Theft prevention system

Abstract

Provided is an acoustic magnetic (AM) anti-theft system with which it is possible to widen the permissible range of a resonance frequency of a tag. The acoustic magnetic anti-theft system comprises a transmission unit 20, a tag 10, a reception unit 30, and a tag detection processing unit 42. The transmission unit 20 transmits a burst signal during a transmission period. The tag 10 resonates with the burst signal that is transmitted from the transmission unit 20, and outputs a ringing-down signal. The reception unit 30 receives the ringing-down signal during a reception period after the transmission period. The tag detection processing unit 42 detects the tag 10 on the basis of the ringing-down signal that is received by the reception unit 30. Each cycle 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.

Description

Anti-theft system

[0001] The present invention relates to an anti-theft system using the acousto-magnetic method.

[0002] As an example of an anti-theft system, a security system that performs two types of electronic article surveillance (EAS), namely, the radio frequency (RF) method and the acousto-magnetic (AM) method, is known.

[0003] The RF anti-theft system includes a transmitter that includes an oscillator that oscillates an RF signal (for example, 8.2 MHz) and a transmission coil, and a receiver that includes a sensor coil. In this type of anti-theft system, although the magnitude of the voltage change due to the RF security label attached to the product is small, the signal from the RF security label can be detected very clearly.

[0004] A characteristic of the RF anti-theft system is that the frequency of the high-frequency magnetic field from the transmission coil takes a method of continuously sweeping (scanning) the frequency instead of a fixed frequency. Usually, the range for sweeping the frequency is (8.2 MHz - 10%) to (8.2 MHz + 10%). When the oscillation frequency of the sweeping transmitter matches the resonance frequency of the LC resonance circuit in the RF security label, the RF security label starts to oscillate, and a clear voltage drop (DIP) occurs in the sensor coil that detects the signal from the RF security label.

[0005] Usually, the management of the resonance frequency of the RF security label is greatly affected by the quality control in the manufacturing process. However, due to the sweeping method in the wide frequency range (8.2 MHz ± 10%) of the excitation magnetic field as described above, the allowable resonance frequency range of the RF security label is as wide as 8.2 MHz ± 10%, and strict quality control is not required. As a result, the cost of the RF security label can be reduced.

[0006] On the other hand, the wide range of acceptable resonant frequencies mentioned above is causing 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-type anti-theft systems operate using a pulse-listening method. In the pulse-listening method, the zero-crossing point of a 50Hz or 60Hz commercial frequency power supply signal is used as the control trigger timing. After a certain period of time from the zero-crossing point, the transmitter's transmit window (TX Window) (usually with a window width of about 1.4ms to 2.0ms) opens, and during this time, a 58kHz burst signal is transmitted from the transmitter. A little later (usually about 0.2ms later), the receiver's receive window (RX Window) opens for a certain period of time (usually about 2.0ms to 5.0ms), during which the response signal from the tag is detected.

[0008] In AM-type anti-theft systems, label tags with a resonant frequency in the 58 kHz band (see, for example, Patent Document 1 below) or hard tags consisting of an LC resonant circuit are used. When these tags receive a 58 kHz burst signal during the burst signal transmission period when the transmitter's transmission window is open, they accumulate excitation energy, and for a certain period after the burst signal transmission period ends, they output a ringing down signal at the tag's resonant frequency. During the reception period when the receiver's reception window is open, the attenuated radio waves (ringing down signals) emitted from the tag are received by the receiver, and based on the time interval, frequency, and degree of attenuation of the ringing down signals, it is determined whether or not the signal is from the tag. If it is determined that the signal is from the tag, an alarm is triggered.

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

[0010] As a quality control standard for AM-type anti-theft systems, a standard has been set that the resonant frequency of the tag should be 58.0 kHz ± 0.52% (58.0 kHz ± 0.3 kHz). This standard ensures that when the transmitter sends a burst signal at 58.0 kHz, the distance from the receiver at which the receiver can detect a tag within the allowable resonant frequency range (tag sensitivity) is at least 70% of the maximum tag sensitivity at a resonant frequency of 58.0 kHz.

