精密卧式加工中心主轴轴向热误差补偿方法

热误差是精密机床最主要的误差源之一。主轴是机床的关键部件,其热误差直接影响机床的加工精度。文章以某型号精密卧式加工中心主轴为对象,对其温度场和热变形进行了仿真分析。根据仿真结果发现主轴轴向热变形更严重,并结合机床结构确定温度传感器布置位置。在此基础上,对不同转速下主轴部分位置温度和轴向热误差进行现场测试。运用最小二乘法建立热误差补偿模型,直接结合机床FANUC数控系统实施主轴轴向热误差补偿。经实验验证,补偿后主轴轴向热误差减小了85%以上。     

A thermal error model for large machine tools that considers environmental thermal hysteresis effects

Environmental temperature has an enormous influence on large machine tools with regards to thermal deformation, which is different from the effect on ordinary-sized machine tools. The thermal deformation has hysteresis effects due to environmental temperature, and the hysteresis time fluctuates with seasonal weather. This paper focused on the hysteresis nonlinear characteristic, analyzing the thermal effect caused by external heat sources. Fourier synthesis, time series analysis and the Newton cooling law were combined to build a time-varying analytical model between environmental temperature and the corresponding thermal error for a large machine tool. A multiple linear regression model based on the least squares principle was used to model the internal heat source effects simultaneously. The two models were united to make up a synthetic thermal error prediction model called the environmental temperature consideration prediction model (ETCP model). A series of experiments were performed using a large gantry type machine tool to verify the accuracy and efficiency of the predicted model under random environments, random times and random machining conditions throughout an entire year. The proposed model showed high robustness and universality, with over 85% thermal error, with up to 0.2 mm was predicted. The mathematical model was easily integrated into the NC system and could greatly reduce the thermal error of large machine tools under ordinary workshop conditions, especially for long-period cycle machining.     

基于GA-SVR的数控机床热误差建模

为了提高数控机床加工精度,消除数控机床热误差对加工精度的影响,文章提出了基于GA-SVR(遗传算法-支持向量回归机)的数控机床热误差建模方法.为了构建机床的热误差模型,首先采用温度传感器与位置传感器测量机床的温度与对应的机床主轴变形量.其次把获得的数据进行支持向量回归机建模训练,同时使用遗传算法寻找支持向量回归机相关参数的最优值.最后建立机床热误差模型,并验证模型的准确度.结果表明,基于GA-SVR的数控机床热误差建模方法具有精度高和鲁棒性强的特点.     

基于改进模糊聚类和最大信息系数的数控机床温度测点选取北大核心

在加工过程中,机床会因热变形而产生误差,这将严重影响加工精度。减少加工过程的热误差是提高加工精度的有效途径,而确定关键温度测点不仅能提高计算效率,还可避免温度数据间复共线性问题,提高热误差模型的预测精度。提出基于改进模糊聚类和最大信息系数(MIC)的温度测点选择方法,通过改进模糊聚类对温度测点进行分类;根据MIC方法选择每类温度数据中的关键温度测点;使用BP神经网络对热误差进行建模。结果表明:与传统温度测点选择方法相比,利用所提方法改进的热误差模型精度更高。     

机床稳健性温度敏感点选择及热误差建模

针对VMC1165B立式加工中心,进行机床热特性及温度场分析,基于试验数据,避免进行热机制分析和计算温度场边界条件。采用模糊聚类结合Pearson相关系数法选出4个稳健性温度敏感点建立热误差模型,验证模型预测性能,并与模糊聚类结合灰色关联度选出的非稳健性温度敏感点热误差预测模型对比。结果表明：稳健性温度敏感点热误差预测模型的机床 X 向最大残差下降了25.44%, Y 向最大残差、平均绝对误差和均方差分别下降了25%、23.03%和33.25%。     

基于粗集方法的机床热补偿误差的温度测点优化

机床热误差是影响机床加工精度稳定性的最大误差源,因此减小热误差对提高机床的加工精度至关重要。采用粗集理论对机床热变形建模及补偿技术中温度测点的选择进行优化,以HMC800A立式三轴加工中心温度测点的选择为例进行研究,结果表明该方法能有效地减少温度测点数量,既可以保证模型的精度,又可节省工作量。     

Compensation of thermo-dependent machine tool deformations due to spindle load: investigation of the optimal transfer function in consideration of rough machining

