Non-destructive inspection method and non-destructive inspection device

Abstract

To provide a nondestructive inspection method and a nondestructive inspection device that enable accurate and easy inspection for damaged portions of reinforcing bars or the like provided in a structure.SOLUTION: A nondestructive inspection method is provided which measures the magnetic flux density of an inspection object P buried in a concrete structure C and extending along a first direction, along the first direction of the inspection object P from the outside of the concrete structure C, and which determines damage of the inspection object P on the basis of a change in the magnetic flux density along the first direction of the inspection object P. The magnetic flux density to be measured includes a magnetic flux density in a second direction that is perpendicular to the first direction of the inspection object P, that goes along a surface CF of the concrete structure C or a tangent to the surface CF of the concrete structure C, and that is perpendicular to the first direction of the inspection object P. The magnetic flux density in the second direction is measured at both sides of a reference surface SA that is parallel to the first direction of the inspection object P and perpendicular to the second direction. Damage of the inspection object P is determined on the basis of the measured magnetic flux density in the second direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-destructive inspection method and a non-destructive inspection device. More specifically, it relates to a non-destructive inspection method and a non-destructive inspection device for detecting damages such as breakage and corrosion of reinforcing bars, steel bars, steel wires, etc. provided in a concrete structure using the leakage magnetic flux method.

Background Art

[0002] Conventionally, there is a leakage magnetic flux method as a non-destructive inspection method for detecting damaged parts of reinforcing bars, steel bars, steel wires, etc. (hereinafter referred to as reinforcing bars, etc.) provided in a concrete structure. In this leakage magnetic flux method, a magnet such as a permanent magnet is moved along the surface of the concrete to magnetize the reinforcing bars, etc., and then the magnetic flux density leaking from the surface of the concrete is measured. And based on the measurement result of the magnetic flux density, the presence or absence of damage to the reinforcing bars, etc. is detected. Technologies for detecting damaged parts of reinforcing bars, etc. using this leakage magnetic flux method are disclosed in Patent Documents 1 to 5.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] By using the techniques disclosed in Patent Documents 1 to 5 described above, it is possible to detect damaged parts such as reinforcing bars provided in a concrete structure with a certain degree of accuracy. However, there is a need for a method and apparatus that can perform inspections with higher accuracy and more simply.

[0005] In view of the above circumstances, an object of the present invention is to provide a non-destructive inspection method and a non-destructive inspection apparatus that can accurately and simply inspect damaged parts such as reinforcing bars provided in a structure.

Means for Solving the Problems

[0006] <Non-destructive Inspection Method> The non-destructive inspection method of the first invention measures the magnetic flux density of an inspection object extending in a first direction embedded in a concrete structure outside the concrete structure along the first direction of the inspection object, and determines the damage of the inspection object based on the variation of the magnetic flux density. The magnetic flux density to be measured includes the magnetic flux density in a second direction that is a direction along the surface of the concrete structure or a direction along the tangent to the surface of the concrete structure and is orthogonal to the first direction of the inspection object. The magnetic flux density in the second direction is measured on both sides of a reference plane that is parallel to the first direction of the inspection object and intersects the inspection object and is orthogonal to the second direction, and the damage of the inspection object is determined based on the measured magnetic flux density in the second direction. The non-destructive inspection method of the second invention, in the first invention, measures the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, respectively, and is spaced apart in the first direction of the inspection object and in the first direction of the inspection object. The magnetic flux density in the third direction orthogonal to both the first direction and the second direction of the inspection object is measured at a third measurement position and a fourth measurement position sandwiching the first measurement position and the second measurement position, respectively, at the same timing as the first measurement position and the second measurement position. Calculate a third-direction differential magnetic flux density that is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position measured at the same timing, and during a period in which the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, the absolute value of the third-direction differential magnetic flux density is set to a predetermined value. The two timings are defined as a first timing and a second timing, and it is characterized in that it is determined that a break has occurred in the inspection object when the following conditions (1) and (2) are satisfied. (1) The sign of the first magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction at the first measurement position measured at the first timing and the magnetic flux density in the second direction at the first measurement position measured at the second timing, and the second magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction at the second measurement position measured at the first timing and the magnetic flux density in the second direction at the second measurement position measured at the second timing, is opposite. (2) The absolute values of the first magnetic flux density variation amount and the second magnetic flux density variation amount are equal to or greater than a predetermined value. The non-destructive inspection method of the third invention, in the first invention, measures the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, respectively, and measures the magnetic flux density in the third direction orthogonal to both the first direction and the second direction of the inspection object at the same timing as the first measurement position and the second measurement position at a third measurement position and a fourth measurement position that are separated in the first direction of the inspection object and sandwich the first measurement position and the second measurement position in the first direction of the inspection object, calculates a second-direction differential magnetic flux density that is the difference between the magnetic flux density in the second direction at the first measurement position and the magnetic flux density in the second direction at the second measurement position measured at the same position in the first direction of the inspection object, calculates a third-direction differential magnetic flux density that is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position measured at the same timing, and sets two timings at which the absolute value of the third-direction differential magnetic flux density becomes a predetermined value as a first timing and a second timing during a period in which the absolute value of the third-direction differential magnetic flux density is equal to or greater than the predetermined value, and determines that a break has occurred in the inspection object when the following conditions (3) and (4) are satisfied. (3) The absolute value of the second-direction differential magnetic flux density measured at the first timing and the second timing is equal to or greater than a predetermined value. (4) The signs of the second-direction differential magnetic flux density at the first timing and the second-direction differential magnetic flux density at the second timing are opposite. The non-destructive inspection method of the fourth invention, in the third invention, uses the timing intermediate between the first timing and the second timing as the reference timing, and determines that a break has occurred in the inspection object when the following condition (5) is satisfied in addition to (3) and (4). (5) The absolute value of the second-direction differential magnetic flux density measured at the reference timing is equal to or less than a predetermined value. The non-destructive inspection method of the fifth invention is, in the second, third, or fourth invention, when measuring the magnetic flux density of the inspection object along the first direction of the inspection object, the timing at which the absolute value of the third-direction differential magnetic flux density exceeds a predetermined value from a value smaller than the predetermined value is defined as the first timing, and the timing at which the absolute value of the third-direction differential magnetic flux density falls below the predetermined value from a value larger than the predetermined value after the first timing is defined as the second timing. The non-destructive inspection method of the sixth invention is, in the first invention, measuring the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, calculating a second-direction differential magnetic flux density that is the difference between the magnetic flux density in the second direction at the first measurement position and the magnetic flux density in the second direction at the second measurement position, both measured at the same position in the first direction of the inspection object, and using, as a reference position, a position where the absolute value of the second-direction differential magnetic flux density in the first direction of the inspection object is equal to or less than a predetermined value, and determining that a break has occurred in the inspection object when the following conditions (6) and (7) are satisfied. (6) The absolute value of the second-direction differential magnetic flux density at a first determination position and a second determination position sandwiching the reference position in the first direction of the inspection object is equal to or greater than a predetermined value. (7) The signs of the second-direction differential magnetic flux density at the first determination position and the second-direction differential magnetic flux density at the second determination position are opposite. The non-destructive inspection method of the seventh invention is, in the sixth invention, at third measurement positions and fourth measurement positions that are spaced apart in the first direction of the inspection object and sandwich the first measurement position and the second measurement position in the first direction of the inspection object, the magnetic flux density in a third direction orthogonal to both the first direction and the second direction of the inspection object is measured at the same timing as the first measurement position and the second measurement position, a third-direction differential magnetic flux density, which is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position measured at the same timing, is calculated, and during a period in which the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, the positions in the first direction of the inspection object at the first measurement position or the second measurement position at two timings at which the absolute value of the third-direction differential magnetic flux density becomes the predetermined value are taken as the first determination position and the second determination position. The non-destructive inspection method of the eighth invention is, in any one of the first to seventh inventions, the magnetic flux density in the second direction, the magnetic flux density in the first direction of the inspection object, and / or the magnetic flux density in a third direction orthogonal to both the first direction and the second direction of the inspection object is measured, and based on the variation of the measured value of the magnetic flux density in the second direction depending on the measurement position and the variation of the measured value of the magnetic flux density in the first direction and / or the third direction of the inspection object depending on the measurement position, the damage of the inspection object is determined. The non-destructive inspection method of the ninth invention is, in the eighth invention, the magnetic flux density in the third direction is measured at a plurality of measurement positions arranged along the first direction of the inspection object, and at least two of the plurality of measurement positions are set so as to sandwich a line connecting at least two measurement positions for measuring the magnetic flux density in the second direction on both sides of the reference plane. The non-destructive inspection method of the tenth invention is, in any one of the first to ninth inventions, the magnetic flux density is measured at a plurality of locations on both sides of the reference plane, and based on the magnetic flux density measured at the plurality of locations, a contour diagram of the magnetic flux density on a plane parallel to the surface of the concrete structure or a plane parallel to the tangent plane of the surface of the concrete structure is created, and based on the contour diagram, the damage of the inspection object is determined. The non-destructive inspection method of the 11th invention is characterized in that, in any one of the 1st to 10th inventions, the periodic fluctuation component of the magnetic flux density included in the measured magnetic flux density is removed by a moving average filter. The non-destructive inspection method of the 12th invention is characterized in that, in any one of the 1st to 11th inventions, at each measurement position, an approximate polynomial of the magnetic flux density in the direction along the first direction of the inspection object is created based on the measured magnetic flux density and the measurement position where the magnetic flux density is measured, a corrected magnetic flux density value is calculated by subtracting the value of the approximate polynomial at the same position as the measurement position where the magnetic flux density is measured from the measured value of the measured magnetic flux density, and the damage of the inspection object is judged based on the corrected magnetic flux density value. <Non-destructive inspection device> The non-destructive inspection device of the 13th invention is a non-destructive inspection device that measures the magnetic flux density of an inspection object extending in a first direction embedded in a concrete structure outside the concrete structure along the first direction of the inspection object and judges the damage of the inspection object, and includes a magnetic flux measurement unit having a plurality of magnetic sensors that measure the magnetic flux density, and the plurality of magnetic sensors are arranged such that one measurement axis is parallel to the first arrangement direction and the non-destructive inspection device is moved along the surface of the concrete structure in the first direction of the inspection object with the first array direction being orthogonal to the first direction of the inspection object and the inspection object being positioned between two of the plurality of magnetic sensors of the first magnetic sensor array to measure the magnetic flux density of the inspection object and is characterized by this. The non-destructive inspection device of the 14th invention is, in the 13th invention, the magnetic flux measurement unit has a second magnetic sensor row arranged side by side along a second arrangement direction intersecting the first arrangement direction and arranged so as to sandwich the first magnetic sensor row in the second arrangement direction, and the two magnetic sensors in the second magnetic sensor row have a function of measuring the magnetic flux density in a third direction orthogonal to the first arrangement direction and the second arrangement direction , a control unit having a function of controlling the plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array to measure the magnetic flux density at the same timing, and an analysis function of analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit, and theWhen the analysis function of the control unit moves the non-destructive inspection device along the surface of the concrete structure in the first direction of the inspection target in a state where the first array direction is orthogonal to the first direction of the inspection target and the inspection target is located between two of the plurality of magnetic sensors in the first magnetic sensor array, the magnetic flux density in the second direction parallel to the first array direction is measured by the plurality of magnetic sensors in the first magnetic sensor array, and the magnetic flux density in the third direction orthogonal to the first array direction and the second array direction is measured by two magnetic sensors in the second magnetic sensor array, it calculates a third-direction differential magnetic flux density, which is the difference between the values of the magnetic flux density in the third direction measured at the same timing by the two magnetic sensors in the second magnetic sensor array. During a period in which the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, it sets two timings at which the absolute value of the third-direction differential magnetic flux density becomes the predetermined value as the first timing and the second timing, and determines that a break has occurred in the inspection target when the following conditions (1) and (2) are satisfied. (1) The sign of the first magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing by one of the two magnetic sensors in the first magnetic sensor array that sandwich the inspection target in the first array direction and the magnetic flux density in the second direction measured at the second timing, and the second magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing by the other of the two magnetic sensors and the magnetic flux density in the second direction measured at the second timing, is opposite. (2) The absolute values of the first magnetic flux density variation amount and the second magnetic flux density variation amount are equal to or greater than a predetermined value. The non-destructive inspection device according to the 15th invention has, in the 13th invention, a second magnetic sensor array having two magnetic sensors arranged side by side along a second array direction intersecting the first array direction and arranged so as to sandwich the first magnetic sensor array in the second array direction. The two magnetic sensors in the second magnetic sensor array have a function of measuring the magnetic flux density in a third direction orthogonal to the first array direction and the second array direction. , a control unit having a function of controlling the plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array to measure the magnetic flux density at the same timing, and an analysis function of analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit, and theThe analysis function of the control unit of the control unit is such that when the first array direction is orthogonal to the first direction of the inspection object and the inspection object is located between two of the plurality of magnetic sensors of the first magnetic sensor array, the non-destructive inspection device is moved along the surface of the concrete structure in the first direction of the inspection object, and the magnetic flux density in the second direction parallel to the first array direction is measured by the plurality of magnetic sensors of the first magnetic sensor array, and the magnetic flux density in the third direction orthogonal to the first array direction and the second array direction is measured by two magnetic sensors of the second magnetic sensor array. Then, a second-direction differential magnetic flux density, which is the difference between the magnetic flux density in the second direction measured by one of the two magnetic sensors of the first magnetic sensor array sandwiching the inspection object in the first array direction and measured at the same position in the first direction of the inspection object and the magnetic flux density in the second direction measured by the other of the two magnetic sensors, is calculated. A third-direction differential magnetic flux density, which is the difference between the magnetic flux density in the third direction measured by the two magnetic sensors of the second magnetic sensor array at the same timing, is calculated. During the period when the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, two timings at which the absolute value of the third-direction differential magnetic flux density becomes a predetermined value are defined as the first timing and the second timing. When the following conditions (3) and (4) are satisfied, it is determined that a break has occurred in the inspection object. (3) The absolute value of the second-direction differential magnetic flux density measured at the first timing and the second timing is equal to or greater than a predetermined value. (4) The signs of the second-direction differential magnetic flux density at the first timing and the second-direction differential magnetic flux density at the second timing are opposite. The non-destructive inspection device according to the 16th invention is, in the 15th invention, characterized in that when the timing intermediate between the second timing and the first timing is defined as the reference timing and the following condition (5) is satisfied in addition to (3) and (4), it is determined that a break has occurred in the inspection object. (5) The absolute value of the second-direction differential magnetic flux density measured at the reference timing is equal to or less than a predetermined value. In the non-destructive inspection apparatus of the 17th invention, in the 14th, 15th, or 16th invention, when the non-destructive inspection apparatus is moved in the first direction of the inspection object along the surface of the concrete structure, the analysis function of the control unit sets the timing at which the absolute value of the third-direction differential magnetic flux density exceeds a predetermined value from a value smaller than the predetermined value as the first timing, and sets the timing at which the absolute value of the third-direction differential magnetic flux density falls below the predetermined value from a value larger than the predetermined value after the first timing as the second timing. The non-destructive inspection apparatus of the 18th invention is the 13th invention, and includes a control unit having an analysis function for analyzing the measured value of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is such that the first arrangement direction is orthogonal to the first direction of the inspection object and the inspection object is located between two of the plurality of magnetic sensors of the first magnetic sensor array. When the non-destructive inspection apparatus is moved in the first direction of the inspection object along the surface of the concrete structure and the magnetic flux density in the second direction orthogonal to the first direction of the inspection object and parallel to the first arrangement direction is measured by the plurality of magnetic sensors of the first magnetic sensor array, a second-direction differential magnetic flux density, which is the difference between the magnetic flux density in the second direction measured by one of the two magnetic sensors of the first magnetic sensor array that sandwich the inspection object in the first arrangement direction at the same position in the first direction of the inspection object and the magnetic flux density in the second direction measured by the other of the two magnetic sensors, is calculated. When the position where the absolute value of the second-direction differential magnetic flux density is equal to or less than a predetermined value in the first direction of the inspection object is used as a reference position and the following conditions (6) and (7) are satisfied, it is determined that a break has occurred in the inspection object. It is characterized by this. (6) The absolute value of the second-direction differential magnetic flux density at the first determination position and the second determination position sandwiching the reference position in the first direction of the inspection object is equal to or greater than the predetermined value. (7) The signs of the second-direction differential magnetic flux density at the first determination position and the second-direction differential magnetic flux density at the second determination position are opposite. The non-destructive inspection apparatus of the 19th invention is, in the 18th invention, the analysis function of the control unit is such that the magnetic flux measurement unit has a second magnetic sensor array arranged side by side along a second arrangement direction intersecting the first arrangement direction and arranged so as to sandwich the first magnetic sensor array in the second arrangement direction. The two magnetic sensors of the second magnetic sensor array have a function of measuring the magnetic flux density in a third direction orthogonal to the first arrangement direction and the second arrangement direction. The control unit has a function of controlling so that a plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array measure the magnetic flux density at the same timing. The analysis function of the control unit calculates a third-direction differential magnetic flux density, which is the difference in the magnetic flux density in the third direction measured by the two magnetic sensors of the second magnetic sensor array at the same timing. During a period when the absolute value of the third-direction differential magnetic flux density becomes equal to or greater than a predetermined value, the position of the inspection object in the first direction of one of the two magnetic sensors or the other magnetic sensor of the first magnetic sensor array at two timings when the absolute value of the third-direction differential magnetic flux density becomes equal to the predetermined value is set as the first determination position and the second determination position. The non-destructive inspection apparatus of the 20th invention is, in the 19th invention, the analysis function of the control unit is such that when the non-destructive inspection apparatus is moved in the first direction of the inspection object along the surface of the concrete structure, after detecting that the absolute value of the third-direction differential magnetic flux density has exceeded a predetermined value from a value smaller than the predetermined value, and then detecting that the absolute value of the third-direction differential magnetic flux density has fallen below the predetermined value from a value larger than the predetermined value, it diagnoses the breakage of the inspection object. The non-destructive inspection apparatus of the 21st invention is, in any one of the 13th to 20th inventions, characterized in that the magnetic flux measurement unit has a second magnetic sensor array formed of a plurality of magnetic sensors arranged side by side along a second arrangement direction intersecting the first arrangement direction. The non-destructive inspection apparatus of the 22nd invention is, in any one of the 13th to 21st inventions, characterized in that the plurality of magnetic sensors are sensors having measurement axes in a plurality of directions. The non-destructive inspection device of the 23rd invention, in any one of the 13th to 22nd inventions, the plurality of magnetic sensors are arranged so that six or more are arranged along the direction of at least one measurement axis, and the control unit has an analysis function for analyzing the measured value of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is based on the measured value of the magnetic flux density measured by the plurality of magnetic sensors and the position where the magnetic flux density is measured, and creates a contour diagram of the magnetic flux density on a plane parallel to the surface of the concrete structure or a plane parallel to the tangent plane of the surface of the concrete structure. It is characterized by having a function. The non-destructive inspection device of the 24th invention, in any one of the 13th to 23rd inventions, includes a control unit having an analysis function for analyzing the measured value of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit has a function of calculating a corrected magnetic flux density value obtained by removing the periodic fluctuation component of the magnetic flux density included in the measured value of the magnetic flux density by a moving average filter. The non-destructive inspection device of the 25th invention, in any one of the 13th to 24th inventions, includes a control unit having an analysis function for analyzing the measured value of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit creates an approximate polynomial in the direction along the first direction of the inspection object based on the measured value of the magnetic flux density and the position where the magnetic flux density is measured, and subtracts the value of the approximate polynomial at the same position as the position where the magnetic flux density is measured from the measured value of the magnetic flux density. It is characterized by having a function of calculating the corrected magnetic flux density value.

