WO2017149461A1

WO2017149461A1 - Method for automatically picking metallic elements of elongated shape and picking device

Info

Publication number: WO2017149461A1
Application number: PCT/IB2017/051178
Authority: WO
Inventors: Simone Rupoli
Original assignee: Schnell S.P.A.
Priority date: 2016-02-29
Filing date: 2017-02-28
Publication date: 2017-09-08
Also published as: EP3423208A1; EP3423208B1; ITUB20161159A1

Abstract

The method for automatically picking metal elements of elongated shape, in particular bar-shaped metal profiles, provides to prearrange a gripping device (10) comprising a magnetic source (11) for picking the metal elements (2), adjustable between a condition of maximum grip and a condition of minimum grip, to adjust the gripping device (10) to a desired degree of grip, and to place it at a picking zone (3) in which the elements (2) to be picked are arranged. The gripping device (10) performs the gripping at the desired degree of grip, handles the elements (2), by holding them, to a discharge zone, and releases the handled elements (2) into the discharge zone, by adjusting the gripping degree to the minimum grip condition.

Description

METHOD FOR AUTOMATICALLY PICKING METAL ELEMENTS OF ELONGATED SHAPE

AND GRIPPING DEVICE

Technical Field

[01 ] The present invention concerns a method for automatically picking metal elements of elongated shape, in particular bar-shaped metal profiles, and a gripping device predisposed to carry out such method.

Background Art

[02] It has been known the use of apparatuses for automatically loading metal elements of elongated shape, in particular bar-shaped metal profiles, from a respective store, generally constituted by a plurality of compartments placed on the floor, inside which said elements are prearranged, separated according to size and type.

[03] The above-mentioned apparatuses are equipped with picking means, for example of the magnetic type, for picking groups of bars from respective compartments, as well as a transfer device, for loading the picked bars, associated with counting and transfer means for transferring a determined number of bars to suitable receiving means. More precisely, the aforementioned receiving means are destined to receive the counted bars and to transfer them to subsequent work stations, for example cut and/or fold stations.

[04] An example of these apparatuses is disclosed in EP1356875 in the name of the same Applicant. In particular, the apparatus disclosed in this patent comprises a transfer device arranged above a collecting store, comprising a body shaping a shelf, tiltable between a substantially horizontal position and a lowered position, substantially vertical, predisposed to free the passage of the bars during the load and unload thereof.

[05] The known apparatuses are generally used to load, in a controlled manner, bars of very different transverse size, usually comprised between 8mm and at least 55mm of diameter. Given the wide variety and diversity of products to be picked, held and handled, the provided picking means are not always able to process the bars in an efficient way.

[06] More precisely, the commonly used picking means comprise magnetic sources of the type of permanent magnets and electromagnets, sized for the maximum nominal load. This means that such magnetic means usually involve high power, effective for manipulating metal elements of large size and heavy weight, but too big to handle standard elements and lower weight.

[07] Consequently, it often happens that at each loading cycle, the elements are picked in excessive number than necessary. Therefore, in addition to the waste of mechanical work to be provided, it is necessary to specially provide a discharge cycle of the exceeding number of elements, lengthening the production time accordingly. In addition, in case of metal elements of reduced diameter or cross-dimension, it is also necessary to consider the phenomenon, very accentuated, of the mutual entanglement of the metal wires, already picked, but in excess. This phenomenon also makes difficult the necessary unloading operations, that is, the operations of return in the source stock. In the following picking cycles from the same stock, the loading operations can then be even more difficult.

WO 2005/095254 disloses a gripping device for gripping pieces by a magnetic force, comprising a casing predisposed to define an internal chamber, a magnet movably mounted in the same housing, and an actuator for moving the magnet towards and away from the inner side of a wall that separates the said inner chamber of the casing from the pieces to be picked. The aforesaid actuator is of pneumatic type.

Disclosure

The task of the present invention is to solve the aforementioned problems, devising a method and a device for automatically feeding elements of elongated shape, in particular bar-shaped metal profiles, that allows to perform the feeding step in an efficient way in any working condition.

Within such task, in is a further scope of the present invention to provide a device of simple constructive and functional conception, provided with safe and reliable use, as well as relatively economic cost.

The cited scopes are reached according to the present invention by the method for automatically picking metal elements of elongated shape according to claim 1 and by the gripping device according to claim 5.

