SUMMARY

Many applications such as automobiles, gyroscopes, machine tools, and automated transfer systems require orientation control of the rotating shaft. Of particular interest in this thesis is the development of a ball-joint-like, brushless, direct-drive actuator capable of offering three-DOF in a single joint, referred to here as spherical wheel motors(SWM), the development of which requires a good understanding of the magnetic field. Unlike existing spherical motors being studied by many others, where the focus has been on the control of the three-DOF angular displacements, the SWM offers a means to control the orientation of its rotating shaft. The objective of the proposed research is to develop a method to characterize the magnetic field for design and control of permanent-magnet based actuators. It begins with physics-based pole models using pre-determined formulations of the elementary potential field. The solution of more complex magnetic field of the SWM can then be obtained by the superposition of the elementary field models. Next, an image method will be applied to handle different shape and material boundary conditions. The proposed modeling method will be validated by comparisons with known analytical solutions as well as results obtained numerically and experimentally. Once it is validated, the methods will be applied to characterize the entire magnetic field of the SWM and to develop a non-contact magnetic sensor to determine the angular position of the rotating shaft, which will be employed to design a controller with observer for the SWM. Finally, we will investigate open-loop and closed-loop control systems of the SWM. While the observer and controller designs have been developed in the context of a spherical wheel motor, these techniques along with the models and analysis tools developed in this research can be applied to design, analysis and control of most electromagnetic devices.