Torque Model for Position Control of Multi-degree of Freedom Electromagnetic Actuator

Abstract

A Spherical Wheel Motor (SWM) is one of electromagnetic actuators capable of providing three degree of freedom (DOF) rotational motions as a single device. The SWM can be applied to many application such as industrial robots, humanoid robots, surgical instrument, etc due to its compactness. However, the existed SWM has to be improved to apply practical applications in the areas of compact design, force and torque, and control systems and so on. The objective of the thesis is to develop the method of torque model for SWM and position control using in open loop control. The torque model requires understanding the design of SWM as well as magnetic fields analysis. In particular, the analysis of magnetic fields of the SWM is very difficult and requires long computational time due to complexity and a number of magnetic poles. The existing models based on numerical methods may not be suitable to control the SWM. Therefore, the simple but accurate torque model is required to real-time control. In previous research, the torque model of SWM was demonstrated the summation of interaction between each permanent magnets and electromagnets as the magnetic circuit is linear. In this work, the equations of interaction between the permanent magnets and electromagnets was simplified using the structural characteristic of SWM. The torque model was suggested in closed-form using simplified torque model. The experiment and other simulations were performed to check the validity of simplified torque model. To verify the simplified torque model, the position control was operated using push-pull principal. To demonstrate that the torque model and position control principal were proper, the experiment was performed the position control in open-loop control. The simplified torque model offers fast computational performance compared with other simulation tools results, and shows that the torque values are reasonable to control. Furthermore, the experiment results show that the SWM is properly controlled the position using the proposed torque model and position control mechanism.