Dynamic Characteristic Parameters Identification Of Key Joints For Ball Screw Feed Drive System And Experiment Research

Ball screw feed drive system has become a key part of computer numerical control(CNC)machine tools owning to its advantages of low friction coefficient,high positioning accuracy and transmission efficiency,compact structures and long operating life,therefore its vibration,modal and frequency response characteristics have significant impact on processing performance,positioning accuracy,abrasion and noise characteristics of a machine tool.The dynamic characteristic of the system not only depends on each component and part,but also has direct relation with joints' dynamic characteristic parameters.Dynamic characteristic parameters identification methods of the joints can be summarized into three kinds: theoretical calculation method,experimental test method,and theoretical calculation combined with experimental test.Considering that the theoretical calculation methods are complicated and relatively unreliable,the experimental test methods are of poor universality and can only be applied to single joint,the theoretical calculation combined with experimental test methods are difficult to obtain the frequency response functions(FRFs)of ball screw joint and bearing joint,the existing methods cannot preciously identify the characteristic parameters identification of joints in assembled ball screw feed drive system.In illusion to the above problems,this paper proposes a dynamic characteristic parameters identification method of the fixed joint based on improved adaptive genetic algorithm,proposes an axial dynamic characteristic parameters identification method of the rolling joints and designs a test device of the ball screw assembly joint's axial dynamic characteristic parameters,and proposes a dynamic characteristic parameters calculation method of the rolling joints based on Hertz contact theory,and studies the dynamic characteristic of the feed drive system and a milling machine tool based on finite element simulation and experiment.The main research contents of this paper are as follows:(1)A method to the dynamic characteristic parameters of the fixed joints based on improved adaptive genetic algorithm was proposed.In this method,the minimum of relative error between natural frequency and damping ratio of finite element calculation and their corresponding experimental results was considered as objective function,the improved adaptive genetic algorithm was utilized to identify the stiffness and damping of the fixed joints.The modeling method of the fixed joint based on spring-damper unit was improved,and an improved adaptive genetic algorithm related to evolving generation was put forward.Modeling,experiment and parameters identification were conducted with a self-designed and manufactured fixed joint model treated as the research object.(2)A method to the dynamic characteristic parameters of the rolling joints in assembled ball screw feed drive system was proposed.This method firstly deduced the axial vibration equations of the system with a harmonic exciting force exerted on its workbench,and established the identification model of the joints' axial stiffness and damping parameters based on the equations;then built the identification equations by measuring the distance between supporting points of the screw,frequency and amplitude of the harmonic exciting force,and amplitude of the screw end's axial vibration velocity;finally identified the rolling joints' axial stiffness and damping parameters by solving the identification equations using genetic algorithm.With a ball screw feed drive system determined as research object,joints' axial stiffness and damping parameters of its ball screw assembly,left bearing group and right bearing group were identified based on the proposed method,and the correctness of the identified results was verified by experiment.(3)A test device of the ball screw assembly joint's axial dynamic characteristic parameters was designed,and the corresponding measure method was proposed.This method first established the identification model of the joints' axial stiffness and damping parameters,then built the identification equations by measuring the distance between supporting points of the screw,frequency and amplitude of the harmonic exciting force,and amplitude of the screw end's axial vibration velocity;finally identified joints' axial stiffness and damping parameters by solving the identification equations with genetic algorithm.Axial dynamic characteristic parameters of the ball screw assembly joints with different diameter and length can be measured by the designed test device combined with the proposed measure method.(4)A method to calculate the dynamic characteristic parameters of the rolling joints in ball screw feed drive system based on Hertz contact theory was proposed.The stiffness parameters of the ball screw assembly,rolling guide pair and bearing joints in a ball screw feed drive system were calculated based on the proposed method,and the stiffness parameters of fixed joint in the system was obtained by Takashi Yoshimura method,upon which a finite element model(FEM)of the feed drive system was established.Then theoretical and experimental modal analysis were conducted,the validity of the FEM was verified by the comparison of vibration mode and natural frequency.According to the established FEM,effect of workbench's mechanical parameters and rolling joints' stiffness parameters on the dynamic characteristic of the b system was analyzed.(5)With a three-axis CNC milling machine determined as research object,dynamic modeling method of its feed drive system was discussed,and fixed and rolling joints' stiffness parameters were calculated.A FEM of the CNC milling machine was established,the correctness of the FEM was verified by comparison of theoretical and experimental modal analysis of the machine workbench.Under the two modeling methods of joints that taking stiffness parameters into consideration and connecting joints rigidly,theoretical modal analysis of the workbench,spindle system and milling machine were implemented separately,harmonic response analysis of the spindle system and workbench were conducted,and the results were analyzed and discussed.