Angle Metrology Research Articles

New Application and Research of Ring Laser Gyroscope in the Field of Angle Metrology

New Application and Research of Ring Laser Gyroscope in the Field of Angle Metrology

A novel approach to using artificial intelligence in coordinate metrology including nano scale

The applications of modern length and angle metrology continue to pose new challenges for manufacturers and operators of measuring equipment, starting from nano scale. One method to support measurement processes is the use of artificial intelligence. As an essential part of Industry 4.0 and Metrology 4.0 strategies, it actively supports humans in executing measurement activities. The use of artificial intelligence in this area is determined by technological and social factors, as the shortage of highly skilled operators is becoming increasingly acute. The paper discusses the possibilities of using artificial intelligence in coordinate metrology. Ideas including the selection of the measurement strategy, conditions, filtering techniques, as well as self-verification or even self-calibration were presented. Schemes of procedures using local and global databases of applications and measuring instruments are presented. A new area application in the analysis of interference fringes is shown, with method descriptions and experimental results.

Calibration of angle standards

Main textOptical polygons and angle gauge blocks are the primary artifacts for disseminating the unit of angle to industry. The Consulative Committee for Length (CCL) has designated the calibration of such angle artifacts as a key comparison topic area in order to ensure world-wide traceability and equivalence of angle measurements at the lowest measurement uncertainties. This report describes the key comparison in the topic area of angle metrology for the SIM region. An optical polygon and six angle gauge blocks were measured by five national metrology institutes (NMI). The comparison was successful and the results of the participants are reported. One NMI reported values that were initially inconsistent with the key comparison reference value for the optical polygon.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Measurement of timing belt angle transfer accuracy in angle metrology applications

The use and characteristics of timing belts are well-known for power transmission, but data regarding their suitability for use in dimensional metrology is far less available. In specific applications, e.g., when comparative measurements are wanted, a mechanical system capable of accurate angle transmission is needed. While belt drives offer excellent flexibility and low cost, their absolute accuracy of angle transfer is not widely researched which makes them difficult to use in precision engineering applications. To improve this lack of information, a comparative measurement system with integrated belt transmission was designed and built. The system comprises of two rotary axes, belt tensioning force adjustment mechanism and force measurement stage. Using this system, a standard timing belt was characterized with respect to the angle transfer error, and the relationship between angle transfer error and belt tensioning force was determined. These measurements provide a detailed insight into the key metrological characteristics of a belt drive system.

Generating and measuring pico-radian angles

The angular performance of a nano-angle generator (NANGO) developed at Diamond Light Source has been characterised using a dual-beam laser interferometer designed and built at the National Physical Laboratory (NPL). NANGO is a flexure-based, piezo actuated device which generates milli- to sub-nano-radian angles for the calibration of metrology instruments used to test the quality of synchrotron x-ray mirrors and angular nano-positioning stages at Diamond. The NPL interferometer provides traceability for small angle measurements made by NANGO. An uncertainty budget has been developed for measurements over a 50 nanoradian range. In closed-loop, using feedback from the NANGO’s angle encoder, for the first time we show that 1 nanoradian steps made by NANGO are measurable by an external metrology device. The 200 kHz acquisition rate of the NPL angle interferometer also reveals new dynamic information about NANGO’s angular motion. The NPL interferometer demonstrates that NANGO in open-loop can make: distinct steps of 500 picoradians; sinusoidal oscillations at 0.4 Hz with an amplitude of 125 picoradians; or 1 nanoradian oscillations at 40 Hz. Traceability to the SI though National Metrology Institute instrumentation for NANGO will provide enhanced accuracy for a wide range of angle metrology applications at Diamond, including inputs to deterministic polishing techniques for the creation of next-generation x-ray mirrors and dynamic characterisation of nano-positioning stages.

