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About This Manual
Conventions ...................................................................................................................xiii
Documentation and Examples .......................................................................................xiv
Chapter 1
Software and Hardware Interaction.................................................................1-2
NI Motion Controller Architecture..................................................................1-2
NI Motion Controller Functional Architecture................................................1-4
NI SoftMotion Controller Communication Watchdog ..................................................1-9
Chapter 2
Creating NI-Motion Applications
Creating a Generic NI-Motion Application...................................................................2-1
Adding Measurements to an NI-Motion Application....................................................2-2
Chapter 3
Tuning Servo Systems
NI SoftMotion Controller for Ormec ..............................................................3-1
Using Control Loops to Tune Servo Motors .................................................................3-1
Control Loop ...................................................................................................3-2
PID Loop Descriptions......................................................................3-4
Velocity Feedback...........................................................................................3-9
NI Motion Controllers with Velocity Amplifiers............................................3-10
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Contents
Chapter 4
NI 73xx Time Base ........................................................................... 4-5
NI 73xx Arc Move Limitations ....................................................................... 4-13
Status Display ................................................................................................. 4-14
Graphing Data................................................................................................. 4-14
Chapter 5
Straight-Line Moves
Velocity-Based Straight-Line Moves............................................................................ 5-10
Algorithm........................................................................................................ 5-11
LabVIEW Code............................................................................................... 5-13
C/C++ Code .................................................................................................... 5-13
Velocity Profiling Using Velocity Override.................................................................. 5-17
Algorithm........................................................................................................ 5-18
LabVIEW Code............................................................................................... 5-19
C/C++ Code .................................................................................................... 5-20
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Chapter 6
Arc Move Algorithm.......................................................................................6-3
LabVIEW Code...............................................................................................6-4
LabVIEW Code...............................................................................................6-10
C/C++ Code.....................................................................................................6-10
Algorithm ........................................................................................................6-14
LabVIEW Code...............................................................................................6-15
Chapter 7
Overview........................................................................................................................7-1
Arbitrary Contoured Moves...........................................................................................7-2
Absolute versus Relative Contouring ...............................................7-4
LabVIEW Code...............................................................................................7-5
Chapter 8
Reference Moves
Reference Move Algorithm.............................................................................8-2
LabVIEW Code...............................................................................................8-3
Chapter 9
Superimpose Two Moves................................................................................9-2
Blend after First Move Is Complete ................................................................9-3
Blend after Delay.............................................................................................9-4
Blending Algorithm.........................................................................................9-5
LabVIEW Code...............................................................................................9-6
C/C++ Code.....................................................................................................9-7
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Contents
Algorithm........................................................................................................ 10-2
Algorithm........................................................................................................ 10-11
Camming Table............................................................................................... 10-12
Master Offset .................................................................................... 10-17
Chapter 11
Algorithm ......................................................................................................................11-2
LabVIEW Code............................................................................................................. 11-4
Single Position Breakpoints............................................................................ 12-8
C/C++ Code .................................................................................................... 12-14
Periodically Occurring Breakpoints .............................................................................. 12-16
Periodic Breakpoints (NI 7350 only).............................................................. 12-17
Periodic Breakpoint Algorithm ........................................................ 12-17
LabVIEW Code ................................................................................ 12-18
C/C++ Code...................................................................................... 12-18
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LabVIEW Code...............................................................................................12-24
LabVIEW Code...............................................................................................12-29
LabVIEW Code...............................................................................................12-34
Real-Time System Integration Bus (RTSI) ...................................................................12-37
RTSI Implementation on the Motion Controller.............................................12-38
Encoder Pulses Using RTSI ............................................................................12-39
LabVIEW Code...............................................................................................13-4
LabVIEW Code...............................................................................................13-10
C/C++ Code.....................................................................................................13-11
Speed Control Based on Analog Feedback Algorithm....................................13-14
LabVIEW Code...............................................................................................13-15
Using Onboard Programs with the NI SoftMotion Controller ......................................14-1
Writing Onboard Programs .............................................................................14-3
Algorithm ........................................................................................................14-4
LabVIEW Code...............................................................................................14-5
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Contents
Running, Stopping, and Pausing Onboard Programs.................................................... 14-8
Algorithm........................................................................................................ 14-15
Branching Onboard Programs....................................................................................... 14-19
Algorithm........................................................................................................ 14-26
Synchronizing Host Applications with Onboard Programs .......................................... 14-26
Onboard Subroutines..................................................................................................... 14-34
Algorithm........................................................................................................ 14-34
C/C++ Code .................................................................................................... 14-38
Automatically Starting Onboard Programs ................................................................... 14-42
Changing a Time Slice .................................................................................................. 14-42
Scanning
Connecting Straight-Line Move Segments ................................................................... 15-1
Raster Scanning Using Straight Lines Algorithm........................................... 15-2
LabVIEW Code............................................................................................... 15-3
C/C++ Code .................................................................................................... 15-4
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LabVIEW Code...............................................................................................15-9
C/C++ Code.....................................................................................................15-10
User-Defined Scanning Path Algorithm..........................................................15-15
LabVIEW Code...............................................................................................15-16
Rotating Knife
Solution..........................................................................................................................16-1
Algorithm ........................................................................................................16-3
LabVIEW Code...............................................................................................16-4
C/C++ Code.....................................................................................................16-5
Appendix A
Sinusoidal Commutation for Brushless Servo Motion Control
Appendix B
Initializing the Controller Programmatically
Appendix C
Technical Support and Professional Services
Glossary
Index
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About This Manual
This manual provides information about the NI-Motion driver software,
including background, configuration, and programming information.
The purpose of this manual is to provide a basic understanding of the
NI-Motion driver software, and provide programming steps and examples
to help you develop NI-Motion applications.
This manual is intended for experienced LabVIEW, C/C++, or other
developers. Code instructions and examples assume a working knowledge
of the given programming language. This manual also assumes a general
knowledge of motion control terminology and development requirements.
This manual pertains to all NI motion controllers that use the NI-Motion
driver software.
Conventions
The following conventions appear in this manual:
<>
Angle brackets that contain numbers separated by an ellipsis represent a
range of values associated with a bit or signal name—for example,
AO <3..0>.
[ ]
Square brackets enclose optional items—for example, [response].
»
The » symbol leads you through nested menu items and dialog box options
to a final action. The sequence File»Page Setup»Options directs you to
pull down the File menu, select the Page Setup item, and select Options
from the last dialog box.
This icon denotes a tip, which alerts you to advisory information.
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash.
bold
Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names.
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italic
Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
monospace
Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames, and extensions.
monospace bold
Monospace bold text indicates a portion of code with structural
significance.
monospace italic
Monospace italic text indicates a portion of code that is commented out.
Documentation and Examples
In addition to this manual, NI-Motion includes the following
documentation to help you create motion applications:
•
•
•
Getting Started with NI-Motion for NI 73xx Motion Controllers—This
document provides installation instructions and general information
about the NI-Motion product.
Getting Started: NI SoftMotion Controller for Ormec
ServoWire SM Drives—Refer to this document for information about
getting started with the NI SoftMotion Controller for Ormec.
Getting Started: NI SoftMotion Controller for Copley CANopen
Drives—Refer to this document for information about getting started
with the NI SoftMotion Controller for CANopen.
•
•
•
•
NI-Motion VI Help—Refer to this document for specific information
about NI-Motion LabVIEW VIs.
NI-Motion Function Help—Refer to this document for specific
information about NI-Motion C/C++ functions.
Measurement & Automation Explorer Help for Motion—Refer to this
document for configuration information.
NI-Motion ReadMe—Refer to this HTML document for information
about hardware and software installation and information about
changes to the NI-Motion driver software in the current version. This
document also contains last-minute information about NI-Motion.
Application notes—For information about advanced NI-Motion
concepts and applications, visit ni.com/appnotes.nsf/.
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About This Manual
•
•
NI Developer Zone (NIDZ)—Visit the NI Developer Zone, at
ni.com/zone, for example programs, tutorials, technical
presentations, the Instrument Driver Network, a measurement
glossary, an online magazine, a product advisor, and a community area
where you can share ideas, questions, and source code with motion
developers around the world.
Motion Hardware Advisor—Visit the National Instruments Motion
Hardware Advisor at ni.com/devzone/advisors/motion/to
select motors and stages appropriate to the motion control application.
In addition to the NI Developer Zone, you can find NI-Motion C/C++
and Visual Basic programming examples in the NI-Motion\
FlexMotion\Examplesfolder where you installed NI-Motion. The
default directory is ProgramFiles\NationalInstruments\
NI-Motion.
You can find LabVIEW example programs under examples\Motion
in the directory where you installed LabVIEW. You can find
LabWindows™/CVI™ examples under samples\Motionin the directory
where you installed LabWindows/CVI.
You can find the NI-Motion C/C++ and LabVIEW example code
referenced in this manual in the NI-Motion\Documentation\
Examples\NI-Motion User Manualfolder where you installed
NI-Motion.
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Part I
Introduction
software, motion control setup, and specific task-based instructions for
creating motion control applications using the LabVIEW and C/C++
application development environments.
Part I covers the following topics:
•
•
Introduction to NI-Motion
Creating NI-Motion Applications
© National Instruments Corporation
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1
Introduction to NI-Motion
About NI-Motion
NI-Motion is the driver software for National Instruments 73xx motion
controllers and the NI SoftMotion Controller. You can use NI-Motion to
create motion control applications using the included library of LabVIEW
VIs and C/C++ functions.
National Instruments also offers the Motion Assistant and NI-Motion
development tools for Visual Basic.
NI-Motion Architecture
The NI-Motion driver software architecture is based on the interaction
between the NI motion controllers and a host computer. This interaction
includes the hardware and software interface and the physical and
functional architecture of the NI motion controllers.
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Chapter 1
Introduction to NI-Motion
Software and Hardware Interaction
NI Motion Assistant
Graphical Prototyping Tool
Creates ADE
Code
Measurement and
Automation Explorer
Configuration Utility
Application Development Environments:
LabVIEW, Visual Basic, and C++
NI-Motion Driver Software
Figure 1-1. NI Motion Control Hardware and Software Interaction
Note The last block in Figure 1-1 is not applicable to the NI SoftMotion Controller.
NI Motion Controller Architecture
This section includes information about the architecture for both the 73xx
family of NI motion controllers and the NI SoftMotion Controller.
NI 73xx Architecture
NI 73xx controllers use a dual-processor architecture. The two processors,
a central processing unit (CPU) and a digital signal processor (DSP), form
the backbone of the NI motion controller. The controller plugs into a
variety of slots, including PCI slots, or to a PC using a high-speed serial
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The controller CPU is a 32-bit micro-controller running an embedded real
time, multitasking operating system. This CPU offers the performance and
determinism needed to solve most complex motion applications. The CPU
performs command execution, host synchronization, I/O reaction, and
system supervision.
The DSP has the primary responsibility of fast closed-loop control with
simultaneous position, velocity, and trajectory maintenance on multiple
axes. The DSP also closes the position and velocity loops, and directly
commands the torque to the drive or amplifier.
Motion I/O occurs in hardware on an FPGA and consists of
limit/home switch detection, position breakpoint, and high-speed capture.
This ensures very low latencies in the range of hundreds of nanoseconds
for breakpoints and high-speed captures. Refer to Chapter 12,
Synchronization, for information about breakpoints and high-speed
capture.
The motion controller processor is monitored by a watchdog timer, which
is hardware that can be used to automatically detect software anomalies and
reset the processor if any occur. The watchdog timer checks for proper
processor operation. If the firmware on the motion controller is unable to
process functions within 62 ms, the watchdog timer resets the motion
controller and disallows further communications until you explicitly reset
the motion controller. This ensures the real-time operation of the motion
control system. The following functions may take longer than 62 ms to
process.
•
•
•
•
•
•
Save Defaults
Reset Defaults
Enable Auto Start
Object Memory Management
Clear Buffer
End Storage
These functions are marked as non-real-time functions. Refer to the
NI-Motion Function Help or the NI-Motion VI Help for more information.
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Chapter 1
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Figure 1-2 illustrates the physical architecture of the NI motion controller
hardware.
NI Motion Controller
Host Computer
Microprocessor
Running a Real-Time
Operating System
Digital Signal
Processor (DSP)
PC
Supervisory/
Communications/
User-defined Onboard
Programs
Control Loop and
Trajectory Generation
FPGAs
Watchdog
Timer
Encoders and Motion I/O
Figure 1-2. Physical NI Motion Controller Architecture
Tip Because the NI SoftMotion Controller is not a hardware device, information about
its architecture is not covered in this section. Refer to the NI SoftMotion Controller
Architecture section for information about the functional architecture that is specific to the
NI SoftMotion Controller.
NI Motion Controller Functional Architecture
Functionally, the architecture of the NI 73xx motion controllers and the
NI SoftMotion Controller is generally divided into four components:
supervisory control, trajectory generator, control loop, and motion I/O. For
the NI SoftMotion Controller, the motion I/O component is separate from
the controller. Refer to Figure 1-3 and Figure 1-4 for an illustration of how
the components of the 73xx and NI SoftMotion Controller interact.
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Chapter 1
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Figure 1-3 shows the components of the NI 73xx motion controllers.
Typical NI 73xx Motion Controller Architecture
Supervisory Control
To drive
Trajectory Generation
Host
Bus
Control Loop
From
feedback
& sensors
Microcontroller running RTOS/DSPs/FPGAs
Figure 1-3. Typical NI 73xx Motion Controller Functional Architecture
Figure 1-4 shows the components of the NI SoftMotion controller.
NI SoftMotion Controller Architecture
Software is separate from the I/O
Supervisory Control
To drive
Trajectory Generation
Host
Bus
Control Loop
From
feedback
& sensors
Any CPU on a real-time environment
Figure 1-4. NI SoftMotion Controller Functional Architecture
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Chapter 1
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Figure 1-5 illustrates the functional architecture of NI motion controllers.
Trajectory Generation
(ms)
Cruise
k
Jer
Jer
k
Supervisory Control
(ms)
Control Loop (µs)
(with Interpolation)
Decel
Accel
User API
Interface
Time
Set Point
dt
Supervisory
Control
Commands for
Trajectory Generator
Interpolation
Output
PID
New
Set Point
Updated
Event Monitoring Interface
Updates Trajectory
Generator Based on
I/O And User
I/O
Sensor
Response
Figure 1-5. NI Motion Controller Functional Architecture
The following list describes how each component of the 73xx controllers
and the NI SoftMotion Controller functions:
•
Supervisory control—Performs all the command sequencing and
coordination required to carry out the specified operation
–
–
System initialization, which includes homing to a zero position
Event handling, which includes electronic gearing, triggering
outputs based on position, updating profiles based on user defined
events, and so on
–
Fault Detection, which includes stopping moves on a limit switch
encounter, safe system reaction to emergency stop or drive faults,
watchdog, and so on
•
•
Trajectory generator provides path planning based on the profile
specified by the user
Control loop—Performs fast, closed-loop control with simultaneous
position, velocity, and trajectory maintenance on one or more axes
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Chapter 1
Introduction to NI-Motion
feedback, and it defines the response and stability of the system. For
stepper systems, the control loop is replaced with a step generation
component. To enable the control loop to execute faster than the
trajectory generation, an interpolation component, or spline engine, the
control loop interpolates between setpoints calculated by the trajectory
generator. Refer to Figure 1-5 for an illustration of the spline engine.
•
Motion I/O—Analog and digital I/O that sends and receives signals
from the rest of the motion control system. Typically, the analog output
is used as a command signal for the drive, and the digital I/O is used
for quadrature encoder signals as feedback from the motor. The motion
I/O performs position breakpoint and high speed capture. Also, the
supervisory control uses the motion I/O to achieve certain required
functionality, such as reacting to limit switches and creating the
movement modes needed to initialize the system.
NI SoftMotion Controller Architecture
The NI-Motion architecture for the NI SoftMotion Controller uses standard
PC-based platforms and open standards to connect intelligent drives to a
real-time host. In this architecture, the software components of the motion
controller run on a real-time host and all I/O is implemented in the drives.
This separation of I/O from the motion controller software components
helps to lower system cost and improve reliability by improving
connectivity. Open standards, such as IEEE 1394 and CANopen, are
used to connect these components.
NI SoftMotion Controller for Ormec
When you use the NI SoftMotion Controller with an Ormec device, you can
daisy chain up to 15 drives together and connect them to the real-time host.
The real-time isochronous mode of the IEEE 1394 bus is used to transfer
data between the drives and the host. Figure 1-6 shows the NI SoftMotion
Controller component architecture that applies when the controller is used
with an Ormec device.
The supervisory control and trajectory generation loops execute every
millisecond. If the control loop is configured to execute faster than every
millisecond, the trajectory data is interpolated before the control loop
uses it.
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Chapter 1
Introduction to NI-Motion
NI SoftMotion Controller on Host Device*
Ormec Drive
I/O**
Supervisory
Control
Trajectory
Generation
Control
Loop
IEEE 1394 Bus
*Host device is a PC or PXI chassis running the
LabVIEW Real-Time Module for RTX Targets
**I/O includes encoder implementation
Figure 1-6. NI SoftMotion Controller Functional Architecture for Ormec
NI SoftMotion Controller for CANopen
When you use the NI SoftMotion Controller with a CANopen device, you
can daisy chain up to 15 drives together and connect them to the real-time
host. The real-time Process Data Objects (PDOs) defined by the CANopen
protocol are used to transfer data between the drives and host.
All I/O required by the motion controller is implemented by CANopen
drives that support the Device Profile 402 for Motion Control. Currently,
the NI SoftMotion Controller supports only CANopen drives from Copley
Controls Corp. When used with CANopen devices, the Supervisory
Control and Trajectory Generation components of the NI SoftMotion
Controller execute in a real-time environment that is running LabVIEW
Real-Time Module (ETS).
If your motion control system uses 8 axes or fewer, the supervisory control
and trajectory generation loops execute every 10 milliseconds. If your
motion control system uses more than 8 axes, the supervisory control and
trajectory generation loops execute every 20 milliseconds. When you use
the NI SoftMotion Controller with a CANopen drive, the drive implements
the control loop and interpolation.
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Chapter 1
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NI SoftMotion Controller
on Host Device*
CANopen Drive
Supervisory Trajectory
Spline
Engine
Control
Loop
I/O**
Control
Generation
CAN Bus
*Host device is a PC or PXI chassis running the
LabVIEW Real-Time Module
**I/O includes encoder implementation
Figure 1-7. NI SoftMotion Controller Functional Architecture for CANopen
In this configuration, the I/O and the control loop execute on the CANopen
drive. The NI SoftMotion Controller uses an NI-CAN device to
communicate to the CAN bus.
NI SoftMotion Controller Communication Watchdog
The supervisory control in the NI SoftMotion Controller continuously
monitors all communication with the drives connected to the host. If any
drive fails to update its data in the host loop update period, the axis
corresponding to that drive is disabled and the communication watchdog
status bit, which is returned by the Read Per Axis Status function, is set to
TRUE. Similarly, all drives connected to the NI SoftMotion Controller are
configured to go into a fault state if the data from the
NI SoftMotion Controller is not updated every host loop update period on
the drives.
The communication watchdog functionality ensures that the NI SoftMotion
Controller operates in real time.
Tip To get an axis or axes out of the communication watchdog state, reset the
NI SoftMotion Controller.
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2
Creating NI-Motion Applications
This chapter describes the basic form of an NI-Motion application and its
acquisition device.
Creating a Generic NI-Motion Application
Figure 2-1 illustrates the steps for creating an application with NI-Motion,
and describes the generic steps required to design a motion application.
