JP2000161935A - Method and instrument for measuring three-dimensional coordinates for slit light projection type three- dimensional visual sensor and recording medium with three-dimensional coordinate measuring program recorded therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional coordinate measuring method with which the rotation axis of slit light can be positioned to an arbitrary position. SOLUTION: After a camera 6 is calibrated by considering that slit light is a plane rotating around an arbitrary axis, the equation on standard slit light planes P0-P2, rotation axis, and an arbitrary slit light plane around the rotation axis is found by measuring three or more slit light rays P0-P2 projected upon calibration target planes X1 and X2 by using the camera 6. Therefore, the three- dimensional coordinates photographed with a camera can be found easily, without having to use precise jig machining, parts machining, nor to conduct accurate mechanical positioning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional coordinate measuring method for three-dimensionally measuring an object using slit light.

[0002]

2. Description of the Related Art A slit light projection type three-dimensional coordinate measuring method for measuring the shape and position of an object in a three-dimensional space using a slit light and a video camera is known as a robot visual sensor or a non-contact shape measuring device. Has been applied to Conventionally, in this type of three-dimensional coordinate measurement method, in order to simplify a coordinate calculation formula, a constraint condition is given to an arrangement of a measurement system such as a positional relationship between a slit light for irradiating an object and a camera. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 7-270137 (scanning with a mirror of spot light, if one direction is fixed, slit light can be regarded as slit light), a plane passing through the center of the camera lens and perpendicular to the imaging surface is assumed. The constraint is that the plane is perpendicular to the slit light plane, and that when the slit light is rotated, the rotation axis must include the slit light plane.

[0003]

However, in the conventional slit light projection type three-dimensional coordinate measuring method, a plane which passes through the center of the camera lens and is perpendicular to the imaging plane is physically obtained in order to keep the above-mentioned constraints. It is necessary to accurately perform mechanical positioning, such as adjusting the slit light plane to the rotation axis or accurately adjusting the rotation axis. Therefore, there is a problem that an error occurs in measurement data because a precise jig or component processing is required or mechanical positioning is difficult.

Accordingly, the present invention has been made in view of the above problems, and has as its object to eliminate the need for precise jigs and parts processing, and to accurately perform mechanical positioning of a camera and slit light. It is an object of the present invention to provide a method for measuring three-dimensional coordinates in which accurate measurement data can be obtained without performing the above operation.

[0005]

According to the first aspect of the present invention,
An image of the object irradiated with the slit light is captured on a camera image plane, and position coordinates of a point on the object corresponding to the reflected light point are obtained from the camera image plane coordinates of the light reflected by the slit light on the image of the object In the slit light projection type three-dimensional coordinate measuring method of calculating the angle using a calculation formula, a camera calibration step of calibrating a camera in advance, and three or more different angles based on the calibration data of the calibration step. A step of obtaining three or more equations of a rotated slit light plane; a step of obtaining an equation of a rotation axis from the equations of the three or more slit light planes; and an arbitrary step of rotating an arbitrary angle around the rotation axis. Obtaining the equation of the slit light plane.

In this method, a slit light is considered as a plane rotating around an arbitrary axis, and after calibrating a camera, different light projected on two or more different calibration target planes using the camera is used. 3
By measuring more than one slit light, a reference slit light plane and a rotation axis are obtained. Once the rotation axis is determined,
The equation of the slit light plane rotated by an arbitrary angle rotating around the rotation axis is calculated. When the equation of the slit light plane rotated by an arbitrary angle is determined, the three-dimensional coordinates of an arbitrary point on the slit light taken by the camera are obtained as the intersection of the straight line between the slit light plane and the line of sight in the three-dimensional space. Can be

As described above, by calibrating the slit light using the camera and the calibration target, even if the slit light projector is arranged at an arbitrary position, any point on the slit light photographed by the camera can be obtained. Since the three-dimensional coordinates can be easily obtained, it is not necessary to mechanically align the rotation axis of the slit light with the slit light plane or the center of the camera as in the related art.

