降低精密数控车床进给轴热误差对切削精度影响的方法

精密数控车床批量加工零件的精度稳定性是衡量机床性能的重要指标,其中加工过程中的进给轴受热伸长是影响加工精度的重要因素之一。对数控车床进给轴热变形方向及伸长量进行研究,对比丝杠预拉伸及数控系统热误差补偿功能,指出这两种降低进给轴热误差方法局限性,提出一种使用中空油冷循环系统降低进给轴热误差的方法。该中空油冷循环系统,一方面通过中空丝杠内循环的冷却油带走丝杠螺母的发热量,另一方面通过轴承室内循环冷却油带走轴承的发热量。进行了系统结构设计与实验验证,结果表明该系统可以使进给系统在加工时保持温度稳定,降低热误差,进而提升批量加工的精度稳定性。     

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.     

Thermal error forecast and performance evaluation for an air-cooling ball screw system

In machine tools such as numerical control machines, thermal error in the ball screw induces a direct position error. A high-speed ball screw system naturally generates more heat and results in greater thermal expansion, adversely affecting the accuracy of positioning. In this paper, we discussed the placement of an air cooling system in a ball screw shaft to overcome thermal errors and achieve temperature equilibrium faster. In order to estimate the thermal error of the ball screw system and effectiveness of the air cooling system, thermal behavior models using the finite element method (FEM) and a modified lumped capacitance method (MLCM) were developed separately. This included heat generation from the main heat source of the ball screw system and other boundary conditions. The completed models were used to simulate temperature distribution, thermal deformation and air cooling performance. Comparing the experiments shows that these methods can well predict thermal behavior of the ball screw system and air cooling performance. And the positioning accuracy will significantly improve with the use of the air cooling system in the ball screw drive system.     

机床丝杠热膨胀零点及补偿技术研究

机床丝杠在运行时转速很高而且换向频繁,热量不能及时散出而产生很高的温升。丝杠为细长杆,对温度的变化敏感。根据丝杠热误差的产生规律,提出丝杠热膨胀零点的选取方法,建立误差补偿模型。研究机床丝杠热膨胀零点的补偿方法,分析丝杠热膨胀误差的补偿流程;通过补偿实验证明丝杠热膨胀零点对误差建模的意义。     

XK714/1数控铣床螺距误差补偿

数控机床的定位精度是影响其高精度性能的一个重要方面,因而也是数控机床验收和检测的重要指标之一。螺距误差是影响定位精度的重要因素,通过螺距误差补偿能够有效改善机床的定位精度和加工精度,对数控机床的使用和维护具有重要意义。对数控机床反向间隙补偿和螺距误差补偿的原理及测量方法进行深入研究,并针对XK714/1数控铣床FANUC 0M系统的螺距误差进行补偿,取得了良好的补偿效果,说明对滚珠丝杆传动机构的反向偏差与螺距误差进行补偿是恢复和提高机床精度的一种重要手段。     

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。     

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.     

机床热误差补偿群控系统研究

为提高热误差补偿精度和实现热误差补偿群控,提出了一种车间机床热误差补偿群控方法,采用分布式采集、补偿控制以及集中式建模计算,有效提高了采集端的扩展性,充分利用了服务端的高性能。基于CAN总线,构建了机床状态信息采集平台,结合PSO-BP神经网络进行了热误差建模研究,开发了热误差补偿群控系统,开展了机床状态信息采集监控及误差补偿实验。实验结果表明:该系统具有较好的扩展性,适应多类型机床信息采集与交互;热误差补偿群控模型有效提高了机床定位精度,具有较好的工程应用前景。     

数控机床的热误差建模与补偿研究

数控机床的热变形误差是影响其加工精度的主要因素。针对当前机床热误差难以解决的问题,提出一种融合模糊聚类理论、灰色关联理论和多元线性回归理论的热误差建模及补偿原理,通过应用于实验室自主研制的AGPM,经机床温度场的测点优化分析、多元线性回归求解,建立了精确的热误差补偿模型。经补偿验证,该原理理论正确、简单易行、稳定可靠,可以大幅减小机床的热变形误差。     

立式加工中心空间误差验证及补偿

为提高某立式加工中心整机加工精度,借助旋量理论建立完备立式加工中心空间误差模型,在此基础上实现机床空间误差有效补偿.以旋量理论为基础推导并建立机床刀具运动链与工件运动链运动学正解,分析机床21项几何误差原理,在考虑21项几何误差的基础上建立该立式加工中心完备空间误差模型;利用九线法完成各项几何误差辨识;基于旋量运动学正解求解机床运动学逆解后得出运动轴实际运动路径,并通过体对角线实验对比补偿前后的效果.结果表明:所提补偿方法补偿效果显著,验证了机床空间误差模型的准确性,实现了提高机床加工精度的目的.     

无限冲激响应网络在数控机床热误差建模中的应用

本文阐述了数控机床热误差补偿技术的基本概念，提出了一种基于无限冲激响应(IIR)网络的数控机床热误差预报模型，讨论了该模型的建立及相关技术问题，对智能预报补偿系统进行了研究，并给出了智能预报的结果和精度评价。     

精密加工中心直线轴复合误差建模研究北大核心

为提高精密机床加工精度,针对直线轴几何误差与热误差两类重要误差项进行分析,并提出一种复合定位误差建模方法。首先对两端固定式丝杠进给系统的热误差机制进行分析,建立正弦函数误差表达式,利用有限元法提取丝杠表面温度并作为输入量代入到热误差模型中。利用切比雪夫多项式建立静态几何误差预测模型。将两模型叠加,得到复合定位误差模型。对精密加工中心直线轴进行检测实验,实验值与预测模型对比后发现预测精度达到85%以上,验证了复合误差模型具有较高的预测精度,为直线轴定位误差补偿提供了参考。     

