WO2011110568A1

WO2011110568A1 - Method for validating a measurement result from a coordinate measuring machine

Info

Publication number: WO2011110568A1
Application number: PCT/EP2011/053482
Authority: WO
Inventors: Ulrich Staaden
Original assignee: Carl Zeiss Industrielle Messtechnik Gmbh
Priority date: 2010-03-11
Filing date: 2011-03-08
Publication date: 2011-09-15
Also published as: DE102010011841B4; DE102010011841A1

Abstract

The present invention relates to a method for validating a measurement result (87) from a coordinate measuring machine (10), which measurement result has a plurality of measurement points (62, 64). In this case, provision is made for determining a validation limit (78) relative to a known desired geometry (66) of a workpiece (14) to be measured and for determining invalid measurement points (64) and valid measurement points (62) using a respective property of the measurement points (62, 64) relative to the validation limit (78). The present invention also relates to a coordinate measuring machine and to a computer program.

Description

Method for validating a measurement result of a coordinate measuring machine

The present invention relates to a method for validating a multiple measurement points having measurement result of a coordinate measuring machine.

Such a method is known for example from the document DE 199 00 737 AI.

Coordinate measuring machines are used today in many areas of industrial technology to measure workpieces. Fields of application arise, for example, in the field of quality control or in the field of reverse engineering, which involves detecting the dimensions of a known workpiece as precisely as possible, in order then to draw conclusions about the manufacturing process and to reconstruct the workpiece as identical as possible. Coordinate measuring machines have a sensor which is movable as a rule. Alternatively, coordinate measuring machines are available in which the sensor is fixed and the workpiece is moved past the sensor. These are then usually used to check a certain type of workpieces in large quantities.

Usually, the sensor is pivotally mounted on a rotary / swivel element about all three spatial axes, wherein the rotary / swivel element itself can be moved in turn in a measuring range, so that by means of the sensor, the workpiece at all points can be detected in any spatial direction.

In the case of the sensor may be an optical sensor, but in the present case, in particular tactile sensors are considered, which touch the workpiece by means of a mounted in a probe stylus and from the position of the rotary / pivot member and the deflection of the stylus in the probe to the probing position.

When checking workpieces as part of a quality control, it is often required to scan a surface as quickly as possible. For example, the surface may be a plane of the workpiece surface that is to be checked to see if it is actually planar, or it may be, for example, a cylindrical surface created by a bore and then checked for actual the required diameter is present.

With respect to the types of measurement is usually between a single point measurement, in which successively several points are touched on the workpiece and the data thus acquired are stored sequentially, and distinguished so-called scanning method in which the stylus in contact with the workpiece a workpiece surface is driven along and in certain time intervals the measuring points are detected. By means of such scanning methods, a high number of measuring points can be detected within a very short time.

If the surface to be scanned has elevations or depressions, for example grooves, the stylus of a probe enters the depression during a scanning process or "jumps" over the elevations. Also during these processes, measuring points are detected, which then have to be filtered out of the measurement result to be evaluated, since they do not characterize the actual surface to be scanned and thus falsify the measurement result.

In particular, overshoots and undershoots are critical, which occur during a scanning process at the beginning and at the end of a survey or a depression.

In order to improve the evaluation of the measurement results, various methods are therefore proposed in the prior art, with which the actually detected measurement result can be validated.

For example, DE 199 00 737 A1 already mentioned suggests that outlier measurement values are determined from the set of measured values that are then identified as invalid measured values. The evaluation should then only be based on the valid measured values. In particular, this should be done for example by means of a high-pass or low-pass filtering, wherein a defined threshold deviation compared to a reference value or replacement element is considered.

The determination of the replacement elements, which generally have geometrically ideal shapes, for example, in Chapter 6 of the textbook Weckenmann, Gawande, "Coordinate Metrology", Carl Hansa Verlag, Munich, 1999, ISBN 3-446-17991-7 described.

There it is proposed to fit a selected geometric element, for example a circle, by means of a predetermined pass condition, for example as a minimum circle, as an enveloping circle or as a circle in the amount of all measuring points. Measuring points that differ by a certain amount from the equivalent element thus approximated should be sorted out as invalid measuring points.

