Measuring method and measuring device for capturing a surface topology of a workpiece

Abstract

A measuring method for capturing a surface topology (2) of a workpiece (3) using a coherence tomograph (28), in which a measuring area (14) of a reference arm (12) of the coherence tomograph (28) is guided along an actual path (19) by means of a manipulator (4) and / or a deflection unit (7; 11), which deviates at least partially from a target path (18) due to disturbances, in particular following errors of the manipulator (4), and an actual distance (dm) is measured at at least one measuring point (17) of the actual path (19) between a zero point (15) of the measuring area (14) and a workpiece surface (10), characterized in that a planning path length (lp) of the reference arm (12) is defined to compensate for the disturbances for the at least one measuring point (17) and that the measured actual distance (dm) is determined by means of the The planning path length (lp) is normalized to a standard distance (dn).

Description

[0001] The present invention relates to a measuring method for capturing a surface topology of a workpiece using a coherence tomograph, in which a measuring area of ​​a reference arm of the coherence tomograph is guided along an actual path by means of a manipulator and / or a deflection unit, which deviates at least partially from a target path due to disturbances, in particular following errors of the manipulator, and an actual distance is measured at at least one measuring point of the actual path between a zero point of the measuring area and a workpiece surface.

[0002] Furthermore, the invention relates to a measuring device for capturing a surface topology of a workpiece with a coherence tomograph for measuring an actual distance between a zero point of a measuring range of the coherence tomograph and a workpiece surface, a manipulator and / or a deflection unit for guiding the measuring range along an actual path, and a computing unit for compensating measurement errors, in particular tracking errors.

[0003] Such measurement methods are well known from the prior art and are used in particular to determine the quality of welds and similar components produced using a laser processing system. Typically, a robot and / or a deflection unit enables relative movement between the workpiece to be measured and a scan head. This allows the surface of the workpiece to be scanned and analyzed. The robot's axis controllers attempt to follow a target path to achieve the most accurate result possible. However, due to the delayed response of the axes to commands, a lag often occurs, which negatively impacts the overall analysis.

[0004] The object of the present invention is therefore to create a measuring method and a measuring device for capturing a surface topology, which reliably determines the quality assurance measurement results.

[0005] The problem is solved by a measuring method and a measuring device with the features of independent claims 1 and 15.

[0006] A measurement method for capturing the surface topology of a workpiece using coherence tomography is proposed. In this method, a measurement area of ​​a reference arm of the coherence tomograph is guided along a defined path by a manipulator and / or a deflection unit. The manipulator is preferably an industrial robot capable of performing positioning and measurement tasks in addition to manufacturing processes. Furthermore, the reference arm of the coherence tomograph can be guided precisely along or across the surface topology to be analyzed by means of the deflection unit, in particular several movable mirrors. The surface topology to be analyzed can, for example, be a weld seam or a cut in the trailing path and / or an edge or a step in the leading path. Based on this surface topology, a motion program is preferably generated so that the measurement area is guided along this path, but especially along a target path.

[0007] At at least one measuring point of the actual path, an actual distance is measured between a zero point of the measuring range and a workpiece surface. The measuring range preferably extends coaxially to the reference arm and / or is approximately 10 to 20 mm in size, whereby in particular only half of the measuring range is usable. The zero point preferably divides the measuring range substantially in half, so that it lies approximately in the middle of the measuring range. When defining the target path within the measuring range, the workpiece surface is positioned slightly above or below the zero point. The actual distance between the zero point and the workpiece surface is measured using the coherence tomograph. To measure the surface topology for at least one scan, several measurements are performed point by point, so that an actual distance is measured for each measuring point.These actual distances can then be stored as height pixels, possibly along with other values ​​such as intensity and / or quality.

[0008] Due to interference, the actual path deviates at least partially from the intended path. For example, the mechanical inertia of the manipulator leads to tracking errors, which essentially represent a pre-development of the planned measurement points of the intended path relative to those of the actual path. Similarly, pendulum motion by the deflection unit can lead to inaccurate measurements.

