Influence of Drive Current to Unbalanced-Magnetic-Pull in Spindle Motor

Both symmetric and asymmetric armature windings are applied in the spindle motors used in hard disk drives. Consider the influence of the drive current in the windings, the analysis to the unbalanced-magnetic-pull (UMP) generated in the motor becomes more difficult. Besides the intrinsic and extrinsic components, the additional UMP can also induced by the current, and the UMP could thus be serious. This paper analyzes this phenomenon, and presents a model which can describe clearly the influence of the drive current to the UMP. For verifying the effectiveness of the analytic method proposed, several spindle motors are analyzed, and compared with the results obtained by using FE method. The comparing proves the effectiveness of the UMP model presented.