Methodology for the assessment of the friction torque of ball slewing bearings considering preload scatter

This manuscript presents an innovative methodology for the assessment of the friction torque of ball slewing bearings. The methodology aims to overcome the limitations of state-of-the-art approaches, especially when the friction torque is conditioned by the preload of the balls. To this end, the authors propose to simulate the preload scatter when solving the load distribution problem, prior to the friction torque calculation. This preload scatter allows to simulate a progressive transition of the balls from a four-point contact state to a two-point contact one. By implementing this capability into an analytical model, the authors achieve a successful correlation with experimental results. Nonetheless, depending on the stiffness of the structures to which the bearing is assembled, it is demonstrated that the rigid ring assumption can lead to inaccurate friction torque results when a tilting moment is applied. The methodology described in this research work is meant to have a practical application. Therefore, the manuscript provides guidelines about how to use and tune the analytical model to get a reliable friction torque prediction tool.