JPH08138160A - Theft preventive device - Google Patents

Abstract

PURPOSE: To simultaneously use different kinds of tag equipments at the same store by providing a filter circuit for transmission and that for reception so as to selectively receive plural signals of different frequencies. CONSTITUTION: A first frequency signal is made by an oscillation circuit 105 and amplified by an output circuit 103 and after then, passes through a filter circuit 101 to be outputted from a transmission antenna 3 as radio. Next, a second frequency signal is amplified by an output circuit 104 and then, passes through a filter circuit 102 to be transmitted from a transmission antenna 4 as radio. At this time, the filter circuit 101 cuts-off the signals of frequencies excepting for the second frequency and the filter circuits 102 cuts-off the signals of frequencies excepting for the second frequency to output both signals from respective transmission antennas 3 and 4. In addition, a filter for reception 201 cutting-off the signals of frequencies excepting for the frequency of a signal to be received is provided for a reception circuit 202 in a reception unit 2 to receive a right signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-theft device for articles displayed in a store, and more particularly to an anti-theft device that is compatible with a plurality of anti-theft tag devices.

[0002]

2. Description of the Related Art In recent years, the introduction of anti-theft devices has been increasing in order to reduce sales loss due to shoplifting in convenience stores, shopping malls and the like. Various types of antitheft devices have been made, and typical examples thereof will be described below.

FIG. 6A is one of the conventional anti-theft devices, which is composed of a transmitting unit 1a, a transmitting antenna 3 connected to the transmitting unit 1a, and a tag device 5. In the transmission unit 1a, 131 is a first frequency signal output circuit, 132 is a first frequency signal oscillator circuit connected to the input of the output circuit 131, and 133 is a power supply circuit for supplying power to these circuits. Tag device 5 here
2A, the receiving antenna 501, the first frequency signal receiving circuit 502 connected to the receiving antenna 501, the detection circuit 503 connected to the output of the receiving circuit 502, An alarm output circuit 504 connected to the output of the detection circuit 503 and the alarm output circuit 504
And a power supply circuit 506 for supplying power to these circuits.

The signal generated by the oscillation circuit 132 in the transmission unit 1a is amplified by the output circuit 131 and transmitted to the transmission antenna 3
Will be transmitted as radio waves. When the tag device 5 comes close to the transmitting antenna 3, the receiving antenna 501 of the tag device 5
A radio wave enters and the receiving circuit 502 receives the signal. This signal is detected by the detection circuit 503, and when the signal level exceeds a certain level, the alarm output circuit 504 is driven and an alarm sound is emitted from the speaker 505 built in the tag device 5.

FIG. 6 (b) is one of the anti-theft devices of a method different from that of FIG. 6 (a), and includes a transmitting unit 1b, a transmitting antenna 4 connected to the transmitting unit 1b, a receiving unit 2b, and It comprises a receiving antenna 7 connected to the receiving unit 2b and a tag device 6. Transmission unit 1
In b, 141 is a second frequency signal output circuit,
It is connected to the output of the second frequency signal oscillator circuit 142. 143 is a sweep circuit, the output of which is connected to the second frequency signal oscillator circuit 142. 144 is a power supply circuit that supplies power to these circuits. The receiving unit 2b further includes a second frequency signal receiving circuit 231 connected to the receiving antenna 7, a detection circuit 232 connected to the output of the receiving circuit 231, and the detection circuit 23.
2 and a warning output circuit 234 connected to the output of the signal judging circuit 233.
A speaker 235 connected to the output of the alarm output circuit 234, and a power supply circuit 2 for supplying power to these circuits.
And 36. Here, the tag device 6 is shown in FIG.
As shown in (b), coil 601 and capacitor 602
It is composed of a parallel connection body of the coil 601 and the capacitor 6
02 forms a resonance circuit having a second resonance frequency.

