Cutter discrimination device

Abstract

To provide a cutter discrimination device that can be used as a walk-through type metal detection gate and can discriminate a magnetic metal cutter.SOLUTION: A cutter discrimination device 10 includes: a transmission panel 1 that has a panel type housing, has magnetic field directivity in a normal direction, a vertical direction and a longitudinal direction of a panel surface and incorporates three systems of transmission coils arranged so that opening surfaces when viewed from the panel surface overlap with each other; a reception panel 2 that has a panel type housing, detects a flux change in an AC magnetic field generated from the three systems of transmission coils and incorporates three systems of reception coils arranged so that opening surfaces when viewed from the panel surface overlap with each other; and a control device 3 that determines whether or not a person 100 carries a magnetic metal cutter 101 on the basis of each signal of the three systems of reception coils when the person 100 passes through a space where the panel surface of the transmission panel 1 faces the panel surface of the reception panel 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cutting tool discrimination device, and more particularly to a device for discriminating whether a person has cutting tools made of magnetic metal or not.

Background Art

[0002] At security inspection sites in airports, a walk-through type metal detector (metal detector) is installed so that people can walk through it directly to inspect whether a person is carrying any metal objects that could be used as weapons such as cutting tools. Generally, magnetic metals passing through a magnetic field have the property that the magnetic flux increases due to magnetization of the metal object itself, while non-magnetic metals have the property that eddy currents are generated in the metal object and the magnetic flux decreases due to the secondary magnetic field. Metal detectors detect metal objects using such properties. Specifically, the metal detection gate has a transmitting coil that generates an alternating magnetic field on one side (left or right) of the gate, a receiving coil that detects the change in magnetic flux of the alternating magnetic field on the other side, and a passage for people to pass through in between. When a person carrying a metal object passes through the passage, the metal object reacts.

[0003] In order to specify not only the presence or absence of metal objects but also their approximate shape and position in the magnetic field, it is necessary to detect changes in magnetic flux in multiple directions, preferably in three mutually perpendicular axes, using a plurality of transmitting coils and receiving coils. However, due to the need to provide a passage for people to pass through, the transmitting coils and receiving coils of the metal detection gate need to be arranged on the left and right sides of the gate. For this reason, conventional metal detection gates address this problem by arranging a plurality of transmitting coils and receiving coils with different directivities vertically or horizontally (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In addition to knives, metal objects that a metal detector reacts to include mixtures of magnetic and non-magnetic metals such as smartphones and safety items made of magnetic metals such as belts. That is, it is difficult for conventional metal detectors to distinguish between knives made of magnetic metals that can be used as weapons and other safe items. For this reason, in security inspections, it is necessary to remove all items made of magnetic metals such as belts and then pass through the metal detection gate, which has the problem of taking a long time for the inspection. Therefore, metal detection gates are installed only in places where a high level of safety is required, such as airport security inspection areas and the entrances of event venues, and are not currently installed at soft targets where a large number of unspecified people come and go, such as railway stations and commercial facilities.

[0006] In addition to using metal detectors, there is also a technology that irradiates millimeter waves onto the object of interest and constructs an image of the belongings from the reflected or transmitted waves. However, in order to accurately identify the shape of the belongings, it is necessary to increase the resolution of the image, which requires arranging a large number of antennas. For this reason, inspection devices using millimeter waves are more expensive than metal detectors and have problems in terms of cost.

[0007] In view of the above problems, an object of the present invention is to provide a knife discrimination device that can be used as a walk-through type metal detection gate and can discriminate knives made of magnetic metals.

Means for Solving the Problems

[0008] According to one aspect of the present invention, there is provided a transmitting panel having a panel-shaped housing, having magnetic field directivity in the normal direction, vertical direction, and horizontal direction of the panel surface, and having first transmitting coils, second transmitting coils, and third transmitting coils whose opening surfaces are arranged to overlap each other when viewed from the panel surface; a receiving panel having a panel-shaped housing, detecting a change in magnetic flux of an alternating magnetic field generated from the first transmitting coil, the second transmitting coil, and the third transmitting coil, and having first receiving coils, second receiving coils, and third receiving coils whose opening surfaces are arranged to overlap each other when viewed from the panel surface; and a control device that determines whether a person passing through a space where the panel surface of the transmitting panel faces the panel surface of the receiving panel is holding a cutting tool made of magnetic metal based on signals from the first receiving coil, the second receiving coil, and the third receiving coil. A cutting tool discrimination device is provided.

Effects of the Invention

[0009] According to the present invention, a cutting tool discrimination device that can be used as a walk-through type metal detection gate in which a transmitting panel and a receiving panel face each other and a person can walk through between them is realized. Further, by detecting a change in magnetic flux of an alternating magnetic field in three orthogonal axes instead of a single magnetic field, it is possible to specify the approximate shape and the presence or absence of magnetism of a metal object held by a person passing through the space between the transmitting panel and the receiving panel, and it is possible to determine that the person is holding a cutting tool made of magnetic metal.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

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Figure 9

Figure 10

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Figure 15

Best Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. However, a more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate understanding by those skilled in the art. The inventor provides the accompanying drawings and the following description to enable those skilled in the art to fully understand the present invention, and does not intend to limit the subject matter described in the claims thereby. Also, the dimensions of each member depicted in the drawings, the detailed shapes of the details, etc. may be different from the actual ones. ≪Outline of the Device≫

[0012] FIG. 1 is a schematic diagram of a cutting tool discrimination device according to an embodiment of the present invention. The cutting tool discrimination device 10 according to the present embodiment is a permanent or portable device that can be used as a walk-through type metal detection gate installed at a security inspection site at an airport or an entrance to an event venue, through which a person 100 can walk and pass directly. Specifically, the cutting tool discrimination device 10 includes, as main components, a transmission panel 1, a reception panel 2, and a control device 3.

