WO2009013479A1

WO2009013479A1 - Shock absorber

Info

Publication number: WO2009013479A1
Application number: PCT/GB2008/002498
Authority: WO
Inventors: Bernard Warren
Original assignee: Rapid Rail International Limited
Priority date: 2007-07-23
Filing date: 2008-07-22
Publication date: 2009-01-29
Also published as: GB0714354D0

Abstract

A single-use shock absorber comprising: a. a support member; b. a spindle member supported on the first support member; and c. a deformable element having a first load application point, the deformable element being rotatably mounted on the spindle member, wherein the deformable element is dimensioned for plastic shock absorbing deformation on application of a predetermined force to the first load application point. Also provided is a fall arrest harness incorporating such a shock absorber.

Description

SHOCKABSORBER

Background to the invention

The present invention relates to a single-use shock absorber.

It is known for fall arrest systems to incorporate a shock absorber in which a textile element tears at stitching and/or stitched fabric to absorb energy in decelerating a falling man prior to the force arising from his full momentum being resisted by a rope or cable alone. If a shock absorber is not provided, much higher shock forces are experience throughout the fall arrest system and indeed by the man. These can be damaging to the system and the man.

A common problem with shock absorbers that incorporate a textile element is that the textile element undergoes significant deterioration over time. If such deterioration goes unnoticed and the shock absorber is not replaced regularly, the shock absorber will not perform properly when required, which could have fatal consequences if the fabric and/or stitching fail during the fall of a user.

It is known to absorb shock by plastic deformation, typically of a single-shock-use metallic element.

By single-shock-use is intended that the element may carry resist forces loads well below the force lead at which it deforms plastically, but once it has deformed plastically, it should be discarded.

A problem with a device that is intended to deform plastically under shock forces is that it may deform appreciably elastically under lesser force loads to such extent as to interfere with other devices under ordinary usage. For instance, it may open elastically and pinch something on closure. In addition, conventional metal shock absorbers are bulky and often heavy and so may be inconvenient to use and add significantly to the load of the person carrying the shock absorber as part of their fall arrest safety equipment.

There is therefore a need for a single-use shock absorber which will not be subject to rapid deterioration, will avoid the bulky nature of existing metal shock absorbers and which is capable of efficiently absorbing the lead force of a falling object.

Summary of the Invention The present invention seeks to address the problems of the prior art.

Accordingly, a first aspect of the present invention provides a single-use shock absorber comprising: a. a support member; b. a spindle member supported on the first support member; and c. a deformable element having a first load application point, the deformable element being rotatably mounted on the spindle member, wherein the deformable element is dimensioned for plastic shock absorbing deformation on application of a predetermined force to the first load application point.

In this way, when a force of a predetermined value is applied to the first load application point e.g. by a falling mass, there is controlled deformation of the deformable element with a resultant absorption of energy by the shock absorber thereby reducing the rate of fall of the falling load, such as an initially free falling man at a level which does not expose him to damaging shock loads, and does not over-load the fall arrest system in which the shock absorber is incorporated. The deformable element may comprise any suitable plastically deformable material such as metal or any suitable plastic or rubberised material or any other suitable material known to the skilled person and appropriate for the purpose.

The form of the deformable element may be produced by laser cutting, casting, pressing, machining, moulding or by any suitable method known to the skilled person.

While it is envisaged that the deformable element may be arranged for its plastic deformation to be in tension, it may also be in torsion.

In one embodiment, the deformable element comprises a continuous longitudinal element extending along a spiral path.

For example, the continuous longitudinal element may comprise a coil.

Preferably, no portion of the longitudinal element makes contact with any other portion of the longitudinal element.

The separation between adjacent coils of the deformable element may be of any desired distance provided that the deformable element completes at least one coil around the spindle. Preferably, the distances between adjacent coils are identical. However, it is to be appreciated that the distances between adjacent coils may be variable.

The deformable element may be of any suitable shape in cross-section. Preferably, the deformable element is circular in cross-section. Alternatively, the deformable element may be rectangular, square or triangular in cross-section. In an alternative embodiment, the deformable element comprises a hollow member mounted on the spindle member.

In one embodiment, the hollow member is provided with a weakened portion defining a spiral path along at least a portion of the hollow member.

In one embodiment, the deformable element is provided with a bridge spanning the spiral path, the bridge being dimensioned to fracture at a predetermined force.

