Abstract: A method of characterizing the surface of an aspheric diffractive structure includes using a metrological apparatus to perform a measurement on the surface of the structure so as to provide a measurement profile representing the z-direction deviations of the surface of the structure; determining parameters relating to the aspheric and diffractive components of the aspheric diffractive structure; producing data having the determined parameters; and comparing the produced data with the measurement profile to determine residual error data.

Abstract: A method of determining a correction parameter for use in effecting alignment of a component of a metrological apparatus in at least one direction is described which includes: positioning an artefact on a support surface of a turntable of the metrological apparatus so that a measurement surface of the artefact is asymmetric with respect to a rotation axis of the turntable in the at least one direction; using a measurement probe of the measurement instrument to make a first measurement of the measurement surface; rotating the turntable; using the measurement probe of the measurement instrument to make a second measurement of the measurement surface after rotation of the turntable; and determining a correction parameter from the first and second measurements.

Abstract: A method of characterising the surface of an aspheric diffractive structure includes using a metrological apparatus to perform a measurement on the surface of the structure so as to provide a measurement profile representing the z-direction deviations of the surface of the structure; determining parameters relating to the aspheric and diffractive components of the aspheric diffractive structure; producing data having the determined parameters; and comparing the produced data with the measurement profile to determine residual error data.

Abstract: A method of determining a correction parameter for use in effecting alignment of a component of a metrological apparatus in at least one direction is described which includes: positioning an artefact on a support surface of a turntable of the metrological apparatus so that a measurement surface of the artefact is asymmetric with respect to a rotation axis of the turntable in the at least one direction; using a measurement probe of the measurement instrument to make a first measurement of the measurement surface; rotating the turntable; using the measurement probe of the measurement instrument to make a second measurement of the measurement surface after rotation of the turntable; and determining a correction parameter from the first and second measurements.

Abstract: A metrological apparatus has a driver (33) that effects relative movement between a support (4) and a measurement probe (8) carriage (7) in a first direction (X) to cause the measurement probe (8) to traverse a measurement path along a surface of an object supported by the support. The measurement probe (8) moves in a second direction (Z) transverse to the first direction as it follows surface characteristics. Respective first and second position transducers (35, 32) provide first and second position data representing the position of the measurement probe in the first and second direction. A calibrator (300) carries out a calibration procedure using measurement data obtained on a surface of known form. The calibrator determines calibration coefficients of an expression relating corrected measurement data and the actual measurement data by using the known form of the reference surface as the corrected measurement data.

Abstract: A metrological apparatus has a driver (33) that effects relative movement between a support (4) and a measurement probe (8) carriage (7) in a first direction (X) to cause the measurement probe (8) to traverse a measurement path along a surface of an object supported by the support. The measurement probe (8) moves in a second direction (Z) transverse to the first direction as it follows surface characteristics. Respective first and second position transducers (35, 32) provide first and second position data representing the position of the measurement probe in the first and second direction. A calibrator (300) carries out a calibration procedure using measurement data obtained on a surface of known form. The calibrator determines calibration coefficients of an expression relating corrected measurement data and the actual measurement data by using the known form of the reference surface as the corrected measurement data.

Abstract: An apparatus and method for the processing of height information indicative of the roughness or texture of a surface which may be used to produce an improved two dimensional recording of the surface. The apparatus or method has particular applicability in the field on metrological instruments. In processing the surface information, the apparatus or method takes account not only of the basic height information but also of gradient information. Such gradient information is furthermore adjusted dependent upon a desired angle of illumination which may be selected by the user.

Abstract: A nominally cylindrical surface of a workpiece is sensed by a stylus displaceable radially of an axis of rotation of the surface relative to a support column defining a reference datum so that the stylus follows the cylindrical surface at a given height along the surface. Relative rotation of the workpiece and the stylus about the axis of rotation of the surface is effected and the displacement of the stylus used to determine information relating to the radial form of the surface at that height. These measurements are represented at different heights along the surface so as to determine its cylindrical form. The displacement of the stylus from a given position on the surface at each height before and after rotation of the stylus and workpiece through 180° are measured and the resulting measurements used to compensate for any error or deviation in the reference datum.

Abstract: An apparatus and method for the processing of height information indicative of the roughness or texture of a surface which may be used to produce an improved two dimensional recording of the surface. The apparatus or method has particular applicability in the field on metrological instruments. In processing the surface information, the apparatus or method takes account not only of the basic height information but also of gradient information. Such gradient information is furthermore adjusted dependent upon a desired angle of illumination which may be selected by the user.

Abstract: A roundness measuring machine is described which measures the position of the surface of an object as the object is rotated on a turntable. The machine determines the circle which is the best fit to the measured points and converts the measurements to distances from the best fit circle. An improved algorithm for determining the best fit circle is used in place of the limacon fit. Calculated differences between the measured surface position and the best fit circle are corrected for the effect of measuring the difference in the direction towards the center of rotation of the turntable instead of in the direction towards the center of the circle. Data values are calculated representing points at equal angles around the center of the best fit circle rather than equal angles around the center of rotation of the turntable. The improved accuracy of correction allows the machine to tolerate greater eccentricity of the workplace relative to the turntable, reducing the necessity for accurate centering of the workpiece.