Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02557985 2013-01-22
FALL ARREST SYSTEM WITH A DEFORMABLE LINK
The present invention relates a mobile mount for attachment of a fall
arrest system.
BACKGROUND OF THE INVENTION
Fall protection of operators working in a situation where a fall can take
place over a sufficient distance to cause injury or death is becoming
generally
required in most industries. Many arrangements are provided for mounting an
anchor post on a structure adjacent the worker so that a personal fall arrest
system
can be attached to the anchor.
Such personal fall arrests systems include a harness together with a
cable system for attachment to the harness and to a suitable anchor where the
cable
system can be paid out to allow the worker to move to a required location but
the
cable system arrests any fall within a short distance. Such devices are well
known
and commercially available and many different designs have been proposed.
In most cases the structure itself provides or has attached a suitable
anchoring post so that the relatively high loading necessary can be readily
provided
by a simple post rigidly attached to the structure.
In the interior buildings, such anchors can be mounted on a rail which
allows the anchor to slide longitudinally along a track attached to the rail.
However some structures are unsuitable for attachment of an anchor
post or have been designed without the possibility of attachment of an anchor
post
so that operators in this environment are often unprotected against fall. In a
particular area where this is problematic is in that related to aircraft where
aircraft
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design does not lead to the suitability of attachment of mounting posts. Up
until now,
therefore, operators working in this environment have remained unprotected
with the
potential of serious injury or death.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided an apparatus
comprising:
a base carried on ground wheels for movement over a ground surface to
an elevated structure on which one or more persons is intended to work;
a ladder upstanding from the base to an elevated position above the base;
the upstanding ladder being adjustable in height relative to the base;
the upstanding ladder including two side rails and transverse rungs such
that said one or more persons can climb the ladder to the elevated structure;
at least one of the side rails of the ladder having mounted thereon a
tubular receptacle;
a post member mounted in the tubular receptacle and shaped and
arranged so as to extend upwardly from the receptacle, wherein the tubular
receptacle
is vertical and the post member includes a vertical post portion and an arm
extending
from the post portion;
a deformable link between the post portion and the arm, the deformable
link comprising a longitudinal member having opposite ends spaced apart by a
first
distance along a longitudinal axis, said deformable link comprising at least
one slot
transverse to the longitudinal axis, said deformable link extending between a
first
connection point on the post portion and a second connection point on the arm
thereby
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2a
supporting the arm on the post portion, the deformable link being adapted to
bend if the
load exceeds the load limit of the apparatus thereby visually indicating
overloading of
the apparatus, the arm being arranged to move during bending of the deformable
link
such that the distance between the ends of the deformable link is decreased;
and at least one support member at an end of the arm remote from the
tubular receptacle for attachment to and loading from a personal fall arrest
system for
attachment to said one or more persons.
Preferably each of the side rails includes a respective tubular receptacle
and a respective post member and wherein the two support member
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each carried on a respective one of the post members and each for receiving
the
personal fall arrest system of a respective one of two separate persons.
Preferably the support members are arranged and mounted on the
ladder so as to allow side to side movernent of the support member relative to
the
6 base.
Preferably the base includes a hitch by which the base can be moved
to the elevated structure by a towing vehicle.
Preferably there is provided a platform at a top of the ladder extending
from the top of the ladder outwardly over the base.
Preferably the post member and the support member are arranged
such that the support member is cantilevered generally over a mid Ilne of the
base.
Preferably the or each support member comprises a loop for receiving
a hook of the personal fall arrest system.
Preferably the post member is inclined forwardly of an upper end of the
side rail to cantilever the support member in front of the ladder.
Preferably there is provided a platform between rails at the top of the
ladder for the person to step onto the elevated structure.
Preferably the tubular receptacle allows adjustment of the post
member relative to the side rail of the ladder.
Preferably the tubular receptacle allows height adjustment of the post
member relative to the side rail of the ladder.
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Preferably the post member is inclined upwardly, forwardly from the
respective rail and outwardly to one side of the respective side rail away
from the
other of the side rails.
Preferably the tubular receptacle is vertical and the post member
includes a vertical post portion and an arm extending from the post portion to
the
support member.
Preferably there Is provided a deformable link between the post portion
and the arm, the deformable link comprising a longitudinal member having
opposite
ends spaced apart by a first distance, said deformable link extending between
the
first and second connection points, thereby supporting the arm on the post
portion;
the deformable link being adapted to bend if the load exceeds the load limit
of the
apparatus thereby visually indicating overloading of the apparatus; and the
arm
being arranged to move during bending of the deformable link such that the
distance
between the ends of the deformable link is decreased.
