The Novel Method For Optimization Design Of Combine Harvester Vibrating Screens

According to the statistics, the grain production of our country was about1.14trillioncatties last year, and this number increases every year. Most of these grain need to beremoved impurities and sorted before being put in storage, and sieving machines will beused during this process. Vibrating screens are the most commonly used sieving machines.In order to improve the screening efficiency and reduce the loss, it’s urgent to research thescreening process and the screening principle of the vibrating screen for improving thedesign level of vibrating screens better.For a long time, the research of the vibrating screen mainly used experimental methodsand traditional continuum mechanics methods. Experimental methods are time-consuming,and the results are usually not ideal. Material particles on the screen are viewed as a wholewhen using traditional continuum mechanics methods. So the error of the results is verysignificant, and it is not possible to research the whole screening process very well too. Inrecent years, researching the screening process using DEM became mainstream. Comparedwith continuum mechanics methods, this method can get the real simulation of the wholescreening process, and the simulation results are also more closer to the real situation. Butthere are also some problems, for example simplified particle models, simplified boundarymodels, approximate mechanical models, and approximate simulation parameters etc.Especially, we can only simulate the screening process of the vibrating screen with straightmovement or circular motion using DEM because of simplified boundary models, but can donothing about vibrating screens with complicated movement. So the method of multi-rigid-body systems dynamics and DEM coupling was put forward to research vibrating screens inthis paper.The discrete element method (DEM) is a numerical Method which was first proposedby Cundall in order to deal with the mechanical behavior of particulate medium systems.The basic thought is to simplify granular materials as a set of particles with a certain kind ofshape and mass, and endue the particle-particle and particle-boundary relationship with acertain kind of contact mechanics model and some parameters. The DEM is applied toresearch the contact effects, which influence the particle-particle and particle-boundaryrelationship, and the different physical and mechanical characteristics between particle andcontacted boundary.The dynamics of multi-rigid-body systems is a new dynamics branch which developedfrom classical mechanics theories. Its research objects are complex mechanisms composedof several rigid bodies, its purpose is to establish kinematics and dynamics analysis modelswhich are suitable for computer program, and seek accurate, efficient and stable numerical methods.With the development of science and technology, the computer simulation technologyhas been more and more mature, and widely used in various fields. Our research group hassuccessfully introduced DEM into the computer simulation technology, and independentlydeveloped the DEM simulation analysis software which is suitable for agriculturalmachinery parts. This software includes the front design module, the calculation module andthe post-processing module. Using it we have successfully simulated and optimizationdesigned agricultural machinery parts, such as seed-metering devices, fertilizer apparatus,furrow openers and so on. Because of these early research results, it is possible to researchvibrating screens using the method of multi-rigid-body systems dynamics and DEMcoupling.According to the structure and the form of movement of the vibrating screen, we hadkinematics analysis of the vibrating screen using the Cartesian method of multi-rigid-bodysystems dynamics in this paper. Firstly, the coordinate system was established, andconstraint equations of different kinematic pairs were derived based on it (including positionconstraint equations, speed constraint equations and acceleration constraint equations).Then this paper introduced the assembly and calculation methods of constraint equations ofthe whole system, and the multi-rigid-body systems kinematics model of the vibrating screenwas finally established. The2D vibrating screens movement analysis software which isall-purpose and stylized was exactly developed based on these theories above.Then we measured the three-dimensional size and the density of selected soybeanparticles, designed and processed the vibrating screen test bench, designed the test schemeand steps, and carried out a bench test of the screening process. We mainly examined theinfluence on oversize fraction, undersize fraction and screening efficiency of the vibratingscreen in different crank speeds, different dip angles of the sieve surface, different aspectratios of the sieve surface and different lengths of the boom, and analyzed the test results.Finally, we established the2D DEM analysis models of the vibrating screen and thesoybean particles, selected the suitable mechanical models and simulation parameters, andcarried out the computer simulation of the screening process using the2D DEM simulationanalysis software. Through comparing the simulation results with the test results, it provedthat using the method of multi-rigid-body systems dynamics and DEM coupling to researchthe screening process is feasible, and the DEM simulation analysis software developed byour research group is available, aiming to establish a kind of new method for optimizationdesign of vibrating screens.