JP2004317246A - Range finder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a range finder for measuring the accurate shape of an object. <P>SOLUTION: A parallel beam is radiated from a laser irradiation device 50 toward the object OB. The object OB is imaged by a camera C having a fixed position relation with a floodlight. When calculating the surface position of the object OB from the image imaged by the camera C, the object OB direction is determined from a camera base position P<SB>c</SB>shifted as much as the displacement V<SB>d</SB>from the reference position to the incident beam relative to each imaged image in consideration of the optical center O of the camera C and the shift quantity of the incident beam entering a lens system of the camera C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a range finder for measuring a shape of an object without contact.
[0002]
[Prior art]
In recent years, three-dimensional measurement using images has become common with the development of CCD cameras and computer image processing. As a three-dimensional measuring device using a CCD camera and computer image processing, there is a range finder. The range finder is a device that irradiates a parallel light beam such as a slit light from a light projector to a target object, images the target object with a camera, and measures the shape of the target object from the captured image. The principle is to calculate a surface position of an object based on triangulation from a positional relationship between a projector and a camera and a position of a parallel ray in a captured image (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-9-287927 (paragraph 0025, FIG. 2, etc.)
[0004]
[Problems to be solved by the invention]
By the way, in the conventional range finder, the light projector irradiates a parallel light beam from a fixed point, and measures the shape on the assumption that the light beam incident on the camera converges to one point. That is, it is assumed that the lens system of the camera is based on the pinhole camera model. In this pinhole camera model, as shown in FIG. 7, only light (incident light) incident through a base position (needle hole: pinhole H) reaches the image plane, and the three-dimensional space is A model associated with a two-dimensional space on a surface. As described above, the pinhole camera model assumes that an image is formed through an incident light beam through a single pinhole.
[0005]
However, not a pinhole camera but a camera having a lens system made of glass or the like does not converge on one point even if the incident light beam is extended. Therefore, an image captured by a camera having a lens system has non-linear distortion, and the distortion is larger in a peripheral visual field.
Therefore, in the conventional range finder, an error occurs in the position measurement result of the object by the amount of the distortion. This error also depends on the distance to the object, and the change in error due to the distance of the object is non-linear. Therefore, if the distance of the object is known, it is possible to calibrate by taking the relationship between the position measurement result and the actual position, but since the distance of the object is unknown until measured, it is completely It could not be calibrated.
[0006]
The present invention has been made in view of the above problems, and in a conventional range finder, removes a root cause of an error based on a pinhole camera model, regardless of a distance between a camera and an object. An object of the present invention is to provide a range finder capable of performing accurate shape measurement.
[0007]
[Means for Solving the Problems]
The present invention has been devised to achieve the above-mentioned object. First, the range finder according to claim 1 irradiates a parallel light beam to an object by a projector and irradiates the object by a camera. An image of an object, a range finder for measuring the shape of the object, from the positional relationship between the light emission position of the light projector and the optical center of the camera, and the irradiation position of the parallel rays in the captured image, A correction means for calculating a shift amount of an incident light beam incident on the lens system with respect to an optical center of the lens system of the camera, and correcting the shape of the object based on the shift amount is provided. .
[0008]
According to such a range finder, the correcting means calculates a shift amount of an incident light beam incident on the lens system of the camera from the optical center, and based on the shift amount, determines each measurement position, that is, the position of the object. Correcting the shape makes it possible to measure the exact shape of the object. The optical center indicates the center position of the lens system, and corresponds to the position of the pinhole in the lens system of the pinhole camera model.
[0009]
Further, the range finder according to claim 2 irradiates a parallel light beam to the object by a light projector, captures an image of the object irradiated by the parallel light beam by a camera, and emits light from the light projector and the optical center of the camera. A range finder for measuring the shape of the object from a positional relationship of the object and an irradiation position of the parallel light beam in the captured image, and image input means for inputting an image captured by the camera; and the image input means. Pixel position detecting means for detecting the pixel position of the irradiated parallel light beam in the image input in step 2, the pixel position of the image picked up by the camera, the direction of the light beam incident on the pixel, and the incident light beam from the reference position. The calibration table based on a pixel position detected by the pixel position detection unit, and a calibration table storage unit that stores a calibration table that associates the displacement amount with the calibration table. A position calculating unit that obtains the direction and displacement of the incident light beam corresponding to the pixel position with reference to the pixel position, and calculates the irradiation position using the direction and the displacement amount of the incident light beam. And
[0010]
In such a range finder, first, a target object is irradiated with a parallel light beam by a projector. The parallel light beam may be light that is irradiated without spreading from the projector, and spot light that is irradiated at one point, slit light that is a band-like light, or pattern light having a specific pattern alone may be used. Alternatively, these can be used in combination.
