Flaw detection device

Abstract

To detect a flaw in a steel plate deck from a pavement body side.SOLUTION: A flaw detection device comprises: a first excitation coil 132a; a second excitation coil 132b that has a winding direction opposite to the first excitation coil; an excitation unit that applies AC current to the first excitation coil and second excitation coil to generate induction current in a steel plate deck through electromagnetic induction; a first detection coil 134a; a second detection coil 134b that has a winding direction opposite to the first detection coil; a detection unit that detects a detection signal based on the induction current through the first detection coil and second detection coil; an electromagnetic wave transmission and reception unit that transmits an electromagnetic wave and receives a reflected wave based on the transmitted electromagnetic wave; a distance calculation unit that calculates the distance from the steel plate deck on the basis of the reflected wave; a difference calculation unit that calculates the difference between a first detection signal detected through the first detection coil and a second detection signal detected through the second detection coil; and a comparison unit that compares the difference with a threshold according to the distance calculated by the distance calculation unit.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a flaw detection device.

Background Art

[0002] Roads such as highways and bridges are composed of a steel floor slab and a pavement such as asphalt laminated on the upper surface of the steel floor slab. The steel floor slab may be damaged, such as cracked, due to aging fatigue caused by vehicles passing over the pavement.

[0003] Therefore, as a technique for inspecting the damage of the steel floor slab, an ultrasonic flaw detection method is used (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the ultrasonic flaw detection method described in Patent Document 1 above, the probe must be brought into contact with the steel floor slab side, that is, directly below the road. For this reason, it is necessary to construct a scaffold or the like under the road, and there is a problem that the cost required for damage inspection becomes extremely large.

[0006] In view of such problems, an object of the present disclosure is to provide a flaw detection device capable of detecting damage to a steel floor slab from the pavement side.

Means for Solving the Problems

[0007] To solve the above problems, a flaw detection device according to one aspect of the present disclosure includes a first excitation coil, a second excitation coil that is juxtaposed in a substantially horizontal direction of the first excitation coil, has a central axis substantially parallel to the central axis of the first excitation coil, has a winding direction opposite to that of the first excitation coil, and is connected in series to the first excitation coil, an excitation unit that applies an alternating current to the first excitation coil and the second excitation coil to generate an induced current in a steel floor slab by electromagnetic induction, a first detection coil that is separated in the direction of the central axis of the first excitation coil and superimposed on the first excitation coil, and has a central axis substantially parallel to the central axis of the first excitation coil, a second detection coil that is juxtaposed in a substantially horizontal direction of the first detection coil, is separated in the direction of the central axis of the second excitation coil and superimposed on the second excitation coil, has a central axis substantially parallel to the central axis of the second excitation coil, and has a winding direction opposite to that of the first detection coil, a detection unit that detects a detection signal based on the induced current through the first detection coil and the second detection coil, an electromagnetic wave transmission and reception unit that includes a transmission unit that transmits an electromagnetic wave and a reception unit that receives a reflected wave based on the transmitted electromagnetic wave, a distance calculation unit that calculates a distance to the steel floor slab based on the reflected wave, a difference calculation unit that calculates a difference between a first detection signal detected through the first detection coil and a second detection signal detected through the second detection coil, and a comparison unit that compares a threshold value corresponding to the distance calculated by the distance calculation unit with the difference.

[0008] Further, the flaw detection device may include a first canceling coil that is separated in the direction of the central axis of the first detection coil and superimposed on the first detection coil, and generates a magnetic field in a direction opposite to the magnetic field formed by the first excitation coil, and a second canceling coil that is separated in the direction of the central axis of the second detection coil and superimposed on the second detection coil, and generates a magnetic field in a direction opposite to the magnetic field formed by the second excitation coil.

[0009] Further, the flaw detection device is provided between the first detection coil and the second detection coil, has a central axis substantially parallel to the central axis of the second detection coil, and has a winding direction opposite to that of the second detection coil. A third detection coil, and a fourth detection coil provided between the first detection coil and the second detection coil, having a central axis substantially parallel to the central axis of the first detection coil and having a winding direction opposite to that of the first detection coil. The difference calculation unit may calculate the difference between the difference between the third detection signal detected through the third detection coil and the second detection signal and the difference between the fourth detection signal detected through the fourth detection coil and the first detection signal.

Advantages of the Invention

[0010] According to the present disclosure, it becomes possible to detect a flaw in the steel floor slab from the paving body side.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 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 this specification and the drawings, elements having substantially the same function and configuration are denoted by the same reference numerals to omit redundant description, and elements not directly related to the present disclosure are not shown.

