AN ENERGY ABSORBING DEVICE

Abstract: An energy absorbing device is for use in an energy absorbing system coupled to an object. The energy absorbing device comprises a body defining a longitudinal slot passing therethrough for receiving at least two layers of lanyard material in a tight fitting relationship. The layers are movable in opposite directions, whereby, in the event of energy absorption demand, the lanyard material is moved relative to said energy absorbing device and friction between said lanyard and said device controls the force supplied to the object. Means is provided for increasing the width of the slot following arrest of the object so as to reduce said friction and permit controlled further movement of the object. The invention provides for a two-stage descent in which after a fall, the second stage allows a controlled descent.

Description: AN ENERGY ABSORBING DEVICE The present invention relates to an energy absorbing device for use in an energy absorbing system coupled to an object, for example 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 object, for example a person. It is known to provide a work person with a general purpose saferj harness which is used in connection with a safety lanyard for attachment to an anchorage point on a roof or other elevated location. The lanyard is extensible and incorporates an energy absorbing device whereby frictional contact between the lanyard and said device controls the force applied to the work person in a fall so that the person is brought to rest without injury. An energy absorbing device of this kind is described in European Patent Application No. 92904028.5 b\ Henry Crawford and comprises a body defining a 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, and communication means for permitting formation of a loop of lanyard material externally of said body, 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. A disadvantage of known energy absorbing devices such as the Crawford device is that after a fall the work person is left suspended in a position from which it may be difficult to rescue him. It is an object of the present invention to provide an energy absorbing device in which the aforesaid disadvantage is obviated or mitigated. According to 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 body defining a 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, 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 supplied to the object, characterised in that means is provided for increasing the width of the slot following arrest of the object so as to reduce said friction and permit controlled further movement of the object. Preferably, said slot is defined by a fixed body part and a movable body part associated with a manually operable adjustment screw. The slot width may be pre-set during manufacture and means is preferably provided for preventing inadvertent operation of said adjustment screw. The preventing means is preferably a sheer pin interconnecting the body with a head of the adjustment screw so as to immobilise said screw. In order to prevent welding together of the layers of lanyard material as a result of heat generated by frictional contact, the slot is preferably divided into two passages by a separating element preventing such contact. The energy absorbing device is preferably provided in combination with a length of lanyard material having looped ends for securing the device by hook means to an anchor point and a harness. An intermediate section of the lanyard material is preferably folded into multiple layers so as to provide sufficient length of material for energy absorption and said further movement. The invention will now be further described by way of example only with reference to the accompanying drawings, in which:- Fig. 1 shows a workman in an elevated position wearing a general purpose safet harness attached to a lanyard incorporating an energy absorbing device in accordance with the invention; Fig. 2 shows the lanyard in greater detail with insets showing the energy absorbing device of the invention to an enlarged scale; Fig. 3 is a longitudinal section of the lanyard of Fig. 2, and Fig. 4 is an exploded view of the energy absorbing device of the invention. Referring now to the drawings, the illustrated lanyard indicated generally at 1 comprises an energy absorbing device 2 and a length of lanyard material 3. As illustrated in Figs. 2 and 3, the energy absorbing device 2 may be encapsulated in tough plastics material 4 in order to prevent tampering. The lanyard material 3 is provided in a continuous length and has a relatively short section 3a extending to one side of the energy absorbing device 2 and a relatively long section 3b extending to the opposite side of the energ absorbing device 2. Each lanyard section 3a, 3b terminates in a loop 5, 6 which is connected by hooks 7, 8 (see Fig. 1) on the one hand to a workman's general purpose safety harness 9 and on the other hand to an anchorage (not shown). The energy absorbing device 2 comprises a body 10 having two halves 10a, 10b defining therebetween a longitudinal slot 1 1. The main body part 10b has a channel 12 flanked by side walls 13, 14 penetrated by holes 15 for socket headed cap screws one of which is shown at 16. The through holes 15 are aligned with tapped holes (not shown) in the underside of the cover body part 10a. The cover part 10a of the body 10 is also provided with a channel 17, facing the channel 12 and having terminal recesses 18, 19. The channels 12, 17 define a longitudinal passageway of fixed width determined by the spacing in between the floors of the channels 12 and 1 . A slipper 20 in the form of a rectangular plate with upturned ends 21, 22 defines between its underside as seen in Fig. 4 and the floor of channel 12 the slot 11 which is of variable width. A separator plate 23 for dividing the slot 11 into two passages to either side of the plate 23 is located by means of side lugs 24, 25 in correspondingly shaped recesses 26, 27 in the side walls 13, 14 of the main body part 10b. The upturned ends 21, 22 of the slipper 20 are slidably located in the recesses 18, 19 respectively. An adjusting screw 28 (see inset to Fig. 2 and Fig. 3) has a head 29 in the form of a manual control knob and is in screw-threaded engagement with a tapped hole 30 in the cover 10a. The adjusting screw 28 extends through the hole 30 into engagement with the upper surface of the central part of the slipper 20 thereby urging the slipper 20 a predetermined distance towards the floor of the channel 12 and fixing the maximum width of the slot 11 for the particular screw setting. The energy absorbing device 2 is factory assembled with the slot 11 set to a predetermined width and the control knob 29 temporarily fixed in the corresponding position by means of a sheer pin 31 (see Figs. 2 and 3) engaged in aligned sockets in the underside of the control knob 29 and the upper surface of the cover 10a. The side walls 13, 14 of the main body part 10b extend beyond the channel 12 to provide locating pins 32, 33 for loops of lanyard material. The lanyard sections 3a, 3b are provided by a continuous length of lanyard material which is looped at its one end about the pin 33, is folded to form the loop 5 at the outer end of the section 3a and is then returned over the underside of the energy absorbing device 2 within the plastics sleeve 4 and via multiple folded layers 34 through the slot 11 in one direction under the separator plate 23, around the pin 32 and back in the opposite direction over the separator plate 23 to terminate in the loop 6 at the outer end of the lanyard section 3b. The lanyard section 3a has its various layers stitched together while the layers of webbing material constituting the lanyard section 3b are encased in a sheath 35 to permit movement in use as will now be described. When a work person falls from an elevated location with the hook 8 of the lanyard 1 connected to an anchorage and the hook 7 connected to the safet harness, an initial free fall is arrested by the energy absorbing device 2 in known manner in that the layers of webbing material trapped in the slot 11 to either side of the separating plate 23 are caused to move relative to each other with consequent extension of the lanyard section 3b as a result of unfolding of the layers 34. Once the fall has been arrested, the work person or a rescuer can turn the control knob 29, after initially shearing the pin 31 so as to release the adjusting screw 28. The slot 11 is thus enlarged to permit relative movement of the webbing material in the slot 11 and enable a controlled decent of the work person to the extent permitted by the webbing material remaining in the lanyard section 3b. It should be noted that full release of the adjusting screw 28 increases the width of the slot 11 to an extent sufficient to permit fairly rapid descent but not completely uncontrolled descent, i.e. with the screw 28 fully retracted the maximum width of the slot 11 relative to the thickness of the webbing material is such that the body 10 still offers substantial frictional resistance to the movement of the webbing material. It will be appreciated that numerous modifications may be made without departing from the scope of the invention. Thus, for example, the means for preventing inadvertent rotation of the control knob may involve, in place of the sheer pin 31, containment of the control knob 29 within the plastic sheath 4, although a sheer pin is preferred as giving a visible indication that the control knob has not been tampered with.

