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M. S. Thesis Abstract
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**A Design
Methodology of a High-torque Multi-degree-of-freedom Spherical Motor**
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David J. Kim
March 1997
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. |