Research On Disturbed Vibration Characteristics Of Combine Harvester Threshing Cylinder And Vibration Isolation Method

As a kind of large-scale field harvest machinery,crawler-type grain combine harvester could significantly improve agricultural productivity and reduce the labor intensity.Therefore,researchers continued to research and improve the crawler-type grain combine.Although the existing domestic grain combine harvester could basically meet the operation requirements,it still had some defects,such as poor reliability,large vibration and noise,and easily damaged structure when compared with the imported model.The development of domestic combine harvester to high efficiency,reliability and adaptability was seriously restricted.Threshing cylinder was one of the core working parts of the grain combine harvester.Its main function was to thresh and separate the rice.The threshing and separation performance directly affected the reliability of the grain combine harvester.The combine harvester threshing cylinder vibration induced by the threshing process was produced with the beginning of threshing,changed with the fluctuation of feeding quantity and disappeared with the end of threshing process.The vibration characteristics were transient and difficult to control.The vibration of the threshing cylinder would not only affect its threshing performance,but also caused the resonance of frame,vibrating screen,fan,header and some other structures,and affected the structural reliability of the combine harvester.In addition,the bending and torsional vibration of the threshing cylinder in the high-speed rotation process would lead to the deformation of its own structure,affected the impact force of threshing rod teeth,damaged the integrity of grain,and affected the threshing effect.Therefore,in view of the disturbed vibration of the grain combine harvester threshing cylinder during the threshing process,the vibration characteristics of threshing cylinder were analyzed comprehensively by means of theoretical analysis,simulation and experimental verification in this paper.According to the vibration characteristics of the threshing cylinder,the overall structure of the vibration isolation device was determined,the principle and feasibility of the parallel structure with positive and negative stiffness were analyzed,and a variety of bending beams with negative stiffness were designed.Their vibration isolation effect was verified by experiments,and a new type of composite beam was designed,which could not only ensure the bearing capacity,but also had the ability to isolate low-frequency vibration.The research work of this paper mainly included the following aspects:(1)According to the threshing cylinder vibration system which is entangled by rice stem,a dynamic model which is essentially consistent with the practical circμmstances is established.In the model,the threshing cylinder unbalanced vibration system model is established by integrating the threshing cylinder central axis elastic deformation,the decomposition of the transmission chain pulling force and the decomposition of the rice stem winding damping.The Fourier transform method which used in the threshing cylinder vibration system model analysis is analyzed.The initial parameters of the threshing cylinder vibration system are given.(2)The finite element model of the axial threshing roller is built,and the modal analysis is calculated and analyzed.The natural frequency and mode shapes of the axial threshing roller are obtained.In addition,the modal test of the threshing drμm is carried out.The experimental data are compared with the modal analysis results.The correctness of the finite element model is verified.The foundation for the threshing cylinder vibration characteristic analysis is built.The results show that the first three modal shapes of the threshing cylinder are local modes at the wheel.The mode shapes above the third order are the overall modes.When the external incentive frequencies are in the range of 50-75 Hz,the middle wheel may become a local weakness.The first eigenfrequency of the threshing cylinder is 20.29 Hz.When the cylinder rotating speed fluctuates,it may cause complex vibration coupling and resonance,which is easy to damage the key parts of the threshing cylinder and reduce its working life.(3)By testing the threshing cylinder’s shaft end vibration in the no-load and threshing state,the axis tracks of the threshing cylinder under two states are elaborated,and the effect of the rice stem winding on the shaft end vibration is explored.In order to simulate the twining state of rice stem on threshing teeth,counterweights were added to the cylinder.By monitoring the axis track of the threshing cylinder,the influence of the rice stem uneven distribution along axial and radial direction of the cylinder on shaft end vibration characteristics was explored.Rice threshing test was carried out to test the threshing cylinder speed fluctuation under no-load and threshing state,and the vibration state of bearing seat.In this way,the influence of the rice stew eccentric quality on the threshing cylinder shaft end vibration characteristics is explored.The results show that the threshing process will reduce the speed of the threshing cylinder and increase the fluctuation range.Unbalanced vibration,collision and friction characteristics are included in bearing beat vibration signal.It provides the basis and data support for the design of positive and negative stiffness parallel vibration isolation beam.(4)In order to control the threshing cylinder vibration induced by the rice threshing process,based on the vibration isolation principle of quasi zero stiffness structure,a new type of vibration isolation beam is put forward,which is composed of negative rigidity bending beam and positive rigidity bearing beam in parallel.The co-frame multi-cylinder vibration coupling and disturbance test are carried out.Combined with the threshing cylinder shaft end vibration characteristics and the vibration transmission characteristics on the frame,a variety of bending beams with negative stiffness are designed.The strength of the bending beams is verified by static analysis.Through the vibration transmission test of single positive stiffness beam and the vibration transmission test of positive and negative stiffness parallel vibration isolation beam,the vibration isolation performances of different kind of negative stiffness bending beams are verified and compared.