Defect inspection system and defect inspection method

Abstract

Depth information is generated by imaging the front and back surfaces of plywood 10 transported on belt conveyors 5U, 5D by using an imaging device of first illumination / imaging units 1F, 1B, shape information is generated by measuring the shape of the plywood 10 by using shape-measuring units 3F, 3B provided at a location different from a gap 51 where the imaging is performed, the depth information is corrected on the basis of the shape information, and any defect in the plywood 10 is detected on the basis of the depth information. Any defect in the plywood 10 is detected on the basis of the depth information corrected by using the shape information, which is measured without the influence of vibration occurring when the plywood 10 is transported over the gap 51; thus, any deformation occurring in the plywood 10 is not flattened due to the correction of the depth information, and defects such as warpage and bending can be accurately detected.

Description

Defect inspection system and defect inspection method

[0001] The present invention relates to a defect inspection system and a defect inspection method, and is particularly suitable for use in a system for detecting defects present in plywood constructed by laminating a plurality of veneers cut from logs.

[0002] Generally, plywood is manufactured by stacking multiple veneers produced by cutting natural logs with a veneer lace and gluing them together with an adhesive. Plywood produced from logs contains a variety of defects. Individual plywood is sorted into one of several quality ranks depending on the type, size, and number of defects. Conventionally, a defect inspection device is used to detect defects present in plywood for this sorting. Plywood defects detected by defect inspection devices include discoloration on the front and back surfaces (mold, dirt, bark inclusions, etc.), holes, dirt, unevenness, warping, bending, etc.

[0003] Conventionally, an inspection device is known that irradiates the surface of a laminated wood lumber with vertical and oblique light, and also irradiates the back surface of the laminated wood lumber with vertical and oblique light, and analyzes image data obtained by photographing the surface and back surface of the laminated wood lumber with a line sensor camera to determine the properties of the surface and back surface, respectively (see, for example, Patent Document 1).

[0004] Also known is a device for inspecting the thickness of an object to be inspected, such as a decorative panel manufactured by bonding plywood and a sheet-like decorative material, in which a pair of displacement sensors are arranged through the object to inspect the thickness of the object based on the difference between a plurality of first displacement data representing the distance from a position on one surface of the object to a predetermined reference point measured by one of the displacement sensors, and a plurality of second displacement data representing the distance from a position on the other surface of the object to the reference point measured by the other displacement sensor (see, for example, Patent Document 2).

[0005] However, when simultaneously photographing or measuring the front and back surfaces of plywood as in Patent Documents 1 and 2, it is necessary to separate the conveying device (conveyor) for transporting the plywood into an upstream and a downstream conveyor, and to arrange the two conveyors with a spatial gap between them. As a result, when the plywood transfers from the upstream conveyor to the downstream conveyor, i.e., when photographing or measuring the plywood, the plywood may bounce, which may result in errors in the photographed or measured data. In particular, when the plywood has a warp or bend, this is likely to cause the bounce.

[0006] In this regard, Patent Document 2 states that stripes appear in the captured image due to vibrations of the test object that occur when the test object passes over the inspection surface of the displacement sensor, but that by taking the difference between the first displacement data and the second displacement data, it is possible to obtain an image in which the change in surface height due to the vibrations of the test object is offset.

[0007] However, the technology described in Patent Document 2 does not detect defects in plywood, but measures the thickness of the plywood. Therefore, if the technology described in Patent Document 2 is applied to a plywood defect inspection device, if the plywood has a defect such as warping or bending, the defect will also be removed by calculating the difference between the first displacement data and the second displacement data, resulting in a problem in that the defect such as warping or bending cannot be detected.

[0008] JP 2023-29260 A JP 2014-222156 A

[0009] The present invention has been made to solve such problems, and has as its object to enable accurate detection of defects such as warping and bending present in plywood.

[0010] To solve the above-mentioned problems, the present invention uses an imaging device to capture images of the front and back surfaces of plywood being transported on a conveyor to generate depth information for both sides of the plywood, and a shape measuring device installed in a location different from the gap between the conveyors where the images are captured measures the shape of the plywood in the thickness direction to generate shape information, and then analyzes the depth information and shape information to detect defects in the plywood. Here, the depth information is corrected based on the shape information, and defects due to deformation of the plywood are detected based on the depth information.

