Singularity Free Mode Changes of a Redundantly Driven Two Limbs Six-Dof Parallel Robot

Abstract

A novel singularity free mode changes of a redundantly driven two limbs six-dof parallel robot ATARIGI is proposed in this paper. ATARIGI uses a total of eight actuators to drive a seven-dof mechanism, six-dof output node plus one-dof built-in differential screw. The parallel robot has multiple solutions to the inverse and forward kinematics. By changing postures from one solution to another, the parallel robot can expand its workspace. For ATARIGI, the bending direction of the elbow (over and under) of each limb and direction of the gripper (up and down) can be switched by the mode changes. Singularity and redundancy of ATARIGI are discussed by two Jacobian matrices which relate the velocity of the actuators and the mechanism. Conditions that ATARIGI loses redundancy but keeps the non-singularity are derived. Using the conditions, singularity free mode changes between “the elbows-over and gripper-down, suitable posture for the bottom working area,” and “the elbows-under and gripper-up, suitable for the upper working area” is proposed.