Bending-limited protective sheath for a light guide

Abstract

Bending-limited protective sheath (10) for a light guide, with several rigid tube segments (20; 31, 32) arranged in the axial direction so that the light guide can be passed through them, characterized in that the rigid tube segments (20; 31, 32) partially overlap in such a way that a relative movement of two overlapping tube segments (20; 31, 32) transverse to the axial direction is only possible up to a maximum tilting angle (α).

Description

[0001] The invention relates to a tubular optical fiber protective sheath with bending limiter. With the increasing use of optical fibers in conjunction with high-power lasers, a reliable, high-strength bending limiter is required to prevent the escape of laser light, even in the event of accidental improper use of the optical fiber. Particularly in so-called fluid optical fibers, in which the light is guided in a liquid core by total internal reflection at a plastic sheath surrounding the core, a safety risk arises from excessive bending of the optical fiber. At the same time, however, the flexibility of the fluid optical fiber should be restricted as little as possible within the permissible bending range.

[0002] Previous bend limiters for hoses are based on the principle of metal wound hoses. The bend limit is achieved either by wrapping one or two wires or flat steel strips into the valleys of the metal wound hose or by clamping the hose. These previous bend limiter solutions are inadequate for a variety of reasons. Friction-based (clamping) wound hoses are difficult to manufacture with reproducible accuracy. While winding two wires allows for a reliable definition of the bend radius, it cannot withstand the required forces, as the wires can snap over each other even under moderate bending forces. Winding just one wire or strip requires a previously unattainable level of accuracy in the dimensions of the wound hose valleys and the wire / strip.Furthermore, it is generally difficult to achieve a sufficiently robust stop with a wound hose that effectively stops the bend when the maximum permissible curvature is reached.

[0003] The object of the present invention is to overcome the disadvantages described above and to provide a functional, reliable and reproducible solution for a bend-limited protective sheath.

[0004] The solution is achieved by the bend-limited protective sheath with the features defined in claim 1. The subclaims relate to preferred embodiments as well as a light guide arrangement comprising the protective sheath and a light guide guided through it.

[0005] According to the invention, the protective sheath contains a plurality of rigid tube segments which are arranged in a row in the axial direction in such a way that the optical fiber can be guided through them, and which are further arranged in an overlapping manner in such a way that a relative movement of two overlapping tube segments transverse to the axial direction is only possible up to a maximum tilt angle.

[0006] In other words, the inventive solution preferably comprises tube segments in the form of interlocking chain links, which determine the bending radius through their length and tilt angle relative to each other. The accuracy of the bending radius is defined by the manufacturing tolerances of the chain links, which can be very precise with current technology. Resistance to high forces is controlled by the choice of material and the wall thickness of the chain links. All rigid and highly bending-resistant materials are suitable, preferably steel or titanium.

[0007] According to a first exemplary embodiment, the individual pipe segments are identical in construction and each have a first pipe section and a second pipe section with different diameters. More precisely, the pipe segments are each stepped such that the outer diameter of the second pipe sections is smaller than the inner diameter of the first pipe sections. Thus, the second pipe section of a pipe segment can be inserted into the first pipe section of an axially adjacent pipe segment. A protective sheath of this design can be manufactured efficiently and is particularly easy to assemble because all pipe segments have the same geometry.

[0008] According to a second embodiment, two different types of pipe segments are used, namely cylindrical first and second pipe segments with different diameters. More precisely, the outer diameter of the second pipe segments is smaller than the inner diameter of the first pipe segments. When assembling the protective jacket, one of the second pipe segments is inserted into two axially adjacent first pipe segments. A protective jacket of this design is particularly cost-effective to manufacture because all pipe segments are simple hollow cylinders, each with a constant diameter.

[0009] Preferably, the protective sheath further contains several ring-shaped elastic elements positioned axially between each pair of tube segments. These elastic elements allow for axial length adjustment of the protective sheath when bent. If the bend-limited protective sheath did not yield, the optical fiber to be protected would be compressed or stretched upon bending because the optical fiber is firmly connected to the protective sheath. In practice, a compressibility and stretchability of ≥ 1% is required. For this purpose, the chain links or tube segments are each held at a distance from one another by an elastic element. The elastic ring elements serving as spacers are preferably made of an elastomer such as silicone.

[0010] The protective sheath according to the invention preferably further comprises an overtube made of an elastomer that holds the pipe segments together. For example, a shrink tube made of a polyolefin, a PVC tube, or a silicone tube can be used.

[0011] If necessary, the protective sheath is additionally covered with a wire mesh braided sleeve. This prevents overstretching, for example, when high forces are applied and the outer sleeve is too flexible, or when elevated temperatures are expected during use.

[0012] The invention is explained in more detail below using several exemplary embodiments with reference to the figures. The figures show: Fig. 1 a cross-sectional view of the protective sheath according to the invention according to a first embodiment in straight orientation; Fig. 2 a cross-sectional view of the protective sheath according to the invention according to the first embodiment in a curved orientation; Fig. 3 a cross-sectional view of the protective sheath according to the invention according to a second embodiment in a straight orientation; and Fig. 4 a cross-sectional view of the protective sheath according to the invention according to the second embodiment in a curved orientation.

[0013] The one in the Fig. The protective sheath 10 shown in Figure 1 comprises an over-hose 11 enclosing several identical pipe segments 20 arranged axially next to one another, with annular elastic elements 12 serving as spacers. The pipe segments 20 are stepped, i.e., each has a first pipe section 21 with an inner diameter D and a second pipe section 22 with a smaller outer diameter d.

