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Many industrial processes call for determining not only the front but also the rear surface shape, i.e., the material thickness. This is crucial for identifying weak points or potential material savings, for instance, in ampoules. Existing methods for the simultaneous measurement of surface shape and material thickness (e.g., computer tomography) are complex, expensive, slow, and cannot be integrated into production lines. As a result, e.g., container glass manufacturers are actively seeking an alternative solution.
We aim to provide such a solution by enhancing our current process. Instead of a CO2 laser line at λ = 10.6 μm wavelength, which is absorbed at the object’s surface and does not penetrate the material, we use a wavelength in the short-wave infrared (SWIR). At this shorter wavelength, the laser radiation travels through commercially available glasses. At the rear surface, the radiation is partly reflected and reaches the front surface again. Along its path, the radiation is absorbed and leaves a heat trace behind. Whereas common glasses are translucent in the SWIR, they are generally opaque in the LWIR range. Consequently, while some SWIR radiation penetrates the object, LWIR cameras detect heat only at its front surface: (1) at the entering laser line and (2) at the position of the exiting line. Our goal is to use these two thermal signal positions to determine both the front and rear 3D surface shape, and thus the material thickness. In this paper, we investigate our approach theoretically using a simulation model. The model is used to generate thermal points on static measurement objects and determine appropriate parameters such as laser power, angle of incidence, and irradiation time. Furthermore, we analyze the temporal and spatial behavior of the thermal points, considering the material parameters. With the obtained simulated results, we subsequently demonstrate an initial experimental setup. In this setup, the two thermal signals are evaluated on a glass plate for different angles of incidence to determine the material thickness.
In this contribution, we present new 3D sensor technologies based on three different methods of near-infrared projection technologies in combination with a stereo vision setup of two cameras. We explain the optical principles of an NIR GOBO projector, an array projector and a modified multi-aperture projection method and compare their performance parameters to each other. Further, we show some experimental measurement results of applications where we realized fast, accurate, and irritation-free measurements of human faces.
We propose a novel approach of phase unwrapping without using additional pattern projection. Based on a stereo camera setup, an image segmentation of each view in areas without height jumps larger than a fringe period is necessary. Within these segments, phase unwrapping is potentially without error. Alignment of phase maps between the two views is realized by an identification process of one correspondence point.
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