JP2010140099A - Rfid tag reading device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio frequency identification (RFID) tag reading device which determines whether or not an object is approaching an antenna communicatable area of the RFID tag reading device, without using a dedicated sensor. <P>SOLUTION: The RFID tag reading device constantly emits a radio wave whose intensity is weaker than that of an inquiry radio wave from an antenna. The RFID tag reading device detects an approach of an object to a vicinity of the antenna, based on the reflected status of the weak radio wave. When the approach of the object is detected, the RFID tag reading device emits an inquiry radio wave from the antenna. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless tag reading apparatus and method for reading information on a wireless tag using radio waves.

  In recent years, a wireless tag (also referred to as an IC tag, an RFID tag, an electronic tag, a transponder, etc.) having an IC chip and a wireless tag reader are provided, both of which communicate data via an antenna, respectively. RFID (Radio Frequency Identification) systems that can read information on a wireless tag in a non-contact manner in a wireless tag reader have become widespread.

  In this RFID system, the wireless tag reader normally radiates a high frequency signal for wireless tag inquiry from the antenna as a radio wave. When the radio tag receives a radio wave from the radio communication device via the antenna, the radio tag performs back scatter modulation by changing the amount of reflection of the high-frequency signal using information stored in the IC chip. When the wireless tag reader receives a backscatter modulated wave from the wireless tag with the antenna, the wireless tag reader demodulates it and reads the information of the wireless tag.

  Here, the radio wave for querying a radio tag radiated from the radio tag reader has a strength of about 500 mW to 1 W and is relatively strong. For this reason, always radiating may affect other wireless systems. There are also concerns about adverse effects on the human body. Therefore, conventionally, a detector such as an optical sensor is used to monitor whether or not an object has approached the antenna communication area of the RFID tag reader. A method of emitting radio waves for inquiries was used.

For example, Patent Document 1 discloses a radio wave sensor in an electronic lock system that reads a user ID of an electronic key in a non-contact manner by a wireless communication function and releases a lock when a user ID registered in advance is read. A technique is disclosed in which an object approaching a door knob is monitored using a detector such as an electronic device, and an electronic key is read when the object is detected.
JP 2005-325573 A

  Conventionally, in order to construct an RFID system that monitors whether an object has approached the antenna communication area of the RFID tag reader and emits radio tag inquiry radio waves on the condition that the object has been approached, It was necessary to use a dedicated sensor to detect this.

  The present invention has been made based on such circumstances, and the purpose of the present invention is that the wireless tag reader has a monitoring function as to whether or not an object has approached its own antenna communication area, and is dedicated. This is to eliminate the need for sensors.

  The present invention includes an antenna, radiates an inquiry radio wave to the radio tag from the antenna, performs radio communication with the radio tag that has received the inquiry radio wave via the antenna, and reads information on the radio tag. The device emits a radio wave with a lower output intensity than the interrogation radio wave from the antenna, detects the approach of the object to the periphery of the antenna from the reflection state of the radio wave, and on condition that the approach of the object is detected. Inquiry radio waves are emitted.

  According to the present invention in which such a measure is taken, the wireless tag reader can be provided with a monitoring function as to whether or not an object has approached its antenna communication area, and a dedicated sensor can be dispensed with.

The best mode for carrying out the present invention will be described below with reference to the drawings.
Note that this embodiment is a case where the present invention is applied to a wireless tag reader of an RFID system provided with a gate type antenna.

  A schematic configuration of the RFID system in the present embodiment is shown in a system diagram of FIG. In this embodiment, a gate type antenna 5 is used in which a plurality (four in the figure) of antennas 1, 2, 3, and 4 are arranged to face each other. The four antennas 1, 2, 3, 4 incorporated in the gate antenna 5 are connected to the wireless tag reader 10 via communication cables 6, 7, 8, 9 respectively. The wireless tag reader 10 is connected to a host device 30 such as a personal computer via a communication cable 20.

  In such an RFID system, normally, when a wireless tag passes between the gate type antennas 5, information on the wireless tag is read in a non-contact manner by wireless communication with any one of the antennas 1 to 4. Information of the read wireless tag is transmitted to the host device 30 via the wireless tag reader 10.

The principal part structure of the wireless tag reader 10 is shown in the block diagram of FIG. The wireless tag reading device 10 includes a device main body 11 and an antenna selection switch 12.
The apparatus main body 11 includes a communication unit 41, a storage unit 42, a control unit 43, a transmission unit 44, a reception unit 45, and a circulator 46. The communication unit 41 manages data communication between the control unit 43 and the host device 30.

  The transmission unit 44 includes a modulation unit 441, an amplification unit 442, and an output switching unit 443. The modulation unit 441 modulates a predetermined carrier wave with the transmission data signal given from the control unit 43. The amplification unit 442 amplifies the output signal from the modulation unit 441. The output switching unit 443 changes the signal amplification factor in the amplification unit 442. The signal amplified by the amplifying unit 442 is supplied to one of the antennas 1 to 4 through the circulator 46 and is radiated as a radio wave from the antennas 1 to 4. When the signal amplification factor is set large, the intensity of radio waves radiated from the antennas 1 to 4 is increased. When the signal amplification factor is set small, the intensity of the radio waves radiated from the antennas 1 to 4 is weakened.

  The circulator 46 outputs the signal input from the transmission unit 44 to the antenna selection switch 12 and outputs the signal input from the antenna selection switch 12 to the reception unit 45. From the antenna selection switch 12, a signal from the wireless tag received by any one of the antennas 1 to 4 is given to the circulator 46.

  The reception unit 45 includes an amplification unit 451, a demodulation unit 452, and a VSWR calculation unit 453. The amplifying unit 451 amplifies the signal input via the circulator 46. The demodulator 452 demodulates the signal amplified by the amplifier 451. The received data signal demodulated by demodulator 452 is applied to controller 94.

  The VSWR calculation unit 453 calculates a voltage standing wave ratio (VSWR) based on the signal amplified by the amplifier 451. A radio wave (traveling wave) radiated from an antenna and a reflected wave thereof are added or canceled while propagating in opposite directions to generate a wave in the voltage amplitude. The VSWR calculation unit 453 calculates the ratio of the maximum value and the minimum value of the voltage amplitude wave as the voltage standing wave ratio VSWR by the following equation (1).

VSWR = (1+ | G |) / (1- | G |) (1)
In the formula (1), G is a voltage reflection coefficient, and is defined by the following formula (2).

G = V _R / V _F (2)
(2) In the equation, _{V F} is the traveling wave voltage, _{V R} is the reflected wave voltage.

  The control unit 43 generates a transmission data signal in response to a command from the host device 30 received via the communication unit 91, and provides tag information from the function to be given to the transmission unit 44 and the reception data signal given from the reception unit 45. And a function to be given to the host device 30 via the communication unit 41. Further, it has a function of switching the output switching unit 443 and a function of switching the antenna selection switch 12. These functions are controlled based on a program stored in the storage unit 42. The storage unit 42 stores a threshold value SH of the voltage standing wave ratio VSWR in addition to the above program.

  The antenna selection switch 12 is interposed between the circulator 46 and the antennas 1, 2, 3, and 4. The antenna selection switch 12 is sequentially switched by a switching control signal from the control unit 43 to connect the antennas 1, 2, 3, 4 to the circulator 46 in order.

  The main control procedure executed by the control unit 43 is shown in the flowchart of FIG. The control unit 43 waits for a command from the host device in a process waiting state after power-on (ST1). When a command is received (YES in ST1), the type of the command is determined (ST2, ST3).

  If the received command is a threshold setting command (YES in ST3), the control unit 43 waits for threshold data sent from the host device 30 following this command (ST4). If threshold data is received (YES in ST4), control unit 43 rewrites threshold data SH stored in storage unit 42 with the received threshold data (ST5: threshold setting). means). This completes the process when the threshold command is received. The control unit 43 waits for the next command.

  When the received command is a reading start command (YES in ST2), the control unit 43 controls transmission of sensor radio waves (ST6). That is, the control unit 43 instructs the modulation unit 441 to transmit an unmodulated signal after setting the signal amplification factor = “small” to the output switching unit 443. In addition, a switching control signal is periodically transmitted to the antenna selection switch 12.

  As a result, radio waves (sensor radio waves) corresponding to unmodulated carrier wave signals are sequentially emitted from the antennas 1 to 4 of the gate type antenna 5. Since the signal amplification factor of the amplifying unit 442 is set to “small”, the sensor radio wave is radiated as a weaker radio wave than a tag inquiry radio wave described later. As described above, when an object such as a person, metal, or cardboard approaches the gate antenna 5 in the state where the sensor radio wave is radiated from the gate antenna 5, the amount of reflection from the object increases. The amount of reflection increases as the object approaches the antenna 5. As a result, the value of the voltage standing wave ratio VSWR is increased.

  Therefore, the control unit 43 controls the transmission of the sensor radio wave and then monitors the voltage standing wave ratio VSWR calculated by the VSWR calculation unit 453 (ST7). And it is judged whether voltage standing wave ratio VSWR exceeded threshold value SH memorize | stored in the memory | storage part 42 (ST8: object detection means).

  When the object is not approaching the gate-type antenna 5, the voltage standing wave ratio VSWR does not exceed the threshold value SH. In this case (NO in ST8), the control unit 43 continues to transmit the sensor radio wave and monitor the voltage standing wave ratio VSWR.

  When an object approaches the periphery of the gate type antenna 5, the voltage standing wave ratio VSWR exceeds the threshold value SH. In this case (YES in ST8), the control unit 43 controls the transmission of the tag inquiry radio wave (ST9: reading control means). That is, the control unit 43 sets the signal amplification factor = “large” to the output switching unit 443 and then instructs the modulation unit 441 to transmit a tag inquiry command. In addition, a switching control signal is periodically transmitted to the antenna selection switch 12.

  As a result, radio waves (tag inquiry radio waves) corresponding to the carrier wave signals modulated by the tag inquiry command are sequentially emitted from the antennas 1 to 4 of the gate type antenna 5. The tag inquiry radio wave is radiated as a radio wave stronger than the sensor radio wave because the signal amplification factor of the amplifying unit 442 is set to “large”. When the wireless tag receives the tag inquiry radio wave, the wireless tag returns a response signal including its own ID. This response signal is received by any one of the antennas 1 to 4 of the gated antenna 5, and is input to the amplification unit 451 of the reception unit 45 via the circulator 46. Then, after being amplified and demodulated by the demodulator 452, it is given to the controller 43.

  Therefore, the control unit 43 starts the timer after controlling the transmission of the tag inquiry radio wave (ST10). Then, a response signal from the wireless tag is waited until this timer times out (ST11). The timer measures a sufficient time required for an object approaching the gated antenna 5 to pass through the antenna 5 and leave.

  If the response signal from the wireless tag is received before the timer times out (YES in ST11), the control unit 43 reads the tag data from the response signal (ST12). The read tag data is transmitted to the host device 30 via the communication unit 41. The control unit 43 executes the process of ST12 every time it receives a response signal from the wireless tag.

  When the timer times out (YES in ST13), control unit 43 returns to the process in ST6. That is, the transmission of the sensor radio wave is controlled again.

  Thus, in the present embodiment, the sensor radio wave is constantly radiated from the gate type antenna 5. Here, the sensor radio wave is a weak radio wave (about 10 mW) whose intensity is weaker than the tag inquiry radio wave. For this reason, even if it always radiates, it does not affect other radio systems. Moreover, there is no concern about adverse effects on the human body.

  When an object such as a person, metal, or cardboard approaches the gate-type antenna 5, the sensor radio wave is reflected by the object. As a result, the radio wave condition around the gate type antenna 5 changes. Specifically, the voltage standing wave ratio VSWR based on the sensor radio wave (transmission wave) and the reflected wave thereof increases. When the voltage standing wave ratio VSWR exceeds the threshold SH, the tag inquiry radio wave is radiated from the gate type antenna 5 for a certain period of time.

  Therefore, when a wireless tag is attached to an object approaching the gate antenna 5, information on the wireless tag is read by the wireless tag reader 10 via the gate antenna 5.

  As described above, the tag inquiry radio wave is radiated only when the object approaches the gated antenna 5, so that it is efficient. In addition, it is practical because it does not affect other RFID systems and does not adversely affect the human body. In this case, a special sensor for detecting that the object has approached the gate-type antenna 5 is not required. Therefore, the cost can be reduced as compared with the conventional case where the sensor is used.

  By the way, in the present embodiment, what is the threshold value SH compared with the voltage standing wave ratio VSWR is an important point for improving the tag reading accuracy. Next, a method for setting the threshold value SH will be described.

  FIG. 4 shows the distance (horizontal axis) from the antenna when the object approaching the antenna is a metal (A in the figure), a person (B in the figure), and a cardboard (C in the figure). 4 is a graph showing the relationship with the voltage standing wave ratio VSWR (vertical axis). As is clear from the figure, the voltage standing wave ratio VSWR increases as the object approaches the antenna. However, the degree of ascent varies depending on the material of the object. That is, it is the largest when the object is a metal, and then the case of a person. In the case of cardboard, the degree of ascent is small.

  Therefore, when the material of the object to which the wireless tag to be read is attached is not particularly limited, that is, the wireless tag may be attached to metal, may be attached to a person, or attached to a cardboard. In such a case, as shown in FIG. 4, in any case, the level at which the voltage standing wave ratio VSWR exceeds before the object reaches the antenna is set as the threshold value SH0.

  By doing so, when an object made of metal approaches the antenna, a tag inquiry radio wave is radiated when the distance from the antenna becomes d3. When a person approaches, a tag inquiry radio wave is emitted when the distance from the antenna is d2 (<d3). Further, when a cardboard is approaching, a tag inquiry radio wave is radiated when the distance from the antenna becomes d1 (<d2). As a result, when a wireless tag is attached to an approaching object, information on the wireless tag is stably read by the wireless tag reader 10 regardless of the material of the object.

  Thus, the amount of reflected radio waves is calculated from the voltage standing wave ratio VSWR, and when the voltage standing wave ratio VSWR exceeds a preset threshold value, it is determined that an object has approached the periphery of the antenna. Therefore, the approach of the object can be detected with high accuracy without being limited to the material of the object.

  Next, the case where the material of the object to which the wireless tag is attached is limited will be described. In this case, the threshold value SH is determined by considering how close the object is to the antenna and radiating the tag inquiry radio wave.

  FIG. 5 is a graph showing the relationship between the distance from the antenna (horizontal axis) and the voltage standing wave ratio VSWR (vertical axis) when the object approaching the antenna is a metal. As shown in the figure, when a tag inquiry radio wave is emitted when an object made of metal approaches a distance e1 to the antenna, the level SH1 is set as a threshold value. On the other hand, when a tag inquiry radio wave is radiated when an object made of metal approaches to the distance e2 (> e1) to the antenna, the level SH2 (<SH1) is set as a threshold value. In addition, when a tag inquiry radio wave is emitted when an object made of metal approaches a distance e3 (> e2) to the antenna, the level SH3 (<SH2) is set as a threshold value.

  In this way, the timing at which tag inquiry radio wave radiation is started can be shifted by arbitrarily changing the level of the threshold SH by the threshold setting means for variably setting the threshold.

  Further, the voltage standing wave ratio VSWR varies depending on whether or not there is a metal around the antenna of the RFID tag reader 10. FIG. 6 shows the distance from the antenna (horizontal axis) and voltage standing when a person approaches the antenna when there is no metal around the antenna (B1 in the figure) and when there is metal (B2 in the figure). It is the graph which showed the relationship with wave ratio VSWR (vertical axis). As shown in the figure, when the metal is present around the antenna, the value of the voltage standing wave ratio VSWR as a base is increased as compared with the case where there is no metal.

  For this reason, when the threshold is set to SH, in an environment where there is no metal around the antenna, even if a person approaches the antenna, the tag inquiry radio wave is not radiated until the distance therebetween becomes f1. On the other hand, in an environment where there is a metal around the antenna, a tag inquiry radio wave is radiated when a person approaches the antenna until the distance is f2 (> f1).

  Thus, the distance from the antenna to the object until the voltage standing wave ratio VSWR exceeds the threshold value varies depending on the environment where the antenna is installed. In other words, when deciding how close an object is to the antenna to radiate tag inquiry radio waves, the accuracy can be improved by taking into account the environment in which the antenna is installed. .

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  For example, in the above embodiment, the antenna connected to the wireless tag reader 10 is the gate type antenna 5, but the type of antenna is not limited to the gate type. For example, the present invention can be similarly applied to a wireless tag reader 10 to which a stationary planar antenna is connected.

  In the above embodiment, the voltage standing wave ratio variation is used as means for detecting that an object has approached the antenna. However, the present invention is not limited to this. It is only necessary that the approach of the object can be detected based on the characteristics of the radio wave environment that varies as the object approaches the antenna.

  In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be combined.

1 is an overall configuration diagram of an RFID system according to an embodiment of the present invention. FIG. 2 is a block diagram showing a main configuration of the wireless tag reader according to the embodiment. 4 is a flowchart showing a main part of a control procedure executed by a control unit of the wireless tag reading device in the embodiment. The graph which shows the correspondence of the distance to the antenna of each object, and the voltage standing wave ratio in the case where the object which consists of metal approaches the antenna, the case where a person approaches, and the case where the object which consists of corrugated cardboard approaches. The graph which shows the correspondence of the distance to the antenna of an object, and a voltage standing wave ratio when the object which consists of metals approaches an antenna. The graph which shows the correspondence of the distance to a person's antenna, and a voltage standing wave ratio with and without a metal around an antenna when a person approaches an antenna.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 5 ... Gate type antenna, 10 ... Radio | wireless tag reader, 30 ... Host apparatus, 41 ... Communication part, 42 ... Memory | storage part, 43 ... Control part, 44 ... Transmission part, 45 ... Reception part, 46 ... Circulator, 453 ... VSWR Calculation unit.

Claims (5)

In a wireless tag reader that includes an antenna, radiates an inquiry radio wave to the radio tag from the antenna, performs radio communication with the radio tag that has received the inquiry radio wave via the antenna, and reads information on the radio tag ,
An object detection means for radiating a radio wave having a lower output intensity than the interrogation radio wave from the antenna, and detecting an approach of an object to the periphery of the antenna from a reflection state of the radio wave;
Read control means for radiating the inquiry radio wave from the antenna on the condition that the approach of the object is detected by the object detection means;
A wireless tag reading apparatus comprising:   The object detection means stores a threshold value for the reflection amount of the radio wave, and determines that an object has approached the periphery of the antenna when the reflection amount exceeds the threshold value. The wireless tag reader according to 1.   The wireless tag reader according to claim 2, wherein the object detection unit calculates a reflection amount of the radio wave from a voltage standing wave ratio.   4. The wireless tag reader according to claim 2, further comprising threshold setting means for variably setting the threshold. The radio tag reader radiates inquiry radio waves to the radio tag from the antenna, and the radio tag reader performs radio communication with the radio tag that has received the inquiry radio wave via the antenna, and the radio tag information is obtained. In the wireless tag reading method of reading,
The wireless tag reader radiates a radio wave having a lower output intensity than the interrogation radio wave from the antenna, and monitors whether or not an object approaches the periphery of the antenna from the reflection state of the radio wave. The wireless tag reading method according to claim 1, wherein the interrogation radio wave is radiated from the antenna when detected.

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