[0013] FIG. 1 is a diagram for explaining a road 10 that is a flaw detection target of a flaw detection device 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.

[0014] As shown in FIG. 1, the road 10 is composed of a steel floor slab 20 and a pavement 30. The steel floor slab 20 is a floor slab composed of steel members. The steel floor slab 20 supports the vertical load from the vehicle. The steel floor slab 20 includes a deck plate 40, a main girder web 42, a vertical stiffener 44, a transverse rib 46, and a U-rib 48.

[0015] The deck plate 40 is a steel plate extending in a substantially horizontal direction. The main girder web 42 is a steel plate standing vertically downward from the deck plate 40 and extending in the extending direction of the road 10. The vertical stiffener 44 is a steel plate provided on the main girder web 42. The upper surface of the vertical stiffener 44 is welded to the deck plate 40. The transverse rib 46 is a steel plate standing vertically downward from the deck plate 40 and extending in the width direction of the road 10. The transverse rib 46 is connected to the main girder web 42. The U-rib 48 is a steel plate having a U-shaped vertical cross section. The U-rib 48 is welded to the deck plate 40 so as to extend in the extending direction (road length direction) of the road 10.

[0016] The paving body 30 is laminated on the deck plate 40. The paving body 30 is composed of asphalt or the like.

[0017] Due to the aging fatigue caused by the vehicle passing over the paving body 30, cracks or other damages may occur at the welded parts between the deck plate 40 and the U-rib 48, and the welded parts between the deck plate 40 and the vertical stiffener 44 in the steel floor slab 20. The crack progresses from the welded part towards the deck plate 40.

[0018] Therefore, the flaw detector 100 shown in FIG. 2 below inspects the presence or absence of damages in the steel floor slab 20 from above the paving body 30. In this embodiment, the flaw detector 100 inspects the presence or absence of damages while scanning the road 10 in the passing direction of the vehicle (in the Y-axis direction in FIG. 1, the extending direction of the road 10, that is, the extending direction of the U-rib 48).

[0019] [Flaw Detector 100] FIG. 2 is a view of the vehicle 110 constituting the flaw detector 100 according to this embodiment as seen from directly below in the vertical direction.

[0020] As shown in FIG. 2, the flaw detector 100 includes a vehicle 110, an antenna 120, a probe 130, an encoder 140, a marking mechanism 150, and a control unit 200.

[0021] When inspecting the presence or absence of damages in the steel floor slab 20, the vehicle 110 travels (moves) on the paving body 30. An antenna 120, a probe 130, an encoder 140, and a marking mechanism 150 are integrally fixed to the lower surface 112 of the vehicle 110. In this embodiment, the antenna 120, the probe 130, the encoder 140, and the marking mechanism 150 are provided in this order from the front side in the traveling direction of the vehicle. A control unit 200 is provided inside the vehicle 110.

[0022] Antenna 120 transmits electromagnetic waves based on the current applied from the electromagnetic wave transmitting and receiving unit 250 described later, or receives reflected waves based on the transmitted electromagnetic waves. The electromagnetic waves penetrate the pavement 30 (for example, asphalt). Therefore, the electromagnetic waves are reflected by the steel floor slab 20. Antenna 120 is, for example, a Vivaldi antenna, a quad-ridge horn antenna, or a bowtie antenna.

[0023] Probe 130 is a probe for electromagnetic induction flaw detection (EMIT). Electromagnetic induction flaw detection is a flaw detection method also called eddy current flaw detection.

[0024] FIG. 3 is a first diagram for explaining electromagnetic induction flaw detection. FIG. 4 is a second diagram for explaining electromagnetic induction flaw detection. In FIGS. 3 and 4, the case where excitation and detection are performed with the same coil C is taken as an example.

[0025] As shown in FIG. 3, when an alternating current is applied to coil C, an alternating magnetic field is generated (excitation). Then, by electromagnetic induction, an induced current (eddy current U) is generated in the steel floor slab 20 in a direction that cancels out the alternating magnetic field.

[0026] As shown in FIG. 4, at a damaged location on the steel floor slab 20, the eddy current U is blocked by the damage. Then, at the damaged location, a disturbance occurs in the eddy current U compared to the undamaged location.

[0027] Therefore, in electromagnetic induction flaw detection, the presence or absence of damage is detected by detecting the change amount of the eddy current U obtained through coil C as a change in impedance.

