JPH0962953A - Burglay preventing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of an article with a tag. SOLUTION: A signal of a fixed amplitude obtained by sinewave scanning in 140Hz within the range of 7.4 to 8.9MHz is sent from a transmission antenna 1. A reception side is provided with a signal analyzing part 9 which estimates the generating timing of a signal to be received within a second half period from the generating timing of a signal received within a first half period within one period of the scanning and recognizes the passage of the article at the time of confirming both signals to be in the relation of mutually opposite phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tag in which a resonance circuit is incorporated in an article to be monitored, and when the article with the tag passes between transmitting / receiving antennas arranged opposite to each other, the tag is transmitted from the transmitting antenna. The present invention relates to an anti-theft system that detects passage of a tagged article by receiving radio waves emitted from the resonance circuit and causing them to resonate, and receiving radio waves re-radiated from the resonance circuit.

[0002]

2. Description of the Related Art In the theft prevention system, for example, 8.
The short-wave band centering on 2MHZ is used, and the radio waves emitted from the transmitter are weak, and are easily affected by the electromagnetic waves from fluorescent lamps and OA devices mixed as noise, communication signals, and the like. To reduce the influence of noise, it is relatively easy to deal with it by increasing the transmission output of radio waves, enlarging the resonance circuit, or reducing the detection area.
Unnecessarily increasing the output radio wave is not allowed, and enlarging the resonance circuit makes the tag larger, which is not preferable. Even more, there is a growing tendency for the detection area to be reduced, and there is a growing tendency for the detection area to be expanded. Therefore, conventionally, for example, as described in Japanese Patent Application Laid-Open No. 63-126094, two kinds of resonance circuits having different resonance frequencies are incorporated in one tag, and a radio wave to be transmitted is swept, and every one cycle of sweeping. A technique has been proposed in which a detection signal is output when the re-radiated radio wave is received four times as valid.

[0003]

According to the above technique, the detection accuracy is high because only re-radiated radio waves are detected as targets for ignoring sudden noise, but the tag becomes double in size. It is an eyesore. Further, if a signal confusing with a resonance signal is detected four times within one period of sweep, it is judged as a resonance signal.

[0004]

According to the present invention, the distinction between a resonance signal and noise is discriminated by the number of times and timing of occurrence of a signal between consecutive successive cycles to minimize the possibility of malfunction. It is a theft prevention system that has been lowered to
The configuration is such that a radio wave with a constant amplitude that is periodically swept between predetermined frequencies is transmitted from the transmission antenna, the resonance frequency of the resonance circuit is set to a frequency lower than the upper limit frequency of the transmitted radio wave and higher than the lower limit frequency, and the sweep is performed. Within one cycle, the generation timing of the signal to be received within the latter half cycle is predicted from the generation timing of the signal received within the first half cycle, and the predicted timing is compared with the received signal. However, the analysis means for recognizing the passage of the article is provided when it is confirmed that the phases are opposite to each other. The sweep frequency of the radio wave transmitted from the transmitting antenna is preferably a frequency that can be detected while a person walks between the transmitting and receiving antennas.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the antitheft device according to the present invention will be described with reference to the drawings. FIG. 1 shows the anti-theft system according to the present invention, and FIG. 2 shows the principle of the analyzing means in the anti-theft system. The transmitting antenna 1 is operated by a DDS 3 based on a command from a computer (microcomputer) 2. A signal obtained by sweeping a sine wave at 50 Hz in the range of 0.4 MHz to 8.9 MHz is sent through the amplification unit 4 and a radio wave is radiated. Receiving antenna 5
Then, the radio wave radiated from the transmitting antenna 1 is received, the received signal is sent to the detection unit 7 via the amplification unit 6, and the signal detected there is passed through the band pass filter 8 to the signal analysis unit 9 Is output to. The transmitting antenna 1
When the tag 10 having the resonance circuit 10a enters between the receiving antenna 5 and the receiving antenna 5, the resonance signal is re-emitted from the tag 10, and the re-radiated radio wave and various noises are emitted together with the radio wave emitted from the transmission antenna 1. It is received by the receiving antenna 5.

