GB2357563A

GB2357563A - An energy absorber/ fall arrester

Info

Publication number: GB2357563A
Application number: GB9930232A
Authority: GB
Inventors: Julian Renton; Peter Nott
Original assignee: Latchways PLC
Current assignee: Latchways PLC
Priority date: 1999-12-21
Filing date: 1999-12-21
Publication date: 2001-06-27
Anticipated expiration: 2019-12-21
Also published as: GB9930232D0; GB0005252D0; GB2357564A; GB2357563B; GB2357564B

Abstract

An energy absorber comprises housing means (1), a store (15) of plastically deformable material (8) mounted in the housing means, means (3) for attaching the energy absorber to a structure, means (10) for attaching the plastically deformable material (8) to an elongate safety element (not shown), and means (27, 7, 5, 6) responsive to a predetermined tensile load effective to deploy said plastically deformable material (8) in a controlled manner from its store whereby said material is permanently plastically deformed during said deployment, thereby absorbing energy.

Description

2357563 ENERGY ABSORBER The present invention relates to an energ absorber

and, in particular, to v an energy absorber that absorbs tensile energy and deploys irreversibly at or close to a constant force.

Tension energy shock absorbers are often used to assist the absorption of energy in constrained or partially constrained lines. For example, fall arrest applications require energy from a failing body to be absorbed by a line such as a rope or wire which is usually attached to a!,strong structure at one end or both ends. In such situations, it is desirable to achieve a low combination of stretch in the line and line tension. Lowering lino stretch reduces the distance the body fails before arrest, and also reduces the fall energy. Lowering line tension reduces the loading on the line and also on the anchor or anchors constraining the line. Another example of energy absorption in constrained lines is vehicle crash barriers that absorb vehicle kinetic energy. Lower line stretch reduces the degree to which a vehicle can move across a crash barrier.

Lower line loads reduce the likelihood of line aInd/or anchorage failure in the event of a crash.

The amount of energy absorption in constrained or partially constrained lines is determined by the product of stretch in the line and the line tension.

Typically, line stretch is elastic such that the amount of stretch increases in proportion to the tension in the line. The energy absorbed is therefore the average line tension or half the maximum line tension multiplied by the stretch.

However, in order to minimise the combination of line stretch and line tension, 1 the ideal line system would absorb energy by str 1 etching at a predetermined line tension where the energy absorbed is the predetermined line tension multiplied by the line stretch. This would absorb the some energy as the elastic line system for a given maximum line tension but require only half the line stretch.

Also, such a system would be able to limit maximum line tension to the predetermined force at which stretch occurs.

2 In practice, it is difficult to achieve this ideal, but significant improvement can be made in energy absorption efficiency with respect to the combination of line stretch and line tension by combining low stretch line with an energy absorber that deploys by stretching at a predetermined force. If the extent of deployment stretch in such an absorber is sufficiently large, it could also effectively limit line tension to the predetermined deployment force for all foreseeable energy absorption situations. This is important for establishing with a high degree of certainty safe design criteria for line systems and anchors.

In conventional energy absorbers that deploy at a constant force, the component which is deployed is typically straight, being housed within a further straight component prior to deployment. The overall length of such an absorber prior to deployment is therefore greater that the extent of deployment.

Such energy absorbers typically consist of a component, preferably having a spherical or part-spherical leading portion, which is pulled through a length of tube having a bore smaller in diameter than the outer dimension of the leading portion of said component, such that a force is required effectively to extrude the bore of the tube. One such energy absorber is described in the present Applicants granted European Patent No. EP 0 605 538.

In view of the foregoing analysis, it will be clear to persons skilled in the art that, in applications in which large deployment extents are required, the overall length of the energy absorber also needs to be large.

This is undesirable, not only from the point of view of cost, but also because in many applications such as fall arrest it is important to gain access to a constrained or partially constrained line close to the constraining anchors.

Typically, large deployment extents are useful for containing line loads and also ensuring that line loads never exceed the predetermined deployment force of the energy absorber for all foreseeable situations, and provide a useful energy absorption surplus as a contingency against unforeseeable circumstances.

It is therefore an object of the present invention to provide an energy absorber which gives a long deployment stroke without occupying an inordinate linear extent.

3 According to the present invention, there is provided an energy absorber comprising housing means, a store of plastically deformable material mounted in said housing means, means for attaching thelenergy absorber to a structure, means for attaching the plastically deformable material to an elongate safety element, and means responsive to a predetermined tensile load effective to deploy said plastically deformable material in a controlled manner from its store whereby said material is permanently plastically deformed during said deployment, thereby absorbing energy.

