Hello experts,

I have a system using CU320-2 PN with 3 axes. All 3 are the same type of DriveCLiQ motor(see picture below).

All 3 are managed in the same way, with same mechanical parameters by a Positioning_Axis TO, version 6.0.

I home them using MC_HOME with absolute encoder adjustment, mode 7. Can be done only in manual mode from button on HMI.

Problem is that one of these loses 1/2mm every time I do a STOP -> START of the PLC.

For example,

It is at 80mm, in home position, brake closed, machine stopped and nothing moving; after restart of PLC encoder will show 78.0 mm.

Does anyone have idea why this could be happening? It is not big problem because I rarely download big modifications now, but If I forget to fix the position after, I could create some problems.

Hi there,

you should check this FAQ: https://support.industry.siemens.com/cs/ww/en/view/84133347
Even though from its title it seems to be specifically about having your issue when switching the PLC off and back on again, it is still valid for your issue with only stopping and starting the PLC. The FAQ basically lists all possible reasons for such a behaviour, with explanation and remedy. So if you just follow it step by step, you should find the cause of your issue.

Regards,
daviso

Hello,

I think I found the problem. For some reason this TO had backlash compensation of 2mm activated. So, after START of the PLC the TO updated its position taking the backlash into account.