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Fanuc Y Axis Works perfectly for hours; later rumbles, alarms 401, 420, 421, 424

Jrill

Aluminum
Joined
Feb 11, 2013
Location
Northeast USA
Our 2000 Hardinge with OMD control has had Y axis issues for the 3rd day in a row.

Each day for the past three days, it works perfectly for a few hours and then in the afternoon starts to move extremely coarsely and vibrates the shop floor and the load meter is all over the place, and won't move at all half of the time (the position display moves, though) and throws a 421 or 420 error (Y axis excess). Sometimes it won't move with the handwheel and then will jolt half an inch or so and have a 424 (Y axis detect error) and/or 401 (VRDY off?).

This morning the repair tech came in and it ran perfectly for a few hours, including jogging back and forth at 1181ipm for a few minutes, and now it will barely move at all and when it does it sounds terrible.

The ballscrew turned fine by hand, and I greased it up again yesterday and took off the covers and looked around and everything seemed decent. It seems almost like mechanically it's fine but electrically it's fighting with itself.

We replaced the XY module in the control a few months ago, if that makes a difference.

How does one troubleshoot this? What is a likely cause?
 
Sounds like a bad servo amp to me. If that is what you replaced a few months ago, it's possible it has gone bad again. Did you replace it with a new one from Fanuc, or a rebuild from a non fanuc entity. Results may vary on rebuild amps. I have had both good and bad luck with them. Only replacement amps that seem to last as they should are new ones.
 
Four or five years ago I had a redcap behave exactly like that - turned out to be the pulse coder. I was hesitant to accept that was the problem as I couldn't understand how it could have been intermittent to start with and there were no SPC alarms, just servo like yours. However sure enough after it was replaced everything was back to normal and has been fine ever since.
 
Does this machine have a scale on the Y axis?

I should know, but I don't. How can I tell if it does or not?


If it's a bad servo amp, then swap the amps with another axis, and see if it moves to follow the amp, or stays in the Y axis.

That's a good idea, thanks. We did that before to diagnose the servo amp, but I had forgotten about that technique.


Sounds like a bad servo amp to me. If that is what you replaced a few months ago, it's possible it has gone bad again. Did you replace it with a new one from Fanuc, or a rebuild from a non fanuc entity. Results may vary on rebuild amps. I have had both good and bad luck with them. Only replacement amps that seem to last as they should are new ones.

We got it rebuilt from a non fanuc entity. Interested to see if it's already bad...


Four or five years ago I had a redcap behave exactly like that - turned out to be the pulse coder. I was hesitant to accept that was the problem as I couldn't understand how it could have been intermittent to start with and there were no SPC alarms, just servo like yours. However sure enough after it was replaced everything was back to normal and has been fine ever since.

Where's the pulse coder? I'm not familiar with that. How much was it to replace?
 








 
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