Pattern light projection device, three-dimensional measurement device, and distance image acquisition device

Abstract

To provide a pattern light projection device which is of a simple structure and easy to manufacture, and which makes it possible to obtain a uniform strength distribution over the entire measurement region (pattern light projection region), and high-precision three-dimensional measurement device and distance image acquisition device.SOLUTION: The pattern light projection device comprises: a light emission unit for emitting pattern light; and a projection unit for projecting pattern light to a measurement object. The projection unit is composed of a square pyramid-shaped light guide unit demarcated by one end, the other end, and a side face and tapered off from the one end side toward the other end side. The pattern light entering from the one end side into the light guide unit propagates inside of the light guide unit toward the other end side and forms a plurality of rays of virtual pattern light on the other end side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pattern light projection device that projects pattern light with a two-dimensional distribution onto a measurement object, a three-dimensional measurement device that measures the three-dimensional position of the measurement object from an image of the projected pattern light, and a distance image acquisition device that measures the distance to the measurement object.

Background Art

[0002] In recent years, as a method for acquiring information on the distance to an object and information on the three-dimensional shape of the object, a measurement object is projected with pattern light (structured light) such as a random dot pattern, the measurement object onto which this pattern light is projected is imaged by an imaging unit, and cross-correlation processing is performed using predetermined calibration parameters. By using a pattern matching method or a triangulation method, etc., for each point on the captured image, the distance from the projection reference plane (screen position) is calculated, and technologies for acquiring distance information and three-dimensional shape information of the object have attracted attention (for example, Patent Document 1 and Patent Document 2).

[0003] FIG. 10 is a diagram for explaining the principle of measuring distance information and three-dimensional shape information by such a pattern light projection method. FIGS. 10(a) and (b) show a state in which the dot pattern light emitted from a light source is irradiated onto a predetermined projection reference plane in a situation where the measurement object does not exist in the measurement space. On the other hand, FIGS. 10(c) and (d) show a situation in which the same dot pattern as before is irradiated onto the measurement object. In a situation where the measurement object exists in the measurement space, depending on the height from a predetermined reference plane, that is, the shape of the measurement object, distortion occurs in the image of the dot pattern as shown in FIG. 10(d). From the amount of distortion of this dot pattern image, it becomes possible to measure distance information and three-dimensional shape information from the light source to the measurement object by using an existing pattern matching method or the like.

[0004] As a pattern light projection device used in this type of three-dimensional measurement device or distance image acquisition device, light from an LED (Light Emitting Diode) or an LD laser (Laser Diolde) is converted into structured light by utilizing the diffraction phenomenon caused by a diffractive optical element, and the converted structured light is projected onto a predetermined measurement area on the object to be measured by a projection lens (for example, Patent Document 3).

[0005] In recent years, the cost of vertical cavity surface emitting lasers (VCSELs) has been decreasing, and they are being used in many applications such as gesture control and 3D sensing. For example, smartphones are being equipped with a so-called dot projector that applies the aforementioned pattern projection device as a 3D face authentication function.

[0006] As such a dot projector for smartphones, a configuration is known that includes a VCSEL as a light source, a projection optical system including a diffractive optical element (DOE) that generates predetermined structured light and a projection lens, and a prism optical system that bends the optical path of the projection optical system to make it thinner in order to accommodate the projection optical system within the thickness of the smartphone body (for example, Patent Document 4).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] The above-described dot projector for a smartphone laminates and forms a fine structure of about several millimeters in size, which consists of a prism optical system, a projection lens, and a diffractive optical element (DOE), by wafer-level packaging (WLP) technology.

[0009] However, such a dot projector laminates and forms fine components by WLP technology which consists of multiple processes. As a result, the structure becomes complex and the manufacturing becomes difficult. In addition, due to the nature of the diffractive optical element, particularly due to the decrease in the diffraction efficiency of diffracted light other than the first order, it has the problem that it is difficult to obtain a uniform intensity distribution over the entire measurement region (pattern light projection region).