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Chapter 2
Creating NI-Motion Applications
Determine the system requirements
Getting Started with NI-Motion
Determine the
for NI 73xx Motion Controllers
required mechanical system
Connect the hardware
Configure the controller using
MAX
Measurement & Automation
Explorer Help for Motion
Test the motion system
Plan the moves
Part III:
Programming with NI-Motion
Create the moves
Add measurements with data
and/or image acquisition (optional)
Adding Measurements to an NI-Motion Application
Figure 2-2 illustrates an expanded view of the topics covered in Part III,
Programming with NI-Motion, of this manual. For information about items
in the diagram, refer to Chapter 12, Synchronization.
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1
Define control mechanism for I/O
Breakpoints*
High-speed capture**
2b
2a
Define breakpoint position
Define triggering input type
Enable high-speed capture
Read the captured position
Enable a breakpoint
Set data or image acquisition
device to trigger on breakpoint
Re-enable the breakpoint
after each occurrence
(absolute/relative/modulo
breakpoints only)
Re-enable high-speed capture
after each occurrence
(non-buffered high-speed
capture only)
Chapter 12:
Synchronization
* Breakpoints cause a digital output to change state when a specified position is reached
by an encoder. Breakpoints are not supported by the NI SoftMotion Controller when it is
used with an Ormec or CANopen device.
** A high-speed capture records the position of an encoder when a digital line is used as
a trigger. High-speed captures are not supported by NI SoftMotion Controller for
CANopen. You can use two high-speed captures per axis when you are using the
NI SoftMotion Controller with an Ormec device.
Figure 2-2. Input/Output with Data and Image Acquisition
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Note If you are using RTSI to connect your motion controller to a National Instruments
data or image acquisition device, be aware that the NI SoftMotion Controller does not
support RTSI.
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Part II
Configuring Motion Control
Motion control is divided into two parts: configuration and execution.
Part II of this manual discusses configuring the hardware and software
components of a motion control system using NI-Motion.
Part II covers the following topic:
•
Tuning Servo Systems
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Tuning Servo Systems
When your motion control system includes a servo motor, you must tune
and calibrate the system to ensure proper performance. This chapter covers
general information about tuning and calibrating your servo system using
control loop parameters. Refer to Measurement & Automation Explorer
Help for Motion for more information about and instructions for tuning
servo motors in Measurement & Automation Explorer (MAX).
NI SoftMotion Controller Considerations
This section includes information you need if you are using the
NI SoftMotion Controller.
NI SoftMotion Controller for CANopen
This chapter does not apply if you are using the
NI SoftMotion Controller for CANopen because the control loop is
implemented on the drive. Refer to the drive documentation for
information about tuning the servo motors you are using with the CANopen
drive.
NI SoftMotion Controller for Ormec
If you are using the NI SoftMotion Controller for Ormec with an Ormec
ServoWire drive in position mode, you must tune the control loop using the
drive configuration utility provided by Ormec.
Using Control Loops to Tune Servo Motors
Tuning maximizes the performance of your servo motors. A servo system
uses feedback to compensate for errors in position and velocity.
For example, when the servo motor reaches the desired position, it cannot
stop instantaneously. There is a normal overshoot that must be corrected.
The controller turns the motor in the opposite direction for the amount of
distance equal to the detected overshoot. However, this corrective move
also exhibits a small overshoot, which must also be corrected in the same
manner as the first overshoot.
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A properly tuned servo system exhibits overshoot as shown in Figure 3-1.
Overshoot
Commanded
Position
Time
0
Settling Time
Figure 3-1. Properly Tuned Servo Motor Behavior
The amount of time required for the motors to settle on the commanded
position is called the settling time. By tuning the servo motors, you can
affect the settling time, the amount of overshoot, and various other
performance characteristics.
Control Loop
NI motion servo control uses control loops to continuously correct errors in
position and velocity. You can configure the control loop to perform a
Proportional, Integral and Derivative (PID) loop or a more advanced
control loop, such as the velocity feedback (PIV) or velocity feedforward
(PIVff) loops.
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PID Loop Descriptions
The following are common variables relating to the PID control loop.
Kp (Proportional Gain)
The proportional gain (Kp) determines the contribution of restoring force
that is directly proportional to the position error. This restoring force
functions in much the same way as a spring in a mechanical system.
Each sample period, the PID loop calculates the position error, which is the
difference between the instantaneous trajectory position and the primary
feedback position, and multiplies the position error by Kp to produce the
proportional component of the 16-bit DAC command output.
An axis with too small a value of Kp is unable to hold the axis in position
and is very soft. Increasing Kp stiffens the axis and improves its disturbance
torque rejection. However, too large a value of Kp often results in
instability.
Ki (Integral Gain)
The integral gain (Ki) determines the contribution of restoring force that
increases with time, ensuring that the static position error in the servo loop
is forced to zero. This restoring force works against constant torque loads
to help achieve zero position error when the axis is stopped.
Each sample period, the position error is added to the accumulation of
previous position errors to form an integration sum. This integration sum is
scaled by dividing by 256 prior to being multiplied by Ki.
In applications with small static torque loads, this value can be left at its
default value of zero (0). For systems having high static torque loads, this
value should be tuned to minimize position error when the axis is stopped.
Although non-zero values of Ki cause reduced static position error, they
tend to cause increased position error during acceleration and deceleration.
This effect can be mitigated through the use of the Integration Limit
parameter. Too high a value of Ki often results in servo loop instability.
National Instruments therefore recommends that you leave Ki at its default
value of zero until the servo system operation is stable. Then you can add a
small amount of Ki to minimize static position errors.
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Kd (Derivative Gain)
The derivative gain (Kd) determines the contribution of restoring force
proportional to the rate of change (derivative) of position error. This force
acts much like viscous damping in a damped spring and mass mechanical
system. A shock absorber is an example of this effect.
The PID loop computes the derivative of position error every derivative
sample period. A non-zero value of Kd is required for all systems that use
torque block amplifiers, where the command output is proportional to
motor torque, for the servo loop operation to be stable. Too small a Kd
value results in servo loop instability.
With velocity block amplifiers, where the command output is proportional
to motor velocity, it is typical to set Kd to zero or a very small positive
value.
Kv (Velocity Feedback)
You can use a primary or secondary feedback encoder for velocity
feedback. Setting the velocity feedback gain (Kv) to a value other than
zero (0) enables velocity feedback using the secondary encoder, if
configured, or the primary encoder if a secondary encoder is not
configured.
Kv is used to scale this velocity feedback before it is added to the other
components in the 16-bit DAC command output. Kv is similar to derivative
gain (Kd) except that it scales the velocity estimated from encoder
resources only. The derivative gain scales the derivative of the position
error, which is the difference between the instantaneous trajectory position
and the primary feedback position. Like the Kd term, the velocity feedback
derivative is calculated every derivative sample period and the contribution
is updated every PID sample period.
Velocity feedback is estimated through a combination of speed-dependent
algorithms. Velocity is measured based on the time elapsed between each
encoder count.
Vff (Velocity Feedforward)
The velocity feedforward gain (Vff) determines the contribution in the
16-bit DAC command output that is directly proportional to the
instantaneous trajectory velocity. This value is used to minimize following
error during the constant velocity portion of a move and can be changed at
any time to tune the PID loop.
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Velocity feedforward is an open-loop compensation technique and cannot
affect the stability of the system. However, if you use too large a value for
Vff, following error can reverse during the constant velocity portion, thus
degrading performance, rather than improving it.
Velocity feedforward is typically used when operating in PIVff mode
with either a velocity block amplifier or substantial amount of velocity
feedback (Kv). In these cases, the uncompensated following error is
directly proportional to the desired velocity. You can reduce this following
error by applying velocity feedforward. Increasing the integral gain (Ki)
also reduces the following error during constant velocity but only at the
expense of increased following error during acceleration and deceleration
and reduced system stability. For these reasons, increasing Ki is not a
recommended solution.
Tip In PIVff mode, the Kd and Kv gains are set to zero.
Velocity feedforward is rarely used when operating in PID mode with
torque block amplifiers. In this case, because the following error is
proportional to the torque required, rather than the velocity, it is typically
much smaller and does not require velocity feedforward.
Aff (Acceleration Feedforward)
The acceleration feedforward gain (Aff) determines the contribution in the
16-bit DAC command output that is directly proportional to the
instantaneous trajectory acceleration. Aff is used to minimize following
error (position error) during acceleration and deceleration and can be
changed at any time to tune the PID loop.
Acceleration feedforward is an open-loop compensation technique and
cannot affect the stability of the system. However, if you use too large a
value of Aff, following error can reverse during acceleration and
deceleration, thus degrading performance, rather than improving it.
Kdac
Kdac is the Digital to Analog Converter (DAC) gain. Use the following
equation to calculate Kdac:
20 V
Kdac = -----------
216
20 V represents the 10 V range in the motion controller.
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Ga
Ga is the Amplifier Gain.
Kt
Kt is the Torque Constant of the motor. Kt is represented in Newton Meters
per Amp.
1/J
1/J represents the motor plus load inertia of the motion system.
Ke
Ke represents the conversion factor to revolutions. This may involve a
scaling factor.
Dual Loop Feedback
Motion control systems often use gears to increase output torque, increase
resolution, or convert rotary motion to linear motion. The main
disadvantage of using gears is the backlash created between the motor and
the load. This backlash can cause a loss of position accuracy and system
instability.
The control loop on the motion system corrects for errors and maintains
tight control over the trajectory. The control loop consists of three main
parts—proportional, integral and derivative—known as PID parameters.
The derivative part estimates motor velocity by differentiating the
following error (position error) signal. This velocity signal adds, to the
loop, damping and stability. If backlash is present between the motor and
the same. This difference causes the derived velocity to become ineffective
for loop damping purposes, which creates inaccuracy in position and
system instability.
Using two position sensors for an axis can help solve the problems caused
by backlash. As shown in Figure 3-3, one position sensor resides on the
load and the other on the motor before the gears. The motor sensor is used
to generate the required damping and the load sensor for position feedback.
The mix of these two signals provides the correct position feedback with
damping and stability.
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Σ
Σ
Figure 3-3. Dual Loop Feedback
Tip You can enable dual-loop feedback on the NI motion controller by mapping an
encoder as the secondary feedback for the axis, and then using the velocity feedback gain
instead of the derivative gain to dampen and stabilize the system, as shown in Figure 3-4.
Figure 3-4. Dual Loop Feedback Algorithm
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Velocity Feedback
You can configure the NI motion controller for velocity feedback using the
Kv (velocity feedback) gain. Using Kv creates a minor velocity feedback
loop. This is very similar to the traditional analog servo control method of
necessary for systems where precise speed control is essential.
You can use a less expensive standard torque, or current mode, amplifier
with the velocity feedback loop on NI motion controllers to achieve the
same results you would get from using velocity amplifiers, as shown in
Figure 3-5.
Σ
Σ
Figure 3-5. Velocity Feedback
Setting any non-zero value for Kv allows you to use the Kv term instead of
or in addition to the Kd term to stabilize the system.
scales the velocity estimated from encoder resources only. The derivative
gain scales the derivative of the position error, which is the difference
between the instantaneous trajectory position and the primary feedback
position. Like the Kd term, the velocity feedback derivative is calculated
every derivative sample period, and the contribution is updated every PID
sample period, as shown in Figure 3-6.
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in Addition to Kd
Figure 3-6. Alternate Dual-Loop Feedback Algorithm
NI Motion Controllers with Velocity Amplifiers
Velocity amplifiers close the velocity loop using a tachometer on the
amplifier itself, as shown in Figure 3-7. In this case, the controller must
ensure that the voltage output is proportional to the velocity. Use the
velocity feedforward term (Vff) to ensure that there is minimum following
error during the constant velocity profiles.
Figure 3-7. NI Motion Controllers with Velocity Amplifiers
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Figure 3-8 describes how to use NI motion controllers with velocity
amplifiers.
Figure 3-8. NI Motion Controllers with Velocity Amplifiers Algorithm
You typically use velocity feedforward when using controllers with
velocity amplifiers. The uncompensated following error is directly
proportional to the specified velocity. You can reduce the following error
by applying velocity feedforward. Increasing the integral gain (Ki) also
reduces the following error during constant velocity, but at the expense of
increased following error during acceleration and deceleration and reduced
system stability.
Note National Instruments does not recommend increasing Ki.
Velocity feedforward is rarely used when operating in PID mode with
torque block amplifiers. In this case, following error is typically much
smaller because it is proportional to the torque required rather than to the
velocity. When operating in PID mode with torque block amplifiers,
velocity feedforward is not required.
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Part III
Programming with NI-Motion
You can use the C/C++ functions and LabVIEW VIs, included with
NI-Motion, to configure and execute motion control applications. Part III
of this manual covers the NI-Motion algorithms you need to use all the
features of NI-Motion.
Each task discussion uses the same structure. First, a generic algorithm
flow chart shows how the component pieces relate to each other. Then, the
task discussion details any aspects of creating the task that are specific to
LabVIEW or C/C++ programming, complete with diagrams and code
examples.
Note The LabVIEW block diagrams and C/C++ code examples are designed to illustrate
applications.
Refer to the NI-Motion Function Help or the NI-Motion VI Help for
detailed information about specific functions or VIs.
Part III covers the following topics:
•
•
•
•
•
•
•
•
What You Need to Know about Moves
Straight-Line Moves
Arc Moves
Contoured Moves
Reference Moves
Blending Moves
Electronic Gearing and Camming
Acquiring Time-Sampled Position and Velocity Data
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Programming with NI-Motion
•
Synchronization
•
•
Torque Control
Onboard Programs
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4
What You Need to Know about
Moves
This chapter discusses the concepts necessary for programming motion
control.
Move Profiles
The basic function of a motion controller is to make moves. The trajectory
generator takes in the type of move and the move constraints and generates
points, or instantaneous positions, in real time. Then, the trajectory
generator feeds the points to the control loop.
The control loop converts each instantaneous position to a voltage or to
step-and-direction signals, depending on the type of motor you are using.
Move constraints are the maximum velocity, acceleration, deceleration, and
jerk that the system can handle. The trajectory generator creates a velocity
profile based on these move constraint values.
There are two types of profiles that can be generated while making the
move: trapezoidal and s-curve.
Trapezoidal
When you use a trapezoidal profile, the axes accelerate at the acceleration
Based on the type of move and the distance being covered, it may be
impossible to reach the maximum velocity you set.
The velocity of the axis, or axes, in a coordinate space never exceeds the
maximum velocity loaded. The axes decelerate to a stop at their final
position, as shown in Figure 4-1.
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Velocity
Time
Figure 4-1. Trapezoidal Move Profile
S-Curve
The acceleration and deceleration portions of an s-curve motion profile are
smooth, resulting in less abrupt transitions, as shown in Figure 4-2. This
limits the jerk in the motion control system, but increases cycle time. The
value by which the profile is smoothed is called the maximum jerk or
s-curve value.
Velocity
Time
Figure 4-2. S-Curve Move Profile
Basic Moves
There are four basic move types:
•
•
Reference Move—Initializes the axes to a known physical reference
such as a home switch or encoder index
Straight-Line Move—Moves from point A to point B in a straight
line. The move can be based on position or velocity
Arc Move—Moves from point A to point B in an arc or helix
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•
Contoured Move—Is a user-defined move; you generate the
trajectory, and the points loaded into the motion controller are splined
to create a smooth profile
The motion controller uses the specified move constraints, along with the
move data, such as end position or radius and travel angle, to create a
motion profile in all the moves except the contoured moves. Contoured
moves ignore the move constraints and follow the points you have defined.
Coordinate Space
With the exception of the arc move, you can execute all basic moves on
grouping of axes, such as the XYZ axis shown in Figure 4-3. Arc moves
always execute on a coordinate space.
If you are performing a move that uses more than one axis, you must
specify a coordinate space made up of the axes the move will use, as shown
in Figure 4-3.
Z
X, Y, Z
Y
X
Figure 4-3. 3D Coordinate Space
Use the Configure Vector Space function to configure a coordinate space.
This function creates a logical mapping of axes and treats the axes as part
of a coordinate space.The function then executes the move generated by the
trajectory generator on the vector, and treats all the move constraints as
vector values.
Multi-Starts versus Coordinate Spaces
Coordinate spaces always start and end the motion of all axes
simultaneously. You can use multi-starts to create a similar effect without
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grouping axes into coordinate spaces. Using a multi-start automatically
starts all axes virtually simultaneously. To simultaneously end the moves,
you must calculate the move constraints to end travel at the same time. In
coordinate spaces, this behavior is calculated automatically.
Trajectory Parameters
Use trajectory parameters to control the moves you program in NI-Motion.
All trajectory parameters for servo axes are expressed in terms of
quadrature encoder counts. Parameters for open-loop and closed-loop
stepper axes are expressed in steps. For servo axes, the encoder resolution,
which is expressed in counts per revolution, determines the ultimate
positional resolution of the axis.
For stepper axes, the number of steps per revolution depends upon the type
of stepper drive and motor you are using. For example, a stepper motor with
1.8°/step (200 steps/revolution) used in conjunction with a 10X microstep
drive has an effective resolution of 2,000 steps per revolution. Resolution
on closed-loop stepper axes is limited to the steps per revolution or encoder
counts per revolution, whichever value is more coarse.
Floating-point versus fixed-point parameter representation and time base
are two additional factors that affect the way trajectory parameters are
loaded to the NI motion controller as compared to how they are used by the
trajectory generators.
The NI SoftMotion Controller uses a 64-bit floating point trajectory
generator. The ranges for all move constraints are the full 64-bit range,
which includes maximum velocity, maximum acceleration, maximum
deceleration, maximum acceleration jerk, maximum deceleration jerk, and
velocity override percentage. All arc parameters that use floating point also
support the full 64-bit floating point range.
NI 73xx Floating-Point versus Fixed-Point
Note The information in this section applies only to NI 73xx motion controllers. These
restrictions are not applicable to the NI SoftMotion Controller.
You can load some trajectory parameters as either floating-point or
fixed-point values, but the internal representation on the NI motion
controller is always fixed-point. You must consider this functionality when
working with onboard variables, inputs, and return vectors. This
functionality also has a small effect on parameter range and resolution.
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NI 73xx Time Base
Velocity and acceleration values are loaded in counts/s, RPM, RPS/s,
the trajectory generator updates target position at the Trajectory Update
Rate, which is programmable with the Enable Axes function. This means
that the range for these parameters depends on the update rate selected, as
shown in the following examples.
Table 4-1 lists minimum and maximum update rates for acceleration and
velocity in various units.
Velocity values in RPM are converted to an internal 16.16 fixed-point
format in units of counts (steps) per sample period (update period) before
being used by the trajectory generator. NI-Motion can control velocity to
1/65,536 of a count or step per sample.
Table 4-1 shows the minimum and maximum velocity in counts/min. Use
the formula shown in the Calculation Based on Units column to determine
the counts/min value to RPM.
Table 4-1. Velocity in Counts/Min
Calculation Based
Update Rate
62.5 µs
MIN
MAX
on Units
14.648438 counts/min For servo motors, the
RPMmax = MAX×1/r
maximum counts/min is where r = counts/revolution
1.2 billion independent
of the update rate.
125 µs
7.324219 counts/min
4.882813 counts/min
3.662109 counts/min
2.929688 counts/min
2.441406 counts/min
2.092634 counts/min
1.831055 counts/min
187.5 µs
250 µs
312.5 µs
375 µs
For stepper motors, the
maximum counts/min
value is dependent on the
controller:
RPMmin = MIN×1/r
where r = counts/revolution
437.5 µs
500 µs
• 480 million
counts/min for 7350
• 240 million
counts/min for 7330,
7340, and 7390
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You can calculate this minimum velocity increment in RPM with the
following formula:
1
Ts
1
R
-----
---
minimum RPM = Vmin ×
× 60 ×
where
Vmin = 1/65,536 counts/sample or steps/sample
Ts = sample period in seconds per sample
60 = number of seconds in a minute
R = counts or steps per revolution
or
1
R
---
minimum RPM = MIN ×
You also can calculate the minimum velocity using the formula shown in
the Calculation Based on Units column in Table 4-1.
