Metal detector

Abstract

To provide a metal detector which is easy to handle by suppressing electrostatic coupling between a transmission coil and a reception coil.SOLUTION: The metal detector 1 includes a housing 11, a transmission coil 12 and reception coils 13A and 13B disposed in the housing 11, a holding member 14 for holding the transmission coil 12 and the reception coils 13A and 13B in the housing 11, and a shield member 16 disposed between the transmission coil 12 and the reception coils 13A and 13B in the housing 11. The electrical resistivity of the shielding member 16 is higher than the electrical resistivity of the housing 11.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a metal detector. [Background technology]

[0002] A metal detector is a device that determines whether or not an object under inspection contains metal by detecting changes that the metal causes in an inspection magnetic field.

[0003] Metal detectors generally use a magnetic field that flows from a transmitter coil, which constitutes the magnetic field output section, to a receiver coil, which constitutes the magnetic field receiver section, to detect metals present in an object passing nearby. However, metal detection is also affected by electric fields (so-called electrostatic coupling) in addition to magnetic fields, which can hinder improvements in the sensitivity and stability of metal detectors. Suppressing electrostatic coupling that occurs between the transmitter coil or receiver coil and the object being inspected is an important factor for conducting proper inspections.

[0004] Patent Document 1 discloses that an electrostatic shield plate is attached to the portion of the test object facing the transmitting coil or the receiving coil, thereby blocking the influence of static electricity. Patent Document 2 discloses an electrostatic shield that reduces electrostatic coupling between the test object and the transmitting coil or the receiving coil. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2614180 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-017118 Summary of the Invention [Problem to be solved by the invention]

[0006] Metal detectors use two receiving coils to detect metals mixed in an object being inspected, based on the balanced voltage (differential voltage) that is the difference between the induced voltages generated in each coil as the object passes through. Ideally, when an object is not being detected, the difference between the induced voltages in the two receiving coils should be zero, and adjustments are made to make this difference zero during the manufacturing and assembly of the metal detector.

[0007] However, the state of the metal detector changes due to factors such as changes in ambient conditions, and when this happens, the difference in the induced voltages between the two receiving coils in the non-detection state gradually fluctuates, making it impossible to accurately detect metals.

[0008] Fluctuations in the balance voltage are particularly affected by changes in ambient conditions. Changes in ambient conditions include changes in the electromagnetic coupling between components such as the transmitter coil, receiver coil, and housing. Conventionally, a mechanical adjustment method has been used to maintain the balance voltage at an ideal state by inserting a metal plate, metal rod, or the like into the metal detector. However, such a method is difficult to address fluctuations in the balance voltage due to changes in ambient conditions, making the metal detector difficult to handle, including the adjustment work.

[0009] The present invention relates to a metal detector that suppresses electrostatic coupling between a transmitting coil and a receiving coil and is easy to handle. [Means for solving the problem]

[0010] The present invention provides a metal detector (1) for determining whether or not a metal is present in an object to be inspected, A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed in the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed within the housing between the transmitting coil and the receiving coil, The electrical resistivity of the shielding member is higher than the electrical resistivity of the housing. It is a metal detector.

[0011] The present invention also provides a metal detector (1) for determining whether or not a metal is present in an object to be inspected, comprising: A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed in the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed within the housing between the transmitting coil and the receiving coil, The electrical resistivity, arrangement, shape, and area of ​​the shielding member are determined so that the amount of magnetic field attenuation caused by the shielding member is 50% or less of the magnetic field generated in the examination region (S) by the transmitting coil when the shielding member is not present. It is a metal detector. [Effects of the Invention]

