Path Tracking Control of a Manipulator Considering Torque Saturation

Abstract

When the minimum-time trajectory of a manipulator along a geometrically prescribed path is planned considering the manipulator dynamics and actuator torque limits, at least one of the joints is at the torque limit. The execution of such a trajectory by a conventional feedback control scheme results in torque saturation. Consequently, the tracking error cannot be suppressed and the manipulator may deviate from the desired path. In this paper, we propose a feedback control method for path tracking which takes the torque saturation into account. Based on the desired path, a coordinates system called“path coordinates”is defined. The path coordinates are composed of the coordinate along the path and the coordinates normal to the path. The equations of motion are described in terms of the path coordinates. Control of the coordinates normal to the path is given priority in order to keep the motion of the manipulator on the path. The simulations by a two-degree-offreedom manipulator show the effectiveness of this method.