For a typical servo axis with 2,000 counts per revolution operating at a
250 µs update rate, the minimum RPM increment is
1
1
1
---------------
---------------
-----------
×
× 60 ×
= 0.00183105 RPM
65,536
250 µs
2000
or
1
-----------
3.662109 ×
= 0.00183105 RPM
2000
You can calculate the maximum velocity in RPM with the following
equation:
1
R
---
maximum RPM = Vmax × 60 ×
where
Vmax = 20 MHz for servos
8 MHz for steppers on a NI 7350 controller
4 MHz for steppers on a NI 7330, NI 7340, or NI 7390
motion controller
R = counts/steps per revolution
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and is constrained by acceleration/deceleration according to the following
equation:
velocity ≤ (65,536 × deceleration) – acceleration
where velocity is in counts/sample and acceleration and deceleration are in
counts/sample2.
From the example, the maximum RPM is
1
6
------------
(20 × 10 ) × 60 ×
= 600,000 RPM
2,000
RPM values stored in onboard variables are in double-precision IEEE
format (f64).
NI 73xx Velocity in Counts/s or Steps/s
Velocity values in counts/s or steps/s are also converted to the internal
16.16 fixed-point format in units of counts or steps per sample (update)
period before being used by the trajectory generator. Although the motion
controller can control velocity to 1/65,536 of a count or step per sample, it
is impossible to load a value that small with the Load Velocity function, as
shown in the following formula:
1
Ts
-----
Velocity in counts or steps/s = Vmin ×
where
Vmin = 1/65,536 counts/sample or steps/sample
Ts = sample period in seconds per sample
Even at the fastest update rate, Ts = 62.5 × 10–6
1
1
---------------
--------------------------
×
= 0.244 counts or steps/s
–6
65,536
62.5 × 10
The Load Velocity function takes an integer input with a minimum value of
1 count/s or step/s. You cannot load fractional values. If you need to load a
velocity slower than one count or step per second, use the Load Velocity
in RPM function.
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You can calculate the maximum velocity with the following equation:
maximum velocity = Vmax
Vmax = 20 MHz for servos
where
8 MHz for steppers on a NI 7350 controller
4 MHz for steppers on a NI 7330, NI 7340, or NI 7390
motion controller
and is constrained by acceleration/deceleration according to the following
equation:
velocity ≤ (65,536 × deceleration) – acceleration
where velocity is in counts/sample and acceleration and deceleration are in
counts/sample2.
NI 73xx Acceleration in Counts/s2
Acceleration and deceleration values are converted to an internal
16.16 fixed-point format in units of counts/s2 before being used by the
trajectory generator.
Table 4-2 shows the minimum and maximum acceleration update rates in
counts/sec2.
Table 4-2. Acceleration Update Rate in Counts/Sec2
Calculation Based
Update Rate
MAX
MIN
on Units
62.5 µs
125 µs
2,048,000,000 counts/sec2
2,048,000,000 counts/sec2
910,222,222 counts/sec2
512,000,000 counts/sec2
327,680,000 counts/sec2
227,555,556 counts/sec2
167,183,673 counts/sec2
128,000,000 counts/sec2
3906 counts/sec2
977 counts/sec2
434 counts/sec2
244 counts/sec2
156 counts/sec2
109 counts/sec2
80 counts/sec2
61 counts/sec2
Accelmax = MAX
187.5 µs
250 µs
312.5 µs
375 µs
Accelmin = MIN
437.5 µs
500 µs
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You can calculate the minimum acceleration increment with the following
formula:
2
1
Ts
-----
minimum acceleration/deceleration = Amin ×
where
Amin = 1/65,536 counts/sample2 or steps/sample2
Ts = sample period in seconds per sample
For a typical servo axis with 2,000 counts per revolution operating at the
250 µs update rate, calculate the minimum acceleration/deceleration
increment using the following equation:
2
1
1
×
= 244 counts/second2
--------------
--------------
65536
250µs
You can calculate the maximum acceleration/deceleration using the
following equation:
2
1
Ts
-----
maximum acceleration/deceleration = Amax ×
where
Amax = 32 counts/sample2
Ts = sample period in seconds per sample
and is constrained according to the following equations:
acceleration ≤ 256 × deceleration
deceleration ≤ 65536 × acceleration
NI 73xx Acceleration in RPS/s
Acceleration and deceleration values in RPS/s are converted to an internal
16.16 fixed-point format in units of counts/sample2 or steps/sample2 before
being used by the trajectory generator.
Table 4-3 shows the minimum and maximum acceleration update rates in
counts/sec2.
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Table 4-3. Acceleration Update Rate in RPS/s
Calculation Based
on Units
Update Rate
MAX
MIN
2,048,000,000 counts/sec2
2,048,000,000 counts/sec2
910,222,222 counts/sec2
512,000,000 counts/sec2
327,680,000 counts/sec2
227,555,556 counts/sec2
167,183,673 counts/sec2
128,000,000 counts/sec2
62.5 µs
125 µs
3906 counts/sec2
977 counts/sec2
434 counts/sec2
244 counts/sec2
156 counts/sec2
109 counts/sec2
80 counts/sec2
61 counts/sec2
RPS/smax = MAX×1/r
where r = counts/revolution
187.5 µs
250 µs
312.5 µs
375 µs
RPS/smin = MIN×1/r
where r = counts/revolution
437.5 µs
500 µs
You can calculate the minimum acceleration increment in RPS/s with the
following formula:
2
1
Ts
1
R
-----
---
RPS/s = Amin ×
×
where
Amin = 1/65,536 counts/sample2 or steps/sample2
Ts = sample period in seconds per sample
R = counts or steps per revolution
or
1
R
---
RPM/s = MIN ×
For a typical servo axis with 2,000 counts or steps per revolution operating
at the 250 µs update rate, calculate the minimum RPS/s increment using the
following equation:
2
1
1
1
---------------
--------------
-----------
×
×
= 0.122070 RPS/s
65,536
250µs
2000
or
1
-----------
244 ×
= 0.122
2000
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You can calculate the maximum RPS/s using the following equation:
2
1
Ts
1
R
-----
---
maximum RPS/s = Amax ×
×
where
Amax = 32 counts/sample2
Ts = sample period in seconds per sample
R = counts or steps per revolution
and is constrained according to the following equations:
acceleration ≤ 256 × deceleration
deceleration ≤ 65536 × acceleration
or
1
r
--
MAX ×
For a typical servo axis with 2,000 counts or steps per revolution operating
at the 250 µs update rate, calculate the maximum RPS/s increment using the
following equation:
2
1
1
--------------
-----------
32 ×
×
= 256,000 RPS/s
250µs
2000
RPS/s values stored in onboard variables are in double-precision
IEEE format (f64).
NI 73xx Velocity Override in Percent
The Load Velocity Override function takes a single-precision
floating-point (f32) data value from 0 to 150%, but velocity override is
internally implemented as a velocity scale factor of 0 to 384 with an
implicit fixed denominator of 256. NI-Motion uses the velocity override to
increase the speed of the calculation for the sake of calculation speed—the
division is a shift right by eight bits. The resolution for velocity override is
therefore limited to 1/256, or about 0.39%.
Note The conversion from floating-point to fixed-point is performed on the host
computer, not on the motion controller. To load velocity override from an onboard variable,
you must use the integer representation of 0 to 384, where 384 corresponds to 150%.
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Note If the distance of the move is too small, it may not be possible to reach the
commanded maximum move constraints. In such instances, NI-Motion adjusts the move
constraints lower to reach the commanded position.
NI 73xx Arc Angles in Degrees
The Load Circular Arc, Load Helical Arc, and Load Spherical Arc
functions take angle parameters in degrees as double-precision
floating-point values. These values are converted to an internal
16.16 fixed-point representation where the integer part corresponds to
multiples of 45° (for example, 360° is represented as 0x0008 0000).
Use the following formula to convert from floating-point to fixed point:
Angle in degrees
---------------------------------------- = Q + R
45°
where
Q = quotient, the integer multiple of 45°
R = remainder
·
R
45°
--------
Angle in 16.16 format = Q.
× 65,536
For example, 94.7° is represented in 16.16 format as follows:
4.7°
45°
---------
Angle in 16.16 format = 2.
× 65,536 = 0x0002.1ABD
The minimum angular increment is
1
---------------
× 45° = 0.000687°
65.536
Note The conversion from floating-point to fixed-point is performed on the host
computer, not on the motion controller. To load arc functions from onboard variables,
you must use the 16.16 fixed-point representation for all angles.
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NI 73xx Arc Move Limitations
The following are limitations to the velocity and acceleration of arc moves.
Arc moves must use the following equations or an
NIMC_invalidVelocityErroris generated:
V × P × 4 ≥ R
and
(V × P2 × 83,443)
-------------------------------------------
1,677,216 ≥
≥ 16
R × I
where
V = Velocity in counts/s
P = PID sample rate in seconds
I = Arc Interval (10 ms or 20 ms) in seconds
R = Radius in counts
Arc moves must use the following equations or an
NIMC_invalidAccelerationErroris generated:
A × P × 4 ≥ R
and
A × P3 × 83,443
--------------------------------------
65,536 ≥
≥ 1
R × I2
where
P = PID sample rate in seconds
I = Arc Interval (10 ms or 20 ms) in seconds
R = Radius in counts
A = Acceleration/deceleration in counts/s2
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Timing Loops
National Instruments recommends that you use the loop timings discussed
in the following sections.
Status Display
When you are displaying status information to the user, such as position,
move status, or velocity, an update rate faster than 60 ms has no value.
In fact, there is no need to update a display any faster than 22 Hz because
the human eye can detect flicker only at refresh rates slower than 22 Hz.
However, you might see flicker in monitors at around 60 Hz, because of
interference with artificial light from light bulbs that run on a 60 Hz AC
signal. The recommended standard is 60 ms because one might need
multiple function calls within one loop to acquire all the necessary data.
Graphing Data
Event Polling
When acquiring data for graphing or tracking purposes, a 10 ms update
time suits most applications. MAX, for example, updates its motion graphs
every 10 ms. This update time equates to 100 samples every second and
provides enough resolution for typical applications. Consider how accurate
the graph display is when choosing the timing for the loop.
Use a polling interval of 5 ms when polling for a time-critical event that
must occur before the program continues. This interval is fast enough to
satisfy most time-critical polling needs, although certain high-speed
applications may require a faster interval. Consider the allowable response
time when choosing a polling interval.
For example, to synchronize the motion with the acquisition in an
application where a user places an object under the scan area and clicks a
Scan button, you create periodic breakpoints every 10 counts to trigger a
data acquisition over RTSI. In this example, the loop needs only to read the
position and wait for the move to complete before ending the scan.
Although the program polls for an event (move complete), no action is
being triggered by the move complete. Because there is no need for
instantaneous action, there is no need to update the position any faster than
60 ms, and 60 ms is acceptable for monitoring the move complete status
as well.
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5
Straight-Line Moves
A straight-line move executes the shortest move between two points.
Position-Based Straight-Line Moves
Position-based straight-line moves use the specified target position to
generate the move trajectory. For example, if the motor is currently at
position zero, and the target position is 100, a position-based move creates
a trajectory that moves 100 counts (steps).
The controller requires the following information to move to another
position in a straight line:
•
•
•
Start position—Current position, normally held over from a previous
move or initialized to zero
End position—Also known as the target position, or where you want
to move to
Move constraints—Maximum velocity, maximum acceleration,
maximum deceleration, and maximum jerk
Tip When you are using the NI SoftMotion Controller, you can load separate acceleration
and deceleration jerk values
The motion controller uses the given information to create a trajectory that
never exceeds the move constraints and that moves an axis or axes to the
end position you specify. The controller generates the trajectory in real
time, so you can change any of the parameters while the axes are moving.
Straight-Line Move Algorithm
The straight-line move algorithm includes the following procedures:
•
•
Load target position—Specifies the end position
Load the move constraints—Loads the velocity, acceleration,
deceleration, and jerk values
•
Start motion—Starts the move
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The start position is always the current position of the axis or axes. You can
load the end position as either an absolute position to move to or as a
position relative to the starting position. Although you can update any
parameter while the move is in progress, the new parameter is used only
after a subsequent Start or Blend Move.
Tip You must load the move constraints only if they are different from what was
previously loaded.
Figure 5-1. Position-Based Straight-Line Move Algorithm
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6
1
5
3
4
2
7
8
9
10
11
12
1
2
3
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
4
5
6
Load S-Curve Time
Set Operation Mode
Load Target Position
7
8
9
Start Motion
Read per Axis Status
Motion Error Handler
Figure 5-2. 1D Straight-Line Move in LabVIEW
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6
1
5
3
4
2
7
8
9
10
11
12
1
2
3
4
Configure Vector Space
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
5
Load S-Curve Time
Set Operation Mode
Load Target Position
Start Motion
9
Check Move Complete Status
6
7
8
10 Read per Axis Status
11 Read per Axis Status
12 Motion Error Handler
Figure 5-3. 2D Straight-Line Move in LabVIEW
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C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
1D Straight-Line Move Code
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk - scurve time (in sample periods)
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err = flex_load_scurve_time(boardID, axis, 1000,
0xFF);
CheckError;
// Set the operation mode
err = flex_set_op_mode (boardID, axis,
NIMC_ABSOLUTE_POSITION);
CheckError;
// Load Position
err = flex_load_target_pos (boardID, axis, 5000,
0xFF);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
do
{
axisStatus = 0;
// Check the move complete status
err = flex_check_move_complete_status(boardID,
axis, 0, &moveComplete);
CheckError;
// Check the following error/axis off status for
the axis
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
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// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D, &resourceID,&errorCode);
nimcDisplayError(errorCode,commandID,
resourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
2D Straight-Line Move Code
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 status;
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
// Set the board ID
boardID = 1;
// Set the vector space
vectorSpace = NIMC_VECTOR_SPACE1;
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// Configure a 2D vector space comprised of axes 1
and 2
err = flex_config_vect_spc(boardID, vectorSpace, 1,
2, 0);
CheckError;
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, vectorSpace,
10000, 0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk - scurve time (in sample periods)
err = flex_load_scurve_time(boardID, vectorSpace,
1000, 0xFF);
CheckError;
// Set the operation mode
err = flex_set_op_mode (boardID, vectorSpace,
NIMC_ABSOLUTE_POSITION);
CheckError;
// Load vector space position
err = flex_load_vs_pos (boardID, vectorSpace,
5000/*x Position*/, 10000/*y Position*/, 0/* z
Position*/, 0xFF);
CheckError;
// Start the move
err = flex_start(boardID, vectorSpace, 0);
CheckError;
do
{
axisStatus = 0;
// Check the move complete status
err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &moveComplete);
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CheckError;
// Check the following error/axis off status for
axis 1
err = flex_read_axis_status_rtn(boardID, 1,
&status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 2
err = flex_read_axis_status_rtn(boardID, 2,
&status);
CheckError;
axisStatus |= status;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
ourceID);
//Read the communication status register
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flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Velocity-Based Straight-Line Moves
Some motion applications require moves that travel in a straight line for a
specific amount of time at a given speed. This type of move is known as
velocity profiling or jogging.
You can use a motion control application to move a motor at a given speed
for a specific time, and then change the speed without stopping the axis.
The sign of the loaded velocity specifies the direction of motion. Positive
velocity implies forward motion and negative velocity implies reverse
motion.
Tip You can change the move constraints during a velocity move.
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Loading a second velocity and executing Start Motion causes the motion
controller to accelerate or decelerate to the newly loaded velocity using the
acceleration or deceleration parameters last loaded. The axis decelerates to
a stop using the Stop Motion function. The velocity profile created in the
example code is shown in Figure 5-5.
Velocity
10,000
Time
5,000
10,000
Figure 5-5. Velocity Profile
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LabVIEW Code
6
7
9
10
5
1
3
2
4
8
11 12
1
2
3
4
Load Velocity
5
6
7
8
Set Operation Mode
Start Motion
Read per Axis Status
Load Velocity
9
Start Motion
Load Acceleration/Deceleration
Load Acceleration/Deceleration
Load S-Curve Time
10 Read per Axis Status
11 Stop Motion
12 Motion Error Handler
Figure 5-6. Velocity-Based Straight-Line Move in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 moveTime1;// Time for the 1st segment
i32 moveTime2;// Time for the 2nd segment
i32 initialTime;
i32 currentTime;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
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i32 errorCode;// Error code
// Set the board ID
boardID = 3;
// Set the axis number
axis = NIMC_AXIS1;
// Move time for the first segment
moveTime1 = 5000; //milliseconds
// Move time for the second segment
moveTime2 = 10000; //milliseconds
//-------------------------------------------------
//First segment
//-------------------------------------------------
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk (s-curve value) for the move (in
sample periods)
err = flex_load_scurve_time(boardID, axis, 100,
0xFF);
CheckError;
// Set the operation mode to velocity
err = flex_set_op_mode(boardID, axis,
NIMC_VELOCITY);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
// Wait for the time for first segment
initialTime = timeGetTime();
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do
{
// Check the following error/axis off status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
// Get the current time and check if time is over
for the first //segment
currentTime = timeGetTime();
if((currentTime - initialTime) >= moveTime1)
break;
Sleep (100); //Check every 100 ms
}while (!(axisStatus) && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT)); //Exit on following error/axis
off
//-------------------------------------------------
// Second segment
//-------------------------------------------------
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 6568, 0xFF);
CheckError;
// Start the move - to update the velocity
err = flex_start(boardID, axis, 0);
CheckError;
// Wait for the time for second segment
initialTime = timeGetTime();
do
{
// Check the following error/axis off status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
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CheckError;
// Read the communication status register and
check the modal // errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
// Get the current time and check if time is over
for the //second segment
currentTime = timeGetTime();
if((currentTime - initialTime) >= moveTime2)
break;
Sleep (100); //Check every 100 ms
}while (!(axisStatus) && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT)); //Exit on move
complete/following error/axis off
// Decelerate the axis to a stop
err = flex_stop_motion(boardID, axis,
NIMC_DECEL_STOP, 0);
CheckError;
return;// Exit the Application
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
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flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Velocity Profiling Using Velocity Override
You also can use Load Velocity Override to shift from one velocity to
another while executing moves. When you use this function, you indicate
the new velocity in terms of a percentage of the originally loaded velocity
instead of explicitly stating the velocity you want to change to.
For example, 120 percent of an original velocity of 10,000 changes the
velocity to 12,000.
The transition between velocities follows all other move constraints.
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Algorithm
Figure 5-7 is a generic algorithm applicable to both C/C++ and VI code.
