| Since the 1980's, with the wide applications of electro-hydraulic servo control techniques in industry and requirements for cheap, anti-pollution electro-hydraulic control components, research engineers have begun looking for a new type of electro-hydraulic control components which would replace the nozzle-flapper valve being sensitive to oil contamination and jet pipe servo valve with the leakage and power loss being a lot. In one study, a digital valve was examined, in which a stepper motor was utilized as the electro-mechanical transformer to carry out direct digital control.Compared to other servo valves, 2D digital servo valve has the advantage of insensitivity to oil contamination. In the design, zero lap between holes and spiral groove can be taken to ensure the stability and large static axial stiffness. The axial displacement of the spool is related to the angular displacement and conversion accuracy is high. The leakage is extremely small and its power loss is almost not considered. Control characteristics is ideal and there is no dead zone and hysteresis. To sustain the high resolution and fast response of the digital servo valve, a special algorithm has been developed to control the stepper motor continuously, which is undertaken by a microcomputer system with DSP in the valve controller.In this paper, 2D digital servo valve and controller are designed for study the performance by simulations and experiments. The speed step process is about 9ms. The bandwidth is about 100Hz at -3db gain and 55°phase lag for 25% input signal.The main tasks of this thesis are as follows.In chapter one, a summary of some relevant information about the history and trend of this research is made. The meaning, purpose and the main tasks of this thesis are given. In chapter two, the working principle three-potential four-way digital servo valve is introduced. Based on the mathematical model, dynamic performance and frequency characteristics are simulated using a numerical simulation method.In chapter three, mathematic model of stepper motor is established at first. Then simulations are made to measure angular displacements of the stepper motor under typic input waves and the sinusoidal control signals with different frequency. At last, the frequency characteristics of the controller are given.In chapter four, an embedded controller is designed with an algorithm of continual angular displace control of the stepper motor, which is a specially designed microcomputer system with DSP as CPU. The every part of hardware circuit diagram is given. There are some design experiences in discussion.In chapter five, experiments are designed to get dynamic response and frequency characteristics of the direct actuated digital valve and its controller. First, experimental system and control program are introduced. Then the real angular displacements of the stepper motor under typical input waves and the sinusoidal control signals of different frequency are obtained. The frequency characteristics of the controller are given in the experiment. Finally a typical step response time of digital valve is measured. The real axial displacement responses of the spool to the typical input waves and the different frequent sinusoidal control signals are obtained. The frequency response of the 2D digital valve is experimentally measured and compared with theretical results.In chapter six, a summary and a prospect of this thesis are put forward as the conclusions. |