[0011] Comparing the RF and AM methods, the following points can be made: First, regarding the price of transmitters and receivers, RF methods were traditionally cheaper, but now AM methods are priced similarly to RF methods. Regarding the price of tags, RF methods have always been cheaper, and there is a demand for cheaper AM tags.

[0012] Regarding the management standards for the resonant frequency of tags, the RF method has a wide tolerance range of 8.2 MHz ± 10%, while the AM method, as mentioned above, has a tolerance range of 58.0 kHz ± 0.52% (58.0 kHz ± 0.3 kHz). The AM method has a much narrower tolerance range for the resonant frequency compared to the RF method, resulting in excessive quality control costs.

[0013] Furthermore, regarding stability in terms of false alarms, the RF system is prone to false alarms because its excitation frequency (8.2 MHz) is the same as that of marine radio, and it is susceptible to the influence of products (such as cable coils) whose resonant frequency is 8.2 MHz ± 10%. In contrast, the AM system is more stable than the RF system and rarely produces false alarms.

[0014] U.S. Patent No. 4,510,489

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

[0016] In this regard, the variation in the resonant frequency of AM-type tags has been greatly improved. Therefore, if the allowable range of the resonant frequency of AM-type tags can be expanded from the current 58 kHz ± 0.5% to approximately 58 kHz ± 1.0%, it will be possible to reduce the price of AM-type tags by 40 to 60%.

[0017] This invention has been made in view of the above circumstances, and aims to provide an acoustic-magnetic (AM) anti-theft system that can widen the permissible range of the resonant frequency of the tag.

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

[0019] With this configuration, since the transmission period includes a period in which a burst signal in the 57 kHz band is transmitted at regular intervals, and another period in which a burst signal in the 58 kHz band is transmitted, it becomes possible to widen the tolerance range of the tag's resonant frequency, and thus lower the price of the tag.

[0020] (2-1) A second anti-theft system according to the present invention is an acoustic-magnetic anti-theft system comprising a transmitter, a tag, a receiver, and a tag detection processing unit. The transmitter transmits a burst signal during the 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 the reception period after the transmission period. The tag detection processing unit 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 for transmitting a burst signal in the 57 kHz band and a transmission period for transmitting a burst signal in the 58 kHz band.

[0021] With this configuration, each cycle of the commercial frequency power supply includes 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. This makes it possible to expand the allowable range of the resonant frequency of the acoustic-magnetic tag from the current 58.0 kHz ± 0.5% to at least 58.0 kHz ± 1.0%. By expanding the allowable range of the tag's resonant frequency in this way, the price of the tag can be reduced.

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

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

[0024] (3-1) The third anti-theft system according to the present invention is an acoustic-magnetic anti-theft system comprising a transmitter, a tag, a receiver, and a tag detection processing unit. The transmitter transmits a burst signal during the 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 the reception period after the transmission period. The tag detection processing unit detects the tag based on the ringing-down signal received by the receiver. Each two cycles of the commercial frequency power supply include 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.

[0025] With this configuration, each two-cycle cycle of the commercial frequency power supply includes a transmission period for sending burst signals in the 57 kHz band and a transmission period for sending burst signals in the 58 kHz band. This makes it possible to expand the allowable range of the resonant frequency of the acoustic-magnetic tag from the current 58.0 kHz ± 0.5% to at least 58.0 kHz ± 1.5%. By expanding the allowable range of the tag's resonant frequency in this way, the price of the tag can be reduced.

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

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

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

[0029] With this configuration, the resonant frequency of the tag is detected in advance, and then a burst signal of that resonant frequency is transmitted during the transmission period in each cycle of the commercial frequency power supply, thereby enabling the detection of the tag. This avoids the influence of the anti-resonant frequency (see Patent Document 1) on tag detection.

