EP3219628A1

EP3219628A1 - Apparatus for wrapping products with a film of extensible material

Info

Publication number: EP3219628A1
Application number: EP17161906.7A
Authority: EP
Inventors: Andrea PAZZINI; Andrea Bartoli
Original assignee: Atlanta Stretch SpA
Current assignee: Atlanta Stretch SpA
Priority date: 2016-03-18
Filing date: 2017-03-20
Publication date: 2017-09-20
Also published as: ITUA20161827A1

Abstract

The apparatus for wrapping products with a film of extensible material comprises a framework (2) predisposed to receive a product at an interaction station; a ring-shaped structure (4) carried rotatably about a central wrapping axis by a mobile support frame (3) carried by the framework (2); a dispensing unit (5) associated with the ring-shaped structure (4) and carrying a support station (51) for at least one coil (6) of the above-mentioned film, predisposed to be unwound according to an unwinding path; a translation unit working on the mobile support frame (3) for operating a relative translation, according to the wrapping axis, between the dispensing unit (5) and the product to be wrapped; a mobile diverter unit (9), for maintaining a determined degree of tensioning of the film.

Description

Technical Field

The present invention concerns an apparatus for wrapping products with a film extensible material.

Background Art

It has been known the use of apparatuses allowing to automatically wrap groups of products, usually arranged on pallets, with a film of extensible material of the type of polyethylene.
For example, EP1963188B1 , in the name of the applicant, discloses an apparatus for wrapping groups of products with a film of extensible material, provided with a ring rotating according to a vertical or horizontal axis. The rotating ring carries a dispensing unit of the film of extensible material, provided, in particular, with a roller carrying a coil of film to be unwound and with a couple of rubber-coated and motorized rollers for performing a determined pre-stretching of the material.
A further example of such kind of machines is disclosed in patent application WO2013/008161 . This application describes a machine provided with a horizontal rotating ring supported by a mobile frame along a vertical direction. The rotating ring is associated with a dispensing unit comprising a coil of film material and a pair of pre-stretching rollers operated in rotation about relative longitudinal axes by respective motor members. The pre-stretching rollers cooperate for unwinding the film material from the coil and to perform a predetermined pre-stretching of the material.
In particular, there is the need to ensure that the extensible film material is wrapped about the product with a substantially constant tensioning, so as to obtain a bandage adherent to the product in uniform manner, thus qualitatively acceptable.
Therefore, these apparatuses are usually provided with an adjustment device for the tensioning of the material, for example constituted by an adjustment roller, so called "dandy roll", about which the same film is diverted, before being wound about the product.
The above-mentioned adjustment roller has a substantially static adjustment function; in substance, in a starting step, the operator sets the actual or estimated size of the product to be packaged, for example by providing the control unit with the apparatus an average size of the perimeter, in plant, of the same product. Consequently, the apparatus is operated in such a manner as to work at a constant unwinding speed according to the theoretical or estimated datum provided in the starting step. The adjustment roller thus serves to compensate for the variations of the tensioning of the film being unwound, due to a discrepancy between the real size and the above-mentioned inserted data and/or to a discontinuity in the shape of the product, for example at any possible edges. Therefore, in the apparatuses of the known type described above, the packaging result of the depends substantially on the correctness of the theoretical data inserted by the operator at the beginning of the working cycle. If this data significantly differs from the actual product measurements, which define the wrapping perimeter, on each cross-section of the wrapping axis, the packaging may be unacceptable, because it is not sufficiently tensioned or, vice versa, for a film break.
In the light of the aforementioned drawbacks, technical solutions have been developed to ensure a dynamic adjustment of the tensioning of the film, which can instantly intervene in case of size variations of the product during wrapping, preventing film breaks and, at the same time, helping a tensioning always effective.
Patent application EP0936141 discloses, for example, a machine for wrapping products comprising a ring-shaped guide frame at the centre of which a product to be wrapped is arranged. A dispensing unit is mounted slidable on the frame, and comprises a motorized coil of material to be unwound and a series of deflection rollers of the film material defining a unwinding pathway of the material. The dispensing unit also comprises tensioning means which include a sensor connected to a control circuit predisposed to detect the tension of the film so as to continually control, by interfacing with the circuit, the operating parameters of the motor associated with the coil such as torque, rotation speed and rotation direction.

