Magnetic field modeling based on geometrical equivalence principle for spherical actuator with cylindrical shaped magnet poles

Spherical actuator is a device that can achieve multiple degree-of-freedom (DOF) rotary motions in a single joint. It has a bright application prospect on moment gyros and satellite systems. Cylindrical shaped PM pole is widely used because of easy fabrication and pattern of magnetization. However, its topology and structure cause difficulties in accuracy magnetic modeling. Thus, the structure optimization and performance design become complicated. This paper proposes a novel magnetic field method for spherical actuator with cylindrical shaped PM poles based on geometrical equivalence principle. For convenient expression of magnetic field, three types of approximated dihedral cone shaped magnet poles are put forward based on different equivalent principles. On the basis of optimal equivalent principle, accurate harmonic model is set up with the magnetic field formulated. In addition, the analytical result is confirmed by numerical simulation from different dimensions. A research prototype with 8-PM-poles outer rotor and 24-coils stator is assembled and an experimental setup is established. The experimental results show experimental curves, analytical curves and FEM curves match with each other well which proves the accuracy of the proposed model. Thus, the indirect method of modeling magnetic field for spherical actuator with cylindrical shaped PM poles can be an effective tool. The magnetic field results can be the foundation for further study.