Valveless electrohydraulic servo system

Valveless electrohydraulic servo system

The traditional electro-hydraulic servo control system has large energy loss in work, is very sensitive to medium pollution, has high requirements for manufacturing accuracy and high cost, is difficult to find the cause of failure, has extremely high management and maintenance costs, and is also sensitive to temperature changes. These drawbacks greatly limit the application and popularity of traditional systems. In recent years, servo proportional control, digital control and other technologies have made many new achievements, but most of them have not fundamentally overcome the above shortcomings. Valveless electro-hydraulic servo control system is a technological innovation in the international hydraulic technology field in recent years. It overcomes some defects of the traditional system and has the remarkable characteristics of strong anti pollution ability, energy saving, low cost, high reliability, simple installation and connection, etc.

1. Principle and structure

The traditional system mainly uses the electro-hydraulic servo valve to control the actuator to obtain the servo action. The hydraulic energy output by the hydraulic pump has to undergo cumbersome electrical and mechanical displacement conversion, in order to finally achieve the direction, position and speed requirements of the system. Because the electro-hydraulic servo valve is a high-precision component, the cleanliness of the working medium is very demanding, so its manufacturing cost and use cost are very high.

Figure 46 is the principle block diagram of valveless electro-hydraulic servo system. It can be seen that the valveless system uses the AC servo motor to directly drive the two-way quantitative hydraulic pump. Because it gives full play to the characteristics of the AC servo motor without using the electro-hydraulic servo valve, it overcomes many disadvantages brought by the electro-hydraulic servo valve to the servo system, and its manufacturing cost and use cost are greatly reduced. In addition, it can also easily integrate the motor, hydraulic pump, oil tank, actuator and position sensor, It forms a valveless electro-hydraulic servo control device for direct use (see Figure 47). Because the AC servo motor can directly realize speed change, direction change and torque limit, the valveless device can easily change the direction and speed of the actuator. In the closed-loop system, the position control adopts displacement sensor for feedback, and the control accuracy can be effectively guaranteed. AC servo motor can be easily controlled by microcomputer. Therefore, valveless system has strong adaptability in automatic control. By changing the control program, the valveless device can easily get sine wave, square wave and other special forms of motion.

2. Technical performance and Application

To illustrate the technical performance of the valveless system, the traditional and valveless electro-hydraulic servo systems are listed and compared. See the following table for details.

Performance comparison between traditional system and valveless system

It is not difficult to see from the above table that the traditional system has obvious advantages in control accuracy and frequency response, but in practical industrial applications, the frequency response of 2 ~ 5Hz can fully meet the requirements of most servo systems. In terms of control accuracy, in order to obtain high control accuracy in the traditional system, only the servo valve with zero overlap (zero opening) characteristics can make the system obtain satisfactory accuracy and stability. In fact, the valveless system can also achieve high control accuracy through reasonable adjustment of control parameters when the load is relatively stable. In other aspects, the valveless system has the advantages of high efficiency, energy saving, small integration, simple operation and installation, etc. In recent years, valveless systems have been successfully applied in a variety of equipment and production devices produced abroad. According to the characteristics of the valveless system, the valveless system can obtain satisfactory application results in several aspects, such as ship steering gear control, continuous casting molten steel flow control (mold liquid level control), valve control, six degree of freedom simulation platform (simulation system), hydraulic robot (manipulator), hydraulic turbine speed regulation system, hydraulic punching and forging equipment (multi cylinder synchronous system), engineering machinery hydraulic control system, etc.