[0012] According to the present invention, it is possible to suppress electrostatic coupling between the transmitting coil and the receiving coil, and to make the metal detector easier to handle. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram of a metal detector. [Figure 2] FIG. 2 is a perspective view of the metal detector according to the first embodiment, and particularly shows the configuration of the detection head. [Figure 3] FIG. 3 is a side view of the metal detector according to the first embodiment, and in particular shows the side and interior of the detection head. [Figure 4] FIG. 4 is a side view of the metal detector according to the second embodiment, and in particular shows the side and interior of the detection head. [Figure 5] FIG. 5 is a side view of the metal detector according to the third embodiment, and in particular shows the side and interior of the detection head. [Figure 6]FIG. 6 is a perspective view of a metal detector according to the fourth embodiment, and particularly shows the configuration of the detection head. [Figure 7] FIG. 7 is a side view of the metal detector according to the fourth embodiment, and in particular shows the side and interior of the detection head. [Figure 8] FIG. 8 is a diagram showing another example of the shielding member. [Figure 9] FIG. 9 is a diagram showing an example in which two shielding members are arranged. [Figure 10] FIG. 10 is a diagram showing another example in which a double shielding member is arranged. [Figure 11] FIG. 11 is a diagram showing an example in which a transmission coil is surrounded by a cylindrical shield member. [Figure 12] FIG. 12 is a diagram showing an example of a coaxial detection head in which a shield member extending in the axial direction is disposed in the gap between the transmission coil and the reception coil. [Figure 13] FIG. 13 is a diagram showing another example of a coaxial detection head in which a shield member extending in the axial direction is disposed in the gap between the transmission coil and the reception coil. [Figure 14] FIG. 14 is a diagram showing another example of the arrangement of shield members in a single-sided detection head. [Figure 15] FIG. 15 is a diagram showing another example of the arrangement of shield members in a single-sided detection head. [Figure 16] FIG. 16 shows an example of grounding of the fence-like shielding member. [Figure 17] FIG. 17 shows another example of grounding the fence-shaped shielding member. [Figure 18] FIG. 18 is a diagram for explaining the relationship between the distance from the ground point and the shielding effect. [Figure 19] FIG. 19 is a diagram showing an example in which the shielding member is grounded at multiple points. [Figure 20] FIG. 20 is a diagram showing an example in which a divided shield member is grounded. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Overall configuration of metal detector) 1 is a block diagram of a conventionally known metal detector. Metal detector 1 is a device that determines whether or not metal is present in an object to be inspected W. Metal detector 1 includes a detection head 10, a quadrature detection unit 20, and band-pass filters (BPFs) 31 and 32.

[0015] The detection head 10 has a transmitting coil 12 (see FIG. 2) that constitutes a magnetic field output unit and receiving coils 13A and 13B (see FIG. 2) that constitute a magnetic field receiving unit. The detection head 10 detects metal mixed in an object W under test that passes near the transmitting coil 12 and receiving coils 13A and 13B, using a magnetic field directed from the transmitting coil 12 to the receiving coils 13A and 13B. Details of the detection head 10 will be described with reference to FIG. 2 and subsequent figures.

[0016] The magnetic field is modulated by the passage of the object W under test. The quadrature detection unit 20 demodulates (quadrature detects) the modulated received signal to extract the modulated component. The band-pass filters 31 and 32 demodulate the detected signal A from the quadrature detection unit 20. I , A Q By filtering out the desired frequency band, the detection signal D I , D Q A determination circuit (not shown) outputs the detection signal D I , D Q By analyzing the above, it is possible to determine whether or not metal has been mixed into the object W to be inspected as it passes.

[0017] (Embodiment 1) Fig. 2 is a perspective view of the metal detector 1 according to the first embodiment, and in particular shows the configuration of the detection head 10. Fig. 3 is a side view of the metal detector 1 according to the first embodiment, and in particular shows the side of the detection head 10, but also shows the interior. The detection head 10 of the metal detector 1 includes a housing 11, a transmitting coil 12, receiving coils 13A and 13B, a holding member 14, a conductive plate 15, and a shielding member 16.

[0018] The housing 11 is made of an electrostatic shielding material such as metal (for example, aluminum alloy or stainless steel). The housing 11 has a hollow rectangular shape, and an inspection space S (inspection area) is formed inside the housing 11. A transport conveyor (not shown) for transporting the object to be inspected W is disposed so as to pass through the inspection space S.

