JP2015190856A - Imaging device and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that can provide uniform and high-contrast images even when an object to be imaged is a mixture of glossy and uneven surface such as metal and non-glossy surface such as resin and the amount of light is required not to have much influence on imaging.SOLUTION: The imaging device includes: dome-type lighting means; a line camera; a conveying mechanism conveying the imaging target to a direction intersecting at right angles with a direction in which the line camera extends; and opening amount adjusting means at the opening of the dome-type lighting means in an optical system with the line camera installed having an imaging angle inclination from a direction perpendicular to an imaging target.

Description

  The present invention relates to an image capturing apparatus including a camera and illumination.

  At the manufacturing site, for the purpose of automation, machine vision is used in which an apparatus itself identifies an object such as a product based on an image picked up by a CCD camera or the like, and determines operation based on the image.

  Machine vision at the manufacturing site generally consists of a camera and light source for acquiring images, hardware and software for processing the acquired images, and operating mechanisms such as input / output devices such as sensors and stages. It is.

  The performance of machine vision is greatly influenced by the optical system, such as the sharpness of the acquired image. When an image is unclear due to noise or the like, preprocessing for recognizing the image is necessary, and the cost of software increases. In addition, hardware for operating the software is required to have high performance.

  When machine vision is used for automatic inspection of products, an optical system that can ensure the contrast between the product and an identification target such as a defective portion is required.

  Furthermore, in order to accurately recognize the identification target, it is desirable that other portions can be stably imaged with uniform luminance.

  Various illuminations are used for stable imaging, and there are mainly two types of illuminations: transmitted illumination and reflected illumination.

  In the case of inspecting the shape, the transmitted illumination that irradiates from a position that is paired with the camera with the object interposed therebetween can easily obtain contrast, and stable imaging can be performed.

  In addition, there are many cases where it is desired to check the surface condition of an inspection object such as inspection of foreign matter. In this case, if the object does not transmit illumination, it is common to use reflected illumination that illuminates the object from the same side as the camera.

  However, in the reflected illumination, non-uniform reflected light from the object may hinder stable imaging, and the type and position of the illumination must be considered.

  In particular, when the object is a highly reflective material such as a metal, it is difficult to obtain uniform reflected light when the surface is further curved or uneven, or the angle varies. Affects.

  For example, when coaxial illumination that irradiates an object parallel to the optical axis of the camera from the front of the lens using a half mirror is used, and when the object is perpendicular to the optical axis of the camera The reflected light reflects and returns brightly, and when there is an angle, the light that is regularly reflected on the surface of the imaging object does not return to the camera and appears dark.

  In order to solve this problem, the use of dome illumination is known as a method of trying to perform uniform imaging even when the imaging target has an angle by irradiating light from various angles.

  The dome illumination has a structure in which a substantially hemispherical reflecting plate extends from the periphery of the lens to the imaging target, and a slit for the lens to look into the imaging target is provided at the apex portion of the hemisphere.

  When dome illumination is used, when the object to be imaged is vertical, it reflects light from the slit (lens) part, and when it has an angle, it reflects the hemispherical reflector part. As a result, it may be non-uniform.

  Therefore, in Patent Document 1 and Patent Document 2, an optical system using both dome illumination and coaxial epi-illumination is used.

  However, even if these methods are used, there is a difference between the amount of light due to the coaxial incident light and the amount of light due to the reflector of the dome illumination, and the difference between the part that does not emit light at the boundary between the two is uneven. Cause.

  Furthermore, if a sufficiently large dome illumination is not used for the imaging range, the brightness of the end tends to decrease, and there is a problem that the apparatus becomes large or difficult to install.

  On the other hand, there are two main types of imaging methods: a method using an area camera that captures an arbitrary range including an imaging target at once, and a method using a line camera that repeats imaging on a straight line in accordance with the movement of the imaging target. is there.

  When an area camera is used, it is necessary to make the imaging range wide and uniform. However, when a line camera is used, it is sufficient that only the straight line to be imaged is made uniform.

  Therefore, in order to obtain a uniform image, it may be advantageous to use a line camera.

