JP2016148596A - Linear array camera calibration method for surface inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear array camera calibration method for a surface inspection device capable of easily and accurately calibrating the field of view of a linear array camera disposed in a detection unit of the surface inspection device, when, in inspecting the surface of a material to be inspected (for example, a metal band such as a steel band) with the surface inspection device, the inspection position is set as a position at which the material to be inspected is wound on a roll.SOLUTION: A mark M for calibration includes: a virtual reference horizontal line 21; a virtual vertical line 22; a first diagram (rectangular triangle) 23; a second diagram (rectangular triangle) 24; a third diagram (rectangle) 25; a fourth diagram (rectangle) 26; a fifth diagram (circle) 27; and a sixth diagram (circle) 28. By pasting the mark M for calibration on a roll 2, the field of view of a linear array camera 13 is calibrated.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a linear array camera calibration method for a surface inspection apparatus for calibrating the field of view of a linear array camera provided in a detection unit of the surface inspection apparatus.

  In general, in a surface inspection apparatus, an illumination device that irradiates a strip-shaped parallel light beam and a linear array camera (hereinafter also simply referred to as a “camera”) are provided in a detection unit, and a material to be inspected that is irradiated by the illumination device. The surface of the material to be inspected is inspected by imaging (for example, a metal strip such as a steel strip) with a camera.

  In general, when inspecting the surface of a material to be inspected by a surface inspection apparatus, a method of aligning the visual field position of a camera (that is, a calibration method) is performed by using a reference plate ( Calibration mark) is arranged, and the visual field position of the camera is aligned with the reference plate as a target (for example, Patent Documents 1 and 2).

JP 2009-243920 A JP 2009-288165 A

  When surface inspection is performed by the surface inspection apparatus, it is desirable that there is no vertical fluctuation (pass line fluctuation) of the material to be inspected.

  Therefore, when the material to be inspected is a metal strip or the like, as shown in FIG. 1, the inspection position (camera field of view) is set to a position where the material to be inspected 1 is wound around the roll 2 and the object irradiated by the illumination device 11 is used. The inspection material 1 is often imaged by the camera 13.

  On the other hand, in the above Patent Documents 1 and 2, as shown in FIG. It is said. Therefore, if the calibration method described in Patent Documents 1 and 2 is applied when the camera field of view as shown in FIG. 1 is used as a roll surface, a position (offline position) different from the actual inspection position (online inspection position). After calibrating the field of view of the camera 13 with the off-line reference plate, the camera 13 is moved to the online inspection position. However, there are the following problems 1 and 2.

  (Problem 1) The roll surface serving as the on-line inspection position is subject to wear due to aging, so the position does not exactly match the off-line reference plate. This problem can be avoided by frequently adjusting the position of the online inspection position and the offline reference plate. However, the adjustment of the position of the offline reference plate and the calibration of the camera 13 are carried out, resulting in a heavy work load. Become.

  (Problem 2) When the online inspection position and the position of the offline reference plate are aligned, the installation accuracy of the actual camera 13 and the offline reference plate has an error of about ± 0.5 mm. When the imaging angle of the camera 13 is the regular reflection direction of the irradiation light from the illumination device, even if the position of the camera 13 is aligned with the offline reference plate, there is a high possibility that the reflection intensity will be greatly different if it is moved to the online position. In particular, when the surface of the material to be inspected 1 is close to a mirror surface, most of the reflection in the specular reflection direction occupies the target 13 of the material to be inspected if the field of view of the camera 13 is slightly deviated from the specular reflection position. There is a high possibility that it will not be detected.

Patent Document 2 discloses a calibration method for a line sensor camera in which a reference plate having a pattern that satisfies the following conditions (a) to (c) is installed so that a virtual reference line coincides with a predetermined reference position. Have been described.
(A) It has five or more linear elements that intersect the virtual reference line.
(B) The linear elements are not all parallel.
(C) The extension lines of the linear elements do not all intersect at one point.

  However, this calibration method has the following problems 3 to 6 when applied to the case where the camera field of view is the roll surface.

  (Problem 3) When the field of view of the camera 13 is tilted with respect to the roll axis, it is unclear how much tilted.

  (Problem 4) It is difficult to accurately determine how much the visual field of the camera 13 is in the vertical relationship with the reference plate.

  (Problem 5) When the plate thickness of the material 1 to be inspected is thin, the reference plate must also be thin and long, and it is necessary to apply it directly to the roll. Not.

