Design of single-degree-of-freedom four-bar seedling-taking and throwing manipulator

With the demand for vegetables is increasing, and by the advantages of climate compensation and early growth of crops, seedling transplanting technology has become the main means to ensure the increase of vegetable production. But seedling raising and transplanting belong to labor-intensive operation, which is time-consuming and labor-consuming, low efficiency and high cost. Therefore, in order to promote seedling transplanting technology, vegetable transplanting mechanization must be carried out. As a key component of transplanting machinery, seedling taking and throwing mechanism has become the focus of research by scholars at home and abroad. Aiming at the problems of the complex structure and high manufacturing cost of the automatic seedling-picking mechanism of vegetable seedlings, in this paper, an open hinge four-bar mechanism for seedling taking and throwing manipulator was designed. Through the analysis of mechanical characteristics of seedlings, the basis for shape design of seedling claws was provided. According to the working process of artificial seedling taking and throwing and the existing seedling taking and throwing mechanism, the design requirements of seedling fetching mechanism were formulated. The motion path of the mechanism and the motion of each pair were planned and designed，the planetary gear train was used to restrain the rotating pair consisting of connecting rod 1 and connecting rod 2, cam high pair mechanism was used to restrain the rotating pair consisting of connecting rod 2 and connecting rod 3, cam mechanism was also used to control the movement of seedling claw opening and closing and the seedling pusher. Finally, a single-degree-of-freedom fully mechanical seedling taking and throwing mechanism was designed, which significantly reduced the cost and improved the reliability of the work, and made the seedling taking and throwing mechanism suitable for harsh working environment of farmland. The coordinate system and mathematical model of the seedling-taking mechanism were established, and the trajectory of each connecting rod was calculated with MATLAB, and the motion trajectory of the mechanism was simulated and analyzed. The simulated results showed that the simulation results were consistent with the design requirements. Detailed structural design of the seedling taking and throwing mechanism was carried out, and the experimental prototype was made. The motion trajectory of the grasping point of the seedling claw of the seedling-feeding mechanism was analyzed by high-speed camera, and the imaging results showed that the trajectory of the grasping point of the seedling claw was similar to the trajectory of the theoretical simulation results. The transplanting experiment was carried out with the prototype, and 3 groups of experiments were organized and 3 plates of seedlings were continuously grabbed and put in each group. The overall success rate of transplanting seedlings was 91.32%, the damage rate of bowl was 3.13%, and the reliability of the mechanism was high. The design of this mechanism provides a fully automatic method for seedling taking and throwing, and provides a reference for the full automation research of transplanting equipment.