The measurement of ultra low aspect ratio fluid film thickness is very crucial technique both for the verification of lubrication media characteristics and for the clearance design in many precision components such as MEMS, precision bearings and other slideways. Many technologies are applied to the measurement of ultra low aspect ratio fluid film thickness (i.e. elastohydrodynamic lubrication film thickness). In particular, in-situ optical interferometric method has many advantages in making the actual contact behaviors realized with the experimental apparatus. This measurement method also does the monitoring of the surface defects and fractures happening during the contact behavior, which are delicately influenced by the surface conditions such as load, velocity, lubricant media as well as surface roughness. Careful selection of incident lights greatly enhances the fringe resolutions up to ~1.0 nanometer scale with digital image processing technology. In this work, it is found that coaxial aligning trichromatic incident light filtering system developed by the author can provide much finer resolution of ultra low aspect ratio fluid film thickness than monochromatic or dichromatic incident lights, because it has much more spectrums of color components to be discriminated according the variations of film thickness. For the measured interferometric images of ultra low aspect ratio fluid film thickness it is shown how the film thickness is finely digitalized and measured in nanometer scale with digital image processing technology and space layer method. The developed measurement system can make it possible to visualize the contact deformations and possible fractures of contacting surface under the repeated loading condition.

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Many EHL (elastohydrodynamic lubrication) experiments have been performed with the regard to measuring the film thickness variations according to contact conditions, such as contact load, sliding-rolling ratio, contact accelerations for the verification purpose of lubricant characteristics. The measured images of film thickness by the interferometry system are easily converted into film thickness values even both in nanometer scale and resolution with the help of image processing technology. However, only the measurement of the EHL film thickness is not enough to verify the lubricant characteristics under the various contact conditions, because the lubricant is under very high contact pressures above 500MPa, where the lubricant is suddenly solidified and is no longer considered as a fluid itself. In this work, the EHL fluid film pressures are computed from the measured interferometric image of contact film thickness ranging from 10nm to several hundred nano meter, which should be taken with nano-scale resolution. The image processing technique makes it possible to convert the measured film thickness into contact fluid film pressures if the contact geometry and material properties are known. Without the nano-scale resolution for the measured film thickness, the converting computation from the measured film thickness to fluid film pressure is not possible due to the severe noises of interferometric image over the contact area. Measuring technology of the EHL film thickness with nano-scale is also explained with regards to nano scale resolution.

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