This work attempts to study the vibration response of a double-row self-aligning ball bearing due to surface and localized imperfections. For the contact deformation at the ball–race interactions, the Hertzian load–deflection relation is used for the evaluation of time-varying contact stiffness. The elastohydrodynamic theory is applied to find out the central film thickness. For both the inner and outer race waviness cases, the system response is observed as periodic (with vibrations of high amplitude) at [Formula: see text], i.e. multiples of Nb and its vicinity, but gradually turns to quasi-periodic as the value of waviness order reach some intermediate value. In the case of a localized defect, the double impulse phenomenon marks the entry and exit events of the rolling element in and out of the rectangular spall. Hence, this analysis can be used as a diagnostic tool with system dynamic characteristics for distributed and localized defect identification.

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This paper presents an autonomous method to diagnose a double-row self-aligning ball bearing for any dynamic misalignment or localized defects, using vibration signals. The frequency spectra from the experimental investigation revealed that irrespective of the health condition of the bearing i.e. either healthy or defective, the frequency spectrum had a clear cage frequency peak whenever the system was under dynamic-misalignment. An improved version of Harmonic Product Spectrum (HPS) called sideband product spectrum (SPS) was used to identify the cage frequency peaks which was preprocessed using kurtosis-based band-pass filter and parameter-optimized variational mode decomposition (VMD) algorithm. A mathematical model is also presented to analyze the dynamic behavior of double-row self-aligning ball bearing under such conditions. From the model, it was realized that during misalignment, the contact load shared by the rolling elements, generates some moment which has a tendency to rotate the bearing’s inner-race about the radial axis and thus resulting in a wobbly rotary motion. This wobbly motion of the inner race in fact characterizes the bearing for dynamic misalignment. The simulated results were in accordance with the experimentally obtained results.