Note: Descriptions are shown in the official language in which they were submitted.
CA 02697299 2010-03-04
WO 2009/029965 PCT/AT2008/000307
Profile shape for a crane jib
The present invention concerns a crane boom for a crane having a longitudinal
axis and a notional contour line extending in a transverse plane relative to
an axis of
symmetry in at least approximately mirror-symmetrical relationship, wherein
the
contour line intersects the axis of symmetry at a first and a second
intersection point
and wherein the contour line has a straight portion whose notional extension
in the
direction of the second intersection point intersects the axis of symmetry and
includes
an acute angle therewith.
Such a crane is shown for example in Figure 13 of EP 583 552 B1.
In practice that crane boom is of a relatively large structural shape and is
thus
severely limited in its usability. For exaniple it is not suitable for the
loading crane
sector.
The object of the invention is to provide an improved crane boom.
That object is attained by a crane boom having the features of claim 1.
It will be appreciated that a real crane arm has both an outside contour and
an
inside contour by virtue of the material thickness of the components forming
it. The
'notional contour line' refers to the outside contour of the crane boom.
The term centroid is used in the context of this disclosure to denote the
center of
gravity of the overall region enclosed by the notional contour line (the dash-
dotted area
in Figure l h). The term 'centroid' is therefore not to be interpreted in
relation to the area
enclosed between the outside and inside contours.
The choice of the configuration of the notional contour line such that the
centroid of the region enclosed by the notional contour line is between the
first
intersection point and the center point provides that there is a free choice
in respect of
the sheet metal thickness of the crane boom enclosed by the notional contour
line, in a
relatively wide material thickness range. Unlike the situation in the state of
the art (for
example EP 583 552 Bi) the position of the zero crossing on the axis of
symmetry (that
position at which the tensile forces prevailing in the upper region of the
crane boom
change into the compression forces prevailing in the lower region of the crane
boom) is
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set not by the selection of the sheet metal thickness but by the configuration
of the
notional contour line. Even with the same sheet metal thickness in all
portions it is
possible by means of the invention to shift the zero crossing into the lower
region of the
crane arm.
Further advantageous embodiments are defined in the appendant claims.
The invention further concerns a jib system for a crane, wherein at least one
jib
and/or jib extension is in the form of a crane boom as set forth in one of
claims 1
through 26. Preferably there are provided between one and twenty, preferably
between
five or ten, jib extensions. It is particularly preferable for more than five
jib extensions
to be provided.
The invention further concerns a crane, in particular a loading crane, having
a
crane boom according to one of the aforementioned embodiments or a jib system
of the
aforementioned kind as well as a utility vehicle equipped with such a crane.
Further advantages and details of the invention will be apparent from the
Figures and the related specific description. In the Figures:
Figure 1 a shows a first embodiment of the notional contour line of a crane
boom according to the invention,
Figures Ib and 1c show the construction of a contour line (Figure lb) and the
corresponding sheet metal structure (Figure 1 c) of an embodiment in which the
arcuate
portion ki is approximated by a polygonal line,
Figure ld shows a jib system having three jib extensions as shown in Figure
lb,
Figure 1 e shows the crane boom of Figures 1 a through 1 c, showing the
position
of the centroid,
Figure 1f shows a jib system having a jib extension, showing the arrangement
of mounting elements,
Figure 1g shows a jib system with a jib extension, wherein the arcuate portion
in the jib and the jib extension was approximated by different polygons,
Figure 1 h shows the crane boom of Figures 1 a through 1 c and 1 e, wherein
that
area to which the centroid relates has been shown in dash-dotted lines
representatively
for all embodiments,
Figure 2 shows a second embodiment of the notional contour line of a crane
boom according to the invention,
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Figure 3 shows a third embodiment of the contour line of a crane boom
according to the invention,
Figure 4 shows a perspective view of a jib system as shown in Figure 1 d, and
Figure 5 shows a utility vehicle with a crane according to the invention.
It will be presupposed that all Figures are true to scale insofar as the
lengths of
the individual contour portions and the illustrated angles are shown in the
correct ratio
to each other. All angle references relate to degrees, so that a full angle
corresponds to
360 degrees. An angle of less than 1/4 full angle is interpreted as an acute
angle. An
angle of greater than 1/4 and less than V2 full angle is interpreted as an
obtuse angle. An
angle equal to '/4 full angle is identified as a right angle.
Figure 1 a shows a first embodiment of the configuration of the notional
contour
line of the crane boom in a transverse plane of the crane boom. In this
respect the term
transverse plane is used to identify a plane through which the longitudinal
axis of the
crane boom passes in orthogonal relationship. All crane booms according to the
invention have an axis of symmetry s which is arranged in the transverse plane
and in
relation to which the contour line of the crane boom extends in the transverse
plane in
at least approximately mirror-image relationship. For the situation where the
crane
boom is of the same cross-sectional shape over a large part of or its entire
longitudinal
extent, that axis of symmetry s represents the straight section line of the
transverse
plane with the plane of symmetry extending along the longitudinal axis (median
plane).