Waits the duration of time you specified
for the originally loaded velocity
Waits the duration of time you specified
for the newly loaded velocity
Figure 5-7. Velocity Override Algorithm
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Straight-Line Moves
LabVIEW Code
6
7
9
5
1
3
10
Read per Axis Status
10 Stop Motion
11 Motion Error Handler
11
8
2
4
1
2
3
4
Load Velocity
5
6
7
8
Set Operation Mode
Start Motion
Read per Axis Status
Load Velocity Override
9
Load Acceleration/Deceleration
Load Acceleration/Deceleration
Load S-Curve Time
Figure 5-8. Velocity-Based Move Using Velocity Override in LabVIEW
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Straight-Line Moves
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 moveTime1;// Time for the 1st segment
i32 moveTime2;// Time for the 2nd segment
i32 initialTime;
i32 currentTime;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 3;
// Set the axis number
axis = NIMC_AXIS1;
// Move time for the first segment
moveTime1 = 5000; //milliseconds
// Move time for the second segment
moveTime2 = 10000; //milliseconds
////////////////////////////////
//-------------------------------------------------
//First segment
//-------------------------------------------------
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
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// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk (s-curve value) for the move (in
sample periods)
err = flex_load_scurve_time(boardID, axis, 100,
0xFF);
CheckError;
// Set the operation mode to velocity
err = flex_set_op_mode(boardID, axis,
NIMC_VELOCITY);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
// Wait for the time for first segment
initialTime = timeGetTime();
do
{
// Check the following error/axis off status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
// Get the current time and check if time is over
for the first //segment
currentTime = timeGetTime();
if((currentTime - initialTime) >= moveTime1)
break;
Sleep (100); //Check every 100 ms
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}while (!(axisStatus) && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT)); //Exit on move
//complete/following error/axis off
//-------------------------------------------------
// Second segment
//-------------------------------------------------
//Change the velocity to 80% of the initially loaded
value
err = flex_load_velocity_override(boardID, axis, 80,
0xFF);
CheckError;
// Wait for the time for second segment
initialTime = timeGetTime();
do
{
// Check the following error/axis off status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
// Get the current time and check if time is over
for the second //segment
currentTime = timeGetTime();
if((currentTime - initialTime) >= moveTime2)
break;
Sleep (100); //Check every 100 ms
}while (!(axisStatus) && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT)); //Exit on move
complete/following error/axis off
// Decelerate the axis to a stop
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err = flex_stop_motion(boardID, axis,
NIMC_DECEL_STOP, 0);
CheckError;
// Reset velocity override back to 100%
err = flex_load_velocity_override(boardID, axis,
100, 0xFF);
CheckError;
return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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6
Arc Moves
An arc move causes a coordinate space of axes to move on a circular,
spherical, or helical path. You can move two-dimensional vector spaces in
a circle only on a 2D plane. You can move a 3D vector space on a spherical
or helical path.
algorithm that ensures the smoothest arc. This also ensures negligible
chordal error, which is error caused when two points on the surface of the
arc join with each other using a straight line. A cubic spline algorithm
generates multiple points between every two points of the arc, ensuring
smooth motion, minimum jerk, and maximum accuracy at all times. The
data path is shown in Figure 6-1.
Output to DACs or
Stepper Output
Cubic Spine
Arc Generation
Figure 6-1. Arc Move Data Path
Circular Arcs
A circular arc defines an arc in the XY plane of a 2D or 3D coordinate
space. The arc is specified by a radius, starting angle, and travel angle.
Also, like all coordinate space moves, the arc uses the values of move
constraints—maximum velocity, maximum acceleration, and maximum
deceleration.
Tip For the NI SoftMotion Controller, the arc generation also uses acceleration jerk and
deceleration jerk while calculating the arc move.
Note When you use an NI 73xx motion controller to move a motor in an arc, you can use
only trapezoidal profiles. You do not use jerk to calculate the profile for arc moves.
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Arc Moves
To move axes in a circular arc, the motion controller needs the following
information:
•
•
Radius—Specifies the distance from the center of the arc to its edge
Start Angle—Orients the arc on its plane using the starting point as an
axis to spin around. Because the starting point for a new arc is fixed
based on the current position, moving its center around the starting
point alters the orientation of a new arc. For example, Figure 6-2 shows
the effect of changing the start angle from 0° to 180°.
1
0°
180°
2
1
Original Arc
2
Arc with 180° Start Angle
Figure 6-2. Rotating Start Angle
•
Travel Angle—Indicates how far the arc travels in a 360° circle. For
example, a travel angle of 90° executes a quarter-circle, a travel angle
of 360° creates a full circle, and a travel angle of 720° creates two full
circles. A positive travel angle always creates counterclockwise
circular motion. A negative travel angle reverses the direction to create
clockwise circular motion, as shown in Figure 6-3.
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Chapter 6
Arc Moves
1
2
1
Positive Travel Angle
2
Negative Travel Angle
Figure 6-3. Positive and Negative Travel Angles
Arc Move Algorithm
Load Velocity
Move
Constraints
Load Acceleration/
Deceleration
Load Circular Arc
Radius, Start Angle,
and Travel Angle
Start Motion
Loop Waiting for Move Complete
Perform Measurements
(Optional)
Figure 6-4. Circular Arc Move Algorithm
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LabVIEW Code
4
5
6
1
2
3
7
8
9
10
1
2
3
4
Configure Vector Space
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
5
6
7
Load Circular Arc
Start Motion
Check Move Complete Status
8
9
Read per Axis Status
Read per Axis Status
10 Motion Error Handler
Figure 6-5. Circular Arc Move in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 status;
u16 moveComplete;
//Variables for modal error handling
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u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the vector space number
vectorSpace = NIMC_VECTOR_SPACE1;
////////////////////////////////
// Configure a 2D vector space comprising of axes 1
and 2
err = flex_config_vect_spc(boardID, vectorSpace,
NIMC_AXIS1, NIMC_AXIS2, 0);
CheckError;
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, vectorSpace,
10000, 0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Load Spherical Arc
err = flex_load_circular_arc (boardID, vectorSpace,
5000/*radius*/, 0.0/*startAngle*/,
180.0/*travelAngle*/, 0xFF);
CheckError;
//Start the move
err = flex_start(boardID, vectorSpace, 0);
CheckError;
do
{
axisStatus = 0;
//Check the move complete status
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err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &moveComplete);
CheckError;
// Check the following error/axis off status for
axis 1
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 2
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
// Read the communication status register and
check the modal // errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
//////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID and the
error code of the //modal error from the
error stack on the device
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flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Spherical Arcs
A 3D spherical arc defines a 2D circular arc in the X'Y' plane of a
coordinate system that is transformed by rotation in pitch and yaw from the
normal 3D coordinate space (XYZ), as shown in Figures 6-6 and 6-7.
Z
Y
X
Figure 6-6. Changing Pitch by Rotating the X Axis
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Z
Y
X
Figure 6-7. Changing Yaw by Rotating the Z Axis
In the transformed X'Y'Z' space, the 3D arc is reduced to a simpler 2D arc.
The 3D arc is defined as a 2D circular arc in the X'Y' plane of a transformed
vector space X'Y'Z'. This transformed vector space, X'Y'Z', is defined in
orientation only, with no absolute position offset. Its orientation is relative
to the XYZ vector space, and is defined in terms of pitch and yaw angles.
When rotating through the pitch angle, the Y and Y' axes stay aligned with
each other while the X'Z' plane rotates around them. When rotating through
the yaw angle, the Y' axis never leaves the original XY plane, as the
newly-defined X'Y'Z' vector space rotates around the original Z-axis.
The radius, start angle, and travel angle parameters also apply to a spherical
arc that defines the arc in two dimensions.
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Chapter 6
Arc Moves
Algorithm
Load Velocity
Move
Constraints
Load Acceleration/
Deceleration
Load Spherical Arc
Radius, Start Angle,
Travel Angle, Yaw, and Pitch
Start Motion
Loop Waiting for Move Complete
Perform Measurements
(Optional)
Figure 6-8. Spherical Arc Algorithm
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LabVIEW Code
5
6
2
4
1
9
3
7
8
10
11
1
2
3
4
Configure Vector Space
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
5
Load Spherical Arc
Start Motion
Check Move Complete Status
Read per Axis Status
9
Read per Axis Status
6
7
8
10 Read per Axis Status
11 Motion Error Handler
Figure 6-9. Spherical Arc Move in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 status;
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
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///////////////////////////////
// Set the board ID
boardID = 1;
// Set the vector space number
vectorSpace = NIMC_VECTOR_SPACE1;
////////////////////////////////
// Configure a 3D vector space comprising of axes 1,
2 and 3
err = flex_config_vect_spc(boardID, vectorSpace,
NIMC_AXIS1, NIMC_AXIS2, NIMC_AXIS3);
CheckError;
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, vectorSpace,
10000, 0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Load Spherical Arc
err = flex_load_spherical_arc (boardID, vectorSpace,
5000/*radius*/, 45.0/*planePitch*/,
45.0/*planeYaw*/, 0.0/*startAngle*/,
180.0/*travelAngle*/, 0xFF);
CheckError;
//Start the move
err = flex_start(boardID, vectorSpace, 0);
CheckError;
do
{
axisStatus = 0;
//Check the move complete status
err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &moveComplete);
CheckError;
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// Check the following error/axis off status for
axis 1
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 2
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 3
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS3, &status);
CheckError;
axisStatus |= status;
//Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
//////////////////////
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
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//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Helical Arcs
A helical arc defines an arc in a 3D coordinate space that consists of a circle
in the XY plane and synchronized linear travel in the Z-axis. The arc is
specified by a radius, start angle, travel angle, and Z-axis linear travel.
Linear travel is the linear distance traversed by the helical arc on the Z-axis,
as shown in Figure 6-10.
Z
X
Z
4
Y
X
Y
X
1
2
3
1
Side View of Helix
2
Top View of Helix
3
Isometric View of Helix
4
Linear Travel
Figure 6-10. Helical Arc
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Arc Moves
Algorithm
Load Velocity
Move
Constraints
Load Acceleration/
Deceleration
Load Helical Arc
Radius, Start Angle,
Travel Angle, Linear Travel
Start Motion
Loop Waiting for Move Complete
Perform Measurements
(Optional)
Figure 6-11. Helical Arc Algorithm
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LabVIEW Code
5
6
1
9
2
3
4
7
8
10
11
1
2
3
4
Configure Vector Space
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
5
6
7
8
Load Helical Arc
Start Motion
Check Move Complete Status 11 Motion Error Handler
Read per Axis Status
9
Read per Axis Status
10 Read per Axis Status
Figure 6-12. Helical Arc Move in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void){
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 status;
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
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// Set the board ID
boardID = 1;
// Set the vector space number
vectorSpace = NIMC_VECTOR_SPACE1;
////////////////////////////////
// Configure a 3D vector space comprising of axes 1,
2 and 3
err = flex_config_vect_spc(boardID, vectorSpace,
NIMC_AXIS1, NIMC_AXIS2, NIMC_AXIS3);
CheckError;
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, vectorSpace,
10000, 0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Load Helical Arc
err = flex_load_helical_arc (boardID, vectorSpace,
5000/*radius*/, 0.0/*startAngle*/,
720.0/*travelAngle*/, 5000 /*linear travel*/, 0xFF);
CheckError;
//Start the move
err = flex_start(boardID, vectorSpace, 0);
CheckError;
do
{
axisStatus = 0;
//Check the move complete status
err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &moveComplete);
CheckError;
// Check the following error/axis off status for
axis 1
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err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 2
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for
axis 3
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS3, &status);
CheckError;
axisStatus |= status;
//Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
//////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
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flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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7
Contoured Moves
A contoured move moves an axis or a coordinate space of axes in a pattern
that you define. The trajectory generator on the motion controller is not
used during a contoured move. The controller takes position data in the
form of an array, and splines the data before outputting it to the DACs or
stepper outputs, as shown in Figure 7-1.
User-Defined
Points
Output to DACs or
Stepper Output
Cubic Spine
Figure 7-1. Contoured Move Data Path
Overview
All positions in a contouring buffer are relative to the current position when
starting. There is an assumed 0 point that the firmware adds to the front of
the buffer of points. For example, if the contour buffer is [10, 20, 30, 40],
the positions are [0, 10, 20, 30, 40] in the firmware.
When a contour move starts it takes a snap shot of the current position
according to the following equation:
StartPosition = currentPosition.
The start position is added to each point in the buffer to get the actual
position to move through according to the following equation:
Point = StartPosition + bufferPosition[n].
If the current position is 100, and the buffer is [10, 20, 30, 40], the contour
move follows these points: [100, 110, 120, 130, 140].
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Contoured Moves
The difference between absolute contouring and relative contouring is how
the points in the buffer are treated. The previous example was of an absolute
contour move. A relative contour move treats the points as deltas according
to the following formula:
Point[n] = Point[n-1] + bufferPosition[n]
For a relative contour move that starts at position 100 and includes a buffer
with the following values: [10, 20, 30, 40], the points the contour move
follows are [100, 110, 130, 160, 200].
For contoured moves, no two consecutive points can differ by more than
215 – 1. For absolute position mode, the first position in the array passed to
the controller must be less than 215 – 1, and any two consecutive points
must be less than 215 – 1. For relative position mode, no point passed to the
controller can be greater than 215 – 1.
Arbitrary Contoured Moves
Contoured moves are useful when you want to generate a trajectory that
cannot be constructed from straight lines and arcs. To ensure that the
motion is smooth with minimum jerk, the motion controller creates
intermediate points using a cubic spline algorithm.
The move constraints commonly used to limit other types of moves, such
as maximum velocity, maximum acceleration, maximum deceleration,
and maximum jerk, have no effect on contoured moves. However, the
NI Motion Assistant prototyping tool can remap a user-defined trajectory
based on specified move constraints, preserving move characteristics and
move geometry.
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Contoured Move Algorithm
Set Operation Mode
Specify absolute or
relative contouring
• Set the Buffer Type as Position
• Total Points is the total number of
countoured points you want to load
• Buffer Size is the size of the buffer you
Configure the buffer
on the device
want to create on the device
• Set Old Data Stop to TRUE if you do
not want old data to be used
• Requested Interval is the time interval
between points
Write Buffer
Write the array of points and the
number of points you are writing
Start Motion
Loop Waiting for Move Complete
Update Contoured Data (Optional)
Check the buffer on the device
Number of points consumed
Write Buffer
Write remaining points
to onboard buffer
Perform Measurements
(Optional)
Clear the buffer that stores
contoured move points
Restore Operation Mode
Set operation mode back to absolute
position to clear contouring data
Figure 7-2. Contoured Move Algorithm
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Contoured Moves
All contoured moves are relative, meaning motion starts from the position
of the axis or axes at the time the contouring move starts. This behavior is
similar to the way arc moves work. Depending on the operation mode you
use, you can load absolute positions in the array or relative positions, which
imply incremental position differences between contouring points.
Absolute versus Relative Contouring
If an axis starts at position 0 and uses either of the following sets of
contouring points, the axis ends up at position 28. If the axis starts at
position 10, it ends up at position 38 in both cases.
1
1
3
2
6
10
14
18
22
25
27
2
28
1
Figure 7-3. Absolute Contouring Buffer Values
3
4
4
4
4
3
Figure 7-4. Relative Contouring Buffer Values
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Contoured Moves
1
2
1
Check Buffer
2
Write Buffer
Figure 7-6. Contoured Move True Case in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 status;// Temporary copy of status
u16 moveComplete;// Move complete status
i32 i;
i32 points[1994] =NIMC_SPIRAL_ARRAY;// Array of 2D
points to move
u32 numPoints = 1994;//Total number of points to
contour through
i32 bufferSize = 1000;// The size of the buffer to
allocate on the //motion controller
motion controller can // really contour
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i32* downloadData = NULL;// The temporary array that
is created to // download the points to the motion
controller
u32 currentDataPoint = 0;// Indicates the next point
in the points // array to download
i32 backlog;// Indicates the available space to
download more //points
u16 bufferState;// Indicates the state of the onboard
buffer
u32 pointsDone;// Indicates the number of points that
have been // consumed
u32 dataCopied = 0;// Keeps track of the points
copied
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the vector space number
vectorSpace = NIMC_VECTOR_SPACE1;
////////////////////////////////
// Configure a 2D vector space comprising of axes 1
and 2
err = flex_config_vect_spc(boardID, vectorSpace,
NIMC_AXIS1, NIMC_AXIS2, NIMC_NOAXIS);
CheckError;
//Set the operation mode to absolute position
err = flex_set_op_mode(boardID, vectorSpace,
NIMC_ABSOLUTE_CONTOURING);
CheckError;
// Configure buffer on motion controller memory (RAM)
// Note requested time interval is hardcoded to 10
milliseconds
err = flex_configure_buffer(boardID, 1 /*buffer
number*/, vectorSpace, NIMC_POSITION_DATA,
bufferSize, numPoints, NIMC_TRUE, 10,
&actualInterval);
CheckError;
// Send the first 1,000 points of the data
downloadData = malloc(sizeof(i32)*bufferSize);
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for(i=0;i<bufferSize;i++){
downloadData[i] = points[currentDataPoint++];
}
err = flex_write_buffer(boardID, 1/*buffer number*/,
bufferSize, NIMC_REGENERATION_NO_CHANGE,
downloadData, 0xFF);
free(downloadData);
downloadData = NULL;
CheckError;
// Start Motion
err = flex_start(boardID, vectorSpace, 0);
CheckError;
for(;;){
axisStatus = 0;
// Check for available space and download
remaining points // every 50 milliseconds
Sleep(50);
// Check to see if there are more points to
download
if(currentDataPoint < numPoints){
err = flex_check_buffer_rtn(boardID,
1/*buffer number*/, &backlog,
&bufferState, &pointsDone);
CheckError;
if(backlog >= 300){
downloadData =
malloc(sizeof(i32)*backlog);
dataCopied = 0;
for(i=0;i<backlog;i++){
if(currentDataPoint >
numPoints) break;
downloadData[i] =
points[currentDataPoint++];
dataCopied++;
}
err = flex_write_buffer (boardID, 1
/*buffer number*/, dataCopied,
NIMC_REGENERATION_NO_CHANGE,
downloadData, 0xFF);
free(downloadData);
downloadData = NULL;
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CheckError;
}
}
// Check the move complete status
err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &moveComplete);
CheckError;
if(moveComplete) break;
// Check for axis off status/following error or
modal errors
//Read the communication status register check
the modal errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
// Check the motor off status on all the axes or
axis
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
if( (axisStatus & NIMC_FOLLOWING_ERROR_BIT) ||
(axisStatus & NIMC_AXIS_OFF_BIT) ){
break;//Break out of the for loop because an axis
was killed
}
}
// Set the mode back to absolute mode to get the
motion controller out of // contouring mode
err = flex_set_op_mode(boardID, vectorSpace,
NIMC_ABSOLUTE_POSITION);
CheckError;
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// Free the buffer allocated on the motion controller
memory
err = flex_clear_buffer(boardID, 1/*buffer
number*/);
CheckError;
return;// Exit the Application
//////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
// Get the command ID, resource ID, and the
error code of the // modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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8
Reference Moves
Use reference moves to move the axes to a known starting location and
orientation. Reference functions include Find Reference, Check Reference,
Wait Reference, Read Reference Status, Load Reference Parameters, and
Get Reference Parameters.
Use the Check Reference function to determine if the Find Reference
operation is complete. This function is often placed in a loop that continues
until the status for the Find Reference operation is shown to be complete.
You can use the Wait Reference function if there is no need to monitor the
status of the Find Reference function.
Find Reference Move
Use a Find Reference move to initiate a search operation to find a reference
position. Available search operations include home switch, index pulse,
forward limit switch, reverse limit switch, center, or run sequence. Refer to
the NI-Motion VI Help or the NI-Motion Function Help for information
about reference move options.
