Sanitary paper defect inspection device and manufacturing method

Abstract

To enable accurate detection of the sizes and shapes of holes appearing on a sheet-like object.SOLUTION: A defect inspection device 200 for sheet-like object S is provided, comprising an image capturing device 211 located on one side of an inspection target portion of the sheet-like object S and configured to capture an image of a surface of the inspection target portion, and a light source 212 located on a side of the other surface of the inspection target portion to illuminate a shooting range of the image capturing device 211 from the side of the other surface of the inspection target portion, the light source 212 being located outside an angle of view range of the image capturing device 211.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a defect inspection device for a sheet-like material such as toilet paper, and a method for manufacturing a sheet-like material using the same.

Background Art

[0002] Conventionally, regarding household toilet paper such as toilet paper and tissue paper, as a method for inspecting defects (holes, stains, streaks, foreign substances, etc.) generated during the manufacturing process, while the base paper of the toilet paper is being conveyed at high speed by a roller or the like, the paper surface is photographed with a camera during the conveyance to detect defects generated on the paper surface. This is known.

[0003] Regarding a defect inspection technique for a test object of a sheet-like material such as paper or film, Patent Document 1 discloses an inspection device including an illumination device that irradiates light on the sheet-like material and an imaging device that continuously images the transmitted light transmitted through the sheet-like material, and performing a pass / fail determination by analyzing the captured image of the sheet-like material. In this way, an inspection method of detecting the light irradiated from the illumination device and transmitted through the sheet-like object with a camera is also called the "transmission method".

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a conventional defect inspection apparatus of the "transmission method", an illumination device is arranged on the optical axis of an imaging device. However, when the illumination device is arranged on the optical axis of the imaging device in this way, when there are hole-shaped defects or perforations in the sheet-like object, diffraction of light occurs when the light irradiated from the illumination device passes through these holes, and these holes may be imaged larger than actual or their shapes may not be accurately detected. In particular, in a sheet-like object with perforations formed in advance, when a hole is formed on the paper surface, it is necessary to distinguish whether it is a known perforation or an unknown defect. However, if the size and shape of the hole cannot be accurately detected due to light diffraction, it becomes difficult to determine whether the hole is a perforation or a defect.

[0006] Therefore, a main object of the present invention is to provide a defect inspection technology capable of more accurately detecting the size and shape of holes formed in a sheet-like object.

Means for Solving the Problems

[0007] As a result of earnestly studying means for solving the above-mentioned problems of the conventional invention, the inventor of the present invention has obtained the finding that, in a defect inspection apparatus of the transmission method, by arranging a light source outside the angle-of-view range of the imaging device, the size and shape of holes formed in a sheet-like object can be detected more accurately. And based on the above finding, the inventor of the present invention has conceived that the problems of the prior art can be solved and has completed the present invention. Specifically described, the present invention has the following configurations or steps.

[0008] A first aspect of the present invention relates to a defect inspection apparatus for a sheet-like object. The defect inspection apparatus according to the present invention includes an imaging device and one or more light sources. The imaging device is disposed on one surface side of an inspection site of the sheet-like object and images the surface of the inspection site. The light source is disposed on the other surface side of the inspection site and illuminates the imaging range of the imaging device from the other surface side of the inspection site. At this time, the one or more light sources are disposed outside the angular range of the imaging device. That is, in the present invention, there is no light source within the angular range of the imaging device, and the imaging range of the imaging device is illuminated by the light source provided outside the angular range thereof.

[0009] As described above, since the light source is not disposed on the optical axis of the imaging device, even when the sheet-like object has perforations or hole-shaped defects, it is possible to suppress the diffracted light from directly entering the imaging device through the holes. As a result, the holes formed in the sheet-like object can be accurately imaged by the imaging device. As a result, it is also easy to distinguish the perforations and the hole-shaped defects from the captured image obtained by the imaging device. Further, by inspecting the defects of the sheet-like object by the transmission method as in the present invention, even when the sheet-like object is laminated in two or more layers, the hole-shaped defects generated only in one layer and other defects such as the adhesion of foreign matters can be effectively detected.

