JPH10105720A - Optical measurement method for hole position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract a picture part corresponding to a work face, whose position should be measured, of a light-sectioned picture to accurately measure its position with respect to the method which measures the center position in a space coordinate system of a hole of a work in accordance with center coordinates of a hole picture and the position of the light-sectioned picture of the work. SOLUTION: Attribute information RIN and ROUT which indicate a measurement range, where the work face whose position should be measured exists, based on the center of a hole B are stored at the time of teaching (A-1, B-1, C-1). A picked-up image of a light-sectioned picture (s) is subjected to masking processing, where a part other than the measurement range is masked based on said attribute information, based on coordinates of a center (m) of the hole picture (A-3, B-3, C-3). A template TPs is used for the masked image to obtain an approximate position of the light- sectioned picture (s) existing in the measurement range by pattern matching. Plural measurement positions are set based on this approximate position so as to cross the light-sectioned picture existing in the measurement range. The position of the light- sectioned picture existing in the measurement range is obtained in accordance with coordinates of picture points coinciding with individual measurement positions of the light-sectioned picture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for optically measuring the position of a hole provided in a work.

[0002]

2. Description of the Related Art Conventionally, this type of method has been disclosed in
According to the publication No. 0428, a first imaging step of capturing an image of a hole in a work by an imager directly facing the work, and irradiating the work with slit light along a plane oblique to an optical axis of the imager, A second imaging step of imaging the optical cut image of the work drawn by the slit light applied to the work with the imager;
A first measurement step of measuring the center coordinates on the screen of the hole image appearing on the imaging screen obtained in the imaging step, and a position on the screen of the light-section image appearing on the imaging screen obtained in the second imaging step is measured. Calculating a displacement of the workpiece in the optical axis direction of the imager from the position of the light-section image on the screen in the second measurement step, and calculating a center position of the hole in a spatial coordinate system from the displacement and the center coordinates; The method comprising the steps is known.

In this method, in the second measurement step, two measurement points intersecting the light-section image are set at a predetermined distance to one and the other in the diameter direction of the hole image, respectively, and each measurement point of the light-section image is set. The coordinates of the image points that match the location are detected, and the position of a straight line connecting these image points is defined as the position of the light-section image on the screen.

[0004]

A large work such as an automobile body has a plurality of holes to be measured.
There are a plurality of types, such as those provided on a plane portion of a work and those provided on a stepped seating surface of the work.

Here, when measuring the holes provided on the stepped seating surface of the work, the light-section image is not linear, and if the measuring places are set as described above, the measuring places will be the work outside the seating surface. Intersect the part of the light section image drawn on the general surface,
The portion of the light-section image where the measurement location intersects, for example, intersects with the portion of the light-section image drawn on the seat surface, causing a measurement error.

SUMMARY OF THE INVENTION In view of the above, the present invention makes it possible to reliably set a measurement position in a light-section image portion drawn on a predetermined work surface, thereby improving the measurement accuracy of a hole position. The task is to provide a method.

[0007]

Means for Solving the Problems In order to solve the above problems,
The present invention is a method for optically measuring the position of a hole provided in a work, comprising: a first image pickup step of picking up an image of a hole in a work by an imager directly facing the work; A second imaging step of irradiating the workpiece with slit light along a surface oblique to the axis and capturing a light cut image of the workpiece drawn by the slit light applied to the workpiece by the imager;
A first measurement step of measuring the center coordinates on the screen of the hole image appearing on the imaging screen obtained in the imaging step, and a position on the screen of the light-section image appearing on the imaging screen obtained in the second imaging step is measured. Calculating a displacement of the workpiece in the optical axis direction of the imager from the position of the light-section image on the screen in the second measurement step, and calculating a center position of the hole in a spatial coordinate system from the displacement and the center coordinates; In the method, the second measuring step reads out attribute information stored in advance, which represents a measuring range in which a work surface whose position is to be measured is present with reference to the center of the hole, and performs the measuring in the first measuring step. Masking a portion other than the measurement range of the imaging screen obtained in the second imaging process based on the center coordinates based on the attribute information; and performing pattern matching on the masked screen. Calculating the approximate position of the light-section image existing in the measurement range, and setting a plurality of measurement locations so as to intersect the light-section image existing in the measurement range based on the determined approximate position. And detecting the coordinates of image points that match each measurement point in the light section image;
Obtaining the position of the light-section image on the screen from the coordinates of these image points.

