RT multi-motor motion control in a closed loop system

Hello NI Community,
We have 12 stepper motors with load cells attached in line on each motor that are connected to a RT PXI chassis. We use an optical system to gather 3D data on the host computer which is used to calculate relative angles between 2 connected objects. This data is passed to the RT target as one of several feedback based control strategies that are used (relative angles, force on each load cell, motor position, etc.). Our Labview code is setup to utilize any of these control strategies for any motor, often using multiple strategies for different motors at the same time. The code deployed to our RT target is currently a single timed loop that incorporates the load cell reads, PID control calculations, motor command writes and position reads. In determining the timing of this loop we find it to be ~18Hz. We would like to integrate a new control strategy that is inefficient below 30Hz and are trying to determine how we can achieve this. It seems that our limiting factor is the constant writing/reading of each motor at ~4.6ms/motor, although this doesn't seem correct with the posted 62us speeds shown in the specs for the motion controllers. I'm not sure if this there is a setting that I am missing somewhere that is preventing me from achieving these speeds or if this is a function limitation of our hardware setup. We would like to achieve this with all 12 motors, although not all motors are always in use. The PXI components we are using are listed below.
PXI-1050 Chassis
PXI-8105 RT Controller
PXI-7344 Motion Controllers
UMI-7774 Motion Interface
Would any of the following be more advantageous than the others or is there another method someone has found useful in speeding up their systems.
Split motor read/write into another timed loop with a higher priority over the PID loop. (deterministic approach)
Create a unique read/write loop for each of the 3 Motion Controllers
Create boolean activation to ensure only the motors that are being used are incorporated in the control scheme
Sorry for the long post but I wanted to make sure I included as many details as possible. Thank you in advance for your help with this.
Brian

Hey,
Have you tried diagnosing where the problem is by seperating the processes and timing them to see what is causing the delay of the motor control to ~5ms?
Regards,
A. Zaatari
National Instruments
Applications Engineer

Similar Messages

Problem using PID toolkit and control design toolkit to design the closed loop system. (for DC motor closed loop)

Hi, i have facing some problem during i upgrade a project. This project is an opened loop system, it only achieved up to controlling the speed of motor, detecting the speed of motor, and switching the direction of motor while controlling the motor (This motor is a 12 VDC motor).
In order to improve the project, closed-loop dc motor control system will be implemented to correct the error of the motor's speed and maintaining the speed for the initial setting. I would like to use PID control method to do the closed loop system.
I already installed the PID toolkit V8.2 and control design toolkit V2.1.2, and i'm using DAQ usb 6221, LabVIEW 8.5
Below is my problem.
http://img177.imageshack.us/my.php?image=howtocreatethesetpointnx2.jpg
question: 1. How to generate a icon for set point? my setpoint is duty cycle...
2. How to feedback the output duty cycle to summing junction?
below this is my basic concept
http://img237.imageshack.us/my.php?image=closedloopbz5.jpg
Problem 2:
http://img357.imageshack.us/my.php?image=problem1yk2.jpg
question: Why PID toolkit icon cannot wire to cd series.vi?
Below is my original program...
http://rapidshare.com/files/140538836/pwm_generate-final_PSMII.vi.html

Hi Cyrus
Have you had the opportunity to see our
developer zone site on the PID toolkit? This article also has sample
code at the bottom that may help you in developing your application. I
have also linked below knowledge bases regarding setting a point
profile and generating a PWM from a digital output line.
PID toolkit
http://zone.ni.com/devzone/cda/tut/p/id/6440
How to generate a set point profile:
http://digital.ni.com/public.nsf/allkb/125F27AC143B6AFD86256C2B0004A4DC?OpenDocument
How to generate a PWM on a digital output line:
http://digital.ni.com/public.nsf/allkb/1561D31534F07D608625727900391114?OpenDocument
Thank You
Eric Reid
Thank You
Eric Reid
National Instruments
Motion R&D

In a motion Control System, What is a following error?