[0009] According to the invention, a planning path length of the reference arm is defined to compensate for disturbances at least at one measuring point, particularly prior to the measurement. This planning path length corresponds to a planned length of the reference arm at the respective measurement time, which is assumed or determined to be unobstructed and is not actually measured. The planning path length can be defined by a user based on experience to reduce computational effort. The actual measured distance between the zero point and the material surface is then normalized to a standard distance using the planning path length. This references this and all subsequent measuring points to the same starting point, thus making the height pixels comparable. Only then is it ultimately possible to draw error-free conclusions about the surface topology from the height pixels.The interfering influences that distort the result can thus be easily compensated for computationally, without having to fundamentally change the measuring device.

[0010] It is advantageous to store a measurement data set for at least one measuring point as input information for calculating the standard distance. This measurement data set is defined by the optical actual path length of the reference arm, the measured actual distance, and the planned path length. The optical actual path length of the reference arm is determined by the distance between an internal light source and the zero point of the measuring range. The optical actual path length is therefore a known length that can be individually adjusted using the manipulator and / or the deflection unit. Starting from the zero point, which is essentially located at the workpiece-side end of the reference arm, the actual distance is measured. The planned path length can be calculated as a distance value or defined almost arbitrarily. The measurement data set is stored in a memory unit.Based on the measurement data set, sufficient data can be collected for quality assurance purposes, enabling the measurements to be traced in detail even after normalization to the standard distance.

[0011] Furthermore, it is advantageous if the standard distance is calculated from the difference between a calculated value derived from the measurement data set and the planned path length. The calculated value is derived from the sum or the difference of the actual optical path length and the measured actual distance. Whether the calculated value is derived from the sum or the difference ultimately depends on the location of the zero point. The location of the normalization point is initially irrelevant but may need to be considered in specific cases. In an advantageous embodiment of the invention, the zero point of the measuring range and the normalization point are positioned above the workpiece. In another alternative embodiment of the invention, the zero point of the measuring range is positioned above the workpiece and the normalization point is positioned below the workpiece.In both of these cases, where the zero point is located above the workpiece, the calculated value is determined by summing the actual optical path length and the actual distance. If, however, the zero point is located below the workpiece, the calculated value is determined by the difference between the actual path length and the actual distance. Both the zero point of the measuring range and the normalization point can be positioned below the workpiece. Conversely, it is also possible to position the zero point of the measuring range below the workpiece and the normalization point above it. Due to the simple calculation of the normalization distance and the various options for positioning the calculation components during the measurement process, this method can be easily adapted to a wide range of conditions.

[0012] Advantageously, a normalization line is defined to standardize multiple measured actual distances, typically by a user based on experience. Corresponding to the point-by-point measurement from which the actual path is ultimately generated, a normalization point is defined for each measurement. The individual normalization points are then connected to form the normalization line. However, it is not strictly necessary to define a corresponding normalization point for every measurement point. In principle, a single normalization point is sufficient to reference the actual distance. The normalization point or the normalization line can be positioned above or below the workpiece. The normalization line allows the standard distance to be easily established, thus compensating for disturbances with minimal effort.

[0013] It is also advantageous if the normalization line is defined independently or dependently on the target path. Typically, the surface topology is recorded by trained personnel who, based on experience, position the normalization line close to the target path. However, to avoid errors due to an incorrect definition of the normalization line, it can also be determined completely independently of the target path. Alternatively, it can also be advantageous to define the normalization line according to the expected or specified target path.

[0014] The normalization line can be defined to be at least partially identical to the target path. It is also conceivable that the normalization line resembles the target path. Furthermore, only individual values, particularly a start and / or end value, can be identical to it. The normalization line can be defined independently of the user's knowledge, thus ensuring the accuracy of the normalization in every case.

[0015] The normalization line is advantageously defined as a straight line and / or curve, at least in some areas. Alternatively or additionally, it is beneficial if the normalization line is positioned at least in some areas above and / or below the workpiece surface. The design of the normalization line is chosen depending on the user's expertise and the complexity of the surface. When defining the target path, however, care should be taken to ensure that the component remains above or below the workpiece throughout the entire measurement. The selected area should remain unchanged during the measurement if possible, as it is not possible to determine from the measurement data afterward which side the measurement was ultimately performed.

[0016] Advantageously, the corresponding planning path length of the reference arm is determined and / or stored for each individual measuring point using the normalization curve, particularly with the aid of a processing unit. This allows a standard distance to be measured for each actual distance of the respective measuring point.

[0017] A further advantage arises when the planning path lengths are determined as the distance between the normalization line and an internal reference point, depending on the respective measuring point. The planning path lengths are purely planning data that enable the calculation of tracking errors and the like. In principle, it would also be conceivable to define the planning path lengths using any system-independent value.

