JP5194529B2 - Surface defect inspection system, method and program - Google Patents

Description

  The present invention relates to a surface defect inspection system, method, and program for detecting a surface defect of a measurement object such as a steel plate.

  In recent years, a light-cutting optical shape measuring method has been used in various fields. Even in a steel plate production line, the surface of a steel plate surface, such as dents and wrinkles, is emitted by irradiating the surface of the steel plate with linear laser light, imaging the surface of the steel plate with a delay integration camera, and outputting a light cut image. It has been proposed to detect defects (see Patent Document 1).

JP 2004-3930 A

  In the above-mentioned Patent Document 1, it is considered that a steel plate having a relatively flat surface is mainly assumed as a measurement object. For example, when a rail or a shaped steel is used as a measurement object, the surface is relatively flat. Instead of a surface, both ends may be curved surfaces that become lower (or higher).

  By the way, when the measurement object is conveyed in the longitudinal direction, the measurement object may meander or vibrate in the width direction. Then, if the surface of the measurement object is a curved surface as described above, image processing is performed only by slight deviation at the end of the measurement object due to meandering or vibration in the width direction. There is a risk of being recognized as a large shape change (unevenness) in (shading correction processing or the like).

  In addition, when the surface of the measurement object is a curved surface as described above, for example, in floating average processing (image processing that takes a difference between the original data and the data obtained by moving average processing in the width direction for each line) In the derived image, hunting may occur at sites corresponding to the steep shapes at both ends of the measurement object.

  Unevenness and hunting parts in these images after image processing are erroneously detected as surface defects when performing binarization processing for detecting surface defects and determining processing by calculating shape and unevenness information. There is.

  The present invention has been made in view of the above points, and it is an object of the present invention to improve surface defect detection accuracy even when the surface of a measurement object is not a flat surface in surface defect detection using a light-cut image. To do.

The surface defect inspection system of the present invention uses the irradiation means for irradiating the surface of the measurement object with a linear laser beam and the delay integration type imaging means for imaging the reflected light from the measurement object, and performs the measurement. While continuously shifting the irradiation position of the linear laser beam on the object, the reflected light from the measurement object is imaged by the imaging means and a light section image is output to detect a surface defect of the measurement object In the surface defect inspection system, the measurement object has a curve in which both end portions are lowered or raised in a cross-sectional shape, and includes the measurement object imaged by the imaging means or other imaging means Edge position detection means for detecting the edge position of the measurement object based on the luminance image, and an image obtained by the imaging means based on the edge position detected by the edge position detection means Centering processing means for performing centering processing, and first shape correction processing means for performing a fitting process using an even function on the image after the centering processing and performing a difference operation between the image after the fitting processing and the image after the centering processing When the only longitudinal direction of the predetermined length of the difference image the object to be measured after the operation and the average or integrated, the difference between the image after the average or the image subjected to the low pass filter process after the accumulated difference operation Second linear correction processing means for performing calculation or division calculation, wherein the linear laser beam is periodically modulated, and the luminance image is captured by the imaging means. And
The surface defect inspection method of the present invention uses the irradiation means for irradiating the surface of the measurement object with linear laser light and the delay integration type imaging means for imaging the reflected light from the measurement object. While continuously shifting the irradiation position of the linear laser beam on the object, the reflected light from the measurement object is imaged by the imaging means and a light section image is output to detect a surface defect of the measurement object In the surface defect inspection method, the measurement object has a curve in which both end portions become lower or higher in the cross-sectional shape, and includes the measurement object imaged by the imaging means or other imaging means A procedure for detecting an edge position of the measurement object based on the luminance image; a procedure for performing a centering process on the image obtained by the imaging means based on the detected edge position; Performing fitting processing by an even function to the image after the ring processing, the longitudinal direction of the fitting process after the image and the procedure of performing a difference operation between the image after the centering process, the measurement target image after the difference operation the average or integrated by a predetermined length, and a procedure for performing difference operation or division operation between the image after the average or accumulated image and the difference operation which has been subjected to low-pass filtering after, the linear laser The light is periodically modulated, and the luminance image is picked up by the image pickup means.
The program of the present invention uses an irradiation unit that irradiates the surface of a measurement object with linear laser light, and a delay integration type imaging unit that images reflected light from the measurement object. For continuously detecting the irradiation position of the linear laser light, imaging the reflected light from the measurement object by the imaging means, outputting a light cut image, and detecting a surface defect of the measurement object The measurement object is based on a luminance image including the measurement object imaged by the imaging means or other imaging means, having a curve in which both end portions become lower or higher in the cross-sectional shape. A procedure for detecting an edge position of the measurement object, a procedure for performing a centering process on the image obtained by the imaging means based on the detected edge position, and the centering Performing fitting processing by an even function to the image after physical, and procedures for performing a difference operation between the image after the centering process the image after the fitting process, the image after the difference operation in the longitudinal direction of the measurement target Average or integrate a predetermined length, and cause the computer to execute a procedure for performing a difference operation or a division operation between an image subjected to low-pass filter processing after the average or integration and the image after the difference calculation , and the linear The laser light is periodically modulated, and the luminance image is picked up by the image pickup means.

