Information acquisition device and method

Abstract

When measuring information about an object by exciting the object inside it and measuring it in response to the magnetic field generated by eddy currents, it becomes possible to perform measurements even when the object being measured is deep. [Solution] The information acquisition device 1 comprises an excitation unit 1a that energizes a plurality of reinforcing bars 2a1, 2a2, and 2a3 inside the reinforced concrete 2; a magnetic field measurement unit 1b that measures the magnetic field generated by eddy currents in the reinforcing bars 2a1, 2a2, and 2a3; a measurement result approximation unit 1d that approximates the measurement result of the magnetic field measurement unit 1b with the sum AF0 of a plurality of predetermined functions AF1, AF2, and AF3; and a distance derivation unit 1e that determines the distance between each of the reinforcing bars 2a1, 2a2, and 2a3 based on the positions b1, b2, and b3 where each of the plurality of predetermined functions AF1, AF2, and AF3 takes its maximum value. However, the result M measured by the magnetic field measurement unit 1b for each of the reinforcing bars 2a1, 2a2, and 2a3 is approximated by a predetermined function AF.

Description

Technical Field

[0001] The present invention relates to measurement of information (such as pitch, cover thickness or number) of a measurement target (such as a reinforcing bar) inside an object (for example, reinforced concrete).

Background Art

[0002] There are three methods for non-destructively measuring the position of reinforcing bars in reinforced concrete: the electromagnetic wave radar method, the electromagnetic induction method, and the X-ray method. Among these three methods, the electromagnetic induction method excites the reinforcing bar to generate eddy currents, and measures the position of the reinforcing bar (for example, pitch or cover thickness) according to the magnetic field generated by these eddy currents. The electromagnetic induction method has an excellent advantage of not being affected by various influences (such as voids and coarse aggregates in concrete, humidity and water content of concrete, etc.) that are always present in concrete (for example, see Non-Patent Document 1).

[0003] In addition, for the inspection of reinforcing bars using a magnetic field such as the electromagnetic induction method, there are a method that is not completely non-destructive (perforation is required) (for example, see Patent Document 1), and a non-destructive method. The non-destructive method includes an inspection of only a single reinforcing bar, and those in which the influence of adjacent reinforcing bars is not considered (for example, see Patent Document 2). In addition, there are a method for inspecting damage and breakage of a reinforcing bar using a three-axis magnetic sensor (for example, see Patent Document 3), or a method for inspecting damage and breakage of a reinforcing bar using an evaluation index that is easily affected by noise such as a fluctuation curve and differentiation (for example, see Patent Document 4).

[0004] In addition, for the inspection of reinforcing bars using a magnetic field such as the electromagnetic induction method, there are a method for estimating the plate thickness of a corrosion damage part at the ground surface of concrete using a Gaussian function (for example, see Patent Document 5), a method for estimating the position of a reinforcing bar or detecting damage without using a Gaussian function (for example, see Patent Documents 6, 7, and 8), and a method for estimating the position of a reinforcing bar (however, kernel regression using a Gaussian function having a high dispersion value in a kernel function is used as a filter and applied to the measured magnetic field) (for example, see Patent Document 9).

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-178365 [Patent Document 2] Japanese Patent Publication No. 2018-132426 [Patent Document 3] Japanese Patent Publication No. 2020-012851 [Patent Document 4] Japanese Patent Publication No. 2023-184337 [Patent Document 5] Japanese Patent Publication No. 2014-194382 [Patent Document 6] Japanese Patent Publication No. 2020-148554 [Patent Document 7] Japanese Patent Publication No. 2024-095901 [Patent Document 8] Japanese Patent Publication No. 2020-148565 [Patent Document 9] Japanese Patent Publication No. 2018-081070 [Non-patent literature]

[0006] [Non-Patent Document 1] Japan Society for Nondestructive Inspection, "NDIS 3435 (2015) 'Nondestructive Testing of Concrete - Types and Selection of Test Methods for Reinforcement Planar Position and Concrete Cover Thickness'", 2015. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, with the conventional electromagnetic induction method described above, the magnetic field used to excite the reinforcing bars and the magnetic field due to eddy currents attenuate when the depth of the reinforcing bars in the reinforced concrete (e.g., the concrete cover thickness) is large. Therefore, with the above electromagnetic induction method, it is difficult to measure the position of reinforcing bars when they are deep within the reinforced concrete.

[0008] Therefore, the present invention aims to enable measurement even when the object being measured is deep, in a case where information about the object being measured (e.g., position) is measured in response to a magnetic field generated by eddy currents that occur when the object being measured is excited inside the object. [Means for solving the problem]

[0009] The first information acquisition device according to the present invention comprises an excitation unit for exciting a plurality of measurement targets inside an object; a magnetic field measurement unit for measuring the magnetic field generated by eddy currents in the measurement targets; a measurement result approximation unit for approximating the measurement results of the magnetic field measurement unit with the sum of a plurality of predetermined functions; and a distance derivation unit for determining the distance between each of the measurement targets based on the position where each of the plurality of predetermined functions takes its maximum value, wherein the device is configured such that the results of measuring each of the measurement targets by the magnetic field measurement unit are approximated by the predetermined functions.

[0010] According to the first information acquisition device configured as described above, the excitation unit excites multiple objects to be measured inside an object. The magnetic field measurement unit measures the magnetic field generated by eddy currents in the objects to be measured. The measurement result approximation unit approximates the measurement result of the magnetic field measurement unit with the sum of a plurality of predetermined functions. The distance derivation unit determines the distance between each of the objects to be measured based on the position where each of the plurality of predetermined functions takes its maximum value. The result of measuring each of the objects to be measured by the magnetic field measurement unit is approximated by the predetermined functions.

[0011] The second information acquisition device according to the present invention comprises an excitation unit for exciting a plurality of measurement targets inside a body; a magnetic field measurement unit for measuring the magnetic field generated by eddy currents in the measurement targets; a measurement result approximation unit for approximating the measurement results of the magnetic field measurement unit with the sum of a plurality of predetermined functions; and a depth derivation unit for determining the depth of the measurement targets in the object based on the maximum value of each of the plurality of predetermined functions, wherein the results of measuring each of the measurement targets by the magnetic field measurement unit are approximated by the predetermined functions.

[0012] According to the second information acquisition device configured as described above, the excitation unit excites a plurality of measurement targets inside the object. The magnetic field measurement unit measures the magnetic field generated by the eddy current generated in the measurement target. The measurement result approximation unit approximates the measurement result of the magnetic field measurement unit by the sum of a plurality of predetermined functions. The depth derivation unit obtains the depth of the measurement target in the object based on the maximum value of each of the plurality of predetermined functions. The result of measuring each of the measurement targets by the magnetic field measurement unit is approximated by the predetermined function.

[0013] The third information acquisition device according to the present invention includes an excitation unit that excites a plurality of measurement targets inside an object, a magnetic field measurement unit that measures a magnetic field generated by an eddy current generated in the measurement target, a measurement result approximation unit that approximates the measurement result of the magnetic field measurement unit by the sum of a plurality of predetermined functions, and a number derivation unit that sets the number of the predetermined functions that minimize the approximation residual in the measurement result approximation unit to the number of the measurement targets, and is configured such that the result of measuring each of the measurement targets by the magnetic field measurement unit is approximated by the predetermined function.

[0014] According to the third information acquisition device configured as described above, the excitation unit excites a plurality of measurement targets inside the object. The magnetic field measurement unit measures the magnetic field generated by the eddy current generated in the measurement target. The measurement result approximation unit approximates the measurement result of the magnetic field measurement unit by the sum of a plurality of predetermined functions. The number derivation unit sets the number of the predetermined functions that minimize the approximation residual in the measurement result approximation unit to the number of the measurement targets. The result of measuring each of the measurement targets by the magnetic field measurement unit is approximated by the predetermined function.

[0015] In addition, the first, second, and third information acquisition devices according to the present invention may be configured such that the predetermined function is a Gaussian function.

[0016] In addition, the first, second, and third information acquisition devices according to the present invention may be configured such that the predetermined function is the first derivative of a Gaussian function.

[0017] In addition, the first, second, and third information acquisition devices according to the present invention may be such that the predetermined function is based on a theoretical formula of a magnetic field generated by the measurement target when the measurement target is assumed to be a magnet having a size of 0.

