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

Because sliding leadscrews used in precision positioning systems are directly driven by motors with higher speed, it becomes necessary to evaluate more accurately their friction losses to estimate the required motor power or the amount of heat generated It has been proved experimentally that the interface between the screw shaft and the nut achieves a hydrodynamic condition under higher rotational speed. However, a method of calculating the friction has not yet been established. This study aims at proposing a theoretical formula to describe the frictional characteristics of sliding leadscrews under the hydrodynamic condition and at verifying 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 the nut. The infinitely short bearing theory is applied to the shape model in order to derive some dimensionless numbers.