JPH08161661A - Shoplifting preventing device - Google Patents

Abstract

PURPOSE: To surely synchronize a frequency change in a detection signal at a transmitter side with a detection signal at a receiver side with by initializing the operation of a frequency conversion control means every time transmission stop of a detection signal is detected at the receiver side. CONSTITUTION: A transmission stop means stops the operation of a transmission means and a frequency control means for a prescribed time every time the frequency control means changes a frequency of a detection signal by one pattern so as to stop once the transmission of the detection signal from a transmission antenna. Then a transmission stop detection means detects it that the transmission of the detection signal is stopped based on a level of an output signal from the frequency control means, and when the transmission stop detection means detects the transmission stop of the detection signal, a synchronization control means initializes the operation of the frequency conversion control means. Thus, the frequency change start timing of the detection signal at the transmitter side is always coincident with an oscillator control start timing of an oscillator at the receiver side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing shoplifting, and in particular, a resonance circuit having a predetermined resonance frequency as an object to be detected is previously attached to a product or the like, and the resonance circuit is used as a doorway or the like. The present invention relates to a shoplifting prevention device that electrically detects the existence of a shoplifting action and notifies the occurrence of shoplifting.

[0002]

2. Description of the Related Art Conventionally, as this type of device, for example, a transmitting antenna and a receiving antenna installed at a doorway of a library or a store that sells a predetermined product, and a resonance circuit (preliminarily attached to a rental exhibition or product) (Detection object) A transmitting device that sends out a detection signal of the same frequency as the resonance frequency from the transmitting antenna, and a receiving device that detects the occurrence of shoplifting by detecting the signal level of the received signal from the receiving antenna. Things have been put to practical use. That is, in this type of device,
Resonant circuits attached to products resonate, and there are products with resonant circuits attached between the transmitting antenna and the receiving antenna based on the level change of the received signal accompanying absorption and release of the energy of the transmitted signal. When the presence of the shoplifter is detected, a buzzer is sounded or a lamp is lit to detect the occurrence of shoplifting.

Further, in this type of shoplifting prevention device, since the resonance frequency f0 of the resonance circuit attached to the product or the like varies in manufacturing, the frequency of the detection signal is set to a predetermined frequency on the transmitter side including the resonance frequency f0. A sweep oscillator that sweeps in the range f1 to f2 is provided, and a signal of a frequency (f1 ± fi to f2 ± fi) obtained by adding or subtracting a predetermined frequency fi to the frequency of the detection signal is detected on the receiving device side. Local oscillator that is generated at the same sweep speed as that of the local oscillator, and an oscillation signal (f1 ± fi to f2) from this local oscillator.
± fi) and the received signal from the receiving antenna (f1 to f2)
And a mixer (mixer) for converting the frequency of the received signal to a predetermined frequency fi, and detecting the presence or absence of the product (resonant circuit) based on the signal level from the mixer. That is, a so-called heterodyne method is adopted in which the frequency of the received signal, which periodically changes according to the frequency change of the detection signal, is converted into a specific frequency fi and then the received level is detected.

By the way, in the device using the heterodyne system as described above, unless the sweep of the sweep oscillator provided on the transmitter side and the sweep of the local oscillator provided on the receiver side are synchronized, the receiver side is required. The reception level cannot be detected. Therefore, conventionally, as a configuration for synchronizing the sweep on the transmitting side and the sweep on the receiving side, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 282698, instead of providing a sweep oscillator on the transmitter side, an oscillation signal (f1 ± fi to f2) of a local oscillator is transmitted from the receiver side to the transmitter side.
(± fi) is transmitted as a synchronization signal, and the oscillation signal (f1 ± fi to f2 ± fi) and the frequency are fi on the transmitting device side.
The frequency is f1 to f
It has been proposed to generate two detection signals.

[0005]

However, in the conventional shoplifting prevention device, in addition to the transmitting / receiving antenna for transmitting / receiving the detection signal, the synchronizing signal (f1 ±
Since a transmission / reception antenna for transmitting / receiving fi to f2 ± fi) is additionally required, there is a problem that the device becomes complicated.

It is also possible to transmit the synchronization signal between the transmitter and the receiver via a dedicated cable, but in this case, extra wiring is provided at the entrance and exit of a store or the like. Then, there is a problem that it gets in the way of people. The present invention has been made in view of these problems, in a shoplifting prevention device using a heterodyne system,
An object is to reliably synchronize the transmitting side and the receiving side with a simple configuration.