According to the present invention, only the light-section image existing in the measurement range is extracted by masking, and the measurement location is set based on the approximate position of the light-section image determined by pattern matching in this state. This measurement location surely intersects the light-section image existing in the measurement range. For example, when measuring a hole provided in a stepped seating surface of a workpiece, image formation is performed by creating and storing attribute information representing the inner diameter and outer diameter of the seating surface with respect to the center of the hole with the seating surface as a measurement range. By masking a portion of the screen that does not match the seat surface, only the light-section image drawn on the seat surface can be extracted, and the measurement location can reliably cross the light-section image drawn on the seat surface. Thus, the position of the cut image obtained from the coordinates of the image point that matches the measurement point represents the position of the seat, and the displacement of the hole in the optical axis direction of the imager can be accurately determined using the seat as the measurement reference plane. Measurement accuracy and the hole position measurement accuracy is improved.

[0009]

FIG. 1 shows a work A such as an automobile body.
1 shows an outline of an optical measuring device used for measurement of the object A. The device includes a slit light source 1 composed of a slit laser or the like for irradiating a workpiece A with a slit light, an imager 2 composed of a CCD camera, and an imager 2 composed of a CCD camera. It comprises a spot light source 3 composed of a group of light emitting diodes arranged in a ring around the lens 2a, and an image processing circuit 4 for inputting an image signal from the image pickup device 2.

The slit light source 1, the image pickup device 2, and the spot 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 located at a position facing a plurality of measuring parts of the work A. Move in order to measure each measurement site. The slit light source 1 and the image pickup device 2 are mounted on the measuring head in such a positional relationship that the optical axis of the image pickup device 2 obliquely intersects the optical surface SP of the slit light at a predetermined angle θ (for example, 45 °).

FIG. 1 shows a state in which a measuring head is moved to a position facing a hole B provided in a work A to perform hole measurement. At the time of hole measurement, the work A is first irradiated with a spot light from the spot light source 3 in a state where the image pickup device 2 is directly opposed to the work A. (With shading) is transmitted to and stored in the image processing circuit 4, and then the work A is irradiated with the slit light from the slit light source 1 while the spot light source 3 is turned off. Then, the image data (with shading) is transmitted and stored in the image processing circuit 4.

When the spot light is radiated, the image is displayed on the imaging screen as shown in FIG.
As shown in (A), the hole image b appears as a dark portion, and a light cut image S corresponding to the cross-sectional shape of the work A drawn by the slit light on the surface of the work A at the time of the irradiation of the slit light is captured. As shown in FIG. 3 (B), the light-section image s appears as a bright portion on the imaging screen. Incidentally, when the slit light is applied so as to straddle the hole B, the light cut image s becomes the hole B
Is divided at the part corresponding to.

By the way, the point of intersection of the optical axis of the imaging device 2 and the slit optical surface SP is the origin 0, the optical axis of the imaging device 2 is the Z axis, and the coordinate axis parallel to the slit optical surface SP orthogonal to the Z axis is the Y axis. Consider a spatial coordinate system in which a coordinate axis orthogonal to the Y axis and the Z axis is the X axis. Assuming that a projected image of the spatial coordinate system on the XY coordinate plane is taken by the image pickup device 2, the screen of the image pickup device 2 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 0 as the origin, the x-axis coordinate values and the y-axis coordinate values of the screen are spatial coordinates It represents the horizontal distance and vertical distance from the origin 0 on the XY coordinate plane of the system.
Then, as shown in FIG. 2, the ratio between the x, y coordinates mx, my on the screen of the center m of the hole image b and the X, Y coordinates MX, MY in the spatial coordinate system of the center M of the hole B is obtained from the image pickup device 2. Origin 0
Is equal to the ratio of the distance L from the imager 2 to the work A, and therefore, the displacement amount of the work A in the Z-axis direction is d.
As Z, MX = mx · (L−dZ) / L, and MY = my · (L−dZ) / L, and Z coordinate MZ in the spatial coordinate system of the center M of the hole B
Becomes MZ = dZ.

