Method for automatically generating reference positioning systems, RPS, and alignment programs for measuring the shape of a workpiece.

Abstract

This invention provides a method for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of a workpiece. [Solution] A method comprising: step S1 obtaining a datum target of a workpiece from CAD, computer-aided design, or model information of the workpiece; step S2 generating a coordinate system based on the datum target; step S3 determining the alignment of the workpiece; and step S4 using the coordinate system to generate a collision-free workpiece program and / or collision-free movement path for a measuring probe of a shape measuring system.

Description

Technical Field

[0001] The present disclosure relates to a reference positioning system for shape measurement of a workpiece, a reference point system (RPS), a method for automatically generating an alignment program, each computer-readable program, and a shape measurement system configured to execute the method.

[0002] One method of measuring the accuracy of a manufactured workpiece is provided by contact measurement in which a probe contacts specific points on the surface of the workpiece. It can be measured whether the manufactured workpiece is within a predetermined tolerance, particularly in an assembly, to ensure proper functioning of the workpiece.

[0003] The probe is used to measure the geometric shape of the workpiece and can measure parameters such as diameter, length, hole depth, radius, etc. The probe is moved to contact specific points that are important for determining the shape accuracy of the workpiece.

[0004] In order to identify and define the specific contact points (datum targets), it is necessary to identify important parts of the workpiece, namely, surfaces or holes (datum features). Selecting the datum features and datum targets is extremely important for obtaining accurate and reliable measurement values. This is usually done manually and requires experienced operators.

[0005] To assist an operator in generating datum features and / or datum targets, information from a computer-aided design (CAD) model of the workpiece to be measured can be used.

[0006] Known workflows involve importing CAD model datum targets defined as Visible Product Manufacturing Information (PMI) data within CAD files and / or on separate (paper) design drawings. The operator interprets the PMI data and / or design drawings to determine which datum features should be measured as datum targets. Each RPS, reference positioning system, and alignment is performed only until a minimum number of points fully constrain the coordinate system.

[0007] Therefore, in traditional workflows, the user is entirely responsible for selecting the correct data and / or handling excessive constraint information, which is typically prevented rather than automatically handled.

[0008] The demand for experienced operators to determine datum features and datum targets is increasing, but their availability is low. Therefore, alternatives are needed to manually determine datum features and datum targets and manually generate reference positioning systems, RPS, and alignment programs for measuring the shape of the workpiece.

[0009] Therefore, an object of the present invention is to provide a method and system for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of a workpiece, particularly based on CAD model information. [Overview of the Initiative]

[0010] This objective is resolved by the features of the independent claims according to the present invention. Specific embodiments of the present invention are the subject matter of the dependent claims.

[0011] One embodiment relates to a method for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of a workpiece, the method comprising the steps of: obtaining a datum target of the workpiece from CAD, computer-aided design, or model information of the workpiece; generating a coordinate system (datum reference frame) based on the datum target; determining the alignment of the workpiece; and using the coordinate system, generating a collision-free workpiece program and / or collision-free movement path for a measuring probe of the shape measuring system.

[0012] In each method, CAD model information can be used to automatically determine datum features and / or datum targets and to generate collision-free work program and / or collision-free movement paths for measuring probes to measure workpieces. This improves the accuracy of data selection and, in particular, avoids the need for qualified operators to manually perform the steps. Thus, fewer qualified operators are required, which in particular avoids processing delays due to a lack of available workforce. Furthermore, this method can provide enhanced identification of datum features for obtaining improved tolerance measurements.

[0013] In some cases, datum features (and in particular the corresponding reference positioning systems, RPS, or datum systems for geometric components for design and / or manufacturing) are established in accordance with ISO 5459:2024.

[0014] In some examples, a datum target is a portion of the datum features of a workpiece. Datum features are actual tangible features of a workpiece, or their corresponding features, typically important functional surfaces or holes. Specifically, a datum target is, or refers to, theoretically accurate points, lines, and / or axes, etc., established or potentially established from datum features and simulated by a measuring instrument. Datum features are, in particular, actual features of a workpiece that are physically measured, or their corresponding features.

