JP2009186337A - Metal detection device and metal detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal detection device capable of performing highly accurate measurement with simple structure and method, and detecting a position or the size of a reinforcement or a metal pipe buried inside concrete. <P>SOLUTION: This device is equipped with: a gage head 11 for measuring a magnetic field at a measuring point P; an inside coil 12 for generating the first magnetic field to the measuring point P; and an outside coil 13 constituted separately from the inside coil 12, for adjusting a resultant magnetic field of the first magnetic field and the second magnetic field at the measuring point P approximately to be zero, by generating the second magnetic field in the opposite direction to the first magnetic field relative to the measuring point P. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal detection device and a metal detection method for detecting metal.

  Conventionally, metal detection has been performed for various purposes. For example, detection of rebars and metal pipes embedded in the concrete that constitutes the walls and floors of buildings, detection to monitor the entry and exit of metals in special areas such as airports and MRI (Magnetic Resonance Imaging) rooms, or There are detections to monitor metal contamination in food. As one principle for performing such metal detection, an electromagnetic induction method is known.

  For example, Patent Document 1 discloses an electromagnetic induction type metal piece sorting apparatus. This apparatus includes a pair of sensors. In each of these sensors, a drive coil and a detection coil are arranged concentrically with each other. An AC signal source for exciting and driving the drive coil is connected to the drive coil of each sensor, and a differential amplifier that outputs a differential signal of the detection signal of the detection coil is connected to the detection coil of each sensor. It is connected. In such a structure, a sample metal piece is set in the detection coil of one sensor, and a standard sample metal piece is set in the detection coil of the other sensor. When excitation driving is performed, an eddy current is generated in each sample metal piece by the magnetic flux generated by the driving coil. The eddy currents of each sample metal piece differ from each other according to the difference in the composition and external dimensions of the sample metal piece. Therefore, each eddy current difference is amplified by a differential amplifier and analyzed. The difference in composition of the sample metal pieces can be determined.

JP 59-43349

  However, since the metal piece sorting device described in Patent Document 1 sorts metal pieces by calculating the difference between eddy currents generated by each of the pair of sensors, in order to increase measurement accuracy In order to perform this removal process, it is necessary to remove the manufacturing error between the sensors, the displacement of the arrangement position of the sample metal piece relative to each sensor, the production error of the standard sample metal piece, etc. Adjustment and electrical processing such as obtaining a reference signal in advance are required. In addition, this metal piece sorter can detect only the difference in composition relative to the standard sample metal piece, and cannot detect the position and size of reinforcing bars and metal pipes embedded in concrete. It was.

  The present invention has been made in order to solve such problems caused by the prior art, and can perform high-accuracy measurement with a simple structure and method, and can be used as a reinforcing bar or metal embedded in concrete. An object of the present invention is to provide a metal detection device and a metal detection method capable of detecting the position and size of a pipe.

  In order to solve the above-described problems and achieve the object, the present invention according to claim 1 includes a magnetic field measuring unit that measures a magnetic field at a measurement point, and a first magnetic field that generates a first magnetic field with respect to the measurement point. The coil and the first coil are configured separately, and the measurement point is generated by generating a second magnetic field in a direction opposite to the first magnetic field with respect to the measurement point. And a second coil that makes the combined magnetic field of the first magnetic field and the second magnetic field substantially zero.

  The present invention according to claim 2 is the present invention according to claim 1, wherein the second coil is positioned concentrically with the first coil and surrounds the first coil from the outside. It is characterized by being arranged at a position.

  According to a third aspect of the present invention, in the second aspect of the present invention, the one end surface along the axial direction of the first coil is the same as the one end surface along the axial direction of the second coil. It is arranged in a plane.

  According to a fourth aspect of the present invention, in the present invention according to the second or third aspect, the magnetic field measuring means includes a pickup coil disposed at a position surrounded by the first coil from the outside, and the pickup The coil is composed of a pair of coils each having an axis parallel to the axis of the first coil and the axis of the second coil, and the coils are differentially connected to each other. And

  According to a fifth aspect of the present invention, in the present invention according to any one of the second to fourth aspects, the first coil has a plurality of first coils that have different diameters and are arranged concentrically with each other. One coil is provided, and switching means for switching the plurality of first coils to each other is provided.

  According to a sixth aspect of the present invention, in the present invention according to any one of the second to fourth aspects, the second coil has a plurality of first coils that have different diameters and are arranged concentrically with each other. 2 is provided, and switching means for switching the plurality of second coils to each other is provided.

  According to a seventh aspect of the present invention, in the present invention according to any one of the first to sixth aspects, the ratio of the number of turns of the first coil to the number of turns of the second coil is set to the first coil. And the first coil and the second coil are differentially connected to each other.

  The present invention according to claim 8 is the present invention according to any one of claims 1 to 7, wherein a magnetic field in a direction opposite to the first magnetic field is generated for the measurement point, or the second A correction coil for adjusting the strength of the synthetic magnetic field at the measurement point is provided.

  According to a ninth aspect of the present invention, in the present invention according to any one of the first to eighth aspects, the coil unit comprising the first coil and the second coil is arranged such that the measurement points are collinear. It is characterized by being arranged in parallel on the same straight line.

  According to a tenth aspect of the present invention, in the present invention according to the ninth aspect, a coil unit including the first coil and the second coil is arranged in the same straight line so that the measurement points are aligned on the same straight line. A plurality of coil unit groups are formed by arranging a plurality of coil units on the line, and the plurality of coil unit groups are arranged side by side so that the measurement points of the coil units of the plurality of coil unit groups are aligned on the same straight line. It is characterized by that.

  According to an eleventh aspect of the present invention, in the present invention according to the ninth or tenth aspect, the peak depth of the synthetic magnetic field by at least a part of the plurality of coil units is set to the depth of the coil unit other than the part. It is characterized in that the depth is different from the peak depth of the synthetic magnetic field.

  According to a twelfth aspect of the present invention, there is provided a metal detection method for detecting a metal contained in a measurement object, and a magnetic field measurement unit for measuring a magnetic field at a measurement point, and a first magnetic field is generated for the measurement point. The first coil and the first coil are configured separately, and generating a second magnetic field in a direction opposite to the first magnetic field with respect to the measurement point, In the metal detection method using the metal detection device configured to include a second coil whose combined magnetic field of the first magnetic field and the second magnetic field at the measurement point is substantially zero, the metal detection One of the apparatus and the measurement object is moved relative to the other, and at each moving position during the movement, based on a change in the strength of the synthetic magnetic field measured by the magnetic field measuring means. And the metal contained in the measurement object Characterized in that it detected.

  According to the first aspect of the present invention, the presence or absence of a metal in a measurement object, the position of the metal in the measurement object, the size of the metal, and whether the metal is a conductor or a magnetic body can be determined. So it is useful for various metal detection. In particular, since the synthetic magnetic field at the measurement point is set to substantially zero, even if the output change is small, it can be easily determined, and the minute magnetic field change can be captured, so that a high S / N ratio can be detected. In addition, in order to determine the presence or absence and type of metal, it is only necessary to provide one pair of the first coil and the second coil. Since it is not necessary to prepare a sample metal piece to be used, a metal detector can be manufactured easily and inexpensively.

  According to the second aspect of the present invention, since the second coil is arranged concentrically with the first coil, the second coil is composed of a pair of the first coil and the second coil as compared with the case where they are arranged in parallel. It is easy to multiplex the measurement units to be miniaturized by nesting them. Furthermore, if each of the first coil and the second coil is formed in a cylindrical shape and arranged concentrically with each other, the combined magnetic field from these coils to the outside will be isotropic. Since the same magnetic field change can be caused even when the measurement object is arranged at the position, the measurement accuracy can be further improved.

  According to the third aspect of the present invention, by aligning the one end face of the first coil and the one end face of the second coil, the measurement point having a substantially zero composite magnetic field can be brought closest to the measurement object. Therefore, the S / N ratio of metal detection can be further improved.