[0019] The transmitting coil 12 and the receiving coils 13A and 13B are disposed within the housing 11. The transmitting coil 12 and the receiving coils 13A and 13B are disposed along the direction in which the object W passes (passing direction A shown in FIG. 2 ), with the two receiving coils 13A and 13B positioned before and after the transmitting coil 12. The transmitting coil 12 generates magnetic field lines parallel to the passing direction A of the object W. In other words, the detection head 10 of the metal detector 1 according to this embodiment is a coaxial detection head in which the transmitting coil 12 and the receiving coils 13A and 13B are disposed coaxially along the passing direction of the object W.

[0020] In the detection head 10, in an examination space S continuous with the inside of the transmitting coil 12 and the receiving coils 13A and 13B, induced voltages V1 and V2 of mutually opposite phases are generated in the two receiving coils 13A and 13B that intersect with the magnetic flux of the alternating magnetic field of the central transmitting coil 12. The receiving coils 13A and 13B are disposed at equal distances from the transmitting coil 12, and in a non-detection state where the object under test W is located far from the examination space S, the induced voltages V1 and V2 are equal in magnitude and the difference is zero.

[0021] For example, when an object W under test containing metal travels in the passage direction A and moves into the receiving coil 13A on the front side, the magnetic flux density in the receiving coil 13A increases, while the magnetic flux density in the receiving coil 13B on the rear side decreases. As a result, the induced voltage V1 in the receiving coil 13A becomes larger than the induced voltage V2 in the receiving coil 13B. Next, when the traveling object W under test reaches the receiving coil 13B, the magnetic flux density in the receiving coil 13B becomes larger than that in the receiving coil 13A, and the induced voltage V2 becomes larger than the induced voltage V1. In this way, based on the change in the difference between the induced voltages V1 and V2 output from the detection head 10 (magnetic field fluctuations), it is possible to determine whether or not the object W under test that has passed through the inspection space S contains metal.

[0022] The holding material 14 is a member for holding the transmitter coil 12 and the receiver coils 13A and 13B within the housing 11, and is made of an insulating material such as epoxy resin. The holding material 14 in this embodiment fills the internal space of the housing 11, but does not necessarily need to completely fill the internal space; it is sufficient if it functions to hold the transmitter coil 12 and the receiver coils 13A and 13B within the housing 11.

[0023] The conductive plate 15 is disposed between the transmitting coil 12 and the receiving coils 13A and 13B and the inner surface of the housing 11 on the side of the inspection space S. The transmitting coil 12 and the receiving coils 13A and 13B are wound around the inner surface of the housing 11 on the side of the inspection space S via the conductive plate 15. The conductive plate 15 is conductive and reduces electrostatic coupling between the transmitting coil 12 and the receiving coils 13A and 13B and the object W under inspection passing through the inspection space S, thereby reducing the influence of the object W under inspection and the influence of external noise, thereby suppressing a decrease in metal detection accuracy.

[0024] The shield member 16 is a uniform plate-like (sheet-like) member that is disposed between the transmitting coil 12 and the receiving coils 13A and 13B inside the housing 11. The shield member 16 serves as an electrostatic shield that reduces the degree of electrostatic coupling between the transmitting coil 12 and the receiving coils 13A and 13B. The electrical resistivity, arrangement, shape, and area of ​​the shield member 16 are determined so that the amount of magnetic field attenuation caused by the shield member 16 is 50% or less of the magnetic field that would be generated by the transmitting coil 12 in the examination space S if the shield member 16 were not present.

[0025] As described above, the metal detector 1 uses the two receiving coils 13A and 13B to detect metal contained in the object W based on the balanced voltage (differential voltage) that is the difference between the induced voltages V1 and V2, which are in opposite phases as the object W passes. Ideally, when the object W is not being detected, the difference between the induced voltages in the two receiving coils 13A and 13B should be zero.

[0026] However, the state of the metal detector changes due to factors such as changes in ambient conditions, and when this happens, the difference in the induced voltages between the two receiving coils in the non-detection state gradually fluctuates, making it impossible to accurately detect metals.

