Design and experiment of system for picking up and delivering seedlings in automatic transplanter

Abstract: Plug seedlings transplanting, which has comprehensive benefits including high and stable yield, climate compensation and improving land utilization, is an important part in the process of dry land crops production. At present, the crops, such as maize, sugar beet, rapeseed, cotton, tobacco and vegetables, apply dry land seedlings transplanting in China, with total planting area of nearly 50 million hm2 in 2014 which goes in advance in the world. At the same time, semi-automatic transplanting machine is the main equipment for dry land crops transplanting domestically, and the work of picking up and delivering seedlings is finished manually. It results in high-intensive labor and high producing cost. Aiming at some existing problems in China, such as low level of automation in vegetable transplanter and high rate of injuries during picking up and delivering seedlings, a system for picking up and delivering seedlings in automatic transplanter is designed in this paper. In this tester, step mechanism is used to realize the vertical and horizontal movement of plug seedlings, row type of seedlings pushing up mechanism and clamps are adopted to implement the work of pushing up and clamping plug seedlings, and seedlings catching, seedlings stirring up, seedlings delivering, seedling dropping mechanism, etc. are applied to finish the task of delivering plug seedling from bowl plate to transplant instruments. During the whole operation all actions of the system are finished through the programmable logic controller (PLC), which controls pneumatic cylinders and hydraulic motors. Theoretical analysis and MATLAB simulation have been done, and the results show optimum working pressures of 2 drive cylinders which drive seedlings pushing up mechanism and control the opening-closing of clamps' clamping piece are 0.2-0.4 and 0.1-0.3 MPa respectively for pepper seedlings. In order to verify optimization results, single-factor experiment is carried out respectively. The results show that the optimal working pressure of the drive cylinder driving seedlings pushing up mechanism is 0.4 MPa and that of the drive cylinder controlling the opening-closing of clamps' clamping piece is 0.25 MPa. The functional relationship among 3 parameters which are the frequency of picking up seedlings, the speed of delivering seedlings, and the forward speed of transplanting machine are obtained through theoretical analysis. Besides, levels of these 3 factors are optimized, the 4 groups of best combinations of the factors are achieved, and orthogonal experiment is conducted, in which experimental indices are missing ratio of seedling transplanting, seedling repeated planting ratio, seedling lodging ratio, and seedling damage ratio. Using an experimental automatic vegetable high-speed transplanting machine cooperatively developed by College of Mechanical Transportation of Xinjiang Agriculture University, the experiment is conducted in the farm of Regiment 22, Division 2 of Xinjiang construction Corps in Hejing County, Xinjiang. Pepper seedlings which come from the farm of Toudun river, Urumqi, Xinjiang serve as the test sample. The age of seedlings is 52 days, and their plant height is 142 mm. Through analysis on the experiment result, it reflects that the system achieves the best quality of seedlings picking up and delivering when the frequency of picking up seedlings is 7 times/min, the speed of delivering seedlings is 42 m/min, and the forward speed of transplanting machine is 20 m/min.