  According to the present invention, when the measurement object is a long material having a curve whose both end portions are low or high in the cross-sectional shape, when the measurement object meanders or vibrates in the width direction. In addition, the surface defect detection accuracy can be increased.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of a surface defect inspection system according to an embodiment of the present invention as viewed from a direction orthogonal to a moving direction of a measurement object 2. The surface defect inspection system according to the embodiment of the present invention includes a laser device 10, a rod lens 20, a delay integration camera (TDI camera) 30, a timing signal generator 40, an image processing device 50, and a display device 60. With.

  Such a surface defect inspection system measures the shape of the measuring object 2 optically by an optical cutting method. Here, as the measuring object 2, as shown in FIG. 2, a long length material (long length plate or bar) having a curved line that lowers (or increases) both upper end portions irradiated with laser light in a cross-sectional shape. Material), that is, a long material having a curved surface whose surface is lowered (or increased) at both ends, for example, a rail or a shape steel. In the present embodiment, it is assumed that the surface has a height difference of about 6 mm. The measuring object 2 is transported at a constant speed in the longitudinal direction (arrow in the figure), and the surface defect inspection system according to the present embodiment measures the shape of the measuring object 2 while it is being transported. Surface defects such as dents and wrinkles on the surface of the object 2 are detected. Note that the measurement object 2 is not limited to the long material, and it is obvious that the present invention can be applied to the short material.

  The laser device 10 generates a continuous wave laser beam. The rod lens 20 spreads the laser beam emitted from the laser device 10 in a fan shape along the width direction of the measurement object 2 (direction perpendicular to the paper surface of FIG. 1). Thereby, the laser beam emitted from the laser device 10 is irradiated onto the measurement object 2 as a linear laser beam. At this time, the linear laser light is incident obliquely on the surface of the measurement object 2. Thus, on the surface of the measuring object 2 irradiated with the linear laser beam, a linear bright part is formed along the width direction of the measuring object 2. Further, since the measurement object 2 moves in the longitudinal direction, when viewed from the measurement object 2, the linear bright part also moves along the longitudinal direction of the measurement object 2. The reflected light (linear reflected image) from such a linear bright part is picked up by the TDI camera 30.

  The timing signal generator 40 generates a sine waveform signal having a predetermined frequency ω, and sends the sine waveform signal to the laser device 10. The laser device 10 can continuously change its oscillation intensity by an external signal, and generates a laser beam whose output changes in a sine waveform when receiving a sine waveform signal sent from the timing signal generator 40. To do. That is, in this embodiment, the oscillation intensity of the laser light emitted from the laser device 10 is periodically modulated. The timing signal generator 40 generates a camera shift pulse signal having a frequency M times the frequency ω, and sends the camera shift pulse signal to the delay integration camera 30. The laser device 10 can be configured using a semiconductor laser. In addition to continuous oscillation, the laser device 10 may oscillate a pulse at a frequency several digits higher than the frequency ω to modulate the peak intensity of the pulse.

  The TDI camera 30 captures a linear reflection image of the moving measurement object 2. FIG. 3 is a diagram for explaining the structure and operation of the TDI camera. In the TDI camera 30, as shown in FIG. 3A, a large number of photoelectric conversion elements 35 are arranged in a matrix on the light receiving surface. Here, for example, it is assumed that n photoelectric conversion elements 35 are arranged in the row direction and N in the column direction. Each row is numbered sequentially from the top with the top row as the first row, and each column is numbered sequentially from the left with the leftmost column as the first column.

