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In order to measure the plant leaf area conveniently and quickly in an indoor laboratory and outdoor field, a set of scaffold leaf area measurement systems was designed and manufactured. A 2D in situ method for measuring plant leaf area with camera correction and background color calibration was proposed. The method integrates three subalgorithms: fast calibration and distortion correction algorithm, background color calibration algorithm, and edge error correction algorithm. At the same time, the Visual Studio 2015 and OpenCV 3.4.0 were used to develop and test the algorithm. In order to verify the measurement speed and environmental adaptability of the system, the test was carried out in the complex light disturbance outdoors, and the results were consistent with those in the room. In order to verify the measurement accuracy of the system, this method was used to measure the standard rectangular gauge block of known area and the real leaf area, respectively, and its data were compared with the data measured by Wanshen LA-S plant image analyzer. The results show that both methods have a good stability, and the algorithm proposed in this paper performs better in measurement accuracy and environmental adaptability.

Line structured light systems have been widely applied in the measurement of various fields. Calibration has been a hot research topic as a vitally important process of the line structured light system. The accurate calibration directly affects the measurement result of the line structured light system. However, the external environment factors, such as uneven illumination and uncertain light stripe width, can easily lead to an inaccurate extraction of light stripe center, which will affect the accuracy of the calibration. An image analysis-based framework in the calibration process was proposed for the line structure light system in this paper. A three-dimensional (3D) vision model of line structure light system was constructed. An image filtering model was established to equalize the uneven illumination of light stripe image. After segmenting the stripe image, an adaptive window was developed, and the width of the light stripe was estimated by sliding the window over the light stripe image. The light stripe center was calculated using the gray centroid method. The light plane was fitted based on the calibration points coordinates acquired by the camera system. In the measurement experiment of standard gauge block width, the maximum and minimum average deviations of 0.021 pixels and 0.008 pixels and the maximum and minimum absolute deviations of 0.023 pixels and 0.009 pixels could be obtained by using the proposed method, which implies the accuracy of the proposed method.

The example 9.5 from JCGM-SI “Gauge block calibration” with a nominal length of 50 mm by the comparison method using a comparator and a reference measure of the same nominal length and the same material as the original standard is analyzed. In JCGM-SI compares the procedures for uncertainty evaluation, performed on the basis of the law of propagation of uncertainty (GUM) and the Monte Carlo method. The report uses the procedure developed by the authors, which consists Taylor-series expansion of the measurement model into a second-order series taking into account the kurtosis of input quantity distributions. To facilitate engineering calculations, the finite increment method is used. The excess method is used to find the expanded uncertainty. The good agreement of the results obtained by the proposed method with the results obtained by the Monte Carlo method is shown.

A calibration pattern with linear light method for profile vision measurement is proposed. A plan for calibration pattern is made which of the pattern pins can fold back to pattern plate in accordance with rows separately. The unfolding pattern pins are photographed with linear light crossing that vertically one row at a time. The mathematical expression of transforming physical plane into pixel plane is derived by physical coordinates and pixel coordinates. With the least-square method the calibration coefficient is made. The method is validated through the means that magnetic gauge block used as a higher precision measurement standard is close to the profile. The experiment indicates that it is avoided that the pattern pins from different rows interrupt the linear light, and the profile measurement error is better than 0.2 mm.

A simple technique for measuring the phase change on reflection with application to gauge block calibration is presented. The proposed technique measures the optical constants of the steel gauge block and the auxiliary platen which is made of fused silica using polarized light. The presented method considers the principal angle of incidence method and avoids the deviation of the quarterwave plate from exact λ/4 value. The phase change angle could be determined with high accuracy (±2o) and the uncertainty contribution of the phase change correction in the gauge block calibration could be reduced to (± 2 nm). The resulted phase change correction value was compared to the value obtained by interferometry using the stack method. The presented method is proposed to be convenient with the contactless measurement of gauge block length using the double ended interferometer

