JP5573205B2 - Detection device - Google Patents

Description

  The present invention relates to a detection device.

  In Patent Document 1, the excitation means for generating an alternating magnetic field in the detection area, and the position of the owner who holds the detected object in order to change the positional relationship between the alternating magnetic field and the detected object are indicated in the detection area. An object detection device is described that includes a moving means for forcibly moving and a detecting means for detecting the detected object based on a signal generated from a magnetic material applied to the detected object by application of an alternating magnetic field. .

JP 2008-46004 A

  An object of this invention is to provide the detection apparatus which can detect a magnetic body even when a magnetic material is contained in an installation surface.

According to a first aspect of the present invention, there is provided a detection device comprising two antenna units each provided with an excitation coil that generates an alternating magnetic field that causes magnetization reversal in a magnetic material and a detection coil that detects a change in magnetic field due to magnetization reversal of the magnetic material. And a non-magnetic metal that shields propagation of the alternating magnetic field to the installation surface so that the noise detected by the detection coil is less than a predetermined allowable level due to the alternating magnetic field acting on the installation surface. A shielding portion is provided at least in part , and is formed integrally with the two antenna portions in a state where the two antenna portions are separated from each other by a predetermined distance , and from the bottom surface of the two antenna portions And a plate-like support base for supporting.

  A detection device according to a second aspect of the present invention is the detection device according to the first aspect, wherein the antenna unit includes two detection coils, and alternating currents induced in the alternating magnetic field are opposite to each other. A removal means for removing noise having the same frequency as the frequency of the alternating current that generates the alternating magnetic field from an electrical signal that is connected in series so as to be in phase and that flows through a series circuit in which the two detection coils are connected in series. ing.

  A detection device according to a third aspect of the present invention is the detection device according to the first or second aspect, wherein the permissible level is a current value of a pulse current generated in the detection coil by the magnetization reversal.

A detection device according to a fourth aspect of the present invention is the detection device according to any one of the first to third aspects , wherein the entire support base is made of a nonmagnetic metal.
In addition, a detection device according to a fifth aspect of the present invention is the detection device according to any one of the first to fourth aspects, wherein the antenna unit includes two detection coils, and the support base. The AC currents are arranged in a direction parallel to the plane, and are connected in series so that the alternating currents induced by the alternating magnetic field have opposite phases.
Further, a detection device according to a sixth aspect of the present invention is the detection device according to any one of the first to fifth aspects, wherein the shielding portion is made of nonmagnetic stainless steel.

  According to the first aspect of the present invention, it is possible to detect a magnetic material even when a magnetic material is included in the installation surface, as compared with a case where a shielding portion is not provided on a support base that supports two antenna portions from the bottom surface. It becomes easy.

  According to the invention of claim 2, the noise due to the eddy current generated in the support base is compared with the case where noise having the same frequency as the frequency of the alternating current that generates the alternating magnetic field is generated from the electric signal flowing through the series circuit. Even when the two detection coils are detected differently, the detection accuracy of the magnetic material can be improved.

  According to the invention of claim 3, it is easier to detect the magnetic material by comparing the amount of change in the signal level with the threshold value as compared with the case where the allowable level is larger than the current value of the pulse current. .

  According to the fourth aspect of the present invention, it is easy to enhance the noise shielding effect as compared with the case where a part of the support base is formed of a nonmagnetic metal.

It is a perspective view which shows the schematic structure of the detection apparatus which concerns on 1st Embodiment. It is a block diagram which shows the detailed structure of the detection apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the large Barkhausen effect. It is a wave form diagram which shows an example of the air signal which generate | occur | produces in a detection coil. It is a wave form diagram which shows an example of the electric signal which generate | occur | produces in the detection coil of the detection apparatus which concerns on embodiment. It is a perspective view which shows schematic structure of the detection apparatus which concerns on 2nd Embodiment. It is a block diagram which shows the detailed structure of the detection apparatus which concerns on 2nd Embodiment. It is a figure which shows an example of the frequency characteristic of the filter circuit which concerns on 2nd Embodiment. It is a figure which shows an example of the signal output from a differential amplifier.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
1A to 1C are plan views showing the configuration of the detection apparatus according to the embodiment of the present invention. 1A is a top view of the detection device, FIG. 1B is a front view of the detection device, and FIG. 1C is a side view of the detection device.