Preferably, the plastically deformable Material is a length of yielding material such as metal, the length being relative to the maximum extension required for absorbing energy. One end of the length of material preferably has provision for attaching the material to a line or rail anchorage and, close to such attachment provision, the material is prefe i ably constrained in a non-linear path by a structure that also has provisio for attachment to a line or anchorage. In such an arrangement, when thematerial is pulled relative to the structure, the material is forced by the structure to move in a non- linear path and its movement is therefore resisted primarily by the reluctance of the material to yield. Movement of the material is:enabled when the pulling force is sufficiently great to overcome the yielding resistance, thus having the effect of absorbing energy as a result of the product of the tensile force needed to overcome the resistance to movement of the material and the extent of movement of the material relative to the structure. The tensile forces required to effect deployment are substantially determined by the yielding and therefore plastic deformation properties of the material, its section shape and the degree of non-linearity of its path as constrained by the housing means.

The length of material can have any c ross-section such as rectilinear, round, tubular or any other shape. In some ebodiments, the section shape can vary along the length of the material, for e' ample, in applications in which it is desirable to vary the resistant force between the housing means and the material. The length of material prior to de loyment may be wound into a spiral or coil or other form such that the length of space it occupies when stored is small relative to the overall deployed l,ength of the material. The non- i 4 linear path of the material when pulled and as constrained by the housing means is typically defined by two dimensional inclinations but it may also be defined by three dimensional inclinations, causing the material to twist about its section. Alternatively, a combination of both two or three dimensional inclinations can be used.

Preferably, the elements of the housing means constraining the path of movement of the material when pulled relative to the housing means can be circular shafts or rollers, each roller rotating about its own axis, or any other shape constraining the path of the material, all such elements being fixed to or constrained relative to the housing means or else forming an integral part of the housing means.

The invention will now be described by way of example only with reference to the drawings, in which:

Figure 1 is a perspective view of a first embodiment of the invention with the length of material spirally wound; Figure 2 shows a side elevation of the embodiment depicted in Figure 1; Figure 3 shows a side view of an alternative embodiment of the invention in which the length of material is wound in a helical coil; Figure 4 shows a top view of the embodiment in Figure 3; Figure 5 shows an alternative embodiment to that depicted in Figures 3 and 4,.

Figure 6 shows a top view of the embodiment in Figure 5; Figure 7 shows a further alternative embodiment to that depicted in Figures 3 and 4; Figure 8 shows a top view of the embodiment depicted in Figure 7, and Figure 9 shows an alternative method of coiling the material that may be applied to the embodiments depicted in Figures 3 to 8.

As shown in Figures 1 and 2, an energy absorber has a structure 1 comprising a housing means formed of plates 1 and 2 that are spaced apart 1 and fixed to pins 5, 6 and 7 such that plates 1 and 2 are rigidly linked. Fixing means 3 and 4 are provided at one end of the plates for attaching them to a rigid anchor or wire or rope termination. Length of material 8 is shown as strip material that is wound into a spiral 15 and bent at 16 and 17 to f it beneath pin and above pin 6, respectively, with attach' nlent means 9 at one end for attaching to a rigid anchor or wire or rope termination. The spiral winding enables a long length of material to be stored within a relatively short linear space. Plate 10 is held to the end of length of material 8 by means of rivets 11 and 12 in order to strengthen attachment means 9. In some embodiments not illustrated here, it may not be necessary to include plate 10. Alternatively, plate 10 could be fixed to the end of length of material 8 by some other means, such as by welding.

When the energy absorber is required to absorb energy, an increasing tension force is applied to attachment means 3 and 4, and 9 in the direction of arrows 13 and 14 until the applied force bed omes sufficiently high to pull material 8 around pins 5 and 6 such that th absorber extends to absorb energy. Pin 7 assists in unwinding spiral 15. Feature 27 is a sharp bend at the end of material 8 which becomes trapped between pins 5 and 7 or between pins 5 and 6 to provide a limit to the deployment of material 8. If material 8 is consistent in nature and crosssection, the tension force required to move the material in the direction of arrow 14 should be approximately constant in relation to the degree of movement of material 8. However, in the first embodiment described here in relation to Fi g yres 1 and 2, the function of unwinding spiral 15 will tend to result in such tension force increasing because of the need to unwind a material in which the curl diameter of the spiral decreases as material 8 is deployed.

Figures 3 and 4 show a second embodiment of the invention in which a length of material 20 is wound as a helical coil 21. The curl diameter of the helical coil 21 remains constant, thereby avoiding an increase in applied tension force as material 20 deploys from its stored condition.. Tube 23 holds the i 6 helical coil 21 of material in position and is an alternative means of assisting the function of uncoiling in comparison to pin 7 in Figures 1 and 2. Loop 22 formed at one end of the helical coil 21 of material serves the same function as sharp bend 27 discussed above in relation to the first illustrated embodiment, and prevents the length of material from becoming completely separated from the housing means.

