Thanks for all the responses. I now know what the source of the vibration I hear during a G33 can be attributed to.
First a correction. I said something yesterday that was incorrect and misleading. The oscillation I was seeing in the velocity waveform (also in the DDT of the position information, of course) DID NOT go away on coast (I said yesterday that it did). What I was thinking of was that as the spindle coasted down it became low enough to be unnoticeable. It was happening though after I shut off the spindle for several seconds before trailing off, zooming in on the graph revealed that. I was thinking (to continue to blame the vfd :-) that it wasn’t truley coasting that it must still be interfering some…. After spending today doing more testing and peering at Halscope traces, oscilloscope traces I ended up convincing myself that the VFD was causing the speed variation. I talked to Automation Direct tech support and theyagreed that the variation could be due to the VFD having a slight variation of the frequency output. I put a high voltage probe on one of the motor output leads from the VFD and could see the PWM fluctuating (in frequency) and talked myself into that being the culprit. Later I realized that the PWM would fluctuate in frequency to make up the output waveform but that by itself is NOT the output waveform frequency (and hence was a red herring). Anyway, one of my shop mates had the idea to just wire the motor directly to the 3-phase AC line voltage to completely remove the VFD form the picture. The motor spins at 1755 rpm at AC line voltage. With everything wired normally I first watched motion.spindle-speed-in in Halscope after commanding 1468rpm in Axis (with gear reduction that means motor at 1755rpm) just to be able to compare it when connected directly. I then re-wired directly to AC and fired it back up. I fully expected the fluctuation to be gone. But it wasn’t! So much for assumptions. Doing some calculations on the resulting plot revealed two things. The period was almost dead on once per rotation of the spindle, the variation is about 9rpm (so the spindle is fluctuating between +4.5 and -4.5 rpm of commanded speed), and that the motor itself was not causing it because otherwise the period of the variation would be at the motor gear reduction (0.8313). The frequency of the variation is about 25-30Hz and this jibes which what you can hear when running a G33 (a low rumbly vibration). If you look at the link I posted which shows a picture of the spindle you see a long mechanism that the spindle motor is turning. https://www.flickr.com/photos/37438950@N00/16941293785/in/album-72157651167328249/ This includes the Rohm collet closer, the casting mount (bearings inside) for the spindle and the head. Somewhere in that 18+” long contraption is a slight imbalance that is causing the spindle to vary as it spins. There is no noticeable noise with the spindle alone and nothing you can feel - I think the variation is just too small given the mass. BUT, if you run G33 it is trying to synchronize with the spindle. So, my Z-axis stepper is amplifying the 25Hz rumble. I will post a video (in another thread) showing the G33 knurling routine but you can’t really hear the vibration in the video, maybe a little, it definitely sounds different than a non-coordinated move though... Anyway, the G33 runs fine, I know the source of the vibration, and I am declaring victory and moving on. Thanks again for all your help, -Tom ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
