IT202000019636A1 - MULTI-BLADE MULTIPLE CROSS CUTTING MACHINE FOR CUTTING TO SIZE OF WOODEN BOARDS - Google Patents

Description

MULTI-BLADE MULTIPLE CROSS CUTTING MACHINE FOR CUTTING TO SIZE OF WOODEN BOARDS.

DESCRIPTION

The invention relates to a multi-blade multiple cross cutting machine for cutting wooden planks to size.

Special automatic machines configured for cutting a wooden board to size, which is in turn obtained from the longitudinal cut of a trunk, are currently known in the field of industrial processing of wooden materials.

Each plank obtained from a log cut lengthwise must then be brought to the right length based on the intended final use.

A wooden board extracted from a trunk can have a length between 1.5 and 6 meters.

Similar wooden planks are aimed at the wooden pallets industry, but also in other sectors, such as the construction of coffins, and other similar fields which envisage the production of wooden elements.

Such wooden planks normally need to be cut into smaller pieces. court, depending on the specific intended use.

In order to reduce the timing of cutting operations in sawmills, industrial machines configured to cut the same board, generally between 1.5 meters and 6 meters in length, plus lengths, have been developed and are known today. points at the same time.

These multiple transversal cutting machines comprise a base on which a certain number of circular saws can slide on the same guide, each of which is mounted on a corresponding movable frame; some of the movable frames can translate on the guide, so as to adjust their cutting position to the length of the part of the board to be cut.

These multiple cutting machines are configured in such a way that the coaxial cutting blades are pivoted on the respective frame around a fixed axis, and in such a way that a table to be cut is pushed in translation against these fixed axis blades .

There are therefore pushers that push a board against the blades until the board ? been cut across its entire width. Although these multiple cutting machines are used profitably, they have some drawbacks.

A first drawback? linked to the fact that wood, being an originally natural product, can? show up with numerous imperfections including the so-called ?canastro?; with the term ?canastro? refers to a wood in which a compressive stress (wind, asymmetrical crown), has originated a modification of the cell walls which are substantially more? thick and thicker lignified.

The major drawbacks caused by the canastro are the difficulty? of processing and from the tendency to split and to movements following variations in humidity.

The transversal cut of planks of wood taken from conifers, in which the cane is very present, it is particularly difficult to achieve with a multiple cutting machine as described above, since? a certain lateral thrust implemented in a certain area of the table pu? be sufficient to determine the regular advancement and the transversal cut of the table in that area, while the same lateral thrust in a different area of the same table can? not be sufficient, if in that area there is a thickening and therefore a typical hardening of the cane.

A similar situation makes the operation of contemporary cut in pi? points of a very problematic table, since? the board could tend to move from the ideal cross-cut arrangement, giving rise to semi-finished board products that do not conform to the expected geometric shapes and dimensions, where such conformity? inevitably lead to scraps or new piece rework operations, in both cases with undesirable cost increases.

Task of the present invention ? that of developing a multi-blade multiple transversal cutting machine for cutting wooden planks to size, capable of overcoming the aforementioned drawbacks and limitations of the prior art.

In particular, a purpose of the invention ? that of developing a multi-blade machine capable of correctly cutting a board without moving the latter from the correct set-up required to perform the cut.

Another purpose of the invention? to develop a multi-blade machine pi? precise and fast than similar machines of known type.

A further purpose of the invention ? that of developing a multi-blade machine capable of precisely cutting all areas of a wooden board, even those with imperfections such as cane and the like.

The task as well as the aforementioned purposes are achieved by a multi-blade machine for multiple transversal cutting to size of wooden boards according to claim 1.

Further characteristics of the multi-blade machine according to claim 1 are described in the dependent claims. The aim and the aforesaid objects, together with the advantages which will be mentioned hereinafter, are highlighted by the description of an embodiment of the invention, which is given, by way of example but not in limitation, with reference to the attached drawings, where: - Figure 1 is a side view of a multi-blade machine for cutting wooden planks to size according to the invention;

figure 2 is a cross-sectional view of a machine according to the invention in a first operating stage;

- figure 3 represents the same cross-sectional view of figure 2, in a second operative phase;

figure 4 is a side view in section of a part of the machine according to the invention;

- figure 5 is a plan view of a machine according to the invention;

- figure 6 is a further side view of the machine according to the invention;

- figure 7 is a perspective view of a part of the machine according to the invention;

figure 8 represents another perspective view of the same part of the machine of figure 7;

- figure 9 is a perspective view of a detail of a multi-blade machine according to the invention;

- figure 10 represents a perspective view of a detail of figure 9.

