VALIDATION OF TEST PLANS FOR OBJECT SURVEYING USING A COORDINATE MEASURING DEVICE

Description

[0001] The invention relates to a method and a computer device for validating test plans for object measurement with or, in other words, by a coordinate measuring machine. The object measurement can preferably comprise a three-dimensional coordinate determination, in particular of the surface coordinates of the object. In other words, the test plan can be intended for a coordinate measuring machine and / or can be executed by a coordinate measuring machine.

[0002] The following provides background information on the technical field of object measurement using test plans. All features, variants, and designs may also be provided for or applicable to the invention disclosed herein.

[0003] It is common practice to create so-called test plans for the inspection or measurement of workpieces. Such a test plan defines the parameters of a testing process through which the quality of a workpiece or object to be measured can be determined. Such a test plan can be defined, for example, based on certain general standards or manufacturer or customer specifications.

[0004] The inspection plan can be executed by a testing or measuring device, for example, a coordinate measuring machine (CMM), which preferably records three-dimensional coordinates of an object, in particular surface coordinates, during the inspection. The inspection plan can include digital data, digital parameters, program instructions, and / or an algorithm that causes a testing device (e.g., a CMM) to execute the inspection process according to the inspection plan (e.g., according to the relationships and / or parameters defined therein).

[0005] In general, the test plan may be a file or a computer program that is readable and / or executable by a control device, wherein the control device is preferably comprised by a testing device (for example a CMM) that is intended to implement the test plan.

[0006] For example, the test plan (particularly digital and / or programmed) can specify work instructions for performing a desired object test, e.g., in the form of commands. Additionally or alternatively, the test plan can define the test parameters to be set for execution and data generation, e.g., lighting parameters or contact forces, and / or the test components to be used for execution, e.g., sensors. A test plan can also contain test parameters that can be set or changed during the test run, e.g., to adapt subsequent test (sub)processes.

[0007] Furthermore, in addition or alternatively, a test trajectory to be followed to perform the test, e.g., a sensor, can be specified in the test plan. The test result documentation can also be specified in the test plan.

[0008] The test plan can also contain information about the position and shape of the workpiece to be tested, e.g., in a test coordinate system, and / or information about the target values ​​of test characteristics. Information about the shape can be included in the test plan, for example, in the form of a CAD model. Such a CAD model can also be used to define the target values ​​explained. Additionally or alternatively, the test plan can include tolerance specifications for a test characteristic.

[0009] Actual information generated during the execution of the test plan, e.g. measuring points, coordinate values, images or measured values, can also be saved in the test plan.

[0010] Based on the test plan, measurement points to be recorded by a measuring device or, in other words, a measuring instrument can be defined and / or read out, which are necessary for evaluating the test characteristics defined in the test plan. A measurement sequence can then be defined in order to record measurement points, for example on the surface of the workpiece to be measured. In a test step or measuring step, the measurement sequence defined in this way is processed by the measuring instrument (for example in the form of a CMM), whereby the required measurement points (and in particular their spatial coordinates) are then recorded and saved according to the measurement sequence defined in the test plan. The individual test characteristics of the test plan are then evaluated based on the recorded measurement points and / or the obtained coordinates, and this provides the data required to create a measurement report.

[0011] Generally speaking, a test plan can contain instructions (for example in the form of measuring points to be recorded) which directly or indirectly describe a desired measurement procedure.

[0012] In particular, the test plan can contain or define the test characteristics of a workpiece to be measured and / or information about these test characteristics. Test characteristics can be quality criteria, particularly of a dimensional nature, compliance with which is to be verified during the testing process. In other words, a test characteristic can represent a dimensional property of at least one defined geometric element (measuring element) on a measuring object. Examples of test characteristics are the distance between the centers of two holes, the deviations of measuring points on a free-form surface from a desired shape, the position of the center of a hole, the diameter of a hole, the position of a measuring element in a reference coordinate system, etc.

[0013] When creating test plans, the test characteristics to be inspected are usually identified first. These test characteristics are each assigned measuring elements that must be measured to verify the test characteristics. More precisely, in order to quantify a test characteristic that relates to a specific measuring element or, in other words, is defined as a function of it, it is usually necessary to record measuring points of this measuring element. In the field of coordinate metrology considered here, a coordinate measurement value is typically determined for such a measuring point. From this, spatial degrees of freedom (in particular, the complete spatial position and orientation, i.e., the position) and / or dimensions of the measuring element can then be calculated.

[0014] A dependency between a test characteristic and a measuring element is generally referred to here when the measuring element must be touched and / or measured to check (especially quantify) the test characteristic. Such a measuring element represents a reference element for the test characteristic, as it forms a reference to be measured for quantifying the test characteristic.

[0015] The relationship between inspection features and reference elements, as well as their potential impact on the accuracy of an object measurement, is difficult to understand, especially for less experienced operators. It has been shown that, as a result, an unnecessary non-conformity assessment of inspection features often occurs during object measurement, even though this does not correspond to the conditions on the actual object or component.

[0016] A solution for planning inspection strategies using virtual coordinate measuring machines is disclosed in: Yang Hu et al.: "Design, Implementation, and Testing of Advanced Virtual Coordinate-Measuring Machines", IEEE Transactions on Instrumentation and Measurement, IEEEService Center, Piscataway, NJ, US, Vol. 61, No. 5, May 1, 2012 (2012-05-01), pages 1368-1376, XP011440639, ISSN: 0018-9456, DOI: 10.1109 / TIM.2011.2175828.