[0011] In the present invention configured as described above, the shape of the plywood in the thickness direction measured at a location other than the gap between the conveyors is a shape measured without being affected by vibrations that occur when the plywood passes through the gap as it is transported, and defects due to deformation of the plywood are detected based on depth information corrected on the basis of this shape information. As a result, only errors in the depth information caused by the influence of vibrations that occur when the plywood passes through the gap as it is transported are eliminated by correction based on the shape information, and defects due to deformation such as warping and bending that occur in the plywood can be accurately detected without being flattened by correcting the depth information.

[0012] FIG. 1 is a diagram illustrating an example of the overall configuration of a defect inspection system according to the present embodiment. FIG. 2 is a block diagram illustrating an example of the functional configuration of an analysis device according to the present embodiment. FIG. 3 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 4 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 5 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 6 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 7 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 8 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 9 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 10 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 11 is a diagram illustrating an example of depth information of a plywood acquired by a depth information acquisition unit. FIG. 12 is a diagram illustrating an example of shape information of a plywood acquired by a shape information acquisition unit. FIG. 13 is a diagram for explaining the processing contents of a correction processing unit. FIG. 14 is a flowchart illustrating an example of the operation of an analysis device according to the present embodiment. FIG. 15 is a diagram illustrating an example of the overall configuration of a defect inspection system according to a modified example. FIG. 10 is a block diagram illustrating an example of a functional configuration of an analysis device according to a modified example.

[0013] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing an example of the overall configuration of a defect inspection system according to this embodiment. Fig. 1(a) shows the defect inspection system as seen from the side, Fig. 1(b) shows the defect inspection system as seen from above, and Fig. 1(c) shows the defect inspection system as seen from the downstream side in the transport direction. In Figs. 1(a) and 1(b), the right side is the upstream side in the transport direction, and the left side is the downstream side in the transport direction.

[0014] As shown in FIG. 1, the defect inspection system of this embodiment is configured with first lighting / imaging units 1F, 1B (sometimes collectively referred to as first lighting / imaging unit 1), second lighting units 2F, 2B (sometimes collectively referred to as second lighting unit 2), shape measurement units 3F, 3B (sometimes collectively referred to as shape measurement unit 3), and an analysis device 4, and detects multiple types of defects present in plywood 10 transported by belt conveyors 5U, 5D (sometimes collectively referred to as belt conveyor 5).

[0015] The belt conveyor 5 has an upstream belt conveyor 5U and a downstream belt conveyor 5D, which are spaced apart in the conveying direction. Therefore, a gap 51 exists in the conveying direction between the two belt conveyors 5U and 5D. As shown in FIG. 1(b), the belt conveyor 5 is configured by arranging multiple elongated belts in the width direction, which is perpendicular to the conveying direction. Therefore, multiple gaps 52 also exist in the width direction. The plywood 10 is conveyed sequentially from the upstream belt conveyor 5U configured in this manner to the downstream belt conveyor 5D.

[0016] Each of the first illumination / imaging units 1F and 1B includes a first illumination and an imaging device. The first illumination emits first illumination light for capturing color images. The first illumination light can be visible light, such as white, blue, or green. The first illumination / imaging units 1F and 1B are installed vertically above and below the gap 51 between the belt conveyors 5U and 5D, respectively, and vertically emit the first illumination light toward the front and back surfaces of the plywood 10 located in the gap 51. That is, the first illumination / imaging unit 1F installed above the gap 51 emits the first illumination light toward the front surface of the plywood 10 located in the gap 51. The first illumination / imaging unit 1B installed below the gap 51 emits the first illumination light toward the back surface of the plywood 10 located in the gap 51.

[0017] Each of the second lighting units 2F and 2B includes a second lighting element. The second lighting element emits second illumination light for acquiring depth information. The second illumination light can be, for example, a line-shaped laser light for light-section measurement, which has a different color from the first illumination light. The second lighting units 2F and 2B are installed downstream (or upstream) of the center position of the gap 51 of the belt conveyors 5U and 5D in the conveying direction, and obliquely emit the second illumination light toward the front and back surfaces of the plywood 10 located in the gap 51. That is, the second lighting unit 2F installed above the gap 51 obliquely emits the second illumination light toward the front surface of the plywood 10 located in the gap 51. The second lighting unit 2B installed below the gap 51 obliquely emits the second illumination light toward the back surface of the plywood 10 located in the gap 51.

