Design and experiments of high-speed cutting device for vegetable seedlings for grafting

Abstract: The existing grafting machines have some problems, such as immature technology, high price and difficulty in large-scale popularization and application. After a thorough study of the basic characteristics of artificial grafting pipeline, we find that there are problems of high labor intensity and low production efficiency in cutting and conveying links in the process of vegetable seedling artificial grafting. Then a new type of grafting mode, which uses high-speed seedling cutting and conveying device combined with artificial grafting, is proposed to improve the production efficiency of vegetable seedling grafting. Under this grafting mode, scion seedlings and stock seedlings are cut automatically by parallel automatic cutting devices, and then sent to artificial grafting station by conveying device. The final connection and fixing operation between stocks and scions are completed by the grafting workers. Based on the analysis of the basic characteristics of the existing seedling cutting devices, the basic geometric and mechanical characteristics of vegetable seedlings, a high-speed cutting and conveying device for vegetable seedlings is proposed, which includes a seedling conveying device, a seedling pulling device, a cutting device and a scion conveying device. The working principle is that the seedling trays reach the cutting device through the conveying device, the seedlings are cut off by the cutting device, and the upper scions are separated from the seedling trays under the action of the seedling pulling device to reach the scion conveying device. The seedling pulling device which consists of a rotating wheel and three paddles is designed to separate scions from the seedling trays after cutting. This seedling pulling method can realize continuous cutting of seedlings which can greatly improve cutting efficiency. According to the structure and working principle of the cutting device, the kinematics models of the cutting tool and the scion are established. And the theoretical relationship between the transporting speed of seedling, the rotating speed of the seedling pulling wheel and the cutting frequency of the cutting tool is analyzed. The results of theoretical analysis show that when the spacing of vegetable seedlings is fixed, the rotation angular speed of the seedling pulling wheel is proportional to the transportation speed of the vegetable seedling tray and inversely proportional to the number of paddles, and the cutting frequency is proportional to the transportation speed of the vegetable seedling tray. In order to study the performance of the cutting device, cutting experiments of vegetable seedlings are carried out, and the effects of seedling types and cutting parameters on cutting performance are studied. The results show that the cutting efficiency of vegetable seedlings reaches 37 000 plants/h, which meets the needs of 37 artificial grafting sites in the grafting pipeline and the design requirements. The cutting effect of the cutting device is influenced by the characteristics of vegetable seedlings themselves. The higher the hardness and consistency of the seedling is, the better the cutting effect. For the seedlings with softer stems, it is easy to leak of cutting because of the tilt of the seedlings, and it will increase the rate of injured seedlings because of the entanglement of the seedlings. The cutting effect of the harder seedlings is better than that of the softer seedlings. The main factor affecting the rate of seedling injury is the rotational speed of the pulling wheel. When the transporting speed of vegetable seedlings is fixed, the cutting frequency is too low to cause leakage cutting. The change of cutting frequency will affect the success rate of cutting when it increases to a certain value. There is an optimal rotating speed which makes the cutting injury rate the lowest, and when rotational speed of the pulling wheel deviates from the optimal rotating speed, the injury rate increases. The experimental results are in good agreement with the theoretical results. The theoretical analysis and experimental results show that the transporting speed of seedling, the rotating speed of the seedling pulling wheel and the cutting frequency need to satisfy certain relations in order to obtain higher cutting efficiency and lower seedling injury rate. The development of the device provides a high efficiency and low cost man-machine collaborative production mode for large-scale grafted seedling production