  According to the fourth aspect of the present invention, by performing magnetic field measurement using a pickup coil composed of a pair of differentially connected coils, it is possible to cancel each other's magnetic field mutually, Since it becomes easier to make the synthetic magnetic field substantially zero, the S / N ratio of metal detection can be further improved.

  According to the fifth aspect of the present invention, the peak depth of the synthetic magnetic field can be adjusted by switching the plurality of first coils to each other, and the depth from the surface of the measurement object to the metal can be specified. In particular, since the peak depth of the synthesized magnetic field can be adjusted by preparing only one pair of a plurality of first coils and second coils, the apparatus cost can be reduced compared to the case of preparing a plurality of measurement units. At the same time, the detection work can be performed easily and quickly.

  According to the sixth aspect of the present invention, the depth of the peak of the synthetic magnetic field can be adjusted by switching the plurality of second coils to each other, and the depth from the surface to be measured to the metal can be specified. In particular, since the peak depth of the synthesized magnetic field can be adjusted by preparing only one pair of the first coil and the plurality of second coils, the apparatus cost can be reduced compared to the case of preparing a plurality of measurement units. At the same time, the detection work can be performed easily and quickly. In addition, when a plurality of second coils disposed outside are provided, a second coil can be added or changed more easily than when a plurality of first coils disposed inside are provided. it can.

  According to the seventh aspect of the present invention, the first magnetic field and the second magnetic field can be made opposite to each other and have the same strength, and with a simple configuration, the combined magnetic field is substantially omitted. Can be zero.

  According to the eighth aspect of the present invention, since the strength of the synthetic magnetic field can be finely adjusted by providing the correction coil, a high S / N ratio can be detected. In particular, since it is not necessary to strictly adjust the number of turns of the first coil and the second coil, the measurement unit can be manufactured easily and inexpensively.

  According to the present invention of claim 9, by arranging a plurality of coil units in a straight line, it is possible to collectively measure in a linear measurement region as compared with the case where the coil units are arranged alone. It is possible to measure the linear measurement region more quickly.

  According to the tenth aspect of the present invention, by arranging a plurality of coil unit groups, it is possible to perform measurement in a planar measurement region in a lump compared to the case where the coil unit groups are arranged alone. Further, the measurement of the planar measurement region can be performed more rapidly.

  According to the eleventh aspect of the present invention, in the measurement in the linear or planar measurement region, the depth direction in the measurement target is changed by changing the depth of the peak of the synthesized magnetic field by at least a part of the plurality of coil units. Even if it is not known in advance in which position the metal is mixed, the metal can be detected quickly.

  According to the present invention of claim 12, either the metal detection device or the measurement object is moved relative to the other, and the metal is changed based on the intensity change of the synthetic magnetic field at each movement position. By detecting the metal, it is possible to detect the metal quickly even when the measurement object is wide.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [I] First, the basic concept common to each embodiment was explained, then [II] the specific contents of each embodiment were explained, and [III] Finally, modifications to each embodiment Will be described. However, the present invention is not limited to each embodiment.

[I] Basic concept common to the embodiments First, the basic concept common to the embodiments will be described. The metal detection device and the metal detection method according to each embodiment detect a metal included in a measurement target. In this apparatus and method, it is possible to determine 1) presence or absence of metal, 2) position of metal, 3) size of metal, and 4) whether the metal is a conductor or a magnetic body. The metal to be detected and the status of detection are arbitrary. For example, detection of pipes embedded in concrete, detection to monitor the entry and exit of metals in special areas, or monitoring of metal contamination in food It is applicable to the detection to do. In the following example, a case where a reinforcing bar embedded in concrete is detected will be described.

  One of the features common to the respective embodiments is a magnetic field measuring means for measuring the magnetic field at the measurement point, a first coil for generating a first magnetic field at the measurement point, and the measurement point. By generating a second magnetic field in a direction opposite to the first magnetic field, a second coil that uses a combined magnetic field of the first magnetic field and the second magnetic field at the measurement point to be substantially zero is used. . That is, by using at least two coils and devising the mechanical or electrical configuration of each coil, the magnetic fields generated by each coil automatically cancel each other out at a predetermined measurement point. To do. In this way, by making the composite magnetic field substantially zero, it is not necessary to make the difference in the magnetic field generated in each coil zero by signal processing, and metal detection is performed based on the fluctuation of the magnetic field with the zero point as a reference. By doing so, minute fluctuations in the magnetic field can be easily grasped and measurement accuracy can be improved.

  In addition, when the synthetic magnetic field is set to “substantially zero”, the synthetic magnetic field cannot be completely zero, but the synthetic magnetic field that does not hinder measurement accuracy remains. Including meaning. Further, the configuration in which the combined magnetic field is “substantially zero” may not be achieved by only the first coil and the second coil, but may be achieved by magnetic field adjustment by a correction coil described later.

[II] Specific Contents of Each Embodiment Next, specific contents of the metal detection device and the metal detection method according to each embodiment will be described.

[Embodiment 1]
First, the first embodiment will be described. The first embodiment is a basic form in which a pair of coils are arranged in a double concentric cylindrical shape.

(Configuration of metal detector)
FIG. 1 is a schematic diagram showing a metal detection apparatus according to Embodiment 1 together with a measurement object. The measurement object 1 in the first embodiment is concrete 1b in which a reinforcing bar 1a is embedded. The metal detector 2 includes a measurement unit 10, an oscillator 20, an amplifier 30, and a lock-in amplifier 40 (in FIG. 1 and FIGS. It is shown as a vertical cross-sectional view, and the other components are shown as a perspective view, where the vertical cross-section means a cross-section taken along a cut surface along the central axis direction of the coil. Then, the copper wire which comprises each coil is simplified and shown).

  The measurement unit 10 is disposed close to the measurement object 1 and corresponds to the coil unit in the claims. The measurement unit 10 includes a probe 11, an inner coil 12, and an outer coil 13.

  The measuring element 11 measures the magnetic field at the measurement point P and corresponds to the magnetic field measuring means in the claims. The measuring element 11 is configured by winding a pickup coil 11b around a position near the tip of a cylindrical measuring element main body 11a, and an electromotive force is generated in the pickup coil 11b due to a change in magnetic flux passing through the pickup coil 11b. A current corresponding to the change in the magnetic flux is output from the pickup coil 11b. That is, the central position on the central axis of the pickup coil 11b is the measurement point P in the present embodiment.

  The inner coil 12 generates a first magnetic field with respect to the measurement point P, and corresponds to the first coil in the claims. The inner coil 12 is formed by winding a copper wire in a cylindrical shape, and the current output from the amplifier 30 is passed through the inner coil 12 so that the inner coil 12 includes the inner coil 12. A first magnetic field is formed along the axial direction. Here, the inner coil 12 is disposed so that the axial direction of the inner coil 12 is along the vertical direction, and the first magnetic field is a vertically upward magnetic field.

  The outer coil 13 generates a second magnetic field with respect to the measurement point P, and corresponds to the second coil in the claims. The outer coil 13 is formed by winding a copper wire in a cylindrical shape. By passing the current output from the amplifier 30 through the outer coil 13, the outer coil 13 has the outer coil 13. A second magnetic field is formed along the axial direction. The second magnetic field is formed in the opposite direction to the first magnetic field (details of this point will be described later). Here, the outer coil 13 is arranged so that the axial direction of the outer coil 13 is along the vertical direction, and the second magnetic field is a vertically downward magnetic field.

  The interrelationship between the measuring element 11, the inner coil 12, and the outer coil 13 will be described. FIG. 2 is a plan view of each coil in the measurement unit 10 of FIG. The pickup coil 11 b of the measuring element 11 is disposed inside the inner coil 12 and at a position that is concentric with the inner coil 12. The outer coil 13 is disposed at a position that is concentric with the inner coil 12 and that surrounds the inner coil 12 from the outside. Here, the inner coil 12 and the outer coil 13 are differentially connected to each other. Therefore, by passing the current output from the amplifier 30 through the end of the inner coil 12 and the end of the outer coil 13, the first magnetic field by the inner coil 12 and the second magnetic field by the outer coil 13 are mutually The reverse direction.

