Interlocking strain relief

Abstract: A strain relief (9) for a fiber optic cable (2) comprises, a tubular length of flexible material provided with a cylindrical axial bore (18) sized for receiving the fiber optic cable (2), and formed with narrow openings (24), a tongue (27) in each of the openings (24) and a groove (29) across from each tongue (27), whereby bending of the tubular length causes the tongues (27) to lodge in the grooves (29).

Description: The invention relates to a strain relief for protective coupling of an optical fiber cable. It is known from EP-A2-0 260 774 to provide a strain relief for protectively coupling a fiber optic cable with a connector, comprising a generally tubular length of flexible material, provided with a cylindrical axial bore sized for receiving said fiber optic cable therewithin, profiled at a first end, to be anchored thereat to said connector while clamping onto said fiber optic cable characterized in that the tubular length is formed to have narrow openings aligned normally with respect to the axis of said bore, with a predetermined number of said openings each being provided on one side with a small bump of predetermined shape and size not quite extending to the opposite side. It is known from US-A-3 032 737 to provide a cable strain relief for an electrical connector which comprises a tubular length of flexible material provided with an axial bore for receiving a cable therethrough and having a plurality of slit-like openings substantially normal to the axis and arranged in an ascending spiral line. The slits are separated by narrow cross-pieces distributed about the axis along the spiral in circumferential rows which are staggered with respect to adjacent rows. The invention is defined as a strain relief exhibiting all of the features as set out in independent claim 1. Dependent claims 2-4 exhibit advantageous, non-trivial improvements of the subject-matter of claim 1. The present invention relates to an interlocking strain relief. The interlocking strain relief comprises a tubular length of flexible material provided with a bore receiving the fiber optic cable. The tubular length is profiled at a first end to be anchored to the connector while clamping onto the fiber optic cable. The tubular length is formed with a series of narrow openings extending transverse to the axis of the bore. The tubular length has corresponding tongues imposing into corresponding openings, and has corresponding, complementary grooves across the corresponding openings opposing the corresponding tongues, whereby upon bending of the tubular length into an arc or curve, the corresponding tongues lodge in the corresponding grooves to maintain the tubular length in a self supporting, curved relationship. The invention will now be described by way of example with reference to the accompanying drawings, according to which; FIGURE 1 is a fragmentary perspective view of a bayonet type connector together with an optical fiber cable, a crimp ferrule and an interlocking strain relief of the present invention configured at a right angle to the plane of connection between the boot and the connector; FIGURE 2 is a perspective view of assembled optical fiber cable and interlocking strain relief; FIGURE 3 is a front elevation view of a known strain relief; FIGURE 4 is a front elevation view of a strain relief of the present invention; FIGURE 5 is a perspective view of the strain relief shown in Figure 4; FIGURE 6 is a front elevation view, in section, through line 6-6, of the strain relief shown in Figure 4 and Figure 5; FIGURE 7 is an elevation view of another strain relief; and FIGURES 8, 9 and 10 are fragmentary views of portions of the strain relief of Figure 7. Referring to Figures 1 and 2, shown, by way of example, is a connector 1 for an optical fiber cable 2. As shown in Figure 1, the cable 2 includes an elongated central optical fiber 3 concentrically encircled by a buffer 4 together comprising a buffer covered fiber 3,4. The cable 2 includes a load bearing portion in the form of elongated strength members 5 that extend axially along the cable 2. The strength members 5 are distributed over the outer diameter of the buffer covered fiber 3,4. The cable 2 further includes an outer jacket 6 of polymeric material enclosing the strength members 5. Parts of the cable 2 are cut away as shown to provide a length of fiber 3 projecting from the buffer 4, and a length of the buffer covered fiber 3,4 projecting from the strength members 5, and lengths of the strength members 5 projecting from the jacket 6. The connector 1 includes an optical connector assembly 7 and a crimp ferrule 8. An interlocking strain relief 9 is also shown. The connector assembly 7 includes a rigid alignment ferrule 11 enclosed by a protective dust cover 10. The alignment ferrule 11 has an axial central passage (not shown) for aligning the optical fiber 3 of the cable 2. The passage emerges from the rear end 12 of the alignment ferrule 11 for accepting the optical fiber cable 2. A coupling nut 13 encompasses the alignment ferrule 11 of the connector 1, and has J-shaped bayonet type slot 14 for connection with a known complementary connector bushing (not shown). The front end of the alignment ferrule 11, shown protected by the dust cover 10, is rigid and is constructed to enter an alignment sleeve, not shown, within the complementary connector bushing. The interlocking strain relief 9 is shown configured into a right angle alignment with the plane of connection between the strain relief 9 and the optical connector assembly 7. The strain relief 9 provides heavy duty, crush and abrasion protection to fiber optic cable 2 while permitting bending of the cable to a tolerated, or allowed, minimum radii. The strain relief 9 has a short generally cylindrical end portion 15 and a generally cylindrical main body 16 which ultimately tapers towards the other end 17. A cylindrical bore 18 is axially aligned through the strain relief 9 and is sized to comfortably accommodate the exterior diameter of a fiber optic cable 2. In Figure 3 is shown a known strain relief 19 described further in European Patent Application EP-A2- 0 260 774. Figure 3 is a front elevation showing a short generally right-cylindrical end portion 20 followed by a generally cylindrical portion 21 which ultimately tapers towards the other end 22. A cylindrical bore 23 axially aligned through the strain relief 19 is sized to accommodate the exterior diameter of a fiber optic cable. Shown is an overlapping, alternately positioned, staggered series of cut openings 24 provided in the tapered portion 21 of strain relief 19 to provide flexibility. Each cut opening 24 is provided with a generally semi-circular, mid position internal side extension 25 of predetermined size on one long side of each of the openings 24 which ensures that the tapered portion 21 and individual optical fibers of a cable contained therewithin will not be bent to too small a radius. In contrast, shown in Figures 1, 2, 4, 5 and 6, is the interlocking strain relief 9 of the present invention. The strain relief 9 is a hard thermoplastic material for example, an ethylene propylene copolymer. Normally, this material resists bending. Bending of the strain relief 9 is required, however. Shown is the short, generally cylindrical end portion 15 and generally cylindrical main body 16 ultimately tapering, in outer diameter, toward the other end 17. A stepped cylindrical bore 18 is axially aligned through the strain relief 9 and is sized to comfortably accommodate the exterior diameter of the fiber optic cable 2. The strain relief 9 is characterized by multiple series of openings 26 provided lengthwise in the tapered portion 16. Each opening 26 is a narrow, elongated opening extending transversely to, and aligned normally with, the longitudinal axis of the bore of the strain relief 9. Each opening 26 is provided with a generally semi-circular, mid-position, internal side, extended tongue 27 of predetermined size on one long side of each of the openings 26. Each tongue 27 is curved, contoured to provide prominent shoulders on enlarged head 28, and each imposes into each opening 26, with a complementary groove or socket 29 located on a side across the opening 26 in opposed relationship to each tongue 27. Each socket 29 has a narrowed entry 30 which is formed of a shape so as to provide for close fit interlocking with a reduced neck 35 adjacent the head 28 of each complementary tongue 27 therewithin. Each of the series is circumferentially, ninety degrees from two adjacent series. The openings of each of one series is overlapped by openings of each of the two series, and the openings of each series are staggered spaced along the length of the strain relief 9. With particular reference to Figure 6, the strain relief 9 has bore 18 in four sections 31, 32, 33 and 34. Each of sections 31, 32 and 33 is of gradually tapering diameter toward main bore section 34. Sections 33 and 31 are of respective diameters so as to provide complementary friction fit to corresponding rear end 12 and adjacent portion of corresponding alignment ferrule 11. The strain relief 9 is connected to the connector assembly 7 by inserting the rear end 12 of ferrule 11 into axial bore 18 of strain relief 9 and displacing the strain relief 9 along the body 16 of ferrule 11 until rear end 12 is fitted to within sections 31 and 33. The strain relief 9 of the present invention, after assembly to the cable 2 and the connector assembly, may be bent along an arc configuration along any one of the series thereby forcing closure of the corresponding series of openings 26 along the inside of the curvature, along a line passing along urging the corresponding heads 28 of each of tongues 27 into the corresponding entries 30 of complementary grooves 29. Each of the heads 28 snap by the construction of the corresponding entry 30, and each groove 29 retains each complementary tongue 27 therewithin to lodge the tongue 27 in the groove and maintain the orientation of the strain relief 9 at a predetermined curvature, to project the cable 2 along the curvature and along a line extending at an angle, preferably at a right angle, to the plane along which extends the connector assembly 7 and the cable 2, without overstressing or kinking of the cable 2. The arc is constrained to a tolerable, or allowable, minimum radius of curvature, because the tongues 27 are lodged in the grooves 29 and prevent further closure of the openings 26 in response to increased bending force applied to the strain relief 9. With reference to Figure 7, a strain relief 9 of different shaped tongues 27 and grooves or sockets 29 are described as follows. The first tongue 27 and socket 29 in each of the series, as shown in Figure 7 from left to right, has a geometry shown in Figure 8, wherein, a narrowed entry 30 is narrower than the remainder of the socket 29 is wide, and the socket 29 is slightly deeper than the length of the socket 29, with outside corners 36 and inside corners 37 being rounded. The tongue 27 is wider at a front end, and has rounded outside corners 38, with each of the corners 38 being tangent to rounded inside corners 39. The inside corners 39 also reduce the width of the tongue 27. The tongue 27 will enter the socket 29 as described previously with reference to Figures 1, 2, 4, 5 and 6. A second tongue 27 and socket 29 in each of the series, as shown in Figure 7 from left to right, has a geometry shown in Figure 9, that is smaller than that of the first tongue 27 and socket 29 of the series. The tongues 27 and corresponding sockets 29 decrease in size along the series. A third and a fourth tongue 27 and corresponding sockets 29 in each of the series, as shown in Figure 7 from left to right, has a geometry shown in Figure 10, which is less than the previous tongues 27 and sockets 29 of the series.

