On 10/2/22 19:34, John Dammeyer wrote:
Oh boy does that bring back memories.
I started with the US Digital Encoders on the DC Servos. According to the
designer of the PIC upgrade board for the HP_UHU Servo drive the US Digital
were crap and caused nothing but problems.
I switched to CUI and it appeared to be better. Until one day circle milled
inside a piece was off center. See photo.
That’s when I started doing what you did and discovered that at very slow
speeds I could return to the same 0 position but faster moves lost steps. The
error happened in only one direction.
Eventually I discovered that if I swapped the motor+encoder with the Y axis the
problem moved to the Y so it wasn’t the HP_UHU drive. Further research showed
the X axis motor winding resistance was almost double that of the working Y
axis motor.
It's possible I might have been able to fix the problem by doubling the current
setting on the motor. They were bought at the same time and were supposed to
be identical.
I don't know why the HP_UHU servo drive didn't catch the position loss. Like
yours, the encoder signals looked nice. The CUI encoders seem to be high
One other point. I switched to the Bergerda AC Servo drives which to date have
been great. Talking to Donald Chen the sales guy at Bergerda he mentioned that
their encoders are Japanese and more expensive than ones used on a lot of their
competitors. After that conversation I took one apart and checked part
numbers. Sure enough, Japanese design made in China.
So try different encoders.
Yes, I did see some really strange signals on the scope
before. I tore the whole motor/encoder set apart and cleaned
the inside of the encoder. But, optical components in the
encoder are held in place with glue, 39 year old glue! I'm
having doubts that everything is still properly aligned in
there.
So, I'm leaning toward replacing the encoders with newer
high-end encoders with higher line count. But, that will
require machining adapter plates and making sure the
encoders are well-centered.
Thanks,
Jon
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