Effect of the Invention

[0007] <Non-destructive Inspection Method> According to the first invention, since the magnetic flux density in the second direction is measured on both sides of the reference plane, the damage of the inspection object can be accurately grasped. According to the second invention, even when there is a large difference in the DC component of the magnetic flux density in the second direction between the first measurement position and the second measurement position, the breakage of the inspection object can be accurately grasped. According to the third invention, since the presence or absence of a break in the object to be inspected is determined based on the difference in the magnetic flux density in the second direction measured at the first determination position and the second determination position, the break in the object to be inspected can be determined simply and accurately. Moreover, since the first timing and the second timing are set based on the difference in the magnetic flux density in the third direction measured at the third determination position and the fourth determination position along the first direction of the object to be inspected, the accuracy of detecting a break in the object to be inspected can be increased. According to the fourth invention, since the reference timing is utilized, the accuracy of detecting a break in the object to be inspected can be increased. According to the fifth invention, it becomes easier to appropriately set the first timing and the second timing. According to the sixth invention, since the presence or absence of a break in the object to be inspected is determined based on the difference in the magnetic flux density in the second direction measured at the first determination position and the second determination position, the break in the object to be inspected can be determined simply and accurately. According to the seventh invention, since the first determination position and the second determination position are set based on the difference in the magnetic flux density in the third direction measured at the third determination position and the fourth determination position along the first direction of the object to be inspected, the accuracy of detecting a break in the object to be inspected can be increased. According to the eighth invention, since the variation in the measured value of the magnetic flux density in the second direction due to position is compared with the variation in the measured value of the magnetic flux density in the first direction and / or the third direction due to position, the damage to the object to be inspected can be accurately grasped. According to the ninth invention, the accuracy of detecting damage to the object to be inspected when the magnetic flux density in the third direction is utilized can be increased. According to the tenth invention, the accuracy of detecting damage to the object to be inspected can be increased. According to the eleventh invention, the influence of members other than the object to be inspected, such as steel bars for reinforcement and spacers, embedded in the concrete structure can be removed. According to the twelfth invention, the influence of the magnetic gradient along the first direction of the object to be inspected can be removed. <Non-destructive inspection device> According to the 13th invention, the device is arranged on the surface of the concrete structure such that the measurement axis of the magnetic sensor is parallel to the first direction of the inspection object, orthogonal to the surface of the concrete structure or the tangent plane of the surface of the concrete structure, and orthogonal to the reference plane intersecting the inspection object. , and in a state of being positioned between two of the plurality of magnetic sensors The device is moved along the first direction of the inspection object. Then , base On both sides of the reference plane magnetic flux density Measurement can be performed, so the damage of the inspection object can be accurately grasped. According to the 14th invention, even when a large difference occurs in the DC component of the magnetic flux density in the second direction between the first measurement position and the second measurement position, the breakage of the inspection object can be accurately grasped. According to the 15th invention, since the presence or absence of breakage of the inspection object is determined based on the difference in the magnetic flux density in the second direction measured by a plurality of magnetic sensors in the first magnetic sensor array, the breakage of the inspection object can be simply and accurately determined. Moreover, since the reference timing, the first timing, and the second timing are set based on the difference in the magnetic flux density in the third direction measured by two magnetic sensors in the second magnetic sensor array, the accuracy of detecting the breakage of the inspection object can be increased. According to the 16th invention, since the reference timing is used, the accuracy of detecting the breakage of the inspection object can be increased. According to the 17th invention, it becomes easier to appropriately set the first timing and the second timing. According to the 18th invention, since the presence or absence of breakage of the inspection object is determined based on the difference in the magnetic flux density in the second direction measured by a plurality of magnetic sensors in the first magnetic sensor array, the breakage of the inspection object can be simply and accurately determined. According to the 19th invention, since the first determination position and the second determination position are set based on the difference in the magnetic flux density in the third direction measured by two magnetic sensors in the second magnetic sensor array, the accuracy of detecting the breakage of the inspection object can be increased. According to the 20th invention, the breakage of the inspection object can be quickly determined. According to the 21st invention, if the first array direction is arranged parallel to the first direction of the inspection object and the device is moved along the first direction of the inspection object in that state, the magnetic flux density in the second direction can be measured on both sides of the reference plane by a plurality of magnetic sensors in the first magnetic sensor array. Further, the magnetic flux density in the third direction orthogonal to the first and second directions of the inspection object can be measured at different positions along the first direction by a plurality of magnetic sensors in the second magnetic sensor array. Then, since the change in the magnetic flux density in the second direction of the inspection object due to position and the change in the magnetic flux density in the third direction of the inspection object due to position can be compared, the damage of the inspection object can be accurately grasped. According to the 22nd invention, the damage of the inspection object can be accurately grasped. According to the 23rd invention, if three magnetic sensors are respectively positioned on both sides of the reference plane, a contour map of the magnetic flux density on both sides of the reference plane can be created, so the accuracy of detecting the damage of the inspection object can be increased. According to the 24th invention, the influence of members other than the inspection object such as steel bars for reinforcement and spacers buried in the concrete structure can be removed. According to the 25th invention, the influence of the magnetic gradient along the first direction of the inspection object can be removed.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] The non - destructive inspection method of this embodiment is a method for detecting damage to an inspection target embedded inside a concrete structure using the magnetic flux leakage method, and can detect damage such as breakage and corrosion of an inspection target extending along one direction, such as a reinforcing bar, steel bar, steel wire, etc.

[0010] The concrete structure in which the inspection object inspected by the non-destructive inspection method of the present embodiment is embedded (hereinafter sometimes simply referred to as the concrete structure to be inspected) is not particularly limited. For example, bridge girders, bridge piers, floor slabs, etc. of roads and railways can be cited as the concrete structures to be inspected by the non-destructive inspection method of the present embodiment.

[0011] The concrete structure to be inspected by the non-destructive inspection method of the present embodiment is not limited to those having a flat surface, and those having a cylindrical surface are also included. For example, a columnar body having a cylindrical surface can also be cited as the concrete structure to be inspected by the non-destructive inspection method of the present embodiment.

[0012] The inspection object inspected by the non-destructive inspection method of the present embodiment is not particularly limited, and it may be an inspection object that extends in one direction parallel to the surface of the concrete structure to be inspected and is likely to be damaged such as breakage. For example, PC steel bars (high-strength steel with a diameter of 10 mm or more), PC steel wires (wire rods made of high-strength steel with a diameter of 8 mm or less), PC steel strands (formed by combining PC steel wires), etc., and steel materials such as steel bars for reinforced concrete can be used as the inspection object. Also, in the case of a concrete column in a concrete structure, PC steel bars and PC steel wires can be inspected for high-strength steel and wire rods made of high-strength steel with a diameter of 7 mm or 9 mm or less.

[0013] Hereinafter, the case where the surface of the concrete structure to be inspected by the non-destructive inspection method of the present embodiment is flat will be described as a representative.

[0014] In the following description, the surface of the concrete structure to be inspected is a concept including the tangent plane in a structure (curved surface concrete structure) whose surface is a cylindrical surface. In the case of a cylindrical curved surface concrete structure, the reinforcing bars and the like to be inspected extend along the axial direction (the central axis direction of the cylindrical surface) of the surface of the curved surface concrete structure. For this reason, the device used in the non-destructive inspection method of the present embodiment measures the magnetic flux density while moving along the axial direction of the surface of the curved surface concrete structure. Then, the magnetic sensor described later for measuring the magnetic flux density measures the magnetic flux density while moving while maintaining a state parallel to the tangent plane of the surface of the curved surface concrete structure when the device moves along the axial direction of the surface of the curved surface concrete structure. Therefore, in the following description, when the surface of the concrete structure is used as a reference, in the case of a curved surface concrete structure, it means using the tangent plane as a reference.

[0015] <Concrete structure C> First, the concrete structure C inspected by the non-destructive inspection method of the present embodiment will be briefly described.

[0016] The concrete structure C to be inspected is, for example, a structure such as a concrete column, a bridge girder, a bridge pier, or a floor slab, and an inspection target P such as a reinforcing bar, a steel bar, or a steel wire is embedded inside the structure (see FIG. 1). Specifically, the concrete structure C to be inspected has a planar surface CF, and the inspection target P is embedded so as to extend in one direction parallel to the surface CF. The direction in which the inspection target P extends, that is, the axial direction of the inspection target P (the left-right direction in FIG. 1) is hereinafter referred to as the first direction of the inspection target P.

[0017] In the following, there may be cases where the first direction of the inspection target P is the X-axis direction, the direction parallel to the surface CF of the concrete structure C and orthogonal to the X-axis direction is the Y-axis direction, and the normal direction of the surface CF of the concrete structure C is the Z-axis direction (see FIG. 1). This Y-axis direction is the second direction referred to in the claims, and the Z-axis direction is the third direction referred to in the claims.

[0018] Note that the concrete structure C to be inspected may have members other than the inspection target P, such as steel bars for reinforcement and spacers, embedded in it.

[0019] In addition, the parallelism between the surface CF of the concrete structure C and the inspection target P is a concept that includes not only the case where both are completely parallel over the entire inspection target P, but also the case where a part of the inspection target P has a slight inclination with respect to the surface CF of the concrete structure C to be inspected.

[0020] <The non-destructive inspection device 1 of the present embodiment> Next, before explaining the non-destructive inspection method of the present embodiment, the non-destructive inspection device 1 used in the non-destructive inspection method of the present embodiment will be explained.

[0021] <Moving body 2> As shown in FIG. 1, the non-destructive inspection device 1 has a moving body 2. This moving body 2 has a structure that can move smoothly in one direction along the surface CF of the concrete structure C to be inspected. More specifically, the moving body 2 has a structure that can move linearly along the direction of its central axis B (see FIG. 1(B)). Moreover, the moving body 2 has a function of being able to move while maintaining a constant distance between the surface CF of the concrete structure C to be inspected and the magnetic flux measurement unit 5 described later. Note that hereinafter, the direction of the central axis B of the moving body 2 (that is, the moving direction of the moving body 2) may be referred to as the x-axis direction (see FIG. 1).

[0022] Specifically, the moving body 2 includes its main body 2a and a plurality of wheels 2r rotatably attached to the main body 2a (see Fig. 1(A)). The plurality of wheels 2r are provided such that their rotation axes are orthogonal to the central axis B of the moving body 2. Moreover, the plurality of wheels 2r are provided such that their rotation axes are parallel to the surface CF of the concrete structure C to be inspected when the moving body 2 is placed on the surface CF of the concrete structure C to be inspected. In the following, the direction parallel to the rotation axes of the plurality of wheels 2r may be referred to as the y-axis direction, the x-axis direction, and the direction orthogonal to the y-axis direction may be referred to as the z-axis direction (see Fig. 1). The z-axis direction is parallel to the normal direction (Z-axis direction) of the surface CF of the concrete structure C when the moving body 2 is placed on the surface CF of the concrete structure C.

[0023] Further, the plurality of wheels 2r are provided so as to be able to move while maintaining a constant distance H (distance in the z-axis direction) between the magnetic flux measurement unit 5 (more specifically, the magnetic sensor 6) and the surface CF of the concrete structure C to be inspected. That is, if the plurality of wheels 2r are rolled in a state where the plurality of wheels 2r are in contact with the surface CF of the concrete structure C to be inspected, the moving body 2 can be moved along the x-axis direction on the surface CF of the concrete structure C to be inspected while maintaining the distance in the z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected at a constant distance H. In the following, when explaining the movement of the moving body 2, it is assumed that the moving direction is along the x-axis direction.

[0024] Note that the number of wheels 2r provided on the moving body 2 is not particularly limited. As described above, as long as the moving body 2 can be moved in the x-axis direction while maintaining a constant distance in the z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected, the number of wheels 2r may be three or four or more.

[0025] In addition, the moving body 2 only needs to be able to maintain a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected, and to be able to move smoothly along the X-axis direction on the surface CF of the concrete structure C to be inspected. Its structure is not particularly limited. In the above example, the case where the moving body 2 has wheels 2r was described. However, even if a guide rail or the like is laid parallel to the surface CF of the concrete structure C to be inspected and along the X-axis direction, and the moving body 2 is moved along this guide rail or the like, the above functions can be exerted. Further, an acrylic sliding plate may be provided on the bottom surface of the moving body 2 to maintain a constant distance between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected. Note that maintaining a constant distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected includes the case where there is a variation of about 20 mm or less in the distance H between the two when the moving body 2 moves along the surface CF of the concrete structure C.

[0026] In addition, when there are irregularities on the surface CF of the concrete structure C to be inspected, a virtual plane obtained by averaging the irregularities on the surface of the region corresponding to the range where the magnetic sensor 6 is provided in the magnetic flux measurement unit 5 to be described later (the region with the width W in FIG. 1(B)) corresponds to the surface CF of the concrete structure C to be inspected. Therefore, when there are irregularities on the surface CF of the concrete structure C to be inspected, the distance H in the Z-axis direction between the magnetic flux measurement unit 5 and the surface CF of the concrete structure C to be inspected is the distance from the virtual plane in the Z-axis direction to the magnetic flux measurement unit 5. Note that hereinafter, when referring to the surface CF of the concrete structure C to be inspected, it also includes the virtual plane obtained by averaging the irregularities on the surface of the region corresponding to the magnetic flux measurement unit 5.

[0027] In addition, when the concrete structure to be inspected is a columnar body having a cylindrical surface (corresponding to the curved surface concrete structure described above), in the direction orthogonal to the axial direction of the columnar body, the distance between the magnetic flux measurement unit 5 and the surface of the concrete structure varies depending on the position. However, when the moving body 2 of the non-destructive inspection device 1 of the present embodiment is moved in the axial direction of the columnar body (that is, the axial direction of the inspection object, corresponding to the first direction of the inspection object in the claims), the moving body 2 has a function of being able to move while keeping the distance between each magnetic sensor 6 of the magnetic flux measurement unit 5 and the surface of the concrete structure C constant. For example, when a tangent plane that contacts the intersection line of the surface of the columnar body and the plane passing through the central axis of the columnar body and the central axis B of the moving body 2 is set, the moving body 2 of the non-destructive inspection device 1 of the present embodiment has a function of being able to move while maintaining a constant distance between this tangent plane and each magnetic sensor 6 of the magnetic flux measurement unit 5.

[0028] <Magnetic flux measurement unit 5> The magnetic flux measurement unit 5 measures the magnetic flux density of the surface CF of the concrete structure C to be inspected, and includes a plurality of magnetic sensors 6 (eight in FIG. 1(B)). Each magnetic sensor 6 can measure at least the magnetic flux density in the y-axis direction, and is arranged at intervals along the first arrangement direction (the direction along line A in FIG. 1(B), hereinafter sometimes referred to as the first arrangement direction A) orthogonal to the central axis B of the moving body 2 on the base member 5a of the magnetic flux measurement unit 5 (see FIG. 1(B)). Specifically, each magnetic sensor 6 is arranged such that the measurement axis for measuring the magnetic flux density in the y-axis direction is coaxial and parallel to the first arrangement direction A. Note that the magnetic sensor 6 only needs to be able to measure at least the magnetic flux density in the y-axis direction, and various known magnetic sensors can be used. For example, a Hall element sensor, an MR sensor, an MI sensor, a TMR sensor, etc. can be used as the magnetic sensor 6.

[0029] Also, the distance between the magnetic sensors 6 and the width of the region where the magnetic sensors 6 are provided are not particularly limited. The magnetic sensors 6 may be provided with appropriate distances and widths of the regions according to the depth and distance at which the inspection target P is embedded. For example, if the distance from the inspection target P to the surface CF of the concrete structure C to be inspected is about 100 to 200 mm, the distance between the magnetic sensors 6 (i.e., the measurement interval) is preferably about 50 to 100 mm, and the width of the region where the magnetic sensors 6 are provided is preferably about 300 to 1000 mm.

[0030] In addition, when the moving body 2 is arranged on the surface CF of the concrete structure C to be inspected, the plurality of magnetic sensors 6 are arranged on the base member 5a so that the first arrangement direction A is parallel to the surface CF of the concrete structure C to be inspected.

[0031] Moreover, the plurality of magnetic sensors 6 are arranged symmetrically with respect to the center line B of the moving body 2. That is, the plurality of magnetic sensors 6 are provided such that the same number of magnetic sensors 6 are arranged on both sides of the center line B of the moving body 2. For example, taking the plane including the center line B of the moving body 2 and orthogonal to the first arrangement direction A as the reference plane SA, the plurality of magnetic sensors 6 are provided symmetrically with respect to this reference plane SA. In FIG. 1(B), four magnetic sensors 6 are arranged on each side of the reference plane SA.

