Method of automatically generating a reference positioning system alignment procedure for shape measurement of a workpiece

Abstract

The present application relates to a method for automatically generating a reference positioning system (RPS) alignment program for shape measurement of a workpiece, the method comprising the steps of: obtaining a reference target of the workpiece from computer aided design (CAD) model information of the workpiece; generating a coordinate system based on the reference target; determining an alignment of the workpiece; and generating a collision-free workpiece program and / or a collision-free movement path for a measurement probe of a shape measurement system using the coordinate system.

Description

Technical Field

[0001] This disclosure relates to a method for automatically generating a reference positioning system (RPS) alignment procedure for shape measurement of a workpiece, a corresponding computer-readable program, and a shape measurement system configured to perform the method. Background Technology

[0002] Contact measurement (where a probe contacts a specific point on the surface of a workpiece) provides a way to measure the accuracy of a manufactured workpiece. It can measure whether the manufactured workpiece is within predetermined tolerances to ensure proper functioning (especially in assemblies).

[0003] The probe is used to measure the geometry of a workpiece, and it can measure parameters such as diameter, length, hole depth, and radius. The probe is moved to make contact with specific points that are crucial for determining the geometric accuracy of the workpiece.

[0004] To identify and define the specific contact point (reference target), it is necessary to identify key parts of the workpiece, namely surfaces or holes (reference features). Selecting the reference features and reference target is crucial for obtaining accurate and reliable measurements. This is typically done manually and requires experienced workers.

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

[0006] The known workflow involves importing CAD model datum targets, defined as visible Product Manufacturing Information (PMI) data in the CAD file and / or on a separate (paper) blueprint. Workers interpret the PMI data and / or blueprint and determine which datum features should be measured as datum targets. The corresponding RPS (Reference Positioning System) alignment is completed only when a minimum number of points fully constrain the coordinate system.

[0007] Therefore, in traditional workflows, users are fully responsible for selecting the correct data and / or handling over-constraint information, where over-constraints are usually not handled automatically but are prevented.

[0008] Due to the increasing demand for experienced workers who can determine datum features and datum targets, but the limited availability, there is a need for an alternative to manually determining datum features and datum targets and manually generating the Reference Positioning System (RPS) alignment procedure for workpiece shape measurement.

[0009] Therefore, the object of the present invention is to provide a method and system for automatically generating a reference positioning system (RPS) alignment procedure for workpiece shape measurement, particularly based on CAD model information. Summary of the Invention

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

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

[0012] Using appropriate methods, CAD model information can be used to automatically determine datum features and / or datum targets, and generate collision-free workpiece programs and / or collision-free movement paths for measuring probes on the workpiece. This increases the accuracy of data selection and, in particular, avoids the necessity of manually performing these steps by qualified workers. Therefore, fewer qualified workers are required, which in particular avoids processing time delays due to a lack of available labor. Furthermore, this method can provide enhanced identification of datum features for improved tolerance measurement.

[0013] In some instances, datum features (and in particular, the corresponding reference positioning system RPS or datum system for the design and / or manufacture of geometric parts) are established according to ISO 5459:2024.

[0014] In some instances, a datum target is a portion of a workpiece's datum feature. A datum feature is, or corresponds to, a real, tangible feature of the workpiece, and is typically an important functional surface or hole. Specifically, a datum target is, or refers to, a theoretically precise point, line, and / or axis, which is, or can be established from, a datum feature and simulated by a measuring device. A datum feature, in particular, corresponds to, the real feature of the workpiece to be physically measured.

[0015] This method allows for automated workflows that may include one or more of the following: importing a workpiece's CAD file, reading necessary information from the CAD file, and, based on semantic PMI data that can be read from the CAD file, determining which reference features need to be automatically generated based on the CAD geometry and measured using an automatically generated workpiece program. This may, for example, include tolerances or flatness read from the CAD file, and, based on said tolerances or flatness, determining that the relevant geometry (such as several surfaces) should be measured as a plane.

