Surface Texture Evaluation on Mirror Finish Surface Using Patterned Area Illumination Method

摘要

Mirror finish surface products are widely used in many industries such as aerospace, optics, semiconductor and biomedical device manufacturing. The surface texture of mirror finish products is usually measured by off-line instruments such as coherence scanning or phase shifting interferometers. However, most commercial interferometers are expensive and must be operated in a clean and vibration-free laboratory environment. In order to achieve both insitu surface quality control and automated tool changing for the polishing process, fast and non-contact surface texture measurement are required. To address these in-situ measurement challenges, a surface texture measuring system based on fringe pattern illumination method is proposed in this paper. By analyzing the luminance contrast ratio of the fringe pattern reflection image and comparing to the measurement results from the referenced coherence scanning interferometer, the experimental results showed that the proposed system was able to measure different mirror finish surfaces with Sa and Sq values in the range of 15 nm to 120 nm and 30 nm to 160 nm respectively. In addition, the luminance contrast ratio was also correlated with directions of the machining marks and the projected fringes at different measurement angles. The surface texture aspect ratio parameter Str which provides information about the strength of the machining marks was experimentally evaluated and compared with luminance contrast change. In conclusion, the proposed measuring system was able to measure surface texture with a relative error less than 10% at measurement angle between 20° to 160°, and indicate machining pattern effects on the mirror finish surface.