A comparison of traceable spatial angle autocollimator calibrations performed by PTB and VTT MIKES

Autocollimators are versatile devices for angle metrology used in a wide range of applications in engineering and manufacturing. A modern electronic autocollimator generally features two measuring axes and can thus fully determine the surface normal of an optical surface relative to it in space. Until recently, however, the calibration capabilities of the National Metrology Institutes were limited to plane angles. Although it was possible to calibrate both measuring axes independently of each other, it was not feasible to determine their crosstalk if angular deflections were present in both axes simultaneously. To expand autocollimator calibrations from plane angles to spatial angles, PTB and VTT MIKES have created dedicated calibration devices which are based on different measurement principles and accomplish the task of metrological traceability in different ways. Comparing calibrations of a transfer standard makes it possible to detect systematic measurement errors of the two devices and to evaluate the validity of their uncertainty budgets. The uncertainty levels of the devices are comparable to each other, with an expanded uncertainty U = 0.014 arcsecond (95.5% coverage probability) over a measuring range of ±1000 arcsecond in the case of PTB and U = 0.015 arcsecond over a range of ±500 arcsecond and U = 0.020 arcsecond over ±1000 arcsecond in the case of VTT MIKES. Over a range of ±1000 arcsecond with regards to both measuring axis of an Elcomat 3000 autocollimator as a transfer standard, no statistically significant differences between the calibrations were detected. The results thus confirm the calibration capabilities of PTB and VTT MIKES as stated in the calibration and measuring capability database of Bureau International des Poids et Mesures.

Optimization of crystal phase-matching angle metrology instrument and error analysis

Finding the optimal phase matching angle of a potassium dihydrogen phosphate (KDP) crystal is vital for increasing the harmonic conversion efficiency, which plays a key role in Inertial Confinement Fusion (ICF). The aim of this study was to build and optimize an instrument, which can measure the optimal phase matching angle of a KDP crystal accurately. We designed and tested a new beam path, which made the alignment process much simple. We studied the temperature compensation method and applied it in the instrument. Several methods were used to investigate and reduce the errors of the instrument. The errors from laser energy, transmission unit, alignment system, energy meter, temperature, and environmental vibration were analyzed and optimized. The measurement accuracy of the instrument is 10 μradians in phase matching angle. The instrument had been manufactured and applied well in the laser fusion facility, which can save a lot of time and money.

Precision Angle Measurement Systems on the Basis of Ring Laser Gyro.

The main application of a ring laser gyroscope is navigation. It is currently the most widely used device for strapdown inertial navigation systems. However, it is also applicable for high-precision angle metrology systems. This paper discusses the properties of a laser dynamic goniometer (LDG) based on the ring laser gyroscope and designed for the calibration of optical polygons and digital angle converters, and for the measurement of angles between external mirrors (theodolite operating mode). We consider the main sources of uncertainty, such as the ring laser gyro bias due to an external magnetic field and the instability caused by the velocity of rotation along with applicable methods of their compensation. The reversal method providing separation of uncertainties of the LDG and the calibrated angle converter is analyzed in detail. The simplified cross-calibration method is also considered. The results of calibration of optical encoders of various designs—with and without their own rotors (on-axis and off-axis in Euramet terminology)—are presented. Some results of the dynamic goniometer for the measurement of angles between external mirrors are presented. It is shown that the LDG in this mode of operation demonstrates better accuracy than modern theodolites and total stations.

Frequency induced rotation of high-contrast angular intensity fringes from an uncoated SPP device.

High-contrast angular intensity fringes are generated by reflecting laser light from an uncoated spiral phase plate (SPP) device for the first time, to the best of our knowledge. As the laser frequency going into the device is tuned, the fringes rotate. Measured transverse fringe patterns match their theoretical predicted values. They have unity contrast, and their measured intensity varies with laser frequency in a fashion similar to a Fabry-Perot etalon. This effect can be used to enable new miniature devices for angle metrology, imaging, and microscopy.

Perspektywy współczesnej metrologii

The most up-to-date trends in development of length and angle metrology were presented. This development falls within a concept of Industry 4.0 and is understood as Metrology 4.0. Basic elements of these concepts and their connections were shown during years in relation to consecutive industrial revolutions. Specific issues regarding additive technologies were described with a view to functional filtration. Achievements of coordinate measuring technique in macro scale were also presented including optical scanning and computed tomography. In conclusions standardization works regarding the mentioned topics were described.

