I have never used servo drives that close the loop.. I have always had great luck with normal closed loop within linuxcnc. (cheap used amc drives)
(Actually - I take that back - I have used the stmbl drives. so far only for a spindle..) This is of course using mesa analog interface hardware. The only time I had issues with encoder counting was when I thought I could get by with single ended encoders going over 8 ft... Look at something like this.. 20000 counts per rev, 2 axis with 4000? counts per rev... (and the encoders came installed on the servo, single ended and I think they are us-digital) If I was missing counts during these complicated sync moves - you would certainly see it. https://www.youtube.com/watch?v=-4sKHBh6rDk (plus no 3rd party software to tune...) - Granted you have the drives and are familiar with them - at what point do you give up? sam On Sun, Sep 19, 2021 at 12:59 PM John Dammeyer <jo...@autoartisans.com> wrote: > 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:rmoscol...@gmail.com] > > 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 (<jo...@autoartisans.com > >) > > 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 > > > Emc-users@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
