The ability to measure lubricant film thickness in elastohydrodynamic point contacts was greatly improved when the method of interferometry was introduced in the late 1960s. Constant refinements of the technique have made it possible to measure the thickness of thin films with an accuracy of a few nanometers. In order to further develop the technique and provide a tool for advanced lubricant experiments, a Ball and Disc Apparatus was developed. The aim was to accomplish an apparatus with an “open architecture” for easy expansion and the ability to use several sub-methods for film thickness determination.
The combination of suitable computer programming, electronics, mechanics, optics and fluid dynamics made it a complex task since several individuals had to merge their ideas into one design where the result had to be satisfying in all aspects. Even though the apparatus is under constant development, the basics are the same: a mainly computer controlled apparatus able to measure film thicknesses with high accuracy down to zero, friction force from zero to 120 N, contact loads from zero to 140 N (solely dependent on the disc used), running speeds, apart from static, from at least 1×10-3 to 4 m/s and producing detailed digital interferograms directly onto the computer's hard drive for analysis.
Analyzing images is itself a tedious and sometimes difficult task if the appropriate tools are not available. However, a multi-channel method was also developed concurrently which does not depend on the usual colorimetric calibration problems, but rather on a trichromatic light source. This method of determining film thicknesses reduces the time spent to a few seconds per image captured during operation.