JP2005241573A - Method and apparatus for inspecting defect - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for the inspection of defects, wherein internal defects inside a specimen such as a concrete structure or the like is detected, and information regarding defects can be detected quantitatively. <P>SOLUTION: A heating device 17 receives a command from a heating control means 11 and heats the specimen so that temperatures of at least one point inside the specimen are elevated for a heating stop period, after stopping heating. A temperature-measuring device 19 measures the surface temperature of the specimen in a time series manner and outputs the measured data to a data-recording means 13 of a defect inspection controller 10. At this time, the heating period is set shorter than the measurement period. A decision is made by a defect deciding means as to whether the measured data recorded by the data-recording means 13 receiving the output refer to the internal defect, and its result is output, e.g. as image data. The cycle of a reference waveform for carrying out a correlation processing is changed, whereby the internal defects in the specimen can be detected quantitatively. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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 quantitatively determines the information such as the depth and shape of the defective part when detecting the internal defect of the inspected object composed of a low thermal conductivity material such as a concrete structure. Moreover, the invention about the defect inspection method and its apparatus which can detect with high precision is disclosed (for example, refer patent document 1).

JP 2003-83923 A

  However, in the method disclosed by the applicant in the above document, although it is possible to detect the internal defect of the object to be inspected quantitatively and with high accuracy, it is necessary to repeatedly heat and cool the concrete having low thermal conductivity. Therefore, there is a problem that the time required for the inspection becomes long.

  In addition, if the heater, which is a heat source, is too close to the object to be inspected in order to heat the object to be inspected in a short time, the surface of the object to be inspected cannot be heated uniformly, resulting in heating spots and reduced inspection accuracy. There was a problem to do.

  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, An object of the present invention is to provide a defect inspection method and apparatus capable of detecting information such as a shape quantitatively and with high accuracy, and capable of efficiently inspecting by shortening an inspection time.

  It is another object of the present invention to provide a defect inspection method and apparatus capable of effectively inspecting an object to be inspected without generating heating spots.

(1) In the defect inspection method according to the present invention,
In order to increase the temperature at at least one point inside the object to be inspected during the heating stop period after stopping the heating, the surface of the object to be inspected is heated over the entire measurement region,
At least in the heating stop period after stopping the heating,
For each unit area of the measurement area, measure the time change of the surface temperature,
A defect inspection method for finding a defect in the object to be inspected based on a relative difference between each unit region with respect to a temporal change in surface temperature in each unit region,
The heating time is shorter than the measurement time.

  Therefore, heat can be continuously applied to the inside of the object to be inspected even during the cooling process that is the heating stop period. Thereby, the heating time can be shortened without reducing the inspection accuracy, and the inspection efficiency as a whole is improved.

(2) In the defect inspection method according to the present invention,
Heating is performed at a depth of a detection target point inside the object to be inspected, with a strength and abruptness that cause a temperature rise after the heating is stopped.

  Therefore, it is possible to reliably capture the increase in surface temperature caused by the diffusion of heat that reaches the defect. Thereby, inspection accuracy improves. In particular, since the temperature rises more remarkably as the defect becomes shallower, the defect can be reliably detected.

(3) In the defect inspection method according to the present invention,
The measurement is characterized in that at least the heat due to heating continues for a period of time after reaching the depth of the detection target point after the heating is stopped.

  Therefore, at least defects up to the depth point where the heat reaches can be captured. Thereby, the rise in the surface temperature due to the defective part can be reliably detected.

(A) In the defect inspection method according to the present invention,
Heating is performed while moving along the surface of the object to be inspected, and defects in the object to be inspected are found based on the surface temperature of the measurement region after the heating.

  Therefore, the surface of the object to be inspected can be heated uniformly. Thereby, the defect inspection of the inspection object can be performed efficiently.

(4) In the defect inspection method according to the present invention,
The object to be inspected is characterized by being composed of a low thermal conductivity material.

  Therefore, it can be applied to defect inspection of concrete structures and composite materials having low thermal conductivity. Moreover, since the temperature fluctuation is gentle due to the low thermal conductivity, the number of times of measurement can be reduced. For example, even when measuring a plurality of continuous measurement areas, the measurement efficiency can be improved by performing heating and measurement in order for each measurement area.

(5) In the defect inspection method according to the present invention,
It is characterized in that the position of the defect in the object to be inspected is specified based on the relative difference between the unit regions with respect to the temporal change of the surface temperature in each unit region.

  Therefore, an accurate defect position can be specified by clearly expressing the difference between the unit areas.

(6) In the defect inspection method according to the present invention,
The present invention is characterized in that a relative difference between the unit regions with respect to the temporal change of the surface temperature in each unit region is presented as a visually recognizable image.

