Anti-theft system

Abstract

An acoustic magnetic (AM) anti-theft system is provided that can widen the allowable range of the tag's resonance frequency. [Solution] The acoustomagnetic anti-theft system includes a transmitter 20, a tag 10, a receiver 30, and a tag detection processor 42. The transmitter 20 transmits a burst signal during a transmission period. The tag 10 resonates with the burst signal transmitted from the transmitter 20 and outputs a ringing down signal. The receiver 30 receives the ringing down signal during a reception period following the transmission period. The tag detection processor 42 detects the tag 10 based on the ringing down signal received by the receiver 30. The transmission period includes a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted at regular intervals.

Description

[Technical field]

[0001] The present invention relates to an acoustomagnetic anti-theft system. [Background technology]

[0002] 2. Description of the Related Art Known examples of anti-theft systems include security systems that perform two types of Electronic Article Surveillance (EAS): a radio-frequency (RF) system and an acousto-magnetic (AM) system.

[0003] An RF-type anti-theft system includes a transmitter including an oscillator that oscillates an RF signal (e.g., 8.2 MHz) and a transmitting coil, and a receiver including a sensor coil. In this type of anti-theft system, the voltage change caused by the RF security label attached to the product is small, but the signal from the RF security label can be detected very clearly.

[0004] A feature of RF anti-theft systems is that the frequency of the high-frequency magnetic field from the transmitting coil is not fixed, but is swept continuously. Usually, the frequency is swept from (8.2MHz-10%) to (8.2MHz+10%). When the oscillating frequency of the sweeping transmitter matches the resonant frequency of the LC resonant circuit in the RF security label, the RF security label starts to oscillate, and a clear voltage dip (DIP) occurs in the sensor coil that detects the signal from the RF security label.

[0005] Normally, the management of the resonant frequency of RF security labels is heavily influenced by the quality control of the manufacturing process. However, by using the sweep method over a wide frequency range (8.2MHz±10%) of the excitation magnetic field as described above, the allowable resonant frequency range of RF security labels is as wide as 8.2MHz±10%, so strict quality control is not required, and as a result, the cost of RF security labels can be reduced.

[0006] On the other hand, the wide tolerance range of the resonant frequency as described above causes other technical problems. For example, if products such as cable coils and LAN cables sold in stores have a resonant frequency within the range of 8.2 MHz ±10%, false alarms may occur when these products pass near the sensor coil.

[0007] In contrast, AM anti-theft systems operate using a pulse listen method. In this method, the zero crossing point of a 50Hz or 60Hz commercial frequency power signal is used as the trigger timing for control, and a certain time after the zero crossing point, the transmitter's transmission window (TX window) (usually about 1.4ms to 2.0ms wide) is opened, during which the transmitter transmits a 58kHz burst signal. Shortly after this (usually about 0.2ms later), the receiver's reception window (RX window) is opened for a certain time (usually about 2.0ms to 5.0ms), during which the response signal from the tag is detected.

[0008] In the AM anti-theft system, a label tag having a resonant frequency in the 58 kHz band (see, for example, Patent Document 1 below) or a hard tag consisting of an LC resonant circuit is used. When these tags receive a 58 kHz burst signal during a burst signal transmission period when the transmitter's transmission window is open, they store excitation energy and output a ringing down signal at the tag's resonant frequency for a certain period after the burst signal transmission period ends. During a reception period when the receiver's reception window is open, the receiver receives an attenuated radio wave (ringing down signal) coming from the tag, and determines whether the signal is from a tag based on the time interval, frequency, and attenuation of the ringing down signal, and if it is determined to be from a tag, an alarm is issued.

[0009] The label tag used in AM anti-theft systems is made of multiple thin amorphous metal plates arranged in parallel, and is designed to resonate with radio waves of 58 kHz (see, for example, Patent Document 1 below). On the other hand, in hard tags used in AM anti-theft systems, an LC resonant circuit is formed by connecting a capacitor (C) to a ferrite core coil (L), and the resonant frequency is set to 58 kHz.

[0010] The quality control standard for AM anti-theft systems is a tag resonance frequency of 58.0kHz ±0.52% (58.0kHz ±0.3kHz). This standard guarantees that when a transmitter transmits a 58.0kHz burst signal, the distance from the receiver at which the receiver can detect a tag within the allowable resonance frequency range (tag sensitivity) is at least 70% of the maximum tag sensitivity for a resonance frequency of 58.0kHz.

[0011] A comparison of RF and AM systems is as follows: First, the price of transmitters and receivers used to be cheaper for RF systems, but now the price of AM systems is about the same as that of RF systems. As for the price of tags, RF systems have traditionally been cheaper, and inexpensive AM tags are desired.

[0012] Regarding the control standard for the tag's resonant frequency, the RF method has a wide tolerance range of 8.2 MHz ±10%, whereas the AM method has a tolerance of 58.0 kHz ±0.52% (58.0 kHz ±0.3 kHz) as mentioned above, meaning that the tolerance range for the resonant frequency is much narrower than that of the RF method, resulting in excessive quality control costs.

[0013] As for stability against false alarms, the RF system is prone to false alarms because its excitation frequency (8.2MHz) is the same as marine radio and it is susceptible to the influence of products (cable coils, etc.) whose resonant frequency is 8.2MHz±10%. On the other hand, the AM system is more stable than the RF system and almost never causes false alarms. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] U.S. Pat. No. 4,510,489 Summary of the Invention [Problem to be solved by the invention]

[0015] As mentioned above, the prices of transmitters and receivers are becoming similar for RF and AM systems. Therefore, if the price of AM tags can be reduced, AM anti-theft systems, which are less likely to produce false alarms and more stable, may become mainstream.

