Measuring large 3D structures using four portable tracking laser interferometers

A new concept that allows measuring 1D–3D objects in the range of several centimeters to 5 m × 5 m × 5 m is presented. In general terms the concept can be seen as a task specific correction of geometrical errors of coordinate measuring machines (CMMs). The developed system comprises a commercial CMM, its measurement and its evaluation software and a set of at least four high accurate tracking laser interferometers. The CMM is simply used as a mover which allows to capture points on the surface of a measuring object. In parallel the tracking laser interferometers follow a retro-reflector located close to the stylus tip of the tactile probe of the CMM. Based on a multi-lateration algorithm 3D-positions are calculated from the measured interferometric distances. Finally, two sets of coordinates emerged, namely, one by the CMM and the second from the metrological frame of the tracking laser interferometers. The interferometrically measured positions are usually more precise than the positions measured by the CMM. This is due to the high accuracy of the interferometric system and also due to the fact that the measurement positions are taken in a manner which almost avoids Abbe errors. Because of that, the measurement positions of the CMM are substituted with the more accurate measurement points calculated from distance measurements of the tracking interferometers. The position coordinates thus obtained are used for the further computerized evaluations, which yield the geometric parameters of the object measured. First measurements under laboratory condition show very promising results. It has been demonstrated that the concept is suitable for the high precision calibration of large workpieces with small tolerances, for instance, for the calibration of large gears for the windmill industry.     

Development of high-precision micro-coordinate measuring machine: Multi-probe measurement system for measuring yaw and straightness motion error of XY linear stage

Today, with the development of microsystem technologies, demands for three-dimensional (3D) metrologies for microsystem components have increased. High-accuracy micro-coordinate measuring machines (micro-CMMs) have been developed to satisfy these demands. A high-precision micro-CMM (M-CMM) is currently under development at the National Metrology Institute of Japan in the National Institute of Advanced Industrial Science and Technology (AIST), in collaboration with the University of Tokyo. The moving volume of the M-CMM is 160 mm × 160 mm × 100 mm (XYZ), and our aim is to achieve 50-nm measurement uncertainty with a measuring volume of 30 mm × 30 mm × 10 mm (XYZ). The M-CMM configuration comprises three main parts: a cross XY-axis, a separate Z-axis, and a changeable probe unit. We have designed a multi-probe measurement system to evaluate the motion accuracy of each stage of the M-CMM. In the measurement system, one autocollimator measures the yaw error of the moving stage, while two laser interferometers simultaneously probe the surface of a reference bar mirror that is fixed on top of an XY linear stage. The straightness motion error and the reference bar mirror profile are reconstructed by the application of simultaneous linear equations and least-squares methods. In this paper, we have discussed the simulation results of the uncertainty value of the multi-probe measurement method using different intervals and standard deviations of the laser interferometers. We also conducted pre-experiments of the multi-probe measurement method for evaluating the motion errors of the XY linear stage based on a stepper motor system. The results from the pre-experiment verify that the multi-probe measurement method performs the yaw and straightness motion error measurement extremely well. Comparisons with the simulation results demonstrate that the multi-probe measurement method can also measure the reference bar mirror profile with a small standard deviation of 10 nm.     

Measurements of dimensional standards and etalons with feature size from tens of micrometres to millimetres by using sensor strengthened nanomeasuring machine

A laser focus sensor and a contact inductive sensor have been coupled to an ultra high precision positioning stage, referred to as a nanomeasuring machine (NMM), for measurements of dimensional standards with a large measurement volume of 25 mm × 25 mm × 5 mm. Control and measurement software have been designed and complemented. The measurement uncertainty of strengthened NMM has been analyzed and discussed. Groove depth and step height standards with feature heights of tens of micrometres to millimetres as well as aspherical surface etalons are calibrated by nanomeasuring machine. The paper also introduces a method for characterising the measured aspheric surface by least square fitting the measured data to a quadratic paraboloid function. The obtained quadratic coefficients are compared to that measured by a conventional coordinate measuring machine (CMM) and a stylus profiler, showing a good agreement.     