[0010] In the defect inspection apparatus according to the present invention, it is preferable that the imaging device is disposed such that its optical axis is substantially orthogonal to the inspection site, and the one or more light sources are disposed such that their optical axes are inclined with respect to the inspection site. By disposing the imaging device such that the optical axis is orthogonal to the inspection site of the sheet-like object in this way, the imaging device and the sheet-like object are substantially facing each other, so that the shape of the holes formed in the sheet-like object can be accurately imaged. In this case, by inclining the optical axis of the light source with respect to the inspection site of the sheet-like object, the illuminance of the inspection site can be maintained high. In particular, it is preferable that the imaging device and the light source are disposed such that the optical axis of the imaging device and the optical axis of the light source intersect within the plane of the inspection site of the sheet-like object.

[0011] The defect inspection apparatus according to the present invention may further include one or a plurality of light sources that are disposed on one surface side of the inspection target part (i.e., the same side as the imaging device) and illuminate the imaging range of the imaging device from one surface side of the inspection target part. In this way, by disposing the light source on the same side as the imaging device, the above-described inspection by the transmission method and the inspection by the reflection method can be performed simultaneously. For example, by using the reflection method in combination, it is possible to effectively detect thin stains attached to the sheet-like object.

[0012] The defect inspection apparatus according to the present invention preferably further includes an image analysis device that analyzes the captured image of the imaging unit. This image analysis device includes a database that stores the characteristics of non-defect parts (for example, perforation holes) that do not need to be detected as defects. Then, the image analysis device distinguishes, among the defects occurring in the sheet-like object in the captured image, the defects that match the characteristics of the non-defect parts stored in the database from the other defects. Thereby, even when perforation holes or the like are formed in the sheet-like object, it is possible to avoid that they are detected as defects. In particular, according to the present invention, since the size and shape of the holes generated in the sheet-like object can be detected more accurately as described above, it becomes easier to distinguish known perforation holes from other unknown hole-shaped defects.

[0013] A second aspect of the present invention relates to a method for manufacturing a sheet-like object. The method for manufacturing a sheet-like object according to the present invention includes a step of obtaining a sheet-like object and a step of inspecting the presence or absence of defects in this sheet-like object using the defect inspection apparatus according to the first aspect described above.

Effects of the Invention

[0014] According to the present invention, the size and shape of the holes generated in the sheet-like object can be detected more accurately.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes those appropriately modified by those skilled in the art within an obvious range from the following embodiments.

[0017] [1. First Embodiment] Referring to FIGS. 1 and 2, a first embodiment of the present invention will be described. The present invention relates to a defect inspection apparatus for a sheet-like material and a method for manufacturing a sheet-like material using the defect inspection apparatus. Examples of the sheet-like material include those made of paper or plastic. In particular, the sheet-like material is preferably household sanitary paper used as tissue paper or toilet paper. "Sanitary paper" means "sanitary paper" defined in JIS's "Paper, Paperboard and Pulp Terms" (JISP 0001). "Sanitary paper" includes towels, sanitary napkins, tissue paper, toilet paper, and waste paper. The sanitary paper manufactured by the present invention is preferably thin paper with a basis weight in the range of 10 to 25 g / m 2 . Also, the sanitary paper may be a single-ply product consisting of one sheet, or a multi-ply product of two or more sheets stacked, such as a two-ply or three-ply or more product. In the example shown in FIG. 1, after laminating two layers of sheets to form a laminated sheet, embossing and perforations are formed in this laminated sheet to obtain sanitary paper. Also, defect inspection of the sanitary paper is to be performed after the perforation process.

