Adaptive impedance control with variable viscosity for motion and force tracking system

An adaptive impedance control method was proposed to establish a desired dynamical relationship between the robot end point and its environment. Although impedance control-based position or force controllers or hybrid position/force controllers with respect to each axis defined at the contact point, have been successfully applied to various systems, simultaneous control of position tracking and force generation at the end point or at the contact point between the robot and the human has not been proposed. In this study, we propose an adaptive impedance control with variable stiffness which was adjusted on-line based on the tracking error of motion trajectory. We introduce control parameters of weighted control action priorities of the motion tracking task and force generation task, based on the tracking error of the motion trajectory. With the weighted control action priorities, the robot puts higher priority on motion tracking at the robot end point when the position tracking error is large, and also on force generation when the position tracking error is small. Through this control method can make human simultaneously track the motion trajectory and force easily. Through some simulations results, we show the usefulness of the proposed control method.