| The utilization rate of traditional large wood-gathering equipment featuring sole function has decreased since 1990s.However,with the progress in science and technology,and accordingly the increase in labor cost of livestock gathering,the livestock gathering operation mode will eventually be replaced by the economic and ecological multi-functional small skidder.To satisfy the needs in production,a kind of environment-friendly multi-function wheeled skidder was already devised.However,this wheeled vehicle is hardly applicable in the forest because of the environment's complexity.In order to solve this problem,a triangle crawler was implemented to replace the traditional tyre considering its ability to increase the ground area,reduce the earth pressure,improve the trafficability and enhance the adhesion,traction,gradeability and loads of the equipment.Under slope conditions,the split-body structure has a higher ground area than that of a traditional unibody structure.Therefore,the triangle crawler skidder combining the advantages of tire and traditional crawler type,is a direction of skidder development.The working conditions of the triangle crawler skidder are very complicated.In addition to supporting the weight of the body,the crawler also bears the operating loads from collecting materials,loading,unloading,and road repairing.Moreover,in the process of moving,the random impact generated by the uneven road surface makes the force of the crawler more even complicated.The frame structure of the crawler is the main supporting part.The safety and stability of the frame structure plays a very important role in the safe operation of the triangle crawler skidder If the destruction occurs in the production,it will not only lead to the damage of the wood collecting machine,but will also affect the wood production schedule,producing a certain economic loss.Therefore,it is very necessary to carry out the research on the frame structure,which is of practical significance to ensure the safe production of the triangle crawler wood-gathering machine.This paper makes a systematic study on the structure of triangular crawler frame for skidder.In the process of research,the methods mainly include:the field investigation,theoretical analysis and mathematical model of optimization,the virtual prototype and physical prototype test simulation analysis.For the purpose of deciding the main parameters,all the mentioned methods are coherent and complementary,during which the statics,dynamics,optimization design and fatigue life analyses on the frame structure were conducted to give the full picture of the devised machine.The specific research contents are as follows:(1)Through the analysis of the composition and function of the triangle crawler,combined with the working conditions in the forest,the overall layout scheme of the triangle crawler suitable for skidder was proposed.The selection principle and method of key parameters are put forward.The key parameters are obtained and optimized by MATLAB software.On this basis of these,the structural form of the frame structure is selected and its parameters are determined.(2)By using the mechanical theory and adopting the holistic to local stress analysis method,the stress conditions of the speed straight running condition,the straight running condition of the uniform speed ramp,the transverse straight running condition of the uniform speed ramp and the uniform turning condition are obtained,and the summary table of load values of the frame structure under four working conditions is established.Based on this,the numerical simulation of four working conditions was carried out with the help of ANSYS Workbench platform.Through numerical calculation,it is found that the third working condition is the most dangerous among the four working conditions.After optimization,the wall thickness of the square steel tube of the main material is changed from 5mm to 3.5mm,and other parameters remain unchanged.The next step of dynamic simulation analysis is needed to verify whether the optimized frame structure can be applied to actual production.(3)The dynamic simulation platform of triangular crawler wood-gathering machine was built by using SolidWorks software and RecurDyn software,and the rigid and flexible coupling simulation model was created by combining ANSYS Workbench platform.On this basis,the stress cloud map of the frame structure and the occurrence position and time history of the maximum equivalent stress are obtained by rigid and flexible coupling simulation of the frame structure.The maximum equivalent stress ratio is obtained by numerical finite element optimization analysis of the rigid-flexible coupling simulation.(4)The vibration time history of the frame structure under D,E and F levels of pavement conditions was obtained by using MATLAB and the random dynamic simulation platform of triangular crawler skidder.The fast Fourier transform(ffourier transform)is used to transform the vibration signal in frequency domain.The vibration of rear wheel is larger when there is no load.With the deterioration of road quality,the frequency of vibration peak gradually decreases,and the peak of total amplitude increases.From the tri-axial decomposition vibration,the peak amplitude on the X-axis(the moving direction)is gradually reduced.However,the amplitude peaks on the Y and Z axes are gradually higher.(5)physical prototype tests were carried out on three pavement conditions,and the time history of tri-axial vibration of the frame structure under three conditions was obtained.The data is processed and compared with the simulation data.The simulation results of D and E pavement conditions are basically consistent with the vibration test results.However,compared with the vibration test results,the error of the simulation analysis results of F pavement condition is relatively large.Therefore,it is not recommended to use the results from dynamic simulation platform of triangular crawler skidder to replace the measured real value.(6)ANSYS Workbench was used to analyze the random vibration of the frame structure.The maximum equivalent stress values of the frame structure with or without anti-turnover device were compared in the two working conditions of high and low speed.The results show that the anti-rollover device not only plays an anti-rollover role in the delta crawler system,but also can improve the stress condition of the triangle crawler frame.Therefore,anti-rollover device should be installed in practical application.By reference to the calculation formula and experience coefficient of passenger vehicle suspension system,the spring stiffness K and shock absorber damping coefficient delta value were calculated.Based on these values,with the gradient of 500,a larger and smaller values were selected respectively.Then the maximum equivalent stress summary table was built using permutation and combination based on random vibration analysis on the road load of the frame structure F.According to the data in the table,the optimal solutions are K=24635 and ?=63443,respectively.(7)According to the transient fatigue life analysis,the position of the minimum failure cycle is the same as that of the maximum equivalent stress in the random vibration analysis of the pavement condition of machine F with anti-turnover device,which proves the feasibility of the test method and verifies the reliability of the test data.The service life of the frame structure is 2767 days,and the fatigue reliability of the frame structure is verified. |
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