JPH047825B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a method for imaging the stress distribution of a test object by performing infrared measurement on the test object and performing computer processing on the temperature data input into a computer. .

(Prior Art) When designing mechanical devices, parts, structures, etc., it is an important issue from a safety standpoint to know how much stress is applied to which parts. In recent years, a method has been proposed for measuring the stress distribution of such an object in a short time without contact (Japanese Patent Application No. 56,691/1982). The principle of this method will be briefly explained below.

The inventor of this application discovered that when compressive and tensile loads are repeatedly applied to a test object, the surface temperature of the test object repeatedly rises and falls around the temperature at zero load in synchronization with the cycle of the load application. .

For example, as shown in FIG. 4A, when a load is applied to the test object in a sinusoidal manner, the test object surface synchronously with the compressive load corresponding to the positive half cycle and the tensile load corresponding to the negative half cycle. The temperature repeats rising and falling in a sinusoidal manner as shown in FIG. 4B. Furthermore, when a compressive load or a tensile load is applied in a rectangular wave manner (as shown in Figure 4 C and E, respectively), the surface temperature increases or decreases in synchronization with these (as shown in Figure 4 D and F). ).

It is known that there is a proportional relationship between the amount of change in surface temperature and stress change, so if a load is repeatedly applied to the test object and the width of temperature change at a specific point is detected, the width of the temperature change can be calculated. You can know the magnitude of stress at a point.

A conventional stress distribution imaging method based on such a principle will be briefly explained with reference to FIG.

The example shown in Figure 5 is one point on the subject.
This method performs infrared measurement during each scan to visualize the stress distribution. A load is applied to the object 1 by the load shaker 2, the scanner 3 is stopped at each point, and the infrared detector 4 reads the temperature data at each point. For example, in the case of a sinusoidal load,
The detected analog temperature data is switched between a positive half cycle and a negative half cycle by the switch 5 and converted into A/D.
After being sent to the converter 6 (6a and 6b) where it is converted into digital temperature data, it is stored in the corresponding memories 7a and 7b in the computer 7, respectively.
From this stored temperature data, within the same cycle,
The first and second temperature data at the two points in time when the load amplitude difference is maximum are read individually and in each cycle, and averaged by the averaging circuit 7c. In this example, the first temperature data can be the data at the time of the maximum positive amplitude, and the second temperature data can be the data at the time of the maximum negative amplitude. It is also possible to average the detected temperature data within the temperature range, obtain a weighted average of these averaged values obtained for each cycle, and use these as the first and second temperature data. A difference calculator 7d calculates the difference between these first and second temperature data.
This difference, ie, temperature information including stress information, is supplied to a display device 8, such as a CRT, so that the stress distribution of the subject can be displayed as an image.

In addition, the load shaker 2, the switching device 5, the A/D converter 6a,
6b, memories 7a, 7b, averaging circuit 7c, and difference calculator 7d are determined by a timing signal from a timing circuit 9.

This point measurement method requires time to measure temperature data point by point for the entire image and convert it into an image. Therefore, a method of shortening the measurement time by performing measurement by scanning a line or one screen may also be considered.

In this case, analg temperature data detected by scanning part or all of the subject while the load is being applied is stored in each of the memories 7a and 7b of the computer 7 in the same manner as described above. This scanning may be one line scanning, several line scanning, or one field scanning. Then, for example, 256 to 512 points are taken in one line, one line is scanned at high speed many times, and each of the first and second temperature data of each point on these one line is stored in the memory 7a described above. ,7
After storing the respective data in the memory area b, the average value of the first and second temperature data is obtained by the averaging circuit 7c. (not shown). After the temperature information per screen is recorded, this temperature information is sent to the display device 8 in the same manner as described above, and an image of the stress distribution is displayed.

Similarly, in single-screen scanning, except for the fact that the subject 1 needs to be scanned at a scanning speed comparable to that of television scanning, other points are processed in the same way as in the case of line scanning described above. , it is possible to image the stress distribution.

(Problem to be solved by the invention) However, when a load is applied to this test object and compression or tension is performed, in addition to the temperature change caused by the stress, the original change due to the positional shift of the test object occurs. Temperature data at another point shifted from the measurement point is measured, which causes measurement errors. Particularly, if there is a large temperature gradient in the object due to some reason, a large error in the measured temperature will occur.

The length of the subject 1 shown in FIG. 6 is, for example, l=
Assume that the length of the test object 1 is 100 mm, and the elongation of the test object 1 is 0.2 mm when a load of about ±22 Kg/mm ² is applied to it. On the other hand, the temperature gradient of specimen 1 is ~ for a width of ~30 mm ~
Assuming the temperature is about 30℃, there is a gradient of 1℃ per 1mm.