  As an imaging method combining a line camera and indirect illumination such as a dome illumination, Patent Document 3 discloses a method for stably identifying a plated portion with a base metal such as copper or iron as an inspection application for a lead frame or the like. Has been tried.

  However, this method was effective in improving the contrast for distinguishing between two types of metal and plating, and avoiding imaging of rolling flaws on the metal surface, but is insufficient in obtaining images with uniform brightness. was there.

  In particular, in recent years, there are imaging objects that combine three or more types, such as a combination of metal and plating, as well as resin, etc., and more stable uniformity is required for each stable identification. It is required to acquire an image with

  In the method of Patent Document 3, the illumination applied to the product is reflected by indirect illumination such as a dome, thereby causing a problem that the luminance varies at the start and end of product imaging and during product passage.

JP 2006-153580 A JP2009-174857 JP2009-204311

  The present invention has been made in view of the above-described problems, and relates to an imaging method for imaging an image capable of obtaining uniform and contrast.

  The present invention has a dome-shaped illumination means, a line camera, and a transport mechanism that transports an imaging target in a direction orthogonal to the extension direction of the line camera, and the line camera captures an imaging angle from a direction perpendicular to the imaging target. In an optical system installed with an inclination of (2), an imaging apparatus having an opening amount adjusting means at the opening of the dome-shaped illumination means is provided.

  The light emitted from the dome type illumination means becomes indirect light illumination. For example, in the case of dome illumination, the imaging target is illuminated from various angles by a dome-shaped reflector, and the imaging target surface has an angle such as unevenness. Even in the state, light from the reflecting plate surface corresponding to the surface is incident, and a uniform image can be obtained.

  In particular, oblique illumination makes it possible to relatively emphasize edge changes, and is effective in detecting scratches and chips.

  However, in the state where the imaging target is directly under the illumination, the light irradiated to the imaging target is reflected into the dome-shaped illumination means, and this is further reflected by the reflector of the illumination, but the imaging target covers only half of the illumination. If there is, light reflected from the imaging target into the illumination is also reduced, so that a phenomenon in which brightness is different between the both ends and the center of the imaging target occurs in the captured image.

  Further, when the optical axis of the camera is tilted, the imaging start and imaging end positions of the imaging target are not directly under the center of the illumination, but are positions shifted forward or backward depending on the tilt of the camera.

  Therefore, for example, if the camera tilt captures the traveling direction side of the imaging target from directly below the illumination center, the imaging target is shifted to the traveling direction from directly below the illumination at the end of imaging, and reflected from the imaging target to the illumination. The amount of light emitted will be further reduced.

  Therefore, by providing a mechanism that can adjust the aperture by closing the illumination opening in the direction opposite to the direction in which the imaging position is shifted from the illumination center due to the tilt of the camera, the change in luminance when passing through the imaging target is suppressed. I can do things. Further, by adjusting the opening amount by limiting the opening, there is an effect of increasing the amount of light in the imaging portion.

  In addition, when it is desired to obtain a contrast between a glossy surface such as a regularly reflecting metal and a non-glossy surface such as a resin that is irregularly reflected with respect to an imaging target, the image capturing position is shifted from the center of the illumination due to the tilt of the camera. By providing an opening amount adjusting means capable of closing the illumination opening in the same direction, the opening amount can be appropriately adjusted, and a uniform image and a high-contrast image can be obtained.

  On the glossy surface, light from the reflection plate in the regular reflection direction is imaged, and even if the angle of irradiation is reduced by adjusting the amount of opening such as limiting the opening, the amount of light changes little.

  On the other hand, the non-glossy surface captures a component in which light from various angles is irregularly reflected. Therefore, when the irradiation angle is limited, the amount of light incident on the camera is reduced.

  It is particularly preferable that the image pickup apparatus is characterized in that the opening amount adjusting means is a shielding plate.

  Moreover, the line camera side surface of a shielding board is a mirror surface, and the imaging device characterized by absorbing the illumination wavelength which the imaging object side surface irradiates is preferable.

  In addition, it is preferable that the shielding plate be a tilting-side shielding plate extending from a direction opposite to the direction in which the imaging angle of the line camera is tilted.

  In addition to the tilt source side shield plate, the image pickup apparatus is preferably formed of an inclined tip side shield plate extending from a direction in which the imaging angle of the line camera is tilted.

  In addition, an imaging device in which the shielding plate is movable is preferable.

  An imaging device having an imaging angle within 10 degrees and not completely 0 degrees is preferable.

  An imaging method characterized in that, using such an imaging apparatus, an aperture amount of the opening of the dome-shaped illuminating means is adjusted to image an imaging target conveyed in a direction orthogonal to the extension direction of the line camera. I will provide a.

  According to the present invention, even if the object to be imaged is a glossy surface such as a metal having unevenness on the surface, the image can be captured with uniform brightness, and high contrast is obtained between the glossy surface and the non-glossy surface. This enables significant imaging in the field of machine vision.

It is a schematic cross-sectional view showing a conventional optical system related to an embodiment of the present invention, (A) at the start of imaging, (B) at the middle of imaging, and (C) at the end of imaging. It is a schematic cross section showing an optical system showing an example of an embodiment of the present invention, where (A) shows the start of imaging, (B) shows the middle of imaging, and (C) shows the end of imaging. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section for demonstrating this invention, (A) is explanatory drawing of the indirect light used as the light imaged on a glossy surface, (B) becomes the light imaged on a non-glossy surface. It is explanatory drawing of indirect light, (C) is explanatory drawing of the beam light used as the light imaged to a resin surface. It is a schematic cross section which shows the optical system which shows an example of embodiment of this invention, (A) is a light shielding board also provided with the inclination origin side light shielding board, when (A) becomes a light shielding board only from the inclination origin side light shielding board. The case consisting of It is a schematic cross section explaining the present invention, and is a figure for explaining the required width of a slit.

  The imaging apparatus of the present invention includes a dome-shaped illumination unit, a line camera, and a transport mechanism that transports an imaging target in a direction orthogonal to the extension direction of the line camera.

  The line camera is an optical system installed with an inclination of the imaging angle from the vertical direction with respect to the imaging target, and has means for adjusting the opening amount at the opening of the dome-shaped illumination means Yes.

  The dome-shaped illuminating means is a hemispherical dome, and a slit having a shape that can be imaged by a later-described line camera is provided near the top. The direction of the slit is the same as the direction of the line camera, and is a slit perpendicular to the transport direction of the transport mechanism described later. Further, the shape and size of the slit are set in accordance with the shape and size of the visual field of the line camera.

  In addition to the hemispherical dome illumination, a half-pipe type line dome illumination can be used. The use of line dome lighting is effective in saving installation space.

  Further, such a hemispherical line dome need not be strictly a hemispherical shape or a line dome, and may have any shape as long as uniform illumination is required.

  In addition, this dome-shaped illumination means can irradiate many angular components including the coaxial direction by irradiating the object to be imaged with a solid angle of 2π, so that it is effective for revealing defects generated in the side tapered portion. It is. Such a dome-shaped illuminating means includes a type in which a light exit is formed on the inner surface of the dome and light is irradiated from the direction of the solid angle 2π to the object to be inspected, and a light exit is formed on the inner surface of the dome. There is a type that irradiates the object to be imaged with light reflected by the inner surface, but either type may be used as long as the same effect can be produced.

  In order to reduce the influence of shading as much as possible, the inner diameter of the dome-shaped illuminating means is set to at least twice the width of the imaging target so that the entire surface of the imaging target can be imaged with one imaging. Is preferred. As the light source, a metal halide light source, a halogen light source, an LED light source, or the like is selected and used in consideration of the amount of light necessary for imaging.

  Further, an opening amount adjusting means is provided at the opening. Conventionally, an annular plate from the edge to the inside was attached to the edge of the hemisphere in order to suppress irregular reflection, but such an annular plate is only for suppressing irregular reflection, and the inner side of the line camera side Although the surface was a mirror surface, since it was an extremely narrow annular plate, the opening amount of the opening was not substantially adjustable.

  This time, instead of or in addition to such an annular plate, an opening amount adjustment is provided. Such an opening amount adjusting means can be realized by adjusting the transmissive part and the reflective part with a liquid crystal shutter, but in the case of using a liquid crystal shutter, the transmissive part is also reflected by the glass surface, and so on. It is not easy to make adjustments, and the reflection part is also inferior in reflection performance when controlled by a liquid crystal shutter. Therefore, adjustment using a shielding plate is preferable.