Disclosure

The task of the present invention is that of solving the aforementioned problems, devising an apparatus for wrapping products with a film of extensible material that allows to adjust in continuous manner the tensioning in the wrapping step.
Within such task, it is a further scope of the present invention to provide an apparatus for wrapping products with a film of extensible material of simple constructive and functional conception, provided with surely reliable functioning, versatile use, as well as relatively economic cost.
The cited scopes are reached, according to the present invention, by the apparatus for wrapping products with a film of extensible material according to claim 1.
The apparatus for wrapping products with a film of extensible material comprises a framework predisposed to receive a product at an interaction station, a mobile support frame, carried by the framework, a ring-shaped support structure, carried in rotatable manner about a central wrapping axis, by the above mentioned mobile support frame, a dispensing unit, carried by said ring-shaped structure and carrying a support station for at least one coil of film of extensible material, a handling unit operable according to a relative rotation motion about said wrapping axis, between said dispensing unit and the above-mentioned product, such as to allow the wrapping of the above-mentioned film of extensible material about the above-mentioned product.
With "product" is meant generally, but not exclusively, a series of items arranged on a load structure, for example of the type of the so called standardized pallet.
The apparatus comprises, as well, a translation unit for performing a relative translation according to the above-mentioned wrapping axis, between the above-mentioned dispensing unit and the above-mentioned product to be wrapped.
Along the unwinding path of the film, from the coil to the product, a diverter unit is arranged, comprising at least one mobile diverting roller, carried mobile by the same ring-shaped structure, to divert the unwinding path of the film so as to produce a desired degree of tensioning of the film being unwound.
A control unit, preferably external to the ring-shaped structure is provided to set the unwinding speed of the dispensing unit, that is, the dispensing speed of the film of extensible material from the coil.
The same control unit can as well control, for example, the rotation of the ring-shaped structure and the translation of the mobile support frame.
The apparatus also comprises a sensor element associated with the above-mentioned diverter unit, to detect an instantaneous direct measurement of the displacement of the at least one diverting roller, indicating a measurement of the instantaneous deviation of the unwinding path, predisposed to compensate for example for a variation in the shape or size of the product, along the wrapping axis.
The sensor element is associated with a continuous dispensing device comprising a wireless transmission system mounted on the ring-shaped structure, predisposed to receive and transmit the cited instantaneous direct measurement detected by the sensor element, and to transfer it in continuous manner to the cited control unit and, thus, performing the instantaneous correction of the unwinding speed of the film, in order to perform an instantaneous adjustment of the degree of tensioning imparted to the film.
The apparatus can also comprise, preferably, a pre-stretching device, made up of a first pre-stretching roller and a second counterrotating pre-stretching roller, about which the film is predisposed to be unwound along the above-mentioned unwinding path, to perform a stretching of the film, required for wrapping the product. Such stretching is determined by the ratio, generally fixed, between the angular speed of the first roller and the second roller.
According to a feature of the invention, the above mentioned at least one diverting roller is carried by a tilting arm, hinged to the same ring-shaped structure, about a tilting pin, substantially parallel to the above-mentioned unwinding axis.
In practice, the at least one diverting roller, preferably rubber-coated, is placed on the unwinding path of the feeding coil, to tension in a determined way the film of extensible material, being subjected to the action of contrast means, preferably of elastic, pneumatic, or hydraulic type.
According to an aspect of the invention, the tilting arm has a curved profile. Such curved profile is more advantageous than other profiles of different shape, such as for example a substantially linear profile, as it ensures compactness to the diverter unit, thus optimizing the required space, at equal support surface available for the diverting roller to be mounted.
According to the invention, the cited angular sensor element is preferably arranged coaxially to the tilting pin of the diverter unit, to detect an angular direct measurement of the above-mentioned adjustment tilting.
In substance, the sensor element directly measures the angular movement of the at least one diverting roller, along the unwinding path of the feeding coil of the film. The direct measurement of the angular movement contributes to speed up the continuous adjustment process of the degree of tensioning of the material and also ensures a more reliable measurement. A smaller of bigger angular displacement is indicative, along with the direction of movement, of an instantaneous demand for more or less stretching speed of the film of extensible material, to properly wrap the product being processed.
The angular sensor element is connected with a receiving/transmitting unit mounted on the above-mentioned ring-shaped structure, predisposed to receive the data from the sensor element, preferably via cables, and to transmit them to a control unit of the apparatus, through a transmission system of wireless type.
More precisely, the detected angular measurement is transmitted, through the wireless transmission means, to the control unit of the apparatus, mounted externally to the rotating ring-shaped structure, to perform an instantaneous adjustment of the unwinding speed of the film of extensible material. In particular, the control unit acts on the operation unit of the cited dispensing unit, to vary, in corresponding way, the instantaneous unwinding speed of the film and, thus, the instantly dispensed quantity of film.
The above-mentioned wireless transmission means are preferably of the Bluetooth or Wi-Fi or of other equivalent type, without wiring between parts in relative motion, so they can be mounted on the ring-shaped structure independently.
According to an advantageous aspect of the invention, the above-mentioned adjustment device, in particular the sensor element and the wireless transmission system, is powered by at least one independent power supply unit, mounted on the same rotating ring-shaped structure, for example of the type of one or more batteries.
Alternatively or in addition, the angular sensor element may be powered by at least one dynamo or brushless generator member, mounted on the same rotating ring-shaped structure.
Such generator member may advantageously be kinematically connected to the same kinematic chain that operates the rotation of the ring-shaped structure about the wrapping axis, thereby optimizing the overall energy consumption. In substance, the power supply unit may use, in this case, the mechanical work of the film wrapping motion about the product, when the apparatus is in operation, as the source of the necessary electrical power.
A prerogative of the invention is therefore to allow, thanks to the wireless transmission system, an instantaneous adjustment, based on current needs, of the amount of film being dispensed.
In other words, the operator does not need to set any dimensional parameter for the product to be wound, even at the initial setting, since, thanks to the continuous adjustment device associated with the wireless transmission system, such adjustment is carried out automatically by the control unit of the apparatus. Therefore, in the apparatus according to the invention, the resulting wrapping does not require the operator to estimate the size of the product to be packaged.
Moreover, thanks to the instantaneous correction made by the adjusting device, the same wrapping result is also optimal even in the presence of a product whose shape is irregular and/or variable along the wrapping axis.
This instantaneous adjustment is enabled reliably and continuously thanks to the structural and electrical complete autonomy of the components essential to the adjustment. In other words, the presence of an independent power supply unit as well as a wireless transmission system ensure independent, reliable and continuous operation of the adjusting device according to the invention.

