Method and apparatus for characterising instrument error
First Claim
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1. A method for characterising instrument error in a surface measurement instrument, the method comprising:
- obtaining first calibration measurement data representing a known surface form of a first reference object;
obtaining second calibration measurement data representing a known surface form of a second reference object, wherein at least a portion of the second calibration measurement data represents a measurement range that overlaps with at least a portion of a measurement range of the first calibration measurement data, wherein the known surface form of the second reference object is different from the known surface form of the first reference object;
fitting a model of the known surface forms and of the expected form of the instrument error to both the first calibration measurement data and the second calibration measurement data together to determine;
first parameters describing the known surface form of the first reference object;
second parameters describing the known surface form of the second reference object; and
an error function representing the instrument error common to both the first calibration measurement data and the second calibration measurement data;
wherein the error function determined by said fitting characterises the instrument error, wherein the instrument error comprises at least one of error due to gauge non-linearity and error due to stylus tip geometry.
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Abstract
A method for characterising instrument error in a surface measurement instrument, comprising obtaining first calibration measurement data representing a known surface form of a first reference object and obtaining second calibration measurement data representing a known surface form of a second reference object. At least a portion of the second calibration measurement data represents a measurement range that overlaps with at least a portion of a measurement range of the first calibration measurement data. A common error function is obtained that characterises the instrument error.
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20 Claims
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1. A method for characterising instrument error in a surface measurement instrument, the method comprising:
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obtaining first calibration measurement data representing a known surface form of a first reference object; obtaining second calibration measurement data representing a known surface form of a second reference object, wherein at least a portion of the second calibration measurement data represents a measurement range that overlaps with at least a portion of a measurement range of the first calibration measurement data, wherein the known surface form of the second reference object is different from the known surface form of the first reference object; fitting a model of the known surface forms and of the expected form of the instrument error to both the first calibration measurement data and the second calibration measurement data together to determine; first parameters describing the known surface form of the first reference object; second parameters describing the known surface form of the second reference object; and an error function representing the instrument error common to both the first calibration measurement data and the second calibration measurement data; wherein the error function determined by said fitting characterises the instrument error, wherein the instrument error comprises at least one of error due to gauge non-linearity and error due to stylus tip geometry. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A surface measurement instrument comprising:
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a measurement probe configured to follow a surface to be measured; a measurement data obtainer configured to; obtain first calibration measurement data representing the known surface form of a first reference object in a first measurement range to be calibrated; obtain second calibration measurement data representing the known surface form of a second reference object in a second measurement range to be calibrated, wherein at least a portion of the second measurement range overlaps with at least a portion of the first measurement range, wherein the known surface form of the first reference object is different from the known surface form of the second reference object; a data fitter configured to fit a model of the known surface forms and of the expected form of the instrument error to both the first calibration measurement data and the second calibration measurement data to determine; first parameters describing the known surface form of the first reference object; second parameters describing the known surface form of the second reference object; and an error function representing the instrument error common to both the first calibration measurement data and the second calibration measurement data; wherein the error function obtained by fitting the model to both the first calibration measurement data and the second calibration measurement data characterises the instrument error, wherein the instrument error comprises at least one of error due to gauge non-linearity and error due to stylus tip geometry.
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Specification