[0018] As shown in FIGS. 1B and 1C, the first illumination / imaging units 1F and 1B and the second illumination units 2F and 2B are installed in pairs in the width direction perpendicular to the conveyance direction (the second illumination units 2F and 2B are not shown in FIG. 1C). Note that the number shown here is an example, and one pair or three or more pairs may be used. This allows the first illumination light and the second illumination light to be irradiated without omission across the entire width of the plywood 10. Here, the first illumination light for capturing color images is irradiated in a planar manner onto the plywood 10. On the other hand, the second illumination light for acquiring depth information is irradiated in a linear manner onto the plywood 10.

[0019] The imaging device included in first lighting and imaging unit 1F on the front side of plywood 10 and the imaging device included in first lighting and imaging unit 1B on the back side of plywood 10 are installed in positions that are aligned vertically, and by simultaneously capturing images of the front and back surfaces of plywood 10 conveyed sequentially by belt conveyors 5U and 5D in gap 51, planar color images and depth information of the front and back surfaces of plywood 10 are generated. That is, the imaging device captures images of the front and back surfaces of plywood 10 in gap 51 while being irradiated with first illumination light and second illumination light, thereby generating planar color images and depth information. The depth information is information that indicates the distance from a reference position to the front surface of plywood 10 in the thickness direction and the distance to the back surface of plywood 10 in the thickness direction.

[0020] That is, the imaging device receives the reflected light of the first illumination light and the second illumination light irradiated onto the plywood 10 and performs photoelectric conversion to generate a two-dimensional color image. The generated two-dimensional color image includes the trajectory of the second illumination light irradiated in a line shape. The imaging device generates depth information by performing image processing based on a known light-section method on the line-shaped trajectory of the second illumination light included in the two-dimensional color image. The imaging device photographs the plywood 10 at predetermined sampling times while the plywood 10 is transported on the belt conveyor 5, and sequentially outputs the obtained two-dimensional color images and depth information to the analysis device 4.

[0021] Although an example of the configuration of the first lighting / imaging unit 1F, 1B in which the first lighting and the imaging device are integrally provided has been shown here, the first lighting and the imaging device may also be configured as separate entities.

[0022] The shape measuring units 3F, 3B correspond to the shape measuring devices in the claims, and are installed in locations different from the gap 51 in the conveying direction of the belt conveyors 5U, 5D to measure the shape of the plywood 10 in the board thickness direction and generate shape information. In the example of Fig. 1, the shape measuring units 3F, 3B are installed at positions vertically above and below the gap 51 at a sufficient distance on the downstream belt conveyor 5D side from the gap 51. A position on the downstream belt conveyor 5D that is sufficiently distant from the gap 51 is a position where the plywood 10 can be stably conveyed without being affected by bouncing at the gap 51.

[0023] The shape measuring units 3F, 3B are configured to include, for example, laser displacement sensors. The laser displacement sensors acquire information indicating the distance in the thickness direction from a reference position, the same as the depth information described above, to the front surface of the plywood 10 and the distance in the thickness direction to the back surface of the plywood 10 as shape information of the plywood 10. Here, the shape measuring unit 3F, which is installed above the downstream belt conveyor 5D, measures the shape of the front surface of the plywood 10. Meanwhile, the shape measuring unit 3B, which is installed below the downstream belt conveyor 5D, measures the shape of the back surface of the plywood 10.

[0024] As shown in Figures 1(b) and 1(c), three shape measurement units 3F and 3B are installed: one on each of the outer sides of the downstream belt conveyor 5D in the width direction, and one in the central gap 52. This allows the thickness-wise shape of the plywood 10 to be measured at multiple locations near both ends and the center. Because the shape of the plywood 10 is measured at a position where the plywood 10 can be transported stably, it is possible to accurately measure the shape of the plywood 10 at the three locations where the shape measurement units 3F and 3B are installed without being affected by the plywood 10 bouncing in the gap 51. Note that the number of shape measurement units 3F and 3B shown here is merely an example and is not limited to three. For example, a total of five shape measurement units 3F and 3B may be installed by installing a shape measurement unit 3F and 3B at each gap 52.