The thermal behavior of a machine tool is an important indicator for the grade of production accuracy and indirectly for the market success. The load-dependent temperature distribution and the resulting deformation of the machine tool are influenced by a variety of design and thermo-technical parameters. The main spindle of a machine tool is, without any doubt, the major heat source within the machine structure. The object of the scientific investigation presented in this article is the development of an approach to robust compensation of thermo-dependent machine tool deformations due to spindle load in consideration of rough machining. The focus of the work concentrates on the identification of the model with the highest compensation performance. The underlying concept for the compensation of thermo-dependent machine tool deformations is the indirect approach by using the speed and the effective power of the main spindle for the calculation of the Tool Center Point (TCP) displacement. The presented modeling approach requires the knowledge of the TCP displacement in X-, Y- and Z-direction depending on the speed and the effective power of the main spindle. As a tool for modeling the thermo-dependent behavior of a milling machine, a load test rig for repeatable, defined long-term loading of the main spindle has been developed. It simulates the cutting force depending on the spindle speed and the torque and applies load to the main spindle. The spindle speed and the spindle effective power can be taken directly from the numerical control of the machine tool. An important advantage of the presented compensation method is the fact that it does not require any external sensors. The displacement of the TCP has to be measured, but only during modeling. The relationship between the speed/power of the main spindle as a cause and the displacement of the TCP in X-, Y- and Z-direction as an effect can be determined by a transfer function. This paper compares the compensation results depending on the transfer function and identifies the model with the best compensation performance. The validation of the compensation method is executed by using the example of two different speed and power spectra of the main spindle.     

基于单温度传感器的数控机床主轴热误差建模方法研究

为了提高热误差模型的预测精度和减少布置在机床内部的温度传感器数量,提出一种基于单个温度传感器数据的主轴轴向热误差辨识模型。该模型的输入由单个温度传感器采集的数据处理生成,内部参数少,利用智能优化算法的全局寻优能力辨识模型参数,减少人工干预,使得模型泛化性更强。以某型号三轴机床为实验对象,通过机床切削工件,验证模型辨识效果。通过与神经网络主轴热误差预测模型对比分析及实验验证,结果表明：提出的热误差模型预测主轴轴向热误差的残差较小,预测精度较高,且具有内部参数少和泛化能力强等优点,可支持数控机床的集成应用。     

滑枕综合热补偿研究

新设计的滑枕热伸长补偿机构消除了滑枕达到热平衡之前因热变形造成的瞬态热误差。通过试验,测出机床达到热平衡后主轴的温度误差和机床对应的温度场,并利用最小二乘法拟合出该误差和温度值之间的数学模型,将数学模型输入数控系统中进行机床主轴的稳态热补偿,即温度误差补偿。这两种热补偿相结合的方式进一步提高了机床的加工精度,保证了数控龙门柔性生产线各种零件的加工精度要求。     

Thermal error mode analysis and robust modeling for error compensation on a CNC turning center

In this paper a novel concept of thermal error mode analysis is proposed in order to develop a better understanding of the thermal deformation on a turning center. The thermal error of the machine can be treated as the superposition of a series of thermal error modes with corresponding mode shapes and time constants. The selection of sensor location can then be improved based on the thermal error mode analysis. A robust modeling approach is also proposed to minimize the errors due to temperature measuring noise and the adverse effect of environmental changes. Through the use of thermal error mode analysis and the robust modeling approach, the number of thermal sensors has been reduced from 16 to four. The thermal error compensation system has been applied to a turning center in daily production for more than two years and it has kept year-round accuracy. The thermal drift in workpiece diameter on the turning center has been reduced from 35 μm to 6 μm from its center of tolerance.     

基于ARM_Linux的数控机床热误差补偿控制器的设计

以减小机床热误差,提高加工精度为主要目标,设计以S3C2440A处理器与嵌入式Linux操作系统为控制平台,运用BP神经网络建立误差模型的热误差补偿控制器。首先,控制器通过布置在机床关键温度点上的温度传感器采集加工中心的温度信号,该信号经温度采集模块处理后送到CPU处理器计算出温度值。同时,用激光干涉仪检测出机床对应时刻的误差值。BP神经网络模型根据温度值与误差值计算出综合误差补偿值。然后,将计算出的补偿值通过接口传送给CNC控制中心,CNC控制中心做出误差控制指令,修正机床热变形造成的被加工工件的尺寸误差。仿真实验结果表明了补偿效果的可行性。     

数控机床热变形误差补偿技术

热变形误差是影响机床加工精度的重要因素之一,通过实时热变形误差补偿可以提高数控机床加工精度.本文在分析产生机床热误差的原理的基础上, 探讨了热误差的测量方法,利用多元线性回归方法建立了机床热变形与温升之间的数学模型.应用数控系统的PLC补偿功能,对XH178加工中心加工过程中的热误差进行了实时补偿.实验结果表明误差补偿量达到80%以上.     