It will be appreciated that the dimensions of the bridge which may be varied to allow the bridge to fracture at a predetermined load include but are not limited to the width, shape, contours of the bridge. In addition, it will be appreciated that the material of which the bridge is composed will also influence the load at which the bridge will fracture. All of these factors may be used to produce a bridge which will fracture at a predetermined force less than that at which the deformable element deforms plastically.

The bridge is preferably located adjacent the first load application point. However, it will be appreciated that the bridge may be located at any position along the spiral path. In addition, it will be appreciated that more than one bridge may be provided, each bridge spanning a different portion of the spiral path.

The weakened portion may comprise a region of thinner material defined by a groove, the weakened portion being dimensioned to fracture at a predetermined force. In one embodiment, the groove is of a uniform depth along its length, thereby ensuring that the weakened portion is of uniform thickness.

However, it will be appreciated that alternative embodiments are envisaged where the groove is of varying depth along its length, and thus the weakened portion is of varying thickness along its length. Varying the depth of the groove along its length will affect the deformable properties of the deformable element. For example, if the force required for deformation of the element is constant as it would be if the groove was of constant depth, the lighter the falling mass lead, the greater higher will be the deceleration rate G-forces experienced by the mass lead. Therefore, when used for arresting the fall of a falling person, it may be desirable to provide a shock absorber with a groove with a decreasing depth of groove along its length in a direction away from the first load application point in order to reduce the G forces experienced by have more effective fall arrest properties for a lighter individual while maintaining an acceptable fall arrest distance for the heavier individual Although a decreasing groove depth may also be used for a heavier person, the groove depths used may be relatively shallower than those used in respect of a person of lessor weight.

In one embodiment, the groove may be of uniform cross-sectional shape along its length.

However, it will be appreciated that alternative embodiments are envisaged where the groove is of varying cross-sectional shape along its length. By varying the cross-sectional shape of the groove and therefore the cross-sectional profile of the weakened portion, it is possible to vary the fracture tolerances of the deformable element.

The fracturing of the weakened portion defined by the groove absorbs energy from the fall of a mass attached to the shock absorber.

The single-use shock absorber may be further provided with a shear component mounted on the deformable element and spanning at least a portion of the spiral path. Such a shear element may comprise any suitable material such as metal or the like and may be mounted on the deformable element by any suitable method known to the skilled person, for example, by riveting, welding, screwing, or other suitable bonding means, provided that the shear component shears under a force less than that at which the mounting means fails.

A shock absorber in accordance with the present invention could be used in any situation where a shock absorber would typically be employed as part of a fall arrest safety system.

A further aspect of the present invention provides a fall arrest device incorporating a shock absorber in accordance with a first aspect of the present invention. Such a fall arrest device may incorporate one or more shock absorbers in accordance with a first aspect of the present invention.

When multiple single-shock-use shock absorbers are used in a single fall arrest device, they may be provided in series such that the combination of shock absorbers acts to absorb a greater amount of energy than would be absorbed by a single shock absorber. Thus, a user may select the appropriate number of shock absorbers to be used in combination to provide a shock absorber capable of withstanding fracture until application of a force greater than could be withstood by a single shock absorber.

A further aspect of the present invention provides a fall arrest harness comprising an integral single-use shock absorber according to any preceding Claim. In such a harness, the harness would be discarded after a single fall arrest event and replaced with a new harness incorporating a new shock absorber. Conventional fall arrest harnesses are intended to be discarded after a single fall arrest event, due to potential failure of the stitching and fabric over time and after the forces experienced through the harness after a fall event. However, although the shock absorber may be replaced, the harnesses are often reused, sometimes with tragic consequences. By integrating a shock absorber in accordance with the present invention into the fall arrest harness, after a single fall arrest event, the harness will require replacement as the shock absorber will have deformed and require replacement. The shock absorber would typically be stitched into the straps of the harness, the shock absorber providing the first load application point for attachment of a karabiner or the like to allow the harness to be used as part of a fall arrest system.