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

[0031] With this configuration, the tag detection sensitivity can be improved by setting the transmission and reception periods while avoiding phase timings where there is a lot of environmental noise and the tag detection sensitivity is poor.

[0032] (6) The anti-theft system may further include an alarm processing unit that issues an alarm when the intensity of the ringing down signal received by the receiving unit is equal to or greater than a threshold. In this case, different thresholds may be set for each of the multiple reception periods.

[0033] With this configuration, different thresholds are set for each of the multiple reception periods, and notification is given based on whether the intensity of the ringing-down signal received by the receiver during each reception period is above the threshold. This allows for sensitive detection and notification of tags across a wide permissible resonant frequency range.

[0034] (7) The tag detection processing unit may detect the tag if the frequency of the ringing down signal received by the receiving unit is within the permissible resonant frequency range.

[0035] With this configuration, the accuracy of tag detection can be improved by detecting the tag only when the frequency of the ringing-down signal received by the receiver is within the allowable resonant frequency range.

[0036] According to the present invention, it is possible to provide an acoustic-magnetic (AM) anti-theft system that can widen the permissible range of the resonant frequency of the tag.

[0037] This is a block diagram illustrating an example configuration of an anti-theft system according to one embodiment of the present invention. This figure shows an example of the strength of the ringing down signal output when non-disabled tags with different resonant frequencies are excited with a 58.0 kHz burst signal from an AM antenna. This figure shows an example of the strength of the ringing down signal output when disabled tags with different resonant frequencies are excited with a 58.0 kHz burst signal from an AM antenna. This figure shows the relationship between the strength of the ringing down signal and the sensitivity of the tag. This figure is for explaining the operation timing of the anti-theft system in a first embodiment. This figure is 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. This figure is 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. This figure is 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. This is a diagram illustrating the permissible 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. This is a diagram illustrating the permissible 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. This is a diagram illustrating the operating timing of the anti-theft system in the second embodiment. This is a block diagram illustrating the third embodiment.

[0038] 1. Overall Configuration Diagram 1 of the Anti-Theft System is a block diagram showing an example configuration of an anti-theft system according to one embodiment of the present invention. This anti-theft system is a security system that performs acoustic-magnetic (AM) electronic article surveillance (EAS) and includes a tag 10, a transmitter 20, a receiver 30, a control unit 40, and a speaker 50. The transmitter 20 and receiver 30 are installed at the entrance or exit of a store.

[0039] Tag 10 is a label tag attached to products that are subject to theft prevention monitoring. The label tag 10 used in the AM-type anti-theft system has a structure in which multiple thin amorphous metal plates are arranged in parallel and has a magnet inside. However, tag 10 is not limited to a label tag, but may also be a hard tag that constitutes an LC resonant circuit with a magnetic coil made by winding wire around a ferrite core and a capacitor.

[0040] If the magnetic force of the magnet inside the tag 10 is erased at the store's cash register, the tag 10 becomes inactive and cannot be detected by the receiver 30. In other words, the tag 10 attached to a product before purchase is activated, and if the product is taken out of the store, the receiver 30 will detect the tag 10 and sound an alarm. However, after the product is purchased, the tag 10 is deactivated at the cash register, so the product can be taken out of the store without the receiver 30 detecting the tag 10.

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

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

[0043] The receiving unit 30 includes a receiving antenna 31, a receiving amplifier 32, a narrowband filter 33, etc. When the tag 10 is within a certain distance range from the receiving antenna 31 and the tag 10 is oscillated by the burst signal, the receiving antenna 31 can receive the ringing down signal from the tag 10.

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

[0045] The control unit 40 includes a processor such as a CPU (Central Processing Unit), and the processor executes a program to perform the processing necessary for the operation of the anti-theft system. The control unit 40 may be composed of one control device or a plurality of control devices. For example, a configuration in which reception control is performed by an MPU (Micro Processor Unit) controller and other controls are performed by a system controller may also be used.