[0025] The analysis device 4 detects defects in the plywood 10 by analyzing the planar color images and depth information of the plywood 10 acquired by the imaging devices of the first illumination and imaging units 1F and 1B, and the shape information of the plywood 10 acquired by the shape measurement units 3F and 3B. Here, the analysis device 4 detects multiple types of defects in the plywood 10, such as discoloration, holes, and irregularities, based on the planar color images, and detects defects due to deformation, such as warping or bending, of the plywood 10, based on the depth information. At this time, the analysis device 4 corrects the depth information based on the depth information and the shape information.

[0026] 2 is a block diagram showing an example of the functional configuration of the analysis device 4 according to this embodiment. As shown in Fig. 2, the analysis device 4 according to this embodiment includes, as its functional configuration, a color image acquisition unit 41, a depth information acquisition unit 42, a shape information acquisition unit 43, a correction processing unit 44, and a defect detection unit 45.

[0027] These functional blocks 41 to 45 execute the processes described below through cooperation between hardware and software. For example, the processes of the functional blocks 41 to 45 are executed by the operation of a program stored in a storage medium such as RAM, ROM, a hard disk, or a semiconductor memory under the control of a microcomputer including a CPU, RAM, ROM, etc. In addition to the microcomputer, a DSP (Digital Signal Processor) or the like may also be included.

[0028] The color image acquisition unit 41 acquires planar color images of the front and back surfaces of the plyboard 10 generated by the imaging devices of the first lighting and imaging units 1F, 1B. The depth information acquisition unit 42 acquires depth information of the front and back surfaces of the plyboard 10 generated by the imaging devices of the first lighting and imaging units 1F, 1B. As described above, the planar color images acquired by the color image acquisition unit 41 and the depth information acquired by the depth information acquisition unit 42 are generated by the imaging devices photographing the plyboard 10 in the gap 51 in the conveying direction of the belt conveyors 5U, 5D.

[0029] 3 (FIGS. 3A to 3H) are diagrams showing an example of depth information (depth information generated by an imaging device) of a plywood 10 acquired by the depth information acquisition unit 42. Here, an example of depth information is shown acquired as a warped plywood 10 is conveyed sequentially from the upstream belt conveyor 5U to the downstream belt conveyor 5D through the gap 51. The warp refers to a state in which the cross-sectional shape of the plywood 10 in the conveying direction is bowed (arcuate) across the entire width of the plywood 10.

[0030] 3, D1 is depth information for the front surface of the plywood 10, and D2 is depth information for the back surface of the plywood 10, both of which indicate depth information at a specific location in the width direction of the plywood 10. For the sake of explanation, the reference positions for the depth information for the front and back surfaces are both the surface position (a position above the surface of the belt conveyor 5 by the thickness of the plywood 10) when the plywood 10 is assumed to be flat across its entire surface.

[0031] 3A shows a state in which the portion of the plyboard 10 near the leading edge on the downstream side in the conveyance direction is located in the gap 51, and the portion near the leading edge is lower than the reference position. Therefore, the depth information of the plyboard 10 is acquired as information indicating a shape that is recessed downward from the reference position. The portion near the leading edge of the plyboard 10 continues to descend until the leading edge of the plyboard 10 rests on the downstream belt conveyor 5D, as shown in FIG. 3B. Therefore, the depth information also continues to recess downward.

[0032] As shown in Figure 3C, the plywood 10 bounces upward due to the impact the moment its leading edge touches the downstream belt conveyor 5D. Therefore, the depth information acquired shows a shape that protrudes above the reference position. As shown in Figure 3D, the plywood 10 may bounce multiple times. Figure 3E shows the depth information acquired after the bouncing has stopped, at a position where the surface of the plywood 10 is higher than the reference position due to warping.

[0033] The plywood 10 is transported stably until its rear end on the upstream side in the transport direction falls into the gap 51, and the depth information acquired during this time is as shown in FIG. 3F. FIG. 3G shows a state in which the rear end of the plywood 10 is positioned in the gap 51 and is lower than the reference position. Therefore, the depth information of the plywood 10 is acquired as information indicating a shape that is recessed below the reference position. At this point, the plywood 10 may bounce slightly. After that, the plywood 10 is transported while the rear end portion is gradually raised upward along the overall warp, and the depth information as shown in FIG. 3H is acquired.

