WO2005044384A1

WO2005044384A1 - Energy absorbing anchor for fall protection systems

Info

Publication number: WO2005044384A1
Application number: PCT/GB2004/004296
Authority: WO
Inventors: Luke Stratton
Original assignee: Uniline Safety Systems Limited
Priority date: 2003-10-21
Filing date: 2004-10-11
Publication date: 2005-05-19
Also published as: GB0324494D0

Abstract

An energy absorbing anchor for a fall protection system includes a support (1), a cable attachment member (3) and a deformable rod (5). The support (1) is adapted to be secured to a structure. The cable attachment member (3) is pivotally mounted on the support and is provided with means for attaching a cable. The deformable rod (5) extends from the support and passes through a part of the cable attachment member. The deformable rod (5) is configured such that pivoting of the cable attachment member (3) causes deformation of the rod (5) and the consequent absorption of energy.

Description

ENERGY ABSORBING ANCHOR FOR FALL PROTECTION SYSTEMS

This invention relates to an energy absorbing anchor for fall protection systems. The energy absorbing anchor may be used, for example, in cable-based fall protection systems, in particular, for vertical use. However, the anchor may also be used in other fall protection systems, such as inclined and horizontal cable-based fall protection systems .

The anchor may particularly be a termination, or end, anchor, which is fitted at the end of a cable-based fall protection system and is fixed to a supporting structure. The supporting structure may be, for example, a building, a tower leg of angled iron, a ladder rung, or a side stringer, or indeed any other supporting structure which would benefit from an energy absorbing fall protection system to protect the structure from damage, as well as the user, in the event of a worker falling on the fall protection system.

European legislation requires that, in the event of a fall, the maximum force on the user does not exceed 6kN. Essentially, there are two ways in which the force can be limited. One is to provide an energy absorbing device in the user's attachment device, and the other is to provide an energy absorbing device in or adjacent to the anchor.

When an energy absorber is employed in conjunction with an anchor in a vertical fall arrest system, the energy absorber is generally in the form of an in-line energy absorber attached to the termination anchor rather than being integral with the anchor.

It is often difficult with such in-line energy absorbers to determine whether they have been loaded (or deployed) , in particular if the structure to which they are attached is very high, such as an electricity pylon. It is important to be able to determine whether the energy absorber has been loaded because the absorber needs to be replaced and the system inspected before the fall arrest system is used once more .

A further disadvantage of an in-line energy absorber is that it reduces the effective working length of the fall protection system. For example, when a worker is trying to reach the top of a ladder, it may be necessary to detach from the system before reaching the top of the ladder. This is a potentially dangerous operation and it is therefor desirable to avoid reducing the effective working length of the fall protection system as far as possible.

It is therefore an object of the present invention to provide an energy absorbing anchor for fall protection systems which provides effective energy absorption without significantly reducing the effective working length of the fall protection system. It is also an object of the present invention to provide an energy absorbing anchor in which it is relatively easy to determine whether the anchor has been loaded. According to the present invention there is provided an energy absorbing anchor for a fall protection system, the anchor comprising: support means adapted to be secured to a structure; a cable attachment member pivotally mounted on the support means, the cable attachment member being provided with means for attaching a cable thereto; and deformable rod means extending from the support means and passing through a part of the cable attachment member, the deformable rod means being configured such that pivoting of the cable attachment member causes deformation of the rod means and the consequent absorption of energy.

Thus, when a load applied to the cable attaching member exceeds a predetermined level, the cable attachment member begins to pivot relative to the support means and moves along the deformable rod means. Movement of the cable attachment member along the deformable rod means causes plastic deformation of the rod means, which plastic deformation involves the absorption of energy.

It is relatively easy to determine whether the anchor has been loaded because a load in excess of a predetermined value, for example 6 kN, will cause the cable attachment member to pivot relative to the support means and the change in direction will be readily apparent.

The anchor may include at least one friction washer means provided on the deformable rod means on that side of the cable attachment member remote from the support means. If desired, a plurality of friction washer means may be provided. The friction washer means is able to absorb further energy as the cable attachment member pivots relative to the support means .

The friction washer means may be dished, for example with the rim of the washer means bearing against the cable attachment member. The friction washer means may be formed with slits extending radially outwardly from a central region thereof.

The support means may be provided with means, such as a D- ring for receiving adjustable clamp means, for securing the anchor to the structure.

The support means may have a cross-section, for example an L-shaped cross-section, adapted to abut against the structure.

