Reader / writer and transmission waveform determination method

Abstract

To provide a reader / writer capable of properly detecting changes in transmission waveform due to the influence of metal.SOLUTION: A reader / writer (1) is provided, comprising: a detection unit (6) configured to acquire a transmission waveform transmitted from an antenna (5) to detect a Low voltage amplitude and a High voltage amplitude of the transmission waveform; and a determination unit (14) configured to determine whether or not a value representing a relationship between the Low voltage amplitude and the High voltage amplitude is within a given range.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a reader / writer. [Background technology]

[0002] Readers and writers are known that communicate with communication media such as RF (Radio Frequency) tags without contact, reading and writing data from the communication media. The reader / writer communicates with the RF tag by supplying power to it through electromagnetic induction. However, if there is metal around the location where the RF tag and reader / writer are installed, the transmission output from the reader / writer may be affected by the metal and may not be received properly by the RF tag.

[0003] In preparation for such a situation, Patent Document 1 discloses a communication device (reader / writer) that uses the transmission output voltage output from a loop antenna during polling operation and detects nearby metal by comparing the maximum value with a reference value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-3303 Summary of the Invention [Problem to be solved by the invention]

[0005] The influence of metal surrounding the reader / writer can cause the modulation depth of the transmitted waveform to deviate from the intended modulation depth. If the modulation depth falls outside the specified range, the RF tag cannot receive the signal properly. With the conventional technology described above, even if the transmitted output voltage is above the reference value, it is not possible to detect, for example, that the modulation depth is inappropriate.

[0006] One aspect of the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a reader / writer that can appropriately detect changes in a transmission waveform due to the influence of metal. [Means for solving the problem]

[0007] In order to solve the above problem, a reader / writer according to one embodiment of the present invention is a reader / writer that performs wireless communication with an RF tag, and includes an antenna, a detection unit that acquires a transmission waveform transmitted from the antenna and detects a low voltage amplitude and a high voltage amplitude in the transmission waveform, and a determination unit that determines whether a value indicating the relationship between the low voltage amplitude and the high voltage amplitude is within a predetermined range.

[0008] According to the above configuration, the reader / writer detects a transmission waveform transmitted from its antenna. In particular, the reader / writer determines whether a value indicating the relationship between the low voltage amplitude and the high voltage amplitude in the transmission waveform is within a predetermined range indicating normal values. This allows the reader / writer to properly detect changes in the transmission waveform due to the influence of metal.

[0009] The determination unit may determine whether a first modulation index, which is a modulation index of the transmission waveform, is within the predetermined range. With the above configuration, the reader / writer determines whether the first modulation index is within a predetermined range indicating a normal value. This allows the reader / writer to appropriately detect changes in the transmission waveform due to the influence of metal.

[0010] The reader / writer may also be characterized in that, during a first predetermined period, it transmits a first transmission waveform corresponding to one of the binary values, and during a second predetermined period, it transmits a second transmission waveform having a larger amplitude than the first transmission waveform corresponding to the other of the binary values, the detection unit detects the amplitude value of the first transmission waveform as a low voltage amplitude, and detects the amplitude value of the second transmission waveform as a high voltage amplitude, and the first predetermined period and the second predetermined period are longer than the period during which the low voltage amplitude and the high voltage amplitude of the transmission waveform continue during wireless communication, respectively.

[0011] According to the above configuration, the reader / writer can accurately identify the modulation degree.

[0012] The detection unit may be a transmission waveform detection circuit that detects the transmission waveform by obtaining an envelope of the transmission waveform.

[0013] The reader / writer may further include a notification control unit that notifies a user of the quality of the reader / writer installation based on the determination result of the determination unit.

[0014] The reader / writer may further include a transmission circuit that generates the transmission waveform, and a modulation correction unit that corrects a second modulation factor, which is a modulation factor applied by the transmission circuit, based on the determination result of the determination unit. With this configuration, the reader / writer can set the second modulation factor taking into account changes in the transmission waveform due to the influence of metal. Therefore, the reader / writer can properly communicate with RF tags.

[0015] Furthermore, when the first modulation degree is lower than the predetermined range, the modulation degree correction unit may correct the second modulation degree to be higher. With the above configuration, the reader / writer can appropriately set the second modulation degree taking into consideration a decrease in the first modulation degree due to the influence of metal.

[0016] In order to solve the above problem, a transmission waveform determination method according to one embodiment of the present invention includes an acquisition step of acquiring, in a reader / writer that performs wireless communication with an RF tag, a transmission waveform transmitted from an antenna possessed by the reader / writer; a detection step of detecting a low voltage amplitude and a high voltage amplitude in the transmission waveform; and a determination step of determining whether a value indicating the relationship between the low voltage amplitude and the high voltage amplitude is within a predetermined range. [Effects of the Invention]

[0017] According to one aspect of the present invention, it is possible to appropriately detect a change in a transmission waveform due to the influence of metal. [Brief explanation of the drawings]

[0018] [Figure 1] 10A and 10B are diagrams illustrating changes in the frequency characteristics of an antenna due to the influence of surrounding metal in a typical reader / writer. [Figure 2] 10A and 10B are diagrams illustrating changes in the transmission waveform due to the influence of surrounding metal in a typical reader / writer. [Figure 3] 1 is a block diagram showing a schematic configuration of a reader / writer according to an embodiment of the present invention; [Figure 4] FIG. 2 is a diagram illustrating an example of the configuration of a transmission waveform detection circuit of the reader / writer. [Figure 5] 4A and 4B are diagrams illustrating a method for detecting the voltage amplitude of a transmission waveform in the transmission waveform detection circuit. [Figure 6] 10 is a flowchart illustrating an example of processing performed by the reader / writer. [Figure 7] 10 is a flowchart illustrating an example of processing performed by the reader / writer. [Figure 8] FIG. 10 is a block diagram showing a schematic configuration of a reader / writer according to another embodiment of the present invention. [Figure 9] 10A and 10B are diagrams illustrating how modulation degree is corrected in the reader / writer. [Figure 10] 10 is a flowchart illustrating an example of processing performed by the reader / writer. [Figure 11]10 is a flowchart illustrating an example of processing performed by the reader / writer. [Figure 12] 10 is a flowchart illustrating an example of processing performed by the reader / writer. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings. However, the present embodiment described below is merely an example of the present invention in all respects. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention. In other words, when implementing the present invention, specific configurations according to the embodiment may be appropriately adopted.

[0020] §1 Application Examples FIG. 1 is a diagram showing how the frequency characteristics of an antenna in a typical reader / writer change due to the influence of surrounding metal. Reference numeral 1A in FIG. 1 shows an example of the frequency characteristics of an antenna when there is no influence of metal. Reference numeral 1B in FIG. 1 shows an example of the frequency characteristics of an antenna when there is influence of metal. When metal is placed near the reader / writer antenna, the characteristics of the reader / writer antenna are affected by the metal.

[0021] As shown by reference numeral 1A in FIG. 1, when there is no influence of metal, the transmission power of the antenna reaches a maximum value in the 13.56 MHz band, for example. That is, the antenna has a resonant frequency in the 13.56 MHz band. On the other hand, as shown by reference numeral 1B in FIG. 1, when there is influence of metal, the transmission power of the antenna reaches a maximum value at a frequency higher than the resonant frequency (13.56 MHz) band. That is, when there is influence of metal, the transmission power of the antenna in a specific resonant frequency band is lower than when there is no influence of metal.

[0022] FIG. 2 is a diagram showing changes in the transmission waveform of a typical reader / writer due to the influence of surrounding metal. Reference numeral 2A in FIG. 2 shows an example of the transmission waveform of the reader / writer when there is no influence of metal. Reference numeral 2B in FIG. 2 shows an example of the transmission waveform of the reader / writer when there is influence of metal. FIG. 2 shows the envelope of the transmission waveform (modulated wave).

[0023] As shown by reference symbol 2A in Figure 2, when there is no influence from metal, the transmission waveform consists of a waveform with voltage amplitude A corresponding to the binary value "0" and a waveform with voltage amplitude B corresponding to the binary value "1." The reader / writer writes data by sending these transmission waveforms to the RF tag. On the other hand, as shown by reference symbol 2B in Figure 2, when there is influence from metal, the transmission waveform consists of a waveform with voltage amplitude A' corresponding to the binary value "0" and a waveform with voltage amplitude B' corresponding to the binary value "1." As shown in Figure 1, because the transmission power in the resonant frequency band is reduced, voltage amplitude A' and voltage amplitude B' are lower than voltage amplitude A and voltage amplitude B, respectively.

[0024] Furthermore, the ratio (A' / B') of voltage amplitude A' to voltage amplitude B' is greater than the ratio (A / B) of voltage amplitude A to voltage amplitude B. In other words, the modulation degree of the reader / writer's transmission waveform when there is the influence of metal is lower than the modulation degree of the reader / writer when there is no influence of metal. The modulation degree of the transmission waveform is expressed by the following formula:

[0025] (Modulation depth of transmitted waveform) = ((Voltage amplitude corresponding to binary value "1") - (Voltage amplitude corresponding to binary value "0")) / ((Voltage amplitude corresponding to binary value "1") + (Voltage amplitude corresponding to binary value "0")) In the case shown by reference symbol 2A in FIG. 2, (modulation depth of transmission waveform)=(BA) / (B+A).

[0026] As shown in Figures 1 and 2, when a reader / writer antenna is affected by metal, the antenna's transmission power in the resonant frequency band decreases. This causes problems such as a shorter communication distance between the reader / writer and RF tag. In addition, when the reader / writer antenna is affected by metal, the modulation depth of the transmission waveform decreases. This causes problems such as the RF tag being unable to read the signal accurately and data not being able to be written to the RF tag correctly.

[0027] A reader / writer 1 according to one embodiment of the present invention (see FIG. 3) detects a transmission waveform transmitted from its own antenna. In particular, the reader / writer 1 determines whether the modulation degree of the transmission waveform is within a predetermined range indicating a normal value. This allows the reader / writer 1 to appropriately detect changes in the transmission waveform due to the influence of metal.

[0028] §2 Configuration example [Embodiment 1] (Schematic configuration of reader / writer 1) Fig. 3 is a block diagram showing a schematic configuration of the reader / writer 1 according to this embodiment. As shown in Fig. 3, the reader / writer 1 includes a transmission circuit 2, a reception circuit 3, a resonance circuit 4, a transmission waveform detection circuit (detection unit) 6, and a control unit 10. The reader / writer 1 writes and reads data to and from RF tags.

[0029] The transmission circuit 2 transmits a high-frequency carrier wave to be supplied to the RF tag. Here, the transmission circuit 2 modulates the high-frequency carrier wave with a second modulation factor based on a transmission command input from the control unit 10. The second modulation factor is set in advance. The transmission circuit 2 outputs the modulated high-frequency carrier wave to the resonant circuit 4.

[0030] The receiving circuit 3 demodulates the carrier wave transmitted from the RF tag and received by the resonant circuit 4. The receiving circuit 3 outputs the demodulated carrier wave to the control unit 10 as a response signal from the RF tag.

[0031] The resonant circuit 4 communicates with the RF tag at a predetermined frequency (resonant frequency). The resonant circuit 4 transmits the carrier wave from the transmitting circuit 2 to the RF tag. The resonant circuit 4 outputs the carrier wave from the RF tag to the receiving circuit 3.

[0032] The resonant circuit 4 includes a coil (antenna) 5. The coil 5 is an antenna coil that transmits a carrier wave to the RF tag by electromagnetic induction. The coil 5 also receives the carrier wave transmitted from the RF tag by electromagnetic induction.

[0033] The transmission waveform detection circuit 6 directly acquires from the transmission circuit 2 the waveform of the carrier wave (transmission waveform) transmitted from the transmission circuit 2 to the resonant circuit 4. The transmission waveform detection circuit 6 also detects voltage amplitudes (low voltage amplitude VL and high voltage amplitude VH) from the transmission waveform. Here, the low voltage amplitude VL is the voltage amplitude of the transmission waveform corresponding to the binary value "0" in the transmission command. The high voltage amplitude VH is the voltage amplitude of the transmission waveform corresponding to the binary value "1" in the transmission command. A detailed method for detecting voltage amplitudes by the transmission waveform detection circuit 6 will be described later with reference to FIGS. 4 and 5.

[0034] The control unit 10 includes a communication unit 11, a transmission / reception unit 12, a modulation index specifying unit 13, a determination unit 14, and a notification control unit 15. While Fig. 3 illustrates a configuration in which the reader / writer 1 includes the control unit 10, the configuration is not limited to this. For example, the modulation index specifying unit 13 and the determination unit 14 may be included in a higher-level device (e.g., a controller or a personal computer) of the reader / writer 1.

[0035] The communication unit 11 receives a transmission command from a higher-level device. The communication unit 11 outputs the transmission command to the transmission circuit 2 via the transmission / reception unit 12. The communication unit 11 also receives a response signal from the RF tag input from the reception circuit 3 via the transmission / reception unit 12. The communication unit 11 outputs the response signal from the RF tag to the higher-level device.

[0036] For example, the transmission command is a command to transmit a signal to write data to a specific address in the RF tag, or a command to transmit a test signal to detect changes in the transmission waveform due to the influence of metal.

[0037] The modulation degree specifying unit 13 acquires the low voltage amplitude VL and the high voltage amplitude VH from the transmission waveform detection circuit 6. The modulation degree specifying unit 13 specifies the modulation degree (first modulation degree) of the transmission waveform based on the low voltage amplitude VL and the high voltage amplitude VH.

[0038] The determining unit 14 includes a voltage value determining unit 14a and a modulation degree determining unit 14b. The determining unit 14 outputs the determination results of the voltage value determining unit 14a and the modulation degree determining unit 14b to the notification control unit 15.

[0039] The voltage value determination unit 14a acquires the high voltage amplitude VH from the transmission waveform detection circuit 6. The voltage value determination unit 14a determines whether the high voltage amplitude VH is equal to or greater than a reference value. This allows the reader / writer 1 to detect a decrease in the antenna transmission power due to the influence of metal. Note that the voltage value determination unit 14a may also detect a decrease in the antenna transmission power using the low voltage amplitude VL instead of the high voltage amplitude VH.

[0040] The modulation degree determining unit 14b acquires the first modulation degree of the transmission waveform from the modulation degree specifying unit 13. The modulation degree determining unit 14b determines whether the first modulation degree of the transmission waveform is within a predetermined range. As a result, the reader / writer 1 detects a change in the modulation degree of the transmission waveform due to the influence of metal.

[0041] The modulation index specifying unit 13 may specify a value indicating the relationship between the low voltage amplitude VL and the high voltage amplitude VH (for example, the ratio between the low voltage amplitude VL and the high voltage amplitude VH) instead of the first modulation index. In this case, the modulation index determining unit 14b determines whether the value indicating the relationship between the low voltage amplitude VL and the high voltage amplitude VH, instead of the first modulation index, is within a predetermined range.

[0042] The notification control unit 15 outputs whether the installation state of the reader / writer 1 is appropriate to the notification unit 20 based on the determination results of the voltage value determination unit 14a and the modulation degree determination unit 14b, and causes the notification unit 20 to notify the same. If the voltage value determination unit 14a determines that the High voltage amplitude VH is equal to or greater than the reference value and if the modulation degree determination unit 14b determines that the first modulation degree of the transmission waveform is within a predetermined range, the notification control unit 15 outputs to the notification unit 20 that the installation state of the reader / writer 1 is appropriate. If the determination result is other than the above-mentioned determination results, the notification control unit 15 outputs to the notification unit 20 that the installation state of the reader / writer 1 is not appropriate.

[0043] The notification unit 20 notifies the user whether the reader / writer 1 is properly installed or not, based on instructions from the notification control unit 15. The notification unit 20 is, for example, a display that provides guidance using text or images. In the example shown in FIG. 3, the notification unit 20 is provided outside the reader / writer 1, but is not limited to this. For example, the notification unit may be an LED (light-emitting diode) or the like built into the reader / writer 1.

[0044] (Configuration of transmission waveform detection circuit 6) FIG. 4 is a diagram showing an example of the configuration of the transmission waveform detection circuit 6. The transmission waveform detection circuit 6 includes resistors R1 to R3, a diode D1, and a capacitor C3. One end of the resistor R1 is connected to a node between one end (output end) of the transmission circuit 2 and one end (input end) of the resonant circuit 4. The other end of the resistor R1 is connected to the anode of the diode D1. The cathode of the diode D1 is connected to the input terminal of the control unit 10. The resistor R2 is connected between the other end of the resistor R1 and ground. The resistor R3 is connected between the cathode of the diode D1 and ground. The capacitor C3 is connected between the cathode of the diode D1 and ground.

[0045] FIG. 5 is a diagram illustrating a method for detecting the voltage amplitude of a transmission waveform in the transmission waveform detection circuit 6. In FIG. 5, the horizontal axis represents time and the vertical axis represents voltage. FIG. 5 shows the transmission waveform of the modulated wave input from the resonant circuit 4 to the transmission waveform detection circuit 6 and the voltage E output from the transmission waveform detection circuit 6 to the control unit 10. The transmission waveform detection circuit 6 acquires the transmission waveform envelope (voltage E) from the transmission waveform. The transmission waveform detection circuit 6 then detects the transmission waveform. The slope of the voltage drop in the envelope is determined by the time constant τ. The time constant τ is determined by the resistance value of resistor R3 and the capacitance value of capacitor C3. A larger time constant τ results in a smoother voltage change, but also a longer time for the voltage to change from high voltage amplitude VH to low voltage amplitude VL. In order for the control unit 10 to accurately distinguish between the period of high voltage amplitude VH and the period of low voltage amplitude VL, the respective periods must be sufficiently large relative to the time constant τ. The control unit 10 averages the voltage amplitudes at multiple points in time during a certain period to identify the voltage amplitude for that period. When the voltage amplitude changes from the high voltage amplitude VH to the low voltage amplitude VL, it is preferable that the control unit 10 refer to the voltage amplitude at the point in time after the voltage amplitude has completely changed.

[0046] (Example 1) Fig. 6 is a flowchart showing an example of processing by the reader / writer 1. An example of operation in which the reader / writer 1 acquires a transmission waveform based on a first transmission command and determines whether the installation state of the reader / writer 1 is good or bad will be described with reference to Fig. 6.

[0047] The first transmission command is a command for transmitting a signal for writing data to a specific address of the RF tag. The first transmission command may be a command used during actual wireless communication, or may be a test command.

[0048] First, the communication unit 11 receives a first transmission command from the host device (step S1). The communication unit 11 outputs the first transmission command to the transmission circuit 2 via the transmission / reception unit 12.

[0049] Next, the transmission circuit 2 modulates the high-frequency carrier wave with the second modulation index based on the first transmission command input from the transceiver 12. The transmission circuit 2 outputs the high-frequency carrier wave thus modulated to the resonant circuit 4 (step S2).

[0050] Next, the transmission waveform detection circuit 6 acquires the waveform (transmission waveform) of the carrier wave transmitted from the transmission circuit 2 to the resonant circuit 4 (step S3). The transmission waveform detection circuit 6 acquires the envelope of the transmission waveform and detects the low voltage amplitude VL and the high voltage amplitude VH (step S4).

[0051] Next, modulation index specifying unit 13 acquires the low voltage amplitude VL and the high voltage amplitude VH from transmission waveform detection circuit 6. Based on the low voltage amplitude VL and the high voltage amplitude VH, modulation index specifying unit 13 specifies a first modulation index of the transmission waveform (step S5). The actual modulation index (first modulation index) of the transmission waveform may be changed from the second modulation index applied to the carrier wave by transmission circuit 2 due to the influence of metal or the like placed around coil 5.

[0052] Next, the voltage value determination unit 14a acquires the high voltage amplitude VH from the transmission waveform detection circuit 6. The voltage value determination unit 14a determines whether the high voltage amplitude VH is equal to or greater than a reference value (step S6). If the high voltage amplitude VH is equal to or greater than the reference value (YES in step S6), the process proceeds to step S7. If the high voltage amplitude VH is not equal to or greater than the reference value (NO in step S6), the process proceeds to step S9.

[0053] Next, the modulation degree determining unit 14b acquires the first modulation degree from the modulation degree specifying unit 13. The modulation degree determining unit 14b determines whether the first modulation degree is within a predetermined range (step S7). For example, the predetermined range is a range of modulation degrees in which the RF tag can properly recognize the signal. If the first modulation degree is within the predetermined range (YES in step S7), the process proceeds to step S8. If the first modulation degree is not within the predetermined range (NO in step S7), the process proceeds to step S9.

[0054] Next, if the High voltage amplitude VH is equal to or greater than the reference value and the first modulation index is within a predetermined range, the notification control unit 15 outputs to the notification unit 20 a message that the installation state of the reader / writer 1 is appropriate (step S8). On the other hand, if the High voltage amplitude VH is not equal to or greater than the reference value or the first modulation index is not within the predetermined range, the notification control unit 15 outputs to the notification unit 20 a message that the installation state of the reader / writer 1 is not appropriate (step S9). The notification unit 20 notifies (displays) to the user whether the installation state of the reader / writer 1 is appropriate or not, based on an instruction from the notification control unit 15. After step S8 or step S9, the reader / writer 1 ends the processing.

[0055] In this way, the reader / writer 1 identifies the modulation degree (first modulation degree) of the transmission waveform it transmits, and if the first modulation degree is not within a predetermined range, it can notify the user that the installation state of the reader / writer 1 is not appropriate. The influence of metal around the reader / writer 1 can cause the actual modulation degree (first modulation degree) to vary from the set second modulation degree. If the actual modulation degree is not within the predetermined range in which the RF tag can be read, the user can reconsider the placement of the reader / writer 1 or the placement of surrounding structures.

[0056] (Example 2) Fig. 7 is a flowchart showing an example of processing by the reader / writer 1. An example of operation will be described with reference to Fig. 7 when the reader / writer 1 acquires a transmission waveform based on the second transmission command and determines whether the installation state of the reader / writer 1 is good or bad.

[0057] The second transmission command is a command for transmitting a test signal to detect changes in the transmission waveform due to the influence of metal. Upon receiving the second transmission command, the reader / writer 1 transmits a first transmission waveform corresponding to a plurality of binary values ​​"0" during a first predetermined period, and transmits a second transmission waveform corresponding to a plurality of binary values ​​"1" with an amplitude greater than that of the first transmission waveform during a second predetermined period. Either the first or second predetermined period may be transmitted first. In order for the control unit 10 to accurately determine the voltage amplitude during the first and second predetermined periods, the first and second predetermined periods must each be longer than the time constant τ in the transmission waveform detection circuit 6. Furthermore, the first and second predetermined periods may be longer than the duration of the low voltage amplitude VL and the duration of the high voltage amplitude VH of the transmission waveform during wireless communication, respectively. That is, the first and second predetermined periods may be longer than at least the upper limit (for example, 9.44 μs) of the period during which the Low voltage amplitude VL (waveform corresponding to the binary value “0”) continues during wireless communication.

[0058] First, the communication unit 11 receives the second transmission command from the higher-level device (step S11). The communication unit 11 outputs the second transmission command to the transmission circuit 2 via the transmission / reception unit 12.

[0059] Next, the transmission circuit 2 modulates the high-frequency carrier wave so as to superimpose a signal of binary value "0" on the high-frequency carrier wave for a first predetermined period based on the second transmission command input from the transceiver unit 12. The transmission circuit 2 outputs the modulated high-frequency carrier wave to the coil 5 via the resonant circuit 4 for the first predetermined period (step S12).

[0060] Next, the transmission waveform detection circuit 6 acquires the waveform of the carrier wave (first transmission waveform) on which a signal of binary value "0" is superimposed and transmitted from the resonant circuit 4 to the coil 5 (step S13). The transmission waveform detection circuit 6 acquires the envelope of the first transmission waveform and detects the amplitude value of the first transmission waveform as the low voltage amplitude VL (step S14). For example, the control unit 10 may determine the voltage amplitude from a period other than the first unit period (a period corresponding to one binary value in the signal) among the periods corresponding to multiple consecutive binary values ​​"0". This is to avoid the transition period in which the voltage amplitude changes from VH to VL.

[0061] Next, the transmission circuit 2 modulates the high-frequency carrier wave so as to superimpose a signal of binary value "1" on the high-frequency carrier wave for a second predetermined period based on the second transmission command input from the transceiver unit 12. The transmission circuit 2 outputs the modulated high-frequency carrier wave to the coil 5 via the resonant circuit 4 for the second predetermined period (step S15).

[0062] Next, the transmission waveform detection circuit 6 acquires the waveform of the carrier wave (second transmission waveform) on which the signal of binary value "1" is superimposed and transmitted from the resonant circuit 4 to the coil 5 (step S16). The transmission waveform detection circuit 6 acquires the envelope of the second transmission waveform and detects the amplitude value of the second transmission waveform as the High voltage amplitude VH (step S17).

[0063] After a first predetermined period, the modulation degree specifying unit 13 acquires the low voltage amplitude VL from the transmission waveform detection circuit 6. After a second predetermined period, the modulation degree specifying unit 13 acquires the high voltage amplitude VH from the transmission waveform detection circuit 6. The modulation degree specifying unit 13 specifies a first modulation degree of the transmission waveform based on the low voltage amplitude VL and the high voltage amplitude VH (step S18).

[0064] S6 to S9 are the same as in Operation Example 1. After step S8 or step S9, the reader / writer 1 ends the process.

[0065] When the time constant τ is large, the slope of the envelope is small, so the control unit 10 can accurately determine, for example, the voltage amplitude. On the other hand, the transition period from the high voltage amplitude VH to the low voltage amplitude VL also becomes long. If the voltage amplitude is measured during this transition period, the voltage amplitude cannot be accurately obtained.

[0066] In the second operational example, the first transmission waveform (a waveform followed by a low voltage amplitude VL) is divided into a first predetermined period and a second predetermined period of the second transmission waveform (a waveform followed by a high voltage amplitude VH). Therefore, even if the time constant τ is increased, the control unit 10 can identify the voltage amplitude while avoiding the transient period. Therefore, the modulation index identifying unit 13 can accurately identify the modulation index.

[0067] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0068] Fig. 8 is a block diagram showing a schematic configuration of a reader / writer 101 according to this embodiment. The reader / writer 101 according to this embodiment is different from the reader / writer 1 shown in Fig. 3 in that a control unit 110 is provided instead of the control unit 10, but the other configurations are the same. Furthermore, the control unit 110 is different from the control unit 10 shown in Fig. 3 in that it includes a modulation degree correction unit 16 and a resonance frequency correction unit 17, but the other configurations are the same.

[0069] The modulation degree correction unit 16 obtains the determination result regarding the first modulation degree from the determination unit 14. When the first modulation degree is not within a predetermined range, the modulation degree correction unit 16 corrects the second modulation degree so that the first modulation degree falls within the predetermined range. For example, the modulation degree correction unit 16 includes a plurality of modulation circuits corresponding to a plurality of modulation degrees, and corrects (changes) the second modulation degree by selecting a modulation circuit to be used. The modulation degree correction unit 16 outputs the corrected second modulation degree to the transmission circuit 2. A detailed method for correcting the second modulation degree by the modulation degree correction unit 16 will be described later with reference to FIG. 9.

[0070] Note that the modulation degree correction unit 16 may obtain, from the determination unit 14, a determination result regarding a value indicating the relationship between the Low voltage amplitude VL and the High voltage amplitude VH instead of the first modulation degree. In this case, when the value indicating the relationship between the Low voltage amplitude VL and the High voltage amplitude VH is not within the predetermined range, the modulation degree correction unit 16 corrects the Low voltage amplitude VL and the High voltage amplitude VH set in the transmission circuit 2 to correct the second modulation degree.

[0071] The resonance frequency correction unit 17 obtains a determination result regarding the High voltage amplitude VH from the determination unit 14. When the High voltage amplitude VH is not greater than the reference value, the resonance frequency correction unit 17 corrects the parameter regarding the resonance frequency applied to the resonance circuit 4 so that the High voltage amplitude VH becomes greater than or equal to the reference value. Examples of the parameter regarding the resonance frequency include the inductance of the coil and the capacitance of the capacitor in the resonance circuit 4. Thereby, the resonance frequency correction unit 17 can correct the deviation of the resonance frequency of the resonance circuit 4 due to the influence of the metal (see FIG. 1) so that the resonance frequency coincides with the frequency of the carrier wave. The resonance frequency correction unit 17 applies the corrected parameter regarding the resonance frequency to the resonance circuit 4.

[0072] FIG. 9 is a diagram showing the state of correction of the modulation degree in the reader / writer 101. In the graph of FIG. 9, the vertical axis represents the Low voltage amplitude VL of the transmission waveform, and the horizontal axis represents the High voltage amplitude VH of the transmission waveform. Also, the straight lines L1 to L4 represent transmission waveforms in which the first modulation degrees are m1 to m4 (m1 < m2 < m3 < m4), respectively. Also, the point M1 represents a transmission waveform in which the High voltage amplitude is VH1 and the Low voltage amplitude is VL1. The point M2 represents a transmission waveform in which the High voltage amplitude is VH2 and the Low voltage amplitude is VL2.

[0073] The region surrounded by the straight lines L2 and L3 represents the optimal range (predetermined range) of the first modulation degree. Also, the regions surrounded by the straight lines L1 and L2 and the straight lines L3 and L4 represent the communicable ranges. Note that the communicable range represents a range in which communication between the reader / writer 1 and the RF tag is possible but unstable.

[0074] The transmitter circuit 2 modulates the high-frequency carrier wave with a second modulation index so as to output a transmission waveform represented by point M1 in Figure 9, which is within a predetermined range of the first modulation index. That is, the transmitter circuit 2 modulates the high-frequency carrier wave with the second modulation index so that the high voltage amplitude is VH1 and the low voltage amplitude is VL1. Here, due to the influence of metal, the carrier wave transmission waveform is distorted to a transmission waveform represented by point M2 in Figure 9, which is within the communication range. That is, the transmission waveform detection circuit 6 detects a transmission waveform with a high voltage amplitude of VH2 and a low voltage amplitude of VL2.

[0075] To correct for this deviation in modulation index due to the influence of metal, modulation index correction unit 16 calculates a corrected high voltage amplitude VH3 and a corrected low voltage amplitude VL3 so that the first modulation index falls within a predetermined range. Transmission circuit 2 modulates the high-frequency carrier wave with the corrected second modulation index so that the high voltage amplitude is VH3 and the low voltage amplitude is VL3. This allows transmission waveform detection circuit 6 to detect a transmission waveform represented by point M3 in Figure 9, which falls within the predetermined range of the first modulation index. This means that reader / writer 1 can successfully write data to the RF tag with an appropriate modulation index.

[0076] For example, the modulation degree correction unit 16 may calculate the corrected high voltage amplitude VH3 by adding the difference (VH1-VH2) resulting from the reduction in high voltage amplitude due to the influence of metal to the high voltage amplitude VH1. Alternatively, the modulation degree correction unit 16 may calculate the corrected high voltage amplitude VH3 by multiplying the high voltage amplitude VH1 by the ratio (VH1 / VH2). Alternatively, the modulation degree correction unit 16 may calculate the corrected high voltage amplitude VH3 by adding a predetermined correction value to the high voltage amplitude VH1. In this case, the modulation degree correction unit 16 sweeps the high voltage amplitude VH until the first modulation degree of the transmission waveform detected by the transmission waveform detection circuit 6 falls within a predetermined range. The low voltage amplitude VL3 can be calculated in a similar manner.

[0077] (Example 3) 10 is a flowchart showing an example of processing by the reader / writer 101. An example of operation when the resonance frequency correction unit 17 corrects the resonance frequency based on the determination result of the determination unit 14 will be described with reference to FIG.

[0078] Steps S1 to S9 are the same as those in Operation Example 1. If the High voltage amplitude VH is not equal to or greater than the reference value (NO in step S6), the process proceeds to step S21. If the first modulation index is not within a predetermined range (NO in step S7), the process proceeds to step S21. If the voltage value determination unit 14a determines that the High voltage amplitude VH is not equal to or greater than the reference value, or if the modulation index determination unit 14b determines that the first modulation index of the transmission waveform is not within a predetermined range, the determination unit 14 outputs the determination result to the resonance frequency correction unit 17.

[0079] Next, the resonance frequency correction unit 17 obtains the determination result from the determination unit 14. The resonance frequency correction unit 17 determines whether the resonance frequency can be corrected (step S21). That is, it determines whether the parameters related to the resonance frequency of the resonance circuit 4 can be corrected any further. If the resonance frequency can be corrected (YES in step S21), the process proceeds to step S22. If the resonance frequency cannot be corrected (NO in step S21), the process proceeds to step S9.

[0080] If the resonance frequency can be corrected, the resonance frequency correction unit 17 corrects the parameters related to the resonance frequency applied to the resonance circuit 4 so that the High voltage amplitude VH is equal to or greater than the reference value (S22). The reader / writer 101 applies the corrected parameters related to the resonance frequency to the resonance circuit 4, and receives a transmission command from the host device again (return to step S1), or outputs a transmission waveform based on a transmission command that has already been received (return to step S2).

[0081] (Example 4) 11 is a flowchart showing an example of processing by the reader / writer 101. An example of operation when the modulation degree correcting unit 16 corrects the second modulation degree based on the determination result of the determining unit 14 will be described with reference to FIG.

[0082] Steps S1 to S9 are the same as those in Operation Example 1. If the High voltage amplitude VH is not equal to or greater than the reference value (NO in step S6), the process proceeds to step S31. If the first modulation index is not within the predetermined range (NO in step S7), the process proceeds to step S31. If the voltage value determination unit 14a determines that the High voltage amplitude VH is not equal to or greater than the reference value, or if the modulation index determination unit 14b determines that the first modulation index of the transmission waveform is not within the predetermined range, the determination unit 14 outputs the determination result to the modulation index correction unit 16.

[0083] Next, the modulation degree correction unit 16 obtains the determination result from the determination unit 14. The modulation degree correction unit 16 calculates a corrected high voltage amplitude VH3 and a corrected low voltage amplitude VL3 so that the first modulation degree falls within a predetermined range (step S31). Next, the modulation degree correction unit 16 determines whether the corrected high voltage amplitude VH3 and the corrected low voltage amplitude VL3 are settable values ​​(step S32). That is, it determines whether the high voltage amplitude VH and the low voltage amplitude VL (i.e., the modulation degree) can be corrected further. If the corrected high voltage amplitude VH3 and the corrected low voltage amplitude VL3 are settable (YES in step S31), the reader / writer 101 applies the corrected high voltage amplitude VH3 and the corrected low voltage amplitude VL3 to the transmission waveform and receives a transmission command from the higher-level device again (return to step S1). If the corrected high voltage amplitude VH3 and the corrected low voltage amplitude VL3 cannot be settable (NO in step S31), the reader / writer 101 proceeds to step S9.

[0084] (Example 5) Fig. 12 is a flowchart showing an example of processing by the reader / writer 101. An example of operation will be described with reference to Fig. 12 when the resonance frequency correction unit 17 corrects the resonance frequency based on the determination result of the determination unit 14, and then the modulation degree correction unit 16 corrects the second modulation degree based on the determination result of the determination unit 14.

[0085] S1 to S9 are the same as in Operation Example 1. S21 and S22 are the same as in Operation Example 3. S31 and S32 are the same as in Operation Example 4. If the resonance frequency cannot be corrected (NO in step S21), the process proceeds to step S31. That is, in Operation Example 5, if the High voltage amplitude VH does not become equal to or greater than the reference value or the first modulation index does not fall within a predetermined range as a result of correcting the resonance frequency, the reader / writer 101 next corrects the modulation index.

[0086] According to the reader / writer 101 of this embodiment, even when there is an influence of metal surrounding the reader / writer 101, the actual modulation degree (first modulation degree) of the transmitted waveform can be made appropriate by correcting the resonant frequency or the second modulation degree.

[0087] The modulation index determining unit 14b (or the determining unit 14) may determine whether a value indicating the relationship between the low voltage amplitude VL and the high voltage amplitude VH, instead of the first modulation index, is within a predetermined range. For example, the modulation index determining unit 14b (or the determining unit 14) may determine whether a point (coordinate) corresponding to the low voltage amplitude VL and the high voltage amplitude VH is within the communicable range (predetermined range) shown in FIG. 9. The communicable range in FIG. 9 is surrounded by four line segments. Therefore, for example, the modulation index determining unit 14b can determine whether a point (coordinate) corresponding to the low voltage amplitude VL and the high voltage amplitude VH is within the communicable range by determining whether a linear inequality corresponding to each line segment is satisfied.

[0088] [Software implementation example] The control blocks of the reader / writer 1 (particularly, the control units 10, 110, the communication unit 11, the transmission / reception unit 12, the modulation index identification unit 13, the judgment unit 14, the notification control unit 15, the modulation index correction unit 16, and the resonance frequency correction unit 17) may be realized by a logic circuit (hardware) formed on an integrated circuit (IC chip) or the like, or may be realized by software.

[0089] In the latter case, the reader / writer 1 includes a computer that executes instructions from a program, which is software that realizes each function. This computer includes, for example, one or more processors and a computer-readable recording medium that stores the program. The object of the present invention is achieved when the processor in the computer reads and executes the program from the recording medium. The processor may be, for example, a central processing unit (CPU). The recording medium may be a "non-transitory tangible medium," such as a read-only memory (ROM), tape, disk, card, semiconductor memory, or programmable logic circuit. The computer may also include a random access memory (RAM) for expanding the program. The program may be supplied to the computer via any transmission medium (such as a communication network or broadcast waves) capable of transmitting the program. Note that one aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[0090] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0091] 1, 101 Reader / Writer 2. Transmitting circuit 3. Receiving circuit 4 Resonant circuit 5 Coil (antenna) 6. Transmitted waveform detection circuit (detection section) 10, 110 control unit 11 Communications Department 12 Transmitter / Receiver 13 Modulation degree determination section 14 Judgment section 14a Voltage value determination unit 14b Modulation degree determination section 15 Notification control section 16 Modulation correction section 17 Resonant frequency correction section 20. Information Department

Claims

1. A reader / writer that performs wireless communication with an RF tag, The antenna and a detection unit that acquires a transmission waveform transmitted from the antenna and detects a low voltage amplitude and a high voltage amplitude in the transmission waveform; a determination unit that determines whether a value indicating the relationship between the Low voltage amplitude and the High voltage amplitude is within a predetermined range, the reader / writer transmits a first transmission waveform corresponding to one of the binary values ​​during a first predetermined period, and transmits a second transmission waveform corresponding to the other of the binary values ​​and having an amplitude larger than that of the first transmission waveform during a second predetermined period; the detection unit detects an amplitude value of the first transmission waveform as a low voltage amplitude and an amplitude value of the second transmission waveform as a high voltage amplitude; The reader / writer, characterized in that the first predetermined period and the second predetermined period are longer than the period during which the low voltage amplitude of the transmission waveform continues and the period during which the high voltage amplitude of the transmission waveform continues, respectively, during wireless communication.

2. The detection unit is electrically connected to the antenna, The reader / writer according to claim 1 , wherein the determining unit determines whether a first modulation factor, which is a modulation factor of the transmission waveform, is within the predetermined range.

3. 3. The reader / writer according to claim 1, wherein the detection unit is a transmission waveform detection circuit that detects the transmission waveform by obtaining an envelope of the transmission waveform.

4. The reader / writer according to claim 1 , further comprising a notification control unit that notifies whether the installation state of the reader / writer is good or bad based on the determination result of the determination unit.

5. a transmission circuit for generating the transmission waveform; 5. The reader / writer according to claim 1, further comprising: a modulation degree correction unit that corrects a second modulation degree, which is a modulation degree applied in the transmission circuit, based on a determination result of the determination unit.

6. a transmission circuit for generating the transmission waveform; a modulation degree correction unit that corrects a second modulation degree that is a modulation degree applied in the transmission circuit based on a determination result of the determination unit, The reader / writer according to claim 2 , wherein the modulation degree correcting section corrects the second modulation degree to be higher when the first modulation degree is lower than the predetermined range.

7. an acquiring step of acquiring, by the reader / writer, a transmission waveform transmitted from an antenna included in the reader / writer that performs wireless communication with the RF tag; a detection step of detecting a low voltage amplitude and a high voltage amplitude in the transmission waveform; a determining step of determining whether a value indicating the relationship between the Low voltage amplitude and the High voltage amplitude is within a predetermined range; the reader / writer transmits a first transmission waveform corresponding to one of the binary values ​​during a first predetermined period, and transmits a second transmission waveform corresponding to the other of the binary values ​​and having an amplitude larger than that of the first transmission waveform during a second predetermined period; In the detecting step, an amplitude value of the first transmission waveform is detected as a low voltage amplitude, and an amplitude value of the second transmission waveform is detected as a high voltage amplitude; The transmission waveform determination method, wherein the first predetermined period and the second predetermined period are longer than the period during which the Low voltage amplitude of the transmission waveform continues and the period during which the High voltage amplitude of the transmission waveform continues, respectively, during wireless communication.

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