Four-Joint Redundant Wrist Mechanism and Its Control

It is known that conventional three-joint wrists of robot manipulators have two conical regions of degeneracy in which the ability of the wrist to orient the end-effector is poor, A four-joint wrist mechanism is proposed in this paper as a means of overcoming this degeneracy problem. The manipulating ability of this wrist with respect to the end-effector orientation is analyzed using the manipulability measure. A pseudoinverse control algorithm for this redundant wrist mechanism is developed and its effectiveness is shown by experiments.