The design concept of a spherical stepper motor capable of three-degrees-of-freedom (DOF) motion in a single joint is presented. The ball-joint-like motor has no singularities except at the boundary of the workspace and can perform isotropic manipulation in all three directions. Due to its relatively simple ball-like structure, undesired cross-coupling and centrifugal components of wrist rotor dynamics can be effectively minimized or eliminated. The spherical stepper motor has potential in robotic applications as a three-DOF shoulder or an eyeball, as well as a wrist actuator. In particular, the systematic conceptualization of a spherical stepper is presented, and the feasibility of constructing the spherical stepper is examined. Along with the experimental data, an analytical approach based on the permeance formula was used to predict the driving forces generated by a neodymium-iron permanent magnet. The force-displacement curves provide useful information for rational spherical motor design and control.>

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.>