[0008] Thus, accurate measurement data can be obtained even if the precision of machining or assembling of each part is low without requiring precise jigs and parts processing. Further, even when the position of the camera or the slit light projector is shifted due to an impact or the like, the measurement can be performed with the same accuracy as before the position shift without returning to the original position by performing the above calibration.

According to a second aspect of the present invention, an image of the object irradiated with the slit light is captured on a camera image plane, and the reflected light is obtained from the camera image plane coordinates of the light reflected by the slit light on the image of the object. In a slit light projection type three-dimensional coordinate measuring apparatus for calculating a position coordinate of a point on an object corresponding to a point using a calculation formula, camera calibration means for calibrating a camera in advance, and calibration data of the calibration means A slit light plane calculating means for obtaining three or more equations of a slit light plane rotated by three or more different angles based on
A rotation axis calculation means for obtaining an equation of a rotation axis from an equation of one or more slit light planes, and an arbitrary slit light plane calculation means for obtaining an equation of an arbitrary slit light plane when rotated by an arbitrary angle around the rotation axis; It is characterized by having. This eliminates the need for precise jigs and parts processing, and allows accurate measurement data to be obtained even when the machining and assembly precision of each part is low. Further, even when the position of the camera or the slit light projector is shifted due to an impact or the like, the measurement can be performed with the same accuracy as before the position shift without returning to the original position by performing the above calibration.

According to a third aspect of the present invention, an image of the object irradiated with the slit light is captured on a camera image plane, and the reflected light is obtained from the camera image plane coordinates of the point of the light reflected by the slit light on the image of the object. A recording medium storing a slit light projection type three-dimensional coordinate measurement program for calculating a position coordinate of a point on an object corresponding to the point using a calculation formula, wherein the program causes the camera to calibrate in advance, Based on the data, three or more equations of the slit light plane rotated by three or more different angles are obtained, and the equation of the rotation axis is obtained from the three or more equations of the slit light plane. It is characterized in that an equation of an arbitrary slit light plane when it is rotated around by an arbitrary angle is obtained. This eliminates the need for precise jigs and parts processing, and allows accurate measurement data to be obtained even when the machining and assembly precision of each part is low. Further, even when the position of the camera or the slit light projector is shifted due to an impact or the like, the measurement can be performed with the same accuracy as before the position shift without returning to the original position by performing the above calibration.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Slit light projection type three-dimensional coordinate measuring device according to the present embodiment (hereinafter, “three-dimensional coordinate measuring device”)
That. 1) a three-dimensional visual sensor head mechanism 5, a three-dimensional coordinate measurement control panel 14 connected to the three-dimensional visual sensor head mechanism 5, and a calibration target plane of the positions of X1 and X2, as shown in FIG. 3 and 4 to measure the position coordinates of a point on the object three-dimensionally.

The three-dimensional visual sensor head mechanism 5 includes a slit light projector 7 for irradiating a slit light composed of a band-shaped laser light while diffusing it on a horizontal plane, a stepping motor 9 for changing the slit light projector 7 to an arbitrary angle, X1
And a camera 6 for imaging the slit light projected on the calibration target planes 3 and 4 at the position of X2.

The above-mentioned camera 6 has a lens and an imaging member, and the imaging member has an imaging surface on which slit light is projected via the lens. On this imaging surface, an image is projected on the left and right objects with the lens center as the center.

The above-mentioned imaging member has a plurality of light-receiving elements (pixels) for generating electric charges corresponding to the amount of light in a matrix in the x direction and the y direction. As shown in FIG. It is connected to the control panel 14. This imaging member reads out the electric charge of the light receiving element unit as a voltage output in, for example, a raster scan format and outputs it to the three-dimensional coordinate measurement control panel 14 as coordinate data such as calibration target coordinate data.

As shown in FIG. 2, the calibration target planes 3 and 4 at the positions X1 and X2 are mounted on the slide table 2 at right angles to the slide direction. As shown in FIG. 3, a mark 17 serving as a reference for obtaining a position (coordinate) on the camera image plane captured by the camera 6 is drawn on the surfaces of the planes 3 and 4 on the camera 6 side. For example, if this mark (hereinafter, referred to as “calibration target”) 17 is drawn as a black circle, the three-dimensional coordinate measuring device 1 performs the binarization processing of the camera image and the calculation of the center of gravity of the black area. The position (coordinate) on the image can be easily obtained.

