Apparatus for visual inspection and method for visual inspection

Abstract

To provide a visual inspection device that, while simplifying a configuration, makes it possible to easily acquire a plurality of images with varied optical conditions.SOLUTION: The visual inspection device comprises: a stage 30 on which a metal mask M is placed; a conveyance table 20 that moves the stage 30 in a one-dimensional direction; a line illumination 42 that irradiates the metal mask M moving on the conveyance table 20 with illumination light L; a line camera 52 that captures an image of the metal mask M so that a section of the metal mask M irradiated with the illumination light L is included; and a base unit 10 that supports the conveyance table 20, the line illumination 42, and the line camera 52 independently of each other. The base unit 10 moves the line illumination 42 so as to change the angle of the illumination light L with which the metal mask M is irradiated, and moves the line camera 52 so as to change the imaging angle of the line camera 52 at which images of the metal mask M are captured, causing the conveyance table 20 to be rotated around a revolving shaft L1 with respect to the line illumination 42 and the line camera 52.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an appearance inspection apparatus and an appearance inspection method.

Background Art

[0002] In the production of an organic EL display, a metal mask is used to vaporize an organic EL material on the surface of a substrate in a predetermined shape. The metal mask is a rectangular metal plate having a thickness of several tens of μm. The metal mask includes through holes having a width of several tens of μm. In the production of an organic EL display, an organic EL material corresponding to the shape of the through holes provided in the metal mask is formed on the surface of the substrate.

[0003] In the manufacturing process of the metal mask, an appearance inspection is performed to check for various defects such as scratches and discoloration by visual inspection or an appearance inspection apparatus. For example, Patent Document 1 describes an inspection apparatus including a plurality of lighting devices and imaging devices with different optical conditions in order to detect various defects.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Providing a plurality of lighting devices and imaging devices with different optical conditions in an appearance inspection apparatus leads to an increase in the size and complexity of the appearance inspection apparatus.

Means for Solving the Problems

[0006] A visual inspection apparatus for solving the above problems includes a stage having a mounting surface on which a metal plate is placed, a transport table supporting the stage, the transport table having a transport unit that moves the stage between a first position and a second position on the transport table, through an imaging position between the first position and the second position, along a one-dimensional transport direction, line illumination that irradiates the metal plate on the stage passing through the imaging position with line-shaped illumination light extending in a direction intersecting the transport direction, and the metal plate on the stage passing through the imaging position that is illuminated by the illumination light. The system comprises a line camera that captures images including a portion of the metal plate, a base portion that separately supports the transport table, the line lighting, and the line camera, the base portion comprising: a lighting drive unit that changes the irradiation angle of the lighting light onto the metal plate by moving the line lighting, a camera drive unit that changes the imaging angle of the line camera onto the metal plate by moving the line camera, and a transport table drive unit that rotates the transport table relative to the line lighting and the line camera, with a perpendicular line passing through a point on the imaging position and perpendicular to the aforementioned mounting surface as the axis of rotation.

[0007] With the above configuration, the optical conditions, such as the illumination angle and imaging angle of the illumination light on the metal plate placed on the stage, can be changed by driving the lighting drive unit, camera drive unit, and transport table drive unit. Therefore, multiple images with different optical conditions can be easily acquired according to the type of defect.

[0008] In the above-described visual inspection apparatus, a support portion may be further provided to support the stage from below at the imaging position. With this configuration, as the metal plate passes through the imaging position, the stage is supported by the support portion, making it possible to image the metal plate placed on a flat stage. In addition, since the position of the metal plate in the height direction can be kept constant, the focus of the line camera can be adjusted with greater precision.

[0009] In the above-described appearance inspection apparatus, the metal plate contains a ferromagnetic metal, the stage is non-magnetic, and the support portion may be equipped with a magnet that magnetically attracts the metal plate downward from below the stage at the imaging position. With this configuration, at the imaging position, the metal plate is attracted toward the mounting surface by the magnet provided in the support portion. This suppresses the floating of the metal plate relative to the mounting surface, thereby enabling imaging of a flatter metal plate.

[0010] In the above-described visual inspection apparatus, the transport table drive unit may be configured to rotate the transport table within a range of 0 degrees to 45 degrees, where the angle between the direction in which the line lighting and the line camera are aligned and the transport direction is between 0 degrees and 45 degrees. With this configuration, the optical conditions for the metal plate placed on the stage can be changed without excessively increasing the space required for the rotation of the transport table.

[0011] In the above-described visual inspection apparatus, the line illumination may be configured to allow the intensity of the illumination light to be changed. With this configuration, the intensity of the illumination light can be changed according to the type of defect. By adjusting the intensity of the illumination light in conjunction with the illumination angle and imaging angle to the optimal conditions, the accuracy of defect detection can be further improved.

[0012] A visual inspection method to solve the above problem involves placing a metal plate on a mounting surface provided on a stage supported by a transport table, moving the stage from a first position to a second position on the transport table along a one-dimensional transport direction through an imaging position between the first and second positions, irradiating the metal plate on the stage from the first position through the imaging position with a line illumination that extends in a direction intersecting the transport direction, and after imaging the portion of the metal plate irradiated with the illumination light using a line camera, moving the line illumination to change the irradiation angle of the illumination light on the metal plate. At least one of the following is performed: moving the line camera to change the imaging angle of the line camera with respect to the metal plate; and rotating the transport platform with respect to the line lighting and the line camera, using a perpendicular line perpendicular to the aforementioned surface passing through a point on the imaging position as the axis of rotation; moving the stage from the second position to the first position through the imaging position; illuminating the metal plate on the stage as it passes from the second position through the imaging position with the illumination light using the line lighting, and imaging the metal plate with the line camera so as to include the portion of the metal plate illuminated by the illumination light.

