Study On Contact Characteristics And Load Spectrum Extraction Method Of Ball Screws

With the development of modern mechanical manufacturing technology toward the direction of intelligentization,flexibility,integration and high automatization,which requires that the NC machines can still maintain some good characteristics,such as high accuracy,low noise,high reliability and long life in the case of high speed and overload.As a key functional component of NC machines,the contact characteristics of ball screw influences the performance of NC machines greatly.When Ball screw working at high-speed condition,the working accuracy,reliability and longevity will be reduced due to the existence of friction surface heat and contact deformation.So the research on the contact characteristics of ball screw is particularly important.This paper not only establishes a model of load distribution for single-nut ball screw based on the deformation compatibility condition and the Hertz contact theory and analysis the contact dynamics characteristics of ball screw,but also analysis the collision characteristics of re-circulating mechanism based on classical collision theory.The contents of the study are as follows:(1)Based on the Hertz contact theory and differential geometry theory,establishing the geometric equation of the screw and nut raceways surface and then establishing a model of load distribution for single-nut ball screw based on the deformation compatibility theory.Moreover,the influence of axial load on the distribution characteristics of ball screw load and contact angle of the ball screw is analyzed.(2)With using the theory of load distribution for single-nut ball screw,the kinematic analysis model of single-nut ball screw under the high rotation speed was established.And Numerical analysis of the impacts of axial force and rotation speed to contact angle,contact deformation and slip between the ball and nut or screw raceway are analyzed by numerical method based on the kinematic and mechanical equation,which considering the load distribution.Besides,the reliability and correctness of the theoretical analysis results are verified by ANS YS.(3)Using the classical collision theory to build the dynamic model of the collision between the ball and re-circulating mechanism and discuss the variation law of the collision force with time of the single-ball ball screw during collision under the conditions of different collision angle and screw speed,respectively.Moreover,the reliability of the theoretical analysis results through ADAMS are verified.For multi-ball system,the collision exists between the balls and between the ball and the re-circulating mechanism during the circulation,and ADAMS was used to obtain the variation law of acceleration and velocity of the balls with the time during the collision,which were analyzed and discussed from the viewpoint of energy transfer as well.(4)Establishing the dynamic model between ball and raceway.The variation law of the axial force on the ball screw during the cutting process is derived according to the data of experimental cutting force.By the load distribution characteristics,the variation law of the contact load between ball and raceway during the cutting process is obtained indirectly,and and then taking statistical analysis.The load spectrum of ball screw is established through the statistical analysis in the process of cutting and fit the contact load with the normal distribution and lognormal distribution function.According to the Miner damage theory which considers the cumulative effect of the contact load order on fatigue damage,the fatigue characteristics of the contact point between the ball and the ball screw and nut raceway are analyzed.