基于蒙特卡罗仿真方法的大尺寸测量不确定度分析

为评价大尺寸测量不确定度,特别是多站融合测量不确定度,引入蒙特卡罗仿真方法.该方法根据各传感器单元的概率特性重复采样,生成测量结果的样本,统计样本得到坐标测量不确定度,并利用计算机可视化样本的三维散点图.通过不同样本数对运算时问和准确性影响的实验,确定样本数为500.以激光跟踪仪为例进行实验,比较蒙特卡罗法、统计法和解析法三种方法得到的不确定度结果,吻合情况较好,其中与解析法比较最大偏差仅为2.7 um实验结果表明,蒙特卡罗仿真方法可以准确评价大尺寸测量仪器及多站融合测量不确定度,融合精度优于各局部精度.     

综合建站误差的激光跟踪仪测量不确定度评估

针对航空制造业中面向大尺寸空间的激光跟踪仪测量不确定度评估问题,提出了综合建站误差的激光跟踪仪测量不确定度评估方法.在构建激光跟踪仪测量模型与误差模型的基础上,将测量设备建站误差引入优化模型,并通过跟踪仪建站、空间点测量等环节,对受建站误差和测量误差双重因素影响的跟踪仪空间点测量不确定度进行了仿真测试和数据分析.以某工...     

激光跟踪仪多边测量的不确定度评定

激光跟踪仪多边测量是大型高端装备制造现场溯源的重要手段,正确评定其不确定度是确保制造过程量值统一、结果可靠的关键。本文提出了一种准确、快速的激光跟踪仪多边测量的不确定度评定方法。从仪器误差、环境干扰及靶球制造误差等方面分析激光跟踪仪多边测量的不确定度来源。针对多边测量的输出量为多维向量的特点,重点研究基于多维不确定度传播律(GUM法)的不确定度合成方法,同步评定目标点坐标和跟踪仪站位的不确定度。最后,介绍了点到点长度的不确定度计算方法。实验表明:GUM法评定的不确定度结果与蒙特卡洛法(MCM法)的结果相比,坐标不确定度偏差小于0.000 2 mm,相关系数偏差小于0.01,满足数值容差,且GUM法用时仅为MCM法的0.08%;点到点长度测试的En值均小于1。因此,基于GUM法评定激光跟踪仪多边测量的不确定度具有可行性及高效性,且评定结果正确、可靠。     

基于拟蒙特卡罗方法的测量不确定度评定

测量不确定度是表征测量结果可靠性的一个重要参数.针对蒙特卡罗方法在测量不确定度评定时存在的收敛速度较慢以及仿真结果不稳定的不足,利用拟蒙特卡罗方法进行测苗不确定度的评定.拟蒙特卡罗方法使用拟随机数进行仿真计算.在测量不确定度的评定中,先基于Halton序列产生分布较为均匀的随机数,再利用数学变换转换成服从相应概率分布的随机数进行仿真评定计算.对圆柱体积测量不确定度的模拟评定结果表明,拟蒙特卡罗方法收敛速度快,计算结果较为稳定,可以简单高效地用于测量不确定度的评定.     

基于QMC的齿轮测量中心测量不确定度评定方法

为评定齿轮测量中心测量不确定度,提出了一种基于拟蒙特卡罗法(quasi Monte-Carlo method,QMC)的齿轮测量不确定度评定方法。研究了齿轮测量中心的几何误差源,应用坐标变换法建立了齿轮测量中心精密测量模型,采用拟蒙特卡罗仿真法对齿轮测量中心测量不确定度进行了评定,并分析了评定的稳定性。评定实验表明,该方法可准确评定齿轮测量中心测量不确定度,评定结果最大偏差为2.35%,评定方法稳定。     

大直径在线高精度测量不确定度分析

讨论了基于"弓高弦长法"测量原理,由3只精密激光位移传感器组成的大直径非接触在线测量装置的测量不确定度。针对被测大轴的尺寸,选择固定的弦长;基于两标准尺寸的外圆盘进行弦长参数的标定;通过3只传感器的对称布置、相对测量、多次测量求平均值等措施,简化了测量装置的结构、方便了标定和测量过程、提高了直径测量精度。对于直径500 mm~510 mm的大轴,当其圆度误差不超过30μm、3只传感器光线的不平行度误差小于0.5°、上下传感器的不对称小于1 mm、标定和测量时中间传感器光线不对中误差小于1 mm时,直径测量结果的不确定度小于3μm。     

激光跟踪仪现场测量的系统不确定度研究

在分析激光跟踪仪系统不确定度的基础上,通过对Leica激光跟踪仪LTD840进行相关实验,提出了一种激光跟踪仪现场测量不确定度的评估方法,并通过实验验证了相关结果.     

