Bojan Ačko

Standards for testing freeform measurement capability of optical and tactile coordinate measuring machines

For decades three-dimensional (3D) measurements of engineering components have been made using fixed metrology-room based coordinate measuring machines (CMMs) fitted most commonly with single point or to a much lesser extent, scanning tactile probes. Over the past decade there has been a rapid uptake in development and subsequent use of portable optical-based 3D coordinate measuring systems. These optical-based systems capture vast quantities of point data in a very short time, often permitting freeform surfaces to be digitized. Documented standards, for example ISO 10360, for the verification of fixed CMMs fitted with tactile probes are now widely available, whereas verification procedures and more specifically verification artefacts for optical-based systems are still in their infancy. Furthermore, the industry is seeking traceability in 3D measurements of high precision components. A recent requirement is the demand for highly accurate measurements of large gears with diameters up to 1000 mm as used in gear boxes of wind turbines. Up until now it has been impossible to ensure traceability of 3D measurements of big gears, since no traceable standards were available. This paper describes three different types of artefacts that were developed during the project, namely tetrahedron artefacts for testing the basic measurement capability of optical 3D devices, freeform verification artefacts for testing the capability of measuring complex geometry, and a large gear artefact for task related calibration of different types of CMMs. In addition, artefact calibration data and associated measurement uncertainties and international intercomparisons are presented. These developments will be of considerable value to end users, calibration laboratories and producers of optical and tactile CMMs.

SIMULATION OF LINE SCALE CONTAMINATION IN CALIBRATION UNCERTAINTY MODEL

Precise calibration of quartz line scales is very important for assuring traceability of microscopic measurements. Very significant influence in calibration uncertainty budget is represented by uncertainty of line centre detection. Line centre is usually detected through video signal processing using different types of algorithms. This paper is presenting calibration procedure that was developed in the Laboratory for Production Measurement at the Faculty of Mechanical Engineering in Maribor. It is focused in uncertainty analysis and especially in the influence of line scale contamination on determination of line centre position. Different types of line scale contamination like dirt spots, scratches, line edge incorrectness, and line intensity were simulated in order to test the ability of the line centre detection algorithm to eliminate such influences from the measurement results.

Final report on EUROMET Key Comparison EUROMET.L-K7: Calibration of line scales

The results of the EUROMET key comparison on line scales (EUROMET.L-K7) are reported. The comparison involved measurements of thirty measurands ranging from 0.1 mm to 100 mm on two glass scales. Each glass scale circulated in a separated loop. Thirty participants (20 from EURAMET, 10 from other RMOs) were divided into two groups with two linking laboratories. Participating laboratories have used different measurement techniques, which are normally used for calibration services. The results are in quite good agreement: out of the 900 results reported, 80 were not in agreement (within their k = 2 uncertainties) with the weighted mean values taken to be the key comparison reference values. The results of this key comparison will contribute to the Mutual Recognition Arrangement. 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).

Optimization of Calibrating HeNe Laser Interferometers by Sample-Period Simulation

The calibration procedure for the frequency determination of HeNe laser interferometers used for length metrology is described and high-level traceability at the Metrology Institute of the Republic of Slovenia (MIRS) consistent with the Mutual Recognition Arrangement drawn up by the International Committee for Weights and Measures (CIPM MRA) is presented in the article. The analyses of radiation frequency regarding stabilization time, repeatability and reproducibility are given for a case of an industrial and of a laboratory HeNe laser interferometer. Allan-deviation calculations at different sampling periods provided information for setting the optimal sampling period and proved that 100 000 samples at onesecond or 10 000 samples at ten-second long period are usually the most appropriate sets for one-day calibration measurements. (Received in August 2012, accepted in March 2013. This paper was with the authors 3 months for 2 revisions.)

Metrological set-up for Calibrating 1D Line Scales with Sub-Micrometre Precision

The use of the optical standards in the industry is constantly growing. A high resolution 1D measurement instrument developed for calibrating precision line scales with sub-micrometre measurement uncertainty is presented in this paper. The mechanical foundation of this instrument is based around a custom designed, numerically controlled multi-axis granite stage manufactured by Newport Micro-Controle Spectra-Physics, but specifically designed to meet the metrological requirements of the Laboratory for Production Measurement (LTM) at the University of Maribor. The system integrates a numerically controlled multi-axis stage, a laser interferometer, and a vision system for detecting line position. The measurement and the analysis processes are completely automated in order to minimize manual labour during the calibration process, but also increase the calibration accuracy. Increasing calibration accuracy leads up to better quality of industrial measurements which is required by modern precision industry. The metrological capabilities of the presented measurement set-up were verified by some practical test measurements. Indirect users of the results of this research will be all manufacturers of precise products such as automotive and other industries.