Analysis of pole configurations of permanent-magnet spherical actuators

This paper presents a generic design concept of three degree-of-freedom (3-DOF) permanent-magnet (PM) spherical actuators. A ball-shaped rotor mounted with multiple layers of PM poles is concentrically housed in a spherical-shell-like stator with multiple layers of air-core coils. This design allows more rotor and stator poles to be incorporated to increase torque output and motion range of the actuator. The magnetic field and torque modeling methods are generalized to multiple layers of poles, which provides a convenient way to analyze field distribution and torque performance of spherical actuators with various pole configurations. The simulation results of flux distribution and torque variation of double-layer configuration are compared with those of single-layer one. It shows that the magnetic field distribution and torque variation for both configurations are coincident with PM-pole arrangement on the rotor surface. The tilting torque of double-layer design is larger than that of single layer, and the torque variation is more uniform. The spinning torque of single layer is relatively large. The proposed analyzing methods of field and torque could be employed for preliminary study of other PM spherical actuators.