Research On Design And Seed Spacing Uniformity Experiment Of The Variable-volume Hole Precision Seeder

Increasing soybean yield has essential strategic significance for enhancing our soybean international competitiveness and safeguarding national food security. The study of seed spacing distribution in precision sowing is an important part of precision seeding theory research. Improving seed spacing uniformity plays a key role in grain harvest. In this paper, there are two prerequisites raised for improving seeder`s seed spacing uniformity, one is the formation of equitime interval seed flow when discharging seeds, the other one is that all seeds are expelled from the same location and have consistent trajectory.A forced seed-discharging device designed which is virtually a cam follower mechanism is applied to the variable-volume hole precision seeder. Based on theoretical analysis this seedmeter reduces seed-discharging types(leaving only the forced seed-discharging type), meanwhile, not only this seeding apparatus is not affected by the variability of seed shape and size, but is the seeder able to meet the ?two prerequisites?. That provides a theoretical fundamental for improving seed spacing uniformity of the traditional vertical plate seeder.The overall design of the variable-volume hole precision seeder is accomplished. When the hole rotates to the bottom of the seeder the seed begins being discharged. The forced seed-discharging device belongs to the disc cam mechanism of spring force closure with bottom tip of the driven member. The parameter of the hole-disc and the cam mechanism are as follows: diameter of the disc is 200 mm, number of the hole is 30, diameter of the hole varies from 8 mm to 10 mm, depth of the cell varies between 6.4 mm and 7 mm, chamfer of the cell varies from 1 mm to 3 mm; base circle radius of the cam is 49 mm, push-travel motion angle is 24°, lift is 5 mm, farthest dwell angle is 12°, return-travel motion angle is 36°. The cam profile polar equations are designed by using the ?parabolic-linear-parabolic? follower motion model. Finally, the transfer method and whole structure of the seeder are designed, the CATIA software are employed in creating components models, virtual assembly and interference analysis at the same time.The hole`s parameter experimental and optimal design method is the Box-Behnken design of the Response Surface Model. In discrete element software EDEM, the experimental scheme is implemented. The Design-Expert software is used for Response Curved Surface Regression Analysis and Forecasting Optimization, eventually obtains the following results:(1) The precision index and miss index are significantly affected by diameter and chamfer;(2) Regression equation of precision index and miss index;(3) Optimal parameters of the hole are as follows: diameter is 10 mm, depth is 6.5 mm, chamfer is 2 mm. In order to verify Discrete Element Method for the hole`s parameter optimization, Discrete Element Method and JPS-12 seeder test bench comparison test are carried out. The results confirm that Discrete Element Simulation test results are accurate and the hole`s optimal parameters are credible.In order to prove that the variable-volume hole precision seeder can increase seed spacing uniformity, the seed spacing distribution comparison experiments between variable-volume hole precision seeder and brush-wheel seeder are conducted. For studying the qualified seed spacing consistency accurately, this paper introduce a method by which the qualified seed spacing longitudinal consistency(seed spacing longitudinal consistency) and the qualified seed spacing lateral consistency(seed spacing lateral consistency) are formed into the qualified seed spacing consistency. The seed spacing longitudinal consistency and the seed spacing lateral consistency are measured by the standard deviation of seed spacing() and standard deviation of the seed deviate from the centerline() respectively. The results show:(1) The seed spacing longitudinal consistency and the seed spacing lateral consistency of the two seeders deteriorates with increasing operating speed;(2) The variable-volume hole precision seeder is 14% to 21% higher than brush wheel seeder of seed spacing longitudinal consistency, the former is 18% to 26% higher than the latter of seed spacing lateral consistency, the variable-volume hole precision seeder can improve seed spacing consistency.In order to further analyze the reasons that the variable-volume hole precision seeder improve seed spacing uniformity, the two seeder`s contrast test of seed dropping is conducted under the help of the high-speed imaging technology. The experiments are analyzed from the perspective of the time interval between seeds dropping and the seeds dropping trajectory. The results show: the reasons that the variable-volume hole precision seeder with cam follower mechanism realizing forced seed-discharging are the time interval of seeds dropping are stable and the seeds dropping trajectory are uniform, that satisfy the ?two prerequisites? which are essential for improving seeder`s seed spacing uniformity.This paper makes useful exploration on precision seeding theory and precision seeder research.