Imaging device

Abstract

This imaging device comprises: an illumination unit 20 that includes a light source 21 for emitting illumination light 2, and a lens group 22 for irradiating an imaging object 1 with the illumination light 2 emitted from the light source 21; and an imaging unit 10 for imaging the imaging object 1. The imaging device is configured so as to block some of the illumination light 2 emitted from the light source 21 by using a light-shielding component 40.

Description

[Technical Field]

[0001] The present invention relates to an imaging device such as a stereo camera that captures an image of an object while irradiating the object with light. [Background technology]

[0002] Stereo cameras and other imaging devices are used in a variety of industries. For example, industrial robots operating on automated production lines in factories are sometimes equipped with stereo cameras to recognize the shape of workpieces, the distance to the workpieces, and other information. Many imaging devices, including stereo cameras of this type, are equipped with an illumination unit to compensate for insufficient exposure of the object being imaged.

[0003] Generally, the lighting unit built into an imaging device is set to illuminate the object to be imaged almost uniformly. However, when observing the captured image, there is still a difference in brightness between the center and periphery of the image area. Specifically, the center of the captured image is often brighter and the periphery is darker. When this type of brightness difference occurs in a captured image, there is a risk that the accuracy of image analysis using that image will decrease, and so a solution has been desired.

[0004] 3 of Patent Document 1 discloses an illumination device (4) having a first light-emitting section (43b) provided in the center of a light source (41) and second light-emitting sections (44b, 45b) provided around the first light-emitting section (43b). Note that the reference numerals in parentheses are the reference numerals given in Patent Document 1. In this lighting device (4), the first light-emitting section (43b) in the center is set to the lowest brightness, and the brightness of the second light-emitting sections (44b, 45b) is set to successively higher toward the outside. This configuration realizes a light source (41) in which the brightness gradually increases from the center to the periphery of the light-emitting section, thereby improving the uniformity of the illumination distribution on the projection surface (7).

[0005] However, the lighting device (4) disclosed in the document 1 has an improved internal structure of the light source (41), which requires the light source to be produced as a dedicated product, which has the drawback of increasing the production cost compared to conventional devices that use general-purpose LEDs or the like as light sources. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-157488 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide an imaging device that can obtain an image with uniform brightness and that can suppress increases in product costs that may accompany improvements. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides an imaging device comprising an illumination unit including a light source that emits illumination light and a group of lenses for irradiating the illumination light emitted from the light source toward an imaging target, and an imaging unit that images the imaging target, wherein the illumination unit is provided with a shading component that blocks a portion of the illumination light emitted from the light source.

[0009] By blocking a portion of the illumination light in this way, it is possible to correct the difference in brightness between the center and periphery of the captured image and make the brightness of the entire captured area uniform. Furthermore, the imaging device of the present invention can be manufactured by adding light-blocking components to existing components, so the increase in product costs associated with improvements can be suppressed compared to the invention of Patent Document 1, which uses an improved and specialized high-priced light source.

[0010] The light-shielding component can be configured by laminating a light-shielding pattern recording layer on a thin transparent substrate, which can be manufactured inexpensively and can be easily arranged without occupying a large space on the optical path of the illumination light emitted from the light source.

[0011] The shading pattern can be configured to include, for example, a central shading portion that shades the central portion of a cross section perpendicular to the optical axis of the illumination light emitted from the light source, and an annular intermediate shading portion that shades the intermediate portion between the optical axis and the outer edge in a cross section perpendicular to the optical axis of the illumination light.

[0012] As mentioned above, captured images are often bright in the center and dark in the periphery. Therefore, by blocking the central portion of the cross section perpendicular to the optical axis with respect to the illumination light and reducing the brightness of the center of the irradiation area of ​​the imaged object, the brightness of the center of the captured image is also reduced, approaching the brightness of the periphery, and making the brightness of the entire captured area uniform. Furthermore, by blocking the intermediate portion between the optical axis and the outer edge in the cross section perpendicular to the optical axis of the illumination light, the brightness can be reduced in stages from the center to the intermediate portion and then to the outer peripheral portion, thereby smoothly achieving uniform brightness across the entire imaging area.

