滚珠丝杠螺母副热态特性建模方法

以某外循环滚珠丝杠螺母副为研究对象，对其热态特性及其建模方法进行研究。在分析滚珠丝杠进给系统的热源和边界条件的基础上，建立了丝杠稳态温度分布的数学模型，并通过软件编程求解得到丝杠温度场和滚道的存在对丝杠稳态温度的影响；建立了考虑滚道影响的滚珠丝杠进给系统有限元分析模型，获得了滚珠丝杠进给系统稳态和瞬态热特性分析结果；最后通过滚珠丝杠螺母副热特性试验，获得了滚珠丝杠进给系统关键点的温度及其变化情况。研究结果表明：所建立的滚珠丝杠螺母副热特性分析数学模型可以较准确地获得滚珠丝杠的温度场，忽略滚道会使滚珠丝杠螺母副的温度场仿真结果产生15%～20%的误差。     

考虑运行条件的Elman网络丝杠驱动系统热误差建模

研究了建立滚珠丝杠副热误差模型的方法,以进一步提高半闭环丝杠驱动系统的定位精度。分析了滚珠丝杠副的热源和温度场的动态特性并考虑丝杠驱动系统运行条件提出了基于Elman神经网络的热误差建模方法。首先,根据滚珠丝杠副的结构特点,确定其内部热源及温度场分布特性。然后,基于丝杠温度分布函数,研究丝杠热变形与其内部热源之间的动态非线性函数关系。最后,综合考虑丝杠驱动系统运行条件对其热误差的影响,建立了基于Elman神经网络的热误差预测模型。实验结果表明,当丝杠驱动系统的运行条件较为复杂时,采用文中提出的预测模型得到的热变形估计残差为-3.1μm~2.4μm。结果显示:考虑运行条件的Elman神经网络比BP和Elman网络(仅考虑温升数据)具有更好的预测精度和鲁棒性,有较强的工程应用前景。     

TX1600G数控镗铣加工中心滚珠丝杠热特性分析

以TX1600G数控镗铣加工中心为例,主要研究在移动热源施加条件下,不同的进给速度以及冷却液流量对系统热平衡的影响。为得到滚珠丝杠在实际工作中的状态,利用ANSYS建立丝杠的简化三维模型,施加移动热源来模拟螺母和轴承的传动热量,从而得到丝杠的温度模型,建立热误差补偿模型。结果表明,进给速度的增加可以缩短系统的热平衡时间,但热平衡温度有所升高; 冷却液可以有效地降低热平衡温度和缩短热平衡时间。热误差模型建立和温度场分析,为系统的热补偿提供必要的理论依据。     

伺服系统中滚珠丝杠的温度场模型

分析了伺服系统中丝杠螺母的热特性规律,并对丝杠温度场进行了简化建模,以快速准确地预测丝杠温度分布及变化.简化模型能较好地预测丝杠温升过程,但稳态误差较大;通过引进时间修正系数修正了该简化模型,修正后的模型能较好地预测丝杠的稳态温度,但对温度上升过程的预测误差较大;鉴于两个模型的特点,基于分段建模的思想,建立了丝杠温度场...     

高速机床滚珠丝杠副及其热特性分析

根据高速机床滚珠丝杠副结构组成特点和工作原理,结合高速切削实验结果,分析了引起滚珠丝杠副温升变形的主要热源及其影响因素,获得了温升随丝杠转速和预紧力的变化规律.基于能量守恒定律和傅里叶热传导定律,推导了滚珠丝杠副热传导微分方程并确定了其定解条件,建立了丝杠副温度变化的数学模型,为滚珠丝杠系统温度场仿真分析提供理论依据,可用于进一步研究高速进给系统热变形误差和提高定位精度.     

中空滚珠丝杠副热动态特性分析

以传热学理论为基础,研究滚珠丝杠进给系统主要热源分布及热传导计算,分析中空滚珠丝杠副的热态特性及达到热稳定状态后进给系统的温度场。探讨了多热源作用下滚珠丝杠的一维温度响应,给出了滚珠丝杠系统的热传导方程。通过实验验证了理论结果的正确性,根据滚珠丝杠系统各主要部件的升温曲线对比,获得滚珠丝杠系统的温度场变化规律,并在此基础上分析了滚珠丝杠的热变形,确定滚珠丝杠的热伸长量,从而为滚珠丝杠的优化设计提供了参考。     

多变化热源下的滚珠丝杠热动态特性

以传热学理论为基础,研究了滚珠丝杠受周期变化的端热源影响而产生的温度响应及其变化特性。探讨了热源信号作用下滚珠丝杠的温度响应,并用叠加法求解了多变化热源作用下滚珠丝杠的温度场函数。通过有限元仿真,验证了理论结果的正确性,得出了滚珠丝杠在行程内热误差动态变化的曲面图。     