The gripping device according to the invention comprises a magnetic source to which metal elements, in particular bar-shaped metal profiles, are responsive. Preferably, the magnetic source is a permanent magnet capable of exerting a force of attraction on such elements. A feature of the invention consists in the fact of enabling the adjustment of such force of attraction. Such result is made possible by the provision of an adjustable spacer associated with the cited magnetic source and in in the fact that the spacer and the magnetic source are mobile relatively one another between a condition of maximum grip and a condition of minimum grip or discharge.

Such provision allows to adjust in corresponding manner the force of attraction exerted by the magnetic source on the elements when they are arranged in abutment against said spacer.

In particular, it is possible to control in a precise manner the force of attraction exerted on the elements to be picked or released, by adjusting it according to the type, in particular size and weight, of the elements to handle, as well as according to the exigencies of the working cycle. Therefore, the device allows, thanks to the adjustable spacer, to handle in a controlled manner an adequate number, not excessive, of elements from a loading zone to an unloading zone and vice versa.

Moreover, the device according to the invention allows to handle the metal elements to be picked and/or released in ordered manner. Such result is possible, in particular, thanks to the adjustable spacer that can space in controlled manner, for example maximum, as it was previously described, the force of attraction exerted on the elements by the magnetic source and, simultaneously, be approached to a releasing plane at a distance comparable to the transverse size of the elements to be ordered, so as to arrange them, at the unloading zone, substantially on a single plane or in equivalent manner, in a substantially flat single row. In such release operation, according to a feature of the invention, the magnetic source is brought to and kept in the condition of minimum or null grip, so as not to interfere with the ordering action of the elements exerted by the adjustable spacer.

According to a particular aspect of the invention, the abutment screen is shaped by a structure preferably but not limitedly nonmagnetic inside which the magnetic source is arranged, sliding according to a longitudinal grip direction.

The magnetic source can be mobile along a longitudinal adjustment direction, inside a containment structure shaping the adjustable spacer, alternatively between a backed position, of minimum grip, predisposed to release the elements, and an advanced position, for example protruding from the structure through a respective opening end of the same structure, of maximum grip of the elements.

The above-mentioned structure is operated, carrying the magnetic source, in a grip direction, for picking the elements, in particular bars or similar pieces, and for downloading them in a release zone.

The structure can be tubular or box-like, extending along the cited longitudinal adjustment direction, and shaping the above-mentioned spacer. Such spacer can provide a perimetral extension, for example box-like, about the magnetic source.

In practice, according to a particular aspect of the invention, preferred, the spacer shapes a perimetral frame, inside which the magnetic source is arranged mobile.

Between the spacer and the magnetic source a relative movement of controlled sliding, along the longitudinal adjustment direction, is allowed. The spacer can then limit at pleasure the distance between the elements to be handled and the source, interposing in controlled manner, thereby limiting the force of attraction exerted on the elements in a manner directly proportional to the respective controlled distance. This advantageously allows to adjust the intensity of the force of attraction also using as source a permanent magnet, incapable per se of any adjustment. The adjustment motion is preferably operated by command means of linear type, for example of the type comprising an endless screw member.

The spacer, if nonmagnetic, can have the advantageous effect of laterally shielding, in the condition of maximum grip, the magnetic field produced by the magnetic source, limiting the force of attraction substantially along the longitudinal grip direction.

In substance, the presence of the spacer eases the ordered picking of the elements, allowing to adjust, in particular also to direct, in a controlled manner, the efficiency of the grip.

The grip device according to the invention allows to solve the problem complained for the devices of known type that, in presence of elements of small transverse size, cannot prevent to pick or handle an excessive quantity of elements, in particular bars, and arrange them on more overlapped layers. This causes, in the known devices, significant handling, counting and managing problems.

As an alternative, the above-mentioned structure can shape at least a plurality of walls, mutually adjacent and opposite, which end portions can act as adjustable spacer for the elements to be picked or discharged orderly.

According to an aspect of the invention, a gripping unit can be provided comprising a couple of gripping devices, each, as previously described, aligned along the longitudinal extension of the elements to pick, operable selectively or simultaneously, to allow the safe grip of the elements, in a controlled manner according to the weight and/or the size of said elements. In particular, the couple of gripping devices can be operated to handle elements of high weight, while a single device can be operated in case elements of reduced weight, easily interchangeable.

