基于改进有序聚类法的立式加工中心进给系统温测点优化

为解决立式加工中心热误差补偿关键技术中温测点难选取的问题，提出了一种基于改进有序聚类法的机床进给系统温测点优化方法。首先，结合试验数据计算反映温测点温度变量与热误差相关性的互信息值，初步筛选机床各部件的温测点，消除测点间的耦合性；然后，根据筛选出的温测点，通过建立类直径矩阵和计算各类的最小误差函数，获得温度变量分类；最后，基于多元线性回归建立包含多个不同温测点的热误差模型，并对模型进行统计学综合分析，确定了最佳聚类数和最佳温测点。结果表明：在不同加工条件下采用改进有序聚类法建立的热误差模型的均方根误差和平均残差分别降至1.05 μm和1 μm以下，相较于采用传统有序聚类法和灰色关联度模糊聚类法建立的热误差模型，它具有更高的热误差预测精度和更好的鲁棒性。所提方法在中小型加工中心进给系统的温测点研究中具有广阔的应用前景。     

基于热态信息挖掘的机床主轴系统热误差建模方法研究

针对数控机床热误差建模问题,通过对精密卧式加工中心主轴系统热变形数据特征进行分析,提出了一种利用均值理论进行数据分类、利用粗糙集理论进行数据挖掘和利用线性回归分析构建误差模型的机床热误差建模方法.该方法首先进行机床主轴的热误差实验,利用传感器同时检测机床主轴所选各检测点的温升和主轴轴端的热变形,然后利用均值理论和粗糙集理论对获得的数据进行分类和数据挖掘精简,最后通过线性回归分析进行热误差建模.为了评价所建模型的有效性,将所建模型与BP神经网络模型进行了对比,结果表明这种基于热态信息挖掘的热误差建模方法在机床主轴热误差预测方面有较高的准确性和实用价值.     

基于CSO-SVM的数控机床主轴热误差建模

针对数控机床多热源所致的温升与主轴热误差之间复杂的非线性关系问题,提出一种鸡群优化（chicken swarm optimization, CSO）算法与支持向量机（support vector machines, SVM）相结合的主轴热误差预测模型（以下简称热误差模型）。以某精密数控机床的主轴单元为研究对象,采用五点法对其在空转状态下的轴向热变形进行测量,并借助热电偶传感器对机床的4个关键温度测点的温度进行采集。以SVM为理论基础,随机选取75%的数据样本进行训练,进而构建主轴热误差模型。其中,利用CSO算法优化SVM模型的惩罚参数c和核参数g,以提升热误差模型的预测能力及鲁棒性。以余下的25%的样本作为测试数据集,对所得热误差模型进行验证。利用CSO-SVM模型对不同工况下主轴的热误差进行预测,并将预测结果与测量结果进行对比。结果表明：当主轴转速为3 000 r/min时,CSO-SVM模型的平均预测精度高达97.32%,相较于多元线性回归模型和基于粒子群优化的SVM模型分别提升了6.53%和4.68%;当主轴转速为2 000, 4 000 r/min时,CSO-SVM模型的平均预测精度分别为92.53%、91.82%,表明该模型具有较高的预测能力和良好的鲁棒性。CSO-SVM模型具有较强的实用性和工程应用价值。     

基于最小包容区域法的平面度误差的快速评定法——新测点分类法

在平面度误差评定的最小包容区域法中提出一个新的、快速的实施方法:通过将测点向某特殊平面投影并利用在投影面中直线度评定的信息确定原测点的平面度误差.同时证明了从距最小二乘拟合面最远的高(低)点开始的搜索路线可减少测点分类法搜索的次数.本文通过一个常用的算例验证了该算法的正确性,并用随机产生若干算例验证了该算法的有效性.该算法对225个测点的平面度误差评定平均耗费时间只有0.5s左右.     

精密车削中心热误差和切削力误差综合建模

热误差和切削力误差是影响数控机床精度的最重要的两个误差源,误差补偿技术是一种消除机床误差经济有效的方法,而有效的误差补偿依赖于准确的误差模型。在对切削加工过程中的热变形和切削力分析的基础上,选取合理的参量,采用BP神经网络和PSO算法相结合的优化方法建立了热误差和切削力综合模型。BP-PSO建模方法改善了网络模型的收敛速度和预测精度。基于所建误差模型,对一台精密车削中心加工实时补偿后使得径向加工误差从27μm提高到8μm,大大提高了车削加工中心的加工精度,验证了模型精度。     

