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Two orthogonal least squares methods of the points approximation by a set of parallel planes are presented. Such an approximation can be used to study the measurement details of using a coordinate measuring machine (CMM). A calibrated gauge block and a CMM with a touch measuring probe were used in the experimental verification. A comparison of the different CMM strategies is provided. [ABSTRACT FROM AUTHOR]

This paper describes a diameter measurement method for micro-spheres via coherent scanning interferometry (CSI) with a gauge block as the reference. The CSI system measures the height difference between the sphere and gauge block surface from both the front and back sides; then, the diameter is calculated from the measured heights via CSI and the gauge block length. For the glass sphere measured in this study, the diameter was found to be 270.556 µm with an uncertainty of 0.16 µm (k=2). Interestingly, by selecting a gauge block that matches the sphere diameter, the measurement uncertainty remained virtually unchanged, even for different sphere diameters; the proposed method achieved a relative uncertainty of 10-3–10-4. By utilizing the calibrated reference and the highly sensitive CSI system, and based on the comparator principle, the proposed method enables accurate diameter measurement without requiring specific measurement instruments. [ABSTRACT FROM AUTHOR]

The paper discusses the derivation of an accurate coordinate measuring system consisting of two, three, or four sensors based on the records of four fixed laser triangulation sensors done for a gauge block in movement. Three-dimensional case is considered. In the simulations, using a set of distances quadruplets, parameters of sensors in a local sensors coordinate system are determined through a least squares minimization process using the Differential Evolution approach. The influence of the measurement and rounding inaccuracy on the identification accuracy using numerical simulation methods are assessed.

This paper presents a contactless system for automatic gauge blocks calibration based on combination of 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 the measurement. The optical setup is combined with compact gauge block changer with a capacity of 126-ga blocks, which makes the resulting system fully automatic. The paper also presents in detail a set of optimization steps which have been done in order to transform the original experimental setup into the automatic system which meets secondary 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. [ABSTRACT FROM AUTHOR]

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.

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.

This paper presents the evaluation of the uncertainty for the length measurement of gauge blocks by optical interferometry. In order to improve the gauge block calibration method and to decrease measurement uncertainty the old Zeiss-Kösters gauge block interferometer has been modified and improved by DMDM (Directorate of Measures and Precious Metals of Serbia). The main modification of the interferometer covers introduction of two laser sources, as new wavelength standards, as well as new hardware system and interferometer software, developed to completely automate the calibration process. The validation of the new measurement procedure details the uncertainty budget. The measurement method and model equation, which serves as the basis for the uncertainty evaluation is described. The uncertainty evaluation is performed in accordance with the document JCGM 100:2008-Evaluation of measurement data – Guide to the expression of uncertainty in measurement (GUM).

A compact and inexpensive iodine-stabilized diode laser system with an output at 531 nm has been applied to long gauge block measurements. Although the optical frequency of the output beam was widely modulated (modulation width of ∼22 MHz), the coherence length and interference phase stability are sufficiently long and high, respectively, for the interferometric measurement of long gauge blocks of up to 1000 mm in length. The effective uncertainty of laser frequency in the interferometric measurement was theoretically and experimentally confirmed to be less than 10 −9 . [ABSTRACT FROM AUTHOR]

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 (±2°) 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a micro-coordinate measuring machine (micro-CMM) for large-scale dimensional measurement of a micro-slit on a precision die coater by using a shear-mode micro-probe. A glass micro sphere with a nominal diameter of 52.3 urn was attached on one end of a tapered glass capillary tube as a probe tip ball. The micro-slit width of a slot die coater with a nominal slit width of 85 um was measured by the micro-CMM. The probe tip was placed in the slit for the measurement. The effective working length of the probe was confirmed experimentally to be at least 1 mm. In order to measure the gap width uniformity over the entire slot die length of 200 mm, an air-bearing linear slide with a travelling stroke of 300 mm was employed in the micro-CMM to position the probe along the length direction of the slot die. The angular alignment error and the motion error of the air-bearing linear slide as well as those of the stages for positioning the probe along the direction perpendicular to the length direction of the slot die were investigated for evaluation of the expanded uncertainty of gap width measurement. [ABSTRACT FROM AUTHOR]

This article describes principles and methods of intercomparison measurement (Round-Robin), as well as the results and analysis of the seventh intercomparison measurement of standard length gauge blocks and standard cylinder in Yugoslavia. The analysis emphasizes the problem of correct application of used measurement methods, elaboration and presentation of results, and especially of their uncertainty. In the article the function dependence of reproducibility (uncertainty) and measured length of gauge blocks is given; and therefore the length measurement possibility in range of 100 mm in Metrology System of Yugoslavia based on the seventh intercomparison measurement.

