Abstract
Shape from focus is an accurate, but relatively time-consuming, 3D profilometry technique (compared to e.g., laser triangulation or fringe projection). This is the case because a large amount of data that needs to be captured and processed to obtain 3D measurements. In this paper, we propose a two-step shape-from-focus measurement approach that can improve the speed with 40%. By using a faster profilometry technique to create a coarse measurement of an unknown target, this coarse measurement can be used to limit the data capture to only the required frames. This method can significantly improve the measurement and processing speed. The method was tested on a 40 mm by 40 mm custom target and resulted in an overall 46% reduction of measurement time. The accuracy of the proposed method was compared against the conventional shape from focus method by comparing both methods with a more accurate reference.
Highlights
Topography Measurement Method.With the industrial integration of additive manufacturing into the standard production process comes the need for proper metrology on additive manufactured parts
By applying coarse depth information to shape from focus, the measurement time for stitched measurements can be reduced by limiting the measurement ranges of the individual sub-frames
The added margin to the limits set by the coarse measurement
Summary
Topography Measurement Method.With the industrial integration of additive manufacturing into the standard production process comes the need for proper metrology on additive manufactured parts. Many techniques exist to recover the shape from an unknown object. Most techniques are developed for inspection and metrology of finished parts. To improve the quality of additive manufactured products it is of interest to develop these shape recovery techniques for use in at-line or even on-line metrology. In terms of precision and repeatability compared to other techniques like stereo vision or laser triangulation, shape from focus (SFF), otherwise known as depth from focus (DFF), is a good candidate for micrometer precision measurements [1,2,3]. SFF has fewer problems with occultations compared to laser triangulation and has the possibility to create an all-in-focus image that could be used in the analysis for surface defects. Throughout the different techniques for optical shape recovery, SFF is somewhat of an outsider. Most 3D surface shape measurement techniques like Laser
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