LED light irradiation device and inspection system

Abstract

In order to provide an LED light radiating device with which it is possible to improve illumination intensity uniformity in a system equipped with a telecentric optical system, this LED light radiating device is provided with: an LED light source 1 equipped with a light emitting surface; a plano-convex lens 2 provided in such a way that the convex surface faces the light emitting surface; and a rod lens 3 provided in such a way that light emitted from the planar surface of the plano-convex lens 2 is incident on an incident end surface.

Description

[Technical Field]

[0001] The present invention relates to an LED light irradiation device used to detect scratches or marks on products, for example, and an inspection system using an LED light irradiation device. [Background technology]

[0002] One example of an inspection system used for product inspection, etc., is one in which a telecentric optical system is installed between an LED light irradiation device and the workpiece to be inspected, and the light-emitting surface of the LED light irradiation device is imaged onto the workpiece (Patent Document 1).

[0003] In such inspection systems, it is necessary to maximize the utilization efficiency of light irradiated onto a specific area on a workpiece. Therefore, a device called a spotlight is used as an LED light irradiation device. Specifically, as shown in Figure 8, a spotlight 100A comprises an LED light source 1A with a light-emitting surface, a plano-convex lens 2A, and a rod lens 3A, arranged in this order on the optical axis. The plano-convex lens is oriented so that light emitted from the LED light source 1A enters the planar surface and light emitted from the convex surface enters the incident end face of the rod lens 3A. This was because it was believed that the desired performance could be achieved by preventing sharp refraction in the plano-convex lens 2A, reducing the effects of spherical aberration, and minimizing the bias in the light distribution characteristics.

[0004] However, after careful investigation, the inventors of the present application discovered for the first time that in an inspection system equipped with a telecentric optical system as described above, the uniformity of the illuminance on the workpiece can be improved by having a large bias in the light distribution characteristics rather than by supplying light using the conventional spot lighting 100A. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-109520 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention was made based on the above-mentioned discovery, and aims to provide an LED light irradiation device that can improve the uniformity of illuminance in a system equipped with a telecentric optical system. [Means for solving the problem]

[0007] That is, the LED light irradiation device of the present invention is characterized by comprising an LED light source having a light-emitting surface, a plano-convex lens arranged so that its convex surface faces the light-emitting surface, and a rod lens arranged so that light emitted from the flat surface of the plano-convex lens is incident on its incident end surface.

[0008] In this case, because the convex surface of the plano-convex lens faces the light-emitting surface, the influence of spherical aberration can cause a bias in the light distribution characteristics of the light emitted from the exit end face of the rod lens. Specifically, the light intensity can be made highest at a position shifted by a predetermined angle from the optical axis rather than on the optical axis. When light having such a light distribution characteristic is incident on a telecentric optical system, the uniformity of the illuminance at the surface where the telecentric optical system is focused can be improved compared to conventional methods.

[0009] In other words, while it has been conventionally thought that spherical aberration must be minimized to improve light utilization efficiency, the present invention goes beyond this common technical knowledge and intentionally generates spherical aberration, thereby enabling the present invention to achieve desirable light distribution characteristics in a telecentric optical system.

[0010] In order to obtain favorable light distribution characteristics in a telecentric optical system and also to increase the light utilization efficiency, it is sufficient to set the distance between the light-emitting surface and the front principal point of the plano-convex lens to be shorter than twice the focal length of the plano-convex lens. This is because making the distance shorter than twice, that is, by bringing the light-emitting surface and the plano-convex lens closer together, makes it possible to increase spherical aberration and the amount of light incident on the plano-convex lens.

[0011] In an inspection system equipped with the LED light irradiation device according to the present invention and a telecentric optical system into which the light emitted from the exit end face of the rod lens is incident, the light emitted from the telecentric optical system can be irradiated onto a workpiece, thereby enabling highly uniform light to be irradiated within a certain area of ​​the workpiece, thereby improving the accuracy of detecting scratches and marks on the workpiece compared to conventional methods.

[0012] In order to align the direction of the incident light rays at each point on the workpiece and further improve inspection accuracy, it is sufficient to set the focal position of the telecentric optical system on the workpiece to be illuminated.

