ENERGY ABSORBING DEVICE

Abstract: An energy absorbing device (10; 30; 50, 82) for use in a fall arresting system is described comprising a housing (16, 20; 38, 40; 52; 58; 82, 82a) for receiving webbing (12; 32; 62; 86) of a harness coupled to a person or object, the housing being adapted to be coupled to an anchor point. The webbing passes through the device and an external loop (24; 34; 74) of webbing is formed and at least two layers of webbing (12a, 12b; 32a, 32b; 62; 86) are sandwiched in a close fitting relationship in a longitudinal channel (18; 42; 60) of the device. In the event of a fall a force is applied to the object or body and the loop, which is free-running, takes up the initial force and limits the force applied to the body to a first value (F1). Once the free loop is taken up, slippage between the webbing layers and between the webbing and the surfaces of the housing creates friction which controls the maximum force (F2) applied to the body or object. Embodiments of the invention are described.

Description: ENERGY ABSORBING DEVICE The present invention relates to an energy absorbing device for use in a fall arresting system. In particular, the invention relates to a device which is used with a lanyard and uses friction to absorb the kinetic energy of the falling body. General purpose safety harnesses are harnesses which incorporate thigh straps and shoulder straps and which are used in conjunction with safety lanyards for attachment to anchorage points which are usually sited on a roof or on a similar high point. Such harnesses may be built into lightweight suits. General purpose safety harnesses are intended for use with freedom of movement as required, but where the combined effect of the position of the anchorage, the length of the lanyard and the attachment point of the harness and the length of any extensible webbing, limits the potential drop of the wearer to a particular maximum length. British Standard BS1397 requires that the safety harness should absorb the energy of an articulated dummy of a 100 kg weight falling 2 metres before the onset of the arrest; this approximates to a work person working no higher than the structural anchorage. In accordance with this standard, the total energy absorption capacity has been of the order of 2.75 kilojoules (kJ) including extension of any energy absorbing medium. The requirements for future safety harnesses are outlined in a draft European Standard prEN 355, there is a fall of 4 metres allowed before onset of arrest. This implies that a work person can work at a lanyard length above the structural anchorage point, plus extension of the medium. Thus, in this particular standard, the maximum travel would be 5.75 metres with a possible 5.75k total energy absorption requirement. Many existing energy absorbing products may be able to meet the former British Standard requirement. However, they are highly unlikely to stay within the 6kN arrest force maximum specified in the draft European Standard prEN355. Accordingly, it is an object of the present invention to provide an improved energy absorbing device which obviates or mitigates the disadvantages associated with existing devices and which complies with existing British Standards and proposed European Standards in this area. This is achieved in the broadest concept by providing an energy absorbing device which is clamped around a lanyard in a tight-fitting relationship and providing an aperture in the device through which a loop of the lanyard material is formed external to the device. In one arrangement, the device is used with fabric webbing although the device can be modified for use with a rope or the like. Accordingly, in one aspect of the present invention, there is provided an energy absorbing device for use in an energy absorbing system coupled to an object, said energy absorbing device comprising a housing defining a first generally longitudinal slot passing therethrough for receiving at least two layers of lanyard material in a tight-fitting relationship, the layers being movable in opposite directions, the housing having upper and lower elements defining at least one aperture therein and forming a communication means between said longitudinal slot and the exterior of said housing, said upper and lower elements being spaced apart and shaped so that a loop of lanyard material can be formed external to said housing, whereby in the event of energy absorption demand, said lanyard material is moved relative to said energy absorbing device and friction between said lanyard and said device controls the force applied to the object. Conveniently, said elements are defined by lower and upper walls in a surface of said housing, said upper and lower walls defining said aperture through which said loop of lanyard material is adapted to be pulled. Preferably, said lanyard material passes over a hook means for securing the device to an anchor point. Alternatively, a hook means is coupled directly to said housing, said hook means having a first portion for securing to an anchor structure and a second portion around which a layer of lanyard is passed to form part of said loop of lanyard material. Conveniently, said hook means is integrally coupled to said housing, and said first portion being integral