Phantom Axis Stoppage

I have a three color offset printer application in which three axis are mastered to a phantom axis and the phantom axis is mastered to an aux axis feedback channel which is driven by an idler roller which tracks the paper as it passes through the machine. Intermittently, the whole system comes to an abrupt stop in a fashion that suggests the motors are being driven to zero speed, as opposed to coasting. The sudden stop damages the press plates.

 

Mtr 1-3 Parker motors with GPH 30/60 Amps

Mtr 4 phantom axis using stepper electronic feedback

Mtr 6 aux axis

 

This is a Turbo PMAC2 VME frimware version 1.938, with Sick/Stegmann absolute encoders and ACC51P Opt2 for all four channels.

 

A fault on Mtr 1-3 generates a kill command that allows the rolls to coast and not damage the plates.

 

A loss of feedback on Axis 6, with all other axis following, would step command the motors to zero speed, causing this proglem. I am in process of replacing the ACC51P and all cables and encoders to mtr 6.

 

This problem would also be created if the phantom axis were to suddenly drop to zero speed. This occurred three years ago when the system was upgraded to the current processor. The original code was written using an integrated output feedback method that was not backwardly compatible with the current firmware version. The code was rewritten using the stepper method for phantom axis generation. The problem went away for about 18 months then reappeared with higher frequency.

 

What possible causes are there for a stepper method phantom axis to suddenly stop when setup for position following of an aux. encoder?

Having replaced all components on the hardware feedback side, all evidence points to a failure of the stepper setup phantom axis to sustain ongoing position following. Any ideas why this would occur?

Check for any software setup variable that could be overwritten to stop the operation of this function.