Design and experiments of the mechanism of blowing leaves and replanting of plug seedlings

In the seedling filling operation, there were some damaged leaves of plug seedlings around the vacancy tray cell to be filled, particularly on those plug seedlings under leaf covered. In this study, a feasible device with jetting air tubes was proposed to integrate with blowing leaves and filling plug seedlings. The main part of the blowing leaves mechanism was a jetting air tube with an inner diameter of 5 mm. There were 8 jetting holes with a diameter of 1.2 mm in the horizontal section near the top, where the jetting air tube was closed. During the operation, the high-pressure airflow in the jetting air tube moved upward from the seepage hole at the bottom of the hole to be filled, thereby blowing away the sheltered leaves, concurrently cooperated with the seedling filling manipulator to complete the seedling filling. A Fluent 15.0 software was selected to simulate the airflow field produced by the jetting air tube, in order to investigate the distribution of flow velocity at the outlet of jetting air tube. The number of jetting holes was set as 6, 7 and 8 in the simulation. The ratio C was defined as the section area ratio of air tube to that of all jetting holes, which was set as 1, 2 and 3. The results of fluid simulation showed that an ideal surface of jetting flow radiation was obtained when the number of jetting holes was 8, and the jetting flow cannot contact the substrate block of plug seedlings. A performance test was selected to determine the optimal C value. An experimental device was performed on six types of plug seedlings with different leaf coverage, including Anthurium, Spathiphyllum, Chinese kale, Guangfu No.1 flowering cabbage, Chinese pakchoi, and Italy elite lettuce. The blowing leaves mechanism was integrated with the seedling filling manipulator that attached to the Denso manipulator. The results showed that the filling success rate of seedlings was related to the initial leaf coverage rate of plug seedling leaves (the area ratio of holes to be filled covered by the leaves of adjacent plug seedlings to that of all holes), the inclination angle of plug seedling leaves, and the pressure of jetting air tube. There were obvious peaks in the filling success rates of two flowers plug seedlings, while there was only a slight increase in those of four leafy vegetables, as the flow pressure of jetting air tube increased. The filling success rates of all types showed first increased and then decreased with the increasing of ratio C. Therefore, a better performance was achieved, where the C value was selected as 2, the diameter of jetting holes was 1.2 mm, the pressure range of jetting air tube was 0.10-0.31 MPa, and the number of jetting holes was 8. In the Anthurium plug seedlings with an initial leaf coverage rate of 59.4%, the filling success rate of seedlings reached 92%, when the pressure of jetting air tube was 0.28 MPa. In the Spathiphyllum plug seedlings with a 56.2% initial leaf coverage rate, the filling success rate was 94%, when the pressure of jetting air tube was 0.22 MPa. In the plug seedlings of Chinese kale with a 35.4% initial leaf coverage rate, the filling success rate was 90%, when the pressure of jetting air tube was 0.22-0.31 MPa. When the pressure of jetting air tube was 0.16-0.31 MPa, the filling success rate all reached 90% in the plug seedlings of Guangfu No.1 flowering cabbage, Chinese pakchoi, and Italy elite lettuce with an initial leaf coverage rate of 29.7%-35.8%.