Patent Description:
In an optical fiber cable used for communication, a tension member such as steel wire is disposed to prevent an optical fiber core from being stretched more than necessary, for the purpose of securing quality of the communication. In an optical cable connection closure that is used for connection and the like of the optical cable, the optical fiber cable is fixed to prevent bending and damage of optical fibers caused by movement of the optical fiber cable.

For example, Patent Literature <NUM> discloses that steel wire is suitable for the tension member. Further, Patent Literature <NUM> discloses a mechanism for bending and press-contact of the tension member and a member for holding an end of a cable.

To lay the optical fiber cable in a section where suppression of electromagnetic induction is required, it is necessary to use a cable including a nonmetallic tension member. An example of the nonmetallic tension member is made of, for example, glass fiber or chemical fiber as a main material. The optical fiber cable is typically required to be housed and fixed in the closure for connection and the like.

Typically, the optical fiber cable is fixed at two positions in the closure. At one of the two positions, the optical fiber cable is held by bending and pressure-contact of the tension member as disclosed in Patent Literature <NUM>. At the other position, the optical fiber cable is held in such a manner that a cable jacket is sandwiched. When the former method is applied to the nonmetallic tension member, the tension member may be damaged because the material of the tension member is fragile unlike a metal, and a holding method to fix the tension member itself is cannot be used. Therefore, the cable is required to be fixed only by the latter method; however, it is not possible to hold the cable with strength sufficient to fix the cable at the single position because large sandwiching force causes buckling deformation of the cable jacket and damages the optical fiber core.

<CIT> discloses a prior art cable gripping device.

The present disclosure is to solve the above-described issues, and an object of the present disclosure is to fix an optical fiber cable having a nonmetallic tension member in a closure without damaging the tension member and a core.

The invention to solve the above-described issues is a method to fix an optical fiber cable having a nonmetallic tension member in a closure by using a holding band, and the holding band causes appropriate gripping force and appropriate frictional force to act on the cable, which enables fixing of the cable by holding at a single point and eliminates damage by press-contact of the nonmetallic tension member.

More specifically, an optical fiber cable holding device according to the present invention includes all the features specified in appended claim <NUM>.

According to the present disclosure, it is possible to fix the optical fiber cable having the nonmetallic tension member in the closure without damaging the tension member and the core.

Some embodiments of the present disclosure are described in detail below with reference to drawings. Note that the present disclosure is not limited to the embodiments described below. These embodiments are merely examples, and the present disclosure can be implemented in forms obtained by variously alternating or modifying the embodiments based on the knowledge of those skilled in the art. Note that, in the present specification and the drawings, components denoted by the same reference numerals mutually denote the same components.

<FIG> is a perspective view of a holding band according to the present disclosure. A holding band <NUM> according to the present disclosure functions as an optical fiber cable holding device, and includes a thin plate portion <NUM>, a band-diameter adjuster <NUM>, a binding mechanism portion <NUM>, and protrusion fitting holes <NUM>.

The holding band <NUM> is manufactured by processing a metal such as stainless steel or a nonmetallic synthetic resin. The band-diameter adjuster <NUM> and the binding mechanism portion <NUM> housing the band-diameter adjuster <NUM> are connected and fixed to one end of the thin plate portion <NUM>. The protrusion fitting holes <NUM> to be screwed onto protrusions of the band-diameter adjuster <NUM> are provided on the other end of the thin plate portion <NUM>. The thin plate portion <NUM> can pass through the binding mechanism portion <NUM> by being wound, and the band-diameter adjuster <NUM> fitted to the protrusion fitting holes <NUM> is tightened to adjust a diameter of a rough circle formed by the thin plate portion <NUM> and to have a firm grip on an optical fiber cable <NUM>.

<FIG> is a cross-sectional view of the optical fiber cable <NUM>. The optical fiber cable <NUM> may have a self-supporting structure used for a case where the optical fiber cable <NUM> is laid between utility poles or is laid from a utility pole to a subscriber home. In this case, a supporting line is separated and the optical fiber cable <NUM> includes only a main body portion. The optical fiber cable <NUM> includes optical fibers <NUM>, tension members <NUM> and a jacket <NUM> that is made of thermoplastic resin. Note that the configuration of the optical fiber cable <NUM> is not limited hereto as long as the optical fibers <NUM> are disposed inside an inner cavity <NUM>. The optical fibers <NUM> transmit optical signals used for communication. The tension members <NUM> have a function to prevent the optical fibers <NUM> from being damaged by application of excessive tension on the optical fibers <NUM> in a longitudinal direction. The tension members <NUM> are each made of nonmetallic material such as glass fiber reinforced plastic, and does not cause electromagnetic induction.

