New optical sensing system for obtaining the three‐dimensional shape of specular objects

Abstract

A specular surface reflects light only in the direction such that the angle of incidence equals the angle of reflection. Due to this charac- teristic, conventional approaches to obtain the shape of specular objects have not guaranteed accurate results. Taking into account this charac- teristic, an optical sensing system is proposed to obtain the three- dimensional surface shape of specular objects. Its principle is that a highly focused laser beam strikes the object surface and the specular components of the reflected light are then detected by a beam receiving unit. To achieve this, the system is to be composed of a galvanometer that steers the laser beam's direction to the desired surface point, a parabolic mirror that reflects the specular component of surface reflec- tion toward its center line and a beam receiving unit positioned along the mirror center line. To evaluate the performance of the proposed optical sensing system, a series of experiments was performed for various mea- surement conditions. The sensing principle and measurement accuracy are discussed in detail for various objects of simple geometrical shapes. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: specular reflection; optical sensing system; parabolic mirror; gal- vanometer scanning unit; recovered shape; sensing-system design; hexagonal sensing unit; specular objects.