[0015] This method enables an automated workflow that may include one or more of the following: importing a workpiece's CAD file, reading necessary information from the CAD file based on semantic PMI data that can be read from the CAD file, and automatically generating which datum features based on the CAD geometry and determining which need to be measured in the automatically generated workpiece program. This may include, for example, tolerances or planarity read from the CAD file, and based on this, it may be determined that certain relevant geometric shapes, such as surfaces, can be measured as planes.

[0016] Based on CAD file information, it may be possible to further (especially automatically) determine how to align the workpiece for an improved shape measurement process.

[0017] Where advantageous, datum target optimization (especially automatically) can be performed by, for example, using "remove outliers" and / or "prioritize datum features and / or datum targets," as further explained below.

[0018] Furthermore, this method can automatically generate collision-free work programs and / or movement paths for the measurement probe using the generated coordinate system.

[0019] The datum target of the workpiece can be obtained or derived directly from the workpiece's CAD model information, particularly from the PMI (Product Manufacturing Information) and product manufacturing information of the workpiece's CAD model.

[0020] Alternatively or additionally, the step of obtaining a workpiece datum target from the workpiece CAD model information may include one or more of the following steps: reading at least a portion of the PMI, product manufacturing information, from the workpiece CAD model information; identifying one or more datum features of the workpiece; measuring the datum features of the workpiece; and generating one or more datum targets for the datum features.

[0021] PMI, or Product Manufacturing Information, may include one or more of the following: manufacturing technology, surface properties, color, material, material properties, and similar properties of the workpiece.

[0022] Therefore, the characteristics of the workpiece, separate from its geometric shape, are considered in determining the datum features. This can lead to improved results, particularly through proper consideration of other relevant characteristics of the workpiece that might otherwise be ignored.

[0023] This method may further include automated handling of overconstraints by optimizing datum targets to obtain the minimum number of datum targets. To reduce complexity and computation time, specific datum targets can be selected from several possible datum targets.

[0024] Different optimization strategies may be implemented by this method.

[0025] For example, datum target optimization may include reducing the number of datum targets based on identifying and removing outlier datum targets.

[0026] This can be particularly advantageous when there is a small number of datum targets, i.e., a small number of datum targets exceeding the minimum number of datum targets necessary to adequately define a datum feature, such as 6 or 3 or less, and especially 1. For example, 3+1 for planes, 2+1 for lines, and 1+1 for points. Further details are explained below with reference to the figures.

[0027] Alternatively or additionally, datum target optimization may include prioritizing datum targets. This strategy may be particularly advantageous when there is a large number of excess datum targets, for example, five or seven or more, as it can more efficiently determine the optimal datum targets.

[0028] For example, prioritizing data targets can include prioritizing all data targets with the same priority, or prioritizing data targets that decrease along the order of the data targets, and / or prioritizing a first group of data targets higher than a second group of data targets, and optionally, prioritizing a third group of data targets lower than the second group of data targets, and / or prioritizing possible contact points higher than possible non-contact points.

[0029] Different prioritization strategies may be determined based on, for example, information regarding the manufacturing method and / or materials and / or other characteristics of the work.

[0030] An exemplary prioritization strategy may be based on the quality of the data targets. For example, if a data target is located near a defect, the data target may be considered of low quality and they may be weighted lower than data targets located far from the defect, which may be considered of higher quality.

[0031] Another exemplary prioritization strategy may include grouping the data targets given by PMI and prioritizing said groups of data targets. In particular, data targets within one group may be prioritized with the same priority. In particular, data targets for use as primary data targets may be grouped and prioritized higher than data targets for use as secondary data targets.

[0032] Further exemplary strategies may be based on workpiece stability information. For example, if knowledge of appropriate alignment that takes stability (of workpiece features) into account is available, stability can be increased by individually prioritizing the points of those features with high or low weights. Stability information may be based, for example, on the material, shape (e.g., non-metallic shape) and / or reinforcing / frame-like structure of the workpiece or its features.

