Fiber Optic Strain Sensor Vibration Separation for Detection of Seeded Faults in Rotorcraft Transmissions

Abstract

This paper presents a refined methodology for performing helicopter transmission anomaly detection through the use of vibration separation techniques applied to the output of a fiber optic sensor array. Fiber Bragg grating (FBG) sensors—distributed about the exterior of a planetary gearbox annulus—record the local strain response of the annulus surface due to tooth-mesh interactions. These strain profiles are collected for a number of loading conditions both with and without seeded faults. The profiles are separated and synchronously averaged to illustrate the effect of damage to planetary gears on local strain variation. Results of experiments conducted on the University of Maryland Transmission Test Rig (UMTTR) are included. Additional processing and comparison to traditional vibration-based diagnostic methods indicate the potential for increased sensitivity to damage of such a system and the feasibility of fiber optic strain sensors for in situ health and usage monitoring.