Claims: CLAIMS: 1. An energy absorbing device for use in an energ absorbing system coupled to an object, said energy absorbing device comprising: a body defining a 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, 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 supplied to the object, characterised in that means is provided for increasing the width of the slot following arrest of the object so as to reduce said friction and permit controlled further movement of the object. 2. A device as claimed in claim 1, wherein said slot is defined by a fixed body part and a movable body part associated with a manually operable adjustment screw. 3. A device as claimed in claim 2, wherein the slot width is pre-set during manufacture and means is provided for preventing inadvertent operation of said adjustment screw. 4. A device as claimed in claim 3, wherein said preventing means is a sheer pin interconnecting the body with a head of the adjustment screw so as to immobilise said screw. 5. A device as claimed in any one of the preceding claims, wherein the slot is divided into two passages by a separating element preventing contact between the layers of lanyard material in use. 6. A device as claimed in any one of the preceding claims, in combination with a length of lanyard material having looped ends for securing the device by hook means to an anchor part and a harness. 7. A device as claimed in claim 6, wherein an intermediate section of the lanyard material is folded into multiple layers so as to provide sufficient length of material for energy absorption and said further movement. 8. An energy absorbing device with lanyard material, substantially as herein described with reference to the accompanying drawings.

Inventors: FARR PAUL, FARR, PAUL
Applicants: FARR PAUL, SPANSET INTER AG, FARR, PAUL, SPANSET INTER. A.G.
Application year: 1996
Main classification: A62B35
IPC codes: A62B35