[0017] US 2004 / 157861 A1 discloses a solution for correcting temperature deviations during serial measurement of similar workpieces.

[0018] Further technological background can be found in WO 2017 / 121468 A1 and in the following two publications: Giovanni Moroni et al.: "Optimal inspection strategy planning for geometric tolerance verification", Precision Engineering, Vol. 38, No. 1, 1 January 2014 (2014-01-01), pages 71-81, XP055683426, Amsterdam, NL, ISSN: 0141-6359, DOI: 10.1016(j.precisioneng.2013.07.006;

[0019] Giovanni Moroni et al.: "Coordinate Measuring Machine Measurement Planning", January 1, 2011 (2011-01-01), Geometric Tolerances, Springer, Page(s) 111-158, XP099177945, ISBG: 978-1-84996-310-7.

[0020] An object of the present invention is to improve the measurement of workpieces with a coordinate measuring machine, in particular to the extent that workpieces are less likely to be incorrectly assessed as not being OK.

[0021] This object is achieved by a method and a computer device according to the appended independent claims. Advantageous further developments are specified in the dependent claims.

[0022] It should be emphasized again that the features, embodiments, and definitions mentioned in the introductory description can also be provided individually or in any combination in the solution disclosed here. This applies in particular to all embodiments and definitions of test plans, test features, measuring elements, and reference elements, whereby the scope of protection of the described invention is determined by the appended claims.

[0023] According to the invention, it was recognized that a frequent cause of unjustified non-conformity assessments of test characteristics is that the measurement of these test characteristics is carried out with insufficient accuracy. In particular, it was recognized that even the measurement of the reference elements is often only possible with limited and sometimes insufficient accuracy. If the test characteristics are then to be determined mathematically (i.e., quantified) based on these measurements of the reference elements, for example, non-conformity assessments can occur, even though this is not reflected in the actual component.

[0024] More precisely, it has so far been only possible for an operator to reliably determine the cause of a negative evaluation of test characteristics to a limited extent. Of course, the object itself, and more specifically its poor quality, can be a cause of measurement results outside of a permissible tolerance. On the other hand, however, the definition of the test plan and the characteristics and measuring elements it includes can also be at least partially causal for such an evaluation and / or measurement results. For example, a test characteristic may be assessed as not satisfactory primarily because the underlying measuring elements that are assigned to this characteristic as reference elements or serve as reference elements for this test characteristic and are measured for this purpose can only be measured with insufficient accuracy.

[0025] However, identifying such a cause of error becomes particularly complex when measurement results of the reference elements were determined at least partially based on measurements of other measuring elements, i.e. the test characteristic depends on a plurality of successive measuring elements.

[0026] It can require considerable experience and time for an operator to determine whether a test characteristic rated as non-conforming is actually primarily due to the component itself or primarily to the definition of the test plan and the reference elements specified therein, which may be imprecisely measurable. Failure to perform such a check can lead to high scrap rates, as objects are rated as non-conforming to an unnecessarily high degree.

[0027] It is therefore proposed to consider accuracy parameters for reference elements on which a test characteristic depends. These can generally indicate the accuracy with which such a reference element can be measured or, in other words, the accuracy with which a measurement result of the reference element can be determined.

[0028] This can be used, for example, to determine whether the test characteristic depends on reference elements that can only be measured imprecisely. Such a determination can be performed automatically, for example, based on an automatically determined (in particular, calculated) error influence of the reference elements on the quantification of the test characteristic. The error influence can indicate a particularly distorting effect or falsifying effect that the reference element has on the quantification of the test characteristic.

[0029] In this way, it can be determined, for example, that the cause of unacceptable test characteristic values ​​may be the measuring elements that can only be measured inaccurately and not necessarily the object itself.

[0030] An operator can then take appropriate countermeasures and / or corresponding countermeasures can be automatically determined and / or automatically suggested and / or, if necessary, automatically implemented. The countermeasures can include adjusting the measurement of the reference features to increase accuracy, redefining the inspection feature and / or reselecting the measured reference features, for example, by adjusting the dependencies.

[0031] This creates opportunities to detect and / or display to the operator (for example, by determining the error influence) any impairments in the quantification of the test characteristic caused by reference elements that can only be measured imprecisely. This relieves the operator of their own error determinations, which also reduces the requirements for operator qualification and experience. Furthermore, test plan setup is accelerated because potential error influences do not have to be determined iteratively, and the quality of a generated test plan and the test characteristic values ​​that can be determined with it is increased. Consequently, the risk of objects that meet test characteristics being incorrectly assessed as non-conforming is also reduced. This is because the determination of test characteristics is prone to errors and subject to high measurement uncertainty due to its dependence on reference elements that can only be measured imprecisely.

[0032] In detail, a method for validating a test plan for object measurement using a coordinate measuring machine is proposed, wherein the test plan contains at least one test feature that is to be quantified as part of the object measurement, wherein the quantification of the test feature is to be carried out on the basis of a measurement result of at least one reference element of the object; wherein the method comprises: Obtaining at least one accuracy value that indicates an accuracy of the measurement result of the reference element; determining an error influence of the reference element on the quantification of the test feature based on the accuracy value.

[0033] The coordinate measuring machine can be a measuring machine for recording three-dimensional (i.e., spatial) measurement point coordinates, wherein the measurement points can preferably be located on a component surface and / or in the interior of a component (for example, in the case of a computer tomography coordinate measuring machine). The coordinate measuring machine can be designed according to any common type, in particular as a device preferably comprising a plurality of controllable machine axes for positioning a measuring sensor relative to the object. For example, at least two linear axes can be provided, which are preferably orthogonal to one another. In particular, the coordinate measuring machine can be designed as a gantry or bridge structure.

