Toward subnanometer uncertainty in interferometric length measurements of short gauge blocks

A primary-level comparator, with a reproducibility of 0.2 nm and intended for realization of a Systeme International length unit in the range of 1-100 mm, is reported. High-precision differential measurements of phase change on reflection from blocks and end plates are demonstrated. A set of experiments has been developed to measure systematic error associated with nonideal interferometer optics and deviations from flatness of an auxiliary plate. For specially selected high-grade 6-mm blocks, reproducible wringing has been achieved with a random uncertainty in length measurements of 0.1-0.2 nm. Subnanometer wear-off of the blocks as a result of the cleaning has been detected. Under the conditions of reproducible wringing, the accuracy of the length measurements is evaluated to be in the 2-3-nm range for 6-mm blocks.     

新型移相量块干涉仪的研制

研制了一台用于0.5~100 mm量块测量的新型移相量块干涉仪,分别以波长为633 nm和543 nm的两台稳频激光器作为测量光源,通过一根单模光纤引入到干涉仪内。高精密移相器实现5步移相干涉测量,CCD相机采集干涉条纹并计算干涉条纹小数,被测量块长度采用多波长的小数重合法计算。移相量块干涉仪的测量不确定度达到U=0.015μm+0.07×10~(-6)L(L为量块长度,mm)。     

Ring interferometer for two-sided measurement of the absolute lengths of end standards

Special features of a two-sided interferometer based on a ring optical scheme previously proposed [V. M. Khavinson and L. F. Khavinson, in Investigations in the Field of Length and Angle Measurements, N. P. Gerasimov, ed., Proceedings of the D. I. Mendeleyev Institute for Metrology (Energoatomizdat, Leningrad, 1983), pp. 14-18], which exploits an alternative measurement method to the conventional method for measuring absolutely the lengths of precision gauge blocks. Both measuring surfaces of a gauge are viewed directly without an auxiliary platen wrung onto one of them. The two-sided method results in improved consistency of measurement results because the elimination of wringing avoids the contact error that can occur in the gauge length obtained when the conventional method is used. A variety of means to control the optical phase differences in the interferometer are considered.     

计算机图像技术在高温锻件尺寸测量中的应用

利用彩色CCD和红外滤光片等搭建了高温锻件的尺寸测量平台,通过数字滤光与物理滤光技术提高锻件图像质量,采用比较测量法精确测量锻件二维尺寸。通过采集标准量块图像并应用畸变校正、噪声抑制、亚像素边缘提取等标定出系统的像素尺寸当量,然后选用其它标准量块进行验证,测量系统的横向测量不确定度为0.005 1 mm,纵向测量不确定度为0.008 7 mm。温度在1 000 ℃时采集45#锻件的图像并进行解算,所得测量尺寸与理论值的绝对误差小于1 mm,满足该系统的测量精度要求。     

光干涉法高精度材料线膨胀系数测量

中国计量科学研究院研制的高精度材料线膨胀系数测量装置,满足温度范围为5～40 ℃、被测件长度在20～1 000 mm之间的线膨胀系数测量。采用激光干涉法测量被测件长度变化量,用高精度温度传感器测量温度值。设计了热平衡式干涉镜,利用空气折射率修正和零位误差补偿技术,保证在5～40 ℃变温范围内激光干涉仪的测量精度。以500 mm标准量块作为测量对象,线膨胀系数测量结果与德国物理技术研究院(PTB)测量结果的相对偏差为0.2%。材料线膨胀系数测量不确定度达到3×10^-8K^-1。     

Highest-accuracy interferometer alignment by retroreflection scanning

One important prerequisite for interferometric length measurements of high accuracy is autocollimation adjustment. This guarantees that the direction of the length scale represented by light waves is parallel to the length direction of the object investigated. First we describe the conventional visual autocollimation adjustment method used at Physikalisch-Technische Bundesanstalt since the beginning of interferometric length measurements. Then a new autocollimation method based on scanning the retroreflection from the interferometer is described. Check measurements are performed in order to investigate the quality of the adjustment. As a result of the method applied the uncertainty contribution originating from the cosine error could be reduced drastically for the interferometer used.     