  In addition, the diameter of the inner coil 12 and the number of turns of the copper wire, the diameter of the outer coil 13 and the number of turns of the copper wire are determined so that the strength of the first magnetic field and the strength of the second magnetic field are the same. ing. Specifically, the inner coil 12 and the outer coil 13 have a diameter ratio equal to the ratio of the number of turns of the copper wire of the inner coil 12 and the number of turns of the copper wire of the outer coil 13. 12 and the outer coil 13 are formed. For example, the diameter of the inner coil 12 is 200 mm, the diameter of the outer coil 13 is 400 mm, the number of turns of the copper wire of the inner coil 12 is 155, and the number of turns of the copper wire of the outer coil 13 is 310.

  As described above, since the first magnetic field and the second magnetic field are opposite to each other, and the strength of the first magnetic field and the strength of the second magnetic field are the same as each other, The combined magnetic field at the measurement point P between the first magnetic field and the second magnetic field is substantially zero. FIG. 3 is a diagram illustrating changes in magnetic flux density, where the horizontal axis represents the distance from the measurement point P, and the vertical axis represents the magnetic flux density. Here, the “distance” means a distance along the axial direction of the inner coil 12 and the outer coil 13 starting from the measurement point P (the same unless otherwise specified). As shown in FIG. 3, at the measurement point P (at a point where the distance from the measurement point P = 0), it can be seen that the combined magnetic field (the magnetic field of the outer coil 13−the magnetic field of the inner coil 12) becomes zero. . Theoretically, when the inner coil 12 and the outer coil 13 are arranged completely at the same position, the first magnetic field and the second magnetic field are completely mutually different at positions other than the measurement point P. This is not preferable because the magnetic field change according to the presence or absence of metal does not occur. Therefore, here, the case where the inner coil 12 and the outer coil 13 are arranged in the same position is excluded, in other words, the inner coil 12 and the outer coil 13 are configured separately from each other. It is a condition.

  In order to improve the workability of measurement, it is preferable that the measuring element 11, the inner coil 12, and the outer coil 13 have a structure that can be held integrally with each other. For example, it is preferable to configure the measurement unit 10 by arranging the measuring element 11, the inner coil 12, and the outer coil 13 in a non-metallic cylindrical case (not shown) and integrating them.

  In FIG. 1, an oscillator 20 is a reference current source that outputs a current having a predetermined frequency (for example, 1 KHz to several MHz). The amplifier 30 amplifies the current output from the oscillator 20 and outputs it to the end of the inner coil 12 and the end of the outer coil 13. To the lock-in amplifier 40, the current output from the pickup coil 11b of the probe 11 is input as a measurement signal, and the current output from the oscillator 20 is input as a reference signal. Accordingly, the lock-in amplifier 40 outputs a voltage value having a frequency component equal to the current output from the oscillator 20 out of the current output from the pickup coil 11 b of the probe 11. In addition, the electric wire 50 which mutually connects the amplifier 30 and the inner coil 12 or the outer coil 13, the electric wire 50 which mutually connects the pickup coil 11b and the lock-in amplifier 40, and the inner coil 12 and the outer coil 13 are mutually connected. As the electric wire 50 connected to, it is preferable to use a twisted conductive wire in order to reduce the influence of the magnetic field generated by the electric wire 50 itself as much as possible.

(Metal detection method)
Next, a metal detection method performed using the metal detection device 2 configured as described above will be described. In this method, zero adjustment is performed first. Specifically, in a state where there is no metal around the metal detector 2, the oscillator 20 is started and a current is passed, so that the output (voltage value) of the lock-in amplifier 40 becomes zero. The position of the probe 11 with respect to the coil 13 is adjusted. However, when the position is adjusted in advance in the manufacturing process of the metal detection device 2, the zero adjustment may be omitted.

  Next, the measurement unit 10 is moved closer to the measurement object 1. During this movement, the first magnetic field formed outside the inner coil 12 out of the first magnetic field, or the second magnetic field formed outside the outer coil 13 out of the second magnetic field is measured 1. When the metal is a magnetic material, it is magnetized in substantially the same phase as the applied magnetic field. On the other hand, when the metal is a conductor, an induced voltage is generated by electromagnetic induction, and an induced current flows. At this time, the phase is further delayed by 90 degrees compared to the induced voltage due to the inductivity (inductance) of the metal. Due to the change in the magnetic field, the first magnetic field or the second magnetic field is affected, and the resultant magnetic field at the measurement point P is out of balance and has a value other than zero. By measuring the intensity of the synthetic magnetic field and the phase angle with respect to the reference signal with the lock-in amplifier 40, the presence or absence of metal in the measurement target 1, the position of the metal in the measurement target 1, the size of the metal, and the metal are conductors. Or a magnetic material can be determined. The reason why such a determination can be made will be described below.

(Metal detection method-identification of presence or absence of metal)
The presence or absence of metal in the measurement object 1 can be determined based on whether or not the output of the lock-in amplifier 40 is other than zero. That is, as described above, when there is no metal around the metal detection device 2, the output of the lock-in amplifier 40 is adjusted to be zero, so that the output of the lock-in amplifier 40 is other than zero. In this case, it can be seen that the measurement object 1 contains metal.

(Metal detection method-identification of metal position)
The position of the metal in the measuring object 1 is the depth from the surface of the measuring object 1 to the metal (the vertical distance in FIG. 1) and the position in the plane orthogonal to the depth direction (the paper surface in FIG. 1). It is possible to specify in a three-dimensional manner.

  The position in the plane orthogonal to the depth direction can be specified based on the position of the measurement unit 10 with respect to the measurement object 1. That is, the output of the lock-in amplifier 40 is monitored while moving the measurement unit 10 horizontally in the plane, and the position where the output is maximized is the position of the metal.

  Moreover, the depth from the surface of the measuring object 1 to the metal can be specified by changing the depth of the peak of the synthetic magnetic field. FIG. 4 is a diagram showing the relationship between the diameter of the outer coil 13 and the depth from the surface of the measuring object 1 to the peak of the synthesized magnetic field, where the horizontal axis is the diameter of the outer coil 13 and the vertical axis is the peak of the synthesized magnetic field. Indicates depth. As shown in FIG. 4, the peak of the synthesized magnetic field can be deepened as the diameter of the outer coil 13 is increased. Therefore, in the configuration of FIG. 1, the peak of the composite magnetic field is increased by increasing the diameter of the inner coil 12 and the outer coil 13 while maintaining the ratio of the diameter of the inner coil 12 and the outer coil 13. The depth can be adjusted.

  FIGS. 5 to 8 are diagrams showing the relationship between the coil diameter and the peak depth of the synthesized magnetic field, in which (a) is a longitudinal section of the inner coil 12 and the outer coil 13, and (b) is (a), respectively. ), The horizontal axis indicates the distance from the measurement point P, and the vertical axis indicates the magnetic flux density. 5A to 8A, the ratio of the diameter of the inner coil 12 to the diameter of the outer coil 13 is 1: 2, but the diameter of the inner coil 12 and the diameter of the outer coil 13 are respectively set. It is changed as shown. As is clear from FIGS. 5B to 8B, the peak of the synthesized magnetic field becomes deeper from FIG. 5A to FIG. 8A. Accordingly, a plurality of measurement units 10 in which the diameters of the inner coil 12 and the outer coil 13 are changed in this way are prepared, for example, the first measurement is performed in the measurement unit 10 having a shallow peak of the synthesized magnetic field, and the synthesized magnetic field is obtained. The measurement unit 10 gradually switches to the measurement unit 10 where the peak of the peak gradually increases, and the depth of the peak of the synthetic magnetic field of the measurement unit 10 when the metal is detected is the depth from the surface of the measuring object 1 to the metal. Can be determined.

(Metal detection method-metal size discrimination)
Next, the size of the metal can be determined based on the maximum output value of the lock-in amplifier 40. FIG. 9 is a diagram showing a change in the output of the lock-in amplifier 40. Here, the pickup coil 11b has a diameter of about 40 mm, the number of turns of 700, the inner coil 12 has a diameter of 60 mm, a length of 120 mm, a number of turns of 120, and the outer coil 13 has a diameter of 115, a length of 230, and a number of turns of 230. Shows the voltage value and phase angle of the lock-in amplifier 40 when different metals are arranged at a plurality of positions with respect to the measurement unit 10 (actually, this measurement result is provided with a correction coil 14 having two turns and a resistance of about 70 mm). The correction coil 14 will be described in the second embodiment). As can be seen from FIG. 9, the voltage value of the lock-in amplifier 40 becomes maximum when a metal is disposed at a distance of zero with respect to the measurement unit 10, and at least this maximum value is 10 mm in diameter and 15 mm in diameter of the reinforcing bar. The diameter increases as the diameter increases to 20 mm. Therefore, the size of the metal can be determined by acquiring these maximum values in advance and comparing the maximum value obtained by the measurement with a known value.

(Metal detection method-distinguishing whether a metal is a conductor or a magnetic substance)
Next, whether the metal is a conductor or a magnetic material can be determined based on the phase angle of the synthetic magnetic field. FIG. 10 is a diagram illustrating a change in the phase angle according to the distance from the measurement unit 10, where the horizontal axis represents the distance from the measurement unit 10 and the vertical axis represents the phase angle of the measurement signal with respect to the reference signal. Here, using the same measurement unit 10 as in FIG. 9, the results when metals of different types and sizes are arranged at a plurality of positions with respect to the measurement unit 10 are shown. As can be seen from FIG. 10, in the case of a magnetic material such as a reinforcing bar or steel plate, the phase angle is delayed (plus), and in the case of a conductor such as a brass plate, an aluminum plate, and a copper plate, the measurement unit 10 When the distance from is about 130 mm or less, the phase angle advances (minus). Therefore, based on this phase angle, it can be determined whether the metal is a conductor or a magnetic body. The point that the type of metal can be discriminated in this way is particularly important when monitoring the entry and exit of the MRI room. That is, in the MRI room, since the magnetic substance is attracted to the MRI apparatus and dangerous, it is prohibited to bring in the magnetic substance. However, there is a case where the electric conductor such as the patient bed should be allowed in and out. Therefore, it is important to distinguish between the two.

  In addition, there is a possibility that the metal detector 2 can be applied to the measurement of the concrete-containing salt concentration. That is, since the electrical conductivity of concrete changes depending on the salt content, the higher the salt content, the more eddy current is generated, and the voltage value of the lock-in amplifier 40 becomes larger. Accordingly, it is possible to determine the concrete-containing salt concentration based on the voltage value.

(Effect of Embodiment 1)
As described above, according to the first embodiment, the presence or absence of the metal in the measurement object 1, the position of the metal in the measurement object 1, the size of the metal, the determination of whether the metal is a conductor or a magnetic body, and the inclusion of concrete Since salinity concentration can be determined, it is useful for detecting various metals.

  In particular, since the composite magnetic field at the measurement point P is set to zero, even if the output change is small, it can be easily determined, and the minute magnetic field change can be captured, so that a high S / N ratio can be detected.

  Further, in order to determine the presence or absence and type of metal, only one measurement unit 10 needs to be provided. As in the prior art, a plurality of sensors composed of a plurality of coils are provided, or a standard sample metal piece is provided. Since it is not necessary to prepare, the metal detector 2 can be manufactured easily and inexpensively.

[Embodiment 2]
Next, a second embodiment will be described. In the second embodiment, a correction coil is provided. However, about the component substantially the same as Embodiment 1, the same code | symbol or name as used in Embodiment 1 is attached | subjected as needed, and the description is abbreviate | omitted.

  FIG. 11 is a diagram conceptually showing the measurement unit 10 according to the second embodiment. The measurement unit 10 includes a correction coil 14 in addition to a probe 11 (not shown), an inner coil 12, and an outer coil 13. The correction coil 14 is attached to the end of the inner coil 12 to generate a magnetic field in the opposite direction to the first magnetic field with respect to the measurement point P by magnetic flux due to electromagnetic induction, or is attached to the end of the outer coil 13. And adjusting the strength of the combined magnetic field at the measurement point P by generating a magnetic field in the opposite direction to the second magnetic field with respect to the measurement point P by the magnetic flux by electromagnetic induction. Corresponding to In other words, in the configuration of the first embodiment, the diameter of the inner coil 12 and the number of turns of the copper wire and the diameter of the outer coil 13 and the number of turns of the copper wire are such that the strength of the first magnetic field and the strength of the second magnetic field are mutually. To be the same. However, in practice, it may be difficult to set the number of turns of the copper wire to a desired number. As a result, one of the first magnetic field and the second magnetic field becomes slightly stronger, and the combined magnetic field at the measurement point P May not be completely zero. In order to eliminate this point, the correction coil 14 can finely adjust the strength of the synthesized magnetic field.

  Specifically, the correction coil 14 includes a copper wire 14a having a small number of turns (for example, 1 to 3 turns) and a resistor (for example, a resistor of several tens of ohms) 14b connected in parallel to the copper wire. It is wound without being connected to the terminal of either the inner coil 12 or the outer coil 13 (however, it is preferable that the coil is wound at the terminal of the outer coil 13 because the connection work is easier). For example, after the inner coil 12 and the outer coil 13 are formed with a substantially predetermined number of turns, the combined magnetic field at the measurement point P is measured. Then, the number of turns of the copper wire 14a in the correction coil 14 and the size of the resistor 14b are determined in accordance with the composite magnetic field, and the correction coil 14 is attached so as to generate magnetic flux by electromagnetic induction and adjust the composite magnetic field to zero. To do. According to this configuration, since the magnetic field generated by the correction coil 14 is generated at the measurement point P, the combined magnetic field at the measurement point P can be finely adjusted to zero, and thereafter measurement is performed without performing zero adjustment. Can be implemented. Alternatively, the resistance 14b may be a variable resistance, and the zero adjustment may be performed more simply by adjusting the value of the variable resistance after the correction coil 14 is wound around the end of the inner coil 12 or the outer coil 13. .

(Effect of Embodiment 2)
As described above, according to the second embodiment, the strength of the synthesized magnetic field can be finely adjusted, so that a high S / N ratio can be detected. In particular, since it is not necessary to strictly adjust the number of turns of the inner coil 12 and the outer coil 13, the measurement unit 10 can be manufactured easily and inexpensively.

[Embodiment 3]
Next, Embodiment 3 will be described. In the third embodiment, a plurality of inner coils 12 are provided in one measurement unit 10. In addition, about the component similar to Embodiment 1, the same code | symbol or name as used in Embodiment 1 is attached | subjected as needed, and the description is abbreviate | omitted.

  FIG. 12 is a diagram showing the metal detection device 2 according to the third embodiment together with the measurement target 1. The measurement unit 10 includes a probe 11, a plurality of inner coils 12a to 12c, and an outer coil 13. The plurality of inner coils 12a to 12c have different diameters and are arranged concentrically with each other. The plurality of inner coils 12a to 12c are switched to each other, and any one of the inner coils 12a to 12c is switched. By selectively using it, the depth of the peak of the synthetic magnetic field is changed to measure the ease of identifying the position of the metal.

