JPH07260428A - Method for measuring position of work - Google Patents

Abstract

PURPOSE:To measure the central position of a dark part, e.g. a hole part, on a work in a spatial coordinate system using a single camera. CONSTITUTION:A work A is irradiated with a light from a spot light source 2 and the image of the work is picked up by means of a camera 1. The image of the work is also picked up by irradiating the work with a slit light from a slit light source 3 such that the optical plane thereof intersects the optical axis (Z axis) of the camera obliquely. Variation of the work A in the direction of Z axis is measured based on the position on a screen of a slit optical image picked up during irradiation with slit light. The central coordinates on the screen of the image at an objective part B being picked up during irradiation with the slot light is then measured. Subsequently, the central position of the objective part B in a spatial coordinates is determined based on the central coordinates thus measured and the variation of the work A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work position measuring method for optically measuring a center position of a measurement target portion such as a hole portion of a work which appears dark when a work is imaged.

[0002]

2. Description of the Related Art Conventionally, as a method of optically measuring the center position of a hole of a work, two image pickup means arranged so that their optical axes intersect each other are used to irradiate the work with spot light. In this state, the work is imaged by both imaging means, the center coordinates on the screen of the image of the hole appearing as a dark part on the screen of each imaging means are measured, and from these center coordinates, the hole part in the spatial coordinate system is calculated by the principle of triangulation. A method for obtaining the center position is known.

Here, in measuring the center coordinates of the image of the hole, in general, the screen of the image pickup means is scanned in the horizontal x-axis direction so as to match the edges of the image of the hole with two peripheral edges. Repeating the calculation of the point coordinates while shifting the position in the vertical y-axis direction, the x-coordinates of the midpoints of the two peripheral points in the x-axis direction are averaged to obtain the x-coordinate of the center of the hole, and similarly, Repeatedly scanning the top in the y-axis direction to find the coordinates of the peripheral points at the two y-axis directions while shifting the position in the x-axis direction, averaging the y-coordinates of the midpoints of the peripheral points at the two y-axis directions. The y-coordinate of the center of the image of the hole is obtained (JP-A-56)
155804).

Further, the applicant of the present invention has previously filed Japanese Patent Application No. 5-679.
As proposed in No. 77, a plurality of points on the periphery of the image of the hole are picked up, a regression ellipse representing the image of the hole is obtained from the coordinates of these points, and the central coordinates of this regression ellipse are set to the center of the hole. There is also a method of using the center coordinates of the image.

[0005]

It takes time to measure the center coordinates of the image of the hole regardless of which method is used, and this measuring process is executed for each of the screens of the two image pickup means. However, it may be difficult to perform online measurement due to time constraints, and the cost of the measurement equipment may increase due to the use of the two imaging means.

In view of the above points, an object of the present invention is to provide a method capable of efficiently measuring the center position of the measurement target portion in the spatial coordinate system with a single image pickup means.

[0007]

[Means for Solving the Problems] In order to achieve the above object,
The present invention relates to a work position measuring method for optically measuring the center position of a measurement target portion of a work that appears dark when the work is imaged, and the work is imaged by an imaging means in a state where the work is irradiated with spot light. And a step of capturing an image of the work by the image capturing means while irradiating the work with slit light along a surface obliquely intersecting the optical axis of the image capturing means, and as a dark portion on the screen of the image capturing means during irradiation of the spot light. A step of measuring the center coordinates on the screen of the image of the measurement target portion that appears, and a workpiece in the optical axis direction of the image pickup means from the position on the screen of the slit light image that appears as the bright portion on the screen of the image pickup means during irradiation of the slit light. And a step of obtaining the center position of the measurement target portion in the spatial coordinate system from the displacement amount and the center coordinates.

[0008]

When the workpiece is displaced in the optical axis direction of the image pickup means, the slit light image is displaced in parallel on the screen because the slit light extends along the surface obliquely intersecting the optical axis, and thus the slit light image on the screen is displaced. The displacement amount of the work in the optical axis direction can be obtained from the position of. Therefore, the center position of the measurement target portion in the spatial coordinate system can be obtained even if there is only one imaging unit.

