Measurement method and measurement apparatus for capturing the surface topology of a workpiece

Abstract

A measuring device and measuring method for capturing a surface topology of a workpiece uses an optical coherence tomograph having a reference arm guided by a manipulator or a deflection unit to position a measuring region of the scanner. The reference arm is guided along an actual track, which at least partially deviates from an intended track due to disturbing influences like lag errors of the manipulator. An actual distance (d.sub.m) between a zero point of the measuring region and a workpiece surface is measured at at least one measuring point of the actual track. A planning path length (I.sub.p) of the reference arm is established for the at least one measuring point for the compensation of the disturbing influences, and the measured actual distance (d.sub.m) is normalized to a standard distance (d.sub.n) with the aid of the planning path length (I.sub.p).

Claims

1. A measuring method for capturing a surface topology of a workpiece with the aid of an optical coherence tomograph, in which a measuring region of a reference arm of the optical coherence tomograph is guided, with the aid of a manipulator and/or a deflection unit, along an actual track which at least partially deviates from an intended track due to disturbing influences, the method comprising the steps of: measuring an actual distance between a zero point of the measuring region and a workpiece surface at at least one measuring point of the actual track, establishing for the compensation of disturbing influences for the at least one measuring point, a planning path length of the reference arm and using the planning length to normalize the measured actual distance to a standard distance.

2. The measuring method as recited in claim 1, wherein a measuring data record and the planning path length are stored in a memory unit, for the at least one measuring point, as the starting information for calculating the standard distance.

3. The measuring method as recited claim 2, wherein the measuring data record includes an optical path length of the reference arm and the measured actual distance.

4. The measuring method as recited in claim 1, wherein the standard distance is calculated from the difference between a computed value formed from the measuring data set and the planning path length.

5. The measuring method as recited claim 4, wherein the computed value is formed from the sum or difference of the optical actual path length and the measured actual distance.

6. The measuring method as recited in claim 1, wherein a normalization line is established by a user on the basis of empirical values in order to normalize multiple measured actual distances.

7. The measuring method as recited in claim 1, wherein the normalization line is defined independently of the intended track.

8. The measuring method as recited in claim 1, wherein the normalization line is situated above the workpiece surface in some areas and below the workpiece in other areas.

9. The measuring method as recited in claim 1, wherein a processing unit is used to determine the associated planning path length of the reference arm stored for each individual measuring point with reference to the normalization line.

10. The measuring method as recited in claim 1, wherein the planning path length is determined, depending on the particular measuring point, as the distance between the normalization line and a system-internal reference point.

11. The measuring method as recited in claim 1, wherein a movement program for the deflection unit and/or the manipulator is generated depending on the intended track and/or the normalization line.

12. The measuring method as recited in claim 1, wherein the intended track defines a course and is established before the measurement in such a way that the workpiece surface to be measured is located within the measuring region when the measuring region is moved along the intended track.

13. The measuring method as recited in claim 1, wherein the intended track is adjusted in such a way that the course of the optical actual path length of the reference arm is adjusted within the course of the intended track.

14. The measuring method as recited in claim 1, wherein a normalized scan of the workpiece is generated in a path-dependent diagram or a time-dependent diagram with the aid of the calculated standard distances.

15. The measuring method as recited in claim 1, wherein the normalized scan of the workpiece is analyzed with the aid of evaluation algorithms.

16. The measuring method as recited in claim 1, wherein multiple normalized scans are combined in order to form a height map.

17. A measuring device for detecting a surface topology of a workpiece, the measuring device comprising: an optical coherence tomograph configured for measuring an actual distance between a zero point of a measuring region of the optical coherence tomograph and a workpiece surface, a manipulator and/or a deflection unit configured for guiding the measuring region along an actual track, and a processing unit configured for the compensation of measuring errors; wherein the processing unit is designed in such a way that the measured actual distance can be normalized to a standard distance with the aid of a measuring method as recited in claim 1.

18. The measuring method as recited in claim 1, wherein the normalization line is defined dependently of the intended track, wherein the normalization line is at least partially identical to the intended track, is similar to the intended track, and/or at least individual values of the normalization line are identical to the intended track.

19. The measuring method as recited in claim 1, wherein the normalization line is established to include a straight line and a curve line.