  The basic concept of switching the inner coils 12a to 12c will be described. In the description of the first embodiment, referring to FIG. 5 to FIG. 8, the depth of the peak of the composite magnetic field changes by changing the diameter of the inner coil 12 and the diameter of the outer coil 13. And the point from which the depth from the surface of the measuring object 1 to a metal can be specified if the several measurement unit 10 which changed the diameter of the outer side coil 13 is switched and used sequentially was demonstrated. However, it is not preferable in terms of apparatus cost to prepare a plurality of measurement units 10 in this way, and it is not preferable to switch and use a plurality of measurement units 10 because the detection work becomes complicated.

  On the other hand, by changing the ratio between the diameter of the inner coil 12 and the diameter of the outer coil 13 without changing both the diameter of the inner coil 12 and the outer coil 13, the peak depth of the synthesized magnetic field can be changed. Can do. FIG. 13 shows changes in the peak depth of the synthetic magnetic field, the horizontal axis indicates the diameter of the inner coil 12, and the vertical axis indicates the peak depth of the synthetic magnetic field. Here, the outer coil 13 was fixed to a diameter of 90 mm and a length of 50 mm, and the peak depth of the synthesized magnetic field was measured when only the diameter of the inner coil 12 was changed from about 1 mm to about 81 mm. Here, a point where the peak depth of the synthesized magnetic field = 0 mm indicates a state where the peak of the synthesized magnetic field is located at the center position (measurement point P) in the length direction of the outer coil 13 and the inner coil 12. A range where the peak depth is 25 mm or more indicates a state where the peak of the synthetic magnetic field is located outside the outer coil 13. As can be seen from FIG. 13, the larger the diameter of the inner coil 12, the deeper the peak of the synthesized magnetic field.

  Therefore, in the third embodiment, as shown in FIG. 12, the diameter and length of the outer coil 13 are fixed, and the inner coils 12 a to 12 c used for measurement are selectively switched by switching the inner coils 12 a to 12 c. By changing only the dimensions, the peak depth of the synthetic magnetic field can be adjusted. However, since the synthetic magnetic field at the measurement point P needs to be substantially zero, the inner coils 12a to 12c and the outer coil 13 are differentially connected to each other, and the diameters of the inner coils 12a to 12c and The number of turns of the copper wire, the diameter of the outer coil 13, and the number of turns of the copper wire are determined so that the strength of the first magnetic field and the strength of the second magnetic field are the same. For example, when the outer coil 13 has a diameter of 180 mm and the number of turns 60, the inner coil 12a has a diameter of 30 mm, the number of turns 10, and the inner coil 12b has a diameter of 60 mm, the number of turns 20, and the inner coil 12c has a diameter of 90 mm and a number of turns 30. .

  Although the specific structure for switching these inner coils 12a-12c mutually is arbitrary, for example, the differential connection position between each inner coil 12a-12c and the outer coil 13, and each inner coil 12a-12c A changeover switch SW is provided at a connection position between the wires extending from the power supply to the amplifier 30 and the changeover switch SW is manually changed by a measurer or at a predetermined interval by a control device (not shown). Switch automatically sequentially.

(Effect of Embodiment 3)
As described above, according to the third embodiment, the depth of the peak of the synthetic magnetic field can be adjusted by switching the plurality of inner coils 12a to 12c to each other, and the depth from the surface of the measuring object 1 to the metal can be specified. . Particularly, since the depth of the peak of the synthesized magnetic field can be adjusted only by preparing one measurement unit 10, the apparatus cost can be reduced and the detection operation can be performed easily and quickly compared to the case of preparing a plurality of measurement units 10. It becomes possible to do.

[Embodiment 4]
Next, a fourth embodiment will be described. In the fourth embodiment, a plurality of outer coils 13 are provided in one measurement unit 10. In addition, about the component similar to Embodiment 3, the same code | symbol or name as used in Embodiment 3 is attached | subjected as needed, and the description is abbreviate | omitted.

  FIG. 14 is a diagram showing the metal detection device 2 according to the fourth embodiment together with the measurement target 1. The measurement unit 10 includes a measuring element 11, an inner coil 12, and a plurality of outer coils 13a to 13c. The plurality of outer coils 13a to 13c have different diameters and are arranged concentrically with each other. The plurality of outer coils 13a to 13c are switched to each other, and any one of the outer coils 13a to 13c is switched. By selectively using it, the depth of the peak of the synthetic magnetic field is changed to measure the ease of identifying the position of the metal.

  That is, in the fourth embodiment, contrary to the third embodiment, the diameter and length of the inner coil 12 are fixed, and the outer coils 13a to 13c are selectively switched, whereby the outer coils 13a to 13 used for measurement are changed. Only the dimension 13c is changed so that the peak depth of the synthesized magnetic field can be adjusted. Even in this case, the inner coil 12 and the outer coils 13a to 13c are differentially connected to each other, and the diameter of the inner coil 12 and the number of turns of the copper wire, the diameter of the outer coils 13a to 13c and the number of turns of the copper wire are The strength of the first magnetic field and the strength of the second magnetic field are determined to be the same. For example, when the inner coil 12 has a diameter of 30 mm and the number of turns of 10, the outer coil 13a has a diameter of 60 mm, the number of turns of 20, and the outer coil 13b has a diameter of 90 mm, the number of turns of 30, and the outer coil 13c has a diameter of 180 mm and a number of turns of 60. .

(Effect of Embodiment 4)
As described above, according to the fourth embodiment, the depth of the peak of the synthesized magnetic field can be adjusted by switching the plurality of outer coils 13a to 13c to each other, and the depth from the surface of the measuring object 1 to the metal can be specified. . Particularly, since the depth of the peak of the synthesized magnetic field can be adjusted only by preparing one measurement unit 10, the apparatus cost can be reduced and the detection operation can be performed easily and quickly compared to the case of preparing a plurality of measurement units 10. It becomes possible to do. Further, when a plurality of outer coils 13a to 13c are provided, the addition and change of the outer coils 13a to 13c can be performed more easily than when a plurality of inner coils 12 are provided.

[Embodiment 5]
Next, a fifth embodiment will be described. In the fifth embodiment, one end face of the inner coil 12 and one end face of the outer coil 13 are arranged at the same position, and the measuring element 11 is provided with a pickup coil 11b composed of a pair of coils. . In addition, about the component similar to Embodiment 1, the same code | symbol or name as used in Embodiment 1 is attached | subjected as needed, and the description is abbreviate | omitted.

  15 is a plan view showing the metal detector 2 according to the fifth embodiment together with the measuring object 1, FIG. 16 is an enlarged plan view schematically showing the coil portion of FIG. 15, and FIG. 17 is a longitudinal sectional view of FIG. 18 is a longitudinal sectional view schematically showing the coil portion of FIG. As shown in FIGS. 17 and 18, in this metal detector 2, one end surface along the axial direction of the inner coil 12 (the end surface on the side close to the measuring object 1) and the axial direction of the outer coil 13. One end face along (the end face close to the measuring object 1) is arranged at the same position in the height direction, and is arranged in the same plane. According to this structure, as shown in FIG. 18, the measurement point P having a substantially zero synthetic magnetic field can be brought closest to the measurement object, so that the S / N ratio of the metal detection can be further improved. As a specific structure for disposing the inner coil 12 and the outer coil 13 at such positions, various structures can be adopted. Here, as shown in FIG. 17, the inner coil 12 and the outer coil are arranged. An annular position adjusting ring 17 corresponding to the space portion is disposed between the inner coil 12 and the outer coil 13. The inner coil 12 and the outer coil 13 can be fixed to the position adjusting ring 17.

  Moreover, in this Embodiment, as shown to FIGS. 15-17, the pick-up coil 11b of the measuring element 11 is comprised from a pair of coils 11c and 11d. The pair of coils 11c and 11d are formed with substantially the same diameter and length, and at least one end (the end on the side close to the measuring object 1) is outside with the inner coil 12. It is arrange | positioned inside this inner coil 12 so that it may be enclosed from. The axial directions of the coils 11c and 11d are substantially parallel to the axial directions of the inner coil 12 and the outer coil 13. Here, these coils 11c and 11d are so-called eight-shaped planar differential coils and are differentially connected to each other. Specifically, as shown by arrows in FIG. 16, the coils 11c and 11d are arranged so that the winding direction of the copper wire of the coil 11c and the winding direction of the copper wire of the coil 11d are opposite to each other. It is connected. In this structure, the magnetic fields of the coils 11c and 11d themselves can be canceled each other, and the combined magnetic field at the measurement point P can be made almost zero, so that the S / N ratio of the metal detection is further improved. be able to. In the structure shown in FIG. 17, the bottom plate 18b is disposed with respect to the height adjusting plate 18a disposed on the inner side of the inner coil 12, and the height adjusting rod 18c is disposed with respect to the screw hole provided in the bottom plate 18b. , 18d are screwed together. A coil 11c is fixed to the height adjusting rod 18c, and a coil 11d is fixed to the height adjusting rod 18d. The height adjusting rod 18c, 18d is rotated about the axis and moved up and down to thereby move the coil 11c. Since the height of 11d can be adjusted, the position where the synthetic magnetic field at the measurement point P becomes zero can be easily finely adjusted.

  Next, the measurement result by the metal detector 2 according to the present embodiment will be described. FIGS. 19A and 19B are schematic diagrams for explaining the measurement situation, in which FIG. 19A is a plan view showing the measurement object 1 together with the metal detection device 2, and FIGS. 19B and 19C are side views of the measurement object 1. This measuring object 1 is configured by embedding a reinforcing bar 1a and a synthetic resin flexible electric wire pipe (hereinafter referred to as a CD pipe) 1c in a concrete 1b having a width of 300 mm, a length of 1000 mm, and a thickness of 100 mm. Here, the inner coil 12 and the outer coil 13 of the metal detector 2 are arranged in the vicinity of the upper surface of the measuring object 1, and the measuring object 1 is moved in the going direction and the returning direction along the longitudinal direction. At the position, the output from the lock-in amplifier 40 (not shown in FIG. 19) of the metal detector 2 was obtained. Moreover, although the example of FIG. 19 shows only the example in which the reinforcing bar 1a is embedded in the concrete 1b, the measurement was also performed when this reinforcing bar 1a was not embedded (when only the CD tube 1c was embedded).

  20 to 23 are diagrams showing changes in the output of the lock-in amplifier 40. The vertical axis shows the output voltage of the lock-in amplifier 40, and the horizontal axis shows the measurement position. Here, the position of measurement position = 10 cm is the position of the CD tube 1c. FIG. 20 shows a case where only the CD tube 1c is embedded, and the frequency of the oscillator 20 is about 450 kHz. The inner coil 12 and the outer side are located at the position of the CD tube 1c in both the going direction and the returning direction. When the coil 13 is arranged, the output voltage shows the maximum value (or the minimum value).

  FIG. 21 shows a case in which the reinforcing bar 1a and the CD tube 1c are embedded, and the frequency of the oscillator 20 is about 450 kHz. Although not as clear as in FIG. When the inner coil 12 and the outer coil 13 are arranged at the position of the tube 1c, since the output voltage shows the maximum value, there is a possibility that the position of the CD tube 1c can be specified.

  FIG. 22 shows a case where only the CD tube 1c is embedded and the frequency of the oscillator 20 is about 80 kHz, and it is difficult to grasp the correspondence between the position of the CD tube 1c and the output voltage. In FIG. 22, only the measurement result in the direction of travel is shown.

  FIG. 23 shows a case where only the CD tube 1c is embedded and the frequency of the oscillator 20 is about 4.5 kHz. As in FIG. 22, the correspondence between the position of the CD tube 1c and the output voltage is shown. It is difficult to grasp.

  As can be seen from FIGS. 20 and 21, since the position where the output voltage shows the maximum value and the position of the CD tube 1c correspond to each other, the peak of the output voltage is detected to detect the peak of the CD tube 1c. The position can be specified. From this, the metal detector 2 can be used for measurements other than metal by configuring the metal detector 2 and improving its S / N ratio as shown in FIGS. 15 to 18.

  Furthermore, as can be seen from comparison between FIGS. 20 and 21 and FIGS. 22 and 23, the position of the CD tube 1c can be specified by setting the frequency of the oscillator 20 to about 450 kHz. Therefore, in order to specify the position of the CD tube 1c, it is preferable to set the frequency of the oscillator 20 to about 450 kHz. This is because by increasing the frequency of the inner coil 12 and the outer coil 13 which are exciting coils by one digit, the electromotive current (electromotive voltage) in the concrete is increased by one digit, and the pickup coil 11b generated by the magnetic flux of this electromotive current further increases. This is because the electromotive voltage increases by an order of magnitude, so that the SN ratio is improved by an order of two.

(Effect of Embodiment 5)
As described above, according to the fifth embodiment, by aligning one end face of the inner coil 12 and one end face of the outer coil 13, the measurement point P having a substantially zero synthesized magnetic field can be brought closest to the measurement target. Therefore, the S / N ratio of metal detection can be further improved. Further, by performing magnetic field measurement using the pickup coil 11b composed of a pair of differentially connected coils 11c and 11d, the magnetic fields of the coils 11c and 11d themselves can be canceled each other, and the combined magnetic field at the measurement point P Can be made substantially zero, so that the S / N ratio of metal detection can be further improved.

[Embodiment 6]
Next, a sixth embodiment will be described. In the sixth embodiment, a plurality of measurement units 10 are arranged side by side on the same straight line so that the measurement points P are arranged on the same straight line. In addition, about the component similar to Embodiment 1, the same code | symbol or name as used in Embodiment 1 is attached | subjected as needed, and the description is abbreviate | omitted.

  24 is a plan view of the metal detector 2 according to the sixth embodiment, and FIG. 25 is a cross-sectional view taken along the line AA in FIG. The metal detector 2 includes a measurement gate 60, and the coil unit group 15 is built in the measurement gate 60. The coil unit group 15 includes a plurality of measurement units 10. The plurality of measurement units 10 are configured identically to each other and have the same peak depth of the synthesized magnetic field. With such a plurality of measurement units 10 aligned in the axial direction of each measurement unit 10, the end of each measurement unit 10 is positioned in the same plane, and the measurement points of each measurement unit 10 are They are arranged in the vicinity of the bottom surface of the measurement gate 60 so as to be arranged in a straight line. Although not shown, the oscillator 20, the amplifier 30, and the lock-in amplifier 40 are individually provided in each measurement unit 10, and individually output the strength and phase angle of the combined magnetic field of each measurement unit 10. . Alternatively, only one set of the oscillator 20, the amplifier 30, and the lock-in amplifier 40 may be provided for the plurality of measurement units 10, and in this case, each measurement unit 10 is displayed on the screen of the lock-in amplifier 40. The intensity and phase angle may be displayed by color coding or the like, or only the largest intensity may be displayed.

  A metal detection method using the metal detection device 2 configured as described above is as follows. That is, a linear region below the measurement gate 60 is set as a measurement region, and the measurement object 1 is relatively moved so as to cross the linear measurement region. For example, the belt conveyor 70 is arrange | positioned under the measurement gate 60, and the foodstuff which is the measuring object 1 is conveyed in multiple parallel form by this belt conveyor 70. FIG. If a metal is mixed in any of the foods in parallel, the metal can be detected by the output of the lock-in amplifier 40. Therefore, an alarm is output when the metal is detected. Further, by determining which of the plurality of measurement units 10 has detected the metal, the position of the food in which the metal is mixed can be specified, so that only the food in which the metal has been detected is automatically conveyor belted. To discharge from.

(Effect of Embodiment 6)
As described above, according to the sixth embodiment, by arranging a plurality of measurement units 10 in a straight line, the measurement in the linear measurement region is collectively performed as compared with the case where the measurement units 10 are arranged alone. Therefore, the measurement of the linear measurement region can be performed more rapidly.