However, such methods have a disadvantage in practice, since it is not known before the start of the evaluation where and how the replacement element will run. For example, when a family of measurement points acquired during a scanning process on a flat surface is to be approximated by a straight line, it may happen that the straight line does not run parallel to the expected course of the scanned plane, but rather approximates it obliquely becomes. Ultimately, this has to do with the above-described overshoots and undershoots and the measured values recorded in this context, which result in the minimum condition then being fulfilled for an inclined plane, for example.

The approximation with an absolute minimum straight line, for example by means of an L1 approximation, can not lead to the desired result, for example, in the case of several grooves crossing the path of a scanning process. Although the use of an absolute minimum line leads to obtain a straight line with the actual orientation by the approximation, the approximation by means of an absolute minimum line ignores largely deviations from the ideal or actual geometry. If there are more measuring points on the scanned workpiece surface than measuring points in the groove, then the approximated straight line runs on the surface to be scanned. If, however, the other way round is exactly the same, ie more measuring points were recorded in a groove than on the surface to be scanned, the approximated straight line runs in the groove. A priori is therefore not known where the replacement element will be, so that a determination of outliers is not possible. Furthermore, since it is not possible to make a preliminary statement as to which type of approximation is best for a specific measurement result, validation by means of an outlier analysis generally fails completely relative to an approximated replacement element.

Various proposals have been made in the prior art which can be carried out in addition to the determination of valid measured values. For example, the document DE 197 35 975 A1 proposes to smooth the measured values by means of a spline function in order to arrive at a better usable measurement result.

For example, US 5,724,745 suggests, in addition to the coordinates of the measuring points, to use variables such as the deflection of the probe or the speed of movement of the probe at the time of detection of the corresponding measuring point in order to subject the measurement results to additional filtering.

Finally, the publication WO 2008/074989 proposes to skip existing grooves in a surface to be scanned by means of appropriate control specifications. This means that the stylus lifts before the start of a groove from the surface to be scanned and restarts on the surface when the groove and the stylus were passed to each other over. At the same time it is proposed to switch a signal that causes detected during the lifting of the stylus measuring points are marked from the outset as invalid. However, this procedure assumes that the position of the grooves in the surface to be scanned is known in advance.

Starting from this prior art, therefore, an object of the present invention, an improved method for validating a plurality Specify measuring points having measuring results of a coordinate measuring machine, which provides a validated measurement result in particular in existing in the geometry to be measured depressions and / or surveys without the position of these depressions or surveys must be known in advance.

According to a first aspect of the invention, it is therefore proposed to further develop the method mentioned at the outset, such that the steps of determining a validation boundary relative to a known desired geometry of a workpiece to be measured, and determining invalid and valid measurement points based on a respective property of the measurement points relative to the validation boundary.

According to the invention is thus not intended to first approximate a replacement element and then to determine from this valid and invalid measurement points, but it is a known setpoint geometry assumed, for example, a hole along a certain axis with a certain diameter, and relative to this Target geometry determines a dependent of the measurement result validation limit. The validation limit is therefore not necessarily a certain threshold, which is applied to a still to be determined geometry, but just the opposite, the geometry is required and the position of the validation limit to this setpoint geometry is determined or approximated.

This not only allows greater flexibility in the manner of validating the measurement results, but also prevents validation of the measurement result from being rendered unusable due to completely incorrect approximations of the reference element, ie the replacement element. Furthermore, the flexible setting of the validation limits relative to a known desired geometry also makes it possible to reliably filter measurements deviations or elevations without knowledge of the position of the depressions or elevations. As described in detail below, can the validation limits to be determined are set appropriately during the course of the procedure.

According to a second aspect of the invention, a coordinate measuring device with a sensor for measuring a workpiece and an evaluation device is proposed, which is characterized in that the evaluation device validates a measurement result of the sensor by means of a method according to the first aspect of the invention.