[0018] In addition, the first, second, and third information acquisition devices according to the present invention may be such that the predetermined function is based on a first-order derivative of a theoretical formula of a magnetic field generated by the measurement target when the measurement target is assumed to be a magnet having a size of 0.

[0019] In addition, the first, second, and third information acquisition devices according to the present invention may include a measurement result averaging unit that takes an average of the measurement results of each of the magnetic field measurement units while aligning the positions where the measurement results of each of the magnetic field measurement units reach the maximum value with a predetermined position, and the measurement result approximation unit approximates the output of the measurement result averaging unit with the sum of the plurality of predetermined functions, and there may be a plurality of the magnetic field measurement units.

[0020] In addition, the first, second, and third information acquisition devices according to the present invention may include a multivariate analysis unit that performs multivariate analysis on the measurement results of each of the magnetic field measurement units while aligning the positions where the measurement results of each of the magnetic field measurement units reach the maximum value with a predetermined position, and the measurement result approximation unit approximates the output of the multivariate analysis unit with the sum of the plurality of predetermined functions, and there may be a plurality of the magnetic field measurement units.

[0021] In addition, in the first information acquisition device according to the present invention, the measurement result approximation unit approximates the measurement result of the magnetic field measurement unit added with a plurality of types of offsets with the sum of the plurality of predetermined functions, and the distance derivation unit determines the distance between each of the measurement targets based on the position where each of the sums obtained by adding the optimal offset, which is the offset that minimizes the approximation residual in the measurement result approximation unit, to the plurality of predetermined functions reaches the maximum value.

[0022] Furthermore, in the second information acquisition device according to the present invention, the measurement result approximation unit approximates the measurement result of the magnetic field measurement unit with the sum of a plurality of predetermined functions, and the depth derivation unit determines the depth of the object to be measured based on the maximum value of each of the plurality of predetermined functions obtained by adding the optimal offset, which is the offset that minimizes the approximation residual in the measurement result approximation unit, to the plurality of predetermined functions.

[0023] Furthermore, the first information acquisition device according to the present invention includes a depth derivation unit that determines the depth of the object to be measured based on the maximum value of each of the plurality of predetermined functions, and the measurement result approximation unit may set the maximum value of each of the plurality of predetermined functions and the position where the maximum value is taken so that the approximation residual in the measurement result approximation unit is less than a predetermined threshold.

[0024] Furthermore, the first, second, and third information acquisition devices according to the present invention may be configured such that the object is reinforced concrete and the object to be measured is reinforcing steel.

[0025] Furthermore, the first, second, and third information acquisition devices according to the present invention may comprise a plurality of substrates on which the magnetic field measuring units are arranged, and the substrates may be stacked in the direction normal to a plane at a constant distance from the object to be measured.

[0026] Furthermore, the first, second, and third information acquisition devices according to the present invention may be configured such that the excitation unit is excited by a combined signal obtained by combining a first signal of a first frequency suitable for approximation by the measurement result approximation unit and a second signal of a second frequency suitable for corrosion detection of the object to be measured.

[0027] Furthermore, in the first, second, and third information acquisition devices according to the present invention, the excitation unit may be excited by a first signal of a first frequency suitable for approximation by the measurement result approximation unit for a specific duration, and the excitation unit may be excited by a second signal of a second frequency suitable for corrosion detection of the object to be measured for a specific duration, separately.

[0028] The first information acquisition method according to the present invention comprises an excitation step of exciting a plurality of measurement targets inside an object; a magnetic field measurement step of measuring the magnetic field generated by eddy currents in the measurement targets; a measurement result approximation step of approximating the measurement results of the magnetic field measurement step with the sum of a plurality of predetermined functions; and a distance derivation step of determining the distance between each of the measurement targets based on the position where each of the plurality of predetermined functions takes its maximum value, wherein the result of measuring each of the measurement targets by the magnetic field measurement step is approximated by the predetermined functions.

[0029] A second information acquisition method according to the present invention comprises an excitation step of exciting a plurality of measurement targets inside an object; a magnetic field measurement step of measuring the magnetic field generated by eddy currents in the measurement targets; a measurement result approximation step of approximating the measurement results of the magnetic field measurement step with the sum of a plurality of predetermined functions; and a depth derivation step of determining the depth of the measurement targets in the object based on the maximum value of each of the plurality of predetermined functions, wherein the results of measuring each of the measurement targets by the magnetic field measurement step are approximated by the predetermined functions.

[0030] A third information acquisition method according to the present invention comprises an excitation step of exciting multiple measurement targets inside an object; a magnetic field measurement step of measuring the magnetic field generated by eddy currents in the measurement targets; a measurement result approximation step of approximating the measurement results of the magnetic field measurement step with the sum of a plurality of predetermined functions; and a number derivation step of determining the number of measurement targets as the number of predetermined functions that minimize the approximation residual in the measurement result approximation step, wherein the result of measuring each of the measurement targets by the magnetic field measurement step is approximated by the predetermined functions. [Brief explanation of the drawing]

[0031] [Figure 1] This is a functional block diagram showing the configuration of an information acquisition device 1 according to the first embodiment of the present invention. [Figure 2] These are a plan view (Figure 2(a)) and a front view (Figure 2(b)) of the substrate 1s of the information acquisition device 1 according to the first embodiment. [Figure 3] These are cross-sectional views (Figure 3(a)) and plan views (Figure 3(b)) of reinforced concrete (object) 2. [Figure 4] This diagram illustrates the scanning of reinforced concrete 2 by the information acquisition device 1. [Figure 5] This figure shows the measurement results M1 and M2 obtained by the magnetic field measurement unit 1b, with Figure 5(a) showing the case where the cover thickness cd is small and Figure 5(b) showing the case where the cover thickness cd is large. [Figure 6] Figure 6(a) shows a graph of the measurement result M of one of the reinforcing bars 2a1, 2a2, or 2a3 measured by the magnetic field measurement unit 2b; Figure 6(b) shows a graph of the approximation function AF that approximates the measurement result M; and Figure 6(c) shows a superimposed graph of the measurement result M and the approximation function AF. [Figure 7] This figure shows the measurement results M1 and M2 from the magnetic field measurement unit 1b, the approximation functions AF1, AF2, and AF3, and the sum AF0 of the approximation functions AF1, AF2, and AF3, illustrating the case where the cover thickness cd is small (Figure 7(a)) and the case where the cover thickness cd is large (Figure 7(b)). [Figure 8] This graph shows the relationship between the maximum value (amplitude) of the approximation function and the cover thickness. [Figure 9] This is a functional block diagram showing the configuration of an information acquisition device 1 according to a second embodiment of the present invention. [Figure 10] This is a functional block diagram showing the configuration of an information acquisition device 1 according to a third embodiment of the present invention. [Figure 11] These are cross-sectional views (Figure 11(a)) and plan views (Figure 11(b)) of reinforced concrete 2 when reinforced concrete (object) 2 has orthogonal reinforcements 2c1 and 2c2. [Figure 12] This diagram illustrates the magnetic field gradient ΔT that occurs in the measurement results of the magnetic field measurement unit 1b. [Figure 13] This is a functional block diagram showing the configuration of an information acquisition device 1 according to a fourth embodiment of the present invention. [Figure 14] This is a functional block diagram showing the configuration of an information acquisition device 1 according to the fifth embodiment of the present invention. [Figure 15]This is a functional block diagram showing the configuration of an information acquisition device 1 according to the sixth embodiment of the present invention. [Figure 16] This figure illustrates the scanning of reinforced concrete 2 by the information acquisition device 1 in the seventh embodiment. [Figure 17] Figure 17(a) shows the measurement result M1 by the magnetic field measuring unit 1b in the seventh embodiment, and Figure 17(b) shows the measurement result M1 by the magnetic field measuring unit 1b and the approximation functions AF1, AF2, and AF3. [Figure 18] Figure 18(a) shows the measurement result M1 from the magnetic field measuring unit 1b in the seventh embodiment with the offset OF added, and Figure 18(b) shows the measurement result M1 from the magnetic field measuring unit 1b with the offset OF added, along with the approximation functions AF1, AF2, and AF3. [Figure 19] This graph shows the relationship between the offset OF and the approximate residual FE (Fitting Error). [Figure 20] This graph shows the approximate function AF, which approximates the measurement result M, when the magnetic field direction is the Y-axis direction. [Figure 21] These are cross-sectional view (Figure 21(a)) and plan view (Figure 21(b)) of reinforced concrete (object) 2 according to the eighth embodiment. [Figure 22] This flowchart shows the operation of the measurement result approximation unit 1d in the eighth embodiment. [Figure 23] These are a plan view (Figure 23(a)) and a front view (Figure 23(b)) of the substrate 1s of the information acquisition device 1 according to the second embodiment. [Modes for carrying out the invention]

[0032] Embodiments of the present invention will be described below with reference to the drawings.

