基于敏感度分析的机床关键几何误差元素辨识与评定

为了正确识别和判定机床关键几何误差元素对机床精度设计的影响,以PCV-620立式加工中心为研究对象,采用多体系统理论建立机床空间误差模型,从而得到机床几何误差元素与机床精度之间的关联函数。对空间误差模型进行灵敏度分析,获得机床各运动方向的局部灵敏度系数,完成机床关键几何误差元素的初步辨识。以局部灵敏度系数为基础,提出一种与局部灵敏度系数和工作空间中任意位置处的几何误差元素值相关的全局灵敏度系数计算方法,将其作为机床关键几何误差元素的辨识和评定标准,分析得到PCV-620立式加工中心的关键几何误差元素包含3项定位误差、3项垂直度误差和5项直线度误差。     

立式加工中心关键几何误差判定与量化验证

针对现阶段机床空间误差模型不完整且传统灵敏度分析存在局限性,导致其关键几何误差溯源不准确,以及关键几何误差判定结果难以量化验证的问题,以某立式加工中心为研究对象,提出一种机床关键几何误差判定与量化验证方法。以旋量理论为基础,研究某立式加工中心空间误差建模,以输出机床完整空间误差模型;在此基础上,以基于传统局部灵敏度分析为基础,利用误差贡献度因子判定机床关键几何误差;借助数值模拟实验对判定结果进行量化验证。结果表明：相较于传统灵敏度分析结果,利用误差贡献度因子判定关键几何误差的结果更准确;基于误差贡献度因子的判定结果,不仅能量化几何误差相对机床空间误差的影响程度,同时可为机床部件制造精度设计提供理论参考。     

内螺纹磨床的几何误差建模及灵敏度分析

为提高内螺纹磨床的加工精度，建立了内螺纹磨床的几何误差模型并对其进行全局灵敏度分析。首先，基于多体系统理论和齐次坐标变换的方法，建立了砂轮磨削加工系统和砂轮修整系统的几何误差模型，通过误差传递推导出整机加工精度模型；其次，考虑到几何误差作用的随机性和耦合性，建立基于Sobol的拟蒙特卡洛法的全局灵敏度分析模型，识别出影响磨床加工精度的关键几何误差因素。利用MATLAB编写软件，以SCS-180TB的内螺纹磨床的加工误差模型进行灵敏度计算，并验证模拟次数的收敛性。     

五轴联动数控磨床旋转进给机构静力学分析

随着现代制造技术的发展,对特型刀具的品种和刃形的要求越来越高,而普通工具磨床和传统生产工艺方法很难加工这些刃形复杂的刀具。针对这一现状自主开发一种五轴联动数控工具磨床,其中五轴联动数控工具磨床旋转进给机构的受力和位移情况将直接影响磨床的工作性能。利用SolidWorks中的Simulation模块对五轴联动数控磨床的旋转进给机构进行静力学分析,研究旋转进给机构各处的位移和应力情况。分析结果表明:B轴旋转工作台和C轴旋转工作台最大应力均小于材料的屈服应力,说明B轴和C轴工作台结构是安全可靠的。     

五轴联动数控工具磨床加工精度影响因素仿真分析

自主研发的五轴联动数控工具磨床能够实现对球头立铣刀等多种硬度高、刃形复杂刀具的磨削加工,且一次装夹完成所有的精加工。利用多体动力学理论分别建立磨床的多刚体动力学模型和刚柔耦合动力学模型。利用所建立的动力学模型,分析在其它因素相同,X、Y、Z三轴在不同进给加速度、动静质量比、主轴结合部不同相对刚度下的加工误差。得到了3种影响因素对磨床加工精度的影响,研究结果对磨床的设计与结构优化具有一定的参考意义。     