[0018] Furthermore, it is advantageous if the motion program for the deflection unit and / or the manipulator is generated based on the target path and / or the normalization line. An axis controller transmits a target position to the manipulator or deflection unit for each measuring point. The manipulator or deflection unit is then adjusted according to the specified target value by means of the axis controller. However, since the adjustment of the manipulator or deflection unit cannot be infinitely fast, a lag occurs that distorts the measurement; this lag is compensated for by the standard distance.

[0019] The target path is advantageously defined before measurement in such a way that the workpiece surface to be measured is within the measuring range when the workpiece is moved along the target path. This ensures that the measurements can be carried out reliably.

[0020] To ensure the workpiece remains within the measuring range throughout the entire measurement, it is advantageous to adjust the optical actual path length of the reference arm as it approaches the target path. The user defines the target path based on the workpiece being measured, ensuring the workpiece is positioned within the measuring range for the entire duration of the ideal measurement. The axis control then directs the manipulator or deflection unit to move sequentially to the planned measuring points, ultimately forming the actual path. While specifying the target path and controlling the manipulator or deflection unit accordingly cannot guarantee that the workpiece will always remain within the measuring range due to tracking errors or settling-in.However, the probability is very low, since at least in the course of the intended path the rough geometry of the workpiece has been taken into account, so that the errors are ultimately only caused by the component's inertia. These defects can also be compensated for by adopting the normalization curve.

[0021] Advantageously, a normalized scan of the workpiece is generated in a diagram, particularly one dependent on path and / or time, using the calculated standard distances. The normalized scan essentially represents a sampling rate over the area of ​​the workpiece to be measured. The entire scan is divided into path segments, with each segment representing a measurement point. These are plotted on the x-axis of the diagram. The standard distance for each path segment is then plotted on the y-axis. Alternatively, instead of individual path segments, the duration of the scan can be divided into its measurement points. The scan is two-dimensional. This allows the user to easily evaluate the surface topology of the workpiece.

[0022] Furthermore, it is advantageous to analyze the standardized scan of the workpiece using evaluation algorithms. Based on this preferably mathematical evaluation algorithm, further measures can be defined, for example, to rework a defective weld.

[0023] Furthermore, it is advantageous to combine multiple scans to create a height map. The values ​​plotted in the diagram give the measurement a purely two-dimensional character, meaning the user can only draw conclusions about the surface topology based on a single scan. However, it is often necessary to analyze the entire surface topology. This is made possible by combining the individual scans in their sequence. This creates a three-dimensional image of the workpiece in the form of a height map. This allows, for example, a simple evaluation of weld quality.

[0024] Furthermore, a measuring device for capturing the surface topology of a workpiece is proposed. The measuring device comprises at least one coherence tomograph, a manipulator and / or a deflection unit, and a processing unit. The coherence tomograph is designed to measure the actual distance between a zero point of a measuring range of the coherence tomograph and a workpiece surface. The measuring range can be guided along an actual path by means of the manipulator or the deflection unit. The processing unit is designed to compensate for measurement errors, in particular for tracking errors.

[0025] According to the invention, the computing unit is designed such that the measured actual distance can be normalized using a measuring method as described above, whereby the aforementioned features can be present individually or in any combination. This makes it possible to design a measuring device with a significantly reduced error rate without any structural modifications.

[0026] Further advantages of the invention are described in the following exemplary embodiments. These show:

[0027] Fig. 1 a schematic representation of a processing scanner with measuring device,

[0028] Fig. 2a a schematic process for recording a surface topology,

[0029] Fig. 2b a schematic sequence of the acquisition of a surface topology according to a further embodiment,

[0030] Fig. 3. A schematic flowchart for compensating for disturbances,

[0031] Fig. 4 a schematic representation for the normalization of a measuring point,

[0032] Fig. 5 a schematic representation of a second embodiment for the normalization of a measuring point,

[0033] Fig. 6 a schematic representation of the acquisition of a workpiece via several measuring points and

[0034] Fig. 7 A path-dependent diagram to represent determined standard distances.

