Knowledge Base

General

Cogging torque designates a phenomenon with electrical motors, which possess permanent magnets in the stator and a slotted anchor from electric sheets or a slotted stand and an anchor with permanent magnets.

With motors slotted both in the stator and in the anchor, cogging torque arises during operation, too. By the change of the air gap during the change of core tooth to slot opposite to the permanent magnets the magnetic resistance and thus the force  on the anchor varies. This effect is unwanted with most electrical motors, however with reluctance motors it is purposefully used.

Cogging torque lead to varying torques (jerky run in particular at low speed, bad synchronism). The rotor stops after switching the machine off only in certain positions. Motors with ironless anchor do not possess cogging torque.

The S300 and S700 servo amplifers have an intelligent function to compensate the cogging torque, see page Cogging Suppression.

Cogging Specification for Kollmorgen Motors