Barrier Function-Based Adaptive Control of Twisted Tendon-Sheath Actuated System With Unknown Rigid–Flexible Coupling for Robotic Ureteroscopy

Due to the existence of unknown rigid–flexible coupling characteristics, the robust and accurate tracking control of the twisted tendon-sheath actuated system (TAS) is a challenging problem. In this research, a novel adaptive control scheme is proposed to achieve accurate trajectory tracking of the twisting angle of TAS. For the first time, a “hybrid” model is built by combining the rigid-link dynamics with the hysteresis phenomenon model, accounting for the unknown rigid–flexible coupling effects. Then, time-delay estimation is utilized to evaluate the lumped dynamics of the system. Based on the estimation results, a barrier function-based adaptive method is designed for the estimation, of which the updating speed is constrained and intuitive to adjust. With the estimation of the lumped uncertainties and adaptive law, a model-free control scheme is designed for TAS. Finally, the stability of the closed-loop system is theoretically guaranteed by the Lyapunov-based analysis. The effectiveness and robustness of the proposed controller are adequately validated through a series of experiments on a robotic ureteroscopy prototype. To the best of the authors' knowledge, it is the first thorough investigation of control issues related to “flexible endoscope twisting in catheter” in the field of medical robots.