[0007]

The present invention as set forth in claim 1 made in order to achieve the above object, comprises a transmitting antenna and a receiving antenna, which are installed at a predetermined interval, as illustrated in FIG. Transmission means for transmitting a detection signal of a predetermined frequency from the transmission antenna, frequency control means for changing the frequency of the detection signal within a predetermined frequency range and in a predetermined pattern set in advance, and a reception signal from the reception antenna , A frequency conversion means for converting the frequency of the received signal into a different frequency by mixing the received signal with a transmission signal from a predetermined oscillator, and the received signal converted by the frequency conversion means. The oscillation frequency of the oscillator is set to a predetermined pattern according to the frequency change of the detection signal by the frequency control means so that the frequency is always the predetermined measurement frequency. A frequency converter control means for changing,
Based on the level detection means for detecting the signal level of the output signal from the frequency conversion means and the signal level detected by the level detection means, a resonance frequency between the transmission antenna and the reception antenna is in the frequency range. Shoplifting prevention including determination means for determining whether or not an article having a resonance circuit set therein is present, and informing means for informing that the article is present according to the determination result of the determination means In the device, every time the frequency of the detection signal is changed by one pattern by the frequency control unit, the operation of the transmission unit and the frequency control unit is stopped for a predetermined time, and the transmission of the detection signal is temporarily stopped. A transmission stop detection means for detecting that the transmission of the detection signal is stopped based on the signal level of the output signal from the stop means and the frequency conversion means. And a synchronization control means for initializing the operation of the frequency conversion control means when the transmission stop detection means detects the transmission stop of the detection signal. There is.

The present invention according to claim 2 is the shoplifting prevention device according to claim 1, wherein the level detecting means is the oscillator by the frequency conversion control means, as illustrated by the one-dot chain line in FIG. Signal level detection for detecting the signal level of the output signal from the frequency conversion means in the same detection cycle as the cycle in which the oscillating frequency is changed by one pattern and at predetermined time intervals within each detection cycle. Means, storage means for sequentially storing the signal levels detected by the signal level detection means, and signal levels for a predetermined detection cycle stored in the storage means are read out, and detected at the same time in each detection cycle. An average value calculating means for calculating the average value of the signal level respectively, further, the determining means, based on the average value calculated by the average value calculating means, the article Determining whether standing, it is summarized as anti-shoplifting device according to claim.

[0009]

In the shoplifting prevention device according to the first aspect of the present invention configured as described above, the transmitting antenna and the receiving antenna are installed with a predetermined space therebetween, and the transmitting means is provided with a predetermined distance from the transmitting antenna. A frequency detection signal is transmitted, and the frequency control means changes the frequency of the detection signal transmitted by the transmission means within a predetermined frequency range and in a predetermined pattern set in advance.

The frequency change of the detection signal by the frequency control means may be of a sweep type which continuously changes the frequency, or hopping which changes the frequency with time based on a predetermined change pattern. It can be a mold. On the other hand, the frequency conversion means inputs a reception signal from the reception antenna, mixes the reception signal with a transmission signal from a predetermined oscillator, converts the frequency of the reception signal to a different frequency, and performs frequency conversion control. The means changes the oscillation frequency of the oscillator in a predetermined pattern according to the frequency change of the detection signal by the frequency control means so that the frequency of the reception signal converted by the frequency conversion means is always the predetermined measurement frequency. Then, the level detection means detects the signal level of the output signal from the frequency conversion means, and the determination means determines the resonance frequency between the transmission antenna and the reception antenna based on the signal level detected by the level detection means. It is determined whether or not there is an article having the resonance circuit set within the frequency range, and the notification means notifies that the article is present according to the determination result of the determination means.

Here, in the shoplifting prevention device according to the first aspect, the transmission stopping means causes the operation of the transmitting means and the frequency controlling means to be predetermined every time the frequency of the detection signal is changed by one pattern by the frequency controlling means. It is stopped for a certain period of time to temporarily stop the transmission of the detection signal from the transmitting antenna. Then, the transmission stop detection means detects that the transmission of the detection signal is stopped based on the signal level of the output signal from the frequency conversion means, and when the transmission stop detection means detects the stop of the transmission of the detection signal. The synchronization control means initializes the operation of the frequency conversion control means.

That is, in the shoplifting prevention device according to the first aspect of the invention, on the receiving side, from the oscillator (local oscillator) whose frequency is changed in a pattern according to the frequency change of the received signal from the receiving antenna and the detected signal. By mixing with the oscillation signal of, the frequency of the received signal is converted to a constant measurement frequency, the signal level of the received signal after the frequency conversion is detected, a so-called heterodyne method is adopted,
At the transmitting side, every time the frequency of the detection signal is changed by one pattern, the transmission of the detection signal is temporarily stopped.

When the transmission of the detection signal is once stopped in this way, the signal level of the output signal from the frequency conversion means (hereinafter, also simply referred to as the reception level) is lowered on the receiving side, so that the transmission is stopped. The detection means detects that the transmission of the detection signal is stopped based on the signal level, and initializes the operation of the frequency conversion control means every time the stop of the transmission of the detection signal is detected. The frequency change start timing of the detection signal in 1 is always matched with the oscillation control start timing of the oscillator on the receiving side.