[0010] The present invention has been made in consideration of such conventional problems, and an object thereof is to provide a pattern light projection device having a simple configuration, easy to manufacture, and capable of obtaining a uniform intensity distribution over the entire measurement region (pattern light projection region), a high-precision three-dimensional measurement device, and a distance image acquisition device.

Means for Solving the Problems

[0011] As means for solving the above problems, it is as follows. That is, the pattern light projection device of the present invention is a pattern light projection device that projects pattern light having a two-dimensional distribution onto a measurement object, and includes a light emitting unit that emits pattern light of a predetermined pattern, and a projection unit that projects the pattern light from the light emitting unit onto the measurement object. The projection unit is partitioned by one end portion, the other end portion, and a side surface, and is composed of a frustum of a square pyramid-shaped light guide portion that tapers from the one end portion side toward the other end portion side. The one end portion is disposed facing the light emitting unit, and the pattern light incident into the light guide portion from the one end portion side propagates through the light guide portion toward the other end portion side and forms a plurality of virtual pattern lights on the other end portion side. The pattern light having a two-dimensional distribution including the virtual pattern lights is projected onto the measurement object by the projection lens.

[0012] Further, in the above invention, when the opening diameter of one end of the light guide part is D and the opening diameter of the other end is d in the pattern light projection device, it is preferable that 0.425 < d / D < 0.475.

[0013] Further, in the above invention, the pattern light projection device has a projection lens optically connected to the frustum-shaped light guide part, and the surface on the measurement object side of the projection lens is an aspherical surface, and it is preferable that the conic coefficient k satisfies the following conditions. -0.16 < k < -0.21

[0014] Further, the three-dimensional measurement device of the present invention includes the pattern projection device in which the light emitting part emits structured light, and an image acquisition device that acquires an image on the measurement object projected by the pattern projection device.

[0015] Further, in the above invention, it is preferable that the structured light in the three-dimensional measurement device is a dot pattern.

[0016] Further, in the above invention, it is preferable that the three-dimensional measurement device has an asymmetric region in the structured light.

[0017] Further, in the above invention, it is preferable that the structured light in the three-dimensional measurement device is a random dot pattern.

[0018] Further, the distance image acquisition device of the present invention includes the three-dimensional measurement device.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a pattern light projection device that has a simple structure, is easy to mold, and can obtain a uniform intensity distribution over the entire measurement region (pattern light projection region), and a high-precision three-dimensional measurement device and a distance image acquisition device.

Brief Description of the Drawings

[0020]

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Embodiments for Carrying Out the Invention

[0021] [Pattern Light Projection Device] [First Embodiment] Hereinafter, the pattern light projection device according to the first embodiment will be described with reference to the drawings. Note that the following description is given by way of example in order for those skilled in the art to fully understand the present invention, and the present invention is not limited thereto.

[0022] FIG. 1 is (a) a front view, (b) a right side view, and (c) a left side view showing the pattern light projection device according to the first embodiment. The pattern light projection device 1 includes a light emitting unit 10 that emits pattern light (structured light) of a predetermined pattern, and a projection unit 20 that projects the pattern light from the light emitting unit 10 onto a measurement object (not shown).

[0023] As the light emitting unit 10, a vertical cavity surface emitting laser (VCSEL) that emits light in a direction perpendicular to one end portion 211 which is the light incident surface of the projection unit 20 is preferably used, and the VCSEL elements of this vertical cavity surface emitting laser are arranged in an array of 25×25 vertically and horizontally at a pitch of 30 microns as shown in FIG. 3.

[0024] The projection unit 20 is composed of a frustum-shaped light guide unit 21 defined by one end portion 211 facing the light emitting unit 10, the other end portion 212, and the side surface 213, and a projection lens 22 optically connected to the light guide unit 21. The frustum-shaped light guide unit 21 is formed of a transparent solid material, and as shown in FIG. 1, it has a tapered shape from the one end portion 211 side toward the other end portion 212 side. Note that, in this embodiment, an example in which the light guide unit 21 and the projection lens 22 are integrally formed is shown, but they may be formed separately and optically connected to each other.

