JP6357999B2 - RFID tag reader - Google Patents

Description

  The present invention relates to an RFID tag reader that reads information stored in an RFID tag.

  At present, each article to be managed is attached with an RFID tag. By reading this RFID tag with an RFID tag reader, the management status of each article can be easily grasped, and the management of each article is made more efficient. I am trying. In such a management state, there is a request to search for a specific article from a shelf or the like in which a plurality of articles are stored using an RFID tag attached to the article.

  For example, a reader / writer disclosed in Patent Document 1 is known as an RFID tag reading apparatus that enables a search using such an RFID tag. When this reader / writer searches for an RFID tag having an ID number designated by an operator, the control circuit transmits an interrogation radio wave from the transmission unit and receives a response signal from the RFID tag by the reception unit. The information of all RFID tags existing in the communication area is read. If the target RFID tag exists in the communication area, this is displayed and the communication area is automatically reduced. If the RFID tag does not exist, the position of the reader / writer is changed and A display for prompting the reading operation is made. When the display for prompting the reduction of the communication area and the position change of the reader / writer is repeated, the search by the control circuit ends when only the target RFID tag is read.

JP 2009-0985951 A

  By the way, in the configuration for searching for an RFID tag as described above, it is necessary to gradually reduce the communication area in which the RFID tag can be read in accordance with the result of the reading process. As described above, since the communication area is gradually reduced, it may take a long time to find a desired RFID tag, and there is a problem that a desired RFID tag cannot be found efficiently.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an RFID tag reader capable of efficiently searching for an RFID tag.

In order to achieve the above object, the invention described in claim 1 of the claims is an RFID tag reader (10) for reading information stored in an RFID tag (50), which is subject to predetermined transmission conditions. A transmission means (30) for transmitting radio waves with corresponding transmission parameters, a reception means (30) for receiving a response signal transmitted from the RFID tag in response to a transmission radio wave from the transmission means, and the response signal A calculation means (21) for calculating received signal strength, a distance estimation means (21) for estimating a distance to the RFID tag based on the received signal strength and the transmission parameter, and a distance estimated by the distance estimation means and control means for performing control based on the (21), wherein the distance estimating means, the species of the RFID tag in addition to the received signal strength and the transmission parameter As described above, the distance to the RFID tag is estimated based on at least one of RFID tag sensitivity, tag conversion loss, and tag antenna gain, and the type of the RFID tag is the response signal received by the receiving unit. It is obtained from and wherein Rukoto.
In addition, the code | symbol in each said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

  According to the first aspect of the present invention, when a radio wave is transmitted by the transmission means using a transmission parameter corresponding to a predetermined transmission condition, a response signal transmitted from the RFID tag in response to the transmission radio wave is received by the reception means. When the received signal strength of the response signal is calculated by the calculating means, the distance to the RFID tag is estimated by the distance estimating means based on the received signal strength and the transmission parameter.

  When the transmission parameter (transmission condition), for example, the antenna gain and the transmission output are constant, the received signal strength of the response signal changes according to the distance to the RFID tag. That is, since the distance to the RFID tag can be estimated based on the received signal strength and the transmission parameter, the desired RFID tag to be searched is searched by using the distance to the RFID tag. Can be efficiently searched.

Further , the distance estimation means determines the distance to the RFID tag based on at least one of the RFID tag sensitivity, tag conversion loss, and tag antenna gain as the RFID tag type in addition to the received signal strength and the transmission parameter. Estimated . Since the received signal strength varies slightly depending on the sensitivity of the R FID tag (hereinafter also referred to as tag sensitivity), tag conversion loss, tag antenna gain, etc., the distance to the RFID tag is estimated by taking the RFID tag type into account. By doing so, estimation accuracy can be improved.

In particular , since the type of the RFID tag is acquired from the response signal received by the receiving means, it is possible to eliminate an input operation for acquiring the type of the RFID tag in advance.

In the second aspect of the invention, the distance estimation unit estimates the distance to the RFID tag using the received signal strength obtained by smoothing the calculation result of the calculation unit by the moving average. In this way, by smoothing the moving average to obtain the received signal strength, the received signal strength can be calculated with high accuracy even in a work environment where the received signal strength is relatively variable. The distance estimation accuracy can be improved.