Claims: A strain relief for protective coupling of a fiber optic cable with a connector, comprising: a) a generally tubular length of flexible material provided with an axial bore (18) for receiving a fiber optic cable (2) therewithin, b) the tubular length being provided with narrow elongate openings (24) extending transversally to the axis of said bore (18), c) wherein each of said openings (24) is provided on one long side thereof with a tongue (27) extending towards the other long side thereof; characterized by d) a complementary socket (29) located on the other long side of said openings (24) in opposed relationship to the corresponding tongue (27), e) whereby upon bending the tubular length said tongues (27) lodge in said sockets (29). The strain relief as recited in claim 1, characterized in that each socket (29) has a narrow entry for interlocking with a narrow neck (35) of a corresponding tongue (27). The strain relief as recited in claim 1 or 2, characterized in that the openings are spaced from one another at ninety degree intervals around the circumference of the tubular length. A strain relief as recited in claim 1, 2 or 3, characterized in that the tubular length is curved and each tongue (27) along the constricted arc of the curved tubular length is interlocked with a corresponding socket (29).

Inventors: MONROE KEVIN THOMAS, WEBER ROBERT NEY, MONROE, KEVIN THOMAS, WEBER, ROBERT NEY
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1991
Main classification: G02B6
IPC codes: H01R13, G02B6