JPH04181106A - Calibration device of position dimension measuring device - Google Patents

Abstract

PURPOSE:To achieve a constantly accurate calibration by forming a plurality of figures in mutually different shapes and memorizing the pattern and then comparing figure shape on an image surface with the memorized shape pattern. CONSTITUTION:A picture signal of a surface of a plate for calibration 5 which is picked up by a camera 1 is A/D converted 7 and is memorized on a picture element surface of M columns X N rows of a frame memory part 8. Then, a binary processing part 9 reads out an image data of an extraction part 6a from the memory part 8, digitizes it, specifies each mark 6, and then sends it to a correlation operation part 11. The operation part 11 compares the picture element surfaces of m columns X n rows of numeric shape pattern with the picture element surface of M columns X N rows picked up by the camera 1 based on a binary data of numeric shape pattern which is memorized in a numeric shape pattern/numeric position memory 10 and then performs correlation processing and then outputs it to a parameter setting part 12 corresponding to a position of absolute coordinates system. Then, the setting part 12 sets parameters so that a position of the absolute coordinates system matches a position of absolute coordinates system which is memorized 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applied to a measuring device that measures the position and dimensions of an object to be measured by capturing an image of the object with an imaging means. The present invention relates to a device that can accurately calibrate an imaging means.

[Conventional technology]

Conventionally, two cameras are placed side by side at the same height, and the two cameras take images of the object to be measured, respectively.
A measuring device is known that measures the three-dimensional position, depth, and other actual dimensions of an object from the parallax. Such three-dimensional measurement is performed based on the imaging results of each camera and parameters specific to each camera, such as focal length, camera mounting position, etc.

Therefore, in order to perform three-dimensional measurement accurately, it is necessary to perform calibration to accurately determine the values of the above parameters before measurement. Examples of parameters include the following.

■Camera installation position relative to the reference origin.

■Position of camera optical axis (camera optical axis is not guaranteed to be at the center of the image).

■Aberration coefficient of camera lens.

■Camera lens focal length These parameters are normally calibrated when the measuring device is shipped, and the determined values are stored in the device's memory and read out and used during three-dimensional measurement. Parameter values often change after the equipment is introduced and installed at the site. For example, when an external force is applied to the camera, the camera may be mounted out of position.

Therefore, in order to calibrate the camera while it is still attached before taking measurements, multiple (9 The marks are regularly arranged on the plate 5, and the plate 5 is placed on an inspection table or the like so that the plurality of marks are within the field of view of the two cameras. At this time, since the position of each mark in the absolute coordinate system is known in advance, the arrangement of marks appearing in the image taken by the camera is compared with the mark arrangement pattern stored in advance.
The position of each mark on the image plane of the camera is associated with the stored absolute coordinate position of each mark, and calibration is performed based on the positional relationship between them.

[Problem to be solved by the invention]

In order for the above-mentioned calibration to be performed accurately, it is necessary for each mark that the mark on the plate surface corresponds accurately to the mark appearing on the image. That is, when the plate 5 is captured by a camera, marks a', b', and
c ---- are marks a, b, c, etc. on plate 5.
・There is no problem if it corresponds to ((a) in the same figure), but
If there are poor lighting conditions at the site where the camera is installed,
If there is a problem with the mark setting, if there is a problem with the way the plate 5 is installed, or if the camera is tilted more than 45 degrees from its normal state, it may not be possible to image all the marks and the above correspondence may not be correct. For example, there is a risk that the mark b' on the image plane 14a may be mistakenly recognized as the mark a on the plate 5. For this reason, accurate correspondence between the mark position on the image plane 14a of the camera and the stored absolute coordinate position of the mark cannot be obtained, and there is a possibility that an inaccurate calibration run may be performed.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide an apparatus that can always perform accurate calibration even under the influence of poor lighting conditions.

