DG4s-8020 Driver issues

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DG4s-8020 Driver issues

Postby native34 » Tue Dec 17, 2019 4:52 pm

Good Morning,

I am having an issue with my DG4s-8020 Servo drivers. I have been having this problem since i bought them in 2015. I have not been able to get them successfully tuned. By this i mean that they are tuned but when i make a move and come to a stop, the motors will still oscillate and make a slight vibrating noise. When this happens i have to move the motors in the opposite direction in order for this to stop. Sometimes i have to move the motors back and forth several times. I am at the point with these drives that im thinking about replacing them, but feel that i could be spending money needlessly, as they still function. I would just like to get this awful oscillations to stop and be more stable. Does anyone know how i can accomplish this. I have tryed talking to Arturo from CNC4PC and Balaz the maker of the drives. Arturo has not been very good in getting this issue fixed and Balaz has not been returning my emails in order to get this issue fixed.

Native34
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Re: DG4s-8020 Driver issues

Postby native34 » Wed Dec 18, 2019 2:10 am

Anybody??
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Re: DG4s-8020 Driver issues

Postby cncdrive » Wed Dec 18, 2019 2:32 am

Make sure to not have a backlash between the encoder and the motor shaft. Also try to reduce cogging torgue (Physical backlash on the axis) as it can easily upset the control loop if there is a high torque requirement on the axis and if there is a backlash which requires little torque to overcome.
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Re: DG4s-8020 Driver issues

Postby Derek » Wed Dec 18, 2019 11:15 am

I'm not going to be much help but I have 14 of those drives in operation and don't have oscillation issues so it's probably a tuning or mechanical issue and not drive design. One thing I have noticed is they tend to buzz and dither when I use AMT encoders. US Digital not so much. Even with US Digital encoders I do get some buzz when they stop. No oscillations though. What encoders and counts are you using?
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Re: DG4s-8020 Driver issues

Postby cncdrive » Wed Dec 18, 2019 1:05 pm

The problems with the AMT encoder is that it is a capacitive encoder and it interpolates the position with capacitive sensors to output the incremental signals.
This interpolation requires time which causes lag in the output position which can cause instability in the control loop. This is a problem especially on high encoder resolution.

Also I remember a few cases at customers when the plastic lock of the AMT encoder was made with bad tolerances causing some mechanical cogging of the encoder on the shaft which can also cause instabilities in the control loop.
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Re: DG4s-8020 Driver issues

Postby native34 » Wed Dec 18, 2019 5:16 pm

I am using AMT 102V encoder, I believe that my machine is buzzing or dithering as you put it, and not full out oscillating. One of my a is doesn't do this it is very stable, but the other two do it constantly. I am using the same hardware on all axis, with the similar backlash on all axis, even the one which is not experiencing the issues
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Re: DG4s-8020 Driver issues

Postby cncdrive » Fri Dec 20, 2019 9:20 pm

Check the ring and the outer sleeve on the shaft of the motor/encoder. Check if it has any cogging between eachother. If it does then some glue can fix it, however then you will have a hard time removing it later if it has to be removed anytime.
Also you can try to lower the encoder resolution, that lowers the lag of the signals and so it can help to solve the issue if it is cogging.
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Re: DG4s-8020 Driver issues

Postby native34 » Fri Dec 20, 2019 9:36 pm

What do you mean by cogging? I have the encoders resolution set to 250 cpr, pair that with the 2X from the drive should give me 500 cpr. I would like to be able to at least move the axis in .0002 increments
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Re: DG4s-8020 Driver issues

Postby cncdrive » Fri Dec 20, 2019 11:25 pm

I mean a gap between the encoder shaft positive and negative sleeve which causes cogging. (No movement of the encoder for a small shaft rotation)
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Re: DG4s-8020 Driver issues

Postby native34 » Sat Dec 21, 2019 1:16 pm

I think i understand what you are referrong to , but do you have a diagram of cogging so i can have a visual aid to solidify my understanding? Also would this cogging cause loss of motion errors or missed steps, leading to part dimensional errors?
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