Methodology for the application of velocimetry by molecular tagging of hypersonic flows

A laser-induced NO fluorescence technique was applied to measure velocity in a hypersonic shock tunnel nozzle exit. For the application of the technique, a detailed study of the density and fluorescence lifetime of the tracer radical, flow velocity and effective test time is proposed, resulting in a methodology for the application of the technique in hypersonic pulsed facilities. The study has demonstrated that it is necessary to jointly evaluate the flow velocity, the fluorescence lifetime of the radical and the width at half height of the laser beam, resulting in a kind of indicator for the feasibility of the technique. The variation of the laser incidence time with respect to the Pitot signal showed that it is not enough to select a stable Pitot pressure signal region to define the laser incidence time, preliminary trial and error analysis are necessary for each device used. Furthermore, the analysis of the velocity values calculated from the linear fit method shows that the adoption of such a method eliminates the effect of the systematic error of the measurements.     

Comprehensive simulation software for teaching camera calibration by a constructivist methodology

This paper describes the Metrovisionlab computer application implemented as a toolbox for the Matlab program. It is designed to teach the most important camera calibration aspects in dimensional metrology applications such as laser triangulation sensors and photogrammetry or stereovision systems. This software is used in several industrial vision courses for senior undergraduate mechanical engineering students. The application: simulates a virtual camera, providing a simple and visual understanding of how various characteristics of a camera influence the image that it captures; generates the coordinates of synthetic calibration points, both in the world reference system and the image reference system; and can calibrate with the most important and widely-used methods in the area of vision cameras, using coplanar or non-coplanar calibration points. Thus, the main goal is to have a simulation tool that allows characterizing the accuracy, repeatability, error mechanisms and influences for different measurement conditions and camera calibration algorithms. In the realized tests, the software has demonstrated to be a very effective educational tool.     

影响待测物面测量误差的因素及补偿

分析被测物面对激光三角法测量技术的影响,从原理、位移传感器的非线性补偿、被测表面倾角、被测表面特征(颜色、粗糙度、光泽)几方面分析误差产生的原因。探讨各因素的误差补偿方法,对传感器进行非线性误差标定,测量出其非线性误差曲线图;使用标注件标定激光头本身倾角误差,对绘制倾角误差测量结果做曲线拟合;对被测件表面的颜色处理;在非特定条件下,可以忽略表面光泽度和粗糙度;最后综合上述过程,得出测量结果。该方法提高了测量精度。对于小型机电,电子产品外形反求测量,提高其生产过程中的测量精度,具有一定指导作用。     

Enhancing multisensor data fusion on light sectioning coordinate measuring systems for the in-process inspection of freeform shaped parts

A method for automatic determination of sensors positions and orientations in multisensor laser triangulation coordinate measuring systems is presented. Based on a series of measurements on a conical artifact without the use of external light sources, the approach allows for both optimized adjustment of the physical sensors alignment and improved 3D data registration by software. Simulations were conducted to quantify the sensitivity of the method. Experimental results based on measurements of steep details of complex shaped parts show a 5-times reduction of deviations between measurements of sensors with respect to an already optimized adjustment by manual methods.     

Locating Error Considering Dimensional Errors Modeling for Multistation Manufacturing System

Multistation machining process is widely applied in contemporary manufacturing environment.Modeling of variation propagation in multistation machining process is one of the most important research scenarios.Due to the existence of multiple variation streams,it is challenging to model and analyze variation propagation in a multi-station system.Current approaches to error modeling for multistation machining process are not explicit enough for error control and ensuring final product quality.In this paper,a mathematic model to depict the part dimensional variation of the complex multistation manufacturing process is formulated.A linear state space dimensional error propagation equation is established through kinematics analysis of the influence of locating parameter variations and locating datum variations on dimensional errors,so the dimensional error accumulation and transformation within the multistation process are quantitatively described.A systematic procedure to build the model is presented,which enhances the way to determine the variation sources in complex machining systems.A simple two-dimensional example is used to illustrate the proposed procedures.Finally,an industrial case of multistation machining part in a manufacturing shop is given to testify the validation and practicability of the method.The proposed analytical model is essential to quality control and improvement for multistation systems in machining quality forecasting and design optimization.     

A regression model for analysing the non-linearity of laser triangulation probes

A study on the non-linearity of laser triangulation probes is presented in this paper. The influences of design variables on non-linearity were studied by response surface methodology, and the significant factors were identified. A regression model was developed with which non-linearity can be conveniently evaluated in the design stage of laser triangulation probes. The sensitivities of non-linearity to the design variables are evaluated.     