[0033] First Embodiment Figure 1 is a functional block diagram showing the configuration of an information acquisition device 1 according to a first embodiment of the present invention. The information acquisition device 1 according to the first embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a distance derivation unit 1e, and a depth derivation unit 1f.

[0034] The information acquisition device 1 may include only one of the distance derivation unit 1e and the depth derivation unit 1f. However, in the first embodiment, the information acquisition device 1 includes both the distance derivation unit 1e and the depth derivation unit 1f.

[0035] Figure 2 shows a plan view (Figure 2(a)) and a front view (Figure 2(b)) of the substrate 1s of the information acquisition device 1 according to the first embodiment.

[0036] The excitation unit 1a and the magnetic field measurement unit 1b are located on the substrate 1s (see Figure 2(b)). The excitation signal generation unit 1c, the measurement result approximation unit 1d, the distance derivation unit 1e, and the depth derivation unit 1f are located at a distance from the substrate 1s. The magnetic field measurement unit 1b is located on the substrate 1s.

[0037] Referring to Figure 2(a), the excitation unit 1a is, for example, an elliptical excitation coil. However, the shape of the excitation coil is not limited to an ellipse; it may be circular, square, or linear. Also, referring to Figure 2(b), the excitation unit 1a is located directly above one magnetic field measuring unit 1b. However, the magnetic field measuring unit 1b does not have to be located directly below the excitation unit 1a; it may be located on the substrate 1s.

[0038] Figure 3 shows a cross-sectional view (Figure 3(a)) and a plan view (Figure 3(b)) of reinforced concrete (object) 2. Referring to Figure 3, reinforced concrete 2 has reinforcing bars 2a and concrete 2b, and reinforcing bars 2a1, 2a2, and 2a3 are arranged inside the reinforced concrete 2.

[0039] The excitation unit 1a energizes multiple measurement targets inside the object. As an example of an object and measurement targets, in this embodiment of the present invention, the object is reinforced concrete 2, and the multiple measurement targets are reinforcing bars 2a1, 2a2, and 2a3.

[0040] Note that reinforcing bars 2a1 and 2a2 are adjacent (with a distance of pitch P), and reinforcing bars 2a2 and 2a3 are adjacent (with a distance of pitch P). Also, the diameters of reinforcing bars 2a1, 2a2, and 2a3 are D. Furthermore, the covering depth of reinforcing bars 2a1, 2a2, and 2a3 is cd for all of them.

[0041] The magnetic field measuring unit 1b measures the magnetic field generated by eddy currents in the reinforcing bars (objects to be measured) 2a1, 2a2, and 2a3.

[0042] In embodiments of the present invention, the magnetic field measuring unit 1b is a magnetic sensor. The magnetic sensing direction of the magnetic field measuring unit (magnetic sensor) 1b is the Z-axis direction or the X-axis direction. Note that the magnetic field measuring unit 1b does not have to be a magnetic sensor; it may be a coil that detects magnetism.

[0043] The Z-axis direction is the normal direction to the plane at a constant distance from the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3. The Y-axis direction is parallel to the extension direction of the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3. The X-axis direction is perpendicular to the Z-axis and Y-axis directions.

[0044] The excitation signal generation unit 1c provides an excitation signal (for example, an electrical signal) to the excitation unit 1a. The waveform of the excitation signal is, for example, a sine wave.

[0045] The measurement result approximation unit 1d approximates the measurement results of the magnetic field measurement unit 1b with the sum of several predetermined functions. However, the results of the measurement of each of the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3 by the magnetic field measurement unit 2b are approximated by a predetermined function (approximation function AF).

[0046] The specified function is, for example, a Gaussian function (see the approximation function AF in Figure 6(b) and equation (1)).

[0047] The distance derivation unit 1e calculates the distances between each of the reinforcing bars (objects to be measured) 2a1, 2a2, and 2a3 based on the position where each of a plurality of predetermined functions takes its maximum value.

[0048] The depth derivation unit 1f determines the depth (e.g., cover thickness cd) of the reinforcing bars (objects to be measured) 2a1, 2a2, and 2a3 in the reinforced concrete (object) 2 based on the maximum value of each of a plurality of predetermined functions.

[0049] Next, the operation of the first embodiment will be described.

[0050] Figure 4 illustrates the scanning of reinforced concrete 2 by the information acquisition device 1.

[0051] First, the substrate 1s of the information acquisition device 1 is moved in the X-axis direction. More specifically, the X-coordinate of the centroid of the magnetic field measuring unit 1b on the substrate 1s is moved from 0 to X0. This scans the reinforced concrete 2.

[0052] However, the Z coordinate of the substrate 1s is kept constant, and this constant value is assumed to be greater than the maximum value of the Z coordinate of the reinforced concrete 2. Also, the X coordinates of the reinforcing bars 2a1, 2a2, and 2a3 are b1, b2, and b3, respectively. Here, b1 is sufficiently greater than 0. X0 is sufficiently greater than b3. Also, b2-b1=b3-b2=P (see Figure 3(a)).

[0053] While the substrate 1s is moving in the X-axis direction as described above, the excitation signal generation unit 1c supplies an excitation signal with a sinusoidal waveform to the excitation unit 1a. As a result, the reinforcing bars 2a1, 2a2, and 2a3 are excited by the excitation unit 1a, and eddy currents are generated in the reinforcing bars 2a1, 2a2, and 2a3. The magnetic field generated by these eddy currents is measured by the magnetic field measurement unit 1b.

[0054] Figure 5 shows the measurement results M1 and M2 obtained by the magnetic field measurement unit 1b, illustrating the case where the cover thickness cd is small (Figure 5(a)) and the case where the cover thickness cd is large (Figure 5(b)).

[0055] Referring to Figure 5(a), when the concrete cover thickness cd is small (for example, cd is less than or equal to P / 1.5), the measurement result M1 (magnetic field amplitude [nT]) takes a maximum value at X coordinates b1, b2, and b3. Therefore, by finding the X coordinates at which the measurement result M1 takes a maximum value, b1, b2, and b3 can be determined. Furthermore, the distance between reinforcing bars 2a1 and 2a2 can be determined as b2-b1. Also, the distance between reinforcing bars 2a2 and 2a3 can be determined as b3-b2.

[0056] Referring to Figure 5(b), when the concrete cover thickness cd is large (for example, cd exceeds P / 1.5), the measurement result M2 (magnetic field amplitude [nT]) does not take a maximum value at X coordinates b1, b2, and b3. Therefore, the distance between reinforcing bars 2a1, 2a2, and 2a3 cannot be determined by the method described with reference to Figure 5(a) (i.e., the method using the X coordinate where the measurement result takes a maximum value).

[0057] However, by using the measurement result approximation unit 1d and distance derivation unit 1e according to the first embodiment, b1, b2, and b3 can be determined even when the cover thickness cd is large, and the distances between reinforcing bars 2a1, 2a2, and 2a3 can also be determined.

[0058] Figure 6 shows a graph (Figure 6(a)) showing the result M obtained by measuring one of the reinforcing bars 2a1, 2a2, or 2a3 using the magnetic field measurement unit 2b, a graph (Figure 6(b)) showing the approximation function AF that approximates the measurement result M, and a graph (Figure 6(c)) showing the measurement result M and the approximation function AF superimposed.

[0059] The approximation function (a predetermined function) AF that approximates the measurement result M is a Gaussian function. The approximation function AF is defined as shown in equation (1) below.

[0060]

number

[0061] Referring to Figure 6(c), the measured result M and the approximation function AF are in close agreement. The measured result M is better approximated by the approximation function AF.

[0062] The measurement result approximation unit 1d approximates the measurement result of the magnetic field measurement unit 1b with the sum of a plurality (e.g., three) predetermined functions (approximation function AF).

[0063] The sum fm(x) of multiple (N) approximation functions AF is expressed as shown in equation (2) below. The amplitude a and variance c of each approximation function (Gaussian function) AF are common. However, the phase b is different for each approximation function (Gaussian function) AF.

[0064]

number

[0065] AF0 = AF1 + AF2 + AF3. Also, the phase of the approximation function (Gaussian function) AF1 is b1, the phase of the approximation function (Gaussian function) AF2 is b2, and the phase of the approximation function (Gaussian function) AF3 is b3.

[0066] Referring to Figure 7(a), if the concrete cover thickness cd is small (for example, cd is less than or equal to P / 1.5), instead of finding the X coordinate where the measurement result M1 (magnetic field amplitude [nT]) takes its maximum value, the X coordinates of reinforcing bars 2a1, 2a2, and 2a3 can be determined by finding the positions (phases b1, b2, b3) where the approximation functions AF1, AF2, and AF3 take their maximum values. Furthermore, the distance between reinforcing bars 2a1 and 2a2, and the distance between reinforcing bars 2a2 and 2a3 can also be determined.

[0067] Referring to Figure 7(b), when the concrete cover thickness cd is large (for example, cd exceeds P / 1.5), the measurement result M2 (magnetic field amplitude [nT]) does not take a maximum value at X coordinates b1, b2, and b3. However, by finding the positions (phases b1, b2, b3) where the approximation functions AF1, AF2, and AF3 take their maximum values, the X coordinates b1, b2, and b3 of reinforcing bars 2a1, 2a2, and 2a3 can be determined, and furthermore, the distance between reinforcing bars 2a1 and 2a2 and the distance between reinforcing bars 2a2 and 2a3 can be determined.

[0068] In other words, the measurement result approximation unit 1d approximates the measurement results M1 and M2 of the magnetic field measurement unit 1b with AF0 = AF1 + AF2 + AF3.

[0069] Furthermore, the measurement result approximation unit 1d provides the distance derivation unit 1e with the positions (phases b1, b2, b3) where the approximation functions AF1, AF2, and AF3 take their maximum values.

[0070] The distance derivation unit 1e calculates the distances between each of the reinforcing bars (objects to be measured) 2a1, 2a2, and 2a3 based on the positions (phases b1, b2, b3) where each of the approximation functions (predetermined functions) AF1, AF2, and AF3 takes its maximum value. For example, the distance between reinforcing bars 2a1 and 2a2 is calculated as b2-b1. The distance between reinforcing bars 2a2 and 2a3 is calculated as b3-b2.

[0071] Furthermore, the measurement result approximation unit 1d provides the maximum value (amplitude a) of the approximation functions AF1, AF2, and AF3 to the depth derivation unit 1f.

[0072] Figure 8 is a graph showing the relationship between the maximum value (amplitude) of the approximation function and the concrete cover thickness. Before scanning with the information acquisition device 1, the maximum values ​​(amplitudes) (Aa, Ab, Ac) of the approximation function in reinforced concrete 2 with known concrete cover thicknesses (CDa, CDb, CDc) are determined, and from these, the relationship CD between the concrete cover thickness and the maximum value (amplitude) of the approximation function is determined and recorded in the depth derivation unit 1f. The relationship CD is expressed by the following equation (3). In equation (3), d is the concrete cover thickness, fa(d) is the maximum value (amplitude) of the approximation function, κ=5, and p and q are unknowns, and p and q were estimated using the Levenberg-Marquardt method. Note that equation (3) differs for each diameter D of the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3.

[0073]

number

[0074] According to the first embodiment, when the reinforcing bars 2a1, 2a2, and 2a3 inside the reinforced concrete 2 are excited and the magnetic field generated by the resulting eddy currents is used to measure information (e.g., position) of the reinforcing bars 2a1, 2a2, and 2a3, it becomes possible to measure the distance between each of the reinforcing bars 2a1, 2a2, and 2a3 and the cover thickness cd, even when the depth of the reinforcing bars 2a1, 2a2, and 2a3 in the reinforced concrete 2 is deep (e.g., cover thickness cd).

[0075] In other words, when the depth (e.g., cover thickness cd) of the reinforcing bars 2a1, 2a2, and 2a3 in the reinforced concrete 2 is deep, the measurement result M2 does not take a maximum value at the X coordinates b1, b2, and b3 of the reinforcing bars 2a1, 2a2, and 2a3, as shown in Figure 5(b). However, if the measurement result M2 is approximated by the sum AF0 of the approximation functions AF1, AF2, and AF3, each of the approximation functions AF1, AF2, and AF3 takes its maximum value at b1, b2, and b3. Therefore, the positions (phases b1, b2, b3) where each of the approximation functions (predetermined functions) AF1, AF2, and AF3 takes its maximum value can be considered as the X coordinates of the reinforcing bars 2a1, 2a2, and 2a3, and based on this, it becomes possible to measure the distance between each of the reinforcing bars 2a1, 2a2, and 2a3 and the cover thickness cd.

[0076] Second Embodiment The information acquisition device 1 according to the second embodiment differs from the first embodiment in that it has multiple magnetic field measuring units 1b and a measurement result averaging unit 1g.

[0077] Figure 9 is a functional block diagram showing the configuration of an information acquisition device 1 according to a second embodiment of the present invention. The information acquisition device 1 according to the second embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a distance derivation unit 1e, a depth derivation unit 1f, and a measurement result averaging unit 1g. Hereinafter, parts the same as those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0078] The excitation unit 1a and the excitation signal generation unit 1c are the same as in the first embodiment, and their description will be omitted.

[0079] Figure 23 shows a plan view (Figure 23(a)) and a front view (Figure 23(b)) of the substrate 1s of the information acquisition device 1 according to the second embodiment. Unlike the first embodiment, multiple magnetic field measuring units 1b are arranged on the substrate 1s.

[0080] Referring to Figure 23, multiple magnetic field measuring units (magnetic sensors) 1b are arranged on the substrate 1s at equal intervals vertically (Y-axis direction) and horizontally (X-axis direction). An excitation unit (excitation coil) 1a is positioned directly above the central magnetic field measuring unit 1b.

[0081] The measurement result averaging unit 1g takes the average of each measurement result from the magnetic field measurement unit 1b while aligning the position (X coordinate) where each measurement result from the magnetic field measurement unit 1b takes its maximum value to a predetermined position.

[0082] The position (X coordinate) where each measurement result of the magnetic field measuring unit 1b takes its maximum value corresponds to the X coordinate of the magnetic field measuring unit 1b. For example, if the predetermined position described above is the position (X coordinate) where the measurement result of the magnetic field measuring unit 1b, which is located directly below the excitation unit 1a, takes its maximum value, then the measurement results are adjusted to the predetermined position as follows.

[0083] However, ΔX is defined as the magnitude of the difference between the X-coordinate of the centroid of the magnetic field measuring unit 1b located directly below the excitation unit 1a and the X-coordinate of the centroid of the magnetic field measuring unit 1b that is the target of alignment to a predetermined position.

[0084] (1) If the X-coordinate of the centroid of the magnetic field measuring unit 1b that is the target of alignment to a predetermined position is smaller than the X-coordinate of the centroid of the magnetic field measuring unit 1b that is located directly below the excitation unit 1a, the measurement result of the magnetic field measuring unit 1b that is the target of alignment is shifted by -ΔX in the X-axis direction (shifted to the left).

[0085] (2) If the X-coordinate of the centroid of the magnetic field measuring unit 1b located directly below the excitation unit 1a is the same as the X-coordinate of the centroid of the magnetic field measuring unit 1b that is to be aligned to a predetermined position, the measurement result of the magnetic field measuring unit 1b that is to be aligned will be used as is.

[0086] (3) If the X-coordinate of the centroid of the magnetic field measuring unit 1b that is to be aligned to a predetermined position is greater than the X-coordinate of the centroid of the magnetic field measuring unit 1b that is located directly below the excitation unit 1a, the measurement result of the magnetic field measuring unit 1b that is to be aligned is shifted by ΔX in the X-axis direction (shifted to the right).

[0087] The measurement result averaging unit 1g aligns the measurement results to a predetermined position as described above, and then outputs the average of each measurement result from the magnetic field measurement unit 1b.

[0088] The measurement result approximation unit 1d approximates the output of the measurement result averaging unit 1g with the sum of a plurality of predetermined functions. The sum of the plurality of predetermined functions is the same as in the first embodiment and will not be explained.

[0089] The distance derivation section 1e and the depth derivation section 1f are the same as in the first embodiment, and their description will be omitted.

[0090] Next, the operation of the second embodiment will be described.

[0091] First, the substrate 1s of the information acquisition device 1 is moved in the X-axis direction (see Figure 4). This scans the reinforced concrete 2. The scanning is the same as in the first embodiment, so a detailed explanation is omitted.

[0092] Furthermore, during scanning, eddy currents are generated in the reinforcing bars 2a1, 2a2, and 2a3, similar to the first embodiment. The magnetic field generated by these eddy currents is measured by the magnetic field measuring unit 1b. The average of each measurement result from the magnetic field measuring unit 1b is output from the measurement result averaging unit 1g. However, the position (X coordinate) where each measurement result from the magnetic field measuring unit 1b takes its maximum value is set to a predetermined position (for example, the position (X coordinate) where the measurement result of the magnetic field measuring unit 1b located directly below the excitation unit 1a takes its maximum value).

[0093] The output of the measurement result averaging unit 1g is approximated by the measurement result approximation unit 1d as AF0 = AF1 + AF2 + AF3, similar to the first embodiment.

[0094] The operation of the distance derivation unit 1e and the depth derivation unit 1f is the same as in the first embodiment, and therefore will not be described.

[0095] The second embodiment provides the same effects as the first embodiment. Moreover, the second embodiment allows the measurement result averaging unit 1g to reduce random noise generated during measurement by the magnetic field measurement unit 1b.

[0096] Furthermore, according to the second embodiment, when the reinforced concrete 2 has orthogonal reinforcing bars 2c1, 2c2 (see Figure 11) perpendicular to the reinforcing bars (measurement targets) 2a1, 2a2, 2a3, it is possible to reduce the magnetic field gradient ΔT (see Figure 12) that occurs in the measurement results of the magnetic field measurement unit 1b.

[0097] Figure 11 shows a cross-sectional view (Figure 11(a)) and a plan view (Figure 11(b)) of reinforced concrete 2 when reinforced concrete (object) 2 has orthogonal reinforcements 2c1 and 2c2.

[0098] Referring to Figure 11, the orthogonal reinforcing bars 2c1 and 2c2 are orthogonal to the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3.

[0099] Figure 12 is a diagram illustrating the magnetic field gradient ΔT that occurs in the measurement results of the magnetic field measurement unit 1b.

[0100] If there are no orthogonal reinforcing bars 2c1 and 2c2, as shown in Figure 5, the measurement result of the magnetic field measuring unit 1b is almost 0 near the X coordinate 0 and near X0. However, as shown in Figure 11, if the reinforced concrete 2 has orthogonal reinforcing bars 2c1 and 2c2 that are orthogonal to the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3, the measurement result of the magnetic field measuring unit 1b becomes ΔT, which is not almost 0, near X0. The magnetic field gradient ΔT is caused by the magnetization distribution of the orthogonal reinforcing bars 2c1 and 2c2 (i.e., reinforcing bars extending parallel to the scanning direction) and slight positional displacements (for example, the displacement between the extension direction of the orthogonal reinforcing bars 2c1 and 2c2 and the X-axis direction).

[0101] The magnetic field gradient ΔT at multiple magnetic field measurement units 1b contains a mixture of positive and negative gradients. Therefore, the magnetic field gradient ΔT can be reduced by averaging the measurement results from multiple magnetic field measurement units 1b.

[0102] Third Embodiment The information acquisition device 1 according to the third embodiment differs from the second embodiment in that it includes a multivariate analysis unit 1h instead of a measurement result averaging unit 1g.

[0103] Figure 10 is a functional block diagram showing the configuration of an information acquisition device 1 according to a third embodiment of the present invention. The information acquisition device 1 according to the third embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a distance derivation unit 1e, a depth derivation unit 1f, and a multivariate analysis unit 1h. Hereinafter, parts the same as those in the second embodiment are denoted by the same reference numerals and their description is omitted.

[0104] The excitation unit 1a, magnetic field measurement unit 1b, excitation signal generation unit 1c, measurement result approximation unit 1d, distance derivation unit 1e, and depth derivation unit 1f are the same as in the second embodiment and will not be described.

[0105] The multivariate analysis unit 1h performs multivariate analysis (for example, principal component analysis) on each measurement result from the magnetic field measurement unit 1b, while aligning the position (X coordinate) where each measurement result from the magnetic field measurement unit 1b takes its maximum value to a predetermined position.

[0106] The measurement result approximation unit 1d approximates the output of the multivariate analysis unit 1h with the sum of a plurality of predetermined functions. The sum of the plurality of predetermined functions is the same as in the first embodiment and will not be explained further.

[0107] Next, the operation of the third embodiment is the same as that of the second embodiment, so we will omit the explanation.

[0108] However, the multivariate analysis unit 1h outputs the results of a multivariate analysis of each measurement result from the magnetic field measurement unit 1b. Here, the position (X coordinate) where each measurement result from the magnetic field measurement unit 1b takes its maximum value is set to a predetermined position (for example, the position (X coordinate) where the measurement result of the magnetic field measurement unit 1b located directly below the excitation unit 1a takes its maximum value).

[0109] The output of the multivariate analysis unit 1h is approximated by the measurement result approximation unit 1d as AF0 = AF1 + AF2 + AF3, similar to the first embodiment.

[0110] The third embodiment provides the same effects as the first embodiment. Moreover, the third embodiment allows the multivariate analysis unit 1h to reduce random noise generated during measurement by the magnetic field measurement unit 1b.

[0111] Fourth Embodiment The information acquisition device 1 according to the fourth embodiment differs from the first embodiment in that it includes a number derivation unit 1i instead of a distance derivation unit 1e and a depth derivation unit 1f.

[0112] Figure 13 is a functional block diagram showing the configuration of an information acquisition device 1 according to a fourth embodiment of the present invention. The information acquisition device 1 according to the fourth embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, and a number derivation unit 1i. Hereinafter, parts the same as in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0113] In the first embodiment, the number of reinforcing bars (measurement targets) 2a1, 2a2, and 2a3 (3 bars) is known, but in the fourth embodiment, the number of reinforcing bars (measurement targets) 2a1, 2a2, and 2a3 is unknown, and the number of reinforcing bars is derived by the number derivation unit 1i.

[0114] The excitation unit 1a, magnetic field measurement unit 1b, and excitation signal generation unit 1c are the same as in the first embodiment, and their description will be omitted.

[0115] The measurement result approximation unit 1d approximates the measurement result of the magnetic field measurement unit 1b with the sum of a plurality of predetermined functions. However, unlike the first embodiment, the measurement result approximation unit 1d approximates the measurement result of the magnetic field measurement unit 1b with the sum of a plurality of predetermined functions of a certain number (for example, 2, 3, 4, and 5).

[0116] The measurement result approximation unit 1d outputs the approximate residual (Fitting Error) of the measurement result approximated by the magnetic field measurement unit 1b for each of several different numbers (e.g., 2, 3, 4, and 5), and provides it to the number derivation unit 1i.

[0117] For example, the measurement result approximation unit 1d uses the measurement result of the magnetic field measurement unit 1b. The approximate residual of the approximation using the sum of two predetermined functions, The approximate residual of the approximation using the sum of three predetermined functions, The approximate residual of the approximation using the sum of four predetermined functions, The approximate residual of the approximation using the sum of five predetermined functions, The output is provided to the number derivation unit 1i.

[0118] The number derivation unit 1i determines the number of objects to be measured (number of reinforcing bars) by determining the number of predetermined functions that minimize the approximate residual in the measurement result approximation unit 1d. For example, when measuring reinforced concrete 2 as shown in Figure 3, the number of predetermined functions that minimize the approximate residual in the measurement result approximation unit 1d is 3, so the number derivation unit 1i determines the number of objects to be measured (number of reinforcing bars) to be 3.

[0119] Next, the operation of the fourth embodiment will be described.

[0120] First, the substrate 1s of the information acquisition device 1 is moved in the X-axis direction (see Figure 4). This scans the reinforced concrete 2. The scanning is the same as in the first embodiment, so a detailed explanation is omitted.

[0121] Furthermore, during scanning, eddy currents are generated in the reinforcing bars 2a1, 2a2, and 2a3, similar to the first embodiment. The magnetic field generated by these eddy currents is measured by the magnetic field measuring unit 1b.

[0122] The measurement results from the magnetic field measurement unit 1b are approximated by the measurement result approximation unit 1d as the sum of a predetermined number of multiple types of functions (for example, 2, 3, 4, and 5).

[0123] For each of several different numbers (for example, 2, 3, 4, and 5), the approximate residual of the approximate measurement result of the magnetic field measurement unit 1b is provided to the number derivation unit 1i from the measurement result approximation unit 1d.

[0124] For example, the measurement result approximation unit 1d uses the measurement result of the magnetic field measurement unit 1b. The approximate residual of the approximation using the sum of two predetermined functions, The approximate residual of the approximation using the sum of three predetermined functions, The approximate residual of the approximation using the sum of four predetermined functions, The approximate residual of the approximation using the sum of five predetermined functions, The output is provided to the number derivation unit 1i.

[0125] The number of predetermined functions that minimize the approximate residual in the measurement result approximation unit 1d is determined by the number derivation unit 1i to be the number of items to be measured (number of reinforcing bars).

[0126] For example, when measuring reinforced concrete 2 as shown in Figure 3, the number of predetermined functions that minimize the approximate residual in the measurement result approximation unit 1d is 3. Therefore, the number derivation unit 1i determines that the number of items to be measured (number of reinforcing bars) is 3.

[0127] According to the fourth embodiment, the same effects as those of the first embodiment are achieved.

[0128] Furthermore, according to the fourth embodiment, even if the number of items to be measured (number of reinforcing bars) is unknown, the number of items to be measured (number of reinforcing bars) can be determined by the number derivation unit 1i.

[0129] Fifth Embodiment The information acquisition device 1 according to the fifth embodiment differs from the second embodiment in that it includes a number derivation unit 1i instead of a distance derivation unit 1e and a depth derivation unit 1f.

[0130] Figure 14 is a functional block diagram showing the configuration of an information acquisition device 1 according to the fifth embodiment of the present invention. The information acquisition device 1 according to the fifth embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a measurement result averaging unit 1g, and a count derivation unit 1i. Hereinafter, parts the same as those in the second embodiment are denoted by the same reference numerals and their description is omitted.

[0131] The excitation unit 1a, magnetic field measurement unit 1b, excitation signal generation unit 1c, and measurement result averaging unit 1g are the same as in the second embodiment, and their description is omitted.

[0132] The measurement result approximation unit 1d and the count derivation unit 1i are the same as in the fourth embodiment and will not be described. However, the measurement result approximation unit 1d receives the output of the measurement result averaging unit 1g and operates in the same manner as in the fourth embodiment.

[0133] Next, the operation of the fifth embodiment will be described.

[0134] The scanning of the reinforced concrete 2, the operation of the excitation unit 1a, the magnetic field measurement unit 1b, the excitation signal generation unit 1c, and the measurement result averaging unit 1g are the same as in the second embodiment, and therefore will not be described.

[0135] The operation of the measurement result approximation unit 1d and the count derivation unit 1i is the same as in the fourth embodiment, and therefore will not be described. However, the measurement result approximation unit 1d receives the output of the measurement result averaging unit 1g and performs the same operation as in the fourth embodiment.

[0136] The fifth embodiment provides the same effects as the second and fourth embodiments.

[0137] Sixth Embodiment The information acquisition device 1 according to the sixth embodiment differs from the third embodiment in that it includes a number derivation unit 1i instead of a distance derivation unit 1e and a depth derivation unit 1f.

[0138] Figure 15 is a functional block diagram showing the configuration of an information acquisition device 1 according to the sixth embodiment of the present invention. The information acquisition device 1 according to the sixth embodiment comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a multivariate analysis unit 1h, and a number derivation unit 1i. Hereinafter, parts the same as those in the third embodiment are denoted by the same reference numerals and their description is omitted.

[0139] The excitation unit 1a, magnetic field measurement unit 1b, excitation signal generation unit 1c, measurement result approximation unit 1d, and multivariate analysis unit 1h are the same as in the third embodiment, and their description is omitted.

[0140] The measurement result approximation unit 1d and the count derivation unit 1i are the same as in the fourth embodiment, and their description is omitted. However, the measurement result approximation unit 1d receives the output of the multivariate analysis unit 1h and performs the same operation as in the fourth embodiment.

[0141] Next, the operation of the sixth embodiment will be described.

[0142] The scanning of the reinforced concrete 2, the operation of the excitation unit 1a, the magnetic field measurement unit 1b, the excitation signal generation unit 1c, and the multivariate analysis unit 1h are the same as in the third embodiment, and therefore will not be described.

[0143] The operation of the measurement result approximation unit 1d and the count derivation unit 1i is the same as in the fourth embodiment, and therefore will not be described. However, the measurement result approximation unit 1d receives the output of the multivariate analysis unit 1h and performs the same operation as in the fourth embodiment.

[0144] The sixth embodiment provides the same effects as the third and fourth embodiments.

[0145] Seventh Embodiment The information acquisition device 1 according to the seventh embodiment differs from the first embodiment in that the measurement result approximation unit 1d approximates the measurement result of the magnetic field measurement unit 1b by adding multiple types of offsets, and the measurement is performed using the optimal offset, which is the offset that minimizes the approximation residual.

[0146] The information acquisition device 1 according to the seventh embodiment (see Figure 1) comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a distance derivation unit 1e, and a depth derivation unit 1f. Hereinafter, parts the same as those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0147] The configuration of the information acquisition device 1 according to the seventh embodiment is the same as that shown in Figure 1.

[0148] The excitation unit 1a, the magnetic field measurement unit 1b, and the excitation signal generation unit 1c are the same as those in the first embodiment, and the description thereof is omitted.

[0149] The measurement result approximation unit 1d approximates, by the sum of a plurality of predetermined functions, the measurement result of the magnetic field measurement unit 1b to which a plurality of types of offsets are added. Further, the measurement result approximation unit 1d outputs an optimal offset OF0 (see FIG. 19), which is an offset that minimizes the approximation residual in the measurement result approximation unit 1d, among the plurality of types of offsets.

[0150] The distance derivation unit 1e obtains the distance between each of the reinforcing bars (measurement targets) 2a1, 2a2, 2a3 based on the positions where each of the results obtained by adding the optimal offset OF0 to the plurality of predetermined functions reaches the maximum value.

[0151] The depth derivation unit 1f obtains the depth (for example, cover thickness cd) of the reinforcing bars (measurement targets) 2a1, 2a2, 2a3 in the reinforced concrete (object) 2 based on the maximum value of each of the results obtained by adding the optimal offset OF0 to the plurality of predetermined functions.

[0152] Next, the operation of the seventh embodiment will be described.

[0153] FIG. 16 is a diagram for explaining the scanning of the reinforced concrete 2 by the information acquisition device 1 in the seventh embodiment.

[0154] First, the substrate 1s of the information acquisition device 1 is moved in the X-axis direction. More specifically, the X coordinate of the centroid of the magnetic field measurement unit 1b on the substrate 1s is moved from X1 to X2. Thereby, the reinforced concrete 2 is scanned. However, 0 < X1 < b1 < b3 < X2 < X0. Also, X1 is closer to b1 than 0, and X2 is closer to b3 than X0. That is, the X coordinates of the start point and the end point of the scanning are not sufficiently separated from the X coordinates of the reinforcing bars 2a1, 2a2, 2a3.

[0155] However, as in the first embodiment, the Z coordinate of the substrate 1s is kept constant, and this constant value is set to be greater than the maximum value of the Z coordinate of the reinforced concrete 2. Also, as in the first embodiment, the X coordinates of the reinforcing bars 2a1, 2a2, and 2a3 are set to b1, b2, and b3, respectively. Here, b1 is sufficiently greater than 0. X0 is sufficiently greater than b3. Also, b2-b1=b3-b2=P (see Figure 3(a)).

[0156] While the substrate 1s is moving in the X-axis direction as described above, the excitation signal generation unit 1c provides the excitation unit 1a with an excitation signal having a sinusoidal waveform, similar to the first embodiment. As a result, the reinforcing bars 2a1, 2a2, and 2a3 are excited by the excitation unit 1a, and eddy currents are generated in the reinforcing bars 2a1, 2a2, and 2a3. The magnetic field generated by these eddy currents is measured by the magnetic field measurement unit 1b.

[0157] Figure 17 shows the measurement result M1 by the magnetic field measurement unit 1b in the seventh embodiment (Figure 17(a)), and the measurement result M1 by the magnetic field measurement unit 1b and the approximation functions AF1, AF2, and AF3 (Figure 17(b)).

[0158] If, hypothetically, the X-coordinate of the centroid of the magnetic field measuring unit 1b on the substrate 1s were moved from 0 to X0, the measurement result M1 by the magnetic field measuring unit 1b would be as shown in Figure 5(a). However, in the seventh embodiment, the X-coordinate of the centroid of the magnetic field measuring unit 1b on the substrate 1s is only moved from X1 to X2, so the measurement result M1 by the magnetic field measuring unit 1b would be as shown in Figure 17(a). That is, Figure 17(a) is roughly similar to the range in Figure 5(a) where the X-coordinate is between b1 and b3, and the vicinity of that range.

[0159] In Figure 5(a), we can see a region where the amplitude [nT] is almost zero (near the X coordinate 0 and near X0). However, in Figure 17(a), there is almost no region where the amplitude [nT] is almost zero.

[0160] If the measurement result M1 shown in Figure 17(a) is approximated by AF0 = AF1 + AF2 + AF3, as in the first embodiment, the maximum value (amplitude a0) of the approximation functions AF1, AF2, and AF3 (Figure 17(b)) becomes considerably smaller than the amplitude a (Figure 7(a)). If the depth (cover thickness) of the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3 is then determined using the amplitude a0 by the depth derivation unit 1f, the depth will be determined to be significantly smaller than the true value.

[0161] Figure 18 shows the measurement result M1 from the magnetic field measurement unit 1b with the offset OF added (Figure 18(a)), and the measurement result M1 from the magnetic field measurement unit 1b with the offset OF added, along with the approximation functions AF1, AF2, and AF3 (Figure 18(b)).

[0162] The offset OF is added to the measurement result M1 obtained by the magnetic field measurement unit 1b (Figure 18(a)). Furthermore, this is approximated by the measurement result approximation unit 1d as AF0 = AF1 + AF2 + AF3 (Figure 18(b)). As a result, the maximum value (amplitude a1) of the approximation functions AF1, AF2, and AF3 (Figure 18(b)) becomes larger than the amplitude a0 (Figure 17(b)).

[0163] As the offset OF increases, the amplitude a1 increases, approaching amplitude a (Figure 7(a)), and eventually becoming equal to amplitude a. Further increasing the offset OF will cause the amplitude a1 to increase even more, eventually becoming larger than amplitude a.

[0164] Figure 19 is a graph showing the relationship between the offset OF and the approximate residual FE (Fitting Error).

[0165] Referring to Figure 19, as the offset OF is gradually increased from 0, the approximate residual FE due to the measurement result approximation section 1d decreases. Eventually, when the offset OF becomes the optimal offset OF0, the approximate residual FE takes its minimum value FE0 (at this point, amplitude a1 becomes equal to amplitude a). Further increasing the offset OF leads to an increase in the approximate residual FE.

[0166] The distance derivation unit 1e determines the distance between each of the reinforcing bars (measurement targets) 2a1, 2a2, and 2a3 based on the position where each of the sums obtained by adding the optimal offset OF0 to a plurality of predetermined functions takes its maximum value. The method of determination is the same as in the first embodiment.

[0167] The depth derivation unit 1f determines the depth (e.g., cover thickness cd) of the reinforcing bars (objects to be measured) 2a1, 2a2, and 2a3 in the reinforced concrete (object) 2 based on the maximum value of each of the results obtained by adding the optimal offset OF0 to a plurality of predetermined functions. The method of determination is the same as in the first embodiment.

[0168] The seventh embodiment provides the same effects as the first embodiment. Furthermore, according to the seventh embodiment, even when the X coordinates of the start and end points of scanning the reinforced concrete 2 are not sufficiently far from the X coordinates of the reinforcing bars 2a1, 2a2, and 2a3, the cover thickness cd and other parameters can be determined more accurately by performing the measurement using the optimal offset OF0, which is the offset that minimizes the approximate residual.

[0169] In addition, in the seventh embodiment, it is possible to use the measurement result averaging unit 1g as in the second embodiment, or to use the multivariate analysis unit 1h as in the third embodiment.

[0170] Eighth Embodiment The information acquisition device 1 according to the eighth embodiment differs from the first embodiment in that the concrete cover thickness of the reinforcing bars 2a1, 2a2, and 2a3 are all different.

[0171] The information acquisition device 1 according to the eighth embodiment (see Figure 1) comprises an excitation unit 1a, a magnetic field measurement unit 1b, an excitation signal generation unit 1c, a measurement result approximation unit 1d, a distance derivation unit 1e, a depth derivation unit 1f, and a measurement result averaging unit 1g. Hereinafter, parts the same as those in the first embodiment are denoted by the same reference numerals and their description is omitted.

[0172] The configuration of the information acquisition device 1 according to the eighth embodiment is the same as that shown in Figure 1.

[0173] The excitation unit 1a, magnetic field measurement unit 1b, excitation signal generation unit 1c, distance derivation unit 1e, and depth derivation unit 1f are the same as in the first embodiment and will not be described.

[0174] Figure 21 shows a cross-sectional view (Figure 21(a)) and a plan view (Figure 21(b)) of reinforced concrete (object) 2 according to the eighth embodiment. Referring to Figure 21, the reinforced concrete 2 has reinforcing bars 2a and concrete 2b, and reinforcing bars 2a1, 2a2, and 2a3 are arranged inside the reinforced concrete 2.

[0175] Reinforcement bars 2a1 and 2a2 are adjacent (with a distance of pitch P), and reinforcement bars 2a2 and 2a23 are adjacent (with a distance of pitch P). The diameters of reinforcement bars 2a1, 2a2, and 2a3 are D. Furthermore, the covering depths of reinforcement bars 2a1, 2a2, and 2a3 are cd1, cd2, and cd3, respectively. Note that cd1, cd2, and cd3 are all different values.

[0176] The measurement result approximation unit 1d sets the maximum value (amplitude a1, a2, a3) and the position where the maximum value is taken (phase b1, b2, b3) for each of a plurality of predetermined functions so that the approximation residual in the measurement result approximation unit 1d is less than a predetermined threshold.

[0177] However, the phases b1, b2, and b3 are the same as in the first embodiment. The amplitudes a1, a2, and a3 are obtained by replacing a with a in equation (2) in the first embodiment. k (However, this is the result of substituting k=1,2,3).

[0178] Next, the operation of the eighth embodiment will be described.

[0179] Except for the operation of the measurement result approximation unit 1d, the configuration is the same as in the first embodiment.

[0180] Figure 22 is a flowchart showing the operation of the measurement result approximation unit 1d in the eighth embodiment.

[0181] First, assuming that amplitudes a1, a2, and a3 are all equal to a, the measurement result of the magnetic field measuring unit 1b is approximated by AF0 = AF1 + AF2 + AF3 (S10). This is the same as in the first embodiment, so the explanation is omitted.

[0182] Next, in equation (2), change a to a k (However, when k=1,2,3) the phases b1, b2, and b3 are fixed, and the amplitudes a1, a2, and a3 are determined (S12). For example, in equation (2), a is a k (However, when k=1,2,3) the phases b1, b2, and b3 are fixed, and the amplitudes a1, a2, and a3 are found such that the approximate residual is less than or equal to a predetermined value.

[0183] Next, in equation (2), change a to a k (However, when k=1,2,3) the amplitudes a1, a2, a3 are fixed and the phases b1, b2, b3 are determined (S14). For example, in equation (2), a is a k (However, when k is replaced with k=1,2,3), the amplitudes a1, a2, and a3 are fixed, and the phases b1, b2, and b3 are found such that the approximate residual is less than or equal to a predetermined value.

[0184] Furthermore, if the approximate residual of the measurement result obtained by the magnetic field measurement unit 1b using the amplitudes a1, a2, a3 and phases b1, b2, b3 in equation (2) obtained in this way is less than or equal to a threshold (S16, Yes), the measurement result approximation unit 1d outputs the amplitudes a1, a2, a3 and phases b1, b2, b3 and terminates processing by the measurement result approximation unit 1d.

[0185] On the other hand, if the approximate residual of the measurement results by the magnetic field measuring unit 1b, based on the amplitudes a1, a2, a3 and phases b1, b2, b3 in equation (2) obtained in this way, exceeds a threshold (S16, No), the process returns to the step of fixing the phases b1, b2, b3 in equation (2) and determining the amplitudes a1, a2, a3 (S12).

[0186] According to the eighth embodiment, even if the concrete cover thickness of the reinforcing bars 2a1, 2a2, and 2a3 are different, both the concrete cover thickness and the distance between each of the reinforcing bars 2a1, 2a2, and 2a3 can be determined.

[0187] Furthermore, various modifications of the embodiments of the present invention are possible, as shown below.

[0188] <Example 1> Although the magnetic field measuring unit (magnetic sensor) 1b in the embodiments of the present invention has been described as having a magnetic sensing direction in the Z-axis direction or the X-axis direction, the magnetic sensing direction may also be in the Y-axis direction.

[0189] However, if the magnetic field measurement unit 1b's sensing direction is the Y-axis direction, the predetermined function is the first derivative of the Gaussian function.

[0190] Figure 20 is a graph showing the approximation function AF that approximates the measurement result M when the magnetic field direction is the Y-axis direction. The approximation function AF is defined as shown in equation (4) below. Furthermore, the sum of multiple (N) approximation functions AF, fym(x), is expressed as shown in equation (5) below. This fym(x) approximates the measurement result from the magnetic field measurement unit 1b.

[0191]

number

[0192] However, the approximation function AF can be anything other than the Gaussian function or its first derivative.

[0193] For example, the approximation function AF can be defined as being based on the Biot-Savart law and the theoretical formula for the magnetic field generated by the reinforcing bar (object of measurement) 2a1, assuming that the reinforcing bar 2a1 is a magnet of size 0, when the magnetic field measurement unit 1b is sensitive in the Z-axis direction or the X-axis direction (see equation (6) below). Furthermore, the sum of multiple (N) approximation functions AF, f(x), is expressed as shown in equation (7) below. The measurement result by the magnetic field measurement unit 1b is approximated by this f(x) in equation (7).

[0194]

number

[0195]

number

[0196] <Modification 4> It is also conceivable that the information acquisition device 1 according to an embodiment of the present invention could be used for corrosion detection of reinforcing bars 2a1, 2a2, and 2a3. In that case, the frequency at which the excitation unit 1a is excited may differ depending on whether it is suitable for approximation by the measurement result approximation unit 1d (let's call it excitation frequency f1) or suitable for corrosion detection (let's call it excitation frequency f2), as explained in previous embodiments.

[0197] In this case, the excitation signal generator 1c outputs a combined signal of the signal with frequency f1 (first signal) and the signal with frequency f2 (second signal) to excite the excitation unit 1a. Alternatively, the excitation signal generator 1c could output the signal with frequency f1 (first signal) to excite the excitation unit 1a for a period of time, and the excitation unit 1a could output the signal with frequency f2 (second signal) for a period of time, and these periods could be separated.

[0198] Furthermore, the above embodiment can be realized as follows: A computer equipped with a CPU, hard disk, and media (USB memory, CD-ROM, etc.) reader is made to read a media containing a program that implements each of the above parts, for example, the measurement result approximation unit 1d, the distance derivation unit 1e, the depth derivation unit 1f, the measurement result averaging unit 1g, the multivariate analysis unit 1h, and the count derivation unit 1i, and install it on the hard disk. The above functions can also be realized by this method. [Explanation of Symbols]

[0199] 1 Information acquisition device 1a Excitation part 1b Magnetic field measurement section 1c Excitation signal generation unit 1d Measurement result approximation part 1e Distance derivation part 1f Depth Derivation Section 1g measurement result average part 1h Multivariate Analysis Department 1i Number derivation part 1s circuit board 2. Reinforced concrete (object) 2a1, 2a2, 2a3 Reinforcement bars (measurement target) 2b Concrete 2c1, 2c2 orthogonal reinforcement bars P pitch D diameter CD, CD1, CD2, CD3 Covering depth AF, AF1, AF2, AF3 Approximation function function) M, M1, M2 measurement results a, a1, a2, a3 amplitude b1, b2, b3 Phase ΔT magnetic field gradient OF Offset OF0 Optimal Offset FE approximation residual (Fitting Error)

Claims

1. An excitation unit that energizes multiple measurement targets inside an object, A magnetic field measuring unit for measuring the magnetic field generated by eddy currents in the object to be measured, A measurement result approximation unit that approximates the measurement results of the magnetic field measurement unit with the sum of a plurality of predetermined functions, A number derivation unit that determines the number of the number of the measurement targets as the number of predetermined functions that minimize the approximate residual in the measurement result approximation unit, Equipped with, The results of measuring each of the aforementioned objects by the magnetic field measuring unit are approximated by the predetermined function. Information acquisition device.

2. An information acquisition device according to Claim 1, The aforementioned predetermined function is a Gaussian function. Information acquisition device.

3. An information acquisition device according to Claim 1, The aforementioned predetermined function is the first derivative of a Gaussian function. Information acquisition device.

4. An information acquisition device according to Claim 1, The predetermined function is based on a theoretical formula for the magnetic field generated by the object being measured, assuming the object is a magnet of size 0. Information acquisition device.

5. An information acquisition device according to Claim 1, The predetermined function is based on the first derivative of the theoretical formula for the magnetic field generated by the object being measured, assuming the object is a magnet of size 0. Information acquisition device.

6. An information acquisition device according to Claim 1, The system includes a measurement result averaging unit that takes the average of the measurement results of each of the magnetic field measuring units while aligning the position where each measurement result of the magnetic field measuring unit takes its maximum value to a predetermined position. The measurement result approximation unit approximates the output of the measurement result averaging unit with the sum of the plurality of predetermined functions, The aforementioned magnetic field measuring unit has multiple units. Information acquisition device.

7. An information acquisition device according to Claim 1, The system includes a multivariate analysis unit that performs multivariate analysis on the measurement results of each of the magnetic field measurement units while aligning the position where each measurement result of the magnetic field measurement unit takes its maximum value to a predetermined position. The measurement result approximation unit approximates the output of the multivariate analysis unit with the sum of the plurality of predetermined functions, The aforementioned magnetic field measuring unit has multiple units. Information acquisition device.

8. An information acquisition device according to Claim 1, The aforementioned object is made of reinforced concrete, The object being measured is reinforcing steel. Information acquisition device.

9. An information acquisition device according to claim 1, The system comprises multiple substrates on which the magnetic field measuring units are arranged. The substrate is superimposed in the direction normal to a plane at a constant distance from the object to be measured. Information acquisition device.

10. An information acquisition device according to Claim 1, The excitation unit is excited by a combined signal obtained by combining a first signal of a first frequency suitable for approximation by the measurement result approximation unit and a second signal of a second frequency suitable for corrosion detection of the object to be measured. Information acquisition device.

11. An information acquisition device according to Claim 1, The excitation unit is excited by a first signal of a first frequency suitable for approximation by the measurement result approximation unit for a certain period of time, The excitation unit is excited by a second signal of a second frequency suitable for detecting corrosion of the object to be measured for a certain period of time, They are separate. Information acquisition device.

12. An excitation process in which multiple objects to be measured inside an object are energized, A magnetic field measurement step for measuring the magnetic field generated by eddy currents in the object to be measured, A measurement result approximation step in which the measurement result of the magnetic field measurement step is approximated by the sum of a plurality of predetermined functions, A number derivation step in which the number of the number of objects to be measured is determined to be the number of predetermined functions that minimize the approximate residual in the measurement result approximation step, Equipped with, The results of measuring each of the aforementioned objects by the magnetic field measurement step are approximated by the predetermined function. How to obtain information.

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