Description of Drawings

Details of the invention shall be more apparent from the detailed description of a preferred embodiment of the apparatus for wrapping products with a film of extensible material according to the invention, illustrated for indicative purposes in the attached drawings, wherein:

Figure 1 shows a perspective view of the apparatus according to the invention;
Figure 2 shows a perspective view of a portion of the same apparatus;
Figures 3 and 4 respectively show a plant and side view of the portion shown in figure 2;
Figure 5 shows a magnified, plant, down-up view of a detail of the portion of the apparatus according to the invention shown in Figure 2.

Best Mode

With particular reference to such Figures, the apparatus for wrapping products with a film of extensible material according to the present invention is indicated in its entirety with 1.
According to a specific embodiment, the apparatus 1 comprises a support framework 2, built for example in the shape of a portal 21 and a base 22 secured to each other.
The portal 21 extends in substantially vertical way from the horizontal base 22, that is predisposed to receive the product to be packaged in support, for example on a roller conveyor 23.
As previously said, by "product" is usually and preferably meant a plurality of items ordinately arranged on a load standardized structure 100 of the pallet type.
The framework 2, at the portal 21, preferably carries, embossed, a mobile support frame 3, on which there is a translation unit translating along a wrapping axis of the product.
The mobile support frame 3 carries a rotatable ring-shaped structure 4, under which the product to be packaged is arranged in use (see Figure 1).
More precisely, the ring-shaped structure 4 is operated in rotation according to the above-mentioned central wrapping axis, by a motor unit, preferably mounted on the crossbar of the support frame 3, through the interposition of suitable transmission means, preferably of flexible type. In the illustrated case, the wrapping axis is substantially vertical. Alternatively, the wrapping axis of the apparatus can be inclined, for example substantially horizontal.
The apparatus 1 has as well a film dispensing unit 5, comprising at least one support roller 51 for a coil 6 of film of extensible material to be unwound. The support roller 51 is arranged according to an axis substantially parallel to the aforesaid wrapping axis (see Figure 2).
The dispensing unit 5 can be operated in rotation for unwinding the film of extensible material, at a determined unwinding speed, by an operation unit, for example mounted on the mobile support structure 3, through the interposition of transmission means, for example of flexible of belt or chain type.
The dispensing unit 5 comprises as well, preferably, a pre-stretching device 7 made up of a first pre-stretching roller 71 and a second pre-stretching roller 72 about which the film is predisposed to be unwound from the coil 6, so as to be counter-rotating. In particular, the first roller 71 and the second roller 72 are operated in rotation by the operation unit of the dispensing unit 5, at different peripheral speeds, so as to produce a pre-tensioning of the film, thus a "stretching", generally determined in fixed way by the above-mentioned difference between the peripheral speeds of the first roller 71 and of the second roller 72.
For example, the above-mentioned operation unit can operate in rotation one of the two pre-stretching rollers 71, 72, so as to unwind the film of extensible material from the coil 6 at the desired dispensing speed. In practice, the rotation of the ring-shaped structure 4 produces the unwinding of the coil 6, drawing it in rotation at a speed generally excessive for a correct packaging of the product. Therefore, the operation unit that operates the dispensing unit 5 serves, preferably, to adjust, in the sense of reducing, the speed produced by the rotation of the ring-shaped structure 4 until reaching the desired unwinding speed, suitable for the packaging requirements.
The apparatus 1 comprises as well a diverter unit 9, predisposed to keep the film of extensible material in a desired tensioned state, during the unwinding step from the coil 6.
In particular, the diverter unit 9 comprises a tilting arm 91, hinged to the ring-shaped structure 4, carrying one or more diverting rollers 92, about which the film of extensible material is unwound, along the unwinding path.
The above-mentioned tilting arm 91 is hinged about a tilting pin 93 to the same ring-shaped structure 4.
