JP2552966B2 - Correction method of error in optical measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an optical measuring device provided with a projector for irradiating a work with slit light and an imager for picking up a light section image drawn by the slit light irradiated on the work. The present invention relates to a method for correcting an error when measuring the shape and position of a work from a light section image on the screen.

[0002]

2. Description of the Related Art When a work is irradiated with slit light, a cross section of the work surface when the work is cut by a light cutting plane parallel to the slit light including the optical axis by the slit light irradiated on the work surface. A light-section image that matches the shape is drawn, this light-section image is captured by an imager, the position of a specific point of the light-section image on the screen of the imager is measured, and on the light-section plane corresponding to that point. There is known a method of calculating the coordinate value of the point and measuring the shape and position of the work. Further, when the measurement is performed using an image pickup device, as seen in JP-A-62-200207 and JP-A-1-221632,
It is also known to measure the image distortion of an image pickup device in advance and correct the error due to the image distortion.

[0003]

By the way, in the case of measuring the shape and position of the work as described above by using the optical measuring device provided with the projector for irradiating the work with slit light and the image pickup device, the above-mentioned image pickup device is used. In addition to the error due to the image distortion, the error due to the focus shift and the error due to the shift in the relative positional relationship between the projector and the image pickup device may occur, and it is desirable that these errors can be collectively corrected. ing. An object of the present invention is to provide an error correction method that meets such a demand.

[0004]

In order to achieve the above object,
The present invention uses an optical measurement device that includes a light projector that irradiates a work with slit light and an imager that captures a light-sectioned image drawn by the slit light that is irradiated onto the work. Is a method of correcting an error when measuring the shape or position of a work, in which a reference block having the same shape as or similar to the work is arranged facing the optical measuring device, and the reference block is set to the optical axis of the slit light. The light cutting image of the reference block is taken while moving to a plurality of measurement points on the light cutting surface parallel to the slit light including the moving amount on the light cutting surface of the reference block and the light of the reference block for each measurement point. The amount of deviation from the predetermined correspondence with the amount of movement of the cut image on the screen is measured as an error, the correction formula for the error is calculated from the measured error, and the measurement value obtained from the optical cut image when measuring the workpiece is calculated. In the correction formula And correcting me.

[0005]

[Operation] The reference block is moved on the light cutting plane, the amount of movement of the light cutting image of the reference block on the screen of the image pickup device is measured for each measurement point, and the geometrical position is determined based on the relative positional relationship between the image pickup device and the projector. Indexing the movement amount on the light cutting surface of the reference block corresponding to the movement amount on the screen of the light cutting image based on the correspondence between the coordinate value on the screen and the coordinate value on the light cutting surface, The deviation amount between this movement amount and the actual movement amount of the reference block is measured as an error. This error includes all the errors that the optical measuring device has, such as the error due to the image distortion of the image pickup device, the error due to the focus shift, and the error due to the shift of the relative positional relationship between the projector and the image pickup device. By correcting the measurement value at the time of measuring the work using the correction formula obtained from, all the errors can be corrected collectively and the work can be accurately measured.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The illustrated embodiment is an optical measuring device for measuring the position of the work A based on a light section image of the work A formed of the roof side rails of the vehicle body shown in FIG. The present invention is applied to the correction of
As shown in FIG. 2, the measuring device includes a projector 1 including a laser or the like for irradiating a work A with vertical slit light,
The image pickup device 2 formed of a CCD camera for picking up the light section image S ′ of the work A, which is an image of the slit light on the surface of the work A, and the optical axis of the slit light and the optical axis of the image pickup device 2 have a required angle θ. The base plate 3 is attached to the common base plate 3 in such a positional relationship as to be obliquely crossed. Reference numeral 4 in the figure is an electronic control circuit for performing image processing.

As shown in FIG. 3, the screen W of the image pickup device 2 has a maximum part in the X-axis direction with the horizontal and vertical coordinate axes of the screen W as the X-axis and the Y-axis, respectively. Y for department
A light-section image S having a curved portion on the upper side in the axial direction and a linear portion on the lower side is formed. In this image S, since the maximum portion is rounded and there is no clear corner portion suitable for the position determination reference,
Screen W of the intersection Q of the curved line S ₁ and the straight line S ₂
The above X and Y coordinate values are calculated from the equation of the curve S _{1 and} the equation of the straight line S ₂ , and the position of the work A is measured with the intersection Q as a reference point.