[0013] Furthermore, the light-shielding pattern can be formed, for example, by a collection of a large number of light-shielding dots, and the large number of light-shielding dots can be arranged so that the density is highest in the central part of the cross section perpendicular to the optical axis of the illumination light emitted from the light source, and the density decreases as the distance from the central part increases radially. By blocking the illumination light with such a light-blocking pattern, the brightness can be gradually reduced from the center to the middle and then to the outer periphery, making it possible to more smoothly uniform the brightness across the entire imaging area.

[0014] In addition, in an imaging device in which the illumination unit includes, in a lens group, a condenser lens that focuses illumination light from the light source and an illumination system lens that irradiates the illumination light that has passed through the condenser lens toward the object to be imaged, it is preferable that the light-shielding component be arranged in a position on the optical path of the illumination light emitted from the light source that is not optically conjugate with the object to be imaged. This prevents the light blocking pattern from being imaged on the object to be imaged, making it possible to smoothly achieve uniform brightness across the entire imaging area.

[0015] Specifically, it is preferable that the position optically conjugate with the object to be imaged is set midway between the condenser lens and the illumination system lens, and in an imaging device in which the condenser lens is composed of multiple lenses, the shading component is positioned between the multiple lenses that make up the condenser lens without coming into contact with the surfaces of those lenses. More specifically, it is preferable to place the light-shielding component between the first lens of the multiple lenses constituting the condenser lens that is closest to the light source and the second lens that is adjacent to the first lens. By placing the light-shielding component in such a position, the light-shielding component can be separated significantly from the position optically conjugate with the imaging target, allowing the light-shielding pattern to be projected onto the imaging target in a significantly blurred state, thereby achieving smoother uniformity of brightness across the entire imaging area.

[0016] Alternatively, a spacer can be provided between the first and second lenses to form a gap, and a light-shielding component can be attached to the spacer and incorporated into the condenser lens. The spacer allows the light-shielding component to be positioned without coming into contact with the lens surface.

[0017] In addition, in an imaging device in which the position optically conjugate with the object to be imaged is set midway between the condenser lens and the illumination system lens, the light-shielding component can also be placed between the light source and the condenser lens.

[0018] As described above, according to the present invention, it is possible to obtain a captured image with uniform brightness, and furthermore, it is possible to suppress an increase in product costs due to improvements. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the overall structure of an imaging device according to an embodiment of the present invention. [Figure 2] FIG. 2 shows captured images obtained through an experiment by the present inventors. [Figure 3] FIG. 3A is a front view showing an example of a light-shielding component, and FIG. 3B is a right side view of the same. [Figure 4] FIG. 4 is a diagram for explaining the arrangement position of the light blocking component in the lighting unit. [Figure 5] FIG. 5 is a cross-sectional view for explaining the specific arrangement positions of the light blocking components in the condenser lens. [Figure 6] FIG. 6A is a cross-sectional view showing the structure in which a light-shielding component is incorporated into a condenser lens, and FIG. 6B is a cross-sectional view showing an enlarged view of part I. [Figure 7] FIG. 7 is a front view showing an example of the configuration of a light-shielding pattern formed on a light-shielding component. [Figure 8] FIG. 8 is a front view showing another example of the configuration of the light-shielding pattern formed on the light-shielding component. [Explanation of symbols]

[0020] 1: Image capture target, 2: Illumination light, 10: imaging unit, 11: imaging element, 12: imaging lens, 20: lighting unit, 21: light source, 22: lens group, 23: condenser lens, 24: lighting system lens, 25: first lens, 26: second lens, 27: lens barrel, 28: pressing part, 29: annular spacer, 29a: step portion, 29b: adhesive surface, 30: support part, P: conjugate position, 40: Light-shielding component, 41: Light-shielding pattern, 41a: Central light-shielding portion, 41b: Intermediate light-shielding portion, 41c: Light-shielding dot, 42: Transparent substrate, 43: Recording layer BEST MODE FOR CARRYING OUT THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the overall structure of an imaging device according to an embodiment of the present invention. This embodiment shows an example of a configuration in which the present invention is applied to a stereo camera as an imaging device. As is well known, a stereo camera is a device that captures an image of an object 1 using two imaging units 10 (cameras) and processes the captured image data to obtain three-dimensional image data including data in the depth direction.

