Hi Sam, I must admit there's a certain amount of fear every time I press the go button for a CNC program. Especially when I started mucking around with tool #'s and offsets. My hand now overs over ESTOP when I press start. Watching a tool that appears too low scream over to the part held in the vise at a G0 180 ipm is not for the faint of heart.
But then the first time I apply power to a newly assembled power supply my heart is also in my throat. For one product, if the Pick and Place people didn't use enough solder under the ground pad of the regulator chip (the only ground connection too), it would fry and take out the 8 SMD power transistors for the dual supply. Very difficult to repair. On the servo side, the caps are 200V rated as are the 50A transistors so theoretically I could run one with 115VAC as the 165VDC supply. That would certainly provide the force to drive more current into the motor windings and create the speed desired. With 105V the motor can reach 3000 RPM with a lighter load, otherwise it would never work on the X axis but the torque might also just be on the edge during acceleration in one direction and not the other. Or build up a small circuit so I can measure the instantaneous DC current with the scope (don't have a current probe) and see how much current the motors are really drawing. Torque is Amps x Turns and if the voltage isn't there to push the amps then following errors are likely. John > -----Original Message----- > From: Sam Sokolik [mailto:samco...@gmail.com] > Sent: September-19-21 12:11 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] DC Servo issues > > Lol.. I certainly love the electrics part more than the machining most of > the time... > > On Sun, Sep 19, 2021, 2:07 PM John Dammeyer <jo...@autoartisans.com> wrote: > > > Hi Sam, > > See below. > > > From: Sam Sokolik [mailto:samco...@gmail.com] > > > > > > 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 > > > > That's the question. One possibility to try is to grab 110VAC line > > voltage. Put a bridge and caps on it and drive that motor with more than > > the 105VDC power supply. I'll have to check if my transistors are rated > > for the 165VDC rectified voltage and I really would rather have them be > > 250V transitors. And then there's the filters on the board too. The UHU > > circuit was originally for up to about 75V. The HP_UHU came about for > > higher voltage drives; Just don't know if I built mine for more than > > 125VDC although the circuit design parts are for 11A. > > > > I _have_ tried one these motors with the STMBL but could never get it > > tuned and support from the designers was inadequate to help me so I gave > > up. > > > > I'd rather be machining... > > > > John > > > > > > > > > > > > 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 > > > > > > > > _______________________________________________ > > 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