This paper presents a micro-coordinate measuring machine (micro-CMM) for large-scale dimensional measurement of a micro-slit on a precision die coater by using a shear-mode micro-probe. A glass micro sphere with a nominal diameter of 52.3 μm was attached on one end of a tapered glass capillary tube as a probe tip ball. The micro-slit width of a slot die coater with a nominal slit width of 85 μm was measured by the micro-CMM. The probe tip was placed in the slit for the measurement. The effective working length of the probe was confirmed experimentally to be at least 1 mm. In order to measure the gap width uniformity over the entire slot die length of 200 mm, an air-bearing linear slide with a travelling stroke of 300 mm was employed in the micro-CMM to position the probe along the length direction of the slot die. The angular alignment error and the motion error of the air-bearing linear slide as well as those of the stages for positioning the probe along the direction perpendicular to the length direction of the slot die were investigated for evaluation of the expanded uncertainty of gap width measurement.

Abstract: For a national metrology laboratory and holder of national standard for length, capability of performing gauge block calibration by mechanical comparison with lowest possible uncertainty is of highest importance. Uncertainty of gauge block calibration at national metrology laboratory namely enters budgets of uncertainty evaluation of all industrial length calibration laboratories throughout the country. In present paper the uncertainty budget of mechanical calibration of gauge blocks, as a results of extensive analytical and experimental research, is presented in details. Very low measurement uncertainty was achieved and procedure was accredited and entered as Calibration and measurement capability (CMC) into the key comparison database at BIPM. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

The environment parameters, i.e. temperature, pressure, humidity and CO2 concentration affecting the refractive index of air play an important role on the long gauge block measurement using interferometer. In this paper, the environment parameters in a measurement chamber had been continuously investigated more than 24h. The refractive index was then calculated by using an updated Edlén equation. The stability of the refractive index of air in the experiment is 0.1×10−6 with the measurement uncertainty of 4.32×10−8 at the confidential level k =2. While the sensitivity of the pressure of air was small, it was an evidence that the pressure of air mainly contributed to the stability of the refractive index of air due to its large variation. Furthermore, the calculated refractive index of air was employed to correct the length of long gauge blocks. The correction for 1m long gauge block in interferometer system is 0.270mm, 0.269mm and 0.267mm which are respectively based on the three laser wavelengths at 532nm, 633nm and 780nm. [ABSTRACT FROM AUTHOR]

We have developed an interferometer for gauge block calibration based on phase shifting algorithms. The measurement process can provide flatness, parallelism, and length. Wavelength values need to be corrected according to the refractive index of air. This correction is obtained indirectly using Edlén's equation. High-resolution sensors provide the temperature, pressure, and relative humidity readings. To preserve stability, the interferometer is encapsulated in a chamber with active temperature control. Its design, measurement principle, calibration, stability, and reproducibility are analyzed. Since one goal is to employ robust and cheap diode lasers as light sources, we describe the system developed to stabilize a red laser diode using a mode locking technique with a reference gas cell. The instruments and assembly are used to avoid the Doppler effect in the gas cell, which would limit wavelength resolution. Several experiments are carried out to restrict the influence of environmental changes, which affect laser diode frequency. [ABSTRACT FROM AUTHOR]

For a national metrology laboratory and holder of national standard for length, capability of performing gauge block calibration by mechanical comparison with lowest possible uncertainty is of highest importance. Uncertainty of gauge block calibration at national metrology laboratory namely enters budgets of uncertainty evaluation of all industrial length calibration laboratories throughout the country. In present paper the uncertainty budget of mechanical calibration of gauge blocks, as a results of extensive analytical and experimental research, is presented in details. Very low measurement uncertainty was achieved and procedure was accredited and entered as Calibration and measurement capability (CMC) into the key comparison database at BIPM. [ABSTRACT FROM AUTHOR]

As it is know, the gauge blocks sizes should remain within a desired dimensional constancy in time. Many users have reported a change of the dimension of the hardened and aged gauge steel blocks. This dimensional instability has been report as shrinkage, growth or as change from one to the other at different times of measurement. Dimensional stability is a prime requirement for gage blocks, and stability could be affect by the structure and stresses within materials. The used steels have a metastable structure, which has a tendency to martensite transformation with an expected reduction in volume effect. After tempering operations, the phases are also metastable and can transform into bainite upon ageing at room temperature with an increasing effect. Residual stresses can induce in the gauge blocks at room temperature, a growth or shrinkage depending on the sign and orientation of the stress. Several other characteristics and properties are necessary in addition to dimensional stability: a high degree of surface finishing; flatness of surfaces; a parallelism of opposite faces for precise measurements, characteristics that are related to the surface hardness and structure. The coefficient of thermal expansion should be equal to those of high carbon steel. The materials with zero or very low coefficients are the best. Accuracy temperature control is essential and both gauge block and the measured piece must to come to the same temperature. [ABSTRACT FROM AUTHOR]

