Adaptive Output-Feedback Control of a Class of Nonlinear Systems with Unknown Sensor Sensitivity and Its Experiment for Flexible-Joint Robots

Abstract

This paper investigates an adaptive output-feedback stabilization problem for a class of uncertain nonlinear systems with an unknown sensor sensitivity. A high-gain observer based on an inexact system output is designed to estimate unmeasurable state variables and an adaptive output-feedback dynamic surface control strategy is established to accomplish the robust stabilization in the presence of the unknown sensor sensitivity. Compared with the existing control results dealing with the unknown sensor sensitivity, the primary contribution of this paper is that the proposed adaptive control strategy does not require the information of the sensor sensitivity and its bound where the effect of the unknown sensor sensitivity is compensated by designing an adaptation structure. From the Lyapunov stability analysis, the ultimate uniform boundedness of all closed-loop signals and the convergence of the stabilization error to an adjustable neighborhood of the origin are ensured. A simulation for a numerical example and an experiment for a flexible-joint robot are provided to validate the effectiveness of the proposed theoretical approach.