JP2689064B2 - Measuring method of hole position - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hole position measuring method for picking up an image of a circular hole formed in a work and measuring the center position of the circular hole based on image data of the circular hole on the screen of an image pickup means. .

[0002]

2. Description of the Related Art Conventionally, in this type of measuring method, the coordinates of two hole edge points in the x-axis direction which match the hole edges of the image of the circular hole are obtained by scanning the screen in the horizontal x-axis direction. Is repeated while shifting the position in the vertical y-axis direction, and the x-coordinates of the midpoints of the two hole edge points in the x-axis direction are averaged to determine the x-axis of the center of the circular hole.
Obtaining the coordinates and scanning the screen in the y-axis direction to obtain the coordinates of the hole edge points at the two points in the y-axis direction are repeated while shifting the position in the x-axis direction. The y-coordinates of the center points are averaged to find the y-coordinate of the center of the circular hole. By the way, the unevenness due to noise or the like may appear on the edge of the image of the circular hole and the hole edge does not form a continuous curve. In this case, an error due to the unevenness is incorporated into the scan data, and the measurement accuracy deteriorates. In order to solve such a problem, according to Japanese Patent Laid-Open No. 56-155804,
The deviation amount of each hole edge point with respect to the reference circle of the predetermined diameter centered on the center position calculated as described above is obtained, and the change of this deviation amount at each hole edge point is examined to determine the normality from its continuity. It is also known to determine whether the image is an image and delete the hole edge point having a discontinuous change from the scan data to obtain the center position.

[0003]

As described above, in order to check the continuity of the change in the shift amount with respect to the reference circle, the screen is scanned at a fine pitch to detect and store the coordinates of many hole edge points. It is necessary and there is a problem that data processing becomes complicated. Further, when the work is tilted with respect to the optical axis of the image pickup means, a measurement error is likely to occur in the above method for determining the center position on the assumption that the image of the circular hole becomes an ellipse and the image of the circular hole becomes a circle. . In view of the above points, an object of the present invention is to provide a method capable of measuring a hole position with high accuracy by using coordinates of a relatively small number of hole edge points.

[0004]

In order to achieve the above object,
The present invention images a circular hole formed in a workpiece and measures the center position of the circular hole based on the coordinates of a plurality of hole edge points in the circumferential direction that match the hole edge of the image of the circular hole on the screen of the image pickup means. In this method, the regression ellipse that represents the image of the circular hole on the screen is obtained from the coordinates of these hole edge points, the deviation amount of each hole edge point with respect to this regression ellipse is calculated, and the deviation amount of these hole edge points is calculated. When the maximum deviation amount of is greater than or equal to the predetermined value, the regression ellipse is repeatedly obtained from the coordinates of the remaining hole edge points after deleting the hole edge points of the maximum deviation amount until the maximum deviation amount becomes less than the predetermined value.
It is characterized in that a regression ellipse whose maximum deviation amount is less than a predetermined value is obtained as a target ellipse on the screen corresponding to the circular hole, and the center position of the circular hole is calculated from the center coordinates of this target ellipse.

[0005]

By calculating the regression ellipse, the image of the circular hole is approximated as a circle if the image of the circular hole is a circle and as an ellipse if the image of the circular hole is an ellipse. Then, since the hole edge points located in the abnormal image portion where irregularities etc. appear have a large deviation amount with respect to the regression ellipse, they are deleted in the process of repeatedly obtaining the regression ellipse, and finally correspond to the normal image of the circular hole. The target ellipse is sought.
If large irregularities appear on the hole edge of the image of the circular hole, if a regression ellipse is begun in a state including the hole edge points located in this uneven portion, the regression ellipse required to reach the target ellipse Since the number of calculations increases, before determining the first regression ellipse, it is determined whether or not each hole edge point exists within a predetermined annular area set on the screen based on the image center of gravity of the circular hole. Therefore, it is desirable to delete the hole edge points existing outside the area, that is, the hole edge points that largely deviate from the normal image. Further, when the work may be displaced three-dimensionally, the circular holes are imaged by two image pickup means arranged so that the optical axes are oblique to each other, and the image is displayed on the screen of one image pickup means. From the center coordinates of the target ellipse and the center coordinates of the target ellipse on the screen of the other imaging means, the center position of the circular hole in the spatial coordinate system is calculated by the principle of triangulation. By the way, in the process of calculating the target ellipse by repeating the calculation of the regression ellipse, the deviation amount of the hole edge point in the part of the normal image, which is rare, exceeds the deviation amount of the hole edge point of the abnormal image part, The hole edge may be deleted and the target ellipse may no longer match the normal image of the circular hole. In this case, the center position of the circular hole in the spatial coordinate system calculated from the center coordinates of the two target ellipses on the screens of both imaging means and the points on the two target ellipses, both of which are circular holes. When the distance between the center of the circular hole and the common point is calculated from the position of the common point in the spatial coordinate system calculated from the coordinates of the points corresponding to the common point on the edge, the target ellipse is the normal circular hole. If the image is matched, this distance will be equal to the radius of the circular hole, but if not matched, the distance will deviate significantly from the radius of the circular hole. Thus, comparing this distance with the radius of the circular hole,
By determining the center position as the normal center position of the circular hole when the difference is within the allowable range, the center position of the circular hole is erroneously determined based on the center coordinates of the target ellipse that does not match the normal image. Can prevent making decisions.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the outline of an apparatus for measuring the center position of a circular hole b having a predetermined diameter formed as a reference hole in a work a such as an automobile body. 1, a pair of _first and second cameras 2 ₁ and 2 ₂ for imaging the work a, and a computer 3 for inputting image signals from the cameras 2 ₁ and 2 ₂ . The spot light source 1 and both cameras 2 ₁ and 2 ₂ are mounted in a supporting frame (not shown) attached to the operating end of a robot or the like in a required positional relationship, and are moved and set to a predetermined measuring position facing the hole forming portion of the work a. It