[0033] As a specific example, prioritizing datum targets may be based on minimizing the sum of the squared distances between the nominal point ni and the actual (measured) point ai of the datum target Ti. In this strategy, it is desirable to determine the translational T and rotational R such that the set of nominal points {n_i} fits the set of actual (measured) points {a_i} ("best fit"). Further details are explained below with respect to the figures.

[0034] As another specific example, prioritizing datum targets may be based on minimizing the maximum distance between the nominal point n of the datum target and the actual point a associated with it.

[0035] Optionally, prioritizing may involve weighting each datum target so that specific characteristics of the workpiece are appropriately considered. For example, if a workpiece is configured as part of an assembly, key datum targets that are crucial for ensuring a proper assembly may be weighted highly to dominate the optimization.

[0036] The distribution of weights and their magnitudes may depend on the strategy for automatic prioritization. The method for selecting the weight distribution and their magnitudes may depend on the strategy chosen for automatic prioritization.

[0037] For example, given primary datum targets a_1, a_2, a_3, secondary datum targets b_1, b_2, and tertiary datum target c_1, the weighting for prioritizing different groups of datum targets, where the order of datum targets is a_1, a_2, a_3, b_1, b_2, c_1, could be w = 100 / 14, which is (3w, 3w, 3w, 2w, 2w, w). Therefore, the group of primary datum targets is weighted higher than the group of secondary datum targets, and this group of secondary datum targets is weighted higher than the group of tertiary datum targets.

[0038] Prioritizing datum targets may involve prioritizing datum features in the workpiece. This is particularly advantageous in ensuring that key datum features are properly considered in shape measurement.

[0039] For example, key datum features may be the largest surface of the workpiece, the vertical surface of the workpiece, the mounting surface of the workpiece, and / or the mounting holes of the workpiece (e.g., bearing holes).

[0040] Furthermore, this method may include the additional use of CAD entities for coordinate system calculations.

[0041] Furthermore, this method can automatically generate "mating features" and / or "contact features."

[0042] Contact features may be planar or spherical. PMI information may include datum features defined as contact features, such as datum features with the modifier "CF".

[0043] Any contact feature may also be a mating feature.

[0044] Any type of entity attached to and / or included in PMI information may be used to describe datum features.

[0045] Another aspect relates to a computer-readable program that, when loaded and executed on a suitable system, includes instructions causing the system to perform steps of the method according to the aspect disclosed herein.

[0046] A computer-readable program may include instructions for obtaining datum targets from the workpiece's CAD, computer-aided design, and model information, generating a coordinate system based on the datum targets, determining the workpiece's alignment, and using the coordinate system to generate collision-free workpiece programs and / or collision-free movement paths for a shape measurement system's measuring probe.

[0047] Further embodiments relate to a shape measuring system comprising a host computer configured to perform a method according to the embodiments disclosed herein.

[0048] The shape measuring system may further include one or more of the following: a table for placing the workpiece to be measured; a measuring probe for contacting the workpiece; a moving mechanism for moving the measuring probe; and a control unit for controlling the position of the measuring probe and operating the moving mechanism to measure the position of the datum features of the workpiece.

[0049] The movement mechanism is advantageously configured to move the measuring probe within the 3D space on which the workpiece is placed on the table. The movement of the measuring probe may be linear, for example, in the X, Y, and Z directions.

[0050] The present invention is further described in detail below and by accompanying drawings, in which specific embodiments are described as examples, and the present invention is by no means limited by these specific embodiments. Although embodiments are described separately, it should be understood that their single features may be combined into additional embodiments. [Brief explanation of the drawing]

[0051] [Figure 1]This diagram shows an exemplary method for automatically generating a reference positioning system (RPS) and alignment program for measuring the shape of a workpiece. [Figure 2] A flowchart illustrating an exemplary datum target optimization process is shown. [Figure 3] An exemplary shape measurement system for measuring the shape of a workpiece is shown. [Figure 4a] This example shows how to prioritize datum targets. [Figure 4b] This example shows how to prioritize datum targets. [Modes for carrying out the invention]

[0052] Figure 1 shows a flowchart illustrating an exemplary method for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of workpiece 12, and for performing shape measurement of workpiece 12.

