A Simulation Study on the Effect of Lubricant Ageing on Ball Screws Behaviour

Ball screws are used to replace traditional sliding screws when high positioning precision and high performances are requested. In order to preserve their characteristics and extend their life, grease lubrication is usually adopted. The grease's base oil separates the contacting surfaces of the spheres and the grooves under the action of hydrodynamic pressure. When, due to prolonged and intensive usage, the lubricant degrades, its capacity to separate the mating bodies weakens. This paper investigates the effect of lubricant ageing on the macroscopic performance of a ball screw by using a high-fidelity multi-body dynamic model in which both lubricant ageing and grooves' wear models are inserted and mutually interactive. The coupling between these two degradations are studied for different speeds, ageing severity levels and external forces. This work represents a preliminary step in the definition and feasibility study of a prognostic and health management framework for electro-mechanical actuators and, in particular, for ball screws.