Design aspects and performance of a slotless PM motor for hard disk drives

The spindle motor is one of the most important elements in a disk drive, and in many ways determines the drive capacity and performance through its design and configuration. This paper describes the design of a new slotless spindle motor which improves the performance with respect to static cogging and harmonic torques. A three-phase printed circuit winding has been designed into a multilayered flex which can be wrapped around the slotless armature and placed in the airgap. This construction eliminates variations in the gap, and hence any torque-variation is eliminated. Some sample prototype motors have been built and tested and were found to perform well. Design details and test results are presented in this paper, Results from this design are also compared to those obtained from similar but slotted motors.