The above-described three-dimensional coordinate measurement control panel 14 is shown in FIG.
As shown in FIG. 1, I / O units 10a and 10b connected to an imaging member, a slit light projector 7, and the like, and these I / O units 1
An arithmetic unit 11, a RAM 12, a ROM 13, and a motor driving unit 16 are connected to 0 a and 10 b via a signal bus 15. The ROM 13 stores a slit light plane equation calculation routine 13a. The slit light plane equation calculation routine 13a
Is to be executed.

The RAM 12 includes a camera calibration target storage area 12a, a camera parameter storage area 12b, a coordinate value storage area 12c, a slit light plane equation storage area 12d, and a rotation axis equation storage area 12e. , An arbitrary slit light plane equation storage area 12f. As shown in FIG. 4, the camera calibration target storage area 12a stores calibration target coordinate data obtained by calculating the calibration target 17 of the camera 6 in the world coordinate system. Further, the camera parameters calculated from the calibration target coordinate data are stored in the camera parameter storage area 12b. Further, in the coordinate value storage area 12c, as shown in FIG. 6, two arbitrarily determined points on a straight line on the X1 plane 3 and one arbitrarily determined point on a straight line on the X2 plane 4 are stored. , Coordinate data in a three-dimensional space calculated using camera parameters. The slit light plane equation storage area 12d stores the slit light plane equation calculated from the coordinate data. Furthermore, the rotation axis equation storage area 12e stores the rotation axis equation calculated from the slit light plane equation. In addition, an equation for an arbitrary slit light plane that rotates around a rotation axis is stored in an arbitrary slit light plane equation storage area 12f.

A three-dimensional coordinate measuring device 1 according to the present embodiment
As shown in FIG. 10, the equation of the slit light plane rotated by an arbitrary angle is obtained by the slit light plane equation calculation routine 13 a, and from the intersection of the plane equation and the line of sight (straight line) of the camera 6, The three-dimensional coordinates of an arbitrary point on the slit light are measured.

In the above configuration, the operation of the three-dimensional coordinate measuring device 1 will be described with reference to the drawings. As shown in FIG. 11, the camera 6 is calibrated (S
1). That is, as shown in FIG. 4, camera parameters are calculated by a calibration method using a pinhole camera model. The position of the calibration target (black circle) 17 of the camera 6 in the world coordinate system is X
The coordinates are determined by the distance of the slide table 2 from the origin, and Y,
The Z coordinate is determined as a coordinate having a reference point on the planes 3 and 4 (a fixed point on the planes 3 and 4) as an origin. Specifically, as shown in FIG. 4, the plane 3 is set at the position X1 on the slide table 2, and the plane 4 is set at the position X2.
Then, four black circles are positioned on the planes 3 and 4 (Y1, Z
1), (Y2, Z2), (Y3, Z3), (Y4, Z
It is drawn in 4).

In this case, eight calibration targets (black circles) 17 are arranged in the three-dimensional space, and their coordinates P1 to P8 are (X1, Y1, Z1),
(X1, Y2, Z2), (X1, Y3, Z3), (X
1, Y4, Z4), (X2, Y1, Z1), (X2, Y
2, Z2), (X2, Y3, Z3), (X2, Y4, Z
4). These calibration targets (black circles) 17 are imaged by the camera 6 and output to the I / O unit 10a as calibration target coordinate data. When the I / O unit 10a receives the calibration target coordinate data, the positions Q1 to Q8 on the image are obtained by the three-dimensional coordinate measurement control panel 14, respectively.
, Q1 to Q8 are (x1, y1), (x
2, y2) (x8, y8).