[0034] The coordinate measuring machine can measure the object tactilely (for example, by probing it with a measuring probe) or non-contact (for example, using an optical sensor). The object can be an industrially manufactured component. The measurement can be performed as part of a quality inspection, for example, in serial object or component production.

[0035] The measurement result can contain at least one measured value or be such a measured value. The test characteristic can be quantified based on, and in particular by calculating, the measurement result and / or the measured value. Depending on the test characteristic, predetermined calculation rules can be applied for this purpose. For example, the center coordinates of two circles or holes can be determined as the measurement result, and the distance between these centers can be determined as the test characteristic by simply calculating the difference.

[0036] As part of the invention presented herein, it may also be provided to actually execute the test plan, determine measurement results of a reference element, and quantify the test characteristic. However, this is not mandatory. The invention is directed to test plan validation in the sense of preparing for a subsequent implementation or execution of the test plan.

[0037] The accuracy quantity, which generally defines at least one quantified value or can be such a value, can also be referred to as measurement uncertainty and / or indicate such a measurement uncertainty. Examples of specific accuracy quantities are explained below.

[0038] The error influence can specify at least one quantified value. It can be a scale value and / or a value specifying a ranking, for example, to indicate which of a plurality of possible reference elements has the greatest error influence on the test feature quantification. For this purpose, for example, the accuracy values ​​of the reference elements can be compared with each other and / or a ranking can be determined based on this. Preferably, however, the error influence is determined based on a utilized and / or claimed tolerance range of the test feature, explained below, which can be attributed to the reference element under consideration.

[0039] As mentioned, reference elements whose measurement results are used to quantify a test characteristic can have a dependency relationship with the test characteristic. In other words, the test characteristic can be defined and / or determined as a function of these reference elements, so that the test characteristic can be said to be dependent on these reference elements. However, the reference elements themselves can also be dependent on further measurement elements, i.e., their measurement result can be determined at least partially based on a measurement result from another measurement element. Such further measurement elements can thus serve at least indirectly as a reference for the test characteristic and are therefore also referred to herein as reference elements.

[0040] The method is computer-implemented. In principle, all method steps and measures described herein can be automated and / or executed without requiring specific user input. For example, a method according to any variant described herein, or all measures encompassed therein, can be executed using a computer device of the type disclosed herein.

[0041] One aspect of the invention of method and computer device provides for determining whether the error influence meets an error criterion and if so: Classify the reference element as a critical reference element.

[0042] The failure criterion can, for example, be the exceeding of a predetermined and maximum permissible threshold value of the failure influence, which can indicate a quantified value. Classification can include providing the reference element with corresponding data-based and / or digital information or assigning such information to it. The classification can be displayed to a user, for example, on a display device of a computer device disclosed herein. For this purpose, a critical reference element can be visually highlighted, for example, in a graphically displayed test plan. Additionally or alternatively, the reference element can be provided with a corresponding designation (for example, "critical") and / or a failure influence (for example, in the form of a corresponding failure influence value) can be displayed.

[0043] A further development of the method and computer device provides that the measurement result of the reference element is to be determined based on the measurement result of at least one further reference element, or, in other words, should be determined or is determined. The above-described dependence of the reference element on at least one further measuring element can therefore exist. Again, the determination of the measurement result can optionally be included in the solution described here, but preferably only takes place at a later point in time after validation of the test plan. For this further reference element, a (further) error influence on the achievable accuracy of the quantification is then preferably determined. This further reference element can accordingly indirectly influence the accuracy of the test feature quantification.

[0044] Thus, in the sense of a dependency tree or a multi-level breakdown of dependencies, it is possible to consider which reference elements the test characteristic is at least indirectly dependent on, and to determine (error) influences on the quantification of the test characteristic, especially from reference elements to which there is only an indirect dependency. This enables an even more precise analysis of any error cause, since possible error influences on the quantification of the test characteristic can be considered even more comprehensively and across multiple dependency levels.

[0045] In general, the reference element can be a geometric element of the object. It can also be referred to as a form element or measuring element. In particular, it can be a real, physical geometric element that can be touched, for example, by a coordinate measuring machine, as part of an object measurement. However, it can also be a virtual and / or computationally determined geometric element that cannot be touched in reality, but is determined, for example, as an auxiliary element based on measured values ​​for other elements. One example is the intersection point of bore axes that lies outside an object volume.

[0046] According to a further development of the method and the computer device, the measurement result of the reference element is determined based on at least one coordinate value (which can also be referred to as the actual value) of this reference element. In particular, the coordinate values ​​can be determined based on a real or simulated object measurement. Simulated object measurements are known. Real component tolerances and measurement uncertainties can be taken into account using random variables. In particular, it is known in the context of simulations to determine coordinate values ​​based on distributions determined, for example, from a Monte Carlo simulation, random distributions, or using the Box-Muller method. In this case, properties of the specific coordinate measuring machine under consideration, and in particular its accuracy class, can also be taken into account.

[0047] In general, it can further be provided that the measurement result of the reference element specifies at least one spatial degree of freedom and / or at least one dimension of the reference element. A spatial degree of freedom can be any degree of freedom with which a position (i.e., position and orientation) of the reference element can be described, for example, in a reference coordinate system. In a manner known per se, three translational and three rotational degrees of freedom defined in a Cartesian coordinate system can be provided. The dimension can be an extension along at least one axis of a reference coordinate system.