I am trying to understand what a "Following Error" is. I get the error number 70150 which is called a following error. When trying to execute the find home VI in the NI library

The following error only occurs in closed loop systems. It is simply the difference, in counts, between the commanded trajectory position and the actual feedback position. A good way to characterize your following error is to go into the Advanced menu of the 1-D Interactive portion of MAX, run your motors at a very low velocty (1 rpm), and watch the Following Error indicator. If it is increasing slow and steady, then you probably have the encoder resolution wrong. If it jumps up in spurts, then the encoder may be damaged. If it is increasing very fast, then either the encdoder isn't plugged in, the encoder isn't working at all, or the encoder is plugged in backwards.
I hope this helps.
Kyle V
Applications Engineer
National Instruments
www.ni.com/ask

Closed Loop or Open Loop

Dear All,
I'm currently using the DAQ card PIC-6221 to control a DC servomotor with an encoder displacement feedback. I'm using the labview program with a motor amplifier to start the motor and stop it at a specific rotational displacement, where it works by stopping the motor when the encoder feedback value reaches the input desired displacement value. The final displacement of the motor before it stops always exceeds the desired value marginally. May I know for my case,am I using an open or closed loop control? Is a PID controller a MUST for closed loop control? Is my DAQ card capable of desigining a PID controller? If so may I know how?
Also, my project requires me to toggle between the current and voltage mode control. May I know if that is possible to carry out digitally using the Labview Program as my current motor amplifier requires me to push a switch manually to toggle between Voltage and Current mode. Finally, I hope my last question is not out of this world but is it possible to use 2 amplifiers(drivers) for a single motor such that there's a chance to use both the current and voltage modes of control?
Really looking forward to the replys of you kind souls out there! Thanks!
Regards,
Oompa

Oompa,
to learn more about the general concepts of motion control, please visit this link.
In general I widely agree with JB's suggestions. I'll just add some more comments to your questions.
If you need closed loop control depends on what you try to accomplish. If you just want to generate a certain torque (current mode) that is proportional to the output voltage of your control device, you may not need to run a closed loop system. A similar statement is true for the voltage mode.
Closed loop control is especially important if you need to control the position, or if you need to run a special trajectory profile (position/velocity/torque over time)
Maybe it's possible to control the current/voltage mode of your drive with a digital signal. You will have to find out in the manual or check with the vendor.
Using two drives with a single motor doesn't seem to be recommendable. If you want to do something like that, you will need to switch the power signals with relays between the two drives, but as you are working with inductive loads this might become quite tricky and there is a risk to burn both, the motor and the drives...
Regards,
Jochen Klier
National Instruments

Closed loop control of step motors possible with 7344?

Hi All
I have been looking around here for a while for an answer to this question.
For me, a closed loop control system is correcting for following errors all the time, also when the move is complete.
If the load on a system changes, there will often be a need for compensation in order to keep the position right. Then you need a closed loop control system.
I have made a system using DC motors with a 7342 controller. We are in the process og getting a new similar system, where the manufacturer chosed stepmotors in the believe that it can be used in closed loop.
Is it really true that the NI version of closed loop is only performing a what you call a "pull-in" at the end of the move in order to correct for lost steps or flexibility of the connection between motor and object/encoder?
I would call this "backlash compensation" or something like that.
Why dont you make a real closed loop option. The control voltage from your servo motor control, could be fed into a voltage-frequency converter with a matchin sign signal.
This shouldn't be too complicated to accomplish.
/b

You are right. NI motion control boards don't apply a control algorithm
during moves when configured in closed loop stepper mode. In this mode
the board monitors the following error during the move and generates an
error when the following error limit is exceeded and they start the
pull-in moves at the end of the move if necessary.
If you really want to do PID control with stepper motors you still
could connect an external V/f converter to the DAC outputs of the board
and control the axes like DC motor axes. Some vendors implement this
feature on their board but NI has decided not to do that as we don't
think that this approach provides a good solution. Here are some reasons:
The most important issue is the fact that you could easily exceed
the maximum rate of change of the motor frequency in the case that the
following error increases during the move. For a DC motor this would mean that the
voltage of the controller increases to compensate for this error and
the motor will follow - probably with some delay, but it will follow. For
the stepper this could mean that the acceleration becomes so high
that the motor stops immediately as it can't follow with a delay like a DC motor. What
should the controller do then? Restart the move automatically? Generate
an error? There is a big chance that you end up with a system moving in a stop and go mode.
The second issue is related to the control algorithm itself. The transfer function of a stepper motor is not really linear so it will be quite hard to find good tuning parameters. A DC motor can be tuned by analyzing the step response and the Bode plot. For the reasons that I have described in 1.) this won't work for a stepper so how should you tune it?
I have talked to some motion control engineers who have tried to control steppers with a PID algorithm and they all agree that this is a real pain and it's not recommended.
So if your system requirements involve online following error compensation I strongly recommend using a DC motor.
Best regards,
Jochen Klier
National Instruments Germany

