Hi Rick, It may also have something to do with the DC Servo drive electronics. Although it's differential encoder signalling the design may have internal issues that are somewhat corrected by the Henk Olsson module. I had both a small electrolytic and ceramic capacitors right by the US Digital encoders, which BTW, have been discontinued for a few years. Perhaps that's why? Issues?
I swapped the X and Y motor/encoder pair and sure enough the problem moved to the Y axis along with now only 120 IPM instead of 150 IPM. Above that I get following errors. Given that this motor has a higher winding resistance I'm going to guess it's not a 90VDC motor but is more likely a 180VDC motor that was shipped as a 90VDC. Maybe the loading introduces noise in one direction that fools the quadrature encoder. It's very strange that the following errors are only in one direction. At $145US plus shipping, since Automation Technologies won't replace it, I'm going to cast a new mounting plate for one of the slightly smaller 1.27NM Bergerda AC servos. They were destined for the ball screw upgrade (and I'd ordered the wrong size thinking they were the same torque as the DC ones). So we'll see. If the Bergerda does well on the heavier Y axis then problem solved. More as it unfolds. Oh I swapped motor/encoder sets between X and Y,and with the Y motor running the X axis the test program that runs the table back and forth no longer has a slightly different sound between changing direction CW compared to CCW. So it appears that's also on the motor and not LinuxCNC nor the MESA. And absolutely no errors in position on X. Only now on the Y instead. That lets the HP_UHU servo drive off the hook too. John > -----Original Message----- > From: Rick Moscoloni [mailto:[email protected]] > Sent: September-19-21 10:12 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] DC Servo issues > > us digital encoders with a capacitor across dc+and- works without a > fault.... > > El dom, 19 sept 2021 a las 2:49, John Dammeyer (<[email protected]>) > escribi�: > > > Over 10 years ago I bought two of these for the XY axis of the mill. > > > > https://www.automationtechnologiesinc.com/products-page/dc-servo-motor/nema34-1125ozin-dual-shaft-servo-motor > > > > Also from US Digital the 250 line encoders. > > I had assembled HP_UHU kits and had on standby the Henrik Olsson > > replacement PIC processor modules although this photo shows the original > > processor. > > http://www.autoartisans.com/mill/HP_UHU_Modified.jpg > > > > One of the things that showed up right away was that with identical drives > > one motor ran hotter than the other. Further investigation showed the > > resistance of the windings was different with the warmer motor having the > > lower resistance and inductance which matched the spec sheet. By then it > > was too late to return the high resistance one so I decided to put what > > appeared to be the on spec motor on the Y axis since it had to carry more > > weight. The X axis got the cooler and higher resistance motor. > > > > When I finally got it all together I had a lot of position errors and > > Henrik convinced me to trash the US Digital encoders which appeared to be > > losing counts and replace them with the CUI. Changing to Henrik's module > > improved things and positioning was now reasonably accurate. Until a short > > while ago on the X axis. > > > > I pulled the encoder off remounted things and the problem seemed to go > > away. Well last week, after the center drilled holes were off from where > > the 1/4" drill bit went down I realized the problem had returned. After > > much mucking around it seems that the real issue is still with that X axis > > out of spec motor. > > > > What I did is swap motor+encoder from X <=> Y. The cumulative position > > errors on X are now gone so that shows the HP_UHU drive was not the issue. > > What's really interesting is the heavier Y axis now regularly faults at 140 > > ipm where before the other motor could do 150 ipm. > > > > Also interesting when I drop the speeds to below 130 it doesn't fault but > > I started seeing position errors. > > > > The G-Code test program > > G01 X0 Y0 F60 > > X-4 > > Y-1.1 > > Y0 > > X0 > > Y-1.1 > > Y0 > > X5 > > And so on for about 5 cycles. > > > > Now the X axis returns to 0 every single time from either side of 0. But > > the Y axis accumulates -0.020 or so error every time the program runs just > > like X used to with that motor. Always only negative values. So strange. > > > > Also when that motor was on the X axis the sound of the system when > > changing direction was clunky sounding in one direction and not the other > > under G-Code. The change direction with jogging keys wasn't like that. > > > > I don't think it's worthwhile to spend the time to figure out what's > > wrong. Seems pointless to continue to use a motor that isn't up to spec. > > Probably better to just install one of the Bergerda AC Servos I have here > > that I was saving for the Ball Screw upgrade. Especially since > > AutomationTechnologies wouldn't replace the motor even though it was > > clearly out of spec. Not about to buy anything else from them. > > > > John Dammeyer > > > > > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
