Development of insertion and ejection type seedling taking device for vegetable plug seedlings

Abstract: Seedlings cultivation and transplantation are commonly used in the commercial large-scale planting of most vegetable crops, thereby to improve the vegetables quality, yield, and land use efficiency. However, there are still some challenges in the process of transplanting, such as high labor intensity, low transplanting efficiency, and high cost, due to the manual and semi-automatic transplanting are mainly found in most areas of China. There are also complicated structures in most automatic seedling taking devices, showing a relatively low performance of seedling. In this study, a new kind of insertion and ejection mechanism in a seedling taking device was designed and optimized for a fully automatic transplanter in vegetable plug seedlings. The newly developed device was mainly composed of various mechanisms for conveying plug seedling tray, combing, insertion and ejection, plate turning, conveying plug seedling, and collecting empty tray. The process of plug seedlings taking was as follows: The conveying mechanism of plug seedling tray first aligned the bottom holes of tray with the seedling taking holes one by one; The seedling ejection cylinder then drove the ejector pins out; The ejector pins passed through the seedling taking holes and the bottom holes of tray, and thereby to push the whole row of plug seedlings onto the conveyor; The plate turned 90° in clockwise; The ejector pins were retracted, and the plug seedlings fell into the given grids of conveyor; The plate returned to the original position to complete one row of seedling taking. The kinetics analysis was performed on the process of plug seedling ejection, and the kinematic analysis on the oblique throwing process of plug seedling. The angle between the center line of plug and the ejection direction of ejector rod was set to reduce the initial angular velocity of plug seedling, the angle of oblique throwing, and the vertical height when dropping plug seedlings, thereby to alleviate the seedling rolling during the oblique throwing process. Coupling the mechanism of tray conveying, insertion, and ejection, the optimal angle of tray conveying device was 75°, and the tip length of thimble was 25 mm. Taking 72-hole pepper plug seedlings as the experimental objects, an orthogonal experiment was carried out, where the influencing factors were the moisture content of plug, seedling age, and frequency of seedling, whereas, the inspection indexes were the qualified rate of seedling taking, the loss rate of substrate, and the injury rate of seedlings. The experimental results demonstrated that when the pepper seedling age was 30 days, an optimal configuration was achieved, where the moisture content of plug was 60%, and the frequency of seedling taking was 120 plants /min, the qualified rate of seedling taking was 97.22%, the loss rate of substrate was 18.06%, and the comprehensive injury rate of seedlings was 1.39%. Taking 72-hole plug seedlings of 25-day cabbage and cauliflower as the experimental objects, the seedling taking experiment was carried out, where the moisture content of plug was controlled to 60%, and the frequency of seedling taking was 120 plants/min. In plug seedlings of cabbage and cauliflower, the qualified rates of seedling taking were 93.75% and 95.14%, the loss rates of substrate were 17.21% and 16.67%, and the comprehensive injury rates of seedlings were 4.17% and 3.47%, respectively, indicating the newly developed device can meet the requirements of fully automatic transplanter for vegetable plug seedlings. The finding can provide a sound references to optimize the operating parameters in a fully automatic transplanter for plug seedlings in the large-scale vegetable production.