Abstract
Rotating machinery encounter throughout their lifetime various problems. Among them, a rotor-stator rubbing problem is one of the most common. This paper proposes a procedure, which applies the instantaneous angular speed (IAS) measurement as a starting step for rotor-stator partial rub detection. There are various approaches regarding counting techniques and processing of signal. In this paper, an application of analog signals from toothed wheel encoder or zebra tape encoder is considered at low to moderate sampling rates. As the rubbing process is nonlinear, this paper is proposing a variational mode decomposition (VMD) as the second step of the detection procedure. The VMD is relatively new method with promising results especially interesting for machinery fault detection. Detection tool is tested on laboratory test rig at two different rotor operating conditions i.e. without rotor-stator rubbing and with light partial rotor-stator rub. Measurements were performed with non-contact eddy current displacement sensors pointed to toothed wheel encoder. Results are presented in the shape of rotor orbits, IAS signals, FFT spectra of IAS signals and VMD spectrograms. Developed fault detection procedure based on IAS measurement and VMD decomposition was successfully tested on laboratory test rig for no rubbing and light rotor to stator partial rub condition.
Highlights
Rotor–stator contact or rubbing is occasional problem faced by rotating machines especially during startups and shut downs when passing through their critical speeds
If measurements have to be performed on toothed wheel encoder or zebra tape encoder with analog signals and acquired with a general purpose ADC system at low to moderate sampling rates, such a system can experience problems with non-uniformity of encoder segments geometry
It can be concluded that variational mode decomposition (VMD) spectrogram can detect light partial rotor–stator rub condition and give clear difference between no-rubbing and rubbing condition
Summary
Rotor–stator contact or rubbing is occasional problem faced by rotating machines especially during startups and shut downs when passing through their critical speeds. If measurements have to be performed on toothed wheel encoder or zebra tape encoder with analog signals and acquired with a general purpose ADC system at low to moderate sampling rates, such a system can experience problems with non-uniformity of encoder segments geometry In such cases a correction procedure has to be performed using of normalized time passage ratio [14]. IMFs of original version of HHT (EMD) suffer from the lack of mono-component property for the real signals containing noise Bearing this in mind Dragomiretskiy and Zosso have recently proposed a new approach called Variational Mode Decomposition (VMD) [18]. To decrease the error caused by low sampling frequency, raw signal is up-sampled by a factor 50 performing cubic spline interpolation To resolve another source of error i.e. geometric non-uniformity, a correction procedure was performed using normalized time passage ratio of encoder segments. It can be concluded that VMD spectrogram can detect light partial rotor–stator rub condition and give clear difference between no-rubbing and rubbing condition
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