[0034] The shape information acquisition unit 43 acquires shape information of the front and back surfaces of the plyboard 10 generated by the shape measurement units 3F, 3B. As described above, the shape information acquired by the shape information acquisition unit 43 is measured by using a laser displacement sensor to irradiate the plyboard 10 with laser light at a position sufficiently separated from the gap 51 in the conveying direction of the belt conveyors 5U, 5D.

[0035] 4 is a diagram schematically illustrating an example of shape information of plyboard 10 acquired by shape information acquisition unit 43 (shape information generated by shape measurement units 3F, 3B). Here, an example of shape information acquired for plyboard 10 shown in FIG. 3 is shown. In FIG. 4, F1 is shape information of the front surface of plyboard 10, and F2 is shape information of the back surface of plyboard 10. The reference positions of the shape information of the front and back surfaces are both assumed to be the same as the reference positions of depth information D1, D2.

[0036] As described above, the shape measurement units 3F and 3B can accurately measure the shape of the plywood 10. Therefore, as shown in FIG. 4 , the shape information acquired by the shape information acquisition unit 43 matches the actual shape of the plywood 10.

[0037] The correction processing unit 44 corrects the depth information acquired by the depth information acquisition unit 42 based on the shape information acquired by the shape information acquisition unit 43. For example, when the shape of the plyboard 10 in the thickness direction indicated by the depth information acquired by the imaging device of the first lighting and imaging units 1F, 1B differs from the shape of the plyboard 10 in the thickness direction indicated by the shape information acquired by the laser displacement sensor of the shape measurement units 3F, 3B at the same position as the position where the depth information was acquired, the correction processing unit 44 corrects the depth information based on the shape information.

[0038] The position where the depth information is acquired and the position where the shape information is acquired are the same means that the position of the plywood 10 photographed by the imaging device in the gap 51 between the belt conveyors 5U and 5D is the same as the position of the plywood 10 measured after the plywood 10 is transported from there to the position of the shape measurement units 3F and 3B. The same position on the plywood 10 can be identified, for example, based on the transport distance from when the edge of the plywood 10 is detected in the captured image. Alternatively, it can also be identified from the transport distance from the first lighting / imaging units 1F and 1B to the shape measurement units 3F and 3B and the transport speed of the belt conveyor 5.

[0039] The correction processing unit 44 calculates a difference value between the depth information and the shape information at the same position described above, and corrects the depth information using the difference value as a correction value for the depth information. Fig. 5 is a diagram for explaining the processing content of the correction processing unit 44. Fig. 5 shows the depth information D1, D2 generated by the first illumination and imaging units 1F, 1B as in Fig. 3 and the shape information F1, F2 generated by the shape measurement units 3F, 3B as in Fig. 4, superimposed so that the same positions correspond to each other.

[0040] 5, the portion indicated by reference numeral 501 represents a period during which the portion of plywood 10 near the leading edge falls into gap 51 and a period during which plywood 10 bounces. Furthermore, the portion indicated by reference numeral 502 represents a period during which the portion of plywood 10 near the trailing edge falls into gap 51. During these periods 501 and 502, the shape of plywood 10 represented by depth information D1 and D2 does not match the exact shape of plywood 10 represented by shape information F1 and F2. At the portions where the shapes do not match, correction processing unit 44 calculates the difference between depth information D1 and D2 and shape information F1 and F2 as a correction value, and corrects the depth information by adding this correction value to depth information D1 and D2.

[0041] When correction is performed in this manner, the depth information D1 and D2 is corrected in a manner that removes only the difference from the actual shape of the plywood 10, without removing defects such as warping or bending of the plywood 10. As a result, the corrected depth information accurately represents the shape of the plywood 10, similar to the shape information F1 and F2 in FIG.

[0042] Although the depth information D1 and D2 are corrected here when the shape of the plywood 10 indicated by the depth information D1 and D2 differs from the shape of the plywood 10 indicated by the shape information F1 and F2, the depth information D1 and D2 may be corrected without determining whether the shapes differ. In this case, for portions where the shape of the plywood 10 indicated by the depth information D1 and D2 is the same as the shape of the plywood 10 indicated by the shape information F1 and F2, correction is performed by setting the difference between the depth information D1 and D2 and the shape information F1 and F2 to zero, which is essentially equivalent to correcting the depth information D1 and D2 only for portions where the shapes differ.