According to a third aspect of the invention there is provided a computer program comprising program code means adapted to perform all the steps of a method according to the first aspect of the invention when the computer program is executed on a computer.

The coordinate measuring machine according to the second aspect of the invention and the computer program according to the third aspect of the invention therefore have the same advantages as the method according to the first aspect of the invention.

The object initially posed is thus completely solved.

In a preferred embodiment of the method according to the first aspect of the invention, it is provided that the validation limit is determined by determining an extreme point outside or inside the target geometry whose distance in normal directions is farthest from the desired geometry, and this distance is reduced by a predetermined distance to a validation boundary distance so that the validation boundary distance validation boundary extends in parallel to the desired geometry.

[0030] Whether the extreme point lies within or outside the desired geometry depends on whether elevations or depressions in or on the workpiece be expected. For depressions, an extreme value point lying within the setpoint geometry is determined, and in the case of elevations, an extreme point point lying outside the setpoint geometry is determined. Of course, it can also be provided that first a validation boundary within the desired geometry, ie for depressions, is determined and then a validation limit outside the desired geometry for surveys is determined.

In this way, first of all a validation limit is defined which extends through the measuring point furthest from the desired geometry parallel to the desired geometry. This distance of the validation boundary from the desired geometry is then reduced by a predetermined distance. The measure of the predetermined distance then influences how many measurement points are determined to be invalid, ie how rigorously the validation is performed. It has been proven to set the predetermined distance relative to a true immersion depth (t ₀ ). The true immersion depth corresponds to the distance by which a stylus can dip into the desired geometry to the maximum extent. As a rule, the true immersion depth corresponds to the greatest depth of a groove present in the desired geometry. The same is true for surveys. The predetermined distance can thus be set, for example, to half the true immersion depth.

According to a development it can be provided that a final validation limit is determined by an average of the distances of all measuring points is formed whose distance in the normal direction to the desired geometry is greater than the validation limit distance, and that the mean by a predetermined distance to a final validation boundary distance is reduced such that the final validation limit in the validation boundary distance extends parallel to the target geometry.

By means of this further step, an improved validation can be provided, since this is suitable for marking even more measuring points as invalid. Having first as described above, starting from the If the desired geometry and an extreme value point a first validation limit has been determined, then all measuring points are determined whose distance in the normal direction to the desired geometry is greater than the validation limit distance. In other words, all measurement points that are farther from the target geometry than the validation limit are identified. From the distances of these measurement points, the mean value is formed, which is correspondingly closer to the desired geometry than the extreme value point, which was initially used to determine the validation boundary distance. If this mean value by the predetermined distance, for example, t is _0/2 is reduced, so that the final validation boundaries distance is closer to the desired geometry as the validation limits removal or the original or first validation distance limits. Accordingly, more measurement points are flagged as invalid and the validation leads to a better result.

According to yet another embodiment of the method according to the first aspect of the invention can be provided that the validation limit is determined by the measured values are approximated with a replacement element, the geometric shape of which corresponds to the desired geometry, and the replacement element forms the validation boundary, where before determining the validation limit, it is determined that a normal direction of the replacement element corresponds to a normal direction of the target geometry.

In this development, it is thus provided that the validation limit is determined by means of one of the known approximation methods. This procedure differs from methods known from the prior art, according to which a reference element, ie the element relative to which the validation limit is determined, for example, by means of a specific distance, is determined by approximation. This element, referred to herein as desired geometry, is known and defined from the outset according to the present method. If, for example, a surface is present which is penetrated by grooves, a set of measuring points is obtained in which a plurality of measuring points lie on the surface to be measured and a plurality of measuring points lie within the grooves. If one now approximates the family of measuring points with, for example, a minimum straight line, ie a straight line which has a minimum distance from the measuring points, one obtains a straight line which runs somewhere between the bottom of the grooves and the surface to be measured. This line can then be used as a validation limit. By defining the normal direction as a further boundary condition, it is avoided that the replacement element has a different orientation than the surface to be measured.

The replacement element may thus be, for example, a minimum element or an absolute minimum element.

