The first thing that comes to my mind when I read your problem
description is: Why are you using a stepper motor for this task? The
application you describe is predestined to be solved with a servo
motor. In fact the best solution would be to use a servo motor with
analog feedback.
What you try to do is in fact a force control application running under
Windows. As Windows is not a real-time operating system you will never
reach a stable cycle time of 0.01 s. There will always be a
considerable amount of jitter destabilizing your control algorithm.
Even if you use a PID algorithm in your loop I'm pretty sure that the
result won't be very satisfying. Additionally stepper motors can't
handle varying loads very well and they tend to oscillate in this
scenario making it even harder to find stable control parameters.
If you use a servo motor with analog feedback you can use your analog
force signal directly as a feedback signal for the PID loop that runs
on the DSP of the 7344 under real-time conditions.
You can either use the normal move constraints as velocity and
acceleration to control the way the force increases or you could even
use contouring mode for a more sophisticated control.
This method will speed up your application very much, you will get smooth moves and stable system behavior.
Best regards,
Jochen Klier
National Instruments Germany