Nanometer profile measurement of large aspheric optical surface by scanning deflectometry with rotatable devices: Uncertainty propagation analysis and experiments

High-accuracy mirrors and lenses with large dimensions are widely used in huge telescopes and other industrial fields. Interferometers are widely used to measure near flat surfaces and spherical optical surfaces because of their high accuracy and high efficiency. Scanning deflectometry is also used for measuring optical near flat surfaces with sub-nanometer uncertainty. However, for measuring an aspheric surface with a large departure from a perfect spherical surface, both of these methods are difficult to use. The key problem for scanning deflectometry is that high-accuracy autocollimators usually have a limited measuring range less than 1000″, so it cannot be used for measuring surfaces having a large slope. We have proposed a new method for measuring large aspheric surfaces with large slopes based on a scanning deflectometry method in which rotatable devices are used to enlarge the measuring range of the autocollimator. We also proposed a method to connect the angle data which is cut by the rotation of the rotatable devices. An analysis of uncertainty propagation in our proposed method was done. The result showed that when measuring a large aspheric surface with a diameter over 300 mm and a slope of 10 arc-deg, the uncertainty was less than 10 nm. For the verification of our proposed method, experimental devices were set up. A spherical optical mirror with a diameter of 35 mm and curvature radius of 5000 mm was measured. The measuring range of the autocollimator was successfully enlarged by our proposed method. Experimental results showed that the average standard deviation of 10 times measurement was about 20 nm.     

Uncertainty analysis of a laser calibration system for evaluating the positioning accuracy of a numerically controlled axis of coordinate measuring machines and machine tools

This paper presents an uncertainty analysis of a Positional Error Calibrator based on a laser interferometer system. This laser calibration system is capable of evaluating the positioning accuracy of a numerically controlled axis of machine tools and coordinate measuring machines (CMM) under dynamic conditions. In order to assess the measurement uncertainty of this calibrator, an analysis of the uncertainty components that make up the uncertainty budget of this calibrator has been carried out. These uncertainty components can be classified into three categories as follows: (1) uncertainties intrinsic to the laser system; (2) uncertainties due to environmental effects; (3) measuring uncertainties due to the installation. The procedure for evaluating the uncertainty of this calibrator follows GUM (“Guide to the Expression of Uncertainty in Measurement”). This uncertainty analysis was carried out when this calibrator was used to assess the positional errors of the “X” axis of a moving bridge type CMM.     

提高CCD激光自准直测角精度的硬件方法

设计了一个CCD激光自准直测角系统。为提高系统的测量精度和实时性,对系统中的硬件参数进行研究,有效改善了采集到图像的质量。降低数据处理难度的同时,缩短了图像处理时间和提高了系统的测量精度。对系统中小孔光阑的直径,CCD的积分时间,会聚镜头的焦距值,采集卡的亮度和对比度参数分别进行分析,寻找优化值对系统进行改进。对改进前后的系统进行对比实验,实验结果表明,改进后系统的测角精度由原来的5.0″提高到了1.0″,处理一帧图像的时间缩短到了0.417s。     

Evaluation of a multi-sensor horizontal dual arm Coordinate Measuring Machine for automotive dimensional inspection

Multi-sensor coordinate measuring machines (CMM) have a potential performance advantage over existing CMM systems by offering the accuracy of a touch trigger probe with the speed of a laser scanner. Before these systems can be used, it is important that both random and systematic errors are evaluated within the context of its intended application. At present, the performance of a multi-sensor CMM, particularly of the laser scanner, has not been evaluated within an automotive environment. This study used a full-scale CNC machined physical representation of a sheet metal vehicle body to evaluate the measurement agreement and repeatability of critical surface points using a multi-sensor horizontal dual arm CMM. It was found that there were errors between CMM arms and with regard to part coordinate frame construction when using the different probing systems. However, the most significant effect upon measurement error was the spatial location of the surface feature. Therefore, for each feature on an automotive assembly, measurement agreement and repeatability has to be individually determined to access its acceptability for measurement with a laser scanner to improve CMM utilisation, or whether the accuracy of a touch trigger probe is required.     

