Inspection system and spot illumination device for inspection

Abstract

To increase the brightness when imaging in an inspection system with a coaxial incident-light structure having a high-magnification object-side telecentric optical system.SOLUTION: The inspection system includes: a spot illumination device for inspection, having a light source body and a light emission surface for emitting light from the light source body as inspection light; and an imaging device having an object-side telecentric optical system for imaging a workpiece. The inspection system is formed to radiate the inspection light emitted from the light emission surface to the workpiece from the same axis as the optical axis of the imaging device. The light source body uses a semiconductor laser.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an inspection system for irradiating light onto a workpiece, for example, to capture an image of the workpiece's appearance, scratches, defects, etc., and to an inspection spot lighting device used in the inspection system. [Background technology]

[0002] Conventionally, there has been known an inspection system having a so-called coaxial epi-illumination structure, which includes an illumination device that emits inspection light to be irradiated onto a workpiece, and an imaging device having an object-side telecentric optical system that images the workpiece using light scattered or reflected by the workpiece, and is configured so that the inspection light emitted from the illumination device can be irradiated onto the workpiece from a position coaxial with the optical axis of the imaging device (for example, Patent Document 1). Conventionally, in this inspection system, a surface light source in which a number of LED chips are arranged on a plane is used as the light source body of the illumination device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-085815 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors have discovered for the first time that in an inspection system having a coaxial epi-illumination structure with an object-side telecentric optical system as described above, the F-number tends to increase as the optical magnification of the optical system is increased, and there is a problem in that when imaging is performed at a high magnification of, for example, 2x or more, the brightness (exposure amount) during imaging is reduced compared to when imaging is performed at a low magnification.

[0005] As a result of intensive research to solve such problems, the inventors of the present invention have come to the conclusion that by narrowing the light distribution characteristic (for example, 5° or less) in an illumination device that emits inspection light and increasing the radiance of the light emission surface of the illumination device, it may be possible to improve the brightness during imaging even in a high-magnification object-side telecentric optical system. However, with conventional illumination devices that use an LED, which has a Lambertian light distribution characteristic and is a surface light source, as a light source, it has been difficult to realize an illumination device with such narrow light distribution characteristic and high brightness.

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and its main object is to improve the brightness during imaging in an inspection system having a coaxial epi-illumination structure with a high-magnification object-side telecentric optical system. [Means for solving the problem]

[0007] In other words, the inspection system of the present invention is an inspection system comprising a light source body, an inspection spot lighting device having a light emission surface that emits light emitted from the light source body as inspection light, and an imaging device having an object-side telecentric optical system that images a workpiece, and is configured to irradiate the inspection light emitted from the light emission surface onto the workpiece coaxially with the optical axis of the imaging device, and is characterized in that the light source body is configured using a semiconductor laser.

[0008] According to the inspection system of the present invention configured in this manner, the light source of the inspection spotlight device is configured using a semiconductor laser, which is a point light source, so that the light distribution characteristics are narrower and the radiance of the light exit surface is higher than in conventional devices that use a light source using an LED. Therefore, when combined with a high-magnification object-side telecentric optical system, the irradiance on the image plane of the imaging device can be increased, improving the brightness during imaging.

[0009] However, when constructing a light source using a semiconductor laser, if the laser light emitted from the semiconductor laser is directly irradiated onto a work surface, there is a risk that the uniformity of the irradiance on the work surface will decrease due to the asymmetry of the distribution of the laser light.

[0010] Therefore, it is preferable that the inspection system is one in which the light source body emits the laser light emitted from the semiconductor laser as is, and the inspection spot lighting device has a light diffusion section that diffuses the laser light emitted from the light source body. In this way, the symmetry of the light distribution can be improved by diffusing the laser light emitted from the light source using the light diffusion section, thereby improving the brightness during imaging while also improving the uniformity of the irradiance on the work surface.