In addition, it can of course also be determined in this procedure that a final validation limit is determined by the validation limit determined by the replacement element is reduced by a predetermined distance to the final validation limit, as already described above.

In the above-mentioned embodiments can be provided that the respective property of the measuring points is a position relative to the validation limit, and that a measurement point is determined to be invalid when the validation boundary between the measuring point and the desired geometry is.

The validation limit in this case then forms a limit up to which measurement points are considered valid. Measurement points that deviate from the target geometry further than the validation limit are considered to be invalid. In yet a further development, it can be provided that intersections of a measurement curve connecting the measurement points with the validation boundary are determined, and that measurement points in regions defined relative to the intersection points are determined to be invalid measurement points.

If one connects the measuring points in chronological order, ie successively according to their recording time, one obtains a curve which roughly describes the movement of a scanning element which touches the surface to be measured, for example a probe ball. The intersections of this curve with the validation limit can be determined. Since a probe ball always moves into a depression, for example a groove, and moves out of it again or moves up to and from an elevation, the points of intersection roughly mark the beginning and the end of an elevation or depression. Since, due to oscillatory movements, the measuring points just before and shortly after these elevations and depressions can not regularly be used for validation, it can be defined, for example, that all measuring points located 5 mm before or after an intersection are determined to be invalid. The direction of the specific distance is usually parallel to the desired geometry. The defined ranges are thus determined only on the basis of the previously determined validation limit and the measurement curve. The target geometry has no direct influence on the position of the defined areas. Rather, an actual geometry represented by the measurement curve of the workpiece to be measured has a direct influence on the position of the defined areas. The defined areas are determined depending on an actual geometry of the workpiece to be measured. Thus, the defined areas are determined, wherein a location of obstacles, especially elevations or depressions, may be previously unknown. In particular, no obstacles, in particular elevations or depressions, are defined in the desired geometry. The desired geometry can only be formed from a basic geometric shape, such as a circle, an ellipse or a cylinder, in particular a cylinder with a circular base. Accordingly, it can be provided that the defined regions are defined with a distance value before and / or behind a respective intersection.

As areas thus arise, for example, strips of a certain width, which extend normal to the desired geometry. In this way, measurement results in certain areas can be excluded entirely from the validation. It is particularly advantageous that a location of elevations and / or depressions does not have to be known in advance in order to define the areas. The position of the depressions and / or elevations is rather determined by determining the intersection of the trace with the validation boundary.

In this way, all measuring points that were recorded in a groove can be determined. Either areas in front of and / or behind the intersection points can be defined correspondingly large such that they overlap, or it can be provided, for example, that a region between two intersection points is completely accommodated. From the knowledge of the order in which the measuring points were recorded, a "first" point of intersection and a "second" or later point of intersection can be determined and the area between the points of intersection, which actually represents the groove, can be reliably excluded. Otherwise, under certain circumstances, with a circular desired geometry and only two points of intersection, it would not be absolutely clear which region forms the groove and which region has the actual desired measurement results.

In a further embodiment of the method according to the first aspect of the invention, it may be provided that the validation boundary is determined by defining a cone limit angle, and the respective property of the measurement points is the direction of a probing force of a tactile sensor detecting the measurement points, and that the measuring points where the detection of the direction of the probing force is outside the cone limit angle are determined as invalid measuring points. The direction of the probing force during a scanning operation is determined by vector addition of the normal direction probing force and the sliding frictional force acting on the surface between the workpiece and the probe element. In practice it has been found that a cone limit angle of about 11 °, ie the angle between the conical surface and the normal is about 11 °, is suitable for providing a sufficiently good validation result. In principle, however, the cone angle can also be made smaller in order to exclude more measuring points or be chosen larger in order to exclude fewer measuring points. The cone boundary angle can thus be in a range between 0 ° and 45 °, in particular between 5 ° and 30 °.

