Anti-theft system

Abstract

The present application provides an anti-theft system of an acoustic magnetic (AM) method capable of expanding the allowable range of the resonance frequency of a tag. The anti-theft system of the acoustic magnetic method includes a transmitting section 20, a tag 10, a receiving section 30, and a tag detection processing section 42. The transmitting section 20 transmits an excitation pulse signal during a transmission period. The tag 10 resonates due to the excitation pulse signal transmitted from the transmitting section 20 and outputs a ring-down signal. The receiving section 30 receives the ring-down signal during a reception period after the transmission period. The tag detection processing section 42 detects the tag 10 based on the ring-down signal received by the receiving section 30. The transmission period in which the excitation pulse signal of the 57 kHz band is transmitted and the transmission period in which the excitation pulse signal of the 58 kHz band is transmitted are included in each certain period.

Description

Technical Field

[0001] This invention relates to an acoustic-magnetic anti-theft system. Background Technology

[0002] As an example of an anti-theft system, there are two known electronic article surveillance (EAS) security systems that use radio frequency (RF) and acousto-magnetic (AM) methods.

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

[0004] The characteristic of RF-based anti-theft systems is that the high-frequency magnetic field from the transmitting coil is not a fixed frequency, but rather a continuously scanning frequency. Typically, the scanning frequency ranges from (8.2MHz-10%) to (8.2MHz+10%). When the oscillation frequency of the transmitter during the scan matches the resonant frequency of the LC resonant circuit in the RF security sign, the RF security sign begins to oscillate, and a significant voltage drop (DIP) occurs in the sensor coil that detects the signal from the RF security sign.

[0005] Typically, the management of the resonant frequency of RF safety tags is significantly affected by the quality control of the manufacturing process. However, by using a scanning method with a wider frequency range (8.2MHz ± 10%) of the excitation magnetic field as described above, the permissible resonant frequency range of the RF safety tag is 8.2MHz ± 10%, which is a wide range and does not require strict quality control. As a result, the cost of the RF safety tag can be reduced.

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

[0007] In contrast, AM (Advanced AM) anti-theft systems employ pulse-listening. Pulse-listening involves using the zero-crossing of a 50Hz or 60Hz commercial frequency power signal as the trigger. After a certain time following the zero-crossing, the transmitter's transmit window (TX window) (typically 1.4ms to 2.0ms wide) opens, during which a 58kHz burst signal is emitted. Shortly afterward (usually about 0.2ms later), the receiver's receive window (RX window) opens for a short period (typically 2.0ms to 5.0ms), during which the system detects the response signal from the tag.

[0008] In AM-based anti-theft systems, label tags with a resonant frequency in the 58kHz band (see, for example, Patent Document 1 below) or hard tags composed of LC resonant circuits are used. When these tags receive a 58kHz excitation pulse signal during the transmission period of the excitation pulse signal when the transmitter's transmission window is open, they accumulate excitation energy. After a certain period following the end of the excitation pulse signal transmission period, they output a ringing down signal at the tag's resonant frequency. Subsequently, during the reception period when the receiver's reception window is open, the receiver receives the attenuated radio waves (ringing down signal) emitted from the tag. Based on the time interval, frequency, and attenuation of the ringing down signal, it is determined whether the signal originates from the tag. If it is determined to be a signal from the tag, an alarm is triggered.

[0009] The identification tags used in AM-type anti-theft systems are structures made of multiple parallel amorphous metal thin plates, designed to resonate with 58kHz 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 coil (L) of a ferrite core, and its resonant frequency is set to 58kHz.

[0010] As a quality management standard for AM-based anti-theft systems, the tag's resonant frequency is set at 58.0kHz ± 0.52% (58.0kHz ± 0.3kHz). This standard ensures that when the transmitter emits a 58.0kHz excitation pulse signal, the receiver can detect tags within the permissible resonant frequency range at a distance (tag sensitivity) of approximately 70% or more of the maximum tag sensitivity at the resonant frequency of 58.0kHz.

[0011] A comparison of RF and AM methods yields the following results. First, regarding the price of transmitters and receivers, RF methods were previously cheaper, but now AM methods are priced at a level comparable to RF methods. Regarding tag prices, RF methods have historically been cheaper, and there is a strong demand for low-cost AM tags.

[0012] Regarding the management standards for the resonant frequency of tags, compared to the wider allowable range of 8.2MHz ± 10% in the RF method, the AM method, as mentioned above, has a very narrow allowable range of 58.0kHz ± 0.52% (58.0kHz ± 0.3kHz) for the resonant frequency. This results in excessively high quality management costs.

[0013] Furthermore, regarding stability issues such as false alarms, the RF method is prone to false alarms due to the excitation frequency (8.2MHz) being the same as the ship's radio frequency, and its susceptibility to interference from products (such as cable coils) with a resonant frequency of 8.2MHz ± 10%. In contrast, the AM method offers higher stability compared to the RF method, with almost no false alarms.

[0014] Patent documents Patent Document 1: US Patent No. 4,510,489 Summary of the Invention As mentioned above, the prices of transmitters and receivers for RF and AM methods have become comparable. Therefore, if the price of AM tags can be reduced, AM-based anti-theft systems, which are less prone to false alarms and highly stable, are likely to become mainstream.

[0015] Regarding this point, the deviation of the resonant frequency of AM tags has been greatly improved. Therefore, if the permissible range of the resonant frequency of AM tags can be expanded from the current 58kHz±0.5% to about 58kHz±1.0%, the price of AM tags can be reduced by 40-60%.

[0016] The present invention was made in view of the above-mentioned actual situation, and its purpose is to provide an acousto-magnetic (AM) anti-theft system that can expand the permissible range of the resonant frequency of the tag.

