Abstract: The instantaneous rotating speed carries a lot of useful information about the running condition of rotating machinery. It is also a key parameter for the condition monitoring and fault diagnosis. Traditional rotating speed estimation methods suffer from large estimation error due to low frequency resolution of short-time Fourier transform. To overcome this limitation, an instantaneous speed estimation method based on short-time Chirp-Fourier transform is proposed. In addition, an adaptive chirp rate selection scheme is further established. The analyzed signal could be decomposed in an adaptive way according to its time-frequency distribution in the proposed method. Hence the smearing problem could be avoided, and the computational efficiency is enhanced as well. On this basis, a tacho-less amplitude and phase demodulation technique is further proposed to detect the incipient fault of a gearbox during the non-stationary working conditions.

Key words: Chirp-Fourier transform, instantaneous rotation speed, ridge searching, short-time Fourier transform