with said hook means and said housing. Alternatively, said hook means is defined by a separate U-shaped element coupled to said housing by a second portion which is separate. Conveniently, the device is coupled to a webbing-based harness adapted to be worn by a user for use as a fall arresting device, said hook being adapted to be coupled to a roof anchor structure whereby in the event of a fall, the friction between the device and the webbing controls the force applied to said user. According to a further aspect of the present invention there is provided a method of absorbing energy applied to an object coupled to an anchor point via a harness and an energy absorbing device, said harness having at least two layers of webbing fed through said energy absorbing device in frictional engagement, the object undergoing a sudden displacement resulting in the creation of a force applied to the object, said method comprising the steps of; absorbing an initial force at a first level applied to the object via a loop of webbing extending from the interior of the device to form an exterior loop, then after said loop is taken up, absorbing a further higher force applied to said object by permitting said layers of webbing to slip relative to each other within said device whereby friction between the layers of webbing and between the webbing and the device limits the maximum force applied to said object. Preferably, the energy absorbing system is a fall arresting system and said loop of webbing extends from the interior of the device through at least one aperture which extends generally transversely to a longitudinal slot which extends through the device and accommodates said at least two layers of webbing. Preferably, the energy absorbing device is box-shaped and is of generally rectangular cross-section. The longitudinal slot extends perpendicular to the rectangular cross-section and also has a generally rectangular cross-section for receiving two layers of a fabric webbing lanyard. The aperture is an elongated slot which is perpendicular to the longitudinal slot and is located about half-way along the length of said housing. Conveniently, the upper and lower walls defining the aperture have a profile shaped to just engage with the webbing, said profile controlling the degree of friction between the webbing and the energy absorbing device. In one arrangement the spacing between the upper and lower wall is designed so that the loop of material is substantially free running. Alternatively, the lanyard is a rope with two lengths of rope disposed side-by-side in said longitudinal slot, the lengths being movable in opposite directions and a transverse aperture or slot is located in a side wall of the housing through which a loop is formed from one layer of rope. Conveniently, the energy absorbing device can have its frictional or energy absorbing characteristics varied by varying the material of the device, the roughness and spacing of the longitudinal slot surface, and the spacing and shape of the walls defining said aperture. These and other aspects of the invention will become apparent from the following description when taken in combination with the accompanying drawings in which:- Fig. 1 is a diagrammatic view of an energy absorbing device in accordance with an embodiment of the present invention fitted to a webbing lanyard for use in a fall arresting system; Fig. 2 is a side view of the energy absorbing device and part of the lanyard shown in Fig. 1; Fig. 3 is an enlarged and longitudinal cross-sectional view taken through the energy absorbing device shown in Figs. 1 and 2; Fig. 4 is a graph of load versus time for the force applied to a body being arrested using the energy absorbing device shown in Figs. 1-3; Fig. 5 is a diagrammatic view similar to Fig. 1 of an alternative embodiment of energy absorbing device for use with a rope lanyard; Figs 6a, b and c are diagrammatic longitudinal sectional, front and bottom views of an alternative embodiment of an energy absorbing device where the hook for the webbing is integral with the device; Fig. 7 is a diagrammatic front elevation of a further alternative embodiment of an energy absorbing device in accordance with the invention; and Fig. 8 is a front elevation similar to Fig. 7 in which the device has been modified to receive a U-bolt which acts as a hook. Reference is first made to Figs. 1 and 2 of the drawings which depicts an energy absorbing device 10 in accordance with an embodiment of the invention fitted to receive the fabric webbing 12 of a lanyard which is part of a safety harness for use in a fall arresting system. The lanyard 12 being part of the work person's safety harness, has an upwardly movable side 12a and a downwardly movable side 12b looped around a hook or karabiner 14 which can be secured to a structural anchorage on a roof or the like, which is not shown in the interests of clarity. As will be later described in detail, the device 10 is designed to use friction between the device 10 and webbing 12 to absorb the kinetic energy of a falling body so that the maximum energy or force applied to the body is less than a predetermined threshold. The device 10 consists of a first plate 16 having a recessed channel 18 therein for receiving a double thickness (2 layers 