Gauge Blocks – A Zombie Technology

Gauge blocks have been the primary method for disseminating length traceability for over 100 years. Their longevity was based on two things: the relatively low cost of delivering very high accuracy to users, and the technical limitation that the range of high precision gauging systems was very small. While the first reason is still true, the second factor is being displaced by changes in measurement technology since the 1980s. New long range sensors do not require master gauges that are nearly the same length as the part being inspected, and thus one of the primary attributes of gauge blocks, wringing stacks to match the part, is no longer needed. Relaxing the requirement that gauges wring presents an opportunity to develop new types of end standards that would increase the accuracy and usefulness of gauging systems.     

High-resolution laser speckle correlation for displacement and strain measurement

A laser speckle correlator with high optical magnification is presented, and its performance in the measurement of strain is demonstrated experimentally. Two separated areas on a test specimen are illuminated with laser beams, and displacements of each area are measured by performance of laser speckle correlation on successive magnified images. The interplay of magnification, lens aperture, surface roughness, pixel spacing on the CCD array sensor, and the attainable precision of correlation are investigated theoretically and experimentally. Resolutions that are usually considered accessible only to interferometric techniques are achieved: displacement resolutions of less than 50 nm and strain measurements of less than 10 mustrain across distances of the order of 10 mm are demonstrated. At high magnification, speckle decorrelation due to out-of-plane displacement becomes a stringent restriction, and surface height correlation effects may limit speckle contrast and broaden speckle correlation peaks.     

Measurement of absolute distance employing a tunable CW dye laser

With a tunable CW dye laser oscillating in a single longitudinal mode, measurement of an absolute distance is demonstrated with the method of excess fractions. Five beams which have different wavelengths are emitted sequentially from the dye laser, and the interferometric phase is measured for each wavelength. An interferometric order number for a wavelength can be calculated from values of wavelengths and phases. Then a precise value of length is obtained. This method is similar to measuring distances by using group delay as used in VLBI and microwave ranging. The measured accuracy was within ±8.8 nm between 0 and 10 mm (at an absolute distance of 0.1-10.1 mm)     

动态流导法真空校准装置的性能测试

介绍了动态流导法真空校准装置的校准原理、校准方法,测试了性能指标,校准了分离规和磁悬浮转子规.实验结果表明,校准范围为(2.6×10-7～2.4×10-1)Pa,不确定度小于1.4%,磁悬浮转子规的校准结果与德国PTB的校准结果的一致性好于1.6%.     

大距离运动的直线度测量

机床轴沿轴向运动的直线度是最重要的性能指标.描述了不同的直线度测量方法(直尺法、钢丝绳法、激光干涉仪法、局部垂直度测量及球板和球杆法等),并讨论了这些方法对测量移动长度超过2000 mm的机床的适用性.详细叙述了无重叠的球板拼接,估计了测量的不确定度,测量结果不确定度U为3.4μm(因子κ=2).给出了减小主要影响测量不确定度,也就是影响机床轴重复性的主要因素的一些可能性.示出了500mm×500mm球板拼接测量,并且和轴向移动量900mm的比较仪进行了比对,两种测量结果的偏差小于0.6μm.因此不会超出原有的测量不确定度范围.球板拼接法也可应用于大距离移动中的垂直度测量.无论是利用垂直平面进行测量或者用近来引进的精密三维机床检测,无重叠的球板拼接均可用于水平和垂直的直线度测量,还可用于定位、倾斜、俯视及偏转等方面的测量.     

Measurement of surface strains in GRP products

Current work on fibre composite materials required the measurement of surface strains on glass reinforced plastics (GRP) products subjected to static loading. A study undertaken to account for anomalous results obtained with electrical resistance strain gauges showed that strains measured at a given load, increased with decreasing gauge length and foil gauge resistance. Measurement of localised strains using gauges of length up to 25 mm are subject to considerable discrepancy when compared with gauge lengths of less than 13 mm.     

