Method and apparatus for calculating the distance between two points on a workpiece - Patents.com

Abstract

To provide determining an accurate two-point size of a workpiece while enabling quick measurement of the workpiece.SOLUTION: A computer implemented method for determining a two-point size of a workpiece comprises the steps of: receiving a set of measuring points (50) of a workpiece (30); determining a longitudinal axis (L) of the workpiece (30) based on the set of measuring points (50); projecting at least a part of the set of measuring points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; and determining a two-point size of the workpiece (30) based on the projection points.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of measuring workpieces, and more particularly to a method and apparatus for determining the distance between two points on a workpiece. [Background technology]

[0002] A "distance (dimension) between two points on a workpiece" refers to a local dimension between two points on the surface of the workpiece. For example, if the workpiece is substantially cylindrical, a "distance (dimension) between two points on the workpiece" refers to a local dimension between two points on the workpiece surface that are opposite each other across the longitudinal axis of the workpiece. If the workpiece is cylindrical, the two points are opposite each other across the central axis of the cylinder.

[0003] Hereinafter, "the distance (dimension) between two points on a workpiece" will be referred to as "the distance between two points on a workpiece." In addition, in the following explanation, "cylinder" and "circular cylinder" will be used, but there is no need to distinguish between a cylinder and a circular cylinder, and it should be understood that a cylindrical shape includes a cylindrical shape and vice versa.

[0004] Known methods for calculating the distance between two points require measurement data (e.g. measurement points) obtained by measuring the workpiece in a circumferential direction around the longitudinal axis of the workpiece (e.g. the central axis of a cylindrical workpiece) and measuring the workpiece at different positions along the longitudinal axis. The measurement points obtained by measuring the workpiece in a circumferential direction around the longitudinal axis at a certain position correspond to measurement points around one circumference of the workpiece around the axis, which are approximately located in a plane perpendicular to the longitudinal axis of the workpiece. In order to measure the workpiece as precisely as possible, several measurements are required, i.e. several measurements at different positions along the longitudinal axis of the workpiece. Furthermore, the measurement points around each circumference must be separated from each other along the longitudinal axis of the workpiece. In addition, when measuring a workpiece, the probe that measures the workpiece must be positioned for each measurement of one circumference, i.e., the probe must be positioned at a new position along the longitudinal axis of the workpiece one by one. (Positioning the probe includes positioning the probe's measuring point and adjusting the attitude so that the measurement axis of the probe (e.g., the probe coordinate system) is parallel to the axis (longitudinal axis) of the workpiece.) When multiple measurements must be made, each measurement must be repeated multiple times, each time for a single measurement, and the measurement point data is not obtained in a continuous, uninterrupted series of measurements. Therefore, in order to obtain accurate distances between two points on the workpiece, the measurements of the workpiece must be lengthy and cumbersome. Summary of the Invention [Means for solving the problem]

[0005] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a method and an apparatus therefor that enable rapid measurement of a workpiece in order to precisely calculate the distance between two points on the workpiece.

[0006] That is, the present invention makes it possible to shorten the time required to measure a workpiece, while also enabling accurate calculation of the distance between two points on the workpiece.

[0007] This object is solved by the subject matter defined in the independent claims. Preferred embodiments are also defined in the dependent claims.

[0008] One aspect of the present invention is A computer-implementable method for calculating a distance between two points on a workpiece, comprising: The method comprises: receiving a series of sets of measurement points on the workpiece; calculating a longitudinal axis of the workpiece based on the set of measurement points; projecting at least a portion of the set of measurement points onto a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; and calculating a distance between two points on the workpiece based on the set of projected points.

[0009] To further benefit, The method comprises: It allows for the calculation of distances between two points on a workpiece using measurement points that are measured consecutively and that may not lie in a plane perpendicular to the longitudinal axis of the workpiece. This is because the measurement points are projected onto the projection plane, and the distance between the two points is calculated based on the projected points. By "continuously measured" it is meant that the measurement points are taken in a single measurement. Thus, not only can the distance between two points be calculated accurately, but measurements of the workpiece can be performed more quickly.