  The photoelectric conversion element 35 accumulates charges corresponding to the intensity of the received light. In the present embodiment, it is assumed that the linear reflection image of the measurement object 2 is incident on the photoelectric conversion element 35 with a width corresponding to one row via the lens 31 of the TDI camera 30. In the TDI camera 30, each photoelectric conversion element 35 transfers the accumulated charge to a photoelectric conversion element located in the same row as the photoelectric conversion element 35 and located in the next column. The timing of this transfer is the same for all the photoelectric conversion elements 35, and is controlled by a camera shift pulse signal sent from the timing signal generator 40. That is, each time a camera shift pulse signal is input, each photoelectric conversion element 35 transfers charges. In this embodiment, the frequency of the camera shift pulse signal (camera shift frequency) is Mω. Then, when the camera shift pulse signal is input, the photoelectric conversion element 35 located in the Nth column (final column) sends the accumulated charge to the read register. In synchronization with the movement of the linear reflection image on the light-receiving surface due to the movement of the measurement object 2, the charge corresponding to the linear reflection image is sequentially transferred by the camera shift pulse signal in accordance with the camera shift pulse signal. The light cut image is output.

  In general, in the TDI camera 30, as shown in FIG. 3B, when light is incident on each photoelectric conversion element 35 while the charge is being transferred, a charge corresponding to the intensity of the incident light is added. Is done. However, in this embodiment, as described above, a linear reflection image having a width corresponding to one column is incident on the photoelectric conversion element 35. For this reason, the charge is hardly added in each photoelectric conversion element 35 during the transfer of the charge. In particular, even when background light becomes a problem, this can be suppressed by installing an optical filter that transmits only the laser wavelength in front of the lens.

  Since the measuring object 2 moves along the longitudinal direction, the laser beam is irradiated from the laser device 10 onto the measuring object 2, and a linear reflection image of the measuring object 2 is used for a predetermined time using the TDI camera 30. When the image is taken, it is possible to sequentially obtain light-cut images at each position in the longitudinal direction of the measuring object 2. Therefore, an image representing the entire measurement object 2 can be obtained by sequentially arranging the light section images thus obtained.

  In this embodiment, the linear laser light is periodically modulated, and the intensity of the linear laser light changes with time, so that the amount of charge accumulated in each photoelectric conversion element in the column direction in each row The distribution of (light reception intensity) also changes periodically. Therefore, an image obtained by sequentially arranging the light section images output from the TDI camera 30 becomes a fringe image in which the density (intensity) of each light section image periodically changes along the array direction. . FIG. 4 shows an example of a stripe image. Here, the light section image corresponding to one period of density change is referred to as “stripe”. In such a striped image, the direction parallel to the stripe corresponds to the width direction of the measurement object 2, and the direction orthogonal to the stripe corresponds to the longitudinal direction of the measurement object 2. When the ratio of the camera shift frequency of the TDI camera 30 to the modulation frequency of the laser light is M: 1, M light-cut images, that is, M pixels in the arrangement direction form one stripe.

  By the way, since the laser beam is incident on the surface of the measurement object 2 at an angle, for example, if there is a recessed portion in the measurement object 2, the reflection point of the laser beam is shifted to the right in FIG. Therefore, the position of the light section image on the photoelectric conversion element 35 is also shifted in the column direction in the right side, that is, in FIG. For this reason, in the fringe image, the light cut image corresponding to the laser light reflected by the concave portion is output earlier in time than the light cut image corresponding to the laser light reflected by the non-dented portion. It will be. Therefore, in the image obtained by arranging the images output from the TDI camera 30 in order, the recessed portion can be clearly recognized as a stripe shift.

  This fringe shift will be described in more detail. FIG. 5A is a schematic enlarged view of a certain fringe image. In FIG. 5A, the position where the maximum density is given for each stripe is shown by a solid line. For example, in this fringe image, when the maximum density position is examined along the arrangement direction at the position A in the width direction, the maximum density positions are located at equal intervals, and no stripe deviation occurs. That is, the measurement object 2 has a flat shape at the position A in the width direction along the arrangement direction. In this case, the density distribution of the fringe image (slice fringe image data) along the arrangement direction at the position A in the width direction has a clean sine wave shape as shown in FIG.

