| The increasing demands of advanced manufacturing processes have motivated the development of novel actuators. A unique example is an electromagnetic spherical actuator, which offer attractive features of combining three degrees-of-freedom (DOF) motion in one joint, isotropic properties, and simplicity in structure. The thesis presents a detailed analytical investigation on the design, modeling and performance evaluation of a practical bearing system for ball-joint-like actuators. Unlike previous studies, where the focus has been on the method of controlling the three DOF orientations, this thesis addresses the method of regulating the three DOF translations and thereby improving the dynamic performance of the orientation motion manipulation by reducing contact frictions.; The different methods of regulating the rotor displacement have been explored analytically; namely, a passive air bearing system, an active air-bearing system, and an electromagnetic levitation system. The investigation has led to the modeling and design of a potentially useful air-bearing system capable of eliminating frictions in spherical and yet, it provides an effective means to evaluate a spectrum of design configurations. Along with a design methodology which has been established to strategically arrange point bearings around the limited spherical surface of a stator, the forward and inverse kinematics for relating the rotor displacement and the air gaps have been derived in closed-forms, which are essential for the design optimization, dynamic simulation and for motion control. With a detailed modeling of the pressure-flow relationship as a function of the rotor position, the dynamic performance of the air bearing system has been evaluated analytically by simulation. Simulation results suggest that the fluid forces could be generated to passively stabilize the otherwise open loop unstable electromagnetic system. The innovative spherical air bearing design has been used to regulate the rotor translations to within sub-millimeter motion precision. It is expected that this research will be a basis for designing, modeling, and evaluating an improved VR spherical motor with enhanced torque capability by eliminating mechanical friction. |
