Siemens drive issues

Hi,

Maybe some of you can help or point in the right direction regarding one problem that is causing headache.
We have a couple of manipulators driven by SIEMENS double motor modules and the system is operated with the SIMOTION drive based solution. One motor module drives vertical and horizontal axis. Encoder is set on the motor side and it is multiturn absolute encoder.
The issue appears within one vertical axes - first there was issue with one but now they say it is happening with the other vertical axis/motor module as well.
It looks like the axis is "slipping", absolute encoder is showing right position but this 0 position happens to be 10mm and declining from the wanted zero position.
The problem is even more stranger because it is showing up randomly. One day you don't experience it at all while the other you may experience it with almost every cycle.
One day we had this problem with every automatic cycle, it was frustrating to rehome the machine every time so we left the machine OFF for 15min or so. After that we had no problem for couple of hours..
It is really strange because this randomness doesn't look like mechanics problem, encoder also does not give any faults. It is strange to show "wrong" position with absolute encoder as well..
Maybe someone experience similiar and knows more where to look?

I'm assuming there are some sort of encoder wheels . . . Have you made certain
all of them are tight - all the setscrews tightened down so that nothing can slip?

And you might try checking the DC power supplies for AC ripple.
(I use a fluke digital meter. Read the DC volts, then switch to AC and see if there is anything there.)

Poet.

Mad_Poet said:

I'm assuming there are some sort of encoder wheels . . . Have you made certain
all of them are tight - all the setscrews tightened down so that nothing can slip?

And you might try checking the DC power supplies for AC ripple.
(I use a fluke digital meter. Read the DC volts, then switch to AC and see if there is anything there.)

Poet.

Click to expand...

Thanks for the reply. Yes, we will check mechanics, funny thing is it is so random and unexplainable that we crossed out mechanics. Especially that when you turn off the machine for some time problem can go away. That is why we accused electronics first.. or ghosts