[0027] Fluctuations in the balance voltage are particularly affected by changes in ambient conditions. Changes in ambient conditions include changes in the electromagnetic coupling between components such as the transmitter coil 12, receiver coils 13A and 13B, and housing 11. Conventionally, a mechanical adjustment method has been used to maintain the balance voltage at an ideal state by inserting a metal plate, metal rod, or the like into the metal detector. However, such a method is difficult to address fluctuations in the balance voltage due to changes in ambient conditions, making handling the metal detector 1, including the adjustment work, difficult.

[0028] Therefore, in this embodiment, the shield member 16 serves to reduce the degree of electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B. Because the shield member 16 reduces the degree of electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B, it is possible to suppress fluctuations in the balance voltage due to changes in the degree of electrostatic coupling, making it easier to perform balance adjustments, while still ensuring accurate metal detection functionality.

[0029] The shield member 16 has a certain degree of conductivity and its electrical resistivity is kept low in order to reduce the degree of electrostatic coupling between the transmitting coil 12 and the receiving coils 13A and 13B. However, if the electrical resistivity of the shield member 16 is too low (if the conductivity is too high), the magnetic field generated by the transmitting coil 12 in the examination space will be significantly attenuated, so the shield member 16 needs to have a certain degree of electrical resistivity.

[0030] Therefore, in this embodiment, the electrical resistivity of the shield member 16 is set to be higher than the electrical resistivity of the housing 11, which is made of a highly conductive material (low electrical resistivity) such as metal. As a result, in order to ensure the functionality of the metal detector, the shield member 16 suppresses excessive attenuation of the magnetic field generated in the inspection space by the transmitter coil 12, while suppressing electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B, making the metal detector 1 easier to handle.

[0031] From the viewpoint of electrostatic shielding, it is important to set the electrical resistivity of the shield member 16 based on the square resistance (Ω / □), which is the resistance per area. -2 Ω / □~10 3 The square resistance is set in the range of Ω / □. The square resistance is also called surface resistance or sheet resistance. This makes it possible to reduce electrostatic coupling between the transmitter coil and the receiver coil while suppressing excessive attenuation of the magnetic field generated in the examination space by the transmitter coil 12. Note that a numerical range expressed using "~" means a range that includes the numerical values ​​written before and after "~" as the lower and upper limits.

[0032] The metals used in the housing 11, etc. are 10 -4 Ω / □~10 -3 The shielding member 16 has a square resistance of about Ω / □, and the electrical resistivity of the shielding member 16 is higher than the electrical resistivity of the housing 11. The holding material 14 is an insulating material, and the electrical resistivity of the shielding member 16 is lower than the electrical resistivity of the holding material 14.

[0033] The material constituting the shielding member 16 is not particularly limited, but it can be formed, for example, by applying or attaching a conductive material to a predetermined substrate. The substrate may be a resin substrate such as Bakelite. The conductive material may include, for example, conductive carbon. The use of carbon makes it easy to form the shielding member 16. The material of the shielding member 16 may be the same as or different from the material of the conductive plate 15.

[0034] In this embodiment, the transmitting coil 12 and the receiving coils 13A and 13B constitute a coaxial detection head 10 that is arranged coaxially along the passing direction A of the test object W. Because the detection head 10 is of a general coaxial type, it can be easily assembled.

[0035] In this embodiment, the shielding member 16 is, for example, a ring-shaped body having a hollow rectangular cross section, and is made by combining plate-shaped members to surround the periphery (each side) of the receiving coils 13A and 13B. Therefore, the shielding member 16 entirely covers the receiving coils 13A and 13B. This allows for a simple and efficient reduction in electrostatic coupling between the transmitting coil 12 and the receiving coils 13A and 13B. However, the shielding member 16 does not need to completely cover the receiving coils 13A and 13B, and slits or the like may be provided in the shielding member 16. The size of the slits or the like is preferably equal to or less than ¼ of the wavelength of the electromagnetic waves to be reduced.

[0036] (Embodiment 2) FIG. 4 is a side view of a metal detector 1 according to a second embodiment, particularly showing the side of the detection head 10, but also showing the interior. The basic configuration of the detection head 10 is the same as that of the first embodiment. In this embodiment, the shield member 16 surrounds the periphery (each side) of the transmitter coil 12. Therefore, the shield member 16 covers the entire transmitter coil 12. This makes it possible to simply and efficiently reduce electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B. The structure of the shield member 16 is the same as that of the first embodiment. Furthermore, the first and second embodiments may be combined, and both the transmitter coil 12 and the receiver coils 13A and 13B may be surrounded by the shield member 16.

