Design analysis of a dual-cylinder electrohydraulic load simulator for motion tracking by individual metering under feedforward-PI control

Abstract

This thesis presents a comprehensive analysis of the design and performance of a dual-cylinder electrohydraulic load simulator (EHLS) for motion tracking applications. The EHLS serves as a crucial component in hardware-in-loop (HIL) experiments, particularly in the aerospace and automotive industries. The objective of the EHLS is to generate desired force profiles using a hydraulic cylinder, while simultaneously achieving precise motion tracking despite varying external loads. The study focuses on the challenges posed by nonlinearities in electrohydraulic systems, including the pressure-discharge relationship in variable openings of metering valve ports, friction effects, and oil compressibility. These challenges require advanced control strategies beyond simple PID feedback. Moreover, low-cost systems utilizing proportional valves and high-friction cylinder pairs exhibit additional nonlinear features, necessitating careful controller design to achieve comparable tracking performance to more expensive servo systems. Furthermore, the thesis investigates the energy efficiency and tracking accuracy of electrohydraulic systems. The use of variable-displacement pumps, proportional valves, individual metering valve (IMV) and combined individual metering valve (CIMV) arrangements are examined to reduce power losses and improve system efficiency. A composite feedforward position-force controller coupled with a feedback controller is designed. in developing the feedforward control, order-separation technique is used to estimate motion inducing terms, compressibility, and leakage related terms. Comparison of position and force response, FFPI control voltages of metering valves and chamber pressures for CIMV & IMV configurations is explored. Different combinations of position and load demands are explored to study the position and force tracking performances. Additionally, the thesis also cited the area to be explored in future. Different control strategies, valve and cylinder arrangements, are referred in the last chapter. As this thesis is entirely a simulation-based studies, hence a real-time experiment of the configurations should be carried out in future.The research findings provide insights into the design and control of electrohydraulic systems for motion tracking applications. The analysis contributes to the development of improved control strategies, energy-efficient designs, and enhanced tracking accuracy in EHLS and electrohydraulic force systems. The results have implications for industries such as aerospace, automotive, robotics, and fault-tolerant fields, where precise motion control and force tracking are crucial.