Flaw detection device

Abstract

To detect a flaw in a steel plate deck from a pavement body side.SOLUTION: A flaw detection device 100 comprises: excitation coils (first excitation coil 132a, second excitation coil 132b); an excitation unit 210 that applies, to the excitation coils, AC current with a first frequency and AC current with a second frequency that is a frequency lower than the first frequency to generate induction current in a steel plate deck through electromagnetic induction; a detection unit 230 that detects a detection signal based on the induction current; and a depth estimation unit 268 that estimates the depth of a flaw formed in the steel plate deck on the basis of a first frequency detection signal based on the induction current according to the AC current with the first frequency and a second frequency detection signal based on the induction current according to the AC current with the second frequency.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This disclosure relates to a flaw detection device. [Background technology]

[0002] Highways, bridges, and other road structures are composed of steel decks and pavement layers, such as asphalt, laid on top of the steel decks. The steel decks may develop cracks or other damage due to fatigue over time caused by vehicles passing over the pavement.

[0003] Therefore, ultrasonic testing is used as a technique for inspecting defects in steel decks (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-14513 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the ultrasonic flaw detection method described in Patent Document 1 requires the probe to be brought into contact with the steel deck, that is, directly beneath the road. This necessitates the construction of scaffolding or similar structures beneath the road, resulting in enormous costs for inspecting for defects.

[0006] In view of these challenges, this disclosure aims to provide a flaw detection device capable of detecting defects in steel decks from the pavement side. [Means for solving the problem]

[0007] To solve the above problems, a flaw detection device according to one aspect of this disclosure is provided. 1 Excitation coil and A second excitation coil having a winding direction opposite to that of the first excitation coil and connected in series with the first excitation coil, a first detection coil, a second detection coil having a winding direction opposite to that of the first detection coil, a third detection coil having a winding direction opposite to that of the second detection coil and connected in series with the second detection coil, a fourth detection coil having a winding direction opposite to that of the first detection coil and connected in series with the first detection coil, a first cancellation coil provided vertically above or vertically below the first detection coil, and a second detection coil provided vertically above or vertically below the second detection coil. Cancellation coil and first frequency 1 AC current and a second frequency lower than the first frequency 2nd with an alternating current 1 excitation coil and the second excitation coil is applied to the steel floor slab, and an induced current is generated in the steel floor slab by electromagnetic induction, and the Third alternating current of the first frequency and the 4th alternating current of the second frequency 1 are applied to the and the second cancellation coil canceling coil 1 to generate a magnetic field opposite to the magnetic field generated by the and the second excitation coil excitation coil, and a detection unit that detects the Through the first detection coil, second detection coil, third detection coil, and fourth detection coil, according to the first AC current detection signal high frequency based on the induced current, and a depth estimation unit that estimates the depth of the defect formed in the steel floor slab, based on the And a low-frequency detection signal based on the induced current corresponding to the second AC current. detection signal. The excitation unit A difference calculation unit calculates the difference between a high-frequency detection signal and a low-frequency detection signal, and the difference calculated by the difference calculation unit does the following. The detection unit generates a first AC current by amplifying the third AC current and applies it to the first and second excitation coils, generates a second AC current by amplifying the fourth AC current and applies it to the first and second excitation coils, detects a first high-frequency detection signal and a first low-frequency detection signal through the first detection coil, detects a second high-frequency detection signal and a second low-frequency detection signal through the second detection coil, and detects a third high-frequency detection signal and a third low-frequency detection signal through the third detection coil. The fourth detection coil detects a fourth high-frequency detection signal and a fourth low-frequency detection signal. The difference calculation unit calculates the difference DaH between the first high-frequency detection signal and the fourth high-frequency detection signal, and the difference DcH between the second high-frequency detection signal and the third high-frequency detection signal, and the difference DaL between the first low-frequency detection signal and the fourth low-frequency detection signal, and the difference DcL between the second low-frequency detection signal and the third low-frequency detection signal, and the depth estimation unit estimates the depth of the defect formed in the steel deck based on the difference DcH and the difference DcL.

[0008] In addition, the flaw detection device includes an electromagnetic wave transmission / reception unit including a transmission unit that transmits electromagnetic waves and a reception unit that receives a reflected wave based on the transmitted electromagnetic waves, a distance calculation unit that calculates the distance to the steel floor slab based on the reflected wave, and a correction unit that corrects the Difference calculated by the difference calculation unit based on the calculated distance. The depth estimation unit may estimate the depth of the defect formed in the steel floor slab based on the difference corrected by the correction unit.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to detect a defect in the steel floor slab from the paving side.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a diagram for explaining a road that is a flaw detection target of the flaw detection device according to the embodiment. [Figure 2] FIG. 2 is a diagram of the vehicle constituting the flaw detection device according to the embodiment as viewed vertically downward. [Figure 3] FIG. 3 is a first diagram for explaining the electromagnetic induction flaw detection method. [Figure 4] FIG. 4 is a second diagram for explaining the electromagnetic induction flaw detection method. ​ [Figure 5] FIG. 5 is a top view of the probe according to the embodiment. [Figure 6] FIG. 6 is a first side view of the probe according to the embodiment. [Figure 7] FIG. 7 is a second side view of the probe according to the embodiment. [Figure 8] FIG. 8 is a functional block diagram of the flaw detector according to the embodiment. [Figure 9] FIG. 9 is a diagram for explaining the relationship between the distance between the probe and the steel floor slab and the signal intensity. [Figure 10] FIG. 10 is a diagram for explaining the relationship between the flaw detection frequency, the skin depth, and the signal intensity. [Figure 11] FIG. 11 is a diagram for explaining the relationship between the signal intensity of the detection signal according to the flaw detection frequency and the depth of the defect. [Figure 12] FIG. 12 is a flowchart showing the processing flow of the flaw detection method according to the embodiment. [Figure 13] FIG. 13 is a diagram for explaining the probe 430 according to the modification.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in such embodiments are merely examples for facilitating understanding, and do not limit the present disclosure unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to omit redundant descriptions, and elements not directly related to the present disclosure are not shown.

[0012] FIG. 1 is a diagram for explaining a road 10 which is a flaw detection target of a flaw detector 100 according to the present embodiment. In FIG. 1 of the present embodiment, and FIGS. 2, 5 to 7, and 11 described later, an X-axis (horizontal direction, road width direction), a Y-axis (horizontal direction, road length direction), and a Z-axis (vertical direction) that intersect perpendicularly are defined as shown in the drawings.

