EHL AND THE USE OF IMAGE-ANALYSIS

This paper describes three cases where image analysis has been used to evaluate transient phenomena in elastohydrodynamic lubrication (EHL). In the first case, a CCD camera and image analysis are used to evalua te the ball trajectory after impact in the ''jumping ball apparatus'' for subsequent calculation of the limiting shear stress-pressure coeff icient. The error of the method is <1%. In the second case, the motion of the rollers in a roller bearing is traced with a video camera and image analysis. The rolling and sliding motion in the loaded and unloa ded parts of the bearing was clearly visible. Although the shaft speed was only 23.6 rpm, the method can easily be used up to 1500 rpm using a conventional high speed video and up to 27 000 rpm with a 6000 pict ures per second video camera. In the third case, the method was applie d to interferograms of an EHL point contact to investigate lubricant f ilm thickness. The method uses hue, saturation and intensity values fr om digitized colour interferometric images together with calibration v ales. It can be used to evaluate transient as well as quasistatic phen omena in the contact. The method makes it possible to determine absolu te values of film thickness without prior knowledge about the fringe o rder in the interferogram. The method has been shown to work well in t he range 140-700 nm with white light but preliminary tests for conside rably thicker films are very promising.