JPS6298202A - Detecting device for crack tip position of fatigue test piece - Google Patents

Abstract

PURPOSE:To accurately eliminate an image blur and to detect a crack tip position by providing strobe lighting devices and picking up the crack of a fatigue test piece and a reference line in the same visual field. CONSTITUTION:The strobe lighting devices 26 and 27 emit light alternately at a period longer than the after-image time of ITV camera heads 22 and 23 tin synchronism with the output signal of a frequency dividing circuit 35. Then, a video signal in light emission is sent to a scribing line detecting means 32 and a crack tip position detecting means 23. The means 32 calculates the integral value of the luminance level of the video signal by a horizontal integration circuit 38 and an integral value peak detection part 39 detects the maximum luminance level from the luminance distribution to find the position of a scribing line 13. The means 33, on the other hand, passes the video signal through a filter circuit 40 and converted it into a binarization signal by a circuit 41 to detect the crack 12. For the purpose, a noise removing circuit 42 removes noise components to find the tip position of the crack 12. The position of this line 13 and the tip position are sent to a distance detection part 43, which finds the distance from the line 13 to the crack tip position and displays it on a display part 44,.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a fatigue test piece crack tip position detecting device for detecting the crack tip position of a fatigue test piece used for metal materials.

[Conventional technology]

For fatigue measurement of metal materials, shape and dimensions are B, 55762-
1979 (Methods for cr.
ack opening display
lent testing) etc.
As shown in Fig. 1, a fatigue test piece (hereinafter abbreviated as test piece) 1 with a rack (fatigue crack) 2 in it was used. In addition, this test piece 1 has a crack 2 of a predetermined length made from the tip of a mechanical notch (hereinafter abbreviated as notch) 3 machined in the center of the test piece 1 using a fatigue testing machine. Therefore, this crack 2
In the machining operation, it is necessary to monitor the length of the crack 2, that is, the position of the crack tip.

By the way, there is an apparatus for detecting the position of the tip of a crack, for example, as disclosed in Japanese Patent Application No. 12098/1983. this is,
A test piece with a marked line as a reference line is set in a fatigue testing machine, and a repeated load is applied to this test piece. In addition,
This load has an amplitude of several hundred microns and a frequency of about 30H2. While such a load is being applied, the surface of the test piece is illuminated and an m-image is taken using an ITV camera (industrial television camera) through a microscope. The video signal output from this ITV camera is then processed to detect the distance between the tip position of the crack that occurs in the test piece and the cut line to determine the degree of fatigue and the like.

[Problem that the invention seeks to solve]

However, in the above apparatus, since the test piece is illuminated with continuous light, the obtained image of the test piece is blurred. In other words, as mentioned above, the load has an amplitude of several hundred microns and a frequency of about 30Hz, but on the other hand, IT
The field of view when taking an image with a V-camera must be approximately several 1/1 meter in consideration of resolution, and therefore, if continuous illumination is used to image 1/1/2 inch, the image of the test piece will be blurred due to vibration. It becomes impossible to detect the crack tip position with high precision.

Furthermore, the width of a crack that occurs in a test piece varies from several microns to several tens of microns depending on the internal and surface conditions of the test piece. Therefore, if a particularly narrow portion of a crack is not illuminated with appropriate illuminance, it may not be imaged and cannot be detected.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a highly accurate fatigue test piece crack tip position detection device that can eliminate image blur and accurately detect the crack tip position.

[Means for solving problems]

In order to achieve the above object, the present invention provides an imaging means that images the crack and the reference line in the same field of view of a fatigue test piece on which a reference line has been applied to obtain the position of the tip of the crack, and irradiates illumination light onto the surface of the fatigue test piece. A strobe illumination device, a lighting control means for controlling the light emission timing of the strobe illumination device to a desired timing, and a video signal from an imaging means, and the luminance level is integrated in the same direction as the reference line direction to find the maximum level. The video signal from the reference line detection means for detecting the reference line position and the imaging means is subjected to binarization processing of the brightness level in the direction perpendicular to the crack direction, and then the continuity of the high level value is determined to determine the tip of the crack. Crack tip position detection means for detecting the position, and a crack tip position for calculating the distance from the reference line to the crack tip position from the reference line position determined by the reference line detection means and the crack tip position determined by the crack tip position detection means. 1 is a fatigue test specimen crack tip position detection device comprising a tip position calculation means.