  Therefore, by associating each unit area with a constituent unit of image data, the entire measurement area can be output as image data, and the defect position can be identified visually. For example, the relative difference between the unit areas can be expressed as a contrast difference on the image data.

(7) In the defect inspection method according to the present invention,
The relative difference is characterized in that it is determined on the basis of a comparison of a feature value in a predetermined waveform and a waveform due to a time change of the surface temperature in each unit region.

  Therefore, even if disturbance data is included in the measurement data, highly accurate defect detection can be performed by referring to the predetermined waveform. For example, in the case of an inspected object such as a concrete structure, disturbance data may be generated due to dirt, solar radiation or reflection on concrete surface such as soot and free lime, and whether it is a disturbance by comparing with a predetermined waveform. Judgment can be made.

(8) In the defect inspection method according to the present invention,
The feature quantity comparison is characterized in that it is performed based on a specific value indicating the correlation between the two waveforms of the waveform due to the time change of the surface temperature in each unit region and the predetermined waveform, or on the phase difference between the two waveforms.

  Therefore, when comparing feature amounts, information regarding defects can be acquired as a quantitative value corresponding to the degree of the comparison result. In other words, accurate defect inspection can be performed by using various indexes indicated by the waveforms as feature quantities.

(9) In the defect inspection method according to the present invention,
While performing heating and heating stop for a predetermined period, measuring by changing the period of the predetermined waveform,
It is characterized in that the defect depth is estimated based on a predetermined waveform period in which a difference in relative temperature change between each unit region becomes significant.

  Therefore, it is possible to accurately estimate the depth at which the internal defect exists. Moreover, the depth of the internal defect can be estimated more accurately by changing the cycle of the predetermined waveform and repeating the measurement. Furthermore, the size and thickness of internal defects can be estimated simultaneously.

(10) In the defect inspection method according to the present invention,
It is characterized in that the depth of the defect is estimated based on a table in which the depth of the defect is associated with a predetermined waveform period in advance.

  Therefore, a more accurate depth of the internal defect can be estimated by referring to the table. Thereby, the number of measurements can be reduced and the inspection efficiency can be improved.

(11) In the defect inspection apparatus according to the present invention,
Heating start command to a heating device that heats the entire surface of the object to be inspected so that the temperature rises at at least one point inside the object to be inspected during the heating stop period after the heating is stopped Heating control means for performing,
Data recording means for inputting data from a temperature measuring instrument after stopping heating and recording it as temperature data of each unit area;
Based on the recorded temperature data, it is possible to detect a relative difference between the unit regions with respect to the temporal change of the surface temperature in each unit region, and include a defect determination unit that determines a defect in the inspection object.
The heating time is shorter than the measurement time.

  Therefore, heat can be continuously applied to the inside of the object to be inspected even during the cooling process that is the heating stop period. Thereby, the heating time can be shortened without reducing the inspection accuracy, and the inspection efficiency as a whole is improved.

(12) In the data collection device according to the present invention,
Heating start command to a heating device that heats the entire surface of the object to be inspected so that the temperature rises at at least one point inside the object to be inspected during the heating stop period after the heating is stopped Heating control means for performing,
Data recording means for inputting data from a temperature measuring instrument after heating is stopped and recording it as temperature data of each unit area,
The heating time is shorter than the measurement time.

  Therefore, heat can be continuously applied to the inside of the object to be inspected even during the cooling process that is the heating stop period. Thereby, the heating time can be shortened without reducing the inspection accuracy, and the inspection efficiency as a whole is improved.

(B) In the defect inspection control device or data collection device according to the present invention,
A heating device control means for giving a movement command to the heating device so as to heat the measurement region while moving along the surface of the object to be inspected,
Furthermore, it is characterized by providing.

  Therefore, the measurement area of the object to be inspected can be heated uniformly. Thereby, heating spots can be reduced and inspection accuracy can be improved.

(13) In the defect judgment device according to the present invention,
The surface in each unit area based on the temperature data of each unit area of the measurement area recorded after the heating of the surface of the object to be inspected is heated so that the temperature rises at at least one point inside the object. A defect determination means for detecting a relative difference between the unit regions with respect to a temporal change in temperature and determining a defect in the inspection object;
It is characterized by having.

  Therefore, the defect can be accurately detected based on the measured surface temperature data of the object to be inspected.

(C) In the heating device according to the present invention,
A heating device that heats the entire surface of the object to be inspected,
The measurement area is heated while moving along the surface of the object to be inspected.

  Therefore, the measurement area of the object to be inspected can be heated uniformly.

  Embodiments of the present invention will be described below with reference to the drawings.

1. First Embodiment 1-1. About heating conditions 1-1-1. Heating distance and heating time FIG. 1a shows that the heating distance and the heating time are changed, and the surface of the object to be inspected as a concrete structure is heated and cooled (heating stopped) using a heater. 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.

