Design and test of the blocking type air-suction seed metering device for maize plot seeder

Thousands of plots can be required to sow in the breeding fields. The seeds cannot be mixed among plots, due to different varieties need to be sown in each plot. A plot seeder can be used to fully meet the requirements, such as continuous and interval sowing. Therefore, the seeder needs to be frequently cleaned and replace seeds, which is different from the field seeder. Fortunately, neatly arranged aisles can be expected to strengthen the isolation between varieties and mutual influence. At the same time, it is convenient to walk in the aisle between plots, in order to conduct the field surveys during harvesting. However, the seeds can be inevitably sown on the aisle between plots, particularly in the existing maize plot planters. Two reasons can be attributed to the excessive seeding in the seed metering device. One, the seeds in the seed filling cavity cannot be cleaned in time, resulting in the seed plate absorbing the excess seeds. Another, the seed plate is filled with the seeds too early at the moment when the seeds of the next plot enter the seed-filling cavity. Furthermore, air-suction seed metering devices have been widely used in most plot precision seeders, due to their better seeding performance. In this study, a blocking-type air-suction seed metering device was designed to improve the consistency of aisle width between maize plots. The technical idea was extended to accurately block the excess seeds that were adsorbed by the seed plate into the seed-throwing area. A blocking function was added to the traditional plot seed metering device. The filling-cleaning-changing functions were shifted to the continuous filling-blocking-cleaning-changing operations of the plot seed metering device. The movement trajectory of the blocked seeds was reasonably planned. Mechanical and kinematic analyses were conducted on the maize seeds in the seed-blocking stage. The key parameters of the blocking mechanism were determined, according to the brachistochrone curve. The brachistochrone curved surface was used to simulate the contact surface between the blocking plate and the blocked seed. The main parameters of the rotating circle corresponding to the brachistochrone curved surface were determined as a radius of 53.70 mm and a rotation angle of 0.482π. The linkage plate in the blocking mechanism was used to prevent the seed cleaning airflow from sucking away the seeds to be sown on the seed plate during seed cleaning, thus causing missed sowing. The key parameters of the blocking mechanism were determined after optimization. A two-factor six-level full factorial bench test was carried out to take the test factors as the reaction distance of the blocking plate triggering the closing action and the closing state duration distance. The results showed that the probability of adsorbing one more seed at the end of the previous plot was 33.33%, and the probability of adsorbing one more seed in advance of the next plot was 10.00%. The blocking effect was dominated by the reaction distance after the blocking plate triggered the closing action and the closing state duration distance. When the reaction and duration distance were 1.2 and 0.8 m, respectively, the device was used to successfully block 4 suction holes between the neighboring plots of the seed discharging plate. The optimal combination of operation parameters was verified by the field tests, indicating the normal seeds to be sown. The blocking success rate of the blocking-type air-suction seed metering device was 100%, and the coefficient of variation of aisle width between plots was 4.19%. The coefficient of variation was reduced by 9.47%, compared with the traditional device. There was a better alignment of the aisle between plots in the maize plot after the operation using the blocking-type air-suction seed metering device. The blocking mechanism fully met the actual operational requirements. The finding can also provide the technical reference to promote the maize plot seeder.