EP2252540B1 - Jib comprising a metal hollow profile with a reinforcement layer consisting of a fibre-plastic composite and sensor element - Google Patents

Description

The invention relates to a boom for end-side receiving loads according to the preamble of claim 1. Furthermore, the invention relates to a method for producing such a boom.

Lightweight boom parts are an important prerequisite to meet the demands of mobile machinery such. As work platforms, cranes, concrete pumps u. s. w. in terms of high load capacity, long boom length and long range to meet. By means of lightweight construction, these performance data can be increased compared to conventional designs without increasing the overall weight of the machine or unfavorably shifting the center of gravity. So z. As in mobile cranes, mobile work platforms and mobile concrete pumps, the negative impact of the boom weight on the vehicle size and mass, the support base, the number of axles and the necessary counterweights are kept low.

Monolithic construction methods of fiber-plastic composite (FKV), as z. As used in aerospace, are a way to realize such a lightweight construction. Although they are very light, but for economic and safety aspects for the construction of mobile machines unsuitable. The production of box girders in monolithic fiber composite construction is very costly due to the complicated fiber structure in force applications or bearings. In addition, monolithic FRPs are impact-sensitive, so they are not suitable for construction sites for use in construction machinery such as cranes.

An alternative to pure FKV construction is the hybrid construction, in which metallic materials are combined with FKV. A boom in this hybrid construction is known from the EP 0 968 955 A2 , The DE 195 08193 A1 discloses a boom according to the preamble of claim 1.

From the US 6,786,233 B1 is a truck-mounted concrete pump with a boom, which consists of a boom-hollow profile with an affiliated reinforcement system of a fiber-plastic composite. Furthermore, the describes GB 1 389 139 already a load measuring device for a telescopic mast with at least one Strain gauge, which is preferably arranged in the upper or lower parts of the telescopic mast.

It is an object of the present invention to develop a boom of the type mentioned in such a way that the reinforcing layer can be dimensioned exactly to the particular application, in particular the construction site suitability and thus safety should be increased.

This object is achieved by a boom with the features specified in claim 1.

The sensor element according to the invention serves, for example, for detecting a bending moment. In this case, for example, in a test phase of the cantilever and / or in the first application of a hybrid designed according to the invention with a metallic cantilevered hollow section and a fiber-plastic composite reinforcing layer, it can be detected whether damage occurs in the structure of the cantilevered hollow section. The reinforcing layer can be dimensioned according to the load forces measured by the sensor element. Also, aging-related or overload-induced deformations of the structure of the cantilever can be reliably detected via the sensor element. Costly inspection procedures for fiber-plastic composites, such as thermography or ultrasonic inspection, can be avoided. In the hybrid construction according to the invention, ie the use of a metallic component and a fiber-plastic component, the specific properties of the fibers of the reinforcing layer are used to improve the bending stiffness and the bending strength of the metallic boom hollow profile. In contrast to a pure fiber-plastic composite component without a metallic component, a large part of, for example, the shear transmission and the introduction of force can be taken over by the metallic boom hollow profile in the boom according to the invention. The boom can also have a plurality of sensor elements. By interconnecting a plurality of inventive sensor elements, for example, bending moments and a normal force in the boom can be detected. With a suitable arrangement of the sensor elements, it is possible to detect a change in the distribution of the expansions between, on the one hand, the metal boom hollow profile and, on the other hand, the FRP. Such a change of distribution is a Indication of damage, for example delamination or fiber breakage. An inner reinforcing layer, that is to say a reinforcing layer arranged in the cantilevered hollow profile, is protected against external influences. This, too, is a decisive advantage over a structure as it is known from the EP 0 968 955 A2 It is known where the shock-sensitive FKV is located outside. A boom with such an inner reinforcing layer of a fiber-plastic composite in a metallic boom hollow profile can also be used without a sensor element for detecting load forces, since such a boom without the sensor element advantages over the example of EP 0 968 955 A2 known prior art has. Also, a protection of the reinforcing layer from the weather is given. Overall, the construction site suitability and thus the safety of the boom is increased. The boom hollow profile or the profile sections thereof can then simultaneously serve as a tool for producing the hybrid boom. Investment costs for a winding system or for a corresponding tool eliminated. Attachments attached externally on the arm are not hindered by any possibly interfering fiber-plastic composite there. Attachments can then be welded in particular to the boom hollow profile. An arrangement of at least one of the sensor elements on an inner wall of the reinforcing layer and at least one further of the sensor elements between the reinforcing layer and the boom hollow profile allows, in particular, detection of undesired delamination of the reinforcing layer from the boom hollow profile.