[0013] According to the above visual inspection method, the optical conditions when the stage is moved from the first position to the second position and the optical conditions when the stage is moved from the second position to the first position can be easily changed. Therefore, multiple images with different optical conditions depending on the type of defect can be easily obtained. [Effects of the Invention]

[0014] According to the present invention, the configuration of the visual inspection device can be simplified while easily acquiring multiple images with different optical conditions. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic side view of the visual inspection device. [Figure 2]FIG. 2 is a top view schematically showing an appearance inspection apparatus. [Figure 3] FIG. 3 is a top view showing a state where the transfer stage is rotated with respect to the base portion. [Figure 4] FIG. 4 is a side view showing an enlarged view of a support portion that supports the stage. [Figure 5] FIG. 5 is a top view showing a state where the stage is located at the first position. [Figure 6] FIG. 6 is a top view showing a state where the stage is located at the second position. [Figure 7] FIG. 7 is a top view showing a state where the stage is located at the first position and the transfer stage is rotated 45 degrees with respect to the base portion. [Figure 8] FIG. 8 is a side view showing a modified example of a support portion that supports the stage. [Figure 9] FIG. 9 is a side view showing a configuration in which support rollers are provided on the transfer stage. [Figure 10] FIG. 10 is a schematic diagram showing an incident angle of illumination light and an imaging angle with respect to a metal mask. [Figure 11] FIG. 11 is a top view showing a configuration using oblique illumination of Comparative Example 2. [Figure 12] FIG. 12 is a side view showing a configuration using ring illumination and an area camera of Comparative Example 3.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9. [Metal Mask] As shown in FIG. 1, the appearance inspection apparatus 1 is an apparatus for inspecting the appearance of the metal mask M by image inspection. The metal mask M is used, for example, in the manufacture of an organic EL display. The metal mask M has, for example, a sheet-like shape that is rectangular in plan view. The metal mask M is an example of a metal plate, has a thickness of 10 μm or more and 50 μm or less, and has a rectangular outer shape. The long side of the metal mask M is, for example, 530 mm or more and 1300 mm or less. The short side of the metal mask M is, for example, 50 mm or more and 350 mm or less. A plurality of through holes having a predetermined shape are arranged in the central portion of the metal mask M. The through holes may be circular holes, square holes, or elliptical holes. The width of the through hole is, for example, 20 μm or more and 100 μm or less.

[0017] The metal mask M contains a ferromagnetic metal that is attracted by a magnet. The ferromagnetic metal is, for example, any one selected from the group consisting of iron, cobalt, nickel, and an alloy containing any of these. An example of the alloy is an Invar material containing iron and nickel.

[0018] [Appearance Inspection Apparatus] The appearance inspection apparatus 1 includes a base portion 10, a transfer table 20, a stage 30, a lighting portion 40, and an imaging portion 50. The base portion 10 supports the transfer table 20, the lighting portion 40, and the imaging portion 50. The base portion 10 has a rectangular outer shape in which the direction along the X axis (hereinafter referred to as the X-axis direction) is the long side and the direction along the Y axis (hereinafter referred to as the Y-axis direction) is the short side. Hereinafter, the direction in which the long side of the base portion 10 extends will be described as the X axis, the direction in which the short side of the base portion 10 extends will be described as the Y axis, and the height direction will be described as the Z axis.

[0019] The base portion 10 includes a rotation support portion 11 and a shaft support portion 12. The rotation support portion 11 supports the transfer table 20 so as to be rotatable about a rotation axis L1 parallel to the Z axis. The shaft support portion 12 supports each of the lighting portion 40 and the imaging portion 50 so as to be rotatable.

[0020] The transport platform 20 supports the stage 30. The transport platform 20 has a rectangular shape with the longer side in the X-axis direction and the shorter side in the Y-axis direction. The rotation axis L1 is, for example, located in the center of the longer side of the transport platform 20. The transport platform 20 is divided at the center in the X-axis direction, with one side being the first part 20A and the other side being the second part 20B.

[0021] The transport platform 20 includes a rail section 21. The rail section 21 comprises two rail members 21A and 21B that extend along the long side (X-axis direction in Figure 1) of the transport platform 20, from a first section 20A to a second section 20B. The rail section 21 constitutes the movement path of the stage 30. The transport platform 20 moves the stage 30 along the rail section 21 by a first drive mechanism, such as an electric actuator with a motor or an air actuator with a cylinder. The rail section 21 and the first drive mechanism are an example of a transport section for moving the stage 30 in a one-dimensional transport direction. The X-axis direction is an example of a transport direction in which the transport platform 20 moves the stage 30. The transport direction coincides with the direction in which the long side of the transport platform 20 extends.

[0022] The transport platform 20 moves the stage 30 in a one-dimensional transport direction between a predetermined first position in the first section 20A and a predetermined second position in the second section 20B. In Figure 1, the stage 30 and metal mask M located at the first position are shown with solid lines, and the stage 30 and metal mask M located at the second position are shown with dashed lines. The first transport direction D1 when the stage 30 moves from the first position to the second position is shown with a solid arrow. The second transport direction D2 when the stage 30 moves from the second position to the first position is shown with a dashed arrow.

