Nonlinear and Non-stationary Vibration Analysis for Mechanical Fault Detection by Using EMD-FFT Method

Abstract

The Hilbert-Huang transform (HHT) is a powerful method for nonlinear and non-stationary vibrations analysis. This approach consists of two basic parts of empirical mode decomposition (EMD) and Hilbert spectral analysis (HSA). To achieve the reliable results, Bedrosian and Nuttall theorems should be satisfied. Otherwise, the phase and amplitude functions are mixed together and consequently, the confidence of resultant frequencies are reduced. To prevent such an event, various methods as improved Hilbert-Huang transforms have been proposed. Yet, another method is introduced in this paper that has a high ability to identify the mechanical defects easily. According to this method, the signal is decomposed to its intrinsic mode functions (IMFs) and then each of the IMF is analyzed by fast Fourier transform (FFT). As the proposed method, which is called EMD-FFT, used, the mechanical defects of an electro motor have been detected in Kerman combined power plant. While, the classical FFT method is unable to detect all the defects and the HHT, due to the mixing phase and amplitude functions, does not provide accurate results.