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

Next, a method of obtaining the center coordinates mx and my of the hole image b will be described. First, a differentiated screen is created by differentiating the brightness distribution of the imaging screen with shading. Since the luminance distribution of the imaging screen changes sharply at the edge of the hole in the hole image b, the differential value increases at the edge of the hole, and the differentiated screen corresponds to the edge of the hole as shown in FIG. A ring-shaped image br appears. Next, a template TP representing the shape of the hole edge of the hole image b is created by graphic processing based on the hole diameter data stored at the time of teaching for measuring the master work, and FIG.
As shown in (B), pattern matching is performed on the differentiated screen by the normalized correlation method or the like, and the position of the approximate center m 'of the hole image b is determined. In order to reduce the processing time of the pattern matching, the pattern matching is performed by reducing the differentiated screen and the template TP at the same ratio (for example, 1/4). By the way, it is possible to binarize the imaging screen with shading and make the area center of gravity of the dark part of the binarized screen the approximate center of the hole image b. However, the dark area of the binarized screen is reflected by light reflected from the inner surface of the hole. May be deformed. In this case, since the area center of gravity of the dark part is greatly deviated from the normal center of the hole image, it is more accurate to determine the position of the approximate center m 'of the hole image b by pattern matching with the differentiated screen as described above.

Next, as shown in FIG. 4 (C), a plurality of scanning lines LSC, which are measurement locations along a plurality of radiation directions centered on the approximate center m ', are set on the imaging screen with shading. Each scanning line LSC is set to extend over a predetermined range inside and outside the hole edge of the hole image b based on the hole diameter data stored at the time of teaching. And each scanning line L
Based on the luminance distribution on the SC, the coordinates of the hole edge point Pb that matches each of the scanning lines LSC at the hole edge of the hole image b are detected.

FIG. 5A shows a luminance distribution curve on the scanning line LSC, and the luminance sharply decreases at the edge of the hole. Therefore, when a differential curve obtained by differentiating the luminance distribution curve is created, a peak appears at a position corresponding to the edge of the hole as shown in FIG. In this case, the position of the vertex of the differential curve may be set as the position of the hole edge point Pb, but it is difficult to uniquely specify the vertex, and there is variation. Therefore, in the present embodiment, the vertices of the differential curve are determined temporarily, and the points on the differential curve at each of two pixels before and after the pixel (pixel) that matches this vertex are determined. , The equation of the parabola LP approximating the vertex of the differential curve is calculated by regression processing, and the position of the vertex of the parabola is defined as the position of the hole edge point Pb.

Incidentally, the above-described scanning line LS in the radial direction is used.
Instead of C, a scanning line parallel to the x-axis direction and a scanning line parallel to the y-axis direction are formed on both sides in the y-axis direction at the approximate center of the hole image b so as to intersect the hole edge of the hole image b. It is also conceivable to set both sides in the x-axis direction. However, in this case, the scanning line obliquely intersects the edge of the hole, the luminance distribution on the scanning line changes slowly, and the peak of the differential curve becomes low and gentle. Therefore, even when the approximate parabola LP is obtained as described above, the positions of the vertices are apt to fluctuate, and it becomes difficult to obtain the detection accuracy of the hole edge point Pb. On the other hand, if the scanning line LSC is set in the radial direction as in the present embodiment, the scanning line LSC becomes substantially orthogonal to the edge of the hole, and the luminance distribution on the scanning line LSC changes suddenly. The peak of the differential curve is high and steep, and the detection accuracy of the hole edge Pb is improved.