Preferably the load is supported on the arm at a loading point distally
spaced from the post.
Preferably the deformable link further comprises a plurality of slots
spaced along the deformable link between the opposite ends thereof, said slots
extending into said deformable link from a first side thereof.
Preferably the deformable link comprises a U-shaped cross section
defining a central portion separating two spaced apart side portions, said
side
portions extending from the central portion toward the first side of the
deformable
link such that the plurality of slots are spaced along and extend into each of
said
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side portions.
Preferably the slots in the side portions of the longitudinal member do
not extend to the central section thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
5 One
embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
Figure 1 is an isometric view of a first embodiment which is the subject
of Application Serial No. 10/841,838 filed May 10th 2004 which is now issued
as US
Patent 7,740,106.
Figure 2 is an isometric view of a first embodiment according to the
present invention.
Figure 3 is an isometric view of a modified version of the embodiment
of Figure 2 incorporating two of the components of Figure 2 connected
together.
Figure 4 is an isometric view of a second embodiment according to the
present invention which is similar to that of Figure 2 but includes a number
of
modifications.
Figure 5 is a side elevational view of the embodiment of Figure 4.
Figure 6 is an isometric view of a davit used in the embodiment of
Figures 4 and 5.
Figure 7 is an isometric view of the deformable link used in the davit of
Figure 6 of the embodiment of Figures 4 and 5.
Figure 8 is a cross-sectional view of the deformable link of Figure 7.
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Figure 9 is a plan view of a metal panel to be bent to form the
deformable link of Figure 7.
DETAILED DESCRIPTION
In Figure 1 is shown a first embodiment according to the present
invention which includes a base 10 and a support 11 for supporting anchors or
receptacles 12 and 13 at a raised position above the base.
The base comprises a pair of side rails 14 and 14A extending forwarding
from a rear frame structure 15. At the outer end of each side rail is provided
a
ground engaging wheel 16 for rolling over the ground supporting the base.
The frame 15 comprises a pair of rails 17 and 18 which are parallel
and generally at right angles to the side rails 14 and 14A. The rails 17 and
18 are
parallel and interconnected by a number of cross members 19 which hold the
rails
parallel. The rails 14 and 14A are attached to respective ends of the rails 17
and 18
so as to form a rigid structure. Some of the cross members 19 extend outwardly
beyond the rails 17 and 18 and provide a support for a ground wheel 20 which
co-
operates with a ground wheel 16 in supporting the base for movement across the
ground. The number of ground wheels and arrangement of ground wheels depends
upon the weight to be supported and the type of ground wheel to be used. The
base
provides a relatively wide area for support over the ground to prevent
toppling of the
structure when load is applied.
At opposite ends of the frame 15 is provided a pair of upstanding posts
22 and 23 which form a part of the support 11. The upstanding posts are formed
in
two sections including upper portions 22A and 23A which are slidable
vertically
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relative to the lower portions 22B and 23B. Suitable mounting using bearings
can be
provided between the portions to allow the vertical sliding movement required
to
elevate the upper section relative to the lower section, A cross member 24
connects
the upper end of the lower portions 22B and 23B to retain the structure rigid.
A
similar cross member 25 is provided across the top of the upper portions 22A
and
23A to maintain the upper section rigid. The upper section is raised relative
to the
lower section by chains 26 and 26A carried on lower pulleys 27 and 28
respectively
operated by manually rotatable handle 29 attached to a shaft 30. The shaft 30
extends between the two pulleys 27 and 28 so the rotation of the handle 29
pulls the
chains 26 and 26A over an upper pulley 31, 32 respectively at the top of the
respective posts portions 22B and 23B so as to pull on the lower end of the
upper
portions 22A and 23A pulling them upwardly along the slide mounting indicated
at
34.
Thus the upright portion of the support 11 defined by the posts and the
cross members can be raised and lowered to a required height. At the top of
the
upper portion of the posts is provided a cantilever arm section generally
indicated at
35 forming part of the support 11. The cantilever arm structure comprises a
rail 36
parallel to the cross beams 25 and 24 and cantilevered outwardly therefrom on
support rails 37, 38, 39 and 40. The rails 38 and 40 form a brace at an angle
to the
rails 37 and 39 thus maintaining the rail 36 at a position approximately
midway
across the base from the frame 15 towards the wheels 16.
The rail 36 is formed by a structural tube together with a transport track
attached to the underside of the structural tube so the track carries a pair
of trolleys
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41 and 42 which can slide along the track 43 independently of one another.