The cable attachment member may be pivotably mounted on the support means by way of a pair of spaced members extending from the support means .

The cable attachment member may be substantially L-shaped and may be pivotably mounted on the support means in the region of one end thereof. The cable attachment member may be provided with means for attaching to a cable in the region of the other end thereof . A free end of the other end of the cable attachment member may be inclined relative to the remainder of the member such that the free end is inclined towards the support means. The deformable rod means may pass through the cable attachment member in the region where the two arms of the L-shape join.

The cable attachment member may be provided with a laterally extending element through which the deformable rod means passes. The laterally extending element may lie adj acent to the support means .

The deformable rod means may pass through an aperture in the cable attachment member and through an aperture in the support means . One or both of the apertures may be chamfered at least on that side thereof remote from the other of the support means and the cable attachment member. The deformable rod means may be provided with an end stop at one or both ends thereof. A plurality of deformable rod means may be provided.

The deformable rod means may be profiled along its length so as to define an axial path which is different to the path defined by that part of the cable attachment member through which the deformable rod means passes when the cable attachment member pivots relative to the support means .

The deformable rod means may be profiled, for example curved, in the plane of the defined path. Alternatively or additionally, the deformable rod means may be profiled in a direction transverse to the plane of the defined path. For example, the deformable rod means may diverge from the plane of the defined path. For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a perspective view of one embodiment of an energy absorbing anchor in accordance with the present invention for use in a fall arrest system, the anchor being shown in its normal configuration;

Figure 2 is a perspective view of the energy absorbing anchor shown in Figure 1 in a configuration after loading;

Figure 3 is a perspective view of a cable attachment member forming part of the energy absorbing anchor shown in Figures 1 and 2 ;

Figure 4 is a perspective view of part of the energy absorbing anchor shown in Figures 1 and 2 ;

Figure 5 is a perspective view, to a different scale, of a friction washer forming part of an energy absorbing structure of the anchor shown in Figures 1 and 2 ; and

Figure 6 is an elevational view, to a different scale, of a rod of deformable material forming part of an energy absorbing structure of the anchor shown in Figures 1 and 2.

The energy absorbing anchor shown in the figures comprises a support means in the form of a base 1 for mounting on a supporting structure (not shown) , a cable attachment member 3 pivotably mounted on the base 1 and an energy absorbing structure including a plastically deformable rod 5.

As shown, the base 1 comprises a generally L-shaped member 7 which is adapted to abut against and be secured to a supporting structure by any suitable means as is well known by the skilled person. In the case of the illustrated embodiment, provided at one end (the upper end as shown in the drawings) of the member 7 is a D-shaped ring 13 which may be used for securing the anchor to a supporting structure by way of an adjustable clamp (not shown) .

In the case of the illustrated embodiment the supporting structure will have a suitably configured portion adapted to receive the L-shaped member 7. In the event the supporting structure is a generally flat surface, the member 7 can readily be adapted to have a generally planar region for securing to the supporting structure. Thus, the anchor can readily be adapted to a wide range of structures including buildings, electricity and other pylons, ladder rungs, stringers and monopoles.

Provided at the other end (the lower end as shown in the drawings) of the member 7 are a pair of support members 9 for a pivot point 11. In the illustrated embodiment the support members 9 together form a generally Y-shaped configuration with the arms of the Y secured to the member 7, for example by means of welding, and the leg being formed by portions of the support members 9 which extend from the member 7 in a manner parallel to, and spaced apart from, each other. Pivotably mounted on the member 7, by way of a bolt 15 passing through the pivot point 11 and a corresponding pivot point 17 formed in the member 3, is the cable attachment member 3, which is generally L-shaped. The cable attachment member 3 has one arm 19 which extends in normal use generally parallel to the member 7 from the pivot point 17 at the free end of the arm 19 and another arm 21 which is generally perpendicular to the arm 19. The free end 23 of the arm 21 is angled to the major portion of the arm 21 generally in a direction towards that end of the member 7 provided with the support members 9 (that is, downwardly as shown in the drawings) . The purpose of the angled free end 23 will be described in more detail hereinafter.

The outer end of the arm 21 is connected in use to a swaged cable termination of a cable 25 by way of a pivot point 27 which allows the end of the cable to pivot relative to the cable attachment member 3.

The region of the cable attachment member 3 where the arms 19 and 21 join is connected to the member 7 by way of the energy absorbing structure. The region where the arms 19 and 21 join is formed with a laterally extending portion 29 which is shaped to lie adjacent to and to complement the shape of the member 7. In the illustrated embodiment the portion 29 is generally V-shaped and has two arms 29A and 29B as best shown in Figure 3.