[0028] FIG. 5 is a top view of probe 130 according to the present embodiment. FIG. 6 is a first side view of probe 130 according to the present embodiment. FIG. 7 is a second side view of probe 130 according to the present embodiment.

[0029] As shown in FIGS. 5 to 7, the probe 130 includes a first excitation coil 132a, a second excitation coil 132b, 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.

[0030] The first excitation coil 132a and the second excitation coil 132b are juxtaposed adjacent to each other in a substantially horizontal direction (the Y-axis direction in FIGS. 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 FIG. 5, when 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 to the first excitation coil 132a.

[0031] The first excitation coil 132a and the second excitation coil 132b are installed on the paving body 30 such that the central axis is substantially parallel to the orthogonal direction (the Z-axis direction in FIGS. 5 to 7) of the surface of the paving body 30 laminated on the steel floor slab 20.

[0032] The first detection coil 134a is superimposed on the first excitation coil 132a at a distance in the direction of the central axis of the first excitation coil 132a (the Z-axis direction in FIGS. 5 to 7). The first detection coil 134a has a central axis substantially parallel to the central axis of the first excitation coil 132a.

[0033] The second detection coil 134b is juxtaposed in a substantially horizontal direction (the Y-axis direction in FIGS. 5 to 7) with respect to the first detection coil 134a. The second detection coil 134b is superimposed on the second excitation coil 132b at a distance in the direction of the central axis of the second excitation coil 132b (the Z-axis direction in FIGS. 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 FIG. 5, when 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 the present embodiment, the third detection coil 134c is provided in the same plane (XY plane in FIGS. 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 FIG. 5, when 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 spaced apart from the third detection coil 134c in the direction of the central axis of the third detection coil 134c (Z-axis direction in FIGS. 5 to 7) and is superimposed on the third detection coil 134c. The fourth detection coil 134d has a central axis substantially 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 FIG. 5, when the winding direction of the first detection coil 134a is clockwise, the winding direction of the fourth detection coil 134d is counterclockwise.

[0037] That is, the winding directions of the first detection coil 134a and the third detection coil 134c are the same. The winding directions of the second detection coil 134b and the fourth detection coil 134d are the same. The winding directions of the first detection coil 134a and the third detection coil 134c are opposite to the winding directions 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. Also, the second detection coil 134b and the third detection coil 134c are directly connected.

[0039] The first cancellation coil 136a is superimposed on the first detection coil 134a at a distance in the direction of the central axis of the first detection coil 134a. The first cancellation coil 136a generates a magnetic field in a direction opposite to the magnetic field formed by the first excitation coil 132a.

[0040] As will be described in detail later, a first detection signal based on an induced current is detected through the first detection coil 134a. However, in addition to the voltage based on the induced current, a voltage based on the first excitation coil 132a is directly applied to the first detection coil 134a. Therefore, the first cancellation coil 136a that generates a magnetic field in a direction opposite to the magnetic field formed by the first excitation coil 132a is superimposed on the first detection coil 134a. Thereby, the first cancellation coil 136a can cancel the voltage directly applied from the first excitation coil 132a to the first detection coil 134a. Therefore, the voltage based on the first excitation coil 132a is applied to the first detection coil 134a after being reduced. For this reason, the first detection coil 134a can accurately acquire the voltage based on the induced current.

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

[0042] As will be described in detail later, a second detection signal based on an induced current is detected through the second detection coil 134b. However, in addition to the voltage based on the induced current, a voltage based on the second excitation coil 132b is directly applied to the second detection coil 134b. Therefore, a second canceling coil 136b that generates a magnetic field in the direction opposite 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 the voltage directly applied from the second excitation coil 132b to the second detection coil 134b. Therefore, the voltage based on the second excitation coil 132b is applied to the second detection coil 134b after being reduced. For this reason, the second detection coil 134b can accurately acquire the voltage based on the induced current.

[0043] The first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first canceling coil 136a, and the second canceling coil 136b are installed on the paving body 30 so that the orthogonal direction (Z-axis direction in FIGS. 5 to 7) of the surface of the paving body 30 laminated on the steel floor slab 20 is substantially parallel to the central axis.

[0044] Returning to FIG. 2 and explaining, the encoder 140 acquires path information indicating the distance of the path along which the probe 130 has moved. The path information acquired by the encoder 140 is output to the control unit 200.