基于GA-BP神经网络系统的滚珠丝杠热误差建模

滚珠丝杠是数控机床进给系统的关键部件,其热变形影响机床的定位误差。为提高数控机床的精度,提出一种基于GA-BP神经网络的热误差预测方法。以TX1600G镗铣加工中心进给系统的滚珠丝杠为研究对象,运用有限元法对丝杠进行热特性分析,并据此获得其温度和热误差数据。针对BP神经网络模型训练时间长,容易陷入局部极值等缺点,运用遗传算法优化BP神经网络的阈值和权值,并建立滚珠丝杠的热误差预测模型。通过MATLAB完成仿真实验,结果证明,GA-BP神经网络模型比BP神经网络模型拟合性能更好,预测能力更强。     

进给系统滚珠轴承热特性分析

为了研究数控机床滚珠丝杠进给系统成对安装的角接触球轴承其工作状态下热特性,精确计算滚珠轴承热源和轴连部分的温度场。建立轴承的准静态模型,考虑轴承的离心力、陀螺力矩等因素,利用牛顿-拉弗逊法求解,继而计算轴承系统的发热率。根据数控机床轴承部件的结构特点,建立其有限元模型,使用ANSYS软件计算轴承系统的温度场,研究轴承部件内部发热特点,实现精确预测工作状态下进给系统滚珠轴承热特性。研究为机床滚珠丝杠进给系统的热误差建模和热动力学分析奠定有力基础。     

进给系统热特性分析与测温点的选取

滚珠丝杠副由于摩擦产生的热变形是进给系统热误差产生的主要原因.论文以TX1600数控镗铣加工中心为例,首先对丝杠建立了简化的三维模型,根据实际运动状态,通过施加移动热载荷,利用Ansys仿真出丝杠的温度场和热变形,得到了丝杠表面温度场的分布趋势和达到热平衡的时间,确定了滚珠丝杠的热变形.其次通过模糊聚类法对温度变量进行分组,找到关键的测温点的数量和位置,为后续建立补偿模型奠定基础.     

Thermal characteristics of a CNC feed system under varying operating conditions

In high-speed and high-precision feed systems, thermal positioning errors are mainly caused by the non-uniform temperature variations and resulting time-varying thermal deformations under different operating conditions. The research presented here ultimately aims to develop a generic method capable of evaluating the thermal characteristics (such as temperature rise of heat sources, thermal positioning error) of the feed system induced by varying operating conditions (feed speed, cutting load and preload of ball screw). The thermal contact resistance between the balls and the inner and outer rings of supporting bearing is calculated using the Hertzian theory and JHM method. Experiments were carried out on a high-speed feed system experimental bench, and the influences of operating conditions on temperature rises of supporting bearings and ball screw nut were analyzed. Based on a WNN-NARMAL2 model, the relationship between temperature rise of supporting bearings and operating conditions was established. Furthermore, with the temperature of the ball screw nut set to be a moving heat source load, the temperature and thermal deformation distributions of the ball screw were simulated. The work described lays a solid foundation for thermal error prediction and compensation of a feed system under varying operating conditions.     

Time-varying positioning error modeling and compensation for ball screw systems based on simulation and experimental analysis

Thermal expansion of ball screw systems affects the machining accuracy of machine tools significantly. This paper intends to provide a comprehensive error compensation method for the time-varying positioning error of machine tools. To confirm the thermal deformation mechanism of ball screw systems, experiments have been designed to study the thermal behaviors of a ball screw system under varying temperature conditions. An exponential algorithm is proposed to predict the temperature variation pattern of the ball screw based on finite element analysis, and the actual thermal boundary conditions of the ball screw system are exactly defined according to the proposed algorithm and the experimental results. Then, a comprehensive compensation model is established based on the decomposition of the initial geometric error and thermal error components. Finally, a real-time error compensation system is developed for machine tools based on the function of external machine original coordinate shift and fast Ethernet data interaction, and satisfactory results have been achieved for the compensation experiments on a machining center.     

