Research Of Air-suction Mechanical Combined Soybean High-speed And Precision Seed Metering Device

High-speed precision seeding is a main developing trend of soybean planting,and the seeding quality is significantly affected by the performance of the seed metering device,the core part of a seeder.Air-suction seed metering devices characterized by high adaptability to seeds,low damages to seeds,and high seed metering frequency are the mainstream seed metering pattern.However,these devices are limited by the high requirement for negative pressure,and the induction of instable negative pressure in case of insufficient power output,which would induce missed seeding.To reduce the negative-pressure dependence of air-suction seed metering devices and improve the seed metering performance in case of pressure instability,we designed an air-suction mechanical combined seed metering device for soybean planting according to the principles of air-suction seed picking and mechanical seed picking.(1)The physical parameters of soybean seeds(thousand-grain weight,density,triaxial sizes)and mechanical parameters of seed-material contact(dynamic & static friction coefficients,collision restitution coefficient,elastic modulus)were measured,and the relationships between mechanical parameters and water content were explored.(2)The seed-metering monomer structures of a 2BDB-6 seeder were introduced,including a double-V-shaped furrow opener,a 2BDB seed metering device,a three-disc soil covering device,and a profiling elastic press roller.The 2BDB seed metering device was composed of a vertical-disc seed metering plate and a seed clearing pole equipped with a hairpin negative-pressure chamber.Based on the 2BDB seed metering device,an air-suction mechanical combined seed metering device was designed,and after the removal of the seed clearing pole,the combined seed metering plate was reconstructed by adding a seed protection board.The edges of the combined seed metering device were uniformly distributed with multiple seed-picking pores,in which seed-stirring slots were opened at the top and suction pores were set at the bottom.The seed protection board was installed at the upper part of the seed metering plate.Meanwhile,to study the effects of chamber shape on the seed metering performance,we designed a chamber adjusting plate installed in between the seed metering plate and the chamber and used it to change the initial and final angles of the chamber.The seed picking,seed clearing,seed moving and seed dropping performances of the combined seed metering device were theoretically analyzed,and its seed picking mechanism and working process were studied.(3)During simulation of the combined seed metering device on the discrete element method software EDEM,firstly the dynamic and static friction coefficients of seeds were calibrated using the repose angle to be 0.044 and 0.6,respectively.The static friction coefficients between seeds and friction materials(organic glass and resin)were calibrated by using the seed & inclined-plane sliding friction angle to be 0.51 and 0.45,respectively.The collision restitution coefficients between seeds and different materials(organic glass and resin)were calibrated by using the drop collision to be 0.33 and 0.32,respectively.The combined seed metering device was simulated in the Hertz-Mindlin slide-free model.Firstly,the population structures were simulated,and the populations were divided into a rising zone,a fall zone,a reflux zone and a relatively static zone by using the seed speeds and directions on vectorgraphs.The effects of population quantity and seed metering plate rotation speed on the population movement status were studied.Simulations showed the population inclination angles were maintained around 40° and were not significantly affected by either the population quantity or metering plate rotation speed.However,the seed filling rate was promoted by the population quantity,but reduced by the metering plate rotation speed both significantly.Simulation of seedstirring slots showed the seed-stirring and-guiding performances were the optimal at the slot depth of 2 mm and inclination angle of 45°.Double-factor(seed-picking pore size,advancing speed)five-level quadratic orthogonal rotation combined simulation experiments were conducted,which showed both factors significantly affected the seed filling performance.When the upside and downside of the front wall surfaces of seedpicking pores were 10.2 and 6.0 mm distant from the posterior wall surface,respectively,and at depth 6.3 mm and width 10.2 mm,the seed filling qualified rate exceeded 96% and the missed filling rate was smaller than 3%.Based on the seed metering plate optimal design parameters determined from simulation experiments,we used the resinmade processing seed metering trays using the SLA fast molding technology.(4)The airflow field of the seed metering device was analyzed by using a JPS-12 seed metering platform and a U-shaped pressure device.When the rotation speeds of the air blowers were the same,the outlet negative pressure at the chamber of the combined seed metering device was smaller than that of the 2BDB seed metering device.Compared with the soybean and corn seed metering devices,the suction pore number and diameter were both reversely proportional to the chamber negative pressure.The negative pressures of suction pores at different positions of the chamber were measured.It was found the negative pressure farther from the outlet was smaller,but the negative pressure opposite to the outlet was slightly smaller than that near the outlet.Airflow field simulation on Solidworks Flow Simulation was conducted to observe the air flow motion laws when the seed metering plate was static or revolving.The rotation of the seed metering plate drove the air flow in the chamber to flow spirally,and the air flow rate in the chamber declined.The air flow near the suction pores of the combined seed metering device decreased at smaller rate than that of the 2BDB seed metering device,indicating the suction pores contributed to the negative pressures.The thickness and initial/final angles of the chamber were changed by the chamber adjusting plate,and when the chamber thickness increased by 20 mm,the negative pressures in the chamber were the most uniform.(5)With the seed metering platform and a high-speed camera,the seed filling and seed metering performances of the combined seed metering device were tested under the working states of air suction,mechanical mode and their combination.Under the air-suction state,the initial filling angle significantly affected the seed filling performance,which stabilized when the initial filling angle exceeded 50°.The rotation speed and negative pressure of the seed metering plate significantly affected the seed filling performance.As the metering plate rotation speed rose,the seed filling performance was gradually weakened,and the downtrend decreased with the rise of negative pressure.The seed dropping angle significantly affected the seed metering performance,and the regression equation indicated the qualified rate maximized at the seed dropping angle of 39.5°.The rotation speed and negative pressure of the seed metering plate significantly affected the seed metering performance.As the metering plate rotation speed rose,the seed metering performance was gradually weakened,and the downtrend decreased with the rise of negative pressure.The high-speed camera showed when the seeds departed from the seed metering plate,the instantaneous position and time both differed,and thereby the falling positions of the seeds differed,which were manifested as a larger seed filling performance than the seed metering performance.Under the mechanical state,the use of a protection board ensured the seeds would not fall off the seed-picking pores during the moving process.The initial angle of the protection board significantly affected the seed filling performance,and the regression equation indicated the seed filling performance was the optimal at the initial angle of 35.7°.When the protection board was equipped with a flexible buffer device,the fractured rate was reduced,and when the buffer length was 60 mm,the seed filling performance was the optimal and the fractured rate was 0.The results under the combined state outperformed both the air suction state and the mechanical state.The results of the field tests conducted in Boli County,Heilongjiang Province,were smaller than the platform tests.The seed metering performance of the air-suction mechanical combined seed metering device was better than the 2BDB seed metering device,and satisfied the requirements of soybean precision seeding operations when the speeds were between 6 and 12 km/h.