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Research paper : High accuracy three-dimensional shape measurements for supporting manufacturing industries (S. Osawa et al.)−100−Synthesiology - English edition Vol.2 No.2 (2009) metrology institues participated with this comparison. Figure 9 shows the results of the international comparison[7]. In the international comparison, the participating institutes conduct measurements independently based on the national standard of their respective countries, and therefore none of the labs know which of their results are the closest to the true value. The weighted average value considering the uncertainties of measurements of the participating labs is designated as a value that is probably the most certain (reference value), and the deviation of the data of each lab is calculated. However, in this international comparison, it was found that the measurement data of some of the participating labs were greatly deviant. Ultimately, the measurements of four countries, Japan (NMIJ/AIST), U.S.A. (NIST), Switzerland (METAS), and Germany (PTB) were in good agreement, and therefore the average values of these four laboratories were used as a reference value. The graph of Fig. 9 is a plot showing the deviation from the reference value for each lab (the values of AIST run only to 720 mm due to the limitations of the measurement system). From this result, the reliability of the step gauge calibration system developed at AIST was confirmed, and the high level of the calibration technology of AIST was presented to the world.3.3.2 International comparison of ball platesThe international comparison of ball plate calibration (CCL-K6) was conducted from 2001 to 2004. There were 12 participating institutes. Figure 10 shows the result of this international comparison. The plotted points in this graph show the difference between the AIST result and the reference value, which is the average value of all participating institutes for the distances from 1st sphere to each sphere (2nd to 25th). The number of spheres is shown below the error bar. The error bar shows the uncertainly (66 % confidence interval) for measurement values of AIST, and the blue line shows the uncertainty (66 % confidence interval) against the reference value. It can be seen from this graph that the AIST values and the reference value match within the range of uncertainty. From this result, the reliability of the developed system was confirmed and the high-level calibration technology of AIST was presented to the world.3.4 Calibration service of standards by private companiesThe mission of AIST is to have the technology confirmed in the above international comparison be used widely in industry. Since the number of calibration services that can be undertaken by AIST is limited, private companies with high-level calibration technology can conduct the service and participate as the middle tier of the traceability system, and diffuse the highly reliable three-dimensional shape measurement technology to industry. The Japan Calibration Service System (JCSS) based on the Measurement Act is a mechanism for officially accrediting private companies with proper calibration capacity. The service provider accredited under this system can issue calibration certificates that certify that a standard is traceable to the Japanese national standard. To establish a calibration system for step gauges using this system, a technological committee was established in the National Institute of Technology and Evaluation (NITE), and a draft of Guidelines for Technological Requirements[8] needed for accredited service providers was drafted under the leadership of AIST. Immediately after the establishment of the system, several service providers were accredited, and the traceable step gauges are now employed in several industries.4 Reliability assessment of the CMM4.1 Accreditation of calibration service providers for CMMAs mentioned in chapter 3, it became possible to calibrate the CMM appropriately since the standard for step gauges was established. In this situation, the service providers that Fig. 9 Result of international comparison for step gauge (CCL-K5).Deviation from reference value (µm)Measured length (mm)-3-0.5-1-1.5-2-2.500.510020020040040060060080080010001000PTB (Germany)CEM (Spain)CENAM (Mexico)KRISS (Korea)METAS (Switzerland)NIM (China)NMIJ (Japan)CSIRO (Australia)NIST (U.S.A.)

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