Need Help!- Suddenly I have Servo Jitters on the Z-axis

[Deltic_Engine]

Hi,

I have a GN 6Mb with Fanuc Black Cap Servos.

I had run a series of programs all morning with no problems.
I shut the machine down for a couple hours while I did some
programming in Gibbs.

When I powered the machine back up it booted fine.
but when I started to bring the spindle down to check my origins
the Z started jittering and then the control threw a **Y** axis
resolver error (notice I said Y, not Z).

After first getting all axis off the limits I cleared the alarm by
powering back up with the 'reset/delete' combo.

Now there is no Y axis issue at all but the jittery Z persists.
Basically if I move the Z in 1/10000 increments it is OK.
But as I try to move it faster by say, using the 10 thou increment
it will get progressively more jittery the faster I try to move it,
until a 401 alarm is finally thown.

Is there something to clean on Black Cap serrvos (Model 5)?
Commuters and such?

Or does this sound like a voltage or board problem.
As I said it came on very suddenly.

All parameters have been verified so it is not a BMU problem.

Help! I'm in the middle of a job.

[Deltic_Engine]

I went into mt Fanuc/GN 6Mb Maintanance Manual and found the 'Gain' adjustment
on the Velocity Board for the Z-Axis. It is a Pot labeled 'RV1'.

I turned brought the Z Axis down (slowly) so I could play with the hand wheel
after turning Pot a little each way. The clockwise direction of the RV1 pot had
the effect of dampening out the jitters so at least for the time being my problem
is solved.

However since the jitters manifested suddenly (and the RV1 pot is now full-clockwise)
I suspect this adjustment may be just a bandaid for a developing board problem.
6 running hours so far since the fix and things are stable for now.

Regards,
Jeff Krause
http://www.Polyradial.com

[ClassicDoors]

Had a similar problem with a motor on a tool changer carosel...had to replace the circuit board...solved the problem.

[underthetire]

I would take apart the servo and clean up the carbon before you purchase anything.