20. The measuring method as recited in claim 1, wherein the normalization line is established in order to normalize multiple measured actual distances.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages of the invention are described in the following exemplary embodiments. Wherein:

(2) FIG. 1 shows a schematic representation of a machining scanner comprising a measuring device,

(3) FIG. 2a shows a schematic progression of the capture of a surface topology,

(4) FIG. 2b shows a schematic progression of the capture of a surface topology according to yet another exemplary embodiment,

(5) FIG. 3 shows a schematic flow chart for the compensation of disturbing influences,

(6) FIG. 4 shows a schematic representation of the normalization of a measuring point,

(7) FIG. 5 shows a schematic representation of a second exemplary embodiment for the normalization of a measuring point,

(8) FIG. 6 shows a schematic representation of the capture of a workpiece via multiple measuring points, and

(9) FIG. 7 shows a path-dependent diagram for representing ascertained standard distances.

DETAILED DESCRIPTION

(10) FIG. 1 shows a schematic representation of a measuring device 1 for capturing a surface topology 2 of a workpiece 3. In doing so, the measuring device 1, spaced apart from the workpiece 3, is moved over the workpiece 3 with the aid of a manipulator 4. According to the present exemplary embodiment, the manipulator 4 is a multiaxial industrial robot, on the free end of which the measuring device 1 is situated. The measuring device 1 comprises a point distance sensor which is designed as an optical coherence tomograph 28 in this case. By way thereof, a measuring beam 31, in particular a laser beam, is directed onto the workpiece surface 10. The measuring device 1 also comprises a measuring scanner 6, with the aid of which the measuring beam 31 can be deflected via at least one rotatably mounted mirror 13.

(11) The measuring device 1 can also include a machining scanner 5 which is installed downstream from the measuring scanner 6. The machining scanner 5 includes a first deflection unit 7. With the aid of the first deflection unit 7, a machining beam 8 of the machining scanner 5, in particular a laser beam, can be deflected via at least one movable mirror 9. The workpiece 3 is machined with the aid of the machining beam 8 of the machining scanner 5, i.e., in particular being marked, cut, or welded. In doing so, the surface topology 2 to be investigated by the measuring device 1, in particular the measuring scanner 6, is changed.

(12) According to the present exemplary embodiment, the measuring scanner 6 is fixedly coupled to the machining scanner 5. The measuring scanner 6 and the machining scanner 5 are therefore jointly moved by the manipulator 4. Alternatively, said measuring scanner and said machining scanner can also comprise separate manipulators 4, however. The measuring scanner 6 can also be situated so as to be detached from the manipulator 4, however. The measuring beam 31 of the measuring scanner 6 can be additionally moved relative to the manipulator movement with the aid of a second deflection unit 11 in order to perform a distance measurement. For this purpose, the second deflection unit 11 comprises at least one second mirror 13.

(13) According to FIG. 1, the position of the measuring point 17 of the measuring beam 31 is therefore influenced by the manipulator movement, the deflection movement of the first deflection unit 7, and the deflection movement of the second deflection unit 11. Therefore, these are mutually superimposed movements.

(14) The optical coherence tomograph 28 comprises a reference arm 12 which is formed by one portion of the beam path of the measuring beam 31. In the area of its end, the reference arm 12 comprises a measuring region 14. The end of the reference arm 12 forms a zero point 15 of the measuring region 14 in this case. The optical coherence tomograph 28 measures a distance between the workpiece surface 10 located in the measuring region 14 and the zero point 15.

(15) The length of the reference arm 12 and the position of the measuring region 14 in the z-direction can be changed with the aid of an adjusting device which is not represented here. Preferably, the adjusting device is integrated in the optical coherence tomograph 28. The length of the reference arm 12 is preferably controlled in such a way that the workpiece surface 10 is located in the measuring region 14 during the entire measurement. The length of the reference arm 12 is furthermore selected in such a way that the zero point 15 is located above or below the workpiece surface 10 during the entire measurement. According to FIG. 1, the measuring region 14 extends from a region above the workpiece 3, in particular from a side facing the measuring device 1, to below the workpiece 3. In any case, the measurement relates to the zero point 15 of the measuring region 14, which essentially halves this measuring region 14. In the represented exemplary embodiment, the zero point 15 of the measuring region 14 is located just above the workpiece 3. It is also conceivable, however, to locate the zero point 15 below the workpiece 3.

(16) The reference arm 12 is displaced, with the aid of an axis control 16, across the surface topology 2 to be captured, and therefore an actual distance d.sub.m between the zero point 15 and the workpiece surface 10 can be measured at at least one measuring point 17. In doing so, the axis control 16 can influence the adjusting device, the manipulator, the first deflection unit, and/or the second deflection unit. The position of the zero point 15 or of the entire measuring region 14 can be changed via an axis control 16 by way of the reference arm 12, in particular, being displaced. In the represented exemplary embodiment, the measuring point 17 is at the same level as the zero point 15 of the measuring region 14. It is also conceivable, however, that the measuring point 17 is located above or below the zero point 15.