<FIG> illustrates a configuration in which the optical fiber cable <NUM> is held by the holding band <NUM> in a closure. The holding band <NUM> is attached and wound around the optical fiber cable <NUM>. The binding mechanism portion <NUM> has a shape engageable with a screwing tool such as a driver and a wrench, and can apply appropriate tightening pressure to the optical fiber cable <NUM>. The optical fiber cable <NUM> is fixed only by the holding band <NUM>. The tension members <NUM> themselves are not directly and mechanically press-fixed in the closure. Therefore, even when the tension members <NUM> are each made of a nonmetallic material, the tension members <NUM> are not damaged. In addition, fixing only by the holding band <NUM> makes it possible to improve work efficiency. Note that a member to be fixed to the closure may be attached to the holding band <NUM>.

<FIG> illustrates the holding configuration as viewed from the cable longitudinal direction, and illustrates a mechanism applying pressure to the optical fiber cable <NUM>. One end 10A of the thin plate portion <NUM> is fixed to the binding mechanism portion <NUM>. The other end 10B of the thin plate portion <NUM> is provided with the protrusion fitting holes <NUM>, and the protrusion fitting holes <NUM> fit onto protrusions of a convex portion <NUM> of the band-diameter adjuster <NUM>. The holding band <NUM> can have a firm grip on the optical fiber cable <NUM> such that the thin plate portion <NUM> comes into close contact with the optical fiber cable <NUM>, and can uniformly apply the pressure in a circumferential direction. The holding band <NUM> can prevent buckling deformation of the optical fiber cable <NUM> and the jacket <NUM> in a case where the pressure is applied to the optical fiber cable <NUM> and the jacket <NUM> in one direction.

Deformation of the jacket <NUM> occurred by applying the pressure to the optical fiber cable <NUM> causes contraction of an area of the inner cavity of the optical fiber cable <NUM>. The plurality of optical fibers <NUM> stored in the optical fiber cable <NUM> closely contact with one another to generate excessive bending, which influences communication. In a condition where pressure p in a radial direction is applied to the circular optical fiber cable <NUM> along the circumference, a reduction amount ΔR of a radius R of the inner cavity of the optical fiber cable <NUM> can be determined by an expression (<NUM>) with use of a Young's module E of the jacket <NUM>. <NUM>) <MAT>.

In a condition where the optical fiber cable <NUM> is gripped by the holding band <NUM>, a cross-sectional area S that is a limit for influence on the communication is determined by an expression (<NUM>). <NUM>) <MAT> Therefore, the pressure p to fix the optical fiber cable <NUM> can be increased to a value determined by an expression (<NUM>). <NUM>) <MAT>.

As an example, a test in which crushing pressure is applied so as to sandwich two points of a commercially-available optical fiber cable having specifications of <FIG> was performed. As a result, loss occurred on the optical fiber when the cross-sectional area S reached <NUM><NUM>. Therefore, the holding band <NUM> satisfies an expression of the pressure p ≤ <NUM> MPa to fix the optical fiber cable, as gripping force.

When the optical fiber cable <NUM> is stretched in such a manner that one end of the optical fiber cable <NUM> is held in the closure and the other end is anchored to a utility pole or the like, tension in the longitudinal direction occurs on the optical fiber cable <NUM> due to action of a weight of the cable itself, a wind pressure load applied to the cable, and the like. Hereat, to fix the optical fiber cable <NUM> in the closure, it is necessary to satisfy an expression (<NUM>),
(Math. <NUM>) <MAT> where w is a width of the thin plate portion <NUM> of the holding band <NUM>, µ is a static friction coefficient between the thin plate portion <NUM> and the optical fiber cable <NUM>, and F is the tension applied to the optical fiber cable in the longitudinal direction of the optical fiber cable. Therefore, the holding band <NUM> satisfies the gripping force expressed by an expression (<NUM>). <NUM>) <MAT>.

<FIG> illustrates an example of a holding configuration according to the claimed invention. The holding band <NUM> according to the claimed invention further includes a thin plate elastic body <NUM>, an elastic curved portion <NUM>, and a protrusion <NUM>.

