JP2022111555A - Photographing device and structure inspection system - Google Patents

Abstract

To install a lighting at the lowest possible position and reduce the necessary illuminance, as well as secure a photographing range.SOLUTION: Provided is a photographing device mounted to a moving body, the moving body moving in parallel to the surface of a structure while performing inspection. The photographing device comprises: a lighting unit arranged behind the moving body, for irradiating the surface of the structure with light extending in a line direction that crosses the direction of movement and equipped with a linear irradiation light source arranged in plurality along the line direction; and at least three or more line cameras arranged in plurality along the line direction for photographing the structure. Each of a pair of line cameras on at least the outermost side in the line direction among the line cameras is arranged facing the outside, with the line cameras being arranged such that the light receiving face of the imaging element of a line camera, the principal plane of optical system of the line camera and the surface of the structure satisfy the Scheimpflug condition.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to imaging devices.

In order to inspect the road surface for cracks, etc., a photographing device such as a camera is installed in a vehicle such as an automobile, and the road surface is photographed while the vehicle is running. ing.

For example, Patent Literature 1 discloses an apparatus for inspecting road surface properties by using an imaging device mounted on a vehicle and photographing the vehicle with the imaging device pointing directly downward from the vehicle.

Japanese Unexamined Patent Application Publication No. 2017-181396

By the way, lighting is also necessary to capture an image of the road surface. The lighting and camera are installed at approximately the same height. If the camera is installed at a high position in order to widen the shooting range as much as possible, the distance from the road surface to the lighting will increase, and the illuminance required for shooting will also increase. On the other hand, if the camera is installed at a lower position, that is, at a lower position, the shooting range will be narrowed.

In view of the above, an object of the present disclosure is to provide an imaging device and a structure inspection system that can reduce the necessary illuminance by installing illumination at a position as low as possible and also ensure an imaging range.

An imaging apparatus according to an embodiment of the present disclosure is an imaging apparatus that is mounted on a moving body and that inspects the surface of a structure while the moving body is moving parallel to the surface of the structure. A lighting unit equipped with a plurality of linear irradiation light sources arranged along the line direction for irradiating the surface of the object with light extending in a line direction that intersects with the movement direction, and a line direction for photographing the structure. and at least three or more line cameras arranged in plurality along the line, wherein at least a pair of the line cameras that are the outermost in the line direction of the line cameras are each arranged facing outward, and the imaging elements of the line cameras The line camera is arranged such that the light-receiving surface, the main surface of the optical system of the line camera, and the surface of the structure satisfy the Scheimpflug condition.

Further, the structure inspection system according to the embodiment of the present disclosure includes a moving body, and an imaging device mounted behind the moving body for performing inspection while the moving body moves parallel to the surface of the structure. an illumination unit including a plurality of linear illumination light sources arranged along the line direction for illuminating the surface of the structure with light extending in a line direction that intersects with the moving direction; and photographing the structure. and at least three or more line cameras arranged in plurality along the line direction, wherein each of at least a pair of the line cameras located on the outermost side in the line direction among the line cameras faces outward. The line camera is arranged such that the light receiving surface of the imaging device of the line camera, the main surface of the optical system of the line camera, and the surface of the structure satisfy the Scheimpflug condition.

Advantageous Effects of Invention According to the present disclosure, it is possible to provide an imaging device and a structure inspection system that can reduce the required illuminance by installing illumination at a position as low as possible and also ensure an imaging range.

1 is a diagram showing the configuration of an imaging device according to an embodiment of the present disclosure and a structure inspection system using the same; FIG. It is a figure for demonstrating the conditions of Scheimpflug. It is a figure for demonstrating an illumination part. FIG. 4 is a diagram for explaining the relationship between the optical axes of the imaging optical system and the illumination optical system; It is a figure for demonstrating an example of an illumination optical system. It is a figure which shows the simulation result of the required illuminance in an Example, and the irradiance in an irradiation surface.

A structure inspection system according to an embodiment of the present disclosure will be described below with reference to the drawings. FIG. 1 is a diagram showing an overview of an imaging device according to an embodiment of the present disclosure and a structure inspection system using this imaging device.

