Optical Surface Roughness Measurement Using a Two-Dimensional Gaussian Function

Abstract

A new noncontact optical technique for rapidly measuring the surface roughness was proposed. The surfaces of ground specimens were illuminated with a LED light. The reflected light intensity distribution was measured with a CCD optical sensor, and it was approximated by a two-dimensional (2-D) Gaussian function. The standard deviations of the 2-D Gaussian function, σ_x and σ_y, with respect to the x and y axes were calculated for evaluating the broadness of the reflected intensity distribution curve in the two directions. The standard deviation σ_x with respect to the axis perpendicular to the ground direction increased with increasing the center line-averaged surface roughness Ra, giving the experimental relationship Ra = 21.9σ²_x-6.8σ_x+0.6. On the other hand, the standard deviation σ_y with respect to the ground direction remained unchanged, independent of the surface roughness Ra. This technique allows optical measurement of the surface roughness in two perpendicularly intersecting directions simultaneously.