Bionic Research On Mechanism Of Damage Reduction And Efficiency Increase Of Mechanical Threshing Of Wheat And Critical Components

Wheat was the main food crop,and wheat grain loss and damage along with mechanical harvesting seriously affected grain yield and quality.Innovating mechanism of wheat threshing and reforming wheat threshing component are the key steps to promote technology upgrading of damage reduction and efficiency increase of wheat harvester.The biological in nature formed to contact properties of low damage and high efficiency after one hundred million years of evolution.It provided natural biological template to solve damage reduction and efficiency increase of wheat harvesting.It had important scientific significance and value of technology to research mechanism and critical components of bionic threshing.This study based on the material properties of wheat and the principle of traditional mechanical wheat threshing.The characteristics of contact mechanics of papillae was the basis of bionic design.Geometric characteristics and mechanical properties of wheat was the basis of the research on contact characteristics of threshing interface.This research showed that a wheat ear unit was composed of two layers of glume and a kernel.Many units staggered about the ear axis to form a contact surface of regular morphology.The static friction factor of wheat and metal was 0.536,and was 0.670 of silica gel plate.The tensile strength of lower part of stem was largest,the central section was second,and the top was least.The nonlinear characteristic of stem's tensile property was outstanding.The tensile strength of ear axis decreased from the bottom up.In this study,the threshing laws of impact,rubbing,combing,and grinding was analyzed in using the method of building geometry model of mechanical threshing interface.It was found tht the threshing parts contacted with wheat under mechanical movement.Kernels were separated from ear axis when the wheat overcame the biological contact forces by energy transferring.Each threshing principle had significant characteristics.Impacting threshing generated the highest efficiency,but damage rate and loss rate were largest at the same time.Rubbing threshing produced the highest threshing rate,but the working performance was relatively low.To solve the contradictions between threshing rate and damage rate was the key point to innovating threshing principle and optimize threshing parts.The tongue of many herbivores in nature had contact functions of low damage and high efficiency for plant materials.This study found that cattle's feeding characteristics were of high frequency and large amount of feed as they were typical ruminant.Many filiform papillae were distributed regularly on the tongue apex of cattle by scanning electron microscope.They tilted oral cavity and kept a angle from 34.69 degree to 38.86 degree with tongue surface.The papillae shaped cone and had spherical top.Herz model,fracture model,statics model and gelling model of function surface of cattle tongue's apex were builted respectively with mechanics modeling method.The formation,extension,stabilization and decomposition of contact interface between cattle tongue's apex and material were quantitative analyzed.It was found that filiform papillae were in favor of enhancing material contact strength and reducing material damage.It was suggested that the cattle tongue could reduce power dissipation in the process of movement based on the law of cattle tongue motion and the kinetic analysis of contact interface.The bionic threshing was inspired by the contact function of low damage and high efficiency of cattle tongue's apex supplied beneficial enlightenment for exploring the mechanism of bionic threshing.The bionic threshing interface studied in this thesis was a new threshing interface of damage reduction and efficiency increase.In this surface,arch-shaped tooth was the struct body,bionic papillae were the surface morphology,and lateral side of wheat was contacted vertically.The mechanical wheat threshing principle and contact mechanism of low damage and high efficiency were analyzed in this study.Based on analyzing the contact characteristics of mechanical threshing interface and cattle tongue's apex,the threshing interface was optimized and we got that:first,there were five basic morphologic units such as cattle papillae,incline and flat papillae,vertical and bulb papillae,vertical and flat papillae and cylindrical surface of arch-shaped teeth.Second,the maximum threshing efficiency and optimum threshing quality were realized in the bionic threshing interface.The rigid-flexible coupling mechanism made wheat ear and kernel have different contact,which could reasonably adjust energy distribution between them.Thirdly,the contact form between threshing parts and wheat ear was improved by morphology bionic in bionic threshing interface.The force way,kernel deformation and effective coverage of threshing interface.The traditional global force form was changed into local microscopic force based on morphology and structure bionic.As a result,high efficiency and low damage of threshing were realized.Bionic threshing mechanism could lay a theoretical foundation of bionic design,and realize low damage and high efficiency of threshinng by optimization of threshing interface.In this study,bionic arch-shaped tooth was designed based on the mechanism of low damage and high efficiency.The tangential flow threshing drum was the tooth's application environment.The tooth was the rigid unit of bionic arch-shaped tooth.The filiform papillae were the prototype of bionic design.The geometrical characteristic of wheat was the boundary conditions.The bionic arch-shaped teeth were mounted on the tangential flow drum.The key components were designed by the SolidWorks software.Their simulation analysis was conducted by the Abaqus software.The test bench of bionic tooth profile and arch-shaped teeth laid a foundation for verificating the principle of bionic damage reduction and efficiency increase.Compared with the working theory of standard threshing tooth,both lateral sides of the front and rear of bionic threshing teeth could contact wheat ear in the same time.Bionic threshing teeth could apply micro moments on wheat ear unit.But both lateral sides of stander threshing teeth scarely contacted with wheat.It indicated that bionic threshing teeth had significant characteristics of improving stress distribution and reducing stress amplitude.The flexible units could reduce stress distribution and amplitude,thus the loss rate of kernel was reduced in the mechanical threshing.The elasticity modulus of flexible units was smaller than wheat kernel.So the flexible units could absorb kinetic energy of wheat kernel and turn it into transformation.The energy of transformation damage was reduced after total energy of kernel reduced.Regression model of threshing rate and damage rate was builted after bench test,respectively.It was found that magnification diameters and dip angle of bionic profile reduced the negative impact from threshing clearance and rasied threshing rate significantly.When the value of K was 2.75,L was 8.9 mm,? was 38 degree,threshing rate was 98.55 percent.Bionic arch-shaped tooth could raise threshing rate and reduce damage rate simultaneously.When rotate speed of drum was 350 rpm,the maximum of threshing rate was 98.33 percent,and damage rate was 1.361 percent at this point.Bionic threshing arch-shaped teeth could provide a higher threshing rate under slower rotate speed of drum.One reason was that the arch structure of bionic threshing teeth could apply impact on the entire wheat.The other reason was that the bionic tooth profile could act micro mechanical friction on local sections of wheat.The entire engery absorbed could transform into falling work under dual function of impact and friction.Bench test indacated that bionic arch-shaped teeth had good threshing functions of damage reduction and efficiency increase.