JP2014009997A - Range finding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately measure a distance to an object or a shape by preventing reduction of measurement accuracy caused by the distance to the object.SOLUTION: A range finding device includes a semiconductor laser 21 for emitting illumination light, a diffraction optical element 22 for applying diffractive pattern light generated by diffracting the illumination light to an object 41, a plurality of imaging lenses 12 for forming an image of the diffractive pattern light reflected by the object, a plurality of image pickup devices 13 for capturing a plurality of images of the object based on the diffractive pattern light image-formed by the imaging lenses, range finding means 31 for calculating a distance from the object from parallax information among the plurality of images, and irradiation control means 32 for controlling the diffractive pattern light according to the distance information obtained from the range finding means.

Description

  The present invention relates to a distance measuring device including a pattern illumination device that projects pattern light onto an object, and in particular, the distance measuring accuracy is improved by controlling the pattern light to be projected according to the distance measuring conditions. The present invention relates to a distance measuring device.

  Conventionally, a “stereo ranging” technique is known in which an object is photographed by two cameras and distance information to the object is obtained using the two obtained images. In stereo ranging, the depth distance is calculated based on the principle of triangulation using the parallax generated between two captured images. In order to obtain parallax in stereo ranging, it is necessary to perform window matching to find corresponding points (corresponding points) in each image.

FIG. 15 and FIG. 16 are diagrams for explaining the principle of the distance measuring method using the principle of triangulation used in “stereo distance measurement”. In stereo ranging, two cameras are configured by combining a pair of two-dimensional sensors and a pair of lenses, and the distance (parallax) of an object is detected to determine the distance based on the principle of triangulation. measure.
Consider a case in which two cameras 102 a and 102 b having the same optical system are arranged in the stereo camera device 106 shown in FIG. 15 and the light from the object 101 is photographed by each camera 102.
Each camera 102 (102a, 102b) includes a lens 103 (103a, 103b) on which an optical image of the object 101 is incident and an optical image (object image 104: 104a, 104b) of the object 101 incident on each lens 103. Two-dimensional sensor 105 (105a, 105b).
The object image 104a obtained through the lens 103a of the camera 102a and the object image 104b obtained through the lens 103b of the camera 102b are shifted from each other by the parallax Δ between the same points on the object 101 and two-dimensional sensors 105a and 105b (FIG. 16), the light is received by a plurality of light receiving elements (pixels) and converted into electrical signals.

Here, the distance between the optical axes of the lenses 103a and 103b is called a baseline length. When the base line length is D, the distance between the lens 103 and the object 101 is A, and the focal length of the lens 103 is f, the following equation holds when A >> f.
A = Df / Δ Expression (1)
As shown in FIG. 15, since the baseline length D and the focal length f of the lens are known, the distance A to the object 101 can be calculated from the equation (1) by detecting the parallax Δ.

By the way, the window matching is a method of finding the corresponding point 104c of the object image 104a based on the distribution characteristic of the luminance value of the pixel. Therefore, for example, when the target object 101 is an object having a single color surface, the luminance distribution on the surface of the target object 101 is uniform, and it is difficult to change the luminance value in the captured image. Since it becomes difficult to find the point 104c, there is a problem that an accurate distance cannot be calculated.
On the other hand, Patent Document 1 discloses a technique for solving the above-described problem by irradiating a predetermined pattern on an object whose luminance value is unlikely to change in a photographed image and applying a pattern to the surface of the object. It is disclosed. Specifically, this document discloses an imaging apparatus including an AF (autofocus) auxiliary light emitting unit using laser light and a hologram. A pattern is given to the surface of the object by irradiating the object with laser light having a predetermined pattern diffracted by the hologram plate.

By the way, in order to detect corresponding points with high accuracy in window matching, it is necessary that an appropriate luminance value distribution exists in the object portion of the acquired image.
In Patent Document 1, the pattern switching unit switches the hologram in accordance with the shooting angle of view or AF area of the shooting optical system, thereby irradiating the entire range necessary for distance measurement. However, when the same pattern is irradiated to objects with different distances from the imaging device, due to the nature of the light, the luminance value distribution in the object portion of the acquired image is different between the objects close to and far from the imaging device. There will be a difference. As a result, there is a problem that a large difference in measurement accuracy occurs depending on the distance to the object.
The present invention has been made in view of the above-described circumstances, and aims to prevent a decrease in measurement accuracy due to the distance to the object and to measure the distance and shape to the object with high accuracy. .

  In order to solve the above-described problem, a distance measuring device according to claim 1 includes: a light source that emits illumination light; and a diffractive optical element that irradiates an object with diffraction pattern light generated by diffracting the illumination light. A plurality of imaging lenses that image the diffraction pattern light reflected by the object, and a plurality of images that capture a plurality of images related to the object based on the diffraction pattern light imaged by the imaging lenses. Imaging means; distance measuring means for calculating a distance from the object based on parallax information between the plurality of images; and pattern control for controlling the diffraction pattern light according to distance information obtained from the distance measuring means And means.

  According to the present invention, since the pattern light to be irradiated is controlled according to the distance to the object, an image having an appropriate luminance value distribution according to the distance to the object can be obtained. Accordingly, it is possible to prevent a decrease in measurement accuracy due to the distance to the object and to measure the distance and shape to the object with high accuracy.

It is the schematic diagram which showed the distance measuring device which concerns on 1st embodiment of this invention. It is a block diagram of the ranging apparatus shown in FIG. It is the figure shown about the pattern light irradiated from a laser irradiation apparatus, and the image imaged with a stereo camera. (A)-(c) is a figure which shows the ranging example in the case of not performing pattern illumination. (A)-(c) is a figure which shows the ranging example at the time of performing pattern illumination. It is the schematic diagram which showed the example which changes the irradiation angle of view of pattern light according to the distance to a target object. It is a block diagram of a wavelength variable laser. (A)-(c) is an example of pattern light with a narrow irradiation angle of view, (d)-(f) is a figure which shows the example of pattern light with a wide irradiation angle of view. It is the schematic diagram which showed an example of the laser irradiation apparatus. (A), (b) is a figure explaining operation | movement when the ranging apparatus which concerns on 1st embodiment of this invention is attached to a robot arm. (C), (d) is a figure explaining operation | movement when the ranging apparatus which concerns on 1st embodiment of this invention is attached to a robot arm. (A)-(c) is an example of pattern light with a low density, (d)-(f) is a figure which shows the example of pattern light with a high density. It is a figure which shows the laser irradiation apparatus which concerns on 3rd embodiment. (A), (b) is a schematic diagram which shows an example of a polarization rotation element. It is a figure explaining the principle of the ranging method using the principle of triangulation. It is a figure explaining the principle of the ranging method using the principle of triangulation.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
<First embodiment>
A distance measuring apparatus according to a first embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing a distance measuring apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram of the distance measuring apparatus shown in FIG. The distance measuring device according to the present embodiment is a device that measures the distance to an object by “stereo ranging” using the principle of triangulation shown in FIGS. 15 and 16. The distance measuring apparatus according to the present embodiment is characterized in that the pattern light applied to the object is controlled according to the distance information obtained from the distance measuring means.

As shown in FIGS. 1 and 2, the distance measuring device 1 includes a stereo camera 10 that captures two object images with parallax and a laser irradiation apparatus that irradiates the object 41 with a predetermined pattern light. 20, and a control unit 30 having a distance measuring unit 31 that calculates a distance from a parallax image captured by the stereo camera 10 to an object and an irradiation control unit 32 that controls the laser irradiation apparatus 20.
The laser irradiation device 20 includes a semiconductor laser 21 (light source) that emits illumination light, and a diffractive optical element 22 that irradiates an object 41 with pattern light (diffraction pattern light) generated by diffracting the illumination light. Yes. The stereo camera 10 includes a plurality of monocular cameras 11 (11a and 11b), and each camera 11 forms a plurality of imaging lenses 12 (images of the pattern light reflected by the object 41). 12a, 12b) and a plurality of image pickup devices 13 (13a, 13b: image pickup means) for picking up a plurality of images related to the object 41 based on the pattern light imaged by each image pickup lens 12. .
The distance measuring means 31 of the control unit 30 calculates the distance to the target object 41 based on the parallax information between the images captured by the image sensors 13. The irradiation control means 32 functions as a means for controlling on / off of the semiconductor laser 21 and also functions as a pattern control means for controlling pattern light according to the distance information obtained from the distance measuring means 31.

  Each camera 11 of the stereo camera 10 has a predetermined imaging angle of view α (see FIG. 3). In the distance measuring apparatus 1, the distance between the optical axes (base line length) of the imaging lenses 12a and 12b of the two cameras 11a and 11b is D, the distance between the imaging lens 12 and the object 41 is A, and the focal length of the imaging lens is f. When A >> f, “A = Df / Δ” (Δ: parallax) as shown in the above-described equation (1). Since the base length D and the focal length f of the imaging lens are known, the distance A to the target 41 can be calculated by detecting the parallax Δ of the target 41 reflected on each image sensor 13. Note that the image sensor 13 is a two-dimensional sensor such as a CCD or a CMOS.