It is understood that the abovementioned possibilities for determining the validation limit can be applied not only alternatively but also cumulatively. In this case, the individual developments can be carried out simultaneously or in succession. For example, it may be provided to first determine a validation limit by means of an extreme value point, so that one obtains a validation limit which extends in the validation boundary distance parallel to the desired geometry and a first number of measurement points can be excluded by means of this validation limit. Subsequently, it can then be provided, for example, to mark further measurement points as invalid by means of a cone limit angle and a determination of the direction of the probing forces in the measurement points. Accordingly, other combination options are given. Furthermore, the method is applicable to all geometries and any free-form surfaces. The geometries can be arbitrary two-dimensional geometric elements or arbitrary three-dimensional geometric bodies. Of course, the desired geometry or nominal free-form surface must be known, but a position of recesses (grooves) or elevations on the desired geometries or predetermined free-form surfaces need not be known.

It is therefore understood that the features mentioned above and those yet to be explained not only in each case Combination, but also be used alone, without departing from the scope of the present invention.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

1 shows an embodiment of a coordinate measuring machine according to a second aspect of the invention,

2 is a detail view of a probe in an embodiment of the coordinate measuring machine in Fig. 1,

3 shows an embodiment of a method according to a first aspect of the invention,

4 shows a further embodiment of a method according to the first

Aspect of the invention,

Fig. 5 is another illustration for explaining the method in Fig. 4, and

Fig. 6 shows yet another embodiment of the method according to the first aspect of the invention.

The coordinate measuring machine 10 has a measuring surface 12 on which a workpiece 14 is arranged. On the measuring surface 12, a portal 16 is movably mounted in a Y-direction. At the portal 16, a carriage 18 is movably mounted in an X direction. In turn, a quill 20 is displaceably mounted in the carriage 18 in the Z direction. At one end of the sleeve 20 is a probe 22 which receives a stylus 24 with a Tastkugel 26 in itself.

In this way, the stylus 18 can be approached in any direction to the workpiece 14 and the workpiece 14 are touched with the probe ball 26.

There are scales 28, 29, 30 are provided, along which the portal 16, the carriage 18 and the sleeve 20 are moved. By means of suitable sensors, the position of the portal 16, the carriage 18 and the quill 20 can be determined on the basis of the scales 28, 29, 30. The probe 22 has a further sensor (not shown), which can be designed active or passive measuring. By means of this sensor, a deflection of the stylus 18 relative to the probe 22 and the sleeve 20 can be determined, so that a position of the probe ball 26 is known.

The coordinate measuring machine 10 further comprises a control device 32, which may be formed, for example, as a conventional computer. In a conventional embodiment, the control device 32 then has an output device 34 and an input device 36, so that a user can read results of measurements at the output device 34 or, for example, start a sequence program for a measurement process. By means of the input device 36, for example, various modifications with regard to the speed of the measuring process, the surfaces to be touched, etc., can be made. Furthermore, an evaluation device 38 is provided, which is provided to evaluate the measurement data acquired by the coordinate measuring device 10 by means of a method described below. The evaluation device 38 is shown as part of the control device 32, but in principle the evaluation device 38 can also be provided separately.

The control device 32 is capable of automatically measuring the workpiece 14. Of course, as an alternative or cumulatively, too an operating device 40 may be provided to perform a measuring operation manually. Thus, for example, a certain measuring operation can be taught or, in the event of failure of the control device 32, the control of the coordinate measuring machine 10 can be taken over manually.

The control device 32 may, as shown, have a cable connection to the other elements of the coordinate measuring machine 10, but it may also be wirelessly connected. Of course, it can also be provided that the control device 32 is an integral part of the remaining elements, for example, in the measuring surface 14 or in the portal 16 is arranged. There, the output device 34 or the input device 36 may be arranged.

Fig. 2 shows a simplified schematic representation of the basic operation of the probe 22. The probe 22 is designed as an active probe, with which a probing force with which the probe ball 26, the workpiece 14 touches, can be controlled. The probe 22 has a fixed part 40 and a movable part 42, which are connected to each other via two leaf springs 44, 46. The leaf springs 44, 46 form a spring parallelogram, which allows movement of the part 42 in the direction of the arrow 48. Thus, the stylus 24 can be deflected by a distance 50 from its rest position. The reference numeral 24 ', the stylus 24 is shown schematically in the deflected position.

