Optical fiber cable with ripcords

BACKGROUND THE INVENTION

Field of Invention

The present invention relates to an optical cable having ripcords that are easily accessible, and wherein the ripcords can be used reliably without damaging the optical cable and without breakage.

Background of Related Art

EP-A-0 893 722 discloses an optical fiber cable comprising an armor layer in a cylindrical form. The armor layer includes a first end and a second end overlapped by the first end at an overlap point, one or more ripcords disposed within the cylindrical form, a jacket surrounding the cylindrical form and two diametrically opposed longitudinal strength members embedded In the jacket. The longitudinal strength members extend substantially parallel to the axis of the optical fiber cable. In an embodiment the optical fiber cable comprises an armor layer In a cylindrical form including an overlap point, wherein one of the longitudinal strength members is disposed in front of the overlap point of the armor layer such that the other longitudinal strength member is disposed 180 degrees from the overlap point. Two ripcords are disposed 180 degrees from each other within the cylindrical form in such manner, that each ripcord is disposed away from the overlap point.

An optical cable may include a ripcord that facilitates the removal of portions of cable armor or other protective sheathing disposed about a fiber bundle in order to gain access to the fiber bundle. However, the placement of ripcords in conventional optical cables may result in the ripcord being cut by the edge of the protective armor tape when the ripcord is used. When the ripcord becomes cut, the cable must be re-prepped, which is a time-consuming and tedious process.

Additionally, the ripcord may also be cut due to wearing against a radial strength member (RSM). This occurs when the ripcord is pulled through the wrong portion of the sheath. In such a situation, the intervening RSM may also prevent the ripcord from adequately tearing through the cable sheathing. Conventional placement of the ripcord, which permits the ripcord to be pulled incorrectly through the cable housing, may also cause damage to the fiber bundle in the central cavity of the optical cable.

Ripcords placed without due regard to the above considerations may also be accidentally cut when the cable is being prepped. Furthermore, random placement of the ripcords may not provide a sufficient window opening in the sheath, which makes it difficult to extract the cable core from its housing.

SUMMARY OF THE INVENTION

Starting from EP-A-0 893 722 as the most pertinent prior art of record, the present invention provides an optical fiber cable comprising: <ul id="ul0001" list-style="dash" compact="compact"><li>an armor layer disposed in a cylindrical form, said armor layer including a first and a second end, said first end overlapping said second end at an overlap point;</li><li>a first and a second ripcord disposed essentially 180 degrees from each other within the cylindrical form of said armor layer, each of said first and second ripcords being disposed more than 45 degrees from said overlap point (3) within the cylindrical form;</li><li>a jacket surrounding the cylindrical form of said armor layer; and</li><li>a first and a second radial strength member disposed In said jacket,</li></ul> characterized In that said first and second radial strength members are disposed more than essentially 45 degrees from sold overlap point, and In that said first ripcord is positioned at a location proximate to said first radial strength member and towards said overlap point, and said second ripcord is positioned at a location proximate to said second radial strength member and located in a direction away from said overlap point.

Further embodiments according to the invention are disclosed in the subclaims.

The present invention obviates the above deficiencies of known fiber cables by placing the ripcords included in the cable armor with reference to the position of the cable armor overlap and also with reference to radial strength members included in the cable. In particular, ripcords are placed at least 45 degrees, preferably 90 degrees ± 20 degrees, off the center from the armor tape overlap.

The cable and ripcords can also be marked by color coding, texturing or printed matter so that the ripcord is pulled in the correct direction to avoid being damaged by the RSM. Preferred embodiments of the invention with be described below with reference to the attached drawings where: <ul id="ul0002" list-style="none" compact="compact"><li>Fig. 1 illustrates an optical cable with ripcords according to the invention.</li><li>Fig. 2 illustrates an optical cable with ripcords according to the invention.</li></ul>

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Fig. 1, the ripcords 1, 1' are disposed at 90° ± 20° relative to the center of armor tape overlap 3. The reason for this is that each of the edges of the corrugated armor tape is like a serrated knife. If the ripcord rubs against this edge as it is being used to cut through the sheath, the ripcord will be cut and the cable must be re-prepped. Ripcords should be 180 degrees apart in order to provide a bisected cable sheath that permits the fiber core to be most easily extracted. Accordingly, to provide the bisected sheath, the best position that the ripcords can be from the armor overlap is 90 degrees. To provide this degree of ripcord displacement relative to the center tape and relative to the other ripcord, the ripcords can simply be guided into this position during cable manufacturing or the ripcords can be glued to the armor tape at the appropriate angular displacement from the armor overlap, using an appropriate adhesive.

Referring to Fig. 2, the placement of the ripcords 1, 1' relative to reinforcing radial strength members 2, 2' disposed in an optical cable should also be considered, in addition to their replacement relative to the armor overlap 3. In an optical cable including the RSMs, ideally ripcord 1 should be pulled in direction A through jacket 4 and ripcord 1' should be pulled in direction A'. However, without adequate indicators, a service person may pull ripcord 1 in direction B or ripcord 1' in the direction of B'. Either situation could cause the ripcord to break due to the shearing action against the RSM 2 or 2'. Accordingly, as a further feature of the invention, when the ripcords and RSMs are disposed as shown in Fig. 2, the ripcords and one or more sides of the cable sheath are color coded so that each ripcord can be identified and pulled through the corresponding side of the cable sheath. The color coding or other marking, such as texturing or printing, is provided to orient the ripcord with the appropriate side of the cylindrical jacket with respect to the RSMs.