  (Problem 6) With respect to the distribution of the signal intensity of the black triangle mark that is the target of the visual field of the camera 13, the positional deviation in the roll axis direction of the camera 13 can be recognized by monitoring the width difference between the signals. If the width difference between the signals becomes small, it becomes difficult for the calibration operator to recognize, and the work load increases.

  The present invention has been made in view of the above circumstances, and when inspecting the surface of a material to be inspected (for example, a metal strip such as a steel strip) by a surface inspection device, the material to be inspected rolls the inspection position. To provide a linear array camera calibration method for a surface inspection apparatus capable of easily and accurately calibrating the visual field of the linear array camera provided in the detection unit of the surface inspection apparatus when the position is wound around the surface. It is the purpose.

  In order to solve the above problems, the present invention has the following features.

[1] When inspecting the surface of the material to be inspected by the surface inspection device, when the inspection position is set to a position where the material to be inspected is wound around the roll, the linear array camera provided in the detection unit of the surface inspection device A linear array camera calibration method for a surface inspection apparatus for calibrating a field of view, comprising:
Irradiation of strip-shaped parallel rays from the illumination device so that the linear array camera can receive the reflected rays from the illumination device provided in the detection unit of the surface inspection device. A lighting position adjustment step for adjusting the position;
A reference line setting step of irradiating the roll with strip-shaped parallel light rays from an illumination device, and setting a reference line in the roll axis direction along a light band formed on the roll surface;
A reference plate that satisfies the following conditions (a) to (d) is placed at a roll position that enters the field of view of the linear array camera by matching a virtual reference horizontal line provided on the reference plate with the reference line in the roll axis direction. A reference plate pasting step to be pasted;
(A) It has a virtual reference horizontal line provided in the horizontal direction, a virtual vertical line perpendicular to the virtual reference line, and an intersection of the virtual reference horizontal line and the virtual vertical line.
(B) On one side in the vertical direction of the virtual reference horizontal line, a right triangle having the intersection as an acute vertex, a side perpendicular to the virtual reference horizontal line and a side parallel to the virtual reference horizontal line It has a certain first figure.
(C) On the other side in the vertical direction of the virtual reference line, a second figure that is a right triangle that is point-symmetric with the first figure with respect to the intersection point, and the second figure in the second figure An acute vertex that is not on the virtual reference horizontal line is used as a shared vertex, the second figure has one side that is an extension of a side parallel to the virtual reference horizontal line, and the virtual reference horizontal line And a fourth figure which is a rectangle which is line-symmetric with the third figure with respect to the virtual vertical line.
(D) having a fifth graphic that is a circle centered on the virtual reference horizontal line and a sixth graphic that is a circle symmetrical to the fifth graphic with respect to the virtual vertical line ing.
An imaging step of obtaining a one-dimensional image by imaging the figure on the reference plate with the linear array camera;
And a camera position adjusting step of adjusting a vertical position of the field of view of the linear array camera and a tilt angle of the field of view of the linear array camera with respect to the roll axis direction based on the light intensity pattern of the one-dimensional image. A linear array camera calibration method for a surface inspection apparatus, characterized in that

  In the present invention, when inspecting the surface of a material to be inspected (for example, a metal strip such as a steel strip) by the surface inspection device, the surface inspection device is set to a position where the material to be inspected is wound around the roll. The field of view of the linear array camera provided in the detector can be easily and accurately calibrated.

It is a figure which shows the test | inspection position (test | inspection state) in one Embodiment of this invention. It is a figure which shows the illumination position adjustment step in one Embodiment of this invention. It is a figure which shows the reference line setting step in one Embodiment of this invention. It is a figure which shows the reference line setting step in one Embodiment of this invention. It is a figure which shows the reference | standard board in one Embodiment of this invention. It is a figure which shows the reference | standard board sticking step in one Embodiment of this invention. It is a figure which shows the imaging step in one Embodiment of this invention. It is a figure which shows the test | inspection position (inspection state) in a prior art (patent documents 1, 2).

  An embodiment of the present invention will be described with reference to the drawings.

  In one embodiment of the present invention, as shown in FIG. 1, when the surface of a material to be inspected (for example, a metal strip such as a steel strip) 1 is inspected by a surface inspection device, the inspection material 1 is positioned at the inspection position. As a method for calibrating the field of view of the linear array camera 13 provided in the detection unit of the surface inspection apparatus when the position is wound around the roll 2, an illumination position adjustment step and a reference line setting step as shown below , A reference plate pasting step, an imaging step, and a camera position adjusting step.