[0035] The Fig. Figure 1 shows a schematic representation of a measuring device 1 to capture a surface topology 2 a workpiece 3 The measuring device 1 This is done using a manipulator. 4 from the workpiece 3 moved at a distance across it. According to the present embodiment, the manipulator is 4a multi-axis industrial robot, at whose free end the measuring device 1 is arranged. The measuring device 1 features a point distance sensor, which in this case is a coherence tomograph 28 is trained. A measuring beam is emitted from this. 31 , in particular a laser beam, onto the workpiece surface 10 guided. Furthermore, the measuring device includes 1 a measuring scanner 6 , by means of which the measuring beam 31 via at least one rotatably mounted mirror 13 is easily distracted.

[0036] The measuring device can also 1 a processing scanner 5 include the measuring scanner 6 downstream. The processing scanner 5 includes a first deflection unit 7 . By means of the first deflection unit 7 can a processing beam 8 of the processing scanner 5, in particular a laser beam, via at least one movable mirror 9 be distracted. The workpiece 3 is used with the processing beam 8 of the processing scanner 5 processed, i.e., in particular marked, cut or welded. In this process, the material is measured by the measuring device. 1 , especially the measuring scanner 6 , surface topology to be investigated 2 changed.

[0037] According to the present embodiment, the measuring scanner 6 firmly attached to the processing scanner 5 coupled. The measuring scanner 6 and the processing scanner 5 are therefore jointly controlled by the manipulator 4 moved. Alternatively, these can also be separate manipulators. 4 exhibit. The measuring scanner 6 However, it can also be independent of the manipulator. 4 be arranged. The measuring beam 31 the measuring scanner 6can be achieved by means of a second deflection unit 11 For distance measurement, the second deflection unit must also be moved relative to the manipulator movement. 11 at least a second mirror 13 on.

[0038] According to Fig. 1 will therefore be the position of the measuring point. 17 of the measuring beam 31 through the manipulator movement, the deflection movement of the first deflection unit 7 and the deflection movement of the second deflection unit 11 influenced. These are therefore superimposed movements.

[0039] The coherence tomograph 28 features a reference arm 12 on, which passes through part of the path of the measuring beam 31 is formed. In the region of its end, the reference arm exhibits 12 a measuring range 14 The end of the reference arm forms the base. 12 a zero point 15 of the measuring range14 The coherence tomograph 28 measures a distance between the points in the measuring range 14 located workpiece surface 10 and the zero point 15 .

[0040] The length of the reference arm 12 or the position of the measuring range 14 The position in the z-direction can be changed via an adjustment device not shown here. This is preferably located in the coherence tomograph. 28 integrated. The length of the reference arm 12 is preferably controlled in such a way that the workpiece surface 10 throughout the entire measurement within the measuring range 14 The length of the reference arm is located. 12 is furthermore chosen such that the zero point 15 throughout the entire measurement above or below the workpiece surface 10 is located. The measuring range 14 extends according to Fig. 1 of an area above the workpiece 3, in particular from one of the measuring devices 1 facing side, up to under the workpiece 3 In any case, the measurement refers to the zero point. 15 of the measuring range 14 , which this measuring range 14 essentially halved. In the illustrated embodiment, the zero point 15 of the measuring range 14 just above the workpiece 3 arranged. However, it is also conceivable to define the zero point as... 15 under the workpiece 3 to place.

[0041] The reference arm 12 is achieved by means of an axle control system 16 above the surface topology to be recorded 2 adjusted so that at least one measuring point 17 an actual distance d m between the zero point 25 and the workpiece surface 10 can be measured. The axle control 16This can affect the adjustment mechanism, the manipulator, the first deflection unit, and / or the second deflection unit. The position of the zero point. 15 or the entire measuring range 14 can be controlled via an axle 16 be changed, in particular by altering the reference arm 12 is adjusted. The measuring point 17 In the illustrated embodiment, it is at the same height as the zero point. 15 of the measuring range 14 However, it is also conceivable that the measuring point 17 above or below zero 15 is arranged.

[0042] The Fig. 2a and Fig. Figure 2b shows a schematic sequence of the surface topology recording process. 2 In both Fig. 2a, Fig. 2b depends on the surface topology to be recorded. 2 Each initially a target path 18 specified, according to which the reference arm 12with the axle control not shown 16 , the manipulator 4 and / or the second deflection unit 11 the measuring device 1 It is to be adjusted for distance measurement. The goal is therefore to find the zero point. 15 of the measuring range 14 on the planned path 18 to move along.

