Fringe Projection Profilometry in Production Metrology: A Multi-Scale Comparison in Sheet-Bulk Metal Forming

Fringe projection profilometry in combination with other optical measuring technologies has established itself over the last decades as an essential complement to conventional, tactile measuring devices. The non-contact, holistic reconstruction of complex geometries within fractions of a second in conjunction with the lightweight and transportable sensor design open up many fields of application in production metrology. Furthermore, triangulation-based measuring principles feature good scalability, which has led to 3D scanners for various scale ranges. Innovative and modern production processes, such as sheet-bulk metal forming, thus, utilize fringe projection profilometry in many respects to monitor the process, quantify possible wear and improve production technology. Therefore, it is essential to identify the appropriate 3D scanner for each application and to properly evaluate the acquired data. Through precise knowledge of the measurement volume and the relative uncertainty with respect to the specimen and scanner position, adapted measurement strategies and integrated production concepts can be realized. Although there are extensive industrial standards and guidelines for the quantification of sensor performance, evaluation and tolerancing is mainly global and can, therefore, neither provide assistance in the correct, application-specific positioning and alignment of the sensor nor reflect the local characteristics within the measuring volume. Therefore, this article compares fringe projection systems across various scale ranges by positioning and scanning a calibrated sphere in a high resolution grid.

Full Scale Calibration of a Combined Tactile Contour and Roughness Measurement Device

In current production metrology contour and roughness of work pieces has to be controlled in demanding small tolerances. It is important that the results not only have to be accurate, but also the measurement has to be performed effective and fast. It would be convenient to have the possibility measuring first a continuous surface profile and than performing different evaluations on adjacent segments. We describe a measurement system which is based on a tactile probe with a diamond tip. The position of each axis is measured by high resolution and high accuracy digital scales. The instrument is calibrated and traced back by only using one precision sphere covering approximately the whole measuring range of 24 mm. It is shown that with only that macroscopic calibration and adjustment the accuracy for roughness measurement in all arbitrary vertical positions is reached in the nm-range. The calibration and adjustment process is described and we show the verification of the accuracy by measuring several surface specimens. The results are compared to a Physikalisch-Technische Bundesanstalt (PTB) calibration certificates for those surface roughness standards.

Design of a Silicon Micromachined Artifact for Hybrid Dimensional Measurement

We are developing calibration artifacts for mesoscale metrology (especially vision probing) by using silicon bulk micromachining. We evaluate these artifacts on both high accuracy coordinate measuring machines (CMMs) and on typical production vision-based measurement systems. This will improve the accuracy of vision-based measurement equipment used in production. Successful realization of these mesoscale artifacts will enhance both production metrology capabilities and reduce manufacturing costs.