[0010] Preferably, the series of sets of measurement points are obtained from measuring a surface of the workpiece with a measuring device. Each measurement point may represent three-dimensional (3D) position information of the measured portion of the surface of the workpiece relative to a reference point (fiducial point) whose position is known, for example by measurement, in three-dimensional coordinate values. The measurement points may preferably be obtained from a coordinate measuring device that measures the workpiece. An exemplary coordinate measuring device may obtain the measurement points using a probe that detects the workpiece. The probe may measure the workpiece by contacting the surface of the workpiece, for example with a stylus tip, or may measure the surface of the workpiece in a non-contact manner, for example by optical methods, computer tomography and / or X-rays. Furthermore, it is preferred that the measuring device and / or the probe measures the workpiece in a single scan, i.e. the measurement points are preferably obtained in that single scan.

[0011] Moreover, each projection point of the set of projection points projected onto the projection plane corresponds to each measurement point of the series of measurement points. For example, each projection point of the set of projection points corresponds to a different measurement point of the series of measurement points. By projecting a part of the series of measurement points onto the projection plane, each projection point of the set of projection points is represented by two-dimensional (2D) position information, for example, two-dimensional coordinates.

[0012] Preferably, the entire set of measurement points is projected onto the projection plane, i.e. all measurement points of the set of measurement points are projected onto the projection plane to obtain a set of projection points. Also, a normal to the projection plane perpendicular to the longitudinal axis of the workpiece may be parallel to the longitudinal axis of the workpiece, and the set of measurement points may be pre-analyzed to determine incorrect measurement points (i.e., outliers) that are not projected onto the projection plane, thereby allowing only a portion of the set of measurement points to be projected onto the projection plane.

[0013] Preferably, the set of measurement points may consist of measurement points obtained from a helical measurement of the workpiece, which may have a substantially cylindrical shape.

[0014] Advantageously, helical measurement of a substantially cylindrical workpiece allows for faster measurement of the workpiece as compared to the known methods described above. In helical metrology, the surface of a workpiece may be measured along a path having a generally helical trajectory, for example a path having the form of a thread, and the helical metrology results in a successive set of measurement points. Successive or adjacent measurement points in a series of measurement points obtained by helical measurement have a non-zero, substantially constant axial difference when viewed along the longitudinal axis of the workpiece (e.g., the central axis of a cylindrical workpiece). That is, compared to conventional measurement methods in which the measurement points of one revolution are substantially in a plane perpendicular to the longitudinal axis of the workpiece, the measurement points of one revolution obtained by helical measurement are not in a plane perpendicular to the longitudinal axis of the workpiece. Furthermore, helical measurements eliminate the need to position the probe relative to the longitudinal axis of the workpiece to obtain measurements for each revolution of the workpiece, and therefore measurements can be made more quickly. Additionally, the helical measurement can be applied to workpieces having an approximately cylindrical shape.

[0015] Further, the set of measurement points acquired in the helical measurement includes measurement points acquired from at least one revolution about the longitudinal axis of the workpiece (the central axis of a generally cylindrical workpiece). Preferably, the set of measurement points may include measurement points acquired from multiple revolutions about the longitudinal axis of the workpiece (the central axis of a generally cylindrical workpiece). A revolution may be determined by summing up the angular differences between successive or adjacent measurement points about the longitudinal axis of the workpiece (the central axis of a generally cylindrical workpiece) up to 360 degrees.

[0016] Preferably, The step of calculating the longitudinal axis of the workpiece comprises: calculating a geometric model of the workpiece based on the set of measurement points; determining a longitudinal axis of the shape model as a longitudinal axis of the workpiece; may include. Typically, the workpiece does not have a perfect shape, such as a perfect cylinder. That is, in the case of a cylindrical workpiece, the diameter of the workpiece may vary depending on the measurement location. Such deviations are reflected in the set of measurement points so that the shape model becomes a better approximation of the workpiece shape, thereby allowing the calculation of the workpiece's longitudinal axis.

[0017] Preferably, for a workpiece having an approximately cylindrical shape, the shape model may be a model of the cylindrical shape, preferably a Gaussian cylindrical model, with the longitudinal axis of the workpiece corresponding to the central axis of the cylindrical model. The Gaussian cylinder model may be fitted as a model that is as close as possible to the entire set of measurement points or at least a portion of the set of measurement points, for example, by using a least squares method for the set of measurement points.

