Development of a screw-internal grooved wheel combination precision alfalfa seed-metering device

High-quality alfalfa sowing generally requires the precision seeder applied in strip sowing. However, conventional grooved wheel seed-metering devices have suffered from inaccurate seeding amounts and uneven seed distribution. In this study, a precision seed-metering device with a screw-internal grooved wheel was designed for alfalfa. A seed-pushing screw was employed to convey seeds. An internal grooved wheel was used for quantitative seed filling, and staggered grooved teeth were used for the uniform seed discharge, thereby achieving a uniform and continuous seed flow. According to the material properties of alfalfa seeds and the agronomic requirements for planting, the structural parameters were designed for the key components of the seeding wheel. The kinetics of seeds were analyzed during the seed-filling and seed-discharging stages. The key parameters were identified on seed-metering performance. The movement patterns and distribution of seeds were simulated using extended discrete element simulation software (EDEM). Different grooved tooth types and numbers were also selected during filling and discharging. A two-factor optimization and validation were conducted on the screw-internal grooved wheel combination seed-metering device using a seed-metering performance testing platform. Thereby, the optimal performance was achieved to define the fundamental structure of the seeding wheels. Single-factor simulation with different types of grooved tooth indicated that the linear type of grooved tooth was used to more effectively discharge all seeds from the perforations than the arc or the vertical type of grooved tooth. The seeding wheel achieved a single-revolution seeding amount of 2.26 g under this configuration, which was consistent with the actual measurement. Once the number of grooved teeth was 9, the seed flow was more continuous and uniform, compared with the grooved teeth of six or twelve. The seeding rate exhibited minimal fluctuation during seed discharging over a single rotation of the seed wheel, with a standard deviation of 0.024 g/s. Bench experiments indicated that the optimal seed-metering performance was achieved after a two-factor regression equation, when the inclination angle of the tooth surface was 52.5°, and the working speed was 9 km/h. Validation experiments demonstrated that the seed-metering device exhibited a coefficient of variation of displacement of 1.80% under the optimal parameters, a coefficient of variation of uniformity of 15.00%, a seed damage rate of 0.03%, and a blocking rate of 0.07%. There was a largely consistence with the optimization from the two-factor experiments. Furthermore, the coefficients of variation of displacement, coefficients of variation of uniformity, seed damage rate, and blocking rate were 2.80, 2.60, 0.03, and 0.02 percentage points lower, respectively, compared with the toothed type of external grooved wheel seed-metering device. The device can fully meet the large-scale requirements for precision strip seeding of alfalfa. The findings can also provide a valuable reference to enhance the seeding quality of the precision strip seeder for small-particle seeds.