JP2913370B2 - Optical position measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical position measuring method for measuring a center position in a spatial coordinate system of a circular portion to be measured such as a circular hole provided in a work.

[0002]

2. Description of the Related Art Conventionally, as a measuring method of this kind, two cameras arranged so that their optical axes are oblique to each other are used. The method of calculating the center position of the measured part in the spatial coordinate system from the center coordinates of the image of the measured part on the screen of the other camera and the center coordinates of the image of the measured part on the screen of the other camera is based on the principle of triangulation. Are known. Here, when measuring the center coordinates of the image of the measured part on the screen of the camera, generally, a horizontal x
Scanning in the axial direction and obtaining the coordinates of two peripheral points in the x-axis direction that match the peripheral edge of the image of the measured portion are repeated while shifting the position in the vertical y-axis direction, and the two peripheral points in the x-axis direction are obtained. The x-coordinate of the midpoint is averaged to obtain the x-coordinate of the center of the image of the measured portion. Similarly, scanning the screen in the y-axis direction to obtain the coordinates of two peripheral points in the y-axis direction is called x. This is repeated while shifting the position in the axial direction, and the y coordinate of the middle point of the two peripheral points in the y axis direction is averaged to obtain the y coordinate of the center of the image of the measured portion (Japanese Patent Application Laid-Open No. 56-155804). No.).

[0003]

In the above method, the center coordinates of the image to be measured are accurately obtained when the image of the portion to be measured is a perfect circle. The image becomes an ellipse having the shift direction as a short axis, and in the above-described method, a measurement error of the center coordinates of the image easily occurs. Also,
When measuring the center position of the measured part in the space coordinate system using two cameras as described above, one camera can be arranged so that its optical axis matches the normal direction of the work surface, while the other camera can be arranged. The optical axis of the camera is oblique to the work surface. In this case, the projection plane of the screen of the other camera onto the spatial coordinate system is inclined with respect to the work surface, and as a result, the projected image of the measured section on the projection plane viewed from the other camera is the same as the real image of the measured section. Are not exactly similar. Here, the image of the measured portion on the screen of each camera matches the projected image of the measured portion viewed from each camera on the projection plane of the screen of each camera onto the spatial coordinate system. Conventionally, the equation of the line of sight of each camera in a spatial coordinate system, which passes through the center of the projected image on each projection plane that matches the center of the image of the measured part on the screen of each camera, is obtained. The position is calculated by using the intersection of as the center of the measured part in the space coordinate system.
However, as described above, when the projected image of the measurement target on the projection plane of the screen of the other camera onto the spatial coordinate system does not resemble the real image of the measurement target, the line of sight of the other camera passing through the center of the projection image is affected. It does not pass through the center of the measuring unit, and causes a measurement error of the center position. In view of the above points, an object of the present invention is to provide a measurement method capable of accurately measuring the center position of a measurement target in a spatial coordinate system from image data of two cameras.

[0004]

In order to achieve the above object,
The present invention captures an image of a circular object to be measured provided on a workpiece by two first and second cameras arranged so that their optical axes are oblique to each other, and uses image data of both cameras in a spatial coordinate system. In the method of measuring the center position of the measured portion, the first camera is arranged so that its optical axis coincides with the normal of the surface of the work, and the first camera coincides with the periphery of the image of the measured portion on the screen of the first camera. Obtaining a first regression ellipse representing the image of the measured part on the screen of the first camera based on the coordinates of the peripheral points at a plurality of circumferential points; The coordinates of the peripheral points at a plurality of positions in the circumferential direction corresponding to the peripheral edge are converted into coordinates when the respective peripheral points are projected along the line of sight from the second camera on the projection plane of the screen of the first camera onto the spatial coordinate system. Based on the transformed coordinates of these peripheral points, A step of calculating a second regression ellipse representing an image, and a step of calculating a center position of the measured part in a spatial coordinate system from the center coordinates of the first regression ellipse and the center coordinates of the second regression ellipse. It is characterized by the following.