The oscillating circuit 142 of the transmitting unit 1b is a variable frequency oscillating circuit, and the function of the sweep circuit 143 causes the signal frequency to periodically change with a constant width above and below the second frequency. The signal generated by the oscillation circuit 142 is amplified by the output circuit 141 and transmitted as a radio wave from the transmission antenna 4. Radio waves from the transmitting antenna 4 enter the receiving antenna 7 and are received by the receiving circuit 231 of the receiving unit 2b. This signal is detected by the detection circuit 232 and input to the signal determination circuit 233. Here, when the tag device 6 passes between the transmitting antenna 4 and the receiving antenna 7, the input signal of the determination circuit 233 changes, so that the determination circuit 233.
Reads this change, determines that the tag device 6 is passing, and drives the alarm output circuit 234. As a result, an alarm sound is emitted from the speaker 235 built in the receiving unit 2b.

FIG. 7a shows an example of sweeping the signal frequency of the transmitting unit 1b, and FIG. 7b shows the change of the detection signal in the receiving unit 2b. In this example, the frequency is swept stepwise, but it may be continuously changed. When the second frequency and the resonance frequency of the tag device 6 are the same, the detection signal suddenly drops, so that the existence of the tag device 6 can be known.

FIG. 8 is a diagram showing an example of installation of the anti-theft device in the store 31, where 32, 33 and 34 are product shelves, 35 is a checkout counter (cash register), 36 is an entrance / exit of the store, 3, 4
Is a transmitting antenna of the anti-theft device, and 7 is a receiving antenna of the anti-theft device provided facing the transmitting antenna 4. Although not shown, the anti-theft tag device is attached to each product on the product shelf. When purchasing a product normally, the clerk removes the tag device at the cash register, but if the product is taken out of the store without permission, the tag device of the product responds to the radio waves from the transmitting antennas 3 and 4 at the entrance and exit. As described in 6 (a) and 6 (b), the speaker of the tag device 5 or the receiving unit 2b gives an alarm to notify the theft.

As can be seen from the above description, there are various types of anti-theft devices, but since the tag device 5 itself has an alarm function in FIG. 6A, the theft item and the criminal can be identified. It is easy, but the circuit is complicated and the shape is large.
Further, in FIG. 6B, the tag device 6 does not have an alarm function, but there is an advantage that it is inexpensive and can be made small and thin. Therefore, anti-theft devices of different types are used properly depending on the product to which the tag is attached.

[0010]

However, when it is desired to use antitheft devices of different methods in the same store, a large space is required for installing the antenna and the transmission / reception unit, and the number of connection cables and power cables increases, which is an obstacle. Become.
Further, there is a fundamental problem that the transmitted radio waves interfere with each other and a normal signal is not output, or noise is superimposed, so that predetermined performance cannot be obtained.

The present invention solves the above-mentioned problems of the prior art by incorporating a plurality of signal output circuits / reception circuits having different frequencies in one transmission unit / reception unit, and simultaneously installing tag devices of different types in the same store. It is an object of the present invention to provide a usable antitheft device.

[0012]

In order to achieve this object, the anti-theft device of the present invention, as a first means, shuts off a signal of a frequency output from another output unit to each output unit of the transmission unit. The transmission filter circuit is provided, and the reception unit that receives the output signal of the transmission unit is further provided with the reception filter circuit that cuts off signals other than the frequency of the signal to be received.

As a second means, the transmission unit is provided with a time division circuit for sequentially switching signals of different frequencies at regular time intervals and outputting signals one by one, and the reception unit is further provided with a signal transmitted from a transmission antenna. A receiving circuit for selecting and receiving a signal of at least one of the frequencies, and a determining circuit for determining whether or not at least one of the tag devices exists in the specific area from the time-division received signal. It has a different configuration.

[0014]

According to the first structure of the anti-theft device of the present invention, even if a plurality of signals having different frequencies are output from one transmitting unit, only the target frequency is output between each transmitting antenna and the output circuit. Since the transmission filter circuit for passing the signal is provided, signals do not interfere with each other in the output circuits. Further, since the receiving unit is also provided with the receiving filter circuit between the receiving antenna and the receiving circuit, it is possible to select and receive a plurality of signals having different frequencies. According to the second configuration, the output signal frequency of the transmission unit is switched one by one in a time division manner, so that signal interference does not occur. In each case, since different types of tag devices can be used at the same time in the same store with one set of anti-theft device, the installation space is small and the cost is low, and the most suitable anti-theft device for each product is possible and the crime prevention effect is further enhanced. Can be increased.