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Reference Moves
Reference Move Algorithm
Load Velocity
Load Acceleration/
Deceleration
Move
Constraints
Load Jerk
Find Reference
Typically a Find Home
Loop Waiting for Find Complete
Check Reference
Find Reference
Typically a Find Index
Loop Waiting for Find Complete
Check Reference
Figure 8-1. Find Reference Move Algorithm
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Reference Moves
LabVIEW Code
1
2
3
4
5
6
7
8
1
2
3
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
4
5
6
Load S-Curve Time
Find Reference
Check Reference
7
8
9
Read per Axis Status
Check Reference
Motion Error Handler
Figure 8-2. Find Reference Move in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void){
u8 boardID;// Board identification number
u8 axis;// Axis number
f64 acceleration=100;// Acceleration value in RPS/s
f64 velocity=200;// Velocity value in RPM
u16 found, finding;// Check reference statuses
u16 axisStatus;// Axis status
u16 csr = 0;// Communication status register
i32 position;// Current position of axis
i32 scanVar;// Scan variable to read in values not
supported by
// the scanf function
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//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
//Get the board ID
printf("Enter the Board ID: ");
scanf("%d", &scanVar);
boardID=(u8)scanVar;
//Check if the device is at power up reset condition
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
if (csr & NIMC_POWER_UP_RESET ){
printf("\nThe FlexMotion device is in the reset
condition. Please initialize the device before
");
printf("running this example. The
\"flex_initialize_controller\" function will
initialize the ");
printf("board with settings selected through
Measurement & Automation Explorer.\n");
return;
}
//Get the axis number
printf("Enter the axis: ");
scanf("%d",&scanVar);
axis=(u8)scanVar;
//Flush the Stdin
fflush(stdin);
//Load acceleration and deceleration to the axis
selected
err = flex_load_rpsps(boardID, axis, NIMC_BOTH,
acceleration, 0xFF);
CheckError;
//Load velocity to the axis selected
err = flex_load_rpm(boardID, axis, velocity, 0xFF);
CheckError;
//Start the Find Reference move
NIMC_FIND_HOME_REFERENCE);
CheckError;
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//Wait for Find Reference to complete on the axis AND
also check //for modal errors at the same time
do{
//Read the current position of axis
err = flex_read_pos_rtn(boardID, axis,
&position);
CheckError;
//Display the current position of axis
printf("\rAxis %d position: %10d", axis,
position);
//Check if the axis has stopped because of axis
off or following //error
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
//Check if the reference has finished finding
err = flex_check_reference(boardID, axis, 0,
&found, &finding);
CheckError;
//Read the communication status register - check
the modal //error bit
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
if (csr & NIMC_MODAL_ERROR_MSG)
{
flex_stop_motion(boardID,NIMC_AXIS1,
NIMC_DECEL_STOP, 0);//Stop the Motion
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
//test for find reference complete, following
error, or axis //off status
}while (!(axisStatus & (NIMC_FOLLOWING_ERROR_BIT |
NIMC_AXIS_OFF_BIT)) && finding);
printf("\nAxis %d position: %10d", axis, position);
if (found)
printf("\rAxis found reference");
else
printf("\rAxis did not find reference");
printf("\n\nFinished\n");
return;// Exit the Application
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///////////////////////////////////////////////////////
/////////////
// Error Handling
//
nimcHandleError;
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the error
code of the modal
//error from the error stack on the device
flex_read_error_msg_rtn(boardID,&commandID,&reso
urceID, &errorCode);
nimcDisplayError(errorCode,commandID,resourceID)
;
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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9
Blending Moves
Use blending moves to create continuous motion between two or more
move segments.
Blending
Blending, also called velocity blending, superimposes the velocity profiles
of two moves to maintain continuous motion. Blending is useful when
continuous motion between concatenated move segments is important.
Examples of some applications that can use blending are scanning,
welding, inspection, and fluid dispensing.
Blending must occur on velocity profiles of two move segments, so the end
positions of each move segment may or may not be reached. For example,
if you are blending two straight-line moves that form a 90º angle, the
blended move must round the corner to make the move continuous. In this
case, the move never reaches the exact position where the two straight lines
meet, but instead follows the rounded corner, as shown in Figure 9-1.
2
3
1
1
Starting Position
2
End Point
3
Corner Rounded by Blending
Figure 9-1. Two Blended Straight-Line Moves
Motion controllers can perform blending between two straight-line moves,
between two arc moves, or between straight-line and arc moves. Blending
does not work for reference and contoured moves.
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Blending Moves
There are three ways you can start the second move in a blend:
•
Superimpose the two moves by starting the second move as the first
•
•
Start the second move after the first profile is complete
Start the second move after the first profile is complete and the added
delay time has elapsed
Refer to the Move Profiles section of Chapter 4, What You Need to Know
about Moves, for more information about move profiles.
Superimpose Two Moves
Superimposing two moves is the most common use of blending. In this
case, the motion controller tries to maintain continuous motion by
superimposing the two move segments such that the second move segment
starts its profile while the first move is decelerating, as shown in
Figure 9-2.
1
2
3
Velocity
Time
1
Blending Starts
2
Blend is Complete
3
Actual Velocity
Figure 9-2. Superimposing Two Moves
The velocity during the superimposition depends on the cruising velocity,
deceleration, and jerk of the first move segment, and the jerk, acceleration,
and cruising velocity of the second move segment.
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Blend after First Move Is Complete
Blending moves after the first move is complete causes the first move
segment to come to a complete stop before starting the profile of the second
segment, as shown in Figure 9-3.
1
2
Velocity
Time
1
Blending Starts
2
Blend is Complete
Figure 9-3. Blending after Move Complete
This type of blending is useful if you want to start two move segments, one
after the other, with no delay between them.
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Blending Moves
Blend after Delay
You can blend two moves after a delay at the end of the first move, as
shown in Figure 9-4.
1
2
Velocity
Time
3
1
Blending Starts
2
Blend is Complete
3
User-Defined Delay
Figure 9-4. Blending after a Delay
Blending in this manner is useful if you want to start two move segments
after a deterministic delay. The two move segments can be either
straight-line moves or arc moves.
Because blending occurs on velocity profiles, the effect of reaching the end
positions of the move segments and the maximum velocity depends on the
velocity, acceleration, deceleration, and jerk loaded for the two move
segments.
Because two move segments are always used while blending, it is very
important that you wait for the blend to complete before loading the next
move segment you want to blend.
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Chapter 9
Blending Moves
Blending Algorithm
Figure 9-5 illustrates a generic algorithm for blending moves.
Load Move Segment 1
Coordinate Space,
Move Constraints, etc.
Start Motion
Load Move Segment 2
Blend Motion
Loop Waiting for Blend Complete
Perform Measurements
(Optional)
Load Move Segment n
Blend Motion
Loop Waiting for Blend Complete
Perform Measurements
(Optional)
Figure 9-5. Blending Algorithm
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C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 vectorSpace;// Vector space number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 status;
u16 complete;//Move or blend complete status
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the vector space number
vectorSpace = NIMC_VECTOR_SPACE1;
////////////////////////////////
// Configure a 2D coordinate space comprised of axes 1,
and 2
err = flex_config_vect_spc(boardID, vectorSpace,
NIMC_AXIS1, NIMC_AXIS2, NIMC_NOAXIS);
CheckError;
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, vectorSpace, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in counts/sec^2)
err = flex_load_acceleration(boardID, vectorSpace,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk or s-curve in sample periods
err = flex_load_scurve_time(boardID, vectorSpace, 1,
0xFF);
CheckError;
// Set the operation mode to absolute position
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err = flex_set_op_mode(boardID, vectorSpace,
NIMC_ABSOLUTE_POSITION);
CheckError;
// Load the first straight-line segments to position
5000, 5000
err = flex_load_vs_pos(boardID, vectorSpace, 5000,
5000, 0, 0xFF);
CheckError;
// Start the move
err = flex_start(boardID, vectorSpace, 0);
CheckError;
// Load Circular Arc - making a counter-clockwise
semi-circle
err = flex_load_circular_arc (boardID, vectorSpace,
5000/*radius*/, 0.0/*startAngle*/,
180.0/*travelAngle*/, 0xFF);
CheckError;
// Blend the move
err = flex_blend(boardID, vectorSpace, 0);
CheckError;
// Wait for blend to complete before loading the next
segment
do
{
axisStatus = 0;
// Check the blend complete status
err = flex_check_blend_complete_status(boardID,
vectorSpace, 0, &complete);
CheckError;
// Check the following error/axis off status for axis
1
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for axis
2
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
//Read the communication status register and check
the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
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{
}
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
Sleep(50); //Check every 50 ms
}while (!complete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT)); //Exit on move
//complete/following error/axis off
// Load the final straightline segments to position 0, 0
err = flex_load_vs_pos(boardID, vectorSpace, 0, 0, 0,
0xFF);
CheckError;
// Wait for move to complete because this is the final
segment
do
{
axisStatus = 0;
// Check the move complete status
err = flex_check_move_complete_status(boardID,
vectorSpace, 0, &complete);
CheckError;
// Check the following error/axis off status for axis
1
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS1, &status);
CheckError;
axisStatus |= status;
// Check the following error/axis off status for axis
2
err = flex_read_axis_status_rtn(boardID,
NIMC_AXIS2, &status);
CheckError;
axisStatus |= status;
//Read the communication status register and check
the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
Sleep(50); //Check every 50 ms
}while (!complete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
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Chapter 9
Blending Moves
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the error
stack on the device
flex_read_error_msg_rtn(boardID,&commandID,
&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,resou
rceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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10
Electronic Gearing and
Camming
Use electronic gearing or camming to synchronize the movement of one or
more slave axes to the movement of a master device, which can be an
encoder, ADC, or the trajectory of another axis. The movement of the slave
axes may be at a higher or lower gear ratio than the master. For example,
every turn of the master axis may cause a slave axis to turn twice.
Gearing
Electronic gearing allows one slave motor to be driven in proportion to a
master motor or feedback sensor, such as an encoder or torque (analog)
sensor.
As the slave follows the master position at a constant ratio, the effect is
similar to that of two axes mechanically geared.
Electronic gearing has several advantages over mechanical gears. The most
notable is flexibility because you can change gear ratios on-the-fly. The
other major advantage to electronic gearing is that you can superimpose a
move over a geared axis. The superimposed move is added to the geared
profile of the slave axis, which allows the slave axis to be synchronized
on-the-fly.
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Algorithm
The device can be one of the following:
• the trajectory generator of another axis
• an encoder driven externally
• αν analog sensor connected to one
of the analog channels of the motion
controller
Designate a Master Device
Set the Gear Ratio
Gearing
Enable gearing on the
Slave Axis
The slave axis now moves in
proportion to the master device.
Load Move Constraints
Set Operation Mode
Load Target Position
Superimposed
Straight-line Move
(optional)
Start Motion on Slave Axis
Figure 10-1. Electronic Gearing Algorithm
The gear ratio is used to determine how far the slave axis must move in
proportion to the master when gearing is enabled. The gear ratio can be
absolute or relative.
Slave axis move = Master axis position × Gear ratio
Relative gearing allows you to change the gear ratio on-the-fly. The master
move is calculated based on the master reference position, which is updated
when gearing is enabled and is updated each time a new gear ratio is loaded.
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For example, if you have a gearing ratio of 2:1 (slave:master), the slave
moves 20 counts when the master device moves 10 counts.
Master Position at Enable
Master Position
Move
After Move
Master Position
1000
1010
Slave Position at Enable
Slave Position
After Move
Move
3000
Slave Position
3020
Figure 10-2. Relative Gearing at Enable
Absolute gearing behaves similarly to relative gearing in that when gearing
is enabled, the slave axis follows the master axis movement as it is defined
by the gear ratio. The difference between relative and absolute gearing is
that the reference position calculated for the master axis is updated only
when gearing is enabled. This difference is apparent when the gear ratio is
updated on-the-fly.
For example, if the gear ratio is 2:1, the current master position is 1010, the
current slave position is 3020, and the gear ratio is changed to 3:1, the slave
axis jumps from 3020 to 3030 but the master position remains the same.
Master Position
at Enable
Master Position
After Move
Move
Master Position
1000 1010
Slave Position
After Gear Change
Slave Position
at Enable
Jump
Slave Position
3000
3020 3030
Slave Position
After Move
Figure 10-3. Absolute Gearing at Gear Ratio Change
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Changing a gear ratio on-the-fly during absolute gearing allows you to
quickly synchronize the slave axis with the master axis.
Note When the gear ratio is changed on-the-fly, the slave axis moves at full torque to the
new position.
Gear Master
An axis can be geared to another axis, or to an encoder or ADC.
When you gear an axis to another axis, the slave axis follows the trajectory
generation of the master axis. For example, if you manually move the
master axis, the slave axis does not move because the trajectory generator
of the master axis is not active.
When you gear an axis to an encoder, or feedback device, the slave axis
follows the feedback generated by the encoder. If the encoder detects
movement, the slave moves proportionally to information returned by the
encoder. For example, if you twist the master axis connected to the encoder,
the slave axis also turns because it is using the position information
gathered by the encoder.
When an axis is geared to an ADC, the slave axis follows the binary value
of the ADC as if it were a position. For example, if the binary code for 2 V
is 6553, the slave axis tracks to this position.
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LabVIEW Code
1
2
3
4
5
6
7
8
9
10
11
12
1
2
3
4
5
6
Configure Gear Master
Load Gear Ratio
Enable Gearing
Wait
Load Velocity
Load Acceleration/Deceleration
7
8
9
Set Operation Mode
Load Target Position
Start Motion
10 Wait for Move Complete
11 Enable Gearing Single Axis
12 Read per Axis Status
Figure 10-4. Tracking an Encoder Using Electronic Gearing with Superimposed Move
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID; // Board identification number
u8 slaveAxis; // Slave axis number
u8 master; // Gear master
u16 csr = 0; // Communication status register
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The command ID of the function
u16 resourceID;// The resource ID of the function
i32 errorCode;// Error code
///////////////////////////////
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Chapter 10
Electronic Gearing and Camming
// Set the board ID
boardID = 1;
// Set the axis number
slaveAxis = NIMC_AXIS1;
// Master is encoder 4
master = NIMC_ENCODER4;
////////////////////////////////
// Set up the gearing configuration for the slave
axis
err = flex_config_gear_master(boardID, slaveAxis,
master);
CheckError;
//Load Gear Ratio 3:2
err = flex_load_gear_ratio(boardID, slaveAxis,
NIMC_RELATIVE_GEARING, 3/* ratioNumerator*/, 2/*
ratioDenominator*/, 0xFF);
CheckError;
//-------------------------------------------------
// Enable gearing on slave axis
//-------------------------------------------------
err = flex_enable_gearing_single_axis (boardID,
slaveAxis, NIMC_TRUE);
CheckError;
// Wait for 5,000 ms (5 seconds)
Sleep(5000);
//-------------------------------------------------
// Set up the move parameters for the superimposed
move
//-------------------------------------------------
// Set the operation mode to relative
err = flex_set_op_mode(boardID, slaveAxis,
NIMC_RELATIVE_POSITION);
CheckError;
// Load velocity in counts/s
err = flex_load_velocity(boardID, slaveAxis, 10000,
0xFF);
CheckError;
// Load acceleration and deceleration in counts/s^2
err = flex_load_acceleration(boardID, slaveAxis,
NIMC_BOTH, 100000, 0xFF);
CheckError;
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// Load the target position for the registration
(superimposed) //move
err = flex_load_target_pos(boardID, slaveAxis, 5000,
0xFF);
CheckError;
// Start registration move on the slave
err = flex_start(boardID, slaveAxis, 0);
CheckError;
err = flex_wait_for_move_complete (boardID,
slaveAxis, 0, 1000/*ms timeout*/,
20/*ms pollInterval*/, &moveComplete);
CheckError;
//-------------------------------------------------
// Disable gearing on slave axis
//-------------------------------------------------
err = flex_enable_gearing_single_axis (boardID,
slaveAxis, NIMC_FALSE);
CheckError;
return;// Exit the Application
///////////////////////
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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Electronic Gearing and Camming
Camming
Electronic camming operates similarly to electronic gearing in that the
move distance of an axis is proportional to the move distance of its master
device. Camming differs from gearing in how the master/slave ratio is
handled by the motion controller. Gearing is used in applications where a
constant gear value creates a linear slave position profile, as shown in
Figure 10-5.
Slave
Gear ratio = ∆ Slave/∆ Master
Master
∆ Master
Figure 10-5. Master/Slave Ratio in Gearing
Camming creates a more flexible profile by using more master/slave ratios.
These ratios are handled automatically by the motion controller, allowing
precise switching of the gear ratios, as shown in Figure 10-6. Camming is
used in applications where the slave axis follows a non-linear profile from
a master device.
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Chapter 10
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Slave
Master Cycle
Begins to Repeat
Master
Ratio Ratio Ratio Ratio
Ratio Ratio
1
2
3
4
1
2
Figure 10-6. Multiple Camming Gear Ratios
An example of a motion control system that can benefit from the flexibility
of electronic camming is welding parts as they travel on a conveyor belt.
Figure 10-7 shows that the welding point moves to the first position, and
then welds the material for a couple of seconds. Because the conveyor belt
keeps moving at a constant rate, the welding point must follow the material
at the same speed as the conveyor belt during the weld process. When the
welding process is finished for one item, the welding point must quickly
return to its initial position and the process repeats.
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Chapter 10
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3
1
2
Conveyor belt
Movement of the welder as it follows the object, and then returns to the initial
position
3
Welding point
Figure 10-7. Welding Application
In this application, the master device is the position encoder attached to the
conveyor belt, and the slave axis is the actuator that moves the welding
point. The slave axis repeatedly performs a two-segment movement:
1. First, it follows the material with the same speed as the conveyor belt.
2. Next, it returns to the initial position as the next material approaches.
Each segment of the move is represented with a gear ratio that dictates how
fast and which direction the welding point is moving in relative to the
conveyor belt.
This application requires the slave axis to switch from one ratio to the other
at the correct master position, otherwise the welding process is not
repeatable. If this application used gearing instead of camming, the latency,
or delay, of loading a new gear ratio might cause an accumulation of
position errors.
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Algorithm
Similar to gearing, in a camming application, a slave axis can perform any
move when camming is enabled. The move profile is superimposed over
the camming profile.
Designate a Master
Camming Device
The device can be one of the following:
• an axis
• an encoder
• an analog sensor
Set the Master Cycle
Configure the Buffer
for Slave Positions
Camming
Load the Slave Positions
to the Cam Table
Set the Master and
Slave Offset (optional)
Enable Camming
The slave axis now moves in
proportion to the master device.
Load Move Constraints
Set Operation Mode
Load Target Position
Superimposed
Straight-line Move
(optional)
Start Motion on Slave Axis
Figure 10-8. Camming Algorithm
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Camming Table
When a camming operation is active, the slave axis follows a profile that is
established using a list of master and slave positions pairs, called the
camming table. Refer to Table 10-1 for an example of a camming table.
Figure 10-9 shows that, in the welding example defined in Figure 10-7, the
conveyor belt is moving at 1,000 counts/s and the parts to be welded are
6,000 counts apart. To weld the part, the welding point must follow the part
down the conveyor belt for 2 seconds.
Time to dwell
during welding
(2 seconds)
6,000
counts
between
welding
spots
Conveyor belt speed
(1000 counts/s)
Figure 10-9. Welding Application Time and Speed Constraints
In this welding application, the slave axis must follow the part with the
same velocity as the conveyor belt while welding is in progress. Because it
takes two seconds to weld each part, the welding point and conveyor belt
have both moved 2,000 counts by the time the welding is complete. This
part of the welding application creates the first move segment.
For the second move segment, the welding point must return to its original
position so that it can weld the next part on the conveyor belt. To move the
welding point to its original position at the same time that the next part is
in the correct position on the conveyor belt, the welding point must travel
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Chapter 10
Electronic Gearing and Camming
2,000 counts in the opposite direction of the conveyor belt at half the speed
that the conveyor belt is traveling at. Figure 10-10 shows the move profile
of the first and second move segments.
Slave
2000
1000
Master
2000
4000
6000
Figure 10-10. First and Second Move Segment Profile
Table 10-1 shows the camming table that corresponds to the move profile
in Figure 10-10
.
Table 10-1. Welding Application Cam Table
Master
Time
(seconds)
Position
(counts)
Slave Position
(counts)
Ratio*
—
0
2
4
6
0
0
2000
4000
6000
2000
1000
0
1
–0.5
–0.5
* Ratio = ∆SlaveDistance / ∆MasterDistance
Table 10-1 shows that the camming cycle is 6,000 counts and is divided into
equal length segments.
Tip Because the camming cycle is 6,000 counts, the master cycle must also be
6,000 counts.