[0013] Both the transmitting panel 1 and the receiving panel 2 have panel-shaped housings made of a lightweight, rigid, non-magnetic material with low dielectric constant and conductivity, such as synthetic resin. As an example, their size is 2100 - 2250 mm in the longitudinal direction, 600 - 850 mm in the short transverse direction, and 50 - 60 mm in thickness. As will be described later, the transmitting panel 1 has a transmitting coil for transmitting an alternating magnetic field, and the receiving panel 2 has a receiving coil for detecting the change in magnetic flux of the alternating magnetic field built into their respective housings. The transmitting panel 1 and the receiving panel 2 are supported by self-standing or unspecified supports and are used in a state where their panel surfaces face each other at an interval of 720 - 750 mm and stand vertically with the longitudinal direction vertical. Further, in the standing state of the transmitting panel 1 and the receiving panel 2, connecting members 11 such as beams or ceiling plates are attached to the upper part of the panel as needed to stabilize the standing state of the panel and prevent lateral sway of the panel.

[0014] In addition to the above, photoelectric or ultrasonic sensors 4a and 4b are provided at appropriate positions at both ends in the short transverse direction of the panel surfaces of the transmitting panel 1 and the receiving panel 2 facing each other. That is, one part of the transmission and reception of the sensor 4a is provided at an appropriate position at one end in the short transverse direction of the panel surface of the transmitting panel 1, and the other part is provided at the corresponding position on the receiving panel 2. One part of the transmission and reception of the sensor 4b is provided at an appropriate position at the other end in the short transverse direction of the panel surface of the transmitting panel 1, and the other part is provided at the corresponding position on the receiving panel 2. These sensors 4a and 4b are for detecting the entry and exit of a person 100 into and out of the space (hereinafter sometimes referred to as the "inspection space") where the panel surface of the transmitting panel 1 and the panel surface of the receiving panel 2 face each other. The inspection space serves as a passage for the person 100 to pass through.

[0015] The transmission panel 1 and the reception panel 2 are connected to the control device 3 by cables. Further, a camera 5 for imaging the overall image of a person 100 passing through the inspection space is installed on the connecting member 11 or a support (not shown), and the camera 5 is also connected to the control device 3. The control device 3 includes an oscillation circuit that supplies a signal to a transmission coil built in the transmission panel 1, a reception circuit that acquires the signal of the reception coil built in the reception panel 2, and an electronic circuit such as a sensor circuit that controls the sensors 4a and 4b. In addition, the control device 3 includes a processor that processes the signals obtained from the reception circuit and the sensor circuit. By signal processing by this processor, it is determined whether or not the person 100 passing through the inspection space is carrying a cutting tool 101 made of magnetic metal. The determination result can be displayed on a display device (not shown) of the control device 3 together with the captured image of the camera 5, recorded in a storage, or displayed in real time on a terminal 7 located remotely via a communication network 6 such as the Internet.

[0016] ≪Transmission and reception coils≫ Next, the coils built in the transmission panel 1 and the reception panel 2 will be described in detail. For convenience, hereinafter, as shown in FIG. 1, the normal direction, the vertical direction (longitudinal direction), and the horizontal direction (lateral direction) of the panel surfaces of the transmission panel 1 and the reception panel 2 will be described as the x-axis, the y-axis, and the z-axis, respectively. When viewed from the person 100 passing through the inspection space, the x-axis corresponds to the horizontal direction, the y-axis corresponds to the vertical direction (vertical direction), and the z-axis corresponds to the traveling direction.

[0017] FIG. 2 is a diagram for explaining an example of the shape and arrangement of a transmission coil incorporated in the transmission panel 1. The depth direction of the figure is the x-axis, the vertical direction is the y-axis, and the horizontal direction is the z-axis. FIG. 2(a) shows an example of the arrangement of all the coils when the transmission panel 1 is viewed from the panel surface. The remaining area of the transmission panel 1 excluding the portion where the connecting member 11 is attached is roughly divided into four zones in the vertical direction. The uppermost zone is located at a height generally above the chest of the person 100 passing through the inspection space, the second zone from the top is located at a height around the waist to the chest, the third zone from the top is located at a height around the thigh to the waist, and the lowermost fourth zone is located at a height generally below the knees. The vertical width of each zone is the same. Transmission coils having magnetic field directivity in the xyz axis directions are arranged in each zone. FIG. 2(b) is a drawing showing only the transmission coil Ta having high magnetic field directivity in the x-axis direction, FIG. 2(c) is a drawing showing only the transmission coil Tb having high magnetic field directivity in the y-axis direction, and FIG. 2(d) is a drawing showing only the transmission coil Tc having high magnetic field directivity in the z-axis direction. For convenience, the transmission coil Ta is drawn with a thick line, the transmission coil Tb is drawn with a thin line, and the transmission coil Tc is drawn with a dashed line, but actually these lines are coil windings formed by copper wires, printed wirings of printed circuit boards, etc. The arrows in the figure represent the direction of the current, or more precisely, the polarity of the current.

[0018] As shown in Fig. 2(b), one transmission coil Ta is arranged for each zone. For convenience, these transmission coils Ta are called Ta1, Ta2, Ta3, and Ta4 in order from the topmost zone. The transmission coils Ta1 to Ta4 are all loop coils in which a conductor is wound in the same substantially rectangular shape and current flows in the same direction. The transmission coils Ta1 to Ta4 are formed by winding the conductor so that the opening area is as wide as possible within each zone. For example, as shown in the figure, the conductor is wound around the entire zone frame. Thereby, from each coil, a high directivity in the x-axis direction can be obtained, and a stronger magnetic field can be generated. Also, the transmission coils Ta1 to Ta4 are formed by winding with conductors of different systems from each other. For this reason, it is possible to apply signals of different frequencies for each zone, and the detection sensitivity of metal and the discrimination accuracy of the holding position for each zone can be improved.

