|
The rapid developments in the micro camera industry, driven by the smartphone sector, offer a wide range of innovations with respect to the performance and miniaturization of endoscopic instruments. For the fast 3D inspection of inaccessible components such as turbine blades in partially disassembled aircraft engines, a borescopic fringe projection system was developed. This study provides a methodology for the comparison of different camera and projection configurations within borescopic fringe projection. Furthermore, the current limits for the use of multimedia sensors in metrological applications are shown and quantified. The projection unit of the developed measuring system is based on a digital micromirror device, which generates structured light that is imaged into the measurement scene by means of an objective lens and a borescope. Threedimensional, high-resolution reconstructions are carried out via chip-on-the-tip miniature cameras based on the MIPI interface by forming a triangulation base with the projection unit. To enable inspections in confined spaces, the cameras are connected to external framegramer boards. In this study, 1/6” and 1/4” sensors with fixedfocus lenses are evaluated to assess the trade-off between the physical sensor size and the possible reconstruction accuracy. Typical camera parameters such as the sensitivity with respect to the signal-to-noise ratio are determined by means of a standardized test setup. In addition, the application in the triangulation system is evaluated through the modulation signal strength as well as the suitability for typical system calibrations based on the widely used pinhole camera model in combination with a distortion polynomial correction according to the approach of Conrady and Brown. Finally, the sensors are compared regarding 3D reconstructions of calibrated geometric features in accordance with ISO/IEC Guide 98-3:2008 and VDI/VDE 2634-2.
|