  The shielding plate can be made of any material, but the surface on the line camera side is mirrored to increase the illumination efficiency and suppress unnecessary incident light, and the opposite imaging target side absorbs the illumination wavelength. This is preferable because it suppresses unnecessary incident light that causes noise to the camera.

  The shielding plate is preferably composed of a tilting-side shielding plate extending in a direction in which an imaging angle of a line camera described later is inclined, that is, in a direction opposite to the imaging direction. This is because the line camera captures an image of the opening in the direction in which the imaging angle of the line camera in the opening is inclined, and the opposite direction is not an imaging target. In addition, the line camera has a linear imaging range due to its characteristics, and if an inclined tip side shielding plate is provided so that only the part necessary for imaging is opened, the opening becomes slit-like and efficient and uniform. Illumination is possible, and a desired image can be obtained.

  If the imaging angle is not constant and is changed, the imaging area changes, so it is desirable that the position of the shielding plate can be changed accordingly. The mechanism of the change is also manual movement, automatic movement, refit, etc. Various means are used.

  The line camera is appropriately selected from monochrome, color, specific color, ultraviolet light, and the like depending on the imaging target and application. Also, the gradation is appropriately selected from 256 gradations, a coarser image, a more precise image, etc. depending on the application.

The angle of the line camera may be fixed as long as the type of image to be captured and the image to be obtained is constant, but is preferably variable in consideration of quality fluctuations. The adjustment at this time may be automatic or manual. The angle can be selected freely as long as the optical axis of the line camera is within the range of the reflector of the dome illumination when it is regularly reflected on the object to be imaged. Although the range that can be obtained changes, it is theoretically possible from about 1 degree to 70 degrees, but about 3 degrees to about 5 degrees is generally safe and desirable.

  The object to be imaged is more preferably a structure on a flat plate, but may have another shape.

  The transport mechanism has a function of transporting in the direction orthogonal to the extension direction of the line camera, and the flow may be continuous or intermittent, and may be belt transport or other transport.

  Hereinafter, the optical system of the present invention will be described.

  FIG. 1 is a conceptual side cross-sectional view showing a state in which a shielding plate is not used. (A) shows the respective optical systems at the start of imaging, (B) at the middle of imaging, and (C) at the end of imaging. Show.

  The imaging target 20 flows to the optical system by the line camera 10 and the dome illumination 11 installed at an angle of 4 degrees with respect to the vertical direction of the imaging target.

  Since there is no light-shielding plate 1, the illumination light 33 from the front is reflected by the imaging object 20 to be reflected light 32 and returns into the dome at the start of imaging A. However, the illumination light 34 from behind is transmitted as it is because the imaging target 20 does not exist in the hit portion. At an intermediate time B, not only the illumination light 33 from the front but also the illumination light 34 from the rear is reflected by the imaging object 20 to become reflected light 35 and return into the dome. At the end of imaging C, the illumination light 34 from behind is reflected by the imaging target 20 and becomes reflected light 35, which returns to the inside of the dome. However, the illumination light 33 from the front is transmitted as it is because the imaging target 20 does not exist in the hit portion.

  That is, the amounts of light at the start of imaging (A), at the middle of imaging (B), and at the end of imaging (C) are different, and the captured images are different, and the purpose cannot be achieved.

  On the other hand, in the present application, since the light shielding plate 1 is present, as shown in FIG. 2, not only the illumination light from the front but also the illumination light from the rear at the start of imaging A, at the intermediate time B, or at the end of imaging C. Also, except for the imaging part, the light is reflected by the light shielding plate 1 and returned to the dome as reflected light.

  As described above, in order to acquire a uniform image, a uniform image can be acquired by partially blocking the irradiation port of the dome illumination.

  That is, when there is no light-shielding plate 1, the light from the front half is reflected on the product and returns into the dome when imaging the head and center. On the other hand, when the light shielding plate 1 is provided, the reflected light is prevented from entering the dome, and the back half of the light is reflected by the light shielding plate 1 to return to the inside of the dome, thereby concentrating near the visual field of the camera. Can be irradiated.