[0043] In Fig. 2a will be the reference arm 12 of the measuring scanner 6 from the manipulator 4 (cf.) Fig. 1) along the planned path 18 moved to measure at several points 17 to perform a distance measurement in each case. Since the manipulator 4 However, it cannot move infinitely fast, the reference arm 12 not exactly along the planned path 18 guided, but along an existing path 19 In this case, it is called a following error. Of the actual path 19 training measuring points 17, especially from the zero point 15 (cf.) Fig. 1), starting from, is done using the measuring scanner not shown 6 per measuring point 17 the actual distance d m measured. The actual distance d m This is therefore the actually measured distance between zero point, distorted by the following error. 15 and workpiece surface 10 .

[0044] The reference arm 12 of the in Fig. The process shown in 2b is only intended to be described by the second deflection unit. 11 (cf.) Fig. 1) along the planned path 18 to be guided. However, here too, the situation deviates, particularly due to the stabilization of the second mirror. 13 the second deflection unit 11 , the actual path 19 from the planned target route 18 away.

[0045] The following Fig. 3 and Fig. Section 4 now shows how the previously described disturbances can be compensated for. Fig. Figure 3 shows a schematic flowchart for compensating for disturbances. For illustration, in Fig. Figure 4 schematically illustrates the standardization of the measurement. First, the target path is defined by a user (not shown). 18 specified. The target path. 18 depends on the workpiece surface to be measured 10 such that the workpiece surface 10 throughout the entire measurement within the measuring range 14 (cf.) Fig. 1, Fig. 4) is ordered. The determination of the target path 18 This is done based on empirical data.

[0046] This is done by an unseen user in a programming environment. 20 or generally in a control unit 21 the desired target path 18 specified. Depending on the target path. 18 is from the programming environment 20 an exercise program 22for the axle control 16 generated so that the measuring beam 31 or the reference arm 12 so along the workpiece surface 10 is caused to the workpiece surface 10 throughout the entire measurement within the measuring range 14 (cf.) Fig. 4) is located. Based on the exercise program 22 Preferably, the movement of the manipulator not shown will also be included. 4 or the second deflection unit 11 influenced.

[0047] Furthermore, in the programming environment 20 , especially by the user, a standardization line 23 specified, which in Fig. Figure 4 shows the normalization line. 23 is in the illustrated embodiment (see Fig. 4) as well as the target path 18 above the workpiece surface 10 arranged. The normalizing line 23 is stored as a data set in the control unit 21determined. Based on the normalization curve. 23 is in a computing unit 24 (cf.) Fig. 3) a planning route length l p of the reference arm 12 determined. The planning route length l p could one according to Fig. 4 as distance between one in the measuring device 1 , especially in the measuring scanner 6 , located, system-internal reference point 25 and one on the normalization line 23 lying normalization point 26 View. Ultimately, the planning distance is l p However, this is a fictitious value that does not necessarily have to correspond to the actual measurement method. The planning path length l p is stored in a storage unit 27 saved.

[0048] The measurement itself is carried out according to Fig. 3 by the coherence tomograph 28 performed using coherence tomography. 28 can the actual distance d m from zero15 of the measuring range 14 up to the workpiece surface 10 (cf.) Fig. 4) be determined. In addition, an optical actual path length l is determined. i determines which extends from a scan head not shown to the zero point 15 of the measuring range 14 extends. In addition to the optical actual path length l i will the actual distance d m and also the planning route length l p in the storage unit 27 as a measurement data set 29 deposited.

[0049] In order to compensate for the interference, the measurement data set is 29 according to Fig. 3 from the computing unit 24 further processed. For this purpose, a standard distance d is used for each individual measurement. n (cf.) Fig. 4) determined. In order to determine the standard distance d for the illustrated embodiment. n To determine this, the sum of the actual optical path lengths l must first be calculated. iand the measured actual distance d m The result is calculated. This yields a value for further processing. The difference between this value and the planned route length l is then calculated. p formed. The value calculated in this way is the standard distance d. n This is a reference to the normalization line. 23 referenced distance, which is thereby normalized.

[0050] The same procedure can be used for multiple measuring points. 17 The procedure is carried out whereby for each measuring point 17 an individual planning route length l p , the measured actual distance d m as well as the optical actual path length l i determined and in the storage unit 27 to be recorded. By stringing together several actual measurement points. 17 The current path will be used. 19 trained.

