JP4602811B2 - Tag detection device - Google Patents

Description

  The present invention relates to a tag detection device that monitors the movement of an article by a tag attached to a product or the like and prevents the theft of the article.

  There is a tag detection device that attaches a magnetic tag to an article to prevent the article from being stolen. FIG. 5 shows a configuration of a tag detection device 40 conventionally used. The tag detection device 40 presets the excitation coil 20, the receiving coil 24, the processing means 16 for extracting only the harmonic component of the received signal from the receiving coil 24, and the amplitude of the voltage signal of the extracted harmonic component. And a determination unit 42 that determines that a magnetic tag that has not expired is present if the signal is larger than the threshold and is a signal larger than the threshold. The term “revocation” as used here refers to the case where goods are purchased properly and taken out of a store or the like without any problem, and a strong magnetic field is applied to the magnetic tag using a revocation device, causing the large Barkhausen effect described later. Say not to state. It is determined whether or not the money item has been properly paid by determining the presence or absence of an expired magnetic tag.

  The exciting coil 20 and the like are provided in the gate. In general, the gate is formed by opposing two plates or the like with a predetermined interval. An exciting coil 20 or the like is provided in each plate or the like. The gate width is, for example, about 900 mm, and allows an article to which a tag is attached to pass therethrough. There are two receiving coils 24, and the receiving coil 24 is provided inside the exciting coil 20, as shown in FIG. The number of turns of the exciting coil 20 and the receiving coil 24 is arbitrary. In order to perform differential amplification, which will be described later, the number of turns of the two receiving coils 24 is the same.

  The magnetic tag is made of amorphous metal. The magnetization reversal phenomenon of a magnetic tag made of amorphous metal in an alternating magnetic field excited at a predetermined frequency is a phenomenon called a large Barkhausen effect. The large Barkhausen effect is a high permeability and low coercivity metal. When the external magnetic field exceeds a certain threshold value inherent to the metal, a reverse magnetic domain is suddenly formed in the metal, and the domain wall moves to move the metal. This is a phenomenon in which the magnetization reversal ends. A magnetic tag using an amorphous metal having high permeability and low coercivity easily causes a large Barkhausen effect (FIG. 7). The change in the magnetic field due to the sudden magnetization reversal due to the large Barkhausen effect is a harmonic component of a specific frequency and is received by the receiving means 14 together with the predetermined frequency component of the alternating magnetic field. The large Barkhausen effect can be prevented from being generated by a defeater.

  The processing means 16 includes a differential amplifier circuit 26, a high-pass filter 28, a low-pass filter 30, an AC amplifier circuit 32, and the like. The differential amplifier circuit 26 is a circuit that takes and amplifies the potential difference between the received signals from the two receiving coils 24. FIG. 8 is a graph showing an example of differential amplification. In order from the top, the differentially amplified signal, the reception signal of one of the two reception coils 24, the reception signal of the other reception coil 24, and the other reception coil 24 of FIG. Received signal. The vertical axis of the graph is 2 V / div, and the horizontal axis is 1 msec / div. Each waveform has an amplitude center of 0V.

  The high pass filter 28 and the low pass filter 30 may be replaced with band pass filters. In the processing means 16, a band pass filter and an AC amplifier circuit 32 are connected in multiple stages.

  The processing means 16 obtains and amplifies the difference between the received signal potentials of the two receiving coils 24 by differential amplification. Only the harmonic components associated with the large Barkhausen effect are extracted from the difference received signal by a circuit including the high-pass filter 28 and the low-pass filter 30. If there is a revoked magnetic tag, or if there is no magnetic tag, the received signal is almost 0V as shown in FIG. 9A, and if there is a magnetic tag that has not been revoked, it is large as shown in FIG. 9B. The voltage due to Barkhausen jump appears.

  An arithmetic unit 46 such as a microcomputer compares the amplitude of the signal due to the extracted harmonic component with an amplitude threshold value stored in advance in the storage means 44. If the signal is larger than the threshold value, the magnetic tag is not expired. Is determined to be present (Patent Document 1). For example, as shown in FIG. 10, if there is an invalid magnetic tag or if there is no magnetic tag, only noise having the same frequency as the signal to be detected appears. Further, as shown in FIG. 11, when there is a magnetic tag that has not expired at 100 mm from the receiving coil, a signal to be detected appears. Since this signal is larger than the noise, there is no possibility that the tag detection device 40 malfunctions.

JP-A-8-235460 (Claim 5 or page 6)

  However, when the distance between the magnetic tag and the receiving means 14 is large, the magnitude of the change in the magnetic field due to the large Barkhausen effect becomes smaller in inverse proportion to the square of the distance and is received by the receiving means 14. The signal amplitude of the harmonic component generated by the magnetic tag has a magnitude equal to or less than that of the disturbance noise, and cannot be detected by a method for comparison with the threshold value. For example, when there is a magnetic tag that has not expired at a distance of 500 mm from the receiving coil as shown in FIG. 12, the noise becomes larger.

