I'm well on my way to getting this machine running. Starting from a bare-boned chunk of iron with stock motors and encoders, I've brought this Frankenstein to life. Now I'm in the tuning phase, trying to eliminate following errors and get everything just so. It's an Ex-Cell-O 605 CNC.
I'm using a 70V Keling 7220 1400W supply, AMC 30A8 PWM brushed-servo AMPs (which, in the case of the Z-axis has been tuned to a critically damped square-wave per the servo-loop tuning instructions.) The motors are Electrocraft E727 38 006 (about 1.125 HP each) with tach feedback and 500ppr encoders. All axis are 10:1.
I've tuned the Z-axis so that errors are less than 2.5m on the scope (viewed from 500u/div), and multiple sequential moves in the same direction are as smooth as glass.
On reversal however, I get a huge oscillation. I believe I've tried compensating with backlash up to .004 (or was it .0004?) in hopes that EMC would neglect this part of the error tracking, but I still get a "thunk" when the axis reverses. No amount of D appears to make this stop without introducing instability (as far as I have experimented thus far.)
It is the "THUNK" that concerns me. I also tried moving the ballscrew shaft looking for axial play, but no movement was apparent.
I figure this is simply a tuning issue, and that I've screwed up the tuning parameters so that while I think I've tuned them properly, I have in fact only half-tuned, or I've tuned them to some mysterious harmonic that manifests in proper movement only in the same direction.
If tuning parameters are suspect, let me know and I'll post the z-axis params. From memory (I'm on the train right now), they're something along the lines of:
p: 200
i: 15
d: 1.72
FF0: 0
FF1: -.0142
FF2: 0.003
Torin...