Nonsingular Spherically Constrained Clemens Linkage Wrist

Abstract

The parallel connection of a revolute-spherical-revolute Clemens linkage with a revolute-universal joint (RU) spherical linkage realizes a two-axis spherical pointing device suitable for use in a robot wrist. The design is derived from a Clemens linkage constant-velocity coupling having a spherical constraint. A novel transverse orientation of the RU linkage facilitates control of the pointing direction through actuation of a pair of revolute joints at the base of the device, a capability not otherwise required when this type of mechanism is employed as a constant-velocity coupling. As the mechanism is confined to spherical space, spherical trigonometry and related geometric reasoning may be employed in the analysis of mobility and actuation. The analysis derives the forward and inverse kinematic relations, showing that the mechanism allows a full 180 deg of deflection of the pointer from the center before encountering a singularity.