Evaluation of measurement uncertainty for a high-precision angle comparator with a vacuum preloaded structure

Angle measurement is widely used in various fields of science and technology. With the development of technology, the measurement uncertainty of angle metrology becomes more and more demanding. To achieve high-precision calibration of a high-precision angle comparator with a sub-arc-second level, a method of angle position error calibration and measurement uncertainty evaluation based on no material reference was established. Firstly, the structure of the angle comparator with a vacuum preloaded air bearing driven by an ultrasonic motor drive and the construction of the whole calibration system are briefly introduced. Then, the basic principle, algorithm and error separation principle of angle calibration based on the optical angle measurement method were studied, and the test process is introduced. Finally, the measurement results and error sources were analyzed, the measurement uncertainty model was established and the measurement uncertainty was evaluated. The experimental results show that the high-precision angle comparator with a vacuum preloaded structure has an angle position error of 0.12″ and a measurement uncertainty of 0.05″ (k = 2). Through many experiments, it is shown that the measurement system has a stable high-precision calibration capability with a sub-arc-second level for circular division artifacts.

A dynamic angle metrology system based on fibre-optic gyroscope and rotary table

A dynamic angle metrology system based on fibre-optic gyroscope and rotary table

A precision crystal phase-matching angle metrology instrument

An instrument has been developed to measure the optimal phase-matching angle of large-aperture potassium dihydrogen phosphate (KDP) crystal. KDP crystal in the frequency converter is applied to generate a third harmonic generation, which is important to achieve inertial confinement fusion (ICF). To achieve high harmonic conversion efficiency, the tuning angle of KDP crystal should be optimal when the frequency converter is working online in ICF facilities. The optimal tuning angle of KDP crystal must be measured off-line before KDP crystal is mounted in the facility. The Crystal Phase-matching angle Metrology Instrument (CPMI) can measure the optimal phase-matching angle and harmonic conversion efficiency of KDP crystal off-line. The CPMI is housed in ISO 5 clean room and several methods are taken to keep the temperature stable. The automatic alignment system is built in the CPMI which makes the measurement convenient and fast. The working posture adjustment system is applied to measure the optimal phase-matching angle when KDP crystal is in the working posture. The integration control system is assisted to measure the phase-matching angle automatically, which can increase the work efficiency immensely. Some experiments are done to test the measuring accuracy. The experiments indicate that the measuring error does not exceed 10 μrad and the repeated accuracy does not exceed 3 μrad. The CPMI can replace on-line measuring of the optimal phase-matching angle, which is economical and time-saving.

Environmental influences on autocollimator-based angle and form metrology.

Deflectometric profilometers are indispensable tools for the precision form measurement of beam-shaping optics of synchrotrons and x-ray free electron lasers. They are used in metrology labs for x-ray optics worldwide and are crucial for providing measurement accuracy dictated by the form tolerances for modern state-of-the-art x-ray optics. Deflectometric profilometers use surface slope (angle) to assess form, and they utilize commercial autocollimators for the contactless slope measurement. In this contribution, we discuss the influences of environmental parameters, such as temperature and air pressure, including their gradients, on high-accuracy metrology with autocollimators in profilometers. They can cause substantial systematic errors in form measurement, especially in the case of large and strongly curved optical surfaces of high dynamic range. Relative angle and form measuring errors of the order of 10-4 are to be expected. We characterize environmental influences by extended theoretical and experimental investigations and derive strategies for correcting them. We also discuss the possibility to minimize the contributions of some errors by the application of sophisticated experimental arrangements and methods. This work aims at approaching fundamental limits in autocollimator-based slope and form metrology.

Digitalizacja powierzchni w aplikacjach mikro, mezo i makro

In the paper a concept of length and angle metrology in fourth industrial revolution known as Industry 4.0 was presented. Problems and conditions as well as limitations connected with measurement possibilities from devices and man point of view were shown. Scale as metrology term with its division to different ranges, i.e. macro, micro and meso were described. For each of these areas digitization and its tasks were presented.

