Order analysis based on FS-STFT and its application to varying speed machinery fault diagnosis

An order analysis method was proposed which utilizes short time Fourier transforms(STFT) based on frequency shift(FS-STFT).In the algorithm,by using the convolution properties of Fourier transforms in the frequency domain,the original signal is multiplied by e^-j2πf_it in the time domain,and the spectrum energy of f_i is shifted to the position of zero frequency.Other spectrum energies can be got at the position of zero frequency when f_i is changed according to a certain frequency interval.As a result,the frequency resolution of STFT is improved in the time-frequency analysis.Then local threshold de-noising was used in the time-frequency domain,and the change of speed signals was tracked.Eventually,the mothod was applied to the order analysis of varying speed machinery.A comparison of analysis results between STFT and FS-STFT shows that the method can track actual speed signals accurately.The order analysis for faulty bearings using the method in the deceleration process also demonstrates that the fault frequency can be extracted successfully.