CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2019/033190, filed Aug. 23, 2019, which claims priority to Japanese Patent Application No. 2018-176918, filed Sep. 21, 2018, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

The present invention relates to a lighting for defect inspection of sheet-shaped objects, a defect inspection apparatus for sheet-shaped objects, and a method of defect inspection of sheet-shaped objects.

BACKGROUND OF THE INVENTION

Conventionally, for the purpose of inspecting the presence or absence of defects such as scratches in a sheet-shaped object having a smooth surface, inspection apparatuses and inspection methods are available that apply light to a sheet-shaped object and, if a defect such as a scratch is present, detect the defect such as a scratch in the sheet-shaped object by reading out the scattered light caused by the scratch. In such an inspection apparatus, a linear light-application unit, such as a fluorescent lamp, and an imaging unit are typically arranged parallel to or almost parallel to the width direction of the sheet-shaped object to receive and detect the scattered light caused by defects.

The severity of a defect (such as a scratch) is typically determined by the magnitude of the amount of received scattered light (the magnitude of light amount value) to prevent the outflow of products with serious defects that pose a quality problem, and to perform quality control.

With the method for detecting a defect such as a scratch in a transparent sheet-shaped object described above, light may be reflected on the sheet-shaped object for inspection, or light may be transmitted through the sheet-shaped object for inspection. Referring toFIGS. 13 to 16, the principle of detecting defects such as scratches in a transparent sheet-shaped object that is continuously transferred in the above method is now described.FIGS. 13 and 14are diagrams illustrating the defect detection principle of an inspection that is performed with light reflected on the inspection target, andFIGS. 15 and 16are diagrams illustrating the defect detection principle of an inspection performed with light transmitted through the inspection target. InFIGS. 13 and 14, a linear application light source12is arranged so as to extend in a direction perpendicular to the plane of the drawing, and a defect100(seeFIGS. 14 and 16) in a sheet-shaped object5also extends in a direction perpendicular to the plane of the drawing. In general, since the width direction of the sheet-shaped object5often coincides with the longitudinal direction of the linear application light source12, a direction perpendicular to the plane of the drawing (Y direction) is referred to as a sheet width direction (light source longitudinal direction), a right-left direction on the plane of the drawing (X direction) is referred to as a transfer direction in which the sheet-shaped object5is continuously transferred, and is also referred to as a sheet longitudinal direction (light source lateral direction), and an up-down direction on the plane of the drawing (Z direction) is referred to as a sheet vertical direction (imaging unit optical-axis direction).

FIGS. 13 and 14illustrate a situation in which the linear application light source12and an imaging unit6are arranged at the same side of the sheet-shaped object5, and the reflected scattered light caused by a defect100, which is located in the surface of the sheet-shaped object5and parallel to the width direction (Y direction), is detected to detect the defect. Here, an optical center line8of the imaging unit6is arranged so as to be offset from an optical axis10(specular reflection optical axis) of the light that is emitted by the linear application light source12and specularly reflected on the sheet-shaped object. As such, when the surface of the sheet-shaped object5is free of a defect, light is reflected only in a direction that is linearly symmetrical with the incident light with respect to the normal to the surface of the sheet-shaped object5(the Z direction in this example) as illustrated inFIG. 13, so that no light enters the imaging unit6. However, when the surface of the sheet-shaped object5has a defect100parallel to the width direction (Y direction), reflected scattered light14is created by the defect100parallel to the width direction (Y direction) as illustrated inFIG. 14. Of the reflected scattered light14, a component15directed toward the imaging unit6enters the imaging unit6, enabling the detection of the defect.

FIGS. 15 and 16illustrate a situation in which the linear application light source12and the imaging unit6are arranged at opposite sides of the sheet-shaped object5, and the transmitted scattered light caused by a defect100, which is located in the surface of the sheet-shaped object5and parallel to the width direction (Y direction), is detected to detect the defect. Here, the optical center line8of the imaging unit6is arranged so as to be offset from the optical axis of the linear application light source12. As such, when the surface of the sheet-shaped object5is free of a defect, light is not scattered and transmitted linearly through the sheet as illustrated inFIG. 15, so that no light enters the imaging unit6. However, when the surface of the sheet-shaped object5has a defect100parallel to the width direction (Y direction), transmitted scattered light16is created by the defect100parallel to the width direction (Y direction) as illustrated inFIG. 16. Of the transmitted scattered light16, the component17directed toward the imaging unit6enters the imaging unit6, enabling the detection of the defect.

However, in the above method, the scattered light is strong and the sensitivity is high when light is applied, the incidence plane of which is perpendicular to the direction of the scratch, while the scattered light is weak and the sensitivity is low when light is applied, the incidence plane of which is parallel to the direction of the scratch. Consequently, when the above method uses a light source such as a fluorescent lamp or a parallel-bundle optical fiber light, which are common linear application light sources, the detection sensitivity for a scratch that is parallel to the sheet width direction (Y direction) is high, but there is the problem that the detection sensitivity for a scratch that is parallel to the sheet longitudinal direction (X direction) is low.

Patent Literature 1 discloses a technique for detecting scratches parallel to the sheet longitudinal direction (X direction) with high sensitivity.FIG. 17is a perspective view schematically illustrating an embodiment disclosed in Patent Literature 1. As illustrated inFIG. 17, Patent Literature 1 discloses an inspection apparatus including a linear light-application unit18formed by optical fibers, an imaging unit6, and the like. It is disclosed that the imaging unit6performs reading with a monitor camera, such as a line CCD camera, as a solid-state imaging device that detects light. The linear light-application unit18, which is formed by optical fibers, consists of at least two systems of optical fiber bundles18aand18b, which are arranged such that an optical axis directions of the light emitted from optical fiber emission ends form an angle of θ7aand an angle of θ7b, respectively, with the Z direction. InFIG. 17, the optical fiber bundles18aand18bhave light emission ends that are directed in different directions. This inspection apparatus is of a technique that detects a defect101parallel to the longitudinal direction X of the sheet-shaped object5by applying light, the incidence plane of which is perpendicular to the defect101. The angles θ7aand θ7bare uniform over the X direction in each system, and such lighting is referred to as oblique lighting. The oblique lighting with the angles θ7aand θ7bof crossing is referred to as cross oblique lighting.

Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. 2008-216148

SUMMARY OF THE INVENTION

However, the inspection method of Patent Literature 1 has the following problem. This problem is described with reference toFIG. 17. When detecting a defect101that is parallel to the longitudinal direction (X direction), the inspection method of Patent Literature 1 creates transmitted scattered light16having a certain degree of directivity and intensity distribution. The distribution and intensity of the transmitted scattered light16depend on the intensity of application light13, the angles θ7aand θ7bthat the application light13forms in the X direction with the axis in the Z direction, and the severity, shape, size, etc. of the scratch, but do not depend on the position of the scratch. As such, the transmitted scattered light16created by a defect101that is parallel to the longitudinal direction (X direction) is stronger when the severity of the scratch is greater, and is weaker when the severity of the scratch is lower. In general, an inspection apparatus determines the severity of a scratch based on the amount of received light. With the example described above, a scratch of low severity may fail to create a sufficient amount of light to be received, causing the defect to be overlooked.

In order to avoid such oversight, the angles θ7aand θ7bthat are formed by the application light13in the X direction with the axis in the Z direction are typically reduced to an extent that does not cause incident light to directly enter the imaging unit6and thus hinder the inspection. This reduction increases the intensity of the transmitted scattered light16caused by a scratch relative to the severity of the scratch, thereby achieving a sufficient amount of light to be received and thus the detection of the defect.

However, in the inspection method of Patent Literature 1, optical fibers are used as a mechanism of controlling the angles θ7aand θ7bof the light emitted by the linear light-application unit18. With an optical fiber, the light aperture angle φ (the angle of spreading of light from the optical fiber emission end) is generally determined by the material of the optical fiber. For example, the light aperture angle φ is 70 degrees for a commonly used multicomponent glass fiber, the light aperture angle φ is 60 degrees for an inexpensive plastic fiber, and the light aperture angle φ is 25 degrees for an expensive quartz fiber. In the distribution of the light intensity with respect to the light emission direction, the light intensity is highest in the center direction perpendicular to the fiber end, and the component spreading away from the center in the peripheral direction is gradually weakened. As such, the aperture angle of an optical fiber has a certain extent, and reductions in light intensity are inevitable in the peripheral angular portion. This imposes a limitation on the detection of a scratch with low severity.

Additionally, as described above, in the distribution of the light intensity with respect to the light emission direction, the light intensity of the light emitted by an optical fiber is highest in the center direction perpendicular to the fiber end, and the component spreading away from the center in the peripheral direction is gradually weakened. However, even though the component spreading in the peripheral direction is weak, there is a certain amount of light component leaking as diffused light from the light emission end surface and the side surface, for example, of the optical fiber. Consequently, when the linear light-application unit18formed by optical fibers is placed directly under the center of the optical axis of the imaging unit6, it is inevitable that some light components leaking from the optical fibers will directly enter the imaging unit6. For this reason, the amount of light is set low enough to avoid saturation of the brightness value, which hinders the detection of scratches, when the leaking light component is imaged by the imaging unit6. In this case, the intensity of the transmitted scattered light16caused by scratches cannot be relatively increased, so that a sufficient amount of light may not be obtained. This imposes a limitation on the detection of a scratch with low severity.

The linear light-application unit18formed by optical fibers can be inclined in the sheet longitudinal direction (X direction) from the position directly under the center of the optical axis of the imaging unit6, so that the light component leaking from the optical fibers does not directly enter the imaging unit6, avoiding the saturation of the brightness value when the light is imaged by the imaging unit6. This allows the amount of light to be increased. However, in this case, since the light application direction is a combination of the longitudinal direction (X direction) and the width direction (Y direction), light cannot be applied in a direction perpendicular to a defect101that is parallel to the longitudinal direction (X direction), failing to achieve a sufficient detection sensitivity for the defect101parallel to the longitudinal direction (X direction).

For the reasons described above, it is significantly advantageous to detect scratches parallel to the sheet longitudinal direction (X direction) with high sensitivity.

In view of the above, the present invention provides lighting for defect inspection of sheet-shaped objects, a defect inspection apparatus for sheet-shaped objects, and a method of defect inspection of sheet-shaped objects that detect a scratch parallel to the transfer direction of a sheet-shaped object with high sensitivity.

Solution to Problem

A lighting for defect inspection of sheet-shaped objects according to the present invention to solve the problem is to be used for defect inspection of sheet-shaped objects. The lighting includes: an elongated light application unit configured to apply illumination light to a sheet-shaped object, the light application unit extending in a second direction that is orthogonal to a first direction on a surface of the sheet-shaped object, the first direction being a direction in which the sheet-shaped object moves relative to the lighting; a first light shielding unit that is located on a light path from the light application unit to the sheet-shaped object, the first light shielding unit having light shielding sections and opening sections alternately arranged in a direction parallel to the second direction; and a second light shielding unit that is located, between the first light shielding unit and the sheet-shaped object, on the light path from the light application unit to the sheet-shaped object, the second light shielding unit having light shielding sections and opening sections alternately arranged in a direction parallel to the second direction. The opening sections of the first light shielding unit are located between the light shielding sections of the second light shielding unit and the light application unit in a third direction orthogonal to the first and second directions, and the opening sections of the first light shielding unit have a smaller length in the second direction than the light shielding sections of the second light shielding unit have.

In the lighting for defect inspection of sheet-shaped objects according to the present invention, it is preferable that the light shielding sections of the first light shielding unit and/or the light shielding sections of the second light shielding unit include, on sides facing the light application unit, light reflection members that protrude toward the light application unit.

A defect inspection apparatus for sheet-shaped objects according to the present invention to solve the problem includes: the lighting for defect inspection of sheet-shaped objects according to the present invention; an imaging unit configured to image light that is emitted by the lighting for defect inspection and transmitted through the sheet-shaped object; and an image processing unit configured to detect a defect occurring in the sheet-shaped object based on imaging data obtained by the imaging unit.