[0053] The illustrated method includes the following steps.

[0054] In relation to step S1 of obtaining a datum target for workpiece 12 from the CAD, computer-aided design, and model information of workpiece 12, the datum target for workpiece 12 may be obtained directly from the CAD model information of workpiece 12, for example, from the PMI of the CAD model information. Alternatively or additionally, obtaining a datum target for workpiece 12 from the CAD model information of workpiece 12 may include identifying one or more datum features of workpiece 12, optionally measuring the datum features of workpiece, and generating a datum target for said datum features.

[0055] In step S2, a coordinate system is generated based on a datum target, and this coordinate system (also called a datum reference frame) forms the basis for measuring the workpiece 12 in particular. Specifically, the geometric dimensions and tolerances of the workpiece are defined with reference to such a coordinate system. The coordinate system includes three orthogonal planes defined by the datum target.

[0056] In relation to step S3, which determines the alignment of the workpiece 12, robust workpiece alignment can be determined by horizontal or spatial alignment, rotation or planar alignment, and / or origin or axial translation.

[0057] In connection with step S4, which uses a coordinate system to generate a collision-free work program and / or collision-free movement path for the measurement probe 6 of the shape measurement system 1, one or more commands may be generated to cause the measurement probe 6 to move to multiple datum targets of the work 12, each to a datum feature, taking into account the geometric shape and alignment of the work 12.

[0058] In connection with step S5, which involves performing shape measurement of the workpiece, the shape measurement of the workpiece may be performed by moving or displacing a measuring probe 6, as described below in relation to Figure 3, relative to the datum target of the workpiece 12, relative to the datum feature, respectively.

[0059] Optionally, this method may further include a step of datum target optimization performed particularly between step S1 and step S2. An example is shown in Figure 2 and described below.

[0060] Figure 2 shows a flowchart of an exemplary datum target optimization process for use in the manner shown in Figure 1 and described herein.

[0061] Identifying and removing outlier datum targets according to the example in step S1-3a can be used for datum target optimization. This approach is particularly advantageous when finding a reference plane suitable for a particular measurement and / or when the workpiece is expected to be accurate due to its manufacturing method.

[0062] If at least one additional datum target is available for a datum feature in addition to the minimum required number of datum targets (step S1-2), this approach may be considered to efficiently and reliably handle excess constraints. Preferably, the number of excess datum targets is 6 or less, more preferably 3 or less, and most preferably 1 with respect to this approach.

[0063] For example, the minimum number of datum targets required for a plane is 3 plus 1 additional datum targets (i.e., A1 to A4 for a datum plane pA).

[0064] Optimization may include the following steps:

[0065] First of all, the datum targets are distributed into three sets: A, B, and C.

[0066] Distribution may be manually assigned and / or based on PMI information from the CAD model.

[0067] For example, set A may include datum targets A1-A4, set B may include datum targets B1-B3, and set C may include datum targets C1-C2.

[0068] Next, the datum target of set A is passed to the tangent plane solver, which creates the resulting plane pA and separates the points into "contact points" A0 located on the resulting plane pA and "outlier points" A1 located "below" that plane. Three or more points lie on the resulting (linear) plane pA.

[0069] If applicable, the same steps are performed for the (quadratic) plane pB.

[0070] The datum targets in set B are passed to the tangent plane solver, which creates the resulting plane pB with constraints on pA, separating the datum targets into a "contact point" B0 and an "outlier point" B1, where pB is perpendicular to pA. Two or more points lie on the resulting plane pB.

[0071] If applicable, the same steps are performed for the (cubic) plane pC.

[0072] The datum targets in set C are passed to the tangent plane solver, which creates a resulting plane pC with constraints on pA and pB, separating the datum targets into a "contact point" C0 and an "outlier point" C1, where pC is perpendicular to pA and pB. One or more points lie on the resulting plane pC.

[0073] In particular, a tangent plane solver may be configured to calculate the parameters of a plane such that the plane is substantially tangent to a datum feature represented by a corresponding datum target. The resulting parameters describe the plane, which includes at least some of the datum targets, which are defined as "contact points."

