A New Model-Based Control Structure for Position Tracking in an Electro-Hydraulic Servo System With Acceleration Constraint

Abstract

A new variable structure control strategy consists of two separate sliding mode controllers (SMCs) with a switching mechanism designed to address position tracking problem of electro-hydraulic servo systems (EHS) with acceleration constraint, which can be found in numerous mechatronics and industrial control system applications. Examples include fatigue testing systems, plate hot rolling systems, injection molding machines, hydraulic elevators, and robotic arms. In this paper, first, a complete model of an electro-hydraulic system is proposed in which detailed mathematical descriptions for all elements are included. Not only is a more accurate model capable of providing a fertile ground for simulation studies but also it could contribute toward better results in the control approach. Furthermore, based on the variable dynamic behavior of EHS in forward and return motions, two separate SMCs synchronizing with a switching mechanism are applied. This novel approach calculates two separate control input in each instance for each dynamic behavior of the system and the switching mechanism decides which one should utilize. It is shown that the proposed control method, despite model uncertainties and external disturbances, tracks the reference position with error in scale of 10−3, and its remarkable accuracy in tracking trajectories with acceleration constraint, which has a great deal of importance in the sense of many industrial applications, is proved.