[0016] Regarding this point, the variation in the resonant frequency of AM tags has been greatly improved at present, so if the tolerance range of the resonant frequency of AM tags could be expanded from the current 58kHz ±0.5% to around 58kHz ±1.0%, it would be possible to reduce the price of AM tags by 40 to 60%.

[0017] The present invention has been made in view of the above circumstances, and has an object to provide an acoustomagnetic (AM) anti-theft system that is capable of widening the allowable range of the tag's resonance frequency. [Means for solving the problem]

[0018] (1) A first anti-theft system according to the present invention is an acousto-magnetic anti-theft system, comprising a transmitter, a tag, a receiver, and a tag detection processor. The transmitter transmits a burst signal during a transmission period. The tag resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal. The receiver receives the ringing down signal during a reception period following the transmission period. The tag detection processor detects the tag based on the ringing down signal received by the receiver. The system includes a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted at regular intervals.

[0019] With this configuration, a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted are included at regular intervals, making it possible to widen the allowable range of the tag's resonant frequency and reducing the price of the tag.

[0020] (2-1) A second anti-theft system according to the present invention is an acousto-magnetic anti-theft system, comprising a transmitter, a tag, a receiver, and a tag detection processor. The transmitter transmits a burst signal during a transmission period. The tag resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal. The receiver receives the ringing down signal during a reception period following the transmission period. The tag detection processor detects the tag based on the ringing down signal received by the receiver. Each cycle of a commercial frequency (60 Hz or 50 Hz) power supply includes a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted.

[0021] With this configuration, since each cycle of the commercial frequency power supply includes a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted, it becomes possible to expand the allowable range of the resonant frequency of acoustomagnetic tags from the current 58.0 kHz ±0.5% to at least about 58.0 kHz ±1.0%. If it becomes possible to widen the allowable range of the resonant frequency of tags in this way, it becomes possible to reduce the price of tags.

[0022] (2-2) Each cycle of the commercial frequency power supply may include a transmission period in which a 57.7 kHz burst signal is transmitted, a transmission period in which a 58.0 kHz burst signal is transmitted, and a transmission period in which a 58.3 kHz burst signal is transmitted.

[0023] With this configuration, it becomes possible to detect tags with a wider range of resonant frequencies, approximately 58.0 kHz ±1.0%, based on the combination of transmission period / phase of whether or not a ringing down signal of a certain strength or greater is received from the tag for burst signals of different frequencies transmitted during three transmission periods in each cycle of the commercial frequency power supply.

[0024] (3-1) A third anti-theft system according to the present invention is an acousto-magnetic anti-theft system, and includes a transmitter, a tag, a receiver, and a tag detection processor. The transmitter transmits a burst signal during a transmission period. The tag resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal. The receiver receives the ringing down signal during a reception period following the transmission period. The tag detection processor detects the tag based on the ringing down signal received by the receiver. Every two cycles of the commercial frequency power supply include a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted.

[0025] With this configuration, every two cycles of the commercial frequency power supply include a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted, making it possible to expand the allowable range of the resonance frequency of acoustomagnetic tags from the current 58.0 kHz ±0.5% to at least about 58.0 kHz ±1.5%. If it becomes possible to widen the allowable range of the resonance frequency of tags in this way, the price of tags can be reduced.

[0026] (3-2) Every two cycles of the commercial frequency power supply may include a transmission period for transmitting a 57.25 kHz burst signal, a transmission period for transmitting a 57.55 kHz burst signal, a transmission period for transmitting a 57.85 kHz burst signal, a transmission period for transmitting a 58.15 kHz burst signal, a transmission period for transmitting a 58.45 kHz burst signal, and a transmission period for transmitting a 58.75 kHz burst signal.

[0027] With this configuration, it becomes possible to detect tags with a wider range of resonant frequencies, approximately 58.0 kHz ±1.5%, based on whether a ringing down signal of a certain strength or greater is received from the tag in response to burst signals of different frequencies transmitted during six transmission periods in every two cycles of the commercial frequency power supply.

[0028] (4) The anti-theft system may further include a resonant frequency detection processing unit that causes the transmitter to transmit burst signals of different frequencies in the 57 kHz or 58 kHz band during a transmission period of each cycle over multiple cycles of the commercial frequency power supply, and detects the frequency at which the output of the ringing down signal received by the receiver is the highest as the resonant frequency of the tag. In this case, during the transmission period of each cycle of the commercial frequency power supply after detecting the resonant frequency of the tag, transmission is performed with a transmission pattern including a burst signal of the resonant frequency (fr). The transmission pattern may be a pattern of (fr-0.1 kHz, fr, fr+0.1 kHz) (see Table 4 below).

[0029] According to this configuration, the tag can be detected by detecting the resonant frequency of the tag in advance and transmitting a burst signal of the resonant frequency during the transmission period in each cycle of the commercial frequency power supply thereafter. This makes it possible to avoid the influence of the anti-resonant frequency (see Patent Document 1) on tag detection.

[0030] (5) Phase timing of the transmission period and the reception period may be adjustable with respect to the phase of a commercial frequency power supply.

[0031] According to such a configuration, the detection sensitivity of the tag can be improved by setting the transmission period and the reception period so as to avoid phase timings where there is a lot of environmental noise and the detection sensitivity of the tag is poor.

[0032] (6) The anti-theft system may further include a notification processor that issues an alarm when the strength of the ringing down signal received by the receiver is equal to or greater than a threshold value. In this case, different threshold values ​​may be set for the plurality of reception periods.