[0013] A specific example of a configuration that can achieve both uniformity of illuminance on the workpiece and efficiency of utilization of light emitted from the LED light source is one that is configured to satisfy 250≦EV≦325, where θ is the angle between the optical axis and a tangent drawn from the intersection of the light-emitting surface and the convex surface, D is the diameter of the opening through which light enters at the incident end face of the rod lens, Y is the diameter of the light-emitting surface, and EV=D×θ×(1 / Y) is the evaluation value. [Effects of the Invention]

[0014] As described above, with the LED light emitting device according to the present invention, the convex surface of the plano-convex lens faces the light emitting surface of the LED light source, and therefore it is possible to obtain a biased light distribution characteristic that can improve the uniformity of illuminance in a system equipped with a telecentric optical system used, for example, for inspection, by utilizing spherical aberration. Note that the present invention can be applied not only to LED light sources that irradiate visible light, but also to LED light sources that emit light other than visible light, such as ultraviolet light or infrared light, and in such cases, it is possible to obtain a light distribution characteristic that can improve the uniformity of irradiance (illuminance in the case of visible light). [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing the configuration of an LED light irradiation device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an inspection system using the LED light irradiation device according to the embodiment. [Figure 3] FIG. 2 is a schematic diagram showing an irradiation optical system of the inspection system in the embodiment. [Figure 4] 10 shows simulation results of light distribution characteristics on the optical axis of a conventional LED light irradiation device and an LED light irradiation device according to an embodiment. [Figure 5] 10 shows simulation results of light distribution characteristics at 10 degrees from the optical axis of a conventional LED light irradiation device and an LED light irradiation device according to an embodiment. [Figure 6] FIG. 2 is a schematic diagram showing each design parameter of the LED light irradiation device of the present embodiment. [Figure 7] 10 is a simulation result showing the change in the uniformity of irradiance on the workpiece and the light utilization efficiency with respect to the evaluation value in this embodiment. [Figure 8] FIG. 1 is a schematic diagram showing the configuration of a conventional LED light irradiation device. [Explanation of symbols]

[0016] 200: Inspection system 100:LED light irradiation device 1:LED light source 2: Plano-convex lens 3: Rod lens 4: Casing 5: Telescope tube 6: Imaging lens 7: Beam splitter 8: Camera TL: Telecentric optical system ST: Aperture W: Work DETAILED DESCRIPTION OF THE INVENTION

[0017] An LED light irradiation device 100 according to one embodiment of the present invention and an inspection system 200 using this LED light irradiation device 100 will be described with reference to the accompanying drawings. As shown in Fig. 1, the LED light irradiation device 100 of this embodiment is a so-called spot light in which an LED light source 1 that emits near-infrared light, a glass plano-convex lens 2, and a glass rod lens 3 are housed in a casing 4 in this order from the base end to the tip end. The casing 4 is roughly a two-stage cylindrical shape tapered toward the tip end, and a heat dissipation support member (not shown) is arranged on the base end where the LED light source 1 is provided.

[0018] The LED light source 1 has a light-emitting surface of a predetermined area. That is, it is not a point light source, but is configured so that light rays are emitted from the entire light-emitting surface of a predetermined size.

[0019] In this embodiment, the plano-convex lens 2 is a hemispherical lens in which one of its surfaces, the convex surface, is formed in a hemispherical shape. Note that the convex surface is not limited to a hemispherical shape, and it may be aspherical. The other surface of the plano-convex lens 2 is flat. As shown in FIG. 1 , the plano-convex lens 2 is arranged so that its convex surface faces the light-emitting surface of the LED light source 1, and light emitted from the light-emitting surface is incident on the convex surface. Light emitted from the flat surface of the plano-convex lens 2 is incident on the incident end surface of the rod lens 3.

[0020] The distance between the LED light source 1 and the plano-convex lens 2 is set so that the distance between the light-emitting surface of the LED light source 1 and the front principal point of the plano-convex lens 2 is shorter than twice the focal length of the plano-convex lens 2. Here, the front principal point refers to H shown in Figures 1 and 6. In this embodiment, the plano-convex lens 2 is a hemispherical lens, so the front principal point is at the vertex of the hemispherical lens.