[0032] Note that the first arrangement direction A being parallel to the surface CF of the concrete structure C to be inspected includes not only the case where the surface CF of the concrete structure C to be inspected and the first arrangement direction A are completely parallel when the moving body 2 is arranged on the surface CF of the concrete structure C to be inspected, but also the case where there is a slight inclination between the surface CF of the concrete structure C to be inspected and the first arrangement direction A.

[0033] In addition, when the concrete structure is for inspecting a columnar body having a cylindrical surface, when the plurality of magnetic sensors 6 are arranged on the surface of the columnar body with the moving body 2, the first arrangement direction A thereof becomes parallel to the tangent plane described above. The fact that the tangent plane and the first arrangement direction A are parallel is not limited to the case where the tangent plane and the first arrangement direction A are completely parallel, but also includes the concept where there is a slight inclination between the tangent plane and the first arrangement direction A. In this case, the reference plane SA is a plane that passes through the tangent line between the columnar body and the tangent plane and is orthogonal to the tangent plane. Here, the fact that the tangent plane and the reference plane SA are orthogonal includes the concept where a slight inclination occurs between the tangent plane and the reference plane SA.

[0034] In addition, the fact that the measurement axes (y measurement axes) for measuring the magnetic flux density in the y-axis direction of each magnetic sensor 6 are coaxial includes both the case where the y measurement axes of all the magnetic sensors 6 are completely coaxial and the case where there is a slight deviation between the y measurement axes of each magnetic sensor 6. The deviation between the y measurement axes of each magnetic sensor 6 includes both the case where there is a deviation in position in the direction (x-axis direction or z-axis direction) intersecting the y measurement axis and the case where there is an inclination between the y measurement axes of each magnetic sensor 6.

[0035] In addition, each magnetic sensor 6 only needs to be arranged such that the y measurement axes are parallel to each other, and it is not necessary for the y measurement axes of all the magnetic sensors 6 to be coaxial. Here, the fact that the y measurement axes of all the magnetic sensors 6 are parallel to each other includes both the case where the y measurement axes of all the magnetic sensors 6 are completely parallel and the case where there is a slight inclination between the y measurement axes of each magnetic sensor 6.

[0036] The case where there is a deviation in position in the direction intersecting the y measurement axis between the y measurement axes of each magnetic sensor 6 described above means the case where there is a deviation of about ±20 mm in the x-axis direction or z-axis direction between the y measurement axes of each magnetic sensor 6. In addition, the case where there is a slight inclination between the y measurement axes of each magnetic sensor 6 means the case where the y measurement axis of each magnetic sensor 6 has a slight inclination with respect to the first arrangement direction A.

[0037] In addition, a magnetic sensor 6 capable of measuring the magnetic flux density in three axial directions may be used. In this case, it is desirable to arrange the three measurement axes (x measurement axis, y measurement axis, z measurement axis) of each magnetic sensor 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above, respectively. The three measurement axes of each magnetic sensor 6 being parallel to the x-axis direction, y-axis direction, and z-axis direction described above respectively includes both the case where the three measurement axes of each magnetic sensor 6 are completely parallel to the x-axis direction, y-axis direction, and z-axis direction, and the case where the three measurement axes have a slight inclination with respect to the x-axis direction, y-axis direction, and z-axis direction. When measuring the magnetic flux density in three axial directions, instead of the magnetic sensor 6, three magnetic sensors for measuring the magnetic flux density in one axial direction may be used to measure the magnetic flux density in three axial directions. For example, three magnetic sensors for measuring the magnetic flux density in one axial direction may be arranged adjacent to each other to measure the magnetic flux density in three axial directions. Also in this case, it is desirable to arrange the measurement axes of each magnetic sensor 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above, respectively. Of course, when measuring the magnetic flux density of multiple axes, the magnetic flux density in two axial directions may be measured. For example, the two axes in the x-axis direction and y-axis direction, the two axes in the x-axis direction and z-axis direction, or the two axes in the y-axis direction and z-axis direction may be measured. Also in this case, it is desirable to arrange the measurement axes of each magnetic sensor 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above, respectively.

[0038] <Control unit 4> As shown in FIG. 2, the control unit 4 has a position calculation function for calculating the positions of the respective magnetic sensors 6 of the magnetic flux measurement unit 5 and an operation control function for controlling the operation of the respective magnetic sensors 6 of the magnetic flux measurement unit 5. Further, the control unit 4 has a storage function of associating and storing in a storage unit such as a memory the data of the measured values of the magnetic flux density measured by the respective magnetic sensors 6 of the magnetic flux measurement unit 5 and the positions of the respective magnetic sensors 6 of the magnetic flux measurement unit 5 calculated by the position calculation function.

[0039] Furthermore, the control unit 4 has an analysis function that creates a graph showing the variation in the measured value of the magnetic flux density, specifically the variation in the measured value of the magnetic flux density along the moving direction (X-axis direction) of the moving body 2, using the data stored in the storage unit. If the control unit 4 is provided with a data communication function to transmit and receive measurement data and the like to and from an external personal computer or cloud computer, it is also possible to cooperate the storage function, analysis function, etc. of the control unit 4 with an external personal computer or the like.

[0040] <Position calculation function> The control unit 4 has a position calculation function that calculates the amount of movement of the moving body 2, in other words, the amount of movement of each magnetic sensor 6 of the magnetic flux measurement unit 5. This position calculation function calculates the moving distance of each magnetic sensor 6 of the magnetic flux measurement unit 5 from the initial position (the position where the moving body 2 is placed on the surface CF of the concrete structure C to be inspected) to the current position, in other words, calculates the current position of each magnetic sensor 6 of the magnetic flux measurement unit 5 with respect to the initial position. For example, if the relative positions of each magnetic sensor 6 with respect to the reference position (for example, the position of the wheel 2r) in the moving body 2 are stored in the storage unit, the position calculation function is based on the reference position at the initial position, and based on the amount of movement in the x-axis direction of the moving body 2 from the initial position and the relative positions of each magnetic sensor 6 with respect to the reference position, the moving distance of each magnetic sensor 6 in the X-axis direction and the position of each magnetic sensor 6 in the X-axis direction after the above movement can be calculated.

[0041] Note that the method for obtaining the moving distance of each magnetic sensor 6 of the magnetic flux measurement unit 5 from the initial position is not particularly limited. As shown in FIG. 2, a detector 4c for detecting the moving distance of the moving body 2 from the initial position may be provided on the moving body 2. For example, as the detector 4c, an encoder capable of detecting the rotation amount (rotation angle) of the wheel 2 may be provided. In this case, the position calculation function can calculate the moving distance of each magnetic sensor 6 of the magnetic flux measurement unit 5 in the X-axis direction with respect to the initial position and the position of each magnetic sensor 6 of the magnetic flux measurement unit 5 in the X-axis direction with respect to the initial position after the above movement, based on the rotation angle of the wheel 2 detected by the detector 4c and the diameter of the wheel 2.

[0042] In addition, the detector 4c that detects the moving distance of the moving body 2 from the initial position described above is not limited to detecting the moving distance of the moving body 2 based on the number of rotations of the wheel 2r like the encoder described above. An optical mouse, an accelerometer, or the like may be used as the detector 4c for grasping the moving distance.

[0043] Furthermore, the method for grasping the current position of each magnetic sensor 6 (in other words, the position where each magnetic sensor 6 measures the magnetic flux density) is not limited to the method described above. For example, position markers may be provided on the concrete structure C or in its vicinity, and the relative position of the magnetic flux measurement unit 5 at the timing when the magnetic flux density with respect to this position marker is measured may be measured to grasp the position (the position in the X-axis direction) where the magnetic flux measurement unit 5 measures the magnetic flux density.

[0044] <Actuation control function> The control unit 4 has an actuation control function for controlling the operation of each magnetic sensor 6 of the magnetic flux measurement unit 5. This actuation control function determines the timing at which each magnetic sensor 6 of the magnetic flux measurement unit 5 measures the magnetic flux density, and has a function of causing each magnetic sensor 6 of the magnetic flux measurement unit 5 to measure the magnetic flux density at that timing and a function of transmitting the measured value to the storage function. For example, when a measurement start signal is input by an operation button or the like, thereafter, the magnetic flux density is measured by each magnetic sensor 6 at a predetermined time interval (for example, every 10 milliseconds) and the measured value is transmitted to the storage function (hereinafter, causing each magnetic sensor 6 to measure the magnetic flux density and transmitting the measured value to the storage function may be referred to as measurement, etc.), or the actuation control function has a function of causing each magnetic sensor 6 to measure the magnetic flux density, etc. at every predetermined distance based on the amount of movement of the moving body 2 in the x-axis direction calculated by the position calculation function. Of course, the control unit 4 may be configured to continuously measure the magnetic flux density by each magnetic sensor 6 and continuously transmit the measured value to the storage function when a measurement start signal is input by an operation button or the like. Note that the control unit 4 may cause all of the plurality of magnetic sensors 6 to perform measurement, etc. at the same timing, or may cause each magnetic sensor 6 to perform measurement, etc. at an appropriate timing. For example, each magnetic sensor 6 may be caused to perform measurement, etc. at the timing when the amount of movement of each magnetic sensor 6 reaches a predetermined amount of movement.

[0045] In addition, when the position calculation function has the detector 4c as described above, the signal transmitted by the detector 4c may be directly supplied to the operation control function, and the operation control function may cause each magnetic sensor 6 to measure the magnetic flux density based on the signal transmitted by the detector 4c. For example, if the detector 4c is an encoder, the operation control function may cause each magnetic sensor 6 to measure the magnetic flux density according to the rotation angle of the wheel 2r detected by the detector 4c (that is, when the wheel 2r rotates by a predetermined angle). Also, the timing for starting the measurement of the magnetic flux density by the magnetic sensor 6 may be determined based on the signal transmitted by the detector 4c. For example, when the detector 4c detects that the wheel 2r has started rotating from a state where the wheel 2r is not rotating and transmits a signal, the measurement of the magnetic flux density may be started for each magnetic sensor 6 based on that signal.

[0046] Also, each magnetic sensor 6 of the magnetic flux measurement unit 5 may always be in a state of measuring the magnetic flux density regardless of the command of the operation control function. In this case, the operation control function only needs to have a function of transmitting the signal from each magnetic sensor 6 to the storage function at each of the above-described time intervals or predetermined moving distances after the measurement start signal is input.

[0047] <Storage function> The storage function is a function of storing the moving distance of the magnetic flux measurement unit 5 calculated by the position calculation function and the measured value of the magnetic flux density measured by each magnetic sensor 6 of the magnetic flux measurement unit 5 in association with each other. Specifically, the storage function has a function of storing in the storage unit the measured value of the magnetic flux density measured by each magnetic sensor 6 of the magnetic flux measurement unit 5, the time when each magnetic sensor 6 measures the magnetic flux density, and the position (moving distance or signal of the detector 4c) of each magnetic sensor 6 at that time, in association with each other.

[0048] Also, information regarding the position (for example, the initial position) where each magnetic sensor 6 starts measurement and the start time thereof is stored in the storage unit in association with each magnetic sensor 6.

[0049] Therefore, if the information stored in the memory unit is acquired, it is possible to identify at which position the magnetic flux density measured by each magnetic sensor 6 of the magnetic flux measurement unit 5 was measured.

[0050] <Analysis function> The control unit 4 also has an analysis function of creating a graph showing the variation of the measured values of the magnetic flux density of each magnetic sensor 6 using the data stored in the memory unit. Specifically, the analysis function of the control unit 4 has a function of creating a graph showing how the measured values of the magnetic flux density of each magnetic sensor 6 change along the moving direction of the moving body 2, that is, the moving direction (X-axis direction) of each magnetic sensor 6. The graph created by the control unit 4 is not particularly limited, but for example, a graph showing the position (position in the X-axis direction) where the magnetic flux density was measured and the measured value at that position, that is, a graph showing the variation of the magnetic flux density according to the position in the X-axis direction can be cited. Also, a graph showing the relationship between the time (measurement timing) when the magnetic flux density was measured and the variation of the measured magnetic flux density can be cited (see FIG. 12).

[0051] In addition, if each magnetic sensor 6 can measure the magnetic flux density in the three-axis directions, a graph showing the variation of the magnetic flux density according to the position in the X-axis direction for each measurement axis direction (x measurement axis direction (X-axis direction), y measurement axis direction (Y-axis direction), z measurement axis direction (Z-axis direction)) (see FIG. 5) or a graph showing the relationship between the measurement timing and the variation of the magnetic flux density in each measured axis direction can be created.

[0052] Further, the control unit 4 does not necessarily have the analysis function (the function of creating a graph showing the variation according to the position in the X-axis direction of the magnetic flux density and the relationship with the measurement timing) as described above, and may have only the above-described position calculation function, operation control function, and storage function. In this case, a function for supplying the data stored in the control unit 4 to the outside may be provided, and the data may be analyzed by an analysis device provided separately from the non-destructive inspection device 1. In that case, the data may be supplied from the control unit to the analysis device by wire or wirelessly, or the data may be stored in a storage device such as a USB and supplied from the control unit to the analysis device.

[0053] Further, in the case of detecting a break in real time as described later, if only the presence or absence of a break needs to be grasped, the position calculation function may not be provided. For example, in the case where the measured magnetic flux density is directly graphed and displayed, the position calculation function may not be provided.

[0054] <The non-destructive inspection method of the present embodiment> A method (first determination method) for inspecting the damage of the inspection target P embedded in the concrete structure C to be inspected by the non-destructive inspection device 1 of the present embodiment described above will be described. Note that, in the following, it is described on the premise that the surface CF of the concrete structure C to be inspected is a horizontal plane. Of course, even if the surface CF of the concrete structure C to be inspected is a vertical surface or an inclined surface, the inspection can be performed in the same manner using the non-destructive inspection device 1 of the present embodiment. Further, it is described on the premise that each magnetic sensor 6 can measure the magnetic flux density in three axial directions.

[0055] First, move a magnet along the surface of the concrete structure C to be inspected to magnetize the inspection target P embedded in the concrete structure C to be inspected. Note that the method of magnetizing the inspection target P is not particularly limited. In the following description, a case will be described where the magnet is moved along the first direction of the inspection target P with the N pole and S pole of the magnet arranged in the first direction of the inspection target P, with the N pole on the right side in FIG. 1. Also, after magnetizing the inspection target P, it is desirable to demagnetize it. The method of demagnetizing the inspection target P is not particularly limited either.

[0056] After magnetizing the inspection target P, place the moving body 2 of the non-destructive inspection device 1 on the surface CF of the concrete structure C to be inspected (see FIG. 1(A)). At this time, the moving body 2 is arranged such that its reference plane SA is parallel to the first direction of the inspection target P (see FIG. 1(B)). In other words, when viewed from the normal direction (Z-axis direction) of the surface CF of the concrete structure C to be inspected, the moving body 2 is arranged such that the first arrangement direction A is orthogonal to the inspection target P. Then, when the moving body 2 is moved along the surface CF of the concrete structure C to be inspected and the first direction (X-axis direction) of the inspection target P (moved rightward in FIG. 1), the moving body 2 can be moved while maintaining the state where the first arrangement direction A is orthogonal to the axial direction of the inspection target P.

[0057] Note that in plan view, it is desirable to arrange the moving body 2 such that the same number of a plurality of magnetic sensors 6 exist on both sides of the inspection target P. For example, if the moving body 2 is arranged such that the central axis of the inspection target P is included in the reference plane SA (see FIG. 1(B)), the above state can be achieved. Also, the moving body 2 may be arranged such that the central axis of the inspection target P is located in the vicinity of the reference plane SA. For example, in the Y-axis direction, the reference plane SA of the moving body 2 and the central axis of the inspection target P may be offset by about 0 to 10 mm.

[0058] When the moving body 2 is placed, a measurement start signal is input by an operation button or the like, and the moving body 2 is moved along the first direction (X-axis direction) of the inspection object P. Then, the magnetic flux density along the moving path of each magnetic sensor 6 is measured by each magnetic sensor 6 of the magnetic flux measurement unit 5. That is, the magnetic flux density along the first direction of the inspection object P at the position of each magnetic sensor 6 is measured. And the measured values of the magnetic flux density measured by each magnetic sensor 6 are associated with the measurement position and the measurement time, and are stored in the storage unit by the storage function.

[0059] The area for inspecting the inspection object P, that is, the inspection is completed when the moving body 2 is moved by the distance for inspecting the inspection object P.

[0060] When the measurement is completed, a graph showing the variation of the magnetic flux density along the X-axis direction of each magnetic sensor 6 is created by the analysis function of the control unit 4, and the damage of the inspection object P is confirmed based on the graph. For example, a graph is created with the magnetic flux density obtained from the measured value of the magnetic flux density on the vertical axis and the measurement position (the position in the first direction of the inspection object P, that is, the position in the X-axis direction) on the horizontal axis (see FIG. 5).

[0061] If the inspection object P is broken, the magnetic flux density in the three-axis directions forms a graph as shown in FIG. 5, and at the break position, the measured values of the magnetic flux density all show characteristic variations. Among them, in the graph in the Y-axis direction (see FIG. 5(B)) and the graph in the Z-axis direction (see FIG. 5(C)), at the break position, the magnetic flux density intersects the reference line (the line formed by the magnetic flux density when there is no break), and before and after that (before and after the break position in the X-axis direction), the magnetic flux density shows a waveform with peaks in opposite directions (plus direction and minus direction). And in the X-axis direction and the Z-axis direction, the magnetic flux density measured on one side and the other side with respect to the reference plane SA, that is, on both sides sandwiching the inspection object P, has the same variation waveform (see FIGS. 5(A) and (C)), but in the magnetic flux density in the Y-axis direction, on one side (right side passing) and the other side (left side passing) with respect to the reference plane SA, that is, on both sides sandwiching the inspection object P, the waveforms show opposite variations (see FIG. 5(B)).

