Active cogging torque construction by the weld slot design in a positioning servo system

The cogging torque is usually considered as an adverse effect of the PM machine servo system. This paper presents a new perspective that the cogging torque can be exploited in many practical situations as long as the speed ripple can be suppressed. By the proposed cogging torque design scheme, the local core saturation on the stator yoke can be constructed by specially designing the yoke structure. With this idea, the cogging torque distribution can be designed, with the transmission ratio, generating a series of designated auxiliary positioning forces on the load side. This weak positioning force will be amplified by the reduction gears and make the terminal servo load prone to stop at the designated stable equilibrium positions. This feature can help humans conveniently move the load to some designated positions by manual mode with a certain precision. Considering the negative impact of this constructed cogging effect, a speed ripple suppression method is applied to guarantee that the cogging torque machine can provide a good servo performance. The designated cogging torque and performances are verified by prototype machines, testing, and motion control experiments.