M. S. Thesis Abstract
A Design Methodology of a High-torque Multi-degree-of-freedom Spherical Motor
David J. Kim
A permanent-magnet (PM) spherical motor containing permanent magnets in its rotor assembly was proposed. Although the structure of the PM spherical motor was similar to the structure of a variable-reluctance (VR) spherical motor, the operating principle of the PM spherical motor differed from that of the VR spherical motor: Unlike the VR spherical motor which relies only on attraction between iron rotor poles and stator poles, the PM spherical motor relies on both attraction and repulsion between PM rotor poles and stator poles. A two-dimensional finite-element (FE) analysis was conducted to study the repulsive force. The results indicated that for a low coil current input the PM spherical motor operates only on attraction due to the strong demagnetizing field of the permanent magnet. Based on the FE results, the linear magnetic circuit model of the PM spherical motor was constructed, and the static torque model of the motor was derived. The torque model suggested that the torque output of a PM spherical motor can be divided into three different components: (1) component representing an interaction between electrical and magnetic power inputs, (2) component representing an interaction among magnetic power inputs, and (3) component representing an interaction among electrical power inputs. Among these components, the component representing an interaction among magnetic power inputs remains constant for a specific rotor orientation. Although the torque output of a PM spherical motor can be characterized by a similar approach used to characterize that of a VR spherical motor, the torque output of a PM spherical motor cannot be expressed as the torque-to-input-power ratio used by the VR spherical motor. Therefore, a constrained optimization must be performed in order to compute the maximum torque output.