Coaxial lighting device

Abstract

In order to provide a coaxial lighting device that is small but has a wide field of view and can simplify adjustment work, the device is provided with a half mirror 1 arranged diagonally on an observation axis A1 connecting the work W to be observed and an observation section M where the work W is observed, a light source 2 arranged to irradiate light onto the half mirror 1 from a direction different from the observation axis A1 so that the light reflected by the half mirror 1 is irradiated onto the work W, a lens 3 arranged between the half mirror and the work, and a first aperture 4 arranged between the light source 2 and the half mirror 1, and the first aperture 4 is arranged at the focus of the lens 3 on an irradiation axis A2 connecting the light source 2 and the half mirror 1.

Description

Technical Field

[0001] The present invention relates to a coaxial illumination device.

Background Art

[0002] For example, as a lighting device for surface inspection, as shown in Patent Document 1, coaxial illumination is known in which light emitted from a light source in a direction different from the observation direction is reflected by a half mirror in the same direction as the observation direction by a camera or the like to illuminate a workpiece that is an observation target.

[0003] Such a coaxial illumination device holds not only a light source and a half mirror but also optical elements such as lenses in a housing, and for example, the relative positional relationship between them is configured to be adjustable so that an image captured by a camera can be adjusted to be suitable for surface inspection.

[0004] However, when a plurality of lenses such as a lens on the light source side and a lens on the camera side are provided, adjustment is required for each of them, which is time-consuming and difficult to adjust to obtain an appropriate image.

[0005] In addition, when trying to increase the field of view in which the workpiece can be observed, a plurality of members have to be enlarged respectively, and the housing for holding them inside also becomes larger, resulting in an increase in the size of the entire coaxial illumination device. In addition, with the increase in size, the manufacturing cost significantly increases.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above-described problems, and an object thereof is to provide a coaxial illumination device that is small in size but can widen the field of view and simplify the adjustment work.

Means for Solving the Problems

[0008] That is, the coaxial illumination device according to the present invention includes a half mirror obliquely disposed on an observation axis connecting a work as an observation target and an observation unit that observes the work, and irradiates the half mirror with light from a direction different from the observation axis, and a light source arranged such that the light reflected by the half mirror irradiates the work, a lens provided between the half mirror and the work, and a first diaphragm provided between the light source and the half mirror, and the first diaphragm is arranged at the focal point of the lens on the irradiation axis connecting the light source and the half mirror.

[0009] With such a configuration, a telecentric optical system can be constituted by the light source, the first diaphragm, and the lens to irradiate the work with parallel light, and the lens can also be shared on the observation unit side. Therefore, the number of lenses used can be reduced compared to conventional coaxial illumination devices, and the labor of the adjustment work can be reduced.

[0010] In addition, since the number of components can be reduced, it is possible to widen the field of view in the observation unit without making the coaxial illumination device so large.

[0011] Furthermore, the light emitted from the light source can be irradiated onto the workpiece as parallel light, and the NA of the light source can also be adjusted by the first aperture. Therefore, for example, it is easy to appropriately adjust the brightness of the workpiece observed in the observation unit. For example, due to minute undulations on the surface of the workpiece, reflected light or scattered light from the object to be observed and its surroundings may not easily reach the observation unit. In such a case, by increasing the NA of the light source, the amount of reflected light or scattered light incident within the field of view of the observation unit increases, and even if there are undulations on the surface, it becomes possible to clearly capture the object to be observed.

[0012] In order to simplify the adjustment operation of the light irradiated onto the workpiece and make it easier to miniaturize the entire apparatus, only the first aperture needs to be provided as an optical element between the light source and the half mirror.

[0013] In order to irradiate parallel light that is uniform and has little luminance unevenness to each point of the workpiece, it is sufficient that the light source has a planar light emitting surface, and the light emitting surface is arranged such that the irradiation axis and the observation axis are orthogonal.

[0014] In order to be able to further finely adjust the manner in which the light reflected or scattered by the workpiece is observed in the observation unit, it is sufficient that a second aperture is further provided between the half mirror and the observation unit.

[0015] In order to prevent undulations or the like on the surface of the workpiece W from making it difficult for reflected light or scattered light from the surface to reach the observation unit and enable accurate surface inspection, the NA defined by the first aperture may be larger than the NA defined by the second aperture, or may be configured to be made larger.

[0016] For example, in order to be able to limit the location that requires adjustment work to only the first aperture and significantly reduce the labor of the adjustment work compared to the prior art, it is sufficient that a housing is further provided to fix the positional relationship between the half mirror, the light source, the first aperture, and the lens and hold each of them.

