Microscopic laser triangulation in harsh industrial conditions for the inspection of microstructured surfaces

Laser triangulation is a well-established technique for three-dimensional measurement of surface geometries. The majority of available laser triangulation systems is, however, not capable of measuring microstructured surfaces with sufficient accuracy. This article introduces a measurement system for the inspection of microstructured surfaces and describes adjustments in comparison to a conventional triangulation system. On the one hand, the adjustments regard the generation of a laser light section. The presented measurement system is able to project a narrow light section with a width of approximately 10 mu m. On the other hand, the necessary adjustments regard the digital processing of the raw triangulation measurement data to achieve more precise laser line detection, because in the microscopic scale, laser triangulation is very sensitive to fluctuations of the surface reflectivity. For the presented system, a robust algorithm for the calculation of the laser line positions from camera images was developed. This algorithm carries out image segmentation based on the Chan-Vese method. The measurement system is designed for application in very harsh industrial conditions, such as the inspection of microstructutred surfaces in the aviation industry. Here, the surfaces are used on a large scale to reduce drag. This planned large-scale application requires the use of measurement systems which are able to efficiently monitor the manufacturing process. For this purpose, the measurement system must be located directly on the manufacturing tool. Therefore, the measurement system must be able to cope with all harsh conditions during the manufacturing process, including impurities such as dust, coolants or lubricants.