Here, it takes time to measure the center coordinates of the image of the measurement target portion on the screen, but since the slit light image is linear, its position can be measured instantaneously, and from this position, simple calculation is possible. Since the amount of displacement of the work can be obtained, the processing time is greatly shortened as compared with the case where the measurement processing of the center coordinates of the images of the measurement target portions is performed on the screens of the two image pickup means.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of an apparatus for measuring the center position of a circular hole B formed as a reference hole in a work A such as an automobile body. The apparatus is one CCD as an image pickup means.
A camera 1 and a spot light source 2 for emitting spot light,
It is composed of a slit light source 3 which emits slit light, and an image processing circuit 4 which inputs an image signal from the camera 1. The camera 1, the spot light source 2, and the slit light source 3 are mounted on a measuring head (not shown) attached to the operating end of a moving mechanism such as a robot, and the measuring head is moved to a predetermined position facing the hole B of the work A by the operation of the moving mechanism. The position of the hole B is measured by moving to the measurement position.

Here, the camera 1 and the slit light source 3 are
The measuring head is mounted on the measuring head in a required positional relationship so that an optical surface SP of the slit light (hereinafter referred to as a slit light surface) obliquely intersects the optical axis of the camera 1, and the light of the camera 1 at the measuring position. The axis CD is oriented in the normal direction of the work A.

When the measuring head is moved to the measuring position, first, the work A is irradiated with the spot light from the spot light source 2, the work A is imaged by the camera 1 in this state, and the image data is processed by the image processing circuit 4. Then, the work A is irradiated with the slit light from the slit light source 3, the work A is also imaged by the camera 1 in this state, and the image data is transmitted and stored in the image processing circuit 4.

When the spot light is radiated, the image b of the hole B appears as a dark portion on the screen of the camera 1 as shown in FIG. 3A, and when the slit light is radiated, the work A is lit by the slit light. Illuminated in a linear shape indicated by S, a linear slit light image s appears as a bright portion on the screen of the camera 1 as shown in FIG. When the slit light is applied so as to straddle the hole B, the slit light image s is divided at the portion b ′ with respect to the hole B.

The intersection of the optical axis of the camera 1 and the slit light surface SP is the origin 0, the optical axis of the camera 1 is the Z axis, and the coordinate axes parallel to the slit light surface SP orthogonal to the Z axis are the Y axis and the Y axis. And a spatial coordinate system having a coordinate axis orthogonal to the Z axis as the X axis and a projection image of the spatial coordinate system on the XY coordinate plane is taken by the camera 1, the origin 0 on the screen of the camera 1 When the horizontal X-axis corresponding to the X-axis and the vertical y-axis corresponding to the Y-axis are taken with the center point corresponding to the origin as the origin, the x-axis coordinate value and the y-axis coordinate value of the screen are X- of the spatial coordinate system. It represents the horizontal distance and the vertical distance from the origin 0 on the Y coordinate plane.
Then, as shown in FIG. 2, the ratio of the x, y coordinates mx, my on the screen of the center m of the image b of the hole B and the X, Y coordinates MX, MY in the spatial coordinate system of the center M of the hole B is It becomes equal to the ratio of the distance L from the camera 1 to the origin 0 and the distance from the camera 1 to the work A. Therefore, assuming that the displacement amount of the work A in the Z-axis direction is dZ, MX = mx · (L−dZ) / L Similarly, MY = my · (L−dZ) / L, and the Z coordinate M in the spatial coordinate system of the center M of the hole B.
Z becomes MZ = dZ.

