| Small-seed crops play an important role in planting industry in China.By2011, the total sown area of crops was reached162283thousands of hectares and the sown area of small-seed crops such as oil, cotton, vegetables etc was a total of42056thousands of of small-seed crops should be put on the semi mechanized or artificial seeding with the problems of lower efficiency, higher cost and larger labor intensity of field management etc, which made comprehensive benefit lower and limited the sowing area of small-seed crops expansion.Given the problem of small-seed crops such as small size, easy damage and complex structure cased by traditional single metering device, the pneumatic cylinder-type precision metering device based on the principle of positive and negative pressure combined was developed, which simplified metering device structure and quantity, and improved the work efficiency and work quality. The research work in this paper are as follow:(1) There are carried on test and analysis of the mechanical and physical properties of small-seed crops, which provided theoretical basis for design of pneumatic cylinder precision centralized metering device. With Guangdong Chinese cabbage and Huaza "No. four" rapeseed as the research object, it mainly test three shaft size, weight, moisture content, the sliding friction angle and angle of repose in this paper. And there are focusing on the analysis of the growth characteristics of cabbage seeds under different compression. The experiments indicated that compression damage had significant influence on germination rate, germination vigor, length of radicles and seedling and vigor index. The germination vigor and germination rate had significant positive correlation while it showed negative correlation between germination vigor and the length of radicles. The germination didn’t been influenced when the force was less than6.4IN or the compression deformation was less than26.9percent.This result of test could provide the significant basis to suction hole, vacuum pressure, rotate-speed of the seed metering device.(2) There was conducting out the system metering device that was designed. The principle of pneumatic cylinder-type precision metering device for small seeds was analyzed and the main structure and operation parameters was determined. Basing on the physical characteristics of seed testing of small seed in the early stage, the external diameter of cylinder, the diameter of absorbing hole and the radial number of absorbing hole were determined. The theoretical analysis and experiments showed that the pneumatic cylinder centralized metering device was made of the external diameter of cylinder, the diameter of absorbing hole, the radial number of absorbing hole, the central angle to the adjacent suction holes, the radial distance in the cylinder surface and the axial distance that is (p165m,1.2mm,20,18°,26mm and30mm respectively, based on which the seedmeter performance and various consistency met the requirement of production. The rotational speed and limited positive and negative value of the pneumatic cylinder centralized metering device are analyzed. The rotational speed range froml7.8r/min to34.7r/min, the negative value from93pa to37200pa and the positive value from Opa to65.6kpa though the theoretical analysis are obtained.(3)There are carried out the character of force for pneumatic cylinder centralized metering. The model of dynamic and kinematic in main seeding process was established absorbing model. There are using the JPS-12test-rig to conduct out the single experiment. The experiment indicated that the quality index reaches90%and higher when the rotational speed is20r/min, the pressure is2200Pa and the vacuity is2200Pa. This research indicates that the experimental conclusion is in agreement with the result of analytical calculation, which provides theoretical foundation for optimizing operation and structure parameters of the metering device.(4) The pneumatic cylinder centralized metering device for small seeds was simulated and analyzed by using ANSYS/CFX software. The centralized metering device was simulated and analyzed with the number of absorbing hole, the structure of absorbing hole, the space of axial and the way of air out as the research object. And the simulation results were verified by test. The experiment showed that the structure of absorbing hole was the main influence factors of the size of pressure in the end surface, for which step hole and column hole was obviously better than cone hole. The way of air out influencesd the velocity of the end surface. The outlet of both ends can improve seeding reliability with more uniformity flow and less zero speed region. The combination of parameter optimization in pneumatic cylinder centralized metering device were30absorbing hole with stepped hole structure and20mm spacing with two air way.(5)There are carried out the experiments of performance for the centralized metering device.The single factor and orthogonal experiments which used the rotation speed, positive pressure and negative pressure as the experiment factor were conducted so as to achieve the good seeding performance. The bench experiments showed that the damage rate was below0.5%, the quality index was94.02%, the loss index was below4.0%, and the variation coefficient of the consistency of each line displacement and stability of the total displacement were5.73%,1.21%respectively when the rotating speed was20r/min, the positive pressure was2200Pa, and the negative pressure was2200Pa.(6) There are carrying out performance experiment in the pavement and field. In order to study the working parameters on seeding performance of centralized metering device influence and field test process of vibration, dust, a seed conveying pipe inclination angle, the tractor speed, road conditions, a land wheel slip rate on seeding performance of centralized metering device, there are finding the optimized combine of working parameter for centralized metering device. With positive value, rotational speed of centralized metering device, speed of Rotary blade, speed of tractor and the inclination angle of a seed conveying pipe as the factor, there are carrying out performance experiment in the pavement and field. The pavement and field experiment indicated that in the work process of centralized metering device, the seeding performance is stable and reliable. In the tractor down forward process, consistency variant of each output was2.68%-3.63%and coefficient of variation of total output stability was1.01%-4.02%, which met the national standard of discharging device requirements. And field test showed that centralized metering device has no seed damage and seed germination was significantly better than that of artificial seeding. |
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