[0033] According to this configuration, a different threshold value is set for each of multiple receiving periods, and an alert is issued based on whether the strength of the ringing down signal received by the receiving unit in each receiving period is equal to or greater than the threshold value, thereby making it possible to sensitively detect tags with a wide range of allowable resonance frequencies and issue an alert.

[0034] (7) The tag detection processing unit may detect the tag when a frequency of the ringing down signal received by the receiving unit is within an allowable resonance frequency range.

[0035] According to such a configuration, a tag is detected only when the frequency of the ringing down signal received by the receiver is within the allowable resonance frequency range, thereby improving the accuracy of tag detection. Effect of the Invention

[0036] According to the present invention, it is possible to provide an acoustomagnetic (AM) anti-theft system that can widen the allowable range of the resonance frequency of the tag. [Brief description of the drawings]

[0037] [Figure 1] 1 is a block diagram showing a configuration example of an anti-theft system according to an embodiment of the present invention; [Diagram 2] FIG. 13 is a diagram showing an example of the strength of the ringing down signal output when non-neutralizable tags with different resonant frequencies are excited with a 58.0 kHz burst signal from an AM antenna. [Diagram 3] FIG. 13 is a diagram showing an example of the strength of the ringing down signal output when deactivatable tags with different resonant frequencies are excited with a 58.0 kHz burst signal from an AM antenna. [Figure 4] FIG. 13 is a diagram showing the relationship between the strength of the ringing down signal and the sensitivity of the tag. [Diagram 5] FIG. 2 is a diagram for explaining a first embodiment of the operation timing of the anti-theft system. [Figure 6A] FIG. 2 is a diagram for explaining the allowable range of the resonant frequency of the tag 10 in the first embodiment, showing the case where the resonant frequency of the tag is 57.4 kHz to 57.6 kHz. [Figure 6B] FIG. 1 is a diagram for explaining the allowable range of the resonant frequency of the tag 10 in the first embodiment, showing the case where the resonant frequency of the tag is 57.7 kHz to 57.9 kHz. [Figure 6C] FIG. 2 is a diagram for explaining the allowable range of the resonant frequency of the tag 10 in the first embodiment, showing the case where the resonant frequency of the tag is 58.0 kHz. [Figure 6D] FIG. 2 is a diagram for explaining the allowable range of the resonant frequency of the tag 10 in the first embodiment, showing the case where the resonant frequency of the tag is 58.1 kHz to 58.3 kHz. [Figure 6E] FIG. 2 is a diagram for explaining the allowable range of the resonant frequency of the tag 10 in the first embodiment, showing the case where the resonant frequency of the tag is 58.4 kHz to 58.6 kHz. [Figure 7] FIG. 11 is a diagram for explaining a second embodiment of the operation timing of the anti-theft system. [Figure 8] FIG. 13 is a block diagram for explaining a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] 1. Overall configuration of the anti-theft system 1 is a block diagram showing an example of the configuration of an anti-theft system according to an embodiment of the present invention. This anti-theft system is a security system that performs Acousto-Magnetic (AM) type Electronic Article Surveillance (EAS), and includes a tag 10, a transmitter 20, a receiver 30, a controller 40, and a speaker 50. The transmitter 20 and receiver 30 are installed at the entrance or exit of a store.

[0039] The tag 10 is a label tag attached to a product that is to be monitored to prevent theft. The label tag 10 used in the AM-type anti-theft system has a structure in which multiple thin plates made of amorphous metal are arranged in parallel, and has a magnet inside. However, the tag 10 is not limited to a label tag, and may be a hard tag that configures an LC resonant circuit with a capacitor and a magnetic coil with a wire wound around a ferrite core.

[0040] If the magnetic force of the magnet inside the tag 10 is erased at a store's cash register or the like, the tag 10 is deactivated and cannot be detected by the receiving unit 30. In other words, the tag 10 attached to an item before purchase is activated, and if an attempt is made to take the item out of the store, the tag 10 is detected by the receiving unit 30 and an alarm is sounded. However, after the item is purchased, the tag 10 is deactivated at a cash register or the like, making it possible to take the item out of the store without the tag 10 being detected by the receiving unit 30.

[0041] The transmitting unit 20 includes an oscillator 21, a transmitting amplifier 22, and a transmitting antenna 23. The oscillator 21 has an oscillator circuit for transmitting a burst signal in the 57 kHz band and an oscillator circuit for transmitting a burst signal in the 58 kHz band. A transmission window (TX Window) is opened during each transmission period of a fixed cycle, during which the 57 kHz band and 58 kHz band burst signals are transmitted from the transmitting antenna 23 via the transmitting amplifier 22.

[0042] When the tag 10 is within a certain distance from the transmitting antenna 23, the tag 10 oscillates due to the burst signal transmitted from the transmitting antenna 23. Specifically, when the tag 10 receives a burst signal with a frequency close to its resonant frequency, the tag 10 accumulates excitation energy during the transmission period when the transmission window of the transmitter 20 is open, and outputs a ringing down (attenuation) signal at the resonant frequency of the tag 10 for a certain period after the transmission period of the burst signal ends.

[0043] The receiving unit 30 includes a receiving antenna 31, a receiving amplifier 32, and a narrow-band filter 33. When the tag 10 is present within a certain distance from the receiving antenna 31, the receiving antenna 31 can receive a ringing down signal from the tag 10 when the tag 10 oscillates due to a burst signal.

[0044] Specifically, a little after (usually about 0.2 ms) the transmission period (transmission window) of the burst signal (usually 1.4 ms to 2.0 ms), the reception window (RX Window) of the receiver 30 is opened for a certain period of time (usually about 2.0 ms to 5.0 ms). During the reception period when the reception window of the receiver 30 is open, the ringing down signal from the tag 10 is received by the reception antenna 31 and input to the control unit 40 via the reception amplifier 32 and narrowband filter 33.