[0018] The process of manufacturing the base paper for sanitary paper basically includes a preparation process of obtaining a papermaking raw material (pulp slurry), which is a suspension of raw pulp fibers, and a papermaking process of forming a fiber web by papermaking the raw pulp fibers from the papermaking raw material and drying it. In the preparation process, the papermaking raw material (pulp slurry) used as the raw material for sanitary paper is adjusted. The papermaking raw material mainly uses pulp. Examples of the raw pulp include kraft pulp (KP) such as hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP); chemical pulp such as sulfite pulp (SP) and soda pulp (AP); semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP); mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP); or non-wood pulp made from raw materials such as kozo, mitsumata, hemp, kenaf, cotton-based pulp such as cotton linter and cotton lint, and deinked pulp made from waste paper. The papermaking raw material may use one type of raw pulp or a plurality of types of raw pulp in any ratio according to the use and required performance of the tissue paper. The raw pulp may be unbeaten pulp or may be wholly or partly beaten. The papermaking raw material adjusted in the preparation process is papermade in the papermaking process to become sanitary paper. The papermaking process can be carried out using a known papermaking machine. In this way, the original reel of the base paper of sanitary paper is generated, and sanitary paper can be obtained by overlapping the base paper drawn from a plurality of original reels while pulling it out, or by performing various processes (such as embossing and perforation).

[0019] Specifically, the base paper of the toilet paper is conveyed from the upstream of the device on the right side of FIG. 1 toward the downstream of the device on the left side. Upstream of the device, a first base roll 11 and a second base roll 12 are positioned. A long first sheet S1 is wound around the first base roll 11, and a long second sheet S2 is wound around the second base roll 12. When the first sheet S1 and the second sheet S2 are respectively fed out from the first base roll 11 and the second base roll 12, each sheet S1, S2 is conveyed to the downstream side of the device via a driving and rotating conveying roller and a driven and rotating guide roller, and at the first overlapping portion 20 (overlapping roller 21), they are overlapped with each other. Here, a plurality of layers of sheets in which the first sheet S1 and the second sheet S2 are overlapped are referred to as a laminated sheet. The laminated sheet is conveyed to the downstream side of the device.

[0020] Downstream of the first overlapping portion 20, an embossing portion 30 is positioned. In the example shown in FIG. 1, the laminated sheet is separated again into the first sheet S1 and the second sheet S2 in the embossing portion 30, and embossing is performed on each sheet. The embossing portion 30 includes, for example, embossing rollers 31, 32 and receiving rollers 33, 34 at positions facing each other across the conveying path of each sheet. The first sheet S1 is introduced between the first embossing roller 31 and the first receiving roller 33, and the second sheet S2 is introduced between the second embossing roller 32 and the second receiving roller 34. Each of the embossing rollers 31, 32 has a plurality of convex portions corresponding to the pattern of the embossing to be applied to each sheet S1, S2. On the other hand, for each of the receiving rollers 33, 34, a metal roller having, for example, a concave pattern complementary to the pattern of the convex portions of the embossing rollers 31, 32 formed on the outer peripheral surface, or a rubber roller whose outer peripheral surface is covered with rubber can be used. In the embossing portion 30, by introducing the sheets S1, S2 between the embossing rollers 31, 32 and the receiving rollers 33, 34 and sandwiching and pressing them, an embossing of a pattern corresponding to the convex portions of the embossing rollers 31, 32 can be applied to the paper surface of each sheet S, S2.

[0021] On the downstream side of the embossing section 30, a second laminating section 40 (laminating roller 41) is located. In the second laminating section 40, the first sheet S1 and the second sheet S2, which have been embossed separately in the embossing section 30, are laminated on each other. Thereby, a laminated sheet having a two-layer structure with embossing on each layer is obtained. Also, for example, when manufacturing kitchen paper, an adhesive may be applied between the layers after embossing to bond the two layers.

[0022] On the downstream side of the second laminating section 40, a perforating section 50 is located. In the perforating section 50, perforations extending in the width direction (a direction planar orthogonal to the conveyance direction) are formed in the laminated sheet at regular intervals. By forming the perforations, it becomes easier to cut the laminated sheet at predetermined lengths. The perforating section 50 includes, for example, a fixed blade 51 and a rotary blade 52. A plurality of blades are intermittently provided on the peripheral surface of the fixed blade 51 in a perforation pattern along the axial direction of the roller, and by sandwiching the laminated sheet between the fixed blade 51 and the rotary blade 52, perforations are formed in the laminated sheet by the blades. Examples of sheet products that require perforations include toilet paper and kitchen paper.

