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Position feedback for stepper motor


yfleong
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I am using Pmac2, I need to set-up a stepper motor with encoder feedback. Encoder counts x4 decode is 8192cts/rev. Most of the stepper driver do not have exact matching step size, example stepping set to 12800 pulse/rev. When running the motor, it seems that require very long settling time to reach the actual position. Any parameter need to change instead Ix30 servo loop gain?
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The most important thing to do is to ask yourself if you really want to be controlling the motor this way. Virtually everyone who tries this method runs into this type of problem due to mismatch between the command interval and the feedback interval. Your best tool for improving the settling will be to create some deadband in the control loop with Ix64 and Ix65 so that fractional count errors do not keep the servo loop active.

 

Most people get better performance from commanding the stepper drive open loop (in PMAC, feed the pulse train back to the counter with I9n0=8) and just using the encoder for confirmation, not as part of the feedback loop. This requires an extra encoder channel on the PMAC; do you have one available?

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  • 4 weeks later...

The most important thing to do is to ask yourself if you really want to be controlling the motor this way. Virtually everyone who tries this method runs into this type of problem due to mismatch between the command interval and the feedback interval. Your best tool for improving the settling will be to create some deadband in the control loop with Ix64 and Ix65 so that fractional count errors do not keep the servo loop active.

 

Most people get better performance from commanding the stepper drive open loop (in PMAC, feed the pulse train back to the counter with I9n0=8) and just using the encoder for confirmation, not as part of the feedback loop. This requires an extra encoder channel on the PMAC; do you have one available?

 

 

Thanks for your advise... I have tested the Ix30 & Ix33 need to be sensitive in order to get less position error. Not recommended to do such a way. The optimize still matching the same step and encoder resolution.

 

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