11 February 2011 3D triangulation system based on out-of-axis aperture configuration for micro-scaled objects shape measurement
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In three-dimensional (3-D) measurement systems based on triangulation, a stereoscopic angle between two distinct viewpoints encodes the depth information. This angle generally generates some distortion known as keystone distortion. In this paper an original 3-D optical configuration in addition with a digital light processing system (DLP) is presented which prevents keystone distortion, resulting in less calibration and post-processing work. The DLP is used to project incoherent white light fringes pattern at high frame rate (30 Hz) on a specimen and a CCD camera dynamically captures this projected pattern. Using a phase shifting algorithm, the reconstruction of the 3-D shape of the specimen is finally computed. This optical configuration is based on an « out of axis » aperture method combined with an afocal design for both projection and acquisition. With the combination of these two properties, the stereoscopic effect is obtained without any keystone distortion and a unique objective lens instead of two in a classical 3-D measurement system is used. As a result of this unique objective lens, the global volume of the measurement device can be easily minimized. This system was designed with the optical software Zemax to limit geometric and chromatic aberrations and to control the diffraction effect. Experiments showed that high surface profile accuracy can be obtained on a variety of surfaces, allowing reverse engineering on micro-scaled objects or precise 3-D measurements of macro-scaled objects. Also a depth resolution value under 2 μm for a scanned area around 7.5x5.5mm is obtained under experimental conditions.
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Erwan Dupont, Frederic Lamarque, Christine Prelle, Tanneguy Redarce, "3D triangulation system based on out-of-axis aperture configuration for micro-scaled objects shape measurement", Proc. SPIE 7932, Emerging Digital Micromirror Device Based Systems and Applications III, 79320F (11 February 2011); doi: 10.1117/12.874796; https://doi.org/10.1117/12.874796

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