Vol.2 No.2 2009

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Research paper : High accuracy three-dimensional shape measurements for supporting manufacturing industries (S. Osawa et al.)−104−Synthesiology - English edition Vol.2 No.2 (2009) AIST established a consortium for creating a standard for the precision assessment of noncontact CMM in 2005. The consortium developed standards for use in the assessment of the noncontact CMM (metrological standards) and devised an assessment method using these standards.Since there are many different types of noncontact CMMs, it is important to create standards that enable assessment of these various measuring machines. In optical measuring machine, error tends to occur in the presence of luster in the measured area of the standard. Therefore, the surface of the standard must have optically diffusing surface. To select an ideal diffusing surface, through cooperation of the consortium members, several spheres were created with slightly different processing methods, conditions, and surface coatings. Figure 16 shows some examples. Processing were done with over 100 different conditions, the spheres were measured using several types of noncontact CMMs, and a sphere for which relatively stable measurements could be obtained in all measuring machines was selected. Next, using the selected sphere, a ball bar, which would be the standard for a precision assessment of the measuring machines, was created (see Fig. 17). A carbon frame was used so it would not be affected by environmental temperature, since many noncontact CMMs were portable and they were unlikely to be used in a room with constant temperature at 20 ºC. Therefore, a standard that was stable against temperature change was needed. Hence, a standard traceable to the national standard was created by the consortium so it could be used for assessment of measuring machines. After conducting comparative measurements, the assessment of noncontact CMM using this standard was standardized as Japan Industrial Standard (JIS). Currently, the drafted JIS is undergoing deliberation at the Japan Industrial Standards Committee as JIS B 7441. It has also been submitted to the ISO committee at the same time. We are collaborating with Digital Human Research Center, AIST, for the standardization of the assessment method of noncontact CMM for the measurement of the human body.The x-ray CT device that was previously used for the detection of cast pores is now being employed in industry as a CMM that can measure internal structures. Therefore, there are demands from manufacturers and users for the development of a common phantom (standard) to assess the x-ray CT devices, as well as for the standardization of assessment method using the phantom, and AIST is preparing for this study.6.2 Cooperation with regional public research laboratoriesSince CMMs are expensive instruments, the financial strain on small to medium businesses is great. Therefore, CMMs are installed in almost all regional public laboratories to provide services, such as requested measurements and the use of the instrument by the local companies. AIST is engaging in activities to improve three-dimensional measurement technology in the Shape Measurement Subcommittee, Intellectual Infrastructure Committee, which is one of the technical committees of the Council of Promotion of Industrial Technology Collaboration. The subcommittee has engaged in comparative measurement of ball plates, demonstration experiment for the calculation of uncertainty in deliberation at the ISO, and assessment experiment of video probe CMM. Also, a project to maintain reliability of CMM measurements is conducted as a local collaborative innovation creation undertaking with public laboratories in the wider Kanto area from FY 2008. Through such activities we are contributing to the improvement of three-dimensional shape measurement technology at the site of production. We hope these technologies will be transferred from public laboratories to local small and medium businesses to vitalize Japanese manufacturing.6.3 Operator trainingAIST has engaged in technological developments and diffusion activities for the three-dimensional shape measurement. We feel that the technological development for establishing metrological traceability had been sufficiently organized. In the future, we shall strengthen activities to diffuse daily maintenance methods for CMM to further improve the reliability of the three-dimensional measurement, and train the users. Recent measuring machines including CMMs are digital rather than analog, and the values are shown on the display. Therefore, the operator tends to think that the figures are always correct. However, in measurement, the reliability of the values changes depending Fig. 16 Spheres manufactured under different conditions.Dispersion eutectoid coating (B-MOS) (leftmost)Sandblast: Cr coating (2nd from left), TiN coating (center)Chemical etching (FeCl2) (two on right)Fig. 17 Ball bar for noncontact CMM assessment.

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