Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1998-09-25
2001-03-06
Tokar, Michael (Department: 2819)
Communications: electrical
Selective
Interrogation response
C340S010300, C342S164000
Reexamination Certificate
active
06198381
ABSTRACT:
INTRODUCTION AND BACKGROUND
THIS invention relates to radio frequency (RF) electronic identification systems comprising an interrogator and a plurality of transponders. The invention more particularly relates-to operational modes for transponders forming part of such a system.
A known system of the aforementioned kind includes a reader comprising a transmitter for transmitting an RF energizing signal to the transponders and a receiver for receiving a response signal from the transponders. A microprocessor in the reader identifies a particular transponder by identification code data modulated on the response signal by the transponder when in a normal operational mode. Upon receipt of the data by the reader and thus upon identification of the transponder, the reader transmits a first signal to the transponder to switch it to a catnap mode wherein it no longer is responsive and thus stops responding to the interrogation signal, even while still being energized. After energization of the transponder has been removed for a period longer than a short reset period (typically shorter than 2 to 10 seconds) the transponder reverts to the normal operational mode, wherein it will again respond with identification code data upon being energized.
The aforementioned known transponders are also adapted to be switched from the operational mode to a sleep mode upon receipt of a second signal from the reader. When so switched, the transponders internal clock is stopped and it remains in this mode wherein it is not responsive to any signal for a period as long as an internal capacitor providing the transponder with power, remains charged. It will be appreciated that this period is not of a predictable length, but is dependent on the discharge rate of the capacitor. which rate in turn is dependent on various other variables.
Other disadvantages of the mode of operation described hereinbefore and which is charactefised by the rapid reset from the catnap mode to the normal operational mode, are that scattering and reflections of the interrogation signal may lead to multiple readings of a single transponder; and that there is no method of controlling misreading of transponders, so that transponder reading or interrogation has to be performed under strictly controlled conditions. Furthermore, once the transponder has switched to the aforementioned sleep mode, it cannot be switched to the normal operational mode and it will only revert to the normal operational mode after elapse of the aforementioned period.
OBJECT OF THE INVENTION
Accordingly, it is an object of the present invention to provide an alternative electronic identification system, transponder and a method of operating an identification system with which the applicant believes the aforementioned disadvantages may at least be alleviated.
SUMMARY OF THE INVENTION
According to the invention there is provided an electronic identification system including
at least one reader;
a plurality of transponders to be read by the at least one reader;
each transponder having a first or normal operational mode wherein it, in response to an interrogation signal from said at least one reader, transmits a code to the reader; and a second or monitor mode wherein it is still sensitive and responsive to signals from said at least one reader, but wherein it does not transmit the code;
said at least one reader being adapted to cause a transponder of which the code is received, to switch from said first mode to the second mode by transmitting a first signal to the transponder;
the transponder while being in the second mode being sensitive to a second signal and responsive upon receipt of the second signal to reset to the first mode.
In one embodiment of the invention the transponder, when in the second mode and whether energized or not, remains in the second mode until the second signal is received.
In another embodiment, the transponder may be arranged to remain in the second mode for a predetermnined period, after which it automatically resets to the first mode, if by then the second signal has not yet been received by the transponder.
The invention also includes within its scope a transponder for use in an electronic identification system including at least one reader and a plurality of transponders to be read by the at least one reader, the transponder including:
a controller having a first mode wherein it, in response to an interrogation signal from said at least one reader, causes a code to be transmitted to the reader, and a second mode wherein it is still sensitive and responsive to signals from said at least one reader, but wherein it does not cause the code to be transmitted;
the controller being responsive to a first signal from said reader by switching from said first mode to said second mode; and
the controller also being responsive to a second signal from said at least one reader by switching from said second mode to said first mode.
In one embodiment of the transponder, the controller when in the second mode and whether the transponder is energized or not, remains in the second mode until the second signal is received.
In another embodiment, the controller may be adapted to remain in the second mode for a predetermined period after which it automatically resets to the first mode, if by then the second signal has not yet been received from said at least one reader.
The predetermined time period may be programmable and may be in the order of 15 minutes to 30 minutes.
Also included within the scope of the present invention is a method of operating an electronic identification system including at least one reader and a plurality of transponders, the method including the steps of:
transmitting by means of said reader an interrogation signal to the transponders which are in a first or normal operational mode;
receiving from a transponder a response signal;
transmitting a first signal to said transponder to cause the transponder to switch from the first mode to a second or monitor mode
causing the transponder in the second mode still to be responsive to signals from the reader, but to cease transmitting the response signal; and
transmitting a second signal to said transponder to cause the transponder to switch from said second mode to said first mode.
In one embodiment the method may include the step of causing the transponder, when in the second mode and whether energized or not, to remain in the second mode until the second signal is received.
In another embodiment, the method may include the steps of causing the transponder to remain in the second mode for a predetermined time period after which the is caused automatically to switch to the first mode, if the second signal has not been received by then.
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U.S. Ser. No. 09/138,560 filed on Aug. 24, 1998.
U.S. Ser. No. 09/143,711 filed on Aug. 28, 1998.
Kruger Johan Dawid
Turner Christopher Gordon Gervase
Data Investments Limited
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Jeanglaude Jean B.
Tokar Michael
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