JP2015010987A - Pattern illumination device and distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pattern illumination device that can increase an output and luminance while configured to be focus-free.SOLUTION: The pattern illumination device includes: a plurality of semiconductor laser light sources 2a to 2e; a plurality of coupling lenses 3a to 3e for converting light emitting from the semiconductor laser light sources 2a to 2e into parallel beams 60a to 60e; volume holograms 50a to 50e for synthesizing the converted parallel beams and aligning outgoing directions of the beams to one direction; and a diffraction optical element 4 for diffracting the synthesized parallel beams to generate random pattern beams 5 and projecting the beams onto a measurement object.

Description

  The present invention relates to a pattern irradiation apparatus that projects a predetermined diffraction pattern light onto a measurement target and a distance measuring apparatus including the pattern irradiation apparatus.

2. Description of the Related Art Conventionally, a technique called “stereo distance measurement” is known in which a measurement (distance measurement) object is photographed by two cameras and distance information to the measurement object is obtained using the two obtained images.
Such a distance measuring apparatus to which “stereo distance measurement” is applied can be suitably used for a self-propelled robot or a movable robot arm.
In “stereo ranging”, the depth distance is calculated based on the principle of triangulation using the parallax generated between two images. To obtain the parallax in stereo ranging, window matching is performed on each image. It is necessary to find points corresponding to each other (corresponding points).

FIGS. 13 and 14 are diagrams illustrating the principle of a distance measuring method using the principle of triangulation used in “stereo distance measurement”.
In the distance measurement method using “stereo distance measurement”, two cameras are configured by combining a pair of two-dimensional sensors and a pair of lenses to detect a deviation (parallax) of a measurement object, The distance is measured by the principle of triangulation.
Consider a case where the stereo camera device 106 shown in FIG. 13 shoots light from the measurement object 101 by arranging two cameras 102a and 102b made of the same optical system.
The measurement object image 104a obtained through the lens 103a of the camera 102a and the measurement object image 104b obtained through the lens 103b of the camera 102b are different from each other in that the same point on the subject (measurement object 101) is shifted by the parallax Δ. Each of the dimension sensors 105a and 105b (FIG. 15) is received by a plurality of light receiving elements (pixels) and converted into an electrical signal.

Here, the distance between the optical axes of the lenses 103a and 103b is called a base line length, which is D, where A is the distance between the lens and the subject, and f is the focal length of the lens. Equation 1 holds.
A = Df / Δ (Expression 1)
Since the base length D and the focal length f of the lens are known, the distance A to the subject can be calculated by detecting the parallax Δ using (Equation 1).
In addition, said method is a method of searching the corresponding point for the measurement object 101 reflected in the two two-dimensional sensors based on the distribution characteristics of the luminance values of the pixels.
Therefore, when the measurement object 101 is an object having a single-color surface, the luminance distribution of the surface is uniform, and it is difficult for the luminance value to change in the captured image, it is difficult to perform the association (that is, Because the corresponding point 104c shown in FIG. 14 cannot be detected), the distance cannot be calculated.
Japanese Patent Application Laid-Open No. 2004-133260 discloses a technique that enables a stereo camera to accurately associate an object having no texture (pattern) by projecting a pattern using a projector.

However, when a pattern is irradiated onto an object using a projector as in Patent Document 1, the range in which the irradiation pattern is focused is limited due to the optical characteristics of the projector.
Therefore, if the object to be measured is within the focus range of the projection screen of the projector, the distance can be detected accurately, but if it is outside the focus range, a defocused pattern will be emitted and it will be accurate. The distance cannot be detected.
On the other hand, if a laser light source is used as a light source for pattern projection and a pattern light obtained by diffracting the laser light by a diffraction element is applied to the object, the focus can be focused anywhere. That is, regardless of the distance between the object and the stereo camera, it is possible to irradiate the object with a pattern that is always in focus.

