Correlation between preload and no-load drag torque of ball screws

Abstract

This paper examines the relationship between the preload and no-load drag torque of ball screws. Based on a new equation to calculate the normal contact load between balls and the screw raceway under no external load, a new correlation between preload and no-load drag torque is proposed. Meanwhile, a novel preload-adjustable ball screw mechanism and a drag torque measuring system are constructed. Three LCM300 load cells and a force sensor are implemented for obtaining the experimental data from the constructed systems. Preload and no-load drag torque are obtained and analyzed. It is found that there is a large gap between the calculated preload by traditional formula and the measured value. The experimental results, agreeing well with the theoretical values calculated in this paper, show there exists a linear correlation between preload and drag torque in a preloaded ball screw mechanism. Furthermore, the derivation of the drag torque would be decreased when increasing the preload, which can improve the stability of the screw during its operation. This study provides an accurate correlation to obtain the preload through the no-load drag torque for preloaded ball screws, which is significant for better performance of ball screws as well as the CNC machine tools.