Bearing health monitoring using optical fiber sensors

Abstract

Bearings are vital elements in rotating machinery. Failures in bearings can result in irreversible damage. Therefore, early detection of bearing damage and monitoring of fault severity are necessary for optimization of maintenance decisions.The classical methods for bearing monitoring are based on analysis of vibration signals captured by accelerometers, usually located on the machine case. Two difficulties arise when diagnosing bearings in that manner. The first difficulty is the distortion of the signals due to the transmission path to the sensor. The second difficulty is the characteristic low signal to noise ratio, resulting from the weak bearing signals in the presence of the strong surrounding noise, originating from the vibrations of other rotating components in the machine.The goal of the present study was to research the possibility of using an optical fiber sensor of the Fiber Bragg Grating (FBG) type, which senses strain and temperature changes, for bearing diagnostics. Due to its small dimensions, this sensor can be embedded close to, or even inside the bearing, suggesting a possible solution to the two difficulties which were discussed above.The results of this study open new options to monitor and detect early failure signs in critical bearings. FBG-based diagnostics was found applicable and useful for detecting damage in bearings.The analysis of signals measured on bearings with various widths of spall, demonstrates the power of the FBG-based local sensing methodology. In addition, the study also aimed to understand the capabilities and limitations of FBG for wideband sensing, and the effect of different sensor attaching techniques on the signal.