A novel method of gauge block measurement without wringing onto a glass platen is proposed. By using tandem low-coherence interferometry to perform remote measurements, wringing is rendered unnecessary. To measure its length, a gauge block for measurement without wringing is set several millimeters above a glass platen that is positioned on a triangle interferometer such that the distances between the surfaces of the block and the reflection surface of the platen can be measured from opposite directions. By using tandem low-coherence interferometry with a He-Ne laser as a reference length standard, gauge blocks with nominal lengths of 5, 10 and 75 mm have been measured remotely with an expanded uncertainty of about 86 nm [ABSTRACT FROM AUTHOR]

In this paper we describe the progress we have made in our simultaneous length measurement and the femtosecond comb interferometric spectroscopy in a conventional arrangement with a moving mirror. Scanning and detection over an interval longer than the distance between two consecutive pulses of the frequency comb allow for a spectral resolution of the individual frequency modes of the comb. Precise knowledge of comb mode frequency leads to a precise estimation of the spectral characteristics of inspected phenomena. Using the pulse train of the frequency comb allows for measurement with highly unbalanced lengths of interferometer arms, i.e. an absolute long distance measurement. Further, we present a non-contact (double sided) method of measurement of the length/thickness of plane-parallel objects (gauge blocks, glass samples) by combining the fs comb (white light) with single frequency laser interferometry. The position of a fringe packet is evaluated by estimating the stationary phase position for any wavelength in the spectral band used. The repeatability of this position estimation is a few nanometres regardless of whether dispersion of the arms is compensated (transform limited fringe packet ∼10 fringes FWHM) or highly different (fringe packet stretched to >200 fringes FWHM). The measurement of steel gauge block by this method was compared with the standard method, and deviation (+13 ± 12) nm for gauge blocks (2 to 100) mm was found. The measurement of low reflecting ceramic gauges or clear glass samples was also tested. In the case of glass, it becomes possible to measure simultaneously both the thickness and the refractive index (and dispersion) of flat samples. [ABSTRACT FROM AUTHOR]

We developed a Fabry-Perot etalon to select high-frequency parts of repetition-frequency modes of a short pulsed, mode-locked fiber laser at the wavelength of 1.55 µm. The 2 GHz repetition-modified laser is transmitted to an unbalanced Michelson interferometer with gauge blocks wrung on a platen. Two interference fringes were generated from the gauge block and platen at different positions. The interference fringes have a temporal coherence pattern and can make positioning in space easy. The length of the gauge block was directly determined from different positions of the two interference fringes, without using the excess fractions method. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical comparison calibration of gauge blocks with dissimilar materials at the highest level is not wide spread because bigger national laboratories tend to calibrate non-steel gauge blocks with reference gauge block of like material. For smaller laboratories this is not viable economically due to the high costs of reference gauge block sets. Therefore, steel reference sets are used for calibrating gauge blocks from other materials. Lack of knowledge about material properties is causing a significant rise in calibration uncertainty. In order to improve best measurement capabilities, we have performed extensive research on gauge block material behaviour. For this purpose we have bought sample gauge blocks from all leading producers and evaluated their influences on the uncertainty budget, based on experimental measurements. The uncertainty budget of gauge blocks with dissimilar materials mechanical calibration, as well as the results of analytical and experimental research, is presented in this paper in detail. Significantly smaller uncertainty of gauge block calibration of dissimilar materials is achieved. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Based on dual polarization competition laser, we develop a new height gauge. By inserting a quartz crystal plate into the laser cavity, one laser beam splits into two orthogonally linear polarized laser beams, which appear one after another with the change in cavity length. After detecting their intensities, we obtain two power-turning curves. The longitudinal mode spacing is divided into 4 equal zones and each one has different intensity phenomena, which provides a new method of height measurement. According to experiments, the direct measuring range of this new method is 12mm with resolution of 79.1nm, and the indirect measuring range can be increased using first grade gauge blocks and a liftable platform. Compared to other height gauges such as vernier gauge, inductance sensor and gauge block interferometer, this new instrument has the advantage of self-calibration and simple structure without frequency stabilization system. [ABSTRACT FROM AUTHOR]