  On the other hand, when the maximum density position is examined along the arrangement direction at the position B in the width direction shown in FIG. 5A, the interval between the maximum density positions gradually widens from the left to the right, and a stripe shift occurs. ing. That is, the measurement object 2 has a dent along the arrangement direction at the position B in the width direction. In this case, the density distribution (slice fringe image data) of the fringe image along the arrangement direction at the position B in the width direction is compared with the sine wave shown in FIG. 5B as shown in FIG. Out of phase. As described above, the fringe shift due to the dent of the measurement object 2 appears as a phase shift in the slice fringe image data. Actually, the phase shift and the dent (depth) of the measuring object 2 are in a proportional relationship. The greater the depth, the greater the phase shift in the slice fringe image data. In the surface defect inspection system of the present embodiment, information related to the phase shift is calculated based on the fringe image, and the shape of the measurement object 2 is measured based on the information related to the phase shift. If this method of calculating the phase shift is used, for example, when the ratio of the camera shift frequency to the modulation frequency of the laser beam is 4: 1, it is possible to detect the irregularity even if the stripe does not clearly shift by one pixel or more. There is sensitivity.

  Here, the fringe image shown in FIG. 4 is that of a measurement object having a flat surface. On the other hand, in the measurement object 2 assumed in the present embodiment, that is, a long material having a curve in which both end portions are lowered (or increased) in a cross-sectional shape such as a rail or a shape steel, it is shown in FIG. Thus, it becomes a fringe image in which both ends of each fringe are curved.

  Next, the relationship between the phase shift in the slice fringe image data and the depth of the measurement object 2 will be described. FIG. 7 is a diagram for explaining the relationship between the phase shift in the slice fringe image data and the depth of the measurement object 2.

  Now, as shown in FIG. 7, the incident angle at which the linear laser light is incident on the surface of the measuring object 2 is defined as θ. Further, it is assumed that the measurement object 2 has a recess, and the linear laser light is reflected at a depth d from the surface of the measurement object 2 and enters the TDI camera 30 when entering the recess. At this time, the linear laser beam reflected at the depth d is reflected by the distance h in the longitudinal direction (right direction) of the measuring object 2 as compared with the linear laser light reflected by the flat surface of the measuring object 2. The point shifts. Here, h = d · tan θ. As a result of the deviation of the reflection point of the linear laser beam by the distance h in the longitudinal direction, a phase shift occurs in the slice fringe image data. This phase shift is denoted by φ.

Assuming that the imaging resolution in the column direction of the photoelectric conversion element 35 in the TDI camera 30 is s (mm / pixel), the distance h that the reflection point of the linear laser beam is displaced in the longitudinal direction corresponds to the h / s pixel in the striped image. To do. When the ratio between the camera shift frequency of the TDI camera 30 and the modulation frequency of the laser beam is M: 1, M pixels in the arrangement direction form one stripe in the stripe image. That is, when the fringes are shifted by M pixels, the phase shift is 2π. Therefore, the phase shift φ in the slice fringe image data when the reflection point of the linear laser beam is shifted by the distance h in the longitudinal direction is
M / 2π = (h / s) / φ
Than,
d = {M · s / (2π · tan θ)} φ
It becomes. From this, it can be seen that the phase shift φ in the slice fringe image data and the depth d of the measurement object 2 are in a proportional relationship.

  Strictly speaking, when a normal lens is used, the imaging resolution s changes according to the depth d and needs to be corrected. However, as in the case of measuring a dent in a steel plate, the lens working distance is not affected. When the depth change is small, such a change in the imaging resolution s can be ignored in practice. If a telecentric lens is used, the imaging resolution s can be made constant regardless of the depth d.

  The image processing device 50 performs processing for generating an image representing the shape of the measurement object 2 based on each light cut image output from the TDI camera 30, and processing for detecting a defect based on the image. is there. FIG. 8 shows a schematic block diagram of the image processing apparatus 50. The image processing apparatus 50 includes an A / D conversion unit 501, a pre-filter unit 502, an orthogonal sine wave generation unit 503, low-pass filter units 504a and 504b, a phase calculation unit 505, a phase continuation processing unit 506, A centering processing unit 507, a shape correction processing unit 508, a defect detection processing unit 509, an amplitude calculation unit 510, and an edge position detection unit 511 are included. The results processed by each part of the image processing device 50 are displayed on the screen of the display device 60.

  FIG. 14 is a flowchart for explaining the processing operation of the image processing apparatus 50. Hereinafter, the processing operation of each unit of the image processing apparatus 50 will be described with reference to FIG.

