U.S. patent application number 14/171667 was filed with the patent office on 2014-07-31 for inductive device assemblies and methods.
The applicant listed for this patent is PULSE ELECTRONICS, INC.. Invention is credited to Alan H. Benjamin, Michael T. Gilmartin, Fredrick J. Kiko.
Application Number | 20140211427 14/171667 |
Document ID | / |
Family ID | 34083353 |
Filed Date | 2014-07-31 |
United States Patent
Application |
20140211427 |
Kind Code |
A1 |
Gilmartin; Michael T. ; et
al. |
July 31, 2014 |
INDUCTIVE DEVICE ASSEMBLIES AND METHODS
Abstract
Improved form-less electronic apparatus and methods for
manufacturing the same. In one exemplary embodiment, the apparatus
comprises a shape-core inductive device having a bonded-wire coil
which is formed and maintained within the device without resort to
a bobbin or other form(er). The absence of the bobbin simplifies
the manufacture of the device, reduces its cost, and allows it to
be made more compact (or alternatively additional functionality to
be disposed therein). One variant utilizes a termination header for
mating to a PCB or other assembly, while another totally avoids the
use of the header by directly mating to the PCB. Multi-core
variants and methods of manufacturing are also disclosed.
Inventors: |
Gilmartin; Michael T.;
(Tuam, IE) ; Kiko; Fredrick J.; (Carlsbad, CA)
; Benjamin; Alan H.; (Elfin Forest, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PULSE ELECTRONICS, INC. |
San Diego |
CA |
US |
|
|
Family ID: |
34083353 |
Appl. No.: |
14/171667 |
Filed: |
February 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13758875 |
Feb 4, 2013 |
8643456 |
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14171667 |
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13351182 |
Jan 16, 2012 |
8368500 |
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13758875 |
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13012616 |
Jan 24, 2011 |
8098125 |
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13351182 |
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12572168 |
Oct 1, 2009 |
7876189 |
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13012616 |
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10885868 |
Jul 6, 2004 |
7598837 |
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12572168 |
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60485801 |
Jul 8, 2003 |
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Current U.S.
Class: |
361/748 ;
336/192 |
Current CPC
Class: |
H01F 2027/065 20130101;
H01F 3/08 20130101; H01F 41/02 20130101; H05K 1/18 20130101; H05K
1/181 20130101; H01F 27/027 20130101; H05K 2201/1003 20130101; Y10T
29/4913 20150115; H01F 27/306 20130101; H01F 27/29 20130101; H01F
27/292 20130101; H01F 17/043 20130101; H05K 1/182 20130101; Y10T
29/49147 20150115 |
Class at
Publication: |
361/748 ;
336/192 |
International
Class: |
H01F 27/29 20060101
H01F027/29; H05K 1/18 20060101 H05K001/18 |
Claims
1.-45. (canceled)
46. An electronic assembly, comprising: at least three core
elements mated to one another, the mated core elements collectively
forming a plurality of winding channels, each winding channel
having a respective aperture associated therewith; a plurality of
windings, each having a plurality of turns and disposed at least
partly within respective ones of the plurality of winding channels,
each of the plurality of windings further comprising at least two
ends which are routed through their respective aperture; and a
termination element comprising a plurality of electrically
conductive terminals associated therewith, the at least two ends of
each of the windings being coupled with ones of the terminals.
47. The assembly of claim 46, wherein at least two of the mated
core elements are substantially identical to one another and are
oriented in a face-to-face fashion.
48. The assembly of claim 47, further comprising a printed circuit
board having a signal interface for use with a broadband data
connection.
49. The assembly of claim 48, wherein the printed circuit board
further comprises an electronic circuit that, in combination with
the plurality of windings and the mated core elements, is compliant
with a prescribed DSL configuration or service.
50. The assembly of claim 49, wherein the at least three core
elements are utilized in conjunction with a single termination
element so as to reduce and/or eliminate the spacing or stand-off
required between conventional designs that necessitate the use of
multiple termination elements.
51. The assembly of claim 50, wherein the at least three core
elements are disposed together so as to form an array.
52. The assembly of claim 51, wherein each of the plurality of
electrically conductive terminals are in signal communication with
the printed circuit board.
53. An electronic assembly useful in a digital subscriber line
(DSL) application, comprising: a printed circuit board (PCB) having
an inductive device mounted thereon, the inductive device
comprising: a plurality of core elements that are mated to one
another, at least a portion of the plurality of core elements
comprising a plurality of winding channels, each of the plurality
of winding channels having a post foiled from a magnetically
permeable material disposed therein; wherein the plurality of mated
core elements also collectively form a plurality of apertures that
communicate with respective ones of the winding channels; a
plurality of windings, each comprising a plurality of turns and
disposed at least partly within one of the winding channels, each
winding further comprising at least two ends which are routed
through respective ones of the plurality of apertures; and a
termination element comprising a plurality of electrically
conductive terminals associated therewith.
54. The assembly of claim 53, wherein at least two of the mated
core elements are substantially identical to one another and are
oriented in a face-to-face fashion.
55. The assembly of claim 54, wherein the plurality of mated core
elements comprises at least three core elements that are ganged
together in an array.
56. The assembly of claim 55, further comprising a printed circuit
board having a signal interface for use with a broadband data
connection.
57. The assembly of claim 56, wherein the termination element
comprises: a body having a bottom surface; wherein the plurality of
electrically conductive terminals protrude from the bottom surface,
the plurality of electrically conductive terminals being in
electrical communication with a plurality of traces disposed on the
PCB.
58. The assembly of claim 57, wherein the plurality of core
elements are utilized in conjunction with a single termination
element so as to reduce and/or eliminate the spacing or stand-off
required between conventional designs that necessitate the use of
multiple termination elements.
59. The assembly of claim 53, wherein the plurality of core
elements are disposed together so as to form an array.
60. An electronic assembly, comprising: at least three core
elements mated to one another so as to form a plurality of winding
channels, each winding channel comprising a respective aperture
associated therewith; a winding having a plurality of turns and
disposed at least partly within at least one of the winding
channels; and a termination element comprising a plurality of
electrically conductive terminals associated therewith that
protrude from a bottom surface of the termination element, the
winding being coupled with at least a portion of the terminals.
61. The assembly of claim 60, wherein the at least three core
elements are disposed in a substantially side-by-side fashion that
includes a face-to-face mating orientation, and at least one other
type of orientation.