[0013] As shown in Figure 1, the road 10 is composed of a steel deck 20 and a pavement 30. The steel deck 20 is a deck made of steel members. The steel deck 20 supports vertically downward loads from vehicles. The steel deck 20 includes a deck plate 40, a main girder web 42, vertical reinforcement members 44, transverse ribs 46, and U-ribs 48.

[0014] The deck plate 40 is a steel plate that extends in a substantially horizontal direction. The main girder web 42 is a steel plate that is erected vertically downward from the deck plate 40 and extends in the direction of the road 10's extension. The vertical reinforcement members 44 are steel plates provided on the main girder web 42. The upper surface of the vertical reinforcement members 44 is welded to the deck plate 40. The transverse ribs 46 are steel plates that are erected vertically downward from the deck plate 40 and extend in the width direction of the road 10. The transverse ribs 46 are connected to the main girder web 42. The U-ribs 48 are steel plates with a U-shaped vertical cross-section. The U-ribs 48 are welded to the deck plate 40 so as to extend in the direction of the road 10's extension (road length direction).

[0015] The pavement 30 is stacked on the deck plate 40. The pavement 30 is made of asphalt or the like.

[0016] Due to fatigue caused by vehicles passing over the pavement 30, cracks and other defects may occur in the steel deck 20, such as in the welds between the deck plate 40 and the U-rib 48, and between the deck plate 40 and the vertical reinforcement members 44. The cracks propagate from the welds into the deck plate 40. In other words, the cracks propagate from bottom to top in a direction perpendicular to the surface of the steel deck 20 (deck plate 40).

[0017] Therefore, the flaw detection device 100 shown in Figure 2 below inspects the steel deck slab 20 for defects from above the pavement 30. In this embodiment, the flaw detection device 100 inspects the road 10 for defects while scanning it in the direction of vehicle passage (in Figure 1, the Y-axis direction, the direction of extension of the road 10, that is, the direction of extension of the U-rib 48).

[0018] [Flaw detection equipment 100] Figure 2 is a view of the vehicle 110, which constitutes the flaw detection device 100 according to this embodiment, as seen from vertically below.

[0019] As shown in Figure 2, the flaw detection device 100 includes a vehicle 110, an antenna 120, a probe 130, an encoder 140, a marking mechanism 150, and a control unit 200.

[0020] Vehicle 110 travels (moves) on the pavement 30 when inspecting the steel deck 20 for defects. An antenna 120, a probe 130, an encoder 140, and a marking mechanism 150 are integrally fixed to the underside 112 of vehicle 110. In this embodiment, the antenna 120, probe 130, encoder 140, and marking mechanism 150 are provided in this order from the front in the direction of travel of the vehicle. A control unit 200 is provided inside vehicle 110.

[0021] Antenna 120 transmits electromagnetic waves based on a current applied from the electromagnetic wave transmitting / receiving unit 250 (described later) and receives reflected waves based on the transmitted electromagnetic waves. The electromagnetic waves penetrate the pavement 30 (e.g., asphalt). Therefore, the electromagnetic waves are reflected by the steel deck 20. Antenna 120 is, for example, a Vivaldi antenna, a Quadrich horn antenna, or a bowtie antenna.

[0022] Probe 130 is a probe for electromagnetic induction testing (EMIT). Electromagnetic induction testing is a type of flaw detection method also known as eddy current testing.

[0023] Figure 3 is the first diagram illustrating the electromagnetic induction flaw detection method. Figure 4 is the second diagram illustrating the electromagnetic induction flaw detection method. In Figures 3 and 4, the example shows the case where excitation and detection are performed using the same coil C.

[0024] As shown in Figure 3, when an alternating current is applied to coil C, an alternating magnetic field is generated (excitation). Then, due to electromagnetic induction, an induced current (eddy current U) is generated in the steel deck 20 in a direction that cancels out the alternating magnetic field.

[0025] As shown in Figure 4, in areas of the steel deck 20 where there are defects, the eddy current U is blocked by the defects. As a result, disturbance occurs in the eddy current U in the areas with defects compared to areas without defects.

[0026] Therefore, in electromagnetic induction testing, the presence or absence of defects is detected by detecting the change in eddy current U acquired through coil C as a change in impedance.

[0027] Figure 5 is a top view of the probe 130 according to this embodiment. Figure 6 is a first side view of the probe 130 according to this embodiment. Figure 7 is a second side view of the probe 130 according to this embodiment.

[0028] As shown in Figures 5 to 7, the probe 130 includes an excitation coil 132, a first detection coil 134a, a second detection coil 134b, a third detection coil 134c, a fourth detection coil 134d, a first cancellation coil 136a, and a second cancellation coil 136b.

[0029] In this embodiment, the excitation coil 132 includes a first excitation coil 132a and a second excitation coil 132b.

[0030] The first excitation coil 132a and the second excitation coil 132b are placed side by side in close proximity in a substantially horizontal direction (Y-axis direction in Figures 5 to 7). The second excitation coil 132b has a central axis substantially parallel to the central axis of the first excitation coil 132a. The winding direction of the second excitation coil 132b is opposite to that of the first excitation coil 132a. For example, in Figure 5, if the winding direction of the first excitation coil 132a is clockwise, the winding direction of the second excitation coil 132b is counterclockwise. The second excitation coil 132b is connected in series with the first excitation coil 132a.

[0031] The first excitation coil 132a and the second excitation coil 132b are installed on the pavement 30 such that the direction perpendicular to the surface of the pavement 30, which is laminated on the steel deck 20 (the Z-axis direction in Figures 5 to 7), is approximately parallel to the central axis.

[0032] The first detection coil 134a is superimposed on the first excitation coil 132a, spaced apart in the direction of the central axis of the first excitation coil 132a (the Z-axis direction in Figures 5 to 7). The first detection coil 134a has a central axis that is approximately parallel to the central axis of the first excitation coil 132a.

[0033] The second detection coil 134b is positioned parallel to the first detection coil 134a in a substantially horizontal direction (Y-axis direction in Figures 5 to 7). The second detection coil 134b is superimposed on the second excitation coil 132b, spaced apart in the direction of the central axis of the second excitation coil 132b (Z-axis direction in Figures 5 to 7). The second detection coil 134b has a central axis substantially parallel to the central axis of the second excitation coil 132b. The second detection coil 134b has a winding direction opposite to that of the first detection coil 134a. For example, in Figure 5, if the winding direction of the first detection coil 134a is clockwise, the winding direction of the second detection coil 134b is counterclockwise.

[0034] The distance from the proximity portion of the first excitation coil 132a and the second excitation coil 132b to the first detection coil 134a is substantially equal to the distance from the proximity portion to the second detection coil 134b.

