360° shape measurement system for objects having from Lambertian to specular reflectance properties utilizing a novel rangefinder

Abstract

This paper describes a 360° shape measurement system for objects with various reflectance properties. To date, ordinary laser rangefinding techniques have rarely been used to measure objects having specular reflectance. The ordinary rangefinder is also difficult to apply to objects having hybrid reflectance, i.e. those whose reflectance properties lie between Lambertian and specular. We previously proposed a rangefinder that can be applied to specular objects. The concept of that rangefinder involved the use of a light-stripe projected at a constant incident angle upon the image sensor through the use of shield masks. We propose here a new rangefinder which improves on the previous rangefinder. The main improvements are the placement of a field stop using multiple slits, automatically controlled scanning of the light source, and an automatic gain control for the image sensor. As a result, the new rangefinder allows the automatic measurement of the 360° shapes of objects exhibiting both hybrid reflectance and non-uniform reflectance. We constructed a prototype automatic 360° shape measurement system which utilizes the proposed rangefinder. The experimental results demonstrate that the system can measure the shapes of hybrid objects with almost the same level of accuracy as it can those of Lambertian objects and specular objects. The proposed rangefinder is especially valuable for industrial purposes, since it assures consistent accuracy and high reliability even for objects with unknown reflectance properties.