WO1997008672A1

WO1997008672A1 - Burglarproof system

Info

Publication number: WO1997008672A1
Application number: PCT/JP1996/002397
Authority: WO
Inventors: Michinari Hayashi
Original assignee: Maspro Denkoh Co., Ltd.
Priority date: 1995-08-29
Filing date: 1996-08-27
Publication date: 1997-03-06
Also published as: JPH0962953A

Abstract

A burglarproof system improving a tagged article detecting accuracy. A signal of a predetermined amplitude obtained by sine-wave sweeping a range of 7.4 MHz-8.9 MHz by 140 Hz is sent out from a transmitting antenna (1). At a signal reception side, a signal analysis unit (9) is provided which is adapted to predict the time of generation of a signal, which is to be received in the second half cycle in one cycle of the sweeping, on the basis of the time of generation of the signal received in the first half cycle in the same one cycle, compare the predicted time with the reception signal, and recognize the passage of an article when the predicted time and reception signal have reverse-phase relation with each other.

Description

Specification

Anti-theft system [Technical field]

According to the present invention, an evening with a built-in resonance circuit is attached to an article to be monitored, and when the evening article passes between transmitting and receiving antennas arranged opposite to each other, the article is transmitted from the transmitting antenna. The present invention relates to an anti-theft system for detecting the passage of an evening article by receiving a radio wave by the resonance circuit, causing resonance, and receiving a radio wave re-emitted from the resonance circuit by a receiving antenna.

[Background Art]

In the anti-theft system, for example, a short wave band centered at 8.2 MHZ is used, and a radio wave radiated from a transmitter is weak, and a fluorescent light mixed as noise, an electromagnetic wave from a 0 A device, a communication signal, And so on.

In order to reduce the influence of noise, it is relatively easy to respond by increasing the transmission output of radio waves, increasing the size of the resonance circuit, or reducing the detection area. It is not allowed to increase, and it is not preferable to increase the size of the resonance circuit because the evening becomes larger.

Furthermore, the shrinking of the detection error is not likely to be accepted by consumers, as there is a growing desire to expand the detection error.

Therefore, conventionally, for example, as described in Japanese Patent Application Laid-Open No. 63-126904, two types of resonance circuits having different resonance frequencies are incorporated into one tag, and the transmitted radio wave is swept. However, a technique has been proposed in which a detection signal is output when four re-radiated radio waves are received every one cycle of a sweep. According to the above-mentioned technology, detection accuracy is high because only re-radiated radio waves are targeted for detection ignoring sudden noise, but the size of the evening wave is doubled, which is annoying. In addition, within one cycle of the sweep, a confusing signal such as a resonance signal is detected only four times, and is determined to be a resonance signal.

DISCLOSURE OF THE INVENTION

The present invention provides an anti-theft system that distinguishes between a resonance signal and noise based on the number of times and timing of occurrence of a signal between successive cycles, thereby minimizing the possibility of malfunction. The configuration consists of transmitting a constant-amplitude radio wave periodically swept between predetermined frequencies from the transmitting antenna, and setting the resonance frequency of the resonance circuit to be lower than the upper-limit frequency of the transmitted radio wave and higher than the lower-limit frequency. , Within the period of the sweep, the timing of occurrence of a signal to be received within the second half period is predicted from the occurrence timing of the signal received within the first half period, and the predicted timing and reception are performed. An analysis means is provided for comparing the signals with each other, and recognizing the passage of the article when it is confirmed that the signals have the opposite phases.

It is preferable that the subtraction frequency of the radio wave transmitted from the transmitting antenna is a frequency that can be detected while a person walks between the transmitting and receiving antennas.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an anti-theft system according to the present invention.

Figure 2 is an explanatory diagram of the principle of analysis.

FIG. 3 is a flowchart of the analysis process.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the anti-theft storage rack according to the present invention will be described with reference to the drawings.

Fig. 1 shows the principle of the anti-theft system according to the present invention, and Fig. 2 shows the principle of the analysis means in the anti-theft system. The transmission antenna 1 has a DDS 3 based on a computer (microcomputer) 2 command. A signal obtained by sine-wave sweeping in the range of 7.4 MHz to 8.9 MHz at 5 QHz is sent through the amplifier 4, and a radio wave is emitted.

The receiving antenna 5 receives the radio wave radiated from the transmitting antenna 1 and The detected signal is sent to the detection unit 7 via the amplification unit 6, and the detected signal is output to the signal analysis unit 9 via the bandpass filter 8.

When an antenna 10 having a resonance circuit 10a enters between the transmission antenna 1 and the reception antenna 5, a resonance signal is re-emitted from the tag 10, and the re-emitted radio wave and various noises are generated. The reception antenna 5 receives the radio wave radiated from the transmission antenna 1 together with the radio wave. The transmitted signal is in the range of 7.4 MHz to 8.9 MHz, based on experimental results that are most suitable for detecting while passing between the transmitting and receiving antennas at an average speed of human walking. For example, from a resonant circuit whose sinusoidal sweep is performed at 140 Hz and the resonance frequency f _Q is set within that band, as shown in FIG. In this case, resonance occurs once in the first half cycle and once in the second half cycle.