[0037] (Embodiment 3) FIG. 5 is a side view of a metal detector 1 according to a third embodiment, particularly showing the side of the detection head 10, but also showing the interior. The basic configuration of the detection head 10 is the same as in the first and second embodiments. In this embodiment, a shield member 16 is disposed between the transmitter coil 12 and the receiver coils 13A and 13B in the coaxial direction of the detection head 10 (the left-right direction in FIG. 5, the direction A in which the object W passes (see FIG. 2)). The shield member 16 is, for example, a plate member extending along each side of the transmitter coil 12 (or the receiver coils 13A and 13B). While the shield member 16 does not surround the transmitter coil 12 or the receiver coils 13A and 13B, it can easily and efficiently reduce electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B.

[0038] (Embodiment 4) FIG. 6 is a perspective view of a metal detector 1 according to a fourth embodiment, particularly showing the configuration of the detection head 10. FIG. 7 is a side view of the metal detector 1 according to the fourth embodiment, particularly showing the side of the detection head 10, but also showing the interior. In this embodiment, the upper surface of the detection head 10 is the inspection area (inspection space), and the object W under inspection travels over the upper surface of the detection head 10 in a passing direction A. The transmitter coil 12 and receiver coils 13A and 13B constitute a single-sided detection head 10, arranged coaxially along a direction perpendicular to the passing direction A of the object W under inspection. The single-sided detection head 10 can determine whether or not metal is present in the object W under inspection using the same principle as the coaxial detection heads 10 of the first to third embodiments.

[0039] The shield member 16 is disposed between the transmitter coil 12 and the receiver coils 13A and 13B in the coaxial direction (the passing direction A of the subject W). The shield member 16 is, for example, a plate-shaped member, and does not surround the transmitter coil 12 or the receiver coils 13A and 13B, but can simply and efficiently reduce electrostatic coupling between the transmitter coil 12 and the receiver coils 13A and 13B.

[0040] (Another example of a shielding material) In each of the above-described embodiments, the shielding member 16 is made of a material having a predetermined electrical resistivity (for example, 10 -2 Ω / □~10 3 In this example, a uniform plate-like (sheet-like) member having a resistance (Ω / □) is used to function as an electrostatic shield without significantly interfering with the magnetic field. However, the shielding member is not limited to the above. For example, if it is desired to further reduce interference with the magnetic field, the shielding members 16a and 16b having a fence-like structure ((a) is comb-like, (b) is zigzag-like) shown in FIGS. 8(a) and (b) or the shielding member 16c having a mesh-like (lattice-like) structure shown in FIG. 8(c) can be used as the shielding member to be placed between the transmitting coil and the receiving coil.

[0041] Also, for example, 10 -2If a uniform plate material with low electrical resistivity (less than Ω / □) is used as a shielding material, large eddy currents will be generated when a magnetic field is applied, thereby attenuating the magnetic field. In this case, by shaping the shielding material to limit the path of eddy currents, as shown in Figures 8(a), (b), and (c), it is possible to function as an electrostatic shield without significantly impeding the magnetic field. The electrical resistivity, arrangement, shape, and area of ​​each of the shielding members 16a, 16b, and 16c shown in Figure 8 are determined so that the magnetic field attenuation caused by each shielding member 16a, 16b, and 16c is 50% or less of the magnetic field generated by the transmitting coil 12 in the inspection region when each shielding member 16a, 16b, and 16c is not present. The shielding members 16a, 16b, and 16c having such shapes can be constructed using, for example, a metal mesh or a printed circuit board. Here, the shielding member 16c (Figure 8(c)) has a mesh pattern and can form a large loop R. For this reason, although shield member 16c attenuates the magnetic field more easily than shield members 16a and 16b, it is believed that the paths through which eddy currents occur are more limited than in the uniform plate-like shield member 16. Therefore, it is believed that the magnetic field attenuation effect of shield member 16c is smaller than in the case of shield member 16 having a uniform plate shape.