Stepper motor closed loop control using 7344

I have some question about the closed loop control of stepper motor using 7344. From the NI website I got that closed loop steppers work differently from closed loop servos. Instead of adjusting the output on each PID iteration like a servo system, closed loop steppers will do a pull-in move at the end of a move to adjust for any difference between the target position and the encoder feedback. By default, it will attempt the pull-in move three times.
Now for example I got five points: (0,0) (10,20) (30 40) ( 31 60) (50 65). The request time interval I set as 10ms. This mean that in the first 10ms, the machine should move from (0 0) to (10 20). But for some reasons the machine can not move to (10, 20), it moves to (8,16) and the first 10ms passed. In the second 10ms, how it move? Move from (8 16) to (30 40), If like this, the following error will accumulated. In practise, it is not accumulated. Is there anyone can explain something about the closed loop control of stepp motor? Thanks a lot!

Requested Interval is additional data for the Position buffer type. The Position buffer type requires a Requested Interval parameter, and indicates the time between contouring data points in milliseconds. For all other buffer types, the Requested Interval parameter is ignored.
The controller will use the closest value it can that is greater than or equal to the interval value you requested. Your time interval must be an even multiple of the PID rate.
For example, given a PID rate of 250 ms, a time interval of 11.2 ms between points is physically impossible, so a call to configure buffer with an interval of 11.2 causes the buffer to actually be configured for 11.25 ms, since 11.25 is the nearest possible interval greater than 11.2. The following table shows valid intervals for each PID rate.
My question is like this. For example I got five points: (0,0) (10,20) (30 40) ( 31 60) (50 65). The request time interval I set as 10ms. This mean that in the first 10ms, the machine should move from (0 0) to (10 20). If it is impossible for the machine to move from (0 0) to (10 20), there are two ways to solve this problem. First is the time interval is 10ms and assume it move to (8 16) within 10ms and take (8 16) as the start point and (30 40) as the end point of the second move. Second is extend the time interval, assume it takes 14ms to move from (0 0) to (10 20). After 14ms, the (10 20) is the new start point for the second move. I think it works as the second ways.If not, the following error will accumulated. Is there anyone can explain something about the closed loop control of stepp motor in detail? Thanks a lot!

Closed loop control of DC motor drive using PCI 6251

Hi
i am using NI PCI 6251 for closed loop control of dc drive.(shunt motor,220v, 0.5HP, 2.5A rated, 1500RPM)
the dc motor is fed from a bidirectional dc-dc converter. this converter works in boost mode(forword motoring) and buck mode(braking mode/battery charging)
the converter is built using mitsubishi IGBT module. at low voltage side of the converter a battery bank of 48V is connected and high voltage side the motor is connected.
An IR sensor is developed to measure the speed of the motor and a hall current sensor is used to sense the converter current.
in the control part i have an inner current control loop(PWM controller) and a outer speed control loop.both controllers are PI controller. To measure the speed i have used counter of the DAQ assistant, then frequency. then this frequency is converted to RPM using labview.after giving the speed and current signals to the controllers , then i started tunning the PI gain, but at the starting the duty cycles was 100%, so the IGBT got damaged immediately. now how to tune the controllers during the closed loop operation. the switching frequency of the converter is 20KHz.
can any body suggest me how to run the dc drive in closed loop ?
thanking you.

