U.S. patent application number 10/904635 was filed with the patent office on 2005-05-05 for system and method for selective communication with rfid transponders.
This patent application is currently assigned to ZIH CORP., A DELAWARE CORPORATION WITH ITS PRINCIP. Invention is credited to Gawelczyk, Robert, Hohberger, Clive P., Tsirline, Boris Y..
Application Number | 20050092838 10/904635 |
Document ID | / |
Family ID | 32961158 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092838 |
Kind Code |
A1 |
Tsirline, Boris Y. ; et
al. |
May 5, 2005 |
System and Method for Selective Communication with RFID
Transponders
Abstract
A system having an RFID transceiver is adapted to communicate
exclusively with a single RFID transponder located in a
predetermined confined transponder target area. The system includes
a magnetic coupling device comprising a magnetic flux generator
responsive to a radio frequency input signal and a magnetic field
pattern former. The pattern former is configured to collect flux
produced by the flux generator and to form a field pattern in the
location of the transponder target area. The system establishes, at
predetermined transceiver power levels, a mutual magnetic coupling
which is selective exclusively for a single transponder located in
the transponder target area.
Inventors: |
Tsirline, Boris Y.;
(Libertyville, IL) ; Hohberger, Clive P.;
(Highland Park, IL) ; Gawelczyk, Robert; (Chicago,
IL) |
Correspondence
Address: |
BABCOCK IP LLC
24154 LAKESIDE DRIVE
LAKE ZURICH
IL
60047
US
|
Assignee: |
ZIH CORP., A DELAWARE CORPORATION
WITH ITS PRINCIP
3 Gorham Road
Hamilton
BM
|
Family ID: |
32961158 |
Appl. No.: |
10/904635 |
Filed: |
November 19, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10904635 |
Nov 19, 2004 |
|
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|
10249039 |
Mar 11, 2003 |
|
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6848616 |
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Current U.S.
Class: |
235/449 ;
340/572.1 |
Current CPC
Class: |
G06K 7/0008 20130101;
G06K 7/087 20130101; G06K 17/0025 20130101 |
Class at
Publication: |
235/449 ;
340/572.1 |
International
Class: |
G06K 007/08 |
Claims
What is claimed is:
1. A method of establishing communication between a transceiver and
a single RFID transponder located in a predetermined confined
transponder target area, comprising: generating a magnetic flux
field which varies in response to a radio frequency input signal;
and collecting and forming said magnetic field pattern in the
location of said transponder target area; and establishing at
predetermined power levels of the transceiver a mutual magnetic
coupling which is selective exclusively for a single transponder
located in said transponder target area.
2. The method defined by claim 1 including locating in said
magnetic flux field a ferrite structure having a gap, said field
pattern being formed within and adjacent to said gap.
3. The method defined by claim 1 including transporting a web of
labels through said target area, at least some of which labels have
an RFID transponder, and wherein said method includes printing on
said labels.
4. The method defined by claim 1 including suppressing electric
fields associated with said generating of said magnetic flux field,
which fields would otherwise reach said target area.
5. A magnetic coupling device, comprising: a coil having a first
side and a second side; a magnetic field pattern former; and the
magnetic field pattern former covering the first side of the coil
and at least a portion of the second side of the coil.
6. The magnetic coupling device of claim 5, wherein the coil is
formed as at least a first trace on a printed circuit board.
7. The magnetic coupling device of claim 5, wherein the magnetic
field pattern former has a magnetic permeability of at least
20.
8. The magnetic coupling device of claim 5, wherein the magnetic
field pattern former is ferrite.
9. The magnetic coupling device of claim 8, wherein the ferrite is
flexible and the ferrite is applied to cover the first side of the
coil, around at least a first edge and at least a portion of a
second side of the coil.
10. The magnetic coupling device of claim 9, wherein the portion of
the second side of the coil that is covered by the ferrite is at
least 30 percent.
11. The magnetic coupling device of claim 5, further including a
first RF shield covering a first side of the coil.
12. The magnetic coupling device of claim 11, wherein the first RF
shield has a loop shape with an open circuit.
13. The magnetic coupling device of claim 11, wherein the first RF
shield is coupled to an electrical ground.