[0019] As shown in Fig. 2(d), one transmission coil Tc is arranged for each zone. For convenience, these transmission coils Tc are called Tc1, Tc2, Tc3, and Tc4 in order from the topmost zone. The transmission coils Tc1 to Tc4 are loop coils in which a pair of sub-coils in which a single conductor is wound in opposite loop shapes are arranged in the left-right direction of the panel surface. When using a pair of sub-coils wound in opposite directions to each other as the transmission coil, a magnetic field with high directivity can be generated in the direction in which the sub-coils are arranged, that is, the z-axis direction. The sub-coils of the transmission coils Tc1 to Tc4 are formed by winding the conductor so that the opening area is as wide as possible within each zone and the centers of the opening areas are as far apart as possible. For example, as shown in the figure, the zone is divided into two parts left and right, and the conductor of the sub-coil is wound around the entire divided area. Thereby, from each coil, a high directivity in the z-axis direction can be obtained, and a stronger magnetic field can be generated. Also, the transmission coils Tc1 to Tc4 are formed by winding with conductors of different systems from each other. For this reason, it is possible to apply signals of different frequencies for each zone, and the detection sensitivity of metal and the discrimination accuracy of the holding position for each zone can be improved.

[0020] As shown in Fig. 2(c), the transmitting coil Tb is a loop coil in which pairs of sub-coils, each formed by winding a single wire in mutually reverse loop shapes, are arranged in the vertical direction of the panel surface. When using such pairs of sub-coils wound in mutually reverse directions as the transmitting coil, it is possible to generate a highly directional magnetic field in the direction in which the sub-coils are arranged, i.e., the y-axis direction. However, unlike the transmitting coils Ta and Tc, the transmitting coil Tb is formed by winding a single wire commonly for all zones, without winding the wire for each zone in a separate system. Also, unlike the transmitting coil Tc, the transmitting coil Tb arranges pairs of sub-coils not for each zone but for two adjacent zones. This is because the vertical width of each zone is narrow compared to the horizontal width, and if pairs of sub-coils were arranged vertically in each zone, it would not be possible to secure a large enough opening area for each sub-coil, and the centers of the opening areas could not be sufficiently separated. Conversely, as shown in the figure, by arranging one sub-coil in each zone, it is possible to increase the opening area of each sub-coil and greatly separate the centers of the opening areas with the pair of sub-coils, resulting in high directivity in the y-axis direction and the ability to generate a stronger magnetic field.

[0021] As shown in Fig. 2(a), the transmitting coils Ta, Tb, and Tc are arranged in the transmitting panel 1 with their respective opening surfaces overlapping each other. Although the opening surfaces of the transmitting coils Ta, Tb, and Tc overlap in this way, by applying signals of different frequencies to these coils simultaneously, it is possible to suppress the interference of their magnetic fields. Also, when viewed from the panel surface, the windings of the transmitting coils Ta, Tb, and Tc overlap at points without linearly overlapping each other, i.e., the windings are shifted so as to cross, preferably orthogonally, as much as possible. By arranging the transmitting coils Ta, Tb, and Tc in this way, even when current flows through multiple coils simultaneously, the current flowing through the winding of one transmitting coil can be minimized from affecting the current flowing through the winding of another transmitting coil.

[0022] If the signal frequencies of the transmitting coils Ta, Tb, and Tc are too low, it becomes difficult for eddy currents to be generated in non-magnetic metals, making it difficult to detect non-magnetic metals. Conversely, if the frequency is too high, electrostatic induction due to static electricity, such as the clothing of a person 100 passing through the inspection space, may affect the detection, resulting in a risk of misdetecting metal objects. Additionally, the need to take EMC countermeasures also arises. Therefore, the signal frequencies of the transmitting coils Ta, Tb, and Tc are preferably up to 100 kHz, and more preferably 1 kHz to 50 kHz.

[0023] Figure 3 is a diagram for explaining an example of the shape and arrangement of the receiving coils incorporated in the receiving panel 2. The depth direction of the figure is the x-axis, the vertical direction is the y-axis, and the horizontal direction is the z-axis. Figure 3(a) shows an example of the arrangement of all the coils when the receiving panel 2 is viewed from the panel surface. Similar to the transmitting panel 1, the remaining area of the receiving panel 2 excluding the portion where the connecting member 11 is attached is partitioned into four zones in the vertical direction. The uppermost zone is located at approximately the height above the chest of a person passing through the inspection space, the second zone from the top is located at approximately the height around the chest to the waist, the third zone from the top is located at approximately the height around the waist to the thigh, and the lowermost fourth zone is located at approximately the height below the knees. The vertical width of each zone is the same. Receiving coils for detecting the magnetic flux change of the magnetic field generated from each of the transmitting coils Ta, Tb, and Tc are arranged in each zone. Figure 3(b) is drawn by extracting only the receiving coil Ra for detecting the magnetic flux change of the alternating magnetic field generated from the transmitting coil Ta, Figure 3(c) is drawn by extracting only the receiving coil Rb for detecting the magnetic flux change of the alternating magnetic field generated from the transmitting coil Tb, and Figure 3(d) is drawn by extracting only the receiving coil Rc for detecting the magnetic flux change of the alternating magnetic field generated from the transmitting coil Tc. For the sake of convenience, Ra is drawn with a thick line, Rb is drawn with a thin line, and Rc is drawn with a dashed line, but in reality, these lines are coil windings formed by copper wires or printed wirings on a printed circuit board.

[0024] As shown in FIG. 3(b), one receiving coil Ra is arranged for each zone. For convenience, these receiving coils Ra are called Ra1, Ra2, Ra3, and Ra4 in order from the topmost zone. The receiving coils Ra1 to Ra4 are all loop coils in which a conductor is wound in the same substantially rectangular shape. The receiving coils Ra1 to Ra4 are formed by winding the conductor so that the opening area is as wide as possible within each zone. For example, as shown in the drawing, the conductor is wound around the entire zone frame. Thereby, in each coil, the change in magnetic flux of the alternating magnetic field generated from the transmitting coil Ta can be detected with high sensitivity. Further, the receiving coils Ra1 to Ra4 are connected to receiving circuits of different systems from each other. For this reason, signals independent of each other can be acquired from these coils.

