Nonlinear Hysteresis Modeling and Compensation of Tendon-Sheath System via Piecewise Linear Approximation

Tendon-sheath system (TSS) provides a simple yet dexterous solution of force transmission for remote actuation. However, the nonlinear friction determines the control performance of TSS. This paper proposes a simplified piecewise linear model to construct backlash hysteresis. An inverse transmission of this model is used to control distal-end force. Considering the effect of velocity on the transmission model, a piecewise inverse mode method with variable parameters is designed to reduce the force tracking error. The performance of the proposed methods is evaluated by force-tracking experiments with different velocities. The results show that the proposed compensator achieves good force-tracking performance and reduces root mean square error (RMSE) from 3.95 N (without compensator), 1.03 N (traditional compensator), and 0.79 N (piecewise compensator) to 0.43 N (piecewise compensator with varying parameters).