Mechanism and method for the full-scale quantitative diagnosis of ball bearings with an inner race fault

A full-scale quantitative diagnostic method is proposed in this study for inner-race fault-size estimation of ball bearings. The fault size is generally estimated using time interval between double impacts if the fault size is smaller than ball angular spacing. This method may be inapplicable when fault sizes become larger than integral multiples of ball angular spacing, which means they have the same time intervals. The analysis of dynamic modelling reveals the existence of a zone where load distribution is unaffected by the inner-race fault and the range of the zone varies monotonously with the fault size. The monotonic relationship between the proportion of fault-free components in axis-orbit time history and fault size can be explored using this mechanism. Hence, a novel evaluation indicator called the axis-orbit deterioration degree (AODD) is proposed in this study. The expression of this indicator is derived from theoretical analysis and signal processing methods. AODD in the simulation and experimental studies can be used to distinguish between faults that differ in size by integral multiples of the ball angular spacing. A new idea is proposed for the quantitative diagnosis method of ball bearings to improve the accuracy of fault size estimation. (C) 2020 Elsevier Ltd. All rights reserved.