Design on opposed inclined-plate high-speed precision seed-metering device and its working mechanism analysis

Abstract: Mechanical precision seed-metering device has low price, compact structure, good manufacturability and other advantages. However, in recent years, the pneumatic precision seed-metering device has occupied the dominant position, mainly because of the fatal flaw of the hole filling rate declining rapidly in high speed for mechanical precision seed-metering device, which resulted in grievous decline in the quality of operation and serious seed-leakage phenomenon. Due to the structure characteristic of seed-metering device and mixing characteristic of granular soybean seeds, the value of filling force in the form of compressive stress was limited. For this reason, how to improve the filling force was a crucial factor for mechanical precision seed-metering device. In this paper, the model of filling force of hole was built. And an opposed inclined seed-metering device was innovatively designed by theoretical analysis, which combined the advantages of a variety of mechanical seed-metering devices. It could improve seeding frequency by using double-plate to seed in single line. It changed the seed filling pattern from structure, made full use of the structure of the shell space, improved the compaction force and the filling force type, and further improved the qualified rate and its performance under high-speed operation to adapt to the modern high-speed operation requirements. Relying on gravity cleaning of seed, it effectively avoided the injury of seeds. The double-cavity composite vertical seed-metering device was chosen as a comparison, which also had high speed operation ability. The mathematical models were established according to the working principle. The filling force of the vertical disk seed-metering device and opposed inclined-plate seed-metering device was contrasted and analyzed. Through analyzing the filling force changing rule of the seed-metering device in different angles, and drawing the function image by Matlab (MATrix LABoratory) software, the effective ways to improve the filling ability were found and the best angle was determined to 20°. The single-factor experiments were carried out under the condition of different inclined angles, and the operation indices under 20° were better, which proved the accuracy of the theoretical analysis. The seed-metering device structure both retained the advantages of traditional vertical seed-metering device and solved the problems of seed-leakage increasing phenomenon under high speed. The simulation was done for opposed inclined-plate seed-metering device and double-cavity composite vertical seed-metering device by EDEM (engineering discrete element method) software, and a physical prototype test was performed to verify the superiority of this kind of structure further. The results showed that the simulated and experimental values of variation trend of filling rate were basically the same, and the relative error was small. At the low speed section of 5-8 km/h, the qualified rate was increased by 2% on average, and in 8-12 km/h high speed section, the average qualified rate was increased by 3.6%. The results of simulation and experiment showed the performance of opposed inclined-plate seed-metering device was significantly optimized when its speed was increased and the speed range of mechanical allowing operation was improved. This verifies the gravity and interaction force between seeds as composite force can make a contribution to filling seeds and can be obviously helpful for seeds to come into the hole when increasing the rotational speed of seed-plate, and provides the guidance for the design and development of high-speed precision mechanical seed-metering device.