Reliability Analysis Of Static Stiffness Of Ball Screw

Ball screw is widely used infeed systems of mechanical products,especially for the CNC machine tool feed system.The axial contact stiffness of the ball screw is the weakest link in the CNC machine tool feed system.Therefore,this dissertation analyzes the machining error caused by the deformation of the ball screw due to the influence of the cutting force.The reliability and sensitivity of the ball screw are researched in this dissertation.At the same time,the ball screw test bench is established in order to verify the theoretical results.In this paper,the reliability and sensitivity of the ball screw is studied,which aims to provide the theoretical basis for the reasonable design of the ball screw parameters,and then lay the foundation for improving the machining precision.The specific work content is as follows:(1)Based on the theory of Hertz contact,the theoretical model of axial contact deformation of single nut ball screw pair is established by using lead,contact angle,nominal diameter of ball screw,raceway curvature ratio,working load and other technical parameters of single nut ball screw pair.Then,based on the structural characteristics of double nut ball screw pairs,the theoretical model of axial contact deformation of double nut unloaded ball screw pair was established.At last,according to the deformation coordination equation,the theoretical model of the axial contact deformation of the double nut preload ball screw pair under load is established.(2)According to the theoretical model of axial contact deformation of single nut ball screw,the influence of the change of working load,contact angle and helix angle on contact stiffness was analyzed.At the same time,the reliability model of single nut ball screw is established according to the principle that the axial contact deformation of single nut ball screw is less than machining precision.The reliability and sensitivity of the static stiffness of the single nut ball screw are analyzed and calculated by using the improved second order moment method.(3)According to the theoretical model of axial contact deformation of double nut ball screw pairs,the influence of the change of working load,contact angle,helix angle and preload on the contact stiffness was analyzed.At the same time,the reliability model of double nut ball screw pair is established according to the principle that the axial contact deformation of double nut ball screw is less than the machining precision.The Kriging method is used to analyze and calculate the static rigidity reliability and sensitivity of the double nut ball screw.(4)According to the components of screw and guide rail used in upscale numerical control machine tool,the static rigidity test bench of single nut ball screw is designed independently.Through the axial loading and testing of single nut ball screw pair,the experimental results of the ball screw pair under different load are compared with the theoretical values of axial contact deformation of single nut ball screw pairs,and the correctness of the theoretical model of single nut ball screw is verified.