Stability and control of robotic manipulators during contact/noncontact task transition

A control methodology that addresses the problem of control of robotic manipulators during a general class of task that requires the manipulator to make a transition from noncontact motion to contact motion and contact motion to noncontact motion is proposed. During noncontact motion, a control suitable for the noncontact phase of motion is applied; during contact, another control, suitable for contact motion, is applied. These different control schemes are applied to the manipulator in such a way that the overall control is discontinuous in nature. The following closed-loop behavior is achieved: (1) the closed-loop system exhibits global asymptotic stability; (2) asymptotic trajectory tracking of generalized force and position inputs is achieved; and, significantly, (3) upon inadvertent loss of contact by the manipulator, contact is reestablished and generalized forces and positions are again achieved asymptotically. Experimental results, performed on a two-degree-of-freedom direct-drive robot, support the theoretical claims.>