[0025] In the first embodiment, since the surface shape of one end portion 211 of the projection unit 20 is a convex surface with a curvature r centered on the other end portion 212 surface on the central axis of the light guide unit 21, it is possible to efficiently take in the light emitted from the light emitting unit 10 into the light guide unit 21. Note that the surface shape of one end portion 211 is not limited to this example and may be a flat surface.

[0026] As shown in the front view (a) and the left side view (c) of FIG. 1, the side surface 213 of the light guide unit 21 has side surfaces 213A and 213C and side surfaces 213B and 213D arranged opposite to each other, and the four side surfaces 213A to 213D form a frustum shape that tapers from the one end portion 211 side toward the other end portion 212 side.

[0027] In the pattern light projection device 1 of the first embodiment, the overall length L of the pattern light projection device 1 is 4.56 mm, the overall length L1 of the light guide part 21 is 2.9 mm, the thickness L2 of the projection lens 22 is 1.66 mm, the diameter N of the projection lens 22 is 2.8 mm, the length L of the VCSEL element as the light emitting part 10 and the opening length D of one end part 211 of the light guide part 21 are 0.8 mm, and the length d of one end part 212 of the light guide part 21 is 0.36 mm.

[0028] Also, in the pattern light projection device 1 according to the present embodiment, when the opening diameter of one end part 211 of the light guide part 21 is D and the opening diameter of the other end part 212 is d, it is preferable that 0.425 < d / D < 0.475. Further, d / D = 0.45 is particularly preferable for realizing a regular two-dimensional repetitive arrangement of virtual pattern light described later.

[0029] The projection lens 22 has a main body part 22 on a cylinder and a lens surface 23 whose surface on the measurement object side is a convex surface. The surface shape of the lens surface 23 is not particularly limited, but it is preferably an aspherical lens for correcting various aberrations.

[0030] When the lens part 23 is an aspherical lens, the aspherical shape, taking the optical axis direction as z and the direction orthogonal to the optical axis as y, and the conic coefficient (conic constant) as K and the aspherical coefficients as A4, A6, A8, A10 ···, is represented by the following formula (I). z=(y 2 / r) / [1+{1-(1+K)(y / r) 2} 1 / 2 +A4y 4 +A6y 6 +A8y 8 +A10y 10 ···(I) Note that in the aspherical coefficients, E indicates a power of 10. For example, 2.3×10 -2 is represented as 2.3E - 002. Also, the symbols of these specification values are common in the numerical data of the examples described later.

[0031] The pattern light projection device 1 according to the present embodiment preferably satisfies the following conditions as the cone coefficient K in the formula (I). -0.16 < k < -0.21 By setting the cone coefficient K within this range, various aberrations of the projection lens 22 are appropriately corrected, and a particularly clear dot pattern is projected.

[0032] [Principle of forming pattern light] Next, the principle of forming virtual pattern light of the pattern light projection device of the present invention will be described. FIG. 2 is a cross-sectional view for explaining the behavior of light rays in the pattern light projection device 1 and the principle of forming virtual pattern light in the present embodiment.

[0033] As described with reference to FIG. 1, the light guide portion 21 having a frustum of a square pyramid shape is a transparent solid tube shape having reflective inner walls formed by four side surfaces 213A to 213D, and constitutes a so-called kaleidoscope. The light incident from the one end portion 211 side travels while repeating total reflection at the air interfaces of the side surfaces 213A to 213D having a tapered shape from the one end portion 211 side toward the other end portion 212 side, and propagates through the light guide portion 21 toward the other end portion 212 side. Note that the light guide portion 21 is preferably configured to perform total reflection at the air interfaces of the side surfaces 213A to 213D as a solid transparent resin, but may also be a reflective film formed with an aluminum vapor deposition film or the like.

