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Calibration of a Metrological Apparatus

  • US 20080234963A1
  • Filed: 08/16/2006
  • Published: 09/25/2008
  • Est. Priority Date: 08/18/2005
  • Status: Active Grant
First Claim
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1. A metrological apparatus for measuring surface characteristics of a surface of an object, the apparatus comprising:

  • a support for receiving an object to be measured;

    a carrier for carrying a measurement probe so that the measurement probe is movable relative to the measurement probe support;

    a mover operable to effect relative movement between the support and the carrier in a first direction to cause the measurement probe carried by the carrier to traverse a measurement path along a surface of an object supported by the support so that the measurement probe moves in a second direction transverse to the first direction as it follows surface characteristics along the measurement path;

    a first position transducer responsive to relative movement between the support and the carrier to provide first position data representing the position of the measurement probe in the first direction;

    a second position transducer responsive to movement of the measurement probe in the second direction to provide second position data representing the position of the measurement probe in the second direction;

    a measurement data obtainer operable to obtain from the first and second position transducers measurement data comprising the first and second position data for each of a plurality of measurement points along the measurement path;

    a surface characteristic determiner operable to determine data relating to at least one surface characteristic of the surface using the measurement data obtained by the measurement data obtainer; and

    a calibrator operable to carry out a calibration procedure, the calibration comprising;

    a controller operable to cause the measurement data obtainer to obtain calibration measurement data representing the known surface form of a reference object by controlling the mover to cause the measurement probe carried by the carrier to traverse a calibration measurement path on the reference object surface such that, during the traverse of the measurement path, the measurement probe moves through a measurement range to be calibrated;

    a data fitter operable to determine calibration coefficients of at least one expression representing the relationship between corrected measurement data and the calibration measurement data by using the known form of the reference surface as the correction measurement data and by varying the calibration coefficients for a number calibration points spaced within the calibration measurement data and fewer in number than the measurement points until the at least one expression provides a fit to the data; and

    a measurement data corrector operable to correct measurement data representing measurements made on a surface of a workpiece using the results of the calibration procedure.

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