Research On Application Of Morphological Filter In Diagnosis Of Roling Element Bearing With Local Defect

The vibration of rolling element bearing with local defect presents properties of amplitude-modulating vibration. Its carrier wave is a kind of the bearing's inherent vibration with high frequency, and its modulating wave is a pass vibration corresponding to the local defect. Therefore making diagnosis of the local defect needs to demodulate the vibration to get the modulating wave. Because the morphological filter can availably identify the features of fringe and shape of signal, the demodulation based on morphological filter has been used in this thesis to extract the impulsive signals due to the local defects from the vibration of the rolling element bearing. Thus the diagnosis of local defects of rolling element bearing has been successfully realized by means of this technique. Moreover, the technique of wavelet filtering has been applied in envelope-demodulation to validate the results of morphological filtering. The main contents and the results of this thesis are as follows:Selection of morphological operator: Morphological filtering is a kind of operation based on morphologic arithmetic between a signal to be studied and a structuring element specified by morphology. Different morphologic arithmetic, which forms a morphologic filter namely morphologic operator, could get different result of filtering. Comparing the filtering results from different morphological operators, the close-operator of morphologic arithmetic is selected to identify the plus impulse caused by the local defect.Selection of structuring element: The structuring element also affects the result of morphological filtering. In general, only structuring signal, which matches the structuring element both in scale and shape, could remain after morphological filtering. Based on study of the relationship between noises in bearing vibrations and pulses extracted by flat structuring elements with different scales, a line structuring element with 0.6T in length and zero in width has been used in this thesis for morphological filtering to perfectly extract required impulses caused by local defects of bearing. It has been shown by experiment results that using the line structuring element for morphological filtering of bearing vibration can availably identify the information of local defects of the bearings. Application of morphological filtering in diagnosis of the local defect of ball bearing and the criterions corresponding to the diagnosis: Using the close-operator and line structuring element mentioned above, a series of signals of bearing vibrations have been processed by means of morphological filtering. Then the filtered signals, which are modulating signals with envelope amplitude, are transferred by FFT into their envelope-spectra. Based on analysis of envelope-spectra of the signals, the criterions corresponding to the diagnosis are given finally.Application of wavelet filtering in envelope-demodulation, and verification of results of morphological filtering: Band-pass filtering is important in envelope- demodulation. The wavelet filtering has the properties of band-pass filtering and has its unique advantages, so it has been used for envelope-demodulation in this thesis to replace common digital filter, and its corresponding arithmetic has been given also. Through analysis of and comparison wavelet filtering with morphological filtering, the validity of morphological filtering has been verified. Meantime, the advantages of demodulation based on morphological filter are known, such as its high Signal-to-Noise Ratio (SNS) , good adaptability to non-linear vibration , good adaptability to monitor on line and so on.