[0016] The CAD file information can be used to further (especially automatically) determine how to align the workpiece to improve the shape measurement process.

[0017] If advantageous, benchmark target optimization can be performed, for example, by using "removing anomalies" and / or by "prioritizing benchmark features and / or benchmark targets" (particularly automatically), as further described below.

[0018] Furthermore, this method can automatically generate a collision-free workpiece program and / or movement path for the measuring probe using the generated coordinate system.

[0019] The baseline target of a workpiece can be obtained or exported directly from the workpiece's CAD model information, especially from the PMI (Product Manufacturing Information) of the workpiece's CAD model information.

[0020] Optionally or additionally, obtaining the reference targets of a workpiece from the workpiece's 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's CAD model information; identifying one or more reference features of the workpiece; measuring the reference features of the workpiece; and generating one or more reference targets for the reference features.

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

[0022] Therefore, the datum features are determined by considering the characteristics of the workpiece in addition to its geometry. This allows for improved results, especially because other relevant characteristics of the workpiece are properly considered, which might otherwise be ignored.

[0023] This method may also include automatically handling over-constraints through optimization of the baseline objective to obtain a minimum number of baseline objectives. Specific baseline objectives can be selected from multiple possible baseline objectives to achieve reduced complexity and computation time.

[0024] Different optimization strategies can be implemented using this method:

[0025] For example, optimizing a baseline objective can include reducing the number of baseline objectives by identifying and removing anomalous baseline objectives.

[0026] This can be particularly advantageous if the number of redundant reference targets (i.e., the amount of reference targets that exceeds the minimum necessary number of reference targets to sufficiently define the reference feature) is low (e.g., equal to or less than 6 or 3, especially 1). For example, 3+1 for a plane, 2+1 for a line, and 1+1 for a point. Further details are described below with reference to the accompanying drawings.

[0027] Alternatively or additionally, optimizing the baseline objective may include prioritizing the baseline objectives. This strategy may be particularly advantageous if the number of redundant baseline objectives is high (e.g., equal to or greater than 5 or 7), as it can more effectively determine the optimal baseline objective.

[0028] For example, prioritizing benchmark targets may include: prioritizing all benchmark targets with the same priority; or prioritizing benchmark targets in descending order of priority along the sequence of benchmark targets; and / or prioritizing the first group of benchmark targets over the second group of benchmark targets, optionally prioritizing the third group of benchmark targets over the second group of benchmark targets; and / or prioritizing possible contact points over possible non-contact points.

[0029] Different prioritization strategies can be determined, for example, based on information about the manufacturing method and / or material and / or other properties of the workpiece.

[0030] An exemplary prioritization strategy can be based on the quality of a benchmark target. For example, if a benchmark target is located near a defect, it may be considered low-quality, and its weight may be lower than that of a benchmark target located far from the defect, which may be considered to have higher quality.

[0031] Another exemplary prioritization strategy may include grouping benchmark targets given by the PMI and prioritizing said groups of benchmark targets. Specifically, benchmark targets within a group may be prioritized using the same priority. In particular, benchmark targets used as primary benchmark targets may be grouped together and assigned a higher priority than benchmark targets used as secondary benchmark targets.

[0032] Another exemplary strategy could be based on workpiece stability information. For example, if knowledge of the appropriate alignment of stability (of workpiece features) is available, stability can be increased by specifically prioritizing points of that feature using individual higher or lower weights. Stability information could be based, for example, on the material, form (e.g., freeform metal) and / or reinforcement / frame structure of the workpiece or its features.

[0033] As a specific example, prioritizing benchmark targets can be based on minimizing the sum of squared distances between nominal points ni and actual (measured) points ai of the benchmark target Ti. In this strategy, it is desirable to determine translations T and rotations R such that the set of nominal points {n_i} fits the set of actual (measured) points {a_i} (“best fit”). Further details are described below with reference to the accompanying figures.

[0034] As another specific example, the priority of dividing benchmark targets can be based on minimizing the maximum distance between the nominal point n of the benchmark target and the associated actual point a.

