Research Of Key Technologies Of Digital Control For2D Servo Valve

Since the electro-hydraulic servo system has the advantages of high power to weight ratio, fast dynamic response, large load stiffness and so on, it is widely being used in the application of aeronautics&astronautics, marine and equipment manufacturing area. In the electro-hydraulic servo system, the electro-hydraulic servo valve has the functions of both electro-mechanical signal transformation and power amplification, and therefore has a crucial influence on the performance of whole system. The development of electro-hydraulic servo valve is always associated with the development course of electric-hydraulic control technology. With the development of information technology, computational technology and microelectronics, digital control of electro-hydraulic servo valve is being an inevitable trend as digital control not only improves the control quality and management level of whole system but also bring an overall opportunity to entirely enhance static and dynamic characteristics of servo valve itself.The2D servo valve achieves power amplification through servo screw mechanism, whose working principle is based on the usage of dual DOFs of spool radial rotation and axial movement. Compared to other types of servo valve,2D servo valve possesses benefits of simple structure, high anti-pollution capability, neglectable null position leakage of pilot stage, high natural frequencies and fast dynamic response. In this thesis the key technologies of digital control for2D servo valve are researched and the main contents are as follows:1. The digital control technology for inductor-type synchronous motor (also called as hybrid stepping motor), which is used as electro-mechanical converter of2D digital servo valve, is researched. The static and dynamic mathematical model of inductor-type synchronous motor is established. The frequency response of input-output characteristics under voltage control and current control are studied. Since the frequency width under current control is mainly limited by phase lag, the linearization method and phase plane method are used to analyze phase lag problem and a phase compensation method is proposed. Finally a novel continuous synchronous tracking control algorithm is put forward to ensure rotor of electro-mechanical converter to continuously track input signal without step loss and therefore possesses excellent static and dynamic characteristics.2. The digital dither compensation for nonlinearities of2D digital servo valve is studied. To suppress and even eliminate hysteresis caused by backlash of valve transmission mechanism, the mathematical model of hysteresis compensation is established and simulation is performed. To eliminate dead zone of flow characteristic caused by positive overlap, the principle of dead zone compensation is proposed and the simulation of dither compensation for dead zone of flow characteristics of2D servo valve is performed. Finally the effectiveness of dither compensation technology and theoretical analysis are validated by experimental study.3. According to synchronous tracking control algorithm and dither compensation for nonlinearities of2D digital servo valve, an embedded controller based on high speed DSP chip is developed and experiment of static and dynamic characteristics of electro-mechanical converter is performed. The experimental results illustrate that the electro-mechanical converter has excellent static and dynamic characteristics whose repeatability is less than1%, linearity is less than0.5%, frequency width is approximately245Hz at-3dB and-90°,and rising time of step response is about5.5ms.4. The static and dynamic characteristics of2D digital servo valve are researched. The theoretical analysis of null position leakage of pilot stage, static and dynamic characteristics of servo screw mechanism are performed and the influence of main structure parameters to valve frequency characteristics and step response such as initial chord height, radius of high&low pressure hole, length of sensitive chamber and system pressure, are all studied.5. The test rig for performance of2D servo valve is built. The experiments of null position leakage of pilot stage, flow characteristics, repeatability and dynamic characteristics of2D servo valve are performed. The experimental results reveal that the2D digital servo valve has excellent response speed, repeatability and dynamic performance. Its frequency width is about140Hz approximately at-3dB and-90°, rising time of step response is only about8ms, the overshoot of maximum percentage is about5.3%.