WO2013140211A1

WO2013140211A1 - Improved apparatus and method for wrapping a palletized load

Info

Publication number: WO2013140211A1
Application number: PCT/IB2012/056070
Authority: WO
Inventors: Emilio Murarotto
Original assignee: Bema S.R.L.
Priority date: 2012-03-20
Filing date: 2012-10-31
Publication date: 2013-09-26
Also published as: EP2828166B1; ITVR20120050A1; EP2828166A1; ES2569726T3

Abstract

An apparatus (1) and a method for wrapping a palletised load (2), having a base (21) and a top (22), the apparatus (1) comprises a platform (3) for supporting the palletised load (2), a wrapping head (4) for distributing the plastic film (5) to be wrapped around the side parts of the palletised load (2), means (7) for moving the wrapping head (4), a rotating presser device (6), equipped with a cover (61) that is rested with a suitable resting force on the top (22) of the load (2), and a control unit (10) that drives and controls variations of the angular position of the presser device (6) with respect to the angular position of the platform (3).

Description

"IMPROVED APPARATUS AND METHOD FOR WRAPPING A PALLETIZED LOAD"

Designated inventor: Murarotto Emilio

TECHNICAL FIELD OF THE INVENTION

The present invention concerns an apparatus of the improved type for wrapping a palletised load and a method for wrapping a palletised load with such an apparatus .

STATE OF THE ART

From European patent EP-1514800B1, to the same Applicant, a wrapping apparatus is known for wrapping palletised loads comprising a wrapping head for wrapping the side walls of a palletised load through a plastic covering film.

During the wrapping step, the load rests on a rotary support table and, on the top of the load, a downward presser device, i.e. a cover that is rested on the load is also used.

In the case of the apparatus of European patent EP- 1514800B1, the presser device, which is used for stabilising and keeping the various layers of the load in the correct position, is rotated in sync with the rotating support table of the load.

In other types of more simple machines, the presser device is free to rotate and is pulled in rotation by the load itself.

Moreover, in the case of wrapping apparatuses with a fixed table and wrapping head that is mobile around the load, the presser device can simply be stationary .

The wrapping process foresees the arrangement of the load to be wrapped on the support table, the table is then set in rotation, whereas the wrapping head, which is actuated by suitable movement means, for example a robot of the anthropomorphous type or of the Cartesian-type or other equivalent movement means, is moved vertically so as to obtain a wrapping of the plastic covering film with a substantially helical pattern.

In the case of wrapping apparatuses with a fixed table, the load is arranged on the table, which is indeed fixed, and the wrapping head is made to rotate in a substantially helical manner around the load.

During the wrapping process, the presser element is rested on the top of the palletised load, so as to stabilise the products that constitute the load itself and keep them in the correct position, preventing the movement of said products that would otherwise occur in the upper layers of the load during wrapping due to the rotation of the support table and to the tension of the plastic covering film that acts on the products.

However, the palletised loads thus wrapped, in any case have the tendency to become twisted, especially during the subsequent transportation steps.

For example, in the case in which they are transported by road, due to the stress induced by the obstacles present on the road surface, such as holes, traffic calming measures, ditches, bumps and, in general, obstacles that can generate strong vertical accelerations temporarily nullifying the weight force of the products that form the palletised load, in particular in the upper layers. Such a situation can in any case occur in all cases in which the load undergoes strong vertical accelerations which nullify the weight force of the products that form the palletised load.

Since the products do not have weight force, there is no friction force between one layer and the other of the load and therefore the tension left over in the plastic covering film causes a twisting on the products causing the load to become twisted, i.e. the upper layers of the product tend to rotate with respect to the lower layers. There is therefore an increase in the volume of the palletised loads when they are stacked, adjacent and alongside one another inside warehouses or inside load areas of means of transport.

This problem is particularly serious in the means of transport, since it prevents the load volume of the means of transport themselves from being maximised.

PURPOSES OF THE INVENTION

One purpose of the present invention is to improve the state of the art.

Another purpose of the present invention is to propose an apparatus that is suitable for wrapping palletised loads in a more stable and resistant manner with respect to the wrapping obtained with apparatuses belonging to the state of the art.

In accordance with one aspect of the present invention it is foreseen for there to be an apparatus for wrapping palletised loads according to claim 1.

A further purpose of the present invention is to have a method for wrapping palletised loads based on the present invention.

According to another aspect of the present invention it is foreseen for there to be a method for wrapping palletised loads as specified in claim 12. The dependent claims refer to preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention shall become clearer from the detailed description of a preferred, but not exclusive, embodiment of an apparatus for wrapping palletised loads, illustrated as an indication and not for limiting purposes, in the attached drawing tables, in which:

figure 1 is a schematic side view of an apparatus for wrapping palletised loads according to the invention;

figure 2 is a schematic perspective view of the apparatus according to figure 1;

figure 3 is a schematic perspective view of a further embodiment of an apparatus according to the present invention;

figure 4 is a schematic perspective view of yet another embodiment of the apparatus according to the invention;

figure 5 is a schematic perspective view of another embodiment of the apparatus according to the invention .

EMBODIMENTS OF THE INVENTION With reference to the attached figures, reference numeral 1 schematically indicates an apparatus for wrapping palletised loads.

