Abstract: The motion of passive joints of under-actuated robots is driven by dynamic coupling between the actuated joints and the passive one. The coupling always encounters dynamic singularity, which result in poor manipulability of system. Dealing with the arbitrary under-actuated manipulator, a dynamic optimal method is proposed. The core is construct a finite subspace motion sequences that cover with the full dynamic coupling space according as the coupling measure, the motion occurred in the subspace has redundancy, and can be utilized to optimize the coupling. A simulation on a four links under-actuated manipulator verifies this method.

Key words: Dynamic coupling, Motion planning, Optimal control, Under-actuated manipulator