[0042] The shielding effect may be further enhanced by arranging the shielding members 16a, 16b, and 16c in a double layer. For example, when arranging the shielding members 16a in a double layer, the shielding effect can be further enhanced by minimizing gaps through which the electric field leaks, as shown in FIGS. 9 and 10. In each of the examples in FIGS. 9 and 10, the two shielding members 16a are arranged so that they overlap in the thickness direction. In each of FIGS. 9 and 10, (a) is a top view, and (b) is a side view viewed from below in (a). In the example in FIG. 9, the two shielding members 16a are arranged so that the multiple strips P constituting one shielding member 16a are parallel to the multiple strips P constituting the other shielding member 16a and are positioned in the gaps G between the strips P of the other shielding member 16a. In the example in FIG. 10, the two shielding members 16a are arranged so that the multiple strips P constituting one shielding member 16a are perpendicular to the multiple strips P constituting the other shielding member 16a. When the shielding material is arranged in a double layer, the electrical resistivity, arrangement, shape, and area are determined so that the amount of magnetic field attenuation caused by the doubled shielding material is 50% or less of the magnetic field that the transmitting coil 12 would create in the examination area if the shielding material were not present.

[0043] In the first and second embodiments, the shielding member 16 is formed by combining plate-like members to surround the transmitting coil 12 or the receiving coils 13A and 13B, but the arrangement of the shielding member is not limited to this. For example, as shown in FIG. 11 , the transmitting coil 12 may be surrounded by a cylindrical shielding member, or a sheet-like or wire-like member may be wound around the transmitting coil 12. Of course, the cylindrical shielding member may surround each of the receiving coils 13A and 13B instead of the transmitting coil 12, or may surround both the transmitting coil 12 and the receiving coils 13A and 13B. Furthermore, a sheet-like or wire-like member may be wound around each of the receiving coils 13A and 13B, or may be wound around each of the transmitting coil 12 and the receiving coils 13A and 13B.

[0044] In the third embodiment, as shown in FIG. 5 , the shield member 16 is a plate member extending along each side of the transmitter coil 12 (or the receiver coils 13A and 13B) and is provided separately from the conductive plate 15. However, for example, a shield member in which the shield member 16 and the conductive plate 15 are integrated on each side may be used. According to this configuration, by disposing the shield member between the transmitter coil 12 and the receiver coils 13A and 13B, the transmitter coil 12 is surrounded by the shield member, and a portion of the shield member also functions as a shield between the inspection space and the coil. That is, when the shield member is inserted between the transmitter coil 12 and the receiver coils 13A and 13B, a portion of the shield member is simultaneously disposed between the transmitter coil 12 and the inspection space. In general, in metal detectors, an electrostatic shield is inserted between the coil and the inspection space to reduce the influence of the object under test. However, according to the above configuration, there is no need to separately install a shield member between the transmitter coil and the receiver coil, which is advantageous for improving manufacturability and reducing costs.

[0045] As shown in FIG. 12 , the positions and sizes of the transmitter coil 12 and the receiver coils 13A and 13B may be slightly changed so that they do not overlap when viewed in the direction A of passage of the subject W, but rather a gap is formed between them, and a shield member 16e may be placed in this gap. In FIG. 12 , the outer shape of the transmitter coil 12 is smaller than the outer shapes of the receiver coils 13A and 13B when viewed in the direction A of passage, and the shield member 16e is placed outside the transmitter coil 12 and inside the receiver coils 13A and 13B. Note that FIG. 12 shows a state in which the shield member 16e is placed on one side of the transmitter coil 12 and one side of the receiver coils 13A and 13B, but similar shield members 16e may also be placed in gaps on each of the other three sides. Alternatively, as shown in FIG. 13 , the outer shape of the transmitter coil 12 may be set larger than the outer shapes of the receiver coils 13A and 13B, and the shield member 16e may be placed in gaps formed inside the transmitter coil 12 and outside the receiver coils 13A and 13B. According to this configuration, the shielding member does not protrude in a direction perpendicular to the passage direction A, making it easy to install the shielding member.

