Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Applicants: Lennart Holgersson and Berne Mahl
Title of the invention: Ladder
The present invention relates to a ladder which is designed as a so-called
ladder set with several different sections which may be interconnected to
one another such -that the effective length of the ladder may be varied. The
ladder according to the invention is, furthermore, manufactured of profiled
material and is designed in such a manner that, in the unassembled state,
it may be distributed and sold for assembly at the site of use.
The art abounds in different types of ladder sets manufactured of aluminium
profiles. These prior art ladders are, however, manufactured and assembled
at one and the same place, rivet connections being often used to connect
the different co~ponents which make up the ladder. This entails that the
ladder must be transported in the fully assembled state which, because of
the bulky nature of the ladder, is an expensive matter in itself and which,
moreover, entails that a purchaser of the ladder must pay for the assembly
work even though he himself would perhaps have preferred to carry out this
work. In the handling and use of a ladder in such a manner that the ladder
is subjected to oblique loading, extremely high demands are placed on the
points of connection oF the ladder. This applies not only to connections
between the different sections of the ladder but also between the different
fittings which form part of a ladder section. Thus, for example, older
ladders in which the different ladder sections are interconnected to one
another by means of catches may be experienced as highly unstable in many
situations. Furthermore, it is not entirely possible that such a ladder may
inadvertently come apart even under loading.
One form of loading which is particularly difficult to deal with in a
satisfactory manner is rotation of the ladder about its longitudinal axis.
Such loading occurrences may arise if, for example, the ladder is placed
on uneven ground, if the one upright of the ladder sinks into the ground or
if the ladder is placed with its uppermost rung resting against a corner,
a narrow tree or the like so that the support area will be asymmetrically
located. In such oblique loading, the joint between the different ladder
sections will, naturally, be subjected to extreme loading, but an even more
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serious problem is the twisting load or torsion which occurs in the rungs
themselves and in their anchorage in the uprights. Since deformation of
the ladder rungs and their anchorages is slight but the forces that much
greater, this will entail, in particular if the material of which -the ladder
is manufactured consists of an easily-deformable aluminium material, that
extremely great care must be devoted to these details. If, for example,
the ladder is joined together by rivet connec-tions, the ex-treme loadings
which occur more or less as point loading in these rivet connections will
rapidly deform the rivet connections so that play occurs whereby the ladder
will feel completely unstable. As a rule, it is not possible to subsequently
adjust or reset the rivet connections.
The object of the present invention is to realize a so-called ladder set
which may be manufactured as an easily-assemblable kit and which, in the
assembled state, possesses very good resis-tant forces to the extreme loadings
to which the ladder is often subjected when in use.
This object is achieved according to the invention by means of a ladder of
the type intimated by way of introduction which, in each section, comprises
two uprights and a number of rungs fixedly mountable therein, both the up-
rights and the rungs being designed of profiled material and the uprights
having a longitudinal, substantially enclosed, channel portion, and a
longitudinal projection member so tha-t the projection members on one ladder
section are torsionally rigidly disposable as longitudinally shiftable in
the channels of another ladder section, if the ladder according to the present
invention is characterized in that the cross-section of the rungs has an
enclosed profile, that each end of the rungs has at least one projection
which, on assembly of the ladder, is torsionally rigidly fixable in a recess
in the upright, and that the rung is urgable against the upright by means
of anchorage members discrete from the projections.
In one practical embodiment, the ladder according to the present invention
is suitably characterized in that the rungs possess non-rotational symmetric
cross-sectional profile and that the projection and anchorage members are
disposed on opposing sides thereof.
A particularly simple and advantageous embodiment of the present invention
will be attained if the ladder is characterized in that the projection consists
of a portion of the wall material of the rung projecting beyond the end
surface of the rung.
In order to eliminate play between di-fferent ladder sections, and in order
to improve the slide running therebe-tween, the ladder is also suitably
charac-teri~ed in that interconnec-ted ladder sections are in guiding
engagement with one another by the intermediary of a number of longitudinal
guiding ribs, preferably disposecl interiorly in -the channels.