An active MEMS probe for fine position and force measurements

This paper deals with the development and calibration of a single degree-of-freedom probe that is capable of regulating an input position and measuring force or applying a constant input force and measuring deflection. Such a probe is useful in making sensitive measurements on thin films, nano- and microstructures, and fluids. The probe is actuated by an electrostatic comb drive with an integrated capacitive sensor. COTS electronics and a capacitance-to-voltage IC are used to develop a closed-loop controller for the system, capable of regulating position over a range of about 40 μm to within a 5 nm resolution and controlling forces up to 300 μN with a resolution of 25 nN. The design and fabrication of the probe are discussed. The calibration of the device is performed using multiple methods to cross check each other. The use of the probe is demonstrated in the measurement of surface tension and probing the response of a soft polymer to small forces.     

二维光学自准直微角度传感器

为实现表面微形貌测量以及精密平台的定位测量,设计了一种结构简单的小体积二维微角度传感器。该微角度传感器基于激光自准直原理,主要由作为光源的激光二极管、自准直光路和作为位置探测器的四象限光电二极管组成。分析计算发现,角度传感器的灵敏度与光路中物镜的焦距无关,因此选用了焦距较短的物镜,以实现小体积、高灵敏度的目的。四象限光电二极管具有二维位置探测能力,利用其作为光电转换装置,微角度传感器可以同时探测两轴角度变化值。实验结果表明,微角度传感器的体积可达到25×20×13 mm3,角度测量范围±1 200 arcsec,分辨率为0.1 arcsec。实验中利用激光自准直仪进行对照,有效验证了这种新型二维光学自准直微角度传感器的可行性。     

基于三维激光扫描的移动大尺寸圆柱体工件长度快速检测系统

针对移动大尺寸圆柱体工件两端的表面形貌特征,利用三维激光扫描仪设计了一种快速长度在线检测系统。基于三维激光扫描仪可在短时间内连续高速获取大量测量数据的特点,系统在虚拟环境下构造出自适应测量形状的虚拟测量基准面,采用二维误差分离方法抑制系统误差和运动误差,识别定位工件两端端点并计算其到虚拟测量基准面的位移;最后结合多传感器融合模型获取三维位移场测量结果。另外,测试前用三坐标测量机精密测量过的相似形状圆柱体工件对系统进行了校准修正。为验证系统的精度和可靠性,分别对处于（1 000±25）mm内不同直径的圆柱体工件进行了长度检测。结果显示,系统可在1 s完成直径约为50 mm工件的长度测量,检测分辨力为0.010 mm,检测精度达到0.050 mm。实际运行结果表明,该设计系统具有高自动性和高效性,可满足在线生产中对大尺寸工件控制和检测的要求。     

An innovative algorithm for statistic sampling of measured points and simplifying measuring probe orientation for sculpture surfaces

As living standards have improved, the requirements of appearance modeling variables have also increased. Although several CAD systems can design and modeling needed products with complicated geometric, but the questions of measuring methods and workpiece error-detection are also growing. For the contact measuring method, besides measuring collision and probe orientation, the sampling points and their distributed locations are the important factors that influence measuring time as well as precision. In this paper, the sampling statistics technique was used to calculate the minimum number of sampling points, which will tally the contour tolerance requirements of the measured surface. Next, the suitable locations for sampling points will be carried out using the one-half sampling distribution method. Finally, the 2D space picture of measuring characteristic of five-axis CMM (CMM-space) was developed for measuring probe’s orientation in the measuring process. As a result, an algorithm of measuring characteristic matrix of five-axis CMM (CMM-matrix) and the minimum times of the measuring probe’s placement was derived to reduce the measuring time and improve the measuring efficiency.     