[0062] Therefore, if a plurality of magnetic sensors 6 of the magnetic flux measurement unit 5 are provided and the measured values of the magnetic flux density in the Y-axis direction are measured on both sides with respect to the reference plane SA, a graph of the magnetic flux density as shown in Fig. 5(B) can be formed, so that the presence or absence of breakage and the breakage position of the inspection object P can be accurately grasped. In particular, if the measured value of the magnetic flux density in the Z-axis direction is used in combination with the measured value of the magnetic flux density in the Y-axis direction, the accuracy of grasping the breakage position of the inspection object P can be further improved.

[0063] Note that, to grasp the breakage position of the inspection object P, a graph of the measured value of the magnetic flux density in the Y-axis direction and a graph of the measured value of the magnetic flux density in the X-axis direction may be used, or graphs of the measured values of the magnetic flux density in all directions of the X-axis direction, Y-axis direction, and Z-axis direction may be used.

[0064] <Contour diagram> The analysis function of the control unit 4 may have a function of creating a contour diagram of the magnetic flux density in a plane parallel to the plane along the surface CF of the concrete structure C to be inspected. For example, if the magnetic sensor 6 of the magnetic flux measurement unit 5 can measure the magnetic flux density in three axial directions, it may have a function of creating a contour diagram of the magnetic flux density in a plane parallel to both the x measurement axis and the y measurement axis of each magnetic sensor 6 (in other words, the X-Y plane).

[0065] Note that the analysis function of the control unit 4 may also have a function of creating a contour diagram of the magnetic flux density on a plane orthogonal to the plane along the surface CF of the concrete structure C to be inspected, in addition to the above-mentioned plane. For example, if the plurality of magnetic sensors 6 of the magnetic flux measurement unit 5 can measure the magnetic flux density in three axial directions, a plane parallel to both the x measurement axis and the z measurement axis of each magnetic sensor 6 of the magnetic flux measurement unit 5 (in other words, the X-Z plane), or a plane parallel to both the y measurement axis and the z measurement axis of each magnetic sensor 6 of the magnetic flux measurement unit 5 (in other words, the Y-Z plane) may have a function of creating a contour diagram of the magnetic flux density. In this case, since the distribution of the magnetic flux density in the depth direction of the concrete structure C to be inspected can be grasped, it becomes easier to determine whether the change in the magnetic flux density is due to damage to the inspection target P or due to something other than the inspection target such as steel bars like reinforcement or spacers. Furthermore, it also becomes easier to grasp the damage position of the inspection target P in the depth direction of the concrete structure C to be inspected.

[0066] As described above, if a plurality of magnetic sensors 6 are provided in the magnetic flux measurement unit 5 and the magnetic flux density is measured in a state where four magnetic sensors are respectively located on both sides of the reference plane SA (in other words, on both sides of the inspection target P, see Fig. 1(B)), it becomes possible to create a contour diagram of the magnetic flux density based on the measured values of the magnetic flux density of the plurality of magnetic sensors 6. That is, it is possible to form a distribution diagram of the magnetic flux density around the fracture position of the inspection target P.

[0067] Specifically, if the magnetic sensor 6 of the magnetic flux measurement unit 5 can measure the magnetic flux density in the three-axis directions, a contour diagram of the magnetic flux density in the three-axis directions showing a distribution as shown in FIG. 6 can be created. This contour diagram simplifies the actually measured contour diagram of the magnetic flux density in the three-axis directions (see FIG. 7). The hatched circles indicate the positions where the magnetic flux density of the plus component with respect to the reference line (see FIG. 5) is distributed, and the white circle portions indicate the positions where the magnetic flux density of the minus component with respect to the reference line (see FIG. 5) is distributed. Note that the signs of the plus component and the minus component are reversed depending on the magnetization state. FIGS. 6 and 7 show an example in which the N pole and the S pole in the broken portion are magnetized as shown in FIG. 5. As shown in FIG. 6, when a contour diagram is formed, in the contour diagram formed by the measured value of the x measurement axis of the magnetic sensor 6 (magnetic flux density in the X-axis direction) (hereinafter sometimes simply referred to as the contour diagram of the x measurement axis), the break position of the inspection target P exists near the center of the position where the magnetic flux density of the minus component is distributed. In the contour diagram formed by the measured value of the y measurement axis of the magnetic sensor 6 (magnetic flux density in the Y-axis direction) (hereinafter sometimes simply referred to as the contour diagram of the y measurement axis), the break position of the inspection target P exists near the center of the position surrounded by the position where the magnetic flux density of the plus component is distributed and the position where the magnetic flux density of the minus component is distributed. In the contour diagram formed by the measured value of the z measurement axis of the magnetic sensor 6 (magnetic flux density in the Z-axis direction) (hereinafter sometimes simply referred to as the contour diagram of the z measurement axis), the break position of the inspection target P exists between the position where the magnetic flux density of the plus component is distributed and the position where the magnetic flux density of the minus component is distributed.

[0068] In particular, in the contour diagram of the y measurement axis, the break position of the inspection target P exists near the center of the position surrounded by the position where the magnetic flux density of the plus component is distributed and the position where the magnetic flux density of the minus component is distributed. Therefore, by using the contour diagram of the y measurement axis, it becomes easier to grasp the break position of the inspection target P than by using the contour diagram of the x measurement axis or the contour diagram of the z measurement axis.

[0069] In addition, depending on the distance from the inspection target P, a difference occurs in the region where the magnetic flux density measured by each magnetic sensor 6 of the magnetic flux measurement unit 5 is measured. Specifically, the deeper the depth at which the inspection target P is embedded, that is, the distance from the surface CF of the concrete structure C to be inspected, the wider the region where the magnetic flux density is measured. Therefore, in the contour diagram of the y measurement axis as shown in FIG. 6(B), the positions of the circles formed at the positions surrounding the fracture position of the inspection target P are in a state where the distance between them increases as the depth at which the inspection target P is embedded increases. That is, the distance between the circles is correlated with the depth at which the inspection target P is embedded. Therefore, if the area of the quadrangular region CA connecting the centers a1 to a4 of the four circles C1 to C4 surrounding the fracture position of the inspection target P is calculated in the contour diagram of the y measurement axis, it is also possible to estimate the depth of the fracture position of the inspection target P based on the area of the region CA.

[0070] If the magnetic sensor 6 of the magnetic flux measurement unit 5 can measure the magnetic flux density in the three-axis directions, as described above, the contour diagrams of the x measurement axis, the y measurement axis, and the z measurement axis can be formed respectively. However, as long as the magnetic sensor 6 of the magnetic flux measurement unit 5 can measure the magnetic flux density in at least the y-axis direction, the contour diagram of the y measurement axis can be formed. Similarly, if the magnetic sensor 6 in the first arrangement direction A of the magnetic flux measurement unit 5 can measure the magnetic flux density in at least the x-axis direction and the z-axis direction, the contour diagrams of the x measurement axis and the z measurement axis can be formed respectively.

[0071] In addition, when the region CA is created in the contour diagram of each measurement axis, the area of the region CA changes not only depending on the depth at which the inspection target P is embedded but also depending on the length of the fracture gap of the inspection target P. Therefore, it is possible to estimate the length of the fracture gap of the inspection target P based on the area of the region CA.

[0072] <Removal of the influence of the magnetic field formed by the reinforcement> In the concrete structure C to be inspected, generally, reinforcing bars (steel reinforcements) are laid approximately at equal intervals in the vertical and horizontal directions immediately below the surface CF of the concrete structure C to be inspected. That is, immediately below the surface CF of the concrete structure C to be inspected, the steel reinforcements are laid in a generally grid pattern. In the case where the PC steel material is the inspection target P, the PC steel material is usually embedded at a position deeper than the steel reinforcements, that is, at a position farther from the surface CF of the concrete structure C to be inspected than the steel reinforcements. Therefore, if the inspection target P, the PC steel material, is magnetized, the steel reinforcements will also be magnetized together with the PC steel material. Then, the measured value of the magnetic flux density measured by the plurality of magnetic sensors 6 of the magnetic flux measurement unit 5 will be a value including the magnetic flux density of the magnetic field formed by the steel reinforcements. Specifically, since the steel reinforcements are arranged at approximately equal intervals, each time the magnetic sensor 6 passes through the position of the steel reinforcements, the measured values of the magnetic flux density in each axial direction (X-axis direction, Y-axis direction, Z-axis direction) will fluctuate in a peak-like manner on the plus side and the minus side with respect to the reference line. Then, the fluctuation of the magnetic flux density of the magnetic field formed by the steel reinforcements may interfere and make it impossible to accurately grasp the fracture position of the inspection target P. Also, in the contour diagram of the magnetic flux density, regions where the magnetic flux density of the plus or minus component is distributed due to the steel reinforcements will occur. Then, it becomes difficult to grasp the fracture position of the inspection target P from the contour diagram.

[0073] Generally, since the steel reinforcements are laid at equal intervals, the magnetic field formed by the steel reinforcements is generated at a certain period approximately along the moving direction of the moving body 2. For this reason, the measured values of the magnetic flux density in each axial direction measured by the magnetic sensor 6 include the periodically fluctuating magnetic flux density due to the influence of the steel reinforcements. In the first direction of the inspection target P, that is, in the X-axis direction parallel to the moving direction of the moving body 2, the fluctuation rate of the magnetic flux density due to the influence of the steel reinforcements is much larger (higher frequency) than the fluctuation rate of the magnetic flux density due to the fracture of the inspection target P. Therefore, by using a digital signal filter with periodic (frequency) selectivity, the magnetic flux density due to the influence of the steel reinforcements can be removed from the measured values of the magnetic flux density in each axial direction.

[0074] Here, the reason why the rate of change of the magnetic flux density due to the influence of the reinforcement bars varies greatly is generally that when the inspection target P is a PC steel material and the moving body 2 is arranged on the surface CF of the concrete structure C to be inspected, the distance (referred to as L1) between the inspection target P (fracture position) and the magnetic sensor 6 becomes several times the distance (referred to as L2) between the reinforcement bars and the magnetic sensor 6 (see Fig. 1(A)). For this reason, at the position of the magnetic sensor 6, the rate of change of the magnetic flux density due to the fracture of the inspection target P is significantly different from the rate of change of the magnetic flux density due to the influence of the reinforcement bars. For example, when L1 / L2 is 3, the rate of change of the magnetic flux density due to the influence of the reinforcement bars is more than 9 times the rate of change of the magnetic flux density due to the fracture of the inspection target P.

[0075] Therefore, in order to more accurately estimate the fracture position of the inspection target P, the analysis function of the control unit 4 may have a function of calculating a corrected magnetic flux density value obtained by removing the periodic variation component of the magnetic flux density due to the influence of the reinforcement bars from the measured values of the magnetic flux density in each axial direction (X-axis direction, Y-axis direction, Z-axis direction) measured by each magnetic sensor 6.

[0076] Specifically, a function of removing the periodic variation component of the magnetic flux density in each axial direction by a moving average filter is provided from the measured values of the magnetic flux density in each axial direction. That is, for the magnetic flux density in each axial direction measured by each magnetic sensor 6, the magnetic flux density variation period (fundamental frequency) in each axial direction due to the influence of the reinforcement bars is calculated from the FFT spectrum of the measured value of the magnetic flux density in each axial direction, and a moving average filter that selectively removes the period (fundamental frequency) component from the measured value of the magnetic flux density in each axial direction is applied. The moving average filter has the property of selectively and strongly removing periodic signals (all of the fundamental frequency and its higher harmonics) having a period equal to the averaging data length and a period that is one integer fraction thereof. The periodic variation due to the influence of the reinforcement bars is not a sine wave but a distorted wave including higher harmonics, but all of its components can be removed by applying the moving average filter. Therefore, for the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6, a corrected magnetic flux density value (hereinafter sometimes referred to as the first corrected magnetic flux density value) from which the periodic variation component of the magnetic flux density due to the influence of the reinforcement bars is removed can be calculated.

[0077] If the control unit 4 creates a graph or a contour map showing the variation of the measured values of the magnetic flux density of each magnetic sensor 6 using such a first corrected magnetic flux density value, the presence or absence of breakage and the breakage position of the inspection target P can be grasped more accurately.

[0078] Note that the magnetic flux density variation period may be obtained from the FFT spectrum of the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6. However, when the magnetic flux density variation period is clear from the reinforcement layout drawing of the concrete structure C to be inspected, the magnetic flux density variation period due to the influence of the reinforcement may be calculated based on that information.

[0079] In addition, the variation of the magnetic flux density in each axial direction measured by each magnetic sensor 6 due to the influence of the reinforcement also occurs when the moving direction of the moving body 2 and the axial direction of the reinforcement are not parallel. The reinforcement is generally laid in a grid pattern with its longitudinal and transverse reinforcements. However, there may be a case where the moving direction of the moving body 2, that is, the first direction of the inspection target P, is not parallel to either the longitudinal or transverse reinforcement. In this case, the magnetic flux density measured in each axial direction by each magnetic sensor 6 includes two periodic variations: the variation of the magnetic flux density due to the influence of the longitudinal reinforcement and the variation of the magnetic flux density due to the influence of the transverse reinforcement. In this case, for the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6, the magnetic flux density variation period (fundamental frequency) is calculated for each of the variation of the magnetic flux density due to the influence of the longitudinal reinforcement and the variation of the magnetic flux density due to the influence of the transverse reinforcement. Then, by using a moving average filter, the periodic variation components of the magnetic flux density of both are sequentially removed from the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6. Then, a first corrected magnetic flux density value can be calculated by removing the periodic variation components of the magnetic flux density due to the influence of both the longitudinal and transverse reinforcements from the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6.

[0080] In addition, when the magnetic sensor 6 measures the magnetic flux density in three axial directions, it is desirable to calculate the first corrected magnetic flux density value for the measured values of the magnetic flux density in the three axial directions. However, the first corrected magnetic flux density value may be calculated for the measured values of the magnetic flux density in one or two selected axial directions out of the three axial directions. Further, when the magnetic sensor 6 measures the magnetic flux density in one axial direction or two axial directions, the first corrected magnetic flux density value may be calculated for the measured values of the magnetic flux density in the one axial direction or two axial directions.

[0081] <Removal of Influence of Magnetic Gradient> When magnetizing the inspection object P along the first direction of the inspection object P, a non-linear magnetic gradient is generated along the first direction of the inspection object P. Therefore, the measured values of the magnetic flux density in each axial direction measured by the plurality of magnetic sensors 6 in the magnetic flux measurement unit 5 become values including the magnetic gradient (see FIG. 8). Then, even if a graph of the magnetic flux density in the Y-axis direction and the Z-axis direction is created based on the measured value of the magnetic flux density, the position where the graph of the magnetic flux density intersects the reference line (the line formed by the first corrected magnetic flux density value when there is no break) may deviate from the original break position. Further, even if a contour map of the magnetic flux density is created, in the contour map of the y measurement axis, the break position of the inspection object P may deviate from the vicinity of the center of the position surrounded by the position where the magnetic flux density of the positive component is distributed and the position where the magnetic flux density of the negative component is distributed with respect to the reference line.

[0082] Since the frequency component of this magnetic gradient is a much lower frequency variation than the variation of the magnetic flux density generated by the break of the inspection object P, it is possible to remove the influence of the magnetic gradient from the measured values of the magnetic flux density in each axial direction by performing baseline correction using a polynomial.

[0083] Therefore, in order to more accurately estimate the fracture position of the inspection target P, the analysis function of the control unit 4 may have a function of calculating a corrected magnetic flux density value (hereinafter sometimes simply referred to as the second corrected magnetic flux density value) obtained by removing the influence of the magnetic gradient from the measured values of the magnetic flux density in each axial direction measured by the plurality of magnetic sensors 6 of the magnetic flux measurement unit 5. When both the removal of the influence of the magnetic gradient and the removal of the periodic fluctuation component of the magnetic flux density due to the influence of the reinforcement described above are performed, it is desirable to calculate the first corrected magnetic flux density value obtained by removing the periodic fluctuation component of the magnetic flux density due to the influence of the reinforcement and then remove the influence of the magnetic gradient to calculate the second corrected magnetic flux density value.

[0084] When removing the influence of the magnetic gradient, the analysis function of the control unit 4 is provided with a function of forming an approximate polynomial by the least squares method. That is, based on the measured values of the magnetic flux density in each axial direction measured by each magnetic sensor 6 and the positions where the magnetic flux density is measured by each magnetic sensor 6, an approximate polynomial by the least squares method with the position where the magnetic flux density is measured by each magnetic sensor 6 as a variable, that is, an approximate polynomial by the least squares method in the direction along the first direction of the inspection target, is provided in the analysis function of the control unit 4. And a function of calculating a second corrected magnetic flux density value obtained by subtracting the value of the approximate polynomial at the same position as the position where the magnetic flux density is measured by each magnetic sensor 6 from the measured value of the magnetic flux density in each axial direction measured by each magnetic sensor 6 is provided in the analysis function of the control unit 4. If a graph of the magnetic flux density as shown in FIG. 5 is formed using this second corrected magnetic flux density value, the position where the graphs of the magnetic flux density in the Y-axis direction and the Z-axis direction intersect the reference line (the line formed by the second corrected magnetic flux density value when there is no fracture) can be made to coincide with the fracture position. Similarly, if a contour map of the magnetic flux density as shown in FIG. 6 is created using this second corrected magnetic flux density value, a contour map of the y measurement axis can be formed such that the fracture position of the inspection target P is located near the center of the position surrounded by the position where the magnetic flux density of the plus component is distributed and the position where the magnetic flux density of the minus component is distributed.

[0085] As described above, if the control unit 4 creates a graph or a contour diagram showing the variation in the measured values of the magnetic flux density of each magnetic sensor 6 using the second corrected magnetic flux density value from which the influence of the magnetic gradient has been removed, it is possible to more accurately determine the presence or absence of a break in the inspection target P and the break position.

[0086] Note that the degree of the approximate polynomial to be formed is not particularly limited, and it should be appropriately selected so that it sufficiently follows the magnetic gradient but does not follow the variation in the magnetic flux density at the break position of the inspection target P. The selection of the degree of the approximate polynomial to be formed may be determined in advance, or it may be adjusted to an appropriate degree while checking a graph or the like of the magnetic flux density created by the analysis function of the control unit 4. For example, in the case where PC steel materials are used as the inspection target P in a general PC floor slab or the like, if a 1st to 5th order curve approximation polynomial is created as the approximate polynomial to be formed, it becomes easier to form an approximate polynomial that satisfies the above conditions.

