GB2470284A - Aerial signal conductor holder having strength member(s) with weakening section(s) - Google Patents

Abstract

An elongated aerial signal conductor holder 1 is configured to hold one or more elongated signal conductors 9 and has at least one elongated strength member 4, which contains at least one weakening section 6 to locally weaken that member. The conductor holder is suspended from supports (S1, S2, figure 1) and the supports are less likely to break when there is a collision and/or a mechanical load is placed on the holder. There may be a series of spaced-apart weakening sections.

Description

Title: Aerial signal conductor holder The invention relates to an elongated aerial signal conductor holder, configured to hold one or more elongated signal conductors, the holder being provided with at least one elongated strength member.

Such a holder is known from practice. For example, W02007/073386 discloses an aerial selfsupporting optical fiber cable that can be suspended between poles. The cable is provided with a central strength member, which is capable of withstanding and controlling the significant tensile and thermo stresses that the cable may be subject to, while keeping the elongation of the signal conductor within predetermined limits in all weather conditions.

Generally, an aerial signal conductor holder will be suspended from at least one support, for example between two supports, such as between two poles or between a pole and an end user location (a building, home). The elongated strength member strengthens the holder.

A problem of such configurations is a risk that an accidental grip of the signal conductor holder (for example caused by an object colliding with the holder) leads to breaking of a respective support.

The present invention aims to find a solution to this problem.

According to an aspect of the invention, to this aim, there is provided an elongated aerial signal conductor holder that is characterized by the features of claim 1.

Preferably, the strength member contains at least one weakening section to locally weaken that member. In this way, the problem of breakage of a support (for example a wooden pole) due to a mechanical loading of the signal conductor holder can be prevented in a relatively simple, inexpensive manner. Particularly, during use, the strength member breaks at a respective weakening section upon a predetermined loading of the respective aerial signal conductor holder, to prevent overloading a support from which the signal conductor holder has been suspended.

In a further elaboration, each weakening section locally weakens the strength member by 10% or more, for example at least 20%. For example, in yet a further embodiment, each weakening section locally weakens the strength member by a factor 2 (two) or more, for example a factor 3 (three) or more (with respect to remaining non-weakened strength member sections).

For example, according to a further embodiment, each strength member of the signal conductor holder (for example an aerial tube or cable) can be weakened at regular intervals. Preferably, the weakening section leads to a decrease of a maximum breaking load of the signal conductor holder (with respect to a holder that includes one or more strength members without weakening sections), whereas an elastic modulus of the holder is hardly affected. In this way, a minimal strain of the holder can be guaranteed at worst case load conditions.

The invention will now be further elucidated by means of, non-limiting, examples referring to the drawings. Therein shows: Fig. 1 schematically a side view of an embodiment; Fig. 2 a perspective, partly opened cross-sectional view of part of a first non-limiting embodiment of the invention; Fig 3 a similar view as Fig. 2 of a second embodiment; Fig. 4 a longitudinal cross-section of part of the second embodiment, over line A-A of Fig. 3 Fig. 5 a similar view as Fig. 2 of a third embodiment; and Fig. 6 a similar view as Fig. 2 of a fourth embodiment.

Similar or corresponding features are denoted by similar or corresponding reference signs in this patent application.

Figure 1 shows an example of a signal transmission system. The present system includes supports si, s2, (in this case a wooden pole si and a support provided by a building s2), and one or more flexible, elongated aerial signal conductor holders 1 (only one being shown), suspended from (and extending between) the supports si, s2. In a further embodiment, two aerial signal conductor holders 1 are suspended between the supports si, s2.

Each holder 1 extends between mounting points p1, p2 of the supports si, s2, the mounting points for example having connector devices (such as brackets) to connect the holder 1 to the supports si, s2.

Particularly, the holder 1 is aerial, extending above ground level G (for example at least at several meters height above ground level G).

In the example, the supports si, s2 are spaced-apart over a relatively large distance L, for example a distance larger than 5 m, and particularly larger than 10 m and more particularly larger than 50 m. In a further elaboration, a maximum distance between the supports si, s2 can be m. In the examples, a length of the holder 1 is larger than the distance L between the supports si, s2. For example, a length of the holder 1 can be least 50 m, for example more than 100 rn. Preferably, the length of a holder section that extends between the mounting points pi, p2 is slightly larger (for example significantly smaller than 1% during installation, and between 1% and 2% during heavy, load conditions) than the distance L between those two points p1, p2. Thus, the flexible aerial signal conductor holder follows a slightly curved path between the supports si, s2.

