Cable grips for pulling, holding and supporting elongated objects such as cables, ropes and the like are well known in the art. These grips typically comprise an open mesh sleeve formed from braided or interwoven metallic wire strands which may be expanded radially by longitudinal compression to enable them to readily receive the cable and radially contracted by longitudinal stretching to frictionally engage the periphery of the cable. Tensile forces tending to separate the grip from the cable or to move the grip along the cable produce a firmer gripping of the cable.
Such grips are suitable for the fairly rugged electrical cable, but significant problems arise when the cable to be pulled is fragile. An example of the latter is fiber optic cable which comprises a flexible jacket encasing a single optical fiber or a bundle of optical fibers therein. Such fragile cable can be easily crushed or its optical characteristics can be distorted if the radial compressive forces on the cable are localized and become too great. Also, the optical fiber can be easily broken when subjected to excessive bending forces. In addition, it is typical to have pre-assembled on the end of fiber optic cable one or more fragile optical connectors receiving one or a bundle of optical fibers therein and secured by an epoxy resin and a crimp. This fragile connector is highly susceptible to crushing radial compressive forces as well as longitudinal tensile forces which could easily snap the connector from the cable. Moreover, the facial end of the connector must be protected from damage which would deleteriously affect its optically finished surface.
Moreover, fiber optic cable is much smaller in diameter than the typical electrical cable. These small diameters in most cases are much less than the conventional wire mesh grips can adequately hold. Also, the fiber optic connector at the end of the fiber optic cable has a much larger outside diameter than the cable so that a conventional grip selected to fit and adequately grip the cable cannot expand enough to accept the larger connector diameter or diameters. Conversely, a grip designed to receive a large diameter connector cannot compress enough to grip the smaller cable diameter. A typical example is a connector with a 0.5 inch outer diameter and a cable with a 0.073 inch outer diameter.
A method presently used to protect a fiber optic cable connector during pulling comprises wrapping the connector in a layer of foam rubber and then inserting this into a plastic sleeve which in turn is inserted into an oversized wire mesh grip. This method, however, is expensive and time consuming since conventional wire mesh grips are relatively stiff, thereby creating extreme difficulty in inserting the small and flexible cable with a connector attached. In addition, after assembly of this combination, the holding capability of the oversized wire mesh is marginal and may allow slippage of the cable and pulling out of the pre-assembled connector.
In addition to these qualifications, a grip for pulling fiber optic cable must adequately grip the cable and not damage the cable or the connector. There are four basic cable configurations that must be contended with by the grip designer. The first is a cable by itself, containing one or a plurality of fiber optic cables all without preassembled connectors. This provides only one rather uniform diameter for the grip to contend with.
A second configuration involves a single fiber optic cable with a preassembled connector, with both the cable and the connector diameter being within the grip diameter range so that the grip can be compressed longitudinally and therefore expand sufficiently in the radial direction to accept the combined cable and connector and also then be stretched longitudinally to thereby reduce the radius of the wire mesh into a sufficient gripping engagement of the cable.
A third cable configuration involves a single fiber optic cable with a preassembled connector where the connector size is beyond the expansion of the wire mesh that is made to suit the cable diameter. Lastly, a fourth basic cable configuration involves a plurality of fiber optic cables with preinstalled conconnectors where the connector diameter build-up is beyond the expansion capability of the wire mesh.
In my copending U.S. patent application Ser. No. 213,856 filed Dec. 8, 1980 and assigned to the same assignee as the instant application, there is disclosed a cable grip which is especially suitable for pulling fiber optic cables and provides the necessary protection to the fragile connector ends of such cables by means of a tubular protective sheath. The particular embodiment of the sheath disclosed in that patent application is one of a rigid metal body formed of, for example, metal tubing. While this particular embodiment of a sheath body provides excellent protection for the fiber optic connector inserted therein, for certain installations involving angled or curved conduits through which the cable must be pulled, a sharp curvature of the conduit walls may pose an obstruction to the passage of an elongated rigid tubular member.