  FIG. 3 is a diagram showing pattern light irradiated from the laser irradiation apparatus and an image captured by the stereo camera. As shown in the drawing, a laser beam (pattern light) of a predetermined pattern is irradiated from the laser irradiation device 20. The irradiation direction of the pattern light is adjusted to coincide with the direction of the stereo camera 10. The irradiation field angle β of the pattern light emitted from the laser irradiation device 20 is set to be approximately equal to the imaging field angle α of the stereo camera 10. Therefore, regardless of the distance to the object, the pattern light irradiation range 23 and the imaging range 14 of the stereo camera 10 are substantially the same, and the pattern light can be applied to substantially the entire imaging range 14 of the stereo camera 10.

Next, differences in distance measurement results depending on the presence / absence of pattern illumination will be described with reference to FIGS. FIG. 4 is a diagram illustrating an example of distance measurement when pattern illumination is not performed. FIG. 5 is a diagram illustrating an example of distance measurement when pattern illumination is performed.
In the following description, “the luminance distribution is uniform” or “the luminance value hardly changes” may be expressed as “no contrast” or “low contrast”.

First, the case where there is no pattern illumination will be described. As shown in FIG. 4A, consider a case where an object 41 (in this example, a rectangular parallelepiped) placed on a plane 40 is photographed with a stereo camera 10. The plane 40 and the object 41 are both objects having no contrast. In this case, an image captured by the stereo camera 10 is as shown in FIG.
The distance measuring means 31 obtains the parallax from two images taken by each camera 11 (see FIG. 2) of the stereo camera 10 and obtains the distance to the plane 40 and the object 41.
When the distance image is calculated based on the obtained distance, the result is as shown in FIG. In the distance image, the distance obtained by the distance measuring unit 31 is expressed on the image by, for example, a color difference. As shown in FIG. 4C, the distance is calculated only for the edge portion 41a of the object 41, and the distance is not calculated for the flat surface 40 without contrast and the upper surface portion 41b of the object 41 without contrast. This is because, based on the principle of a stereo camera, an object having no contrast hardly changes in luminance value in a captured image, and it is difficult to find a corresponding point (corresponding point) by performing window matching.

On the other hand, the case where there is pattern illumination will be described. As shown in FIG. 5A, when pattern light is irradiated to the object 41 placed on the plane 40, a predetermined pattern (pattern) is formed on the surface of the plane 40 and the object 41. In this case, the stereo camera 10 captures an image as shown in FIG.
The distance measuring means 31 obtains the parallax from two images taken by each camera 11 (see FIG. 2) of the stereo camera 10 and obtains the distance to the plane 40 and the object 41.
When the distance image is calculated based on the obtained distance, the result is as shown in FIG. As shown in FIG. 5C, not only the edge portion 41a of the object 41 but also the plane 40 and the upper surface portion 41b of the object 41 are calculated. This is because a pattern is irradiated onto an object with no contrast, which causes a change in the brightness value on the surface of the object, and it is now possible to find corresponding points (corresponding points) by performing window matching. is there.
By performing pattern illumination in this way, distances can be obtained even for objects without contrast, and the shape dimensions of the object can also be known from the angle of view of the camera and the size of the image formed on the image sensor. it can.

By the way, depending on the distance between the stereo camera and the object, the following problems occur. Hereinafter, a description will be given with reference to FIG.
First, there is a problem that the light intensity per unit area of the irradiation pattern becomes weaker as the object 41 is farther from the stereo camera 10. The irradiation area of the light emitted from the laser irradiation device 20 increases as the distance increases. However, since the output of the laser mounted on the laser irradiation device 20 is constant, the light intensity per unit area becomes weaker as the distance increases. When the light intensity becomes weak, the contrast becomes small, so that an error is likely to occur when searching for corresponding points by performing window matching, and accurate distance measurement cannot be performed.
Second, there is a problem that the object image formed on the image sensor 13 becomes smaller as the object 41 is farther from the stereo camera 10. As shown in FIG. 3, when the target object 41 is close to the stereo camera 10, the area of the target object 41 occupying the imaging range 14 is large, so that the target object 41 is greatly projected on the screen. Conversely, when the object is located far from the stereo camera 10, the area of the object 41 occupying the imaging range 14 becomes small, and the object 41 appears only small on the screen. On the other hand, the pattern (for example, dot) of the pattern light is small on the surface of the target object 41 when the target object 41 is at a position close to the laser irradiation apparatus 20, and the target object 41 is at a position far from the laser irradiation apparatus 20. In some cases, it becomes larger on the surface of the object 41. Therefore, for example, if the pattern of the pattern light is a dot, the number of pattern light dots applied to the object 41 decreases as the object 41 is further away from the laser irradiation apparatus 20, and an accurate distance and shape are measured. The problem that it becomes impossible.
The above-mentioned problem is particularly noticeable when the distance and direction to the object change every moment because the distance measuring device is attached to a movable part such as a robot arm or a self-running robot. In order to solve this problem, in the present embodiment, the pattern irradiated from the laser irradiation apparatus is switched according to the distance to the object.