With reference to the cited figures, a multi-blade machine for cutting wooden planks to size according to the invention ? indicated as a whole with the number 10.

This multi-blade machine 10 comprises:

- a crankcase 11,

- a guide 12 having a development direction X1,

- a plurality? of load-bearing frames 13, 14, 14a, 14b, 14c, 14d, 14e at least part of which are constrained to translate with movement means 15 on the guide 12 in the development direction X1.

In the present, non-limiting embodiment of the invention, there are seven bearing frames 13, 14, 14a, 14b, 14c, 14d, 14e.

These load-bearing frames are understood to be able to be even more? of seven or less than seven.

In a variant embodiment of the invention, not illustrated for the sake of simplicity, the multi-blade machine according to the invention comprises a plurality of blades. of movable bearing frames, i.e. at least two movable bearing frames, and no fixed bearing frames.

In the present embodiment, a first supporting frame 13 is fixed to the guide 12 and then to the base 11.

In the present embodiment, at least two supporting frames, for example six other supporting frames 14, 14a, 14b, 14c, 14d and 14e, are movable with respect to the guide 12 and can translate on this guide 12 with respective movement means 15 more? better described below.

In figures 2 to 5 ? shown is a supporting frame 14 by way of example, meaning the other supporting frames 13, 14a, 14b, 14c, 14d and 14e substantially the same.

Each of the supporting frames 13, 14, 14a, 14b, 14c, 14d, 14e has: - a rotating cutting blade 18, with an axis of rotation parallel to the development direction X1, and corresponding drive means 19 for the rotating blade 18 ,

- handling means 17 for moving the rotating blade 18 between a rest position and an operating position in correspondence with a cutting area 22 of the supporting frame 14,

- movement means 20 for the translation of a table T in a transversal direction X2 with respect to the development direction X1, from a first side 23, for loading, to a second opposite side 24, for unloading, of the supporting frame 14,

- locking means 21 for the reversible locking of a table T being worked in correspondence with the cutting area 22.

For each of the supporting frames 13, 14, 14a, 14b, 14c, 14d, 14e, the rotating blade 18, the locking means 21 and the cutting area 22 are configured in such a way as to hold and work a table T with this It is last positioned with its main axis, i.e. the longitudinal development axis of the table T, arranged parallel to the development direction X1 of the guide 12.

Therefore, a table T being machined positioned in this cutting area 22 ? positioned with its axis of longitudinal development that ? parallel to the X1 development direction of guide 12.

In the embodiment of the multi-blade machine 10 according to the invention described here by way of non-limiting example of the invention, the movement means 17 for moving the rotating blade 18 comprise:

- a movable bracket 16 constrained to the supporting frame 14,

- the rotating blade 18 with rotation axis parallel to the development direction X, and the corresponding actuation means 19 for the rotating blade 18 being mounted on the mobile bracket 16;

- handling means 50 for moving the movable bracket 16 between a rest position, i.e. non-operative, of the rotating blade 18, and an operating position, i.e. an attitude in which the rotating blade performs a cutting operation on a table T.

The drive means 19 comprise, for example, an electric motor 26 and a belt or chain transmission 27, this belt or chain transmission 27 being configured to transmit motion from a driving pulley 26a, integral with the drive shaft of the electric motor 26, to a driven pulley 18a integral and coaxial with the rotating blade 18.

In particular, in the embodiment described here by way of non-limiting example of the invention, the movable bracket 16 is rotatably constrained to the supporting frame 14.

The mobile bracket 16 ? hinged to the supporting frame 14 by means of a pin 28 with an axis parallel to the axis of rotation of the rotating blade 18. This movable bracket 16 comprises at one end? a blade holder plate 16a, at the opposite end? a motor holder plate 16b and a central portion 16c, for connection between the blade holder plate 16a and the motor holder plate 16b.

The mobile bracket 16 ? pivoted to the supporting frame 14 at the central portion 16c.

This movable bracket 16, clearly visible in figures 2 and 3, in the present embodiment? ?S? shaped; ? to be understood that this movable bracket 16 can? also be shaped differently, depending on the need? and specific technical requirements.