  The detection device detects whether or not a tag embedded with a magnetic material having a large Barkhausen effect has passed, and issues an alarm when the tag passes.

  The detection device detected two security gates 10, a support base 14 that supports the two security gates 10 in parallel, a control unit 20 that controls the operation of each security gate 10, and the passage of a tag. A warning light 40 that emits light in some cases. The control unit 20 may be provided inside one of the two security gates 10, may be provided in the support base 14, or may be provided separately from the two security gates 10. Good. The warning light 40 may also be provided in either of the two security gates 10 or may be provided separately from the two security gates 10. In the detection device according to the present embodiment, an adjustment member 16 is provided between the security gate 10 and the support base 14 so that the height of the security gate 10 can be adjusted.

  In the detection device, the space between the two security gates 10 is a detection region for detecting a tag. For example, if an article 41 that should not be taken out from a certain space such as an important document is attached with a tag and the security gate 10 is installed at the entrance of the space, the important document with the tag is removed from the space. A warning light 40 is turned on when the document is taken out, and the taking out of important documents is restricted.

  Here, each security gate 10 includes an exciting coil 11 that generates an alternating magnetic field, and detection coils 12 and 13 that are induced by an external magnetic field and through which a current flows. In the present embodiment, the detection coils 12 and 13 are provided symmetrically in the horizontal direction.

  FIG. 2 is a diagram illustrating a detailed configuration of the detection device according to the first embodiment.

  The security gate 10 includes an excitation coil 11, detection coils 12 and 13, an excitation current supply unit 15 that supplies an excitation current for generating a magnetic field in the excitation coil 11, and an analog that is induced in the detection coils 12 and 13. A signal processing unit 21 that converts an electrical signal into a digital signal and a controller 22 that detects passage of a tag based on the converted digital signal are provided.

  Here, the detection coils 12 and 13 are arranged so that they are adjacent to each other on the plane and the winding directions are reversed. One end of the detection coil 12 is connected to the signal processing unit 21, and the other end of the detection coil 12 is connected to one end of the detection coil 13. The other end of the detection coil 13 is connected to the signal processing unit 21.

  The controller 22 includes a microcomputer and includes a CPU (Central Processing Unit) 22A, a ROM (Read Only Memory) 22B, a RAM (Random Access Memory) 22C, a nonvolatile storage unit 22D including a flash memory, Control overall operation.

  The exciting current supply unit 15 supplies an alternating current to the exciting coil 11 under the control of the controller 22.

  The exciting coil 11 is excited by being supplied with an alternating current from the exciting current supply unit 15, and generates an alternating magnetic field in which the magnetic field changes like a sine wave. In the detection coils 12 and 13, an alternating current is induced by the alternating magnetic field generated by the exciting coil 11, and when a tag including a magnetic material having a large Barkhausen effect exists in the alternating magnetic field, A pulse current is generated by the inversion.

  3A and 3B are diagrams for explaining the large Barkhausen effect.

  The large Barkhausen effect is obtained from a BH characteristic shown in FIG. 3A, that is, from a material having a relatively small hysteresis loop and a relatively small coercive force (Hc), for example, Co—Fe—Ni—B—Si. This is a phenomenon in which steep magnetization reversal occurs when an amorphous magnetic material is placed in an alternating magnetic field. A magnetic material having a large Barkhausen effect undergoes magnetization reversal when a magnetic field having a strength greater than the positive and negative strengths is applied. For this reason, when an excitation current is passed through the excitation coil 11 to generate an alternating magnetic field and a tag is placed in the alternating magnetic field, a pulsed current is generated in the detection coils 12 and 13 disposed near the tag at the time of magnetization reversal. Flowing.

