| Paddy rice is one of the most important fine food crops whose total production accounts for about 40%. Therefore the rice production plays a very important part in grain production. The hybrid rice planting area accounts for about 60% of total rice planting area. There are two planting patterns of paddy rice called direct seeding and transplant. At the moment, paddy rice is planted mostly by transplant. Every hole only needs 2±1 strains while the hybrid rice was transplanted in transplanting pattern, while every hole needs 2~4 seeds in direct seeding pattern. Compared with transplanting pattern, direct seeding can save power, time and seeding bed, improve efficacy and economy. What is more, the direct seeding pattern is easier to operate. Rice direct seeding has very important significance for achieving the lightweight, specialization and scale of rice production.In order to meet the rice direct seeding needs, a pneumatic seed metering device for rice budded seed was designed based on the combination of agricultural machinery and agronomic technology and the seeding principle of air suction-air blowing. The seed metering device used cam, pushing rod and combing strips to solve the problem of rice budded seeds’ mobility. The seeding plate which had groups of suction holes could absorb 2~4 rice budded seeds. The home and abroad research status of rice direct seed metering device was elaborated in the paper. The double-sided pneumatic precision seed metering device for rice budded seed hill-drop was studied and explored based on the physical and mechanical characteristics of rice budded seed and the combination of theory and practice. The main contents include:⑴The objects of study were Huang Huazhan, E Zao 18 and E Jing 912 which were planted widely in Hubei province. The physical characteristics of 3 rice budded seed were studied in the paper, which contained three axis size,weight of one thousand seeds,suspension velocities and so on. The solution of these problems provided basic data for pneumatic seed metering device for rice budded seed.⑵A pneumatic seed metering device for rice budded seed based on the seeding principle of air suction-air blowing was designed in the paper. The method which used cam, pushing rod and combing strips to increase the rice budded seed was first raised and the structural and working parameters of seed metering device was analyzed and determined. The force on rice budded seed and motion of rice budded seed in period of seed filling, seed carrying and seed dropping was analyzed and the necessary conditions of a single suction hole absorbing one rice budded seed was determined. The vacuum degree in suction chamber of seed filling and carrying period had relationships with the speed of rice budded seed, diameter of suction hole, physical characteristics of rice budded seed and so on. The moving equation of rice budded seed was set up in the paper.⑶ANSYS/CFX was used to simulate the airflow field of seed metering device in the paper, getting the distribution of pressure and airflow velocity in negative suction chamber. The different structural parameters of seed metering device were analyzed with diameters of suction hole in chamber from 6~12mm, the rows of suction holes from 8~12 and inner diameter of negative suction chamber from 52~68mm. The simulation results showed that the pressure of suction chamber increased with the suction holes’ increasing firstly and then decreased. When the diameter of suction hole was 1.6mm, the pressure and airflow velocity of suction chamber reached the maximum, the pressure was-3392.33 Pa and the airflow velocity was 75.4683m/s. However the number of suction hole and volume of negative suction chamber did little effect on pressure and airflow velocity in negative suction chamber.⑷The paper which took pneumatic seed metering device as studying object, used Pro/E and EDEM to set up the three-dimensional model and simulation model of seed metering device. It could be seen from the EDEM simulation that the rice budded seed nearby the seeding plate face separated from budded seed group more easily caused by the friction of seeding plate and combing strips. From the simulation of seed filling performance the paper got relationship curve between velocity, force, distance and time of the budded seeds nearby the seeding plate and combing strips. What is more, the paper obtained the relationship curve of average velocity, average force and average distance, the contact curve of budded seed and budded seed, budded seed and combing plate.⑸The paper used the high-speed camera technology to shoot the motion procession of rice budded seed in seed metering device. The paper obtained the initial state of budded seeds group in filling area, the motion state of rice budded seed while seeding plate working, the filling state of suction hole absorbing seeds and the dropping trajectory of budded seeds. At last, the fitting equation of budded seed motion was set up in the paper, which provided the theoretical basis for seeding tube.⑹ The paper launched bench experiment of pneumatic seed metering device and studied the relationship between seeding performance and diameter of suction hole, distribution of suction, vacuum degree of air chamber, speed of seeding plate and the height of rice budded seed group. The experiment result showed that vacuum degree, speed of seeding plate and other factors had a significant effect on the qualified rate, and the best diameter of suction was 1.6mm. The experiment of two factors(speed of seeding plate and vacuum degree in air chamber) and three levels showed that while the vacuum degree was 4.5KPa,the speed of seeding plate was 10r/min, the performance of seed metering device was the best, whose qualified rate reached 94%. The orthogonal test indicated that the optimal condition for the seed metering device is when the rotational speed is 15r/min, the vacuum degree is 3.5kPa and the diameter of suction hole is 1.6mm. This condition meets the requirement of precise direct seeding of hybrid rice. This study provided a reference for further improving quality and optimizing the parameter for pneumatic seed metering device. |
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