[0022] The imaging unit 10 is configured, for example, by combining an imaging element 11 and an imaging lens 12 that receives reflected light from the imaging target 1 and directs the light to the imaging element 11. For example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) is used for the imaging element 11. The two imaging units 10 are arranged at a fixed distance apart in the width direction. In addition to the configuration described above, the imaging unit 10 can also be configured with various cameras used in known stereo cameras.

[0023] An illumination unit 20 is disposed at the center position in the width direction between the two imaging units 10. This illumination unit 20 has the function of irradiating illumination light 2 onto the imaging target 1 to compensate for insufficient exposure of the imaging target 1. The illumination unit 20 includes a light source 21 that emits the illumination light 2, and a lens group 22 that irradiates the illumination light 2 emitted from the light source 21 toward the imaging target 1.

[0024] The light source 21 may be, for example, a light emitting diode (LED) or an organic electroluminescence (EL) element. The lens group 22 includes a condenser lens 23 that condenses the illumination light 2 from the light source 21, and an illumination system lens 24 that irradiates the illumination light 2 that has passed through the condenser lens 23 toward the object 1 to be imaged.

[0025] In this embodiment, the lighting unit 20 is disposed at a central position sandwiched between the two imaging units 10, and irradiates the illumination light 2 toward the imaging target 1 from a position facing the imaging target 1.

[0026] These units are incorporated into a main body case (not shown) to form a single imaging device, which is attached to an industrial robot arm or the like and placed at an arbitrary position facing the imaging target 1.

[0027] The lighting unit 20 is set to illuminate the subject 1 almost uniformly. However, in reality, there is a large difference in brightness between the center and the periphery of the captured image. Specifically, the center of the captured image is often brighter and the periphery is darker. This is thought to be due to differences in the reflection characteristics of the object 1 to be imaged and the performance of the central / peripheral light intensity ratio of the imaging lens 12 (i.e., lens performance), which results in a lack of peripheral light intensity compared to the central light intensity reaching the imaging element 11.

[0028] FIG. 2 shows a captured image obtained through an experiment conducted by the inventors. The image was taken by using an anodized aluminum plate with a light-scattering white matte surface as the target 1, irradiating it with illumination light 2 from an illumination unit 20 positioned opposite it, and capturing the surface of target 1 with imaging unit 10. Note that image processing was performed to darken the entire image to clarify differences in brightness depending on the location. In this captured image, the relative brightness of center A of the captured area was 138, while the relative brightness of peripheral B was 54. Therefore, the peripheral / center brightness ratio was 39%, demonstrating the phenomenon of the center being bright and the peripheral being dark.

[0029] Therefore, the imaging device of this embodiment is configured to incorporate a light-blocking component 40 into the lighting unit 20, which blocks part of the illumination light 2, thereby correcting the difference in brightness between the center and periphery of the captured image and making the brightness of the entire imaging area uniform. FIG. 3A is a front view showing an example of a light-shielding component, and FIG. 3B is a right side view of the same. The light-shielding component 40 has a light-shielding pattern 41 formed thereon to block the illumination light 2 from the light source 21 . The light-shielding component 40 can be configured, for example, by laminating a recording layer 43 of a light-shielding pattern 41 onto a thin, transparent substrate 42. The recording layer 43 can be formed by applying a photosensitive emulsion. The light-shielding component 40 configured as described above can be produced using commercially available positive film. The light-shielding pattern 41 can be drawn as an image by exposing the recording layer 43, printing it, and developing it. A light-shielding component 40 configured in this manner can be manufactured inexpensively, and the light-shielding pattern 41 drawn on the recording layer 43 can be easily changed as needed, allowing for flexible design changes depending on the reflection characteristics of the object 1 to be imaged, etc.

