Method and apparatus for determining two-point size of a workpiece

Abstract

The invention provides a method and apparatus for determining a two-point size of a workpiece. One aspect relates to a computer-implemented method for determining a two-point size of a workpiece (30), the method comprising the steps of: receiving a set (50) of measurement points of the workpiece (30); determining a longitudinal axis (L) of the workpiece (30) based on the set (50) of measurement points; projecting at least a portion of the set (50) of measurement points into a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projected points; and determining the two-point size of the workpiece (30) based on the projected points.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of measuring workpieces, and more particularly to a method and apparatus for determining a two-point size of a workpiece. BACKGROUND

[0002] The two-point size of a workpiece, preferably a workpiece having a substantially cylindrical shape, is the (local size) distance between two points of the surface of the workpiece that are opposite each other with respect to the longitudinal axis of the workpiece. In the case of a cylindrical workpiece, these two points are opposite each other with respect to the cylindrical axis of the workpiece.

[0003] Known methods for determining the two-point size require measurement data (e.g. measurement points) obtained by measuring the workpiece circumferentially around the longitudinal axis of the workpiece (e.g. the cylindrical axis of a cylindrical workpiece) and at different positions along the longitudinal axis. The measurement points obtained by measuring the workpiece circumferentially around one position of the longitudinal axis represent a rotation of the workpiece, and these measurement points are substantially located in a plane perpendicular to the longitudinal axis of the workpiece. However, in order to measure the workpiece as accurately as possible, a large number of rotations of the workpiece must be measured (i.e. rotations at different positions along the longitudinal axis of the workpiece), wherein each rotation is displaced along the longitudinal axis of the workpiece. Furthermore, measuring the workpiece requires that the probe measuring the workpiece must be aligned for each single rotation, i.e. at a new position along the longitudinal axis of the workpiece. This results in as many individual measurements as rotations, which are not measured consecutively. Therefore, in order to obtain an accurate two-point size of the workpiece, the measurement of the workpiece is lengthy and cumbersome. SUMMARY

[0004] The present invention has been made in view of the above, and it is an object of the present invention to provide a method and apparatus for determining a two-point size of a workpiece that allows for quickly measuring the workpiece while providing an accurate determination of the two-point size of the workpiece.

[0005] In particular, the present invention allows for determining an accurate two-point size of a workpiece while the measurement of the workpiece can be performed quickly.

[0006] This object is solved by the subject matter of the independent claims. Preferred embodiments are defined in the dependent claims.

[0007] An aspect of the present invention relates to a computer-implemented method for determining a two-point size of a workpiece, the method comprising the steps of:

[0008] receiving a set of measurement points of the workpiece;

[0009] determining a longitudinal axis of the workpiece based on the set of measurement points;

[0010] projecting at least a part of the set of measurement points into a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; and

[0011] determining the two-point size of the workpiece based on the projected points.

[0012] Advantageously, the method allows to determine the two-point size of the workpiece using measured points which have been measured consecutively and which can not lie in a plane perpendicular to the longitudinal axis of the workpiece, since the measured points are projected in the projection plane and the two-point size is determined based on the projected points. Measured consecutively means that the measured points have been captured with a single measurement. Thus, the measurement of the workpiece can be performed faster, while still the two-point size can be determined accurately.

[0013] Preferably, the set of measured points is obtained by measuring the surface of the workpiece with a measuring device. Each measured point can represent three-dimensional (3D) position information (e.g. 3D coordinates) of a measured position of the surface of the workpiece relative to a reference position. The measured points can preferably be obtained from a coordinate measuring device which measures the workpiece. An exemplary coordinate measuring device can use a probe which samples the workpiece to obtain the measured points. The probe can be configured to contact the surface, e.g. with a needle tip, to measure the workpiece, or the probe can be configured to measure the surface contactless, e.g. optically, based on computed tomography and / or x-rays. Further, the measuring device and / or the probe preferably measures the workpiece in a single scan. That is, the measured points are preferably captured with a single scan.

[0014] Further, each projected point of the set of projected points which is projected into the projection plane can correspond to a measured point of the set of measured points. In particular, each projected point of the set of projected points can correspond to a different measured point of the set of measured points. Since a part of the set of measured points is projected into the projection plane, each projected point of the set of projected points can represent two-dimensional (2D) position information, e.g. 2D coordinates.