[0023] The stage 30 comprises a plate-shaped portion 31 having a mounting surface 31S on which the metal mask M is placed, and an engaging portion 32 that engages with the rail portion 21. The stage 30 engages with the rail portion 21 and the engaging portion 32 so as to straddle the two rail members 21A and 21B that constitute the rail portion 21. The material constituting the stage 30 is a non-magnetic metal or inorganic compound that is not attracted to magnets. An example of a non-magnetic metal is aluminum or copper. An example of a non-magnetic inorganic compound is silicon oxide or aluminum oxide. From the viewpoint of suppressing deflection of the central part due to its own weight, aluminum or an aluminum alloy with high deformation resistance per unit weight is preferred for the stage 30. The thickness of the stage 30 is, for example, about 2 mm. The plate-shaped portion 31 has a mounting surface 31S. The metal mask M is placed on the mounting surface 31S.

[0024] The illumination unit 40 and the imaging unit 50 are aligned in the X-axis direction. The illumination unit 40 comprises a first frame unit 41 and line illumination 42. The first frame unit 41 is attached to the pivot unit 12. The first frame unit 41 rotates relative to the pivot unit 12 with an axis parallel to the Y-axis as its axis of rotation, by a second drive mechanism, such as a motor. The line illumination 42 is attached to the tip of the first frame unit 41. The line illumination 42 illuminates the metal mask M, which is placed on a stage 30 that moves along the rail unit 21, with illumination light L in a line. The line illumination 42 is, for example, LED illumination arranged linearly along the Y-axis direction. The first frame unit 41 and the second drive mechanism are an example of an illumination drive unit that changes the illumination angle of the illumination light L on the metal mask M by moving the line illumination 42.

[0025] The line lighting 42 focuses and irradiates the metal mask M with illumination light L such that the optical axis OA of the illumination light L is perpendicular to the light-emitting surface 42S of the line lighting 42. The line lighting 42 is configured to allow the light intensity of illumination light L to be changed. For example, the line lighting 42 changes the light intensity of illumination light L according to the magnitude of the applied voltage. Alternatively, a mesh-like shutter may be used to change the light intensity of illumination light L. The light intensity of illumination light L decreases as it passes through the mesh-like shutter. Therefore, the light intensity of illumination light L may be changed by switching between a state in which a mesh-like shutter is placed in the optical path of illumination light L and a state in which a mesh-like shutter is not placed in the optical path of illumination light L. Alternatively, the light intensity of illumination light L may be changed by switching the transmittance of illumination light L using a liquid crystal shutter.

[0026] The imaging unit 50 is located in the X-axis direction, opposite to the illumination unit 40 relative to the pivot 12. The imaging unit 50 comprises a second frame unit 51 and a line camera 52. The second frame unit 51 is attached to the pivot 12. The second frame unit 51 rotates relative to the pivot 12 with an axis parallel to the Y-axis as its axis of rotation, by a third drive mechanism, such as a motor.

[0027] The line camera 52 is attached to the tip of the second frame section 51. The line camera 52 acquires the brightness of the reflected light from the illumination light L reflected on the metal mask M, which is placed on a stage 30 that moves along the rail section 21. In other words, the line camera 52 images the metal mask M, which is placed on a stage 30 that moves along the rail section 21, including the portion that is illuminated by the illumination light L. In the XZ plane, which includes the X and Z axes, the imaging axis IA of the line camera 52 intersects with the optical axis OA of the line illumination 42 at intersection point P. The second frame section 51 and the third drive mechanism are an example of a camera drive unit that changes the imaging angle of the line camera 52 relative to the metal mask M by moving the line camera 52.

[0028] The first frame section 41 and the second frame section 51 rotate around the pivot point 12 with an axis of rotation parallel to the Y-axis and passing through intersection point P. That is, the axis of rotation of the first frame section 41 and the axis of rotation of the second frame section 51 coincide with intersection point P in the XZ plane. Therefore, the position of intersection point P between the optical axis OA of the line illumination 42 and the imaging axis IA of the line camera 52 is constant regardless of the rotation angle of the first frame section 41 and the second frame section 51. Intersection point P is configured to be at the same height as the surface of the metal mask M placed on the stage 30 which moves along the rail section 21. Intersection point P is located, for example, on the axis of rotation L1 in the XZ plane. The first frame section 41 and the second frame section 51 rotate independently around the pivot point 12, for example, so that the angle they make with the base section 10 is in the range of greater than 0 degrees and less than 180 degrees.

[0029] By rotating at least one of the illumination unit 40 and the imaging unit 50 relative to the base unit 10, the optical conditions when the metal mask M is imaged can be changed. For example, when the reflection angle of the illumination light L matches the imaging angle of the line camera 52, the image acquired by the line camera 52 is a bright-field image. Conversely, when the reflection angle of the illumination light L and the imaging angle of the line camera 52 are different, the image acquired by the line camera 52 is a dark-field image. The optical conditions when the metal mask M is imaged can also be changed by changing the light intensity of the illumination light L.

[0030] The visual inspection device 1 includes a control device 100. The control device 100 includes, for example, a control unit and a memory unit. The control unit controls the operation of each part of the control device 100. The control unit is, for example, a CPU. The control unit drives the transport table 20 to move the stage 30. The control unit drives the first frame unit 41 to rotate the illumination unit 40 relative to the pivot unit 12. The control unit switches between a state in which the line illumination 42 emits illumination light L and a state in which the line illumination 42 does not emit illumination light L. The control unit changes the amount of illumination light L emitted by the line illumination 42. The control unit drives the second frame unit 51 to rotate the imaging unit 50 relative to the pivot unit 12. The control unit causes the line camera 52 to image the metal mask M placed on the stage 30, which moves along the rail unit 21. The control unit processes the image data captured by the line camera 52. The control unit determines whether or not there are defects in the metal mask M from the image data captured by the line camera 52.