In the invention of claim 3, when the estimated distance by the distance estimating means is adjusted to be lower than a predetermined value so that the receiving sensitivity of the receiving means is increased, the received signal of the response signal received with the adjusted receiving sensitivity The intensity is calculated again by the calculating means. Then, the distance to the RFID tag is estimated by the distance estimation unit using the received signal strength calculated again by the calculation unit.

  When the estimated distance by the distance estimation means is sufficiently small relative to the maximum communicable distance (hereinafter also referred to as the maximum communication distance), the reception sensitivity of the reception means is increased (the power level is lowered) for maximum communication. By reducing the distance, the calculation accuracy of the received signal strength can be increased. Therefore, in situations where the estimated distance is less than or equal to a predetermined value, the received signal strength is calculated again with the reception sensitivity increased, thereby improving the received signal strength calculation accuracy and the estimated accuracy of the distance to the RFID tag. Can be improved.

It is a figure which shows the structure outline | summary of the RFID tag reader which concerns on 1st Embodiment. It is a block diagram which illustrates the electric constitution of a RFID tag reader. 2 is a block diagram schematically illustrating an electrical configuration of an RFID tag. FIG. It is explanatory drawing explaining the communication state of a wireless tag process part and an RFID tag. It is a graph which shows the relationship between a communication distance and an RSSI value. It is a graph which shows the relationship between a communication distance and an RSSI value. It is a flowchart which illustrates the flow of the tag search process by a control part. It is a flowchart which illustrates the flow of the RSSI value calculation process in FIG.

[First Embodiment]
Hereinafter, a first embodiment in which an RFID tag reader according to the present invention is embodied will be described with reference to the drawings. 1A and 1B are diagrams showing an outline of the configuration of an RFID tag reading apparatus 10 according to the first embodiment. FIG. 1A is a front view and FIG. 1B is a side view. FIG. 2 is a block diagram illustrating an electrical configuration of the RFID tag reader 10.

  An RFID tag reader 10 shown in FIGS. 1A and 1B is configured as a portable information terminal that is carried by a user and used in various places, and mediates radio waves transmitted and received via an antenna. In addition to a function as a wireless tag reader that reads information stored in an RFID tag (wireless tag) 50, it also has a function as an information code reader that reads an information code such as a barcode or a two-dimensional code. It is a configuration that can be done with.

  As shown in FIGS. 1 (A) and 1 (B), the RFID tag reader 10 has a longitudinal shape constituted by assembling an upper case 11a and a lower case 11b formed of a synthetic resin material such as ABS resin. An outer case is formed by the casing 11. The upper case 11a is provided with a key operation unit 25 such as function keys and numeric keys operated when inputting predetermined information, a display unit 24 for displaying predetermined information, and the like. The lower case 11b has a reading port 12 that opens downward.

  As shown in FIG. 2A, a control unit 21 that controls the entire RFID tag reader 10 is provided in the housing 11 of the RFID tag reader 10. The control unit 21 is composed mainly of a microcomputer, has a CPU, a system bus, an input / output interface, and the like, and constitutes an information processing apparatus together with the memory 22. The control unit 21 is connected to an LED 23, a display unit 24, a key operation unit 25, a vibrator 26, a buzzer 27, an external interface 28, and the like.

  The key operation unit 25 is configured to give an operation signal to the control unit 21, and the control unit 21 receives the operation signal and performs an operation according to the content of the operation signal. Further, the LED 23, the display unit 24, the vibrator 26 and the buzzer 27 are configured to be controlled by the control unit 21, and each operate in response to a command from the control unit 21. The external interface 28 is configured as an interface for performing data communication with an external device or the like, and is configured to perform communication processing in cooperation with the control unit 21. In addition, a power supply unit 29 is provided in the housing 11, and power is supplied to the control unit 21 and various electrical components by the power supply unit 29 and the battery 29 a.

In addition, a wireless tag processing unit 30 and an information code reading unit 40 are connected to the control unit 21.
The wireless tag processing unit 30 performs electromagnetic wave communication with the RFID tag 50 in cooperation with the antenna 34 and the control unit 21, reads data stored in the RFID tag 50, or writes data to the RFID tag 50. It functions to perform. The wireless tag processing unit 30 is configured as a circuit that performs transmission by a known radio wave system. As schematically illustrated in FIG. 2B, the wireless tag processing unit 30 includes a transmission circuit 31, a reception circuit 32, a matching circuit 33, and the like. Have.

  The transmission circuit 31 includes a carrier oscillator, an encoding unit, an amplifier, a transmission unit filter, a modulation unit, and the like, and is configured to output a carrier (carrier wave) having a predetermined frequency from the carrier oscillator. The encoding unit is connected to the control unit 21, encodes transmission data output from the control unit 21, and outputs the transmission data to the modulation unit. The modulation unit is a part to which the carrier (carrier wave) from the carrier oscillator and the transmission data from the encoding unit are input. The carrier (carrier wave) output from the carrier oscillator is encoded at the time of command transmission to the communication target. A modulated signal that is ASK (Amplitude Shift Keying) modulated by the encoded transmission code (modulated signal) output from the encoding unit is generated and output to the amplifier. The amplifier amplifies the input signal (the modulated signal modulated by the modulation unit) with a predetermined gain, and outputs the amplified signal to the transmission unit filter. The transmission unit filter filters the amplified signal from the amplifier. The transmission signal is output to the antenna 34 via the matching circuit 33. When the transmission signal is output to the antenna 34 in this way, the transmission signal is radiated to the outside from the antenna 34 as a transmission radio wave. The wireless tag processing unit 30 may correspond to an example of a “transmission unit” that transmits radio waves using transmission parameters corresponding to a predetermined transmission condition.

  On the other hand, the response signal received by the antenna 34 is input to the receiving circuit 32 via the matching circuit 33. The receiving circuit 32 includes a receiving unit filter, an amplifier, a demodulating unit, a binarization processing unit, a decoding unit, and the like. After the response signal received through the antenna 34 is filtered by the receiving unit filter, The signal is amplified by an amplifier, and the amplified signal is demodulated by a demodulator. The demodulated signal waveform is binarized by the binarization processing unit, decoded by the decoding unit, and then the decoded signal is output to the control unit 21 as received data. The wireless tag processing unit 30 may correspond to an example of a “reception unit” that receives a response signal transmitted from the RFID tag 50.

Here, the RFID tag 50 to be read by the RFID tag reader 10 will be described with reference to FIG. FIG. 3 is a block diagram schematically illustrating the electrical configuration of the RFID tag 50.
As shown in FIG. 3, the RFID tag 50 includes an antenna 51, a power supply circuit 52, a demodulation circuit 53, a control circuit 54, a memory 55, a modulation circuit 56, and the like. The power supply circuit 52 rectifies and smoothes a transmission signal (carrier signal) received from the RFID tag reader 10 via the antenna 51 to generate an operation power supply. The operation power supply is used as the control circuit 54. And other components.

  The demodulating circuit 53 demodulates the data superimposed on the transmission signal (carrier signal) and outputs it to the control circuit 54. The memory 55 is configured by various semiconductor memories such as a ROM and an EEPROM, and stores a control program, identification information (tag ID) for identifying the RFID tag 50, data corresponding to the use of the RFID tag 50, and the like. ing. The control circuit 54 is configured to read the information and data from the memory 55 and output it as transmission data to the modulation circuit 56. The modulation circuit 56 performs load modulation on the response signal (carrier signal) with the transmission data. Thus, the antenna 51 is configured to transmit as a reflected wave.

  The information code reading unit 40 functions to optically read the information code. As shown in FIG. 2C, the information code reading unit 40 includes a light receiving sensor 43 including a CCD area sensor, an imaging lens 42, a plurality of LEDs, It has a configuration including an illumination unit 41 composed of a lens and the like, and functions to read an information code C (bar code or two-dimensional code) attached to a reading target R in cooperation with the control unit 21. To do.

  When reading is performed by the information code reading unit 40, first, the illumination light Lf is emitted from the illumination unit 41 that has been instructed by the control unit 21, and the illumination light Lf is irradiated to the reading object R through the reading port 12. The Then, the reflected light Lr reflected by the information code C from the illumination light Lf is taken into the apparatus through the reading port 12 and is received by the light receiving sensor 43 through the imaging lens 42. The imaging lens 42 disposed between the reading port 12 and the light receiving sensor 43 is configured to form an image of the information code C on the light receiving sensor 43, and the light receiving sensor 43 is an image of the information code C. The light reception signal corresponding to the is output. The light receiving signal output from the light receiving sensor 43 is stored as image data in the memory 22 (FIG. 2A) and used for decoding processing for acquiring information included in the information code C. The information code reading unit 40 is provided with an amplifying circuit for amplifying the signal from the light receiving sensor 43 and an AD converting circuit for converting the amplified signal into a digital signal. Is omitted.

  Next, tag search processing executed by the control unit 21 of the RFID tag reader 10 will be described with reference to FIGS. FIG. 4 is an explanatory diagram for explaining a communication state between the wireless tag processing unit 30 and the RFID tag 50. FIG. 5 is a graph showing the relationship between the communication distance X and the RSSI value. FIG. 6 is a chart showing the relationship between the communication distance X and the RSSI value. FIG. 7 is a flowchart illustrating the flow of tag search processing by the control unit 21. FIG. 8 is a flowchart illustrating the flow of the RSSI value calculation process in FIG.

  When searching for a specific item using a RFID tag 50 attached to the item from a shelf or the like in which a plurality of items are stored, the specific item can be easily estimated by estimating the distance to the RFID tag 50. To explore. Therefore, in the present embodiment, as shown in FIG. 4, the tag search process executed by the control unit 21, the predetermined transmission condition when the transmission radio wave is transmitted toward the RFID tag 50, and the RFID tag 50 The estimated distance (hereinafter also referred to as communication distance X) to the RFID tag 50 is estimated according to the received signal strength (RSSI: dBm) of the response signal (backscanter) received from, and this estimated communication distance Search for a specific article based on X.

  For example, an RFID tag 50 having a tag sensitivity of −16.7 dB, a tag conversion loss of −9 dB, and a tag antenna gain of −5 dBi is set as a search target, and an RFID tag reading is performed as a transmission parameter corresponding to the predetermined transmission condition. Using the RFID tag reader 10 in which the antenna gain of the device 10 (hereinafter also referred to as RW antenna gain) is 0.2 dBi, and the internal loss of the wireless tag processing unit 30 (hereinafter also referred to as receiver internal loss) is −10 dB. When the transmission radio wave is transmitted at a transmission radio wave frequency of 919.2 MHz and a transmission output of 29.4 dBm, the relationship shown in FIGS. 5 and 6 is established between the communication distance X and the RSSI value. To do.

The RSSI estimated values shown in FIGS. 5 and 6 described above are calculated using the communication distance X as a variable based on the following equations (1) to (3).
RSSI estimated value = tag received power + tag conversion loss + tag antenna gain-space loss
+ RW antenna gain + receiver internal loss (1)
Tag reception power = transmission output + tag antenna gain-space loss + RW antenna gain (2)
Space loss = −20 log (4π × communication distance X / λ) (3)
Here, λ shown in Expression (3) for obtaining the space loss (span loss, radio wave propagation loss) is the wavelength of the transmission radio wave, and is obtained from the frequency of the transmission radio wave.
5 and 6, it can be seen that the RSSI actually measured value obtained by actually measuring the RSSI value and the RSSI estimated value have small errors, and in particular, in the vicinity of the maximum communication distance Xm. The maximum communication distance Xm is an eigenvalue determined according to the communication performance of the RFID tag reader 10 and the like.

  Then, the RSSI value can be directly calculated as the received signal strength of the response signal from the RFID tag 50 without using the equation (1). Therefore, when the tag type is specified and the predetermined transmission condition is made constant, the communication distance X can be estimated from the calculated RSSI value (RSSI calculated value). For example, under the conditions illustrated in FIGS. 5 and 6, if the RSSI calculated value is directly calculated as −70 dB, it can be estimated that the communication distance X is approximately 2.5 m. Therefore, in the present embodiment, information corresponding to a relational expression between the RSSI calculated value and the communication distance X (for example, mapping data) is stored in the memory 22 or the like in advance for each parameter using the tag type and transmission condition as parameters. The communication distance X is estimated based on the RSSI calculation value from this relational expression and the like.

  A tag search process for searching for the RFID tag 50 using the estimation method for estimating the communication distance X from the RSSI calculated value will be described in detail with reference to the flowcharts shown in FIGS. It is assumed that identification information such as a tag ID for identifying the RFID tag 50 to be searched has been input in advance.

  When a tag search process is started by the control unit 21 by performing a predetermined operation on the key operation unit 25, a tag type specifying process shown in step S101 of FIG. 7 is performed. In this process, a search target RFID tag 50 (hereinafter also referred to as a search target tag 50) is first extracted from a plurality of communicable RFID tags 50 based on the specific information, and communicated with the search target tag 50. The tag type (tag sensitivity, tag conversion loss, tag antenna gain, etc.) of the search target tag 50 is specified from the acquired information.

  Next, the transmission output setting process shown in step S103 is performed. In this process, the transmission output (power level) when transmitting the transmission radio wave to the search target tag 50 at a predetermined frequency is set to a predetermined value (for example, Lv20 at the power level).

  Subsequently, RSSI value calculation processing shown in step S105 is performed. Since the RSSI value is a value that is relatively easy to vary depending on the work environment in which the RFID tag reader 10 is used, in this RSSI value calculation process, a change amount Y related to the RSSI value is calculated, and according to the change amount Y The moving average method used to calculate the RSSI value is selected. The control unit 21 that executes the process shown in step S105 and the process shown in step S115 described later can correspond to an example of a “calculation unit”.

Specifically, first, the change amount Y calculation process shown in step S201 of FIG. 8 is performed. In this process, the search target tag 50 is read continuously within a unit time Δ (for example, 20 ms) under a certain transmission condition set as described above, and two RSSI values (R (t− Δ), R (t−2Δ)) are directly calculated, and the RSSI value change amount Y is calculated based on the following equation (4).
Y = | R (t−Δ) −R (t−2Δ) | / Δ (4)
Here, R (t−Δ) indicates an RSSI value at time t−Δ, and R (t−2Δ) indicates an RSSI value at time t−2Δ.

  Subsequently, in the determination process shown in step S203, it is determined whether or not the change amount Y is less than a predetermined change amount threshold Z. Here, if the change amount Y is less than the change amount threshold Z, it is determined as Yes in step S203, assuming that the RFID tag reader 10 is used in a work environment in which the RSSI value is relatively difficult to vary.

  In this case, the average value calculation process at n = 5 shown in step S205 is performed. In this process, five RSSI values are directly calculated by reading the search target tag 50 again five times continuously under the constant transmission conditions set as described above, and these five RSSI values are moved. The RSSI calculation value is calculated by smoothing by averaging.

  On the other hand, if the change amount Y is greater than or equal to the change amount threshold Z, it is determined No in step S203, assuming that the RFID tag reader 10 is being used in a work environment in which the RSSI value is relatively variable. In this case, the average value calculation process at n = 50 shown in step S207 is performed. In this process, 50 RSSI values are directly calculated by continuously reading the search target tag 50 again under the constant transmission condition set as described above, and the 50 RSSI values are moved. The RSSI calculation value is calculated by smoothing by averaging.

  In the average value calculation process described above, the number used for the moving average in step S207 is not limited to calculating from five in step S205 or from 50 in step S207. It is sufficient that the number is larger than the number used in the above. As a result, in the work environment in which the RSSI value is relatively difficult to vary (Yes in S203), priority is given to the improvement of the processing speed, and in the work environment in which the RSSI value is relatively variable (No in S203), a decrease in the average value calculation accuracy can be suppressed. .

  When the RSSI calculation value is calculated in step S205 or step S207, communication distance estimation processing is performed in step S107 of FIG. In this process, the RSSI calculated as described above is based on the tag type specified in step S101 and the relational expression stored in advance in the memory 22 corresponding to the transmission output set in step S103. A communication distance X is calculated and estimated based on the calculated value. In addition, the control part 21 which performs the process shown to the said step S107 and the process shown to step S117 mentioned later can correspond to an example of a "distance estimation means."

  Subsequently, a notification process shown in step S109 is performed. In this process, information on the communication distance X estimated as described above is displayed on the display screen of the display unit 24 and notified. Thereby, the worker who sees this display can grasp the distance to the search target tag 50, that is, the distance to the search target article. The control unit 21 that executes the process shown in step S109 and the process shown in step S119 described later may correspond to an example of a “control unit” that performs control based on the estimated distance.

  And it is determined by the determination process shown to step S111 whether the estimated communication distance X is below the predetermined distance threshold value Xo. Here, the distance threshold value Xo is set to a sufficiently small value with respect to the maximum communication distance Xm (for example, a value that is ¼ of the maximum communication distance Xm), and the estimated communication distance X is greater than the distance threshold value Xo. Is larger (No in S111), the processing from step S105 is repeated.

  On the other hand, when the estimated communication distance X becomes smaller than the predetermined distance threshold value Xo when the worker who has seen the notification information on the display screen moves toward the search target article (Yes in S111), step The transmission output adjustment process shown in S113 is performed. In this process, the transmission output (power level) set in step S103 is adjusted (changed) to a lower value (for example, Lv5 at the power level). When the communication distance X calculated with respect to the maximum communication distance Xm is sufficiently small (Yes in S111), the maximum communication distance is adjusted by increasing the reception sensitivity of the wireless tag processing unit 30 (lowering the power level). This is because the accuracy of calculating the RSSI value can be increased by reducing Xm. The control unit 21 that executes the process shown in step S113 can correspond to an example of an “adjustment unit” that can adjust the reception sensitivity.

  When the transmission output (power level) is adjusted to a lower value in this way, RSSI value calculation processing shown in step S115 is performed. In this process, similarly to the RSSI value calculation process in step S105, the process after the change amount Y calculation process shown in step S201 of FIG. 8 is performed, and the direct calculation is performed under the transmission conditions adjusted as described above. The RSSI calculated value is recalculated from the plurality of RSSI values.

  Then, in the communication distance estimation process shown in step S117, from the relational expression etc. stored in advance in the memory 22 or the like corresponding to the tag type specified in step S101 and the transmission output adjusted in step S113. The communication distance X is calculated and estimated based on the RSSI calculated value calculated as described above.

  Subsequently, a notification process shown in step S119 is performed, and information on the communication distance X estimated as described above is displayed on the display screen of the display unit 24 and notified. Then, it is determined No in step S121 until the operator performs an end operation due to the discovery of the search target article, etc., and the processing from step S115 is repeated.

  As described above, in the RFID tag reading apparatus 10 according to the present embodiment, when a radio wave is transmitted with a transmission parameter corresponding to a predetermined transmission condition, a response transmitted from the RFID tag 50 according to the transmission radio wave. A signal is received. When the RSSI value (reception signal strength) of the response signal is calculated, the distance (communication distance X) to the RFID tag 50 is estimated based on the RSSI value and the transmission parameter.

  As described above, since the distance to the RFID tag 50 can be estimated based on the RSSI value and the transmission parameter, the desired RFID tag 50 to be searched for is determined using the distance to the RFID tag 50 (communication distance X). By searching, a desired RFID tag 50 can be searched efficiently.

  In addition to the RSSI value and the transmission parameter, the distance to the RFID tag 50 (communication distance X) is estimated based on the type of the RFID tag. Since the RSSI value varies somewhat depending on the type of RFID tag 50 (tag sensitivity, tag conversion loss, tag antenna gain, etc.), the distance to the RFID tag 50 (communication distance X) is also considered in consideration of the type of RFID tag 50 The estimation accuracy can be improved by estimating.

  Furthermore, since the type of the RFID tag 50 is acquired from the received response signal (S101), it is possible to eliminate an input operation for acquiring the type of the RFID tag 50 in advance. When the type of the RFID tag 50 can be specified in advance, the process in step S101 may be omitted by inputting the type of the RFID tag 50 in advance.

  Furthermore, in the RSSI value calculation process (S105, S115), the distance (communication distance X) to the RFID tag 50 is estimated using the RSSI calculated value obtained by smoothing the RSSI value calculation result by moving average. . As described above, the RSSI value is smoothed by moving average to obtain the RSSI calculation value, so that the RSSI value can be calculated with high accuracy even in a work environment where the RSSI value is relatively easily varied. The estimation accuracy of can be improved.

  In particular, when the estimated distance to the RFID tag 50 (communication distance X) is equal to or less than a predetermined distance threshold value Xo, the reception sensitivity is adjusted to be high (the power level is low) (Yes in S111). The RSSI value of the response signal received with the adjusted reception sensitivity is calculated again. Then, the distance to the RFID tag 50 is estimated using the RSSI value calculated again.

  As described above, in a situation where the estimated distance to the RFID tag 50 is equal to or less than the predetermined distance threshold value Xo, the RSSI value is calculated again with high reception sensitivity, thereby increasing the RSSI value calculation accuracy. Thus, the estimation accuracy of the distance to the RFID tag 50 can be improved.

[Other Embodiments]
In addition, this invention is not limited to the said embodiment, For example, you may actualize as follows.
(1) In the RSSI value calculation process (S105, S115), the RSSI calculated value is obtained by always calculating the same number of RSSI values without considering the change amount Y and smoothing these calculation results by a moving average. It may be calculated. Moreover, in the said RSSI value calculation process, you may calculate not only using a moving average but calculating another RSSI value using another average method. Further, in the RSSI value calculation process, when used in a work environment in which the RSSI value is unlikely to vary, an RSSI value that is directly calculated by one reading without using an average may be used as the RSSI calculated value.

(2) The notification process (S109, 119) is not limited to performing control for notifying the information about the communication distance X by display, but is based on other control based on the estimated distance, for example, the volume according to the communication distance X. Control for notifying information related to the communication distance X by emitting a beep sound or the like that changes may be performed.

(3) The present invention is not limited to being configured as a portable information terminal having a function as an information code reader that optically reads an information code in addition to a function as a wireless tag reader that reads the RFID tag 50, You may comprise as a portable information terminal which has only a function as a tag reader, and may be comprised as a portable information terminal which has another function.

DESCRIPTION OF SYMBOLS 10 ... RFID tag reader 21 ... Control part (Calculation means, distance estimation means, control means, adjustment means)
30 ... RFID tag processing unit (transmission means, reception means)
50 ... RFID tag X ... Communication distance

Claims (3)

An RFID tag reader for reading information stored in an RFID tag,
Transmitting means for transmitting radio waves with transmission parameters corresponding to predetermined transmission conditions;
Receiving means for receiving a response signal transmitted from the RFID tag in response to a transmission radio wave from the transmitting means;
Calculating means for calculating the received signal strength of the response signal;
Distance estimating means for estimating a distance to the RFID tag based on the received signal strength and the transmission parameter;
Control means for performing control based on the distance estimated by the distance estimation means;
Equipped with a,
The distance estimation means is configured to reach the RFID tag based on at least one of RFID tag sensitivity, tag conversion loss, and tag antenna gain as the RFID tag type in addition to the received signal strength and the transmission parameter. Estimate the distance of
The types of RFID tags, RFID tag reader according to claim Rukoto is obtained from the response signal received by the receiving means.   2. The RFID according to claim 1, wherein the distance estimation unit estimates a distance to the RFID tag using the received signal intensity obtained by smoothing a calculation result of the calculation unit by a moving average. Tag reader. Adjusting means adjustable to increase the receiving sensitivity of the receiving means when the estimated distance by the distance estimating means is below a predetermined value;
The calculating means, when the receiving sensitivity of the receiving means is adjusted by the adjusting means, recalculates the received signal strength of the response signal received with the adjusted receiving sensitivity,
The RFID tag reader according to claim 1, wherein the distance estimating unit estimates a distance to the RFID tag using the received signal intensity calculated again by the calculating unit.

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