[0045] The control unit 40 includes a processor such as a CPU (Central Processing Unit), and executes a program to perform processes required for the operation of the anti-theft system. The control unit 40 may be configured with one control device or multiple control devices. For example, the control unit 40 may be configured such that reception control is performed by an MPU (Micro Processor Unit) controller, and other controls are performed by a system controller.

[0046] The control unit 40 functions as various processing units such as a burst signal transmission processing unit 41, a tag detection processing unit 42, and a notification processing unit 43, as a result of the processor executing a program. However, the control unit 40 is not limited to these processing units and may function as other processing units.

[0047] The burst signal transmission processing unit 41 performs processing for transmitting a burst signal from the transmission unit 20. That is, by the processing of the burst signal transmission processing unit 41, a burst signal of a preset frequency is transmitted from the transmission unit 20 during a preset transmission period (transmission window).

[0048] The tag detection processing unit 42 performs processing for detecting the tag 10 based on the signal from the receiving unit 30. Specifically, the tag detection processing unit 42 detects the tag 10 based on the ringing down signal from the tag 10 received by the receiving unit 30 during the above-mentioned reception window period.

[0049] By interposing the narrowband filter 33 between the receiving antenna 31 and the control unit 40, the tag detection processing unit 42 detects the tag 10 only when the ringing down signal received by the receiving unit 30 is within a certain range of frequencies. This improves the detection accuracy of the tag 10. A quadrature mirror filter (QMF) can be used as the narrowband filter 33. However, the narrowband filter 33 may be omitted.

[0050] The notification processing unit 43 performs processing for issuing a notification based on the ringing down signal from the tag 10 received by the receiving unit 30. Specifically, when the tag detection processing unit 42 detects the tag 10 based on the ringing down signal from the tag 10 received by the receiving unit 30, an alarm is output from the speaker 50 to notify the theft of the product to which the tag 10 is attached.

[0051] 2. Details about tags (1) Resonant frequency and anti-resonant frequency of the tag In the tag 10, the accumulation and output of excitation energy are maximized at the resonance frequency (fr), but there is an anti-resonance frequency (fa) slightly higher than the resonance frequency, and at this anti-resonance frequency, the accumulation and output of excitation energy are reduced conversely (see Patent Document 1).

[0052] The tag 10 is classified into two types: a de-activatable tag and a non-de-activatable tag. That is, if the magnetic force of the magnet in the tag 10 can be erased, the tag is a de-activatable tag, and if the magnetic force of the magnet in the tag 10 cannot be erased, the tag is a non-de-activatable tag.

[0053] The deactivatable tag 10 has a small electromagnetic coupling factor. Also, in the deactivatable tag 10, fa-fr is approximately 0.1 kHz, and the anti-resonance frequency (fa) is very close to the resonance frequency (fr).

[0054] In contrast, the non-deactivatable tag 10 has a large electromagnetic coupling factor. Also, in the non-deactivatable tag 10, fa-fr is approximately 0.3 kHz, and the difference between the anti-resonance frequency (fa) and the resonance frequency (fr) is large.

[0055] (2) Details of tags that cannot be disabled 2 is a diagram showing an example of the strength of the ringing down signal output when non-neutralizable tags 10 with different resonant frequencies are excited by a 58.0 kHz burst signal from an AM antenna. In FIG. 2, the horizontal axis shows the resonant frequency of the tag 10, and the vertical axis shows the voltage of the ringing down signal.

[0056] In this example, a burst signal is transmitted at an excitation frequency of 58.0 kHz to resonate the non-neutralizable tag 10 and output a ringing down signal. The measurement conditions were a time width of the transmission window of 1.6 ms, and the voltage of the ringing down signal was measured 0.4 ms after the transmission window was closed.

[0057] As shown in Fig. 2, a voltage drop in the ringing down signal is observed when the resonant frequency of the tag 10 is 57.7 kHz. This is because the excitation frequency of the burst signal, 58.0 kHz, corresponds to the anti-resonant frequency (fa) of the tag 10, which has a resonant frequency of 57.7 kHz. If the allowable range of the resonant frequency of the tag 10 is currently 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), the resonant frequency of 57.7 kHz is included within this allowable range, and although the tag 10 with a resonant frequency of 57.7 kHz exhibits a voltage drop in the ringing down signal for a 58.0 kHz burst signal, the tag can be detected by the receiver 30 of the system.

[0058] (3) Details of tags that can be disabled 3 is a diagram showing an example of the strength of the ringing down signal output when the deactivatable tag 10 is excited with a 58.0 kHz burst signal from the AM antenna. In FIG. 3, the horizontal axis shows the resonant frequency of the tag 10, and the vertical axis shows the voltage of the ringing down signal.

[0059] In this example, a burst signal is transmitted at an excitation frequency of 58.0 kHz to resonate the deactivatable tag 10 and output a ringing down signal. The measurement conditions were a time width of the transmission window of 1.6 ms, and the voltage of the ringing down signal was measured 0.4 ms after the transmission window was closed.

[0060] As shown in FIG. 3, a voltage drop in the ringing down signal is observed when the resonant frequency of the tag 10 is 57.8 kHz to 57.9 kHz. This is because the excitation frequency of the burst signal, 58.0 kHz, corresponds to the anti-resonant frequency (fa) of the tag 10, which has a resonant frequency of 57.8 kHz to 57.9 kHz. If the allowable range of the resonant frequency of the tag 10 is currently 58 kHz ±0.52% (58.0 kHz ±0.3 kHz), the resonant frequency of 57.8 kHz to 57.9 kHz is included in this allowable range. Although the tag 10 with a resonant frequency of 57.8 kHz to 57.9 kHz experiences a drop in the ringing down signal in response to excitation by a burst signal of 58.0 kHz, the tag can be detected by the receiver 30 of the system.