14. The magnetic coupling device of claim 11, further including a
second RF shield covering a second side of the coil.
15. The magnetic coupling device of claim 6, further including a
first RF shield covering the first trace; the first RF shield
formed as a second trace on the printed circuit board.
16. The magnetic coupling device of claim 5, further including: at
least one capacitor in one of series with the coil for series
resonance and across the coil for parallel resonance.
17. A planar coil printed circuit board magnetic coupling device,
comprising: a first trace on the printed circuit board forming the
planar coil; a first RF shield, the first RF shield insulated from
and covering a first side of the first trace; a second RF shield,
the second RF shield insulated from and covering a second side of
the first trace; and a magnetic field pattern former covering a
first side of the printed circuit board area covered by the first
trace and at least a portion of a second side of the printed
circuit board area covered by the first trace.
18. The magnetic coupling device of claim 17, wherein: the first RF
shield is a second trace on the printed circuit board.
19. The magnetic coupling device of claim 17, wherein: the first RF
shield has an open circuit.
20. The magnetic coupling device of claim 17, wherein: the magnetic
field pattern former has a magnetic permeability of at least
20.
21. The magnetic coupling device of claim 20, wherein: the magnetic
field pattern former is flexible ferrite.
22. A method for increasing planar selectivity of a magnetic
coupling device, comprising the steps of: covering an area of the
magnetic coupling device where a magnetic field emanation is not
desired with a magnetic field pattern former.
23. The method of claim 22, wherein the magnetic field pattern
former has a magnetic permeability of at least 20.
24. The method of claim 22, wherein the magnetic field pattern
former is flexible ferrite.
25. The method of claim 24, wherein the flexible ferrite is
arranged to cover a first side of the magnetic coupling device, a
first edge of the magnetic coupling device and at least a portion
of a second side of the magnetic coupling device.
26. A transponder communication selective module, comprising: a
magnetic coupling device partially covered by a magnetic field
pattern former; located proximate a media feed path; the media feed
path arranged to carry a plurality of transponders sequentially
past the magnetic coupling device.
27. The apparatus of claim 26, further including a printhead
arranged to apply indicia upon an outer surface of the
transponders.
28. The apparatus of claim 26, wherein the outer surface is a
label.
29. The apparatus of claim 26 wherein, the magnetic coupling device
is formed as at least a first trace on a printed circuit board.
30. The apparatus of claim 26, wherein the magnetic field pattern
former has a magnetic permeability of at least 20.
31. The apparatus of claim 26, wherein the magnetic field pattern
former is ferrite.
32. The apparatus of claim 31, wherein the ferrite is flexible and
the ferrite is applied to cover the first side of the magnetic
coupling device, around at least a first edge and at least a
portion of a second side of the magnetic coupling device.
33. The apparatus of claim 32, wherein the portion of the second
side of the magnetic coupling device that is covered by the ferrite
is at least 30 percent.
34. The apparatus of claim 26, further including a first RF shield
covering a first side of the magnetic coupling device.
35. The apparatus of claim 34, wherein the first RF shield has a
loop shape with an open circuit.
36. A system for sequentially communicating with a plurality of
RFID transponders, comprising: a magnetic coupling device located
proximate a media supply path arranged to transport RFID
transponders sequentially past the magnetic coupling device; the
magnetic coupling device having a magnetic field pattern former
arranged to minimize magnetic flux emanation away from the magnetic
coupling device, except through a gap; and the gap dimensioned to
enable inductive coupling with only a single RFID transponder at a
time.
37. A method for selectively communicating with a desired RFID
transponder among a plurality of RFID transponders, comprising the
steps of: energizing a magnetic coupling device; and passing the
desired RFID transponder through a magnetic flux field generated by
the magnetic coupling device; the magnetic coupling device covered
on a first side and at least a portion of a second side by a
magnetic field pattern former whereby a magnetic flux field
generated by the magnetic coupling device is in an area small
enough so that only the desired RFID transponder is energized.
38. The method of claim 37, wherein the magnetic field pattern
former is formed from a flexible ferrite material.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to RFID communication systems which
are selective for an individual transponder located in a
predetermined target area, to the exclusion of other transponders,
and to printers and other larger systems having such RFID
communication systems.
