JP4097081B2 - Defect inspection method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for detecting an internal defect in an object to be inspected composed of a low thermal conductivity material such as concrete.

  Conventionally, a thermography method is known as a method for examining internal defects such as floating and peeling of a concrete structure. In this conventional thermography method, the local temperature change region of the concrete surface that occurs when a thermal load is applied to a concrete structure or the like is measured by infrared thermography, and the measurement data is output as an image to inspect internal defects. Do. In other words, the output image represents the distribution of the measured infrared intensity, and the internal defect can be detected based on the contrast difference between the infrared intensity of the defective part and the healthy part.

  As an application of the conventional thermography method, the applicant is able to detect not only the defect site but also the defect depth of a test object composed of a low thermal conductivity material such as a concrete structure. The invention about the method and its apparatus is disclosed (for example, refer patent document 1).

  In this prior art, heating and cooling (heating stop) are alternately performed on the object to be inspected, and a temporal change in the surface temperature at each part of the object to be inspected is detected during cooling. Since the temporal change of the surface temperature is different between the healthy part and the part having a defect inside, the phase difference from the measurement waveform in the healthy part can be detected to detect the defect.

  Furthermore, when the above measurement is performed with different heating / cooling periods (for example, 10 minutes, 20 minutes, 30 minutes, and 40 minutes), the maximum phase difference is obtained when heating and cooling are performed in any period. The depth of the defect can be detected by seeing whether or not (a phase difference from the sound waveform) occurs.

JP 2003-83923 A

  However, in the method disclosed by the applicant in the above document, the depth of the internal defect of the object to be inspected can be detected, but the heating and cooling cycle must be changed, and the measurement must be performed many times. There was a problem that the inspection took a long time. This was especially true for low thermal conductivity materials to be tested.

  In addition, when detecting the presence or absence of defects, in order to accurately detect defects at different depths, it is necessary to perform multiple measurements with different heating and cooling cycles, which requires a long time for inspection. Was.

  The present invention has been made to solve such a problem, and when detecting an internal defect of an object to be inspected composed of a low thermal conductivity material such as a concrete structure, It is an object of the present invention to provide a defect inspection method and apparatus capable of accurately detecting information such as depth and shape, and efficiently inspecting by shortening the inspection time.

(1) A defect inspection method according to the present invention includes:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
The difference in the predetermined periodic component between the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part is calculated for different periodic components, and the difference is obtained based on the difference obtained for each periodic component. A defect inspection method for detecting defects in each unit region of an inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, the presence or absence of a defect can be detected by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(2) The defect inspection method according to the present invention is as follows:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Determining the defect based on the difference in the predetermined periodic component of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part,
The defect is calculated for different periodic components, and based on the difference obtained for each periodic component, a defect inspection method for estimating the defect depth in each unit region of the inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, the presence or absence of a defect can be detected and the defect depth can be estimated by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(3) A defect inspection method according to the present invention includes:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
The difference in the predetermined periodic component of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part is calculated for the predetermined periodic component of a plurality of periods,
Based on the difference obtained for each periodic component, a defect inspection method for estimating the defect depth in each unit region of the inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, the defect depth can be estimated by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(4) In the defect inspection method according to the present invention,
The difference in the predetermined period component of the time change of the surface temperature in each unit region and the time change of the surface temperature in the healthy part is as follows:
It is determined based on a relative difference with respect to a reference waveform having a predetermined period.

  Therefore, the defective part and the healthy part can be determined by relative comparison.

(5) In the defect inspection method according to the present invention,
A unit region in which a difference from an average difference in a predetermined periodic component of a temporal change in surface temperature in all unit regions is smaller than a predetermined value is defined as the healthy portion.

  Therefore, it is possible to detect a defect with high accuracy without preparing data in a healthy part in advance.

(6) In the defect inspection method according to the present invention,
The difference in the predetermined period component is a phase difference.

  Therefore, the defect depth can be estimated with high accuracy.

(7) In the defect inspection method according to the present invention,
The defect depth is estimated based on which one of the plurality of periodic components has the maximum phase difference.

  Therefore, the defect depth can be estimated with high accuracy.

(8) In the defect inspection method according to the present invention,
It is characterized in that the defect depth is estimated based on a phase difference change pattern accompanying a change in the cycle of the predetermined cycle component.

  Therefore, the defect depth can be estimated by a simple method.

(9) (11) A defect inspection apparatus according to the present invention includes:
A heating control means for performing a heating start command and a heating stop command for a heating device that heats the entire surface of the measurement target surface of the object to be inspected;
Data recording means for inputting and recording data from a temperature measuring instrument that measures the surface temperature in each unit region of the object to be inspected at least after stopping heating;
Waveform comparison means for reading temperature data recorded in the data recording means and calculating a phase difference between a time-varying waveform of the surface temperature in each unit region and a reference waveform having a predetermined period for a plurality of reference waveforms having a predetermined period; ,
A defect inspection apparatus comprising a comparison result output means for outputting a phase difference calculated by a waveform comparison means ,
The phase difference is calculated using a plurality of different reference waveforms with respect to measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, information for detecting the presence or absence of a defect can be presented to the operator by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(10) (12) A defect inspection apparatus according to the present invention includes:
A heating control means for performing a heating start command and a heating stop command for a heating device that heats the entire surface of the measurement target surface of the object to be inspected;
Data recording means for inputting and recording data from a temperature measuring instrument that measures the surface temperature in each unit region of the object to be inspected at least after stopping heating;
Waveform comparison means for reading the temperature data recorded in the data recording means and calculating the phase difference between the time change waveform of the surface temperature in each unit region and the reference waveform having a predetermined period;
A defect position output means for detecting a region where the difference from the average phase difference in all regions is a predetermined value or more as a defect portion, and outputting the defect position;
The phase difference is calculated for different periodic components, and the defect depth in each unit region of the object to be inspected is estimated based on the difference between the phase difference of the defective portion and the phase difference of the healthy portion obtained for each periodic component. A defect inspection apparatus comprising a defect depth estimating means for
The phase difference is calculated using a plurality of different reference waveforms with respect to measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, the presence or absence of a defect can be detected and the defect depth can be estimated by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(13) A defect inspection method according to the present invention includes:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Based on the difference in the predetermined periodic components of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part, the defect in each unit region of the object to be inspected is determined,
A defect inspection method for calculating a determinable defect depth based on a cycle of a predetermined cycle component used for the defect determination ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
It is characterized by.

