Design and experiment of the air suction wheel precision seed metering device for vegetables

Pneumatic precision metering device has been mostly used for single crops in recent years. However, there are many types of vegetables with large differences in seed size. It is still lacking the pneumatic precision metering device suitable for the vegetable seeds, such as flowering Chinese cabbage, radish, and hot pepper. In this study, an air-suction wheel pneumatic precision metering device was developed for the vegetables using the seed stirring strip and seed filling. The key structural parameters of the precision metering device were determined, where the diameter of the seed-suction hole was 1.0 mm, and the number of seed-suction holes was 20. The structure of the seed stirring strip was designed with a rectangular strip of length 6 mm and width 2 mm. The direction of the long axis was also tangential to the seed-suction hole. The force of the seeds was analyzed on the seed-stirring strip during the seed-filling stage. The range of the parameters was determined in the seed-stirring strip structure. A seed cleaning device was also designed with the staggered and adjustable seed cleaning distances on both sides. Among them, the force on the seeds was analyzed in the seed-cleaning stage, in order to design the structure of the seed-cleaning finger for the gradual approach of the seed-suction hole. The test objects were selected as the seeds of Sijiu No.19 flowering Chinese cabbage, short leaf No.13 radish, and Dunjiao Chuanqi hot pepper. The preference test was carried out, where the qualified, multiple and missing rates were used as test indexes, and the inclination angle and the thickness of the seed stirring strip were used as test factors. The test results showed that there was a variation in the inclination angle and the thickness of the seed stirring strip on the seed filling performance under the different seeds. The qualified rate of each structural parameter was taken as the average value. The better parameter values were determined as the inclination angle of the seed stirring strip was 30°. The thickness of the seed stirring strip was a kind of seed stirring strip with a slope, where the thickness at the thinnest and thickest points were 0.5 and 1.0 mm, respectively. A three-factor and three-level orthogonal test was carried out with the seeding rotation speed, working negative pressure, and seed cleaning distance as the test factors. The regression analysis was also performed to obtain a better combination of working parameters. In flowering Chinese cabbage seeds, the qualified rate, multiple rate, and missing rate were 99.20%, 0.67%, and 0.13%, respectively, when the working negative pressure was 0.92 kPa, the seeding rotation speed was 13.3 r/min, and the seed cleaning distance was 0.70 mm. In radish seeds, the qualified rate, multiple rate and missing rate were 97.34%, 2.13%, and 0.53%, respectively, when the working negative pressure was 4.47 kPa, the seeding rotation speed was 25.5 r/min, and the seed cleaning distance was 1.20 mm. In hot pepper seeds, the qualified rate, multiple rate and missing rate were 88.27%, 9.06%, and 2.67%, respectively, when the working negative pressure was 1.49 kPa, the seeding rotation speed was 16.9 r/min, and the seed cleaning distance was 0.69 mm. The new device fully met the agronomic requirements of flowering Chinese cabbage, radish, and hot pepper. The finding can provide a strong reference to design the air-suction wheel precision metering device for vegetables.