Abstract: A measurement probe is carried by a carriage movable in a first direction to cause the measurement probe to traverse a measurement path across a surface of an object received by a support surface to provide measurement data representing variations in a second direction different from the first direction of surface features along the measurement path. The support surface is movable in a third direction different from the first and second directions. Measurement of a surface area is effected by controlling the carriage to cause the measurement probe to traverse a plurality of measurement paths across an area of the surface of an object mounted on the support surface and by controlling the support surface to move in the third direction after each measurement path traverse. Measurement data thus obtained for a reference sphere of previously known radius is used to determine the relative orientation of the first and third directions.

Abstract: A position-to-electrical transducer circuit primarily intended for use in meteorological instruments for measuring a characteristic of a surface of a workpiece. An excitation signal generator provides to a transducer an excitation signal whose voltage varies in a known manner with time and a processor analyzes an electrical signal from the transducer to generate a measurement signal. The processor corrects for any phase shift between excitation signal and the electrical signal to provide an accurate measurement. A meteorological instrument for measuring a characteristic of a surface of a workpiece in which a pivotably-mounted arm holding a stylus is traversed relative to the surface of the workpiece and a variable transducer converts the position of the stylus into a corresponding electrical signal.

Abstract: A stylus support assembly for a gauge for a metrological instrument which has a main gauge body and a mounting block for supporting a stylus. The main gauge body and the mounting block each have first and second ends, with the first ends facing in the same direction. A resilient ligament connects the first ends which are arranged at an angle to one another so that the ligament biases the mounting block and thus the stylus to extend at an angle to the main gauge body, thereby providing a biasing force to bias the stylus against the workpiece.

Abstract: A stylus is carried at one end of a support arm mounted so as to be pivotable about a pivot axis to allow the stylus to follow a surface during relative movement between the stylus and the surface. A drive arrangement is responsive to pivotal movement of the support arm to drive the support arm to maintain the support arm at a substantially constant attitude. A measuring arrangement is provided for measuring the displacement of the stylus. The measuring arrangement uses a measuring element mounted to one end of the support arm adjacent the stylus. The measuring arrangement may be an interferometer and the measuring element a corner cube mounted so as to be aligned with the tip of the stylus.

Abstract: A metrological instrument for measuring surface characteristics such as surface form of a component (300). The instrument includes a slideway (32) to cause relative movement between a surface sensing probe (84) and the component which allows the probe to traverse a surface of the component. A probe carriage (80) supports the probe to allow the probe to move as a body in a measurement direction relative to the carriage so as to follow a surface being sensed. An optical sensor (82) provides a signal indicative of the displacement of the probe relative to the probe carriage. A controller (83) acts in response to a signal from the optical sensor, to move the probe carriage so as to maintain the probe in an operational range. A further sensor (11) measures measurement of displacement of the probe in the measurement direction as it follows a surface during use of the instrument.

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.

Abstract: An arrangement for mounting a stylus on a stylus support for a metrological instrument includes a camming pin on a mounting disc of the stylus support, which passes through a mounting hole in a mounting disc of the stylus. A spring applies a sideways force to a sloping cam surface of the camming pin, which is converted into a force pulling the camming pin through the mounting hole and thus holding the mounting discs together. An operator can deform the spring so that it releases the camming pin, allowing the stylus to be mounted or dismounted without applying significant force to the pivot bearing of the stylus support. If excessive radial force is applied to the stylus arm, the spring will ride up the cam surface allowing the stylus to be released from the stylus support, thereby avoiding applying extreme forces to the pivot bearing.

Abstract: A blocking technique and apparatus are used to mount a partially finished lens or other component to an arbor, which is useable to hold the partially finished lens for subsequent machining or mechanical operations. The blocking of the partially finished lens occurs on the same axes of the multi-axis machining device that were used to generate the partially finished lens. The blocking of the partially finished lens occurs without removing the partially finished lens from the workpiece holder which held the partially finished lens during the machining operation. Accurate and repeatable blocking is achieved using the axes of the lens generating equipment.

Abstract: A portable metrological instrument for measuring surface finish parameters has a main housing which sits on a workbench. A slidable arm can be extended or retracted over the bench so as to move a stylus over a workpiece. The stylus is fitted to a gauge mounted to the end of the arm. The mounting includes a vertically movable slider which incorporates a mechanism for lifting the stylus away from the workpiece and lowering it back. The operation of the instrument is controlled by modular software which can be reprogrammed using an external device, and the machine is operated by a control panel on the housing or by an identical control panel on a remote controller. The gauge includes an inductive sensor, and the associated circuit includes automatically adjustable error canceling devices. The control system uses the sensed position of the arm to estimate the speed of the motor which drives the arm, avoiding the need for a shaft encoder on the motor.

