Fringe projection system for high-temperature workpieces-design, calibration, and measurement

In the Collaborative Research Centre 1153, Tailored Forming, the geometry of hot measurement objects needs to be captured quickly, areally, and with high precision. The documentation of the hybrid components' shrinkage behavior directly after the forming process can yield insight into the development of residual stresses. In this paper, we present a fringe projection measurement setup designed for the topography measurement of high-temperature steel shafts, comprising two cameras with different lenses and a projector. In order to separate the measurement signal from light by self-radiation, a green bandpass filter is installed in front of the measurement camera's sensor. The optical sensors are protected from the measurement object's temperature and possible scale by a glass panel and a working distance of at least 250 mm. High-resolution measurements are guaranteed due to a telecentric measurement camera and a triangulation angle of about 30°. The triangulation angle requires an additional entocentric calibration camera to provide a highly accurate projector model estimation. Special attention is therefore devoted to the developed calibration routine, the glass panel effect, and the applied distortion models. The quality of the calibration routine is validated by a reference sphere measurement. Furthermore, the geometry data of a red-glowing heating rod (approximately 1020°C) is acquired to demonstrate the performance of the presented system. In future applications, the presented setup will be used with a force-controlled clamping unit to enable secure and position stable topography acquisition of hot measurement objects.