Effective damage detection on curved structures using a scanning laser Doppler vibrometer

Conventional laser scanning techniques that employ scanning laser Doppler vibrometers (LDVs) excel at inspecting flat, plate-like structures but produce errors when examining complex, three-dimensional (3D) structures without prior knowledge of the structure’s geometry. Herein, we propose a novel approach that integrates an LDV with a laser distance meter (LDM) and performs 3D shape estimation using compensation algorithms to minimize errors caused by the nonuniform scan spacing resulting from curved surfaces. The LDM, in conjunction with Galvo mirrors, facilitates the acquisition of 3D point clouds representing the curved surfaces of the structure, thereby outlining its geometry during the 3D shape estimation process. Spacing errors, calculated by subtracting neighboring points with nonuniform spacing arising from curvature variations, are effectively mitigated. The proposed method not only compensates for these spacing errors but also creates an optimal, adaptive scan grid tailored for different 3D structures. By ensuring uniform laser scan spacing on curved surfaces, this technique reduces potential errors resulting from spacing discrepancies. Experiments conducted on aluminum and composite structures reflecting the curvature of an aircraft wing demonstrated the improved accuracy on curved surfaces achievable using this technique.