SIMPLIFIED ALGORITHM OF COORDINATE MEASUREMENTS UNCERTAINTY EVALUATION

Wojciech Plowucha

Abstract

Long-lasting works on the ISO 15530 series can be a proof for complexity of uncertainty evaluation of coordinate measurements for different characteristics defined according to the rules of geometrical product specification (GPS). There are two most acknowledged and commonly accepted methods. First is described in the document ISO 15530-3:2011 which provides in detail the procedure of uncertainty evaluation with the use of calibrated workpiece or measurement standard. Second procedure is based on the use of computer simulation that is known from many imeko_proceedings and mentioned in ISO/TS 15530-4:2008. <BR />The author is one of the elaborator of the methodology and the software (EMU-CMMUncertainty^TM) which makes possible evaluation of the measurement uncertainty for bridge and horizontal arm CMMs. Some details concerning the software operation have been published. The software is developed with assumptions some of which are similar as in the method using the computer simulation. The most important assumption is that the uncertainty of measurement for particular characteristic (size, dimension, form, orientation, location and run-out) is calculated with the formula describing the characteristic as a function of differences of coordinates of characteristic pointsof the workpiece (the generality condition).<BR />For easier understanding of the methodology a simplified version was developed which includes in the uncertainty budget just the <i>MPE</i>_E instead of the geometrical errors and probing head errors of the CMM. Of course, this assumption gives overestimated uncertainty values but enables the sensitivity analysis. The paper includes some interesting cases of the sensitivity analysis.

Keywords

uncertainty, coordinate measurements, CMM, geometrical product specification

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DOI

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IMEKO TC

TC14 - Measurement of Geometrical Quantities

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