Line light emitting device and inspection system

Abstract

This line light emitting device for emitting line-shaped light that extends along a predetermined longitudinal direction onto a workpiece is provided with a pair of light emitting units arranged such that light emitting surfaces thereof that face the workpiece are symmetrical to one other across a gap when viewed from the longitudinal direction, wherein: each light emitting unit includes a light source and an optical system for guiding light emitted from the light source to the workpiece; in a lateral direction orthogonal to the longitudinal direction and the optical axis of the optical system, an apparent light emitting surface as viewed from the surface of the workpiece to be illuminated is continuous within a collimation half angle with respect to the workpiece; the optical system has a cylindrical lens having a curvature in a plane orthogonal to the longitudinal direction; and a front focal position of the cylindrical lens is positioned closer to the light source side than an image forming position of the light source.

Description

Line light irradiation device and inspection system

[0001] The present invention relates to a line light irradiation device that irradiates a line-shaped light and an inspection device using the same.

[0002] Conventionally, there has been known an inspection system that irradiates light onto a workpiece (inspection object) such as paper or film that is transported in a predetermined direction, captures an image of the irradiated area of ​​the workpiece with an imaging device called a line sensor camera, and imports the obtained image data into an image processing device to inspect the surface for scratches, etc. Patent Document 1 discloses a light irradiation device used in such an inspection system, which is a dome lighting device that is placed between the workpiece and the line sensor camera and irradiates light from various directions from a light-emitting surface facing the workpiece toward the surface of the workpiece.

[0003] Japanese Patent Application Laid-Open No. 2017-166865

[0004] In an inspection system using a line sensor camera, it is necessary to increase the irradiance on the irradiated surface of the workpiece in order to shorten the takt time while ensuring a field of view along the longitudinal direction (line direction) of the line sensor. The dome lighting device of Patent Document 1 described above provides a dome effect by being able to irradiate the irradiated surface of the workpiece from various directions, but because the light emitted from the light-emitting surface is not configured to converge in a line, the efficiency of the energy incident within the field of view is low, resulting in low irradiance on the irradiated surface of the workpiece.

[0005] Therefore, the present invention has been made to solve the above-mentioned problems, and its main objective is to improve the irradiance on the irradiated surface of the workpiece while maintaining the dome effect in a light irradiation device used in conjunction with a line sensor camera.

[0006] In other words, the line light irradiation device of the present invention irradiates a workpiece with line-shaped light along a predetermined longitudinal direction, and is equipped with a pair of light irradiation units arranged so that the light-emitting surfaces facing the workpiece are symmetrical to each other across a gap when viewed from the longitudinal direction, each light irradiation unit having a light source and an optical system that guides light emitted from the light source to the workpiece, and in a short direction perpendicular to the longitudinal direction and the optical axis of the optical system, the apparent light-emitting surface as viewed from the irradiated surface of the workpiece is continuous within a collimation half angle for the workpiece, and the optical system has a cylindrical lens having a curvature in a plane perpendicular to the longitudinal direction, and the forward focal position of the cylindrical lens is configured to be located closer to the light source than the imaging position of the light source.

[0007] According to the present invention configured in this manner, in a light irradiation device used together with a line sensor camera, it is possible to improve the irradiance on the irradiated surface of a workpiece while maintaining the dome effect.

[0008] The present invention relates to an inspection system and a linear light irradiation device, and is a method for irradiating a linear light beam onto a target object.

[0009] A line light irradiation device 100 according to one embodiment of the present invention will be described below with reference to the drawings.

[0010] 1, the line light irradiation device 100 of this embodiment irradiates light onto a workpiece w (object to be inspected), and is used, for example, in a product inspection system X that uses an imaging device C called a line sensor camera to capture an image of a predetermined area of ​​the workpiece w, and then imports the obtained image data into an image processing device (not shown) to inspect for scratches, etc. Note that the workpiece w in this embodiment is, for example, a continuous object such as paper or film that flows in one direction at a constant speed, or an individual item such as cut film or cut glass that is placed on a conveyor and continuously transported.

