We report on the development of measurement facilities for the calibration of ultra-precision displacement sensors and for the dimensional stability validation of materials, joint structures and sensors. A Fabry-Pérot interferometer and a double-ended heterodyne interferometer are discussed, both with a dedicated design aiming for sub-nanometer displacement measurement accuracy.
We have investigated the uncertainty sources that affect the traceability of dimensional measurements using the VIScan
of the Zeiss F25 coordinate measuring machine (CMM). Our experimental results on line-width measurements are
promising, having a repeatability below 120 nm and moreover they are reproducible for all light settings investigated.
The comparison with the measurements performed on a facility used for line-scale calibrations provides very good
agreement. At present we can report an uncertainty below 0.45 μm for line-width calibrations. This would be the first
traceable F25 VIScan, and to our knowledge one of the first truly traceable vision systems for line-width calibrations.
A new universal non-contact measurement machine design for measuring free-form optics with 30 nm expanded uncertainty is presented. In the cylindrical machine concept, an optical probe with 5 mm range is positioned over the surface by a motion system. Due to a 2nd order error effect when measuring smoothly curved surfaces, only 6 position measurement errors are critical (nanometer level). A separate metrology system directly measures these critical errors of the probe and the product relative to a metrology frame, circumventing most stage errors.
An uncertainty estimation has been performed for the presented design, including a calibration uncertainty estimation and a dynamic analysis. Machine dynamics certainly cause relative motion between probe and product, but due to the non-contact nature of the measurement and the short metrology loop, these motions do not cause significant measurement errors. The resulting shape measurement error for aspheres up to medium free-forms is between 24 and 37 nm, and 30 - 85 nm for medium to heavily free-form surfaces. The suitability of the proposed design is herewith confirmed. A detailed design and a prototype of the machine are currently being developed.
This paper focuses on the on the design and calibration of an elastically guided vertical axis that will be applied in a small high precision 3D Coordinate Measuring Machine aiming a volumetric uncertainty of 25 nm. The design part of this paper discusses the principles of this system, the compensation of the stiffness of the vertical axis in the direction of motion, the weight compensation method and the design and performance of the axis precision drive system, a Lorentz actuator. In the metrology part of this paper the calibration methods to determine the linearity as well as motion straightness and axis rotation errors are discussed. Finally first calibration results of this axis show nanometer repeatability of the probing point over the 4 mm stroke of this axis. The causes of the short-term variations with a bandwidth of about ± 10 nm are under investigation. Error compensation may reduce the residual error of the probing point to the nanometer level.
KEYWORDS: Digital signal processing, Laser stabilization, Modulation, Human-machine interfaces, Absorption, Photodiodes, Frequency combs, Process control, Signal processing, Iodine cells
We have developed a digital controller to stabilize one of NMi's iodine stabilized helium-neon lasers using the third harmonic technique. The controller is proven to be a suitable replacement of the analogue electronics, as demonstrated by internal comparisons and a calibration against the frequency comb of the Bureau International des Poids et Mesures.
KEYWORDS: Calibration, Monte Carlo methods, 3D modeling, Temperature metrology, Computer simulations, Metrology, Interferometers, Signal generators, 3D metrology, Laser development
In coordinate measurement metrology, assessment of the measurement uncertainty of a particular measurement is not a straight forward task. A feasible way for calculation of the measurement uncertainty seems to be the use of a Monte Carlo method. In recent years, a number of Monte Carlo methods have been developed for this purpose, we have developed a Monte Carlo method that can be used on CMM's that takes into account, among other factors, the auto correlation of the error signal. We have separated the errors in linearity errors, rotational errors, straightness errors and squareness errors. Special measurement tools have been developed and applied to measure the required parameters. The short-wave as well as the long-wave behavior of the errors of a specific machine have been calibrated. A machine model that takes these effects into account is presented here. The relevant errors of a Zeiss Prismo were measured, and these data were used to calculate the measurement uncertainty of a measurement of a ring gauge. These calculations were compared to real measurements.
Nanosensors are a new class of sensors that has recently appeared. These sensors are characterized by nanometer or sub-nanometer resolution over a range of at least several micrometers. The most well known examples are capacitive and inductive sensors but also laser interferometers, holographic scales, and scanning probe microscopes (SPM's) belong to the class of nanosensors. The accuracy of these nanosensors is not necessarily of the same level as the resolution. Effects like sensitivity errors, non-linearity, hysteresis and drift may cause deviations of many nanometers. In order to determine these errors in a traceable way, a new measuring instrument was developed. The heart of the system is a Fabry-Perot interferometer, which consists of two parallel mirrors separated by a distance L from each other. Light of a so-called slave laser is directed into this Fabry-Perot cavity and stabilized to the cavity length L. When one of the mirrors of this cavity is displaced the frequency of the slave-laser will follow its movement. The frequency of this slave-laser is then compared to the frequency of a primary length standard. In this way the displacement of the mirror is measured. When a nanosensor is placed on top of the mirror it will also follow the movement of the mirror. In this way the nanosensor is calibrated. The range of the instrument is 300 micrometers and the uncertainty is approximately 1 nm. Measurements of different sensors, such as an inductive and a capacitive sensor as well as a laserinterferometer will be presented. A detailed description of the uncertainty budget will also be given.
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