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Electronic Gearing and Camming
Each row of data defines a gear ratio. The camming profile is repeated after
a camming cycle is completed. The master position is always interpreted
inside the modulus defined by the camming cycle.
For example, initially, the master axis moves from 0 to 1000. The gear ratio
used for this move is 1:1 because the master position is in the 0 to 2000
interval. With a gear ratio of 1:1, the slave axis moves at the same speed as
the master device to position 1000.
Figure 10-11 shows that the master position in this interval is inside the
modulus.
Master
0
0
1000
1000
Slave
Figure 10-11. Master and Slave Positions at Enable
Figure 10-12 shows that if the master axis moves to position 2000, the gear
ratio does not change because the current master position is still inside the
0 to 2000 interval.
Master
0
0
1000
1000
2000
2000
Slave
Figure 10-12. Master Axis Moves within Interval
Figure 10-13 shows that when the master axis moves to position 4,000, the
gear ratio changes to –0.5. The slave axis travels half the distance that the
master axis travels, and it travels in the opposite direction.
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Master
Slave
0
0
2000
4000
4000
1000 2000
Figure 10-13. Gear Ratio Change
Figure 10-14 shows that when the master reaches position 6000, the slave
axis moves back the original position, and the camming cycle begins again.
Master
0
0
2000
4000
4000
6000
6000
Slave
1000 2000
Figure 10-14. Camming Cycle Repeats
Slave Offset
In some camming applications, the slave axis might begin and end the
camming cycle at different positions, as shown in Table 10-2.
Table 10-2. Camming Profile with and without Slave Offset
Master Position
(counts)
Slave Position
(counts)
0
0
2000
4000
6000
2000
1000
500
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Figure 10-15 shows that, after three camming cycles, the slave axis end
position is 500 counts away from the starting position (0) with the slave
offset, and that without the slave offset, the slave axis end position is
1500 counts away from the starting position (0).
With a slave offset of 500, the slave axis traverses the positions specified in
the camming table, but it does not maintain the camming ratio.
Without Offset
With Offset
Figure 10-15. Camming without Offset
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Master Offset
If the material and welding point are not initially aligned, as shown in
Figure 10-16, the master offset must be applied to consider the position
difference.
Position = 0
Position = 50
When there is no master offset,
the master cycle begins at
position 0.
Figure 10-16. Misaligned Material and Welding Point
Without the master offset, the master device position is already inside the
first interval as soon as the first material passes the welding point.
Figure 10-16 shows that the master cycle intervals are offset by 50 counts.
The master interval is shifted from 0, 2,000, 4,000, and 6,000 to 50, 2,050,
4,050, and 6,050.
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Camming starts
here at position 50
at position 50.
Figure 10-17. Camming Profile Starts when First Material Passes
Figure 10-18 shows the camming profile used for the application portrayed
in Figure 10-16 and Figure 10-17.
2500
2000
1500
1000
500
Without Master Offset
With Master Offset
Master Offset
0
0
2000
4000
6000
8000
10000
Master
Figure 10-18. Camming Profiles with and without Master Offset
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Chapter 10
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LabVIEW Code
1
2
3
6
7
8
4
5
9
10
11
12
13
1
2
3
4
5
6
7
Configure Camming Master
Configure Buffer
Write Buffer
Enable Camming Single Axis
Wait in a Sequence Structure
Set Operation Mode
Load Move Constraint
8
9
Load Target Position
Start Motion
10 Wait for Move Complete
11 Enable Camming Single Axis
12 Clear Buffer
13 Motion Error Handler
Figure 10-19. Axis to Axis Camming
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
///////////////
// Main Function
void main(void)
{
// Locals
u8 boardID = 1;
// Board ID as assigned by MAX
f64 bufferInterval = 0; // Ignored
// Master axis information
u8 masterAxis = 2;
// Master axis ID
the camming process
// Slave axis information
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u8 slaveAxis = 1;
u8 buffer = 1;
cam table
// Slave axis ID
// Buffer to contain the
i32 positionArr[] = {0, 10000, 40000, 45000, 45000,
40000, 10000, 0}; // Position array
u32 positionSize = sizeof(positionArr) / sizeof(i32);
// Number of positions in the array
NIMC_DATA data;
// Generic data structure
i32 targetPos = 10000; // Position to move to
f64 velocity = 10000; // Velocity limit for this move
u16 moveComplete;
// For error handling
u16 csr;
// Communication status
u16 commandID;
// Command ID that causes the
error
u16 resourceID;
the failed command
i32 errorCode;
controller
// Resource ID that is set on
// Error code from the
// Configuring camming profile.
// Configure the cam master & master cycle
err = flex_configure_camming_master(boardID,
slaveAxis, masterAxis, camCycle);
CheckError;
// Configure the cam table
err = flex_configure_buffer(boardID, buffer,
slaveAxis, NIMC_CAMMING_POSITION, positionSize,
positionSize, TRUE, bufferInterval, &bufferInterval);
CheckError;
// Write the data to the buffer
err = flex_write_buffer(boardID, buffer,
positionSize, NIMC_REGENERATION_NO_CHANGE, positionArr,
0xFF);
CheckError;
// Enable camming immediately
err = flex_enable_camming_single_axis(boardID,
slaveAxis, TRUE, -1.0);
CheckError;
// At this point camming is engaged or started. You
can start the master
// axis or insert other functionality here.
Sleep(5000);
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// Configure the superimposed move (optional)
// Set to absolute mode
err = flex_set_op_mode(boardID, slaveAxis,
NIMC_ABSOLUTE_POSITION);
CheckError;
// Set the maximum velocity
data.doubleData = velocity;
err = flex_load_move_constraint(boardID, slaveAxis,
TnimcMoveConstraintVelocity, &data);
CheckError;
// Set the target position
err = flex_load_target_pos(boardID, slaveAxis,
targetPos, 0xFF);
CheckError;
// Start the master axis movement
err = flex_start(boardID, slaveAxis, 0x0);
CheckError;
// Wait for move to complete
err = flex_wait_for_move_complete (boardID,
slaveAxis, 0x1, 20000, 20, &moveComplete);
CheckError;
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Disable camming
flex_enable_camming_single_axis(boardID, slaveAxis,
FALSE, -1.0);
// Clear (delete) the buffer
flex_clear_buffer(boardID, buffer);
// Check to see if there were any Modal Errors
flex_read_csr_rtn(boardID, &csr);
if (csr & NIMC_MODAL_ERROR_MSG)
{
do
{
// Get the command ID, resource and the error code of the
modal
//error from the error stack on the board
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flex_read_error_msg_rtn(boardID, &commandID,
&resourceID, &errorCode);
nimcDisplayError(errorCode, commandID, resourceID);
//Read the Communication Status Register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
{
nimcDisplayError(err,0,0);
}
return;// Exit the Application
}
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11
Acquiring Time-Sampled
Position and Velocity Data
is firmware-timed. After you command the motion controller to acquire
position and velocity data, a separate acquire data task is created in the
real-time operating system that reads time-sampled position and velocity
data into a FIFO buffer on the motion controller. You can read data in from
this buffer asynchronously from the host computer, as shown in
Figure 11-1.
Step 1: Reads the
position velocity
Acquire data task
Step 2: Copies position and
velocity data to FIFO buffer
Step 3: Reads data from
the buffer asynchronously
Figure 11-1. Acquire Data Path
The acquire data task has higher priority than any onboard programs or
housekeeping tasks, but it has a lower priority than the I/O reaction and host
communication tasks. To achieve the best possible performance, keep host
communications to a minimum when acquiring data.
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Chapter 11
Acquiring Time-Sampled Position and Velocity Data
The FIFO buffer is of a fixed size that can accommodate 4,096 samples for
one axis. One sample consists of position data, in counts or steps, and
velocity data, in counts/s or steps/s. As you increase the number of axes
from which you are acquiring data, you also decrease the total number of
samples you can acquire per axis. For example, you can acquire up to
1,024 samples per axis for four axes. You also can vary the time period
between acquired samples from 3 ms to 65,535 ms.
Algorithm
Acquire Data
Specify the number of axes, sample
period, and number of samples
Wait for Time = Sample Period
Wait until at least one sample
has been achieved
Loop if Wait Period > Sample Period
Read One Sample
Wait more than the sample period
to allow the controller to fill the FIFO
Figure 11-2. Acquire Data Algorithm
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Chapter 11
Acquiring Time-Sampled Position and Velocity Data
The data must be read one sample at a time. A four-axis sample uses the
following pattern for returning the data.
Axis 1 position
Axis 1 velocity
Axis 2 position
Axis 2 velocity
Axis 3 position
Axis 3 velocity
Axis 4 position
Axis 4 velocity
If you request 1,024 samples, you must read each of the 1,024 samples
individually.
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Chapter 11
Acquiring Time-Sampled Position and Velocity Data
LabVIEW Code
Figure 11-3 acquires data for two axes, 200 samples, and three
milliseconds apart.
1
2
3
1
Acquire Trajectory Data
2
Read Trajectory Data
3
Motion Error Handler
Figure 11-3. Acquire Data Using LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u16 csr = 0;// Communication status register
i32 i;
u16 axisMap;// Bitmap of axes for which data is
requested
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i32 axis1Positions[200];// Array to store the
positions (1)
i32 axis1Velocities[200];// Array to store
velocities(1)
i32 axis2Positions[200];// Array to store the
positions (2)
i32 axis2Velocities[200];// Array to store
velocities(2)
u16 numSamples = 200;// Number of samples
i32 returnData[4];// Need size of 4 for 2 axes worth
of data
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Axes whose data needs to be acquired
axisMap = ((1<<1) | (1<<2)); // Axis 1 and axis 2
////////////////////////////////
err = flex_acquire_trajectory_data(boardID, axisMap,
numSamples, 3/* ms time period*/);
CheckError;
Sleep(numSamples * 3/* ms time period*/);
for(i=0; i<numSamples; i++){
Sleep (2);
// Read the trajectory data
err = flex_read_trajectory_data_rtn(boardID,
returnData);
CheckError;
// Two axes worth of data is read every sample
axis1Positions[i] = returnData[0];
axis1Velocities[i] = returnData[1];
axis2Positions[i] = returnData[2];
axis2Velocities[i] = returnData[3];
}
return;// Exit the Application
//////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
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// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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12
Synchronization
You can synchronize NI motion controllers with NI data and image
acquisition devices using breakpoints and high-speed captures.
or velocity. Synchronizing position and velocity information with the
external world allows you to coordinate measurements with moves. You
can program the motion controller to trigger another device at specified
positions using RTSI or a pin on the Motion I/O connector. This
functionality is called breakpoints, which are divided into Absolute
Breakpoints, Relative Position Breakpoints, and Periodically Occurring
Breakpoints.
In some cases, it may be necessary to synchronize position with some
measurement occurring external to the motion controller. For example,
you might be aligning two fiber optic cables, in which case the maximum
optical power needs to correspond with the alignment position. To align the
fibers, the external device that is recording the optical power must trigger
the motion controller so that positions and optical power measurements can
be synchronized and analyzed. This functionality is known as High-Speed
Capture or trigger inputs. The motion controller can be triggered by
another device using RTSI or externally using a pin on the Motion I/O
connector. When triggered, the motion controller can latch the current
position of the encoder, which can be read and recorded.
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Table 12-1 shows the availability of breakpoint modes on each NI motion
controller.
Table 12-1. Breakpoint Modes on NI Motion Controllers
NI 7340, NI 7330, and
Breakpoint Mode
Absolute*
Relative*
NI 7350
NI 7390
Y
Y
Y
N
Y
Y
Y
N
Y
N
Periodic
Modulus
Buffered
* Available in buffered and single operation for NI 7350 and in single operation only for
all other controllers
Note If you are using a data or image acquisition device with your motion control system,
be aware that the NI SoftMotion Controller does not support the RTSI bus.
Note Breakpoints are not supported on the NI SoftMotion Controller.
Note When you are using the NI SoftMotion Controller with an Ormec device, you can
use two high speed captures per axis.
Absolute Breakpoints
Absolute position breakpoints allow you to trigger external activities as
the motors reach specified positions. For example, if you need to use an
image acquisition device to capture an image from a certain position while
the device under test is in continuous motion, the motion controller must be
able to trigger the image acquisition device as it reaches those positions.
The current position is continuously compared against the specified
breakpoint position by the encoder circuitry to produce a latency of less
than 100 ns.
After a breakpoint triggers, you must re-enable it for the breakpoint to work
again. In certain cases, such as buffered and periodic breakpoints, the
motion controller automatically re-enables the breakpoints.
The implementation for absolute breakpoints is divided into the buffered
breakpoint and single position breakpoint methods.
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Note All breakpoints can be affected by jitter in the motion control system. For example,
if you have a very small breakpoint window, the jitter in the motion control system could
cause the position to change enough to reach the breakpoint when a breakpoint is not
intended. Increase the size of the breakpoint window to compensate for system jitter.
Buffered Breakpoints (NI 7350 only)
Instead of enabling breakpoints in your application at the software level,
you can create a buffer of breakpoints that you can pre-load into the motion
controller. The motion controller automatically arms the next breakpoint in
the buffer when the preceding breakpoint triggers. Therefore, enabling
breakpoints occurs on a firmware-timed basis, which enables you to use a
higher bandwidth.
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Buffered Breakpoint Algorithm
Figure 12-1 shows the basic algorithm for implementing buffered
breakpoints.
Load Breakpoint Array
Configure the onboard buffer
• Set the buffer type to breakpoint positions
• Total Points is the total number of
breakpoint positions you want to load
• Buffer Size is the size of the buffer you
want to create on the device.
Write buffer
Write the array of breakpoint
positions and the number of points
• Set Old Data Stop to TRUE if you do not
want old data to be used
• Requested Interval = 0
Configure breakpoint
for buffered mode
Enable the breakpoint
Loop checking for buffered breakpoints usage
Update breakpoint array
Check the onboard buffer
(optional)
Check the number of
breakpoints consumed
Write buffer (optional)
Write remaining breakpoint
positions to onboard buffer
Clear buffer
Figure 12-1. Buffered Breakpoint Algorithm
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LabVIEW Code
3
1
2
4
5
6
7
1
2
3
Configure Buffer
Write Buffer
Configure Breakpoint
4
5
Enable Breakpoint Output
Check Buffer
6
7
Clear Buffer
Motion Error Handler
Figure 12-2. Buffered Position Breakpoint in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main function
void main (void)
{
// Resource variables
u8boardID = 1;// Board identification number
u8axis = NIMC_AXIS1;// Axis number
u8 buffer = 1;// Buffer number
// Modal error handling variables
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
u16 csr = 0;// Communication status
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// Buffer resources
i32 breakpointPositions[] = {1000, 1100, 1200, 1300,
1400, 1500, 1600};
u16 numberOfPoints = 7;// Number of breakpoints
f64 actualInterval;// Required in the function call
but not being //used
f64 requestedInterval = 10.0;// Required in the
function call but //not being used
u32 backLog;// Number of space available in buffer
u16 bufferState;// Buffer state
u32 pointsDone;// Number of breakpoints done or
consumed
// Configure the buffer for buffered breakpoint
err = flex_configure_buffer(boardID, buffer,axis,
NIMC_BREAKPOINT_DATA, numberOfPoints,
numberOfPoints,NIMC_TRUE, requestedInterval,
&actualInterval);
CheckError;
// Write the breakpoint position to the buffer
err = flex_write_buffer(boardID, buffer,
numberOfPoints, NIMC_REGENERATION_NO_CHANGE,
breakpointPositions, 0xFF);
CheckError;
// Configure the breakpoint to be buffered breakpoint
err = flex_configure_breakpoint(boardID, axis,
NIMC_ABSOLUTE_BREAKPOINT, NIMC_PULSE_BREAKPOINT,
NIMC_OPERATION_BUFFERED);
CheckError;
// Enable the breakpoint
err = flex_enable_breakpoint(boardID, axis,
NIMC_TRUE);
CheckError;
// Poll the status of the buffer, if you have more
breakpoint //positions to write, insert
flex_write_buffer call here.
do
{
// Check the buffer status
err = flex_check_buffer_rtn(boardID, buffer,
&backLog, &bufferState, &pointsDone);
CheckError;
Sleep(50);
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} while ((pointsDone != numberOfPoints) ||
(bufferState != NIMC_BUFFER_DONE));
// Clear the buffer
err = flex_clear_buffer(boardID, buffer);
CheckError;
return;
///////////////////////////////////////////////////
/////////////
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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Single Position Breakpoints
Single position breakpoints execute one breakpoint per enabling.
Single Position Breakpoint Algorithm
Figure 12-3 shows the basic algorithm for implementing single position
breakpoints.
Configure breakpoint
Configure breakpoint
for absolute mode
Load breakpoint position
Absolute position where
you want to trigger an event
Enable breakpoint
Wait for
breakpoint to occur
Load a new
breakpoint position
Figure 12-3. Single Position Breakpoint Algorithm
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LabVIEW Code
4
5
1
2
3
1
2
Configure Breakpoint
Load Breakpoint Position
3
4
Enable Breakpoint Output
Read per Axis Status
5
Motion Error Handler
Figure 12-4. Single Position Breakpoint in LabVIEW
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Refer to Figure 12-5 for an example of how to route this breakpoint
using RTSI.
5
6
1
2
3
4
1
2
Select Signal
Configure Breakpoint
3
4
Load Breakpoint Position
Enable Breakpoint Output
5
6
Read per Axis Status
Motion Error Handler
Figure 12-5. Single Position Breakpoint With RTSI Using LabVIEW
After the breakpoint is routed through RTSI, the trigger appears on both
the RTSI line and the breakpoint line on the Motion I/O connector.
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 breakpointPosition[3] = {10000, 15000, 20000};
i32 i;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
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///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
// Route breakpoint 1 to RTSI line 1
err = flex_select_signal (boardID, NIMC_RTSI0
/*destination*/, NIMC_BREAKPOINT1/*source*/);
CheckError;
// Configure the breakpoint
err = flex_configure_breakpoint(boardID, axis,
NIMC_ABSOLUTE_BREAKPOINT /*mode*/,
NIMC_SET_BREAKPOINT /*action*/,
NIMC_OPERATION_SINGLE /*single operation*/);
CheckError;
for(i=0; i<3; i++){
// Load breakpoint position - where breakpoint
should occur
err = flex_load_pos_bp(boardID, axis,
breakpointPosition[i], 0xFF);
CheckError;
// Enable the breakpoint on axis 1
err = flex_enable_breakpoint(boardID, axis,
NIMC_TRUE);
CheckError;
do
{
// Check the breakpoint status
err = flex_read_axis_status_rtn(boardID,
axis, &axisStatus);
CheckError;
// Read the communication status register
and check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check for modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
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}
Sleep (10); //Check every 10 ms
}while (!(axisStatus & NIMC_POS_BREAKPOINT_BIT));
// Wait for breakpoint to be triggered
}
return;// Exit the Application
//////////////////////
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Relative Position Breakpoints
Relative position breakpoints trigger events based on a change in position
relative to the position at which the breakpoint was enabled.
Instead of keeping track of absolute positions and the current position,
you can use relative breakpoints to specify the breakpoint relative to the
position where the breakpoint is enabled.
For example, if you are creating a motion control system to control the
two-dimensional movement of a microscope, you might use relative
position breakpoints to move the microscope a specific distance in a
direction, and then hit a breakpoint that triggers a camera snap. The relative
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breakpoint is useful in this example because the current position is not
important. The application must move the axis a specific number of counts
from wherever it is, and then generate a breakpoint.
Note All breakpoints can be affected by jitter in the motion control system. For example,
cause the position to change enough to reach the breakpoint when a breakpoint is not
intended. Increase the size of the breakpoint window to compensate for system jitter.
Relative Position Breakpoints Algorithm
Figure 12-6 shows the basic algorithm for relative breakpoints.