Preferably, the tilting arm 91 has a curved profile being more advantageous than the profiles of different shape, such as, in particular, a substantially rectilinear profile, as it makes more compact the diverter unit 9, thus optimizing the required space at equal support surface available for the diverting rollers 92 to be mounted.
In particular, in the embodiment shown in the Figures, the tilting arm 91 has a multi-curved profile.
Preferably, the tilting arm 91 has a S-shaped profile.
In the illustrated case, for example, the diverting rollers 92 are a pair mounted in fixed manner on the tilting arm 91.
The presence of more diverting rollers 92 allows to define, along the above-mentioned unwinding path of the film, an accumulation of material, that can be used to compensate for an instantaneous increase in demand for film to be unwound, avoiding excessive stretching of the same film.
The diverter unit 9 is subjected to the contrast action of suitable return means, for example of elastic, pneumatic or hydraulic type, to grant the degree of stretching desired for the film to be unwound from the coil 6, by pre-setting the aforementioned return action.
The diverting roller 92 then pivots about the pin 93, thus automatically positioning, by virtue of said return action by the contrasting means acting thereon, on the angular position predisposed to ensure the correct tensioning of the film according to the set initial settings, for example by means of a suitable calibration of the return means.
The apparatus 1 also comprises an adjustment device 10 of the dispensing of the film, made up of a sensor element 11 associated with a diverting roller 92, and a wireless transmission system 12 of the measurements instantaneously detected by the sensor element 11 mounted on the ring-shaped structure 4, to transfer in continuous manner the abovementioned measurements to the control unit 8 of the apparatus 1 (see in particular Figures 2, 3, 4 and 5).
The sensor element 11 is predisposed to perform direct angular measurements of the deviations of the tilting arm 91. In practice, the sensor element 11 directly measures the angular displacement of the diverting roller 92.
The sensor element 11 is preferably mounted on the axis of the tilting pin 93, so as to detect instantaneous oscillations of the arm 91 carrying the at least one diverting roller 92.
Preferably, the sensor element 11 comprises a magnetic angular position transducer. The wireless transmission system 12 preferably comprises at least one receiving and transmitting data board, preferably of Bluetooth and/or Wi-Fi type, for example inserted in a properly electrically powered box, as it is better described hereinafter, predisposed to transfer the measurements instantly detected by the sensor element 11 to the control unit 8.
The adjustment device 10 is associated with a power supply unit 13 for the sensor element 11 and for the transmission system 12, completely independent, mounted on the ring-shaped structure 4.
The power supply unit 13 can comprise for example one or more electric batteries 14 or, as an alternative or in addition, generator members 15 of the type of the dynamo or brushless, also mounted directly on the ring structure 4.
In an advantageous way, the above-mentioned generator members 15 can be connected with the operation kinematic chain of the same ring-shaped structure 4, through the interposition of transmission means 16 suitable to provide mechanic work for the generation of electric power. In the illustrated case, for example, these transmission means 16 are flexible transmission means of belt type, wound about at least one transmission member 17, in the specific case a pulley, kinematically connected with the operation unit of the ring-shaped structure 4 (see Figure 2).
The functioning of the apparatus for wrapping products with a film of extensible material is easy to understand from the preceding description.
Initially, the product to be wrapped, for example a plurality of products arranged ordinately on a pallet load structure, is arranged at the base 22 of the apparatus, in support on the roller 23, at an interaction station with the ring-shaped structure 4. In particular, the load structure 100 carrying the products to be wrapped is centered with respect to the cited wrapping axis of the apparatus 1. The ring-shaped structure 4, in the starting step, can be spaced from the product, or, preferably, already close to it, for example arranged on a plane transverse to the cited wrapping axis, that intercepts the same product.
In such step, the coil 6 of film is prearranged in the support station 51, unwound about the first roller 71 and second rolled 72 of the pre-stretching device 7 and finally about the mobile diverting roller 9. The free edge of the film of extensible material is then fixed on the product to be wrapped.
