Z Axis Drive Fault

[jeremy_d]

I'm an amateur machinist trying to look after my dad's machine shop for a while. We have a Cincinnatti Milacron Arrow 750 mill that continually gives us problems. This morning, I was unable to run it because I kept getting "Z Axis Drive Fault"s. At first, I could work around them because they were infrequent and only between cycles. Now they happen every minute and even when the machine is mid-cycle. Does anyone know if this is more likely an electrical problem (servo board?) or a mechanical problem (z axis column stuff)? Any help appreciated.

[Torchhead]

All of the above. Check the obvious things first. Servo's fault because the encoder feedback does not match the commanded postion (following error). A dirty encoder can cause problems. Any mechanical binding that would cause the servo to work harder than it's current trip would cause a fault. Since the drive parameters are most likely hardware settings on the card there is not much you can do in software to work around the problem.

Can you cause a fault in the manual jog mode? Can you jog it at full speed and cause a fault? When you said it previously faulted only between cycles what was the last thing it did before it faulted. Was it on a rapid up after a cut? When things start to go south on a servo typically it will start to happen on the fastest moves (G00 moves).

I would carefully clean and lube the Z axis components. Even a tiny bit of scarf in the encoder can cause ugly things.

[NC Cams]

Since any fault the servo amp encounters will only produce a generic "fault" signal, you have to systematically do an analysis to find/fix the problem.

Check motor brushes. Worn brushes might be causing a high than normal current draw thus leading to an overcurrent fault. Endcoder issues could be leading to follower erros. The other issues cited in above post are also quite valid. Do NOT underestimate the problems you could be creating via crudded up ways/ball screws.

We chased a limit swith problem for days that was solved ultimately by wiping down the quill housing OD that slides up and down in the housing. A small chip wouldn't let the darn thing "home". Simple housekeeping instead of "screw it, it ain't that dirty" can gang up and bite you.