Patent Application
20080094182
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-287523, filed on Oct. 23, 2006, and the prior Japanese Patent Application No. 2007-238716, filed on Sep. 14, 2007, the entire content of which is incorporated herein by reference.
The present invention relates to a reader/writer for transmitting and receiving data by radio communication with an RFID (Radio Frequency Identification) tag and a data communication method between the RFID tag and the reader/writer.
In recent years, development for practical use of an RFID tag (also called a radio tag, IC tag, non-contact type ID, non-contact type IC and transponder or the like) has been progressed and thereby an RFID system utilizing such RFID tag has been introduced in various fields.
The RFID tag is roughly classified into a “passive type” and an “active type”.
The active type RFID tag comprises a battery to realize self-feeding of electrical power. On the other hand, the passive type RFID tag does not comprise a battery and therefore cannot realize self-feeding of electrical power. Accordingly, the passive type RFID generates a current when it receives a radio frequency signal transmitted from a reader/writer. The current generated is then supplied, after the rectification, to each circuit of the RFID tag as the regulated supply voltages. The RFID tag can be operated through supply of such electrical power.
Moreover, upon the reader/writer transmitting data to the RFID tag and receiving data from the RFID tag, the reader/writer searches (inventories) the RFID tag existing within the communication-enabled range of an antenna of the read/writer. When a search command of the RFID tag is transmitted to the RFID tag from the reader/writer, the RFID tag is supplied electrical power from the field and receives the search command. Then the RFID tag transmits the own tag ID to the reader/writer as a response to the search command. The reader/writer transmits, upon reception of the tag ID from the RFID tag, a command indicating the completion of identification state (DATA_READ command for ISO/IEC 18000-6 Type B) to switch the RFID tag to the state (DATA_EXCHANGE state for ISO/IEC 18000-6 Type B) for enabling data transmission and reception between the reader/writer and RFID tag. The RFID tag generates, upon reception of the command from the reader/writer, response contents in accordance with contents instructed by the command and then transmits the same contents to the reader/writer. Thereafter, The RFID tag reads the information stored in the memory thereof or writes information to the memory.
In the case where a plurality of RFID tags exist within the communication-enabled range of the antenna of the reader/writer at the time of searching the RFID tag, a plurality of RFID tags transmit simultaneously the responses for the search command. Therefore, the reader/writer sometimes enters the situation that it cannot receive the responses because of mutual interferences among the responses. In view of avoiding such a situation, the reader/writer and the RFID tag are respectively provided with some collision arbitration functions.
ISO/IEC 18000-6 type B and C specifications provide a memory flag function which can temporarily store some information. The memory flag function can be used to reduce the number of tags participating in the collision arbitration by sending a command to indicate a condition for responding to the search command, and therefore to improve the overall performance.
However, since the passive type RFID tag does not comprises a battery as explained above, even when the flag is stored in the temporary memory, feeding of electrical power for maintaining the stored contents in the temporary memory cannot be continued in the case where the tag goes out of the communication-enabled range of antenna or the radio transmission condition is rather bad even when the tag exists within the communication-enabled range. As a result, the flag stored in the temporary memory is sometimes cleared. Therefore, if the flag stored in the temporary memory is cleared, the RFID tag sends a response when it receives the search command from the reader/writer.
In the case where the flag is cleared in adequate time, the RFID tag is allowed to return again to the state for sending a response for the search command. However, if the RFID tag which has already been recognized by the reader/writer returns to the state for sending a response for the search command while other RFID tags are still trying to respond, the problem of interference among the responses of a plurality of RFID tags still cannot be solved.