Here, the equation of the curve S ₁ can be approximately expressed as an equation of a circle passing through the three points in the specific region of the curved portion, and therefore the first to third portions of the upper half of the light section image S are represented. 3 windows W1, W2, W3 are set, and the centers of gravity G1, G of the light section images S in these windows are set.
2. The X and Y coordinate values of G3 were measured, the equation of a circle passing through these three centers of gravity was determined, and this was used as the equation of the curve S ₁ . By the way, the light section image S has a certain width, and the coordinate value of the center of gravity changes due to a subtle difference in whether or not the amount of light received by the pixels located near the boundary line of the image S exceeds a predetermined threshold value. Even if the same work is placed at the same position, the coordinate value of the center of gravity changes slightly. In this case, comparing the change rate of the radius of the circle with respect to the change of the coordinate value of the image center of gravity G2 of the intermediate second window W2 and the change rate of the radius of the circle with respect to the change of the coordinate values of the other center of gravity G1 and G3, The former rate of change is larger, and the error in the coordinate value of the center of gravity G2 greatly affects the calculation accuracy of the equation of the curve S ₁ . On the other hand, the curvature of the work A does not fluctuate to the left for individual products. If this curvature radius is measured in advance, the equation of the curve S ₁ can be calculated from the coordinate values of the two points on the curve S ₁ and the curvature radius. Can be calculated. When the curve equation is sampled and calculated from a minute area, in order to eliminate the influence of the error of the coordinate value of G2 and improve the equation calculation accuracy, the curve S ₁ is calculated from two points and the radius of curvature. It is advantageous to calculate the equation,
Therefore, in this embodiment, as shown in FIG.
The first and third windows W1 and W3 are set in the upper half part of each of the windows, the coordinate values of the image centroids G1 and G3 of the respective windows are measured, and from this and the radius of curvature R, the equation of the curve S ₁ is obtained. Was calculated. When measuring the radius of curvature R,
A master work having the same shape as the work A is placed at a predetermined reference position, a light-section image of the master work is taken, and the three first to third windows W1, W2, and W3 are set on the screen W, and these windows are set. The radius of the curve of the light-cut image of the masterwork is obtained from the image center of gravity, and the average value of the radii obtained by repeating this several times is set as the radius of curvature R, and this value is stored in the electronic control circuit 4. In the case of performing online measurement on a production line, the master work may be a vehicle body flowing through the line. In that case, the first one or several machines at the time of starting the measurement are master works. The equation of the straight line S ₂ of the light-cut image S of the work A is set with the fourth and fifth windows W4 and W5 in the lower half of the image S, and the coordinate values of the image centroids G4 and G5 of the respective windows are set. It is calculated by measuring.

By the way, when the relative positional relationship between the work A and the image pickup device 2 changes, the position of the light section image S on the screen W also changes, and the windows W1 to W5 may be set to the fixed positions of the screen W. , The window is out of the light section image S,
Further, the windows W1 and W3 set in the curved portion may be applied to the image portion having a small radius of curvature, and the curve equation may not be accurately calculated. In this case, as shown in FIG. 4, it is conceivable that the positions of the windows W1 to W5 are set with reference to the leftmost end point P of the maximum portion in the X-axis direction of the light section image S, but the light section image S It is difficult to unambiguously determine the Y-axis coordinate value of the point P unless the maximum part of the is not squared, and the relative positions of the windows W1 to W5 with respect to the light section image S vary in the Y-axis direction. . In view of this, in the present embodiment, as shown in FIG. 5A, the sixth and seventh upper and lower parts that are long in the Y-axis direction are provided at positions separated by a predetermined length to the right with respect to the X coordinate value of the point P. Set a pair of windows W6 and W7,
The coordinate values of the image centroids G6 and G7 of the respective windows are measured, and the coordinate value of a point having a predetermined correlation with the centroids G6 and G7, for example, the coordinate value of the reference point M which is the midpoint of the centroids G6 and G7, is calculated. Based on this point M, the positions of the windows W1 to W5 are determined as shown in FIG. 5 (b).

According to this, even if the position of the light cut image S on the screen W is displaced, the windows W1 to W5 can be accurately set while maintaining a constant correlation with the image S, and thus the curve S ₁ And the straight line S ₂ are correctly calculated, and the coordinate value of the intersection Q can be accurately obtained. In FIG. 5B, dxn and dyn are the positions in the X-axis direction and the Y-axis direction with respect to the reference point M of the upper left corner of each window Wn, Wxn,
Wyn is the length of each window Wn in the X-axis direction and the Y-axis direction, and is stored in the electronic control circuit 4.