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

  As shown in the graph of A of FIG. 1a, when the heating distance is 2 m and the heating time is 20 minutes, the internal temperature at the position of 50 mm depth increases after the heating is stopped (after 20 minutes have elapsed). Yes. Further, as shown in the graph of B of FIG. 1a, when the heating distance is 0.5 m and the heating time is 1 minute, similarly to the above, after the heating is stopped (after 1 minute has passed), the depth is 50 mm. The internal temperature at the location 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. 1A, simulated peeling of polyethylene sheets having thicknesses of 2 and 5 and thickness of 5 mm are simulated peeling at positions d of 100 mm and 50 mm from the surface. Simulated peelings 4 and 7 of polyethylene sheets 3 and 6 and a thickness of 2 mm are embedded, respectively.

  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.).

  B in FIG. 1B is a temperature distribution image when (1) the heating distance is 2 m and the heating time is 20 minutes. C in FIG. 1B is a 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 B in FIG. 1b, 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 C in FIG. 1b, 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). In addition, in the temperature distribution images of B and C in FIG. 1b, the variation in the surface temperature at the simulated defects 5 to 7 is considered to be due to the influence of heating spots 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 greatly improve the inspection efficiency will be described below.

1-2. Defect inspection When a thermal load that fluctuates at a fixed period is applied to an object, wave-like heat transfer occurs inside the object, and the surface temperature of the object also fluctuates at a fixed period and amplitude. If a defect exists in the object, the influence of the defect also appears in the surface temperature distribution that fluctuates in a wave shape. It is possible to measure such a surface temperature fluctuation of a certain period in time series and detect an internal defect of an object based on correlation processing between measurement data and a predetermined waveform.

  For example, the correlation processing is performed by synchronizing the measurement data of the surface temperature fluctuation and the reference waveform of a predetermined period, and outputs the difference in phase lag value (phase difference) from the reference waveform in each unit region as the correlation data. To do. That is, a unit region where a phase difference is generated represents a site where an internal defect exists. Therefore, it is possible to perform defect inspection by converting the correlation data into image data that can be easily recognized visually, and displaying a portion where an internal defect exists as a contrast difference on the image data.

1-2-1. Outline of Defect Inspection System FIG. 1 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 and defect determination means 15 for reading the measurement data recorded in the data recording means 13 and comparing the feature quantity with a predetermined reference waveform to determine an internal defect.

1-2-2. Configuration of Device of Defect Inspection System FIG. 2 shows a configuration diagram of a device that realizes 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 become hotter 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.

  In response to the output of the measurement data, the computer device 29 records the measurement data by the data recording unit 13, determines the internal defect of the inspection object 20 by the defect determination unit 15, and outputs an image.

  1 is realized by a computer device 29 and a signal generator 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.

1-2-3. Hardware Configuration Diagram of Computer Device FIG. 3 shows 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 with other devices. The hard disk 35 stores a program for determining a defect, a reference waveform, a program for displaying an image, and the like.

1-2-4. Flowchart in Defect Inspection Control Device FIG. 4 shows a flowchart in the defect inspection control device 10 when performing defect inspection. First, in the defect inspection control device 10, the CPU 30 of the computer device 29 outputs a preset heating condition to the signal generating device 27 (step S401). Here, the heating condition refers to the time for applying a thermal load to the device under test 20 and the number of repetitions thereof. The amplitude is a constant value and the duty cycle is 50%.

  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.

  In the present embodiment, since the defect inspection is performed based on the knowledge obtained from the above consideration, the heating distance, which is the installation distance between the inspection object 20 and the heater 21, is set to 0.5 m. On the other hand, the defect inspection is performed by setting the heating time, which is the time for applying heat to the heater 21, to 2 minutes.

  While performing heating / heating stop under predetermined heating conditions, the surface temperature of the inspection object 20 is measured using the infrared camera 23, particularly during the heating stop period.

  FIG. 4 a shows the relationship between the heating control signal 40 output from the relay device 25 to the heater 21 and the temperature fluctuation curve 41 on the surface of the test object 20 heated based on the signal 40. That is, the temperature fluctuation data in the measurement period 45 shown in FIG. 4a is measured.

  The measurement data is output to the connected computer device 29 and recorded on the hard disk 35 or the like (step S402). By repeating this measurement process every predetermined time, measurement data of the surface temperature fluctuation at each measurement time in the heating stop period is acquired. The measurement data is surface temperature data for each unit region of the measurement region in the inspection object 20.

  After performing the above processing for a predetermined number of repetitions, the measurement is terminated (step S403). In the present embodiment, the number of repetitions of heating / stopping heating is set to one.

