Sinumerik 802C marker pulse during home referencing

We have a Sinumerik 802C that is not consistently 'homing' or 'referencing' properly.

Basically, when it 'references' it lookes for a 'cam' (limit switch). It then moves in a specified direction until it sees a 'z-pulse' or 'marker pulse' from the encoder. It then determines 'zero position' based on that pulse.

We have watched the pulse with a digital scope and have seen it EVERY time, but the system doesn't always recognize it within the specified distance and faults out with a 20002 fault.

For testing purposes, we have opened the specified distance, and it may recognize the first or the twentieth pulse.

We have also set the MD 36310 to 1, so it the machine will have to see a 'z-pulse' every rotation based on the encoder counts (1024 pulses per revolution). But, it never faults when we jog it. This means the controller sees every 'z-pulse', but chooses not to recognize them sometimes for some reason during the 'referencing'. Has anyone seen something like this? Any suggestions?

I saw somthing simular in a Japanese tubing bender and it turned out to be a faulty encoder. It would actually skip past a specified reference point and would then try to search for it in slow motion. Have you tried to watch the positioner by manually moving the part with the servo off?

ref. problems

Hi IPSI John

Is it possible that the ref.switch and the ref.puls from your encoder is to "good" aligned ?
Take out you encoder and turn the axis 90 degrees and put it back
again. Clockwise or counterclockwise-your decision.

Good luck
Siemon