[0025] As shown in FIG. 3(c), one receiving coil Rb is arranged for each zone. For convenience, these receiving coils Rb are called Rb1, Rb2, Rb3, and Rb4 in order from the topmost zone. The receiving coils Rb1 to Rb4 are loop coils in which a pair of sub-coils in which a single conductor is wound in opposite loop shapes are arranged in the vertical direction of the panel surface. When using a pair of sub-coils wound in opposite directions as a receiving coil in this way, it operates as a differential coil that detects the magnetic flux gradient in the direction in which the sub-coils are arranged, that is, the y-axis direction, and the change in magnetic flux of the alternating magnetic field generated from the transmitting coil Tb can be detected. The receiving coils Rb1 to Rb4 are connected to receiving circuits of different systems from each other. For this reason, signals independent of each other can be acquired from these coils. Further, the sub-coils of the receiving coils Rb1 to Rb4 are formed by winding the conductor so that the opening area is as wide as possible within each zone and the centers of the opening areas are as far apart as possible. For example, as shown in the drawing, the zone is divided into two parts vertically, and the conductor of the sub-coil is wound around the entire divided area. Thereby, in each coil, the magnetic flux gradient in the y-axis direction can be detected with high sensitivity.

[0026] As shown in FIG. 3(d), one receiving coil Rc is arranged for each zone. For convenience, these receiving coils Rc are called Rc1, Rc2, Rc3, and Rc4 in order from the topmost zone. The receiving coils Rc1 to Rc4 are loop coils in which a pair of sub-coils wound in a reverse loop shape with one conductor are arranged in the left-right direction of the panel surface. When using such a pair of sub-coils wound in opposite directions as the receiving coil, it operates as a differential coil that detects the magnetic flux gradient in the direction in which the sub-coils are arranged, that is, the z-axis direction, and can detect the change in the magnetic flux of the alternating magnetic field generated from the transmitting coil Tc. The receiving coils Rc1 to Rc4 are connected to receiving circuits of different systems from each other. Therefore, independent signals can be obtained from these coils. Further, the sub-coils of the receiving coils Rc1 to Rc4 are formed by winding the conductors so that the opening area is as wide as possible within each zone and the centers of the opening areas are as far apart as possible. For example, as shown in the figure, the zone is divided into two parts left and right, and the conductors of the sub-coils are wound over each divided area. Thereby, in each coil, the change in the magnetic flux in the z-axis direction can be detected with high sensitivity.

[0027] As shown in FIG. 3(a), the receiving coils Ra, Rb, and Rc are arranged in the receiving panel 2 with their respective opening surfaces overlapping each other. Although the opening surfaces of the receiving coils Ra, Rb, and Rc overlap in this way, as will be described later, since these coils are connected to different receiving circuits, their respective signals can be obtained without interfering with each other. Also, unlike the transmitting coils Ta, Tb, and Tc, the respective windings of the receiving coils Ra, Rb, and Rc may linearly overlap each other when viewed from the panel surface.

[0028] ≪Receiving Circuit≫ FIG. 4 is a circuit configuration diagram of a receiving circuit according to an example. The receiving circuit 8 is a circuit that acquires the signals of the receiving coils Ra, Rb, and Rc and is mounted on the control device 3. For convenience, in FIG. 4, an example of three receiving circuits of the receiving coils Ra1, Rb1, and Rc1 is shown. Actually, the remaining receiving coils are also connected to similar receiving circuits.

[0029] A capacitor 81 is connected in parallel to each of the receiving coils Ra1, Rb1, and Rc1, and together with the receiving coils, an LC resonance circuit is formed. The LC resonance circuit including the receiving coil Ra1 resonates at the signal frequency of the transmitting coil Ta1, the LC resonance circuit including the receiving coil Rb1 resonates at the signal frequency of the transmitting coil Tb, and the LC resonance circuit including the receiving coil Rc1 resonates at the signal frequency of the transmitting coil Tc1. The capacitance values of the respective capacitors 81 are adjusted accordingly. Each LC resonance circuit is connected to a band-pass filter 82, and a signal of the resonance frequency is extracted by each band-pass filter 82. The output of each band-pass filter 82 is connected to a differential amplifier 83, and the signal of the resonance frequency is differentially amplified by each differential amplifier 83.

[0030] The output of each differential amplifier 83 is connected to an offset removal circuit 84 composed of a half-wave rectifier circuit and a differential amplifier. Each offset removal circuit 84 generates a voltage signal in which the offset voltage of the DC component is canceled. The output of each offset removal circuit 84 is connected to a low-pass filter 85, and the low-frequency components of the voltage signal are cut by each low-pass filter 85. The output of each low-pass filter 85 is connected to an A / D converter 86, and each voltage signal is converted into a digital signal by the A / D converter 86. The digital signal is processed by the processor of the control device 3.

[0031] ≪Metal Object Detection by Coils of Each xyz Axis≫ Next, examples of metal object detection by each of the pairs of the transmitting coil Ta and the receiving coil Ra, the pair of the transmitting coil Tb and the receiving coil Rb, and the pair of the transmitting coil Tc and the receiving coil Rc when a magnetic metal plate and a non-magnetic metal plate pass through the inspection space will be described.

[0032] FIG. 5 is a diagram showing metal object detection by the transmitting coil Ta and the receiving coil Ra when the magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. FIG. 6 is a diagram showing metal object detection by the transmitting coil Ta and the receiving coil Ra when the non-magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. Both figures are end views of the transmitting coil Ta and the receiving coil Ra cut in the xz plane, where the left-right direction in the figure is the x-axis, the depth direction is the y-axis, and the up-down direction is the z-axis. The circles represent the cross-sections of the coil windings, the thick gray lines connecting the circles represent the coil windings, the solid arrows represent the transmitting magnetic field generated from the transmitting coil Ta, especially the thick arrows represent the general direction of the magnetic field, the dashed ellipses and dashed arrows represent the secondary magnetic field generated from the metal plate, especially the thick arrows represent the general direction of the magnetic field. Also, the horizontally long rectangle in the center of the figure represents the metal plate passing through the inspection space. Since the flat surface of the metal plate faces the traveling direction, i.e., the z-axis direction, in FIGS. 5 and 6, only the end faces in the longitudinal or short-side direction of the metal plate, i.e., the thickness part, can be seen.