However, the output power of a semiconductor laser that emits laser light is currently about 300 mW even if it has a high output. Therefore, for example, when trying to irradiate a pattern with a wide area of 1 m square, the brightness per 1 cm ³ is about 30 μW.
With this level of brightness, the brightness of sunlight is buried outdoors, and the brightness of fluorescent lamps becomes noise even indoors.
Therefore, high brightness is required for pattern irradiation using a laser light source and a diffractive optical element.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a pattern irradiation apparatus capable of increasing the brightness of diffraction pattern light in a focused state at all times.

  In order to solve the above-mentioned problems, the invention of claim 1 includes a plurality of light sources, first optical means for combining the light emitted from the plurality of light sources and emitting them in the same direction, and the first The pattern illumination device includes: second optical means for diffracting the light synthesized and emitted by the optical means to generate diffraction pattern light and projecting the diffraction pattern light onto the object.

  Since it comprised as mentioned above, according to this invention, the pattern irradiation apparatus which can make high brightness | luminance of diffraction pattern light always in a focused state is realizable.

The figure which shows the structural example of the pattern illumination apparatus applicable to a compound eye camera apparatus. The figure which showed the relationship between the cross-sectional shape of a diffractive optical element, and diffraction efficiency. The figure which shows the structure of the compound eye camera apparatus applicable to a ranging apparatus. The figure explaining the stereo camera apparatus based on this invention which applied (integrated) the pattern illumination apparatus of FIG. 1 to the stereo camera apparatus of FIG. The figure which showed the relationship between the angle of view of a ranging lens and the output angle of the diffraction pattern light of a pattern illumination apparatus in the stereo camera shown in FIG. BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing of the pattern illumination apparatus which concerns on 1st Embodiment. The figure explaining the characteristic of the 2nd optical element which synthesize | combines a laser beam in detail. The figure shown with the graph which shows the relationship between the incident angle of a volume hologram, and diffraction efficiency. The figure which shows the pattern illumination apparatus which concerns on 2nd Embodiment. The figure explaining the combination of the area which irradiates a pattern, and the laser light source to light-emit. The figure which shows the change of the Bragg angle by the wavelength change of light. The figure which shows the distance measuring device to which the pattern illumination apparatus which concerns on this embodiment is applied. The figure explaining the principle of the ranging method using the principle of the triangulation used in "stereo ranging". The figure explaining the principle of the ranging method using the principle of the triangulation used in "stereo ranging".

Embodiments according to the present invention will be described below in detail with reference to the drawings.
Prior to describing the pattern illumination device according to the present embodiment, a basic configuration of a pattern illumination device applicable to a compound eye camera device will be described.
FIG. 1 is a diagram illustrating a configuration example of a pattern illumination device applicable to a compound eye camera device.
FIG. 1A illustrates each element constituting the pattern illumination device, and the display of the configuration of the compound eye camera to which the pattern illumination device can be applied is omitted. FIG. 1B is a diagram showing the gradation of the multi-gradation luminance distribution.
As shown in FIG. 1, the pattern illumination device 1 according to the present embodiment includes a semiconductor laser light source 2 as a light source, a coupling lens 3 disposed on the optical path of laser light emitted from the semiconductor laser light source 2, and diffraction. And an optical element 4.

The laser light emitted from the semiconductor laser light source 2 is converted into parallel light by the coupling lens 3 disposed on the optical path on the subject side to be measured.
The parallel light that has passed (transmitted) through the coupling lens 3 is then incident on the diffractive optical element 4 and diffracted, and is projected onto the measurement object as diffraction pattern light 5 having a luminance distribution of two or more gradations.
In order to keep the output of the semiconductor laser light source 2 constant, a temperature adjustment function unit 6a and an APC (Auto Power Control) function unit 6b for keeping the temperature constant may be provided.

