【作者】 王威；

【导师】 张义民；

【作者基本信息】 东北大学 ， 机械设计及理论， 2019， 博士

【摘要】 进给系统作为数控机床的控制及运动执行部件,其动态特性直接影响工件的加工质量、决定加工系统的性能及可靠性。考虑安装误差、尺寸误差、连接件弹性变形、动态切削力等因素的影响,数控机床加工过程中进给系统的振动不可避免。因此,开展数控机床进给系统及其连接支撑部件动态特性分析对抑制加工过程振动,提高零件加工精度及数控机床可靠性具有重要意义。本文的主要研究工作及成果如下:(1)分析滚动直线导轨轨道磨损与滚珠动态接触变形之间的耦合规律,提出了改进的滚动直线导轨系统的耦合磨损模型。基于Hertz接触理论和Archard磨损模型,探究了正常使用过程中滚动直线导轨的磨损机理。考虑轨道凹槽的磨损,得到了新的滚动直线导轨系统垂直刚度模型,并建立了系统的分段非线性动力学模型用来分析系统动态载荷下的动态特性。另外,还分析了滑块滑动行程和垂直载荷幅值对轨道磨损速率的影响。使用幅频特性曲线、最大Lyapunov指数、振动时间历程图、相位图、庞加莱截面图分析了轨道磨损对滚动直线导轨系统振动特性的影响。(2)提出了两种多自由度动力学模型分析不同结构形式具有非线性连接部件的进给系统的振动特性。分析进给系统的滚动直线导轨、滚珠丝杠、滚动轴承接触特性,得到进给系统结合面处弹性恢复力关于系统振动位移的非线性分段函数的表达式。系统动力学建模需要的几何参数通过进给系统试验台识别获得,并通过试验验证了进给系统动力学模型的有效性。通过求解动力学方程得到系统振动响应的幅频特性曲线、3-D频谱图、振动时间历程图、频谱图、相位图、庞加莱截面图分析了激励幅值、激励角度、丝杠螺母位置、工件尺寸、导轨安装间距对进给系统振动幅值以及稳定性的影响。(3)以多轴进给龙门铣床为研究对象分析了多轴进给系统切削过程中的振动响应及稳定性。通过分析多轴进给系统每层平台之间的相对位移与偏转,得到了系统主要连接支撑件的非线性弹性恢复力。基于半功率谱带宽法,通过试验测定幅频特性曲线识别了连接结构件的阻尼。由多体动力学理论和刚体假设,得到了相对坐标系下龙门铣床进给系统的多自由度振动微分方程。通过矢量叠加法获得了动态切削力作用下龙门铣床刀具的振动误差。最后,分析了激励频率、工作台质量和位置、连接件初始预紧变形对系统动态特性以及稳定性的影响。(4)分析了参数具有随机性质的进给系统及主要连接件滚动直线导轨的动态可靠性和灵敏度问题。考虑系统参数服从随机正态分布,利用滚动直线导轨的非线性刚度模型分析的系统动态响应特性。根据滚动直线导轨行走平行度定义确定了导轨系统定位精度失效的模式。由四阶矩法获得了导轨系统振动响应状态函数的统计特征,基于Edgeworth级数法给出了系统响应的概率分布以及系统精度失效概率的估计。由于铣床进给系统状态函数是隐式非线性的形式,随机摄动法不再适用求解其可靠度及可靠性灵敏度,本文采用结合主动学习函数的Kriging模型分析系统的加工过程非线性振动的可靠性和灵敏度问题,并通过与Monte Carlo模拟方法获得的可靠度结果对比验证了本文提出方法的有效性及精度。最后,通过分析系统随机参数的均值方差对系统动态特性及精度的影响,可以为进给系统的设计提供理论基础和参考。更多还原

【Abstract】 Feed system is the control and motion actuator of NC machine tool.Its dynamic characteristics directly affect the quality of workpiece and determine the performance and reliability of NC machine tool.Considering the effects of installation error,dimension error,elastic deformation of connectors,dynamic cutting force and other factors,the vibration of feed system is inevitable in the machining process.Therefore,it is important to analyze the dynamic characteristics of feed system and main kinematic joints for restraining the vibration and improving the accuracy and reliability of of NC machine tools.The main research studies and achievements are following:(1)Considering the coupling effects between wear and contact characteristics of linear guide,an improved wear prediction model is proposed.Based on the Hertz contact theory and Archard wear model,the wear evolution is explained to study the dynamic performance of linear guide in the long-age service.Meanwhile,a new contact stiffness and the piecewisenonlinear dynamic model are established to analysis the dynamic behaviors of linear guide system.Moreover,some affecting factors in wear rates such as running distance and vertical load are discussed.To analyze the effects of wear on the dynamics of system,some basic properties such as frequency response,Lyapunov exponents,time histories,phase plane diagram and Poincare mapping are analyzed with numerical simulations.(2)Two multi-degree-of-freedom models are developed to investigate the vibration characteristics of feed system with nonlinear kinematic joints.Linear guide,ball screw,and ball bearing are the main kinematic joints that connect and support the work table of a feed system.Considering the contact behaviors of rolling balls,contact force is a piecewise smooth function of displacements of the system.In terms of modeling,geometry and material parameters are determined according to the experimental feed system and the model is verified by a dynamic experiment.The motion equations of the system are derived to evaluate the effects of force excitation and screw-nut position on the vibration amplitude and stable state of the vibratory system.In order to better investigate the effects of excitation amplitude,excitation angle,installation distance and height of workpiece on the dynamic vibration,frequency-amplitude curves,3-D frequency spectrums,time history,frequency domain,phase diagram,and Poincare section are employed to present the vibration properties.(3)In order to investigate the dynamic vibration of gantry-type machine tool system in the machining process,a typical 3-freedom parallel feeding mechanism is studied.Through analysis of relative displacements and deflections between each axis of feed system,the nonlinear interface forces of main kinematic joints are obtained.Moreover,using the halfpower bandwidth method,the damping ratio is estimated according to the frequency test.Based on the multi-body kinematics theory and rigid-body assumption,multi-degree-of-freedom equations of gantry-type machine tool system is established in relative coordinates.According to the principle of vector addition,the vibration errors of gantry-type machine tool system are obtained,which are caused by dynamic cutting force.Finally,the effects of excitation frequency,mass and position worktable,and initial deformation of kinematic joints on dynamic characteristic and stability of the system are studied.(4)The dynamic reliability and sensitivity analyses of feed system and linear guide with random geometric parameters are carried out,respectively.To analyze the dynamic performance of linear guide system,nonlinear vibration equation is established by employed a stiffness model,which takes the uncertainty of the geometric parameters into account.The failure mode of the linear guide system is defined based on the walking parallelism tolerance.The statistical fourth moment method is introduced to obtain the first four moments of system response and state function.The Edgeworth series is applied to approximately determine the probability distribution function of the state function indicating the positioning precision of the linear guide.The state function of gantry-type machine tool system is implicit and nonlinear.Then,a method,which combines Kriging model and active learning function,is more applicable to analyze the machining nonlinear vibration reliability and sensitivity.Monte Carlo simulations are performed as comparisons to verify the validity of the methods.Finally,the influence of random geometric parameters on dynamic characteristics and positioning precision is carried out to provide theoretical basis and reference for the design of feed system.更多还原