[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 when the processor executes 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 reception unit 30. Specifically, the tag 10 is detected by the tag detection processing unit 42 based on the ringing-down signal from the tag 10 received by the reception unit 30 during the reception window period.

[0049] By interposing a narrowband filter 33 between the reception 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 reception unit 30 is within a certain frequency range. Thereby, the detection accuracy of the tag 10 can be improved. As the narrowband filter 33, a quadrature mirror filter (QMF) can be used. However, the narrowband filter 33 may be omitted.

[0050] The notification processing unit 43 performs processing for notification based on the ringing-down signal from the tag 10 received by the reception 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 reception unit 30, an alarm for notifying theft of the merchandise to which the tag 10 is attached is output from the speaker 50.

[0051] 2. Details concerning the tag (1) Resonance frequency and anti-resonance frequency of the tag The tag 10 has maximum excitation energy storage and output at the resonance frequency (fr), but there is an anti-resonance frequency (fa) at a frequency slightly higher than the resonance frequency, at which the excitation energy storage and output are conversely reduced. (See Patent Document 1)

[0052] Tag 10 is classified into two types: deactivatable tags and non-deactivatable tags. In other words, a tag is deactivatable if it is possible to erase the magnetic force of the magnet inside the tag 10, and it is non-deactivatable if it is not possible to erase the magnetic force of the magnet inside the tag 10.

[0053] In the deactivatable tag 10, the magnetic coupling factor is small. Also, in the deactivatable tag 10, fa - fr ≈ 0.1 kHz, and the anti-resonant frequency (fa) is very close to the resonant frequency (fr).

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

[0055] (2) Detailed view of the non-disableable tag Figure 2 shows an example of the strength of the ringing down signal output when a non-disableable tag 10 with a different resonant frequency is excited with a 58.0 kHz burst signal from an AM antenna. In Figure 2, the horizontal axis represents the resonant frequency of the tag 10, and the vertical axis represents the voltage of the ringing down signal.

[0056] This example describes a case where a burst signal is transmitted at an excitation frequency of 58.0 kHz to resonate the non-disableable tag 10 and output a ringing-down signal. The measurement conditions were as follows: the transmission window time was 1.6 ms, and the voltage of the ringing-down signal was measured 0.4 ms after the transmission window closed.

[0057] As shown in Figure 2, a voltage drop in the ringing-down signal is observed when the resonant frequency of 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 tag 10 with a resonant frequency of 57.7 kHz. If the allowable range of the resonant frequency of tag 10 is the current 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), then the resonant frequency of 57.7 kHz is included within this allowable range, and although a voltage drop in the ringing-down signal is observed for tag 10 with a resonant frequency of 57.7 kHz in relation to the 58.0 kHz burst signal, the tag can still be detected by the system's receiving unit 30.

[0058] (3) Detailed view of the deactivatable tag Figure 3 shows 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 Figure 3, the horizontal axis represents the resonant frequency of the tag 10, and the vertical axis represents the voltage of the ringing down signal.

[0059] This example describes a case where a burst signal is transmitted at an excitation frequency of 58.0 kHz to resonate a deactivatable tag 10 and output a ringing-down signal. The measurement conditions were as follows: the transmission window time was 1.6 ms, and the voltage of the ringing-down signal was measured 0.4 ms after the transmission window closed.

[0060] As shown in Figure 3, a voltage drop in the ringing-down signal is observed when the resonant frequency of tag 10 is between 57.8 kHz and 57.9 kHz. This is because the excitation frequency of the burst signal, 58.0 kHz, corresponds to the anti-resonant frequency (fa) of tag 10 with a resonant frequency of 57.8 kHz to 57.9 kHz. If the allowable range of the resonant frequency of tag 10 is the current 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), then the resonant frequency of 57.8 kHz to 57.9 kHz will be included within this allowable range. Tag 10 with a resonant frequency of 57.8 kHz to 57.9 kHz will have a drop in the ringing-down signal when excited by a burst signal of 58.0 kHz, but the tag can still be detected by the system's receiving unit 30.