五轴联动数控磨床直线进给机构静力学分析

针对普通工具磨床和传统生产工艺方法很难加工出特型刀具的品种和刃形的问题,研发了一种五轴联动数控工具磨床,其中五轴联动数控工具磨床直线进给机构的受力和位移情况将直接影响磨床的工作性能。利用Solid Works中的simulation模块对五轴联动数控磨床的直线进给机构进行静力学分析,研究直线进给机构各处的位移和应力情况。结果表明:X轴工作台的最大应力为2 MPa,出现在X轴工作台的滑块和立柱的下部,X轴工作台的最大位移为0.000 015 88 mm,出现在立柱的中部;Y轴工作台的最大应力为2 MPa,出现在Y轴工作台中部,Y轴工作台的最大位移为0.000 003 584mm,出现在Y轴工作台的中部;Z轴工作台应力的最大值为10.3 MPa,位于Z轴工作台右侧,Z轴工作台位移最大值为0.000 030 88 mm,出现在Z轴工作台中部。     

五轴联动数控机床空间综合误差解耦技术研究

分析五轴联动机床的误差项和拓扑结构,给出伺服轴运动时理想情况和有误差情况下的坐标变换矩阵。以此为基础,给出五轴联动机床空间综合误差的计算方法。基于多体运动学的微分变换原理,给出五轴联动机床综合误差解耦算法。以某RTTTR型五轴联动机床为例,应用MATLAB进行实际综合误差解耦和补偿计算,结果验证了该解耦算法的正确性。     

五轴联动水切割机床回转中心几何误差分析

以机床旋转轴几何中心偏差所产生误差的规律为研究对象,以达到预期的加工精度。以水刀切割锥台为例,根据矢量在空间的旋转变换关系及时间分割法插补原理,采用双转台五轴联动数控机床的刀具矢量加工旋转动作分解的方法,求出在双转台五轴联动数控机床(AC型和BC型)中,由刀具回转中心偏差ε和δ所带来的回转中心几何误差的关系式,表明误差与刀具回转中心具有关联性。     

双转台五轴数控机床的综合误差建模与补偿研究

研究五轴数控机床的综合误差建模与补偿方法.系统地分析了机床几何误差与热误差,并提出了其新的分类方法和一种直观形象的杆、副误差矩阵描述方法,根据这种误差描述方法建立了五轴数控机床的综合误差模型,最后根据矩阵微分法建立了机床综合误差补偿模型.     

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。     

Identification and compensation of geometric errors of rotary axes on five-axis machine by on-machine measurement

The geometric errors of rotary axes are the fundamental errors of a five-axis machine tool. They directly affect the machining accuracy, and require periodical measurement, identification and compensation. In this paper, a precise calibration and compensation method for the geometric errors of rotary axes on a five-axis machine tool is proposed. The automated measurement is realized by using an on-the-machine touch-trigger technology and an artifact. A calibration algorithm is proposed to calibrate geometric errors of rotary axes based on the relative displacement of the measured reference point. The geometric errors are individually separated and the coupling effect of the geometric errors of two rotary axes can be avoided. The geometry error of the artifact as well as its setup error has little influence on geometric error calibration results. Then a geometric error compensation algorithm is developed by modifying the numeric control (NC) source file. All the geometric errors of the rotary errors are compensated to improve the machining accuracy. The algorithm can be conveniently integrated into the post process. At last, an experiment on a five-axis machine tool with table A-axis and head B-axis structure validates the feasibility of the proposed method.     

Accuracy test of five-axis CNC machine tool with 3D probe-ball. Part II: errors estimation

To improve the accuracy of CNC machine tools, error sources and its effects on the overall position and orientation errors must be known. Most motional errors in the error model of five-axis machine tool can be measured with modern laser interferometer devices, but there are still some not measurable geometric errors. These not measurable errors include constant, inaccurate link errors of components such as rotary axes block, main spindle block and tool holder. After setting all measured errors in the error model, a reduced error model is defined, which describes the influence of each unknown and not measurable link error on the overall position errors of the five-axis machine tool. On the other hand, the newly developed probe-ball device can measure the overall position errors of five-axis machine tools directly. Based on the reduced model and the overall position errors, the link errors can be estimated very accurately with the least square estimation method. The error model is then fully known and can be used for advanced purposes such as error prediction and compensation.     