[Effect]

The present invention includes the above-mentioned means, so that when the fatigue test piece is irradiated with illumination light by the strobe lighting device, the fatigue test piece is imaged by the imaging means, and the reference line and crack tip are determined from the video signal obtained at this time. The position is detected and the distance between these reference lines and the crack tip position is calculated.

[Example] Hereinafter, a practical example of the present invention will be described with reference to the drawings.

FIG. 1 is an external view of a fatigue test piece crack tip position detection device, and FIG. 2 is a specific configuration diagram thereof. In each of the figures, reference numeral 10 is a test piece, in which a notch 11 is formed as shown in FIG. is pulled into place. This marking line 13 is C
This is the target position for making a crack 12 in the OD test scissor piece. Further, the surface of this test piece 10 is polished with fine particles of diamond or the like, and is formed into a state almost identical to a mirror surface.

Reference numerals 20 and 21 denote microscopes, which are provided to obtain enlarged images of both surfaces of the test piece 10. ITV camera heads 22.23 are attached to these microscopes 20.21, and ITV camera controllers 24.25 are respectively attached to these microscopes 20.21.
The image magnified through each microscope 20 and 21 is controlled by the microscopes 20 and 21, and the video signal thereof is sent to the marking line detection means 32 and the crack tip position detection means 33 via the camera changeover switch 31 of the signal processing device 3o. It looks like this.

Further, 26.27 is a strobe illumination device, which irradiates the surface of the test piece 10 with illumination light R from a position having a predetermined angle θ, for example, 30° with respect to the optical axis G of each microscope 20.21. It is something. Incidentally, the light emission timing of these strobe lighting devices 26, 27 is set at time intervals such that afterimages in each ITV camera head 22, 23 are sufficiently attenuated. Specifically, as a lighting control means, a frequency dividing circuit 35 receives the synchronizing signal from a synchronizing signal generating circuit 34 that sends a synchronizing signal to each ITV camera controller 24, 25, and divides the frequency of the synchronizing signal at a predetermined frequency division ratio. , and a strobe controller 36, 37 which receives the frequency-divided output of the frequency dividing circuit 35 and operates each strobe lighting device 26, 27 to emit light. Note that the camera changeover switch 31 receives the divided output of the frequency dividing circuit 35 and switches the strobe lighting device! Video signals from the respective ITV camera heads 22 and 23 are alternately passed through in synchronization with the light emission operations of 26 and 27.

Next, the scribing line detection means 32 detects the brightness level of the video signal as the scribing line I! in the image. It has the function of integrating in the same direction as 13 to obtain the maximum 111 degree level, and detecting the position of the diagonal line 13 from this maximum brightness level position. 39.

In addition, the crack tip position detection means 33 converts the video signal into a binary signal, and then high-level values are continuously generated from the image data obtained from the binary signal, and this satisfies a certain continuity condition. Crack 12 to determine whether
The filter circuit 4012 has the function of detecting
It is composed of a value conversion circuit 41 and a noise removal circuit 42.

The distance detection unit 43 has the ability to determine the distance between the slope line position determined by each of the means 32 and 33 and the crack tip position, and this distance is displayed on a display unit 44, for example, on a monitor television. It is now possible to do so.

In addition, the setting value of the distance between the marking $113 and the crack tip position (including when the crack tip position marking line is reached) for stopping the fatigue test type (not shown) is preset for the wooden mounting. a stopping distance setting circuit 45 and a fatigue test station stop signal generation circuit 4 that sends a stop signal K to the fatigue test machine.
6 is provided.

Next, the operation of the g position configured as described above will be explained. The image of the scribe line 13 and the crack 12 magnified by the microscope 20.21 is captured by the ITV camera head 22.2.
The position, etc., are adjusted so that the image appears within one screen of 3 and becomes an image as shown in FIG. 4(a). Further, the illuminance of the strobe lighting devices 26 and 27 is variably adjusted so that the scribe line 13 and the crack 12 are emphasized and imaged. In other words, the diffusely reflected light from the scribe line 13 and the crack 12 is imaged. In addition, Fig. 4 (a
), the colors are reversed.

Now, in this state, when a synchronization signal is sent from the synchronization signal generation circuit 34, each ITV camera controller 24
．． Under the control of 25, each I-V camera head 22, 23 starts capturing an image and outputs its video signal.

