Note: Descriptions are shown in the official language in which they were submitted.
W092/1~01 ~ PCT/GB92/~223
ENERGY ABSQRBING ~y__B ~ ~ 3 ~ ~ ~
The present invention relates to an energy absorbing
device ~or use in a fall arresting syste~. In particular,
the invention relates to a device which is used with a
lany rd and uses friction to absorb the kinetic energy of ~:
the falling body.
General purpose safety harnesses are harn~s~es-which : :
incorporate thigh ~traps and shoulder straps and which are
used in conjunction with safety lanyards ~or attachme~nt to ~
anchorage points which are usually sited on a roof or on a ~ ?
si~ilar high point. Such harnesses may be ~uilt into
lightweight suits. General purpose sa~ety harnesses are
intended for use with ~reedom of movement as required, but
where the combin~d effQct of the position of ~he
anchorage, the length of ~he lanyard and the att~ch~ent
point of the harness and the length of any extensi~le
webbing, limits the potential drop o the wearer to a
parti~ular maximum length. British Standard BS1397
requires that the sa~ety harness should absorb the energy
o~ an arti ulated dummy o~ a 100 kg weigh~ ~alling 2 .
metres be~ore the onset of the arr~s~; this approximates ;,
to a work person working no higher than the structural
anchor~g~. ID accordance with this standard, the total
; ~ energy absorption capaci~y has been of the order of 2. ?5
kilojoules (kJ) including extension of any ener~y
absorbing medium. The requiremen~s for ~uture sa~ety
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~T~9 2 1 ~223
2 ~ '9~
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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 5.75kJ 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 dra~t European Standard
prEN355.
Accordingly, it is an o~ject of the present invention
~o 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 one embodiment of the present
invention, 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,
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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; and communication means for permitting
formation of a loop of lanyard material externally of said
body, rJhereby 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 communication means is in the form
of an aperture defined by lower and upper walls in a
surface of said body.
Preferably, the device is provided in combination
with a length of lanyard material. -
Preferably also, said lanyard material passes over a
hook means for securing the device to an anchor point or ,
to a harness. The hook means may be coupled directly to ;
said body, and said communication means is defined in part
by a portion of the hook means around which a layer of
lanyard is passed.
Conveniently, said hook means is integrally coupled `
to said body.
;~ ~ Alternatively, said hook means is defined by a
separate U-shaped element coupled to said bod~ by said
portion which prior to coupling is separate from the
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~` F~ SUBSTITUT~ S~-~E~
4 2 i ~ ? ~ 9 J~PRIl 1993
remainder of the hook means.
Conveniently, the device is coupled to a
webbing-based harness ada~ted to be worn by a user for use
as a fall arresting device, said hook means belng adapted
to be co~pled to a roof anchor structure whereby in the
event of a fall, the friction between the devicP and the
lanyard material controls the force applied to said user.
Preferably, the body of the energy absorbing device
is box-shaped and is of rectangular cross-section, and the
longitudinal slot extends perpendicular to the rectangular
cro~s-section and also has a rectangular cross-section for
receiving two layers of a fabric webbing lanyarcl. The
communication means may be an aperture transverse to the
longitudinal slot and is located about half-way along the
length o~ said body.
Conveniently, the upper and lower walls of the body
defining the aperture have a~profile shaped to engage with
the webbing, said profile controlling the degree of
friction between the webbins and the enexgy 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 ~ope disposed side-by-side in said longitudinal slot,
the lengths being movable in opposite directions and said
co~municating means is in the form of a transverse
aperture located in a side wall of the body thxough which
a loop is formed from one layer of
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2 5 M~lRCH 199~
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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 surfacec;~ and the spacing
and shape of the walls de~ining said aperture.
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 ~ia a . :
harness and an energy absorbing device, said harne~s ;
having at least two layers of webbing fed through saicl
energy absorbing device in ~rictional engagement, the
object undergoing a sudden displacement resulting in the
creation of a force applied to the~object, said method
compri~ing the StepR 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 ~aid 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 th~ webbing and the device limits the maximum
force applied to said object. .
Preferably, the ~nergy absorbing system i5 a fall
arresting system and said loop of webbing extends from the
interior of the device through at least one aperture which
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P~T/6B 9 2 ~ 2 ~
- 6 - 2~ 23 M~R~ 1993
extends transversely to a lonyitudinal slot which extends
through the device and accommodates said at least two
layers of webbing.