It is also conceivable to binarize a picked-up image with shading, set a long window in the radial direction as a measurement point on the binarized screen, and detect a light-dark boundary in the window as a hole edge point. However, in the binarized screen, the disturbance image portion due to the reflected light from the inner surface of the hole may appear as a bright portion image, so that the detection accuracy of the hole edge point is deteriorated. On the other hand, as in the present embodiment, if the scanning line LSC, which is a measurement location, is set on the imaging screen with shading and the luminance distribution on the scanning line LSC is detected, the luminance change becomes gentle in the disturbance image portion. The disturbance image portion can be determined from the luminance change, that is, the differential curve, and the detection accuracy of the hole edge point Pb is improved.

Incidentally, the brightness in the bright and dark portions of the imaging screen is not uniform, and when the brightness distribution curve on the scanning line LSC is differentiated over the entire area, a plurality of vertices appear in the differential curve. In some cases, it may be difficult to determine whether the hole corresponds to the edge of the hole. Therefore, in the present embodiment, a differential curve is created for a region where the luminance difference before and after the decrease is the largest among the regions where the luminance distribution curve continuously decreases, and the above processing is performed. This prevents erroneous detection due to the above. In this case as well, a plurality of vertices may appear due to noise or the like. However, since vertices due to noise are low, the detection accuracy can be ensured by excluding vertices below a predetermined threshold from processing targets.

When the position of the hole edge point Pb on each scanning line LSC is detected as described above, the x and y coordinates on the screen of each hole edge point Pb are calculated from the setting data of each scanning line LSC.
Next, a regression circle Cb (see FIG. 4D) that approximates the hole image b from the coordinates of the hole edge points Pb (regression processing is performed so that the total amount of deviation of each hole edge point Pb from the circle is minimized). Then, the center coordinates mx and my are obtained by using the center of the regression circle Cb as the center m of the hole image b. When obtaining the regression circle Cb, the shift amount of each hole edge point Pb with respect to the circle calculated by the regression processing is obtained, and when the shift amount of any of the hole edge points Pb is equal to or more than a predetermined value, the hole edge point Pb is determined. Is repeated and the regression processing is performed again until the deviation amounts of all the hole edge points Pb become equal to or less than a predetermined value.

The method of detecting the center coordinates mx and my of the hole image b has been described above. Next, the method of detecting the x coordinate sx of the light-section image s will be described. First, a template TPs representing the fragment shape of the light-section image s is created from the teaching data by graphic processing, and a shaded imaging screen of the light-section image S shown in FIG.
As shown in (E), pattern matching is performed by the normalized correlation method or the like using the template TPs, and the approximate x coordinate sx ′ of the light section image s is determined. Note that, in order to reduce the processing time of the pattern matching, it is desirable to perform the pattern matching by reducing the imaging screen and the template TPs to the same ratio (for example, 1/4).

Next, as shown in FIG. 4F, based on the y-coordinate of the regression circle Cb at the determined x-coordinate sx ', the upper and lower sides of the regression circle Cb are parallel to the x-axis, respectively. A plurality (for example, three) of scanning lines LSC, which are important measurement locations, are set at a predetermined pitch in the y-axis direction. According to this, each scanning line L
The SC surely crosses a predetermined portion of the light section image s. Next, from the luminance distribution on each scanning line LSC, the coordinates of an image point Ps that matches each scanning line LSC of the light-section image s are detected,
From the coordinates of these image points Ps, as shown in FIG.
An equation of a regression line Ls (a line obtained by regression processing so as to minimize the total amount of deviation from the line of each image point Ps) approximating the light section image s is calculated, and the x coordinate of the regression line Ls is calculated. The x-coordinate sx of the light-section image s is set.
If the work A is normal, the image line Ls is parallel to the y-axis. However, if the work A is inclined with respect to the XY coordinate plane of the space coordinate system, the image line Ls is inclined with respect to the y-axis. . In this case, an abnormal display is performed, and the x coordinate of the intersection of the image line Ls and a straight line parallel to the x axis passing through the center of the regression circle Cb is obtained as a temporary x coordinate sx of the light section image s.