[0017] (1) The first anti-theft system of the present invention is an acousto-magnetic anti-theft system, which includes a transmitter, a tag, a receiver, and a tag detection processing unit. The transmitter emits an excitation pulse signal during the transmission period. The tag resonates due to the excitation pulse signal emitted from the transmitter and outputs a ringing attenuation signal. The receiver receives the ringing attenuation signal during a reception period following the transmission period. The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiver. Each fixed cycle includes a transmission period emitting an excitation pulse signal in the 57 kHz frequency band and a transmission period emitting an excitation pulse signal in the 58 kHz frequency band.

[0018] Based on this structure, since each certain period includes a transmission period for transmitting an excitation pulse signal in the 57kHz band and a transmission period for transmitting an excitation pulse signal in the 58kHz band, the permissible range of the tag's resonant frequency can be expanded, thereby reducing the price of the tag.

[0019] (2-1) The second anti-theft system of the present invention is an acousto-magnetic anti-theft system, which includes a transmitter, a tag, a receiver, and a tag detection processing unit. The transmitter emits an excitation pulse signal during the transmission period. The tag resonates due to the excitation pulse signal emitted from the transmitter and outputs a ringing attenuation signal. The receiver receives the ringing attenuation signal during a reception period following the transmission period. The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiver. Each cycle of a commercial frequency (60Hz or 50Hz) power supply includes a transmission period for emitting an excitation pulse signal in the 57kHz band and a transmission period for emitting an excitation pulse signal in the 58kHz band.

[0020] Based on this structure, since each cycle of a commercial frequency power supply includes a transmission period for an excitation pulse signal in the 57kHz band and a transmission period for an excitation pulse signal in the 58kHz band, the permissible range of the resonant frequency of the acousto-magnetic tag can be expanded from the current 58.0kHz ± 0.5% to at least approximately 58.0kHz ± 1.0%. Thus, by expanding the permissible range of the tag's resonant frequency, the price of the tag can be reduced.

[0021] (2-2) Each cycle of the commercial frequency power supply may include a transmission period for transmitting a 57.7 kHz excitation pulse signal, a transmission period for transmitting a 58.0 kHz excitation pulse signal, and a transmission period for transmitting a 58.3 kHz excitation pulse signal.

[0022] Based on this structure, by considering whether a combination of transmission periods / phases during which a ringing attenuation signal of a certain intensity is received at the tag, based on the different frequencies of the excitation pulse signals emitted during the three transmission periods in each cycle of a commercial frequency power supply, tags with a wider resonant frequency range of approximately 58.0 kHz ± 1.0% can be detected.

[0023] (3-1) The third anti-theft system of the present invention is an acousto-magnetic anti-theft system, which includes a transmitter, a tag, a receiver, and a tag detection processing unit. The transmitter emits an excitation pulse signal during the transmission period. The tag resonates due to the excitation pulse signal emitted from the transmitter and outputs a ringing attenuation signal. The receiver receives the ringing attenuation signal during a reception period following the transmission period. The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiver. Each two cycles of a commercial frequency power supply include a transmission period for emitting an excitation pulse signal in the 57kHz band and a transmission period for emitting an excitation pulse signal in the 58kHz band.

[0024] Based on this structure, since each two cycles of the commercial frequency power supply includes a transmission period for an excitation pulse signal in the 57kHz band and a transmission period for an excitation pulse signal in the 58kHz band, the permissible range of the resonant frequency of the acousto-magnetic tag can be expanded from the current 58.0kHz ± 0.5% to at least approximately 58.0kHz ± 1.5%. Thus, by expanding the permissible range of the tag's resonant frequency, the price of the tag can be reduced.

[0025] (3-2) The transmission period of transmitting a 57.25kHz excitation pulse signal, the transmission period of transmitting a 57.55kHz excitation pulse signal, the transmission period of transmitting a 57.85kHz excitation pulse signal, the transmission period of transmitting a 58.15kHz excitation pulse signal, the transmission period of transmitting a 58.45kHz excitation pulse signal, and the transmission period of transmitting a 58.75kHz excitation pulse signal may be included in every two cycles of the commercial frequency power supply.

[0026] Based on this structure, tags with a wider resonant frequency range of approximately 58.0kHz ± 1.5% can be detected by observing whether a ringing attenuation signal of a certain intensity is received from the tag during the six transmission periods within every two cycles of a commercial frequency power supply.

[0027] (4) The aforementioned anti-theft system may further include a resonant frequency detection and processing unit. This unit, within multiple cycles of the commercial frequency power supply, causes the transmitting unit to emit excitation pulse signals of different frequencies in the 57kHz or 58kHz frequency band during the transmission period of each cycle, and detects the highest frequency of the ringing attenuation signal received by the receiving unit 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 tag's resonant frequency, transmission is performed in a transmission mode containing the excitation pulse signal of the resonant frequency (fr). The transmission mode can be a (fr-0.1kHz, fr, fr+0.1kHz) mode (see Table 4 below).

[0028] Based on this structure, the tag can be detected by pre-detecting its resonant frequency and then transmitting an excitation pulse signal at that resonant frequency during the transmission period in each cycle of the subsequent commercial frequency power supply. This avoids the influence of the anti-resonant frequency (see Patent Document 1) on tag detection.

[0029] (5) The phase timing during the above-mentioned transmission and reception periods can be adjusted relative to the phase of the commercial frequency power supply.

[0030] Based on this structure, the detection sensitivity of the tag can be improved by setting the transmission and reception periods to avoid phase timing that is noisy and has poor tag detection sensitivity.

[0031] (6) The above-mentioned anti-theft system may further include a notification processing unit that issues an alarm notification when the strength of the ringing attenuation signal received by the receiving unit is above a threshold. In this case, a different threshold may be set for each of the plurality of receiving periods.

[0032] Based on this structure, different thresholds are set for each of the multiple reception periods, and notifications are made based on whether the intensity of the ringing attenuation signal received by the receiving unit in each reception period is above the threshold. This enables sensitive detection of tags with a wide permissible resonant frequency range and provides notifications.