Hi Premenanda
The freq data receiverd from the daq assistant has the units of Hz, or in terms of motor speed, rps (rotations per second). I can see that you are trying to convert that to rpm (rotation per minute). which can be done by dividing the rps speed by 60. Instead, you are multiplying it by 60 and also comparing with 2000. the resultant multiplied value is displayed in your program only if it is smaller than 2000.which is causing the problem here.( as seen in file 'original code.png)
I have attached a file named 'modified code.png' that shows how the conversion from rps to rpm is done. Please do the required changes in your code and let me know if it works.
Attachments:
modified code.png ‏18 KB
Original code.png ‏15 KB

Simple straight line motion control with brushless motor and encoder/microswitch

I want to go build a motion control system/program using labview. I have a brushless motor and a controller and a National instrument DAC (NI USB-6009). This is how my system looks like: receive an input signal 4-20mA, this should be converted to 0-5V for the controller for speed, controller should move motor till it hits micro switch. The micro switch/encoder should generate a signal (5V) back to shut the controller. I want to record the position of the motor in labview. How do I do this? How do I set the system up? Thank you in advance

Controller from anaheimautomation: MDC151-050301
Motor:BLWSG234D-36V-4000-R3
Controller and motor go together.
The input signal for the system will be 4-20mA. Using this signal I will correlate it to a specific voltage which will drive the speed of the motor. This will displace the lead screw linearly. I will have a microswitch that will be triggered by screw and will relay a signal to shut the motor. I want find a way to record the position of the shaft/leadscrew at that specific point. I want to identify a home position, halfway position and full length travel position. I will use 3 swiches or 1 switch in three positions to identify all these points.
My end result should be whwn I turn on the system or start the program It should detect whether it is at the home position, if not travel to home then respond accordigly given an input signal(4-20mA).
How will I program such on labview...finding all the right icons to record the data is such a mess for me since i'm a beginner.
Thanks

DC motor closed loop control through labview using usb 6008

Hello
i am doing a project in which i want to control the speed of a DC motor (PID control) through labVIEW 2010. I am having a DC motor, a drive unit that regulates the voltage to the motor by getting analog voltage from 0 to 3.3V ( it can be used for both directions) and i also have a NI usb 6008 board. The problem is that i can't feed the usb 6008 with the digital signal from my hall effect speed sensor. Is it posible with this setup to control the motor?? I can also try to use the pulse as analog input and trasform the frequency into rpm's. Then i am thinking of generating an analog signal to feed the motor drive. If you have any further suggestion of a probably better hardware setup would be more than helpfull to me.
Sincerely
Jason Chaloulos

Hello Michael
Thanks for the reply. I came across those topics before and all of them are trying to generate a PWM signal as output i want to use just an analog signal output so timing on the output is not that important i guess. i am struggling on getting the frequency from the digital input signal that my hall effect sensor generates. Since the maximum speed of the motor is 3000 rpm and with my tooth wheel the maximum output frequency of the sensor will be 300Hz which i see its way less than the limitation of my ni board. Is there any tutorial documentation that might help me with this one ? Thank you in advance.
Kind regards
Jason

3_Axis Motion Control

I need to enter target positions in degrees.I am using PCI 7433 Motion controller
and Servo Motors in Closed loop condition with Incremental Encoders
Thanks and regards.
Sunil

We use http://www.jrkerr.com/index.html motor control system. This uses
low cost Pics and a serial network. The drivers are a DLL and can be
called from LabVIEW. I have built multi axis devices and it has worked
real reliable. (No problems).
A company called Compu-Motion has experience building low cost hardware and
software for mult-axis devices. Compu-Motion web site is
www.compu-motion.com. Compu-Motion could help you build the hardware or
software.
John Harmon
330-848-0460
----- Original Message -----
From: Dow Airen
Newsgroups: comp.lang.labview
Sent: Wednesday, November 24, 1999 12:33 AM
Subject: 3 axis motion control- where do I start?
>
> I have to develop a hearing aid hybrid test system which will test an
array
>
> o
f hybrids. I already have the individual hybrid test code but need some
>
> guidance with the motion control. Does anybody have any good references
>
> for me on what aspects should be considered. All I really want to do is
> step
> and test but don't know much about motor types stepper/servo etc, limits,
> calibration etc. Any tips would be greatly appreciated.
>
> Regards,
>
> Dow Airen
> Design Engineer
> Crystalaid Microelectronics P/L

