A tacho-less order tracking technique for large speed variations

• Current tacho-less OT methods are only applicable to small speed variations.
• The instantaneous frequency is estimated by time–frequency analysis.
• Vold–Kalman filter is employed to extract the interested harmonic.
• The established method is applicable to large speed variations.
• Simulation and experimental results verify the established method.

Order tracking is considered as a classic and effective technique of the non-stationary vibration analysis for rotating machinery. Traditionally, a tachometer is required to obtain a reference signal. Some tacho-less order tracking methods have been proposed in the past few years to improve the applicability of traditional order tracking technique. However, current tacho-less order tracking methods are only applicable to those with small speed fluctuations. A new tacho-less order tracking method is established for any speed variations including large speed variation such as run-up or run-down process of machinery. In this method, a Chirplet-based approach is proposed to estimate the instantaneous frequency of a certain harmonic of rotating frequency. The result is accurate and reliable since the chirp basis can be adjusted to match the vibration signal. After that, Vold–Kalman filter is employed to extract the harmonic, because it is particularly suitable for the harmonic extraction under large speed variations. Then, the shaft angular position is recovered from the vibration signal through demodulating the extracted harmonic. The order tracking is carried out by using the shaft angular position thereafter. Simulations and experiments are given to testify the proposed tacho-less method. The results obtained by the proposed method are almost the same as those obtained by a tachometer under large speed variation.