Computed torque method considering the nonlinear terms has been used for precise position control of the robotic system that involves nonlinear dynamics. It is hard to know exact values of robot parameters and the robot arm may receive unpredictable interference from the environment where it resides. These effects are regarded as disturbances which, especially in a direct drive robot, are directly transmitted to actuating motor without reduction. Those characteristics may arise a serious error in a tracking problem. So, it needs a robust controller to overcome this problem. In this paper, we propose a new controller which has the structure that $H_∞$ controller is adapted to linearized robot system by computed torque. And simulations are made for preparing the performance of this new one with that of a nonlinear $H_∞$ controller proposed by Chen and that of computed torque method.
