| Corn is the largest crop in China.The continuous expansion of corn productiondemand gap seriously threatens China’s grain security under the background of rigid growth of corn demand.Corn grain loss and damage caused by mechanical threshing process not only lead to serious loss and waste,but also restrict the transformation of our corn production mode to the promotion of direct grain harvest,which results in increasing difficulty in increasing production output.The lack of low-loss and highefficiency threshing machines hinders the pace of improving the quality and efficiency of corn production.It has become a difficult problem restricting the high efficiency and high quality production of corn in China.Therefore,it is necessary to break through the low-loss and high-efficiency threshing technology to realize the transformation of production mode and loss reduction.Therefore,low-loss and high-efficiency of corn threshing poses a severe challenge to the existing technology,which has great strategic significance and research significance.Aiming at the production issues and technical problems of corn mechanical threshing,this paper starts from the basic research of corn low-loss and high-efficiency,reveals the mechanism of corn threshing,and explores the methods of corn low-loss and high-efficiency threshing;the main guidance is to reduce threshing boundary conditions and the secondary guidance is to regulate the impact force according to the mechanism of loss reduction and efficiency enhancement;the innovative threshing principles are inspired by the behavior of twisting and loosening corn with both hands,and the related threshing technology and implements are created by combining the ripple structure,so as to reduce the threshing boundary conditions and make the grain more easily to detach from the corncob;an extensible multi-dimensional corn threshing model including loose threshing test data is constructed to provide a control model for the precise regulation of impact force to achieve low-loss and high-efficiency threshing of corn.The main research results of this paper are as follows:(1)The material properties are the basis for the study of low-loss and highefficiency corn threshing.The material property parameters such as grain moisture content,grain geometric features,thousand grain weight,density,angle of repose,geometric features of corn ear,grain shear modulus,grain elastic modulus,and grain poisson’s ratio were determined,and the pressure tolerance characteristics of corn ear with different moisture content and the connection force between kernel and corn cob were analyzed.It was found that external conditions could change the material properties of corn threshing,and the pressure resistance characteristics of corn ear increased with the increase of moisture content.At the same time,the change of grain moisture content affected the connection force between grain and corn cob,and the connection force increased with the increase of moisture content.The related researches provide data support and experimental basis for the subsequent numerical simulation and the design of low-loss and high-efficiency threshing system.(2)In order to reveal the mechanism of corn mechanical threshing,a multi-method fusion method was used to analyze it.Display dynamics method and discrete element method were used to study the mechanism of low loss and high efficiency corn threshing based on Hertz contact theory combined with collision dynamics theory analysis method,which provided theoretical basis and direction for loss reduction and efficiency increasing of corn threshing.The study identified two forms of loss reduction and efficiency increasing in corn threshing: changing boundary conditions and controlling impact force;and proposed specific measures for loss reduction and efficiency increasing: reducing threshing boundary conditions and improving damage boundary conditions(reducing moisture content,cultivating suitable varieties),increasing contact area,reducing linear velocity of threshing element,increasing contact time,optimizing threshing element structure(rib clearance,rib angle,and rib width of threshing elements),improving the material of threshing element(using flexible material under the premise of ensuring durability),determining the suitable collision angle and selecting the suitable material quantity.(3)Aiming at reducing threshing boundary conditions,this paper studied the behavior of two-handed twisting to loosen the corn ear,and revealed the loose mechanism and synergistic mechanism of hand torsion.By analyzing the change of torque under different torsion angles and types,the connection force between grain and corn cob,the pressure resistance characteristics and the change trend of threshing performance,the strategies that two-handed twisting corn ear makes the grains detach from the corn cob more easily,and the twisting loosening effectively reduces the threshing boundary conditions to reduce damage and increase efficiency were determined;it also revealed the loose mechanism of two-handed twisting: the corn grains on the ear are disturbed repeatedly during the twisting process,which breaks the original connection state,and then reduces the connection force between grain and corn cob.At the same time,the resistance of threshing will also be reduced after the loose of corn ear,and then the grain breakage rate will be reduced during the subsequent mechanical threshing.(4)The scheme of mechanized loose corn ear was put forward and the loose corrugated roller was created through the integration of the engineering bionic technology and the loose mechanism of two-handed twisting.The corn ear was subjected to forces of different magnitudes and directions at different times by rolling the corrugated roller to complete corn ear loosening operation.It was found that the loose pretreatment based on the loose corrugated roller had a significant effect on changing the boundary conditions of corn threshing by comparing the connection force of loose corn,resistance moment and threshing performance of the loose corrugated roller.The loose pretreatment of loose corrugated roller can effectively reduce the connection force between grain and corn cob,threshing resistance moment and grain breakage rate;when the down-pressing depth was 10 mm,the axial,radial and circumferential connection forces between grain and corn cob were reduced by 48.18%,45.97%,and 22.11%,respectively,and the threshing resistance moment was reduced by 42.75% compared with the unprepared corn ear.In addition,the grain breakage rate was significantly reduced under the same linear speed of threshing element,and the non-threshing rate was much smaller than that of the unpretreated group;combined with the self-designed single longitudinal flow threshing test bench,the threshing performance of loose corn ears and non-loose corn ears was compared under large feeding conditions,and the results proved that the loose corn ears treated by loose corrugated roller could effectively reduce the grain breakage rate and grain loss rate in the process of corn threshing.(5)In order to accurately control the impact force exerted on the corn ear by the threshing system under complex agronomic and agricultural conditions and the coexistence of multiple threshing systems,and to achieve low-loss and high-efficiency corn threshing,this study obtained production data by conducting threshing tests of different varieties,moisture contents,and system structures based on the data from the threshing tests of loose pre-treatment;a prediction model of corn threshing production was constructed based on BP neural network,which included the data of variety,moisture content,location,structure form of threshing system,operation parameters of threshing system,etc.The model could predict the quality of corn threshing in real time to meet the demand of corn threshing prediction;finally,an iterative learning control strategy for constructing threshing quality was proposed by using neural network model. |
PDF Full Text Request