The nature of the present invention ancl its apsects will be more readily
understood from the following brief description of the accompanying drawings,
and discussion relating thereto.
In the accompanying drawings:
Fig. 1 shows, from beneath, a portion of two mutually interconnected ladder
sections; and
Fig. 2 illustrates an end por-tion of a rung.
It will be apparent to the skilled reader of Fig. 1 that -two of the side
pieces, or uprights, in two mutually interconnected ladder sections are
designated 1 on the drawings, whereas the rungs fixed -to the side pieces
are designated 2. Thus, the drawing figure shows adetailed view of two ladders
seen from beneath.
It is further apparent from Fig. 1 that the side pieces are manufactured of
profiled material, preferably aluminium profiles which have U-shaped cross-
section and which, on the one free shank, have two projections 3 and, on the
other free shank, a bent-over portion 4 which forms an as good as enclosed
channel. It will moreover be apparent from the figure tha-t the projections
3 on the one side piece may be accommodated in the channel 4 of the other
side piece, the one shank of the profiled material of the side piece ex-tending
in through the opening 5 in the channel on the adjacen-t side piece. When the
side pieces are interconnected with one another in this manner, they are
freely shiftable in the longitudinal direction, at the same time as the webs
6 in the profiled ,naterial of the side pieces lie in a plane with one another.
This entails that the ladder sections may be identically designed and inter-
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connectable with one another, for which reason a ladder design~d accordingto the present invention may be built up from a number of identical
sections without it being necessary to distinguish between a top section,
central section or foot section or the like.
The interior dimensions of the channels 4 are adapted in such a manner that
the projections 3 and the adjacent portion of the one shank 7 may, along
their major extent~ be accommodated in the channel 4 with relatively large
play, in other words in such a manner that, for example, sand, gravel or
other foreign matter will not cause seizure or in any other way prevent
the relative shifting between mutually cooperatiny aluminium parts on two
interconnected ladder sections.- In order that the ladder not feel unstable
while in use, it is, however, important that cooperation between the side
pieces be such that no play can occur in practice and, moreover, such that
torsion about the longitudinal axis of the ladder efficiently be trans-
mitted from the one ladder section to the other. For this reason, the
.side pieces are provided with a number of guide ribs, also referred to as
"protrusions" of which two guide ribs 8 are placed on the outer side of the
second shank 9 of the side piece. Hence, the guide ribs 8 are placed so as
to face towards the interior of the profied channel 4. Furthermore, the
profiled channel is interiorly provided with two opposingly directed guide
ribs 10 and 17 which are intended to laterally guide the ladder sections
in relation to one another.
Naturally, it would also be possible to place all of the guide ribs on the
first shank 7 of the profiled material of the side pieces and instead render
the second shank 9 and the channel 4 interiorly smooth. The essential
factor is merely that the side pieces possess fully acceptable guiding in
relation to one another, at the same time as there must be space to allow
for the departure of foreign matter without causing damage or without
possibly causing the side pieces to jam in their relative movements.
As has been intimated above, a ladder of this current type is exposed to
great, and many times composite loads while in use. The single loadings
which affect the ladder symmetrically may be exemplified by a bending of
the ladder as a whole, the bending plane lying parallel to the webs 6 of
the side pieces. Loadings of this single type need not be dealt with further~
since they hardly cause problems of any magnitude. If, on the other hand,
the ladder is obliquely loaded, for example in that one side piece sinks
down into the ground on which it is resting or if the ladder i5 placed with
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its upper end against a building corner or a narrow tree, loading phenomena
which are much more difficult to appreciate will occur. Particularly
difficult loadings occur in such situations int al in that the ladder is
exposed to rotation about its longitudinal axis. This twisting or rotation
is transmitted to the rungs by the intermediary of the joints between
the rungs and the side pieces, acting then in the form of a torsion loading.
For this reason, it is vital, on the one hand, that the proFile of the rung
be of such design that it is torsionally rigid and, on the o-ther hand, that
the joint between the rung and the side pieces be capable of transmitting
the torsional forces which occur. The situation will be particularly
troublesome if one takes into account the fact that the subject matter of
the present invention is designed so as to be assembled at the site of use,
in other words to be manufactured and sold in the form of a kit which cannot
be joined together by, for example, welding. Furthermore9 such material
properties as the softness of the aluminium material entail serious problems,
since, on oblique loading of the ladder, extremely great local loadings
easily occur which readily deform the material permanently, giving rise to
play and a consequential instability of the ladder.
According -to the present invention, the rungs 2 are manufactured in the
form of profiled rods which preferably may be extruded. The cross-section
of these profiled rods is designed so as -to impar-t to the rung great load-
absorption capacity in the vertical direction, at the same time as the rung
must be able to withstand great torsional loadings.
The cross-sectional configuration of the rung illustrated in Fig 2 has been
conceived taking into account the above-mentioned factors. Thus, the rung
according to this drawing figure has two vertical and opposing side walls 11
which permit the accommodation and absorption of large vertical loadings. In
order to reduce the risk of slip, but also in order to render the rung safer
and easier to stand on, the upper face 12 of the rung is substantially planar
- and fluted in its surface structure. In the corner regions between the
side-walls 11 and the upper face 12, screw pockets 13 are provided for
accommodating screws which are intended for joining together the rungs and
the side pieces. Furthermore, the rung 2 has a subs-tantially planar underface
14 whereby the cross-section of the rung will be fully enclosed.The presence
of the planar underface 14 entails that it is easy, by simple machining,
to realize a projecting tongue 15 which extends throughout the entire width
of the underface of the rung.
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On mounting of the rungs 2 in the side pieces, openings made pairwise in
the side pieces corresponding to the screw pockets 13 are used so that
screws 15'may be passed there-through. However, a screw connection is not
sufficient to impart to the ladder its requisite stability, in particular
not as regards the torsional loadings which rest upon the rungs. For this
reason, the tongue 15 in the underface 14 of the rung is also employed
for assembly purposes. Consequently, openings are also provided in the
web 6 of the side pieces 1, apart from the openings for the screws 16,
for the tongues 15, these openings being designed for tight fit with the
tongues.
As was mentioned above, the rung 2 is of completely enclosed cross-
sectional configura-tion, which greatly increases its capacity to withstand
torsional loadings. Furthermore, the anchorage points between the rungs 2
and the side pieces are placed in such great spaced apart relationship to
one another as is possible, so as thereby to reduce the effect of those
loadings which occur in the joint regions. Cooperation between the tongue
15 and the corresponding opening in the web 6 of the side piece is also
of particular importance in this context, whereby the torsion-transmitting
capacity of the joint will be increased and the cross-sectional configuration
of the rung will be locked in such a manner that it is highly unlikely that
any alteration of the cross-sectional configuration can occur under extreme
loading conditions.
The described method of joining the rung and side pieces involves greatadvantages partly because assembly may simply and readily be effected
without access to particular tools directly at the site of use of the
ladder. Furthermore, the described joint makes for a high degree of strength
in particular under severe loading situations. Finally, it is also possible
to reset and realign the joints if the ladder were to be damaged as the
result of some form of overloading. Such resetting and realignment of the
anchorage points of the ladder rungs can hardly be carried out to a ladder
having permanent fixation, in particular not if it is manufactured by
folding or riveting.
The invention may be modified without departing from the spirit and scope
of the appended claims. Hence, it is possible to use rungs of a slightly
different cross-sectional configuration than that shown in Fig 2. For
example, such a cross-sectional configuration of the rung could have
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substantially straight lower portions of the side-walls 11, these lower
portions being provided with tongues corresponding to the tongue 15.
Naturally, it is also possible to place projecting tongues at the end of
the rungs at other and, possibly, more places than has been suggested
above; but the considerable weakening which would occur in the web 16 of
the side pieces must, however, be taken into account if far too many and
far too large projections are employed.
