| One of the main ways of harvesting rapeseed is the staged harvesting,which firstly cuts the rapeseed plants and lays them in a concentrated place to dry for a period of time before picking up and threshing them.It makes full use of the post-ripening effect of the plants.Sweating is a key link in segmented harvesting.Due to the need to open furrows for rape planting in Mid-lower Yangtze River,and the plants are tall and have many branches,the operating conditions of the rape windrower are complex and the vibration excitation range is wide.The platform is prone to large vibration,causing fatigue damage to key parts,impacting the dependability and operation stability of the whole machine.Aiming at the problem that the rape windrower is working,based on the elaboration of vibration and structural optimization of agricultural machinery at home and abroad,and takes the rape windrower as the research object.The vibration characteristics of the header and the operating feature of each part are analyzed by mechanical model and test analysis;the optimal design of the header frame structure was carried out by using software such as Creo,Hyper Works and Recur Dyn;through the combination of simulation analysis and experiment,the optimization was compared and analyzed.The stiffness,strength,natural frequency and vibration amplitude of the front and rear header frames,the header amplitude was reduced,and the working parts work stably.The concrete research contents and research conclusions are drawn:(1)Vibration characteristics of rape windrower header under multiple working conditions were tested and analyzed.(1)It was clarified that the vibration excitation of the header comes from the reciprocating motion of the horizontal and vertical cutter,the rotation of the reel and conveyor,the reciprocating motion of the diesel piston,the hydraulic pump working incentives and the road excitation,and the excitation frequency was determined according to the rotational speed of each component,the component excitation frequency range was 0～40Hz.(2)The vibration test of the windrower under different working conditions was carried out,and amplitude of the measuring point and vibration frequency of header were obtained.The test showed that when the working parts of the windrower header and the engine work at the same time,the vibration amplitude of the header was about 2 times higher than that when only the engine working,the amplitude of the horizontal and vertical cutters was higher than that of other measuring points,and there was coupled vibration when the working part was working;the main factors affecting the vibration of the header were determined by the analysis:the range of 4-20Hz,the ignition frequency of the engine(36.7Hz)and its frequency division(18.4Hz),among which the first-order mode of the header was the state frequency of 18.8Hz was close to the frequency division of the engine excitation frequency,which was prone to resonance.(2)The force simulation test of the rape windrower header based on Recurdyn was carried out.Using 3D laser scanner and harmonic superposition method to obtain the elevation data of different pavement,the excitation model of flat pavement(tar road)and field pavement(rural dirt road and rape field)was generated;the test method was established by changing the driving auxiliary function and track contact parameters.The coupling model of the machine-road system under different working conditions was obtained through simulation analysis;the mechanical model of the header was constructed,and the simulation results were compared with that of the header.The force theoretical analysis results showed that the relative error between the two is within 10%,which verified the correctness of the model.(3)Based on the variable density topology optimization,the structure optimization of the header frame was carried out.(1)In order to improve the dynamic and static performance of the windrower header frame,the density of the structural material was the design variable,and the volume fraction was the constraint condition.The header comprehensive objective function of stiffness and frequency was constructed by the compromise programming method,and the weight of each sub-objective was determined according to the AHP method.Based on the multi-body dynamics simulation results and Hypermesh software,an optimization model for three working conditions was established and carried out the structural optimization of the rape windrower header frame.(2)The structure of header was designed with reference to the results of topology optimization combined with manufacturing and actual engineering requirements,and the reconstructed model was subjected to finite element static analysis and modal analysis.The results showed that optimized frame of header achieves rigidity demands,and the maximum deformation decreased from 0.82mm to0.36mm,and the maximum stress value reduced from 107.99MPa to 64.45Mpa;the first three-order modal frequency increased to a certain extent,and the fundamental frequency increased from 18.83Hz to 24.18Hz,avoiding the external excitation frequency.The optimized header frame achieved the expected optimization goal.(4)The vibration test of the optimized rape windrower was carried out.As you can see from vibration test:(1)The amplitude of measuring longitudinal cutter support on the header of the two generations of prototype when the engine and working parts were working at the same time increases and was greater than that of other measuring points when only the engine was working,it showed that the longitudinal cutter has a great influence on the width of the header.(2)The range of the windrower measuring points on different roads was different,which indicated that the influence of road excitation on the vibration of the windrower cannot be ignored.(3)Header amplitude that was optimized is significantly lower than that before optimization.The maximum amplitude of the longitudinal cutter bracket was reduced from 4.83m/s~2 to 1.49 m/s~2,and the amplitude was reduced by 69%,which verified the accuracy of the topology optimization results. |
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