The deflection of the stylus 24 relative to the fixed part 40 may be the result of a probing of the workpiece 14. The deflection of the stylus 24 is taken into account in the determination of the spatial coordinates of the probe ball 26. In addition, the deflection of the stylus 24 can be generated at an active probe 22 using a measuring force generator. On the fixed part 40 and on the movable part 42, a leg 51, 52 is arranged in each case. The legs 51, 52 are parallel to the leaf springs 44, 46 and parallel to each other. Between the legs 51, 52, a sensor 54 (shown here with a scale 55) and a measuring force generator or measuring force generator 57 is arranged. The sensor 54 may be a plunger, a Hall sensor, a piezoresistive sensor or another sensor, with the aid of which the spatial deflection of the stylus 18 relative to the fixed part 40 can be determined. The measuring force generator 57 may be, for example, a plunger coil, by means of which the two legs 51, 52 can be pulled against each other or pushed apart. The probe 22 is correspondingly also connected to the control device 64 so that it can read on the one hand sizes such as the deflection and the probing force and on the other hand can control the measuring force generator 57.

In the simplified illustration in Fig. 2, the probe 22 allows only a deflection of the stylus 18 in the direction of the arrow 10. However, the skilled person is aware that such a probe 22 typically allows a corresponding deflection in two other orthogonal directions in space , An embodiment of such a probe 22 is described for example in the document DE 44 24 225 AI, the disclosure of which is incorporated herein by reference. However, the invention is not limited to this special probe 22 and can also be realized with other measuring or switching probes and sensor heads of other measuring systems, in particular passive probes.

It is known to those skilled in the art that a probe head 22 or sensor head of the kind shown in greatly simplified form in FIG. 2 generally has a receptacle on which the stylus 18 or another sensor is interchangeably attached.

FIG. 3 shows a diagram 60 in which the distance s is plotted on the abscissa. In the ordinate direction f deviations or positions are plotted in the normal direction. Correspondingly, measuring points 62, 64 are obtained which were recorded from left to right in the course of a measuring operation in the illustrated diagram 60. Accordingly, a set of points with the coordinates (s, f) results from the measurement points 62, 64. These measuring points 62, 64 should now be subjected to a validation, ie valid measuring points 62 should be distinguished from invalid measuring points 64.

It is based on a desired geometry 66, which corresponds to the expected position of a surface of the workpiece 14. In the present case, this is a level to be checked to see if it is flat. Accordingly, the desired geometry 66 is a straight line.

The workpiece 14 to be scanned has a groove 68, which represents a depression in the surface to be scanned. Accordingly, a probe ball 26 during scanning can not follow the expected course of the desired geometry 66, but immerse in the groove 68.

To validate the measurement points 62, 64, an extreme value point 70 is first searched. In the present case this is the lowest point 70 in the ordinate direction. For surveys, it would be the highest point 70 'in the ordinate direction f.

Starting from this extreme value point 70, a distance to the desired geometry in the normal direction 72 is determined in a normal direction 72. In the present case, the extreme value point 70 is located exactly at the bottom of the groove 68, so that its removal in the normal direction 72 corresponds to a true immersion depth 74 of a probe ball 26 into the workpiece 14. However, the distance of the extreme value point 70 to the desired geometry 66 in the normal direction 72 may also be less than the true immersion depth 74. This distance of the extreme point 70 from the desired geometry 66 is reduced by a predetermined distance 76. In the present example, it is determined that this predetermined distance 76 corresponds to half the true immersion depth 74. In this way, one obtains a validation limit distance 77, ie the distance of a validation boundary 78 from the desired geometry 66. It is defined that the validation boundary 78 extends parallel to the desired geometry 66, ie in the present case the validation boundary 78 is also a straight line that extends in the validation boundary distance

77 extends parallel to the desired geometry 66.

All measured value points 64, for which the validation limit 78 extends between their location and the desired geometry 66, are marked as invalid measuring points 64. In other words, all those measuring points 64 that are farther than the validation limit 78 from the desired geometry 66 are invalid. Optionally, it can be determined that measurement points that are exactly on the validation boundary 78 are valid or invalid.