Both cameras 2 ₁ , 2 ₂ have their optical axes 0 ₁ , 0 _{2 respectively.}
Are arranged so as to cross each other on the horizontal plane as shown in FIG. 2, and the coordinate axes orthogonal to each other on the horizontal plane are the X axis and the Z axis.
Axis, the coordinate axis orthogonal to the horizontal plane is the Y axis, and the center position of the circular hole b in the spatial coordinate system with the origin 0 at the intersection of the optical axes 0 ₁ and 0 ₂ is the circular hole on the screen of both cameras 2 ₁ and 2 _2. It was calculated from the center coordinates of the image by the principle of triangulation. To explain this in detail, on the screen of each camera 2 ₁ , 2 ₂ ,
As shown in (a) and (b), when the horizontal x-axis and the vertical y-axis are taken with the center point corresponding to the origin 0 as the origin, the x-axis coordinate value and the y-axis coordinate value of the screen are in the spatial coordinate system. The horizontal and vertical distances from the origin 0 on the projection planes Q ₁ and Q _{2 of the} cameras 2 ₁ and 2 ₂ are represented, and considering the center point M of the circular hole b, the first camera 2 ₁ projection surface projection point M ₁ of the point M to Q ₁ is turned to the center point of the first camera 2 ₁ screen, the point M ₁
The horizontal and vertical distances from the origin 0 of the first camera 2 _{1 become} the x-axis coordinate value x ₁ and the y-axis coordinate value y ₁ of the point M ₁ on the screen of the first camera 2 ₁ , and similarly the projection plane of the second camera 2 ₂ The projection point M ₂ of the point M on Q ₂ becomes the center point on the screen of the second camera 2 ₂ , and the point M ₂
The horizontal distance and the vertical distance from the origin 0 of the point are the x-axis coordinate value x ₂ and the y-axis coordinate value y ₂ of the point M ₂ on the screen of the second camera 2 ₂ . Then, X- of the line of sight of the first camera 2 _{1 with} respect to the point M
The equation of the projection line e ₁ to Z coordinate plane with determined from x _1, equation for a projection line e ₂ to X-Z coordinate plane of the second camera 2 ₂ sight for point M from x _2, both projection The X-axis coordinate value and the Z-axis coordinate value of the point M in the spatial coordinate system are calculated as the intersections of the lines, and then one of the two cameras, for example, the first camera 2
₁ based on the calculated distance between the surface and the first camera 2 ₁ including the intersection parallel to the projection plane Q _1, this distance a, the first camera 2 ₁ and between the projection plane Q ₁ The Y-axis coordinate value of the point M is calculated by multiplying y ₁ by the ratio with the distance.

A circular hole b on the screen of each camera 2 ₁ , 2 _2.
The coordinates of the center points M ₁ and M ₂ of the image of ₁ are calculated from the coordinates of the hole edge points at a plurality of circumferential positions that match the hole edges of the image of the circular hole.
In the present embodiment, first, the image center of gravity G of the circular hole b is obtained, four hole edge points intersecting with two x-axis scanning lines symmetrical with respect to the center of gravity G in the y-axis direction, and the center of gravity G in the x-axis direction. A total of eight hole edge points including four hole edge points intersecting the two y-axis scanning lines symmetrical to each other are picked up and their coordinates are detected, and the circles on each screen are detected from the coordinates of these hole edge points. The coordinates of the center points M ₁ and M ₂ of the image of the hole b were calculated.

By the way, considering that the hole edge of the image of the circular hole b may appear uneven due to noise and the like, and the picked-up hole edge point includes a point located in such an abnormal image portion. Then, the coordinates of the center points M ₁ and M ₂ are calculated by the following procedure.

