비례방향제어 밸브를 사용한 유압 실린더의 위치 제어

Abstract

In this study, the author investigates automatic control design schemes to obtain excellent control performances in a hydraulic control system using a proportional directional control valve and a conventional hydraulic cylinder. The object control system consists of a proportional directional control valve with overlap characteristic near the neutral position, an electronic amplifier, a conventional hydraulic cylinder with big frictional resistance, and a personal computer for controller implementation. A proportional control valve with overlap characteristic has a dead zone near the neutral position. The overlap characteristic is apt to be the cause of dull responses and steady-state errors in control outputs. Therefore, it is the goal of this study to overcome the weakness of the valve characteristics, and finally to obtain good control performances in the object control system. In the first stage of this study, the author performs a study to improve the control performance of the valve itself(the unit including the electronic amplifier, the valve and a built-in spool-position sensor), which corresponds to a minor control loop in the object control system. Then, in the second stage, the author investigates controller design schemes to improve the control performances of the total control system mentioned above. Chapter 2 of this thesis handles the contents of the first stage study, and chapter 3 and 4 handle the ones of the second stage study described above. The contents of chapter 2, 3 and 4 are summarized as follows. In chapter 2, a neutral-position-characteristic compensator is devised to compensate the discontinuity control characteristic. And also, in chapter 2, a feed-forward controller in conjunction with a PI-D controller(shortly, FF-PI-D controller) is applied to the minor control loop to improve the control performances of the valve itself. In chapter 3, the introductory part of the chapter describes the composition and the basic characteristics of the object control system. To control the object control system(the total system), In chapter 3, a FF-PI-D controller is applied, and the control performances of the system are verified through the examination of the experimental results. In addition, in chapter 3, the control performances of a synchronizing control of two cylinders are shown, where the controllers are designed with the FF-PI-D controller. In chapter 4, for the same control system(the total control system) a different kind of controller design is applied. The controller in chapter 4 consists of a feedback-linearization compensator and a disturbance observer. The control performances of the system are also verified through the examination of experimental results. Conclusively, it is confirmed that the object control system can be controlled with excellent control performances by using the minor loop control schemes devised in this study for the valve unit and the controllers adopted in this study for the total control system.