Inverse kinematic functions for redundant spherical wrists

By upgrading to a manipulator with a three-axis wrist, it is possible to expand the workspace and largely eliminate the effects of singularities. The author achieves these goals using the inverse kinematic function approach to redundancy. He shows that an ideal wrist should be mounted with its first axis perpendicular to the major axis of the manipulator´s forearm. With regard to commercially available manipulators, he shows that the pointing workspace of a PUMA-560 can be expanded by approximately 20% by using all three wrist axes as compared to using only the first two wrist axes. The results can also be applied to kinematic control of a four-axis spherical wrist applied to three-degree-of-freedom orientation tasks