Tag communication device and tag communication method

• US 8,334,754 B2
• Filed: 03/17/2008
• Issued: 12/18/2012
• Est. Priority Date: 06/01/2007
• Status: Active Grant

• Current Assignee: Omron Corporation
• Original Assignee: Omron Corporation
• Inventors: Kasai, Hirokazu, Kawai, Takehiro
• Primary Examiner(s): Bugg, George
• Assistant Examiner(s): NWUGO, OJIAKO K
• Application Number:
  US12/602,411
• Publication Number:
  US 20100214073A1
• Time in Patent Office: 1,737 Days
• Field of Search: 3405721-5729, 340 51- 56, 340 101- 106, 235375-385, 455 73- 88
• US Class Current: 340/10.4
• CPC Class Codes: G01S 13/38 wherein more than one modulation frequency is used
• CPC Class Codes: G01S 13/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10435 the interrogation device being positioned close to a conveyor belt or the like on which moving record carriers are passing conveying in accordance with bodily destination marks, see B65G47/46, sorting of objects carrying identity markings, see B07C5/34

Abstract

To improve communication between tags by causing a mobile object having a RFID tag attached to transmit an interrogating wave only when moving in a communication range to reduce power consumption and prevent occurrence of tag confusion. By acquiring two Doppler signals from 2-frequency transmission waves (CW) with different frequencies and respective reflected waves and detecting phase difference from the Doppler signals, a cargo (21A) is detected to be moving in the communication range (A). Only when the movement is detected, a reader-writer (1A) transmits the interrogating wave (RW).

Claims

1. A tag communication device for performing wireless communication with an RFID tag by transmitting an interrogating wave from an antenna to a mobile object with the RFID tag attached in a predetermined communication range, the tag communication device comprising:

Doppler measurement means for obtaining a Doppler signal for every frequency from transmission waves with a plurality of frequencies and reflected waves thereof;

phase difference detection means for detecting a phase difference of the Doppler signals of two frequencies of the Doppler signals for every frequency; and

communication control means for controlling the transmission of the interrogating wave so as to transmit the interrogating wave when the phase difference is detected by the phase difference detection means, and so as not to transmit the interrogating wave when the phase difference is not detected by the phase difference detection means.

2. The tag communication device according to claim 1, further comprising:

stop tag detection means for detecting presence of reception of a response wave with respect to the interrogating wave transmitted from the antenna when the phase difference is not detected by the phase difference detection means, and detecting that a stopped RFID tag is present in the predetermined communication range when the response wave is received;

wherein

the communication control means stops the transmission of the interrogating wave after the detection by the stop tag detection means.

3. The tag communication device according to claim 2, further comprising:

distance calculating means for calculating a distance between the mobile object and the antenna from the phase difference detected by the phase difference detection means; and

transmission power adjustment means for adjusting transmission power of the interrogating wave during the wireless communication according to the distance calculated by the distance calculation means.

4. The tag communication device according to claim 1, further comprising:

tagless movement detection means for detecting presence of reception of a response wave with respect to the interrogating wave transmitted from the antenna after the phase difference is detected by the phase difference detection means, and detecting that the mobile object without the RFID tag attached moved in the predetermined communication range when the response wave is not received;

wherein

the communication control means stops the transmission of the interrogating wave after the detection by the tagless movement detection means.

5. The tag communication device according to claim 1, further comprising:

distance calculating means for calculating a distance between the mobile object and the antenna from the phase difference detected by the phase difference detection means; and

transmission power adjustment means for adjusting transmission power of the interrogating wave during the wireless communication according to the distance calculated by the distance calculation means.

6. The tag communication device according to claim 1, further comprising communication abnormality detection means for determining as a communication abnormality when the phase difference is detected by the phase difference detection means and the response wave is not received from the RFID tag.

7. The tag communication device according to claim 1, wherein

the antenna is a scan antenna, including a plurality of antenna elements, for scanning a beam of the transmission wave;

the device including scan antenna control means for controlling an orientation of the transmission wave based on a scan angle of the scan antenna;

the communication control means acquires the scan angle of the scan antenna upon detection when the phase difference detection means detects the phase difference, and sets a directional angle of the interrogating wave according to the scan angle and transmits the interrogating wave; and

the device further includes movement direction detection means for detecting a movement direction of the mobile object based on a transition of the directional angle.

8. The tag communication device according to claim 1, wherein the communication control means transitions a directional angle of the interrogating wave according to a movement direction detected by the movement direction detection means.

9. A tag communication device for performing wireless communication with an RFID tag by transmitting an interrogating wave from an antenna to a mobile object with the RFID tag attached in a predetermined communication range, the tag communication device comprising:

first Doppler measurement means for obtaining a first Doppler signal from a transmission wave with a first frequency and a reflected wave thereof;

second Doppler measurement means for obtaining a second Doppler signal from a transmission wave with a second frequency different from the first frequency and a reflected wave thereof;

phase difference detection means for detecting a phase difference between the first Doppler signal and the second Doppler signal; and

communication control means for controlling the transmission of the interrogating wave so as to transmit the interrogating wave when the phase difference is detected by the phase difference detection means, and so as not to transmit the interrogating wave when the phase difference is not detected by the phase difference detection means.

10. A tag communication method for performing wireless communication with an RFID tag by transmitting an interrogating wave from an antenna to a mobile object with the RFID tag attached in a predetermined communication range, the tag communication method comprising the steps of:

a Doppler measurement step for obtaining a Doppler signal for every frequency from transmission waves with a plurality of frequencies and reflected waves thereof;

a phase difference detection step for detecting a phase difference of the Doppler signals of two frequencies of the Doppler signals for every frequency; and

communication control step for controlling the transmission of the interrogating wave so as to transmit the interrogating wave when the phase difference is detected by the phase difference detection step, and so as not to transmit the interrogating wave when the phase difference is not detected by the phase difference detection step.

11. The tag communication method according to claim 10, further comprising the step of:

a stop tag detection step for detecting presence of reception of a response wave with respect to the interrogating wave transmitted from the antenna when the phase, difference is not detected by the phase difference detection step, and detecting that a stopped RFID tag is present in the predetermined communication range when the response wave is received;

wherein

the communication control step stops the transmission of the interrogating wave after the detection by the stop tag detection means.

12. The tag communication method according to claim 11, further comprising the steps of:

a distance calculating step for calculating a distance between the mobile object and the antenna from the phase difference detected by the phase difference detection step; and

a transmission power adjustment step for adjusting transmission power of the interrogating wave during the wireless communication according to the distance calculated by the distance calculation step.

13. The tag communication method according to claim 10, further comprising the step of:

a tagless movement detection step for detecting presence of reception of a response wave with respect to the interrogating wave transmitted from the antenna after the phase difference is detected by the phase difference detection step, and detecting that the mobile object without the RFID tag attached moved in the predetermined communication range when the response wave is not received;

wherein

the communication control step stops the transmission of the interrogating wave after the detection by the tagless movement detection step.

14. The tag communication method according to claim 10, further comprising the steps of:

a distance calculating step for calculating a distance between the mobile object and the antenna from the phase difference, detected by the phase difference detection step; and

a transmission power adjustment step for adjusting transmission power of the interrogating wave during the wireless communication according to the distance calculated by the distance calculation step.

15. The tag communication method according to claim 10, further comprising the step of:

a communication abnormality detection step for determining as a communication abnormality when the phase difference is detected by the phase difference detection step, and the response wave is not received from the RFID tag.

16. The tag communication method according to claim 10, wherein

the antenna is a scan antenna, including a plurality of antenna elements, for scanning a beam of the transmission wave;

the method includes a scan antenna control step for controlling an orientation of the transmission wave based on a scan angle of the scan antenna;

the communication control step acquires the scan angle of the scan antenna upon detection when the phase difference is detected in the phase difference detection step, and sets a directional angle of the interrogating wave according to the scan angle and transmits the interrogating wave; and

the method further includes detecting a movement direction of the mobile object based on a transition of the directional angle.

17. The tag communication method according to claim 10, wherein the communication control step transitions a directional angle of the interrogating wave according to a movement direction detected by the movement direction detection.

18. A tag communication method for performing wireless communication with an RFID tag by transmitting an interrogating wave from an antenna to a mobile object with the RFID tag attached in a predetermined communication range, the tag communication method comprising the steps of:

a first Doppler measurement step for obtaining a first Doppler signal from a transmission wave with a first frequency and a reflected wave thereof;

a second Doppler measurement step for obtaining a second Doppler signal from a transmission wave with a second frequency different from the first frequency and a reflected wave thereof;

a phase difference detection step for detecting a phase difference between the first Doppler signal and the second Doppler signal; and

a communication control step for controlling the transmission of the interrogating wave so as to transmit the interrogating wave when the phase difference is detected by the phase difference detection step, and so as not to transmit the interrogating wave when the phase difference is not detected by the phase difference detection step.