A structure inspection system 1 includes an imaging device 100 , a mobile body 200 and an analysis device 300 . An imaging device 100 for inspecting a structure is mounted on a moving body 200. While the moving body 200 moves parallel to the surface MS of the structure, the imaging device 100 captures an image of the surface MS of the structure. The surface of the structure is inspected by acquiring an image and analyzing the acquired image by the analysis device 300 .

The mobile object 200 is, for example, a vehicle or an aircraft. Vehicles are not limited to vehicles such as automobiles driven by people, but also include unmanned vehicles that are automatically driven. The flying object includes a remotely controlled flying object such as an unmanned aerial vehicle or an flying object that autonomously flies along a predetermined route and can keep a constant distance from a structure. Therefore, parallel movement is not limited to strictly parallel movement, but includes movement while maintaining a substantially constant distance.

More specifically, the photographing apparatus 100 uses a line camera or a line sensor as a camera. Here, the image is obtained by scanning the line camera with the movement of the moving body 200, so the term "line camera" is unified. That is, the moving direction of the moving body becomes the scanning direction. Note that an area sensor camera may be used as the camera of the image capturing apparatus 100 as long as images captured while scanning can be integrated by image processing.

The line camera includes a light receiving element 110 having pixels arranged in one direction, and an imaging optical system 120 composed of optical elements such as a plurality of lenses. The light receiving element 110 is, for example, an imaging element such as a CCD or CMOS.

The structure is, for example, the road surface of a road, the wall surface of a building, or the like, and the surface is guaranteed to have a certain degree of flatness. The target surface is asphalt as a general road or expressway, and does not have to be completely flat. Therefore, for example, when the road surface is to be inspected, the photographing is performed while the vehicle is running or the aircraft is flying. When a wall is the target, it is also possible to shoot with a moving object or flying object that moves along the wall.

The analysis device 300 is, for example, a computer such as a PC, and includes an analysis device storage section 390 and an analysis section 350 . The analysis device storage unit 390 transfers images transmitted and received from the imaging device 100 or images stored in the imaging device storage unit 190 of the imaging device 100 to the analysis device storage unit 390 via a predetermined storage medium. memorize the image. The analysis unit 350 has a function of reading and analyzing images stored in the analysis device storage unit 390 . More specifically, cracks and the like on the surface of structures such as road surfaces are detected by image analysis.

Furthermore, the analysis device 300 may include an image correction section 360 that corrects the read image. As will be described later, if the captured image is distorted on the outside in the line direction, image processing can be performed to correct the distortion.

In such a structure inspection system 1, if the photographing device 100 is installed above the moving body 200, that is, at a high position in order to widen the photographing range as much as possible, the distance from the illumination to the road surface becomes large. As a result, the illuminance required for photographing also increases. On the other hand, if the photographing device 100 is installed at a lower position, that is, at a lower position, the photographing range will be narrowed.

Unnecessarily increasing the amount of light for illumination results in the adoption of an expensive light source, which is not only uneconomical, but also poses a problem of light safety on general roads and highways.

Also, if the camera is placed obliquely with respect to the road surface in an attempt to widen the shooting range from the state in which the shooting surface is oriented perpendicularly to the road surface, there will be parts that are in focus and parts that are out of focus within the shooting range. There will be places where the focus shifts.

Therefore, in the imaging device 100 according to the embodiment of the present disclosure, the light receiving surface 110S of the light receiving element 110, the main surface 120S of the imaging optical system 120, and the surface MS of the structure to be inspected are Scheimpflug By arranging so as to satisfy the condition of (1), it is possible to shoot an image in focus while widening the shooting range.

In order to satisfy the above requirements, the imaging device 100 according to the embodiment of the present disclosure has a function of adjusting the angle of the light receiving surface 110S of the light receiving element 110 or the main surface 120S of the imaging optical system. More specifically, for example, a lens tilting mechanism is provided that realizes a tilting function of the principal surface of the lens that constitutes the principal surface 120S of the optical system.

