Seeding performance of conical-hole seeding plate of the positive and negative pressure combination precision seed metering device for rapeseed

Abstract: A seed-metering device has been widely applied with the combined positive and negative pressure in various agricultural machinery for medium and small-size seeding. However, the hole-type of seeding plate in the traditional device cannot match the seed size during filling, leading to the low carrying performance. It is a high demand for the high precision and efficiency of equipment for rapeseed seeding. In this study, a conical-hole seeding plate was proposed to increase the local population disturbance in the seed filling area, and reduce the transport resistance of the adsorbed seeds, further improving the operational performance of the precision metering device combined with the positive and negative pressure for the rapeseed in the medium-high speed sowing. The conical suction holes were also circularly distributed in the seeding plate, in order to increase the disturbance of the seed population in the seeding chamber, and the velocity of seed particles in the seed filling area near the holes. A comparison was also made on the seeding performance of the seed metering device with two types of seeding plate, such as the conical and cylindrical suction holes. The seed filling success and carrying stability were greatly improved using the seeding plate with conical suction holes, compared with the cylindrical holes, due to the low tangential resistance of the adsorbed seeds on the holes, when migrating along with the seeding plat. Discrete element simulation and quantitative analysis were implemented to compare the seeding plate with conical suction holes and cylindrical holes under the same number of holes. It was found that the average velocity of seed populations in the seeding chamber increased by 66.72% with the conical holes. Meanwhile, the velocities of seed particles in the seed filling area along the tangential, axial, and radial directions increased by 90.45%, 83.90%, and 165.60%, respectively. Specifically, the tangential resistance in the seed motion decreased by 35.60%, when the seeds were adsorbed on the holes. The bench test showed that the seed metering device with the conical-hole seeding plate greatly promoted the qualified index by 5.49%, but reduced the multiple and missing index by 68.62% and 3.79%, respectively, when the work negative pressure of the air chamber in the range of 800~4 800 Pa, and the rotating speed of seeding plate within 10~50 r/min. More importantly, the qualified, multiple and missing index reached 98.13%, 1.25%, and 0.62%, with the conical-hole seeding plate, under the working conditions of positive pressure in 200 Pa, negative pressure in 2 100 kPa, and the rotating speed of seeding plate in 25 r/min. Consequently, the conical-hole plate effectively improved the seeding performance of the precision seed-metering device without wedge churning and filling, where the holding performance of single seeding was enhanced to reduce the multiple and missing index. The conical-hole plate presented a much greater effective depth and area of seed contact than those of the cylindrical holes plate. The movement of the seed particles was facilitated to effectively implement the single seeds and holding, further to accurately take the single seed from the population and disturb the population. The findings can provide a strong reference for the structural optimization of the combined positive and negative pressure precision seed-metering device for the medium and small-size seeds and medium-high speed sowing.