[0031] The storage unit is, for example, an HDD. The storage unit stores, for example, a program that controls the operation of each part of the control device 100, image data captured by the line camera 52, a program that processes the image data, and a program that determines whether or not there are defects in the metal mask M from the image data.

[0032] As shown in Figure 2, the metal mask M is placed on the mounting surface 31S so that its long side is parallel to the transport direction. The transport table 20 moves the stage 30 from the first position to the second position, or from the second position to the first position, along the transport axis L2 that passes through the center of the rail section 21. At this time, the stage 30 passes through the imaging position between the first position and the second position. The transport axis L2 is parallel to the transport direction in which the transport table 20 moves the stage 30. Figure 2 also illustrates the case where the transport axis L2 coincides with the center line L4 that passes through the center of the Y-axis direction in the base section 10.

[0033] Line illumination 42 irradiates illumination light L onto a metal mask M placed on a stage 30 as it passes the imaging position on the transport table 20. The imaging position on the transport table 20 is a position between the first and second positions on the transport table 20 that is illuminated by the illumination light L of the line illumination 42 and imaged by the line camera 52. For example, the center of the imaging position is the intersection of the transport axis L2 and the center line L3 of the area illuminated by the illumination light L. In Figure 2, the area illuminated by the illumination light L within the visual inspection device 1 is shown by a dashed line when the stage 30 passes the imaging position.

[0034] The line camera 52 captures a linear imaging area, including the portion of the metal mask M placed on the stage 30 that is illuminated by the illumination light L, as it passes through the imaging position on the transport table 20. In other words, the imaging area of ​​the line camera 52 overlaps with the area illuminated by the illumination light L of the line illumination 42. For example, in the X-axis direction, the center of the imaging area of ​​the line camera 52 coincides with the center line L3 of the area illuminated by the illumination light L. Note that the center line L3 is a straight line parallel to the Y-axis.

[0035] Compared to an area camera that images the entire metal mask M at once, the line camera 52 has a smaller imaging area, which allows for a smaller distance between the line camera 52 and the metal mask M. Therefore, by using the line camera 52, the external dimensions of the visual inspection device 1 can be reduced compared to when an area camera is used.

[0036] The illumination unit 40 and the imaging unit 50 rotate around the pivot point 12 with the center line L3 as the axis of rotation. Therefore, regardless of the irradiation angle of the illumination light L to the metal mask M, the position of the area irradiated by the illumination light L within the visual inspection device 1 remains constant. Similarly, regardless of the imaging angle to the metal mask M, the position of the imaging area within the visual inspection device 1 remains constant. The center line L3 passes through intersection point P in Figure 1 in the XZ plane.

[0037] As shown in Figure 3, the rotation support unit 11 rotates the transport table 20 relative to the base unit 10 around a rotation axis L1 parallel to the Z axis, for example, by a fourth drive mechanism such as a motor. The rotation axis L1 is an axis parallel to the Z axis that passes through a point on the imaging position on the transport table 20, and is perpendicular to the XY plane. The rotation axis L1 is perpendicular to the mounting surface 31S. The rotation axis L1 passes, for example, through the intersection of the transport axis L2, which is the center of the imaging position, and the center line L3. The rotation support unit 11 and the fourth drive mechanism are an example of a transport table drive unit that rotates the transport table 20 relative to the line lighting 42 and line camera 52 attached to the base unit 10.

[0038] The rotation support unit 11 rotates the transport table 20 relative to the base unit 10, for example, so that the angle θ1 between the transport axis L2 and the center line L4 passing through the center of the Y-axis direction in the base unit 10 is in the range of 0 degrees to 45 degrees. The center line L4 is a straight line parallel to the X-axis. Also, the center line L4 coincides with the direction in which the illumination unit 40 and the imaging unit 50 are aligned in the base unit 10. In other words, the rotation support unit 11 rotates the transport table 20 relative to the base unit 10 so that the angle θ2 between the transport axis L2, which is parallel to the transport direction, and the center line L3, which is parallel to the Y-axis direction from which the illumination light L extends, is in the range of 45 degrees to 135 degrees.

[0039] By rotating the transport platform 20 relative to the base 10, the direction in which illumination light L is shone on the metal mask M and the direction in which the metal mask M is imaged can be changed relative to the transport direction in which the transport platform 20 moves the stage 30. In other words, by rotating the transport platform 20 relative to the base 10, the optical conditions when the metal mask M is imaged can be changed.

[0040] The longer side of the transport table 20 is larger than the shorter side of the base portion 10 along the Y-axis. Therefore, the larger the angle θ1 between the transport axis L2 of the transport table 20 and the center line L4 of the base portion 10 becomes, as it approaches a right angle, the larger the width of the visual inspection device 1 in the Y-axis direction becomes. Consequently, if the angle θ1 between the transport axis L2 and the center line L4 is between 0 degrees and 45 degrees, the width of the visual inspection device 1 in the Y-axis direction can be reduced compared to a structure that rotates until the angle θ1 approaches 90 degrees.

[0041] The transport table 20 is equipped with a support section 22. The support section 22 supports the stage 30 from below as it passes through the imaging position on the transport table 20. The center of the support section 22 coincides, for example, with the intersection of the transport axis L2, which is the center of the imaging position, and the center line L3. As the stage 30 passes through the imaging position, it is supported by the support section 22, which keeps the stage 30 in a flat state. This allows imaging of the metal mask M placed on the flat stage 30.