[0005]

The regression ellipse is determined by regression processing so as to pass as close as possible to a plurality of peripheral points. Then, by calculating the regression ellipse, if the image of the measured portion is a perfect circle,
In the case of an ellipse, the image of the measured portion is accurately identified as an ellipse, and the center coordinates of the image can be measured with high accuracy. By the way, the projection plane of the screen of the first camera on the spatial coordinate system is parallel to the work surface, and the projected image of the measured section viewed from the first camera on the projected plane is similar to the real image of the measured section. The line of sight of the first camera passing through the center of the regression ellipse of the projection image obtained based on the coordinates of the peripheral point of the image of the measurement target on the screen of the first camera passes through the center of the measurement target. On the other hand, the projection plane of the screen of the second camera onto the spatial coordinate system is inclined with respect to the work surface, and the projected image of the measured section viewed from the second camera with respect to the projection plane does not resemble the real image of the measured section. However, in the present invention, since the coordinates of the peripheral point of the image of the measured portion on the screen of the second camera are converted as described above, the point on the converted coordinates is the first coordinate.
This coincides with the peripheral edge of the projection image of the measured portion viewed from the second camera with respect to the projection plane on the spatial coordinate system of the camera. This projected image is similar to the real image of the measured portion, and the line of sight of the second camera passing through the center of the regression ellipse of the projected image obtained based on the transformation coordinates of the peripheral point passes through the center of the measured portion. Therefore, it is possible to accurately measure the center position of the measured portion in the spatial coordinate system as an intersection between the line of sight of the first camera and the line of sight of the second camera.

[0006]

FIG. 1 shows an outline of an apparatus for measuring the center position of a circular hole b which is a measurement target portion formed as a reference hole in a work a such as an automobile body. First and second light source 1 and CCD camera
Two camera 2 _1, 2 _2, and a image processing circuit 3 for inputting an image signal from the both the camera 2 _1, 2 _2.

The spot light source 1 and the cameras 2 ₁ and 2 ₂ are mounted on a measuring head (not shown) attached to an operating end of a robot or the like, and the measuring head is placed at a predetermined measuring position opposite to a location where the circular hole b is formed. after moving, the spotlight 1 both cameras 2 ₁ by irradiating a spot light from 2 ₂ imaging the workpiece a, the center position of the circular hole b in the spatial coordinate system from both cameras 2 _1, 2 ₂ of the image data measure.

The two cameras 2 ₁ and 2 ₂ are arranged such that the optical axes 0 ₁ and 0 ₂ obliquely intersect at a predetermined angle θ as shown in FIG. 1 the optical axis 0 ₁ of the camera 2 ₁ position of the measuring head is controlled so as to match the direction normal to the surface of the workpiece a.

[0009] Here, both cameras 2 _1, 2 ₂ of the optical axis 0 _1, 0 ₂
Is the origin 0, and the optical axis 0 on a plane including both optical axes 0 ₁ and 0 ₂
Z-axis coordinate axes conform to _1, X-axis coordinate axes orthogonal to the Z axis on the plane, the coordinate axes perpendicular to the plane set the spatial coordinate system with the Y axis, the space of the first camera 2 ₁ Screen the projection plane to Q ₁ to the coordinate system as the X-Y plane, X on the plane, Y
X the first camera 2 ₁ of screen to match the coordinates, y
Set the coordinates, also, X-Z takes on the coordinate plane X 'axis to be perpendicular to the optical axis 0 _2, a projection plane Q ₂ of the second camera 2 ₂ screen space coordinate system of the X'- as Y plane, X on the plane ', sets the x, y coordinate in the second camera 2 ₂ screen to match the Y-coordinate. The distance from both cameras 2 _1, 2 ₂ of the origin and each L.

