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. John > -----Original Message----- > From: Jon Elson [mailto:el...@pico-systems.com] > Sent: October-02-22 3:49 PM > To: emc-users@lists.sourceforge.net > Subject: [Emc-users] losing encoder counts > > I thought I was about done with my R2E3 retrofit project. > But, doing some testing, I found it was losing a little bit > of position when moving. Every axis shows this, but it is > worst on the Y axis. I have a program that moves Y 3" back > and then returns to the indicator. It seems like at 12IPM or > below, it doesn't seem to lose position, but above that > speed it loses from a half to a full thousandth on each > repeat. I've looked at the A and B quadrature signals with a > scope, and they look good, the differential complements look > like complements. I am using my PPMC boards, and I've never > seen this on my older Bridgeport using the same hardware. > > This retrofit is using AMC 30A20AC analog servo amps, and > the original motors. I reterminated the original Bridgeport > encoder cables to the PPMC encoder board, and have checked > all that wiring.� The cables are individually shielded > twisted pairs until the last couple inches at the controller > end. > > Anybody have any suggestions? I'm strongly considering > replacing all the encoders, there are some nice ones on eBay > <http://www.ebay.com/>right now, but I would have to make > shaft and mounting adapters. > > The encoders are DataMetrics S-9481A-250. > > Thanks for any comments, > Jon > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users
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