Dynamic analysis and current calculation of a permanent magnet spherical motor for point-to-point motion

Point-to-point (PTP) motion of the end effector is an essential part for using robot manipulators to perform precision machining task. Traditionally, it is implemented by several motors with complex transmission mechanism, which causes slow responses, low positioning precision and dynamic performance. Therefore, dynamics analysis and modified electrifying method of a permanent magnet spherical motor (PMSM), which can provide up to three degrees-of-freedom independently for PTP motion is presented in this study. First, a new inverse kinematics method for solving PMSM's rotation angle using a cross-product between two points is proposed. Through dynamics analysis, the control torque is designed by using sinusoidal function to plan the PTP motion. Second, a modified electrifying method by combined coils has been proposed based on the current-torque equation, which deduced the calculation burden by reducing the dimensions of characteristic matrix. Finally, the simulations and experimental results show that PTP motion trajectory planning based on sinusoidal function and the modified electrifying control method can not only reduce the torque disturbance and increase the electromagnetic torque, but also has the advantages of relatively simple control and better tracking control performance.