(1) Illumination position adjustment step As shown in FIG. 2, a strip-shaped parallel light beam is irradiated onto the roll 2 from the illumination device 11 provided in the detection unit of the surface inspection device, and the linear array camera 13 applies the reflected light beam to the roll 2. The irradiation position of the strip-shaped parallel light beam from the illumination device 11 to the roll 2 is adjusted so that light can be received.

(2) Reference line setting step When the roll 2 is irradiated with a strip-shaped parallel light beam from the illumination device 11, a light band 12 is formed on the surface of the roll 2 as shown in FIG. 3, so as shown in FIG. The yarn 14 is attached to the entire width of the roll 2 along the upper side (or lower side) of the optical band 12, and this yarn 14 is used as a reference line in the roll axis direction.

(3) Reference plate pasting step The reference plate (calibration mark) enters the field of view of the linear array camera 13 with the virtual reference horizontal line provided on the reference plate aligned with the reference line (thread 14) in the roll axis direction. Affix to the roll 2 surface position. The accuracy of the calibration mark attaching position is set to about ± 0.5 mm.

  Here, as shown in FIG. 5, the reference plate (calibration mark) M satisfies the following conditions (a) to (d).

  (A) It has a virtual reference horizontal line 21 provided in the horizontal direction, a virtual vertical line 22 perpendicular to the virtual reference line 21, and an intersection of the virtual reference horizontal line 21 and the virtual vertical line 22.

  (B) On one side (here, the lower side) of the virtual reference horizontal line 21 in the vertical direction, the intersection point is an acute vertex, and a side perpendicular to the virtual reference horizontal line 21 is parallel to the virtual reference horizontal line 21. It has a right triangle (first figure) 23 having a long side.

  (C) On the other side of the virtual reference line 21 in the vertical direction (here, the upper side), a right triangle (second figure) that is symmetric with respect to the first figure (right triangle) 23 with respect to the intersection. ) 24 and a sharp vertex that is not on the virtual reference horizontal line 21 in the second graphic (right triangle) 24 as a common vertex, and parallel to the virtual reference horizontal line 21 in the second graphic (right triangle) 24 With respect to a rectangle (third figure) 25 having one side that is an extension of the side and having the other side overlapping the virtual reference horizontal line 21, and a virtual vertical line 22, a third figure ( It has a rectangle (fourth graphic) 26 that is line-symmetric with the (rectangular) 25.

  (D) A circle (fifth figure) 27 having a center on the virtual reference horizontal line 21 and a circle (sixth figure) that is symmetrical with the fifth figure (circle) 27 with respect to the virtual vertical line 22 ) 28.

  As shown in FIG. 6, three calibration marks M are pasted in the axial direction of the roll 2 (M1 (camera field left end), M2 (camera field center), M3 (camera field right edge)). At that time, the distance between M1 and M2 and the distance between M2 and M3 are made equal.

  Then, the roll 2 is moved so that the thread 14 is on the center line of the light band 12, that is, so that the virtual reference horizontal line 21 of the calibration mark M coincides with the center line of the light band 12. After completion, the thread 14 is removed from the roll 2.

(4) Imaging step The linear array camera 13 images the figures 23 to 28 on the calibration mark M (M1, M2, M3) to obtain a one-dimensional image.

  FIG. 7 shows an example of the obtained one-dimensional image (light intensity pattern).

  When the camera field of view for the calibration mark M (M1, M2, M3) is in a state as shown in FIG. 7A, a light intensity pattern (signal intensity pattern) as shown in FIG. 7B is obtained.

  When the camera field of view for the calibration mark M (M1, M2, M3) is in a state as shown in FIG. 7C, a light intensity pattern (signal intensity pattern) as shown in FIG. 7D is obtained.

(5) Camera position adjustment step Based on the light intensity pattern (signal intensity pattern) of the one-dimensional image, the tilt angle of the visual field of the linear array camera 13 with respect to the roll axis direction and the vertical position of the visual field of the linear array camera 13 are determined. adjust.

  Incidentally, in the installation of the roll 2, the illumination device 11 and the linear array camera 13, a machine installation error actually occurs. Therefore, here, the position of the roll 2 installed on the site and the optical band by the illumination device 11 are used. The position of 12 is set to “positive”, and the method of ensuring the optical system arrangement of the linear array camera 13 and the illuminating device 11 with high accuracy is adopted by aligning the visual field of the linear array camera 13 with the center line of the optical band 12. .