[0011] This line light irradiation device 100 is disposed between the workpiece w and the imaging device C, and irradiates the workpiece w with a line of light (hereinafter also referred to as line light) along a predetermined direction (hereinafter referred to as the longitudinal direction). Specifically, as shown in FIGS. 1 and 2 , this light irradiation device 100 includes a pair of light irradiation units 1 having light-emitting surfaces 1L facing the workpiece w. Each of the pair of light irradiation units 1 irradiates a line of light toward the workpiece w, and the light-emitting surfaces 1L are arranged symmetrically with each other when viewed from the longitudinal direction. A slit 1S is formed between the pair of light irradiation units 1, allowing light reflected by the workpiece w to pass toward the imaging device C, and the imaging device C can image a predetermined area of ​​the workpiece w through this slit 1S. Each light irradiation unit 1 will be described below.

[0012] As shown in FIG. 3 , the light irradiation unit 1 includes a casing 11 having an opening facing the workpiece w, and a light source unit 12 and an optical system 13 housed within the casing 11 .

[0013] The casing 11 has an elongated shape extending in the longitudinal direction. Specifically, the casing 11 has a generally rectangular bottom wall 11a extending in the longitudinal direction, a pair of side walls 11b (short side walls) provided on both longitudinal sides of the bottom wall 11a, and a pair of side walls 11c (long side walls) provided on both widthwise sides of the bottom wall 11a. These side walls 11b, 11c form a generally rectangular opening facing the bottom wall 11a.

[0014] The light source unit 12 has a board 12a attached to the inner surface of the bottom wall 11a of the casing 11 and a plurality of light sources 12b mounted on the board 12a. The light source unit 12 is controlled to be turned on / off and to have its light intensity adjusted based on a control signal transmitted from a control unit (not shown).

[0015] The substrate 12a has a long rectangular shape extending in the longitudinal direction and is fixed to the bottom wall 11a with screws. The light sources 12b in this embodiment are LEDs, and a large number of them are mounted on the surface of the substrate 12a in the longitudinal direction.

[0016] The optical system 13 guides the light emitted from the light source 12b to the workpiece w and is positioned in front of the light source 12b in the light emission direction. Specifically, the optical system 13 includes an aspherical lens having a curvature in a plane perpendicular to the longitudinal direction (i.e., the axis passing through the center of curvature coincides with the longitudinal direction), specifically an aspherical cylindrical lens 131. The aspherical cylindrical lens 131 closes the opening of the casing 11 and is positioned so that its optical axis 1x coincides with the central axis (or optical axis) of the light source 12b when viewed from the longitudinal direction. Note that the optical axis of the light source 12b refers to the optical axis of the lens if the light source 12b has a lens; if the light source 12b does not have a lens, it refers to an axis passing through the approximate center of the light-emitting element and perpendicular to its light-emitting surface. With this configuration, the optical system 13 focuses light in the lateral direction perpendicular to the optical axis 1x and the longitudinal direction. Furthermore, by blocking the opening of the casing 11 with the aspherical cylindrical lens 131, the apparent light-emitting surface 1L as seen from the workpiece w appears continuous within the collimation half angle (i.e., the size of the apparent light-emitting surface 1L as seen from the irradiated surface of the workpiece w expressed in angle) in the short direction relative to the irradiated surface of the workpiece w, and the light-emitting surface 1L is seamless in the short direction (i.e., the light source 12b can be seen from any angle when viewed from a point on the irradiated surface of the workpiece w within the collimation half angle).

[0017] The optical system 13 of this embodiment has two aspherical cylindrical lenses 131 a and 131 b arranged along the light emission direction of the light source 12 b. The two aspherical cylindrical lenses 131 a and 131 b are both plano-convex lenses, and are arranged so that their optical axes 1 x are aligned and their convex surfaces face each other.

[0018] 3 and 4, the optical system 13 is configured so that the front focal position Pf of the aspherical cylindrical lens 131b located closest to the workpiece w is located closer to the light source 12b than the imaging position Pi of the light source 12b (here, the position of the workpiece w). In other words, the front focal position Pf is provided between the imaging position Pi of the light source 12b and the aspherical cylindrical lens 131b.

[0019] The light irradiation unit 1 of this embodiment further includes a light diffusion plate 14 having a light distribution angle of 5° or less in the short-side direction and a light distribution angle in the long-side direction that is wider than the light distribution angle in the short-side direction. Specifically, the light diffusion plate 14 is a so-called lenticular lens configured by arranging multiple plano-convex cylindrical lenses, each having a curvature in a plane perpendicular to the short-side direction, in the long-side direction. The light diffusion plate 14 is disposed on the workpiece w side of the aspherical cylindrical lens 131b constituting the optical system 13, with its convex surface facing the light source 12b and its flat surface on the opposite side facing the workpiece w. In this embodiment, this flat surface forms the light-emitting surface 1L of the light irradiation unit 1. In this embodiment, the light diffusion plate 14 is configured to have a diffusion angle of approximately 30° in the long-side direction and a diffusion angle of approximately 1° in the short-side direction.

