Hello Everybody,

we are trying to use a direct synchronous motor as a controlled brake to regulate the tension of a film tape.

We are using a S120 driver (CU310-2 + PM240) parameterized with starter and the torque is managed by a S7-1500 via MC_TORQUELIMIT and telegram 105.

We want to use the electrical motor to have the smoothest braking control as possible but the fact is that the synchronous motor present a cogging torque that we are not able to eliminate.

Is possible to eliminate this problem?

Which is the best approach?

Thank you for your support.

Thank you for your suggestion.

In the manual is mentioned the "Cogging Torque Compensation" function that requires an additional license. Before to purchase it do you have experience on it? Is it effectively able to mitigate the problem?

Thank you

jacek d

It is described in SINAMICS S120 Function Manual .

 I've checked the specifications of the cogging torque compensation function but I'm not sure it suits my needs.

The manual says that this is to reduce the cogging torque at low speed but if I rotate the motor at low speed (1 rpm) there is no cogging or ripples in its velocity.

I experience cogging only when the motor operate in torque limit. I suppose this is due to the fact that its p1300 is = 22 (speed control with encoder), probably by using close loop torque control I obtain a better beahviour.

What do you think about it?

Hello,

I want to post the results of the test I've made so they remain also for other Forum users.

The "Cogging compensation" functions of S120 require a license but it can be enabled as a trial for 300 hours so we've been able to test it.

This function does indeed smooths a lot the speed oscillation in velocity mode as you can see in attached picture but it seems to not reduce a lot the cogging in torque limit mode.

The cogging is a natural characteristic of synchronous motors and the ways to reduce it are:

1. Skewed poles motor (the less effective one);
2. Increase the system inertia;
3. Increase the motor speed by using a gear reducer.

For our application we will remove the torque motor and we'll use a smaller motor with an adequate reducer.