[0043] The defect detection unit 45 detects multiple types of defects in the plywood 10 based on the flat color image acquired by the color image acquisition unit 41. The multiple types of defects detected based on the flat color image include discoloration (mold, dirt, bark inclusions, etc.) on the front and back surfaces of the plywood 10, blind holes, loopholes, insect holes, dust inclusions, and dust accumulations. These defects can be detected using known techniques, and detailed explanations will be omitted.

[0044] It is difficult to detect relatively gradual deformations such as warping and bending of the plywood 10 by analyzing only a flat color image. While it is possible to detect warping and bending by utilizing the shadows cast by multiple lighting sources, this is difficult to detect because the difference in pixel values ​​corresponding to the shadows becomes small depending on the degree of unevenness and the angle of the lighting, and in some cases, no shadows are generated at all depending on the angle of the unevenness. Therefore, defects caused by such deformations are detected based on depth information.

[0045] The defect detection unit 45 detects defects due to deformation such as warping or bending of the plywood 10 based on the depth information acquired by the depth information acquisition unit 42. Here, if the depth information has been corrected by the correction processing unit 44, defects such as warping or bending of the plywood 10 are detected based on the corrected depth information. As described above, by correcting the depth information by the correction processing unit 44, the corrected depth information accurately represents the shape of the plywood 10, making it possible to accurately detect defects such as warping or bending.

[0046] 6 is a flowchart showing an example of the operation of the analysis device 4 configured as above. This Fig. 6 shows an example of the operation when detecting defects in one piece of plywood 10.

[0047] In the loop processing of steps S1 to S2, color image acquisition unit 41, depth information acquisition unit 42, and shape information acquisition unit 43 acquire planar color images, depth information, and shape information for the entire plywood 10 from its leading edge to its trailing edge. That is, in step S1, color image acquisition unit 41 and depth information acquisition unit 42 sequentially acquire planar color images and depth information generated sequentially by first illumination and imaging units 1F, 1B from the leading edge to the trailing edge as the plywood 10 is transported, and shape information acquisition unit 43 sequentially acquires shape information generated sequentially by shape measurement units 3F, 3B from the leading edge to the trailing edge as the plywood 10 is transported.

[0048] In step S2, it is determined whether acquisition of planar color images, depth information, and shape information for the entire plywood 10 has been completed. If not, the process returns to step S1 to continue. On the other hand, if it is determined that acquisition of information for the entire plywood 10 has been completed, the correction processing unit 44 corrects the depth information based on the shape information (step S3). Then, the defect detection unit 45 detects multiple types of defects in the plywood 10 based on the color images, and detects defects due to deformations such as warping and bending of the plywood 10 based on the corrected depth information (step S4). This completes the process of the flowchart shown in FIG. 6.

[0049] Although the above description deals with the process of executing the correction processing unit 44 and the defect detection unit 45 after the first lighting and imaging units 1F, 1B and the shape measurement units 3F, 3B have completed their processes for the entire plywood 10, the present invention is not limited to this. For example, the process of the correction processing unit 44 may be executed sequentially while the first lighting and imaging units 1F, 1B and the shape measurement units 3F, 3B are executed from the leading edge of the plywood 10 to the trailing edge thereof, and the process of the defect detection unit 45 may be executed after the processes have been completed for the entire plywood 10.

[0050] As explained in detail above, in this embodiment, the front and back surfaces of the plywood 10 transported on the belt conveyor 5 are photographed by the first lighting and imaging units 1F, 1B to generate depth information for both surfaces of the plywood, and the shape information is generated by measuring the shape of the plywood 10 by the shape measuring units 3F, 3B installed in a location different from the gap 51 between the belt conveyors 5U, 5D where the photographing is performed. The depth information is then corrected based on the shape information, and defects due to deformation of the plywood 10 are detected based on the depth information.