[0014] The outer diameter d of the second pipe section 22 is smaller than the inner diameter D of the first pipe section 21. As a result, two pipe segments 20 can be inserted into one another in a chain-like manner such that the second pipe section 22 of a pipe segment 20 is inserted into the first pipe section 21 of an axially adjacent pipe segment 20 up to a defined insertion depth.

[0015] An elastomer ring 12 positioned axially between the first pipe sections 21 of adjacent pipe segments 20 creates a defined axial flexibility of the arrangement. In the example shown, both pipe sections 21, 22 are the same length. However, the length can also differ, especially if the difference is compensated for by correspondingly longer or shorter elastic ring elements 12.

[0016] In Fig. 2, the protective sheath 10 is shown in a curved orientation. Due to the cylindrical clearance of the nested tube sections 21, 22 defined by the different tube diameters D, d, and the insertion depth of the tube sections 21, 22, which can be selected by the axial length of the ring elements 12, the rigid tube segments 20 can only be tilted transversely to the axial direction to a certain degree. This maximum tilt angle α limits the overall bending radius of the protective sheath 10, thereby protecting a light guide (not shown) that can be passed through the tube segments 20 from excessive curvature.

[0017] As explained above, in the first embodiment, the stepped tube segments 20, manufactured as turned parts, are inserted into one another in a "chain." The cylindrical clearance between the first tube section 21 and the second tube section 22 inserted into it allows the bending radius of the protective sheath 20 to be defined. The bending is not hindered, but the minimum radius is stopped by a robust stop.

[0018] The Fig. 3 and Fig. 4 shows a second embodiment of the invention. Here, the pipe segments are not identical in construction; instead, there are first pipe segments 31 with the inner diameter D and second pipe segments 32 with the smaller outer diameter d. To avoid repetition, only the differences from the first embodiment are explained below.

[0019] As in the Fig. As shown in Figure 3, the elastic rings 12 are positioned as spacers axially between each two adjacent first pipe segments 31. The second pipe segments 32 are arranged axially offset therefrom, so that they each extend halfway into two adjacent first pipe segments 31.

[0020] In the Fig. Figure 4 again illustrates the functionality of the bending limiter. The first tube segments 31 can only be tilted transversely to the axial direction within a cylindrical clearance defined by the different tube diameters D, d, and the insertion depth. This achieves the desired bending limit of the protective sheath 10 and thus the necessary protection of the optical fiber (not shown) guided therein.

[0021] In summary, the present invention succeeds in creating a bending limitation for a light guide protective sheath 10 by arranging several rigid tube segments 20, 31, 32 in the axial direction so as to partially overlap one another that the light guide can be guided through them, and a relative movement of two overlapping tube segments 20, 31, 32 transverse to the axial direction is only possible up to a maximum tilt angle α. List of reference symbols 10 Protective sheath 11 Overhose 12 elastic element 20 pipe segments 21 first pipe section 22 second pipe section 31 first pipe segment 32 second pipe segment D Inner diameter of first pipe section 21 / first pipe segment 31 d Outer diameter of second pipe section 22 / second pipe segment 32 α maximum tilt angle

Claims

[1] Bending-limited protective sheath (10) for a light guide, with several rigid tube segments (20; 31, 32) which are arranged in an axial direction in such a way that the light guide can be guided through them, characterized by that the rigid pipe segments (20; 31, 32) partially overlap in such a way that a relative movement of two overlapping pipe segments (20; 31, 32) transverse to the axial direction is only possible up to a maximum tilt angle (α). [2] Protective sheath (10) according to claim 1, wherein the rigid pipe segments (20) each have a first pipe section (21) with a pipe inner diameter (D) and a second pipe section (22) with a pipe outer diameter (d) which is smaller than the pipe inner diameter (D). [3] Protective sheath (10) according to claim 2, wherein the second pipe section (22) of a pipe segment (20) protrudes or is inserted into the first pipe section (21) of a pipe segment (20) arranged axially adjacent thereto. [4] Protective sheath (10) according to claim 1, wherein the rigid pipe segments (31, 32) comprise first pipe segments (31) having a pipe inner diameter (D) and second pipe segments (32) having a pipe outer diameter (d) which is smaller than the pipe inner diameter (D) of the first pipe segments (31). [5] Protective sheath (10) according to claim 4, wherein one of the second tube segments (32) projects into or is inserted into two axially adjacent first tube segments (31). [6] Protective sheath (10) according to one of the preceding claims, further comprising a plurality of annular elastic elements (12) which are positioned in the axial direction between each two tube segments (20; 31) and which enable a length correction of the protective sheath (10) in the axial direction when the protective sheath (10) is bent. [7] Protective sheath (10) according to one of the preceding claims, further comprising an overtube (11), preferably a shrink tube, which envelops and holds together the rigid tube segments (20; 31, 32). [8] Protective sheath (10) according to one of the preceding claims, wherein the maximum tilt angle (α) is adjustable by determining the different diameters (D, d) of the tube segments (20; 31, 32) and their axial lengths and limits the bending radius of the protective sheath (10). [9] Protective sheath (10) according to one of the preceding claims, wherein the tube segments (20; 31, 32) are made of steel or titanium. [10] Optical fiber arrangement with a light guide, in particular a fluid light guide, and a protective sheath (10) according to one of the preceding claims, wherein the optical fiber is guided through the tube segments (20; 31, 32) of the protective sheath (10) which are arranged in a partially overlapping manner in the axial direction.

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