Analysis And Test Of Dynamic Pre-tightening Ball Screw Pair Static And Dynamic Stiffness

As one of the key functional components of Numerical control machine tools,ball screw pairs directly affect the processing accuracy and overall performance of CNC machine tools.With the deepening of research on ball screw pairs by domestic scholars and engineers,the gap between the overall performance of ball screw produced in China and abroad has gradually narrowed,but there is still a big gap between accuracy retention and reliability of ball screw pairs produced abroad.Improving the accuracy retention and reliability of domestic ball screw pairs is a top priority in the field of domestic CNC machine tools.From the customer satisfaction survey of CNC machine tools initiated by China Quality Association,it can be seen that the loss of pre-tightening force during ball screw operation is one of the main reasons leading to poor accuracy retention of CNC machine tools.In this paper,an adaptive pre-tightening structure of ball screw pair is proposed to solve the problem of retaining pre-tightening force,and the dynamic performance of the structure of ball screw pair is studied.The main contents of this paper are as follows:1)Summarize the research status of pre-tightening and failure of ball screw pairs at home and abroad,analyze and compare different pre-tightening methods of ball screw pairs,and introduce the purpose and main research contents of this paper.2)The relationship between pre-tightening force and deformation of the ball in the ball screw pair is studied.According to the structure and stress characteristics of the ball screw pair with twin nuts,a mathematical model for solving the axial contact deformation and the axial contact stiffness of the ball screw pair with twin nuts is established.3)Firstly,the loosening reason and wedge pre-tightening principle of screw nut pair are introduced,and the structure form of self-adaptive pre-tightening nut is designed based on wedge pre-tightening principle;the relevant dimension parameters of wedge nut are determined by applying mechanical structural mechanics and related knowledge;the transient dynamic model of self-adaptive pre-tightening screw nut pair is established by using ANSYS WORKBENCH software,from the change of pre-tightening force and wedge.The relative slip distance androtation angle between the tightening blocks verify the feasibility of the pre-tightening of the self-adaptive pre-tightening nut.4)Using ANSYS WORKBENCH software to analyze the static stiffness of the self-adaptive pre-tightening ball screw pair.Through ANSYS WORKBENCH software,the static analysis of adaptive pre-tightening is carried out,and the axial deformation and stiffness of the pre-tightened ball screw pair with twin nuts are calculated theoretically.The axial deformation and stiffness changes of the two pairs are compared and analyzed.5)In the dynamic stiffness analysis,considering the different positions of nuts,the modal analysis of two kinds of ball screw pairs in the wear and non-wear state is carried out respectively.Then the modal test of the gasket type ball screw pair nut is carried out,and the harmonic response analysis of the self-adaptive pre-tightening ball screw pair is carried out to verify the feasibility of the self-adaptive pre-tightening ball screw pair.