[Means to solve the problem]

Therefore, in the present invention, the position and dimensions of the object to be measured are measured by a position and dimension measuring device that measures the position and dimensions of the object to be measured based on the imaging result of the object to be measured by the imaging means and the parameters including the arrangement position of the imaging means. In a calibration device for a positional and dimension measuring device that performs calibration to obtain the value of the parameter before measurement, a calibration plate in which five or more figures of mutually different shapes are arranged is arranged so that the plurality of figures are aligned with the image pickup means. a storage means disposed within the field of view and storing the shape pattern of each of the plurality of figures and the absolute coordinate position in the absolute coordinate system; and an image obtained by imaging the calibration plate surface. Matching the shape patterns for each figure, calculating the coordinate position of each of the plurality of figures on the image plane,
a calculation means for reading an absolute coordinate position corresponding to the calculated image plane coordinate position from the storage means and associating the image plane coordinate position and the absolute coordinate position for each figure; The position and dimension measuring device is provided with means for determining the values of the parameters based on a plurality of sets of image plane coordinate positions and stored absolute coordinate positions.

[Effect]

According to this configuration, the shapes of a plurality of figures are made different from each other, and these plurality of shape patterns are stored, so that by matching the figure shape on the image plane with the memory shape pattern, , the positions of the sides of each figure on the image plane can be reliably determined. At this time, since the absolute position of each figure is stored, the correspondence between the absolute position of each figure and the position on the image plane is ensured. In this way, the correspondence between the position on the image plane and the absolute coordinate position of the figure can be reliably obtained for each figure, so that the alignment is performed accurately.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a calibration device for a position measuring device according to the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an apparatus according to an embodiment of the present invention, in which two CCD cameras 1.2 are arranged side by side.
The camera 1.2 on the stand images the same wave meter U1 object,
The three-dimensional position and size of the object to be measured are measured. Note that such three-dimensional measurement itself is not directly related to the purpose of the present application, so detailed explanation thereof will be omitted. Before processing the three-dimensional measurement using the two CCD cameras 1.2, each camera 1.2 must be calibrated. I will explain using 1 as a representative example. Reference numeral 3 shown in the figure is a calibration processing section that performs such calibration processing, and this processing section is assumed to be incorporated into a part of a measuring device that performs three-dimensional measurement. During calibration, a calibration plate 5 on which nine marks 6 are arranged is positioned and placed on the inspection table 4. As shown in FIG. 2, the plate 5 is, for example, a glass substrate, and on the glass substrate there are circular marks 6 made of, for example, chrome, or numbers 1, 2, 31, 118, . Cutout 6a shaped like 9
is deposited leaving behind.

The arrangement of the inspection table 4 and the positioning of the plate 5 are such that the nine marks 6 on the surface of the plate 5 are all connected to the camera 1.2.
It is designed to be within the field of view. In addition, the examination table 4,
The plate 5 may be removed after calibration is completed, or may be left in place during measurement. In this case, it may be installed behind the object to be measured so as not to interfere with the measurement of the object to be measured.

FIG. 4 shows the geometric relationship of each coordinate system when the mark 6 and the observation object 16 including the measured logarithmic object are captured by the camera 1. In other words, the coordinate system X-y-z is a camera coordinate system whose origin is the focal point of the optical axis 15 when an ideal pinhole camera is assumed, and the direction in which the two cameras l and 2 are juxtaposed is the X direction. The height direction is defined as two directions.

The coordinate system xW-yW-2 is an absolute coordinate system on the ground with its origin at an appropriate reference position, and the coordinate system X-Y is a coordinate system indicating the two-dimensional position of the image plane 14 (CCD element) of the camera. .

When observing the observation object 16 existing at the position (x, y, z) in the camera coordinate system ((X -, Yv, Zv) in the absolute coordinate system), the observation object 16 is the image of the camera 1. Assuming that it appears at the coordinate position (Xu, Y,) on the surface 14, in an ideal pinhole camera, the following relationship holds true, where f is the focal length.

Xu-fx/z Y, -fy/z -(1) Using this equation (1), the position (x,
Once y, z) are determined, the position in the absolute coordinate system (x= , y, , Zv )... (
2) Here, r, (i-1 to 9) is a rotation matrix determined by the yaw, pitch, and roll angles that the camera coordinate system has with respect to the absolute coordinate system, and specifically, the mounting of camera 1 is determined by the position means. T, ,T, ,T.

is a vector that adjusts both translation needles.