62. The assembly of claim 61, further comprising a printed circuit
board having an electronic circuit disposed thereon that, in
combination with the at least three core elements and the winding,
is compliant with a DSL compliant standard or service.
63. The assembly of claim 62 wherein the printed circuit board
comprises a signal interface for use with a broadband data
connection.
64. The assembly of claim 63, wherein the at least three core
elements are disposed proximate one another in a common orientation
so as to form an array.
65. The assembly of claim 64, wherein the at least three core
elements are ganged together in a plurality of formations.
Description
PRIORITY CLAIM
[0001] This application is a continuation of and claims priority to
co-owned and co-pending U.S. patent application Ser. No. 13/758,875
entitled "FORM-LESS ELECTRONIC DEVICE ASSEMBLIES AND METHODS OF
OPERATION", filed Feb. 4, 2013, to issue as U.S. Pat. No.
8,643,456, which is a continuation of and claims priority to
co-owned and co-pending U.S. patent application Ser. No. 13/351,182
entitled "FORM-LESS ELECTRONIC DEVICE ASSEMBLIES AND METHODS OF
OPERATION", filed Jan. 16, 2012, now U.S. Pat. No. 8,368,500, which
is a continuation of and claims priority to co-owned U.S. patent
application Ser. No. 13/012,616 of the same title, now U.S. Pat.
No. 8,098,125, which is a continuation of and claims priority to
co-owned U.S. patent application Ser. No. 12/572,168 of the same
title, now U.S. Pat. No. 7,876,189, which is a divisional of and
claims priority to co-owned U.S. patent application Ser. No.
10/885,868 entitled "FORM-LESS ELECTRONIC DEVICE AND METHODS OF
MANUFACTURING", now U.S. Pat. No. 7,598,837, and which claims
priority benefit of co-owned U.S. Provisional Patent Application
Ser. No. 60/485,801, of the same title, filed Jul. 8, 2003, each of
the foregoing being incorporated herein by reference in its
entirety.
COPYRIGHT
[0002] A portion of the disclosure of this patent document contains
material that is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure, as it appears in the
Patent and Trademark Office patent files or records, but otherwise
reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
[0003] 1. Field of Invention
[0004] The present invention relates generally to electronic
elements and particularly to an improved design and method of
manufacturing miniature electronic components including
transformers and inductive devices (e.g., "choke coils") without a
bobbin or other forming component.
[0005] 2. Description of Related Technology
[0006] As is well known in the art, inductive components are
electronic devices which provide the property of inductance (i.e.,
storage of energy in a magnetic field) within an alternating
current circuit. Inductors are one well-known type of inductive
device, and are formed typically using one or more coils or
windings which may or may not be wrapped around a magnetically
permeable core. So-called "dual winding" inductors utilize two
windings wrapped around a common core.
[0007] Transformers are another type of inductive component that
are used to transfer energy from one alternating current (AC)
circuit to another by magnetic coupling. Generally, transformers
are formed by winding two or more wires around a ferrous core. One
wire acts as a primary winding and conductively couples energy to
and from a first circuit. Another wire, also wound around the core
so as to be magnetically coupled with the first wire, acts as a
secondary winding and conductively couples energy to and from a
second circuit. AC energy applied to the primary windings causes AC
energy in the secondary windings and vice versa. A transformer may
be used to transform between voltage magnitudes and current
magnitudes, to create a phase shift, and to transform between
impedance levels.
[0008] Ferrite-cored inductors and transformers are commonly used
in modern broadband telecommunications circuits to include ISDN
(integrated services digital network) transceivers, DSL (digital
subscriber line) modems and cable modems. These devices provide any
number of functions including shielding, control of longitudinal
inductance (leakage), and impedance matching and safety isolation
between broadband communication devices and the communication lines
to which they are connected. Ferrite-core inductive device
technology is driven by the need to provide miniaturization while
at the same time meeting performance specifications set by chip-set
manufactures and standards bodies such as the ITU-T. For example,
in DSL modems, microminiature transformers are desired that can
allow a DSL signal to pass through while introducing a minimal THD
(total harmonic distortion) over the DSL signal bandwidth. As
another example, dual-winding inductors can be used in telephone
line filters to provide shielding and high longitudinal inductance
(high leakage).
[0009] "Shaped" Devices
[0010] A common prior art ferrite-cored inductive device is known
as the EP-core device. EP and similar devices are well known in the
prior art. For example, U.S. Pat. No. 5,489,884 to Heringer, et al.
issued Feb. 6, 1996 and entitled "Inductive Electric Component"
discloses an inductive electric component including a coil body
having coil body flanges defining a winding space, and contact pin
strips integrally formed onto the coil body flanges, the contact
pin strips having extensions and having free ends with undercuts
formed therein being limited outwardly by the extensions. U.S. Pat.
No. 5,434,493 to Woody, et al. issued Jul. 18, 1995 and entitled
"Fixed core inductive charger" discloses an EP-core device, as well
as other shaped core devices, including EE and RS devices. Other
similar well-know devices include inter alia so-called EF, ER, RM,
and pot core devices. See, e.g., the pot core device is described
in U.S. Pat. No. 5,952,907 to McWilliams, et al. issued Sep. 14,
1999 and entitled "Blind Hole Pot Core Transformer Device."
[0011] FIG. 1 illustrates a representative prior art EP transformer
arrangement, and illustrates certain aspects of the manufacturing
process therefore. The EP core of the device 100 of FIG. 1 is
formed from two EP-core half-pieces 104, 106, each having a
truncated semi-circular channel 108 formed therein and a center
post element 110, each also being formed from a magnetically
permeable material such as a ferrous compound. As shown in FIG. 1,
each of the EP-core half-pieces 104, 106 are mated to form an
effectively continuous magnetically permeable "shell" around the
windings 112, the latter which are wound around a spool-shaped
bobbin 109 which is received on the center post element 110. The
precision gap in ground on the ferrite post 110 can be engineered
to adjust the transfer function of the transformer to meet certain
design requirements. When the EP core device is assembled, the
windings 112 wrapped around the bobbin 109 also become wrapped
around the center post element 110. This causes magnetic flux to
flow through the EP core pieces when an alternating current is
applied to the windings. Once the device is assembled, the outer
portion of the EP cores self-enclose the windings to provide a high
degree of magnetic shielding. The ferrous material in the core is
engineered to provide a given flux density over a specified
frequency range and temperature range.
