Application of new materials in the field of therm

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Application of new materials in the field of electro-hydraulic servo valve development

at present, the application of new materials in the field of electro-hydraulic servo valve development is mainly the development of converters based on piezoelectric components, giant magnetostrictive materials and shape memory alloys. Each of them has its own excellent characteristics

piezoelectric element

the characteristic of piezoelectric element is "piezoelectric effect": under the action of a certain electric field, the overall dimension will change, and within a certain range, the deformation is directly proportional to the electric field strength. 7. All equipment is equipped with corresponding mechanical, hydraulic, electrical and other protective measures. The main materials of piezoelectric components are piezoelectric ceramics (PZT), electrostrictive materials (PMN), etc. Typical piezoelectric ceramic materials include stacked piezoelectric telescopic ceramics of tokin company in Japan. The principle of PZT direct acting servo valve is that the two ends of the valve core are respectively connected with two multi-layer piezoelectric elements through steel balls. Through the piezoelectric effect, the piezoelectric material can stretch and drive the valve core to move. Realize electrical mechanical conversion. PMN nozzle flapper servo valve is equipped with a flapper which is fixedly connected with the piezoelectric stack at the nozzle. The gap between the flapper and the nozzle is increased or decreased by the extension and contraction of the piezoelectric stack, so that the differential pressure is generated at both ends of the valve core to drive the valve core to move. At present, the development of piezoelectric electromechanical converter is relatively mature and has been widely used. It has the characteristics of fast frequency response, and the frequency width of the servo valve can even reach thousands of Hertz, but it also has the disadvantages of large hysteresis and easy drift, which restrict the further application of piezoelectric elements in the electro-hydraulic servo valve

giant magnetostrictive material giant magnetostrictive material (GMM) can produce much larger length or volume changes under the action of magnetic field than traditional magnetostrictive materials. The direct acting servo valve developed by using GMM converter connects the GMM converter with the valve core, drives the expansion and contraction of GMM by controlling the current of the driving coil, drives the displacement of the valve core, and controls the output flow of the servo valve. Compared with the traditional servo valve, this valve not only has the characteristics of high frequency response, but also has the advantages of high precision and compact structure. At present, the United States, Sweden and Japan are at the leading level in the development and application of GMM. Zhejiang University in China has used GMM technology to carry out structural design and characteristic research on pneumatic nozzle flapper valve and high-speed powerful solenoid valve of internal combustion engine fuel injection system. From the current situation, compared with piezoelectric materials and traditional magnetostrictive materials, GMM materials have the characteristics of large strain, high energy density, fast response speed and large output force. Countries all over the world attach great importance to GMM electro-mechanical converter and related technical research. GMM technology has developed rapidly, and has gradually entered the market development stage from the laboratory development stage. In the future, it is necessary to solve the problems of thermal deformation, magnetocrystalline anisotropy, material corrosion, manufacturing process and parameter matching of GMM, so as to be widely used in high-tech fields

shape memory alloy shape memory alloy (SMA) is characterized by shape memory effect. After it is shaped at high temperature, it is cooled to low temperature and applied with external force. Generally, metal will have permanent deformation after exceeding its elastic deformation, but SMA will restore its original shape under high temperature after heating it to a certain temperature in normal operation. 4. The specified working temperature is 10~40 ℃, otherwise the viscosity of gear oil is too large or too small. The servo valve developed by using its characteristics is to add a group of SMA actuators wound by shape memory alloy at both ends of the valve core, drive the SMA actuator by heating and cooling, make the shape memory alloy at both ends of the valve core extend or contract, drive the valve core to move, and add position feedback to improve the control performance of the servo valve. From the situation of this valve, although SMA has large deformation, its response speed is slow and its deformation is discontinuous, which also limits its application range

compared with the traditional servo valve, the servo valve developed by using the electric mechanical converter of new materials generally has the advantages of high frequency response, high precision and compact structure. Although there are still some key technologies to be solved, the application and development of new functional materials provide a new way for the technical development of electrohydraulic servo valves

at present, the application of electronic and digital technology in electrohydraulic servo valve technology mainly requires two ways to obtain the vertically arranged carbon nanotube forest: first, add d/a conversion device to the analog control components of electrohydraulic servo valve to realize its digital control. With the development of microelectronics technology, the control components can be installed inside the valve body, and the performance of the valve can be controlled by computer program to realize digital compensation and other functions. However, analog circuits are prone to zero drift and temperature drift, and d/a conversion interfaces are needed. The second is direct acting digital control valve. By driving the valve core with a stepping motor, 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, open-loop control of speed and position and direct digital control, and is widely used. However, in the occasions with high real-time control requirements, such as the conventional step-by-step method, the requirements of quantization accuracy and response speed cannot be taken into account. Zhejiang University of technology adopts the method of continuous tracking control, which eliminates the contradiction between the two and obtains good dynamic characteristics. In addition, many digital servo valve products are formed by various control methods such as digital control through direct drive of valve core by DC torque motor or structural change of servo valve

with the development of various technical levels, a new intelligent servo valve integrating machinery, electronics, sensors and computer self-management (fault diagnosis and troubleshooting) has been developed by using new sensor and computer technology. This kind 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 as flow control servo valve, pressure control servo valve or flow/pressure composite control servo valve according to the control requirements. And the control parameters of the servo valve, such as flow gain, flow gain characteristics, zero point, etc., can be set according to the principle of optimization of control performance. The diagnosis information and key control parameters of the servo valve (including working environment parameters and internal parameters of the servo valve) can be fed back to the main controller in time; In fact, good machine performance and efficiency is a major factor affecting the price. Distance to monitor, diagnose and remote control the servo valve. During the commissioning of the host computer, the control parameters of the servo valve can be downloaded through the bus port or directly set by the upper computer, so that the servo valve can achieve the best match with the control system and optimize the control performance. The servo valve control parameters can be downloaded and updated even when the host is running. In the development of servo valve matching with control system, embedded technology has become a reality for servo valve. According to the embedded system, it should be defined as "a special computer system embedded in the object system". "Embeddedness", "specificity" and "computer system" are the three basic elements of embedded system. It embeds a special microprocessor chip and corresponding control system into the traditional servo valve, constructs a servo valve with optimal control parameters according to the specific application requirements of customers, and completes the corresponding control tasks by the valve's own control system (such as the synchronous control of each control axis), and then embeds it into the whole large control system. From the current technological development and the requirements of the control system for the servo valve, the self diagnosis and self-test functions of the servo valve should have greater development

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