Design and test analysis of the seedling pick-up mechanical equipment for automatic transplanting

Efficient rotation of cropping production is often required for automatic transplanting devices. However, seedling damage can frequently be found during operation. There are some challenges to the success of seedling transplanting. It is very important to understand the force condition of picking up seedlings in the process of automatic transplanting. In this study, a multi-pin pincette mechanical equipment was designed to examine various force conditions. The dynamic analysis was also carried out to pick up the seedlings from the growing tray cells. Among them, the pincette-type end effector was driven by multiple cylinders. Two fingers and four needles were efficiently configured for picking up seedlings. The ball screw linear was constructed to move the pincette-type end effector for picking up seedlings. The displacement sensor was selected to accurately detect the displacement. The tension/pressure sensor was utilized to examine the applied forces in the process of automatic picking. The high precision control and data acquisition were constructed using these sensors. Single-factor and orthogonal tests were conducted to take the target parameters as the size of the sliding needle and the running speed of picking seedlings. The mechanical test of grasping and picking root lumps for automatic transplanting vegetable seedlings was carried out under the different influencing factors. It was found that picking seedlings was a combination of multiple mechanical actions, such as inclined penetration, parallel grasping, and vertical extraction of sliding needles. A better performance was achieved in the sudden squeezing of the seedlings by the sliding needles at the maximum depth of penetration. Their roots were then loosened to take away from the growing tray cells. The grasping deformation of the root lumps was furthermore maintained to completely break away from the adhesion of the tray cells, in order to successfully pick up seedlings. The dynamic analysis was performed on picking up seedlings from their growing tray cells, according to the measured data. The statistical analysis of variance (ANOVA) showed that the size of the sliding needle shared a highly significant effect on the penetrating forces, and the running speed of picking seedlings had a significant effect on the desorption force and the pulling force. Furthermore, the pulling force in picking up seedlings from their growing tray cells was closely related to the desorption force of the root lumps. Specifically, the oblique penetrating force of the thick sliding needles with a diameter of 2 mm was 1.6 times that of the thin sliding needles with a diameter of 1.5 mm at the low-speed operating state. According to the measured seedling, the desorption forces of plug seedlings grown in the 72-cell trays were more than 10 times their own seedling weights. Automatic transplanting of plug seedlings was successfully realized in the growing trays. Among them, the applied forces were mainly used to overcome the adhesion forces between the seedling roots and the cell walls in the process of automatic picking. The better integrity of the seedling root lump was achieved in the fine needle with a diameter of 1.5 mm and a running speed of 25 mm/s. On the whole, the elastic thin needles with less disturbance to the root lumps were better than those of the rigid thick needles. Combined actions included inclined penetration, parallel grasping, and vertical extraction of sliding needles. After that, the plug seedlings transplanting was extracted from their growth cells. The integrity rate of root lumps was more than 97% in the picking up seedlings, indicating the better performance of transplanting. This finding can provide guidance for the optimal design of the high-efficiency and low-damage seedling-picking mechanism