JPH0281200A - Theft preventing device - Google Patents

Abstract

PURPOSE:To simplify the adjustment of a receiving frequency of a tag device and to surely output an alarm by sieving a frequency of a radio wave outputted from a transmitter between the upper limit frequency and the lower limit frequency in accordance with a control voltage. CONSTITUTION:To an oscillating circuit 12 of a transmitter 10 of a theft preventing device, a control voltage generating circuit 16 is connected. An output voltage S1 of the circuit 16 applied to a variable capacity diode 15 is a saw tooth voltage which is varied by a prescribed repeated period as time elapses, and the capacity of the diode 15 is varied, and a frequency of a radio wave is sieved repeatedly to fOL-fO, and fO-fOM by following up a variation of the voltage S1. Therefore, as for an adjustment of a tag device attached to an article to be protected, it will suffice that a coarse adjustment is executed so that a receiving characteristic comes to a range of fOL-fOM. When the radio wave which is sieved coincides with a receiving frequency of the tag device which is brought to coarse adjustment, an alarm is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an anti-theft device that detects when a protected item on display is illegally taken out of a controlled area.

Prior Art FIG. 3 shows the external appearance of a tag device 2 attached to each protected item 1. The tag device 2 is equipped with an alarm 3 as shown in FIG.
A battery 4 and the like are built in, and the operation of the alarm 3 is normally turned off by a switch section 5. Protected items 1
Figures 6 and 7 are on display near the entrance of the store.
As shown in the figure, an antenna device 6 that emits radio waves B is installed in a prescribed area A. Reference numeral 7 indicates a checkout table where customers and shopkeepers receive money and hand over protected items 1, and 8 is an entrance/exit.

In a normal sales format, the store opens at the checkout table 7 and uses a special procedure to remove the tag device 2 from one product to be protected, and only the product is handed over to the customer. Take it, checkout table 7
From here, pass through the designated area A and exit the store from entrance 8.

In a shoplifting situation, when the protected item 1 with the tag device 2 passes through the specified area A, the receiving section 9 of the tag device 2 detects the radio wave B emitted from the antenna device 6 and activates the switch section 5. When activated, the alarm 3 is turned on and an alarm sound and specific radio waves are emitted in the vicinity, promptly notifying the store staff that shoplifting has occurred.

The transmitter 10 giving a signal to the antenna device 6 is a fourth
As shown in the figure, it is composed of a power amplification section 11 and an oscillation circuit 12, and a constant voltage circuit 14 is conventionally connected to a frequency control terminal 13 of the oscillation circuit 12.

15 is a variable capacitance diode.

Problems to be Solved by the Invention In such a conventional configuration, the constant voltage circuit 14 is set so that the frequency of the radio wave B emitted from the antenna device 6 becomes fo.
The output voltage of the oscillator circuit 12 is changed by adjusting the output voltage of the variable capacitance diode 15, and the output frequency of the oscillation circuit 12 is changed, and the receiving frequency of the receiving section 9 of the tag device 2 attached to each protected item 1 is adjusted to the frequency f0. The pitch of the antenna coil of the receiving section 9 is adjusted so that.

FIG. 5 shows how the tag device 2 is adjusted. When the receiving characteristic R1 of the receiving section 9 is at fl, the pitch of a part of the antenna coil is widened and the receiving characteristic is moved in the direction of arrow C.
fine-tuned to match o. In addition, when the receiving characteristic R2 of the receiving section 9 is at f2, the pitch of a part of the antenna coil is narrowed and the receiving characteristic is moved in the direction of the arrow.
g & adjusted to match.

However, since each tag device 2 is attached to each protected item, it not only takes a great deal of effort to adjust each tag device 2 one by one as described above, but also the receiving frequency shift occurs due to aging, external force, etc. In case, tags are included! A serious problem arises in that even if the protected item 1 with the attached protector passes through the specified area A, no alarm is output.

The present invention provides a rough F1 that allows easy adjustment of the reception frequency of the tag device.
′! To provide an anti-theft device which requires only Ii and can reliably output an alarm even if a received frequency shift occurs.

Means for Solving the Problems The anti-theft device of the present invention comprises an antenna device connected to the output of a transmitter and emitting radio waves toward a defined area, and an antenna device attached to an item to be protected that emits radio waves from the antenna device. Tag equipment that detects and issues an alarm! The transmitter is characterized in that a control voltage generation circuit whose output voltage changes at a predetermined repetition period is connected to a frequency control terminal of the oscillation circuit of the transmitter.

Effect: According to this configuration, the frequency of the radio waves output from the transmitter via the antenna device sweeps between the upper limit frequency and the lower limit frequency according to the control voltage, and the tag devices in the specified area have their own reception frequency. Outputs an alarm when it detects radio waves that match.

EXAMPLE Hereinafter, an example of the present invention will be explained based on FIGS. 1 and 2. Components having the same functions as those shown in FIGS. 3 to 7 showing the conventional example will be described with the same reference numerals.

FIG. 1 shows a transmitter 10 in the anti-theft device of the present invention. A control voltage generation circuit 16 is connected to the frequency control terminal 13 of the zero oscillation circuit 12 instead of the constant voltage circuit 14.

The output voltage S1 of the control voltage generation circuit 16 applied to the variable capacitance diode 15 is a sawtooth wave that changes at a predetermined repetition period [for example, about 3 Hz] as time passes, and the capacitance of the variable capacitance diode 15 changes. As shown in FIG. 2, the frequency of the radio wave B changes to f as the output voltage S1 changes. It is repeatedly swept from L to f0 and then to fo""-fou.

With this configuration, when adjusting the tag device 2, the reception characteristic R1 or R2 is f. It is sufficient to make a rough adjustment so that it falls within the range of L to f O6l.

In actual use, f OL""' f OH
An alarm is generated when the radio wave B swept between the two matches the reception frequency of the tag device 2, which has been adjusted by ¥11i, and the deviation in the reception frequency can be compensated for.

According to the present invention, the antenna device has more than the effects of the invention! The frequency of the radio waves emitted from the tag device is not one wave, but sweeps within a predetermined band, so the reception characteristics of each tag device must be fine-tuned to match the frequency of one wave, as in the past. This simplifies the adjustment, as it only requires coarse adjustment to fit within the sweep band.

Furthermore, if the reception characteristics deviate under usage conditions,
In the past, serious situations occurred where no warning was output, but
Since a warning can be reliably output if there is a deviation within the sweep band, reliability is also greatly improved.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of the transmitter in the anti-theft device of the present invention, Figure 2 is an explanatory diagram of the radio wave sweep state of the transmitter, and Figure 3 is an exploded view showing how the tag device is attached to the protected item. A perspective view, FIG. 4 is a configuration diagram of a conventional anti-theft device, FIG. 5 is an explanatory diagram of the radio waves of a conventional transmitter and reception characteristics of a tag device, and FIGS. 6 and 7 are a diagram of a conventional anti-theft device. FIG. 2 is a schematic longitudinal cross-sectional view and a plan view of the vicinity of the entrance and exit of the store. DESCRIPTION OF SYMBOLS 1... Product to be protected, 2... Tag device, 6... Antenna device, 10... Transmitter, 12... Oscillation circuit, 1
3... Frequency control terminal, 16... Control voltage generation circuit. Agent Yoshihiro MorimotoFigure JFigure 1Figure 2Figure 5

Claims (1)

[Claims] 1. An antenna device connected to the output of a transmitter and emitting radio waves toward a defined area, and a tag device attached to the protected item to detect radio waves from the antenna device and issue an alarm; An anti-theft device comprising a control voltage generating circuit whose output voltage changes at a predetermined repetition period, connected to a frequency control terminal of an oscillation circuit of the transmitter.