Yaskawa servo drives, not homing after power failure

Hey all,

I have a couple older style Yaskawa servo drives (not sure on exact model at this moment, but i can get it)

We had a power failure over the weekend. Came in today and two of the motors just keep turning extremely slow. They are acting like they are searching for home position. The prox for each is made every revolution, but they are not stopping....they just keep rotating extremely slow until the timer in the PLC runs out and the machine faults out for not finding home position. I ran across this problem years and years ago but cannot remember the solution.

We have turned them off for 10+ minutes, let the charge bleed down, then powered them back on. Also have tried downloading the parameters again from a backup all with the same results.

did you check your homing position inputs are working/ coming on?

if the controller/ drive doesn't see them, it will continue "hunting" for them.

I got online with the motion card and i can see them coming on and off when the flag passes the prox.

I dont believe they are "searching". They are turning extremely slow. Usually they turn quite a bit faster when they are told to origin.

The homing sequence may also be looking for the encoder C channel (lso known as Z channel) pulse after the homing sensor was detected. This is usually done at much slower speed than the initial home sensor seek(approach) move. There is a single pulse per motor shaft revolution.

It is possible that somehow the encoders inside the motors were damaged so the C pulse is not detected. Usually these motots are very reliable but anything can happen.

I dont think its even starting the homing sequence. Im seeing very very slow, jerky movement from them. The motion card is not telling them to move.

Jerky movements can be related to encoder feedback problem or encoder setup problem.