Quaternion Joint: Dexterous 3-DOF Joint Representing Quaternion Motion for High-Speed Safe Interaction

This paper presents a dexterous three degree-of-freedom (3-DOF) wrist mechanism with a large range of motion and uniform manipulability without singular points throughout the entire range of motion. It has a 2-DOF spherical pure rolling joint surrounded by two pairs of actuating wires, the motions of which directly represent the quaternion values of the joint; this joint is therefore named the quaternion joint. Based on this property, it has simple and clear forward and inverse kinematics and high manipulability. By adding a 1-DOF rotation joint at the distal end of the quaternion joint, it can be extended to a 3-DOF joint mechanism. To precisely approximate the spherical pure rolling motion in a confined central space, a novel parallel mechanism composed of three identical supporting linkages was introduced. Unlike conventional parallel mechanisms, it has a compact and simple structure with no interference among the supporting linkages. Because the wrist mechanism is a tendon-driven mechanism, and is thus suitable for lightweight manipulators, it is mounted to a low-inertia manipulator with high stiffness and strength, namely, LIMS2-AMBIDEX, which is an improved version of the authors' previous research. The basic concept and thorough theoretical analysis of the wrist mechanism are described herein, and the simulations and experiments conducted for a quantitative validation are presented.