Composite adaptive force tracking control for electro-hydraulic system without persistent excitation condition

Abstract

In this article, a composite adaptive control method without persistent excitation condition is proposed to improve force tracking performance of an electro-hydraulic loading system. Due to structure restriction, the force sensor cannot be installed and associated force signals are unable to be obtained by the control hardware. Thus, a composite adaptive control method is designed to estimate the unknown spring stiffness and friction coefficient of the electro-hydraulic loading system. Simultaneously, a modified prediction error is designed to relax the stringent persistent excitation condition of the conventional adaptive method. Then the position trajectory of the cylinder could be optimized by using the estimated stiffness to achieve accuracy loading for the specimen. Furthermore, first-order filters are utilized to produce certain virtual controllers and their derivatives to avoid analytic calculation. At last, the stability analysis of the closed-loop system is given, and the comparative experimental results have verified the effectiveness of the proposed control method.