Here, when the work A is displaced in the Z axis direction, the slit light surface SP is parallel to the Y axis and obliquely intersects with the Z axis, so that the slit light image s is displaced in the x axis direction on the screen. The relationship between the x coordinate sx of the slit light image s and the X coordinate SX of the slit light irradiation portion S on the work A is SX = sx · (L−dZ) / L (1) Further, assuming that the inclination angle of the slit light surface SP with respect to the Z axis is θ, SX = dZ · tan θ (2), and from equations (1) and (2), sx · (L−dZ) / L = dZ · tan θ (3), and by summarizing equation (3) for dZ, dZ = sx · L / (Ltan θ + sx) (4) Thus, if the x coordinate sx of the slit light image s is measured, the Z-axis displacement amount dZ of the work A can be calculated from the equation (4),
The center positions MX, MY, MZ of the hole B in the spatial coordinate system can be obtained from the center coordinates mx, my of the hole image b on the screen and dZ.

The center coordinates mx and my of the image b of the hole B are calculated from the coordinates of the peripheral points at a plurality of circumferential positions that match the periphery of the hole image b. In the present embodiment, first, the image center of gravity g of the hole image b is obtained, and four peripheral points intersecting with two x-axis scanning lines symmetrical with respect to the image center of gravity g in the y-axis direction as shown in FIG. 4A. , And 4 peripheral points intersecting with two y-axis scanning lines symmetrical with respect to the image center of gravity g in the x-axis direction, a total of 8 peripheral points are picked up and their coordinates are detected. By the way, in consideration of the fact that unevenness due to noise or the like may appear on the periphery of the hole image b, and the picked up peripheral point includes a point located in such an abnormal image portion, the following procedure is performed. The central coordinates mx and my are measured.

First, if the hole image b is normal on the screen, the image center of gravity g is set so that the peripheral edge of the hole image b is within the area.
A predetermined annular area as shown by a virtual line in FIG. 4 (a) is set with the center as the center, and among the peripheral points picked up as described above, the peripheral points outside the annular area are points located in the abnormal image portion. And delete it. In the example of FIG. 4, the peripheral points of are deleted.

Next, from the coordinates of the remaining peripheral points, FIG.
A regression ellipse q representing the hole image is obtained as shown in. In this case, even if it is an abnormal image part, if the degree of abnormality is slight, the peripheral points picked up from it will enter the annular area, but such peripheral points have a large amount of deviation from the regression ellipse. Become. Therefore, the deviation amount of each peripheral point with respect to the regression ellipse is calculated, and when the maximum deviation amount of the deviation amounts of these peripheral points is equal to or greater than a predetermined value, the peripheral points of the maximum deviation amount are deleted from the coordinates of the remaining peripheral points. The calculation of the regression ellipse is repeated until the maximum deviation amount becomes less than the predetermined value. The regression ellipse q obtained in this way matches the normal image of the hole B, and thus the center coordinates mx and my of the hole image b are set to the regression ellipse q.
It can be accurately obtained as the center coordinate of. If the hole B faces the camera 1, the hole image b becomes circular,
The hole image b is deformed into an elliptical shape as the hole B is displaced from the optical axis of the camera 1, but if the hole image b is circular, the circle,
If it is an ellipse, a regression ellipse that represents that ellipse is obtained,
The measurement accuracy of the center coordinates mx and my of the hole image b is improved.

When the center coordinates mx and my are measured as described above, the image data at the time of slit light irradiation is called next to measure the x coordinate sx of the slit light image s. In this measurement, the y coordinates of the upper end point qa and the lower end point qb of the regression ellipse q in the y-axis direction are obtained in advance, and as shown in FIG. A pair of symmetrical upper and lower windows Wa, Wb which are long in the x-axis direction and are separated from each other by an equal distance.
The image centroids ga and gb of the slit light image s in b are detected, and the average value of the x coordinates of both centroids ga and gb is obtained as the x coordinate sx of the slit light image s.