[0018] However, depending on the situation, different cylindrical models may be applied, for example the cylindrical model may be the minimum circumscribed cylindrical model or the maximum inscribed cylindrical model.

[0019] The cylindrical model provides a good approximation of the shape of a cylindrical workpiece, i.e., the cylindrical model allows for a good approximation of the longitudinal axis of the workpiece (the central axis of a cylindrically shaped workpiece).

[0020] The step of projecting at least a portion of the series of set of measurement points onto a projection plane perpendicular to the longitudinal axis to obtain a set of projection points may include projecting at least a portion of the series of set of measurement points parallel to the longitudinal axis, where projecting the series of set of measurement points onto the projection plane may include projecting the series of set of measurement points parallel to the longitudinal axis of the workpiece (a central axis of the workpiece in the case of a cylindrical workpiece) to obtain each corresponding projection point of the series of set of measurement points.

[0021] Preferably, the step of calculating the distance between two points of the workpiece includes calculating a circle center of a circle based on the set of projected points, and the circle is preferably a Gaussian circle calculated from the set of projected points, i.e. the circle is calculated from the set of projected points, and the Gaussian circle is a circle that is as central as possible between the set of projected points.

[0022] Furthermore, the step of calculating the distance between two points of the workpiece may include determining a pair of points facing each other with respect to the circle center based on the set of projected points, and calculating the distance between the pair of points to calculate the distance between the two points. Furthermore, the calculation of the circle center may be performed for a cylindrical workpiece.

[0023] Even though the workpiece does not usually have a perfect shape as described above, the calculation of the circle center provides a good approximation of the circle center. Using the calculated circle center allows for accurate calculation of the distance between two points on the workpiece. Furthermore, the circle calculated from the set of projected points is not limited to a Gaussian circle. For example, the calculated circle may be a minimum circumscribed circle model or a maximum inscribed circle model calculated from the set of projected points.

[0024] Preferably, the pair of points may include at least one point of the set of projected points, and if the other point of the pair of points is not included in the set of projected points, the method further comprises calculating the other point by interpolation based on the set of projected points. Alternatively, both points of the pair of points may be derived by interpolation of the set of projected points.

[0025] This makes it possible to calculate the distance between two points even if a set of projection points does not include projection points that face each other with respect to the center of the circle.

[0026] For example, the series of sets of measurement points may include at least one subset of measurement points corresponding to one revolution (circumference) of the workpiece, and the set of projection points includes at least one subset corresponding to the at least one subset of measurement points. The subset of projection points may be obtained by projecting each set of measurement points onto a projection plane parallel to the longitudinal axis. Additionally, the set of measurement points may include more than one subset of measurement points, where each subset of measurement points may correspond to a different rotation of the workpiece. For example, the number of subsets of measurement points may be equal to the number of rotations at which the workpiece is measured. Additionally, each subset of measurement points may be projected onto a projection plane to obtain a respective subset of projection points, i.e., for each rotation the workpiece is measured, a respective subset of projection points is obtained, and thus, for each rotation (each full circumference) of the workpiece, the distance between the two points can be calculated.

[0027] A subset of measurement points corresponding to one revolution of the workpiece can also be determined from the set of measurement points, for example by projecting the set of measurement points perpendicularly onto the longitudinal axis of the workpiece (e.g., the central axis of a cylindrical model) to yield a set of intermediate points distributed along the longitudinal axis. A first midpoint and a second midpoint are selected from the set of midpoints, where the first midpoint and the second midpoint are a pair of points in the set of midpoints that have the longest possible distance. The remaining midpoints in the set of midpoints, i.e., the set of midpoints excluding the first midpoint and the second midpoint, are sorted based on their distance to the first midpoint or the second midpoint. For example, the remaining midpoints may be sorted in ascending order based on their distance to the first midpoint or the second midpoint. The first midpoint, the remaining sorted midpoints, and the second midpoint constitute a sorted set of midpoints, each of which can be a reference point for a corresponding measurement point in the set of measurement points.

[0028] The subset of measurement points corresponding to one revolution (one circumference) can be determined based on a distance criterion or an angle criterion. For example, the distance criterion may be dependent on the measurement process of the workpiece. For example, the distance criterion may correspond to a distance along the scan axis of the workpiece required to measure one revolution of the workpiece (a thickness when the workpiece is sliced). Alternatively, the distance criterion may be user defined.