[0061] (4) Ringing down signal and tag sensitivity 4 is a diagram showing the relationship between the strength of the ringing-down signal and the sensitivity of the tag, in which the horizontal axis represents the voltage of the ringing-down signal and the vertical axis represents the sensitivity of the tag 10 (tag sensitivity).

[0062] "Tag sensitivity" refers to the distance from the receiving antenna 31 (the distance between the tag 10 and the receiving antenna 31) at which the receiving antenna 31 can detect a tag 10 that is within the allowable resonant frequency range. As shown in Fig. 4, there is an approximately proportional relationship between the ringing down signal and the sensitivity of the tag 10. Therefore, in order to detect the tag 10, it is necessary to make the voltage of the ringing down signal equal to or greater than a certain value, and the tag sensitivity is determined in relation to that certain value.

[0063] (5) Tolerance range of the tag's resonance frequency and the excitation frequency of the burst signal As described above, the resonant frequency of tag 10 at which a voltage drop in the ringing down signal is observed relative to the excitation frequency of the burst signal of 58.0 kHz is 57.7 kHz for non-deactivatable tags 10 and 57.8 kHz to 57.9 kHz for deactivatable tags 10. However, currently, the allowable range of the resonant frequency of tag 10 is 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), which includes these resonant frequencies.

[0064] In other words, when the excitation frequency of the burst signal is 58.0 kHz as in the current situation, by providing the necessary excitation to a tag 10 whose allowable range of resonance frequencies is 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), a ringing down signal whose voltage is equal to or greater than a certain value is output from the tag 10, and the tag 10 can be detected without problem. With this as a background, an embodiment of an anti-theft system that is applicable to both non-deactivatable and deactivatable tags 10 and that can expand the allowable resonance frequency range of the tag 10 will be described below.

[0065] 3. Working Example In the following embodiment, one or two cycles of a commercial frequency power supply (50 Hz or 60 Hz) include a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted. That is, in the past, there was only one transmission period in which a burst signal in the 58.0 kHz band was transmitted during one cycle of the commercial frequency power supply, but in the following embodiment, the transmission period in which a burst signal in the 57 kHz band is transmitted and the transmission period in which a burst signal in the 58 kHz band is transmitted are set to appear multiple times with different phases during one or two cycles of the commercial frequency power supply.

[0066] (1) First Example 5 is a diagram for explaining a first embodiment of the operation timing of the anti-theft system. In this example, each cycle of the commercial frequency power supply is divided into three phases, Phase A, Phase B, and Phase C, and a transmission window (transmission period) and a reception window (reception period) are set in each phase. Specifically, at the initial timing of each phase, the transmission window of the transmitter 20 is opened for about 1.4 ms to 2.0 ms, during which a burst signal is transmitted from the transmitter 20. A little after the transmission window in each phase (about 0.2 ms), the reception window of the receiver 30 is opened for a certain period of time (about 2.0 ms to 3.0 ms), during which a ringing down signal is received from the tag 10.

[0067] The frequencies of the burst signals in each of Phase A, Phase B, and Phase C are as shown in Table 1 below. Thus, the frequency of the burst signal in each phase is in the 57 kHz band or the 58 kHz band. That is, each cycle of the commercial frequency power supply includes a transmission period in which a burst signal in the 57 kHz band is transmitted, and a transmission period in which a burst signal in the 58 kHz band is transmitted. The output of the burst signal in each phase is controlled to a constant value by the transmission amplifier 22. [Table 1]

[0068] 6A to 6E are diagrams for explaining the allowable range of the resonance frequency of the tag 10 in the first embodiment. In the diagrams, the vertical line mark portion in the transmission window period is the excitation energy absorption region in the tag 10, and the attenuation mark portion after the transmission window indicates the ringing down signal of the tag 10. FIG. 6A means that when the resonance frequency of the tag 10 is 57.4 kHz to 57.6 kHz, a strong ringing down signal of the tag 10 may appear in the reception window of Phase A. FIG. 6B means that when the resonance frequency of the tag 10 is 57.7 kHz to 57.9 kHz, a strong ringing down signal of the tag 10 may appear in the reception windows of Phase A and Phase B. FIG. 6C means that when the resonance frequency of the tag 10 is 58.0 kHz, a strong ringing down signal of the tag 10 may appear in the reception windows of Phase A, Phase B, and Phase C. Fig. 6D shows a case where the resonant frequency of the tag 10 is 58.1 kHz to 58.3 kHz, and Fig. 6E shows a case where the resonant frequency of the tag 10 is 58.4 kHz to 58.6 kHz. Even if the resonant frequency of the tag 10 does not match the frequency of the burst signal, as long as the resonant frequency of the tag 10 is within a range of ±0.3 kHz of the frequency of the burst signal, the ringing down signal of the tag 10 is output with a detectable intensity equal to or greater than a certain intensity in the receiving window following the transmitting window of the burst signal.

[0069] 6A, when the resonant frequency of the tag 10 is 57.4 kHz to 57.6 kHz, a 57.7 kHz burst signal in Phase A causes the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception window of Phase A. In contrast, a 58.0 kHz burst signal in Phase B and a 58.3 kHz burst signal in Phase C do not cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception windows of Phase B and Phase C. In other words, during each cycle of the commercial frequency power supply, a ringing down signal of a certain intensity or more that can be detected is output from the tag 10 only in one phase of Phase A.

