Simulation and verification of seed-filling performance of pneumatic-combined holes maize precision seed-metering device based on EDEM

Abstract: Pneumatic metering device has been increasingly widespread for the advantages of high planting quality, low seed-injuring rate, strong adaptability to seeds and higher planting speeds when sowing corn seeds. The seed-filling performance of pneumatic metering device is particularly important which basically determines the seeding performance. Studies have shown that motion characteristics of seeds have a greater influence on the seed-filling performance, however, the shape of corn seeds is very irregular and the physical properties of material system of such discrete-state particle are too complicated to describe with conventional motion law of solid and liquid substance. This paper studied the pneumatic-combined holes seed-metering device based on the theory of discrete element method. The EDEM software was used to carry out simulation research, and the Hertz-Mindlin no-slip contact model was selected and the normal force between particles contacts was used as monitoring value of internal friction during the simulation. Four kinds of seed plates with great differences of type hole structures were designed which aimed at creating different interference intensity. The seeds of Zhengdan 958, which was widely adopted, were used as modeling objects of particles. The impact of seeds plates on seeds movement was simulated at different rotational speeds, and variance value of normal force and total normal force were used as indexes for data analysis during simulation. The results indicated that the increase of seeds' interference intensity can't significantly reduce the total normal force but will reduce the transient normal stress of seeds which is also called transient internal friction. It is inferred that the seed-filling performance of D type seeds plate which has the largest variance value of normal force is better than the others. The four kinds of seeds plates were respectively processed and installed on the pneumatic-combined holes seed-metering device to do experiments. The inspection area was designated before experiments, and predetermined the position where type hole leaving away from the seed layer as a starting point and the beginning of seed-clearing area as the end point, and then a High-Speed Video Camera was used to record images of this area and determined the situation as missing-seeding when there was no seeds in the type holes in this region. Experiment results indicated that variance value of normal force has a significantly impact on missing-seeding rate of seeds plate, and the value variance of D type seeds plate was the largest, the missing-seeding rate reached the lowest rate 1.13% when the rotational speed reached the maximum value 37.3 r/min. By comparing the simulation results and experimental results, the relationship among the missing-seeding rate, the rotational speed of seed plate and variance value of normal stress was obtained which verified the simulation conclusion that larger interference intensity can reduce the internal friction of seeds instantaneously and improve the seed-filling rate of metering device.