JP2013190394A - Pattern illumination apparatus and distance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small pattern illumination apparatus which can emit a pattern capable of achieving a precise distance measurement, and a distance measuring apparatus which measures a distance to a measurement object by using the pattern illumination apparatus.SOLUTION: A pattern illumination apparatus 1 according to a first embodiment of the present invention, which projects a pattern to a measurement object to measure a distance to the measurement object that is not shown, comprises: a semiconductor laser (light source) 2 that emits light for projecting pattern light 5; a coupling lens (optical means) 3 that converts the light emitted from the semiconductor laser 2 to parallel light; a diffraction optical element 4 that diffracts the parallel light converted by the coupling lens 3. The pattern light 5 emitted from the diffraction optical element 4 and projected to the measurement object is a pattern formed by randomly arranging pixels each having luminance distribution of multi-gradation which is three gradations or more.

Description

  The present invention relates to a pattern illumination device and a distance measuring device, and in particular, in a distance measurement using a stereo camera, a pattern illumination device that projects a pattern for identifying a measurement target, and a measurement target using the pattern illumination device The present invention relates to a distance measuring device that measures a distance.

  Conventionally, a “stereo distance measurement” technique is known in which a measurement object is photographed simultaneously by two cameras, and distance information from the two obtained images to the measurement object is obtained. In this stereo distance measurement, the distance to the measurement object is calculated based on the principle of triangulation using the parallax generated between two images. In addition, 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. 9 is a diagram illustrating the principle of triangulation, and FIG. 10 is a diagram illustrating the parallax Δ on the two-dimensional sensor. The principle of calculating the distance by obtaining the parallax based on FIGS. 9 and 10 will be described.
From FIG. 9, a pair of two-dimensional sensors (105a, 105b) is combined with a pair of lenses (103a, 103b) to form two cameras (102a, 102b), and the measurement object 101 has two two-dimensional objects. A deviation (parallax) is detected from each image projected on the sensors (105a, 105b), and the distance is measured based on the principle of triangulation. In FIG. 9, consider the case where the light from the measurement object 101 is photographed by arranging two cameras 102a and 102b made of the same optical system. The measurement object image 104a obtained via the lens 103a and the measurement object image 104b obtained via the lens 103b are shifted to the two-dimensional sensors 105a and 105b by shifting the same point of the measurement object 101 by the parallax Δ, respectively. Images are taken as 104a and 104b (see FIG. 10), 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 base line length, which is D, when the distance between the lens and the measurement object 101 is A, and the focal length of the lens is f, and when A >> f. The following equation holds.
A = Df / Δ (1)
Since the baseline length D and the focal length f of the lens are known from the equation (1), the distance A to the measurement object 101 can be calculated by detecting the parallax Δ.

However, the above method is a method of finding the corresponding point 104c shown in FIG. 10 based on the distribution characteristics of the luminance values of the pixels of the measurement object 101 reflected on the two two-dimensional sensors 105a and 105b. Is an object having a surface of a single color, the luminance distribution of the surface is uniform, and it is difficult to perform the association (that is, the corresponding point 104c cannot be detected) when the luminance value does not easily change in the captured image. Therefore, there is a problem that the parallax Δ cannot be calculated, and as a result, the distance cannot be calculated.
In order to solve the problem, Patent Document 1 has a predetermined luminance gradation as a conventional technique for projecting a predetermined light projection pattern on the surface of a measurement object and patterning the surface of the measurement object. It is disclosed to use a random pattern in which luminance blocks are arranged randomly (that is, so that there is no regularity in luminance change).

Patent Document 2 discloses the use of a non-periodic projection pattern having no periodicity in dot size, line length, thickness, position, density, and the like based on uniform random numbers and normal random numbers. Has been. Further, as means for projecting this pattern, means for projecting light emitted from a light source through a slide of a random pattern to form an image with a lens system and projecting it onto a measurement object is disclosed.
Further, Patent Document 3 discloses a method of generating a sequence so that vectors represented by each partial sequence are different in direction from each other as a pattern generation method, and there is a risk of incorrect association. It is disclosed that it can reduce and can perform exact matching. Further, it is disclosed that a projector or a scanning exposure apparatus is used as means for projecting this pattern.

