| Laser control technology belongs to the a hi-tech field related to many subjects such as laser, mechanics, microelectronics and hydraulics. Land leveling with the control of laser technology is an accepted method with highest accuracy among the land leveling techniques at present in the world. It is an important way to increase the land irrigation quality, improve the crop seedbed conditions, actualize "fine agriculture" and build modern agriculture of land irrigation. As a part of the National 863 Magnitude Science and Technology Program "Fine Land Irrigation Research - the Research and Development of the Laser Control Leveling System", the mission of the research is to develop a set of hydraulic control system and study the control performance of the laser land-leveling machine with high precision and efficiency, lower price, simple operation and excellent matching with the middle power tractor in common use in our country.On the basis of the research of the style, characteristics and control methods of leveling machines in common use at present, a general plan is designed according to the farmland environment in our country. And considering the characteristics and parameters of middle power tractor hydraulic system in common use in our country, as well as the task requirements of land leveling machine, an appropriate hydraulic control device is developed with the use of the thread cartridge valves.The thread cartridge hydraulic control valve, which directly determines the working quality of the whole system, is developed with novel structure and excellent performance. And with the aim at improving the anti-break ability of the differential relif valve, an optimum design method is put forward by establishing the optimum objective function with the minimum square error (ISE) so as to obtain the optimum combination parameters of the valve. The mathematical models for the hydraulic control valves are also established with state space method and the influence on the dynamic characteristics of the valve is analyzed with respect to the parameter varieties of the components with the simulation so as to obtain the optimum combination parameters of the valve.The fuzzy inference system for the control system of the laser land leveling machine is edited with the fuzzy control toolbox in the MATLAB software and the emulational model is obtained. The research on the dynamic characteristics simulation is carried out with the 'Simulink' module in the MATLAB software so that a reasonable control system is worked out.It has been testified through indoor experiments that the new hydraulic valves have perfect dynamic characteristics and stability as well as less leak, lower excess quantity and more quick response velocity. The unloading pressure of the hydraulic control device is 0.4MPa, and the rising delay time of the leveling spade is 80ms and the falling delay time is 44ms. It has no static sedimentation and the test results basically accord with results of the theoretical analysis.It can be concluded from several farm experiments of the laser land leveling system that the newly-designed hydraulic control system is perfectly matched with the relative units of the laser land leveling machine and has excellent working performances at high, medium and low rate. The testing parameters basically accord with the indoor results and it entirely satisfies the requirements of the farmland leveling. The standard deviation of the farmland surface after leveling is less than 2.5cm and the working efficiency is 0.81ha/h.
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