Multiple tag reading system

• US 6,538,564 B1
• Filed: 06/15/1999
• Issued: 03/25/2003
• Est. Priority Date: 01/17/1997
• Status: Expired due to Term

• Current Assignee: Tagsys SA
• Original Assignee: Integrated Silicon Design Pty Ltd. (Thales SA)
• Inventors: Cole, Peter Harold
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Brown, Vernal U
• Application Number:
  US09/319,987
• Time in Patent Office: 1,379 Days
• Field of Search: 340/10.4, 340/10.3, 340/825.54, 340/10.2, 340/825.2, 340/10.41, 340/10.1
• US Class Current: 340/10.4
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• 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 7/10039 interrogator driven, i.e. synchronous

Abstract

A system is provided for processing articles in a warehousing or merchandising operation wherein information bearing electronically coded labels are attached to the articles to be processed. The system uses the principle of electromagnetic communication in which an interrogator containing a transmitter generates an electromagnetic signal which is transmitted to electronic labels containing label receiving antennas. The electronic labels are attached to articles as they are processed. Each label antenna receives a proportion of the transmitted energy and operates a reply generation circuit connected either to the label receiving antenna or a separate label reply antenna with the result that an information bearing electromagnetic reply signal is radiated by the label.

Claims

1. A label reading system including:

an interrogator including a transmitter for generating an interrogation signal and a receiver for detecting and decoding a reply signal;

an interrogation field creation means including a transmitter antenna connected to said transmitter for generating from said interrogation signal an electromagnetic interrogation field through which an object possessing a code responding label may pass;

said code responding label including a label receiving antenna for receiving from said interrogation field a label interrogation signal, means for generating label reply signals and means for generating from said label reply signals an electromagnetic reply field;

said label reply signals being generated intermittently by the label at intervals which are timed within the label;

said code responding label further including means for detecting a label excitation level provided by said interrogation field at said label, and means for providing an encoded indication of said label excitation level in said label reply signals;

a receiver antenna connected to said receiver for receiving said reply signals from said reply field;

said receiver including means for detecting starting and stopping times of said reply signals; and

said interrogator providing a timing signal to the labels upon detecting that a reply signal or an overlapping series of reply signals has just ceased.

2. A label reading system according to claim 1 wherein a plurality of labels is simultaneously present in the interrogation field.

3. A label reading system according to claim 2 wherein said timing signal to the labels acts as a time marker in terms of which subsequent signals to labels are interpreted by said labels.

4. A label reading system according to claim 3 wherein said timing signal becomes part of a structured end of reply signal containing additional information.

5. A label reading system according to claim 4 wherein said additional information includes the encoded indication of said label excitation level that was present in the label reply most recently received by said receiver.

6. A label reading system according to claim 1 wherein said intermittent generation of replies by a label is suspended within a label that receives an end of reply signal from the interrogator a predetermined time after completing its reply.

8. A label reading system according to claim 4 wherein the label stores the last label excitation level detected by that label.

9. A label reading system according to claim 8 wherein said intermittent generation of replies by a label is suspended by a label which receives a structured end of reply signal containing an encoded label excitation level which matches the label excitation level stored in the label.

10. A label reading system according to claim 4 wherein command signals to the labels, signals transmitted after an end of reply signal, or signals transmitted within a structured end of reply signal vary characteristics of the label reply signal.

11. A label reading system according to claim 10 wherein said characteristics include duration and timing of the label reply signal, spacing between successive label reply signals, ceasing transmission of a label reply signal, resuming transmission of a label reply signal and adopting a predetermined initial condition.

12. A label reading system according to claim 1 wherein a signal transmitted after an end of reply signal indicates successful decoding within said interrogator of said reply signal.

13. A label reading system according to claim 1 wherein a signal transmitted after an end of reply signal indicates unsuccessful decoding within said interrogator of said reply signal.

14. A label reading system according to claim 13 wherein an unsuccessful decoding signal causes the label which has just completed its reply to resume intermittent generation of replies.

15. A label reading system according to claim 2 wherein a label is adapted to draw energy from said interrogation field.

16. A label reading system according to claim 11 wherein said interrogator includes means for recording an average proportion of time for which labels reply signals are detected compared with a time for which no label reply signals are detected.