[0034] As shown in FIG. 2, the light emitted from a single point of the light emitting portion 10 which is a light source enters the light guide portion 21 from one end portion 211 of the light guide portion 21 and travels toward the other end portion 212 while being internally reflected by the side surface 213. When viewed from the other end portion 212 side, virtual light source images 11 and 12 are continuously observed on the arrangement surface of the light emitting portion 10. In the description of FIG. 2, an example is shown in which two virtual light source images 11 and 12 are observed as a result of two internal reflections by the surface 213A. However, the inclination angles of the respective side surfaces 213A to 213D which are tapered from the one end portion 211 side toward the other end portion 212 side and the number of reflections corresponding thereto can be used to set the positions of the virtual light source images and the number of virtual light sources, that is, the distribution pattern of the two-dimensional light source images.

[0035] The virtual light source image with a two-dimensional distribution formed on the other end portion 212 side of the light guide portion 21 is enlarged and projected at an appropriate magnification onto a predetermined range of a projection reference plane (screen position) at a predetermined distance from the lens surface 23 of the projection lens 22 by the projection lens 22.

[0036] FIG. 3 is a diagram for explaining the configuration of the light emitting portion 10. The light emitting portion 10 in the present embodiment emits pattern light of a dot pattern. Further, as shown in FIG. 3, an asymmetric region 10A is formed on the light emitting surface of the light emitting portion 10 in order to understand the principle of the present invention.

[0037] FIG. 4 shows a projected image in which the pattern light emitted from the light emitting portion 10 is projected onto a predetermined projection reference plane (in this embodiment, a position 400 mm in the optical axis direction from the lens surface 23 of the projection lens 22) by the pattern light projection device 1 in the first embodiment.

[0038] As described above, in the pattern light projection device 1 in the present embodiment, since the light guide portion 21 constitutes a so-called kaleidoscope partitioned by side surfaces 213A to 213D having internal reflection surfaces, the structured light of the dot pattern (in this embodiment, a 25×25 array dot pattern in the vertical and horizontal directions) incident from the light emitting portion 10 into the light guide portion 21 forms a light source image (actual light source image) directly irradiated onto the projection reference plane (not shown) by the projection lens 22 and a large number of virtual light source images formed around the actual light source image.

[0039] That is, as shown in the projected image of FIG. 4, the dot pattern projected by the pattern light projection device 1 has an actual light source image K directly projected at the center, virtual light source images K1 to K8 as primary reflection images are formed around it, secondary reflection images are formed on the outer periphery thereof, and virtual light source images as tertiary reflection images are formed on the outer periphery thereof, respectively.

[0040] Therefore, according to the pattern projection device 1 in the present embodiment, the pattern light that undergoes total internal reflection within the frustum-shaped light guide portion can have the virtual pattern light arranged in a regular two-dimensional repeating pattern on the projection surface including the object.

[0041] In addition, since the light emitting surface of the light emitting portion 10 in the present embodiment has the asymmetric region 10A, the light source image of the dot pattern guided into the light guide portion 20 from the light emitting portion 10 forms an inverted image of the non-target region at the virtual light source images K1 to K8 respectively according to the reflection paths by the respective internal reflection surfaces from the side surfaces 213A to 213D.

[0042] Furthermore, by forming the asymmetric region 10A, that is, the irregular region, in the pattern light of the dot pattern, it becomes easy to identify the projection region (position information) of the measurement object from the position information of the asymmetric region that has been previously known for the image of the projected pattern light, and it becomes possible to reduce the arithmetic processing when calculating the three-dimensional position.

[0043] FIG. 5 shows the virtual light source image on a predetermined projection reference plane in the range where d / D = 0.4 to 0.5 when the opening diameter of one end portion 211 of the light guide portion 21 is D and the opening diameter of the other end portion 212 is d. As shown in FIG. 5, when 0.425 < d / D < 0.475, the dot pattern is projected particularly clearly, and further, when d / D = 0.45, the dot pattern is projected more clearly.