[0033] (7) The tag detection processing unit can detect the tag when the frequency of the ringing attenuation signal received by the receiving unit is within the permissible resonant frequency range.

[0034] Based on this structure, the tag detection accuracy can be improved by detecting the tag only when the frequency of the ringing attenuation signal received by the receiving unit is within the allowable resonant frequency range.

[0035] According to the present invention, an acousto-magnetic (AM) anti-theft system capable of expanding the permissible range of the tag's resonant frequency can be provided. Attached Figure Description

[0036] Figure 1 This is a block diagram illustrating a structural example of an anti-theft system according to one embodiment of the present invention.

[0037] Figure 2 This figure illustrates an example of the ringing-reducing signal output strength when a non-failable tag with a different resonant frequency is excited by a 58.0 kHz excitation pulse signal from an AM antenna.

[0038] Figure 3 This figure illustrates an example of how ringing weakens the signal output when a 58.0 kHz excitation pulse signal from an AM antenna is used to excite a malfunctionable tag with a different resonant frequency.

[0039] Figure 4 A graph illustrating the relationship between the strength of the ringing attenuation signal and the sensitivity of the tag.

[0040] Figure 5 This is a diagram illustrating the timing of the operation of a first embodiment of an anti-theft system.

[0041] Figure 6A The diagram used to illustrate the permissible range of the resonant frequency of the tag 10 in the first embodiment shows the case where the resonant frequency of the tag is 57.4 kHz to 57.6 kHz.

[0042] Figure 6B The diagram used to illustrate the permissible range of the resonant frequency of the tag 10 in the first embodiment shows the case where the resonant frequency of the tag is 57.7 kHz to 57.9 kHz.

[0043] Figure 6C The diagram used to illustrate the permissible range of the resonant frequency of the tag 10 in the first embodiment shows the case where the resonant frequency of the tag is 58.0 kHz.

[0044] Figure 6D The diagram used to illustrate the permissible range of the resonant frequency of the tag 10 in the first embodiment shows the case where the resonant frequency of the tag is 58.1 kHz to 58.3 kHz.

[0045] Figure 6E The diagram used to illustrate the permissible range of the resonant frequency of the tag 10 in the first embodiment shows the case where the resonant frequency of the tag is 58.4 kHz to 58.6 kHz.

[0046] Figure 7 This is a diagram illustrating the timing of the operation of a second embodiment of an anti-theft system.

[0047] Figure 8 This is a block diagram used to illustrate the third embodiment. Detailed Implementation

[0048] 1. Overall structure of the anti-theft system Figure 1 This is a block diagram illustrating a structural example of an anti-theft system according to one embodiment of the present invention. This anti-theft system is an electronic article surveillance (EAS) security system that uses an acoustic-magnetic (AM) method, and includes a tag 10, a transmitter 20, a receiver 30, a control unit 40, and a speaker 50, etc. The transmitter 20 and receiver 30 are installed at store entrances and exits, etc.

[0049] Tag 10 is an identification tag affixed to a product for the purpose of theft prevention and monitoring. In an acousto-magnetic anti-theft system, the identification tag 10 has a structure consisting of multiple parallel amorphous metal sheets with an internal magnet. However, tag 10 is not limited to identification tags; it can also be a hard tag consisting of a magnetic coil with winding wire wound around a ferrite core and a capacitor forming an LC resonant circuit.

[0050] If the magnet inside tag 10 is demagnetized at the store's checkout counter or similar location, tag 10 will become ineffective and will not be detected by the receiving unit 30. In other words, tag 10 is effective when attached to an item before purchase; when attempting to remove the item from the store, the receiving unit 30 will detect tag 10 and issue an alarm. However, after purchase, by deactivating tag 10 at the checkout counter or similar location, tag 10 will not be detected by the receiving unit 30, allowing the item to be removed from the store.

[0051] The transmitting unit 20 includes an oscillator 21, a transmitting amplifier 22, and a transmitting antenna 23. The oscillator 21 has an oscillation circuit for transmitting excitation pulse signals in the 57kHz band and an oscillation circuit for transmitting excitation pulse signals in the 58kHz band. During each transmission period of a certain cycle, the transmission window (TX window) is open, and during this period, the 57kHz and 58kHz excitation pulse signals are transmitted from the transmitting antenna 23 through the transmitting amplifier 22.

[0052] When tag 10 is present within a certain distance relative to transmitting antenna 23, tag 10 oscillates due to the excitation pulse signal emitted from transmitting antenna 23. Specifically, when tag 10 receives an excitation pulse signal with a frequency close to its resonant frequency, during the transmission period when the transmission window of transmitting unit 20 is open, tag 10 accumulates excitation energy, and after a certain period following the end of the transmission period of the excitation pulse signal, it outputs a ringing down signal at the resonant frequency of tag 10.

[0053] The receiving unit 30 includes a receiving antenna 31, a receiving amplifier 32, and a narrowband filter 33. When the tag 10 is present within a certain distance relative to the receiving antenna 31, when the tag 10 oscillates due to the excitation pulse signal, the receiving antenna 31 can receive the ringing reduction signal from the tag 10.

[0054] Specifically, shortly after the transmission of the excitation pulse signal (transmission window) (typically 1.4ms to 2.0ms) (typically about 0.2ms later), the receiving window (RX window) of the receiving unit 30 is only open for a certain period of time (typically about 2.0ms to 5.0ms). During the reception period when the receiving window of the receiving unit 30 is open, the ringing attenuation signal from the tag 10 is received by the receiving antenna 31 and input to the control unit 40 via the receiving amplifier 32 and the narrowband filter 33.

[0055] The control unit 40 includes a processor, such as a CPU (Central Processing Unit), which executes programs to perform the processing required for the operation of the anti-theft system. The control unit 40 may consist of a single control device or multiple control devices. For example, it may be configured to receive control data via an MPU (Micro Processor Unit) controller and perform other controls via a system controller.

