JP2005321853A - Variable transmission cycle active tag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active tag surely performing gate control such as management of entrance/exit to/from a room. <P>SOLUTION: A probe wave transmitted by a reader/writer is received to be combined with a local oscillation frequency for converting the probe wave into that with a predetermined frequency. A received voltage after frequency conversion is measured to be inputted to a CPU after its A/D conversion. The CPU decides a transmission cycle of an iD according to the received voltage and sets a decided time value to start a timer. In this way, the CPU is controlled by the timer to access a memory at a fixed time interval and read the ID, and transmits the read ID to the reader/writer. The reader/writer verifies validity of the received ID and outputs a control signal, by which gate control and the like is carried out, to a controller if validity is confirmed. In this process, a reference cycle is prepared for measuring timing of gate control and compared with the transmission cycle of the ID, and a control signal is outputted if these cycles agree with each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transmission cycle variable type active tag in which a transmission cycle of an ID is variable.

Active tags that automatically send IDs are attached to people and moving objects, and when performing gate control such as entrance / exit management that controls the opening and closing of electric locks and automatic doors, the communication distance is longer than the passive type. This is convenient when you do not need to hold your hand over it and your hands are blocked by luggage.
On the other hand, since the communication distance is long, the timing for detecting the ID is early, and even if people or moving objects are far away, the gate opens at an early stage, making it difficult to ensure security.

On the other hand, since the active tag emits an ID itself, it has a built-in battery and requires battery replacement or charging.
In addition, when the ID is transmitted at a predetermined cycle and the transmission cycle is shortened, the battery is consumed quickly. Therefore, the normal transmission cycle is set to be considerably long, for example, 3 to 30 seconds.
Therefore, since the time when ID is not transmitted is long, the timing for detecting ID is delayed, and the gate may not open even if a person or a moving object approaches.

  The problem to be solved is that it is difficult for conventional active tags to perform gate control at appropriate timing, and gate control becomes uncertain, and the present invention provides an active tag that can reliably perform gate control. It was made for the purpose of doing.

  The present invention relates to a transmitting means for transmitting an ID to an active tag at a constant transmission period, a receiving means for receiving a transmitted radio wave of the interrogator, a measuring means for measuring a received voltage of the transmitted radio wave of the received interrogator, and a measurement And a change means for changing the transmission period in accordance with the received voltage.

According to the present invention, the ID transmission cycle of the active tag is changed in accordance with the reception voltage of the transmitted radio wave of the interrogator. Therefore, the proximity of the active tag can be determined by the ID transmission cycle.
Therefore, gate control can be performed at an appropriate timing.
In addition, since the ID transmission cycle is shortened only when approaching the interrogator, there is no waste in battery consumption of active tags that often spend most of their time away.

  Hereinafter, embodiments of the present invention will be described.

FIG. 1 is a block diagram of a transmission cycle variable type active tag embodying the present invention.
The transmission cycle variable type active tag 1 includes a receiver 12 connected to the receiving side terminal of the antenna duplexer 11, a frequency synthesizer 13, a receiving voltage measuring device 14, a modulator 15 connected to the transmitting side terminal, A transmission circuit unit including a transmitter 16 and a control circuit unit including a CPU 17, a timer 18, and a memory 19 are configured.

The transmission cycle variable type active tag 1 is configured as described above, and the receiver 12 receives the probe radio wave transmitted from the reader / writer 2 via the antenna duplexer 11, and the frequency synthesizer 13 is a variable frequency oscillator. The local oscillation frequency obtained by electrically controlling the signal is synthesized to convert the probe radio wave to a predetermined frequency.
The probe radio wave is assigned with a different frequency channel for each reader / writer 2, and when receiving the probe radio wave, it is necessary to select the frequency of the target reader / writer 2 from among them.
Thus, a plurality of reader / writers 2 are arranged in different gates so that the transmission cycle of the transmission cycle variable type active tag 1 can be individually controlled.

After the frequency conversion, the reception voltage measuring device 14 measures the reception voltage of the probe radio wave and inputs the A / D converted reception voltage to the CPU 17.
The CPU 17 determines the ID transmission cycle according to the received voltage, sets the time value of the determined transmission cycle, and starts the hardware or software timer 18.
As a result, under the control of the timer 18, the CPU 17 accesses the memory 19 at regular time intervals to read the ID, the modulator 15 modulates the read ID, and the transmitter 16 passes the modulated ID through the antenna duplexer 11. To the reader / writer 2.
At this time, the frequency of the transmitted radio wave of ID uses a frequency band different from the frequency of the probe radio wave having a different frequency for each reader / writer 2.
This allows the reader / writer 2 to recognize the IDs of a plurality of variable transmission cycle type active tags 1 by sharing the frequency of the transmission radio wave of the ID of all transmission cycle variable type active tags 1.

When the probe radio wave from the reader / writer 2 is temporarily interrupted, the CPU 17 stops updating the timer 18 and maintains the transmission cycle immediately before the interruption.
Thereby, the reader / writer 2 can temporarily control the transmission cycle of the transmission cycle variable type active tag 1 that temporarily stops the probe radio wave and goes to the gate.
When the probe radio wave from the reader / writer 2 is interrupted for a certain time, the CPU 17 sets a preset time value in the timer 18 and returns it to a predetermined transmission cycle.
As a result, the reader / writer 2 can stop the probe radio wave for a certain period of time and reset the transmission cycle of the transmission cycle variable type active tag 1 that has passed through the gate.

The reader / writer 2 verifies the validity of the received ID, and if it is OK, outputs a control signal for performing gate control to the controller 3.
At this time, a reference cycle for measuring the timing of gate control is prepared in advance, and the control signal is output when the reference cycle coincides with the ID transmission cycle.
Thereby, gate control can be ensured by making the timing of gate control appropriate.

In free space, as shown in FIG. 2, when the transmission power Pt (W) of the probe radio wave transmitted by the reader / writer 2 is constant, the reception voltage E (V / m) of the variable transmission period active tag 1 is the reader. / Attenuation is inversely proportional to the distance d (m) between the writer 2 and the transmission cycle variable active tag 1.
As a result, the reception voltage E received by the transmission cycle variable active tag 1 increases as the transmission cycle variable active tag 1 approaches the reader / writer 2 and the distance d decreases (d1>d2> d3) ( E1 <E2 <E3).
The transmission cycle variable type active tag 1 measures the reception voltage E and shortens the ID transmission cycle t in inverse proportion to the reception voltage E (t1>t2> t3).
When the above-described measurement of the received voltage E and the operation of shortening the transmission period t are continuously performed, the reader / writer 2 accurately determines the position of the transmission period variable active tag 1 because the ID transmission period t and the distance d are linearly proportional. Can be detected. Therefore, the accuracy of gate control is further improved.

It is a block diagram of the transmission period variable type active tag which implemented this invention. It is a figure which shows the change of the transmission period t by the distance d.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission period variable type active tag 11 Antenna duplexer 12 Receiver 13 Frequency synthesizer 14 Reception voltage measuring device 15 Modulator 16 Transmitter 17 CPU
18 Timer 19 Memory 2 Reader / Writer 3 Controller

Claims (6)

A transmission means for transmitting the ID at a constant transmission cycle;
A receiving means for receiving the interrogator's outgoing radio wave;
A measuring means for measuring the reception voltage of the transmitted radio wave of the received interrogator,
Changing means for changing the transmission period according to the measured received voltage;
A transmission cycle variable type active tag characterized by comprising:   2. The variable transmission cycle type active tag according to claim 1, wherein the frequency of the transmission radio wave of the ID and the transmission radio wave of the interrogator are different.   2. The transmission cycle variable type active tag according to claim 1, wherein when the transmission radio wave of the interrogator is temporarily interrupted, the immediately preceding transmission cycle is maintained.   2. The transmission cycle variable type active tag according to claim 1, wherein when a radio wave transmitted from the interrogator is interrupted for a predetermined time, the transmission cycle returns to a preset transmission cycle.   The transmission period variable active tag according to claim 1, wherein the frequency of the transmission radio wave of the interrogator can be selected from one or more frequency channels. 2. The transmission cycle variable type active tag according to claim 1, wherein the changing unit continuously changes the transmission cycle according to the reception voltage continuously measured by the measuring unit.