[0035] The third detection coil 134c is provided between the first detection coil 134a and the second detection coil 134b. In this embodiment, the third detection coil 134c is provided on the same plane (XY plane in Figures 5 to 7) as the first detection coil 134a and the second detection coil 134b. The third detection coil 134c has a central axis substantially parallel to the central axis of the second detection coil 134b. The third detection coil 134c has a winding direction opposite to that of the second detection coil 134b. For example, in Figure 5, if the winding direction of the second detection coil 134b is counterclockwise, the winding direction of the third detection coil 134c is clockwise.

[0036] The fourth detection coil 134d is located between the first detection coil 134a and the second detection coil 134b, and is superimposed on the third detection coil 134c, separated in the direction of the central axis of the third detection coil 134c (the Z-axis direction in Figures 5 to 7). The fourth detection coil 134d has a central axis that is approximately parallel to the central axis of the first detection coil 134a. The fourth detection coil 134d has a winding direction opposite to that of the first detection coil 134a. For example, in Figure 5, if the winding direction of the first detection coil 134a is clockwise, the winding direction of the fourth detection coil 134d is counterclockwise.

[0037] In other words, the winding direction of the first detection coil 134a and the third detection coil 134c is the same. The winding direction of the second detection coil 134b and the fourth detection coil 134d is the same. The winding direction of the first detection coil 134a and the third detection coil 134c is opposite to that of the second detection coil 134b and the fourth detection coil 134d.

[0038] The first detection coil 134a and the fourth detection coil 134d are connected in series. The second detection coil 134b and the third detection coil 134c are directly connected.

[0039] The first cancel-out coil 136a is superimposed on the first detection coil 134a, spaced apart in the direction of the central axis of the first detection coil 134a. The first cancel-out coil 136a generates a magnetic field in the opposite direction to the magnetic field formed by the first excitation coil 132a.

[0040] As will be explained in more detail later, a detection signal based on the induced current is detected through the first detection coil 134a. However, in addition to the voltage based on the induced current, the voltage based on the first excitation coil 132a is directly applied to the first detection coil 134a. Therefore, a first cancel-out coil 136a, which generates a magnetic field in the opposite direction to the magnetic field formed by the first excitation coil 132a, is superimposed on the first detection coil 134a. As a result, the first cancel-out coil 136a can cancel out the voltage directly applied to the first detection coil 134a from the first excitation coil 132a. Consequently, the voltage based on the first excitation coil 132a is reduced and applied to the first detection coil 134a. Therefore, the first detection coil 134a can acquire the voltage based on the induced current with high accuracy.

[0041] The second cancellation coil 136b is superimposed on the second detection coil 134b, spaced apart in the direction of the central axis of the second detection coil 134b. The second cancellation coil 136b generates a magnetic field in the opposite direction to the magnetic field formed by the second excitation coil 132b.

[0042] As will be explained in more detail later, a detection signal based on the induced current is detected through the second detection coil 134b. However, in addition to the voltage based on the induced current, the voltage based on the second excitation coil 132b is directly applied to the second detection coil 134b. Therefore, a second canceling coil 136b, which generates a magnetic field in the opposite direction to the magnetic field formed by the second excitation coil 132b, is superimposed on the second detection coil 134b. As a result, the second canceling coil 136b can cancel out the voltage directly applied to the second detection coil 134b from the second excitation coil 132b. Consequently, the voltage based on the second excitation coil 132b is reduced and applied to the second detection coil 134b. Therefore, the second detection coil 134b can acquire the voltage based on the induced current with high accuracy.

[0043] The first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first counteracting coil 136a, and the second counteracting coil 136b are installed on the pavement 30 such that the direction perpendicular to the surface of the pavement 30, which is laminated on the steel deck 20 (the Z-axis direction in Figures 5 to 7), is approximately parallel to the central axis.

[0044] Returning to Figure 2, the encoder 140 acquires path information indicating the distance traveled by the probe 130. The path information acquired by the encoder 140 is output to the control unit 200.

[0045] The marking mechanism 150 marks the pavement 30 in accordance with a control command from the control unit 200. The marking mechanism 150 includes, for example, a choke and an actuator that drives the choke.

[0046] Figure 8 is a functional block diagram of the flaw detection apparatus 100 according to this embodiment. As shown in Figure 8, the control unit 200 includes an excitation unit 210, a detection unit 230, an A / D converter 240, an electromagnetic wave transmitting and receiving unit 250, a central control unit 260, a memory 280, and a display device 290.

[0047] The excitation unit 210 applies an alternating current of a first frequency substantially simultaneously to the first excitation coil 132a and the second excitation coil 132b, generating an induced current in the steel deck 20 by electromagnetic induction. The excitation unit 210 also applies an alternating current of a second frequency, which is lower than the first frequency, substantially simultaneously to the first excitation coil 132a and the second excitation coil 132b, generating an induced current in the steel deck 20 by electromagnetic induction.

[0048] The first and second frequencies are determined based on the results of flaw detection tests conducted in advance using simulated test specimens, etc. Alternatively, the first and second frequencies may be determined analytically using electromagnetic simulations, etc. Furthermore, the first and second frequencies may be determined taking into account the characteristics of the defects to be detected. The characteristics of the defects include, for example, the depth of the defect (depth of the crack), the length of the defect, and whether or not the defect penetrates. For example, when attempting to detect a defect located far from the pavement 30, the frequency should be lowered. Conversely, when attempting to detect a defect located close to the pavement 30, a frequency with high detection sensitivity (for example, around 700 Hz) should be used.

[0049] Hereinafter, the alternating current of the first frequency may be referred to as "high-frequency alternating current." The alternating current of the second frequency may also be referred to as "low-frequency alternating current." In this embodiment, the excitation unit 210 includes a function generator 212 and an amplifier 214.

[0050] The function generator 212 (indicated as "F / G" in Figure 8) generates a first-frequency AC signal and a second-frequency AC signal at different timings. The first-frequency and second-frequency AC signals from the function generator 212 are output to the amplifier 214 and the detection unit 230. The AC current (high-frequency AC current) based on the first-frequency AC signal from the function generator 212 is applied to the first cancel-out coil 136a and the second cancel-out coil 136b. Similarly, the AC current (low-frequency AC current) based on the second-frequency AC signal from the function generator 212 is applied to the first cancel-out coil 136a and the second cancel-out coil 136b.

