Improved spectral amplitude modulation for tacholess estimation of rotation speed

Abstract

Rotation speed is key information for rotating machinery, whether it’s a negative feedback control method based on speed or equipment status monitoring and fault diagnosis. In order to accurately and efficiently estimate the rotation speed under tacholess condition, a novel method named improved spectral amplitude modulation (ISAM) is proposed in this paper. In ISAM, the vibration signal is first filtered through a band-pass filter to eliminate interference from irrelevant frequency components. Subsequently, an appropriate weight, which modifies the amplitude spectrum of the time–frequency representation (TFR) to decompose different components based on their powers, is selected to enhance the instantaneous frequency (IF) of rotation speed. The modified signal is then reconstructed based on the edited amplitude and original phase. Finally, the IF can be extracted from the TFR of the modified signal with the multiple time–frequency curve extraction (MTFCE) technique. Additionally, entropy is utilized to guide the selection of weight. The effectiveness of the proposed method is evaluated through simulation analysis and case studies. The results show that the ISAM can accurately estimate rotation speed, with the mean absolute error (MAE) at 0.13. Compared to an existing IF estimation method, ISAM can reduce computation time by 95%.