Modeling and Robust Control for Tendon–Sheath Artificial Muscle System Twist With Time-Varying Parameters and Input Constraints: An Exploratory Research

Tendon–sheath artificial muscle (TSAM) is a type of artificial muscle, which is widely used in robotic flexible endoscopies. The characteristics of the tendon force/position transmission were studied recently, but the control issue of the TSAM

twist

is still barely concerned. In this article, an effective robust control scheme is proposed for the TSAM

twist

, which achieves satisfactory tracking performance. First, a rigorous model was developed for the TSAM

twist

with consideration of parameters uncertainty and actuator input constraints, moreover, the disturbance of the discontinuous friction (Coulomb friction) was analyzed. Next, by applying some signal operation methods, a nonlinear robust controller was designed. In addition, the stability of the control strategy was proven theoretically by utilizing Lyapunov-based theory. Finally, a series of hardware experiments were conducted on a robotic flexible ureteroscope test-bed. The feasibility of the proposed model, the effectiveness and robustness of the designed control method were extensively validated.