[0021] An inspection system 200 equipped with a telecentric optical system TL as shown in FIG. 2 is configured using such an LED light irradiation device 100. This inspection system 200 detects scratches and marks on the workpiece W, which is the irradiation target, based on an image captured by a camera 8. The inspection system 200 of this embodiment is a coaxial illumination system configured so that the observation optical axis of the camera 8 and the optical axis of the inspection light irradiating the workpiece W are coaxial. Specifically, the inspection system 200 includes a cylindrical lens barrel 5 that houses various optical devices, and the LED light irradiation device 100 is attached to the side of the center of the lens barrel 5. An imaging lens 6 is provided at one end of the lens barrel 5 facing the workpiece W, and a camera 8 is attached to the other end. A beam splitter 7 is provided at the center of the lens barrel 5, and is configured so that light emitted from the LED light irradiation device 100 is reflected toward the imaging lens 6. Furthermore, the light reflected by the workpiece W returns into the lens barrel 5, passes through the imaging lens 6 and the beam splitter 7, and enters the camera 8 at the other end.

[0022] In this embodiment, an aperture stop ST is provided at the focal position inside the barrel 5 of the imaging lens 6, and the imaging lens 6 and aperture stop ST form a telecentric optical system TL. Furthermore, by placing the workpiece W at the focal position outside the barrel of the imaging lens 6 as shown by the ray trajectories in Figure 2, the chief ray, upper ray, and lower ray of light emitted from each point on the exit end face of the rod lens 3 in the LED light irradiation device 100 are incident on the imaging lens 6 in a parallel state. Therefore, each angular component emitted from each point on the exit end face of the rod lens 3 is focused at one point on the workpiece W.

[0023] Figure 3 shows the trajectory of the light beam on the irradiation side. In Figure 3, the angle between the principal ray of the light beam irradiated to the outermost point in the irradiation area on the workpiece W and the optical axis is Θ, and the light distribution characteristic emitted from the LED light irradiation device 100 is I(Θ). The irradiance on the workpiece W is I(Θ) × cos 3 Θ. Therefore, I(Θ) ∝ 1 / cos 3 The inventors of the present application have found that if the light distribution characteristic of Θ can be realized by the LED light irradiation device 100, the irradiance on the workpiece W will be completely uniform.

[0024] Based on this knowledge, the light distribution characteristic of the light emitted from the LED light irradiation device 100 is expressed as I(Θ)∝1 / cos 3 In order to approach Θ, in this embodiment, the convex surface of the plano-convex lens 2 is arranged to face the light emitting surface of the LED light source 1, so that the influence of spherical aberration is more pronounced.

[0025] 4 and 5 show simulation results of light distribution characteristics when the flat surface of the plano-convex lens 2 faces the light-emitting surface of the LED light source 1 as in the conventional LED light irradiation device 100, and when the convex surface of the plano-convex lens 2 faces the light-emitting surface of the LED light source 1 as in this embodiment. As shown in Fig. 4 and 5, compared to when the flat surface of the plano-convex lens 2 faces the light-emitting surface of the LED light source 1, when the convex surface of the plano-convex lens 2 faces the light-emitting surface of the LED light source 1, it is possible to make the amount of light of angular components at ±10 degrees with respect to the optical axis greater than the amount of light on the optical axis by utilizing the spherical aberration of the plano-convex lens 2 (approaching light distribution characteristics where I(Θ) ∝ 1 / cos3Θ).

[0026] Next, a description will be given of a configuration for improving not only the uniformity of irradiance on the workpiece W but also the utilization efficiency of light emitted from the LED light source 1. The description will be given based on a schematic diagram of Fig. 6 showing each design parameter of the LED light irradiation device 100.

[0027] The angle between the optical axis and a tangent drawn from the intersection of the light-emitting surface of the LED light source 1 and the optical axis to the convex surface of the plano-convex lens 2 is θ, the diameter of the opening through which light enters the incident end face of the rod lens 3 is D, the diameter of the light-emitting surface is Y, and the evaluation value is EV=D×θ×(1 / Y).

