Abstract: A method of calibrating a scanning system comprising a machine and a measuring probe, includes the steps of error mapping the system statically and qualifying the stylus tip so that the system will provide accurate measurements, determining the positions of a number of datum points on the surface of an artefact with the probe stylus in contact with the workpiece and at zero deflection normal to the surface, scanning the surface through the datum points at a nominal stylus deflection and at the maximum speed which provides repeatable position measurements to make a second determination of the positions of the datum points, determining the errors attributable to the scanning process by subtracting the positions obtained in the first and second determinations, and storing the error values for correction of subsequent measurements of similar artefacts.

Abstract: An analogue probe having a stylus with a spherical tip of radius (r) is calibrated using a sphere of known radius (R) mounted on a machine. The stylus tip is driven into the sphere from a plurality of directions (at least 9), each nominally normal to the sphere surface, until the stylus has deflected a predetermined amount. The machine movement is then reversed, and probe (a,b,c) deflection outputs are recorded simultaneously with machine (X,Y,Z) axis positions until the stylus tip leaves the surface. The readings are extrapolated to obtain the (X,Y,Z) readings when the probe radial deflection is zero. The value of (R+r) is determined from these readings along with the position of the sphere center giving a value with zero probe errors. Values of (R+r) are also determined using a pre-selected radial deflection for each of the directions, by converting probe (a,b,c) outputs at that deflection to incremental machine (X,Y,Z) axis values using a trial probe transformation matrix.

Abstract: An analogue probe having a stylus with a spherical tip of radius (r) is calibrated using a sphere of known radius (R) mounted on a machine. The stylus tip is driven into the sphere from a plurality of directions (at least 9), each nominally normal to the sphere surface, until the stylus has deflected a predetermined amount. The machine movement is then reversed, and probe (a,b,c) deflection outputs are recorded simultaneously with machine (X,Y,Z) axis positions until the stylus tip leaves the surface. The readings are extrapolated to obtain the (X,Y,Z) readings when the probe radial deflection is zero. The value of (R+r)is determined from these readings along with the position of the sphere centre giving a value with zero probe errors. Values of (R+r) are also determined using a pre-selected radial deflection for each of the directions, by converting probe (a,b,c) outputs at that deflection to incremental machine (X,Y,Z) axis values using a trial probe transformation matrix.

Abstract: A method of calibrating a scanning system comprising a machine and a measuring probe, includes the steps of error mapping the system statically and qualifying the stylus tip so that the system will provide accurate measurements, determining the positions of a number of datum points on the surface of an artefact with the probe stylus in contact with the workpiece and at zero deflection normal to the surface, scanning the surface through the datum points at a nominal stylus deflection and at the maximum speed which provides repeatable position measurements to make a second determination of the positions of the datum points, determining the errors attributable to the scanning process by subtracting the positions obtained in the first and second determinations, and storing the error values for correction of subsequent measurements of similar artefacts.

Abstract: A method of calibrating a scanning system comprising a machine and a measuring probe, includes the steps of error mapping the system statically and qualifying the stylus tip so that the system will provide accurate measurements, determining the positions of a number of datum points on the surface of an artefact with the probe stylus in contact with the workpiece and at zero deflection normal to the surface, scanning the surface through the datum points at a nominal stylus deflection and at the maximum speed which provides repeatable position measurements to make a second determination of the positions of the datum points, determining the errors attributable to the scanning process by subtracting the positions obtained in the first and second determinations, and storing the error values for correction of subsequent measurements of similar artefacts.

Abstract: Velocity dependent measurement errors made by coordinate measuring machines (CMMs) are corrected by deriving a polynomial expression which relates components of the errors to the relative velocity between the probe and the workpiece. A calibration is performed to establish the constant of the polynomial for different stylus configurations of the probe and these constants are stored. During a measuring process the probe produce analogue output signals from which a trigger signal is generated to latch the output signals of the machine measuring devices. The probe and machine output signals are monitored and recorded at clocked intervals over a range of positions within which lies the position at which the machine readings were latched. Actual relative velocity values are calculated at each position and, using these values and the stored constants, the errors in the machine readings at each position can be calculated from the polynomial.

Abstract: A workpiece surface 30 is digitized by scanning it with the stylus 8 of a scanning probe 5. Digitized coordinate data for many points P1-P6 on the workpiece surface are subjected to a filtering algorithm, in order to remove redundant data when the surface is relatively flat or planar. Top and bottom tolerance vectors TV0,BV0 are defined, starting from a first point P1 and lying at a given tolerance h above and below a second point P2. Next, a direct vector DV1 is defined between the point P1 and a third point P3. If the vector DV1 lies outside the tolerance band between the vectors TV0 and BV0, then point P2 is deemed to be required and is not filtered out. Otherwise, the data for point P2 is deemed to be redundant and is rejected. In this case, new tolerance vectors TV1 and BV1 are now defined, starting from point P1 and passing within a tolerance h above and below point P3.

Abstract: A coordinate positioning machine is equipped with either an optical probe or a contact measuring probe. Movement of the head of the machine to enable the probe to scan an unknown surface is controlled by predicting the position of a subsequent point to which the head of the machine is to be driven upon the basis of three most recently measured points, P.sub.1, P.sub.2, P.sub.3. The prediction of the subsequent point P.sub.4 is performed by machine control in real time.

Abstract: Apparatus with a multi-axis mechanism to perform, say, measurements or tests, has at least one pair of temperature detectors individually for each of selected members of the mechanism, each pair of temperature detectors being arranged to sense temperature differences transversely across the associated member. The required positions of the temperature detectors are predetermined from a preliminary examination of the mechanism, so that the extent and direction of each predetermined aspect of thermal distortion within the mechanism, can be computed from simultaneously detected transverse temperature differences, employing algorithms devised as a result of the preliminary examination of the mechanism. Compensation for corresponding selected errors in the measurements or tests can be calculated from the computed extent and direction of each of the predetermined aspects of thermal distortion within the mechanism.