Positive airflow guidance method and parameter optimization for grafting seedlings

Abstract: At present, in the facilities of horticultural production, how to avoid seedling damage is one of the important problems that need to be solved, and the flexible holding technology that uses the principle of vacuum adsorption is an effective method to prevent seedling damage. But in this case without external assistance, the vacuum adsorption holding hand in the operation is difficult to overcome the holding position deviation caused by variation of seedlings. Such variation in individual seedlings will lead to no fit of holding hands and seedlings, resulting in not stable holding hand to hold seedlings. The solution to this problem is to use the manual operation or through complex machine vision for seedling position judgment, but the manual operation leads to a lower degree of automation, and the structure of machine vision is complex and the machine calibration can consume more time. Aiming at the above problems, in this study, we proposed a method using positive pressure airflow to guide the seedling, it was through the positive pressure airflow to correct the deviation between the seedling and the holding hand so that seedlings and holding hand suction mouth could fit. In this paper, the cucumber seedlings were used as the object for research. First of all, the size parameters and mechanical properties were measured for cucumber seedlings, the results showed that the average max bending force of cucumber seedlings with mean long axis diameter was (1.82 ± 0.07) mm and mean short axis diameter was (1.47±0.02) mm. It was (0.082 ± 0.005) N when bending 5 on 10 mm length. In order to investigate the effect of positive pressure airflow guiding operation, an experiment of single tube positive pressure guiding for cucumber seedlings was carried out, and a high-speed photographic recording was performed during the experiment, so that the details of the guiding operation could be observed. During the experiment, the height difference between the two holding hands was set to 10 mm, the position of the holding hand suction nozzle mouth could ensure that the seedlings were upright after the seeding was guided, and the positive pressure airway was coaxial with one holding hand. The results showed that the highest success rate of up to 93% when the inner diameter of the positive pressure airway was 4 mm, the distance between the air outlet of positive pressure airway and suction nozzle mouth of the negative pressure holding hand was 25-30 mm, and the guiding air pressure was 0.3 MPa. The guide effect was instable for operation method of single tube positive pressure guiding for cucumber seedlings, the relative position of the positive pressure guide tube and the holding hand was required to be high, and the air pressure was difficult to be accurately controlled. Seedlings may easily be damaged or could not fit the suction nozzle mouth of negative pressure holding hand. In order to further improve the guiding effect, an experiment of double tube positive pressure guiding for cucumber seedlings was carried out, using the same test method with the experiment of single tube positive pressure guiding, but the two positive pressure guide tubes were arranged symmetrically with respect to one holding hand. The results showed that under the condition of 4 mm inner diameter of positive pressure airway, when the distance between the air outlet of positive pressure airway and suction nozzle mouth of the negative pressure holding hand was 20-25 mm, and the guiding air pressure was 0.3 MPa, the success rate of cucumber seedling that was guided could reach 100%, in the case of low guide pressure, the cucumber seedlings and the suction nozzle mouth was difficult to fit, so seedlings appeared shaking. Results of this study can provide technical reference for seedling hold operations based on airflow guidance method.