Development of a spherical stepper wrist motor

The design concept is presented of a novel spherical stepper robotic wrist motor capable of three-degree-of-freedom (DOF) motion in a single joint for applications where high-speed manipulation of end-effector orientation is required continuously in all directions. Typical applications are plasma and laser cutting and microassembly. The spherical motor is developed based on the principle of the variable-reluctance stepper motor. The differences between the operation principle of the three-DOF spherical motor and that of the conventional stepper motor are pointed out. The authors seek to establish a theoretical basis for design, prototype development, and performance prediction. An analysis of torque prediction is discussed, along with the presentation of kinematic and dynamic relationships. A laboratory prototype hybrid digital/analog control circuitry has been developed to demonstrate proof of concept feasibility and to assist in achieving an optimum design