In phase measuring deflectometry (PMD), the fringe pattern deformed according to slope deviation of a specular surface is digitized employing a phase-shift technique. Measuring examples for reflective and refractive components are given, demonstrating the potential of the method. Unlike other techniques the presented measuring method does not require particular previous knowledge of the tested component and may be applied to both reflective and refractive optical surfaces. In favor of a high measurement accuracy phase shifting techniques and photogrammetric methods are used in the course of the evaluation of the reference structure and the characterization of the tested optical surface. The grid pattern is taken as a reference object whose resulting image recorded by the camera is evaluated in order to obtain the properties of the tested optical component. With the measuring method presented in this paper the imaging properties of the optical component under test may be determined by making it part of an imaging system consisting of an electronic camera with lens, a special grid pattern and the object itself. For complexly formed and/or large objects, we propose a robot-based inspection setup.ĭue to the increasing use of aspherical optics, there is a demand for innovative measuring methods that allow the flexible testing of a wide variety of optical components. We will show that an inspection of specular and partially specular objects is feasible in an industrially applicable inspection system. After presenting some properties of the deflectometric inspection itself, we describe the qualitative and quantitative evaluation of the deflectometric observation in detail. In this paper, we introduce the theoretical background of deflectometry. Knowing that pattern, it is possible to inspect the surface qualitatively and at least with certain additional knowledge to reconstruct the surface under test. The main principle of deflectometric surface acquisition is to use a highly controllable environment, where a screen on which a well-defined pattern is presented is observed via the specular reflecting surface. The transfer of this observation into automated visual inspection is called deflectometry. In contrast to the non-specular case, the appearance of a specular surface is dominated by the reflections of the environment that are visible in it. The inspection of specular surfaces differs significantly from the case of non-specular surfaces. This is a work in progress and further experiments need to be carried out and several extensions could be considered. Simulations have been performed to validate the system, having obtained errors on the measured vector field that are in the order of less than 1 mrad, suitable for many applications. The system requires only a single camera and an LCD screen, so it is a low cost solution. ![]() Besides that, the proposed system does not require precise positioning of the measured part. Furthermore it is simple, computationally efficient and robust. The method is based on homographies, a mathematical tool that has been widely tested in computer vision. to measure angular deviations between the average normal vector of the surface and the actual vector at each point of the surface (vector field errors). The method presented in this paper makes it possible to evaluate the planarity of quasi-flat surfaces, i.e. ![]() Deflectometric methods have been extensively used, both in research and industry, to measure the shape of specular surfaces.
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