[0051] Amplifier 214 (indicated as "B / P" in Figure 8) amplifies the first frequency AC signal from the function generator 212 and applies a high-frequency AC current to the first excitation coil 132a and the second excitation coil 132b. This generates an induced current in the steel deck 20 due to electromagnetic induction. Similarly, amplifier 214 amplifies the second frequency AC signal from the function generator 212 and applies a low-frequency AC current to the first excitation coil 132a and the second excitation coil 132b. This also generates an induced current in the steel deck 20 due to electromagnetic induction. As described above, since the winding direction of the first excitation coil 132a and the winding direction of the second excitation coil 132b are opposite, current is applied in the same direction in the adjacent portions of the first excitation coil 132a and the second excitation coil 132b. Amplifier 214 is, for example, a bipolar power supply.

[0052] The detection unit 230 is composed of, for example, a lock-in amplifier (indicated as "L / I" in Figure 8). Based on the AC signal (reference signal) output from the function generator 212, the detection unit 230 extracts the frequency components (detection signals based on induced current) of the current applied to the first excitation coil 132a and the second excitation coil 132b from the AC voltage detected by the first detection coil 134a. Hereinafter, the detection signal detected through the first detection coil 134a will be referred to as the first detection signal. The detection unit 230 detects a first detection signal (first frequency detection signal) based on the induced current corresponding to the high-frequency AC current and a first detection signal (second frequency detection signal) based on the induced current corresponding to the low-frequency AC current. Hereinafter, the first detection signal based on the induced current corresponding to the high-frequency AC current may be referred to as the "first high-frequency detection signal." Also, the first detection signal based on the induced current corresponding to the low-frequency AC current may be referred to as the "first low-frequency detection signal."

[0053] Similarly, the detection unit 230 extracts the frequency components (detection signals based on induced current) of the current applied to the first excitation coil 132a and the second excitation coil 132b from the AC voltage of the second detection coil 134b based on the reference signal. Hereinafter, the detection signal detected through the second detection coil 134b will be referred to as the second detection signal. The detection unit 230 detects a second detection signal (first frequency detection signal) based on the induced current corresponding to the high-frequency AC current and a second detection signal (second frequency detection signal) based on the induced current corresponding to the low-frequency AC current. Hereinafter, the second detection signal based on the induced current corresponding to the high-frequency AC current may be referred to as the "second high-frequency detection signal." Also, the second detection signal based on the induced current corresponding to the low-frequency AC current may be referred to as the "second low-frequency detection signal."

[0054] Furthermore, the detection unit 230 extracts the frequency component (detection signal based on induced current) of the current applied to the first excitation coil 132a and the second excitation coil 132b from the AC voltage of the third detection coil 134c based on the reference signal. Hereinafter, the detection signal detected through the third detection coil 134c will be referred to as the third detection signal. The detection unit 230 detects a third detection signal (first frequency detection signal) based on the induced current corresponding to the high-frequency AC current and a third detection signal (second frequency detection signal) based on the induced current corresponding to the low-frequency AC current. Hereinafter, the third detection signal based on the induced current corresponding to the high-frequency AC current may be referred to as the "third high-frequency detection signal." Also, the third detection signal based on the induced current corresponding to the low-frequency AC current may be referred to as the "third low-frequency detection signal."

[0055] Furthermore, the detection unit 230 extracts the frequency component (detection signal based on induced current) of the current applied to the first excitation coil 132a and the second excitation coil 132b from the AC voltage of the fourth detection coil 134d based on the reference signal. Hereinafter, the detection signal detected through the fourth detection coil 134d will be referred to as the fourth detection signal. The detection unit 230 detects a fourth detection signal (first frequency detection signal) based on the induced current corresponding to the high-frequency AC current and a fourth detection signal (second frequency detection signal) based on the induced current corresponding to the low-frequency AC current. Hereinafter, the fourth detection signal based on the induced current corresponding to the high-frequency AC current may be referred to as the "fourth high-frequency detection signal." Also, the fourth detection signal based on the induced current corresponding to the low-frequency AC current may be referred to as the "fourth low-frequency detection signal."

[0056] The A / D converter 240 (indicated as "A / D" in Figure 8) converts the output value (analog signal) of the detection unit 230 into a digital signal.

[0057] The electromagnetic wave transmitting and receiving unit 250 is composed of, for example, a frequency analysis device (shown as "N / A" in Figure 8). The electromagnetic wave transmitting and receiving unit 250 functions as a transmitting unit that applies current to the antenna 120 and transmits electromagnetic waves to the surface of the pavement 30 through the antenna 120. The electromagnetic wave transmitting and receiving unit 250 also functions as a receiving unit that receives reflected waves (reflected electromagnetic waves) reflected from the steel deck 20 through the antenna 120. The electromagnetic wave transmitting and receiving unit 250 then analyzes the signal based on the reflected waves and calculates the frequency components (spectrum) of the reflected waves.

[0058] The central control unit 260 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 260 reads programs and parameters for operating the CPU from ROM. The central control unit 260 works in cooperation with RAM, which serves as the work area, and other electronic circuits to manage and control the entire flaw detection device 100.

[0059] Memory 280 consists of ROM, RAM, flash memory, HDD, etc. Memory 280 stores programs and various data used by the central control unit 260.

[0060] The display device 290 is composed of a liquid crystal display, an organic EL (Electro Luminescence) display, etc.

[0061] The detection signal based on the induced current obtained by the detection unit 230 includes a defect signal (alternating magnetic field change) S based on a defect and a lift-off signal S based on the distance between the probe 130 and the steel floor plate 20. F and a lift-off signal S based on the distance between the probe 130 and the steel floor plate 20. L and includes.

[0062] The defect signal S F is represented by the following formula (1). The lift-off signal S L is represented by the following formula (2). S F =A F exp(iωt) … Formula (1) S L =A L exp(iφ) … Formula (2) In the above formula (1), A F represents the amplitude of the defect signal. i represents a complex constant. ω represents the frequency. t represents the time. In the above formula (2), A L represents the amplitude of the lift-off signal. i represents a complex constant. φ represents the initial phase.

[0063] When the flaw detection device 100 scans the road 10 (vehicle 110 moves along the road 10), one or more wheels 114 of the vehicle 110 may get stuck in depressions such as ruts in the pavement 30, or ride up on protrusions in the pavement 30, causing the distance between the underside 112 of the vehicle 110 and the surface of the pavement 30, i.e., the distance between the probe 130 and the surface of the pavement 30, to fluctuate. In this case, even if the thickness of the pavement 30 is constant, the distance between the surface of the pavement 30 and the probe 130 will fluctuate, and the distance between the probe 130 and the steel deck 20 will fluctuate. Furthermore, if the thickness of the pavement 30 fluctuates due to wear caused by vehicle traffic or increased thickness due to repairs to the pavement 30, the distance between the probe 130 and the steel deck 20 will fluctuate, even if the distance between the surface of the pavement 30 and the probe 130 is constant.