[0074] Alternatively, if there is a larger number of excess datum targets (step S1-2), for example, five or more, preferably seven or more, optimizing the datum targets by prioritizing them may be advantageous as it may enable faster and / or more reliable results.

[0075] An example of datum target optimization using step S1-3b is shown in Figure 4 and will be explained further below.

[0076] Figure 3 shows an exemplary shape measuring system 1 for measuring the shape of a workpiece 12, which can at least partially use the datum targets and / or datum features determined as described above. The illustrated shape measuring system 1 is configured, in particular, to perform a method for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of a workpiece 12 according to one aspect of this specification.

[0077] Specifically, the shape measurement system 1 includes a host computer 2 for performing the method described above.

[0078] The shape measuring system 1 may include a table 4 for supporting the workpiece 12 and / or for providing a mounting base for workpiece support.

[0079] The shape measuring system 1 shown in Figure 3 includes a moving mechanism 8 and a control unit 10 configured to control the moving mechanism 8 by being operated by a host computer 2.

[0080] The moving mechanism 8 includes a Y slider 16, an X slider 14, and a Z movable element 18. The Y slider 16 is slidably mounted on the table 4 in the Y direction. The X slider 14 slides in the X direction along the beam of the Y slider 16. The Z movable element 18 is fixed to the X slider 14. The Z movable element 18 moves in the Z direction by moving upward away from the table 4 or downward toward the table 4.

[0081] The measuring probe 6 is positioned at the tip of the Z-movable element 18 and is configured to contact the workpiece 12 and measure the datum targets and the datum features of the workpiece 12 represented by each datum target.

[0082] The Y slider 16, X slider 14, and Z movable element 18 may each be fitted with one or more drive motors and encoders. The drive of each drive motor may be controlled by a drive control signal from the control unit 10. Each encoder detects the amount of movement of the Y slider 16, X slider 14, or Z movable element 18 and outputs the detected value to the control unit 10 and / or the host computer 2.

[0083] The host computer 2 can operate the control unit 10 and / or the moving mechanism 8 to move the measuring probes 6 to their respective (nominal) datum targets and measure their actual positions on the workpiece 12.

[0084] This feature is specifically for optimizing datum targets to handle excessive constraints by prioritizing them by minimizing the sum of the squared distances between each nominal point ni and the actual (measured) point ai of the datum target Ti.

[0085] In this mode, the measuring probe 6 is moved by the moving mechanism 8 and contacts the workpiece 12 at multiple datum targets, and the position of the contact point is measured.

[0086] For optimization purposes, datum targets can be prioritized by comparing the sum of the squared distances between nominal points and the corresponding contact points that have been actually measured. Optimization may be performed by the host computer 2 of the shape measurement system 1.

[0087] Alternatively, the shape measuring system 1 may be configured to be coupled to a separate machine comprising a table 4, a measuring probe 6, a moving mechanism 8, and a control unit 10.

[0088] Figures 4a and 4b show examples of prioritizing datum targets, including the "best fit" which minimizes the sum of the squared distances between nominal and actual points, for example, as in step S1-3b shown in Figure 2.

[0089] In particular, when there is an excessive number of datum targets, for example, five or more, preferably seven or more, optimizing the datum targets using this approach can be advantageous as it may enable more efficient and / or more reliable results.

[0090] A datum target T_i is considered a pair of nominal points n_i and actual (measured) points a_i. In RPS alignment, it is desirable to find the translational T and rotational R such that the set of nominal points {n_i} fits the set of actual points {a_i}.

[0091] Figures 4a and 4b show two alignments in which the highest priority is given to T_1=(n_1,a_1) (Figure 4a) and the highest priority is given to T_2=(n_2,a_2) (Figure 4b).

[0092] The notation in Figures 4a and 4b is as follows: T = translation, R = rotation, n_i = nominal point, n'_i = R*n_i rotational nominal point, n''_i = T*n'_i = translation (and rotation) nominal point, a_i = measurement point.