  First, the TDI camera 30 images the measurement object 2 and outputs a light cut image (step S101). The A / D conversion unit 501 performs A / D conversion on each light-cut image output from the TDI camera 30 and outputs it as digital multilevel image data. Such digital multilevel image data is stored in an image memory (not shown). By arranging these digital multivalued image data in order, a fringe image is formed.

  From such a fringe image (or digital multi-valued image data), data representing the density distribution of the fringe image along the arrangement direction at each position in the width direction is generated. Data representing the density distribution of the stripe image along the arrangement direction is “slice stripe image data”. Slice fringe image data at each position in the width direction is sequentially output from the image memory.

  The pre-filter unit 502 removes noise and sharpens the stripe state by applying a predetermined filter process to each slice stripe image data. Note that the filtering process by the prefilter unit 502 is not necessarily performed. For example, it may be performed only when many fine noises are generated in the striped image.

Two pieces of slice fringe image data I _j (k) at each position j (j = 0, 1, 2,...) In the width direction are output from the prefilter unit 502. k (k = 0, 1, 2,...) is a position in the arrangement direction. At this time, it is assumed that the slice fringe image data I _j (k) at the position j in the width direction changes sinusoidally. That is,
I _j (k) = A (j, k) {cos ((2πk / M) + φ (j, k)) + 1}
It is. Here, A (j, k) is the amplitude of the slice fringe image data at the pixel position (j, k), and φ (j, k) is the phase shift of the slice fringe image data at the pixel position (j, k). . The influence of the fringe shift generated in the fringe image due to the depression of the measurement object 2 appears as a phase shift φ. Since the amplitude of the linear laser beam is constant, the amplitude A is usually constant. However, when the surface of the measuring object 2 is dirty, the amplitude A may decrease rapidly at the pixel position corresponding to the dirty position. Therefore, in the above equation, the amplitude A is written in a form depending on the pixel position (j, k).

The reason why “1” is added after the term of cos is to guarantee this because slice stripe image data (density value) I _j (k) does not become negative. Therefore, the slice fringe image data I _j (k) varies between 0 and 2A.

The orthogonal sine wave generation unit 503 generates two orthogonal reference sine wave data sin (2πk / M) and cos (2πk / M), which are created in advance on a memory such as a ROM. In particular, the former is also referred to as reference sin data, and the latter is also referred to as reference cos data. These two reference sine wave data are respectively multiplied by the slice fringe image data I _j (k) output from the prefilter unit 502. By this multiplication processing, the following two outputs Ia _j (k) and Ib _j (k) are obtained.

Each of the low-pass filter units 504a and 504b performs predetermined filter processing on the outputs Ia _j (k) and Ib _j (k) obtained by the above multiplication processing, thereby removing the fringe frequency component and its harmonic components. That is, a component including only the phase shift φ is extracted. If the output from the low-pass filter unit 504a is LPF (Ia _j (k)) and the output from the low-pass filter unit 504b is LPF (Ib _j (k)),
LPF (Ia _j (k)) = (A cos φ) / 2
LPF (Ib _j (k)) = − (A sin φ) / 2
It is.

  The phase calculation unit 505 calculates a phase shift φ (j, k) at each pixel position (j, k) based on the results output from the two low-pass filter units 504a and 504b (step S102). The phase shift φ (j, k) can be obtained from the following equation.

In the above equation, the arctan value range is set to −π / 2 to + π / 2, and information on the codes of LPF (Ia _j (k)) and LPF (Ib _j (k)) is used to shift the phase. φ is determined in the range of −π to + π. Here, the phase shift obtained in this range will be described again as φ ′. In this case, the phase shift φ ′ obtained by the above formula has a periodic relationship with the depth of the measurement object 2, and there are a plurality of depths that take a certain value of the phase shift φ ′. Therefore, accurate information on the shape of the measurement object 2 cannot be obtained by using such a phase shift φ ′. For this reason, it is necessary to obtain a phase shift φ that is proportional to the depth of the measurement object 2 from the phase shift φ ′. The process of obtaining a phase shift φ proportional to the depth is performed by the phase continuation processing unit 506. FIG. 9A shows an example of a phase image obtained by the phase calculation unit 505. FIG. 10A shows an example of a characteristic diagram showing the phase characteristics in the phase image.