Description of Drawings

Details of the invention shall be more apparent from the detailed description of a preferred embodiment of the gripping device predisposed to carry out the method for automatically picking elements of elongated shape, illustrated for indicative purposes in the attached drawings, wherein:

figures 1 , 2, 3, 4, 4a and 5 show a side view of the apparatus in which the gripping device has been used according to the invention, respectively in subsequent working steps of picking and handling of the above-mentioned elements;

figures 6 and 7 show a side view of the gripping device according to the invention in different working steps;

figures 8, 9, 10 and 1 1 show a side view of the apparatus shown in figures 1 to 5, in subsequent working steps of a different productive cycle;

figures 12 to 14 show a perspective view of the gripping device according to the invention in different working steps. Best Mode

With particular reference to figures 1 to 5, the apparatus, in which the gripping device predisposed to carry out the method according to the invention has been used, is indicated with 1 . The apparatus 1 is used to automatically feed metal elements 2 of elongated shape, in particular bar-shaped metal profiles.

The apparatus 1 comprises a gripping device 10 intended for picking one or more elements 2 from a picking zone 3 and to place them on a release zone 4. For example, the picking zone 3 can be a compartment of a store 3 or ironworks, while the release zone 4 can be a transfer plane from which the elements 2, in counted number and in ordered succession, are transferred to working stations downstream of the apparatus 1 .

The gripping device 10 is therefore preferably mobile at least between a first position, for example lifted at the above-mentioned transfer plane 4 and a second position, for example lowered, at the store 3, according to any path, for example rectilinear or substantially rectilinear, or of different shape.

The gripping device 10 comprises a magnetic source 1 1 , suitable to exert a force of attraction, also constant, on the elements 2 and a support structure 12, shaping an adjustable spacer 13, intended for modulating the force of attraction exerted on the elements 2 to be picked.

The adjustable spacer 13 is placed at an adjustable distance from the magnetic source 1 1 , for allowing the adjustment of the cited force of attraction exerted on the elements 2 that are placed in abutment against the gripping device 10.

The magnetic source 1 1 and the adjustable spacer 13 are mobile relatively one another, to vary the distance between them, along a longitudinal adjustment direction A and therefore vary the distance between the magnetic source 1 1 and the elements 2 to be handled (see figures 6 and 7).

In particular, the structure 12 can shape for example, but not limitedly, a tubular or box-like structure, having advantageously an open end 15, inside which the magnetic source 1 1 is arranged sliding along the above-mentioned longitudinal adjustment direction A.

The spacer 13 can shape, at the above mentioned open end 15, a perimetral edge of the structure 12 against which the elements 2 can be brought in abutment. The perimetral edge is preferably delimited by a filled surface, intended for facing the elements 3 to be picked. Alternatively, the spacer 13 can be shaped by a plurality of walls, mutually opposite or adjacent, carried by the same structure 12, suitable for the purpose of protecting and possibly abutting, through its own end edge, the elements 2 to be picked (see figures 6 and The magnetic source 1 1 is carried by a linear actuation member 14, mobile along the above- mentioned longitudinal adjustment direction A, alternatively between a maximum grip condition and a minimum grip condition.

The linear actuator can be of the type comprising an endless screw member suitably operated by a motor member.

More precisely, the above-mentioned maximum grip condition corresponds to the maximum extraction of the magnetic source 1 1 from the structure 12 along the longitudinal adjustment direction A and, correspondently, at a minimum distance of the same magnetic source 1 1 from the above-mentioned edge shaped by the spacer 13. In such condition the magnetic source 1 1 is for example protruding from the edge shaped by the spacer 13 (see figure 6) through the open end 15 and then exerts a maximum attraction on the elements 2 in abutment (see figure 14).

The above-mentioned minimum gripping condition corresponds to a condition of maximum insertion of the magnetic source 1 1 inside the structure 12 along the longitudinal adjustment direction A and, correspondently, at a maximum distance of the same magnetic source 1 1 from the edge shaped by the spacer 13. In such condition the magnetic source 1 1 exerts a minimum attraction on the elements 2 close to or in abutment against the edge shaped by the same spacer 13. In the cited condition of minimum grip, the above-mentioned force of attraction can reach a value substantially null, to allow the release of the elements 2 (see figure 13).