激光位移传感器在自由曲面测量中的应用

以点激光位移传感器(HL-C211BE)为对象,研究它在自由曲面测量中的应用。针对激光位移传感器因测点倾角代入的测量误差,提出了一个可以量化的倾角误差模型。基于直射式点激光三角法原理,分析了激光光路的几何关系,从会聚光斑光能质心发生的偏移推导出倾角误差模型。随后,用高精度激光干涉仪和正弦规对激光位移传感器进行校对实验,并用误差模型对测量结果进行补偿。结果显示,补偿后激光位移传感器的测量精度得到明显提高。对一非球面凸透镜进行了实验测量,得到了自由曲面测点倾角的计算方法,并用倾角误差模型修正了测量数据。实验结果表明,量化的倾角误差模型可以将激光位移传感器的测量误差控制到小于10μm,满足激光位移传感器在自由曲面测量中应用的要求。     

测量近中红外激光大气透过率的调制型太阳光度计

为弥补常用红外波段激光大气透过率测量方法成本高或实时性低的不足,通过模拟计算分析研究,提出基于光源调制太阳光度计技术提取红外波段激光大气透过率的方法,提供一种成本低、操作简单、实时性强的有效测量方法。研制的光源调制型红外太阳光度计可测量宽波段大气透过率,再依据建立的宽带和窄带透过率关系进行修正,最终获取可应用的近中红外多波段激光大气透过率。实际测量结果与对比实验表明,与实验室自研的近红外太阳光度计相比统计误差小于4%,与POM-02相比统计误差小于6%。红外调制型太阳光度计获取的实时结果不但可应用于激光大气传输修正中,也对评估激光通信和激光传输等具有重要意义。     

飞秒激光烧蚀石英玻璃表面质量分析

基于不同激光功率线烧蚀试验,研究激光偏振模式对烧蚀线宽度及表面形貌特征的影响。结合线烧蚀优化参数,开展不同线重叠率δ的面烧蚀试验,利用表面轮廓仪进行烧蚀表面粗糙度分析;建立扫描速度和线重叠率对残留高度影响的关系表达式,并进行计算分析。研究表明,当线偏振方向平行于扫描方向时,线偏振光烧蚀线质量优于圆偏振光,且其烧蚀线宽比圆偏振光大。当δ由65%增大到90%时,线偏振光烧蚀面垂直于扫描方向的轮廓算数平均偏差Ra先减小后增大,并在δ=80%时达到最小值1.05 μm;圆偏振光Ra随δ增大而减小,在δ=90%时达到最小值1.63 μm。此外,烧蚀面微观不平度十点高度Rz计算结果与试验结果基本吻合,且Rz与δ呈线性关系,并随δ增大而减小。     

Control of melt pool temperature and deposition height during direct metal deposition process

This paper presents a hybrid control system that is able to improve dimensional accuracy of geometrically complex parts manufactured by direct metal deposition process. The melt pool height is monitored by three high-speed charged couple device cameras in a triangulation setup. The melt pool temperature is monitored by a dual-color pyrometer. A two-input single-output hybrid control system including a master height controller and a slave temperature controller is used to control both height growth and melt pool temperature at each deposition layer. The height controller is a rule-based controller and the temperature controller uses a generalized predictive control algorithm with input constraints. When the melt pool height is above a prescribed layer thickness, the master height controller blocks control actions from the temperature controller and decreases laser power to avoid over-building. When the melt pool height is below the prescribed layer thickness, the temperature controller bypasses the height controller and dynamically adjusts laser power to control the melt pool temperature. This hybrid controller is able to achieve stable layer growth by avoiding both over-building and under-building through heat input control. A complex 3-D turbine blade with improved geometrical accuracy is demonstrated using the hybrid control system.     

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.     

非接触测量激光光学探头

阐明了激光三角测量的原理, 推导了有关的公式, 对影响测量精度的诸因素进行了分析。介绍了基于三角测量原理的非接触激光光学探头的设计, 给出了实验结果, 展望了应用前景。     

Description and characteristics of a 'wave follower' system for energy exchange studies in the vicinity of an air-water interface

This paper describes the design, construction, and testing of an electromechanical servomechanism capable of responding to the vertical displacements of a wavy air-water interface. The device is to be used to maintain various probes at a fixed distance above or below the moving interface in a large wind-wave tank. The measurements so obtained will help to elucidate the mechanisms of mass, momentum, and energy transfer between air and water in the presence of waves. The dynamical characteristics of the wave follower are given. For frequencies below 9 Hz, it possesses a linear reponse characterized below 5 Hz by a 7.4 ms time lag. This is the sum of two time lags, 4.9 and 2.5 ms, which correspond, respectively, to the servomechanism itself and to the capacitance-type wave height measurement system. The maximum position error is found to be +/-2 mm for typical wave amplification by wind studies (maximum wave height of about 6 cm).     

在役套管的激光测量法研究

介绍激光三角测量法在套损检测中的应用，激光三角法的测量原理、结构组成及CCD信号采集。提出双层4探头交叉测量方法对套管内壁腐蚀缺陷的检测，实现了单探头单通道测量，通过数据处理判断腐蚀缺陷的位置和深度。     

Reliability of parameters of associated base straight line in step height samples: Uncertainty evaluation in step height measurements using nanometrological AFM

