Performance Improvement of Operating Three-Degree-of-Freedom Spherical Permanent-Magnet Motor

This paper describes performance of operating three-degree-of-freedom (3-D.O.F.) spherical permanent-magnet motor with a finite-element-analysis and experimental studies. Torque and efficiency comparison was made for two different models; the pure iron processed stator core model with a Guide-frame structure, and powder formed stator core model with a Guide-frame structure. As a post study to compensate the defect of the guide frame structure, a double-air-gap operating three-degree-of-freedom spherical permanent-magnet motor has been proposed. Double air-gap type has a single stator, double air-gap between the outer rotor and the inner rotor. Moreover, the double air-gap type, which does not have a guide frame, has a higher torque density, better efficiency, and greater applicability. Finally, the estimated performance has been proven via experiment conducted under the proposed efficiency measurement method.