By the way, in the method using digitalization as described above, when scanning the object 1 with a length of about 100 mm, the line interval is about 1 mm to 0.5 mm, so a positional deviation error of 0.2 mm will occur. If this occurs, the temperature error component will be 0.2°C. This temperature error is a very large error compared to the signal. In reality, the temperature difference caused by this thermoelastic effect is 0.4° C. under the above-mentioned load, so the temperature error component described above becomes an extremely large error reaching 50% of the temperature difference caused by the thermoelastic effect.

Therefore, it is necessary to correct the temperature error caused by such positional deviation.

When performing this correction, another problem is how much scanning line interval should be scanned. Assuming that one pixel is 1 mm, when the subject moves in units of one pixel, it means that the subject has moved 1 mm when viewed from the center point of the pixel. As above, apply 30°C/30°C to the subject.
If we consider that there is a temperature gradient of 1 mm, the temperature change for a 1 mm positional shift is 1°C, and if we correct such a temperature change at 1 mm intervals, the magnitude of the signal due to the thermoelastic effect (0.4°C In view of the degree of correction, the correction is not sufficient, and correction must be made on the order of one pixel or less.

An object of the present invention is to provide a novel method for imaging the stress distribution of a subject, which solves the above-mentioned problems.

(Means for Solving the Problems) In order to achieve this object, according to the method of the present invention, a load is repeatedly applied to a subject, the subject is scanned using an infrared detector, and the load is measured. The temperature at each point within a predetermined area of the subject during two time periods giving the maximum load amplitude difference for each cycle is detected as first temperature data and second temperature data, respectively, and these first and second temperature data are In order to image the stress distribution of the object by calculating the difference between Detecting the temperature at each point within the predetermined area during two time periods giving the maximum load amplitude difference for each cycle as third temperature data and fourth temperature data, and detecting the temperature from the third and fourth temperature data, respectively. For each point within the predetermined area to which the thermal filter is attached,
obtaining positional deviation correction data for each point on the condition that the temperature at the same point is the same in the two time periods giving the maximum load amplitude difference; and before performing the difference calculation, calculating the positional deviation correction data. The method is characterized in that it includes a step of correcting an error due to positional deviation in the first or second temperature data using the temperature data.

(Function) With this configuration, even when the temperature of the object becomes high and the temperature gradient becomes large, large temperature data measurement errors caused by minute positional displacements of the object can be accurately corrected using position correction data. Therefore, the stress distribution of the object can be imaged more accurately.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. In the case of the present invention, the load waveform shown in FIG. 4 and the circuit shown in FIG. 5 described above can be applied, but detailed explanation thereof will be omitted since it would be redundant.

FIG. 1 mainly shows the functional blocks of the computer 7 (shown in FIG. 5) used in this invention.
Figure 2 shows the object to be inspected with a heat filter attached;
The figure is a diagram for explaining correction of temperature data according to the present invention.

In FIG. 1, the same components as in FIG. 5 are given the same reference numerals. The device shown in Figure 1 is the fifth
The difference from the device shown in the figure is that a correction circuit 7j is inserted between the averaging circuit 7c and the difference calculation circuit 7d, and another set of memories 7e is provided separately from the memories 7a, 7b and the averaging circuit 7c. , 7f and an averaging circuit 7g are provided, and a ΔV, ΔH determination circuit 7h that determines ΔV, ΔH for each image constituting the image based on data from the memories 7e and 7f, and a ΔV, ΔH determining circuit 7h that stores the determined ΔV, ΔH. At the same time, a ΔV and ΔH storage circuit 7i is provided to send data to the correction circuit 7j.

First, position correction will be explained. As with the conventional example shown in FIG. 5, it is assumed that the memory 7a stores the first temperature data at the time of the maximum positive amplitude, and the memory 7b stores the second temperature data at the time of the maximum negative amplitude. Figure 7A shows the memory 7 as the first temperature data.
FIG. 7B shows the temperature distribution image of the subject at the maximum positive amplitude stored in memory 7b, and FIG. 7B shows the temperature distribution image of the subject at the maximum negative amplitude stored in the memory 7b as second temperature data. shows. It can be seen that the specimens A and B are deformed in different directions due to the difference in the load direction, and that if the difference image is obtained as is, an accurate stress image cannot be obtained. For example, a point on the subject that corresponds to point (j, i) in image A at the maximum positive amplitude is in image B at the maximum negative amplitude.
, it has moved to point P due to positional displacement due to deformation.