[0020] In the light irradiation unit 1 of this embodiment, a heat dissipation member 15 such as a heat sink is attached to the outer surface of the long side wall 11c of the casing 11, the long side wall 11c opposite the slit 1S side (the anti-slit side wall). Specifically, this heat dissipation member 15 is configured to include a plurality of rod-shaped members provided upright on the outer surface of the anti-slit side wall 11c. The rod-shaped members are provided spaced apart from one another.

[0021] The pair of light irradiation units 1 configured in this manner are arranged symmetrically with respect to the optical axis Cx of the imaging device C when viewed from the longitudinal direction (this includes not only completely symmetrical but also slightly misaligned (approximately symmetrical)). More specifically, the pair of light irradiation units 1 are arranged at an angle so that the optical axes 1x of their optical systems 13 intersect near the surface of the workpiece w (more specifically, so that the imaging positions Pi of the light sources 12b overlap).

[0022] The line light irradiation device 100 also includes a connecting member 2 that connects the pair of light irradiation units 1. The connecting member 2 is generally plate-shaped, and the bottom wall 11a of each casing 11 is attached to one surface (inward surface 2a) of the connecting member 2 facing the workpiece w with a fixed inclination angle using fasteners such as bolts. The outer surface of the bottom wall 11a of each casing 11 and the inward surface 2a of the connecting member 2 are in surface contact, allowing heat from the casing 11 to be dissipated to the connecting member 2. An observation window 2w is formed in the central region of the connecting member 2, allowing light reflected by the workpiece w and passing through the slit 1S to pass toward the imaging device C. The observation window 2w is configured as an opening that penetrates in the thickness direction and is located opposite the slit 1S. The opening has an elongated rectangular shape extending along the longitudinal direction in a plan view.

[0023] 5, the arrangement and optical design of each light irradiation unit 1 in the line light irradiation device 100 of this embodiment is such that the following angular conditions (1) to (3) are satisfied when viewed from the longitudinal direction: (1) The distance between the end of the apparent light-emitting surface 1L on the slit 1S side and the image formation position P of the light source 12b ｉ (2) The angle θ1 between the virtual line L1 connecting the slits 1S and the optical axis Cx of the image pickup device C is 0° or more and 20° or less. (3) The angle θ2 between the virtual line L1 and the optical axis 1x of the light irradiation unit 1 is 20° or more and 40° or less. (4) The angle θ2 between the end of the apparent light emitting surface 1L on the opposite side to the slit 1S and the imaging position P of the light source 12b is 0° or more and 20° or less. ｉ The angle θ3 formed by the imaginary line L2 connecting the above and the surface of the workpiece is 0° or more and 35° or less.

[0024] According to the line light irradiation device 100 of the present embodiment configured as described above, the optical system 13 has aspherical cylindrical lenses 131a, b having a curvature in a plane perpendicular to the longitudinal direction, so that the light emitted from the light source 12b is focused in the lateral direction perpendicular to the longitudinal direction and the direction of the optical axis 1x of the optical system 13, and the light is focused in a line on the irradiated surface of the workpiece w, thereby increasing the irradiance. Furthermore, by configuring the front focal position Pf of the aspherical cylindrical lens 131b on the workpiece w side to be positioned closer to the light source 12b than the imaging position Pi of the light source 12b, the entrance pupil position can be brought closer to the workpiece w, and the apparent light-emitting surface 1L as viewed from the irradiated surface of the workpiece w can be enlarged. This allows the collimation half angle in the short direction as seen from the irradiated surface of the workpiece w to be increased, and the apparent light-emitting surface as seen from the irradiated surface of the workpiece w appears continuous.Furthermore, since the light-emitting surfaces 1L of the pair of light-irradiation units 1 are arranged in pairs, a sufficient dome effect can be exerted on the irradiated surface of the workpiece w placed between the pair of light-emitting surfaces 1L.

[0025] The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the light source 12b is configured as an LED (light-emitting diode), but this is not limiting. In other embodiments, the light source 12b may be an LD (laser diode), an SLD (superluminescent diode), or the like.

