Structural design and stiffness matching control of bionic variable stiffness joint for human-robot collaboration

The physical compliance of interaction is an important requirement for safe and efficient collaboration between robots and humans, and the realization of human-robot compliance requires robot joints with variable stiffness similar to those of human joints. In this study, based on the tissue structure and driving principle of the human arm muscle ligament, a robot joint with variable stiffness is designed, consisting of an elastic belt and serial elastic actuator in parallel. The variable stiffness of the joint is realized by adjusting the tension length of the elastic belt. Surface electromyography (sEMG) signals of the human arm are used as the characterization quantity of joint stiffness to establish the pseudostiffness model of the elbow joint. The stiffness of the robot joints is adjusted in real-time to match the human arm stiffness based on the changes in sEMG signals of the human arm during operation. Real-time compliant interaction of human-robot collaboration is realized based on an end stiffness matching strategy. Additionally, to verify the effectiveness of the human joint stiffness matching-based compliance control strategy, a human-robot cooperative lifting experiment was designed. The bionic variable stiffness joint shows good stiffness adjustment, and the human-robot joint stiffness matching strategy based on human sEMG signals can improve the effectiveness and comfort of human-robot collaboration. (c) 2022 The Author(s). Published by Elsevier B.V. on behalf of Shandong University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).