[0015] Preferably, the (complete) set of measured points, i.e. all measured points of the set of measured points, is projected into the projection plane to obtain the set of projected points. Further, the projection plane which is perpendicular to the longitudinal axis of the workpiece can have a normal which is parallel to the longitudinal axis of the workpiece. Optionally, the set of measured points can be analyzed to obtain incorrect measured points, i.e. outliers, which are not projected into the projection plane, such that only a part of the measured points is projected into the projection plane.

[0016] Preferably, the set of measured points can consist of measured points obtained from a helical measurement of the workpiece, and / or the workpiece can have a substantially cylindrical shape.

[0017] Advantageously, the helical measurement of a workpiece, which is preferably substantially cylindrical, allows for a faster measurement of the workpiece compared to the known measurement methods described above. With the helical measurement, the surface of the workpiece can be measured along a path having a substantially helical trajectory, e.g. a path in the form of a thread of a screw. In particular, the helical measurement results in a set of measurement points having a substantially regular non-zero axial difference between successive and / or adjacent measurement points of the set of measurement points along a longitudinal axis of the workpiece, e.g. a cylindrical axis of a cylindrical workpiece. That is, in contrast to the conventional measurement methods in which the measurement points of a revolution are substantially located in a plane perpendicular to the longitudinal axis of the workpiece, the measurement points of a revolution obtained with the helical measurement are not located in a plane perpendicular to the longitudinal axis of the workpiece. Furthermore, the helical measurement allows for measuring the workpiece without the need to align the probe along the longitudinal axis for each revolution of the workpiece, and thus, the measurement can be performed faster. Preferably, the helical measurement is applicable to workpieces having a substantially cylindrical shape.

[0018] Furthermore, the set of measurement points obtained with the helical measurement can comprise measurement points obtained from at least one revolution around the longitudinal axis of the workpiece and / or the cylindrical axis of the substantially cylindrical workpiece. Preferably, the set of measurement points can comprise measurement points obtained from a plurality of revolutions around the longitudinal axis of the workpiece and / or the cylindrical axis of the substantially cylindrical workpiece. A revolution can be determined from the measurement points by adding the angular difference between successive and / or adjacent measurement points around the longitudinal axis of the workpiece and / or around the cylindrical axis of the cylindrical workpiece until 360 degrees.

[0019] Preferably, the step of determining the longitudinal axis of the workpiece can comprise determining a shape model of the workpiece based on the set of measurement points and providing the longitudinal axis of the shape model as the longitudinal axis of the workpiece. Typically, the workpiece does not have a perfect shape, e.g. a perfect cylindrical shape. That is, in the case of a cylindrical workpiece, the diameter of the workpiece can vary depending on the measurement location. This deviation is reflected in the set of measurement points and the shape model advantageously provides an approximation of the shape of the workpiece, allowing for determining the longitudinal axis of the workpiece.

[0020] Advantageously, for a substantially cylindrical workpiece, the shape model can be a cylindrical shape model, preferably a Gaussian cylindrical shape model, and the longitudinal axis of the workpiece can correspond to the cylindrical axis of the cylindrical shape model. The Gaussian cylindrical shape model can provide a cylindrical shape model which is arranged as close as possible to a portion of the set of measurement points and / or as close as possible to the set of measurement points. In particular, the Gaussian cylindrical shape model can be obtained by using a least squares method on the set of measurement points.

[0021] However, depending on the case, different cylindrical shape models can be applied. For example, the cylindrical shape model can comprise a minimum circumscribed cylindrical shape model and a maximum inscribed cylindrical shape model.

[0022] Advantageously, the cylindrical shape model provides a good approximation of the shape of a cylindrical workpiece. Thus, the cylindrical shape model allows to provide a good approximation of the longitudinal axis of the workpiece and / or the cylinder axis of the cylindrical workpiece.

[0023] Preferably, the step of projecting at least a part of the set of measurement points into the projection plane and / or projecting the set of measurement points into the projection plane can comprise projecting at least a part of the set of measurement points and / or the set of measurement points parallel to the longitudinal axis. Thus, each projection point of the set of projection points can be obtained by projecting a respective measurement point of the set of measurement points parallel to the longitudinal axis of the workpiece and / or the cylinder axis of the workpiece (in case of a cylindrical workpiece) into the projection plane.

