[0001] The present invention relates to a limit stop device for lifting cranes, particularly
cranes with telescopic arms.
[0002] More specifically, the invention relates to cranes which comprise a base column to
which a first rigid arm is articulated, the arm being controlled by a corresponding
first hydraulic jack adapted to produce its oscillation with respect to said column,
and in which said first arm typically has a second arm articulated thereto, the second
arm comprising telescopic portions and being likewise controlled by a corresponding
second hydraulic jack which is adapted to produce its oscillation with respect to
the first one and includes additional hydraulic jacks which cause the extension and
retraction of the telescopic portions.
[0003] Cranes of this type, typically used to equip trucks and transport vehicles in general,
can use a cable, provided with a lifting hook, which is pulled by a winch being supported
by the arm with telescopic portions, termed telescopic arm for the sake of brevity,
and is guided by a pulley being carried at the free end of the outermost portion of
the arm, considered in its fully extended configuration. In inactive conditions, or
in particular operating conditions (for example during swiveling), in order to prevent
the lifting hook from oscillating and causing damage to objects and/or to people in
the vicinity of the crane, the lifting cable is moderately tensioned and the lifting
hook is made to abut against a mechanical retention element, known as limit stop,
which is designed to keep the hook in a stable inactive position.
[0004] For this purpose, mechanical retention elements or limit stops are known in which
a fork, oscillatably coupled to the pivot of the guiding pulley, has a flat bracket
articulated thereto; the suspension cable passes through the bracket and the lifting
hook abuts against the bracket, which is provided with a reaction slider which engages,
by way of its active surfaces, the pulley, onto which it discharges the stress produced
by the abutment contact of the lifting hook. Thanks to the ability of the fork to
oscillate and to the fact that such bracket is in turn articulated to said fork, the
surface of the flat bracket that acts as abutment for the supporting surface of the
lifting hook is arranged substantially at right angles to the cable, at least for
angular positions of the telescopic arm which are not very far from the horizontal
one. This is designed to prevent, or at least reduce, the onset of torques which tend
to turn the assembly constituted by the fork, the bracket and the reaction slider
about the pivot of the pulley and to prevent the bracket from assuming an angle other
than 90° with respect to the cable, which in this case would be subjected to excessive
stress.
[0005] However, these known limit stops do not provide sufficient assurance of retention
of the lifting hook and substantially are not fully reliable as to the onset of excessive
tensions on the cable caused by the rotation of the pulley.
[0006] The aim of the present invention, starting from the knowledge of these drawbacks
of known types of limit stop, is to eliminate them, and within the scope of this aim
the important particular object of the invention is to provide a limit stop device
which can ensure the correct engagement of the lifting hook by way of its abutment
portion and the consequent correct application of stress to the cable regardless of
the relative angular position of the arms of the crane, accordingly avoiding the disengagement
of the hook from the limit stop even in the presence of considerable tensions applied
to the cable by unintentional and accidental extensions of the telescopic arm of said
crane.
[0007] Another important object of the present invention is to provide a limit stop device
which has an extremely simplified structure and in particular does not have mutually
connected and/or articulated elements and therefore ensures absolute reliability in
operation and no need for maintenance.
[0008] According to the present invention, this aim and these and other objects which will
become better apparent from the detailed description that follows are achieved with
a limit stop device for lifting cranes with telescopic arms, having the specific features
defined in the appended claims.
[0009] Substantially, the invention is based on the concept of accommodating the pulley
for guiding the lifting cable inside a rigid housing which has, at one end, a contact
surface for rigid coupling to the end of the telescopic arm of the crane having an
inlet for the lifting cable that arrives from the winch and, at the other end, an
outlet for the cable that arrives from the guiding pulley, surrounded by contact edges
for the abutment portion of the lifting hook, the profile of said edges being shaped
like an arc traced by the involute to a circle whose evolute is a circular contour
being concentric and internal, external or coincident with respect to the pitch circle
of the guiding pulley.
[0010] In this manner, by selecting a sufficiently wide angle for the involute arc, one
ensures the perpendicular arrangement of the abutment contact surfaces of the lifting
hook with respect to the cable and therefore the perfect stability of such hook in
its inactive position for any angular position of the arms of the crane and also in
the presence of excessive mechanical tensions generated on the cable by maneuvers
for extending the telescopic arm performed inadvertently during work or when the lifting
hook is in said inactive position.
[0011] The characteristics, purposes and advantages of the limit stop device according to
the present invention will become better apparent from the following detailed description
and with reference to the accompanying drawings, given by way of non-limitative example,
wherein:
Figure 1 is a side elevation view of a crane with telescopic arms provided with the
limit stop device according to the present invention;
Figure 2 is an enlarged-scale view of a detail of Figure 1, illustrating the limit
stop in detail;
Figures 3 and 4 are elevation views of corresponding different angular arrangements
of the arms of the crane of Figure 1;
Figures 5 and 6 are partial elevation views of the telescopic arm of the crane of
Figure 1, shown in the corresponding retracted and extended configurations.
[0012] In the drawings, reference numeral 1 generally designates a typical lifting crane
with telescopic arms, which comprises a base column 2, a first rigid arm 3 which is
articulated to the column and is controlled by a corresponding first hydraulic jack
3a being adapted to produce its oscillation with respect to the column, and a second
arm 4, designated as telescopic arm, which is articulated to the arm 3 and is composed
of a plurality of mutually telescopic portions 4a, 4b, etcetera. The arm 4 is in turn
controlled by a hydraulic jack 5 which is adapted to produce its oscillation with
respect to the arm 3 and includes additional hydraulic jacks 4k for the extension
and retraction of the telescopic arms. The telescopic arm 4 further has, at the pivoting
section, a winch 6, preferably of the hydraulic type, which actuates a lifting cable
7 being guided by a pulley 8 which is arranged at the end of the telescopic portion
4b that protrudes furthest (when the arm is in the fully extended configuration) and
ends with the lifting hook 9. The limit stop, generally designated by the reference
numeral 10, is associated with the pulley 8.
[0013] According to the present invention, the device 10 (Figure 2) is constituted by a
sturdy rigid housing 11 made of metal plate, which contains the guiding pulley 8,
being pivoted so that it can rotate freely; the housing has, at one end, a contact
surface 12 for the rigid coupling of said housing, by way of bolts B, to the outer
portion 4b of the telescopic arm; the contact surface 12 is provided with an inlet
13 for the lifting cable 7. At the other end, the housing 11 has an outlet 14 for
the cable 7 which is surrounded by contact edges 15 for the abutment portion of the
lifting hook 9; the profile of the edges is shaped like an arc traced by the involute
to a circle whose evolute is a circular contour being concentric and internal or external
or coincident with respect to the pitch circle of said guiding pulley. In this manner,
the contact edges 15 are, at the involute arc, strictly perpendicular to the cable
7, and the contact force between said contact edges and the abutment surface 9a of
the hook 9 also is strictly perpendicular to the surface and therefore has no transverse
components which can move the hook from the inactive position in abutment against
the edges 15.
[0014] The involute arc covers a convenient angle, typically a center angle of 160°. This
ensures that the abutment surfaces of the lifting hook are perpendicular with respect
to the cable, and therefore ensures that said hook is perfectly stable in its inactive
abutment position, for any angular position of the arms of the crane 1. Figures 3
and 4 clearly illustrate the stable condition of the hook 9 in limit stop conditions
for two extreme configurations of the crane, designated by the reference numerals
1' and 1" respectively, and even in the presence of excessive mechanical tensions
on the cable, caused for example by inadvertent extensions of the telescopic arm 4
(Figures 5 and 6).
[0015] Without altering the concept of the invention, the details of execution and the embodiments
may of course vary extensively with respect to what has been described and illustrated
by way of non-limitative example, without thereby abandoning the scope of the appended
claims.
[0016] The disclosures in Italian Patent Application No. T02000A000220 from which this application
claims priority are incorporated herein by reference.
[0017] Where technical features mentioned in any claim are followed by reference signs,
those reference signs have been included for the sole purpose of increasing the intelligibility
of the claims and accordingly such reference signs do not have any limiting effect
on the scope of each element identified by way of example by such reference signs.
1. A limit stop device (10) for lifting cranes (1), particularly cranes with telescopic
arms (4), characterized in that it is constituted by a rigid housing (11) made of metal plate which contains, so
that it is freely rotatably pivoted, a pulley (8) for guiding a lifting cable (7)
and has, at one end, a contact surface (12) for rigid coupling of said housing (11)
to an outer portion (4b) of a telescopic arm (4) which has an inlet (13) for the lifting
cable (7) and, at the other end, an outlet (14) for the lifting cable (7), surrounded
by contact edges (15) for the abutment portion of a lifting hook (9), the profile
of said edges being shaped like an arc traced by the involute to a circle whose evolute
is a circular contour which is concentric and internal or external or coincident with
respect to a pitch circle of said guiding pulley (8).
2. The device according to claim 1, characterized in that the arc traced by the involute to a circle of said contact edges (15) that surround
the outlet (14) of the cable (7) covers a convenient angle, typically a center angle
of 160°.
3. The device according to claims 1 and 2, characterized in that said rigid housing (11) that contains the guiding pulley (8) is rigidly coupled to
the outer portion (4b) of the telescopic arm (4) by way of a series of bolts (B).
4. The device according to the preceding claims, characterized in that said lifting hook (9) has an abutment surface (9a) adapted to adhere, by strictly
perpendicular contact engagement, to the contact edges (15) that surround the outlet
(14) of said lifting cable (7).