(17) FIGS. 2a and 2b show a schematic progression of the capture of the surface topology 2. In both FIGS. 2a, 2b, an intended track 18 is initially specified depending on the surface topology 2 to be captured, according to which the reference arm 12 is to be displaced with the aid of the axis control 16 (not represented), the manipulator 4, and/or the second deflection unit 11 of the measuring device 1 in order to measure distance. The objective, therefore, is to move the zero point 15 of the measuring region 14 along the intended track 18.

(18) In FIG. 2a, the reference arm 12 of the measuring scanner 6 is moved by the manipulator 4 (cf. FIG. 1) along the intended track 18 in order to carry out a distance measurement at each of multiple measuring points 17. Since the manipulator 4 cannot move infinitely rapidly, however, the reference arm 12 is not guided precisely along the intended track 18, but rather along an actual track 19. In this case, one refers to a lag error. Proceeding from the measuring points 17 forming the actual track 19, in particular proceeding from the zero point 15 (cf. FIG. 1), the actual distance d.sub.m is measured for each measuring point 17 with the aid of the measuring scanner 6 which is not represented. The actual distance d.sub.m is therefore the distance between the zero point 15 and the workpiece surface 10, which is corrupted by the lag error and which is actually measured.

(19) The reference arm 12 of the progression represented in FIG. 2b is to be guided along the intended track 18 only by the second deflection unit 11 (cf. FIG. 1). In this case as well, however, the actual track 19 deviates from the planned intended track 18, in particular due to the reciprocating movements of the second mirror 13 of the second deflection unit 11.

(20) The following FIGS. 3 and 4 now show how the above-described disturbing influences can be compensated. FIG. 3 shows a schematic flow chart for the compensation of the disturbing influences. The normalization of the measurement is schematically represented in FIG. 4 for the purpose of illustration. Initially, the intended track 18 is specified by a user (not represented). The intended track 18 is established, depending on the workpiece surface 10 to be captured, in such a way that the workpiece surface 10 is located in the measuring region 14 (cf. FIG. 1, FIG. 4) during the entire measurement. The intended track 18 is established with reference to empirical values.

(21) For this purpose, the desired intended track 18 is specified by a user (not represented) in a programming environment 20 or, generally, in a control unit 21. Depending on the intended track 18, a movement program 22 for the axis control 16 is generated by the programming environment 20, and therefore the measuring beam 31 and the reference arm 12 are guided along the workpiece surface 10 in such a way that the workpiece surface 10 is located within the measuring region 14 (cf. FIG. 4) during the entire measurement. The movement of the manipulator 4 (not represented) and/or the second deflection unit 11 is preferably also influenced on the basis of the movement program 22.

(22) Moreover, a normalization line 23, which is shown in FIG. 4, is specified in the programming environment 20, in particular by the user. In the represented exemplary embodiment (cf. FIG. 4), the normalization line 23 as well as the intended track 18 are located above the workpiece surface 10. The normalization line 23 is established as a data set in the control unit 21. With reference to the normalization line 23, a planning path length l.sub.p of the reference arm 12 is established in a processing unit 24 (cf. FIG. 3). The planning path length l.sub.p could be considered, according to FIG. 4, to be the distance between a system-internal reference point 25 located in the measuring device 1, in particular in the measuring scanner 6, and a normalization point 26 lying on the normalization line 23. The planning path length l.sub.p is a hypothetical value, however, which does not necessarily need to be related to the actual measuring method. The planning path length l.sub.p is stored in a memory unit 27.

(23) The measurement itself is carried out, according to FIG. 3, by the optical coherence tomograph 28. With the aid of the optical coherence tomograph 28, the actual distance d.sub.m from the zero point 15 of the measuring region 14 to the workpiece surface 10 (cf. FIG. 4) can be determined. In addition, an optical actual path length l.sub.i is determined, which extends from a scan head (not represented) to the zero point 15 of the measuring region 14. In addition to the optical actual path length l.sub.i, the actual distance d.sub.m and the planning path distance l.sub.p are stored in the memory unit 27 as a measuring data set 29.

(24) In order to now be capable of compensating the disturbing influences, the measuring data set 29 according to FIG. 3 is further processed by the processing unit 24. For this purpose, a standard distance d.sub.n (cf. FIG. 4) is determined for each individual measurement. In order to be capable of determining the standard distance d.sub.n for the represented exemplary embodiment, the sum of the optical actual path length l.sub.i and the measured actual distance d.sub.m must be initially calculated. This yields a computed value for the further processing. Subsequently, the difference of the computed value and the planning path length l.sub.p is formed. The value calculated in this way is the standard distance d.sub.n. This is a distance which is referenced to the normalization line 23 and, therefore, is normalized.