[0023] On the downstream side of the perforating section 50, a log forming section 70 is located. In the log forming section 70, after perforating, the laminated sheet is wound by a winding roller until it reaches a predetermined length to form a log. The log of the laminated sheet is then carried out to a cutting section (not shown) and cut to a predetermined width by a log saw or the like to become individual sheet products. In such a process, roll-shaped sheet products such as toilet rolls and kitchen rolls can be manufactured. However, the present invention can also be applied to sheet products such as tissue paper.

[0024] Also, as shown in FIG. 1, a photographing device 211 and a light source 212 of the defect inspection device 200 are arranged between the perforation processing unit 50 and the log forming unit 70. In the present embodiment, the defect inspection device 200 inspects the presence or absence of defects in a laminated sheet in which two layers of sheets S1 and S2 are overlapped (hereinafter also referred to as the toilet paper S). For this reason, the defect inspection device 200 may be provided at least at one location on the downstream side of the overlapping portion of the two layers of sheets S1 and S2. However, when embossing or perforating is performed on each sheet, defects are likely to occur in the sheet in each processing step. Therefore, the defect inspection device 200 may be provided at one location immediately after the embossing unit 30 and at one location immediately after the perforation processing unit 50, respectively.

[0025] The defect inspection device 200 includes a photographing device 211 (camera) installed so as to face the paper surface on one side (front side) of the toilet paper S, and an image analysis device 220 connected to the photographing device 211 by wire or wirelessly. Further, the defect inspection device 200 includes a light source 212 disposed on the other side (back side) of the toilet paper, that is, on the side opposite to the photographing device 211. Also, the toilet paper S is conveyed at a constant speed in a constant direction, particularly in the portion facing the photographing device 211. Further, the back side of the toilet paper S is illuminated by the light source 212, and the light transmitted through the toilet paper S is introduced into the photographing device 211. In this way, the photographing device 211 acquires a photographed image by imaging the light transmitted through the paper surface of the toilet paper S among the irradiation lights from the light source 212. The photographed image of the toilet paper acquired by the photographing device 211 is input to the image analysis device 220, and the image analysis device 220 analyzes whether or not a defect has occurred on the paper surface of the toilet paper. Further, the image analysis device 220 performs a process of determining the type of defect on the paper surface included in the photographed image.

[0026] Figure 2 shows an example of the arrangement of the imaging device 211 and the light source 212 for the defect inspection apparatus 200 according to the first embodiment. As shown in Figure 2, the imaging device 211 is arranged on the front surface side (one surface side) of the sanitary paper S, and the light source 212 is arranged on the back surface side (the other surface side) of the sanitary paper S. Also, in Figure 2, the "defects" occurring on the sanitary paper S are indicated by the symbol D. Examples of defects include quality defects such as holes, stains, streaks, foreign objects, etc., which are not suitable for the sale of sanitary paper. Further, in Figure 2, the "optical axis" of the imaging device 211 (the axis of symmetry passing through the center of the optical imaging system, also referred to as the principal axis) and the "optical axis" of the light source 212 (the central axis of the illumination range of the light) are each indicated by a dashed line. Also, in Figure 2, the "angle of view" of the imaging device 211 is indicated by the symbol W, and the "angle of view range" of the imaging device 211 is indicated by a broken line. Also, in Figure 2, the range on the paper surface of the sanitary paper S photographed by this imaging device 211 is defined as the "photographing range".

[0027] The imaging device 211 is a camera for acquiring still image or moving image data. The image data acquired by the imaging device 211 is transmitted to the image analysis device 220 (see Figure 1) and predetermined image analysis for defect detection is performed. The camera is realized by, for example, an optical-electrical conversion element such as a lens, a mechanical shutter, a shutter driver, a CCD image sensor unit or a CMOS image sensor unit, a digital signal processor (DSP) for reading out the charge amount from the optical-electrical conversion element and generating image data, an IC memory, etc. Note that the camera may be one for photographing still images or one for photographing moving images at a predetermined frame rate.

[0028] The imaging device 211 is preferably arranged such that its optical axis is substantially perpendicular to the paper surface of the sanitary paper S. That is, when a straight line is drawn vertically from the imaging surface of the imaging device 211, the straight line intersects the paper surface substantially perpendicularly. Specifically, the angle θ1 formed by the optical axis of the imaging device 211 and the paper surface of the sanitary paper S is preferably 80 to 100 degrees, and particularly preferably 85 to 95 degrees or 90 degrees. Thereby, the paper surface of the sanitary paper S can be photographed without distortion by the imaging device 211.

[0029] The light source 212 is a light that illuminates the imaging range of the toilet paper S imaged by the imaging device 211. The light source 212 preferably irradiates white light. Examples of the light source 212 include a fluorescent lamp, an LED (light-emitting diode), an OLED (organic light-emitting diode), a lamp, an arc lamp, an incandescent bulb, etc. Further, the light source 212 can adopt a spot light source, a parallel light source (surface light source), or a point light source, but it is most preferable to adopt a spot light source whose illumination range (spot size) and optical axis are easy to control. By using a spot light source, light can be irradiated in a limited direction and range from the light source. In FIG. 2, the illumination range of the light source 212 is indicated by a dashed line, and the optical axis of the light source 212 is indicated by a one-dot chain line. In the example shown in FIG. 2 and the like, as the light source 212, a spot light source whose illumination range (diameter) spreads in a tapered shape around the optical axis is adopted. Note that, as the spot light source, one with the same illumination range at infinity can also be used.

[0030] As shown in FIG. 2, the light source 212 is arranged to illuminate a range including the imaging range on the paper surface of the toilet paper S by the imaging device 211. That is, in the present embodiment, the imaging device 211 images the inspection site on the surface of the toilet paper S, and the light source 212 illuminates the inspection site of the toilet paper S imaged by the imaging device 211 from the back side. For this reason, the light irradiated from the light source 212 and transmitted through the toilet paper S is introduced into the imaging device 211. In this way, the imaging device 211 acquires a captured image of the toilet paper S in a transmission method.

[0031] In the present invention, no light source including the light source 212 is arranged within the angle-of-view range of the imaging device 211. That is, even when the toilet paper S is excluded, the light source 212 does not appear in the image captured by the imaging device 211. In particular, the light source 212 is not located on the optical axis of the imaging device 211. By arranging the imaging device 211 and the light source 212 in this way, even when the toilet paper S has perforations or hole-shaped defects, it is possible to suppress the diffracted light passing through the holes and directly entering the imaging device 211. As a result, the shape of the holes formed in the toilet paper S is accurately reflected in the captured image of the imaging device 211, making it easier to identify the size and shape of the holes.

[0032] Also, the angle-of-view W of the imaging device 211 is preferably 10 to 60 degrees, particularly preferably 15 to 50 degrees or 20 to 30 degrees. When the angle-of-view of the imaging device 211 is widened, it becomes difficult to arrange the light source 212 outside the angle-of-view range of the imaging device 211. Therefore, the angle-of-view of the imaging device 211 is preferably 60 degrees or less, particularly preferably 50 degrees or less.

[0033] Furthermore, as shown in FIG. 2, the imaging device 211 is preferably arranged outside the illumination range of the light source 212. That is, when the toilet paper S is excluded, the light irradiated from this light source 212 does not directly enter the imaging surface of the imaging device 211. By arranging the imaging device 211 outside the illumination range of the light source 212 in this way, it is possible to more reliably prevent the diffracted light passing through the holes of the toilet paper S from directly entering the imaging device 211. Also, if the illumination range of the light source 212 spreads too much, the irradiated light will directly enter the imaging device 211. Therefore, in order to narrow down the illumination range of the light source 213 to a certain extent, it is preferable to adopt a spot light source as this light source 213.

[0034] Also, as shown in FIG. 2, in the longitudinal cross-sectional view of the toilet paper S, the optical axis of the light emitted from the light source 212 is inclined at a predetermined angle θ2 with respect to the plane of the toilet paper S. The inclination angle θ2 of the optical axis of the light source 212 is preferably, for example, 30 degrees to 120 degrees, 40 degrees to 100 degrees, 50 degrees to 90 degrees, or 60 to 80 degrees. In the present embodiment, since it is assumed that the optical axis of the imaging device 211 is arranged so as to be substantially orthogonal to the toilet paper S, in order to arrange the light source 212 outside the angle-of-view range of the imaging device 211, it is necessary to incline the optical axis of the light source 212 with respect to the toilet paper S. From such a viewpoint, it is preferable that the inclination angle θ2 of the optical axis of the light source 212 is 80 degrees or less. In particular, in order to place the imaging device 211 outside the illumination range of the light source 212, it is preferable that the inclination angle θ2 of the optical axis of the light source 212 is 60 to 80 degrees.

[0035] Also, the optical axis of the imaging device 211 and the optical axis of the light source 212 are preferably arranged so as to intersect on the plane of the toilet paper S. Thereby, the imaging range of the imaging device 211 can be illuminated with sufficient illuminance by the light source 212.

[0036] The captured image of the imaging device 211 is analyzed by the image analysis device 220. The image analysis device 220 analyzes the image of the toilet paper acquired by the imaging device 211 to inspect whether there are defects in the toilet paper. A general computer may be used for the image analysis device 220. The image analysis device 220 is provided with an interface for the imaging device, and the image data acquired by the imaging device 211 is input thereto. The image analysis device 220 includes, for example, a control arithmetic unit, a storage unit (database), an operation unit, and a display unit. The control arithmetic unit performs image analysis processing of the image data acquired from the imaging device 211 according to a computer program for defect inspection stored in the storage unit. The control arithmetic unit can be realized by a processor such as a CPU or a GPU. The storage unit can be realized by a non-volatile memory such as an HDD or an SDD, or a volatile memory such as a RAM or a DRAM. The operation unit is composed of input devices such as a mouse, a keyboard, a touch panel, and a microphone, and receives operation information by a person. The display unit is a display device such as a liquid crystal display or an organic EL display, and may display the image data acquired from the imaging device 211.

[0037] The image analysis device 220 (specifically, the control arithmetic unit) basically analyzes the captured image acquired by the imaging device 211 to determine whether there are defects or defects on the surface of the toilet paper. For example, the image analysis device 220 measures the brightness (density) for each pixel or pixel group of the image data of the toilet paper, and when there is a portion darker (or brighter) than the normal brightness range, it determines that there is a defect in the toilet paper of the image data. For example, in the defect inspection by the transmission method, when a hole is formed in the toilet paper, the portion corresponding to the hole in the captured image appears bright in terms of brightness. Further, when foreign matter (for example, soot stain or oil stain) adheres to the toilet paper, the foreign matter portion appears dark in terms of brightness. In this way, the image analysis device 220 determines that the portion where the brightness of the image data is abnormal is the defect portion of the toilet paper. Further, the image analysis device 220 also determines that a defect has occurred in the toilet paper when the perforations are not formed at the locations where they should originally be.

[0038] Further, the image analysis device 220 may include a database storing features (such as size, shape, color, periodicity, etc.) of non-defective parts that do not need to be detected as defects. In this case, the image analysis device 220 identifies the size, shape, and periodicity of feature points that may be defective from the captured image, and among these feature points, distinguishes between defects that match the features of non-defective parts stored in the database and other defects. In this way, by comparing the feature points with the features of non-defective parts stored in the database, it is possible to distinguish between non-defective parts and others. For example, in sanitary paper S such as toilet paper, perforation holes may be formed periodically. Even when the perforation holes are reflected in the captured image, the image analysis device 220 can determine that this is a defective part by comparing it with the features of the perforation holes stored in the database. This can avoid misrecognizing the perforation holes as defects.

[0039] [2. Second Embodiment] FIG. 3 shows a configuration example of the defect inspection device 200 according to the second embodiment. For the following embodiments, the description will focus on the configurations different from the above-described first embodiment, and the same reference numerals will be given to the configurations substantially the same as those in the first embodiment, and the detailed description will be omitted.

[0040] In the second embodiment shown in FIG. 3, in addition to the same first light source 212 as in the first embodiment, a second light source 213 is arranged. Similar to the first light source 212, the second light source 213 is arranged on the back side of the sanitary paper S, that is, on the side opposite to the imaging device 211. In this way, it is also possible to perform defect inspection in a transmission method using a plurality of light sources 212 and 213. Also in this second embodiment, similar to the first embodiment, the first light source 212 and the second light source 213 are arranged outside the angular range of the imaging device 211. Further, it is preferable that the imaging device 211 is arranged outside the illumination ranges of the first light source 212 and the second light source 213. Also, the number of light sources is not limited to the first light source 212 and the second light source 213, and it is of course possible to further add more.

