An experimental study of acoustic emissions from active surface degradation in planetary gears

In this article, the detection of high frequency elastic waves, known as acoustic emission (AE), is used to correlate the events derived from the gear mesh with the surface wear and the operational behaviour in a planetary gearbox. In this regard, AE monitoring is a method that is able to provide information about the friction in the contact between surfaces in relative motion, which enables to employ a monitoring technology that overcomes the lack of sensitivity of traditional technologies under certain working conditions. Therefore, the investigation of the AE generated during the degradation of active gear surfaces can clarify how this process affects the performance in gearboxes. From the results, it has been stated that modifications in the active surfaces are barely reflected through traditional condition indicators (CI), such as AE frequency spectrum and AE signal envelope frequency spectrum, and same processing with accelerometry signals. It has been also observed that AE event width, or event lifetime, related with the gear meshing its a suitable indicator to monitor gear active surfaces. In this respect, a CI related to the AE event width and based in data reduction algorithm is proposed for gears monitoring with AE. For this work, characteristics of the complex studied system, as sensor position or cyclic periods inherent to the planetary gearbox, are assessed and highlighted as important factors in order to develop a valid monitoring.