Modeling and Simulation for the Electro-hydraulic Servo System Based on Simulink  

Abstract- This paper established mathematical model based on control theory for electro-hydraulic position servo system, used Simulink to simulate system model, and applied M files and module mask function to simplify the system simulation process. This electro-hydraulic position servosystem adopted PID controller. The PID control is the abbreviation of proportion, integral and differential control, its value depends on its widely applicable for most of the control system, especially when the mathematical model of the controlled object is known, PID control could be particularly useful. This paper applied digital PID to get ideal system dynamic performance by adjusting the PID parameters. This paper proposed a method that provides a reference for other control systems analysis and design.

Keywords-mathematical model; system simulation; module mask

I.   I NTRODUCTION

Electro-hydraulic servo system refers to the control system which combined two control modes of electrical and hydraulic. Detecting, transmitting and processing the signal by use of electric and electronic components, driving the load with hydraulic transmission in the electro-hydraulic servo control system. So it can make full use of electrical system for its convenience and aptitude, make full use of hydraulic system for its rapid response speed, big load stiffness and accurate positioning characteristics to make the whole system more adaptable. PID control is the abbreviation of proportion, integral and differential control, its value depends on its widely applicable for most of the control system, especially when the mathematical model of the controlled object is known, PID control could be particularly useful. Simulink is a graphical environment for dynamic system modeling, simulation and analysis interactively [1]. Using Simulink environment, can build complex system simulation model, using the mask function to simplify the model, using M files to initial the module variables, which provides great convenience for PID parameters setting and change the variable value of the various modules [2-3]. This paper establish the mathematical and simulation model for the valve controlled asymmetrical hydraulic cylinder position servo system, and optimize system dynamic performance by setting PID parameters

II.   ANALYSIS OF SERVO VALVE WITH ASYMMETRICAL CYLINDER

Fig.1 is the diagram of servo valve controlled asymmetrical cylinder position control system [4]. The electric-hydraulic servo valve is a zero opening and four-way slide valve. This paper studies the load of the hydraulic system compose of the inertial load, viscous load and linearization coulomb friction. The three basic equations of valve control hydraulic cylinder system are as follows [5].

Figure 1.  The diagram of servo valve controlled asymmetrical cylinder position control system

Linearized flow equation of the zero opening and four-way slide valve is

                 (1)

The load flow continuity equation of the cylinder is

       (2)

The force balance equation effected on piston is

   (3)

Integrated (1), (2) and (3) deduce to the transfer function, which is output displacement of the piston rod to input displacement of the valve

        (4)

Where

The response speed of servo amplifier and displacement sensor are far higher than servo valve controlled hydraulic cylinder, so they all can be seen as a proportional link. So, based on every part of the transfer function is known and ignore leakage and linearize the dry friction [6-7], get hydraulic position servo system simulation diagram as shown in Fig.2.

Figure 2.  Electro-hydraulic position servo system simulation diagram

III. CONTROL SYSTEM SIMULATION WITH SIMULINK

In standard Simulink module library contains many modules, such as Sinks(output module group), Source(input module group), Linear(Linear link module group), Nonlinear (non-linear links module group), Math(mathematical operation module group), Continuous and Connections modules group and so on. Each module contains manysub-module [8]. Use these modules can easily convert the system simulation diagram as Fig.2 shows to the simulation model shows as Fig.3.