Brief Description of the Drawings

An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a front view of an embodiment of a shock absorber in accordance with the present invention:

Figure 2 is a side view of the embodiment of figure 1;

Figure 3 is a rear view of the embodiment of figure 1; Figure 4 is a cross-sectional view through B-B of figure 3;

Figure 5 is a perspective view of the embodiment of figure 1;

Figure 6 is an enlarged view of the shear element indicated by circle C in figure 4;

Figure 7 is a view from above of the embodiment of figure 1; Figure 8 is a perspective view of a further embodiment of a shock absorber in accordance with the present invention in use as part of a harness; and

Figure 9 is a perspective view of a further embodiment of a shock absorber in accordance with the present invention for use as part of a roof safety system;

Figure 10 is a perspective view of a further embodiment of a shock absorber in accordance with the present invention; and

Figure 11 is a perspective view of the embodiment of figure 10 in use as part of a harness.

Detailed Description of the Invention An embodiment of a shock absorber in accordance with the present invention will now be described with reference to figures 1 to 7 in which the same reference numbers have been used to indicate common features.

A shock absorber 10 is provided comprising a support member 20 having first and second opposing ends 22, 24. A deformable element 30 is provided mounted on a spindle member 40. Spindle member 40 is held between first and second opposing ends 22, 24 of support member 20, thereby retaining the deformable element 30 in position, deformable element 30 being rotatable relative to spindle member 40.

Deformable element 30 is provided with a first load application point 35 to which a karabiner or the like would be attached in use. The first load attachment point 35 extends transverse to the axis through spindle member 40 such that deformation of the deformable element will result in rotation of the deformable element 30 about the spindle member 40. A groove 50 extends from adjacent first load application point 35 of deformable element 30 across the surface of the deformable element 30 in a spiral path, groove 50 stopping before reaching the end of deformable element 30 distal to first load application point 35, leaving unweakened portion 39 of deformable element 30 which is not expected to fracture under the predetermined force under which a thinner weakened portion 50' defined by the groove portion of deformable element 30 would fracture in use.

Groove 50 may comprise any desired depth or cross-sectional shape to provide the weakened portion 50' with the desired deformation properties such that the deformable element 30 fractures along the spiral path defined by groove 50 and weakened portion 50' at a predetermined force.

An optional shear component (shown as shear component 60 in figure 6) is mounted on deformable element 30 and spans a portion of the spiral path defined by groove 50 and weakened portion 50' at a location adjacent the first load application point 35 of deformable element 30.

In use, a karabiner may be attached to first load application point 35 of deformable element 30 of shock absorber 10, the karabiner then being attached to a cable of a fall arrest system. Support member 20 is then secured to another part of the fall arrest equipment. For example, support member 20 may be stitched into to the harness of a user such that shock absorber 20 is located between the user and the fall arrest support cable.

If a serious accidental force is applied, for example, a man falling from a tower or the like during use of the fall arrest system, the karabiner applies a force to the deformable element in excess of its ability to support.

On application of a first predetermined force to first load application point 35 of deformable element 30, deformable element 30 will begin to fracture along the weakened portion 50', causing plastic deformation of the deformable element and applying force across the shear component 60. The fracturing of the deformable element along the weakened portion absorbs energy from, for example, a falling mass. Continued application of force will lead to the fracture of shear component 60 and the continued fracturing of the deformable element from the first load application point 35 along the weakened helical path defined by groove 50 and the plastic deformation of deformable element. This arrangement is such that the deformable element rotates relative to spindle member 40, progressively straightening from the first load application point 35 along the helical path. It will appreciated that significant work is required for this deformation to take place and that a significant amount of energy can be absorbed in the fracturing and unwinding of the deformable element, as is suitable for reducing the deceleration of an initially free falling individual at a level which does not expose the individual to damaging shock forces, complies to current legislation and does not over-load the fall arrest system in which the shock absorber is incorporated. On continued application of the predetermined force, the deformable element will continue to fracture until the end of groove 50 is reached, but will not fracture across portion 39 of deformable element 30.

It will be appreciated that in an alternative embodiment, deformable element 30 may be pre-cut rather than provided with a groove. However, although no fracturing of deformable element 30 would be needed before plastic deformation could take place, the force applied to first application point 35 of deformable element 30 would have to be sufficient to result in fracture of shear component 60 before full plastic deformation of deformable element 30 can take place.

It will also be appreciated that in alternative embodiments of the shock absorber in accordance with the present invention the shear component may be omitted and the energy absorbance result from fracture and/or plastic deformation of the deformable element only.

Further variants are envisaged also in which the helical path may be partially pre- cut with one or more uncut bridge portions provided along the helical path, fracture of the or each bridge portion being necessary to allow subsequent plastic deformation of corresponding portions of the deformable element.