Step height is widely used as one of the important nanometrological standards for the calibration of nanometrological instruments. In the calculation of step height, a method of determining a base straight line as a reference line is very important. In nanometrology, which is a field of dimensional metrology, an associated feature (Gaussian associated feature), such as a base straight line, is normally calculated from a measured dataset of a metrological instrument on a real feature using the least squares method. The reliability of a base straight line varies depending on the position and number of measured points for the line and the uncertainty in step height calibration also varies depending on the reliability of the base straight line. In this study, we carried the out step height measurement of micropatterned thin films (10, 7, 5, and 3 nm) using an atomic force microscope (AFM) equipped with a three-axis laser interferometer (nanometrological AFM) and evaluated the uncertainty in these measurements. From the uncertainty evaluation results, the uncertainty derived from the reliability of the parameters of the base straight line was one of the major sources of uncertainty when the measured points for the base straight line were varied. An expanded uncertainty (k = 2) of less than 0.4 nm was obtained. Furthermore, the reliable range of an associated base straight line in a single step height, such as that in an atomic step sample, was calculated and in importance of the calculation of the reliable range was shown in the uncertainty evaluation and in determining the measurement strategy.     

Multi-degree-of-freedom motion error measurement in an ultraprecision machine using laser encoder — Review

Recently, in accordance with the increasing market demand for ultraprecision technology, a high precision multi-degree-of-freedom displacement measurement technology has become important for industrial applications such as the field of manufacturing and inspection because those physical quantities, linear and angular displacements, are key parameters for keeping and improving quality control of a production system. A number of instruments capable of precise multi-degree-of-freedom measurements have been built and some novel techniques have been introduced. The current state-of-art techniques for multi-degree-of-freedom motion error measurement in a linear stage using laser encoder-implemented system are reviewed. First, we summarize the basic principles behind the measurement technology of the motion error in a stage and simple encoder system. Next, the basic design principles of practical laser encoder system are discussed using the experience of past and existing cases to refer to the important points and the major scientific results. The current trends in the field are significantly discussed, including the novel techniques under construction and advanced technologies. Lastly, the future of multi-functional laser encoder-implemented system, highlighting the kinds of new science upcoming in the next few years, is discussed.     

Automated three-dimensional analysis of particle measurements using an optical profilometer and image analysis software

The automated collection of topographic images from an optical profilometer coupled with existing image analysis software offers the unique ability to quantify three‐dimensional particle morphology. Optional software available with most optical profilers permits automated collection of adjacent topographic images of particles dispersed onto a suitable substrate. Particles are recognized in the image as a set of continuous pixels with grey‐level values above the grey level assigned to the substrate, whereas particle height or thickness is represented in the numerical differences between these grey levels. These images are loaded into remote image analysis software where macros automate image processing, and then distinguish particles for feature analysis, including standard two‐dimensional measurements (e.g. projected area, length, width, aspect ratios) and third‐dimensional measurements (e.g. maximum height, mean height). Feature measurements from each calibrated image are automatically added to cumulative databases and exported to a commercial spreadsheet or statistical program for further data processing and presentation. An example is given that demonstrates the superiority of quantitative three‐dimensional measurements by optical profilometry and image analysis in comparison with conventional two‐dimensional measurements for the characterization of pharmaceutical powders with plate‐like particles.     

A new methodology to design multi-sensor networks for distributed large-volume metrology systems based on triangulation

Distributed Large-Volume Metrology (LVM) systems are mainly used for industrial applications concerning assembly and dimensional verification of large-sized objects. These systems generally consist of a set of network devices, distributed around the measurement volume, and some targets to be localized, in contact with the measured object's surface or mounted on a hand-held probe for measuring the points of interest. Target localization is carried out through several approaches, which use angular and/or distance measurements by network devices.This paper presents a new methodology to support the design of networks of devices, for distributed LVM systems based on triangulation (i.e., systems in which network devices perform angular measurements only). It is assumed that these systems use multi-sensor networks including two typologies of devices: some are accurate but expensive and other ones are less accurate but cheaper. The goal of the methodology is establishing a link between the following parameters: (i) density of network devices, (ii) mix between the two typologies of network devices, (iii) measurement uncertainty, and (iv) cost. The methodology allows to estimate the most appropriate density and mix between the two typologies of network devices, so that the distributed LVM system is conforming with the required measurement uncertainty and cost.The methodology relies on a large number of simulated experiments, defined and implemented using a dedicated routine; feasibility and practicality is tested by preliminary experiments on a multi-sensor photogrammetric system, developed at Politecnico di Torino—DIGEP.     

Analysis of digitizing errors of a laser scanning system

The digitizing errors of a high-speed 3D laser scanning system are analyzed and characterized in this paper. As the laser scanner is an electro-optical device and based on the principle of optical triangulation, the measurement accuracy is affected by the measured part geometry and its position within the scanning window. Commercial laser scanners are often calibrated in the scanning plane to account for variation of the incident angle of the laser beam. The effects of the scan depth and the projected angle, characterizing the surface normal of the measured part external to the scanning plane, on the measurement accuracy are not considered in the standard calibration process and have been identified by experiments in the present work. Experimental results indicate that the random error of the scanned data is close to the nominal value provided by the manufacturer. The systematic error shows a bilinear relationship with the scan depth and the projected angle and has a maximum value of about 160 μm. The developed empirical model correctly predicts the systematic error with a maximum deviation of only 25 μm.