[0048] In this way, the measurement result can be used, for example, to determine a distance or another property of a relative arrangement to the reference element, knowing the (preferably complete) spatial position and / or the dimension, wherein the dimension or the property can be the test feature.

[0049] In a further embodiment of the method and the computer device, the accuracy value is determined on the basis of at least one of the following, wherein the following coordinates can be obtained in particular by means of the above simulations during a purely computer-based test plan validation or during real measurement, e.g. of a test object: A statistical parameter of a distribution of coordinate values ​​determined to determine the measurement result of the reference element. For example, a range of coordinate values ​​and / or a distribution variable, such as a standard deviation, can be considered. Additionally or alternatively, the statistical parameter can be determined based on a compensation method of the type explained below. The greater the scatter, deviation, or range of coordinate values, the lower the accuracy value that can be selected.

[0050] For example, within the scope of the adjustment procedure, a geometric element can be calculated that is fitted into a plurality of coordinate values ​​(for example, a circle that is fitted into a plurality of coordinate values ​​recorded at a hole edge). As a statistical parameter, for example, an average deviation of the actual coordinate values ​​from the calculated coordinates of the fitted geometric element can be determined. The greater the deviation, the lower the accuracy value that can be selected. A deviation of at least one coordinate value from a measurement result calculated for the reference element from a plurality of coordinate values. This applies in particular to the case in which the measurement result is determined using an explained adjustment method, for example as a calculated or fitted geometric element. The greater the deviation, the lower the accuracy value that can be selected. A adjustment method that is carried out to calculate the measurement result from a plurality of coordinate values. The adjustment method can fit a geometric element of the type mentioned into a plurality of determined coordinate values. The geometric element can be, for example, a straight line, a circle or a plane. The coordinate values, as actual values, are typically not on or within this geometric element, but deviate slightly from it.The larger the deviation (e.g. average or maximum), the smaller the accuracy value that can be selected. A form deviation of the reference element. The form deviation can be calculated in a conventional manner using coordinate values ​​of the reference element, e.g. as the largest deviation of the coordinates within a fitted geometric element and / or as the difference between the maximum and minimum coordinates of the measuring points of a fitted geometric element. In this way, error influences such as a general measurement uncertainty and / or surface deviations of the component at a measuring point can be taken into account, at least indirectly. Analogous to the above statements on compensation methods, the following applies: the larger the form deviation, the smaller the accuracy value that can be selected. An inherent or, to put it another way, systematic measurement uncertainty of the coordinate measuring machine.This can be a measurement uncertainty, which is due, for example, to imperfect kinematics of the coordinate measuring machine. Inherent measurement uncertainties can, for example, be determined by the manufacturer of a coordinate measuring machine prior to delivery using a standardized procedure. Additionally or alternatively, such a determination can take place as part of a machine acceptance test. The inherent measurement uncertainty can indicate the performance of the coordinate measuring machine with regard to the achievable measurement accuracy. The greater the inherent measurement uncertainty, the lower the accuracy value that can be selected.

[0051] According to a further embodiment of the method and the computer device, the error influence of the reference element can be determined based on a possible value spectrum of the measurement result of this reference element, wherein the value spectrum is determined using the accuracy parameter. For example, the accuracy parameter can be used to define an expected variation range (or the expected value spectrum) of the measurement result resulting from the measurement. In particular, a possible upper limit and a lower limit of the value spectrum can be determined, wherein the upper limit and lower limit each represent possible extreme values ​​of the measurement result.

[0052] The value spectrum can be used to determine a resulting range of variation in the quantification of the test characteristic in the manner explained below.

[0053] More specifically, according to another variant of the method and the computer device, a possible quantification value spectrum of the test characteristic can be determined based on the value spectrum of the reference element and compared with a (predetermined) permissible tolerance range of the test characteristic. For example, any extreme values ​​of a value spectrum can be used to determine resulting (external) quantification values ​​of the test characteristic. From this, the expected variation range of the test characteristic can be determined, which results from the possible value spectrum of the measurement result.

[0054] It can then be examined to what extent this variation range and the permissible tolerance range overlap, or what proportion this variation range represents of the tolerance range. If it becomes apparent that a reference element can be measured with such inaccuracy that the quantification values ​​of the inspection characteristic are also subject to increased fluctuations, for example, accounting for more than 10%, more than 20%, or more than 50% of the tolerance range, the error influence can be assessed as critical. This is particularly the case if the inspection characteristic depends on more than one reference element, so that a single reference element should only account for a correspondingly small proportion of the tolerance range.

[0055] In summary, if the quantification value spectrum exceeds a permissible portion of the tolerance range of the inspection characteristic, the defect criterion can be met. Consequently, the corresponding reference element can then be classified as critical.

[0056] According to one aspect of the method and the computer device according to the invention, it is determined whether the error influence meets an error-free criterion (or non-critical criterion), and if this is the case: Classify the reference element as a non-critical reference element.

[0057] In a similar way to the approach described above for critical reference elements, all of the measures mentioned above can be taken to inform the operator of the corresponding classification. In general, this variant offers the advantage of informing the operator which reference elements can be ruled out as error causes and / or do not need to be optimized or measured differently.

[0058] In this context, it can further be provided that at least one measurement parameter, on the basis of which a measurement result of the reference element assessed as non-critical can be determined and which is preferably defined in the test plan, is changed to achieve a higher measurement speed and / or a lower measurement accuracy if the error-free criterion is met.