First, if the image of the circular hole is normal on the screens of the cameras 2 ₁ and 2 ₂ so that the edge of the hole is within the area, the image center of gravity G of the circular hole b is centered. Set a predetermined ring area. Here, since the first camera 2 ₁ is arranged so as to face the work a, the image of the circular hole b on the screen becomes substantially circular as shown in FIG. 3A, while the second camera 2 1 ₂ is arranged so as to image the workpiece a at an angle, the image of the circular hole b on the screen is shown in FIG.
As shown in (b), it becomes elliptical, and in consideration of the reduction and enlargement of the image due to the displacement of the work a in the perspective direction, the screen of the first camera 2 ₁ is as shown by the phantom line in FIG. A circular ring-shaped area is set, while an elliptical ring-shaped area is set on the screen of the second camera 2 ₂ as shown by an imaginary line in FIG. Then, among the hole edge points on the screens of the cameras 2 ₁ and 2 ₂ , the hole edge points existing outside the annular area are judged to be points located in the abnormal image portion and are deleted. In the example of FIG. 3, points on the screen of the second camera 2 ₁ are deleted.

Next, a regression ellipse representing the image of the circular hole b on the screen is obtained from the coordinates of the remaining hole edge points. This will be described by taking the screen of the second camera 2 ₂ as an example. The hole edge point on this screen is picked up from the abnormal image portion, and even if it exists in the above-mentioned annular area, the deviation amount of the hole edge point with respect to the regression ellipse shown by S ′ in FIG. δ becomes large. Therefore, the deviation amount of each hole edge point with respect to the regression ellipse is calculated as the distance between the intersection point of the regression ellipse and the hole edge point on the straight line connecting the center of the regression ellipse and the hole edge point, and the deviation amount of these hole edge points. If the maximum displacement amount of the above is greater than or equal to the predetermined value, the hole edge point having the maximum displacement amount, that is, the hole edge point is deleted, and the regression ellipse is obtained again from the coordinates of the remaining hole edge points. In the example shown in the figure, each hole edge point matches the regression ellipse of S ″ obtained again, and this regression ellipse S ″
Is a target ellipse that corresponds exactly to the normal image of the circular hole b. If the maximum deviation amount of the hole edge point with respect to the regression ellipse obtained for the second time is equal to or greater than the predetermined value, the hole edge point with the maximum deviation amount is deleted to obtain the regression ellipse again, and this processing is performed with the maximum deviation amount of the predetermined value. The target ellipse is repeatedly obtained until it becomes less than the value. By the way, when the number of hole edge points becomes small, the regression ellipse cannot be accurately obtained. Therefore, when the number of hole edge points becomes 5 or less, the fact that measurement is impossible is displayed.

[0012] S ₁ is (a circle if the image is a circle) target ellipse corresponding to the normal image of the circular holes in the first camera 2 ₁ of the screen of FIG. 5 (a), 5 (b), S ₂ is a target ellipse corresponding to a normal image of the circular hole on the screen of the second camera 2 ₁ ,
Camera 2 ₁ on the screen of the target ellipse S ₁ of the center point M ₁ of the coordinates (x _1, y ₁₎ and the second camera 2 ₂ on the screen of the target ellipse S ₂ of the center point M ₂ coordinates (x _2, y ₂ ) and the position of the center point M of the circular hole b in the spatial coordinate system as described above.

Although rare, in the process of repeatedly obtaining the regression ellipse, the hole edge point located in the normal image portion may be deleted, and the target ellipse may not correspond to the normal image. By the way, the position of the point N on the hole edge of the circular hole b shown in FIG. 5C in the spatial coordinate system is the coordinate of the corresponding point N ₁ on the target ellipse S ₁ obtained on the screen of the first camera 2 _1. And the coordinates of the corresponding point N ₂ of the target ellipse S ₂ obtained on the screen of the second camera 2 ₂ are calculated by the principle of triangulation, and the distance L of the point N from the center point M in the spatial coordinate system is calculated. If obtained, both target ellipses S ₁ , S ₂
This distance is equal to the radius of the circular hole b as long as is matched with the normal image.

Therefore, this distance is compared with the radius of the circular hole b, and when the difference is within the allowable range, the position of the center point M calculated as described above is set as the normal center position of the circular hole b. It was decided, and when it was outside the allowable range, it was displayed that it was impossible to measure.

