Note: Descriptions are shown in the official language in which they were submitted.
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APPLYING AN OPTICAL FIBER TO A SUBSTRATE
TECHNICAL FIELD
The invention relates to a method and a device for applying an optical fiber
to a substrate,
in particular for making optical waveguide flexfoils, i.e. flexible sheets
having optical
s waveguides arranged therein or thereon, using optical fibers as the
waveguides.
BACKGROUND
Future demands on communication systems include an increased density of
components
used and higher bandwidths. Due to restriction in space and the high impedance
characteristics of thin electrical lines, increased component density on
printed circuit
,o boards, PCBs, renders difficulties in providing a sufficient number of
electrical
connections to an electrical backplane, BP, and from one circuit board to
another through
such a backplane. Due to the large bandwidth and low signal loss exhibited by
optical
fibers, the use of optical interconnections for inter board communication and
infra board
communication may reduce these problems.
,s However, a large number of loose fibers mounted on or connected to PCBs or
BPs will
give an unmanageable building practice. Optical fiber management is one of the
key
factors that have to be solved in order to successfully implement the use of
short range
optical interconnections. The short range optical interconnect medium here
presented
consists of optical fibers mounted on a flexible substrate, i.e. an optical
fiber flexfoil.
2o The optical flexfoil technique has been presented by the company AT&T, see
U.S. patent
No. 5,259,051 for Burack et al. This patent describes how optical fibers are
routed using
a rotatable wheel on a surface of a substrate coated with an adhesive. The
rotatable wheel
has three parallel grooves and is mounted at the lower end of a manipulator,
i.e. a robot
arm. The fiber is fed from a reel through a fiber guide to pass over a lower
portion of the
is wheel in one of the grooves to be deflected at the wheel by an angle of
about 45 ° . When
the manipulator is moved down to the flat surface having an adhesive coating,
the wheel
will press the piece of optical fiber at its lower surface and partly inside
the groove
against the surface to make the fiber stick to the surface. By moving the
robot arm and
thus the wheel over the surface it is possible to place the optical fiber
along any desired
so path. The optical fiber is placed on the surface in one whole length of
fiber. After placing
the fiber on the surface, the substrate is cut to provide accessible fiber
ends at the cutting
lines, the whole length of fiber then being separated into a plurality of
individual fiber
pieces. It is also mentioned that the optical fiber can be severed after each
interconnection
made, i.e. after applying the optical fiber between e.g. a start tab and an
end tab. The
ss patent also describes how the optical fiber is encapsulated between two
plastic foils, the
surface having' the adhesive coating being an inner surface of one of the
foils. Before
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applying the other foil the optical fibers applied are encapsulated by a layer
of a
thermoplastic material.
Another patent for the company AT&T, U.S. patent No. 5,204,925, focuses on
optical
flexfoils comprising connectorised tongues, i.e. tongues provided with optical
connectors.
s In this case, the tongues extend from the flexfoil, beyond the edges
thereof.
SUMMARY
It is an object of the invention to provide a method and a device for making
flexfoils
using optical fibers allowing that individual pieces of an optical fiber are
applied to a base
foil or sheet.
,o It is another object of the invention to provide a method and a device for
making flexfoils
using optical fibers allowing that a single fiber is applied substantially
only at positions
where it is needed, thus not requiring any fibers loops exterior to the
flexfoil base.
It is another object of the invention to provide a method and a device for
making flexfoils
using optical fibers allowing that the fibers are applied with small
curvatures at fiber
,s bends and with a minimum of mechanical stress on the fibers.
It is another object of the invention to provide a method and a device for
making flexfoils
using optical fibers allowing fiber cross-overs to be produced also for small
angles
between crossing fibers.
Thus, the problem to be solved by the invention is how to apply an optical
fiber to a base
zo flexfoil only at positions where it is needed for forwarding light and in
an accurate
manner with a good control of the applied fiber and with as small curvatures
as possible
with a minimum mechanical stress to the fiber during the application thereof.
In applying an optical fiber to a substrate, such as producing a flexfoil
structure having
optical waveguides located between two flexible plastics sheets which are
laminated to
zs each other, the substrate being one of the two foils to be laminated, this
substrate is
assumed to be coated with a suitable adhesive or at least to have a surface to
which the
optical fiber adheres when pressed against it. A supply of the optical fiber
is located
wound around a reel and the optical fiber is fed in a loose loop providing a
fiber
magazine from the reel to a collet or nozzle, giving the fiber located in
front of or
ao downstream the outlet of the collet a definite, accurately defined
direction. From the
outlet of the_ collet the optical fiber is passed as freely extending fiber
portion, not in
contact with the substrate surface or anything else, to a hold-down means
having a fixed
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bottom surface or pressing surface located at a small distance of the outlet
of the collet.
The hold-down means presses at its bottom or pressing surface the fiber
against the
surface of the substrate, the collet and its outlet then being located at some
small distance
from the substrate surface. The reel, collet and the holding-down means are
moved so that
s the contact point at the substrate surface is moved along a desired path,
where the optical
fiber is to be placed. A fiber cutter is located upstream the collet and it
can cut the fiber
at the places where it is to end so that no loose fiber end portions are
produced. A fiber
feeder is provided behind the cutter to feed more fiber after it has been cut.
The important features comprise firstly that in the laying-out-operation of
the optical fiber
,o the direction is defined by a device, the outlet of the collet, and the
pressing operation of
the fiber against the substrate is performed by a separate device, the hold-
down means, or
that the optical fiber is fed from the supply to contact, with a top side
portion of the fiber,
all the time the same bottom surface of the hold-down means and that
simultaneously a
bottom side portion of the fiber, which is opposite the top side portion, is
pressed by the
,s bottom surface to contact the surface of the substrate. The bottom surface
is thus a fixed
portion of the fixed hold-down means meaning that the fiber will all the time
contact the
same definite area of the bottom surface. The bottom surface is thus not
rotatable or a
portion of some rotatable body. It has a generally straight configuration of
its lower-most
part as see from the outlet of the collet, no guiding means being arranged in
or at the
zo bottom surface for maintaining the fiber in contact with the definite area
of the bottom
surface, the definite area being the central pan of the lower-most portion of
the bottom
surface.
The fiber is thus not guided in lateral directions of the fiber at the bottom
or pressing
surface of the hold-dow means, the lateral directions here being taken as
directions
zs parallel to the substrate surface and perpendicular to the longitudinal
direction of the fiber.
The bottom or pressing surface has no groove or any other guiding means, but
it may be
curved, as seen in the fiber direction, and straight, as seen in a direction
perpendicular to
the fiber direction along the substrate surface, or generally be part of a
circular-cylindrical
surface having its axis parallel to the substrate surface and a diameter of
typically 10 - 20
39 mm. The direction of the fiber along the substrate surface when it is
applied thereto, is
only defined by the collet and the rigidity of the fiber between the outlet of
the collet and
the pressing surface. The distance between the outlet of the collet and the
pressing surface
is selected to be sufficiently small, so that the rigidity of the optical
fiber will substantially
maintain the direction given by the collet up to the pressing surface.
3s It will then be advantageous if the optical fiber when being feed from the
outlet of the
collet up to the pressing surface of the hold-down means will not be sharply
deflected at
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the "pinch" between the pressing surface and the substrate surface. If it was
too sharply
deflected it could, owing to the bending and elastic forces in the fiber,
easily loose its
definite direction and slip away from the central portion of the pressing
surface. Therefor,
the free portion of fiber between the outlet of the collet and the pressing
surface is made
s to form a small angle to the substrate surface, the angle being chosen to be
as small as
possible considering the necessary dimensions of the collet and the free
portion of the
fiber from the collet to the bottom surface. In particular an angle of 5 - 1 S
° , preferably an
angle of 5 - 10°, can be used. The distance from the outlet of the
collet to the substrate
surface, also called the height of the outlet, will then be equivalently
small, e.g. about
,0 0.2 - 0.5 mm, for a free portion of the fiber of about 3 - 5 mm, preferably
substantially 4
mm between the outlet of the collet and the central point of the pressing
surface. Since the
width of the pressing surface or bottom surface of the hold-down means, as
seen in the
fibe direction, can suitably be about 3 - 4 mm, this means that the distance
from the collet
outlet to the most adjacent portion of the pressing surface is about 2 mm or
generally
,s 1.5 - 2 mm. The height of the collet outlet above the substrate surface
should be as small
as possible still allowing that the collet will not contact optical fibers
earlier placed on and
adhering to the substrate. The free portion of the fiber between the outlet of
the collet and
the pressing surface is selected to be as small as possible, considering that
the collet
should not touch earlier placed fibers and that the rigidity of the this
portion should be
2o sufficient to guide the fiber to the same central area at the lowest
surface of the pressing
means.
A second feature comprises the cutting operation which can be performed at any
place at
the substrate and thus allows fiber pieces to start and end at any desired
places. Thirdly,
the magazine portion of the optical fiber between the supply and the contact
point
is configured as a loosely hanging or suspended portion having a curvature
allows a rapid
feeding of the optical fiber at the contact point subjecting the fiber to a
minimum of
mechanical stress during the fiber-placing operation and in particular at
bends of the laid-
out fiber and at starts and stops.
This is in contrast to the teachings of the first cited U.S. patent 5,259,051
assigned to
3o AT&T which among other things does not include any fiber cutting facility.
Instead, the
AT&T patent describes how the fiber is routed as a continuous loop having
portions
placed outside the actual flexfoil area to be used causing substantial lengths
of fiber to be
spent in relation to the actually used fiber lengths in the finished flexfoil.
The patent states
that this is an advantage since it then is possible to determine the quality
of all the fiber
as routed in one measurement sending light through the fiber prior to cutting
the foil and the
fibers to define the usable area of the flexfoil. However, this is only an
advantage if
damage to the fiber by the routing is likely to occur. Possibly, also the
lamination of the
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top foil could be performed before the cutting operation and in the lamination
process then
also there could be a risk a causing damage to the place fiber. Using the
lamination
method described in the simultaneously filed International patent application
entitled
"Lamination of optical fiber flexfoils" together with the routing method as
described
s herein, the risk of such damage is virtually eliminated. The remaining risk
of damage or
malfunctioning will then reside in the activities made for connecting the
optical fibers to
external devices. However, such malfunctioning can only be detected by loss
measurements on the individual fiber pieces in the finished flexfoil
structure.
The fiber routing method and device described herein have the capability of
routing fiber
,o for forming cross-overs even though the angle between the two fibers
crossing each other
is small. If the fiber routing device is equipped with a grooved wheel, as
suggested by the
cited first patent assigned to AT&T, low angle fiber cross-overs may be
difficult to
achieve. The fiber-carrying grooved wheel may be blocked by the adjacent
fiber. If the
wheel would be moved in the Z-direction or height direction away from the
substrate
,s surface, the fiber may loose track due to the small and shallow keyway on
the wheel and
the elasticity of the fiber at the rather sharp bend at the wheel. However,
this patent
describes that the wheel is spring-loaded in order to allow cross-overs what
will make
sharp cross-overs even more difficult. Further, in order to route fiber
curvatures with
small radii, the radius of the wheel must be small. Depending on the depth of
the groove
zo in the wheel, the radius of this wheel may need to be smaller than the
smallest routing
radius used. If the smallest radius used is close to the mechanical safe
bending limit of
approximately 5 mm for conventional glass fiber, that is only valid for short
time periods
of bending - for longer periods substantially larger bending radii are only
allowed, the
bending radius during routing due to the wheel may be harmful to the fiber.
is In the method and device as described herein, the placement definition and
the actual
attachment are separated into two parts by the collet and the sleigh or hold-
down means
instead of being provided by a single part performing simultaneously or
integrated both
functions, the grooved wheel. This avoids all problems associated with using a
grooved
wheel as described above.
ao The use of the pre-cut fiber method as described above allows the use of
flexfoils having
internal tongues without having to get numerous redundant fiber portions in
the production
of the foil which would be the case using continuous routing as in the cited
prior art. The
advantages of internal tongues are described in the simultaneously filed
International
patent application "Flexfoils having connector tabs" .
3s Finally, in the cited U.S. patent 5,259,051 assigned to AT&T the fiber
being routed is
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directly pulled from a reel possessing a significant moment of inertia what
requires a
rather constant speed of feeding fiber from the reel and does not allow rapid
stops and
starts and what can also produce unnecessary tensions in the fiber when making
bends.
Additional objects and advantages of the invention will be set forth in the
description
s which follows, and in part will be obvious from the description, or may be
learned by
practice of the invention. The objects and advantages of the invention may be
realized and
obtained by means of the methods, processes, instrumentalities and
combinations
particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
,o While the novel features of the invention are set forth with particularly
in the appended
claims, a complete understanding of the invention, both as to organization and
content,
and of the above and other features thereof may be gained from and the
invention will be
better appreciated from a consideration of the following detailed description
of non
limiting embodiments presented hereinbelow with reference to the accompanying
,s drawings, in which:
- Fig. 1 is a perspective view of an apparatus for applying an optical fiber
to a substrate,
and
- Fig. 2 is a schematic cross-sectional view of the apparatus of Fig. 1,
- Fig. 3 is a cross-sectional view showing schematically a lower portion of a
cutting tool,
Zo and
- Fig. 4 is a cross-sectional view showing schematically a lower portion of a
feeding unit.
DETAILED DESCRIPTION
In Fig. 2 a schematic cross-sectional view of an apparatus for routing optical
fiber 1 on a
surface of a substrate 3 is shown, the apparatus being shown also in a
perspective view in
2s Fig. 1. The surface of the substrate is made to adhesive to an optical
fiber to be applied
such as by coating with a suitable adhesive or subjecting the surface to some
other
suitable treatment. A vertical flat house 5 is mounted on a robot arm 7 of a
manipulator,
not shown. A feeding collet 9 is attached at a low position of the house S. A
hold-down
means or sleigh 11 is mounted at the lower end of the robot arm 7, so that the
nozzle,
so outlet or mouth of the collet 9 is located at a small distance from and
directed towards the
bottom surface of the sleigh 11. The bottom surface has a part-cylindrical
shape, the
cylindrical surface thus being directed downwards and the axis of the part-
cylindrical
surface being perpendicular to the direction of a fiber passing through the
collet 9 to the
part-cylindrical surface and also horizontal and thus substantially parallel
to the top
as surface of the substrate 3. The manipulator is capable of moving the arm 7
in parallel to
the top surface of the substrate 3 located underneath the apparatus, the
adhesive top
.~.. ,
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surface being horizontal and extending in the X-Y-plane. The manipulator is
also capable
of moving the arm 7 in the vertical direction or Z-direction perpendicular to
said surface
and of rotating it in the ~p-direction about a vertical axis passing through
the center of the
generally vertical arm 7, through the contact point of a routed fiber drawn
from the collet
s 9 and the bottom side of the sleigh 11.
At the top edge of housing 5 a reel 13 having the optical fiber wound thereon
is mounted.
A motor unit 15 is attached to the reel 13 and has control means allowing the
fiber to be
automatically unwound from the reel 13. From the reel 13 the fiber is fed
inside and in
parallel to the vertical large surfaces of the house 5 in a specially designed
path
,o comprising first a loose, freely hanging or freely suspended loop 17,
generally a free,
non-straight portion having a curvature, and from that, as guided by a border
19 of the
house 5, that projects laterally or in a horizontal direction from the large
surfaces of the
house 5, to the inlet of the feeding collet 9. A high precision fiber feeding
unit 21 and a
fiber cutting tool 23 are attached to the plate S behind or upstream the
feeding collet 9.
,s The fiber feeding unit 21 feeds the fiber or fiber-end region before and
during the actual
fiber routing.
The house 5 thus has the shape of a basically inverted, triangular main body
having a
horizontal upper side and containing the fiber freely hanging loop 17. The
reel 13 is
attached to the front upper corner of the triangular shape. From the rear
upper corner of
Zo the triangular shape a channel projects for guiding the fiber to the
feeding unit 21, the
channel being limited in the forward direction of the house by the border 19
and
extending first in a vertical direction to finish in a curved portion having a
forward bend
to end in a small angle to the horizontal plane. A steel plate 24 connects the
main
triangular body of the house 5 and the channel portion for stabilizing the
channel portion.
is A lower portion of the cutting tool 23 is shown in Fig. 3. It comprises a
housing in which
a cylindrical channel 31 is arranged for guiding the optical fiber 1 through
the tool. A
knife 33 is arranged in the housing in order to be moved, as driven by a
suitable motor,
not shown, see the arrow 34, in a direction perpendicular to the that of the
channel 31 for
cutting the optical fiber when required. A cleaning channel 35 is provided
from the
ao outside of the housing to the edge of the knife 33. Particles which can be
formed in the
cutting operation can be sucked out through this channel. The front mouth of
the fiber
channel 31 is connected to the nozzle 9, not visible in Fig. 3.
In the same way a lower portion of the feeding unit 21 is shown in Fig. 4. It
has a
housing in which a cylindrical channel 41 is arranged for guiding the optical
fiber 1
3s through the unit. Two rollers 43 , acting on opposite sides of the optical
fiber to be
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transported, are arranged inside the housing. The rollers 43 can rotate freely
or be rotated
by being driven by a motor, not shown, when required, for feeding the optical
fiber in the
channel 41, both when introducing a new piece of optical fiber and after
cutting the
optical fiber in the cutting tool 23.
s Now the routing of a piece of optical fiber will be described. First the
optical fiber is
manually unwound from the reel 13 and positioned in the desired path inside
the house 5,
first in the loosely hanging loop 17 and then along a semi-circular path
having its central
point located highest, the border 19 and thus the channel portion of the house
being
configured correspondingly. From the semi-circular path the fiber is placed
along a
,o vertical path and is then bent to a direction which is nearly horizontal
and is therefrom
inserted in the inlet of the fiber feeding unit 21. The fiber feeding unit 21
senses the
inserted fiber end and feeds, by activating its motor acting on the rollers
43, a piece of
fiber through the cutter 23 and the collet 9 and up to the central, lowest
point of the
bottom or pressing surface of the sleigh 11.
,s When the end of the fiber is in this position at the profiled bottom
surface of the sleigh
11, the manipulator moves the arm 7 downwards, so that the sleigh 11 is moved
towards
the adhesive-made upper surface of the substrate 11 with the lowest points of
its bottom
surface forming a straight line parallel to the substrate surface. Then the
bottom surface
presses the fiber against the substrate surface, so as to make the fiber 1
adhere to the
zo adhesive surface of the substrate 11. The thickness of an adhesive coated
on the substrate
surface and/or the pressure are adjusted so that the bottom surface of the
sleigh 11 never
touches the adhesive and only the upper side of the fiber I. The manipulator
then moves
the robot arm 7 in parallel to the upper surface of the substrate 3. As the
robot arm 7
moves, the optical fiber I adheres to the substrate along a selected path
determined by the
25 movement of the arm 7 in relation to the substrate 3. The friction or
adhesive forces
between the pressed-down fiber 1 and the adhesive surface causes the optical
fiber to be
automatically fed from the loose loop 17 inside the housing 5 and further
through the
feeding collet 9. As has already been described, the robot arm 7 is rotatable
in the ~p-
direction about its vertical central axis which passes through the contact
point between the
ao sleigh 11 and the fiber 1 during the pressing operation. A change in the
direction of the
path of the fiber to be placed on the adhesive surface requires a rotation of
the robot arm
7 as well as a change of the velocity of its movement in the X- and Y-
directions. The
amount of the rotation (movement in the cp-direction) of the robot arm 7 in
each instant is
determined by the radius of the fiber path curvature. When the robot arm 7
rotates around
3s its vertical central axis, also the house 5 and its attached components
rotate, i.e. the reel
13, the fiber feeding unit 21, the fiber cutting tool 23 and the feeding
collet 9, and of
course also the sleigh 11 which is rigidly attached to the robot arm 7.
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When nearly all of the required length of optical fiber has been routed in the
desired path,
the cutting tool 23 is activated for cutting off the fiber by moving the knife
33. The robot
arm 7 then continues its horizontal movement along a short additional path so
that the
fiber piece between the sleigh 11 and the edge of knife 33 in the cutting
means 23 is
s expelled from the feeding collet 9 and is pressed on to the coated top
surface. Thus a
piece of optical fiber has been placed at the coated surface in a desired
path. Then, the
robot arm 7 is moved upwards, in the Z-direction from the top surface of the
substrate 3.
After the sleigh 11 has lost contact with the upper side of the routed fiber,
the robot arm
7 is free to move to a new starting point for another piece of optical fiber
to be routed,
,o i.e. to perform a movement in the X- and Y-directions. At this starting
point additional
fiber is fed automatically by the feeding unit 21 by activating the motor
acting on the
rollers 43 through the cutting tool 23 and the feeding collet 9 in order to
place the fiber
end in a suitable start position centrally at the bottom surface of the sleigh
11. The robot
arm 7 is then moved downwards, in the Z-direction towards the substrate
surface, which
,s causes the fiber at the lower surface of the sleigh 11 once again to adhere
to the surface
of the substrate 3. Now, a movement of the robot arm 7 in the X- and/or Y-
directions
causes new fiber to be routed, etc.
In the operation described above, when a fiber is routed, friction between the
coated
surface of the substrate 11 all the time causes additional, new fiber 9 to be
automatically
zo and successively fed from the feeding collet 9, the rollers 43 of the
feeding unit 21 then
rotating freely, not interfering with the transport of new fiber. Then new
fiber is fed from
the loop 17 of fiber which loosely hangs down from the reel 13. Because of
this loose
loop, the tension exerted on the fiber during the fiber routing is low enough
not to damage
the fiber and the moment of inertia of the reel 13 does not influence the
automatic fiber
zs feeding operation at the bottom surface of the sleigh 11 when it is moved
pressing the
fiber 1 to contact the coated surface. Using this apparatus having the
described cut-and-
place function requires also a quick stopping and starting of the fiber
feeding process and
of the movement of the arm 7. A control and sensing unit 25 is mounted at a
vertical side
of the house 5 at the location of the loosely hanging fiber loop 17 and it is
arranged to
ao control the amount of fiber contained in this loop. When a certain amount
of fiber has
been fed from the loop 17, the control and sensing unit 25 starts the motor 1
S attached to
the reel 13 for feeding a predetermined length of fiber from the reel 13 to
restore the
original shape of the loosely hanging loop 17. This can made by arranging e.g.
two
sensors 27, 29 such as photodetectors at different heights in the area of the
loosely
3s hanging loop 17. The upper sensor 27 signals when the loosely hanging loop
has 17 been
used sufficiently for feeding more fiber from the reel 13 and the lower sensor
29 signals
that sufficient new fiber has been fed from the reel 13.
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A fiber crossing an already placed fiber may be routed even though the angle
between the
two fibers is small. If a fiber is to cross an adjacent fiber, the manipulator
moves the
robot arm 7 in the Z-direction upwards from the substrate surface at the
starting point of
the fiber crossover. When the bottom surface of the sleigh 11 does not any
more press the
s currently routed fiber against the substrate surface it moves in an oblique
direction, i.e.
simultaneously both in parallel with as well as perpendicular to, the adjacent
fiber. When
the fiber has been crossed, the manipulator moves the arm 7 in the Z-direction
towards
the substrate surface which causes the fiber at the bottom surface of the
sleigh 11 once
again to adhere to the substrate surface.
,o Attached to the robot, that carnes the manipulator, is a unit, not shown,
that makes
alignment marks on the substrate. When the manipulator moves in the X- or Y-
direction
to the substrate surface, it moves relative to the alignment marks. The
alignment marks
are used as reference points in the coordinate system used by a control system
using video
cameras and controlling the manipulator in the same way as in automatic
component
,s mounting machines for e.g. surface mounting of electronic components. The
alignment
marks thus allow that a low accuracy is used when the substrate is placed in a
fixture in
the fiber routing apparatus.
The fibers placed on a substrate as described above are then, for forming a
flexfoil,
encapsulated by a top substrate, not shown, placed on top of the fibers and of
the
zo substrate 11 and adhering to the fibers and the substrate, the substrates
then usually
comprising flexible plastic sheets. The flexfoil thus formed may then be
subjected to a
cutting operation for adjusting the shape of the flexfoil and for forming
tongues, not
shown, used for external optical connections. If the cutting machine is
equipped with a
vision system that locates the alignment marks on the substrate, the
punching/cutting
zs process may be performed using the internal coordinate system given by the
alignment
marks.
The fiber routing technique here described allows a large number of fibers of
arbitrary
lengths to be routed on a substrate surface, i.e. arbitrary lengths in sense
of several fibers
having predetermined lengths or also one continuous fiber. The technique may
be used for
3o any kind of optical fiber, e.g. optical glass fibers and plastics or
polymer optical fibers.
While specific embodiments of the invention have been illustrated and
described herein, it
is realized that numerous additional advantages, modifications and changes
will readily oc-
cur to those skilled in the art. Therefore, the invention in its broader
aspects is not limited
to the specific details, representative devices and illustrated examples shown
and described
as herein. Accordingly, various modifications may be made without departing
from the spirit
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11
or scope of the general inventive concept as defined by the appended claims
and their
equivalents. It is therefore to be understood that the appended claims are
intended to cover
all such modifications and changes as fall within a true spirit and scope of
the invention.
