Vibration Based Condition Monitoring of Planetary Gearboxes Operating Under Speed Varying Operating Conditions Based on Cyclo-non-stationary Analysis

Bearing failures not only increase the cost due to production loss and need for repair or replacement, but also threaten the personnel safety. Manufacturers of rotating machinery tend to adopt new health monitoring services, using regular inspections or embedding sensors for health monitoring systems within each unit. Early failure signs of a bearing defect are usually weak compared to other sources of excitation. Furthermore, fault detection of bearings appears to be more complicated in the case of planetary gearboxes. As a result, a plethora of signal processing tools have been proposed, focusing towards fault detection and diagnosis of rolling element bearings, such as Envelope Analysis through the selection of the filtering band with Kurtogram. Recently, Cyclic Spectral Correlation/Coherence have been presented as powerful tools for condition monitoring of rolling element bearings, exploiting their cyclostationary behaviour. The aforementioned tools perform well under steady speed operating conditions but their effectiveness drops in the case of speed varying operating conditions, which is quite common in applications such as wind turbines and helicopter drive trains. In order to overcome this difficulty, a new diagnostic tool is introduced based on the integration of the Order-Frequency Cyclic Spectral Coherence along a frequency band that contains the diagnostic information. A special procedure is proposed in order to automatically select the filtering band, maximizing the corresponding fault indicators. The effectiveness of the methodology is validated using experimental and real data captured on planetary gearboxes, including various faults with different levels of diagnostic complexity.