Identification of two different geometric error definitions for the rotary axis of the 5-axis machine tools

Geometric errors are clearly among the critical error sources in 5-axis machine tools and directly contribute to the machining inaccuracies. According to the definition of geometric errors of the rotary axis, different understandings have been exist in published studies. It is extremely dangerous as it makes the comprehension of the geometric errors ambiguous and may make the geometric error identification and compensation less effective. This phenomenon has not been noticed so far. In this paper, two different commonly used geometric error definition and modeling methods are firstly identified and analyzed, named as “Rotary axis component shift” and “Rotary axis line shift”. The features and relationships of these two error modeling methods are analyzed. After a detailed comparison, “Rotary axis component shift” is more suitable to definite the geometric errors of rotary axis. An experiment has been conducted on a 5-axis machine tool to show the correctness of our work. The results show that the identified geometric errors of rotary axis based on the two error models are greatly different and need to be concerned.     

五轴数控机床旋转轴误差辨识方法研究进展

随着五轴联动数控机床在先进制造行业的地位越来越重要,机床空间定位精度显得尤为重要。旋转轴误差辨识和补偿是提高零件加工质量的一大重要指标。分析和比较近年来国内外基于球杆仪和R-test装置的五轴机床旋转轴误差辨识方法的主要特点,总结了旋转轴误差在不同定义下的辨识方法,从方法的可靠性、精度指标以及可行性等方面来综述该方法对五轴数控机床的应用价值。根据辨识原理的不足,系统性地指出了目前五轴数控机床旋转轴误差辨识存在的主要问题,并对未来的进一步研究提出了建议,为五轴数控机床旋转轴误差辨识方法提供了参考。     

五轴联动立式磨床几何误差灵敏度研究

以一台五轴联动立式磨床为例,提出了一种分析几何误差灵敏度的方法。基于多体系统理论和齐次坐标变换建立了五轴联动立式磨床的33项几何误差模型,利用求导的方式给出了几何误差灵敏度分析的数学模型。并根据该模型找出了关键几何误差,研究了关键几何误差的灵敏度系数随平移轴运动的变化规律,研究结果为精密机床改进设计和误差的实时补偿提供了理论依据。     

Measurement and verification of position-independent geometric errors of a five-axis machine tool using a double ball-bar

In this study, position-independent geometric errors, including offset errors and squareness errors of rotary axes of a five-axis machine tool are measured using a double ball-bar and are verified through compensation. In addition, standard uncertainties of measurement results are calculated to establish their confidence intervals. This requires two measurement paths for each rotary axis, which are involving control of single rotary axis during measurement. So, the measurement paths simplify the measurement process, and reduce measurement cost including less operator effort and measurement time. Set-up errors, which are inevitable during the installation of the balls, are modeled as constants. Their effects on the measurement results are investigated to improve the accuracy of the measurement result. A novel fixture consisting of flexure hinges and two pairs of bolts is used to minimize set-up error by adjusting the ball's position located at the tool nose. Simulation is performed to check the validation of measurement and to analyze the standard uncertainties of the measurement results. Finally, the position-independent geometric errors of the five-axis machine tool (involving a rotary axis and a trunnion axis) are measured using proposed method.     

基于球杆仪的数控加工中心几何精度解析

论述了数控加工中心几何精度的球杆仪识别技术,分析了数控加工中心的周期误差、垂直度误差和直线度误差,根据球杆仪测量图形,分析误差生成原因,提出了消除数控加工中心几何误差的方法。     

Double ballbar test for the rotary axes of five-axis CNC machine tools

In this paper a new method that uses the double ballbar to inspect motion errors of the rotary axes of five-axis CNC machine tools is presented. The new method uses a particular circular test path that only causes the two rotary axes to move simultaneously and keeps the other three linear axes stationary. Therefore, only motion errors of the two rotary axes will be measured during the ballbar test. The theoretical trace patterns of various error origins, including servo mismatch and backlash, are established. Consequently, the error origins in the rotary block can be diagnosed by examining whether similar patterns appear in the motion error trace. The method developed was verified by practical tests, and the servo mismatch of the rotary axes was successfully detected.     