[0056] The control unit 40 executes programs through a processor and functions as various processing units such as the excitation pulse signal transmission processing unit 41, the tag detection processing unit 42, and the notification processing unit 43. However, the control unit 40 is not limited to these processing units and may also function as other processing units.

[0057] The excitation pulse signal transmission processing unit 41 performs processing for transmitting an excitation pulse signal from the transmission unit 20. That is, through the processing of the excitation pulse signal transmission processing unit 41, an excitation pulse signal of a preset frequency is transmitted from the transmission unit 20 during a preset transmission period (transmission window).

[0058] The tag detection processing unit 42 performs processing for detecting tag 10 based on the signal from the receiving unit 30. Specifically, the tag detection processing unit 42 detects tag 10 based on the ringing attenuation signal from tag 10 received by the receiving unit 30 during the aforementioned receiving window.

[0059] By providing a 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 frequency of the ringing attenuation signal received by the receiving unit 30 is within a certain range. This improves the detection accuracy of the tag 10. The narrowband filter 33 can be a quadrature mirror filter (QMF). However, the narrowband filter 33 can also be omitted.

[0060] The notification processing unit 43 performs notification processing based on the ringing attenuation signal received by the receiving unit 30 from the tag 10. Specifically, when the tag detection processing unit 42 detects the tag 10 based on the ringing attenuation signal received by the receiving unit 30 from the tag 10, it outputs an alarm from the speaker 50 to notify that the item with the tag 10 attached has been stolen.

[0061] 2. Detailed explanation of the label (1) The resonant frequency and anti-resonant frequency of the tag Label 10 shows that the accumulation and output of excitation energy reach their maximum at the resonance frequency (fr: resonance frequency), but there is an anti-resonance frequency (fa: anti-resonance frequency) at a frequency slightly higher than the resonance frequency. At this anti-resonance frequency, the accumulation and output of excitation energy reach their minimum (see Patent Document 1).

[0062] Tag 10 is divided into two types: deactivatable tags and non-deactivatable tags. That is, a tag is deactivatable if the magnetic force of the magnet inside the tag 10 can be eliminated, and a tag is non-deactivatable if the magnetic force of the magnet inside the tag 10 cannot be eliminated.

[0063] The electromagnetic coupling factor of the deactivatable tag 10 is relatively small. Furthermore, in the deactivatable tag 10, fa-fr ≈ 0.1 kHz, and the anti-resonant frequency (fa) is very close to the resonant frequency (fr).

[0064] In contrast, the non-failable tag 10 has a larger electromagnetic coupling factor. Furthermore, in the non-failable tag 10, fa-fr ≈ 0.3 kHz, indicating a significant difference between the anti-resonant frequency (fa) and the resonant frequency (fr).

[0065] (2) Detailed description of the non-expirable label Figure 2 This figure illustrates an example of the ringing attenuation signal strength when a non-failable tag 10 with a different resonant frequency is excited by a 58.0 kHz excitation pulse signal from an AM antenna. Figure 2 In the diagram, the horizontal axis represents the resonant frequency of label 10, and the vertical axis represents the voltage of the ringing attenuation signal.

[0066] In this example, the case where an excitation pulse signal is transmitted at an excitation frequency of 58.0 kHz, causing the non-failable tag 10 to resonate and output a ringing attenuation signal is illustrated. As a measurement condition, the transmission window has a time width of 1.6 ms, and the voltage of the ringing attenuation signal is measured 0.4 ms after the transmission window closes.

[0067] like Figure 2 As shown, when the resonant frequency of tag 10 is 57.7 kHz, a voltage drop in the ringing attenuation signal can be observed. This is because the excitation frequency of the excitation pulse signal, 58.0 kHz, corresponds to the anti-resonant frequency (fa) of tag 10 at the resonant frequency of 57.7 kHz. While the permissible range of the resonant frequency of tag 10 is currently 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), this permissible range includes the resonant frequency of 57.7 kHz. Although a voltage drop in the ringing attenuation signal can be observed relative to the 58.0 kHz excitation pulse signal at the resonant frequency of tag 10, the tag can still be detected by the system's receiving unit 30.

[0068] (3) Detailed description of expiration labels Figure 3 This figure illustrates an example of the ringing attenuation signal output strength when a malfunctionable tag 10 is energized by a 58.0 kHz excitation pulse signal from an AM antenna. Figure 3 In the diagram, the horizontal axis represents the resonant frequency of label 10, and the vertical axis represents the voltage of the ringing attenuation signal.

[0069] In this example, the case where an excitation pulse signal is transmitted at an excitation frequency of 58.0 kHz, causing the deactivated tag 10 to resonate and output a ringing attenuation signal is illustrated. As a measurement condition, the transmission window has a time width of 1.6 ms, and the voltage of the ringing attenuation signal is measured 0.4 ms after the transmission window closes.

[0070] like Figure 3 As shown, when the resonant frequency of tag 10 is 57.8kHz to 57.9kHz, a voltage drop in the ringing attenuation signal can be observed. This is because the excitation frequency of the excitation pulse signal, 58.0kHz, corresponds to the anti-resonant frequency (fa) of tag 10, which is also within the resonant frequency range of 57.8kHz to 57.9kHz. Given that the permissible range of the resonant frequency of tag 10 is currently 58kHz ± 0.52% (58.0kHz ± 0.3kHz), this permissible range includes the resonant frequency range of 57.8kHz to 57.9kHz. Although a drop in the ringing attenuation signal occurs relative to the excitation pulse signal generated by tag 10 with a resonant frequency of 57.8kHz to 57.9kHz at the 58.0kHz resonant frequency, the tag can still be detected by the system's receiving unit 30.