[0026] Furthermore, while the optical system 13 in the above embodiment includes multiple aspherical cylindrical lenses 131a, 131b arranged along the optical axis direction, this is not limited to this. In other embodiments, the optical system 13 may include only one aspherical cylindrical lens 131, or may include three or more aspherical cylindrical lenses 131. When the optical system 13 includes three aspherical cylindrical lenses 131, it is preferable to arrange them so that the flat side of the cylindrical lens closest to the light source faces the light source and the flat side of the cylindrical lens closest to the workpiece faces the workpiece. This minimizes aberrations such as spherical aberration and coma, and focuses light at a single point on the irradiated surface of the workpiece w, resulting in a stronger dome effect.

[0027] In another embodiment, the light diffusion plate 14 may be disposed so that its convex curved surface faces the workpiece w. The light diffusion plate 14 may also be disposed on the light source 12b side, rather than on the workpiece w side of the aspherical cylindrical lens 131b constituting the optical system 13. Each light irradiation unit 1 may not necessarily be provided with the light diffusion plate 14.

[0028] In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. For example, the disclosure of this specification may include the following aspects.

[0029] (Aspect 1) A line light irradiation device that irradiates a workpiece with a line-shaped light along a predetermined longitudinal direction, comprising a pair of light irradiation units that are arranged so that their light-emitting surfaces facing the workpiece are symmetrical to each other with a gap between them when viewed from the longitudinal direction, each light irradiation unit comprising a light source and an optical system that guides light emitted from the light source to the workpiece, wherein an apparent light-emitting surface viewed from the irradiated surface of the workpiece is continuous within a collimation half angle for the workpiece in a short direction that is perpendicular to the longitudinal direction and the optical axis of the optical system, and wherein the optical system has a cylindrical lens that has a curvature in a plane perpendicular to the longitudinal direction, and wherein the front focal position of the cylindrical lens is located closer to the light source than an imaging position of the light source.

[0030] In this configuration, the optical system includes a cylindrical lens having a curvature in a plane perpendicular to the longitudinal direction. Therefore, the light emitted from the light source is focused in a lateral direction perpendicular to the longitudinal direction and the optical axis direction of the optical system. This results in a linear convergence of the light on the irradiated surface of the workpiece, thereby increasing the irradiance. Furthermore, by positioning the front focal position of the cylindrical lens closer to the light source than the light source's imaging position, the entrance pupil position can be moved closer to the workpiece, thereby increasing the apparent light-emitting surface as viewed from the irradiated surface of the workpiece. This increases the collimation half angle in the lateral direction as viewed from the irradiated surface of the workpiece (w). Furthermore, since the light-emitting surfaces of the paired light-emitting units are arranged in pairs, a sufficient dome effect can be achieved on the irradiated surface of the workpiece placed between the pair of light-emitting surfaces.

[0031] (Aspect 2) The line light irradiation device according to Aspect 1, wherein each of the optical systems includes a plurality of the cylindrical lenses arranged along the light emission direction of the light source. In this aspect, by using a plurality of cylindrical lenses, it is possible to position the apparent light emitting surface forward (toward the workpiece) while reducing aberration compared to when an optical system is configured with a single cylindrical lens, and a stronger dome effect can be obtained.

[0032] (Aspect 3) The line light irradiation device according to Aspect 2, wherein the plurality of cylindrical lenses are all plano-convex, and in each optical system, the flat surface of the cylindrical lens closest to the light source faces the light source, and the flat surface of the cylindrical lens closest to the workpiece faces the workpiece. With this aspect, aberrations such as spherical aberration and coma aberration can be minimized, and light is focused at one point on the irradiated surface of the workpiece, resulting in a greater dome effect.

[0033] (Aspect 4) The line light irradiation device according to any one of Aspects 1 to 3, wherein each of the light irradiation units further includes a light diffusion plate having a light distribution angle in the short-side direction of 5° or less and a light distribution angle in the long-side direction wider than the light distribution angle in the short-side direction. In this aspect, by setting the light distribution angle in the short-side direction to 5° or less, high irradiance can be maintained on the irradiated surface of the workpiece. Meanwhile, by widening the light distribution in the long-side direction compared to the short-side direction, the uniformity of the luminance distribution of the light-emitting surface in the long-side direction can be improved. Furthermore, the apparent chipping of the light-emitting surface as viewed from the irradiated surface of the workpiece in the long-side direction can be reduced, further improving the dome effect.

