Design and parameter optimization of a bilateral staggered wheel-spoon precision seed-metering device for millet plot breeding

Precision seeding of micro-sized millet seeds in plot breeding faces critical challenges, including high miss-seeding rates and severe seed cross-contamination during variety changeovers. This study developed a novel bilateral staggered wheel-spoon precision seed-metering device to achieve precise hill-dropping of 5-8 seeds per hole, zero-residue rapid clearing, and high-precision low-speed seeding without seed damage. The device features a horizontal-axis bilateral staggered arrangement of 20 seed spoons, a lateral gravity seed-dropping mechanism and a semi-enclosed seed chamber. Discrete Element Method (DEM) simulation and Central Composite Design (CCD) response surface methodology were applied to optimize seed spoon cavity dimensions, followed by machine vision bench tests and field validation. Kinematic analysis verified that 20 staggered spoons effectively prevent centrifugal seed scattering. The optimized cavity has an effective depth of 4.4 mm, width of 4.1 mm and height of 2.7 mm, with a simulated seeding qualification rate above 92%. Bench tests at 9 rpm delivered a 92.67% qualification rate, 3.33% re-seeding rate and 4.00% miss-seeding rate. Field trials across three millet varieties maintained qualification rates ≥88%, with an 8.5-second zero-residue clearing process. This device resolves the conflict between micro-seed precision hill-dropping and efficient contamination-free clearing, fully satisfying the agronomic demands of millet plot precision breeding.