Uncertainty analysis and variation reduction of three dimensional coordinate metrology. Part 3: variation reduction

In this part of the paper, the uncertainty analysis of coordinate estimation for the case in which the sampled geometric errors are dominated by the random component is investigated. In practice, the uncertainty analysis of coordinate estimation using high-precision datum surfaces often falls into this type. In this paper, a sensitivity matrix, which serves as the theoretical basis of the uncertainty analysis, is presented to establish a linearized relationship between the variations of the coordinate estimation and the geometric errors of the part surface at the measurement points. Based on the sensitivity matrix, quantitative measures are derived for the prediction of coordinate variation. Computer simulation and experiments are conducted to verify the theoretical predictions when the surface geometric errors are small and dominated by the random component.     

螺旋锥齿轮齿面加工偏差的敏感性分析

螺旋锥齿轮齿面复杂,为了研究机床几何误差对齿面偏差的敏感性,在建立螺旋锥齿轮齿面加工偏差模型的基础上,分别采用局部敏感性分析方法和Sobol全局敏感性分析方法,研究输入参数范围变化对输出结果的影响,确定了影响齿面偏差的关键几何误差。从输入参数和输出结果两个方面比较了两种分析方法的特点。明确了敏感性分析方法的选取原则：对于输入参数的分布范围不明确或者分布情况相似的线性或非线性不强的模型,可以考虑采用局部敏感性分析;对于输入参数的分布范围复杂、准确性要求高的非线性模型,适于采用全局敏感性分析方法。     

Kinematic and geometric error compensation of a coordinate measuring machine

In this paper, kinematic modelling of a Coordinate Measuring Machine (CMM) is carried out and the methodology followed in modelling is explained in detail. The model is simplified by certain assumptions which may result in over-simplification of the model. Consequently, the model is investigated and enhanced by adding the relevant and suitable geometric error terms. Different approaches are employed to evaluate the model coefficients. In the first approach, a commercial ring gauge is measured in a structured lattice in the work volume of the CMM. Resulting errors in these measurements are used in conjunction with some statistical methods to arrive at sets of model coefficients values. The second approach is based on measurement of the individual 21 error terms in the CMM by means of laser interferometry. These measurements are used to evaluate another set of model coefficients. A compensation strategy is proposed and tested using the model and the sets of coefficients obtained. Volumetric Performance of the CMM is evaluated according to ASME standards, before and after compensation. Improvement in the CMM volumetric performance is demonstrated and compared.     

球杆仪对数控机床切削参数的优化

主要利用球杆仪在不同的切削进给率下检测数控机床加工的圆度值,采用对比进给率和圆度值的折线图形的方法,分析了数控机床精度的差异,并进行切削参数的优化,提高了零件的加工精度,为从事数控机床编程与加工的人员提供了提高机械零件加工精度的措施。     

Five-axis milling machine tool kinematic chain design and analysis

Five-axis CNC machining centers have become quite common today. The kinematics of most of the machines are based on a rectangular Cartesian coordinate system. This paper classifies the possible conceptual designs and actual existing implementations based on the theoretically possible combinations of the degrees of freedom. Some useful quantitative parameters, such as the workspace utilization factor, machine tool space efficiency, orientation space index and orientation angle index are defined. The advantages and disadvantages of each concept are analyzed. Criteria for selection and design of a machine configuration are given. New concepts based on the Stewart platform have been introduced recently in industry and are also briefly discussed.     

A method of testing position independent geometric errors in rotary axes of a five-axis machine tool using a double ball bar

Ensuring that a five-axis machine tool is operating within tolerance is critical. However, there are few simple and fast methods to identify whether the machine is in a “usable” condition. This paper investigates the use of the double ball bar (DBB) to identify and characterise the position independent geometric errors (PIGEs) in rotary axes of a five-axis machine tool by establishing new testing paths. The proposed method consists of four tests for two rotary axes; the A-axis tests with and without an extension bar and the C-axis tests with and without an extension bar. For the tests without an extension bar, position errors embedded in the A- and C-axes are measured first. Then these position errors can be used in the tests with an extension bar, to obtain the orientation errors in the A- and C-axes based on the given geometric model. All tests are performed with only one axis moving, thus simplifying the error analysis. The proposed method is implemented on a Hermle C600U five-axis machine tool to validate the approach. The results of the DBB tests show that the new method is a good approach to obtaining the geometric errors in rotary axes, thus can be applied to practical use in assembling processes, maintenance and regular checking of multi-axis CNC machine tools.     