  In addition, when disturbance noise with a value larger than the threshold value occurs, it is erroneously determined that there is a magnetic tag that has not been revoked even if there is a revoked magnetic tag or there is no magnetic tag. .

  As described above, the method of comparing and determining the signal amplitude of the harmonic component by the magnetic tag with a preset threshold has a problem in that the receivable distance is limited and erroneous detection occurs.

  Accordingly, an object of the present invention is to provide a tag detection device in which malfunction does not easily occur even when a magnetic tag is separated from a receiving coil 24.

  The tag detection device of the present invention is a tag detection device for detecting a magnetic tag made of amorphous metal attached to an article passing through an inspection region, and an AC magnetic field having a strength exceeding the coercive force of the magnetic tag. Exciting means for applying, receiving means for detecting a change in the magnetic field of the inspection region and outputting it as a received signal, processing means for extracting a voltage waveform caused by magnetization reversal of the magnetic tag from the received signal, and Means for converting the voltage waveform generated due to magnetization reversal into a rectangular wave train; means for storing a predetermined number of rectangular wave trains as a rectangular wave train number set value; and the number of converted rectangular wave trains And means for comparing the stored rectangular wave train number setting value.

  Means is provided for determining that there is a magnetic tag that has not been revoked when the number of rectangular wave trains is greater than the set value of the number of rectangular wave trains.

  The means for converting into the rectangular wave train is means for converting a voltage equal to or higher than a threshold value into a rectangular wave.

  According to the present invention, since the presence or absence of the magnetic tag is determined based on the number of rectangular wave trains, even if the distance between the magnetic tag and the receiving means is increased, the magnetic type is surely not affected by disturbance noise. The tag can be detected. Further, even when there is no expired magnetic tag or magnetic tag, it is no longer possible to determine that there is no expired magnetic tag.

  A tag detection apparatus according to the present invention will be described with reference to the drawings. The tag detection device is a gate-shaped device installed at the entrance of a store that sells or rents articles such as pharmacies, bookstores, jewelry precious metals, glasses, videos, CDs, etc. The tag information at the time of passing through the (detection area) is read, and it is determined whether or not the money has been properly paid. There are two types of tag information reading methods: radio wave type, electromagnetic wave type, and magnetic type. The present invention deals with a tag by a magnetic reading method.

  The magnetic tag is made of an amorphous metal mainly composed of iron, nickel, cobalt, molybdenum or the like. Magnetic tags including amorphous metal include labels and fasteners.

  As shown in FIG. 1, the tag detection apparatus 10 according to the present invention detects the change of the magnetic field in the inspection area by using the excitation means 12 for applying an alternating magnetic field having a strength exceeding the coercive force of the magnetic tag, and as a received signal. The receiving means 14 for outputting, the processing means 16 for extracting the voltage waveform of the harmonic component caused by the magnetization reversal of the magnetic tag from the received signal, and the determining means 18 for determining the presence or absence of the magnetic tag that has not expired. And comprising.

  The exciting means 12, the receiving means 14, the processing means 16, and the judging means 18 are provided at a gate installed at an entrance of a store or the like. The gate has two plates facing each other as in the conventional case, and excitation means 12 is provided on each plate. The area between the two plates is a detection area.

  The excitation means 12 includes an excitation coil 20 and an excitation power source 22 for generating a magnetic field in the excitation coil 20. The excitation power source 22 generates an AC voltage composed of a sine wave having a predetermined frequency in order to generate a magnetic field in the excitation coil 20. The predetermined frequency is about 100 to 400 Hz, preferably about 200 to 400 Hz, and most preferably about 300 Hz. The current flowing through the exciting coil 20 is about 0.5 to 2 A, preferably about 1.0 to 2 A. The exciting coil generates an alternating magnetic field whose strength exceeds the coercive force of the magnetic tag. The magnetic field strength exceeding the coercive force of the magnetic tag is about several tens to several hundreds of milligauss.

  The receiving means 14 includes a receiving coil 24. Two receiving coils 24 are provided for one exciting coil 20. The number of turns of the two receiving coils 24 is the same. The reception coil 24 detects a change in the alternating magnetic field in the detection region and outputs it as a reception signal.

  The processing means 16 comprises an analog circuit that processes the received signal. The analog circuit extracts a waveform generated due to the magnetization reversal of the magnetic tag. Specific circuits include a differential amplifier circuit 26, a high-pass filter 28, a low-pass filter 30, an AC amplifier circuit 32, and the like as described in the prior art. The voltage waveform generated due to the magnetization reversal is a waveform in a specific frequency band of about 3000 to 7000 Hz, preferably about 4000 to 6000 Hz.

  The judging means 18 is a means 34 for converting a voltage waveform generated due to magnetization reversal into a rectangular wave train, a means 36 for storing a predetermined number of rectangular wave trains as a rectangular wave train number set value, and Means for comparing the number of rectangular wave trains with the stored set value of the number of rectangular wave trains. The rectangular wave train is a sequence of rectangular waves, and the number of rectangular wave trains is the number of rectangular waves in the rectangular wave train.

  The means 34 for converting into a rectangular wave train is a circuit that saturates a voltage equal to or higher than a threshold value and converts it into a rectangular wave. As described in the related art, since the voltage due to noise may be higher than the voltage due to the influence of the magnetic tag, the threshold value is generated when the magnetic tag is farthest from the receiving coil 24 in the inspection region. Determine based on the voltage to be used. As shown in FIG. 3 and FIG. 4, the voltage exceeding the threshold and the noise are saturated to a certain voltage and converted into a rectangular wave with a flat apex.

  The set value of the number of rectangular wave trains is the number of rectangular wave trains per unit time when a voltage waveform generated by noise is converted into a rectangular wave even when there is no expired magnetic tag or magnetic tag. The means 36 for storing the rectangular wave train number setting value is a memory used in a computer.

  The means for comparison is an arithmetic device 38 such as a microcomputer or a sequencer. The arithmetic device 38 includes means for determining that there is a magnetic tag that has not expired when the number of rectangular wave trains per unit time is larger than the set value of the number of rectangular wave trains. Since a rectangular wave due to noise is always generated, if a larger number of rectangular waves than the set value of the number of rectangular wave trains are detected, it can be seen that there is a magnetic tag that has not expired.

  FIG. 2 shows a rectangular wave train when there is no magnetic tag. FIG. 3 and FIG. 4 show a rectangular wave train when there are magnetic tags that are not expired at 100 mm and 500 mm from the receiving means. Even if the magnetic tag that has not been revoked is located 500 mm from the receiving coil, it can be seen that there is a magnetic tag that has not been revoked because the number of rectangular wave trains is increased as compared with FIG.

  As described above, the present invention can detect a magnetic tag far from the receiving means 14 without being affected by noise. Further, compared with a radio wave type tag detection device, there is no influence of radio waves of a mobile phone and the like, which is advantageous for tag detection.

  As mentioned above, although this invention was demonstrated, this invention is not limited to the above-mentioned embodiment. In addition, the present invention can be carried out in a mode in which various improvements, modifications, and changes are added based on the knowledge of those skilled in the art without departing from the gist thereof.

It is a figure which shows the structure of the tag detection apparatus of this invention. It is a figure which shows a rectangular wave train when there is no magnetic tag. It is a figure which shows a rectangular wave train when the magnetic tag which is not expired exists in the place of 100 mm from a receiving coil. It is a figure which shows a rectangular wave train when the magnetic tag which has not expired exists in the place of 500 mm from a receiving coil. It is a figure which shows the structure of the conventional tag detection apparatus. It is a figure when an exciting coil and a receiving coil are stored in the gate. It is a figure which shows the hysteresis curve of an amorphous metal. It is a graph which shows differential amplification, and is the signal differentially amplified from the top, the reception signal of one reception coil of two reception coils, and the reception signal of the other reception coil. It is a figure which detects the voltage by a large Barkhausen jump, (a) is a figure when there is no magnetic tag, (b) is a figure when there is a magnetic tag. It is a figure which shows the noise when there is no magnetic tag. It is a figure which shows a reception result when the magnetic type tag which has not expired exists in the place of 100 mm from a receiving coil. It is a figure which shows a reception result when the magnetic tag which has not expired exists in the place of 500 mm from a receiving coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 40: Tag detection apparatus 12: Excitation means 14: Reception means 16: Processing means 18, 42: Determination means 20: Excitation coil 22: Excitation power supply 24: Reception coil 26: Differential amplification circuit 28: High pass filter 30: Low pass Filter 32: AC amplifier circuit 34: Circuit for converting into rectangular wave train 36: Means 38 for storing the set number of rectangular wave trains 46, 46: Arithmetic unit 44: Means for storing amplitude threshold

Claims (3)

A tag detection device for detecting a magnetic tag made of amorphous metal attached to an article passing through an inspection region,
Excitation means for applying an alternating magnetic field having a strength exceeding the coercive force of the magnetic tag;
Receiving means for detecting a change in the magnetic field of the inspection region and outputting as a received signal;
Processing means for extracting a voltage waveform generated due to magnetization reversal of the magnetic tag from the received signal;
Means for converting the voltage waveform generated due to magnetization reversal into a rectangular wave train;
Means for storing a predetermined number of rectangular wave trains as a rectangular wave train number setting value;
Means for comparing the converted number of rectangular wave trains with the stored rectangular wave train number setting value;
A tag detection device comprising: The tag detection device according to claim 1, further comprising means for determining that there is a magnetic tag that has not been revoked when the number of rectangular wave trains is larger than a set value of the number of rectangular wave trains. The tag detection device according to claim 1 or 2, wherein the means for converting into a rectangular wave train is means for converting a voltage equal to or higher than a threshold value into a rectangular wave.

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