[0046] In the fourth embodiment, an example was shown in which a plate-shaped shield member 16 was disposed between the transmitter coil 12 and the receiver coils 13A and 13B in the single-sided detector head 10. However, the shape and arrangement of the shield member are not limited to this. As with the coaxial detector head described above, the material, arrangement, shape, and area of ​​the shield member can be changed in the single-sided detector head. FIGS. 14 and 15 show examples of the arrangement of shield members 16d and 16e relative to the transmitter coil 12 and the receiver coils 13A and 13B within the detector head. As shown in FIG. 14, the transmitter coil 12 may be surrounded by a cylindrical shield member 16d. Although FIG. 14 shows the shield member 16d disposed on only one side of the transmitter coil 12, in practice, cylindrical shield members 16d are also disposed on the other three sides. Alternatively, as shown in FIG. 15, a shield member 16f formed integrally with a conductive plate 161 and a shield member 162 may be used. The conductive plate 161 is disposed between the transmitter coil 12 and the receiver coils 13A and 13B and the subject, and the shielding member 162 is disposed so as to surround the receiver coils 13A and 13B on the inner circumferential side of the transmitter coil 12. With this shielding member 16f, the conductive plate 161 is disposed between the transmitter / receiver coils and the examination space at the same time as inserting the shielding member 162 between the transmitter coil 12 and the receiver coils 13A and 13B. This eliminates the need to separately install a shielding member between the transmitter / receiver coils, which is advantageous for improving manufacturability and reducing costs.

[0047] Furthermore, the method of grounding the shielding member is not limited to the examples in the above-described embodiments. As shown in Fig. 16, each of the multiple straps P constituting the fence-like shielding member 16a may be grounded. Alternatively, as shown in Fig. 17, connecting straps P1 may be provided to electrically connect the multiple straps P, and the connecting straps P1 or the straps P may be grounded. Note that the connecting straps P1 may be provided so as to electrically connect the multiple straps P, and the number, position, shape, etc. of the connecting straps P1 are not limited to those shown in the illustrated example.

[0048] Since the shielding effect decreases with increasing distance from the ground point, as shown in Fig. 18, if a grounding path is provided on one side of the plate-shaped shielding member 16e, the shielding effect may be insufficient at a point r far from the ground point. In such cases, the reduction in shielding effect can be prevented by grounding at multiple points, as shown in Fig. 19. Furthermore, as shown in Fig. 20, by dividing the shielding member 16e into multiple shielding members 16e1 and grounding each shielding member 16e1, the formation of large eddy currents in the shielding member 16e can be prevented.

[0049] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the disclosure.

[0050] Here, the features of the metal detector according to the embodiment of the present invention described above will be briefly summarized and listed below in [1] to [8].

[0051] [1] A metal detector (1) for determining whether or not a metal is present in an object to be inspected, A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed in the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed within the housing between the transmitting coil and the receiving coil, The electrical resistivity of the shielding member is higher than the electrical resistivity of the housing. Metal detector.

[0052] According to the metal detector described in [1], by disposing a shielding member between the transmitter coil and the receiver coil, the degree of electrostatic coupling between the transmitter coil and the receiver coil can be reduced, thereby suppressing fluctuations in the balance voltage due to changes in the degree of electrostatic coupling between the transmitter coil and the receiver coil, thereby facilitating balance adjustment work and making the metal detector easier to handle.

[0053] [2] A metal detector (1) for determining whether or not a test object contains metal, A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed in the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed within the housing between the transmitting coil and the receiving coil, The electrical resistivity, arrangement, shape, and area of ​​the shielding member are determined so that the amount of magnetic field attenuation caused by the shielding member is 50% or less of the magnetic field generated in the examination region (S) by the transmitting coil when the shielding member is not present. Metal detector.

[0054] According to the metal detector described in [2], by disposing a shielding member between the transmitting coil and the receiving coil, the degree of electrostatic coupling between the transmitting coil and the receiving coil can be reduced, thereby suppressing fluctuations in the balance voltage due to changes in the degree of electrostatic coupling between the transmitting coil and the receiving coil, thereby facilitating balance adjustment work and making the metal detector easier to handle.

