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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.>
Lee et al. (Tue,) studied this question.