[0029] A subset of measurement points may be determined from the set of measurement points based on a distance criterion. For example, the subset of measurement points based on the distance criterion may be determined from the set of measurement points by referring to a sequence of ordering points obtained from a set of sorted (ordered) midpoints that satisfy the distance criterion. That is, the distance between a first point in the sequence of ordering points and a last point in the sequence of ordering points satisfies the distance criterion. For example, referring to a corresponding order in the sorted (ordered) set of midpoints, a subset of measurement points may be allocated from the set of measurement points until a distance between a first point in the sequence of ordering points and a last point in the sequence of ordering points is equal to or greater than the distance criterion. This process may be repeated for each rotation. In this case, the first point in the next sequence of ordering points obtained from the sorted (ordered) set of midpoints is the point following the last point in the previous sequence of ordering points obtained from the sorted (ordered) set of midpoints.

[0030] If an angle criterion is used instead of a distance criterion, points from the set of measurement points may be assigned to the subset of measurement points in order, taking into account the order provided by the sorted set of intermediate points, until the sum of the angles between the points of the sequence of measurement points exceeds 360° around the longitudinal axis (the central axis of the cylindrical model). To determine the angles between the points of the sequence of measurement points around the longitudinal axis, the points of the sequence of measurement points may be projected onto a plane perpendicular to the longitudinal axis. This process may be repeated for each rotation, such that for the next rotation, the first point of the next sequence of measurement points is the point following the last point of the previous sequence of measurement points.

[0031] Determining the subset of measurement points based on the sorted set of intermediate points prevents the measurement points from being ordered incorrectly, so that consecutive measurement points in the set of measurement points are close to each other, i.e., have small longitudinal differences along the scan axis. If the calculated longitudinal axis of the shape model (the central axis of the cylindrical model) is tilted with respect to the actual scan axis, the order of consecutive two points in the set of measurement points may be reversed when projected onto the longitudinal axis (central axis) compared to the projection of consecutive two points in the set of measurement points on the scan axis.

[0032] Preferably, the step of calculating the distance between two points on the workpiece comprises: calculating circle centers of each of the circles, preferably Gaussian circles, based on at least a subset of the projected points; determining a pair of points from at least one subset of projected points that are substantially opposed to the circle center; and, This can include calculating the distance between a pair of points to determine the point-to-point distance. Preferably, the distance between two points is the sum of the distances of each point in the pair of points to the circle centre.

[0033] Although the Gaussian circle calculated from at least one subset of projection points is preferred, a circle calculated by another method can also be applied. For example, the calculated circle can include at least one of a minimum circumscribing circle and a maximum inscribing circle calculated from at least one subset of projection points. Furthermore, if more than one subset of projection points is obtained, a respective circle and circle center can be calculated for each subset of projection points. Alternatively, a pair of points facing each other with respect to the circle center of each subset of projection points can be calculated from each subset of projection points, and the distance between the pair of points can be calculated to calculate the two-point distance for each subset of projection points.

[0034] An advantage of the present invention is that it allows for rapid measurement of a workpiece while still allowing for accurate calculation of distances between two points from a series of measured points.

[0035] Preferably, a pair of points of each subset of projected points may include at least one of the subset of projected points, and another point of a pair of points may not include the subset of projected points. In this case, the method may further include determining another point by interpolation based on a subset of the projected points. Alternatively, both points of each pair of points in each subset of projection points may be derived by interpolation of the respective set of projection points.

[0036] The advantage of the present invention is that the two facing points can be found based on the subset of projection points, even though the subset of projection points itself may not include two facing points, so that the distance between two points can be calculated even if the subset of projection points does not include two facing projection points.

[0037] Preferably, the step of calculating the distance between two points on the workpiece may include calculating at least one of the minimum distance between two points on the workpiece, the maximum distance between two points on the workpiece, and the average distance between two points on the workpiece.

[0038] A further aspect relates to an apparatus for calculating a distance between two points on a workpiece, the apparatus comprising: A receiving unit; A calculation unit, the receiving unit receives a series of sets of measurement points of the workpiece; The calculation unit is calculating a longitudinal axis of the workpiece based on the set of measurement points; projecting at least a portion of the set of measurement points onto a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; A distance between two points on the workpiece is calculated based on the set of projected points.