[0064] Damage Signal S F This is the lift-off signal S L Although detected in a different phase, as the distance between the probe 130 and the steel deck 20 increases, the amplitude of the defect signal A F The detection signal decreases, and the defect signal S is lost from the detection signal. F It becomes impossible to identify them.

[0065] Therefore, the flaw detection device 100 according to this embodiment is equipped with four detection coils (first detection coil 134a, second detection coil 134b, third detection coil 134c, and fourth detection coil 134d), and uses the detection signals of each coil to remove the lift-off signal.

[0066] In this embodiment, the central control unit 260 functions as a difference calculation unit 262, a distance calculation unit 264, a correction unit 266, a depth estimation unit 268, and a signal storage unit 270.

[0067] The difference calculation unit 262 calculates the difference DcH (=|DaH-DbH|) between the difference DaH between the first high-frequency detection signal and the fourth high-frequency detection signal and the difference DbH between the second high-frequency detection signal and the third high-frequency detection signal. Similarly, the difference calculation unit 262 calculates the difference DcL (=|DaL-DbL|) between the difference DaL between the first low-frequency detection signal and the fourth low-frequency detection signal and the difference DbL between the second low-frequency detection signal and the third low-frequency detection signal.

[0068] As described above, the first detection coil 134a and the fourth detection coil 134d have opposite winding directions. Therefore, the first detection signal and the fourth detection signal contain the same lift-off signal in opposite directions. As a result, when the difference Da between the first detection signal and the fourth detection signal is calculated, the lift-off signals cancel each other out, making it possible to extract signals other than the lift-off signal (defect signals).

[0069] Similarly, the second detection coil 134b and the third detection coil 134c have opposite winding directions. Therefore, the second detection signal and the third detection signal contain the same lift-off signal in opposite directions. As a result, when the difference Db between the second detection signal and the third detection signal is calculated, the lift-off signals cancel each other out, making it possible to extract signals other than the lift-off signal (defect signals).

[0070] The distance calculation unit 264 calculates the distance between the probe 130 and the steel deck 20 based on the peak times in the spectrum calculated by the electromagnetic wave transmitting / receiving unit 250.

[0071] The correction unit 266 corrects the difference DcH and difference DcL calculated by the difference calculation unit 262 based on the distance calculated by the distance calculation unit 264.

[0072] Figure 9 illustrates the relationship between the distance between the probe 130 and the steel deck 20 and the signal intensity. In Figure 9, the vertical axis represents the signal intensity (amplitude). In Figure 9, the horizontal axis represents the distance (lift-off) [mm] between the probe 130 and the steel deck 20.

[0073] The signal intensity of the detection signal based on defects changes depending on the distance between the probe 130 and the steel deck 20. Specifically, as shown in Figure 9, the signal intensity of the detection signal based on defects decreases as the distance between the probe 130 and the steel deck 20 increases.

[0074] Therefore, in this embodiment, the correction unit 266 multiplies the difference DcH and difference DcL by a correction coefficient corresponding to the distance calculated by the distance calculation unit 264. The correction coefficient becomes smaller as the distance calculated by the distance calculation unit 264 increases.

[0075] The depth estimation unit 268 estimates the depth of the cracks formed in the steel deck 20 based on the difference DcH and difference DcL corrected by the correction unit 266.

[0076] In the electromagnetic induction flaw detection method used in the flaw detection device 100 according to this embodiment, the magnetic field is canceled out by induced current as you penetrate deeper into the steel deck 20, due to the permeability and electrical resistivity of the steel deck 20. Therefore, the higher the frequency of the alternating current applied by the excitation unit 210, the less magnetic flux reaches the interior of the steel deck 20, and eddy currents concentrate on the surface of the steel deck 20. Here, the depth at which the current density is 1 / e is called the skin depth d, and is expressed by the following formula (A). d = √(2ρ / ωμ) …Equation (A) ω = 2πf …Equation (B) In equation (A) above, d is the skin depth, ρ is the electrical resistivity, and μ is the absolute permeability. In equation (B) above, f is the frequency of the alternating current applied by the excitation unit 210. Hereinafter, the frequency of the alternating current applied by the excitation unit 210 may be referred to as the "flaw detection frequency".

[0077] Figure 10 illustrates the relationship between flaw detection frequency, skin depth, and signal strength. In Figure 10, the left vertical axis represents skin depth [mm]. In Figure 10, the right vertical axis represents signal strength (amplitude). In Figure 10, the horizontal axis represents flaw detection frequency [Hz].

[0078] As described above, when the flaw detection frequency is high, most of the eddy currents U are concentrated on the surface of the steel deck 20. Therefore, as shown in Figure 10, when the flaw detection frequency is high, the signal strength of the detection signal based on cracks and other defects is high, but the surface depth d is shallow (short). In other words, when the flaw detection frequency is high, the signal strength of the detection signal based on defects is high, but defects cannot be detected unless the defect depth is long. The defect depth is the length from the base to the tip in the direction of defect propagation (for example, the vertical length of the crack).

[0079] On the other hand, when the flaw detection frequency is low, the magnetic flux reaches the interior of the steel deck 20. Therefore, as shown in Figure 10, when the flaw detection frequency is low, although the surface depth d is deep (long), the signal strength of the detection signal based on cracks and other defects is small. In other words, when the flaw detection frequency is low, defects can be detected even if the defect depth is short, but the signal strength of the detection signal is small.

[0080] Figure 11 illustrates the relationship between the signal strength of the detection signal according to the flaw detection frequency and the depth of the defect. In Figure 11, the vertical axis represents the signal strength. In Figure 11, the horizontal axis represents the depth of the defect. In Figure 11, the black circles represent the signal strength of the detection signal when the flaw detection frequency is high. In Figure 11, the white circles represent the signal strength of the detection signal when the flaw detection frequency is low.

[0081] As shown in Figure 11, when the flaw detection frequency is high, the signal strength of the detection signal based on defects such as cracks is higher than when the flaw detection frequency is low. On the other hand, the defect depth Hf-D at the detection limit of the detection signal when the flaw detection frequency is high is longer than the defect depth Lf-D at the detection limit of the detection signal when the flaw detection frequency is low. In other words, when the flaw detection frequency is low, defects with shorter depths can be detected than when the flaw detection frequency is high.