Therefore, according to the shoplifting prevention device of the first aspect, unlike the conventional device described above, the frequency change of the detection signal on the transmission side and the reception side are eliminated without providing an additional antenna or wiring. It is possible to reliably synchronize with the frequency change of the oscillator. Since the transmitting side and the receiving side can be reliably synchronized in this way, the frequency of the received signal can be surely converted to a predetermined measurement frequency and the reception level can be detected. Therefore, the reception level can be detected only with respect to the frequency of the detection signal actually transmitted at that time, and in addition, the influence of external noise can be minimized to accurately determine the presence or absence of the article having the resonance circuit. Can be determined.

Next, in the shoplifting prevention device according to the second aspect, when the level detecting means detects the signal level of the output signal from the frequency converting means, first, the signal level detecting means causes the frequency conversion controlling means. Detects the signal level of the output signal from the frequency conversion means at the same detection cycle as the cycle in which the oscillation frequency of the oscillator is changed by one pattern, and at predetermined time intervals within each detection cycle, and stores the detected signal level. The means sequentially stores the signal levels detected by the signal level detecting means. Then, the average value calculation means reads out the signal level for a predetermined detection cycle stored in the storage means, and calculates the average value of the signal levels detected at the same time in each detection cycle.

Then, the judging means judges whether or not there is an article based on the average value calculated by the average value calculating means. That is, in the shoplifting prevention device according to the second aspect, the oscillation frequency of the oscillator is the same as the cycle changed by one pattern, in other words, the cycle of the detection signal frequency is changed by one pattern. In addition, by detecting the reception level at each predetermined time interval in each cycle and sequentially storing the detected reception levels, a plurality of reception levels when the detection signal of the same frequency is transmitted are stored. I am trying to do it. Then, the reception level corresponding to the detection signal of the same frequency is averaged for each predetermined period, and whether or not there is an article having a resonance circuit between the transmission antenna and the reception antenna based on each average value. Is determined.

Therefore, according to the shoplifting prevention device of the second aspect, even if a single noise (random noise) occurs within the frequency range in which the frequency of the detection signal is changed (within the frequency band of the detection signal). Since the calculated average value of the reception level does not have a great influence, it is possible to always accurately detect and notify the occurrence of shoplifting without being influenced by noise.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 is a block diagram showing the configuration of the shoplifting prevention device of the embodiment. As shown in FIG.
The shoplifting prevention device of this embodiment has a predetermined resonance frequency f0 (f0 = 8.23 MH in this embodiment) in a store selling video tapes, music compact discs, and the like.
The product M to which the L-C resonance circuit Ma having z) is attached in advance detects that the product M has passed near a specific entrance / exit, and notifies the occurrence of shoplifting. A pair of transmitting antenna 1 and receiving antenna 5, which are installed at a distance of 1.8 m), and a resonance circuit Ma.
Predetermined frequency range f1 to f2 including the resonance frequency f0 (in this embodiment, f1 = 7.38 MHz to f2 = 9.07 MH)
z) the transmitting device 3 for sending out the detection signal swept from the transmitting antenna 1, and the receiving device 7 for detecting and informing the occurrence of shoplifting action based on the received signal from the receiving antenna 5.
It consists of and. The resonance circuit Ma is attached to the product M after being formed on a dedicated tag called a tag, a price tag of the product, or the like.

The transmitting device 3 has a predetermined frequency range (f1 to f1) according to a microcomputer (hereinafter, simply referred to as CPU) 9 having a CPU, a ROM, a RAM, etc., and frequency data (digital data) output from the CPU 9. f2)
Direct digital synthesizer (hereinafter, simply referred to as DDS) 11 that outputs a sine wave signal of
A low-pass filter (LPF) 13 that removes unnecessary harmonic components from the output signal of, and a variable attenuator 15 that attenuates the level of the signal output from the low-pass filter 13.
An amplifier (AMP) 17 for amplifying the output signal of the variable attenuator 15 and sending it as a detection signal from the transmitting antenna 1,
It has. The attenuation value of the variable attenuator 15 is set so that the output level of the detection signal transmitted from the transmitting antenna 1 falls within a predetermined specified value.

On the other hand, the receiving device 7 includes a CPU, a ROM, and an R.
Microcomputer equipped with AM, etc. (hereinafter simply referred to as CP
21), a reception signal from the reception antenna 5, and a bandpass filter (BPF) 23 that attenuates frequency components other than the reception band (f1 to f2) and a reception signal from the bandpass filter 23. Amplifying amplifier (A
MP) 25, a variable attenuator 27 that attenuates the amplified received signal level according to a control voltage from the outside, and C
According to the frequency data (digital data) output from the PU 21, a predetermined frequency range (in this embodiment, 18.08 to which is higher than the frequency of the detection signal by 10.7 MHz).
A direct digital synthesizer (hereinafter simply referred to as DDS) 29 as an oscillator that outputs a sine wave signal of 19.77 MHz), an amplifier (AMP) 31 that amplifies the output signal from the DDS 29, and an output signal of the amplifier 31. To input the required frequency component (18.08 to 19.7).
Band pass filter (BP) that passes only 7MHz
F) 33, the output signal from the band pass filter 33 and the received signal from the variable attenuator 27 are mixed, and the received signal is in the 10 MHz band (intermediate frequency fi = 10.
7 MHz), a mixer 35 as frequency conversion means, an IF band pass filter (IF-BPF) 37 for inputting a received signal from the mixer 35 and attenuating frequency components other than the intermediate frequency fi, and IF. An IF amplifier (I that amplifies the output signal from the bandpass filter 37)
F-AMP) 39, a detector 41 that detects the amplified reception signal, a high-pass filter (HPF) 43 and a low-pass filter (LPF) 45 that shape the waveform of the detection voltage signal output from the detector 41, An A / D converter 47 that converts the waveform-shaped detected voltage signal output from the low-pass filter 45 into a digital signal and outputs the digital signal to the CPU 21, and an output from the IF amplifier 39 to the detector 41 1
A diode 49 for detecting a 0.7 MHz received signal,
The detection voltage from the diode 49 is always the predetermined reference voltage V
The control voltage is output to the variable attenuator 27 so that the detection voltage from the diode 49 and the automatic gain control circuit 51 that keeps the level of the reception signal input to the detector 41 constant becomes a predetermined value or less. A comparator 53 that detects whether or not the voltage is equal to or lower than a predetermined value and outputs a low-level signal ST to the CPU 21, a lamp 55 and a buzzer 57 as notification means for notifying occurrence of shoplifting, Is equipped with.

The control loop composed of the variable attenuator 27, the diode 49, and the automatic gain control circuit 51 uses the detector 41 to determine the overall level of the received signal input from the IF amplifier 39 to the detector 41. This is for stabilizing to a level at which detection is possible, and is set so as not to follow a steep level change (for example, a change of 1 KHz or more) of the received signal.

In the shoplifting prevention device of this embodiment having the above-described structure, the CPU 9 of the transmitter 3 executes the sweeping process (FIG. 3) described later, whereby the transmitter antenna 1
To f1 = 7.38 MHz to f2 = 9.07 MHz, the detection signal is swept and transmitted. Then, C of the receiving device 7
The PU 21 detects the signal level of the reception signal from the reception antenna 5 by executing the article detection process (FIG. 4) described later, and detects the presence or absence of shoplifting action based on the signal level.

Therefore, first, the sweep process executed by the CPU 9 of the transmitter 3 will be described with reference to FIG. It should be noted that this sweeping process is always repeated when the transmitter 3 is powered on. As shown in FIG. 3, when the execution of the sweep process is started, first, in step (hereinafter referred to as S) 110, wait for 0.1 ms, and then in S120, the frequency data to be output to the DDS 11 is initialized. And the minimum value of the sweep range is f1 (= 7.38MHz)
Is output for 1.5 ms.

Then, in the transmitter 3, the DDS 11
Outputs a sine wave signal of 7.38 MHz for 1.5 ms, and this sine wave signal is transmitted as a detection signal from the transmission antenna 1 through the low pass filter 13, the variable attenuator 15, and the amplifier 17. . In this embodiment,
DDS 11, low-pass filter 13, variable attenuator 15,
And the amplifier 17 corresponds to the transmitting means.

When 1.5 ms has elapsed, the subsequent S
At 130, the next frequency data is set and output to the DDS 11. Here, in this embodiment, the frequency of the detection signal is increased from f1 = 7.38 MHz to f2 = 9.07 MHz in 80 steps over a period of 1.6 ms. The frequency data is the frequency Δf (Δf = (f2−f1) / 79 = 2) per step of the frequency of the detection signal currently transmitted.
1.392 KHz) is the data representing the added frequency.

Then, in subsequent S140, the time Δt (Δt = 1.6) per step for changing the frequency of the detection signal.
ms / 79 = 20.253 μs), and then S15
At 0, the frequency data currently output to the DDS 11 is the maximum value in the sweep range f2 (= 9.07 MHz).
It is determined whether or not the value has been reached. And S150
When it is determined that the frequency data has not reached the value indicating f2, the process returns to S130, the frequency data is updated to the DDS 11 (S130), and the time Δ per step Δ.
The waiting for t (S140) is repeated.

In this way, the frequency data to the DDS 11 is updated every Δt by Δf, and when it is determined in S150 that the currently output frequency data has reached the value representing f2. Advances to S160 to stop the output of frequency data, and then returns to S110.

Then, the DDS 11 stops the output of the sine wave signal for the waiting time (0.1 ms) in S110, and the detection signal is sent for 0.1 m.
Stopped for s. Then, when 0.1 ms has elapsed,
After the processing from S120 to S160 is executed again and the frequency of the detection signal is held at f1 for 1.5 ms, Δf is changed every Δt (= 20.253 μs).
It is increased by (= 21.392 KHz) and is increased to f2 again.

That is, as a result of the execution of this sweeping process, the detection signal has a transmission stop period of 0.1 ms (S110, S160) and a 1.5 ms output at 7.38 MHz, as shown in FIG. 6 (A). A constant frequency period (S120) and a 1.6 ms sweep period (S130 to S) in which the frequency is increased in 80 steps from 7.38 MHz to 9.07 MHz.
150), and a total of 3.2 ms is set as one cycle and is transmitted from the transmitting antenna 1. In other words, in the sweep process, the frequency of the detection signal is set to 7.
After maintaining at 38 MHz, the detection signal transmission is stopped for 0.1 ms for each frequency change pattern that increases from 7.38 MHz to 9.07 MHz in 80 steps over 1.6 ms. There is.

In this embodiment, S120 to S1
50 corresponds to the processing as frequency control means, and S
110 and S160 correspond to the processing as the transmission stop means. The 3.2 ms period will be referred to as a sweep period hereinafter. Next, the article detection process executed by the CPU 21 of the reception device 7 will be described with reference to FIG. It should be noted that this article detection process is also repeatedly executed whenever the receiving device 7 is powered on.

As shown in FIG. 4, when the execution of the article detection process is started, first in S210, the CPU 21 is initialized, and the DDS 29 is initialized to the maximum value of the frequency change range of 19.77 MHz (= The frequency data representing f2 + fi) is output. Then, in subsequent S220, the DDS 29 is synchronized with the sweep cycle of the detection signal on the transmitter 3 side.
By changing the transmission frequency of the
The frequency of the received signal from is converted into the intermediate frequency fi, and the data acquisition process of detecting the signal level after the frequency conversion is executed.

This data fetching process is executed as shown in FIG. That is, when the execution of the data acquisition process is started, the signal ST from the comparator 53 is first sent in S410.
It is determined whether or not the level has changed from the high level to the low level, in other words, whether or not the signal ST has fallen.

Here, the signal S output from the comparator 53
T will be described. First, in the reception device 7, the sine wave signal having a frequency higher than the detection signal by fi (= 10.7 MHz) is output from the DDS 29, and the sine wave signal and the reception signal from the reception antenna 5 (variable attenuator 27) are detected. Are mixed by the mixer 35, the frequency of the received signal is converted into the intermediate frequency fi, and the received signal after the frequency conversion is converted into fi
A narrow band IF bandpass filter 37 and an IF amplifier 39 that attenuate frequency components other than
And the diode 49.

Immediately after the receiver 7 is powered on, the DDS 29 outputs a constant sine wave signal of 19.77 MHz (= f2 + fi) by the process of S210. Therefore, after the power to the receiving device 7 is turned on, the IF amplifier 39 outputs a signal of a predetermined level only when the frequency of the detection signal transmitted from the transmitting antenna 1 becomes f2 (= 9.07 MHz).
By extension, the detection voltage from the diode 49 becomes a predetermined value or more, and the signal ST from the comparator 53 becomes High level. Then, after that, when the transmission of the detection signal is stopped as described above, the detection voltage of the diode 49 becomes equal to or lower than a predetermined value (approximately 0 V), and the signal ST from the comparator 53 becomes Low.
Change to a level.

That is, in this embodiment, after the power supply to the receiving device 7 is turned on, the signal ST from the comparator 53 is output at the timing when the transmission of the detection signal from the transmitting antenna 1 is first stopped.
It is configured such that a falling change occurs at this time, and this timing is detected in S410 of the data acquisition process.

If it is determined in S410 that the signal ST has fallen and changed, the process proceeds to S420 and D
Initially set the frequency data to be output to the DS29 to the minimum value of the frequency change range of 18.08 MHz (= f1 +
The frequency data representing fi) is output, and in the subsequent S430, the time (1.6 m) obtained by adding the transmission stop period (0.1 ms) of the detection signal and the constant frequency period (1.5 ms).
s) only wait.

Then, from the DDS 29, 18.08M
A sine wave signal of Hz is output for 1.6 ms, and this sine wave signal is input to the mixer 35 via the amplifier 31 and the bandpass filter 33. And at this time,
As described above, since the detection signal of 7.38 MHz is transmitted from the transmitting antenna 1, in the receiving device 7,
The received signal from the receiving antenna 5 is 1 by the mixer 35.
After frequency conversion into a signal of 0.7 MHz, the detector 4 is passed through the IF band pass filter 37 and the IF amplifier 39.
1, the detected voltage from the detector 41 is waveform-shaped by the high-pass filter 43 and the low-pass filter 45, and then input to the CPU 21 via the A / D converter 47.

Then, in the subsequent S440, the CPU 21 fetches the digital data (hereinafter referred to as level data) from the A / D converter 47 and stores it in the RAM, and in the subsequent S450, sets the next frequency data. DDS29
Output to. The next frequency data set in S450 is also set to the frequency of the sine wave signal currently output by the DDS 29 by one step in the sweep process, just as in S130 of the sweep process executed on the transmitter 3 side. Frequency per hit Δf (=
21.392 KHz).

Then, in the following S460, it is determined whether 80 pieces of level data have been fetched, that is, the processing of S440 is performed by 80.
If it is determined that 80 level data have not been fetched, it is determined in S470 that follows.
After waiting for a time Δt (= 20.253 μs) per step in which the frequency of the detection signal is changed by the sweep process, S
Returning to 440, the processing of S440 to S470 is repeated.
On the other hand, if it is determined in S460 that 80 level data have been captured, the data capturing process ends.