[0051] The following description of the items in the Fig. 5 to Fig. The 6 alternative embodiments shown are for features that differ from those in the Fig. Since the first embodiment shown in section 4 is identical and / or at least comparable in its design and / or mode of operation, the same reference numerals are used. Unless these are explained in detail again, their design and / or mode of operation corresponds to the design and mode of operation of the features already described above.

[0052] This shows Fig. 5. A second embodiment for normalizing the disturbances. Here, the target path is 18 and also the normalization line 23 below the workpiece 3 arranged. The calculated value for determining the standard distance d n is calculated from the difference in the actual path length l i and the actual distance d m formed. The standard distance d n will continue to be calculated from the difference in the planning route length l pcalculated value.

[0053] In a further embodiment not shown, it is also conceivable that the normalizing line 23 above the workpiece 3 and the target path 18 below the workpiece 3 is arranged. Furthermore, it is conceivable that the target path 18 above the workpiece 3 and the normalization line 23 below the workpiece 3 is arranged. It is advantageous if their position is relative to the workpiece surface. 10 during the entire measurement, i.e., that it remains either above or below the workpiece surface. 10 condition.

[0054] In Fig. 6 is a complete survey of the material surface 10 over three measuring points 17 The target path is shown. 18 is according to the workpiece surface assumed by the user 10trained. The standardization line 23 is arranged as a straight line in Cartesian space and is partially identical to the intended path 18 Depending on the target path 18 is from the programming environment 20 an exercise program 22 for the axle control 16 generated (cf.) Fig. 3), so that all three measuring points 17 from the measuring scanner 6 They are controlled sequentially. Due to the inertia of the axis control. 16 will the measuring points 17 however, not according to the planned path 18 not controlled, but subject to interference. This causes the zero points to be affected. 15 per measuring point 17 not on track 18 , but above or below it. By connecting the individual zero points 15 The actual path will be 18 trained.

[0055] From the measuring scanner 6 starting from the respective zero point 15is then performed for each measuring point 17 the actual path length l i determined. Furthermore, the coherence tomograph (not shown) is used. 28 for each measuring point 17 from the zero point 15 starting from the current distance d m determined. Likewise, for each measuring point 17 an associated planning path length l p determined. The planning route length l p extends from the system's internal reference point 25 starting from the normalization point 26 The calculation of the standard distance d n This is done, as already described, by calculating the difference between the calculated value and the planned route length l. p The calculated standard distances d n They can then be analyzed and further processed using mathematical evaluation algorithms.

[0056] In Fig. Figure 7 shows schematically how the standard distances d nin a path-dependent diagram 23 can be represented. The diagram indicates this. 23 an x-axis. The measurement points are located on the x-axis. 14 applied, which are evenly distributed across the measurement. Each measurement point 14 is in Fig. 7 according to the order in which they are measured in the diagram 30 applied and labelled. According to the diagram 23 Consequently, measurements were taken at seven points over the course of the scan. 17 the actual distances d m measured. Per measuring point 17 A standardized standard distance d was used. n calculated. Each of the calculated standard distances d n is on the y-axis of the diagram 23 applied for.

[0057] The present invention is not limited to the embodiments shown and described. Modifications within the scope of the claims are possible, as is a combination of the features, even if these are shown and described in different embodiments. Reference symbol list 1 measuring device 2 Surface topology 3 workpieces 4 Manipulator 5 processing scanners 6 measuring scanners 7 First deflection unit 8 processing beam 9 First Mirror 10 Workpiece surface 11 Second deflection unit 12 Reference arm 13 Second Mirror 14 Measuring range 15 Zero point 16-axis control 17 measuring points 18 Target path 19 Current route 20 Programming environment 21 Control unit 22 Exercise program 23 Normalization line 24 computing units 25 Reference point 26 Normalization point 27 storage units 28 coherence tomographs 29 measurement data set 30 Diagram 31 Measuring beam d m Actual distance d n Standard distance l i Actual path length l p Planning route length