7344 servo motion switching between open and closed loop operation

I have a custom end-of-line test system presently using a 4-axis 7344 servo controller to perform various functional tests on small, brushed DC motors. The system is programmed in C/C++ and uses flex motion functions to control the motor during testing. Motors are coupled to external encoder feedback and third party PWM drives running in closed-loop torque mode from an analog command signal. The system uses all four motion axis channels on the 7344 board to independently and asynchronously test up to four production motors at a time.
In closed-loop mode, the system runs without issue, satisfying the battery of testing protocols executed by this system. I now have a request to add additional test functionality to the system. This testing must be run in open loop mode. Specifically, I need to use my +/- 10v analog output command to my torque drive to send different DAC output levels to the connected motor.drive while monitoring response.
I do not believe the flex motion library or 7344 controller includes functions to easily switch between open and closed loop mode without sending a new drive configuration. I am also under the impression that I cannot reconfigure one (or more) servo controller axis channels without disabling the entire drive. As my system runs each axis channel in an asynchronous manner, any requirement to shutdown all drives each time I change modes is an unworkable solution.
I am open to all ideas that will allow asynchronous operation of my 4 motor testing stations. If the only solution is to add a second 7344 controller and mechanical relays to switch the drive and motor wiring between two separately configured servo channels, so be it. I just want to explore any available avenue before I place a price tag on this new system requirement.
Bob

Jochen,
Thank you for the quick response. The 7344 board does an excellent job running my manufacturing motor assemblies through a custom end-of-line tester in closed loop mode. A portion of the performance history and test result couples the motor through a mechanical load and external shaft. The shaft is in contact with a linear encoder that closes my servo loop.
My new manufacturing requirement is to also sample/document how the small DC motor behaves in open loop operation. Your solution is exactly what I need to perform the additional functional tests on the product I am manufacturing. I see no reason why this cannot work. I was originally concerned that I would need to reinitialize the 7344 board after changing axis configuration. Initialization is a global event and impacts all four channels on the 7344 board.
Using flex_config_axis() to change axis configuration on a single channel without disturbing other potentially running axis channels will solve my concern. It will be several weeks before I can return to the manufacturing facility where the 7344-based testing machine is located. I will update this thread once I verify a successful result.
Bob

Difference between open loop and closed loop mode when finding the index on a stepper motor axis.

I have a test system which uses a PXI-7352 motion controller with a MID-7602 stepper motor drive to position a 200 step/revolution stepper motor with an attached 1000 line encoder. The MID-7602 is configured for 64 microsteps per step, giving 12,800 microsteps and 4000 encoder counts per revolution. The system is controlled using LabView 7.1 and NI-Motion 6.13. To home the motor, I've defined a sequence in MAX which first finds the reverse limit switch and then moves forward to the encoder index pulse.
When finding its reference in open loop mode, the system its reference at the same microstep each time. When findings its reference in closed loop mode, the system finds its reference somewhere within about a 20 microstep wide range.
I hope somebody out there with more experience with this controller can describe the difference between finding the encoder index in open loop mode and finding the encoder index in closed loop mode.
Thanks,
Mark Moss

Hello Mark,
I suspect that the behavior you are experiencing has today
with the resolution difference between your encoder and your
microstepping. Let me illustrate with an
example:
Example Setup
Stepper
Motor
NI
Motion Controller
10
steps per encoder pulse (Every 10 steps the controller gets an encoder
pulse, therefore positions 0-9 all appear to be 0 to the controller)
The
system has a maximum of 3 pull in moves set
Open Loop Scenario
The
system is commanded to go to position 9.
The
controller sends out 9 pulses.
The
motor moves to position 9.
Closed Loop Scenario
The
system is commanded to go to position 9.
The
controller sends out 9 pulses.
The
motor moves to position 9.
The
controller checks its position and sees that it is still at position 0
because it has not received an encoder pulse.
Because
the controller thinks it is still at position 0, it sends another 9 pulses
as its first pull in move.
The
motor moves to position 18.
The
controller checks its position and sees that it is at position 10 because
it has only received one encoder pulse.
Because
the controller thinks it is still at position 10, it sends1 reverse pulse
as its second pull in move.
The
motor moves to position 17.
The
controller checks its position and sees that it is at position 10 because
it has only received one encoder pulse.
Because
the controller thinks it is still at position 10, it sends and additional
single reverse pulse as its third pull in move.
The
motor moves to its final position of 16.
I believe something similar is happening with your
application as it looks for the index pulse.
Because the controller does not compensate for what it perceives as
position error in open loop mode, the motor always goes to the same commanded
position. In closed loop mode, the motor
is bouncing around inside the single index encoder pulse trying to find a
certain position.
There are several recommendations I can make towards
correcting this behavior. These
recommendations are in order of effectiveness:
Setup
your system so that there are more encoder counts per revolution than
steps per revolution.
Turn
off pull-in moves by setting them to 0 in MAX.
Use an
open loop configuration.
Play
around with the pull in window in MAX.
Regards,
Luke H

