The Gravity Pendulum Method for Precise Measurement of the Tooth Surface Friction Coefficient of a Pair of Mating Gears

A new gravity pendulum method has been proposed in order to precisely measure the tooth surface friction coefficient of a pair of mating gears excluding the bearing loss. In this new method, the center-to-center distance between the pair of gears is kept constant with a flexure hinge mechanism in order to reproduce the relative motion, including rolling and sliding, between the tooth surfaces of practical rotating gears. The free damped oscillation of the gravity pendulum was measured, and the tooth surface friction coefficient was calculated by equating the dissipated potential energy of the gravity pendulum during oscillations to the work done by the frictional force between the teeth of mating gears. This method has a big advantage, in that the tooth surface friction coefficient can be measured in a very small region of the tooth profile, because the oscillation amplitude can be set approximately equal to or less than one arc-degree. The distribution of tooth surface friction coefficient on the entire tooth profile can be obtained, as the result. After investigating the influences of the horizontal oscillation of floor and that of the small clearances in the flexure hinge mechanisms on the free oscillation of the gravity pendulum, the distribution of the tooth surface friction coefficient along the tooth profile has been precisely measured for a pair of internal and external gears.