滚珠丝杠副关键加工尺寸误差与预紧转矩关系研究

预紧转矩是决定滚珠丝杠副可靠性的重要影响因素,目前预紧转矩的计算主要依据经验公式,理论计算值与实际预紧 转矩值误差较大。 为了准确计算滚珠丝杠副的预紧转矩,基于接触变形和载荷分布理论,分析关键加工尺寸误差对预紧转矩的 影响,建立中径误差、导程误差与滚珠丝杠副预紧转矩关系模型。 利用滚珠丝杠副导程误差、型面检测试验台测量不同型号丝 杠副的导程误差、中径值,通过导程误差、中径误差计算滚珠丝杠副的预紧转矩理论值。 利用滚珠丝杠副预紧转矩试验台测量 预紧转矩实际值,测量结果表明预紧转矩的理论计算值与试验值的相对误差为 0. 65% ~ 12. 18% ,均小于前人模型的 15. 07% ~ 43. 57% ,理论模型与实际预紧转矩的一致性较好,验证理论模型的正确性。     

Utilization of heat quantity to model thermal errors of machine tool spindle

Thermal error modeling of the spindle plays an important role in predicting thermal deformation and improving machining precision. Even though the modeling method using temperature as the input variable is widely applied, it is less effective due to severe loss of thermal information and pseudo-hysteresis between temperature and thermal deformation. This paper presents a novel modeling method considering heat quantity as the input variable with theoretical analysis and experimental validation. Firstly, the change of thermal state of a metal part being heated is discussed to reveal the essence of the relationship between heat, thermal deformation and temperature, and the theoretical basis of the modeling method proposed in this paper is elaborated. Subsequently, the relationship between thermal deformation and heat quantity is further studied through modeling the thermal deformations of stretching bar and bending beam using heat quantity as the independent variable, and the stretching model is verified based on finite element method. Then, the thermal error models of the spindle are developed with the heat elastic mechanics theory and the lumped heat capacity method. In succession, the parameter identification of thermal error models is carried out experimentally using the least square method. The average fitting accuracy of these models is up to 91.3%, which verifies the good accuracy and robustness of the models. In addition, these models are of good prediction capability. The proposed modeling method deepens the research of thermal errors and will help to promote the application of relevant research results in the actual production.     

闭式冷却塔的数值分析

采用已有的数学模型,利用不同作者试验所得的传热、传质系数经验公式,预测了闭式冷却塔的热力性能,得到了不同工况下的出口温度、换热量,并与Hasan的试验测试结果进行对比,采用Mizushina的经验公式得到的预测换热量与试验值的最大偏差达到37.12%,采用Hasan试验所得的经验公式计算得到的结果与试验结果一致性较好。结果表明:预测闭式冷却塔不同工况下的热力性能时,应采用试验范围内所得的传热、传质系数经验公式,否则会产生较大误差。对闭式冷却塔热力性能的合理预测有一定的指导作用。     

神经外科颅骨磨削温度场预测新模型

基于恒定热流密度的温度场理论计算值与实际温度值的误差较大,是当前磨削温度场理论研究的瓶颈。建立了不同冷却条件下的对流换热系数及材料内部的热传导模型,通过实时采集动态磨削力,利用高次高斯函数拟合建立了动态热流密度模型,并以此为基础建立了神经外科骨磨削温度场预测新模型。在干式磨削、喷雾式及纳米粒子射流喷雾式冷却条件下对骨磨削温度场进行了数值分析,并采用与人体颅骨力学性能最相近的新鲜牛股骨密质骨,采用羟基磷灰石纳米粒子及生理盐水进行了试验验证。结果表明,与试验测得温度值相比,采用基于恒定热流密度的温度场模型计算的温度值误差为18.8%,而采用新模型计算的温度值误差为6.6%,理论分析与试验结果吻合,即骨磨削温度场预测新模型更符合实际工况。     

Thermal influence of the Couette flow in a hydrostatic spindle on the machining precision

Hydrostatic spindles are increasingly used in precision machine tools. Thermal error is the key factor affecting the machining accuracy of the spindle, and research has focused on spindle thermal errors through examination of the influence of the temperature distribution, thermal deformation and spindle mode. However, seldom has any research investigated the thermal effects of the associated Couette flow. To study the heat transfer mechanism in spindle systems, the criterion of the heat transfer direction according to the temperature distribution of the Couette flow at different temperatures is deduced. The method is able to deal accurately with the significant phenomena occurring at every place where thermal energy flowed in such a spindle system. The variation of the motion error induced by thermal effects on a machine work-table during machining is predicated by establishing the thermo-mechanical error model of the hydrostatic spindle for a high precision machine tool. The flow state and thermal behavior of a hydrostatic spindle is analyzed with the evaluated heat power and the coefficients of the convective heat transfer over outer surface of the spindle are calculated, and the thermal influence on the oil film stiffness is evaluated. Thermal drift of the spindle nose is measured with an inductance micrometer, the thermal deformation data 1.35 μm after running for 4 h is consistent with the value predicted by the finite element analysis's simulated result 1.28 μm, and this demonstrates that the simulation method is feasible. The thermal effects on the processing accuracy from the flow characteristics of the fluid inside the spindle are analyzed for the first time.