JP2009064346A - Passive rfid sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passive RFID sensor enabling the use of a sensor requiring stable power supply such as a sensor (distortion gauge) including a bridge circuit using a strain gauge, and being capable of detecting highly reliable data with stable operation even when the sensor is mounted on a metal surface. <P>SOLUTION: The passive RFID sensor includes a sensor for the dynamic monitoring of a structural member, one or a plurality of power supply tags 10A for supplying power required for stable operation of the sensor, and a data acquisition tag 10B for radio communicating data detected by the sensor. The power supply tags 10A and the data acquisition tag 10B are separate passive RFID tags, and each tag is installed in a position apart from the structural member. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a passive RFID sensor that uses a passive RFID tag and is used for a soundness inspection of a structure.

RFID (Radio Frequency Identification) refers to a technology for exchanging information from a tag embedded with ID information by short-range wireless communication using an electromagnetic field or a radio wave.
The “RFID tag” means an IC tag used for RFID, and can be roughly classified into two types, a passive tag and an active tag. The “passive tag” is a tag that operates using radio waves from the sensor reader device as an energy source, and has a feature that a communication distance is short but a battery need not be incorporated. An “active tag” is a tag with a built-in battery, and has a long communication distance.

  In recent years, research and development using RFID for building management has been actively conducted, and various reports and proposals have been made (for example, Non-Patent Documents 1 to 3 and Patent Document 1).

In Non-Patent Document 1, an RFID tag is attached to a member of a building, and an attempt is made to use RFID for management of a building construction process and inspection / repair history.
Non-Patent Document 2 has developed an RFID tag device that can be used even in concrete in a strong alkaline environment, and has expanded the range of installation and use of RFID tags. The aim is to realize a “building traceability system” that can provide information on buildings such as earthquake resistance.

In addition to these, a lot of research and development has been carried out, and the use method and range of RFID for building management are gradually expanding.
In Non-Patent Document 3, the Ministry of Land, Infrastructure, Transport and Tourism showed a direction to actively use RFID for building maintenance management in an interim report of the “Promotion Guidelines for Promotion of Land Transport Innovation” in 2007. The trend of utilizing RFID tags for maintenance management is expected to accelerate further.

Patent Document 1 aims at a state inspection system for a structure that can easily determine the soundness of the structure.
Therefore, in the present invention, as shown in FIG. 6, the maximum value storage type sensor 61 is installed on the column 64, the beam 65, the pile 66 of the structure 60, or on the seismic control device 67 or the seismic isolation device, respectively. The maximum value storage type sensor 61 is connected to the wireless tag via the sensor cable 61a. As the wireless tag, an RF sensor tag 62 using RF communication is used. The RF sensor tag 62 is installed on the wall surface or ceiling surface of the structure 60 so that it can be read by the sensor reader device 63 which is a reading device carried by a person.

Nobuki Yabuki, “Application of RFID (Electronic Tag) and Product Model to the Construction Field”, Japan Construction Information Center Research Grant Program, 2003. YRP Ubiquitous Networking Laboratory, Sumitomo Osaka Cement Co., Ltd .: http: // www. ubin. jp / press / pdf / UNL061204-04. pdf, 2006 Ministry of Land, Infrastructure, Transport and Tourism: http: // www. mlit. go. jp / kisha / kisha07 / 01 / 01223_. html, 2007.

Japanese Patent Laying-Open No. 2005-207867, “Structure State Inspection System”

In the maintenance of buildings, (1) In addition to managing the history of inspection and repair, (2) Knowing the correct repair timing for deterioration and damage due to long-term use of structural members, (3) It is important to detect anomalies such as abnormal strain of building members. These are made possible by performing dynamic monitoring of the building, especially structural members.
However, in many cases, a decorative board or the like is attached as an interior material to a building such as a building or a condominium, and the structural member is usually not directly accessible. Therefore, when dynamic measurement is required, as in Patent Document 1, a sensor and an RF sensor tag (hereinafter referred to as an RFID tag) are attached to a building at the time of construction. Reading by a sensor reader device which is a portable reading device has been proposed.

However, when the RFID tag is an active tag with a built-in battery, there is a problem that long-term measurement cannot be performed because the battery cannot be replaced.
In addition, when the RFID tag is a passive tag that does not incorporate a battery, the power that can be supplied from the sensor reader device 63 is very weak (for example, about 4 mW), and thus the temperature sensor consumes very little power and does not require a stable voltage. There was a problem that was limited to.
That is, for the dynamic monitoring of structural members, for example, it is desired to use a sensor including a bridge circuit using a strain gauge (hereinafter referred to as “strain sensor”), but the bridge circuit requires a stable power supply. For this reason, it is difficult to drive the sensor and simultaneously transmit sensing data with a single RF sensor tag.

Further, since the data detected when the inductive power (power supply) is insufficient is inaccurate, there is a problem that the reliability is low even if the data is obtained from the strain sensor.
Furthermore, although the strain gauge constituting the strain sensor needs to be directly attached to the structural member, the structural member is usually made of metal, and communication using a tag does not work well on a metal surface or the like.

  The present invention has been developed to solve the above-described problems. That is, an object of the present invention is to use a sensor that requires a stable power supply, such as a sensor including a bridge circuit using a strain gauge (strain gauge), and when this sensor is attached to a metal surface. However, an object is to provide a passive RFID sensor that operates stably and can detect highly reliable data.

According to the present invention, a sensor for performing dynamic monitoring of a structural member;
One or more power supply tags for supplying power necessary for stable operation of the sensor;
A data acquisition tag for wirelessly communicating detection data of the sensor,
There is provided a passive RFID sensor, wherein the power supply tag and the data acquisition tag are separate passive RFID tags, and each tag is installed at a position away from the structural member.

According to a preferred embodiment of the present invention, the sensor is attached to a structural member, a strain gauge for measuring the strain, a bridge circuit for measuring a resistance change of the strain gauge, and the bridge circuit An amplification circuit for amplifying the output,
The power supply tag is configured to operate using radio waves from a sensor reader device as an energy source, and to supply power necessary for stable operation of the bridge circuit and the amplifier circuit,
And a voltage dividing circuit for dividing the output voltage of the amplifier circuit into desired detection data,
The data acquisition tag operates using radio waves from the sensor reader device as an energy source, supplies power necessary for stable operation of the voltage dividing circuit, and A / D converts the detection data to the sensor reader device. Send.

  The power supply tag monitors the supply voltage, and transmits an abnormal signal to the sensor reader device when the supply voltage is insufficient for stable operation of the bridge circuit and the amplifier circuit.

  The passive RFID tag includes a built-in antenna that wirelessly communicates with a sensor reader device and generates power therefrom, a power supply circuit that converts received power into a DC voltage, an ADC that performs A / D conversion of detection data, data, and A memory for storing the program, a CPU for executing the program, and an RF circuit are included.

According to the above configuration of the present invention, one or a plurality of power supply tags are provided separately from the data acquisition tag for wirelessly communicating sensor detection data, and power necessary for stable operation of the sensor is supplied from the power supply tag. Therefore, even a sensor that requires stable power supply, such as a sensor (strain sensor) including a bridge circuit using a strain gauge, can supply power necessary for stable operation.
In addition, each tag (data acquisition tag and power supply tag) is installed at a position away from the structural member, so even when this sensor is mounted on a metal surface, it operates stably and detects highly reliable data. can do.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a schematic diagram of a passive RFID tag used in the present invention.
As shown in this figure, the passive RFID tag 10 includes a built-in antenna 1, a power supply circuit 2, an ADC 3, a memory 4, a CPU 5, and an RF circuit 6.
The built-in antenna 1 wirelessly communicates with a sensor reader device (not shown) and generates electric power from the induced radio wave.
The power supply circuit 2 converts the received power into a stable DC voltage.
The ADC 3 is an analog / digital converter that A / D converts an analog signal into a digital signal.
The memory 4 stores data and programs.
The CPU 5 executes a program.
The RF circuit 6 oscillates radio waves in a predetermined frequency band.

  A sensor reader device (not shown) includes an antenna that generates induced radio waves that drive the sensor, an antenna that receives information from the tag, and a circuit that processes the received data.

  In FIG. 1, the passive RFID tag 10 has three terminals 7, 8, and 9. 7 is a ground terminal (GND), 8 is a power supply terminal of a DC power supply, and 9 is a signal input terminal of an analog signal.

FIG. 5A is a circuit diagram showing a conventional usage example of the passive RFID tag 10.
In this figure, R is a pull-up resistor, and Rx is the resistance of a sensor (variable resistance element).
When the pull-up resistor R is a sensor of 18 k to 630 kΩ and the sensor resistor Rx is a sensor on the order of kΩ, if the voltage of the power supply terminal 8 is constant, the voltage (divided voltage) input to the signal input terminal 9 is It has a certain relationship with Rx. In this circuit configuration, the power consumption can be limited to a predetermined allowable range by the size of the resistors R and Rx.
Therefore, with the circuit shown in FIG. 5A, one passive RFID tag 10 supplies necessary power to the sensor circuit, and the measurement data is A / D converted by the passive RFID tag 10 so that the outside is not shown. It can be transmitted to the sensor reader device.

FIG. 5B is a comparative example in which the passive RFID tag 10 is directly applied to a sensor including a bridge circuit using a strain gauge.
In this figure, Rx1 and Rx2 are strain gauges, and are composed of a bridge circuit 51, an amplifier circuit 52, and a voltage dividing circuit 53 using the same.
In this case, in order to operate the bridge circuit 51 and the amplifier circuit 52, larger electric power is required as compared with the circuit of FIG. For this reason, when the bridge circuit 51 and the amplifier circuit 52 are operated by one passive RFID tag 10, the voltage fluctuation of the DC power supply terminal 8 increases due to their operating states, and as a result, sensing data is transmitted simultaneously with driving of the sensor. Even if it is not possible, the detected data is inaccurate and the reliability is low.

For example, when each resistance Rx1, Rx2, R11, R13 in the bridge circuit 51 is 330Ω and a resistance R15 of 1 kΩ is provided for input limitation, the average resistance of the bridge circuit 51 is 1.33 kΩ, If the voltage of the DC power supply terminal 8 is 2.2 V, the power consumption is 3.6 mW.
On the other hand, the power that can be supplied from the passive RFID tag 10 is 2.2 V and 4.4 W, and most of the power that can be supplied by the bridge circuit 51 is consumed, so the amplifier circuit and the voltage dividing circuit are driven. In consideration of the electric power to do so, it becomes impossible to secure the stability of the supply of 2.2V.

The present invention has been developed to solve the above-described problems.
Hereinafter, embodiments of the present invention will be described in detail.

1. The inventors of the present invention have focused on RFID, which is expected to be used for building maintenance in the future. Assuming that RFID tags are pasted for history management such as inspection and repair at the time of construction, if it becomes possible to measure strain and load of structural members at the same time with the pasted RFID tags, the installation cost will be reduced, and the decorative board It is possible to mechanically sense the internal structural member through a shield such as. Therefore, this enables maintenance of advanced buildings.

Therefore, the inventors of the present invention aim to develop an RFID device for building maintenance and management, and use a passive type using a strain gauge driven without a battery using a passive type RFID tag capable of mass production. An RFID sensor was developed.
Some sensing devices using passive RFID tags have been developed in the past, such as a temperature sensor. However, the present invention is limited to those using elements that consume minute power. This is different from the passive type RFID sensor.

As described above, it is difficult to drive a sensor such as a strain gauge that stably supplies a certain amount of power and simultaneously transmit sensing data using only one tag (passive RFID tag). It is.
Therefore, the inventors of the present invention drive passive RFID capable of mass production by separately driving a tag for sensing data communication and a tag for supplying power in one sensor module (passive RFID sensor). We developed a battery-less strain gauge force sensor module (passive RFID sensor described above) that enables stable circuit drive and communication distance maintenance using only tags. This module is called “passive RFID sensor” or simply “RFID sensor”.

2. Passive RFID Sensor 2.1 Passive RFID Tag and Reader / Writer FIG. 1 described above is a schematic diagram of a passive RFID tag used in the present invention. This tag (passive type RFID tag 10) has a communication frequency of 13.56 MHz, and is a passive type RFID tag (Yoshikawa RF System, H56 [mm], W84 [mm]).

  In addition to the general read / write function of the memory 4, the tag 10 has a power supply terminal 8 for supplying the power obtained on the tag side to the outside, and a DC voltage rectified and smoothed in the chip (this example) Then, 2.2V) can be supplied to the outside. A major feature of the tag 10 is that it has an 8-bit ADC function (A / D conversion function) inside the tag. Therefore, as shown in FIG. 5A, the variable resistance element Rx is connected to GND 7-signal input. A resistance change of the variable resistance element Rx can be read by RFID communication by dividing between the terminal 9 and the fixed resistor R connected between the power supply terminal 8 and the signal input terminal 9. That is, simple sensing can be performed by using a sensor such as a thermistor for the variable resistance element Rx.

  As a reader / writer (sensor reader device) used in the present invention, a commercially available RX5300 (Yoshikawa RF System) was used. The antenna 1 uses a H37 [mm], W67 [mm] four-turn antenna, can supply a maximum of 4.4 mW of power to the tag, and about 100 mm at maximum with the power supply terminal 8 unloaded. Communication is possible.

2.2 Force sensor As a sensor, a strain gauge (Kyoritsu Electronics, KFG5-350-C1-11-L1M2R), which is generally used when measuring strain and load of a building, is used.
The strain gauge is deformed in conjunction with the member to be attached, and changes in resistance in response to the deformation. Usually, in order to accurately measure this resistance change, a bridge circuit is configured to change the resistance change into a voltage change. In addition, the differential pressure is amplified by an instrumentation amplifier circuit, and measurement with a meter or digital value becomes possible.
In order to use a strain gauge in a passive RFID sensor, it is necessary to stably drive these circuits with an induced electromotive force from a tag.

  In the present invention, the sensor is not limited to a force sensor using a strain gauge, but can be applied to a gauge pressure sensor using a strain gauge, a platinum resistance temperature sensor driven by a constant voltage, and the like.

2.3 Circuit Configuration of Passive RFID Sensor In order to drive the strain gauge, it is necessary to stably drive the bridge circuit and the amplifier circuit with a minute electric power (for example, a maximum of 4.4 mW) due to the induced electromotive force. However, the communication between the ADC 3 constituting the tag 10 and the tag-reader / writer requires a certain amount of power, and further, the amount of power supplied to the tag is reduced according to the distance between the tag-reader / writer. It is very difficult in terms of power supply to stably perform communication between the ADC 3 and the tag-reader / writer while driving the circuit and the amplifier circuit by applying a stable voltage. Therefore, in order to use a sensor that requires a certain amount of power in this way, some means for supplying stable power is required.

  Therefore, in the RFID sensor 20 of the present invention, the two tags 10A and 10B are driven by separate reader / writers, and one tag 10A is a tag for supplying power to the bridge circuit and the amplifier circuit, and the other tag. 10B is ADC for the power value obtained from the above-described tag and is used as a data acquisition tag for transmitting sensing data to the reader / writer, thereby enabling stable operation of the sensor module.

FIG. 2 is a circuit diagram of a passive RFID sensor according to the present invention.
In this figure, the bridge circuit 12 and the amplifier circuit 14 are driven by power supply from one power supply tag 10A on the right side. Note that the power supply tag 10A is not limited to one, and two or more power supply tags may be arranged in parallel according to the required supply power.

