| Rice is one of the three most important food crops in the world.Recently,with the continuous expansion of rice planting area and the increase of yield,the decentralized management of rural land has been transformed to moderate-scale planting,and the seedling transplanting model is no longer suitable for planting in large fields.Current rice planting methods include mechanical seeding and original manual planting.Compared with the manual planting mode,mechanical live broadcast greatly reduces the intensity of manual operations,improves production efficiency and saves labor costs.At present,more than 30% of the rice planting area in the country has adopted direct seeding.Therefore,the development of high-speed and efficient rice direct seeding machines has become a top priority for rice production.At present,high-speed precision seed metering devices are mostly suitable for soybeans,corn,cotton and other large-grained and highly sphericity seeds.The existing pneumatic rice precision seed metering devices are prone to leakage and injury as the operation speed increases.Serious phenomenon.Aiming at the problems that the existing seed metering device has a higher leakage rate,serious damage to the buds,and poor fluidity at higher speeds,this topic uses air suction on the basis of a comparative analysis of existing seeder devices at home and abroad— The principle of air-blowing seeding,the principle of double-disc opposite staggered seeding,is used to design a double-disc pneumatic precision rice seeder,and its main structural working parameters are determined through theoretical calculations.The overall structure design of the seed meter,the simulation analysis of its working process,and the performance test of the seed meter bench according to the evaluation index of the seed meter are carried out.The main research contents of this article are:(1)Structural design of double-disc pneumatic precision seed metering device and design and parameter determination of key components.Based on the working principle of the double-disc pneumatic seed metering device,combined with agronomic requirements,the overall structure and key component parameters of the metering device were determined,and the seeder filling,cleaning,carrying,and seeding links weremotivated.Based on theoretical analysis and calculation,a method for increasing the filling performance of rice with the structure of the seed layer height adjustment device was proposed,the filling mechanism of rice seeds was analyzed,and the minimum vacuum required for the seeder to absorb the seeds was calculated.(2)Simulation analysis of the flow field of the seed meter.The ANSYS/CFX software was used to simulate and analyze the structural parameters of the negative pressure zone of the pneumatic rice precision seed metering device,and the distribution law and structural design parameters of the suction chamber pressure in the negative pressure zone of the seed metering device were determined.The simulation analysis of the number of suction hole groups and the volume of the negative pressure zone of the seeding plate group were performed.With the increase of the number of suction hole groups,there was little difference in the mean pressure of the flow field inside the air chamber of each negative pressure zone.The pressure distribution of the flow field in the entire gas chamber is relatively uniform.Although the average pressure corresponding to the number of suction hole groups in different groups changes,the change is not obvious,indicating that the change in the number of suction type hole groups affects the air flow in the negative pressure suction chamber.The field influence is not great.When the number of suction hole groups in the seeding plate group is 10,the average pressure inside the negative pressure suction chamber reaches a maximum value,which is-2934.25 Pa.When the radius of the suction chamber is increased from 52 mm to 68 mm,the internal pressure of the airflow field of the suction chamber is less changed,the pressure inside the suction chamber is more stable,and the distribution is more uniform to avoid the vortex phenomenon of the internal pressure.With a radius of 68 mm,the pressure of the airflow field inside the suction chamber reaches the maximum value,which is-2932.52 Pa.With the change of the radius of the negative pressure suction chamber ring,the error value of the change in the pressure of the internal airflow field is small,indicating that the volume of the suction chamber is changed.The size has little effect on the internal pressure of the negative pressure air chamber.In order to investigate the influence of the position of the air chamber interface and the angle of the air inlet on the pressure of the flow field in the negative pressure zone,the horseshoe-shaped negative pressure zone was divided into thefilling zone type pore pressure,the clearing zone type pore pressure,and the carrying zone type pore pressure.Workbench post-processing obtains the average value of negative pressure at each group of experimental holes.A two-factor and three-level full-combined experimental study is conducted.The research analysis shows that the position of the air chamber interface has a significant effect on the flow field pressure in the negative pressure zone,and the inlet angle is negative.The influence of pressure in the nip flow field is not significant,and the optimal angle parameter of the inlet position is determined.(3)Simulation analysis of seeder filling performance.The three-dimensional software Pro/E was used to model the seeder,and the model was imported into the EDEM software to perform a simulation analysis of the filling performance of the double-disc pneumatic seeder.Through simulation,it can be seen that the rice seed model entering the seeding area was rejected.The friction between the seed plate and the comb strips is more susceptible to the disturbance of the seed plate to obtain an initial velocity than the rice seed model far away from the seed plate.The filling performance simulation test obtained the relationship between the particle speed,force,and displacement of the seeds on the surface of the disc and the comb,as a function of time,and obtained the average speed,force,and displacement of the rice seed population over time.Relationship lines.(4)Bench test of seed meter.A single-factor test was conducted on the double-disk pneumatic precision seed metering device with the diameter of the suction hole of the seed-disc,the rotation speed of the seed-disc,the vacuum degree of the suction chamber,and the height of the seed layer as the influencing factors.The test results showed that the degree of vacuum,Factors such as the speed of the seeding plate and the diameter of the suction hole have a significant effect on the seeding effect of the seeding device;as the height of the seed layer continues to increase,the leakage of the seeding device is significantly reduced.The reasons are analyzed.The "outward convex" structure eases the "pressure" of the seed layer thickness on the seeding plate hole.With the increase of the seed layer height,the bud seedlings are driven by the seeding plate,which makes the arc section of the seeding area grow and the seeding hole The increase of the contact time with the bud species verified the rationality of the seed layer height adjustment devicedesign.A quadratic regression orthogonal rotation combination design test was conducted on the effects of seed metering disk speed,suction chamber vacuum,and suction hole diameter on the seed metering performance.The test data was analyzed and a regression equation between test factors and indicators was established.The test results show that when the speed of the seeding tray is 13r/min,the vacuum of the suction chamber is4.4k Pa,the diameter of the suction hole of the seeding tray is 1.6mm,the positive pressure of the seed injection port is 450 Pa,the seeding performance is optimal,and the qualification rate is It is 85.8%,the missed rate is 4.7%,and the replay rate is 8.5%,which meets the agronomic requirements of precision seeding. |
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