Spindle current bouncing 2 to 10% at one speed?

ifixcnc · Apr 16, 2020

Newer Hyundai gear head HMC.
Spindle current bounces at 2500 RPM (motor speed) in any gear?
Lower or higher speeds have less bounce, up to a point when it flattens out?
1900 = OK
3200 = OK
The speed is steady.
The fluctuating current is enough of a problem that the motor over heats.

Mtndew · Apr 16, 2020

Seems like you should change your username.

alphonso · Apr 16, 2020

Something loose (cable, encoder, coffee pot) that the harmonics at 2500 sets it off???????

markz528 · Apr 16, 2020

Does it have an encoder? You really need to know if the drive is causing the current fluctuations or if the drive is reacting to mechanical load.

You look at the speed signal and the current signal with an oscilloscope (or other appropriate device) and see if they are in phase or opposite. It is a much better test if you have an encoder.

If the speed and current are in phase then the drive is the culprit, if opposite then the the drive is reacting to mechanical load. This assumes that the signals you are evaluating are accurate.

And you do have a speed change - it is just a question of how much.

Sounds like a resonance issue to me............

ifixcnc · Apr 21, 2020

Mtndew said:
Seems like you should change your username.

To those who thought I was not worthy of my pocket protector after 40 years, Fanuc just spent a full day and could find nothing. There is some mechanical resonance (around 30HZ) that shows quite clearly with advanced diagnostic tools. Still no joy?

Vancbiker · Apr 21, 2020

I got called to look at a geared head machine that the owner suspected a bearing or something was going out because it made reallllly bad rattly noises at certain rpms. Mechanically, it was fine. Ended up tweaking some gain adjustments on the drive and got rid of most of it without degrading the spindle performance noticeably. Never was able to get it totally quiet unless de-tuned to where it seemed sluggish.

ifixcnc · Apr 21, 2020

This one is quiet.
31i control coupled to Fanuc servo guide software allowed adjustments of all kinds, with a graph to show results.
We could aggravate the condition slightly but never improve it?
Some harmonic resonance demon lives in the head.

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