[0045] The marking mechanism 150 attaches an index (mark) to the paving body 30 in response to a control command from the control unit 200. The marking mechanism 150 includes, for example, chalk and an actuator that drives the chalk.

[0046] FIG. 8 is a functional block diagram of the flaw detector 100 according to the present embodiment. As shown in FIG. 8, the control unit 200 includes an excitation unit 210, a detection unit 230, an A / D converter 240, an electromagnetic wave transmission / reception unit 250, a central control unit 260, a memory 270, and a display device 280.

[0047] The exciting unit 210 applies an alternating current to the first exciting coil 132a and the second exciting coil 132b, and generates an induced current in the steel floor plate 20 by electromagnetic induction. In the present embodiment, the exciting unit 210 includes a function generator 212 and an amplifier 214.

[0048] The function generator 212 (indicated by "F / G" in Fig. 8) generates an alternating signal of a predetermined frequency. The alternating signal by the function generator 212 is output to the amplifier 214 and the detection unit 230. Further, an alternating current based on the alternating signal by the function generator 212 is applied to the first canceling coil 136a and the second canceling coil 136b.

[0049] The amplifier 214 (indicated by "B / P" in Fig. 8) amplifies the alternating signal by the function generator 212 and applies an alternating current to the first exciting coil 132a and the second exciting coil 132b. Then, an induced current is generated in the steel floor plate 20 by electromagnetic induction. As described above, since the winding direction of the first exciting coil 132a and the winding direction of the second exciting coil 132b are opposite, currents are applied in the same direction in the proximity portions of the first exciting coil 132a and the second exciting coil 132b. The amplifier 214 is, for example, a bipolar power supply.

[0050] The detection unit 230 is composed of, for example, a lock-in amplifier (indicated by "L / I" in Fig. 8). The detection unit 230 extracts a frequency component (detection signal based on the induced current) of the current applied to the first exciting coil 132a and the second exciting coil 132b from the alternating voltage detected by the first detection coil 134a based on the alternating signal (reference signal) output from the function generator 212. Hereinafter, the detection signal detected through the first detection coil 134a is referred to as the first detection signal.

[0051] Similarly, the detection unit 230 extracts, based on the reference signal, the frequency components of the current applied to the first excitation coil 132a and the second excitation coil 132b (detection signals based on the induced current) from the AC voltage of the second detection coil 134b. Hereinafter, the detection signal detected through the second detection coil 134b is referred to as the second detection signal.

[0052] Also, the detection unit 230 extracts, based on the reference signal, the frequency components of the current applied to the first excitation coil 132a and the second excitation coil 132b (detection signals based on the induced current) from the AC voltage of the third detection coil 134c. Hereinafter, the detection signal detected through the third detection coil 134c is referred to as the third detection signal.

[0053] Also, the detection unit 230 extracts, based on the reference signal, the frequency components of the current applied to the first excitation coil 132a and the second excitation coil 132b (detection signals based on the induced current) from the AC voltage of the fourth detection coil 134d. Hereinafter, the detection signal detected through the fourth detection coil 134d is referred to as the fourth detection signal.

[0054] The A / D converter 240 (denoted as "A / D" in FIG. 8) converts the output value (analog signal) of the detection unit 230 into a digital signal.

[0055] The electromagnetic wave transmission / reception unit 250 is constituted by, for example, a frequency analysis device (denoted as "N / A" in FIG. 8). The electromagnetic wave transmission / reception unit 250 functions as a transmission unit that applies a current to the antenna 120 and transmits electromagnetic waves to the surface of the pavement 30 through the antenna 120. Also, the electromagnetic wave transmission / reception unit 250 functions as a reception unit that receives the reflected wave (reflected electromagnetic wave) reflected by the steel floor slab 20 through the antenna 120. Then, the electromagnetic wave transmission / reception unit 250 analyzes the signal based on the reflected wave and calculates the frequency components (spectrum) of the reflected wave.

[0056] The central control unit 260 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 260 reads out programs, parameters, etc. for operating the CPU from the ROM. The central control unit 260 manages and controls the entire flaw detection device 100 in cooperation with a RAM as a work area and other electronic circuits.

[0057] The memory 270 is composed of a ROM, a RAM, a flash memory, an HDD, etc. The memory 270 stores programs and various data used by the central control unit 260. In the present embodiment, the memory 270 stores a calibration curve described later.

[0058] The display device 280 is composed of a liquid crystal display, an organic EL (Electro Luminescence) display, etc.