Then, the image input means inputs the image captured by the camera into the range finder, and the pixel position detecting means recognizes the pixel position of the emitted parallel light beam from the image. Further, the position calculating means acquires the direction and the amount of displacement of the incident light beam corresponding to the pixel position with reference to the calibration table, and utilizes the direction of the incident light beam and the amount of displacement from the reference position to irradiate the irradiation position, that is, the target position. Calculate the surface position of an object.
Therefore, the shape of the target object can be measured based on the accurate direction of the incident light beam entering the lens, so that the shape of the target object can be accurately measured.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
First, we explain the non-pinhole property of a camera, which is generally called a pinhole camera model, where incident light does not intersect at one point, which causes image distortion, and quantifies the characteristics of the camera with the non-pinhole property The calibration data obtained will be described. Then, a method of generating a calibration table by measuring calibration data for each imaging pixel of the camera will be described, and a range finder having this calibration table will be described sequentially.
[0012]
[About non-pinhole properties of camera]
First, with reference to FIG. 8, a description will be given of the cause of the occurrence of distortion in an image captured by a camera having a lens system. FIG. 8 is a schematic diagram of a camera having a lens system. Here, for the sake of simplicity, it is assumed that the lens system is a sheet glass G, and the aperture F generates a pinhole H. The incident light beam r1 vertically incident on the plate glass G of the camera C passes through the pinhole H and is captured by the pixel R1 on the imaging surface I. The incident light beams r2 and r3 obliquely incident on the glass sheet G are refracted in the glass sheet G and then imaged on the pixels R2 and R3 on the imaging plane I through the pinhole H.
[0013]
However, this camera C does not intersect at one point r2 ′ and r3 ′, which are extensions of the incident light beams r2 and r3 before passing through the glass sheet G, at one point. It turns out that it has not become. Therefore, the pixel R3 on the imaging surface I captures an incident light r3 that is shifted by the distance D from the incident light rr assumed in the pinhole camera model.
[0014]
As described above, a camera that captures an image with an incident light beam that is incident on a lens system (here, the glass sheet G) has a pinhole property (non-pinhole property). Hereinafter, a camera having a lens system is referred to as a “non-pinhole camera”.
[0015]
[Calibration data]
Next, calibration data obtained by digitizing the characteristics of the non-pinhole camera will be described with reference to FIG. FIG. 9 is an explanatory diagram for explaining the contents of the calibration data. As shown in FIG. 9, the incident light beam R incident on the lens 1 can be specified at two points. Here, when the light emitted from the first light source position P1 and the light emitted from the second light source position P2 are imaged on the same pixel (not shown), the incident light R is changed to the incident light corresponding to the pixel. Is specified.
[0016]
Here, the point at which the sum of the squares of the distances to all the incident rays is the minimum is defined as the optical center O, and the point at which the distance between the incident ray R and the optical center O corresponding to each imaging pixel is the minimum is defined as the optical center O. It is defined as the incident light base point K of the incident light R.
[0017]
That is, the optical center O (x ₀ , y ₀ , z ₀ ) is the light source position P 1 (x ₁ , y ₁ , z ₁ ) and the light source position P ₂ (x ₂ , y ₂ , z ₂ ) for all incident light beams. The position at which the sum of the squares of the distance d from the incident light R (formula (1)) is minimum is the position obtained by the least squares method.
[0018]
d ² = − (A ² / B) + C (1)
[0019]
However,
A = (x ₂ −x ₁ ) (x ₁ −x ₀ ) + (y ₂ −y ₁ ) (y ₁ −y ₀ ) + (z ₂ −z ₁ ) (z ₁ −z ₀ )
B = (x ₂ −x ₁ ) ² + (y ₂ −y ₁ ) ² + (z ₂ −z ₁ ) ²
C = (x ₁ −x ₀ ) ² + (y ₁ −y ₀ ) ² + (z ₁ −z ₀ ) ²
And
[0020]
Thereby, the direction of the incident light beam (the direction specified by the light source positions P1 and P2), the displacement amount from the optical center O to the incident light base point K (expressed by the three-dimensional vector V _D (dx, dy, dz)) The characteristics of the non-pinhole camera can be quantified by making the data associated with the calibration data the calibration data.