[0071] (4) Ringing attenuation signal and tag sensitivity Figure 4 A graph illustrating the relationship between the strength of the ringing attenuation signal and the sensitivity of the tag. Figure 4 In the diagram, the horizontal axis represents the voltage of the ringing attenuation signal, and the vertical axis represents the sensitivity of tag 10 (tag sensitivity).

[0072] "Tag sensitivity" refers to the distance (distance between tag 10 and receiving antenna 31) at which the receiving antenna 31 can detect a tag 10 within its permissible resonant frequency range. For example... Figure 4 As shown, the ringing attenuation signal is approximately proportional to the sensitivity of tag 10. Therefore, in order to detect tag 10, the voltage of the ringing attenuation signal needs to be above a certain value, and the tag sensitivity is determined based on its relationship with this certain value.

[0073] (5) The allowable range of the tag's resonant frequency and the excitation frequency of the excitation pulse signal. The resonant frequency of tag 10, which shows a voltage drop in the ringing weakening signal relative to the excitation frequency of the excitation pulse signal of 58.0 kHz, is as described above. In the case of a non-failable tag 10, it is 57.7 kHz, and in the case of a failable tag 10, it is 57.8 kHz to 57.9 kHz. However, under the current circumstances, 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), which includes these resonant frequencies, can be used as the permissible range of the resonant frequency of tag 10.

[0074] In other words, when the excitation frequency for generating the pulse signal is 58.0 kHz as is currently the case, by applying the necessary excitation to the tag 10, whose resonant frequency has an allowable range of 58 kHz ± 0.52% (58.0 kHz ± 0.3 kHz), a ringing attenuation signal with an output voltage above a certain value will be generated from the tag 10, indicating that the tag 10 can be detected without problems. Against this background, an embodiment of an anti-theft system applicable to both non-failable and failable tags 10, and capable of expanding the allowable resonant frequency range of the tag 10, will be described below.

[0075] 3. Examples In the following embodiments, within one or two cycles of the commercial frequency power supply (50Hz or 60Hz), there is a transmission period for transmitting an excitation pulse signal in the 57kHz band and a transmission period for transmitting an excitation pulse signal in the 58kHz band. That is, conventionally, within one cycle of the commercial frequency power supply, the transmission period for transmitting the 58.0kHz excitation pulse signal occurs only once, while in the following embodiments, it is configured that within one or two cycles of the commercial frequency power supply, the transmission periods for transmitting the 57kHz band excitation pulse signal and the transmission periods for transmitting the 58kHz band excitation pulse signal occur multiple times with different phases.

[0076] (1) First embodiment Figure 5 This diagram illustrates a first embodiment of the timing for the operation 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. Each phase has a transmission window (transmission period) and a reception window (reception period). Specifically, at the initial timing of each phase, the transmission window of the transmitter 20 is opened for approximately 1.4 ms to 2.0 ms, during which an excitation pulse signal is transmitted from the transmitter 20. Furthermore, shortly after the transmission window in each phase (approximately 0.2 ms later), the reception window of the receiver 30 is opened for only a short period (approximately 2.0 ms to 3.0 ms), during which a ringing attenuation signal from the tag 10 is received.

[0077] The frequencies of the excitation pulse signals in each phase, including phases A, B, and C, are shown in Table 1. Thus, the frequencies of the excitation pulse signals in each phase are either in the 57kHz or 58kHz band. That is, each cycle of the commercial frequency power supply includes a transmission period for the 57kHz excitation pulse signal and a transmission period for the 58kHz excitation pulse signal. The output of the excitation pulse signal in each phase is controlled to be constant by the transmitting amplifier 22.

[0078] [Table 1]

[0079] Figures 6A-6E This is a diagram illustrating the permissible range of the resonant frequency of tag 10 in the first embodiment. The vertical lines during the transmission window represent the absorption area of ​​excitation energy in tag 10, and the attenuation marks after the transmission window represent the ringing reduction signal of tag 10. Figure 6A This indicates that when the resonant frequency of tag 10 is 57.4kHz~57.6kHz, a strong ringing weakening signal of tag 10 may appear in the receiving window of phase A. Figure 6B This indicates that when the resonant frequency of tag 10 is 57.7kHz~57.9kHz, a strong ringing weakening signal of tag 10 may appear in the receiving windows of phase A and phase B. Figure 6C This indicates that when the resonant frequency of tag 10 is 58.0kHz, a strong ringing attenuation signal of tag 10 may appear in the receiving windows of phase A, phase B, and phase C. Figure 6D This indicates that the resonant frequency of tag 10 is between 58.1kHz and 58.3kHz. Figure 6E This indicates the case where the resonant frequency of tag 10 is 58.4kHz to 58.6kHz. It should be noted that even if the resonant frequency of tag 10 is not the same as the frequency of the excitation pulse signal, as long as the resonant frequency of tag 10 is within ±0.3kHz of the frequency of the excitation pulse signal, the ringing attenuation signal of tag 10 will be output at a detectable intensity above a certain level in the receiving window of the transmitting window following the excitation pulse signal.

[0080] like Figure 6A As shown, when the resonant frequency of tag 10 is 57.4kHz~57.6kHz, the 57.7kHz excitation pulse signal in phase A will cause tag 10 to output a ringing reduction signal of a certain intensity and detectable strength within the receiving window of phase A. Conversely, with the 58.0kHz excitation pulse signal in phase B and the 58.3kHz excitation pulse signal in phase C, tag 10 will not output a ringing reduction signal of a certain intensity and detectable strength within the receiving windows of phases B and C, respectively. In other words, within each cycle of a commercial frequency power supply, a ringing reduction signal of a certain intensity and detectable strength will only be output from tag 10 in phase A.

