Provident control of an electrohydraulic servo with experimental results

In this study, we propose a novel variable structure control method for output tracking of uncertain nonlinear systems, with experimental application to an electro-hydraulic servo system. First we perform a state transformation to convert the system to the normal form. Then we apply a method that we have termed provident control, so called because of its frugal but judicious use of the input when compared to other variable structure methods which use large control authority to drive the state to the sliding surface. This method combines variable structure control with variable structure adaptation and performs switching with hysteresis between the structures so as to avoid a sliding mode. By completely separating the reaching and tracking phases, a two-degree-of-freedom controller is obtained. Experimental results indicate significant performance improvement over the well-known boundary layer sliding control, together with robustness against parametric uncertainty and external disturbances. Copyright (C) 1996 Elsevier Science Ltd.