Process signatures of the fusion area directly determine the quality of the part in Laser Powder Bed Fusion (LPBF). The geometric contour of the fusion area is one of the most important indicators of manufacturing quality. The accurate detection of the contour has been generating considerable interest. However, due to the complex operating condition in LPBF, the 2D images of the fusion area suffer from shortcomings such as poor contrast, high noise, and vary illumination. This makes the location of the contour extremely difficult for traditional detection methods. In this study, a robust contour detection method of the fusion area in LPBF is proposed. In order to raise the contrast of the contour, the phase image with clear contour details will be calculated from a series of fringe images with phase shift projected onto the fusion area. A phase-guided contour extraction method is conducted to accurately locate the center of contour which reduces significantly the impact of the severe manufacturing condition. Experimental results reveal that the proposed method can obtain the contours of the fusion area in a very short time, with higher accuracy and repeatability. In addition, it also holds the potential to be an effective way to monitor the geometric defects layer-wise.
KEYWORDS: 3D metrology, Cameras, Calibration, Spatial resolution, Temporal resolution, Projection systems, 3D image processing, Phase shifts, 3D acquisition, Computing systems
Numerous fast 3D shape measurement systems based on pattern projection method have been developed in the recent
years, but measuring arbitrary dynamic 3D shape with full resolution, including temporal resolution and spatial
resolution, is still a big challenging problem. This paper presents a real-time 3D measurement system with full spatial
resolution and temporal resolution. In this system, three-step phase-shifting algorithm is employed for full spatial
resolution measurement, and a multi-view phase-shifting correspondence is used to search the corresponding point
independently without additional images. So any adjacent three phase-shifting images in the continuous capturing stream
can be used to reconstruct arbitrary 3D shape, the 3D acquisition speed can be as fast as the camera capturing speed to
achieve full temporal resolution. Moreover, for developing an accurate measurement system the calibration method is
also presented, and it can obtain more accurate internal and external parameters than traditional method in presence of
inaccuracy of calibration target. And a hybrid computing architecture based accelerate calculation method is introduced
to achieve real-time 3D measurement, and the computation speed can be above 280 times faster than before. The
experiments indicate that our system can perform 1024 × 768 full spatial resolution and 220 fps full temporal resolution
3D measurement, and it can also realize real-time 3D measurement at average speed of 50 fps.
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