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

A specular surface reflects light only in the direction such that the angle of incidence equals the angle of reflection. Due to this characteristic, conventional approaches to obtain the shape of specular objects have not guaranteed accurate results. Taking into account this characteristic, 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 reflection 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 measurement conditions. The sensing principle and measurement accuracy are discussed in detail for various objects of simple geometrical shapes. (C) 1996 Society of Photo-Optical Instrumentation Engineers.