Registers – Systems controlled by data bearing records
Reexamination Certificate
2000-08-30
2002-12-31
Le, Thien (Department: 2876)
Registers
Systems controlled by data bearing records
C235S384000
Reexamination Certificate
active
06499656
ABSTRACT:
BACKGROUND OF THE INVENTION
THIS invention relates to a method and apparatus for the identification of objects, and in particular for the identification of a plurality of remote electronic identification tags by a reader using electromagnetic communication means.
Numerous different types of electronic tags, which are typically in the form of transponders, are attached to physical objects such as goods, equipment, people, animals and the like. These tags are programmed to contain identity data, which is used to electronically identify the tagged objects via interrogation by a reader. The read data is typically arranged to be transferred to a computer system for tallying and reading the identity of those objects which are in the interrogation area of the reader.
A large number of patents already cover the situation of a reader and a plurality of transponders with the communication between the reader and the transponders being based on acoustic or electromagnetic radiation principles. In most cases, the prior art protocol requires the transponders to have a unique identification number and the ability to receive and decode a transmission containing a data stream from the reader and match it to all or components of its unique identification number.
Another class of prior art is an identification system that needs neither a unique identity nor a multi-bit receiver and decoder for the transponder, but which relies on the reader communicating with the transponder at the correct time after it has finished its transmission, if the transponder was successfully identified. The communication can be single bit in format, and the message is communicated by the timing of the communication after the completion of transmission, the communication being as simple as disturbing the energising field from the reader at the correct instant. Such a system is described in South African patent 92/0039, which requires the reader and the transponder whose identity is being determined to be synchronised and to remain synchronised after communication has been completed so that the reader may respond at the correct time after the transmission has been completed.
A further category of prior art covers an identification system that uses a selection process to isolate a single transponder so that the transponder's data can be received without being corrupted by transmissions from other transponders. U.S. Pat. No. 5,751,570 describes such a system. A collision signal is initially sent by the reader to place all transponders in to a dead state. Each transponder calculates a random dead state after receiving the collision signal, during which they do not transmit their data. At the end of the dead state each transponder will transmit its data again. If the reader receives data from only one transponder it sends an occupied or busy signal which place, all the transponders except the one busy transmitting into an idle state. The transponders in the idle state no longer transmit data. After the reader has received the complete data from the individual transponders the reader transmits an acknowledge signal which places the identified transponder into a passive or idle state in which it ceases transmission of its data. The rest of the transponders in idle state are reactivated and they recalculate a random dead time. The steps above are repeated until all the transponders have been identified. The drawback of this system is that if the electromagnetic field is changed to send the busy signal, the changes in the electromagnetic field may cause the receiver to misread the data from the transponder because the transponder signal is very much smaller than the changes in the electromagnetic field
A similar system is described in U.S. Pat. No. 5,124,699, where changes in frequency are used to send signals to the transponders, Initially a frequency shift is sent to the transponders to start a selection procedure that will isolate an individual transponder. The transponders calculate a random delay after which they transmit a starting block. Due to the random delay, only a few transponders might transmit a starting block at the same time. When the reader receives a starting block it changes the transmitter frequency which causes the transponders not transmitting a starting block to go into a passive state. The remaining transponders transmit their unique code. If the reader detects that more than one transponder is transmitting its code then the reader signals an error by changing the transmitter frequency which causes these transponders to recalculate a random delay again and to follow the steps above. The transponders in the passive state remain so. This selection process will eventually yield an individual transponder. Once the reader has identified the individual transponder it is placed into a passive state by another frequency change which also causes the remaining unidentified transponders to restart the selection process again. This system requires complex tuned circuitry in the transponder so that the different frequencies can be detected
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of identifying objects by an interrogator, comprising the steps of:
transmitting an interrogation signal from the interrogator to the objects;
transmitting from each object to the interrogator an identification signal having predetermined indicator characteristics in response to the interrogation signal;
receiving the identification signals from the objects at the interrogator and substantially contemporaneously determining at the reader if any identification signal has been individually and correctly received on the basis of the indicator characteristics;
substantially contemporaneously transmitting from the interrogator a common re-transmit or interrupt signal in the event of any identification signal not being individually and correctly received; and
ceasing signal transmission from an object if that object completes its signal transmission without receiving an interrupt signal front the interrogator during such transmission.
Preferably, the method includes the step of temporarily suspending signal transmission from an object if that object is transmitting its identification signal at the time it receives the interrupt signal from the interrogator.
In a preferred form of the invention, the method comprises the further steps of continuing so to receive all identification signals at the interrogator, and to transmit the interrupt signals, until no further identification signal is individually and correctly received for a time period sufficient to ensure that all identification signals from objects have been individually and correctly received by the interrogator.
In one form of the invention, the method may comprise the steps of continuously transmitting the interrogation signal and transmitting the interrupt signals at a time interval which defaults to less than the average transmission time of a valid identification signal in the absence of the receipt of an identification signal at the interrogator.
Conveniently, the method includes the step of transmitting at random time intervals an identification signal from each object which has not ceased its signal transmission and allowing each object which has ceased its transmission to recommence transmission in response to a reset event.
The reset event may include the absence of or variation in the interrogation signal for a predetermined minimum time period.
Advantageously, the method further includes the steps of transmitting a disable signal from the interrogator, receiving the disable signal at at least one of the objects, and setting a memory element in the object preventing it, only after the object has ceased signal transmission, from responding to any subsequent interrogation signal for a minimum predetermined stand-off time period.
The method may include the still further steps of transmitting an enable signal from the interrogator, receiving the enable signal at at least one of the objects, and resetting the memory element
Hodson Trevor Meredith
Marsh Michael John Camille
Le Thien
Scully Scott Murphy & Presser
Trolley Scan (Proprietary) Limited
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