Note: Descriptions are shown in the official language in which they were submitted.
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C4-343
APPARATUS FOR DEACTIVATION OF ELECTRONIC
ARTICLE SURVEILLANCE TAGS
FIELD OF THE INVENTION
This invention relates generally to electronic article
surveillance and pertains more particularly to so-called
~deactivators" for rendering electronic article surveillance tags
inactive.
BACKGROUND OF THE INVENTION
It has been customary in the electronic article surveillance
(EAS) industry to apply to articles to be monitored either hard,
reusable EAS tags or disposable adhesive EAS labels, both
functioning as article monitoring devices. At article checkout
stations in retail stores, a checkout clerk passes the article over
or into deactivation apparatus which deactivates the monitoring
device. ~
Known deactivation apparatus includes coil structure
energizable to generate a magnetic field of magnitude sufficient to
render the monitoring device inactive, i.e., no longer responsive
to incident energy to itself provide output alarm or to transmit an
alarm condition to an alarm unit external to the tag or label
(hereinafter "tag").
One commercial deactivator of the assignee hereof employs one
coil disposed horizontally within a housing and tagged articles are
moved across the horizontal top surface of the housing such that
the tag is deactivated regardless of its orientation.
Another commercial deactivator of the assignee hereof employs
a housing having an open side with a plastic bucket inserted in the
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housing such that an article or a plurality of articles may be made
resident in the bucket. Three coil pairs are disposed about the
bucket in respective x-, y- and z-axis planes.
The coil pairs of each of the two described deactivators
generate a low frequency decaying magnetic field of substantial
strength. In the first deactivator, the field necessarily is
exteriorly above the upper horizontal surface thereof to perform
deactivation. However, the field escapes the housing in other
directions, particularly downwardly of the housing. In the second
deactivator, while the fields are necessarily needed only in the
bucket, they undesirably escape the housing. Thus, in use of
either type of deactivator, it is necessary to keep the deactivator
at a safe distance from other sensitive devices, such a monitors,
magnetic stripe readers and the like.
The known deactivators place an undesirable constraint on EAS
system checkout stations, i.e., the stations can not be as compact
as desired, and otherwise usable space at the stations need be
dedicated to the EAS system. Further, the known deactivators
exhibit relatively high power needs to generate the deactivating
fields.
While shielding has been successfully used in the EAS industry
to overcome interference problems, for example, in transmitting
antenna shielding, as in commonly-assigned U.S. Patent No.
4,769,631, a new approach is requisite due to the extraordinarily
strong fields and low frequencies involved in tag deactivation. An
"evident solution~ to the problem would be to select a suitable
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shielding material of acceptable thickness, driven usually by
weight and cost considerations, which would be placed around the
interfering unit. In the case of the known deactivators, this
approach would have required a substantial gap between the
deactivating coils and the shield to prevent saturation and the
addition of a second layer in a nested arrangement. This would
have resulted in a greatly increased overall size and some magnetic
leakage due to the gap without significant improvement in
efficiency.
SUMMARY OF THE INVENTION
The present invention has as its primary object a solution to
the above-discussed problems attending the described prior art
deactivators.
One more particular object of the invention is to provide
enhanced constraints on magnetic fields unnecessarily exterior to
the described prior art deactivators.
Another more particular object of the invention is lessen
power needs of the described prior art deactivators.
In attaining the above and other objects, in one embodiment
thereof, relating to the first described prior art deactivation
device for deactivating electronic article surveillance tags, the
invention provides a housing, a single coil supported in the
housing and having opposed first and second sides and energizable
to generate a magnetic field issuing from both the first and second
sides thereof and a shielding unit supported in the housing in
juxtaposition with the coil second side, the shielding unit
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comprising a succession of magnetically permeable members. The
shielding unit lessens magnetic fields exteriorly of a portion of
the housing juxtaposed with the last of magnetically permeable
members in the succession and otherwise enhances the magnetic
field.
In a second embodiment thereof, relating to the second
described prior art deactivation device for inactivating electronic
article surveillance tags, the invention provides a housing, at
least first and second pairs of coils supported in the housing each
coil having opposed first and second sides. The coil pairs are
independently energizable to generate respective first and second
magnetic fields issuing from both the first and second coil sides
and shielding units are supported in the housing respectively in
juxtaposition with the second sides of each coil, each shielding
unit comprising a succession of magnetically permeable members.