[0059] In other words, the effort required to measure the reference element considered non-critical can be reduced and, in particular, the measurement speed can be increased, which generally results in less accurate measurements. This can reduce the time required to implement the test plan. The lower measurement accuracy may be acceptable given the non-critical reference element's classification and the achievable time savings.

[0060] The measurement parameter can be adjusted automatically (i.e., user-autonomously), for example, based on predefined rules and / or an adjustment algorithm. The operator can thus be relieved of the burden of determining the appropriate adjustment themselves. Instead, this can be automatically stored in the test plan and / or suggested to the operator for final approval. Relationships between measurement parameters and measurement speed are well known and can be stored, for example, in the aforementioned algorithm. However, it can also be provided that the operator makes the appropriate adjustment themselves by manual input.

[0061] It can also be specified that a measurement parameter, on the basis of which a measurement result of the reference element assessed as critical can be determined, is changed to achieve higher measurement accuracy if the error criterion is met. This can also be done automatically or user-controlled. Relationships between measurement parameter settings and the resulting achievable measurement accuracies are well known. For example, higher measurement accuracy typically requires lower measurement speeds. However, the resulting increase in the time required to execute the test plan can be acceptable if it improves the quantification of the test feature.

[0062] The invention further relates to a computer device for validating a test plan for object measurement with a coordinate measuring machine, wherein the test plan contains at least one test feature to be quantified as part of the object measurement, wherein the quantification of the test feature is to be carried out based on a measurement result of at least one reference element of the object; wherein the computer device is configured to perform the following measures: obtaining (and / or determining) at least one accuracy variable of the measurement result of the reference element; determining an error influence of the reference element on the quantification of the test feature based on the accuracy variable.

[0063] The computer device may comprise at least one processor device (e.g., a microprocessor) for executing program instructions. The program instructions may be stored on a (digital) storage device of the computer device. By executing and / or executing the program instructions, all of the measures described herein may be implemented.

[0064] To obtain the accuracy value, the computer device can be configured to carry out any variant mentioned herein for determining this accuracy value or to read out an accuracy value determined in another way, for example from a storage device and / or a database.

[0065] In order to determine the influence of the error, the computer device can be configured to carry out any of the determination and, in particular, calculation measures described herein.

[0066] In order to carry out the above, but also any other measure, the computer device may comprise suitable program instructions, algorithms and / or software components which are executable, for example, by means of a processor device of the computer device.

[0067] The computer device may include any further development and any further feature to provide or execute all of the above or below steps, operating states, and functions. In particular, the arrangement may be configured to execute a method according to any of the above or below aspects. All of the above statements regarding and further developments of method features may also be provided for or apply to the identical features of the computer device.

[0068] An embodiment of the invention is explained below with reference to the accompanying schematic figures. Features that are identical in type and / or function may be provided with the same reference numerals across the figures. Fig. 1 shows an example of a coordinate measuring machine with a computer device according to an embodiment of the invention, wherein the computer device executes a method according to the invention. Fig. 2 shows a schematically illustrated test plan including dependencies between test feature and reference element for explaining the method according to the invention; Figure 3 shows a general flow chart of a method according to the invention; Figs. 4A-C show a possibility for determining an error influence according to a variant of the method according to the invention; and Figs. 5A-B show a further example of an error influence according to a further variant of the method according to the invention.

[0069] In Figure 1A coordinate measuring machine (CMM) 60 is shown, which is designed purely as an example as a tactile CMM 60 with a gantry design. An optical CMM or a different setup or kinematic structure could also be used. Alternatively, a CMM could be used that uses invasive electromagnetic radiation to scan workpieces, similar to a computer tomography scanner. The CMM 60 generally serves to execute an inspection plan for a measurement object 24 or to measure the object 24 according to this inspection plan.

[0070] In a manner known in principle, the CMM 60 is designed as a gantry and comprises a measuring table 1, over which columns 2, 3 are movable, which, together with a crossbeam 4, form a gantry of the CMM 60. The crossbeam 4 is connected at its opposite ends to columns 2 and 3, respectively, which are mounted on the measuring table 1 for longitudinal displacement.

[0071] The cross member 4 is combined with a cross slide 7, which is movable along the cross member 4 (in the X direction) on air bearings. The current position of the cross slide 7 relative to the cross member 4 can be determined using a scale graduation 6. A vertically movable spindle 8 is mounted on the cross slide 7 and is connected at its lower end to a measuring sensor 5 via a mounting device 10. A tactile scanning probe 9 is removably mounted on the measuring sensor 5. Instead of the probe 9, the measuring sensor 5 could also comprise a non-contact scanning sensor, in particular a laser sensor.

[0072] An additional rotatable measuring table 13 is arranged on the measuring table 1. A measuring object 24 to be measured according to a test plan is arranged on the measuring table 13. The measuring object 24 can be rotated about a vertical axis of rotation by rotating the measuring table 13. Furthermore, a magazine 14 is arranged on the measuring table 1, in which various probe heads can be arranged, which can be exchanged for the probe head 9, or in which various styli can be arranged, which can be exchanged for the stylus carried by the probe head 9.

[0073] Furthermore, Fig. 1schematically shows a computer device 12 according to an embodiment of the invention, wherein the computer device 12 is designed as a control device of the CMM 60. The computer device 12 has a processor device (not separately shown), software or program instructions, and at least one data memory 15. The computer device 12 is connected via signal and control lines to controllable components of the CMM 60, in particular to drives. Furthermore, the computer device 12 is connected via a measurement data connection to those elements of the CMM 60 that are used to determine measured values ​​obtained on the basis of the test plan. Since such elements and devices are generally known in the field of CMM 60, they will not be discussed in detail here.

