[How do I?] Encoder Noise/servo Chatter

native34

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I'm having an issue with two of the three axis on my mill. It appears that the motors are chattering. When I lower the encoder resolution it gets better but never completely goes away. I am using amt102-v encoders. The axis that is not giving me issues is set to 1024. When I set the other two to that setting they chatter horribly. So I have one set to 500 and the other set to 256 but these two still have chattering but not as bad as when set to 1024. Does anyone have an idea what I can do to alleviate this chattering. All hardware is the same brand and model I don't have any mismatched hardware.
 
Was it working correctly at one time then started giving problems? If so I would be looking for a ground/shielding issue, as you say, noise. If you have an oscilloscope, it is a most useful tool for tracking down these kinds of problems.

In an otherwise stable system, the Proportional gain in the PID loop would have the greatest effect in calming the motors down. You might try turning it down a bit.
 
No it has always worked like this. I wish I had an oscilloscope. I have tried tuning these two several times it really doesn't have any affect on it. The only thing that works is lowering the ppr on the encoder which I shouldn't have to do as they all share the same hardware and one axis is able to have resolution at 1024.
 
What motors, drives, motion controller, and software are you using?
 
I am using cnc4pc c32 bob, cncdrive dg4s-8020 drives, kelinginc kl34-170-72 motors, cuiinc amt102-v encoders.
 
I did a little research and the consensus seems to be that lowering the encoder resolution is the fix, which seems a bit counter productive IMHO. Also make sure the encoder cables are shielded and the shield is only connected at the panel end. 2 channel encoders are prone to picking up noise, where 4 channel encoders are almost noise immune. If possible, changing to 4 channel encoders might eliminate the problem. Maybe a used 2 channel scope would be a good purchase, might help track down the problem.

I wish I could be of more help. Too bad we are 2500 miles apart.
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I swapped out the encoders giving me problems with the one not giving me issues and found out that the issue follows the encoders. As soon as I did this the motor that was fine started giving me problems and the one giving me problems previously was working without issue. So it appears that there is a problem with the encoders.
 
I should'a suggested that. Happy to hear you found the problem! :encourage:
 
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