Absolute length calibration of gauge blocks traceable to the definition of meter is an important task of the national metrology institutes responsible for providing reliable length artifacts for industrial use. The length of a gauge block (henceforth, represented as GB) is defined in ISO 3650 as the distance between its one measuring face and the surface of an auxiliary platen on which the other measuring face has been wrung. Accordingly, in central length calibration of K-grade GBs using interferometry, it is required that they be wrung onto an auxiliary platen whose characteristics are the same as the measuring face of the GBs. According to this definition, the length of a GB consists of its mechanical length between two faces and the wringing film thickness. This definition is practical and reasonable in many cases because GBs are used as length standards with wringing. Also this calibration method has the advantage that the thickness of the wringing film is propagated appropriately when lower grade GBs are calibrated by comparison to higher grade GBs via a mechanical comparator. In terms of this paper is briefly described interferometry method of gauge blocks calibration. The paper was written in conjunction with Czech Metrology Institute.

Gauge block plays an important role in dimensional metrology as a standard for calibration. There are several techniques to calibrate gauge block, one of which is an optical method, such as, Michelson interferometer. The interference pattern is recorded for gauge block comparison. The stability of light source is important for the calibration. In this work, we developed a reliable constant current control circuit of 7 mW laser diode for the gauge block interferometer with a closed-loop feedback temperature control, which utilized the advantage of an embedded system. A PID controller was used to maintain the temperature at 25.0 °C within ± 0.5 °C of uncertainty. We tested the system for 60 minutes by monitoring the stability of the laser wavelength. The results showed that the wavelength of the laser was unstable during the first 20 minutes before becoming constant at 655.525 nm.

Double-ended interferometry has several benefits over single-ended gauge block interferometry: there is no need for wringing, which wears surfaces and requires expertise, and there is improved repeatability, since there is no variation due to inconsistent wringing conditions or form errors of the gauge block surfaces. Some disadvantages of double-ended interferometry are that absolute phase change correction is needed for the gauge block and its uncertainty has a double effect on total uncertainty. In addition, elimination of the wavefront error is more complicated than with single-ended interferometry. A simple optical modification that enables double-ended interferometer (DEI) measurements with the MIKES interferometer for long gauge blocks is presented. This modification is applicable to almost any single-ended interferometer (SEI). A procedure for evaluating the wave front correction for different parts of the interferogram of DEI is explained, and a modification and software with capability for nine-point phase stepping is presented. Three independent methods for evaluation of the phase correction were studied. One of them uses integrating sphere for the surface roughness correction and literature values for the phase change due to complex refractive index of material correction. The second evaluates the phase correction from the difference between DEI and SEI results obtained with a quartz platen. The third uses differences-from separate measurements-between the results obtained with quartz or steel auxiliary platens. Only a few gauge blocks per set need testing to obtain phase correction. SEI and DEI results with different phase correction determination methods are presented and evaluated. The uncertainty estimate for gauge block calibration with DEI gives a similar standard uncertainty to that with the best SEIs, u = (10.0 nm)2 + (118*10-9L)2 .

Metrologists at the National Institute for Standards-NIS (Egypt) develop length measuring devices to provide reliable and less expensive metrological systems for accurate measurement. Length Laboratory Group investigates the sources of errors in the absolute measurement of length using the improved Abbe vertical metroscope. The investigation includes analyzing of errors induced by optical alignment, environment, and instrument. Errors due to environment and vibration are reduced by controlling the area in which the technique is placed. The instability in the readings caused by temperature fluctuations is handled by averaging 1000 points/sec. To ensure ideal contact between the probe of the comparator and the surface of the artifact, holographic technique is used in testing the uniformity of the probe at the area of contact. Other factors influencing the measurements such as material expansion of the artifact and optical source used in the measurement are considered in the uncertainty evaluation. The uncertainty in the absolute measurement of gauge block length of 80mm is found to be ±0.2µm. The results of measuring some pieces using the absolute method are in good agreement with the corresponding reference values given in their calibration certificate.