[0074] The computer device 12 receives and / or generates a test plan for an object 24 to be measured according to this test plan. In the illustrated case, the computer device 12 also validates the test plan using a method according to the invention. It is also possible for the computer device 12 to be provided separately from the CMM 60, e.g., as a conventional PC in an office. The CMM 60 would then have a conventional control device that executes the test plan validated by the separate computer device 12.

[0075] In Fig. 2 Test characteristics 12 and reference elements (measurement elements) 14 of a test plan are shown. The representation can also be called a dependency tree and in this form can be Fig. 1 not shown display device of the computer device 12.

[0076] The inspection features 12 and reference elements 14 are each provided with symbols and identifying reference signs, which can also be displayed. Furthermore, percentage values ​​are shown for some of the reference elements 14, which can in turn be displayed to an operator and indicate, in the manner explained below, a portion of a tolerance range of an inspection feature claimed by a reference element.

[0077] All measuring elements from Fig. 2 are referred to as reference elements, since at least one of the test features 12 and, more precisely, its quantification depends at least indirectly on each of the reference elements 14.

[0078] Shown as reference elements 14 are planes EA, EB, EC, cylinders C1, C2, and plane intersection points EP1, EP2. Also shown is a reference coordinate system K, which is not a geometric feature or measuring element of the object to be measured.

[0079] The dependencies from Figure 2 are explained below from bottom to top. First, the spatial position (i.e., position and orientation) of two planes EA, EB of the object that are at an angle to each other is determined. This position forms the measurement result determined for these reference elements 14.

[0080] For this purpose, a plurality of measuring points on the object surface in the area of ​​these planes EA, EB are recorded and the spatial coordinates are thus determined for each of the planes EA, EB. Furthermore, a cylinder C1 (i.e. a cylindrical area of ​​the object) is recorded, for which purpose a plurality of surface points of the cylinder C1 are also probed. The cylinder C1 is oriented relative to the planes EA, EB in such a way that the orientation of a reference coordinate system K can be determined therefrom. Options for generating corresponding reference coordinate systems K by probing selected measuring elements are familiar to the person skilled in the art and are therefore not explained in more detail here. The reference coordinate system K serves as a reference for quantifying the test features 12, for example when distances in predetermined directions or along predetermined axes are to be determined.

[0081] After determining the orientation of the reference coordinate system K, further reference elements 14 in the form of two cylinders C2, C3 and a plane EC are then probed or measured. The spatial positions of these reference elements 14 are again determined as the respective measurement results.

[0082] Based on this, the spatial coordinates of the intersection points EP1, EP2 of the plane EC with the cylinders C2, C3 are determined as a purely mathematically determined measuring element or reference element 14, as well as as a further measurement result. This is done using known geometric calculations based on the determined positions and the coordinates of the plane EC and the cylinders C2, C3.

[0083] Two distances are then checked and quantified as inspection characteristics 12. For example only, these are a distance EP1-EP2 between the two intersection points EP1, EP2 and a distance from one of the intersection points EP2 to an origin of the reference coordinate system K. The designation (Y) in Figure 2 specifies that the distances along the Y-axis of the reference coordinate system K (i.e. in the Y-direction) are to be determined.

[0084] Using the lines in Figure 2Dependencies between the reference elements 14 and, in particular, the inspection characteristics 12 are marked. It can be seen that the inspection characteristic 12, concerning the distance from one of the intersection points EP2 to an origin of the reference coordinate system K, depends directly and immediately on the determined position (i.e., the computationally determined measurement result) of the intersection point EP12. This, in turn, depends on, or is defined by, the cylinders C2, C3, and the plane EC. Thus, the corresponding inspection characteristic 12, or its quantification, is at least indirectly also dependent on the cylinders C2, C3, and the plane EC.

[0085] Since the corresponding test characteristic 12 is intended to determine the distance with respect to the reference coordinate system K, there is also an at least indirect dependence on the initially measured planes EA, EB and the cylinder C1.

[0086] In the same way, the further test characteristic 12 concerning the distance between the individual plane intersection points EP1, EP2 is dependent on all other reference elements 14.

[0087] The measurement results (i.e. the determined coordinate values ​​and / or spatial positions) of the reference elements 14 thus influence the values ​​that are ultimately determined for the test characteristics 12.

[0088] The invention provides for determining these (error) influences and preferably also displaying them directly to an operator. The influences are quantified, and reference elements 14 are classified as critical if predetermined error criteria are met.

[0089] In the example shown, percentages are entered for selected reference elements 14, and in particular for the inspection feature 12 that the distance measurements to the coordinate origin relate to. These percentages indicate the error influences of the reference elements 14 on the quantification of the corresponding inspection feature 12. These are the previously mentioned proportions of an utilized tolerance range of the inspection feature 12.

[0090] For cylinder C1, which has a percentage of 60%, it is also visually highlighted that it is a critical reference element 14. This is the case because the error criterion is defined as exceeding a maximum permissible portion of the tolerance range of (only as an example) 20%.