[0030] The light-shielding component 40 is not limited to a configuration using a positive film. For example, it may be configured by laminating a recording layer 43 made of a thin chromium film on a thin transparent glass substrate. A glass substrate has advantages such as being resistant to thermal expansion and having high heat resistance.

[0031] Furthermore, by forming the light-shielding component 40 in a thin plate shape, it can be easily arranged on the optical path of the illumination light 2 emitted from the light source 21 without taking up a large width, as will be explained next.

[0032] FIG. 4 is a diagram for explaining the arrangement position of the light blocking component in the lighting unit. Illumination unit 20 includes an optical system that collects illumination light 2 from light source 21 with condenser lens 23 and irradiates it onto imaging target 1 through illumination system lens 24. A position (conjugate position P) that is optically conjugate with imaging target 1 is set between condenser lens 23 and illumination system lens 24. When a projection target is placed at this conjugate position P, an image of the projection target is formed on the surface (projection plane) of imaging target 1. Therefore, when light-shielding component 40 is placed at this conjugate position P, a clear image of light-shielding pattern 41 is formed on the surface of imaging target 1, which may cause a discontinuous change in brightness at the boundary between the imaged portion of light-shielding pattern 41 and other portions.

[0033] Therefore, in this embodiment, the light-shielding component 40 is arranged at a position (other than the conjugate position P) that is not in an optically conjugate relationship with the image capture target 1. For example, as shown in FIG. 4, the light-shielding component 40 can be incorporated inside the condenser lens 23. 5, the condenser lens 23 is composed of multiple lenses. If a light-shielding component 40 is arranged between the first lens 25, which is closest to the light source 21, and the second lens 26, which is adjacent to the first lens, the light-shielding component 40 can be spaced farther away from the conjugate position P. The farther away from the conjugate position P is, the more blurred the light-shielding pattern 41 projected onto the surface of the object 1 to be imaged becomes. This makes it possible to make the boundaries where brightness is discontinuous less noticeable and to illuminate the object 1 with illumination light 2 whose brightness changes smoothly.

[0034] Here, it is preferable to arrange the light-shielding components 40 so that they do not come into contact with the surfaces of the lenses, in order to prevent interference fringes from appearing and causing variations in the brightness of the illumination light 2 if the light-shielding components 40 come into contact with the surfaces of the lenses.

[0035] 5, the shading component 40 can also be disposed between the first lens 25 (i.e., the condenser lens 23) and the light source 21. By disposing it in this position, the shading pattern 41 projected onto the surface of the imaging target 1 can be blurred even more.

[0036] 6A and 6B are cross-sectional views showing the structure in which a light-shielding component is incorporated into a condenser lens. 6A, the multiple lenses that make up condenser lens 23 are inserted into cylindrical lens barrel 27 and are fastened axially by retaining parts 28 to ensure no rattle. An annular spacer 29 for adjusting the gap is provided between first lens 25 and second lens 26, and a light-shielding part 40 is attached to this annular spacer 29. First lens 25 is assembled via support part 30.

[0037] 6B, annular spacer 29 is formed with step portion 29a, and an adhesive surface 29b of light-shielding component 40 is formed at a position recessed from the circumferential surface that contacts second lens 26. By adhesively fixing light-shielding component 40 to this adhesive surface 29b, it is possible to arrange light-shielding component 40 without contacting the surface of second lens 26 (and, of course, the surface of first lens 25).

[0038] FIG. 7 is a front view showing an example of the configuration of a light-shielding pattern formed on a light-shielding component. The shading pattern 41 shown in the same figure is assumed to have a virtual cross section perpendicular to the optical axis O of the illumination light 2 emitted from the light source 21, and is composed of a central shading portion 41a that shades the central portion of the illumination light 2 in that virtual cross section, and an annular intermediate shading portion 41b that shades the intermediate portion between the optical axis O of the illumination light 2 and the outer edge.