[0042] As shown in Figure 4, the support section 22 comprises a magnet 22A and two non-magnetic sections 22B. In Figure 4, the magnet 22A is marked with a dot. The magnet 22A and the non-magnetic sections 22B extend in a direction intersecting the transport direction. The magnet 22A is located between the two non-magnetic sections 22B in the transport direction. In Figure 4, the transport direction is shown to coincide with the X-axis direction. The magnet 22A and the non-magnetic sections 22B support the plate-shaped section 31 of the stage 30 from below so that it does not bend due to its own weight and the weight of the metal mask M at the imaging position.

[0043] The magnet 22A is composed of a permanent magnet such as an Alnico magnet, a ferrite magnet, or a neodymium magnet. The non-magnetic part 22B is a non-magnetic metal, an inorganic material, or a resin material such as POM (polyacetal resin). The support part 22 supports the stage 30 as it passes through the imaging position with the non-magnetic part 22B, and the magnetic force of the magnet 22A can attract the metal mask M toward the mounting surface 31S from below. This suppresses the floating of the metal mask M relative to the mounting surface 31S, thereby enabling imaging of a flatter metal mask M. The thickness of the stage 30 is preferably 1 mm to 2 mm, from the viewpoint of maintaining mechanical strength while allowing the magnetic force of the magnet 22A to act sufficiently on the metal mask M.

[0044] [Visual Inspection Method] The visual inspection device 1 inspects the surface of the metal mask M for defects that have occurred during the manufacturing process of the metal mask M. Defects that occur on the metal mask M include, for example, scratches, stains, and holes. Scratches and dents are caused by contact with the edges of manufacturing equipment, other metal plates, or foreign objects. For example, a long sheet of metal like a metal mask M may be manufactured using a roll-to-roll method, in which the sheet is unwound from a roll, processed, and then rolled back into a roll. In the roll-to-roll method, scratches, which are an example of scratches, are likely to form on the surface of the metal mask M, parallel to the winding direction (feed direction), i.e., parallel to the long side of the metal mask M. When detecting scratches parallel to the long side of the metal mask M, it is preferable that the transport direction of the stage 30 is not parallel to the X-axis where the line illumination 42 and the line camera 52 are aligned, i.e., that the angle θ1 is greater than 0 degrees and 45 degrees or less.

[0045] Stain defects are caused by surface-to-surface contact with manufacturing equipment, other metal plates, or foreign objects, or by chemical reactions. Stain defects include rust, discoloration due to chemical reactions, and surface roughness. Compared to flaws, stain defects often reflect less illumination light L. When detecting stain defects, it is preferable to perform imaging in dark-field conditions, for example.

[0046] A hole defect is a shape defect of a through-hole located in the center of the metal mask M. Through-holes are formed, for example, by chemical etching. Hole defects include, for example, a through-hole that is partially or completely incomplete, a through-hole that is too large or too small, or a chip in the edge of the through-hole. Since the through-hole is a portion of the metal mask M that penetrates in the thickness direction, the reflection pattern when illuminated with illumination light L is different from other parts. Therefore, when detecting hole defects, it is preferable to use an optimal amount of light so that the shape of the edge of the through-hole can be identified. Furthermore, in order to clearly image the shape of the edge of the through-hole, it is preferable to image the reflected light of the illumination light L specularly reflected by the metal mask M with the line camera 52. That is, in the XZ plane shown in Figure 1, it is preferable that the angle of incidence between the optical axis OA and the rotation axis L1 of the illumination light L is equal to the imaging angle between the imaging axis IA and the rotation axis L1 of the line camera 52.

[0047] As described above, the metal mask M may have multiple types of defects that exhibit different reflection patterns when illuminated with illumination light L. Furthermore, depending on the shape and size of the defects, they may be difficult to identify in the image at certain illumination or shooting angles. In other words, the optimal optical conditions for detecting defects in the metal mask M may vary depending on the type, size, and shape of the defects.

[0048] Therefore, when performing a visual inspection with the visual inspection device 1, the first to fifth imaging conditions are determined in advance to achieve the optimal optical conditions according to the type and degree of defects to be detected. The imaging conditions are settings for each part of the visual inspection device 1 and are elements that determine the optical conditions when imaging the metal mask M.

[0049] The first imaging condition is the magnitude of the illumination angle L on the metal mask M, that is, the magnitude of the angle of the first frame section 41 relative to the base section 10 in the XZ plane. The second imaging condition is the magnitude of the imaging angle of the line camera 52 on the metal mask M, that is, the magnitude of the angle of the second frame section 51 relative to the base section 10 in the XZ plane. The third imaging condition is the magnitude of the angle θ1 of the transport direction of the stage 30 with respect to the X axis where the line illumination 42 and the line camera 52 are aligned, that is, the magnitude of the angle θ1 of the transport table 20 relative to the base section 10 in the XY plane including the X and Y axes. The fourth imaging condition is the exposure time for the metal mask M as it passes the imaging position. The exposure time depends on the transport speed at which the transport table 20 transports the stage 30. The fifth imaging condition is the amount of light from the illumination L on the metal mask M as it passes the imaging position.

[0050] The control device 100 stores at least one imaging condition pattern, which is a combination of the first to fifth imaging conditions. For example, the control device 100 stores the optimal combination of imaging conditions for detecting scratches as the first imaging condition pattern. The control device 100 stores the optimal combination of imaging conditions for detecting stains as the second imaging condition pattern. The control device 100 stores the optimal combination of imaging conditions for detecting holes as the third imaging condition pattern. Note that if multiple types of defects can be detected simultaneously with a single imaging condition pattern, it is not necessarily required to store an imaging condition pattern for each type of defect. Also, multiple imaging condition patterns may be stored for a single type of defect to improve detection accuracy. Each imaging condition pattern only needs to differ in at least one of the first to fifth imaging conditions.

