Theoretical and experimental study of friction torque of ball screw mechanism considering lubrication

The amount of lubricating oil supply of ball screw mechanism is adjusted only by artificial experience in the computer numerical control (CNC) feed system, which lacks scientific basis and theoretical guidance. On the one hand, the raceway of ball screw mechanism is worn frequently, on the other hand, lubricating oil is wasted and environment is polluted. To meet the requirements of green manufacturing, realize reasonable and accurate lubrication, and improve the accuracy retention and reliability of the ball screw mechanism, it is necessary to study intelligent lubrication control method of the ball screw mechanism based on the actual lubrication state online perception. Firstly, the calculation methods of contact characteristics, oil film thickness distribution, and friction coefficient with the vary of lubrication degradation process were established based on the theory of fractal and point-contact elastohydrodynamic lubrication (EHL) theory. Subsequently, according to the quasi-static force balance equation under the constant screw speed operating condition, the calculation method of friction torque of the ball screw mechanism with the varies of lubrication state was proposed, and the law of friction torque with lubrication degradation process in different screw speeds was determined. Finally, the online monitoring experiment on the lubrication degradation process of the ball screw mechanism was implemented based on the linear relationship between the friction torque of the ball screw mechanism and the current of the driving motor under the no external load and constant screw speed conditions, and the experimental results verified the correctness of the theoretical analysis.