Mathematical modelling and fuzzy logic based position control of an electrohydraulic servosystem with internal leakage

This paper describes an application of a fuzzy logic position control to an electrohydraulic servosystem. Mathematical model of the electrohydraulic servosystem is obtained considering the internal leakage within the servosystem. Electrohydraulic servosystems are one of the most commonly used actuators. However, electrohydraulic servosystems are difficult to control due to nonlinearity and complexity of their mathematical models. In this paper, as a first step, the mathematical models of the main components of the servosystem are obtained. The effect of compressibility, friction, internal leakage in servovalve, leakage in actuator and inertia are included in the model. Since the system has a complex structure and the system characteristics are time dependent. Fuzzy Logic Control (FLC) is applied to the electrohydraulic servosystem. The error and change in error are employed in the FLC. The effect of internal leakage on the mathematical model and performance of the position control system is investigated. Numerical simulation results for position control under a square wave reference input are obtained. Results are presented in graphical form. Physical trends of numerical simulation results are discussed. Although leakage is often ignored in dynamic analysis of servosystems, results shown in the paper indicate that the leakage has a significant effect on the mathematical model and performance of the position control system at small spool displacements. (C) 2009 Elsevier Ltd. All rights reserved.