Acquiring and processing light deflection maps for transparent object inspection

Transparent objects play important roles in different sectors, e.g., they are employed in high precision optical systems or to guide laser beams in surgery. Hence, transparent materials have to meet high quality requirements. However, most of the existing elaborated automated inspection approaches are not applicable for the inspection of transparent materials-especially with respect to scattering inhomogeneities. Scattering material defects mainly cause a deflection of incident light rays away from their original optical path. This article proposes a novel optical system based on a transmission-type laser scanner that acquires so-called deflection maps of transparent objects. By means of two subsequent processing methods-one based on a spatial gradient calculation, the other relying on vector analysis-scattering material defects can be visualized even in test objects with a complex 3D-shape. Experiments performed using a first prototype and different test objects approve the proposed approach.