[0003] 2. Description of Related Art
[0004] Inductively coupled radio frequency identification (RFID)
technology allows data acquisition and or transmission from and or
to active (battery powered) or passive RFID transponders using RF
magnetic induction. To read or write from and or to an RFID
transponder, the RFID transponder is exposed to an RF magnetic
field that couples with and energizes the RFID transponder through
magnetic induction and transfers commands and data using a
predefined "air interface" RF signaling protocol.
[0005] When multiple RFID transponders are within the range of the
same RF magnetic field they will each be energized and attempt to
communicate with the transceiver, potentially causing errors in
reading and or writing to a specific RFID transponder.
Anti-collision management technologies exist to allow near
simultaneous reading and writing to numerous RFIDs in a common RF
magnetic field. However, anti-collision management increases system
complexity and cost. Further, anti-collision management is blind.
It cannot recognize where a responding transponder is located in
the RF magnetic field.
[0006] One way to prevent errors during reading and writing to RFID
transponders without using anti-collision management is to isolate
each RFID transponder from nearby RFID transponders. Previously,
isolation of RFID transponders has used RF shielded housings and or
anechoic chambers through which the RFID transponders are
individually passed for isolated exposure to the interrogating RF
magnetic field. This requires that the individual transponders have
cumbersome shielding or a significant physical separation.
[0007] When RFID transponders are supplied attached to a carrier
substrate, for example in RFID-mounted labels, tickets, tags or
other media supplied in bulk rolls, Z-folded stacks or other
format, an extra portion of the carrier substrate is required to
allow one RFID transponder on the carrier substrate to exit the
isolated field area before the next RFID transponder in line enters
it. The extra carrier substrate increases materials costs and the
required volume of the RFID media bulk supply for a given number of
RFID transponders. Having increased spacing between RFID
transponders may also slow overall throughput.
[0008] When the size or form factor of the utilized RFID
transponder is changed, the RF shielding and or anechoic chamber
configuration may also require reconfiguration, adding cost and
complexity and reducing overall productivity.
[0009] There exists applications wherein it is desired to print on
transponder-mounting media in the same target space in which the
transponder is being read from or written to. This may be very
difficult to accomplish if the transponder must be interrogated in
a shielded housing or chamber.
[0010] Printers have been developed which are capable of on-demand
printing on labels, tickets, tags, cards or other media with which
is associated an RFID transponder. These printers have an RFID
transceiver for on-demand communicating with the RFID transponder
on the individual media. For the reasons given, it is highly
desirable in many applications to present the media on rolls or
other format in which the transponders are closely spaced. However,
close spacing of the transducers exacerbates the task of serially
communicating with each individual transponder without concurrently
communicating with transponders on neighboring media. This
selective communication exclusively with individual transponders is
further exacerbated in printers designed to print on the media in
the same space as the transponder is positioned when being
interrogated.
[0011] Competition in the market for such "integrated"
printer-transceiver systems and selective RFID interrogation
systems has focused attention on minimization of overall costs,
including reduction of the costs of individual RFID transponders,
bulk RFID label and or tag supply carrier substrates, printers and
or interrogators.
[0012] Therefore, it is an object of the invention to provide a
system and method which overcomes deficiencies in such prior
art.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with a general description of the
invention given above, and the detailed description of the
embodiments given below, serve to explain the principles of the
invention.
[0014] FIG. 1 is a side schematic view of a media printer according
to one embodiment of the invention having an improved RFID
interrogation system.
[0015] FIG. 2 is a top view of a magnetic coupling device embodying
principles of the present invention.
[0016] FIG. 3 is a bottom view of the magnetic coupling device of
FIG. 2.
[0017] FIG. 4 is a top view of the magnetic coupling device of FIG.
2, with a magnetic field pattern former applied.
[0018] FIG. 5 is a bottom view of the magnetic coupling device of
FIG. 4.
[0019] FIG. 6A is a cut-away side view of a magnetic coupling
device as shown in FIGS. 4 and 5, illustrating schematically a
mutual magnetic coupling selectively with a single RFID transponder
supplied in-line with other RFID transponders on a carrier
substrate.
[0020] FIG. 6B is a view similar to FIG. 6A of an alternative
embodiment of an aspect of the invention.