The adjustable distance between the edge shaped by the spacer 13 and the magnetic source 1 1 allows then to attenuate at pleasure the force of attraction applied on the elements 2, modulating it depending on the type and the number of elements 2 to be handled.

The substantially flat shape of the surface of the edge shaped by the spacer 13, along with the possibility of graduating the force of attraction exerted by the magnetic source 1 1 , allows as well to align on a release plane, possibly in a single layer, the elements 2 in the releasing step.

More precisely, the spacer 13 can act as pressure member to "flatten", in other words to orderly arrange, substantially on a single row or layer, the elements 2 in the releasing step. Such compression action occurs by interposing in mutual abutment, the elements 2 between the flat surface of the above-mentioned edge shaped by the spacer 13 and the releasing plane, on which the elements 2 are unloaded by the gripping device 10.

The edge shaped by the spacer 13 can then perform a "flattening" action or levelling, accompanying and compressing the elements 2 towards a releasing zone 4 (see figure 4a). By gradually backing the magnetic source 1 1 from the edge 13, it is then possible to approach the same edge 13, carrying the elements 2 in grip, to the releasing zone, without attracting further elements 2 possibly already present therein. At the same time, the flat edge 13 can push the elements 2 to arrange on a single row or layer (see figure 4a).

The structure 12 can advantageously tilting, within a limited angular interval, with respect to a longitudinal gripping direction B, to fit the orientation of the gripping member 1 1 to the spatial arrangement of the elements 2 that, being flexible, can in fact bend and arrange, at respective gripping portions, inclined with respect to a condition perpendicular to such direction.

More precisely, the structure 12 is advantageously divided into at least a pair of box-like or tubular portions, a first portion 12a and a second portion 12b, mutually articulated, through articulations 16, for example of the piston rod type. The first portion 12a is advantageously carried by the fixed framework of the apparatus 1 , and brought sliding, along guide means arranged on a gripping direction B, by suitable operation means, for simplicity not represented, while the second portion 12b, carrying the magnetic source 1 1 and shaping the adjustable spacer 13, is directed towards the elements 2 to be picked and carried by the first portion 12a, through the interposition of the above mentioned articulations 16, so as to allow the above mentioned tilting adjustment to the arrangement of the elements 2 in the picking step and of transport (see in particular figures 12 to 14).

As it is shown in figures 12 to 14 the gripping device 10 can also comprise a sensor unit 17 predisposed to detect the presence of the elements 2 to be picked, for example when approaching to the elements 2 to be picked, or for checking that there are no elements 2 held by the gripping device 10. The sensor unit 1 7 can be of mechanical type, for example providing a touching roll 19 operated in mobile manner, for example tilting about a pin 20 carried by the same structure 12, in particular by the second portion 12b, upon operation of an actuation member 19, for example linear of hydraulic or pneumatic type.

The magnetic source 1 1 can be advantageously realized through a perimetral magnet, made adjustable in the same way as an electromagnet.

The functioning of the picking device 10 for metal elements of elongated shape according to the invention can be understood from the preceding description.

In a starting preparation step, the picking device 10 is prearranged in the cited first position, for example lifted with respect to the store 3, at a respective compartment in which the elements 2 to be picked are prearranged.

In this step, for example the transfer plane 4 is spaced from the gripping device 10 in lifted position, so as not to interfere with the subsequent steps (see figure 1 ).

Subsequently, the gripping device 10 is operated in motion along the above-mentioned gripping direction B, for example along the vertical direction, and brought in the second position, in particular lowered, approached to the top to the above-mentioned compartment of the store (see figure 2). In the same step or in the starting preparation step, the magnetic source 1 1 is handled along the longitudinal adjustment direction A of the same device, so as to adjust the distance from the spacer 13 according to the number or the type of elements 2 to be picked. The magnetic source 1 1 can be for example outwardly protruding from the edge of the spacer 13 through the cited open end 15 (see figure 6).

Then, when the spacer 13 is approached to the top of the heap of elements 2 arranged inside the picking compartment, the elements 2 arranged at the top are subjected to the force of attraction exerted by the magnetic source 1 1 , shielded in desired measure, for example minimum, by the spacer 13 (see figure 2).

The elements 2 arranged at the top of the store 3 are held by the afore-mentioned magnetic action.

The gripping device 10 is then handled again, in particular lifted along the same longitudinal gripping direction B, until the cited second position, adjacent to the transfer plane 4 (see figure 3).