Claims

[1] Measurement method for capturing a surface topology ( 2 ) of a workpiece ( 3 ) using a coherence tomograph ( 28 ), in which a measuring range ( 14 ) of a reference arm ( 12 ) of the coherence tomograph ( 28 ) by means of a manipulator ( 4 ) and / or a deflection unit ( 7 ; 11 ) along an actual path ( 19 ) is carried out, which is due to disturbances, in particular following errors of the manipulator ( 4 ), from a target path ( 18 ) deviates at least partially, and at at least one measuring point ( 17 ) the actual path ( 19 ) between a zero point ( 15 ) of the measuring range ( 14 ) and a workpiece surface ( 10 ) an actual distance (d m ) is measured, characterized by that to compensate for the interference influences for at least one measuring point ( 17 ) a planning route length (lp ) of the reference arm ( 12 ) is determined and that the measured actual distance (d m ) using the planning route length (l p ) to a standard distance (d n ) is standardized. [2] Measuring method according to the preceding claim, characterized by that for at least one measuring point ( 17 ) as input information for calculating the standard distance (d n ) a measurement data set ( 29 ), in particular an optical actual path length (l i ) of the reference arm ( 12 ) and the measured actual distance (d m ), and the planning route length (l p ), in particular in a storage unit ( 27 ). [3] Measuring method according to one or more of the preceding claims, characterized by that the standard distance (d n ) from the difference between one from the measurement data set ( 29) calculated value, in particular from the sum or difference of the actual optical path length (l i ) and the measured actual distance (d m ), and the planning route length (l p ) is calculated. [4] Measuring method according to one or more of the preceding claims, characterized by that to normalize several measured actual distances (d m ) a normalization curve ( 23 ) is determined, in particular by a user based on experience. [5] Measuring method according to one or more of the preceding claims, characterized by that the normalization line ( 23 ) regardless of the target path ( 18 ) or is defined depending on this, where the normalization line ( 23 ) preferably at least partially identical to the target path ( 18 ) is, is similar to it and / or at least individual values, especially the start and / or end value, are identical to it. [6] Measuring method according to one or more of the preceding claims, characterized by that the normalization line ( 23 ) defined at least partially as a straight line and / or curve and / or at least partially above and / or below the workpiece surface ( 10 ) is ordered. [7] Measuring method according to one or more of the preceding claims, characterized by that based on the normalization curve ( 23 ), in particular by means of a computing unit ( 24 ), for each individual measuring point ( 17 ) the associated planning route length (l p ) of the reference arm ( 12 ) is determined and / or stored. [8] Measuring method according to one or more of the preceding claims, characterized by that the planning route length (l p ) depending on the respective measuring point ( 17 ) as the distance between the normalizing line ( 23 ) and an internal reference point ( 25 ) is determined. [9] Measuring method according to one or more of the preceding claims, characterized by that depending on the target path ( 18 ) and / or the normalization line ( 23 ) an exercise program ( 22 ) for the deflection unit ( 7 ; 11 ) and / or the manipulator ( 4 ) is generated. [10] Measuring method according to one or more of the preceding claims, characterized by that the target path ( 18 ) is determined before the measurement in such a way that the workpiece surface to be measured ( 10 ) within the measuring range ( 14 ) is located when it is on the intended path ( 18 ) is moved along. [11] Measuring method according to one or more of the preceding claims, characterized by that the target path ( 18 ) is adjusted so that the optical actual path length (l i ) of the reference arm ( 12 ) during which it is adjusted. [12] Measuring method according to one or more of the preceding claims, characterized by that in a diagram, especially one that is dependent on path and / or time ( 30 ) using the calculated standard distances (d n ) a standardized scan of the workpiece ( 3 ) is generated. [13] Measuring method according to one or more of the preceding claims, characterized by that the standardized scan of the workpiece ( 3 ) is analyzed using evaluation algorithms. [14] Measuring method according to one or more of the preceding claims, characterized by that several standardized scans are combined to create a height map. [15] Measuring device ( 1 ) to capture a surface topology ( 2 ) of a workpiece ( 3 ) with a coherence tomograph ( 28 ) to measure an actual distance (d m ) between a zero point ( 15 ) of a measuring range ( 14) of the coherence tomograph ( 28 ) and a workpiece surface ( 10 ), a manipulator ( 4 ) and / or a deflection unit ( 7 ; 11 ) to guide the measuring range ( 14 ) along an actual path ( 19 ), and a computing unit ( 24 ) to compensate for measurement errors, especially trailing errors, characterized by that the computing unit ( 24 ) is designed in such a way that the measured actual distance (d m ) using a measuring method according to one or more of the preceding claims to obtain a standard distance (d n ) can be standardized.

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