Friction of Sliding Leadscrew under Hydrodynamic Lubrication : 1st Report, Establishment of Clearance Shape Model and Its Analysis Based on Infinitely Short Bearing Theory

Abstract

Because sliding leadscrews used in precision positioning systems are driven by motors directly with higher speed, it becomes necessary to evaluate more accurately their friction losses to estimate the required motor power or heat generation. It has been proved experimentally that the interface between the screw shaft and the nut achieves hydrodynamic condition under higher rotational speed. But the method of calculating the friction has not been established. This study aims at proposing a theoretical formula describing the frictional characteristics of sliding leadscrews under hydrodynamic condition and verify it experimentally. In this report, lead errors of a screw shaft and a nut are measured accurately and discussed to formulate a clearance shape model with respect to the drunkenness error of nut. The infinitely short bearing theory is applied to the shape model so as to derive some dimensionless numbers.