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Velocity ripple


Inert Production
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Having problems controlling velocity ripple at all speeds. Dual motor drive with cross coupling enabled. It's difficult to set Kp i and d gain values manually. Low frequency ripple at around 5 Hz, causing other motors to have trouble holding position. Have a higher frequency ripple also, around 22Hz but less of a problem. Turning off contra-drive doesn't help. Any tips?
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Aloha Inert, Have you verified that there isn't any noise getting into your feedback? I would use the scope feature of the IDE with your motors absolutely still, clamped or something to make sure that your feedback sources aren't noisy. I would prefilter as a last resort since that is really to take out resonances and might masked a larger issue. I would start by removing power from your motor and see if the noise goes away, the closest high current device to the encoder or feedback may be the culprit.

 

If your feedback is clean, I would lower your Kp a little bit or increase your Kd. It could be possible that your Ki is too high. You can zero out your Ki and just working with Kp and Kd for now to see if the ripple goes away.

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You can use trajectory prefilter (a notch at 5 Hz)to attenuate low frequency vibrations.

 

I tried notch filters and they worked very well, the problem is that I lost my positioning accuracy and I need to hold position as close as possible. Everything adds up and the velocity and acceleration following error ripples are what's hurting the most at the moment

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You can use trajectory prefilter (a notch at 5 Hz)to attenuate low frequency vibrations.

 

I tried notch filters and they worked very well, the problem is that I lost my positioning accuracy and I need to hold position as close as possible. Everything adds up and the velocity and acceleration following error ripples are what's hurting the most at the moment

 

Try to increase your Ki gain and decrease your Kd gain a little. Your Ki should decrease your steady state error. Dont add too much Ki or your system will go unstable. Also relatively, whatever change you make to Kd as a rule of thumb make a fraction of that as the change for Ki. To be safe just change one at a time starting with changing Ki a little bit and see how it does.

 

If its not your steady state position accuracy that you need to improve, but your tracking position accuracy, then increase your Kp.

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