[0087] When the magnetic sensor 6 measures the magnetic flux density in three axial directions, it is desirable to calculate the second corrected magnetic flux density value from which the influence of the magnetic gradient has been removed for the measured values in the three axial directions. However, even if it is configured to calculate the second corrected magnetic flux density value from which the influence of the magnetic gradient has been removed for the measured values of the magnetic flux density in one or two selected axial directions out of the three axial directions. Also, when the magnetic sensor 6 measures the magnetic flux density in one axial direction or two axial directions, it may be configured to calculate the second corrected magnetic flux density value from which the influence of the magnetic gradient has been removed for the measured values of the magnetic flux density in the one axial direction or two axial directions.

[0088] <Another example of the magnetic flux measurement unit 5> In the above example, the case where a plurality of magnetic sensors 6 are arranged on the base member 5a of the magnetic flux measurement unit 5 at intervals along the first arrangement direction A orthogonal to the central axis B of the moving body 2 has been described (see FIG. 1(B)). On the other hand, the magnetic flux measurement unit 5 may be provided with a plurality of magnetic sensors 7 arranged along the direction orthogonal to the first arrangement direction A, that is, along the central axis B of the moving body 2. Each magnetic sensor 7 has substantially the same function as the magnetic sensor 6 and can measure at least the magnetic flux density in the z-axis direction.

[0089] As shown in Fig. 3(A), a plurality (two in Fig. 3(A)) of rows of magnetic sensors 6 arranged at intervals along the first arrangement direction A are defined as the first magnetic sensor row CL1, and a plurality (two in Fig. 3(A)) of rows of magnetic sensors 7 arranged in the direction along the central axis B of the moving body 2 (hereinafter referred to as the second arrangement direction B) are defined as the second magnetic sensor row CL2. And each magnetic sensor 7 is arranged such that its z measurement axis is located on the reference plane SA.

[0090] Moreover, the plurality of magnetic sensors 7 in the second magnetic sensor row CL2 are arranged symmetrically with respect to the first magnetic sensor row CL1.

[0091] Even in the non-destructive inspection device 1 provided with the magnetic flux measurement unit 5 having the first magnetic sensor row CL1 and the second magnetic sensor row CL2, in the same manner as the non-destructive inspection device 1 (see Fig. 1(B)) having only the first magnetic sensor row CL1 composed of the plurality of magnetic sensors 6 described above, a graph of magnetic flux density as shown in Fig. 5 and a contour diagram of magnetic flux density as shown in Fig. 6 can be created to grasp the fracture position of the inspection object P.

[0092] On the other hand, in the non-destructive inspection device 1 provided with the magnetic flux measurement unit 5 having the first magnetic sensor row CL1 and the second magnetic sensor row CL2 as shown in Figs. 3 and 4, if the control unit 4 has the function of performing the following analysis, by performing the following analysis, the fracture position of the inspection object P can be accurately grasped.

[0093] That is, the magnetic flux density is measured at the same timing for the two magnetic sensors 7, 7 in the second magnetic sensor row CL2, the difference between the measured values of the magnetic flux density in the Z-axis direction measured by the two magnetic sensors 7, 7 at the same timing is calculated, and a graph of the difference value is formed (see Fig. 9(A)). Then, a graph having a peak at the fracture position of the inspection object P is formed. Note that the position in the first direction (X-axis direction) of the inspection object P on the horizontal axis of Fig. 9 indicates the position in the first direction (X-axis direction) of the magnetic sensor 6 of the first magnetic sensor row CL1 at the timing when the two magnetic sensors 7, 7 in the second magnetic sensor row CL2 measure the magnetic flux density.

[0094] Using this graph and the graph of the measured values of the magnetic flux density on the y - measurement axis of the plurality of magnetic sensors 6 in the first magnetic sensor array CL1 (see FIG. 9(B)), the break position of the object P to be inspected can be accurately grasped. That is, if the position where the graph of the measured values of the magnetic flux density on the y - measurement axis intersects the reference line coincides (or is located in the vicinity) with the position of the peak of the graph of the difference values, it can be determined that there is a break in the object P to be inspected at that position (or in its vicinity). And by using both graphs, even when spiral reinforcing bars for reinforcement are embedded in the concrete structure C to be inspected, the break position of the object P to be inspected can be accurately grasped.

[0095] In the case where no spiral reinforcing bars are embedded, the break position of the object P to be inspected can be grasped with a certain degree of accuracy only from the graph of the difference values of the measured values in the Z - axis direction measured by the two magnetic sensors 7, 7 in the second magnetic sensor array CL2 at the same timing. Therefore, usually, only the graph of the difference values of the magnetic flux density in the Z - axis direction is formed by the analysis function of the control unit 4 to confirm the break position of the object P to be inspected, and only when it is difficult to make a judgment only from the graph of the difference values of the magnetic flux density in the Z - axis direction, the graph of the measured values of the magnetic flux density in the Y - axis direction may be used to confirm the break position of the object P to be inspected.

[0096] Note that the two magnetic sensors 7, 7 in the second magnetic sensor array CL2 do not necessarily have to be symmetric with respect to the first magnetic sensor array CL1. Also, the second magnetic sensor array CL2 may have three or more magnetic sensors 7. In this case too, the plurality of magnetic sensors 7 in the second magnetic sensor array CL2 do not necessarily have to be symmetrically arranged with respect to the first magnetic sensor array CL1, but it is desirable that at least one magnetic sensor 7 is arranged on both sides of the first magnetic sensor array CL1.

[0097] Also, as shown in FIG. 3(B), in the nondestructive inspection device 1 having the first magnetic sensor array CL1 and the second magnetic sensor array CL2, the magnetic sensors 6 of the first magnetic sensor array CL1 and the magnetic sensors 7 of the second magnetic sensor array CL2 may be provided on the main body portion 2a of the moving body 2. In this case, since it is not necessary to provide the base member 5a of the magnetic flux measurement unit 5, the nondestructive inspection device 1 itself can be configured to be compact. Of course, in the nondestructive inspection device 1 shown in FIG. 1(B) as well, the magnetic sensor 6 may be provided on the main body portion 2a of the moving body 2 without providing the base member 5a of the magnetic flux measurement unit 5.

[0098] Note that the z measurement axes of the respective magnetic sensors 7 constituting the second magnetic sensor array CL2 being located on the reference plane SA includes both the case where the z measurement axes of the respective magnetic sensors 7 are located on the reference plane SA and the case where the z measurement axes of the respective magnetic sensors 7 have a slight deviation with respect to the reference plane SA. The deviation of the z measurement axis of each magnetic sensor 7 with respect to the reference plane SA includes both the case where the z measurement axis is inclined with respect to the reference plane SA and the case where the position of the z measurement axis is deviated with respect to the reference plane SA in the y-axis direction (for example, when there is a deviation of about ±20 mm).

[0099] Note that a magnetic sensor 7 capable of measuring the magnetic flux density in three axial directions may be used. In this case, it is desirable to arrange the three measurement axes (x measurement axis, y measurement axis, z measurement axis) of each magnetic sensor 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above, respectively. Here, the three measurement axes of each magnetic sensor 6 being parallel to the x-axis direction, y-axis direction, and z-axis direction described above respectively includes both the case where the three measurement axes of each magnetic sensor 6 are completely parallel to the x-axis direction, y-axis direction, and z-axis direction and the case where the three measurement axes have a slight inclination with respect to the x-axis direction, y-axis direction, and z-axis direction. When measuring the magnetic flux density in three axial directions in the second magnetic sensor array CL2, three magnetic sensors for measuring the magnetic flux density in one axial direction may be used to measure the magnetic flux density in three axial directions. For example, three magnetic sensors for measuring the magnetic flux density in one axial direction may be arranged adjacent to each other to measure the magnetic flux density in three axial directions. Also in this case, it is desirable to arrange the measurement axes of the respective magnetic sensors 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above. Of course, when measuring the magnetic flux density in a plurality of axes in the second magnetic sensor array CL2, the magnetic flux density in two axial directions may be measured. For example, the two axes of the x-axis direction and the z-axis direction, or the two axes of the y-axis direction and the z-axis direction, may be measured. Also in this case, it is desirable to arrange the measurement axes of the respective magnetic sensors 6 to be parallel to the x-axis direction, y-axis direction, and z-axis direction described above.

[0100] <Magnetic sensors 6 and 7> In the above example, the case where the first magnetic sensor array CL1 has two magnetic sensors 6, 6 and the second magnetic sensor array CL2 has two magnetic sensors 7, 7 has been described. However, the number of magnetic sensors 6 constituting the first magnetic sensor array CL1 and the number of magnetic sensors 7 constituting the second magnetic sensor array CL2 are not particularly limited. When creating a contour map of the magnetic flux density, it is desirable to provide four or more magnetic sensors 6 on both sides of the reference plane SA. However, it is also possible to create a contour map of the magnetic flux density even when three magnetic sensors 6 are provided on both sides of the reference plane SA. On the other hand, if the above-described contour map is not created, the number of magnetic sensors 6 in the first magnetic sensor array CL1 may be two. That is, one magnetic sensor 6 may be provided on each side of the reference plane SA for the magnetic sensors 6 in the first magnetic sensor array CL1.

[0101] <Breaking determination function> Further, the control unit 4 of the non-destructive inspection apparatus 1 of the present embodiment may have a breaking determination function for detecting the breakage of the inspection object P by the following method (second determination method).

[0102] First, when implementing the second determination method, the magnetic flux measurement unit 5 is provided with a first magnetic sensor array CL1 having two magnetic sensors 6, 6 arranged on both sides of the reference plane SA in the first arrangement direction A (see Fig. 3). Moreover, the two magnetic sensors 6, 6 of the first magnetic sensor array CL1 are arranged such that the distances from the reference plane SA are the same.

[0103] Note that the distances from the reference plane SA to the two magnetic sensors 6, 6 being the same includes both the case where the distances are exactly the same and the case where the difference between the distance from the reference plane SA to one magnetic sensor 6 and the distance from the reference plane SA to the other magnetic sensor 6 is within 20 mm. Also, three or more magnetic sensors 6 may be provided in the first magnetic sensor array CL1. In that case, among the three or more magnetic sensors 6, two magnetic sensors 6, 6 that sandwich the reference plane SA and have the same distance from the reference plane SA may be adopted as the two magnetic sensors 6, 6 used in the second determination method.

[0104] <Breaking determination function> If it has the magnetic flux measurement unit 5 as described above, the breaking determination function of the control unit 4 can determine the breakage of the inspection object P using the magnetic flux densities measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1.

[0105] Here, when the breaking determination function of the control unit 4 determines the breakage of the inspection object P, the non-destructive inspection device 1 having the magnetic sensors 6, 6 of the first magnetic sensor array CL1 and the magnetic sensors 7, 7 of the second magnetic sensor array CL2 described above is used to measure the magnetic flux density in a method substantially the same as in the case of the first determination method described above. That is, when viewed from the normal direction of the surface of the concrete structure C, the first arrangement direction A is orthogonal to the inspection object P, and the moving body 2 is arranged such that the reference plane SA is parallel to the first direction of the inspection object P and includes the central axis of the inspection object P (or is located near the central axis of the inspection object P). Then, while maintaining that state, the moving body 2 is moved in the first direction of the inspection object P, and the magnetic flux density is measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor array CL2.

[0106] In the following description, on the premise that the magnetic flux density has been measured by the above method, the break determination function of the control unit 4 will be described.

[0107] The break determination function has a function of calculating the difference in the magnetic flux density in the y-measurement axis direction (second-direction difference magnetic flux density) measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1. Specifically, for the magnetic flux density in the y-measurement axis direction of the two magnetic sensors 6, 6 measured at the same position in the first direction (X-axis direction) of the inspection object P, it has a function of calculating the second-direction difference magnetic flux density, which is the difference between the magnetic flux density measured by one magnetic sensor 6 and the magnetic flux density measured by the other magnetic sensor 6. Note that the positions where the two magnetic sensors 6, 6 are provided in the magnetic flux measurement unit 5 correspond to the first measurement position and the second measurement position referred to in the claims.

[0108] Further, the break determination function has a function of detecting, in the X-axis direction, a position (reference position BP, the position of BP in FIG. 9(B)) where the absolute value of the calculated second-direction difference magnetic flux density is equal to or less than a predetermined value (reference value). For example, as shown in FIG. 9(B), based on the magnetic flux density in the y-measurement axis direction measured by the two magnetic sensors 6, 6, a graph (refer to Y3 and Y4 in FIG. 9(B)) is created with the vertical axis being the measured value of the magnetic flux density and the horizontal axis being the measurement position in the X-axis direction. Then, the position where the absolute value of the second-direction difference magnetic flux density becomes 0 μT or the position where the absolute value of the second-direction difference magnetic flux density is equal to or less than the reference value (for example, 100 μT) can be set as the reference position BP. Note that when the position where the absolute value of the second-direction difference magnetic flux density is equal to or less than the reference value is set as the reference position BP, a certain range may be set as the reference position BP (for example, the range L in FIG. 9(B)).

[0109] Furthermore, the break determination function sets a first determination position JP1 and a second determination position JP2 that sandwich the reference position BP in the X-axis direction (JP1 and JP2 in Fig. 9(B)), and has a function of determining whether the absolute values of the second-direction differential magnetic flux densities at the first determination position JP1 and the second determination position JP2 (V1 and V2 in Fig. 9(B)) are equal to or greater than a predetermined value (hereinafter sometimes referred to as a threshold value). For example, the first determination position JP1 and the second determination position JP2 are set at positions 20 mm away from both sides (left and right directions in Fig. 9(B)) of the reference position BP. When the reference position BP has a width, for example, the first determination position JP1 and the second determination position JP2 are set at positions 20 mm away from the middle position of the width. Then, it has a function of determining whether both the absolute value of the second-direction differential magnetic flux density at the first determination position JP1 and the absolute value of the second-direction differential magnetic flux density at the second determination position JP2 are equal to or greater than the threshold value (for example, 200 μT).

[0110] Moreover, when the absolute values of the second-direction differential magnetic flux densities at the first determination position JP1 and the second determination position JP2 are equal to or greater than the threshold value, the break determination function determines whether the signs of the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2 are opposite signs, and if they are opposite signs, it has a function of determining that a break has occurred in the inspection object P. For example, in Fig. 9(B), when the value obtained by subtracting the magnetic flux density of Y4 from the magnetic flux density of Y3 at the first determination position JP1 and the second determination position JP2 has opposite signs, it has a function of determining that a break has occurred in the inspection object P. That is, the break determination function has a function of determining that a break has occurred in the inspection object P when the following conditions (6) to (7) are satisfied. (6) The absolute values of the second-direction differential magnetic flux densities at the first determination position JP1 and the second determination position JP2 that sandwich the reference position BP in the first direction of the inspection object P are equal to or greater than the threshold value. (7) The signs of the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2 are opposite.

[0111] If the presence or absence of breakage of the inspection target P is determined by the above method, it is possible to prevent misjudging the magnetization end such as the edge of the inspection target P as a break when no breakage has occurred. That is, as shown in FIG. 10, based on the magnetic flux densities in the y-measurement axis direction measured by the two magnetic sensors 6, 6, a graph is created with the vertical axis being the measured value of the magnetic flux density and the horizontal axis being the measurement position in the X-axis direction (see Y3 and Y4 in FIG. 10). Then, in the vicinity of the breakage position of the inspection target P, the graphs of the measured values of the magnetic flux densities in the y-measurement axis direction of the two magnetic sensors 6, 6 intersect in the vicinity of the breakage position. That is, in the vicinity of the breakage position of the inspection target P, the above-described reference position BP is formed. On the other hand, in the vicinity of the edge or the like of the inspection target P (hereinafter sometimes referred to as the vicinity of the magnetization end), the graphs of the measured values of the magnetic flux densities in the y-measurement axis direction of the two magnetic sensors 6, 6 do not intersect, and a graph with peaks of opposite signs occurs (see Y3 and Y4 in FIG. 10(A)). That is, since the above-described reference position BP is not formed in the vicinity of the magnetization end, it is possible to prevent misjudging the magnetization end such as the edge of the inspection target P as a break.

[0112] Similarly, if the presence or absence of breakage of the inspection target P is determined by the above method, even if there is a reinforcing bar (transverse bar) or the like that intersects the axial direction of the inspection target P between the inspection target P and the two magnetic sensors 6, 6 (that is, the measurement positions of the magnetic flux density), the above-described reference position is not formed due to the influence of the reinforcing bar or the like (see FIG. 11(A)), so it is possible to prevent misjudging this reinforcing bar or the like as a break.

[0113] Note that when determining the presence or absence of breakage of the inspection target P by the above method, the graphs of the measured values of the magnetic flux densities in the y-measurement axis direction of the two magnetic sensors 6, 6 may be created using the above-described first corrected magnetic flux density value and second corrected magnetic flux density value.

[0114] <Real-time Diagnosis (1)> The break diagnosis by the above-described break determination function may be performed after the measurement of the magnetic flux density at a predetermined distance is completed, or the break diagnosis may be performed while measuring the magnetic flux density. That is, the break diagnosis may be performed while moving the moving body 2 in the first direction (X-axis direction) of the inspection target P. Then, since it is possible to quickly determine the presence or absence of a break at the inspection site, there is an advantage that the diagnostic accuracy and reliability of the break can be improved by immediately measuring the break determination location and the detailed magnetic flux density around it.

[0115] For example, while moving the moving body 2 along the first direction of the inspection target P, the reference position BP is detected by the break determination function. If the reference position BP is not detected until the measurement is completed, it can be tentatively determined that no break has occurred in the inspection target P.

[0116] When the reference position BP is detected, in the same manner as above, the first determination position JP1 and the second determination position JP2 are set at positions separated by a predetermined distance from the reference position BP (for example, positions 20 mm before and after the reference position BP), and the second-direction differential magnetic flux density at the second determination position JP2 is calculated. Then, if the absolute value of the second-direction differential magnetic flux density at the second determination position JP2 is smaller than the threshold value, it can be determined that no break has occurred in the inspection target P.

