Intelligent Cepstrum And The Research Of Its Application In Fault Diagnosis

III The cepstrum is a method of fault diagnosis, the method has a strongdiscrimination ability of sideband in the detection, it is mainly change the sideband into a harmonic signal with FFT, and enhances the R.P.of weak sideband when combined with the logarithmic transformation.Gear failure is one of the main faults in rotating machinery. When eccentric, local fracture scuffing, fatigue, wear is appeared,the sideband around the meshing frequency and its harmonics will be appeared as well.Cepstrum can detect the sidebands effectively. The method of cepstrum is used to research fault diagnosis of the gearbox, the advantages and disadvantages of the method has been expounded, in the base of a detailed theoretical studies on cepstrum,the quantitative analysis problems of cepsctrum has been solved, in order to improve the resolution of the method, the CEFS、the CEES、the CFES has been sdutied.and made quantitative analysis for the mathod.In order to awoid of mistake,combined with full vector spectrum technology,studied the full vector cepstrum.The main research work and results are as follows: Research methods: the method cepstrum analysis is do FFT twice. The first FFT is used to detect the harmonic component of Waveform signal, and represent with the spectrum. There may be a sideband on spectrum, space of sideband response the frequency of fault, logarithmic transformation of the spectrum can reduce the small harmonic signal ignored.The second FFT change sidebands of spectrum into one or a plurality of line, the reciprocal of the inverted frequency is the space of sidebands in spectrum, it can determinethe location of the fault. cepstrum can calculate the amount of harmonic signal in spectrum. If change the second FFT into maximum entropy spectral estimation,get maximum entropy spectrum, and carried on the quantification analysis, it can reflect the sideband of spectrum stably,resolution has been improved as well,The full vector cepstrum can reflect the fault information really.Subjects: When the surface of gear wore, sideband with the space of running frequency will be appeared in spectrum,though the theoretical study of the diagnostic method and object,find that using the cepstrum can determine fault of wear,the method is with high desirability and accuracy.Experiment: in order to verify the feasibility of the theoretical research, the harmonic signal with fixed frequency interval is for research purposes,do FFT twice on it,gain the spectrum and cepstrum, compare the two graphs,The peak in Cepstrum is match with the sideband of corresponding spectrum,change the second FFT into maximum entropy spectral estimation, the correspondence is similar with the cepstrum. but the peak with high resolution.Fault analysis: cepstrum is applied to analysis the fault diagnosis of gearbox. It expounds the process of the practical analysis.It appeared abscissa in cepstrum that reflect the fault feature. And then analysisthe cepstrumwith quantitative strategy,it can estimate severity of breakdown.Methods optimization: the method of CFES is used to research fault of the gear box.and further proves the advantages in the resolution and stability, finally realizes the accurate positioning and quantitative analysis.