Projection of reference points to large scale objects in fringe projection projects
The three dimensional reconstruction of large scale objects, for example a Volkswagen T6 car body, is carried out operationally with fringe projection systems. In comparison to classical touch-probe coordinate measuring systems, which just generate punctual measured data, the optical measuring technology provides a global full-field mesh, a reconstruction of the measurement object. To enable the geometrical data fusion between single fringe projection results from different positions, reference points have to be signalized on the surface of the car body. The three dimensional coordinates of the reference points have to be calculated by a prior photogrammetric measurement and processing.
To avoid the time consuming process of signalizing reference points by fixing circular high contrast targets on the surface it is planned to use a high resolution beamer for the projection of targets on the object being measured.
As the positional accuracy of the reference points has to be 0.1 mm in object space it has to be investigated whether the resolution of a high resolution beamer is acceptable for that task. It has to be examined, if the projection of reference points is stable enough during the whole time of the prior photogrammetric measurement and the following fringe projection process.
The major goal is to reach the same overall accuracy through all parts of the optical measurement of a T6 chassis without mounted targets. Beside the effect of reducing the afford and the gaining of time the merging of the fringe projections has to be ensured to be precise and safe by using projected targets. It has to be proved that projected targets meets the requirements of the common optical measurements, which are frequently used in the industrial manufactory.
Figure 1: Comparison of a real, mounted target (left) with a projected target (right)
Ürün, M.; Wiggenhagen, M.; Nitschke, H.; Heipke, C. (2017): Stabilitätsprüfung projizierter Referenzpunkte für die Erfassung großvolumiger Messobjekte. In: Luhmann, T.; Schumacher, C. (Eds.) Photogrammetrie – Laserscanning – Optische 3D-Messtechnik. Beiträge der Oldenburger 3D-Tage 2017, Wichmann Verlag, Heidelberg 377-387. | file |