The camera parameters are calculated by the three-dimensional coordinate measurement control panel 14 from the eight sets of these coordinate data. As described above, the camera parameters are obtained by calculating the three-dimensional coordinates of arbitrary points on the known planes X1 and X2 by one.
This is because it can be obtained from the camera images of the cameras 6. That is, the positions P1 to P8 in the world coordinate system of an arbitrary point on a plane whose X coordinate is known can be calculated by the position coordinates Q1 to Q8 in the image coordinate system obtained from the camera image.

Note that the position of the calibration target (black circle) 17 in the world coordinate system on the planes 3 and 4 is measured in advance. In the three-dimensional coordinate measuring apparatus 1 according to the present embodiment, a case where eight points are used as an example has been described.
Therefore, it is sufficient that six or more points that are not on the same plane exist independently in the three-dimensional space. In general, when the number of calibration targets 17 is large, the accuracy of coordinate data in a three-dimensional space can be improved by using the least squares method when obtaining camera parameters.

Next, as shown in FIG. 11, an equation (angle θ = θ ₀ ) of one reference slit light plane P _{0 which} is a reference of the slit light rotating around the axis is calculated by the following procedure. (S2). As shown in FIG. 6, the slit light projector 7
Is fixed, and is set as a reference angle θ ₀ . When the calibration target plane 3 is placed at the position X1, an output signal is output to the slit light projector 7 via the I / O unit 10a so that the slit light projector 7 emits slit light. When the slit light applied to the calibration target plane 3 is captured by the camera,
This slit light becomes a straight line on the image plane. This straight line (hereinafter, referred to as a “slit light straight line”) is an X1 plane 3
That the line of intersection of the slit light plane P _0. Next, as shown in FIGS. 6 and 7 (b), two arbitrary points on the slit light straight line are determined to be Qa (ya, xa) and Qb (yb, xb). Then, the coordinate value Q on the image plane of the slit light image
The coordinate data (Xa, Ya, Za) and (Xb, Yb, Zb) in the three-dimensional space are calculated using a, Qb, camera parameters, and the equation of the calibration target plane 3, and the coordinate value storage area 12c. Note that X
a and Xb are equal to X1.

Next, as shown in FIG. 7, the calibration target plane 4 is placed at the position of X2, and an arbitrary point on the slit light straight line of the image is set in the same manner as the calibration target plane 3 at the position of X1. Decision Qc (yc, x
c), and the coordinate data (Xc, Y
c, Zc) is calculated. This coordinate data of a three-dimensional space of three points of the reference slit light plane P ₀ (Xa, Y
a, Za), (Xb, Yb, Zb) (Xc, Yc, Z
c) is required. These three points, determine the equation of the reference slit light plane P ₀ in the three-dimensional space, it is stored in the equation storage area 12d of the plane.

Although the method of obtaining the equation of the reference slit light plane P ₀ from the three points Qa, Qb and Qc has been described, the number of points arbitrarily determined on the slit light straight line may be increased or the position of the calibration target 17 may be increased. May be increased to increase the number of points in the slit light plane to three or more. In this case, the equation of the plane is obtained by the least square, so
Measurement errors can be reduced.

The above-mentioned reference slit light plane P₀Is any
Slit light plane P that rotates by an angle _iOf rotation θ_iBase
The reference slit light plane, for example,
Litt light plane P₀Is the angle θ = θ₀When the plane is
θ₁The rotation angle of the slit light plane rotated by θ is θ₀−θ
₁Can be expressed as The reference slit light plane P₀Is particularly specific
It is not necessary to set the angle, it can be set to any angle
Should be done, but it differs between calibration and measurement
It must not be.

Next, as shown in FIG. 11, the equation of the slit light plane P ₁ in which the angle of the slit light projector 7 is shifted by a certain angle θ ₁ is calculated by the following procedure (S 3). From the reference slit light plane P ₀ , the slit light
_A drive signal is output to the stepping motor 9 via the motor drive unit 16 so as to rotate by _one . Upon receiving the drive signal, the stepping motor 9 rotates the slit light projector 7 by the angle θ ₁ . The equation (angle θ = θ ₁ ) of the slit light plane P _{1 is the same as} the equation of the reference slit light plane P ₀ , and the slit light is used to calibrate two X1 and X2 having different positions in the x direction. After being projected from the camera target planes 3 and 4 and calculated from the camera images captured by the camera 6, they are stored in the plane equation storage area 12 d.