[0035] Optionally, prioritization may include weighting each baseline objective so that specific properties of the workpiece are appropriately considered. For example, if the workpiece is configured as part of a component, key baseline objectives that are critical to ensuring proper assembly may be weighted high enough to dominate optimization.

[0036] The distribution and magnitude of the weights can be determined by the automatic prioritization strategy. The method for selecting the weight distribution and magnitude can also depend on the chosen automatic prioritization strategy.

[0037] For example, for primary benchmark targets a_1, a_2, a_3, auxiliary benchmark targets b_1, b_2, and third benchmark target c_1, the weights used to prioritize different groups of benchmark targets with the benchmark target sequence a_1, a_2, a_3, b_1, b_2, c_1 can be (3w, 3w, 3w, 2w, 2w, w), where w = 100 / 14. Therefore, the weight of the primary benchmark target in this group is higher than that of the auxiliary benchmark targets in this group, and the weight of the auxiliary benchmark targets in this group is higher than that of (one or more) third benchmark targets (groups).

[0038] Prioritizing datum targets can include prioritizing datum features of the workpiece. This is particularly advantageous for ensuring that critical datum features are properly considered in shape measurement.

[0039] For example, key reference features may be the maximum 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] In addition, the method may include the additional use of CAD entities for coordinate system calculations.

[0041] In addition, this method can automatically generate "fitting features" and / or "contact features".

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

[0043] Any contact feature can be a mating feature.

[0044] Entities attached to and / or included in the PMI information can be used to describe one or more data characteristics.

[0045] On the other hand, it relates to a computer-readable program including instructions that, when loaded and executed on a suitable system, cause the system to perform the steps of the method according to the aspects disclosed herein.

[0046] Computer-readable programs may specifically include the following instructions: for obtaining a reference target for the workpiece from CAD (computer-aided design) model information of the workpiece; generating a coordinate system based on the reference target; determining the alignment of the workpiece; and using the coordinate system to generate a collision-free workpiece program and / or a collision-free movement path for the measuring probe of the shape measurement system.

[0047] On the other hand, it relates to a shape measurement system, which includes a host computer configured to perform methods according to aspects disclosed herein.

[0048] The shape measurement system may also include one or more of the following: a worktable for mounting 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 a reference feature of the workpiece.

[0049] The moving mechanism is advantageously configured to move the measuring probe in 3D space, in which the workpiece is mounted on a worktable. The movement of the measuring probe can, for example, be linear in each of the X, Y, and Z directions.

[0050] The invention is further explained in detail below with reference to the accompanying drawings, in which specific embodiments are shown by way of example, and the invention is by no means limited to these specific embodiments. It should be understood that even though embodiments are described individually, their individual features can be combined into additional embodiments. Attached Figure Description

[0051] Figure 1 A flowchart is shown as an exemplary method for automatically generating a Reference Positioning System (RPS) alignment procedure for shape measurement of a workpiece;

[0052] Figure 2 A flowchart illustrating an exemplary baseline target optimization process is shown;

[0053] Figure 3 An exemplary shape measurement system for measuring the shape of a workpiece is shown;

[0054] Figure 4a and 4b An example of prioritizing baseline targets is shown. Detailed Implementation

[0055] Figure 1 A flowchart is shown of an exemplary method for automatically generating a Reference Positioning System (RPS) alignment procedure for shape measurement of workpiece 12 and performing shape measurement of workpiece 12.

[0056] The method shown includes the following steps:

[0057] In conjunction with step S1 – obtaining the reference target of the workpiece 12 from the CAD (Computer-Aided Design) model information of the workpiece 12 – the reference target of the workpiece 12 can be obtained directly from the CAD model information of the workpiece 12, for example, from the PMI of the CAD model information. Alternatively or additionally, obtaining the reference target of the workpiece 12 from the CAD model information of the workpiece 12 may include: identifying one or more reference features of the workpiece 12, and optionally measuring the reference features of the workpiece; and generating a reference target for the reference features.

