Note: Descriptions are shown in the official language in which they were submitted.
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IDENTIFICATION AND LOCATION OF RF TAGGED ARTICLES
This invention relates to system of maintaining the inventory of articles or
objects
provided with radio frequency (RF) transducers such as tags or transponders
containing
electronic codes for recognition and identification of the articles. Such
devices are commonly
known as radio frequency identification devices (RFID). More specifically,
this invention relates
to methods of employing radio frequency for spatial resolution of tags, RFID
tags and tags
activation devices. A RFID consists of a reader-interrogator and a plurality
of transponders; and
the latter are affixed on the objects or articles which are subject to
inventory and may be located
in a storage such as a warehouse.
RFID methods and systems provide the recognition of objects with
identification tags
affixed thereon. The process of tag recognition must be accomplished at high
speed and with
minimum error. In the process, it is necessary to determine the Electronic
Product Code (EPC)
that describes the article to which the tag is attached, and the tag location
or direction relative to a
reader. Some of the interrogators are provided for primarily reading the tag
codes while others
are only for searching for the directions of the tags. An interrogator
transmits a tag activation
signal for all the tags in a predetermined interrogation zone simultaneously.
It adjusts the
activation signal which has been sent in advance to the tags with known ID or
without ID codes
depending on the tag design. If the tag ID is known in advance, it will be
activated accordingly
such that the interrogator can read its tag electronic code with high level of
accuracy because
there are no other response signals from other tags. When a small number of
tags, for example,
one to five tags, without ID codes are activated, because of the differences
in electronic circuit
parameters, the tags are activated in an insignificant time lag. Furthermore,
the interrogator may
activate the tags repeatedly so as to increase the probability of accurate
recognition of the codes.
However, when a large number of tags are to be read by the reader, the
response tag signals reach
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the reader practically simultaneously which may result in failure to recognize
the objects with
adequate accuracy even in the case of tag signal processing with some of the
anti-collision
protocols. Miscellaneous tri-angular methods and reader multi-antenna design
have been
employed for resolving the above problem.
The RFID Handbook by Klaus Finkenzeller, Carl Hansen Verlag, Munich/FRG, 1999
outlines four methods of solving the problem of space, frequency, code and
time descriminations
in RFID.
U. S. Patents No. 6,600,443 and No.6,476,756 both to J. A. Landt, and
No.6,069,564 to
R. Hatano et al illustrate methods and systems tag reading and the
determination of its direction.
The Landt patents illustrate a method of tag signal structure analysis while
the Hantano et al
patent proposes a multi-directional RFID antenna for this purpose.
Canadian Patent No.2,447,975 to P. M. Eisenberg et al, and No.2,399,092 and
No.2,450,189 both to P. A. Sevcik et al describe aspects of the collection and
use of data
obtained by RFID tag interrogation, in particular, by comparing information
obtained through
interrogation of tags with the data recorded during repeated interrogation.
U. S. Patents No.6,317,028 to c. Valinlis; No.5,822,714 to R. T. Cato;
No.6,034,603 to
W. E. Steeves; and Canadian Patent No.2,447,975 to P. M. Eisenberg et al show
RFID systems
of tag recogniation for the case of a plurality of radio frequency
identification tags. To effectively
recognize tags, a number of other technical solutions assume a tag data base
as previously known
and perform its current status control through comparison of the read current
values with the data
of a base as shown in U. S. Patent No.5,822,714 to R. T. Cato.
U. S. Patent No.6,034,603 to W. E. Steeves also shows a method and system of
tag
construction with improved tag interference avoidance in which a tag includes
both a receiver
module and a processor, while the generation of a signal is decided as a
result of analysis of radio
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frequency activity.
U. S. Patent No.7,030,761 to R. Bridgelall et al shows a multi-resolution
object location
system and method for locating objects which employs a long range object
locator together with
a more precise RFID locator. The long range locator is used to first determine
the general
location of the object, and then the RFID locator further determines a more
accurate location of
the object.
U. S. Patent No.7,038,573 to G. Bann shows systems and methods for tracking
the
location of items within a controlled area having a plurality of RFID tags.
