Optimization Design And Test Of Spinach Harvester's Root-cutting Shovel Based On Discrete Element Method

China is a country with a large area of green leafy vegetables planting,but the harvesting mode is relatively backward and the mechanization degree is relatively low.The main method of the harvesting is artificial,which results in the waste of human resources and reduces economic benefits.The rare green leafy harvesting machine is also mainly disordered harvesting machines with stubble cutting.This harvesting mode not only has the problems of large loss and high pollution,but also does not conform to the consumption habits of bundle sales in China.Therefore,it is necessary to develop the orderly harvesting machinery in line with China's national conditions for leafy greens.Soil breaking and root digging are the key links of green leafy vegetable harvesting.The development of root-cutting shovel has become a key step of harvester,In view of this,our project team designed a new type of root-cutting shovel,which can both cut roots and gather roots.In this paper,spinach,which is common in green leafy vegetables,is taken as the research object.Starting from the characteristics of root-soil complex,the simulation analysis and optimization of root-cutting shovel are carried out by using EDEM simulation software and Design-Expert analysis software.The interaction law between soil,plant and component is studied,the relevant parameters are optimized,and a test bench is built for harvesting test and research.This paper mainly includes the following four parts.(1)The experiment of physical properties on spinach roots were carried out.The physical characteristics of spinach root such as three-dimensional appearance size,moisture content and friction coefficient were measured by relevant instruments and equipment.Using the universal testing machine and other equipment to measure the peak shearing force of spinach root is31.2N and the peak compression force is 113.8N,which provided data support for the modeling and theoretical analysis of root-soil complex.(2)The spinach root flexible body model was established.Based on the constitutive equation of the discrete element contact model,combined with the mechanical properties of spinach root,the bonding parameters of spinach root were determined as follows:the normal stiffness coefficient is 5.7×10~6 N/m,the tangential stiffness coefficient is 3.6×10~6 N/m,the critical normal stress is 1.95MPa,the critical tangential stress is 4.2MPa,the bonding radius is0.8mm.And the spinach root-soil complex was established combine with the soil model.Then,the parameters of the root-soil composite model are calibrated by using the method of simulation and experiment,and the final simulation model is determined,which can provide the necessary theoretical basis for the structural design and simulation of the root-cutting shovel.(3)According to the harvesting agronomy and needs of project,a new type of root-cutting shovel is designed,which can reduce the cutting resistance and gather roots.In this study,the stress model of root cutting was established,and the key parameters of the blade were calculated and optimized.Make sure that the blade slide angle is 60°and the blade edge angle is 45°.Using the discrete element method to carry out the cutting simulation,the working mechanism of shovel was clarified,and the main parameters that affect the working performance of the shovel were determined.Combine the response surface and orthogonal experiment,the parameters of the root-cutting shovel were optimized,and the optimal design parameters were determined:the angle of the blade wing is 76°,the length of the blade wing accounts for 57%,and the area of the blade groove accounts for 40%;the optimal working parameters were determined:the depth of penetration is 18mm,the angle of penetration is 5°and the cutting speed is 0.18m/s.(4)In order to verify the accuracy of the simulation and the working performance of the shovel,the spinach extraction and transportation device was developed according to the planting agronomy,and a low damage harvesting test platform was built with the spinach root-cutting shovel.According to the standard of root-cutting qualified efficiency and harvest efficiency on spinach,the indoor tests of spinach harvesting was carried out,and the average value of root-cutting qualified efficiency and harvest efficiency was 93.3%and 90%,respectively.This study can provide theoretical guidance and support for the development of spinach harvester.