In the present embodiment, the movement means 50 of the movable bracket 16 comprise at least one thrust cylinder, which thrust cylinder ? hinged on one side to the supporting frame 14 and on the opposite side to the movable bracket 16.

The lengthening and shortening of the thrust cylinder determine the rotation in one direction or in the opposite direction of the movable bracket 16. The movement means 50 are clearly visible in figures 2 and 3.

The base 11, to be understood obviously as a type in itself? known, ? exemplified as consisting of four columns 11a, configured to support the multi-blade machine 10 at the ends of guide 12.

The guide 12 comprises two horizontal beams 12a and 12b, clearly visible in figure 3, parallel to each other.

In particular, but not exclusively, the horizontal beams 12a and 12b have a quadrangular tubular section.

Above each of the horizontal beams 12a and 12b there is a rail 29 configured to cooperate with a corresponding overlying shoe 30 fixed to a mobile bearing frame 14, 14a, 14b, 14c, 14d and 14e.

The fixed bearing frame 13 does not have any slide and ? fixed at a first end? of the guide 12, as clearly visible in figures 1 and 6.

The fixed bearing frame 13 and the movable bearing frames 14, 14a, 14b, 14c, 14d, 14e are substantially "C" configured; such bearing frames each include:

- a lower crosspiece 31, extending transversely to the direction of development X1,

- a lateral upright 32, extending upwards from one end? of the lower crosspiece 31,

- an upper crosspiece 33, which cantilevers out from the upper part of the lateral upright 32,

- a structural carter 34, mounted on the lower cross member 31 and configured to contain the rotating blade 18 both in the rest position and in the operative position.

The lower crosspiece 31 has at the bottom the runners 30 for sliding the mobile bearing frame 14, 14a, 14, 14c, 14d, 14e on the respective rails 29.

The upper crosspiece 33 extends above the structural casing 34.

The upper crosspiece 33 carries the locking means 21 for the reversible locking of a table T being worked in correspondence with the cutting area 22.

The cutting area 22 ? defined above the structural casing 34.

Between the cutting area 22 and the overlying locking means 21 ? defined the space for a table T being machined.

The structural carter 34 ? also configured to support the displacement means 20 for the translation of a table T in a transverse direction X2.

Said displacement means 20 comprise a driving circuit comprising at least one element with flexible longitudinal development 46 defining an annular path between a plurality of return wheels 40, 41, 42 and 43, and a motor gear 44, in turn driven by a corresponding motor 45.

The 45 engine? fixed to a support 70 placed at one end? of the guide 12, as clearly visible in figures 1 and 6.

The 45 engine, ? for example an electric motor.

The power developed by the 45 engine? transferred to the movable bearing frames 14, 14a, 14b, 14c, 14d and 14e by means of a hexagonal shaft 71 passing through corresponding hexagonal hubs of the motor gears 45; the? tree hexagonal ? schematized by a dashed axis in figures 1 and 6.

The power developed by the 45 engine? transferred to the drive gear 44 of the fixed bearing frame 13 via a cylindrical shaft 71a flanged coaxially to the hexagonal shaft 71 which drives the drive gears 44 of the movable bearing frames.

The hexagonal shaft 71, passing through the hexagonal hubs of the motor gears 44, allows the translation of the mobile bearing frames 14, 14a, 14b, 14c, 14d, 14e and the transmission of the torque useful for the work of the displacement means 20.

Each flexible longitudinal member 46 ? configured in such a way as to allow the surface gripping of a table T and the dragging of the same.

For example, but not exclusively, such at least one element with flexible longitudinal development 46 ? consisting of a chain, and the return wheels 40, 41, 42, 43 are gear wheels.

The external bearing frames, ie the fixed bearing frame 13 and the sixth mobile bearing frame 14e, have a single element 46 with flexible longitudinal development, consisting of a single chain.

The movable internal bearing frames 14, 14a, 14b, 14c, 14d, ie arranged between the two external bearing frames 13 and 14e, have two flexible longitudinally extending elements 46 and 46a, extending in parallel. The structural casing 34 has an upper opening for the passage of the rotating blade 18.

The upper opening? defined on an upper plate 35 of the structural casing 34.

The flexible longitudinally extending elements 46, and also 46a, slide above the upper plate 35 for a distance between a transmission wheel 40 and the driving gear 44.

