How to use the Omni-Wrist III for dexterous motion: An exposition of the forward and inverse kinematic relationships

Abstract

The Omni-Wrist III, invented by Ross-Hime Designs, Inc. (Rosheim, 1999, 2002), is a well known two-degree of freedom wrist mechanism that incorporates parallel links with double universal joints (N-UU). It has the advantage of singularity-free operation over the entire hemispherical work-space and maintains a constant axial distance between the two joints. These characteristics make it an appealing choice for mobile robotic appendages that require dexterous maneuvers. While the two active input joint angles are coupled, this paper presents an accessible exposition of the forward and inverse kinematics for the position and velocity of the mechanism. The novelty of this analysis lies in the parameterization of the kinematics in terms of the vector between the origins of the tool and space frames. The results of this paper provide concise equations that are readily implementable in simulation and on low power microcontrollers enabling the use of the Omni-Wrist III for highly dynamic mobile robot maneuvers.