[0033] Generally, when a magnetic metal plate is placed in a magnetic field with its flat surface facing the same direction as the magnetic field, the metal plate is magnetized by the magnetic field and a secondary magnetic field is generated. Conversely, when a magnetic metal plate is placed in a magnetic field with its flat surface perpendicular to the direction of the magnetic field, due to the influence of the anti-magnetic field, the metal plate is hardly magnetized and hardly generates a secondary magnetic field. On the other hand, when a non-magnetic metal plate is placed in a magnetic field with its flat surface perpendicular to the direction of the magnetic field, eddy currents are generated on the surface of the metal plate and a secondary magnetic field opposite to the surrounding magnetic field is generated. Conversely, when a magnetic metal plate is placed in a magnetic field with its flat surface facing the same direction as the magnetic field, hardly any eddy currents are generated on the surface of the metal plate and hardly any secondary magnetic field is generated to cancel out the surrounding magnetic field.

[0034] Therefore, as shown in FIG. 5, when the magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction, the metal plate is magnetized by the transmitting magnetic field in the x-axis direction, and a secondary magnetic field is generated, causing a change in the magnetic flux passing through the opening surface of the receiving coil Ra. This change in magnetic flux appears as a change in the induced electromotive force generated in the receiving coil Ra. On the other hand, as shown in FIG. 6, when the non-magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction, almost no eddy current is generated on the surface of the metal plate, and almost no secondary magnetic field is generated. Therefore, there is no change in the magnetic flux passing through the opening surface of the receiving coil Ra, and the induced electromotive force generated in the receiving coil Ra hardly changes either.

[0035] FIG. 7 is a diagram showing metal object detection by the transmitting coil Tb and the receiving coil Rb when the magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. FIG. 8 is a diagram showing metal object detection by the transmitting coil Tb and the receiving coil Rb when the non-magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. Both figures are end views of the transmitting coil Tb and the receiving coil Rb cut in the xy plane. The left-right direction in the figure is the x-axis, the up-down direction is the y-axis, and the depth direction is the z-axis. The circles represent the cross-sections of the coil windings, the thick gray lines connecting the circles represent the coil windings, the solid arrows represent the transmitting magnetic field generated from the transmitting coil Tb, especially the thick arrows represent the general direction of the magnetic field, the dashed ellipses and dashed arrows represent the secondary magnetic field generated from the metal plate, especially the thick arrows represent the general direction of the magnetic field, respectively. Also, the two vertically long rectangles in the center of the figure represent the metal plate passing through the inspection space. Since the flat surface of the metal plate faces the traveling direction, that is, the z-axis direction, the flat surface of the metal plate can be seen in FIGS. 7 and 8.

[0036] As shown in FIG. 7, when the magnetic metal plate passes through the inspection space with its flat surface facing the traveling direction, the metal plate is magnetized by the transmitting magnetic field in the y-axis direction, generating a secondary magnetic field, which causes a change in the magnetic flux passing through the opening surfaces of the sub-coil pairs of the receiving coil Rb. This magnetic flux change appears as a change in the induced electromotive voltage generated in the receiving coil Rb. Specifically, if the sub-coil pairs of the receiving coil Rb1 are Rb1' and Rb1'', a positive induced electromotive voltage "VRb1'" is generated in the coil Rb1', and a negative induced electromotive voltage "-VRb1''" is generated in the coil Rb1''. The induced electromotive voltage VRb1 of the receiving coil Rb1 is a positive voltage such as VRb1 = VRb1' - (-VRb1'') = VRb1' + VRb1''. On the other hand, the receiving coil Rb2 adjacent to the receiving coil Rb1 is affected by a magnetic field in the opposite direction to that of the receiving coil Rb1. If the sub-coil pairs of the receiving coil Rb2 are Rb2' and Rb2'', a negative induced electromotive voltage "-VRb2'" is generated in the coil Rb2', and a positive induced electromotive voltage "VRb2''" is generated in the coil Rb2''. The induced electromotive voltage VRb2 of the receiving coil Rb2 is a negative voltage such as VRb2 = -VRb2' - VRb2'' = -(VRb2' + VRb2''). On the other hand, as shown in FIG. 8, when the non-magnetic metal plate passes through the inspection space with its flat surface facing the traveling direction, almost no eddy current is generated on the surface of the metal plate, and almost no secondary magnetic field is generated either. Therefore, there is no change in the magnetic flux passing through the opening surfaces of the coil pairs of the receiving coil Rb, and the induced electromotive voltage generated in the receiving coil Rb hardly changes either.

[0037] FIG. 9 is a diagram showing metal object detection by the transmission coil Tc and the reception coil Rc when the magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. FIG. 10 is a diagram showing metal object detection by the transmission coil Tc and the reception coil Rc when the non-magnetic metal plate passes through the inspection space with the flat surface facing the traveling direction. Both figures are end views of the transmission coil Tc and the reception coil Rc cut in the xz plane, where the left-right direction in the figure is the x-axis, the depth direction is the y-axis, and the up-down direction is the z-axis. Also, the end views when the metal plate is at different positions (point A, point B, point C) in the inspection space are arranged vertically. The circles represent the cross-sections of the coil windings, the thick gray lines connecting the circles represent the coil windings, the solid arrows represent the transmission magnetic field generated from the transmission coil Tc, particularly the thick arrows represent the general direction of the magnetic field, the dashed ellipses and dashed arrows represent the secondary magnetic field generated from the metal plate, particularly the thick arrows represent the general direction of the magnetic field, respectively. Also, the horizontally long rectangle in the center of the figure represents the metal plate passing through the inspection space. Since the flat surface of the metal plate faces the traveling direction, that is, the z-axis direction, in FIGS. 9 and 10, only the end faces in the longitudinal or short-side direction of the metal plate, that is, the thickness part, can be seen.