[0070] As shown in Fig. 6B, when the resonant frequency of the tag 10 is 57.7kHz to 57.9kHz, a 57.7kHz burst signal in Phase A and a 58.0kHz burst signal in Phase B cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception windows of Phase A and Phase B. In contrast, a 58.3kHz burst signal in Phase C does not cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception window of Phase C. That is, during each cycle of the commercial frequency power supply, the tag 10 outputs a ringing down signal of a certain intensity or more that can be detected in two phases, Phase A and Phase B.

[0071] 6C, when the resonant frequency of the tag 10 is 58.0 kHz, a 57.7 kHz burst signal in Phase A, a 58.0 kHz burst signal in Phase B, and a 58.3 kHz burst signal in Phase C cause the tag 10 to output a ringing down signal of a certain intensity or more that is detectable in the reception windows of Phase A, Phase B, and Phase C. That is, during each cycle of the commercial frequency power supply, the tag 10 outputs a ringing down signal of a certain intensity or more that is detectable in all three phases, Phase A, Phase B, and Phase C.

[0072] As shown in Fig. 6D, when the resonant frequency of the tag 10 is 58.1kHz to 58.3kHz, a 58.0kHz burst signal in Phase B and a 58.3kHz burst signal in Phase C cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception windows of Phase B and Phase C. In contrast, a 57.7kHz burst signal in Phase A does not cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the reception window of Phase A. That is, during each cycle of the commercial frequency power supply, the tag 10 outputs a ringing down signal of a certain intensity or more that can be detected in two phases, Phase B and Phase C.

[0073] 6E, when the resonant frequency of the tag 10 is 58.4 kHz to 58.6 kHz, a 58.3 kHz burst signal in Phase C causes the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the receiving window of Phase C. In contrast, a 57.7 kHz burst signal in Phase A and a 58.0 kHz burst signal in Phase B do not cause the tag 10 to output a ringing down signal of a certain intensity or more that can be detected in the receiving windows of Phase A and Phase B. That is, during each cycle of the commercial frequency power supply, a ringing down signal of a certain intensity or more that can be detected is output from the tag 10 only in one phase of Phase C.

[0074] In this way, in the first embodiment, when the resonant frequency of the tag 10 is 57.4 kHz to 57.6 kHz (FIG. 6A), 57.7 kHz to 57.9 kHz (FIG. 6B), 58.0 kHz (FIG. 6C), 58.1 kHz to 58.3 kHz (FIG. 6D), and 58.4 kHz to 58.6 kHz (FIG. 6E), the combination of phases at which a ringing down signal of a certain intensity or more detectable in the receiving window is output from the tag 10 is different. Therefore, it becomes possible to detect tags 10 with a wider resonant frequency range of 57.4 kHz to 58.6 kHz (approximately 58 kHz ±1.0%) based on the combination of phases at which a ringing down signal of a certain intensity or more is received from the tag 10 for burst signals of different frequencies transmitted in each phase (three transmission periods in each cycle of the commercial frequency power supply).

[0075] (2) Second Example Fig. 7 is a diagram for explaining a second embodiment of the operation timing of the anti-theft system. In this example, every two cycles of the commercial frequency power supply are divided into six phases P1 to P6, and a transmission window (transmission period) and a reception window (reception period) are set in each phase. Note that Fig. 7 only illustrates the transmission windows (transmission periods) in each phase P1 to P6, but as in the first embodiment, in each phase, the transmission window of the transmitter 20 is opened for a certain period of time, and shortly thereafter, the reception window of the receiver 30 is opened for a certain period of time.

[0076] [Table 2] The frequency of the burst signal in each phase P1 to P6 is as shown in Table 2 above. Thus, the frequency of the burst signal in each phase is 57 kHz band or 58 kHz band. That is, every two cycles of the commercial frequency power supply include a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted. The output of the burst signal in each phase is controlled to a constant value by the transmission amplifier 22.

[0077] In the receiving window following the 57.25 kHz burst signal at phase P1, tags 10 whose resonant frequencies are within the range of 56.95 kHz to 57.55 kHz (57.25 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0078] In the receiving window following the 57.55 kHz burst signal at phase P2, tags 10 whose resonant frequencies are within the range of 57.25 kHz to 57.85 kHz (57.55 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0079] In the receiving window following the 57.85 kHz burst signal at phase P3, tags 10 whose resonant frequencies are within the range of 57.55 kHz to 58.15 kHz (57.85 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0080] In the receiving window following the 58.15 kHz burst signal in phase P4, tags 10 whose resonant frequencies are within the range of 57.85 kHz to 58.45 kHz (58.15 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0081] In the receiving window following the 58.45 kHz burst signal at phase P5, tags 10 whose resonant frequencies are within the range of 58.15 kHz to 58.75 kHz (58.45 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0082] In the receiving window following the 58.75 kHz burst signal at phase P6, tags 10 whose resonant frequencies are within the range of 58.45 kHz to 59.05 kHz (58.75 kHz ±0.3 kHz) can be detected with a ringing down signal strength equal to or greater than a certain level.

[0083] In this way, in the second embodiment, it is possible to detect tags 10 whose resonant frequencies are within the range of 56.95 kHz to 59.05 kHz, i.e., within the range of 58.0 kHz ± 1 kHz (± 1.7%). In this way, it is possible to detect tags 10 with a wider resonant frequency range of about 58 kHz ± 1.7%, based on whether a ringing down signal of a certain intensity or more is received from tag 10 in a receiving window following the transmission window of the burst signal for burst signals of different frequencies transmitted in each phase (six transmission periods in every two cycles of the commercial frequency power supply).

[0084] (3) Third Example Fig. 8 is a block diagram for explaining the third embodiment. In this embodiment, only the configuration of the control unit 40 in the anti-theft system shown in Fig. 1 is different, and other configurations are the same as those in Fig. 1, so the same components are given the same reference numerals in the figure and detailed description is omitted.