A first aspect of the present invention is a method for controlling a response of an RFID tag for transmitting a response in accordance with an inquiry from a reader/writer, the method includes steps of transmitting, from the reader/writer, a search command for searching the RFID tag within the communication-enabled range of the reader/writer together with a first response control information for determining whether the RFID tag has already transmitted the response, comparing, in the RFID tag, upon reception of the search command from the reader/writer, the first response control information transmitted together with the search command with a second response control information stored in a memory of the RFID tag, controlling, in the RFID tag, the response to the search command when the first response control information is identical to the second response control information, and, transmitting, in the RFID tag, a response to the search command when the first response control information is different from the second response control information, and moreover updates the second response control information stored in the memory of the RFID tag with the first response control information received from the reader/writer.
A second aspect of the present invention is an RFID system has a reader/writer for communication by radio with an RFID tag and a computer for mutual communication with the reader/writer through a network. The computer includes a generating part which generates a first response control information for controlling necessity of a response to a search command of the RFID tag, and a search instructing part which transmits, to the reader/writer, a search instructing command for instructing detection of the RFID tags existing within the communication-enabled range of the reader/writer together with the first response control information generated by the generating part.
The reader/writer includes a receiving part which receives the search instructing command and the first response control information transmitted from the computer, and a search command transmitting part which transmits, to the RFID tag, the search command for detecting the RFID tags existing in the communication-enabled range of the reader/writer together with the received first response control information.
A third aspect of the present invention is a computer-readable storage medium storing a response control information generating program, the response control information generating program includes: a generating function which generates a first response control information to determine necessity of a response to a search command from the reader/writer by accepting an instruction to generate the first response control information, and a transmitting function which transmits a search instructing command for instructing search of the RFID tag to the reader/writer together with the first response control information generated by the generating part.
A fourth aspect of the present invention is a computer-readable storage medium storing a response control program, the response control program includes a receiving function which receives a first response control information together with a search command from a computer, and a transmitting function which transmits the search command for detecting an RFID tag existing in the communication-enabled range together with the received first response control information.
The inventors of the present invention have focused attention to the fact that some passive RFID tags have not only a temporary memory which clears stored contents if the power-feeding is suspended but also a non-volatile memory. When the information showing the completion of a search command is stored in such non-volatile memory, such information is held without relation to feeding of electrical power. Therefore, the RFID tag does not respond to the search command indicating the response condition including the same information after it has once sent a normal response for the search command.
Meanwhile, when the information indicating the completion of the search command is stored in a non-volatile memory, such information is stored continuously. Accordingly, even when the RFID tag enters the state that it must respond again for the search command, the situation is generated again in which the RFID tag does not respond for such search command because of the information stored in the non-volatile memory. A method for sending a command to clear the information stored in the non-volatile memory in the adequate time has also been proposed. However, since data transmission and reception between the reader/writer and the RFID tag are conducted by radio, a situation will be generated depending on the radio transmission condition that the RFID tag cannot receive the update command transmitted from the reader/writer or that even when such update command is received, feeding of electrical power to execute the update command cannot be acquired sufficiently and thereby the information indicating the completion of the search command stored in the non-volatile memory cannot be cleared.
The inventors of the present invention have also focused attention to the fact that, when a method for updating information contained in the response condition of the search command in the predetermined timing is employed in the system side, no other clearing commands to reset the information in the non-volatile memory showing the completion of the previous search command are necessary. The RFID tag changes contents of the information showing the completion of the search command when the command contains new response condition and the processing in the tag is successfully completed. The RFID tag compares the response condition received with the information stored in the non-volatile memory. When these information pieces are identical, the RFID tag does not respond for the search command, but when these are different, the RFID tag sends a response. Thereby, the necessity of response for the search command of the RFID tag can be controlled even when the information stored in the non-volatile memory is not updated.
As explained above, it is an object of the present invention that, once an RFID tag is inventoried by a search command from the reader/writer, the response from the same RFID tag to other search commands is never transmitted multiple times, therefore preventing duplicate processing of the same tag.
The preferred embodiments of the present invention will be explained with reference to the following embodiments.