[0039] Furthermore, the device for calculating the distance between two points on the workpiece may receive a set of measurement points from a measurement device as described above. Alternatively, the device may include a measurement unit for measuring the workpiece. The measurement unit may measure the workpiece using a probe that detects the workpiece. The probe may measure the workpiece by contacting the surface of the workpiece, for example with a stylus tip, or may measure the surface of the workpiece in a non-contact manner, for example by optical methods, computer tomography and / or x-rays.

[0040] The computing unit may also be configured to perform the methods described above.

[0041] A further aspect relates to a computer-readable medium containing instructions that, when executed by a computer, cause the computer to perform the following steps: That is, the computer readable medium containing instructions is receiving a series of sets of measurement points on a workpiece; calculating a longitudinal axis of the workpiece based on the set of measurement points; projecting a series of sets of measurement points onto a projection plane perpendicular to the longitudinal axis to obtain a set of projection points; and calculating a distance between two points on the workpiece based on the set of projected points.

[0042] Additionally, a computer readable medium may include instructions that enable the implementation of the methods described above.

[0043] These and other objects, features and advantages of the present invention will become more apparent from a reading of the following detailed description of the preferred embodiments and the accompanying drawings. Although the embodiments are described separately, it should be understood that a single feature thereof may be combined with another embodiment. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a diagram showing an apparatus for measuring a distance between two points on a workpiece. [Diagram 2] FIG. 1 illustrates a helical measurement of a workpiece. [Diagram 3] FIG. 13 is a diagram illustrating a state in which measurement points are projected onto a projection surface. [Figure 4] FIG. 13 is a diagram showing a circle calculated from a set of projection points. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] FIG. 1 illustrates an apparatus 10 for calculating a distance between two points on a workpiece 30 (eg, a cylindrical workpiece 30 as depicted in FIG. 1). A measurement device 20 communicatively connected to the apparatus 10 is configured to measure the workpiece 30 to obtain a series of sets 50 of measurement points on the workpiece. The set of measurement points is received by a receiving unit 12 of the apparatus 10. Alternatively, the apparatus 10 may comprise a measurement unit (not shown) for measuring the workpiece 30, from which the receiving unit 12 obtains the set of measurement points 50.

[0046] The apparatus 10 further comprises a computing unit 14 . The calculation unit 14 determines a distance between two points on the workpiece 30 based on the set of measurement points 50 received by the receiving unit 12. The distance between two points on the surface of the workpiece 30 is the distance between two points on the surface of the workpiece 30 that are opposite each other across the longitudinal axis L of the workpiece 30. As shown in Fig. 1, the workpiece 30 is an approximately (substantially) cylindrical workpiece 30, and the central axis of the workpiece 30 corresponds to the longitudinal axis L. The terms "approximately" and "substantially" mean that the workpiece 30 does not have a perfect shape, i.e., for example, the diameter of the cylindrical workpiece 30 may vary depending on the position of the measurement.

[0047] The measuring device 20 and / or the measuring unit may measure the workpiece using a probe that detects the workpiece, for example by contacting the surface of the workpiece 30 with a stylus tip, or may measure the surface of the workpiece 30 in a non-contact manner, for example by optical methods, computer tomography and / or x-rays.

[0048] FIG. 2 represents a series of sets 50 of measurement points obtained by measuring a workpiece 30 with a measuring device 20 or measuring unit. In detail, the series of measurement points 50 is obtained by helical measurement of the workpiece 30. Each measurement point of the series of measurement points 50 represents three-dimensional position information (e.g., three-dimensional coordinates expressed by X, Y, and Z coordinates) of a measurement location on the workpiece surface. In the helical measurement, the surface of the workpiece can be measured along a path P having a substantially helical trajectory, for example, a path P having the shape of a screw thread. Then, the series of measurement points 50 is obtained by the helical measurement. Successive or adjacent measurement points in the series of measurement points 50 obtained by the helical measurement have a non-zero, substantially constant axial difference (difference) when viewed in a direction along the longitudinal axis L of the workpiece 30 (e.g., the central axis of the cylindrical workpiece 30).

