A new kinematic design of a parallel spherical wrist with actuator
redundancy is presented. A special feature of this parallel manipulator is the
arrangement of co-axial actuators which allows unlimited rotation about any axis
inside a cone-shaped workspace. A detailed kinematic analysis has shown that
actuator redundancy not only removes singularities but also increases workspace
while improving dexterity. The structure optimization has been performed with a
global dexterity criterion. Using a conditioning measure, a comparison with a
non-redundant structure of the same type was performed and shows that a
significant improvement in dexterity has been obtained.