JP3009579B2 - Infrared stress imaging system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared stress imaging system and, more particularly, to an infrared stress imaging system in which a sample is subjected to repeated compressive / tensile loads to detect the stress of the sample.

[0002]

2. Description of the Related Art Measuring the magnitude of a stress generated in each part of an object is a complete and accurate method for designing a machine or a structure by selecting the shape of each part, the dimensions of the material used, the material, and the like. It is crucial to enable economical design. Therefore, conventionally, a strain gauge has been attached to an object to be measured, and strain generated in the object to be measured has been detected to measure a stress distribution.

[0003] However, there is a problem that it is troublesome to attach the strain gauge to the object to be measured, and it takes much time for the measurement. On the other hand, if a compressive / tensile load is repeatedly applied to an object, heat generation and heat absorption appear, and if this heat generation and heat absorption are repeated in a relatively short cycle, diffusion of heat to the surroundings or interruption of heat from the surroundings is interrupted. With the insulation insulated
Although the surface temperature of the stress concentration portion changes, there is a proportional relationship between the temperature change amount and the stress change. Therefore, it has been proposed to use this to measure the stress distribution (Japanese Patent Publication No. 62-1987). No. 1204, JP-B-62-1205, JP-B-6
3-7333, Japanese Patent Application No. 4-178376, Japanese Patent Application No. 5
-253036). According to such a stress distribution measuring method, as compared to a conventional measuring method using a strain gauge or the like,
It is possible to measure quickly and easily without contact.

FIG. 3 shows a stress distribution based on temperature data obtained by horizontally and vertically scanning an image spot of an infrared detector on an object to which a load is periodically applied by utilizing such a principle. The timing chart at the time of calculation is shown.
Here, the description will be given on the assumption that the phase of the excitation signal fin for applying, for example, a repeated load of tension and compression to the subject and the temperature signal generated by the excitation are in phase. In general, the excitation signal fin is not synchronized with the camera HB signal (camera scan infrared data acquisition signal: signal of one scanning line of an infrared image).

As shown in FIG. 3, a plus trigger is generated in the vicinity of the phase where the stress becomes maximum with respect to the excitation signal fin, and a minus trigger is generated in the vicinity of the phase where the stress becomes minimum. In response to the plus trigger, a temperature signal is taken as plus data at the position of the first camera HB signal, and a temperature signal is taken as minus data at the position of the first camera HB signal in response to the minus trigger.

In general, the plus trigger and the minus trigger are not synchronized with the camera HB signal. In order to detect a minute temperature difference such as 1/1000 ° C. at the time of capturing the temperature signal, the S / N ratio is improved by using a method such as line integration or frame integration. Here, the line integration is to take and add a plurality of data during a half cycle of the excitation signal fin,
The frame integration is to superimpose a plurality of data of the entire image. The example of FIG. 3 shows an example of line integration in which three data are fetched and added in each half cycle on the plus side and the minus side. Then, by taking the difference between the plus data and minus data thus obtained for the entire screen, temperature change distribution data is obtained and can be used as stress distribution data.

[0007]

By the way, in such an infrared stress imaging system, when the line integration is not performed, only the peak value of the temperature signal due to the vibration can be taken out. Although it is possible to accurately correspond to the distribution, when performing line integration, to capture a plurality of temperature signals with a certain width near the peak value of the temperature signal due to vibration,
The added signal data is not proportional to the peak value. This will be described with reference to FIG.

FIG. 4 is an enlarged timing chart showing the plus side of the temperature signal in the timing chart when the line integration is performed three times as shown in FIG. In FIG. 4, when a plus trigger is generated in the vicinity of the peak value of the temperature signal due to the vibration, as described above, the temperature signal is taken in at the timing of three camera HB signals generated immediately after the plus trigger. . In this case, as is clear from FIG. 4, the peak value Y ₀ of the temperature signal by vibrating the temperature signal in generating the position of the positive trigger Y
_t , and obviously Y _t <Y ₀ , all three temperature signals taken in as plus data are Y
a value between the Y ₀ from _t. Here, the camera HB signal is not synchronized with the temperature signal due to the vibration and the plus trigger as described above, and therefore, the values of the three temperature signals are also random. In any case, these three
Sum of pieces of temperature signal becomes smaller than the value of 3 times Y0, in other words, the average value is always smaller than Y _0, the final addition data is excellent in S / N ratio However, there is a problem that the stress is not exactly proportional.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and an object thereof is to detect an accurate temperature change distribution and a stress distribution even when line integration is performed. An infrared stress imaging system is provided.