An example of part of the holder 1 (at a section Q of Fig. 1) is schematically shown in Fig 2. The holder 1 can be configured in various ways. For example, the holder 1 can be a flexible tube or a cable, for example having a cylindrical shape (as in the examples) or another shape.

In the present example, the holder 1 has an elongated flexible wall 2. The wall 2 as such can include one or more wall layers, and can be made of various materials, for example (substantially) a flexible plastic material, for example a polyethylene, HDPE (high density polyethylene) or a different material. In a further embodiment, the wall 2 is made of a plastic material having a density of about 1000 kg/rn3 or lower (such as a HDPE); also, in a further embodiment, the wall 2 is made of a plastic material having an elastic modulus E (Young's modulus) of 10 GPa or lower, for example 1 GPa or lower (such as a HDPE).

The holder 1 is provided with one or more elongated signal conductors 9. In the present example, a section of the holder 1 that extends between the supports si, s2 is provided with at least one continuous signal conductor 9, extending at least over the same distance. For example, each elongated signal conductor 9 can be at least as long as the respective holder 1, or longer (depending for example on a stranding configuration -if any-of the conductor 9 with respect to the holder).

In a preferred embodiment, the signal conductor 9 is an optical signal conductor, for example having one or more optical waveguides (for example optical fibers, or bundles of optical fibers) to transmit optical signals. The holder 1 can also include one or more signal conductors for transmitting other types of signals, for example electrical signals.

Each signal conductor 9 can be held by the holder 1 in various ways, for example loose with respect to the wall, or fixed with respect to the wall. For example, a signal conductor 9 can be embedded in the wall 2, be located externally or internally with respect to the wall 2. The holder 1 may define at least one channel (for example a duct or a groove) receiving the at least one signal conductor 9. The one or more signal conductors 9 can be provided in an interior space 2a defined by the wall 2 (as in the present examples), or one or more signal conductors 9 can be located along an exterior surface of the wall. An interior space 2a can be hollow, or it can be filled with a fluid, for example a liquid or liquid mixture, or a gas or gas mixture. Alternatively, the interior space 2a can be filled with a solid substance or compound. Each signal conductor 9 can extend along various paths with respect to a central line of the holder 1 (for example a straight line, a spiral path, a SZ-stranded path, or differently). The skilled person will appreciate that the signal conductor 9 can also be held in a different manner by the holder 1.

The holder 1 is also provided with at least one elongated strength member 4, two parallel members 4, in this example. The strength members 4 are dimensioned to keep an elongation of the signal conductor within Pre-determined limits. In a further example, the holder 1 can be provided with more strength members 4, for example at least three (parallel) strength members 4.

In the embodiments, a section of the holder 1 extending between the supports si, s2 is provided with strength members 4 extending at least over the same distance (i.e., a length of the respective strength member section is at least equal to the length of the respective section of the holder 1 extending between the points p1, p2). For example, each strength member 4 can be at least as long as the respective holder 1. Preferably, as in the present examples, each strength member 4 is an uninterrupted strength member 4. That is, the respective section of the holder 1 extending between the points p1, p2 is continuously provided with the at least one strength member 4.

The one or more strength members 4 provide a strengthening of the holder 1. Particularly, each strength member 4 is configured to take up longitudinal tensile forces that can be experienced by the holder wall 2, for example tensile forces due to gravity, ice and wind load, acting on the elongated holder 1. In this way, according to a further embodiment, the strength member(s) 4 can prevent or limit longitudinal deformation of the holder 1.

Each strength member 4 can be held by the holder 1 in various ways. Preferably, the strength member 4 is joined with the wall 2 to take up said longitudinal tensile forces. In the present examples, to this aim, each member 4 is embedded in the wall 2. The skilled person will appreciate that the strength member 4 can also be connected to the wall 2 of the holder 1 in a different manner.

