System Identification And Characterisic Comparative Studies On Electro-Hydraulic Servo And Proportional Pressure Control System

Electro-hydraulic Proportional Control has been developing into a vigorous new branch in the field of the Fluid Power and Transmission Control since 1960s. It aims at meeting the special requirements of common engineering systems to emphasize either the traditional fluid transmission technique, which takes open-loop transmission as typical characteristic, or apply electro-hydraulic servo control technique, whose major characteristic is closed-loop control, or take advantage of both of the techniques. It is possible to replace servo valves with the Electro-hydraulic Proportional Control technique considering its advantages such as low cost, antipollution and energy-saving. However, at present, Electro-hydraulic Proportional Control technique needs further study since there are still many problems theoretically and practically. The researches on any kind of Proportional Control techniques will promote and enhance the development of Electro-hydraulic Proportional Control Technique.Targeting at the conditions for replacing servo control with proportional control, taking concrete pressure control system as the research subject, the study researches on proportional system and servo system from the aspects of identification method, the systems'characteristics and the different performances because of the different control strategies and different working conditions. The objective of the study is to figure out the similarities and differences between proportional control and servo control to shed light on the application of the two control techniques.Taking the material testing machine electro-hydraulic proportional pressure control system and servo pressure control system as research subjects, the dissertation sets out to compare and analyze the two systems according to the selections of input signals and sampling time, data processing methods, acquisition of the model structure style parameters, the right identification styles to acquire the mathematical models, and the accuracy of the identified mathematic models. At the same time, based on the comparative and contrastive study on different outputs with different identified mathematic models when inputting signals, with different model structure styles or various identification methods, it finds out the best identification method which is fit for the research subject. On basis of the identified mathematic models, using Genetic Algorithms, the dissertation obtains correct system open-loop parameters.Then, when making sure that all the conditions are the same except for the control element, it compares and analyses the stability, rapidity and accuracy of material testing machine proportion and servo systems, to find out the major parameters which lead to the performance differences of the two systems and which affect the performances of pressure control system. According to theory background and experiment results, it further studies the possibility of replacing servo system with proportional system under certain conditions. In order to avoid unilateral result when analyzing the characteristics of only one control system, the dissertation takes excavator arm cylinder pressure control system as the other research subject. Synthesizing the research consequences of the two subjects, it compares the system characteristics of the proportion and servo systems. It is concluded that under some kinds of working conditions the proportion system can realize the same control effects with that of the servo system.Finally, with the material testing machine as the research subject, using the identified mathematic models and the parameters, adopting PID control and MRAC as control strategies, the dissertation simulates the material testing machine electro-hydraulic proportional pressure control system and the material testing machine electro-hydraulic servo pressure control system. Then experiments are conducted on material testing machine. The study compares the performances of the two systems using both PID control and MRAC, and analyses the practicability of substituting electro-hydraulic servo pressure control system with electro-hydraulic proportional pressure control system in practical systems. The experiments shows that the servo system is superior to the proportion system under this experiment situation. The dissertation point out that proportion system can be applied to realize the proper conditions of controlling system performances.