[0059] The detection signal based on the induced current obtained by the detection unit 230 includes a flaw signal (alternating magnetic field change) S based on a flaw F and a lift-off signal S based on the distance between the probe 130 and the steel floor plate 20 L and includes.

[0060] The flaw 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 flaw signal. i represents a complex constant. ω represents a frequency. t represents time. In the above formula (2), A L represents the amplitude of the lift-off signal. i represents a complex constant. φ represents an initial phase.

[0061] When the flaw detection device 100 scans the road 10 (the vehicle 110 moves on the road 10), one or more wheels 114 constituting the vehicle 110 may get stuck in a recess such as a rut formed in the pavement 30 or ride over a protrusion formed in the pavement 30, causing the distance between the lower surface 112 of the vehicle 110 and the surface of the pavement 30, that is, the distance between the probe 130 and the surface of the pavement 30 to vary. 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 varies, and the distance between the probe 130 and the steel floor slab 20 also varies. Further, when the thickness of the pavement 30 varies due to wear of the pavement 30 caused by the running of the vehicle or an increase in the thickness of the pavement 30 due to repair of the pavement 30, even if the distance between the surface of the pavement 30 and the probe 130 is constant, the distance between the probe 130 and the steel floor slab 20 varies.

[0062] Flaw signal S F is detected with a phase different from that of the lift-off signal S L However, as the distance between the probe 130 and the steel floor slab 20 increases, the amplitude A F of the flaw signal decreases, and it becomes impossible to identify the flaw signal S F from the detection signal.

[0063] Therefore, the flaw detection device 100 according to the present embodiment includes four detection coils (first detection coil 134a, second detection coil 134b, third detection coil 134c, fourth detection coil 134d), and uses each detection signal to remove the lift-off signal.

[0064] In the present embodiment, the central control unit 260 functions as a differential calculation unit 262, a distance calculation unit 264, a comparison unit 266, and a signal storage unit 268.

[0065] The differential calculation unit 262 calculates a difference Dc (=|Da - Db|) between a difference Da between the first detection signal and the fourth detection signal and a difference Db between the second detection signal and the third detection signal.

[0066] As described above, the winding directions of the first detection coil 134a and the fourth detection coil 134d are opposite. Therefore, the same lift-off signal is included in the first detection signal and the fourth detection signal in opposite directions. For this reason, when the difference Da between the first detection signal and the fourth detection signal is calculated, the lift-off signal is canceled out, and it becomes possible to extract a signal (defect signal) other than the lift-off signal.

[0067] Similarly, the winding directions of the second detection coil 134b and the third detection coil 134c are opposite. Therefore, the same lift-off signal is included in the second detection signal and the third detection signal in opposite directions. For this reason, when the difference Db between the second detection signal and the third detection signal is calculated, the lift-off signal is canceled out, and it becomes possible to extract a signal (defect signal) other than the lift-off signal.

[0068] The distance calculation unit 264 calculates the distance between the probe 130 and the steel floor slab 20 based on the time of the peak in the spectrum calculated by the electromagnetic wave transmission / reception unit 250.

[0069] The comparison unit 266 refers to the calibration curve stored in the memory 270 and determines a threshold value from the distance between the probe 130 and the steel floor slab 20 calculated by the distance calculation unit 264.

[0070] FIG. 9 is a diagram for explaining the calibration curve 300. As shown in FIG. 9, the calibration curve 300 is a curve in which the signal intensity (amplitude) determined as a defect and the distance (lift-off) [mm] between the probe 130 and the steel floor slab 20 are associated. The calibration curve 300 is created in advance by detecting a test piece having a predetermined defect with the flaw detector 100. As shown in FIG. 9, in the calibration curve 300, the signal intensity decreases as the distance between the probe 130 and the steel floor slab 20 increases.

[0071] The comparison unit 266 refers to the calibration curve 300 and determines a threshold value from the distance between the probe 130 and the steel floor slab 20 calculated by the distance calculation unit 264. For example, when the distance between the probe 130 and the steel floor slab 20 is 80 mm, the threshold value is determined to be 0.36. Also, when the distance between the probe 130 and the steel floor slab 20 is 50 mm, the threshold value is determined to be 17.3.

[0072] Then, the comparison unit 266 compares the determined threshold value with the difference Dc calculated by the difference calculation unit 262. As a result, if it is determined that the difference Dc is equal to or greater than the threshold value, the comparison unit 266 determines that there is a defect. Then, the comparison unit 266 drives the marking mechanism 150 to mark the pavement 30.

