Modeling and compensation control of a single tendon-sheath actuated system with time-varying parameters

The tendon-sheath actuated system (TSAS) has been widely adopted in many cases due to its merits of compliance, dexterity, and remote transmission. However, realizing precise control of the distal end poses remains a significant challenge due to inherent nonlinear phenomena caused by friction and hysteresis. In this study, a novel adaptive sliding mode compensation control (ASMCC) scheme based on the inverse transmission model was proposed to achieve accurate trajectory tracking of the TSAS. Based on the Coulomb friction model, the static and dynamic models of TSAS were analyzed and the correctness of system's output displacement and output force characteristics was confirmed through simulation and experimental results. Based on the assumptions of the constant curvature of the sheath and the pre-tensioned tendon, the inverse model was calibrated by offline measurements with sensors installed at the proximal end. A novel control strategy was developed based on the inverse model combined with an adaptive algorithm according to Lyapunov stability theory with sliding mode controller for the online estimation of time-varying parameters. Finally, trajectory tracking experiments were conducted with/without external springs to evaluate the feasibility of the proposed control strategy, and its effectiveness and accuracy in parameter identification and accuracy compensation for the single tendon-sheath actuated system was confirmed.