However, the conventional techniques described in Patent Documents 2 and 3 have a problem that the size of the apparatus increases because of the use of a projector or a scanning laser exposure apparatus. In other words, the projector may have a large light source lamp. For example, if an LED is used as the light source, it is possible to reduce the size, but since a lens is used for image formation, a random pattern with high resolution can be irradiated at the image formation position. As a result, the distance cannot be accurately measured.
Further, the scanning laser exposure apparatus disclosed in Patent Document 3 is a method of displaying a random pattern by scanning while modulating laser light. In this method, in order to irradiate the entire measurement object with a random pattern, the time required for scanning becomes long. Therefore, since the shutter speed of the stereo camera is limited by the time required for laser scanning, it is not possible to photograph at a short shutter speed. As a result, there is a problem that it is difficult to perform measurement in a fast moving object or in a dark place.
The present invention has been made in view of such a problem, and is a compact pattern illumination device that can irradiate a pattern that enables highly accurate distance measurement, and a distance measuring device that measures a distance to a measurement object using the device. The purpose is to provide.

  In order to solve this problem, the present invention provides a pattern illumination device that projects a pattern for identifying a measurement object in order to measure a distance to the measurement object, A light source for projecting a pattern, optical means for converting light projected from the light source into parallel light, and a diffractive optical element for diffracting the parallel light converted by the optical means, the diffractive optical element The light emitted from the light and projected onto the measurement object is pattern light in which pixels having a multi-tone luminance distribution of three or more tones are randomly arranged.

  According to the present invention, by using a diffractive optical element to irradiate a pattern in which pixels having a multi-tone luminance distribution are randomly arranged, the measurement object is an object having a single color surface, Stereo correspondence is possible, and the distance to the measurement object can be measured with high accuracy. Furthermore, the pattern illumination device has a small size because it does not have a scanning unit. By using near infrared light as the wavelength, the pattern is always suitable for highly accurate ranging even if the distance to the measurement object changes. Can be irradiated.

(A) is a figure which shows the structure of the pattern illumination apparatus which concerns on one embodiment, (b) is a figure which shows the gradation of multi-tone luminance distribution. It is a figure which shows the relationship between the cross-sectional shape of a diffractive optical element, and diffraction efficiency. (A) is a figure which shows the structure of the stereo camera which concerns on one embodiment, (b) is the figure which looked at the image pick-up element from the top. It is a figure which shows the arrangement | positioning relationship between the pattern illuminating device which concerns on this embodiment, and a stereo camera. It is a figure which shows the position which can arrange | position the pattern illumination apparatus which concerns on this embodiment with respect to a stereo camera. It is a figure showing the relationship between the emission angle of the pattern illuminating device which concerns on this embodiment, and the angle of view of a stereo camera. It is a figure which shows the structure of the refusal apparatus which concerns on this embodiment. (A) is a figure which shows the case where the 0th-order light which arises in a diffractive optical element enters in a pattern, (b) is a figure which shows the case where the 0th-order light which arises in a diffractive optical element does not enter in a pattern. It is a figure which shows the principle of triangulation. It is a figure explaining parallax (DELTA) on a two-dimensional sensor.

  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. .

FIG. 1A is a diagram illustrating a configuration of a pattern illumination device according to an embodiment, and FIG. 1B is a diagram illustrating gradations of a multi-gradation luminance distribution. The pattern illumination device 1 according to the first embodiment of the present invention is a pattern illumination device 1 that projects a pattern onto a measurement object in order to measure a distance to a measurement object (not shown), and includes pattern light 5. Is converted by a semiconductor laser (light source) 2 that emits light for projecting light, a coupling lens (optical means) 3 that converts light emitted from the semiconductor laser 2 into parallel light, and a coupling lens 3. And a diffractive optical element 4 that diffracts the parallel light. The light emitted from the diffractive optical element 4 and projected onto a measurement object (not shown) is randomly arranged with pixels having a multi-tone luminance distribution. Pattern light 5.
That is, the laser light emitted from the semiconductor laser 2 is converted into parallel light by the coupling lens 3. The parallel light enters the diffractive optical element 4 and is diffracted to become light having a multi-tone luminance distribution. This light is not binary, has the multi-tone luminance distribution shown in FIG. 1B, and the size of one pixel as a minimum unit is about 1 mm square. Pattern light 5 in which the minimum unit pixels having the multi-tone luminance distribution are randomly arranged is projected onto the measurement object.

FIG. 2 is a diagram showing the relationship between the cross-sectional shape of the diffractive optical element and the diffraction efficiency. In order to generate multi-tone luminance, the cross-sectional shape of the diffractive optical element 4 has a multi-step shape with different groove depths. The diffraction efficiency changes by changing the number of steps of the diffractive optical element 4 or the depth of the steps. That is, in FIG. 2, the diffraction efficiency increases from about 40%, 55%, 75%, 84%, and 100% in order from the top. By utilizing this, the luminance is bright where the diffraction efficiency is high, and the luminance is dark where the diffraction efficiency is low, so a multi-tone luminance distribution can be formed. As described above, techniques relating to the conversion of the light intensity (luminance) distribution using the diffractive optical element 4 are also disclosed in Patent Documents 4 and 5 and the like.
In this embodiment, the semiconductor laser 2 is assumed to be a laser that emits near-infrared light having a wavelength of about 700 to 900 nm. If the wavelength becomes larger than this, the pattern may not be accurately detected due to being cut by an infrared cut filter built in the stereo camera (compound-eye imaging device) or the sensor sensitivity of the stereo camera being lowered. On the contrary, the wavelength of the semiconductor laser 2 may be visible light of 400 to 700 nm. By making visible light, there is an advantage that the detection sensitivity of the sensor of the stereo camera is improved. However, on the other hand, since the laser beam can be seen with the eyes, there arises a problem that a person feels danger or becomes annoying. Therefore, the wavelength may be properly used depending on the measurement object.

In addition, the semiconductor laser 2 generally instantaneously generates a phenomenon called mode hopping in which the wavelength changes as the temperature rises. When the wavelength changes, the emission angle and diffraction efficiency of the pattern light from the diffractive optical element 4 change, and the pattern irradiation range changes. Thus, when the diffraction efficiency changes, the multi-tone luminance distribution changes relatively. In any case, since it causes a problem in performing stable ranging, it is desirable to provide a temperature adjusting element 6 (FIG. 1) such as a Peltier element in order to keep the temperature of the semiconductor laser 2 constant.
Also, the laser power is desirably kept constant by feeding back the emitted light using an APC (Auto Power Control) circuit 7 (FIG. 1). By keeping the brightness of the pattern illumination constant, it is possible to maintain an optimal shutter time for a stereo camera.
The semiconductor laser 2 is generally very small with a package size of φ3.5 mm and φ5.6 mm. Since the coupling lens 3 and the diffractive optical element 4 are also made with substantially the same size, the pattern illumination device 1 of this embodiment can be made much smaller than the conventional projector or scanning type laser exposure device. In addition to being able to do so, there is no scanning section and the reliability is extremely high.
As described above, the pattern illumination device 1 according to this embodiment can irradiate a pattern that enables highly accurate distance measurement while being small.

FIG. 3A is a diagram illustrating a configuration of a stereo camera according to one embodiment, and FIG. 3B is a diagram of the image sensor as viewed from above. In FIG. 3A, the lens array 11 is formed by integrating lenses 12a and 12b. The lenses 12a and 12b are distance measuring lenses having the same shape and the same focal length, and the optical axes 13a and 13b are parallel to each other. The distance between the optical axis 13a and the optical axis 13b is the baseline length D.
Here, as shown in FIG. 3A, the direction of the optical axes 13a and 13b is the Z axis, the direction perpendicular to the Z axis and the direction from the optical axis 13b to the optical axis 13a is the Y axis, and the Z axis and the Y axis. The direction orthogonal to both of these is the X axis. The lenses 12a and 12b are on the XY plane, and the centers of both lenses are arranged on the Y axis. In this case, the direction in which the parallax Δ is generated is the Y-axis direction.

In addition, as shown in FIG. 3B, the image sensor 14 is an image sensor such as a CMOS or a CCD, and a large number of pixels are formed on a wafer by a semiconductor process. On the image sensor 14, an imaging region 15a where a measurement target is imaged via a distance measuring lens 12a and an imaging region 15b where a measurement target is imaged via a distance measuring lens 12b are spaced apart. Are arranged. The imaging area 15a and the imaging area 15b are rectangular areas having the same size, and the diagonal centers A and B of the imaging area 15a and the imaging area 15b are substantially coincident with the optical axes 13a and 13b of the lenses 12a and 12b. Are arranged to be.
The stereo camera 16 having the above-described configuration can measure the distance to the measurement object based on the principle of triangulation previously described with reference to FIGS. Furthermore, if a random pattern is irradiated by the pattern illumination device 1 shown in FIG. 1, even if the measurement target is an object having a single color surface, stereo correspondence can be performed. In addition, since the pattern illumination apparatus 1 does not have a scanning unit, even a moving object can be accurately measured.

FIG. 4 is a diagram showing an arrangement relationship between the pattern illumination device and the stereo camera according to the present embodiment. Patent Document 3 discloses a configuration in which an illumination device is disposed between two cameras constituting a stereo camera, but the stereo camera 16 of the present invention is extremely small in size and has the largest size in the baseline length direction. It is physically impossible to dispose the lighting device between the two cameras because the width is only about 13 mm. The places where the pattern illumination device 1 can be placed are the surroundings A to D of the stereo camera 16 as shown in FIG.
Here, the relationship between the angle of view of the lenses 12a and 12b of the stereo camera 16 and the pattern emission angle of the pattern illumination device 1 will be described. FIG. 6 is a diagram illustrating the relationship between the emission angle of the pattern illumination device according to the present embodiment and the angle of view of the stereo camera. When the pattern illumination device 1 and the stereo camera 16 are integrated, places where the pattern illumination device 1 can be arranged are places A to D around the stereo camera 16 as shown in FIG. Therefore, in order to irradiate the entire field angle that is the visual field of the stereo camera 16, the pattern emission angle α must be larger than the field angle of the stereo camera 16. However, in order to increase the pattern emission angle α, the diffractive optical element 4 must be processed more finely. Therefore, the pattern emission angle α cannot be increased so much due to processing limitations. Therefore, it is desirable to place the pattern illumination device 1 at the position B or D instead of the position A or C in FIG.

FIG. 7 is a diagram illustrating the configuration of the refusal device according to the present embodiment. This figure shows the relationship between the field angle and the emission angle when the pattern illumination device according to the present invention is disposed at the position shown in FIG. 5D. The measurement refusal device 9 according to the present embodiment includes a pattern illumination device 1, a stereo camera 16 that captures a measurement object irradiated with a pattern projected by the pattern illumination device 1, and an image obtained from the stereo camera 16. And a control unit 17 that calculates the parallax and calculates the distance to the measurement object. Then, the pattern illumination device 1 is arranged at a position where the emission angle β from the diffractive optical element 4 is larger than the lens field angle of the stereo camera 16.
Compared with the emission angle α in the case of FIG. 6, the emission angle β of the pattern illumination device 1 can be made smaller in FIG. 7. This is because when the pattern illumination device 1 is arranged at positions A and C of the stereo camera 16, the pattern illumination device 1 must be arranged so as to cover all the horizontal angles of view with a large angle of view of the stereo camera 16. . In order to cover all the horizontal angles of view, the exit angle α of the pattern illumination device 1 must be increased, and in order to increase the exit angle α, the diffractive optical element 4 must be processed more finely. .
Thus, by arranging the pattern illumination device 1 at a position perpendicular to the direction of the base line length of the stereo camera 16, it is possible to cover the entire field of view of the stereo camera 16 without making the processing of the diffractive optical element 4 difficult. Pattern illumination can be performed. Especially in the vertical direction, the stereo camera 16 can be arranged near the field of view of the stereo camera by arranging it in the vertical direction between the two lenses, and the processing accuracy of the diffractive optical element 4 can be relaxed.