FIG. 6 is a schematic diagram illustrating an example of changing the irradiation angle of view of the pattern light according to the distance to the object.
As shown in FIG. 6, when the object 41 is at a distance A <b> 1 close to the stereo camera 10, the image of the object 41 imaged on the image sensor 13 is large. Therefore, when the distance measuring means 31 (see FIG. 2) recognizes that the object 41 is nearby, the angle of view of the pattern light emitted from the laser irradiation apparatus 20 is increased (irradiation angle of view β). The pattern light is irradiated to the entire object 41 and its peripheral part.
That is, first, the object 41 is imaged by the stereo camera 10, and the distance measuring unit 31 calculates the distance to the object 41 based on the parallax images of the two cameras 11. When the distance calculated by the distance measuring unit 31 is smaller than a predetermined distance (threshold value), the irradiation control unit 32 increases the field angle of the pattern light emitted from the laser irradiation device 20 (irradiation). The laser irradiation apparatus 20 is controlled so that the angle of view becomes β. Then, the pattern light is irradiated to the entire object 41 and its peripheral portion (irradiation range 23β).

On the other hand, when the object 41 is at a distance A2 far from the stereo camera 10, the image of the object 41 imaged on the image sensor 13 is small. Therefore, when the distance measuring unit 31 recognizes that the object 41 is far away, the angle of view of the pattern light emitted from the laser irradiation device 20 is reduced (irradiation angle of view γ).
That is, first, the object 41 is imaged by the stereo camera 10, and the distance measuring unit 31 calculates the distance to the object based on the parallax images of the two cameras 11. When the distance calculated by the distance measuring unit 31 is larger than a predetermined distance (threshold), the irradiation control unit 32 reduces the field angle of the pattern light emitted from the laser irradiation device 20 (irradiation). The laser irradiation apparatus 20 is controlled so that the angle of view becomes γ. Then, the entire target object 41 and its peripheral part (irradiation range 23γ) are irradiated with the pattern light. Even if the irradiation angle of view is reduced here, the distance to the target object 41 is far away, so that the pattern light is irradiated to the entire target object 41 and its peripheral part.

Here, an example of a pattern light switching method will be described.
The output field angle θ of the pattern light from the diffractive optical element 22 is “θ = Arcsin (λ / d)” where λ is the wavelength of the illumination light emitted from the semiconductor laser 21 and d is the periodic structure of the diffractive optical element 22. Given in For example, when the wavelength λ = 0.65 μm and the periodic structure d = 1.0 μm, the emission angle is about 40 °. In order to increase the outgoing angle of view θ, the wavelength λ of the illumination light may be increased or the periodic structure d may be miniaturized.
As a method for changing the wavelength λ of the illumination light, it is conceivable to use a wavelength tunable laser for the semiconductor laser. FIG. 7 is a configuration diagram of a wavelength tunable laser. In the wavelength tunable laser 21A, a laser medium 51 and a modulation medium 52 having an electro-optic effect are disposed between two reflecting mirrors 53 constituting a laser resonator. As the modulation medium 52, LiNbO ₃ , LiTaO _3, or the like can be used. By applying an electric field from the voltage source 54 to the modulation medium 52, the refractive index of the modulation medium 52 changes. Then, since the laser cavity length changes, the oscillation frequency changes. Therefore, the outgoing angle of view θ can be changed.