[0085] 8, the control unit 40 functions not only as the burst signal transmission processing unit 41, tag detection processing unit 42, and notification processing unit 43 described above, but also as a resonance frequency detection processing unit 44. The resonance frequency detection processing unit 44 causes the transmitting unit 20 to transmit burst signals of different frequencies in the 57 kHz band or 58 kHz band during the transmission period of each cycle over multiple cycles of the commercial frequency power supply, and detects the frequency at which the output of the ringing down signal received by the receiving unit 30 is the highest as the resonance frequency.

[0086] The following Table 3 is an example of a burst signal transmitted by the processing of the burst signal transmission processing unit 41. In this example, a case where the power supply frequency is 60 Hz will be described. [Table 3]

[0087] As shown in Table 3 above, each cycle tn of the commercial frequency power supply is divided into three phases, Phase A, Phase B, and Phase C, and a transmission window (transmission period) and a reception window (reception period) are set in each phase. A burst signal of a different frequency is transmitted in each phase. Specifically, the frequency of the burst signal is swept (scanned) by 0.1 kHz in each phase of each cycle tn.

[0088] The frequency sweep range is 57.4kHz to 58.6kHz, and burst signals are repeatedly transmitted within this frequency range. Note that when the commercial power frequency is 60Hz, the time that elapses for each period tn is very short at 16ms, and even if the range of 57.4kHz to 58.6kHz is repeated three times, the elapsed time is approximately 208ms, as shown in Table 3 above.

[0089] When the receiving unit 30 receives a ringing down signal for a burst signal transmitted in each phase of each cycle tn, it is determined whether the output of the ringing down signal is the highest. That is, when the frequency of the burst signal is swept within the range of 57.4 kHz to 58.6 kHz (58.0 kHz ± 0.6 kHz), which is the allowable range of the resonant frequency of the tag 10, the ringing down signal with the highest output is identified, and the frequency of the burst signal corresponding to that ringing down signal is detected as the resonant frequency of the tag 10.

[0090] In this way, after the resonant frequency of the tag 10 is detected by the resonant frequency detection processing unit 44, the burst signal transmission processing unit 41 transmits subsequent burst signals in a transmission pattern that includes a burst signal of the detected resonant frequency.

[0091] Table 4 below shows the frequency of the burst signal at each phase of each period tn when the resonant frequency of the tag 10 is detected to be 57.5 kHz. [Table 4]

[0092] As shown in Table 4 above, the frequency of the burst signal in Phase B of each period tn is set to 57.5 kHz, which is the resonant frequency of the tag 10, the frequency of the burst signal in Phase A is set to 57.4 kHz (57.5-0.1 kHz), and the frequency of the burst signal in Phase C is set to 57.6 kHz (57.5+0.1 kHz). That is, after the resonant frequency of the tag 10 is detected as 57.5 kHz in the resonant frequency sweep process of Table 3, burst signals are repeatedly transmitted at a frequency of 57.5±0.1 kHz in each period tn for a certain period of time to detect the tag 10, and then the process returns to the resonant frequency sweep process of Table 3 again.

[0093] In this way, the resonant frequency of the tag 10 is detected in advance by the processing of the resonant frequency detection processing unit 44, and a burst signal pattern (resonant frequency -0.1 kHz, resonant frequency, resonant frequency +0.1 kHz) related to the resonant frequency is transmitted in each period tn of the commercial frequency power supply thereafter, thereby making it possible to reliably detect the tag 10. This makes it possible to avoid the effect of the anti-resonant frequency on the detection of the tag 10.

[0094] In the above first to third embodiments, an anti-theft system was proposed that includes a transmission period (transmission window) in which a burst signal in the 57 kHz band is transmitted at regular intervals of a commercial frequency (50 Hz or 60 Hz) power supply, and a transmission period (transmission window) in which a burst signal in the 58 kHz band is transmitted, but this transmission control is performed based on the zero crossing points of the commercial frequency power supply. As an application of the present invention, there is also a case where a DC power supply is used instead of a commercial frequency power supply. In this case, it goes without saying that it is possible to detect tags 10 with a wider allowable resonance frequency by setting a transmission window in which the frequency of the burst signal is changed at regular intervals in the same manner as in the above embodiments, and a reception window that opens thereafter.

[0095] 4. Notification Processing The notification processing unit 43 issues a notification when the strength of the ringing down signal received by the receiving unit 30 is equal to or greater than a threshold. As the threshold, a different threshold may be set for each of a plurality of receiving periods (receiving windows). For example, in the case where each cycle of the commercial frequency power supply is divided into three phases, Phase A, Phase B, and Phase C, as in the above-mentioned first to third embodiments, and a transmitting window (transmitting period) and a receiving window (receiving period) are set in each phase, a different threshold may be set in each receiving window of Phase A, Phase B, and Phase C.

[0096] In this case, when the strength of the ringing down signal received by the receiving unit 30 is equal to or greater than a threshold in any one of the receiving windows of Phase A, Phase B, and Phase C, the notification processing unit 43 may issue a notification. Also, when peaks appear in the ringing down signal received by the receiving unit 30 in two or more phases among the receiving windows of Phase A, Phase B, and Phase C, the notification processing unit 43 may issue a notification when the strength of the largest peak is equal to or greater than a threshold.

[0097] 5. Adjusting the phase timing The phase timing of the transmission window (transmission period) and the reception window (reception period) may be adjustable with respect to the phase of the commercial frequency power supply. In this case, the detection sensitivity of the tag 10 can be improved by setting the transmission window and the reception window so as to avoid the phase timing at which the detection sensitivity of the tag 10 is poor due to environmental noise or the like.

