A Practical Output Feedback Controller for Robotic Flexible Endoscope System With Unknown Dynamics and Actuator Uncertainties

Robotic flexible endoscope (RFE) systems are widely preferred in natural orifice transluminal endoscopic surgeries owing to their unique advantages. Nevertheless, some inherent characteristics of RFE systems (e.g., complex dynamics, input hysteresis, etc.) are still challenging issues to be solved for the autonomous steering. Therefore, this article designs a novel adaptive output feedback control method to handle the unknown dynamics and actuator uncertainties for the bending motion of RFE systems. In particular, a group of continuous signals are first constructed to recover unmeasurable velocities <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">without</i> differential calculation. Then, relying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">solely</i> on the accessible bending angle, an output feedback controller is proposed based on an adaptive fuzzy logic system, which can simultaneously approximate the uncertain model and input uncertainties online. The closed-loop system is rigorously proven to exhibit <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">exponential</i> stability based on Lyapunov theory. Finally, the proposed approach is applied on a self-built robotic ureteroscopy prototype to validate its effectiveness and robustness. Compared with traditional approaches, the proposed controller has higher tracking accuracy, stronger robustness, and lower sensing requirements. To the best of the authors' knowledge, this is the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">first</i> output feedback control strategy to achieve accurate autonomous tracking and estimate the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">unmeasurable</i> signals for RFE systems with unknown dynamics and input hysteresis/deadzone.