  Upon completion of the measurement, the CPU 30 of the computer device 29 performs measurement data analysis processing (step S404).

1-2-4-1. Measurement Data Analysis Processing FIG. 5 is 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 temperature at the time t and the unit region i is represented by _Kti . The CPU 30 calls this K _ti from the hard disk 35 for each area and stores it in the memory 31 (step S501).

The CPU 30 calls the reference waveform R _t at time t from the hard disk 35 (step S502). The reference waveform _Rt is an analog signal whose period is, for example, 40 minutes.

The CPU 30 calculates the phase difference P _ti from the reference waveform R _{t at} time t and region i (step S503). The calculation process of the phase difference _Pti will be described below.

The CPU 30 converts the reference waveform _Rt into a square wave, and then generates sin wave and cos wave digital data Sin (t) and Cos (t) having the same frequency.

Next, calculation processing of the following equation is performed between the digital signal V (t) determined by the temperature K _ti in the unit region i at the time t and the reference waveforms Sin (t) and Cos (t).

However, ΔV _sin represents the fluctuation amplitude of the infrared intensity synchronized with the reference waveform, and ΔV _cos represents the fluctuation amplitude of the infrared intensity synchronized with the cosine wave that is 90 degrees out of phase with the reference waveform. N is the number of frames taken in signal processing.

ΔV _cos is 0 when the surface temperature fluctuation completely matches the phase of the fluctuating heat load. When the surface temperature fluctuation is shifted from the phase of the fluctuating heat load due to the influence of thermal diffusion or the like, a component of ΔV _cos appears. In this case, the absolute value ΔV and the phase delay θ of the temperature fluctuation amplitude can be obtained by the following equations.

Here, the obtained θ is defined as a time difference _t and a phase difference P _{ti from} the reference waveform R _t in the unit region i.

The CPU 30 adds 1 to i to obtain i + 1 in order to obtain the phase difference in the next unit area (step S504). Furthermore, until i exceeds the total number of regions I (step S505, YES), repeatedly determining the phase difference P _ti the processing of step S501～504 (step S505, NO).

  Next, the CPU 30 adds Δt to the time t to make the time t + Δt (step S506), and repeats steps S501 to S506 until the predetermined analysis time T is exceeded (step S507, YES) (step S507, NO). .

In this way, the signal processing for _obtaining the phase difference _Pti is performed for each pixel of the infrared sensor in the infrared camera 23, that is, the total number of areas I times and the number of captured frames N times measured by the infrared camera 23.

1-2-4-2. Display of Analyzed Image After finishing the measurement data analysis processing, the CPU 30 calls the phase difference P _Ti at time T for each region, and based on this, generates image data for the entire measurement region (step S405), and the display 33. Is output (step S406). That is, the CPU 30 generates image data by associating the input phase difference with a predetermined display color and displays it.

  FIG. 6A shows an example of display of image data when the defect inspection system described above is applied and a defect inspection is performed on a concrete specimen having an artificial defect. In addition, this image measures the concrete test body which has the artificial defects 1-6 shown in FIG.6 (B). The artificial defects 1 to 6 are produced by embedding defects having different depths and thicknesses in concrete.

  For example, the artificial defects 1 to 3 have a depth of 100 mm from the surface, and the artificial defects 4 to 6 have a depth of 50 mm from the surface. The artificial defects 1 and 4 have a defect thickness of 10 mm, the artificial defects 2 and 5 have a defect thickness of 5 mm, and the artificial defects 3 and 6 have a defect thickness of 2 mm.

  In FIG. 6A, three portions clearly displayed as contrast differences in the right column 61 correspond to the artificial defects 4 to 6, respectively. Although the artificial defects 1 to 3 are displayed in the left column 60, the contrast is not so clear.

FIG. 7 is an example in which the phase difference between the measurement data and the reference waveform in the unit area of the measurement area is shown as a graph. The phase difference P _ti in each unit region i in the measurement region frame measured by the infrared camera 23 is a reference waveform R ₇₁ approximated to the temperature variation curve 71 of the defective portion and a reference waveform approximated to the temperature variation curve 73 of the healthy portion. it can be expressed by a phase difference between R _73.

1-2-5. Summary As described above, by reducing the heating distance between the heater 21 and the object 20 to be inspected, sufficiently accurate defect inspection can be performed even if the heating time is short. In particular, by increasing the measurement time in the cooling period after stopping the heating, it is possible to measure the surface temperature increase due to the heat reaching the deeper defect.

  In addition, the infrared camera used for the measurement in this case should just have the temperature resolution which can distinguish the said surface temperature rise. Here, the amount of heat given from the heater 21 to the object to be inspected 20 is an amount of heat that causes at least a temperature rise at a depth point to be subjected to defect inspection.

