Servo shutters

[Karl_T]

I have a galil 1780 card with a brushed DC servo on the Z axis and an AMC analog servo amp model 25A8E.

For some time now the Z axis has shutterred occasionally. I'd guess maybe 10 cycles per second and maybe 5 degrees in amplitude (very rough guesses). Anyway, the servo is rotating back and forth very rapidly for just a short distance. Estop and reset would stop it.

Now, its starting to do it often. And as of a few minutes ago, constantly, and during very slow motion moves.

I need to repair this before using the machine further.

First, I'm going to inspect if the encoder disk may be loose. Are there any more suggestions?

Karl

[Al_The_Man]

Are you using the drive in the torque mode with no tach feedback?
If so is the tach pot set to minimum and the gain to max?
After this check, do a re-tune of the PID parameters in the 1780.
Al.

[Karl_T]

Yes, torque mode no tach. I'll do your suggestions.

I just tested Z moves down to 0.005 inch/min. problem is no worse than its always been. but, it should be corrected.

I'm making trials with electronic gearing for tapping. This is not working at all, nothing but shutters. So, there may be more to it than just slow Z moves. I just read the galil manual and didn't see anything. Would you know how to change PID values to give an over damped response of the slave axis while in electronic gear mode?

Karl

[Al_The_Man]

I assume the Z is the slave in the gearing setup?
My experience so far is to set the slave axis up first as an independent axis and tune it according to either the Galil S/W , or per the 'Tune the Servo Sytem' method in the Manual, where the KI, KP & KD are tuned in turn until stable moves can be achieved with zero, or close to it error when TE is issued.
Al.

[Karl_T]

Yes, Z is the slave. the spindle with a 3 phase and VFD is master.

I have a utility called Galil WSDK. You just click on tune servos, wait 20 minutes, an it gives you the answer. I'll do all this monday and see if it helps.

karl