Next, the angle of the slit light projector 7 is set to a certain angle.
Degree θ_TwoSlit light plane P shifted_TwoThe equation is
(S4). Reference slit light plane P₀
The slit light projector 7 from the angle θ_TwoJust rotate
The drive signal is stepped through the motor drive unit 16
Output to the motor 9. When the drive signal is received, the step
The ping motor 9 sets the slit light projector 7 to the angle θ._TwoOnly
Rotate. And the slit light plane P_TwoEquation (angle
Degree θ = θ_Two) Is the reference slit light plane P₀Field of equations
As in the case, two slit light beams with different positions in the x direction
X1 and X2 calibration target plane 3,
4 and calculated from the image captured by the camera 6.
After that, it is stored in the equation storage area of the plane. In addition, these
Angle θ ₁, Θ_TwoIs the reference slit light plane P₀From 0
It is sufficient to rotate only two angles. Also, its absolute
The logarithmic value is not necessary for calculation when determining the rotation axis. However
And the angle θ₁, Θ_TwoIs too small, find the axis of rotation
Accuracy becomes worse.

The three slit light planes P₀, P₁, P_Twoof
Once the equations have been obtained, these three
Slit light plane P₀, P₁, P_TwoAny two pickpockets from
The slit light plane, for example, as shown in FIGS.
G light plane P₀And slit light plane P₁Bisecting plane P of₀₁Is calculated
It is issued (S5). Bisection plane P₀₁Is calculated, another
Two planes, for example, slit light plane P₁And slit light
Plane P_TwoBisecting plane P of ₁₂Is calculated (S6). Bisecting
Plane P₀₁, P₁₂Is calculated, the bisecting plane P₀₁And bisecting plane
P₁₂The equation of the intersection (rotation axis) 18 of
Is stored in the equation storage area 12e (S7).

A plurality of rotation axes 18 can be obtained by a combination of the slit light plane and a combination of the bisectors, and the rotation axis 18 closest to the actual rotation axis 18 is selected. Further, since a point on the rotation axis 18 always has a constant distance from any slit light plane, there is also a method of directly obtaining the equation of the rotation axis. In this case, if the number of shift angles is increased and the slit light plane is increased, the equation of the rotation axis can be obtained with high accuracy by the least square method.

[0031] When the rotating shaft 18 is determined, that equation of the slit light plane P _i rotated any angle about an axis of rotation 18 is calculated (S8). The method of calculating the equation of the slit light plane P _i rotated by an arbitrary angle is based on the reference slit light plane P
_{When 0} is rotated by θ with respect to the rotation axis and the angle becomes θx (θ ₀ −θx = θ), the following is performed. First, the rotation axis 18 and the slit light plane are translated so that the rotation axis 18 passes through the origin. After that, the slit light plane is rotated by θ with respect to the rotation axis 18. Finally, the rotation axis 18 and the slit light plane are translated so that the rotation axis 18 passes through the original point. The equation of the slit light plane P _i rotated an arbitrary angle is determined by calculation. Here, the rotation amount θ _i
Shall obtain its absolute value. The detection of the rotation angle is performed based on, for example, the number of steps of a stepping motor attached to the rotation shaft, the number of pulses of an encoder, and the like.

[0032] By calibrating the slit light plane as described above, since the equation of the slit light plane P _i rotated any angle can be calculated, for any point on the imaged slit light plane by the camera 6 coordinate data of a three-dimensional space is obtained as the intersection 19 in a 3-dimensional space with any of the slit light plane P _i and the straight line 20 of the camera's line of sight.

In the present embodiment, a program for causing the arithmetic unit 11 to execute the slit light plane equation calculation routine 13a is stored in the ROM 13 in advance. However, the present invention is not limited to this. ,
It may be recorded on a recording medium such as an optical disk.