R12 and R14 in this figure are strain gauge resistors, and the resistors R11 and R13 and the strain gauges R12 and R14 constitute the bridge circuit 12. The resistor R15 is an input limiting resistor.
As the instrumentation amplifier 15 constituting the amplifier circuit 14, a NUJ7016D operational amplifier of New Japan Radio Co., Ltd., which consumes less power, was used.

FIG. 3A is a schematic diagram of the amplifier circuit 14, and FIG. 3B is a specific example of the amplifier circuit 14. In this figure, 15 is an instrumentation amplifier (NUJ7016D of New Japan Radio Co., Ltd.), and R _{1 to} R ₇ are resistors.
With this circuit, the output voltage V _out can be obtained from the input voltages V ₁ and V ₂ by the following equation (1).
V _out = (R ₆ / R ₄ ) (1+ (R ₂ + R ₃ ) / R ₁ ) (V ₁ −V ₂ ) (1)
Here, since the instrumentation amplifier 15 can be driven by a DC power supply of 1 to 5.5V, when driven by a power supply tag 10A with a power supply of 2.2V, a full swing output can be obtained up to the power supply voltage range.

  On the other hand, in FIG. 2, the left tag 10 </ b> B is a data acquisition tag and drives the voltage dividing circuit 16. Since this tag 10B has a specification in which a fixed resistor between 2.2 V and ADC is connected from the beginning in the chip, the voltage output from the instrumentation amplifier 15 is divided and input to the signal input terminal 9. There is a need.

The divided voltage V _ADC input to the signal input terminal 9 of the tag 10B is V _out that is the voltage output from the instrumentation amplifier 15, and is between V _{out and} V _ADC, between 2.2 V and V _ADC , V _When the conductances between _{ADC and} GND are Y ₁ , Y ₂ , and Y ₃ , they are expressed by Expression (2).
V _ADC = (Y ₁ × V _out + Y ₂ × 2.2) / (Y ₁ + Y ₂ + Y ₃ ) (2)
If Y ₁ >> Y ₂ is set, the output of V _out can be input to the signal input terminal 9 with almost full swing.

3. Experiment 3.1 Trial Production of Passive RFID Sensor A passive RFID sensor having the circuit configuration shown in FIG. The prototype RFID sensor 20 includes two tags (10A and 10B), a strain gauge bridge circuit 12, an amplifier circuit (amplifier circuit 14), and a voltage divider circuit portion 16 for tag ADC input. They were housed in an acrylic container and integrated.

The two tags (10A and 10B) were arranged so that the two tags did not overlap so that the tags did not interfere with each other.
Communication of sensing data by the prototype RFID sensor 20 can be 30 mm from the data acquisition tag 10B through the acrylic container.

In this embodiment, the power supply tag 10A uses almost no function as a passive RFID tag in the prototype RFID sensor 20 and only supplies power by induced electromotive force. Therefore, the power supply tag 10A in the present invention is not limited to a passive RFID tag, and may be a power supply unit having only an antenna and a rectifying / smoothing circuit.
Alternatively, the power supply tag 10A may be configured to monitor the supply voltage, and to transmit an abnormal signal to the sensor reader device when the supply voltage is insufficient for stable operation of the bridge circuit 12 and the amplifier circuit 14. Good.

3.2 Evaluation of Responsiveness In order to confirm the operation of the prototyped RFID sensor 20, the input voltage V _ADC to the signal input terminal 9 of the data acquisition tag 10B was observed with an oscilloscope, and the responsiveness of the RFID sensor 20 was confirmed.
FIG. 4 shows a change in the voltage response of the V _ADC observed with an oscilloscope with respect to deformation of the strain gauge when the prototype RFID sensor 20 is driven. In this example, the strain gauge is once deformed until the output is saturated, and the voltage value of the input voltage V _ADC when the deformation is gradually restored is observed.
FIG. 4A shows a waveform when the deformation is restored stepwise, and FIG. 4B shows a waveform obtained by observing the input voltage V _ADC when the deformation is continuously restored.

4A and 4B, it was confirmed that in any case, the RFID sensor 20 operates stably and can detect highly reliable data.
Therefore, it was confirmed that the RFID sensor 20 of the present invention can use a sensor that requires a stable power supply, such as a sensor (strain gauge) including a bridge circuit using a strain gauge.

4). As described above, the inventors of the present invention use the passive RFID tag 10 having an ADC function that can be mass-produced, and drive and use the power supply tag 10A and the data acquisition tag 10B separately. We have developed a batteryless passive RFID sensor that can stably drive a circuit and maintain a communication distance with only a small amount of electric power from a tag.

According to the configuration of the present invention described above, one or a plurality of power supply tags 10A are provided separately from the data acquisition tag 10B for wirelessly communicating sensor detection data, and are necessary for stable operation of the sensor from the power supply tags 10A. Therefore, even a sensor that requires a stable power supply, such as a sensor including a bridge circuit using a strain gauge (strain sensor), can supply the power necessary for stable operation. .
In addition, each tag (data acquisition tag and power supply tag) is installed at a position away from the structural member, so even when this sensor is mounted on a metal surface, it operates stably and detects highly reliable data. can do.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention. For example, in the example described above, there is one power supply tag 10A, but two or more power supply tags 10A may be arranged in parallel according to the required power supply. Moreover, although the same passive RFID tag 10 is used for the power supply tag 10A and the data acquisition tag 10B, different tags may be used, and communication frequencies may be separated.

It is a schematic diagram of a passive RFID tag used in the present invention. 1 is a circuit diagram of a passive RFID sensor according to the present invention. A schematic diagram (A) of the amplifier circuit and a specific example (B) thereof. It is an Example which shows the characteristic of the prototype RFID sensor. It is a circuit diagram which shows the conventional usage example of a RFID tag. 1 is a schematic diagram of a system of Patent Document 1. FIG.

Explanation of symbols

1 built-in antenna, 2 power supply circuit, 3 ADC,
4 memory, 5 CPU, 6RF circuit,
7 Ground terminal (GND), 8 Power supply terminal, 9 Signal input terminal,
10 Passive RFID tag,
10A power supply tag, 10B data acquisition tag,
12 bridge circuit, 14 amplifier circuit,
15 instrumentation amplifier, 16 voltage divider,
20 Passive RFID sensor

Claims (4)

A sensor for dynamic monitoring of structural members;
One or more power supply tags for supplying power necessary for stable operation of the sensor;
A data acquisition tag for wirelessly communicating detection data of the sensor,
The passive RFID sensor, wherein the power supply tag and the data acquisition tag are separate passive RFID tags, and each tag is installed at a position away from the structural member. The sensor includes a strain gauge attached to a structural member for measuring the strain, a bridge circuit for measuring a resistance change of the strain gauge, and an amplifier circuit for amplifying the output of the bridge circuit. Have
The power supply tag is configured to operate using radio waves from a sensor reader device as an energy source, and to supply power necessary for stable operation of the bridge circuit and the amplifier circuit,
And a voltage dividing circuit for dividing the output voltage of the amplifier circuit into desired detection data,
The data acquisition tag operates using radio waves from the sensor reader device as an energy source, supplies power necessary for stable operation of the voltage dividing circuit, and A / D converts the detection data to the sensor reader device. The passive RFID sensor according to claim 1, wherein the passive RFID sensor transmits.   The power supply tag monitors the supply voltage, and transmits an abnormal signal to the sensor reader device when the supply voltage is insufficient for stable operation of the bridge circuit and the amplifier circuit. Item 2. The passive RFID sensor according to Item 1.   The passive RFID tag includes a built-in antenna that wirelessly communicates with a sensor reader device and generates power therefrom, a power supply circuit that converts received power into a DC voltage, an ADC that performs A / D conversion of detection data, data, and The passive RFID sensor according to claim 1, further comprising a memory that stores a program, a CPU that executes the program, and an RF circuit.

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