These and other aspects of the invention will become
apparent from the following description when taken in
combination with the accompanying draw:ings in which:-
Fig. 1 is a diagrammatic view of an energy absorbingdevice in accordance with an embodiment o~' the present
invention fitted to a webbing lanyard :Eor use in a fall
arresting system;
Fig. 2 is a side view of the energy absorbing device
and part of the la~yard sh~wn in Fi~
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
ab~orbing device shown in Figs. 1 3;
Fig. 5 is a diagrammatic view similar ko Fig. 1 of an
alternatiYe embodimen~ of energy absorbing device for use
with a rope lanyard; :
Figs 6a, b and c are diagrammatic longitudinal
sectional, Pront and bottom views of an alternative
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WO g2~01 ~ ~ ~ 3 ~ ~ ~ P~r/GB9~/00223
embodiment of an energy absorbing device where the hook
for the webhing is integral with the device;
Fig. 7 is a diagrammatic fr~nt 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 a:nd 2 of the
drawings which depicts an energy absorbing device 10 in
accordance with an e~bodiment of the invention fitted to
receive the ~abric webbing 12 o~ a lanyard which is part
o~ a safety harness ~or use in a ~all arresting system.
The lanyard 12 being part o~ the work person's safety
harness, has an upwardly ~ovabl~ 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 }ik~, which is not shown in the int~rests of -:
clari~y. As will be later described in detail, the device
lO is designed to use ~riction be~we~n the device lO and .
webbing I2 to absorb the kinetic energy of a falling body
so that the maximum energy or ~orce applied to the body is
less than a predetermined threshold~
The device 10 consists of a first plate 1-6 having a
recessed channel 18 therein ~or receiving a double
thickn-ss (2 layers laa, 12b~ o~ webbing l~ and a front
plate 20 which is sized and proportioned to mate with the
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WO 92/13601 ~ '3 PCI`/GB92/00223
-- 8 -- .
rear plate 16 to securely compress ~he webbing layers l~a~ -
12b into the recess 18. ~he ~ront plate 20, when fitted
to ~he rear plate, resul~s in the recess :L8 being ~ormed
into a slot which extends the length of ~e energy
absorbing device.
The front plate 20 of the Pnergy absorbing device has
a perpendicular slot 22 disposed ther~in 'i30 that the
exterior of the device communica~e~ wi~h the internal slot
18. The wid~h o~ the slot 22 i5 proportioned a~d
dimensioned so that a loop 24 o~ fabric webbing can be
pulled therethrough as shown in Figs. 1 and 2.
Re~erence is now made to Fig. 3 of ~he drawi~gs which
is an enlarged longitudinal sectional view through the
energy absorbing device 10 when ~i~ted with the lanyard of
webbing 12. It will be appreciated that the internal ~lot
18 is proportioned so that the lanyard webbing 12a, 12b ~.
is compressed in ~he channel. The ~pacing between the ~ ~ .
walls ~5 and 26 defining the slot 22, ici the ~ame or
slightly more than a thickn~ss of 2 layers of webbing 12a,
12b superimposed ~o that the webbing is, at the most~ only
slightly compressed so ~hat the loop 24 is ess~ntially
freie running in the event of a downward force applied to
webbing 12b although there is a tight-fitting relationship
betwe~n the webbing 12a, 12b and the lo~gitudi~al slot
18. It will be appreciated that walls 25 and 26 are
carefully dimensioned and pro~iled as will b~ explained so
as to provide the desired frictional e*~ect between the
WO 92/13601 PCT/GB92~00223
_ g
energy absorbins device 10 and the la~yard 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 de~ice will now be descri~ed with
reference to Figs. 1-3 and also with reference to Fig. 4
o~ the drawin~s. As best ~een in Fig. 4, in the event of
a fall, the force applied to the body inc:reases to a force
Fl as the lanyard 12 has just gone taut; this is about a
load o~ 2kN. At time tl t2, primary ~lippage 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 :-
e~fect is to increase the force F to a peak F2, at time t3 .
where secondary slippage takes place with conseguential
frictional losses between the webbing downside 12~ and
webbing upside 12a, as ~he webbing moves between
compression plate 16 and 18, and be~ween the webbing 12
and the eye 28 of the hook or karabiner 14. This
sequence of events ensure~ that the fall of the work
person is first acted upon by ~hQ relatively low force, F
which aids alignment or orientation of the harness wearer . ~
in readiness ~or the later ~orce F2 which brin~s abou~ the .
arrestment of the wor~ person at a controllnd force. The
design of the energy absorbing d2vice 10 and choice o~
la~yard used resul~s in the struc~ure in this embodiment . .
i~posing a peak secondary force of less than 6kN on the :
work person, t~uc co-plying with tbe propo~d ~uropesn
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WO 92/13601 ~ 3 ~ ~ PCr/GB9t/00223
-- 10 -- _
safety standard in draft prEN 355.