  The phase continuation processing unit 506 detects discontinuous points of the phase shift φ ′ based on the phase image obtained by the phase calculation unit 505, and the phase shift φ ′ so that the phase shift φ ′ is smoothly connected. 'Is corrected (step S103). As described above, since the value range of the phase shift φ ′ calculated by the phase calculation unit 55 is −π to + π, the phase shift φ ′ is discontinuous at −π and + π. For example, in the phase image shown in FIG. 9A, a portion that changes from white (or black) to black (or white) corresponds to a discontinuous point of the phase shift φ ′. If such a phase image is used as it is, it is difficult to recognize the shape of the measuring object 2. Therefore, it is necessary to correct the phase shift φ ′ so that the phase shift φ ′ is smoothly connected at the discontinuous points of the phase shift φ ′. Such correction (phase jump correction) is a process for obtaining a unique phase shift φ proportional to the depth of the measuring object 2 from the phase shift φ ′ defined in the range of 2π.

  Specifically, the phase continuation processing unit 506 detects a discontinuous point of the phase shift φ ′ and corrects the phase shift φ ′ at the discontinuous point. Whether or not the phase shift φ ′ is discontinuous is not known by looking at only one pixel. It is necessary to judge by looking at adjacent pixels. First, the phase continuation processing unit 506 checks the phase image along the arrangement direction at each position in the width direction of the phase image, and compares the phase shift φ ′ between adjacent pixels. If the phase shift φ ′ differs greatly between the adjacent pixels, it is determined that the phase shift φ ′ is discontinuous between the pixels, and the phase shift φ ′ is corrected. Actually, the depth at the surface of the measuring object 2 such as a steel plate does not change abruptly. For this reason, it is considered that the phase shift φ ′ is largely different because the phase shift φ ′ is changed by ± 2π. Therefore, it is only necessary to examine pixels in which the phase shift φ ′ is significantly different from the phase shift φ ′ in the adjacent pixels and smoothly connect the phase shift φ ′.

  For example, when a phase shift φ ′ is close to + π at a certain pixel position and the phase shift φ ′ is close to −π at a pixel position on the right side, the right adjacent pixel At the position, it is recognized that the phase shift φ ′ changes by + 2π. Then, the phase shift φ ′ is corrected by adding + 2π to the phase shift φ ′ at the right adjacent pixel position. Further, when the phase shift φ ′ is a value close to −π at a certain pixel position, and the phase shift φ ′ is a value close to + π at the pixel position on the right side, the pixel on the right side At the position, it is recognized that the phase shift φ ′ changes by −2π. The phase shift φ ′ is corrected by adding −2π to the phase shift φ ′ at the right pixel position.

  Thus, after examining the adjacent pixels along the arrangement direction at each position in the width direction and correcting the phase shift φ ′, the phase continuation processing unit 506 is now arranged in the width direction at each position in the arrangement direction. The adjacent pixels are examined, and similarly, the phase shift φ ′ is corrected. The phase shift at each pixel position after correction is a unique phase shift φ proportional to the depth of the measurement object 2.

  Next, the phase continuation processing unit 506 newly creates a phase image based on the corrected phase shift φ. This new phase image accurately represents the shape of the measuring object 2. This new phase image is referred to as a shape image. FIG. 9B shows an example of a shape image obtained by the phase continuation processing unit 506. FIG. 10B shows an example of a characteristic diagram representing the phase characteristic in the shape image.

On the other hand, the amplitude calculation unit 510 calculates the amplitude A (j, k), that is, the luminance at each pixel position (j, k) based on the results output from the two low-pass filter units 504a and 504b (step S104). ). The amplitude A (j, k) is
A (j, k) = 2 [{LPF (Ib _j (k))} ² + {LPF (Ia _j (k))} ² ] ^1/2
It can be obtained more. Then, an amplitude image (luminance image) is created based on the calculated amplitude A. The amplitude image is expressed as a grayscale image in which the image becomes black as the amplitude is small, for example. FIG. 11 shows an example of an amplitude image obtained by the amplitude calculation unit 510.

  The edge position detection unit 511 detects the left and right edge positions for each line based on the amplitude image (luminance image) obtained by the amplitude calculation unit 506, using a threshold value or the like (step S105).

  The centering processing unit 507 performs centering processing on the shape image obtained by the phase continuation processing unit 506 based on the edge position detected by the edge position detection unit 511 (step S106). In the centering process, as shown in FIG. 12, the center position of the measuring object 2 is calculated for each line based on the left and right edge positions and aligned in the longitudinal direction. Due to the centering process, when the measurement object 2 is a long material having a curved line whose both end portions are low or high in the cross-sectional shape, the measurement object 2 meanders or vibrates in the width direction. Sometimes, the detection accuracy of surface defects can be increased.