Since this point P is not a measurement point, the temperature value is unknown, but if the temperature data Dji' of the point P at the destination of this position shift is known, new data can be created using that Dji' as point (j, i) data. It is possible to create accurate correction data (Fig. 7B'). As can be seen from FIG. 7B', this correction data is obtained by correcting the shape at the maximum negative amplitude to match the shape (state) at the maximum positive amplitude. Therefore, by obtaining a difference image between image A and image B', a stress distribution image in the shape at the maximum positive amplitude can be accurately obtained.

In the present invention, the above-mentioned temperature data Dji' at the positional shift destination is obtained as follows based on an interpolation method using temperature data of surrounding points. That is,
The point (j, i) at the maximum positive amplitude moves by ΔH in the horizontal direction and by ΔV in the vertical direction when the maximum amplitude is negative, assuming that the interval between adjacent measurement points is 1, and moves to the point Pji in Figure 3. If you have already done so, the point
The temperature data Dji′ of Pji is calculated at four points (j,
i), (j, i+1) (j+1, i) (j+1, i+
1) Temperature data Dji, Dji+1, Dj+1i, Dj+1i
It is determined by the following formula based on the interpolation method using +1.

Dji′=Dji×(1−ΔH)×(1−ΔV)+Dji+1×
(ΔH)×(1−ΔV)+Dj+1i+1×(ΔH)×(ΔV)
+Dj+1i×(1−ΔH)×(ΔV)… (1) However, ΔH and ΔV are unknown from the first temperature data and the second temperature data. The present invention is characterized by adding a measurement with a thermal filter attached to the surface of the subject, and determining ΔH and ΔV from the third and fourth temperature data obtained from the measurement.

In this additional measurement, as shown in FIG. 2, a thermal filter 10 is attached to the surface of the subject 1. This thermal filter 10 has a temperature comparable to the temperature distribution of the object 1, and the temperature gradient of the object appears on the surface, but temperature changes due to stress caused by load application are not transmitted. Furthermore, a material that expands and contracts in response to compression and tension of the subject is used. As this thermal filter 10, for example, adhesive tape, vinyl tape, or any other material that satisfies the above-mentioned conditions can be used regardless of its material, size, and thickness. Further, the location where the thermal filter 10 is attached can also be arbitrarily selected.

Next, when a load is applied to the subject 1 to which the thermal filter 10 is attached, the temperature distribution of the subject 1 itself appears in the area of the subject 1 where the thermal filter 10 is attached.
The temperature change component due to stress does not appear. The thermal filter 10 is scanned by infrared rays to detect third and fourth temperature data, and these data are stored in the other memories 7e and 7f of the computer 7 through the switch 5, respectively, as shown in FIG. do.

When a thermal filter is attached to a surface, as described above, the inherent temperature gradient of the object appears on the surface, but temperature changes due to stress caused by load application are not transmitted to the surface. Therefore, on the surface of the thermal filter, only the temperature distribution inherent to the subject appears equally at both the maximum positive amplitude and the maximum negative amplitude. In short, if we focus on the temperature at the same position of the subject to which the thermal filter is attached, it is the same at the maximum positive amplitude and at the maximum negative amplitude. In the present invention,
Focusing on this characteristic, for the third temperature data and the fourth temperature data, for example, by searching for a point at the negative maximum amplitude that has the same temperature as a specific point at the positive maximum amplitude, the positional deviation amount ΔH , ΔV is being determined.

Here, it is assumed that the third temperature data stored in the memory 7e is for the maximum positive amplitude, and that the temperature data stored in the memory 7f is for the maximum negative amplitude. In Fig. 3, the points (j, i), (j, i
+1) (j+1, i) (j+1, i+1) indicates adjacent measurement points that constitute the temperature distribution image stored in each memory, and Dji, Dji+1, Di+1i, Dj+1i+
1 shows temperature data at each measurement point.

On the surface of the thermal filter, only the original temperature distribution of the object appears equally at both the maximum positive amplitude and the maximum negative amplitude, so if there is no deformation due to load application to the object, Memory 7e, 7f
Temperature data at the same position at the time of the maximum positive amplitude and the time of the maximum negative amplitude stored in
1 should be equal.

However, as already mentioned, the measurement point actually moves due to deformation at the time of the maximum positive amplitude and at the time of the maximum negative amplitude. The measurements taken with the heat filter attached are as follows:
Since all the conditions such as field of view and intensity of applied load are the same as the measurements to obtain the first and second temperature data, the deformation appearing in the first and second temperature data will be reflected in the third and fourth temperature data. It appears equally.

That is, in the same way as explained for the first and second temperature data, for the third and fourth temperature data, the interval between the measurement points where the point (j, i) at the maximum positive amplitude is adjacent is set as 1. , at the maximum negative amplitude, it moves by ΔH in the horizontal direction and by ΔV in the vertical direction, and has moved to point Pji in FIG. Even if there is such a positional deviation in the fourth temperature data with respect to the third temperature data, 4 points (j, i), (j, i+1) (j+1, i) from the fourth temperature data
Temperature data Dji, Dji+1 of (j+1, i+1),
If the temperature Dji′ of a certain point in the area surrounded by the four points calculated based on equation (1) using Dj+1i and Dj+1i+1 is equal to Dji of the third temperature data, the point with that temperature Dji′ is the position shift destination. , and ΔH, ΔV at that time
The value represents the amount of positional deviation. This is based on the fact that, as described above, when focusing on the temperature at the same position of the subject to which the thermal filter is attached, the temperature is the same at the maximum positive amplitude and at the maximum negative amplitude.

The points of such temperature Dji' are divided into four points (j, i),
(j, i+1) (j+1, i) (j+1, i+1)
To search within the area surrounded by
By changing and giving in 1/1 step,
Let the position of point Pji be the point (j, i), (j, i+1) (j+
1, i) Set 100×100=10000 points in the area surrounded by (j+1, i+1), and calculate the calculated value based on formula (1) for each point at the point (j, i) stored in the memory 7e.
It is sufficient to compare it with the temperature data Dji of , and find a point that matches the calculated value Dji. When this calculated value matches Dji, ΔH and ΔV are determined as the positional deviation amount at the time of the negative maximum amplitude with respect to the point (j, i) with respect to the time of the positive maximum amplitude.

For example, if we consider the case of tension in the vertical direction, ΔH=0 and equation (1) is simplified, which simplifies the task of finding it. That is, after the third and fourth temperature data taken into the memories 7e and 7f are averaged (integrated) by the averaging circuit 7g,
The ΔV, ΔH determining circuit 7h reads arbitrary data Dji and Dj+1i from the memory 7f, and calculates ΔV.
Calculate Dji′ in 100 ways based on equation (1) by changing Dji′ in 100 ways in 1/100 steps such as 0.01, 0.02, 0.03, …, 0.99, 1.00, and read out the Dji′ in 100 ways from memory 7e. Compared to , Dji=Dji′.
Find Dji′. ΔH and ΔV, which give Dji′ obtained in this way, are determined as the amount of positional deviation regarding the point (j, i).

The ΔH, ΔV determining circuit 7h performs such work for all pixels (temperature data) forming the image. As a result, ΔH and ΔV are obtained for all pixels that make up the image. ΔV, ΔH
The storage circuit 7i stores ΔH and ΔV for all pixels determined by the determination circuit 7h.

After ΔH and ΔV for correction are obtained in this way, the correction circuit 7j performs correction as follows. That is, the correction circuit 7j corrects the point (j, i)
For the correction, four points (j, i), (j, i+1),
(j+1, i), (j+1, i+1) data Dji,
Read Dji+1, Dj+1i, Dj+1i+1, and these 4
The point data and the positional deviation amounts ΔH and ΔV at the point (j, i) read from the storage circuit 7i are substituted into equation (1) to obtain the correction value Dji'. The obtained Dji' is stored in the memory in the correction circuit 7j as data at the point (j, i) of the corrected second temperature data.

The correction circuit 7j then reads out the temperature data of the four surrounding points from the second temperature data stored in the memory 7b for all other points in exactly the same way, and also calculates ΔH,
ΔV is read out from the storage circuit 7i, a correction value is determined based on equation (1), and is stored in the memory. When the second temperature data (see FIG. 7B') corrected for all the temperature data is obtained in this way, the correction circuit 7j uses the first temperature data that has not been corrected at all and the corrected second temperature data. The two temperature data are sent to the difference calculation circuit 7d. If the result of the difference calculation is supplied as stress information to a display device (indicated by 8 in FIG. 5), a stress image that is not adversely affected by positional deviation will be displayed on the display screen.

