JP2019109208A - Surface flaw depth determination device - Google Patents

Abstract

To provide a surface flaw depth determination device capable of accurately determining the depth of even a surface flaw such as a surface crack with a relatively steep shape change that can occur in a steel piece.SOLUTION: A surface flaw depth determination device 100 includes shape measurement devices 2 arranged along lateral faces of a steel piece B for measuring the shapes of the lateral faces of the steel piece by one-dimensional array ultrasonic probes 1 and an optical cutting method, and a signal processing device 3 for generating a two-dimensional image relating to a cross section in a direction orthogonal to a longitudinal direction of the steel piece by applying signal processing to a flaw detection signal outputted from the ultrasonic probe, and determining the depth of a surface flaw that has occurred on a lateral face of the steep piece. The signal processing device detects a surface flaw that occurred on a lateral face of the steel piece on the basis of shape measurement data acquired by the shape measurement devices, and determines the depth of the detected surface flaw on the basis of shape measurement data in the vicinity of the detected surface flaw and the density of the two-dimensional image.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a surface flaw depth determination apparatus. In particular, the present invention relates to a surface flaw depth judging device capable of accurately judging the depth of a surface flaw such as a surface crack accompanied by a relatively sharp shape change generated in a steel piece.

Conventionally, ultrasonic flaw detection methods are widely used to guarantee the quality of billets.
In recent years, as a method capable of accurately determining the position of generated flaws among ultrasonic flaw detection methods, a two-dimensional imaging method using a one-dimensional array-type ultrasonic probe having a plurality of transducers is used. Ultrasonic flaw detection methods are attracting attention.

Specifically, a one-dimensional array type ultrasonic probe is disposed along the side of a steel piece, and a flaw detection signal is output when the one-dimensional array type ultrasonic probe receives an echo from the steel piece By applying signal processing (aperture synthesis processing, TFM (Total Focusing Method), etc.), a two-dimensional image of a cross section in a direction orthogonal to the longitudinal direction of the steel piece is generated, and this two-dimensional image is used to detect defects. An ultrasonic flaw detection method is proposed (see, for example, Patent Documents 1 and 2). Aperture synthesis processing or TFM used as a two-dimensional imaging method divides the coordinate space of the cross section of the test material such as a steel piece in the direction opposite to the one-dimensional array ultrasonic probe into meshes, The propagation time and amplitude value of the flaw detection signal from the reflection source simultaneously measured at multiple points with the probe type ultrasound probe based on the positional relationship between the material to be detected and the one-dimensional array type ultrasound probe and the sound velocity information This is a method of reconstructing the image of the reflection source by integrating in a predetermined mesh.
According to the ultrasonic flaw detection method using the above two-dimensional imaging method, since a two-dimensional image having high spatial resolution can be generated, the position of the flaw in the flaw detection region of each one-dimensional array type ultrasonic probe Can be accurately determined.

  However, in the ultrasonic flaw detection method using the above two-dimensional imaging method, the depth direction (from the surface layer to the surface layer) in the two-dimensional image is caused by the influence of noise (bottom surface echo etc.) generated in the surface layer (side surface of steel). In general, a predetermined range in the vertical direction is considered as a dead zone corresponding to a flaw detection frequency. For example, when the flaw detection frequency is 3 MHz, about 2 mm from the surface layer is considered as a dead zone. For this reason, for example, when a surface crack accompanied by a shape change from the surface layer to the depth direction is generated in the steel piece, the depth of the surface crack is evaluated smaller than the actual, or not generated in the surface layer but generated inside the steel piece. There is also a possibility that it may be misjudged to be a flaw. There is also a possibility that surface cracks can not be detected.

  In order to detect flaws accompanied by a shape change from the surface to the depth direction like surface cracks, not the ultrasonic flaw detection method but the laser light source and the imaging means are provided and the shape of the side of the steel is measured by the light cutting method It is conceivable to detect a flaw based on the shape change measured by this shape measuring device using a shape measuring device.