Alternatively, the length of the flexible longitudinal elements 46 and 46a above the upper plate 35 is between two return wheels, and the motor gear ? engaged in different points of the flexible longitudinally extending elements 46 and 46a.

In the present embodiment, a first return wheel 40 ? positioned on a first side 23, for loading, of the cutting area 22, near? of the upper plate 35; the motor gear 44 ? positioned on the second opposite side 24, unloading, of the cutting area 22, also near? of the upper plate 35.

The return wheels 40, 41, 42, 43 and the driving gear 44 are supported by the structural casing 34.

The return wheels 40, 41, 42, 43 and the driving gear 44 are positioned on board the structural casing 34 in such a way that the respective flexible longitudinally extending elements 46 and 46a determine a circuit which bypasses the areas occupied by the rotating blade 18 in the transition between the rest position and the operational cutting position.

The actuator cylinder of the movement means 50 for the movable bracket 16 ? hinged at one end? to the central portion 16c of the movable bracket 16 and to the end? opposite to an appendix 52 of the structural carter 34, which appendix 52 ? indicated in figures 3 and 7.

In particular, the actuator cylinder ? positioned so that the head of the stem is hinged to the central portion 16c.

In an alternative construction, not illustrated for simplicity? In the description, the moving means for the rotating blade are of the linear and non-rotating type, for example means for moving the rotating blade from bottom to top or from top to bottom.

The locking means 21 for the reversible locking of a table T being worked in correspondence with the cutting area 22, clearly visible in figures 2, 3, 8 and 9, comprise a pressure body 55 moved by displacement means 56 between a raised position , inoperative, schematized in figure 2, and a lowered, operative or thrust position on a table T resting in the cutting area 22, schematized in figure 3.

The pressure body 55 comprises, for example, a metal box open at the bottom to allow the passage of the rotating blade 18.

The lower support edges 55a of the pressure body 55 have gripping teeth, configured to grip the surface of the table T and prevent it from moving during the cutting phase of the same table T.

The displacement means 56 comprise two connecting rods 57 constrained on one side to the upper crosspiece 33 of the supporting frame 13, 14, 14a, 14b, 14c, 14d, 14e and on the opposite side to the pressure body 55, so to be defined as an articulated quadrilateral.

The moving means 56 comprise at least one actuator cylinder 58, for example a single actuator cylinder 58 constrained on one side to the upper crosspiece 33 and on the opposite side to a lever 59 integral with a connecting rod 57.

The upper beam 33 ? consisting of a hollow profile open downwards.

The actuator cylinder 58 ? placed to operate inside the upper crosspiece 33, as clearly visible in figure 10.

The actuator cylinder 58 ? pneumatic type; this actuator cylinder 58 ? it should be understood that it can also be of the hydraulic type.

In general, the displacement means are to be understood as capable of including other actuators, for example electric actuators, and other kinematic systems for guiding the displacements, which are technically similar and equivalent.

With the term ?connecting rod? 57 means a group of elements comprising two opposite symmetrical plates.

The blocking means 21 also comprise a safety system 60 configured to prevent the transversal movement of the table T when this is? in the shear zone T.

This safety system 60 comprises a table stop bar 61, pivoted to the upper crosspiece 33 and operated by an actuator cylinder 62.

The table stop bar 61 ? long enough to be arranged alongside the cutting area 22 when the table-stop bar 61 itself? in operational trim, i.e. rotated downwards.

This stop-table bar 61 ? configured to prevent a table T, placed in the cutting area 22 and subjected to the stresses of a rotating blade 18 during cutting operations, from moving, from the cutting position, in the transversal direction X2 which goes from the first side 23 to the second opposite side 24 of the bearing frame 14.

The six supporting frames 14, 14a, 14b, 14c, 14d and 14e are movable with respect to the guide 12 and can translate on this guide 12 with respective movement means 15.

For each of the mobile bearing frames 14, 14a, 14b, 14c, 14d, 14e, the movement means 15 comprise an electric motor 63 fixed to the lower crosspiece 31 of the mobile bearing frame, for example the mobile bearing frame 14, which electric motor 63 it drives a drive shaft 64 which is in turn configured to drive two pinions 65 each meshed with a corresponding rack 66 which is in turn fixed to a respective horizontal beam 12a and 12b of the guide 12. The electric motors 63 of the looms are of the brushless type; these electric motors are capable of ensuring a fine positioning of each of the movable bearing frames 14, 14a, 14b, 14c, 14d and 14e and at the same time ensure stability? of the position, in the development direction X1, of the movable bearing frames on the guide 12.