Statistical optimization and assessment of a thermal error model for CNC machine tools

The objective of a thermal error compensation system for CNC machine tools is improved machining accuracy through real time error compensation. The compensation capability depends on the accuracy of the thermal error model. A thermal error model can be obtained using an appropriate combination of temperature variables. In this study, the thermal error modeling is based on a correlation grouping and a successive linear regression analysis. During the successive regression analysis, the residual mean square is minimized using a judgement function, which, although simple, is effective in the selection of variables in the error model. When evaluating the proposed thermal error model, the multi-collinearity problem and computational time are both improved through the correlation grouping, and the linear model is more robust against measurement noises than the engineering judgement model, which includes variables with higher order terms. The modeling method used in this study can be effectively and practically applied to real-time error compensation because it includes the advantages of simple application, reduced computational time, sufficient model accuracy, and model robustnesss.     

基于多体系统理论的数控机床加工精度几何误差预测模型

针对多轴联动数控机床加工精度误差补偿问题,从分析数控机床误差产生机制和建立精度误差补偿模型的角度,提出基于多体系统理论的数控机床加工精度几何误差预测模型。分析B-A摆头五轴龙门数控机床的拓扑结构关系、低序体阵列、各典型体坐标变换,推导出B-A摆头五轴龙门数控机床的精度几何误差预测函数模型。采用平动轴十二线法误差参数辨识算法,计算出B-A摆头五轴数控机床21项空间几何误差,为精度几何误差预测函数提供有效的误差参数。该精度误差参数建模方法,对不同结构和运动关系的数控机床具有通用性,为后续数控机床误差动态实时补偿提高切削加工精度提供了理论基础。     

Investigation into effect of thermal expansion on thermally induced error of ball screw feed drive system of precision machine tools

In order to investigate the effect of thermal expansion on the ball screw feed drive system of a precision boring machine tool, theoretical modeling of and experimental study on thermally induced error along with heat generation characteristics are focused in this paper. A series of thermal experiments are conducted on the machine tool to measure and collect the thermodynamic data with the feed drive system operating at different speeds. Based on the heat generation and transfer analysis of ball screw system, thermal expansion of screw shaft in the axial direction is modeled mathematically. Relationships between the thermal error and axial elongation are established to characterize the thermal error distribution considering the thermal expansion coefficient as a temperature-variant parameter. It turns out that the thermal error varies with different working positions through the ball screw length and working time nonlinearly, and there definitely exists certain transform from the thermal expansion to the thermal error obtained by measurement. In addition, regression analysis is employed to carry out the theoretical modeling of thermal error with the temperature data of the critical heat generation points. The relations between temperature rise and thermal error are formulated directly while taking the thermal expansion as an implicit variable. Experiments under a different condition are preformed and the proposed methods for thermal error modeling prove to be effective and accurate enough to be used in the machining process as well.     

数控车床热误差建模与补偿研究

数控机床热变形引起的误差通常占到总体误差的40%~70%。以某公司生产的某型卧式数控车床为研究对象,检测主轴热误差和X进给轴热误差,基于最小二乘法对该机床主轴X、Y、Z向和X进给轴分别建立热误差模型。考虑到实测环境温度相对参考温度20℃时滚珠丝杠伸长的因素,对主轴热误差实测值进行了修正。根据主轴X向修正后的热误差模型和X进给轴热误差模型建立了X轴综合热误差模型,并采用西门子840D系统进行了热误差补偿试验,热误差降低了54.5%,CP值由1.34提升至1.88,证明此该建模与补偿方法有效、可行。     

基于多体系统理论的车铣中心空间误差模型分析

数控机床的误差建模是进行机床运动设计、精度分析和误差补偿的关键技术,也是保证机床加工精度的重要环节.本文利用多体系统理论来构建超精密数控机床的几何误差模型,该模型简便、明确,不受机床结构和运动复杂程度的限制,为计算机床误差、实现误差补偿和修正控制指令提供了理论依据.在机床实际应用中,可以利用由精密机床误差建模所推导出的几何位置误差来修正理想加工指令,控制机床的实际运动,从而实现几何误差补偿,提高机床加工精度.     

丝杠热误差自适应实时补偿分析

目前,针对机床的热误差补偿大都是由实验确定相应的数学模型来进行预测补偿。这样的方式受到了温度条件、加工条件、模型精准度等多因素的限制,使得在非实验条件下这样的方式往往失效。以机床的滚珠丝杠为例,从理论上去探究丝杠的热误差形成机制,再对其进行模拟仿真,并进行实验验证。二者对比表明:基于丝杠理论的仿真结果与实验结果基本吻合且在时间上同步,可实现热误差的自适应实时在线补偿。     

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。     

Accuracy enhancement of five-axis CNC machines through real-time error compensation

Although error modeling and compensation have given significant results for three-axis CNC machine tools, a few barriers have prevented this promising technique from being applied in five-axis CNC machine tools. One crucial barrier is the difficulty of measuring or identifying link errors in the rotary block of five-axis CNC machine tools. The error model is thus not fully known. To overcome this, the 3D probe-ball and spherical test method are successfully developed to measure and estimate these unknown link errors. Based on the identified error model, real-time error compensation methods for the five-axis CNC machine tool are investigated. The proposed model-based error compensation method is simple enough to implement in real time. Problems associated with the error compensation in singular position of the five-axis machine tool are also discussed. Experimental results show that the overall position accuracy of the five-axis CNC machine tool can be improved dramatically.