Further, when the work A is displaced in the optical axis direction of the slit light, the light section image S is displaced in the X axis direction on the screen W and the enlargement ratio of the image S is changed. This will be described with reference to FIG. In FIG. 6, the optical axis of the image pickup device 2 is the Z axis,
The image pickup device 2 is placed at a point C on the Z axis, the X axis and the Y axis are taken on the reference image pickup surface W ′ of the image pickup device 2 which is separated from the point C by a predetermined reference distance L, and the light of slit light is emitted. A U-axis in the optical axis direction and a V-axis orthogonal to the optical-axis are arranged on a light-cutting plane T parallel to the slit light including the axis so that the V-axis coincides with the Y-axis and XY
It shows a state in which the coordinate system is set so that the U axis passes through the origin O of the coordinates. Now, let us say that the image length when an image of length H on the light section plane T, which is located at a distance a in the Z-axis direction from the image plane W ′, is projected onto the image plane W ′ with the point C as the viewpoint. h
Then, the enlargement ratio K = h / H is L / (La).
Here, assuming that the U-axis coordinate value of H is u and the X-axis coordinate value of h is x (the left side of the origin O is positive and the right side is negative), a is ucos θ.
Therefore, the enlargement ratio K is K = L / (L-ucos θ) (1) On the other hand, tan α = x / L, where α is the angle between the Z-axis and the line of sight from point C to H on the X-Z coordinate plane, and the X-axis coordinate value of H is usinθ, so tan α = usinθ / (L−a) = usinθ / (L−ucosθ), from which the relationship between x and u is calculated: x / L = usinθ / (L−ucosθ) That is, u = Lx / (Lsinθ + xcosθ). 2), and by substituting the equation (2) into the equation (1) and rearranging, the enlargement factor K is K = 1 + (x / L) cotθ (3). Therefore, when the work A is displaced in the optical axis direction of the slit light, the light section image S is displaced in the X axis direction on the screen W, and the displacement direction is left when the work A approaches, and right when the work A moves away. Moreover, the size of the image S is enlarged or reduced according to the enlargement ratio of the equation (3).
Therefore, the window W1 to
It is desired to change the position and size of W5. Therefore, in the present embodiment, when the work A is set to the normal position, the optical measuring device is adjusted so that the X-axis coordinate value on the screen W of the point P at the leftmost end of the light section image S becomes zero. Incidentally, when the image S is displaced in the X-axis direction, the X-axis coordinate value Px of the point P is substituted as x in the equation (3) to obtain the enlargement factor K,
As shown in FIG. 7, the Y-axis coordinate value of each window Wn is set to the above d.
The value of yn is multiplied by K, and the size of each window Wn is changed according to the enlargement ratio K so that the windows W1 to W5 can be set at the required positions of the light section image S, respectively.

Further, in the measurement of the shape by image processing, an error due to the distortion of the lens system of the image pickup device 2, an error due to focus shift, a processing error of the base plate 3 and an attachment error of the projector 1 and the image pickup device 2 to the error. An error may occur due to an error in the relative positional relationship between the projector 1 and the image pickup device 2 caused by the error. Therefore, as shown in FIG.
A table 6 which is mounted on the base 5 and is movable in two orthogonal directions on the light cutting plane, that is, the U-axis direction and the V-axis direction, is provided on the surface plate 5, and the table 6 resembles the shape of the work A. The reference block 7 having a shape was placed, and the error was measured in advance. To explain this in detail, the reference block 7 is set to the table 6
Therefore, the virtual corner points of the reference block 7 corresponding to the intersections to be described later are set to a plurality of measurement points U ₁ set on the light cutting plane.
V ₁ , ... Umvm are sequentially moved so as to match each other, and at each point, the reference block 7 is irradiated with slit light from the light projector 1 and a light-section image S ′ on the block 7 is picked up by the image pickup device 2 and picked up. From the light section image on the screen of the container 2, the position of the intersection (the point corresponding to the above Q) of the two lines forming the image is obtained by the same method as above, and the coordinates on the light section plane corresponding to this intersection point are obtained. The errors Δu and Δv in the U-axis direction and the V-axis direction between the value and the coordinate value of the measurement point are measured for each measurement point.
In this embodiment, an edge portion 7a that coincides with the virtual corner point is formed at the base of the reference block 7, and the reference block 7 is accurately measured by using the edge portion 7a as a guide so that the virtual corner point coincides with the measurement point. I was able to set to. FIG. 9 is a diagram three-dimensionally showing each Δu at a plurality of measurement points U ₁ V ₁ , ... UmVm, and a correction formula Δu = f representing Δu by multiple regression from the data of Δu.
₁ (u, v) is calculated, and a correction expression Δy = f ₂ that similarly expresses Δv
(U, v) is obtained, and the correction value obtained by these correction equations is added to or subtracted from the coordinate value on the optical cutting plane of the intersection Q obtained by the measurement of the work A to obtain the coordinate value for determining the position of the work A. ,
The errors due to the above various causes are collectively corrected so that accurate measurement can be performed.

