Parameters optimization of directing precision seeder for large cucurbitaceous seeds

Abstract: A tray seeder is important equipment that greatly increases seeding efficiency and decreases the intensity of labor in the industrial seedlings production. In order to solve the problem of a traditional precision seeder being not suitable for seeding large cucurbitaceous seeds, such as bottle gourd, pumpkin, and watermelon seeds, whose sizes and weights are bigger than ordinary vegetable seeds, a precision directing seeder for large cucurbitaceous seeds was developed to achieve precision seeding in the same direction at a 45° angle. The cotyledons of seedlings could grow up in the same direction as a 45° seeding angle to avoid cotyledons of adjacent seedlings being covered each other.Precision seeding in the same direction at 45° angle was achieved by transporting seeds with a linear vibrator, directing seeds with seed-slots, and seeding with air-suction nozzles. The seeder was controlled by a programmable logic controller. The size of the seed-slot was determined according to the maximum measurements of the 100 normal seeds selected randomly to accommodate almost all the seeds. Optimal operation and structure parameters of the directing seed-slot mechanism and air-suction seeding mechanism were obtained by experimenting with bottle gourd seeds, using a standard tray with 50 cells. The air pressure of the pneumatic system was 0.5 MPa, and the negative pressure of the air-suction nozzle absorbing seed was 0.04 MPa. Results indicated that, with 1.5 mm of the vertical distance from the exit of seed transporting track to seed-slot, 0mm of the horizontal distance and 65 mm/s of the transporting speed of linear vibrator, the success rate of transporting seed into directing seed-slots could reach up to 98.89%; with 40 mm/s of the vertical transporting speed of air-suction nozzle, 3 mm of the depth of the seeds pushed into substrate, and 1 second of the residence time for pushing seeds in substrate, the angular deflection was at the minimum, with 0.8 degree of the mean value of the angular deflection and 15° of the maximum of the angular deflection. The comprehensive operating performance experiment of the precision directing seeder for large cucurbitaceous seeds showed that the seeding productivity of the seeder could reach up to 6 000 cell/h, the single seed rate of the seeding tray could reach up to 97%, the maximum of the angular deflection was less than 25°, and more than 91% of the angular deflections were less than 10 degrees. Compared with the SF70 directing seeder for large cucurbitaceous seeds which was developed by Japan Yanmar Machinery Co., above 95% of the seed angular deflections of seeding operation were less than 15° with our seeder, and they were 30° with a SF70 seeder.There still exists some aspects of the seeder to be improved in the future, such as the size of seed-slot should be designed to be adjustable to be suitable for different batches of seeds. Because the optimal transporting speed of the linear vibrator had reached its maximum, a proper linear vibrator should be further selected to obtain a higher optimal transporting speed for enhancing seeding productivity.