Design and experiment of high-speed sparse transplanting mechanism for hydroponics pot seedlings in greenhouses

Leafy vegetable cultivation with culture solution has become a promising new type of planting technology for the vegetable production in a green house. In processing, the seedlings of plugs need to be taken out from the float trays, and transplanted into the cultivation trough. However, a hand transplanting of seedlings is a major traditional operation with high labor intensity and low efficiency. In this study, a novel high-speed mechanism was designed with multiple end effectors for the sparse transplanting of hydroponics seedlings in greenhouses. Specifically, the operations of picking can realize for the whole row seedlings in the float trays, while plant the seedlings in parallel with variable intervals in the cultivation troughs, particularly with high level automation, and great quality. The test platform of sparse transplanting mechanism was composed of three parts: the sparse transplanting component with multiple end effectors, transportation component of seedling tray, and cultivation trough. The sparse transplanting component with multiple end effectors was utilized to transplant the seedlings to empty cultivation trough, connecting the transportation component of seedling tray and cultivation trough. Concurrently, the transportation component of seedling tray was used to convey the seedlings. The transportation component of cultivation trough was used to convey the empty cultivation trough. A systematic optimization was made for the transplanting mechanism, thereby to obtain the best transplanting effect under the combination optimal parameters. In the transplanting mechanism, a rigid cloth belt was adopted to connect the series of needle-type multiple end effectors for equal separation. An elastic belt was also added to alleviate the unequal velocity that resulted from the variable interval process. The collision simulation of multiple end effectors mechanism was conducted on the ADMS software, indicating a large impact force occurred at the end of cylinder. In order to cushion the movement impact, the hydraulic shock absorbers were installed at the end positions of multiple end effectors in the vertical and horizontal directions. The penetration angle and picking seedling depth were determined for the plug seedlings of leafy vegetable, according to the impact factors of transplanting mechanism. Five impact factors of transplanting effect included the belt elastic coefficient(K), average horizontal velocity(v1), absorption energy of oil buffer at the horizontal end(N1), average velocity in the vertical direction(v2), and absorption energy of oil buffer at the vertical end(N2). An orthogonal test was conducted on the factors in each group. It was found that the transplanting efficiency and transplanting success rate were inversely proportional, K, as well as v1, N1 had a great impact on the transplanting success rate of seedlings. A combination of optimal mechanism parameter was obtained through analysis of variance: K=0.128 N/m, v1=0.49 m/s, v2=0.74 m/s, N1=6 J, and N2=15 J. In this case, the better performance can be achieved for the sparse transplanting operating component with multiple end effectors. The transplantation efficiency was 3 956 plants/h, and the transplantation success rate reached 96.7%. This mechanism can meet the actual production requirements of high-efficiency sparse transplanting.