However, surface cracks that occur in billets often involve relatively sharp shape changes. For this reason, as shown in FIG. 1A, depending on the relationship between the shape of the surface flaw (surface crack) and the direction of the imaging means, the shape of the flaw may be able to be measured accurately. As shown in b), it may not be possible to measure the shape of the deep part of the flaw. That is, by leaving the field of view of the imaging means, there may be a location where the shape measurement data is missing (a location indicated by a white circle in FIG. 1B).
If the shape measurement data is missing, even if it is possible to detect surface flaws, the depth may be determined smaller than the actual depth. That is, when the shape measuring device is used alone, it may be difficult to accurately determine the depth of surface flaws generated in the steel piece.
In addition, in FIG. 1, the code | symbol B is attached | subjected to the steel piece and the code | symbol Y is attached | subjected to the longitudinal direction of the steel piece B. As shown in FIG. The same applies to FIG. 2 described later.

  FIG. 2 illustrates the problems in the surface flaw depth determination by the ultrasonic flaw detection method using the conventional two-dimensional imaging method described above and the problems in the surface flaw depth determination by the light cutting method FIG. Fig.2 (a) shows the problem of the light cutting method when the surface flaw depth is shallow, and Fig.2 (b) shows the problem of the light cutting method when the surface flaw depth is medium, (C) shows the problem of the light cutting method when the depth of surface flaws is deep. Fig. 2 (d) shows the problems of the ultrasonic flaw detection method when the surface flaw depth is shallow, and Fig. 2 (e) shows the problems of the ultrasonic flaw detection method when the surface flaw depth is medium, FIG. 2 (f) shows the problem of the ultrasonic flaw detection method when the depth of surface flaws is deep. Specifically, FIGS. 2 (d) to 2 (f) show an example of a two-dimensional image of a cross section of a steel slab generated by the ultrasonic flaw detection method. Further, the hatched area in FIG. 2 means a dead zone in a surface layer portion (for example, in a range of about 2 mm from the surface layer (side surface of a steel slab) when the flaw detection frequency is 3 MHz) in the ultrasonic flaw detection method.

As shown in FIGS. 2 (a) to 2 (c), according to the light-section method, the shape measurement data is deficient (FIG. 2 (a) to 2 (c)) by being out of the field of view of the imaging means. Even if it is possible to detect the surface flaw itself, the depth may be determined to be smaller than the actual depth, and any surface flaw may be erroneously determined to be equivalent depth even if the detection of the surface flaw itself is possible. is there.
Further, in the example shown in FIG. 2D, since the entire surface flaw is located in the dead zone of the surface layer portion, the surface flaw can not be detected by the ultrasonic flaw detection method.
Furthermore, as shown in FIGS. 2 (e) and 2 (f), according to the ultrasonic flaw detection method, even if it is possible to detect the deep portion located inside the dead zone of the surface layer among the surface flaws, Since the surface layer part located can not be detected, there is a possibility that the depth of the surface flaw may be judged smaller than the actual, or it may be erroneously judged as the flaw generated not inside the surface layer part but inside the steel piece.

JP, 2011-203037, A JP, 2009-236668, A

  Therefore, the present invention is to provide a surface flaw depth judging device capable of accurately judging the depth of surface flaws such as surface cracks with relatively sharp shape change generated in steel slabs. As an issue.

  In order to solve the above problems, as a result of intensive investigations by the present inventors, it is possible to execute both an ultrasonic flaw detection method using a two-dimensional imaging method and an optical cutting method, and an ultrasonic wave using a two-dimensional imaging method The depth of the surface flaw is obtained by combining the advantages of the flaw detection method (the position of the deep portion of the surface flaw can be accurately determined) and the advantages of the light cutting method (the position and the shape of the surface layer of the surface flaw can be accurately determined). In the present invention, the present invention has been completed.

  That is, in order to solve the above problems, according to the present invention, there is provided a one-dimensional array type ultrasonic probe disposed along a side surface of a steel billet, and the present invention is arranged along a side surface of the steel billet according to a light cutting method. A shape measuring device for measuring the shape of the side surface of the steel piece and signal processing on the flaw detection signal outputted from the one-dimensional array ultrasonic probe, a direction orthogonal to the longitudinal direction of the steel piece A two-dimensional image of the cross section of the steel piece, and measuring the shape of the side surface of the steel piece by the shape measuring device, based on the shape measurement data obtained and the generated two-dimensional image; And a signal processing device that determines the depth of surface flaws generated on the side surface.

