Abstract: A method of calibrating a contact probe having a contact element includes measuring with the contact probe a first geometric property of a calibrated artifact and a second geometric property of the or a further calibrated artifact. The first and second geometric properties are such that a deviation between a measured value and the expected value, resulting from a difference between an effective diameter of the contact element and an assumed diameter used for determining the measured value, has the opposite sign for each of the first and second geometric properties. The method further includes identifying a difference in the effective diameter of the contact element from the assumed diameter including comparing deviations of the measured value to the expected value for each of the first and second geometric properties to determine whether there is a difference in the deviations.

Abstract: This invention relates to a method for measuring a feature of an object that comprises obtaining a representation of at least the feature on the object by acquiring multiple data points via surface measurement of at least the feature. A model substantially replicating at least the feature of the object is fitted to the representation. The model comprises parameters defining at least two independently alterable portions that are linked at a common point. The fitting comprises changing the form of the model by altering at least one of the at least two independently alterable portions. The method also comprises obtaining information regarding at least the feature from the fitted model.

Abstract: A method of calibrating a contact probe having a contact element includes measuring with the contact probe a first geometric property of a calibrated artefact and a second geometric property of the or a further calibrated artefact. The first and second geometric properties are such that a deviation between a measured value and the expected value, resulting from a difference between an effective diameter of the contact element and an assumed diameter used for determining the measured value, has the opposite sign for each of the first and second geometric properties. The method further includes identifying a difference in the effective diameter of the contact element from the assumed diameter including comparing deviations of the measured value to the expected value for each of the first and second geometric properties to determine whether there is a difference in the deviations.

Abstract: A method of determining the dimensions and location of a surface feature, for example a valve seat. The surface of the feature is measured, for example using a spiral scan path with a tactile probe and the multiple data points acquired from the scan are used to create a digitized image. The digitized image is fitted to a nominal image (e.g. CAD data) of the surface feature. The deviation of the digitized image from the nominal image is used to determine at least one of the dimensions, location and form deviation of the surface feature.

Abstract: A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least a first axis. The method comprises obtaining a first measurement with the surface sensor at a first angular orientation and obtaining a at least a second measurement with the surface sensor at a second angular orientation. The first and second angular orientations are different to each other such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements. The method then compensates and/or establishes for the offset using the first and second measurements.

Abstract: A method of calibrating a measurement scale in a motorized scanning head using a reference artefact is described. The method comprises the step of rotating a surface sensing device, such as a scanning probe, mounted on the scanning head about at least one axis of the scanning head to move the surface sensing device into a plurality of different angular orientations relative to the reference artefact. A step is then performed of measuring, with the surface sensing device, at least one property of the reference artefact at each of the different angular orientations. An error map or function is then created for at least one measurement scale of the scanning head using the properties of the reference artefact measured and optionally known or calibrated properties of that reference artefact. The method may comprise use of co-ordinate positioning apparatus, such as a co-ordinate measuring machine, to move the scanning head. The reference artefact may comprise a single feature or an array of features.

Abstract: This invention relates to a method for measuring a feature of an object that comprises obtaining a representation of at least the feature on the object by acquiring multiple data points via surface measurement of at least the feature. A model substantially replicating at least the feature of the object is fitted to the representation. The model comprises parameters defining at least two independently alterable portions that are linked at a common point. The fitting comprises changing the form of the model by altering at least one of the at least two independently alterable portions. The method also comprises obtaining information regarding at least the feature from the fitted model.

Abstract: A method of calibrating a probe is disclosed said probe being mounted on a machine and having a stylus with a workpiece contacting tip, comprising calculating calibration information for the probe for a first orientation of the probe, and rotating the calibration information by an angle to obtain a probe calibration information for when the probe is oriented by that angle with respect to the first orientation. Also disclosed is a method of calibrating a probe during a measurement process. The calibration information may include a vector which relates probe head axes to machine axes; a calibration matrix; datum data; an inertial matrix. The stylus tip may be datumed at the orientation of the probe or inferred from datum information obtained at different orientations. The rotation step may be carried out by a software/computer program which may be stored on a controller for the machine.

Abstract: A method of operating a coordinate positioning apparatus having a surface sensor that is rotatable about at least a first axis. The method comprises obtaining a first measurement with the surface sensor at a first angular orientation and obtaining a at least a second measurement with the surface sensor at a second angular orientation. The first and second angular orientations are different to each other such that any offset of the surface sensor from an expected position will have at least a partially opposing affect on the first and second measurements. The method then compensates and/or establishes for the offset using the first and second measurements.

Abstract: A method of determining the dimensions and location of a surface feature, for example a valve seat. The surface of the feature is measured, for example using a spiral scan path with a tactile probe and the multiple data points acquired from the scan are used to create a digitized image. The digitized image is fitted to a nominal image (e.g. CAD data) of the surface feature. The deviation of the digitized image from the nominal image is used to determine at least one of the dimensions, location and form deviation of the surface feature.

Abstract: A method of calibrating a measurement scale in a motorised scanning head using a reference artefact is described. The method comprises the step of rotating a surface sensing device, such as a scanning probe, mounted on the scanning head about at least one axis of the scanning head to move the surface sensing device into a plurality of different angular orientations relative to the reference artefact. A step is then performed of measuring, with the surface sensing device, at least one property of the reference artefact at each of the different angular orientations. An error map or function is then created for at least one measurement scale of the scanning head using the properties of the reference artefact measured and optionally known or calibrated properties of that reference artefact. The method may comprise use of co-ordinate positioning apparatus, such as a co-ordinate measuring machine, to move the scanning head. The reference artefact may comprise a single feature or an array of features.

Abstract: A method of calibrating a probe is disclosed said probe being mounted on a machine and having a stylus with a workpiece contacting tip, comprising calculating calibration information for the probe for a first orientation of the probe, and rotating the calibration information by an angle to obtain a probe calibration information for when the probe is oriented by that angle with respect to the first orientation. Also disclosed is a method of calibrating a probe during a measurement process. The calibration information may include a vector which relates probe head axes to machine axes; a calibration matrix; datum data; an inertial matrix. The stylus tip may be datumed at the orientation of the probe or inferred from datum information obtained at different orientations. The rotation step may be carried out by a software/computer program which may be stored on a controller for the machine.

Abstract: A method of measuring an artefact 5 using a machine 2 on which a measuring probe 6 is mounted. The probe is brought into contact with the artefact and movement continued for a limited distance to deflect the stylus 7. The machine and probe outputs are recorded whilst the probe is free and when the stylus is deflected. A model of the probe and CMM outputs during both contact and non-contact between the probe and artefact is fitted to the data to allow the contact position when the stylus contacts the artefact with zero force to be determined. The probe outputs may be fitted to the model individually to determine a single contact position. By using data during movement of the probe towards and away from the artefact, errors due to time delays may be corrected.

Abstract: A method of measuring an artefact 5 using a machine 2 on which a measuring probe 6 is mounted. The probe is brought into contact with the artefact and movement continued for a limited distance to deflect the stylus 7. The machine and probe outputs are recorded whilst the probe is free and when the stylus is deflected. A model of the probe and CMM outputs during both contact and non-contact between the probe and artefact is fitted to the data to allow the contact position when the stylus contacts the artefact with zero force to be determined. The probe outputs may be fitted to the model individually to determine a single contact position. By using data during movement of the probe towards and away from the artefact, errors due to time delays may be corrected.