[0012] The bobbin 109 includes a terminal array 114 (aka "header")
generally mounted to the bottom of the device 100, with the
windings 112 penetrating through the truncated portions 116 of the
half-pieces 104, 106, the terminal array 114 being mated to a
printed circuit board (PCB) or other assembly. Margin tape (not
shown) may also be applied atop the outer portions of the outer
winding 112 for additional electrical separation if desired.
[0013] For each core shape and size, various differing bobbins are
available. The bobbins themselves (in addition to the other
elements of the parent device) have many different characteristics;
they can provide differing numbers of pins/terminations, different
winding options, different final assembly techniques, surface mount
versus through-hole mount, etc. For example, U.S. Pat. No.
6,587,023 to Miyazaki, et al. issued Jul. 1, 2003 and entitled
"Electromagnetic Induction Device" discloses a flat bobbin with
coaxially aligned through-holes. U.S. Pat. No. 5,350,980 to Dye, et
al. issued Sep. 27, 1994 and entitled "Nonlinear Inductor with
Magnetic Field Reduction" discloses, inter alia, a dumbbell-shaped
ferrite bobbin carrying an inductive coil.
[0014] Magnet wire is commonly used to wind transformers and
inductive devices (such as inductors and transformers, including
the aforementioned EP-type device). Magnet wire is made of copper
or other conductive material coated by a thin polymer insulating
film or a combination of polymer films such as polyurethane,
polyester, polyimide (aka "Kapton.TM."), and the like. The
thickness and the composition of the film coating determine the
dielectric strength capability of the wire. Magnet wire in the
range of 31 to 42 AWG is most commonly used in microelectronic
transformer applications, although other sizes may be used in
certain applications.
[0015] The prior art EP and similar inductive devices described
above have several shortcomings. A major difficulty with EP devices
is the complexity of their manufacturing process, which gives rise
to a higher cost. The use of a bobbin (also called a "form" or
"former") increases not only the cost, but size and complexity of
the final device, since the bobbin is retained within the device
upon completion of the manufacturing process. The bobbin consumes
space within the device which could be used for other
functionality, or conversely eliminated to give the final device a
smaller size and/or footprint.
[0016] Also, the EP core half pieces themselves are relatively
costly to mold and produce. For example, by the time the EP
transformer is assembled and tested, its volume production cost is
high (currently ranging from approximately $0.50 to-$0.70). It
would be desirable to produce a device having performance
characteristics at least equivalent to those of an EP transformer,
but at a significantly lower cost.
[0017] Yet a further disability of "headered" shaped core devices
such as that of FIG. 1 is the use of the header or terminal array
114 itself. This component adds additional cost and manufacturing
steps, and at minimum increases the vertical profile of the device
100. In certain applications, it would be desirable to utilize a
lower profile configuration without a header if possible.
[0018] Bonded Wire
[0019] Bonded wire is a well-established product/process that is
used to produce so-called "air coils". Air coils themselves are
inductors, and are typically use in RFID tags, voice coils,
sensors, and the like. The materials and manufacturing equipment
for producing bonded wire are commercially available from a variety
of sources known to the artisan of ordinary skill.
[0020] Bonded wire is essentially an enamel-coated wire having
additional coating applied (by either the wire vendor or the device
manufacturer) to the outer surfaces of the enamel. Generally,
during winding, the bonded wire coating may be activated (normally
by heat, although other types of processes including radiation
flux, chemical agents, and so forth) to cause the coated wires to
stick/bond together. This approach provides certain benefits and
cost economies in the context of electronic component
production.
[0021] Accordingly, there is a need for an improved electronic
device, and a method of manufacturing the device, that does not
require use of a bobbin or other form(er). Such an improved device
would ideally utilize existing and well understood technologies in
place of the bobbin/form(er) in order to simplify the manufacturing
process and further reduce cost, yet still maintain the desirable
electrical and physical properties of its bobbined counterpart
while reducing the overall size and/or footprint of the device.
[0022] Furthermore, for certain applications, it would be highly
desirable to obviate the header (terminal array) of the prior art
from the shaped core device altogether.
SUMMARY OF THE INVENTION
[0023] The present invention satisfies the aforementioned needs by
providing improved electronic inductive devices, and methods of
manufacturing the same.
[0024] In a first aspect of the invention, an improved form-less
electronic device is disclosed. The device generally comprises a
core and at least one winding, the at least one winding being
formed and disposed within the device without use of an internal
bobbin. In one exemplary embodiment, the device comprises a
bonded-wire coil formed to reside within a shaped core, the bonded
wire of the coil obviating the use of an internal bobbin or other
comparable structure. A termination element is disposed on the
bottom of the device to permit termination of coil windings to the
parent assembly (e.g., PCB).
[0025] In a second aspect of the invention, a multi-core device is
disclosed. In the exemplary embodiment, the multi-core device
comprises a plurality of form-less electronic inductive devices as
described above disposed within a common termination header in
end-to-end (or side-by-side) orientation, thereby economizing on
PCB footprint. Pins with common signals are optionally
consolidated, thereby reducing the required number of terminal
leads as well.
[0026] In a third aspect of the invention, a termination header for
use in terminating a form-less inductive device is disclosed. In
one embodiment, the termination header comprises a molded assembly
with inset SMT terminals which attaches to a single core of the
device using standard gluing techniques. In another embodiment, the
header is adapted to receive a plurality of cores adjacent one
another.
[0027] In a fourth aspect of the invention, a method of
manufacturing the above-referenced form-less electronic devices is
disclosed. The method generally comprises: providing a termination
header; providing a shaped core separated into at least two
elements; providing a bonded winding comprising wire having ends;
forming a shaped core assembly by disposing the winding within the
core components such that the ends are exposed; coupling the shaped
core assembly with a termination element having a plurality of
terminals; and terminating the ends of said winding to ones of the
terminals.
[0028] In a fifth aspect of the invention, an improved "direct
assembly" form-less device is disclosed. In one embodiment, the
device comprises a form-less inductive device as previously
described, yet which mates directly with the parent assembly (e.g.,
PCB), thereby obviating the termination header. The free ends of
the windings protrude from the device through an aperture formed in
the underlying assembly. The ends are soldered to conductive pads
present on the PCB substrate.