[0028] Figure 7 shows the results of a simulation showing the change in the uniformity of irradiance on the workpiece W and the light utilization efficiency versus the evaluation value EV. The three graphs show the simulation results for three change patterns when θ, Y, and D are changed in the configuration of the LED light irradiation device 100. As can be seen from the graphs, as long as the configuration satisfies 250≦EV≦325, it is possible to achieve both desirable uniformity and efficiency, regardless of the configuration of the telecentric optical system TL. Therefore, the LED light irradiation device 100 of this embodiment is configured to satisfy this EV.

[0029] The LED light irradiation device 100 of this embodiment, configured as described above, can utilize the spherical aberration of the plano-convex lens 2 to increase the amount of light at angular components at ±10° relative to the optical axis compared to the amount of light on the optical axis, and can achieve a light distribution characteristic approaching I(Θ)∝1 / cos3Θ. Because such a light distribution characteristic is achieved, the uniformity of irradiance on the focal plane OP of the telecentric optical system TL to which light is supplied from the LED light irradiation device 100 can be improved compared to conventional techniques. Therefore, light with approximately the same light intensity and irradiation pattern can be incident on each point on the focal plane OP of the workpiece W. This allows the conditions for imaging by the camera 8 to be consistent at each point on the workpiece W, thereby improving inspection accuracy compared to conventional techniques.

[0030] Other embodiments will be described.

[0031] Although the LED light irradiation device according to the present invention was used in an inspection system in the above-described embodiment, it may also be used for other purposes. In other words, the LED light irradiation device may be used for purposes where it is preferable that the light distribution characteristics have a higher intensity in the angular components around the optical axis than the intensity on the optical axis.

[0032] Furthermore, the light emitted from the LED light irradiation device does not necessarily have to be incident on a telecentric optical system. In other words, the LED light irradiation device may be used alone. The light emitted from the LED light source 1 is not limited in any way and may be near-infrared light, visible light, ultraviolet light, or infrared light other than near-infrared light. In particular, the present invention is suitable for ultraviolet light and infrared light (including near-infrared light), for which resin reflector lenses often used for visible light are not suitable. By combining the plano-convex lens 2 and rod lens 3, the uniformity of the irradiance can be easily improved.

[0033] The imaging lens is not limited to being composed of a single lens, but may be composed of a combination of multiple lenses. Furthermore, the plano-convex lens is not limited to having a convex surface formed by a continuous curved surface, but may be composed of multiple divided lens elements, such as a Fresnel lens. In short, in a plano-convex lens, the convex surface generates greater spherical aberration than the other surface, and it is sufficient that such a convex surface faces the LED light source.

[0034] In addition, various modifications and combinations of parts of each embodiment may be made as long as they do not go against the spirit of the present invention. [Industrial Applicability]

[0035] According to the present invention, it is possible to provide an LED light emitting device having biased light distribution characteristics that can utilize spherical aberration to improve the uniformity of illuminance in a system equipped with a telecentric optical system used, for example, for inspection, etc. Furthermore, it is possible to provide an inspection system that uses such an LED light emitting device to irradiate a certain area with highly uniform light and improve the accuracy of detecting scratches and marks on a workpiece compared to conventional systems.

Claims

1. an LED light source having a light emitting surface; a plano-convex lens having one surface entirely formed with a continuous curved convex surface and the other surface entirely formed with a flat surface, the convex surface being disposed so as to face the light-emitting surface; a cylindrical rod lens arranged so that its axis direction coincides with the optical axis direction of the plano-convex lens, and arranged so that light emitted from the flat surface of the plano-convex lens is incident on its incident end surface; The LED light irradiation device has a distance between the light emitting surface and the front principal point of the plano-convex lens that is set to be shorter than twice the focal length of the plano-convex lens.

2. The LED light irradiation device according to claim 1; and a telecentric optical system into which the light emitted from the exit end face of the rod lens is incident.

3. 3. The inspection system according to claim 2, wherein the focal position of said telecentric optical system is set on the workpiece to be irradiated.

4. 3. The inspection system according to claim 2, configured to satisfy 250≦EV≦325, where θ is the angle formed by the optical axis and a tangent drawn from the intersection of the light-emitting surface and the optical axis to the convex surface, D is the diameter of the opening through which light is incident at the incident end face of the rod lens, Y is the diameter of the light-emitting surface, and the evaluation value EV=D×θ×(1 / Y).

Images