JP3415921B2 - Length or distance measurement method and calibration jig for measurement - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a length or distance measuring method and a calibration jig therefor. More specifically, a production automation process, useful in precision measurement, etc., non-contact, and an optical measurement method capable of accurately measuring the length or distance even when the surface of the measurement target portion is inclined, It relates to a jig for tilt calibration for this method.

[0002]

2. Description of the Related Art Conventionally, in the production automation process, precision measurement, etc., a method for optically measuring the length and distance on the plane of various objects to be measured in a non-contact manner and an apparatus therefor have been adopted. There is. In these conventional methods, the length and distance between two points such as the size of a predetermined target portion are measured by image processing of a two-dimensional image obtained by using an image pickup device such as a CCD camera.

However, in this optical length or distance measuring method, as shown in FIG. 1, for example, as shown in FIG. 1, a camera (101) is used to mount an object on a target installation surface (104) on an object installation base (103). When measuring the length or distance between two points, there is a problem that an accurate measurement result cannot be obtained when the camera optical axis (102) and the imaging target plane, that is, the focal point (105) are not orthogonal. In particular, as shown in FIG. 1, the installation surface (104) and the measurement target plane (focusing surface) (10
5) are not the same, and it is difficult to measure the length or distance that is displaced in the depth direction when viewed from the camera (101), and complicated measures are required.

As shown in FIG. 2, with respect to the camera optical axis (202) of the camera (201), the object installation base (20
3) Installation surface (204) on top, and target plane (focus point)
If (205) is orthogonal, even if the camera (20
Even if there is a shift in the depth direction as seen from 1), the above problems do not occur in measuring the length and distance. Therefore, in the conventional method, as illustrated in FIG. 1, when the target plane (focus point) has an inclination with respect to the camera optical axis, the camera (101) and the target plane ( By adjusting the level of the in-focus plane), the orthogonality was absolutely ensured.

[0005]

However, in the case of the above-mentioned conventional method, in order to secure the absolute orthogonality by the level or the like, the mechanism for the adjustment becomes complicated, and the adjustment itself has many problems. It had the drawback of requiring labor. In addition, when the level of the plane cannot be easily measured, for example, because the structure around the target plane is complicatedly complicated and the level cannot be used, there is a problem that the conventional technique cannot accurately adjust the level. .

The present invention has been made in view of the above circumstances, solves the drawbacks of the prior art, and even if the optical axis of the camera and the plane of the target portion are not strictly orthogonal, By obtaining the inclination of the target plane and using this inclination as a calibration factor, a new measuring method that can accurately and easily measure the length and distance between two points on the plane and a calibration jig for that purpose. It is intended to be provided.

[0007]

In order to solve the above-mentioned problems, the present invention provides a method of measuring the length or distance on an optical plane by an image pickup device, which comprises a plane portion and its legs. Place the provided calibration jig on the part to be measured, read the reference point of the flat surface of the calibration jig and the coordinate values on the image of the leg end points, and use this coordinate value and the known dimensions of the calibration jig. Provided is a method for measuring a length or a distance, wherein a three-dimensional inclination of a plane of an object to be measured with respect to an optical axis of an imaging device is obtained, and the length or distance of the object to be measured is measured by calibration based on the inclination. .

Further, the present invention is a calibration jig for measuring an optical length or a distance by an image pickup device, which comprises a plane portion and its leg portion and is arranged on the plane of the object to be measured. Also provided is a calibration jig for measuring a length or a distance, characterized in that a three-dimensional inclination of a plane to be measured is obtained from coordinate values on the image and known dimensions of the jig.

[0009]

In the measuring method of the present invention, the inclination angle formed by the optical axis of the camera and the plane of the target portion is obtained by the above-mentioned means, and the length or distance of the target portion is optically measured by the plane equation. More specifically, in the method of the present invention, the above-mentioned calibration jig is placed on a plane on which an object to be measured is placed, and an image is picked up by an image pickup device such as a CCD camera, and a specific point of the calibration jig on the camera image is picked up. The coordinate values of the plane are read, and the three-dimensional inclination of the plane is obtained by geometrical calculation processing from the coordinate values, the known dimensions of each part of the jig, and the dimensions of the system including the image pickup device and the jig. Alternatively, the true length or distance is obtained by performing tilt calibration from the coordinate value of the distance on the camera image.

The calibration jig in this case preferably has a specific point serving as a reference in its plane portion, and at least three legs radially arranged about this point have a known length. At least three other points are set at the positions so that the coordinate values of them can be read. It is assumed that at least these three points are on a plane position parallel to the plane on which the jig is placed.