[0081] like Figure 6BAs shown, when the resonant frequency of tag 10 is 57.7kHz~57.9kHz, the 57.7kHz excitation pulse signal in phase A and the 58.0kHz excitation pulse signal in phase B will cause tag 10 to output a ringing reduction signal of a certain intensity and detectable strength within the receiving windows of phases A and B, respectively. Conversely, with the 58.3kHz excitation pulse signal in phase C, tag 10 will not output a ringing reduction signal of a certain intensity and detectable strength within the receiving window of phase C. In other words, within each cycle of the commercial frequency power supply, a ringing reduction signal of a certain intensity and detectable strength will be output from tag 10 in both phases A and B.

[0082] like Figure 6C As shown, when the resonant frequency of tag 10 is 58.0kHz, the 57.7kHz excitation pulse signal in phase A, the 58.0kHz excitation pulse signal in phase B, and the 58.3kHz excitation pulse signal in phase C will cause tag 10 to output a ringing reduction signal of a certain intensity and detectable strength within the receiving windows of phases A, B, and C. In other words, within each cycle of the commercial frequency power supply, a ringing reduction signal of a certain intensity and detectable strength will be output from tag 10 in all phases of phases A, B, and C.

[0083] like Figure 6D As shown, when the resonant frequency of tag 10 is 58.1kHz~58.3kHz, the 58.0kHz excitation pulse signal in phase B and the 58.3kHz excitation pulse signal in phase C will cause tag 10 to output a ringing reduction signal of a certain intensity and detectable strength within the receiving windows of phases B and C, respectively. Conversely, with the 57.7kHz excitation pulse signal in phase A, tag 10 will not output a ringing reduction signal of a certain intensity and detectable strength within the receiving window of phase A. In other words, within each cycle of the commercial frequency power supply, a ringing reduction signal of a certain intensity and detectable strength will be output from tag 10 in phases B and C.

[0084] like Figure 6EAs shown, when the resonant frequency of tag 10 is 58.4kHz to 58.6kHz, the 58.3kHz excitation pulse signal in phase C will cause tag 10 to output a ringing reduction signal of a certain intensity and detectable strength within the receiving window of phase C. Conversely, with the 57.7kHz excitation pulse signal in phase A and the 58.0kHz excitation pulse signal in phase B, tag 10 will not output a ringing reduction signal of a certain intensity and detectable strength within the receiving windows of phases A and B, respectively. In other words, within each cycle of a commercial frequency power supply, a ringing reduction signal of a certain intensity and detectable strength is only output from tag 10 in one phase of phase C.

[0085] Thus, in the first embodiment, when the resonant frequency of tag 10 is 57.4kHz to 57.6kHz ( Figure 6A ( ), for the case of 57.7kHz~57.9kHz ( Figure 6B ), for the case of 58.0kHz ( Figure 6C (The case where the frequency is 58.1kHz to 58.3kHz) Figure 6D ) and the case of 58.4kHz~58.6kHz ( Figure 6E In various cases, the combination of phases of the ringing attenuation signal with a detectable intensity above a certain strength will be output by tag 10 in the receiving window. Therefore, based on whether the combination of phases of the excitation pulse signal of different frequencies transmitted in each phase (within the three transmission periods of each cycle of the commercial frequency power supply) will be received from tag 10, a wider resonant frequency range of 57.4kHz to 58.6kHz (approximately 58kHz ± 1.0%) can be detected for tag 10.

[0086] (2) Second embodiment Figure 7 This diagram illustrates a second embodiment of the timing system for the operation of an anti-theft system. In this example, every two cycles of the commercial frequency power supply are divided into six phases, P1 to P6, each with a transmission window (transmission period) and a reception window (reception period). It should be noted that... Figure 7 The illustration only shows the transmission window (during transmission) in each phase P1 to P6, but as in the first embodiment, in each phase, the transmission window of the transmitting unit 20 is opened for a certain period of time, and then the receiving window of the receiving unit 30 is opened for a certain period of time shortly thereafter.

[0087] [Table 2]

[0088] The frequencies of the excitation pulse signals in each phase (P1-P6) are shown in Table 2 above. Thus, the frequencies of the excitation pulse signals in each phase are either in the 57kHz or 58kHz band. That is, each two cycles of the commercial frequency power supply includes a transmission period for the 57kHz excitation pulse signal and a transmission period for the 58kHz excitation pulse signal. The output of the excitation pulse signal in each phase is controlled to be constant by the transmitting amplifier 22.

[0089] Within the receiving window of the excitation pulse signal following phase P1 at 57.25 kHz, the tag 10 with a resonant frequency in the range of 56.95 kHz to 57.55 kHz (57.25 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0090] Within the receiving window of the excitation pulse signal following phase P2 at 57.55 kHz, the tag 10 with a resonant frequency in the range of 57.25 kHz to 57.85 kHz (57.55 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0091] Within the receiving window of the excitation pulse signal following phase P3 at 57.85 kHz, the tag 10 with a resonant frequency in the range of 57.55 kHz to 58.15 kHz (57.85 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0092] Within the receiving window of the excitation pulse signal following phase P4 at 58.15 kHz, the tag 10 with a resonant frequency in the range of 57.85 kHz to 58.45 kHz (58.15 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0093] Within the receiving window of the excitation pulse signal following phase P5 at 58.45 kHz, tag 10 with a resonant frequency in the range of 58.15 kHz to 58.75 kHz (58.45 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0094] Within the receiving window of the excitation pulse signal following phase P6 at 58.75 kHz, the tag 10 with a resonant frequency in the range of 58.45 kHz to 59.05 kHz (58.75 kHz ± 0.3 kHz) can be detected with a ringing intensity greater than a certain level to reduce the signal strength.

[0095] Thus, in the second embodiment, tags 10 with resonant frequencies in the range of 56.95kHz to 59.05kHz, i.e., 58.0kHz ± 1kHz (± 1.7%), can be detected. Therefore, based on whether a ringing attenuation signal of a certain intensity or higher is received from tag 10 in the receiving window of the transmission window following the excitation pulse signal, for excitation pulse signals of different frequencies transmitted in each phase (six transmission periods within every two cycles of a commercial frequency power supply), tags 10 with a wider resonant frequency range of approximately 58kHz ± 1.7% can be detected.