[0091] The operator can thus identify which reference element 14 has the greatest and, in particular, a critical error influence on the quantification of a test feature 12 to be inspected. The measurement of critical reference elements 14 can then be specifically adjusted to improve the achievable accuracy, for example, by reducing the measuring speed or increasing the number of contact points. For this purpose, suitable adjustments to the corresponding measurement parameters can be automatically determined and suggested to the operator. Optionally, these adjustments can also be implemented automatically. Another adjustment could be to select other reference elements 14 or to replace critical reference elements 14 with other reference elements 14 to be measured.

[0092] In Figure 3The procedure described above is shown using a flow chart that generally represents a process sequence according to the invention.

[0093] In a step S1, data on the object to be measured is obtained, for example as a CAD data set.

[0094] In a step S2, the inspection features 12 to be checked are defined, for example, by an operator. In a conventional manner, it can then be determined (preferably at least partially automatically and / or through further user input) which reference elements 14 are to be measured to determine the inspection features 12. This also defines the dependencies between the reference elements 14 and the inspection features 12 or can be determined therefrom.

[0095] In a step S3, accuracy values ​​are obtained for the reference elements 14. For example, these accuracy values ​​can be read from a database or obtained from another computer device. Individual accuracy values ​​can also be determined for at least some of the reference elements 14, for example, if they are determined in the manner explained above using fitting or compensation calculations.

[0096] However, it may be provided that, for example, if the accuracy quantity is an inherent measurement uncertainty of the CMM 60, the same accuracy quantity is considered for at least some of the reference elements 14.

[0097] In a step S4, for each test characteristic 12, the error influences of those reference elements 14 on which this test characteristic 12 is at least indirectly dependent are determined. This can be done, for example, in the following using the example of Figures 4A-4Cexplained manner and by reference to the accuracy value.

[0098] In a step S5, the error influences are then used to determine whether reference elements 14 are to be classified as critical. If this is the case, this can be communicated to an operator in Figure 2 displayed and adjustments can be suggested or implemented automatically if necessary.

[0099] In the Figures 4A-4C An example for determining the error influence of a reference element 14 on a test feature 12 is shown. The test feature 12 is determined as a distance D between a circle center M of a circular reference element 14 and a straight line 15 in the vertical direction shown. Only the error influence of the straight line 15 is considered as an example. However, the error influence of the circular reference element 14 can be determined in an analogous manner.

[0100] For line 15, an inherent measurement uncertainty of the coordinate measuring machine 60 used is considered an accuracy parameter. This measurement uncertainty is plotted as a tolerance range around line 15. This is intended to express that a position of line 15 can also be obtained as a measurement result at any position within this tolerance range. The tolerance range thus represents a possible value spectrum of the measurement result of line 15. This measurement result is determined in a conventional manner by recording the coordinates of two points PG1, PG2 on line 15.

[0101] Tolerance ranges 13 are also entered for the distance D and the center point M of the circular reference element 14. The tolerance range 13 of the center point M is also determined from a corresponding accuracy variable, but is not further considered in the following abbreviated representation. The tolerance range 13 of the distance D (the lower tolerance range 13 in Figure 4A ) is determined as explained below and forms (at least partially) a possible range of values ​​for quantifying the inspection characteristic "distance." This range of values ​​can also be influenced by the upper tolerance range 13 of the center point M, but for the sake of simplicity, this will not be considered in detail.

[0102] To determine the tolerance range 13 of the distance D, extreme situations are considered that can lead to the greatest possible value variations of this distance D. More specifically, extreme values ​​or extreme courses of the straight line 15 are considered according to an upper and lower limit of the possible value spectrum of this reference element 14 or its position determined as a measurement result. The term "extreme" refers to the impact on the quantification of the inspection characteristic under consideration, namely that it assumes either a maximum or minimum value.

[0103] In Figure 4BAn extreme situation or a first limit of the measured position of the straight line 15 is shown, which leads to a greatest possible reducing influence on the distance D. This occurs with a dashed line along the straight line 15. Such a course can occur, for example, if the measured coordinates of the first point PG1 of the straight line 15 are influenced by the maximum measurement uncertainty in a first (e.g., negative) way or with such a sign, and the measured coordinates of the second point PG2 are influenced by the measurement uncertainty in the opposite way.

[0104] In Figure 4CThe reverse case is shown, where points PG1 and PG2 are each influenced in the opposite way (e.g., PG1 maximally positive and PG2 maximally negative). This results in the greatest possible distance D, i.e., the greatest possible (or maximizing) error influence of the measured position of straight line 15 on the distance D determined as test characteristic 12.

[0105] In summary, the error influence of this reference element 14 on the quantification of the test characteristic is determined based on an accuracy parameter relating to the accuracy with which a position of the straight line 15 can be determined as a measurement result. This error influence can, for example, be defined as the bandwidth of the value spectrum or the tolerance range 13 of the distance D and / or be quantified based thereon. The error influence can then be compared with an error criterion, whereby the error criterion can, for example, specify a maximum permissible extent of the corresponding value spectrum or tolerance range 13. In this way, it can be determined whether the error influence of the straight line 15, and in particular its measurement or the possible measurement value spectrum, can be classified as critical or not.

[0106] In the Figures 5A-BAnother example of error influence determination is shown, namely for determining the distance between two circles 100. A coordinate system is defined by two planes E1, E2, each of which forms reference elements 14. The position of planes can be determined in a conventional manner, for example, by probing three points in this plane.

[0107] The planes E1 and E2 are perpendicular to the page plane and ideally perpendicular to each other. They define the orientation of an XY coordinate system, whose axes are ideally perpendicular to each other. The XY axes run parallel to a respective plane E1 and E2.

[0108] In Fig. 5A A direct distance D1 between the circles 100 is determined as test characteristic 12. The reference elements 14 have no influence on this.