  For example, when the alternating magnetic field shown in the upper part of FIG. 3B is generated by the exciting coil, a pulse current as shown in the lower part of FIG. 3B flows through the detection coils 12 and 13.

  However, the currents in the detection coils 12 and 13 include not only this pulse current but also an alternating current induced by an alternating magnetic field. In the present embodiment, in order to cancel the alternating current induced in the detection coils 12 and 13, the detection coils 12 and 13 are connected so that the winding directions are reversed.

  As a magnetic material (magnetic material) contained in the tag, generally, a permanent magnet, for example, a rare earth-based neodymium (Nd) -iron (Fe) -boron (B) as a main component, samarium (Sm)- Cobalt (Co) as the main component, Alnico aluminum (Al) -Nickel (Ni) -Cobalt (Co) as the main component, Ferrite-based barium (Ba) or strontium (Sr) and iron oxide There are those containing (Fe2O3) as a main component, soft magnetic materials, oxide soft magnetic materials, and the like. As the magnetic material causing the large Barkhausen effect, it is preferable to use an amorphous magnetic material whose basic composition is Fe—Co—Si or Co—FeNi.

  The shape of the magnetic material is not particularly limited as long as it is suitable for causing the large Barkhausen effect. However, in order to cause the large Barkhausen effect, a length corresponding to the cross-sectional area is required, and thus a linear shape (wire shape) or a strip shape is preferable, and a wire shape is more preferable.

  When the magnetic material is in the form of a wire, it is preferable that the minimum diameter necessary for causing the large Barkhausen effect is 10 μm or more. Further, the maximum diameter is not particularly limited. For example, when a magnetic material is mixed into a recording medium (paper) and integrated with the recording medium (paper), the diameter is suppressed in order to prevent the magnetic material from being exposed on the surface of the recording medium. Depends on the thickness of the recording medium. For example, in the case of a recording medium having a thickness of about 90 μm, it is preferably 60 μm or less, more preferably 50 μm or less.

  The length of the magnetic material is preferably 5 mm or more as the minimum length necessary for causing the large Barkhausen effect. The maximum length of the amorphous magnetic material is not particularly limited so long as it is not exposed from the recording medium when it is contained inside, but is preferably 430 mm or less.

  The signal processing unit 21 (see FIG. 2) includes a differential amplification amplifier 31 that amplifies and outputs the differential of both-end voltages (signal voltages output from the other end of the detection coil 12 and one end of the detection coil 13), A waveform shaping circuit 32 for shaping the waveform of the signal output from the differential amplifier 31; and an analog / digital converter (ADC) 34 for converting the signal shaped by the waveform shaping circuit 32 into a digital signal. Yes. The signal processing unit 21 extracts a band pass filter that extracts and outputs a signal in a predetermined band corresponding to a pulse current generated by magnetization reversal of the magnetic material from the input signal between the waveform shaping circuit 32 and the ADC 34. You may make it provide further.

  The controller 22 determines whether or not the level of the digital signal output from the ADC 34 exceeds a threshold value, or determines whether or not the waveform shape of the digital signal is a waveform shape due to magnetization reversal of the magnetic material by a cross correlation method or the like. By determining whether or not the tag has passed, the warning lamp 40 is turned on when the tag has been passed.

  Next, tag detection by the detection apparatus according to the present embodiment will be described.

  When detecting the tag, the controller 22 controls the excitation current supply unit 15 to supply an alternating current to the excitation coil 11.

  Thereby, the exciting coil 11 generates an alternating magnetic field. An alternating current is induced in the detection coils 12 and 13 by an alternating magnetic field generated by the excitation coil 11. In addition, when the article 41 to which the tag is attached passes between the security gates 10 in the detection coils 12 and 13, a pulse current is generated by the magnetization reversal of the magnetic material included in the tag.

