Detection of the rubbing-caused impacts for rotor-stator fault diagnosis using reassigned scalogram

Impacts generated from the surface of a stator rubbing against the surface of a rotor during its rotation is a common defective phenomenon which often occurs in a rotating machine. The rubbing often occurs at the positions with small clearances in rotating machinery. This defect may deteriorate rapidly and finally cause the catastrophic breakdown of the machine. It will not only interrupt services or production, but also lead to substantial economic loss. To further understand the rubbing-caused impacts, a detailed analysis is presented in this paper to explain the cause of rubbing, its occurrence and phenomenon if the severity of rubbing becomes serious. A comparison has also been conducted to investigate the effectiveness of monitoring the rubbing-caused impacts by using conventional scalograms and reassigned scalograms. The results show that when rubbing occurs, its impacts lead to an increase of magnitudes not only at the fundamental rotational frequency and its harmonics, but also at some high-frequency components. The more severe the rubbing, the higher and the more components at high frequencies. Both the simulated rubbing signals and experimental rubbing signals collected from a test rig have proven that the method of reassigned scalograms is more effective in measuring rubbing-caused impacts as it can provide a better concentration of impacts with less interference. Moreover, the exact occurrence time and frequency of impacts are also easier to be identified. In summary, the phenomenon of having more high-frequency components due to the increasing severity in rubbing, and the clear identification of impacts provided by reassigned scalograms, can definitely help a machine operator to detect the occurrence and determine the severity of rubbing occurring between the stator and the rotor of a rotary machinery.