Empirical estimation of uncertainty in dimensional metrology is a vital part in calibration processes. Uncertainty estimation in gauge block measurement mainly depends on three major areas, thermal effects, dimension metrology system that includes measurement strategy, and end standard surface perfection grades. This paper focuses precisely to estimate the uncertainty due to the geometrical imperfection of measuring surfaces and wringing thickness U ( L g +L w ) in calibration of end standards grade 0. An optomechanical system equipped with Zygo interferometer and AFM techniques have been employed. A novel protocol of measurement covering the geometric form of end standard surfaces and wrung base platen was experimentally applied. Surface imperfection characteristics of commonly used 6.5 mm GB have been achieved by AFM in 2D and 3D to be applied in three sets of experiments. The results show that there are obvious mapping relations between geometrical imperfection and wringing thickness of the end standards calibration. Moreover, the predicted uncertainties are clearly estimated within an acceptable range from 0.132 to 0.202 µm respectively. Experimental and analytical results are also presented and discussed.

Connecting rod is often in high speed movement as one of the main parts of automobile engine. It’s shape error and accuracy of the hole or the plane will directly influence the working performance and the service life of engine. So the production has very strict requirements on the shape error. Connecting rod standard gauge block, as a standard part of manufacturing connecting rod, it’s manufacturing accuracy is higher, and the measurement and calibration of error directly affects the machining efficiency and the precision of the connecting rod. CMM develops so fast that constantly pounding all kinds of special measuring equipment. In the contact, a digital measurement is carried out for the key dimension and the space shape error of connecting rod standard gauge block. so data processing of the measuring results has been obtained, then reconstructed geometry elements of the plane and round hole ,etc., and got the required shape error by the contact CMM, it provides the basis for improving machining precision of the connecting rod.

A simple method for reducing the uncertainty of reference standards has been proposed for gauge block comparator calibration. Errors due to the reference value of the length difference for mechanical comparator evaluation can be reduced by using the average of two reference values. Two reference values of length difference are obtained by the appropriate combination of three gauge blocks. Errors caused by reference gauges are canceled and averaged. An error reduction effect was successfully demonstrated using an actual mechanical comparator.

In order to realize precision measurement for the computer vision measurement system, a system comprehensive calibration method based on straight line imaging characteristics is proposed. The method uses parallel straight line edges of general 00 level gauge groups to comprehensively calibrate the measurement system. It establishes the calibration function that describes the corresponding relationship between the imaging point location and space point position, and then determines the coefficient of the calibration function according to the linear characteristic of gauge block measurement surface edges imaging. This method is simple to operate and is easy to realize and has good versatility. It can comprehensively correct all kinds of system errors such as the optical distortion, the perspective error, the sensor position error and location error of edge detection algorithm. Repeated measurement experiments for the gauges show that the precision of the measurement system can reach by means of this calibration method.

