Line-churning tooth design and metering accuracy experiment of rice pneumatic precision hill-drop seed metering device on pregnant Japonica rice seed

Abstract: There are two rice varieties in China. One is Japonica rice and another is Indica rice, and there are obvious differences between them. Due to the need to accurately obtain seed quantity for each hill in direct rice seeding, a novel precise pneumatic metering device was designed with a group sucking holes plate in a seed metering device, by which 3-4 seeds can be sucked and dropped at the same time. Existing experiments were conducted to investigate the sucking characteristics of the group holes on the sucking plate under vacuum, the diameter of the hole, and the seed-clearing device. For optimization of the pneumatic precise metering device structure and motion parameters, improving its capability on accurately sucking different rice varieties of seed, a kind of line-churning tooth was designed. A quadratic orthogonal rotation regression experiment was conducted to investigate the sucking characteristics of the precise pneumatic metering device under vacuum, the rotation speed of the plate, the distance between the sucking-hole center, and the line-churning tooth and height of the line-churning tooth. A probability about the quantity for each hill was used to evaluate the capability of the pneumatic precise metering device. The experimental equipment consisted of a pneumatic metering device with group holes, a U-shaped manometer, a positive and negative pressure air pipeline, a cut-off valve, and a vortex pump. In the experiments, the rotating speed of a sucking plate was 15-45 r/min and its diameter was 165 mm. The diameter of the sucking hole was 1.8mm, and the distance between sucking holes were 6.5mm, while the distance was 65 mm between the middle hole and the center of the plate. There were ten group holes on the plate, and every group had three sucking holes on a straight line of radius direction. A fingerlike clearing device was set on the plate while the distance was 123.75 mm between it and the center of the plate, its length was 38 mm, and the installation angle was 25° to vertical axis of the plate. The rice variety was pregnant Japonica rice seed whose name was Yanfeng 47. Its moisture content (wet basis) was 21.30%-21.79%, its 1000-grain was 30.03 g, its sphericity was 0.54, and its overall dimension (length×width×thickness) was 6.82 mm×3.23 mm×2.24 mm. Its sliding friction angle was 36.15°, and its natural repose angle was 27.12°. With a probability of (3-4) seeds per hill, a probability of three seeds per hill, a probability of four seeds per hill, and a probability of ≥5 seeds per hill, four regression equations were established. Every equation's evaluation of fitting was very good, and all equations were significant at the 0.05 level. The experimental results showed that there existed an optimization condition on the capability of the metering device to meet the needs of production. The optimization condition included that the vacuum was 2.4 kPa, the rotation speed was 30r/min, the distance between the churning tooth and sucking hole was 8mm, the seed churning tooth height was 3mm, the sucking hole diameter was 1.8 mm, and the distance between the holes was 6.5 mm. With the cleaning device, the probability of (3-4) seeds per hill of the metering device was 77.28%; in addition the ≤2 seeds probability was 3.04%, and ≥5 seeds probability was 19.67%, while the experimental results were very close to the regression model calculation results. The study proved that the metering device could accurately obtain seed quantity for each hill of pregnant Japonica seeds, and the regression model could be used to predict probable seed quantity for each hill. This study was an important reference basis for the pneumatic metering device on structure design and motion parameters optimization on seeding pregnant Japonica seeds.