The transmission signal has a frequency of 7.4 MHz to 8.9 MH.
Determined based on experimental results that are most suitable for sensing in the range of z at an average walking speed of a person while passing between transmitting and receiving antennas, for example, sine wave swept at 140 Hz. As shown in FIG. 2, from the resonance circuit in which the resonance frequency f _Q is set within the band, resonance occurs once in the first half cycle and once in the second half cycle within one sweep cycle. Wake up. Further, since the resonance timing is regular, the resonance timing generated in the latter half cycle can be easily predicted, and the waveform thereof has an opposite phase. In the analysis unit, the signal of the received radio wave is processed according to the flow chart shown in FIG. 3, for example. First, in S1, the detection signal is sampled for each sweep and stored in the memory.
Then, the data for one sweep stored in the memory is read out, and in S3, it is searched whether a signal exists in the first half of the data. If there is any signal,
If the signal is a resonance signal, the timing of the signal to be generated in the second half is predicted from the signal a shown in FIG. 2 received in the first half cycle, and the signal detected in the second half, for example, the signal shown in FIG. It is determined from the generation timing and phase of b whether the signal b is a normal signal corresponding to the signal a, and if it is confirmed that the signal is as expected, then in S5, they are regarded as resonance signals. Recognizing the passage of the article, the signal analysis unit 9 sends a signal with a tag to the notification unit 11
The notification unit 11 is activated by the notification unit 12 such as a lamp or a buzzer. If the signal is not detected in S3 or the corresponding signal is not confirmed in S4, the process returns to S2, the data for the next sweep is read, and the analysis process is repeatedly executed. Therefore,
A signal confusing with a resonance signal in the first half cycle, for example, in FIG.
Even if the signal c shown in is received, the signal corresponding to the signal c is not received in the latter half cycle, or conversely, even if the signal is received in the latter half cycle, the signal is received in the first half cycle. If no signal is received, or if the signal generation timing of the latter half does not match the prediction even if the signals are received in each of the first and second half cycles, then those signals are regarded as noise and the tagged article It is judged that the passage of is not allowed.

As described above, since only the resonance radio wave generated twice in one sweep is reliably identified, noise is not mistaken for a resonance signal. In addition, since the double check is performed based on the generation timing and the phase, it can be used with confidence even in an environment with a lot of noise that is difficult to distinguish from the resonance signal. The phase check is performed by confirming that the peak value of the signal a appears in the order of A, B, and C, and the peak value of the signal b appears in the order of C, B, and A.

The use band of the sweep frequency and the transmission frequency can be changed as appropriate, and the resonance frequency f in the resonance circuit of the tag is f.
_{Q is} also arbitrarily set within a range lower than the frequency f _{H at} the upper limit of the transmitted radio wave and higher than the frequency f _L at the lower limit.

If the sweep frequency is made too high, the pattern of the resonance signal will collapse and it will not be possible to discriminate, and if it is too low, it will pass through the detection band while the sweep of one cycle is completed. When using a band, the sweep frequency is 5
It can be said that 0 to several hundred Hz is practical, but the sweep frequency can be appropriately changed according to the frequency of the radio wave to be used.

The present invention predicts the generation timing of the signal to be received in the latter half cycle from the generation timing of the signal received in the first half cycle within one frequency of the sweep, and the prediction is made. It compares the waveform received at the timing and judges that the tag detection is valid when it is confirmed that they are in the opposite phase to each other.The signal is received within the first half cycle within one frequency of the sweep. The generated signal and the waveform of the signal received in the latter half of the half cycle are compared, and if it is confirmed that both signals have a symmetrical and opposite phase relationship with each other with the middle of one frequency as a boundary, Controls based on the timing and phase of signal generation, such as controlling to judge that the detection is effective, are all included.

[0011]

EFFECTS OF THE INVENTION Even if it is received on a one-off basis or is intermittent, a signal having no regularity in the generation timing is judged as noise, so only the resonance signal to be supplemented is recognized and the detection accuracy is extremely high. . Since the tag only needs to have one resonance circuit built therein, the tag can be miniaturized. In addition, by setting the sweep frequency to 50 to several hundreds of Hz, when the short wave band is used, the discriminating power of the signal is not impaired, and there is no possibility of slipping through the detection area during one sweep.
There is no concern about detection errors, and it has excellent reliability.

[Brief description of drawings]

FIG. 1 is a block diagram showing a theft prevention system according to the present invention.

FIG. 2 is an explanatory diagram of an analysis principle.

FIG. 3 is a flowchart of analysis processing.

[Explanation of symbols]

1 ... Transmission antenna, 2 ... Computer, 3 ... DD
S, 4 ... Amplifying unit, 5 ... Receiving antenna, 6 ... Amplifying unit, 7 ... Detection unit, 8 ... Bandpass filter, 9 ...
Signal analysis unit, 10 ... Tag, 10a ... Resonance circuit, 11
..Notification unit, 12 ...

Claims (2)

[Claims] 1. A tag in which a resonance circuit is incorporated is attached to an article to be monitored, and when the article with a tag passes between transmitting and receiving antennas arranged opposite to each other, a radio wave transmitted from a transmitting antenna is resonated to the resonance. Since the circuit picks up and resonates, the receiving antenna receives the radio wave re-emitted from the resonant circuit, and in the anti-theft system that detects the passage of the tagged article, the transmitting antenna periodically cyclically moves between predetermined frequencies. Sends out a swept constant amplitude radio wave,
The resonance frequency of the resonance circuit is set to be lower than the frequency at the upper limit of the transmitted radio wave and higher than the frequency at the lower limit, and within one cycle of the sweep, from the generation timing of the signal received in the first half cycle, within the latter half cycle. In the analysis means for predicting the generation timing of the signal to be received, comparing the predicted timing with the received signal, and recognizing the passage of the article when it is confirmed that they have a phase opposite to each other. Anti-theft system provided. 2. The antitheft system according to claim 1, wherein the radio waves transmitted from the transmitting antenna are swept at a frequency that can be detected while a person walks between the transmitting and receiving antennas.