[0061] (4) Ringing Down Signal and Tag Sensitivity Figure 4 shows the relationship between the strength of the ringing down signal and the sensitivity of the tag. In Figure 4, 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 its allowable resonant frequency range. As shown in Figure 4, the sensitivity of the ringing down signal and the tag 10 are approximately proportional. Therefore, in order to detect the tag 10, it is necessary to raise the voltage of the ringing down signal above a certain value, and the tag sensitivity is determined in relation to that certain value.

[0063] (5) Permissible range of resonant frequency of the tag and excitation frequency of the burst signal The resonant frequency of the tag 10 in which a drop in the voltage of the ringing down signal is observed relative to the excitation frequency of the burst signal of 58.0 kHz is, as described above, 57.7 kHz for non-disabled tags 10 and 57.8 kHz to 57.9 kHz for disabled tags 10. Currently, however, 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), which includes these resonant frequencies, is applied as the permissible range of resonant frequency for the tag 10.

[0064] In other words, if the excitation frequency of the burst signal is 58.0 kHz as in the current case, then by applying the necessary excitation to a tag 10 whose allowable resonant frequency range is 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), a ringing-down signal with a voltage above a certain value will be output from the tag 10, and the tag 10 can be detected without any problems. Against this backdrop, the following describes an embodiment of an anti-theft system that can be applied to both non-disableable and disableable tags 10 and can widen the allowable resonant frequency range of the tag 10.

[0065] 3. Examples In the following examples, the transmission period for transmitting a burst signal in the 57 kHz band and the transmission period for transmitting a burst signal in the 58 kHz band are included within one or two cycles of the commercial frequency power supply (50 Hz or 60 Hz). That is, conventionally, there was only one transmission period for transmitting a 58.0 kHz burst signal within one cycle of the commercial frequency power supply, but in the following examples, the transmission period for transmitting a burst signal in the 57 kHz band and the transmission period for transmitting a burst signal in the 58 kHz band are set to appear multiple times with different phases within one or two cycles of the commercial frequency power supply.

[0066] (1) Figure 5 of the first embodiment is a diagram illustrating the first embodiment of the operating 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 transmit window (transmitting period) and a receive window (receiving period) are set in each phase. Specifically, at the initial timing of each phase, the transmit window of the transmitter 20 is opened for about 1.4 ms to 2.0 ms, and a burst signal is transmitted from the transmitter 20 during this time. Also, a little after the transmit window in each phase (about 0.2 ms later), the receive window of the receiver 30 is opened for a certain period of time (about 2.0 ms to 3.0 ms), and a ringing down signal from the tag 10 is received during this time.

[0067] The frequencies of the burst signals in each phase, Phase A, Phase B, and Phase C, are as shown in Table 1 below. Thus, the frequencies of the burst signals in each phase are in the 57 kHz band or the 58 kHz band. In other words, 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 transmitting amplifier 22.

[0068] Figures 6A to 6E illustrate the allowable range of the resonant frequency of the tag 10 in the first embodiment. In the figures, the vertical line marks during the transmission window period represent the region where excitation energy is absorbed in the tag 10, and the attenuation marks after the transmission window represent the ringing down signal of the tag 10. Figure 6A means that when the resonant frequency of the tag 10 is between 57.4 kHz and 57.6 kHz, a strong ringing down signal of the tag 10 may appear in the reception window of Phase A. Figure 6B means that when the resonant frequency of the tag 10 is between 57.7 kHz and 57.9 kHz, a strong ringing down signal of the tag 10 may appear in the reception windows of Phase A and Phase B. Figure 6C means that when the resonant 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. Figure 6D shows the case where the resonant frequency of tag 10 is 58.1 kHz to 58.3 kHz, and Figure 6E shows the case where the resonant frequency of tag 10 is 58.4 kHz to 58.6 kHz. Note that even if the resonant frequency of tag 10 does not match the frequency of the burst signal, if the resonant frequency of tag 10 is within a range of ±0.3 kHz from the frequency of the burst signal, the ringing down signal of tag 10 will be output with an intensity that can be detected above a certain level in the receiving window following the transmission window of the burst signal.