[0041] [3. Third Embodiment] FIG. 4 shows a configuration example of the defect inspection apparatus 200 according to the third embodiment. In the second embodiment shown in FIG. 4, in addition to the same first light source 212 as in the first embodiment, a third light source 214 is arranged. Different from the first light source 212, the third light source 214 is arranged on the surface side of the toilet paper S, that is, on the same side as the imaging device 211. Thus, the light irradiated from the first light source 212 passes through the toilet paper S as described above and enters the imaging device 211. On the other hand, the light irradiated from the third light source 214 is reflected on the paper surface of the toilet paper S and enters the imaging device 211. In this way, it is also possible to perform defect inspection of the toilet paper S by using the transmission method using the first light source 212 and the reflection method using the third light source 214 in combination.

[0042] Also, although not shown, as a modification of the third embodiment, it is also possible to arrange another light source on the surface side of the toilet paper S in the same manner as the third light source 214. In this way, when photographing the paper surface of the toilet paper S by the light reflection method, by arranging a plurality of light sources on the same side as the imaging device 211, floating substances (for example, paper dust) existing between the paper surface of the toilet paper S and the imaging device 211 can be illuminated from a plurality of directions. Therefore, the color of the shadow of the floating substances projected on the paper surface can be made lighter. As a result, by analyzing the captured image acquired by the imaging device 211, defects attached to the paper surface can be detected more clearly.

[0043] Also, as a further modification of the third embodiment, in addition to the first light source 212 and the third light source 214, it is also possible to arrange another light source on the back side of the toilet paper S, that is, on the side opposite to the imaging device 211, in the same manner as the second light source 213 (see FIG. 3) of the second embodiment described above. Furthermore, a plurality of light sources can be arranged on the surface side and the back side of the toilet paper S, respectively.

[0044] Above, in this specification of the present application, in order to express the content of the present invention, the embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to the above embodiments, and includes obvious modification forms and improvement forms that those skilled in the art can make based on the matters described in this specification of the present application.

Explanation of Reference Signs

[0045] 11…First original web roll 12…Second original web roll 20…First overlapping part 21…Overlapping roller 30…Embossing part 31…First embossing roller 32…Second embossing roller 33…First receiving roller 34…Second receiving roller 40…Second overlapping part 41…Overlapping roller 50…Perforation processing part 51…Cutter roller 52…Anvil roller 200…Defect inspection device 211…Imaging device 212…First light source 213…Second light source 214…Third light source 220…Image analysis device S1…First sheet S2…Second sheet S…Toilet paper (sheet-like material)

Claims

1. A defect inspection device for a sheet-like object, comprising: an imaging device disposed on one side of the inspection area of ​​the sheet-like material and configured to image a surface of the inspection area; one or more light sources arranged on the other side of the examination site and illuminating an imaging range of the imaging device from the other side of the examination site; The one or more light sources are disposed outside the angle of view range of the imaging device. Defect inspection equipment.

2. the imaging device is disposed so that its optical axis is substantially perpendicular to the region to be examined; The one or more light sources are arranged such that their optical axes are inclined with respect to the region to be inspected. The defect inspection device according to claim 1 .

3. and further comprising one or more light sources arranged on the one side of the examination site and illuminating an imaging range of the imaging device from the one side of the examination site.

3. The defect inspection device according to claim 1 or 2.

4. Further comprising an image analysis device for analyzing the captured image of the imaging unit, The image analysis device comprises: A database storing characteristics of non-defective portions that do not need to be detected as defects, Among the defects occurring on the sheet-like object in the captured image, defects that match the characteristics of non-defective portions stored in the database are distinguished from other defects. The defect inspection device according to any one of claims 1 to 3.

5. Obtaining a sheet-like material; and inspecting the sheet-like object for defects using the defect inspection device according to any one of claims 1 to 4. A method for producing a sheet-like material.

Images