That is, in the data fetching process, the comparator 53
It is detected that the sending of the detection signal is temporarily stopped by detecting the fall of the signal ST from (S).
410), 1.6m from the detection timing as a starting point
During s, the transmission frequency of DDS29 is 18.08MHz
(= F1 + fi) (S420, S430), and thereafter, just like the transmitting device 3, the transmission frequency of the DDS 29 is Δf (= 21.25 μs) every time Δt (= 20.253 μs) elapses. 392 KHz), and finally up to 19.77 MHz (= f2 + fi) in 80 steps (S450 to S470). Therefore, from the DDS 29, fi (= 1
(0.7 MHz), a sine wave signal having a high frequency is output, and by extension, the reception signal from the reception antenna 5 is always converted into a signal having an intermediate frequency fi = 10.7 MHz and input to the detector 41. Will be done.

Further, in the data acquisition process, the DDS
Immediately before increasing the transmission frequency of 29 by Δf, the signal level (detection voltage) of the reception signal detected by the detector 41 is taken in as level data via the A / D converter 47, and each level is acquired. The data is sequentially stored in the RAM (S440).

In this embodiment, S420, S4
30, S450 to S470 correspond to the processing as the frequency conversion control means, and S410 corresponds to the processing as the transmission stop detection means and the synchronization control means. Also, S
Reference numeral 440 corresponds to the signal level detection means and the storage means.

Therefore, after the power is turned on, the data fetching process is 1
When it is executed once, 80 pieces of level data D1.1, D1.2, ..., In the RAM, as shown in the uppermost part of FIG.
D1 79 and D1 80 will be stored. Incidentally, FIG.
In (B), D1 · n is the frequency of the detection signal transmitted from the transmitting antenna 1 is “(f1 + (n−1) · Δ”.
f): However, n represents the level data when it is an integer of 1 to 80.

Next, when the CPU 21 completes the execution of the data fetching process, in S230 of FIG. 4, it is determined whether or not the data fetching process has been executed 16 times,
If it is determined that the process has not been executed 16 times, the process returns to S220 and the processes of S220 and S230 are repeated.

As described above, the data acquisition process S
When the processing after 420 is executed, after that, DDS2
6 outputs a sine wave signal having a frequency higher than that of the detection signal by fi, and the IF amplifier 39 outputs a reception signal of a predetermined level that has been frequency-converted to 10.7 MHz. Therefore, as shown in FIG. Signal S from the comparator 53
T becomes Low level only when the transmission of the detection signal is stopped on the transmitter 3 side. Therefore, when the data acquisition process is performed after the power is turned on to the receiving device 7 for the second time or later, the timing at which it is determined in S410 that the signal ST has fallen and changed, that is, the detection signal. Is resynchronized with the timing at which the transmission of
The substantial process of S470 to S470 is executed.

If it is determined in S230 that the data fetching process has been executed 16 times, the process proceeds to S240. Therefore, when proceeding to S240, a total of 1280 (= 80 × 16) level data are stored in the RAM as shown in FIG. 6B. In FIG. 6B, Dm · n represents the nth level data captured when the mth (mth sweep) data capture process is executed.

Next, in S240, a predetermined counter n
Is reset to "0", and in the subsequent S250, the counter n
Is incremented. Then, in the subsequent S260, each of the data fetching processes executed 16 times as described above is performed n times.
Secondly, the level data Dm · n (m = 1 to 1) stored in the RAM
16) The process as an average value calculating means for calculating the average value Dn is executed.

In subsequent S270, it is determined whether or not the value of the counter n has reached 80, that is, whether or not the calculation of the average value has been completed for all the 1st to 80th level data, and the counter is counted. When it is determined that the value of n is not 80, the process returns to S250 and S250 to S270.
Is repeated. Then, in S270, the counter n
When it is determined that the value of 80 has reached 80, the process proceeds to S280, and all the average values D1 to D8 calculated in S260.
Store 0 in RAM.

Therefore, when the processing of S280 ends, R
As shown in the bottom of FIG. 6B, the AM has level data detected at the same timing in each of the 16 data acquisition processes (that is, the reception level when the detection signal of the same frequency is transmitted). 80 average values (hereinafter, referred to as average data) D1 to D80 are stored.

Then, in S290, calculated as 80
In the average data D1 to D80, a process as a determining unit for determining whether or not data outside a predetermined range set in advance is executed. If data outside the predetermined range exists, In subsequent S300, the lamp 55 and the buzzer 57 are driven for 1 second to notify that the product M exists between the transmitting antenna 1 and the receiving antenna 5 (alarm).
To do.