[0069] As shown in Figure 6A, when the resonant frequency of tag 10 is between 57.4 kHz and 57.6 kHz, a 57.7 kHz burst signal in Phase A causes tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the Phase A receiving window. In contrast, with a 58.0 kHz burst signal in Phase B and a 58.3 kHz burst signal in Phase C, tag 10 does not output a ringing-down signal of a detectable intensity above a certain level in the Phase B and Phase C receiving windows. That is, during each cycle of the commercial frequency power supply, a ringing-down signal of a detectable intensity above a certain level is output from tag 10 only during one phase of Phase A.

[0070] As shown in Figure 6B, when the resonant frequency of tag 10 is between 57.7 kHz and 57.9 kHz, the 57.7 kHz burst signal in Phase A and the 58.0 kHz burst signal in Phase B cause tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the receiving windows of Phase A and Phase B. In contrast, the 58.3 kHz burst signal in Phase C does not cause tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the receiving window of Phase C. In other words, during each cycle of the commercial frequency power supply, tag 10 outputs a ringing-down signal of a detectable intensity above a certain level in both Phase A and Phase B phases.

[0071] As shown in Figure 6C, when the resonant frequency of tag 10 is 58.0 kHz, the burst signals of 57.7 kHz in Phase A, 58.0 kHz in Phase B, and 58.3 kHz in Phase C cause tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the receiving windows of Phase A, Phase B, and Phase C. In other words, during each cycle of the commercial frequency power supply, tag 10 outputs a ringing-down signal of a detectable intensity above a certain level in all three phases of Phase A, Phase B, and Phase C.

[0072] As shown in Figure 6D, when the resonant frequency of tag 10 is between 58.1 kHz and 58.3 kHz, the 58.0 kHz burst signal in Phase B and the 58.3 kHz burst signal in Phase C cause tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the receiving windows of Phase B and Phase C. In contrast, the 57.7 kHz burst signal in Phase A does not cause tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the receiving window of Phase A. That is, during each cycle of the commercial frequency power supply, tag 10 outputs a ringing-down signal of a detectable intensity above a certain level in both Phase B and Phase C phases.

[0073] As shown in Figure 6E, when the resonant frequency of tag 10 is between 58.4 kHz and 58.6 kHz, a 58.3 kHz burst signal in Phase C causes tag 10 to output a ringing-down signal of a detectable intensity above a certain level in the Phase C receiving window. In contrast, with a 57.7 kHz burst signal in Phase A and a 58.0 kHz burst signal in Phase B, tag 10 does not output a ringing-down signal of a detectable intensity above a certain level in the Phase A and Phase B receiving windows. That is, during each cycle of the commercial frequency power supply, a ringing-down signal of a detectable intensity above a certain level is output from tag 10 only during one phase of Phase C.

[0074] Thus, in the first embodiment, the combination of phases at which a ringing-down signal of a certain intensity or higher, detectable in the reception window, is output from the tag 10 differs for each of the following resonant frequencies: 57.4 kHz to 57.6 kHz (Figure 6A), 57.7 kHz to 57.9 kHz (Figure 6B), 58.0 kHz (Figure 6C), 58.1 kHz to 58.3 kHz (Figure 6D), and 58.4 kHz to 58.6 kHz (Figure 6E). Therefore, based on the combination of phases at which a ringing-down signal of a certain intensity or higher is received from the tag 10 for burst signals of different frequencies transmitted during each phase (three transmission periods within each cycle of the commercial frequency power supply), 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%).