[Embodiment 7]
Next, a seventh embodiment will be described. In the seventh embodiment, a plurality of coil unit groups 15 similar to those in the sixth embodiment are arranged in parallel. In addition, about the component substantially the same as Embodiment 6, the same code | symbol or name as used in Embodiment 6 is attached | subjected as needed, and the description is abbreviate | omitted.

  26 is a plan view of the metal detector 2 according to the seventh embodiment, and FIG. 27 is a cross-sectional view taken along the line BB in FIG. The metal detection device 2 includes a plurality of coil unit groups 15. Each coil unit group 15 includes a plurality of measurement units 10. The plurality of coil unit groups 15 are arranged in parallel near the bottom surface of the measurement plate 80.

  A metal detection method using the metal detection device 2 configured as described above is as follows. That is, a two-dimensional or three-dimensional region such as concrete or the ground is set as the measurement object 1 and the surface of the measurement object 1 is scanned in parallel with the measurement plate 80 via the measurement arm 81. When a metal is embedded in the measurement object 1, the metal can be detected by the output of the lock-in amplifier 40. Therefore, an alarm is output when the metal is detected. By determining which of the plurality of measurement units 10 has detected the metal, the position where the metal is embedded can be specified.

(Effect of Embodiment 7)
As described above, according to the seventh embodiment, by arranging a plurality of coil unit groups 15 in parallel, the measurement in the planar measurement region is performed in a lump compared to the case where the coil unit groups 15 are arranged alone. Therefore, the measurement of the planar measurement region can be performed more rapidly.

[Embodiment 8]
Next, an eighth embodiment will be described. In the eighth embodiment, a plurality of measurement units 10 are arranged in a straight line as in the sixth embodiment, and the peak depth of the synthesized magnetic field of each of the plurality of measurement units 10 is changed. is there. In addition, about the component substantially the same as Embodiment 6, the same code | symbol or name as used in Embodiment 6 is attached | subjected as needed, and the description is abbreviate | omitted.

  FIG. 28 is a plan view of the metal detector 2 according to the eighth embodiment, and FIG. 29 is a cross-sectional view taken along the line CC in FIG. The metal detector 2 includes a measurement gate 90, and the coil unit group 16 is built in the measurement gate 90. The coil unit group 16 includes a plurality of measurement units 10a to 10c. The plurality of measurement units 10 are configured so that the peak depths of the synthesized magnetic field are different from each other. Specifically, one of the inner coil 12 and the outer coil 13 has a common diameter and number of turns, and the inner The peak depth of the synthesized magnetic field is changed by changing the other diameter and the number of turns of the coil 12 or the outer coil 13.

  A metal detection method using the metal detection device 2 configured as described above is as follows. That is, the linear area below the measurement gate 90 is set as the measurement area, and the measurement object is relatively moved along the linear measurement area. For example, a belt conveyor 70 is disposed below the measurement gate 90, and the plurality of foods that are the measurement target 1 are conveyed in a row by the belt conveyor 70. This food sequentially passes under the measurement units 10a to 10c having different peak depths of the synthetic magnetic field, the food has a thickness, and metal is mixed in any position in the thickness direction (depth direction). Even if it is not known in advance, since the metal can be detected by the output to the lock-in amplifier 40 from any of the measurement units 10a to 10c, an alarm is output when the metal is detected. Or the food in which the metal is detected is automatically discharged from the belt conveyor. Further, by determining which of the plurality of measurement units 10a to 10c has detected the metal, the position in the depth direction of the food mixed with the metal can also be specified.

(Effect of Embodiment 8)
As described above, according to the eighth embodiment, the plurality of measurement units 10 having different peak depths of the synthesized magnetic field are arranged in a straight line, so that the linear measurement unit 10 is linear compared to the case where the measurement unit 10 is arranged alone. Measurement in the measurement area can be performed more quickly, and even if it is not known in advance where the metal is mixed in the depth direction of the measurement object, the metal is detected quickly. It becomes possible.

[Embodiment 9]
Next, Embodiment 9 will be described. In the ninth embodiment, a plurality of coil unit groups similar to those in the eighth embodiment are arranged in parallel. In addition, about the component similar to Embodiment 8, the code | symbol or name same as what was used in Embodiment 8 is attached | subjected as needed, and the description is abbreviate | omitted.

  30 is a plan view of the metal detector 2 according to the ninth embodiment, and FIG. 31 is a cross-sectional view taken along the line DD in FIG. The metal detection device 2 includes a plurality of coil unit groups 16. Each coil unit group 16 includes a plurality of measurement units 10a to 10d, and the plurality of coil unit groups 16 are juxtaposed in the vicinity of the floor surface 100 of the entrance gate of the MRI room, which is a measurement region. . Each coil unit group 16 includes a plurality of measurement units 10a to 10d as in the eighth embodiment, and the plurality of measurement units 10a to 10d have different peak depths of the synthesized magnetic field. It is configured.

  A metal detection method using the metal detection device 2 configured as described above is as follows. That is, a measurement area is set above the entrance gate, and a bed on which a patient is placed, which is the measurement target 1, is passed through the measurement area. When the patient wears a metal product or the bed contains metal, the metal can be detected by the output from any of the measurement units 10 to the lock-in amplifier 40. In this case, an alarm is output. Further, by determining which of the plurality of measurement units 10a to 10d has detected the metal, the position of the metal product in the horizontal region can be specified. Further, by determining which of the plurality of measurement units 10a to 10d has detected the metal, the position in the depth direction of the metal can also be specified. Furthermore, as described with reference to FIG. 11 in the first embodiment, since it is possible to determine whether the metal is a conductor or a magnetic body, a conductor such as a bed is excluded, and the magnetic body is detected. It is possible to prevent unnecessary alarm output by outputting the alarm only when the alarm occurs.

(Effect of Embodiment 9)
As described above, according to the ninth embodiment, the plurality of measurement units 10a to 10d having different peak depths of the synthesized magnetic field are arranged in a plane shape, compared with the case where the measurement units 10a to 10d are arranged alone. In addition, the measurement in the planar measurement region can be performed more rapidly, and even if it is not known in advance where the metal is mixed in the depth direction of the measurement target, It becomes possible to detect quickly.

[III] Modifications to Each Embodiment While the embodiments of the present invention have been described above, the specific configuration and means of the present invention are within the scope of the technical idea of each invention described in the claims. It can be arbitrarily modified and improved within. Hereinafter, such a modification will be described.

(About problems to be solved and effects of the invention)
The problems to be solved by the invention and the effects of the invention are not limited to the above-described contents, and the present invention solves the problems not described above or produces the effects not described above. In addition, only a part of the described problems may be solved or only a part of the described effects may be achieved.

(About shape and numerical values)
The shapes and numerical values shown in each embodiment are examples, and for example, each dimension value in the embodiment can be arbitrarily changed.

(About the mutual relationship of each embodiment)
A part of the structure or method described in each embodiment can be applied to other embodiments. For example, the correction coil 14 according to the second embodiment may be provided in the metal detection device 2 according to the third to ninth embodiments.

(About coil configuration)
The first coil, the second coil, and the correction coil can be formed in any shape including a rectangular tube shape in addition to the case where the first coil, the second coil, and the correction coil are formed in a cylindrical shape as illustrated.

(About coil arrangement)
The first coil and the second coil can be arbitrarily arranged as long as the combined magnetic field at the measurement point P can be made substantially zero. For example, as conceptually shown in FIG. 32, even when the first coil 12 ′ and the second coil 13 ′ are arranged in series with each other so as to have the same central axis, the first coil 12 ′ and the second coil 13 ′ are arranged in series. The combined magnetic field at the intermediate position between the coil 12 'and the second coil 13' can be made substantially zero. Alternatively, as conceptually shown in FIG. 33, even when the first coil 12 ′ and the second coil 13 ′ are arranged side by side so that the central axes thereof are parallel, these first coils The combined magnetic field at the intermediate position between 12 ′ and the second coil 13 ′ can be made substantially zero. However, as shown in the first to ninth embodiments, the measurement unit 10 is arranged by arranging the first coil (inner coil 12) and the second coil (outer coil 13) concentrically. It becomes easy to multiplex and reduce the size.