  Thereby, the inspection efficiency and the inspection accuracy in the defect inspection of the inspection object as the concrete structure can be further improved. In particular, since the heating process performed using a relatively large-scale heating apparatus can be shortened from the conventional 20 minutes to 1 minute, the work efficiency for inspection can be improved by about 20 times.

  When heat reaches the defective part during heating, the surface temperature change of the defective part appears remarkably. For this reason, there has been a desire to measure changes in surface temperature during heating. However, since there is heat reflection from the surface, it is difficult to accurately measure the surface temperature during heating.

  As shown in the present embodiment, when the heating intensity is increased by reducing the heating distance or the like, the internal temperature near the surface rises even after the heating is stopped. The surface temperature can be measured by causing an internal temperature rise. For this reason, the difference in the surface temperature between the healthy part and the defective part appears more prominently near the surface, and the shallower defect can be detected more accurately.

  Furthermore, the temperature gradient between each deep part inside a to-be-inspected object can be enlarged by heating rapidly in a short time. Thereby, the defect which exists in the deep part is correctly detectable compared with the case where it heats slowly.

2. In a second embodiment the first embodiment, the period of the reference waveform R _t were defect detection as 40 minutes, when considered from a different viewpoint, the heat load (heating distance 0.5 m, the heating time of 2 minutes ) and relationships of the period of the reference waveform R _t (40 minutes) is also considered to have been suitable for detecting the artificial defect 4-6 depth 50 mm.

  In the above, the period of the reference waveform is 40 minutes, but the phase difference between the defective part and the healthy part displayed as image data varies depending on the period of the reference waveform.

  Therefore, by using a reference signal with a period suitable for the temperature fluctuation curve, the phase difference between the healthy part and the defective part can be captured more clearly, and even if the temperature difference in the temperature fluctuation curve is small, the correlation process can be performed. Accuracy can be improved.

  As described above, since the phase difference displayed as image data varies depending on the period of the reference waveform used for the correlation processing, if a reference waveform having an optimal period is used according to the depth of the defect to be inspected, Highly accurate defect inspection can be performed.

  8A to 8C are based on the surface temperature data obtained by measuring the artificial defect specimen shown in FIG. 8D only once, and change the period of the reference waveform to perform the above correlation processing. It is a phase distribution image created based on the processing result.

  As shown in FIGS. 8A to 8C, the contrast difference indicating the defects 4 to 6 having a defect depth of 20 mm is clearly displayed at a period of 20 minutes and 40 minutes, particularly when the period is 40 minutes. The contrast difference is displayed most clearly.

  Similarly, the contrast difference indicating defects 1 to 3 having a defect depth of 30 mm is clearly displayed at a period of 20 minutes and 40 minutes, and particularly, the contrast difference is displayed most clearly at a period of 40 minutes. Has been.

  FIG. 9A shows a graph showing the relationship between the phase difference and the period of the reference signal obtained based on the result of the above experiment performed on the artificial defect specimen with the defect depth changed. Further, FIG. 9B shows an example of a relationship table between the period of the reference waveform and the defect depth created based on this graph.

  As shown in FIG. 9B, the period of the reference waveform when the phase difference becomes the largest at each defect depth is considered to be the optimum period. For example, since the maximum phase difference at the defect depth “10 mm” is “23.5 °”, the optimum reference waveform period when inspecting the defect depth is “20 minutes”.

  Similarly, the maximum phase difference when the defect depth is “20 mm”, “30 mm”, and “50 mm” is “13.0 °”, “3.0 °”, and “1.5 °”, respectively. The optimum reference waveform periods when inspecting these defect depths are “40 minutes”, “20 minutes”, and “40 minutes”, respectively.

  Note that the period of the optimum reference waveform corresponds to the “period of a predetermined waveform in which the difference becomes remarkable” shown in [Claims].

  Therefore, by using the relationship table shown in FIG. 9B, an optimum reference waveform period can be set according to the defect depth to be inspected in the inspection object 20. Thereby, the number of times of measurement can be reduced, and the inspection efficiency can be improved.

  In the present embodiment, a defect inspection method with improved inspection efficiency will be described using a relationship table between the period of the reference waveform and the defect depth.

2-1. Outline of Defect Inspection In the first embodiment, the defect detection is performed on a concrete specimen having an artificial defect. However, in the present embodiment, the present invention is applied to a concrete structure actually having an internal defect due to aging. The case where the defect inspection system according to is applied will be described.

  In addition, the concrete structure which performs a defect inspection shall be produced by the material and environment of the same conditions as the said concrete test body, and showed the relationship between the depth of a defect, and the period of a reference waveform shown to B of FIG. A reference table shall be used.