[0051] An example of a visual inspection method will be explained below with reference to Figures 5 to 7. As shown in Figure 5, first, the metal mask M is placed on the mounting surface 31S of the stage 30, which is located at a first position on the transport table 20. Then, the control device 100 drives each part of the visual inspection device 1 to apply an imaging condition pattern for detecting a desired defect. In this state, the transport table 20 is driven to move the stage 30 along the first transport direction D1 from the first position to the second position. As the stage 30 moves from the first position to the second position, the line camera 52 takes a first image of the metal mask M placed on the stage 30 as it passes the imaging position.

[0052] As shown in Figure 6, the stage 30 is positioned at the second position on the transport table 20 after the first imaging is completed. Next, the control device 100 drives each part of the visual inspection device 1 to apply an imaging condition pattern different from the imaging condition pattern applied in the first imaging. For example, without changing the third to fifth imaging conditions, at least one of the irradiation angle of the illumination light L, which is the first imaging condition, or the imaging angle of the line camera 52, which is the second imaging condition, is changed. In this state, the transport table 20 is driven to move the stage 30 along the second transport direction D2 from the second position to the first position. Then, as the stage 30 moves from the second position to the first position, the line camera 52 performs a second imaging of the metal mask M placed on the stage 30 as it passes the imaging position.

[0053] As shown in Figure 7, the stage 30 returns to the first position on the transport table 20 after the second imaging is completed. The control device 100 then drives each part of the visual inspection device 1 to apply an imaging condition pattern different from the imaging condition patterns applied in the first and second imaging. For example, from the imaging condition pattern applied in the second imaging, the angle θ1 of the transport table 20 relative to the base part 10, which is the third imaging condition, is changed to 45 degrees, while other imaging conditions remain unchanged. In this state, the transport table 20 is driven to move the stage 30 along the first transport direction D1 from the first position to the second position. As the stage 30 moves from the first position to the second position, the line camera 52 performs a third imaging of the metal mask M placed on the stage 30 as it passes the imaging position.

[0054] In this manner, the stage 30 on which the metal mask M is placed is moved between the first and second positions of the transport table 20 to perform multiple imaging cycles. By changing the imaging condition pattern each time imaging is performed, multiple images with different optical conditions can be obtained. Note that the number of imaging cycles is not limited to three; imaging can be performed as many times as necessary to detect defects. Furthermore, the captured images can be converted into a single image data containing the entire metal mask M through image processing, for example. In addition, the presence or absence of defects may be determined from the converted image data using processing techniques such as binarization.

[0055] [Effects of the Embodiment] According to the above embodiment, the following effects can be obtained. (1) The irradiation angle of the illumination light L on the metal mask M, the imaging angle of the line camera 52 on the metal mask M, and the angle θ1 between the X-axis where the line illumination 42 and the line camera 52 are aligned and the transport direction of the stage 30 are all configured to be changeable. This makes it possible to easily change the optical conditions when imaging the metal mask M as it passes through the imaging position by driving each part of the visual inspection device 1. Therefore, multiple images with different optical conditions depending on the type of defect can be easily acquired.

[0056] Furthermore, when determining the optimal imaging condition pattern for detecting defects, each imaging condition can be easily changed, making it possible to easily determine the optimal imaging condition pattern.

[0057] (2) As the stage 30 passes the imaging position, the support part 22 supports the stage 30, allowing imaging of the metal mask M supported on the flat stage 30. In addition, since the position of the metal mask M in the Z-axis direction (height direction) can be kept constant, the focus of the line camera 52 can be adjusted with greater precision.

[0058] (3) The support portion 22 is equipped with a magnet 22A, which suppresses the lifting of the metal mask M relative to the mounting surface 31S. As a result, a flatter metal mask M can be imaged. (4) By keeping the angle θ1 within the range of 0 degrees to 45 degrees, the optical conditions for the metal mask M placed on the stage 30 can be changed without excessively increasing the space required for the rotation of the transport table 20. In particular, the longer the object to be inspected, such as the metal mask M, the wider the Y-axis direction of the visual inspection device 1 becomes as the angle θ1 approaches a right angle. Therefore, the longer the object to be inspected, such as the metal mask M, the greater the above effect.

[0059] (5) The line illumination 42 is configured to allow the light intensity of the illumination light L to be changed, so that the light intensity of the illumination light L can be changed according to the type of defect. By adjusting the light intensity of the illumination light L in conjunction with the irradiation angle of the illumination light L and the imaging angle of the line camera 52 to the optimal conditions, the accuracy of defect detection can be further improved.

[0060] (6) By changing the transport speed at which the transport platform 20 transports the stage 30, the exposure time when the line camera 52 images the metal mask M can be changed. This allows the exposure time to be adjusted to the optimal conditions in conjunction with the illumination angle of the illumination light L and the imaging angle of the line camera 52, thereby further improving the accuracy of defect detection.

[0061] [Example of changes] The above embodiment can be implemented with the following modifications. The transport speed at which the transport platform 20 transports the stage 30 may be constant. In this case, although the exposure time when the line camera 52 images the metal mask M will be constant, the effects similar to those described in (1) to (5) above can be obtained.