[0034] (Aspect 5) The line light irradiation device according to Aspect 4, wherein the light diffusion plate is disposed closer to the workpiece than the cylindrical lens. In this aspect, by disposing the light diffusion plate at a position farther from the light source, it is possible to further improve the uniformity of the luminance distribution of the light-emitting surface in the longitudinal direction, and to obtain a stronger dome effect.

[0035] (Aspect 6) The line light irradiation device according to any one of Aspects 1 to 5, wherein each of the light irradiation units includes a casing that houses the light source and the optical system, each casing having a generally rectangular bottom wall extending along the longitudinal direction and a pair of opposing side walls provided on both widthwise sides of the bottom wall, the space between the pair of side walls being blocked by the cylindrical lens, an LED board on which the LED is mounted is provided on the inner surface of the bottom wall, and a heat dissipation member is provided on the outer surface of the side wall. In this aspect, by providing a heat dissipation member on the outer surface of the casing side wall, the light irradiation device itself can be configured thinner than when a heat dissipation member is provided on the bottom wall. This allows the imaging device to be closer to the workpiece, thereby reducing the working distance.

[0036] (Aspect 7) An inspection system including the line light projection device according to any one of Aspects 1 to 6 and a line sensor camera that captures an image of the irradiated surface of the workpiece and is arranged so that the longitudinal direction of the line sensor camera is parallel to the longitudinal direction of the line light projection device. Such an inspection system can achieve the same effects as the line light projection device described above.

[0037] According to the present invention described above, in a light irradiation device used together with a line sensor camera, the irradiance on the irradiated surface of a workpiece is improved while maintaining the dome effect.

[0038] REFERENCE SIGNS LIST 100: Line light irradiation device 1: Irradiation unit 1L: Light emitting surface 12: Light source unit 12b: Light source 13: Optical system 131a, b: Cylindrical lens w: Workpiece Pf: Front focal position Pi: Imaging position of light source

Claims

1. A line light irradiation device which irradiates a workpiece with a line-shaped light along a predetermined longitudinal direction, comprising a pair of light irradiation units arranged so that their light-emitting surfaces facing the workpiece when viewed from the longitudinal direction are symmetrical to each other with a gap between them, each of the light irradiation units comprising: a light source and an optical system which guides light emitted from the light source to the workpiece, wherein in a short direction perpendicular to the longitudinal direction and the optical axis of the optical system, the apparent light-emitting surface as viewed from the irradiated surface of the workpiece is continuous within a collimation half angle for the workpiece, and wherein the optical system has a cylindrical lens having a curvature in a plane perpendicular to the longitudinal direction, and wherein the front focal position of the cylindrical lens is configured to be located closer to the light source than the imaging position of the light source.

2. A line light irradiation device as described in claim 1, wherein each of said optical systems comprises a plurality of said cylindrical lenses arranged in the light emission direction of said light source.

3. A line light irradiation device as described in claim 2, wherein all of the multiple cylindrical lenses are plano-convex, and in each of the optical systems, the flat surface of the cylindrical lens closest to the light source faces the light source, and the flat surface of the cylindrical lens closest to the workpiece faces the workpiece.

4. A line light irradiation device as described in claim 1, wherein each of the light irradiation units further comprises a light diffusion plate having a light distribution angle in the short side direction of 5° or less and a light distribution angle in the long side direction wider than the light distribution angle in the short side direction.

5. The line light irradiation device according to claim 4, wherein the light diffusion plate is disposed closer to the work than the cylindrical lens.

6. The line light irradiation device according to claim 1, wherein each of the light irradiation units comprises a casing that houses the light source and the optical system, each of the casings having a bottom wall that extends along the longitudinal direction and is roughly rectangular, and a pair of opposing side walls provided on both sides in the width direction of the bottom wall, the space between the pair of side walls being blocked by the cylindrical lens, an LED board on which the LEDs are mounted is provided on the inner surface of the bottom wall, and a heat dissipation member is provided on the outer surface of the side wall.

7. An inspection system comprising: the line light projection device according to claim 1; and a line sensor camera for imaging the irradiated surface of the workpiece, the line sensor camera being positioned so that its longitudinal direction is parallel to the longitudinal direction of the line light projection device.