Dextrous spherical robot wrist

This invention comprises a general redundant spherical linkage capable of producing singularity free relative motion of two arms which intersect at a fixed point. All points of all links of the invention move on spheres that are concentric about this fixed point of intersection of the two arms. In a general way the invention can be considered as a sphere which is divided by a central link that supports two pairs of orthogonally intersecting axes of rotation for four semicircular links that are 180 DEG arcs of great circles. The point of intersection of a pair of orthogonally pivoted semicircular links, directs an arm passing through the center of the sphere. Each pair of orthogonally pivoted links controls the spherical motion of one arm within one hemisphere. By simultaneously controlling all four pivoted links, arbitrary relative motion of the two arms can be achieved.