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Proceedings Volume 12618, Optical Measurement Systems for Industrial Inspection XIII
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Item-typ:Veröffentlichung, Improved 3D form profiler based on extending illumination aperture(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2023-08-15); ; We recently demonstrated that the 3D shape of micro-parts can be measured using LED illumination based on contrast evaluation. The technique is based on imaging the object under test using partially coherent illumination. The limited spatial coherence of LED illumination was utilized to discriminate depth. For a fast depth scan without mechanically moving parts, an electrically tunable lens (ETL) in a 4f optical configuration is used. This approach is efficient, takes less than a second to capture all required images, is eye-safe, and offers a depth of focus of a few millimeters. However, the main limitation of the proposed approach arises from the underlying assumption that a small angle of variation of illumination is required. Such a small illumination aperture affects the axial scan resolution that dominates the measurement uncertainty. In the present paper we propose a method to overcome the main limitation of the above-mentioned profiling technique. The approach combines measurements with multiple illumination directions achieved by illuminating the object simultaneously with several independent light sources. In this way, the full-width half maximum of the contrast envelope is reduced. A tilted metallic plate is used for proof of concept.Konferenzbeitrag32 79 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Indirect geometry measurement method based on confocal microscopy and fluorescent microparticles(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2023-08-15); ; ; The precise production of micro- or micro-structured components of increasingly different materials requires ever more precise and flexibly adjustable geometry measurement methods. Today’s optical metrology offers various innovative approaches for this purpose. A major shortcoming is, however, that not all surfaces and structures to be measured are optically cooperative and return too little light or information to the measurement system for the signal analysis. Therefore, indirect optical geometry measurements are introduced as a new approach: Instead of directly detecting the outer boundary layer of the measuring object, the shape of the object’s imprint in the surrounding medium is examined. For this purpose, the surrounding medium is enriched with fluorescent substances and a confocal microscope scans the space surrounding the measured object. The spanned area above which the fluorescence signal disappears is then determined as the boundary layer between the measurement object and the surrounding medium. As a result, the object geometry is obtained completely independently of the optical response behavior of the object. While first realizations studied measurements in a liquid environment, this work demonstrates for the first time the feasibility of indirect optical geometry measurements in air environments with the aid of fluorescent microparticles. In order to maximize the measurement accuracy, different model-based signal evaluation approaches for determining the interface geometry from the fluorescence signals are investigated and compared, taking both cases (liquid and air environment) into account. Finally, indirect optical measurements are performed on a step geometry, reconstructing the height profiles using the theoretically derived model function.Wissenschaftlicher Artikel85 94