By the way, in order to generate a brightness of two or more gradations in the diffraction pattern light 5 irradiated to the measurement target, the cross-sectional shape of the diffractive optical element 4 is a multi-step staircase shape having different groove depths.
As shown in FIG. 1B, the diffraction pattern light has a multi-tone luminance distribution, and the size of one pixel, which is the minimum unit, is about 1 mm square. The diffraction pattern light 5 in which the minimum unit pixels having the multi-tone luminance distribution are randomly arranged is projected onto the object to be measured (ranging).

FIG. 2 is a diagram showing the relationship between the cross-sectional shape of the diffractive optical element and the diffraction efficiency.
As shown in FIG. 2, the diffraction efficiency can be changed by changing the number of grooves (steps) in the cross-sectional shape of the diffractive optical element 4 and the depth of the steps.
Since the luminance is high (bright) in the portion where the diffraction efficiency is high and the luminance is low (dark) in the portion where the diffraction efficiency is low, the multi-tone luminance distribution can be obtained by appropriately combining the groove shape patterns in the diffractive optical element 4. Can be formed.
As described above, a technique relating to the conversion of the light intensity (luminance) distribution using the diffractive optical element 4 is also disclosed in Japanese Patent Laid-Open No. 2003-270585 and Japanese Patent No. 4333760.

The semiconductor laser light source 2 shown in FIG. 1 can select and emit visible light having a wavelength λ of 400 to 700 nm and near infrared light having a wavelength λ of about 700 to 1000 nm.
If visible light is used, it is possible to irradiate diffraction pattern light with high sensitivity and high resolution to the imaging device of the stereo camera. On the other hand, when using near-infrared light, the sensitivity to the image sensor is low, but the laser light is not visible to the eye (invisible light), so that the user does not feel unnaturalness.
The outgoing angle θ1 from the diffractive optical element 4 is determined by the wavelength λ of the outgoing light from the semiconductor laser light source 2 and the periodic structure of the diffractive optical element 4.
In order to increase the emission angle θ1, the wavelength λ of the semiconductor laser light source 2 must be increased or the periodic structure of the diffractive optical element 4 must be miniaturized.

However, the wavelength of the emitted light from the semiconductor laser light source 2 is limited to the above-mentioned wavelength of 400 to 1000 nm, and the periodic structure of the diffractive optical element 4 is limited to the fine processing capability of the processing apparatus.
Therefore, the actual situation is that the emission angle cannot be increased beyond a certain angle.
For example, when the wavelength λ = 0.65 μm and the periodic structure is 1.0 μm, the emission angle is about 40 °.

3A and 3B are diagrams illustrating a configuration of a compound eye camera device applicable to the distance measuring device, in which FIG. 3A is a cross-sectional view of the compound eye camera device, and FIG. 3B is a top view of an imaging element included in the compound eye camera device. is there.
Note that the present invention can be suitably applied to a stereo camera device including two cameras (an imaging lens and an imaging region) as a compound eye camera, and the stereo camera device will be described as an example.
In FIG. 3, the stereo camera device 20 includes a lens array 11 having a plurality of (for example, two) lenses arranged on the same plane, and reflected light (including diffraction pattern light) from an object transmitted through the lens array 11. An image sensor 14 that receives light and acquires image information.
In the lens array 11, imaging lenses 12a and 12b, which are distance measuring lenses, are integrally formed.

The imaging lenses 12a and 12b have the same optical characteristics, have the same shape and the same focal length, and the optical axes 13a and 13b are parallel to each other. The interval between the optical axis 13a and the optical axis 13b is the baseline length D.
As shown in FIG. 3, the direction of the optical axes 13a and 13b is the Z axis, the direction orthogonal to the Z axis and from the optical axis 13b to the optical axis 13a is the Y axis, and both the Z axis and the Y axis are An orthogonal direction is taken as an X axis.

When the lens array 11 is arranged so that the centers of both lenses are on the Y axis, the imaging lenses 12a and 12b exist on the XY plane.
In this case, the direction in which the parallax Δ is generated is the Y-axis direction.
The imaging device 14 is an imaging device such as a complementary metal oxide semiconductor (CMOS) or a charge coupled device (CCD), and has a large number of pixels (imaging regions) formed on a wafer 14a by a semiconductor process.