[0024] Preferably, the step of determining the two-point size of the workpiece can comprise determining a center of a circle based on the set of projection points, wherein the circle is preferably a Gauss circle determined from the set of projection points. That is, the circle is determined from the set of projection points. Further, the Gauss circle can be a circle that lies in the middle between the set of projection points in the best possible way.

[0025] Further, the step of determining the two-point size of the workpiece can comprise determining a point pair based on the set of projection points, wherein the point pair is opposite to each other with respect to the center of the circle, and determining the two-point size by calculating a distance between the point pair. Further, the determination of the center of the circle can be performed for a cylindrical workpiece.

[0026] Advantageously, the determination of the center of the circle leads to a good approximation of the center of the circle, since the workpiece can typically not have a perfect shape as discussed above. Using the determined center of the circle allows to accurately determine the two-point size of the workpiece. Further, the circle determined from the set of projection points is not limited to a Gauss circle. For example, the determined circle can comprise at least one of a minimum circumscribed circle and a maximum inscribed circle determined from the set of projection points.

[0027] Preferably, the point pair can comprise at least one point of the set of projection points, and in case the other point in the point pair is not comprised in the set of projection points, the method further comprises determining the other point by interpolation based on the set of projection points. Alternatively, both points in the point pair can be derived by interpolation of the set of projection points.

[0028] Advantageously, the two-point size can also be determined for a case where the set of projection points does not comprise projection points that are opposite to each other with respect to the center of the circle.

[0029] Preferably, the set of measurement points can comprise at least one subset of measurement points corresponding to one revolution of the workpiece, and the set of projection points comprises at least one subset of projection points corresponding to the at least one subset of measurement points. The subset of projection points can be obtained by projecting the corresponding subset of measurement points parallel to the longitudinal axis into the projection plane. Furthermore, the set of measurement points can preferably comprise more than one subset of measurement points, each subset of measurement points corresponding to a different revolution of the workpiece. In particular, the number of subsets of measurement points can be equal to the number of revolutions of the workpiece measured. Furthermore, each subset of measurement points can be projected into the projection plane to obtain a corresponding subset of projection points. That is, for each revolution of the workpiece measured, a corresponding subset of projection points is obtained. Thus, a two-point size can be determined for each revolution of the workpiece.

[0030] The subset of measurement points corresponding to one revolution of the workpiece can be determined from the set of measurement points. In particular, the set of measurement points can be projected vertically on the longitudinal axis of the workpiece, i.e. on the longitudinal axis of the shape model (e.g. the cylindrical axis of a cylindrical shape model), thereby obtaining a set of intermediate points distributed on the longitudinal axis. A first intermediate point and a second intermediate point are determined from the set of intermediate points, wherein the first and second intermediate points have a maximum distance to each other among the possible pairs of points of the set of intermediate points. The remaining intermediate points of the set of intermediate points (i.e. the set of intermediate points without the first and second intermediate points) are ordered based on their distance to the first or second intermediate point. For example, the remaining intermediate points can be ordered in ascending order of their distance to the first or second intermediate point. The first intermediate point, the ordered remaining intermediate points, and the second intermediate point constitute an ordered set of intermediate points, wherein each point of the ordered set of intermediate points can be referenced by a corresponding measurement point of the set of measurement points.

[0031] Furthermore, the determination of the subset of measurement points corresponding to one revolution can be based on a distance criterion or an angle criterion. For example, the distance criterion can depend on the measurement process of the workpiece. In particular, the distance criterion can correspond to the distance (e.g. the slice thickness) along the scan axis of the workpiece required for measuring one revolution of the workpiece. Alternatively, the user can define the distance criterion.

[0032] Based on the distance criterion, a subset of the measurement points can be determined from the set of measurement points by referring to subsequent points in the set of ordered intermediate points that just satisfy the distance criterion, i.e. the distance between the first of the subsequent points and the last of the subsequent points just satisfies the distance criterion. For example, points from the set of measurement points can be assigned to the subset of measurement points by referring to the respective subsequent points from the set of ordered intermediate points until the distance between the first of the subsequent points and the last of the subsequent points is greater than or equal to the distance criterion. This process can be repeated for further rotations, wherein the first of the next subsequent points from the set of ordered intermediate points is the successor of the last of the previous subsequent points from the set of ordered intermediate points.