Figure 8 is a perspective view of a further embodiment of a shock absorber 10 in accordance with the present invention comprising part of an integral part of a safety harness 100 worn by a user as part of a fall arrest system.

Shock absorber 10 is retained integrally as part of safety harness 110 by means of support member 20 of shock absorber 10 which is located beneath harness retaining portion 112, harness retaining portion 112 being attached to harness 110 along at least two edges 112', 1 12" to retain support member 20 of shock absorber 10 in place.

Shock absorber 10 is provided with a deformable element 30 mounted on a spindle member 40, spindle member 40 being held between first and second opposing ends

22, 24 of support member 20, thereby retaining the deformable element 30 in position, deformable element 30 being rotatable relative to spindle member 40. A weakened portion 50' defined by groove 50 is provided across the surface of the deformable element 10 in a spiral path in a similar manner as described above in relation to shock absorber 10 shown in figures 1 to 7.

Shock absorber 10 is further provided with an attachment portion 110 defining an aperture 120 therethrough, aperture 120 being suitably dimensioned to receive at least a portion of a karabiner or the like therethrough to allow attachment of the safety harness 100 via a cable to a fall arrest safety system in use.

In use therefore, the harness would be worn by a user and attached, via a karabiner or the like to a fall arrest system. Should the user then fall from height, a force will be applied through the deformable element and, providing the force is sufficient, the deformable element will begin to facture along the weakened portion 50' and absorb the force as described above with respect to the shock absorber 10 shown in figures 1 to 7.

The shock absorber is intended for use for a single fall incident and is integral with the harness. Thus, after use during a fall the deformable element 10 will have undergone some deformation and the harness 100 and integral shock absorber 10 should be replaced.

Figure 9 shows a further embodiment of a shock absorber 10 in accordance with the present invention for use as part of a roof safety system. Shock absorber 10 is provided with a deformable element 30 mounted on a spindle member 40, spindle member 40 being held between first and second opposing supports 220, 240, deformable element 30 being rotatable relative to spindle member 40. A weakened portion 50' is provided across the surface of the deformable element 10 in a spiral path in a similar manner as described above in relation to shock absorber 10 shown in figures 1 to 7. Supports 220, 240 are provided with respective apertures 222, 242 suitably dimensioned to receive a portion of a bolt or nail or other suitable fastening element (not shown) therethrough in order to retain shock absorber 10 securely in place on roof structure 300.

Deformable element 30 is provided with a weakened portion 50' extending along its length and is further provided with an extended portion 32 which supports a cable receiving sleeve 230 through which the cable 250 of a safety support system extends in use.

In use, a user would be connected to the cable by means of a karabiner and support harness or the like. Should the user fall from height whilst connected to the cable, a force will be applied to the deformable element through extended portion 32 and providing the force is sufficient, the deformable element will begin to facture along the weakened portion 50' and absorb the force as described above with respect to the shock absorber 10 shown in figures 1 to 7.

Figure 10 shows a further embodiment of a shock absorber 10 in accordance with the present invention for use as part of a fall arrest system roof safety system. Shock absorber 10 is provided with first and second opposing ends 22, 24. Shock absorber 10 is provided with a deformable element 30 mounted on a spindle member 40. The deformable element 30 comprises a longitudinal member following a spiral path from one end 22 towards opposing end 24. The deformable element is circular in cross-section. However, it is to be appreciated that the deformable element may be of any alternative cross-sectional shape. For example, the deformable element may be rectangular, square or triangular in cross-section. Deformable element 30 is provided with a first load application point 35 to which a karabiner or the like would be attached in use. The first load attachment point 35 extends transverse to the axis through the spindle member 40 such that deformation of the deformable element 30 will result in rotation of the deformable element 30 about the spindle member 40. In use, a karabiner may be attached to first load application point 35 of deformable element 30 of shock absorber 10. The karabiner may then be attached to a cable of a fall arrest system. Support member 20 is then secured to another part of the fall arrest equipment.

On application of a first predetermined force to first load application point 35 of deformable element 30, deformable element 30 will begin to deform away from its spiral pathway and extend away from spindle 40 in a direction in which the force is being applied. The deformable element 30 will thus progressively straighten from the first load application point 35 along the helical path. It will be appreciated that significant work is required for this deformation to take place and that a significant amount of energy can be absorbed during the unwinding of the deformable element.