NI 9505 Closed Loop Position Control Example

Hello, I have a cRIO 9073 with a NI 9505 module that I'd like to use for simple position control of a unit along a lead screw.
I don't have the softmotion module, and am trying to write a program bassed off of the "Position Control (closed loop) - NI 9505" example to control the position the small motor attached to the lead screw (Faulhaber 2342S024CR with a 512 count/rev encoder that we had laying around)
I've reviewed the manual PID tuning example, and have not had much luck getting the response that I'd like when making large position moves simply by adjusting Kp,Ki,Kd gains of the position loop, as the overshoot remains too high for this application when making large moves. The system is also oscillating about the set point, and doesn't ever seem to dampen out unless I change things other parameters on the fly such as the current limit, or current loop parameters (osciallations get worse as current limit is increased).
Can someone advise me if the components of this example are up to this task? Or on the interactions between the current limit, current loop parameters, and position loop parameters from this example, and which parameters would have the most impact on achieving desirable system performance?
Is there a VI available that can autotune such a motor?

Hello - there are many reasons why a closed loop controller can oscillate - from correct settings of controller (kp,ki,kd) to making sure signals act in the appropriate direction to deadband/friction in the actuator to badly sized signals/actuators.
Firstly, have a look at the signal your controller is outputing (ideally in LabVIEW so you can graph it). Does it oscillate - perhaps as a sawtooth, a sinewave or simply switching between maximum and minmum values. I presume the electrical motor driving the screw which is driven from some AO signal from the cRIO (could also be a PWM signal driving the motor).
I expect (from what you say about current limit) the control signal will be oscillating by switching between maximum and minimum (e.g. +10V to -10V) or oscillating like a sinewave. What values of kp, ki, kd are you using ? If kd is non-zero, set it to zero (you only need worry about this if you want to get maximum performance). Is ki non-zero ? Try setting it to zero - any better ? If you are still getting big oscillations in your control signal, keep reducing kp (e.g. half each time?) until oscillations disappear (as you reduce kp, control signal *should* get smaller - maybe not straight way though).
If this does not make oscillations go away, then it may be that you have a sign wrong in your loop - i.e. a positive control signal makes lead screw move in opposite direction controller expects. This should be a fundamental thing sorted out when setting up the loop - you could do an open test to check which way +ve voltage moves lead screw. If you find it moves in opposite direction - you can either re-wire, or put a "-1" gain on controller output.
If there is any more subtle oscillations / obersvations, then try to show some plots of the lead screw motion and control signal, as that always helps when trying to diagnose what is going wrong.
Good luck.
Consultant Control Engineer
www-isc-ltd.com