[0033] In case the angle criterion is used instead of the distance criterion, subsequent points in the set of measurement points can be assigned to the subset of measurement points until the added angle between the subsequent points with respect to the longitudinal axis, e.g. the cylinder axis of the cylindrical shape model, exceeds 360°, taking into account the order provided by the set of ordered intermediate points. To determine the angle between the subsequent points with respect to the longitudinal axis, the subsequent points can be projected into a plane perpendicular to the longitudinal axis. This process can be repeated for further rotations, wherein for the next rotation, the first of the next subsequent points is the successor of the last of the previous subsequent points.

[0034] By determining the subset of measurement points based on the set of ordered intermediate points, errors in the order of the measurement points can be prevented. In particular, subsequent measurement points in the set of measurement points can be close together, such that the longitudinal difference along the scan axis is low. In case the longitudinal axis of the determined shape model and / or the cylinder axis of the cylindrical shape model is tilted with respect to the actual scan axis, the order of two consecutive points in the set of measurement points when projected on the determined longitudinal axis and / or cylinder axis is inverted compared to the projection of the set of measurement points on the scan axis.

[0035] Preferably, the step of determining the two-point size of the workpiece can comprise determining respective circle centers of a circle, preferably a Gaussian circle, based on the at least one subset of projection points, determining a pair of points from the at least one subset of projection points, wherein the pair of points is substantially opposite to each other with respect to the circle center, and determining the two-point size by calculating the distance between the pair of points. Preferably, the two-point size is the sum of the distances of the points in the pair of points to the circle center.

[0036] Although the circle is preferably a Gaussian circle determined from the at least one subset of projection points, other circles are applicable. For example, the determined circle can comprise at least one of a smallest circumscribed circle and a largest inscribed circle determined from the at least one subset of projection points. Furthermore, in case of more than one subset of projection points, a respective circle and circle center can be determined for each subset of projection points. Moreover, for each subset of projection points, the two-point size can be determined by determining a pair of points from each subset of projection points, which pair of points is opposite to each other with respect to the circle center of the respective subset of projection points, and by determining the two-point size by calculating the distance between the pair of points.

[0037] Advantageously, the two-point size can be accurately determined from the set of measurement points, while a fast measurement of the workpiece can be performed.

[0038] Preferably, the respective pair of points for each subset of projection points can comprise at least one point of the subset of projection points, and in case the other point of the pair of points is not comprised in the subset of projection points, the method can further comprise determining the other point by interpolation based on the subset of projection points. Alternatively, both points of the pair of points for each subset of projection points can be derived by interpolation of the set of respective projection points.

[0039] Advantageously, two opposite points can be determined from a subset of projection points, although the subset of projection points can not comprise the opposite projection points. Thus, the two-point size can be determined even in case the subset of projection points does not comprise the opposite projection points.

[0040] Preferably, the step of determining the two-point size of the workpiece can comprise determining at least one of a minimum two-point size of the workpiece, a maximum two-point size of the workpiece, or an average two-point size of the workpiece.

[0041] Another aspect relates to a device for determining a two-point size of a workpiece, the device comprising:

[0042] a receiving unit configured to receive a set of measurement points of the workpiece; and

[0043] a determining unit configured to:

[0044] determine a longitudinal axis of the workpiece based on the set of measurement points;

[0045] project the set of measurement points into a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; and

[0046] determine the two-point size of the workpiece based on the set of projection points.

[0047] Further, the device for determining a two-point size of a workpiece can receive the set of measurement points from a measurement device as discussed above. Optionally, the device can comprise a measurement unit for measuring the workpiece. The measurement unit can measure the workpiece using a probe that samples the workpiece. The probe can be configured to contact the surface, e.g. with a needle tip, to measure the workpiece, or the probe can be configured to measure the surface contactlessly, e.g. optically, based on computed tomography and / or x-rays.