Formed in each of the arms 29A and 29B is an aperture 31 which is chamfered at least on that face of the arms 29A and 29B remote from the member 7. Corresponding apertures 33 (best seen in Figure 4) are formed in the member 7 so as to be substantially coaxial with the apertures 31 in normal use, the apertures 33 being chamfered at least on that face of the member 7 remote from the arms 29A and 29B.

Passing through each pair of apertures 31, 33 is the rod 5 of plastically deformable material (best seen in Figure 6) . Each rod 5 is provided with an end stop 37 at least at that end thereof remote from the member 7. The other end of each rod 5 may be secured behind the member 7 by any suitable means, such as welding. The end stop 37 may be provided, for example, by forming the end of the rods 5 may with a thread and a nut may be screwed onto the threaded end and welded in place. The end stops 37 prevent pivoting of the cable attachment member 3 beyond a predetermined amount .

Provided on each rod 5 at that side of the arms 29A and 29B is an annular friction washer 39 (best seen in Figure 5) .

The friction washers may be made, for example, from stainless steel. As can be seen, the friction washers 39 are dished such that the rim of the washer is adjacent to and bears against the arms 29A and 29B and the centre of the washer is spaced from the arms. The washers are also formed with slits 41 extending radially outwardly from an opening in a central region of the washer and which allow the washer to grip the rod 5 in a manner which generates friction between the washer 39 and the rod 5. The rods 5 are generally made of steel, for example stainless steel, and have a constant cross-section, but are profiled along their length so as to define an axial path which is different to the path defined by each of the apertures 31 as the cable attachment member 3 pivots about the pivot point 11. In the illustrated embodiment, the rods 5 are curved to form an arc having a radius which is different to the radius of the arc defined by the apertures 31. Further, the rods 5 are angled such that they diverge as the distance from the member 7 increases, while the apertures 31 are a constant distance apart.

The components of the energy absorbing anchor may be made of any suitable material. As noted above, the rods 5 and friction washers 31 may be made of stainless steel, but the components of the anchor may be made, for example, of mild steel, galvanised steel, aluminium or titanium.

The energy absorbing anchor according to the present invention is relatively small and lightweight and can conveniently be carried to the top of a structure by a worker for installation.

In use of the energy absorbing anchor shown in the drawings, should a fall occur a force will be exerted on the cable 25 in the direction of the arrow 43. The anchor will begin to deploy once the force exceeds a predetermined load (less than 6 kN) allowing the cable attachment member 3 to rotate about the pivot point 11. As the cable attachment member 3 rotates the free end 23 moves towards the plane of the member 7 and reduces the turning moment exerted on the member 7 (that is, the height of the free end 23 relative to the member 7 is reduced) . In this respect, the free end 23 of the arm 21 is angled such that the free end 23 is closer to the plane of the member 7 than is the remainder of the arm 21, thereby further reducing the turning moment exerted on the member 7.

Deployment takes the form of the arms 29A and 2 B urging the friction washers 39 along the rods 5. This causes the rods 5 to deform plastically and to be pulled substantially straight as shown in Figure 2 thereby absorbing energy, and also for the friction washers to generate friction between the washers and the rods thereby absorbing further energy. Deforming the rods 5, and employing the friction washers, absorbs a substantial amount of energy and reduces the load transmitted to the supporting structure and to the user to an acceptable level . The amount of energy absorbed by the rods 5 can be varied by selecting the material for the rods 5 and the dimensions thereof. In addition the number of friction washers may be varied, with a greater number of washers providing greater friction and, consequently, greater energy absorption. It may be desirable to be able to vary the amount of energy absorbed by the rods and the friction washers, for example to adapt the anchor to the total amount of energy required to be absorbed. Thus, for example, if an anchor is to absorb the energy that may be required to halt the fall of up to three personnel then, although deployment must begin at a load less than 6 kN, the total energy to be absorbed will be significantly greater than for a single person. The parameters of the anchor and its materials can readily be adapted by the skilled person.

Once pivoting movement of the cable attachment member 3 relative to the member 7 has occurred, it will be apparent to an observer that the anchor has been loaded and must be replaced.

In addition to reducing the load transmitted to the supporting structure, the anchor is intended, in combination with other energy absorbing devices if necessary, to limit the load on a falling worker to a maximum of 6 kN.

