S620 / CDDR Overspeed Fault F08

Good morning,

We have a machine with an S620 drive running a C131A-11-2105S motor. Drive, motor, and cables are original and have been in service about 10 years with no problems. The motor drives a rotary table and indexes in 45 degree increments. We execute eight distinct motion tasks from a PLC using digital I/O but the table always rotates 45 degrees at a time, always in the same direction.

Recently we started getting occasional F08-Overspeed faults on the drive. They didn't seem to correspond to any unusual motion of the motor and would occur after the index was complete. The problem got progressively worse so in the drive parameters I increased VOSPD. It had been 60 rpm and we were only commanding the motor to 50 rpm so it should have been sufficient but I changed it to 80 rpm as a test. We are now no longer getting the F08 fault but occasionally the motor is overshooting its target position by about 10 degrees. It then immediately backs up to the target position before signaling motion done. This happens about 1 out of every 50 indexes but is sporadic. So the machine is functioning but the reverse motion puts a lot of stress on the components (and the motor I'm sure). When this funky index occurs you can observe the motor rotating much faster than it normally does--I suspect this was the source of the overspeed fault.

Some time ago we bought an AKD-P02406-NBAN-0000 and new cables with the intent of replacing the obsolete S620 at some point, as the AKD is our standard now. So now seems the time to do that but I'd really like to know the cause of the issues we are seeing. We were not planning to replace the CDDR so is there a chance that these problems are related to the motor or encoder?

Thanks,
John