[0109] In Fig. 5BFor a test characteristic 12, the distance D2 in Y is calculated. The plane E1 has a significant influence on this, as it largely determines the orientation of the Y alignment or Y coordinate axis. Analogous to the previous example, it can then be determined how an expected, tolerance-dependent variation in the plane E1 affects the expected value spectrum of this distance D2.

Claims

1. Computer-implemented method for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature is intended to be implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the method comprises: - obtaining at least one accuracy variable which specifies an accuracy of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error-free criterion, and should this be the case: - classifying the reference element (14) as a noncritical reference element (14), wherein at least one measurement parameter on the basis of which a measurement result of the reference element (14) assessed as noncritical is ascertainable is altered for the purposes of obtaining a faster measurement speed if the error-free criterion is satisfied.

2. Computer-implemented method for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature is intended to be implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the method comprises: - obtaining at least one accuracy variable which specifies an accuracy of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error criterion, and should this be the case: - classifying the reference element (14) as a critical reference element (14), wherein at least one measurement parameter on the basis of which a measurement result of the reference element (14) assessed as critical is ascertainable is altered for the purposes of obtaining a faster measurement speed.

3. Computer-implemented method for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature is intended to be implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the method comprises: - obtaining at least one accuracy variable which specifies an accuracy of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error criterion, and should this be the case: - classifying the reference element (14) as a critical reference element (14), wherein countermeasures which comprise an adaptation of the measurement of the at least one reference element (14), so that the measurement accuracy is increased, or a new definition of the test feature (12) and / or a new selection of the at least one measured reference element (14) are ascertained and / or proposed and / or implemented if the error criterion is satisfied.

4. Method according to any one of the preceding claims, wherein the measurement result of the reference element (14) should be ascertained on the basis of the measurement result of at least one further reference element (14) and an error effect on the achievable accuracy of the quantification is also ascertained for this further reference element.

5. Method according to any one of the preceding claims, wherein the reference element (14) is a geometric element of the object.

6. Method according to any one of the preceding claims, wherein the measurement result of the reference element (14) is ascertained on the basis of at least one coordinate value of said reference element (14); and in particular wherein the coordinate value is ascertained on the basis of a real or simulated object measurement.

7. Method according to any one of the preceding claims, wherein the measurement result of the reference element (14) specifies at least one spatial degree of freedom and / or at least one dimension of the reference element (14) .

8. Method according to any one of the preceding claims, wherein the accuracy variable is ascertained on the basis of at least one of the following: - a statistical characteristic of a distribution of coordinate values which were determined to ascertain the measurement result of the reference element (14) ; - a deviation of at least one coordinate value from a measurement result, which was calculated from a multiplicity of coordinate values, for the reference element (14); - an adjustment method which is carried out to calculate the measurement result from a multiplicity of coordinate values; - a shape deviation of the reference element (14); - an inherent measurement uncertainty of the coordinate measuring machine (60).

9. Method according to any one of the preceding claims, wherein the error effect of the reference element (14) is determined on the basis of a possible value spectrum of the measurement result of said reference element (14), the value spectrum being determined on the basis of the accuracy variable.

10. Method according to Claim 9, wherein, on the basis of the value spectrum of the reference element (14), a possible quantification value spectrum of the test feature (12) is ascertained and compared with an admissible tolerance range of the test feature (12).

11. Method according to either of Claims 2 and 10 or 3 and 10, wherein the error criterion is satisfied if the quantification value spectrum exceeds an admissible portion of the tolerance range of the test feature (12).

12. Method according to Claim 3 or a claim referred back to it, wherein countermeasures are automatically ascertained and / or proposed and / or implemented.

13. Computer device (12) for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature (12) is implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the computer device (12) is configured to carry out the following measures: - obtaining at least one accuracy variable of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error-free criterion, and should this be the case: - classifying the reference element (14) as a noncritical reference element (14), wherein at least one measurement parameter on the basis of which a measurement result of the reference element (14) assessed as noncritical is ascertainable is altered for the purposes of obtaining a faster measurement speed if the error-free criterion is satisfied.

14. Computer device (12) for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature (12) is implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the computer device (12) is configured to carry out the following measures: - obtaining at least one accuracy variable of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error criterion, and should this be the case: classifying the reference element (14) as a critical reference element (14), wherein at least one measurement parameter on the basis of which a measurement result of the reference element (14) assessed as critical is ascertainable is altered for the purposes of obtaining a faster measurement speed.

15. Computer device (12) for validating a test plan for an object measurement using a coordinate measuring machine (60) for preparing an implementation or execution of the test plan that is only carried out thereafter, wherein the test plan contains at least one test feature (12) to be quantified within the scope of the object measurement, wherein the quantification of the test feature (12) is implemented on the basis of a measurement result of at least one reference element (14) of the object; wherein the computer device (12) is configured to carry out the following measures: - obtaining at least one accuracy variable of the measurement result of the reference element (14); - ascertaining an error effect of the reference element (14) on the quantification of the test feature (12) on the basis of the accuracy variable; - ascertaining whether the error effect meets an error criterion, and should this be the case: classifying the reference element (14) as a critical reference element (14), wherein countermeasures which comprise an adaptation of the measurement of the at least one reference element (14), so that the measurement accuracy is increased, or a new definition of the test feature (12) and / or a new selection of the at least one measured reference element (14) are ascertained and / or proposed and / or implemented if the error criterion is satisfied.