A Dichromatic Interference Intensity Modulation Approach to Lubricating Film Thickness Measurement

A dichromatic (red-green) interference intensity modulation (DIIM) approach is proposed for ball-on-disk lubricating film measurement. In this approach,a modulated signal,obtained by intensity subtraction between the red and the green components in the interference outside the contact area,was used to infer the fringe order of characteristic locations. Thereafter the film thickness of other locations can be determined by the intensity. This approach was analyzed with multi-beam interference,and the influences of wavelengths,FWHM of the light source and the lubricants' refractive indices were discussed. To validate the feasibility of this approach,the static contact gap and dynamic film thickness between a steel ball and a glass disc were measured,and the results were well correlated with the classical theories. With the red laser of 653 nm in wavelength and the green laser of 532 nm in wavelength,the measurement range can be as high as 4 μm. Since there were no obvious intensity attenuates and no artificial fringe order counting,this approach can be used to evaluate film thickness efficiently.