[0093] The underlying optimization depends, for example, on finding the best fit that minimizes the sum of squared distances, such as min_{T,R}sum_{i}d(T+R(n_i),a_i)^2.

[0094] Weighting datum targets according to this example corresponds to weighted optimization, where each datum target T_i receives a weight w_i, which can be considered by min_{T,R}sum_{i}w_i*d(T+R(n_i),a_i)^2.

[0095] In Figure 4a, the exemplary weights could be (w_1,w_2,w_3)=(1000,1,1), but in Figure 4b, the exemplary weights could be (w_1,w_2,w_3)=(1,1000,1).

[0096] Determining the weight distribution and their magnitudes may depend on the automated prioritization of the workpieces and / or the strategy for their geometric shapes.

[0097] For example, as further explained above, a prioritization strategy may include prioritizing all datum targets with the same priority, prioritizing datum targets that decrease in order of datum targets, and / or prioritizing the first group of datum targets higher than the second group of datum targets, and optionally prioritizing the third group of datum targets lower than the second group of datum targets, and / or prioritizing possible contact points higher than possible non-contact points.

[0098] Following the optimization step, the coordinate system is generated based on the optimized datum target (see step S2b in Figure 2). [Explanation of Symbols]

[0099] 1. Shape Measurement System 2 Host computer 4 tables 6. Measurement probe 8 Moving mechanism 10 Control Unit 12 Work 14 X Slider 16 Y-slider 18 Z mover

Claims

1. A method for automatically generating a reference positioning system, RPS, and alignment program for measuring the shape of a workpiece (12), wherein the method is Step (S1) of obtaining the datum target of the workpiece (12) from the CAD, computer-aided design, and model information of the workpiece, Step (S2) of generating a coordinate system based on the datum target, Step (S3) of determining the alignment of the workpiece (12), Step (S4) of generating a collision-free work program and / or collision-free movement path for the measuring probe (6) of the shape measuring system (1) using the aforementioned coordinate system, Methods that include...

2. Step (S1) of obtaining the datum target of the workpiece (12) from the CAD model information of the workpiece is, The steps include reading PMI and product manufacturing information from the CAD model information of the workpiece (12), The steps include identifying the datum features of the workpiece (12), The steps include measuring the datum features of the workpiece (12), The steps include generating a datum target for the datum feature, including, The method according to claim 1.

3. This further includes automated processing of over-constraints by optimizing datum targets (S1-1) to obtain the minimum number of target datums. The method according to claim 1 or 2.

4. Datum target optimization includes reducing the number of datum targets based on identifying and removing outlier datum targets. The method according to claim 3.

5. Datum target optimization includes prioritizing datum targets. The method according to claim 3 or 4.

6. Prioritizing datum targets is Prioritizing all datum targets with the same priority, or Prioritizing the datum targets that decrease in the order of the datum targets, and / or, Prioritizing the first group of datum targets higher than the second group of datum targets, and optionally prioritizing the third group of datum targets lower than the aforementioned second group of datum targets, and / or Prioritizing possible contact points above possible non-contact points, including, The method according to claim 5.

7. Prioritizing datum targets is based on minimizing the sum of the squared distances between the nominal point (ni) and the actual point (ai) of the datum target (Ti). The method according to claim 6.

8. This further includes weighting each datum target, The method according to claim 6 or 7.

9. Further including prioritizing the datum features of the workpiece (12), The method according to any one of claims 3 to 8.

10. When loaded and executed in a suitable system, the system includes instructions that cause the system to perform the steps of the method described in any one of the prior claims, Computer-readable program.

11. A shape measuring system (1) comprising a host computer configured to perform the method described in any one of claims 1 to 9, wherein the shape measuring system (1) A table (4) for placing the workpiece (12) to be measured, A measuring probe (6) for contacting the workpiece (12), A moving mechanism (8) for moving the measuring probe (6), A control unit (10) controls the position of the measuring probe (6) and operates the moving mechanism (8) to measure the position of the datum features of the workpiece (12), Furthermore, Shape measurement system (1).

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