JPH08161660A - Shoplifting preventing device - Google Patents

Abstract

PURPOSE: To detect and inform a shoplifting act accurately at all times without being affected by random noise by detecting a level of a reception signal for the same period as a frequency change period of a detection signal for each prescribed time interval within each period. CONSTITUTION: When an object detection means detects the presence of an object, at first a level detection means detects a level of a reception signal from a reception antenna for the same period as a frequency change period of a detection signal for each prescribed time interval within each period, and a storage means stores sequentially the signal level detected by a level detection means. Then a mean value calculation means reads the signal level by a prescribed detection period stored in the storage means and calculates a mean value of the signal levels detected at the same time for each detection period respectively. Then a discrimination means discriminates whether or not an object is in existence based on the mean value calculated by the mean value calculation means and allows a notice means to conduct notification.

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 are installed on both sides of a doorway of a library or a store that sells a predetermined product, and the device is preliminarily attached to a rental item or a product. A detection signal of the same frequency as the resonance frequency of the resonance circuit (object to be detected) is constantly sent from the transmission antenna, the signal level of the reception signal from the reception antenna is detected, and the occurrence of shoplifting is detected. It has 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.

[0003]

However, in general,
In this type of anti-shoplifting device, the resonance frequency of the resonance circuit attached to the product varies due to manufacturing. Therefore, in order to reliably detect the presence (shoplifting) of the resonance circuit, the frequency of the detection signal sent from the transmitting antenna Is swept in a predetermined frequency range, and the receiving side receives signals in the entire frequency range and detects the signal level.

Therefore, in the above-mentioned conventional shoplifting prevention device, only a single noise (random noise) is generated within the frequency band of the detection signal transmitted from the transmission antenna, and the signal level of the reception signal greatly varies. ,As a result,
There has been a problem that even a person who is not a shoplifter is notified of the occurrence of shoplifting.

The present invention has been made in view of these problems, and an object of the present invention is to provide a shoplifting prevention device capable of always accurately detecting and notifying the occurrence of shoplifting.

[0006]

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. Transmitting means for transmitting a detection signal of a predetermined frequency from the transmitting antenna, frequency control means for periodically causing the transmitting means to change the frequency of the detection signal within a predetermined frequency range, and a reception signal of the receiving antenna. Based on a signal level, between the transmitting antenna and the receiving antenna, article detecting means for detecting the presence of an article having a resonance circuit whose resonance frequency is set within the frequency range, and the article detecting means. In the shoplifting prevention device, comprising: a notification means for notifying that the presence of the article has been detected, the article detection means is configured to detect the detection by the frequency control means. Level detection means for detecting the signal level of the received signal at the same detection cycle as the frequency of the signal being changed, and at predetermined time intervals within each detection cycle, and detected by the level detection means. Storage means for sequentially storing the detected signal levels, and a signal level for a predetermined detection cycle stored in the storage means, and an average for calculating the average value of the signal levels detected at the same time in each of the detection cycles. A value calculating means and a determining means for determining whether or not the article exists based on the average value calculated by the average value calculating means, and for determining that the article exists, causing the informing means to perform an informing operation. And a shoplifting prevention device characterized in that

According to a second aspect of the present invention, in the shoplifting prevention device according to the first aspect, the average value calculating means stores the signal level for one detection cycle every time the storage means stores a signal level for one detection cycle. The shoplifting prevention device is characterized in that the average value is calculated using a signal level of the detection cycle and a signal level of a predetermined detection cycle immediately before the detection cycle.

Furthermore, according to the present invention as defined in claim 3, in the shoplifting prevention device according to claim 1 or claim 2, the level detecting means controls the transmission frequency, as illustrated by the dotted line in FIG. Possible transmitter, frequency conversion means for mixing the transmission signal from the transmitter and the reception signal to convert the frequency of the reception signal to a different frequency, and the reception signal converted by the frequency conversion means Frequency conversion control means for controlling the oscillation frequency of the oscillator so that the frequency is always a predetermined measurement frequency, and detection for detecting the signal level of the output signal from the frequency conversion means as the signal level of the reception signal. And means for preventing shoplifting.

[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 causes the transmission means to periodically change the frequency of the detection signal within a predetermined frequency range. And
Article detection means, based on the signal level of the received signal from the receiving antenna, between the transmitting antenna and the receiving antenna,
The presence of an article having a resonance circuit whose resonance frequency is set within the frequency range is detected, and the notification unit notifies that the article detection unit detects the presence of the article.

Here, when the presence of the article is detected by the article detection means, first, the level detection means has the same detection cycle as the cycle in which the frequency of the detection signal is changed by the frequency control means, and The signal level of the received signal from the receiving antenna is detected at predetermined time intervals within each detection cycle, and the storage unit sequentially stores the signal levels detected by the level detection unit. Then, the average value calculation means reads out the signal level for the predetermined detection cycle stored in the storage means, calculates the average value of the signal levels detected at the same time in each detection cycle, and the determination means, Based on the average value calculated by the average value calculation means, it is determined whether or not an article exists, and when it is determined that the article exists, the notification means is caused to perform the notification operation.

That is, in the shoplifting prevention device of the present invention, the signal level of the received signal is detected and detected at the same cycle as the frequency change cycle of the detection signal and at predetermined time intervals within each cycle. By sequentially storing the signal levels, a plurality of signal levels (hereinafter, also simply referred to as reception levels) of the reception signals when the detection signals of the same frequency are transmitted are stored. 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 present invention,
Even if random noise occurs within the frequency range in which the frequency of the detection signal is changed (in the frequency band of the detection signal), the average value of the calculated reception level does not have a significant effect. When there is a resonant circuit, the reception level corresponding to the detection signal of the same frequency continuously fluctuates greatly, and the average value also greatly changes from the steady value, so only the existence of the resonant circuit is accurately detected. be able to. Therefore, according to the shoplifting prevention device of the present invention, the occurrence of shoplifting can always be accurately detected and notified without being affected by random noise.

Next, in the shoplifting prevention device according to the second aspect, every time the average value calculating means stores the signal level for one detection cycle, the average level calculating means stores the signal level of the detection cycle.
The average value is calculated using the signal level of a predetermined detection cycle immediately before the detection cycle. That is, it is conceivable to calculate the average value and determine the presence / absence of the resonance circuit (article) each time the reception level for a predetermined period is detected. In this case, however, the time interval for performing one determination is It gets bigger.

Therefore, in the shoplifting prevention device according to the second aspect, the average value of the reception level is calculated for each detection cycle by using the detection result of that time and the detection result of the predetermined detection cycle immediately before that. By doing so, it is possible to make a stable determination for each detection cycle.
Therefore, according to the shoplifting prevention device of the second aspect, it is possible to detect the presence of the article with good responsiveness.

On the other hand, in the shoplifting prevention device according to the third aspect, when the level detecting means detects the signal level of the received signal, the frequency converting means detects the transmission signal from the oscillator capable of controlling the transmission frequency. The frequency of the received signal is converted to a different frequency by mixing with the received signal from the receiving antenna, and the frequency conversion control means ensures that the frequency of the received signal converted by the frequency conversion means is always the predetermined measurement frequency. First, the oscillation frequency of the oscillator is controlled, and the detection means detects the signal level of the output signal from the frequency conversion means as the signal level of the reception signal.

That is, in the shoplifting prevention device according to the third aspect, the frequency of the received signal that periodically changes according to the frequency change of the detected signal is converted into a constant measurement frequency, and then the received level is detected. The so-called heterodyne system is adopted. Therefore, according to the shoplifting prevention device according to claim 3, the frequency range in which the frequency of the detection signal is changed (that is,
Since the reception level can be detected only for the frequency of the detection signal actually transmitted at that time without detecting the reception level of the entire detection signal frequency band), the influence of external noise is minimized. Therefore, the presence or absence of the article having the resonance circuit can be more accurately determined.

[0017]

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 transmission device 3 has a predetermined frequency range (f1 to f1) according to a microcomputer (hereinafter, simply referred to as CPU) 9 including 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 an 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 bandpass 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 a frequency conversion means, an IF band pass filter (IF-BPF) 37 that inputs the received signal from the mixer 35 and attenuates 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, The 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 the IF amplifier 39 outputs the detected voltage signal to the detector 41.
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 level of the received signal input to the detector 41 is kept constant, and the detection voltage from the diode 49 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 including 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, so that 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.

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 processing as frequency control means for setting the next frequency data and outputting it to the DDS 11 is executed. Here, in the present embodiment, the frequency of the detection signal is f1 = 7.
From 38MHz to f2 = 9.07MHz, 1.6ms
It takes 80 hours to raise it,
The next frequency data output in S130 is the frequency per step of the frequency of the detection signal currently transmitted.
f (Δf = (f2-f1) /79=21.392KH
z) is data representing the frequency added.

Then, in the subsequent S140, the time per step Δt (Δt = 1.6) 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, as shown in FIG. 6 (A), the detection signal has a transmission stop period of 0.1 ms (S110, S160) and a 1.5 ms output at 7.38 MHz. 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 addition, below, this 3.2m
The period of s is called the sweep period.

Next, the article detection processing executed by the CPU 21 of the receiving device 7 will be described with reference to FIG. In addition, in this article detection process, when the receiving device 7 is powered on,
It is repeatedly executed. 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 maximum value of the frequency change range is 19.77 MHz (= f2 + f) to the DDS 29.
Output the frequency data representing i).

Then, in the subsequent S220, the frequency of the reception signal from the reception antenna 5 is converted into the intermediate frequency fi by changing the transmission frequency of the DDS 29 in synchronization with the sweep cycle of the detection signal on the transmission device 3 side. Then, a data acquisition process for 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 receiving apparatus 7 is powered on, the DDS 29 outputs a constant sine wave signal of 19.77 MHz (= f2 + fi) by the above-described processing 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.

When it is determined in S410 that the signal ST has fallen, 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 serves as a detection means (level detection means) and a storage means for fetching the digital data (hereinafter referred to as level data) from the A / D converter 47 and storing it in the RAM. A process is executed, and in the subsequent S450, a process as a frequency conversion control means for setting the next frequency data and outputting it to the DDS 29 is executed.

Note that the next frequency data set in S450 is also swept to the frequency of the sine wave signal currently output by the DDS 29, just as in S130 of the sweep process executed on the transmitter 3 side. Frequency per step 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), DD for 1.6ms from that timing
The transmission frequency of S29 is 18.08 MHz (= f1 + f
i)) (S420, S430), and thereafter, the transmission frequency of the DDS 29 is set to be the same as on the transmitting device 3 side.
Every time t (= 20.253 μs) elapses, Δf (= 2
It is increased by 1.392 KHz) and finally increased to 19.77 MHz (= f2 + fi) in 80 steps (S450 to S470). Therefore, DDS
From 29, fi (= 10.7MH) is always higher than the detection signal.
z), 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. It will be.

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).

Therefore, after the power is turned on, the data acquisition 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 performed 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, S of the data acquisition process
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.

When 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.

Then, in the following 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 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 RAM as 80, and 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, the sweeping cycle is the same as the sweep cycle of the detection signal sent from the transmitting antenna 1 as shown in FIG. The signal level of the reception signal from the reception antenna 5 is sequentially stored in the RAM as level data via the A / D converter 47 at every predetermined time Δt in the 1.6 ms sweep period (S420 to S470). ), The level data when the detection signals of the same frequency are transmitted 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), respectively, and the transmission antenna 1 and the reception antenna 5 based on the respective average values (average data) D1 to D80. It is determined whether or not the product M having the resonance circuit Ma is present therebetween (S290).

Therefore, according to the shoplifting prevention apparatus of this embodiment, random noise occurs within the sweep frequency range (f1 to f2) of the detection signal, and as shown in FIG. Even if a large level change occurs in the level data input from the / D converter 47 to the CPU 21, 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 as a result, the shoplifting action is always generated. It can be accurately detected and notified. Further, 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), 80 level data for one sweep cycle. Each time the data is fetched, the average data D1 to D80 are calculated 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 ( S240-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.

Furthermore, in the shoplifting prevention device of this embodiment,
When the signal level of the reception signal is detected on the reception device 7 side, fi (= 10.7M) is detected from the detection signal from the DDS 29.
A sine wave signal having a high frequency of (Hz) is always output, 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 frequency conversion is performed. The received signal after is detected by the detector 4
I detect it in 1. That is, the shoplifting prevention device of the present embodiment adopts a so-called heterodyne method in which the frequency of the reception signal that periodically changes according to the frequency change of the detection signal is converted into a constant frequency fi and then the reception level is detected. are doing.

Therefore, according to the shoplifting prevention apparatus of this embodiment, the signal level of the received signal can be detected through the narrow band IF bandpass filter 37 that attenuates frequency components other than the intermediate frequency fi. In this case, the reception level can be detected only for the frequency component of the detection signal actually transmitted at that time without detecting the reception level in the entire sweep frequency range (f1 to f1) of the detection signal. The presence or absence of the product M having the resonance circuit Ma can be more accurately determined by minimizing the influence of external noise.

On the other hand, in the shoplifting prevention device of this embodiment, the transmitting device 3 is arranged to stop the transmission of the detection signal only for 0.1 ms at each sweep cycle, and the receiving device 7 side is arranged to It is detected that the sending of the detection signal is once stopped (S
410), resynchronize with the detection timing, and DDS2
9 oscillation frequency control is performed (S420-
S470).

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 difference in the operating speed (operating clock) between the transmitter and the receiver 1, there is no need to provide a special wiring for synchronization between the transmitting and receiving devices 3 and 7, and the frequency change of the detection signal and the DDS 29 on the receiving device 7 side The oscillation frequency can be accurately synchronized, and by extension, the reception signal from the reception antenna 5 can always be surely frequency-converted by the mixer 35, and the reception level can be accurately detected.

[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 (3)

[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 to the transmitting means in a predetermined frequency range. A frequency control means for periodically changing the resonance frequency, and a resonance circuit in which a resonance frequency is set within the frequency range between the transmission antenna and the reception antenna based on a signal level of a reception signal from the reception antenna. In a shoplifting prevention device comprising: an article detecting unit that detects the presence of an article having the item; and an informing unit that notifies that the item detecting unit detects the presence of the item, The same detection cycle as the cycle in which the frequency of the detection signal is changed by the frequency control means, and a predetermined time interval within each detection cycle. A level detection means for detecting the signal level of the received signal; a storage means for sequentially storing the signal levels detected by the level detection means; and a signal level for a predetermined detection period stored in the storage means. An average value calculating means for calculating an average value of signal levels detected at the same time in each detection cycle, and whether or not the article exists based on the average value calculated by the average value calculating means. A shoplifting prevention device comprising: a determination unit that causes the notification unit to perform a notification operation when it is determined that the article is present. 2. The shoplifting prevention device according to claim 1, wherein the average value calculation unit and the detection period each time the storage unit stores a signal level for one detection period. The shoplifting prevention device is characterized in that the average value is calculated using a signal level for a predetermined detection period immediately before. 3. The shoplifting prevention device according to claim 1, wherein the level detecting unit mixes an oscillator capable of controlling an oscillation frequency with an oscillation signal from the oscillator and the reception signal. do it,
Frequency conversion means for converting the frequency of the received signal into a different frequency, and frequency for controlling the oscillation frequency of the oscillator so that the frequency of the received signal converted by the frequency conversion means is always a predetermined measurement frequency. A shoplifting prevention device comprising: conversion control means; and detection means for detecting a signal level of an output signal from the frequency conversion means as a signal level of the received signal.