| The rice planting area and total participation are second only to corn in the world cereal crops,and it is the main food crop in China,and the quality and yield of rice are of great significance to the food production security in China.The degree of rice mechanization is closely related to the development of the rice industry.The rice planting link is a crucial step in the mechanized development of the rice industry,and rice mechanical direct seeding has the advantages of simplifying the process and saving labor and cost.The seed releaser is the core component of the rice direct seeding machine,and the seed releaser currently on the market is mainly divided into two categories:mechanical and pneumatic.In view of the diverse agronomic requirements of rice sowing in different origins and varieties,the existing mechanical seed dispersers in the market can meet the requirements,but there are problems such as low adjustment accuracy and easy to hurt the rice seeds,while the pneumatic seed disperser has low damage to the rice seeds and strong adaptability to the geometric size of the rice seeds.Therefore,this study designs a pneumatic rice seeder with adjustable sowing volume according to the agronomic requirements of hybrid and conventional rice sowing,which can meet the adjustment of 1～8 rice seeds and improve the sowing efficiency.The main studies are as follows:(1)Complete the overall structure design of the pneumatic roller seed rower.According to the agronomic requirements of rice sowing and the characteristics of rice seed material,the working principle of the seed rower and the sowing volume adjustment range are determined,i.e.the seed rower adopts the working mode of negative pressure to suck rice seed and positive pressure to clear the blockage and drop the seed,and the sowing volume adjustment is achieved by adjusting the number of longitudinal suction holes.The main structure of the seed rower includes seed rowing drum,seed box,seed clearing nozzle,seed rowing shaft and external shell,etc.(2)Complete the key structural design of the species.According to the characteristics of rice species,the diameter range of the pore absorption is 1.6mm ～1.8mm.The breeding box adopts a layered diversion design,the thickness of the species plate is 2mm,and the guidance incision is not less than 31 °.Design the structure of the type of the species device to determine the partitioning partition of the type.According to theoretical calculation and industrial production experience,the diameter of the roller roller is determined that the diameter of the roller is 160 mm,and the surface of the roller is provided with a follow-up block.Analyze the working process of the germ device,establish a single-grain rice species force model,and determine that the negative voltage range of the type of the seeder is 2 ～ 4k Pa,and the clearing airflow is 12 ～ 18m/s.(3)Simulation of the flow field of the air chamber of the seed releaser is completed.The airflow of the seed releaser enters from the negative and positive pressure inlet of the air chamber,forming an isolated negative pressure chamber and positive pressure chamber in the seed releaser chamber,and the airflow forms a pressure difference on both sides of the suction hole,so that the suction hole can suck the rice seed to complete the seed filling process.The velocity and pressure changes of the internal flow field of the three types of suction hole structures: straight hole,cone hole and sink hole,and the apertures of 1.6mm and 1.8mm diameter were analyzed,and the suction hole structure was determined to be 1.8mm straight hole structure.The velocity and pressure variation of the internal flow field of the suction orifice length were analyzed,and the orifice length was determined to be 5 mm.different seed cleaning nozzles were studied,and the velocity variation of the four outlets was measured,and the B-type nozzle was selected as the seed cleaning nozzle according to the consistency of the velocity variation and the velocity variation of the four outlets.(4)The design of the seed stirring mechanism and the simulation test on the performance of the seed rower were completed.According to the thickness of the rice seed,the thickness of the seed churning block was set in the range of 1～2mm,and the effect of seed churning was analyzed by discrete element simulation.It was found that when the structure of the seed churning block remained unchanged,the greater the velocity and force on the seed population around the churning block as the thickness of the churning block increased,the more obvious the cavitation phenomenon near the suction hole was,which was more conducive to seed filling,but the excessive force would break the seed.To further investigate the effect of the seed churning block on the seed disperser performance,the seed disperser was simulated by DEM-CFD coupling.The simulation results showed that: when the thickness of the seed stirrer was 1mm,the seed rower had the phenomenon of sowing leakage;when the thickness of the seed stirrer was 2mm,the seed stirrer pushed the rice seed out of the seed box and caused the phenomenon of reseeding to increase,and the phenomenon of sowing leakage and reseeding was obviously reduced when the thickness of the seed stirrer was 1-2mm trapezoidal.(5)Complete the pneumatic roller type rice seed rower seed rowing performance test.According to the design plan and simulation test result analysis,complete the prototype processing.The test results show that,under the condition that other test conditions remain unchanged,with the increase of rotational speed,negative suction pressure and positive suction pressure,the passing rate of the seed rower shows a trend of first increasing and then decreasing,and the passing rate of 15r/min rotational speed,4KPa negative suction pressure and 4KPa positive suction pressure reaches the maximum.The pass rate of the seed rower under different precision was close to the maximum value when the number of suction holes and single-chamber and double-chamber seeding were adjusted longitudinally,indicating that the seed rower could meet the demand of different seeding precision.On the basis of the seeding performance test,the optimum working parameters were determined,and the regression equation between the evaluation index and the test factors was determined by conducting a three-factor,three-level test.The best performance of the seed releaser was determined at 10.85 r/min of seed releasing drum speed,4246.25 Pa of negative vacuum in the air chamber and 3500 Pa of positive pressure,with a passing index of 86.13%,a reseeding rate of 6.64% and a leakage rate of7.23%.The test results showed that the developed pneumatic roller seeder met the design target and met the agronomic requirements of rice direct seeding. |
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