Use of Cyclostationarity to Detect Changes in Gear Surface Roughness Using Vibration Measurements

Wear in gears can usually be detected from the vibration signal once the wear has reached a ‘macro’ level—millimetre-scale variations from the original involute profile. Macro level wear is often preceded and accompanied by micro-level surface roughness changes (micrometre scale), arising from either abrasive wear or contact fatigue pitting. These micro- and macro-level phenomena interact with one another, and so knowledge of surface roughness is needed to be able to predict macro-level wear. It was recently suggested that it may be possible to use the cyclostationary properties of the vibration signal as an indicator of gear surface roughness, and the present paper examines this possibility further. It is thought that roughness information is carried by random high frequency vibrations that are modulated by the gearmesh cycle, and so any speed changes in the system should change both the carrier and modulating frequencies. The paper tests this hypothesis by studying laboratory measurements from a spur gearbox running at different speeds and with gears of different roughnesses. The findings will be very important for the further development of gear prognostics methods.