[0082] Therefore, the depth estimation unit 268 estimates the depth of the defect formed in the steel deck 20 based on the difference DcH (correction value) based on the high-frequency AC current and the difference DcL (correction value) based on the low-frequency AC current. In this embodiment, the depth estimation unit 268 calculates the depth D of the defect using the following formula (C). D={log(DcL´ / DcH´)+α} / β …Formula (C) In the above formula (C), D is the depth of the defect. DcH' is the difference DcH corrected by the correction unit 266. DcL' is the difference DcL corrected by the correction unit 266. α and β are values ​​determined based on the first frequency and the second frequency. α and β are calculated from the results of a flaw detection test (measured value (master curve)) conducted in advance using, for example, a simulated test specimen. It is thought that α and β will vary depending on the properties of the steel deck slab 20 (deck plate 40), the thickness of the pavement 30, etc.

[0083] The depth estimation unit 268 then determines that there is a defect if the estimated defect depth D is greater than or equal to a threshold. The threshold is determined based on the remaining strength of the steel deck slab 20. The depth estimation unit 268 then drives the marking mechanism 150 to mark the pavement 30.

[0084] On the other hand, the depth estimation unit 268 determines that there is no defect if the estimated defect depth D is less than a threshold.

[0085] The signal storage unit 270 stores the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, the fourth low-frequency detection signal, and the distance between the probe 130 and the steel deck 20 in the memory 280, associating them with the path information acquired by the encoder 140.

[0086] [Flaw detection method] Next, a flaw detection method for inspecting a road 10 using the flaw detection device 100 described above will be explained. Figure 12 is a flowchart showing the processing flow of the flaw detection method according to this embodiment. As shown in Figure 12, the flaw detection method according to this embodiment includes a completion determination step S110, a signal acquisition step S120, a difference calculation step S130, a distance calculation step S140, a correction step S150, a depth estimation step S160, a determination step S170, a marking step S180, a storage step S190, a movement step S200, and a remaining intensity estimation step S210. Each step will be explained below.

[0087] [Termination determination process S110] The central control unit 260 determines whether the scanning of a predetermined flaw detection area has been completed. If it determines that the scanning of the flaw detection area has not been completed (NO in S110), the central control unit 260 moves to the signal acquisition step S120. On the other hand, if it determines that the scanning of the flaw detection area has been completed (YES in S110), the central control unit 260 moves to the remaining intensity estimation step S210.

[0088] [Signal acquisition step S120] The excitation unit 210 applies a high-frequency alternating current to the first excitation coil 132a and the second excitation coil 132b substantially simultaneously. The excitation unit 210 also applies a low-frequency alternating current to the first excitation coil 132a and the second excitation coil 132b substantially simultaneously. Furthermore, the excitation unit 210 applies the high-frequency alternating current and the low-frequency alternating current at different timings. The detection unit 230 acquires the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, and the fourth low-frequency detection signal, and the A / D converter 240 converts these detection signals into digital signals.

[0089] The electromagnetic wave transmitting / receiving unit 250 applies an electric current to the antenna 120 and transmits electromagnetic waves to the surface of the pavement 30 through the antenna 120. The electromagnetic wave transmitting / receiving unit 250 then receives the reflected waves reflected from the steel deck 20 through the antenna 120. The electromagnetic wave transmitting / receiving unit 250 analyzes the signal based on the reflected waves and calculates the spectrum.

[0090] Furthermore, the encoder 140 acquires route information and outputs it to the control unit 200.

[0091] [Difference calculation step S130] The difference calculation unit 262 calculates the difference DcH (=|DaH-DbH|) between the difference DaH between the first high-frequency detection signal and the fourth high-frequency detection signal, and the difference DbH between the second high-frequency detection signal and the third high-frequency detection signal, based on the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, and the fourth high-frequency detection signal acquired in the signal acquisition process S120. Similarly, the difference calculation unit 262 calculates the difference DcL (=|DaL-DbL|) between the difference DaL between the first low-frequency detection signal and the fourth low-frequency detection signal, and the difference DbL between the second low-frequency detection signal and the third low-frequency detection signal, based on the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, and the fourth low-frequency detection signal acquired in the signal acquisition process S120.

[0092] [Distance calculation step S140] The distance calculation unit 264 calculates the distance between the probe 130 and the steel deck 20 based on the spectrum acquired in the signal acquisition process S120.

[0093] [Correction process S150] The correction unit 266 corrects the difference DcH and difference DcL calculated in the difference calculation step S130 based on the distance calculated in the distance calculation step S140.

[0094] [Depth estimation process S160] The depth estimation unit 268 estimates the depth D of the defect formed in the steel deck 20 based on the difference DcH' (corrected value) and difference DcL' (corrected value) corrected in the correction process S150.

[0095] [Judgment step S170] The depth estimation unit 268 determines whether the depth D of the defect estimated in the depth estimation step S160 is greater than or equal to a threshold. If it determines that the depth D of the defect is greater than or equal to the threshold (YES in S170), the depth estimation unit 268 moves on to the marking step S180. On the other hand, if it determines that the depth D of the defect is not greater than or equal to the threshold (NO in S170), that is, if it determines that the depth D of the defect is less than the threshold, the depth estimation unit 268 moves on to the storage step S190.

[0096] [Marking process S180] The depth estimation unit 268 drives the marking mechanism 150 to mark the pavement 30.

[0097] [Preservation process S190] The signal storage unit 270 stores the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, the fourth low-frequency detection signal, and the distance between the probe 130 and the steel deck 20 in the memory 280, associating them with the path information acquired by the encoder 140.

[0098] [Moving process S200] The vehicle 110, which constitutes the flaw detection device 100, moves from the first position where the signal acquisition process S120 was performed to the second position within a predetermined time. The second position is a different position from the first position in the direction of movement of the vehicle 110 (Y-axis direction in Figure 2).

[0099] [Residual strength estimation process S210] The depth estimation unit 268 estimates the remaining strength around the defect in the steel deck 20 based on the defect depth D (length in the Z-axis direction in Figure 1) and the defect length (length on the XY plane in Figure 1) estimated in the depth estimation process S160.

[0100] As described above, the flaw detection device 100 according to this embodiment includes an antenna 120, a probe 130, and a control unit 200. Therefore, the flaw detection device 100 according to this embodiment can detect defects in the steel deck 20 from the pavement 30 side.

[0101] Furthermore, as described above, the flaw detection device 100 according to this embodiment includes a first detection coil 134a, a fourth detection coil 134d, and a difference calculation unit 262. The first detection coil 134a and the fourth detection coil 134d have opposite winding directions. As a result, a signal with reduced environmental noise, such as the distance between the probe 130 and the steel deck 20, can be obtained from the difference DaH and DaL calculated by the difference calculation unit 262.

[0102] Similarly, the flaw detection device 100 according to this embodiment includes a second detection coil 134b, a third detection coil 134c, and a difference calculation unit 262. The second detection coil 134b and the third detection coil 134c have opposite winding directions. This allows a signal with reduced environmental noise, such as the distance between the probe 130 and the steel deck 20, to be obtained from the difference DbH and DbL calculated by the difference calculation unit 262.

