Research On Potato Digging Mechanism Based On Discrete Element Method And Design Of Bionic Shovel

With the promotion of potato staple strategy in China,the planting scale is increasing,but the harvesting mechanization level is relatively low,and there are problems such as large traction resistance and high potato injury rate.The digging shovel of potato harvesters,as a key component directly acting on soil,tuber and root system,lacks accurate and reasonable theoretical support in its design,so it is still in the experiential-semi-experiential-design.Combination with the National Science Foundation general program: "Dynamic rupture property of the aggregate of soil-patato tuber-root system and it's coupling mechanism with digging shovel "(5157367)and fund for the Doctoral Program of Higher Education Project " Research on the bionic excavating mechanism of potato based on the spout of boar "(project number: 20122103110009)carrying out,In this paper,the differences in morphology and mechanical properties of potato tubers,roots and surrounding soil in different regions were comprehensively considered,and a discrete element model of soil-tuber-root aggregate was established.The dynamic fracture characteristics of soil-tuber-root aggregate and its coupling effect with digging shovel during potato harvest were studied by numerical simulation.The drag reduction mechanism and energy saving approach of potato mining were discussed.Under the guidance of this basic theory,a bionic excavating shovel based on the boar's arch mouth was designed,and its good drag reduction effect was verified by simulation and field experiments,which provided a theoretical basis for the development of high-performance potato harvester and other block root harvester.The main research contents are as follows:(1)The parameters of soil,tubers and roots during potato harvest were measured.The number,depth and width of potato plants were measured on the spot.The size and proportion of soil particle size were measured by sieving method;Soil samples were collected from the soil near and far from the potato plant(100mm and 300 mm away from the center of the potato plant respectively),and the soil moisture content,density,firmness,cohesion and internal friction Angle of the soil samples in different areas were measured.The accumulation Angle of soil was measured by cylinder lifting method.The moisture content,density and compression properties of potato tuber during harvest were studied.The characteristic parameters of the excavated roots were measured and the density of potato roots was measured by drainage method.It provides data reference for the subsequent establishment of discrete metamodel.(2)A discrete element model of soil-potato tuber-root aggregate was established.According to the measurement results of soil particle size in the previous chapter,four soil discrete element models with different particle sizes were established by using dis crete element EDEM software.The geometric model of tubers and roots was established by using 3d scanning technology and Creo2.0 software,and the discrete element mo del of tubers and roots was obtained by particle filling in EDEM software environmen t.The virtual calibration test of soil particle accumulation Angle was carried out by Pl ackett-burman experiment design,steepest climb test design and response surface test.P hysical parameters and contact models between particles were set in EDEM software t o complete the discrete element model of soil-potato tuber-root system.The effective ness and reliability of the discrete element simulation model are verified by comparing the resistance of field test and simulation test under the same working parameters.(3)Simulation of potato digging process based on discrete element method.Based on the discrete element model,the potato digging process was simulated and analyzed,and the coupling mechanism between digging shovel and soil-tuber-root aggregate was revealed.The change law of soil velocity and the response of force and time under the disturbance of excavator are obtained.The displacement of soil particles in different soil layers(bottom layer,middle layer and surface layer)and different regions(near and far from potato plant)in horizontal and vertical directions under the action of digging shovel was analyzed by simulation,and some differences were found.By marking potato tubers and roots separately,the movement variation of potato tubers under the action of digging shovel was studied from the aspects of displacement and velocity.The influence of working parameters and shape of excavation shovel on working resistance was studied through simulation test.A single factor test was carried out to analyze the different working speed,digging depth and digging shape that affect the working resistance.A single factor test of shovel surface shape was carried out and it was found that the convex shovel has unique advantages in soil crushing capacity and soil mobility improvement.(4)Design of potato digging shovel based on bionic technology.Using the bionics principle and the key technology of reverse engineering,the data collection and surface reconstruction of the boar-bear-touching part were completed,the characteristic curve of the boar-beartouching part was extracted,and the curve fitting equation was generated.Based on the curve equation,the bionic digging shovel of potato was established.Under the condition of the same working parameters,the performance of the bionic digging shovel with the same size parameters and the same surface shovel was compared and analyzed through the simulation test.The results showed that the working resistance of the bionic digging shovel was low and the breaking rate of soil particles was high.In order to explore optimal structure parameters of biomimetic shovel to dig in the process of working resistance and soil particle breaking rate as test indexes,to bionic blade single shovel length,single shovel width and blade Angle as test factors,the Box-Behnken response surface experiment method for multiple factors,each performance index is established with the test parameters,the mathematical model between the Design-Expert software was applied to the bionic structure parameters of the digging shovel for multi-objective optimization.Field validation experiments were carried out on the optimized potato bionic excavator,and the results were compared with those of the plane excavator.The results show that the resistance of the new bionic excavator in the field is less than that of the plane excavator on the whole,and the mining performance is good,which can be used in the actual potato excavator.