[0075] (2) Figure 7 of the second embodiment is a diagram illustrating the second embodiment of the operating timing of the anti-theft system. In this embodiment, every two cycles of the commercial frequency power supply are divided into six phases P1 to P6, and a transmit window (transmit period) and a receive window (receive period) are set in each phase. In Figure 7, only the transmit windows (transmit periods) for each phase P1 to P6 are shown, but as in the first embodiment, in each phase, the transmit window of the transmit unit 20 is opened for a certain period of time, and a little later the receive window of the receive unit 30 is opened for a certain period of time.

[0076] The frequencies of the burst signals in each phase from P1 to P6 are as shown in Table 2 above. Thus, the frequencies of the burst signals in each phase are in the 57 kHz band or the 58 kHz band. In other words, 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 transmitting amplifier 22.

[0077] In the reception window following the 57.25 kHz burst signal at phase P1, tags 10 with a resonant frequency 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 intensity above a certain level.

[0078] In the reception window following the 57.55 kHz burst signal at phase P2, tags 10 with a resonant frequency 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 intensity above a certain level.

[0079] In the reception window following the 57.85 kHz burst signal at phase P3, tags 10 with a resonant frequency 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 intensity above a certain level.

[0080] In the reception window following the 58.15 kHz burst signal at phase P4, tags 10 with a resonant frequency 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 above a certain level.

[0081] In the reception window following the 58.45 kHz burst signal at phase P5, tags 10 with a resonant frequency 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 intensity above a certain level.

[0082] In the reception window following the 58.75 kHz burst signal at phase P6, tags 10 with a resonant frequency 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 above a certain level.

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

[0084] (3) Figure 8 of the third embodiment is a block diagram illustrating the third embodiment. In this example, only the configuration of the control unit 40 in the anti-theft system shown in Figure 1 is different, and the other configurations are the same as those in Figure 1, so the same reference numerals are used in the figure for similar configurations and detailed explanations are omitted.

[0085] As shown in Figure 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 resonant frequency detection processing unit 44. The resonant frequency detection processing unit 44 causes the transmission 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 ringing down signal output received by the reception unit 30 is highest as the resonant frequency.

[0086] Table 3 below shows an example of a burst signal transmitted by the burst signal transmission processing unit 41. This example describes the case where the power supply frequency is 60 Hz.

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

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

[0089] For each phase of each period tn, when the receiving unit 30 receives a ringing-down signal from the transmitted burst signal, it is determined whether the ringing-down signal has the highest output. 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 resonance frequency detection processing unit 44 detects the resonance frequency of the tag 10, the burst signal transmission processing unit 41 then transmits burst signals in a transmission pattern that includes the detected resonance frequency burst signal.

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

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

[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 related to that resonant frequency (resonant frequency - 0.1 kHz, resonant frequency, resonant frequency + 0.1 kHz) is transmitted at each cycle tn of the commercial frequency power supply thereafter, thereby enabling reliable detection of the tag 10. This makes it possible to avoid the influence of the anti-resonant frequency on the detection of the tag 10.

[0094] In the first to third embodiments described above, an anti-theft system was proposed that includes a transmission period (transmission window) for transmitting a burst signal in the 57 kHz band and a transmission period (transmission window) for transmitting a burst signal in the 58 kHz band at regular intervals of a commercial frequency (50 Hz or 60 Hz) power supply. This transmission control is performed based on the zero-crossing point of the commercial frequency power supply. As an application of the present invention, a DC power supply may be used instead of a commercial frequency power supply. In this case, it goes without saying that by changing the frequency of the burst signal in the transmission window and the subsequent reception window at regular intervals using the same method as in the above embodiments, it is possible to detect a tag 10 with a widened allowable resonant frequency.

[0095] 4. Notification Processing The notification processing unit 43 provides notification when the intensity of the ringing down signal received by the receiving unit 30 is above a threshold. The threshold may be set differently for each of the multiple reception periods (reception windows). For example, as in the first to third embodiments above, when each period 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 for each phase, different thresholds may be set for each reception window of Phase A, Phase B, and Phase C.