The movement means 15 also comprise two anti-tip wheels 67 each arranged to slide under a corresponding horizontal beam 12a and 12b; each anti-tip wheel 67 ? pivoted to a bracket 68 extending below the lower cross member 31.

The handling means 15 also include means 80 for fine control of the position, configured to detect with micrometric precision the position of a mobile supporting frame 14, 14a, 14b, 14c, 14d, 14e with respect to the guide 12.

In the present embodiment, these fine control means of the position 80 comprise an electromagnetic bar fixed to one of the horizontal beams 12a and 12b of the guide 12, and a position sensor on board each mobile supporting frame 14, 14a, 14b, 14c, 14d, 14e, positioned facing the electromagnetic bar.

The multi-blade machine 10 according to the invention also comprises a mobile chute 90, positioned at the fixed bearing frame 13, configured and moved in such a way as to be able to assume two configurations:

- a first arrangement, raised, for unloading by fall, thanks to which the scrap S of the head of the table falls below the mobile chute 90, which ? positioned substantially vertically and not ? capable of intercepting the fall of a head scrap of a board that falls from the fixed bearing frame 13; below the mobile slide 90 pu? Is there a conveyor that takes the waste to a grinder, where is the waste ? for example reduced in chips;

- or a second position, lowered, for unloading with sliding, thanks to which the waste slides on the mobile chute 90, positioned inclined, and reaches a collection area, external to the multi-blade machine 10.

The moving slide 90 ? consisting of a hinged plate with horizontal axis and transversal to the development direction X1, to a support fixed to the horizontal beams 12a and 12b of the guide 12.

The moving slide 90 ? moved by one or more? actuator cylinders 91, for example of the pneumatic type.

The command for raising or lowering the mobile chute 90 ? given by a system for measuring the length of the table being worked on; for example, if the board protrudes less than 15 cm. with respect to the rotating blade 18 of the fixed bearing frame 13, the mobile chute 90 is brought into the first trim raised, and the lead scrap is chipped; if the table protrudes more? of 15 cm, the mobile slide 90 ? brought to the second position, lowered, and the material is taken and taken up again for other processes.

Yup ? in practice it has been observed that the invention achieves the intended aim and objects.

In particular, with the? Invention? development of a multi-blade machine capable of correctly cutting a board without moving the latter from the correct set-up required to perform the cut, thanks to the rotating blades that move while the board to be cut is ? held still.

In particular, thanks to the presser consisting of a box-shaped body shaped in such a way as to allow part of the rotating blade to enter inside it, the rotating blade acts on the table to be cut precisely in correspondence with the presser body and substantially in the same direction in which the pressure body pushes on the table, in this way the torque due to the shear forces on one side and the thrust of the pressure body on the other? very low and the table? firm hold with much greater effectiveness than known multi-blade machines.

Furthermore, with? The invention? set up a multi-blade machine pi? precise and fast than similar machines of known type.

Furthermore, with the? Invention? development of a multi-blade machine capable of precisely cutting all areas of a wooden board, even those with imperfections such as cane and the like.

Furthermore, thanks to the fine control means of the position of the mobile bearing frames, the multi-blade machine according to the invention is capable of operating with much greater precision than known multi-blade machines.

The invention so? conceived ? susceptible to numerous modifications and variations, all falling within the scope of the inventive concept; furthermore, all the details may be replaced by other technically equivalent elements.

In practice, the components and materials used, provided? compatible with the specific use, as well as? the contingent dimensions and shapes may be any according to the requirements and to the state of the art.

Where features and techniques mentioned in any claim are followed by reference marks, such reference marks are intended to be affixed for the sole purpose of enhancing intelligibility? of the claims and consequently such reference marks have no limiting effect on the interpretation of each element identified by way of example by such reference marks.