[0015]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block circuit diagram of an anti-theft device according to a first embodiment of the present invention. In FIG. 1, 1 is a transmitting unit, 2 is a receiving unit, 3 is a transmitting antenna for a first frequency connected to the transmitting unit 1,
4 is a transmission antenna for the second frequency connected to the transmission unit 1, 5 is a tag device for the first frequency, 6 is a tag device for the second frequency, and 7 is a first frequency device connected to the reception unit 2. It is a receiving antenna for the second frequency.

The transmission unit 1 has an oscillation circuit 105 as a circuit for the first frequency, a signal output circuit 103 connected to the output of the oscillation circuit 105, and the output circuit 103.
And a transmission filter circuit 101 connected to the output of the. Also, the sweep circuit 1 is used as a circuit for the second frequency.
07, the oscillator circuit 106 connected to the output of the sweep circuit 107, the signal output circuit 104 connected to the output of the oscillator circuit 106, and the transmission filter circuit 102 connected to the output of the signal output circuit 104. And a power supply circuit 108 for supplying power to these circuits, the transmission antenna 3 is connected to the output of the transmission filter circuit 101, and the transmission filter circuit 102 is provided.
The transmission antenna 4 is connected to the output of the.

The receiving unit 2 has a second frequency receiving filter circuit 201 connected to the receiving antenna 7.
A second frequency signal receiving circuit 202 connected to the output of the receiving filter circuit 201, and the receiving circuit 20.
2 is connected to the output of the detection circuit 203, the signal determination circuit 204 connected to the output of the detection circuit 203, and the alarm output circuit 2 connected to the output of the signal determination circuit 204.
05, a speaker 206 connected to the output of the alarm output circuit 205, and a power supply circuit 207 that supplies power to these circuits.

The tag devices 5 and 6 are as shown in FIGS. 2 (a) and 2 (b) and are the same as those described in the conventional example.

The operation of the anti-theft device constructed as above will be described below. First, the signal of the first frequency is generated by the oscillation circuit 105, amplified by the output circuit 103, and then transmitted as a radio wave from the transmission antenna 3 through the filter circuit 101. The tag device 5 is the transmitting antenna 3
When it comes near, the radio wave enters the receiving antenna 501 (see FIG. 2A) of the tag device 5 and the signal is received by the receiving circuit 502. This signal is detected by the detection circuit 503, and when the signal level exceeds a certain level, the alarm output circuit 504 is driven and an alarm sound is emitted from the speaker 505 built in the tag device 5.

Next, the signal of the second frequency is the oscillation circuit 106.
The oscillation circuit 106 is a variable frequency type oscillation circuit, and the function of the sweep circuit 107 causes the signal frequency to periodically change with a constant width above and below the second frequency. The signal generated in this way is amplified by the output circuit 104 and then passed through the filter circuit 102 to be transmitted as a radio wave from the transmitting antenna 4. Radio waves from the transmitting antenna 4 enter the receiving antenna 7 and the filter circuit 201 of the receiving unit 2.
The signal is received by the receiving circuit 202 through the signal. This signal is detected by the detection circuit 203 and input to the signal determination circuit 204. Here, when the tag device 6 passes between the transmitting antenna 4 and the receiving antenna 7, the input signal of the determination circuit 204 changes, so the determination circuit 204 reads this change and determines that the tag device 6 is passing. , Alarm output circuit 20
5 is driven. As a result, an alarm sound is emitted from the speaker 206 built in the receiving unit 2.

An example of sweeping the second frequency signal of the transmitting unit 1 is shown in FIG. 7a, and an example of detecting the presence of the tag device 6 by the change of the detection signal of the receiving unit 2 is shown in FIG. 7b. . Both have the same principle as described in the conventional example.

If the transmitting antennas 3 and 4 are installed close to each other, the radio wave of the first frequency output from the transmitting antenna 3 enters the transmitting antenna 4 and affects the second frequency signal output circuit. And as a result transmit antenna 4
Although there is a possibility that the signal waveform of the second frequency output from is disturbed, since the filter circuit 102 blocks signals of frequencies other than the second frequency, only the signal of the second frequency is transmitted from the transmitting antenna 4. Is output. Conversely, the radio wave of the second frequency output from the transmitting antenna 4 enters the transmitting antenna 3 and affects the first frequency signal output circuit, and as a result, the signal of the first frequency output from the transmitting antenna 3 Although the waveform may be disturbed, since the filter circuit 101 blocks signals of frequencies other than the first frequency, only the signal of the first frequency is output from the transmitting antenna 3.