[0117] On the other hand, if the absolute value of the second-direction differential magnetic flux density at the second determination position JP2 is greater than or equal to the threshold value, the second-direction differential magnetic flux density at the first determination position JP1 is calculated. Then, if the absolute value of the second-direction differential magnetic flux density at the first determination position JP1 is smaller than the threshold value, it can be determined that no break has occurred in the inspection target P. On the other hand, if the absolute value of the second-direction differential magnetic flux density at the first determination position JP1 is greater than or equal to the threshold value and the signs of the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2 are opposite, it can be determined that a break has occurred in the inspection target P.

[0118] In order to more accurately determine the breakage, after the measurement of the magnetic flux density is completed, it is desirable to check the graph of the measured values of the magnetic flux density again. When checking the graph of the measured values of the magnetic flux density after the measurement, it is necessary to provide the control unit 4 with a position calculation function.

[0119] Also, when performing breakage diagnosis while measuring the magnetic flux density, since the measured values will be directly used to determine breakage by the above method, the breakage diagnosis will be performed using the magnetic flux density including the influence of the reinforcement arrangement and the magnetic gradient. Then, errors are likely to occur in the breakage diagnosis. Therefore, after the measurement is completed, based on the magnetic flux densities measured by the two magnetic sensors 6, 6, the above-described first corrected magnetic flux density value and second corrected magnetic flux density value are calculated, a graph is created using the calculated corrected magnetic flux density values, and if the breakage is diagnosed by the above method or the like, the breakage can be determined more accurately.

[0120] <Method for determining reference value, threshold value, first determination position JP1, and second determination position JP2> The method for determining the above-described reference value, threshold value, first determination position JP1, and second determination position JP2 is not particularly limited. A preliminary test may be performed, and based on the results, appropriate values and positions may be set for determining the breakage of the inspection target P in the concrete structure C that is the test subject.

[0121] The preliminary test for determining such a reference value, threshold value, first determination position JP1, and second determination position JP2 can be carried out using a test structure in which a test target (preferably the same material as the inspection target P), which is a member equivalent to the inspection target in the concrete, is embedded. That is, in the test structure in which the test target is embedded in the concrete so as to have the same cover depth as the inspection target P in the concrete structure C, after magnetizing and demagnetizing (or only magnetizing) the test target in the same manner as the inspection, the magnetic flux density is measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1 of the non-destructive inspection device 1, and based on the results, the reference value, threshold value, first determination position JP1, and second determination position JP2 can be determined.

[0122] In addition, since the magnetic permeability of generally dried concrete is almost the same as that of air, the test structure does not necessarily have to be a structure in which the test object is embedded in concrete, and a pseudo-concrete embedded structure may be used as the test structure. The pseudo-concrete embedded structure refers to, for example, a structure that is simply installed as a test structure so that the test object has a predetermined structure and shape, that is, a structure installed with the test object exposed, or a structure provided with a member (for example, a plate-like member formed of a material having magnetic permeability) that covers the test object so that the test object has a predetermined structure and shape. In the case of a structure provided with a member that covers the test object, the surface of the member that covers the test object corresponds to the surface of the concrete in a test structure having a structure in which the test object is embedded in concrete.

[0123] <When using the measurement values of the second magnetic sensor array CL2> In the above-described example, the reference position BP, the first determination position JP1, and the second determination position JP2 were determined based on the difference in the magnetic flux density in the y measurement axis direction (second direction difference magnetic flux density) measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1. The reference position BP, the first determination position JP1, and the second determination position JP2 may be determined by the following method (third determination method).

[0124] First, in addition to the first magnetic sensor array CL1, the magnetic flux measurement unit 5 is provided with a second magnetic sensor array CL2 having magnetic sensors 6 capable of measuring the magnetic flux density in at least the z measurement axis direction (that is, the Z-axis direction). Specifically, in addition to the first magnetic sensor array CL1, the magnetic flux measurement unit 5 is provided with a second magnetic sensor array CL2 having two magnetic sensors 7, 7 disposed on both sides of a line connecting the two magnetic sensors 6, 6 in the second arrangement direction B (see FIG. 3) (line A in FIG. 3(A), hereinafter simply referred to as line A). Moreover, the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 are arranged so that the distances from line A in the second arrangement direction B are the same. Note that the positions where the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 are provided in the magnetic flux measurement unit 5 correspond to the third measurement position and the fourth measurement position referred to in the claims.

[0125] Note that the condition that the distances from line A to the two magnetic sensors 7, 7 in the second array direction B are the same includes both the case where the distances are exactly the same and the case where the difference between the distance from line A to one magnetic sensor 7 and the distance from line A to the other magnetic sensor 7 is within 20 mm. Also, three or more magnetic sensors 7 may be provided in the second magnetic sensor array CL2. In that case, among the three or more magnetic sensors 7, two magnetic sensors 7, 7 that sandwich line A and have the same distance from line A may be adopted as the two magnetic sensors 7, 7 used in the third determination method.

[0126] The control unit 4 is provided with a function to control the plurality of magnetic sensors 6 in the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 in the second magnetic sensor array CL2 to measure the magnetic flux density at the same timing.

[0127] The break determination function is provided with a function to calculate the difference (third-direction difference magnetic flux density) in the magnetic flux density in the z measurement axis direction measured by the two magnetic sensors 7, 7 in the second magnetic sensor array CL2 at the same timing, and to determine the reference position BP, the first determination position JP1, and the second determination position JP2. Specifically, the reference position BP, the first determination position JP1, and the second determination position JP2 are determined as follows.

[0128] First, for the magnetic flux density in the z measurement axis direction of the two magnetic sensors 7, 7 measured at the same timing, the magnetic flux density measured by the magnetic sensor 7 located behind the moving direction of the moving body 2 is subtracted from the magnetic flux density in the z measurement axis direction measured by the magnetic sensor 7 located in front of the moving direction of the moving body 2 to calculate the third-direction difference magnetic flux density, which is the difference between the two. For example, in FIG. 9(B), the magnetic flux density Z2 is subtracted from the magnetic flux density Z1 to calculate the third-direction difference magnetic flux density.

[0129] When the third-direction differential magnetic flux density is calculated, as shown in Fig. 9(A), based on the magnetic flux densities in the z-measurement axis direction measured by the two magnetic sensors 7, 7, a graph is created with the vertical axis representing the third-direction differential magnetic flux density and the horizontal axis representing the position in the X-axis direction of the plurality of magnetic sensors 6 in the first magnetic sensor array CL1 and the timing at which the two magnetic sensors 7, 7 in the second magnetic sensor array CL2 measure the magnetic flux density. In Fig. 9(A), the graph has the upper side as negative and the lower side as positive. Then, the third-direction differential magnetic flux density is small when moving away from the break position, but rapidly increases in the vicinity of the break position (in Fig. 9(A), it increases on the negative side). That is, a period is formed in the vicinity of the break position during which the absolute value of the third-direction differential magnetic flux density becomes equal to or greater than a predetermined value TH (the period W in Fig. 9(A)). More specifically, in the graph of Fig. 9(B), it is the third-direction differential magnetic flux density obtained when the moving body 2 moves from the right direction to the left direction. When the moving body 2 approaches the break position, the third-direction differential magnetic flux density rapidly increases on the negative side in the vicinity of the break position, and when passing through the break position and moving away from the break position, the third-direction differential magnetic flux density rapidly decreases and fluctuates.

[0130] Therefore, when the moving body 2 approaches the break position, the timing (first timing T1) at which the third-direction differential magnetic flux density exceeds a predetermined value TH from a value smaller than the predetermined value TH is determined, and the position in the X-axis direction of the first magnetic sensor array CL1 at this first timing T1 can be set as the first determination position JP1. This first timing T1 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes equal to the predetermined value TH. Also, when the moving body 2 passes through the break position and moves away from the break position, the timing (second timing T2) at which the third-direction differential magnetic flux density drops below the predetermined value TH from a value greater than the predetermined value TH is determined, and the position in the X-axis direction of the first magnetic sensor array CL1 at this second timing T2 can be set as the second determination position JP2. This second timing T2 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes equal to the predetermined value.

[0131] Then, the midpoint between the first determination position JP1 and the second determination position JP2 determined as described above can be used as the reference position BP.

[0132] When the reference position BP, the first determination position JP1, and the second determination position JP2 are determined in such a manner, if the break determination function satisfies the following (6) to (8), it can be determined that a break has occurred in the inspection target P near the reference position BP. On the other hand, if any of the above (6) to (8) is not satisfied, the break determination function can determine that no break has occurred in the inspection target P. (6) The absolute value of the second-direction differential magnetic flux density at the first determination position JP1 and the second determination position JP2 is greater than the threshold value. (7) The signs of the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2 are opposite. (8) The second-direction differential magnetic flux density at the reference position BP is less than or equal to the reference value.

[0133] Note that the predetermined value TH for determining the above-described first timing T1 and second timing T2 can be determined by performing a preliminary test as described above.

[0134] Also, when determining the presence or absence of a break in the inspection target P by the above method, the graphs of the measured values of the magnetic flux density in the y-measurement axis direction of the two magnetic sensors 6, 6 and / or the graphs of the measured values of the magnetic flux density in the z-measurement axis direction of the two magnetic sensors 7, 7 may be created using the above-described first corrected magnetic flux density value and second corrected magnetic flux density value.

[0135] <When not using the reference position BP> Note that when determining the first determination position JP1 and the second determination position JP2 using the first timing T1 and the second timing T2, it is not always necessary to determine the reference position BP (reference timing BT). In this case, if the break determination function satisfies the conditions of (6) and (7), it may determine that a break has occurred in the inspection target P.

[0136] <Real-time Diagnosis (2)> When performing the fracture diagnosis by the above-described fracture determination function while measuring the magnetic flux density, the diagnosis may be performed as follows.

[0137] First, the moving body 2 of the non-destructive inspection device 1 of the present embodiment is arranged on the surface CF of the concrete structure C to be inspected. Next, while measuring the magnetic flux density by the plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 by the control unit 4, the moving body 2 is moved in the first direction (X-axis direction) of the inspection target P. Then, due to the movement of the moving body 2, the plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 move along the first direction (X-axis direction) of the inspection target P. At this time, the control unit 4 calculates the third-direction differential magnetic flux density of the two magnetic sensors 7, 7 sandwiching the first magnetic sensor array CL1 in the second magnetic sensor array CL2 at any time. The third-direction differential magnetic flux density is calculated by subtracting the magnetic flux density in the third direction measured by the rear magnetic sensor 7 (hereinafter sometimes simply referred to as the rear magnetic sensor 7) in the moving direction of the moving body 2 from the magnetic flux density in the third direction measured by the front magnetic sensor 7 (hereinafter sometimes simply referred to as the front magnetic sensor 7) among the two magnetic sensors 7, 7 (hereinafter sometimes simply referred to as the two magnetic sensors 7, 7) sandwiching the first magnetic sensor array CL1 in the second magnetic sensor array CL2.

[0138] If there is a fracture in the inspection target P, as the two magnetic sensors 7, 7 approach the fracture position, the third-direction differential magnetic flux density increases, and eventually, the third-direction differential magnetic flux density exceeds a predetermined value TH (see Fig. 9(A)). Then, the fracture determination function determines the X-axis direction positions of the two magnetic sensors 6, 6 of the first magnetic sensor array CL1 at the timing when the third-direction differential magnetic flux density exceeds the predetermined value TH as the first determination position JP1, calculates the second-direction differential magnetic flux density at that position, and stores the second-direction differential magnetic flux density. In the non-destructive inspection device 1 of the present embodiment, in order to notify that there may be a fracture when the first determination position JP1 is determined, a warning sound may be emitted.

[0139] After the first determination position JP1 is determined and the moving body 2 further moves, the two magnetic sensors 6, 6 pass through the break position and move away from the break position. Eventually, the third-direction differential magnetic flux density changes from a state exceeding a predetermined value TH to a state below the predetermined value TH. Then, the break determination function determines the X-axis direction positions of the two magnetic sensors 6, 6 in the first magnetic sensor row CL1 at the timing when the third-direction differential magnetic flux density falls below the predetermined value TH as the second determination position JP2, calculates the second-direction differential magnetic flux density at that position, and stores the second-direction differential magnetic flux density.

[0140] When the first determination position JP1 and the second determination position JP2 are determined, the break determination function determines the position in the middle of the two as the reference position BP, calculates the second-direction differential magnetic flux density at that position, and stores the second-direction differential magnetic flux density.

[0141] Finally, the break determination function determines whether the second-direction differential magnetic flux densities at the reference position BP, the first determination position JP1, and the second determination position JP2 satisfy a predetermined condition. If the predetermined condition is satisfied, it is determined that a break has occurred. The predetermined condition mentioned here is the following conditions (6) to (8). (6) The absolute values of the second-direction differential magnetic flux densities at the first determination position JP1 and the second determination position JP2 are greater than the threshold value. (7) The signs of the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2 are opposite. (8) The second-direction differential magnetic flux density at the reference position BP is less than or equal to the reference value.

[0142] In the non-destructive inspection device 1 of this embodiment, when it is determined that a break has occurred, a warning sound may be emitted to notify that the break has been detected.

[0143] If the breakage determination is performed by the method as described above, when breakage has occurred in the inspection target P, breakage can be detected rapidly. Therefore, it is desirable in that the diagnostic accuracy and reliability of the breakage can be improved by immediately measuring the breakage determination location and the detailed magnetic flux density around it.

[0144] In addition, even when it is determined that there is breakage by the above method, in order to more accurately determine the breakage, it is desirable to check the graph of the measured values of the magnetic flux density again after the measurement of the magnetic flux density is completed. When checking the graph of the measured values of the magnetic flux density after the measurement, it is necessary to provide the control unit 4 with a position calculation function.

[0145] Also, when performing breakage diagnosis while measuring the magnetic flux density, since the breakage determination is performed by the above method using the measured values as they are, the breakage diagnosis is performed using the magnetic flux density including the influence of the reinforcement arrangement and the magnetic gradient. Then, an error is likely to occur in the breakage diagnosis. Therefore, after the measurement is completed, the first corrected magnetic flux density value and the second corrected magnetic flux density value described above are calculated based on the magnetic flux density measured by the two magnetic sensors 6, 6 or the two magnetic sensors 7, 7, and a graph is created using these calculated corrected magnetic flux density values to diagnose the breakage, then the breakage can be determined more accurately.

[0146] <When not using the reference position BP> Note that when determining the first determination position JP1 and the second determination position JP2 using the first timing T1 and the second timing T2, it is not always necessary to determine the reference position BP. In this case, if the breakage determination function satisfies the conditions (6) and (7), it may be determined that breakage has occurred in the inspection target P.

[0147] <Breakage determination using the measurement timing> In the above example, the first determination position JP1 and the second determination position JP2 were set based on the first timing T1 and the second timing T2, and breakage was determined using the second-direction differential magnetic flux density at the first determination position JP1 and the second-direction differential magnetic flux density at the second determination position JP2. However, without setting the first determination position JP1 and the second determination position JP2, breakage determination may be performed using the second-direction differential magnetic flux density at the first timing T1, the second-direction differential magnetic flux density at the second timing T2, and the second-direction differential magnetic flux density at a timing (reference timing BT) intermediate between the first timing T1 and the second timing T2 (fourth determination method). Hereinafter, a case where breakage determination is performed using the second-direction differential magnetic flux densities of the first timing T1, the second timing T2, and the reference timing BT will be described.

[0148] First, the moving body 2 of the non-destructive inspection device 1 of the present embodiment is arranged on the surface CF of the concrete structure C to be inspected. Next, while measuring the magnetic flux density by the plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 by the control unit 4, the moving body 2 is moved in the first direction (X-axis direction) of the inspection target P. Then, due to the movement of the moving body 2, the plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor array CL2 move along the first direction (X-axis direction) of the inspection target P. At this time, the control unit 4 calculates the third-direction differential magnetic flux density of the two magnetic sensors 7, 7 sandwiching the first magnetic sensor array CL1 in the second magnetic sensor array CL2 at any time. The third-direction differential magnetic flux density is calculated by subtracting the magnetic flux density in the third direction measured by the rear magnetic sensor 7 (hereinafter sometimes simply referred to as the rear magnetic sensor 7) in the moving direction of the moving body 2 from the magnetic flux density in the third direction measured by the front magnetic sensor 7 (hereinafter sometimes simply referred to as the front magnetic sensor 7) among the two magnetic sensors 7, 7 (hereinafter sometimes simply referred to as the two magnetic sensors 7, 7) sandwiching the first magnetic sensor array CL1 in the second magnetic sensor array CL2.

[0149] If there is a break in the inspection target P, as the two magnetic sensors 7, 7 approach the break position, the third-direction differential magnetic flux density increases, and eventually, the third-direction differential magnetic flux density exceeds a predetermined value TH (see Fig. 9(A)). Then, the break determination function determines the timing when the third-direction differential magnetic flux density exceeds the predetermined value TH as the first timing T1 (see Fig. 9(A) and (B)), calculates the second-direction differential magnetic flux density of the two magnetic sensors 6, 6 at the first timing T1, and stores the second-direction differential magnetic flux density. This first timing T1 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes the predetermined value TH. In the non-destructive inspection device 1 of the present embodiment, a warning sound may be emitted to notify that there may be a break when the first timing T1 is determined.

[0150] When the moving body 2 further moves after the first timing T1 is determined, the two magnetic sensors 7, 7 pass through the break position and move away from the break position. Eventually, the third-direction differential magnetic flux density changes from a state exceeding the predetermined value TH to a state below the predetermined value TH. Then, the break determination function determines the timing when the third-direction differential magnetic flux density falls below the predetermined value TH as the second timing T2, calculates the second-direction differential magnetic flux density of the two magnetic sensors 6, 6 at the second timing T2, and stores the second-direction differential magnetic flux density. This second timing T2 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes the predetermined value TH.

[0151] When the first timing T1 and the second timing T2 are determined, the break determination function determines the position in the middle between the two as the reference timing BT, calculates the second-direction differential magnetic flux density at the reference timing BT, and stores the second-direction differential magnetic flux density.

