It is known, in the construction industry, to use cranes, both fixed and truck-mounted, to move and lift weights, even hundreds of tons, to heights that can exceed several dozen meters.
Such cranes are normally provided with an extendable arm, which can be formed by one or more segments connected to each other in an articulated or telescopic manner. In the latter case they are called telescopic cranes, or extendable or telescopic arm cranes.
In some particular applications, in which supplementary performances are required of the crane, it is known to use, to increase the performance of the crane in terms of maximum reachable height, an auxiliary extension device, also known as jib, attached to the free end of the extendable arm. Normally, the auxiliary extension device is made of steel, and generally has a reticular latticed structure. The auxiliary extension device can be made with one or more segments or sections, connected or interconnected to each other.
Known auxiliary extension devices can be assembled by means of pivoting coupling on the free end of the corresponding extendable arm. This allows them to fold back on the extendable arm during transport, and then to be put in their working position, that is, cantilevered with respect to the extendable arm, by means of a rotation carried out on site.
Known auxiliary extension devices can be assembled and positioned both with manual procedures and also using a support crane.
One disadvantage of known auxiliary extension devices is that they are normally very heavy, even in the order of a ton. This can cause a heavier weight of the crane in its entirety, so that moving it by truck can be inconvenient and costly.
The weight of known auxiliary extension devices as above also penalizes the performance of the cranes in terms of the mass of movable load, since this must be added to the weight of the auxiliary extension device itself, already weighing on the extendable arm of the crane.
Another disadvantage connected to the weight of the auxiliary extension device can affect the horizontal distance to which the load can be moved, a distance which is connected to the forces acting on the attachment zone of the auxiliary extension device to the extendable arm of the crane.
Another limitation due to the weight of the auxiliary extension device affects the actual maximum height the arm can reach to position the load.
Another disadvantage of known auxiliary extension devices is connected to the complexity and time needed for the operations to assemble and produce the auxiliary extension devices themselves, since generally, as stated above, they have a latticed structure.
Another disadvantage of known auxiliary extension devices is that they are difficult to assemble on the end of the extendable arms of the cranes, since normally they need one or more support cranes.
It is also known from WO-A-96/26887, EO-A-2012/156807, EP-A-1.361.189, and EP-A-1.090.875 the use of segments of an extendable arm of a crane made with a composite material.
The documents WO-A-96/26887, WO-A-2012/156807 and EP-A-1.361.189, in particular, disclose an extendable arm in which, each segment is reciprocally connected to another segment and cannot be disassembled easily, without removing substantially parts of the extendable aim, such as actuation means able to move telescopically the segments.
The document WO-A-96/26887 discloses a crane for lifting a load, such as a platform. The crane comprises a telescopic aim formed by sections made of composites material. The sections cooperate with each other in sliding so as each section can slide internally or externally with respect to another section.
One of the sections, in particular the section defining the free end of the telescopic arm, is provided with an arm. The arm is also made with a composite material and is designed to support a platform to accommodate a load or people.
The arm has only the function of connection between the extendable arm and the platform, and is provided with regulation means configured to maintain the platform horizontal.
This arm, however, is not suitable to be connected to attachment devices, such as a hook to which a load can be attached.
One purpose of the present invention is to obtain an auxiliary extension device for a crane with an extendable arm which has a limited weight compared with known auxiliary extension devices, which is easy and quick to produce and which allows, given the same performance, to limit, the overall weight of the crane on which it is mounted.
Another purpose of the present invention is to simplify the selective connection operations between an auxiliary extension device and an extendable arm of a crane.
Another purpose of the present invention is to obtain an auxiliary extension device that has optimized mechanical resistance in relation to the stresses to which it is subjected.
Another purpose of the present invention is to obtain an auxiliary extension device for a crane with extendable arm that allows to increase the mass of load movable by the crane on which it is mounted, given the same height that can be reached.
Another purpose of the present invention is to obtain an auxiliary extension device which allows to increase the horizontal distance to which the load can be moved by the crane on whose extendable arm the auxiliary extension device is mounted, given the same mass of the load and the same length of the auxiliary extension device.
Another purpose is to obtain an auxiliary extension device which, given the same weight as a known auxiliary extension device, allows the crane on which it is mounted to reach a greater maximum height at which to position the load.
Another purpose of the present invention is to obtain an auxiliary extension device which, with the same sizes as a known auxiliary extension device, is easier to transport and easier to mount manually on the extendable arm of the crane and which does not need a support crane.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.