Configure breakpoint
Configure breakpoint
for relative mode
Load breakpoint position
Relative position where
you want to trigger an event
Enable breakpoint
Wait for breakpoint
to cause a trigger
Figure 12-6. Relative Position Breakpoints Algorithm
Notice that relative breakpoints are not ideal for periodic breakpoints.
There is a latency between the time a breakpoint generates and is
re-enabled. If the axis is moving at sufficient velocity, the breakpoint
re-enables only after the axis has moved slightly. Because a relative
breakpoint generates relative to the position the axis was in when the
breakpoint was enabled, the latency between generation and re-enabling
For example, the actual breakpoints might occur at positions 5,000; 10,003;
15,006; and 20,012. In this example, the axis moves three counts between
a breakpoint and the subsequent re-enabling. For exact distances between
breakpoints at high speeds, use Buffered Breakpoints (NI 7350 only) or
Periodically Occurring Breakpoints.
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LabVIEW Code
In this example, a breakpoint generates and then is re-enabled 5,000 counts
from where the move starts. The following code examples are designed to
illustrate the relative breakpoint algorithm only. These examples are not
complete.
5
4
1
2
3
6
1
2
Select Signal
Configure Breakpoint
3
4
Load Breakpoint Position
Enable Breakpoint Output
5
6
Read per Axis Status
Motion Error Handler
Figure 12-7. Relative Position Breakpoint with RTSI Using LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 breakpointPosition = 5000;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
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// Set the axis number
axis = NIMC_AXIS1;
///////////////////////////////
// Route breakpoint 1 to RTSI line 1
err = flex_select_signal (boardID, NIMC_RTSI1
/*destination*/, NIMC_BREAKPOINT1/*source*/);
CheckError;
// Configure Breakpoint
err = flex_configure_breakpoint(boardID, axis,
NIMC_RELATIVE_BREAKPOINT, NIMC_SET_BREAKPOINT, 0);
CheckError;
// Load breakpoint position, which is position where
breakpoint should occur
err = flex_load_pos_bp(boardID, axis,
breakpointPosition, 0xFF);
CheckError;
for(;;){
// Enable the breakpoint on axis 1
err = flex_enable_breakpoint(boardID, axis,
NIMC_TRUE);
CheckError;
do
{
// Check the breakpoint status
err = flex_read_axis_status_rtn(boardID,
axis, &axisStatus);
CheckError;
// Read the communication status register
and check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check for modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
Sleep (10); // Check every 10 ms
}while (!(axisStatus & NIMC_POS_BREAKPOINT_BIT));
// Wait for breakpoint to be triggered
}
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return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Periodically Occurring Breakpoints
NI-Motion allows you to program the motion controller to generate
multiple breakpoints at fixed and exact intervals, regardless of the direction
of travel or velocity.
There are two ways to create periodically occurring breakpoints using
NI-Motion functions, depending on which motion controller you have.
For the NI 7350 controller, use periodic breakpoints. For NI 7330, NI 7340,
and NI 7390 controllers, use modulo breakpoints.
Note All breakpoints can be affected by jitter in the motion control system. For example,
if you have a very small breakpoint window, the jitter in the motion control system could
cause the position to change enough to reach the breakpoint when a breakpoint is not
intended. Increase the size of the breakpoint window to compensate for system jitter.
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Periodic Breakpoints (NI 7350 only)
Periodic breakpoints require that you specify an initial breakpoint and an
ongoing repeat period. When enabled, the periodic breakpoints begin when
time the axis moves a distance equal to the repeat period, with no
re-enabling required.
For example, if an axis is enabled at position zero, the initial breakpoint is
set for position 100, and the breakpoint period is set at 1,000, then the axis
behaves as shown in Figure 12-8.
–900 100 1100
2100
3100
Direction
= Current Position
= Breakpoint
= Armed Breakpoint
Figure 12-8. Periodic Breakpoint Every 1,000 Counts/Steps
Periodic Breakpoint Algorithm
Figure 12-9 shows the basic algorithm for periodic breakpoints.
Configure breakpoint
Load breakpoint bosition
Load the initial breakpoint
Load breakpoint modulus
Load the breakpoint period
Enable breakpoint
Figure 12-9. Periodic Breakpoint Algorithm
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LabVIEW Code
1
2
3
4
5
6
7
8
1
2
3
Configure Breakpoint
Load Breakpoint Position
Load Breakpoint Modulus
4
5
6
Enable Breakpoint Output
Load Target Position
Start Motion
7
8
Read per Axis Status
Motion Error Handler
Figure 12-10. Periodic Breakpoint Output
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID; //Board Identification number
u8 axis; // Axis
u16 csr* 0; // Communication Status Register
u8 profileStatus; // Profile Complete Status
u8 bpStatus; // Breakpoint found Status
i32 bpPos; // Breakpoint Position
i32 bpPer; // Breakpoint Period
i32 currentPos; // Current Position
u16 axisStatus; // Status of the axis
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//Variables for modal error handling
u16 commandID; // The commandID of the function
u16 resourceID; // The resource ID
i32 errorCode;
//Get the board ID
printf("Enter the Board ID: ");
scanf("%u", &boardID);
//Get the axis number
printf("Enter a axis number: ");
scanf("%u",&axis);
//Get the Target Position
printf("Enter a target position: ");
scanf("%ld",&targetPos);
//Get the Breakpoint Position
printf("Enter a breakpoint position: ");
scanf("%ld",&bpPos);
//Get the Breakpoint Period
printf("Enter a breakpoint period: ");
scanf("%ld",&bpPer);
//Configure the breakpoint to be absolute
err =
flex_configure_breakpoint(boardID,axis,NIMC_PERIODI
C_BREAKPOINT,NIMC_NO_CHANGE,0);
CheckError;
//Load the position to start breakpoints
err = flex_load_pos_bp(boardID,axis,bpPos,0xFF);
CheckError;
//Set the Period
err = flex_load_bp_modulus(boardID,axis,bpPer,0xFF);
CheckError;
//Enable the breakpoint
err =
flex_enable_breakpoint(boardID,axis,NIMC_TRUE);
CheckError;
//Load a target position
err =
flex_load_target_pos(boardID,axis,targetPos,0xFF);
CheckError;
//Start the motion
err = flex_start(boardID,axis,0);
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CheckError;
printf("\n");
do
{
//Read the axis status
err =
flex_read_axis_status_rtn(boardID,axis,&axisStat
us);
CheckError;
err =
flex_read_pos_rtn(boardID,axis,¤tPos);
CheckError;
//Check the breakpoint bit
bpStatus = !((axisStatus &
NIMC_POS_BREAKPOINT_BIT)==0);
//Check the profile complete bit
profileStatus = !((axisStatus &
NIMC_PROFILE_COMPLETE_BIT)==0);
printf("Current Position=%10d Breakpoint
Status=%d Profile
Complete=%d\r",currentPos,bpStatus,profileStatus
);
//Check for modal errors
err = flex_read_csr_rtn(boardID,&csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
flex_stop_motion(boardID,NIMC_VECTOR_SPA
CE1, NIMC_DECEL_STOP, 0);//Stop the
Motion
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
}while(!profileStatus);
printf("\nFinished.\n");
return; // Exit the Application
///////////////////////////////////////////////////
//////////////////////
// Error Handling
//
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nimcHandleError;
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource and the
error code of the modal
//error from the error stack on the board
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID,&errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the Communication Status Register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else // Display regular error
nimcDisplayError(err,0,0);
return; // Exit the Application
}
Modulo Breakpoints (NI 7330, NI 7340 and NI 7390 only)
Modulo breakpoints use a breakpoint window, which defines an area
around the current position. The two breakpoints around the current
position are always enabled.
breakpoint position is the offset from absolute zero.
For example, to create a breakpoint every 500 counts, set the repeat period
to 500 and the breakpoint position to 0. If the breakpoint is enabled when
the axis is at 710, the breakpoints at 1000 and 500 are both armed, as shown
in Figure 12-11.
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–1000
–500
0
500
1000
= Current Position
= Breakpoint
= Armed Breakpoint
Figure 12-11. Breakpoint Modulus of 500
As another example, if you set the breakpoint repeat period to be 2000
counts and the offset to be –500, breakpoints occur at –4500, –2500, –500,
1500, 3500. If the breakpoint is enabled when the axis is at 2210, the
breakpoints at 1500 and 3500 are both armed, as shown in Figure 12-12.
–4000 –2000
0
2000
4000
–4500
–2500
–500
1500
3500
= Current Position
= Breakpoint
= Armed Breakpoint
Figure 12-12. Breakpoint Modulus of 2000 with an Offset of 500
Each time a breakpoint occurs, re-enable it to load the next breakpoint.
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Modulo Breakpoints Algorithm
Figure 12-13 shows the basic algorithm for modulo breakpoints.
Configure breakpoint
Configure breakpoint for modulo mode
Load breakpoint repeat period
Load breakpoint modulus
Load breakpoint position
Position where you want to trigger an
event every time regardless of direction
Enable breakpoint
Wait for breakpoint
to cause a trigger
Figure 12-13. Modulo Breakpoints Algorithm
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LabVIEW Code
2
1
3
4
5
6
1
2
Configure Breakpoint
Load Breakpoint Modulus
3
4
Load Breakpoint Position
Enable Breakpoint Output
5
6
Read per Axis Status
Motion Error Handler
Figure 12-14. Modulo Breakpoint Using LabVIEW
1
2
3
4
5
6
7
1
2
3
Configure Breakpoint
Load Breakpoint Modulus
4
5
Load Breakpoint Position
Enable Breakpoint Output
6
7
Read per Axis Status
Motion Error Handler
Figure 12-15. Modulo Breakpoint with RTSI Using LabVIEW
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C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
// Route breakpoint 1 to RTSI line 1
err = flex_select_signal (boardID, NIMC_RTSI1
/*destination*/, NIMC_BREAKPOINT1/*source*/);
CheckError;
//Configure Breakpoint
err = flex_configure_breakpoint(boardID, axis,
NIMC_MODULO_BREAKPOINT, NIMC_SET_BREAKPOINT,
NIMC_OPERATION_SINGLE);
CheckError;
// Load Breakpoint Modulus - repeat period
err = flex_load_bp_modulus(boardID, axis, 500,
0xFF);
CheckError;
// Load Breakpoint Position - position at which
breakpoint should //occur every modulo
err = flex_load_pos_bp(boardID, axis, 0, 0xFF);
CheckError;
for(;;){
// Enable the breakpoint on axis 1
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err = flex_enable_breakpoint(boardID, axis,
NIMC_TRUE);
CheckError;
do
{
// Check the move complete
status/following error/axis off //status
err = flex_read_axis_status_rtn(boardID,
axis, &axisStatus);
CheckError;
// Read the communication status register
and check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
Sleep (10); //Check every 10 ms
}while (!(axisStatus & NIMC_POS_BREAKPOINT_BIT));
// Wait for breakpoint to be triggered
}
return;// Exit the Application
//////////////////////
// Error Handling
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the error
code of the modal //error from the error stack on
the device
flex_read_error_msg_rtn(boardID,&commandID,&reso
urceID, &errorCode);
nimcDisplayError(errorCode,commandID,resourceID)
;
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
else// Display regular error
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nimcDisplayError(err,0,0);
return;// Exit the Application
}
High-Speed Capture
Some motion control applications require that you execute a move and
record the locations where external triggers happen. To accomplish this,
you must use the high-speed capture functionality of NI motion controllers.
The implementation for high-speed capture is divided into the buffered and
non-buffered high-speed capture methods.
Buffered High-Speed Capture (NI 7350 only)
Buffered high-speed capture lets you create a buffer that holds captured
positions that you can read asynchronously from the motion controller.
The motion controller automatically arms the next high-speed capture, and
writes the captured high-speed data into its onboard buffer. The enabling of
high-speed capture occurs on a firmware-timed basis, which provides
better frequency than the non-buffered high-speed capture method.
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Buffered High-Speed Capture Algorithm
Configure high-speed capture
• Set the buffer type to be high-speed
capture positions
• Total Points is the total number of
high-speed capture positions you
want to store
• Buffer Size is the size of the buffer
you want to create on the board
• Set Old Data Stop to TRUE if you do
not want old data to be used
Configure a buffer
on the controller
Enable high-speed capture
Loop checking for captured data array usage
Read captured position
Check buffer on the device
(optional)
Check number of captured
positions available to read
Read buffer (optional)
Read captured positions to free
the buffer for more data to be written
Figure 12-16. Buffered High-Speed Capture Algorithm
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LabVIEW Code
4
5
6
7
1
2
3
1
2
3
Configure Buffer
Configure High-Speed Capture
Enable High-Speed Capture
4
5
Check Buffer
Read Buffer
6
7
Clear Buffer
Motion Error Handler
Figure 12-17. Buffered High-Speed Capture in LabVIEW
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// Axis number
u16 csr = 0;// Communication status register
i32 bufferSize = 100;// The size of the buffer to
allocate on the //motion controller
u32 totalPoints = 100;// The number of high speed
capture to //acquire
i32 capturedPositions[100];// Array to store the
captured //positions
f64 actualInterval;// The interval at which the
motion controller can //really contour
u32 backlog;// Indicates the available space for
captured positions
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u32 pointsDone;// Indicates the number of points that
have been //consumed
u16 bufferState;// Indicates the state of the onboard
buffer
u32 currentDataPoint = 0;// Indicates the next points
to be read //from the buffer
i32* readBuffer = NULL;// The temporary array that is
created to //read captured positions
u32 i;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
// Configure buffer on motion controller memory (RAM)
// Notice requested time interval is hardcoded to 10
milliseconds
err = flex_configure_buffer(boardID, 1 /*buffer
number*/, axis, NIMC_HS_CAPTURE_READBACK,
bufferSize, totalPoints, NIMC_TRUE, 10,
&actualInterval);
CheckError;
// Configure High-Speed Capture
err = flex_configure_hs_capture(boardID, axis,
NIMC_HS_LOW_TO_HIGH_EDGE, NIMC_OPERATION_BUFFERED);
CheckError;
// Enable the high-speed capture on axis
err = flex_enable_hs_capture(boardID, axis,
NIMC_TRUE);
CheckError;
do
{
err = flex_check_buffer_rtn(boardID, 1/*buffer
number*/, &backlog, &bufferState, &pointsDone);
CheckError;
// Check backlog for captured position in buffer
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if (backlog > 0)
{
readBuffer =
(i32*)malloc(sizeof(i32)*backlog);
// If captured position available in the
buffer, read the //captured position from
the buffer
err = flex_read_buffer_rtn(boardID,
1/*buffer number*/, backlog, readBuffer);
for(i=0;i<backlog;i++){
if(currentDataPoint > totalPoints)
break;
capturedPositions[currentDa
taPoint] = readBuffer[i];
printf("capture pos %d\n",
capturedPositions[currentDataPoin
t]);
currentDataPoint++;
}
free(readBuffer);
readBuffer = NULL;
CheckError;
}
// Check for axis off status/following error or
any modal //errors; Read the communication status
register and check the //modal errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG){
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
Sleep(60);// Check every 60 ms
} while (bufferState != NIMC_BUFFER_DONE);
memory
err = flex_clear_buffer(boardID, 1/*buffer
number*/);
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CheckError;
return;// Exit the Application
///////////////////////////////////////////////////
//////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
err = flex_read_error_msg_rtn(boardID,
&commandID, &resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
err = flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
Non-Buffered High-Speed Capture
Non-buffered high-speed capture allows you to configure a single
high-speed capture event. For multiple high-speed captures, you must
re-enable the high-speed capture each time it triggers.
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High-Speed Capture Algorithm
Configure high-speed
capture
Enable high-speed
capture
Wait for high-speed
capture
Read the high-speed capture status
Do the required task
on trigger
This could be a starting move on an
axis or vector space, or just reading
the captured position and recording it
Read the captured position
(optional)
Figure 12-18. High-Speed Capture Algorithm
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LabVIEW Code
1
2
3
4
1
2
Configure High-Speed Capture
Enable High-Speed Capture
4
Read per Axis Status
Read Captured Position
Figure 12-19. High-Speed Capture Using LabVIEW
To trigger the high-speed capture from a RTSI line, set the Destination
parameter in Select Signal to High Speed Capture 1, as shown in
Figure 12-20.
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1
2
3
4
5
1
2
3
Select Signal
Configure High-Speed Capture
Enable High-Speed Capture
4
5
Read per Axis Status
Read Captured Position
Figure 12-20. High-Speed Capture with RTSI Using LabVIEW
C/C++ Code
The following section includes C/C++ code for executing a high-speed
capture, as well as using RTSI to execute a high-speed capture. The
following example code is not necessarily complete, and may not compile
if copied exactly. Refer to the examplesfolder on the NI-Motion CD for
files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID; // Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 capturedPositions[6]; // Array to store the
captured positions
i32 i;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
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axis = NIMC_AXIS1;
////////////////////////////////
// Route HSC 1 to RTSI line 1
err = flex_select_signal (boardID, NIMC_HS_CAPTURE1
/*destination*/, NIMC_RTSI1/*source*/);
CheckError;
//Configure High-Speed Capture
err = flex_configure_hs_capture(boardID, axis,
NIMC_HS_LOW_TO_HIGH_EDGE, 0);
CheckError;
for(i=0; i<6; i++){
// Enable the high speed capture on axis
err = flex_enable_hs_capture(boardID, axis,
NIMC_TRUE);
CheckError;
do
{
// Check the high-speed capture status
err = flex_read_axis_status_rtn(boardID,
axis, &axisStatus);
CheckError;
// Read the communication status register
and check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
Sleep (10); //Check every 10 ms
}while (!(axisStatus &
NIMC_HIGH_SPEED_CAPTURE_BIT));
// Wait for high-speed capture to be triggered
err = flex_read_cap_pos_rtn(boardID, axis,
&capturedPositions[i]);
CheckError;
return;// Exit the Application
//////////////////////
// Error Handling
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//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else //Display regular error
nimcDisplayError(err,0,0);
return; //Exit the Application
}
Real-Time System Integration Bus (RTSI)
RTSI is a dedicated high-speed digital bus designed to facilitate system
integration by low-level, high-speed, real-time communication between
National Instruments devices.
Many applications, such as scanning and alignment, synchronize
measurements made with data and image acquisition devices with position
and velocity. This synchronization requires high speeds with low latencies.
Using RTSI, the NI motion controller can share high-speed digital signals
with NI data acquisition devices, NI image acquisition devices, digital I/O,
or other NI motion devices with no external cabling and without consuming
bandwidth on the host bus. The RTSI bus also has built-in switching, so you
can route signals to and from the bus on-the-fly using software.
In addition to the breakpoint and high speed capture signals, you can route
encoder pulses over the RTSI lines, which serves as a way to trigger an
external device on every change in the encoder channels. You can route
phase A, phase B, and the index pulse of the encoder over RTSI.
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You also can create a software trigger by writing to the RTSI lines directly
from software.
You can route position breakpoints and encoder pulses using the RTSI bus
to trigger other devices. You also can configure data and image acquisition
devices to trigger high-speed captures on the NI motion controllers using
the RTSI bus.
RTSI Implementation on the Motion Controller
You can configure an onboard buffer on the motion controller and use the
buffered high-speed capture or breakpoint functionality to synchronize the
motion application with data or image acquisition.
As shown in Figure 12-21, the I/O reaction task automatically re-enables
the breakpoints or high-speed captures on the NI 7350 motion controller.
On NI 7340 motion controllers, you must write an onboard program or use
the host to perform the same re-enabling tasks.
Write the captured position to the buffer
or read the position from the buffer and enable
the breakpoint. You must create the buffer.