Each
trolley carries a respective one of the anchors 12, 13.
Thus the apparatus shown in Figure 1 can be wheeled to a required
location at an elevated structure with the rail 36 supported at a position
above the
6
elevated structure by any necessary adjustment of the height of the support.
The
location of the rail 36 over the elevated structure can be obtained by moving
the
base on the wheels to the required position relative to the elevated
structure. The
arrangement as shown is particularly suitable for location over the wing of an
aircraft
with the rail 36 at a position approximately head height above the operator
standing
on the wing. Thus the base is located under the wing with the rail 36 above
the
wing.
The structure is designed and arranged to provide sufficient loading so
that the anchors can receive the full force obtained by an operator falling
from the
elevated structure.
In practice it has been determined that the necessary loading which
the anchor must accommodate is of the order of 1800 lbs. for a single operator
and
either 2000 lbs. or 3000 lbs. for two operators depending upon the
jurisdiction where
the standards are in force. Thus the anchor is not merely an anchor location
but
must provide sufficient strength so that the fall of a heavy operator
potentially
carrying heavy equipment and the impact of that fall on the personal fall
arrest
system can be applied to the anchor and through the anchor to the ground
without
damaging the structure or allowing the operator to fall beyond the intended
position
arrested by the fall arrest system.
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Turning now to Figure 2, an alternative embodiment is shown including
a base 100 and a support 111 for anchors 112 and 113. In this embodiment the
base 100 is formed by cross beams 101 and 102 carrying ground wheels 103
together with longitudinal rails 104 and 105. The wheels are suitable castor
wheels
or may alternatively be driven wheels for moving the base by powered
operation.
In this embodiment the support 111 is in the form of a ladder structure
114 with side rails 115 and 116 together with transverse rungs 117 and an
upper
platform 118. The ladder structure is again formed in two pieces with an upper
part
120 which can be raised relative to a lower part 121 by actuation of a
manually
operable chain lifting system 124. Thus the upper parts of the rails of the
ladder can
slide upwardly to raise the platform 118 and the anchors 112 and 113 to a
required
height above an elevated structure to operated on, The lower part of the
ladder is
rigidly attached to the cross beam 102 and is supported by braces 125 and 126
extending downwardly to the longitudinal rails 104 and 105. The lower end of
the
braces is attached to slide members 127 which can move longitudinally along
the
respective rails 104, 105 and carry a cross beam 128 which has stabilizing
legs 129
at each end. The stabilizing legs can be moved down into engagement with the
ground so as to transfer some loading from the base from the wheels to the
legs to
maintain the base at a required location.
At the upper end of the rails 115 and 116 of the ladder is provided
tubular receptacles 130, 131 for a pair of davits each defined by a curved
post 132
and 133 respectively which extends upwardly from the receptacle and forwardly
beyond the end of the upper part of the ladder to the upper anchor 112, 113
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respectively. Thus the anchors are cantilevered forwardly beyond the end of
the
ladder by the curvature of the posts 132 and 133. Thus again the anchors 112
and
113 are located approximately over the midline of the base and a cantilevered
structure with the base located underneath the structure. Again this
arrangement is
5 particularly suitable for the wing of an aircraft where the base can be
moved to a
position beneath the wing with the platform moved up to the end of the wing
and the
anchors 112 and 113 located over the wing for the operator to transfer from
the
platform onto the wing for operations on the aircraft.
In Figure 3 is shown an alternative arrangement which utilizes basically
40 the structure of Figure 2 arranged in a pair of such structures
connected together by
cross members 140 and 141. Thus each base 100 and each support 111 is
provided at a position spaced transversely of the base frames and connected
together at spaced positions by the rails 140 and 141. At the top of the
curved posts
132 and 133 is provided a transverse rail 136 similar to the rail 36 which
carries a
track 137 and trolleys 138. Each trolley is attached to a personal safety
arrest
system generally indicated at 145. Thus the basic system shown in Figure 3 can
be
modified to provide an elongated structure defining an elongated protection
system
along the full extent of the rail 136, which may be up to 30 feet in length,
so that a
number of operators can be properly protected by personal fall arrest systems
slidable along the rail 136 in its track 137. The rail 136 can be removed from
the
posts 132 and 133 and the base 100 can be separated to provide two separate
elements which can be used independently. The base structure in Figure 3 is
slightly different in construction from that shown in Figure 2 in that the
side rails
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extend at an angle outwardly and the wheels are attached to the ends of the
side
rails rather than to the ends of the cross rail 101 as shown in Figure Z. It
will be
appreciated that different forms of base structure be designed with the
intention that
the structure merely provides sufficient ground engagement area to accommodate
any side loads which occur as an operator falls to prevent the system from
toppling
and to maintain the rail 136 at its elevated position despite any direction of
fall of one
or more operators from the elevated structure.