[0044] FIG. 6 is a diagram showing the state of the virtual light source image on a predetermined projection reference plane when the conic coefficient (conic constant) K in the above formula (I) representing the aspherical shape on the lens surface 23 of the projection lens 22 is set to K = -0.06, -0.16, and -0.26. As shown in FIG. 6, when the conic coefficient K is -0.06 and -0.26, a not very clear dot pattern is projected. On the other hand, when the conic coefficient K is -0.16, the aberration of the projection lens 22 is appropriately corrected, and a particularly clear dot pattern is projected.

[0045] 〔Second Embodiment〕 Hereinafter, the pattern light projection device according to the second embodiment will be described with reference to the drawings. FIG. 7 shows a perspective view of the pattern light projection device according to the second embodiment, and FIG. 8 shows a cross-sectional view.

[0046] As shown in FIGS. 7 and 8, the pattern light projection device 1 according to the second embodiment includes a quadrangular frustum-shaped light guide portion 21 and a projection lens 22 optically connected to the light guide portion 21. The projection lens 22 has a reflecting surface 24 having a function as an optical prism that reflects the light beam transmitted from the light guide portion 21 in a direction perpendicular to the optical axis of the light guide portion 21. The reflecting surface 24 is preferably configured to cause total internal reflection at an air interface, but may also be a reflecting film formed with an aluminum vapor deposition film or the like. For other identical components, the same reference numerals as those of the pattern light projection device according to the first embodiment described above are given and the description thereof is omitted.

[0047] In the pattern light projection device according to the second embodiment, the light beam transmitted from the light emitting portion 10 to the light guide portion 21 is reflected by the reflecting surface 24 in a direction perpendicular to the optical axis of the light guide portion 21 and exits from the lens portion 23. Therefore, it is possible to accommodate this projection optical system even in a space with a limited thickness of a housing such as a smartphone.

[0048] According to the projection lens of the present invention, the pattern light incident into the light guide portion from one end side of the tapered quadrangular frustum-shaped light guide portion is transmitted to the other end side of the light guide portion while repeating multiple internal total reflections between the opposing surfaces of the quadrangular pyramid in the light guide portion, and a virtual pattern light distributed two-dimensionally is formed on the other end side. This two-dimensionally distributed virtual pattern light is projected onto the object to be measured by the projection lens. Therefore, a virtual pattern light with a two-dimensional distribution can be obtained with a simple configuration. In addition, in order to obtain a virtual pattern with a two-dimensional distribution by internal total reflection, it is not affected by the reduction in diffraction efficiency, which is a problem when obtaining pattern light with a two-dimensional distribution using a diffractive optical element, and it is possible to obtain a uniform intensity distribution over the entire measurement region (pattern light projection region).

[0049] [3D Measuring Device and Distance Image Acquisition Device] Hereinafter, the three-dimensional measuring device of the present invention will be described with reference to the drawings. FIG. 9 is a diagram showing an example of applying the three-dimensional measuring device of the present invention as a 3D face authentication function of a smartphone.

[0050] As shown in FIG. 9, the three-dimensional measuring device 100 of the present invention includes a pattern light projection device 300 described in the first embodiment or the second embodiment, and an image acquisition device 400 that acquires an image on a measurement object projected by the pattern projection device 300, which are respectively arranged at a predetermined interval on the upper part of the housing of the smartphone 2.

[0051] The three-dimensional measuring device 100 of the present invention projects a two-dimensional distributed pattern (dot pattern) formed by the above-described pattern light formation principle from the pattern light projection device 300 onto a measurement object including a predetermined projection reference plane, and the image acquisition device 400 acquires an image including the dot pattern reflected on the measurement object. In the three-dimensional measuring device 100 of the present invention, according to the height from a predetermined reference plane of the measurement object, that is, the shape of the measurement object, distortion occurs in the image of the dot pattern projected from the pattern light projection device. However, it is possible to measure distance information from the light source to the measurement object and three-dimensional shape information using an existing pattern matching method or the like from the amount of distortion of the image of this dot pattern.