  First, the tilt angle of the visual field of the linear array camera 13 with respect to the roll axis direction is adjusted.

  When the camera field of view is parallel to the virtual reference horizontal line 21 of the calibration marks M1 to M3 as shown in FIG. 7A, each calibration mark is displayed as shown in FIG. 7B. The signal intensity patterns of the second figure (right triangle) 24, the third figure (rectangle) 25, and the fourth figure (rectangle) 26 in M1 to M3 are the same (for example, the second figure (right triangle)). 24, the signal widths U1 to U3 are equal, and the signal widths V1 to V3 and W1 to W3 of the third graphic (rectangular) 25 and the fourth graphic (rectangular) 26 are equal.

  When the camera field of view is inclined with respect to the virtual reference horizontal line 21 of the calibration marks M1 to M3 as shown in FIG. 7C, the calibration field is used as shown in FIG. 7D. The signal intensity pattern gradually changes from the mark M1 to the mark M3. In each calibration mark M1, the second figure (right triangle) 24, the third figure (rectangle) 25, and the fourth figure (rectangle). 26. In addition to the second figure (right triangle) 24, the third figure (rectangle) 25, and the fourth figure (rectangle) 26, the calibration mark M2 includes a fifth figure (circle) 27 and The signal intensity pattern is based on the sixth graphic (circle) 28, and the calibration mark M3 is the signal intensity pattern based only on the first graphic (right triangle) 23.

  Therefore, when a light intensity pattern (signal intensity pattern) as shown in FIG. 7D is obtained, the camera field of view is inclined with respect to the virtual reference horizontal line 21 of the calibration marks M1 to M3. Therefore, the horizontal inclination angle of the camera field of view is adjusted so that the signal intensity pattern by the fifth graphic (circle) 27 and the sixth graphic (circle) 28 appears in all of the calibration marks M1 to M3. Thus, the camera field of view may be matched with the virtual reference horizontal line 21 of the calibration marks M1 to M3.

  Subsequently, the vertical position of the visual field of the linear array camera 13 is adjusted.

  However, in FIG. 7A, since the camera field of view does not coincide with the virtual reference horizontal line 21 of the calibration marks M1 to M3, the fifth figure (circle) 27 and the The signal intensity pattern by the figure (circle) 28 of 6 does not appear.

  The detailed procedure in this camera visual field vertical position adjustment step is as follows.

  Procedure 1: The camera position is adjusted so that the center line of the optical band 12 (that is, the virtual reference horizontal line 21 of the calibration marks M1 to M3) is the camera field of view.

  (1.1) The camera tilt (vertical angle) is moved upward so as to see the upper part of the calibration mark M, and the third mark (rectangle) 25 of the calibration mark mark M (M1 to M3) It is assumed that the signal intensity pattern of the fourth figure (rectangle) 26 appears evenly.

  (1.2) When the tilt of the camera is moved downward so as to see the vertical center of the calibration mark M, the signal intensity patterns of the fifth figure (circle) 27 and the sixth figure (circle) 28 are changed. As a result, the signal intensity of the third graphic (rectangular) 25 and the fourth graphic (rectangular) 26 of the calibration mark M decreases.

  (1.3) Stop when the signals of the third figure (rectangle) 25 and the fourth figure (rectangle) 26 of the calibration mark M have just disappeared.

  This completes the alignment of the camera field of view with the center line of the light band.

  Procedure 2: Subsequently, the camera visual field is finely adjusted in order to precisely match the visual field position of the camera 13 with the regular reflection direction of the irradiation light beam from the illumination device 11.

  (2.1) The camera 13 is finely moved upward in the tilt.

  At that time, if the width of the obtained signal intensity pattern (signal intensity waveform) of the second figure (right triangle) 24 of the calibration mark M increases, the signal intensity waveform continues to decrease and disappear. Move the camera tilt downward to find the position where the signal strength waveform disappeared.

  If the width of the obtained signal strength pattern (signal strength waveform) increases by moving the camera tilt downward, the camera's vertical position is below the reference horizontal line, so the opposite direction (upward ).

  (2.2) Confirm that there is no variation in the left and right of the camera field of view by moving the tilt of the camera. Confirmation is made with the widths of the graphic parts 23 to 28 (black parts) of the calibration mark M.