[0058] In step S2, a coordinate system is generated based on a reference target, wherein the coordinate system (also called a reference reference system) specifically forms the basis for measuring workpiece 12. Specifically, the geometric dimensions and tolerances of the workpiece are defined with reference to this coordinate system. The coordinate system includes three orthogonal planes defined by the reference target.

[0059] In conjunction with step S3 - determining the alignment of workpiece 12, robust workpiece alignment can be determined through horizontal or spatial alignment, rotation or planar alignment and / or translation of the origin or axis.

[0060] In conjunction with step S4 - using a coordinate system to generate a collision-free workpiece program and / or collision-free movement path for the measuring probe 6 of the shape measurement system 1, one or more instructions can be generated to move the measuring probe 6 to multiple reference targets (corresponding reference features) of the workpiece 12, taking into account the geometry and alignment of the workpiece 12.

[0061] In conjunction with step S5 - performing workpiece shape measurement, the workpiece shape measurement can be performed by moving or shifting the measuring probe 6 to the reference target (corresponding reference feature) of the workpiece 12, as described below. Figure 3 As stated above.

[0062] Optionally, the method may also include a step for optimizing the baseline objective, particularly a step performed between steps S1 and S2. An example of this is... Figure 2 It is shown in the figure and described below.

[0063] Figure 2 An example of using Figure 1 A flowchart illustrating an exemplary baseline target optimization process for the methods shown and described herein.

[0064] The identification and removal of anomalous reference targets, as illustrated in steps S1-3a, can be used for the optimization of reference targets. This approach is particularly advantageous in situations where a suitable datum plane is needed for a specific measurement and / or if the workpiece is expected to be precise due to its manufacturing method.

[0065] If the minimum necessary number of baseline targets plus at least one additional baseline target can be used for the baseline feature (steps S1-2), then this scheme can be considered for effectively and reliably handling over-constraints. Preferably, for this scheme, the number of redundant baseline targets is 6 or fewer, more preferably 3 or fewer, and most preferably 1.

[0066] As an example, the minimum number of reference targets required for a plane is 3 plus 1 additional reference targets (i.e., A1-A4 of reference plane pA).

[0067] Optimization may include the following steps:

[0068] First, the benchmark targets are divided into three sets: A, B, and C.

[0069] Distributions can be manually assigned and / or based on PMI information from a CAD model.

[0070] In the example, set A may include benchmark targets A1-A4, set B may include benchmark targets B1-B3, and set C may include benchmark targets C1-C2.

[0071] Then, the baseline target of set A is passed to the tangent plane solver, which creates the resulting plane pA and divides the points into "contact points" A0 located on the resulting plane pA and "outliers" A1 located "below" the plane. Three or more points lie on the resulting (primary) plane pA.

[0072] If applicable, perform the same steps for the (auxiliary) plane pB:

[0073] The baseline targets in set B are passed to the tangent plane solver, which creates a resulting plane pB constrained by pA and divides the baseline targets into "contact points" B0 and "anomalies" B1, where pB is perpendicular to pA. Two or more points lie on the resulting plane pB.

[0074] If applicable, perform the same steps for the (third) plane pC:

[0075] The baseline targets in set C are passed to the tangent plane solver, which creates a resulting plane pC with constraints on pA and pB, and divides the baseline targets into "contact points" C0 and "anomalies" C1, where pC is perpendicular to pA and pB. One or more points lie on the resulting plane pC.

[0076] Specifically, the tangent plane solver can be configured to calculate the parameters of the plane such that the plane is substantially tangent to a datum feature represented by a corresponding datum target. The resulting parameters(s) describe a plane containing at least some of the datum targets. The datum targets are defined as "contact points".

[0077] Alternatively, if the number of redundant baseline targets is large (steps S1-2), for example, equal to or greater than 5, preferably equal to or greater than 7, it may be advantageous to optimize the baseline targets by prioritizing them, as this can allow for faster and / or more reliable results.

[0078] Based on the baseline target optimization in the example of step S1-3b Figure 4a and 4b It is shown in the figure and described further below.

