JPH0656281B2 - How to find the tangent position of a curve on an image - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for determining a tangent position of a curve on an image by an image processing technique.

[Conventional technology]

For example, in the measurement of Brinell hardness, it is premised that the diameter of the depression, that is, the indentation of the test piece is measured. Usually, at the production site, the diameter is measured by visually observing the indentation with a portable magnifying glass and reading it from the scale of the magnifying glass. But,
With such a measuring method, continuous measurement in a short time is impossible, so that it is impossible to inspect all products in the production line.

On the other hand, in such a production line, it is also possible to image the indentation to be measured while optically enlarging it, and to obtain the diameter from the image of the indentation by image processing. Even in the measurement by such image processing, the measurement of the diameter is premised on obtaining the intersection of the arc and the straight line in the diameter direction. However, in general, the surface of the test piece is not smooth, unevenness is generated in the contour part of the curve, and when it is enlarged,
Since the boundary is unclear, the measurement accuracy is reduced.

Further, if the lengths of two chords are measured on the arc, the diameter of the circle can be obtained by a calculation formula. Even with this type of measurement method, as with the above case, there are still problems with measurement accuracy.Therefore, the same product is subject to several sampling inspections, and the most probable value is calculated from those measurement values based on error theory. To be However, according to such a measuring method, even if the average value calculation and the statistical processing are performed by the computer, the calculation time becomes longer than the takt time of the production line. It is not suitable as a continuous measurement method for all products.

[Object of the Invention]

Therefore, an object of the present invention is to make it possible to obtain the tangent position of a small arc-shaped curve on an image within a precision that allows image processing, without using a statistical method.

[Outline of Invention]

The diameter of the circle is determined by measuring the distance between two parallel tangents to the arc. Moreover, even if the contour curve of the circle is irregular, the tangent position can be determined relatively easily.

Therefore, the present invention focuses on the above point, images a small arc-shaped curve, expresses the contour of the curve by pixels on the image, and represents the pixel on the arc-shaped curve on a straight line tangential to the contour. The number is counted, and the tangent position of the curve is obtained from the maximum value of the counted values.

Such a method can be easily performed at high speed and with high accuracy by applying image processing technology and computer technology.

[Outline of measuring device]

First, FIG. 1 shows the configuration of a measuring apparatus 1 according to the measuring method of the present invention. This measuring device 1 is for measuring Brinell hardness, that is, for measuring the diameter of an indentation, and is a guide device 4 for moving an optical magnifying glass 2 and a CCD type image sensor 3 connected thereto. A positioning control device 5 for driving the guide device 4 is provided. The magnifying glass 2 has a low magnification, for example, a magnification of 2 times, is directed toward the workpiece 6 of the object to be measured on the side of the objective lens, and is connected to the CCD image sensor 3 on the side of the eyepiece at the upper end thereof. ing. This image sensor 3 is
The image processing device 7 and the image processing CPU 8 are sequentially connected.

The guide device 4 holds the magnifying glass 2 and the image sensor 3 in a three-dimensional space, that is, in a state of being movable in X, Y, and Z directions. The positioning control device 5 moves the magnifying glass 2 to the position of the indentation 9 of the work 6 in relation to the movement of the work 6 and the measurement operation, that is, the control operation of the CPU 8.

The measurement device 1 repeats the following measurement operation.

First, the work 6 of the object to be measured is continuously conveyed to the measuring station within, for example, a tact time of 20 seconds, and positioned there. Subsequently, the positioning control device 5 moves the guiding device 4 to perform the first-stage focusing and light amount adjustment with respect to the magnifying glass 2, and subsequently, the cutting surface 1 of the work 6.
The indentation 9 of the most image object is searched from 0, the optical axis of the magnifying glass 2 is positioned near the indentation 9, and the final focusing is performed by the autofocus function, and subsequently the light amount is adjusted by epi-illumination. To do.

After performing such focusing, light amount adjustment, and positioning control, measurement of the diameter D of the indentation 9 is started.

FIG. 2 shows the relationship between the indentation 9 and the diameter D. Indentation 9
Since it is dish-shaped with respect to the planar cutting surface 10, the contour of the indentation 9 is an arc-shaped curve with a small curvature.

In the first positioning, as shown in FIG. 3, the magnifying glass 2 is set on one of the contour curves 15 of the indentation 9. Here, the image sensor 3 and the image processing device 7 read the optical image of the magnifying glass 2 and, after A-D conversion, store it in the image memory as a one-frame image via the buffer memory or directly, At that position, an imaginary tangent line 11 of the contour curve 15 is obtained, and this tangent line 11 and the first screen 13a
The distance x1 from the upper baseline 14 is measured. When this measurement is completed, the positioning control device 5 moves the magnifying glass 2 in the X-axis direction by an appropriate movement distance d. This moving distance d
Is preset in relation to the desired diameter D. Due to such movement, the magnifying glass 2 is moved to the second screen 13b. Here as well, the tangent 1 of the contour curve 15
The distance x2 between 2 and the baseline 14 is measured. When such distances x1 and x2 and the moving distance d are measured, the diameter D of the indentation 9 to be obtained is obtained by the following calculation formula.