[0049] 2, the workpiece 30 is measured for more than one revolution, and in each revolution, each full revolution measurement point has a displacement along the longitudinal axis L of the workpiece 30. Thus, the series of measurement points 50 is made up of more than one subset of measurement points 52-60. Here, each subset of measurement points 52-60 includes a full revolution of measurement points acquired in a helical measurement, which may be determined from the set of measurement points 50 by summing up the angular differences between successive or adjacent measurement points up to 360 degrees around the longitudinal axis L of the workpiece 30.

[0050] As mentioned above, the workpiece 30 does not have a perfect shape, making it difficult to identify the longitudinal axis of the workpiece 30. Therefore, the calculation unit 14 is configured to calculate the longitudinal axis L based on the set of measurement points 50. For example, the calculation unit 14 may calculate a shape model (not shown) of the workpiece 30 based on the set of measurement points 50. For example, the calculation unit 14 may determine a Gaussian cylindrical model for a cylindrical workpiece 30. The Gaussian cylindrical model can be obtained by applying a least squares method to the entire set of measurement points 50 or at least a part of the set of measurement points 50. Thereby, the Gaussian cylindrical model can be adjusted as a model that is as close as possible to the entire set of measurement points 50 or at least a part of the set of measurement points 50. The calculation unit 14 may then determine the central axis of the Gaussian cylindrical model as the longitudinal axis L of the workpiece 30.

[0051] Please refer to Figure 3. The calculation unit 14 is further configured to project at least a part of the set of measurement points 50, in particular substantially the entire set of measurement points 50, onto a projection plane perpendicular to the determined longitudinal axis L of the workpiece 30 to obtain a corresponding set of projection points. Furthermore, a normal to the projection plane may be parallel to the longitudinal axis L. Furthermore, at least a part of the measurement points 50, in particular the entire set of measurement points 50, may be projected parallel to the longitudinal axis L determined from the shape model. If the set of measurement points 50 includes more than one subset of measurement points, in particular each subset of measurement points 52-60 may be projected onto the projection plane to obtain a corresponding subset of projection points 62. For the sake of simplicity, FIG. 3 shows the projection of one subset of projection points 62 onto a projection plane perpendicular to the longitudinal axis L to obtain a (one) corresponding subset of projection points 62.

[0052] Please refer to Figure 4. The calculation unit 14 is further configured to calculate a distance between two points on the workpiece 30 based on the set of projected points. For simplicity, FIG. 4 depicts the calculation of the point-to-point distance based on a subset 62 of the projected points. Based on the subset of projection points 62, the calculation unit 14 calculates a circle C that corresponds to the subset of projection points 62. For example, the circle C may be at least one of a Gaussian circle, a minimum circumscribing circle, and a maximum inscribing circle. As depicted in Fig. 4, the circle C is preferably a Gaussian circle that is centered between the subset of projected points 62 in the best possible way, the minimum circumscribing circle is the circle for which the subset of projected points 62 are inside the circle and at the same time the circle is as small as possible, and the maximum inscribing circle is the circle for which the subset of projected points 62 are outside the circle and at the same time the circle is as large as possible.

[0053] Once the circle C is determined, the calculation unit 14 can calculate a circle center CP of the circle C. To calculate the distance between two points on the workpiece 30, the calculation unit 14 can determine the distance between two points on the workpiece 30 by determining a pair of points 70, 72 that are substantially opposite each other with respect to the circle center CP based on the subset of projected points 62. Using the pair of points 70, 72, the calculation unit 14 may calculate the distance between the two points based on a distance D between the pair of points 70, 72.

[0054] The pair of points 70, 72 as depicted in FIG. 4 need not be actual projected points of the subset of projected points 62. For example, in FIG. 4, one point 70 of the pair of points 70, 72 may be a point of the subset of projected points 62, and the other point 72 of the pair of points 70, 72 may be calculated by interpolation. For example, the interpolation method may include calculating a connecting line passing through a first projected point 70 and a circle center CP for a first projected point 70 selected from the subset of projected points 62, and determining a second projected point 72 from the subset of projected points 62, the second projected point being closest to the connecting line and having a distance to the first projected point 70 greater than the radius of the circle C. The first projected point 70 and the first projected point 72 may form a point pair, and the distance between the two points may be the sum of the distance from the first projected point 70 to the circle center CP and the distance from the second projected point 72 to the circle center CP.