[0021] FIG. 7 is a partial cut-away top schematic view of the
magnetic coupling device and carrier substrate mounted RFID
transponders of FIG. 6A; a printhead and platen roller have been
omitted for clarity.
[0022] FIG. 8A is a test chart showing relative power levels
delivered for activation by a magnetic coupling device of the
invention of several different types of RFID transponders, in
"landscape" orientation, as a function of location of the
transponder along a feed path of a hypothetical media printer.
[0023] FIG. 8B is a test chart similar to that of FIG. 8A but with
the transponders in a "portrait" orientation.
[0024] FIG. 9 is a test chart showing successful RFID transponder
writes with respect to the position of an RFID transponder along a
feed path of a label printer containing a magnetic coupling device
according to one embodiment of the invention having a constant
magnetic coupling device power level.
[0025] FIG. 10 is a chart showing a range of acceptable RFID
transponder locations and substrate dimensions for use with a
magnetic coupling device according to one embodiment of the
invention.
DETAILED DESCRIPTION
[0026] The present invention concerns apparatus and method which
enables an RFID transceiver (sometimes termed herein an
"interrogator") to communicate selectively and exclusively with a
single RFID transponder when one or more other transponders are in
close proximity, without the need for physical isolation or
cumbersome shielded housings or chambers.
[0027] The invention is useful in the loading or reading of
transponders, for example on an assembly line, in distribution
centers or warehouses where on-demand RFID labeling is required,
and in a variety of other applications. In many applications a
transponder or a number of transponders are mounted on a label,
ticket, tag, card or other media carried on a liner or carrier. It
is often desirable to be able to print on the media before, after,
or during communication with a transponder. Although this invention
is disclosed here in a specific embodiment for use with a direct
thermal or thermal transfer printer, it may also be used with any
other type of printer using other printing technologies, including
inkjet, dot-matrix, and electro-photographic methods.
[0028] In some applications a print station may be at a distance
from the RFID transceiver; in others it may be necessary to
accomplish the print function in the same general space occupied by
the transponder when it is being interrogated (sometimes herein
termed the "transponder target area").
[0029] FIG. 1 illustrates by way of example only an implementation
of the invention in a thermal transfer label printer 12 in which
both printing and transponder communication are accomplished, but
at different locations in the printer.
[0030] As shown in FIG. 1, the printer 12 includes a printhead
sub-assembly 15 comprising a conventional thermal printhead 14 and
platen roller 16, as in a direct thermal printer for printing on
thermally-sensitive media. A web 24 of media, such as labels,
tickets, tags or cards, is directed along a feed path 26 to the
printhead 14 where the printhead 14 applies on demand text and/or
graphics under control of a computer or microprocessor (not shown).
After being printed, the media may be peeled off the underlying
carrier substrate 20 at a tear bar 32 and follows a media exit path
34. The liner or carrier substrate 20 for the media is guided out
of the printer 12 by a roller 36 where it exits the printer along
an exit path 38.
[0031] When a thermal printer is configured for use as a thermal
transfer printer, a ribbon supply roll 18 delivers a thermal
transfer ribbon (not shown for clarity) between printhead 14 and
the media on web 24. After use, the spent ribbon is collected on a
take-up reel 22.
[0032] In accordance with an aspect of the present invention, the
printer includes a transceiver 42 and a magnetic coupling device 1
located proximate the media feed path 26. As will be explained and
illustrated in detail hereinafter, the system (including
transceiver 42 and magnetic coupling device 1) forms a magnetic
flux field pattern in the location of a transponder target area 44
(see FIG. 6A). The system is configured to establish at
predetermined transceiver power levels a mutual magnetic coupling
which is selective exclusively for a single transponder located in
the transponder target area 44.
[0033] As labels or other media with embedded transponders move
along the media feed path 26, through target area 44, data may be
read from and or written to transponder 10. Information indicia
then may be printed upon an external surface of the media as the
media passes between the platen roller 16 and the printhead 14 by
selective excitation of the heating elements in the printhead 14,
as is well known in the art. When the thermal printer 12 is
configured as a direct thermal printer, the heating elements form
image dots by thermochromic color change in the heat sensitive
media; when the thermal printer 12 is configured as a thermal
transfer printer, then ink dots are formed by melting ink from the
thermal transfer ribbon (not shown for clarity) delivered between
printhead 14 and the media on web 24 from supply roll 18. Patters
of printed dots thus form the desired information indicia on the
media, such as text, barcodes or graphics.
[0034] Media conveyance is well known in the art. Therefore the
media conveyance 25 portion of the printer that drives the media
with transponders along the media feed path 26 is not described in
detail.
[0035] The magnetic coupling device 1 and its manner of operation
will now be described with reference to FIGS. 2-7. One embodiment
of the magnetic coupling device 1 is configured for use, for
example, with 13.56 MHz RFID transponders 10. Transponders 10 are
bulk supplied on a carrier substrate 20 in label, ticket, card or
tag form with a printable facestock 30.
[0036] The magnetic coupling device 1 comprises a magnetic flux
generator and a magnetic field pattern former, as will be
described. The magnetic flux generator may comprise one or more
coils responsive to RF signals supplied by the transceiver 42. The
coils may take the form of a planar elongated coil created, for
example, by conductor(s) coupled with a coil support structure. The
conductors and coil support structure may comprise, for example, a
coil trace(s) 50 on and or within a multi-layered printed circuit
board (PCB) 60. Coil trace(s) 50 may be formed without sharp
corners to minimize creation of impedance discontinuities.
[0037] Because the wavelength at 13.56 MHz is approximately 22
meters, design of a small, low-cost antenna for coupling to an RFID
transponder using electromagnetic radiation is difficult.
Therefore, the magnetic coupling device 1 is configured to mutually
couple to RFID transponder(s) operating at frequencies with long
wavelengths using only magnetic induction coupling. As will be
described hereinafter, electric fields emitted by coil trace 50 are
suppressed by a grounded E-field suppressor shield 90.
[0038] The dimensions of the magnetic coupling device 1 and the
number of turns, for example three to five turns, used in the
coil(s) are determined in part by the intended range from and
longitudinal dimensions of the RFID transponder 10 which the
magnetic field of the magnetic coupling device will selectively
mutually inductively couple with. Capacitors 80, for example
surface mounted to the PCB 60 local to the coils trace(s) 50, may
be used for impedance matching (for example, 50 ohm) and tuning of
the magnetic coupling device 1, to zero the imaginary component of
impedance at a desired resonant frequency. Other impedance matching
and or magnetic coupling device tuning components that may be
applied include matching transformers, inductors and a tap of the
magnetic coupling device coil. one or more resistor(s) 85 may be
used to adjust a Q-factor of the magnetic coupling device.
[0039] The E-field suppressor shield 90 may be created, for
example, by forming another conductive layer on one or both sides
of the PCB 60 containing coil trace 50, as shown in FIGS. 2, 3, 4
and 6A and 6B. The E-field suppressor shield 90 may be formed as a
gapped loop that covers the magnetic coupling device radiating coil
trace(s) 50 completely with the exception of a small open circuit
100, as shown in FIGS. 1 and 2. The purpose of the open circuit 100
is to prevent Eddy current flow in the E-field suppressor shield 90
which would cause signal losses.
[0040] Without more, the coil trace(s) of the magnetic coupling
device 1 may be expected to emit magnetic flux lines in a generally
omnidirectional toroid pattern about the coil trace(s) 50. A
transponder-selective magnetic field pattern former 110 is provided
to collect flux produced by the flux generator (coil trace(s) 50 in
the illustrated embodiment) and to form a field pattern 70 in the
location of a predetermined transponder target area 44.
[0041] FIG. 6A illustrates an arrangement wherein a transceiver 42
and magnetic coupling device 1 are located in a printer having a
printhead 14 and associated platen roller 16 which are located
proximate the transponder target area 44. With the printhead 14
within or near the transponder target area 44, a label or other
media carrying a transponder can be interrogated (read and or
write) and the carrying media can be printed in essentially the
same space. This is important in on demand systems, particularly
portable or compact systems, where it would be impractical to have
a print station located remotely from the transponder interrogation
station.
[0042] The field pattern former 110 increases the amount of
magnetic flux by inserting into the field space a material of
higher magnetic flux permeability than free space. The field
pattern former 110 has a gap 112 within and adjacent to which the
field pattern is formed. The gap 112 is defined as areas of the
magnetic coupling device 1, and in the present embodiment
particularly coverage of the coil trace 50, which are not covered
by the field pattern former 110. The resulting field pattern is
therefore positioned and influenced by the configuration and
position of the gap 112. In the FIG. 6A embodiment, the gap 112 may
be, for example, approximately the width of one side of the coil
traces 50 or may be about 50% of the top surface area of the PCB 60
(if the coil trace 50 is centered on the PCB 60) and is located at
the end of the magnetic coupling device 1 nearest the printhead 14.
Configurations that cover more or less of the coil traces 50 and
or, for example, all edges of the PCB 50 are also usable to create
a magnetic field pattern 70 that matches a desired transponder
target area 44. A top view of the arrangement shown in FIG. 6A is
illustrated in FIG. 7.
[0043] Alternatively, a simplified RFID transponder read and or
write system may be formed without printing capabilities by
positioning a magnetic coupling device 1 coupled to a transceiver
42 proximate a media conveyance moving sequential RFID transponders
through a target area 44 of the magnetic coupling device 1.
[0044] Such an alternative embodiment is shown in FIG. 6B wherein
the gap 112 in coverage by a field pattern former 110 is disposed
intermediate the ends of magnetic coupling device 1. The FIG. 6B
embodiment is configured for applications wherein an associated
printing function in the same physical space is not necessary. The
FIG. 6B embodiment contemplates that any printing or other function
to be performed is accomplished at another station. The printer 12
illustrated in FIG. 1 and described above is an example of an
execution of the invention wherein the interrogation of the
transponders is accomplished at a distance from the printhead
14.
[0045] The field pattern former 110 may be formed using a material
preferably having a magnetic relative permeability of 20 or more.
The material may be, for example, a ferrite composition. Ferrite is
a general name for a class of materials having a powdered,
compressed, and sintered magnetic material having high resistivity,
consisting chiefly of ferric oxide combined with one or more other
metals. The high resistance of ferrite compositions makes
eddy-current losses extremely low at high frequencies. Examples of
ferrite compositions include nickel ferrite, nickel-cobalt ferrite,
manganese-magnesium ferrite and yttrium-ion garnet. The field
pattern former 110 may be a rubberized flexible ferrite, ferrite
polymer film or stennite material. Flex Suppressor (trademark)
material available from Tokin EMC is also a suitable material. The
selected field pattern former 110 may be connected to the PCB 60,
for example, with an adhesive. Alternatively, the field pattern
former 110 may be applied in a liquid or semi liquid form, upon the
desired areas of the PCB 60 or other coil support structure and
solidified and or cured to leave, for example, only a desired gap
112 uncovered by the material comprising the field pattern former
110.
[0046] The embodiment shown in FIGS. 4-7 may have a field pattern
former 110 of flexible ferrite. For example, for the embodiment
shown in FIGS. 4, 5, 6A and 7, the field pattern former 110 covers
the magnetic coupling device 1 area of the bottom side of the PCB
60 and extends, wrapped about the PCB 60 in a single portion to
cover approximately one half of the top side of the coil traces 50,
resulting in the concentration of flux and the formation of a
magnetic field pattern 70 within and adjacent the gap 112.
[0047] In accordance with an aspect of the present invention, the
system is configured to establish at predetermined transceiver
power levels a mutual magnetic coupling which is selective
exclusively for a single transponder located in the predetermined
transponder target area 44. As will become evident from the
description of FIGS. 8A and 8B, the mutual coupling will vary
depending upon the mechanical and electrical characteristics of the
coupled transponder, the applied power levels of the transceiver
42, the size and other properties of any media 20 which supports
the transponder, the characteristics of the pattern former, and
other factors.
[0048] Obviously, at some exaggerated transceiver power level
transponders outside the transponder target area 44 may be excited.
However, by this invention, at power levels in the range of normal
transceiver operations, and, for example, allowing for a 3 dB or
greater tolerance margin, the mutual coupling created will be
highly selective for the transponder 10 in the transponder target
area 44.
[0049] The compact size of the magnetic coupling device 1 and the
lack of any other shielding requirements allows the economical
addition of sequentially spaced multiple RFID transponder format
read and or write capability to a range of sequential RFID
transponder transport devices, for example label printers, to form
a selective transponder communication module.
[0050] Because the magnetic coupling device 1 may be configured to
be selective exclusively for a single transponder located in the
transponder target area 44, it is now possible by this invention to
use a web of media having transponders which are closely spaced on
the web, as shown in the figures of this application. Prior to this
invention it was extremely difficult to communicate with just one
transponder in a closely spaced series of transponders without
simultaneously activating adjacent transponders.
[0051] FIGS. 8A and 8B are test charts showing relative power
levels delivered for activation by a magnetic coupling device
according to the invention of several different types of
rectangular transponders as a function of location along the feed
path 26 of printer 12, and the orientation of these transponders
along the web 24. FIG. 8A shows data for selected transponders in
the "landscape" orientation similar to FIG. 7. FIG. 8B shows data
for selected transponders in the "portrait" orientation, in which
the long axis of the transponder is along feed path 26. The FIGS.
8A and 8B charts reveal how highly sensitive the system of the
invention is for a transponder located in the transponder target
area 44, and how highly non-sensitive the system is for any
transponder outside the target area 44.
[0052] The different curves in the FIGS. 8A and 8B charts are
associated with different commercially available 13.56 MHz RFID
transponders, as labeled. Here, the RFID integrated types, antenna
geometries and/or manufacturers of the selected transponders are
not in themselves important, as they are used only as examples to
demonstrate the effect of the invention. The curves themselves
reflect how the mutual coupling with the various selected
transponders results in different position sensitivity to
excitation within the transponder target area 44.
[0053] The different curves shown in the charts of FIGS. 8A and 8B
are not magnetic field distributions, but rather estimates of the
available power margin over the reading threshold for each type of
transponder as a function of orientation and position relative the
target area 44. This measurement is made by applying a
constant-power RF signal to the magnetic coupling device 1 through
a variable RF attenuator; then increasing the attenuation in
decibels until the reading of data from transponder 10 stops; and
finally recording the attenuation value as a function of position
and orientation on the appropriate chart in FIG. 8A or 8B. These
charts are used to select an optimal location within the labels,
tickets, tags or cards for embedding the transponders, and
determine the minimum allowable spacing between transponders along
the web 24.
[0054] To better understand the FIGS. 8A and 8B charts, an
explanation with respect to one of the curves, identified as
describing the characteristics of a "Lintec I*CODE 16.times.47 mm"
RFID transponder, will be made in detail. In the example shown in
FIG. 8A, the curve begins at a first position where the front edge
of the coil of the transponder 10 is located in the target area 44
at a distance of 16 mm from a reference "0" line defined by the
sharp corner edge of the tear bar 32. At this point, the leading
edge of the transponder 10 antenna coil is also located 2 mm back
of a second reference line labeled "print line" of printhead 14.
The print line is analogous to the print line in FIG. 6A where the
printhead 14 engages a media to be printed. The Lintec I*CODE
16.times.47 mm transponder curve shows that, at the designated
transceiver test power level, the transponder cannot be
activated.
[0055] In this printer configuration, moving the transponder back
only 2 mm to a position 18 mm from the reference "0" line and 4 mm
behind the "print line", the transponder is responsive until the
test transceiver power level is suppressed 6 dB. If the transponder
is moved back another 4 mm, to a position 8 mm behind the "print
line" the transceiver test power level must be attenuated a full 13
dB before the transponder will not respond normally.
[0056] The back side of the Lintec I*CODE 16.times.47 mm curve is
equally steep. With the transponder moved back only 14 mm from the
print line; the transponder responds normally with the test
transceiver power level suppressed up to 12 dB. However, with the
transponder moved back just 20 mm from the print line, the
transponder will not respond to the transceiver delivering the test
power level.