Figure 11 shows a the deformable element and spindle arrangement of figure 10 comprising part of a safety harness 100 worn by a user as part of a fall arrest system. This arrangement operates in a similar way to the shock absorber and harness arrangement of figures 8, however, the shock absorber 10 shown in figure 11 is a longitudinal member or coil which follows a spiral-like pathway around spindle member 40.

In use, the harness would be worn by a user and attached, via a karabiner or the like to a fall arrest system. Should the user then fall from a height, a force will be applied through the deformable element and, providing the force is sufficient, the deformable element will begin to deform and progressively straighten along the helical path. As a significant work is required for this deformation to take place, a significant amount of energy can be absorbed during the unwinding of the deformable element.

Shock absorber 10 is a single-use item and after a fall event has occurred the shock absorber should be replaced.

Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort. For example, For example, although the shock absorber is described mainly in terms of absorbing the shock from a falling person, it will be readily appreciated that the shock absorber of the present invention may find equal application in the support of loads such as lifts or over-running machinery for example where machinery runs past safety buffers, or may be used in any other suitable application where shock forces may occur. Further, although the embodiment shown in figures 8 and 9 is a roof mounted shock absorber for use as part of a roof mounted fall arrest safety system for a person, it will be appreciated that the shock absorber may be mounted on any elevated structure and may be used to arrest the fall of an object, for example signage or the like mounted on an elevated structure, to prevent the object from ground impact damage during a fall and to prevent injury to anyone located beneath the object during a fall e.g. due to high winds and/or fastenings failure and the like.

Claims

1. A single-use shock absorber comprising: a. a support member; b. a spindle member supported on the first support member; and c. a deformable element having a first load application point, the deformable element being rotatably mounted on the spindle member, wherein the deformable element is dimensioned for plastic shock absorbing deformation on application of a predetermined force to the first load application point.

2. A single-use shock absorber according to Claim 1 or Claim 2, wherein plastic deformation of the deformable element occurs under torsion.

3. A single-use shock absorber according to Claim 1 or Claim2, wherein plastic deformation of the deformable element occurs under tension.

4. A single-use shock absorber according to any preceding Claim, wherein the deformable element comprises a continuous longitudinal element extending along a spiral path.

5. A single-use absorber according to Claim 4, wherein the continuous longitudinal element comprises a coil.

6. A single-use shock absorber according to Claim 4 or Claim 5, wherein no portion of the longitudinal element makes contact with any other portion of the longitudinal element.

7. A single-use shock absorber according to any preceding Claim, wherein the deformable element is circular in cross-section.

8. A single-use shock absorber according to any preceding Claim, wherein the deformable element comprises a hollow member.

9. A single-use shock absorber according to any preceding Claim, wherein the hollow member is provided with a weakened portion defining a spiral path along at least a portion of the hollow member.

10. A single-use shock absorber according to Claim 9, wherein the deformable element is provided with a bridge spanning the spiral path, the bridge being dimensioned to fracture at a predetermined loadforce less than that at which the deformable element deforms plastically.

11. A single-use shock absorber according to Claim 10, wherein the bridge is located adjacent the first load application point.

12. A single-use shock absorber according to Claim 10 or Claim 11, wherein deformable element is provided with a series of bridges.

13. A single-use shock absorber according to any one of Claims 9 to 12, wherein the weakened portion comprises a groove, the groove being dimensioned to fracture at a predetermined.

14. A single-use shock absorber according to Claim 13, wherein the groove is of a uniform depth along its length.

15. A single-use shock absorber according to Claim 13 or Claim 14, wherein the groove is of varying depth along its length.

16. A single-use shock absorber according to any one of Claims 13 to 15, wherein the groove is of uniform cross-sectional shape along its length.

17. A single-use shock absorber according to any one of Claims 13 to 15, wherein the groove is of varying cross-sectional shape along its length.

18. A single-use shock absorber according to any preceding Claim, further comprising a shear component mounted on the deformable element and spanning at least a portion of the spiral path, the shear component designed to fracture at a predetermined force slightly greater than that at which the deformable element deforms plastically.

19. A fall arrest harness comprising an integral single-use shock absorber according to any preceding Claim.

20. A single-use shock absorber substantially as hereinbefore described and with reference to the accompanying drawings.

21. A fall arrest harness substantially as hereinbefore described and with reference to the accompanying drawings.