Evolution of gear condition indicators for diagnostics of planetary gearboxes

In the last decades diagnostics of planetary gearboxes became a necessity in different fields, such as Industry and Army, and a plethora of gear condition indicators (CI) were proposed. Among the others: FM4, NA4, ER and SI. All of these CIs have proved to be effective in specific conditions, but it is a matter of fact that several indicators may lead to different decisions, while the literature only reports case studies with positive responses for each CI. In this paper a critical comparison among different CIs is carried out during a complete life of a gearbox. In particular a test bench runs a three-stage gearbox for a non-stop target period of 700 hours. At the end of the test the presence of faults are evident from the analysis of the vibrations. Moreover two original CI, namely RV and CRV, have been introduced and tested. The evolution of CIs response is monitored during the test, showing different behavior in both parameter sensitivity and response dynamics. The data analysis allows a choice of the most promising indicators