| American ginseng is a precious tonic medicine with special therapeutic value,and its economic benefits are significant,the planting area of American ginseng has been expanding,and it has become the third largest producer and largest consumer of American ginseng after the United states and Canada,but the domestic planting of American ginseng has a high density,and the seeding method is still dominated by manual pressure point on demand,which has problems such as low work efficiency,high labor cost and poor seeding quality.Existing agronomy of American ginseng cultivated in China,which is using narrow row spacing and precision seeding,have persistent challenges that employ a seeder to improve efficiency and guarantee precision,highlighting a need for narrow row spacing precision sowing technology and equipment.The purpose of this research was to explore an innovated prototype of multi narrow rows parallel pneumatic needle centralized seeding device to addresses the challenge,which combine positive and negative air pressure to suck and discharge the 24 rows seed respectively.The main research contents and results are as follows:1)Measured and analyzed the physical and mechanical properties of American ginseng seedsTaking germination and non-germination American ginseng seeds as research object,the basic physical parameters,tribological properties,compressive mechanical properties and collision recovery coefficients of American ginseng seeds were measured.The result showed that:The triaxial size of the germination and non-germination American ginseng seeds are in a normal distribution,The average triaxial size of the germination ginseng seeds was 6.24 mm×5.04 mm×3.35 mm,and the sphericity was 75.69%,which was slightly larger than the average triaxial size of the non-germination seeds 6.20 mm×4.92mm×2.91 mm,and the sphericity was 72.06%,it has low sphericity and irregular shape.The angle of repose and the sliding friction angle of ginseng seeds were 38.45°,36.72°respectively,which were larger than the angle of repose 37.63°and the sliding friction angle 33.34°of the non-germination ginseng seeds,it can be seen that the seed fluidity is poor.The seed coat was hard and closed,and the seed yield stress fracture was 45.535 N and average yield point strain reaches 0.277 before the germination,which was greater than 29.671 N and 0.195 of germination ginseng seeds.The collision recovery coefficient of the non-promoted American ginseng seeds and the iron plate was 0.682,after soaking and germination treatment,the fiber structure of seed coat became soft,and the embryo expanded to a crack,which led to an increase in the amount of deformation during collision and more energy loss than the non-germination American ginseng seed,so the collision recovery coefficient with the iron plate was 0.206.This study provides a parameters basis for the design and optimization of key components of American ginseng precision planter.2)Proposed the overall scheme of pneumatic needle precision centralized seeding device for American ginsengBased on systematic analysis of the research status of American ginseng seeding technology and pneumatic centralized seeding device,aiming at the requirements of single grain precision seeding of American ginseng narrow spacing,combined with physical and mechanical properties of American ginseng seeds,A 24-row pneumatic needle precision needle precision centralized seeding device for American ginseng was proposed.Introduced the working principle of the prototype device,determined the number of tube needle rotating unit fixedly connected radially cicumferential on the air chamber rotating disk,and the seed adsorption surface diameter is 3.00 mm.In the filling room,Designed inner each bridge evenly distributed,which divided filling room into 12filling units,theoretical calculations show that adjacent inner arch bridge spacing is 17.60mm,the bending radius of the filling chamber floor is 190 mm,the angle of the filling plate is 51°,and the diameter of the avoiding holes on the falling tube is 10 mm×85 mm.The efficiency of centralized seeding device reached 540~900 m~2/h.3)Analyzed the seed metering processThrough the establishment and analysis of the mechanical model of the seed absorbing process,the seeding process and the unloading process,the size and influencing factors of the required adsorption force for each seeding process were clarified.The main factors affecting the seeding performance are seeding axis speed w,the suction negative pressure,the seed adsorption surface diameter at the end of needle,the physical and mechanical properties,the motion radius at the end of needle r,and the suction angle?,determined test suction negative pressure value of the seeding performance is 3.50~5.50 kPa.4)Carried out the airflow distribution uniformity simulation test of the key execution componentsIn order to verify the feasibility of the structural parameters of the tube needle rotating unit and the uniformity of the needle airflow in parallel rows,the Fluent software was used for the simulation test.The test shows:the airflow field in tube needle rotating unit is symmetrically distributed in the middle,and the energy loss of the two ends of tube is smaller than that of the middle part.the average flow velocity variation coefficient of the seed adsorption surface at the 12 needles was 2.923%,and the pressure coefficient of variation was 5.772%,which indicated that the structural parameters of the tube needle rotating unit were reasonable,and the uniformity of the needle airflow in parallel rows was better.5)Carried out the seeding performance bench test of pneumatic needle precision centralized seeding device for American ginsengThe single factor test shows that the single row qualified index of seeding device can reached more than 90.00%,determined according to the single factor test result that the range of working parameters in the quadratic regression orthogonal combination test,which is the seeding axis speed 12.00~24.00 r/min,the suction negative pressure 3.90~5.1kPa,and positive pressure 2.70~3.90 kPa.Combined with response surface analysis showed that the primary and secondary factors affecting seeding qualified index and missing index were rotating speed of the seed meter shaft,the negative pressure and the positive pressure successively,the optimal working parameters combination was optimized as the row axis speed 13.10~17.70 r/min,the negative pressure 4.20~4.50 kPa,the positive pressure 2.90 kPa,within this optimal condition range,the qualified index of a single row was greater than 88.50%,missing index was less than 5.00%and multiple index was less than 7.50%.The difference working conditions in the optimal condition range were selected to estimate the overall performance of the prototype device,the result showed that each row qualified index of centralized seeding device was greater than86.30%,the consistency coefficient of variation for each row was less than 1.80%and the stability coefficient of variation for each row was less than 6.20%,which confirmed that the seed metering device worked stably and achieved the precision seed metering requirements for American ginseng sowing.The research provides the core device for further developing American ginseng seeder adapted to the precision planting agronomic requirements.The study has new innovative in the design of key seeding component for applicable equipment for narrow row spacing intensive cropping. |
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