The transfer plane 4 is handled in a working position suitable for transferring the picked elements 2, in particular below the portion of the elements 2, for example a portion central with respect to the longitudinal extension of the same, held by the gripping device 10 (see figure 4).

In this step, the elements 2, in grip at the grip device 4, can be brought up to contact with the surface of the transfer plane 4 (see figure 4a).

Subsequently, the magnetic source 1 1 is spaced from the spacer 13, in particular backed along the longitudinal direction A, so as to correspondently reduce the force exerted on the picked elements 2. Preferably, such spacing is progressive, so as to correspondently produce also a progressive and ordered releasing of the elements 2. The progressive releasing of the elements 2 prevents undesired dynamic reactions, such as flicks and, consequently, rebound motions of the elements 2 that would move the elements 2 in uncontrolled manner.

In the releasing step and, in particular, when the magnetic source 1 1 is at a distance from the spacer 13 such as to minimize the exerted force of attraction, the spacer edge 13 can be operated towards, that is approached and slightly pushed against, the transfer plane 4 or any releasing plane, so as to align on the same plane the elements 2.

The pressure exerted by the spacer 13, while the magnetic source 1 1 is in position of minimum or null grip, allows then to order the elements 2 on a single layer, for example eliminating undesired overlaps, on the transfer plane 4 (see figure 5, in which the final result of such "flattening" effect is shown). In such condition, the magnetic source 1 1 , arranged in position of minimum grip, does note exert, advantageously, any interference action that could interfere, otherwise, with the operation of alignment on the transfer plane 4. Thanks to such alignment operation, the spacer edge 13 eases a subsequent counting and handling step of the picked elements 2, thus acting as leveller or controller, and preventing the further entanglement of the same elements.

If the elements 2 have been picked in excess than necessary in the working cycle of the apparatus 1 , the gripping device 10 can also perform the reverse cycle, of picking from the transfer plane 4 and back to the store 3 from which the elements 2 had been previously picked. In this way, it is possible to prevent the elements 2 from freely falling into the store

3 below, with risk of entanglement, or from falling out of the store of provenance.

The gripping device 10 is then arranged above the transfer plane 4 on which the elements

2 to be downloaded again in the store 3 are arranged (see figure 8).

The magnetic source 1 1 is approached to the spacer edge 13, along the longitudinal adjustment direction A, in a way suitable to exert a certain force of attraction on the same elements 2 themselves.

Subsequently, the gripping device 10 is approached to the transfer plane 4, now picking zone, up to abutting the elements 2 (see figure 9). The elements 2 are attracted and suitably held at the gripping device 10.

The transfer plane 4 is then spaced from the gripping device 10, so as not to occupy the working space of picking and unloading (see figure 10).

Finally, the gripping device 10 is handled towards the lowered position, along the longitudinal gripping direction B, at the compartment of the store 3 in which the elements 2 must be left. By progressively backing the magnetic source 1 1 from the spacer edge 13, along the longitudinal adjustment direction A, the gripping attractive force on the elements

2 is shielded and thus progressively reduced, releasing them ordinately in the same store

3 of provenience (see figure 1 1 ).

Advantageously, the adjustment capability of the gripping device 10 according to the invention allows to pick the elements 2 with an adequate force of attraction. Moreover, the same adjustment capability allows, in the unloading step, to prevent falls for the force of gravity of the picked elements, performing, instead, an ordered and controlled downloading. More precisely, in the unloading step, the spacer 13 can act as pressure member, to arrange the elements on the transfer plane, while the source 1 1 can be spaced from the same elements 2, along the adjustment direction, not to interact with the same unloading step. In practice, the used materials as well as the size and shape may vary according to the needs.

Should the technical characteristics mentioned in the claims be followed by reference signs, such reference signs were included for the sole purpose of increasing the understanding of the claims and thus they shall not be deemed limiting the scope of the element identified by such reference signs by way of example.

Claims

1 . Method for automatically picking metal elements of elongated shape, in particular bar- shaped metal profiles, characterized in that it comprises the steps of:

(a) , prearranging a gripping device (10) mobile along a picking direction (B), comprising a magnetic source (1 1 ), predisposed to exert a force of attraction on said elements (2) and a structure (12) of containment of said magnetic source (1 1 ), having an open end (15) and shaping at said open end (15) an adjustable spacer (13), predisposed for modulating said force of attraction, said magnetic source (1 1 ) being mobile inside said structure (12) along a longitudinal adjustment direction (A), alternately between a condition of minimum grip, backed, and a condition of maximum grip, close to or outwardly protruding, from said spacer (13) shaped by said structure (12) through said open end (15);

(b) . adjusting said gripping device (10) through said spacer (13) to a desired degree of grip, by varying the distance along said longitudinal adjustment direction (A) between said magnetic source (1 1 ) and said adjustable spacer (13) shaped by said structure (12);

(c) . operating along said longitudinal gripping direction (B) said gripping device (10), placing it at a picking area (3) in which said elements to be picked (2) are arranged;

(d) . picking a number of said elements (2) through said gripping device (10) adjusted to said desired degree of grip, by approaching said gripping device (1 0) to said elements (2);

(e) handling said elements (2) held by said gripping device (10) towards a discharge zone (4);

(f) discharging said handled elements (2) at said discharge zone (5), by performing the adjustment of said gripping device (10) to said condition of minimum grip or discharge.

2. Method according to claim 1 , characterized in that said step of (f). discharging said elements (2) occurs, while said gripping device (10) is carried and rests in said minimum grip or discharge condition, exerting a compression action through said adjustable spacer (13) of said gripping device (10) on said elements (2), interposed in abutment between said adjustable spacer (13) and said discharge zone (3, 4), in order to rearrange said elements (2) in a corresponding manner, in particular in a manner substantially aligned in a row of elements (2) on said discharge zone (3, 4).

3. Method according to claim 2, characterized in that said step of (f) discharging said elements (2) provides to approach said spacer (13) to said discharge zone (3, 4) at a distance substantially equal to the transverse size of said elements (2) to be discharged, so allowing to place said elements (2) rearranged in a single row on said discharge zone.

4. Gripping device for metal elements of elongated shape, in particular bar-shaped metal profiles, comprising a magnetic source (1 1 ), predisposed to exert a force of attraction on said elements (2), said gripping device (10) being brought mobile along a gripping direction (B) to bring said elements (2) from a picking zone (3, 4) to a discharge zone (3, 4) characterized in that it comprises a containment structure (12) of said magnetic source

(1 1 ) , having an open end (15) and shaping at said open end (15) an adjustable spacer (13), intended for modulating said force of attraction, said magnetic source (1 1 ) being mobile inside said structure (12) along a longitudinal adjustment direction (A), alternately between a condition of minimum grip, backed inside said structure (12), and a condition of maximum grip, approached to or outwardly protruding from said spacer (13) shaped by said structure

(12) through said open end (15), said gripping device (10) being adjustable between said condition of maximum grip and said condition of minimum grip or discharge.

5. Device according to claim 4, characterized in that said structure (12) is tubular or box-like, said adjustable spacer (13) being shaped by said structure (12) as a continuous perimetral edge.

6. Device according to claim 5, characterized in that said adjustable spacer (13) has a substantially flat abutment surface for abutting said elements (2), predisposed to serve as pressure member, to arrange said elements (2) in aligned manner on a release plane, when said magnetic source (1 1 ) is arranged in said minimum grip position.

7. Device according to one of claims 4 to 6, characterized in that said adjustable spacer (13) is borne on respective perimetral walls of said structure (12), around said open end (15), so as to be interchangeable.

8. Device according to one claim from 4 to 7. characterized in that said magnetic source (1 1 ) is operated by a linear actuator member (14) or the type of the operating screw, being constrained to said structure (12).

9. Device according to one of claims 4 to 8, characterized in that said structure (12) is divided into at least one first portion (12a) and a second portion (12b), said first portion (12a) being operated mobile along said gripping direction (B), said second portion (12b) carrying inside said magnetic source (1 1 ) and shaping said adjustable spacer (13), said second portion 12b) being carried by said first portion (12a) through the interposition of articulations (16), so as to enable said second portion (12b) an oscillation of adjustment to the direction of said elements (2) in the picking and/or transport step of said elements (2).

10. Gripping assembly comprising a couple of gripping devices, each one according to one of the previous claims, aligned along the longitudinal length of said elements (2) to be picked, said gripping devices being selectively or simultaneously operable to allow a safe grip of elements (2), in a controlled way according to the weight and/or size of said elements (2).