Contributions to the analysis of vibrations and acoustic emissions for the condition monitoring of epicyclic gearboxes

Condition monitoring of machines through vibration analysis has been successfully applied on different types of machines for several decades. However, there are still some mechanical systems where its use has not given the same good results. Epicyclic gearboxes (EG) belong to this group of systems. Due to its special characteristics, EG are used in a wide range of applications within the drive technology, mostly when high power transmission is required. Machines dealing with high power transmission are typically critical, which means that a large part of the process in which they are involved depends on their appropriate operation. Hence, there is a high interest on a solution which can effectively diagnose failures in EG at an early stage, before they evolve and produce major breakdowns. Probably the most important reason for the deficient results of failure detection on epicyclic gearboxes (EG) through vibration analysis is the poor understanding of the characteristics of the vibrations generated in EG. This situation is even more critical in the case of the acoustic emissions (AE), whose application for the machine condition monitoring has been increasingly explored in the past years, but not in the case of EG. This work contributes to the problem of failure diagnosis in EG by providing valuable information regarding the characteristics of the vibrations and AE generated in EG. The analysis considers the special kinematics of the gearbox and the measurement arrangement, both decisive factors in the structure of the generated vibrations and AE. The phenomenon is thoroughly explained through the development of two models: one for the vibrations and one for the AE generated in a planetary gearbox, when measured with a sensor installed on the outer part of the ring gear. The models are used to explore the most appropriate signal processing tools for the analysis of both types of signals. The tools are finally used for the analysis of real signals measured in different planetary gearboxes.