A fiber optic sensor for surface roughness measurement

A fiber optical interferometer system is described for non-contact measurement of surface topography. The system employs a fiber optic guide and lens arrangement that forms an interferometric cavity between the lens front face and the test surface. Changes in the surface topography are manifested as phase changes between the light reflected from the surface and the front face of the lens. An electronic control and data acquisition system converts the phase change into a voltage signal proportional to surface height. The system is calibrated and compared with stylus surface profile measurements performed on a standard set of machined surface samples. Comparison of the amplitude parameter, R-a, shows differences of between 17 percent and 34 percent across the set of samples, whereas, two spatial parameters, frequency and peak count, consistently compare within 1 percent to 12 percent throughout the R-a range: 0.42 mu m less than or equal to R-a less than or equal to 2.89 mu m.