Unbalanced-magnetic-pull induced by the EM structure of PM spindle motor

The electromagnetic structure of the permanent-magnet spindle motor may induce intrinsic unbalanced-magnetic-pull (UMP). In the paper, this kind of UMP is analyzed with a method developed from the magnetic-circuit and magnetic field analysis. The principle of the method is introduced in the paper. The analysis shows that using the even slot can avoid the generation of the intrinsic UMP. Several spindle motors are used as example to explain the application, and the results prove the effectiveness of the proposed method.