17. A label reading system according to claim 13 wherein said interrogator includes means for comparing a duration during which a label reply signal or an overlapping sequence of label reply signals is detected with a known duration of a single label reply signal.

18. A label reading system according to claim 13 wherein said labels encode their replies by phase modulation of a sub-carrier signal, said interrogator includes means for analyzing, during each interval in which a label reply signal is detected, variation in amplitude of the recovered label reply sub-carrier signal, and a judgment of correct decoding made by said interrogator requires that said variation in amplitude does not exceed a predetermined value.

19. A label reading system according to claim 1 in which the end of reply signal is achieved via a substantial reduction in amplitude of said interrogation signal for a time which is short relative to the energy storage time of a circuit contained in the associated code responding label.

20. A label reading system according to claim 1 wherein the label includes DC energy storage means for sustaining operation of the label between periods of reduction of the interrogation power supply signal, said operation including transfer of information from the interrogator to the label.

21. A label reading system according to claim 20 wherein the label includes further DC storage means, and volatile but relatively low power consuming information storage circuits, which preserve information generated during operation of the label, and in particular whether or not it has ceased to offer its intermittent replies, and the information defining the interval at which those replies are offered, for a period which is greater than the duration of several complete label reply signals, even if no interrogator power is available therein.

22. A label reading system according to claim 1 wherein said interrogation field creation means includes a plurality of transmitter antennas, said transmitter antennas being arranged to create in one region a plurality of spatial directions of magnetic field and wherein two of the transmitter antennas are in the form of loops which intersect at an angle along a line of intersection falling within the interrogation field.

23. A label reading system according to claim 1 wherein said interrogation field creation means includes a plurality of transmitter antennas, each one of said plurality of antennas being connected to set the transmitter for a time sufficient for receiving just one label reply signal.

24. A label reading system according to claim 23 wherein a plurality of antennas is connected to said transmitter in a sequence which is varied to avoid synchronism between the interval between offerings of a label reply signal with an interval which establishes the cycle of connection of the interrogation antennas.

25. A label reading system according to claim 1 wherein said label receiving antenna forms part of a resonant circuit having a resonant frequency which is adjusted in response to an interrogator command.

7. A label reading system according to claim 7 wherein said suspension takes place before the reply signal from the label has been decoded by the interrogator.

26. A label reading system including:

an interrogator including a transmitter for generating an interrogation signal and a receiver for detecting and decoding a reply signal;

an interrogation field creation means including a transmitter antenna connected to said transmitter for generating from said interrogation signal an electromagnetic interrogation field through which an object possessing a code responding label may pass;

said code responding label including a label receiving antenna for receiving from said interrogation field a label interrogation signal, means for generating a label reply signal and means for generating from said label reply signal an electromagnetic reply field;

a receiver antenna connected to said receiver for receiving said reply signal from said reply field; and

said interrogation field creation means including a plurality of interrogation transmitter antennas, said interrogation transmitter antennas being connected to said transmitter in sequence and the sequence in which the plurality of interrogation transmitter antennas is connected to said transmitter being varied to avoid synchronism between the interval between offerings of a label reply signal with an interval which establishes the cycle of connection of the interrogation transmitter antennas.

27. A label reading system according to claim 26 wherein the sequence in which the plurality of antennas is connected to said transmitter is varied in a substantially random manner.

28. A label reading system including:

an interrogator including a transmitter for generating an interrogation signal and a receiver for detecting and decoding a reply signal;

an interrogation field creation means including a transmitter antenna connected to said transmitter for generating from said interrogation signal an electromagnetic interrogation field through which an object possessing a code responding label may pass;

said code responding label including a label receiving antenna for receiving from said interrogation field a label interrogation signal, means for generating a label reply signal and means for generating from said label reply signal an electromagnetic reply field;

a receiver antenna connected to said receiver for receiving said reply signal from said reply field; and

said interrogation field creation means including a plurality of transmitter antennas, said transmitter antennas being arranged to create in one region a plurality of spatial directions of magnetic field and two of the transmitter antennas being in the form of loops which intersect at an angle along a line of intersection falling within the electromagnetic interrogation field.