Impact of manufacturing errors of ball screw system on performance characteristics

To convert rotary motion into translational motion in modern metal-cutting machine tools, screw-nut rolling transmissions are widely used. Special requirements are placed on the stability of the operational characteristics of the screw-nut rolling transmission. The influence of the accuracy of manufacturing screw-nut transmission on the main transmission characteristics: axial stiffness and the moment of idling is considered. When analyzing the quality of the manufacture of the transmission, the following manufacturing errors were taken into account: the pitch errors of the screw and nut threads; errors in thread diameter of screw and nut; deviation of the thread profile of the screw and nut; the error of the diameter of the ball. Since these errors are independent random variables, on the basis of the basic propositions of the theory of probability, analytical dependencies were obtained to determine the coefficients connecting the variances of the design parameters and the variance of the probabilistic distribution of the axial force and the idling torque. Based on the calculation results from the obtained dependencies, it was concluded that the errors in the thread pitch of the screw and nut have a prevailing influence on the dispersion of the probabilistic distribution of the axial force ( and, consequently, the axial stiffness) and the idling torque. The results obtained allow us to outline further ways of improving the transmission of the screw-nut rolling.