An external control device according to claim 2 can process further information, such as hydraulic pressures, with which a construction machine, within which the boom is used, works, an inclination of the boom against the vertical or a tensile force in optionally existing guy elements. The information obtained by the sensor elements according to the invention supplement this further, processable by the external control device information. This allows the external control device to more reliably detect unsafe conditions of the boom-mounted construction machines and to prevent them, for example, by switching off a hoist or a luffing mechanism. As an external control device, in particular a control device which is regularly present in modern mobile cranes can be used.

A structure of the fiber-plastic composite according to claim 3 leads to a stable reinforcement with low weight.
A fiber arrangement according to claim 4 in particular increases the flexural rigidity of the cantilever.

In particular, a part of the fibers of the reinforcing layer can be arranged according to claim 5 obliquely or diagonally with respect to the boom longitudinal axis. In particular, there may be two fiber groups crossing each other. Thus arranged fibers assist in the transmission of shear forces from torsion and shear and increase flexural rigidity of cross-sectional parts of the cantilever.

An electrically insulating intermediate layer according to claim 6 protects the metallic boom hollow profile from corrosion, in particular when the FKV reinforcing layer has carbon fibers. In this case, a fiber layer, in particular a glass fiber layer, is preferably used.

Profile sections according to claim 7 simplify the production of the boom according to the invention.

A U-profile shape of the profile sections allows, for example, an arrangement of the reinforcing layers, in which they are spatially well separated from the connecting sections between the profiled sections constituting the boom-hollow profile. The profile sections can then be welded together, for example via the legs of the U, without the risk of damaging the reinforcing layer arranged, for example, at the bottom of the U. Alternatively to a U-profile shape, the profile sections can also be flat, designed as an L-profile or in cross-section with several kinks. Such a cross-sectional design of the cantilever with profile sections bent several times in cross-section yields, for example, a boom with a hexagonal or octagonal cross-section.

A sensor element group according to claim 8 allows in particular a temperature-compensated measurement occurring load forces, for example, occurring bending moments.

Another object of the invention is to provide a low cost manufacturing process indicate for the boom according to the invention.

This object is achieved by a method according to claim 9.

A manufacturing method according to claim 9 uses in particular the advantages of a subdivision of the boom hollow profile in profile sections according to claim 7. If an already complete boom hollow section is provided as an output element for connection to the reinforcing layer, the reinforcing layer can also be inserted into the hollow profile or, as far as the Reinforcement layer is mounted outside of the hollow profile to be applied to this. The sensor element can be introduced into the boom together with the reinforcement layer or can already be provided together with the boom hollow profile. Alternatively, it is possible to attach the sensor element before the application of the reinforcing layer or only thereafter. Under certain circumstances, can be dispensed with the introduction of a sensor element, in particular when the reinforcing layer is arranged in the cavity of the boom-hollow profile.

An application of the reinforcing layer according to claim 10 is suitable for an automated manufacture of the cantilever. The fiber-plastic composite is produced when applying the reinforcing layer of the fiber layer and the polymeric resin. After laying the fiber layer, the injection of the resin / hardener mixture can be done under vacuum. There is no need to provide ready pre-produced fiber-plastic composite. The reinforcing layer can easily adapt to the boom hollow profile or the profile section thereof in this manufacturing process. The boom hollow profile or the profile section thereof then serves as a tool for producing the hybrid boom.

