Design and testing of the mechanical automatic precision seed metering device for pepper

Floating seedlings have been widely used in recent years, because of the small footprint, short nursery cycle, and high quality of pepper seedlings. The seeding link of pepper floating seedling is required for one hole and one-grain precision seeding. Among them, manual spot seeding can usually sow with high labor intensity and low seeding efficiency. The high seeding quality is confined to the complex and costly structure of the pneumatic precision seed-metering device. While the mechanical seed-metering device is more suitable for the round or pelletized vegetable seeds, rather than the small pepper seeds. In this study, a low-cost, lightweight, and simplified mechatronic precision seed-metering device was designed for the pepper floating seedlings, according to the magnetic return-type seed-metering device. A series of mechanisms were designed for the reciprocating motion, rotating, and seed dropping. The seed metering device was improved from the filling and discharging of magnetic return-type seed-metering device by means of various mechanisms. The important factors were selected as the diameter of the filling hole and the depth of the seed-dropping hole in the magnetic return-type seed-metering device. The single grain rate was improved for the high quality of sowing. The triaxial dimensions of the pepper seeds were then measured to determine the size of the filling and dropping holes. In reciprocating motion, the crank radius and seed displacement were determined for the minimum radius of the crank. In rotating, the minimum torque of the motor was determined by the center of mass and force analysis. The influencing factors were selected as crank diameter, crank motor speed, rotating motor angular speed, rotation angle, and seed volume in the trial test. One-factor test was carried out to obtain better ranges in the crank diameter, crank motor speed, rotating motor angular speed, rotation angle, and seed volume. Among them, the crank diameter, crank motor speed, and seed volume shared a significant influence on the performance of the seed-metering device. A three-factor and three-level orthogonal test was conducted to establish a regression model, where the crank diameter, crank motor speed, and seed volume were taken as test factors, while the target variables were the single-seed qualified, reseeding, and missed seeding indexes. The bench test was also carried out to verify the model under the optimal combination of parameters. The test results show that the crank diameter of 30 mm, crank motor speed of 230 r/min, and seed volume of 4 000 grains under the rotation angle of 30° and rotating motor angular speed of 0.07 rad/s (i.e., productivity of 240 trays/h). The seed-metering device performed better with a single-seed qualified index of 91.04%, a reseeding index of 5.21%, and a missed seeding index of 3.75%. The seeding performance fully met the industrial requirements of floating seedlings in pepper production and small-seeded seed-metering devices.