FIG. 8 is a diagram showing the relationship between the angle of view of the pattern light and the obtained distance image. 8A to 8C are examples of pattern light having a narrow irradiation angle of view, and FIGS. 8D to 8F are examples of pattern light having a wide irradiation angle of view. The photographed image, the angle of view of the irradiation pattern, and the obtained distance image are shown. As shown in the figure, in FIGS. 8A to 8C, the field angle to be irradiated is narrower than that in FIGS. 8D to 8F, but at the same time the pattern density is increased. It turns out that a more accurate distance and shape can be obtained.
In this way, by switching the pattern light emitted from the laser irradiation device 20, even when the object is far away, the power of the laser irradiation device 20 can be used effectively, sufficiently bright against the object, and High contrast pattern light can be irradiated. Accordingly, the corresponding points can be found from the captured image with high accuracy, and accurate ranging can be performed.

In order to change the periodic structure d, there is a method of switching a plurality of diffractive optical elements having different periodic structures d. FIG. 9 is a schematic diagram illustrating an example of a laser irradiation apparatus. The laser irradiation apparatus 20A includes a semiconductor laser 21 that emits illumination light (laser light) that is linearly polarized light with a predetermined wavelength λ, a coupling lens 61 that converts the illumination light emitted from the semiconductor laser 21 into parallel light, And a plurality of diffractive optical elements 22 (22A and 22B: holograms) that generate pattern light obtained by diffracting parallel light.
The diffractive optical element 22 generates pattern light having different angles of view. Further, the two diffractive optical elements 22 are arranged adjacent to each other, and constitute one optical plate 62.
The irradiation control means 32 performs switching control of the diffractive optical elements 22A and 22B on which the parallel light is incident. In this example, the optical plate 62 is slid by a driving mechanism (not shown), and the diffractive optical element 22 on which a desired pattern is formed is arranged on the optical path, thereby directing pattern light having different angles of view toward the object. Can be irradiated.
When the irradiation field angle of the pattern light is changed by changing the wavelength λ of the semiconductor laser 21, the pattern density changes with the angle of view as shown in FIG. When different diffractive optical elements are selectively used, it is possible to irradiate pattern light with only the angle of view changed without changing the pattern density.

Hereinafter, the operation when the distance measuring device 1 of the present invention is actually attached to the robot arm will be described with reference to FIGS. 10 and 11. 10 and 11 are diagrams for explaining the operation when the distance measuring device according to the first embodiment of the present invention is attached to the robot arm. Since the distance measuring device 1 is attached to a freely moving robot arm, the distance and direction to the object change every moment. Hereinafter, an example in which the irradiation angle of view of the pattern light is changed using the laser irradiation apparatus 20A shown in FIG. 9 will be described.
As shown in FIG. 10A, the distance measuring device 1 attached to the robot arm 80 first calculates the distance to the object 41 without emitting the pattern light from the laser irradiation device 20. The stereo camera 10 captures the object 41, and the distance measuring means 31 (see FIG. 2) performs stereo matching to obtain a distance image to the object 41. Here, since the surface of the object 41 has a uniform luminance distribution, the shape of the object 41 cannot be accurately determined. However, since the distance to the edge part of the target object 41 can be calculated, it can be determined from the calculated distance information that the target object 41 is at a position far from the robot arm. The distance information calculated by the distance measuring means 31 is sent to the irradiation control means 32.

The irradiation control unit 32 controls the angle of view of the pattern light emitted from the laser irradiation device 20 based on the distance information calculated by the distance measuring unit 31. In this example, since the object 41 is located far from the robot arm 80, pattern light having a small angle of view is emitted from the laser irradiation device 20 (FIG. 10B). That is, the irradiation control means 32 slides the optical plate 62, arranges the diffractive optical element 22A having a small irradiation angle of view on the optical path, and allows parallel light to enter the diffractive optical element 22A. As a result, the pattern light is irradiated onto the object 41 having no contrast at a narrow irradiation angle of view γ. By forming a predetermined pattern (pattern) on the surface of the object 41, not only the edge portion of the object 41 but also the shape of the entire object 41 can be understood.
Although the distance to the object 41 is long, the angle of view of the pattern light emitted from the laser irradiation device 20 is small, so that the object can be irradiated with a sufficiently bright and high-contrast pattern. A distance image can be obtained.

  Since an accurate distance image of the object is obtained in FIG. 10B, the robot arm 80 approaches the object 41 based on the information. In addition, calculation of the distance to the target object 41 by the distance measuring means 31 is continuously performed. As the object 41 is approached, the object 41 becomes larger in the shooting screen of the stereo camera 10. Although the object 41 appears to be large, if the irradiation angle of the pattern light emitted from the laser irradiation device 20 remains small, a part of the object 41 is not irradiated with the pattern light (FIG. 11 ( c)).