[0055] Further, the calculation unit 14 may be configured to determine at least one of the minimum inter-point distance of the workpiece 30, the maximum inter-point distance of the workpiece 30, and the average inter-point distance of the workpiece 30 by analyzing a series of sets of projection points.

[0056] Examples of the shape of the workpiece include those that are entirely or partially cylindrical or columnar, but the shapes of the workpieces to which the present invention can be applied are not limited to these. For example, the workpiece may be entirely prismatic or tubular, or may include a prismatic or tubular shape in part. In this case, the bottom surface (cross section) is typically a regular polygon, but it does not have to be a regular polygon. If the workpiece has a three-dimensional part with an axis (longitudinal axis, central axis) as the axis of symmetry (axis of rotational symmetry), the present invention can be applied to that part. The surface to be measured may be the outer surface of a workpiece (for example, the outer surface of a cylinder (column)) or the inner surface (the inner surface of a cylindrical hole). A spiral is generally defined as a curved line, but it should be interpreted more broadly depending on the shape of the workpiece, and any measurement that takes continuous measurement sampling points along a line (which may be curved or straight) that moves at a constant pitch in a direction perpendicular to the plane of rotation while rotating should be interpreted as being included in spiral measurement. The measuring device includes, for example, a three-dimensional coordinate measuring machine, a roundness measuring machine, and an image measuring machine. [Explanation of symbols]

[0057] 10. Apparatus for calculating distance between two points on a workpiece 12 Receiving unit 14 Calculation Units 20 Measuring Equipment 30 work pieces A series of 50 measurement points 52-60 Subset of measurement points 62 Subset of Projected Points 70, 72 Pair of points C Yen CP Yen Center D Distance between a pair of points P Spiral measurement path L Longitudinal / Central Axis of the Workpiece

Claims

1. A computer-implemented method for calculating a distance between two points on a workpiece (30), comprising the steps of: The method comprises: receiving a series of sets (50) of measurement points of the workpiece (30); calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the set of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; and calculating a distance between two points on the workpiece (30) based on the set of projected points; The series of measurement points (50) including measurement points obtained from a helical measurement of the workpiece (30). A method comprising:

2. The method of claim 1, The step of calculating the longitudinal axis (L) of the workpiece (30) comprises: calculating a geometric model of the workpiece (30) based on the set of measurement points (50); calculating the longitudinal axis (L) of the shape model as the longitudinal axis of the workpiece (30). A method comprising:

3. The method according to claim 2, The shape model is a cylindrical model, The central axis of the cylindrical model corresponds to the longitudinal axis (L) of the workpiece (30). A method comprising:

4. In the method according to any one of claims 1 to 3, The step of projecting at least a portion of the series of sets of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points includes: and projecting at least a portion of the set of measurement points (50) parallel to the longitudinal axis (L). A method comprising:

5. A computer-implemented method for calculating a distance between two points on a workpiece (30), comprising the steps of: The method comprises: receiving a series of sets (50) of measurement points of the workpiece (30); calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the set of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; and calculating a distance between two points on the workpiece (30) based on the set of projected points; The step of calculating the distance between two points of the workpiece (30) includes: Calculating a circle center (CP) of a circle (C) based on the set of projection points; calculating a pair of points (70, 72) based on the set of projected points; At this time, the pair of points (70, 72) are located opposite each other with the circle center (CP) therebetween, calculating the distance (D) between the pair of points (70, 72) to calculate the distance between the two points. A method comprising:

6. The method according to claim 5, the pair of points (70, 72) includes at least one point of the set of projected points; If the other point of the pair of points is not included in the set of projected points, the other point is calculated by interpolation based on the set of projected points. A method comprising:

7. A computer-implemented method for calculating a distance between two points on a workpiece (30), comprising the steps of: The method comprises: receiving a series of sets (50) of measurement points of the workpiece (30); calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the set of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; and calculating a distance between two points on the workpiece (30) based on the set of projected points; the series of measurement points (50) includes at least one subset of measurement points (52-60) corresponding to one revolution of the workpiece; The set of projection points includes at least one subset of projection points (62) corresponding to the at least one subset of the measurement points. A method comprising:

8. The method according to claim 7, The step of calculating the distance between two points of the workpiece (30) includes: calculating a circle center (CP) of each circle (C) based on the at least one subset (62) of the projection points; calculating a pair of points (70, 72) based on the at least one subset (62) of projected points, At this time, the pair of points (70, 72) are located opposite each other with the circle center (CP) therebetween, calculating the distance (D) between the pair of points (70, 72) to calculate the distance between the two points. A method comprising:

9. The method according to claim 8, the pair of points (70, 72) includes at least one point of the at least one subset (62) of projected points; if the other point of the pair of points (70, 72) is not included in the at least one subset (62) of projected points, and calculating the other point by interpolation based on the at least one subset of the projected points. A method comprising:

10. A computer-implemented method for calculating a distance between two points on a workpiece (30), comprising the steps of: The method comprises: receiving a series of sets (50) of measurement points of the workpiece (30); calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the set of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; and calculating a distance between two points on the workpiece (30) based on the set of projected points; The series of measurement points (50) including measurement points obtained from a helical measurement of the workpiece (30); perpendicularly projecting the set of measurement points onto the longitudinal axis of the workpiece to produce a set of intermediate points distributed along the longitudinal axis; By referring to the arrangement order of the intermediate points on the longitudinal axis, a set of measurement points corresponding to one rotation of the spiral measurement is identified from the series of sets of measurement points. A method comprising:

11. An apparatus for calculating a distance between two points on a workpiece (30), comprising: A receiving unit (12); A calculation unit (14), The receiving unit (12) receives a series of sets (50) of measurement points of the workpiece (30); The series of measurement points (50) including measurement points obtained from a helical measurement of the workpiece (30); The calculation unit (14) Calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the series of sets of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; Calculating a distance between two points on the workpiece (30) based on the set of projected points. An apparatus comprising:

12. An apparatus for calculating a distance between two points on a workpiece (30), comprising: A receiving unit (12); A calculation unit (14), The receiving unit (12) receives a series of sets (50) of measurement points of the workpiece (30); The calculation unit (14) Calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the series of sets of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; Calculating a distance between two points on the workpiece (30) based on the set of projected points; The distance between two points on the workpiece (30) is calculated as follows: Calculating a circle center (CP) of a circle (C) based on the set of projection points; calculating a pair of points (70, 72) based on the set of projected points; At this time, the pair of points (70, 72) are located opposite each other with the circle center (CP) in between, and the distance (D) between the pair of points (70, 72) is calculated to calculate the distance between the two points. An apparatus comprising:

13. An apparatus for calculating a distance between two points on a workpiece (30), comprising: A receiving unit (12); A calculation unit (14), The receiving unit (12) receives a series of sets (50) of measurement points of the workpiece (30); The calculation unit (14) Calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the series of sets of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; Calculating a distance between two points on the workpiece (30) based on the set of projected points; the series of measurement points (50) includes at least one subset of measurement points (52-60) corresponding to one revolution of the workpiece; The set of projection points includes at least one subset of projection points (62) corresponding to the at least one subset of the measurement points. An apparatus comprising:

14. An apparatus for calculating a distance between two points on a workpiece (30), comprising: A receiving unit (12); A calculation unit (14), The receiving unit (12) receives a series of sets (50) of measurement points of the workpiece (30); The calculation unit (14) Calculating a longitudinal axis (L) of the workpiece (30) based on the set of measurement points (50); projecting at least a portion of the series of sets of measurement points (50) onto a projection plane perpendicular to the longitudinal axis (L) to obtain a set of projection points; Calculating a distance between two points on the workpiece (30) based on the set of projected points; The series of measurement points (50) including measurement points obtained from a helical measurement of the workpiece (30); perpendicularly projecting the set of measurement points onto the longitudinal axis of the workpiece to produce a set of intermediate points distributed along the longitudinal axis; By referring to the arrangement order of the intermediate points on the longitudinal axis, a set of measurement points corresponding to one rotation of the spiral measurement is identified from the series of sets of measurement points. An apparatus comprising:

15. A computer readable medium comprising instructions which, when executed by a computer, cause the computer to perform the method of any of claims 1 to 10.

23. A computer readable medium comprising:

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