Optical high-speed 3D metrology in harsh environments: Recording structural data of railway lines

This paper reports measurement results and some design details of railway measurement systems based on optical principles. The quality of railway lines is crucial for reliability and safety and therefore to be controlled regularly. Special measuring vehicles operate permanently on all railway lines, even during regular traffic situations. Therefore the measurement systems used to record the data have to be fast enough even at high speeds and robust enough to provide reliable data under almost any environmental conditions. The application of optical methods is advantageous concerning accuracy and speed but of course limited by external influences. We report here measures enabling even a sensitive optical measurement principle, the phase measurement technique, to be applied under these harsh environmental conditions. Exemplarily the optical and mechanical design of a clearance profile scanner is described. It is shown how to make the sensor insensitive against environmental conditions like contamination by dust or water or temperature changes. Measurement results of this scanner and of another system to measure the position of the contact wire are presented.