U.S. patent application number 12/249613 was filed with the patent office on 2009-02-05 for fiber optic cables suitable for automated preconnectorization.
Invention is credited to Warren W. McAlpine, Allen M. Miller.
Application Number | 20090034923 12/249613 |
Document ID | / |
Family ID | 37996403 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090034923 |
Kind Code |
A1 |
Miller; Allen M. ; et
al. |
February 5, 2009 |
Fiber Optic Cables Suitable for Automated Preconnectorization
Abstract
Fiber optic drop cables are disclosed that are suitable for
automated preconnectorization. In one embodiment, an optical
waveguide is disposed in a buffer tube that has two strength
components disposed on opposite sides thereof and a plurality of
strength members. The plurality of strength members are disposed at
a plurality respective interstices located between the buffer tube
and the two strength components and shaped into a plurality of
substantially triangular shapes for improving the balancing of the
residual stresses in the fiber optic cable caused by the shrinkage
of a cable jacket during cooling. In another embodiment, a fiber
optic cable includes a tonable lobe connected by a web that is
frangible and the web includes predetermined ratios for easily and
reliable separation of the tonable lobe.
Inventors: |
Miller; Allen M.; (Newton,
NC) ; McAlpine; Warren W.; (Hickory, NC) |
Correspondence
Address: |
CORNING INCORPORATED
INTELLECTUAL PROPERTY DEPARTMENT, SP-TI-3-1
CORNING
NY
14831
US
|
Family ID: |
37996403 |
Appl. No.: |
12/249613 |
Filed: |
October 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11264241 |
Nov 1, 2005 |
7454107 |
|
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12249613 |
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Current U.S.
Class: |
385/113 |
Current CPC
Class: |
G02B 6/4433 20130101;
G02B 6/447 20130101 |
Class at
Publication: |
385/113 |
International
Class: |
G02B 6/44 20060101
G02B006/44 |
Claims
1. A fiber optic drop cable comprising: a main cable body, the main
cable body having at least one optical waveguide, at least one
strength component, and a cable jacket; and a tonable lobe, the
tonable lobe having a toning wire that includes a copper material
for locating the fiber optic drop cable, the tonable lobe being
connected to the cable jacket of the main cable body by a web that
is frangible, wherein the web has a first radius R1 adjacent to the
main cable body and a second radius R2 adjacent to the tonable
lobe, and a radius ratio is defined as the ratio between the second
radius and the first radius (R2/R1), wherein the radius ratio is
greater than 2.
2. The fiber optic drop cable of claim 1, the main cable body
further comprising at least one strength member.
3. The fiber optic drop cable of claim 2, the at least one optical
waveguide being disposed within a buffer tube.
4. The fiber optic drop cable of claim 3, the buffer tube having a
thixotropic grease therein.
5. The fiber optic drop cable of claim 2, the web having a first
thickness t1 adjacent to the main cable body and a second thickness
t2 adjacent to the tonable lobe and a thickness ratio is defined as
the ratio between the second thickness and the first thickness
(t2/t1), wherein the thickness ratio is greater than 1.
6. The fiber optic drop cable of claim 2, the main cable body
having a width of about 10 millimeters or less and a height of
about 5 millimeters or less.
7. The fiber optic drop cable of claim 1, the optical waveguide
being housed in a buffer tube, the main cable body having two
strength components and a plurality of strength members disposed at
a plurality interstices between the buffer tube and the two
strength components.
8. The fiber optic drop cable of claim 7, the plurality of strength
members being shaped into a plurality of substantially triangular
shapes for improving the balancing of the residual stresses in the
fiber optic cable due to shrinkage of a cable jacket during
cooling.
9. The fiber optic drop cable of claim 2, the web having a first
thickness t1 adjacent to the main cable body and the tonable lobe
having a minimum wall thickness t3, wherein a tear control ratio is
defined as the ratio between the minimum wall thickness and the
first thickness (t3/t1), wherein the tear control ratio is greater
than about 0.7.
10. The fiber optic drop cable of claim 2, the tonable lobe having
a separation force from the main cable body between about 10
Newtons and about 50 Newtons along a X-X axis.
11. A fiber optic drop cable comprising: a main cable body, the
main cable body having at least one optical waveguide, at least one
strength component, and at least one strength member; and a tonable
lobe, the tonable lobe having a toning wire that includes a copper
material for locating the fiber optic drop cable and the tonable
lobe being connected to the main cable body by a web that is
frangible, wherein the web has a first thickness t1 adjacent to the
main cable body and the tonable lobe has a minimum wall thickness
t3, and a tear control ratio is defined as the ratio between the
minimum wall thickness and the first thickness (t3/t1), wherein the
tear control ratio is greater than about 0.7.
12. The fiber optic drop cable of claim 11, the web having a first
radius R1 adjacent to the main cable body and a second radius R2
adjacent to the tonable lobe and a radius ratio is defined as the
ratio between the second radius and the first radius (R2/R1),
wherein the radius ratio is greater than 1.
13. The fiber optic drop cable of claim 12, the radius ratio being
greater than about 2.0.
14. The fiber optic drop cable of claim 11, the main cable body
having two strength components and a plurality of strength members
disposed at a plurality of interstices between a buffer tube and
the two strength components.