Material 20 in Figures 3 and 4 is constrained to move in a non-linear path by both pins 5 and 6. However, Figures 5 and 6 show a similar embodiment to that in Figures 3 and 4 except material 20 is only constrained by a single pin, pin 5.

In the embodiment depicted in Figures 7 and 8, there is no constraining pin, the force resisting pulling material 20 in the direction of arrow 14 being provided by the plastic deformation required to straighten material 20 relative to its coiled state.

Such resisting force being provided by the uncoiling of material from a substantially coiled state to a relatively straight state could apply to any embodiment of the invention, including any coiling means and any cross section of material.

Figure 9 shows a convenient attachment means 25 for pulling length of material 24 relative to plates 1 and 2 substantially in the centre of length of material 24.

If present, pins 5 and 6 in the embodiments depicted in Figures 1 to 9 could each be the same or differing shapes. For example, they could be round in cross-section, or some other shape, or they could be integrally incorporated in some other structure having the functionally of plates 1 and 2 and one or more pins. There could be more than two constraining pins or rollers to provide further constraining non-linearity if required in order to increase the force resisting the movement of material 20. Pins 5 and 6 andlor any further pins could be rollers having the ability to rotate about axes that are substantially fixed to plates 1 and 2. The path of movement of the length of material constrained by abutments such as pins 5 and 6 in Figures 1 to 9 could be any non-linear path. Lengths of material 8, 21 and 24 could be any cross section 7 and also such cross section could vary along the length of the material particularly in circumstances in which it is des iralble to vary the tension required to deploy such material from its stored condition.

In Figures 1 to 9, the length of material!! is shown as coiled to provide convenient and compact storage prior to deployment. However, the material could be stored as a straight length or in any Other form.

In Figures 1 to 9 the length of material and/or pins 5 and 6 may be coated in a lubricating and/or insulating material to reduce friction andlor to avoid sufficient heating to cause welding of the material to the constraining elements such as pins 5 and 6. Alternatively pins 5 and 6 may be plated in a material having the effect of providing a sacrificial layer to avoid damaging andlor assist with lubrication and/or heat insulation.

Although the invention has been particularly described above with reference to specific embodiments, it will be understood by persons skilled in the art that these are merely illustrative and that, variations are possible without departing from the scope of the claims whic h follow.

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Claims

1 An energy absorber comprising housing means, a store of plastically deformable material mounted in said housing means, means for attaching the energy absorber to a structure, means for attaching the plastically deformable material to an elongate safety element, and means responsive to a predetermined tensile load effective to deploy said plastically deformable material in a controlled manner from its store whereby said material is permanently plastically deformed during said deployment, thereby absorbing energy.

2. An energy absorber as claimed in claim 1 wherein the plastically deformable material is a length of yielding material such as metal, the length being relative to the maximum extension required for absorbing energy.

3. An energy absorber as claimed in claim 1 or claim 2 wherein one end of the length of material has provision for attaching the material to an elongate safety element or an anchorage.

4. An energy absorber as claimed in claim 3 wherein the material is constrained in a substantially non-linear manner.

5. An energy absorber as claimed in any preceding claim wherein the housing means has provision for attachment to an elongate safety element or an anchorage.

6. An energy absorber as claimed in any preceding claim wherein the length of material has a cross-sectionai configuration selected from the group consisting of rectilinear, round, tubular or a combination of the foregoing.

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7. An energy absorber as claimed in anypreceding claim wherein the configuration of the plastically deformable material varies along its length.

8. An energy absorber as claimed in any preceding claim wherein the length of material prior to deployment is wound into p spiral, coil or other compact i form such that the length of space it occupies when stored is small relative to the overall deployed length of the material.

9. An energy absorber as claimed in any preceding claim wherein the nonlinear path of the material when pulled and as constrained by the housing means is defined by two-dimensional inclinations.

10. An energy absorber as claimed in any one of claims 1 to 8 wherein the non-linear path of the material when pulled and, as constrained by the housing means is defined bythreedimensional inclinations, causingthe materialtotwist about its section.

11. An energy absorber as claimed in claims and 10 wherein the non-linear path of the material when pulled and as constrained by the housing means is defined by a combination of both two- and three-dimensional inclinations.

12. An energy absorber as claimed in any preceding claim wherein the elements of the housing means constraining:, the path of movement of the material when pulled relative to the housing means are selected from the group consisting of circular shafts or rollers, or any other shape constraining the path of the material, all such elements being fixed to or constrained relative to the housing means or forming an integral part of the housing means.

13. An energy absorber as claimed in claim ill 2 wherein the elements of the housing means constraining the path of movernent of the material when pulled relative to the housing means are rollers, each roller rotating about its own axis.

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14. An energy absorber substantially as described herein with reference to Figures 1 and 2; Figures 3 and 4; Figures 5 and 6; Figures 7 and 8, or Figure 9 of the drawings.