In addition, in the above example, the positional deviation amounts ΔH and ΔV of the temperature data at the negative maximum amplitude (fourth temperature data) were calculated based on the data at the positive maximum amplitude (third temperature data), so the correction At this time, the temperature data at the maximum negative amplitude (second temperature data) was corrected. Conversely, if the positional deviation amount of the temperature data at the maximum positive amplitude (third temperature data) is calculated based on the temperature data at the maximum negative amplitude (fourth temperature data), Needless to say, correction must be made to the data at the maximum amplitude (first temperature data).

As mentioned above, if a load is applied to the test object and the test object generates heat for some reason and the temperature gradient becomes large, large temperature data will be generated even if the position of the test object is small. A measurement error occurs, but according to the present invention, this measurement error can be corrected. Therefore, to summarize the method of imaging the temperature distribution of a specimen according to the present invention, (a) temperature changes due to thermoelastic effects are not transmitted to the surface of the specimen, but the temperature distribution is almost equal to the temperature distribution of the specimen itself, and A thermal filter made of a material that can withstand expansion and contraction is attached, and the temperature data at the two points in time when the difference in load amplitude between the thermal filters attached to the test object is maximum is input into a computer, and the temperature at the same point is calculated by computer processing. (b) A step of importing temperature data into a computer for a subject to which a thermal filter is not attached; (c) ) Using the positional deviation correction amount obtained in step (a),
(b) correcting the position of the temperature data of the object without a thermal filter obtained in step (b) by interpolation to a resolution of one pixel or less, for example, to about 1/100 of one pixel, by computer processing; (d) position; The method includes a step of calculating a difference between the corrected temperature data of the subject to which the thermal filter is not attached and performing imaging.

In the above-described embodiments, metal was used as the object to be examined, but the present invention can be applied to other materials having a large temperature gradient.

Further, in the present invention, the scanning may be point scanning, line scanning, or single screen scanning.

(Effects of the Invention) As is clear from the above explanation, according to the method of the present invention, even when a load is applied to the test object and heat is generated and the temperature gradient becomes large,
Since large temperature data measurement errors caused by minute positional fluctuations of the subject can be corrected accurately, there is an advantage that the temperature distribution of the subject can be imaged more accurately.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram of a computer for explaining one embodiment of the method of the present invention, FIGS. 2 and 3 are diagrams for explaining the embodiments of the present invention, and FIGS. F is a line diagram and signal waveform diagram showing the object part to explain the conventional principle and the principle of this invention, FIG. 5 is a diagram showing the apparatus system used to explain the conventional system and this invention, and FIG. FIG. 7 is a diagram for explaining the drawbacks of the above method, and FIG. 7 is a diagram for explaining the concept of positional deviation correction. 1... Subject, 2... Load shaker, 3... Scanner, 4...
Infrared detector, 5...switcher, 6a, 6b...A/D
Converter, 7... Computer, 7a, 7b, 7e,
7f...Memory, 7c, 7g...Averaging circuit, 7d...
Difference calculator (or difference calculation circuit), 7h...ΔV and ΔH
Determination circuit, 7i... Interpolation data determination circuit, 7j... Correction circuit, 8... Display device, 9... Timing circuit, 1
0...Heat filter.

Claims (1)

[Claims] 1. A load is repeatedly applied to a test object, and the test object is scanned using an infrared detector to obtain the maximum load amplitude difference for each cycle of the test object during two time periods. The temperature at each point within a predetermined area of is detected as first temperature data and second temperature data, respectively, and the difference calculation between these first and second temperature data is performed to image the stress distribution of the subject. A thermal filter is attached to the surface of the predetermined region of the subject, and the predetermined region is scanned with an infrared detector to detect each region within the predetermined region during two time periods giving a maximum load amplitude difference for each cycle of the load. Detecting the temperature at each point as third temperature data and fourth temperature data, respectively; and from the third and fourth temperature data, for each point in the predetermined area to which the thermal filter is attached,
obtaining positional deviation correction data for each point on the condition that the temperature at the same point is the same in the two time periods giving the maximum load amplitude difference; and before performing the difference calculation, calculating the positional deviation correction data. and correcting errors due to positional deviation in the first or second temperature data using the method. 2. In the method for imaging stress distribution in a subject as set forth in claim 1, the material of the thermal filter is heated to a temperature comparable to the temperature distribution of the subject so that the temperature gradient of the subject is However, temperature changes caused by stress caused by load application are not transmitted to the surface, and the material is characterized by expanding and contracting in response to compression and tension of the specimen. Distribution imaging method. 3. In the method for imaging stress distribution in a subject as set forth in claim 1, the scanning by the infrared detector is performed by any one of point scanning, line scanning, or single screen scanning. Distribution imaging method.