As shown in detail in FIG. 3B, on the image sensor 14, an imaging region (imaging means) 15a on which a subject image is formed via the imaging lens 12a, and a subject image is formed via the imaging lens 12b. The imaging region 15b is spaced apart.
The imaging area 15a and the imaging area 15b are rectangular areas having the same size, and the diagonal centers of the imaging area 15a and the imaging area 15b are substantially coincident with the optical axes 13a and 13b of the imaging lenses 12a and 12b. Is arranged.

The stereo camera device 20 having the above configuration can measure the distance from the subject based on the principle of triangulation described above with reference to FIGS.
Further, if the pattern is illuminated by the pattern illumination device shown in FIG. 1, even if the measurement target is an object having a single color surface, stereo correspondence can be performed, so that the object can be measured with high accuracy.

4 is a diagram illustrating a stereo camera device according to the present invention in which the pattern illumination device of FIG. 1 is applied (integrated) to the stereo camera device of FIG.
4A is a cross-sectional view in the longitudinal direction (length direction of the lens array) of the stereo camera device, and FIG. 4B is a cross-sectional view in the short side direction (width direction of the lens array).
FIG. 5 is a diagram showing the relationship between the angle of view of the distance measuring lens and the emission angle of the diffraction pattern light of the pattern illumination device in the stereo camera shown in FIG.
In FIG. 4 and subsequent figures, the same components as those in FIGS. 1 and 3 are denoted by the same reference numerals, and detailed description thereof is omitted.

The distance measuring device 30 shown in FIG. 4 is configured by combining the stereo camera device 20 described in FIG. 3 with the configuration of the pattern illumination device shown in FIG.
That is, the pattern illumination device as shown in FIG. 1 is arranged between the two cameras (the imaging lens 12a and the imaging region 15a, the imaging lens 12b and the imaging region 15b) constituting the stereo camera device 20 described in FIG. ing.
In addition, a parallax calculation unit (ranging unit) 40 that performs distance measurement based on parallax of images captured by the two cameras is provided.

As shown in FIG. 4B, the semiconductor laser light source 2 of the pattern illumination device included in the distance measuring device 30 is attached to the side surface of the housing 30 a of the distance measuring device 30. 31 is installed. The light emitted from the semiconductor laser light source 2 is reflected by the mirror 31 toward the subject to be measured, and converted into parallel light by the coupling lens 3 (see FIG. 1).
The parallel light is diffracted by the diffractive optical element 4 (see FIG. 1), is emitted as diffraction pattern light 5 having a predetermined emission angle, and is irradiated onto the object.

In the distance measuring device 30 shown in FIG. 5, the distance measurement possible area A is an area where the field angles of the two imaging lenses 12 a and 12 b overlap.
However, the emission angle θ1 of the diffraction pattern light 5 emitted from the diffractive optical element 4 is equal to the angle of view θ2 of the imaging lenses 12a and 12b of the stereo camera device 20.
Therefore, even if the distance between the object and the stereo camera device 20 changes, the pattern is irradiated to the entire range A that can be measured.
Therefore, as shown in FIG. 5, distance measurement using the diffraction pattern light can be performed in the entire distance measuring area A regardless of the distance to the object to be measured.
In this way, the diffractive optical element 4 is disposed between the optical axes of the two imaging lenses 12a and 12b of the stereo camera so that the angle of view of the stereo camera and the angle of view (spread angle) of the diffractive optical element 4 are matched.
Thereby, the area that can be measured by the stereo camera and the area that illuminates the diffraction pattern light can always be matched.
Thereby, even if the distance to the object changes, the area A that can be measured by the stereo camera and the area that illuminates the diffraction pattern light can always be matched. Further, it is possible to irradiate the distance measuring area A with the diffraction pattern light 5 emitted from the semiconductor laser light source 2 without waste.