The gripping force expressed by the above-described expression (<NUM>) is realized by the thin plate elastic body <NUM> illustrated in <FIG>. The thin plate elastic body <NUM> includes the elastic curved portion <NUM> that is curved in an elliptical shape so as to externally contact with the jacket <NUM> of the optical fiber cable. When the pressure occurring on an external contact point between the elastic curved portion <NUM> and the optical fiber cable <NUM> is increased by tightening the band-diameter adjuster <NUM>, a curvature of the elastic curved portion <NUM> is reduced.

The elastic curved portion <NUM> includes the protrusion <NUM> on a rear surface of the external contact point with the optical fiber cable <NUM>. When the pressure is applied to the optical fiber cable <NUM> and the above-described curvature is reduced, the protrusion <NUM> is caused to fit into one of the protrusion fitting holes <NUM> as illustrated in <FIG>, and the band-diameter adjuster <NUM> is not rotated any more.

In a configuration illustrated in <FIG>, a frictional force application portion <NUM> is added to a surface of the thin plate portion <NUM>. The frictional force application portion <NUM> increases frictional force on a surface of the holding band <NUM> contacting with the optical fiber cable <NUM>, which makes it possible to fix the optical fiber cable <NUM> in the closure when the tension in the cable longitudinal direction occurs on the optical fiber cable <NUM>. The frictional force application portion <NUM> is realized by, for example, application of a friction material or formation of roughnesses on the thin plate portion. The configuration according to the present example is applicable to the example and the embodiment previously described.

<FIG> illustrates an example of holding protrusions <NUM> formed by the friction material added to the frictional force application portion <NUM> or the roughnesses provided on the thin plate portion <NUM>. A shape of each of the holding protrusions <NUM> does not damage the jacket <NUM>, and does not influence on the optical fibers <NUM> inside the optical fiber cable <NUM> and on communication. Further, the shape of each of the holding protrusions <NUM> may have a height smaller than a thickness of the jacket of the optical fiber cable <NUM>, and may be a symmetric protrusion or may be an asymmetric shape to bite into the jacket <NUM>, which is deformed due to the tension applied in the longitudinal direction.

The above-described frictional force application portion and the above-described holding protrusions are added to increase the static frictional coefficient µ acting between the jacket of the optical fiber cable and the holding portion, thereby sufficiently satisfying the following expression. This makes it possible to surely fix the optical fiber cable without applying pressure causing loss of the optical fibers. <NUM>) <MAT>.

The above-described embodiments do not limit the present invention, which is defined by the appended claims.

Claim 1:
An optical fiber cable holding device, comprising:
a thin plate portion (<NUM>) configured, by bending a rectangular thin plate in a length direction thereof into a shape of a rough circle, to hold an outer periphery of an optical fiber cable (<NUM>);
a binding mechanism portion (<NUM>) fixed on one end of the thin plate portion (<NUM>) and configured to bind the thin plate portion (<NUM>) wound around the optical fiber cable (<NUM>) on the one end of the thin plate portion (<NUM>);
protrusion fitting holes (<NUM>) provided on the other end of the thin plate portion (<NUM>) wound around the optical fiber cable (<NUM>); and
a band-diameter adjuster (<NUM>) fixed to the binding mechanism portion (<NUM>), including a band diameter adjuster protrusion (<NUM>) fittable into each of the protrusion fitting holes (<NUM>), and configured to adjust a diameter of the rough circle by changing from one hole to another hole of the protrusion fitting holes (<NUM>) to be fitted onto the band diameter adjuster protrusion (<NUM>),
characterized in that
the thin plate portion (<NUM>) includes a mechanism to limit pressure, applied from the thin plate portion (<NUM>) to the optical fiber cable (<NUM>), to a predetermined value or less,
wherein the thin plate portion (<NUM>) includes a thin plate elastic body (<NUM>)
wherein the thin plate elastic body (<NUM>) comprises an elastic curved portion (<NUM>), which is curved to protrude toward the optical fiber cable (<NUM>) to externally contact with it,
wherein the elastic curved portion (<NUM>) includes, on a rear surface not contacting with the optical fiber cable (<NUM>), a thin plate elastic body protrusion (<NUM>),
wherein the thin plate portion (<NUM>) is configured such that,
by predetermined pressure occurring between the thin plate elastic body (<NUM>) and the optical fiber cable (<NUM>), a curvature of the thin plate elastic body (<NUM>) is reduced, the thin plate elastic body protrusion (<NUM>) is caused to fit into one of the protrusion fitting holes (<NUM>) of the thin plate portion (<NUM>), and the diameter of the rough circle is fixed.