  Therefore, information on the defect depth that can be determined can be presented to the operator by one heating and measurement. Thereby, the inspection time concerning heating and measurement can be shortened, and the inspection efficiency as a whole is improved.

(14) A defect inspection method according to the present invention includes:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Temporal change in the surface temperature of each unit region, the temporal change of the surface temperature at the healthy part, based on the difference in a predetermined period component, a defect inspection method for determining defects in each unit area of the device under test,
The difference is calculated using a plurality of different periodic components for measurement data in one time series obtained by performing the heating and the measurement once.
The depth of the defect to be inspected is determined, and the period of the predetermined period component is selected as an appropriate period for detecting the defect depth.

  Therefore, an appropriate cycle for detecting the defect depth can be selected by one heating and measurement, and defect inspection can be performed efficiently.

(15) In the shape estimation method according to the present invention,
Divide the measurement target surface of the object under test into multiple unit areas,
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the object to be inspected,
Calculate the difference in the predetermined period component of the time change of the surface temperature in each unit region and the time change of the surface temperature in the reference part,
The difference is calculated for different periodic components, and based on the difference obtained for each periodic component, the thickness in the depth direction in each unit region of the inspected object is estimated to estimate the shape of the inspected object It is characterized by this.

  Therefore, the shape of the back side of the object to be inspected whose shape is unknown can be easily estimated by one heating and measurement.

(15) A defect inspection method according to the present invention includes:
Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
A defect inspection method for detecting a defect in each unit region of an object to be inspected based on a difference in a predetermined periodic component of a temporal change in surface temperature in each unit region and a temporal change in surface temperature in a healthy part,
The difference is calculated using a plurality of different periodic components for measurement data in one time series obtained by performing the heating and the measurement once.
As the predetermined period, a period longer than the heating period is used.

  Therefore, it is possible to detect a deep defect with a short heating time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1. First embodiment 1-1. About heating conditions 1-1-1. Heating distance and heating time FIG. 2 shows that the surface of the object to be inspected as a concrete structure is heated and cooled (heating stopped) by changing the heating distance and the heating time. It is a graph at the time of measuring the time-dependent change of the temperature in a deep part (50 mm). The heating intensity of the heater was constant, and the temperature was measured using a thermocouple installed on the object to be inspected.

  FIG. 2A is a graph when the heating distance between the surface of the object to be inspected and the heater is 2 m and heating is performed for 20 minutes. FIG. 2B is a graph when the heating distance between the surface of the object to be inspected and the heater is 0.5 m and heating is performed for 1 minute.

  As shown in the graph of FIG. 2A, when the heating distance is 2 m and the heating time is 20 minutes, the internal temperature at the position of 50 mm in depth increases after the heating is stopped (after 20 minutes have elapsed). In addition, as shown in the graph of FIG. 2B, when the heating distance is 0.5 m and the heating time is 1 minute, the heating is stopped (after 1 minute has passed) at a position where the depth is 50 mm as described above. The internal temperature is rising.

  In particular, when the heating distance is 0.5 m, the internal temperature at the point where the depth is 50 mm is hardly seen during the heating period of 1 minute, but the internal temperature is reduced after the heating is stopped. It is gradually rising. That is, even when the heating time is shortened and the heating distance is shortened, the temperature rises at a point where the depth is 50 mm.

1-1-2. Thermography An example of a case where an object to be inspected (artificial defect specimen) having an artificial defect is heated under the above-described heating conditions, and a surface temperature distribution is measured using an infrared thermography method to detect a defect.

  In the artificial defect specimen 1 shown in FIG. 3A, simulated peeling 2 and 5 of a polyethylene sheet having a thickness of 10 mm, simulated peeling 3 of a polyethylene sheet having a thickness of 5 mm, at positions where the depth d from the surface is 100 mm and 50 mm, 6. Simulated peelings 4 and 7 of a polyethylene sheet having a thickness of 2 mm are embedded.

  For the artificial defect specimen 1, heating is stopped when (1) the heating distance is 2 m and the heating time is 20 minutes, and (2) the heating distance is 0.5 m and the heating time is 1 minute. (After 25 minutes), the surface temperature distribution was measured by infrared thermography (detection wavelength: 8-13 μm, NETD value: 0.1 ° C.).

  FIG. 3B is a surface temperature distribution image when (1) the heating distance is 2 m and the heating time is 20 minutes. FIG. 3C is a surface temperature distribution image when (2) the heating distance is 0.5 m and the heating time is 1 minute.

  In the temperature distribution image of FIG. 3B, the vicinity of b1, b2, and b3 is displayed at a high temperature. This has shown that the defect detection about the simulated defects 5-7 is possible. In the temperature distribution image of FIG. 3C, the vicinity of c1, c2, and c3 is displayed at a high temperature. This indicates that defect detection can be performed for simulated defects 5 to 7 having a depth of 50 mm.

  The simulated defects 2 to 4 having a depth of 100 mm could not be detected under any of the heating conditions shown in the above (1) and (2). Further, in the temperature distribution images of FIGS. 3B and 3C, the variation in the surface temperature at the simulated defects 5 to 7 is considered to be due to the influence of heating spots and the like during heating.

1-1-3. Consideration Considering the above points, when a large amount of heat exceeding a certain amount is given to the surface of the object to be inspected with low thermal conductivity, a so-called heating layer is generated inside the object to be inspected. It is expected that the heat conduction to the inside will be continued during the cooling period in which the temperature decreases.

  That is, when a thermal load is applied to the surface of an object composed of a low thermal conductivity material such as a concrete structure, the greater the amount of heat generated by the applied thermal load, the greater the amount of heat generated during the heating stop period after the heating is stopped. Heat conduction to is sustained.

  Therefore, if the continuous heat conduction to the inside reaches the depth point of the defect to be detected and the change in the surface temperature based on the temperature rise caused by the arrival of heat can be measured, at least to the point It is possible to detect a defect existing at a depth even after the heating is stopped.

  Based on this knowledge, a defect inspection method in which the inspection object as a concrete structure is heated to improve the inspection efficiency will be described below.

1-2. Defect Inspection As described above, even after heating is applied to the surface of the object to be inspected, heat conduction to the inside is maintained during the cooling period even if heating is stopped. If there is a defect in the object to be inspected, the heat conduction is hindered by the defective portion, and as a result, the surface temperature of the defective portion becomes higher than the surface temperature of the healthy portion. Therefore, a defect can be detected by comparing the temporal change waveform of the surface temperature after stopping the heating at the inspection site with the temporal change waveform of the surface temperature of the healthy part.

  FIG. 4 shows a temporal change waveform of the surface temperature after heating. A waveform γ is a waveform of a healthy part, and a waveform α and a waveform β are waveforms when there is an internal defect. There is an internal defect at a deeper position in the case of the waveform β than in the case of the waveform α. Since the waveform of the part with the defect is clearly different from the waveform of the healthy part, the defect can be found.

  The comparison of the waveforms can be performed by calculating a phase difference in a predetermined periodic component. In calculating the phase difference, the phase difference between the temporal change waveform of the surface temperature at the examination site and a reference waveform (such as a sine wave) having a predetermined period is calculated, and the temporal change waveform of the surface temperature of the healthy part and the predetermined waveform are calculated. It can be obtained by calculating the phase difference between the period and the reference waveform and further calculating the difference between the two phase differences.

  This phase difference is converted into visually recognizable image data, and a defect inspection can be performed by displaying a portion where an internal defect exists as a contrast difference on the image data.

  Note that the temporal change waveform of the surface temperature at the inspection site also changes depending on the depth of the defect (distance from the surface of the object to be inspected to the shallowest part of the defect). This is because the deeper the defect, the slower the onset of the effect of the defect on the surface temperature. In FIG. 4, the defect in the case of the waveform β is located deeper than the defect in the case of the waveform α.

  Therefore, if the change corresponding to the defect depth in the temporal change waveform is detected, the depth of the defect can be estimated. In the following embodiments, the phase difference is calculated using a reference waveform having a plurality of periods, and the defect depth is estimated based on the phase difference in each period.

1-3. Outline of Defect Inspection System FIG. 1a is a functional block diagram showing a schematic configuration of a defect inspection system for realizing the present invention. In this figure, the defect inspection control device 10 inputs heating control means 11 for controlling heating / stopping heating to the heating device 17 and measurement data of the surface temperature of the object measured by the temperature measuring device 19. Data recording means 13 for recording, waveform comparison means 16 for reading the measurement data recorded in the data recording means 13 and comparing the waveform with the reference waveform, and comparison result output means 18 for outputting the result of waveform comparison I have.

  By adjusting the distance between the heating device 17 and the object to be inspected, the amount of heat given to the object to be inspected per unit time can be adjusted. In the following embodiments, this distance is set to 0.5 m.

1-3-1. Configuration of Device of Defect Inspection System FIG. 5 shows a specific configuration example of the defect inspection system. The inspected object 20 represents a concrete wall for inspecting internal defects. A heater 21 that applies a thermal load to the inspection object 20 is installed opposite to the inspection object 20. The heater 21 is connected to a relay device 25 that can adjust the output of the thermal load in order to give a uniform thermal load to the device under test 20. By providing the relay device 25, the irradiation amount at the center of the heater 21 is adjusted so that the center of the device under test 20 does not reach a higher temperature than the periphery.

  The signal generator 27 is connected to the relay device 25 and the computer device 29, and generates a signal for controlling the relay device 25 based on the heating start command received from the computer device 29.

  The infrared camera 23 is installed opposite to the inspection object 1 and is connected to the computer device 29, measures the surface temperature of the inspection object 1 in time series, and outputs the measurement data to the computer device 29. To do.

  Receiving the output of the measurement data, the computer device 29 records the measurement data, and based on the data, judges an internal defect of the inspection object 20 and outputs an image to estimate the defect depth.

  The defect inspection control device 10 in FIG. 1 a is realized by a computer device 29 and a signal generation device 27. The heating device 17 is realized by the heater 17 and the relay device 25. The temperature measuring device 19 is realized by the infrared camera 23. In addition, you may make it control the heating apparatus 17 directly from the computer apparatus 29, without providing the signal generator 27. FIG.

1-3-2. Hardware Configuration Diagram of Computer Device FIG. 6 is a hardware configuration diagram of the computer device 29. This apparatus includes a CPU 30, a memory 31, a display 33, a hard disk 35 (storage device), a keyboard / mouse 37, and a communication circuit 39.

  The communication circuit 39 is a circuit for connecting to the signal generator 27, the infrared camera 23, and the like. The hard disk 35 stores an operating system and a defect inspection program. The program for defect inspection achieves its function in cooperation with the operating system.

1-3-3. Defect Inspection Processing FIG. 7 shows a flowchart of the defect inspection program. First, the CPU 30 outputs heating conditions to the signal generator 27 via the communication circuit 39 (step S401). In this embodiment, the heating conditions are output such that the heating time is 2 minutes and the heating intensity is constant at 38.8 kW (heater output).

  The heating condition is given to the signal generator 27, converted into a waveform signal, and output to the relay device 25. The relay device 25 operates the heater 21 based on the input waveform signal. Thereby, a thermal load is given to the to-be-inspected object 20 on predetermined heating conditions. Here, as shown in FIG. 8, a heat load is applied such that the heating time is 2 minutes and the heating intensity is constant at 38.8 kW.

  Next, the CPU 30 records the output (surface temperature data) of the infrared camera 23 on the hard disk 35 via the communication circuit 39 (step S402). The surface temperature data is recorded at least after the heating stop time. Of course, data before the heating stop may be recorded, but as described later, in this embodiment, the defect is determined only by the surface temperature data after the heating stopping time.

  As shown in FIG. 9, the infrared camera 23 outputs the surface temperature of each unit region P1,1 to Pk, j to be measured. That is, the surface to be measured is a matrix of length k and width j, and the surface temperature of each unit region is measured.

  FIG. 10 shows temperature data recorded on the hard disk 35. For each unit region P1,1 to Pk, j, the temporal change of the surface temperature is recorded. Time t1 is when heating is stopped, and time tN is when measurement ends. In this embodiment, the measurement time interval is the image frame period of the infrared camera 23. In this embodiment, measurement was performed for 60 minutes from the heating stop time t1.

  When the measurement process is finished, the CPU 30 sets the smallest period among the preset reference waveform periods as the target period (step S403). Here, 20 minutes, 30 minutes, and 40 minutes are set as the cycles, and the smallest cycle of 20 minutes is set as the target cycle.

  The CPU 30 performs measurement data analysis processing using the reference waveform having the target period (step S404). FIG. 11 shows a flowchart of measurement data analysis processing. Here, the surface temperature data for each unit region of the measurement region in the inspection object 20 is represented by K, and the temperatures at the time t and the unit regions x, y are represented by Kt, x, y. The CPU 30 calls this Kt, x, y from the hard disk 35 for each area and stores it in the memory 31.

  First, in step S501, the CPU 30 sets the unit area indices x and y to “1”. Next, the phase difference between the surface temperature data waveform of the unit region P1,1 and the reference waveform (sin wave) with a period of 20 minutes is calculated (step S502). In this embodiment, the phase difference is calculated based on the following.

  First, the fluctuation amplitude ΔKsin of the surface temperature waveform synchronized with the reference waveform and the fluctuation amplitude ΔKcos of the surface temperature waveform synchronized with the COS wave 90 degrees out of phase with the reference waveform are calculated by the following formula.

  Here, N is the number of frames for capturing surface temperature data (N from t1 to tN in FIG. 9). K (t) represents the surface temperature data value of P1,1 at time t. Sin (t) indicates the amplitude value of the reference waveform (sin wave) at time t. Cos (t) indicates the amplitude value of a waveform (cos wave) that is 90 degrees out of phase with the reference waveform at time t. For example, the maximum value of the amplitude value of the reference waveform may be “1”.

  Next, the absolute value ΔK and the phase difference θ of the temperature fluctuation amplitude are calculated by the following equations.

  The CPU 30 records the phase difference θ1,1 in the unit area P1,1 calculated in this way on the hard disk 35 in association with the period of the reference waveform.

  Next, x is incremented by 1, and step S502 and subsequent steps are repeated. That is, the phase difference θ1.2 is calculated and recorded for the unit areas P1 and P2 in the same manner as described above. When x exceeds the number J of pixels in one line, that is, when the phase difference is calculated for all pixels in one line (step S504), y is increased by 1, x is set to “1”, and step S502 and subsequent steps are repeated. That is, for the unit area P2,1, the phase difference θ2,1 is calculated and recorded in the same manner as described above. Thereafter, this process is repeated to calculate the phase differences θ1,1 to θJ, K for all the unit regions up to the unit regions PJ, K.

  When the calculation of the phase difference for the reference waveform with a period of 20 minutes is completed in this way, step S405 in FIG. 7 is executed. In step S405, it is determined whether there is an unprocessed cycle.

  Here, since there is an unprocessed cycle, the process proceeds to step S403. In step S403, the analysis process of step S404 is performed in the same manner as described above, with the next period of 30 minutes as the target period. Thereby, the phase differences θ1,1 to θJ, K with respect to the reference waveform having a period of 30 minutes can be obtained. Subsequently, in the same manner as described above, phase differences θ1,1 to θJ, K with respect to a reference waveform having a period of 40 minutes are calculated.

  After calculating the phase differences for all phases in this way, the CPU 30 next calculates the phase differences θ1,1 to θJ, K in the unit regions P1,1 to PJ, K for the reference waveforms of the respective periods. An image expressed as a density difference is generated. Further, this is displayed on the display 33. Alternatively, it is printed out from a printer (not shown).

  12A to 12C, the above-described inspection is performed on the inspected object having the simulated defect as shown in FIG. 12D, and the phase differences θ1, 1 to θJ, K with the reference waveforms of 10 minutes, 20 minutes, and 40 minutes are calculated. The image obtained by doing is shown.

  Six simulated defects are provided as shown in FIG. 12D. Defects 1, 2, and 3 have a depth of 30 mm, and defects 4, 5, and 6 have a depth of 20 mm. Defects 1 and 4 have a thickness of 10 mm, defects 2 and 5 have a thickness of 5 mm, and defects 3 and 6 have a thickness of 2 mm. When the period is 10 minutes, as shown in FIG. 12A, a clear contrast between the healthy part and the defective part cannot be obtained. In the case of a period of 20 minutes, as shown in FIG. 12B, although the defect having a depth of 20 mm is clear, the contrast is not clear for the defect having a depth of 30 mm. When the period is 30 minutes, as shown in FIG. 12C, the contrast is clear even for the defect having a depth of 30 mm. In FIG. 12A, the range of the phase difference of −0.1 to 0.7 radians is imaged, the phase difference of −2.4 to −2.1 radians in FIG. 12B, and the phase difference of −2.4 to − in FIG. 12C. 2.2 The range of radians is imaged.

  Thus, it is considered that the reason why the phase difference due to the reference waveform having a long cycle becomes large between the healthy part and the defective part when the defect becomes deep is as follows. FIG. 13A shows the surface temperature waveforms of the healthy part and the defective part in the case of a shallow defect. FIG. 13B shows the surface temperature waveforms of the healthy part and the defective part in the case of a deep defect.

  As shown in FIG. 13A, when the defect is shallow, the effect of the defect appears early, and the waveform immediately after the heating is stopped is greatly different between the healthy part and the defective part (waveform 73a and waveform 71a). Immediately after the heating is stopped, the surface temperature changes greatly, so that a difference between the two is found as a phase difference in a relatively high frequency component. Further, since the waveform of the healthy part is lowered earlier than that of the defective part, the phase of the defective part is delayed from that of the healthy part. In the figure, it is schematically represented as a phase difference Δθ1 (> 0) between the reference waveforms R′71a and R′73a.

  Further, as shown in FIG. 13B, when the defect is deep, the influence of the defect appears late (waveform 73a and waveform 72a). Therefore, the difference between the two is found as a phase difference in a relatively low frequency component. Further, since the waveform of the defective portion changes more gently, a lower frequency component appears earlier than the waveform of the healthy portion, and the phase of the defective portion advances more than the healthy portion. In the figure, it is schematically represented as a phase difference Δθ2 (<0) between the reference waveforms R ″ 72a and R ″ 73a. On the other hand, the waveform immediately after the heating is stopped does not differ greatly between the healthy part and the defective part (waveform 73a and waveform 72a). Therefore, the phase difference in the high frequency component does not occur so much. In the figure, it is schematically represented as a phase difference Δθ1 (= 0) between the reference waveforms R′72a and R′73a.

  For the reasons described above, it is considered that the phase difference between the healthy part and the defective part becomes remarkable when a reference waveform having a long period is used.

  The operator looks at the image of FIG. 12 and determines the presence or absence of a defect based on the contrast difference. In this embodiment, since the phase difference with respect to the healthy part is calculated using the reference waveforms having a plurality of periods, the possibility of overlooking the defect can be reduced.

  FIG. 14 shows the relationship between the “phase difference of the defective portion relative to the healthy portion” and the “reference signal period” for each “defect depth in the defective portion”. In this figure, “the phase difference of the defective portion relative to the healthy portion” is defined as a value obtained by subtracting “the phase difference of the defective portion relative to the reference signal” from “the phase difference relative to the reference portion of the defective portion”.

  For example, the point 149 indicates that the phase of the “defect portion waveform” is about “5 °” ahead of the “healthy portion waveform”.

  Thus, when the defect depth is different, the phase change pattern when the period of the reference waveform is changed also differs. Therefore, if the phase difference is output (displayed or printed) numerically (or in a graph or density diagram as shown in FIG. 14A) for each defective unit area, the operator can detect the defect based on the above pattern. Depth can be estimated.

  For example, a variation curve according to the period of each reference waveform with respect to the phase difference of the unit region can be applied to the graph shown in FIG. 14A, and the defect depth of the unit region can be estimated from the correlation.

  For example, the variation value of each reference waveform with respect to the phase difference of the unit region is applied to a variation pattern table as shown in FIG. 14B, and the defect depth of the unit region can be estimated from the correlation.

  FIG. 15 shows a measurement example in which an inspected object (concrete) having a defect is inspected. FIG. 15A is a sectional view. A defect D exists at a depth of 10 mm from the surface. In the figure, the defect D is indicated by oblique lines. Concrete C remains in the cavity of the defect D. FIG. 16 shows the concrete C remaining in the defect D. FIG. 15B shows the shape of the defect D viewed from the surface side.

  FIG. 17 shows an image showing a phase difference calculated with reference waveforms of periods of 20 minutes, 30 minutes, and 40 minutes. In the figure, the darker the portion, the larger the phase difference (the phase difference is positive). As is clear from FIG. 14, it is clear that the deeper the defect, the higher the density (positive phase difference) when the reference waveform having a longer period is used. Also in FIG. 17, the darker portion of FIG. 17C is larger than that of FIG. 17A, and is more consistent with the defect shape of FIG.

  In the above embodiment, the period of the reference waveform is longer than the heating period (since it is a heating period of 2 minutes, it is a period of 4 minutes when considered as a pulse period). This makes it possible to detect deep defects even with a short heating time. If the measurement time is not a problem, the heating cycle and the reference waveform cycle may be equal, or the heating cycle may be made longer.

  In the above embodiment, the phase difference is calculated using a plurality of reference waveforms, but the phase difference may be calculated using only one reference waveform to find a defect.

  Step S401 corresponds to the heating control means, step S402 corresponds to the data recording means, step S404 corresponds to the waveform comparison means, and step S406 corresponds to the comparison result output means.

2. Second Embodiment In the above embodiment, an operator determines a defect based on an image displayed (printed) by a computer. However, the computer device 29 may be made to determine whether or not there is a defect and / or both of the defect depth.

  The overall configuration of the system is shown in FIG. In this figure, the defect inspection control device 10 inputs heating control means 11 for controlling heating / stopping heating to the heating device 17 and measurement data of the surface temperature of the object measured by the temperature measuring device 19. The data recording means 13 for recording, the measurement data recorded in the data recording means 13 are read, the above-mentioned phase difference is calculated, the defect position output means 15 for outputting the position of the internal defect, and the depth of the internal defect. Defect depth estimation means 9 for estimation is provided.

  By adjusting the distance between the heating device 17 and the object to be inspected, the amount of heat given to the object to be inspected per unit time can be adjusted. In the following embodiments, this distance is set to 0.5 m.

  The hardware configuration and the like are the same as those in the first embodiment. However, the defect inspection program is different. FIG. 18 shows a flowchart of the defect inspection program. Steps S401 to S404 are the same as those in FIG. In step S1501, the CPU 30 calculates the average value of the phase differences of all unit regions for the reference waveform of the first period (for example, 20 minutes). Instead of this phase difference, a known phase difference of the healthy part may be used.

  Next, the average phase difference is subtracted from the phase difference of each unit area (step S1502). It is determined whether or not the absolute value of the subtraction value exceeds a predetermined value (threshold value) (step S1503). If not, it is determined that the unit area is not a defect, and the same process as described above is performed for the next unit area. If it exceeds, the unit area is determined to be defective, and the coordinates (x, y) of the unit area are recorded in the hard disk 35. Thereafter, the same processing as described above is performed for the next unit area.

  When the above process is completed for all the unit areas, the defect position detected by the reference waveform of that period is recorded on the hard disk 35. Thereafter, the CPU 30 repeatedly executes step S403 and subsequent steps with the next cycle (for example, 30 minutes) as the target cycle. Thereby, the defect position detected by the reference waveform of each cycle is recorded on the hard disk 35. The CPU 30 determines that a unit area determined to be defective in the reference waveform of at least one of the periods is a defect.

  Next, the CPU 30 estimates the defect depth for each unit area determined to be a defect as described above. In order to perform this estimation, a pattern table (periodic pattern) as shown in FIG. 14B is recorded on the hard disk 35. This pattern table represents the relationship between the period of the reference waveform and the positive / negative phase difference for each defect depth.

  CPU30 reads the phase difference in each period of the unit area | region judged to be a defect, and obtains the code | symbol. For example, the phase difference in the unit area is “2 degrees” for a 10-minute reference waveform, “−3 degrees” for a 20-minute reference waveform, and “−10 degrees” for a 30-minute reference waveform. If it is “−12 degrees” with respect to the reference waveform for 40 minutes, “+ −−−” is obtained as the code string. Subsequently, the CPU 30 finds what matches the later code string pattern from the table of FIG. 14B. Here, since the defect depth 20 mm matches, it is estimated that the defect depth is 20 mm. The CPU 30 records the defect depth estimated in this way together with the coordinates (x, y) of the unit basin (step S1507).

  The CPU 30 returns to step S1507 for the defect unit area and repeats the above processing. In this way, the defect depth is recorded for all defect unit areas. If a matching pattern is not found, it may be determined based on the defect depth of the surrounding defect unit area.

  Next, the CPU 30 generates a phase difference image (step S1509). This is the same as step S406 in FIG. Subsequently, the CPU 30 outputs the phase difference image, the defect position coordinates, and the defect depth to the display 33 or the printer.

  Step S404 corresponds to the waveform comparison means, steps S1502 to S1506 correspond to the defect position output means, and steps S1507 and S1508 correspond to the defect depth estimation means.

3. Third Embodiment In the above, an example in which defect inspection is performed with the heating distance between the heater 21 and the inspection object 20 set to 0.5 m in order to give a strong thermal load to the inspection object 20 has been described. .

  However, if the heater 21 is too close to the object 20 to be inspected, heating spots may occur, and there may be a problem that the inspection accuracy is lowered.

  Therefore, a defect inspection system that can solve the problem of heating spots will be described below.

  The functional block diagram of the defect detection system in the present embodiment is the same as that in FIGS. 1 and 2 shown in the first and second embodiments. The hardware configuration of the computer device 29 according to the defect inspection control device is the same as that shown in FIG.

  FIG. 20 shows a configuration diagram of an apparatus for realizing the defect inspection system in the present embodiment. The inspected object 20 represents a concrete wall for inspecting internal defects.

  A heater 21 and a heater moving device 22 that apply a thermal load to the device under test 20 are installed opposite to the device under test 20. The heater 21 is connected to the relay device 25 as in the first embodiment. The heater moving device 22 is a device for moving the heater along the surface of the inspection object 20 and is connected to a computer device 29 that controls the movement.

  The signal generator 27 is connected to the relay device 25 and the computer device 29 as in the first embodiment.

  The infrared camera 23 and the camera moving device 24 are installed so as to face the object 1 to be inspected, and each is connected to the computer device 29.

  The camera moving device 24 is a device for moving the infrared camera along the surface of the object 20 to be inspected, and is connected to a computer device 29 that controls the movement.

  The CPU 30 of the computer device 29 outputs a preset heating condition to the signal generator 27 and outputs a movement condition to the heater moving device 22.

  Here, the moving condition is to give a moving speed and a moving distance to the heater moving device 22.

  For example, the heater moving device 22 drives a motor for rotating the wheel based on the moving speed, and moves the heater at a predetermined moving speed. Further, after moving a predetermined moving distance, the motor is stopped to complete the movement.

  Thereby, the heater 21 can perform heating while moving along the surface of the inspection object 20. For example, when the irradiation width of the heater 21 is 1 m, if the heater moving device 22 is moved at a speed of 0.5 m per minute, a measurement area of 1 m can be heated substantially for about 2 minutes.

  When the region 91 (imaging range by the infrared camera) in a predetermined range is heated by the movement of the heater 21, the CPU 30 acquires the surface temperature by the infrared camera 23.

  Furthermore, when the heater 21 moves and the adjacent region 93 in the predetermined range is heated, the CPU 30 gives a movement command to the infrared camera moving device 24 and moves the infrared camera 23 to a position where the region 93 can be imaged. When the movement is completed, the CPU 30 acquires surface temperature data from the infrared camera 23.

  By repeating the above operation, surface temperature data is also acquired for the regions 95 and 97. Note that the CPU 30 stops the heater moving device 22 at a place where the heater 21 is completely removed from the region 97.

  Thereafter, the CPU 30 moves the infrared camera 23 to a position where the temperature data of the area 91 can be acquired again, and acquires the temperature data again in the order of the areas 93, 95, and 97. Further, this operation is repeated to acquire temperature data in each region.

  The processing after temperature data acquisition is the same as in the first and second embodiments.

4). Other Embodiments In the above embodiment, a concrete material is used as the object 1 to be inspected. However, the present invention can also be applied to a defect inspection in a composite material composed of a low thermal conductivity material such as CFRP. is there.

  In the above embodiment, heating and measurement are performed only once. However, under the same conditions, reheating may be performed after the measurement, and further measurement may be performed. In this way, more accurate detection can be performed by performing heating measurement a plurality of times and averaging the calculated phase differences. In this case, if the reflection of the heat source on the surface of the object to be measured is not affected, temperature fluctuations in both the heating and heating stop periods may be continuously measured.

  In the above-described embodiment, the phase difference between the waveform obtained from the measurement data and the predetermined reference waveform is used as the feature amount when obtaining the defective part. However, another index may be used as the feature amount. For example, temperature gradient data in time change of measurement data, time change data of the temperature gradient data, frequency component data when Fourier analysis is performed on the measurement data, peak value of measurement data waveform or time to reach the peak value, etc. May be used as the feature amount.

  In addition, Fourier analysis data of the temperature waveform of the healthy part and Fourier analysis data of the temperature waveform of the defective part may be calculated, and the presence / absence of a defect may be determined by a phase difference at any frequency. . Furthermore, the defect depth may be estimated by determining at which frequency the phase difference is large.

  In addition, although a sine wave / cosine wave curve is used as a reference waveform, a logarithmic curve or other polynomial curves may be used.

  Furthermore, when comparing these feature quantities, the measurement data is indirectly compared by correlation processing between each measurement data and a predetermined reference waveform, but even if each measurement data is directly compared, Good. For example, this corresponds to comparing peak values of measurement data.

  In the above embodiment, quantitative information related to the defect site is acquired using the relationship table between the period of the reference waveform and the defect depth, but the relationship table further including the defect thickness may be used. Good. In this case, it is possible to detect a defect with higher accuracy.

  In the above-described embodiment, the defect inspection control device 10 includes the computer device 29 and the signal generation device 27. However, the defect inspection control device 10 includes a data collection device that realizes the heating control means 11 and the data recording means 13, and a defect. The defect determination device that realizes the determination unit 15 may be configured by different devices. For example, by connecting these devices using a communication line, remote operation in defect inspection becomes possible.

  In the above embodiment, the heat load is applied to the device under test 20 using the heater 21, but other methods may be used as long as the surface of the device under test 20 can be heated strongly. For example, the surface of the test object 20 may be moistened, and a microwave may be irradiated from a remote location to apply a heat load.

  In the above embodiment, the heating distance is 0.5 m and the heating time is 2 minutes. However, heating may be performed under different heating conditions. For example, the heating distance may be 2 m and the heating time may be 20 minutes.

  In each of the above embodiments, the defect is detected, but the shape of the back surface that cannot be seen from the front surface may be detected. In this case, a phase difference is obtained for a standard piece having a standard thickness and is compared with the phase difference in each part to be detected to estimate the thickness of each part to be detected to obtain a back surface shape. be able to.

  In the above embodiment, the phase difference is calculated for the reference waveforms of all periods recorded in advance. However, if the maximum defect depth is known in advance by, for example, investigating a part of the inspection target in advance, the shortest cycle in which the maximum defect depth can be detected may be used.

  The relationship between the period of the reference waveform and the detectable defect depth may be stored as a table, and the detectable defect depth may be output according to the used reference waveform.

  Moreover, in the said embodiment, although the said process is implement | achieved using the computer, an operator may perform these processes.

It is a figure which shows the functional block diagram of the defect detection system in one Embodiment of this invention. It is a figure which shows the functional block diagram of the defect detection system in one Embodiment of this invention. It is an example of the graph which shows the time-dependent change of the temperature in one Embodiment of this invention. It is an artificial defect specimen and temperature distribution image in one Embodiment of this invention. It is a temporal change waveform of the surface temperature after heating in one Embodiment of this invention. It is an example which shows the block diagram of the apparatus which implement | achieves the defect detection system in one Embodiment of this invention. It is an example which shows the hardware block diagram of the computer apparatus in one Embodiment of this invention. It is a figure which shows the flowchart in the defect inspection process in one Embodiment of this invention. It is a figure which shows the relationship between the signal which gives the thermal load in one Embodiment of this invention, and a reference waveform. It is a figure which shows each unit area | region of measurement object in one Embodiment of this invention. It is a figure which shows the example of the temperature data recorded in one Embodiment of this invention. It is a figure which shows the flowchart in the analysis process of the measurement data in one Embodiment of this invention. It is an example (AC) of the display screen of the image data when measuring the artificial defect (D) and this artificial defect in one Embodiment of this invention. It is the example which showed the phase difference of the measurement data and the reference waveform in the unit area | region of the measurement area | region in one Embodiment of this invention with the graph. It is the example of the graph and reference table which showed the relationship between the period of a reference waveform, and a phase difference for every depth of defect in one Embodiment of this invention. It is an example of the screen which estimated the shape of the defect based on the quantitative information concerning the defect site | part in one Embodiment of this invention. It is an example when the internal defect part of the measured concrete structure in one Embodiment of this invention is extract | collected. It is a display screen of image data when measuring the concrete structure with an internal defect in one embodiment of this invention. It is a figure which shows the flowchart in the case of performing a defect inspection by changing the reference waveform in one Embodiment of this invention. It is a figure which shows the flowchart in the case of performing a defect inspection by changing the reference waveform in one Embodiment of this invention. It is an example which shows the block diagram of the apparatus which implement | achieves the defect detection system in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Defect inspection control apparatus 11 ... Heating control means 13 ... Data recording means 16 ... Waveform comparison means 17 ... Heating apparatus 18 ... Comparison result output means 19 ... Temperature measuring device

Claims (15)

Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
The difference in the predetermined periodic component between the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part is calculated for different periodic components, and the difference is obtained based on the difference obtained for each periodic component. A defect inspection method for detecting defects in each unit region of an inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection method characterized by Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Determining the defect based on the difference in the predetermined periodic component of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part,
The defect is calculated for different periodic components, and based on the difference obtained for each periodic component, a defect inspection method for estimating the defect depth in each unit region of the inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection method characterized by Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
The difference in the predetermined periodic component of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part is calculated for the predetermined periodic component of a plurality of periods,
Based on the difference obtained for each periodic component, a defect inspection method for estimating the defect depth in each unit region of the inspection object ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection method characterized by In the defect inspection method of Claim 2 or 3,
The difference in the predetermined period component of the time change of the surface temperature in each unit region and the time change of the surface temperature in the healthy part is as follows:
A defect inspection method characterized by being determined based on a relative difference with respect to a reference waveform having a predetermined period. The defect inspection method according to claim 4,
A defect inspection method , characterized in that a unit region in which a difference from an average difference in a predetermined periodic component of a temporal change in surface temperature in all unit regions is smaller than a predetermined value is defined as the healthy portion. In the defect inspection method according to claim 1,
The defect inspection method , wherein the difference in the predetermined period component is a phase difference. In the defect inspection method in any one of Claims 2-6,
A defect inspection method , wherein a defect depth is estimated based on which one of a plurality of periodic components has a maximum phase difference. In the defect inspection method in any one of Claims 2-6,
A defect inspection method , wherein a defect depth is estimated based on a change pattern of a phase difference accompanying a change in period of a predetermined period component. A heating control means for performing a heating start command and a heating stop command for a heating device that heats the entire surface of the measurement target surface of the object to be inspected;
Data recording means for inputting and recording data from a temperature measuring instrument that measures the surface temperature in each unit region of the object to be inspected at least after stopping heating;
Waveform comparison means for reading temperature data recorded in the data recording means and calculating a phase difference between a time-varying waveform of the surface temperature in each unit region and a reference waveform having a predetermined period for a plurality of reference waveforms having a predetermined period; ,
A defect inspection apparatus comprising a comparison result output means for outputting a phase difference calculated by a waveform comparison means ,
The phase difference is calculated using a plurality of different reference waveforms with respect to measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection device characterized by. A heating control means for performing a heating start command and a heating stop command for a heating device that heats the entire surface of the measurement target surface of the object to be inspected;
Data recording means for inputting and recording data from a temperature measuring instrument that measures the surface temperature in each unit region of the object to be inspected at least after stopping heating;
Waveform comparison means for reading the temperature data recorded in the data recording means and calculating the phase difference between the time change waveform of the surface temperature in each unit region and the reference waveform having a predetermined period;
A defect position output means for detecting a region where the difference from the average phase difference in all regions is a predetermined value or more as a defect portion, and outputting the defect position;
The phase difference is calculated for different periodic components, and the defect depth in each unit region of the object to be inspected is estimated based on the difference between the phase difference of the defective portion and the phase difference of the healthy portion obtained for each periodic component. A defect inspection apparatus comprising a defect depth estimating means for
The phase difference is calculated using a plurality of different reference waveforms with respect to measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection device characterized by. A defect determination device that estimates the defect depth of an object to be inspected based on surface temperature data in each unit region of the surface of the object to be inspected, which is recorded after stopping the heating of the surface of the object to be inspected.
A waveform comparison means for calculating a phase difference between a time-varying waveform of the surface temperature in each unit region and a reference waveform having a predetermined period for a plurality of reference waveforms having a predetermined period;
A defect determination device comprising a comparison result output means for outputting a phase difference calculated by a waveform comparison means ,
The surface temperature data is measurement data in one time series obtained by performing heating and measurement on the surface of the object to be inspected once.
The waveform comparison means calculates the phase difference using a plurality of different reference waveforms for the measurement data in one time series.
A defect judgment device characterized by the above. A defect determination device that estimates the defect depth of an object to be inspected based on surface temperature data in each unit region of the surface of the object to be inspected, which is recorded after stopping the heating of the surface of the object to be inspected.
Waveform comparison means for calculating the phase difference between the time variation waveform of the surface temperature in each unit region and the reference waveform having a predetermined period;
A defect position output means for detecting a region where the difference from the average phase difference in all regions is a predetermined value or more as a defect portion, and outputting the defect position;
The phase difference is calculated for different periodic components, and the defect depth in each unit region of the object to be inspected is estimated based on the difference between the phase difference of the defective portion and the phase difference of the healthy portion obtained for each periodic component. A defect determination device comprising defect depth estimation means for
The surface temperature data is measurement data in one time series obtained by performing heating and measurement on the surface of the object to be inspected once.
The waveform comparison means calculates the phase difference using a plurality of different reference waveforms for the measurement data in one time series.
A defect judgment device characterized by the above. Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Based on the difference in the predetermined periodic components of the temporal change of the surface temperature in each unit region and the temporal change of the surface temperature in the healthy part, the defect in each unit region of the object to be inspected is determined,
A defect inspection method for calculating a determinable defect depth based on a cycle of a predetermined cycle component used for the defect determination ,
The difference is calculated using a plurality of different periodic components for the measurement data in one time series obtained by performing the heating and the measurement once.
Defect inspection method characterized by Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
Temporal change in the surface temperature of each unit region, the temporal change of the surface temperature at the healthy part, based on the difference in a predetermined period component, a defect inspection method for determining defects in each unit area of the device under test,
The difference is calculated using a plurality of different periodic components for measurement data in one time series obtained by performing the heating and the measurement once.
A defect inspection method comprising: determining a depth of a defect to be inspected, and selecting a period of the predetermined periodic component as an appropriate period for detecting the defect depth . Heat the entire surface of the object to be inspected,
At least in the heating stop period after stopping the heating, measure the time change of the surface temperature in each unit region of the measurement target surface of the object to be inspected,
A defect inspection method for detecting a defect in each unit region of an object to be inspected based on a difference in a predetermined periodic component of a temporal change in surface temperature in each unit region and a temporal change in surface temperature in a healthy part,
The difference is calculated using a plurality of different periodic components for measurement data in one time series obtained by performing the heating and the measurement once.
The defect inspection method, wherein the predetermined period is longer than the heating period.

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