Kinematic analysis and test on automatic pick-up mechanism for chili plug seedling

Abstract: Seedlings transplanting plays an important role in the process of vegetable production, and mechanized transplanting can reduce the labor intensity, improve the production efficiency and ensure the work quality. The chili seedling transplanting mechanization technology has been vigorously developing in Xinjiang region. However, at present, there is no automatic vegetable transplanting machine available in Xinjiang. The chili seedling transplanting work basically relies on manual operation, and some transplanters used are semi-automatic machines, which still need manual work to pick up and drop seedlings. Therefore, it is very important and urgent to study the automatic pick-up mechanism for chili plug seedling. Based on the situations above, a kind of automatic pick-up mechanism for chili plug seedling was studied and analyzed in order to replace the manual work. The mechanism consisted of a planetary gear train, a curvy cam, a connecting rod and a pick-up seedling arm in which 2 seedling claws were installed. As the transmission of the mechanism, the planetary gear train drove the seedling pick-up arm to carry out reciprocating movement in curvy cam for picking up seedlings once every rotation. Compared with the existing pick-up mechanisms for vegetable seedlings, the mechanism proposed in this paper was simplified and its stability was improved. It could not only pick up and transport seedlings, but also drop seedlings in the vertical direction at the same time, which ensured that plug seedling had good planting upright degree. Moreover, the endpoint trajectory of the seedling needle was more easier to control. Based on the analysis of structure features and working principle of the automatic seedling pick-up mechanism, its kinematic mathematical model was established, and the displacement, velocity and acceleration equations were also analyzed. Then, a computer-aided analysis program based on Visual Basic 6.0 was developed for optimizing structural parameters of the mechanism. By means of the human-computer interaction analysis method and the software of Adams, certain structural parameters influencing the regularities of the seedling needle endpoint trajectory were analyzed, and then optimized to satisfy the requirements of picking up chili seedling. Therefore, the ideal movement locus of seedling pick-up needle endpoint and a group of optimized structural parameters were acquired conveniently. According to the optimized structural parameters, the three-dimensional entity model of mechanism was established and the automatic seedling pick-up test-bed was developed. The kinematic simulation analysis and seedling pick-up prototype tests were carried out in the Key Laboratory for Xinjiang Production and Construction Corps Agricultural Machinery. The results showed that the seedling needle endpoint's relative trajectories obtained from high-speed camera were consistent with the theoretical ones. According to the seeding pick-up experiment, the success rate of seedling pick-up reached 98.6%, the loss percentage of plug seedling substrate was 4.2%, and the success rate of dropping seedlings attained to 94.2%, which indicated that manufactured pick-up mechanism met the requirement of actual testing. The seedling pick-up experiment further proved that the mechanism could not only satisfy the demands of chili seedlings automatic mechanical pick-up, but also apply to other vegetables, such as tomato. The research method was also proved to be accurate. The study for the automatic pick-up mechanism provides very important theoretical basis and reference for the design, analysis and further study on automatic pick-up and transplanting mechanism.