[0057] The transponder is 16 mm wide and 47 mm long. In a landscape
orientation with respect to the direction of media travel, as soon
as the leading edge of the transponder coil clears either side of a
roughly 17 mm target area, it is unable to be activated. The other
curves demonstrate responses of a range of different RFIDs using
the same test configuration. Allowing for the possible use of all
the different transponders with the same magnetic coupling device
configuration provides a usable target area of 25 mm or less. With
this degree of selectivity provided by the present invention,
transceiver power levels can be raised to provide a comfortable
safety margin without concern for energizing adjacent transponders
even when the transponders are closely spaced. Conversely, the
target area is wide enough that pinpoint positioning of the
transducer is not necessary for reliable communication.
[0058] Results in the portrait orientation shown in FIG. 8B are
less closely defined. When the longer dimension of the RFID
transponder is along the feed path 26, the magnetic coupling device
1 may inductively couple along any portion of the extended length
of RFID transponder 10, even if a majority of the transponder area
is outside the target area 44.
[0059] Another way to measure the system performance is shown in
FIG. 9. FIG. 9 is a test chart demonstrating the number of
successful write operations out of ten attempts as a typical
Phillips I*Code (trademark) 13.56 MHz RFID transponder with a
12.times.38 mm antenna coil is moved across the print media path of
a Zebra Technologies, Inc. model R402 label printer/RFID
programmer, equipped with a magnetic coupling device 1 according to
the present invention. The RFID transponder location for each test
series is shown relative to either side of the printer's tear bar
(representing "0" on the tag position axis), along the print media
path. Results of three different test series taken with 13.56 MHz
RF excitation and the magnetic coupling device 1 resonant at
frequencies 13.31, 13.56, and 13.81 MHz respectively are shown for
each location at 1 mm increments. FIG. 9 demonstrates that the
focused magnetic field pattern 70 generated by the present
invention may be configured to cause successful inductive coupling
with an RFID transponder only within a very closely defined target
area, permitting the RFID transponders to be closely sequentially
spaced together without causing read and or write collisions
through accidental activation of multiple transponders.
[0060] FIG. 10 shows an RFID transponder placement map, also for
I*Code 12.times.38 mm RFID transponders, derived from testing on
the model R402 similar to that shown in FIGS. 8 and 9 for a
plurality of different transponder locations. Labels having a width
"a" of at least 21 mm; a length "b" of between 29 and 102 mm; a
lead edge distance "y" of between 8 and 22 mm; and a label spacing
"s" of a minimum of 1 mm are possible. From this form of testing,
specific to each RFID transponder, a minimum periodicity "P" for a
specific RFID transponder may be calculated as P=a+s. The value of
"P" then becomes the same as the minimum RFID transponder spacing,
leading edge to leading edge (as well as the minimum label repeat
distance along the web) required to ensure that read and or write
collisions do not occur for the selected RFID transponder and
magnetic coupling device 1 combination.
[0061] The magnetic field pattern former 110 may be easily adjusted
for different desired magnetic field directions and or shapes
during manufacture by varying the size, configuration and or
location of the magnetic field pattern former 110 applied to the
PCB 60 or other coil support structure.
1 Table of Parts 1 magnetic coupling device 10 transponder 12
printer 14 printhead 15 printhead sub-assembly 16 platen roller 18
supply roll 20 carrier substrate 22 take up reel 24 web 25 media
conveyance 26 feed path 30 facestock 32 tear bar 34 label exit path
36 roller 38 carrier exit path 42 transceiver 44 target area 50
coil trace 60 printed circuit board 70 field pattern 80 capacitors
85 resistor 90 E-field suppressor shield 100 open circuit 110 field
pattern former 112 gap
[0062] Where in the foregoing description reference has been made
to ratios, integers or components having known equivalents then
such equivalents are herein incorporated as if individually set
forth.
[0063] While the present invention has been illustrated by the
description of the embodiments thereof, and while the embodiments
have been described in considerable detail, it is not the intention
of the applicant to restrict or in any way limit the scope of the
appended claims to such detail. Additional advantages and
modifications will readily appear to those skilled in the art.
Therefore, the invention in its broader aspects is not limited to
the specific details, representative apparatus, methods, and
illustrative examples shown and described. Accordingly, departures
may be made from such details without departure from the spirit or
scope of applicant's general inventive concept. Further, it is to
be appreciated that improvements and/or modifications may be made
thereto without departing from the scope or spirit of the present
invention as defined by the following claims.
* * * * *