Advantages of the Invention

[0017] As described above, according to the coaxial illumination device of the present invention, the lens acts as a telecentric lens with respect to the light source and also acts as a condenser lens that condenses the reflected light or scattered light from the workpiece with respect to the observation unit. Therefore, it is not necessary to provide a lens for each of the light source and the observation unit, reducing the number of components and miniaturizing the entire device, while easily enlarging the field of view. In addition, since the number of lens arrangements can be reduced, the adjustment work for appropriately observing the workpiece can be simplified compared to the prior art.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Explanation of Reference Numerals

[0019] 200 ··· Surface inspection system 100 ··· Coaxial illumination 1 ··· Half mirror 2 ··· Light source 3 ··· Lens 4 ··· First aperture 5 ··· Second aperture 7 ··· Housing

Embodiments for Carrying Out the Invention

[0020] The coaxial illumination device 100 according to the first embodiment of the present invention and the surface inspection system 200 using the same will be described with reference to FIGS. 1 to 3. The coaxial illumination device 100 of the first embodiment is used for surface inspection, for example, irradiating light onto an object such as a product, i.e., a workpiece W, and observing scratches, characters, etc. on the surface of the workpiece W with a camera or the like for automatic inspection. Specifically, as shown in FIG. 1, on the observation axis A1 connecting the workpiece W and an observation unit M such as a camera for observing the workpiece W, the coaxial illumination device 100 is installed between the workpiece W and the observation unit M. The surface inspection system 200 is configured by the coaxial illumination device 100 and the observation unit M arranged in this way.

[0021] Hereinafter, the details of the coaxial illumination device 100 will be described.

[0022] As shown in FIGS. 1 to 3, the coaxial illumination device 100 includes a half mirror 1 arranged on the observation axis A1, a light source 2 that irradiates light toward the half mirror 1, a lens 3 arranged between the half mirror 1 and the workpiece W, a first diaphragm 4 arranged between the half mirror 1 and the light source 2, a second diaphragm 5 arranged between the half mirror 1 and the observation unit M, an observation-side lens 6 arranged between the second diaphragm 5 and the observation unit M, and a housing 7 that houses these components.

[0023] The half mirror 1 is a cube half mirror formed by combining two prisms. The joint surface of each prism is coated with a dielectric multilayer film or a metal thin film, and the joint surface is arranged to form an angle of 45 degrees with respect to the observation axis A1 and the irradiation axis A2 of the light source 2, respectively.

[0024] The light source 2 emits light from a rectangular, for example, square light-emitting surface, and emits diffused light that has been homogenized from the light-emitting surface. This light source 2 is formed, for example, by arranging a large number of LED chips in an array on a substrate. In the first embodiment, there are no optical elements other than the first aperture 4 between the light source 2 and the half mirror 1. Also, the light source 2 is fixed to the housing 7, and its position within the housing 7 is fixed.

[0025] The lens 3 is composed of a single or a plurality of lenses, and is fixed around the work-side opening 71 of the housing 7. The light emitted from the light source 2 and reflected by the half mirror 1 is refracted by this lens 3 and irradiated perpendicularly to the work W. Also, the light reflected or scattered by the work W is condensed by this lens 3, transmitted through the half mirror 1, and then incident on the observation unit M. In this way, the lens 3 is shared by both the light source 2 and the observation unit M. The lens 3 is arranged such that its focal point exists between the light source 2 and the half mirror 1 on the irradiation axis A2, and between the half mirror 1 and the observation unit M on the observation axis A1.

[0026] The first aperture 4 is arranged at the focal point of the lens 3 on the irradiation axis A2. That is, the light source 2, the first aperture 4, and the lens 3 form a telecentric optical system, and the light emitted from the light source 2 is parallelized by the lens 3 and irradiated onto the work W. The first aperture 4 is a variable aperture, and is configured such that its aperture diameter can be appropriately adjusted by an adjustment knob 41 that protrudes outside the housing 7. Also, in the coaxial illumination device 100 of the first embodiment, only this first aperture 4 is configured to be adjustable. The position of this first aperture 4 is also fixed within the housing 7.

[0027] The second aperture 5 is disposed at the focal point of the lens 3 on the observation axis A1. That is, the workpiece W, the lens 3, and the second aperture 5 form a telecentric optical system, and only the light having an optical axis in the direction parallel to the observation axis A1 among the light reflected or scattered by the workpiece W can pass through the second aperture 5 and reach the observation unit M. In the first embodiment, the second aperture 5 is a fixed aperture, and its aperture diameter is fixed to a predetermined size. Also, the NA defined by the first aperture 4 is configured to be larger than the NA defined by the second aperture 5.

[0028] The observation-side lens 6 refracts the light that has passed through the second aperture 5 and makes it incident on the observation unit M. For example, the focal point of the observation-side lens 6 may be made to exist on the second aperture 5 so that the light passing through the observation-side lens 6 is parallelized and incident on the observation unit M.

