04-17-2010 08:45 AM
04-19-2010 03:55 AM
ERTUGRUL,
what kind of hardware are you using to control the motors and what deployment platform are you using for your application (e. g. PC, cRIO, PXI,...).
Thanks,
Jochen Klier
National Instruments
04-19-2010 06:50 AM
04-19-2010 08:42 AM
I'm wondering a bit how you would use a USB data acquisition device for motion control, but as long as long as you don't use this for closed loop control it could be ok.
But anyway. Here are some links to example that might help you. As you could imagine NI doesn't provide examples for labjack products, but you should be able to adapt the examples to your hardware:
Joystick Inputs with DAQ Card Outputs
Motion Control with USB Joystick
For more example code and tutorials please search ni.com for "joystick LabVIEW"
Kind regards,
Jochen
04-19-2010 10:45 AM
I don't see a problem with closed loop control. You measure things, and adjust your output accordingly.
Is this a basic potentiometer type joystick? If so, excite it with a DAC (analog output) set to perhaps ~2.4 volts. Then if you measure excitation voltage and output signal(s), you can determine the joystick ratio(s).
What type of motors do you have? Do you have a motor controller or driver of any sort, and what type of control signal does it take? Do you have feedback of desired information from the motors (position, speed), or do you not need feedback?
04-20-2010 01:29 AM
My concerns about closed loop control are related to deterministic closed loop control with loop timings in the ms- or even µs-range. This type of control requires accurate loop timing with low jitter which can't be provided by a non-deterministic operating system like Windows. USB with high first byte latencies makes things even worse.
E. g. in case of a PID controller stable loop timing is at least as important as properly tuned PID parameters.
Jochen
04-20-2010 11:18 AM
Agreed. I don't see a problem with closed loop control in general, but if the system can't tolerate jitter of up to a few milliseconds then a Windows/USB solution is likely to have problems.