For a further evaluation, then only the valid measuring points 62 are used accordingly.

Furthermore, it can then be provided that an average value of the invalid measured values 64 is formed in the ordinate direction. This mean value 80 can then also be reduced by the predetermined distance 76 ', which may possibly deviate from the predetermined distance 76, in the direction of the desired geometry 66, so that a final validation limit distance 77' results. Accordingly, a final validation limit 82 can be found which extends in the validation boundary distance 77 'parallel to the desired geometry 66.

Correspondingly, all points that are further away from the desired geometry 66 than the final validation limit can again be marked as invalid measuring points 64.

Optionally, an average value of the measuring points 64, which are now marked as invalid, may again be formed and the above be repeated process described. In this way, a kind of iterative process can be formed. However, it is preferably provided to form an average of the invalid measuring points 64 only once and then to set the final validation limit 82.

Accordingly, the method described above can also be carried out for surveys. For the sake of clarity, the method described above can be carried out once again for depressions and once for elevations, so that a corresponding validation can also be carried out for workpieces 14 which have both elevations and depressions.

FIG. 4 shows a further embodiment for the determination of invalid measuring points 64. The entry of the individual measuring points was not made in FIG. 4 for reasons of clarity. In this embodiment, defined areas 84, 85 are provided, wherein it is determined that measurement points 64 located in the areas 84, 85 are determined to be invalid. The defined regions 84, 85 are intended to mark existing measurement points as invalid, in particular at the beginning and at the end of the groove 68, since these regions are predominantly characterized by overshoots or undershoots and have a corresponding course of measurement points 64 which is not to be used ,

Since it may not be known where elevations or depressions such as, for example, the groove 68 are present, a possibility is indicated in FIG. 5 how the defined regions 84, 85 can be defined.

FIG. 5 shows a measurement curve or a measurement result 87 for this purpose, which is obtained by connecting the measurement points 82, 84 in chronological order. Furthermore, the validation limit 78 is to be determined, for example by means of one of the preceding methods, or by approximating a replacement element 88, for example, as a minimum straight line with a defined normal direction 72. The further boundary condition of the predefined normal direction 72 avoids that the minimum straight line is approximated obliquely to the desired geometry 66. In this way, it is achieved in any case that the additional element 88 runs parallel to the desired geometry 66.

Of course, the validation limit 78 may also have been determined in one of the other ways described above.

Now, intersections 91, 92 between the validation boundary 78 and the measurement curve 87 are determined.

The intersections 91, 92 give an indication of the approximate location of the groove 68 by describing their beginning and end in approximately.

Starting from the intersection points 91, 92, the defined regions 84, 85 are defined, in the present example, for example, by defining a distance in the negative s direction starting from the intersection point 91 and starting from the intersection point 92, a distance in positive s direction is defined. All measuring points 64 whose s-coordinates lie within these defined regions 84, 85 are now marked as invalid.

In addition, it can be provided, for example, that it is determined that the point of intersection 91 lies "in front" of the intersection point 92 and all measuring points between the intersection points 91, 92 are also marked as invalid. Furthermore, the described method can also be cumulated with the methods described above, for example the determination of invalid measuring points 64 based on a validation limit 78 determined on the basis of an extreme value point at a predetermined distance. In this way, measuring points produced reliably in the groove 68 and at the edges of the groove due to overshoots or undershoots can be identified and excluded from a further evaluation, which leads to the finally validated measuring curve 89.

Fig. 6 shows another embodiment of the validation method which can be used alternatively or cumulatively to the embodiments presented above. In this case, a cone limit angle 94 is set to the normal direction 72 of the desired geometry 66, it being true that only those measuring points 62 are considered valid, the detection of the direction of the contact force between the Tastkugel 26 and the workpiece 14 was within this Kegelgrenzwinkels 94.

In this case, of course, together with the coordinates of a measuring point, a vector 96 of the probing force at the detection time point must also be recorded. For this purpose, for example, the probe shown in Fig. 2 is suitable.

