Application Note: Seeking A Smoother Way To Measure Roughness

By Hank Hogan

Christopher A. Brown, a professor of mechanical engineering at Worcester Polytechnic Institute in Massachusetts, also could be thought of as a topographic mapmaker working on a very fine scale because of his interest in the texture of surfaces.

From surface-height measurements taken as a function of position, Brown, founder and director of the institute's surface metrology laboratory, hopes to develop a way to abstract the measurements into numbers that could summarize the potentially more than a quarter million heights from a 512 x 512 array of points and help discriminate between the two surfaces. The same information could be correlated to physical characteristics.

In seeking a way to measure surface texture, Brown found confocal technology among the most versatile in terms of dealing with surfaces and roughness. The technique can tackle highly reflective or absorbing surfaces, both of which cause problems for other optical methods. It also deals with a variety of textures, including abrasives with very steep slopes.