[0048] Further, the determining unit can be configured to perform the method as discussed above.

[0049] Another aspect relates to a computer readable medium comprising instructions which, when executed by a computer, cause the computer to perform a method comprising the steps of:

[0050] receiving a set of measurement points of a workpiece;

[0051] determining a longitudinal axis of the workpiece based on the set of measurement points;

[0052] projecting the set of measurement points into a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; and

[0053] determining a two-point size of the workpiece based on the set of projection points.

[0054] Further, the computer readable medium can comprise instructions allowing to perform the method as discussed above. BRIEF DESCRIPTION OF DRAWINGS

[0055] These and other objects, features, and advantages of the present application will become apparent in light of the following detailed description of preferred embodiments, as illustrated in the accompanying drawings. It should be understood, of course, that even though a preferred embodiment is described in detail, the single features of the embodiment can be combined with additional embodiments.

[0056] Figure 1 A device for measuring a two-point size of a workpiece is depicted.

[0057] Figure 2 A helical measurement of a workpiece is depicted.

[0058] Figure 3 Projecting measurement points into a projection plane is depicted.

[0059] Figure 4 A circle determined from a set of projection points is depicted.

[0060] List of reference signs

[0061] 10 Device for determining a two-point size of a workpiece

[0062] 12 Receiving unit

[0063] 14 Determining unit

[0064] 20 Measuring equipment

[0065] 30 workpieces

[0066] A collection of 50 measurement points

[0067] 52~60 measurement point subset

[0068] 62 projection point subsets

[0069] 70,72 points

[0070] C Circle

[0071] CP Center

[0072] D The distance between pairs of points

[0073] P Path of spiral measurement

[0074] L longitudinal axis / cylindrical axis of the workpiece DETAILED DESCRIPTION

[0075] Figure 1 Depicted is a diagram for determining a workpiece 30 (e.g., Figure 1 The apparatus 10 is configured to measure the workpiece 30 at two points (e.g., a cylindrical workpiece 30 shown in FIG. 1 ). A measuring device 20, communicatively coupled to the apparatus 10, is configured to measure the workpiece 30 to obtain a set 50 of measured points of the workpiece. The set of measured points is received by a receiving unit 12 of the apparatus 10. Alternatively, the apparatus 10 may include a measuring unit (not shown) for measuring the workpiece 30, and the receiving unit 12 receives the set 50 of measured points from the measuring unit.

[0076] The device 10 further includes a determining unit 14 for determining a two-point size of the workpiece 30 based on the set 50 of measurement points received by the receiving unit 12. The two-point size of the workpiece 30 is the distance between two points on the surface of the workpiece 30 that are opposite to each other about the longitudinal axis L of the workpiece 30. Figure 1 As depicted in FIG, the workpiece 30 is a generally cylindrical workpiece 30 , wherein the cylindrical axis of the workpiece 30 corresponds to the longitudinal axis L. The term “generally” means that the workpiece 30 does not have a perfect shape, and the diameter of the cylindrical workpiece 30 may vary depending on the measurement location.

[0077] The measuring device 20 and / or the measuring unit may be configured to measure the workpiece using a probe that samples the workpiece. The probe may be configured to, for example, contact the surface of the workpiece 30 with a needle tip to measure the workpiece 30, or the probe may be configured to measure the surface of the workpiece 30 contactlessly (e.g., optically, based on computed tomography and / or x-rays).

[0078] Figure 2A set 50 of measurement points obtained by measuring the workpiece 30 with the measuring device 20 or the measuring unit is depicted. In particular, the set 50 of measurement points is obtained by a helical measurement of the workpiece 30, wherein each measurement point of the set 50 of measurement points represents 3D position information (e.g. 3D coordinates represented by X, Y and Z coordinates) of a measurement position of the surface of the workpiece. With the helical measurement, the surface of the workpiece can be measured along a path P having a substantially helical trajectory (e.g. a path P having the form of a thread of a screw). In particular, the helical measurement is such that the set 50 of measurement points has a substantially regular non-zero axial difference between consecutive and / or adjacent measurement points of the set 50 of measurement points along a longitudinal axis L of the workpiece 30 (e.g. a cylindrical axis of a cylindrical workpiece 30).

