Application regime, problems and some solutions in triangulation ranging Available to Purchase

Optical triangulation is one of the techniques used to determine the range from a measuring instrument to an observed surface. Some other techniques are based upon time-of-flight ranging, focusing, and interferometry. Presently, triangulation occupies a unique middle ground among these techniques in terms of its qualities of range resolution, speed, and measurement reliability. For example, this approach can provide resolution down to about one thousandth of an inch (one mil) in three dimensions, at measurement rates up to millions of points per second. Finer resolution is less convenient at high speed because the transmitted beam cannot be held to cross sectional dimensions much less than a mil over a substantial depth of focus. Measurement reliability can be very good but can be compromised by local variations in reflectivity, by laser speckle and in particular by multiple reflections off shiny surfaces. The effects of multiple scattering are illustrated in video recordings of triangulation scans of screw threads, which will be shown during the talk. These results also illustrate a general method for reducing multiple scattering measurement errors which is used in a number of commercially available instruments. Examples of the effectiveness of this approach will be shown.