2-2. Defect depth estimation method First, for the concrete structure to be inspected, the concrete thickness and the rebar cover thickness in the inspection range are examined, and the maximum depth for defect inspection is determined. Note that when examining the thickness of the reinforcing bar cover, an inspection device using ultrasonic waves, microwave radar, electromagnetic induction, or the like may be used.

  Next, the number of times of measurement is determined from the required inspection efficiency, and measurement is performed by determining the period of the reference waveform corresponding to the maximum depth from the reference table shown in FIG. 9B. For example, in the present embodiment, as a result of the investigation, the maximum depth is considered to be 50 mm. Therefore, the reference waveform period is set to 20 to 40 minutes, the number of times of measurement is set to 1, and the heating time is set to 2 minutes.

  FIG. 10 shows image data obtained by applying the defect inspection system according to the present invention to a concrete structure. 10A to 10C are measured by changing the period T of the reference waveform to 20 to 40 minutes, respectively, and it is clear that a defect exists in the center of the image in each image. Is displayed.

  As shown in (i) to (iii) below, quantitative information related to this defect can be estimated from these images and the reference table.

  (i) In FIG. 10A, the outline 101 of the defect at the center of the image is clearly displayed as a contrast difference with respect to the whole. When this contrast difference indicates a phase difference of about 20 °, it can be estimated from the reference table that the defect depth in this range is around 10 mm. That is, a defect exists around 10 mm from the surface.

  (ii) In FIG. 10B, the contrast difference indicating the defect contour 103 at the center of the image is displayed so as to expand toward the center as compared with FIG. When this contrast difference indicates a phase difference of about 7 °, the reference table indicates that the defect depth in this range is around 20 mm, and the defect in this range has a larger cavity than the defect in the range of 10 mm. Can be estimated.

  (iii) In FIG. 10C, the contrast difference indicating the defect contour 105 at the center of the image is displayed so as to further expand toward the center as compared with FIG. 10B. When this contrast difference indicates a phase difference of about 3 °, the reference table indicates that the defect depth in this range is about 30 mm, and the defect in this range has a larger cavity than the defect in the range of 20 mm. Can be estimated.

  Thereby, this internal defect exists in the position of depth 10mm-30mm from the surface of a concrete structure, and it can be estimated that it is a float of the shape which tapered toward the perpendicular direction from the surface to the inside.

  In addition, in FIG. 11, the example when the internal defect part of the concrete structure measured this time is extract | collected is shown. As shown in FIG. 11A, the internal defect portion has a contour that is substantially the same shape as the contour portion of the contrast difference of the internal defect in the image shown in FIG. Moreover, FIG. 11 (B) has shown the side surface of this internal defect part, and the thickness was 20-30 mm.

  In this way, by performing a defect inspection of a concrete structure using the defect inspection system to which the present invention is applied, the depth of the internal defect is identified, and the internal defect such as its size and thickness is quantitatively determined. It is possible to estimate accurate information. As a result, inspection efficiency in defect inspection can be increased, and risk-based maintenance can be performed in which effective countermeasures are taken according to the defect probability of defects.

2-3. Flowchart in Defect Inspection Control Device FIG. 6 is a flowchart in the defect inspection control apparatus 10 that automatically estimates internal defects using the defect depth estimation method shown in FIG.

  First, in the computer device 29 that is the defect inspection control device 10, the maximum depth of the defect to be detected is input (step S1201). The maximum depth input at this time is 2-2. As shown in Fig. 4, it may be determined by a preliminary survey of concrete structures.

  Next, based on the required inspection efficiency, the number of times of measurement and the range of the period of the reference waveform to be used are input (step S1202). The period of this cycle may be automatically determined by the CPU 30 according to the maximum depth.

  In the defect inspection control device 10, the CPU 30 of the computer device 29 outputs a heating condition to the signal generator 27 (step S1203). Here, the heating condition refers to the time for applying a thermal load to the device under test 20 and the number of repetitions thereof. The heating distance is 0.5 m, the heating time is 2 minutes, the amplitude is a constant value, and the duty cycle is 50%.

  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.

  While performing heating / heating stop under predetermined heating conditions, the surface temperature of the inspection object 20 is measured using the infrared camera 23, particularly during the heating stop period. The measurement data is output to the connected computer device 29 and recorded on the hard disk 35 or the like (step S1204). By performing this measurement process only once, measurement data of the surface temperature at each measurement time in the heating stop period is acquired. The measurement data is surface temperature data for each unit region of the measurement region in the concrete structure that is the inspection object 20.

  When the measurement process is finished, the CPU 30 reads the reference waveform cycle set in step 1202 (step S1205). For example, when 20 minutes, 30 minutes, and 40 minutes are set as the period, 20 minutes that is the smallest period is read.