Further, since two types of signals are output from the transmitting antennas 3 and 4, two types of signals also enter the receiving antenna 7, but the filter circuit 201 blocks signals of frequencies other than the second frequency. Therefore, the receiving circuit 202 can accurately receive the signal of the second frequency.

As described above, according to the present embodiment, each output circuit of the transmission unit 1 cuts off the signal of the frequency output from the other output circuit, and the transmission filter circuits 101 and 102.
Is provided to prevent signals having different frequencies from invading each other's circuits, and to provide the receiving circuit of the receiving unit 2 with a receiving filter circuit 201 for cutting off signals other than the frequency of the signal to be received. Can receive signals. Therefore, one anti-theft device can accurately detect a plurality of types of tag devices 5 and 6 having different frequencies and issue an alarm.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a block circuit diagram of the anti-theft device in the second embodiment of the present invention. In FIG. 3, 11 is a transmitting unit, 12 is a receiving unit, 13 is a transmitting antenna for the first frequency connected to the transmitting unit 11, 14 is a transmitting antenna for the second frequency connected to the transmitting unit 11, Reference numeral 15 is a tag device for the first frequency, 16 is a tag device for the second frequency, and 17 is a receiving antenna for the second frequency connected to the receiving unit 12.

The transmission unit 11 has an oscillator circuit 115 as a circuit for the first frequency, an analog switch 113 connected to the output of the oscillator circuit 115, and a signal output circuit 111 connected to the output of the analog switch 113.
It has and. Further, a sweep circuit 117 as a circuit for the second frequency, an oscillator circuit 116 connected to the output of the sweep circuit 117, an analog switch 114 connected to the output of the oscillator circuit 116, and the analog switch 114. A signal output circuit 112 connected to the output, and the analog switches 113 and 114.
And a power supply circuit 119 that supplies power to the above circuits, and a time division circuit 118 that is connected to the input of the analog switch 113 and 114 to control ON / OFF of the analog switches 113 and 114. And
The transmission antenna 13 is connected to the output of the output circuit 111, and the transmission antenna 14 is connected to the output of the output circuit 112.

The receiving unit 12 includes the receiving antenna 1
Filter circuit 21 for reception of the second frequency connected to 7
1, a second frequency signal receiving circuit 212 connected to the output of the receiving filter circuit 211, and the receiving circuit 2
12 is connected to the output of the detection circuit 213, a signal determination circuit 214 connected to the output of the detection circuit 213, an alarm output circuit 215 connected to the output of the signal determination circuit 214, and the alarm output circuit 215 And a power supply circuit 217 that supplies power to these circuits.

The tag devices 15 and 16 are respectively shown in FIG.
It is the same as the tag devices 5 and 6 shown in (b).

The operation of the anti-theft device constructed as above will be described below. First, the signal of the first frequency is generated by the oscillation circuit 115, and the analog switch 113
The signal is amplified by the output circuit 111 through and is transmitted as a radio wave from the transmitting antenna 13. Next, the signal of the second frequency is generated by the oscillating circuit 116. This oscillating circuit 116 is a frequency variable type oscillating circuit, and the function of the sweeping circuit 117 causes the oscillating circuit 117 to periodically oscillate with a constant width above and below the second frequency. The signal frequency changes. The signal thus created passes through the analog switch 114, is amplified by the output circuit 112, and is transmitted as a radio wave from the transmitting antenna 14.

The time division circuit 118 is an analog switch 11
3 and 114 are turned on and off alternately at a constant cycle. Therefore, the signal of the first frequency is output only when the analog switch 113 is on, while the signal of the second frequency is not output because the analog switch 114 is off. Next, according to the cycle of the time division circuit 118, the analog switch 113 is turned off after a fixed time and the signal of the first frequency is not output.
14 is turned on and the signal of the second frequency is output.