Now, the data actually obtained as a result of imaging by the camera 1 is not a position (x, , y,) on the image plane 14, but a quantized position on a frame memory, which will be described later. The position obtained by this frame memory is (X+
-Yl). (X., Y.) and (XISYr) have a one-to-one correspondence, but what is the scale and difference between them?
A factor exists. The problem here is that the origin of the image plane 14 does not necessarily coincide with the optical axis 15, and the lens 1a of the camera 1 has aberrations (Xu).

Y, ) and (X+, Yl) do not have a simple proportional relationship. Correct measurements cannot be made unless parameters are found to correct these. By determining this parameter and the parameters in equations (1) and (2) above, calibration is performed, that is, the position (X,
, Yl) and the position in the absolute coordinate system (X w % yv
−, Z v ). In this embodiment, the position of the mark 6 in the absolute coordinate system is stored as known, and the above is based on the stored position and the position obtained on the frame memory when the mark 6 is captured by the camera 1. Perform calibration to determine each parameter. It should be noted that each parameter can be determined if there are at least five marks 6, but in this embodiment, the number is nine in order to improve accuracy. Note that the 5th side of the plate on which the marks 6 are arranged is x
, -y, , -2, and the z v = 0 plane of the coordinate system facilitates calculation to obtain the above parameters.

The procedure of the calibration process will be explained below.

As shown in FIG. 1, the image signal of the surface of the plate 5 scanned and imaged by the camera 1 is applied to the A/D conversion section 7 of the calibration processing section and output as image data. The frame memory section 8 takes in this image data and
Images of five surfaces of the plate are stored on the pixel plane of the column. This pixel surface of M rows and N columns has one pixel of 2'' gradation as one unit.Therefore, the imaged mark 6 will appear with a predetermined gradation at an appropriate location on the pixel surface of M rows and N columns. .- side, the number shape pattern/number position memory 10 has numbers 1, 2, .
Shape patterns representing the shapes of 3, . . . , 9 are set and stored using each number as an address.

The shape pattern of these numbers 1, 2, 3, ..., 9 is
Each pixel surface has m rows and n columns, and the number shape part is a logical “
1°, and the other background parts are logic “0°” and so on, 2
It is stored as digitized data.

In addition to this, mark 6...X * "f w
The position of the mark in the Z w absolute coordinate system is P, (xwl, y, l), number 2
The mark position where is the punched part is P2 (xw2, y92
), . . . (assuming z v = 0), each number is stored as an address. Binarization processing section 9
is provided to extract only the extracted portion 6a from the image data in the frame memory section 8, and converts the 2'' gradation image data in the frame memory section 8 into binary image data of logical "1" and "0". At the same time as converting the mark to

The resulting binary image data of each mark is applied to the correlation calculation section 11. On the other hand, the binary data of the number shape pattern in the number shape pattern/number position memory section 10 is also added to the correlation calculation section 11. The correlation calculation unit 11 performs a process of comparing the pixel surface of the M rows and XN columns of the numerical shape pattern with the pixel surface of the M rows and XN columns captured by the camera 1 to obtain a correlation. This correlation process is performed in order from number 1 to number 2, 3, and so on. Regarding the number 1, the image of the pixel surface of m rows x n columns indicating the number 1 is M
It is matched against the upper left of the pixel plane of rows and columns of N, and from this position, the pixel plane of m rows and columns of n is sequentially shifted and scanned one pixel at a time, and correlation coefficients are sequentially determined. Once all the correlation coefficients have been determined, the largest correlation coefficient among these determined correlation coefficients is determined as a matching point. The position on the pixel surface of the camera 1 obtained by this matching becomes the imaging position of the cutout 6a of the number 1, and the matching position P-+(X++,
Y, , ) is obtained. At this time, number 1 from memory 10
The absolute coordinate system position P1 corresponding to is read out, and P- and Pl are associated with each other and output to the parameter setting section 12. Similarly, matching positions P-2 (Xr2, Y, 2) and P-i (Xr3, Y
, 3)... are obtained, and these are the absolute coordinate system position P2
, P3 . . . and output to the parameter setting unit 12.

