Multi-DOF Orientation Detection of a Permanent Magnet Spherical Motor Based on Back EMF

In order to achieve the motion with multi-degree-of-freedom (multi-DOF) of the permanent magnet spherical motor, it is necessary to accurately obtain the rotor orientation of the spherical motor. In this article, a detecting system of spherical rotor orientation based on back EMF is designed, which combines the special electromagnetic relationship between the stator and rotor of the tiered-type spherical motor. First, the deriving process of the expression between the phase difference of back EMF for the tilting stator and the rotor orientation is introduced. Then, a phase difference detecting method of the back EMF combining the algorithm of the fundamental component extraction and crossing-zero phase demodulation is proposed. Next, a dual-dimensional iterative algorithm is presented, which can quickly observe the rotor orientation according to the phase difference of the back EMF. Finally, the effectiveness of the method is experimentally verified on a DSP-based platform.