In all embodiments the contour line intersects the axis of symmetry s at first
and second
intersection points SI, S2. The center point M arranged on the axis of
symmetry s
equidistantly relative to the first and second intersection points SI, S2
represents the
position of half the height of the crane boom in the transverse plane.
Starting from the
center point M in the direction of the intersection point S2, that affords a
region of the
crane boom which, in operation, is predominantly subjected to a tensile
loading. The
region of the crane boom, that is between the center point M and the first
intersection
point SI, is substantially subjected to a compression loading in operation.
The configuration of the contour line of the crane boom shown in Figure 1 has
four portions kl, gl, g2, g3 which can be distinguished from each other.
The portion k, which is arranged in the region of the compression loading that
is greatest in operation is of an arcuate configuration since, as is known per
se, that
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cross-sectional shape has reduced compression stresses and involves a
reduction in the
risk of buckling. It is sufficient if that portion is at least approximately
arcuate in the
sense that it can be approximated by a polygon, as is shown in Figures lb and
lc.
Approximation of the arcuate portion kl by a polygon permits easier
manufacture by
folding of the metal sheets forming the crane boom. It will be appreciated
however that
an arcuate configuration can be implemented by means of a rolling operation.
The arcuate portion kl can also be only approximately arcuate in the sense
that
it can be formed for example by one or more ellipse portions of suitably
slight
eccentricity. It would also be possible to envisage a configuration for the
arcuate
portion ki by arranging in joining relationship suitably short straight,
elliptical and/or
arcuate segments.
As shown in Figure 1 it is particularly advantageous if the arcuate portion kl
is
in the form of a quarter-circle arc, that is to say it extends over an angle
of about 90
degrees. It is possible in that way for the large part of the configuration of
the contour
line between the first intersection point S1 and the point M to be produced in
the form
of an arcuate portion kl. The variant shown in Figure 1 is particularly
preferred, in
which the center point of curvature K of the arcuate portion k, is in the
proximity of or
on the axis of symmetry s and the center point of curvature K of the arcuate
portion ki
is between the first intersection point S, and the center point M. Unlike the
situation
shown in Figure 1 the arcuate portion kl can certainly extend as far as the
first
intersection point Si. In that case therefore the entire contour line in the
region of the
intersection point SI and the center point M is in the form of an arcuate
portion kl .
The embodiment shown in Figure 1 is particularly preferred however in which a
third straight portion g3 tangentially adjoins the arcuate portion k, in the
direction of the
first intersection point S1, the third portion g3 including an angle y of less
than 90
degrees with the axis of symmetry s (here the angle y is about 72 degrees).
That affords
good weldability of the crane boom, better suitability for clamping for the
welding
operation by virtue of the portions which meet each other inclinedly and the
possibility
of producing a longitudinal weld seam without additional edge preparation.
Overall that
affords a configuration which is more reliable in terms of process
implementation.
The angle is preferably less than 80 degrees. Preferably the angle y is
greater
than 70 degrees.
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In the Figure 1 embodiment the center point of curvature K of the arcuate
portion kl is disposed directly on the axis of symmetry s between the center
point M
and the first intersection point S1. Unlike the situation shown the center
point of
curvature K can also be arranged displaced somewhat relative to the axis of
symmetry
s. It should however always be in the region between the center point M and
the first
intersection point S1.
The first straight portion gi adjoins the arcuate portion kl in the direction
of the
second intersection point S2 tangentially to the auxiliary circle illustrated
in Figures 1 a
and lb, the first portion gl extending over the large part of the contour
configuration
between the center point M and the second intersection point S2. That straight
configuration which is extended in length in the upper region of the crane
boom and the
resulting narrowing in cross-section forms a zone which is better suited than
in the state
of the art to carrying the tensile forces occurring here and the bearing and
reaction
forces which occur when arranged in a jib system. The notional extension gl'
of the
straight portion gi (see Figure lb) includes with the axis of symmetry s an
acute angle (3
which in the illustrated embodiment is about 18 degrees. Quite generally the
acute
angle 0 can also be in a range of greater than 10 degrees, preferably greater
than 15
degrees. In that respect an upper limit of 25 degrees is preferred in each
case in order to
exclude an excessively shallow configuration in respect of the straight
portion gi.
In the embodiment shown in Figure 1 a second straight portion g2 directly
adjoins the first straight portion gl, the second portion extending as far as
the axis of
symmetry s and intersecting it at the second intersection point S2. As can be
seen in
particular in Figure 1 c, for reasons relating to manufacturing technology it
may be
desirable if the second straight portion gZ (unlike the situation shown in
Figure la) is
connected to the first straight portion gi not directly but by way of a
preferably curved
further portion.
In the Figure 1 embodiment the second straight portion g2 includes with the
axis
of symmetry s an angle a which is smaller than 90 degrees (in the Figure 1
embodiment the angle a is about 65 degrees). A range for the angle a of less
than 70
degrees is particularly preferred. The angle a in this embodiment should
however be
larger than 60 degrees.
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In a further embodiment as shown in Figure 2 the second straight portion
includes a right angle with the axis of symmetry s.
The second straight portion g2 affords the advantage that this arrangement, in
the region around the tip of the crane boom, permits favorable local
application of
forces, as occurs for example when supporting slide packets between individual
jib
extensions. The short limb length affords a favorable relationship between the
sheet
metal thickness and the limb length so that deformation of the crane boom is
prevented
in the upper region.
It will be noted however that basically it would also be possible for the
contour
configuration in that region to be in the form of a second arcuate portion k2
(see Figure
3). That however only represents a special variant of a more general idea,
namely the
idea that the contour line ends in a rounded configuration at the line of
symmetry s. As
an alternative to the illustrated configuration of the rounded configuration
in the form
of an arcuate portion k2 the rounded configuration could for example also be
in the
form of an edge configuration 7.
In the embodiment of Figure 2 the notional contour line does not have an
arcuate portion kl, but only straight portions gl, g2, g3, g4.
Quite generally it must be said in relation to all configurations of the crane
according to the invention that the centroid F of the area enclosed by the
contour line in
the transverse plane lies in a region between the center point M and the first
intersection point Si, that is to say below half the height of the crane boom.
That
provides that the cross-section concentration of the crane boom is displaced
as much as
possible downwardly into the compression zone, thereby affording a lower
compression stress component.
As can be seen from the Figures the contour line of all embodiments has,
between the first intersection point S1 and the second intersection point S2,
an extreme
point E at maximum distance e from the axis of symmetry S. The spacing D
between
the first intersection point and the second intersection point Si, S2 can in
that case be at
least twice as great as the distance e. Preferably the spacing D is at least
two and a half
times as great, particularly preferably 2.75 times as great, as the distance
e. The spacing
D can be in each case less than three times the distance e.
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It can be provided that the spacing d of the contour line from the axis of
symmetry s, at approximately a quarter of the spacing D between the first and
second
intersection points Si, S2, starting from the second intersection point S2, is
less than or
equal to 0.8 times the maximum distance e.
In the Figure 1 embodiment the extreme point E is between the center point M
and the first intersection point S1 approximately at the height of the center
point of
curvature K. In the Figure 1 a configuration the contour line has only one
single extreme
point E, that is to say the width of the crane boom decreases both in the
direction of the
first intersection point S, and also in the direction of the second
intersection point S2,
starting from the extreme point E. When the arcuate portion kl is approximated
by a
polygonal line, as shown in Figure 1 c, it will be appreciated that all points
on the
polygonal portion, by which the arcuate portion kl is approximated in the
region of the
extreme point E, involve that maximum distance e.
Starting from the auxiliary circle shown in Figure 1 a, of the radius r, the
embodiment of Figure 1 involves a profile width b in accordance with b- 2r, a
profile
height D in accordance with D - 3r and a profile width upward bl in accordance
with bl
- r. Those particularly advantageous dimensions can be provided quite
generally in
crane booms according to the invention.
Figure 1 e shows for the embodiment of Figure 1 the position of the centroid F
between the center point M and the first intersection point S1 on the axis of
symmetry s.
In this case the centroid F refers to the area shown in dash-dotted lines in
Figure lh,
that is to say the entire area enclosed by the notional contour line
(corresponds to the
outside contour).
Figure lf shows a jib system 5 with a jib extension, showing in addition the
mounting of the jib system 5 by way of a mounting element 1 and mounting of
the jib
extension in the jib by way of mounting elements 2. It will be appreciated
that the
illustrated embodiment is intended purely by way of example in relation to the
number
of illustrated jib extensions. The same mounting elements can be used in jib
systems
having any number of jib extensions.
The embodiment of Figure 1 g shows two crane booms which involve for
example a jib extension arranged in a jib. It is of significance that the
arcuate portion ki
is approximated by different polygons. The inwardly disposed cross-sectional
profile
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has fewer edges in the region of the arcuate portion, which can be of
advantage in
particular when dealing with small profiles, in terms of manufacturing
technology.
Production of a crane boom according to the invention can be effected for
example in such a way that the crane boom is formed from two shells which are
shaped
in mirror image relationship with each other, wherein one of the shells
respectively
corresponds to one of the embodiments. The two shells can be joined together,
for
example welded, in the region of the first intersection point S1 and the
second
intersection point S2.
It will be noted however that it is particularly preferably provided that the
crane
boom is produced from a single metal sheet at least along a portion of its
longitudinal
extent, the metal sheet being suitably shaped and then closed along a single
line (for
example by welding). That line can extend for example in the region of the
first
intersection point S, or the second intersection point S2.
Shaping of the metal sheets can be effected in known manner or by folding or
bending and/or rolling, and for example welding.
If different gauges are required, the outside contour should preferably remain
the same and the sheet metal thickness should be applied inwardly.
Figure 4 shows by way of example a jib system 5 having a jib extension
arranged in a jib.
Figure 5 shows by way of example a utility vehicle 3 on which a crane 4
according to the invention is arranged. The crane 4 has a jib system 5
according to the
invention, in which case the individual jib extensions can be telescopically
displaced
relative to each other by way of thrust cylinders 6. It will be appreciated
that telescopic
displaceability can also be ensured by other drive means. A loading structure
(not
shown) could be arranged for example in the rearward region of the utility
vehicle 3.
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