In the parameter setting unit 12, the positions P −+ , P −2 . . . obtained by the correlation calculation unit 11 and the positions P 1 , P 2 . The position in the absolute coordinate system obtained by calculating equations (1) and (2) using parameters from positions P-, p-2, etc. corresponds to the position in the stored absolute coordinate system. Processing is performed to set the values of parameters (r + -r 9 , T t -T*, f, and lens aberration coefficient) so as to match P1, P2, . . . . Note that the method of determining the parameters itself is well known and is not directly related to the purpose of the present application, so a detailed explanation will be omitted.

Note that similar calibration will be performed for the other camera 2 as well.

In the embodiment, nine marks 6 were prepared for calibration, but if a large number of marks 6, for example 20 to 30, are prepared and their position data obtained, the accuracy of calibration can be further improved. can be done.

In addition, in the example, it was assumed that 3D measurement was performed using two cameras, but of course the calibration itself is performed for each camera, so this example is not applicable when performing 2D measurement using one camera. It is possible to apply this method to the calibration of one camera, and when measurements are performed using three or more cameras, it is also possible to apply the method to the calibration of each of these three or more cameras.

In the embodiment, different numbers 1, 2, etc. are formed in each of the plurality of marks 6, but
As shown in FIG. 3(a), it is also possible to form a cutout 6'a of a different Alphabella ASB in the mark 6', and as shown in FIG. 3(b), the mark 6゛-
It is also possible to form circular cutouts 6-a in a different number and arrangement. In short, the shape of the punched portion may be any shape as long as it can be distinguished from other marks. Furthermore, it is conceivable to identify each mark by a different barcode.

In addition, in the embodiment, a cutout for mark identification is formed in the circular mark 6, but the point is that the mark only needs to be distinguishable from other marks in shape, so the mark itself cannot be distinguished from other marks. It is also possible to implement different shapes that are distinguishable from each other.

For example, it is conceivable that the shape of the mark itself is the shape of the numbers 1, 2, . . . .

[Effects of the Invention] As explained above, according to the present invention, each of a plurality of marks can be reliably identified even if there is an influence such as poor lighting conditions. Therefore, accurate calibration can always be performed, and the position measuring device can always provide accurate measurement results, greatly improving the reliability of the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a calibration device for a position measuring device according to the present invention, and FIG.
An enlarged view showing marks arranged on the surface of the calibration plate shown in the figure, FIGS. 3(a) and 3(b) are views showing other embodiments, and illustrate marks arranged on the surface of the calibration plate. Figure 4 is a diagram explaining the principle applied to the present invention, and Figure 5 is a diagram showing the geometric relationship of each coordinate system centered on the camera coordinate system, and Figure 5 is a diagram explaining the principle applied to the present invention. FIG. 3 is a diagram used to compare the state of the arrangement and the arrangement of marks captured by a camera. 1.2... CCD camera, 3... Calibration processing section, 5... Calibration plate, 6
．． 6″, 6----7-ri, 6a, 6a-16, l″
...Extraction part. To figure 2 figure 3 (0) figure 3 (b)

Claims (1)

[Claims] Position and dimensions by a position and dimension measuring device that measures the position and dimensions of the object to be measured based on the imaging result of the object by the imaging means and parameters including the arrangement position of the imaging means. In a calibration device for a position measuring device that performs calibration to obtain the value of the parameter before measurement, a calibration plate in which five or more figures of mutually different shapes are arranged is arranged so that the plurality of figures are in the field of view of the imaging means. storage means for storing the shape pattern of each of the plurality of figures and the absolute coordinate position in the absolute coordinate system; The shape patterns are matched for each figure, the coordinate positions of each of the plurality of figures on the image plane are calculated, and the absolute coordinate positions corresponding to the calculated image plane coordinate positions are read out from the storage means and the image plane coordinates are calculated. a calculation means for associating a position with an absolute coordinate position for each figure; a means for determining the value of the parameter based on a plurality of sets of image plane coordinate positions and stored absolute coordinate positions associated by the calculation means; A calibration device for a positional dimension measuring device, wherein the positional dimension measuring device is provided with: