Parameter optimization and test on pick-up mechanism of planetary gear train with ellipse gears for vegetable plug seedling

Abstract: In order to develop a simpler and more reliable high-efficiency pick-up mechanism for vegetable plug seedlings, a new type of vegetable plug seedling pick-up mechanism with planetary gear train with five congruent ellipse gears was proposed. The mechanism consists of a transmission part, including an ellipse gear planetary gear train, and two identical pick-up seedling arms. Two symmetrically distributed arms permit the mechanism to pick up seedlings twice for each rotation of transmission. Compared to existing similar pick-up mechanisms at home and abroad, the mechanism was significantly simplified and the pick-up efficiency was improved. After this summary, the requirements of pick-up mechanism as the design basis were introduced, and work principle was clarified in the following. The mechanism imitates artificial action, picking up seedlings from the seedling tray, holding the seedlings while moving forward, and releasing them into a seedling-planting mechanism for the following planting work. Then, it goes back to its original position and be in ready condition for next the set picking. During the process, a particular locus with two straight and close-set curve part has been formed which sufficiently satisfies the requirement of automatically picking up seedlings. On the other hand, in terms of the specific actions of the finger-like pick-up claws fixed on the mechanical arms that pick up seedlings, it can be divided into four phases. Before entering the hole of the seedling plug, the claws are completely open to stay in the prepared state for picking up seedlings. When reaching the seedling tray surface, the claws will start to be clamped slowly, until they enter into the bottom of the hole in the seedling tray after which they turn to be fully clamped to pull the seedling out of the hole of the tray. Then, the seedling is held reliably and moved to a particular location with a set of seedling-plant mechanisms placed below, and the claws start to open until a new seedling-picking process starts. Afterwards, based on the above analysis of the principle of mechanism, the mathematical equation of mechanism kinematics is established. Therefore, a computer-aided analysis and optimization software on the platform of Visual Basic for this vegetable plug seedlings pick-up mechanism was developed on the basis of the established mathematical equation. With the man-computer interaction of this visualization software and by using the method of controlling single variables at a time, a group of combinative analysis by trial and error was carried out, and the regularity of how the structure parameters changed in value influence work locus of the mechanism was analyzed in a convenient way. Then, one group of non-inferior parameters that well satisfy the demands of forming ideal work locus in accordance with design requirements was presented. Based on these non-inferior parameters, the mechanism 3D model was set up. Subsequently, simulation analysis and prototype tests were carried out. The mechanism ran smoothly with a pick-up success rate reached 95%. The results showed the feasibility of the mechanism’s theoretical model and will provide technical support for the research and development of core components of automatic transplanting machine.