JP3635990B2 - Reader / writer for ID tag - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ID tag reader / writer that transmits and receives data by communicating with an ID tag by radio waves.
[0002]
[Problems to be solved by the invention]
For example, there is a remote ID system using high-frequency radio waves as a mobile object identification system. In this method, communication by radio waves is performed between the reader / writer and the ID tag, and data of the ID tag at a remote position is read or data is written to the ID tag.
[0003]
In such a remote ID system, as the ID tag, a power supply externally dependent type not equipped with a battery is mainly used. For the power supply externally dependent ID tag, a radio signal for operating power is sent from the reader / writer, and the ID tag operates by receiving this radio signal.
[0004]
By the way, the antenna of the ID tag is composed of a coil, and the ID tag receives the radio signal when the magnetic flux generated from the reader / writer is linked to the coil for the antenna. For this reason, even if the ID tag is within the communication range of the reader / writer, the ID tag does not operate if the antenna coil of the ID tag is parallel to the magnetic flux emitted as a radio wave signal from the reader / writer and does not link. It becomes impossible.
[0005]
Further, even when the antenna coil of the ID tag is linked with the magnetic flux from the reader / writer, the magnitude of the received electric power varies depending on the amount of the linked magnetic flux. For example, if the ID tag is away from the reader / writer, the amount of magnetic flux interlinked with the antenna coil may be reduced, and electric power necessary for the operation may not be obtained. On the contrary, when the ID tag is near the reader / writer and the amount of magnetic flux interlinked with the antenna coil is large, more power than necessary may be obtained, which may be a waste of power.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is for an ID tag capable of detecting whether or not the power necessary for operation can be supplied to the antenna coil of the ID tag. To provide a reader / writer.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, when communicating with the ID tag, the resonance when the frequency tuning of the inductance value of the transmitting antenna including the coil connected in series with the resonance capacitor is completed. A configuration is adopted in which the magnetic coupling with the antenna coil of the ID tag is estimated based on the inductance value obtained from the capacitance of the capacitor for use.
[0008]
When the reader / writer communicates with the ID tag, the antenna coil of the reader / writer and the antenna coil of the ID tag are electromagnetically coupled to each other to cause mutual induction action, and the inductance value of the antenna coil changes. In this case, in the reader / writer, the inductance value of the transmission antenna coil represents the strength of electromagnetic coupling with the reception antenna coil of the ID tag. The strength of electromagnetic coupling with the ID tag transmission antenna coil indicates the magnitude of electromotive force induced in the ID tag reception antenna coil when a radio signal is transmitted from the reader / writer transmission antenna coil. It will be. Therefore, according to the above configuration, it can be determined whether or not communication with the ID tag is possible based on the inductance value of the coil for the transmission antenna of the reader / writer.
[0009]
The invention according to claim 2 controls the output of the transmitting antenna in accordance with the magnetic coupling degree estimated by the coupling degree obtaining means. For example, when the ID tag is far away from the reader / writer, the transmission output of the reader / writer is increased, so that communication is possible even when communication with the ID tag is impossible in the past. it can.
[0010]
The invention according to claim 3 determines whether or not communication with the ID tag is possible based on the magnetic coupling degree estimated by the coupling degree acquisition means, and issues a warning when it is judged that communication is impossible. It is possible to prevent the communication operation from being terminated while the ID tag is left.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The ID tag 1 shown in FIG. 9 and FIG. 10 is configured by incorporating the electric circuit shown in FIG. The electric circuit of the ID tag 1 includes an antenna coil 3 for transmitting and receiving radio signals, a resonance capacitor 4, a control IC 5, and a smoothing unit 6. The resonance capacitor 4, the control IC 5 and the smoothing unit 6 is mounted on a printed wiring board 7.
[0012]
The control IC 5 is a single-chip semiconductor element constituting the rectifier 9, modulator / demodulator 10, memory 11 and the like in addition to the MPU (microprocessor unit) 8 as a controller. Here, the memory unit 11 has an EEPROM as an erasable nonvolatile memory for temporary storage. Further, the smoothing unit 6 includes a smoothing capacitor, a Zener diode, and the like (not shown).
[0013]
The antenna coil 3 is connected in parallel with the resonance capacitor 4 to form a resonance circuit. When a radio wave signal for power having a predetermined high frequency is transmitted from a reader / writer which is an external transmission / reception device, Is supplied to the rectifying unit 9. The rectification unit 9 constitutes an operation power supply circuit together with the smoothing unit 6, rectifies the electric power radio signal transmitted from the resonance circuit, smoothes it by the smoothing unit 6, and has a constant voltage DC power (operation power). ) And supplied to the MPU 8 or the like.
[0014]
A signal such as data transmitted from the reader / writer is transmitted by being superimposed on a power radio signal, and the signal is demodulated by the modem 10 and given to the MPU 8. The MPU 8 operates in accordance with an operation program stored in the ROM included in the memory unit 11. The MPU 8 executes processing according to a signal input from the modem unit 10 and writes received data to the EEPROM included in the memory unit 11. The data is read from the memory unit 11, modulated by the modem unit 10, and transmitted from the antenna coil 3 as a radio wave signal.
Such an ID tag 1 is attached to an article in a delivery system, an inventory management system, a sales management system, or the like and used to identify the article.
[0015]
As a reader / writer that communicates with the ID tag 1, there is a hand-held reader / writer 12 shown in FIGS. This handheld reader / writer 12 is provided with a head portion 13b at the tip of an operation portion 13a that also serves as a grip portion, and a battery 14 (see FIG. 5) is built in as a power source for operation. And the display part 15 (refer FIG. 5) which consists of a liquid crystal is provided in the front side of the head 13b. The operation unit 13 is provided with, for example, a plurality of key switches 16, and the operation content is designated by these key switches 16 and data is input.
[0016]
The handheld reader / writer 12 includes a main control unit 17 and a remote control unit 18 (corresponding to reading / writing means and resonance frequency changing means) as shown in FIG. The key switch 16 group is connected to the main control unit 17 via a switch circuit 19, and a communication unit 20 that exchanges data between the display unit 15 and a host device (for example, a personal computer). Etc. are connected. The switch circuit 19 transmits a signal corresponding to the operated key switch to the main control unit 17. The remote control unit 18 is in charge of data communication with the ID tag 1. The antenna unit 21 transmits and receives radio signals to and from the ID tag 1 and the sound generation unit 22 as a warning means such as a buzzer. Is connected.
[0017]
FIG. 6 schematically shows the configuration of the main control unit 17 of the hand-held reader / writer 12. As shown in FIG. 6, the main control unit 17 includes an MPU 23, a ROM 24 that stores an operation program, a RAM 25 that temporarily stores data, a communication unit 26 that performs communication with the remote control unit 18, and the like. Yes. The MPU 23 processes data and controls peripheral devices. The MPU 23 executes a process according to a signal sent from the remote control unit 18 or the switch circuit 19, and the processing content or process being executed. The result is displayed on the display 15.
[0018]
FIG. 7 schematically shows the configuration of the remote control unit 18. As shown in FIG. 7, the remote control unit 18 includes an MPU 27 as a control unit, a ROM 28 that stores an operation program, a RAM 29 that temporarily stores data, and a communication unit 30 that performs communication with the main control unit 17. , A transmission unit 31, a reception unit 32, and the like.
[0019]
Here, the antenna unit 21 includes a transmission antenna coil 33 and a reception antenna coil 34, the transmission antenna coil 33 is connected to the transmission unit 31, and the reception antenna coil 34 is connected to the reception unit 32. . These antenna coils 33 and 34 are arranged close to each other in the same direction on the front side (the right side in FIGS. 8 and 9) in the head 13b in the same direction.
[0020]
The MPU 27 of the remote control unit 18 controls the sound generation unit 22 and also controls communication with the ID tag 1. When communicating with the ID tag 1, the MPU 27 first modulates the reference signal by the transmission unit 31 and transmits the signal as a power radio signal from the transmission antenna coil 33, and then converts the data to be transmitted into the power radio signal. The signal is modulated by the transmission unit 31 so as to be superimposed and transmitted from the transmission antenna coil 33.
[0021]
The radio wave signal transmitted from the ID tag 1 is received by the receiving antenna coil 34, demodulated by the receiving unit 32, and discriminated as data. Then, the MPU 27 of the remote control unit 18 temporarily stores the data demodulated by the reception unit 32 in the RAM 29, and then transmits the data to the main control unit 17 side via the communication unit 30. Yes.
[0022]
Now, the transmitter 31 of the remote control unit 18 is provided with an automatic tuning function for automatically tuning the resonance frequency of the transmission antenna coil 33 to the frequency of the transmission signal. Will be described.
[0023]
First, the principle of automatic tuning will be described.
In the series resonance circuit including the coil L, the capacitor C, and the resistor R as shown in FIG. 3, the voltage difference between both ends of the coil L (corresponding to the transmission antenna coil 33) becomes the transmission output. When the resonance tuning is matched, the maximum current flows through the series resonance circuit and the transmission output becomes maximum. At this time, the signal waveform at both ends of the coil L is 90 ° out of phase with the waveform of the transmission signal. On the other hand, when the resonance is not tuned when the frequency of the transmission signal and the resonance signal is shifted, the voltage at both ends of the coil L is lower than that at the time of resonance tuning as shown by the broken line in FIG. At this time, the phase shift of the signal waveform at both ends of the coil L is out of 90 °. For this reason, the transmission output from the coil L falls compared with the resonance tuning.
[0024]
FIG. 4 shows the relationship between the phase difference of the voltage across the coil L and the transmission output. In FIG. 4, it can be seen that the transmission output is maximized when the phase difference is 90 °, and the transmission output decreases as the phase difference deviates from 90 °. It can also be seen that there is a correlation between the phase shift at both ends of the coil L and the transmission output (resonant current). Therefore, by changing the capacitance of the capacitor C and adjusting the phase shift within an allowable range, automatic tuning of adjusting the resonance frequency of the transmission antenna coil 33 to the transmission frequency can be realized, and the resonance current (transmission output) ) Can be adjusted to be sufficient.
[0025]
FIG. 2 schematically shows the configuration of the transmission unit 31. In FIG. 2, the transmission circuit 35 of the transmission unit 31 is connected to a series resonance circuit 36 and a first level conversion circuit 37, and a reference signal (transmission signal) having a predetermined frequency is transmitted to the series resonance circuit 36 and the first level conversion circuit 37. Output to the level conversion circuit 37. The series resonance circuit 36 is configured by connecting a transmission antenna coil 33 and a resonance capacitor circuit 38 in series.
[0026]
The resonance capacitor circuit 38 is configured by connecting a reference capacitor 39 and a correction circuit 40 in parallel, and the overall capacitance of the resonance capacitor circuit 38 is equal to the capacitance of the reference capacitor 39 and the correction circuit 40. It is the value which added the electrostatic capacity of. The correction circuit 40 includes a plurality of first to n-th unit circuits 41 connected in parallel. One unit circuit 41 includes a capacitor 41a (corresponding to a correction capacitor) and a capacitor 41b (corresponding to a correction capacitor). ) Are connected in series, and a switch 41c is connected in parallel with the capacitor 41b. Therefore, the capacitance of the correction circuit 40 as a whole, and hence the capacitance of the resonance capacitor circuit 38, is determined according to the on / off state of the switch 41c of each unit circuit 41.
[0027]
Here, when the capacitance of the capacitor 41a and the capacitor 41b in each unit circuit 41 is set to the same capacitance, for example, 2C, the capacitance of the unit circuit 41 becomes C when the switch 41c is in the OFF state, and the switch 41c. Since the capacitance of the unit circuit 41 is 2C in the ON state, the capacitance of the unit circuit 41 can be increased from C to 2C by turning on the switch 42.
[0028]
When the correction circuit 40 is composed of the first to sixth unit circuits 41, the capacitances of the capacitors 41a and 41b in the first to sixth unit circuits 41 are 64C, 32C, 16C, The relations 8C, 4C, and 2C are set. Therefore, in the state where the switches 41c of the first to sixth unit circuits 41 are independently turned on, the capacitance of the entire correction circuit 40 increases by 32C, 16C, 8C, 4C, 2c, and 1C. . This means that the electrostatic capacity of the entire correction circuit 40 can be adjusted in units of 1C in the range of 0 to 63C according to the combination pattern of the on / off state of the switch 41c of each unit circuit 41.
[0029]
In this case, the correction circuit 40 is designed so that the series resonance circuit 36 is in a resonance tuning state with the switch 41c of the first unit circuit 41 turned on. This is because when the capacitance of the correction circuit 40 is increased or decreased by setting the resonance frequency of the series resonance circuit 36 as a design value at the center of the frequency adjustable range of the correction circuit 40, the frequency increase / decrease correction is performed. This is to make it effective.
[0030]
A voltage dividing circuit 42 is connected in parallel to the resonance capacitor circuit 38 configured as described above. The voltage dividing circuit 42 is formed by connecting a capacitor 42a and a capacitor 42b in series, and outputs a voltage level at a common connection point between the capacitor 42a and the capacitor 42b to the second level conversion circuit 43. A capacitor having a small capacitance is used so as not to affect the capacitance of the circuit 38.
[0031]
The first and second level conversion circuits 37 and 43 convert the input signal into a binarized signal, and output the binarized signal to the exclusive OR circuit 44.
The exclusive OR circuit 44 outputs an exclusive OR of the binarized signals input from the first and second level conversion circuits 37 and 43 to the phase difference voltage conversion circuit 45. The exclusive OR circuit 44 outputs a phase difference signal indicating the phase difference between the reference signal from the transmission circuit 35 and the resonance signal of the series resonance circuit 36. When the phases of both signals do not match, the phase difference signal is output. Output a pulse-like phase difference signal indicating the magnitude and phase difference direction.
[0032]
The phase difference voltage conversion circuit 45 converts the phase difference signal output from the exclusive OR circuit 44 into a voltage indicating a phase difference and a phase difference direction, and transmits a transmission tuning error determination circuit 46 (corresponding to transmission tuning error acquisition means). Output to. The transmission tuning deviation determination circuit 46 outputs the phase difference and the phase difference direction to the C (capacitor) on / off control circuit 47 (corresponding to the counting means) and the MPU 27 based on the voltage output from the phase difference voltage conversion circuit 45. The C on / off control circuit 47 controls the on / off of the switch 41c of the unit circuit 41 of the correction circuit 40 so that the signal phase difference between both ends of the transmitting antenna coil 33 becomes 90 °. Adjust the capacitance. Further, the MPU 27 determines whether or not frequency tuning has been performed based on a signal from the transmission tuning deviation determination circuit 46 (tuning determination means).
[0033]
Here, the inductance value of the transmission antenna coil 33 changes depending on the surrounding environment, in particular, the relationship with the antenna coil 3 of the ID tag 1 that is electromagnetically coupled to the transmission antenna coil 33. The inductance value 33 changes. That is, as the distance between the transmission antenna coil 33 and the antenna coil 3 of the ID tag 1 increases, the inductance value increases. Accordingly, whether or not the distance from the ID tag 1 is detected by detecting the inductance value of the transmission antenna coil 33, or whether the ID tag 1 can receive operable power from the power radio signal. Can be detected.
[0034]
Therefore, when the frequency tuning is completed, the MPU 27 obtains the on / off information for each switch 41c of the resonance capacitor circuit 38 from the C sound off control circuit 47, and obtains the capacitance of the resonance capacitor circuit 38 from the on / off information. I have to. The MPU 27 calculates the inductance value of the transmission antenna coil 33 from the capacitance of the resonance capacitor circuit 38.
[0035]
Next, the operation of the above configuration will be described in the case where data is read from the ID tag 1 with reference to the flowchart shown in FIG.
When the read switch of the operation unit 13a is operated, the remote control unit 18, in other words, the MPU 27 determines “YES” in step S1, and in the next step S2, a small output for measurement is transmitted from the transmission antenna coil 33. The radio wave signal is output, and an automatic tuning operation command is given to the C on / off control circuit 47 in the subsequent step S3.
[0036]
When giving the automatic tuning operation command, the MPU 27 controls the C on / off control circuit 47 so that only the switch 41c of the first unit circuit 41 of the correction circuit 40 is turned on. The capacitance is adjusted to the middle of the capacitance correction possible range.
[0037]
Incidentally, although the series resonance circuit 36 is designed to be in a resonance state (tuned state) with a maximum current corresponding to the output of the reference signal from the transmission circuit 35, the transmission antenna coil 33 of the handheld reader / writer 12. The inductance value is changed by being magnetically coupled to the antenna coil 3 of the ID tag 1 or the like. Since the resonance frequency of the transmission antenna coil 33 is determined by the inductance and the capacitance of the resonance capacitor, when the inductance value of the transmission antenna coil 33 changes, the resonance frequency of the transmission antenna coil 33 changes.
[0038]
Therefore, in this embodiment, the MPU 27 detects the signal phase difference between both ends of the transmission antenna coil 33 based on the determination result by the transmission tuning deviation determination circuit 46 of the transmission unit 31, so that the phase difference is within the reference range. (Synchronization determination means). At this time, if the phase difference between the reference signal and the resonance signal exceeds the allowable range, it is determined that the resonance tuning state is not established, and a switching command is given to the C on / off control circuit 47. As a result, the on / off pattern of the switch of the correction circuit 40 is switched in a short time, and the resonance frequency of the transmission antenna coil 33 approaches the frequency of the reference signal. When the phase difference between both ends of the transmitting antenna coil 33 falls within a predetermined range, it is determined that the resonance tuning state has been established.
[0039]
When the resonance tuning state is established in this way, the MPU 27 reads the capacitance of the resonance capacitor from the switching information of the C on / off control circuit 47 (switch on / off pattern information of the correction circuit 40) in step S4. In S5, a calculation for estimating the inductance value of the transmission antenna coil 33 is performed (inductance value acquisition means). Then, the MPU 27 compares the inductance value of the transmission antenna coil 33 obtained by this calculation with the reference value to determine whether or not communication with the ID tag 1 is possible, in other words, the transmission antenna coil 33 and the ID tag 1. The degree of magnetic coupling with the antenna coil 3 is estimated, and it is determined whether or not the degree of coupling can transmit operating power to the ID tag 1 (step S6; coupling degree acquisition means, judgment means).
[0040]
Next, when communication with the ID tag 1 is possible, the MPU 27 becomes “YES” in Step S6 and proceeds to Step S7. In step S7, the MPU 27 obtains an output corresponding to the inductance value by, for example, calculation, and outputs a radio wave signal from the transmission antenna coil 33 at the output level. As a result, the ID tag 1 acquires sufficient operating power from the operating radio signal, and outputs identification information in response to a request from the handheld reader / writer 12. When the MPU 27 of the handheld reader / writer 12 reads the identification information from the ID tag 1 (step S8), the MPU 27 notifies the reception by ringing the sound generator 22 (step S9), and ends.
[0041]
On the other hand, as shown in FIG. 9, the ID tag 1 is at a position far away from the handheld reader / writer 12, or the antenna coil 3 of the ID tag 1 is transmitted by the handheld reader / writer 12 as shown in FIG. When the magnetic flux output from the antenna coil 33 is not parallel and interlinked, the inductance value of the transmission antenna coil 33 is at a level indicating that communication is impossible, and the MPU 27 determines “NO” in step S6. Then, the process proceeds to step S10.
