| Citrus is the largest fruit produced in China.The demand for seedlings is high,and factory container seedling cultivation is an effective way to achieve large-scale production of citrus seedlings.In the process of grafting seedlings with substrate in the factory container cultivation of citrus,both the filling of the seedling bowl and the formation of the transplanting hole are completed by manual operation.The labor intensity is high,the efficiency is low,and the quality of the operation is poor.The existing container seedling filling and hole-forming machines are mostly suitable for standardized hard containers.However,China’s citrus container seedling cultivation often uses thinwalled plastic seedling bowls,which have small mouths,deep bags,and soft texture.Compared with the hard containers commonly used for vegetable,flower and tree container seedling cultivation,it is more difficult to mechanize the filling and holeforming operations.In view of the above problems,in order to improve the efficiency and quality of filling and hole-forming operations,combined with actual seedling factory production,a citrus seedling bowl filling and hole-forming production line suitable for factory container cultivation was developed.The main research contents and conclusions are as follows:(1)Overall design of the machine.Combined with the agronomic requirements of citrus factory seedling in China and the relevant machinery for filling and hole-making of seedling bowls at home and abroad,the design requirements and performance indicators of the production line for filling and hole-making of citrus seedling bowls were determined,and the overall structure composed of filling module,irrigation module,punching module and seedling bowl transfer frame was designed.(2)Design of key components.The design of the seedling bowl transfer frame was carried out.The multi-compartment structure was adopted to assist in supporting and protecting the seedling bowl during operation.The slider groove pin mechanism was used to switch between the placement and unloading states of the transfer frame.The key dimensions of the mechanism were calculated.The design of baffle lifting machine was carried out.The size of hopper and unloading height were calculated.According to the theoretical analysis of unloading process,the adjustment range of unloading height was designed.The design of diversion-scraper device was carried out.The scraping structure and lifting structure of diversion cover plate were designed and calculated.The selection of linear module and electric push rod was determined.The design of irrigation device was carried out.The device composition and installation sequence of irrigation pipeline were determined.According to the water infiltration rate test,the parameters of irrigation pipeline were determined,based on which the key components of irrigation pipeline were selected,and the efficiency of irrigation process was analyzed.The design of punching device was carried out.In view of the lightweight installation plate of punching column,servo electric cylinder parameters were determined,and the influence of punching process on nutrient soil and seedling bowl was analyzed.(3)Design and development of control system.A distributed control system based on STM32 controller and CAN bus technology was built,which consists of four parts:main controller,filling module controller,punching module controller and irrigation module controller,realizing collaborative control among various modules.The components of hardware circuit in each module control system were calculated and selected,and an emergency stop control system independent from STM32 control system was designed.At the same time,modular design method was adopted.C language was used as development language,Keil5 software was used as development environment to develop main programs and subprograms for filling,irrigation,punching and main control modules respectively.Incremental PID feedback control algorithm was added to irrigation program at the same time.Human-machine interaction interface with serial port screen was designed,USART serial port communication protocol and CAN communication application layer protocol data frame specific definition were compiled.(4)The prototype was manufactured,debugged and tested.The processing and construction of the prototype were completed,and the electromagnetic interference problem was solved during the debugging process.The PID parameters of the irrigation control program were tuned,and the uniformity of water flow from each outlet of the irrigation circuit was adjusted to ensure that the variation coefficient of the water output after adjustment was less than 1.3%.The positioning test of the seedling bowl transfer frame was carried out,and the results showed that the belt conveyor speed of the loading station met the positioning accuracy requirements within the range of 0.4-0.7 m/s,and the optimal working speed of the chain plate conveyor belt of the punching station was 0.25m/s.The filling test was carried out with filling volume and filling uniformity as evaluation indexes.The results showed that when the water content of nutrient soil volume was 3%,the lifting speed of hoist was 0.25 m/s,and the unloading height was580 mm,the filling effect was best.The irrigation-punching test was carried out with aperture shrinkage rate,seedling bowl collapse height and nutrient soil settlement height as evaluation indexes.The results showed that when the total irrigation amount was 450 m L,the infiltration time was 19 s,the punching column cone angle was 35°,the punching speed was 200 mm/s,and the punching column hole bottom stay time was 2 s,the punching effect was best.Under the optimal parameter combination,the working efficiency of the whole machine is greater than 2300 bowls/hour,and the filling effect is good enough to meet online automatic production requirements for citrus seedling bowls. |
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