The structure shown in Figure 1 can also be extended by providing
additional posts and increasing the length of the rails 24, 25 and 36. Thus
for
example the basic rail 36 may be of the order of 20 ft. which should be
increased to
30 ft. by providing an additional post to provide three such posts in a row.
Figures 4 and 5 show isometric and side views respectively of the
embodiment of Figure 2. It will be noted that additional side panels 145 and
146 are
added in Figure 4 on the sides of the platform 118 to inhibit falling by the
user.
These can be attached to suitable mounting brackets 147 on the rails 115 and
116.
The side rails and the platform can be extended by sliding an outer part
inwardly and
outwardly relative to an inner part.
The davits of Figure 2 which include the curved post construction are
replaced in Figure 4 by an alternative form of the davit which is shown in
Figure 6.
This includes an upright post 232 and an arm 238 supported by a deformable
link
210.
Figure 6 illustrates the davit assembly 150 featuring the first
embodiment of a deformable link or overload indicator 210 as described
hereinafter.
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In this particular assembly 150, the first member consists of a vertically
arranged
post 232 having a pair of side plates 234 attached at points 233 and 235 by
means
of bolting arrangements including bolts, washers and nuts. The plates 234
extend
vertically upward from the post 232 to an upper end 237. The second member in
the
davit assembly 150 is a longitudinal support member or arm 238 extending
upward
and out to one side of the post 232 and side plates 234. The support member
238 is
connected to the side plates 234 at an attachment point 236 near the upper end
237
of the plates by a bolting arrangement that will resist moments about that
point. The
support member 238 is arranged to support a load (not shown) at a loading
point
242 near a distal end 243 opposite the plates 234 and post 232 by means of a U-
bracket 244 which forms the support 112 or 113.
The overload indicator 210 is mounted between the support member
238 and the side plates 234 such that the side 223 from which slots 224 extend
into
the indicator 210, as described in more detail hereinafter, face upward toward
the
support member 238 and side plates 234. The overload indicator 210 is attached
to
the side plates 234 at a first connection point 241 by bolting arrangements
including
appropriate spacers. The indicator 210 is attached to the support member 238
at a
second connection point 245 on brackets 240 provided on the support member
238,
again by bolting arrangements.
The post 232 is mounted in the tubular support or sleeve 130 as a
sliding fit such that the post can be rotated relative to the sleeve and can
be adjusted
in height relative to the sleeve 130.
The post includes holes 251 and 252 which cooperate with selected
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holes in the sleeve so as to set a selected height and orientation of the post
in the
sleeve. When the post is at a raised height the top of the post is
approximately at a
height of 6 feet from the platform and the support arm 238 extends upwardly at
an
inclined angle to the horizontal from the top of the post to a height of the
order of 8
feet which is above the head of the user. In this way the safety fall arrest
system is
located above head height. However it will be noted that the arms extend
upwardly
and outwardly away from the platform 118 so that the arms do not extend over
the
platform but are at all times maintained to one side of the platform. The arms
thus
are arranged at an angle to one another inclined outwardly away from one
another,
This directs the arm along the elevated structure to which the platform meets
away
from the platform allowing the user to walk along the elevated structure away
from
the platform when exiting from the platform. Also the height adjustment of the
post
in the sleeve allows the post and the arm to be lowered to a reduced height in
which
the outer end of the arm is below head height. In this way the platform can be
brought up to the underside of an elevated structure and the operator can
reach up
to the elevated structure from the plafform without the danger of the arm
impacting
on the structure and casing damage thereto. The post can of course also be
fully
removed from the sleeve as shown in Figure 6 allowing the ladder and platform
to be
used without the davit.
The supports 112 and 113 are directly attached to the end of the
support arms 238 and there is no safety rail which extends horizontally from
the end
of the support arm above and over the platform.
The deformable link 210 is shown in Figure 7. The overload indicator
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210 is made of a longitudinal member 212 having a U-shaped cross section as
shown in Figure 8. The U-shaped member 212 has a central portion 218 extending
perpendicularly between parallel side portions 220. Between opposite ends 214
and
216, the longitudinal member 212 has a series of slots 224 extending from a
side
223 opposite the central portion 218 toward the central portion 218 in each
side
portion 220. These slots 224 define teeth 222, each of which is positioned
between
two adjacent slots 224. At each of the ends 214 and 216, there is provided a
pair of
holes for mounting the deformable link on an appropriate load supporting
apparatus.
