Design trends of spindle motors for high performance hard disk drives

Reducing the unbalanced radial force and reduction of cogging torque are important for the future high performance spindle motors. In this paper, the effects of the pole and slot number combinations on the cogging torque and unbalanced radial force are discussed and a detail investigation on the unbalanced radial force is made using FEM. It is shown that the unbalanced radial force is substantial in the starting condition and in the delta connection winding. The unbalanced radial force can be largely reduced by optimization of the pole arc to pitch ratio.