Reference is now made to Fig. 5 of the drawings which
depicts a furt:her embodiment of an energy a~sorbing device
3 0 . In this case, the lanyard is a rope .32 which has a
free loop 34 which pass~s through a side aperture 36 as
shown. The rope 32 has an upwardly mova~le lerlgth 32a and
a downwardly mo~able length 32b of which :Loop 34 is part.
The rope is compressed b~tween plates 38,40 which de~ine a
channel 42 and the device 30 works in the same way as t:hat
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 ~irst cast aluminium body poxtion
52 with an integral eye or hook 54 and which has a
recessed portion 56 ~or receiving a cast alumini~m webbing
compression plate 58 (Fig. 6c) to define a longitudinal
slot 60 for receiving lanyard webbing 62 a~ will b~ later
described in detail. The webbiny 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 stepp~d so that the plate 58
abuts shoulders 64 and the plate 58 ls fastened to the
body portion 52 by means of 6 capscrews ~not ~hown) which
fit into the capscr~w recesses 66. In this embodiment
the eye or ~ook 54 is integral with the body portion ~2
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/q~H 1993
and also has a circular integral cross-bar 68, the
crossbar 68 and the wall 70 of the body portion 52
together defining a transverse slot 72 through which a
loop 74 of fabric webbing can be pulled therethrouyh as
shown in Fig. 6a. It will be appreci~ted 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 which
replaces eye 28 as shown in Figs. 1 and 2. As with the
device described in the first em~odiment, the slots 60 and
72 are dimensioned and proportioned to re~eive 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 p~sses 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 ~orce
being applied to the webbing 62b (Fig. 6a).
Operation of the device 50 will now be described with
re~erence to Figs. 6a, b and c and Fig. 4. In the event
o~ a fall, the force applied to the body increases to F
as webblng 62 goes taut, ~or a load of about 2~N~ At
time tl - t2 p~imary slippage o~ webbing 62b takes place
by the free loop 74 being drawn into the device hetween
body portion 52 and front compression plate 58. At time
t2, the "free loop" is taken up and the force on the body
increase~ to a p~ak F2 at t3. At this time secondary
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~71!03~88 P~T/6B9 2 t 0~223
~ 23 MAR~ 1993
- 12
slippage occurs wi~h 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 embodlments to comply with the proposed
draft European Safety Standard prEN 355. An advantage of
this embodiment is that the body portion can be cast S~ith
an integral eye or hook minimising components and
assembly. Another advantage of this embodiment is that
the friction round the integral crossbar 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 forme~ by
a U-shaped forging secured to upstanding lugs of body `
porti~n 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 num~rals denote like parts except with the
suf~ix 'a' added, except that internal sur~aces 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
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~103.~ 2~ MAR~ 1993
that of Fig. 7. An advantage of the devices shown in
Figs. 7 and 8 is that a single castin~ can be used (then
milled for Fig. 8) so minimising stock and the maximum
reaction ~orces are taken between the upper surface of the
cross-bars 84, 84a and the underside of the forged
U-shaped hook 80,8Oa.
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 al~ays
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 o~ the webbing and khe energy
absorbing device, the degree o~ 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
a}so the shape of the walls or surfaces defining the
aperture. In addition, the surface texture of the slots
or parts in contac~ with the moving webbing will affect
the friction. Because t~e energy absorption
characteristics of ~he device are affected by all these
factors, it i8 possible, therefore, to design the ener~y
: :absorption device so as to produce 2 particular load-time
; profile with a particular lanyard in the event of a fall
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~092/1~01 ~ 14 - PCT/GB92/00~23 _
occurring.
It will also be appreciated ~hat various
modifications may be made to the device~ hereinbefore
described without departing ~rom the scope of the
invention. The device could be used as a back-up Oll a
crane so that in the event of ~ailure ~f the lifting
tackle or rapid arrest o~ the crane, the ~nergy absorption
device is actuated ~o con~rol the ~orce applied to ~he
payload being moved by the crane~ In addition, although
only one free loop is shown, two or more apertures can ~e
provided to provide two or ~ore free loops to produce a
particular load-time profile.
In addition, although the compression plate is
ceparate and ~hown fastened to th~ back face with screws,
it will be appreci~ted thak, o~ course, this could be
hinged to ~acilitate ease of ~ixing around the webbi.ng or
rope when used as the lanyard. It will be appreciated
that the external shape of the energy absorbing device i~
not critical. Although generally box-shaped in the
e~bodiments, it will be appreciated that this hape 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 o~ .
each aperture may be adjustable to accom~odate different ::
webbing thicknesses and to control the friction between ~ :
the loop and th~ device. Further, ~he device may be
provided as a separate accessory for use in c~njunction
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W092/1~01 l5 ~ PCT/GB92/~223
with a conventional harness. Also, as ~he operation of
the device is ~ot dependent on orientation, the device may
b~ 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.
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