Noncontact optical measurement system of three-dimensional shapes of objects with various kinds of surface reflectance

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In this research, we have developed a new triangulation-based laser rangefinder for measuring the 3-D shapes of objects with hybrid reflectance, which combines Lambertian reflectance and specular reflectance. Ordinary laser rangefinding techniques at present have rarely been applied to the measurement of the shapes of this type of object, since the equations for the computation of 3-D position based on tnangulation do not hold for objects with specular reflectance.Like the ordinary rangefinder, the proposed rangefinder consists of a light-stripe generator, a lens system, and an image sensor. The lens system hes at the core of the scheme of our rangefinder. It consists of a field stop, a lens, and shield masks. The field stop is placed in front of the lens and parallel to the lens, and has horizontal slits. The shield masks are located between the lens and the image sensor, and composed of multiple thin plates which stand vertically at a constant angle with respect to the lens.We measured shape measurements of object with hybrid surfacesThe experimental results demonstrate that the proposed rangefinder allows the measurement of hybrid objects with almost the same level of accuracy as that of Lambertian object, and specular objects Since the rangefinder does not require a reflectance model of the object's surface, it has the advantages of higher accuracy and reliability over other shape extraction techniques for Lambertian surfaces and/or specular surfaces. The proposed rangefinder is especially available for industrial purposes since a consistent accuracy and high reliability are assured even for objects with unknown reflectance properties. In conclusion the rangefinder is promising for many common industrial tasks including measurement of the shapes of metal objects and the inspection of solder joint surfaces.