Path Tracking Control of a Manipulator Considering Torque Saturation

Hirohiko Arai, Kazuo Tanie and Susumu Tachi

IEEE Transactions on Industrial Electronics, Vol.41, No.1, pp.25-31, 1994.


When the minimum-time trajectory of a manipulator along a geometrically prescribed path is planned taking into consideration the manipulator's dynamics and actuator's torque limits, at least one of the joints should be 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 coordinate system called path coordinates is defined. The path coordi-nates are composed of the coordinate along the path and the coordinates normal to the path. The equation of motion is 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. Simulations by a two-degree-of-freedom manipulator show the effectiveness of this method.