Design and experiment of horizontal disc seed metering device for maize seeder

Abstract: Seed metering device as the core component of seeding machine, plays a vital role in seeding performance of a seeder. At present, most of the corn seeder in Northeast China use pneumatic seed metering device or finger-clamping metering device which is accurate but expensive, while horizontal disc seed metering device has the advantages of easy falling into the hole, simple structure and low price, but it's not suitable for high seeding speed. To meet the precision seeding requirements under high speed conditions, the working principle of the metering device was analyzed. As corn accurate seeding requires uni-grain, i.e. into each hole only a seed, the state of the seed falling into the hole can only be side lying or side standing. By studying the shape and size of flat corn seeds used in Northeast China, longitudinal rectangular holes adequate for flat seeds were determined with specific size of 11 mm length, 6 mm width and 6 mm depth. Combined with stress analysis and kinematic analysis, a seed metering disc with inclination hole and small fillet chamfer, which was suitable for high working speed, was designed. Small fillet on the rear edge was bound to accelerate the speed of seeds falling into holes, so as to improve the filling rate of the holes. Front chamfer and side chamfer of the holes on seeding disc could effectively improve the relative speed of seeds, and it made the nearby seeds more stable and more efficient to fall into the holes. Inclination hole was a type of hole which was opposite to the rotation direction of the seed metering disc. When the seeds fell from the filling hole, the force at the vertical direction it suffered not only contained its own gravity, but also the component of vertical downward force given by the reverse slope of the inclined holes. The vertical force could ensure the seed to drop from the holes to the guide tube effectively. It changed the way of the traditional horizontal disc metering device relying solely on seed gravity free falling movement, and ensured the seeding process could be completed successfully. In order to improve the working performance and get the best performance parameters of the seed metering device, a quadratic orthogonal rotary composite experiment was designed. The seed metering device's rotational speed, chamfer length and inclination angle of hole were taken as experimental factors, and the qualified index, the multiple index and the missing index were evaluated. The experiment was carried out on the JPS-12 seeding test bench. Using Design-expert 8.0.6 software, the mathematical models of experimental factors and test indices were established based on the experimental data obtained from the bench test. Response surface methodology (RSM) was used for multi-objective optimization of the regression equation. Test results showed that when the rotational speed of seed metering device was 33 r/min, the chamfer length was 7 mm and the inclination angle of hole was 61°, the qualified index was 92.47%, the multiple index was 3.56%, and the missing index was 3.97%. On this basis, field experiment was carried out to verify the working performance of the seed metering device and to test the adaptability of different corn seed varieties. Field validation test showed that when the seed metering device speed was 33 r/min, the line speed of seeding disc was 0.41 m/s, and the unit forward speed was 8.6 km/h, the seeding performance index could meet the agronomic requirements of precision seeding. It also proved that the seed metering device had a good adaptability for different corn varieties and a good seeding performance. The research provides a reference method for designing and analysis of mechanical precision seed metering device.