DESIGN OPTIMIZATION OF A 3-DEGREES-OF-FREEDOM VARIABLE-RELUCTANCE SPHERICAL WRIST MOTOR

This paper presents the basis for optimizing the design of a three deg rees-of-freedom (DOF) variable reluctance (VR) spherical motor which o ffers some attractive features by combining pitch, roll, and yaw motio n in a single joint The spherical wrist motor offers a major performan ce advantage in trajectory planning and control as compared to the pop ular three-consecutive-rotational joint wrist. Since an improved perfo rmance estimate is required a method for optimizing the VR spherical m otor's magnetics was developed. This paper begins with a presentation of the geometrical independent and dependent variables which fully des cribed 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, ampl ifier specifications, iron saturation, and leakage flux are derived. F inally, 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 character istics is discussed with respect to the optimization methodology. It i s expected that the resulting analysis will improve the analytical tor que prediction model by the inclusion of constraint equations, aid in developing future VR spherical motor designs, improve estimates of per formance, and therefore will offer better insight into potential appli cations.