FIG. 4 is a timing chart showing the above operation. In FIG. 4, a signal of the first frequency is output at timings 1 and 3, and a signal of the second frequency is output at timings 2 and 4. Here the tag device 15
Comes near the transmitting antenna 13, the detection circuit of the tag device 15 obtains the detection signal of the first frequency as shown in FIG. When the detection signal has a signal level above a certain level, the tag device 15 emits an alarm sound. In the case of this example, the alarm sound is an intermittent sound because the detection signal is intermittent, but it is also possible to insert an integrating circuit into a continuous sound. On the other hand, when the tag device 16 passes between the transmitting antenna 14 and the receiving antenna 17, the detection signal of the second frequency as shown in FIG. 4 is input to the determination circuit 214 in the period of timings 2 and 4. As described with reference to FIGS. 7A and 7B of the conventional example, when the second frequency matches the resonance frequency of the tag device 16, the detection signal changes momentarily. Since the width of this change is smaller than the intermittent period of the detection signal, the determination circuit 214 reads the width of this change and determines that the tag device 16 is present, and the speaker 2
A warning sound is emitted from 16.

When the signal of the first frequency is output from the transmitting antenna 13, the signal of the first frequency also enters the receiving antenna 17 for the second frequency, but the filter circuit 2
Since 11 cuts off signals of frequencies other than the second frequency, the receiving circuit 212 can accurately receive signals of the second frequency.

As described above, according to the present embodiment, each signal output from the transmission unit 11 is alternately switched and output according to the cycle created by the time division circuit, so that the frequency can be changed without the transmission filter circuit. It is possible to prevent the different signals from interfering with each other and disturbing the waveform. Further, a correct signal can be received by providing the receiving circuit of the receiving unit 12 with a filter circuit 211 that blocks signals other than the frequency of the signal to be received. Therefore, one anti-theft device can accurately detect a plurality of types of tag devices 15 and 16 having different frequencies and issue an alarm.

(Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 5 shows a block circuit diagram of an anti-theft device in a third embodiment of the present invention. In FIG. 5, 21 is a transmitting unit, 22 is a receiving unit, 23 is a transmitting antenna for the first frequency connected to the transmitting unit 21, 24 is a transmitting antenna for the second frequency connected to the transmitting unit 21, Reference numeral 25 is a tag device for the first frequency, 26 is a tag device for the second frequency, 27 is a receiving antenna for the first frequency connected to the receiving unit 22, and 28 is a first receiving antenna for the receiving unit 22. It is a receiving antenna for the second frequency.

The transmission unit 21 includes a signal output circuit 121 and this output circuit 121 as a circuit for the first frequency.
Of the analog switch 123, the signal output circuit 122 serving as a circuit for the second frequency, the analog switch 124 connected to the input of the signal output circuit 122, and the inputs of the analog switches 123 and 124. The oscillator circuit 126, the sweep circuit 127 connected to the input of the oscillator circuit 126, and the analog switch 12
3, 124 and a time division circuit 125 connected to the inputs of the sweep circuit 127 to control the analog switches 123, 124 and the sweep circuit 127, and a power supply circuit 128 for supplying power to these circuits.

The receiving unit 22 has a receiving filter circuit 221 connected to the receiving antenna 27 as a circuit for the first frequency, a receiving circuit 223 connected to the output of the receiving filter circuit 221, and the receiving circuit 223. Circuit 223
And a detection circuit 225 connected to the output of the receiving antenna 28 as a circuit for the second frequency.
And a receiving circuit 224 connected to the output of the receiving filter circuit 222.
And the detection circuit 2 connected to the output of the receiving circuit 224
26 and. Further, the detection circuit 22
5, a signal determination circuit 227 connected to the outputs of 226,
The configuration includes an alarm output circuit 228 connected to the output of the signal determination circuit 227, a speaker 229 connected to the output of the alarm output circuit 228, and a power supply circuit 230 that supplies power to these circuits. ing.

The tag devices 25 and 26 are both shown in FIG.
The tag device 6 is the same as the tag device 6 shown in FIG. 2 and does not include a tag device such as the tag device 5 having an alarm circuit built therein.

The operation of the anti-theft device constructed as above will be described below. The signal of the first frequency or the second frequency is generated by the oscillating circuit 126. The oscillating circuit 126 is a variable frequency oscillating circuit, and the sweep circuit 12
The function of 7 causes the signal frequency to periodically change with a constant width above and below the first frequency or the second frequency. Of the signals thus produced, the signal of the first frequency passes through the analog switch 123, is amplified by the output circuit 121, and is transmitted as a radio wave from the transmitting antenna 23. The signal of the second frequency passes through the analog switch 124, is amplified by the output circuit 122, and is transmitted as a radio wave from the transmitting antenna 24.

The time division circuit 125 works so that the sweep circuit 127 alternately selects either the first frequency or the second frequency for the center frequency in a constant cycle, and at the same time, the analog switches 123 and 124 are alternately switched in the same cycle. Work to turn on and off. That is, when the first frequency is selected, the analog switch 123 is turned on and the signal of the first frequency is output from the transmitting antenna 23. At this time, the analog switch 124 is turned off and no signal is output from the transmitting antenna 24. In the next cycle, the second frequency is selected, the analog switch 123 is turned off, and the analog signal is not output from the transmission antenna 23.
Is turned on and the signal of the second frequency is transmitted to the transmitting antenna 24.
Output from

A timing chart of the above operation will be described with reference to FIG. 4 similarly to the second embodiment. In FIG. 4, a signal of the first frequency is output at timings 1 and 3, and a signal of the second frequency is output at timings 2 and 4.
Here, when the tag device 25 passes between the transmitting antenna 23 and the receiving antenna 27, the detection circuit 226 obtains the detection signal of the first frequency as shown in FIG. 4 in the periods of timings 1 and 3. As described with reference to FIGS. 7A and 7B of the conventional example, when the first frequency matches the resonance frequency of the tag device 25, the detection signal changes for a moment. Since the width of this change is smaller than the intermittent period of the detection signal, the determination circuit 227 reads the width of this change, determines that the tag device 25 is present, and issues a warning sound from the speaker 229. Next, when the tag device 26 passes between the transmitting antenna 24 and the receiving antenna 28, a detection signal of the second frequency as shown in FIG. Similarly to the case of the frequency of, the determination circuit 227 reads the width of the change of the detection signal and determines that the tag device 26 is present, and the speaker 229 issues an alarm sound.

When the transmitting antenna 23 outputs the signal of the first frequency, the receiving antenna 28 for the second frequency also receives the signal of the first frequency.
The reception circuit 224 can accurately receive the signal of the second frequency because the signal 22 blocks the signal of the frequency other than the second frequency. On the contrary, when the signal of the second frequency is output from the transmitting antenna 24, the signal of the second frequency is also input to the receiving antenna 27 for the first frequency, but the filter circuit 221 has a frequency other than the first frequency. Since the signal having the frequency of 1 is cut off, the receiving circuit 223 can accurately receive the signal having the first frequency.

As described above, according to this embodiment, the signals output from the transmission unit 21 are alternately switched and output according to the cycle created by the time division circuit 125, so that signals having different frequencies interfere with each other. The waveform is prevented from being disturbed. Further, since the receiving circuit of the receiving unit 22 is provided with the filter circuits 221, 222 for cutting off signals other than the frequency of the signal to be received, correct signals can be received. Therefore, a single anti-theft device can accurately identify a plurality of types of tag devices 25 and 26 having different frequencies and issue an alarm.

[0043]

As described above, according to the present invention, as a first means, each output section of the transmission unit is provided with a transmission filter circuit for cutting off a signal of a frequency output from another output section, and further, the transmission unit. Even if a single transmission unit outputs a plurality of signals with different frequencies, the input unit of the reception unit that receives the output signal is equipped with a reception filter circuit that blocks signals other than the frequency of the signal to be received. The signals do not interfere with each other in the circuits, and the receiving unit can correctly select and receive any of the plurality of signals having different frequencies.

