MEASURING INSTRUMENTS CATALOG No.E2019
591/608

N-22Figure 6 Target points of measurement for Single Stylus Form ErrorThis measurement was included in the dimensional measurement in ISO 10360-2: 2001. However, it is specied as "CMMs using single and multiple stylus contacting probing systems" in ISO 10360-5: 2010.The measurement procedure has not been changed, and the following procedure should be performed.Measure the dened target points on a standard sphere (25 points, as in Figure 6) and use all the results to calcu-late the center position of the sphere by the least squares method.Then, calculate the radial distance from the center position of the sphere by the least squares method for each of the 25 measurement points, and obtain the radial difference Rmax - Rmin. If this difference, to which a compound uncertainty of forms of the stylus tip and the standard test sphere are added, is equal to or less than the specied value, it can be judged that the probe has passed the test.Maximum Permissible Single Stylus Form Error PFTU, MPE [ISO 10360-5: 2010]22.5゜22.5゜a22.5゜22.5゜22.5゜Example of circle measurement by CMMQuantication of CMM uncertainty elements by experimentMajor contributions that cause uncertainty in CMM measurement resultsMeasurement uncertainty is an indication used for evaluating reliability of measurement results.In ISO 14253-1: 1998, it is proposed to consider the uncertainty when evaluating the measurement result in reference to the specification. However, it is not easy to estimate the uncertainty of the measurement performed by a CMM.To estimate the uncertainty of the measurement, it is necessary to quantify each source of uncertainty, and determine how it propagates to the measurement result. The CMM is subject to all types of settings that determine how the measurement should be performed, such as measurement point distribution, or datum denition, according to the drawing instruction or operator's intention. This fact makes it harder to detect the sources of uncertainty inuencing the result. Taking circle measurement as an example, just a difference of one measurement point and its distribution causes the necessity of recalculation of the uncertainty.Also, there are many sources of uncertainty to be considered with the CMM and their interactions are complex. Because of the above, it is almost impossible to generalize on how to estimate measurement uncertainty of the CMM.The Virtual CMM software* enables straightforward, automated estimation of the measurement uncertainty of a CMM. The software simulates a CMM on a PC based on its machine characteristics and performs virtual (simulated) measurements. The simulated measurements are performed according to the part program created by the machine operator. The machine's perfor-mance is evaluated from experimental values based on geometri-cal characteristics of the actual machine, probing characteristics, and temperature environment, etc., and the measurement uncer-tainty of the CMM is estimated by the software package.ISO15530 Part 4 (ISO/TS 15530-4 (2008)) denes how to verify the validity of task-specic measurement uncertainty using computer simulations.Virtual CMM conforms to this specication.* Virtual CMM is a software package originally developed by PTB (Physikalisch-Technische Bundesanstalt).Relevant parts of ISO 15530: Geometrical Product Specications (GPS) -- Coordinate measuring machines (CMM): Technique for determining the uncertainty of measurement --Part 3: Use of calibrated workpieces or measurement standardsPart 4: Evaluating task-specic measurement uncertainty using simulation [Technical Specication]Measurement Uncertainty of the CMMMeasurement uncertainty of the CMM and the Virtual CMM softwareUncertainty of circle proleUncertainty of center positionPositioning of measuring pointsUncertainty of measurementCMMProbeEnvironmentWorkpieceEnvironmentData processingMeasurement taskProbeCMMN

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