[0029] In a sixth aspect of the invention, a method of
manufacturing the form-less and header-less inductive device
previously described is disclosed. The method generally comprises:
providing a shaped core separated into at least two elements;
providing at least one length of wire having ends; forming the wire
into a core winding having a plurality of turns, also comprising
treating the wire so as to form the turns into a substantially
unitary component; and disposing the winding within the core
elements such that the ends of said winding are exposed for
termination. In one exemplary embodiment, the wire comprises
thermally activated bonding wire which is wound around a mandrel
and then heated, thereby obviating the bobbin. The assembled device
is then direct-assembled onto the PCB or other device as described
above.
[0030] In a seventh aspect of the invention, a self-leaded
electrical device adapted for surface mounting is disclosed,
generally comprising a bobbin-less inductive element and a
self-leaded termination element coupled to the inductive element,
the self-leaded termination element comprising a plurality of
terminal elements each adapted to receive at least one of the
winding ends of the inductive winding thereon so as to permit
surface mounting. In one exemplary embodiment, the termination
element comprises a molded plastic header with terminal posts
around which the core windings are wrapped.
[0031] In an eighth aspect of the invention, a low profile, low
cost electronic assembly, is disclosed, generally comprising: a PCB
having a first aperture formed therein and a plurality of contact
pads formed thereon; and a bobbin-less inductive device having a
shaped core with a second aperture formed therein and a winding
having a plurality of free ends, the first and second apertures
substantially communicating with each other such that the free ends
pass through both apertures and are each terminated to ones of the
contact pads. At least a portion of the winding is received within
the second aperture, thereby permitting the inductive device to be
reduced in overall (installed) height.
[0032] In a ninth aspect of the invention, a reduced footprint
multi-core electronic assembly is disclosed. The assembly generally
comprises a plurality of bobbin-less and header-less inductive
devices disposed in substantially mated and in-line configuration.
In one exemplary embodiment, the devices are disposed in adjacent,
juxtaposed (side-by-side) fashion and direct-assembled to the
parent device (e.g., PCB), thereby occupying the smallest possible
footprint.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The features, objectives, and advantages of the invention
will become more apparent from the detailed description set forth
below when taken in conjunction with the drawings, wherein:
[0034] FIG. 1 is an exploded view of a typical prior art EP
transformer design having a two-piece EP core and bobbin,
illustrating the components thereof.
[0035] FIG. 2a is an exploded perspective view of a first exemplary
embodiment of the improved electronic device of the present
invention.
[0036] FIG. 2b is a side plan view of the device of FIG. 2a.
[0037] FIG. 2c is a cross-sectional view of the device of FIG. 2a,
taken along line 2c-2c.
[0038] FIG. 2d is a logical flow diagram illustrating one exemplary
method of manufacturing the device of FIGS. 2a-2c.
[0039] FIG. 2e is a top elevational view of a first exemplary
embodiment of a self-leaded improved electronic device of the
present invention,
[0040] FIG. 2f is an end elevational view of a second exemplary
embodiment of a self-leaded improved electronic device of the
present invention.
[0041] FIG. 3 is a perspective view of second embodiment of the
form-less device of the present invention, having multiple
inductive cores and a unitary termination header.
[0042] FIG. 4 is a top perspective view of another embodiment of
the form-less electronic device of the invention adapted for direct
assembly to a parent device (e.g., PCB).
[0043] FIG. 4a is a bottom perspective view of the device of FIG.
4, illustrating one exemplary termination scheme used
therewith.
[0044] FIG. 4b is a front plan view of another exemplary
configuration of a "direct assembly" inductive device according to
the invention, for use on PCBs or other equipment not having an
aperture or recess.
[0045] FIG. 4c is a top plan view of a typical prior art multi-core
arrangement disposed on a PCB, illustrating its comparatively large
footprint.
[0046] FIGS. 4d and 4e are top and bottom plan views, respectively
of an exemplary "ganged" multi-core arrangement (on a PCB)
according to the present invention, illustrating its reduced
footprint as compared to that of the prior art arrangement of FIG.
4c.
[0047] FIG. 5 is a logical flow diagram illustrating one exemplary
method of manufacturing the device of FIGS. 4-4a.
[0048] FIG. 6a is an exploded perspective view of another
embodiment of the inductive device of the invention, illustrating
the use of a substrate and interface element.
[0049] FIG. 6b is a perspective view of the device of FIG. 6a fully
assembled.
[0050] FIG. 6c is an exploded perspective view of yet another
embodiment of the inductive device of the invention, illustrating a
simplified structure without an interface element.
[0051] FIG. 6d is an exploded perspective view of still another
embodiment of the inductive device of the invention.
[0052] FIGS. 6e and 6f illustrate still another embodiment of the
inductive device of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0053] Reference is now made to the drawings wherein like numerals
refer to like parts throughout.
[0054] As used herein, the term "inductive device" refers to any
device using or implementing induction including, without
limitation, inductors, transformers, and inductive reactors (or
"choke coils".
[0055] As used herein, the terms "bobbin" and "form" (or "former")
are used to refer to any structure or component(s) disposed on or
within an inductive device which helps form or maintain one or more
windings of the device.
[0056] As used herein, the term "signal conditioning" or
"conditioning" shall be understood to include, but not be limited
to, signal voltage transformation, filtering and noise mitigation,
signal splitting, impedance control and correction, current
limiting, and time delay.
[0057] As used herein, the term "digital subscriber line" (or
"DSL") shall mean any form of DSL configuration or service, whether
symmetric or otherwise, including without limitation so-called
"G.lite" ADSL (e.g., compliant with ITU G.992.2), RADSL: (rate
adaptive DSL), VDSL (very high bit rate DSL), SDSL (symmetric DSL),
SHDSL or super-high bit-rate DSL, also known as G.shdsl (e.g.,
compliant with ITU Recommendation G.991.2, approved by the ITU-T
February 2001), HDSL: (high data rate DSL), HDSL2: (2nd generation
HDSL), and IDSL (integrated services digital network DSL), as well
as In-Premises Phoneline Networks (e.g., HPN).
[0058] Overview
[0059] In one primary aspect, the present invention provides
improved bobbin-less electronic apparatus and methods for producing
the same, The electronic apparatus may be used in any number of
electrical circuits including for example those used for signal
conditioning or in DSL circuits. One significant benefit of winding
the coil independent of a bobbin (or "former") is that the space
normally taken up by the bobbin inside the device can be utilized
for additional functionality, or the design made smaller in size
and/or footprint.
[0060] Specifically, more winding space inside the device allows
any of the following (or combination thereof) to be utilized in the
design: (i) more winding turns can be used on a given design,
therefore more inductance/performance can be achieved in a given
form factor (i.e., higher winding density); (ii) alternatively,
heavier gauge wire can be used and yet maintain the same number of
turns, thereby providing other electrical performance benefits;
(iii) the performance of a given design using a bobbin can be
achieved in a smaller "bobbinless" design. Smaller devices are
generally lower cost. In addition to the cost benefit, smaller size
for a given perform also offers the end application space and
footprint reduction benefits that can be very attractive in
high-density applications.
[0061] In addition to the significant electrical design benefits,
bobbinless designs offer other significant advantages, including
the flexibility to terminate the windings of the device before or
after core assembly, and the use of different termination
approaches which take full advantage of the bobbinless design
construction and manufacturing methodology.
[0062] Exemplary Apparatus
[0063] It will be recognized that while the following discussion is
cast in terms of an exemplary shaped core transformer, the
invention is equally applicable to other inductive devices (e.g.,
inductors) and core configurations. Conceivably, any device having
a plurality of winding turns and requiring electrical insulation
may benefit from the application of the approach of the present
invention. Accordingly, the following discussion of the shaped core
transformer is merely illustrative of the broader concepts.
[0064] Referring now to FIGS. 2a-2c, an exemplary embodiment of a
bobbinless (form-less) inductive device (e.g. shaped core
transformer) is described. As shown in FIGS. 2a-2c, the device 200
generally comprises a core element 202, wound coil 204, and a
termination element or header 206. The core element in the
illustrated embodiment is "E-shaped" with an oval-shaped center leg
203; it will be recognized that various different shapes may be
used (such as EF, EE, ER, and RM, and even pot core), however. In
addition, it will be recognized that the core element and the wound
coil together may be at any angle relative to the header. For
example, FIG. 6 illustrates one embodiment where the "E-shaped"
core element 602a, 602b and wound coil 604 is positioned such that
the core's open plane is perpendicular to the printed circuit board
plane on which the header is positioned. The core element 202
comprises two pieces 202a, 202b of similar configuration. The core
is fashioned from a magnetically permeable material such as a soft
ferrite or powdered iron, as is well known in the electrical arts.
The manufacture and composition of such cores is well understood,
and accordingly is not described further herein. The cores are
assembled onto the wound coil 204 and the termination element
206.
[0065] In the illustrated embodiment, an adhesive is used to mate
the core 202 to the molded polymer termination element 206, due
primarily to ease of manufacturing and low cost However, other
techniques for fastening the two components (i.e., core 202 and
termination element 206) together may be utilized. For example,
metallic "spring" clips of the type well known in the art may be
used. Alternatively, a frictional arrangement can be used as well,
such as where two side risers (not shown) disposed lateral to the
outer sides of the core elements 202a, 202b are formed as part of
the termination element 206; the assembled core 202 is disposed
atop the termination element 206 and then forced into frictional
cooperation with the risers to maintain the core 202 in stationary
position on the element. As yet another option, the core portions
202a, 202b may be cemented or bonded together, and the wires of the
core in effect stretched taught and terminated (e.g., wire wrapped
and/or soldered) to the terminals 210 of the element 206. Hence,
the terminated wires act to maintain tension on the wound coil 204
(and therefore the core 202), thereby acting to maintain the core
assembly in communication with the termination element 206.
Different combinations of the foregoing may also be used as
desired.
[0066] The termination element 206 includes a plurality (e.g.,
eight) terminals 210 for physical and electrical mating to another
device, such as a PCB or the like. These terminals 210 may be of
literally any configuration, including for example, substantially
rectangular cross-section adapted for surface mount (SMT), circular
or elliptical cross-section for through-hole mounting, ball-grid
array, etc. They may also be notched or shaped to facilitate wire
wrapping if desired. Furthermore, it will be appreciated that the
termination element 206 may comprise a self-leaded arrangement (not
shown) of the type described in co-owned U.S. Pat. No. 5,212,345 to
Gutierrez issued May 18, 1993 entitled "Self leaded surface mounted
coplanar header", or U.S. Pat. No. 5,309,130 to Lint issued May 3,
1994 and entitled "Self leaded surface mount coil lead form", both
of which are incorporated herein by reference in their entirety.
For example, in one embodiment, the termination element 206 is a
molded polymer device having eight (8) self-leading terminals
formed therein, upon which various of the conductors of the coil
204 are wound. FIG. 2e shows a first embodiment of an electronic
device comprising self-leaded termination elements 250 according to
the principles of the present invention. FIG. 2f shows a second
embodiment of an electronic device comprising self-leaded
termination elements 250 according to the principles of the present
invention.
[0067] It is further recognized that the termination element 206
may take any number of different forms or configurations in terms
of its shape. For example, the termination element 206 may comprise
a substantially square, circular, or polygonal form, depending on
the needs of the particular application. Additionally, the exact
placement of the terminals 210 within the element 206 can be
optimized based upon circuit placement and mounting considerations
at the system level.
[0068] Also, if desired, the termination element may be obviated
altogether through, e.g., the approach described subsequently
herein with respect to FIGS. 4 and 4a, or alternatively direct
bonding of the conductive terminals 210 to the core itself.
[0069] As shown in FIG. 2a, the wound coil 204 comprises one or
more windings of wire which, when formed, is inserted between the
core portions 202a, 202b and into the termination element 206. The
coil windings consist of bonded wire of the type described
previously herein, and is wound independent of an internal bobbin
or form(er), such as on a removable die, winding mandrel or steel
former. The shape of the coil is defined by the dimensions of the
winding mandrel. In one exemplary embodiment, the winding mandrel
comprises a polished steel shaft with a centrally disposed groove
or recess. The groove/recess if formed by the extension of a
selectively retractable pin or shaft. The bonded wire is held by a
first of two small radial pins or dowels disposed adjacent the
groove of the shaft. The bound wire source (e.g., spool) is then
laterally aligned over the groove, and the shaft rotated to build
up the winding coil 204. Once the winding is complete, the terminal
end of the wire is then brought and held by a second radial pin
disposed adjacent the other side of the groove. The winding is then
heated (such as by blowing hot air over the mandrel, or heating the
mandrel itself, etc.) so that the wires of the coil are bonded.
[0070] It will be recognized that many variations of this approach
exist, such as where the shaft (mandrel) is stationary and the wire
source rotated around the mandrel. Such winding techniques are well
known in the mechanical arts, and accordingly not described further
herein.
[0071] Additionally, it will be appreciated that different winding
lay patterns may be used in order to achieve certain design
objectives. For example, a substantially parallel lay pattern may
provide the tightest spatial packing, thereby reducing the size of
the winding as a whole. Alternatively, other lay patterns may
provide the most desirable electrical and/or magnetic performance
for certain applications. All such variations will be recognized by
those of ordinary skill.
[0072] When the single or multiple winding has been completed, the
retractable center pin on the winding mandrel (which forms the
groove) is withdrawn allowing the formed and bonded coil to be
removed, or drop due to gravity, and winding of a new coil can
commence again.
[0073] In the exemplary embodiment, the bonded wire comprises 35
AWG-42 AWG bondable wire manufactured by the Bridgeport Insulated
Wire Company of Bridgeport, Conn., although other manufacturers,
configurations and sizes of wire may be used. The wire comprises
round copper magnet wire with a polyurethane base coating. The
polyurethane base coat has a polyamide (Kapton) and self-bonding
overcoat. The wire of the illustrated embodiment complies with the
NEMA MW29-C and IEC 317-35 international standards for wire,
although this is not required. It will be understood, however, that
suitable wire may be purchased and then subsequently coated
(whether before, during, or after the mandrel forming process
previously described) in order to produce the desired windings
204.
[0074] It will be recognized that the foregoing "form-less" wire
bonding process may be applied to (i) a single continuous winding;
(ii) multiple windings bonded into a unitary physical group or
structure; or (iii) single or multiple windings bonded into two or
more discrete groups which may or may not themselves ultimately be
bonded together using the aforementioned bonding techniques or
others. Hence, the present invention contemplates various
winding/bonding configurations which may be driven for example by
dielectric withstand requirements, the need for multiple windings
within the same core, and so forth.
[0075] Furthermore, while bonded wire is preferred, the device 200
may also utilize a wound coil formed and coated as described
generally in co-owned U.S. Pat. No. 6,642,827 issued Nov. 4, 2003
and entitled "Advanced Electronic Miniature Coil and Method of
Manufacturing", which is also incorporated herein by reference in
its entirety. Specifically, a Parylene coating is applied to a
plurality of individual wires formed into a layer or group using
for example a vapor or vacuum deposition process. Parylene is
chosen for its superior properties and low cost; however, certain
applications may dictate the use of other insulating materials.
Such materials may be polymers such as for example fluoropolymers
(e.g., Teflon, Tefzel), polyethylenes (e.g., XLPE),
polyvinylchlorides (PVCs), or conceivably even elastomers.
Additionally, dip or spray-on coatings may be used to form the
wound coil 204 of the illustrated invention.
[0076] Note that in the present embodiment, the free ends 220 of
the windings (see FIG. 2c) are stripped of insulation prior to
winding, after winding, or during soldering (so-called "solder
stripping"), using techniques well known in the art. This stripping
facilitates the formation of good electrical contacts with the
terminals 210 to which the free ends 220 are mated.
[0077] Because the coil is wound independent of an internal bobbin
or form(er), additional space inside the device 200 is available in
its final assembled configuration. This additional space permits
the inclusion of greater turns on a given core design, therefore
advantageously increasing the inductance and/or performance of a
given shaped core. Conversely, the additional space created by
obviating the bobbin allows the use of heavier gauge wire, while
maintaining the same number of turns, thereby providing other
electrical performance benefits such as reduced DC resistance and
insertion loss.
[0078] Furthermore, the additional space may be used to decrease
the overall size and/or footprint of the device 200, as well as its
weight. Smaller cores not only have a cost benefit (due to use of
less material), but also offer the end application space benefits,
which is especially attractive in high-density applications. For
example, the larger prior art (bobbined) counterpart device having
the required electrical performance simply may not fit in certain
applications. It can be appreciated that these design variations,
as well as other design variations available uniquely due to the
"bobbin-less" or form-less feature of the invention, may be used
independently or in combination with each other.
[0079] FIG. 2d illustrates one exemplary method 270 of
manufacturing the inductive device 200 of FIGS. 2a-2c. It will be
appreciated that while various steps are described in terms of
forming or manufacturing components of the inductive device 200,
such steps may be obviated by alternatively procuring the
pre-manufactured component from a third party.
[0080] As shown in FIG. 2d, the method 270 generally comprises
first forming a termination header 206 (step 272), including
forming the terminals 210 and disposing them within the header
(step 274). Next, a shaped core 202 is provided, separated into its
component elements 202a, 202b (step 276). Bonded wire is next
provided in sufficient quantity (step 278). Per step 280, the
bonded wire is then formed on an external form, and cured (e.g.,
heated, exposed to chemical agents, irradiated, etc.). The cured
coil 204 is then removed from the form and prepared, which includes
properly positioning the free ends of the windings and stripping
them if required (step 282). The prepared coil is then disposed
between the core halves, the latter being optionally bonded
together if desired (step 284). The assembled core is then disposed
onto the termination element 206 using adhesive (step 286), and the
free ends 220 terminated to their respective terminals 210 (step
288). The device is then optionally tested per step 290.
[0081] Referring now to FIG. 3, another embodiment of the inductive
device of the present invention is described. FIG. 3 shows a device
assembly 300 having multiple inductive devices 301 (e.g., four)
ganged together in an array which is disposed within a combined
termination header 306. In the illustrated embodiment, the devices
301 are disposed with their longer dimension being co-linear,
although other orientations (e.g., side-by-side) and array
formations may be used. The multiple core assembly 300 of FIG. 3
provides many advantages over single core assemblies. Specifically,
multiple cores 301, on a single header 306 reduce and/or eliminate
the spacing or stand-off required between cores on a single header
in conventional designs. This spacing represents wasted PCB area,
since the individual devices can be placed only so close to one
another. The space-conserving benefits of the invention are
magnified as greater numbers of devices are ganged; e.g., eight,
twelve, and so forth.
[0082] Multiple core termination headers 306 also reduce the number
of terminations to the printed circuit board (PCB), as common pins
or terminals 310 on a discrete design may be consolidated onto
single termination points in a multiple core header design such as
that of FIG. 3.