[0062] The amount of illumination light L emitted by the line lighting 42 may be constant. Even in this case, the effects similar to those described in (1) to (4) and (6) above can be obtained. If there are no spatial constraints when installing the visual inspection device 1, the angle θ1 between the X-axis where the line lighting 42 and the line camera 52 are aligned and the transport direction of the stage 30 may exceed 45 degrees. For example, the base part 10 may be circular, and the transport table 20 may rotate 360 ​​degrees around the rotation axis L1. Even with such a configuration, the effects similar to those described in (1) to (3), (5), and (6) above can be obtained.

[0063] For example, if the metal mask M is thick, and wrinkles or undulations are unlikely to occur when it is placed on the mounting surface 31S, and lifting relative to the mounting surface 31S is unlikely, then the support part 22 does not need to be equipped with a magnet 22A. For example, instead of the magnet 22A, the entire support part 22 may be made of a non-magnetic part 22B. Even with such a configuration, effects similar to those described in (1), (2), (4) to (6) above can be obtained. Also, if the support part 22 does not have a magnet 22A, the stage 30 may be made of a ferromagnetic material, or the metal mask M may be made of a non-magnetic material. Furthermore, instead of providing a magnet 22A on the support part 22, a magnet may be provided on the side of the stage 30 opposite to the mounting surface 31S.

[0064] Furthermore, as shown in Figure 8, the support portion 22 may be a roller. With such a configuration, the stage 30 can be supported as it passes through the imaging position, while the stage 30 can be moved smoothly. Alternatively, a support portion 22 equipped with a magnet 22A and a roller-shaped support portion 22 may be arranged side by side.

[0065] If the plate-shaped portion 31 of the stage 30 has sufficient rigidity to prevent it from bending under its own weight and the weight of the metal mask M, the support portion 22 may be omitted. Also, the support portion 22 may be attached to the base portion 10 instead of the transport table 20. The plate-shaped portion 31 of the stage 30 may be reinforced with a non-magnetic material such as aluminum to prevent it from bending.

[0066] As shown in Figure 9, the conveyor table 20 may be equipped with support rollers 23. The support rollers 23 are provided, for example, at the lower part of the conveyor table 20 at each end in the conveying direction (longitudinal direction). The support rollers 23 support the conveyor table 20 from below while rotating on the base portion 10 as the conveyor table 20 rotates relative to the base portion 10. If the ends of the conveyor table 20 in the conveying direction are free ends, the larger the dimension in the conveying direction, the more susceptible it becomes to bending due to its own weight, the weight of the stage 30, and the metal mask M. By providing support rollers 23, the ends in the conveying direction can be supported while the conveyor table 20 can be rotated smoothly relative to the base portion 10.

[0067] The object to be inspected by the visual inspection device 1 is not limited to the metal mask M, but can be any flat metal plate. For example, the metal plate to be inspected is made of a ferromagnetic material, but if a magnet 22A is not provided in the support part 22, it may be made of a non-magnetic material.

[0068] [Examples] Examples and comparative examples will be described below with reference to Figures 10 to 12. Note that the following examples are merely illustrative examples for illustrating the effects of the above embodiments and do not limit the present invention.

[0069] [Example 1] A metal mask M with a thickness of approximately 30 μm was used as the object of inspection. The metal mask M was placed on a stage 30. Line illumination 42 was used to concentrate and irradiate illumination light L. To suppress the floating of the metal mask M relative to the stage 30, a support part 22 equipped with a magnet 22A was used. The stage 30 was made of an aluminum plate with a thickness of 2 mm. To ensure sufficient rigidity, the outer circumference of the stage 30 was reinforced with an aluminum frame, and further supported from the back surface of the stage 30 with a roller, which is an example of a support part 22. In other words, in Example 1, a support part 22 equipped with a magnet 22A and a roller-shaped support part 22 were arranged side by side. In this state, the appearance of the metal mask M was imaged using a line camera 52.

[0070] As shown in Figure 10, in the XZ plane, the incident angle between the optical axis OA of the illumination light L and the rotation axis L1 is defined as θ3, and the imaging angle between the imaging axis IA of the line camera 52 and the rotation axis L1 is defined as θ4. In Example 1, the angle θ1 between the transport axis L2 and the center line L4 of the base unit 10 was set to 45 degrees. Then, with both the incident angle θ3 and the imaging angle θ4 set to 30 degrees, the first imaging was performed. Subsequently, with only the incident angle θ3 changed from 30 degrees to 24 degrees, the second imaging was performed.

[0071] [Comparative Example 1] Except for the fact that the base portion 10 does not have a rotating support portion 11 and the transport table 20 does not rotate relative to the base portion 10, imaging with the line camera 52 was performed in the same manner as in Example 1. Therefore, in Comparative Example 1, the angle θ1 is fixed at 0 degrees. Then, the first imaging was performed with both the incident angle θ3 and the imaging angle θ4 set to 30 degrees. Subsequently, the second imaging was performed with only the incident angle θ3 changed from 30 degrees to 24 degrees.

[0072] [Comparative Example 2] As shown in Figure 11, imaging with the line camera 52 was performed in the same manner as in Example 1, except that the base portion 10 does not have a rotating support portion 11, the transport table 20 does not rotate relative to the base portion 10, and oblique light illumination 43 was used instead of line illumination 42. Therefore, in Comparative Example 2, the angle θ1 is fixed at 0 degrees. The oblique light illumination 43 irradiates illumination light L such that it forms a constant angle θ5 with respect to the X axis when viewed from a viewpoint opposite the XY plane. The angle θ5 was set to 30 degrees. Then, the first imaging was performed with both the incident angle θ3 and the imaging angle θ4 set to 30 degrees. After that, the second imaging was performed with only the incident angle θ3 changed from 30 degrees to 24 degrees.