[0079] As Figure 2 depicted, the workpiece 30 is measured with more than one revolution, each revolution being displaced along the longitudinal axis L of the workpiece 30.

[0080] Thus, the set 50 of measurement points comprises more than one subset 52-60 of measurement points, each subset 52-60 of measurement points comprising measurement points of one revolution obtained with the helical measurement. One revolution can be determined from the set 50 of measurement points by adding the angular difference between consecutive and / or adjacent measurement points around the longitudinal axis L of the workpiece 30 until 360 degrees.

[0081] As discussed above, the workpiece 30 can not have a perfect shape, such that it is difficult to identify the longitudinal axis L of the workpiece 30. Thus, the determining unit 14 is configured to determine the longitudinal axis L based on the set 50 of measurement points. In particular, the determining unit 14 can determine a shape model (not shown) of the workpiece 30 based on the set 50 of measurement points. For example, the determining unit 14 can determine a Gaussian cylindrical shape model of a cylindrical workpiece 30. The Gaussian cylindrical shape model can be obtained by using a least squares method on the set 50 of measurement points and / or at least a portion of the set 50 of measurement points. Thus, the Gaussian cylindrical shape model is arranged to be as close as possible to the set 50 of measurement points and / or the portion of the set 50 of measurement points. Further, the determining unit 14 can provide a cylindrical axis of the Gaussian cylindrical shape model as the longitudinal axis L of the workpiece 30.

[0082] With reference to Figure 3The determining unit 14 is further configured to project at least a portion of the set of measurement points 50, in particular substantially the entire set of measurement points 50, into a projection plane perpendicular to the longitudinal axis L of the determined workpiece 30 to obtain a respective set of projection points. Moreover, a normal of the projection plane can be parallel to the longitudinal axis L. Furthermore, at least a portion of the measurement points 50, in particular the set of measurement points 50, can be projected parallel to the longitudinal axis L determined according to the shape model. In case the set of measurement points 50 comprises more than one subset of measurement points, in particular each subset of measurement points 52-60 is projected into the projection plane to obtain a respective subset of projection points 62. For the sake of clarity, Figure 3 A subset of projection points 62 is depicted being projected into a projection plane perpendicular to the longitudinal axis L to obtain a respective subset of projection points 62.

[0083] Referring to Figure 4 The determining unit 14 is further configured to determine a two-point size of the workpiece 30 based on the set of projection points. For simplification, Figure 4 Only the determination of the two-point size based on the subset of projection points 62 is depicted. Based on the subset of projection points 62, the determining unit 14 determines a circle C representing the subset of projection points 62. For example, the circle C can be at least one of a Gaussian circle, a minimum circumscribed circle and a maximum inscribed circle. As Figure 4 indicated, the circle C is preferably a Gaussian circle which is located in the middle between the subset of projection points 62 in the best possible way. Furthermore, the minimum circumscribed circle is a circle within which the subset of projection points 62 is located and which is as small as possible at the same time. The maximum inscribed circle is a circle outside which the subset of projection points 62 is located and which is as large as possible at the same time.

[0084] Once the circle C is determined, the determining unit 14 can determine a circle center CP of the circle C. For determining the two-point size of the workpiece 30, the determining unit 14 can determine the two-point size of the workpiece 30 by determining a pair of points 70, 72 based on the subset of projection points 62, wherein the pair of points 70, 72 is substantially opposite to each other with respect to the circle center CP. Based on the pair of points 70, 72, the determining unit 14 can determine the two-point size based on a distance D of the pair of points 70, 72.

[0085] As Figure 4 indicated, the pair of points 70, 72 need not be actual projection points of the subset of projection points 62. And, for example, as Figure 4As shown, one point 70 in the pair of points 70, 72 may be a point in the projection point subset 62, and the other point 72 in the pair of points 70, 72 may be determined by interpolation. An exemplary interpolation method may include: for a first projection point 70 in the projection point subset 62, determining a connecting line passing through the first projection point 70 and the center point CP, and determining a second projection point 72 from the projection point subset 62, the second projection point being closest to the connecting line and having a distance from the first projection point 70 that does not exceed the radius of the circle C. The first projection point 70 and the second projection point 72 may form a point pair, and the size of the two points may be the sum of the distance from the first projection point 70 to the center point CP and the distance from the second projection point 72 to the center point CP.