数控机床热误差建模及预测方法分析

热误差作为制约数控机床加工精度的关键因素,在重型数控机床上表现得尤为明显。以重型落地镗铣床为例,根据热误差测量试验数据,分析重型数控机床温度场特性,并基于兼顾相关系数和欧式距离的系统聚类准则,对温度测点系统进行优化,以减小温度测点间共线性。通过优化温度测点,采用多元线性回归分析,建立重型数控机床热误差预测模型。由现场试验可知,建立的热误差预测模型可将均方根误差控制在10μm以内,有效地提高了热误差预测精度。     

Thermal analysis for the feed drive system of a CNC machine center

A high-speed drive system generates more heat through friction at contact areas, such as the ballscrew and the nut, thereby causing thermal expansion which adversely affects machining accuracy. Therefore, the thermal deformation of a ballscrew is one of the most important objects to consider for high-accuracy and high-speed machine tools. The objective of this work was to analyze the temperature increase and the thermal deformation of a ballscrew feed drive system. The temperature increase was measured using thermocouples, while a laser interferometer and a capacitance probe were applied to measure the thermal error of the ballscrew. Finite element method was used to analyze the thermal behavior of a ballscrew. The measured data were compared with numerical simulation results. Inverse analysis was applied to estimate the strength of the heat source from the measured temperature profile. The generated heat sources for different feed rates were investigated.     

数控机床切削力间接测量研究

在数控加工中，切削力的大小直接影响着数控机床的加工精度与效率，因此对切削力的准确测量非常重要。传统利用力传感器直接测量切削力的方法存在许多缺陷，为此提出一种新的间接测量切削力的方法。即通过测量进给伺服电机电流来间接检测切削力。在详细分析了进给电机电流与切削力之间关系的基础上，建立了数学模型并进行了实验验证。实验证明该方法切实可行，具有重要的应用价值。     

飞机蒙皮镜像加工变形迭代预测方法

飞机蒙皮尺寸大、壁厚小,易发生加工变形,并且切削力与加工变形之间存在着复杂的耦合关系,普通的无迭代加工变形预测方法难以实现较好的预测效果。针对飞机蒙皮镜像加工变形现象,在建立镜像铣定制刀具切削力模型的基础上,提出一种加工变形迭代预测方法,该方法较好地解决了切削力与加工变形之间的复杂耦合关系问题,并通过仿真和试验证明了该方法的有效性。相对普通无迭代预测方法,该方法预测加工变形量的变化趋势和变化幅值更符合实际蒙皮镜像加工,加工变形仿真预测值与实际加工变形的差值更稳定,预测误差更小,可以更准确有效地预测出蒙皮镜像加工变形量。     

Tools with built-in thin film thermocouple sensors for monitoring cutting temperature

The ability to monitor in real time, the thermal activation and thermal impact to cutting tools has been very appealing to the manufacturing industries. Such responses can be measured with appropriate sensors such as thin film thermocouples (TFTs) built in cutting tools. The challenges have been to instrument the tool, equipment and sensors, which can withstand high stress and temperature in machining process. In this work, the sequence of fabricating the built-in TFTs and experimental setups are proposed and demonstrated. The cutting experiments are carried out under different cutting conditions for A6061-T6 aluminum alloy and finally cutting temperature is measured at very high cutting speeds up to 16 m/s.     

数控车床热误差实时补偿研究

热误差是数控加工中的主要误差源之一,对零件加工精度有非常大的影响。对数控车床热误差进行补偿可以有效地提高机床的加工精度。在数控车床的加工过程中,采用铂电阻温度传感器对数控加工中关键点的温度进行实时测量,再配合线性回归理论建立数控车床的热误差模型。最后根据热误差模型对数控车床的加工误差进行实时补偿,经验证该技术是可靠有效的。     

数控机床热变形误差超前预测研究

针对当前数控机床热变形误差实施补偿存在的预测值滞后实际补偿值问题，提出基于长短期记忆(LSTM)神经网络算法热误差超前预测解决方案，详细探讨LSTM神经网络算法的解析流程，建立基于LSTM神经网络算法热误差超前预测模型，并进行关键温测点及热变形误差超前预测实验。实验结果表明：热变形误差实际值与预测值的最大残差、平均值和均方差均在可控范围内，超前预测的准确度为86.3%，进一步论证了机床热变形误差超前预测的有效性。     

An error control approach to tool path adjustment conforming to the deformation of thin-walled workpiece

Producing an accurate part mainly depends on the position and orientation of the cutting tool with respect to the workpiece which is mainly influenced by the rigid body motion of the workpiece and the elastic deformation of workpiece-fixture-cutter system. For the purpose of minimizing the machining error, a new modification strategy of the nominal tool path is not that directly compensate the control commands of the machine tools, but that modify the cutter location source file (CLSF) from the computer aided manufacturing (CAM) system by means of the proposed modification model on the basis of the prediction deviation, namely, the deviation of the cutting tool relative to the workpiece in computer numerical control (CNC) machining operation. Therefore, it is not only simpler, but also easier implemented by common manufacturing engineer. The effectiveness of the proposed strategy is verified by a machining example.