Effect of laser pulsing on the composition measurement of an Al–Mg–Si–Cu alloy using three-dimensional atom probe

The effect of laser pulse energy on the composition measurement of an Al–Mg–Si–Cu alloy (AA6111) specimen has been investigated over a base temperature range of 20–80 K and a voltage range of 2.5–5 kV. Laser pulse energy must be sufficiently higher to achieve pulse-controlled field evaporation, which is at least 0.9 nJ with a beam spot size of about 5 μm, providing an equivalent voltage pulse fraction, ∼14% at 80 K for the alloy specimen. In contrast to the cluster composition, the measured specimen composition is sensitive to base temperature and laser energy changes. The exchange charge state under the influence of laser pulsing makes the detection of Si better at low base temperature, but detection of Cr and Mn is better at a higher temperature and using higher laser energy. No such effect occurs for detection of Mg and Cu under laser pulsing, although Mg concentration is sensitive to the analysis temperature under voltage pulsing. Mass resolution at full-width half-maximum is sensitive to local taper angle near the apex, but has little effect on composition measurement.     

Integration Planning Model of IDEF0 and STEP Product Data Representation Methods in a CMM Measuring System

The measuring process using a CMM involves a large amount of data. It is necessary to understand and clearly define the data required by the measuring process and the relationships of these data before incorporating automation into a CMM system. This paper uses the IDEF0 model to analyse the measuring function requirements for solving the problem of ambiguous internal information flow and material flow during the measuring process. A data module for the CMM measuring system was developed using the EXPRESS language in STEP, to support the IDEF0 function process module. An information flow design model was also established, which integrated the IDEF0 process requirement analysis model and the EXPRESS data module. The objective is to enhance the efficiency of the development of measuring systems by system designers, and to provide a basis for future development of measuring information systems using STEP data formats.     

Multi-probe scanning system comprising three laser interferometers and one autocollimator for measuring flat bar mirror profile with nanometer accuracy

This paper describes a multi-probe scanning system comprising three laser interferometers and one autocollimator to measure a flat bar mirror profile with nanometer accuracy. The laser interferometers probe the surface of the flat bar mirror that is fixed on top of a scanning stage, while the autocollimator simultaneously measures the yaw error of the scanning stage. The flat bar mirror profile and horizontal straightness motion error are reconstructed by an application of simultaneous linear equations and least-squares method. Measurement uncertainties of the flat bar mirror profile were numerically evaluated for different installation distances between the laser interferometers. The average measurement uncertainty was found to be only 10 nm with installation distances of 10 and 21 mm between the first and second, and first and third interferometers, respectively. To validate the simulation results, a prototype system was built using an X–Y linear stage driven by a stepper motor with steps of 1 mm along the X direction. Experiments were conducted with fixed interferometers distances of 10 and 21 mm, as in the simulation, on a flat bar mirror with a profile known to an accuracy of λ = 632.8 nm. The average value of two standard deviations (95%) of the profile calculated over ten experiments was approximately 10 nm. Other results from the experiment showed that the system can also measure the yaw and horizontal straightness motion errors successfully at a high horizontal resolution. Comparing with the results measured by ZYGO's interferometer, our measured data excluding some edge points showed agreement to within approximately 10 nm. Therefore, we concluded that our measurement profile has an accuracy in the nanometer range.     

Profile measurement of a wide-area resist surface using a multi-ball cantilever system

In the semiconductor industry, a device that can measure the surface profile of thin film like photoresist with high accuracy and high speed is needed. Since the surface of photoresist is very smooth and deformable, a device is required that will measure vertically with nanometer resolution and not damage the film during the measurement. We developed an apparatus using a multi-ball cantilever and white light interferometer to measure the surface profile of thin film. However, this system, as assessed with a scanning method, suffers from the presence of a moving stage and systematic sensor errors. Therefore, this paper describes an approach using a multi-ball cantilever as coupled distance sensors together with an autocollimator as an additional angle measuring device, which has the potential for self-calibration of a multi-ball cantilever. Using this method, we constructed an experimental apparatus and made measurements on resist film. The results demonstrated the feasibility of the constructed multi-ball cantilever system with the autocollimator for measuring thin film with high accuracy.     