[First Embodiment]
Next, a first embodiment of the present invention will be described.
In the basic configuration described above, the semiconductor laser light source 2 and the coupling lens 3 included in the pattern illumination device are a set, and sufficient output and luminance cannot be ensured.
The embodiment described below aims to solve such a problem.

FIG. 6 is a schematic explanatory diagram of the pattern illumination device according to the first embodiment of the present invention.
The pattern illumination device 1 includes a plurality of semiconductor laser light sources 2 (2a to 2e), a plurality of coupling lenses 3 (3a to 3e), a first optical element (optical means 50, and a second optical element (optical). And a diffractive optical element 4 as means.
The semiconductor laser light sources 2 (2a, 2b, 2c, 2d, and 2e) are semiconductor lasers that emit infrared light having the same wavelength.
The coupling lens 3 (3a, 3b, 3c, 3d, 3e) converts the light emitted from the plurality of semiconductor laser light sources 2 (2a, 2b, 2c, 2d, 2e) into parallel light 60a, 60b, 60c, 60d, respectively. , 60e.

The first optical element 50 combines the parallel lights 60 (60a to 60e) emitted from the coupling lenses 3 so that the traveling directions thereof coincide with each other. Although the configuration of the first optical element 50 will be described in detail later, the first optical element 50 includes a plurality of volume holograms 50a to 50e.
The diffractive optical element 4 diffracts the incident light beam and irradiates the object with a desired diffraction pattern light 5.

In the following description, a pattern illuminating device having five semiconductor laser light sources 2, five coupling lenses 3, and five volume holograms 50 is exemplified, but the number of these elements is not limited to this. Not too long.
As the number of the laser 2 light sources is increased, the diffraction pattern 5 having higher luminance can be irradiated.
The semiconductor laser light source 2 is disposed on the optical axis of the coupling lens 3 (3a, 3b, 3c, 3d, 3e), respectively.
Since the light can be converted into parallel light by the coupling lens 3, an LED that diffuses light more than the semiconductor laser light source may be used as the light source.
The collimated light 60 emitted from the coupling lens 3 is incident on the first optical element 50 (50a, 50b, 50c, 50d, 50e) at different angles, and the traveling direction is matched.

FIG. 7 is a diagram for explaining in detail the characteristics of the second optical element that combines laser beams.
As shown in FIG. 7, the first optical element 50 includes five volume holograms that diffract only the corresponding parallel light 60. Specifically, it has a configuration in which five volume holograms are arranged in the light emission direction.
In FIG. 7, five volume holograms are stacked, but a gap may be provided between the volume holograms.
The volume hologram 50a diffracts only the parallel light 60a emitted from the coupling lens 3a, and transmits the parallel lights 60b, 60c, 60d, and 60e emitted from the other coupling lenses.
Similarly, the volume hologram 50b diffracts only the parallel light 60b emitted from the coupling lens 3b and transmits the other parallel lights 60a, 60c, 60d, and 60e.

The volume holograms 50c, 50d, and 50e diffract only the parallel lights 60c, 60d, and 60e, and transmit the other parallel lights.
At this time, the five light beams guided to the diffractive optical element 4 are all diffracted by the volume holograms 50a to 50e so as to enter the diffractive optical element 4 at the same angle.
Thus, in realizing the fact that only a specific light beam is diffracted and the other light beam is transmitted, the feature of the volume hologram which is “angle selectivity” is used.
“Angle selectivity” is a characteristic in which only light incident at a specific incident angle is diffracted with high efficiency, and light incident at other angles is transmitted.

According to “Lightwave Electro-Optics” (Corona), pages 117-132, by Jiro Koyama and Hiroshi Nishihara, a volume hologram is defined as a hologram having a Q value of 10 or more expressed by equation (2).
Q = 2π · λ0 · T / (n0Λ2) (Formula 2)
However, λ0: wavelength of incident light, T: thickness of hologram, n0: refractive index of hologram element substrate, Λ: period of hologram Volume hologram is light with an incident angle satisfying a specific diffraction condition (so-called Bragg condition) Only strongly diffracts.

