Dimensional inspection of rough surfaces by optical triangulation

Abstract

An optical noncontact microtopographer based on discrete active triangulalion procedure which allows submicron range revolutions is described. The system is based on a simple triangulation procedure where the topographic information is obtained from the horizontal shift incurred by the bright spot created by an oblique collimated light beam on a vertical surface. A lazer beam is focused on to a small, difraction-limited spot on the surface and is made to scan over the desired region. The bright spot is perpendicularly imaged on to a linescan camera and its position obtained from the data on the individual detectors that are activated above a certain controllable intensity threshold level. The shift in the corresponding horizontal spot on the reference plane is then computed. The distance between the surface and a reference plane at each sampled point is then easily calculated. A map of the surface topography can be built and Statistical surface characterization parameters calculated.