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Research paper : High accuracy three-dimensional shape measurements for supporting manufacturing industries (S. Osawa et al.)−98−Synthesiology - English edition Vol.2 No.2 (2009) the baseline length of the scale (that is, position of the probe is separated from the scale itself) (in technological terms, it “does not fulfill Abbe’s Principle”).2. There are several other factors of error, and assessment of uncertainty of measurement data is difficult.Although Issue 1 is a major problem in conducting high-precision measurement, the effect is kept small by allowing correction by software[1], by improving repeatability through increased rigidity of the machine itself. Most of the current CMMs have software correction functions, and it is necessary to obtain accurate correction data in advance to conduct effective correction. Specifically, there are two types of correction data. One is the correction data for the probing system. By measuring a calibration sphere, for which the value of the diameter has been precisely measured in advance and which has extremely small shape error (with 50 nm or less deviation from circularity), the diameter, deflection, and characteristic of this probing system of the spherical tip of the probe (stylus) used can be calculated (specifically, when the cross-section of the sphere is measured with a CMM, the shape may not turn out circular, but may be triangular or square depending on the characteristic of the probing system). The other type of correction data is the movement error of the instrument including scale error (of attachment of the scale), squareness error (orthogonality among each axis), straightness error (distortion in each axis guide), and rotational error (error due to changes in position). The errors of scale, squareness, straightness, and rotation are called geometrical errors[2] that can be calculated using various standards. Standards for CMM are necessary to obtain precise measurements of the two types of correction data, as described in the next section.Issue 2 refers to the difficulty in assessment of uncertainty because CMM has multiple factors of error, and also because of complicated processing where the measurement data is calculated by concentrating the discretely distributed measurement points into one factor. We looked at a new calculation method for uncertainty using software simulation, and conducted research to solve this problem. This will be explained in detail in section 4.2.3.2 Development of standards for CMM3.2.1 Step gaugeTo check the measurement accuracy of the CMM or to obtain the data for software correction, various standards such as gaugeblocks and ball plates that can be traced to higher-level national standards (iodine stabilized He-Ne laser) are used. Unless calibration of these standards is conducted accurately, highly precise assessment of CMMs that is in the lower level of the traceability system cannot be done. Therefore, development of standard calibration technology is important, and the metrology labs of other countries are engaging in the development of calibration technology and calibration services.AIST has been engaging in the development of a standard calibration system for about 10 years. In Japan, end measures (gaugeblock or step gauge) are generally used in the precision assessment of CMMs. For assessment of CMM, a step gauge (see Fig. 5), where short gaugeblocks are lined up and used as standards for varying lengths, is used more often than the gaugeblock. In major national metrology labs, step gauges are calibrated using a special instrument that combines a laser interferometer and a moving stage[3]. AIST developed a system for calibrating the step gauge by combining the CMM and the laser interferometer[4]. Figure 6 shows the developed system. In this system, by using a four optical path interferometer, the measured length shows the distance between the center of the sphere at the tip of the stylus and the interferometer at all times, even if rotation errors such at pitching and yawing occur in the stylus. When the step gauge with measured length 500 mm was calibrated using this system, uncertainty of 0.30 µm (95 % confidence interval) was achieved.Fig. 4 Relationship between traceability system and Full Research.Fig. 5 Exterior view of step gauge (measurement surface is arranged in comb-tooth form). SI basic unit “m”Construction of calibration service accreditation systemIndustrial standardization①Development of technologies for CMMcalibration and assessment gauge calibrationProductCMMGaugeblock, step gauge, ball plate, etc.Practical-use stabilized He-Ne laserIodine stabilized He-Ne laser-Development of gauge calibration system-International comparison with national standard labs of other countries-JCSS application of gauge calibration②Technological development for building CMM traceability system-JCSS application of CMM calibration-Development of uncertainty assessment method-Development of remote calibration service③Development of high-precision three-dimensional coordinate measurement technology-Development of calibration technology for large CMMs-Development of high-precision measurement technology using CMMs

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