In the transportation industry, especially in the shipbuilding process, 3D surface measurement of large-scale hull pieces is needed for fabrication and assembly. We suggest an efficient method for checking the shape of curved plates under the forming operation with short time by measuring 3D profiles along the multi lines of the target surface. For accurate profile reconstruction, 2D camera calibration and 3D calibration using gauge blocks were performed. The evaluation test shows that the measurement accuracy is within the boundary of tolerance required in the shipbuilding process. Keywords: 3D profile measurement, multi-slit beams, 2D camera calibration, 3D calibration, gauge block I. 서론 선박, 항공기, 자동차로 대표되는 운송기 제조분야에 형상정밀도를 요구하는 대형구조물의 제작이 요구된다. 특히 후판(thick plate)을 소성변형시켜 물리적 결합을 하는 선박제조 공정에서는 추가 소성변형량을 결정하기 위해 중간재의 형상을 주기적으로 측정하여야 하는 필요가 요구된다. 아직도 대부분의 선박제조 현장에서는 그림 1과 같이 목형 템플릿(wooden template)를 이용해 곡판의 깊이를 목측으로 측정하는 것이 현실이지만, 점차 측정자동화를 위한 노력을 진행 중에 있다. 대형 곡판의 형상 측정에서 고려해야 할 사항으로는 첫째, 성형 중 실시간 측정을 통해 추가로 요구되는 성형량을 빠르게 결정할 수 있어야 한다. 둘째, 측정 대상이 대형구조물이므로 측정장비가 가능한 간단한 구조를 가져야 한다. 셋째, 수 미터 크기의 전체 형상에 대해 수 밀리미터 수준의 측정 정밀도를 만족시켜야 한다. 넷째, 기존 전통적인 측정방식인 목형 템플릿 사용법에서 알 수 있듯이 일련의 가로방향 형상 측정만으로도 곡판의 형상 특징을 결정할 수 있다[1]. 대형 곡판의 형상측정을 위해 사용 가능한 상업용 장비는 3차원측정기(CMM: Coordinate Measuring Machine), 레이져트랙커(LTS: Laser Tracking System) [2], 위성항법장치(GPS: Global Positioning System) [3,4] 등이 있다. 이들은 모두 공간상에 존재하는 한 점의 좌표를 정밀하게 측정하는 것을 목적으로하는 상업용 측정장비로서 가공 중 대형가공물의 형상에 대해 실시간 측정이 불가능하고, 고가인 단점이 있다. 따라서 상기 요구조건들을 만족시킬 수 있는 특성화된 머신비젼이 필요한데, 이는 다수의 슬릿빔광원(multi-slit beam)과 1대의 카메라를 이용해 구성할 수 있다. 다중 구조광(structured beam)을 이용한 사례에서 물체의 3차원 정보를 획득하기 위해 다른 파장광, 원패턴[5] 또는 일련의 렌즈군을 사용한 경우[6]가 있었으나 선박 곡판측정에 적용하기에는 복잡한 측정법과 장비구조를 가지고 있다. 머신비젼에서의 보정과정(calibration process)은 2D, 3D 측정의 성공을 좌우하는 필수요소이다. 특히 측정 대상물이 형상 정밀도를 요구하는 가공 중간재 또는 완성품인 경우, 가공의 성패는 보정 정밀도와 깊은 연관을 가진다. 실좌표계(real-world coordinates)상에 존재하는 물체의 형상은 빛이라는 매개체를 통해 카메라의 스크린 좌표계(screen coordinates)로 변환(mapping)하는 과정을 거치게 된다. 이 과정에서 실좌표계 상에 존재했던 물체의 형상정보는 스크린 상에서 화소수(number of pixels)라는 이질적인 정보로 변경된다. 따라서 두 좌표계 사이의 상관관계를 결정짓는 과정이 요구되며 이 과정을 보정과정이라 정의한다. 이상적으로는 결상렌즈의 배율로써 두 좌표계 사이의 상관관계를 정의할 수 있지만, 실제적으로는 결상된 영상의 영역에 따라 배율이

This is a study of the measurement system capability and analysis of a gauge block comparator aimed at improving the quality requirements of calibration instruments that ensure system stability. The total variance of measuring instruments includes the following: different measuring environments, precision of measuring equipment, the experience of the measuring staff, and the specifications of the workpiece. The source variations must be converted into data and charted to show the measuring capability of the system.The main items in a measurement system analysis are the following: stability, bias, linearity, repeatability, and reproducibility. Different experimental models are designed according to different characteristics. After running the data, we can evaluate the data using statistical methods which include the following: hypothesis test, one-sample t-test, two-sample t-test, linear regression analysis, and analysis of variance (F test). We then use statistical software (MINITAB) to do a relia...

Uncertainty in gauge block measurement depends on three major areas, thermal effects, dimension metrology system that includes measurement strategy, and end standard surface perfection grades. In this paper, we focus precisely on estimating the uncertainty due to the geometrical imperfection of measuring surfaces and wringing gab in calibration of end standards grade 0. Optomechanical system equipped with Zygo measurement interferometer (ZMI-1000A) and AFM technique have been employed. A novel protocol of measurement covering the geometric form of end standard surfaces and wrung base platen was experimentally applied. Surface imperfection characteristics of commonly used 6.5 mm GB have been achieved by AFM in 2D and 3D to be applied in three sets of experiments. The results show that there are obvious mapping relations between the geometrical imperfection and wringing thickness of the end standards calibration. Moreover, the predicted uncertainties are clearly estimated within an acceptable range from 0.132 µm, 0.164 µm and 0.202 µm, respectively. Experimental and analytical results are also presented.