The operator can then proceed with operating the rotation of the ring-shaped structure 4.
In particular, the operator does not need, at this step, to indicate to the control unit 8 its own estimation of the external dimensions of the product to be wrapped, as such indication is overcome by the continuous and automatic activity of the adjusting device 10 in combination with the angular sensor element 11 associated with the diverter unit 9, in particular on the axis of the oscillation pin 93, as it is described in the following.
The ring-shaped structure 4 starts rotating about the product, carrying the dispensing unit 5 and unwinding the film from the coil 6 along the unwinding path. At the same time, the diverting roller 92 moves, in particular rotates about the tilting pin 93, so as to tension the film, in order to fit the above-mentioned path to the instantaneous demand for film.
The sensor element 11 then detects a direct measurement of the angular movement of the at least one diverting roller 92 and transmits such information through the transmission and receiving means of the wireless transmission system 12, mounted on the ring-shaped structure 4 itself.
The wireless transmission system 12 then transfers to the control unit 8 the data received by the sensor element 11, indicating the required unwinding speed, based on shape and size of the product, among other data, in order to adjust in corresponding way, the unwinding speed of the film. In particular, the control unit 8 processes data received from the sensor element 11 through the wireless transmission system 12, thus adjusting the dispensing speed of the dispensing unit 5, for a correct wrapping of the product, in particular acting on the dispensing unit 5.
In practice, the wireless transmission system 12 associated with the angular sensor element 11 allows to fit, in a continuous manner, the feeding speed of the film to the peripheral size of the product, during the wrapping step, allowing to fit the same to possible size and/or shape variations of the product along the wrapping axis.
Once the product has been completely wrapped, for example after a pre-established number of loops, the rotation of the ring-shaped structure 4 is stopped either automatically or at the operator's command.
The film is cut at a terminal winding portion, close to the product, which can then be released and removed from the wrapping station of the apparatus 1.
The apparatus according to the invention thus achieves the scope of performing a uniform bandage of the product, adequately compensating for any shape discontinuities, both along the wrapping axis and, above all, at possible edges of the product. This result is mainly achieved thanks to the presence of the adjusting device that enables the continuous transmission, to the data control unit, of data concerning the instantaneous wrapping film demand, provided by the continuous detection performed by the sensor element.
It is to be considered that the sensor element performs direct angular measurements, and therefore more immediate, and contributes for speeding up the aforementioned compensation process of any possible discontinuity in the shape of the product.
It is specified that by "direct" measurement is a measure based on the detection of a physical or chemical quantity of interest by comparing it with reference values.
"Indirect" measurement, on the other hand, is a measure based on the detection of specific physical or mathematical relationships that intervene among directly measurable variables differing from the variable of interest. These directly measurable variables can be of the same kind as the variable of interest or may belong to different kinds.
It is noted, therefore, that the direct measurement of the angular displacements is, in addition to rapid, more reliable considering that it is not subject to uncertainty linked to the indirect derivation of the measurement.
In addition, the wireless transmission system of the adjustment device is electrically autonomous, thanks to the power supply unit, mounted on the ring-shaped structure.
Lastly, the continuous adjustment made by the wireless transmission system according to the invention greatly simplifies the initial setting of the apparatus, preventing the operator from entering data manually into the control unit 8 such as the shape and size of the product to be wrapped. Such insertion is in fact rendered superfluous by the transmission of the recurring detections performed by the sensor element which, therefore, is able to ensure a continuous and precise adjustment of wrapping parameters.
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