[0073] On the other hand, if it is determined that the difference Dc is less than the threshold value, the comparison unit 266 determines that there is no defect.

[0074] The signal storage unit 268 associates the first detection signal, the second detection signal, the third detection signal, the fourth detection signal, and the distance between the probe 130 and the steel floor slab 20 with the path information acquired by the encoder 140 and stores them in the memory 270.

[0075] [Flaw detection method] Subsequently, a flaw detection method for detecting flaws in the road 10 using the flaw detection device 100 will be described. FIG. 10 is a flowchart showing the processing flow of the flaw detection method according to the present embodiment. As shown in FIG. 10, the flaw detection method according to the present embodiment includes an end determination step S110, a signal acquisition step S120, a difference calculation step S130, a distance calculation step S140, a threshold determination step S150, a comparison step S160, a marking step S170, a storage step S180, and a movement step S190. Each step will be described below.

[0076] [End determination step S110] The central control unit 260 determines whether the scanning of a predetermined flaw detection range has been completed. As a result, if it is determined that the scanning of the flaw detection range has not been completed (NO in S110), the central control unit 260 transfers the process to the signal acquisition step S120. On the other hand, if it is determined that the scanning of the flaw detection range has been completed (YES in S110), the central control unit 260 ends the flaw detection method.

[0077] [Signal acquisition step S120] The excitation unit 210 applies an alternating current to the first excitation coil 132a and the second excitation coil 132b. The detection unit 230 acquires the first detection signal, the second detection signal, the third detection signal, and the fourth detection signal, and the A / D converter 240 converts these detection signals into digital signals.

[0078] The electromagnetic wave transmission / reception unit 250 applies a current to the antenna 120 and transmits electromagnetic waves to the surface of the pavement 30 through the antenna 120. Then, the electromagnetic wave transmission / reception unit 250 receives the reflected wave reflected by the steel floor slab 20 through the antenna 120. The electromagnetic wave transmission / reception unit 250 analyzes the signal based on the reflected wave and calculates the spectrum.

[0079] Also, the encoder 140 acquires path information and outputs it to the control unit 200.

[0080] [Difference calculation step S130] The difference calculation unit 262 calculates the difference Dc (=|Da - Db|) between the difference Da between the first detection signal and the fourth detection signal and the difference Db between the second detection signal and the third detection signal based on the first detection signal, the second detection signal, the third detection signal, and the fourth detection signal acquired in the signal acquisition step S120.

[0081] [Distance calculation step S140] The distance calculation unit 264 calculates the distance between the probe 130 and the steel floor slab 20 based on the spectrum acquired in the signal acquisition step S120.

[0082] [Threshold determination step S150] The comparison unit 266 refers to the calibration curve 300 stored in the memory 270, and determines a threshold value from the distance between the probe 130 and the steel floor slab 20 calculated in the distance calculation step S140.

[0083] [Comparison step S160] The comparison unit 266 determines whether the difference Dc calculated in the difference calculation step S130 is equal to or greater than the threshold value determined in the threshold value determination step S150. As a result, if it is determined that the difference Dc is equal to or greater than the threshold value (YES in S160), the comparison unit 266 transfers the process to the marking step S170. On the other hand, if the difference Dc is not equal to or greater than the threshold value (NO in S160), that is, if it is determined that the difference Dc is less than the threshold value, the comparison unit 266 transfers the process to the storage step S180.

[0084] [Marking step S170] The comparison unit 266 drives the marking mechanism 150 to mark the pavement 30.

[0085] [Storage step S180] The signal storage unit 268 associates the first detection signal, the second detection signal, the third detection signal, the fourth detection signal, and the distance between the probe 130 and the steel floor slab 20 with the path information acquired by the encoder 140, and stores them in the memory 270.

[0086] [Movement step S190] The vehicle 110 constituting the flaw detector 100 moves from the first position where the signal acquisition step S120 was executed to the second position within a predetermined time. The second position is a position where the position in the moving direction of the vehicle 110 (the Y-axis direction in FIG. 2) is different from the first position.

[0087] As described above, the flaw detector 100 according to the present embodiment includes the antenna 120, the probe 130, and the control unit 200. Therefore, the flaw detector 100 according to the present embodiment can detect the flaw of the steel floor slab 20 from the pavement 30 side.