Since the resonance timing is regular, the resonance timing occurring in the latter half cycle can be easily predicted, and the waveform thereof has the opposite phase.

In the analysis unit, the signal of the received radio wave is processed, for example, according to a flowchart shown in FIG.

First, the detected signal is sampled for each sweep in S1 and stored in a memory, and in S2, the data for one sweep stored in the memory is read out. In S3, the data is read out. A search is made for the presence of a signal in the first half of the evening.

If any signal is present and it is assumed that 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. For example, from the detected timing and phase of the detected signal b shown in FIG. 2, it is determined whether the signal b is a normal signal corresponding to the signal a, and it is confirmed that the signal b is as predicted. Then, in S5, they are regarded as resonance signals, the passage of the article is recognized, the signal with evening is sent from the signal analysis unit 9 to the notification unit 11, and the notification unit 11 outputs a signal such as a lamp or buzzer. Such a notification means 1 or 2 emits a chirp report.

If a signal is not detected in S3 or a corresponding signal is not confirmed in S4, the process returns to S2, where data for the next sweep is read out, and the analysis process is repeatedly performed. Is performed.

Therefore, even if a signal confusing with the resonance signal in the first half period, for example, the signal c shown in FIG. 2 is received, a signal corresponding to the signal c is not received in the second half period, and conversely, Even if a signal is received in the first half cycle but no signal is received in the first half cycle, or even if signals are received in each of the first and second half cycles, the second half of the signal generation If they do not match the predictions, those signals are regarded as noise, and it is determined that the passage of tagged articles is not allowed. In this way, only the resonance radio waves generated twice in one sweep are reliably identified, so that noise is not mistaken for a resonance signal.

In addition, since the chip is double-checked for the generation timing and phase, it can be used safely even in an environment with many noises that are difficult to distinguish from the resonance signal.

The phase check is based on the confirmation that, for example, if the peak value of the signal a appears in the order of A, B, C, the peak value of the signal b appears in the order of C, B, A. The band used for the sweep frequency and the transmission frequency can be changed as appropriate, and the resonance frequency fo of the tag's resonance circuit can be arbitrarily set within a range below the upper limit fn of the transmitted radio wave and below the lower limit: ft. Is set. If the sweep frequency is too high, the pattern of the resonance signal will be distorted and it will not be possible to discriminate, and if it is too low, it will pass through the detection band during the completion of one cycle of the sweep. When using a band, it is considered practical to use a sweep frequency of 50 to a hundred and several hundred Hz, but the sweep frequency can also be changed as appropriate according to the frequency of the radio wave used. The present invention predicts the timing of occurrence of a signal to be received in the latter half cycle from the timing of occurrence of a signal received in the first half cycle within one frequency of the sweep, and calculates the predicted timing The tag detection is judged to be valid when it is confirmed that the tag detection is in the opposite phase with the waveform received in the first half. Signal and received within the second half cycle The timing and waveforms of the generated signals are compared, and if it is confirmed that both signals are symmetrical and out of phase with respect to the middle of one frequency, control is performed to determine that tag detection is valid. For example, all controls based on the timing and phase of signal generation as criteria are included.

【The invention's effect】

Even if the signal is received sporadically or intermittently, the signal whose occurrence timing is not regular is judged as noise, so only the resonance signal to be supplemented is recognized, and the detection accuracy is extremely low.

In addition, only one resonance circuit needs to be built in the tag, so that the size of the evening can be reduced.

In addition, by setting the sweep frequency to 50 to a hundred and several hundred Hz, the short-wave band is used, so that the signal discriminating power is not impaired. There is no worry about mistakes and the reliability is excellent.

Claims

The scope of the claims

1. A tag with a built-in resonant circuit is attached to the monitored article, and when the tagged article passes between the transmitting and receiving antennas arranged opposite to each other, the resonant circuit transmits radio waves transmitted from the transmitting antenna. The antenna then picks up and resonates, so the receiving antenna receives the radio waves re-emitted from the resonant circuit, and in the anti-theft system that detects the passage of tagged items, the transmitting antenna periodically sweeps between predetermined frequencies. A signal having a constant amplitude that is lower than the upper limit of the transmission frequency and higher than the lower limit, and the signal received within the first half of the sweeping cycle. From the occurrence timing of the signal, the occurrence timing of the signal to be received in the latter half cycle is predicted, and the predicted evening Anti-theft system in which a analyzing means for recognizing the passage of the article when compared with the items, to be in a relationship of opposite phases was confirmed.

2. The anti-theft system according to claim 1, wherein the radio wave transmitted from the transmitting antenna is swept at a frequency that can be detected while a person walks between the transmitting and receiving antennas.