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Comparison of Volumetric Analysis Methods for Machine Tools with Rotary Axes

Longstaff, Andrew P., Fletcher, Simon, Poxton, Anthony and Myers, Alan (2009) Comparison of Volumetric Analysis Methods for Machine Tools with Rotary Axes. In: Laser Metrology and Machine Performance. Euspen Ltd, Euspen Headquarters, Cranfield University, pp. 87-96. ISBN 978-0-9553082-7-7

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    Abstract

    Confidence in the ability of a production machine to meet manufacturing
    tolerances requires a full understanding of the accuracy of the machine.
    However, the definition of “the accuracy of the machine” is open to
    interpretation. Historically, this has been in terms of linear positioning accuracy
    of an axis with no regard for the other errors of the machine. Industry awareness
    of the three-dimensional positioning accuracy of a machine over its working
    envelope has slowly developed to an extent that people are aware that
    “volumetric accuracy” gives a better estimation of machine performance.
    However, at present there is no common standard for volumetric errors of
    machine tools, although several researchers have developed models to predict
    the effect of the combined errors.
    The error model for machines with three Cartesian axes has been well
    addressed, for example by the use of homogenous transformation matrices.
    Intuitively, the number of error sources increases with the number of axes
    present on the machine. The effect of the individual axis geometric errors can
    become increasingly significant as the chain of dependent axes is extended.
    Measurement of the “volumetric error” or its constituents is often restricted
    to a subset of the errors of the Cartesian axes by solely relying on a laser
    interferometer for measurement. This leads to a volumetric accuracy figure that
    neglects the misalignment errors of rotary axes. In more advanced models the
    accuracy of the rotary axes are considered as a separate geometric problem
    whose volumetric accuracy is then added to the volumetric accuracy of the
    Cartesian axes.
    This paper considers the geometric errors of some typical machine
    configurations with both Cartesian and non-Cartesian axes and uses case studies
    to emphasise the importance of measurement of all the error constituents.
    Furthermore, it shows the misrepresentation when modelling a five-axis
    machine as a three-plus-two error problem. A method by which the five-axis
    model can be analysed to better represent the machine performance is
    introduced.
    Consideration is also given for thermal and non-rigid influences on the
    machine volumetric accuracy analysis, both in terms of the uncertainty of the
    model and the uncertainty during the measurement. The magnitude of these
    errors can be unexpectedly high and needs to be carefully considered whenever
    testing volumetric accuracy, with additional tests being recommended.

    Item Type: Book Chapter
    Subjects: T Technology > TJ Mechanical engineering and machinery
    Schools: School of Computing and Engineering > Centre for Precision Technologies
    School of Computing and Engineering
    School of Computing and Engineering > Centre for Precision Technologies > Engineering Control and Machine Performance Research Group
    Related URLs:
    Depositing User: Helene Pickles
    Date Deposited: 17 Sep 2009 16:31
    Last Modified: 25 Nov 2010 09:24
    URI: http://eprints.hud.ac.uk/id/eprint/5555

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