[0010]

In order to achieve the above object, an infrared stress imaging system of the present invention applies a load to a subject periodically, and detects a temperature change of a sample surface due to heat generation and heat absorption by infrared rays. In an infrared stress imaging system that detects a stress distribution based on a temperature change distribution by detecting with a camera, the plus temperature distribution data and the minus temperature distribution data are line-integrated a predetermined number of times, respectively, and the plus temperature distribution obtained by the line integration The temperature change distribution is obtained by taking difference data between the data and the minus temperature distribution data, and correcting the difference data with a correction coefficient obtained using the vibration frequency for the subject and the horizontal scan frequency of the infrared camera. It is characterized in that it is obtained.

[0011]

According to the present invention, the line-integrated temperature data is corrected by the correction coefficient obtained by using the vibration frequency for the subject and the horizontal scan frequency of the infrared camera according to the principle described later. , S / N ratio, and accurate stress distribution can be detected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle and embodiments of an infrared stress imaging system according to the present invention will be described below with reference to the drawings. FIG.
5 is a timing chart for explaining the principle of the infrared stress imaging system according to the present invention.

Here, first, when the line integration is performed, it is considered which position the average value of the plurality of added temperature signals corresponds to. In this case, considering that the camera HB signal that captures the plurality of temperature signals is not synchronized with any of the temperature signal due to the vibration and the plus trigger, the plurality of temperature signals become the temperature signals from the time of occurrence of the plus trigger. Are taken in at random timings up to the peak value of. Therefore, from the viewpoint of probability theory, the average value has the highest probability corresponding to a position that divides the interval T ₁ between the plus trigger and the peak value into two, that is, a position of T ₂ = T _1/2 .

Next, the value Y ₁ of the temperature signal in a phase shifted from the peak value by T ₂ will be examined. Here, each variable and constant are defined as follows.

[0015] f _0: vibration frequency T _0: vibration period _{(T 0 = 1 / f 0} ) f s: camera horizontal scanning frequency T _s: camera horizontal scanning period _{(T s = 1 / f s} ) L 0: Line integration number Y ₀ : peak value of temperature signal Y ₁ : average value of taken-in temperature signal x: angle of phase corresponding to the average value (angle from phase of peak value) As shown in FIG. The phase of the value is 90 ° and corresponds to １ ／ of the excitation period T ₀ . Further, as a condition for performing the line accumulation range to be taken of the temperature signal from the time point of generation of the positive trigger is [T _s × L _0], because this corresponds to twice the T _1, wherein T ₂
Is equivalent to １ ／ of this [T _s × L ₀ ].

From such a relationship, the following proportional expression can be established. T _0/4: 90 ° _{= [T s × L 0]} / 4: if x deforming the proportional expression, x = 90 ° _{× (T s × L 0/} 4) / (T 0/4) is obtained Can be

Therefore, if Y ₁ = αY ₀ , the value of α is α = sin (90 ゜ −x) = sin [90 ゜ −90 ゜ × (T _s × L ₀ ) according to the teaching of the trigonometric function. / 4) / (T ₀ /
4)] = sin [90 ° -90 ° _{× (L 0 / 4f s)} / (1 / 4f
₀ )].

Therefore, the error in the plus data, that is, the difference ΔY between the peak value Y ₀ and the detected average value Y ₁ is:
Using this α, it can be expressed as ΔY = Y ₀ −Y ₁ = (1−α) Y ₀ . That is, the coefficient of the error of the plus data is represented by (1−α).

Since the final data is the difference between the plus data and the minus data as described above, the difference ΔY from the peak value in the finally obtained difference data is doubled. Here, if the error coefficient in the final difference data is β, β = 2 (1−α). Then, assuming that the difference data actually obtained is D and the accurate difference data is D ₀ , D = D ₀ −βD ₀ = D ₀ (1-β) = D ₀ [1-2 (1-α) ]. Therefore, the accurate difference data D ₀ is D ₀ = D / [1-2 (1-α)], that is, for the difference data D actually obtained,
By performing correction with a predetermined correction coefficient obtained from the excitation frequency f ₀ and the camera horizontal scan frequency f _s , accurate difference data can be obtained while performing line integration.