The shielding units lessen magnetic fields exteriorly of respective
portions of the housing juxtaposed with the last of magnetically
permeable members in the respective successions and enhance the
magnetic field inside of the housing.
The magnetically permeable members are comprised of magnetic
steel, preferably, silicon iron.
In contrast to the ~evident solution" to the prior art problem
above addressed, the invention overcomes the problem by placing a
heavier shield in very close proximity to the coils (zero gap in
the case of the first embodiment) making it an integral part of the
magnetic circuit where it acts as a pole piece as well as a shield.
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The resulting deactivators are only slightly larger that than the
prior art deactivators and are much more efficient due to the
improved flux path without the leakage of the "evident solution~.
The reduction of the undesirable external field is achieved in part
through a reduction in coil current proportional to the enhancement
of the internal field so that the same deactivation field is
maintained.
The foregoing and other objects and features of the invention
will be further understood from the following detailed description
of preferred embodiments thereof and from the drawings, wherein
like reference numerals identify like components throughout.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is an exploded, perspective view of a first embodiment
of a deactivator in accordance with the invention.
Fig. 2 is a perspective view of the single deactivating coil
of the first embodiment.
Fig. 3 is front elevational view of the shielding unit of the
first embodiment.
Fig. 4 is an exploded, perspective view of a second embodiment
of a deactivator in accordance with the invention.
Fig. 5 is a left side elevational and schematic view of the
Fig. 4 deactivator.
Fig. 6 is front elevational view of one of the four identical
panels of the shielding units of the second embodiment.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PRACTICES
Referring to Fig. 1, deactivator 10 includes a housing jointly
defined by cover 12 and base 14. A product identifier/logo decal
12a is seatable in a circular open recess 12b of cover 12.
Transmit/receive coil structure 16 is disposed adjacently
interiorly of cover 12 for effecting communication with a tag prior
to deactivation to initiate the same and following deactivation
thereof to assure, through associated processing circuitry known in
the EAS art in the described prior art deactivators, that the tag
is indeed deactivated.
Deactivation coil 18 is disposed interiorly of transmit/
receive coil structure 16. As is seen in Figs. 1 and 2,
deactivation coil 18 is energized through conductors 22 and 24 and
generates a necessary magnetic field above its upper side, i.e., to
deactivate tags disposed adjacent the outer surface of cover 12.
Shielding unit 34 has an upper side thereof in Fig. 1 juxtaposed
with the lower side of coil 18. Base 14 includes various
registration and assembly securing members 36 and, on assembly of
deactivator 10, they extend through holes 38 in shielding unit 34
and holes 40 in transmit/receive coil structure 16, and abuttingly
bound coil 18, to maintain the various components of the
deactivator in desired position. Members 36 are exteriorly
threaded at free ends thereof and interiorly threaded securement
members (not shown) are secured to members 36 atop transmit/receive
coil structure 16 to assemble the deactivator.
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Referring to Fig. 3, shielding unit 34 will be seen to be
comprised of ten layers, 34a, 34b,...34j. As is indicated for
layer 34a (all layers are identical), it includes an exterior
coating layer 34a-1, in the nature of the material of a transformer
lamination, i.e., electrically insulative material, such as C5 type
inorganic matter in a very thin coating of about two ten
thousandths of an inch, an interior layer 34a-2, comprised of
magnetically permeable matter, preferably commercially-available
#24 gauge .025", 64mm) Ml9 grade, non-oriented silicon steel
(SiFe), and an interior layer 34a-3, constituted identically with
layer 34a-1.
Layers 34a and 34b are mutually secured, as are all juxtaposed
layers of shielding unit 34, by a double-sided adhesive film 42,
forming shielding unit 34 as a laminated structure.
Each deactivation cycle requires an amount of energy (power-
time product) which is measured in watt seconds. The first
described prior art deactivator, i.e., without shielding unit 34,
requires two hundred watt seconds per deactivation, or a power
consumption of two hundred watts for deactivation once every
second.
With the shielding unit 34 so formed and present,
experimentation has established that the deactivator of Figs. 1-3
requires only seventy watt seconds per deactivation or seventy
watts for deactivation once every second. Applicants attribute
such improvement to the modification of the reluctance path in the
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deactivator, strongly influenced by the presence of shielding unit
34, which can be regarded as a shielding unit/pole piece.
A further advantage of the first embodiment is a substantial
lessening of escaping magnetic field below the deactivator.
Turning to Fig. 4, the second prior art deactivator above
discussed includes bulk deactivator unit 44 having opening 44a and
plastic bucket 46 having opening 46a. Shield unit 48 is configured
as a sleeve for deactivator unit 44, having opening 48a and a
rightward opening (not shown).
The interior structure of deactivator unit 44 is seen in Fig.
5. One coil pair (x-axis) has coils shown at 44b-la, 44b-lb and
44b-2a, 44b-2b. A second coil pair (y-axis) has coils shown at
44c-la, 44c-lb and 44c-2a, 44c-2b. One coil of a third coil pair
(z-axis) is shown at 44d. The three coil pairs are thus arranged
in a Helmholz like configuration. The coil pairs are driven one
pair at a time resulting in a three step sequence.
Fig. 6 illustrates the configuration of each of the four
sidewalls of shield unit 48, which will be seen to be comprised of
seven layers, 48a, 48b,...48g. As is indicated for layer 48a (all
layers are identical), it includes an exterior coating layer 48a-1,
of material and thinness noted above for coating layer 34a-1, , an
interior layer 48a-2, comprised of magnetically permeable matter,
preferably commercially-available #24 gauge, Ml9 grade, non-
oriented silicon steel (SiFe), and an interior layer 48a-3,
constituted identically with layer 48a-1.
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Layers 48a and 48b are mutually secured, as are all juxtaposed
layers of shielding unit 48, by screws passing therethrough and
into securement with support member 50, which may be plywood and
provides an outer wall of the shielding unit. Given that
shielding unit 48 has open ends, and that the z-axis coils
accordingly do not have walls ~uxtaposed with sides thereof but,
rather are bounded perimetrically by the magnetic steel layers, the
principal field containment and enhance occurs for the fields
generated by the x- and y-axis coils. However, it has been found
that the z-axis experiences a ten percent reduction in external
field strength as well as a ten percent field strength enhancement
inside the deactivation chamber. Accordingly, if the z-axis coil
pair drive is reduced by ten percent, and yet the field strength of
the prior art deactivator is achieved, the external z-axis field is
reduced by some nineteen percent.
Since only one open end is needed, for entry of tagged
articles into the bucket, the invention may be practiced with a
single z-axis shielding unit wall or floor as desired.
The power-time product for the second above-noted prior art
deactivator, i.e., without shielding unit 48, is four hundred and
sixty watt seconds per deactivation. Experimentation has
established that the power-time product for the subject deactivator
with shielding unit 48 is two hundred watt seconds per
deactivation.
The invention contemplates the use of plural, spaced shielding
panels for each coil. In a preferred arrangement, a first panel is
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configured with an inner panel comprised of five layers of #26
gauge, M 19 grade non-oriented silicon steel and an outer panel
comprised of five layers of #29 gauge, M6 gauge grain oriented
silicon steel. The inner panel is located 20mm from the coil and
the outer panel is spaced 6mm from the inner panel. The grades and
gauges are selected optimally for different fields encountered.
This approach results in the highest attenuation for a given amount
of magnetic material. In this connection, while the double panel
arrangement maximizes shielding performance (attenuation), it is
not as effective as a pole piece and therefore does not achieve the
same field enhancement because only the inner shield functions as
an effective pole piece. Thus, the double panel arrangement finds
best usage in situations where maximum external field attenuation
need be achieved at the expense of other parameters, such as
efficiency, size and cost.
Silicon iron emerged as applicants' principle magnetic stee~
choice based on its following characteristics: high permeability
resulting in good shielding performance (attenuation); high
intrinsic induction limit (saturation flux density) making it
suitable for strong fields; low hysteresis losses and low eddy
current losses; desired shielding unit thickness readily obtained
by stacking thin sheets, also reducing eddy current; easily
cuttable by simple shearing operations; relatively low cost, some
one and one-half to two times compared to ordinary steel depending
on grade; and commercially supplied annealed and with a protective
coating (transformer lamination).
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Various changes in structure to the described systems and
apparatus and modifications in the described practices may
evidently be introduced without departing from the invention.
Accordingly, it is to be understood that the particularly disclosed
and depicted embodiments are intended in an illustrative and not in
a limiting sense. The true spirit and scope of the invention are
set forth in the following claims.