  The CPU 30 performs measurement data analysis processing using the read reference waveform period (step S1206). The measurement data analysis process shown in step S1206 is the same as the process shown in FIG. 5 of the first embodiment.

CPU30 completing the analysis processing of the measurement data at each period of the reference waveform, call for each region the phase difference P _Ti at time T, to determine the presence or absence of a defect based on this. Further, the CPU 30 determines the depth at which the defect exists based on the correlation data indicating the phase difference of the area determined to be a defect (step S1207). That is, referring to the phase difference of each region and the reference table 120 showing the relationship between the period of the reference waveform and the defect depth, the depth of the region determined to indicate a defect is determined.

  After completing the analysis process in step S1206 and the determination process in step S1207, the CPU 30 determines whether or not the analysis process has been performed for all the set cycles (step S1208). If there is an unprocessed cycle, the flow returns to step S1205 to read another cycle and repeat steps S1206 to 1207. For example, the above steps S1206 to S1207 are repeated for each set period of 20 minutes, 30 minutes, and 40 minutes.

  The CPU 30 generates image data of the entire measurement area and outputs the image data shown in FIG. 10 to the display 33 (step S1209). In the present embodiment, it is assumed that the value of the depth of the defective portion is simultaneously displayed on each screen (not shown).

  Further, a defect shape estimation screen as shown in FIG. 13 may be displayed simultaneously using the defect depth determined in step S1207. Thereby, quantitative information on the defective part is displayed as image data, and it is easy to confirm the inspection result in the defect inspection, and even a person who does not have special judgment knowledge can find the internal defect. In addition, in FIG. 13, although the defective part is expressed two-dimensionally, you may express as a three-dimensional shape. As a result, more detailed information on the defect can be acquired.

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.

3-1. Device Configuration of Defect Inspection System The functional block diagram of the defect detection system in the present embodiment is the same as FIG. 1 shown in the first embodiment. The hardware configuration of the computer device 29 according to the defect inspection control device is the same as that shown in FIG. 3 in the first embodiment.

  FIG. 14 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.

  1 is realized by a computer device 29 and a signal generator 27. The heating device 17 is realized by the heater 17, the heater moving device 22, and the relay device 25. The temperature measuring device 19 is realized by the infrared camera 23 and the camera moving device 24.

3-2. Flowchart in Defect Inspection Control Device FIG. 15 shows a flowchart in the defect inspection control device 10 when performing defect inspection. In the defect inspection control device 10, 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 (step S1400).

  Here, as in the first embodiment, the heating condition is a time for applying a thermal load to the device under test 20 and the number of repetitions thereof. Further, the movement condition is to give a movement speed and a movement 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 heating by the heater 21 is finished, the heater moving device 22 stops after moving a predetermined distance. Thereafter, the CPU 30 outputs measurement conditions to the infrared camera 23 and outputs movement conditions to the camera moving device 24 (step S1401).

  Here, the measurement conditions refer to measurement time and measurement timing for the infrared camera 23 to measure the surface temperature of the inspection object 20. Further, the moving condition is to give a moving speed and a moving distance to the camera moving device 24 as in the case of the heater moving device 22.

  After the heating by the heater 21 is completed, the camera moving device 24 moves the infrared camera 23 to the front of the measurement area that has just been heated. The infrared camera 23 measures the surface temperature of the measurement region based on the measurement time and the measurement timing (step S1402).

  After performing the above processing under predetermined heating conditions, measurement conditions, or movement conditions, the CPU 30 ends the measurement (step S1403).

  The measurement data analysis process (step S1404), the image data generation process (step S1405), and the image data output process (step S1406) after the measurement are the same as in the first embodiment.

  Thereby, even when the heater 21 as a heat source can be brought close to the inspection object 20, the surface of the inspection object can be uniformly heated by preventing heating spots, and the inspection accuracy can be further improved. it can.

  Further, by using the heater moving device 22 and the camera moving device 24, by repeatedly heating with the heater 21 and measuring the temperature with the infrared camera 23 while moving along the surface of the inspection object 20 (for example, step S1400 above). S1403), defect inspection can be continuously performed for a plurality of continuous measurement regions of the inspection object 20.

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

  In the above embodiment, the number of repetitions of heating / stopping heating is set to one, but may be repeated a plurality of times depending on the property of the object to be inspected. In this case, if the reflection of the heat source on the surface of the object to be measured is not affected, the temperature fluctuation 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.

  Further, the correlation processing is performed using the sine wave / cosine wave curve, but 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.