  As described above, when the object 41 is closer than a certain distance, the angle of view of the pattern light emitted from the laser irradiation device 20 is increased (FIG. 11D). Specifically, based on the distance information calculated by the distance measuring means 31, the irradiation control means 32 slides the optical plate 62 and arranges the diffractive optical element 22B having a large irradiation angle of view on the optical path, and the diffractive optical element. Parallel light is incident on the element 22B. The irradiation field angle β of the diffractive optical element 22 of this example is substantially the same as the imaging field angle α of the stereo camera 10, and the entire target object 41 can be irradiated with pattern light. As a result, the distance and shape of the entire object 41 can be accurately grasped, and the robot arm 80 can grasp the object 41 accurately.

As described above, according to the present embodiment, the object is photographed with the stereo camera, the parallax is calculated based on the captured image, and the distance from the parallax to the object is calculated.
By changing the irradiation angle of the pattern according to the calculated distance, the optimum pattern according to the distance is irradiated from the laser irradiation apparatus. Even when the distance to the object changes, the pattern is not irradiated to a portion where the object does not exist. Therefore, the pattern light can be efficiently irradiated onto the object. As a result, even a distant object can be irradiated with a sufficient amount of pattern light, so that a bright and high-contrast distance image can be obtained, and the distance to the object and the shape of the object can be accurately measured.
Moreover, since the irradiation angle of the pattern is changed according to the distance, the output of the limited laser light source can be used effectively. Therefore, even if a small and low-cost semiconductor laser is used as the light source of the laser irradiation apparatus, a sufficient amount of light can be secured.

<Second Embodiment>
A distance measuring apparatus according to a second embodiment of the present invention will be described. The distance measuring device according to the present embodiment is characterized in that the density of the pattern light applied to the object is controlled according to the distance information obtained from the distance measuring means.
FIG. 12 is a diagram showing the relationship between the density of pattern light and the obtained distance image. 12A to 12C are examples of pattern light having a low density, and FIGS. 12D to 12F are examples of pattern light having a high density.
In the first embodiment, the angle of view is changed according to the distance to the object, but the pattern density may be changed according to the distance to the object. Specifically, the pattern density is sparse when the object is far, and the pattern density is dense when the object is close. By doing this, even when pattern irradiation is performed on an object that is far away, the light intensity of each pattern formed by the pattern light does not decrease, and accurate distance measurement is possible.

As shown in FIGS. 12A to 12C, when the irradiation angle of pattern light is wide and the density is low, there is a pattern (for example, dot) of pattern light although distance information of the entire imaging range can be obtained. The part which does not increase also increases. Since the light intensity is secured at the spot irradiated with the dot, the distance can be measured accurately, but the distance cannot be measured accurately at the portion where the dot does not exist, and as a result, the distance image becomes rough (FIG. 12C). .
On the other hand, as shown in FIGS. 12D to 12F, when the density of the pattern light is increased without changing the irradiation angle of view, the density of the distance image is also increased, and the object has a more accurate distance and shape. Information can be obtained.
Therefore, as shown in FIG. 10B, when the robot arm 80 is far from the object 41, control is performed to irradiate pattern light having a low density. Further, as shown in FIG. 11D, when the object 41 approaches the robot arm 80, control is performed to irradiate a pattern having a high density. By doing so, the accurate distance and shape can be grasped, and the robot arm 80 can finally easily grasp the object 41.

For example, in the case of a factory production line, since the shape of the object to be grasped by the robot arm and the movement locus of the object are constant, it is not always necessary to obtain a distance image for the entire imaging range. That is, as in the first embodiment, there is no problem even if the irradiation field angle is narrowed when the object is far away.
However, when the target object to be grasped by the robot arm does not have a certain shape or the position where the target object is placed is different each time, the pattern is irradiated on the entire target object by reducing the angle of view of the pattern to be irradiated. There are cases where it is not done. In such a case, it is effective to change the pattern density without changing the angle of view.
In the present embodiment, the density of the pattern to be irradiated can be changed by switching a plurality of diffractive optical elements having different pattern densities using the laser irradiation apparatus 20A shown in FIG. Since the specific control method is the same as that of the first embodiment, the description thereof is omitted.
Of course, when the object is far, a diffractive optical element that irradiates a pattern with a narrow angle of view and a low density is used, and when the object is close, a diffractive optical element that irradiates a pattern with a wide angle of view and a high density May be used.

  As described above, according to the present embodiment, control for changing the density of the pattern is performed based on the distance information obtained from the stereo camera. Specifically, the pattern is made low density at a long distance and the pattern is made high density at a short distance. By doing so, it is possible to prevent the brightness of the pattern from being lowered even at a long distance, and it is possible to prevent a reduction in distance measurement accuracy due to a reduction in the amount of light.

