Force/Torque Sensing and Micro-Motion Manipulation of a Spherical Stepping Wrist Motor

Recent developments in robotics and high precision manufacturing automation have provided the motivation for the re-examining of unusual designs of electromechanical transducers. This paper presents the coarse-fine motion strategy of the spherical stepper wrist motor which combines pitch, roll, and yaw motion in a single joint. By presenting the trade-off between the torque generated and the resolution for a realistic wrist motor design, the needs of a micro-motion mechanism as part of the spherical wrist motor are discussed. The design concept of a series-parallel actuated micro-motion mechanism to enhance the resolution and to provide an effective means of torque sensing is addressed. The micro-motion actuation is achieved by piezo-electric actuating devices which have relatively short response time and essentially infinite positioning resolution.