Motion-copying system with variable impedance based on scaled bilateral control in one-degree-of-freedom robot

A motion-copying system is a kind of autonomous robotic system. This system reproduces human motion on the basis of haptic information (i.e., position and force information) extracted using a bilateral control system. However, in conventional motion-copying systems, control stiffness always remains constant. Thus, conventional systems show poor adaptability to differences in environmental locations during the reproduction phase. The objective of this study is to develop a motion-copying system with variable impedance. The proposed method includes an approach to determine the control stiffness of the motion-copying system on the basis of position, force, and impedance information. The haptic information is acquired using a scaled bilateral control system. For calculating the impedance, dynamic programming matching and the least-squares method are utilized. Dynamic programming matching accommodates the motion speeds in the saved data. The derived impedance is fed into a compliance control system, where it is reproduced. To validate the proposed method the task of removing a sarcoma is performed in experiments, in which three different types of target positions are set. The proposed motion-copying system succeeded in removing the sarcoma phantom, whereas the conventional method either failed to grasp it or applied excessive force. The proposed method succeeded in increasing the adaptability of the motion-copying system to different environmental locations.