[0088] Further, as described above, the flaw detection device 100 according to the present embodiment includes a first detection coil 134a, a fourth detection coil 134d, and a differential calculation unit 262. The first detection coil 134a and the fourth detection coil 134d have opposite winding directions. Thereby, a signal with reduced environmental noise such as the distance between the probe 130 and the steel floor slab 20 can be obtained from the difference Da between the first detection signal and the fourth detection signal calculated by the differential calculation unit 262.

[0089] Similarly, the flaw detection device 100 according to the present embodiment includes a second detection coil 134b, a third detection coil 134c, and a differential calculation unit 262. The second detection coil 134b and the third detection coil 134c have opposite winding directions. Thereby, a signal with reduced environmental noise such as the distance between the probe 130 and the steel floor slab 20 can be obtained from the difference Db between the second detection signal and the third detection signal calculated by the differential calculation unit 262.

[0090] Furthermore, as described above, the differential calculation unit 262 calculates the difference Dc between the difference Da and the difference Db. Thereby, the differential calculation unit 262 can obtain a signal with further reduced environmental noise such as the distance between the probe 130 and the steel floor slab 20.

[0091] In this way, since the flaw detection device 100 according to the present embodiment can obtain a signal with reduced environmental noise such as the distance between the probe 130 and the steel floor slab 20, it is possible to detect a flaw without removing the pavement 30.

[0092] Further, as described above, the flaw detection device 100 according to the present embodiment includes a first canceling coil 136a. Thereby, the first detection coil 134a can be placed in a zero magnetic field environment. Therefore, it is possible to reduce the influence of the magnetic field by the first excitation coil 132a on the first detection coil 134a.

[0093] Similarly, the flaw detection device 100 according to the present embodiment includes a second cancellation coil 136b. Thereby, the second detection coil 134b can be placed in a zero magnetic field environment. Therefore, it is possible to reduce the influence of the magnetic field by the second excitation coil 132b on the second detection coil 134b.

[0094] Note that the fourth detection coil 134d is superimposed on the third detection coil 134c and has the opposite winding direction. For this reason, 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 fields by the first excitation coil 132a and the second excitation coil 132b on the third detection coil 134c and the fourth detection coil 134d.

[0095] Also, as described above, the comparison unit 266 compares the threshold value corresponding to the distance between the probe 130 and the steel floor plate 20 with the difference Dc. Thereby, the comparison unit 266 can detect flaws with high accuracy.

[0096] Also, as described above, the flaw detection device 100 according to the present embodiment includes a marking mechanism 150. Thereby, it becomes possible for the user to visually recognize the position of the flaw.

[0097] Also, as described above, the flaw detection method using the flaw detection device 100 repeats from the end determination step S110 to the movement step S190. That is, the flaw detection device 100 detects the presence or absence of flaws in a time-division manner according to the running of the vehicle 110. Thereby, the flaw detection device 100 can comprehensively detect all regions on the road 10 where the vehicle 110 has traveled.

[0098] As described above, the embodiments have been described with reference to the accompanying drawings. Needless to say, the present disclosure is not limited to the above embodiments. It is obvious that those skilled in the art can conceive of various modification examples or correction examples within the scope described in the claims, and it is naturally understood that those also belong to the technical scope of the present disclosure.

[0099] For example, in the above-described embodiment, the case where the probe 130 includes one each of the first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first cancellation coil 136a, and the second cancellation coil 136b was taken as an example. However, the probe 430 may include a plurality of these.

[0100] FIG. 11 is a diagram for explaining the probe 430 according to a modified example. As shown in FIG. 11, the probe 430 includes a first excitation coil 132a, a second excitation coil 132b, and a plurality of coil units 440.

[0101] The coil unit 440 includes the first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first cancellation coil 136a, and the second cancellation coil 136b. The positional relationship among the first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first cancellation coil 136a, and the second cancellation coil 136b in the coil unit 440 is substantially the same as the positional relationship in the above-described embodiment.

[0102] The coil units 440 are provided in parallel in the X-axis direction in FIG. 11. That is, the coil units 440 are provided in a direction orthogonal to the road length direction (Y-axis direction in FIG. 11).

[0103] When including one each of the first detection coil 134a, the second detection coil 134b, the third detection coil 134c, the fourth detection coil 134d, the first cancellation coil 136a, and the second cancellation coil 136b having a length in the X-axis direction corresponding to a plurality of coil units 440, an average AC voltage with respect to the coil area can be obtained, and the detection limit for damage will decrease.

[0104] Therefore, by providing the probe 430 with a plurality of coil units 440, it becomes possible to improve the detection limit for damage.

