Friction and 2D position measurements in small journal bearings

• Simultaneous detection of friction and eccentricity on small journal bearings.
• Consideration of relative displacement to determine friction.
• Method of identification and consideration of tolerances to determine friction.
• Detection of whirling phenomena.

Shaft position and friction torque as a function of radial loading and rotational speed are important parameters in the theory of lubrication. However, to date values for small bearings taking into account manufacturing tolerances are not available. The method described in this work allows precise friction torque and 2D position measurements on small journal bearings under variation of the important parameters: speed, radial loading, lubricant and gap width. The system developed is able to capture simultaneously the friction torque as well as the 2D relative displacement between shaft and bearing using laser-triangulation which reveals the displacement trajectory under variation of speed and the dynamic behavior (half-frequency whirling and critical speeds). If displacement is considered for the friction torque measurement, an improvement in measurement accuracy is achieved when compared to previously reported techniques. Geometrical tolerances, which are of high importance in miniature bearings, are identified by two measurements in opposite direction of rotation and corrected.