Abstract: A theoretical model for calculating the friction torque of ball screw considering the influences of the reverser is presented. Based on the theories of Hertz contact and elastic collision, the dynamic behavior and force conditions of the steel balls at the entrance and exit of the reverser, are analyzed respectively, explaining how the elastic collision and the preloaded pressure affect the friction torque when the balls are entering or leaving the reverser. Then, experimental tests are performed for a certain type of ball screw under different working conditions (i.e., rotating speed and axial load). Comparative analyses indicate that the additional friction torque caused by the reverser is an important part of the ball screw’s total friction torque, and the influence of the entrance is relatively greater than that of the exit, mainly due to the pileups between the balls. Using the proposed calculation model, good agreements between the theoretical and experimental results could be obtained under different axial loads and rotating speeds of ball screw, which proves the accuracy of the model.

Key words: ball screw, elastic collision, friction torque, Hertz theory, reverser