[0105] Also, in the above embodiment, the case where the first canceling coil 136a is provided vertically above the first detection coil 134a was taken as an example. However, the first canceling coil 136a may be provided in the vertical direction of the first detection coil 134a. Therefore, the first canceling coil 136a may be provided vertically below the first detection coil 134a.

[0106] Similarly, the case where the second canceling coil 136b is provided vertically above the second detection coil 134b was taken as an example. However, the second canceling coil 136b may be provided in the vertical direction of the second detection coil 134b. Therefore, the second canceling coil 136b may be provided vertically below the second detection coil 134b.

[0107] Also, in the above embodiment, the case where the flaw detection device 100 includes the first canceling coil 136a and the second canceling coil 136b was taken as an example. However, the flaw detection device 100 may not include the first canceling coil 136a and the second canceling coil 136b.

[0108] Also, in the above embodiment, the case where the flaw detection device 100 includes the third detection coil 134c and the fourth detection coil 134d was taken as an example. However, the flaw detection device 100 may not include the third detection coil 134c and the 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 comparison unit 266 compares the difference between the first detection signal and the second detection signal with a threshold value. Also, in this case, instead of the first detection coil 134a and the second detection coil 134b, a magnetic sensor may be provided.

[0109] Also, in the above embodiment, the case where the control unit 200 is provided in the vehicle 110 was taken as an example. However, the control unit 200 may be provided at a location separated from the vehicle 110.

[0110] The present disclosure can contribute, for example, to Goal 12 of the Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns."

Description of reference numerals

[0111] 100 Flaw detector 132a First excitation coil 132b Second excitation coil 134a First detection coil 134b Second detection coil 134c Third detection coil 134d Fourth detection coil 136a First cancellation coil 136b Second cancellation coil 20 Steel floor slab 210 Excitation unit 230 Detection unit 250 Electromagnetic wave transmission / reception unit 262 Difference calculation unit 264 Distance calculation unit 266 Comparison unit

Claims

1. a first excitation coil, a second excitation coil juxtaposed in a substantially horizontal direction of the first excitation coil, having a central axis substantially parallel to the central axis of the first excitation coil, having a winding direction opposite to that of the first excitation coil, and connected in series with the first excitation coil; an excitation unit that applies an alternating current to the first excitation coil and the second excitation coil to generate an induced current in the steel floor slab by electromagnetic induction; a first detection coil spaced apart in the direction of the central axis of the first excitation coil and superimposed on the first excitation coil, having a central axis substantially parallel to the central axis of the first excitation coil; a second detection coil juxtaposed in a substantially horizontal direction of the first detection coil, spaced apart in the direction of the central axis of the second excitation coil and superimposed on the second excitation coil, having a central axis substantially parallel to the central axis of the second excitation coil, and having a winding direction opposite to that of the first detection coil; a detection unit that detects a detection signal based on the induced current through the first detection coil and the second detection coil; an electromagnetic wave transmitting and receiving unit including a transmitting unit that transmits an electromagnetic wave and a receiving unit that receives a reflected wave based on the transmitted electromagnetic wave; a distance calculation unit that calculates a distance between the steel floor slab based on the reflected wave; a difference calculation unit that calculates a difference between a first detection signal detected through the first detection coil and a second detection signal detected through the second detection coil; a comparison unit that compares a threshold value corresponding to the distance calculated by the distance calculation unit with the difference; a flaw detection device comprising:

2. a first canceling coil spaced apart in the direction of the central axis of the first detection coil and superimposed on the first detection coil, generating a magnetic field in a direction opposite to the magnetic field formed by the first excitation coil; a second canceling coil spaced apart in the direction of the central axis of the second detection coil and superimposed on the second detection coil, generating a magnetic field in a direction opposite to the magnetic field formed by the second excitation coil; The flaw detection device according to claim 1, comprising:

3. a third detection coil provided between the first detection coil and the second detection coil, having a central axis substantially parallel to the central axis of the second detection coil, and having a winding direction opposite to that of the second detection coil; a fourth detection coil provided between the first detection coil and the second detection coil, having a central axis substantially parallel to the central axis of the first detection coil, and having a winding direction opposite to that of the first detection coil; comprising: The difference calculation unit is The flaw detection device according to claim 1 or 2, which calculates a difference between a difference between a third detection signal detected through the third detection coil and the second detection signal and a difference between a fourth detection signal detected through the fourth detection coil and the first detection signal.

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