<Third embodiment>
A distance measuring apparatus according to a third embodiment of the present invention will be described with reference to FIG. The distance measuring apparatus according to the present embodiment is characterized in that a plurality of diffractive optical elements are switched and used without driving the diffractive optical element (plate). FIG. 13 is a diagram showing a laser irradiation apparatus according to the third embodiment.
Light emitted from the laser irradiation device is converted into a predetermined pattern by the diffractive optical element. In order to irradiate a plurality of different patterns, a plurality of diffractive optical elements (holograms) may be used as shown in the first embodiment (FIG. 9). In the laser irradiation apparatus 20A of FIG. 9, a drive unit for switching the plurality of diffractive optical elements 22A and 22B is necessary, so that the laser irradiation apparatus 20A is enlarged. Further, since the diffractive optical element 22 is mechanically moved, the diffractive optical element 22 vibrates at the time of switching. Since the pattern light vibrates in accordance with the vibration of the diffractive optical element, there is a possibility that a defocused pattern is photographed by the stereo camera. If such a phenomenon occurs, a clear distance image cannot be obtained, and the operation speed of the robot arm decreases. Therefore, in the present embodiment, a method is proposed in which the pattern can be switched at high speed without mechanically moving the diffractive optical element (hologram) when the pattern to be irradiated is switched.

A laser irradiation apparatus 20B shown in FIG. 13 includes a semiconductor laser 21 (light source) that emits linearly polarized light (illumination light) having a wavelength λ, and a coupling lens 61 that converts the illumination light emitted from the semiconductor laser 21 into parallel light. A polarization rotation element 63 capable of controlling the polarization direction of the transmitted parallel light, and at least one polarization film 64A (polarization means) that transmits or reflects the light emitted from the polarization rotation element 63 according to the polarization direction. A light splitting element 64 and a plurality of diffractive optical elements 22 (22A, 22B) that diffract each light transmitted or reflected by the polarizing film 64A and generate different pattern lights are provided. The irradiation control means 32 (pattern control means) switches the diffractive optical element on which the illumination light enters by controlling the polarization direction of the light transmitted through the polarization rotation element 63.
The polarization rotation element 63 converts the polarization direction of the illumination light emitted from the semiconductor laser 21. For example, when the illumination light is S-polarized light, it is transmitted as S-polarized light or changed to P-polarized light and emitted.
The light splitting element 64 is a beam splitter, for example, and has a polarizing film 64A and a total reflection surface 64B in this example.
The two diffractive optical elements 22 are disposed on the optical path of light reflected by different films. The diffractive optical element 22A is an element on which the light reflected by the polarizing film 64A is incident, and generates long-distance diffraction pattern light to be irradiated when the object is at a long distance. The diffractive optical element 22B is an element on which light reflected by the total reflection surface 64B is incident, and generates short-distance diffraction pattern light to be irradiated when the object is at a short distance.

A method for making illumination light incident on different diffractive optical elements 22A and 22B will be described. In the following description, it is assumed that the parallel light transmitted through the coupling lens 61 is S-polarized light, and the polarizing film 64A has a characteristic of reflecting S-polarized light by 100% and transmitting P-polarized light by 100%.
First, the parallel light (S-polarized light) transmitted through the coupling lens 61 passes through the polarization rotation element 63 and enters the light splitting element 64. When the light emitted from the polarization rotation element 63 is S-polarized light, the light is reflected 100% by the polarizing film 64A. The reflected light enters the diffractive optical element 22A and becomes pattern light. The diffractive optical element 22A converts the incident light into pattern light having a narrow angle of view for irradiating an object at a far position.
In this state, when generating pattern light having a large angle of view for irradiating an object located at a close position, the polarization rotating element 63 converts S-polarized light into P-polarized light. P-polarized parallel light is incident on the light splitting element 64 and passes through the polarizing film 64A by 100%. The light transmitted through the polarizing film 64A is reflected 100% by the total reflection surface 64B. The reflected light enters the diffractive optical element 22B and becomes pattern light. The diffractive optical element 22B converts the incident light into pattern light having a wide angle of view for irradiating an object located at a close position.
Thus, by using the polarization rotation element 63 and the light splitting element 64, it is possible to select a diffractive optical element on which the laser light is incident. Accordingly, different diffraction pattern light can be generated by different diffractive optical elements 22.