Abstract: A system for measuring the angle of a beam of light is arranged so that a periodically varying pattern is formed on a photodetector, with a waveform property such as wavelength or phase of the pattern varying with the angle of the light. This may be done by creating interference between the light beam to be measured and a reference light beam having a fixed angle, or by forming a shadow on the detector array of one or more masks having a periodically varying transmission characteristic. One convenient way of processing the output of the photodetector array is to perform a fast Fourier transform, obtain therefrom one or more spatial frequency components, and extract therefrom a part which provides a measure of the angle of the light beam. The use of a periodically varying pattern on the photodetector array enables a substantial length of the array to be used in any particular measurement operation, and averages out individual performance differences between different elements of the photodetector array.

Abstract: A metrological apparatus has a movable arm 15 which moves up and down between two bearing members 13, both of which define datum positions for the arm 15. The arm 15 has air bearings on the bearing members 13, so that it adopts a position equidistant between the bearing members 13. In this way, the position of the arm 15 contains the average of the errors in the two datum positions defined by the bearing members 13. Where the bearing members 13 have symmetric errors, these will be cancelled. Since the path of maximum straightness of movement of the arm 15 is spaced from the bearing members 13, it is possible to put a workpiece 3 in this path and a turntable 5 for supporting the workpiece 3 is arranged to have its rotational axis in line with the path of maximum straightness.

Abstract: Apparatus for surface measurement has a grating interferometer with a curved diffraction grating carried on a pivotal support arm of a probe for contacting a surface. The probe is biased into contact with a surface by an electromagnetic coil acting on an armature, or a pair of such biasing arrangements. A laser diode illuminates the grating to produce a pair of first order diffracted beams of opposite sign which are reflected from internal faces of a prism, and combined by a diachronic central layer of the prism and a pair of beam splitters. Output signals from the beam splitters are supplied to a signal processing circuit having a fringe counter and an interpolator. The fringe counter detects zero crossings of the signals and the interpolator maintains a digital estimate of the phase of the signals and updates the estimate when the phase difference between the estimate and the input signals exceeds a predetermined threshold.

Abstract: Apparatus for measuring surface roughness utilizes diffraction patterns derived from the surface under test. The energies in the different orders are detected and processed utilizing various different algorithms dependent upon a number of factors such as the number of orders in the diffraction pattern and asymmetry in the diffraction pattern. Various filter functions both for the diffraction pattern itself and for values of surface roughness after measurement are disclosed. One algorithm for measuring surface roughness involves comparison of values representing the energy orders with reference values, preferably reference values obtained by an interpolation operation between one set of reference values representative of a diffraction pattern from a symmetrical surface and another set representative of a diffraction pattern from an asymmetrical surface.

Abstract: A metrological apparatus for measuring form and texture of a surface employs an inductive transducer producing an AC gauge signal, and a tracking AC analogue to digital converter. In order to avoid errors in the output signal at a relatively high speed of traverse of the surface due to a non-flat frequency response of the converter, the output signal is processed by a digital filter to provide a combined frequency response which is flat over a desired range. In order to avoid errors in the output signal due to non-linearity of the transducer, a square or cubic correction is applied to the signal. A method calibrating the apparatus to obtain coefficients for the square and cube terms in the correction process is also described.

Abstract: An interpolator, particularly for use with an optical grating for detecting position in a metrological apparatus, receives input signals in quadrature. One of the input signals is squared and the two signals are multiplied together to provide further signals in quadrature at twice the frequency of the input signals. One of the further signals is also squared and the further signals are multiplied together to provide output signals at four times the frequency of the input signals. Filtering is provided to remove DC components, such as due to drift. In the illustrated metrological apparatus, the zero crossing points of the output signals are detected to effect sampling, with high resolution, of a surface sensor output. Interpolation noise occurs at a high frequency and is removed by low pass filtering of the sample signal from the surface sensor.

Abstract: In order to measure the surface profile of a workpiece, a yoke having two fixed feet is held in contact with the surface as the workpiece is rotated. A dynamic probe is mounted on the yoke by means of a transducer which outputs a signal dependent upon the position of the dynamic probe relative to a transducer datum. The fixed feet and the foot of the dynamic probe have a similar shape and size so that they detect irregularities in the workpiece surface with equal sensitivity. Fourier analysis of the signal caused by movement of the dynamic probe directly by the workpiece and also by movement of the yoke enables the profile of the workpiece to be determined. In order to improve the frequency response of the transducer output over the range of harmonics considered, the angles between the dynamic probe and the fixed probes are unequal. The apparatus does not require a precision spindle type machine to rotate the workpiece and is therefore particularly suitable for in situ measurement of workpiece profiles.