[0098] For example, when multiple anti-theft systems (such as transmitting antennas 23) are installed close to each other, it is extremely important to properly synchronize their transmission and reception windows. Specifically, when two or more transmitting antennas 23 are installed close to each other, it is important to match the phase of the transmission window (usually 1.4 ms to 2.0 ms) of the transmitting antenna 23 with the phase of the transmission window of the adjacent transmitting antenna 23 so that the phase of the burst signal from the other adjacent transmitting antenna 23 does not overlap with the reception window of this system.

[0099] If the phase of the transmission window of another transmitting antenna 23 nearby overlaps with the phase of the receiving window of this system and synchronization is not achieved properly, problems such as false alarms and reduced detection sensitivity of the tag 10 may occur. Therefore, by adjusting the phase timing of the transmission window and receiving window to the phase of the commercial frequency power supply and achieving proper synchronization, problems such as false alarms and reduced detection sensitivity of the tag 10 can be prevented. In particular, caution is required with the AM system, since the wavelength is longer than that of the RF system and anti-theft systems located relatively far from each other (for example, 100 m) are likely to affect each other.

[0100] Also, a mode in which the transmission window and the reception window are controlled (label detection mode) and a mode in which the transmission window and the reception window are not controlled (noise measurement mode) may be provided. In this case, in the noise measurement mode, a burst signal is not transmitted in the transmission window, and the reception signal (noise) from the reception antenna 31 may be measured in terms of the phase relationship with the transmission window / reception window of the phases (Phase A, Phase B, Phase C) of each cycle of the commercial frequency power supply.

[0101] Furthermore, if large noise is measured at a specific phase in noise measurement mode, and the phase in which the noise was detected overlaps with the receiving window, the influence of the noise will be large, so adjustments can be made by moving the receiving window to a phase where the influence of the noise is smaller. [Explanation of symbols]

[0102] 10 Tags 20 Transmitter 21 Oscillators 22 Transmitting amplifier 23 Transmitting Antenna 30 Receiving section 31 Receiving antenna 32 Receiving amplifier 33 Narrow Band Filter 40 Control section 41 Burst signal transmission processing unit 42 Tag detection processing unit 43 Notification processing section 44 Resonant frequency detection processing unit 50 Speakers

Claims

1. An acoustomagnetic anti-theft system, comprising: a transmitter for transmitting a burst signal during a transmission period; a tag that resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal; a receiving unit that receives the ringing down signal during a receiving period after the transmitting period; a tag detection processing unit that detects the tag based on the ringing down signal received by the receiving unit, An anti-theft system including a transmission period in which a burst signal in the 57 kHz band is transmitted and a transmission period in which a burst signal in the 58 kHz band is transmitted at regular intervals.

2. An acoustomagnetic anti-theft system, comprising: a transmitter for transmitting a burst signal during a transmission period; a tag that resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal; a receiving unit that receives the ringing down signal during a receiving period after the transmitting period; a tag detection processing unit that detects the tag based on the ringing down signal received by the receiving unit, An anti-theft system, comprising a transmission period for transmitting a burst signal in the 57 kHz band and a transmission period for transmitting a burst signal in the 58 kHz band during each cycle of a commercial frequency power supply.

3. 3. The anti-theft system according to claim 2, wherein each cycle of the commercial frequency power supply includes a transmission period in which a 57.7 kHz burst signal is transmitted, a transmission period in which a 58.0 kHz burst signal is transmitted, and a transmission period in which a 58.3 kHz burst signal is transmitted.

4. An acoustomagnetic anti-theft system, comprising: a transmitter for transmitting a burst signal during a transmission period; a tag that resonates with the burst signal transmitted from the transmitter and outputs a ringing down signal; a receiving unit that receives the ringing down signal during a receiving period after the transmitting period; a tag detection processing unit that detects the tag based on the ringing down signal received by the receiving unit, An anti-theft system, comprising a transmission period for transmitting a burst signal in the 57 kHz band and a transmission period for transmitting a burst signal in the 58 kHz band during every two cycles of a commercial frequency power supply.

5. 5. The anti-theft system according to claim 4, wherein every two cycles of the commercial frequency power supply include a transmission period for transmitting a 57.25 kHz burst signal, a transmission period for transmitting a 57.55 kHz burst signal, a transmission period for transmitting a 57.85 kHz burst signal, a transmission period for transmitting a 58.15 kHz burst signal, a transmission period for transmitting a 58.45 kHz burst signal, and a transmission period for transmitting a 58.75 kHz burst signal.

6. a resonant frequency detection processing unit that transmits burst signals of different frequencies in the 57 kHz band or the 58 kHz band during a transmission period of each cycle over a plurality of cycles of a commercial frequency power supply, and detects a frequency at which the output of the ringing down signal received by the receiving unit is the highest as a resonant frequency of the tag; 2. The anti-theft system according to claim 1, wherein during a transmission period of each cycle of the commercial frequency power supply after the resonant frequency of the tag is detected, transmission is performed in a transmission pattern including a burst signal of the resonant frequency.

7. 2. The anti-theft system of claim 1, wherein phase timing of said transmit and receive periods is adjustable relative to the phase of a mains frequency power source.

8. a notification processing unit that issues an alarm when the strength of the ringing down signal received by the receiving unit is equal to or greater than a threshold, The theft prevention system according to claim 1 , wherein different threshold values ​​are set for each of a plurality of the reception periods.

9. 2. The anti-theft system according to claim 1, wherein the tag detection processing unit detects the tag when a frequency of the ringing down signal received by the receiving unit is within an allowable resonance frequency range.

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