  The alternating currents induced by the alternating magnetic fields in the detection coils 12 and 13 are connected to each other so that the winding directions of the detection coils 12 and 13 are reversed. The pulse current induced by the magnetization reversal is converted into a digital signal by the signal processing unit 21.

  The controller 22 detects whether or not the tag has passed based on the waveform data indicated by the input digital signal. When the tag is detected to pass, the controller 22 illuminates the warning lamp 40 to detect that the tag has passed. Notice.

  Incidentally, if a magnetic material (iron-based material) is included in the installation surface (floor surface) on which the security gate 10 is installed, when an alternating magnetic field is generated from the excitation coil 11, as shown in FIG. The installation surface is magnetized by the magnetic field generated from the noise, and noise from the installation surface is detected by the detection coils 12 and 13, making it difficult to detect the pulse current that should be detected.

  Therefore, in the detection device according to the present embodiment, the support base 14 is formed of a nonmagnetic metal material. By forming the support base 14 with a nonmagnetic metal material in this way, the alternating magnetic field generated from the exciting coil 11 is consumed as an eddy current in the support base 14, and the alternating magnetic field is difficult to reach the installation surface. As a result, as shown in FIG. 5, noise from the installation surface due to the excitation magnetic field is difficult to be incident on the detection coils 12 and 13, so that the article 41 to which the magnetic material is added can be discriminated with high accuracy. In addition, although current is generated in the detection coils 12 and 13 at the same cycle as the alternating magnetic field due to the eddy current generated in the support base 14 by the alternating magnetic field, the detection coils 12 and 13 are arranged in the horizontal direction in this embodiment. Since the detection coils 12 and 13 are symmetrical with respect to the support base 14 and are connected so that the winding directions of the detection coils 12 and 13 are reversed, they cancel each other.

As the non-magnetic metal material used in the support base 14, for example, non-magnetic stainless steel, the material of specific permeability 1.1, such as SUS316 or SUS304 to obtain a higher effect. Materials such as non-magnetic stainless steel and aluminum may be appropriately selected depending on cost, strength, etc. In particular, non-magnetic stainless steel is desirable in order to lower the center of gravity and avoid stability and to ensure stability. Furthermore, the two security gates 10 and the support base 14 are integrally formed by screwing or the like, so that the fulcrum distance at the time of the fall becomes larger, so that the fall than the case where one excitation detection antenna is attached to the installation base. It becomes a structure difficult to do.

[Second Embodiment]
Next, a second embodiment will be described.

  FIG. 6 shows a detection apparatus according to the second embodiment. Note that the same portions as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the security gate 10 according to the present embodiment, the detection coils 12 and 13 are provided symmetrically in the vertical direction.

  FIG. 7 is a diagram illustrating a detailed configuration of the detection apparatus according to the second embodiment. Note that the same portions as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The signal processing unit 21 further includes a filter circuit 33 that performs filtering to remove noise having the same frequency as the frequency of the alternating current that generates an alternating magnetic field from the signal shaped by the waveform shaping circuit 32.

  FIG. 8 shows an example of the frequency characteristic of the filter circuit 33. The filter circuit 33 according to the present embodiment has a negative peak at the same frequency as the frequency of the alternating current that generates the alternating magnetic field, and removes noise generated in synchronization with the frequency of the alternating magnetic field.

  Here, when an alternating magnetic field is generated from the exciting coil 11 when detecting the tag, an eddy current generated in the support base 14 is generated in the support base 14 by the alternating magnetic field. Current is generated in the detection coils 12 and 13 by this eddy current, but in this embodiment, the detection coils 12 and 13 are arranged in the vertical direction, and the distance from the support base 14 is different. The amount of current generated in the coils 12 and 13 is different. For this reason, in the signal output from the differential amplifier 31, as shown in FIG. 9, noise having the same frequency as the frequency of the alternating magnetic field is generated together with the pulse current. The filter circuit 33 performs filtering to remove noise synchronized with the frequency of the alternating magnetic field. Thereby, noise generated by the eddy current from the support base 14 is removed.