This paper shows the result of work of the Institute of Micromechanics and Photonics at Warsaw University of Technology and the Length and Angle Division of Central Office of Measures (GUM) [1] in building an automatic multiwavelength interferometric system with extended measurement range for calibration of long (up to 1 m) gauge blocks. The design of a full working setup with environmental condition control and monitoring systems, as well as image analysis software, is presented. For length deviation determination the phase fraction approach is proposed and described. To confirm that the system is capable of calibrating gauge blocks with assumed accuracy, a comparison between the results of 300 mm length gauge block measurement obtained by using other systems from the Central Office of Measures is made. Statistical analysis proved that the system can be used for high precision measurements with assumed standard uncertainty (125 nm for a length of 1 m). Finally the comparison between our results obtained for a long gauge block set (600 mm to 1000 mm long) and previous calibrations made by the Physikalisch-Technische Bundesanstalt (PTB) [2] is shown

This paper presents a method implemented in a system for automatic contactless calibration of gauge blocks designed at ISI ASCR. The system combines low-coherence interferometry and laser interferometry, where the first identifies the gauge block sides position and the second one measures the gauge block length itself. A crucial part of the system is the algorithm for gauge block alignment to the measuring beam which is able to compensate the gauge block lateral and longitudinal tilt up to 0.141 mrad. The algorithm is also important for the gauge block position monitoring during its length measurement.

The question of traceability of measurement standards used for calibration is a crucial one. Optimized or not, calendar periodicity is one of the accepted pillars of quality in measurement standard verification. Aware that this practice by itself cannot guarantee the metrological performance of measurement standards, laboratories make a point of also resorting to monitoring. In fact, calibrating independent and diverse instrumentation should of itself provide the means to detect problems with the reference gauges. Indeed, there is no logical reason why a collection of independent measurement instrumentation should, on average, have a common bias. If such a bias were observed, it would most likely point to a bias in the reference gauge used for the calibrations. In this paper, this argument is investigated with reference to a practical example of gauge block calibration.

This paper presents a contactless method for gauge blocks calibration combining laser interferometry and low-coherence interferometry. In the presented system, the contactless measurement of the absolute gauge block length is done as a single-step operation without any change in optical setup during measurement, giving complete information about the gauge block length. The paper also presents a set of optimization steps which have been done in order to transform the original experimental setup into the automatic system which meets legal length metrology requirements. To prove the measurement traceability, we conducted a set of gauge block length measurement comparing data from the optimized system and the established reference systems TESA NPL A.G.I. 300 and TESA–UPC operated in Czech Metrology Institute laboratory.

Load and age of rails can result in problems such as breakage, depletion, and expansion that can lead to accidents. Rail inspection has been done manually by operator tracing the rails by walking or riding a special inspection vehicle. These methods obviously are inefficient and inaccurate, as operators might be missing some of the defects. In this research depletion detection of rails are conducted by analyzing changes of the area as well as position shifting of laser spot on captured images by utilizing the triangulation principle. Accuracy and efficiency improvement of rail inspection are expected from this method. Prior calibration of the system was conducted using gauge blocks with thickness varying from 19 to 1 mm with 1 mm decrement. Area changes and position shifting of laser spot are later analyzed through image processing. The system was also implemented on R-54 rail type based on the calibration and later be compared to the manual measurement data. It was shown that the system can detect depletion in rail type R-54. The calibration result shows that the deviation percentage of the measurement of laser area are ranging from 11.41% to 13.48% while for the measurement of laser spot position shift is from 6.91% to 8.80%. Implementation on rail type R-54 shows the deviation percentages between proposed method and manual measurement are ranging from 1.52% to 10.04% for the area measurement, while for the position shifting ranged from 1.11% to 12.68%.

In this paper, a novel principle of contactless gauge block calibration is presented. The principle of contactless gauge block calibration combines low-coherence interferometry and laser interferometry. An experimental setup combines Dowell interferometer and Michelson interferometer to ensure a gauge block length determination with direct traceability to the primary length standard. By monitoring both gauge block sides with a digital camera gauge block 3D surface measurements are possible too. The principle presented is protected by the Czech national patent No. 302948.