High precision (Advanced) angle metrology: pushing the limits for nanoradian uncertainty demands

Precise angle measuring devices – such as angle encoders, angle interferometers, small angle generators and autocollimators – are extensively used in various applications where high precision is demanded. Recently, an angle metrology project supported under European Metrology Research Programme (EMRP) has been completed. This project has made a significant contribution to traceable angle metrology targeting at nanoradian uncertainty (less than 50 nrad) for stringent demands and achieved milestones. It has provided novel methods, tools, instruments, guides and knowledge that will help to ensure use of precise angle metrology equipment for the demands which have not been answered before. Some of the new devices are already commercially available and have been started to be used for critical needs. This paper gives highlights of the project’s outputs and inform the community about recent developments in high precision advanced angle metrology.

Determination of correct sign in primary angle calibrations

This paper discusses the critical issue of correct sign determination of angle deviations during primary calibration of angle standards and practical realisation of SI angle unit radian. The cases referring to reading direction of angle measuring devices and standards are presented and correct sign determination process is illustrated for primary method, cross calibration. The information should be of use to the laboratories contemplating the establishment of primary angle measurements or high precision angle metrology applications.

Influence of the air’s refractive index on precision angle metrology with autocollimators

In this paper, we discuss a substantial—though previously neglected—error source in precision metrology with autocollimators, specifically, changes in the air’s refractive index, with a focus on the dominant impact of pressure changes. Pressure decreases with increasing elevation above sea level and is subject to substantial variation due to weather changes. It causes changes in an autocollimator’s angle response which are proportional to the measured angle and which increase linearly with the beam length and air pressure. We characterise this important influence in detail by using extended theoretical and experimental investigations and derive strategies for correcting it. We discuss its implications for the comparison of autocollimator calibrations performed at different metrology institutes which is crucial for validating their calibration capabilities. This work aims at approaching fundamental limits in angle metrology with autocollimators.

Investigations of interpolation errors of angle encoders for high precision angle metrology

Interpolation errors at small angular scales are caused by the subdivision of the angular interval between adjacent grating lines into smaller intervals when radial gratings are used in angle encoders. They are often a major error source in precision angle metrology and better approaches for determining them at low levels of uncertainty are needed. Extensive investigations of interpolation errors of different angle encoders with various interpolators and interpolation schemes were carried out by adapting the shearing method to the calibration of autocollimators with angle encoders. The results of the laboratories with advanced angle metrology capabilities are presented which were acquired by the use of four different high precision angle encoders/interpolators/rotary tables. State of the art uncertainties down to 1 milliarcsec (5 nrad) were achieved for the determination of the interpolation errors using the shearing method which provides simultaneous access to the angle deviations of the autocollimator and of the angle encoder. Compared to the calibration and measurement capabilities (CMC) of the participants for autocollimators, the use of the shearing technique represents a substantial improvement in the uncertainty by a factor of up to 5 in addition to the precise determination of interpolation errors or their residuals (when compensated). A discussion of the results is carried out in conjunction with the equipment used.

Angle comparison using an autocollimator

Autocollimators are versatile optical devices for the contactless measurement of the tilt angles of reflecting surfaces. An international key comparison (KC) on autocollimator calibration, EURAMET.L-K3.2009, was initiated by the European Association of National Metrology Institutes (EURAMET) to provide information on the capabilities in this field. The Physikalisch-Technische Bundesanstalt (PTB) acted as the pilot laboratory, with a total of 25 international participants from EURAMET and from the Asia Pacific Metrology Programme (APMP) providing measurements. This KC was the first one to utilise a high-resolution electronic autocollimator as a standard. In contrast to KCs in angle metrology which usually involve the full plane angle, it focused on relatively small angular ranges (±10 arcsec and ±1000 arcsec) and step sizes (10 arcsec and 0.1 arcsec, respectively). This document represents the approved final report on the results of the KC.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).