Impedance control of a direct-drive manipulator without using force sensors

This research is concerned with impedance control of a manipulator which carries out stable contact tasks. The method controls the dynamic interaction between a robot and its environment by changing the apparent mechanical impedance of the manipulator. Conventional impedance control methods required force or torque sensors, which made the manipulator system very complex. In this paper a new method is proposed for controlling the impedance of a manipulator without using force or torque sensors. The angular velocity and angular acceleration of the manipulator joints are estimated, and by using a computer model of the manipulator, the necessary torque for each joint is calculated and applied to the joint to attain the desired impedance. The feasibility of the method is verified by surface-following experiments and collision experiments using a two-degree-of-freedom direct-drive manipulator.