Design and experiment on manipulator for transplanting leaf vegetables seedling cultivated by coco-peat

Abstract: Currently, cultivated area of facilities horticulture is growing rapidly in China, while the level of mechanization is very low, and the production of hydroponic leafy vegetables during the seedlings transplanting is mainly manual. So it is needed to develop a plug tray seedlings transplanting machine which fits the mode of China's hydroponics leafy vegetables production. The main operation object of the current transplanting machine in facilities horticulture is potted flowers that use different culture-substrate comparing with hydroponics leafy vegetables. In contrast, the production of hydroponics leafy vegetables uses coco-peat as the main culture-substrate in the South of China. Coco-peat has characteristics of small bulk density, large porosity, poor water-retention capacity, and poor adhesion between particles. Therefore, the existing facility horticultural transplanting manipulators are not suitable for such substrate. In view of the above problems, a 4-needle-type transplanting manipulator for hydroponics leafy vegetables for coco-peat substrate was designed in this paper. In the transplanting manipulator, we used a non-shrinkable needle structure that depended on the angle of the telescopic needle which can reduce the disturbance of the coco-peat as well as avoided the spallation of the substrate cube. In order to compare the adhesion characteristics between coco-peat and peat moss, a cube compression test has been done. The test results showed that coco-peat was more likely to be scattered than peat moss because the coco-peat has the characteristics of large porosity and difficulty forming adhesion between particles, and this trend was intensified with the increasing of substrate moisture content. The percentage of scattered substrate mass in the transplanting process and the remaining component on seedling root growth needed to be evaluated. As such, a comprehensive evaluation method that the percentage of scattered substrate mass combined with scored scattered area was proposed in this study. An experiment was carried out that used hydroponics leafy vegetables of kale (Brassica oleracea) seedlings as transplanting target, and the plug tray for seedlings cultivation was a 50 (5×10) standard plug tray, the culture-substrates were coco-peat, peat moss and perlite with mass ratio of 8:2:1. Through the design and experiment study, the structure parameters of 4-needle-type transplant manipulator were as follow, telescopic needle diameter, 2.5 mm, the angle that telescopic needles insert into the substrate cube, 76°, the distance from the insert point of telescopic needles to the substrate cube edge, 5 mm. The results indicated that the root situations of hydroponics leafy vegetables seedlings had the greatest effects on the transplanting success rate, and the movement accelerations of the robot manipulator also had influences. The success rate of kale seedling transplantation was 100% , under the condition that the seedlings was in the status of normal growth, the vertical acceleration was 0.3 m/s2, the horizontal acceleration was 1.5 m/s2 and the substrate moisture content was 81.01%. This study provides a technical reference for developing transplanting manipulator which transplanted the hydroponics leafy vegetables seedlings that use coco-peat as the main culture substrate.