[0038] The upper part of FIG. 9 shows metal object detection when the magnetic metal plate is near point A, that is, near the opening surface of one sub-coil of the transmission coil Tc. At point A, the transmission magnetic field in the x-axis direction by the sub-coil is dominant. Therefore, the metal plate is magnetized by the transmission magnetic field in the x-axis direction and a secondary magnetic field is generated, causing a change in the magnetic flux passing through the opening surface of the sub-coil pair of the reception coil Rc. This magnetic flux change appears as a change in the induced electromotive voltage generated in the reception coil Rc. Specifically, if the sub-coil pair of the reception coil Rc is Rc’ and Rc”, a positive induced electromotive voltage “VRc’” is generated in the coil Rc’, and a negative induced electromotive voltage “-VRc”” is generated in the coil Rc”. The induced electromotive voltage VRc of the reception coil Rc becomes a positive voltage such as VRc = VRc’ - (-VRc”) = VRc’ + VRc”.

[0039] The middle part of Fig. 9 represents the detection of a metallic object when the magnetic metal plate is at point B, that is, at the boundary of the sub-coil pair of the transmitting coil Tc. At point B, the transmitting magnetic field in the z-axis direction is dominant. Therefore, the metal plate is hardly magnetized and the induced electromotive force generated in the receiving coil Rc hardly changes either.

[0040] The lower part of Fig. 9 represents the detection of a metallic object when the magnetic metal plate is at point C, that is, near the opening surface of the other sub-coil of the transmitting coil Tc. At point C, the transmitting magnetic field in the x-axis direction by the said sub-coil, and in the direction opposite to that at point A, is dominant. Therefore, the metal plate is magnetized by the transmitting magnetic field in the x-axis direction to generate a secondary magnetic field, which causes a change in the magnetic flux penetrating the opening surface of the sub-coil pair of the receiving coil Rc, and this change in magnetic flux appears as a change in the induced electromotive force generated in the receiving coil Rc. Specifically, if the sub-coil pair of the receiving coil Rc is denoted as Rc’ and Rc”, a positive induced electromotive force “VRc’” is generated in the coil Rc’, and a negative induced electromotive force “-VRc”” is generated in the coil Rc”. The induced electromotive force VRc of the receiving coil Rc becomes a positive voltage similar to that at point A, i.e., VRc = VRc’ - (-VRc”) = VRc’ + VRc”.

[0041] The upper part of Fig. 10 represents the detection of a metallic object when the non-magnetic metal plate is at point A, that is, near the opening surface of one of the sub-coils of the transmitting coil Tc. At point A, the transmitting magnetic field in the x-axis direction by the said sub-coil is dominant. Therefore, almost no eddy current is generated on the surface of the metal plate and almost no secondary magnetic field is generated either. As a result, there is no change in the magnetic flux penetrating the opening surface of the sub-coil pair of the receiving coil Rc, and the induced electromotive force generated in the receiving coil Rc hardly changes either.

[0042] The middle part of Fig. 10 represents the detection of a metallic object when the non-magnetic metal plate is at point B, that is, at the boundary of the sub-coil pair of the transmitting coil Tc. At point B, the transmitting magnetic field in the z-axis direction is dominant. Therefore, eddy currents are generated on the surface of the metal plate, and a secondary magnetic field in the opposite direction of the z-axis is generated to cancel out the transmitting magnetic field in the z-axis direction generated by the transmitting coil Tc. The generation of the secondary magnetic field from the metal plate causes a change in the magnetic flux passing through the opening surface of the sub-coil pair of the receiving coil Rc, and this change in magnetic flux appears as a change in the induced electromotive voltage generated in the receiving coil Rc. Specifically, if the sub-coil pair of the receiving coil Rc is denoted as Rc' and Rc'', a positive induced electromotive voltage "VRc'" is generated in the coil Rc', a negative induced electromotive voltage "-VRc''" is generated in the coil Rc'', and the induced electromotive voltage VRc of the receiving coil Rc becomes a positive voltage such as VRc = VRc' - (-VRc'') = VRc' + VRc''.

[0043] The lower part of Fig. 10 represents the detection of a metallic object when the non-magnetic metal plate is at point C, that is, near the opening surface of the other sub-coil of the transmitting coil Tc. At point C, the transmitting magnetic field in the x-axis direction by the sub-coil, and in the direction opposite to that at point A, is dominant. Therefore, almost no eddy currents are generated on the surface of the metal plate and almost no secondary magnetic field is generated either. As a result, there is no change in the magnetic flux passing through the opening surface of the sub-coil pair of the receiving coil Rc, and the induced electromotive voltage generated in the receiving coil Rc hardly changes either.

[0044] Figure 11 is a table summarizing the characteristics of the signal waveforms of metal object detection by each coil when a magnetic metal plate and a non-magnetic metal plate pass through the inspection space with their flat surfaces facing the advancing direction. The vertical axis of each graph in the table represents the induced electromotive voltage generated in the receiving coil, and the horizontal axis represents the elapsed time from when the metal plate enters the inspection space until it exits. Note that since the receiving coil Ra is not a differential coil unlike the other receiving coils, the induced electromotive voltage is not zero but a certain positive value in the metal non-detection state. Also, Figure 12 is a table summarizing the characteristics of the signal waveforms of metal object detection by each coil when a magnetic metal plate and a non-magnetic metal plate pass through the inspection space with their flat surfaces facing the panel surface. Figure 13 is a table summarizing the characteristics of the signal waveforms of metal object detection by each coil when a magnetic metal plate and a non-magnetic metal plate pass through the inspection space with their flat surfaces facing the floor surface.

[0045] ≪Method for Discriminating Possession of Cutting Tools≫ As shown in Figures 11 to 13, the signal waveforms of the receiving coils vary differently depending on the presence or absence of magnetism of the metal plate and the direction when passing through the inspection space. Figure 14 is a diagram showing examples of the signal waveforms of each receiving coil in the zone corresponding to the height when a stainless-steel kitchen knife, a smartphone, and a steel beverage can pass through the inspection space at a certain height. In terms of type, the stainless-steel kitchen knife corresponds to a magnetic metal plate, and the smartphone corresponds to a non-magnetic metal plate. The vertical axis of each graph represents the signal voltages of the receiving coils Ra, Rb, and Rc, and the horizontal axis represents the elapsed time from when a person enters the inspection space until they exit.

[0046] When comparing the signal waveforms of each metal object, for the Ra signal, a small peak is seen in the stainless-steel kitchen knife, while relatively large downward peaks are seen in the smartphone and the steel beverage can. Also, for the Rc signal, there is one downward peak in the stainless-steel kitchen knife, two downward peaks in the smartphone, and two downward and one upward peak in the steel beverage can. Thus, different characteristics can be seen in the signal waveforms depending on the difference in the shape of the metal object and the presence or absence of magnetism.

[0047] In an actual scenario, since people carry magnetic metal objects, non-magnetic metal objects, and even composite objects of these in various orientations in various places and pass through the inspection space, the signal waveform of the receiving coil becomes more complex. As a means of accurately discriminating magnetic metal knives from such complex signal waveforms, a neural network is used. There are various types of neural networks, but in this embodiment, a convolutional neural network (CNN) that can process the signal waveform as image data as it is is used.

[0048] FIG. 15 is a schematic diagram of an example of a CNN model for tool discrimination. The CNN model 30 is configured by sequentially connecting a first convolutional layer 31, a first pooling layer 32, a second convolutional layer 33, a second pooling layer 34, a fully connected layer 35, and an output layer 36. A total of 12-channel signals of the receiving coils Ra, Rb, and Rc in four zones A / D-converted by the receiving circuit are preprocessed and then input as image data into the CNN model 30. For example, when the time from when a person enters the inspection space until they exit is divided into 100 points, image data of 12 pixels in height × 100 pixels in width is input into the CNN model 30. The preprocessing is performed by the processor of the control device 3. Specifically, a moving average is taken for the signals of each channel to remove noise, data is decimated if the number of data points is large, and data is interpolated if it is small to absorb the walking speed difference of the person passing through the inspection space. As filters for the first convolutional layer 31 and the second convolutional layer 33, filters of size 3n×m (where n is a natural number less than or equal to the number of zones and m is a natural number less than or equal to the number of horizontal pixels of the input image) are used so as to simultaneously extract the features of the signals of the receiving coils Ra, Rb, and Rc. Note that the vertical pixels of the input image are arranged in the order of Ra, Rb, and Rc for each zone. The output layer 36 is composed of two nodes: a node representing that a person passing through the inspection space is carrying a tool made of magnetic metal and a node representing that they are not carrying such a thing, and probability values are output from each node. The CNN model 30 is pre-trained by providing actual signals obtained using various samples other than the tool made of magnetic metal, which is the object to be discriminated, such as a steel can or a smartphone, as training data.

[0049] Various parameters of the pre-trained CNN model 30 are stored in the built-in storage or external storage of the control device 3. The processor of the control device 3 reconstructs the pre-trained CNN model 30 by reading the parameters from the storage. Then, by preprocessing the newly acquired signals of the receiving coils Ra, Rb, and Rc and inputting them into the CNN model 30, it is possible to determine whether a person passing through the inspection space is carrying a tool made of magnetic metal.

[0050] <<Effect>> As described above, the cutting tool discrimination device 10 according to the present embodiment can be used as a walk-through type metal detection gate in which the transmission panel 1 and the reception panel 2 face each other and a person can walk between them and pass through as it is. Further, by detecting the change in the magnetic flux of the alternating magnetic field of the orthogonal three axes instead of a single magnetic field, it is possible to specify the approximate shape and the presence or absence of magnetism of the metal objects possessed by a person passing through the space where the transmission panel 1 and the reception panel 2 face each other, and it is possible to discriminate that the person possesses cutting tools made of magnetic metal.

[0051] Furthermore, by dividing the reception panel 2 into a plurality of zones in the vertical direction and detecting the change in the magnetic flux of the alternating magnetic field of the orthogonal three axes in each zone, even if a person passing through the space where the transmission panel 1 and the reception panel 2 face each other possesses both cutting tools made of magnetic metal and other safe objects at the same time, a signal waveform peculiar to the cutting tools made of magnetic metal is detected by the reception coil of the zone corresponding to the possession position of the cutting tools made of magnetic metal, and the cutting tools can be accurately discriminated.

[0052] Therefore, in the cutting tool discrimination device 10 according to the present embodiment, it is not necessary to pass through the metal detection gate after removing all the possessed items made of magnetic metal such as a belt as in the conventional case, and security inspection can be performed more easily. For this reason, it can be expected to be introduced into soft targets where an unspecified number of people come and go, such as railway stations and commercial facilities.

[0053] <<Modification Example>> Instead of applying signals of different frequencies to the transmission coils Ta, Tb, and Tc at the same time, signals of the same frequency may be applied in a time-division manner. In that case, it is not necessary to arrange the coil windings of the transmission coils Ta, Tb, and Tc so as to be shifted from each other. For example, the coil windings may be arranged so as to overlap linearly when viewed from the panel surface.

[0054] It is not necessary to match the number of zones between the transmission panel 1 and the reception panel 2. For example, the zones of the reception panel 2 can remain as they are, and the transmission panel 1 can reduce the number of zones and increase the opening area of each transmission coil accordingly so that a stronger alternating magnetic field is generated. Also, the number of transmission coils Ta, Tb, and Tc can be different. For example, the transmission coil Ta can be arranged throughout each zone frame that divides the transmission panel 1 into four parts, and the transmission coil Tc can be arranged throughout each zone frame that divides the transmission panel 1 into two parts.