Next, a configuration is proposed in which zero-order light generated by the diffractive optical element 3 does not enter into the pattern light to be illuminated. FIG. 8A shows a case where the 0th-order light generated by the diffractive optical element enters the pattern, and FIG. 8B shows a case where the 0th-order light generated by the diffractive optical element does not enter the pattern. It is.
In the case of the pattern illuminating device described so far as shown in FIG. 8A, if there is light (0th order light) that is transmitted without being diffracted by the diffractive optical element 4, it is exactly the center of the pattern to be irradiated. The spot light 8 having the same size as the beam diameter of the laser beam incident on the diffractive optical element 4 is irradiated. In the portion irradiated with the 0th-order light 8, the multi-tone luminance distribution is disturbed, and the center of the screen irradiated with the 0th-order light 8 cannot be accurately measured.
Therefore, as shown in FIG. 8B, it is prevented from entering the pattern irradiated with the 0th-order light 8. That is, zero-order light can be avoided by the positional relationship between the stereo camera 16 and the pattern illumination device 1 shown in FIG. By doing so, the luminance distribution is not disturbed by the 0th-order light, and accurate ranging can be performed on the entire screen. In the configuration of FIG. 8B, the diffraction efficiency is lowered and the pattern to be irradiated becomes dark. However, if the light output of the semiconductor laser 2 is increased, the pattern becomes brighter and the reduction in the diffraction efficiency can be covered.

  The pattern illumination device 1 and the stereo camera 16 described above may be detachable so that the measurement object is an object having a surface of a single color and the case where it is not. By integrating the pattern illumination device 1 and the stereo camera 16, there is no deviation between illumination and shooting, and stable distance measurement is possible even with changes over time and vibration.

DESCRIPTION OF SYMBOLS 1 Pattern illumination apparatus, 2 Semiconductor laser, 3 Coupling lens, 4 Diffractive optical element, 5 Pattern light, 6 Temperature control element, 7 APC circuit, 80th-order light, 9 Measurement rejection apparatus, 11 Lens array, 12a, 12b Lens , 13a, 13b Optical axis, 14 Image sensor, 15a, 15b Image area, 16 Stereo camera, 17 Control unit

JP 2001-91247 A JP 2001-147110 A JP 2007-17355 A JP 2003-270585 A Japanese Patent No. 4333760

Claims (5)

A pattern illumination device that projects a pattern for identifying a measurement object in order to measure a distance to the measurement object,
A light source that projects the pattern;
Optical means for converting light projected from the light source into parallel light;
A diffractive optical element that diffracts the parallel light converted by the optical means,
The light emitted from the diffractive optical element and projected onto the measurement object is pattern light in which pixels having a multi-tone luminance distribution of three or more gradations are randomly arranged. Lighting device.   The pattern illumination device according to claim 1, a compound eye imaging device that images the measurement object irradiated with the pattern light projected by the pattern illumination device, and a parallax from each image captured by the compound eye imaging device And a control unit that calculates the distance to the measurement object by calculating   3. The distance measuring device according to claim 2, wherein the pattern illumination device is arranged at a position where an emission angle from the diffractive optical element is larger than a lens field angle of the compound-eye imaging device.   The distance measuring device according to claim 2, wherein the pattern illumination device is arranged in a direction perpendicular to a direction of a base line length that is a distance between optical axes of the compound-eye imaging device.   3. The pattern illumination device is arranged so that pattern light emitted from the diffractive optical element and projected onto the measurement object does not include zero-order light generated by the diffractive optical element. The distance measuring device according to any one of 1 to 4.

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