Frequency and Time-Frequency Analysis of Cutting Force and Vibration Signals for Tool Condition Monitoring

Diagnosis of turbo-compressors during start-up is a particularly challenging task. One of the reason is the reduced set of instruments that monitor this procedure. It is cumbersome to adjust lubrication and steam valves while controlling the speed and dynamic stability. In order to get the turbo-compressor out of a high vibration zone, it is important to be able to predict instabilities associated to the start-up process. Thus, it is necessary to have a measurement system with the ability of fault detection, especially at early stages of fault appearance. In this way, the start-up time can be significantly reduced. Although recent developed diagnosis methods use information from different sources and measurements, data structures are not designed to carry predictive information related to the turbo-compressor health. Therefore, it is important to extract early warning signals related to instability conditions. Vibration signals during machine start-up are non-stationary in nature, and conventional techniques, such as Fourier transforms and time series analysis, have difficulties to extract the full features of the vibrations signature. In this paper, the features of start-up vibrations in rotational systems like those found in turbo compressors are investigated by time-frequency analysis, and appropriate analysis of the transient vibration during compressor start-up is presented.

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TVAR Time-frequency Analysis for Non-stationary Vibration Signals of Spacecraft

Chinese Journal of Aeronautics ◽

10.1016/s1000-9361(08)60055-2 ◽

2008 ◽

Vol 21 (5) ◽

pp. 423-432 ◽

Cited By ~ 6

Author(s):

Yang Hai ◽

Cheng Wei ◽

Zhu Hong

Keyword(s):

Frequency Analysis ◽

Vibration Signals ◽

Time Frequency Analysis ◽

Time Frequency ◽

Stationary Vibration

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Stationarity test of vibration signals with surrogate data and time–frequency analysis

Advances in Structural Engineering ◽

10.1177/1369433216677602 ◽

2016 ◽

Vol 20 (8) ◽

pp. 1143-1154

Author(s):

Zuo-Cai Wang ◽

Feng Wu ◽

Wei-Xin Ren

Keyword(s):

Frequency Analysis ◽

Surrogate Data ◽

Transform Method ◽

Vibration Signals ◽

Time Frequency Analysis ◽

Time Frequency ◽

Analysis Methods ◽

Stationarity Test ◽

Modulated Signals ◽

Short Time

The stationarity test of vibration signals is critical for the extraction of the signal features. In this article, the surrogate data with various time–frequency analysis methods are proposed for stationary test of vibration signals. The surrogate data are first generated from the Fourier spectrum of the original signal with keeping the magnitude of the spectrum unchanged and replacing its phase by a random sequence. The local and global spectra of the original signal and the surrogate data are then estimated by four time–frequency analysis methods, which are short-time Fourier transform, multitaper spectrograms, wavelet transform, and S-transform methods. The index of nonstationarity is then defined based on the distances between the local and global spectra. Three kinds of synthetic signals, which are stationary signals, frequency-modulated signals, and amplitude-modulated signals, are tested to compare the efficiency of the four time–frequency analysis methods as mentioned. The results show that with a certain observation scale value, the index of nonstationarity based on the short-time Fourier transform or wavelet transform method may fail to test the stationarity of the signal. The parametric studies and sensitivity analysis of the observation scale and noise-level effect are also extensively conducted. The results show that the index of nonstationarity calculated using the multitaper spectrograms’ method is more suitable for stationarity test of frequency-modulated signals, while the index of nonstationarity calculated using the S-transform method is more suitable for stationarity test of amplitude-modulated signals. The results also show that the noise has a significant effect on the stationarity test results. Finally, the stationarity of a real vibration signal measured from a cable is tested, and the results show that the proposed index of nonstationarity can effectively test the stationarity of real vibration signals.

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