According to the surface flaw depth judging device according to the present invention, the signal processing device is based on the shape measurement data obtained by the shape measuring device using the light cutting method, the surface layer of the surface flaw generated on the side of the steel piece It is possible to detect the part accurately (the position and the shape of the surface layer part of the surface flaw can be accurately determined). In addition, the signal processing device can accurately detect the deep portion of the surface flaw generated on the side of the steel piece based on the two-dimensional image generated using the flaw detection signal output from the one-dimensional array ultrasonic probe ( The position of the deep part of the surface flaw can be determined with high accuracy). For this reason, the signal processing apparatus measures shape measurement data in the vicinity of the surface flaw (surface layer portion of the surface flaw) detected based on the shape measurement data (data of a portion positioned in the vicinity of the surface layer portion of the surface flaw). It is possible to determine the depth of the surface layer of surface flaws based on In addition, the depth of the surface flaw is determined based on the density of the two-dimensional image in the vicinity of the detected surface flaw (the density of pixels located in the vicinity of the surface layer of the surface flaw among the pixels constituting the two-dimensional image) It is possible. That is, since a pixel having a density equal to or higher than a predetermined threshold can be considered to be a pixel corresponding to a surface flaw, the depth of the surface flaw is determined based on the pixel corresponding to the surface flaw. It is possible. Therefore, the depth of the surface flaw can be determined with high accuracy by taking into consideration the depth of the surface layer of the surface flaw determined based on the shape measurement data and the depth of the depth of the surface flaw determined based on the density of the two-dimensional image is there.
In the surface flaw depth determination apparatus according to the present invention, the shape measurement data is used as a trigger for surface flaw detection (that is, the surface layer portion of the surface flaw is first detected based on the shape measurement data and then detected). Since the depth of the surface flaw is determined using the density of the two-dimensional image in the vicinity of the position), it is not necessary to make the vicinity of the surface layer of the two-dimensional image a dead zone as in the prior art.

  Specifically, the signal processing device detects a portion where the shape measurement data is missing and uses the first step as a starting point, and the pixels constituting the two-dimensional image with respect to the starting point. A second step of identifying a pixel located in the depth direction of the billet and having a concentration equal to or more than a predetermined threshold value, and of the pixels identified in the second step, the most from the side face of the billet Preferably, the method further comprises the third step of determining the depth of the surface flaw based on the position of the separated pixel.

  According to the above preferable configuration, the first step performed by the signal processing device enables detection of surface flaws such as surface cracks accompanied by a sharp shape change such that shape measurement data is lost (position of surface layer portion of surface flaws) (The point of origin can be detected). Next, since surface flaws such as surface cracks generated in the steel piece progress in the depth direction of the steel piece, the second step performed by the signal processing device is the first of the pixels constituting the two-dimensional image. It is possible to specify a pixel corresponding to the surface flaw detected in one step. Finally, in the third step performed by the signal processing apparatus, the depth of the surface flaw can be accurately determined by specifying the position of the most distant pixel, that is, the pixel corresponding to the deepest portion of the surface flaw. It is possible.

  Preferably, in the second step, a plurality of threshold values are set according to the distance from the side surface of the billet, and the plurality of threshold values are smaller as they are separated from the side surface of the billet.

  When a flaw detection signal of a surface flaw such as a surface crack generated in a steel piece is two-dimensionally imaged, the strength of the flaw detection signal tends to decrease as the depth increases. For this reason, as in the above-described preferable configuration, by setting the threshold value smaller as it is separated from the side surface of the steel piece, the pixel corresponding to the surface flaw is accurately identified, and the depth of the surface flaw is accurate. It is possible to determine.

  According to the present invention, it is possible to accurately determine the depth of a surface crack such as a surface crack accompanied by a relatively sharp shape change generated in a steel piece.

It is explanatory drawing explaining the problem in the depth determination of the surface flaw by the light cutting method. It is explanatory drawing explaining the problem in the depth determination of the surface flaw by the ultrasonic flaw detection method using the conventional two-dimensional imaging method, and the problem in the depth determination of the surface flaw by the light cutting method. It is a schematic block diagram of the depth judging device of a surface crack concerning one embodiment of the present invention. It is explanatory drawing explaining each step which the signal processing apparatus shown in FIG. 3 performs.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings.
FIG. 3 is a schematic block diagram of a surface flaw depth determination apparatus according to an embodiment of the present invention. FIG. 3A is an overall configuration diagram. FIG. 3B is an enlarged view of the one-dimensional array ultrasonic probe as viewed in the direction of arrow Y in FIG. 3A. FIG.3 (c) is an enlarged view of the shape measuring apparatus seen from the arrow mark Y direction of Fig.3 (a).
As shown in FIG. 3, the surface flaw depth determination device (hereinafter, appropriately referred to as “depth determination device”) 100 according to the present embodiment includes a one-dimensional array type ultrasonic probe 1 and a shape measurement device 2. And the signal processing device 3.