As a second means, the transmitting unit is provided with a time division circuit for sequentially switching signals of different frequencies at regular intervals to output signals one by one, and further, a signal transmitted from the transmitting antenna to the receiving unit. A receiving circuit for selecting and receiving a signal of at least one frequency among them, and a judging circuit for judging whether or not at least one of the tag devices exists in the specific region from the time-divided received signal. As a result, the output signal frequency of the transmitted radio wave is switched one by one in a time division manner, so that signal interference does not occur.

In each case, a set of anti-theft devices allows different types of tag devices to be used at the same time in the same store, and the installation space is small and the cost is low, and optimal anti-theft according to each product is possible. The crime prevention effect can be further enhanced.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an anti-theft device according to a first embodiment of the present invention.

FIG. 2A is a block circuit diagram of the tag device 5 included in the first embodiment. FIG. 2B is a block circuit diagram of the tag device 6 included in the first embodiment.

FIG. 3 is a block circuit diagram of an anti-theft device according to a second embodiment of the present invention.

FIG. 4 is a timing chart of the anti-theft device according to the second embodiment.

FIG. 5 is a block circuit diagram of an anti-theft device according to a third embodiment of the present invention.

6A is a block circuit diagram of a conventional anti-theft device, and FIG. 6B is a block circuit diagram of another conventional anti-theft device.

FIG. 7 is a frequency sweep timing chart of the transmission unit of the conventional antitheft device of FIG. 6 (b).

FIG. 8 is a layout diagram showing an installation example of an anti-theft device in a store

[Explanation of symbols]

 1 transmitting unit 2 receiving unit 3 transmitting antenna 4 transmitting antenna 5 tag device 6 tag device 7 receiving antenna 101 transmitting filter circuit 102 transmitting filter circuit 201 receiving filter circuit 118 time division circuit 204 judgment circuit

Claims (7)

[Claims] 1. A transmission unit for outputting a plurality of signals having different frequencies, a plurality of transmission antennas for transmitting an output signal of the transmission unit to a specific area, and a plurality of units mounted on a product and responsive to the plurality of transmission signals. Of the tag device, a receiving antenna provided in the area for receiving the transmission signal, and a receiving unit for discriminating the signal received by the receiving antenna and issuing an alarm. Theft, characterized in that a transmission filter circuit that passes only the signal of the frequency output from the output unit is provided, and a reception filter circuit that passes only the frequency of the signal to be received is provided at the input unit of the receiving unit. Prevention device. 2. At least one of the plurality of tag devices receives a signal having a certain strength or more and a receiving circuit that selects and receives a signal of one frequency among signals transmitted from a transmitting antenna. The anti-theft device according to claim 1, further comprising an alarm circuit for issuing an alarm at times. 3. The anti-theft device according to claim 1, wherein at least one of the plurality of tag devices is formed of an LC resonance circuit having a resonance frequency that is the same as the frequency of one of the signals transmitted from the transmission antenna. apparatus. 4. A transmission unit which outputs a plurality of signals having different frequencies, a plurality of transmission antennas which transmits an output signal of the transmission unit to a specific area, and a plurality of which is attached to a product and reacts to the plurality of transmission signals. Of the tag device, a receiving antenna provided in the area for receiving the transmitting signal, and a receiving unit for discriminating the signal received by the receiving antenna and issuing an alarm. A time division circuit for sequentially switching and outputting one kind of signal for each type, the reception unit selecting a reception signal of at least one frequency of the signals transmitted from the transmission antenna, And a determination circuit for determining whether at least one of the tag devices exists in the specific area from the divided reception signal. Characteristic anti-theft device. 5. At least one of the plurality of tag devices receives a signal having a certain strength or more and a receiving circuit that selects and receives a signal of one frequency among signals transmitted from a transmitting antenna. An anti-theft device according to claim 4, further comprising an alarm circuit for issuing an alarm at times. 6. The anti-theft device according to claim 4, wherein at least one of the plurality of tag devices comprises an LC resonance circuit having a resonance frequency that is the same as the frequency of one of the signals transmitted from the transmission antenna. apparatus. 7. A transmission unit, wherein a plurality of analog switches are inserted between a plurality of frequency oscillation circuits having different frequencies and a transmission circuit, and the time division circuit sequentially turns on / off the analog switches to sequentially switch a plurality of transmission signals. The antitheft device according to claim 4, wherein the antitheft device is provided.