[0096] In this case, if the intensity of the ringing-down signal received by the receiving unit 30 is greater than or equal to a threshold in any of the receiving windows of Phase A, Phase B, and Phase C, the notification processing unit 43 may provide notification. Furthermore, if peaks appear in the ringing-down signal received by the receiving unit 30 in two or more phases of each of the receiving windows of Phase A, Phase B, and Phase C, the notification processing unit 43 may provide notification if the intensity of the largest peak is greater than or equal to a threshold.

[0097] 5. Adjustment of Phase Timing The phase timing of the transmission window (transmission period) and reception window (reception period) may be adjustable relative 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 reception window to avoid phase timings where the detection sensitivity of the tag 10 is poor due to environmental noise, etc.

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

[0099] If the phase of the receiving window overlaps with the phase of the transmitting window of another transmitting antenna 23 located nearby, and proper synchronization is not achieved, problems such as false alarms or a decrease in the detection sensitivity of the tag 10 may occur. Therefore, by adjusting the phase timing of the transmitting and receiving windows with respect to the phase of the commercial frequency power supply and properly synchronizing them, problems such as false alarms or a decrease in the detection sensitivity of the tag 10 can be prevented. In particular, with the AM system, the wavelength is longer than with the RF system, and interference is more likely to occur between anti-theft systems located relatively far apart from each other (for example, 100m), so caution is necessary.

[0100] Furthermore, a mode for controlling the transmit and receive windows (label detection mode) and a mode for not controlling the transmit and receive windows (noise measurement mode) may be provided. In this case, in noise measurement mode, the burst signal may not be transmitted in the transmit window, and the received signal (noise) from the receiving antenna 31 may be measured in terms of the phase relationship between the transmit / receive windows and the phase of each period (Phase A, Phase B, Phase C) of the commercial frequency power supply.

[0101] Furthermore, if a large amount of noise is measured at a specific phase in noise measurement mode, and the phase in which the noise is detected coincides with the reception window, the influence of the noise will be large. In such cases, the reception window may be adjusted by moving it to a phase where the influence of the noise is small.

[0102] 10 Tag 20 Transmitter 21 Oscillator 22 Transmitting Amplifier 23 Transmitting Antenna 30 Receiving Unit 31 Receiving Antenna 32 Receiving Amplifier 33 Narrowband Filter 40 Control Unit 41 Burst Signal Transmission Processing Unit 42 Tag Detection Processing Unit 43 Notification Processing Unit 44 Resonant Frequency Detection Processing Unit 50 Speaker

Claims

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

2. An acoustic magnetic anti-theft system comprising: a transmitting unit that transmits a burst signal during a transmission period; a tag that resonates with the burst signal transmitted from the transmitting unit and outputs a ringing-down signal; a receiving unit that receives the ringing-down signal during a reception period after the transmission period; and a tag detection processing unit that detects the tag based on the ringing-down signal received by the receiving unit, wherein each cycle of the commercial frequency power supply includes 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.

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

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

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

6. The anti-theft system according to claim 1, further comprising a resonant frequency detection processing unit that transmits burst signals of different frequencies in the 57 kHz band or the 58 kHz band from the transmitting unit 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 is highest as the resonant frequency of the tag, wherein, after the resonant frequency of the tag has been detected, transmission is performed with a transmission pattern that includes the burst signal of the resonant frequency during the transmission period of each cycle of the commercial frequency power supply.

7. The anti-theft system according to claim 1, wherein the phase timing of the transmission period and the reception period is adjustable with respect to the phase of the commercial frequency power supply.

8. The anti-theft system according to claim 1, further comprising an alarm processing unit that issues an alarm when the intensity of the ringing down signal received by the receiving unit is equal to or greater than a threshold, wherein different thresholds are set for each of the multiple reception periods.

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

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