(About coil connection)
The first coil and the second coil do not necessarily need to be differentially connected to each other. For example, the first coil and the second coil are connected to different amplifiers 30 and the amplifiers 30 are the same. A reverse magnetic field may be formed by flowing a current in the reverse direction in phase.

  The present invention is for detecting a metal, and is suitable for a hand-held metal detection device or an installation-type metal detection device.

It is a schematic diagram which shows the metal detection apparatus which concerns on Embodiment 1 of this invention with a measuring object. It is a top view of each coil in the measurement unit of FIG. It is a figure which shows the change of magnetic flux density. It is a figure which shows the relationship between the diameter of an outer side coil, and the depth of the peak of a synthetic magnetic field. It is a figure which shows the relationship between the diameter of a coil, and the depth of the peak of a synthetic magnetic field, (a) is a longitudinal cross-section of an inner side coil and an outer side coil, (b) is a figure which shows the change of the magnetic flux density in the case of (a). It is. It is a figure which shows the relationship between the diameter of a coil, and the depth of the peak of a synthetic magnetic field, (a) is a longitudinal cross-section of an inner side coil and an outer side coil, (b) is a figure which shows the change of the magnetic flux density in the case of (a). It is. It is a figure which shows the relationship between the diameter of a coil, and the depth of the peak of a synthetic magnetic field, (a) is a longitudinal cross-section of an inner side coil and an outer side coil, (b) is a figure which shows the change of the magnetic flux density in the case of (a). It is. It is a figure which shows the relationship between the diameter of a coil, and the depth of the peak of a synthetic magnetic field, (a) is a longitudinal cross-section of an inner side coil and an outer side coil, (b) is a figure which shows the change of the magnetic flux density in the case of (a). It is. It is a figure which shows the output change of the lock-in amplifier according to the dimension of a metal. It is a figure which shows the change of the phase angle according to the distance from a measurement unit. It is a figure which shows notionally the measuring unit which concerns on Embodiment 2. FIG. It is a figure which shows the metal detection apparatus which concerns on Embodiment 3 with a measuring object. It is a figure which shows the change of the depth of the peak of a synthetic magnetic field. It is a figure which shows the metal detection apparatus which concerns on Embodiment 4 with a measuring object. It is a top view which shows the metal detection apparatus which concerns on Embodiment 5 with a measuring object. FIG. 16 is an enlarged plan view schematically showing a coil portion of FIG. 15. It is a longitudinal cross-sectional view of FIG. It is a longitudinal cross-sectional view which shows typically the coil part of FIG. It is a schematic diagram explaining a measurement condition, (a) is a top view which shows a measuring object with a metal detector, (b) (c) is a side view of a measuring object. It is a figure which shows the output change of lock-in amplifier. It is a figure which shows the output change of lock-in amplifier. It is a figure which shows the output change of lock-in amplifier. It is a figure which shows the output change of lock-in amplifier. It is a top view of the metal detection apparatus which concerns on Embodiment 6. FIG. It is AA arrow sectional drawing of FIG. It is a top view of the metal detection apparatus which concerns on Embodiment 7. FIG. It is BB arrow sectional drawing of FIG. FIG. 10 is a plan view of a metal detection device according to an eighth embodiment. It is CC sectional view taken on the line of FIG. FIG. 10 is a plan view of a metal detection device according to a ninth embodiment. It is DD sectional view taken on the line of FIG. It is a figure which shows notionally the arrangement | positioning relationship of the coil which concerns on a modification. It is a figure which shows notionally the arrangement | positioning relationship of the coil which concerns on a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement object 1a Reinforcing bar 1b Concrete 1c CD pipe 2 Metal detector 10, 10a-10d Measuring unit 11 Measuring element 11a Measuring element main body 11b Pickup coil 11c, 11d coil 12, 12a-12c Inner coil 12 '1st coil 13, 13a to 13c Outer coil 13 'Second coil 14 Correction coil 15, 16 Coil unit group 17 Position adjustment ring 18a Height adjustment plate 18b Bottom plate 18c, 18d Height adjustment rod 20 Oscillator 30 Amplifier 40 Lock-in amplifier 50 Electric wire 60, 90 Measurement Gate 70 Belt Conveyor 80 Measurement Plate 81 Measurement Arm P Measurement Point SW Switch

Claims (12)

Magnetic field measuring means for measuring the magnetic field at the measurement point;
A first coil for generating a first magnetic field with respect to the measurement point;
The first coil is configured separately from the first coil, and the second magnetic field in a direction opposite to the first magnetic field is generated with respect to the measurement point, whereby the first coil at the measurement point is generated. A second coil having a combined magnetic field of one magnetic field and the second magnetic field substantially zero;
A metal detection device comprising: The second coil is disposed at a position that is concentric with the first coil and that surrounds the first coil from the outside;
The metal detection device according to claim 1. The one end surface along the axial direction of the first coil and the one end surface along the axial direction of the second coil are arranged in the same plane,
The metal detection device according to claim 2. The magnetic field measuring means includes a pickup coil disposed at a position surrounded by the first coil from the outside,
The pick-up coil is composed of a pair of coils each having an axis parallel to the axis of the first coil and the axis of the second coil, the coils being differentially connected to each other. ,
The metal detection device according to claim 2, wherein: As the first coil, a plurality of first coils having different diameters from each other and arranged concentrically with each other are provided.
Providing a switching means for switching the plurality of first coils to each other;
The metal detection device according to any one of claims 2 to 4, wherein As the second coil, a plurality of second coils having different diameters from each other and arranged concentrically with each other are provided.
Providing a switching means for switching the plurality of second coils to each other;
The metal detection device according to any one of claims 2 to 4, wherein The ratio of the number of turns of the first coil and the number of turns of the second coil is made equal to the ratio of the diameter of the first coil and the diameter of the second coil;
Differentially connecting the first coil and the second coil to each other;
The metal detector according to any one of claims 1 to 6, wherein A magnetic field in the same direction as the first magnetic field is generated at the measurement point, or a magnetic field in the same direction as the second magnetic field is generated at the measurement point, Providing a correction coil for adjusting the strength of the synthetic magnetic field;
The metal detection device according to claim 1, wherein A plurality of coil units including the first coil and the second coil arranged side by side on the same line so that the measurement points are arranged on the same line;
The metal detection device according to claim 1, wherein: Forming a coil unit group by arranging a plurality of coil units including the first coil and the second coil on the same straight line so that the measurement points are arranged on the same straight line;
A plurality of the coil unit groups arranged side by side so that the measurement points of the coil units of the plurality of coil unit groups are aligned on the same straight line;
The metal detector according to claim 9. The depth of the peak of the synthetic magnetic field by at least a part of the plurality of coil units is different from the depth of the peak of the synthetic magnetic field of the coil unit other than the part,
The metal detection device according to claim 9 or 10, wherein: A metal detection method for detecting a metal contained in a measurement object,
The magnetic field measuring means for measuring the magnetic field at the measurement point, the first coil for generating the first magnetic field with respect to the measurement point, and the first coil are configured separately, By generating a second magnetic field in a direction opposite to the first magnetic field with respect to the measurement point, a first magnetic field obtained by combining the first magnetic field and the second magnetic field at the measurement point is substantially zero. In the metal detection method using the metal detection device configured to include two coils,
Either one of the metal detector or the measurement object is moved relative to the other,
Detecting a metal contained in the measurement object based on a change in strength of the synthetic magnetic field measured by the magnetic field measurement means at each movement position during the movement;
Metal detection method characterized by.

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