Motion control with slow and rapid adaptation for smooth reaching movement under external force disturbance

We proposed a nonlinear reference shaping controller for a manipulator which shares its workspace with humans. In this paper, two adaptation methods to external force; “slow adaptation” and “rapid adaptation” are proposed for smoother reaching movements and submissive behavior to follow the force. These make smooth endpoint speed profiles and movements flexible to follow external force without detecting the force. The slow adaptation moderates the manipulator's endpoint acceleration, and it also enables the manipulator to handle subsequent changes of target endpoint positions. If the endpoint position is significantly changed by excessive external force, the rapid adaptation works to follow the force and restart the reaching movement smoothly. The validity of the proposed method is confirmed through computer simulations.