[0010] The first camera 2 ₁ of the screen, the first camera 2 ₁
Matches the projected image of the circular hole b relative to the projection plane Q ₁ as viewed from the hole portion image appears as shown in FIG. 3, The second camera 2 ₂ screens, the projection viewed from the second camera 2 ₂ matches the projected image of the circular hole b to the surface Q _2, such as holes image appears shown in Figure 4 (a).

[0011] Referring now to FIG. 2, a peripheral point in the radial direction two portions of the circular hole b A, B, the first camera 2 ₁ of the center C _1, the second center of the camera 2 ₂ C ₂ , a to projection plane Q ₁ as seen from the first camera 2 _1, a _1, B ₁ the projected point B, a of the projection plane Q ₂ to which seen from the second camera 2 _2, the projected point B a ₃ , B ₃
Then, since the projection plane Q ₁ is parallel to the surface of the work a, the triangle C ₁ AB and the triangle C ₁ A ₁ B ₁ are similar, but the projection plane Q ₂ is θ with respect to the surface of the work a. Therefore, the triangle C ₂ AB and the triangle C ₂ A ₃ B ₃ are not similar to each other. Thus, the hole portion image of the first camera 2 ₁ on the screen is a shape corresponding to the circular hole b, the hole image on the second camera 2 ₂ screens distorted not correspond exactly to the circular hole b Shape. Since the center of the circular hole b to the optical axis 0 ₁ of the first camera 2 ₁ in the illustrated example is offset laterally, the first
Hole image on the screen of the camera 2 ₁ has an elliptical.

[0012] Then, the first camera 2 ₁ line of sight with respect to the center M ₁ of the projected image on the projection plane Q ₁ from the center coordinates of the hole portion image of the first camera 2 ₁ on the screen, i.e., a line C ₁ M ₁ If the equation is obtained, this line of sight passes through the center M of the circular hole b. In contrast, the second camera 2 ₂ sight to the center M ₃ of the projected image on the projection plane Q ₂ from the center coordinates of the hole image on the second camera 2 ₂ images, that is, the equation of the line C ₂ M ₃ Does not pass through the center M of the circular hole b.

Meanwhile, A ₃ and a second camera 2 _{and second} sight for B _3, i.e., when the intersection relative to the projection surface to Q ₁ line C ₂ A ₃ and line C ₂ B ₃ to A ₂ and B _2, triangle C ₂ AB and triangle C ₂ A
₂ B ₂ become to similar, second camera 2 ₂ sight relative to the center M ₂ of the projected image of the circular hole b relative to the projection plane Q ₁ as seen from the second camera 2 _2, i.e., a line C ₂ M ₂ is When the coordinates of the intersection of both lines passing through the center M of the circular hole b and obtained from the equations of the line C ₁ M ₁ and the line C ₂ M ₂ are obtained, this is the center position of the circular hole b in the circular hole in the space coordinate system. Becomes

Hereinafter, the procedure for measuring the center position of the circular hole b based on the image data of the cameras 2 ₁ and 2 ₂ will be described in more detail. First, to detect the coordinates of each camera 2 _1, 2 ₂ of the screen on the peripheral points of the plurality of circumferential locations that match the periphery of the hole image. In detecting these coordinates, first, each camera 2 ₁ ,
Obtains an image centroid of the hole image on the 2 ₂ window, intersect the symmetrical two x-axis scanning line in the y-axis direction with respect to the center of gravity, the peripheral points of the four points that match the periphery of the hole image - and 4 intersects two y-axis scanning lines symmetric with respect to the center of gravity in the x-axis direction
A total of eight peripheral points, i.e., the peripheral points of the points, are picked up and their coordinates are detected.

[0015] Then, a regression ellipse S ₁ representing the hole image of the first camera 2 ₁ on the screen determined by regression processing from the coordinates of the peripheral points. The center coordinates of this regression ellipse S ₁ are (x ₁ ,
y ₁ ), the spatial coordinates of the center M ₁ of the projected image on the projection plane Q ₁ are (x ₁ , y ₁ , 0), and the first camera 2 ₁
The spatial coordinates of the center C ₁ of the (0,0, L) is to determine the equation of the line of sight C ₁ M ₁ from these space coordinates.