Accuracy enhancement of five-axis machine tool based on differential motion matrix: Geometric error modeling,identification and compensation

This paper presents the precision enhancement of five-axis machine tools according to differential motion matrix, including geometric error modeling, identification and compensation. Differential motion matrix describes the relationship between transforming differential changes of coordinate frames. Firstly, differential motion matrix of each axis relative to tool is established based on homogenous transformation matrix of tool relative to each axis. Secondly, the influences of errors of each axis on accuracy of tool are calculated with error vector of each axis. The sum of these influences is integration of error components of machine tool in coordinate system of tool. It endows the error modeling clear physical meaning. Moreover, integrated error components are transformed to coordinate frame of working table for integrated error transformation matrix of machine tools. Thirdly, constructed Jacobian is established using differential motion matrix of each axis without extra calculation to compensate the integrated error components of tool. It makes compensation easy and convenient with reuse of intermediate. Fourthly, six-circle method of ballbar is developed based on differential motion matrix to identify all ten error components of each rotary axis. Finally, the experiments are carried out on SmartCNC500 five-axis machine tool to testify the effectiveness of proposed accuracy enhancement with differential motion matrix.     

双摆台五坐标铣削后置处理软件Star-Fpost研究

针对MIRON UCP800双摆台立式五坐标加工中心,研究其五坐标加工的数学模型.推导出刀心和刀轴矢量六坐标转换成AC双摆台式五坐标的算法公式.利用坐标矩阵转换的方法实现直线圆弧插补刀轨源文件到机床代码的后置处理过程.使用面向对象程序,采取逐行读取刀轨文件关键字触发的方式,开发了专用的五坐标铣削后置处理软件Star-Fpost,在VERICUT仿真环境中完成五坐标机床的建模,在UGNX通过三元整体轴径流式叶轮的仿真加工,仿真结果验证了后置处理软件的功能,可以为MIKRON UCP800五坐标机床实际加工提供参考.     

斜轧缺陷的漏磁检测

无缝钢管表面的斜轧缺陷，因位于漏磁纵横向检测机组的盲角区域，检测灵敏度低，容易漏检，通过改变检测传感器－探靴内检测线圈的轴向夹角，提高了斜轧缺陷的检测灵敏度，同时对斜轧缺陷漏磁检测的机理进行了研讨。     

回转体零件的数控加工工艺性分析

以典型的回转体类零件为例,介绍零件的数控加工工艺性分析方法。根据零件的结构特点选择机床,然后进行零件的图样分析、结构工艺性分析和安装方式的选择,为后续的数控加工工艺路线的设计研究做好准备。     

振动摆动辗压动力学分析

在建立振动摆动辗压的力学模型的基础上,根据不同类型的摆辗力建立了模具－工件振动动系统的动力学模型,并进行了相应的动态特性分析。     

高强度钢冲压回弹量对板料力学性能参数的灵敏度分析

回弹是板料冲压成形中影响冲压件质量的关键因素之一。本文采用正交试验方法,以典型高强钢DP钢U形件弯曲为例,对影响回弹的板料力学性能参数进行了灵敏度分析。考虑各参数按照相同百分比波动时的灵敏度分析结果表明：弹性模量对板料回弹量的影响最大,其次分别为硬化系数、初始屈服应力、硬化指数以及各向异性参数r0,而各向异性参数r45及r90对回弹量的影响可忽略。考虑各参数按照不同百兮比波动时的灵敏度分析结果表明：弹性模量对回弹量的影响最大,其次分别为硬化系数、硬化指数、初始屈服应力以及备向异性参数r0,而r45及r90对回弹量的影响则可忽略。所以,板料的力学性能参数中弹性模量对回弹的影响最明显,其次为硬化系数、硬化指数、初始屈服应力及各向异性参数r0,而r45及r90对回弹量几乎没有影响。     

基于球杆仪的PRS-XY型混联数控机床关键结构参数误差快速检测技术

对PRS-XY型混联数控机床的关键结构参数误差的快速检测技术进行了研究.提出了影响机床运动精度的关键结构参数,并建立了误差计算模型,进而提出了能够反映机床运动性能的球杆仪测试方案.通过仿真计算,得到了关键结构参数误差对检测结果的影响,并通过实验进行了验证.最终建立了PRS-XY型混联数控机床关键参数误差与检测相关结果的对应关系,为快速误差诊断提供了依据.