柴油发动机烟度测量的不确定度分析

通过对柴油发动机烟度测量过程的分析,并对测量过程中不确定度来源进行分析,找出影响不确定度的主要原因,以提高在检验工作中的检测能力。     

谈谈测量不确定度及其应用

我们过去常用测量误差(相对误差和绝对误差)的概念来表征某一质量特性的测量结果，这样的表述存在首许多不确定性(因素)，有时无法可靠地预知其测量结果的分布范围。介绍了测量不确定度的形成过程，测量不确定度的来源，并通过举例来介绍其应用方法。     

单目视觉测量系统不确定度的分析

基于光学测头特征点成像的单目视觉坐标测量系统是一种新兴的高精度、大尺寸、三维整体、在线测试系统,在现代工业生产中具有重要应用价值。为评价这种单目视觉测量系统的测量精度,对基于测量不确定度的评定方法进行研究。在对影响单目视觉坐标测量系统测量精度的主要因素进行深入分析研究的基础上,建立测量不确定度评定表达式,实现对测量系统测量精度的评定;通过测量试验对评定方法加以验证,试验证明测量系统的测量精度与分析结果相吻合。     

Experimental evaluation of software estimates of task specific measurement uncertainty for CMMs

Estimation of the uncertainty of Coordinate Measuring Machine (CMM) measurements for real, imperfect parts is a very complex undertaking. Not only are there many contributors to the uncertainty that may interact in a non-linear fashion, making it difficult to mathematically determine an uncertainty estimate, but it is also difficult to predict the long-term variation of these parameters. Our work seeks to provide experimental validation of the uncertainties predicted by two different commercial software packages that purport to predict the task-specific measuring uncertainty of CMM measurement results. The validation procedure uses repeated measurements of calibrated artifacts to experimentally determine measurement uncertainties. These measurements can then be simulated in the commercial software packages. The comparison will allow the software to be tested to see if it appropriately accounts for the influences of the operator, environment, and part placement. This paper reports the results of actual part measurements and the predicted uncertainty provided by commercial simulation packages. Differences between experimental and simulated uncertainties are highlighted, and their causes examined.     

Influence of measurement noise and laser arrangement on measurement uncertainty of laser tracker multilateration in machine tool volumetric verification

This paper aims to present different techniques and factors that affect the measurement accuracy of a commercial laser tracker responsible for capturing checkpoints used in machine tool volumetric verification. This study was conducted to uncover various sources of error affecting the measurement uncertainty of the laser tracker, additional sources of error that further contributed to the uncertainty, and the factors influencing these techniques. We also define several noise reduction techniques for the measurements.The improvement in the accuracy of captured points focuses on a multilateration technique and its various resolution methods both analytically and geometrically. Similarly, we present trilateration and least squares techniques that can be used for laser tracker self-calibration, which is an essential parameter in multilateration.This paper presents the influence of the spatial distribution of laser trackers (LTs) in measurement noise reduction by multilateration, which produces an improvement in volumetric error machine tool reduction. A study of the spatial angle between LTs, the distance and the visibility of the point to be measured are presented using a synthetic test. All of these factors limit the scope of multilateration. Similarly, a comparison of self-calibration techniques using the least squares and trilateration methods with which to determine the relative position of the laser tracker employees is presented. We also present the influence of the relationship between the radial and angular measurement noise self-calibration processes as it relates to the volumetric error reduction achieved by the machine tool with multilateration. All studies were performed using synthetic tests generated using a synthetic data parametric generator.     

