Ph.D. Thesis Summary


Tian He

August 2000


Automation of repetitive jobs, which are usually accomplished manually, has been a topic of persistent research for a long time. Repetitive motions in stressful working environment have a potential to cause wrist and shoulder disorders. For this reason, significant efforts have been directed toward addressing this problem by exploring the use of alternative multiple degree-of-freedom (DOF) actuators for replacing manual repetitive motions. Among the efforts is a variable-reluctance (VR) spherical motor that provides 3 DOF smooth motion in a single joint.

This research begins with a critical investigation of a prototype VR spherical motor developed at Georgia Tech with emphasis on improving the torque-to-weight ratio and the uniformity of the torque generation. An analytical design method has been developed to optimize the actuator design, specially providing an effective means to visualize the torque generated by the VR spherical motor, which is characterized by a non-linear, orientation dependent function of currents. Simulation results show that the rotor pole configuration has significant influences on the torque performance of a spherical motor. The study provides useful guidelines for increasing the magnitude of the torque generated as well as improving the uniformity of the torque distribution by altering rotor pole layout.

In addition, the effects of permanent magnets on the torque generation were investigated both analytically and experimentally. The study has led to the development of a prototype rotor, which consists of a pair of permanent magnets sandwiched between three layers of iron poles. While the inclusion of permanent magnets significantly improves the torque-to-weight ratio, the trade-off is the complexity in modeling the torque, which has led to another contribution made in this thesis. The potential application of the VR spherical motor has been demonstrated using a chicken deboning process.

Major contributions of this research include an in-depth study on the influences of alternative rotor pole layout on the torque performance of the electromagnetically actuated VR spherical motor and the development of a torque model for design of a spherical motor utilizing permanent magnets. This research has established a basis for design optimization of a VR spherical motor with emphasis in improving the torque performance of the spherical motor.