12a, 12b) of webbing 12 and a front plate 20 which is sized and proportioned to mate with the rear plate 16 to securely compress the webbing layers 12a, 12b into the recess 18. The front plate 20, when fitted to the rear plate, results in the recess 18 being formed into a slot which extends the length of the energy absorbing device. The front plate 20 of the energy absorbing device has a perpendicular slot 22 disposed therein so that the exterior of the device communicates with the internal slot 18. The width of the slot 22 is proportioned and dimensioned so that a loop 24 of fabric webbing can be pulled therethrough as shown in Figs. 1 and 2. Reference is now made to Fig. 3 of the drawings which is an enlarged longitudinal sectional view through the energy absorbing device 10 when fitted with the lanyard of webbing 12. It will be appreciated that the internal slot 18 is proportioned so that the lanyard webbing 12a, 12b is compressed in the channel. The spacing between the walls 25 and 26 defining the slot 22, is the same or slightly more than a thickness of 2 layers of webbing 12a, 12b superimposed so that the webbing is, at the most, only slightly compressed so that the loop 24 is essentially free running in the event of a downward force applied to webbing 12b although there is a tight-fitting relationship between the webbing 12a, 12b and the longitudinal slot 18. It will be appreciated that walls 25 and 26 are carefully dimensioned and profiled as will be explained so as to provide the desired frictional effect between the energy absorbing device 10 and the lanyard 12 in the event of a fall. In the embodiments shown the radius of curvature of walls 25 and 26 is 2mm. Operation of the device will now be described with reference to Figs. 1-3 and also with reference to Fig. 4 of the drawings. As best seen in Fig. 4, in the event of a fall, the force applied to the body increases to a force Fi as the lanyard 12 has just gone taut; this is about a load of 2kN. At time t^-t2, primary slippage of the webbing 12b takes place by drawing the free loop 24 into the lower portion between the compression plates 16 and 20. When the "free loop" is taken up at time t2, the effect is to increase the force F to a peak F2, at time t 3 where secondary slippage takes place with consequential frictional losses between the webbing downside 12b and webbing upside 12a, as the webbing moves between compression plate 16 and 18, and between the webbing 12 and the eye 28 of the hook or karabiner 14. This sequence of events ensures that the fall of the work person is first acted upon by the relatively low force, which aids alignment or orientation of the harness wearer in readiness for the later force F2 which brings about the arrestment of the work person at a controlled force. The design of the energy absorbing device 10 and choice of lanyard used results in the structure in this embodiment imposing a peak secondary force of less than 6kN on the work person, thus complying with the proposed European safety standard in draft prEN 355. Reference is now made to Fig. 5 of the drawings which depicts a further embodiment of an energy absorbing device 30. In this case, the lanyard is a rope 32 which has a free loop 34 which passes through a side aperture 36 as shown. The rope 32 has an upwardly movable length 32a and a downwardly movable length 32b of which loop 34 is part. The rope is compressed between plates 38,40 which define a channel 42 and the device 30 works in the same way as that described with reference to Figs. 1 to 4. Reference is now made to Figs. 6a, b and c of the drawings which depict an alternative embodiment of an energy absorbing device, generally indicated by reference numeral 50, which has a first cast aluminium body portion 52 with an integral eye or hook 54 and which has a recessed portion 56 for receiving a cast aluminium webbing compression plate 58 (Fig. 6c) to define a longitudinal slot 60 for receiving lanyard webbing 62 as will be later described in detail. The webbing 62 is part of a safety harness worn by the user and the eye 54 can be secured, via a hook or karabiner, to a structural anchorage point on a roof or the like (not shown) . As best seen in Fig. 6c the recessed portion 56 is stepped so that the plate 58 abuts shoulders 64 and the plate 58 is fastened to the body portion 52 by means of 6 capscrews (not shown) which fit into the capscrew recesses 66. In this embodiment the eye or hook 54 is integral with the body portion 52 and also has a circular integral cross-bar 68, which together with the compression plate 58 of the body portion 52 defines a transverse slot 72 through which a loop 74 of fabric webbing can be pulled therethrough as shown in Fig. 6a. It will be appreciated that slots 72 and 60 are in communication for receiving the webbing 62 as shown in Fig. 6a and it will also be seen that the webbing loops around the integral cross-bar 68 replaces eye 28 shown in Figs. 1 and 2. As with the device described in the first embodiment, the slots 60 and 72 are dimensioned and proportioned to receive the webbing in the same way. Slot 60 is dimensioned so that when plate 58 is fastened to the body portion the two layers of webbing 62 are compressed and in this case only one layer of webbing 62 passes