Development of a parametric model and virtual machine to estimate task specific measurement uncertainty for a five-axis multi-sensor coordinate measuring machine

Any combination of contact and non contact sensors on a single coordinate measuring machine makes it a multi-sensor or hybrid coordinate measuring machine. The ability to change the probing device without re-establishing the part coordinate system is a significant advantage and consequently the reason for their wide acceptance and usage. In addition to the existing three linear stages in a conventional or hybrid coordinate measuring machine, the number of axes can be augmented with two rotary stages in order to make them more versatile. This not only complicates the metrology loop but also adds more parametric errors to existing list of known 21 errors for a three stage conventional measuring machine. Also different probing sensors in the system have different metrology loops. Literature survey reveals that there is no previous or current work on estimation of task specific uncertainty for machines of this class with a wide potential for measuring complex parts quickly and with great ease. The current work focuses on developing a virtual measuring machine of this class which incorporates a parametric model of a five-axis multi-sensor coordinate measuring machine, techniques to estimate the parametric errors in the model and error correction strategies for the same. The virtual machine is used to mimic real time measurements in order to come up with estimates for task specific measurement uncertainty.     

Laser trackers for large-scale dimensional metrology: A review

Thirty years since their invention, laser trackers are now recognized as the measurement tool of choice in the manufacture and assembly of large components. The general design of laser trackers, i.e., a ranging unit on a two-axis gimbal, has not changed significantly over the years. However, innovations in ranging technology, for example, the emergence of increasingly accurate absolute distance meters (ADMs), are providing users with an alternative to interferometers (IFMs). Hand-held accessories such as touch probes and line scanners are expanding the scope and applicability of laser trackers. In this paper, we survey the literature in all areas of laser trackers as applied to large-scale dimensional metrology (LSDM), with emphasis on error modeling, measurement uncertainty, performance evaluation and standardization.     

Analytical estimation of coordinate measurement uncertainty

The paper presents the assumptions and theoretical background of analytical method of estimation the coordinate measurement uncertainty. The uncertainty for each characteristic is estimated separately. Mathematical model for each characteristic uses the minimal number of so-called “characteristic points” of the measured workpiece. Each characteristic is defined by a formula presented in a form where it is a function of coordinates’ differences’ of characteristic points. The uncertainty budget for the coordinates’ differences includes influences of particular geometrical errors of CMM, probing system errors, as well as temperature errors. The applied algorithms of uncertainty estimation use the type B method according to the rules of GUM.     

Water jet velocity uncertainty in laser Doppler velocimetry measurements

The present work deals with the uncertainty evaluation in water jet velocity measurements carried out by means of a laser Doppler dual-incident-beam velocimeter in reference-beam configuration developed at the WJLab (Water Jet Laboratory of Dipartimento di Meccanica of Politecnico di Milano). The applied experimental procedure makes it possible to calculate the measurement uncertainty through the determination of its various components. Once uncertainty is known, the laser Doppler system is suitable for objective and significant velocity evaluations but also for improvements allowed by the knowledge of the most effective uncertainty sources. Such a subject is typically not considered by the specific water jet literature, but is becoming more and more important due to the evolution of water jet machining towards high precision applications.     

Word error rate measurement uncertainty estimation in digitizing waveform recorders

The paper proposes a method to measure the Word Error Rate (WER) affecting digitizing waveform recorders, suitable to be included, as addendum, into the IEEE Std.1057. In particular, a reliable estimation of the confidence interval and the design of efficient test sessions are provided. The proposed method has been experimentally verified by means of two WER test setups. Test results, carried out by means of WER measurements on actual digitizing waveform recorders, have been compared to those achieved by implementing the method described in the IEEE Std.1057.     

The detection of rotary axis of NC machine tool based on multi-station and time-sharing measurement

At present, the detection of rotary axis is a difficult problem in the errors measurement of NC machine tool. In the paper, a method with laser tracker on the basis of multi-station and time-sharing measurement principle is proposed, and this method can rapidly and accurately detect the rotary axis. Taking the turntable measurement for example, the motion of turntable is measured by laser tracker at different base stations. The redundant equations can be established based on the large amount of measured data concerning the distance or distance variation between measuring point and base station. The coordinates of each measuring point during turntable rotation can be accurately determined by solving the equations with least square method. Then according to the error model of rotary axis, the motion error equations of each measuring point can be established, and each error of turntable can be identified. The algorithm of multi-station and time-sharing measurement is derived, and the error separation algorithm is also deduced and proved feasible by simulations. Results of experiment show that a laser tracker completes the accuracy detection of the turntable of gear grinding machine within 3 h, and each error of the turntable are identified. The simulations and experiments have verified the feasibility and accuracy of this method, and the method can satisfy the rapid and accurate detecting requirements for rotary axis of multi-axis NC machine tool.