[0079] Figure 3 An exemplary shape measurement system 1 for measuring the shape of workpiece 12 is shown, which can at least partially utilize the reference targets and / or reference features as determined above. The illustrated shape measurement system 1 is specifically configured to perform a method according to aspects herein for automatically generating a reference positioning system (RPS) alignment procedure for measuring the shape of workpiece 12.

[0080] Specifically, the shape measurement system 1 includes a host computer 2 for performing the method.

[0081] The shape measurement system 1 may include a worktable 4 for supporting the workpiece 12 and / or providing a mounting base for the workpiece support.

[0082] Figure 3 The shape measurement system 1 includes a moving mechanism 8 and a control unit 10, which is configured to control the moving mechanism 8 by operation of a host computer 2.

[0083] The moving mechanism 8 includes a Y-slider 16, an X-slider 14, and a Z-moving block 18. The Y-slider 16 is configured to slide along the Y direction on the worktable 4. The X-slider 14 slides along the beam of the Y-slider 16 in the X direction. The Z-moving block 18 is fixed to the X-slider 14. The Z-moving block 18 moves in the Z direction by moving upward away from the worktable 4 or downward toward the worktable 4.

[0084] The measuring probe 6 is positioned on top of the Z-shift block 18 and configured to contact the workpiece 12 to measure the reference target and the corresponding reference feature of the workpiece 12 represented by the reference target.

[0085] The Y slider 16, X slider 14, and Z shift block 18 can each be attached with one or more drive motors and encoders. The drive of each drive motor can be controlled by a drive control signal from the control unit 10. Each encoder detects the movement of the Y slider 16, X slider 14, or Z shift block 18 and outputs the detected value to the control unit 10 and / or the main computer 2.

[0086] The host computer 2 can operate the control unit 10 and / or the moving mechanism 8 to move the measuring probes 6 to the corresponding (nominal) reference targets and measure their actual positions at the workpiece 12.

[0087] This function is specifically designed to optimize the baseline target by minimizing the sum of squares of the distances between the corresponding nominal point ni and the actual (measured) point ai of the baseline target Ti, thereby prioritizing the baseline target to handle over-constraints.

[0088] In this mode, the measuring probe 6 is moved by the moving mechanism 8 to contact the workpiece 12 at multiple reference targets and measure the position of the contact point.

[0089] For optimization, the priority of the reference targets can be determined by comparing the sum of the squares of the distances between the nominal point and the corresponding contact point measured in the actual measurement. Optimization can be performed by the main computer 2 of the shape measurement system 1.

[0090] Alternatively, the shape measurement system 1 can be configured to be coupled to a separate machine, which includes a corresponding worktable 4, a measuring probe 6, a moving mechanism 8, and a control unit 10.

[0091] Figure 4a and Figure 4b Examples of prioritizing baseline objectives are shown, such as including a "best fit" that minimizes the sum of squares of the distances between nominal and actual points, for example, as... Figure 2 Steps S1-3b are shown in the diagram.

[0092] In particular, if the number of redundant baseline targets is large, for example equal to or greater than 5, preferably equal to or greater than 7, it may be advantageous to optimize the baseline targets by using this scheme, as it can allow for more efficient and / or more reliable results.

[0093] The reference target T_i is considered as a pair of nominal points n_i and actual (measured) points a_i. For RPS alignment, the goal is to find translations T and rotations R such that the set of nominal points {n_i} fits the set of actual points {a_i}.

[0094] exist Figure 4a and 4b The diagram shows two alignments, where for T_1 = (n_1, a_1) Figure 4a) has the highest priority, and for T_2 = (n_2, a_2) Figure 4b It has the highest priority.

[0095] Figure 4a and 4b The symbols in the table are as follows: T = translation, R = rotation, n_i = nominal point, n'_i = nominal point of R*n_i rotation, n''_i = nominal point of T*n'_i translation (and rotation), a_i = measurement point.