15. The fiber optic drop cable of claim 14, the strength members
being shaped into a plurality of substantially triangular shapes
for improving the balancing the residual stresses in the fiber
optic cable due to shrinkage of a cable jacket during cooling.
16. The fiber optic drop cable of claim 11, the at least one
optical waveguide being disposed within a buffer tube.
17. The fiber optic drop cable of claim 16, the buffer tube having
a thixotropic grease therein.
18. The fiber optic drop cable of claim 11, the web having a first
thickness t1 adjacent to the main cable body and a second thickness
t2 adjacent to the tonable lobe and a thickness ratio is defined as
the ratio between the second thickness and the first thickness
(t2/t1), wherein the thickness ratio is greater than 1.
19. A fiber optic drop cable comprising: a main cable body, the
main cable body having at least one optical waveguide, at least one
strength component, and at least one strength member, the main
cable body having a width of about 10 millimeters or less and a
height of about 5 millimeters or less; a tonable lobe, the tonable
lobe having a toning wire that includes a copper material for
locating the fiber optic drop cable and the tonable lobe being
connected to the main cable body by a web that is frangible,
wherein the web has a first thickness t1 adjacent to the main cable
body and the tonable lobe has a minimum wall thickness t3, wherein
a tear control ratio is defined as the ratio between the minimum
wall thickness and the first thickness (t3/t1), wherein the tear
control ratio is greater than about 0.7.
20. The fiber optic drop cable of claim 19, the tonable lobe having
a separation force from the main cable body between about 10
Newtons and about 50 Newtons along a X-X axis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
11/264,241, filed Nov. 1, 2005, the entire contents of which are
hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to fiber optic
cables suitable for routing optical fiber toward the subscriber
such as fiber to the home applications. More particularly, the
present invention relates to fiber optic cables having separable
toning lobes and/or that are suitable in automated
preconnectorization processes, although the invention is not
limited to such applications.
BACKGROUND
[0003] Communication networks are used to transport a variety of
signals such as voice, video, data transmission, and the like.
Traditional communication networks use copper wires in cables for
transporting information and data. However, copper cables have
drawbacks because they are large, heavy, and can only transmit a
relatively limited amount of data. On the other hand, an optical
waveguide is capable of transmitting an extremely large amount of
bandwidth compared with a copper conductor. Moreover, an optical
waveguide cable is much lighter and smaller compared with a copper
cable having the same bandwidth capacity. Consequently, optical
waveguide cables replaced most of the copper cables in long-haul
communication network links, thereby providing greater bandwidth
capacity for long-haul links. However, many of these long-haul
links have bandwidth capacity that is not being used. This is due
in part to communication networks that use copper cables for
distribution and/or drop links on the subscriber side of the
central office. In other words, subscribers have a limited amount
of available bandwidth due to the constraints of copper cables in
the communication network.
[0004] As optical waveguides are deployed deeper into communication
networks, subscribers will have access to increased bandwidth.
Deployment of optical waveguides toward the subscriber is generally
called fiber to the location x (FTTx) applications and includes
fiber-to-the-curb (FTTC) and fiber-to-the-home (FTTH) applications.
There are certain obstacles that make it challenging and/or
expensive to route optical waveguides closer to the subscriber. For
instance, making a suitable optical connection between optical
waveguides is much more complicated than making an electrical
connection between copper wires. Additionally, as the communication
network pushes toward subscribers, the communication network
requires more connections, which compounds the difficulties of
providing optical waveguides to the premises of the subscriber.
Thus, routing fiber optic cables towards the subscribers requires a
quick and easy solution for streamlining the installation process.
Also, on the end of the network closest to the subscriber, smaller
cables housing fewer optical fibers are typically used. Such cables
have their own set of particular location, installation,
termination, and connectorization issues generally not found with
long haul cables.
[0005] For example, fiber optic cables routed toward the premises
of the subscriber may be buried in the yard of the subscriber.
Consequently, these buried fiber optic cables are preferably
located and marked to prevent damage to the same before the
subscriber or others dig. Generally speaking, the craft prefers
dielectric cables since they do not have to be grounded and the
like. However, dielectric cables are difficult to locate when
buried. To address this problem, fiber optic cables have included a
toning wire for locating the buried cable. The toning wire is
typically a conductor such as copper wire that can be used to
locate the buried fiber optic cable by sending a signal along the
toning wire that can be detected above ground to locate the cable.
Specifically, the route of a buried fiber optic cable having a
toning wire is found by attaching a tone generator device to an
exposed portion of the toning wire so as to generate an electrical
toning signal along the toning wire. A detector is then used by the
craft to find the buried portions of the toning wire by detecting
the toning signal, thereby allowing marking of the cable
location.
[0006] By way of example, U.S. Patent App. Pub No. 2005/0053342,
the disclosure of which is incorporated herein by reference,
discloses a preconnectorized fiber optic cable having a toning wire
disposed in a toning lobe that is connected by a web to a main
cable body. The preconnectorized cable includes a plug connector
that allows the craft to quickly and reliably optically connect the
cable. Before the plug connector can be attached to the end of the
cable the toning lobe must be separated from a portion of the main
cable body.
[0007] However, conventional toning lobes may not have been as
readily or reliably separable from the main cable body as desired.
At times, during separation of the toning lobe from the main cable
body, the cable surface at the tear was not as smooth as desired
after separating the toning lobe. In extreme cases, the toning
lobes may have undesired separation from the main cable body or the
toning wires may be inadvertently torn from their lobes without the
desired separation at the web. In any event, leaving a poor tear
and/or non-uniform surface at the point of removal can cause
problems during the preconnectorization of the fiber optic cable.
For instance, a poor tear or non-uniform surface where the tonable
wire was removed may require further attention by the craft during
connectorization to either remove the poorly torn section and/or
use additional sealing elements, etc., to ensure environmental
sealing of the cable in the connector. This is especially true for
automated connectorization processes that require reliable and
repeatable separation performance of the toning lobe. Thus,
improved fiber optic cable designs incorporating a toning lobe that
is easily separated from the main cable body without damage or
leaving irregular surfaces are desirable.
SUMMARY
[0008] One aspect of the present invention is directed to a fiber
optic drop cable having a main cable body with at least one optical
waveguide disposed in a buffer tube, two strength components
disposed on opposite sides of the buffer tube, and a plurality of
strength members. The plurality of strength members are disposed at
a plurality of respective interstices located between the buffer
tube and the two strength components, wherein the plurality of
strength members are shaped into a plurality of substantially
triangular shapes. The substantially triangular shapes are useful
for improving the balancing of the residual stresses in the fiber
optic cable due to shrinkage of a cable jacket during cooling.
[0009] Another aspect of the present invention is a fiber optic
drop cable having a main cable body with at least one optical
waveguide, at least one strength component, and
[0010] a tonable lobe for locating the cable. The tonable lobe is
connected to the main cable body by a web that is frangible. The
web has a first radius R1 adjacent to the main cable body and a
second radius R2 adjacent to the tonable lobe and a radius ratio is
defined as the ratio between the second radius and the first radius
(R2/R1). The radius ratio is greater than about 1 and more
preferably greater than about 2.
[0011] Yet another aspect of the present invention is directed to a
fiber optic drop cable having a main cable body having at least one
optical waveguide disposed within a buffer tube, two strength
components disposed on opposite sides of the buffer tube, a
plurality of strength members, and a tonable lobe. The plurality of
strength members being disposed at a plurality of respective
interstices located between the buffer tube and the two strength
components. The strength members each have a substantially
triangular shape for improving the balancing of the residual
stresses in the fiber optic cable due to shrinkage of a cable
jacket during cooling. The tonable lobe is connected to the main
cable body by a web that is frangible and the web has a first
radius R1 adjacent to the main cable body and a second radius R2
adjacent to the tonable lobe. A radius ratio is defined as the
ratio between the second radius and the first radius (R2/R1),
wherein the radius ratio is greater than 1.
[0012] The present invention is also directed to a fiber optic drop
cable having a main cable body with at least one optical waveguide
and at least one strength component. A tonable lobe is connected to
the main cable body by a web that is frangible. The web has a first
thickness t1 adjacent to the main cable body and the tonable lobe
has a minimum wall thickness t3, wherein a tear control ratio is
defined as the ratio between the minimum wall thickness and the
first thickness (t3/t1). The tear control ratio being greater than
about 0.7.
[0013] It is to be understood that both the foregoing general
description and the following detailed description present
embodiments of the invention, and are intended to provide an
overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are
included to provide a further understanding of the invention, and
are incorporated into and constitute a part of this specification.
The drawings illustrate various embodiments of the invention, and
together with the description serve to explain the principals and
operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross-sectional view of one example of a fiber
optic cable incorporating multiple aspects of the present
invention.
[0015] FIGS. 1a and 1b depict cross-sectional views of fiber optic
cable having uneven coupling of the cable jacket that can cause
problems in an automated preconnectorization process.
[0016] FIG. 2 is a schematic cross-sectional representation showing
tip entry and die exit outlines of one example of a die head design
useful for extruding cables as in FIG. 1.
[0017] FIG. 3 is a schematic cross-sectional representation of the
die head design of FIG. 2 showing tip exit and die exit
outlines.
[0018] FIG. 4 is an enlarged view of a portion of a cable similar
to the cable of FIG. 1 showing the toning lobe and web portions in
greater detail and identifying certain parameters thereon.
[0019] FIG. 5 is a schematic representation of a testing jig used
for measuring a separation force of a tonable lobe from the fiber
optic cable of FIG. 1.
DETAILED DESCRIPTION
[0020] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Whenever possible, the
same reference numerals will be used throughout the drawings to
refer to the same or like parts. With reference to FIG. 1, one
example of a fiber optic cable 10 according to the present
invention will be described. Fiber optic cable 10 includes an
optical transmission component 15, at least one strength component
18, at least one strength member 20, and a cable jacket 22 having a
main cable body 23 and a toning lobe 28 that are connected by a web
30. Web 30 is frangible for separating toning lobe 28 from main
cable body 23 in a clean and reliable manner as discussed below,
thereby making cable 10 suitable for automated preconnectorization
processes. In this cable, optical transmission component 15
includes a single optical waveguide such as an optical fiber 12 and
a buffer tube 14, but other configurations of the optical
transmission component are possible. For instance, optical
transmission component 15 may include multiple optical fibers or
the buffer tube may be eliminated such as in a tubeless
configuration. Optical fiber 12 can be any type of optical fiber
including, for example, a single-mode, multi-mode or dispersion
shifted optical fiber. Likewise, optical transmission component 15
may include tight-buffered fibers, fiber bundles, fiber ribbons or
other optical fiber configurations/groupings. In this cable, buffer
tube 14 is sized to contain up to twelve optical fibers 12, but
only a single optical fiber is depicted. Specifically, buffer tube
14 has a nominal outer diameter D1 of about 3.0 millimeters and an
inner diameter of about 1.8 millimeters, but other suitable
diameters such as smaller diameters are possible for other suitable
fiber counts. The inner diameter is sized to accommodate a suitable
excess fiber length (EFL) for the desired tensile and contraction
windows for the intended fiber count. Additionally, buffer tube 14
may also house at least one waterblocking and/or water-swellable
substance 16, for example, a gel, thixotropic grease, and/or a
water-swellable tape, thread, or yarn for inhibiting the migration
of water within buffer tube 14. Buffer tube 14 may be formed from a
suitable polymer such as polypropylene, polyethylene, PVC and/or
blends thereof.
[0021] As shown, cable 10 has two strength components 18 and four
strength members 20, thereby providing a flexible cable design
having the desired tensile rating with a relatively small
cross-sectional footprint. The combination of strength components
18 and strength members 20 allows cables of the present invention
to withstand the predetermined tensile loads and yet have a
suitable overall bending flexibility, while still maintaining a
relatively small cross-sectional footprint. Stated another way,
cable 10 has an improved flexibility compared with another cable
having the same tensile rating without the strength members since
the GRPs would have to be larger making the cable stiffer and which
may also increase the cross-sectional footprint. Consequently,
cable 10 provides the craft with a cable having the desired tensile
strength without surpassing a desired maximum level of cable
stiffness, thereby allowing a cable to be bent or coiled to a
predetermined radius of curvature as required for installation,
slack storage, and the like.
[0022] Specifically, strength components 18 are relatively stiff
rods such as glass reinforced plastic (GRPs) that provide the main
source of anti-buckling strength and tensile strength, whereas
strength members 20 are tensile yarns that generally lack
anti-buckling strength but provide a significant amount of tensile
strength. Strength components 18 may optionally include a
water-swellable coating or the like disposed thereon for inhibiting
the migration of water along the cable. Strength members 20 are
tensile yarns that provide tensile strength, but generally lack
anti-buckling strength and generally speaking do not resist
bending. Strength members 20 may be formed from a group of
fiberglass strands, aramid fibers or other suitable tensile yarns,
and may also include a superabsorbent material thereon for
inhibiting the migration of water along the cable. By way of
example, strength components 18 are GRP components having a
rod-like shape with a diameter of about 1.6 millimeters and
strength members 20 are 800 tex fiberglass yarns, but other
suitable materials may be used for either the strength components
and/or strength members. In this example, each of the four
individual strength members 20 has about 20% of the tensile
strength rating of one of the strength components. In other words,
the total tensile strength rating of all four strength members 20
is about 80% of one of the strength components 18.
[0023] During the manufacture of cable 10 the coupling of cable
jacket 22 around the other cable elements can occur unevenly,
thereby resulting in uneven or unbalanced residual stresses in
cable jacket 22 due to shrinkage of a cable jacket during cooling.
Generally speaking, coupling refers to load transfer mechanism that
enables certain cable components to act as a composite structure,
which is generally caused by the radial shrinkage of the jacket
during cooling. In other words, shrinkage of the cable jacket in
the radial direction enables coupling of certain cable components.
It has been discovered that uneven coupling occurs when the
strength components and/or the strength members are not uniformly
located about optical transmission component 15 along the length of
cable 10. Uneven coupling can cause bending or deflection of the
end of the cable when cut. For instance, cable 10 will have uneven
coupling of cable jacket 22 when the surface area of the optical
transmission component contacting cable jacket 22 is non-uniform on
opposing sides and/or changes along the length of the cable.
[0024] Illustratively, FIGS. 1a and 1b depict explanatory
cross-sectional views of fiber optic cables similar to cable 10
having unbalanced cable jacket coupling. FIG. 1a depicts a cable
10' where the strength members 20 on the right-side of the optical
transmission component have migrated to cover a larger area thereof
compared with the left-side of the optical transmission component.
Consequently, the coupling of the cable jacket with the optical
transmission component on the right-side is reduced compared with
the left-side since it has been covered by the strength members
that have spread out to cover a larger area of the optical
transmission component. FIG. 1b depicts a cable 10'' where the top
strength member 20 on the left-side of the cable has migrated about
strength component 18 on the left-side. Again, this reduces the
coupling of the cable jacket on the left-side of the cable compared
with the right-side of the cable. Consequently, when cables 10' or
10'' are cut they will deflect or bend to relieve the unbalanced
residual stresses due to the unbalanced coupling.
[0025] Generally speaking, the cables shown in FIGS. 1a and 1b
perform adequately with respect to the intended use even with the
unbalanced residual stresses caused by uneven coupling of the cable
jacket; however, such unbalanced residual stresses can be
troublesome for the automation of cable preconnectorization.
Specifically, when the cable is cut to length for connectorization
or the like, it may deflect or bend in an unpredictable manner due
to localized release of the residual stresses due to unbalanced
coupling. In other words, any unbalanced residual stresses residing
in the cable jacket are allowed to act longitudinally adjacent to
the cut end of the cable, thereby causing the cable to deflect or
bend unpredictably. Such unpredictable deflections or bending of
the cable may pose problems during an automated connectorization
process since the location of the cable end/cable components will
vary. Thus, one embodiment of the present invention, generally
balances the strength members and strength components about the
optical transmission component so that the cable may be cut without
causing undue deflection or bending of the cable end, thereby
aiding automation of cable preconnectorization. Suitable shapes and
orientations of the above tensile components, in particular after
extrusion, will be discussed below. Of course, the concepts of the
present invention can be practiced with cables designs that do not
include the toning lobe such as a cable similar to cable 10 but
without web 30 and attached toning lobe 28. Likewise, cables
employing the concepts of the present invention can have other
shapes beside the generally flat configuration of cable 10, i.e.,
having end sections 24 that are generally arcuate and a pair of
generally flat-side sections 26.
[0026] As shown in FIG. 1, strength members 20 are formed in four
locations within cable 10. Specifically, strength members 20 are
disposed within interstitial spaces between buffer tube 14 and
strength components 18 in a compact manner. Before cable
manufacture is completed, the strength members have a generally
rectangular cross-sectional shape. For example, strength members
20' may have cross-sectional dimensions of about 0.25 millimeters
by about 2.5 millimeters when passing into the extrusion tooling as
generally shown by FIG. 2. During manufacture, strength members 20
are shaped in the die head to the desired shape as shown in cable
10 of FIG. 1. As shown, the four strength members 20 are disposed
in the interstices with a substantially triangular shape after
manufacture, thereby allowing relatively even coupling of the cable
jacket with the other cable components. Consequently, when an end
of cable 10 is cut for connectorization, the bending or deflection
of the end is reduced compared with the cables shown in FIGS. 1a
and 1b because the unbalanced residual stress is reduced.
[0027] Cable 10 may be manufactured by operation of pressure
extrusion tooling, using an exemplary die and tip design as
schematically illustrated in FIGS. 2 and 3. However other methods
and structures may also be used to manufacture the cable of FIG. 1
and variations thereof described herein. As schematically depicted
in FIGS. 2 and 3, the extrusion tooling extrudes jacketing material
about the strength components 18, strength members 20, optical
transmission component 15, and a toning wire 32 as the components
are fed into the tooling. As the cable components are fed into the
extrusion tooling, a jacketing compound, e.g., polyethylene or
other suitable compound, is supplied under suitable temperature and
pressure conditions to the tooling. The jacketing compound
generally surrounds the cable components thereby forming cable
jacket 22 therearound. Of course, cable jacket 22 may be formed
from other suitable thermoplastics, such as a medium density
polyethylene (MDPE), polypropylene, PVC, or the like. By way of
example, cable jacket 22 has a width w1 of about 8-9 millimeters, a
width w2 of toning lobe 28 and web 30 of about 2-3 millimeters, and
a height of about 4-5 millimeters. Of course, other suitable
dimensions are possible for the cable jacket.
[0028] Specifically, FIG. 2 shows a cross-section of a tip entrance
profile 40 superimposed on an outline of the die exit 42. FIG. 3
shows a cross-section of a tip exit profile 44 superimposed on the
die exit profile. For purposes of this disclosure, die exit profile
42 is considered coextensive with the outer surface of cable 10,
although some shrinkage in jacket material is to be expected during
cooling. One skilled in the art is able to fine tune the tip and
die profiles as needed to achieve the various designs disclosed
herein without undue experimentation, taking into account typical
jacketing material shrinkages, tolerances, etc.
[0029] During travel through the tooling and in particular the die
tip, the various cable components are placed so as to achieve the
orientation of cable components shown in FIG. 1. In particular,
strength members 20 are compressed from the generally rectangular
shape into substantially triangular shapes, within interstices
between buffer tube 14 and strength components 18. Of course, the
substantially triangular shape of the strength member can have some
variation in shape while still providing generally balanced
coupling such as conforming to the round shape of buffer tube 14
and respective strength components 18 on respective sides. In FIG.
2, four such strength members 20' are shown within tip entrance
profile 40 prior to compression within the tip to achieve the shape
and orientation within tip exit profile 42. It should be understood
that variations in the number and shape of strength member yarns
20', as well as changes to tip profiles 40 and 42, are possible
within the scope of the present invention.
[0030] One or more of the following attributes may be achieved
during extrusion. For example, strength components 18 are located
generally adjacent to the optical transmission component and
preferably contact the same, thereby allowing for a cable having a
compact cross-sectional footprint. Further, strength members 20 are
placed in interstitial areas between buffer tube 14 and strength
components 18. Strength members 20 are generally in contact with
buffer tube 14 and an adjacent strength component 18 so as to form
a substantially triangular shape that conforms to the sides of
buffer tube 14 and strength component 18. Additionally, the
respective centers of strength components 18 and buffer tube 14 are
preferably generally aligned along an X-X axis, thereby creating a
preferential bend characteristic for the cable.