FIG. 8 is a graph showing the relationship between the incident angle of the volume hologram and the diffraction efficiency.
As shown in FIG. 8, the diffraction efficiency (%) of the volume hologram has a peak value when the incident angle satisfies the Bragg condition.
Only when the incident angle of light coincides with the Bragg angle, a high diffraction efficiency close to 100% is obtained, and when the incident angle is other than that, the diffraction efficiency is almost 0% and the light is transmitted. This is “angle selectivity”.
Parallel light beams 60a to 60e from the semiconductor laser light sources 2a to 2e are made incident on the volume holograms 50a to 50e at different angles, respectively.
The volume holograms 50a to 50e can synthesize the light beams from the semiconductor laser light sources 2a to 2e into one light beam traveling in the same direction by optimizing the periodic structure so as to diffract only the light beam having a specific incident angle.

Furthermore, a specific design example will be described.
According to the above-mentioned “Lightwave Electro-Optics” (Corona) pages 107-108 by Jiro Koyama and Hiroshi Nishihara, the condition for the maximum diffracted wave to appear is expressed by equation (3).
Λ (sin θi + sin θm) = ± mλ (3)
However, if θi: incident angle, θm: outgoing angle, λ: wavelength, Λ: hologram period, m: integer m = 1, and the wavelength of light is 900 nm infrared light, the incident angle is 20 ° and the outgoing angle is 0 °. In order to achieve this, the period of the hologram may be 2.631 μm.

For example, if the period of the volume hologram 50a is 2.631 μm, only the parallel light beam 60a having an incident angle of 20 ° can be diffracted.
Similarly, in order to emit a parallel light beam having an incident angle of 10 ° with an exit angle of 0 °, the period of the hologram may be set to 5.183 μm.
Therefore, if the period of the volume hologram 50b is 5.183 μm, only the parallel light beam 60b having an incident angle of 10 ° can be diffracted.
As described above, the period of the volume holograms 50a to 50e is designed in accordance with the parallel light beams 60a to 60e incident at different angles, so that the parallel light beams 60a to 60e from the plurality of semiconductor laser light sources 2a to 2e travel in the same direction. It can be combined with the luminous flux of the book.
It is also possible to combine a plurality of light beams having the same wavelength using a beam splitter. In that case, it combines using the difference in polarization. However, in this case, since only two (P-polarized light / S-polarized light) beams can be synthesized, the luminance is only doubled.

On the other hand, if volume holograms are used, they can be combined with a slight difference in incident angle, so that light beams from a larger number of laser light sources can be combined and irradiated with pattern light with high brightness.
The light combined by the first optical element 50 into a single light beam enters the diffractive optical element 4 to become diffracted light, and is irradiated onto the object as random diffraction pattern light 5.
The number of random pattern divisions, the angle of view, and the number of gradations are optimized according to the size and shape of the target to be measured.

  As described above, pattern light with high brightness can be irradiated by combining light beams from many laser light sources. This makes it possible to realize a stereo camera that is resistant to ambient light and can accurately measure the distance even outdoors.

[Second Embodiment]
FIG. 9 is a diagram showing a pattern illumination device according to the second embodiment of the present invention.
As described above, in the pattern illumination device of the present invention, high-luminance pattern light can be irradiated by combining light beams from a plurality of laser light sources.
Thereby, for example, even when pattern illumination (pattern light 5a) is performed on a wide area of 1 m square with a distance to the object to be measured, the brightness per 1 cm ³ is increased to about several hundred μW, and the ambient brightness Even when is bright, pattern light strong against disturbance light can be irradiated.
Conversely, when pattern irradiation is performed on a narrow area (pattern light 5b) that is close to the object to be measured, or when the surrounding brightness is dark, the beam incident on the diffractive optical element 4 needs to have a high light intensity. There is no.
In this case, rather than lowering the light output of all the laser light sources and lowering the overall light intensity, it is better not to emit some of the lasers but to leave only the remaining lasers to emit light at normal light intensity.
It should be noted that the distance to the object to be measured can be the result of distance measurement by the distance measurement control unit 40 provided in the distance measuring device to which the pattern illumination device is applied. The ambient brightness can be measured by providing a light amount sensor in the distance measuring device.

FIG. 10 is a diagram for explaining an example of a combination of an area to be irradiated with a pattern and a laser light source for emitting light.
As shown in FIG. 10, when irradiating the pattern light 5a with a large area in FIG. 9, all the semiconductor laser light sources 2a to 2e are turned on, but when irradiating the pattern 5b with a small area, the semiconductor laser light sources 2a and 2e are turned on. Turn off and turn on only the semiconductor laser light sources 2b to 2d.
In order to control the laser light source to emit light, for example, the distance measurement control unit 40 shown in FIG. 4 includes a light source control unit that switches ON / OFF of the light source.
Since the semiconductor laser generates heat according to the light output, the wavelength λ of the laser oscillated by this heat varies by Δλ.

  In this embodiment, since light is selectively diffracted using a volume hologram, when wavelength fluctuation occurs, there arises a problem that the angle selectivity of light in the volume hologram is lowered as described below.

FIG. 11 is a diagram illustrating changes in the Bragg angle due to changes in the wavelength of light.
As described above, for example, if the period of the volume hologram 50a is 2.631 μm, the parallel light beam 60a having a wavelength of 900 nm and an incident angle of 20 ° can be diffracted at a high emission angle of 0 °. At this time, the black angle is 9.85 °.
However, when the oscillation wavelength of the semiconductor laser 2a changes to 910 nm due to temperature change in this state, the black angle becomes 9.96 °.
In this case, when light of 910 nm enters a volume hologram designed so that the maximum diffraction efficiency can be obtained with light of 900 nm, the maximum diffraction efficiency cannot be obtained and the brightness of the pattern light is lowered. Therefore, it is necessary to suppress the wavelength variation of the laser light source as much as possible.
For this purpose, it is effective not to greatly change the output of each laser.

When the area to illuminate the pattern is small or when sufficient distance measurement is possible even with low-luminance pattern illumination, instead of lowering the light output of all laser light sources and reducing the overall light intensity as shown in FIG. , Stop the emission of some lasers.
It is desirable to keep the light output as constant as possible so that the emitting laser emits light with the same light intensity as usual.

[Third Embodiment]
Next, it is a figure which shows the distance measuring device to which the pattern illumination apparatus 1 shown in 1st, 2nd embodiment is applied.
FIG. 12 is a diagram illustrating a distance measuring device to which the pattern illumination device according to the present embodiment is applied.
Basically, the pattern illuminating device in the distance measuring device 30 shown in FIG. 4 is replaced with the pattern illuminating device 1 described with reference to FIGS. 6 and 9, and therefore a detailed description of the distance measuring device is omitted.
Using the principle described with reference to FIGS. 13 and 14, a stereo camera (cameras 12a and 12b) is used to detect a shift (parallax) in the image of the measurement object and measure the distance based on the principle of triangulation.
A stereo camera that performs distance measurement based on such a principle is effective means of pattern illumination as described above, because a corresponding point cannot be found in a portion without a texture (pattern) and a distance cannot be measured.
Furthermore, in order to illuminate pattern illumination light without wasteful viewing range of the camera, it is desirable that pattern light is emitted from between two cameras of a stereo camera.

However, the distance (base line length) between two stereo cameras is generally about 30 cm, and it is physically difficult to arrange a high-luminance pattern illumination device including a plurality of laser light sources therein.
If it is a small pattern illumination device provided with a small number of laser light sources, it can be arranged, but it has low luminance and cannot be used outdoors as described above.
Therefore, in this embodiment, only the diffractive optical element 4 that generates the pattern light is disposed between the two cameras, and the other components of the pattern illumination device 1 are disposed at different positions.