The one-dimensional array type ultrasonic probe (hereinafter referred to as “ultrasound probe” as appropriate) 1 of the present embodiment is a steel piece (hereinafter referred to as billet) B having a substantially rectangular cross section conveyed by the conveyance roll R There are four arranged along each side of. The ultrasound probe 1 includes a plurality of (for example, 64) transducers 11 arranged in one direction. The ultrasound probe 1 is disposed such that the arrangement direction of the transducers 11 is substantially parallel to the side surfaces of the billet B.
Further, a shoe (not shown) made of resin is attached to the ultrasonic probe 1, and a contact medium such as water is introduced between the shoe and the side surface of the billet B. The ultrasonic wave transmitted from the ultrasonic probe 1 is incident on the inside of the billet B from the side surface of the billet B facing the ultrasonic probe 1 via the shoe and the contact medium, and the defect present in the billet B The echo reflected at the point is received by the ultrasound probe 1 through the contact medium and the shoe.

  The four shape measurement devices 2 of the present embodiment are arranged along each side surface of the billet B. The shape measuring device 2 is provided with a laser light source (not shown) for emitting a laser slit light 2L extending in the direction (X direction or Z direction) orthogonal to the longitudinal direction (Y direction) of the billet B along the side of the billet B And an imaging unit (not shown) for imaging the laser slit light 2L, and is an apparatus for measuring the shape of the side surface of the billet B by a light cutting method.

The signal processing device 3 of the present embodiment controls transmission and reception of ultrasonic waves from each of the four ultrasonic probes 1 and irradiation and imaging of the laser slit light 2 L from each of the four shape measurement devices 2. In addition, the signal processing device 3 performs signal processing on flaw detection signals output from the four ultrasonic probes 1 to obtain a cross section in a direction orthogonal to the longitudinal direction (Y direction) of the billet B. Generate a two-dimensional image. The signal processing device 3 combines the generated two-dimensional images (total four two-dimensional images) of each ultrasonic probe 1 as necessary to generate an entire two-dimensional image of the entire one cross section of the billet B It is also possible.
The signal processing device 3 according to the present embodiment performs aperture combining processing as signal processing, and generates an aperture combined image as a two-dimensional image. In addition, the signal processing device 3 of the present embodiment does not generate an entire two-dimensional image (whole aperture synthetic image), but uses four aperture synthetic images for each ultrasonic probe 1 individually to produce an aperture synthetic image. The following determination is made each time.
The signal processing device 3 generates a plurality of aperture composite images in the longitudinal direction in a state where the billet B is conveyed in the longitudinal direction (direction of arrow Y) by the roll R. Specifically, a plurality of aperture composite images are generated in the longitudinal direction of the billet B, for example, at a pitch of 10 mm.

  The signal processing device 3 controls the transmission and reception of the above-mentioned ultrasonic waves by including known means provided in a so-called flaw detector such as a pulser, a receiver, an amplifier, an A / D converter, and a waveform memory. Further, the signal processing device 3 generates an aperture composite image by performing aperture combining processing on the flaw detection signal stored in the waveform memory. Then, the signal processing device 3 generates surface flaws generated on the side surface of the billet B based on the shape measurement data obtained by measuring the shape of the side surface of the billet B by the shape measurement device 2 and the generated aperture composite image. In order to determine the depth of the program, a predetermined program that executes each step described later is installed. In addition, since the well-known content as described in the above-mentioned patent document 2 is applicable, for example about the opening synthetic | combination processing, description of the specific content is abbreviate | omitted here.

  The signal processing device 3 performs the following first to third steps in order to determine the depth of surface flaws generated on the side surface of the billet B. Hereinafter, each step performed by the signal processing device 3 will be sequentially described with reference to FIG. 4 as appropriate.

