Zhaopeng Chen, Neal Y. Lii, Thomas Wimböck, Shaowei Fan, Hong Liu, and Alin Albu-Schäffer
Dexterous robot hand, friction observer, impedance control, object frame, joint torque
This paper presents an experimental study on impedance control in both Cartesian and object level with adaptive friction compensation for dexterous robot hand based on joint torque feedback. To adaptively decrease the effects of high friction caused by complex transmission systems and joint coupling, a friction observer is proposed based on the extended Kalman filter (EKF) in this paper. A Cartesian impedance controller is implemented on a multi-fingered dexterous robot hand with identical fingers, based on the modelling of each modular finger. In addition, a flexible n-fingered object frame is proposed in this paper, applicable to any finger configuration with three or more fingers (n ≥ 3). This enables the design of a 6-DoF spatial impedance controller. Stability of the closed-loop system with friction observer is analysed. A position error of less than 0.16◦ is achieved using joint impedance control with adaptive friction compensation, which shows significant improvement in performance, as compared to 1.5◦ without compensation, and 0.5◦ with fixed-parameters friction compensation. Experimental results confirm the improvement in performance for the robot hand with Cartesian impedance control and adaptive joint friction compensation, demonstrating the effectiveness of spatial impedance controller with the proposed object frame and estimation strategy.
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