through the slot 72 with the width of the channel being dimensioned to allow loop 74 to be essentially free-running in the event of a downward force being applied to the webbing 62b (Fig. 6a) . Operation of the device 50 will now be described with reference to Figs. 6a, b and c and Fig. 4. In the event of a fall, the force applied to the body increases to F^ as webbing 62 goes taut, for a load of about 2kN. At time ti - t2 primary slippage of webbing 62b takes place by the free loop 74 being drawn into the device between body portion 52 and front compression plate 58. At time t2, the "free loop" is taken up and the force on the body increases to a peak F2 at t 3 . At this time secondary slippage occurs with frictional losses between webbing 62b and 62a, between webbing layers 62a,b and the inside of the slot 60, and between webbing 62 and the cross-bar 68. This brings about arrestment in the same way as the earlier described embodiments to comply with the proposed draft European Safety Standard prEN 355. An advantage of this embodiment is that the body portion can be cast with an integral eye or hook minimising components and assembly. Another advantage of this embodiment is that the friction round the integral hook bar gives flexibility in design for various applications and materials. Reference is now made to the embodiment shown in Fig. 7 which is similar in material construction to that shown in Figs. 6a, b and c except that the hook 80 is formed by a U-shaped forging secured to upstanding lugs of body portion 82 by means of a riveted cross-bar 84. The webbing 86 (shown in broken outline) loops around cross-bar 84 and a loop extends through slot 88 as in the previous embodiment. The device operates in the same way as described above to comply with prEN 355. Reference is also made to the embodiment shown in Fig. 8 which is identical to that shown in Fig. 7, and in which like numerals denote like parts except with the suffix 'a' added, except that internal surfaces 90,92 of the upper lugs are milled out so that a U-shaped hook 80a can be received as shown and secured by riveted cross-bar 84a. The device of Fig. 8 operates in the same way as that of Fig. 7. An advantage of the devices shown in Figs. 7 and 8 is that a single casting can be used (then milled for Fig. 8) so minimising stock and the maximum reaction forces are taken between the upper surface of the cross-bars 84, 84a and the underside of the forged U-bolt hook 80,80a. It will be understood that the maximum primary and secondary slippage forces can be varied by altering the degree of compression of the webbing between the plates or by introducing an agent such as PTFE film within the longitudinal slot, and that the primary force is always less than the secondary force. It should also be understood that the friction between the webbing and the energy absorbing device is dependent on a number of factors such as the material of the webbing and the energy absorbing device, the degree of compression exerted on the webbing upside and webbing downside within the longitudinal slot, the length of the free loop and the width of the aperture through which the loop passes, and also the shape of the walls or surfaces defining the aperture. In addition, the surface texture of the slots or parts in contact with the moving webbing will affect the friction. Because the energy absorption characteristics of the device are affected by all these factors, it is possible, therefore, to design the energy absorption device so as to produce a particular load-time profile with a particular lanyard in the event of a fall occurring. It will also be appreciated that various modifications may be made to the devices hereinbefore described without departing from the scope of the invention. The device could be used as a back-up on a crane so that in the event of failure of the lifting tackle or rapid arrest of the crane, the energy absorption device is actuated to control the force applied to the payload being moved by the crane. In addition, although only one free loop is shown, two or more apertures can be provided to provide two or more free loops to produce a particular load-time profile. In addition, although the compression plate is separate and shown fastened to the back face with screws, it will be appreciated that, of course, this could be hinged to facilitate ease of fixing around the webbing or rope when used as the lanyard. It will be appreciated that the external shape of the energy absorbing device is not critical. Although generally box-shaped in the embodiments, it will be appreciated that this shape could be cylindrical or oval or any other convenient shape as long as the functional requirements of the device are satisfied. It will also be understood that the width of each aperture may be adjustable to accommodate different webbing thicknesses and to control the friction between the loop and the device. Further, the device may be provided as a separate accessory for use in conjunction with a conventional harness. Also, as the operation of the device is not dependent on orientation, the device may be used as described above, or the karbiner 14, eye 54 or hook 80 may be attached to the harness and a hook at the other extremity of the webbing attached to the anchorage.

