Dimensional inspection of rough surfaces by optical triangulation

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.