  In particular, the problem that the presence or absence of the light shielding plate 1 near the end of imaging (C) of the imaging target affects the imaging result is substantially eliminated.

  As described above, it is advantageous in terms of an increase in the amount of light if the light shielding plate can be selected so that the illumination inner surface has a high reflectance. Further, if the outer surface on the imaging target side has a low reflectance, the influence of reflection from the product can be suppressed.

  An embodiment capable of obtaining a contrast between a glossy surface such as metal and a non-glossy surface such as resin will be described.

  In order to obtain a contrast between the glossy surface and the non-glossy surface, attention is paid to how each surface reflects light from the illumination.

  As shown in FIG. 3 (A), the light incident on the line camera is due to regular reflection at the glossy portion, so that light from a specific angle is strongly reflected, and light from other angles is reflected in luminance. Does not affect much.

  On the other hand, as shown in FIG. 3B, since the resin surface is due to irregular reflection, it is considered that light incident from various angles affects the luminance of the resin surface.

  As shown in FIG. 3C, if the light beam is incident only from the angle at which the regular reflection is performed on the line camera, the reflection due to the regular reflection is relatively bright on the plating surface, and the resin surface is attenuated by the irregular reflection. It will be relatively dark and the most contrast can be obtained.

  However, the beam light causes a problem in terms of uniform imaging as described above.

  Therefore, as shown in FIG. 4, a light shielding plate 2 for limiting the irradiation angle is added to limit the direction in which the light is incident, and irradiation is performed from a certain range of angles.

  The light shielding plate 2 can darken the non-glossy surface while maintaining the luminance of the glossy surface, and can extract the contrast.

  The light shielding plate 1 and the light shielding plate 2 can be used simultaneously. The mounting position differs depending on the installation angle of the camera, the object to be imaged, and the position of illumination. FIG. 5 shows the mounting position.

  In this way, since the slit having only the imaging width of the line camera cannot receive the reflected light of the light reflected from the incident light, the incident from the opposite direction of the imaging angle (π−θ) as shown in FIG. It is necessary to provide a slit having a width that allows light of an angle (π−θ) to enter.

  By using the optical system according to the present invention, for example, various imaging objects such as an imaging object in which a glossy material having an uneven surface and a resin are mixed can be uniformly imaged under various conditions such as high contrast. As a result, it is possible to provide a machine vision with a higher degree of accuracy than before.

1 ... Shading plate (tilting side shading plate)
2 ... Shading plate (tilt side shading plate)
DESCRIPTION OF SYMBOLS 10 ... Line camera 11 ... Dome type illumination 20 ... Imaging object 31 ... Imaging light 32, 35 ... Reflected light 33, 34 ... Illumination light

Claims (8)

  A dome-shaped illumination means, a line camera, and a transport mechanism for transporting the imaging target in a direction orthogonal to the extension direction of the line camera, and the line camera has an imaging angle inclination from the vertical direction with respect to the imaging target An image pickup apparatus having an opening amount adjusting means at an opening of the dome-shaped illumination means.   The imaging apparatus according to claim 1, wherein the opening amount adjusting means is a shielding plate.   The imaging apparatus according to claim 2, wherein the line camera side surface of the shielding plate is a mirror surface and absorbs the illumination wavelength irradiated by the imaging target side surface.   The imaging apparatus according to claim 2, wherein the shielding plate is a tilting-side shielding plate extending from a direction opposite to a direction in which an imaging angle of the line camera is tilted.   The imaging apparatus according to claim 4, wherein the shielding plate is an inclined tip-side shielding plate extending from a direction in which an imaging angle of the line camera is inclined in addition to the tilting-source shielding plate.   The imaging apparatus according to claim 2, wherein the shielding plate is movable.   The imaging apparatus according to any one of claims 1 to 6, wherein the imaging angle is within 10 degrees and is not completely 0 degrees.   The imaging apparatus according to claim 1, wherein an opening amount of the opening portion of the dome-shaped illumination unit is adjusted, and an imaging target conveyed in a direction orthogonal to the extending direction of the line camera is imaged. Imaging method.

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