The strength members 4 can be made of various materials. For example, each strength member 4 can be metallic (e.g. steel). Preferably, each strength member is non-metallic. For example, the strength member 4 can be made of fiber reinforced plastic (FRP) or more particular glass fiber reinforced plastic (GFRP). Preferably, the strength member 4 has a Young's modulus higher than 40 GPa. The strength members 4 as such provide a main part of a total (longitudinal) strength and spring constant (quotient of force and elongation) of the holder 1 and respective signal conductor(s) 9.

In the present embodiments, each strength member 4 contains one or more weakening sections 6 to locally weaken that member 4 (for example a local weakening by 10% or more, for example at least 20%, with respect to non-weakened strength member sections, or for example, a locally weakening by a factor two or more, for example a factor three or more, with respect to weakened strength member sections).

In the present example, the two strength members 4 have respective weakening sections 6 located at the same longitudinal location in the holder 1,to provide a joint locally weakening.

As an example, the one or more weakening sections 6 are configured to provide breaking of the holder upon a tensile load (on the holder 1) between 1350 N and 1550 N, particularly in the case that two holders 1 are suspended from supports si, s2, and in case at least one of the supports is a wooden pole. In this way, the holder can break (at a respective the weakening section 6) upon the predetermined loading thereof, to prevent overloading the supports si, s2. In case only a single holder 1 is suspended between the supports si, s2, the respective one or more weakening sections 6 may be configured to provide breaking of the holder upon a higher tensile load (on the holder 1), in this example between 2700 and 3100 N. However, the operator might prefer to select only one type of holder 1, with a maximum breaking load between 1350 N and 1550 N in this example, and allowing a maximum number (two in this example) of holders 1 suspended between the supports si, s2. It will be appreciated that a predetermined minimum loading level at which the support 1 will locally break (locally, at a respective weakening section 6 of the strength member(s)) can have other values than the above-mentioned examples, depending for example on the configuration of the supports si, s2.

Preferably, at least one of the one or more strength member's weakening sections 6 is spaced-apart from the supports sl, s2 (see Figures 1-2). For example, each strength member 4 may contain a plurality of spaced-apart weakening sections 6. Typically, a distance between nearest weakening sections 6 (in case of application of an array of weakening sections 6 in the strength member 4) can be about 1 to several meters (for example a range of about 1-10 meter).

According to a non-limiting embodiment, a sum of the length of the weakening sections 6 of the strength member 4 (measured in a longitudinal direction along the holder 1) can be at most 5% of a length of the holder, particularly at most 1% of the length of a section of the holder 1 that extends between the mounting points p1, p2. For example, a sum of the lengths of the weakening sections 6 of the section of the strength member 4 that extends between the mounting points p1, p2, can be at most 10 cm, to provide a local weakening of the strength member 4.

In the example of Figures 1-2, each weakening section 6 has a reduced cross-section with respect to remaining parts of the strength member 4. Thus, both a height and a width of the strength member 4 have been locally reduced, to provide the local weakening section 6.

Particularly, in the first embodiment, each strength members 4 may be provided with one or more weaker sections 6 having a smaller diameter than a diameter of the remaining parts strength members 4. For example the smallest diameter of the strength member at the weakening sections 6 can be at most 80%, and more particularly at most 50%, of the diameter of the remaining strength member 4 part (i.e. the notweakened part).

In the first embodiment, each strength member 4 has a rod-like cylinder shape. Each weakening section 6 is provided by tapered (frusco-conical or double conical) rod sections, extending towards an intermediate weakening section part of smallest diameter. Besides a reduced cross-sectional area in the weakening section 6, this also provides stress concentration at that section during operation, such that the two strength members 4 (and respective holder) will break at those weakened sections.

Particularly, during operation, a local breaking of the strength members 4 will lead to breaking (for example rupture) of the bolder wall 2, at the same location. This can also hold for the signal conductor(s) 9, particularly in case the conductor(s) 9 is/are connected to the wall 2. The effect of stress concentration can be enhanced by providing relatively short weakening sections 6 (for example having a maximum length of 1 cm, measured in a longitudinal direction along the holder 1).

