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Articulated arm coordinate measuring machines (AACMM or CMA) have conquered a market share in the actual dimensional metrology field, overall when their role implies the inspection of geometrical and dimensional tolerances in an accurate 3D environment for medium-size parts. However, the unavoidable fact of AACMM manual operation constrains its reliability to a great extent, avoiding rigorous evaluation and casting doubt upon the usefulness of external calibration. In this research, a dimensional gauge especially aimed at AACMM evaluation has been developed. Furthermore, the operator skill will be revealed through the use of this gauge. A set of geometrical features, some of them oriented to evaluate the operator and others the equipment, have been collected for the gauge. The proposed evaluation methodology clearly distinguishes between dimensional and geometrical tolerances (with or without datum references), whereas actual verification standards only consider the former. Next, quality indicators deduced from the measurement results are proposed in order to compare AACMM versus coordinate measuring machine (CMM) performance, assuming that CMM possess the maximum accuracy that AACMM could reach, because CMM combines maximum contact accuracy with minimum operator influence. As a result, AACMM evaluation time could be significantly reduced since this gauge allows us to perform a customized evaluation of only those specific tolerances of interest to the user.

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This paper presents a study for assessing the dynamic structural deformations of one of the most modern, and portable, measurement equipment: the Coordinate Measuring Arms (CMAs or AACMMs). The study of the measurement errors derived from the use of these instruments is still controversial due to a certain lack of traceability and reliability in measurements due to the influence of the human factor acting on a complex 3D structure (with 6 or 7 degrees-of-freedom). When contact measurements are taken into account, the human factor variable originates non-uniform contact forces, lack of stability, different velocities and accelerations, among unpredictable probing trajectories. All these factors lead to conclude that in every manual measurement involving a CMA there is a structural dynamic deformation caused by the approach movement before probing a contact point as well as by the force exerted during probing. In order to determine the amplitude of this deformation and its distribution along the CMA structure a new methodology has been developed. Both depend on the followed trajectory and on the probing force amplitude and orientation. This work presents the methodology and steps required for the construction of the virtual simulation model. The method employs 3D modelling of all elements of the CMA structure, Finite Element Analysis (FEA) software and multibody simulation techniques with flexible bodies. This set of software tools is nowadays capable of creating dynamic virtual models for the dynamic analysis of complex mechanisms (machines, vehicles…) in optimization tasks. The application of these tools supposes a novel approach to the study of the CMA metrological behaviour.

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