  The shape correction processing unit 508 performs shape correction processing on the shape image after the centering processing. In the shape images shown in FIGS. 9 (b) and 10 (b), the surface shape of the measurement object 2 itself is not flat. Therefore, even if the binarization process is performed to determine the surface defect, the surface of the steel plate is recessed. It is impossible to extract surface defects such as rust and wrinkles. Therefore, a shape correction process is performed in which the curved surface shape of the measuring object 2 is baked into a flat surface.

  Specifically, the shape image after the centering process is subjected to a fitting process using an even function (for example, a quartic function) for each line (step S107), and a difference calculation with the original data (the shape image after the centering process) is performed. (Step S108). By this fitting process, even when both ends of the measurement object 2 have a steep shape, a sharp signal change at both ends is alleviated.

Subsequently, the shape image after the difference calculation is averaged (integrated) by a predetermined length in the traveling direction (longitudinal direction) of the measurement object 2 (step S109), and low-pass filter processing is performed (step S110), and the original data difference calculation between (shape image after difference calculation) (or division operation) (step S111). By this shading correction, flattening is performed while retaining unevenness information that is a surface defect candidate.

  As described above, as the shape correction processing, two-stage processing such as fitting processing using an even function and further shading correction is performed. The image after the shape correction process is referred to as a depth image. FIG. 9C shows an example of a depth image obtained by the shape correction processing unit 508. FIG. 10C shows an example of a characteristic diagram representing the phase characteristic in the depth image.

  The defect detection processing unit 509 binarizes the depth image obtained by the shape correction processing unit 508 (step S112). In the binarization process, a threshold value is set, and 0 is applied to a portion within the threshold value, and 1 is applied to a portion exceeding the threshold value.

  Then, surface defect determination is performed using the binarized image (step S113), and the surface defect is detected (step S114). FIG. 13A shows how surface defect determination is performed based on the area, length, width, aspect ratio, etc. of the binarized image. In addition to the binarized image, as shown in FIG. 13B, surface defect discrimination is performed based on the maximum and minimum depths of the depth image, and as shown in FIG. 13C. The surface defect determination may be performed based on the maximum luminance, the minimum luminance, the average luminance, or the like of the amplitude image (luminance image) obtained by the amplitude calculation unit 506.

  FIG. 15 shows a hardware configuration example of a computer system that functions as the image processing apparatus 50. As shown in the figure, a CPU 51, an input device 52, a display device 53, and a recording device 54 are included, and each unit is connected via a bus 55. The recording device 54 includes a ROM, a RAM, an HD, and the like, and stores a computer program that controls the operation of the image processing device 50 described above. The function or processing of the image processing apparatus 50 is realized by the CPU 51 executing the computer program. Note that the image processing apparatus 50 does not have to be a single apparatus, and may include a plurality of devices.

  As mentioned above, although this invention was demonstrated with various embodiment, this invention is not limited only to these embodiment, A change etc. are possible within the scope of the present invention. For example, in the above embodiment, the luminance image for detecting the edge position is acquired by the TDI camera 30, but may be acquired by an imaging device different from the TDI camera 30.

1 is a schematic configuration diagram of a surface defect inspection system according to an embodiment of the present invention. It is a figure which shows the example of the cross-sectional shape of a measuring object. It is a figure for demonstrating the structure and operation | movement of a delay integration type camera. It is a figure which shows an example of a fringe image. It is a figure for demonstrating the shift | offset | difference of the stripe in a stripe image. It is a figure which shows an example of a fringe image. It is a figure for demonstrating the relationship between the shift | offset | difference of the phase in slice fringe image data, and the depth of a measuring object. It is a schematic block diagram of an image processing apparatus. It is a figure which shows the photograph of the image in each step, (a) is a figure which shows the photograph of a phase image, (b) is a figure which shows the photograph of a shape image, (c) is a figure which shows the photograph of a depth image. is there. It is a characteristic diagram showing the phase characteristic in each stage, (a) is a characteristic figure showing the phase characteristic in a phase image, (b) is a characteristic figure showing the phase characteristic in a shape image, (c) is a phase in a depth image. It is a characteristic view showing a characteristic. It is a figure which shows the photograph of an amplitude image. It is a figure for demonstrating the outline | summary of a centering process. It is a figure which shows the photograph of the image used for surface defect discrimination | determination, (a) is a figure which shows the photograph of a binarized image, (b) is a figure which shows the photograph of a depth image, (c) is a photograph of a brightness | luminance image. FIG. It is a flowchart for demonstrating the processing operation of an image processing apparatus. It is a figure which shows the hardware structural example of the computer system which functions as an image processing apparatus.