<First step>
In the first step, the signal processing device 3 detects a point where the shape measurement data obtained by measuring the shape of each side of the billet B by the four shape measuring devices 2 is detected as a starting point .
Specifically, as shown in FIG. 4A, the signal processing device 3 has a standard curvature of the corner according to the size of the billet B based on the information input from the process computer (not shown). Identify the radius r. Next, the signal processing device 3 minimizes the circle with the radius of curvature r (the circle indicated by a symbol r in FIG. 4A) in the shape measurement data obtained by combining the four shape measurement data obtained by the four shape measurement devices 3 Shape measurement data (flat portion measurement data) of a portion corresponding to the flat side surface (flat side surface if there is no crack) of the billet B located between the contacts of each circle r and each shape measurement data after fitting by the square method or the like Identify). Finally, the signal processing device 3 detects a portion where there is no shape measurement data in the allowable area in the depth direction (the hatched area shown in FIG. 4A) based on the flat portion measurement data. Let this be the starting point S0.

  The signal processing device 3 resamples the shape measurement data obtained by the shape measurement device 2 according to the resolution of the aperture synthetic image, and aligns the position measurement data with the aperture synthetic image. In the present embodiment, as described above, in the state where the billet B is transported in the longitudinal direction (Y direction), a plurality of aperture composite images are generated at a pitch of 10 mm, for example. The ultrasonic probe 1 also has a Y direction of 10 mm / voxel. Further, the resolution of the aperture synthetic image generated for the pair of ultrasonic probes 1 facing in the X direction in FIG. 3 is 2.5 mm / voxel in resolution direction of the transducers 11 (Z direction in FIG. 3). The resolution of the ultrasonic wave transmission direction (X direction) is 0.15 mm / voxel. Similarly, the resolution of the aperture synthetic image generated for the other pair of ultrasonic probes 1 facing in the Z direction is 2.5 mm / voxel in resolution of the arrangement direction (X direction) of the transducers 11, The resolution of the transmission direction (Z direction) of is 0.15 mm / voxel. The signal processing device 3 resamples the shape measurement data with the same resolution in accordance with the resolution of the aperture composite image, and aligns with the voxels forming the aperture composite image (alignment in the X, Y, and Z directions) )I do. The geometrical positional relationship between the ultrasonic probe 1 and the shape measuring device 2 in the XZ plane is used for the alignment in the X direction and the Z direction. In addition, for alignment in the Y direction, the geometrical positional relationship between the ultrasonic probe 1 and the shape measuring device 2 in the Y direction and the transport speed of the billet B measured by a speed sensor (not shown) Is used. In general, since the resolution of the shape measurement data obtained by the shape measuring device 23 is higher than the resolution of the aperture synthetic image, a series expansion is applied to the shape measurement data as necessary in the above resampling. It is desirable to interpolate data.

Second step
In the second step, the signal processing device 3 forms an aperture synthetic image because the aperture synthetic image is generated in a state in which the billet B is conveyed in the longitudinal direction, which constitutes the aperture synthetic image. In the following description, the case where the pixels constituting the aperture composite image are voxels will be described)), which is located in the depth direction of the billet B with respect to the starting point S0, and Identify voxels having a density above the threshold.
Specifically, as shown in FIG. 4B, the signal processing unit 3 determines the density of each voxel Bi (i.gtoreq.1) of the aperture composite image located immediately below the starting point S0 with respect to the starting point S0. A threshold value set in advance is compared in order from voxel B1, and a voxel Bi having a density equal to or higher than the set threshold value is specified. At this time, in the present embodiment, a plurality of threshold values are set according to the distance from the side surface of the billet B (the side surface where the starting point S0 exists), and the plurality of threshold values are separated from the side surface of the billet B It is considered to be small.

More specifically, in the present embodiment, two threshold values Th1 and Th2 are set, and Th2 <Th1. The signal processing device 3 compares the density of each voxel Bi with the threshold Th1 in order from the voxel B1 closest to the starting point S0, and specifies the voxel Bi having a density equal to or higher than the threshold Th1. Then, when there is no voxel Bi having a density equal to or higher than the threshold Th1, the threshold Th1 is switched to the threshold Th2. The signal processing device 3 determines the concentration of each voxel Bi and the threshold Th2 for the voxel Bi located below the voxel Bi which has a concentration equal to or higher than the threshold Th1 and is located farthest from the side surface of the billet B. And a voxel Bi having a density equal to or greater than a threshold Th2 is identified.
In the example shown in FIG. 4B, voxels B1 and B2 are specified as voxels having a density equal to or higher than the threshold Th1, and voxels B3 and B4 are specified to have a density equal to or higher than the threshold Th2.