  In each of the above embodiments, the case where the entire support base 14 is formed of a nonmagnetic metal material as a shielding portion that shields an alternating magnetic field has been described. However, the present invention is not limited to this. For example, a metal layer made of a non-magnetic metal may be provided on the support base 14 as a shielding part to suppress the alternating magnetic field from reaching the installation surface.

  The range in which the shielding portion is provided needs to cover at least a range where the noise detected by the detection coils 12 and 13 due to the alternating magnetic field acting on the installation surface is greater than a predetermined allowable level. It is preferable to cover a range where noise from the installation surface due to the alternating magnetic field is smaller than the pulse current generated by the magnetic field reversal. The shielding part is not necessarily provided on the surface of the support base. If there is no magnetic body at the top, it may be inside the support base.

  Moreover, although each said embodiment demonstrated the case where the filter circuit 33 was provided when the detection coils 12 and 13 were arrange | positioned along with the vertical direction, this invention is not limited to this. For example, even when the detection coils 12 and 13 are arranged side by side in the horizontal direction and the detection coils 12 and 13 are symmetrical with respect to the support base 14 as in the first embodiment, the detection coil 12 is caused by eddy current. , 13 may generate noise that is synchronized with the frequency of the alternating magnetic field in the signal output from the differential amplifier 31. For this reason, the filter circuit 33 may be provided also in the first embodiment.

  Further, in each of the above embodiments, the case where the detection coils 12 and 13 are connected so that the winding directions are reversed and the alternating currents induced by the alternating magnetic field in the detection coils 12 and 13 are mutually canceled is described. It is not limited to this. For example, after the analog signals of the detection coils 12 and 13 are converted into digital signals, the difference may be obtained to cancel the alternating current.

  In the present invention, the support base may be provided with more than two antenna portions.

  Further, the present invention is not limited to the above-described embodiment, and it is needless to say that the present invention can also be applied to a design modified within the scope of the claims.

DESCRIPTION OF SYMBOLS 10 Security gate 11 Excitation coil 12, 13 Detection coil 14 Support stand 33 Filter circuit

Claims (6)

Two antenna units provided with an excitation coil that generates an alternating magnetic field that causes magnetization reversal in the magnetic material and a detection coil that detects a change in the magnetic field due to magnetization reversal of the magnetic material;
A shield made of a non-magnetic metal that shields propagation of the alternating magnetic field to the installation surface so that noise detected by the detection coil is less than a predetermined allowable level due to the alternating magnetic field acting on the installation surface. Are provided at least in part , and are formed integrally with the two antenna units in a state where the two antenna units are separated from each other by a predetermined distance , and are supported from the bottom surfaces of the two antenna units. A plate-shaped support base;
A detection device comprising: The antenna unit is provided with two detection coils, and is connected in series so that alternating currents induced in the alternating magnetic field are in opposite phases,
The detection device according to claim 1, further comprising a removing unit that removes noise having the same frequency as the frequency of an alternating current that generates the alternating magnetic field from an electric signal flowing in a series circuit in which the two detection coils are connected in series. The detection device according to claim 1, wherein the allowable level is a current value of a pulse current generated in the detection coil by the magnetization reversal. The detection device according to claim 1, wherein the entire support base is formed of a nonmagnetic metal.   The antenna unit is provided with two detection coils arranged in parallel to the surface of the support base, and connected in series so that alternating currents induced by an alternating magnetic field have opposite phases to each other. The detection device according to any one of claims 1 to 4.   The detection device according to claim 1, wherein the shielding portion is made of nonmagnetic stainless steel.

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