The polarization rotation element will be described with reference to FIG. FIGS. 14A and 14B are schematic diagrams illustrating an example of a polarization rotation element.
FIG. 14A shows an example in which the polarization rotation element 63A is a half-wave plate. When the optical axis of the half-wave plate is inclined by 45 ° with respect to the incident S-polarized light, the half-wave plate can emit P-polarized light by rotating the polarization direction of the incident light by 90 °. Accordingly, a drive mechanism (not shown) for rotating the polarization rotation element 63A is provided, and the polarization direction of the light emitted from the polarization rotation element 63A is switched by controlling the drive mechanism by the irradiation control means 32 (see FIG. 13). Can do. Although this method mechanically moves the half-wave plate, since the diffractive optical element is not moved, the pattern light to be irradiated does not vibrate when the polarization direction is switched.
As another example, FIG. 14B shows an example in which the polarization rotation element 63B uses a rotation element having an electro-optic effect or a magneto-optic effect. When using the electro-optic effect, materials such as LiNbO ₃ , LiTaO ₃ , KTP, BBO, and KTN can be used. By applying an electric field to these materials from the voltage source 54, the polarization direction can be rotated. The voltage source 65 is controlled by the irradiation control means 32. When a material having a magneto-optic effect is used, the polarization direction can be rotated by applying a magnetic field to the material. (Faraday effect). The method shown in FIG. 14B does not require a mechanical drive unit, so that the pattern light can be switched at high speed.

  As described above, according to the present embodiment, the polarization direction of light from the laser light source can be switched between S-polarized light and P-polarized light by using the polarization rotation element. By adopting an optical system in which the diffractive optical element on which the S-polarized light is incident and the diffractive optical element on which the P-polarized light is incident, only the polarization direction is rotated, and the diffractive optical element is moved at high speed without mechanical movement. Irradiation can be performed by switching patterns. Therefore, a mechanical drive unit for moving the diffractive optical element is not required, and the irradiation apparatus can be downsized and highly reliable.

  As described above, the distance measuring device having the stereo camera and the laser irradiation device described in the example of each embodiment efficiently targets the light emitted from the laser irradiation device regardless of whether the object is near or far away. Can irradiate objects. Therefore, it is possible to accurately measure the distance even when the object is far away.

  DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 10 ... Stereo camera, 11 ... Camera, 12 ... Imaging lens, 13 ... Imaging element, 14 ... Imaging range, 20 ... Laser irradiation apparatus, 21 ... Semiconductor laser, 22 ... Diffractive optical element, 23 ... Irradiation Range: 30: control unit, 31: distance measuring means, 32: irradiation control means, 40: plane, 41: object, 41a: edge part, 41b: upper surface part, 51: laser medium, 52: modulation medium, 53 ... Reflector, 54 ... voltage source, 61 ... coupling lens, 62 ... optical plate, 63 ... polarization rotation element, 64 ... light splitting element, 64A ... polarizing film, 64B ... total reflection surface, 65 ... voltage source, 80 ... robot Arm, 101 ... object, 102 ... camera, 103 ... lens, 104 ... object image, 104c ... corresponding point, 105 ... two-dimensional sensor, 106 ... stereo camera device, α ... imaging angle of view, β ... irradiation angle of view, γ Irradiation angle

JP 2006-163174 A

Claims (4)

A light source that emits illumination light;
A diffractive optical element that irradiates an object with diffraction pattern light generated by diffracting the illumination light; and
A plurality of imaging lenses that image the diffraction pattern light reflected by the object;
A plurality of imaging means for imaging a plurality of images related to the object based on the diffraction pattern light imaged by the imaging lenses;
Ranging means for calculating a distance from the object from parallax information between the plurality of images;
Pattern control means for controlling the diffraction pattern light according to distance information obtained from the distance measuring means;
A distance measuring device comprising:   The distance measuring apparatus according to claim 1, wherein the pattern control unit controls the density of the diffraction pattern light.   The distance measuring apparatus according to claim 1, wherein the pattern control unit controls an angle of view of the diffraction pattern light. A polarization rotation element capable of controlling the polarization direction of transmitted light;
At least one polarizing means for transmitting or reflecting the light emitted from the polarization rotation element according to the polarization direction;
A plurality of the diffractive optical elements that diffract each light transmitted or reflected by the polarizing means to generate different diffraction pattern lights, and
The said pattern control means switches the said diffractive optical element in which the said illumination light injects by controlling the polarization direction of the light which permeate | transmitted the said polarization rotation element, The Claim 1 thru | or 3 characterized by the above-mentioned. The described distance measuring device.

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