<Third step>
In the third step, the signal processing device 3 determines the depth of the surface flaw based on the position of the voxel Bi most distant from the side surface of the billet B among the voxels Bi specified in the second step.
Specifically, in the example shown in FIG. 4C, the signal processing device 3 selects one of the voxels B1 to B4 specified in the second step, based on the position of the voxel B4 most distant from the side surface of the billet B. Determine the surface flaw depth. More specifically, by replacing the coordinates of the starting point S0 with the coordinates of the voxel B4, as shown by a thick line in FIG. 4C, the shape measurement data is corrected, and the surface is corrected based on the corrected shape measurement data. Determine the flaw depth H.

According to the depth determination device 100 according to the present embodiment described above, the signal processing device 3 is generated on the side surface of the billet B based on the shape measurement data obtained by the shape measurement device 2 using the light cutting method. It is possible to accurately detect the surface layer portion of the surface flaw (determine the position and shape of the surface layer portion of the surface flaw with high accuracy). In addition, the signal processing device 3 can accurately detect the deep portion of the surface flaw generated on the side surface of the billet B based on the aperture composite image generated using the flaw detection signal output from the ultrasonic probe 1 (surface flaw The position of the deep part of can be determined with high accuracy). For this reason, the signal processing device 3 detects the shape measurement data in the vicinity of the surface flaw (surface layer portion of the surface flaw) detected based on the shape measurement data (data of the portion located in the vicinity of the surface layer portion of the surface flaw). It is possible to determine the depth of the surface layer portion of the surface flaw on the basis of. In addition, the depth of the surface flaw is determined based on the density of the aperture synthetic image in the vicinity of the detected surface flaw (the density of pixels located in the vicinity of the surface layer of the surface flaw among the voxels constituting the aperture synthetic image) It is possible. That is, since it is possible to consider that a voxel having a density equal to or higher than a predetermined threshold value Th1 or Th2 is a pixel corresponding to a surface flaw, the depth of a deep portion of the surface flaw is determined based on the voxel corresponding to the surface flaw. It is possible to determine
Therefore, based on the shape measurement data corrected as described above (in other words, the depth of the surface layer portion of the surface flaw determined based on the shape measurement data and the depth of the surface flaw deep as determined based on the density of the aperture composite image And the depth H of the surface flaw can be determined with high accuracy.

1 ··· One-dimensional array type ultrasonic probe 2 ··· Shape measuring device 3 ··· Signal processing device 100 ··· Surface flaw depth judging device B ··· Billet (steel billet)

Claims (3)

A one-dimensional array type ultrasound probe disposed along the side of the billet,
A shape measuring device which is disposed along the side of the billet and measures the shape of the side of the billet by a light cutting method;
A signal processing is performed on a flaw detection signal output from the one-dimensional array type ultrasonic probe to generate a two-dimensional image of a cross section in a direction orthogonal to the longitudinal direction of the steel piece, and the shape measurement Signal processing to determine the depth of surface flaws generated on the side surface of the steel piece based on the shape measurement data obtained by measuring the shape of the side surface of the steel piece using the device and the generated two-dimensional image A device,
A surface flaw depth determination apparatus comprising: The signal processing device
A first step of detecting and detecting a portion where the shape measurement data is missing;
A second step of identifying, among the pixels constituting the two-dimensional image, a pixel located in the depth direction of the steel slab with respect to the origin and having a density equal to or greater than a predetermined threshold value;
Performing a third step of determining the depth of the surface flaw based on the position of the pixel most distant from the side surface of the steel piece among the pixels specified in the second step;
The surface flaw depth judging device according to claim 1 characterized by things. In the second step, a plurality of threshold values are set according to the distance from the side surface of the billet, and the plurality of threshold values are smaller as they are separated from the side surface of the billet,
The surface flaw depth determination apparatus according to claim 2, wherein the surface flaw is determined.