Mechanism And Experimental Study Of Pneumatic Precision Hill-drop Technology With Adjustable Seeding Rate Of Rice

Rice is the main economic and food crop in the world.Rice is the staple food for more than half of the global population.At present,the rice mechanized planting level is low in China.According to statistics,the mechanization level of rice planting in China was only 44.45% in 2015.The main ways of planting are artificial seeding and transplanting.The mechanization of rice direct seeding technology mainly includes mechanical seeding,mechanical drilling,and hill-direct-seeding.Compared to mechanical transplanting,mechanical direct seeding can avoid the process of raising rice seedlings,reduce the input of prophase cost,and does not affect yield.It is expected to be the developing trend in mechanized rice planting in the future.At present,more than 50% of China’s rice planting area is hybrid rice.Compared to conventional rice,hybrid rice has higher tillering ability and higher yield.By using direct seeding technology,the precision seeding is required.Because the mechanical seed metering device has large amount of seeding rate,and the mechanical seeding is easy to damage the rice seeds.It is not suitable for precision seeding of hybrid rice.The pneumatic rice precision direct seeding technique is a combination of machinery and air flow.This technique has the advantages of high seeding precision,low seed damage rate,and strong adaptability and can satisfy the seeding demands of hybrid rice.To meet the cultivation requirements of different varieties and seeding rate of hybrid rice,a rice pneumatic seeding metering device with adjustable seeding rate and a rice pneumatic seeder with adjustable seeding rate were designed in this study.The working principle of seed metering device was analyzed.The mechanism of precision seeding was expounded.The laboratory and field experiments were carried out to verify the seeder and seeding metering device,which provided a reference for the technology of adjustable seeding rate of rice.The main research contents include:(1)The physical characteristic parameters of five kinds rice were measured,and the influence of water content on the physical parameters of rice was analyzed.The results showed that the angle of repose and sliding friction angle of rice increased with the increase of water content.The relationship formula between germination rate of rice seeds and field seeding rate was established,which provided data support for the selection of rice seed seeding rate.(2)The influence law of air pressure distribution of the flow-path structure in rice pneumatic metering device was studied.The flow-path structure of rice pneumatic metering device was simulated and analyzed by ANSYS-CFD software.The simulation results show that the negative pressure interface was located in the middle position,which was advantageous to improve the uniformity of air pressure distribution.The increase size parameters of flow-path thickness and width was advantageous to increase the average negative pressure of suction holes and reduce the loss of air pressure.The fluctuation and uniformity of air pressure in the flow-path were studied by using high precision air pressure sensor under different motor frequencies and different rotational speeds of seed metering plate.The results show that the air pressure distribution is uniform and stable when the seed metering plate was in a static state.The fluctuation and loss of air pressure will increase when the seed metering plate was rotates.The reason of pressure fluctuation and loss were analyzed.It provides a basis for optimizing the structure of negative pressure flow-path of pneumatic seed metering device.(3)Aiming at the problems of high seeds sucking resistance and low seeding precision,the seed stirring device was optimized.A mechanical model between rice seed,seed stirring device and sucking hole was established.The EDEM software was used to simulate and analyze the stirring process inside the seed metering device.The results showed that the average speed of seed movement(namely,effect of stirring)was positively correlated with the size of the seed stirring device.The structural parameters of seed stirring device were tested and analyzed.When the thickness of seed stirring device was 2 mm and the diameter was 5 mm,the seeding effect was good.The average qualified rate was 94.89%,and the average missed rate was 2.02%.It provided a reference for the auxiliary seed sucking structure of pneumatic seed metering device.(4)A rice pneumatic seeding metering device with adjustable seeding rate was designed in this study.This seed metering device adopted multiple independent negative pressure flowpath to control the accuracy of seed suction.The working principle of seed metering device was analyzed.The method of adjusting seeding rate was explained.The whole factor experiments were carried out under different negative pressures,rotational speeds of the sucking plates,and group number of suction holes.The results also showed that the optimal negative pressure was 1.6 k Pa,and the optimal group number of suction holes was 12.The average qualified rate of 1 hole was 78.37% under the optimal condition.The average qualified rate of 2 holes was 96.01%.The average qualified rate of 3 holes was 92.03%.The average qualified rate of 4 holes was 90.63%.The average qualified rate of 5 holes was 86.00%.It also showed that a rice pneumatic seeding metering device with adjustable seeding rate could meet the requirements of different seeding rate for hybrid rice in direct seeding.It provided a reference for the field application of pneumatic seed metering device with adjustable seeding rate.(5)The seed throwing mechanism and seed throwing in hill of pneumatic seed metering device with adjustable seeding rate were studied.The seeding trajectory of seed metering device was analyzed theoretically and modeled mathematically.High-speed photography technology was used to photograph and analyze the trajectory of seed throwing.The difference between theory and actual of seeding trajectory was compared and analyzed.The influence factors the trajectory of seed throwing were analyzed.It provides a theoretical basis for the seed throwing parameters of seed metering device.To improve the qualified rate of seeding hill,the seeds dropping time difference was used to optimize the sucking holes distribution position of the seeding plate.The optimized sucking holes were arranged nonlinearly.The models of seeding throwing in hill under different conditions were established,and the Verifying tests were carried out.The experimental results show that the hill seeding qualified rate of the optimized sucking holes was higher than that of the not optimized sucking hole.When the positive pressure was 0.15 k Pa,the rotational speed of seeding plate was 20 r/min,which could reach the best qualified rate of hill seeding.The qualified rate was 97.34% in 3-hole seeding,90.36% in 4-hole seeding and 87.36% in 5-hole seeding.This study provides a theoretical basis for seeding trajectory and hill seeding,and provides a reference for optimum design of seed metering device structure.(6)In order to meet the requirements of hybrid rice production in the field,a pneumatic seeder with adjustable seeding rate was innovatively designed.The working principle of the prototype is analyzed.Pipeline pressure distribution test was carried out,and the pipeline structure was optimized.The reasons of air pressure loss were analyzed.It provided a reference for the uniform and stable distribution of air pressure.The Wuyou 1179 rice seeds were selected as the experimental object,and the field seeding precision test was carried out.The results also showed that the optimal negative pressure was 2.0 k Pa.The average qualified rate of 2 hole was 93.35% under the optimal condition.The optimal negative pressure was 1.6 k Pa.The average qualified rate of 3 holes was 87.21%.The optimal negative pressure was 1.6 k Pa.The average qualified rate of 4 holes was 83.73%.The optimal negative pressure was 1.6 k Pa.The average qualified rate of 5 holes was 79.86%.The main factors affecting the precision of seeding were analyzed.The feasibility of pneumatic seeder with adjustable seeding rate was verified by field experiments,which provided a basis for its practical production and application.In summary,the seeding mechanism of pneumatic seeder with adjustable seeding rate was studied in this study.A pneumatic seed metering device and seeder with adjustable seeding rate were innovatively designed.The results show that the machine can realize precision seeding of hybrid rice.