An investigation on the implementation of different controllers for an electrohydraulic servo system

Abstract

Electro Hydraulic Servo Systems (EHSS) are distinguished by tremendous torque-to-inertia ratios, relatively high stiffness, self-lubrication of the fluid, and their potential to transmit huge forces at high speeds. Hence they are extensively applied in many industrial motion systems such as aircraft surface control systems, weapon control systems and hydraulic press machines. A hydraulic press is a metal forming machine which uses a linear hydraulic actuator to generate a compressive force. Hydraulic presses have a major advantage than mechanical presses by delivering full pressing force anywhere within the range of stroke. In this research, a typical hydraulic system is converted into an electro hydraulic servo system by replacing the directional control valve with a two stage flapper nozzle servo valve. The dynamics of Electro Hydraulic Servo Systems (EHSS) are highly nonlinear on account of compressibility of the hydraulic fluid, complex fluid flow properties of the servo-valve, valve overlap and friction in the hydraulic actuators. They show a large extent of model uncertainties in modelling external disturbances and leakages. Hence contemporary control methodologies have to be investigated. The experimental setup used in this investigation has three stages. The first stage is the power developing unit with a vane pump driven by a three phase electric motor. The second stage is the control unit, which consists of a two stage flapper nozzle servo valve and a data acquisition system. The third stage of the system is power transmitting unit which consists of the asymmetric hydraulic cylinder and Linear Variable Displacement Transducer (LVDT). The measured displacement of the LVDT and spool position of the servo valve is fed to the data acquisition system. newline newline newline