Explanation of symbols

2 Measurement object 10 Laser device 20 Rod lens 30 Delay integration type camera 40 Timing signal generation unit 50 Image processing device 60 Display device 501 A / D conversion unit 502 Pre-filter unit 503 Orthogonal sine wave generation unit 504a, 504b Low-pass filter unit 505 Phase calculation unit 506 Phase continuation processing unit 507 Centering processing unit 508 Shape correction processing unit 509 Defect detection processing unit 510 Amplitude calculation unit 511 Edge position detection unit

Claims (3)

Using the irradiation means for irradiating the surface of the measurement object with the linear laser light and the delay integration type imaging means for imaging the reflected light from the measurement object, the linear laser light with respect to the measurement object A surface defect inspection system for detecting a surface defect of the measurement object by imaging the reflected light from the measurement object and outputting a light-cut image by continuously shifting the irradiation position,
The measurement object has a curve in which both end portions become lower or higher in the cross-sectional shape,
Edge position detection means for detecting an edge position of the measurement object based on a luminance image including the measurement object imaged by the imaging means or other imaging means;
Centering processing means for performing a centering process on the image obtained by the imaging means based on the edge position detected by the edge position detecting means;
First shape correction processing means for performing an even function fitting process on the image after the centering process, and performing a difference operation between the image after the fitting process and the image after the centering process;
The only longitudinal direction of the predetermined length of the difference image the measurement object after the operation and the average or integrated, or the difference calculation between images after the average or the image subjected to the low pass filter process after the accumulated difference operation Second shape correction processing means for performing a division operation,
The linear laser beam is periodically modulated,
The surface defect inspection system according to claim 1, wherein the luminance image is captured by the imaging means. Using the irradiation means for irradiating the surface of the measurement object with the linear laser light and the delay integration type imaging means for imaging the reflected light from the measurement object, the linear laser light with respect to the measurement object A surface defect inspection method for detecting a surface defect of the measurement object by imaging the reflected light from the measurement object by the imaging means and outputting a light cutting image while continuously shifting the irradiation position,
The measurement object has a curve in which both end portions become lower or higher in the cross-sectional shape,
A procedure for detecting an edge position of the measurement object based on a luminance image including the measurement object imaged by the imaging means or another imaging means;
A procedure for performing a centering process on the image obtained by the imaging means based on the detected edge position;
A procedure for performing an even function fitting process on the image after the centering process and performing a difference calculation between the image after the fitting process and the image after the centering process;
The only longitudinal direction of the predetermined length of the difference image the measurement object after the operation and the average or integrated, or the difference calculation between images after the average or the image subjected to the low pass filter process after the accumulated difference operation A procedure for performing a division operation,
The linear laser beam is periodically modulated,
The surface defect inspection method, wherein the luminance image is taken by the imaging means. Using the irradiation means for irradiating the surface of the measurement object with the linear laser light and the delay integration type imaging means for imaging the reflected light from the measurement object, the linear laser light with respect to the measurement object A program for detecting a surface defect of the measurement object by imaging the reflected light from the measurement object by the imaging means and outputting a light cutting image while continuously shifting the irradiation position,
The measurement object has a curve in which both end portions become lower or higher in the cross-sectional shape,
A procedure for detecting an edge position of the measurement object based on a luminance image including the measurement object imaged by the imaging means or another imaging means;
A procedure for performing a centering process on the image obtained by the imaging means based on the detected edge position;
A procedure for performing an even function fitting process on the image after the centering process and performing a difference calculation between the image after the fitting process and the image after the centering process;
The only longitudinal direction of the predetermined length of the difference image the measurement object after the operation and the average or integrated, or the difference calculation between images after the average or the image subjected to the low pass filter process after the accumulated difference operation The computer executes the procedure for performing the division operation,
The linear laser beam is periodically modulated,
The luminance image is a program imaged by the imaging means.

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