Claims: 601 _ _. — ID — CLAIMS 1. An energy absorbing device for use in an energy absorbing system coupled to an object, said energy absorbing device comprising a housing defining a first generally longitudinal slot passing therethrough for receiving at least two layers of lanyard material in a tight-fitting relationship, the layers being movable in opposite directions, the housing having upper and lower elements defining at least one aperture therein and forming a communication means between said longitudinal slot and the exterior of said housing, said upper and lower elements being spaced apart and shaped so that a loop of lanyard material can be formed external to said housing, whereby in the event of energy absorption demand, said lanyard material is moved relative to said energy absorbing device and friction between said lanyard and said device controls the force applied to the object. 2. A device as claimed in claim 1 wherein said elements are defined by lower and upper walls in a surface of said housing, said upper and lower walls defining said aperture through which said loop of lanyard material is adapted to be pulled. 3. A device as claimed in claim 1 or claim 2 wherein said lanyard material passes over a hook means for securing the device to an anchor point or to a harness. 4. A device as claimed in claim 3 wherein said hook means is separate. 5. A device as claimed in claim 3 including hook means coupled directly to said housing, said hook means having a first portion for securing to an anchor structure or harness and a second portion around which a layer of lanyard is passed. 6. A device as claimed in claim 5 wherein said hook means is integrally coupled to said housing, and said first portion being integral with said hook means and said housing. 7. A device as claimed in claim 5 wherein said hook means is defined by a separate U-shaped element coupled to said housing by a second portion which is separate. 8. A device as claimed in any preceding claim in which said at least one aperture is generally transverse to said longitudinal slot. 9. A device as claimed in any preceding claim in which said housing is generally box-shaped and is of generally rectangular cross-section. 10. A device as claimed in any preceding claim wherein said housing has a first housing portion and a second housing portion adapted to be secured to said first housing portion to define said longitudinal slot for receiving said layers of lanyard material. 11. A device as claimed in claim 2 wherein the upper and lower walls defining the aperture have a profile shaped to just engage with the lanyard material, said profile controlling the degree of friction between the lanyard material and the energy absorbing device. 12. A device as claimed in claim 11 wherein the spacing between the upper and lower wall is designed so that the loop of material is substantially free running. 13. A device as claimed in claim 11 where the lanyard is a rope with two lengths of rope disposed side-by-side in said longitudinal slot, the lengths being movable in opposite directions and a transverse aperture or slot is located in a side wall of the housing through which a loop is formed from one length of rope. 14. A device as claimed in any preceding claim coupled to a webbing-based harness adapted to be worn by a user for use as a fall arresting device, said device being adapted to be coupled to a roof anchor structure whereby in the event of a fall, the friction between the device and the lanyard material controls the force applied to said user. 15. A method of absorbing energy applied to an object coupled to an anchor point via a harness and an energy absorbing device, said harness having at least two layers of webbing fed through said energy absorbing device in frictional engagement, the object undergoing a sudden displacement resulting in the creation of a force applied to the object, said method comprising the steps of: absorbing an initial force at a first level applied o the object via a webbing loop extending from the interior of the device to form an exterior loop, then after said loop is taken up, absorbing a further higher force applied to said object by permitting said layers of webbing to slip relative to each other within said device whereby friction between the layers of webbing and between the webbing and the device limits the maximum force applied to said object. 16. A method as claimed in claim 15 wherein the higher force is absorbed by friction between said webbing layers and between said webbing and hook means for securing said device to an anchor point or to the harness. 17. A method as claimed in claim 15 or 16 where the object is a person wearing said harness secured to an anchor point, and in the event of a fall, the initial force is such that it facilitates user orientation or alignment and the energy absorbed by the friction during slippage is such that the maximum force applied to the user is less than a predetermined safety value.

Inventors: CRAWFORD HENRY, CRAWFORD, HENRY
Applicants: CRAWFORD HENRY, CRAWFORD, HENRY
Application year: 1992
Main classification: A62B35
IPC codes: A62B35