[0051] The shape of the plywood 10 in the thickness direction, which is measured at a location other than the gap 51 between the belt conveyors 5U and 5D, is a shape measured without being affected by vibrations that occur when the plywood 10 passes through the gap 51 while being transported, and defects due to deformation such as warping or bending of the plywood 10 are detected based on depth information corrected on the basis of this shape information. As a result, only errors in the depth information that occur due to the influence of vibrations that occur when the plywood 10 passes through the gap 51 while being transported are removed by correction based on the shape information, and defects due to deformation such as warping or bending that occur in the plywood 10 can be accurately detected without being flattened out by correcting the depth information.

[0052] In the above embodiment, an example has been described in which laser displacement sensors are installed above and below the belt conveyors 5U and 5D as an example of a shape measuring device that measures the shape of the plywood 10 at a location other than the gap 51 between the belt conveyors 5U and 5D, but the present invention is not limited to this. For example, instead of or in addition to the laser displacement sensors, a configuration may be provided in which a side image capturing device is provided that captures an image of the side of the plywood 10 and generates image information of the side.

[0053] Fig. 7 is a diagram showing an example of the overall configuration of a defect inspection system according to this modified example. Fig. 8 is a block diagram showing an example of the functional configuration of an analysis device 4' in the defect inspection system according to this modified example. Note that in Figs. 7 and 8, components having the same functions as those shown in Figs. 1 and 2 are denoted by the same reference numerals.

[0054] As shown in Figure 7, the defect inspection system according to the modified example is provided with side image pickup devices 6L, 6R on the left and right sides, at a sufficient distance from the gap 51 toward the downstream belt conveyor 5D. The distance from the gap 51 to the positions where the side image pickup devices 6L, 6R are installed is the same as the distance from the gap 51 to the positions where the shape measuring units 3F, 3B are installed. As shown in Figures 7(b) and (c), in the defect inspection system according to the modified example, only one set of shape measuring units 3F, 3B is installed at the center position in the width direction of the downstream belt conveyor 5D. However, three or more sets may be installed, as in Figure 1.

[0055] As shown in FIG. 8 , the analysis device 4′ according to the modified example further includes a side image acquisition unit 46 and a side shape recognition unit 47 as functional components. Furthermore, the analysis device 4′ includes a defect detection unit 45′ instead of the defect detection unit 45. The side image acquisition unit 46 acquires side color images generated by the side image capture devices 6L, 6R. The side image acquisition unit 46 supplies the acquired side color images to the defect detection unit 45′ and the side shape recognition unit 47.

[0056] The defect detection unit 45' detects multiple types of defects present on the front and back surfaces of the plywood 10 based on the planar color images acquired by the color image acquisition unit 41, and also detects defects present on the side surfaces of the plywood 10 based on the side color images acquired by the side image acquisition unit 46.

[0057] The side surface shape recognition unit 47 generates shape information in the thickness direction of the plywood 10 by analyzing the side surface color image acquired by the side surface image acquisition unit 46. The analysis performed here can be performed by applying a known image recognition process that detects the shape of an object from a captured image.

[0058] By analyzing the side color images taken by the left and right side image capture devices 6L, 6R, shape information in the thickness direction at the left and right ends of the plywood 10 can be obtained, and shape measurement units 3F, 3B can obtain shape information in the thickness direction at the center of the plywood 10. Furthermore, the left and right side image capture devices 6L, 6R can be used both as a means for obtaining shape information in the thickness direction at the left and right ends of the plywood 10 and as a means for detecting defects present on the side of the plywood 10.

[0059] In addition, Figure 7 shows an example in which the shape measurement units 3F, 3B and the side image capture devices 6L, 6R are installed at positions at the same distance from the gap 51, but it is not necessarily required to install them at positions at the same distance.

[0060] 7 and 8 show an example of a shape measuring device including side image capturing devices 6L and 6R and a side shape recognition unit 47 of an analyzer 4′, but the present invention is not limited to this. In other words, any means capable of measuring the shape of plywood 10 in the thickness direction can be used as the shape measuring device. For example, shape measurement using an optical cutting method may be used. Alternatively, a method of measuring the shape of plywood 10 using a contact-type physical sensor may be used.

[0061] In addition, in the above embodiment and modified example, an example is shown in which the shape measurement units 3F, 3B and the side image capturing devices 6L, 6R are all installed on the downstream belt conveyor 5D side, but either one or both may be installed on the upstream belt conveyor 5U side.