Application of a diffraction grating and position sensitive detectors to the measurement of error motion and angular indexing of an indexing table

In this paper, two systems for the measurement of the error motion and angular indexing of a rotary indexing table have been developed. A laser diode, a laser holder and a position sensitive detector (PSD) are integrated as a simple measuring device for the measurement of the rotary error without using a precision reference artifact (a cylinder or a sphere), multiple probes or error separation methods. The laser diode is assembled in the laser holder and fixed on the rotary table. The PSD is set up above the laser holder to detect the position of an incident laser beam from the laser diode. When the rotary table rotates, the rotary error changes the direction of the incident beam and also the position of the spot on the PSD. For the measurement of the angular indexing, a reflective diffraction grating and two PSDs are integrated as a high-resolution angle measuring device without using an autocollimator or a laser interferometer system. The diffraction grating is set at the center of the rotary table and reflects an incident laser beam into several diffractive rays. Two PSDs were set up for detecting the positions of ±1st-order diffraction rays. A simple algebraic method is used to solve the angular indexing through an optical analysis. The experimental results showed the feasibility of the proposed test devices.     

基于三坐标测量的模具反求设计

论述了从三坐标测量机得到的数据重建模具CAD模型的工作过程,包括点云的预处理如点云对齐、误差点剔除;曲面重构:包括点云的网格化、孔洞填充、边界处理、曲面拟合及曲面评估.利用Geomagic软件完成了对某梁的逆向设计,证明了反求工程理论的可行性.     

Modeling and verification of a five-axis laser scanning system

Today several new kinds of laser beam sensors appear with high resolution and accuracy and find their applications in reverse engineering and quality control. Due to the incapability of changing their orientations continuously in response to the surface fluctuation of a part to be measured, they are not competent for measuring parts with complicated structures. In this paper a five-axis laser scanning system integrated with a CMM, a laser beam sensor and a PH10 rotary head is proposed, which can measure complicated parts by frequently indexing the laser sensor approximately consistent with the normal direction of the surface. As the laser value is a 1-D data and the measured data must be given in 3-D expression in the world coordinate system, a system model for coordinate transformation is established. An “equivalent probe” approach is presented for system verification, and an iterative verifying process is adopted to eliminate the verification error caused by the inclination error of the laser sensor. Experiment study shows that the system can measure a part from any direction with an accuracy of 30 μm.     

Approach to accuracy improvement and uncertainty determination of radius of curvature measurement on standard spheres

In high accuracy radius of curvature (ROC) measurement, significant discrepancy may exist in results on the same optical surface obtained by different techniques. Metrological standard sphere is a potential solution to this problem. Mathematical models are built up to characterize the relationship between the ROC of standard spheres and the roundness error as well as the aperture angle. Equations for calculating the uncertainty of ROC are derived and tested on several ROC measuring methods. The reason for the inconsistency between results of different techniques is analyzed and solutions are proposed. A method is developed which can remarkably reduce the uncertainty of ROC. Experiments are carried out on a set of high quality spheres whose diameters are from 11 mm to 93 mm and roundness below 0.1 μm, measured by instruments with relative accuracy of 10⁻⁵–10⁻⁶, which are a length measuring machine, a profilometer and a homemade differential confocal system. Relative uncertainties of ROC are calculated and analyzed against several factors. Experimental results show good consistency with theoretical analysis. Approaches to trace the ROC to the metrological length standard area discussed.     

基于激光干涉仪的直线度误差测量

机床导轨直线度误差的测量方法有很多种,其中最常用的是水平仪法、自准直仪法和平尺法。主要介绍的是用激光干涉仪测量直线度误差的方法、原理及误差分析,并提出为减少测量误差在测量过程中应注意的几个问题。