| Rice is one of the three major food crops in China.The planting area accounts for about 19% of the total rice planting area in the world.It plays an important role in agricultural production.It is an important guarantee for China's food security.With the acceleration of urbanization in China,the rural labor force is gradually decreasing.The traditional rice cultivation mode of cultivating seedlings and then transplanting is facing the problem of labor shortage.After years of trials and research,Direct seeding of machinery is an agronomic planting model that saves time and effort,saves resources and increases farmers' income.The most important one is the precision spot direct seeding technology.According to the rice agronomic requirements,the rice seed is distributed in the field according to the required plant spacing,row spacing and number of seeds per hole.It is a relatively advanced rice planting technology.The key technology for precision seeding is the design and development of the seed metering device.Based on the in-depth analysis of the agronomic technical requirements for direct seeding of rice,this paper develops the precise seeding equipment and key components,and explores the use of vacuum adsorption theory to develop a gas suction metering device suitable for precise seeding of rice.At the same time,based on the full analysis and based on the mechanical and physical properties of rice seeds,the theoretical research,structural development and simulation research of the air-suction rice precision seed metering device were carried out,and a series of performance verification tests were carried out.The main research contents are as follows:(1)By reading a large number of relevant domestic and foreign literatures,the types,working processes,working principles and research status at home and abroad of the seed metering device were analyzed and studied.(2)Three different varieties of rice seeds were selected as research objects.Calibration of physical and mechanical parameters such as triaxial size,water content,friction angle and stacking angle of the treated seeds.(3)Based on the principle of vacuum adsorption,a seed metering device suitable for rice is designed.The key structural parameters of the seed metering device and the amount of chamber vacuum required for seed adsorption were determined.(4)Establish a simulation model of the airflow field of the seed metering device,and divide the model into a structured grid using the meshing software ICEM.The divided grid is imported into the finite element analysis software FLUENT for airflow field simulation analysis.By changing the rotation speed of the seed metering device,the negative pressure value of the gas chamber and the diameter of the suction hole,the influence of the above three factors on the airflow field inside the negative pressure gas chamber is explored,which provides a theoretical reference for the design of the structural parameters of the seed metering device.(5)Establish a 3D model of rice seeds in SolidWorks and import them into EDEM.Simulation model for generating rice seeds by manual filling.This paper designs three types of seed trays.The effect of different seed trays on seed group agitation was analyzed by EDEM simulation.Generate a rice seed simulation model using API replacement and save the result file as a 0s file.Simulation study by coupling EDEM with FLUENT.The simulation results show that the adsorption of the seeds is consistent with the actual working state of the seed metering device.This laid the foundation for the subsequent optimization of the structural parameters of the rice seed metering device by simulation analysis.(6)The seed metering device was tested on a self-made test bench.The factors affecting the working performance of the seed metering device,such as the arrangement of the seeding hole,the diameter of the suction hole,the rotation speed of the seed trays and the vacuum of the air chamber,were tested by single factor.Three-factor and four-level orthogonal tests were carried out on the diameter of the suction hole,the rotation speed of the seed tray,and the vacuum of the chamber.The primary and secondary order of the influence of the above three factors on the working parameters of the seed metering device and the optimal parameter combination are clarified.The test results show that the order of the above threefactors affecting the seeding performance is the diameter of the suction hole,the rotation speed of the seed tray and the vacuum of the gas chamber.The suction hole adopts a cylindrical hole,the layout is a circular double hole,the diameter of the suction hole is 1.4mm,the rotation speed of the seeding disk is 35r/min,and the displacement of the seeding device is best when the vacuum degree of the gas chamber is-3.5kpa.The test results were as follows: the seeding pass rate was84.22%,the replay rate was 8.81%,and the missed broadcast rate was 5.97%.Meet the parameter indicators in JB/T 10293-2013 "Technical Conditions for Single Grain(Precision)Planters". |
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