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There exists an increasing need in industry, particularly for machined parts, for higher accuracy profile measurements. Structured lighting techniques have proven valuable for such profile measurements, but have typically been limited in their accuracy by focus and sensor limitations. This paper describes a different approach to a structured light type of system which instead takes full advantage of the high accuracies and range available with precision measurement positioning stages. The resulting system, the optical guillotine, provides an optical equivalent of the commonly used mechanical guillotine and feeler gages used for making measurements, except with much greater speed and measurement capability. The optical guillotine effect is created by translating a collimated sheet of light relative to the object's surface along the line of sight of the viewing system such that the line will cut across a constant cross-section of the object at the points on the object which are at the depth as indicated by the stage. This system takes advantage of a compensated focus of both the illumination beam and the viewing system so that the system is not limited by the depth-of-focus of the viewing lens. For high slopes surfaces, very little data processing is required and the signal to noise ratio is inherently very high. These properties make the system capable of very fast measurements, covering a depth of over 15 centimeters in one second with a measurement accuracy of a few microns. The theoretical and design considerations of this approach, including the sources of errors for this type of system in general, are discussed in this paper. The results of a breadboard system, based on this design analysis, is also presented.
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