Design Optimization of a Three Degrees-of-Freedom Variable-Reluctance Spherical Wrist Motor

[+] Author and Article Information
R. B. Roth

HV Technologies, Inc., Trenton, GA 30752

Kok-Meng Lee

Georgia Institute of Technology, Atlanta, GA 30332-0405

J. Eng. Ind 117(3), 378-388 (Aug 01, 1995) (11 pages) doi:10.1115/1.2804344 History: Received April 01, 1993; Revised March 01, 1994; Online January 17, 2008


This paper presents the basis for optimizing the design of a three degrees-of-freedom (DOF) variable reluctance (VR) spherical motor which offers some attractive features by combining pitch, roll, and yaw motion in a single joint. The spherical wrist motor offers a major performance advantage in trajectory planning and control as compared to the popular three-consecutive-rotational joint wrist. Since an improved performance estimate is required, a method for optimizing the VR spherical motor’s magnetics was developed. This paper begins with a presentation of the geometrical independent and dependent variables which fully described the design of a VR spherical motor. These variables are derived from examination of the torque prediction model. Next, a complete set of constraint equations governing geometry, thermal limitations, amplifier specifications, iron saturation, and leakage flux are derived. Finally, an example problem is presented where the motor’s geometry is determined by maximizing the output torque at one rotor position. The concept of developing a spherical motor with uniform torque characteristics is discussed with respect to the optimization methodology. It is expected that the resulting analysis will improve the analytical torque prediction model by the inclusion of constraint equations, aid in developing future VR spherical motor designs, improve estimates of performance, and therefore will offer better insight into potential applications.

Copyright © 1995 by The American Society of Mechanical Engineers
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