Liquid crystal range finder - a high-speed range-imaging system using liquid crystal shutter

The range image measured by the structured light projection has a merit in that the high-density three-dimensional data of the object can be obtained with a high speed, in a stable way and without ambiguity, independently of the smoothness of the object. In this study, a high-speed driven structured light projector is realized by applying a liquid crystal shutter to the projection system. By incorporating the technique with the Gray code pattern projection spatially coded three-dimensional measurement system, a highspeed range-imaging system (Liquid Crystal Range Finder) is constructed. For the liquid crystal range finder, several elaborations are presented, such as stabilization of the measurement and improvement of the accuracy. As to the stabilization, a projection pattern extraction method is developed which excludes the effect of the texture of the object surface or the effect of the environmental illumination, using two complementary projection patterns. As to the improvement of the accuracy, the following elaborations are made. A double-precision pattern is generated by shifting the liquid crystal shutter by a half-pitch, utilizing the feature of Gray code pattern. The projector coordinate is determined with a high accuracy by the interpolation of the spatial code and the interpolation of the projection pattern boundary based on the gray level of the pixel. The usefulness of those techniques is demonstrated by actual measurement.