A summary of the above processing procedure is shown in FIG.
It becomes the street. That is, first, the correction formula f ₁ ,
f ₂ is obtained, then the radius of curvature R is obtained using the master work, and then the mass production vehicle body is measured. In this measurement, as shown in FIG. 11, first, the position of the leftmost point P of the light section image S is measured (S1), and then the sixth point is set with reference to the point P.
The window W6 is set (S2), and the position of the image center of gravity G6 on the window W6 is measured (S3). Further, the seventh window W7 is set based on the point P (S4), and the position of the image center of gravity G7 on the window W7 is measured (S4).
5) Then, the reference point M is determined from the positions of the center of gravity G6 and G7 (S6). Next, the first window W1 is set on the basis of the reference point M, the position of the image center of gravity G1 of the window W1 is measured (S7, S8), and the third to fifth windows W3, W4, W5 are similarly processed. Are sequentially set and the positions of the image centroids G3, G4, and G5 of each window are measured (S9 ... S14).
Here, the setting processing procedure of each window W1 to W5 is as shown in FIG. 12, that is, the parameters dxn, dyn, Wxn, indicating the position and size of each window Wn from the memory.
Wyn is read (), then the enlargement factor K corresponding to the X-axis coordinate value Px of the point P is obtained (), and dyn is K · dyn, W
xn and Wyn are changed to K · Wxn and K · Wyn, respectively (), and Wxn, dxn, dyn at the position from the reference point M to dxn, dyn
A window Wn having a size of Wyn is set (). FIG.
After returning to 1 and measuring the positions of the respective centers of gravity G1 to G5,
The equation of the curve S ₁ is calculated from 1 and G3 and the radius obtained by multiplying the radius of curvature R by the enlargement factor K (S15), and then G
Calculate the equation of the straight line S ₂ from 4 and G5 (S16),
The position of the intersection Q is obtained from both equations (S17), then the coordinate value of the screen W of the intersection Q is converted into the coordinate value on the light cutting plane (S18), and this coordinate value is calculated from the correction formulas f ₁ and f _2. The calculated correction values are added and subtracted (S19), and the coordinate values thus corrected are transmitted as position data of the work A to a host computer that determines the assembly accuracy of the vehicle body (S20), and one measurement process is completed. To do.

[0014]

As is apparent from the above description, according to the present invention, the error due to the image distortion of the image pickup device, the error due to the focus shift, the error due to the shift of the relative positional relationship between the projector and the image pickup device, etc. All the errors that the optical measuring device has can be corrected at once, and the calculation process for correction becomes easy,
Moreover, since the error measurement is performed using the reference block having a shape close to the shape of the work, the error can be measured by the same image processing as the image processing of the light section image at the time of measuring the work, and the error at the time of measuring the work can be accurately corrected. Have an effect.

[Brief description of drawings]

FIG. 1 is a perspective view of a work.

FIG. 2 is a plan view of an example of an optical measuring device to which the present invention is applied.

FIG. 3 is a diagram showing an image processing method of a light section image.

FIG. 4 is a diagram showing another image processing method of a light section image.

5A is a diagram showing how to obtain a reference point for setting a window for image processing, and FIG. 5B is a diagram showing window setting parameters based on the reference point.

FIG. 6 is a diagram showing the principle of image change due to displacement of the workpiece in the optical axis direction.

FIG. 7 is a diagram showing changes in window setting parameters according to image changes.

FIG. 8 is a perspective view showing a device layout in error measurement according to the present invention.

FIG. 9 is a three-dimensional view of an error measured on a coordinate plane that matches a light-section plane.

FIG. 10 is a flowchart showing the overall measurement procedure.

FIG. 11 is a flowchart showing a processing procedure when measuring a workpiece.

FIG. 12 is a flowchart showing a window setting procedure.

[Explanation of symbols]

1 Projector 2 Imager 7 Reference block A Work W screen S Light section image

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Claims (1)

(57) [Claims] 1. A light cutting device on a screen of an image pickup device using an optical measuring device comprising a light projector for irradiating a work with slit light and an image pickup device for picking up a light cutting image drawn by the slit light irradiating the work. A method of correcting an error when measuring the shape or position of a work from an image, in which a reference block having the same shape or a similar shape as the work is arranged facing the optical measuring device,
While moving the reference block to a plurality of measurement points on a light cutting plane parallel to the slit light including the optical axis of the slit light, a light cut image of the reference block is captured, and the light cut of the reference block is performed for each measurement point. The amount of deviation from the predetermined correspondence between the amount of movement on the surface and the amount of movement of the optical cut image of the reference block on the screen is measured as an error, and the correction formula for the error is calculated from the measured error, and the workpiece is measured. A method for correcting an error in an optical measuring device, characterized in that a measurement value obtained from a light-section image is corrected by a correction equation.