[0021]
Note that the calibration data is not limited to this. For example, in the above described example, the optical center O as a reference position, but the vector from the optical center O to the perpendicular foot dropping off the incident light is a displacement V _D, the reference position is not limited to the optical center, the camera Any point may be used as long as it is a fixed point that has a fixed relationship with. The displacement V _D may be any vector directed to any point on the incident light from the reference position is not limited to the vector directed to a foot of the perpendicular line which down to incident light from the reference position.
[0022]
[Method of generating calibration table]
Next, a method of generating a calibration table in which calibration data obtained by quantifying characteristics of a non-pinhole camera is associated with each photographed pixel (corresponding to a projected pixel) of the camera will be described with reference to FIG. FIG. 10 is a conceptual diagram illustrating the principle of a method for generating a calibration table. FIG. 10A is a conceptual diagram illustrating the principle of measuring calibration data by changing the pan and tilt of a camera with respect to a specific incident light beam, and FIG. FIG. 7 is a conceptual diagram showing a principle of measuring calibration data by changing an incident light beam with respect to a camera that has been made.
[0023]
As shown in FIG. 10A, in order to generate a calibration table in which calibration data is associated with each photographing pixel, the light source position is set in one direction of P1 and P2 with respect to the camera C having the non-pinhole property. The camera is moved (one-axis movement) to determine the incident light beam R specified by the light source positions P1 and P2, and the camera is set so that the lights emitted from the light source positions P1 and P2 are both incident on the imaging pixels to be measured. By adjusting the pan and tilt of C (two-axis rotation), the direction of the incident light R incident on each imaging pixel of the camera C is specified.
[0024]
Further, as shown in FIG. 10B, the camera C is fixed, and the light source positions P1 and P2 are set so that the incident light rays R emitted at the two light source positions P1 and P2 are incident on the measurement pixels. May be moved in the XYZ directions (three-axis movement) to specify the direction of the incident light beam R defined by two points of the light source positions P1 and P2 incident on the measurement pixel.
[0025]
10A or 10B, the direction of the incident light R and the incident light base point K from the optical center O on the basis of the incident light R specified for each of the imaging pixels for which the measurement was performed (see FIG. 9). The calibration table can be generated by associating the amount of displacement with respect to each of the imaging pixels (projection pixels) as calibration data.
[0026]
[Configuration of Range Finder]
Next, the range finder will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a range finder according to an embodiment of the present invention. The range finder 1 shown in FIG. 1 captures light (parallel rays) irradiated on the object OB by the laser irradiation device 50 with the camera C, and detects the three-dimensional position of the object OB from the obtained image. Is what you do. Then, the shape of the object OB is measured by shaking the direction of the light beam of the laser irradiation device 50 up and down, left and right, and measuring three-dimensional positions at many points.
Here, the range finder 1 includes a laser irradiation device (light emitter) 50, a camera C, an image input unit 10, a pixel position detection unit 20, a calibration table storage unit 30, and a position calculation unit 40. did.
[0027]
As shown in the block diagram of FIG. 2, the laser irradiation device 50 includes a laser emitting unit 51 that emits a laser beam, and a condensing lens 52 that condenses the laser beam emitted from the laser emitting unit 51 into a narrow beam. And a diffraction grating 53 for dividing the laser light condensed by the condenser lens 52 into a plurality of beams. The diffraction grating 53 separates the beam in a direction perpendicular to the plane of the drawing.
Further, a beam diffusion lens 54 for diffusing the split beam in one direction to generate slit light is provided downstream of the diffraction grating. The beam diffusion lens 54 is configured by a cylindrical lens or the like. Each of the plurality of beams is diffused by the beam diffusion lens 54 at an angle of 60 °.
FIG. 3 illustrates the state of irradiation of the laser beam. As shown in FIG. 3, the laser light LB emitted from the laser irradiation device 50 is diffused in a conical shape, forms a quadratic curve locus RL on the plane PL, and is reflected and scattered. This reflection / scattering indicates the irradiation position referred to in the claims. The laser beam LB is divided into five beams (laser beam LB) by the diffraction grating 53, and the five beams are diffused by 60 ° by the beam diffusion lens 54. These laser beam LB is emitted as radiating from different origin O _L in each beam which is divided into five.
In FIG. 3, the number of beams is set to “5” for easy viewing, but in practice, the laser light is divided at smaller intervals. For example, the angle B shown in FIG. 3 is 32 °, and the angle C between adjacent laser beams is 1.6 °. That is, the number of beams is “21”.