[0016] On the other hand, for the second camera 2 ₂ of the screen,
It converted into coordinates in projecting the respective peripheral point coordinates of the peripheral points of the aperture image on the projection plane Q ₁ along the line of sight from the second camera 2 _2. That is, to convert the coordinates of each perimeter point to the coordinates of the intersection of the second camera 2 ₂ line of sight for each peripheral point (line corresponding to line _{C 2 A 3, C 2 B} 3 described above) and the projection plane Q ₁ . With this transform coordinates, the position of the peripheral edge point and the hole portion image on the second camera 2 ₂ screen is modified as shown in FIG. 4 (b), a regression ellipse S obtained from these peripheral point coordinates ₂ would be indicative of a projected image of the circular hole b relative to the projection plane Q ₁ as seen from the second camera 2 _2. Spatial coordinates of the center M ₂ of-projecting imaging is the center coordinates of the regression ellipse _{(x 2, y 2) (} x 2, y 2, 0) , and the addition, the second camera 2 ₂ spatial coordinates of the center C ₂ Is (L sin θ, 0, L cos θ), and the equation of the line of sight C ₂ M ₂ is obtained from these spatial coordinates. Finally, the coordinates of the center M of the circular hole b in the space coordinate system are converted to the two lines of sight C ₁ M ₁ as described above. , C ₂ M ₂ .

In calculating the regression ellipses S ₁ and S ₂ , the amount of deviation of each peripheral point from the regression ellipse is calculated,
When the maximum deviation amount among the deviation amounts of these peripheral points is equal to or more than a predetermined value, the hole edge point with the maximum deviation amount is deleted, a regression ellipse is obtained again from the coordinates of the remaining peripheral points, and this process is repeated. Iteratively calculating the final regression ellipse until is less than a predetermined value. In this case, if the number of peripheral points decreases, the regression ellipse cannot be calculated accurately. Therefore, when the number of peripheral points decreases to five or less, the fact that measurement is impossible is displayed.

[0018]

As is apparent from the above description, according to the present invention, the center position of the measured portion in the spatial coordinate system can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a measuring apparatus used for carrying out the method of the present invention.

FIG. 2 shows the principle of measurement.

FIG. 3 is a diagram showing an image of a first camera.

4A is a diagram illustrating an image of a second camera, and FIG. 4B is a diagram illustrating an image after coordinate transformation.

[Explanation of symbols]

a Workpiece b Circular hole (measured part) 2 ₁ First camera 2 ₂ Second camera Q ₁ Projection plane of first camera Q ₂ Projection plane of second camera S ₁ First regression ellipse S ₂ Second regression ellipse

Claims (1)

(57) [Claims] An image of a circular portion to be measured provided on a workpiece is captured by first and second cameras arranged so that optical axes are oblique to each other, and a spatial coordinate system is obtained from image data of both cameras. In the method for measuring the center position of the measured part in the method, the first camera is arranged so that its optical axis coincides with the normal of the surface of the work, and the first camera is arranged on the periphery of the image of the measured part on the screen of the first camera. A step of obtaining a first regression ellipse representing an image of the measured part on the screen of the first camera based on the coordinates of the peripheral points at a plurality of matching circumferential points; and an image of the measured part on the screen of the second camera. Are converted into coordinates when the respective peripheral points are projected along the line of sight from the second camera on the projection plane of the first camera screen on the spatial coordinate system, which coincides with the peripheral edge of the camera. Then, based on the transformation coordinates of these peripheral points, the measurement on the projection surface as viewed from the second camera is performed. Calculating a second regression ellipse representing a projected image of the following; calculating a center position of the measured part in a spatial coordinate system from the center coordinates of the first regression ellipse and the center coordinates of the second regression ellipse; An optical position measuring method, comprising: