THEORETICAL DESIGN AND BENCH VALIDATION OF AN AIR-SUCTION PRECISION SEED METERING DEVICE FOR MULTIPLE SEEDS PER HILL OF SMALL-SEED CROPS

To meet the agronomic requirements for multiple-seed-per-hill sowing of millet, broomcorn millet, and rapeseed under plastic-film mulching in Northwest China, an air-suction precision seed metering device was designed and evaluated through theoretical analysis and bench testing. The device integrates seed agitation, suction, staged cleaning, conveying, unloading, and placement, and is equipped with ten hill-forming units with a hill spacing of 16 cm. The airflow field and seed motion during operation were theoretically analyzed, and seed trajectories were captured using a 300 fps high-speed imaging system at an operating speed of 3 km/h. By adjusting the inlet negative pressure and suction-hole diameter, the preliminary stable operating ranges were determined. The results showed that the observed processes of seed agitation, adsorption, cleaning, unloading, and detachment were consistent with the proposed seed-motion model. The stable negative-pressure ranges were 0.61–3.54 kPa for millet, 0.83–4.15 kPa for broomcorn millet, and 0.74–3.59 kPa for rapeseed, while the corresponding suction-hole diameter ranges were 0.6–1.2 mm, 0.8–1.4 mm, and 0.7–1.2 mm, respectively. In 1000-hill bench tests, the qualified rates reached 90.6%, 92.7%, and 91.6% for millet, broomcorn millet, and rapeseed, respectively. These results demonstrate the feasibility of the proposed device and provide a basis for further optimization and field validation.