Contact force detection and control for robotic polishing based on joint torque sensors

Abstract

In robotic polishing applications, the rotating polisher will generate strong vibration disturbance, which makes it more difficult to detect and control the contact force. This paper proposes a novel and practical method to detect and control the contact force using the built-in sensors (motor encoders and joint torque sensors) for actual robotic polishing in harsh conditions of strong vibration disturbance. An extended state observer based on the robot dynamic model is developed to estimate the contact force in real time, and a new and efficient adaptive filter combining insights of the notch filter with the tracking differentiator is designed to relieve the strong vibration disturbance of torque signals from the eccentrically rotating polisher. On the basis of efficient force detection, a hybrid position/force control method based on the inner joint torque controller is proposed to realize accurate force control in actual robotic polishing of curved surfaces. With the proposed contact force detection and control methodology, the robot is potential to achieve satisfied polishing applications in which some usual accessories, such as the six-axis force/torque sensor or Remote Center Compliance device are absent. Experimental results confirm the effectiveness and accuracy of the proposed contact force detection method in conditions of strong vibration disturbance from the rotating polisher. In addition, the curved surface polishing experiments indicate that the new hybrid position/force control framework performs well on rejecting the strong disturbances while maintaining high force control accuracy of polishing, and the quality of polished surface is greatly improved.