As the core component of electro-hydraulic servo control system, the performance of servo valve directly affects the control accuracy, response speed and stability of the system. Hysteresis is a common nonlinear error phenomenon in the practical application of servo valve, which refers to the phenomenon that the output response does not coincide during the rising and falling of the input signal. The existence of hysteresis will reduce the accuracy of system control and may lead to the poor dynamic response of the system. Therefore, it is of great significance to study how to reduce the hysteresis of servo valve for improving the overall performance of servo control system.
First, the cause analysis of servo valve hysteresis
The servo valve hysteresis is mainly related to the following aspects:
1. Friction and clearance of mechanical structure: the friction between the slide valve and the valve body in the servo valve and the clearance of mechanical connecting parts will lead to hysteresis.
2. Elastic deformation hysteresis of materials: During the movement of the valve core, due to the elastic hysteresis characteristics of materials, a certain nonlinear output will also be produced.
3. Hysteresis effect: Hysteresis characteristic of magnetic circuit material is one of the important reasons for hysteresis in electromagnetic driven servo valve.
4. Compressibility and flow loss of hydraulic oil: Compressibility of hydraulic oil under high pressure and pressure loss during flow will also affect the dynamic response of servo valve and aggravate hysteresis.
Second, the main methods to reduce the hysteresis of servo valve
1. Optimize the mechanical structure design
-Improve the machining accuracy and reduce the clearance between the slide valve and the valve body;
-Use low-friction materials or surface treatment techniques (such as hard anodizing, coating, etc.) to reduce friction;
-Pre-tightening structure design is adopted to eliminate the influence of clearance in mechanical connection.
2. Improve the magnetic circuit design
-using magnetic materials with low hysteresis characteristics, such as permalloy or amorphous alloy;
-Optimize the design of electromagnetic coil, improve the symmetry of magnetic circuit and reduce the nonlinear change of magnetic field.
3. Adopt high-precision manufacturing technology
-improve the smoothness and parallelism of the mating surface between the valve core and the valve body;
-Strictly control the assembly accuracy to ensure the coaxiality and verticality of moving parts.
4. Introduce feedback control and compensation technology.
-Real-time detection of spool position by displacement sensor (such as LVDT);
-Feed-forward or PID compensation algorithm is introduced into the control system to dynamically compensate the hysteresis;
-Intelligent control methods such as fuzzy control and neural network are applied to improve the adaptability of the system to nonlinear errors.
5. Optimize working medium and hydraulic system.
-Use hydraulic oil with low compressibility and high stability;
-Keep the oil clean and reduce the interference of particles on the movement of the valve core;
-Reasonable matching of oil supply pressure and flow rate is designed to reduce energy loss during flow.
6. Temperature control and thermal compensation
-The servo valve may cause thermal expansion due to friction or electromagnetic heating in the working process, thus affecting the position accuracy of the spool;
-Thermal error compensation is realized through heat dissipation design or temperature sensor feedback.
Third, the conclusion
To sum up, the causes of servo valve hysteresis are complex, and reducing hysteresis needs to start from mechanical structure, material selection, manufacturing technology, control strategy and other aspects. With the development of advanced manufacturing technology and intelligent control theory, the hysteresis problem of modern servo valves has been significantly improved. In the future, with the continuous application of new materials, new processes and intelligent algorithms, the hysteresis of servo valve will be further reduced or even close to the ideal state, which will provide a more solid guarantee for the development of high-precision servo control system.