Application of EMD method and Hilbert spectrum to the fault diagnosis of roller bearings

Based upon empirical mode decomposition (EMD) method and Hilbert spectrum, a method for the fault diagnosis of roller bearings is proposed in this paper. The local Hilbert spectrum and local Hilbert marginal spectrum are introduced. The orthogonal wavelet bases are used to translate vibration signals of a roller bearing into time-scale representation. Then, an envelope signal can be obtained by envelope spectrum analysis of wavelet coefficients of high scales. By applying EMD method and Hilbert transform to the envelope signal, we can get the local Hilbert marginal spectrum from which the faults in a roller bearing can be diagnosed and fault patterns can be identified. Practical vibration signals measured from roller bearings with out-race faults or inner-race faults are analysed by the proposed method. The results show that the proposed method is superior to the traditional envelope spectrum method in extracting the fault characteristics of roller bearings.