Due to their advanced weight-specific mechanical properties, the application of fibre-reinforced plastics (FRP) has been established as a key technology in several engineering areas. Textile-based reinforcement structures (Preform) in particular achieve a high structural integrity due to the multi-dimensional build-up of dry-fibre layers combined with 3D-sewing and further textile processes. The final composite parts provide enhanced damage tolerances through excellent crash-energy absorbing characteristics. For these reasons, structural parts (e.g. frame) will be integrated in next generation airplanes. However, many manufacturing processes for FRP are still involving manual production steps without integrated quality control. The non-automated production implies considerable process dispersion and a high rework rate. Before the final inspection there is no reliable information about the production status. This work sets metrology as the key to automation and thus an economically feasible production, applying a laser light-section sensor system (LLSS) to measure process quality and feed back the results to close control loops of the production system. The developed method derives 3D-measurements from height profiles acquired by the LLSS. To assure the textile's quality a full surface scan is conducted, detecting defects or misalignment by comparing the measurement results with a CAD model of the lay-up. The method focuses on signal processing of the height profiles to ensure a sub-pixel accuracy using a novel algorithm based on a non-linear least-square fitting to a set of sigmoid functions. To compare the measured surface points to the CAD model, material characteristics are incorporated into the method. This ensures that only the fibre layer of the textile's surface is included and gaps between the fibres or overlaying seams are neglected. Finally, determining the uncertainty in measurement according to the GUM-standard proofed the sensor system's accuracy. First tests under industrial conditions showed that applying this sensor after the drapery of each textile layer reduces the scrap quota by approximately 30%.

Date Published: 18 May 2009
PDF: 12 pages
Proc. SPIE 7356, Optical Sensors 2009, 73560P (18 May 2009); doi: 10.1117/12.820584

Published in SPIE Proceedings Vol. 7356:
Optical Sensors 2009
Francesco Baldini; Jiri Homola; Robert A. Lieberman, Editor(s)