[0011] Specific examples of the light diffusion portion include a speckle reducer provided between the light source body and the light exit surface, and a light diffusion surface formed by, for example, applying a embossing process to the light exit surface.

[0012] In addition, in the inspection system, as another aspect for improving the uniformity of the irradiance on the work surface, it is preferable that the light source body is equipped with the semiconductor laser and a phosphor, and is configured to emit secondary light generated by irradiating and exciting the phosphor with the laser light emitted from the semiconductor laser. In such a device, the light source is configured using a so-called laser phosphor method, in which laser light (excitation light) emitted from a semiconductor laser is irradiated onto a phosphor to excite it, causing the phosphor to emit light.This means that the light distribution has a higher symmetry than laser light, and it is possible to emit light with high brightness like laser light.This makes it possible to improve the brightness during imaging while also improving the uniformity of the irradiance on the work surface.

[0013] The optical characteristics of the spot lighting device provided in the inspection system are as follows: the etendue of the light source body is 1 mm 2·sr or less, and the directivity angle of the inspection light emitted from the light exit surface is preferably within ±5°. With such light distribution characteristics, when combined with a high-magnification object-side telecentric optical system, the inspection light can reach the workpiece with high utilization efficiency, sufficiently increasing the irradiance on the image plane of the imaging device and improving the brightness during imaging. Here, "etendue of the light source body" means the etendue of the semiconductor laser when the light source body is configured to emit the laser light emitted from the semiconductor laser as is, and means the etendue of the phosphor when the light source body is configured to emit secondary light generated from a phosphor irradiated with laser light.

[0014] Furthermore, when the inspection system includes an optical system between the light source body and the light exit surface for directing light emitted from the light source body to the light exit surface, the etendue at each position of the optical system is 1 mm 2 sr or less, and the etendue in front of the light exit surface is preferably 1 mm 2 It is more preferable that it is sr or less.

[0015] In addition, an embodiment in which the effect of the present invention is prominently exhibited is one in which the optical magnification of the object-side telecentric optical system is 2x or more.

[0016] In addition, the inspection spot lighting device of the present invention is used together with an imaging device having an object-side telecentric optical system for imaging a workpiece, and is characterized in that it comprises a light source body and a light exit surface that emits light emitted from the light source body as inspection light, and that the light source body is constructed using a semiconductor laser. Such an inspection spotlight device can provide the same effects as the inspection system of the present invention described above. Effect of the Invention

[0017] According to the present invention thus configured, it is possible to improve the brightness during imaging in an inspection system having a coaxial epi-illumination structure and a high-magnification object-side telecentric optical system. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an inspection system according to a first embodiment and a second embodiment. [Diagram 2] FIG. 1 is a diagram illustrating a schematic configuration of an inspection spot illumination device according to a first embodiment. [Diagram 3] FIG. 13 is a diagram illustrating a schematic configuration of an inspection spot illumination device according to a second embodiment. [Figure 4] 13A and 13B are diagrams showing simulation results of light distribution characteristics of a plurality of inspection spotlight devices having different light source body configurations. [Diagram 5] 13A and 13B are diagrams showing simulation results of the uniformity of irradiance of the inspection spot lighting device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] <First embodiment> An inspection system 100 using an inspection spot illumination device 1 according to a first embodiment of the present invention will be described below with reference to the drawings.

[0020] This inspection system 100 includes an inspection spot lighting device 1 that emits inspection light to be irradiated onto a workpiece W, and an imaging device 2 having an object-side telecentric optical system that images the workpiece W using light scattered or reflected by the workpiece W. As shown in Fig. 1, this inspection system 100 has a so-called coaxial epi-illumination structure that uses a half mirror 232 to irradiate the inspection light emitted from the inspection spot lighting device 1 onto the workpiece W from the same axis as the optical axis C2 of the imaging device 2.