[0055] The transmission panel 1 and the reception panel 2 do not necessarily have to be divided into a plurality of zones. For example, the transmission coils Ta, Tb, Tc and the reception coils Ra, Rb, Rc can each be formed by a single coil having a large opening area. Note that if the zones are eliminated in the reception panel 2, it becomes difficult to accurately discriminate magnetic metal blades when a person holds magnetic metal blades and other safe objects at the same time. Therefore, it is preferable that the reception panel 2 is divided into a plurality of zones.

[0056] Electronic circuits such as an oscillation circuit that supplies signals to the transmission coils Ta, Tb, Tc, a reception circuit that acquires the signals of the reception coils Ra, Rb, Rc, and a sensor circuit that controls the sensors 4a, 4b can be incorporated into the connecting member 11 instead of the control device 3. As a result, when the transmission panel 1 and the reception panel 2 are installed at positions far from the control device 3, it is not necessary to lay out a large number of copper wire cables connected to each coil. Only lightweight signal cables that are easy to lay can be laid out, or wireless communication can be adopted to make it cableless, facilitating the installation of the blade discrimination device 10.

[0057] On the other hand, for the discrimination of magnetic metal blades, an RNN (Recurrent Neural Network) model that processes each signal of the reception coils Ra, Rb, Rc as a time-series signal can be used instead of the CNN model 30. Also, machine learning such as support vector machines and multiple regression analysis can be used in addition to neural networks such as CNN and RNN.

[0058] As described above, as an example of the technology in the present invention, embodiments have been described. For that purpose, the accompanying drawings and detailed description have been provided. Therefore, among the components described in the accompanying drawings and the detailed description, there may be not only the components essential for solving the problems, but also the components not essential for solving the problems for the purpose of exemplifying the above technology. Therefore, just because those non-essential components are described in the accompanying drawings or the detailed description, it should not be immediately determined that those non-essential components are essential. Also, since the above-described embodiments are for exemplifying the technology in the present invention, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the equivalent scope thereof.

Explanation of Signs

[0059] 10 Tool Discrimination Device 1 Transmission Panel 2 Reception Panel Ta Transmission Coil (First Transmission Coil) Tb Transmission Coil (Second Transmission Coil) Tc Transmission Coil (Third Transmission Coil) Ra Reception Coil (First Reception Coil) Rb Reception Coil (Second Reception Coil) Rc Reception Coil (Third Reception Coil) 3 Control Device 30 CNN Model (Machine Learning Model)

Claims

1. A transmitting panel having a panel-shaped housing, having magnetic field directivity in the normal direction, vertical direction, and horizontal direction of the panel surface, and incorporating a first transmitting coil, a second transmitting coil, and a third transmitting coil whose opening surfaces are arranged to overlap each other when viewed from the panel surface; A receiving panel having a panel-shaped housing, detecting a change in magnetic flux of an alternating magnetic field generated from the first transmitting coil, the second transmitting coil, and the third transmitting coil, and incorporating a first receiving coil, a second receiving coil, and a third receiving coil whose opening surfaces are arranged to overlap each other when viewed from the panel surface; A control device that determines whether a person is carrying magnetic metal knives or not based on signals of the first receiving coil, the second receiving coil, and the third receiving coil when the person passes through a space where the panel surface of the transmitting panel faces the panel surface of the receiving panel. A knife discrimination device comprising:

2. The first transmitting coil and the first receiving coil are each a loop coil formed by winding a single conductor in a loop shape. The second transmitting coil and the second receiving coil are each a loop coil in which sub-coil pairs formed by winding a single conductor in loop shapes in opposite directions are arranged in the vertical direction of the panel surface. The third transmitting coil and the third receiving coil are each a loop coil in which sub-coil pairs formed by winding a single conductor in loop shapes in opposite directions are arranged in the horizontal direction of the panel surface. The knife discrimination device according to claim 1.

3. The first transmitting coil, the second transmitting coil, and the third transmitting coil are arranged in each of a plurality of zones partitioned in the vertical direction of the transmitting panel. The first transmitting coil and the third transmitting coil are each wound with different conductors for each zone. The second transmitting coil is wound with a single conductor across the plurality of zones. The knife discrimination device according to claim 2.

4. The winding wires of the first transmitting coil, the second transmitting coil, and the third transmitting coil intersect without linearly overlapping each other when viewed from the panel surface. The knife discrimination device according to claim 3.

5. The first receiving coil, the second receiving coil, and the third receiving coil are arranged in each of a plurality of zones partitioned in the vertical direction of the receiving panel. The knife discrimination device according to claim 2.

6. The cutting tool discrimination device according to claim 2, wherein the first transmission coil, the second transmission coil, and the third transmission coil, and the first reception coil, the second reception coil, and the third reception coil are each wound so that the opening area in the zone is as wide as possible.

7. The cutting tool discrimination device according to any one of claims 1 to 6, wherein signals having different frequencies are simultaneously applied to the first transmission coil, the second transmission coil, and the third transmission coil.

8. The cutting tool discrimination device according to any one of claims 1 to 6, wherein the control device inputs the signals of the first reception coil, the second reception coil, and the third reception coil newly acquired into a machine learning model that has been machine-learned in advance using the signals of the first reception coil, the second reception coil, and the third reception coil as teacher data, to determine whether or not the person is holding a cutting tool made of magnetic metal.

9. The cutting tool discrimination device according to claim 7, wherein the control device inputs the signals of the first reception coil, the second reception coil, and the third reception coil newly acquired into a machine learning model that has been machine-learned in advance using the signals of the first reception coil, the second reception coil, and the third reception coil as teacher data, to determine whether or not the person is holding a cutting tool made of magnetic metal.

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