The host computer 30 roughly includes a processing unit 300 and a network interface 306, while the processing unit 300 includes a controller 301, an application 302, a generator 303, and a storage unit 304. The controller 301 controls various processes of the host computer 30. The application 302 is operated in cooperation with the reader/writer 10 in order to transmit various instructions to the reader/writer 10 and receive information from the reader/writer 10. The generator 303 generates a parameter to be transferred to the reader/writer 10 when the host computer 30 instructs the reader/writer 10 to detect (hereinafter referred to as “inventory process”) the RFID tag 20 existing in the communication-enabled range of the reader/writer 10. This parameter is the information (hereinafter, referred to as the “response control information”) used for controlling the RFID tag 20 detected by the reader/writer 10 to not send responses many times in the sequence of the inventory process.
The reader/writer 10 comprises a processing unit 100, a radio-transmission interface 110, a network interface 120, and an antenna 130.
The radio-transmission interface 110 includes a transmitter 111 and a receiver 112. The transmitter 111 modulates a sending signal to transmit data to the RFID tag 20 via the antenna 130. The receiver 112 receives and demodulates a radio frequency signal transmitted from the RFID tag 20 via the antenna 130. Transmission of the sending signal to the RFID tag 20 and reception of the receiving signal from the RFID tag 20 are conducted through the antenna 130. Moreover, the radio-transmission interface 110 generates a radio frequency signal and transmits the same signal to the RFID tag 20 via the antenna 130 in order to activate the RFID tag.
A processing unit 100 includes a controller 101, an application cooperating unit 102, a command receiver 104, a command transmitter 105, and a storage unit 106. The controller 101 controls operations of the reader/writer such as sending of instructions to each section and transmission of the result of processes in each section in accordance with a command issued from the application 302 through communication with application of the host computer 30 via the network interface 120. The application cooperating unit 102 obtains, upon reception of the instruction to execute the inventory process from the host computer 30, the parameter included in the executing instruction, generates a search command and transmits such search command to the reader/writer 10 via the command transmitter 105 and the transmitter 111. The command receiver 104 receives the receiving signal demodulated in the receiver 112. The command transmitter 105 sends the command and data to be transmitted to the RFID tag 20 through the transmitter 111. The data required for processes in each section is stored or updated in the storage unit 106.
The RFID tag 20 includes a data processor 200, a non-volatile memory 240, a temporary memory 250, a modulator 211, a demodulator 212, a rectifier 220, and an antenna 230. The demodulator 212 executes a demodulating process for the signal received from the reader/writer 10 via the antenna 230 and transfers the demodulated signal to the data processor 200. The rectifier 220 generates a current upon reception of the signal from the reader/writer 100 via the antenna 230 and supplies, after implementation of the rectifying process to the generated current, an electrical power to a processor of the data processor 200 and a storage unit of each memory. The data processor 200 executes the processes in accordance with instructions (search command, various write/read commands or the like) transmitted from the reader/writer 10. The modulator 211 executes modulation process upon reception of the processing result from the data processor 200 and then transmits the processing result, after the modulation process, to the reader/writer 10 via the antenna 230. Moreover, the data processor 200 comprises, as a characteristic of the present invention, a response controller 210 for controlling transmission of responses to thereby prevent the sending of a response until a request for repeated response is generated for the RFID tag 20 which has succeeded in sending of the response for the search command when the search command is received from the reader/writer 10. ISO/IEC 18000-6 Type B specification conformant tags have implemented this component as a function of data processor because this is a mandatory feature. The non-volatile memory 240 and the temporary memory 250 store and retrieve data in accordance with write and read operations of data executed by the data processor 200. The non-volatile memory 240 is in the state for receiving supply of necessary electrical power for operation by assuring the electrical power and is capable of holding the stored contents for a long period of time. The temporary memory 250 receives supply of electrical power with the rectifier 220 and therefore it can hold the stored contents for the period for operation by receiving the electrical power supplied with the rectifier 220.
The application 302 of the host computer 30 determines the start of a processing period (#201 of
(1) When a plurality of products with RFID tags are placed in a cart being moved with a belt conveyor or the like, the start timing is determined as the timing detected by a sensor in the case where the processing period is started in the application at the timing that the cart which has reached the predetermined location is detected with the sensor.
(2) In the case of an application where the processing period is started at the time that an operator inputs an instruction with manual operation, the start timing is determined as the timing at which the input of instruction by the operator is accepted.
(3) In the case of an application where the next process is started immediately after the preceding process has been completed until matching with the predetermined completing condition is attained, the start timing is determined as the timing at which an instruction for triggering start of the next process is detected.
When the start timing of processing period is determined (Yes in #201 of
The following method, for example, has been proposed as a method of generating the response control information.
(1) The time when generation of response control information is instructed by the application 302 is obtained from the system time as the response control information.
(2) A random number generated by the random number generating program is set as the response control information.
In this embodiment, an example in which the time in paragraph (1) is obtained first as the response control information will be explained. The generator 303 accesses, upon acceptance of an instruction for generating the response control information, to a timer (not illustrated) provided in the host computer 30, or to a server (not illustrated) for time distribution which is connected via the network 40 for mutual communication to obtain the time information at this time and defines the obtained time information as the response control information. In the case where the acquired time information is “AM 9:00 of Oct. 10, 2006”, such time information is set as the response control information. As an expression format of the time information, it is convenient that the elapsed time from the predefined base time can be used as response control information. In this embodiment, an example where the time and day indicated as an example are used directly will be utilized to simplify the explanation below.
Next, the application 302 sets the response control information generated by the generator 303 as a parameter, generates a command (hereinafter referred to as the “search instructing command”) for instructing detection of the RFID tag 20 existing in the communication-enabled range of the antenna 130, and transmits such command to the reader/writer 10 (#203 in
Upon reception of the processing result from the reader/writer 10 (#204 of
The application cooperating unit 102 of the reader/writer 10 acquires, upon reception of the search instructing command transmitted from the host computer 30 (#301 of
An example of the search command is shown in
The address area 502 indicates offset of a memory region of the non-volatile memory 240 of the RFID tag 10 for comparison of the value designated in the parameter area 503 with a value written in the offset position designated by the address area 502. The example does not contain data length of the parameter area 503 explicitly because the predetermined fixed size is assumed (for example, eight bytes). However, in the case of considering a parameter of variable length, the parameter length information may also be designated.
In the parameter area 503, the parameter (AM 9:00, Oct. 10, 2006) obtained from the search instructing command received from the host computer 30 is set as the eight bytes numerical number expressed by its decimal format “200610100900”. The numerical number expresses directly the time and date for easier understanding of contents of the invention. However, this parameter can be obtained from different sources and expressed in another format for easier processing in the computer.
The application cooperating unit 102 converts the generated search command into the signal which the RFID tag 10 can receive through the command transmitter 105 and transmitter 111 and thereafter transmits this signal as the radio wave from the antenna 130 (#303 of
The controller 101 determines the situation of response (#304 of
In the case where the response situation is “one-tag-response” (“one-tag-response” in #305 of
When the controller 101 receives a response for the DATA_READ command from the RFID tag 20 (#307 of
When the response from the RFID tag 20 for the search command is in the state of “collision” (“collision” in #305 of
When the response to the search command from the RFID tag 20 is in the “no-response” state (“no-response” in #305 of
The RFID tag 20 executes the demodulating process of the signal received with the demodulator 212, upon reception of the radio wave (including a command) transmitted from the reader/writer 10 via the antenna 2300 and also starts feeding of electrical power via the rectifier 220 for setting the RFID tag 20 to the condition being ready for operation (#410 of
The data processor 200 acquires the response control information 503 included in the search command in the case where the signal demodulated with the demodulator 212 is the search command (#402 of
The larger the number of RFID tags 20 existing in the communication-enabled range of the antenna 130 of the reader/writer 10 is, the higher the probability of collision of the responses from the RFID tag 20 for the search command becomes. When the collision occurs, the reader/writer 10 transmits the FAIL command to the RFID tag 20 in the communication-enabled range. When the RFID tag 20 receives the FAIL command, if it is in the ID state, the collision arbitration process is conducted to control transmission of response to the reader/writer 10 and to resolve the collision of responses (#405 of
Here, it is assumed that the RFID tag 20 having the tag ID of “ID0001” is allowed to send a response to the search command after the collision arbitration process.
The data processor 200 of RFID tag 20 transmits “ID0001” as its own tag ID 601 to the reader/writer 10 (#406 of
After transmission of the tag ID, the data processor 200 receives the command transmitted from the reader/writer 10 (#407 of
When the command received from the reader/writer 10 is the DATA_READ command (DATA_READ command in #407 of
When the response control information write command is received from the reader/writer 10 (Yes in #410 of
Thereafter, upon reception of the INITIALIZE command from the reader/writer 10 (INITIALIZE COMMAND IN #412 OF
As shown in
Next,
Since the response control information 503 (“200610100900”) of the search command is identical to the response control information 603 (“200610100900”) stored in the non-volatile memory 240, the RFID tag 20 having the tag ID “ID0001” determines that a response is not required and does not transmit a response to the reader/writer 10. Therefore, it is prevented that the RFID tag 20 having completed the normal response to the previous search command sends the response for the search command with the same response control information many times. As such, the transmission of responses for the search command can be adequately reduced.
Meanwhile, since the RFID tag 20 having the tag ID of “ID0002” does not yet complete the response for the search command, the response control information 603 remains as “000000000000”. Since the response control information 503 (“200610100900”) of the search command is different from the response control information 603 (“000000000000”) stored in the non-volatile memory 240, the response control unit 201 determines that the response is required for the search command and transmits the response for the search command to the reader/writer 10.
When the response for the search command is completed normally, content of the response control information 603 is changed to “200610100900” from “000000000000” as in the case of the RFID tag 20 having the tag ID of “ID0001”. Thereafter, the RFID tag 20 having the tag ID of “ID0002” does not send the response for the search command including the response control information 503 of “200610100900”.
These processes are repeated, as explained with reference to
Next, the process will be explained required for the situation where an RFID tag 20 receives another search command after all RFID tags have been completed to process to the previous search commands.
When the processing period is changed (Yes in #201 of
The reader/writer 10 having received the new search instructing command sets the parameter “20061010905” included in the search instructing command to the response control information 503 of the search command, then generates a search command with the response control information “20061010905” in the decimal format (#302 of
The RFID tag 20 compares, upon reception of the search command (#402 of
Moreover, when the normal response is completed for the new search command, the response control information 603 of the non-volatile memory 240 of RFID tag 20 is changed to “200610100905”. Accordingly, since the response for the search command is suspended as explained above while the search command setting “1200610100905” to the response control information 503 is valid, repeated response by the RFID tag 20 having completed the response for the new search command can be prevented.
In the embodiment explained above, an example of using the time information for the response control information has been explained, but a random number may also be used in place of the time information. In this case, a random number generator (not illustrated) for generating random numbers is provided in the host computer 30. The generator 30 generates a random number with the random number generator, upon reception of instruction for generation of the response control information and sets the generated random number as the response control information. The subsequent flow of the process will not be explained below in detail because these processes may be implemented by replacing the time information with the random number.
Moreover, any other method than using the time information or random number can be used if it can generate a different value whenever it is required, so long as it can be verified that the new response control information is same as or different from the previous one.
This embodiment explains in case of using ISO/IEC 18000-6 Type B specification conformant tags.
