Actuation Redundancy of A Closed Link Manipulator

In this paper, we propose a closed link mechanism for kinematically redundant direct-drive manipulators and discuss its redundant actuation. The mechanism is kinematically equivalent to four joints of the shoulder through the elbow of an anthropomorphic 7 DOF manipulator. The mechanism uses five direct-drive motors to control 3 DOF position of the end effector. One DOF exhibits kinematical redundancy and another DOF demonstrates actuation redundancy. We show that the previous parameterization of actuation redundancy involves algorithmic singularity and cannot take full advantage of actuation redundancy in some situation. A new singularity-free parameterization is proposed. The advantage of actuation redundancy and the difference due to the pararmeterizations are numerically demonstrated.