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.)−102−Synthesiology - English edition Vol.2 No.2 (2009) In this study, AIST conducted comparative measurement of a normally workpiece, and assessed the practical usability of the virtual CMM. The diffusion of this virtual CMM technology helped the construction of a traceability system for three-dimensional measurement. The calculation method of uncertainty by simulation was standardized as ISO/TS 15530-4.4.3 Remote calibration of CMMTo calculate the uncertainty using the method mentioned in the previous section, it is necessary to obtain data for geometrical error for the entire measurement space using standards. Since extremely specialized technique is needed to obtain the geometrical error data of measurement space of the CMM, this measurement is preferably done by a specialized calibration service. However, time and money costs are needed when the calibration specialist is dispatched to the site of production. Therefore, AIST developed a system to conduct this work easily using the Internet[12].Figure 13 shows the outline of remote calibration of CMM using the Internet. The calibration service provider first sends a standard to the CMM user. Changes during transportation such as temperature, humidity, and vibrations are monitored by an accompanying sensor with a recording function. The calibration service determines whether the standard has changed by looking at the recorded information of the sensor. Next, the user’s CMM is calibrated using a two-dimensional standard. The standard is set in position by the user, while the setting procedure is monitored by a specialist of the calibration service using the network camera. The user’s CMM is controlled by the calibration specialist via the Internet. The environmental temperature during calibration is measured using the thermometer delivered along with the standard. The temperature measurement data are also sent using the Internet and are stored by the calibration service. The parameter setting and the creation of a coordinate system of the probing system are done by talking directly with the user via telephone or Internet camera phone. After completing the measurement, the calibration service uses these measurement data to calculate the geometrical error of the user’s CMM. The calculated geometrical error is sent to the user, and used for calculating uncertainty and error corrections. The calibration service specialist does not have to be present at the site of calibration, and we call this remote calibration. This technological development enables traceability of three-dimensional measurement without requiring the user to have knowledge in standards and geometrical error calculation, and can be done at low cost.AIST has been conducting CMM calibration service using the remote method as a requested test since 2005. This service is conducted by the assessment method based on ISO standards using gaugeblocks and step gauges rather than two-dimensional standards, just as in the CMM calibration in the JCSS.5 Sophistication of three-dimensional shape measurement5.1 Calibration of large CMMsFor shape measurement of automobile body or aircraft fuselage, a large CMM with measurement space such as 5 m × 3 m × 2 m is used. For calibration of such large CMM, large standards may be used, although there are issues of weight and time cost. Therefore, AIST suggested a calibration system using laser tracking laser interferometer (or laser tracker) as one of the methods to calibrate large CMMs without using a standard. The CMM calibration system using the laser tracker was studied at the National Physical Laboratory (NPL) of U.K., the Physikalisch-Technische Bundesanstalt (PTB) of Germany, and AIST. All devices calculate the coordinates by the principle of trilateration from distance measurement of the device. The devices of NPL[13]and PTB[14] use repeated measurements of the target position by transferring one laser tracker to several positions, while the AIST method is to install four laser trackers to measure the positions of the target at once[15]. Since the AIST method allows calculation of coordinates in one shot, it has merit of having shorter measurement time compared to the NPL and PTB methods. Therefore, the external environment effect such as a shift in coordinates of the workpiece due to changes in temperature can be kept to a minimum.Figure 14 is a photograph of the laser tracker developed at AIST. The characteristic of this system is to reduce Fig. 12 Outline of virtual CMM. Measurement result : Actual measurementUncertainty : Calculated by simulatorMeasurement result and information for simulationShape error of measured object+uncertaintySimulation by virtual CMM modeland othersLong-term stabilityFactors of uncertaintyActual measurementMeasurement procedureEnvironmental conditions such as temperatureGeometrical errorProbingParameter setting for simulationMeasurement result CMMController1. Transportation of gauge4. Image and sound3. Send measurement result2. Control of CMM5. Send assessments and resultsCameraInternetFig. 13 Remote calibration technology for CMM.

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