(25) The same approach can be applied for multiple measuring points 17, wherein an individual planning path length l.sub.p, the measured actual distance d.sub.m, and the optical actual path length l.sub.i are determined for each measuring point 17 and are stored in the memory unit 27. The actual track 19 is formed by stringing together multiple actual measuring points 17.

(26) In the following description of the alternative exemplary embodiments represented in FIGS. 5 to 6, identical reference signs are utilized for features which are identical and/or at least comparable in terms of their design and/or mode of operation as compared to the first exemplary embodiment represented in FIG. 4. Provided said alternative exemplary embodiments are not explained again in detail, their design and/or mode of operation correspond to the design and mode of operation of the features already described above.

(27) FIG. 5 shows a second exemplary embodiment for the normalization of disturbing influences. In this case, the intended track 18 and the normalization line 23 are located below the workpiece 3. The computed value for calculating the standard distance d.sub.n is formed from the difference of the actual path length l.sub.i and the actual distance d.sub.m. The standard distance d.sub.n is also formed from the difference of the planning path length l.sub.p with respect to the computed value.

(28) In yet another exemplary embodiment (not represented), it is furthermore conceivable that the normalization line 23 is located above the workpiece 3 and the intended track 18 is located below the workpiece 3. Moreover, it is conceivable that the intended track 18 is located above the workpiece 3 and the normalization line 23 is located below the workpiece 3. It is advantageous when their position relative to the workpiece surface 10 does not change during the entire measurement, i.e., they are each located either above or below the workpiece surface 10.

(29) Represented in FIG. 6 is an overall capture of the workpiece surface 10 via three measuring points 17. The intended track 18 is formed according to the workpiece surface 10 assumed by the user. The normalization line 23 is situated, as a straight line, in the Cartesian space and partially identically to the intended track 18. A movement program 22 for the axis control 16 is generated (cf. FIG. 3) by the programming environment 20 depending on the intended track 18, and so all three measuring points 17 are controlled in succession by the measuring scanner 6. Due to the inertia of the axis control 16, the measuring points 17 are not controlled according to the intended track 18, however, but rather with a disturbing influence. As a result, the zero points 15 for each measuring point 17 do not lie on the intended track 18, but rather above or below said intended track. The actual track 19 is formed by connecting the individual zero points 15.

(30) The actual path length l.sub.i is then determined for each measuring point 17 proceeding from the measuring scanner 6 to the particular zero point 15. Moreover, the actual distance d.sub.m is determined by the optical coherence tomograph 28 for each measuring point 17, proceeding from the zero point 15. In addition, an associated planning path length l.sub.p is established for each measuring point 17. In this case, the planning path length l.sub.p extends, proceeding from the system-internal reference point 25, to the normalization point 26. The calculation of the standard distance d.sub.n takes place, as described above, by forming the difference of the computed value and the planning path length l.sub.p. The calculated standard distances d.sub.n can then be analyzed and further processed with the aid of mathematical evaluation algorithms.

(31) FIG. 7 shows a schematic representation of how the standard distances d.sub.n can be represented in a path-dependent diagram 30. For this purpose, the diagram 30 comprises an x-axis. The measuring points 17, which are uniformly distributed across the measurement, are plotted on the x-axis. Each measuring point 17 is plotted and labeled in the diagram 30 in FIG. 7 according to the sequence in which said measuring points are measured. According to the diagram 30, the actual distances d.sub.m were therefore measured at seven measuring points 17 over the period of time of the scan. A normalized standard distance d.sub.n was calculated for each measuring point 17. Each of the calculated standard distances d.sub.n is plotted on the y-axis of the diagram 30.

(32) The present invention is not limited to the exemplary embodiments which have been represented and described. Modifications within the scope of the claims are also possible, as is any combination of the features, even if they are represented and described in different exemplary embodiments.

LIST OF REFERENCE SIGNS

(33) 1 measuring device 2 surface topology 3 workpiece 4 manipulator 5 machining scanner 6 measuring scanner 7 first deflection unit 8 machining beam 9 first mirror 10 workpiece surface 11 second deflection unit 12 reference arm 13 second mirror 14 measuring region 15 zero point 16 axis control 17 measuring point 18 intended track 19 actual track 20 programming environment 21 control unit 22 movement program 23 normalization line 24 processing unit 25 reference point 26 normalization point 27 memory unit 28 optical coherence tomograph 29 measuring data set 30 diagram 31 measuring beam

(34) d.sub.m actual distance

(35) d.sub.n standard distance

(36) l.sub.i actual path length

(37) l.sub.p planning path length