It is a figure which shows the functional block diagram of the defect detection system by one Embodiment of this invention. It is an example of the graph which shows the time-dependent change of the temperature by one Embodiment of this invention. It is an artificial defect specimen and temperature distribution image by one Embodiment of this invention. It is an example which shows the block diagram of the apparatus which implement | achieves the defect detection system by one Embodiment of this invention. It is an example which shows the hardware block diagram of the computer apparatus by one Embodiment of this invention. It is a figure which shows the flowchart in a defect inspection control apparatus. It is a figure which shows the relationship between the signal for heating control, and the temperature fluctuation curve in the surface of a to-be-inspected object. It is a figure which shows the flowchart in the analysis process of measurement data. It is an example (A) of a display screen of an artificial defect (B) and image data when this artificial defect is measured. It is the example which showed the phase difference of the measurement data in the unit area | region of a measurement area | region, and a reference waveform with the graph. It is an example of the display screen of image data when the period of a reference waveform is changed and an artificial defect is measured. 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 a defect. It is a display screen of image data when changing the period of a reference waveform and measuring a concrete structure having an internal defect. It is an example when the internal defect part of the measured concrete structure was extract | collected. It is a figure which shows the flowchart in the defect inspection control apparatus at the time of reference table use. It is an example of the screen which estimated the shape of the defect based on the quantitative information concerning a defective part. It is an example which shows the block diagram of the apparatus which implement | achieves the defect detection system by one Embodiment of this invention. It is a figure which shows the flowchart in a defect inspection control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Defect inspection control apparatus 11 ... Heating control means 13 ... Data recording means 15 ... Defect judgment means 17 ... Heating apparatus 19 ... Temperature measuring device

Claims (13)

In order to increase the temperature at at least one point inside the object to be inspected during the heating stop period after stopping the heating, the surface of the object to be inspected is heated over the entire measurement region,
At least in the heating stop period after stopping the heating,
For each unit area of the measurement area, measure the time change of the surface temperature,
A defect inspection method for finding a defect in the object to be inspected based on a relative difference between each unit region with respect to a temporal change in surface temperature in each unit region,
The heating time is shorter than the measurement time. The defect inspection method according to claim 1,
The heating is performed with a strength and abruptness at which the temperature rises after the heating is stopped at the depth of the detection target point inside the object to be inspected. The defect inspection method according to claim 1 or 2,
The measurement is continued for at least a time until the heat due to the heating reaches the depth of the detection target point after the heating is stopped. In the defect inspection method in any one of Claims 1-3,
The object to be inspected is composed of a low thermal conductivity material. In the defect inspection method in any one of Claims 1-4,
The position of a defect in the object to be inspected is specified based on a relative difference between the unit regions with respect to a temporal change in surface temperature in each unit region. In the defect inspection method according to claim 1,
The present invention presents a relative difference between the unit regions with respect to the temporal change of the surface temperature in each unit region as a visually recognizable image. The defect inspection method according to claim 6,
The relative difference is determined on the basis of a comparison of a feature value in a predetermined waveform and a waveform due to a temporal change in surface temperature in each unit region. The defect inspection method according to claim 7,
The feature amount comparison is performed based on a specific value indicating a correlation between both waveforms of a waveform due to a time change of the surface temperature in each unit region and a predetermined waveform or a phase difference between the two waveforms. thing. In the defect inspection method in any one of Claims 1-8,
While performing heating and heating stop for a predetermined period, changing the cycle of the predetermined waveform and measuring,
The defect depth is estimated based on a predetermined waveform period in which the difference in relative temperature change between each unit region becomes significant. The defect inspection method according to claim 9.
Furthermore, the depth of the defect is estimated based on a table in which the depth of the defect is associated with a predetermined waveform period in advance. Heating start command to a heating device that heats the entire surface of the object to be inspected so that the temperature rises at at least one point inside the object to be inspected during the heating stop period after the heating is stopped Heating control means for performing,
Data recording means for inputting data from a temperature measuring instrument after stopping heating and recording it as temperature data of each unit area;
Defect inspection comprising defect determination means for detecting a relative difference between the respective unit regions with respect to the temporal change of the surface temperature in each unit region based on the recorded temperature data, and determining a defect in the inspection object A control device,
The heating time is shorter than the measurement time. Heating start command to a heating device that heats the entire surface of the object to be inspected so that the temperature rises at at least one point inside the object to be inspected during the heating stop period after the heating is stopped Heating control means for performing,
A data collecting device comprising data recording means for inputting data from a temperature measuring instrument after stopping heating and recording it as temperature data of each unit region,
The heating time is shorter than the measurement time. The surface in each unit area based on the temperature data of each unit area of the measurement area recorded after the heating of the surface of the object to be inspected heated so that the temperature rises at at least one point inside the object to be inspected A defect determination means for detecting a relative difference between the unit regions with respect to a temporal change in temperature and determining a defect in the inspection object;
A defect determination apparatus for defect inspection, comprising:

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