[0096] (3) Third embodiment Figure 8 This is a block diagram used to illustrate the third embodiment. In this example, only... Figure 1 The control unit 40 in the anti-theft system shown has a different structure; other structures are the same. Figure 1 Since the structures are the same, the same symbols are used to label the same structures in the figure and their detailed descriptions are omitted.

[0097] like Figure 8 As shown, in addition to the excitation pulse signal transmission processing unit 41, tag detection processing unit 42, and notification processing unit 43, the control unit 40 also functions as a resonant frequency detection processing unit 44. The resonant frequency detection processing unit 44 causes the transmitting unit 20 to transmit excitation pulse signals of different frequencies in the 57kHz or 58kHz frequency band during the transmission period of each cycle of the commercial frequency power supply, and detects the highest frequency of the ringing attenuation signal received by the receiving unit 30 as the resonant frequency.

[0098] Table 3 below shows an example of an excitation pulse signal emitted after processing by the excitation pulse signal emission processing unit 41. In this example, the case where the power supply frequency is 60Hz will be explained. [Table 3]

[0099] 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. Each phase has a transmission window (transmission period) and a reception window (reception period). Excitation pulse signals of different frequencies are transmitted in each phase. Specifically, in each phase of each cycle tn, the frequency of the excitation pulse signal is swept at 0.1 kHz intervals.

[0100] The scanning frequency range is 57.4kHz to 58.6kHz, and the excitation pulse signal is repeatedly emitted at frequencies within this range. It should be noted that with a commercial power supply frequency of 60Hz, the elapsed time within each cycle tn is 16ms, which is very short. Even if the range of 57.4kHz to 58.6kHz is repeated 3 times, as shown in Table 3 above, the elapsed time is approximately 208ms.

[0101] When the receiving unit 30 receives a ringing attenuation signal after receiving the excitation pulse signal emitted in each phase of each period tn, it determines whether its output is at its highest. That is, when the frequency of the excitation pulse signal is scanned within the permissible range of the resonant frequency of the tag 10, which is 57.4kHz to 58.6kHz (58.0kHz ± 0.6kHz), the ringing attenuation signal with the highest output is identified, and the frequency of the excitation pulse signal corresponding to the ringing attenuation signal is detected as the resonant frequency of the tag 10.

[0102] In this way, after the resonant frequency of the tag 10 is detected by the resonant frequency detection processing unit 44, the excitation pulse signal transmission processing unit 41 transmits the subsequent excitation pulse signal in a transmission mode that includes the detected resonant frequency.

[0103] Table 4 below shows the frequency of the excitation pulse signal in each phase of each period tn when the resonant frequency of tag 10 is detected to be 57.5 kHz.

[0104] [Table 4]

[0105] As shown in Table 4 above, the frequency of the excitation pulse signal in phase B of each period tn is set to the resonant frequency of tag 10, 57.5 kHz; the frequency of the excitation pulse signal in phase A is set to 57.4 kHz (57.5 ± 0.1 kHz); and the frequency of the excitation pulse signal in phase C is set to 57.6 kHz (57.5 ± 0.1 kHz). That is, in the resonant frequency scanning process in Table 3, after detecting that the resonant frequency of tag 10 is 57.5 kHz, the excitation pulse signal is repeatedly emitted and tag 10 is detected at a frequency of 57.5 ± 0.1 kHz in each period tn for a certain period, and then the process returns to the resonant frequency scanning process in Table 3.

[0106] Thus, the resonant frequency of tag 10 is pre-detected through the resonant frequency detection processing unit 44, and in each cycle tn of the subsequent commercial frequency power supply, an excitation pulse signal pattern related to this resonant frequency (resonant frequency -0.1kHz, resonant frequency, resonant frequency +0.1kHz) is emitted, thereby enabling reliable detection of tag 10. This avoids the influence of the anti-resonant frequency on the detection of tag 10.

[0107] In the first to third embodiments described above, an anti-theft system was proposed that includes a transmission period (transmission window) for transmitting an excitation pulse signal in the 57kHz band and a transmission period (transmission window) for transmitting an excitation pulse signal in the 58kHz band within each certain cycle of a commercial frequency (50Hz or 60Hz) power supply. However, this transmission control is based on the zero-crossing point of the commercial frequency power supply. As an application of the present invention, there are also cases where a DC power supply is used instead of a commercial frequency power supply. In this case, it goes without saying that by setting a transmission window in each certain cycle that changes the frequency of the excitation pulse signal in the same way as in the above embodiments, and then opening a receiving window thereafter, it is possible to detect the tag 10 with an expanded permissible resonant frequency.

[0108] 4. Notification Processing The notification processing unit 43 issues a notification when the strength of the ringing attenuation signal received by the receiving unit 30 is above a threshold. This threshold can be set differently for each of the multiple receiving periods (receiving windows). For example, as shown in the first to third embodiments described above, when each cycle of a commercial frequency power supply is divided into three phases—phase A, phase B, and phase C—and a transmission window (transmission period) and a receiving window (receiving period) are set for each phase, different thresholds can be set within the respective receiving windows of phase A, phase B, and phase C.

[0109] In this situation, if the intensity of the ringing attenuation signal received by the receiving unit 30 is above a threshold in any of the receiving windows of phases A, B, and C, a notification can be sent via the notification processing unit 43. Furthermore, if a peak value appears in the ringing attenuation signal received by the receiving unit 30 in two or more phases within each of the receiving windows of phases A, B, and C, a notification can also be sent via the notification processing unit 43 if the intensity of the maximum peak value is above a threshold.

[0110] 5. Phase timing adjustment The phase timing of the transmission window (during transmission) and the reception window (during reception) can be adjusted relative to the phase of the commercial frequency power supply. In this case, by setting the transmission and reception windows to avoid phase timing issues that would negatively impact the detection sensitivity of the tag 10 due to environmental noise, the detection sensitivity of the tag 10 can be improved.

