Demodulation Analysis Technology In Dynamic Signal Analysis And Fault Feature Extracting Of Gearbox

The importance of Gearbox-Fault-Diagnosis consists not only in cutting time and cost of repairing, but also in raising diagnosing accurate, which improves repairing quality and acquires economic benefits dramatically.Demodulation analysis is widely used for diagnosing machine fault diagnosis. Extracting information from modulation signal is an effective method to diagnose damaging faults fixed with gears and bearings. Each demodulation analysis technique has its merits and limitations. In this paper, the principal and limitations of the Hilbert transform and generalized detection-filtering demodulation analysis are systematically studied. From theoretical analysis, we know the existing demodulation methods have limitations as following: one is that the subtraction of the two signals frequencies will display as the result of demodulation when we demodulate two time-domain adding signals without modulating information (fault information); The other one is that aliasing phenomenon will occur as a result of getting absolute value, detection or square in the process of generalized demodulation analysis, Such phenomenon will result in some superfluous frequency composition on the frequency spectrum, which will puzzle the detection of mechanical vibration. If the sampling frequency is selected from a suitable range, the aliasing phenomenon will be avoided; The last one is that aliasing frequencies will be produced in zoom demodulation analysis because this algorithm cannot employ digital low-pass filtering to avert the folding frequencies of higher harmonics in the process of zoom sub-sampling. These will result in wrong diagnosis and some superfluous frequency composition, which will puzzle the detection of mechanical vibration.Fault feature extracting plays very important role in gearbox fault diagnosing process. This paper investigates the vibration features of various typical gearbox faults including profile error, broken tooth, symmetrical tooth wear, serious unbalance of shaft, on the base of theoretic analyses and plenty of cases. It provides guide for further gearbox-fault-automatic-diagnosis.