Fluorescence based scanless areal surface texture measurement technique using lubricating oil with in-situ calibration

Abstract

We proposed a new scanless areal surface texture measurement method suitable for in-process/in-situ application, utilizing fluorescence emitted from a lubricating oil film applied to a machined surface. By placing a reference surface on the oil-coated surface, surface height information can be converted from the measured fluorescence intensity, enabling scanless measurement. An in-situ calibration method was also developed, using a known reference step height to relate fluorescence intensity to oil film thickness. The measurement system employs a commonly used optical microscope with Köhler illumination and an imaging optical system. The proposed method shows that a linear relationship between fluorescence intensity and oil film thickness was maintained for oil film thicknesses ranging from 50 to 120 μm, and demonstrated high reproducibility of surface texture measurement within ±5 %. Comparative measurements were conducted between the proposed method and a white light interferometer for grinding and EDM surfaces with different roughness levels in the sub-micrometer to several-micrometer range. The results showed good agreement, with differences in surface roughness (Sa) within 25 % and in auto-correlation length (Sal) within 20 %. Furthermore, the surface profiles at identical measurement locations also exhibited good consistency. These results suggest that the fluorescence-based, scanless surface texture measurement method is a promising approach for in-process/in-situ application.