Sinamics S120 and Overspeed alarm

I attached another roller table trace where speed, speed set point and torque were shown, Only one motor is used. In the attahecd trace you can see we are getting some spike on the actual speed : what is the reason - is it mechanical or electrical ? How to eliminate thatbecause that causing overspeed alarm and stopping roller table.

It looks like you have configuration issue.
With new graph the drive shows working fine through ramp up and stable at the high speed for about 1 sec. then you get fluctation for about 1 sec. and then the load reduced and speed stabilized again until drive stopped.
You have this problem because the load sharing is not configured and there is a fight between the two roller tables when load is on both at the same time.
Not sure about the total width of the rolls and the coil diameter but when your one coil is on two groups you must be seeing this.
Just compare two, threeadjacent tables on one graph and check if the speed fluctuation happens at the same time?
Most likely you might have to use just V/F control or increase overspeed thresholdbecause the PLC program will be more complicated if your coil tracking is not very good.
Hope this helps.
Thanks

Hi Monirul,
problem at your location could be because you have multiple roller tables and the way they are configured.
What is happening is when the coil enters say 1st roller table you see the speed ramp up and going to the set speed just fine. The problem starts when the part of the coil enters the next roller table. That is when 2 of these drives are fighting with each other. Now you would say I'm using the encoder and there should not be a problem because all the tables are running at the same speed.
Question is
1.Are you starting all the tables at the same time?- if not the speed mismatch between 2 tables sharing same load can cause fluctuations.
2. If you are starting the tables at the same time even then the fluctuation can happen because the roller table MPM could be different due to multiple factors like gear box play and the roll diameter. (which can have effect due to temperature too)

Normally when the two drives are in vector control it should have sharing configuration other wise they fight and you see the effect on the speed or load current. If it is in V/F mode these effects are minimum but you may get issues with sudden load changes.

Key is you record multiple roller table on one graph you will get the idea when exactly it is happening. And then you can precisely attend the problem. Like if scenario 1 then change sequence to start all together. If scenario 2- add some multiplying factor on second roller table to minimize the speed difference (0.994 or 1.003 to make 1000mpm speed to 999.992or 1000.021 something like that.)
Let me know what you find.