Thus the present invention provides an energy absorbing anchor for a fall protection system which can readily be attached to a range of structures and which combines an anchor with an energy absorber, thereby minimising the number of components required and simplifying installation. The anchor provides a means for reducing the energy transmitted to the structure, which is particularly beneficial for relatively weak structures such as ladder rungs .

Claims

1. An energy absorbing anchor for a fall protection system, the anchor being characterised by: support means (1) adapted to be secured to a structure; a cable attachment member (3) pivotally mounted on the support means, the cable attachment member being provided with means for attaching a cable thereto; and deformable rod means (5) extending from the support means and passing through a part of the cable attachment member, the deformable rod means being configured such that pivoting of the cable attachment member (3) causes deformation of the rod means (5) and the consequent absorption of energy.

2. An anchor as claimed in claim 1 and including at least one friction washer means (39) provided on the deformable rod means (5) on that side of the cable attachment member (3) remote from the support means (1) .

3. An anchor as claimed in claim 2, characterised in that a plurality of friction washer means (39) are provided.

4. An anchor as claimed in claim 2 or 3 , characterised in that the friction washer means (39) is dished.

5. An anchor as claimed in claim 4, characterised in that the rim of the washer means (39) bears against the cable attachment member (3) .

6. An anchor as claimed in any one of claims 2 to 4, characterised in that the friction washer means (39) is formed with slits (41) extending radially outwardly from a central region thereof .

7. An anchor as claimed in any preceding claim, characterised in that the support means (1) is provided with means (13) for securing the anchor to the structure.

8. An anchor as claimed in claim 7, characterised in that the securing means comprises a D-ring (13) for receiving adjustable clamp means.

9. An anchor as claimed in any preceding claim, characterised in that the support means (1) has a cross- section adapted to abut against the structure.

10. An anchor as claimed in claim 9, characterised in that the support means (1) has an L-shaped cross-section (7) .

11. An anchor as claimed in any preceding claim, characterised in that the cable attachment member (3) is pivotably mounted on the support means (1) by way of a pair of spaced members (9) extending from the support means.

12. An anchor as claimed in any preceding claim, characterised in that the cable attachment member (3) is substantially L-shaped (19, 21) and is pivotably mounted on the support means (1) in the region of one end thereof.

13. An anchor as claimed in claim 12, characterised in that the cable attachment member (3) is provided with means for attaching to a cable (25) in the region of the other end thereof .

14. An anchor as claimed in claim 12 or 13, characterised in that a free end (23) of the other end of the cable attachment member (3) is inclined relative to the remainder of the member such that the free end is inclined towards the support means (1) .

15. An anchor as claimed in any one of claims 12 to 14, characterised in that the deformable rod means (5) passes through the cable attachment member (3) in the region where two arms (19, 21) of the L-shape join.

16. An anchor as claimed in any preceding claim, characterised in that the cable attachment member (3) is provided with a laterally extending element (29A, 29B) through which the deformable rod means (5) passes.

17. An anchor as claimed in claim 16, characterised in that the laterally extending element (29A, 29B) lies adjacent to the support means (1) .

18. An anchor as claimed in any preceding claim, characterised in that the deformable rod means (5) passes through an aperture (31) in the cable attachment member (3) and through an aperture (33) in the support means (1) .

19. An anchor as claimed in claim 18, characterised in that at least one of the apertures (31, 33) is chamfered at least on that side thereof remote from the other of the support means (1) and the cable attachment member (3) .

20. An anchor as claimed in any preceding claim, characterised in that the deformable rod means (5) is provided with an end stop (37) at least at one end thereof.

21. An anchor as claimed in any preceding claim, characterised in that a plurality of deformable rod means (5) is provided.

22. An anchor as claimed in any preceding claim, characterised in that the deformable rod means (5) is profiled along its length so as to define an axial path which is different to the path defined by that part of the cable attachment member (3) through which the deformable rod means passes when the cable attachment member pivots relative to the support means (1) .

23. An anchor as claimed in claim 22, characterised in that the deformable rod means (5) is profiled in the plane of the defined path.

24. An anchor as claimed in claim 23, characterised in that the deformable rod means (5) is curved in the plane of the defined path.

25. An anchor as claimed in any one of claims 22 to 24, characterised in that the deformable rod means (5) is profiled in a direction transverse to the plane of the defined path.

26. An anchor as claimed in claim 25, characterised in that the deformable rod means (5) diverges from the plane of the defined path.