U.S. patent application number 13/866678 was filed with the patent office on 2013-09-12 for dielectric armored fiber optic cable with armor profile.
This patent application is currently assigned to CORNING CABLE SYSTEMS LLC. The applicant listed for this patent is CORNING CABLE SYSTEMS LLC. Invention is credited to Gregory Blake Bohler, Julian Latelle Greenwood, III, Keith Alan Greer, Allen Michael Miller, Wesley Brian Nicholson, Kimberly Dawn Slan.
Application Number | 20130236148 13/866678 |
Document ID | / |
Family ID | 42103251 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130236148 |
Kind Code |
A1 |
Bohler; Gregory Blake ; et
al. |
September 12, 2013 |
DIELECTRIC ARMORED FIBER OPTIC CABLE WITH ARMOR PROFILE
Abstract
An armored fiber optic cable includes fiber optic assembly,
including at least one optical fiber, and dielectric armor in the
form of an extruded polymeric tube surrounding the fiber optic
assembly. The dielectric armor has at least one layer formed from a
rigid material having a Shore D hardness of about 65 or greater.
Further, the dielectric armor has an armor profile such that the
dielectric armor has an undulating surface along its length.
Inventors: |
Bohler; Gregory Blake;
(Lenoir, NC) ; Greenwood, III; Julian Latelle;
(Hickory, NC) ; Greer; Keith Alan; (Morganton,
NC) ; Miller; Allen Michael; (Lenoir, NC) ;
Nicholson; Wesley Brian; (Hickory, NC) ; Slan;
Kimberly Dawn; (Ft. Worth, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING CABLE SYSTEMS LLC |
HICKORY |
NC |
US |
|
|
Assignee: |
CORNING CABLE SYSTEMS LLC
HICKORY
NC
|
Family ID: |
42103251 |
Appl. No.: |
13/866678 |
Filed: |
April 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13494129 |
Jun 12, 2012 |
8428406 |
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13866678 |
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12718044 |
Mar 5, 2010 |
8218925 |
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13494129 |
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12261645 |
Oct 30, 2008 |
7702203 |
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12718044 |
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Current U.S.
Class: |
385/103 ;
385/107 |
Current CPC
Class: |
G02B 6/4429 20130101;
G02B 6/443 20130101 |
Class at
Publication: |
385/103 ;
385/107 |
International
Class: |
G02B 6/44 20060101
G02B006/44 |
Claims
1. An armored fiber optic cable, comprising: fiber optic assembly
comprising at least one optical fiber; dielectric armor in the form
of an extruded polymeric tube surrounding the fiber optic assembly,
wherein the dielectric armor has at least one layer formed from a
rigid material having a Shore D hardness of about 65 or greater,
wherein the dielectric armor has an armor profile such that the
dielectric armor has an undulating surface along its length.
2. The armored fiber optic cable of claim 1, wherein the armor
profile has a pitch between about 5 millimeters and about 30
millimeters.
3. The armored fiber optic cable of claim 1, wherein the armor
profile has a pitch and a groove length that is between about 20
percent and 80 percent of the pitch.
4. The armored fiber optic cable of claim 1, wherein the armor
profile has a band thickness and a web thickness, and wherein the
web thickness is less than the band thickness.
5. The armored fiber optic cable of claim 4, wherein the web
thickness is greater than or equal to 0.1 times the band
thickness
6. The armored fiber optic cable of claim 5, wherein the band
thickness is between about 0.5 millimeters and about five
millimeters.
7. The armored fiber optic cable of claim 1, wherein the armor
profile comprises an exterior groove that spirals around the fiber
optic assembly and, thereby, extends along the length of the
armored fiber optic cable.
8. The armored fiber optic cable of claim 7, wherein the armor
profile further comprises an inner groove that spirals around the
fiber optic assembly and, thereby, extends along the length of the
armored fiber optic cable.
9. The armored fiber optic cable of claim 7, wherein the at least
one layer formed of the dielectric armor has a modulus of
elasticity of about 1200 MPa or greater.
10. The armored fiber optic cable of claim 9, wherein the at least
one layer of dielectric armor has a continuous annular
cross-section.
11. The armored fiber optic cable of claim 1, wherein the armored
fiber optic cable has a diametral deflection of 3.3 millimeters or
less during a crush resistance test, the crush resistance test
applies a load of 300 Newtons/centimeter over a 10 centimeter
length of the armored fiber optic cable for a period of ten
minutes.
12. The armored fiber optic cable of claim 1, wherein the at least
one optical fiber has a delta attenuation of 0.2 dB or less at
reference wavelengths of 850 nm during a crush resistance test of
the armored fiber optic cable.
13. The armored fiber optic cable of claim 1, wherein the at least
one optical fiber has a delta attenuation of 0.2 dB or less at
reference wavelengths of 850 nm during an impact test of the
armored fiber optic cable using a 2-kilogram mass.
14. The armored fiber optic cable of claim 1, wherein the armored
fiber optic cable is a stranded tube cable such that the fiber
optic assembly comprises stranded tubes that support the at least
one optical fiber.
15. The armored fiber optic cable of claim 14, wherein the fiber
optic assembly further comprises a central strength member.
16. An armored fiber optic cable, comprising: fiber optic assembly
comprising at least one optical fiber; dielectric armor in the form
of an extruded polymeric tube surrounding the fiber optic assembly,
wherein the dielectric armor has at least one layer formed from a
rigid material having a Shore D hardness of about 65 or greater,
wherein the dielectric armor has an armor profile such that the
dielectric armor has an undulating surface along its length,
wherein the armor profile comprises an exterior groove that spirals
around the fiber optic assembly and, thereby, extends along the
length of the armored fiber optic cable, and wherein the armor
profile has a groove length that is between about 20 percent and 80
percent of a pitch of the armor profile.
17. The armored fiber optic cable of claim 16, wherein the pitch of
the armor profile is between about 5 millimeters and about 30
millimeters.
18. An armored fiber optic cable, comprising: fiber optic assembly
comprising at least one optical fiber; dielectric armor in the form
of an extruded polymeric tube surrounding the fiber optic assembly,
wherein the dielectric armor has at least one layer formed from a
rigid material having a Shore D hardness of about 65 or greater,
wherein the dielectric armor has an armor profile such that the
dielectric armor has an undulating surface along its length,
wherein the armor profile has a band thickness and a web thickness,
wherein the web thickness is less than the band thickness, wherein
the web thickness is greater than or equal to 0.1 times the band
thickness, and wherein the band thickness is between about 0.5
millimeters and about five millimeters.
19. The armored fiber optic cable of claim 18, wherein the armor
profile comprises an exterior groove that spirals around the fiber
optic assembly and, thereby, extends along the length of the
armored fiber optic cable.
20. The armored fiber optic cable of claim 18, wherein the armored
fiber optic cable has a diametral deflection of 3.3 millimeters or
less during a crush resistance test, the crush resistance test
applies a load of 300 Newtons/centimeter over a 10 centimeter
length of the armored fiber optic cable for a period of ten
minutes.
Description
PRIORITY APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 13/494,129 filed Jun. 12, 2012, which is a continuation of U.S.
application Ser. No. 12/718,044 filed Mar. 5, 2010, which issued on
Jul. 10, 2012 as U.S. Pat. No. 8,218,925 and which is a divisional
of U.S. application Ser. No. 12/261,645 filed Oct. 30, 2008, which
issued on Apr. 20, 2010 as U.S. Pat. No. 7,702,203, the content of
each of which is relied upon and incorporated herein by reference
in its entirety, and the benefit of priority under 35 U.S.C.
.sctn.120 is hereby claimed.
RELATED APPLICATIONS
[0002] This application is related to U.S. Provisional Application
No. 61/174,059, filed Apr. 30, 2009, and U.S. Provisional
Application No. 61/168,005, filed Apr. 9, 2009.
FIELD OF THE DISCLOSURE
[0003] The present invention relates generally to optical fiber
assemblies, and in particular relates to armored fiber optic
assemblies having a dielectric armor along with methods of making
the same.
TECHNICAL BACKGROUND
[0004] Conventional fiber optic cables include optical fibers that
conduct light for transmitting voice, video and/or data. The
construction of fiber optic cables should preserve optical
performance when deployed in the intended environment while also
meeting the other additional requirements for the environment. For
instance, indoor cables for riser and/or plenum spaces may require
certain flame-retardant ratings to meet the demands of the space.
In other words, these flame-retardant ratings are addition to
mechanical requirements or desired characteristics for the space.
Mechanical requirements or characteristics such as crush
performance, permissible bend radii, temperature performance, or
the like are desired to inhibit undesirable optical attenuation or
impaired performance during installation and/or operation within
the space. In addition to the mentioned requirements riser and/or
plenum spaces may require a ruggedized design for meeting the
demands of the space.
[0005] By way of example, some indoor applications use a fiber
optic cable disposed within an armor layer for providing improved
crush performance in riser and/or plenum spaces. For instance,
conventional armored constructions have a fiber optic cable
disposed within a metallic interlocking armor for creating a robust
construction. Specifically, one type of well-known metallic
interlocking armor is a "BX armor" or a "Type AC" cable. This metal
armor is spiral wound about the fiber optic cable so that the edges
of the adjacent wraps of armor mechanically interlock, thereby
forming a robust armor layer that also acts as a bend limiting
feature for the assembly. However, there are disadvantages for this
conventional interlocking armor construction. For instance, fiber
optic cables having a metallic armor require additional hardware
and/or installation procedures for grounding the metallic armor to
meet safety standards, thereby making installation time-consuming
and expensive.
[0006] FIG. 1 shows several prior art examples of interlocking
armored cables 10 having a metallic armor layer 12 (typically
aluminum) that serves to protect and preserve optical performance
of cables 14 therein. Since metallic armor layer 12 is conductive
it must be grounded to comply with the National Electrical Code
(NFPA 120) safety standard. This adds to the complexity and expense
of installing a metal-armored fiber optic cable. Additionally, the
metallic armor can be plastically deformed (i.e., permanently
deformed) which can pinch the cable and cause elevated levels of
optical attenuation. Nevertheless, the market and craft prefer the
design and handling of this rugged cabling.
[0007] Manufacturers have attempted to design dielectric armor
cables to overcome the drawbacks of the conventional metallic armor
constructions, but to date a commercial solution is lacking. For
instance, U.S. Pat. No. 7,064,276 discloses a dielectric armor
cable having two synthetic resin layers where the hard resin layer
has continuous spiral groove cut completely through the hard resin
layer along the length of the armor. The hard resin layer is
intended for bend control by having adjoining edge portions of the
spiral groove abut at the desired minimum bend radius. However, one
skilled in the art would recognize this design does not provide the
craft with all of the desired features. Moreover, it can be
difficult for the craft to recognize the cable of the '276 patent
as an armored cable layered because it has a smooth outer surface,
whereas conventional metal armored cables are easily identified by
the craft as depicted by FIG. 1.
[0008] Therefore, there is a need in the art for an armored fiber
optic cable with superior mechanical properties that does not
require grounding as with metallic interlocking armor, but that
also resembles the metallic, interlocking armored cables while
providing robust characteristics.
SUMMARY
[0009] The disclosure is directed to armored fiber optic assemblies
having a dielectric armor along with methods for manufacturing the
same. The dielectric armor can have an armor profile, thereby
resembling conventional metal armored cable to the craft. Moreover,
the dielectric armor provides additional crush and impact
resistance to the optical fibers and/or fiber optic assembly
therein. The dielectric armor is also advantageous to the craft
since it provides the desired mechanical performance without
requiring the time and expense of grounding like conventional metal
armored cables. Additionally, armored fiber optic assemblies can
have any suitable flame and/or smoke rating for meeting the
requirements of the intended space; however, the assemblies may
have outdoor applications or indoor/outdoor applications.
[0010] 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 further understanding of the invention, and are
incorporated into and constitute a part of this specification. The
drawings illustrate the various example embodiments of the
invention and, together with the description, serve to explain the
principals and operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of three different prior art
interlocking armor cables and illustrates the characteristic
helical shape of the metal, interlocking armor layer;
[0012] FIG. 2A is a side cut-away view of a first example
embodiment of an armored fiber optic assembly having a dielectric
armor according to the present invention;
[0013] FIG. 2B is a side cut-away view of a second example
embodiment of an armored fiber optic assembly having a dielectric
armor according to the present invention;
[0014] FIG. 3A is a cross-section of the armored fiber optic
assembly of FIG. 2A taken along the line 3A-3A;
[0015] FIG. 3B is a cross-section of the armored fiber optic
assembly of FIG. 2B taken along the line 3B-3B;
[0016] FIG. 3C is a cross-section similar to FIGS. 3A and 3B, but
generically depicts a fiber optic assembly disposed within a
dielectric armor in order to show a radius R.sub.C of the fiber
optic assembly and an inner radius R.sub.I of the dielectric
armor;
[0017] FIG. 4 is a schematic diagram of an example embodiment of an
armored fiber optic assembly formed in a bend radius (i.e., a
loop);
[0018] FIG. 5A is an enlarged perspective view and FIG. 5B is a
close-up view of the armored fiber optic assembly of FIG. 2A
showing a partial longitudinal cross-section of the dielectric
armor superimposed on a grid for reference of the shapes of the
layers;
[0019] FIG. 6A is an enlarged view of a portion of the dielectric
armor of FIG. 5B further showing various dimensions associated
therewith;
[0020] FIG. 6B is an enlarged perspective view of a portion of a
generic armored profile showing the geometry of used for
finite-element modeling of the dielectric armor;
[0021] FIG. 7 is a plot of the true stress (Pa) vs. the true strain
(%) for two different representative rigid materials and a
representative non-rigid material that are suitable for use as a
portion of the dielectric armor;
[0022] FIG. 8A is a table of design parameters determined by
finite-element modeling at two different minimum strain levels for
the non-rigid material shown in the true stress vs. true strain
graph of FIG. 7;
[0023] FIGS. 8B through 8E respectively set forth tables of design
parameters determined by finite-element modeling at different
minimum strain levels for two different rigid materials shown in
the true stress vs. true strain graph of FIG. 7;
[0024] FIGS. 9A and 9B are plots of the data in FIG. 8A depicting
the dielectric armor band thickness (T1) vs. the groove-length to
pitch ratio (2L2/P) for the non-rigid material with the two
different minimum strain levels on the same plot;
[0025] FIGS. 9C and 9D are plots of the data in FIGS. 8B and 8C
depicting the dielectric armor band thickness (T1) vs. the
groove-length to pitch ratio (2L2/P) for the first rigid material
for two different strain levels on respective plots;
[0026] FIGS. 9E and 9F are plots of the data in FIGS. 8D and 8E
depicting the dielectric armor band thickness (T1) vs. the
groove-length to pitch ratio (2L2/P) for the second rigid material
for two different strain levels on respective plots;
[0027] FIG. 10A is a perspective view of another embodiment of an
armored fiber optic assembly having an inner and outer layer;
[0028] FIG. 10B is a perspective view of yet another embodiment of
an armored fiber optic assembly;
[0029] FIG. 10C is a perspective view of the inner layer of the
dielectric armor of FIG. 10B still another embodiment of an armored
fiber optic assembly;
[0030] FIG. 10D is a perspective view of still another embodiment
of an armored fiber optic assembly;
[0031] FIG. 11 is a schematic diagram of an explanatory extrusion
system for making dielectric armor;
[0032] FIG. 12 is a schematic cross-sectional view of the crosshead
of the extrusion system of FIG. 11;
[0033] FIG. 13 is a schematic side view illustrating another method
of forming the dielectric armor;
[0034] FIG. 14 is a partial, cross-sectional view of another
explanatory example of a crosshead wherein the profiling feature is
within the crosshead die;
[0035] FIG. 15 is a side view of an example extrusion system
wherein the profiling feature is located external to the crosshead
and impresses the profile into the dielectric armor;
[0036] FIG. 16 is a perspective view of an example roller-type
deforming member that is used to impress the armor profile into the
dielectric armor; and
[0037] FIG. 17 is a front view illustrating the use of two
roller-type deforming members to impress the armor profile into the
dielectric armor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Reference is now made in detail to the present preferred
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Whenever possible, identical or similar
reference numerals are used throughout the drawings to refer to
identical or similar parts. It should be understood that the
embodiments disclosed herein are merely examples with each one
incorporating certain benefits of the present invention. Various
modifications and alterations may be made to the following examples
within the scope of the present invention, and aspects of the
different examples may be mixed in different ways to achieve yet
further examples. Accordingly, the true scope of the invention is
to be understood from the entirety of the present disclosure in
view of, but not limited to the embodiments described herein.
[0039] FIGS. 2A and 2B depict side cut-away views of two different
armored fiber optic assemblies 20 having at least one optical fiber
40 disposed within a dielectric armor 120. Dielectric armor 120 is
non-conductive and has an outer surface (not numbered) that
includes an armor profile (not numbered) and in this embodiment is
generally formed in a spiral manner along a longitudinal axis. As
used herein, armor profile means that the outer surface has an
undulating surface along its length that looks similar to the
conventional metal armor (i.e., a undulating shape along the length
of the armor). Dielectric armor 120 includes one or more layers
such as an inner layer 72 and an outer layer 74, but other
constructions are possible. For instance, dielectric armor 120 may
consist of a single layer such as inner layer 72. Preferably, inner
layer 72 is a rigid material and outer layer 74 is a non-rigid
material; however, it is possible to use a non-rigid material for
inner layer 72 and have the rigid material as outer layer 74. As
used herein, "rigid material" means the material has a Shore D
hardness of about 65 or greater and "non-rigid material" means the
material has a Shore D hardness of about 60 or less. The dielectric
armor 120 is advantageous since it provides crush resistance, meets
the desired flame or smoke rating, and/or other desirable
characteristics, but does not require grounding like conventional
metal armor. For instance, armored fiber optic cables can have a
diametral deflection of 3.3 millimeters or less during a crush
resistance test as discussed below.
[0040] FIG. 2A depicts a dielectric armor 120 having multiple
layers with the armor profile formed essentially in the inner layer
72 (i.e., the rigid layer) and the outer layer 74 (i.e., the
non-rigid material) having an essentially uniform thickness over
inner layer 72. Another embodiment of dielectric armor 120 is
constructed by eliminating outer layer 74. As shown, a fiber optic
assembly 30 is housed within dielectric armor 120. In this
embodiment, fiber optic assembly 30 is a fiber optic cable that
includes a cable jacket. However, fiber optic assemblies of other
embodiments can have other constructions and/or structures such as
assemblies that eliminate the cable jacket. By way of example, the
fiber optic assembly may be a stranded tube cable, monotube cable,
micromodule cable, slotted core cable, loose fibers, tube
assemblies, or the like. Additionally, the fiber optic assemblies
can include any suitable components such as water-blocking or
water-swelling components, flame-retardant components such as
tapes, coatings, or other suitable components. Specifically, fiber
optic assembly 30 of FIG. 2A includes a central strength member
having a plurality of tight-buffered optical fibers stranded
thereabout and a cable jacket. Any fiber optic assemblies 30 may
have any suitable fiber count such as a 6-fiber MIC cable or
24-fiber MIC cable available from Corning Cable Systems of Hickory,
N.C.
[0041] FIG. 2B depicts another multi-layer dielectric armor 120
with the armor profile essentially in the outer layer 74 (i.e., the
non-rigid material) with inner layer 72 (i.e., the rigid material)
having an essentially uniform thickness under outer layer 74. Fiber
optic assembly 30 of FIG. 2B includes a plurality of ribbons 56
disposed in a tube 32, thereby forming an assembly. In both
embodiments of FIG. 2A and FIG. 2B, inner layer 72 has a
"continuous annular cross-section". As used herein, "continuous
annular cross-section" means there are not spiral grooves, opening,
or slits that cut entirely thru the layer. Additionally, outer
layer 74 of the embodiments of FIG. 2A and FIG. 2B are formed from
a non-rigid material. Using a non-rigid material as the outer layer
is advantageous for several reasons such as providing impact
protection for the assembly and/or allowing the selection of a
material having a low-smoke characteristic or flame-retardant
property.
[0042] One skilled in the art will appreciate the extreme
difficulty in meeting the desired mechanical characteristics,
low-smoke characteristics, and/or flame-retardant characteristics
and the like with the armored fiber optic assemblies of the present
invention. This difficulty is especially true for the NFPA262
plenum rating. Simply stated, the polymer mass of the armored fiber
optic assemblies provides a relatively large combustible mass,
thereby making it difficult to meet both mechanical requirements
and flame/smoke requirements. Advantageously, certain embodiments
of the armored fiber optic assemblies meet both the mechanical and
the flame/smoke requirements such as riser-ratings and/or
plenum-ratings. Of course, assemblies disclose herein can have
outdoor or indoor/outdoor applications.
[0043] FIGS. 3A and 3B respectively depict cross-sectional views of
armored fiber optic assemblies 20 of FIGS. 2A and 2B taken
respectively along the lines 3A-3A and 3B-3B. For the purposes of
simplicity in illustration, the dielectric armor 120 is depicted
with a uniform cross-section that does not reflect the spiral of
the armor profile. As shown, armored assemblies 20 may include a
free space 90 disposed between an outer surface of fiber optic
assembly 30 and a dielectric armor inner surface. FIG. 3C shows a
generic illustration of an armored fiber optic assembly 20 having
an outer radius R.sub.C and dielectric armor 120 having an inner
radius R.sub.I. The amount of free space 90 is characterized by a
separation .DELTA.R between outer surface of fiber optic assembly
30 and the inner surface of dielectric armor 120, wherein
.DELTA.R=R.sub.I-R.sub.C. Including free space 90 in the
construction aids in preserving optical performance during crush
events and the like as discussed below. By way of example, free
space 90 is typically about 2 millimeters or less, but free space
values larger than 2 millimeters are possible.
[0044] If intended for indoor use, embodiments preferably are
flame-retardant and have the desired flame-retardant rating
depending on the intended space such as plenum-rated, riser-rated,
general-purpose, low-smoke zero-halogen (LSZH), or the like. For
instance, suitable materials for the layers of dielectric armor 120
may be selected from one or more of the following materials to meet
the desired rating: polyvinyl chloride (PVC), polyvinylidene
fluoride (PVDF), flame-retardant polyethylene (FRPE), chlorinated
polyvinyl chloride (CPVC), polytetra flourethylene (PTFE),
polyether-ether keytone (PEEK), Fiber Reinforced Polymer (FRP),
low-smoke zero-halogen (LSZH), polybutylene terephthalate (PBT),
polycarbonate (PC), polyethylene (PE), polypropylene (PP),
polyethylene terephthalate (PETE), and aerylonitaile butadiene
styrene (ABS). The skilled artisan understands that many factors of
the design can affect flame-ratings and finding a suitable designs
and/or materials to meet a given rating can be extremely
challenging. One example of an armored fiber optic assembly similar
to FIG. 2A having a riser rating includes inner layer 72 formed
from a PVC available from Teknor Apex under the tradename 8015 and
outer layer 74 is formed from a plenum-grade PVC jacket material
available from AlphaGary under the tradename 1070L. Additionally,
this PVC/PVC combination results not only in the desired
flame-retardant rating, but also meets the desired mechanical
robustness. Of course, other suitable material combinations are
also possible.
[0045] Besides flame- or smoke-ratings, mechanical characteristics
of interest include minimum bend radius, impact resistance,
crush-resistance, durability of the dielectric armor, susceptibly
to plastic deformation, etc. Material characteristics such as the
hardness, modulus, etc. along with geometry can influence the
desired characteristics/optical performance for the armored fiber
optic assemblies. For instance, the inner layer and/or the outer
layer should have a suitable modulus of elasticity. By way of
example, a modulus of elasticity at 1% strain for the rigid
material is about 1200 MPa or greater and the modulus of elasticity
at 1% strain for the non-rigid material is between about 300 MPa
and about 1200 MPa. Of course, these are merely explanatory
examples and other values for the modulus of elasticity are
possible with the concepts disclosed herein.
[0046] One mechanical property provided by the dielectric armor is
its resistance to being crushed (i.e., crush resistance). One test
that quantifies crush resistance applies a load of 300
Newtons/centimeter over a 10 centimeter length of the armored fiber
optic assembly (i.e., 3000 N total load) for a period of ten
minutes at which time a diameteral deflection is measured under
load. An optical-performance based crush test is given by the
ICEA596 crush standard, which applies a load of 300
Newtons/centimeter for ten minutes and then measures delta
attenuation of the optical fibers under load. The ICEA596 crush
standard requires a maximum delta attenuation of less than 0.60 dB
for multimode (MM) optical fibers at a reference wavelength of 1300
nm and a maximum delta attenuation of 0.40 dB or less for
single-mode (SM) optical fibers at a reference wavelength of 1550
nm. Armored fiber optic assemblies 20 were tested according to the
ICEA596 crush standard as well as other performance tests as
discussed herein. Additionally, assemblies disclosed herein can
meet other standards such as GR409 or the like.
[0047] Specifically, mechanical testing was conducted on MM optical
fiber versions of armored fiber optic assemblies similar to FIG. 2A
having 24-fiber MIC cables for fiber optic assembly 30 and other
embodiments having a 6-fiber MIC cables. MM versions were tested
since they are more sensitive to optical attenuation and a better
indicator of optical performance than SM versions. The testing of
the MM versions was also conducted at two different reference
wavelengths. Additionally, the dielectric armor 120 for the two
different structures (24-fiber and 6-fiber) had different
geometries as discussed below and shown in detail in FIG. 5B. For
instance, the armor profile for the 24-fiber MIC cable embodiments
had an average pitch of 10.+-.1 millimeters, an average web
thickness of 1.+-.0.2 millimeters, and an average band thickness of
1.6.+-.0.2 millimeters for the inner layer. The armor profile for
the 6-fiber MIC cable embodiments had an average pitch of 10.+-.1
millimeters, an average web thickness of 0.8.+-.0.2 millimeters,
and an average band thickness of 1.3.+-.0.2 millimeters for the
inner layer.
[0048] The dielectric armor provided exceptional crush performance.
Specifically, Table A lists the results for the two different
versions under the ICEA596 crush standard along with similar
testing under elevated crush loads of 3500 Newtons and 4000
Newtons. Table A lists the delta optical attenuation results for
each crush load with the results at 1300 nanometers listed first
and the result at 850 nanometers second.
TABLE-US-00001 TABLE A Crush Performance Testing 3000 Newtons 3500
Newtons 4000 Newtons Fiber Optic (1300 nm/ (1300 nm/ (1300 nm/
Assembly 850 nm) 850 nm) 850 nm) Assembly with 0.14 dB/0.12 dB 0.09
dB/0.08 dB 0.24 dB/0.16 dB 6-Fiber MIC Cable Assembly with 0.06
dB/0.05 dB 0.05 dB/0.05 dB -- 24-Fiber MIC Cable
[0049] As shown, the crush performance results for the tested
armored fiber optic assemblies were much lower than the under the
ICEA596 crush standard. The results for both the MM fiber counts
were about 0.20 dB or less at 1300 nm and 3000 Newtons, which is
one-third of the pass value for the ICEA596 crush standard, which
is 0.60 dB or less. Moreover, the load was increased to 4000
Newtons and the results still were less than half of the pass value
at 3000 Newtons. Additionally, the values for SM armored fiber
optic assemblies were not tested but should have delta attenuation
of about 0.20 dB or less at 1300 nm and 3000 Newtons since they are
less sensitive than MM optical fibers.
[0050] Another mechanical property of the armored fiber optic
assemblies is their flexibility (e.g., the ability to bend without
damage and/or causing elevated levels of attenuation). Generally
speaking, the maximum amount of bending that armored assemblies can
withstand without kinking, cracking, separating and/or causing
elevated optical attenuation is characterized by its minimum bend
radius. FIG. 4 shows a loop 94 of armored fiber optic assembly 20
formed into a bend radius R.sub.B. In other words, the bend radius
R.sub.B is the distance from the center to the inner surface of the
assembly when formed into a coil as shown by FIG. 4. The bend
radius R.sub.B may be related to other dimensions and/or
characteristics of the armored fiber optic assembly. For instance,
the minimum bend radius R.sub.B may be related to the maximum outer
diameter of armored fiber optic assembly (2 times the maximum
armored fiber optic assembly radius R.sub.T). By way of example, if
armored fiber optic assembly 20 has an outer diameter of 2R.sub.T
then minimum bend radius R.sub.B may be a multiple of the outer
diameter of 2R.sub.T such as R.sub.B(min).gtoreq.10R.sub.T. Of
course, the assembly can have a minimum bend radius that is smaller
than provided by the relationship.
[0051] Table B lists the delta optical attenuation results for two
different bend radii, specifically, at 10R.sub.T and 8R.sub.T for
the armored fiber optic assemblies described above.
TABLE-US-00002 TABLE B Bend Radii Testing Fiber Optic 10R.sub.T
Bend Radius 8R.sub.T Bend Radius Assembly (1300 nm/850 nm) (1300
nm/850 nm) Assembly with 6- 0.01 dB/0.01 dB 0.02 dB/0.01 dB Fiber
MIC Cable Assembly with 24- 0.04 dB/0.05 dB -- Fiber MIC Cable
As shown, the delta optical attenuation performance for the bend
radius testing was relatively low for the assembly with the 6-fiber
MIC cable and for the assembly with the 24-fiber MIC cable at a
bend radius of 20R.sub.T. Data for the smaller bend radius of
16R.sub.T is not given since the values at 20R.sub.T were somewhat
elevated. Thus, the tested assemblies performed extremely well in
the bend radii testing when compared with the ICEA596 standard.
Other variations or embodiment can have much higher levels of
optical attenuation such as 0.60 dB or less during bending so long
as the performance is acceptable.
[0052] Table C lists the delta optical attenuation results for
impact testing for the armored fiber optic assemblies described
above. Impact testing was conducted using two different masses,
specifically, 2 kg and 6 kg at reference wavelengths of 1300 nm and
850 nm. Impact testing included two impacts at three separate
locations (e.g., about 150 millimeters apart) for each assembly and
the maximum delta attenuation for impacts of each assembly is
listed in Table C.
TABLE-US-00003 TABLE C Impact Testing Fiber Optic 2 kg 6 kg
Assembly (1300 nm/850 nm) (1300 nm/850 nm) Assembly with 6- 0.00
dB/0.00 dB 0.00 dB/0.01 dB Fiber MIC Cable Assembly with 24- 0.00
dB/0.00 dB 0.00 dB/0.01 dB Fiber MIC Cable
As shown, the delta optical attenuation performance for the impact
testing showed little to no delta optical attenuation for either
assembly at either mass. Overall, the tested armored fiber optic
assemblies proved comparable with, or better, than conventional
metallic armor cable assemblies.
[0053] FIG. 5A is an enlarged perspective view and FIG. 5B is a
close-up view of the armored fiber optic assembly of FIG. 2A
showing a partial longitudinal cross-section of the dielectric
armor superimposed on a grid G for referencing the shapes of the
layers. Armored profile has a pitch P (i.e., a generally repeating
shape that forms the armored profile in a spiral manner along the
longitudinal axis) that includes a web 102 and a band 110. The
geometry of the armored profile is discussed below in more detail
with respect to finite-element modeling performed. As best shown in
FIG. 5B, armored profile of this embodiment is generally formed
with inner layer 72 having a curvilinear profile formed in a spiral
along the longitudinal axis and outer layer 74 has a generally
uniform thickness formed over the curvilinear profile of inner
layer 72. Two factors that influence the mechanical performance of
the dielectric armor are geometry of the armored profile and the
material characteristics of the layers.
[0054] FIG. 6A depicts an enlarged cross-sectional view of a
portion of the dielectric armor of FIG. 5B superimposed on grid G
with certain dimensions of the armor profile shown. As shown, the
dielectric armor includes web 102 and band 110. Inner layer 72 of
band 110 has a thickness T1 and the web 102 of inner layer 72 has a
thickness T2 as shown. As shown on grid G, web thickness T2 is
defined as T2=T1-d.sub.o-d.sub.i, where an outer groove depth
d.sub.o is the height difference between the band and the web of
inner layer 72, and an inner groove depth d, is the height
difference between the band and the web of inner layer 72.
Moreover, a total groove depth d.sub.o+d.sub.i is the sum of the
outer groove depth d.sub.o and inner groove depth d.sub.i. In this
illustration, outer layer 74 has a thickness T3 that is essentially
uniform along the length of the armor profile, but the either or
both of the layers could have the armor profile. Dielectric armor
120 has an inner radius R.sub.I and an outer radius that is
R.sub.I+T.sub.1.
[0055] FIG. 6B is an enlarged perspective view of a portion of the
layer of the dielectric armor having the armor profile showing
generic geometry/dimensions used for finite-element modeling of the
same. FIG. 6B depicts an armor profile that is shaped very closely
to a step profile, which provides excellent mechanical
characteristics when the proper geometry is selected. However, in
practice it is difficult to manufacture the armor profile nearly as
a step profile at relatively high line speeds as shown in FIG. 6B.
Consequently, manufactured dielectric armor with the armored
profile has a profile that is shaped in a rounded, sloped or the
like fashion as generally depicted in FIG. 6A.
[0056] Finite-element analysis was conducted on the model of FIG.
6B to simulate the shape of manufactured profiles like shown in
FIG. 6A. Using finite-element analysis, the inventors discovered
certain dimension and/or relationships that provide desired
mechanical characteristics for the armored profile. FIG. 6B depicts
one-half pitch P/2 for the armored profile (i.e., the one-half
pitch P/2 only depicts a fraction of the web 102 and a fraction of
band 110. The one-half pitch P/2 of the armor profile has a length
given by the sum of length L1 (i.e., the fractional portion of the
band), length L.sub.T (i.e., a transitional portion between the
band and web), and length L2 (i.e., the fractional portion of the
web). Additionally, for the purpose of simplicity only the layer
with the armor profile of the dielectric armor was modeled since it
contributes to the majority of the mechanical characteristics for
the dielectric armor. Consequently, the web has a length referred
to as a groove length 2(L2) herein, which is two times the length
L2.
[0057] FIG. 7 is a graph having three different curves of true
stress (Pa) vs. true strain (%) representing two different generic
dielectric materials. Specifically, as labeled the first and second
curves represent different rigid materials and the third curve
represents a non-rigid material as defined herein, and may be
employed in dielectric armor 120. Specifically, the first rigid
material is a PVC available from Teknor Apex under the tradename
SRP 2009, the second rigid material is also a PVC available from
Teknor Apex under the 8015 family name, and the non-rigid material
is a flame-retardant PVC available from AlphaGary under the
tradename AG2052. Examples of rigid materials are rigid
thermoplastics (such as rigid PVC, CPVC, glass/fiber reinforced
plastics, etc.), while examples of non-rigid materials are flexible
thermoplastics (such as polyolefins, PVC, PVDF, FRPE, etc.). As
shown, after the knee in the curve of the rigid materials a
negative slope or near zero (i.e., small) positive slope occurs in
a respective region RG1 or RG2. On the other hand, the curve for
the non-rigid material does not have a negative slope or a near
zero slope like the rigid materials.
[0058] Dielectric materials that exhibit a region with a negative
slope or a near zero positive slope in the stress-strain curve at
or below the limiting design strain such as at the region RG1 of
the first rigid material in FIG. 7, require special attention to
inhibit bending strains from locally concentrating in the web of
the armor profile. Simply stated, if the first rigid material
operates in region RG1 of FIG. 7 (e.g., the 5% to 25% strain zone,
which is material specific) it localizes the strain at one location
of the web during bending, which may cause the web 102 to
undesirably separate from band 110. Thus, region RG1 of strain with
a negative slope or a near zero positive slope should be avoided.
On the other hand, outside region RG1 (i.e., a strain level that
significantly exceeds 25%) the strain is more evenly distributed
along the web, thereby inhibiting band/web separation during
bending. In other words, the failure strain for the rigid material
should be beyond the region RG1 (i.e., the failure strain level for
this material should exceed 25%), thereby inhibiting undesirable
band/web separation for the intended application. Whereas the
failure strain level for materials without the region RG1 such as
the non-rigid material depicted in FIG. 7 may allow for a wider
range of failure strain levels.
[0059] Likewise, the region RG2 for the second rigid material
should be avoided for the same reasons as discussed above. However,
the second rigid material has a relatively low positive slope
beyond region RG2 so that significantly exceeding the region RG2
means that a much higher strain level is required to inhibit
band/web separation. Consequently, different rigid materials may
require different minimum strain levels for inhibiting web-band
separation. By way of example, a minimum strain level of about 80%
is necessary for the second rigid material to inhibit web-band
separation.
[0060] Moreover, it was determined that the total groove length
2(L2) should be greater for rigid materials that exhibit a region
with a near zero positive slope or a negative slope in the
stress-strain curve at or near the failure strain as indicated by
region RG1 or RG2 to inhibit separation of the web from the band of
the armor profile. Consequently, material characteristics along
with band/web geometry for the material characteristics should be
selected for providing the desired performance (e.g., crush,
bending, optical performance, etc) for the armored fiber optic
assemblies.
[0061] Additionally, the modulus of elasticity at 1% strain for the
materials of FIG. 7 was determined from the true stress-true strain
curves. The modulus of elasticity for the non-rigid material
(AG2052) was about 320 MPa. Whereas, the modulus of elasticity for
the first rigid material (SRP 2009) was about 1537 MPa and the
modulus for the second rigid material (8015) was about 3088 MPa,
which is about twice the value of the first rigid material.
[0062] FIG. 8A depicts Table 1 which has exemplary dimensions in
millimeters for the design window of a first modeled material
(i.e., the non-rigid material AG2052). Specifically, Table 1 lists
exemplary dimensions for T1, T2, groove length, groove depth, and
groove pitch for minimum design strains of 40% and 80% with the
armor carrying 100% of the load. In other words, the loading for
the modeling was performed with the dielectric armor carrying 100%
of the applied 3000 Newton crush load with a deflection of 3
millimeters or less in order to provide an acceptable performance
for the design window. However, the fiber optic assembly within the
dielectric armor may carry some of the crush load depending on
several factors such as amount of free space, type of fiber optic
assembly, and the like. Simply stated, all of the modeling
represented in FIGS. 8A-8F model the extreme case where the
dielectric armor would carry 100% of the crush load and bending
load. Consequently, some armored fiber optic cable designs may have
acceptable performance, but not fall within the design window of
the curves shown in FIGS. 9A-9F because the fiber optic assembly
was carrying a fraction of the crush load. Simply stated, some
assemblies may have the dielectric armor carrying a portion of the
load along with the fiber optic assembly carrying a portion of the
load, thereby providing a larger design window. Likewise, during
bending the fiber optic assembly within the dielectric armor may
contribute to the bending performance, but this was not considered
in the finite element modeling. Illustratively, dielectric designs
with relatively longer groove lengths and relatively larger total
groove depths may not perform well in modeling that carries 100% of
the load, but when constructed with a suitable fiber optic assembly
can have acceptable performance due to the fiber optic assembly
carrying a fraction of the load. Some parameters that affect load
sharing between the fiber optic assembly and the dielectric armor
include free space, construction of the fiber optic assembly such
as jacket thickness, and the like.
[0063] The minimum design strain is the minimum percent true strain
at which failure occurs (i.e., the ultimate strain), which is the
case for all of the modeling. For instance, the first column of
data of Table 1 lists armor profile dimensions that have strain of
80% strain or more while meeting the desired bend and crush
criteria. The desired bend criteria permits a bending radius
R.sub.B of 5 diameters of the fiber optic assembly (i.e., 10 radii
of the fiber optic assembly) with no band/web separation and the
crush criteria has an optical attenuation of 0.6 dB or less.
Likewise, the next four columns of data in Table 1 represent
respective sets of armor profile dimensions that result in failure
with a strain of 40% or greater while meeting the same bending and
crush performance. In a similar fashion, the remaining columns of
Table 1 list other sets of armor profile dimensions that result in
failure at the indicated strain levels. Additionally, all of the
different dielectric armor modeled in Table 1 had the same inner
radius R.sub.I slightly below 6 millimeters.
[0064] Using the data from Table 1 (FIG. 8A), families of curves
for the band thickness versus a dimensional ratio for the armor
profile of an exemplary non-rigid material were determined and
plotted in FIGS. 9A and 9B. Specifically, FIGS. 9A and 9B
illustrate six curves for the band thickness T1 vs. a ratio (i.e.,
(2L2)/P) of groove length 2L2 to pitch P for the two different
minimum strain limits (i.e., strain of 40% or more and strain of
80% or more) and the three different total groove depths (do+di).
As shown, families of curves are plotted based upon the total
groove depths (do+di) of 0.5 millimeters, 0.75 millimeters, and 1.0
millimeters for the two different strain levels, which are depicted
on the same graph to illustrate the changes in the design window.
Alternatively, the total groove depth is calculated by T1-T2, which
is equivalent to do+di as shown in FIG. 6B. Further, FIG. 9B is an
enlarged view of the lower left-hand corner of the plot of FIG. 9A,
thereby showing the detail of the extended design window for the
curves directed to the 80% minimum design strain.
[0065] The respective areas bounded by the different curves
represent respective design windows for the given total groove
depth at the given strain level. For instance, the area bounded by
the bold solid line curve represents the total groove depth of 1.0
millimeter at a strain of 40% or more. Designs outside the area
bounded by the 1.0 millimeter/40% minimum strain curve may have
issues with elevated levels of strain, and/or failure (band/web
separation) during bending and the like. For instance, a design
with a 3.1 millimeter band thickness and groove length/pitch ratio
of 0.5 at a groove depth of 1.0 millimeter and 40% minimum strain
falls outside of this bounded area and may have issues with passing
crush performance. On the other hand, these dimensions have
suitable crush performance when the groove depth is 0.75
millimeters and 40% minimum strain since it is bounded by that 0.75
groove depth curve as shown by FIG. 9A. Simply stated, for the
given loading and design parameters for the respective curve: (a)
points below the curve did not meet the desired crush performance;
(b) points to the left of the curve did not meet the desired
bending performance; and (c) points to the right of the curve did
not meet the desired aesthetic appearance (i.e., the groove was too
long relative to the pitch). By way of example, suitable aesthetic
appearance has the groove length between about 20 percent and about
80 percent of the pitch.
[0066] The enlarged view shown in FIG. 9B, depicts that the design
windows for the 80% minimum strain curves are larger than the
counterpart design windows (i.e., the same total groove depths) for
the 40% minimum strain design windows. For instance, the 80%
minimum strain windows extend farther to the left as shown in the
lower left corner of FIG. 9B. Thus, as shown by plotting of the
modeling of Table 1 in FIGS. 9A and 9B, certain ratios and/or
dimension relationships along with the material characteristics
provide the armor profile with the desired performance during
bending and the like.
[0067] FIGS. 8B and 8C respectively depict Tables 2 and 3 with
exemplary dimensions in millimeters for the design window of a
first modeled rigid material, namely, SRP 2009. Like Table 1, Table
2 lists exemplary dimensions for T1, T2, groove length, groove
depth, and groove pitch for minimum strains of 40% and Table 3
lists data for minimum strains of 80%. Like before, the modeled
data from Tables 2 and 3 was used for creating graphs of the
modeled design window with the dielectric armor carrying 100% of
the load.
[0068] Specifically, FIGS. 9C and 9D are similar to FIG. 9A since
they graphically show the curves plotting the band thickness T1 vs.
a ratio (i.e., (2L2)/P) of groove length 2L2 to pitch P for the
given total groove depths (d.sub.o+d.sub.i) at a given minimum
strain level. Specifically, the graph of FIG. 9C illustrates the
design space with a strain of 40% or more and the graph of FIG. 9D
depicts the design space with a strain of 80% or more. As shown,
FIGS. 9C and 9D show that the difference in the design space
between the two different strain levels is more pronounced with the
first rigid material (FIGS. 9C and 9D) compared with the non-rigid
material (FIGS. 9A and 9B). For instance, the designs windows at
40% minimum strain are more sensitive to changes in the total
groove depth (d.sub.o+d.sub.i). This pronounced difference is due
to the negative slope of the stress vs. the strain curve as shown
in FIG. 7 in the proximity of the 40% strain limit for the
high-strength material. Consequently, greater groove-length to
pitch ratios and thicknesses (T1) are required for meeting bending
requirements (e.g., without band/web separation, etc.) when
designing with materials that exhibit small positive slopes or
negatives slopes (i.e., a trough in the stress strain curve) in the
proximity of the failure strain.
[0069] Simply stated, if a material has such a trough in the stress
vs. strain curve (i.e., a small positive or negative slope in the
stress vs. strain curve like as shown in FIG. 7) while the failure
strain is significantly greater than the strain level at the
trough, then smaller groove/pitch ratios and thicknesses T1 can be
employed. Strains initially concentrate in web 102 of dielectric
armor 120 as it is bent. If sufficient strain hardening is not
available before the failure strain is reached (i.e., if the trough
region of the stress vs. strain curve is too close to the failure
strain), then web 102 of thickness T2 will fail and separate.
[0070] FIGS. 8D and 8E respectively depict Tables 4 and 5 with
exemplary dimensions in millimeters for the design window of a
second modeled rigid material, namely, a material from the 8015
family. Tables 4 and 5 list exemplary dimensions for T1, T2, groove
length, groove depth, and groove pitch for respective minimum
strains of 80% and 110%. Higher minimum strains were required for
the second rigid material because the region RG2 is larger and the
true stress-true strain curve has a shallower slope than the first
rigid material. Like above, the modeled data from Tables 4 and 5 is
used for creating graphs of the modeled design window. The loading
for the modeling of the second rigid material was performed with
the dielectric armor carrying 100% of the applied 3000 Newton crush
load with a deflection of 3 millimeters or less and 100% of the
bending load in order to provide an acceptable performance for the
design window.
[0071] FIGS. 9E and 9F graphically show the curves plotting the
band thickness T1 vs. a ratio (i.e., (2L2)/P) of groove length 2L2
to pitch P for the given total groove depths (d.sub.o+d.sub.i) at a
given minimum strain level for the second rigid material.
Specifically, the graph of FIG. 9E illustrates the design window
with a minimum strain of 80% and the graph of FIG. 9F depicts the
design window with a minimum strain of 110%.
[0072] Thus, as shown by the tables and graphs example embodiments
of the armor profile can have dimensions within ranges based on the
materials for providing the desired crush and bending
characteristics. For instance, the dielectric armor may have inner
layer formed from a first rigid material with minimum strain of 80%
and an optional outer layer formed from a non-rigid material, where
the band thickness T1 is between about 1 millimeters and about 5
millimeters and web thickness T2 is between about 0.1T1 and about
T1 for the inner layer. The non-rigid material does not
significantly contribute to the crush and bending characteristics,
but can influence impact resistance and the like. By way of
example, outer layer has a suitable thickness such as about 0.5
millimeters to about 2.0 millimeters such as about 1 millimeter.
Additionally, suitable armored fiber optic assemblies can have
designs outside of the modeled design windows using the same
materials because the fiber optic assembly can carry a portion of
the crush and/or bending load.
[0073] For instance, one example of an armored fiber optic assembly
design similar to FIG. 2A where the fiber optic assembly
contributes to carrying the load uses a 24-fiber MIC cable
available from Corning Cable Systems of Hickory, N.C. as the fiber
optic assembly. The 24-fiber MIC cable includes a cable jacket that
supports the dielectric armor during crush and bending because the
free space is relatively small such about 0.5.+-.0.2 millimeters.
The dielectric armor is formed from an inner layer of 8015 rigid
material and has a band thickness of about 1.5 millimeters, a web
thickness of about 1 millimeter, and a pitch of about 10 with a
non-rigid outer layer formed from 910A-18 available from Teknor
Apex, which is plenum-rated. This 24-fiber embodiment
advantageously meets the desired mechanical characteristics such as
crush and bending while also being riser-rated. Other similar
embodiments can meet the mechanical characteristics and have a
plenum-rating. Another suitable example where the fiber optic
assembly contributes to the load carrying uses a 6-fiber MIC cable
available from Corning Cable Systems. In this embodiment, the
dielectric armor is again formed from an inner layer of 8015 rigid
material and has a band thickness of about 1.3 millimeters, a web
thickness of about 0.8 millimeter, and a pitch of about 10 with a
non-rigid outer layer formed from 910A-18 and is similar to the
design of FIG. 2A. This 6-fiber embodiment advantageously meets the
desired mechanical characteristics such as crush and bending while
also being plenum-rated.
[0074] Other variations of armored fiber optic assemblies are also
possible that may have other shapes for the dielectric armor. For
instance, FIG. 10A is a perspective view of an armored fiber optic
assembly 220 that includes a dielectric armor 120' having an inner
layer 72 that is a rigid material and an outer layer 74 that is a
non-rigid material. As with the other embodiments, dielectric armor
120' includes the armored profile and is disposed about fiber optic
assembly 30 configured as a fiber optic cable. As stated above, one
or both of inner layer 72 and/or outer layer 74 includes web 102
and band 110. In this embodiment, the armored profile has web 102
and band 110 that have a fixed longitudinal orientation instead of
having a spiral configuration along the length of the dielectric
armor. In other words, the web 102 and band 110 do not travel
longitudinally along the fiber optic assembly (i.e., the lead is
0).
[0075] FIG. 10B illustrates armored fiber optic assembly 320 having
a dielectric armor 120'' with an inner layer 72 formed from a strip
200 that is wound or extruded around fiber optic assembly 30 in a
spiral manner. In other words, strip 200 which forms inner layer 72
does not have a continuous annular cross-section, but has a space
between successive wraps of the same. As shown, strip 200 has a
rectangular cross-section, but it may have rounded edges for
inhibiting "zippering" of outer layer 74. In other embodiments,
inner layer 72 is corrugated for providing flexibility for wrapping
around the fiber optic assembly 30, or is interlocked for increased
mechanical strength.
[0076] As shown, outer layer 74 conforms to inner layer 72 formed
by strip 200 and generally takes on a corresponding helical shape
of the armor profile. However, the shape of outer layer 74 can vary
from that formed by strip 200. In an example embodiment, inner
layer 120'' is wound around fiber optic assembly 30 using spinning,
wrapping, and/or stranding methods. The winding methods may include
spinning fiber optic assembly 30. Additionally, strip 200 may be
pre-heated to soften the same before being wound around or
otherwise applied to fiber optic assembly 30 in order to reduce the
rigidity of the inner layer. It is also possible to extrude strip
200 and then wrapping the same or creating the gap thru the wall of
the inner layer. Additionally, other types of materials are
possible for portions of the dielectric armor. By way of example,
inner layer 72 may be an ultraviolet (UV)-light curable material
(i.e., UV curable material) that is helically wrapped about fiber
optic assembly 30, and then cured using a suitable dose of
radiation. This process may include applying or adding a resin to
strip 200.
[0077] Finite element modeling was also performed on the embodiment
of FIG. 10B to determine designs that met the desired crush
criteria as discussed above where the strip 200 carries about 82%
of the crush loading (about 2468 Newtons of the 3000 Newtons).
Bending was not considered since strip 200 has a gap G so there is
no band-web separation issue like the embodiments having an inner
layer with the continuous annular cross-section. Again, other
embodiments can have the fiber optic assembly carry a fraction of
the loading so that other variations having the desired performance
are possible.
[0078] Table D below lists example dimensions for the strip 200
used as inner layer 72 at different pitches about the fiber optic
assembly while meeting the desired crush criteria. FIG. 10C shows
the dimensions for strip 200 as listed in Table D. Specifically,
Table D lists different pitches (P) for the strip 200 formed from
the first rigid material (SRP 2009) with an inner diameter ID of
about 6.8 millimeters, a thickness of about 2.2 millimeters
(thereby yielding an outer diameter of about 11.2 millimeters), and
a normal width W as listed. Additionally, Table D lists gap GAP, an
actual band width BW (i.e., the deformed width of the strip), and a
material ratio per length of the fiber optic assembly (i.e., the
band width divided by the pitch). As depicted in Table D, a range
of pitches P and normal widths W are possible for meeting the
desired crush loading for the embodiment of FIG. 10B. Moreover, if
fiber optic assembly carries a fraction of the loading the possible
ranges for the dimensions are larger. By way of example, the
embodiments of FIG. 10B can have a pitch P between about 5
millimeters and about 30 millimeters and a thickness between about
1 millimeter and about 5 millimeters. As given in Table D, the
material ratio represents the percentage of material usage of the
strip (i.e., the smaller the material ratio the less material is
needed per meter). For instance, the design having a pitch P of 26
has the most efficient use of material to meet the desired criteria
since only 47.1% of the longitudinal length of the assembly has the
strip therearound.
TABLE-US-00004 TABLE D Example Dimensions for the strip of FIG. 10B
Band Width Pitch (P) Width (W) Gap (BW) mm Mm mm mm Material Ratio
32 10.7 15.843 16.157 50.5% 26 9.01 13.766 12.766 47.1% 20 7.71
10.560 9.440 47.2% 14 6.03 7.267 6.733 48.1%
[0079] Other embodiments may look similar to FIG. 10B using the
strip, but have a different construction. For instance, FIG. 10D
depicts armored fiber optic assembly 420 having a dielectric armor
120''' that looks similar to FIG. 10B, but the inner layer 72 is
extruded about fiber optic assembly 30, and outer layer 74 is then
extruded around the inner layer 72. In this embodiment, both the
inner layer 72 and the outer layer 74 have a continuous annular
cross-section. Specifically, inner layer 72 has a uniform
cross-section (i.e., a smooth tube) and the armor profile is
disposed in the outer layer 74. More specifically, outer layer 74
has a very thin web thickness such as about 0.5 millimeters or
less, but other values are possible. Embodiments having a smooth
tube for inner layer 72 may have a relatively low minimum strain
level such as a minimum strain of about 10% or more. For instance,
one smooth tube inner layer has as a minimum strain of about 12% at
a bend radius R.sub.B of about 8R.sub.T (i.e., 4 diameter of the
armored fiber optic assembly).
[0080] One method of forming the dielectric armor includes using
one or more extrusion-based methods for forming the armor profile.
For instance, FIG. 11 depicts a schematic side view of an extrusion
system 300 that includes an extruder 302 that defines an interior
301, having a barrel 303 and a screw 310 therein that is attached
to a crosshead assembly ("crosshead") 304. X-Y-Z Cartesian
coordinates are shown for the sake of reference, and the view in
FIG. 11 is in the X-Y plane. Extruder 302 includes screw 310 that
is mechanically connected to and driven by a motor assembly 320.
Motor assembly 320 includes a motor 322 and a drive system 324 that
connects the motor to screw 310. A material hopper 330 provides
extrusion material 332--here, the dielectric material that
ultimately makes up dielectric armor 120--to extruder 302. An
explanatory extrusion system that is suitable for being adapted for
use as extrusion system 300 is disclosed in U.S. Pat. No.
4,181,647.
[0081] FIG. 12 is a close-up, partial cross-sectional schematic
view of an explanatory crosshead 304 as viewed in the Y-Z plane.
Crosshead 304 includes a tip 348 that defines a central channel 350
having an output end 352 and in which is arranged a profile tube
360 having an outer surface 361, an inner surface 362 that defines
a tube interior 363, a proximal (output) end 364, and a distal end
365. A profiling feature 370 is located on outer surface 361 at
output end 352. In an example embodiment, profiling feature 370 is
a nub or a bump. Profile tube interior 363 is sized to accommodate
fiber optic assembly 30 axially. Profile tube distal end 365 is
centrally engaged by a gear 374 that, in turn, is driven by a motor
(not shown) in a manner such that profile tube 360 rotates within
channel 350.
[0082] Crosshead 304 further includes a die 378 arranged relative
to tip 348 to form a cone-like material channel 380 that generally
surrounds central channel 350 and that has an output end 382 in the
same plane as channel output end 352. Material channel 380 is
connected to extruder interior 301 so as to receive extrusion
material 332 therefrom and through which flows the extrusion
material during the extrusion process to form one or more layers of
the dielectric armor. In the example embodiment of crosshead 304 of
FIG. 12, profile tube output end 365 extends beyond channel output
end 352 such that profiling feature 370 thereon resides adjacent
material channel output end 382. In an example embodiment, profile
tube 360 and tip 348 are integrated to form a unitary tool.
[0083] In forming armored fiber optic assemblies 20, extrusion
material (not shown) flows through material channel 380 and out of
material channel output end 382. At the same time, fiber optic
assembly 30 is fed through profile tube interior 363 and out of
profile tube output end 364 (and thus through tip 348 and die 378).
In the meantime, profile tube 360 is rotated via gear 374 so that
profiling feature 370 redirects (i.e., shapes) the flow of the
extrusion material as it flows about fiber optic assembly 30. As
fiber optic assembly 30 moves through profile tube output end 364,
the circular motion of profiling feature 370 diverts the flow of
extrusion material. When motion of the profiling feature 370 is
combined with the linear motion of fiber optic assembly 30 the flow
of the extrusion material forms an armored profile. The speed at
which profile tube 360 rotates relative to the motion of fiber
optic assembly 30 (which may also be rotating) dictates the pitch
of the same. For instance, all things being equal higher rotational
speeds for the profiling feature 370 results in a shorter pitch.
The size and shape characteristics of profiling feature 370
dictate, at least in part, the particular armor profile imparted to
an outer surface 80 of the dielectric armor. Though the extrusion
flow is primarily diverted on the interior of the armor, the
drawdown of the material moves the groove partially or completely
to the outer surface of the armor. Of course, this type of
extrusion set-up may be used on any desired layer of the dielectric
armor.
[0084] Additionally, there are other suitable methods for forming
the armor profile. By way of example, FIG. 13 schematically
illustrates the dielectric armor 120 initially being extruded as a
smooth-surfaced tube (i.e., having a smooth outer surface as shown
on the right-side). Thereafter, the armor profile of the outer
surface 80 is then formed in the smooth-surfaced tube, prior to
hardening, by the application (e.g., pressing) of a profiling or
deforming member 402 (e.g., a nub or a finger) into the layer so as
to shape outer surface 80 in a manner similar to that used in a
lathe. In this example, the deforming member 402 may simply divert
material from the web to the band, or it may remove material
entirely from the dielectric armor 120. In one example embodiment,
deforming member 402 is stationary and cable 20 is rotated, while
in another example embodiment, deforming member 402 rotates around
the dielectric armor 120 as it passes. In still another example
embodiment, both the dielectric armor 120 and deforming member 402
rotate. Deforming member 402 may also be integrated into the
extrusion tooling (die).
[0085] FIG. 14 is a close-up, schematic cross-sectional view of
another explanatory embodiment of crosshead 304' similar to that
shown in FIG. 12, wherein tip 348 and die 378 are configured so
that central channel 350 is combined with the material channel that
flows extrusion material 332 therethru. A portion of profile tube
360 resides in an interior region 349 of tip 348, while the
proximal end portion of the profile tube resides within channel 350
so that profiling feature 370 resides within central channel 350
adjacent to channel output end 352. This geometry allows for
controlling the flow of extrusion material 332 while confining the
material within die 378.
[0086] In another explanatory embodiment similar to that shown in
FIG. 13 and as illustrated in FIGS. 15 and 16, the dielectric armor
is initially extruded as a smooth-surfaced tube (i.e., having a
smooth outer surface on the right-side) using dielectric material
332. The armor profile of outer surface 80 is then formed prior to
hardening, by the application (e.g., pressing) of profiling or
deforming member 402 (e.g., a set of gears) having one or more
features 404 that press into the dielectric armor in order to shape
outer surface 80. FIG. 16 shows a perspective view of an exemplary
embodiment of a roller-type deforming member 402 having an outer
edge 403 in which features 404 are formed. In this embodiment,
deforming member 402 of FIG. 15 may be formed in sets of two,
three, four, or more for forming the desired armor profile.
Roller-type deforming member 404 rolls over the outer surface 80 of
the dielectric armor before it hardens, thereby impressing features
404 and forming the armor profile.
[0087] Additionally, deforming member 402 may press extrusion
material 332 against fiber optic assembly 30 to eliminate free
space 90. Deforming member 402 may also press against dielectric
armor 120 in a manner that maintains the desired amount of free
space 90. FIG. 17 is a front view that illustrates the use of two
roller-type deforming member to impress the desired armor profile
into the dielectric armor. Of course, the roller-type deforming
member can have any desired pattern for creating the desired
armored profile.
[0088] 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.
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