What is it about?
This work evaluates the performance and operative limits to dimensional accuracy of 3D Optical scanning based on Blue-Light fringe projection technology. This technology, also known as Structured Light 3D scanning, is widely used in many Reverse Engineering applications. It allows to quickly capture and create point clouds, by using images taken at different orientations of white or blue light fringe projected patterns on the part. For the survey, a large and feature-based gauge has been used with optical specific properties. The gauge is endowed with canonical geometrical features made of matt white ceramic material. The gauge was calibrated using a Coordinate Measuring Machine (CMM) by contact. Therefore, it is possible to compare the measurements obtained by the structured Blue-Light sensor with those obtained by the CMM, which are used as reference. In the experimentation, the influence of the scanner software in the measurement results was also analysed. Besides, different tests were carried out for the different fields of view (FOV) of the sensor. The survey offers some practical values and limits to the accuracy obtained in each configuration.
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Why is it important?
The main Highlights are: - A new optimized qualification procedure is presented for Structured Light scanners - Study of scanning strategies applied over large parts exceeding the Field of View - Scanning data treatment influence on the results of measurement accuracy - Use of a feature-based gauge for qualification of optical scanners The analysis performed have led to reliable results about the accuracy of measurements derived from 3D scanning using several geometric features. The experimentation was carried out under usual working conditions for this type of equipment, that is, in terms of “in-situ” measuring procedures. Scanner configuration led to define two different types of tests: 400 FOV and 850 FOV. Using these tests, several point-clouds were acquired over a feature-based gauge. After post-processing, reconstruction of geometrical entities was possible in order to compare their metrological characteristics with the reference alues measured previously with a CMM. This analysis was performed feature-by-feature in the gauge, aiming at comparing form errors and dimensional deviations, and also by considering the global gauge, aiming at comparing distance deviations.
Perspectives
This work let to establish reliability values for the accuracy that this type of equipment can achieve in metrological tasks performed in “in-situ” usual conditions. On the other hand, this work validates a specific feature-based gauge developed for optical metrology. It was proved appropriate for generating high-quality point-clouds, due to the white and matte ceramic elements. However, the linear arrangement of the geometric features is not the most suitable for an equipment based on the Structured Light technique, as location of spheres following a straight line avoids an accurate fitting of the point-clouds. As a future task derived from this survey, development of a new gauge specifically for this technology is proposed. An artefact in which the reference entities could be captured from very different angles or spatial orientations. Thus, it would be possible to reconstruct the entities with the highest precision, as the same coordinate system would be maintained for different captures.
Eduardo Cuesta
University of Oviedo
Read the Original
This page is a summary of: New procedure for qualification of structured light 3D scanners using an optical feature-based gauge, Optics and Lasers in Engineering, November 2018, Elsevier,
DOI: 10.1016/j.optlaseng.2018.06.002.
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