We have a 1987 Sharnoa SDC-80D with Fanuc Motors and drives. The Z axis is having an issue.
The Z axis Drive is a A06B-6047-H003 Velocity Control Unit
The Z axis Motor is a DC 20M Servo # A06B-0652-B005
This machine has a proprietary (Sharnoa) control with a PC motion card that receives the encoder feedback and directs the drives to move. The motors have feedback to the drives only.
The issue we are having is that the Z axis physical position is drifting from indicated position, and we have to re reference to bring it back into position.
I do not understand why, if the ball-screw encoders feed back to the motion card, how this can happen. I would think that the motion card would either have a fault indicated or require the drive to continue moving till it is in position.
Any ideas as to where to start ??