FIG. 2 is a diagram for explaining the Scheimpflug conditions. This figure shows the positional relationship between the light receiving element 110 of one of the line cameras arranged outside in the line direction in a cross section perpendicular to the moving direction, the imaging optical system 120 of the light receiving element 110, and the surface MS of the structure. ing. The Scheimpflug principle states that when the light-receiving surface 110S of the light-receiving element 110, the main surface 120S of the optical system, and the surface MS of the structure to be inspected intersect on the same straight line C, the object is in focus. The plane (the surface MS of the structure) also intersects on the same straight line C. Therefore, the condition based on the Scheimpflug principle is that the light receiving surface 110S of the light receiving element 110, the main surface 120S of the optical system, and the surface MS of the structure should intersect on the same straight line C. This makes it possible to focus on a wide shooting range.

The photographing device 100 arranged to satisfy the Scheimpflug condition in this way is the outermost line camera 100R, 100L among the plurality of line cameras 100R, 100C, 100L arranged in a row along the line direction. is. Each of the line cameras 100R and 100L is arranged obliquely outward so that its orientation satisfies the Scheimpflug condition between vertical and horizontal with respect to the road surface.

In addition, since the outermost line cameras 100R and 100L are arranged on the outer side as described above, the photographing area in the middle, that is, the middle portion is missing. Therefore, it is preferable to arrange at least one line camera 100C inside the pair of outer line cameras as well. The arrangement angle can be appropriately set, and for example, it can be arranged perpendicular to the road surface. As a result, even if the at least three line cameras 100R, 100C, and 100L are placed at a low position, it is possible to photograph a wide range in a focused state.

In this way, since the line cameras are arranged so as to satisfy the Scheimpflug condition, the image on the outside in the line direction is distorted. In order to correct this, a calibration unit 160 may be provided that corrects the distortion of the acquired image by adjusting the internal parameters of the camera. The calibration unit 160 has a function of correcting the photographed image using the internal parameters of the camera. The internal parameters of such a camera are obtained based on a plurality of photographed images obtained by photographing each reference point of a reference object whose relative positional relationship is known from different positions. For example, a camera calibration method described in Japanese Patent No. 3696336 can be used.

In such an imaging apparatus 100, an illumination unit 150 that emits light extending in the line direction is provided to illuminate the imaging range. FIG. 3 is a diagram for explaining the lighting unit 150. As shown in FIG. The illumination unit 150 has, for example, a plurality of linear illumination light sources 150LA, 150LB, . . . 150LF, 150RA, 150RB, . The number of arranged linear irradiation light sources is not limited to the number shown in this figure.

Each linear irradiation light source divides light emitted from a solid-state light source such as an LED (light-emitting diode) or an LD (laser diode) into a plurality of optical paths, such as optical fibers, and propagates through the optical paths to finally A linear light source shaped by an illumination optical system is output on the output side. When an LD is used as the light source, speckles may occur in the image due to coherence, so a mode scrambler may be provided in the optical path to reduce coherence.

The wavelength of light emitted from the light source is, for example, 940 nm. Such light has a wavelength that is absorbed by water vapor, which reduces the influence of sunlight such as shadows of roadside trees, and provides stable performance regardless of day or night. Therefore, the light source preferably contains light with a wavelength of 940 nm.

The illumination optical system of each linear light source may be composed of a lens unit composed of, for example, a combination of a collimator lens provided on the output side of the fiber and a cylinder lens (cylindrical lens). In such a lens unit, light emitted from a fiber is collimated by a collimator lens, and then a cylinder lens (for example, a so-called semi-cylindrical lens having a substantially circular entrance surface and a flat exit surface) is used to form a linear beam. It can be shaped into light. By using such a lens unit, a plurality of linear irradiation light sources demultiplexed from the fiber can be arranged as desired.

By arranging a plurality of such linear irradiation light sources along the line direction so that the linear direction in which the light is irradiated and the line direction are combined, irradiation is performed from each linear irradiation light source in the line direction. The light is superimposed and irradiated to appropriately illuminate the shooting range of the line camera. Although the arrangement of the linear irradiation light sources is arbitrary, for example, they can be arranged symmetrically in the line direction from the center of the moving body 200 or the photographing device 100 as shown in FIG.