D = d-x1 + x2 [Method of obtaining curve position on tangent line of the present invention] The above measurement is premised on obtaining tangent lines 11 and 12 on the image. The present invention provides a tangent line 1 as described above.
This is effective for obtaining the positions of 1 and 12. The details will be described below.

On the screen 13a, the indentation 9 and the cutting surface 10 are represented as a brightness difference. However, usually, bright points exist as noise inside the indentations 9 and dark points exist on the cutting surface 13 as image noise.

Therefore, first, for a stored image as shown in FIG. 4, area division and area binarization are performed for noise removal. In this area division, as shown in FIG. 5, a square area having a certain number of images is set as one unit, and the overall brightness, that is, the sum of the brightness of each pixel in the area is compared with a reference value, and the comparison result is obtained. Based on this, the area is binarized, that is, it is determined as white or black. In this way, the noise in the divided area is removed, and the boundary portion between the indentation 9 and the cutting surface 10, that is, the contour curve 15 is binary-represented by the rough divided area. In this way, the noise of the image is eliminated in the coarse divided screen.

Next, on the image, the range of the contour curve 15 is extracted between the black screen and the white screen which are adjacent to each other in the X direction orthogonal to the desired tangent line, as shown in FIG. Within this range, a point at which the brightness changes abruptly is expressed as a black level point 16 for each pixel unit, as shown in FIG. In this way, the contour curve 15 of the indentation 9 is pixelated by the group of discontinuous points 16.

Of course, this point 16 corresponds to the resolution of the image memory inside the image sensor 3 or the image processing device 7, that is, the pixel of the minimum unit of the image. The measurement accuracy of the image processing device 7 corresponds to the size of the pixel and is ± 3/100 (mm)
It will be about.

Subsequently, as shown on the left side of FIG. 7, by counting the number of pixels on the straight line, that is, the distribution frequency of the points 16 in the tangential direction, that is, the Y direction, the total number of distributions of the points 16 in the tangential direction is obtained. . The position on the X axis corresponding to the maximum value of the total distribution is obtained as the position of the tangent line 11 of the contour curve 15 of the indentation 9. The above processing and counting are performed by the CPU 8
Done at high speed by. The position of the tangent line 11 is obtained by such image processing. In addition, at the time of this measurement, the image can be confirmed on the monitor TV. The above image processing is similarly performed for the other tangent line 12.

[Scope of application of the invention]

In the above embodiment, the closed loop, that is, the two parallel tangents 11 and 12 of the contour curve 15 are obtained in relation to the diameter D of the indentation 9. However, the present invention is a closed loop such as a quadratic curve or a cubic curve. It can also be applied when finding extreme values such as maximum or minimum values of a curve from tangent lines.

〔The invention's effect〕

In the present invention, the tangent position to be obtained is obtained as the maximum number of pixels (points) in the same direction as the tangent line, so that even if the tangent line position is an enlarged image, measurement can be performed with high accuracy. Further, in such a measurement, since a statistical method is not required for the measurement value, the processing calculation time can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a measuring device for carrying out the present invention, FIG. 2 is an enlarged cross-sectional view of an indentation portion, FIG. 3 is an explanatory view for calculating a diameter, and FIGS. The figure is an explanatory view of the process of obtaining the tangent position from the screen. 1 ... Measuring device, 2 ... Magnifying glass, 3 ... CCD image sensor, 4 ... Guide device, 5 ... Positioning control device, 6 ... Work, 7 ... Image processing device, 8 ... CP
U, 9 ... Indentation, 10 ... Cutting surface, 11, 12 ... Tangent line, 13a, 13b ... Screen, 14 ... Baseline, 15 ...
Contour curve, 16 ... points.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Hasegawa No. 1 133-1, Futano-cho, Fukuno-cho, Higashi-Tonami-gun, Toyama Prefecture Rosef Co., Ltd. (72) Kenji Ueda Fukka-cho, Fukuno-cho, Higashi-Tonami-gun, Toyama No. 1331 1 Rosef Co., Ltd. (56) References JP-A-55-83972 (JP, A)

Claims (2)

[Claims] 1. A method for imaging a measured object to obtain a tangent line in a predetermined direction from a contour shape of the measured object, wherein a contour curve is extracted from the contour shape on a picked-up image to be pixelated, and the tangent line is obtained. Count the number of pixels of the contour curve on a straight line in the direction,
A method for obtaining the tangent position of a curve on an image, characterized in that the tangent position of the contour curve is obtained from the linear position corresponding to the maximum value of the count value. 2. A captured image is divided into regions and binarization processing is performed for each divided region to eliminate noise on the image that is smaller than the area of the divided regions, and the boundary between the high-luminance portion and the low-luminance portion. After determining the range where the curve forming the is present on the image, the change position from low luminance to high luminance within that range is converted into points, and the contour curve is represented on the image by the point group. A method for obtaining a tangent position of a curved line on an image according to claim 1.