Schnelle und genaue 3D-Formvermessung mittels Musterprojektion und Stereobildaufnahme im thermischen Infrarot

Three-dimensional shape measurement has become essential in many areas, such as quality control in industrial production or digitization of complex free-form surfaces. Stereo recording based on the principle of pattern projection is often used on diffusely reflecting surfaces. Objects with non-cooperative surfaces, such as transparent, shiny, absorbent, or translucent objects, could not be reliably recorded with this technology until now. In previous studies it was shown that the shape from heating approach can be used to record non-cooperative surfaces in three dimensions. This method is based on pattern projection in the thermal infrared, absorption under generation of a heat pattern, and stereo recording of the reemission. However, the measurement time in the double digit second range has been relatively long and the measurement accuracy insufficient for many applications. In this study, a simulation model for the entire thermal measurement process is developed. With the help of this tool, the interaction between the infrared radiation and the object as well as the generation of a temperature contrast is investigated. From this, limits of the multi-fringe projection are concluded and the novel projection principle of sequential fringes is developed. Instead of an areal multi-fringe projection, the new method irradiates the object only in locally strongly restricted areas. This results in irradiation times in the millisecond range, which drastically reduces the influence of thermal diffusion. The new 3D sensor based on sequential fringe projection has impressively demonstrated the advantages over multi-fringe projection. Besides the significant reduction of measurement times and improvement of measurement accuracy, the recordable material classes are extended to objects with higher thermal conductivity. The presented sensor is thus the world’s fastest and most accurate measurement system for high-resolution optical 3D shape measurement of non-cooperative surfaces.