Moreover, it is preferable that the arrangement intervals of the plurality of linear irradiation light sources become smaller toward the outside in the line direction. Since the intensity of light is inversely proportional to the square of the distance according to the inverse square law, it is necessary to increase the illuminance on the irradiated surface toward the outside in the line direction in order to make the brightness in the photographed image more uniform. . In particular, in the embodiment of the present disclosure, since both outer line cameras are tilted outward so as to satisfy the Scheimpflug condition, more illuminance is emitted to the outer side than when all the line cameras are arranged vertically. is necessary. For this reason, it is preferable that the arrangement intervals of the plurality of linear irradiation light sources become smaller toward the outside in the line direction and that they are arranged more densely. By doing so, it is possible to equalize the illuminance, which is insufficient on the outside in the line direction and decreases on the light receiving surface, as will be described later.

Further, it is preferable to arrange the linear irradiation light source so as to be positioned between the line cameras in the line direction. Thereby, a desired illuminance distribution can be realized.

Alternatively, the output of the linear irradiation light source arranged on the outer side may be increased so that the illuminance distribution on the irradiated surface is larger on the outer side. A desired illuminance distribution can be achieved.

Moreover, it is preferable that the optical axis of the illumination optical system and the optical axis of the imaging optical system have different angles with respect to the surface of the structure. FIG. 4 is a diagram for explaining the relationship between the optical axes of the imaging optical system and the illumination optical system. shows the optical axis of In this figure, the optical axis of the imaging optical system by the line camera 100L is oriented perpendicularly to the surface MS of the structure (with respect to the line direction, both outer line cameras satisfy the Scheimpflug condition). . On the other hand, the optical axis of the illumination optical system of the illumination unit 150 is incident at an angle different from this angle, for example, an angle inclined by 5 to 20 degrees from this vertical direction. It should be noted that the drawings are drawn for the sake of clarity, and do not necessarily have the above angular relationship. Since the illumination system and the photographing system are not placed on the same plane, cracks in the road are obliquely illuminated, and shadows are likely to occur. This makes it easier to obtain the contrast between the road surface and cracks.

An example of the structure inspection system according to the embodiment of the present disclosure described above will be shown. The photographing device 100 can be attached to the rear of a moving body 200, which is, for example, an ordinary automobile, using a predetermined attachment jig or the like. In this case, it is preferable that the height is 0.8 m or less from the road surface, for example, the height is 0.7 m. In addition, for example, three line cameras, ie, line cameras 100R, 100C, and 100L, can be installed as the photographing device. , and the middle line camera 100C is arranged in a direction perpendicular to the road surface. Also, the distance from the line camera 100R to the line camera 100L is, for example, 1.4 m in the line direction. According to such arrangement, it is possible to secure a photographing range of, for example, 3.8 m in the direction of the line, to photograph one lane, and to confirm the road surface properties of general roads and highways. .

Also, the illumination unit 150 is arranged obliquely so that the illumination system and the imaging system are not placed on the same plane, for example, arranged at an angle of 5 to 20 degrees from the vertical direction. For each linear irradiation light source, for example, 9 linear irradiation light sources on one side and 18 linear irradiation light sources on both sides may be arranged. Note that the number of line cameras and the number of linear irradiation light sources can be appropriately determined according to the required illuminance and imaging range, and are not limited to this example.

FIG. 6 shows simulation results of required illuminance and irradiance on the irradiation surface in such an example. In this figure, the horizontal axis represents the position (mm) in the line direction, the vertical axis represents the illuminance (W/mm ² ), and the solid curve indicates the required illuminance on the irradiation surface. Also plotted by dots is the irradiance based on the simulation results. According to this figure, it can be seen that the irradiance exceeds the required illuminance in all areas in the line direction, and the necessary light is supplied to the irradiation surface.

As described above, the imaging device and the structure inspection system according to the embodiments of the present disclosure are an imaging device mounted on a moving body for performing inspection while the moving body moves parallel to the surface of the structure. an illumination unit that is arranged behind the body and has a plurality of linear illumination light sources that are arranged along the line direction to irradiate the surface of the structure with light that extends in a line direction that intersects with the moving direction; and at least three or more line cameras arranged in a plurality along the line direction for photographing, wherein at least a pair of the line cameras that are the outermost in the line direction are each arranged facing outward. By arranging the line camera so that the light receiving surface of the image sensor of the line camera, the main surface of the optical system of the line camera, and the surface of the structure satisfy the Scheimpflug condition, the illumination is kept as low as possible. It can be installed at any position to reduce the required illuminance and secure the shooting range.