Closed loop velocity control based on load cell force

Hello,
My application is for a drill, that drills into rocks of various densities for the purpose of collecting rock core samples.
My setup has 2 motors which get controlled, one spins the drill bit at a constant velocity, the other moves the drill mechanism along a Z axis.
For efficient cutting, it is desired to apply a constant force between the drill bit and the rock. I have a load cell which measures the force being exerted by the drill bit on the rock surface, and this force can be adjusted by changing the velocity of the Z axis. So I would like to employ closed loop control to adjust the Z axis velocity to maintain a constant force on the rock.
Platform: cRIO 9073, with NI 9505 & 9215 Modules, Labview 2010 Full with RT and FPGA modules.
The load cell is by Transducer Techniques, and I use their TMO-1 module to condition the signal, the output of which is attached to an input of the 9215 module, where 0-100 lbs equates to 0-8VDC.
The motors and encoders for the Drill and Z axis are connected directly to the 9505 modules.
Right now I am using a modified version the example found in ...\examples\CompactRIO\Module Specific\NI 9505\Velocity Control (closed loop)\Velocity Control (closed loop) - NI 9505.lvproj to accomplish velocity control of the motors.
My questions are:
1) Do I have the appropriate NI hardware/software for this task?
2) With my current hardware setup, what would be an appropriate way to control my Z axis velocity rate based on Analog feedback from the load cell?
3) Development time is a critical factor, so are there any toolkits etc that are easy to get started with that would drastically decrease my development time, or do I already have everything I need?
Thank you for your time
-MK Hokie

1. Your hardware and software look appropriate assuming the motors are compatible with the 9505s. You didn't mention the NI SoftMotion module in your software list which is something you will need.
2. There are a few ways of doing this. One method would be to have a force PID loop that would attempt to maintain a force setpoint by directly outputting values to your torque loop. In this case, the drill would essentially move as fast as it could while maintaining the force setpoint. Another option is to have the force loop output a velocity setpoint. You would then have a velocity PID loop that outputs torque values to the torque loop. By adding this additional velocity loop you could have control over your maximum and minimum velocities. There are likely other alternatives as well, but these are the first two that come to mind.
3. Unfortunately there are no shipping examples that close the loop on force feedback. My advice would be to start with the NI 9505 shipping example and adapt it to your needs. There are quite a few things you will want to change though. Do you know if you will need to use the trajectory generator to move the drill into position before starting the force control?
Assuming you don't need any trajectory generation, you can scrap the entire RT portion of the NI 9505 example and just create the necessary FPGA code. On the FPGA, you won't need the Spline or Synchronization code either because this information would no longer be coming from RT. You could take these out and replace the position loop with a force loop and possibly a velocity loop and your FPGA program would basically be finished. In fact the only real motion IP that you will need is for the encoders (assuming you want velocity control) and PID. Then you would need to create an RT VI that allows you to send down enable, disable, PID gains, and setpoints.
If you do need trajectory generation, you would want to keep most of the example code the way that it is, but then program in a 'Force Mode' that utilizes the force and velocity controly as described above. You could think of it as having two different routines programmed side by side.
Regards,
Burt S

3 axis motion control- where do I start?

I have to develop a hearing aid hybrid test system which will test an array
of hybrids. I already have the individual hybrid test code but need some
guidance with the motion control. Does anybody have any good references
for me on what aspects should be considered. All I really want to do is
step
and test but don't know much about motor types stepper/servo etc, limits,
calibration etc. Any tips would be greatly appreciated.
Regards,
Dow Airen
Design Engineer
Crystalaid Microelectronics P/L

We use http://www.jrkerr.com/index.html motor control system. This uses
low cost Pics and a serial network. The drivers are a DLL and can be
called from LabVIEW. I have built multi axis devices and it has worked
real reliable. (No problems).
A company called Compu-Motion has experience building low cost hardware and
software for mult-axis devices. Compu-Motion web site is
www.compu-motion.com. Compu-Motion could help you build the hardware or
software.
John Harmon
330-848-0460
----- Original Message -----
From: Dow Airen
Newsgroups: comp.lang.labview
Sent: Wednesday, November 24, 1999 12:33 AM
Subject: 3 axis motion control- where do I start?
>
> I have to develop a hearing aid hybrid test system which will test an
array
>
> o
f hybrids. I already have the individual hybrid test code but need some
>
> guidance with the motion control. Does anybody have any good references
>
> for me on what aspects should be considered. All I really want to do is
> step
> and test but don't know much about motor types stepper/servo etc, limits,
> calibration etc. Any tips would be greatly appreciated.
>
> Regards,
>
> Dow Airen
> Design Engineer
> Crystalaid Microelectronics P/L

RT multi-motor motion control in a closed loop system

Similar Messages

Maybe you are looking for