Next, FIG. 2 is a block diagram showing one embodiment of the infrared stress imaging system of the present invention based on the above principle. This system includes a vibrator 1 for vibrating a subject S
And an infrared camera 2 for capturing an image of the subject S that is repeatedly subjected to a load by the vibrator 1.
Plus trigger generating circuit 3, minus trigger generating circuit 4,
It comprises a frequency detection circuit 5, a plus data memory 6, a minus data memory 7, a difference data memory 8, a computing device 9, and a display device 10.

In the operation, each of the plus trigger generating circuit 3, the minus trigger generating circuit 4, and the frequency detecting circuit 5 receives the vibration signal fin as shown in FIG. The positive trigger generating circuit 3 and the negative trigger generating circuit 4 generate a positive trigger near the phase position where the stress with respect to the excitation signal fin becomes maximum, and generate a negative trigger near the phase position where the stress becomes minimum. At the same time, the frequency of the excitation signal fin is detected by the frequency detection circuit 5 and the data is input to the arithmetic unit 9. It should be noted that the arithmetic unit 9 also receives data on the horizontal scan frequency from the infrared camera 2.

A camera HB signal repeatedly input from the infrared camera 2 for a horizontal scanning line at a predetermined vertical position;
The plus trigger signal generated by the plus trigger generation circuit 3 is input to the plus data memory 6, and a predetermined number of plus temperature data is taken into the plus data memory 6 and added in accordance with the generation of the plus trigger signal. . Also,
The camera HB signal and the negative trigger signal generated by the negative trigger generating circuit 4 are input to the negative data memory 7, and a predetermined number of negative temperature data are stored in the negative data memory 7 in response to the generation of the negative trigger signal.
And added.

The plus temperature data and minus temperature data taken into the plus data memory 6 and minus data memory 7 are sent to a difference data memory 8 under the control of the arithmetic unit 9, and the difference between them is taken. Then, the arithmetic unit 9 corrects the difference data based on the information on the vibration frequency and the camera horizontal scan frequency, and the corrected difference data is stored in the difference data memory 8.

In this manner, temperature change distribution data for one horizontal scanning line is obtained. Next, the horizontal scanning position of the infrared camera 2 is advanced to the next scanning line based on a signal from the difference data memory 8, for example. The temperature change distribution data of the scanning line is similarly obtained, and the same is performed for the entire screen, thereby obtaining the two-dimensional temperature change distribution data of the subject S. The temperature change distribution data stored in the difference data memory 8 is displayed as an image on, for example, the display device 10 to determine the stress distribution of the subject S.

Although the infrared stress imaging system of the present invention has been described based on the embodiments, it is obvious to those skilled in the art that the present invention is not limited to these embodiments and various modifications are possible.

[0026]

As is apparent from the above description, according to the infrared stress imaging system of the present invention, when the temperature signal is line-integrated, the difference is obtained by using the correction coefficient based on the vibration frequency and the camera horizontal scan frequency. Since the data is corrected, accurate S / N ratio and accurate stress data can be detected.

[Brief description of the drawings]

FIG. 1 is a timing chart for explaining the principle of an infrared stress imaging system according to the present invention.

FIG. 2 is a block diagram of one embodiment of the infrared stress imaging system of the present invention.

FIG. 3 is a timing chart for explaining a conventional infrared stress imaging system.

FIG. 4 is a timing chart for explaining a conventional infrared stress imaging system.

[Explanation of symbols]

 S: Subject 1 ... Exciter 2 ... Infrared camera 3 ... Positive trigger generating circuit 4 ... Negative trigger generating circuit 5 ... Frequency detecting circuit 6 ... Positive data memory 7 ... Minus data memory 8 ... Difference data memory 9 ... Computing device 10 … Display device

Claims (1)

(57) [Claims] 1. A method in which a load is periodically applied to a subject to generate heat,
In an infrared stress imaging system in which a temperature change on a sample surface based on an endothermic action is detected by an infrared camera and a stress distribution is detected based on the distribution of the temperature change, positive temperature distribution data and negative temperature distribution data are respectively determined a predetermined number of times. Each line is integrated, and the difference data between the plus temperature distribution data and the minus temperature distribution data obtained by the line integration is taken, and the difference data is obtained by using the vibration frequency for the subject and the horizontal scan frequency of the infrared camera. An infrared stress imaging system characterized in that a temperature change distribution is obtained by correcting with the obtained correction coefficient.