[0028]
The laser irradiation device 50 is not limited to the one that diffracts and diffuses by a lens system, but mechanically rotates a laser beam that emits a single spot light in an upward direction (x direction) and a lateral direction (y direction). You may. In this case, if the rotation mechanism is configured so that the laser light is emitted radially from one point, the position of the target object can be easily calculated.
[0029]
The image input means 10 is for inputting an image of the object OB captured by the camera C. The input image is input as a color image or a multi-tone black and white image. The image input means 10 includes a memory (not shown) for temporarily storing each image captured by the camera C. The image stored in this memory is stored in a pixel position detecting means 20 described later. Shall be referred to.
[0030]
The pixel position detecting means 20 detects the irradiation position of the laser beam in the image input by the image input means 10 and specifies the pixel position. Specifically, a pixel having a peak brightness is detected by looking at the brightness distribution on the image. The pixel position of each image detected here is input to the position calculating means 40.
[0031]
The calibration table storage unit 30 is a general storage medium such as a hard disk, and stores a calibration table 31 in which calibration data is associated with each imaging pixel of the camera C. For example, as shown in FIG. 4, the calibration table 31 stores a displacement amount V _D (dx, dx, _d) from the optical center O as information for specifying a ray incident on the pixel for a combination of the x coordinate and the y coordinate of the pixel. dy, dz) and angles α, β are stored in association with each other. As shown in FIG. 5, the angle alpha, beta is the origin O _L in which the laser beam LB of the laser irradiation apparatus 50 is irradiated as the origin of the coordinate axes, X-axis relative to the orientation of the laser irradiation device 50, Y-axis, Z An axis is set, and the angle of the incident light with respect to the XZ plane in FIG. 5 is α, and the angle of the incident light with respect to the XY plane in FIG. 5 is β.
[0032]
The position calculating unit 40 determines the position of the control object OB based on the calibration data (the direction of the incident light beam and the amount of displacement V _D ) of the calibration table 30 corresponding to the pixel position of each image detected by the pixel position detecting unit 20. The position (three-dimensional position) is calculated.
[0033]
[Operation of range finder]
Next, the operation of the range finder 1 will be described with reference to FIGS. FIG. 6 is a flowchart showing the operation of the range finder 1.
First, the range finder 1 irradiates the object OB with the laser beam LB (step S1), and captures an image of the object OB with the camera C (step S2). Then, the captured image is input by the image input means 10 (step S3).
Next, the range finder 1 detects the peak of the brightness by the pixel position detection unit 20 in each image input by the image input unit 10, and outputs the pixel corresponding to the irradiation position of the laser beam LB on the object OB. The position is detected (step S4).
[0034]
Then, the range finder 1 obtains the calibration data corresponding to the pixel position by the position calculating means 40 with reference to the calibration table 31 (step S5), and based on the calibration data, the camera base position P _C (Cx, Cy, Cz) is calculated (step S6). As shown in FIG. 5, the camera base point position is a position serving as a base point for extending a vector in the line-of-sight direction from the camera C. In the coordinate system of FIG. 5, the coordinates of the optical center O of the camera C, O (Ox, Oy, Oz) and when the camera base position _{P C (Cx, Cy, Cz} ) is
Cx = Ox + dx
Cy = Oy + dy
Cz = Oz + dz
Is represented by In the present embodiment, the calibration table 31 associates the pixel positions with dx, dy, and dz, and Cx, Cy, and Cz are separately calculated, but the calibration table 31 includes the pixel positions and Cx , Cy, and Cz may be stored in association with each other. In that case, the reference position is referred to in the claims, the coordinate system of the origin of the 5, i.e., the origin O _L in which the laser beam LB is irradiated.
[0035]
Then, the irradiation position is calculated based on the camera base position P _C (Cx, Cy, Cz), the angles α and β obtained from the calibration table 31, and the angles ω and φ specifying the direction of the laser beam. Note that, when the distance to the object to be measured is limited in advance, only a predetermined laser beam exists within a certain range on the image, so that the laser beam can be determined from the pixel position. The angle can also be determined. When the laser irradiation device is configured to mechanically shake the spot light, the direction in which the spot light is directed is measured mechanically or electrically, and the angle ω and the angle θ are synchronized with the image. What is necessary is just to take in by the position calculation means 40, and to use for calculation.
[0036]
The calculation of the position is performed, for example, as follows.