The application cooperating unit 102 of the reader/writer 10 acquires, upon reception of the search instructing command transmitted from the host computer 30 (#301 of
An example of the search command based on the ISO/IEC 18000-6 Type B specification is shown in
The address area 502 indicates offset of a memory region of the non-volatile memory 240 of the RFID tag 10 for comparison of the value designated in the data area 505 with a value written in the offset position designated by the address area 502. The example does not contain data length of the data area 505 explicitly because the predetermined fixed size is assumed (for example, four bytes). However, in the case of considering a parameter of variable length, the parameter length information may also be designated.
A mask area 504 contains BYTE MASK information for data matching, and in this example data “F0” in hexadecimal format is used.
In the data area 505, the parameter (“1156987662”) obtained from the search instructing command received from the host computer 30 is set as the four bytes numerical number expressed by its hexadecimal format “44F63B0E”. The numerical number is the elapsed time at the point of creating this command from the predefined base time. However, this parameter can be obtained from different sources and expressed in another format for easier processing in the computer.
A CRC area 506 contains an error detection code.
The application cooperating unit 102 converts the generated search command into the signal which the RFID tag 10 can receive through the command transmitter 105 and transmitter 111 and thereafter transmits this signal as the radio wave from the antenna 130 (#303 of
The controller 101 determines the situation of response (#304 of
In the case where the response situation is the “one-tag-response” (“one-tag-response” in #305 of
When the controller 101 receives a response for the DATA_READ command from the RFID tag 20 (#307 of
When the response from the RFID tag 20 for the search command is in the state of “collision” (“collision” in #305 of
When the response to the search command from the RFID tag 20 is in the “no-response” state (“no-response” in #305 of
The RFID tag 20 executes the demodulating process of the signal received with the demodulator 212, upon reception of the radio wave (including a command) transmitted from the reader/writer 10 via the antenna 230 and also starts feeding of electrical power via the rectifier 220 for setting the RFID tag 20 to the condition being ready for operation (#410 of
The data processor 200 acquires the response control information 503 included in the search command in the case where the signal demodulated with the demodulator 212 is the search command (#402 of
In the example shown in
The larger the number of RFID tags 20 existing in the communication-enabled range of the antenna 130 of the reader/writer 10 is, the higher the probability of collision of the responses from the RFID tag 20 for the search command becomes. When the collision occurs, the reader/writer 10 transmits the FAIL command to the RFID tag 20 in the communication-enabled range. When the RFID tag 20 receives the FAIL command, if it is in the ID state, the collision arbitration process is conducted to control transmission of response to the reader/writer 10 and to resolve the collision of responses (#405 of
Here, it is assumed that the RFID tag 20 having the tag ID of “ID0001” is allowed to send a response to the search command after the collision arbitration process.
The data processor 200 of RFID tag 20 transmits “ID0001” as its own tag ID 601 to the reader/writer 10 (#406 of
After transmission of the tag ID, the data processor 200 receives the command transmitted from the reader/writer 10 (#407 of
When the command received from the reader/writer 10 is the DATA_READ command (DATA_READ command in #407 of
When the response control information write command is received from the reader/writer 10 (Yes in #410 of
Thereafter, upon reception of the INITIALIZE command from the reader/writer 10 (INITIALIZE COMMAND IN #412 OF
As shown in
Next,
Since the response control information 503 (“44F63B0E”) of the search command is identical to the response control information 603 (“44F63B0E”) stored in the non-volatile memory 240, the RFID tag 20 having the tag ID “ID0001” determines that a response is not required and does not transmit a response to the reader/writer 10. Therefore, it is prevented that the RFID tag 20 having completed the normal response to the previous search command sends the response for the search command with the same response control information many times. In this manner, the transmission of responses for the search command can be adequately reduced.
Meanwhile, since the RFID tag 20 having the tag ID of “ID0002” does not yet complete the response for the search command, the response control information 603 remains as “00000000”. Since the response control information 505 (“44F63B0E”) of the search command is different from the response control information 603 (“00000000”) stored in the non-volatile memory 240, the response control unit 201 determines that the response is required for the search command and transmits the response for the search command to the reader/writer 10.
When the response for the search command is completed normally, content of the response control information 603 is changed to “44F63B0E” from “00000000” as in the case of the RFID tag 20 having the tag ID of “ID0001”. Thereafter, the RFID tag 20 having the tag ID of “ID0002” does not send the response for the search command including the response control information 505 of “44F63B0E”.
These processes are repeated, as explained with reference to
Next, the process will be explained required for the situation where an RFID tag 20 receives another search command after all RFID tags have been completed to process to the previous search commands.
When the processing period is changed (Yes in #201 of
The reader/writer 10 having received the new search instructing command sets the parameter “20061010905” included in the search instructing command to the response control information 505 of the search command, then generates a search command with the response control information “44F63B88” in the hexadecimal format (#302 of
The RFID tag 20 compares, upon reception of the search command (#402 of
Moreover, when the normal response is completed for the new search command, the response control information 603 of the non-volatile memory 240 of RFID tag 20 is changed to “44F63B88”. Accordingly, since the response for the search command is suspended as explained above while the search command setting “44F63B88” to the response control information 505 is valid, repeated response by the RFID tag 20 having completed the response for the new search command can be prevented.
In the embodiment explained above, an example of using the time information for the response control information has been explained, but a random number may also be used in place of the time information. In this case, a random number generator (not illustrated) for generating random numbers is provided in the host computer 30. The generator 30 generates a random number with the random number generator, upon reception of instruction for generation of the response control information and sets the generated random number as the response control information. The subsequent flow of processes will not be explained below in detail because these processes may be implemented by replacing the time information with the random number.
Moreover, any other method than using the time information or random number can be used if it can generate a different value whenever it is required, so long as it can be verified that the new response control information is same as or different from the previous one.
An elimination information storage unit 305 is provided in the storage unit 304. In the case that a random number is used for response control information or that a series of application processes are executed via a plurality of reader/writers 10 and it is required to execute the new search command for each reader/writer 10, a situation arises in which no response is sent for the search command to which a certain response should be sent if the same response control information is used.
In view of avoiding such a situation, the response control information which has been once generated is stored in the elimination information storage unit 305 and it is confirmed that, upon generation of the new response control information, the new response control information is not stored in the elimination information storage unit 305.
Accordingly, when it is requested, for example, to send a response for the search command whenever the RFID tag 20 passes the communication-enabled range of each antenna 130 of the reader/writers 10 on the situation that the processes are executed while the tag 20 is passing through a couple of reader/writers 10, a response can also be issued for the search command from the second reader/writer 10, because the response control information written when the response is issued to the first reader/writer 10 is never used as the response control information of the search command to the second reader/writer 10.
In the case of the passive type RFID tag 20, since the power supply for operating the processors and storage units is acquired particularly by generating a current using the radio transmission received from the reader/writer 10 as explained above, if the radio transmission is in bad condition, the response control information is sometimes not written normally due to insufficient supply of electrical power even when the response control information write command is received from the reader/writer 10. In such a case, there is no problem when any part of the response control information is not written at all, but it causes a problem if such response control information is stored partially. For example, in the case of the first embodiment, it is assumed here that when the response control information recorded as “200610100900” is attempted to be updated to the newly generated “200610100955”, only the last two letters happen to be updated resulting in the future time of “200610100955”. If the newly regenerated response control information happens to be changed thereafter to “200610100955”, the RFID tag 20 to which the response control information is erroneously written can no longer send a response for the new search command to which the response should be made. For example, in the case of the second embodiment, it is assumed here that when the response control information recorded as “44F63B88” is attempted to be updated to the newly generated “44F63C00”, only the first three bytes happen to be updated resulting in the future time of “44F63C88”. If the newly regenerated response control information happens to be changed thereafter to “44F63C88”, the RFID tag 20 to which the response control information is erroneously written can no longer send a response for the new search command to which the response should be made.
If writing of the response control information into the RFID tag 20 fails for some reasons, write error information is sometimes notified to the reader/writer 10. When such write error information has been received, the reader/writer 10 can recover from the write error state by instructing the RFID tag to write repeatedly the response control information up to the predetermined number of times as the upper limit.
Otherwise, when the response control information is generated regularly in the ascending or descending sequence like the timestamp as the above example, the response control information 603 written in the RFID tag 20 can be compared with the response control information 503 included in the search command. In the case where the response control information written in the RFID tag 20 is unreasonably larger or smaller in comparison with the response control information 503 included in the search command, the response control information of such RFID tag 20 can be assumed to be in the erroneous state. As explained above, the situation can be prevented that the RFID tag 20 does not send a response for the search command to which the response should be made because of the response control information which has been written erroneously by acquiring the response control information written erroneously to the RFID tag 20 beforehand, storing such information to the elimination information storage unit 305, checking whether the generated response control information happens to be equal with that stored in the elimination information storage unit 305 at the time of generating a new response control information, and then generating again a new response control information without using the generated response control information when the above response control information happens to be equal.
The host computer 30 stores the illegal response control information notified from the reader/writer 10 to the elimination information storage unit 305. Therefore, the response control information which is inadequately stored in the RFID tag 20 can be excepted when the generator 303 generates the response control information and it is also possible that the normal response can be made for the RFID tag 20 to which an erroneous response control information is stored.
In the first to fourth embodiments, an example that the response control information for determining whether the RFID tag 20 has normally completed the processing for the search command from the reader/writer 10 is generated in the host computer 30 has been explained, but it is also possible that such response control information is generated by the reader/writer 10.
In place of the generator 303 of the host computer 30 in the first to third embodiments, the reader/writer 10a is provided with a generator 103. Moreover, a host computer 30b comprises an instructor 307 in place of the generator 303. The host computer 30 does not generate the response control information and the instructor 307 instructs the reader/writer 10 to generate the response control information, upon detection in change of the processing period. The application cooperating unit 102 of reader/writer 10 instructs the generator 103 to generate the response control information, upon acceptance of the instruction to generate the response control information from the instructor 307 of host computer 30b. Thereafter, a search command is generated using the response control information generated by the generator 103. Explanation of the subsequent process is skipped because it is similar to that in the step #303 of
Here, it is more preferable that the response control information generated by the generator 103 of reader/writer 10a is notified to the host computer 30b and necessity for use of the generated response control information is inquired to the host computer 30b. Moreover, since the response control information of the same content may be generated by a plurality of reader/writers 30a in the case where a plurality of reader/writers 30a exist under the control of the host computer 30a and the situation may occur that no response is issued from the RFID tag 20 from which the response should be made when such response control information is used as the parameter 503 of the search command, it is preferable that the response control information generated by the reader/writer 10a is administrated by the host computer 30b in order to eliminate occurrence of such a state.
Moreover, even in the case where the reader/writer 10a generates the response control information, use of inadequate response control information can be prevented by combining the first to third embodiments.
In the first to fifth embodiments, contents of the information (parameter (response control information) 503 included in the search command) indicating that the normal response for the search command is completed are stored in the non-volatile memory 240 of the RFID tag 20. However, in recent years, with development in the electrical power saving technology, contents stored in the temporary memory 250 can be maintained for a longer period of time. In the case where a longer period of time can be acquired for maintaining the contents stored in the temporary memory 250 without any problem on the processes, contents of the information (parameter (response control information) included in the search command) 503 indicating that the normal response for the search command is completed may also be stored in the temporary memory 250, in addition to the non-volatile memory 240.
According to the present invention, a response can be sent effectively to the reader/writer from the RFID tag by preventing duplicate responses from the RFID tag once detected by the reader/writer at the time of later search commands for RFID tags existing within the communication-enabled range of the reader/writer.
The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-287523 | Oct 2006 | JP | national |
| 2007-238716 | Sep 2007 | JP | national |