The predetermined range used in the determination of S290 is, as illustrated in FIG. 7B, more than the value of the average data calculated when the product M does not exist between the transmitting / receiving antennas 1 and 5. It is a range between the upper limit value VthH which is set larger by a predetermined value and the lower limit value VthL which is set smaller by a predetermined value than the value of the average data, and in S290, 80 pieces of average data D1 are set.
If any one of D80 to D80 exceeds the upper limit value VthH or falls below the lower limit value VthL, it is determined that the product M exists.

When the process of S300 is executed, or when it is determined that there is no average data outside the predetermined range in S290, the process proceeds to S310, and among the level data stored in the RAM. Oldest 1
Data for the sweep cycle, that is, 80 level data D1.1-D1-80 stored in the first data acquisition process is deleted, and each level data stored in the mth data acquisition process Level data D (m-1) .. 1 to D (m-1) .Dm.1 to Dm.80 stored in the (m-1) th data loading process.
It is re-stored in the RAM as 80, and then in S320, S2.
In exactly the same manner as in the case of 20, the data fetching process shown in FIG. 5 is executed. The 80 level data stored in the RAM in the data fetching process executed in S320 is
The latest level data D16-1 to D16.80 are stored in the RAM.

Then, when the execution of the data acquisition process is completed in S320, the process returns to S240 again and S240
~ The process of S320 is repeated, and thereafter,
Every time 80 level data for one sweep cycle is acquired,
The average data D1 to D80 are calculated using the level data for the total of 16 sweep cycles consisting of the level data for the current time and the level data for the last 15 sweep cycles, and the average data D1 to D80 are used. Product M
The presence or absence of is sequentially determined.

As described above, in the shoplifting prevention device of this embodiment, when the signal level of the received signal is detected at the receiving device 7 side (S440), fi () is detected rather than the detected signal from the transmitting antenna 1. = 10.7 MHz), a sine wave signal with a high frequency is always output from the DDS 29 (S42
0, S430, S450 to S470), the sine wave signal and the reception signal from the reception antenna 5 are mixed by the mixer 35, the frequency of the reception signal is converted to the intermediate frequency fi, and the reception signal after the frequency conversion is converted. The wave is detected by the wave detector 41. That is, in the shoplifting prevention device according to the present embodiment, the frequency of the reception signal that periodically changes according to the frequency change of the detection signal is converted into the constant frequency fi,
A so-called heterodyne method for detecting the reception level is adopted.

In particular, in the shoplifting prevention device of this embodiment, as shown in FIG. 6A, every time the frequency of the detection signal is changed by one pattern on the transmitting device 3 side (S12).
0 to S150), the transmission of the detection signal is stopped only for 0.1 ms (S110, S160), and the transmission of the detection signal is once performed on the receiving device 7 side based on the signal ST from the comparator 53. It is detected that it has been stopped (S41
0), the oscillation frequency of the DDS 29 is controlled again in synchronization with the detection timing (S410: YE).
S).

Therefore, according to the shoplifting prevention device of this embodiment, the CPU 9 on the transmitting device 3 side and the CPU 2 on the receiving device 7 side.
Even if there is a deviation in the operating speed (operating clock) from the transmitter 1, there is no need to provide any special wiring for synchronization between the transmitters / receivers 3 and 7, and there is no change in the oscillation frequency of the DDS 11 on the transmitter 3 side (detection). The change in the frequency of the signal) and the change in the oscillation frequency of the DDS 29 on the receiving device 7 side can be reliably synchronized.

Since the transmitting side and the receiving side can be surely synchronized in this way, the frequency of the received signal from the receiving antenna 5 is always surely converted by the mixer 35 to accurately detect the receiving level. Therefore, the existence of shoplifting can be accurately determined. That is, since the signal level of the received signal can be reliably detected through the narrow band IF band pass filter 37 that attenuates frequency components other than the intermediate frequency fi, the detection signal actually transmitted at that time is detected. It is possible to detect the reception level only for the frequency component, which allows
Resonance circuit Ma with minimal influence of external noise
It is possible to accurately determine the presence or absence of the product M having the.

Further, in the shoplifting prevention device of this embodiment, the detection signal is sent from the transmitting antenna 1 as shown in FIG. 6A at the same period as the sweep period and within each sweep period. Predetermined time Δt in 1.6ms sweep period
The signal level of the received signal from the receiving antenna 5 is
Sequential RA as level data via the A / D converter 47
The data is stored in M (S440), whereby the level data when the detection signals of the same frequency are sent are stored for a plurality of sweep cycles (16 cycles in this embodiment).
Then, the level data for 16 cycles corresponding to the detection signals of the same frequency are averaged (S240 to S280),
Based on each of the average values (average data) D1 to D80, it is determined whether or not the product M including the resonance circuit Ma exists between the transmitting antenna 1 and the receiving antenna 5 (S290). . Therefore, according to the shoplifting prevention device of the present embodiment, within the sweep frequency range of the detection signal (f1 to f
Random noise is generated in 2), and as shown in FIG. 7A, in the receiving device 7, from the A / D converter 47 to the CPU 2
Even if a large level change occurs in the level data input to 1, as shown in FIG. 7B, the calculated average data D1 to D80 do not have a great influence. On the other hand, when the resonance circuit Ma (commodity M) is present between the transmitting antenna 1 and the receiving antenna 5, the level data corresponding to the detection signal of the same frequency continuously fluctuates, and As shown in (B), the average data also greatly changes from the steady value.

Therefore, according to the shoplifting prevention device of the present embodiment, only the existence of the resonance circuit Ma can be accurately detected without being affected by random noise, and in turn, the shoplifting action is always generated. It can be accurately detected and notified. Furthermore, in the shoplifting prevention device of the present embodiment, after the receiving device 7 is powered on and after the level data has been captured for 16 sweep cycles (S230: YES), 1
Every time 80 level data for the sweep cycle are fetched, the average data D1 to 1 are obtained by using the level data for a total of 16 sweep cycles consisting of the level data for the current cycle and the level data for the immediately preceding 15 sweep cycles. D80 is calculated (S240 to S320).

That is, it is conceivable to calculate the average data every time the level data for 16 sweep cycles is fetched to judge the presence / absence of the resonance circuit Ma (commodity M). The time interval for making the determination becomes large. On the other hand, according to the shoplifting prevention apparatus of this embodiment, after the average data is first calculated after the power is turned on, the oldest level data for one sweep cycle is discarded and the level data for the latest one sweep cycle is discarded. Each time you import
Since the average data D1 to D80 are calculated, it is possible to make a stable determination for each sweep cycle and to detect the presence of the product M with good responsiveness.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of the present invention.

FIG. 2 is a block diagram showing a configuration of a shoplifting prevention device according to an embodiment.

FIG. 3 is a flowchart showing a sweep process executed on the transmitter side.

FIG. 4 is a flowchart showing an article detection process executed on the receiving device side.

FIG. 5 is a flowchart showing a data acquisition process executed in the article detection process.

FIG. 6 is an explanatory diagram illustrating an operation of a sweep process and an article detection process.

FIG. 7 is an explanatory diagram illustrating an operation of the shoplifting prevention device according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transmitting antenna 3 ... Transmitting device 5 ... Receiving antenna 7 ... Receiving device 9,21 ... Microcomputer (CPU) 11, 29 ... Direct digital synthesizer (D)
DS) 13,45 ... Low-pass filter 15, 27 ... Variable attenuator 17, 25, 31 ... Amplifier 23, 33 ... Band-pass filter 35 ... Mixer 37 ... IF band-pass filter 3
9 ... IF amplifier 41 ... Detector 43 ... High-pass filter 47 ... A
/ D converter 49 ... Diode 51 ... Automatic gain control circuit 53
... Comparator 55 ... Lamp 57 ... Buzzer M ... Product Ma ...
LC resonance circuit

Claims (2)

[Claims] 1. A transmitting antenna and a receiving antenna, which are installed at a predetermined interval, transmitting means for transmitting a detection signal of a predetermined frequency from the transmitting antenna, and a frequency of the detection signal within a predetermined frequency range and in advance. A frequency control unit that changes in a set predetermined pattern and a reception signal from the reception antenna are input, and the reception signal and a transmission signal from a predetermined transmitter are mixed to change the frequency of the reception signal to a different frequency. And a frequency conversion means for converting the frequency of the detection signal by the frequency control means so that the frequency of the received signal converted by the frequency conversion means is always a predetermined measurement frequency. Frequency conversion control means for changing the signal in a predetermined pattern according to the change, and a register for detecting the signal level of the output signal from the frequency conversion means. Whether there is an article having a resonance circuit in which the resonance frequency is set within the frequency range between the transmitting antenna and the receiving antenna based on the signal level detected by the level detecting means and the level detecting means. In the shoplifting prevention device, comprising: a judging means for judging whether or not the article exists, and a notifying means for notifying that the article is present according to the judgment result of the judging means, wherein the frequency of the detection signal is changed by the frequency control means. Each time the pattern is changed by one pattern, the operation of the transmission means and the frequency control means is stopped for a predetermined time, and the transmission stop means for temporarily stopping the transmission of the detection signal; and the signal of the output signal from the frequency conversion means. Transmission stop detection means for detecting that the transmission of the detection signal is stopped based on the level, and stop of the transmission of the detection signal by the transmission stop detection means Once detected, anti-shoplifting device for the synchronous control means for initializing, comprising the operations of the frequency conversion control means. 2. The shoplifting prevention device according to claim 1, wherein the level detection unit has the same detection cycle as a cycle in which the oscillation frequency of the oscillator is changed by one pattern by the frequency conversion control unit, and Signal level detection means for detecting the signal level of the output signal from the frequency conversion means and storage means for sequentially storing the signal levels detected by the signal level detection means at predetermined time intervals within each detection cycle. And an average value calculating means for reading out a signal level for a predetermined detection cycle stored in the storage means and calculating an average value of the signal levels detected at the same time in each of the detection cycles. A shoplifting prevention device, wherein the determination means determines whether or not the article exists based on the average value calculated by the average value calculation means.