Investigation of Preload Variation for Double-Nut Ball Screw Based on Hertz Contact Theory and Experimental Vibration Frequency

With the rapid development of manufacturing industries, especially the woodworking industry, with high speed and precision, computer numerical control (CNC) machine tools are widely used. Among the best solutions for machining large-sized products is the ball screw since it provides outstanding efficiency due to the rolling contact between the screw and ball nut. In this study, we investigated the relationship between preload levels and the overall stiffness of double-nut ball screws through Hertz contact theory and natural frequency. The preload values are determined theoretically and then adjusted incrementally, thereby increasing the stiffness of the ball nut. This change in the ball nut stiffness can be monitored through the natural frequency and measured experimentally. From previous studies, it has been shown that the axial frequency of the ball screw can be evaluated as effective in monitoring the preload level. The calculated and experimental measurement results are compared with each other to evaluate the effectiveness of this study. Results from this study can be applied to adjust or compensate for preload loss on ball screws after long-term operation. From there, this is a theoretical model for establishing a process to monitor the level of preload to ensure the condition of the ball screw feed drive system (BFDS).