[0015] Incidentally, in order to determine the spatial coordinates of a point on the hole edge of the circular hole b, circular in the first camera 2 ₁ side of the target ellipse S ₁ and on the second camera 2 ₂ side target ellipse S ₂ above It is necessary to pick up a point corresponding to the common point on the edge of the hole b, but since the optical axes 0 ₁ and 0 _{2 of} both cameras 2 ₁ and 2 ₂ are located on the XZ coordinate plane, each camera 2 ₁ , 2 ₂ is located. The intersections of the x-axis coordinate axes on the screens 2 ₁ and 2 ₂ and the target ellipses S ₁ and S _{2 correspond} to the intersections of the hole edges of the circular hole b and the XZ coordinate plane, and the target ellipse S 1 The upper and lower end points of ₁ , S _{2 in} the y-axis direction correspond to the upper and lower end points of the edge of the circular hole b in the Y-axis direction, and the coordinates of any of these points on both target ellipses S ₁ , S ₂ From this, the position of the point on the edge of the circular hole b in the spatial coordinate system can be calculated. In the example shown in FIG. 5, the Y-axis lower end point N of the circular hole b in the spatial coordinate system is calculated from the coordinates of the y-axis lower end points N ₁ and N ₂ of both target ellipses S ₁ and S _2.
The position of is calculated. Further, the Y-axis coordinate values of the points M and N in the spatial coordinate system can be calculated from the y-axis coordinate values of the points M ₁ and N ₁ with the first camera 2 ₁ as a reference, and the second camera 2 ₂ It can also be calculated from the y-axis coordinate values of the points M ₂ and N ₂ with reference to the distance between the point M and the point N whose Y-axis coordinate values have been calculated with reference to the first camera 2 ₁ , and the second It is desirable to compare the distance between the point M and the point N, the Y-axis coordinate values of which are calculated with the camera 2 ₂ as a reference, with the radius of the circular hole b to make a pass / fail judgment.

[0016]

As is apparent from the above description, according to the present invention, a regression ellipse corresponding to a normal image of a circular hole is obtained from the coordinates of a relatively small number of hole edge points on the hole edge of the image of the circular hole. In addition to being able to accurately measure the center position of the circular hole, the data processing is easier and the measurement accuracy is improved as compared with the conventional technology in which the coordinates of a large number of hole edge points need to be detected and stored. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing the outline of a measuring device used for carrying out the method of the present invention.

FIG. 2 is a plan view of the main part.

3A and 3B are diagrams showing screens of respective cameras.

FIG. 4 is a diagram showing a relationship between a regression ellipse and each hole edge point.

5A and 5B are diagrams showing a target ellipse obtained on the screen of each camera, and FIG. 5C is a diagram showing a center of a circular hole and points on a hole edge in a spatial coordinate system calculated from the target ellipse. Figure

[Explanation of symbols]

a workpiece b circular hole 2 _1, 2 ₂ camera (imaging means) ~ Anaenten G image centroid S ', S "regression ellipse S _1, S ₂ target ellipse M _1, M ₂ target ellipse center point M circular hole Center point N ₁ , N ₂ Corresponding point on target ellipse N Common point on the edge of circular hole

Claims (4)

(57) [Claims] 1. A circular hole formed in a work is imaged, and the center position of the circular hole is determined based on the coordinates of a plurality of hole edge points in the circumferential direction that match the hole edge of the image of the circular hole on the screen of the image pickup means. In the measuring method, a regression ellipse that represents an image of a circular hole on the screen is obtained from the coordinates of these hole edge points, the deviation amount of each hole edge point with respect to this regression ellipse is calculated, and the deviation amount of these hole edge points is calculated. If the maximum amount of deviation is greater than or equal to the predetermined value, the regression ellipse is repeatedly obtained from the coordinates of the remaining hole edge points after deleting the hole edge points of the maximum amount of deviation until the maximum deviation amount is less than the predetermined value. A method for measuring a hole position, characterized in that a regression ellipse whose maximum deviation amount is less than a predetermined value is obtained as a target ellipse on the screen corresponding to the circular hole, and the center position of the circular hole is calculated from the center coordinates of the target ellipse. . 2. Before determining the first regression ellipse, it is determined whether or not each of the hole edge points exists within a predetermined annular area set on the screen based on the image centroid of the circular hole, The hole position measuring method according to claim 1, wherein the hole edge points existing outside the area are deleted. 3. A circular hole is imaged by two imaging means arranged so that their optical axes are oblique to each other, and the center coordinates of the target ellipse on the screen of one imaging means and the screen of the other imaging means. The center position of the circular hole in the spatial coordinate system is calculated from the center coordinates of the target ellipse above.
Alternatively, the hole position measuring method described in 2). 4. The center position of the circular hole in the spatial coordinate system calculated from the center coordinates of the two target ellipses on the screens of the both imaging means, and the points on the two target ellipses, both of which are circular holes. The distance between the center of the circular hole and the common point is obtained from the position of the common point in the spatial coordinate system calculated from the coordinates of the points corresponding to the common point on the hole edge, and this distance and the radius of the circular hole are calculated. The hole position measuring method according to claim 3, wherein the center position is determined as a normal center position of the circular hole when the difference is within an allowable range.