[0055] [3] A coaxial detection head is configured in which the transmitting coil and the receiving coil are arranged to form a coaxial line along the direction in which the object under test passes. [1] or [2]. A metal detector according to the present invention.

[0056] According to the metal detector described in [3], the detection head is of a general coaxial type, so that the detection head can be easily assembled.

[0057] [4] The shielding member covers the entire receiving coil. [3] The metal detector according to [3].

[0058] According to the metal detector described in [4], the electrostatic coupling between the transmitting coil and the receiving coil can be reduced simply and efficiently.

[0059] [5] The shielding member covers the entire transmitting coil. [3] The metal detector according to [3].

[0060] According to the metal detector described in [5], the electrostatic coupling between the transmitting coil and the receiving coil can be reduced simply and efficiently.

[0061] [6] The shielding member is disposed between the transmitting coil and the receiving coil in the coaxial direction. [3] The metal detector according to [3].

[0062] According to the metal detector described in [6], the electrostatic coupling between the transmitting coil and the receiving coil can be reduced simply and efficiently.

[0063] [7] A one-sided detection head is configured in which the transmitting coil and the receiving coil are arranged coaxially along a direction perpendicular to the passing direction of the object under test, the shield member is disposed between the transmitting coil and the receiving coil in the coaxial direction. [1] or [2]. A metal detector according to the present invention.

[0064] According to the metal detector described in [7], the detection head is a typical one-sided type, so that the detection head can be easily assembled and the electrostatic coupling between the transmitting coil and the receiving coil can be easily and efficiently reduced.

[0065] [8] The electrical resistivity of the shielding material is 10 -2 Ω / □~10 3 In the range of Ω / □, [1] The metal detector described in [1].

[0066] According to the metal detector described in [8], it is possible to reduce the electrostatic coupling between the transmitting coil and the receiving coil while suppressing excessive attenuation of the magnetic field generated in the inspection space by the transmitting coil due to the shielding member. [Explanation of symbols]

[0067] 1 metal detector 10 Detector head 11. Housing 12 Transmitting coil 13A receiving coil 13B Receiving coil 14 Retaining material 15 Conductive plate 16, 16a, 16b, 16c, 16d, 16e, 16f Shielding members S inspection space

Claims

1. A metal detector (1) for determining whether or not a metal is present in an object to be inspected, A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed within the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed between the transmitting coil and the receiving coil within the housing; The electrical resistivity of the shielding member is higher than the electrical resistivity of the housing. Metal detector.

2. A metal detector (1) for determining whether or not a metal is present in an object to be inspected, A housing (11), a transmitting coil (12) and a receiving coil (13A, 13B) disposed within the housing; a holding member (14) for holding the transmitting coil and the receiving coil within the housing; a shield member (16) disposed between the transmitting coil and the receiving coil within the housing; The electrical resistivity, arrangement, shape, and area of ​​the shielding member are determined so that the amount of magnetic field attenuation by the shielding member is 50% or less of the magnetic field generated in the examination region (S) by the transmitting coil when the shielding member is not present. Metal detector.

3. The transmitting coil and the receiving coil constitute a coaxial detection head arranged to form a coaxial line along the direction in which the object under test passes.

3. The metal detector according to claim 1 or 2.

4. The shield member covers the entire receiving coil.

4. The metal detector of claim 3.

5. The shielding member covers the entire transmitting coil.

4. The metal detector of claim 3.

6. the shield member is disposed between the transmitting coil and the receiving coil in the coaxial direction.

4. The metal detector of claim 3.

7. a single-sided detection head is configured in which the transmitting coil and the receiving coil are arranged coaxially along a direction perpendicular to the passing direction of the object under test, The shield member is disposed perpendicular to the coaxial direction.

3. The metal detector according to claim 1 or 2.

8. The electrical resistivity of the shielding member is 10 －２ Ω / □ to 10 ３ Ω / □ range, 2. The metal detector of claim 1.

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