Xiang Ling

A Novel Approach of Impulsive Signal Extraction for Early Fault Detection of Rolling Element Bearing

The fault signals of rolling element bearing are often characterized by the presence of periodic impulses, which are modulated high-frequency harmonic components. The features of early fault in rolling bearing are very weak, which are often masked by background noise. The impulsiveness of the vibration signal has affected the identification of characteristic frequency for the early fault detection of the bearing. In this paper, a novel approach based on morphological operators is presented for impulsive signal extraction of early fault in rolling element bearing. The combination Top-Hat (CTH) is proposed to extract the impulsive signal and enhance the impulsiveness of the bearing fault signal, and the envelope analysis is applied to reveal the fault-related signatures. The impulsive extraction performance of the proposed CTH is compared with that of finite impulse response filter (FIR) by analyzing the simulated bearing fault signals, and the result indicates that the CTH is more effective in extracting impulsive signals. The method is evaluated using real fault signals from defective bearings with early rolling element fault and early fault located on the outer race. The results show that the proposed method is able to enhance the impulsiveness of early bearing fault signals.

Notice of Retraction Oil Film Instability Fault Diagnosis Using Hilbert Huang Transform

The Hilbert-Huang Transform (HHT) consists of the following steps: First, decomposition of time sequenced data by empirical modes (EMD), followed by a Hilbert transform to obtain a new method of spectrum treatment. The theory and algorithm of the HHT is explained and an experiment of oil film instability (oil whirl and oil whip) simulated on rotor kit, the full process of oil whirl occurrence, development and oil whip recorded through the rotor run-up test. HHT applied in analysis of oil film instability signal. The experiment results show that the whirl frequency is raised following rotating speed, but the exactly ratio of the two frequency is not fixed in different speed; The half frequency component appearance is the main characteristic of oil whirl, it should be constant, same with the critical speed, when oil whip occurred. The fundamental frequency component is frequency modulated throughout the oil film instability process, and frequency modulation phenomenon appears in half-frequency component when oil whip occurres under some certain speed. Compare to traditional methods, HHT method can represent the characteristics of oil film instability signal more accurately and detect the oil whirl fault earlier.