Vehicles configured to
transport the items being tracked are provided with two RFID interrogators to
obtain the location
of the vehicle.
U. S. Patent No.7,042,358 to S. E. Moore shows a method and apparatus for
tracking
items automatically in which a passive tag is used with remote sensing
antennas placed at each
remote location and a host computer communicates with the interrogators to
determine item
locations to an exacting measure.
U. S. Patent No.7,046,145 to W. Maloney shows RFID an object tracking and
control
system having a storage receptacle with a tray provided with an array of slots
for receiving ID
tags bearing touch memory devices. A computer-based controller detects the
absence or presence
and identity of ID tags disposed in the slots.
None of the above patents teach any RFID method and system possessing features
which
can perform recognition and locating functions of a plurality of objects as
well as reading the
codes and locating tags of both single decoding or working simultaneously with
large numbers of
articles under conditions of locating the inventory objects on a plane or in a
random volume with
minimization of errors caused by the reflection of signals form surrounding
surfaces.
Furthermore, the prior art patents fail to suggest, any RFID method of tag
recognition and
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location in an interrogator close zone - Fresnel Zone when the distance
between the tag and the
reader antenna is relatively small and comparable with the antenna aperture.
The principal object of the present invention is to provide recognition
systems with radio
frequency identification devices (RFID) and, more specifically, to provide
radio frequency
methods of three-dimensional tag selection, creation of tag activation devices
and their
algorithms as well as the tag design.
The read range of the reader is determined according to dimensions of an
interrogation
zone and a search starting point. The possible location of the tags is
selected in the form of a
small spatial domain namely a local interrogation zone. The interrogator
starts the transmission
fo the tag activation signals through at least two spatially separated
antennas. The time of each
signal transmission and delay ( or delays in case of more than two antennas
are employed )
between the signals is calculated in accordance with the tags assumed location
which is entered
into the interrogator memory. This transmits a time-spatial information
forming activating
signals would create a maximum of electromagnetic field intensity at the
position at which a tag
is supposed to be activated. The signals from different antennas should enter
the local
interrogation zone in phase. The signals are received by each one of the tags,
and only the tag for
which the interrogator signals are calculated and transmitted according to the
specific formulas,
will be activated. Since it is possible that tags situated close to the
antenna but not located within
a local interrogation zone may also receive activating signal of an intensity
large enough to
become activated, the duration of the activation signal and the number and
location of the
transmitting antennas are made variable.
The activated tag emits its own identification signal which carries the
information about
the individual tag code. This identification signal is received by the reader
and a tag code is
selected and entered into the reader memory according to the preliminary
calculated tag location.
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Following the assumed location of a tag has been selected, calculated, and
entered into the reader
memory, the next signal sequence transmission will be calculated and the
signals are transmitted
through the reader antennas, etc. The entire sequence is repeated for scanning
the entire
interrogation zone.
The invention possesses numerous benefits and advantages over known RFID
systems. In
particular, the invention permits the reduction of time of search and
recognition of tags when
there are a large number of tags to be recognized within a particular
interrogation zone. It can
locate each one of a plurality of objects or articles and increases the
probability of reading the
codes without error. Noise immunity is achieved due to the elimination of
false responses when
receiving signals are reflected from random surfaces such as the warehouse
walls, shelves,
adjacent articles, container surfaces, etc. One embodiment of the invention
can be used with
existing tags Generation l, 2 without any modifications of the existing
transponders, including
SAW tags. It may be used in a single channel, or two-channel, or multi-channel
systems. The
universal character of the system allows it to be used selectively either as a
mobile or a stationary
device, as well as a two dimensional or three dimensional space version.
The present invention resolves the complex problem in object location,
tracking and
recognition all in cases of a single decoding, as well as with a large number
of articles
simultaneously located in an inventory object location in diverse conditions;
and it is applicable
in a wide variety of fields in manufacturing, shipping or storage.
The RFID method and system of the present invention are based on the
implementation
of a tag activator for creating specific signals which perform tag
interrogation zone multi-step
scanning, selected transponder activation, and processing the transponder
signal by the reader
for:
-Determina.tion of the total interrogation zone coordinates and writing them
into the reader
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memory;
-Determination of local interrogation zone start point coordinates and writing
them into the
reader memory;
-Determination of the number of group of interrogator antennas and the number
and position for
each antenna in a group;
-Calculation of the number of transmission of activation signals;
-Calculation of activation signal parameters for each interrogator antenna in
a group for each
group of antennas for the assumed tag location, i.e. local interrogation zone;
-Creating signals for tag activation at the tag activator coder;
-Transmitting of signals by the first group of interrogator antennas;
-Transmitting of signals by the second group of interrogator antennas;
- The procedure of transmitting of signals repeats until the number of
transmission coincides with
the calculated in advance number of transmitting or signal form activated tag
received by the
reader;
-The selected tag signal has been received by a reader, then the tag
electronic code is retrieved
from a signal and memorized by the reader, and the reader memory keeps the tag
coordinates
which indicate the location of the object with a tag;
-If in the course of time determined by a search area range and no response
signal has been
received, then the following step of search is performed by shifting the local
interrogation zone
on the coordinate off one step, which is determined by the tag activator
resolution;
-The procedure of activation signals creation, transmitting and processing,
tag signal receiving is
repeated until the total interrogation zone is completely examined;
- Tag electronic codes, their location and other tag information are indicated
on the reader data
base and monitor.
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Figure 1 is a schematic layout of the location of the tags and antennas
transmitting the
first group of activating signals relating to the concept of tag activation
according to the present
invention.
Figure 2 is a schematic layout of the location of tags and antennas
transmitting the second
group of activating signals relating to the concept of tag activation
according to the present
invention.
Figure 3 is a graph showing the voltage path of the charging capacitor of a
tag relating to
the concept of selected tag activation according to the present invention.
Figure 4 is a graph showing the voltage path of the charging capacitor of a
tag relating to
the concept of all tags in the interrogation zone activation according to the
present invention.
Figure 5 is a schematic layout of the interrogator antennas transmitting the
activating
signals relating to the concept of selected tag activation according to the
present invention.
Figure 6 is a graph showing the activation signal relating to the concept of
two phase
charging according to the present invention.
Figure 7 is a schematic layout of the reader interrogation zone in the
Cartesian
coordinates in one embodiment according to the present invention.
Figure 8 is a graph showing the voltage path of the charging capacitor of a
tag and signals
from groups of antennas at the local interrogation zone according to the
present invention.
Figure 9 is a schematic block diagram of the two-antennas RFID interrogator
with tag
activator according to the present invention.
Figure 10 is a schematic block diagram of one array antenna RFID interrogator
with tag
activator according to the present invention.
With reference the drawings, the procedure of the activation of tags located
within an
interrogation zone is shown on Figures 1 and 2. A tag can be located randomly
in points, for
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example, from Point 1 to Point 4 within a local interrogation zone
representing tags I to 4
locating at these points on a flat surface in a two dimensional interrogation
zone. If a tag is
located at Point 2 and is transmitting a response signal, the signal is
received by the antennas Al
and A2 with time delays t12 and t23 as shown by positions 10 and 11 in Figure
1. Similarly, the
time delays received by a plurality of N number of antennas An will be t4n as
shown by position
12 in Figure 2. Whereas in a reversed situation, namely, if signals being
transmitted by antennas
Al and A2 in which the signal from Al is delayed by the time t12 will reach
tag 2 simultaneously
and in phase with an amplitude of the sum of two signals increased two times
in comparison with
separate signal. In the event when signals are transmitted by three antennas
with the proper
delays to provide in-phase signals arriving at the tag location, the amplitude
gain at the selected
tag is equal to 3. Thus, for any location in an interrogation zone for N
number of antennas sent
properly time delayed signals at a selected tag, the amplitude gain is equal
to N. At the same
time, for any other tag location in the interrogation zone, because of the
time delayed signals are
not in phase, the amplitude gain would be less than N. Actually, any
interrogation zone consists
of a plurality of local zones with a main maximum corresponding in phase
signal summing from
all antennas and auxiliary maximum of corresponding summing of signal from
some of the
antennas would result in a minimum of electromagnetic field intensity because
of signal
summing with opposite phases, and it would cause a false activation for some
tags not supposed
to be activated. For this reason, tag activation must be created in a two step
procedure using time-
spatial forming of activation signal to initialize selected tags in two or
three dimensional spaces.