The mounting eccentric error is one of the largest error sources for circular grating angle sensors (CGASs). To improve the measuring accuracy of CGASs, one error compensation method based on mounting eccentricity is proposed in this paper. The mounting eccentricity and measuring error of CGASs was modeled after analysis. Six joints mounted with CGASs were used in the eccentric error compensation experiment. The rotation error of the joints was calibrated with a coordinate measuring machine and a gauge block. Then with the calibration data, the parameters of the eccentric error compensation model were calculated. The experimental result shows that after error compensation the rotation angle errors of the joints are reduced about 58 to 543 times.

In ISO/IEC Guide 99:2007, i.e. the International Vocabulary of Basic and General Terms in Metrology-3rd edition (VIM 3), the term “traceability” is replaced by “metrological traceability”, giving it a new definition as property of a measurement result which can be related to a reference. In essence, “metrological traceability” can offer an evidence of measurands tracing to the primary standards which can realize the SI units, and offer a documented unbroken chain of calibrations, thus considered as one of the most important terms in VIM 3. National Measurement Laboratory (NML, Chinese Taipei) has long operated its main mission of calibration implemented along with peer assessed traceability of its measurement systems, which demonstrate a calibration hierarchy conventionally in schematic approach. In dealing with definition of the new term “metrological traceability” in VIM 3, this paper elaborates in taking additionally a newly mathematical approach rather than schematic approach only to realize the practical interpretation of “metrological traceability” to show how the unbroken calibration chain is functioning seamless and robust on the gauge block measurement system in NML. Through such study activities, we well assure our strong confidence on technology inheritance of gauge block and the other measurement systems with sufficient metrological know-how in NML, which can continually pass to each entry level metrologist.

The requirement of improved certainties in the measurement of the diameter and the form of cylindrical artifacts is increasing day-by-day. Such requirements become indispensable in typical applications, like the inspection of the fuel injection systems and calibration of pressure balances. A new experiment is set to measure the diameter of a cylindrical artifact, particularly the piston of a pressure-measuring device. Three displacement sensors are used to scan the cross-section of a cylinder and a reference gauge block. At the same time, the scanning process is simulated for ideal conditions. The coordinate data thus obtained in the scanning is fused on to a circle. The misalignments in the experimental setup are refined by iterative scanning the artifacts under test until the experimentally obtained surface profiles match with the simulated ones. Then, the fused circle represents the diameter of the cylindrical object. According to substitution technique, the deviation of the diameter of the artifact under test is determined from the size of the gauge block. Finally, the expanded measurement uncertainty is estimated.

In this paper, a 3D artifact is proposed to calibrate the kinematic parameters of articulated arm coordinate measuring machines (AACMMs). The artifact is composed of 14 reference points with three different heights, which provides 91 different reference lengths, and a method is proposed to calibrate the artifact with laser tracker multi-stations. Therefore, the kinematic parameters of an AACMM can be calibrated in one setup of the proposed artifact, instead of having to adjust the 1D or 2D artifacts to different positions and orientations in the existing methods. As a result, it saves time to calibrate the AACMM with the proposed artifact in comparison with the traditional 1D or 2D artifacts. The performance of the AACMM calibrated with the proposed artifact is verified with a 600.003 mm gauge block. The result shows that the measurement accuracy of the AACMM is improved effectively through calibration with the proposed artifact.

Biometric analyses of quantitative traits in eyes of mice can reveal abnormalities related to refractive or ocular development. Due to the small size of the mouse eye, highly accurate and precise measurements are needed to detect meaningful differences. We sought a non-contact measuring technique to obtain highly accurate and precise linear dimensions of the mouse eye. Laser micrometry was validated with gauge block standards. Simple procedures to measure eye dimensions on three axes were devised. Mouse eyes from C57BL/6J and rd10 on a C57BL/6J background were dissected and extraocular muscle and fat removed. External eye dimensions of axial length (anterior-posterior (A-P) axis) and equatorial diameter (superior-inferior (S-I) and nasal-temporal (N-T) axes) were obtained with a laser micrometer. Several approaches to prevent or ameliorate evaporation due to room air were employed. The resolution of the laser micrometer was less than 0.77 microns, and it provided accurate and precise non-contact measurements of eye dimensions on three axes. External dimensions of the eye strongly correlated with eye weight. The N-T and S-I dimensions of the eye correlated with each other most closely from among the 28 pair-wise combinations of the several parameters that were collected. The equatorial axis measurements correlated well from the right and left eye of each mouse. The A-P measurements did not correlate or correlated poorly in each pair of eyes. The instrument is well suited for the measurement of enucleated eyes and other structures from most commonly used species in experimental vision research and ophthalmology.

This paper presents a detailed measurement uncertainty analysis for the calibration of gauge blocks made from like materials using a mechanical comparator consisting of opposing styli and a digital readout. After discussing the influence parameters affecting the calibration process, a mathematical model is developed that leads to a measurement equation relating the length of the client's gauge block to measurements of the standard gauge block and associated temperature corrections. Following the ISO “Guide to the Expression of Uncertainty in Measurement,” all of the uncertainty components and their sensitivity components are calculated. These components include factors related to the calibration of the standard, the measured difference between the client's gauge and the standard gauges, and various temperature differences. After discussing a specific measurement process in a typical laboratory environment, all of the uncertainty components are quantified and then combined in quadrature. The resul...

Vertical metro-scopes using Abbe’s principle AVM are used for different dimensional measurements. The accuracy of their measurement is low compared to other available techniques used in the calibration of gauge blocks. This uncertainty can be improved through the use of laser interferometer system in combination with it. This paper describes the improvement, the results of the calibration of a set of gauge blocks and the uncertainty budget for such a calibration. The uncertainty of such calibration is estimated to be within ± (0.06+L/650) *m; L in mm; for gauge blocks less than 200 mm. An inter-comparison between the results of such improved AVM and the results obtained from one of the gauge block electronic comparators available on the market proved that the differences in the mean results are insignificant.

The proficiency level of the calibration laboratories within a global organization has been evaluated by conducting a series of international round robin measurements. This comparison is carried out every 3 years to maintain the high measuring accuracy. For the proper estimation of measurement, two specimens in the same nominal length in several length gauges are used, and the estimation of measured values is carried out by using the value of En and the Youden diagram at an industrial level comparison. In the first comparison in 1995, almost all results indicate satisfactory coincidence and correlation, although a few results obtained display an unexpected bias due to the assigned value of the reference standard. In the second comparison in 1998, all participating calibration laboratories attain excellent results. The discussion on the results of this study shall contribute to the deeper understanding and performance of the length standard traceability.

This paper presents a method for active angular alignment of gauge block implemented in a system for automatic contactless calibration of gauge blocks designed at ISI ASCR. The system combines low-coherence interferometry and laser interferometry, where the first identifies the gauge block sides position and the second one measures the gauge block length itself. A crucial part of the system is the algorithm for gauge block alignment to the measuring beam which is able to compensate the gauge block lateral and longitudinal tilt up to 0.141 mrad. The algorithm is also important for the gauge block position monitoring during its length measurement.

The machine vision measurement system was established to measure 2D sizes of parts. The 5 Megapixels CCD sensors, bi-telecentric lenses, telecentric back illumination and image acquisition modes were chosen to establish hardware part, according to the requirement of views and precision. The software system was developed to extract the edge of the part from the digital image and transform it to a polynomial curve. The optimal estimation of expected value and the measured value was calculated based on contour tangential continuity, to eliminate the effects of random error. The gauge block set was set on the four quadrants of the visual field, and their edges were extracted. Distortion correction and system calibration was done combining with the distortion model. The actual size of each pixel is 4.584μm after using subdivision, Kalman filter, distortion correction and calibration. Tests and analyses show that the measurement precise is ±3μm class.

An international comparison of gauge block measurements by interferometry has been carried out. The comparison is part of the set of key comparisons established by the Consultative Committee for Length (CCL) and contributes to the mutual recognition of calibration certificates issued by national metrology institutes (NMIs). Eleven laboratories representing the four major metrology regions participated in this comparison, which took place in 1998/1999. The standards to be calibrated were ten steel gauge blocks and ten tungsten carbide gauge blocks with nominal lengths between 0.5 mm and 100 mm. The measurand was the central length determined by optical interferometry, as defined in International Standard ISO 3650. The agreement between the measurement results was satisfactory, the major problems encountered being due to the determination of the corrections, taking into account the different properties of the measurement surfaces and the reference platens. The arithmetic mean was found to be the most adequate method for calculating the key comparison reference values.

The LVDT probe is a very important component used in gauge blocks calibration via a mechanical comparative method. The probe is used to determine the central length difference between a reference gauge block and gauge block under-tested (UTC). Typically, an UTC and a reference gauge block have the same nominal length. However, some gauge blocks UTC are specially made for specific purpose where the reference gauge blocks with the same nominal length are not commercially available. Various reference gauge blocks are wrung in order to provide nominal length the same as that of the UTC. Wringing process is the troublesome step and causes larger measurement uncertainty. The lower accuracy is higher number of gauge block used to create reference gauge block, in order to improve accuracy of measurement, the LVDT probe was used at the longer range where the reference gauge block and the UTC don't need to be the same nominal length. In this paper, characteristics of LVDT probe was investigated as it is related to the accuracy of the measurement result. Errors of LVDT probe came from non-linearity, calibration factor, retrace error, repeatability and maximum difference in length. A pair of gauge block, calculated by the Twyman-Green interferometer, length different range 5 μm to 230 μm was used in the study. Non-linearity of LVDT is evaluated by a simple linear regression model. The non-linearity of LVDT probe, calibration factor, retrace error, repeatability and maximum difference in length are 25 nm, 1.0003, 3 nm, 6 nm and 80 nm, respectively. Therefore, by using this technique, central length difference between the 2 gauge blocks up to 80 nm can be calibrated with the uncertainty due to non-linearity of 15 nm The experiment shows the large error of retrace closes to 0.02 μm at 0.09 μm. This can be determined the maximum difference in length to calibrate gauge blocks at difference nominal lengths. The measurement uncertainty of non-linearity is evaluated and it is close to 15 nm.

In this work we demonstrate how absolute length measurements by interferometry, as used for regular gauge block calibration, can be applied to measure the dimensional drift behavior of connections joined by gluing or screwing and how these joining techniques are influenced by thermal treatment. While it is common to investigate the intrinsic stability of material samples by repeated length measurements, there exist growing demands in precision engineering to characterize the stability of assemblies, i.e. of joined material pieces. In order to enable investigation of joining techniques representative joints were fabricated by a number of methods as wringing, screwing and gluing. By using gauge block shaped samples as joining parts parallelism and flatness could be achieved which is needed for interferometric length measurements. The stability of the joints has been investigated longitudinally and laterally to the connection interface, and also mutual tilting of the parts was detected by analysis of the phase topographies. With the use of sample joints, the behavior of connection elements used in ultrahigh-precision instruments can now be examined on an accuracy level of about one nanometer. Results of approximately one year of observation show that screwed joints do not exhibit a significant change of length or orientation. They also did not show response to temperature variations of ±10°C, which is different for adhesive joints where dimensional changes of up to 100 nm were observed.

The uncertainty of a wavemeter has been evaluated taking into account all contributions. This wavemeter was developed to give traceability to the frequency of external cavity diode lasers. These lasers were stabilized and used as light source in the assembly of a new interferometric system for the gauge block calibration. The wavemeter experimental setup is also presented and is based in a Michelson interferometer, a He-Ne laser used as a reference wavelength and a Vernier counter that allowed us to reduce the uncertainty below 1ppm.

A Michelson wavemeter was developed to test the accuracy and give traceability to the wavelength of external cavity diode lasers. These lasers were stabilized using a Littrow configuration and an iodine gas cell as frequency reference, and they will be used as light sources in the assembly of a new interferometric system for gauge block calibration. Previously, the uncertainty evaluation of the Michelson wavemeter with a Vernier counter had to be made, in which, as it is usual, the counting set starts and stops when the interference phases of the reference and unknown wavefronts coincide.

This paper presents a method for active angular alignment of gauge block implemented in a system for automatic contactless calibration of gauge blocks designed at ISI ASCR. The system combines low-coherence interferometry and laser interferometry, where the first identifies the gauge block sides position and the second one measures the gauge block length itself. A crucial part of the system is the algorithm for gauge block alignment to the measuring beam which is able to compensate the gauge block lateral and longitudinal tilt up to 0.141 mrad. The algorithm is also important for the gauge block position monitoring during its length measurement.