[0062] Furthermore, the above-described embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereby. In other words, the present invention can be carried out in various forms without departing from the gist or main characteristics thereof.

[0063] 1F, 1B First lighting and imaging unit (imaging device) 2F, 2B Second lighting unit 3F, 3B Shape measurement unit (shape measurement device) 4, 4' Analysis device 5U, 5D Belt conveyor 6L, 6R Side imaging device 41 Color image acquisition unit 42 Depth information acquisition unit 43 Shape information acquisition unit 44 Correction processing unit 45, 45' Defect detection unit 46 Side image acquisition unit 47 Side shape recognition unit 51 Gap

Claims

1. imaging devices that are arranged vertically above and below a gap between conveyors spaced apart in the conveying direction, and that capture images of the front and back surfaces of the plywood sequentially conveyed by the conveyors in the gap between the conveyors, and generate depth information in the board thickness direction based on the captured images of the front and back surfaces of the plywood; a shape measuring device that measures the shape in the plate thickness direction at a location different from the gap between the conveyors and generates shape information; an analysis device that detects defects in the plywood due to warping or bending by analyzing the depth information acquired by the imaging device and the shape information acquired by the shape measurement device; The analysis device a correction processing unit that corrects the depth information based on the shape information; a defect detection unit that detects defects due to deformation of the plywood based on the depth information. A defect inspection system comprising:

2. The depth information and the shape information are information indicating a distance in the board thickness direction from a reference position to the front surface or the back surface of the plywood, The correction processing unit calculates a difference value between the depth information and the shape information, and corrects the depth information using the difference value as a correction value for the depth information.

2. The defect inspection system according to claim 1.

3. The defect inspection system described in claim 1, characterized in that the correction processing unit corrects the depth information based on the shape information when the shape in the plate thickness direction indicated by the depth information acquired by the imaging device differs from the shape in the plate thickness direction indicated by the shape information acquired by the shape measuring device at the same position as the position where the depth information was acquired.

4. The defect inspection system described in claim 1, characterized in that the imaging devices are installed in positions vertically above and below the gap between the conveyors, in a straight line above and below, and simultaneously photograph the front and back surfaces of the plywood.

5. a first illuminator for irradiating a first illumination light for color image capture onto the front and back surfaces of the plywood; a second illuminator that irradiates a second illumination light for acquiring depth information toward the front and back surfaces of the plywood, the imaging device captures images of the front and back surfaces of the plywood in a gap between conveyors while being irradiated with the first illumination light and the second illumination light, thereby generating a planar color image and the depth information; The analysis device detects a plurality of types of defects in the plywood based on the planar color image, and detects defects due to deformation of the plywood based on the depth information.

5. The defect inspection system according to claim 1, wherein:

6. 6. The defect inspection system according to claim 5, wherein the second illumination light is illumination light for light section measurement.

7. The shape measuring device is a side image capturing device for capturing an image of a side surface of the plywood to generate a side color image; a side shape recognition unit included in the analysis device, The side surface shape recognition unit generates shape information of the plywood in the thickness direction by analyzing the side surface color image acquired by the side surface imaging device.

5. The defect inspection system according to claim 1, wherein:

8. 8. The defect inspection system according to claim 7, wherein the analysis device further detects defects present on the side surface of the plywood based on the side color image.

9. A process in which imaging devices are arranged at positions vertically above and below the gap between conveyors spaced apart in the conveying direction to capture images of the front and back surfaces of the plywood sequentially conveyed by the conveyors in the gap between the conveyors, and depth information in the board thickness direction is generated based on the captured images of the front and back surfaces of the plywood; a step of measuring the shape in the plate thickness direction at a location different from the gap between the conveyors using a shape measuring device to generate shape information; and a step of detecting a deformation defect due to warping or bending in the plywood by analyzing the depth information acquired by the imaging device and the shape information acquired by the shape measuring device using an analysis device, The step of detecting defects in the plywood using the analysis device includes: a first step in which a correction processing unit of the analysis device corrects the depth information based on the shape information; a second step in which the defect detection unit of the analysis device detects defects due to deformation of the plywood based on the depth information corrected by the correction processing unit. A defect inspection method comprising: