U.S. patent application number 09/031482 was filed with the patent office on 2001-11-08 for optical fiber connecting structure and connecting member for connecting an optical fiber cable to a ferrule.
This patent application is currently assigned to Adams & Wilks. Invention is credited to KOSHIGOE, TATSUO, MINAMI, KOUJI, NAKAJIMA, MASAHIRO, SUZUKI, ESTATE OF NOBUO, SUZUKI, SAYOKO, TAIRA, JUNJI, TOKITA, HIROYUKI.
Application Number | 20010038770 09/031482 |
Document ID | / |
Family ID | 26384238 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038770 |
Kind Code |
A1 |
NAKAJIMA, MASAHIRO ; et
al. |
November 8, 2001 |
OPTICAL FIBER CONNECTING STRUCTURE AND CONNECTING MEMBER FOR
CONNECTING AN OPTICAL FIBER CABLE TO A FERRULE
Abstract
A clamp ring for connecting a tensile strength member to the
periphery of a rear end portion of a ferrule retaining part for
holding a ferrule, in which an optical fiber of an optical fiber
cable incorporating a coated optical fiber and the tensile strength
member surrounding the coated optical fiber is inserted and fixed
with an outer covering of the optical fiber cable stripped off from
its terminal portion, the clamp ring comprising a first annular
portion which fits on the periphery of the rear end portion of the
ferrule retaining part, a second annular portion located in the
back of the first annular portion, the second annular portion
having a smaller diameter than the first annular portion, a step
portion interconnecting the second annular portion and the first
annular portion, and a clamping portion extending inward from the
rear end of the second annular portion in such a way that the
extreme end of the clamping portion secures the periphery of the
optical fiber cable, in which the first annular portion, the second
annular portion, the step portion and the clamping portion are
formed as a single piece of metal having approximately the same
wall thickness.
Inventors: |
NAKAJIMA, MASAHIRO; (TOKYO,
JP) ; TOKITA, HIROYUKI; (TOKYO, JP) ; TAIRA,
JUNJI; (TOKYO, JP) ; MINAMI, KOUJI; (TOKYO,
JP) ; KOSHIGOE, TATSUO; (TOKYO, JP) ; SUZUKI,
ESTATE OF NOBUO; (TOKYO, JP) ; SUZUKI, SAYOKO;
(TOKYO, JP) |
Correspondence
Address: |
BRUCE L. ADAMS
ADAMS & WILKS
50 BROADWAY
31ST FLOOR
NEW YORK
NY
10004
|
Assignee: |
Adams & Wilks
|
Family ID: |
26384238 |
Appl. No.: |
09/031482 |
Filed: |
February 26, 1998 |
Current U.S.
Class: |
403/275 |
Current CPC
Class: |
Y10T 403/4908 20150115;
G02B 6/3888 20210501; G02B 6/3887 20130101 |
Class at
Publication: |
403/275 |
International
Class: |
F16G 011/05 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 1997 |
JP |
9-044371 |
Sep 5, 1997 |
JP |
9-241527 |
Claims
What is claimed is:
1. A clamp ring for connecting a tensile strength member to the
periphery of a rear end portion of a ferrule retaining part for
holding a ferrule, in which an optical fiber of an optical fiber
cable incorporating a coated optical fiber and said tensile
strength member surrounding the coated optical fiber is inserted
and fixed with an outer covering of said optical fiber cable
stripped off from its terminal portion, said clamp ring being
characterized in that it comprises: a first annular portion which
fits on the periphery of the rear end portion of said ferrule
retaining part; a second annular portion located in the back of
said first annular portion, said second annular portion having a
smaller diameter than said first annular portion; a step portion
interconnecting said second annular portion and said first annular
portion; and a clamping portion extending inward from the rear end
of said second annular portion in such a way that the extreme end
of said clamping portion secures the periphery of said optical
fiber cable; and that said first annular portion, said second
annular portion, said step portion and said clamping portion are
formed as a single piece of metal having approximately the same
wall thickness.
2. A clamp ring according to claim 1, said clamp ring being
characterized in that it is formed by press-forming operation.
3. An optical fiber terminating structure for connecting a tensile
strength member to the periphery of a rear end portion of a
ferrule, in which an optical fiber of an optical fiber cable
incorporating a coated optical fiber and said tensile strength
member surrounding the coated optical fiber is inserted and fixed
with an outer covering of said optical fiber cable stripped off
from its terminal portion, said optical fiber terminating structure
being characterized in that said tensile strength member is
connected to the periphery of a rear end portion of said ferrule by
crimping a clamp ring with its one end fitted on the periphery of
the rear end portion of said ferrule and the other end fitted on
the periphery of said optical fiber cable.
4. An optical fiber terminating structure according to claim 3,
said optical fiber terminating structure being characterized in
that said clamp ring comprises: a first annular portion which fits
on the periphery of the rear end portion of said ferrule; a second
annular portion located in the back of said first annular portion,
said second annular portion having a smaller diameter than said
first annular portion; a step portion interconnecting said second
annular portion and said first annular portion; and a clamping
portion extending inward from the rear end of said second annular
portion in such a way that the extreme end of said clamping portion
secures the periphery of said optical fiber cable; and that said
first annular portion, said second annular portion, said step
portion and said clamping portion are formed as a single piece of
metal having approximately the same wall thickness.
5. An optical fiber terminating structure according to claim 3,
said optical fiber terminating structure being characterized in
that the periphery of the rear end portion of said ferrule is
formed into a surface having pits and protrusions.
6. An optical fiber terminating structure according to claim 4,
said optical fiber terminating structure being characterized in
that the periphery of the rear end portion of said ferrule is
formed into a surface having pits and protrusions.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to clamp rings such as those
used in optical connectors which are located between optical fiber
transmission lines for switching, connecting or disconnecting the
transmission lines and those directly fitted to ferrules, as well
as to optical fiber terminating structures.
[0002] Presently, detachable optical connectors are used for
connecting optical fiber cables and optical fiber cords intended
for short-distance applications such as in-building wiring and
wiring to equipment. Since optical fibers are so thin and flexible
that they are usually secured by using ferrules. An optical
connector is constructed of a plug incorporating a ferrule and an
adaptor incorporating a sleeve.
[0003] FIG. 6 shows a cross section of an optical connector
employing a conventional crimp ring. As shown in FIG. 6, a ferrule
101 in which an optical fiber 201 is inserted and fixed has a
flange 102, and a stopper 104 is fitted behind a rear end portion
of the ferrule 101 in the back of the flange 102 with a compression
spring 103, which is mounted on the outer periphery of the rear end
portion of the ferrule 101, placed in between. This means that the
ferrule 102 is fitted in such a way that it can move relative to
the stopper 104 in its axial direction with the aid of the
compression spring 103. A coated optical fiber 202 is inserted into
the compression spring 103 and the stopper 104 with a tensile
strength member 204 of an optical fiber cable 203 located at the
rear end of the stopper 104, and the tensile strength member 204 is
secured around the outer periphery of a rear end portion of the
stopper 104 by crimping a crimp ring 105.
[0004] The crimp-on ring 105 is formed of a first cylindrical
portion 111 whose inside diameter fits the outer periphery of the
rear end portion of the stopper 104, a second cylindrical portion
112 which fits on the outer periphery of the optical fiber cable
203, and a connecting part 113 interconnecting the first and second
cylindrical portion 111, 113, as shown in FIG. 7. The first
cylindrical portion 111 is crimped to secure the tensile strength
member 204 between an inside curved surface 111a of the first
cylindrical portion 111 and the stopper 104 and, then, the second
cylindrical portion 112 is crimped to firmly hold the optical fiber
cable 203 in position with a compressive effect provided by an
inside curved surface 112a of the second cylindrical portion
112.
[0005] Since the optical fiber cable 203 is held in position with
compressive and frictional forces exerted by the inside curved
surface 112a of the second cylindrical portion 112 of the crimp-on
ring 105 as described above, its total securing force varies as a
result of changes in the outside diameter of the optical fiber
cable 203. It is therefore necessary to design the crimp-on ring
105 with varying inside diameters of the second cylindrical portion
112 to cater for such changes in the outside diameter of the
optical fiber cable 203. In addition, the outside diameter of the
second cylindrical portion 112 should be made suitable for diameter
rating of a crimping tool to be used. Thus, one problem is that the
crimp-on ring 105 is remarkably expensive, because it is
conventionally produced by cutting an aluminum material, for
instance. Another problem is that the second cylindrical portion
112 becomes relatively thick as a result of a relationship between
the outside diameter of the optical fiber cable 203 and the
diameter rating of the crimping tool, thereby requiring a great
force in crimping operation.
[0006] This invention is intended to solve these problems and has
as an object the provision of clamp rings which are easy to crimp
and manufacture.
[0007] Also known in the prior art are structures for terminating
optical fiber ends by directly fitting a ferrule to each end of an
optical fiber cord. An example of such structures is shown in FIGS.
8A-8B. As shown in FIGS. 8A-8B, after inserting a coated optical
fiber into a ferrule, a tensile strength member 204 of an optical
fiber cable 203 is placed around the periphery 302 of a rear end
portion of the ferrule 301, a ring member 303 is fitted, and both
ends of the ring member 303 is fixed in position by an adhesive 304
to thereby secure the individual components in integral form.
[0008] Such conventional structure has such a problem that a
sufficient tensile strength (about 10 kgf) can not be achieved
since the tensile strength member 204 is fixed by using the
adhesive 304.
[0009] Another problem of this conventional structure is that it
increases the chance of fiber breakage. This is because the
adhesive 304 is sucked into the tensile strength member 204 and
that portion of the tensile strength member 204 where the adhesive
304 has been sucked looses flexibility.
[0010] The structure has yet another problem in that it requires a
good deal of man hours for assembly work, because the adhesive 304
needs a long time to cure.
[0011] The invention aims at solving these problems. Accordingly,
it is also an object of the invention to provide a structure which
makes it possible to directly secure an optical fiber cable to a
ferrule without using an adhesive, as well as an optical fiber
terminating structure which provides a sufficient tensile strength
without causing a loss of optical fiber cable flexibility, yet
permitting ease of production.
SUMMARY OF THE INVENTION
[0012] In a first mode of carrying out the invention, a clamp ring
for connecting a tensile strength member to the periphery of a rear
end portion of a ferrule retaining part for holding a ferrule, in
which an optical fiber of an optical fiber cable incorporating a
coated optical fiber and the tensile strength member surrounding
the coated optical fiber is inserted and fixed with an outer
covering of the optical fiber cable stripped off from its terminal
portion, is characterized in that it comprises a first annular
portion which fits on the periphery of the rear end portion of the
ferrule retaining part, a second annular portion located in the
back of the first annular portion, the second annular portion
having a smaller diameter than the first annular portion, a step
portion interconnecting the second annular portion and the first
annular portion, and a clamping portion extending inward from the
rear end of the second annular portion in such a way that the
extreme end of the clamping portion secures the periphery of the
optical fiber cable, and that the first annular portion, the second
annular portion, the step portion and the clamping portion are
formed as a single piece of metal having approximately the same
wall thickness.
[0013] The aforementioned clamp ring of the invention is formed by
press-forming operation, for example.
[0014] In a second mode of carrying out the invention, an optical
fiber terminating structure for connecting a tensile strength
member to the periphery of a rear end portion of a ferrule, in
which an optical fiber of an optical fiber cable incorporating a
coated optical fiber and the tensile strength member surrounding
the coated optical fiber is inserted and fixed with an outer
covering of the optical fiber cable stripped off from its terminal
portion, is characterized in that the tensile strength member is
connected to the periphery of a rear end portion of the ferrule by
crimping a clamp ring with its one end fitted on the periphery of
the rear end portion of the ferrule and the other end fitted on the
periphery of the optical fiber cable.
[0015] In this structure, it is preferable that the clamp ring
comprises a first annular portion which fits on the periphery of
the rear end portion of the ferrule, a second annular portion
located in the back of the first annular portion, the second
annular portion having a smaller diameter than the first annular
portion, a step portion interconnecting the second annular portion
and the first annular portion, and a clamping portion extending
inward from the rear end of the second annular portion in such a
way that the extreme end of the clamping portion secures the
periphery of the optical fiber cable, and that the first annular
portion, the second annular portion, the step portion and the
clamping portion are formed as a single piece of metal having
approximately the same wall thickness.
[0016] Preferably, the periphery of the rear end portion of the
ferrule is formed into a surface having pits and protrusions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view of a clamp ring according
to an embodiment of the invention;
[0018] FIG. 2 is a cross-sectional view of an optical connector
employing the clamp ring of the invention;
[0019] FIGS. 3A-3B are exploded cross-sectional diagrams showing an
optical fiber terminating structure according to a second
embodiment of the invention;
[0020] FIG. 4 is a diagram showing one variation of the optical
fiber terminating structure according to the second embodiment of
the invention;
[0021] FIGS. 5A-5B are exploded cross-sectional diagrams showing an
optical fiber terminating structure according to a third embodiment
of the invention;
[0022] FIG. 6 is a cross-sectional view of an optical connector
employing a crimp-on ring of the prior art;
[0023] FIG. 7 is a cross-sectional view of the clamp ring of the
prior art; and
[0024] FIGS. 8A-8B are diagrams illustrating one example of an
optical fiber fixing method using a clamp ring of the prior
art.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Embodiments of the invention is now described in detail with
reference to the drawings.
[0026] FIG. 1 shows a cross section of a clamp ring according to an
embodiment of the invention. As shown in FIG. 1, the clamp ring 10
of this embodiment comprises a first annular portion 11, a second
annular portion 12 having a smaller diameter than the first annular
portion 11, a step portion 13 connecting the first annular portion
11 and the second annular portion 12 to each other, and a clamping
portion 14 which is provided immediately adjacent to the rear end
of the second annular portion 12 and extends inward, all these
potions being formed as a single piece. The inside diameter of an
opening 14b formed by an end face 14a of the clamping portion 14 is
made slightly larger than the outside diameter of the earlier
mentioned optical fiber cable, and the outside diameter of the
second annular portion 12 is set to fit diameter rating of a
crimping tool to be used in crimping operation. The first annular
portion 11 has such inside diameter that fits a rear end portion of
a stopper as described earlier, and is so constructed that a
tensile strength member is secured between an inside curved surface
11a of the first annular portion 11 and an inside surface 13a of
the step portion 13 when the first annular portion 11 is crimped
from around its outer periphery.
[0027] FIG. 2 shows a general construction diagram of an optical
connector which employs the clamp ring of this embodiment. As shown
in FIG. 2, a ferrule 31 in which an optical fiber 21 is inserted
and fixed has a flange 32, and the stopper 34 is fitted behind a
rear end portion of the ferrule 31 in the back of the flange 32
with a compression spring 33, which is mounted on the outer
periphery of the rear end portion of the ferrule 31, placed in
between. A coated optical fiber 22 is inserted into the compression
spring 33 and the stopper 34 with a tensile strength member 24 of
an optical fiber cable 23 located at the rear end of the stopper
34, and the tensile strength member 24 is secured between the clamp
ring 10 and an outer peripheral surface of the rear end portion of
the stopper 34 by crimping.
[0028] As stated above, the inside diameter of the opening 14b
formed by the end face 14a of the clamping portion 14 is slightly
larger than the outside diameter of the above-mentioned optical
fiber cable, and the outside diameter of the second annular portion
12 is set to fit diameter rating of the crimping tool used in
crimping operation. The optical fiber cable 23 is clamped by the
clamping portion 14 by crimping the second annular portion 12 with
the crimping tool while the tensile strength member 24 is secured
between the inside curved surface 11a of the first annular portion
11 and the stopper 34, and between the inside surface 13a of the
step portion 13 and the stopper 34, by crimping the first annular
portion.
[0029] The clamp ring 10 of this embodiment provides such
advantageous effects that it can be produced extremely easily by
press forming, for instance, and its crimping operation can be
performed relatively easily.
[0030] Clamp rings of the invention and optical connectors
employing the clamp rings are not limited to the above-described
embodiment in their basic construction. For example, an optical
connector may be a resin-molded product in which a flange, a
compression spring and a stopper are integrally formed.
[0031] FIGS. 3A-3B show an optical fiber terminating structure
according to a second embodiment of the invention. A clamp ring 40
used in this embodiment comprises a main annular portion 41 which
fits on the outer periphery of a rear end portion of a ferrule and
a clamping portion 42 which extends inward from the rear end of the
main annular portion 41 and so that its innermost end clamps the
outer periphery of an optical fiber cable 23. The main annular
portion 41 and the clamping portion 42 are formed as a one-piece
metallic part having approximately a uniform thickness.
[0032] The inside diameter of an opening 42a formed by the clamping
portion 42 is made slightly larger than the outside diameter of the
aforementioned optical fiber cable 23, and the outside diameter of
the main annular portion 41 is set to fit diameter rating of a
crimping tool used in crimping operation. Further, the inside
diameter of the main annular portion 41 is made slightly larger
than the diameter of the outer periphery 53 of the rear end portion
of the ferrule 51 so that the tensile strength member 24 is secured
between an inside curved surface 41a of the main annular portion 41
and the outer periphery 53 of the ferrule 51 to be joined by
crimping both ends of the main annular portion 41 from around its
outer periphery.
[0033] The ferrule 51 of this embodiment in which an optical fiber
21 is inserted and fixed has a flange 52, and the outer periphery
53 of the rear end portion of the ferrule 51 on which the
aforementioned clamp ring 40 is fitted is located in the back of
the flange 52. In this embodiment, three stepped ridges 54a-54c are
integrally formed on the surface of the outer periphery 53.
[0034] It is needless to say that the flange 52 may be produced
either as a discrete component of stainless steel, for instance, or
as an integral part of the ferrule when producing it.
[0035] The following discussion deals with a procedure for making a
terminating structure in which the optical fiber cable 23 is
connected to the ferrule 51 by using the aforementioned clamp ring
40.
[0036] As shown in FIG. 3A, the clamp ring 40 is passed over the
optical fiber cable 23 at first, and an outer covering, or jacket,
of the optical fiber cable 23 is removed near its end to expose the
coated optical fiber 22, the tensile strength member 24 and the
optical fiber 21. Then, the optical fiber 21 is inserted into an
optical fiber insertion hole 25 of the ferrule 51 while the coated
optical fiber 22 is inserted into a core insertion hole 26 of the
ferrule 51. The optical fiber 21 and the coated optical fiber 22
are secured in position with an adhesive readily filled in the
aforementioned optical fiber insertion hole 25 and the core
insertion hole 26.
[0037] The tensile strength member 24 of the optical fiber cable 23
is located around the outer periphery 53 of the rear end portion of
the ferrule 51 thus attached at this point. With the tensile
strength member 24 disposed between the clamp ring 40 and the outer
peripheral surface of the rear end portion of the ferrule 51 in the
back of the flange 52, the clamp ring 40 is crimped and fixed by
using the crimping tool as shown in FIG. 3(b). Thus, the tensile
strength member 24 can be secured in position by crimping the
ferrule side of the clamp ring 40, while the jacket (formed of PVC,
for instance) of the optical fiber cable 23 can be secured by
crimping the optical fiber cable side of the clamp ring 40.
[0038] Subsequently, the far end of the ferrule 51 is polished
together with the optical fiber 21 to complete an optical fiber
cable product already fitted with a ferrule, for instance.
[0039] As shown in the foregoing discussion, the present embodiment
provides such advantageous effects that it becomes unnecessary to
fix with the conventionally used adhesive, the optical fiber cable
23 and the ferrule 51 can be joined together in an extremely simple
and easy way, and the optical fiber cable does not loose its
flexibility.
[0040] Tensile tests carried out on ferrules each joined to an
optical fiber cable have proved that they could withstand tensile
stresses of about 15 kgf. On the other hand, a structure employing
the conventional adhesive bond disjoined under tensile stresses
ranging from 3 to 4 kgf.
[0041] Although there are formed three stepped ridges 54 for
clamping on the outer periphery 52 of the rear end portion of the
ferrule 51 in this embodiment, the number of the stepped ridges 54
is not limited thereto in this invention. Moreover, the outer
periphery 53 of the rear end portion of the ferrule 51 may feature
small pits and protrusions on its surface (to form a so-called
knurled surface) instead of forming the aforementioned stepped
ridges so that the tensile strength member 24 is firmly retained by
the small pits and protrusions when the clamp ring is fitted.
[0042] Although there is formed the flange 52 on the ferrule 51 in
this embodiment, its structure may be varied by employing another
type of clamp ring as shown in FIG. 4, in which the outer periphery
of the clamp ring 40 and that of a ferrule 51 have the same
diameter and an outer peripheral part 73 of the rear end portion of
the ferrule 71 is made slightly smaller than an inside curved
surface 41a of the clamp ring 40 in diameter so that the optical
fiber cable and the ferrule would look like a one-piece
element.
[0043] Next, FIGS. 5A-5B show an optical fiber terminating
structure according to a third embodiment of the invention.
[0044] As shown in FIG. 5, a clamp ring 60 used in this embodiment
comprises a first annular portion 61, a second annular portion 62
having a smaller diameter than the first annular portion 61, a step
portion 63 connecting the first annular portion 61 and the second
annular portion 62 to each other, and a clamping portion 64 which
is provided immediately adjacent to the rear end of the second
annular portion 62 and extends inward, all these potions being
formed as a single piece, in a manner similar to the first
embodiment shown in FIG. 1. The inside diameter of an opening 64b
formed by an end face 64a of the clamping portion 64 is made
slightly larger than the outside diameter of the earlier mentioned
optical fiber cable, and the outside diameter of the second annular
portion 62 is set to fit diameter rating of a crimping tool to be
used in crimping operation. Further, the diameter of the first
annular portion 61 is made slightly larger than the diameter of the
outer periphery 53 of the rear end portion of the ferrule 51 so
that the tensile strength member 24 is secured between an inside
curved surface 61a of the first annular portion 61 and the outer
periphery 53 of the ferrule 51 to be joined by crimping both ends
of the first annular portion 61 from around its outer
periphery.
[0045] The optical fiber terminating structure of this embodiment
is made by joining the optical fiber cable 23 to the ferrule 51 by
using the clamp ring 60 in a manner similar to the second
embodiment.
[0046] Specifically, the clamp ring 60 of this embodiment is passed
over the optical fiber cable 23, the optical fiber 21 is inserted
into the optical fiber insertion hole 25 of the ferrule 51, the
coated optical fiber 22 is inserted into the core insertion hole 26
of the ferrule 51, and the optical fiber and the coated optical
fiber 22 are secured in position with an adhesive, as shown in FIG.
5A.
[0047] The tensile strength member 24 of the optical fiber cable 23
located around the outer periphery 53 of the rear end portion of
the ferrule 51 thus attached is disposed between the inside curved
surface of the clamp ring 60 and the outer peripheral surface of
the rear end portion of the ferrule 51 in the back of the flange
52, and the clamp ring 60 is crimped and fixed by using the
crimping tool as shown in FIG. 5B. Thus, the tensile strength
member 24 can be secured between the outer periphery 53 of the rear
end portion of the ferrule 51 and the inside curved surface 61a of
the first annular portion 61 by crimping the first annular portion
61 of the clamp ring 60 from around its outer peripheral surface.
The tensile strength member 24 can also be secured between the
outer periphery 53 of the rear end portion of the ferrule and an
inside curved surface 63a of the step portion 63 to provide
increased fixing strength by crimping the first annular portion 61
of the clamp ring 60 from around its outer peripheral surface.
Furthermore, the jacket (formed of PVC, for instance) of the
optical fiber cable 23 can be secured by clamping it by the end
face 64a at the clamping portion 64.
[0048] As shown in the foregoing discussion, the present embodiment
provides such advantages, as does the earlier-described embodiment,
that it becomes unnecessary to fix with the conventionally used
adhesive, the optical fiber cable 23 and the ferrule 51 can be
joined together in an extremely simple and easy way, and the
optical fiber cable does not loose its flexibility. This embodiment
makes it possible to join the optical fiber to the ferrule even
more firmly.
[0049] The clamp rings of the invention are easy to produce and
their crimping operation can be performed relatively easily,
because they are formed to have approximately a uniform thickness
throughout their whole structure and the outer periphery of the
optical fiber cable is clamped by the end face of the clamping
portion which extends inward from the rear end of the second
annular portion as described above with reference to the
embodiments.
[0050] On the other hand, the optical fiber terminating structures
of the invention provide such advantageous effects that they
facilitate fixing operation due to their construction in which the
clamp rings have approximately a uniform thickness throughout and
the tensile strength member is secured by crimping the clamp ring
fitted over the outer periphery of the rear end portion of each
ferrule, and that the number of processes and labor hours required
for the fixing operation can be reduced since the individual
components can be fixed together without using an adhesive unlike
the conventional structure.
* * * * *