[0086] Furthermore, the determination unit 14 may determine at least one of a minimum two-point size of the workpiece 30 , a maximum two-point size of the workpiece 30 , or an average two-point size of the workpiece 30 by analyzing the set of projection points.

Claims

1. A computer-implemented method for determining two-point sizes of a workpiece (30), the method comprising the steps of: receiving a set (50) of measurement points of the workpiece (30); determining a longitudinal axis (L) of the workpiece (30) based on the set (50) of measurement points; projecting at least a portion of the set (50) of measurement points into a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; as well as determining two point sizes of the workpiece (30) based on the projection points, The set of measurement points consists of measurement points obtained from spiral measurement of the workpiece, wherein the spiral measurement measures the workpiece along a path having a substantially spiral trajectory, and the two-point size is the distance between two points of the surface of the workpiece that are opposite to each other about the longitudinal axis of the workpiece.

2. The method according to claim 1, wherein The workpiece (30) has a generally cylindrical shape.

3. The method according to claim 1 or 2, wherein: The step of determining the longitudinal axis (L) of the workpiece (30) comprises: determining a shape model of the workpiece (30) based on the set (50) of measurement points, and The longitudinal axis (L) of the shape model is provided as the longitudinal axis of the workpiece (30).

4. The method according to claim 3, wherein: The shape model is a cylindrical shape model, and the longitudinal axis (L) of the workpiece (30) corresponds to the cylinder axis of the cylindrical shape model.

5. The method according to claim 4, wherein: The shape model is a Gaussian cylindrical shape model.

6. The method according to claim 1 or 2, wherein: Projecting at least a portion of the set (50) of measurement points into the projection plane comprises projecting at least a portion of the set (50) of measurement points parallel to the longitudinal axis (L).

7. The method according to claim 1 or 2, wherein: Determining the two-point size of the workpiece (30) includes: determining a center point (CP) of a circle (C) based on the set of projection points, wherein the circle (C) is a Gaussian circle; determining a pair of points (70, 72) based on the set of projected points, wherein the pair of points (70, 72) are opposite to each other about the circle center (CP); and The two point sizes are determined by calculating the distance (D) between the point pair (70, 72).

8. The method according to claim 7, wherein: The point pair (70, 72) includes at least one point in the set of projected points, and in the case where the other point in the point pair is not included in the set of projected points, the method further includes: determining the other point by interpolation based on the set of projected points.

9. The method according to claim 1 or 2, wherein: The set (50) of measurement points includes at least one subset (52-60) of measurement points corresponding to one rotation of the workpiece, and the set of projection points includes at least one subset (62) of projection points corresponding to the at least one subset of measurement points.

10. The method according to claim 9, wherein: Determining the two-point size of the workpiece (30) includes: determining a corresponding center point (CP) of a circle (C) based on the at least one subset of projection points (62), wherein the circle (C) is a Gaussian circle; determining corresponding pairs of points (70, 72) based on the at least one subset of projected points (62), wherein the pairs of points (70, 72) are opposite to each other about the circle center (CP); and The two point sizes are determined by calculating the distance (D) between the point pair (70, 72).

11. The method according to claim 10, wherein: The point pair (70, 72) includes at least one point in the at least one projection point subset (62), and in the case where the other point in the point pair (70, 72) is not included in the at least one projection point subset (62), the method further includes: determining the other point by interpolation based on the at least one projection point subset (62).

12. A device (10) for determining the size of two points of a workpiece (30), the device (10) comprising: a receiving unit (12) configured to receive a set (50) of measurement points of the workpiece (30); as well as A determination unit (14) configured to: determining a longitudinal axis (L) of the workpiece (30) based on the set (50) of measurement points; projecting at least a portion of the set (50) of measurement points into a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; as well as determining two-point sizes of the workpiece (30) based on the set of projection points, The set of measurement points consists of measurement points obtained from spiral measurement of the workpiece, wherein the spiral measurement measures the workpiece along a path having a substantially spiral trajectory, and the two-point size is the distance between two points of the surface of the workpiece that are opposite to each other about the longitudinal axis of the workpiece.

13. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 11.

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