Figure as in 5, the irradiation position from the origin OL laser beam _{BL P 0 (X, Y,} Z) the distance to r, the camera C camera base point _{P C} from the irradiation position _{P 0 (X, Y, Z} ) Let R be the distance to.
Therefore, the irradiation position P ₀ (X, Y, Z) is geometrically expressed by the following formulas (2) to (4) where X = rcos ω in relation to the direction vector of the laser beam BL and the distance r. 2)
Y = rsinω (3)
Z = −rcosωsinω (4)
In the relationship between the line-of-sight direction vector and the distance R, the following expressions (5) to (7) are used: X = Rcosαcosβ + Cx (5)
Y = Rsinαcosβ + Cy (6)
Z = −Rsinβ + Cz (7)
There is a relationship.
When r and R are obtained from these equations (2) to (7),
(0 ≦ Cy and 0 ≦ ω) or (Cy <0 and ω <0) R = (− B + (B ² -4AC)) / 2A
R = -Cy / sinαcosβ when ω = 0
When (0 ≦ Cy and ω <0) or (Cy <0 and 0 ≦ ω), R = (− B−√ (B ² -4AC)) / 2A
When ω = 0, r = (Rsinαcosβ + Cy) / sinω
However,
^{A = cos 2 αcos 2 β +} sin 2 β - cos 2 ωsin 2 αcos 2 β / sin 2 ω
B = cosαcosβ Cx - sinβ Cz - cos 2 ωsinαcosβ Cy / sin 2 ω
C = Cx ² + Cz ² −cos ² ω Cy ² / sin ² ω
It becomes.
[0037]
In this way, the range finder 1 can correct the non-pinhole property of the camera C and accurately detect the irradiation position. Then, if the three-dimensional position is calculated for all the irradiation positions of the laser beam LB, the three-dimensional shape of the object OB can be measured.
The range finder 1 can be used by being incorporated in a mobile robot, an automobile, or the like. For example, when the present invention is applied to a mobile robot and the mobile robot detects the shape of the floor, the unevenness of the floor can be accurately recognized, and the mobile robot can stably walk.
[0038]
【The invention's effect】
As described above, according to the range finder according to the present invention, in consideration of the non-pinhole property of the camera, the shift between the optical center and the light actually incident on the lens system of the camera is corrected, and the accurate position of the object is corrected. Position and shape can be measured.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a range finder according to an embodiment.
FIG. 2 is a block diagram of a laser irradiation device.
FIG. 3 is a perspective view showing a laser irradiation state.
FIG. 4 is a diagram illustrating an example of a calibration table.
FIG. 5 is a diagram illustrating a method of calculating an irradiation position.
FIG. 6 is a flowchart illustrating an operation of the range finder according to the embodiment.
FIG. 7 is a diagram illustrating the concept of a pinhole camera model.
FIG. 8 is a schematic view of a camera having a lens system.
FIG. 9 is a diagram illustrating the contents of calibration data.
FIG. 10 is a diagram illustrating a method for generating calibration data.
[Explanation of symbols]
1 Range finder 10 Image input means 20 Pixel position detecting means 30 Calibration table storage means 31 Calibration table 40 Position calculating means 50 Laser irradiation device C Camera

Claims (2)

The projector irradiates the object with parallel rays, captures an image of the object illuminated by the camera, and positions the light emitting position of the projector and the optical center of the camera, and the parallelism in the captured image. From the irradiation position of the light beam, a range finder for measuring the shape of the object,
A correction means for calculating a shift amount of an incident light beam incident on the lens system with respect to an optical center of the lens system of the camera, and correcting a shape of the object based on the shift amount is provided. Range finder. The projector emits a parallel light beam to the object, and the camera captures an image of the object irradiated with the parallel light beam.The positional relationship between the light emission position of the light projector and the optical center of the camera, and the parallelism in the captured image. From the irradiation position of the light beam, a range finder for measuring the shape of the object,
Image input means for inputting an image captured by the camera,
In an image input by the image input unit, a pixel position detection unit that detects a pixel position of the irradiated parallel light beam,
Pixel position of the image captured by the camera, a calibration table storage means that stores a calibration table that correlates the direction of the incident light beam to the pixel and the displacement amount from the reference position to the incident light beam,
Based on the pixel position detected by the pixel position detection means, referring to the calibration table, obtain the direction and displacement of the incident light corresponding to the pixel position, and use the direction and displacement of the incident light. And a position calculating means for calculating the irradiation position.

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