Orienting fibers according to claim 11 may result in an improvement in the properties of the cantilever with respect to a given load, for example increasing the flexural rigidity.

The intermediate layer according to claim 12 can provide protection against contact corrosion of the metallic hollow profile.

A tearable layer on the fiber layer before injecting the polymeric Synthetic resin / hardener mixture can be applied, layers that are present after the production of the boom as a result of the manufacturing process, but do not form part of the final product, easy to separate from the reinforcing layer.

A dispensing ply that can be applied to the fiber ply prior to injection and over which the injected resin is first distributed transversely of the cantilever longitudinal axis enhances embedding of the fiber ply in the resin when performing a manufacturing process in which a polymeric resin is injected into the fiber ply becomes.

In a manufacturing method according to claim 13, a prefabricated reinforcing layer made of a fiber-plastic composite can be used. In particular, in geometrically simple design boom hollow sections, this can result in a result in a cost-effective production. In this manufacturing process, the sensor elements can be integrated in advance in the FKV reinforcements.

In a bonding according to claim 14 results in a secure bond of the reinforcing layer with the boom-hollow profile or the profile section thereof.

The use of a pressure hull according to claim 15 elegantly uses the geometry of the boom hollow profile in the introduction of two reinforcing layers simultaneously.

A pressure body disposed between the reinforcing plies in the interior of the cantilevered hollow profile along the cantilever longitudinal axis may be used in the manufacture of the cantilever to facilitate connection of the reinforcing plies to the cantilevered hollow profile in the manufacture of the cantilever. The pressure body can be a pressurizable hose.

A fluid filling according to claim 16 allows a defined pressurization of the pressure hull in the bonding of the reinforcing layers. A tempering, for example, for curing the adhesive is possible via such a pressure body by a corresponding temperature of the fluid.

• Fig. 1 einen Querschnitt durch einen Ausleger zur endseitigen Aufnahme von Lasten, ausgeführt als Kastenträger, in einem perspektivischen Ausschnitt;
• Fig. 2 einen auch als Profilsegment bezeichneten Profilabschnitt des Auslegers, ebenfalls in perspektivischer Darstellung, während der Verbindung einer Verstärkungslage mit dem Profilabschnitt im Zuge einer Herstellung des Auslegers;
• Fig. 3 einen Querschnitt durch eine weitere Ausführung eines Auslegers, ebenfalls ausgeführt als Kastenträger, während der Verbindung einer Verstärkungslage mit einem Ausleger-Hohlprofil im Zuge einer weiteren Variante eines Verfahrens zur Herstellung des Auslegers;
• Fig. 4 in einer zu Fig. 1 ähnlichen, schematischen Darstellung die Anordnung von vier Sensorelementen am Ausleger nach 1 zum temperaturkompensierten Messen eines Biegemoments bei einer Biegung des Auslegers in einer in der Fig. 4 vertikal verlaufenden Biegeebene;
• Fig. 5 eine Verschaltung der vier Sensorelemente nach Fig. 4;
• Fig. 6 eine weitere Ausführung eines Auslegers im Längsschnitt, wobei zwei Gruppen jeweils miteinander nach Fig. 5 verschalteter Sensorelemente zu je vier nach Fig. 4 angeordneter Sensorelementen vorgesehen sind; und
• Fig. 7 schematisch einen Querschnitt eines Ausleger-Hohlprofils einer weiteren Ausführung eines Auslegers.