基于SAPSO-GA算法的高速曲轴随动数控磨床几何误差辨识方法

以某型数控曲轴磨床作为研究对象,对其结构和运动进行分析,推导出曲轴磨削时理想的砂轮轨迹方程。根据多体系统理论建立含有误差参数的模型,并推导出机床-工件和机床-刀具的运动链位置矩阵,得出机床精密加工的约束方程。对磨床的几何误差进行研究,建立几何误差模型。为快速、准确辨识出各项几何误差,提出一种混合SAPSO-GA算法。通过对比球杆仪测量补偿前后的运动轨迹,分析补偿效果。结果表明:所提方法提高了辨识准确性,通过补偿大大提高了曲轴随动磨床的加工精度。     

Analysis of geometric errors associated with five-axis machining centre in improving the quality of cam profile

A five-axis machine is presently one of the most versatile machine tools available and they are becoming increasingly common. To increase the accuracy capabilities of such machines, it is crucial to be able to study the geometric errors of the components and its effect on the quality of machined products. In five-axis machine tools, all linear axes are theoretically perpendicular (dot product, cos 90°=0) to each other and directed along or around the X, Y and Z of the cartesian coordinate system; but in working machines, the axes are nearly perpendicular (cos89.90°≠0) because of manufacturing error and assembly error or quasi-static error. The present paper discusses the development of a generalised error model for the effects of geometric errors of the components of the kinematic chain of a machine in the workspace and the results obtained by this model have been verified experimentally. The effect of geometric error has been studied further for cam profile generation using a five-axis machining centre and an improvement in the profile has been obtained.     

Construction of an error map of rotary axes on a five-axis machining center by static R-test

This paper proposes an efficient and automated scheme to calibrate error motions of rotary axes on a five-axis machining center by using the R-test. During a five-axis measurement cycle, the R-test probing system measures the three-dimensional displacement of a sphere attached to the spindle in relative to the machine table. Location errors, defined in ISO 230-7, of rotary axes are the most fundamental error factors in the five-axis kinematics. A larger class of error motions can be modeled as geometric errors that vary depending on the angular position of a rotary axis. The objective of this paper is to present an algorithm to identify not only location errors, but also such position-dependent geometric errors, or “error map,” of rotary axes. Its experimental demonstration is presented.     

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.     

Prediction and identification of rotary axes error of non-orthogonal five-axis machine tool

This paper proposes an efficient and automated scheme to predict and identify the position and motion errors of rotary axes on a non-orthogonal five-axis machining centre using the double ball bar (DBB) system. Based on the Denavit-Hartenberg theory, a motion deviations model for the tilting rotary axis B and rotary C of a non-orthogonal five-axis NC machine tool is established, which considers tilting rotary axis B and rotary C static deviations and dynamic deviations that total 24. After analysing the mathematical expression of the motion deviations model, the QC20 double ball bar (DBB) from the Renishaw Company is used to measure and identify the motion errors of rotary axes B and C, and a measurement scheme is designed. With the measured results, the 24 geometric deviations of rotary axes B and C can be identified intuitively and efficiently. This method provides a reference for the error identification of the non-orthogonal five-axis NC machine tool.     

基于Sobol’法的机床关键几何误差元素辨识方法研究

针对机床几何误差元素多、误差测量与辨识过程繁琐等问题,利用Sobol’全局灵敏度分析方法对空间误差模型中的几何误差元素进行灵敏度分析,筛选出影响较大的几何误差元素,从而降低误差测量与辨识过程的复杂度,简化空间误差模型。以螺旋理论为建模基础,建立机床空间误差模型;对所有几何误差元素进行Sobol序列抽样并通过蒙特卡洛估计法求解灵敏度,计算各误差元素的一阶灵敏度值及全局灵敏度值,从21个误差项中筛选出对机床空间误差影响较大的12项;将简化模型与完备模型进行对比,空间误差元素简化率为48%,其预测精度大于80%,说明了误差元素筛选的有效性,为机床空间误差建模、误差元素辨识以及空间误差补偿工作的简化提供参考。