[0152] Finally, the break determination function determines whether the second-direction differential magnetic flux densities at the reference timing BT, the first timing T1, and the second timing T2 satisfy a predetermined condition, and determines that a break has occurred when the following conditions (3) to (5) are satisfied. (3) The absolute value of the second-direction differential magnetic flux density measured at the first timing T1 and the second timing T2 becomes a predetermined value or more. (4) The signs of the second-direction differential magnetic flux density at the first timing T1 and the second-direction differential magnetic flux density at the second timing T2 are opposite. (5) The absolute value of the second-direction differential magnetic flux density measured at the reference timing BT is a predetermined value or less. Note that in the non-destructive inspection apparatus 1 of the present embodiment, when it is determined that a break has occurred, a warning sound may be emitted to notify that the break has been detected.

[0153] If the break determination is performed by the above method, when a break has occurred in the inspection object P, the break can be detected quickly. Therefore, by immediately measuring the break determination location and the detailed magnetic flux density around it, it is desirable in terms of improving the diagnostic accuracy and reliability of the break.

[0154] Note that when performing the break diagnosis by the break determination function using the reference timing BT, the first timing T1, and the second timing T2 instead of the reference position BP, the first determination position JP1, and the second determination position JP2, the advantage is obtained that it is not necessary to measure the moving distance in the X-axis direction. On the other hand, when performing the break diagnosis by the break determination function using the reference position BP, the first determination position JP1, and the second determination position JP2, the advantage is obtained that the break position determination position in the X-axis direction can be specified more accurately than when using the reference timing BT, the first timing T1, and the second timing T2.

[0155] Also, even when it is determined that there is a break by the above method, in order to more accurately determine the break, it is desirable to confirm the graph of the measured magnetic flux density values again after the measurement of the magnetic flux density is completed. When confirming the graph of the measured magnetic flux density values after the measurement, it is necessary to provide a position calculation function in the control unit 4.

[0156] Also, in the above method, for more accurately determining breakage, after the measurement of the magnetic flux density is completed, it is desirable to check the graph of the measured values of the magnetic flux density again. When performing breakage diagnosis while measuring the magnetic flux density, since the breakage determination is made by using the measured values as they are in the above method, the breakage diagnosis is performed using the magnetic flux density including the influence of the reinforcement arrangement and the magnetic gradient. Then, errors are likely to occur in the breakage diagnosis. Therefore, after the measurement is completed, based on the magnetic flux density measured by the two magnetic sensors 6, 6 or the two magnetic sensors 7, 7, the first corrected magnetic flux density value and the second corrected magnetic flux density value are calculated, a graph is created using these calculated corrected magnetic flux density values, and if the breakage is diagnosed by the above method or the like, the breakage can be determined more accurately.

[0157] <When the reference timing BT is not used> When determining the first determination position JP1 and the second determination position JP2 using the first timing T1 and the second timing T2, it is not always necessary to determine the reference timing BT. In this case, if the conditions (3) and (4) are satisfied, the breakage determination function may determine that breakage has occurred in the inspection target P.

[0158] <Breakage determination using the measurement timing> In the above-described example, when creating a graph as shown in FIG. 9(B) based on the measured values of the two magnetic sensors 6, 6 of the first magnetic sensor array CL1, the case where the breakage determination function determines the breakage of the inspection target P on the premise that two graphs intersect, that is, the reference position BP exists, was described.

[0159] However, due to the influence of the magnetization state and the reinforcement arrangement of the inspection target P, there may be a large difference in the DC component of the magnetic flux density in the second direction measured by the two magnetic sensors 6, 6 of the first magnetic sensor array CL1. That is, even when creating a graph as shown in FIG. 9(B) based on the measured values of the two magnetic sensors 6, 6 of the first magnetic sensor array CL1 measured in a state where breakage has occurred in the inspection target P, the two graphs may not intersect (see Y3 and Y4 in FIG. 12(B)).

[0160] Even under the above conditions, if there is a break in the inspection target P, as shown in FIG. 5(B), the magnetic flux densities in the second direction measured by the two magnetic sensors 6, 6 are in a state where the waveforms are inverted on both sides of the inspection target P, and moreover, they show fluctuations having peaks before and after the break position. Therefore, if the break is judged by the following method, even under conditions where the two graphs do not intersect, it is possible to prevent the detection omission of the break in the inspection target P. Hereinafter, the method (the fifth judgment method) will be described.

[0161] First, the moving body 2 of the non-destructive inspection device 1 of the present embodiment is arranged on the surface CF of the concrete structure C to be inspected. Next, while measuring the magnetic flux density by the plurality of magnetic sensors 6 of the first magnetic sensor row CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor row CL2 by the control unit 4, the moving body 2 is moved in the first direction (X-axis direction) of the inspection target P. Then, due to the movement of the moving body 2, the plurality of magnetic sensors 6 of the first magnetic sensor row CL1 and the two magnetic sensors 7, 7 of the second magnetic sensor row CL2 move along the first direction (X-axis direction) of the inspection target P. At this time, the control unit 4 calculates at any time the third-direction differential magnetic flux density of the two magnetic sensors 7, 7 sandwiching the first magnetic sensor row CL1 in the second magnetic sensor row CL2. The third-direction differential magnetic flux density is calculated by subtracting the magnetic flux density in the third direction measured by the rear magnetic sensor 7 (hereinafter sometimes simply referred to as the rear magnetic sensor 7) in the moving direction of the moving body 2 from the magnetic flux density in the third direction measured by the front magnetic sensor 7 (hereinafter sometimes simply referred to as the front magnetic sensor 7) among the two magnetic sensors 7, 7 (hereinafter sometimes simply referred to as the two magnetic sensors 7, 7) sandwiching the first magnetic sensor row CL1 in the second magnetic sensor row CL2.

[0162] If there is a break in the inspection target P, as the two magnetic sensors 7, 7 approach the break position, the third-direction differential magnetic flux density increases, and eventually, the third-direction differential magnetic flux density exceeds a predetermined value TH (see Fig. 12(A)). Then, the break determination function determines the timing when the third-direction differential magnetic flux density exceeds the predetermined value TH as the first timing T1 (see Fig. 12(A) and (B)). This first timing T1 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes the predetermined value TH. In the non-destructive inspection apparatus 1 of the present embodiment, in order to notify that there may be a break when the first timing T1 is determined, a warning sound may be emitted.

[0163] When the moving body 2 further moves after the first timing T1 is determined, the two magnetic sensors 7, 7 pass through the break position and move away from the break position. Eventually, the third-direction differential magnetic flux density changes from a state exceeding the predetermined value TH to a state below the predetermined value TH. Then, the break determination function determines the timing when the third-direction differential magnetic flux density falls below the predetermined value TH as the second timing T2 (see Fig. 12(A) and (B)). This second timing T2 corresponds to one of the two timings at which the absolute value of the third-direction differential magnetic flux density referred to in the claims becomes the predetermined value TH.

[0164] When the first timing T1 and the second timing T2 are determined, the break determination function determines that a break has occurred if the following conditions (1) to (2) are satisfied. (1) The sign of the first magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing T1 and the magnetic flux density in the second direction measured at the second timing T2 by one of the two magnetic sensors 6, 6 in the first magnetic sensor array CL1, and the second magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing T1 and the magnetic flux density in the second direction measured at the second timing T2 by the other of the two magnetic sensors 6, 6, is opposite. (2) The absolute values of the first magnetic flux density variation amount and the second magnetic flux density variation amount are equal to or greater than a predetermined value.

[0165] For example, assume that the fluctuation graphs of the magnetic flux density measured by two magnetic sensors 6, 6 are as shown in Fig. 12(B). In this case, if the graph of the magnetic flux density measured by one magnetic sensor 6 is Y3 and the graph of the magnetic flux density measured by the other magnetic sensor 6 is Y4, the first magnetic flux density fluctuation amount is V3 and the second magnetic flux density fluctuation amount is V4. Then, if the first magnetic flux density fluctuation amount V3 and the second magnetic flux density fluctuation amount V4 satisfy the above conditions (1) and (2), the breakage determination function determines that a breakage has occurred.

[0166] Note that in the non-destructive inspection apparatus 1 of the present embodiment, when it is determined that a breakage has occurred, a warning sound may be emitted to notify that the breakage has been detected.

[0167] If the breakage determination is performed by the above method, when a breakage has occurred in the inspection object P, the breakage can be detected quickly. Therefore, it is desirable in that the diagnostic accuracy and reliability of the breakage can be improved by immediately measuring the breakage determination location and the detailed magnetic flux density around it.

[0168] Also, even when it is determined that there is a breakage by the above method, in order to more accurately determine the breakage, it is desirable to check the graph of the measured values of the magnetic flux density again after the measurement of the magnetic flux density is completed. When checking the graph of the measured values of the magnetic flux density after the measurement, it is necessary to provide a position calculation function in the control unit 4.

[0169] Also, when performing breakage diagnosis while measuring the magnetic flux density, since the breakage determination is performed by the above method using the measured values as they are, the breakage diagnosis is performed with the magnetic flux density including the influence of the reinforcement arrangement and the magnetic gradient. Then, an error is likely to occur in the breakage diagnosis. Therefore, after the measurement is completed, the first corrected magnetic flux density value and the second corrected magnetic flux density value described above are calculated based on the magnetic flux density measured by the two magnetic sensors 6, 6 or the two magnetic sensors 7, 7, a graph is created using the calculated corrected magnetic flux density values, and if the breakage is diagnosed by the above method or the like, the breakage can be determined more accurately.

[0170] <Real-time diagnosis using only a plurality of magnetic sensors 6 of the first magnetic sensor array CL1> In the above example, real-time diagnosis was performed using a plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and two magnetic sensors 7, 7 of the second magnetic sensor array CL2. However, real-time diagnosis may also be performed using only a plurality of magnetic sensors 6 of the first magnetic sensor array CL1. That is, after detecting the reference position BP, the second-direction differential magnetic flux density at the first determination position JP1 is calculated. When the second magnetic sensor array CL2 reaches the second determination position JP2, the second-direction differential magnetic flux density may be immediately calculated to determine breakage. It is desirable to perform real-time diagnosis using a plurality of magnetic sensors 6 of the first magnetic sensor array CL1 and two magnetic sensors 7, 7 of the second magnetic sensor array CL2 in that it can prevent misdiagnosis due to the influence of steel bar arrangement or the like.

Example

[0171] It was confirmed that the damage of the steel material embedded in the concrete structure can be detected by using the non-destructive inspection method of the present invention.

[0172] <Example 1> In Example 1, a test structure in which a PC steel wire (diameter 32 mm) inserted into a sheath pipe made of steel plate was embedded in a concrete structure was used. After magnetizing the PC steel wire in the test structure, the non-destructive inspection device was moved along the surface of the test structure and the axial direction of the PC steel wire to measure the magnetic flux density.

[0173] As the non-destructive inspection device, the non-destructive inspection device shown in FIG. 1 was used. Eight magnetic sensors of the non-destructive inspection device were arranged at intervals of 50 mm. As the magnetic sensors, TMR sensors capable of measuring magnetic fields in three axial directions were used.

[0174] In the test structure, cross steel bars (diameter 16 mm) were arranged in a grid pattern at intervals of 125 mm. The PC steel wire was arranged parallel to the longitudinal steel bars of the cross steel bars and not directly above the longitudinal steel bars. Also, the embedding depth of the PC steel wire is at a position 110 mm from the surface of the test structure.

[0175] Magnetization of the PC steel wire was performed by using a magnet unit (180×165×134 mm) to make a round trip along the axial direction directly above the PC steel wire.

[0176] The contour diagram of the experimental results is shown in Fig. 7. Note that the contour diagram in Fig. 7 was created using the corrected magnetic flux density values obtained by removing the influence of the magnetic field formed by the reinforcement bars and the influence of the magnetic gradient from the measured magnetic flux density.

[0177] As shown in Fig. 7, in the contour diagram, the magnetic flux density of the plus component is distributed in the part surrounded by the thick line, and the magnetic flux density of the minus component is distributed in the part surrounded by the thin line. And in the contour diagram of the Y-axis, the break position of the PC steel wire is at the center of the part surrounded by the four circles, and it can be confirmed that the break position of the PC steel wire can be easily specified by the contour diagram of the Y-axis.

[0178] <Example 2> In Example 2, a reinforcing bar (diameter 8 mm) with a break as the inspection object was installed horizontally, and a test piece covered with a vinyl chloride cover on this reinforcing bar was used. The nondestructive inspection device was moved along the axial direction of the reinforcing bar on the surface of the cover to measure the magnetic flux density. Note that the test piece used was one with only the reinforcing bar to be inspected installed, and there was no reinforcement arrangement or the like. Note that the distance from the reinforcing bar to the surface of the cover was set to 20 mm.

[0179] In the experiment, the nondestructive inspection device shown in Fig. 3(B) was used. Two magnetic sensors were arranged vertically and horizontally at intervals of 50 mm each. A TMR sensor capable of measuring magnetic fields in three axial directions was used for the magnetic sensors.

[0180] Note that magnetization of the reinforcing bar was performed by using a magnet unit (180×165×134 mm) to make a round trip along the axial direction directly above the reinforcing bar.

[0181] The graph of the magnetic flux density of the experimental results is shown in Fig. 10. Note that the graph of the magnetic flux density in Fig. 10 shows the measured magnetic flux density on the vertical axis and the timing (time) at which the magnetic flux density was measured on the horizontal axis. The upper graph is a graph of the magnetic flux density measured by four magnetic sensors. Y3 and Y4 are graphs of the magnetic flux density in the second direction (Y-axis direction) measured by two magnetic sensors 6 and 6 in the first magnetic sensor row CL1 in Fig. 3. Z1 and Z2 are graphs of the magnetic flux density in the third direction (Z-axis direction) measured by two magnetic sensors 7 and 7 in the second magnetic sensor row CL2 in Fig. 3. Z1 is a graph of the magnetic flux density in the third direction (Z-axis direction) measured by the magnetic sensor 7 in front of the traveling direction of the nondestructive inspection device, and Z2 is a graph of the magnetic flux density in the third direction (Z-axis direction) measured by the magnetic sensor 7 behind the traveling direction of the nondestructive inspection device. The lower graph is a graph of Z1 - Z2.

[0182] As shown in Fig. 10(A), in the graph of Z1 - Z2, there are regions where the magnetic flux density drops significantly below a predetermined value (-100 μT) at the two magnetization ends and the fracture position. However, at the fracture position, Y3 and Y4 intersect, but at the two magnetization ends, Y3 and Y4 do not intersect.

[0183] From this result, it was confirmed that by using the magnetic flux density in the second direction (Y-axis direction) measured by the two magnetic sensors 6 and 6 in the first magnetic sensor row and the magnetic flux density in the third direction (Z-axis direction) measured by the two magnetic sensors 7 and 7 in the second magnetic sensor row, even if there are magnetization ends that would be judged as fractures based only on the magnetic flux density in the third direction (Z-axis direction), it is possible to distinguish between the fracture and the magnetization ends of the inspection object and judge the fracture.

[0184] <Example 3> In Example 3, as a test piece, a reinforcing bar that was not broken as the inspection object was installed, and an experiment was conducted under the same conditions as in Example 3 except that a reinforcing bar (diameter 3 mm, hereinafter referred to as a cross bar) orthogonal to this reinforcing bar was arranged between the reinforcing bar to be inspected.

[0185] The graph of the magnetic flux density of the experimental results is shown in Fig. 11(A). Note that the graph of the magnetic flux density in Fig. 11(A) shows the measured magnetic flux density on the vertical axis and the timing (time) at which the magnetic flux density was measured on the horizontal axis.

[0186] As shown in Fig. 11(A), in the graph of Z1 - Z2, there is a region where the magnetic flux density exceeds a predetermined value (100 μT in absolute value) before and after passing through the horizontal bar, but Y3 and Y4 do not intersect.

[0187] From this result, it was confirmed that by using the magnetic flux density in the second direction (Y-axis direction) measured by the two magnetic sensors 6, 6 of the first magnetic sensor array and the magnetic flux density in the third direction (Z-axis direction) measured by the two magnetic sensors 7, 7 of the second magnetic sensor array, even if there is a horizontal bar that intersects the inspection object that would be judged as broken by only the magnetic flux density in the third direction (Z-axis direction), it is possible to prevent misidentifying the horizontal bar as broken.

[0188] <Example 4> In Example 4, an experiment was conducted under the same conditions as in Example 2, except that a spiral steel bar (diameter 3 mm) with a break was arranged as the inspection object.

[0189] The graph of the magnetic flux density of the experimental results is shown in Fig. 11(B). Note that the graph of the magnetic flux density in Fig. 11(B) shows the measured magnetic flux density on the vertical axis and the timing (time) at which the magnetic flux density was measured on the horizontal axis. Also, in the graph of the magnetic flux density in Fig. 11(B), a line parallel to the vertical axis indicates the position where the spiral back bar was arranged.

[0190] As shown in Fig. 11(B), there are regions where Z1 - Z2 exceeds a predetermined value (100 μT in absolute value) even outside the break position, but Y3 and Y4 do not intersect. On the other hand, near the break position, there are regions where Z1 - Z2 exceeds a predetermined value (100 μT in absolute value), and Y3 and Y4 intersect.

[0191] From these results, it was confirmed that even if the inspection target is a spiral back muscle, appropriate judgment of breakage can be made by using the magnetic flux density in the second direction (Y-axis direction) measured by the two magnetic sensors 6, 6 of the first magnetic sensor array and the magnetic flux density in the third direction (Z-axis direction) measured by the two magnetic sensors 7, 7 of the second magnetic sensor array.

Industrial Applicability

[0192] The non-destructive inspection method of the present invention is suitable as a method for detecting damages such as breakage and corrosion of reinforcing bars, steel bars, steel wires, etc. provided in a concrete structure.