That is, the above-described program may be executed by using these recording media. In this case, if the camera 6 and the slit light projector 7 can be connected to an information processing device such as a personal computer instead of the three-dimensional coordinate measurement control panel 14, by reading the above program from a recording medium, Since the information processing apparatus such as a personal computer can execute the slit light plane equation calculation routine 13a, the camera 6 and the slit light projector 7 can be calibrated.

The invention according to any one of claims 1 to 3 performs the calibration of slit light using a camera and a calibration target,
This eliminates the need for precise jigs and parts processing, and provides an effect that accurate measurement data can be obtained even when the machining and assembly precision of each part is low. Further, even when the position of the camera or the slit light projector is shifted due to an impact or the like, it is possible to perform the measurement with the same accuracy as before the position shift without returning to the original position by performing the above calibration.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a three-dimensional coordinate measurement control panel.

FIG. 2 is a side view of the three-dimensional measuring device.

FIG. 3 is a front view of the three-dimensional measuring device.

FIG. 4 is a diagram illustrating camera calibration.

FIG. 5 is a diagram illustrating target images at positions X1 and X2.

FIG. 6 is a diagram illustrating a method for obtaining a slit light plane.

FIG. 7 is a diagram illustrating a slit light image.

FIG. 8 is a diagram for explaining a method of obtaining a rotation axis.

FIG. 9 is an enlarged view in a circle of FIG. 8;

FIG. 10 is a diagram illustrating a slit light plane and a line of sight of a camera.

FIG. 11 is a flowchart for obtaining an equation of a slit light plane rotated by an arbitrary angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 3D coordinate measuring device 2 Slide base 3 X1 calibration target plane 4 X2 calibration target plane 5 3D visual sensor head mechanism 6 Camera 7 Slit light projector 8 Slit light 9 Stepping motor 10 I / O section 11 Operation section 12 RAM 13 ROM 14 Three-dimensional coordinate measurement control board 15 Signal bus 16 Motor driver 17 Calibration target 18 Rotation axis 19 Intersection 20 Straight line of camera line of sight

Claims (3)

[Claims] 1. An image of an object irradiated with slit light is captured on a camera image plane, and an object corresponding to the reflected light point is determined from camera image plane coordinates of a light point reflected by the slit light on the image of the object. In the slit light projection type three-dimensional coordinate measuring method of calculating the position coordinates of the point by using a calculation formula, a camera calibration step of calibrating the camera in advance, and three points based on the calibration data of the calibration step A step of obtaining three or more equations of the slit light plane rotated by the above different angles; a step of obtaining an equation of the rotation axis from the equations of the three or more slit light planes; and rotation of an arbitrary angle about the rotation axis. Obtaining an equation of an arbitrary slit light plane in the case of performing the slit light projection method three-dimensional coordinate measurement method. . 2. An image of an object irradiated with slit light is captured on a camera image plane, and an object corresponding to the reflected light point is determined from camera image plane coordinates of the light reflected by the slit light on the image of the object. In a slit light projection type three-dimensional coordinate measuring apparatus that calculates the position coordinates of a point using a calculation formula, camera calibration means for calibrating a camera in advance, and three points based on calibration data of the calibration means A slit light plane calculating means for obtaining three or more equations of the slit light plane rotated by the above different angles; a rotation axis calculating means for obtaining a rotation axis equation from the three or more slit light plane equations; Arbitrary slit light plane calculation means for obtaining an equation of an arbitrary slit light plane when rotated by an arbitrary angle around the axis. Slit light projection method 3, wherein Rukoto
Dimensional coordinate measuring device. 3. An image of an object irradiated with the slit light is captured on a camera image plane, and an object corresponding to the reflected light point is obtained from the camera image plane coordinates of the light point reflected by the slit light on the image of the object. A slit light projection type three-dimensional coordinate measurement program for calculating a position coordinate of a point using a calculation formula, the program causing the camera to calibrate in advance, and based on the calibration data, Three or more equations of the slit light plane rotated by at least two different angles are obtained, and an equation of the rotation axis is obtained from the three or more equations of the slit light plane. A recording medium in which a slit light projection type three-dimensional coordinate measurement program is recorded, wherein an equation of an arbitrary slit light plane in the case is obtained.