Endoscopic 3D Inspection of Technical Components Using Structured Light and Structure-from-Motion

The inspection and maintenance of aircraft engines is a crucial task in ensuring the safety and reliability of modern passenger aircraft. Conventional inspection methods, such as visual inspections, are limited by difficult access to engine components. In recent years, there has been increasing usage of non-destructive testing methods such as borescopic inspection. Modern borescopes are capable of generating high-resolution 2D images of the engine interior. Reproducible 3D measurements however remain a challenge. Two applications are relevant in the context of 3D defect measurement: The determination of the defect geometry and the determination of the defect location. The aim of this work is the development of a miniaturized fringe projection sensor for reproducible measurement of the defect geometry inside aircraft engines. The sensor is based on the phase shift method and is equipped with a high-resolution micro camera. An evaluation of the fringe projection sensor was performed with artificial reference specimens. The results show that the sensor provides reproducible measurement results with a low measurement uncertainty on smooth surfaces with diffuse and specular reflectivity. Rough surfaces pose a challenge for the sensor. A structure-from-motion algorithm is used for accurate quantification of the defect location. In the experimental evaluation of the algorithm, surfaces with different reflective properties and textures, as well as homogeneous and structured illumination concepts were investigated. The results show low measurement uncertainty for well-textured diffuse reflective surfaces. For lowtextured diffuse reflective surfaces, the textured illumination leads to a significant improvement of the measurement results. Lack of texture and strong specular reflection can lead to insufficient 3D reconstructions by the algorithm.The results indicate that the combination of fringe projection and structure-frommotion offers the potential to significantly improve aircraft engine inspection processes, reduce maintenance time and costs, and increase the safety of flight operations.