Figures 3-4 depict a second embodiment (said signal conductor has not been shown), which differs from the example shown in Fig. 2 in that one transversal dimension (the height) of the strength member 4, measured in a first orthogonal direction (i.e. a vertical direction), is constant along the strength member 4. Thus, that dimension remains the same at each weakening section 106. However, a second transversal dimension (the width) of the strength member 4, measured in a second orthogonal direction (i.e. a horizontal direction), has been varied to provide the local weakening sections 106. Particularly, the lateral width of the strength member 4 is smaller at the weakening sections 106 than the width at a remaining part of the strength member 4 (see Fig. 4). For example the smallest width Wi of the strength member at the weakening sections 106 can be at most 80%, and more particularly at most 50%, of the width W2 of the remaining strength member 4 part (i.e. the not-weakened part). For example, each weakening section 106 can include two concave sections, located in opposite sides of the strength member (see Fig. 4). In the present example, each concave section 106 has a curved shape, inwardly located tops of the two curves being laterally aligned with respect to each other. In this way, a reduction in bending stiffness in a horizontal longitudinal plane A-A can be minimal, resulting in minimal vulnerability to kinking. A bending stiffness in a virtual vertical plane (orthogonally to plane A-A), can be much larger, and is hardly influenced. In a preferred embodiment, the holder is provided with three or more (parallel) strength members; in that case, the stiffness of the cable hardly depends anymore on the alignment (rotation) of the weakening sections.

Figure 5 depicts a further elaboration, in a third embodiment. In this case, each strength member 4' consists of a bundle of fibers (filaments), for example aramide or polyester yarns 4', or yarns made of different materials. As in the embodiment of Fig. 34, in this case, weakening sections 206 can be provided by locally reducing the width of the bundle of fibers, for example by local cut-outs 206 (each cut out 206 including part of the fibers being locally removed, without cutting through all of the fibers of the respective bundle 4'). Preferably, in case each strength member 4' is provided with an array of spaced-apart weakening sections 206, the interval between those weakening sections 206 is selected such that slip between fibers in each bundle 4' does not occur after mounting, or only over a short length For example, an interval between subsequent cuttings 206 of each bundle 4' can be sufficiently large, such that the cut filaments slip only with respect to the other filaments of the yarn 4' over a length that is much shorter compared to said interval. In this way, the respective holder 1 can maintain a relatively high effective elastic modulus, approximately determined by a total amount of filaments in the yarns. Preferably, the configuration is such that a length over which internal slip between fibers in the strength member 4' occurs (if any) is shorter than a minimal span of the holder 1 (i.e. a minimal length of a holder part that extends between mounting points pl.p2, after mounting to the supports si, s2).

Figure 6 shows a further alternative embodiment, which differs from the example of Fig. 5 in that each strength member 4" is a twisted fiber bundle (i.e. the fibers being mutually twisted, with respect of a longitudinal virtual centre line thereof), having one or more cuts 306 to provide local weakening section(s). Thus, tangling of the fibers is enhanced, so that slip between fibers can be reduced.

Besides, according to a further embodiment, the holder 1 can be provided with at least a first strength member made of a first material and a second strength member made of a second material, the first material being different from the second material. For example, combinations of rod-like strength members and yarns as strength members, at least one of which contains one or more weakening sections, are also possible, for example a combination with three rod-like strength members with weakening sections and polyester yarns without weakening.

Example

A test has been done on non-metallic strength members 4, consisting of elongated cylindrical GFRP rods of 1.15 mm diameter.

Measuring stress (N) versus strain (elongation, in %) at a test bank on samples with effective sample lengths of 0.5 m resulted in a Young's modulus of around 55 GPa. This was hardly affected after having weakened the rod 4 by locally machining to provide concave sections 106 (as in Fig. 4) to 0.48, 0.40 and 0.33 mm, resulting in strengths of 0.47, 0.31 and 0.27 GPa, respectively (a measured strength of a non-weakened sample was at least 0.66 GPa). The Young's modulus of the samples remained practically the same (about 53-55 GPa).

Therefore, the present invention can provide aerial drop tubes or cables 1, where strength members 4 are weakened (preferably at regular intervals). As follows from the above, a breaking strength can be tuned, for example by selecting dimensions (such as a depth of cut-outs) of the weakening sections. Elastic properties of the holder 1 can remain almost unchanged. This makes it possible to design a drop tube or cable 1, being sufficiently durable for normal operating conditions, and providing a timely local breaking upon a mechanical impact (collision), to prevent overloading the supports si, s2.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word comprising' does not exclude the presence of other features or steps then those listed in a claim.

Furthermore, the words a' and an' shall not be construed as limited to only one', but instead are used to mean at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.