Application of digital technology in electro-hydraulic servo valve technology

Electro-hydraulic servo valve is a key component in electro-hydraulic servo control. It is a kind of hydraulic control valve that receives analog electrical signals and outputs modulated flow and pressure accordingly. Electro-hydraulic servo valve has the advantages of fast dynamic response, high control precision and long service life. It has been widely used in the electro-hydraulic servo control system in the fields of aviation, aerospace, naval ships, metallurgy, chemical industry and so on.

At present, there are two main ways to apply electronic and digital technology in electro-hydraulic servo valve technology: first, add D/A conversion device to the analog control components of electro-hydraulic servo valve to realize its digital control. With the development of microelectronics technology, control components can be installed in the valve body, through the computer program to control the valve performance, digital compensation and other functions. However, the analog circuit is prone to zero drift and temperature drift, and D/A conversion interface needs to be added. Second, for the direct - moving digital control valve. By using the stepping motor to drive the spool, the input signal is converted into the stepping signal of the motor to control the flow output of the servo valve. The valve has the advantages of compact structure, controllable speed and position of open ring and direct digital control, and is widely used. However, in the case of high real-time control requirements, such as the conventional stepping method, the requirements of quantization precision and response speed cannot be considered. The method of continuous tracking control is adopted in Zhejiang University of Technology to eliminate the contradiction between the two and obtain good dynamic characteristics. In addition, there are dc torque motor direct drive spool to achieve digital control and other control methods or servo valve structure changes to form a number of digital servo valve products.

With the development of various technical levels, a new intelligent servo valve integrating mechanical, electronic, sensor and computer self-management (fault diagnosis and troubleshooting) has been developed by adopting new sensor and computer technology. This type of servo valve can determine the control target according to the needs of the system: speed, position, acceleration, force or pressure. The same servo valve can be set according to the control requirements into flow control servo valve, pressure control servo valve or flow/pressure composite control servo valve. And the control parameters of the servo valve, such as flow gain, flow gain characteristics, zero, etc., can be set according to the principle of optimal control performance. The diagnostic information and key control parameters of the servo valve (including working environment parameters and internal parameters of the servo valve) can be timely fed back to the main controller. Servo valves can be remotely monitored, diagnosed and remotely controlled. All rights reserved in the control engineering network during the host debugging. The control parameters of the servo valve can be downloaded through the bus port or set directly by the upper computer, so that the servo valve and the control system can achieve a good match and optimize the control performance. And the servo valve control parameters download and update, even in the host operation can also be carried out. In the development of servo valve and control system matching technology, embedded technology for servo valve has become a reality. According to embedded system, it should be defined as "special computer system embedded in the image system". "Embeddedness", "specificity" and "computer system" are three basic elements of embedded system. It is embedded in the traditional servo valves dedicated microprocessor chip and the corresponding control system, based on customer's specific application requirements and build it into the optimal control parameters of the servo valve and the valve's control system to complete the corresponding task (e.g., the control shaft synchronous control), and then embedded in the whole control system. From the current technical development and control system requirements for servo valve control engineering network copyright, servo valve self-diagnosis and self-detection function should have a greater development.