100 mm一等量块自动测量仪测量不确定度评定

分析了100mm一等量块自动测量仪的误差来源，确定了测量量块的合成标准不确定度和扩展不确定度。     

Interferometric measurement of phase change on reflection

We show an interferometric method for measuring phase change with known uncertainty. Because this measurement uses the backreflection from a sample, the height is intrinsically removed, and only the phase change is measured. The uncertainty in the phase change measurement is +/-3.8 degrees and is dominated by the background subtraction method. We also investigate the effect of the phase change on the interferometric radius measurement. The theoretical worst-case error in the interferometric radius measurement due to the phase change is 30 nm.     

Differential wavelength-scanning heterodyne interferometer for measuring large step height

An interferometer based on the differential heterodyne configuration and wavelength-scanning interferometry for measuring large step heights is presented. The proposed interferometer is less sensitive to environmental disturbances than other interferometers and can accurately measure interference phases. A tunable diode laser is utilized to illuminate the interferometer and thus solve the phase ambiguity problem. Counting the interference fringes as the wavelength is scanned through a known change in wavelength directly determines the step height. Three gauge blocks of different lengths, 5, 10, and 50 mm, are individually wrung on a steel plate to simulate large step heights. Comparing the results measured by the proposed interferometer with those by the gauge block interferometer reveals that the accuracy is approximately 100 nm.     

Determination of absolute emission cross sections for electron-impact-induced line radiation in the vacuum ultraviolet

A method and an experimental setup have been developed for measuring absolute photoemission cross sections for electron-impact-induced line radiation in the vacuum ultraviolet (VUV). Unparalleled low uncertainties for the cross sections were achieved mainly from the use of the Berlin electron storage ring as a primary standard source in the VUV for the determination of the responsivity of the spectrometer-detector system used and from the use of a spinning rotor gauge as a secondary standard for the determination of the target gas density. As the first result we present a photoemission cross section for the Ar II 3s3p(6)(2)S(?)-3s(2)3p(5)(2)p?(3/2) transition at 91.98 nm for 2-keV electron-impact energy of 1.167 × 10(-18) cm(2) with a relative uncertainty of 4.4% (√3σ value). This low uncertainty demonstrates the suitability of the setup for further cross-section measurements.     

陶瓷量块的研制

介绍了氧化锆精细陶瓷材料性能及二氧化锆陶瓷量块的优点 ,重点介绍了陶瓷量块的主要技术参数的检测结果 ,陶瓷量块的高硬度、耐磨损、不锈蚀和氧化、线膨胀系数接近于钢、尺寸稳定、研合性好、易维护的特性使之有着良好的市场发展前景。     

MEASURING STRAINS UNDER WELDS BY THE MOIRÉ FRINGE TECHNIQUE

A method of measuring strains very close to weld deposits has been developed using moiré fringe technique and mismatch gratings. It is necessary to compromise between accuracy and gauge length, but an accuracy of 100μin/in (-10^-4) can be achieved with a gauge length of 0.2 in (5mm). Strains parallel to the weld deposit can be measured right up to the fusion line, but in the direction normal to the weld deposit the first strain reading is controlled by the gauge length, as defined by the distance between successive fringes.     

Equipment for highly accurate and repeatable strain gauge factor determination

Special beams for gauge–factor calibration are bent under four–point loading in a rig with less than ±0–02% asymmetry and less than 0–1 µmUm/m strain perturbation. Inductive extensometers with spherically pointed pins at 10 mm (0.394 in) gauge length, calibrated under test conditions by laser interferometry, are placed next to the gauge to eliminate the effect of variations in the value of Young's modulus along the beam. Careful determination of the 2S (two standard deviations) values for the accidental errors of all the quantities affecting the measured gauge factor shows that the sum of the 2S–values is ±0.35%, perhaps ±0.25%, whereas the corresponding RMS value is ±0.15%, perhaps ±0.10%. A method is shown to account for the systematic errors.