[0083] Furthermore, there are economies associated with the
fabrication of a single termination header 306 as opposed to two or
more discrete ones.
[0084] Direct Assembly Soldering Termination Method
[0085] In addition to the foregoing design benefits, the form-less
inductive devices of the present invention provide the ability to
terminate the wires before or after core assembly, rather than
requiring the termination of wires to pins on the bobbin prior to
core assembly as required under the prior art. The flexibility to
terminate the wires before or after coil assembly not only allows
for flexibility within the manufacturing process (e.g., the
permutation of the order of steps in making the device 200), but
also permits at least two distinct termination approaches: (i) the
use of termination elements (headers) as described with respect to
FIGS. 2a-2c above; and (ii) direct assembly soldering. The latter
technique is now described in detail with respect to FIGS. 4 and
4a. While the following discussion is cast in terms of EP-type
cores, it can be appreciated that the invention is in no way
limited to such core designs.
[0086] As shown in FIGS. 4 and 4a, the direct assembly soldering
approach of the present invention advantageously eliminates the
need for bobbin(s) or header(s). In this method, the inductive
device 400 is directly mounted and/or assembled onto the final
assembly or parent device, which may be for example a PCB 403 or
other electronic component. In the exemplary embodiment, the
assembly or parent device includes one or more apertures 405 formed
therein adapted to receive the free conductor ends 420 of the
device coil 404. The inductive device 400 may be glued or bonded to
the PCB 403 or other assembly to which it is mounted as shown in
FIG. 4, or alternatively friction-fit, such as by providing the
outer periphery of the core portions 402a, 402b with a tapered or
ridged construction (not shown), such that the device 400 in effect
"snaps" into the PCB aperture 405. Yet other techniques for
maintaining the device 400 in a substantially constant orientation
with respect to the parent assembly 403 may be used as well, such
as dowel pins, clips, etc.
[0087] As shown in FIG. 4a, the free ends 420 of the coil windings
are brought through the aperture 405 and terminated directly to PCB
contact pads 450 disposed on the underside 417 of the PCB 403. In
the illustrated embodiment, this termination comprises soldering of
the free ends 420 to the pads 450 (such as via a hand or wave
soldering process), although other approaches for termination may
also be used. It will be further appreciated that the invention is
in no way limited to the use of contact pads 450 such as those
shown in FIG. 4a; raised or embedded terminals, pins, etc. may be
used as well consistent with the invention. The illustrated
embodiment, however, has the advantage of simplicity and ease of
manufacture. For example, the depth of the coil 404 in the aperture
405 can be adjusted as desired (whether through device design, PCB
thickness, or use of an intervening spacer, not shown) to permit
use of a wave soldering process which is highly efficient in
providing mass termination of electrical contacts. To this end, the
interior edges 452 of the aperture 405 can be notched if desired
(not shown) in order to retain the routed free winding ends 420 in
the desired orientation with respect to the pads 450 before such
mass soldering is performed.
[0088] It will also be appreciated that while the embodiment of
FIGS. 4 and 4a utilizes pads 450 disposed on the disengaged or
underside of the PCB 403, such pads may also be disposed on the
upper (engaged) side 425 ("same side") of the PCB 403. In one
embodiment (FIG. 4b), the free ends 420 of the windings are simply
routed out from under the device 400 within the thickness of the
adhesive/bonding agent 470 applied between the device 400 and PCB
403 (i.e., the adhesive is applied in sufficient thickness to
permit insulated routing of the leads to pads 450 disposed on the
upper side 425. In another embodiment, the leads 420 are routed out
through notches formed in the core elements 402a, 402b. Other
approaches may be used as well.
[0089] Similarly, it will be recognized that the "same side" pad
arrangement described above may be used with or without the PCB
aperture or recess 405 previously discussed. For example, as shown
in FIG. 4b, the core elements 402 may be configured such that the
winding (when assembled) does not protrude below the plane of the
base of the core elements, thereby obviating the need for such
recess or aperture 405. This approach, however, makes the overall
installed height of the device 400 on the PCB (or other device)
somewhat higher than if the recess/aperture 405 is utilized. This
"aperture-less" configuration, however, may be desirable in cases
where the PCB or other equipment to which the device 400 is mounted
does not (or cannot) have apertures 405.
[0090] Note also that when mounted to a substrate or PCB, at least
portions of the inductive device(s) 400 of the present invention
may also optionally be encapsulated using an epoxy or polymer
encapsulant (such as silicone) as is well known in the art. The
devices may also be shielded against EMI as is well known in the
art, such as by using a well known tin or metallic Faraday
shield.
[0091] The foregoing "direct assembly" approach exemplified in
FIGS. 4-4a not only eliminates the cost of both a bobbin and,
termination header 206 in the device 400 (thereby providing an
appreciably simpler and less costly device for the same electrical
performance), but also advantageously reduces the overall installed
height of a given inductive device design. The approach of FIG. 4b
similarly has no bobbin or header, yet in effect trades greater
vertical height for the absence of a PCB aperture or recess to
accommodate the lower portion of the winding.
[0092] It will also be recognized that the direct assembly approach
generally described above can be used with multiple cores, akin to
the configuration of FIG. 3 previously discussed. Specifically,
multiple cores can be "ganged" together or placed in side-by-side
fashion on the parent device (e.g., PCB) so as to minimize the
footprint used by these devices. The devices 400 may be physically
coupled together if desired (not shown), such as by bonding them
together via adhesive or the like, using a metallic clip
arrangement, using a molded plastic frame which holds the devices
in constant relationship, etc. As yet another alternative, the left
and right core pieces 402a, 402b for the interior devices can be
fabricated as a unitary component (i.e., a left core piece of one
device 400 which has a right core piece for the immediately
adjacent device 400 as an integral part thereof), with the two end
core pieces of the assembly being of the type shown in FIG. 4. In
this fashion, when the cores are assembled, the individual devices
400 are inherently physically attached.
[0093] Under prior art approaches to multiple shaped cores (FIG.
4c), each of the bobbined and headered EP cores would need to be
spaced somewhat from one another to prevent interference between
their footprints (e.g., surface mount terminals). Contrast the
exemplary "direct assembly" configuration of the present invention
(FIGS. 4d and 4e), wherein the individual devices 400 may be
literally mated with one another, either side-by-side as in FIG.
4d, or end-to-end (not shown). This reduces the overall footprint
of the aggregated devices 400 (whether in length as shown in FIG.
4e, or width when the devices are disposed end-to-end).
[0094] Furthermore, the aperture-less approach of FIG. 4b can be
implemented in a multi-device assembly akin to that of FIGS. 4d and
4e (except with no PCB apertures 405), again trading greater
vertical height for the absence of the apertures/recesses.
[0095] Referring now to FIG. 5, a method 500 of direct assembly of
EP cores is described in detail. In the first step 502, the process
previously described with respect to FIG. 2d herein is utilized to
form the core of the device (specifically, steps 276-284). The
aperture 405 or recess adapted to accept the protruding coil (and
the lower contacting portion of the core, if desired) is then
formed in the PCB per step 504 (or the PCB acquired with such
feature already present). Next, the core is adhered, mated to, or
bonded to the PCB if required (step 506). As previously described,
such mating or bonding may be accomplished via adhesive,
silicone-based compounds, use of a "snap in" configuration. etc.
Termination is then completed to the pads 450 disposed on the side
of the PCB opposite to the side on which the device 400 sits; i.e.
the free ends of the coil wire(s) are routed from the core assembly
through the aperture (step 508) and terminated on the pads 450
(step 510).
[0096] Additionally, in another embodiment of the method, the coil
404 may be pre-positioned within the aperture (and optionally
terminated to the pads 450 first) before the core elements 402a,
402b are "sandwiched" around the coil, and adhered to one another
and/or the PCB 403.
[0097] Other Embodiments
[0098] Referring now to FIGS. 6a and 6b, yet another embodiment of
the "formerless" inductive device of the present invention is
described. As shown in FIG. 6a, this device 600 includes a core
assembly 602 with two core elements 602a, 602b and is generally
similar to those previously described with respect to FIGS. 2a-2c,
yet instead of using a header to terminate the windings of the
core, the windings 606 are terminated to a substrate 604 such as a
PCB. In the illustrated configuration, the terminal ends of the
windings 606 are soldered to the pads 609 or traces of the
substrate 604 (which may be disposed on the upper and/or lower
surfaces of the substrate 604); however, welding (such as using
standard electronics welding techniques known to those of ordinary
skill) may be substituted if desired.
[0099] A conventional PCB section is chosen as the substrate in the
illustrated embodiment for low cost; i.e., such PCBs are ubiquitous
in manufacturing, and have very low per unit costs since, inter
alia, many can be formed simultaneously.
[0100] The device 600 of FIG. 6a also comprises an interface
element 608 which electrically separates and mechanically locates
the core 602 and windings 606 on top of the substrate 604. The
interface element 608 of the present embodiment is formed of a
polymer (e.g., low cost plastic) fabricated using injection,
transfer, or other common molding techniques, although other
materials and formation techniques may be substituted if desired.
The substrate 604 optionally includes one or more apertures 611
which cooperate with corresponding pins 612 on the interface
element underside which permit registration of the interface
element 608, although other means may be used to mechanically align
the device 600 with respect to the substrate 604. For example, the
edge features 614 that cooperate with the substrate edges 616 (also
shown in FIG. 6a) may be used alone or in conjunction with the
aforementioned apertures/pins to provide the desired alignment.
[0101] In yet another embodiment (FIG. 6c), the lower portion of
each of the core elements are selectively extended to eliminate the
cost and labor associated with the interface element 608 of the
embodiment of FIG. 6. Specifically, one variant uses two core
halves 622a, 622b each with an extended skirt or lower portion 625
adapted to receive the substrate 604, the core halves each with
individually formed (or cut) apertures 627 through which the
winding conductors are routed, thereby allowing termination of the
winding ends to the substrate 604. The lower portion of the core
hence provides the mechanical registration otherwise provided by
the interface element 608 of the embodiment of FIG. 6a.
Alternatively other means for providing the desired mechanical
alignment may be used, such as forming or machining the core
portions 622a, 622b with one or more small alignment pins that
cooperate with apertures formed on the substrate 604.
[0102] In another variant (FIG. 6d), a plurality (e.g., eight) of
perforations or apertures 630 are formed in the substrate 604, with
the insulated conductors routed through the apertures 630 to
contact pads or traces 632 on, e.g., the bottom of the substrate.
These contact pads or traces, or others in electrical communication
therewith, act as an electrical interface to the parent device
(e.g., motherboard).
[0103] In still another embodiment (FIGS. 6e and 60, the substrate
604 is partly recessed into the bottom portion of the core elements
602a, 602b. The winding leads (not shown) can then be routed either
out through the gap 650 formed on the sides between the core
elements and the substrate, through apertures formed in the
substrate, or even directly onto contacts or pads on the substrate
upper surface under the winding (i.e., within the footprint" of the
core). The substrate 604 may also be outfitted with electrical
terminals of the type well known in the art if desired, such as by
adhering them directly to the substrate, or inserting them through
apertures formed in the substrate.
[0104] It will be further appreciated that although described in
the context of a single inductive device, the techniques described
above can also be readily extended to multi-inductor devices such
as those of FIG. 3. For example, multiple devices 600 of the type
shown in FIGS. 6a-6f can be mated to a common substrate 604 and
interface element 608, such as in the "row" configuration of FIG.
3, or alternatively in another pattern (such as e.g., in an
rectangular or square array). Myriad other configurations will be
recognized by those of ordinary skill given the present
disclosure.
[0105] It will be recognized that while certain aspects of the
invention are described in terms of a specific sequence of steps of
a method, these descriptions are only illustrative of the broader
methods of the invention, and may be modified as required by the
particular application. Certain steps may be rendered unnecessary
or optional under certain circumstances. Additionally, certain
steps or functionality may be added to the disclosed embodiments,
or the order of performance of two or more steps permuted. All such
variations are considered to be encompassed within the invention
disclosed and claimed herein.
[0106] While the above detailed description has shown, described,
and pointed out novel features of the invention as applied to
various embodiments, it will be understood that various omissions,
substitutions, and changes in the form and details of the device or
process illustrated may be made by those skilled in the art without
departing from the invention. The foregoing description is of the
best mode presently contemplated of carrying out the invention.
This description is in no way meant to be limiting, but rather
should be taken as illustrative of the general principles of the
invention. The scope of the invention should be determined with
reference to the claims.
* * * * *