Use of bispectral-based fault detection method in the vibroacoustic diagnosis of the gearbox

Abstract

The central issue is extract the relevant diagnostic information from vibroacoustic signal of mating gears and use it in the forecasting process. Thus the research focuses in particular on the methods of analyzing the relations between various frequency bands and their links to various types of defects or phase of their development. The value of the information contained in the bispectrum consists of, among others, the fact that it enables examination of statistical relations between individual components of the spectrum as well as to detect the components generated as a result of occurrence of non-linear effects and the additional feedback associated with the emerging defects. This results from the fact that in contrast with the power spectrum, which is positive and real, the bispectrum function is a complex value which retains the information on both the distribution of power among individual components of the spectrum as well as the changes of phase. Let us note that the bispectrum enables one to determine the relations between essential frequencies of the examined dynamic system. High value of bispectrum for defined pairs of frequency and combinations of their sums or differences will point to the existence of frequency coupling between them. This may mean that the contemplated frequencies, being the components of the sums, have a common generator, which in the presence of non-linearity of higher order may lead to synthesizing the aforementioned new frequency components. Thus mean that bispectral measures like: diagonal bispectrum, row bispectrum, max bispectrum, can be useful in detection of gear’s fatigue crack.