  Procedure 3: Final confirmation of pan position (horizontal angle) of the camera is performed.

  (3.1) Check the number of pixels in each section between the calibration mark M1 and the calibration mark M2 and between the calibration mark M2 and the calibration mark M3.

  If the number of pixels in the two sections is the same, the center line of the visual field of the camera 13 and the axis of the roll 2 are in a vertical positional relationship. If the number of pixels in the two sections is different, it is necessary to adjust the pan direction position of the camera. Therefore, the horizontal position or the horizontal angle of the camera is finely adjusted so that the number of pixels in each section is uniform. Then, readjustment is performed from step 1.

  This completes the calibration work of the linear array camera 13.

  Thus, in this embodiment, the visual field of the linear array camera 13 can be calibrated easily and accurately.

  That is, in this embodiment, the following effects can be achieved by clarifying the calibration mark M used in the calibration work of the linear array camera 13 of the surface inspection apparatus and the adjustment work.

  1) The visual field position of the current linear array camera 13 can be clearly confirmed visually. In addition, by attaching calibration marks M (M1, M2, M3) to the three points of the left end of the field of view, the center of the field of view, and the right end of the field of view, The position of the horizontal angle (pan angle) and horizontal position) can be adjusted.

  2) Conventionally, the calibration operation of the linear array camera 13 has been difficult to perform unless it is an expert, but can be performed without depending on the operator.

  3) The work time for the calibration work of the linear array camera can be shortened.

  4) After the calibration of the linear array camera is completed, the positional accuracy of the illuminating device 11 and the linear array camera 13 (particularly the specular reflection camera) is increased, and stable inspection of the surface inspection device can be realized.

1 Inspected material (metal strip)
2 rolls 5 support rolls 6 support rolls 11 lighting device 12 optical band 13 linear array camera 14 thread 21 virtual reference horizontal line 22 virtual vertical line 23 first figure (right triangle)
24 Second figure (right triangle)
25 3rd figure (rectangle)
26 Fourth figure (rectangle)
27 Fifth figure (circle)
28 Sixth figure (circle)
M, M1, M2, M3 Calibration marks

Claims (1)

When inspecting the surface of the material to be inspected by the surface inspection device, the field of view of the linear array camera provided in the detection unit of the surface inspection device is calibrated when the inspection position is set to the position where the material to be inspected is wound around the roll A linear array camera calibration method for a surface inspection apparatus for performing
Irradiation of strip-shaped parallel rays from the illumination device so that the linear array camera can receive the reflected rays from the illumination device provided in the detection unit of the surface inspection device. A lighting position adjustment step for adjusting the position;
A reference line setting step of irradiating the roll with strip-shaped parallel light rays from an illumination device, and setting a reference line in the roll axis direction along a light band formed on the roll surface;
A reference plate that satisfies the following conditions (a) to (d) is placed at a roll position that enters the field of view of the linear array camera by matching a virtual reference horizontal line provided on the reference plate with the reference line in the roll axis direction. A reference plate pasting step to be pasted;
(A) It has a virtual reference horizontal line provided in the horizontal direction, a virtual vertical line perpendicular to the virtual reference line, and an intersection of the virtual reference horizontal line and the virtual vertical line.
(B) On one side in the vertical direction of the virtual reference horizontal line, a right triangle having the intersection as an acute vertex, a side perpendicular to the virtual reference horizontal line and a side parallel to the virtual reference horizontal line It has a certain first figure.
(C) On the other side in the vertical direction of the virtual reference line, a second figure that is a right triangle that is point-symmetric with the first figure with respect to the intersection point, and the second figure in the second figure An acute vertex that is not on the virtual reference horizontal line is used as a shared vertex, the second figure has one side that is an extension of a side parallel to the virtual reference horizontal line, and the virtual reference horizontal line And a fourth figure which is a rectangle which is line-symmetric with the third figure with respect to the virtual vertical line.
(D) having a fifth graphic that is a circle centered on the virtual reference horizontal line and a sixth graphic that is a circle symmetrical to the fifth graphic with respect to the virtual vertical line ing.
An imaging step of obtaining a one-dimensional image by imaging the figure on the reference plate with the linear array camera;
And a camera position adjusting step of adjusting a vertical position of the field of view of the linear array camera and a tilt angle of the field of view of the linear array camera with respect to the roll axis direction based on the light intensity pattern of the one-dimensional image. A linear array camera calibration method for a surface inspection apparatus, characterized in that

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