Examples will be shown below to describe the method of the present invention in more detail.

[0012]

EXAMPLES Example 1 FIG. 3 illustrates the outline of the method of the present invention.
Let the optical axis of the camera be the Z axis, and let point C be the principal point position. The camera apparently images from this point C, and each point on a straight line drawn radially from the point C appears to be the same point when viewed from the camera. The calibration jig (301) has a plane with its center point Co 'as a plane of Z = 0. Also, the camera is Z = Zn
It is assumed that it is focused on the plane of and has a sufficient depth of field. Co is the projection of Co ′ on the focusing surface as seen from the camera side, and what can be observed as the coordinate value on the camera image is Co.
Is. Qi (i = 1, 2, 3) is a calibration jig (301)
, And Pi (i = 1, 2, 3) is a projection from the camera surface onto the focusing surface of Qi. Therefore, only Pi can be observed on the camera image.

FIG. 4 shows the three-dimensional representation system shown in FIG.
It is shown in a two-dimensional representation by a certain cross section. Ri
(I = 1,2,3) is the distance between Co ′ and Qi,
It is a known amount by actual measurement. Co ′ coordinates in space are the straight line between the principal point C and the center point Co on the projection plane, and the plane Z =
It is obtained as the intersection with 0 by the following method.

That is, the detection point coordinates (center point) Co (X
0, Y0, Z0), the true coordinates in space Co ′ (α, β,
0), the straight line formula:

[0015]

[Equation 1]

Therefore, by substituting Co ′,

[0017]

[Equation 2]

[0018] Therefore,

[0019]

[Equation 3]

Is required. Next, based on the coordinate values on the image, a straight line formed by the jig end point Qi in the space and the jig end point Pi on the projection plane, the known amount distance Ri as the radius, and Co ′ as the center. It is calculated by the following method as the intersection with the sphere. In this case, the central coordinates Co ′ (α, β,
0), C (CX, CY, CZ), Pi (Xi, Yi, Z
i).

[0021]

[Equation 4]

From the equation of the straight line between C and Pi,

[0023]

[Equation 5]

Therefore, by substituting this into the above sphere equation,

[0025]

[Equation 6]

Lead to Therefore,

[0027]

[Equation 7]

Where the two-dimensional coefficient of ti is Ati ²
If + 2 · Bti + C = 0,

[0029]

[Equation 8]

It becomes By substituting this value into the above-described straight line formula of C and Pi, the jig end point coordinates Qi in space can be obtained. Next, the three points Qi (i = 1, 2,
The plane equation including 3) is obtained by the following method.

That is, first, the jig end point coordinates are Qr (X
qn, Yqn, Zqn). (N = 1 to 3) If the plane normal vector is (a, b, c),
From the plane equation, the following equation holds.

[0032]

[Equation 9]

Therefore, the following equations are successively derived.

[0034]

[Equation 10]

Here, it is assumed that a = 1. By substituting this result into the above (1), the principal point C is obtained by the following equation.

[0036]

[Equation 11]

Further, d can be obtained by the following equation.

[0038]

[Equation 12]

Next, the spatial coordinates of one end of the two observation points whose lengths are to be obtained are obtained. First, the plane equation is ax + by + cz + d = 0, and the observation point PR is (XR, Y
R, ZR)

[0040]

[Equation 13]

Is derived. Therefore, it can be expressed as the following equation.

[0042]

[Equation 14]

Since this point is on the plane, the following equations are successively derived.

[0044]

[Equation 15]

By substituting this into the above-mentioned straight line equation, the coordinates (XR ', YR', ZR ') in space are obtained. By the same means, the spatial coordinates of the other end of the three observation points whose lengths are to be obtained are obtained, and the coordinates (X ″, Y ″,
Z ″). At this time, the length L in the space to be obtained is obtained by the following equation.

[0046]

[Equation 16]

As described above, even if the optical axis of the camera and the target plane are not exactly orthogonal to each other, the equation of the target plane with respect to the optical axis can be easily obtained by a calculation process, and two accurate points can be obtained using this equation. It is possible to find the length of the interval. In addition,
FIG. 5 is a side sectional view showing an example of the arrangement of the calibration jig in the above measuring method. For example, as illustrated in FIG. 5, when measuring the length or the distance on the installation surface (502) on the object installation base (501), the calibration jig (503) is arranged thereon. This calibration jig has a flat surface (5
04) and legs (505).

By the above method using this jig, the length and distance on the inclined plane can be easily and accurately measured without employing special means such as a level or complicated adjustment method. Becomes Embodiment 2 FIGS. 6 (a), 6 (b) and 6 (c) exemplify a calibration jig used in the present invention. For example, as illustrated in FIG. 5, this jig has a center point Co ′ as one base point on a flat installation surface (601) on which the jig is installed on the plane of the object to be measured. It has three legs (602) and their end points (603) for obtaining the inclination of (601) with respect to the camera optical axis. These three leg end points (6
03) is preferably radially separated from the reference point Co ′ of the installation surface in the direction of 120 ° in order to ensure accuracy. Further, the plane including these three points needs to be parallel to the installation surface.

Further, when using this jig, the lengths Ri of the reference point on the installation surface and each of the three end points are treated as known quantities, and therefore it is necessary to obtain them in advance. With the above-described calibration jig, as described in the first embodiment, even if the camera optical axis and the target plane are not exactly orthogonal to each other, the angle of the target plane with respect to the optical axis is obtained by a calculation process, In addition, the length or distance can be measured accurately.

[0050]

As described in detail above, in general, when the optical axis of the camera and the target plane are not exactly orthogonal,
Although it is not possible to accurately determine the length between the two points from the camera image, the method of the present invention does not make the points exactly orthogonal to each other and uses a simple jig to measure the target plane with respect to the optical axis. The angle can be easily obtained by a calculation process, and an accurate length between two points can be obtained.

Further, the calibration jig of the present invention has, in the simplest form, the structure necessary for accurately carrying out the above-mentioned measuring method.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a measurement system for explaining problems of a conventional method.

FIG. 2 is a schematic diagram of a measurement system showing a case where a camera optical axis and a target plane are orthogonal to each other.

FIG. 3 is a schematic diagram showing a measuring method of the present invention.

FIG. 4 is a side sectional view corresponding to FIG.

FIG. 5 is a side cross-sectional view illustrating the arrangement of a calibration jig.

6A, 6B, and 6C are a plan view, a front view, and a perspective view, respectively, illustrating a calibration jig of the present invention.

[Explanation of symbols]

101, 201 camera 102,202 Camera optical axis 103, 203 Installation base 104, 204 Installation surface 105, 205 Imaging target plane (focus plane) 301 Calibration jig 501 installation stand 502 Installation surface 503 Calibration jig 504 Flat part 505 leg 601 plane installation surface 602 legs 603 Leg end point

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-52703 (JP, A) JP-A-61-277012 (JP, A) Special Table 3-505924 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01B 11/00-11/30

Claims (2)

(57) [Claims] 1. A flat surface portion and a calibration jig which includes a three legs were placed onto the target portion, the reference point of the flat portion of the calibration jig
And the coordinate values of the leg end points on the image are read, the three-dimensional inclination of the plane of the object to be measured with respect to the optical axis of the imaging device is obtained from this coordinate value and the known dimension of the calibration jig, and the measured object is calibrated by this inclination. A method of measuring length or distance, which comprises measuring the length or distance of a target portion. 2. A calibration jig which includes a flat surface portion and three legs
Is placed on the part to be measured , and the camera optical axis is the Z-axis.
In the dimensional coordinate system, the coordinates of the principal point C of the camera (CX, C
Y, CZ), detection of the center point of the plane on the camera focal plane.
The coordinates of the origin coordinates Co are (X0, Y0, Z0)
Coordinates of the detection points Pi at each end of the three legs on the focal plane
However, the coordinates of i = 1, 2, 3) are (Xi, Yi, Zi)
(However, i = 1, 2, 3), and the center point and each end
From the distance Ri (however, i = 1, 2, 3) from
The coordinates of the true center point of the coordinates of Co '(α, β, 0)
A, [number 1] The first step of calculating as
Coordinates Qn of each true end (where n = 1, 2,
3) coordinates (Xqn, Yqn, Zqn) (where n =
1, 2, 3), [number 2] The second step of calculating
Coordinates of the detection point (observation point 1) PR on the plane (X
R, YR, ZR), and the true observation point 1 in space
The coordinates (XR', YR', ZR') a, [number 3] As the third step, and then the third step
The coordinates of the true observation point 2 in space, similar to
Fourth step of calculating (X ″, Y ″, Z ″)
When, Equation 4] The length or distance L between the observation points 1 and observation point 2 Fifth length or distance measuring method according to claim 1 Rukoto wherein a and a step of calculating a.