| In the process of ultra-precision machine tools,the vibration of machine tools has a significant influence on machining accuracy,surface quality and service life of the machine tools.The vibration of machine tool can be divided into two types: external vibration from the external environment and internal vibration from the machine tool itself.It is generally believed that exogenous vibration has a great influence on the machining accuracy of ultra-precision machine tools.However,due to the electromechanical coupling effects between control system and mechanical structure of different axes,if the bandwidth of the control system of one axis is close to the inherent frequency of another axis,when the control system is driving the axis,the periodic repeated impact of motor output force will pass through the machine tool bed to another axis and be magnified.This phenomenon will cause the workpiece and tool tip of the mechine tool vibrate violently,thus forming vibration marks on the machining surface of the workpiece,which will affect the processing quality seriously.In this paper,this phenomenon will be studied,so as to provide a reference for the control system design and structural optimization of ultra-precision machine tools.Firstly,the finite element model of air film of X-axis and Z-axis air static guide rail of ultra-precision lathe is established,and the vertical and lateral stiffness of guide rail of X-axis and Z-axis is studied.The finite element model of the machine tool is established,and the modes of X-axis guide and Z-axis guide are analyzed,and the weak links of the machine tool affected by the biaxial coupling vibration are found.The correctness of the finite element model is verified by carrying out modal test on the machine tool.On this basis,the influence of workpiece mass on the X-axis mode of machine tool is analyzed.Secondly,the influence degree of mechanical system parameters such as vertical and lateral stiffness of X-axis guide,bed mass and vibration isolation system stiffness on the biaxial coupling vibration of machine tool is analyzed by using orthogonal test,and the parameter combination to minimize the coupling vibration is preliminarily obtained.On the basis of the orthogonal test,the influence of the parameters of mechanical system on the biaxial coupling vibration is further analyzed.Thirdly,the servo control system model of Z-axis is established in MATLAB/Simulink,and the parameters of the control system are fixed.The multi-body dynamic model of the machine tool is established in Adams,and the dynamic response of the machine tool under the action of cutting force and different motor force of Z-axis is analyzed.According to the input-output relationship betweenthe servo control system and the mechanical system of the machine tool,the electromechanical coupling model of the machine tool is established,with which dynamic analyses are carried out.The influence of workpiece quality,Z-axis load quality,bed quality and control system parameters on the biaxial coupling vibration of the machine tool is analyzed.Finally,a biaxial coupling vibration experiment is carried out on the ultra-precision lathe.The influence of air film stiffness of X-axis guide rail on coupled vibration is studied by measuring and analyzing the coupling vibration acceleration under different stiffness of X-axis guide rail.The influence of Z-axis bandwidth on the coupling vibration is studied by measuring and analyzing the coupling vibration acceleration under different Z-axis bandwidth.By comparing the simulation results with the experimental results,the correctness of the simulation results is verified. |
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