[0021] 2, the inspection spot lighting device 1 emits inspection light from a light exit surface 1s formed at the tip, and includes an illumination housing 11, a light source body 12 built into the illumination housing 11, and an optical system 13 provided in front of the light exit direction of the light source body 12. Note that the inspection spot lighting device 1 refers to an illumination device 1 whose light exit surface 1s can be installed near a position conjugate with the position of the aperture stop 22a of the object-side telecentric optical system without using an optical fiber.

[0022] The lighting housing 11 has a shape of a body of revolution and includes a cylindrical body 111 that houses the light source body 12, a wiring board, etc., and a cylindrical tip portion 112 that is provided coaxially with the body portion 111. The tip portion 112 has a smaller diameter than the body portion 111, and the above-mentioned light emission surface 1s is formed on its tip surface. The tip portion 112 is inserted into a lighting attachment port 231a provided on a camera lens 22 of the imaging device 2 described later, and is configured to be able to emit light into the camera lens 22.

[0023] The light source 12 has a smaller light emitting area than an LED (for example, 0.1 mm 2 The light source body 12 of this embodiment is configured to emit laser light (primary light) emitted from the semiconductor laser 12a as it is toward the optical system 13, and is provided on the optical axis C1 of the optical system 13 so that the emission optical axis coincides with the optical axis C1 of the optical system 13.

[0024] The optical system 13 is provided between the light source body 12 and the light exit surface 1s, and guides the laser light emitted from the light source body 12 to the light exit surface 1s. Specifically, the optical system 13 includes, in this order along its optical axis direction from the base end to the tip end 112, a collimator lens 131, a light diffusion element 132, and a rod lens 133. The collimator lens 131, the light diffusion element 132, and the rod lens 133 are provided so that their optical axis directions coincide with each other.

[0025] The collimator lens 131 collects the laser light emitted from the light source 12 placed at a focal position 13f thereof and makes the light closer to parallel light (collimated light).

[0026] The light diffusion element 132 is for reducing speckle noise by diffusing the laser light that has passed through the collimator lens 131 and reducing its coherence, and is specifically a speckle reducer. The specific configuration of the light diffusion element 132 is not particularly limited, but an example thereof may be one in which a frosted diffusion plate is vibrated by a vibration motor or the like.

[0027] The rod lens 133 is columnar and is provided inside the tip of the lighting housing 11 so that its axial direction coincides with the optical axis C1 of the optical system 13. The rod lens 133 guides the light that has passed through the light diffusing element 132 from a base end face along the axial direction to the inside, reduces unevenness in the amount of light traveling inside, and outputs the light to the outside from a light output surface 1s formed on the tip face. The tip face of the rod lens 133, which is the light output surface 1s, is textured so that the light output surface 1s functions as a light diffusing surface that diffuses the output light.

[0028] The optical characteristics of the inspection spotlight 1 of this embodiment thus configured will be described. The inspection spotlight 1 uses the semiconductor laser 12a to configure the light source body 12, thereby increasing the radiance of the light output surface 1s and narrowing its light distribution characteristics. The inspection spotlight 1 of this embodiment has a directivity angle (or half-value angle) of the inspection light output from the light output surface 1s within ±5°. This directivity angle means the angle at which the relative radiation intensity is 50% or more of the peak value, with the direction in which the radiation intensity is strongest in the light distribution characteristics being 0°. In addition, the etendue of the light source body 12 (semiconductor laser 12a in this embodiment) is 1.0 mm. 2 Less than sr, more specifically 0.01 mm 2 ·sr or less. This etendue is expressed by the product of the cross-sectional area of ​​the light beam and the solid angle (steradian), and is expressed by the following formula (1). E = S × sinθ 2 ×π (1) Here, E: Etendue [mm 2 sr], S: light-emitting area of ​​the light source [mm 2 ], θ: the azimuth angle of the light source.

[0029] In this embodiment, the etendue at each position (preferably in front of the light exit surface 1s) of each optical system 13 provided between the light source body 12 and the light exit surface 1s is 1 mm. 2 - It is configured to be sr or less.

[0030] The imaging device 2 includes a camera body 21 having an imaging element 21a, and a camera lens 22 attached to the camera body 21 to form an image of light reflected or scattered by the workpiece W.

[0031] The camera lens 22 has an object-side telecentric optical system (hereinafter also referred to as an object-side telecentric lens) configured so that the optical axis C2 and the principal ray are parallel on the work W side (object side), and includes a plurality of lenses and an aperture stop 22a housed in a cylindrical lens housing 221 extending along the optical axis direction (imaging direction). In the camera lens 22, the aperture stop 22a is disposed at the focal position 22f of the front lens group among the plurality of lenses, thereby forming an object-side telecentric optical system. In the camera lens 22, the lenses are disposed so that the optical magnification is a high magnification of 2x or more.

[0032] The camera lens 22 includes a coaxial incident light section 23 that introduces the inspection light emitted from the inspection spot lighting device 1 and changes the direction of the introduced inspection light to match the imaging direction. Specifically, as shown in Fig. 1, the coaxial incident light section 23 includes a lighting attachment section 231 to which the tip 112 of the inspection spot lighting device 1 is attached, and a half mirror 232 that reflects the inspection light and changes its direction.

[0033] The illumination attachment part 231 is provided on the side surface of the lens housing 221 and has a cylindrical shape extending in a direction perpendicular to the axial direction of the lens housing 221. At the tip of the illumination attachment part 231, an illumination attachment opening 231a into which the tip part 112 of the inspection spot illumination device 1 is inserted is formed.

[0034] The half mirror 232 is provided in the lens housing 221 on the workpiece W side of the aperture stop 22a and at a position facing the light exit surface 1s inserted from the illumination mounting port 231a. The half mirror 232 is inclined at about 45° with respect to the imaging direction.

[0035] In the coaxial illumination section 23 having such a configuration, the tip 112 of the inspection spot illumination device 1 is inserted into the illumination mounting port 231a, so that the light exit surface 1s of the inspection spot illumination device 1 is located near a position conjugate with the position of the aperture stop 22a of the camera lens 22.

[0036] According to the inspection system 100 of the first embodiment configured as described above, the light source body 12 of the spot lighting device 1 is configured using the semiconductor laser 12a which is a point light source, and the laser light emitted from the semiconductor laser 12a is configured to be emitted as is, so that the radiance of the light emission surface 1s can be made higher and the light distribution characteristic can be made narrower than in the case where an LED is used as the light source body 12. Therefore, when combined with a high-magnification object-side telecentric optical system, the inspection light can reach the workpiece with high utilization efficiency, the radiance on the image plane of the imaging device 2 can be increased, and the brightness during imaging can be improved.

[0037] Moreover, this inspection spot lighting device 1 is equipped with a speckle reducer 132 that diffuses the laser light emitted from the light source body 12, and its light emission surface 1s is provided with a light diffusion surface formed by embossing. Therefore, by diffusing the laser light emitted from the light source body 12, the symmetry of the light distribution can be improved, and the uniformity of the irradiance on the surface of the workpiece W can be improved while improving the brightness during imaging.

[0038] <Second embodiment> Next, an inspection system 100 using an inspection spot illumination device 1 according to a second embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0039] The inspection system 100 of the second embodiment has the same overall configuration as the inspection system 100 of the first embodiment shown in FIG. 1. The inspection spot lighting device 1 of the second embodiment is characterized in that the light source body 12 is of the laser phosphor type. Specifically, as shown in FIG. 3, the light source body 12 includes a plurality of semiconductor lasers 12a and a phosphor 12b, and is configured to emit secondary light generated from the phosphor 12b by irradiating the phosphor 12b with laser light (excitation light) emitted from the plurality of semiconductor lasers 12a to excite the phosphor. The light source body 12 is also called an SLD (Super Luminescent Diode) light source, etc., and has a broad spectrum like a light emitting diode (LED), has lower coherence than the semiconductor laser 12a, and can emit light with high brightness like the semiconductor laser 12a.

[0040] In this embodiment, phosphor 12b is pellet-shaped with a rectangular light-emitting surface of approximately 0.5 mm square, and is provided on optical axis C1 so that the light-emitting surface is perpendicular to optical axis C1 of optical system 13. Here, multiple semiconductor lasers 12a emit blue wavelength laser light, and are arranged to irradiate the light-emitting surface of phosphor 12b from an oblique front. Specifically, each semiconductor laser 12a is provided so that the angle between its emission optical axis and the light-emitting surface of phosphor 12b is approximately 45°.

[0041] In this embodiment, the inspection spot lighting device 1 includes, as the optical system 13, a collimating lens 131 provided in front of the light source body 12. The collimating lens 131 is provided so that its optical axis C1 is coaxial with the tip portion 112 of the cylindrical illumination housing 11. In this embodiment, the inside of the tip portion 112 is hollow and no optical element such as a rod lens 133 is provided, and an internal space S through which light passing through the collimating lens 131 passes is formed. The tip surface of the tip portion 112 where the internal space S opens serves as a light exit surface 1s.

[0042] The optical characteristics of the inspection spotlight 1 of this embodiment thus configured will be described. This inspection spotlight 1 uses a laser phosphor type light source 12, thereby increasing the radiance of the light exit surface 1s and narrowing its light distribution characteristics. Specifically, the inspection spotlight 1 of this embodiment has a directivity angle (or half-value angle) of light emitted from the light exit surface 1s within ±5°, more specifically within ±3.5°. The etendue of the light source 12 (specifically, the phosphor 12b) is 1.0 mm. 2 sr or less, more specifically 0.6 mm 2 -SR or below.

[0043] According to the inspection system 100 of the second embodiment configured as described above, by using the semiconductor laser 12a, which is a point light source, as the light source body 12 of the spot lighting device 1, the radiance of the light emission surface 1s can be made higher and the light distribution characteristic can be made narrower than when an LED is used as the light source body 12. Therefore, when combined with a high-magnification object-side telecentric optical system, the inspection light can reach the workpiece with high utilization efficiency, increasing the radiance on the image plane of the imaging device 2 and improving the brightness during imaging.

[0044] Moreover, this inspection spot lighting device 1 uses a so-called laser phosphor type light source 12, in which laser light (excitation light) emitted from a semiconductor laser 12a is irradiated onto the phosphor 12b to excite it, causing the phosphor 12b to emit light. Therefore, the light distribution has a higher symmetry than laser light and it can emit light with high brightness like laser light, so that it is possible to improve the brightness during imaging while also improving the uniformity of the irradiance on the surface of the workpiece W.

[0045] <Light distribution characteristic simulation> Next, the results of simulating the light distribution characteristics of several inspection spot lighting devices with different light source body configurations are shown in Figure 4. The simulation results show the light distribution characteristics of each of (i) an inspection spot lighting device (denoted as LD) whose light source body is configured to emit light emitted from a semiconductor laser as is, (ii) an inspection spot lighting device (denoted as SLD) whose light source body is configured to emit secondary light generated by irradiating and exciting a phosphor with laser light emitted from a semiconductor laser, and (iii) an inspection spot lighting device (denoted as LED) whose light source body is configured to emit light emitted from a light-emitting diode. In this simulation, in the inspection spot illumination device (i) (LD), a collimating lens and a speckle reducer are provided in front of the light emission direction of the light source body (configuration obtained by removing rod lens 133 from FIG. 2), in the inspection spot illumination device (ii) (SLD), a collimating lens is provided in front of the light emission direction of the light source body (same configuration as FIG. 3), and in the inspection spot illumination device (iii) (LED), a collimating lens and a rod lens are provided in front of the light emission direction of the light source body.

[0046] As shown in Figure 4, in a light source configured to directly emit the laser light from the semiconductor laser (LD), it was confirmed that the beam angle at which the relative radiation intensity is 50% or more of the peak value is within approximately ±5°. In addition, in a light source configured to emit secondary light generated by irradiating and exciting a phosphor with laser light (SLD), it was confirmed that the beam angle is within approximately ±3.5°.

[0047] <Simulation of uniformity of irradiance> Next, a simulation result of the uniformity of irradiance on the surface of the workpiece W when the optical magnification of the camera lens 22 having an object-side telecentric optical system is changed (2x, 4x) using the inspection spot illumination device of the second embodiment is shown in Fig. 5. In this simulation, the sensor size of the imaging element 21a of the camera body 21 that captures the image is equivalent to 2 / 3 inch.

[0048] As shown in Figure 5, the simulation results confirmed that the uniformity of the irradiance on the surface of the workpiece W was good at both optical magnifications of 2x and 4x. In particular, it was confirmed that the uniformity of the irradiance on the surface of the workpiece W could be improved more as the optical magnification was increased.

[0049] <Other embodiments> The present invention is not limited to the above-described embodiment.

[0050] For example, in the first embodiment, the optical system 13 includes both the speckle reducer 132 and the light diffusion surface formed on the light exit surface 1s as the light diffusion section, but it may include only one of them, or may not include the light diffusion section. The light diffusion section may be a light diffusion member such as a diffusion plate or a phosphor.

[0051] In the second embodiment, the light source body 12 is configured to irradiate the phosphor 12b with laser light from the multiple semiconductor lasers 12a, but is not limited to this. The light source body 12 in other embodiments may be configured to include only one semiconductor laser 12a and to excite the phosphor 12b with the single semiconductor laser 12a.

[0052] In each of the above embodiments, the etendue of the light source body 12 and the etendue at each position of the optical system 13 are 1 mm 2 In the above embodiment, the etendue at each position of the light source body 12 and the optical system 13 is set to 1 mm. 2May exceed sr.

[0053] Furthermore, 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 and scope of the present invention. [Explanation of symbols]

[0054] 100 ···Inspection System 1. Spot lighting device for inspection 12a Semiconductor laser 13...Optical system 1s...Light exit surface 2. Imaging device 22 Camera lens (telecentric lens) W ···Work

Claims

1. An inspection system comprising: an inspection spot lighting device having a light source body, a light exit surface that emits light emitted from the light source body as inspection light; and an imaging device having an object-side telecentric optical system that images a workpiece, the inspection system being configured to irradiate the inspection light emitted from the light exit surface onto the workpiece from a position coaxial with an optical axis of the imaging device, The inspection system, wherein the light source is configured using a semiconductor laser.

2. The light source body is configured to emit the laser light emitted from the semiconductor laser as it is, 2. The inspection system according to claim 1, wherein the inspection spotlight device includes a light diffusion section that diffuses the laser light emitted from the light source body.

3. The inspection system according to claim 1 , wherein the light source unit includes the semiconductor laser and a phosphor, and is configured to emit secondary light generated by irradiating and exciting the phosphor with laser light emitted from the semiconductor laser.

4. The etendue of the light source is 1 mm ２ The inspection system according to any one of claims 1 to 3, wherein the distance is sr or less.

5. 5. The inspection system according to claim 1, wherein the inspection light emitted from the light exit surface has a directivity angle within ±5°.

6. 6. The inspection system according to claim 1, wherein the object side telecentric optical system has an optical magnification of 2 or more.

7. A spot illumination device for inspection is used together with an imaging device having an object-side telecentric optical system for imaging a workpiece, and includes a light source body and a light exit surface that emits light emitted from the light source body as inspection light, The inspection spot lighting device, wherein the light source body is configured using a semiconductor laser.

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