[0029] The housing 7 has a longitudinal cross section along the observation axis A1 that is approximately horizontally T-shaped. This housing 7 is configured such that the separation distance between the half mirror 1 and the lens 3 is longer than the separation distance between the light source 2 and the half mirror 1. Also, the diameter of the observation hole 72, which is the opening on the observation unit M side rather than the opening on the workpiece W side, is formed to be small.

[0030] In the case of the coaxial illumination device 100 of the first embodiment configured as described above, since the lens 3 is provided only at the workpiece-side opening 71 of the housing 7, the number of lenses used can be reduced compared to the prior art. Therefore, such labor can be significantly reduced compared to the case where adjustment work was performed for each of the lenses on the light source side and the observation unit side as in the prior art.

[0031] Also, since the number of components constituting the coaxial illumination can be reduced, the field of view in the observation unit M can be increased without making the entire device so large.

[0032] Furthermore, since the light source 2, the first aperture 4, and the lens 3 form a telecentric optical system, the light emitted from the light source 2 can be irradiated onto the work W as parallel light, and the NA (numerical aperture) of the light source 2 can also be adjusted by the first aperture 4. Specifically, as shown in FIGS. 4(a) and 4(b), when the NA of the light source 2 is changed by the first aperture 4, the range of the solid angle at which light can be incident on each point on the surface of the work W can be uniformly changed. In the first embodiment, since the NA of the observation unit M is fixed by the second aperture 5 which is a fixed aperture, by changing the aperture diameter of the first aperture 4, the NA of the light source 2 can be made sufficiently larger than the NA of the observation unit M.

[0033] For example, when inspecting the characters printed on the work W on a plane by machine vision as shown in FIG. 5(a), if there is a region D with minute undulations on the surface other than the characters, as shown in FIG. 5(b), not only in that region D but also the amount of reflected light or scattered light reaching the observation unit M from the characters decreases, and the inspection by machine vision may not be accurately performed. This is because the reflected light and scattered light do not travel in a direction parallel to the observation axis A1 due to the undulations and cannot be incident on the observation unit M. In such a situation, when the NA of the light source 2 is increased as shown in FIGS. 4(a) to 4(b), a component traveling in a direction parallel to the observation axis A1 is generated in a part of the light reflected or scattered in the region D of the work W and can be incident on the observation unit M. Therefore, as shown in FIG. 5(c), a certain amount of reflected light and scattered light can reach the observation unit M even for the undulated region D, and the inspection by machine vision can be accurately performed.

[0034] Also, in the first embodiment, since the irradiation mode of the light onto the work W can be adjusted only by the aperture diameter of the first aperture 4, it is easy to realize an irradiation mode such as luminance and brightness suitable for surface inspection with only a simple adjustment operation.

[0035] Next, the coaxial illumination device 100 according to the second embodiment of the present invention will be described with reference to FIG. 6. Note that the members corresponding to the members described in the first embodiment will be given the same reference numerals.

[0036] The coaxial illumination device 100 of the second embodiment is different from the first embodiment in that it includes a second aperture 6 which is a variable aperture between the half mirror 1 and the observation unit M.

[0037] By providing such a second aperture 6, it becomes possible to adjust the amount of light incident on the observation unit M, and further it becomes possible to easily obtain an image suitable for surface inspection.

[0038] Other embodiments will be described.

[0039] The coaxial illumination device according to the present invention is not only used for surface inspection, but can also be used in other inspections such as other appearance inspections.

[0040] The light source is not limited to an LED, and other types may be used. The lens is not limited to a convex lens, and a Fresnel lens or the like may be used. In addition, the irradiation axis may not be orthogonal to the observation axis, and may be configured to simply intersect.

[0041] In addition, as long as it does not go against the gist of the present invention, parts of various embodiments may be combined and modified.

Industrial Applicability

[0042] According to the present invention, it is possible to provide a coaxial illumination device that is small in size but can widen the field of view and has a simple adjustment operation.

Claims

1. For inspection by machine vision, A half mirror obliquely arranged on the observation axis connecting the work to be observed and the observation unit for observing the work, A light source arranged to irradiate the half mirror with light from a direction different from the observation axis, so that the light reflected by the half mirror irradiates the work, A lens provided between the half mirror and the work, A first aperture provided between the light source and the half mirror, A second aperture provided between the half mirror and the observation unit, The first aperture is directly arranged at the focal point of the lens on the irradiation axis connecting the light source and the half mirror, The light source, the first aperture, and the lens constitute a telecentric optical system, The NA defined by the first aperture is larger than, or can be made larger than, the NA defined by the second aperture, The light source has a planar light emitting surface larger than the aperture diameter of the first aperture, and the light emitting surface is arranged so that the irradiation axis and the observation axis are perpendicular to each other. The coaxial illumination device is characterized by this.

2. The coaxial illumination device according to claim 1, further comprising a housing for fixing and holding the positional relationships between the half mirror, the light source, the first aperture, and the lens respectively.

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