High-Speed Surface Roughness Measurement

Abstract

A prototype apparatus is described that performs a real-time optical measurement of surface roughness in the 2 to 20 microinch AA range, typical of high-quality grinding, honing, and lapping. Ground metal manufactured parts, with surface roughness in the stated range, are illuminated with a 3.39 micron helium-neon laser. The scattering pattern from the surface is scanned across a linear array of lead selenide detectors. Analog and digital electronics control the scanning and measure the intensity incident on each detector. The electronics computes both reflected (specular) and total incident intensity. These two values are used to compute the surface roughness. The system completes a scan and the electronics computes surface roughness in 20 milliseconds. The fast measurement time allows a large area to be scanned. The results demonstrate the feasibility of using the apparatus for online inspection.