Elastohydrodynamic film thickness response to harmonic vibrations

Many machine components, which work in the Elastohydrodynamic (EHD) lubrication regime, including transportation bearings, reciprocating engines, geared transmissions also experience vibrations, which result in a rapid variation of contact load or entrainment speed. The bearings supporting the main spindle of machine tools are subjected to vibrations generated by the cutting process, the gearbox, geometrical inaccuracies and also vibrations from the surrounding environment. It is very important to understand how these vibrations affect the functioning of the bearings supporting the main spindle, in order to maintain the desired precision and accuracy of the cutting process. The present study uses optical interferometry to monitor the response of the EHD films to forced harmonic vibrations. The contact is formed between a transparent disc and a ball pressed one against the other at desired loads. The disc is coated with a thin chromium layer and a silica layer, on the face contacting the ball. White light is shown onto the contact through a specially built microscope. The interferometric fringes formed by the rays reflected by the chromium layer and by the ball's surface are captured by a high speed CCD camera. These images are subsequently analysed and converted to film thickness maps, according to calibration curves.