[0111] For example, when multiple anti-theft systems (such as transmitting antennas 23) are arranged close to each other, it is extremely important to properly synchronize their transmission and reception windows. Specifically, it is important that when two or more transmitting antennas 23 are arranged close to each other, the phase of the transmission window (typically 1.4 ms to 2.0 ms) of the transmitting antenna 23 is aligned with the phase of the transmission window of the neighboring transmitting antenna 23, and that the phase of the excitation pulse signal from the other neighboring transmitting antennas 23 does not overlap with the reception window of these systems.

[0112] If the phase of the transmission window of other nearby transmitting antennas 23 overlaps with the phase of these receiving windows, and they are not properly synchronized, problems such as false alarms or decreased detection sensitivity of tag 10 may occur. Therefore, adjusting the phase timing of the transmission and receiving windows relative to the phase of the commercial frequency power supply and properly synchronizing them can prevent false alarms or decreased detection sensitivity of tag 10. In particular, in AM mode, the wavelength is longer than in RF mode, and interference can easily occur even between anti-theft systems located at greater distances (e.g., 100 meters), so this needs to be considered.

[0113] Additionally, a mode that controls the transmission and reception windows (identification detection mode) and a mode that does not control the transmission and reception windows (noise measurement mode) can be set. In the noise measurement mode, instead of transmitting an excitation pulse signal in the transmission window, the received signal (noise) from the receiving antenna 31 is measured in terms of the phase relationship between the transmission window and the phase (phase A, phase B, phase C) of each cycle of the commercial frequency power supply.

[0114] Furthermore, when a large amount of noise is measured at a specific phase in the noise measurement mode, if the phase of the noise is detected to overlap with the receiving window, the impact of the noise will be amplified. Therefore, the receiving window can be adjusted by moving it to a phase where the impact of the noise is smaller.

[0115] Symbol Explanation 10 tags 20 Launching Section 21 Oscillators 22 Transmitter Amplifier 23 Transmitting Antenna 30 Receiving Department 31 Receiving Antenna 32 Receiver Amplifier 33 Narrowband Filter 40 Control Department 41 Excitation Pulse Signal Transmission Processing Unit 42 Label Inspection and Processing Department 43 Notification Processing Department 44 Resonant Frequency Detection and Processing Unit 50 speakers.

Claims

1. An anti-theft system, which is an acousto-magnetic anti-theft system, comprising: The transmitter emits an excitation pulse signal during the emission period; The tag resonates due to an excitation pulse signal emitted from the transmitter and outputs a ringing reduction signal; The receiving unit receives the ringing attenuation signal during a receiving period following the transmission period; as well as, The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiving unit. Each certain cycle includes a transmission period for transmitting an excitation pulse signal in the 57kHz frequency band and a transmission period for transmitting an excitation pulse signal in the 58kHz frequency band.

2. An anti-theft system, which is an acousto-magnetic anti-theft system, comprising: The transmitter emits an excitation pulse signal during the emission period; The tag resonates due to an excitation pulse signal emitted from the transmitter and outputs a ringing reduction signal; The receiving unit receives the ringing attenuation signal during a receiving period following the transmission period; as well as, The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiving unit. Each cycle of a commercial frequency power supply includes a transmission period for transmitting an excitation pulse signal in the 57kHz band and a transmission period for transmitting an excitation pulse signal in the 58kHz band.

3. The anti-theft system as described in claim 2, wherein, Each cycle of the commercial frequency power supply includes a transmission period for transmitting a 57.7 kHz excitation pulse signal, a transmission period for transmitting a 58.0 kHz excitation pulse signal, and a transmission period for transmitting a 58.3 kHz excitation pulse signal.

4. An anti-theft system, which is an acousto-magnetic anti-theft system, comprising: The transmitter emits an excitation pulse signal during the emission period; The tag resonates due to an excitation pulse signal emitted from the transmitter and outputs a ringing reduction signal; The receiving unit receives the ringing attenuation signal during a receiving period following the transmission period; as well as, The tag detection processing unit detects the tag based on the ringing attenuation signal received by the receiving unit. Each two cycles of a commercial frequency power supply includes a transmission period for transmitting an excitation pulse signal in the 57kHz band and a transmission period for transmitting an excitation pulse signal in the 58kHz band.

5. The anti-theft system as described in claim 4, wherein, Every two cycles of the commercial frequency power supply include a transmission period for transmitting a 57.25kHz excitation pulse signal, a transmission period for transmitting a 57.55kHz excitation pulse signal, a transmission period for transmitting a 57.85kHz excitation pulse signal, a transmission period for transmitting a 58.15kHz excitation pulse signal, a transmission period for transmitting a 58.45kHz excitation pulse signal, and a transmission period for transmitting a 58.75kHz excitation pulse signal.

6. The anti-theft system as described in claim 1, wherein, Furthermore, it includes a resonant frequency detection and processing unit. This unit, within multiple cycles of a commercial frequency power supply, causes the transmitting unit to emit excitation pulse signals of different frequencies (57kHz or 58kHz) during the transmission period of each cycle, and detects the highest frequency of the ringing attenuation signal received by the receiving unit as the resonant frequency of the tag. During each cycle of the commercial frequency power supply after the resonant frequency of the tag is detected, transmission is performed in a transmission mode that includes an excitation pulse signal containing the resonant frequency.

7. The anti-theft system as described in claim 1, wherein, The phase timing during the transmission and reception periods can be adjusted relative to the phase of the commercial frequency power supply.

8. The anti-theft system as described in claim 1, wherein, Furthermore, it includes a notification processing unit that, when the strength of the ringing attenuation signal received by the receiving unit is above a threshold, issues an alarm notification. A different threshold is set for each of the multiple receiving periods.

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

Images