Apparatus for wrapping products with a film of extensible material, comprising a framework (2) predisposed to receive a said product at an interaction station; a mobile support frame (3) carried by said framework (2); a ring-shaped structure (4) carried in rotatable manner by said mobile support frame (3), rotating about a central wrapping axis upon operation of a drive motor unit; a dispensing unit (5), carried by said ring-shaped structure (4) and carrying a support station (51) for at least one coil (6) of said film of extensible material, predisposed to be unwound through the operation of said dispensing unit (5) along an unwinding path between said coil (6) and said product; a translation unit working on said mobile support frame (3) for operating a relative translation according to said wrapping axis, between said dispensing unit (5) and said product to be wrapped; a diverter unit (9) comprising at least one mobile diverting roller (92), arranged along said unwinding path and carried in mobile manner by said ring-shaped structure (4), for diverting said unwinding path of said film so as to produce a desired tensioning degree of the film being unwound; a control unit (8), predisposed to intervene on the operation of said dispensing unit (5), to set the unwinding speed of said coil (6), characterized in that it comprises a continuous adjustment device (10) comprising a sensor element (11) associated with said mobile diverting roller (92) for detecting an instantaneous measurement of the displacement of said mobile diverting roller (92), and a wireless transmission system (12) for the data, installed on said ring-shaped structure (4), predisposed to receive said instantaneous measurement detected by said sensor element (11) and to transfer it in a continuous manner to said control unit (8), to carry out the continuous adjustment of said unwinding speed produced by said dispensing unit (5) and in that said at least one diverting roller (92) is mounted in tilted manner about a tilting pin (93) hinged to said ring-shaped structure (4), said instantaneous measurement detected by said sensor element (11) being a direct angular measurement, indicating said instantaneous deviation.
Apparatus according to claim 1, characterized in that said sensor element (11) is arranged coaxially to said tilting pin (93).
Apparatus according to claim 1 or 2, characterized in that said sensor element (11) comprises a magnetic angular position transducer.
Apparatus according to one of the preceding claims, characterized in that said diverter unit (9) comprises a tilting arm (91) hinged about said tilting pin (93) to said ring-shaped structure (4), said tilting arm (91) carrying said at least one diverting roller (92).
Apparatus according to claim 4, characterized in that said tilting arm (91) has a curved profile.
Apparatus according to any one of the previous claims, characterized in that said wireless transmission system (12) comprises at least one data reception and/or transmission board, of Bluetooth and/or Wi-Fi type, installed on said ring-shaped structure (4).
Apparatus according to one of the previous claims, characterized in that said wireless transmission system (12) is powered by an independent electric power supply unit (13), mounted on said ring-shaped structure (4).
Apparatus according to claim 7, characterized in that said power supply unit (13) comprises one or more electric batteries (14), or, alternatively or in addition, at least a generator member (15) of the dynamo or brushless type.
Apparatus according to claim 8, characterized in that said at least one generator member (15) is connected with a kinematic chain of operation of said ring-shaped structure (4) through the interposition of transmission means (16) predisposed to provide mechanical work for generating of electrical energy, when said ring-shaped structure (4) is operated in motion.
Apparatus according to one of the preceding claims, characterized in that said dispensing unit (5) comprises a pre-stretching device (7) arranged along said unwinding path, comprising a first pre-stretching roller (71) and a second pre-stretching roller (72), counter-rotating, about which said film is predisposed to be unwound along said unwinding path, to carry out a stretching of said film.
Apparatus according to claim 10, characterized in that said operation of said dispensing unit (5), for unwinding said film of extensible material at said preset unwinding speed, occurs by driving in rotation one between said first pre-stretching roller (71) and said second pre-stretching roller (72).