A tribo-dynamics model of ball screws based on flexible body element

Abstract

Dynamic actuation accuracy of ball screws is dramatically affected by screw flexible deformation and the behaviors of ball-groove interface such as friction, stiffness and damping. However, few dynamics studies have considered the screw flexible deformation and rubbing interface behaviors in ball screws. In this study, a dynamics model is developed by including both the screw flexible deformation and lubrication interface behavior. Discretization of the screw/nut is completed using the 6 degree-of-freedom Timoshenko beam element. The tribological properties of ball-groove interface are solved by the mixed lubrication model. Comparison with experimentally tested nut acceleration frequencies verifies the correctness of theoretical model. On this basis, the effects of nut motion, nut position and rough surface on the dynamic response are analyzed. With the increase of time, the screw axial displacement decreases with a certain slope and is accompanied by periodic vibrations. The centers of axis trajectories at different nut positions are far apart. From Hertz, smooth surface to rough surface, the interface stiffness coefficient decreases and the nut vibration amplitude grows. The novel tribo-dynamics model can provide a theoretical basis for fault diagnosis and performance optimization of ball screws.