Design and experiment of the spoon clip type seed metering device for Allium chinense

Allium chinense, as a characteristic vegetable, is exported to Southeast Asian countries such as Japan and South Korea with remarkable economic benefits. Aimed at the problems of Allium chinense planting, main including high labor intensity and artificial planting process cost, a spoon clip seed metering device for Allium chinense was designed. It consists of a seed metering disc, spoon, seed taking and discharging cam, seed box, mounting plate, and other components. The working principle of the spoon clip seed metering device for Allium chinense, and the mechanism of seed taking, seed carrying, and seed discharging were expounded by analyzing the stress state and movement state of Allium chinense seeds in the working process of seed metering device. The seed taking process of the seed metering device was simulated using discrete element simulation software to optimize the spoon for different structures. The Plackett-Burman test method was used to select the significant factors of spoon diameter, spoon depth, start angle of seed taking, ratio of seed surface height to seed box height, and speed of seed taking. Qualified rate of seed taking and missing rate of seed taking were used as test indexes. Orthogonal regression tests were carried out with spoon diameter, start angle of seed taking, and ratio of seed surface height to seed box height as experimental factors. Regression models of qualified rate of seed taking and missing rate of seed taking were established, and parameters were optimized. Field test were conducted to examine the field seeding performance of the seed metering device for Allium chinense based on obtaining optimal parameters. Simulation results show that the type of spoon has a high significance on the qualified rate of seed taking (P<0.01). Qualified rate of seed taking of the round spoon is more excellent than the other two spoons at different speeds, with an average value of 91.14%, and the round spoon is selected as the preferred structure through comprehensive analysis. According to the results of the Plackett-Burman test, diameter of spoon has a highly significant effect on the missing rate of seed taking (P<0.01), and ratio of seed surface height to seed box height has a significant effect on both the qualified rate of seed taking and missing rate of seed taking (P<0.05). The analysis of the effects of the test factors and their interactions on the test indicators in the Box-Behnken test shows that the test regression model is highly significant (P<0.01). The interaction of spoon diameter and start angle of seed taking have a significant effect on the qualified rate of seed taking. Under the condition that other factors are determined, the qualified rate of seed taking increases with the increase of pickup diameter and then decreases. The qualified rate of seed taking decreases with the increase of the start angle of seed taking for smaller spoon diameters and increases with the increase of the start angle of seed taking for spoon diameters larger than 25 mm. The optimal parameters are as follows: spoon diameter is 27mm, start angle of seed taking is 30°, and ratio of seed surface height to seed box height is 92.5%. Under the optimal parameter combination, the filling qualified rate and missing rate of seed taking were obtained, they were 91.17% and 6.17% respectively, which were consistent with the predicted results of the model. Observations of the field test process indicate that the seed metering device can complete the whole process of seed taking, seed carrying, and seed discharging in the field environment. The results of the field seeding test show that the average seeding qualified rate is 63.10%, and the average multiples rate and seeding missing rate are 12.76% and 24.14%, respectively, at the forward speed of 0.1-0.2 m/s. According to the operating quality for single seed metering device can satisfy the field operation. However, stability and efficiency can still be further optimized and improved. The research can provide a reference for the research and design of planting machinery for Allium chinense.