[0096] The underlying optimization relies on a best fit, for example, minimizing the sum of squared distances, such as min_{T,R}sum_{i}d(T+R(n-1), a_i)^2.

[0097] The baseline objectives are weighted according to this example corresponding to weighted optimization, where each baseline objective T_i receives a weight w_i, which can be considered by min_{T,R}sum_{i}w_i*d(T+R(n-1), a_i)^2.

[0098] exist Figure 4a In the example, the weights could be (w_1, w_2, w_3) = (1000, 1, 1), while... Figure 4b In this example, the weights could be (w_1, w_2, w_3) = (1, 1000, 1).

[0099] The distribution and magnitude of the weights can be determined by the strategy used for automatic partitioning priorities and / or geometry of the workpiece.

[0100] For example, as further described above, a prioritization strategy may include: prioritizing all benchmark targets with the same priority; or prioritizing benchmark targets in descending order of priority along the sequence of benchmark targets; and / or prioritizing the first group of benchmark targets over the second group of benchmark targets, optionally prioritizing the third group of benchmark targets over the second group of benchmark targets; and / or prioritizing possible contact points over possible non-contact points.

[0101] Following the optimization step, a coordinate system is generated based on the optimized baseline target (see...). Figure 2 Step S2b in the process.

[0102] List of reference numerals

[0103] 1 Shape Measurement System

[0104] 2. Main computer

[0105] 4 workbench

[0106] 6. Measuring probe

[0107] 8. Mobile mechanism

[0108] 10 Control Unit

[0109] 12 workpieces

[0110] 14 X slider

[0111] 16 Y Slider

[0112] 18 Z-block shift

Claims

1. A method for automatically generating a reference positioning system (RPS) alignment procedure for shape measurement of a workpiece (12), the method comprising the following steps: (S1) Obtain the reference target of the workpiece from the computer-aided design CAD model information of the workpiece (12); A coordinate system (S2) is generated based on the aforementioned benchmark target; Determine (S3) the alignment of the workpiece (12); and Using the coordinate system, generate (S4) a collision-free workpiece program and / or collision-free movement path for the measuring probe (6) of the shape measurement system (1).

2. The method according to claim 1, wherein, The reference targets for the workpiece (12) obtained from the CAD model information of the workpiece (S1) include: Product manufacturing information (PMI) is read from the CAD model information of the workpiece (12); Identify the reference features of the workpiece (12); Measure the reference features of the workpiece (12); and Generate a benchmark target for the benchmark feature.

3. The method according to claim 1 or 2 further includes automatically handling over-constraints through optimization of the baseline target (S1-1) to obtain a minimum number of baseline targets.

4. The method according to claim 3, wherein, Optimization of the baseline targets includes reducing the number of baseline targets by identifying and removing anomalous baseline targets.

5. The method according to claim 3 or 4, wherein, Optimization of the baseline objective includes prioritizing the baseline objective.

6. The method according to claim 5, wherein, Prioritizing baseline targets includes: Prioritize all baseline targets using the same priority level; or Prioritize the benchmark targets in descending order of their sequence; and / or The first group of benchmark targets has a higher priority than the second group of benchmark targets, and optionally, the third group of benchmark targets has a lower priority than the second group of benchmark targets; and / or Identifying potential contact points takes precedence over identifying potential non-contact points.

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

8. The method of claim 6 or 7 further includes weighting each benchmark target.

9. The method according to any one of claims 3 to 8 further includes prioritizing the reference features of the workpiece (12).

10. A computer-readable program comprising instructions that, when loaded and executed on a suitable system, cause the system to perform the steps of the method according to any one of the preceding claims.

11. A shape measurement system (1) comprising a host computer configured to perform the method according to any one of claims 1 to 9, the shape measurement system (1) further comprising: The worktable (4) is used to mount the workpiece (12) to be measured. A measuring probe (6) for contacting the workpiece (12); The moving mechanism (8) for moving the measuring probe (6); and Control unit (10) is used to control the position of the measuring probe (6) and operate the moving mechanism (8) to measure the position of the reference features of the workpiece (12).

Images