自回归分布滞后模型在数控机床热误差建模中的应用

对多元线性回归模型、回归与残差AR叠合模型和自回归分布滞后模型3种热误差建模方法进行了介绍与比对分析。多元线性回归模型方法简单快捷,但因热误差呈非线性且具有互交作用,较难获得精确热误差数学模型。后两个模型均属时间序列分析方法,其优点是能够比较精确地建立热误差数学模型,两者的区别是叠合模型把参数估计分成两部分,而自回归分布滞后模型是统一估计参数,因此叠合模型的精度要低于自回归分布滞后模型精度,并通过实例验证,自回归分布滞后模型在精密数控机床热误差建模中具有较好的建模精度。     

基于灰色线性回归组合模型的机床热误差建模方法

为了控制机床热误差和提高机床加工精度,考虑到测得的热误差数据同时存在着线性和非线性因素,提出了采用具有处理线性和非线性能力的灰色线性回归组合热误差模型的建模方法.用此方法对某卧式加工中心热误差进行了建模和预测,并引入BP神经网络对热误差模型的残差进行修正,从而获得了比较准确的热误差预测值.与用指数函数来模拟生成数据的灰色模型所获得的预测值进行了比较,证明了灰色线性回归组合及BP神经网络模型在机床热误差补偿建模应用中的优越性.     

空间光学窗口的热光学灵敏度分析

在试验测点温度值的基础上，利用Zernike多项式拟合出玻璃表面的温度分布，对特定的周向、径向、轴向温差和温度水平，进行窗口外玻璃热弹性分析，把节点的热变形拟合为Zernike多项式并代入ZEMAX软件求得系统波前误差的RMS。分析结果表明，在温度变化相同时，窗口外玻璃的周向温差对系统波差影响最大。     

考虑结构热变形的机床进给系统热误差研究

为系统研究精密机床进给系统热误差的形成机理及其影响因素，提出了一种考虑结构热变形的进给系统热误差建模方法。在考虑进给系统内生热源及冷却系统对丝杠螺母副的温升和丝杠热变形作用机制的前提下，同时考虑了进给系统内生热源对精密机床结构大件（床身、立柱、溜板）热态特性的影响规律。通过分析结构热变形引起的进给系统电机座和轴承座相对位置的变化，建立了综合考虑结构大件和丝杠热变形的进给系统热误差模型。以JIG630精密卧式加工中心为例，进行了考虑结构热变形和不考虑结构热变形的进给系统热误差建模与仿真分析，并开展了相应的测试验证实验。结果表明考虑结构热变形的进给系统热误差模型仿真值与实验结果具有更高的一致性。该建模方法对精密机床进给系统热平衡设计、热误差的控制与补偿具有重要参考意义。     

热变形、维卡软化点温度测定仪温度校准方法探讨

本文通过分析现有热变形、维卡软化点温度测定仪温度校准情况,总结并指出热变形、维卡软化点温度测定仪温度指示误差的现有各种计量方法存在的问题。通过对该测量设备在实际应用中的使用场景分析,提出更优的计量方法,同时研制一种以温度信号控制图像采集测试数据的温度校准装置,可以精确测量使用温度点的误差,并减小测量过程中的人为误差。     

Study on the thermally inducedspindle angular errors of a five-axis CNC machine tool

Thermally induced spindle angular errors of a machine tool are important factors that affect the machining accuracy of parts. It is critical to develop models with good generalization abilities to control these angular thermal errors. However, the current studies mainly focus on the modeling of linear thermal errors, and an angular thermal error model applicable to different working conditions has rarely been investigated. Furthermore, the formation mechanism of the angular thermal error remains to be studied. In this study, an analytical modeling method was proposed by analyzing the formation and propagation chain of the spindle angular thermal errors of a five-axis computer numerical control (CNC) machine tool. The effects of the machine tool structure and position were considered in the modeling process. The angular thermal error equations were obtained by analyzing the spatial thermoelastic deformation states. An analytical model of the spindle angular thermal error was established based on the geometric relation between thermal deformations. The model parameters were identified using the trust region least squares method. The results showed that the proposed analytical model exhibited good generalization ability in predicting spindle pitch angular thermal errors under different working conditions with variable spindle rotational speeds, spindle positions, and environmental temperatures in different seasons. The average mean absolute error (MAE), root mean square error (RMSE) and R² in twelve different experiments were 4.7 μrad, 5.6 μrad and 0.95, respectively. This study provides an effective method for revealing the formation mechanism and controlling the spindle angular thermal errors of a CNC machine tool. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00409-x     

基于单光束干涉仪的机床主轴热误差实时测量

主轴热误差是数控机床的主要热误差源,本提出了一种使用三路单光束干涉仪（SBI3）进行机床主轴热误码差的非接触式实时测量方法。可以快速准确地测量主轴热误差。实验结果表明,所测立式加工中心主轴热误差沿Z轴方向最大,约为50μm,测量误差约为1.0μm。     

