Dynamics-based visual inspection through real-time modal analysis

In this study, we propose the concept of dynamics-based visual inspection for the verification of structural dynamic properties of a vibrating object; the inspection method involves the analysis of the vibration distribution of the object by using a high-frame-rate video. Under unknown ambient excitation, modal parameters of an excited object are simultaneously estimated to determine its input-invariant dynamic properties by using a fast output-only modal analysis algorithm, SSI-CPAST. The algorithm was implemented on a 2000-fps vision platform, and it facilitates non-destructive monitoring of the structure of beam-shaped objects vibrating at dozens of hertz; the algorithm detects small changes in the dynamic properties of the objects caused by internal defects such as fatigue cracks. The modal parameters resonant frequency and mode shape were actually estimated for beam-shaped objects excited by human finger tapping to verify the performance of 2000-fps real-time dynamics-based visual inspection.