Host can read/update
the buffers asynchronously
To/From
data/image
acquisition device
*NI 7350 only
Latches position on
Generate trigger (breakpoint)
external trigger
at a given position
(high-speed capture)
Figure 12-21. RTSI Implementation on the Motion Controller
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Position Breakpoints Using RTSI
You can use the Select Signal function to route position breakpoints using
one of the RTSI lines. In this case, the motion controller triggers the
external device at a given position, as shown in Figure 12-22.
Source:
Destination:
Position
RTSI line
breakpoint
Figure 12-22. Position Breakpoint Using RTSI
Encoder Pulses Using RTSI
You may need to trigger the external device to acquire data every encoder
phase or on an encoder index pulse, as shown in Figure 12-23.
Source: Encoder
Destination:
phase A, phase B,
RTSI line
or index
Figure 12-23. Encoder Pulses Using RTSI
Software Trigger Using RTSI
You can use the Set I/O Port MOMO function to write directly to the RTSI
lines to trigger other devices, as shown in Figure 12-24.
Source: RTSI
software port
Destination:
RTSI line
Figure 12-24. Software Trigger Using RTSI
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High-Speed Capture Input Using RTSI
When the RTSI line receives the trigger from a data or image acquisition
device, the corresponding high-speed capture occurs, as shown in
Figure 12-25.
Destination:
High-speed
capture line
Source: RTSI line
Figure 12-25. High-Speed Capture Input Using RTSI
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13
Torque Control
To maintain constant torque or force, the sensor that returns the feedback
to the motion controller must return a value proportional to the torque or
force. The motion controller operates torque-control and position-control
systems in much the same way. The main difference is that the feedback in
position-control systems returns the current position, while the feedback in
torque-control systems returns a voltage proportional to the current force or
torque.
You can implement force feedback on NI motion controllers using either
analog feedback or by monitoring force.
Note The NI SoftMotion Controller does not support analog feedback.
Analog Feedback
In this mode, the torque or force sensor is connected to one of the analog
inputs on the NI motion controller. That analog channel is used as the
feedback sensor.
Figure 13-1. Torque Control Using Analog Feedback Flowchart
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Tuning the control loop with a force sensor, which is an analog feedback
sensor, produces the same results as with a position feedback sensor.
Depending upon the resolution you are using, the system may require
higher gains to ensure a faster response. NI motion controllers have 12-bit
or 16-bit analog inputs, whose ranges can be set from 0 V to 5 V, –5 V to
+5 V, 0 V to 10 V, and –10 V to +10 V. When you use counts for entering
the values of position, velocity, acceleration, and deceleration, you do not
need to enter the counts/revolution value for the axis.
Refer to the motion controller user manual for information about analog
input ranges.
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Torque Control Using Analog Feedback Algorithm
Map the analog sensor as
the primary feedback for
the axis that is to maintain
a constant torque or force
Load target position in
terms of volts. If you want to
maintain 5 V, load 2047
counts. This applies to a 5 V range
for ADC Channel & 12-bit ADC
Load move constraints:
max velocity, max
acceleration, and max
deceleration in volts
Set operation mode
Set to absolute mode
Start motion
Loop waiting for move complete
Update target position
(optional)
Start motion
(optional)
Figure 13-2. Torque Control Using Analog Feedback Algorithm
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LabVIEW Code
1
2
3
4
5
6
7
8
1
2
3
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
4
5
6
Set Operation Mode
Load Target Position
Start Motion
7
8
Read per Axis Status
Motion Error Handler
Figure 13-3. Torque Control Using Analog Feedback Using LabVIEW
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C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
u16 moveComplete;
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
//-------------------------------------------------
//Is is assumed that the axis being moved has an ADC
channel mapped //as its primary feedback. Position is
treated as binary volts. //Hence velocity is loaded
in binary volts/sec and acceleration as //binary
volts/sec^2.
//-------------------------------------------------
// Set the velocity for the move (in binary
volts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in binary
volts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in binary
volts/sec^2)
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err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk - s-curve time (in sample periods)
err = flex_load_scurve_time(boardID, axis, 1000,
0xFF);
CheckError;
// Set the operation mode
err = flex_set_op_mode (boardID, axis,
NIMC_ABSOLUTE_POSITION);
CheckError;
// Load Position corresponding to the voltage which
you want the //motor to maintain (2047 ~ 5V in this
example)
err = flex_load_target_pos (boardID, axis, 2047,
0xFF);
CheckError;
//Start the move
err = flex_start(boardID, axis, 0);
CheckError;
do
{
axisStatus = 0;
//Check the move complete status
err = flex_check_move_complete_status(boardID,
axis, 0, &moveComplete);
CheckError;
// Check the following error/axis off status for
axis 1
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
//Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
//Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
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}
}while (!moveComplete && !(axisStatus &
NIMC_FOLLOWING_ERROR_BIT) && !(axisStatus &
NIMC_AXIS_OFF_BIT));
//Exit on move complete/following error/axis off
return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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Chapter 13
Torque Control
Monitoring Force
You can use this second force-feedback mode if you have a position sensor
on the motor, in addition to the torque sensor. The control loop on the
motion controller closes the position and velocity loops as usual. Use MAX
to map the encoder as the feedback device for the axis.
Figure 13-4. Torque Control Using Analog Feedback Flowchart
For monitoring force, create an outer loop to monitor the torque sensor, and
move the motor based on the value read from the torque sensor.
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Torque Control Using Monitoring Force Algorithm
Map the position sensor
(encoder) as the primary
feedback for the axis that is
to maintain a constant
torque or force
Load move constraints:
max velocity, max
acceleration, and max
deceleration
Set operation mode
Set to relative mode
Loop reading the analog channel that is
connected to the force or torque sensor
Read analog sensor
Check against
required value
Update target position
(optional)
Start motion
(optional)
Figure 13-5. Torque Control Using Monitoring Force Algorithm
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Chapter 13
Torque Control
LabVIEW Code
1
2
3
4
5
6
7
8
9
1
2
3
Load Velocity
Load Acceleration/Deceleration
Load Acceleration/Deceleration
4
5
6
Set Operation Mode
Read ADC
Load Target Position
7
8
9
Start Motion
Read per Axis Status
Motion Error Handler
Figure 13-6. Torque Control Using Monitoring Force in LabVIEW
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C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 constant;// Constant force
i16 adcValue;// ADC value read
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
// constant force needed to be maintained
// corresponds to 5V for a +/- 5V ADC settings
constant = 2047;
////////////////////////////////
//-------------------------------------------------
//Is is assumed that the axis being moved has an
encoder mapped as //its primary feedback
//-------------------------------------------------
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
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err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
// Set the jerk (s-curve value) for the move (in
sample periods)
err = flex_load_scurve_time(boardID, axis, 100,
0xFF);
CheckError;
// Set the operation mode to velocity
err = flex_set_op_mode(boardID, axis,
NIMC_RELATIVE_POSITION);
CheckError;
do
{
// Read the ADC channel number 1 and calculate the
position to //be updated
err = flex_read_adc16_rtn(boardID, NIMC_ADC1,
&adcValue);
CheckError;
if( (constant - adcValue) != 0){
err = flex_load_target_pos(boardID, axis,
(constant - adcValue), 0xFF);
CheckError;
// Move based on delta force
err = flex_start(boardID, axis, 0);
CheckError;
}
// Check the move complete status/following
error/axis off //status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
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}
Sleep (50); //Check every 50 ms
}while (!(axisStatus & NIMC_AXIS_OFF_BIT)); //Exit
on axis off
return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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Chapter 13
Torque Control
Speed Control Based on Analog Value
In a system where a feed roll must run at speeds based on an input voltage,
the algorithm to maintain the speed consists of reading the analog voltage
connected to one of the analog channels on the motion controller, and
updating the speed of the axis based on the value of the voltage read. In this
system, the feedback is a normal position sensor, such as an encoder.
Speed Control Based on Analog Feedback Algorithm
Load move constraints
Set operation mode
Set to velocity mode
Start motion
Loop waiting for move complete
Read analog input
Compute new velocity
based on analog input
Load new velocity
Figure 13-7. Speed Control Based on Analog Feedback Algorithm
The analog input could be connected to a force sensor, which ensures that
the tension of a web being fed is maintained.
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Torque Control
LabVIEW Code
1
2
3
4
5
6
7
8
9
10
1
2
3
4
Load Velocity
5
6
7
Start Motion
Read ADC
Load Velocity
8
9
Start Motion
Read per Axis Status
10 Motion Error Handler
Load Acceleration/Deceleration
Load Acceleration/Deceleration
Set Operation Mode
Figure 13-8. Speed Control Based on Analog Feedback Using LabVIEW
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Torque Control
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis;// Axis number
u16 csr = 0;// Communication status register
u16 axisStatus;// Axis status
i32 constant;// Constant multiplier
i16 adcValue;// ADC value read
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
// constant to multiply the ADC value read to
calculate the //required velocity
constant = 10;
////////////////////////////////
// Set the velocity for the move (in counts/sec)
err = flex_load_velocity(boardID, axis, 10000,
0xFF);
CheckError;
// Set the acceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_ACCELERATION, 100000, 0xFF);
CheckError;
// Set the deceleration for the move (in
counts/sec^2)
err = flex_load_acceleration(boardID, axis,
NIMC_DECELERATION, 100000, 0xFF);
CheckError;
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// Set the jerk (s-curve value) for the move (in
sample periods)
err = flex_load_scurve_time(boardID, axis, 100,
0xFF);
CheckError;
// Set the operation mode to velocity
err = flex_set_op_mode(boardID, axis,
NIMC_VELOCITY);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
do
{
// Read the ADC channel number 1 and calculate the
velocity to //be updated
err = flex_read_adc16_rtn(boardID, NIMC_ADC1,
&adcValue);
CheckError;
// Set the velocity based on the ADC value read
err = flex_load_velocity(boardID, axis, (adcValue
* constant), 0xFF);
CheckError;
// Update the velocity
err = flex_start(boardID, axis, 0);
CheckError;
// Check the move complete status/following
error/axis off //status
err = flex_read_axis_status_rtn(boardID, axis,
&axisStatus);
CheckError;
// Read the communication status register and
check the modal //errors
err = flex_read_csr_rtn(boardID, &csr);
CheckError;
// Check the modal errors
if (csr & NIMC_MODAL_ERROR_MSG)
{
err = csr & NIMC_MODAL_ERROR_MSG;
CheckError;
}
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Torque Control
Sleep (50); //Check every 50 ms
}while (!(axisStatus & NIMC_AXIS_OFF_BIT)); //Exit
on axis off
return;// Exit the Application
///////////////////////////////////////////////////
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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14
Onboard Programs
This chapter provides information about how onboard programs work for
the NI SoftMotion Controller and for NI 73xx motion controllers.
Using Onboard Programs with the NI SoftMotion
Controller
To use onboard programs with the NI SoftMotion Controller, use the
LabVIEW Real-Time Module (RT) to target your application to run in the
same environment as the NI SoftMotion Controller.
Because the NI SoftMotion Controller onboard program shares the same
processor and system resources with the NI SoftMotion Controller, ensure
you consider the following points before running your application in
LabVIEW RT:
•
•
•
•
Ensure that your top level VI is configured to run at normal, above
normal, or high priority. If you are targeting LabVIEW RT for ETS,
use the timed loop instead of changing the priority of your top level VI.
Follow the guidelines in the LabVIEW Real-Time Module User
Manual. The guidelines regarding memory allocation and using shared
resources are especially important.
The jitter of the system increases with the number of devices used in
your RT system. Enable only the devices you need to use for the
current application.
Because interrupts cause jitter, National Instruments recommends you
configure your application to poll for data periodically rather than wait
on an interrupt.
You can further decrease the jitter under ETS by configuring the
Ethernet mode to be polling. You configure these settings for the RT
controller in Measurement & Automation Explorer (MAX).
Under LabVIEW RT, the NI SoftMotion Controller runs in the
background at time critical priority. The NI SoftMotion Controller is
designed to consume less than 40% of the processor bandwidth. The
rate at which the NI SoftMotion Controller updates its data is typically
1 KHz for Ormec and 100 Hz for CANopen.
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Onboard Programs
Using Onboard Programs with NI 73xx
Motion Controllers
You can use the real-time operating system on the NI 73xx motion
controller to run custom programs. This functionality allows you to offload
some motion-specific tasks from the host processor and onto the motion
controller. Using onboard variables, which are global data on the device,
arithmetic and loop operations, and efficient wait functions, you can write
onboard programs to execute parts of the motion application with almost
no host interaction. You can execute up to 10 onboard programs
simultaneously.
Onboard programs have the least priority in a preemptive multitasking
environment running on the embedded microprocessor because the primary
function of the embedded processor is supervisory control and I/O reaction.
Instead, the onboard programs run in a time-sliced manner at the lowest
priority. Each onboard program gets a default time slice of
two milliseconds, after which it relinquishes control of the processor to the
next onboard program or housekeeping task.
The host communication and I/O reaction tasks take higher priority than the
onboard programs and housekeeping tasks, as shown in Figure 14-1.
The onboard programs and housekeeping tasks are time-sliced among
themselves.
For greater control and determinism for the motion control system,
National Instruments offers the LabVIEW Real-Time (RT) module motion
control system, which consists of a PXI chassis, PXI motion controller or
controllers, LabVIEW RT, and NI-Motion driver software.
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I/O reaction
Host communications
pre-emptive tasks
2 ms time-sliced tasks
Figure 14-1. Onboard Program Priority
Note If you continuously poll data from the host, the onboard program gets preempted and
has less time to run. To keep this from happening, insert a small delay in the polling loops
on the host. Refer to the Timing Loops section of Chapter 4, What You Need to Know about
Moves, for information about programming delays in the loops.
Writing Onboard Programs
Note This section and the sections that follow it apply only to the NI 73xx motion
controllers.
Almost all NI-Motion functions that execute on the host can run onboard.
You can store up to 32 onboard programs on the motion controller. These
onboard programs remain on the motion controller until you reset it. If you
want the onboard programs to persist through a reset of the motion
controller, save them to FLASH, as shown in Figure 14-2.
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Chapter 14
Onboard Programs
1
Write the program you want to load onto onboard memory. You can use any NI-Motion functions between
Begin and End Store.
2
3
Transfer the program to onboard RAM using the host communication handler.
Store the program to FLASH memory for more permanent storage (optional).
Figure 14-2. Writing Onboard Programs
Algorithm
Begin store
Put motion controller in store mode
Load move parameters
Load the move type
Start move
End store
End the store mode
Figure 14-3. Basic Onboard Program Algorithm
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LabVIEW Code
1
2
3
4
5
7
6
1
2
3
4
Begin Program Storage
Load Target Position
Load Velocity in RPM
5
6
7
Load Accel/Decel in RPS/s
Start Motion
End Program Storage
Load Accel/Decel in RPS/s
Figure 14-4. Onboard Program in LabVIEW
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Onboard Programs
C/C++ Code
The following example code is not necessarily complete, and may
not compile if copied exactly. Refer to the examplesfolder on the
NI-Motion CD for files that are complete and compile as is.
// Main Function
void main(void)
{
u8 boardID;// Board identification number
u8 axis; // Axis number
u16 csr = 0;// Communication status register
//Variables for modal error handling
u16 commandID;// The commandID of the function
u16 resourceID;// The resource ID
i32 errorCode;// Error code
///////////////////////////////
// Set the board ID
boardID = 1;
// Set the axis number
axis = NIMC_AXIS1;
////////////////////////////////
//------------------------------------------------
// Onboard program 1. This onboard program moves axis
one clockwise //5,000 counts (steps). To execute this
onboard program call the //Run Program function.
//------------------------------------------------
// Begin onboard program storage - program number 1
err = flex_begin_store(boardID, 1);
CheckError;
// Set the operation mode to relative
err = flex_set_op_mode(boardID, axis,
NIMC_RELATIVE_POSITION);
CheckError;
// Load Target Position to move clockwise 5,000
counts(steps)
err = flex_load_target_pos(boardID, axis, 5000,
0xFF);
CheckError;
// Load Velocity in RPM
err = flex_load_rpm(boardID, axis, 100.00, 0xFF);
CheckError;
// Load Acceleration and Deceleration in RPS/sec
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err = flex_load_rpsps(boardID, axis, NIMC_BOTH,
50.00, 0xFF);
CheckError;
// Start the move
err = flex_start(boardID, axis, 0);
CheckError;
// End Program Storage
err = flex_end_store(boardID, 1);
CheckError;
return;// Exit the Application
//
// Error Handling
//
nimcHandleError; //NIMCCATCHTHIS:
// Check to see if there were any Modal Errors
if (csr & NIMC_MODAL_ERROR_MSG){
do{
//Get the command ID, resource ID, and the
error code of the //modal error from the
error stack on the device
flex_read_error_msg_rtn(boardID,&commandI
D,&resourceID, &errorCode);
nimcDisplayError(errorCode,commandID,res
ourceID);
//Read the communication status register
flex_read_csr_rtn(boardID,&csr);
}while(csr & NIMC_MODAL_ERROR_MSG);
}
else// Display regular error
nimcDisplayError(err,0,0);
return;// Exit the Application
}
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Chapter 14
Onboard Programs
Running, Stopping, and Pausing Onboard Programs
Use the Run Program, Stop Program, and Pause/Resume Program
functions to run, stop, and pause an onboard program that resides in the
onboard memory of a motion controller.
Running an Onboard Program
Run Program executes previously stored programs from RAM or FLASH.
Typically, you must call the Run Program function from the host, because
it is not possible for an onboard program to run itself. However, it is
possible to configure the motion controller to automatically run an onboard
program upon powering up the motion control system. You also can call an
onboard program from another onboard program using the Run Program
function.
Note Recursively calling an onboard program generates an error.
Stopping an Onboard Program
Stop Program ends the execution of an onboard program that is currently
running.
Stopping an onboard program using the Stop Program function completely
ends execution. It is not possible to resume execution of the stopped
onboard program, but you can re-run the program from the beginning.
You can stop an onboard program with a Stop Program function call from
the host or from another onboard program.
Note It is not possible for an onboard program to stop itself.
Tip Stopping an onboard program is different from stopping the motion of the axis or
axes. When you stop an onboard program, any moves that have started continue to run. You
must separately call the Stop Motion function to stop the motion of the axis or axes.
Pausing/Resuming an Onboard Program
The Pause/Resume Program function suspends execution of a running
onboard program, or resumes execution of a previously paused onboard
You can pause an onboard program with a function call from the host, from
the onboard program itself, or from another running onboard program.
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You can resume an onboard program with a function call from the host or
from another running onboard program.
Note It is not possible for an onboard program to resume itself.
Tip Similarly to the Stop Program function, Pause/Resume Program has no effect on
moves that have started.
Automatic Pausing
Any run-time error that occurs during execution automatically pauses the
onboard program.
An onboard program also pauses automatically when it executes the Start
function or the Blend Motion function on an axis that has been stopped by
the host, or when an axis is stopped due to a limit, home, software limit, or
following error condition.
Single-Stepping Using Pause
You can use the Pause/Resume Program function to effectively single-step
through an onboard program. To single-step, add a Pause/Resume Program
call after each function, and then resume the onboard program from the
host.
Conditionally Executing Onboard Programs
You can set conditions that affect the execution of the onboard programs.
For example, you may want the onboard program to wait until a specific
event occurs, and then continue executing.
The Wait on Condition function allows you to create onboard programs that
programs can send functions to start moves and wait for moves to complete.
The onboard program uses almost no processor time while waiting for an
event such as move complete. When the move is complete, the trajectory
generator enables the I/O reaction task, which causes the onboard program
to continue executing the next function in its sequence, as shown in
Figure 14-5.
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Onboard Programs
Onboard Program Conditional Execution Algorithm
Begin store
Put motion controller in store mode
Load move parameters
Load the move type
Start move
Wait for move event signal
End store
End the store mode
Figure 14-6. Onboard Program Conditional Execution Algorithm
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