[0039] Central light-shielding portion 41a and intermediate light-shielding portion 41b are each formed in an elliptical ring shape, and it is preferable to set the thickness, diameter, etc. of each portion through appropriate simulations according to the shape of the light-emitting surface of the light source and the imaging target 1. By forming each portion in an elliptical ring shape, it is possible to dim the illumination light 2 while projecting it onto imaging target 1 with a blurred outline due to the light being deflected, so that boundaries where brightness is discontinuous are made less noticeable and imaging target 1 can be illuminated with illumination light 2 whose brightness changes smoothly.

[0040] FIG. 8 is a front view showing another example of the configuration of the light-shielding pattern formed on the light-shielding component. The light-shielding pattern 41 shown in the figure is formed by a collection of many light-shielding dots 41c. The many light-shielding dots 41c are arranged on an imaginary cross section perpendicular to the optical axis O of the illumination light 2 emitted from the light source 21, so that the illumination light 2 has the highest density in the center of the cross section and decreases in density as it moves away from the center in the radial direction. By blocking the illumination light 2 with such a light blocking pattern 41, it is possible to gradually reduce the brightness from the center to the intermediate portion and then to the outer peripheral portion.

[0041] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications and applications are possible as required. For example, the shading pattern 41 of the shading part 40 is configured to shade the central part of the illumination light 2, but when the area other than the central part of the captured image becomes brighter than other areas, it is preferable to configure it to shade the part corresponding to the bright area in accordance with such individual phenomenon.

Claims

1. an illumination unit including a light source that emits illumination light and a lens group that irradiates the illumination light emitted from the light source toward an imaging target; an imaging unit that captures an image of the imaging target, a light-shielding component for blocking a part of the illumination light emitted from the light source is provided in the illumination unit; the light-shielding component is configured to block a portion of the illumination light corresponding to an area that is brighter than other areas in the image of the object captured by the imaging unit, the illumination unit includes, in the lens group, a condenser lens that condenses illumination light from the light source, and an illumination system lens that irradiates the illumination light that has passed through the condenser lens toward the imaging target; Furthermore, a position optically conjugate with the imaging target is set at an intermediate portion between the condenser lens and the illumination system lens, and the condenser lens is composed of a plurality of lenses, The imaging device is characterized in that the light-shielding component is disposed between the plurality of lenses constituting the condenser lens without contacting the surfaces of the lenses.

2. 2. The imaging device according to claim 1, wherein the light-shielding component is disposed between a first lens of the plurality of lenses constituting the condenser lens that is closest to the light source and a second lens that is adjacent to the first lens.

3. 3. The imaging device according to claim 2, wherein a spacer is provided between the first lens and the second lens to form a gap, and the light-shielding component is attached to the spacer and incorporated into the condenser lens.

4. An illumination unit including a light source that emits illumination light and a lens group that irradiates the illumination light emitted from the light source toward an imaging target; an imaging unit that captures an image of the imaging target, a light-shielding component for blocking a part of the illumination light emitted from the light source is provided in the illumination unit; the light-shielding component is configured to block a portion of the illumination light corresponding to an area that is brighter than other areas in the image of the object captured by the imaging unit, the illumination unit includes, in the lens group, a condenser lens that condenses illumination light from the light source, and an illumination system lens that irradiates the illumination light that has passed through the condenser lens toward the imaging target; Furthermore, a position optically conjugate with the imaging target is set at an intermediate portion between the condenser lens and the illumination system lens, The imaging device is characterized in that the light blocking component is disposed between the light source and the condenser lens.

5. 5. The imaging device according to claim 1, wherein the light-shielding component is configured by laminating a recording layer of a light-shielding pattern on a thin transparent substrate.

6. The imaging device described in claim 5, characterized in that the shading pattern includes a central shading portion that shades the central portion of a cross section perpendicular to the optical axis of the illumination light emitted from the light source, and an annular intermediate shading portion that shades an intermediate portion between the optical axis and an outer edge in a cross section perpendicular to the optical axis of the illumination light.

7. the light-shielding pattern is formed by a collection of a large number of light-shielding dots, The imaging device described in claim 5, characterized in that the numerous light-shielding dots are arranged so that the density is highest in the central part of a cross section perpendicular to the optical axis of the illumination light emitted from the light source, and the density decreases as the distance from the central part increases radially.

Images