Sinamics S120 vector control problem

Hello, please, I need help with the problem with vector control Sinamics S120. We have this drive for the Shear control in our rolling mill - close loop control with encoder feedback. The shears normály are waiting in the start position (pulse enabled) and after the cut command they accelerate and after the cut decelerate and positioning to the start position. Normaly is everything OK. Sometimes (once every few weeks) is the control of the shears after the cut wrong. There is full negative braking torque on the drive (only displayed in the trace, not in the reality) and the drive accelerate (really - encoder measurement). Important thing - there is no mechanical reason for this behaviour - it is drive control problem. Do you have any idea? Thank you, Tomas.

Hello,

in that case I would open a service request

https://support.industry.siemens.com/my/ww/en/requests/

So you should send the actual traces as .trc file and the STARTER project.

Hello, thank you for your answer. I made service request 3 years ago (SR= 1-4021583326 Shear with asynchron motor and S120, Simotion). But they didnt want to understand, that it is no problem from the load - mechanic. In the moment, when there is max. negative braking torque, there is only motor, gearbox and knives on the drive site, no other mechanical force for the acceleration the drive!!!!!!!!!!!

 Last service answer:

Assuming that the current transformers are working properly,
then the problem comes into being due to the process!

The drive depends on the torque-limit of 6000 Nm and can no longer go higher!

At this moment, the drive is probably taken by the load!

Hence the actual speed is reversed!

I advise to test the current-transformers by a trace in the time-cycle of current loop clock to see that the flows are symmetric.

Remedy is a greater drive and a larger motor!

The behavior of the temperature profile is irrelevant since it is only within +/- 2 degrees.

I send in attachement the right drive behaviour, we have normaly always this, but only sometimes is the cut wrong.

Tomas.