Time-Frequency Postprocessing Methods Based On Wavelet Transform With Application To Vibration Signals Analysis Of Excavator

Modern construction machineries are widely applicated in mineral resource mining,national infrastructure construction,industrial production and other fields because of their strong power,high degree of automation,and good functional adaptability.Vibration generated during construction machinery has a great influence on the running state of equipment and the operating comfort of diver.With the continuous improvement of people’s demands for low noise and operating comfort,ever-stricter limits of construction machinery and human body vibrations promulgated by domestic and foreign standards,vibration and noise reduction has increasingly attracted the attentions of enterprises and researchers.Therefore,carrying out research on vibration and noise properties is crucial in guiding the formulation of targeted passive vibration and nosie reduction for construction machinery,as well as improving its performance.Measuring vibration signals processing is an effective tool to obtain the useful information related to the vibration laws of vibration sources and their transmission path,in which accurately extracting the features and separating signal components are two core subjects.However,construction machinery has complex structure,many vibration sources,and various transmission paths,making the collected vibration signals exhibit complex nonstationary characteristics,such as strongly nonlinear frequency modulation,shock,and correlation.Existing signal processing methods often cannot meet the requirements of nonstationary features extraction and signal components separation.To this end,this dissertation takes excavator,a typical construction machinery as the research object,based on the existing postprocessing time-frequency analysis(TFA)methods,from the perspective of improving the energy concentration and estimation accuracy of time-frequency(TF)spectrum,to explore new TFA methods and their applications in features extraction of different types of nonstationary vibration signals.The main research contents are as follows:(1)Analyzing the existing problems in wavelet transform(WT)when estimating the information about frequency components and time position of analyzed signal.The distribution law of wavelet coefficients in the TF domain,and the inherent relationship between the wavelet coefficients lying in the position of instantaneous frequency(IF)and the essential TF features of the analyzed signal is studied,the existence of fixed points in the WT spectrum of is discussed.(2)To overcome the drawbacks of standard synchrosqueezing wavelet transform(SWT)in feature extaction when processing nonstationary signals with strong frequency modulated characteristics,the multisynchrosqueezing wavelet transform(MSWT)is proposed.The principles of obtaining WT coefficients at the fixed point by this method is analyzed,and its IF estimation and signal reconstruction accuracy are studied.Second-order IF estimation is integrate in MS WT to enhance its capability in processing strong frequency modulated siganls and improve the iterative convergence rate.Finally,simulation and practical signals are employed to verify the effectiveness of proposed methods in processing strongly frequency modulated signals.(3)To eliminate the disturbance of noise and other signal component in extracting features,the synchro-extracting method which can directly obtain the wavelet coefficients related to the essential TF features of the analyzed signal is proposed.The theory concerned such as IF estimation accuracy,signal reconstruction and discrete algorithm implementation are presented.Numerical simulations and experimental data are employed to test the performance of the proposed method in capturing the modulation information related to nonstationary signals.(4)Aiming at the problem that characterization of impulse signals,the distribution law of WT coefficients of impulse signal,the relationship between the WT coefficients located in the position of group delay trajectory and the essential TF features of impulse signals are studied,and then the transient-extracting method based on WT proposed.Theory concerned such as group delay estimation and signal reconstruction are analyzed using a signal modeled in frequency domain.Moreover,taking the TF energy concentration center of impulse signal as the occurrence time of impulse,it is used to estimate repetition period of successive impulses,which improves the accuracy of processing results and reduces the disturbance of noise and irrelevant components.Simulation and practical engineering signals are used to verify the effectiveness of the proposed method in extracting TF feature and locating the occurrence time of impulse signal.(5)Aiming at solving the challenging problem of distinguishing different vibration source with correlated signal features in excavator,the proposed postprocessing TFA methods are employed to analyze modulation and impulsive characteristics of vibration sources’ vibration signals,and the TF features that can reflect the vibration laws of different vibration sources are figured out based on their vibration formation mechanism,and then the mapping relationship between the TF features and vibration source are established.According to the established mapping relationship,applying the ideal of TF feature matching to solve the problem of excavator vibration source identification and their transmission paths location is explored,and the effectiveness of the proposed solution is verified through cases analysis.Aiming at the analysis needs of different types of nonstationary vibration signals of excavator,this paper proposes three time-frequency post-processing methods based on WT:multiple synchro-squeezing,synchro-extracting,transient-extracting,and studies related theories.The proposed methods are employed to study the vibration characteristics of excavator,and the problem of vibration resource identification with relevant characteristics is solved.The research results are of great significance to make up for the shortcomings of the existing TFA methods,enrich and improve the TFA theoretical system,and provide effective technology for the study of vibration characteristics of construction machinery.