Subsequently, for each of the measuring points 62, 64, the direction of the probing force is interrogated and compared with the cone boundary angle 94. Now only the measuring points 62 are determined to be valid, in which the direction 96 of the probing force is within the cone limit angle 94.

Since, as a rule, measuring points which are detected in a free-floating probe ball 26 have a significantly different vector 96 than those measuring points which are recorded in the event of contact between the workpiece 14 and the probe ball 26, a suitable one can also be used here Validation of the measuring points 62, 64 make. It is also understood for this embodiment that it can be used not only alternatively but also cumulatively with the embodiments described above.

Claims

claims

Method for validating a measurement result (87) of a coordinate measuring machine (10) having a plurality of measurement points (62, 64), characterized by the following steps:

Determining a validation limit (78) relative to a known desired geometry (66) of a workpiece (14) to be measured,

• determining invalid (64) and valid (62) measurement points based on a respective property of the measurement points (62, 64) relative to the validation limit (78).

2. The method according to claim 1, characterized in that intersections (91, 92) of a measuring points (62, 64) connecting the measuring curve (87) with the validation limit (78) are determined, and that measuring points (62, 64) in relative to the points of intersection (91, 92) defined areas (84, 85) are determined as invalid measuring points (64).

3. The method according to claim 2, characterized in that the defined regions (84, 85) are defined with a distance value before and / or behind a respective intersection point (91, 92).

4. Method according to one of claims 1 to 3, characterized in that the validation limit (78) is determined by determining an extreme value point (70) located outside and / or within the desired geometry (66) whose distance in the normal direction (72) farthest from the desired geometry (66), and that the distance is reduced by a predetermined distance (76) to a validation boundary distance (77) such that the validation limit (78) in the validation boundary distance (77) extends parallel to the desired geometry (66).

5. The method according to claim 4, characterized in that a final validation limit (82) is determined by forming an average value (80) of the distances of all measurement points whose distance in the normal direction (72) to the desired geometry (66) is greater than that Validation Boundary Distance (77), and that the average (80) is reduced by a predetermined distance (76) to a final validation boundary distance (77) such that the final validation limit (78) in the final validation boundary distance (77) is parallel to the desired geometry (77). 66).

6. The method according to any one of claims 1 to 3, characterized in that the validation limit (78) is determined by the measured values (62, 64) are approximated with a replacement element (88) whose geometric shape corresponds to the desired geometry (66) and the replacement element (88) forms the validation boundary (78), wherein before determining the validation boundary (78) it is determined that a normal direction (72) of the replacement element (88) corresponds to a normal direction (72) of the desired geometry (66).

7. The method according to claim 6, characterized in that the replacement element (88) is a minimum element or an absolute minimum element.

8. The method according to claim 1 or any one of claims 4 to 7, characterized in that the respective property of the measuring points (62, 64) is a position relative to the validation limit (78), and that a measuring point (64) determines invalid when the validation limit (78) is between the measuring point (64) and the desired geometry (66).

9. The method according to claim 1, characterized in that the validation limit (78) is determined by setting a cone limit angle (94) and the respective characteristic of the measuring points (62, 64) is the direction of a probing force (96) of a tactile sensor (22, 24, 26) detecting the measuring points (62, 64), and in that the measuring points (62, 64), when the detection of the direction of the probing force (96) outside the cone limit angle (94), as invalid measuring points (64) are determined.

10. The method according to claim 4 or 5, characterized in that the predetermined distance (76) of half a true immersion depth (74) of a tactile sensor (22, 24, 26) of the coordinate measuring machine (10) in the workpiece to be measured (14). equivalent.

11. Coordinate measuring machine with a sensor (22, 24, 26) for measuring a workpiece (14) and an evaluation device (38), characterized in that the evaluation device (38) has a measurement result (87) of the sensor (22, 24, 26) validated by a method according to any one of claims 1 to 10.

A computer program comprising program code means adapted to perform all the steps of a method according to any one of claims 1 to 10 when said computer program is executed on a computer (32).