Spatial forming is the process of using a group of different spatially
distributed antennas for each
sequential step in a process of each tag activation with the proper time
delays for in phase signal
summing at a local interrogation zone. Time forming is the process of using
activation signal in
the form of pulses having proper duration, transmitted outward by each group
of antennas for
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each sequential step in a process of each tag activation.
In order to realize the time forming of activation signals, the induced
voltage generated in
the tag by the effect of the alternating electromagnetic field from the
interrogator is rectified for
charging the tag capacitor to supply the power to the tag. The voltage path 13
of a tag capacitor is
shown in Figure 3 in which
S-charging phase is the phase of the voltage for charging selected tags;
Reading phase is the phase of transmitting signal contents electronic code by
the tag to
the reader; and
Discharging phase is the phase to set up voltage at the tag battery at zero.
The activation signal from the interrogator charges the tag batteries for any
tag located
inside an interrogation zone especially for interrogator with omni directional
antennas. Spatial
forming of activating signal creates a maximum electromagnetic field intensity
at the local
interrogation zone. However, in some cases, the electromagnetic field
magnitude is sufficiently
large to charge another tag located close to the interrogator tag, for
example, the tag 1 in Figure
1, especially when the tag to be activated is situated far enough form the
interrogator tag 4. To
avoid this situation, the time of S-charging is divided by intervals 0 - tl,
t1 - t2, ...., tm-1 - t,,, as
shown in Figure 4, and the interrogator antennas are united in groups A1 - A2 -
A3, A3 - A4 - An
etc., as shown in Figure 2. The number of groups is equal to the number of
time intervals.
The position of each group and time of activating signal transmitting is
chosen to provide
proportional distribution of electromagnetic field in the interrogation zone
for non-phased
signals. In this situation, even for the tag which is not to be activated and
nevertheless its tag
capacitor is charged due to a strong electromagnetic field during the time
interval tO - t 1;
however, at the next time interval tl - t2 it would receive much less induced
energy because the
antenna group positions and the antennas in the group have changed.
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As shown in Figure 4, the voltage path 14 of the capacitor in a selected tag
is at the time
t,,, of the end of the S-charging phase, and the tag is ready for its
electronic code transmission,
namely entering into the reading phase, meanwhile the voltage 14 at the
capacitor of the tag
which is not intended to be activated is lower than the sufficient level for
it to transmit the
information signal.
As shown in Figure 5, the fixed time delay between signals emitted outward by
the
interrogator antennas corresponds, for example, to any point on the hyperbolic
curve 15 for
antennas A1 and A2. Thus, only one local interrogation zone can be created by
the chosen proper
time delays for any interrogator antennas because there is only one point of
intersection of the
hyperbolic curves 15, 16, 17 and 18 for the antennas A 1- A2, A2 - A3, A3 -
A4, and A4 - A5.
When the S-charging phase, Reading phase and Discharging phase have terminated
for a
selected tag, some other tags may also still remain charged; however, their
level of their induced
voltage would be sufficient to activate the transmission of their signals to a
reader yet it may
cause unselected tag initiation while the next step of the selected tag
activation is in progress. To
avoid this undesirable situation, all tags in the interrogation zone are being
activated by the signal
as shown in Figure 6 during the A-charging phase i.e. all tags are being
charged, followed by
the discharging phase for the selected tag after its information signal has
been received by the
reader and the activation signal 19 for the selected has already advanced to
the A-charging phase.
As shown in Figure 7, the reader interrogation zone in shown in the Cartesian
coordinates
20 X, Y, and it explains the calculation of time delays between signals for
the activation of selected
tags. To facilitate estimations, antennas A 1 and A3 are placed symmetrically
relative to the
center of the coordinates, at which an antenna A2 is placed. In the general
case, antennas can be
placed on the surface within the X and Y coordinates randomly. The search
area, namely the
interrogation zone has, for example, the shape of a rectangle defined by four
points, points 24,
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25, 26, and 27. d is the distance between the antennas; t12 and t23 are time
delays between signals
emitted by antennas Al - A2; A2 - A3 accordingly to provide in phase
activation signal summing
at point 4; Rl, R2 and R3 are distances between antennas and the tag to be
activated at the
coordinates ( Xa, Y4 ).
Scanning of the interrogation zone is performed step-by-step starting from
point 25 with
the step size on the X axis, for example, determined by the range definition (
i.e. the direction
shown by the pointer ). To calculate the parameters of the activating signals
and the delay times
relative to each other, the following equations are used:
R1 =-ir (X4+ d)2 +(Y4)2,
R2(X4 )2 +(Y4)2, (1)
R3(X4-d)2+(Y4)2,
t12=(Rl-R2)/C; t23=(R2-R3)/C, (2)
where C is a signal propagation velocity in the given environment.
To activate a tag in the three dimensional coordinates, the fourth antenna
should be place
outside of the coordinate plate X, Y.
Figure 8 shows the sequence of activating signals from the interrogator
antennas at the
local interrogation zone, where the activating signals 28, 29, 30 and 31
represent an amount of
separate antenna signals as the group signals of antennas Al-A2-A3, A3-A4-A5,
A1-A3-A5, and
A 1-A4-A5 accordingly in the form of pulses with RF carrier. Each activating
signal 28 to 31 has
the same amplitude and limited duration equal to time interval ot designated
by the reference
numeral 47 and displaced for same time et.
A block diagram of an embodiment of the RFID interrogator according to the
present
invention is shown in Figure 9. The interrogator includes a RFID reader 44 and
a tag activator 45
which is operable for activating the transponder of the tag. The reader 44 is
operable to receive
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the information signal from the tag through its antenna 32. The information is
received by a
receiver 33 and is recorded and analyzed by a signal processor 34. A
controller 35 in
combination with the signal processor 34 controls the transmission and
reception of the
information which is recorded and stored in a data base 36 supervised by a
monitor 37 for
displaying the digital, text and graphic information about the transponder and
the code and the
location of the tag. The tag activator 45 has a plurality of antennas Al, A2,
A3 through An
operable for emitting the activation signals to the tags. A tag activator
controller 41 calculates the
activating signal parameters for the creation of the signals by an activation
signal former 42. The
activation signal former 42 creates the activating signals with the proper
parameters namely,
frequency, amplitude, and duration for transmission through a transmitter 43
and compensated
delay lines 40 which provide the proper delays for each signal in the antenna
outputs. The tag
activator controller 41 also controls the group of antennas in accordance with
a rule of the tag
located in the interrogation zone. The tag activator antennas A1 through An
may be operable
with a controlled directivity pattern so as to avoid false activation of the
tag and to ensure noise
immunity.
A second embodiment of the system of the present invention is shown in Figure
10 which
utilizes the same antenna for transmitting the activating signals to the tag
as well as receiving the
tag information from the latter. A dual directional coupler 46 is provided
between each one of the
compensated delay lines 40 and its associated antennas A1 through An. The dual
directional
couplers 46 operate to transmit activation signals from the tag activator 45
outward to receive the
tag signals as well as to provide power to the tag transmitter 43. The dual
directional couplers 46
also uncouple the transmitter 43 and receiver 33 and the compensated delay
lines 40 such that the
antennas A1 through An may alternately broadcast the activation signals to the
tag and to receive
through the receiver 33 the information data signals from the tag for storage
in the data base 36.
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It is to be understood that variations and modifications of the present
invention can be
made without departing from the scope of the invention. It is also to be
understood that the scope
of the invention is not to be interpreted as limited to the specific
embodiments disclosed herein,
but only in accordance with the appended claims when read in the light of the
foregoing
disclosure.
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