Claims (10)

1) Multi-blade (10) multiple cross cutting machine for cutting wooden planks to size, characterized by the fact that it includes: - a base (11), - a guide (12) having a development direction (X1), - a plurality? of bearing frames (13, 14, 14a, 14b, 14c, 14d, 14e) at least part of which are constrained to translate with movement means (15) on said guide (12) in said development direction (X1), each of said supporting frames (13, 14, 14a, 14b, 14c, 14d, 14e) presenting: - a rotating cutting blade (18), with rotation axis parallel to said direction of development (X1), and corresponding actuation means (19) for said rotating blade (18), - handling means (17) for moving said rotating blade (18) between a rest position and an operating position in correspondence with a cutting area (22) of said supporting frame (13, 14, 14a, 14b, 14c , 14d, 14e), - displacement means (20) for the translation of a table (T) in a transverse direction (X2) with respect to said development direction (X1), from a first loading side (23), to a second opposite side ( 24), unloading, of the supporting frame (13, 14, 14a, 14b, 14c, 14d, 14e), - locking means (21) for the reversible locking of a table (T) being worked in correspondence with said cutting area (22). 2) Multi-blade machine according to claim 1, characterized in that said handling means (17) for handling said rotating blade (18) comprise: - a movable bracket (16) constrained to said load-bearing frame (14), - on said movable bracket (16) being mounted said rotating blade (18) with axis of rotation parallel to the development direction (X1), and the corresponding drive means (19) for said rotating blade (18); - handling means (50) for moving said movable bracket (16) between a rest position, i.e. non-operative, of said rotating blade (18), and an operating position, i.e. an attitude in which said rotating blade (18 ) performs a cutting operation on a table (T). 3) Multi-blade machine according to one or more? of the preceding claims, characterized in that said drive means (19) comprise an electric motor (26) and a belt or chain transmission (27), said belt or chain transmission (27) being configured to transmit motion from one driving pulley (26a), integral with the driving shaft of said electric motor (26), with a driven pulley (18a) integral and coaxial with said rotating blade (18). 4) Multi-blade machine according to one or more? of the preceding claims, characterized in that said movable bracket (16) ? rotatably constrained to the corresponding said bearing frame (13, 14, 14a, 14b, 14c, 14d, 14e), said movable bracket (16) being hinged to said bearing frame (13, 14, 14a, 14b, 14c, 14d, 14e) by means of a pin (28) having an axis parallel to the axis of rotation of said rotating blade (18). 5) Multi-blade machine according to one or more? of the preceding claims, characterized in that said movable bracket (16) comprises at one end? a blade holder plate (16a), at the opposite end? a motor holder plate (16b) and a central portion (16c), for connection between said blade holder plate (16a) and said motor holder plate (16b), said movable bracket (16) being pivoted to the respective supporting frame (13, 14, 14a, 14b, 14c, 14d, 14e) in correspondence with the central portion (16c). 6) Multi-blade machine according to one or more? of the preceding claims, characterized in that said guide (12) comprises two horizontal beams (12a, 12b) parallel to each other, above each of said horizontal beams (12a, 12b) there being a rail (29) configured to cooperate with a corresponding overlying shoe (30) fixed to a mobile bearing frame (14, 14a, 14b, 14c, 14d, 14e). 7) Multi-blade machine according to one or more? of the preceding claims, characterized in that a fixed bearing frame (13) and the movable bearing frames (14, 14a, 14b, 14c, 14d, 14e) are substantially "C"-shaped, said bearing frames each comprising: - a lower crosspiece (31), extending transversely to said direction of development (X1), - a lateral upright (32), extending upwards from one end? of the lower crosspiece (31), - an upper cross member (33), projecting from the upper part of the lateral upright (32), - a structural carter (34), mounted on the lower crosspiece (31) and configured to contain the rotating blade (18) both in the rest position and in the operational position, said upper crosspiece (33) extending above said structural carter (34). 8) Multi-blade machine according to one or more? of the preceding claims, characterized in that said lower crosspiece (31) has said shoes (30) at the bottom for sliding a mobile bearing frame (14, 14a, 14, 14c, 14d, 14e) on the respective rails (29). 9) Multi-blade machine according to one or more? of the preceding claims, characterized in that said structural carter (34) ? configured to support the displacement means (20) for the translation of a table (T) in a transversal direction (X2) with respect to said development direction (X1). 10) Multi-blade machine according to one or more? of the preceding claims, characterized in that said displacement means (20) comprise a driving circuit comprising at least one element with flexible longitudinal development (46, 46a) defining an annular path between a plurality of return wheels (40, 41, 42, 43), and a motor gear (44), in turn driven by a corresponding motor (45).