[0073] [Comparative Example 3] As shown in Figure 12, imaging was performed in the same manner as in Example 1, except that an annular ring light 44 was used instead of line lighting 42, and an area camera 53 was used instead of line camera 52. In Figure 12, the ring light 44 is schematically shown cut at the center in the Y-axis direction. The ring light 44 and the area camera 53 are positioned directly above the metal mask M on the stage 30, which passes through the imaging position. The ring light 44 illuminates the entire metal mask M with illumination light L from directly above. The area camera 53 images the entire metal mask M from directly above in one image. In Comparative Example 3, there is no significant difference in the image that can be captured even if the angle θ1 is changed. Also, the illumination angle of the ring light 44 is constant, and the imaging angle θ4 is fixed at 0 degrees. Therefore, in Comparative Example 3, only the first imaging was performed.

[0074] [evaluation] The location of defects was determined in advance by visual inspection of the metal mask M to be inspected, and then it was determined whether the defects could be confirmed at the same location in the captured image data. Those in which no defects could be confirmed by visual inspection in the captured image were classified as defective (×). Those in which a slight defect could be confirmed by visual inspection in the captured image were classified as average (△). Those in which a defect could be clearly confirmed by visual inspection in the captured image were classified as good (〇). Evaluation was performed for each type of defect: scratches, stains, and holes. In addition, for each defect, the image data obtained from both the first and second imaging was evaluated, and the result in which the defect was more clearly confirmed was adopted. The evaluation results for Example 1 and Comparative Examples 1-3 are shown in Table 1.

[0075] [Table 1]

[0076] As shown in Table 1, in Example 1, images with clear contrast were captured for all types of defects: scratches, stains, and holes. In Comparative Examples 1, 2, and 3, examples of scratches such as dents and scratches parallel to the long side of the metal mask M could not be captured with clear contrast. Furthermore, in Comparative Examples 1, 2, and 3, stain defects could not be captured with clear contrast compared to Example 1. It is thought that in Comparative Examples 1 to 3, the number of adjustable imaging condition elements (number of movable axes) was smaller compared to Example 1, making it impossible to construct optimal imaging conditions for detecting stain defects. [Explanation of Symbols]

[0077] θ1, θ2…Angle θ3…Incidence angle θ4…Imaging angle L…Illumination light L1... Rotation axis L2...Conveyor axis 1…Visual inspection device 10...Base section 20… Transport platform 21... Rail section 22...Support part 22A...Magnet 30… Stage 31...Plate-like part 31S… Mounting surface 40…Lighting Department 41...First frame 42…Line lighting 50…Imaging Unit 51...2nd frame 52... Line Camera 100...Control device

Claims

1. A stage having a mounting surface on which a metal plate is placed, A transport table supporting the stage, the transport table comprising a transport unit that moves the stage between a first position and a second position of the transport table, through an imaging position between the first position and the second position, along a one-dimensional transport direction, Line illumination is provided, which irradiates the metal plate on the stage, which passes through the imaging position, with line-shaped illumination light extending in a direction intersecting the transport direction, A line camera that takes images of the metal plate on the stage that passes through the imaging position, including the portion of the metal plate that is illuminated by the illumination light, The system comprises a base portion that separately supports the transport platform, the line lighting, and the line camera, The base portion is A lighting drive unit that changes the irradiation angle of the illumination light onto the metal plate by moving the aforementioned line lighting, A camera drive unit that changes the imaging angle of the line camera relative to the metal plate by moving the line camera, The system includes a transport platform drive unit that rotates the transport platform relative to the line illumination and the line camera, using a perpendicular line passing through the point on the imaging position and perpendicular to the aforementioned mounting surface as the axis of rotation. Visual inspection device.

2. The imaging position further includes a support portion that supports the stage from below. The appearance inspection apparatus according to claim 1.

3. The aforementioned metal plate contains a ferromagnetic metal, The aforementioned stage is nonmagnetic, The support portion includes a magnet that, at the imaging position, magnetically attracts the metal plate downward from below the stage. The appearance inspection apparatus according to claim 2.

4. The transport platform drive unit rotates the transport platform within a range of 0 degrees to 45 degrees, where the angle between the direction in which the line lighting and the line camera are aligned and the transport direction is between 0 degrees and 45 degrees. The visual inspection apparatus according to any one of claims 1 to 3.

5. The aforementioned line lighting is configured to allow the amount of light from the illumination to be changed. The visual inspection apparatus according to any one of claims 1 to 3.

6. A metal plate is placed on the mounting surface of the stage supported by the transport platform. The stage is moved along the one-dimensional transport direction from the first position to the second position of the transport table, through the imaging position between the first position and the second position. Line illumination is used to illuminate the metal plate on the stage, passing from the first position through the imaging position, with line illumination extending in a direction intersecting the transport direction, and after imaging is performed by a line camera to include the portion of the metal plate illuminated by the illumination light, By moving the aforementioned line lighting, the angle at which the illumination light is projected onto the metal plate is changed. By moving the line camera, the imaging angle of the line camera relative to the metal plate is changed, and At least one of the following is performed: rotate the transport platform relative to the line illumination and the line camera, using a perpendicular line perpendicular to the aforementioned mounting surface passing through the point on the imaging position as the axis of rotation. The stage is moved from the second position towards the first position through the imaging position, The line lighting illuminates the metal plate on the stage as it passes from the second position through the imaging position, and the line camera captures an image of the metal plate including the portion illuminated by the lighting. Visual inspection method.

Images