Nonlinear Adaptive Robust Observer for Velocity Estimation of Hydraulic Cylinders Using Pressure Measurement Only

Abstract

This paper considers the design of an observer to estimate the velocity of an electro-hydraulic system using pressure measurements only. The difficulties involved in the design of an observer for such a system include the highly nonlinear system dynamics, severe parametric uncertainties like large variation of inertial load and unmatched model uncertainties. In order to tackle these problems a nonlinear model based Adaptive Robust Observer (ARO) is designed which provides not only a robust estimate of the velocity of the system but also the robust identification of the system parameters. Online monitoring of certain persistence of excitation conditions allow us to improve the quality of the parameter and velocity estimates. Simulation and experimental results on the swing motion control of a three-degree-of freedom hydraulic robot arm demonstrate the effectiveness of the proposed observer.