STABILITY AND CONTROL OF ELASTIC-JOINT ROBOTIC MANIPULATORS DURING CONSTRAINED-MOTION TASKS

Within the robotics literature, the stability of robotic manipulators during contact tasks has been the focus of attention. These investigations have begun to examine the effects of structural compliance of both the robot manipulator and objects contacted by the manipulator on overall system stability. The source of an observed chattering phenomenon during which the manipulator end-effector repeatedly makes and breaks contact with objects in the work environment is still the subject of speculation. This paper examines the effect of a major source of manipulator compliance, namely, the elasticity of manipulator joints, on the overall stability of robot manipulators during constrained-motion task execution. The stability of the elastic-joint manipulator during constrained-motion contact is investigated separately for the case of two controls applied to the manipulator. Using results from the theory of singular perturbations, the stability of the robotic system is established with a "rigid" control law applied. Secondly, the stability of the robotic system is again established using the above technique for the case of a "rigid" control law with a corrective term applied to compensate for joint flexibility applied. It is theoretically established that the presence of joint elasticity does not lead to a destabilizing effect on the manipulator. The results of this work assume exact knowledge of both kinematic and dynamic parameters of the manipulator and contacted objects. Numerical simulation results of a two-degree-of-freedom flexible-joint manipulator during constrained-motion task execution confirm the theoretical claims of this communication.