[0103] Furthermore, as described above, the difference calculation unit 262 calculates the difference DcH between the difference DaH and the difference DbH, and the difference DcL between the difference DaL and the difference DbL. As a result, the difference calculation unit 262 can obtain a signal with environmental noise, such as the distance between the probe 130 and the steel deck 20, further reduced.

[0104] Thus, the flaw detection device 100 according to this embodiment can obtain a signal with reduced environmental noise, such as the distance between the probe 130 and the steel deck 20, making it possible to detect defects without removing the pavement 30.

[0105] Furthermore, as described above, the flaw detection device 100 according to this embodiment includes a first canceling coil 136a. This allows the first detection coil 134a to be placed in a zero magnetic field environment. Therefore, it is possible to reduce the influence of the magnetic field from the first excitation coil 132a on the first detection coil 134a.

[0106] Similarly, the flaw detection apparatus 100 according to this embodiment includes a second cancellation coil 136b. This allows the second detection coil 134b to be placed in a zero magnetic field environment. Therefore, it is possible to reduce the influence of the magnetic field from the second excitation coil 132b on the second detection coil 134b.

[0107] Furthermore, the fourth detection coil 134d is superimposed on the third detection coil 134c, and its winding direction is reversed. As a result, the third detection coil 134c and the fourth detection coil 134d are in a zero magnetic field environment. Therefore, it is possible to reduce the influence of the magnetic field from the first excitation coil 132a and the second excitation coil 132b on the third detection coil 134c and the fourth detection coil 134d.

[0108] Furthermore, as described above, the flaw detection device 100 is equipped with a correction unit 266. This allows the correction unit 266 to correct for fluctuations in signal intensity that occur depending on the distance between the probe 130 and the surface of the steel deck 20. Therefore, even if the distance between the probe 130 and the surface of the steel deck 20 fluctuates, the depth estimation unit 268 can estimate the depth D of the defect with high accuracy.

[0109] Furthermore, as described above, the depth estimation unit 268 can estimate the depth of the defect formed in the steel deck 20 based on the difference DcH based on the high-frequency alternating current and the difference DcL based on the low-frequency alternating current.

[0110] Cracks that propagate from the weld into the deck plate 40 are only discovered when they penetrate the deck plate 40, due to water leakage during rainfall or other events. In other words, cracks that propagate from the weld into the deck plate 40 cannot be detected until they penetrate the deck plate 40. Cracks that penetrate the deck plate 40 may cause the pavement 30 to collapse.

[0111] Therefore, the depth estimation unit 268 detects cracks and other defects before they penetrate the deck plate 40 and estimates the depth D and length of the defects. Then, based on the depth D and length of the defects, the depth estimation unit 268 estimates the remaining strength around the defects in the steel deck 20. This allows for priority repair of areas in the steel deck 20 with low remaining strength.

[0112] Furthermore, as described above, the flaw detection device 100 according to this embodiment includes a marking mechanism 150. This makes it possible for the user to visually understand the location of the flaw.

[0113] Furthermore, as described above, the flaw detection method using the flaw detection device 100 repeats the process from the completion determination step S110 to the movement step S200. In other words, the flaw detection device 100 detects the presence or absence of defects in a time-division manner according to the movement of the vehicle 110. As a result, the flaw detection device 100 can comprehensively inspect the entire area on the road 10 that the vehicle 110 has traveled.

[0114] While embodiments have been described above with reference to the attached drawings, it goes without saying that this disclosure is not limited to the embodiments described above. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of this disclosure.

[0115] For example, in the embodiment described above, the probe 130 was given as an example in which it comprises one first detection coil 134a, one second detection coil 134b, one third detection coil 134c, one fourth detection coil 134d, one first canceling coil 136a, and one second canceling coil 136b. However, the probe 430 may comprise multiple of these.

[0116] Figure 13 is a diagram illustrating a modified probe 430. As shown in Figure 13, the probe 430 comprises a first excitation coil 132a, a second excitation coil 132b, and a plurality of coil units 440.

[0117] The coil unit 440 comprises a first detection coil 134a, a second detection coil 134b, a third detection coil 134c, a fourth detection coil 134d, a first cancel-out coil 136a, and a second cancel-out coil 136b. The positional relationship of the first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first cancel-out coil 136a, and the second cancel-out coil 136b in the coil unit 440 is substantially the same as the positional relationship in the above embodiment.

[0118] The coil units 440 are arranged in parallel along the X-axis direction in Figure 13. In other words, the coil units 440 are arranged in a direction perpendicular to the road length direction (Y-axis direction in Figure 13).

[0119] When a single unit is provided with a first detection coil 134a, a second detection coil 134b, a third detection coil 134c, a fourth detection coil 134d, a first cancellation coil 136a, and a second cancellation coil 136b, each having a length in the X-axis direction of multiple coil units of 440, an average AC voltage relative to the coil area is obtained, resulting in a higher lower limit for detecting defects.

[0120] Therefore, by having multiple coil units 440 in the probe 430, it becomes possible to improve the detection limit of defects.

[0121] Furthermore, in the above embodiment, an example was given in which the first canceling coil 136a is provided vertically above the first detection coil 134a. However, the first canceling coil 136a only needs to be provided vertically above the first detection coil 134a. Therefore, the first canceling coil 136a may be provided vertically below the first detection coil 134a.

[0122] Similarly, an example was given in which the second cancellation coil 136b is provided vertically above the second detection coil 134b. However, the second cancellation coil 136b only needs to be provided vertically above the second detection coil 134b. Therefore, the second cancellation coil 136b may also be provided vertically below the second detection coil 134b.

[0123] Furthermore, in the above embodiment, an example was given in which the flaw detection device 100 is equipped with a first canceling coil 136a and a second canceling coil 136b. However, the flaw detection device 100 does not necessarily have to be equipped with a first canceling coil 136a and a second canceling coil 136b.

[0124] Furthermore, in the above embodiment, an example was given in which the flaw detection device 100 is equipped with a third detection coil 134c and a fourth detection coil 134d. However, the flaw detection device 100 does not necessarily have to be equipped with a third detection coil 134c and a fourth detection coil 134d. In this case, the difference calculation unit 262 calculates the difference between the first detection signal detected through the first detection coil 134a and the second detection signal detected through the second detection coil 134b. Then, the correction unit 266 corrects the difference between the first detection signal and the second detection signal. Then, the depth estimation unit 268 estimates the depth of the defect formed in the steel deck 20 based on the difference between the first detection signal and the second detection signal. In this case, a magnetic sensor may be provided instead of the first detection coil 134a and the second detection coil 134b.

