ROBUST JOINT AND CARTESIAN CONTROL OF UNDERACTUATED MANIPULATORS

Underactuated manipulators are robot manipulators composed of both act ive and passive joints in serial chain mechanisms. The study of undera ctuation is significant for the control of a variety of rigid-body, sy stems such as free-floating robots in space and gymnasts, whose struct ure include passive joints. For mechanisms with large degrees of freed om, such as hyper-redundant snake-like robots and multi-legged machine s, the underactuated structure allows a more compact design, weight de crease, and energy saving. Furthermore, when one or more joints of a s tandard manipulator fail, it becomes an underactuated mechanism; a con trol technique for such system will increase the reliability and fault -tolerance of current and future robots. The goal of this study is to present a robust control method for the control of underactuated manip ulators subject to modeling errors and disturbances. Because an accura te modelling of the underactuated system is more critical for control issues than it is for standard manipulators, this method is significan t in practice. Variable structure controllers are proposed in both joi nt space and Cartesian space, and a comprehensive simulation study is presented to address issues such as computation, robustness, and feasi bility of the methods. Experimental results demonstrate the actual app licability of the proposed methods in a real two-degrees-of-freedom un deractuated manipulator. As it will be shown, the proposed variable st ructure controller provides robustness against both disturbances and p arametric uncertainties, a characteristic not present on previously pr oposed PID-based schemes.