It is to be noted that a binarized image is prepared by binarizing the imaging screen with shading, and a window that is long in the x-axis direction, which is a measurement point, is set at the position of the scanning line LSC. Can be determined as the image point Ps, but the image portion due to noise or disturbance light may appear as a bright portion together with the light cut image on the binarized screen, so that the detection accuracy deteriorates.

Therefore, in this embodiment, as shown in FIG. 6A, a brightness distribution graph representing the brightness distribution on the scanning line is created, and from this graph the peak degree P of the brightness change at each point on the scanning line is obtained. The coordinates of the image point Ps that matches the light section image s are detected based on the peak degree P. The peak degree P of a point on the scanning line whose x coordinate is n is defined as an an luminance point on the luminance distribution graph at the point, and luminance at both ends of a measurement range W of a predetermined width set on the scanning line with the point as the center. The luminance points on the distribution graph are defined as bn and cn, respectively, and are obtained as values representing the height of an with respect to the connection line connecting bn and cn. In this case, the height of an with respect to the middle point of the connection (= {2an− (bn + cn)} / 2) may be used as the peak degree P, and the length of a perpendicular line descending from an in the connection is defined as the peak degree P. It is good. Here, FIG.
, The peak degree P at the point X = n1 has a positive value, and the peak degree P at the point X = n2 has a negative value. Then, a zero point P0 at which the peak degree becomes zero appears on both sides of the peak of the peak degree distribution curve, and a section between the zero points P0 is a part which is not affected by the background illumination by the illuminator on the line. Therefore, as shown in FIG.
If the area centroid G ′ in the section between 0 is obtained and the position is set as the position of the image point, the position of the image point can be accurately detected without the influence of the background illumination.

However, the inclination of the peak of the luminance distribution graph on the imaging direction side (right side) tends to be gentler than the inclination on the opposite side, so that the area center of gravity G 'of the peak is the position of the peak of the peak. From the camera to the imaging direction. On the other hand, the peaks of the peak degree distribution graph have substantially the same inclination on both sides even if the inclinations of the peaks of the luminance distribution graph are different on both sides. Therefore,
The area center of gravity G of the peak in the section between the zero points P0 of the peak degree distribution graph does not shift to the left from the position of the peak of the peak.
Therefore, in order to improve the detection accuracy of the image points, the area centroid G of the section between the zero points P0 of the peak degree distribution graph is obtained,
It is desirable that the position of the center of gravity G be the x coordinate of the image point Ps.

By the way, depending on the measurement site of the work A, as shown in FIG.
P exists or the work A as shown in FIG.
Hole B is provided in the stepped seating surface AS of FIG.
As shown in 1), the hole B may be formed of a cylindrical member AC such as a collar or a nut welded to the work A. At the measurement site in FIG. 7 (A-1), the light-section image s also appears inside the hole as shown in FIG. 7 (A-2), and in the measurement site in FIG. 7 (B-1). 7 (B-2), the light-section image s has a stepped shape, and at the measurement site in FIG. 7 (C-1), the light-section image s as shown in FIG. 7 (C-2). Is divided into an image corresponding to the surface of the work A and an image corresponding to the end surface of the tubular member AC.

When pattern matching using the template TPs is performed on an imaged screen on which such a light-section image s appears, the template TPs matches the image in the hole in FIG. In FIG. 7 (B-2), the template TPs matches the image corresponding to the work general surface outside the seating surface, and in FIG. 7 (C-2), the template TPs matches the image corresponding to the end surface of the tubular member AC. In some cases, it is not possible to determine whether the template TPs matches the light-section image s present in the predetermined measurement range of the work A, and the displacement dZ of the work A cannot be accurately detected.