[0031] As shown in FIG. 1, the shape of strength members 20 is
substantially triangular as it is placed into the interstice,
however, such shape is not required for all aspects of the
invention since other cable configurations are possible such as
using strength components having shapes other than round. Also, it
is noted that strength members 20 are generally speaking
symmetrically disposed about the buffer tube or optical component
and do not extend all the way around optical transmission component
15, thereby influencing the coupling of cable jacket 22 therewith.
Specifically, a top portion 46 and a bottom portion 47 (hereinafter
portions 46,47) of buffer tube 14 contact cable jacket 22 directly.
As depicted, portions 46, 47 extends through about the same
respective angles along the buffer tube or the optical component.
In cable 10, the respective angles are about 45 degrees about the
circumference of buffer tube 14, although in other configurations
the angles may vary. Preferably, portions 46 and 47 are
substantially equal in size and symmetrical in location about the
buffer tube or optical component for purposes of uniform coupling
of cable jacket 22. As shown in FIG. 3, tip exit profile 44 is
generally constructed to form strength members 20 into the desired
shape, i.e., substantially triangular, while maintaining a pair
angles .alpha. and .beta. are about equal so that portions 46,47 in
cable 10 end up about equal. In other words, the tooling inhibits
the strength members from migrating out of their desired positions
and/or shapes.
[0032] In preferred embodiments, strength members 20 do not extend
beyond (up and down as shown in FIG. 1) buffer tube 14 toward side
sections 26 of cable 10, but may extend therebeyond by design
and/or in manufacturing variation. Consequently, the preferred
embodiments have minimum jacketing thickness requirements that are
defined by the diameter D1 of buffer tube 14. Were strength members
material to extend beyond buffer tube 14 so as to become the
outermost element (vertically, as shown), then additional jacketing
material may be required, at least adjacent strength members 20, to
form a minimum jacket thickness. If a uniformly flat side section
26 were desired, then the additional thickness would generally
extend along the entire side sections 26. The illustrated cable
construction of FIG. 1 thus uses less jacketing material and/or
allows for a smaller cable cross-sectional footprint (i.e., the
cable height is reduced). Also, allowing jacketing material to
contact buffer tube 14 at points 46 and 47 allows for coupling that
is beneficially improved for automation of preconnectorization
and/or uniformly distributed along the cable, thereby inhibiting
the unpredictable bending or deflection of the cable when cut.
[0033] It may also be noted that strength members 20 are in contact
with less than 180 degrees of the circumference about strength
components 18. In other words, strength components 18 are in
contact with the jacketing material for more than 180 degrees of
the circumference of the strength components. As above, increasing
the amount of strength component 18 in contact with jacket 22 aides
in improving the evenness of coupling of the jacketing material,
thereby leading to more uniform residual stresses within the cable
and inhibiting the deflection or bending of the resulting cable
when cut. Also, symmetry along horizontal and vertical axis (as
shown in FIG. 1) of the location of strength members 20 in
interstitial spaces between strength components 18 and buffer tube
14, as well as symmetry of locations of buffer tube 14 and strength
components 18 relative to each other, also helps provide for more
even coupling within the cable.
[0034] It should be understood however, that each and every
characteristic above is not required to practice the concepts of
the present invention, whether related to strength element design,
shapes, and/or location as described above, or whether related to
toning lobe and web design as described below.
[0035] The orientation of cable components 15, 18, and 20 within
jacket 22 is achieved by virtue of the tip entrance and exits shown
in FIGS. 2 and 3. Thus, the various elements are fed into the tip
and the reduced size of the opening within the tip squeezes the
elements together in a desired configuration. While it is
impossible as a practical matter to perfectly align such cable
components entirely uniformly along an entire cable, one of skill
in the art can design tooling achieve the resulting orientation as
shown in FIG. 1, in view of the disclosures related to FIGS.
1-3.
[0036] As stated above, it would be possible to modify the
structure above in various ways to modify their attributes of the
resulting cable product. For example, two strength members 20'
could be used instead of four, with a portion of the strength
members being disposed between strength components 18 and buffer
tube 14. Also, instead of the optical transmission component shown,
different optical transmission components or structures may be
used. Also, depending upon the desired tensile and bending
characteristics, the relative diameters of the strength components
and the size and amount of strength member material used could be
varied to achieve desired ratings. Additionally, in certain
situations, nonsymmetrical designs could be used, for example using
only one strength component 18 or differing numbers and or
placements of other cable components.
[0037] Turning now to FIG. 4, an enlarged view of toning lobe 28
and web 30 of a cable similar to cable 10. Specifically, the
enlarged view of FIG. 4 is similar to cable 10 except it depicts a
concentricity error of the toning wire with the tonable lobe as may
occur during manufacturing. FIG. 4 also illustrates certain
dimensions related to these portions that can influence tear
performance so that toning lobe 28 and web 30 are reliably and
cleanly separated from an end portion 24 of cable 10 with the
application of a predetermined separation force. Moreover, the
preferred separation force for the toning lobe prevents an
excessive separation force while inhibiting inadvertent separation
during cable bending, coiling, and the like. Preferably, the
separation force is between about 10 Newtons and about 50 Newtons
for the desired performance and more preferably between about 15
Newtons and about 30 Newtons. The separation force is measured as
the toning lobe is pulled away from the main cable body along the
X-X axis as shown in FIG. 1; however, the toning lobe may be
separated by pulling in other directions. As shown in FIG. 5, a
preferred way of measuring the separation force uses a testing jig
(not numbered) that routes the toning lobe portion being pulled
about a sheave 50 that rotates. Additionally, the testing jig
allows the cable to move in a direction generally perpendicular to
an applied force F as it is applied during separation. Thus, the
force measured is the separation force applied along the X-X
axis.
[0038] As shown in FIG. 4, cable 10 has a first radius R1 that is
defined between end portion 24 and base portion 48 of web 30. A
second radius R2 is defined between distal portion 50 of web 30 and
lobe 28. According to one aspect of the present invention selecting
a predetermined relationship between R1 and R2, i.e., a radius
ratio of R2/R1, improves the separation of web 30 and toning lobe
28 from end portion 24. FIG. 4 also shows a first thickness t1, a
second thickness t2, and a third thickness t3. First thickness t1
is the thickness at the base portion 48 of web 30, second thickness
t2 is the thickness at the distal portion 50 of web 30, and third
thickness t3 is a thickness of lobe 28 near R2. Third thickness t3
is measured at a point of a minimal wall thickness 52 facing end
section 24, measured radially outwardly from the center of wire 32
generally in the direction of arcuate section 24 of main cable body
23. Third thickness t3 is a point at which stresses will increase
during the separation of toning lobe 28 and web 30 from main cable
body 23. If toning wire 32 is perfectly concentrically located
within toning lobe 28, then t3 is the difference in radii between
toning lobe 28 and the toning wire 32. However, toning wire 32 is
not always concentrically disposed within toning lobe 28 in a
manufactured cable. By way of example, FIG. 4 shows toning wire 32
having a concentricity error with respect to toning lobe 28 so that
thickness t3 is not the difference in radii between toning lobe 28
and toning wire 32. Generally speaking, the concentricity error can
occur during the normal manufacture of cable 10 and can affect the
separation/tear performance.
[0039] Aspects of the present invention involve selecting a
predetermined relationship of certain combinations of thicknesses
t1, t2 and t3 (either along with or separate from the R1 and R2
relationship) for improving the separation of web 30 and toning
lobe 28 from end portion 24 from main cable body 23. By way of
example, the desired reliable and clean separation of toning lobe
28 and web 30 along base portion 48 is more likely to occur when t2
is greater than t1, i.e., a thickness ratio t2/t1 is greater than
unity. Also, it has been determined that desired separation of
toning lobe 28 and web 30 at base portion 48 is more likely to
occur if a tear control ratio t3/t1 is greater than about 0.7,
thereby inhibiting tearing along the minimal thickness portion 52
where t3 is measured. Likewise, if R2 is greater than R1, (i.e. the
radius ratio of R2/R1 is greater than unity) web 30 is more likely
to be torn at base portion 48 rather than another location on the
web towards the distal portion 50 when the separation force is
applied.
[0040] Stated numerically, preferably the tear control ratio t3/t1
is greater than 0.7; more preferably, the ratio is greater than
about 0.74; and, most preferably the ratio is greater than about
0.81. Also, for the desired separation performance, the thickness
ratio t2/t1 is greater than about 1.0, and more preferably greater
than about 1.10, and most preferably greater than about 1.15.
Moreover, for desired separation, the radius ratio R2/R1 is greater
than about 1.0, more preferably about 2.0 or greater, and most
preferably about 4.0 or greater. It should be understood that all
of these relationships need not be satisfied simultaneously
according to the scope of the present invention to achieve improved
separation of the web and toning lobe from the main cable body.
[0041] The above stated parameters tend to induce stress
concentrations in the desired location (across base 48), leading to
desired separation performance. This desired separation performance
is especially advantageous in automated preconnectorization
applications, but is also advantageous for separation by hand.
Simply stated, the above mentioned dimension ratios inhibit
stretching and/or tearing of web material in undesired locations
(and/or tearing out of the toning wire from the toning lobe) and
instead concentrates the tearing stress at base 48, thereby
achieving separation/tear characteristics resulting in a reliable
and clean separation. Thus, an uneven distribution of stress across
base portion 48 whereby, for example, high stresses are induced
along a surface of base portion 48 and relatively lower stresses
are induced across the central portion of base portion 48 may not
produce the desired tear, in particular if higher and more evenly
distributed stresses are induced at distal portion 50 or a minimum
wall thickness 52. However, the separation performance may be a
function of more than one parameter, for instance, the same value
of the tear control ratio t3/t1 may perform differently based on
varying other web dimensions and/or toning lobe dimensions.
[0042] Illustratively, table 1 below includes information regarding
a number of exemplary simulated, iterative designs using suitable
modeling software in which R1, R2, t1, and t2 parameters were set
and the t3 parameter was iteratively varied, so as to investigate
the affect the tear control ratio t3/t1. In the simulated design,
toning lobe 28 had an outer diameter (not labeled) of 1.0
millimeter with a 24 AWG copper wire and the length 1 of web 30 was
0.5 millimeters. As depicted in Table 1, different values of the
ratios of t2/t1 and R2/R1 can influence the values for "acceptable"
and "unacceptable" separation performance. A rating of "acceptable"
means the simulated model indicated tearing at web base portion 48
and a rating of "unacceptable" means the simulated model indicated
tearing at minimum wall thickness 52. Additionally, further
iteration could identify a more precise cross-over between the two
values for each tear control ratio t3/t1, meaning the acceptable
ratio for each set of parameters wherein tearing is at the desired
base portion 48 is likely between the acceptable and unacceptable
values shown in Table 1. Likewise, the other ratios may perform
differently based on varying other web dimensions and/or toning
lobe dimensions.
TABLE-US-00001 TABLE 1 t3/t1 T2/t1 R2/R1 Acceptable Unacceptable
1.11 3.00 0.81 0.77 1.17 10.00 0.78 0.75 1.15 5.00 0.75 0.71 1.13
8.33 0.70 0.67 1.10 1.20 0.77 0.73 1.03 1.20 0.77 0.74 1.09 2.00
0.74 0.70 1.03 2.00 0.74 0.71
[0043] Of course, other suitable dimensions and/or combinations of
dimensions may be used to arrive at a cable having a suitable
separation performance. In one preferred embodiment, toning wire 32
is a 24 AWG copper wire having a diameter of about 0.5 millimeters,
toning lobe 28 has an outer diameter (not labeled) of about 1.7
millimeters, and web 30 has a length 1 of about 0.9 millimeters. In
this embodiment, the length 1 was about 0.9 millimeters (almost
double of the simulated model) to allow a sufficient amount of
cooling water to contact web 30 during manufacture, thereby aiding
in generally uniform cooling and inhibiting deformation of the
extruded shape. Tooling was designed and a cable was manufactured
according to this preferred embodiment dimensions so that it had
suitable separation/tear characteristics, thereby making it
suitable for an automated preconnectorization process.
Specifically, the dimensions of a cross-section of the manufactured
cable were examined and measured. One skilled in the art
understands that variations in manufacturing, shrinkage and the
like can cause the same cable or other cables manufactured using
the same tooling to have other values when measured at different
cross-sections along the cable. Typical values for the
cross-section of the manufactured cable were examined and measured
as follows, R2 was about 0.25 millimeters and R1 was about 0.05
millimeters for a radius ratio of R2/R1 of about 5; t2 was about
0.6 millimeters and t1 was about 0.3 millimeters for a thickness
ratio of t2/t1 or about 2.0; and t3 was about 0.3 millimeters for a
tear control ratio t3/t1 of about 1.0. Cables of the present
invention can have other suitable dimensions for the toning lobe,
toning wires, and/or web, thereby resulting in different
ratios.
[0044] As utilized herein, R1 and R2 refer to a radius of curvature
at the illustrated locations. It is recognized, however, that the
radius of curvature of complex shapes often varies, either
according to a formula (for example along an ellipse) or otherwise
in two or three dimensions. Therefore, the radius of curvature
discussed herein is not limited to circular, arcuate
two-dimensional shapes. Also, the radius of curvature illustrated
applies generally to the identified region (i.e., along the base
portion 48 of web 30), not just at the exact point illustrated. The
same concepts apply to the thicknesses t1, t2, and t3 as to
localized two- and three-dimensional variation. Therefore, it is
within the scope of the invention to utilize the radius and
thickness information discussed herein in various ways within and
along the portions of the structures discussed. Moreover, FIG. 4
illustrates that the web 30 is generally symmetrical about the X-X
axis (FIG. 1); however, the web may optionally be asymmetric about
the X-X axis. By way of example, web 30 and toning lobe 28 can be
designed to have preferential tear direction (i.e., the web 30
prefers to tear in one direction) by using different radii on the
one side of the X-X axis. For instance, the values of R1 and R2 on
the opposing side of the X-X axis can be larger to create a
preferential tear direction for web 30. The preferential tear
direction can be marked with an indicia 33 such as a stripe,
protrusion in the extrusion or the like. Likewise, web 30 can
optionally include a rip stop 35 of increased material disposed
periodically along the length of web 30 for inhibiting the tear
from propagating unless a sufficient force is provided. Rip stop 35
can be formed along the cable by pulsating the extrusion at the web
or in other suitable ways as known to one skilled in the art.
[0045] Also, persons of ordinary skill in the art will appreciate
that variations and modifications of the foregoing embodiments may
be made without departing from the scope of the appended claims.
For example, optical transmission component may comprise at least
one tight buffered fiber and/or a bundle of optical fibers. As an
alternative to glass reinforced plastic, strength components can be
metallic or aramid fibers impregnated with a suitable plastic
material so as to provide added stiffness. Although a circular
cross section for strength components and a substantially
triangular cross section for strength members 20 are disclosed,
other cross sectional shapes may be used as well. The concepts
described herein can be applied to many cable designs, for example,
self-supporting, buried, indoor, and indoor/outdoor cable
applications. Flame retardant jacket materials can be selected to
achieve plenum, riser, or LSZH flame ratings. Also additional water
blocking protection can be added. For example, at least one
water-swellable tape or yarn (not shown) can be disposed adjacent
to the optical transmission component. Cables according to the
present invention may also include at least one electrical
conductor for power or data transmission, for example, at least one
coaxial or single wire, or a twisted pair of wires. Ripcords and/or
an armor layer can be added adjacent buffer tube 14.
[0046] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *