A Novel Tiered Type Permanent Magnet Spherical Motor and Its Rotor Orientation Measurement Principle

This paper proposes a novel tiered type permanent magnet spherical motor (T-PMSpM), which has the advantage of relatively larger torque ability compared with most existing spherical motors. The proposed T-PMSpM is capable of continuously rotating while the rotating shaft can tilt in all directions. Considering that it is usually much difficult to measure the multi-DOF rotor orientation of a spherical motor in an easy and convenient way, this paper also proposes a specific rotor orientation measurement method, aiming at providing an idea of simple solution for detecting the multi-DOF rotor orientation based on phase difference. In order to clearly reveal the intrinsic relationship between the phenomenon of phase shift and the tilting motion, a simplified back-EMF model of the T-PMSpM is put forward according to the geometric changes as the rotor tilts. Based on the simplified back-EMF model, both the initial phase and the magnitude of the back-EMF are calculated analytically and verified by the 3D FEM. The full region forward relationship between the rotor tilting position and the phase difference is further obtained. Therefore, the rotor tilting position can be easily identified based on the inverse solution. Finally, a prototype motor of the investigated T-PMSpM has been manufactured. The experimental results validate that the multi-DOF orientation can be detected effectively with enough accuracy.