Therefore, in the present embodiment, the attribute information indicating the measurement range in which the work surface whose position is to be measured exists based on the center of the hole B, that is, the data of the inner diameter RIN and the outer diameter ROUT of the measurement range is taught. Measured and stored at the time, and when measuring at each measurement site, FIG. 7 (A-3)
(B-3) As shown in (C-3), the inside of the circle having a radius of RIN and the outside of the circle having a radius of ROUT centered on the hole center m obtained as described above from the hole image b are masked. Then, pattern matching is performed in this state.
According to this, the template TPs matches the portion of the light section image s corresponding to the predetermined measurement range. Then, by setting the scanning line LSC as described above between the y coordinate of the circle having the radius of RIN and the y coordinate of the circle having the radius of ROUT in the approximate x coordinate of the light-section image s obtained from the pattern matching. Thus, the x coordinate sx of the light-section image s corresponding to the work surface in the predetermined measurement range can be correctly obtained, and the displacement dZ of the work A can be accurately detected. Note that, at the measurement site shown in FIG.
7 is set based on the diameter of ROUT, and there is no ROUT.
At the measurement site (B-1), RIN and ROUT are
7C is set based on the inner and outer diameters of the S. At the measurement site in FIG.
Set based on the diameter of the mounting hole.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of an optical measuring device.

2A is a diagram viewed from the Y-axis direction in FIG. 1, and FIG. 2B is a diagram viewed from the X-axis direction in FIG.

FIG. 3A is a diagram illustrating an imaging screen of a hole image, and FIG. 3B is a diagram illustrating an imaging screen of a light-section image.

FIG. 4A is a diagram showing a differentiation screen of a hole image, and FIG.
A diagram showing a situation of pattern matching, (C) a diagram showing setting of scanning lines, (D) a diagram showing a regression circle approximating a hole image,
(E) A diagram showing the state of pattern matching of the light-section image with respect to the imaging screen, (F) a diagram showing the setting of scanning lines,
(G) Diagram showing image lines

5A is a diagram illustrating a luminance distribution on a scanning line in FIG. 4C, and FIG. 5B is a diagram illustrating a differential curve and an approximate parabola of the luminance distribution.

6A is a diagram illustrating a luminance distribution on a scanning line in FIG. 6B, and FIG. 6B is a diagram illustrating a method for detecting image points;

FIG. 7 (A-1), (B-1), and (C-1) are diagrams showing the cross-sectional shapes of respective measurement sites, (A-2), (B-2), and (C-2).
The figure which shows the imaging screen of the light-section image of each measurement part, (A-
3) (B-3) (C-3) A diagram showing a masked imaging screen

[Explanation of symbols]

Reference Signs List 1 slit light source 2 imager 3 spot light source 4 image processing circuit A work B hole b hole image m center of hole image s light cut image TPs template for pattern matching sx 'approximate position of light cut image LSC scanning line Ps image point sx light Cutting image position

Claims (1)

[Claims] 1. A method for optically measuring the position of a hole provided in a work, comprising: a first image pickup step of picking up an image of a hole in the work by an imager directly facing the work; A second imaging step of irradiating the workpiece with slit light along a plane oblique to the optical axis and capturing an optical cut image of the workpiece drawn by the slit light applied to the workpiece by the imager; and a first imaging step. A first measurement step of measuring the center coordinates of the hole image appearing on the obtained imaging screen on the screen, and a second measurement measuring the position on the screen of the light-section image appearing on the imaging screen obtained in the second imaging step From the step of calculating the amount of displacement of the workpiece in the optical axis direction of the imager from the position of the light section image on the screen, and calculating the center position of the hole in the spatial coordinate system from the amount of displacement and the center coordinates. The method comprising: The measuring step is a step of reading out attribute information stored in advance, which represents a measurement range in which a work surface whose position is to be measured is present with reference to the center of the hole, and using the center coordinates measured in the first measurement step as a reference, Masking a portion of the imaging screen obtained in the step other than the measurement range based on the attribute information, and determining a rough position of the light-section image existing in the measurement range by pattern matching on the masked screen. Setting a plurality of measurement points so as to intersect the light-section image existing in the measurement range based on the determined approximate position; and detecting coordinates of an image point matching each measurement point of the light-section image And a step of obtaining the position of the light-section image on the screen from the coordinates of these image points.