Reduction of cogging torque in spindle motors for CD-ROM drive

In this paper an approach to design a low cogging torque spindle motor without skewing stator slots or magnet poles is proposed. The effects of the slot and pole number combination and optimal choice of the width ratio of armature teeth to magnet pole are are investigated. A finite element method based on a combination of electromagnetic field and circuit equations for magnetic field modeling and torque prediction is presented. Results show that increasing the number of the least common multiple of slot and pole gives only sufficient conditions to decrease the level of cogging torque. To obtain smaller amplitude of the cogging torque, it is also necessary to choose the width ratio of armature teeth to magnet pole are properly.