In the defect inspection apparatus for sheet-shaped objects according to the present invention, it is preferable that a longitudinal direction of the light application unit is parallel to an imaging direction of the imaging unit, in the imaging unit, optical axes at positions along the imaging direction are parallel to each other, and at each position at which light emitted by the lighting for defect inspection is transmitted through the sheet-shaped object, an angle formed by a transmission direction of light transmitted through the sheet-shaped object with an optical axis of the imaging unit is larger than an aperture angle of the imaging unit.

A defect inspection apparatus for sheet-shaped objects according to the present invention to solve the problem includes: the lighting for defect inspection of sheet-shaped objects according to the present invention; an imaging unit configured to image light that is emitted by the lighting for defect inspection and reflected on the sheet-shaped object; and an image processing unit configured to detect a defect occurring in the sheet-shaped object based on imaging data obtained by the imaging unit.

In the defect inspection apparatus for sheet-shaped objects according to the present invention, it is preferable that a longitudinal direction of the light application unit is parallel to an imaging direction of the imaging unit, in the imaging unit, optical axes at positions along the imaging direction are parallel to each other, and at each position at which light emitted by the lighting for defect inspection is reflected on the sheet-shaped object, an angle formed by a reflection direction of light specularly reflected on the sheet-shaped object with an optical axis of the imaging unit is larger than an aperture angle of the imaging unit.

In the defect inspection apparatus for sheet-shaped objects according to the present invention, it is preferable that the imaging unit includes a telecentric lens.

The defect inspection apparatus for sheet-shaped objects according to the present invention, it is preferable that the imaging unit includes a one-dimensional light receiving unit having a same length as a length in the imaging direction.

The defect inspection apparatus for sheet-shaped objects according to the present invention, it is preferable that the one-dimensional light receiving unit is a contact image sensor.

A method of defect inspection of sheet-shaped objects according to the present invention to solve the problem is a method for inspecting presence or absence of a defect of a sheet-shaped object by using a lighting unit and an imaging unit and by imaging light that is emitted by the lighting unit and transmitted through the sheet-shaped object with the imaging unit. The method includes: emitting, with the lighting unit, light with which an angle formed by a transmission direction of light transmitted through the sheet-shaped object with an optical axis of the imaging unit is larger than an aperture angle of the imaging unit at each position at which the light emitted by the lighting unit is transmitted through the sheet-shaped object, along a second direction orthogonal to a first direction on a surface of the sheet-shaped object, the first direction being a direction in which the sheet-shaped object moves relative to the lighting unit; imaging with the imaging unit whose imaging direction is parallel to the second direction of the sheet-shaped object and whose optical axes at positions along the imaging direction are parallel to each other; and determining presence or absence of a defect of the sheet-shaped object by using image data imaged by the imaging unit.

A method of defect inspection of sheet-shaped objects according to the present invention to solve the problem is a method for inspecting presence or absence of a defect of a sheet-shaped object by using a lighting unit and an imaging unit and by imaging light that is emitted by the lighting unit and reflected on the sheet-shaped object with the imaging unit. The method includes: emitting, with the lighting unit, light with which an angle formed by a reflection direction of specular reflection light reflected on the sheet-shaped object with an optical axis of the imaging unit is larger than an aperture angle of the imaging unit at each position at which the light emitted by the lighting unit is reflected on the sheet-shaped object, along a second direction orthogonal to a first direction on a surface of the sheet-shaped object, the first direction being a direction in which the sheet-shaped object moves relative to the lighting unit; imaging with the imaging unit whose an imaging direction is parallel to the second direction of the sheet-shaped object and whose optical axes at positions along the imaging direction are parallel to each other; and determining presence or absence of a defect of the sheet-shaped object by using image data imaged by the imaging unit.

According to the present invention, when detecting scratches parallel to the transfer direction of a sheet-shaped object, it is possible to detect defects with high sensitivity.

