Siemens SINAMICS S120, Function Manual

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Function modules
8.15 Cogging torque compensation
Drive functions
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Function Manual, 11/2017, 6SL3097-4AB00-0BP5
8.15 Cogging torque compensation
8.15.1 Overview
For synchronous motors, the cogging torque can be compensated to improve radial
eccentricity as there is a fixed connection between the absolute location and cogging force in
these motors. Induction motors are not suitable for cogging torque compensation.
The entire cogging torque compensation is executed via a compensation table which,
depending on the position of the motor measuring system, is read out and precontrolled. The
cogging torque compensation can also be performed based on the direction. For this reason,
a separate table can be used for the compensation for each direction of motion (p5260,
p5261).
The tables for the cogging torque compensation must be filled out using a “Learning
process”. During this learning process, the cogging torque can be measured when moving
the motor and stored in the table. If you want to use direction-based cogging torque
compensation, you have to perform corresponding learn runs for each direction of motion.
Note
The activation of this function module leads to a significant increase in the required
computing time per drive axis.
The operation of 6 servo axes on one Control Unit can no longer be guaranteed in all
constellations and should be reduced to 5 axes.
Requirement
● This function module is only available for the SERVO drive object.
Restrictions
● A motor encoder is always required for the cogging torque compensation.
● Transistor-transistor logic or HTL encoders are not suitable for cogging torque
compensation.
● The encoder must have absolute information, thus it must be an absolute value encoder
or have a clear zero mark or be distance-coded. Due to the premature validity message
of absolute information, DQI encoders are only suitable with a bypass (Encoder Data Set
switchover after start-up).
SINAMICS encoder evaluations with actual hardware required (SMC 10/20, SME12x, ≥
6SL xxxx-xxxxx-xxx3) and SINAMICS firmware > 04.50.22).
● The compensation is then applied to the torque-generating current setpoint. It is only
effective if neither current nor voltage limiting intervenes and the frequency is not higher
than the current controller bandwidth.