A modeling method for predicting friction torque of the preload double-nut ball screw based on thermal elastohydrodynamic lubrication

Ball screw has become a key functional component commonly used in actuators of high-end machine tools because of its high transmission efficiency, low environmental impact, and strong universality of working conditions. For the high-precision ball screw, the proper and constant preload is the premise to maintain the transmission accuracy and reliable dynamic characteristics of the ball screw. The direct measurement of the preload is difficult to be achieved. Usually, the preload of the ball screw is indirectly determined by the friction torque of the ball screw under no-load condition. In previous studies, the influence of lubrication on friction torque of the ball screw was not considered, and the influence of operating conditions on performance of lubricant was ignored, and the influence of contact elastic hysteresis effect and the sliding friction effect was not considered, which seriously affected the modeling accuracy of friction torque for the ball screw. Therefore, on the basis of considering the contact elastic hysteresis friction and the sliding friction of the ball screw in the paper, a calculation model of friction torque for the ball screw based on the coupling of the ball load distribution and the thermal elastohydrodynamic lubrication is proposed. The mechanism of different friction terms on the friction torque of the ball screw is analyzed, and the coupling relationship among preload, rotational speed, and friction torque is established. The experimental results show that the proposed method, which the ball load distribution, the thermal elastohydrodynamic lubrication, the elastic hysteresis, and the sliding friction are comprehensively considered, has a good reference significance for improving the internal preload and predicting the precision degradation of the ball screw.