At the same time, the frequency of the synchronization signal is divided by the frequency dividing circuit 35, and the synchronization signal is divided by, for example, the afterimage time of the ITV camera head 22, 23.
It is output as a frequency-divided signal with double the period. Therefore, by alternately sending this frequency-divided signal to each strobe controller 36, 37, each strobe lighting device 26, 27
will emit light alternately in synchronization with the frequency-divided signal. As a result, each strobe lighting device f26.27 is
Light is emitted at a cycle longer than the afterimage time of the TV camera head 22, 23. Thus, the video signals when the strobe lighting devices 26 and 27 emit light are sent through the camera changeover switch 31 to the marking line detection means 32 and the crack tip position detection means 33.

In the scribe line detection means 32, first, the horizontal integration circuit 38
The integrated value of the brightness level of the video signal can be obtained.

That is, in the image shown in FIG. 4(a), the marking line 13
Find the integral value of the brightness level in the same direction as . Then, the brightness level in the horizontal direction as shown in FIG.
Find the position of. Here, the brightness level is high because the crack 12 is imaged in white, but the brightness level due to the crack 12 is removed because it is integrated in the direction of the marking line 13.

On the other hand, simultaneously with the operation of the scribe line detection means 32, the crack tip position detection means 33 performs the following operation.

That is, the video signal on A--A shown in FIG. 4(a) has a high level value in the cracked portion as shown in FIG. 5(a). The video signal is passed through a filter circuit 40 in order to emphasize this crack portion and to prevent it from being affected by changes in the overall brightness level due to changes in the measurement target or the like. This filter circuit 40
The video signal that has passed through has a waveform as shown in FIG. 5(b), for example, and this signal is sent to the binarization circuit 41 and binarized to detect the crack 12. That is, the binarization circuit 41 detects the maximum value of the video signal in each scanning line, and detects that the crack 12 exists at the position on the scanning line where this maximum value is detected. However, since it is meaningless to detect the maximum value on a scanning line where no crack 12 exists, a certain threshold level L is set, and the maximum value is detected only for signals above this threshold level. . The image obtained from the binarized signal in this way is the image shown in FIG. 5(C), but it is not possible to sufficiently extract only the crack 12 at the threshold level, and noise components are included. It has become very popular. This noise component is, for example, a polishing flaw that occurs when the test piece 10 is polished, or a waveform of the same kind as the waveform detected in the crack portion at the scratch line 13 portion, and these polishing flaws and the same kind of waveform are incorrectly detected as noise. It is to be done.

Therefore, the noise component is removed by the noise removal circuit 42. In other words, in the noise removal circuit 42, as shown in FIG.
I am using a window like the one shown. This window is based on a certain point B and has a predetermined length from this point B in the horizontal and vertical directions, and the number of high levels (R large 1i1) in this window, that is, the density of points in the window is a predetermined value. If it is above, the point is determined to be part of a crack, and if it is less than a predetermined value, it is erased as noise. Therefore, it is determined whether the high level portions are occurring continuously. FIG. 6(b) shows the 21a signal level in the noise component portion Q1 shown in FIG. 7, and the high level portion (different color in No. 61J(b)) is irregular. Further, FIG. 6(C) shows a portion Q2 of the crack 12, where a high level continuously occurs. When the noise components are removed in this way, the image becomes as shown in FIG. 5(d). Then, the tip position 112a of the crack 12 is detected. After this, a window is applied again to determine cracks, but this window has a lower window density threshold, which lowers the probability that even crack 2 will be determined as noise. There is.

Then, the scratched line position and crack tip position determined by each means 32 and 33 are sent to the distance detection section 43, where the distance from the scored line 13 to the crack tip position 12a is determined and displayed on the display section 44. will be displayed. Furthermore, when this distance becomes less than or equal to the distance set in the stop distance setting circuit 45, the fatigue test stop signal generation circuit 46 sends a fatigue test stop signal K to the fatigue testing machine. Note that the display section 44
The images displayed are intermittent images because they are images when each of the strobe lighting devices 26 and 27 emit light. Therefore, if an image memory is provided and one frame of image data is stored in the image memory, the surface image of the test piece 10 can be displayed as a still image, and the operator will not have to worry about monitoring.

As described above, in the above embodiment, when the fatigue test piece 10 is irradiated with strobe illumination light by the strobe illumination device 26.27, the fatigue test piece 10 is imaged by the ITV camera head 22.23, and the image obtained at this time is Since the configuration is such that the scribe line 13 and the crack tip position fif 12a are detected from the video signal and the distance between them is calculated,
The rack tip position 12a can be accurately measured without blurring in the fatigue test piece 1o (11 image).In other words, since the test piece 10 is imaged at the moment when the strobe lighting devices 26 and 27 emit light, the test piece 10 Even if the camera is vibrating, it is not affected by the vibration and can capture images that do not blur.Furthermore, since the light emission timing of the strobe lighting devices 26 and 27 is set every afterimage time of the ITV camera head 22 and 23 or more, the influence of afterimages can be captured. In other words, since television cameras generally have afterimages of several fields, the strobe illumination device 26, 27 is synchronized with the field scanning of the ITV camera head 22, 23, and is emitted every time.
When an image is captured, the following afterimage occurs.

In other words, after one field has elapsed from the current image shown in FIG. 8(a), the marking line 13 is
This results in an image in which the crack tip position 12a changes in position.

Therefore, this can be done using conventional equipment using continuous illumination.
When the i-image is taken, the afterimage of the ITV camera head results in a superimposed image as shown in FIG. In this case,
Although the scribe line 13' is detected, there is a risk that the afterimage 12 may be detected at the crack tip position, making it impossible to accurately detect the rack tip position.

However, in the device of the present invention, images are taken at a time interval longer than the afterimage time, so the rack tip position 12- can be accurately detected without being affected by the afterimage, and the marking line 1
3 and the crack tip position 12a can be accurately measured.

Furthermore, this device can provide the following effects.

■Crack tip position can be measured automatically using a non-contact method.

■Since the crack tip position 12a can be measured completely unaffected by the shape and steel type of the test piece 1o,
There is no need for calibration even if the type of 0 is changed.

(2) Cracks on both sides of the test piece 10 can be detected, and the average value of the crack tip positions on both sides can be measured as the crack tip position of the test piece 10.

■Furthermore, it is also possible to perform the detection on two ITV camera heads individually, and when detecting cracks 12 on both sides of one test piece 100 in this way, two cracks can be detected from the images obtained by two ITV camera heads. It is also possible to determine the distance by determining the distance between the melting lines and detecting the average warpage value.

Note that the present invention is not limited to the above-mentioned embodiment, and can be modified without departing from the spirit thereof.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a highly accurate fatigue test specimen crack/tip position detection device that can eliminate image blur and accurately detect the crack tip position.

[Brief explanation of drawings]

Fig. 1 is an external view showing an embodiment of a fatigue test specimen crack tip position detection device according to the present invention, Fig. 2 is a specific configuration diagram of the device of the present invention, and Fig. 3 is a diagram applied to the device of the present invention. FIG. 4(a) is a side view of a fatigue test piece; FIG. 4(a) is a diagram showing an image of the test piece obtained by the apparatus of the present invention; FIG. 4(b) is a brightness distribution diagram for detecting marked lines; FIG. 5(a) to 5(d) are diagrams for explaining the crack detection operation, and FIGS. 6(a), (b), (c) to 7 are diagrams for explaining the noise component removal in the apparatus of the present invention. Figures, Figures 8 to 1
Figure 0 is a diagram to explain the afterimage of the ITV camera head.
FIG. 11 is a side view of the fatigue test piece. 10...Fatigue test piece, 20.21...Microscope, 22
゜23-I TV camera head, 24.25・IT
V camera controller, 26. 27... Strobe lighting device, 30... Signal processing device, 31... Camera changeover switch, 32... Marking line detection means, 33... Crack tip position detection means, 34... Synchronization signal generation circuit, 35... Frequency dividing circuit, 36.37... Strobe controller, 43... Distance detection section.

Claims (3)

[Claims] (1) an imaging means for capturing an image of a crack in a fatigue test piece on which a reference line for obtaining a crack tip position has been applied and the reference line in the same field of view; and a strobe illumination device for irradiating illumination light onto the surface of the fatigue test piece; lighting control means for controlling the light emission timing of the strobe lighting device to a desired timing;
a reference line detection means for detecting the reference line position by integrating the luminance level in the same direction as the reference line direction from the video signal from the imaging means to find the maximum level; A crack tip position detection means performs binarization processing on the brightness level in a direction perpendicular to the crack direction, and then determines the continuity of the high level value to detect the crack tip position, and the reference line detection means determines the crack tip position. crack tip position calculation means for calculating the distance from the reference line to the crack tip position from the reference line position determined by the reference line and the crack tip position determined by the crack tip position detection means. Single crack tip position detection device. (2) The strobe illumination device is installed at a predetermined angle to produce a predetermined amount of diffusely reflected light from the crack and the reference line with respect to the surface of the fatigue test piece. Position detection device. (3) The illumination control means causes the strobe illumination device to emit light at a time interval longer than the afterimage time of the imaging means.
1) The fatigue test piece crack tip position detection device described in item 1).