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International Journal of Optics
Volume 2017, Article ID 4134205, 13 pages
https://doi.org/10.1155/2017/4134205
Research Article

High Precision Laser Scanning of Metallic Surfaces

Mid Sweden University, Sundsvall, Sweden

Correspondence should be addressed to Benny Thörnberg; es.nuim@grebnroht.ynneb

Received 8 February 2017; Accepted 5 June 2017; Published 6 July 2017

Academic Editor: E. Bernabeu

Copyright © 2017 Yousaf Muhamad Amir and Benny Thörnberg. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Speckle noise, dynamic range of light intensity, and spurious reflections are major challenges when laser scanners are used for 3D surface acquisition. In this work, a series of image processing operations, that is, Spatial Compound Imaging, High Dynamic Range Extension, Gray Level Transformation, and Most Similar Nearest Neighbor are proposed to overcome the challenges coming from the target surface. A prototype scanner for metallic surfaces is designed to explore combinations of these image processing operations. The main goal is to find the combination of operations that will lead to the highest possible robustness and measurement precision at the lowest possible computational load. Inspection of metallic tools where the surface of its edge must be measured at micrometer precision is our test case. Precision of heights measured without using the proposed image processing is firstly analyzed to be ±7.6 μm at 68% confidence level. The best achieved height precision was ±4.2 μm. This improvement comes at 24 times longer processing time and five times longer scanning time. Dynamic range extension of the image capture improves robustness since the numbers of saturated or underexposed pixels are substantially reduced. Using a high dynamic range (HDR) camera offers a compromise between processing time, robustness, and precision.