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

Feng Chai,Lei Chen,Lei Gan

doi:10.1109/access.2020.2966786

Abstract

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.

Highlights

Spherical motors are gaining increasing popularity in robotics and industrial applications in recent years
Different from other spherical motors, the type permanent magnet spherical motor (T-PMSpM) are asymmetric in the three directions, i.e., the output shaft can rotate continuously but only tilt in a limited range
The T-PMSpMs are more suitable for wheels, propellers, and machine tools that require orientation control of the rotating shaft [9]

Summary

INTRODUCTION

Spherical motors are gaining increasing popularity in robotics and industrial applications in recent years. A multiDOF rotor orientation measurement method based on phase difference is proposed It can avoid complex calculation of magnetic field distribution in spherical motors. When the rotor revolves with electrical radian frequency ω, a constant upward electromagnetic force will be produced as long as the stator magnetic field rotates in the same direction with the same electrical radian frequency It can be concluded from the working principle that the rotating motion and tilting motion can be controlled by different stators respectively. The circumferential angular position (point P) is measured using the polar angle γ in the polar coordinate system, which is located in the cross-sectional plane The relationship between this polar angle γ and the corresponding azimuth angle γs in the rotor spherical coordinate system is shown, where the tilting angle is denoted as β. The coil’s induced voltage and the phase back-EMF can be expressed by the phasor as

BACK-EMF IN THE ROTATING STATOR

CONCLUSION