[0042]
The MPU 27 rings the sound generator 22 in step S10 to notify that communication is disabled, and returns to step S3. Thereafter, “N0” in steps S4, S5, and S6, step S10, and step S3. Repeat the operation. Then, the user knows that communication is impossible due to the notification sound of the sound generator 22, and moves the handheld reader / writer 12 closer to the ID tag 1 or changes the orientation of the handheld reader / writer 12. Then, since communication is possible, the MPU 27 becomes “YES” in step S6, performs the operations after step S7 described above, and ends.
[0043]
As described above, according to the present embodiment, is it possible to estimate the magnetic coupling degree between the transmission antenna coil 33 and the antenna coil 3 of the ID tag 1 and to communicate by obtaining the inductance value of the transmission antenna coil 33? It can be determined whether or not.
[0044]
When it is determined that communication is possible, the radio signal is transmitted with an output value corresponding to the inductance value, so there is no waste of transmitting a radio signal with a large output even though the ID tag 1 is nearby, and power saving is achieved. Become.
Further, when it is determined that communication is impossible, the sounding unit 22 issues a warning to that effect, so that the handheld reader / writer 12 can be brought close to the ID tag 1 or the direction thereof can be changed so that communication can be performed immediately. There is no risk of ending communication with the uncommitted ID tag 1 left.
[0045]
The present invention is not limited to the embodiments described above and shown in the drawings, and can be expanded or changed as follows.
When transmitting a radio signal with an output corresponding to the inductance value, the output value may be obtained by calculation, or the inductance value and the output value may be stored in advance as data and obtained by referring to the data.
The warning means may be displayed on the display unit 15.
The reader / writer is not limited to a hand-held type, and may be a fixed type.
[Brief description of the drawings]
FIG. 1 is a flowchart showing control contents in an embodiment of the present invention. FIG. 2 is a circuit diagram showing an outline of an electrical configuration of a transmission unit. FIG. Waveform diagram [FIG. 4] A diagram showing a relationship between a signal phase difference between both ends of a coil and a transmission output. [FIG. 5] A block diagram showing an electrical configuration of a hand-held reader / writer. [FIG. 6] An electrical configuration of a main control unit. FIG. 7 is a block diagram showing the electrical configuration of the remote control unit. FIG. 8 is a block diagram showing the electrical configuration of the ID tag. FIG. 9 is an example of a communication disabled state between the ID tag and the handheld reader / writer. FIG. 10 is a diagram showing another example of the communication disabled state between the ID tag and the handheld reader / writer.
In the figure, 1 is an ID tag, 3 is an antenna coil, 12 is a handheld reader / writer, 18 is a remote control unit (inductance value acquisition means, coupling degree acquisition means, determination means, control means), and 22 is a sound generation unit (warning). Means).

Claims (3)

In an ID tag reader / writer equipped with reading / writing means for reading / writing data from / to an ID tag,
When communicating with the ID tag, an inductance value acquisition means for obtaining an inductance value of a transmitting antenna including a coil connected in series with a resonance capacitor from a capacitance of the resonance capacitor when frequency tuning is completed;
An ID tag reader / writer comprising coupling degree obtaining means for estimating a magnetic coupling degree with the ID tag based on an inductance value obtained by the inductance value obtaining means. 2. The ID tag reader / writer according to claim 1, further comprising control means for controlling the output of the transmission antenna in accordance with the magnetic coupling degree estimated by the coupling degree obtaining means. A determination unit that determines whether or not communication with the ID tag is possible based on the magnetic coupling degree estimated by the coupling degree acquisition unit; and a warning unit that issues a warning when the determination unit determines that communication is impossible. The ID tag reader / writer according to claim 1 or 2, further comprising:

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