A displacement generator is realized which enables the calibration of a wide variety of displacement-measuring probes, such as probes of roundness testers, roughness testers and stand-alone type scanning probe microscopes (SPMs), in the range of 12 µm with a standard uncertainty below 1 nm. A digital piezo translator (DPT) drives a flat mirror which serves as the calibration platform. This mirror is locked to an elastic, hysteresis-free, monolithic parallel guide. Calibration of the platform displacement is carried out by various methods including tunable and stabilized lasers, Fabry-Pérot interferometry and laser interferometry. The system is calibrated with a standard uncertainty of about 0.1 nm using three independent methods. As an example the calibration of an SPM using 0.5 µm generated steps is shown.
Within the Dutch standards laboratory (NMi Van Swinden Laboratorium) a traceable atomic force microscope (AFM) is currently being developed where we aim at a measurement uncertainty of 1 nm. As part of this development novel methods have been developed for the calibration of this instrument. The SPM has been constructed using a commercial AFM head that has been embedded in a metrology frame using an accurate 3D translation stage. The position of the AFM probe relative to the sample is determined along three orthogonal measurement axes by three individual laser interferometers. Due to the properties of the 3D translation stage the Abbe offset between the probe position and the measurement axes should remain below 0.1 mm in order to realize an overall measurement uncertainty of 1 nm. Since the laser interferometers use a four-pass optical configuration the measurement axis is defined by the virtual centre of the four positions of the laserspots onto the plane retro mirror. In order to accurately determine this virtual centre and therefore the position of the measurement axis a device has been designed to measure the four laserspot positions of each axis within the SPM. Since the AFM probe position is determined in 3D accurate calibration of the angles between the measurement axes is important if the measurement error is to be minimized to 1 nm. Different calibration setups to accurately determine these angles will be presented. Additionally, a method for the alignment of the optical axes of the laser interferometers with respect to the end mirrors of the interferometers will be discussed. In order to calculate the overall measurement uncertainty of the scanning probe microscope we decided to use the virtual measurement machine concept since a purely analytical approach for these types of measurement instruments is nearly impossible (Schwenke et al 2000 Ann. CIRP 49 395–8). The model or virtual SPM that has been developed for the simulation of the instrumental characteristics will be presented.
The results of the inter-RMO key comparison EUROMET.L-K5.2004 on the calibration of a step gauge are reported. Eighteen National Metrology Institutes and one Designated Institute from four different metrological regions all over the world participated in this comparison which lasted three years, from December 2004 to December 2007.A lack of stability was observed through the shifting of some of the inserted gauges. In order to save the comparison and get valuable and useful conclusions, it was agreed to exclude four gauges from calculation and assume that only seven gauges were reasonably stable so as to get the corresponding reference values. It was also agreed to divide the participants into two groups, analyze separately their results and, taking the pilot as the linking laboratory, refer the results to common reference values.The inverse-variance weighted mean was taken as reference value. Due to the significant instability of the step it was also considered an artefact uncertainty. The reported uncertainties ranged from 0.045 µm to 1.2 µm (k = 1). The uncertainty of the artefact ranged from 0.018 µm (for the 20 mm face) to 0.176 µm (for the 400 mm face).The compatibility of all participants for measuring step gauges was demonstrated with the only exception of a participant showing very high systematic (both positive and negative) errors. Five participants communicated higher uncertainties than the corresponding approved CMCs. A set of Recommendations and Actions were agreed therefore.Main text. 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 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).
An interferometer is realized, based on the Twyman-Green Interferometer principle for the calibration of long gauge blocks and length bars in the 100 -1000 mm range with an uncertainty ofO,02 jim + 0,1 pm/rn. Also the expansion coefficient of gauge blocks and even of rod-shaped materials with non-optical flat faces can be calibrated in the I 8 -22 °C range with an uncertainty below 1107/K. The set-up basically follows the most commonly used interferometer arrangements for long gauge blocks as they are described by Darnedde1, Ikonen2 and Lewis3 where the most similarities with the latter occur. The set-up has some peculiarities which make the measurement straightforward, accurate and reliable. These features are: -A Zeeman-stabilized laser (TESA, type SR), calibrated against a Iodine-stabilized laser, is used as the reference. In addition, two two-mode stabilized He-Ne lasers ('green' and 'yellow') are used. The wavelength of these two lasers is calibrated with an uncertainty of 1.108 using gauge-block measurements in a step-up method. These three lasers can simultaneously be used for two more short-gauge block interferometers.-Temperatures are measured using 20 k thermistors calibrated in the 18 -22°C range. Thermistors have a higher temperature-sensitivity, higher stability and a lower seift-heating when compared to e.g. Pt-100 elements.-The optical alignment is carried out with an autocollimator which is, after adapting the optics, used for viewing the interference pattern in the same position.The fraction is determined from a linearized voltage which is applied to a piezo system which can both tilt and move the reference mirror parallel.-The temperature inside the interferometer is controlled by a thermostatic bath. -Special tools are applied to enable a calibration of the expansion coefficient of any rod-shaped material; reflecting and optical quality surfaces are not necessary.
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.
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