| As an indispensable part of cotton harvesting equipment,self-propelled cotton picker bears heavy responsibility in cotton harvesting and processing industry.In the working process,the self-propelled cotton picker frame will be stimulated by vibration sources such as engine,wind conveying system and picking.The previous study found that the interaction between vibration sources will produce vibration coupling,resulting in complex vibration conditions of the frame,thus affecting the performance of the cotton picker.At present,most domestic cotton pickers are imitations of imported cotton pickers,and there are few basic researches on the frame vibration.In order to deeply understand the vibration characteristics of self-propelled cotton picker frame under multiple excitation,improve the shortcomings of the original frame,and improve the performance,this thesis takes a domestic self-propelled cotton picker model as the object,analyzes the frame vibration,and puts forward a frame theory improvement scheme.The research work mainly includes the following aspects:(1)Three-dimensional modeling was carried out on the frame of the cotton picker,and the load status of the frame was analyzed.The stress and strain of the frame under different working conditions were obtained through static analysis.The maximum stress of the frame was 126 MPa,and the total deformation range was 0-0.939 mm.Finite element software,force hammer,acceleration sensor and other equipment were used to analyze the finite element mode and test mode of the frame respectively,and the first six mode frequencies and mode shapes of the frame were solved.Combined with the comparison of the two mode analysis results,the maximum error of the mode parameters was 3.1%,which verified the accuracy of the model.(2)The test is carried out with the engine,wind transmission system and picking head as the main vibration sources,and the collected signals are analyzed and summarized.Under the first and second gear conditions,the engine excitation characteristics are mainly based on its own excitation frequency,and the excitation direction is mainly concentrated on the X-axis.The fan excitation characteristics are mainly based on the coupling excitation frequency of the fan,and its own excitation frequency amplitude is far less than the coupling excitation amplitude,and the excitation direction is mainly concentrated on the YZ axis.Under the three-gear working condition,the coupling excitation frequency is the main excitation frequency of the engine,and the excitation frequency amplitude of the fan itself is large,but the coupling excitation frequency is still the main excitation frequency.Picking head is characterized by fuzzy excitation frequency and large noise range.The excitation direction is concentrated on the X axis.The main excitation frequency is concentrated around 220 Hz and 320 Hz under the first and second gear conditions,and the main excitation frequency is concentrated around 320 Hz and 400 Hz under the third gear conditions.(3)By dividing the frame vibration measurement points,collecting signals and analyzing,the engine excitation has the greatest influence on the frame vibration,while the fan and picking head have less influence;The vibration of the rear longitudinal beam and longitudinal beam is mainly in the X direction,and the vibration is the strongest.The vibration of the welding frame of the picking head is mainly in the XY axis direction,and the vibration of the front axle is mainly in the YZ axis direction.The overall XYZ three-axis vibration frequency of the frame is dominated by the engine excitation frequency in the first gear,the engine excitation frequency in the second gear and the coupling frequency in the second gear,and the coupling frequency in the third gear,among which the coupling frequency of 235 Hz,260Hz and 330 Hz account for the largest proportion.(4)The structure size of each part of the frame was analyzed,and 20 design variables were selected to calculate the modal sensitivity.The optimization scheme was solved based on the response surface and multi-objective genetic algorithm.The optimal scheme was selected by combining entropy weight method and linear weighting method,and topology optimization was used to improve the frame mass,which was reduced from 1827 kg to 1740 kg.The power spectral density function was calculated by selecting the signal of the maximum root mean square acceleration of the vibration measuring point of the frame,and the frequency amplitude of 1000(m/s2)2/Hz was used as the load function to solve the frame life.The fatigue of the weak part of the frame is greatly improved after the improvement of the local thickening and so on.The statics and modal analysis show that the maximum stress of the improved frame is 114.8MPa and the total deformation range of the frame is 0-0.96 mm under the three working conditions. |