As shown in FIG. 12, only the diffractive optical element 4 that generates pattern light is disposed between two cameras of a stereo camera.
In FIG. 12, the plurality of semiconductor laser light sources 2a to 2e, the coupling lenses 3a to 3e, and the combining optical elements 50a to 50e are located at positions different from those of the stereo camera (lenses 12a and 12b). By arranging in this way, pattern light can be emitted from between the two cameras. Since the light source and the like can be arranged at different positions, even if it is large, the base line length is not limited, and the design freedom of the stereo camera is not lost.
Since the stereo camera measures the distance to the object by performing block matching from the images of the left and right cameras and detecting corresponding points, the distance cannot be detected if the object is an object without a texture.

On the other hand, by applying the pattern illumination device of this embodiment to a distance measuring device, even if the object is an object without a texture, stereo correspondence is possible, and the distance to the object to be measured is measured with high accuracy. can do.
In addition, since the pattern illumination apparatus according to the present embodiment is a pattern illumination using a laser light source, the pattern to be irradiated is not out of focus (focus-free) regardless of where the object is located, regardless of the size and position of the object. The distance can be measured with high accuracy.
As a result, it is possible to irradiate a sharp pattern that is always in focus regardless of the size and position of the object, and therefore distance measurement can be performed with high accuracy.
Furthermore, since light from a plurality of laser light sources is synthesized, a high-brightness random pattern can be irradiated, which is resistant to disturbance light and can be used outdoors.

Further, as described above, since a volume hologram is used instead of a beam splitter or the like as a means for synthesizing the light from the laser light source, the light from more light sources can be synthesized, not limited to about two to four. Can do.
As a result, it is possible to realize a distance measuring device that is resistant to disturbance light and can be used outdoors.

DESCRIPTION OF SYMBOLS 1 Pattern illumination apparatus, 2 Laser light source, 3 Coupling lens, 4 Diffractive optical element, 5 Diffraction pattern light, 6a Temperature control function part, 6b Function part, 11 Lens array, 12a Imaging lens, 12b Imaging lens, 13a Optical axis, 13b Optical axis, 14 Image sensor, 14a Wafer, 15a Image area, 15b Image area, 20 Stereo camera device, 50 Volume hologram, 60 Parallel light

JP 2007-17355 A

Claims (7)

Multiple light sources;
First optical means for combining and emitting light emitted from the plurality of light sources in the same direction;
Diffracting the light synthesized and emitted by the first optical means to generate diffraction pattern light, and projecting the diffraction pattern light onto an object;
A pattern illumination device comprising: The pattern illumination device according to claim 1,
The pattern illumination apparatus according to claim 1, wherein the first optical means is a plurality of volume holograms that diffract light beams having different incident angles emitted from the plurality of light sources in the same emission direction. The pattern illumination device according to claim 1 or 2,
The pattern illumination device, wherein the plurality of light sources are laser light sources that emit light having the same wavelength. The pattern illumination device according to claim 3.
The pattern illumination apparatus according to claim 1, wherein the light having the same wavelength emitted from the plurality of light sources is infrared light. The pattern illumination device according to any one of claims 1 to 4,
A pattern illumination device comprising light source control means for selectively lighting the plurality of light sources according to a distance to the object or ambient brightness. The pattern illumination device according to any one of claims 1 to 5, and a plurality of imaging lenses that image diffraction pattern light emitted from the second optical means and reflected by the object;
A plurality of imaging means for imaging a plurality of images related to the subject based on the diffraction pattern light imaged by each imaging lens;
A distance measuring device comprising: a distance measuring device that calculates a distance from the object based on parallax information between the plurality of images. The distance measuring device according to claim 6,
The second optical means is disposed between the plurality of imaging lenses, and the plurality of light sources and the first optical means are not disposed between the plurality of imaging lenses. apparatus.

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