[0125] Furthermore, in the above embodiment, an example was given in which the excitation coil 132 is composed of a first excitation coil 132a and a second excitation coil 132b. However, the excitation coil 132 may be a single coil.

[0126] Similarly, in the above embodiment, the probe 130 was given as an example in which it comprises a first detection coil 134a, a second detection coil 134b, a third detection coil 134c, and a fourth detection coil 134d. However, the probe 130 only needs to have one detection coil. In this case, the difference calculation unit 262 can be omitted. Therefore, in this case, the depth estimation unit 268 estimates the depth of the defect formed in the steel deck 20 based on a first frequency detection signal based on an induced current corresponding to a first frequency AC current, and a second frequency detection signal based on an induced current corresponding to a second frequency AC current, both acquired by one detection coil. In this case, a magnetic sensor may be provided instead of the detection coil.

[0127] Furthermore, in the above embodiment, an example was given in which the correction unit 266 corrects the difference DcH and difference DcL calculated by the difference calculation unit 262. However, the correction unit 266 may also correct the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, and the fourth low-frequency detection signal based on the distance calculated by the distance calculation unit 264. In this case, the difference calculation unit 262 calculates the difference DcH and difference DcL based on the corrected first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, and the fourth low-frequency detection signal.

[0128] Furthermore, in the above embodiment, an example was given in which the flaw detection device 100 comprises an electromagnetic wave transmitting / receiving unit 250, a distance calculation unit 264, and a correction unit 266. However, if the variation in the distance from the probe 130 to the steel deck 20 is within a predetermined range, or if the variation in signal strength due to the distance from the probe 130 to the steel deck 20 is negligibly small, the flaw detection device 100 may omit the electromagnetic wave transmitting / receiving unit 250, the distance calculation unit 264, and the correction unit 266.

[0129] Furthermore, in the above embodiment, an example was given in which the function generator 212 generates a first frequency AC signal and a second frequency AC signal at different timings. However, the function generator 212 may also generate the first frequency AC signal and the second frequency AC signal in parallel as a composite wave.

[0130] Furthermore, in the above embodiment, the case in which the detection unit 230 is configured as a lock-in amplifier was given as an example. However, the detection unit 230 is not limited in its configuration as long as it can detect the first high-frequency detection signal, the second high-frequency detection signal, the third high-frequency detection signal, the fourth high-frequency detection signal, the first low-frequency detection signal, the second low-frequency detection signal, the third low-frequency detection signal, and the fourth low-frequency detection signal. For example, the detection unit 230 may analytically calculate the signal strength of the first frequency and the signal strength of the second frequency from the reference signal and the input value (AC voltage) of the detection coil (digital lock-in). Alternatively, the detection unit 230 may analyze the first frequency and the second frequency from the reference signal and extract the detection signals of the first frequency and the second frequency by performing a Fourier transform on the input value (AC voltage) of the detection coil (digital lock-in). Alternatively, the detection unit 230 may adjust the phase and intensity of the reference signal to match the input value (AC voltage) of the detection coil, and then use the phase intensity as the signal intensity (digital lock-in).

[0131] Furthermore, in the above embodiment, the control unit 200 was given as an example in which it is installed on the vehicle 110. However, the control unit 200 may be installed in a location separated from the vehicle 110.

[0132] This disclosure can contribute, for example, to Sustainable Development Goal (SDG) 12, "Ensure sustainable consumption and production patterns." [Explanation of symbols]

[0133] 100 Flaw detection equipment 132 Excitation Coil 210 Excitation section 230 Detection unit 250 Electromagnetic wave transmitting and receiving unit 264 Distance Calculation Unit 266 Correction section 268 Depth Estimation Unit

Claims

1. A first excitation coil, A second excitation coil having a winding direction opposite to that of the first excitation coil and connected in series with the first excitation coil, First detection coil and A second detection coil having a winding direction opposite to that of the first detection coil, A third detection coil having a winding direction opposite to that of the second detection coil and connected in series with the second detection coil, A fourth detection coil having a winding direction opposite to that of the first detection coil and connected in series with the first detection coil, A first cancellation coil provided vertically above or vertically below the first detection coil, A second cancellation coil is provided vertically above or vertically below the second detection coil, An excitation unit that applies a first alternating current of a first frequency and a second alternating current of a second frequency lower than the first frequency to the first and second excitation coils to generate an induced current in the steel deck by electromagnetic induction, and applies a third alternating current of a first frequency and a fourth alternating current of a second frequency to the first and second cancellation coils to generate a magnetic field in the opposite direction to the magnetic field generated by the first and second excitation coils, A detection unit that detects a high-frequency detection signal based on the induced current corresponding to the first AC current and a low-frequency detection signal based on the induced current corresponding to the second AC current through the first detection coil, the second detection coil, the third detection coil, and the fourth detection coil, A difference calculation unit that calculates the difference between the high-frequency detection signal and the low-frequency detection signal, A depth estimation unit estimates the depth of a defect formed in the steel deck based on the difference calculated by the difference calculation unit, Equipped with, The excitation unit generates the first AC current by amplifying the third AC current and applies it to the first and second excitation coils, and generates the second AC current by amplifying the fourth AC current and applies it to the first and second excitation coils. The detection unit is The first high-frequency detection signal and the first low-frequency detection signal are detected through the first detection coil. The second high-frequency detection signal and the second low-frequency detection signal are detected through the second detection coil. The third high-frequency detection signal and the third low-frequency detection signal are detected through the third detection coil. The fourth high-frequency detection signal and the fourth low-frequency detection signal are detected through the fourth detection coil. The difference calculation unit, The difference DaH between the first high-frequency detection signal and the fourth high-frequency detection signal, and the difference DcH between the second high-frequency detection signal and the third high-frequency detection signal, are calculated. The difference DaL between the first low-frequency detection signal and the fourth low-frequency detection signal, and the difference DcL between the second low-frequency detection signal and the third low-frequency detection signal, are calculated. The depth estimation unit, A flaw detection device that estimates the depth of a defect formed in the steel deck based on the difference DcH and the difference DcL.

2. An electromagnetic wave transmitting and receiving unit comprising a transmitting unit that transmits electromagnetic waves and a receiving unit that receives reflected waves based on the transmitted electromagnetic waves, A distance calculation unit that calculates the distance between the steel deck and the reflected wave, A correction unit corrects the difference calculated by the difference calculation unit based on the calculated distance, Equipped with, The flaw detection apparatus according to claim 1, wherein the depth estimation unit estimates the depth of a defect formed in the steel deck based on the difference corrected by the correction unit.

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