Internal Preload Control of redundantly actuated Parallel Manipulators - Backlash avoiding Control

Redundant actuation of parallel manipulators admits internal forces without generating end-effector forces (preload). Preload can be controlled in order to prevent backlash during the manipulator motion. Such controlis based on the inverse dynamics. The general solution of the inverse dynamics of redundantly actuated parallel manipulators is given. For the special case of simple over actuation an explicit solution is derived in terms of a single preload parameter. With this formulation a computational effcient open-loop preload control is developed and applied to the elimination of backlash. Its simplicity makes it applicable in real-time applications. The approach is exemplified for a planar 4RRR manipulator.