Detection of Generalized Roughness on Ball Bearing by Cyclostationarity Technique

This paper deals with the detection of generalized roughness on ball bearing. In literature most of the authors focus on the detection of incipient single defects. In the early stage of the damage the vibration signal of the bearing contains characteristics components in the frequency spectrum that reveal both the presence of the fault, and on which element of the bearing the damage is placed. In time the damage develops and important parts of the bearing surface (usually the external or the internal rings) become faulted, and the bearing is said to be affected by generalized roughness. In that case the vibration level of the bearing increases and the characteristic frequencies of the damage are no longer recognizable. In this paper the authors propose the use of cyclostationarity to analyse the vibration signal in the generalized roughness condition. The cyclostationarity allows to detect phenomena which happens repeatedly in a signal. In particular the second-order cyclostationarity has been proved to be suitable for bearing diagnostics, since the periodic impact between a ball and a faulted ring happens with a variable period due to slippery between the bearing elements. So far the cyclo-stationarity has been used to detect single defects, in this paper its use is extended to distributed defects. Experimental results are reported. In particular a degreased bearing is placed on a test-rig and radially loaded to accelerate wear phenomena. The vibration signal is then analysed with two techniques compared to each other: the envelope analysis (which is a well-known method taken from the literature) and cyclostationarity.