By the way, in this embodiment, since the XY coordinate plane is made parallel to the work A when the measuring head is moved to the measuring position by the moving mechanism, the slit light image s is the y-axis of the screen. Parallel to the center of gravity ga, gb
X-coordinates are equal to each other, but when the work A tilts around the X-axis of the spatial coordinate system, the slit light image s tilts with respect to the y-axis,
The x-coordinates of the center of gravity ga and gb have different values.
Therefore, when the deviation between the centers of gravity ga and gb exceeds a predetermined value, the fact is displayed. Even if the work A is tilted around the X axis, if the Z-axis displacement amount dZ of the work A is measured as the Z-axis displacement amount of the center M of the hole B, the center coordinates mx and my of the hole image b are measured. And the center coordinates MX and MY of the hole B have the same relationship as above. Here, the amount of displacement of the center M of the hole B in the Z-axis direction is calculated from the x-coordinate of the intersection point of a line parallel to the x-axis passing through the center m of the hole image b and a line matching the slit light image s. It can be obtained by the equation (4). Since this intersection is the midpoint between the centers of gravity ga and gb, the average value of the x-coordinates of the centers of gravity ga and gb is the x-coordinate of the intersection. Therefore, even if the work A is tilted around the X axis with respect to the XY coordinate plane, the position of the center M of the hole B can be measured by the same processing as that when the work A is parallel to the XY coordinate plane. .

The measurement of the center position of the hole B of the work A has been described above. However, when the center position of the screw hole of the nut C fixed to the work A is measured as shown in FIG. Since the outline of the image of the screw hole is sometimes blurred by the reflected light from the inner surface of the nut C, the screw D is screwed onto the nut C, and the head of the screw D is colored black so that the head looks dark. It is conceivable to measure the center position of the head as the center position of the screw hole. Also in this case, the spot light and the slit light are emitted in the same manner as above, the center coordinates of the image of the screw head at the time of the spot light irradiation, and the position of the slit light image at the time of the slit light irradiation are measured, and the space is measured. The center position of the screw head in the coordinate system can be accurately obtained.

By the way, if the camera 1 and the slit light source 3 are arranged so that the slit light surface SP obliquely intersects the optical axis of the camera 1 as described above, the cross-section measurement of the workpiece by the light cutting method can be performed. When the work is an automobile body, it becomes possible to measure the cross section of the roof side rail, side sill, pillar, etc. and the position of the measurement target part such as a hole that appears dark in the same measuring device, which is advantageous. is there.

[0023]

As is apparent from the above description, according to the present invention, the center position in the spatial coordinate system of the measurement target portion of the work can be measured by a single image pickup means, and the cross section of the work can be measured by the same equipment. Since measurement can also be performed, the cost of measurement equipment can be reduced, the time required for measurement can be shortened, and online measurement on a line with a short takt time can be performed without difficulty.

[Brief description of drawings]

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

2A is a view seen from the Y-axis direction of FIG. 1, and FIG. 2B is a view seen from the X-axis direction of FIG.

FIG. 3 (a) is a diagram showing a screen at the time of spot light irradiation,
(B) The figure which shows the screen at the time of slit light irradiation

4A and 4B are views showing image processing for measuring the center coordinates of the hole image.

FIG. 5 is a diagram showing image processing for measuring the position of a slit light image.

FIG. 6 is a sectional view showing another example of a work whose position is measured by the method of the present invention.

[Explanation of symbols]

1 camera (imaging means) 2 spot light source 3 slit light source 4 image processing circuit A work B hole part (measurement target part) b hole image SP slit light surface s slit light image

Claims (1)

[Claims] 1. A method for measuring the position of a work, which optically measures the center position of a measurement target portion of the work that appears dark when the work is imaged. A step of capturing an image, a step of capturing an image of the work by the image capturing means while irradiating the work with slit light along a surface obliquely intersecting the optical axis of the image capturing means, and a dark portion on the screen of the image capturing means during irradiation of the spot light. And a step of measuring the center coordinates on the screen of the image of the measurement target portion appearing as, in the optical axis direction of the imaging means from the position on the screen of the slit light image appearing as the bright portion on the screen of the imaging means during irradiation of the slit light. A step of obtaining a displacement amount of the work; and a step of obtaining the center position of the measurement target portion in the spatial coordinate system from the displacement amount and the center coordinates. Position measurement method.