数控机床热误差的建模与预补偿

研究了数控机床热误差的预补偿方法。建立了基于主轴转速的热误差自回归模型,从而不需要测量机床的温度场就可以预测热误差。在加工前通过修改工作的数控加工程度即可进行补偿,大大简化了误差补偿过程。可应用于中等精度的数控机床。     

带冷却系统的XK717数控铣床主轴部件热特性分析

机床主轴系统是机床的核心部件，其热特性的好坏，直接影响机床的加工精度；以建立主轴系统的有限元模型，结合主轴系统与普通水箱之间的冷却模型，对带有冷却套的主轴系统进行了热特性分析，得出了主轴系统的热特性曲线；根据分析结果，对XK717数控铣床主轴部件冷却套的布局进行了改进设计，为优化数控铣床主轴系统提供了理论依据。     

New algorithm to minimise kinematic tool path errors around 5-axis machining singular points

The singular points of a given 5-axis CNC machine could be found in the domain of the joint variables of the machine. In the neighbourhood of a singular point, even for a small change of the tooltip position, an enormous change of axis displacements of the machine is often required. This causes a large deviation between the real cutting path and the desired tool path, and the machining surface could be destroyed. This paper provides with an analytical scheme for identifying singular configuration of 5-axis CNC machines. In particular, an efficient and robust algorithm is proposed to compute the cutter path across the neighbourhood of the singular points identified such that the computed cutter path tracks the desired tool path within a controllable error. Numerical examples and real cutting parts are carried out and discussed to show the effectiveness and the efficiency of the presented method.     

A control algorithm for improving the accuracy of five-axis machine tools

An algorithm for reducing the influence of geometrical, thermal, kinematic and stiffness errors in five-axis machine tool components on the desired tool position and orientation is given. This new algorithm is based on the calculation of the cutting tool error matrix for orthogonal machine tools. In the new model of this matrix, all angular errors of the machine links are considered as infinitesimal rotations. The error matrix is a function of the commanded machine component positions and the errors in these positions. To correct errors in the three translational and two angular tool positions, a matrix of commanded tool position and orientation is multiplied by the inverse error matrix in every period of the tool trajectory interpolation. This corrected matrix of the tool position and orientation provides the inverse kinematics used for calculation of the successive links positions required for achieving the given tool trajectory. The control algorithm for five-axis machine tools with the error compensation is implemented both in the CNC system and in the postprocessor. The proposed algorithm is applied on a vertical five-axis turning centre with two translational and three rotational axes. Twenty-four errors that could cause inaccurate machining are recognised on this machine. The machine links and their coordinate frames are denoted using the Denavit–Hartenberg parameters.     

Machining conditions-based preventive maintenance

In this study we propose an operating conditions-based preventive maintenance (PM) approach for computer numerical control (CNC) turning machines. A CNC machine wears according to how much it is used and the conditions under which it is used. Higher power or production rates result in more wear and higher failure rates. This relationship between the operating conditions and maintenance requirements is usually overlooked in the literature. On CNC turning machines we can control the machining conditions such as cutting speed and feed rate, which in turn affect the PM requirements of the CNC machine. We provide a new model to link the PM decisions to the machining conditions selection decisions, so that these two decision-making problems can be solved together by considering their impact on each other. We establish that our proposed geometric programming model captures the related cost terms along with the technological restrictions of CNC machines. The proposed preventive maintenance index function can be used to provide an intelligent CNC machine degradation assessment.     

Virtual simulation of five-axis machine tool with consideration of CNC interpolation,servo dynamics,friction, and geometric errors

Abstract

A virtual machine tool (VMT) simulation system which considers tool center point (TCP) interpolation, geometric errors, servo dynamics, and friction effects for a five-axis machine tool is developed in this paper. A novel five-axis interpolation method is proposed to ensure that maximum velocity constraints for each axis can be satisfied. The geometric error model, including lead screw, straightness, angular and squareness errors is built to analyze the volumetric errors within the working space. The model which includes rigid body motion, friction model and servo control loops is utilized to evaluate servo dynamics and non-linear effects. The errors caused by the locations, servo dynamics, and friction effects are integrated into the VMT simulation program. Simulation results of TCP trajectory are represented by small line segments to generate NC codes. Then the NC codes are fed into VERICUT software to perform virtual cutting. To evaluate the interpolation design, cutting experiments are carried out on the five-axis engraving machine with a PC-based controller. The performances using the proposed interpolation method are comparable with the commercial CNC controller from Heidenhain. The effects of different error sources on the surface are demonstrated by cutting the sculpture of a human face. Path overcut caused by servo dynamics is found at sharp corners, and volumetric errors cause obvious tool marks and poor surface roughness. The proposed methodology can serve as a useful tool in evaluating the behaviors of error sources during the design stage.