[0052] Specifically, in a state where there is no measurement object, a pattern image of structured light at a predetermined distance from the three-dimensional measuring device is acquired as a reference image (reference). Note that the reference image may be stored in a storage device or the like in advance with an image at a desired distance. Next, the same dot pattern of structured light as at the time of acquiring the reference image is projected from the pattern light projection device onto the measurement object, and a measurement image including the dot pattern reflected on the measurement object is acquired. In this case, since the distance from the pattern light projection device to the measurement object changes according to the shape of the measurement object, the dot pattern is also distorted according to the distance to the measurement object. Then, three-dimensional information is acquired by performing a predetermined calculation on both the reference image and the measurement image.

[0053] As the pattern projection device 300 of the present invention used as a 3D face authentication function, a vertical cavity surface emitting laser (VCSEL) that emits an infrared dot pattern is preferably used. Further, as the image acquisition device 400 that acquires an image of the dot pattern projected onto the object to be measured (such as a face), an infrared camera is preferably used. When the three-dimensional estimation device 100 of the present invention is used as a 3D face authentication function, the distance to the object to be measured (face) can be appropriately selected, but is usually set to about 30 to 60 cm. Further, the number of dot patterns can be appropriately selected, but the total number of dot patterns of the light source image (actual light source image) directly irradiated onto the non-measured object by the projection lens 22 described in the first embodiment and a large number of virtual light source images around the actual light source image is preferably 30,000 or more dots.

Explanation of Signs

[0054] 1, 300 Pattern Light Projection Device 10 Light Emitting Unit 20 Projection Unit 21 Trapezoidal Prism-shaped Light Guide Unit 22 Projection Lens 23 Lens Surface 211 One End 212 The Other End 213 Side Surface 100 Three-dimensional Measurement Device 400 Image Acquisition Device

Claims

1. A pattern light projection device that projects pattern light with a two-dimensional distribution onto an object to be measured, comprising: a light emitting unit that emits pattern light of a predetermined pattern; a projection unit that projects the pattern light from the light emitting unit onto the object to be measured, wherein the projection unit is composed of a light guide unit in the shape of a frustum of a square pyramid that is defined by one end portion, the other end portion, and side surfaces, and tapers from the one end portion side toward the other end portion side; the one end portion is disposed facing the light emitting unit; pattern light incident into the light guide unit from the one end portion side propagates through the light guide unit toward the other end portion side and forms a plurality of virtual pattern lights on the other end portion side, and the pattern light with a two-dimensional distribution including the virtual pattern lights is projected onto the object to be measured.

2. When the opening diameter of one end portion of the light guide unit is D and the opening diameter of the other end portion is d, the pattern light projection device according to claim 1, wherein 0.425 < d / D < 0.

475.

3. The pattern light projection device according to claim 1 or claim 2, wherein the projection unit has a projection lens optically connected to the frustum of a square pyramid-shaped light guide unit, and the lens surface of the projection lens is an aspherical surface, and the conic coefficient k satisfies the following condition. -0.16 < k < -0.21

4. A three-dimensional measurement device comprising the pattern projection device according to claim 1 and an image acquisition device that acquires an image on the object to be measured projected by the pattern projection device.

5. The three-dimensional measurement device according to claim 4, wherein the pattern light emitted by the pattern light projection device has an asymmetric region.

6. The three-dimensional measurement device according to claim 4, wherein the pattern light emitted by the pattern light projection device is random pattern light.

7. The three-dimensional measurement device according to claim 4, wherein the pattern light emitted by the pattern light projection device is structured light.

8. A distance image acquisition device comprising the three-dimensional measurement device according to claims 4 to 7.

Images