Compensating Periodic Position Errors - Siemens SINAMICS S120 Function Manual

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Compensating periodic position errors

You can also compensate periodic position errors using the "Cogging torque compensation"

function module. As a result of how the encoder is mounted (not centrally mounted, encoder

coupling, encoder radial runout), measuring errors can occur in the speed and position actual

value with 1 or 2 periods per revolution. You can compensate for these errors, therefore

improving precision and concentric accuracy along with smooth running properties.

In spite of this compensation function, we recommend that encoders are optimally mounted.

This minimizes imbalance and the load and stress on couplings and bearings.

To compensate periodic position errors, proceed as follows:

1. Determine the compensation data for the periodic position errors using the rotating motor

data identification routine (p1959.0 = 1, p1960).

It is not permissible that a load is connected to the motor shaft when performing this routine.

The motor must be fixed as tightly as possible so that when rotating the stator cannot move.

When accepting the identified data, p5265...p5268 are preassigned, which are necessary

for the compensation.

2. Set p5250.2 = 1 to activate the compensation of periodic position errors.

The following diagram shows the speed traces for a toothed wheel encoder before (orange) –

and after (green) compensation when coasting down. The blue curve shows one mechanical

revolution. The periodic speed error was able to be eliminated.

Drive functions

Function Manual, 06/2019, 6SL3097-5AB00-0BP2

Function modules

9.15 Cogging torque compensation