a1 Département de génie mécanique, Université de Moncton, Moncton, Nouveau-Brunswick, Canada
a2 Robotics and Mechanisms (RAM) Laboratory, Department of Mechanical Engineering, University of Victoria, Victoria, British Columbia, Canada
In this work, accuracy enhancement through backlash elimination is considered. When a nonredundantly actuated parallel manipulator is subjected to a wrench while following a trajectory, required actuator torque switching (going from positive to negative or vice versa) may occur. If backlash is present in the actuation hardware for a manipulator, torque switching compromises accuracy. When in-branch redundant actuation is added, a pseudoinverse torque solution requires smaller joint torques, but torque switching may still occur. A method is presented where concepts of exploiting a nullspace basis of the joint torques are used to ensure that single sense joint torques can be achieved for the actuated joints. The same sense torque solutions are obtained using nonlinear optimization. The methodology is applied to several examples simulating parallel manipulators in machining applications.
(Received June 10 2011)
(Accepted June 09 2011)
(Online publication July 11 2011)