Dynamic Response Of Threshing Drums To Stalk Winding Study On The Mechanism Of Rice Grain Damage

Threshing device is one of the main working parts of combine harvester.Its working performance directly affects the harvest effect of the whole machine.During the working process,the threshing device often has problems such as unstable threshing performance,strong vibration and grain damage.In this paper,aiming at the complex vibration problem of threshing drum caused by straw winding,the vibration response characteristics and modal frequencies of threshing drum under different working conditions are studied,the influence of straw winding on the vibration response of threshing drum is analyzed,and the mechanism of drum vibration and modal change is revealed.By analyzing the unbalanced excitation characteristics of threshing drum caused by stalk winding,the stability and vibration response of single beam and composite beam under unbalanced excitation are compared,and the vibration suppression effect of composite beam is further analyzed.A composite beam vibration isolation system is designed to isolate the disturbed vibration of threshing drum,and the prestressed beam structure with stable threshing conditions and good vibration damping performance is analyzed.The loading characteristics of rice grain during threshing were analyzed,and the extraction method of micro stress damage crack region of rice grain was proposed.The dynamic response characteristics of the threshing drum by the winding of the stalk studied in this paper have theoretical and practical value for the suppression method of the vibration of the threshing device and for revealing the mechanism of rice grain damage.It is of great significance for promoting the development of Agricultural Mechanization in China towards high efficiency and intelligence and for improving the quality and reducing the loss of rice in the process of machine harvesting.The main research work includes:1.Combined with the actual situation of rice threshing,the loading characteristics of rice plants were studied,and the tensile and compressive tests were carried out on different parts of rice plants.Through two-point tensile test,three-point tensile test and extrusion test,the load limit of different parts of rice plant and the state after rupture were studied,and the stress condition and failure form of rice stem during threshing were analyzed.The morphology of rice stems after threshing is analyzed from a macro point of view.The load-bearing form of the stems in the threshing drum is analyzed through the general fracture position and fracture morphology of the stems.After threshing,the outer tissue of the stem was completely destroyed,the parenchyma in the middle layer of the stem was deformed,the vascular bundle in the inner layer of the stem was completely deformed,and the internal tissue was cracked.After threshing,the parenchyma of rice leaves was completely destroyed,and serious deformation and fracture occurred.During threshing,most of the failure forms of the stems are fracture after stretching and extrusion,most of which are caused by pulling.Most of the fracture positions of the stems are at the connection between the stem nodes.2.By analyzing the vibration response characteristics and modal frequencies of the cutting flow drum and the transverse axial flow drum under no-load and threshing conditions,the vibration signals of the bearing pedestal of the threshing drum’s constraint model and the threshing model under idle and load conditions are tested.Compared with the no-load state,the amplitude increase of the bearing pedestal at the free end of the threshing drum under threshing state has obvious changes.The eccentric force,eccentric mass and eccentric vibration characteristics of the threshing drum were studied according to the material flow and distribution law in the threshing device.The residual stalk mass of the threshing drum decreased gradually along the cutting flow.The vibration amplitude and frequency of threshing drum under eccentric load were measured and analyzed by using the constraint conditions and model of threshing drum.By adjusting the running state of each drum on the multi drum test-bed,the axial motion track of the axial threshing drum and the vibration of the bearing seat are tested,and the vibration coupling and interaction between the threshing drums are analyzed.3.In view of the instability of the threshing drum due to the winding of the straw,the motion differential equation of the support beam under the action of simple harmonic force is established by the modal superposition method,and the dynamic response of the support beam of the threshing drum under the unbalanced excitation of the threshing system is studied.The composite beam structure is used as the support element of the threshing system to optimize the unbalanced response of the threshing drum.The vibration response of the main beam and auxiliary beam is solved by using the established vibration response model of the composite support beam system and the influence of the excitation frequency on the time-domain response of the main beam and auxiliary beam is analyzed.Test and compare the stability and vibration response of single beam and composite beam under different excitation frequencies,as well as the vibration response changes of composite beam under different support stiffness,excitation frequency and damping value,so as to analyze the vibration suppression effect of composite beam.4.The finite element modal analysis and vibration test were carried out on the transverse axial flow drum and the frame,and the unbalanced response characteristics and vibration transmission characteristics of the threshing drum were analyzed.Combined with the threshing device and its supporting beam structure,four prestressed supporting beam structures are designed to suppress the dynamic characteristics of the threshing device in the threshing process.The straw winding state of threshing drum was simulated by adding counterweight,and compared with the transverse axial flow threshing device under normal threshing.The vibration signals of five measuring points were measured,the excitation frequency and vibration mode characteristics were analyzed,and the suppression effect of four kinds of prestressed support beams on the transmission of dynamic characteristics in the threshing process of the threshing device was studied.5.According to Hertz theory,the mechanical properties and impact damage characteristics of rice grains were analyzed,and the critical impact force and critical linear velocity of rice grains caused by threshing elements were obtained.The tensile and extrusion tests were conducted to simulate the load of threshing elements on rice grains,test the breaking force of grain stalk on Rice Panicle head and the compressive bearing capacity of grains,and obtain the average threshing force required by rice grains.Test the force and threshing force of threshing elements during rice threshing,and analyze the stress state of rice grains in the threshing drum.In the threshing process,the tension and pressure of nail teeth on rice and the concentration range of threshing force were tested.The threshing force is far more than the connecting force between grain and grain stalk,and less than the critical impact force for plastic deformation and brittle fracture of grain.Therefore,the threshing force is safe and effective,which can achieve the effect of threshing rice without plastic and brittle deformation damage.The quantitative model of grain internal damage was established,and the extraction method of grain micro stress damage crack region was proposed.The effects of loading times,loading forces and loading methods on the degree of grain internal damage were analyzed through experiments.Under static load,the destructive force of positive pressure > lateral pressure > vertical pressure;The deformation at failure is as follows: vertical deformation > lateral deformation > positive deformation.