KINEMATIC ANALYSIS OF A 3-DEGREES-OF-FREEDOM SPHERICAL WRIST ACTUATOR

This paper presents the kinematic analysis of a three-degrees-of-freedom (DOF) spherical motor which offers some attractive features by combining pitch, roll, and yaw motion in a single joint. The spherical motor, which operates on the principle of variable-reluctance (VR), achieves high positioning resolution by using continuous-amplitude current control and thus allows the use of few but evenly spaced ferromagnetic poles for three-DOF actuation. As a result, the mechanical structure and the control circuitry of a VR spherical motor are much simplified for manufacture. The kinematic model of the VR spherical motor has been derived as a function of the derivative of the overlapping area between the stator and rotor poles in a three-dimensional space. This paper presents the first detailed kinematic analysis of a three-DOF VR spherical motor. The model permits a spectrum of design configurations to be analyzed. A unique, potentially useful design of a prototype VR spherical motor has been developed. The prototype allows the kinematic model to be examined experimentally and the implementation issues related to design and manufacture of a VR spherical motor to be addressed. These results offer some interesting insights to the design, manufacture, modeling, and motion feasibility study of a VR spherical motor.