A hole 228 is provided through each side portion 220 at each of the ends 214
and 216
for use as a connection point by means of which the deformable link 210 can be
installed for use in a load supporting apparatus.
The absence of material in the side portions 220 created by the slots
224 weakens the ability of these side portions 220 to resist compression
loading
along a longitudinal axis of the deformable link 210. The central portion 218
however, remains intact as a solid piece having and thus has a greater
strength than
the side portions 220. As a result, longitudinal loading of the deformable
link 10 will
tend to cause the longitudinal member 212 to bend, or bow, forming a concave
curvature along the side 223 as the slots 224 close and the teeth 222 move
together
such that the deformable link 210 takes on a curved form. With adjacent teeth
222
coming into contact, the strength of the deformable link 210 is increased as
the slots
24 close up. While weakened by the presence of the slots 224, it should be
noted
that the longitudinal member 212 will not bend under any longitudinal loading,
but
rather will only do so under excessive loading in which a predetermined limit
is
CA 02557985 2006-08-23
exceeded. The slot dimensions, slot spacing and longitudinal member material
are
all chosen so as to provide the deformable link 210 with the appropriate
bending
characteristics for use in a specific load supporting apparatus having a
particular
loading limit. The deformable link 210 therefore will only begin to bend when
the
5
apparatus has been loaded beyond the upper limit of its recommended load
range,
thereby indicating to a user that the apparatus has been overloaded.
Figure 9 shows the deformable link at an intermediate stage of its
manufacture. Using dies, a 3/16" steel plate is formed having the two
dimensional
shape shown in the figure. In order to obtain the U-shaped cross section of
the final
10
product, as shown in Figure 8, the side portions 220 are bent 90 degrees along
the
broken lines shown in Figure 9. A series of six slots nearest each of the ends
214
and 216 of each side portion 220 is longer than the slots 224 between the two
series
of each side portion 220. Each tooth 222 is rounded at its outermost edge 225
opposite the central portion 218 between the respective pair of adjacent
slots. Each
15 slot
224 or 226 is tapered moving from the side 223 of the longitudinal member 212
toward the central portion 218, where it is rounded at its end 227, which is
spaced
from the central portion 218. Each corner 229 of the longitudinal member 212
is
also rounded. As described above, the material and dimensions of the
deformable
link 210 can be modified to alter the bending characteristics as needed.
Arranged as described above, the deformable link 210 will bow under
overloading conditions. This bowing or bending action first serves as an
indicator
that the apparatus has been overloaded. As mentioned previously, the davit
assembly 150 is arranged such that the support member 238 from which the load
is
CA 02557985 2006-08-23
le
suspended extends upwardly, defining an angle between the support member 238
and side plates 234 greater than 90 degrees. In such an arrangement, the
deformable link 210 will not act to reduce the effect of overloading on the
other
assembly components unless it is overloaded enough to bend to an extent such
that
the angle between the support member 238 and the side plates 234 is reduced to
90
degrees or less. This is due to the fact that the moment exerted about the
attachment point 236 is greatest when the support member 238 and side plates
234
are at right angles to each other. So preliminary bending causing the angle
between
the support member 238 and the plates 234 to decrease from the original angle
to
90 degrees will only serve to indicate to a user that the apparatus has been
overloaded, while further bending will decrease the magnitude of the moment
created about the attachment point 237 by the load, thereby increasing the
assembly's ability to support it.
The deformable link 210 is designed to undergo bending at loads
exceeding this value such that it takes on the bow shape. This bending or
bowing
action serves to visually indicate to a user that the apparatus has been
overloaded
and prevent damage to members that would otherwise be caused by the excessive
load. When the user sees the deformable link start to bend, he or she can
respond
to the visual feedback by removing the load to prevent further bending and
possible
accidents. In the case where the angle between members is 90 degrees or less
before bending, the deformable link 210 also serves to reduce the effect of
the load
on the apparatus during exposure to overloading. When the deformable link 210
bends as shown, the angle between the members decreases, thereby moving the
=
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17
load closer to the post. This reduces the magnitude of the moment induced
about
the attachment point by the loading of the second member, increasing the
effective
resistance of the fastening means and thereby reducing the likelihood of
further
collapse of the apparatus.
The scope of the claims should not be limited by the preferred embodiments
set forth in the examples, but should be given the broadest interpretation
consistent
with the description as a whole.