Embodiments will be explained in more detail with reference to the drawing. In this show:

• Fig. 1 a cross section through a boom for end-side recording of loads, designed as a box girder, in a perspective cutout;
• Fig. 2 a profile section of the cantilever also referred to as a profile segment, likewise in a perspective view, during the connection of a reinforcing layer to the profile section in the course of production of the cantilever;
• Fig. 3 a cross section through a further embodiment of a boom, also designed as a box girder, during the connection of a reinforcing layer with a boom hollow section in the course of another variant of a method for producing the boom;
• Fig. 4 in one too Fig. 1 Similarly, the schematic arrangement of the arrangement of four sensor elements on the boom of Figure 1 for temperature compensated measuring a bending moment in a bending of the cantilever in a in the Fig. 4 vertical bending plane;
• Fig. 5 an interconnection of the four sensor elements after Fig. 4 ;
• Fig. 6 a further embodiment of a cantilever in longitudinal section, wherein two groups each with each other after Fig. 5 interconnected sensor elements to four each Fig. 4 arranged sensor elements are provided; and
• Fig. 7 schematically a cross section of a boom-hollow profile of another embodiment of a boom.

An Indian Fig. 1 in perspective and in sections illustrated boom 1 is used for end-side recording of loads. The boom 1 may for example be part of a working platform, a crane or a concrete pump. The boom 1 has a runner designed as a box beam hollow profile 2 with a dashed line in Fig. 1 longitudinal axis 3. The boom hollow section 2 is made of metal. The boom hollow section 2 is composed of two profile sections 4, 5, each with a U-shaped Cross-section assembled. The two profile sections 4, 5 are connected to each other via welds 6, which extend along the boom longitudinal axis 3.

Depending on a reinforcing layer 7 is applied to the bottom of the profile sections 4, 5. The two reinforcing layers 7 are constructed the same, so that it is sufficient, the force applied to the profile section 5 reinforcing layer 7, in the Fig. 1 is described below. The reinforcing layer 7 is arranged as a reinforcing lining in the cavity of the boom hollow section 2, so it abuts against an inner wall 8 of the profile section 5. The reinforcing layer 7 is made of a fiber-plastic composite. This is in particular a carbon fiber-resin composite. Carbon fibers 9 of a fiber layer 10 of the reinforcing layer 7 are connected to one another and to the inner wall 8 via a polymeric synthetic resin matrix 11.

The fibers 9 of the reinforcing layer 7 may have different orientations. They can be arranged for the most part with a parallel to the longitudinal axis 3 of the boom 1 level component. They may also be arranged predominantly diagonally with respect to the longitudinal axis 3.

In particular, all the fibers 9 may be arranged diagonally with respect to the longitudinal axis 3. There may be two groups of fibers whose paths cross each other. These two fiber groups may belong to different and superimposed individual fiber layers of the fiber layer 10.

In the area of the reinforcing layer 7, a sensor element 12 is arranged. Signal or supply lines 12a, which are connected to the sensor element 12, are guided a little way along the boom hollow profile 2 and then led to the outside. The sensor element 12 serves to detect load forces acting on the boom 1. The sensor element 12 is designed as a strain sensor and in particular as a strain gauge. Via a signal connection, not shown, the sensor element 12 is in signal communication with an external control device 13. The latter processes, in addition to measured values which the sensor element 12 receives, also further information, acquired by additional sensors, about the condition of a working or construction machine, the part of which represents the boom 1. at This additional information may be, for example, hydraulic pressures, an inclination of the boom 1 against the vertical or a tensile force in a guy element of the work machine, not shown.

The sensor element 12 may be embedded in the reinforcing layer 7. Alternatively, it is possible to arrange the sensor element 12 on the side facing the cavity of the boom hollow profile 2 side of the reinforcing layer 7. Finally, it is possible to arrange the sensor element 2 between the reinforcing layer 7 and the profile section 5.

In practice, the boom 1 has a plurality of sensor elements 12, which are all in signal communication with the control device 13.

The sensor element 12 is used in particular for detecting a bending moment and for detecting the presence of a damage of the jib 1.

Several of the sensor elements 12 may be part of a common measuring arrangement and z. B. be interconnected in a Wheatstone bridge. This interconnection can in particular be such that the influence of an uneven heating of the cantilever 1 on the measurement result of the sensor elements 12 is compensated.

Between the reinforcing layer 7 and the inner wall 8, an electrically insulating intermediate layer 14 is arranged, which is designed as a glass fiber layer.

The following is based on the Fig. 2 a method of manufacturing the cantilever 1 is described. This is a vacuum injection method in which the profile sections of the boom hollow section 2 take over the function of a tool. Compared to Fig. 1 shows the 2, the profile section 5 of the boom 1 with greater detail.

On the intermediate layer 14, the fiber layer 10 is initially placed with non-matrix-connected fibers 9. During or after placing the fiber layer 10, the fibers 9 of the fiber layer 10 are oriented, that is aligned with the longitudinal axis 3, wherein an orientation of the fibers 9 is adjusted according to what was stated above. On the oriented fiber layer 10 is a tear-able layer 15 launched. In turn, a distribution layer 16 in the form of a distribution fabric is placed on the tearable layer 15. Between the distributor fabric 16 and a resin-impermeable, but air-permeable film 17 disposed therealong, a resin conduit 18 extending along the longitudinal axis 3 is arranged. Over along the longitudinal axis 3 extending and attached to the inner wall 8 of the profile section 5 sealing strip 19, the film 17 is sealed against the profile section 5. Above the film 17, a further air-impermeable film 20 is disposed between the legs of the profile section 5 and sealed by a further pair of sealing strips 19 against the inner wall 8 of the profile section 5. Between the two superimposed films 17, 20, a nonwoven layer 21 is arranged. Between the nonwoven layer 21 and the upper in the upper air-impermeable film 20, an air line 22 is arranged, which also extends parallel to the longitudinal axis 3. The air line 22 is in fluid communication with a vacuum pump 24 via a connection element 23.

The resin pipe 18 is branched via a mixing element 25 into a resin pipe section 26 and a hardener pipe section 27. The resin conduit section 26 communicates with a resin reservoir 28 and the hardener conduit section 27 is in fluid communication with a hardener reservoir 29. In the mixing element 25, a combination of resin and harder in a predetermined mixing ratio, wherein a chemically reactive resin / hardener mixture is generated.

With the help of in the Fig. 2 illustrated construction, the reinforcing layer 7 can be laminated directly to the profile section 5, wherein then according to the reinforcing layers 7 prepared profile sections 4, 5 are connected to the boom 1 with each other. When laminating the reinforcing layer 7, the profile sections 4, 5 simultaneously serve as forming tools for the reinforcing layer 7.

The intermediate layer 14 is placed on the bottom of the profile section 5 after a surface treatment of the profile section 5, for example after degreasing and sandblasting of the profile section 5. Subsequently, the fibers 9 are laid dry as a fiber layer 10 on the intermediate layer 14 and oriented. The oriented fibers are in particular designed as continuous fibers. This also applies if the boom hollow profile 2 over its course along the longitudinal axis 3 has a variable cross-section. As a rule, only a smaller proportion of the carbon fibers 9 has an orientation parallel to the longitudinal axis 3.

To produce the reinforcing layer 7, polymeric synthetic resin, mixed with a hardener, is injected into the fiber layer 10 via the resin line 18. The synthetic resin adheres the fibers 9 to the bottom of the profile section 5. The resin emerging from the distribution line 16 is distributed over the distribution layer 16 transversely to the longitudinal axis 3 of the profile section 5, penetrates the tearable layer 15 and penetrates into the fiber layer 10 , The resin-impermeable film 17 ensures that no resin / hardener mixture can undesirably penetrate into other regions outside the fiber layer 10.

Via the air line 22 of the fleece 21 containing space between the sheets 17, 20 are evacuated. The evacuation prevents trapped air, which can lead to a potential delamination and thus to a material inconsistency. A pressure difference generated by the evacuation drives the resin / hardener mixture into the spaces between the fibers of the fiber layer 10.

Curing of the resin / hardener mixture in the fiber layer 10 may be carried out at room temperature or at elevated temperatures, e.g. B. at 80 ° C, take place.

A heating for curing takes place in a heating furnace or by placing a heating mat.

After curing, the distributor fabric 16 and the two films 17, 20 with the intermediate nonwoven 21 and the two lines 18, 22 are removed by tearing off the tearable layer 15.

The thus prepared with reinforcing layers 7 profile sections 4, 5 are then welded, wherein the welds 6 are produced.

The sensor elements 12 can be mounted in the boom 1 either directly in the production of the reinforcing layers 7 or in the connection of the reinforcing layers 7 and the profile sections 4, 5 or only after the production of the hybrid structure of the profile sections 4 and 5 and the reinforcing layers 7.

Fig. 3 shows a cross section of a further variant of a boom 1, which can be produced by means of a variant of a manufacturing process. Components and procedural details corresponding to those described above with reference to FIGS Fig. 1 and 2 have the same reference numbers and will not be discussed again in detail. In this production variant, first the profile sections 4, 5 are made separately and assembled to the boom hollow section 2 via the welds 6. The reinforcing layers 7 are also produced in a separate method step. In this case, the fibers 9 of the fiber layers 10 of the reinforcing layers 7 are oriented in such a way that, after being connected to the profile sections 4, 5, they have an orientation which corresponds to what has been described above in connection with FIGS Fig. 1 and 2 was explained.

Subsequently, the reinforcing layers 7 are coated on one side with an adhesive 30, for example an epoxy resin-based adhesive. The reinforcing layers 7 are then inserted into the boom hollow section 2, so that the adhesive sides of the reinforcing layers 7 each face the inner walls 8 of the profile sections 4, 5. After inserting the reinforcing layers 7 two pressure plates 31 and a pressure body 32 in the form of a fluidbefüllbaren tube are inserted into the boom-hollow section 2. The pressure body 32 has a course along the longitudinal axis 3 of the boom. 1 The two pressure plates 31 are each arranged between the pressure body 32 and one of the two reinforcing layers 7.

The pressure body 32 is, in particular, a hollow pressure pad made of a rubber-elastic material. After inserting the pressure plates 31 and the pressure body 32, the latter is filled with a pressure fluid, that is to say a gaseous or liquid medium, so that a pressure p is generated in the pressure body 32. By this pressure, the reinforcing layers 7 are pressed against the inner wall 8 and thus against the two adhesive layers 30 via the pressure plates 31. This takes place until the adhesive 30 has cured. This hardening can again take place at room temperature or at elevated temperature. To harden the adhesive 30, the boom 1 is introduced into a heating furnace or a correspondingly preheated liquid, for example water or oil, is introduced into the pressure body 32.

After curing, the pressure body 32 and the two pressure plates 31 are removed from the boom hollow section 2.

The stiffening layers 7 are already prepared with the sensor elements 12. The sensor elements 12 may be arranged relative to the reinforcing layers 7 as explained above in connection with the embodiment according to FIGS. 1 and 2. Alternatively, it is possible to embed the sensor elements 12 in the adhesive layer 30 as well.

Fig. 4 schematically shows one to Fig. 1 similar perspective view of a boom 1 with a total of four sensor elements 12 ₁ , 12 ₂ , 12 ₃ and 12 _4th which are housed in the manner of the sensor element 12 or the sensor elements 12 of the embodiments described above. The sensor elements 12 ₁ to 12 ₄ serve for the temperature-compensated measurement of a bending moment of the cantilever 1 in a perspective view according to Fig. 4 vertically extending bending plane 33. The sensor elements 12 ₁ to 12 ₄ are designed as strain gauges. The sensor elements 12 ₁ and 12 ₃ are arranged on opposite profile walls of the boom hollow section 2 at the same height. The sensor elements 12 ₂ and 12 ₄ are also arranged on opposite profile walls of the boom hollow section 2 at the same height. The sensor element 12 ₁ is adjacent to the sensor element 12 ₂ . The sensor element 12 ₃ is adjacent to the sensor element 12 ₄ .

The sensor elements 12 ₁ and 12 ₃ are aligned in the longitudinal direction of the boom 1. The sensor elements 12 ₂ and 12 ₄ are aligned transversely to the longitudinal direction and perpendicular to the bending plane 33.

When bending the boom 1 in the bending plane 33, the sensor elements 12 ₁ and 12 _{3 are} stretched or compressed and therefore provide a signal contribution in the bending moment measurement. The sensor elements 12 ₂ and 12 ₄ are used in the measurement of the bending moment in the bending plane 33 for temperature compensation to compensate for uneven heating of the boom. 1

Fig. 5 shows the interconnection of the sensor elements 12 ₁ to 12 _4th These are interconnected in the manner of a measuring bridge, wherein at coupling points 34, 35 a supply voltage U _sp coupled and tapped at tapping points 36, 37 a signal voltage U _{si is} tapped. The sensor element 12 ₁ is arranged between the coupling-in point 34 and the tapping point 36. The sensor element 122 is arranged between the injection point 35 and the tapping point 36. The sensor element 12 ₃ is arranged between the coupling-in point 34 and the tapping point 37. The sensor element 12 ₄ is disposed between the injection point 35 and the tapping point 37.

Fig. 6 shows a further embodiment of a boom 1. Components which correspond to those described above with reference to the Fig. 1 to 5 have already been explained, bear the same reference numbers and will not be explained again in detail. When longitudinal section through a further embodiment of a jib 1 after Fig. 6 the reinforcing layer 7 is arranged as a reinforcing lining in a section of the boom hollow section 2. A first sensor element group 38 with four sensor elements 12 ₁ to 12 ₄ on the type of sensor elements 12 ₁ to 12 ₄ after the 4 and 5 is disposed on an inner wall 39 of the reinforcing layer 7. A second sensor element group 40, likewise with four sensor elements 12 ₁ to 12 ₄ in the manner of the sensor elements 12 ₁ to 12 ₄ of FIGS. 4 and 5, is arranged between the reinforcing layer 7 and the boom hollow profile 2.

With the two sensor element groups 38, 40 is the detection of unwanted delamination of the reinforcing layer 7 in a region L between a wedge-shaped towards the inner wall 8 expiring end portion 41 of the reinforcing layer 7 and the sensor elements 12 ₁ to 12 _{4 of} the sensor element group 38 possible, the end portion 41st As long as a connection between the boom hollow section 2 and the reinforcing layer 7 is intact in the region L, the two sensor element groups 38 and 40 provide very similar measuring signals U _si for the same supply voltage U _sp . The two sensor element groups 38, 40, ie the two measuring bridges formed thereby, are then redundant.

As soon as a delamination of the reinforcement layer 7 from the boom hollow section 2 has occurred in the region L, the stretching or compression of the sensor elements 12 ₁ and 12 _{3 of} the inner sensor element group 38 decreases with a bending load of the extension arm 1 in the bending plane 33. The sensor element group 38 shows then at a bending load of the boom 1 in the bending plane 33 a different measurement signal U _si than the outer sensor element group 40. An occurrence of a deviation of the measurement signals U _si of the groups of sensor elements 38, 40 from each other is therefore an indicator for an occurring delamination of the reinforcing layer 7 from the boom hollow profile 2 ,

Fig. 7 shows a further variant of a boom 1. Shown is a boom-hollow profile of the boom 1 in cross section. Not shown is a reinforcing layer, which is arranged as a reinforcing lining in the boom hollow section 2 according to the embodiments discussed above. The boom hollow section 2 is composed of two profile sections 4, 5 and has a total of octagonal cross-section. Each of the two profile sections 4, 5 is folded four times parallel to the longitudinal axis 3.

The reinforcing layer 7 can be arranged in the described embodiments along the entire boom hollow profile or only along sections thereof.

A boom assembly may be constructed of a plurality of such cantilevers 1, which may for example be telescoped into each other or may be connected to each other via joints.

Claims (16)

1. A jib (1) for receiving loads at its end including a metallic jib hollow profile (2) extending along a jib longitudinal axis (3) and a reinforcing layer (7) of a fibre-plastic composite, which is present at least in sections, wherein the reinforcing layer (7) is arranged in the form of a reinforcing lining in the cavity of the boom hollow profile (2), characterised in that sensor elements for detecting load forces acting on the jib are arranged in the vicinity of the reinforcing layer and that at least one of the sensor elements (12₁ to 12₄) is arranged on an inner wall (39) of the reinforcing layer (7) and at least one further sensor element (12₁ to 12₄) is arranged between the reinforcing layer (7) and the boom hollow profile (2).
2. A jib as claimed in Claim 1, characterised in that the sensor element (12₁) is in signal connection with an external control device (13).
3. A jib as claimed in one of Claims 1 to 2, characterised in that the fibre-plastic composite is constructed with carbon fibres.
4. A jib as claimed in one of Claims 1 to 3, characterised in that at least a predominant proportion of the fibres (9) of the reinforcing layer (7) is arranged with a lengthy component parallel to the longitudinal axis (3) of the jib (1).
5. A jib as claimed in one of Claims 1 to 4, characterised in that at least a predominant proportion of the fibres (9) of the reinforcing layer (7) is arranged obliquely to the longitudinal axis of the jib (1), wherein, in particular, different and particularly intersecting fibre orientations are present.
6. A jib as claimed in one of Claims 1 to 5, characterised in that arranged between the reinforcing layer (7) and the jib hollow profile (2) there is an electrically insulating intermediate layer (14), which is preferably constructed in the form of a fibre layer, particularly a glass fibre layer.
7. A jib as claimed in one of Claims 1 to 6, characterised in that the jib hollow profile (2) is composed of at least two profile sections (4, 5), which are connected together along the jib longitudinal axis (3).
8. A jib as claimed in one of Claims 1 to 7, characterised by at least one group (38, 40) with four sensor elements (12₁ to 12₄) connected together in the form of a measuring bridge for detecting load forces acting on the jib (1).
9. A method of manufacturing the jib (1) as claimed in one of Claims 1 to 8 including the following method steps:

   - providing the boom hollow profile (2) or the profile sections (4, 5) thereof,

   - applying the reinforcing layer (7) to the beam hollow profile (2) or the profile section (4, 5),

   - connecting the profile sections (4, 5), if necessary.
10. A method as claimed in Claim 9, characterised in that the application of the reinforcing layer (7) is effected by

    - placing a fibre layer (10) into the boom hollow profile (2) or onto the profile sections (4, 5) thereof,

    - injecting a polymer synthetic resin/curing agent mixture into the fibre layer (10),

    - curing the synthetic resin/curing agent mixture.
11. A method as claimed in Claim 10, characterised in that after the placing process or during the placing process orientation of the fibres (9) of the fibre layer (10) is effected.
12. A method as claimed in one of Claims 9 to 11, characterised in that the intermediate layer (14) is introduced between the fibre layer (10) and the jib hollow profile (2) or the profile section (4, 5) thereof.
13. A method as claimed in one of Claims 9 to 12, characterised in that the reinforcing layer (7) is secured by adhesive to the jib hollow profile (2) or the profile section (4, 5) thereof.
14. A method as claimed in Claim 13, characterised in that the reinforcing layer (7) is pressed during the securing by adhesive to the jib hollow profile (2) or the profile section (4, 5) thereof.
15. A method as claimed in Claim 14, characterised in that two reinforcing layers (17) are secured simultaneously by adhesive in the jib hollow profile (2), wherein arranged between the two reinforcing layers (7) there is a pressure body (32).
16. A method as claimed in Claim 15, characterised in that the pressure body (32) is filled with a fluid, particularly with water or oil, during the pressing of the reinforcing layers (7).

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