Current Spike in Servo Index Drive

[Tigerdawg]

I am testing an index table with a servomotor driven gearbox drive. I am seeing a spike in the accel. and decel. portions of the index. The system starts fine, then drifts away from its goal value (not accelerating fast enough) and spikes to compensate. In decel. mode, the table starts fine, but then it 'runs away' and spikes to increase the deceleration. The spike is repeatable within each program recipe, but the only common factor between recipees is the spike occurs at about 18-20 amps.
Does anyone have any ideas what could cause this?

I was thinking it was a mechanical 'binding' or friction problem, but you would normally decererate faster than you want, not 'run away'. All mechanical couplings have been checked and the drive (amp) has been replaced. Also, the spike is only under full load. Turning the gearbox off of the table does not cause a spike.

 

[sreid]

Clearly something is going into a limit. If you are not hitting the amplifier current limit, it is possible that there is not enough B+ voltage to support the motor IR drop plus the back EMF of the motor.