Explanation of Symbols

[0193] 1 Non-destructive inspection device 2 Moving body 5 Magnetic flux measurement unit 6 Magnetic sensor 7 Magnetic sensor A First array direction B Central axis of moving body 2, second array direction CL1 First magnetic sensor array CL2 Second magnetic sensor array SA Reference plane C Concrete structure CF Surface of concrete structure C P Inspection target BP Reference position BT Reference timing T1 First timing T2 Second timing

Claims

Claim 1 A method for measuring the magnetic flux density of an inspection target extending in a first direction embedded in a concrete structure outside the concrete structure along the first direction of the inspection target, and determining damage to the inspection target based on fluctuations in the magnetic flux density, comprising: The magnetic flux density to be measured is a magnetic flux density in a second direction that is a direction along the surface of the concrete structure or a direction along the tangent to the surface of the concrete structure and is orthogonal to the first direction of the inspection target, measuring the magnetic flux density in the second direction on both sides of a reference plane that intersects the inspection target and is parallel to the first direction of the inspection target and orthogonal to the second direction, determining damage to the inspection target based on the measured magnetic flux density in the second direction A non-destructive inspection method characterized by the above. Claim 2 Measuring the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, respectively, At third and fourth measurement positions that are spaced apart in the first direction of the inspection target and sandwich the first and second measurement positions in the first direction of the inspection target, measuring the magnetic flux density in a third direction that is orthogonal to both the first direction and the second direction of the inspection target at the same timing as the first and second measurement positions, respectively, Calculating a third-direction differential magnetic flux density that is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position measured at the same timing, In a period in which the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, setting two timings at which the absolute value of the third-direction differential magnetic flux density becomes a predetermined value as a first timing and a second timing, Determining that a break has occurred in the inspection target when the following conditions (1) and (2) are satisfied The non-destructive inspection method according to claim 1, characterized by the above. (1) The signs of a first magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction at the first measurement position measured at the first timing and the magnetic flux density in the second direction at the first measurement position measured at the second timing, and a second magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction at the second measurement position measured at the first timing and the magnetic flux density in the second direction at the second measurement position measured at the second timing, are opposite. (2) The absolute values of the first magnetic flux density variation amount and the second magnetic flux density variation amount are equal to or greater than a predetermined value. Claim 3 Measure the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, respectively. Measure the magnetic flux density in a third direction orthogonal to both the first direction and the second direction of the inspection object at a third measurement position and a fourth measurement position that are separated in the first direction of the inspection object and sandwich the first measurement position and the second measurement position in the first direction of the inspection object, at the same timing as the first measurement position and the second measurement position. Calculate a second-direction differential magnetic flux density that is the difference between the magnetic flux density in the second direction at the first measurement position and the magnetic flux density in the second direction at the second measurement position, measured at the same position in the first direction of the inspection object. Calculate a third-direction differential magnetic flux density that is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position, measured at the same timing. In a period when the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, set two timings when the absolute value of the third-direction differential magnetic flux density becomes the predetermined value as a first timing and a second timing. When the following conditions (3) and (4) are satisfied, determine that a break has occurred in the inspection object. The non-destructive inspection method according to claim 1, characterized in that. (3) The absolute value of the second-direction differential magnetic flux density measured at the first timing and the second timing is equal to or greater than a predetermined value. (4) The signs of the second-direction differential magnetic flux density at the first timing and the second-direction differential magnetic flux density at the second timing are opposite.

4. Set the timing intermediate between the first timing and the second timing as a reference timing. When the following condition (5) is satisfied in addition to (3) and (4), determine that a break has occurred in the inspection object. The non-destructive inspection method according to claim 3, characterized in that. (5) The absolute value of the second-direction differential magnetic flux density measured at the reference timing is equal to or less than a predetermined value.

5. When measuring the magnetic flux density of the inspection object along the first direction of the inspection object, set the timing when the absolute value of the third-direction differential magnetic flux density exceeds a predetermined value from a value smaller than the predetermined value as the first timing, and set the timing when the absolute value of the third-direction differential magnetic flux density falls below the predetermined value from a value larger than the predetermined value after the first timing as the second timing. The non-destructive inspection method according to claim 2, 3 or 4, characterized in that.

6. Measure the magnetic flux density in the second direction at a first measurement position and a second measurement position sandwiching the reference plane, respectively. Calculate a second-direction differential magnetic flux density, which is the difference between the magnetic flux density in the second direction at the first measurement position and the magnetic flux density in the second direction at the second measurement position, measured at the same position in the first direction of the inspection object. Set, as a reference position, a position in the first direction of the inspection object where the absolute value of the second-direction differential magnetic flux density is equal to or less than a predetermined value. When the following conditions (6) and (7) are satisfied, it is determined that a break has occurred in the inspection object. The non-destructive inspection method according to claim 1, characterized in that. (6) The absolute values of the second-direction differential magnetic flux densities at a first determination position and a second determination position sandwiching the reference position in the first direction of the inspection object are equal to or greater than a predetermined value. (7) The signs of the second-direction differential magnetic flux density at the first determination position and the second-direction differential magnetic flux density at the second determination position are opposite.

7. Measure the magnetic flux density in a third direction perpendicular to both the first direction and the second direction of the inspection object at a third measurement position and a fourth measurement position that are separated in the first direction of the inspection object and sandwich the first measurement position and the second measurement position in the first direction of the inspection object, at the same timing as the first measurement position and the second measurement position. Calculate a third-direction differential magnetic flux density, which is the difference between the value of the magnetic flux density in the third direction at the third measurement position and the value of the magnetic flux density in the third direction at the fourth measurement position, measured at the same timing. During a period when the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, set the positions in the first direction of the inspection object at the first measurement position or the second measurement position at two timings when the absolute value of the third-direction differential magnetic flux density is equal to the predetermined value as the first determination position and the second determination position. The non-destructive inspection method according to claim 6, characterized in that.

8. Measure the magnetic flux density in the second direction, the magnetic flux density in the first direction of the inspection object, and / or the magnetic flux density in a third direction perpendicular to both the first direction and the second direction of the inspection object. Judge the damage of the inspection object based on the variation of the measured value of the magnetic flux density in the second direction according to the measurement position, and the variation of the measured value of the magnetic flux density in the first direction and / or the third direction of the inspection object according to the measurement position. The non-destructive inspection method according to any one of claims 1 to 7, characterized in that.

9. Measure the magnetic flux density in the third direction at a plurality of measurement positions arranged along the first direction of the object to be inspected. Among the plurality of measurement positions, set at least two measurement positions on both sides of the reference plane to sandwich, in the first direction of the object to be inspected, at least two measurement positions for measuring the magnetic flux density in the second direction. The non-destructive inspection method according to claim 8, characterized by the above.

10. Measure the magnetic flux density at a plurality of locations on both sides of the reference plane respectively. Based on the magnetic flux density measured at a plurality of locations, create a contour diagram of the magnetic flux density on a plane parallel to the surface of the concrete structure or a plane parallel to the tangent plane of the surface of the concrete structure, and determine the damage of the object to be inspected based on the contour diagram. The non-destructive inspection method according to any one of claims 1 to 9, characterized by the above.

11. Remove the periodic fluctuation component of the magnetic flux density included in the measured magnetic flux density by a moving average filter. The non-destructive inspection method according to any one of claims 1 to 10, characterized by the above.

12. At each measurement position, create an approximate polynomial of the magnetic flux density in the direction along the first direction of the object to be inspected based on the measured magnetic flux density and the measurement position where the magnetic flux density is measured. Calculate a corrected magnetic flux density value by subtracting the value of the approximate polynomial at the same position as the measurement position where the magnetic flux density is measured from the measured value of the measured magnetic flux density, and determine the damage of the object to be inspected based on the corrected magnetic flux density value. The non-destructive inspection method according to any one of claims 1 to 11, characterized by the above.

13. A non-destructive inspection device for measuring the magnetic flux density of an object to be inspected extending in the first direction embedded in a concrete structure outside the concrete structure along the first direction of the object to be inspected and determining the damage of the object to be inspected, comprising: A magnetic flux measurement unit having a plurality of magnetic sensors for measuring the magnetic flux density. The magnetic flux measurement unit: The plurality of magnetic sensors have a first magnetic sensor array arranged side by side along the first arrangement direction. The plurality of magnetic sensors: One measurement axis is arranged parallel to the first arrangement direction. The first arrangement direction is orthogonal to the first direction of the object to be inspected, and the non-destructive inspection device is moved along the surface of the concrete structure in the first direction of the object to be inspected in a state where the object to be inspected is located between two of the plurality of magnetic sensors of the first magnetic sensor array to measure the magnetic flux density of the object to be inspected. The non-destructive inspection device, characterized by the above.

14. The magnetic flux measurement unit has a second magnetic sensor array including two magnetic sensors arranged side by side along a second array direction intersecting the first array direction and arranged so as to sandwich the first magnetic sensor array in the second array direction, and the two magnetic sensors of the second magnetic sensor array have a function of measuring the magnetic flux density in a third direction orthogonal to the first array direction and the second array direction, and includes a control unit having a function of controlling the plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array to measure the magnetic flux density at the same timing, and an analysis function of analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is such that when the first array direction is orthogonal to the first direction of the inspection object and the inspection object is located between two of the plurality of magnetic sensors of the first magnetic sensor array, the non-destructive inspection device is moved along the surface of the concrete structure in the first direction of the inspection object, and the magnetic flux density in the second direction parallel to the first array direction is measured by the plurality of magnetic sensors of the first magnetic sensor array, and the magnetic flux density in the third direction orthogonal to the first array direction and the second array direction is measured by the two magnetic sensors of the second magnetic sensor array, a third-direction differential magnetic flux density, which is the difference between the values of the magnetic flux density in the third direction measured at the same timing by the two magnetic sensors of the second magnetic sensor array, is calculated, in a period in which the absolute value of the third-direction differential magnetic flux density becomes equal to or greater than a predetermined value, two timings at which the absolute value of the third-direction differential magnetic flux density becomes equal to the predetermined value are defined as a first timing and a second timing, and it is determined that a break has occurred in the inspection object when the following conditions (1) and (2) are satisfied. The non-destructive inspection device according to claim 13, characterized in that. (1) The sign of the first magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing and the magnetic flux density in the second direction measured at the second timing by one of the two magnetic sensors of the first magnetic sensor array sandwiching the inspection object in the first array direction, and the second magnetic flux density variation amount, which is the difference between the magnetic flux density in the second direction measured at the first timing and the magnetic flux density in the second direction measured at the second timing by the other of the two magnetic sensors, is opposite. (2) The absolute values of the first magnetic flux density variation amount and the second magnetic flux density variation amount are equal to or greater than a predetermined value.

15. The magnetic flux measurement unit has a second magnetic sensor array in which two magnetic sensors are arranged side by side along a second arrangement direction intersecting the first arrangement direction and are arranged so as to sandwich the first magnetic sensor array in the second arrangement direction, and the two magnetic sensors of the second magnetic sensor array have a function of measuring the magnetic flux density in a third direction orthogonal to the first arrangement direction and the second arrangement direction, and includes a control unit having a function of controlling the plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array to measure the magnetic flux density at the same timing, and an analysis function of analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit When the first arrangement direction is orthogonal to the first direction of the inspection object and the inspection object is located between two magnetic sensors among the plurality of magnetic sensors of the first magnetic sensor array, the non-destructive inspection device is moved along the surface of the concrete structure in the first direction of the inspection object, and the magnetic flux density in the second direction parallel to the first arrangement direction is measured by the plurality of magnetic sensors of the first magnetic sensor array, and the magnetic flux density in the third direction orthogonal to the first arrangement direction and the second arrangement direction is measured by the two magnetic sensors of the second magnetic sensor array, calculates a second direction differential magnetic flux density, which is the difference between the magnetic flux density in the second direction measured by one of the two magnetic sensors of the first magnetic sensor array sandwiching the inspection object in the first arrangement direction and the magnetic flux density in the second direction measured by the other of the two magnetic sensors, measured at the same position in the first direction of the inspection object, calculates a third direction differential magnetic flux density, which is the difference between the magnetic flux density in the third direction measured by the two magnetic sensors of the second magnetic sensor array at the same timing, in a period in which the absolute value of the third direction differential magnetic flux density is equal to or greater than a predetermined value, the two timings at which the absolute value of the third direction differential magnetic flux density becomes a predetermined value are defined as a first timing and a second timing, and determines that a break has occurred in the inspection object when the following conditions (3) and (4) are satisfied. The non-destructive inspection method according to claim 13, characterized in that. (3) The absolute value of the second-direction differential magnetic flux density measured at the first timing and the second timing is equal to or greater than a predetermined value. (4) The signs of the second-direction differential magnetic flux density at the first timing and the second-direction differential magnetic flux density at the second timing are opposite.

16. The analysis function of the control unit is using the timing midway between the second timing and the first timing as a reference timing, and when the conditions of (5) are satisfied in addition to (3) and (4) above, determining that a break has occurred in the inspection target. The non-destructive inspection method according to claim 15, characterized in that. (5) The absolute value of the second-direction differential magnetic flux density measured at the reference timing is equal to or less than a predetermined value.

17. The analysis function of the control unit is when moving the non-destructive inspection device in the first direction of the inspection target along the surface of the concrete structure, using the timing when the absolute value of the third-direction differential magnetic flux density exceeds a predetermined value from a value smaller than the predetermined value as the first timing, and using the timing when the absolute value of the third-direction differential magnetic flux density falls below the predetermined value from a value larger than the predetermined value after the first timing as the second timing. The non-destructive inspection device according to claim 14, 15 or 16, characterized in that.

18. It is provided with a control unit having an analysis function for analyzing the measured value of the magnetic flux density measured by the magnetic flux measurement unit, and the analysis function of the control unit is with the first array direction being orthogonal to the first direction of the inspection target and the inspection target being located between two of the plurality of magnetic sensors of the first magnetic sensor array, when moving the non-destructive inspection device in the first direction of the inspection target along the surface of the concrete structure and measuring the magnetic flux density in the second direction orthogonal to the first direction of the inspection target and parallel to the first array direction by the plurality of magnetic sensors of the first magnetic sensor array, calculating a second-direction differential magnetic flux density, which is the difference between the magnetic flux density in the second direction measured by one of the two magnetic sensors of the first magnetic sensor array sandwiching the inspection target in the first array direction and measured at the same position in the first direction of the inspection target and the magnetic flux density in the second direction measured by the other of the two magnetic sensors, using, as a reference position, a position where the absolute value of the second-direction differential magnetic flux density in the first direction of the inspection target is equal to or less than a predetermined value, and when the following conditions (6) and (7) are satisfied, determining that a break has occurred in the inspection target. The nondestructive inspection device according to claim 13, characterized in that... (6) The absolute value of the second-direction differential magnetic flux density at the first determination position and the second determination position sandwiching the reference position in the first direction of the inspection object is equal to or greater than a predetermined value. (7) The signs of the second-direction differential magnetic flux density at the first determination position and the second-direction differential magnetic flux density at the second determination position are opposite.

19. The magnetic flux measurement unit... has a second magnetic sensor array in which two magnetic sensors are arranged side by side along a second arrangement direction intersecting the first arrangement direction and are arranged so as to sandwich the first magnetic sensor array in the second arrangement direction. The two magnetic sensors of the second magnetic sensor array... have a function of measuring the magnetic flux density in a third direction orthogonal to the first arrangement direction and the second arrangement direction. The control unit... has a function of controlling so that the plurality of magnetic sensors of the first magnetic sensor array and the two magnetic sensors of the second magnetic sensor array measure the magnetic flux density at the same timing. The analysis function of the control unit... calculates a third-direction differential magnetic flux density, which is the difference in the magnetic flux density in the third direction measured by the two magnetic sensors of the second magnetic sensor array at the same timing. During a period when the absolute value of the third-direction differential magnetic flux density is equal to or greater than a predetermined value, the position of one of the two magnetic sensors of the first magnetic sensor array or the other magnetic sensor in the first direction of the inspection object at two timings when the absolute value of the third-direction differential magnetic flux density becomes a predetermined value is set as the first determination position and the second determination position. The nondestructive inspection device according to claim 18, characterized in that...

20. The analysis function of the control unit... When moving the nondestructive inspection device in the first direction of the inspection object along the surface of the concrete structure, after detecting that the absolute value of the third-direction differential magnetic flux density has exceeded a predetermined value from a value smaller than the predetermined value, and then detecting that the absolute value of the third-direction differential magnetic flux density has fallen below the predetermined value from a value larger than the predetermined value, it diagnoses the breakage of the inspection object. The nondestructive inspection device according to claim 19, characterized in that...

21. The magnetic flux measurement unit... has a second magnetic sensor array formed by a plurality of magnetic sensors arranged side by side along a second arrangement direction intersecting the first arrangement direction. The nondestructive inspection device according to any one of claims 13 to 20, characterized in that...

22. The plurality of magnetic sensors... are sensors having measurement axes in a plurality of directions. The nondestructive inspection apparatus according to any one of claims 13 to 21, characterized in that...

23. The plurality of magnetic sensors are arranged so that six or more are aligned along the direction of at least one measurement axis, and include a control unit having an analysis function for analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is to create a contour diagram of the magnetic flux density in a plane parallel to the surface of the concrete structure or a plane parallel to the tangent plane of the surface of the concrete structure, based on the measured values of the magnetic flux density measured by the plurality of magnetic sensors and the positions where the magnetic flux density was measured. The nondestructive inspection apparatus according to any one of claims 13 to 22, characterized in that...

24. and include a control unit having an analysis function for analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is to calculate a corrected magnetic flux density value obtained by removing the periodic fluctuation component of the magnetic flux density included in the measured value of the magnetic flux density by a moving average filter. The nondestructive inspection apparatus according to any one of claims 13 to 23, characterized in that...

25. and include a control unit having an analysis function for analyzing the measured values of the magnetic flux density measured by the magnetic flux measurement unit. The analysis function of the control unit is to create an approximate polynomial in the direction along the first direction of the inspection object based on the measured value of the magnetic flux density and the position where the magnetic flux density was measured, and to calculate a corrected magnetic flux density value obtained by subtracting the value of the approximate polynomial at the same position as the position where the magnetic flux density was measured from the measured value of the magnetic flux density. The nondestructive inspection apparatus according to any one of claims 13 to 24, characterized in that...

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