In addition, the difference in the angle of the optical axis of the optical system of the line camera with respect to the structure and the angle of the optical axis of the lighting unit with respect to the surface of the structure in the cross section orthogonal to the surface and line direction of the structure causes cracks in the road. is obliquely illuminated, making it easier to create shadows, making it easier to obtain contrast between the road surface and cracks.

In addition, the moving body is a vehicle, and the illumination unit and the line camera are installed at a distance of 0.8 m or less from the surface of the structure, so that the required amount of illumination light can be reduced.

In addition, since the arrangement intervals of the plurality of linear irradiation light sources become smaller toward the outside in the line direction, it is possible to equalize the illuminance that is insufficient on the outside in the line direction and decreases on the light-receiving surface.

The illumination optical system of the illumination unit includes a collimating lens arranged on the output side of the fiber light source and a lens unit consisting of a cylinder lens, so that the multiple linear illumination light sources separated from the fiber can be arranged in a desired arrangement. can do.

Further, by providing a calibration unit for correcting an image captured by the line camera, it is possible to correct an image captured with the outer side distorted due to arrangement under Scheimpflug conditions.

This completes the description of the embodiments of the present disclosure, but the aspects of the present disclosure are not limited to these embodiments.

1 Structure Inspection System 100 Imaging Device 110 Light Receiving Element 110S Light Receiving Surface 120 Imaging Optical System 120S Principal Surface 121 Collimating Lens 122 Cylinder Lens 150 Illumination Section 150LF Linear Irradiation Light Source 160 Calibration Section 190 Imaging Device Storage Section 200 Moving Body 300 Analysis Device 350 analysis unit 360 image correction unit 390 analysis device storage unit C straight line MS surface

Claims (7)

An imaging device mounted on a moving body for performing inspection while the moving body moves parallel to the surface of a structure,
arranged behind the moving body,
an illumination unit including a plurality of linear illumination light sources arranged along the line direction for illuminating the surface of the structure with light extending in a line direction that intersects with the moving direction;
At least three or more line cameras arranged along the line direction for photographing the structure,
At least a pair of the line cameras that are the outermost in the line direction of the line cameras are each arranged facing outward, and the light-receiving surface of the imaging device of the line camera, the main surface of the optical system of the line camera, The photographing device, wherein the line camera is arranged so that the surface of the structure satisfies the Scheimpflug condition. In a cross section perpendicular to the surface of the structure and the line direction, the angle of the optical axis of the optical system of the line camera with respect to the structure and the angle of the optical axis of the illumination unit with respect to the surface of the structure are different. The photographing device according to claim 1 . 3. The photographing device according to claim 1, wherein said moving body is a vehicle, and said lighting unit and said line camera are installed at a location where the distance from the surface of said structure is 0.8 m or less. 4. The photographing device according to claim 1, wherein the arrangement intervals of the plurality of linear irradiation light sources become smaller toward the outside in the line direction. 5. The photographing apparatus according to claim 1, wherein the illumination optical system of said illumination section includes a lens unit comprising a collimating lens arranged on the exit side of the fiber light source and a cylinder lens. The imaging device according to any one of claims 1 to 5, further comprising a calibration section that corrects an image captured by the line camera. A structure inspection system,
a mobile object;
an imaging device mounted behind a moving object for inspecting the structure while the moving object moves parallel to the surface of the structure;
an illumination unit including a plurality of linear illumination light sources arranged along the line direction for illuminating the surface of the structure with light extending in a line direction that intersects with the moving direction;
At least three or more line cameras arranged along the line direction for photographing the structure,
At least a pair of the line cameras that are the outermost in the line direction of the line cameras are each arranged facing outward, and the light-receiving surface of the imaging device of the line camera, the main surface of the optical system of the line camera, A structure inspection system, wherein the line camera is arranged such that the surface of the structure satisfies Scheimpflug conditions.

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