Measuring a Real Contact Area Using White Light Interferometry for a Low Reflecting Rough Surface under Nonlubricated Conditions

摘要

A method of measuring real contact area for low reflectivity rough surface contacted against a glass plate under nonlubricating and static contact was proposed based on a white light interference image obtained using a stereomicroscope. First, under a Hertzian contact for a steel ball against a glass plate, the correspondence of the magnitude of the real contact area using Hertz theory to the result by the proposed method with the binary threshold determining method (threshold method) was confirmed. Also, in the case of contact for paper material against a glass plate, by compensating image processing for a nonuniformly illuminated background of the optical interference image was obtained, it was made clear from the result of the contact pressure dependency of an intensity histogram and a real contact ratio that this threshold method was effective. Furthermore, the real contact area has been extracted simply and correctly without specifying an strict threshold value by extracting the pixel portion darker than the illuminated background average of each RGB interference color images and with performing logic operation AND (RGB-AND method) between each of those images. Both the threshold and RGB-AND methods were also applied to the measurement of a real contact ratio for phenol resin against a glass plate, and then the same result was obtained. By using the RGB-AND method, we clearly showed that the measurement of a real contact area for low reflectivity rough surface against a glass plate under nonlubricating and static contact is possible without setting a clear threshold value for binarization.