Such an apparatus according to the present invention makes it possible to obtain palletised loads, wrapped with a plastic covering film, provided with high stability and resistance to twisting induced during the transportation step of the loads themselves .

In the rest of the description we shall describe in detail the new parts object of the present invention, whereas the components of an apparatus for wrapping palletised loads that are already known to a man skilled in the art shall be described briefly .

With reference to the embodiment of figure 1, the apparatus 1 for wrapping palletised loads comprises a platform 3 for supporting a palletised load 2 having a base 21 and a top 22, a wrapping head 4 for distributing the plastic film 5, which is wrapped around the side walls of the palletised load 2 and means 7 for moving the wrapping head 4.

In the illustrated example, the movement means are an anthropomorphous robot 7, but they could also be a Cartesian-type robot, or a simple upright on which a trolley carrying the wrapping head 4 translates vertically.

In the following description we shall, in some cases, specifically refer to the anthropomorphous robot 7, but it should be kept in mind that the means for moving the wrapping head 4 could be of any type without for this reason departing from the scope of the present invention.

The apparatus 1 also comprises a presser device 6, which is suitable for resting with a suitable resting force on the top 22 during the wrapping of the palletised load 2, first motor means 11 that are operatively connected to the platform 3, a control unit 10 that is suitable for driving and controlling the angular position of the presser device 6 as a function of certain vertical displacements of the wrapping head 4 with respect to the top 22.

The platform 3 is set in rotation, through the first motor means 11, around a first rotation axis 13 that is perpendicular to the ground.

Basically, the first motor means comprise a first electric motor 11 that can be of any type, and that according to one version of the present invention is an AC electric motor.

The distance of the presser device 6 with respect to the platform 3 can be varied, as a function of the height of the palletised load 2 to be wrapped, through guide means 8.

The presser device 6 comprises a cover 61 that is actuated in rotation, around a second rotation axis 62, through second motor means 12.

Also in this case, basically the second motor means comprise a second electric motor 12 that can be of any type, and according to one version of the present invention it is an AC electric motor.

The second rotation axis 62 substantially coincides with the first rotation axis 13. During the wrapping of the plastic film 5, the palletised load 2 is set in rotation around the first rotation axis 13 and the cover 61 is rested, exerting a suitable force, on the top 22 through technical solutions that are known in the field.

The control unit 10 comprises first means 14 for detecting the position of the platform 3, and first means 15 for actuating the first motor 11.

Such first actuation means can be of any type and essentially comprise an electric motor the speed of which can be varied through a respective device for controlling the speed.

For example, the device for controlling the speed can comprise a first encoder 14 and a first inverter 15 that are connected to the first motor 11. As it is known an inverter makes it possible to vary the rotation speed of an AC electric motor.

According to other versions of the present invention, the electric motor can be of the DC type which may or may not have brushes, i.e. of the so called brushless type. In the case of the DC electric motor with brushes, the variation of the rotation speed of the electric motor can occur with a simple rheostat, in the case of the electric brushless motor the speed is adjusted with suitable electronic devices.

The control unit 10 also comprises second means 16 for detecting the position of the cover 61 of the presser device 6, and second means 17 for actuating the second motor means 12.

Also in this case the second actuation means can be of any type and, for example, they can comprise a second encoder 16 and a second inverter 17 that are connected to the second motor means 12.

The apparatus moreover comprises, according to one aspect of the present invention, actuation means for varying the angular position of the cover 61 with respect to the angular position of the platform 3, as a function of the vertical displacements of the wrapping head 4 between the base 21 and the top 22 of the load 2.

As shall become clearer in the rest of the description, said actuation means, in the present embodiment, are made up of the second motor means 12 and of the respective actuation means 17.

The control unit 10 also comprises third means 18 for detecting the position of the wrapping head 4 and that can be of any type.

Based upon the position detected by the detection means 18, the movement means 7 are suitably actuated so as to obtain the desired position of the wrapping head .

In the illustrated example third detection means can comprise a third encoder 18 that is connected or already present since it is incorporated in the robot 7 itself.

In general, as already indicated above, after the position has been detected by the encoder 18, the robot 7 is suitably actuated so as to obtain the desired position of the wrapping head 4.

The control unit 10 also comprises control means 19 that are operatively connected to the aforementioned means 14, 16, 18 for detecting the position, to the actuation means 15 and 17 of the motor means 11 and 12, and to the movement means 7.

In the illustrated example, the control unit 10 comprises a control card 19 that is connected to the aforementioned first, second and third encoder 14, 16, 18, to the first and to the second inverter 15 and 17 and to the robot 7.

The first, the second and the third encoder 14, 16 and 18 send electrical signals to the control card 19, through which the instantaneous position of the wrapping head 4, the rotation speed of the platform 3 and of the cover 61 are determined.

In particular, during the wrapping step and according to methods explained more in detail in the rest of the description, the control unit 10 can vary the rotation speed of the cover 61 with respect to the rotation speed of the platform 3, as a function of certain vertical displacements of the wrapping head 4 with respect to the top 22, obtaining an angular displacement of the cover 61 with respect to the platform 3.

The control unit 10 comprises electronic control means that detect, through the third encoder 18, the position of the wrapping head 4 with respect to the top 22 and suitably actuate the second motor 12 according to what is explained in greater detail in the rest of the description.

It should be noted that the control unit 10 can process the signals from the means 14, 16, 18 for detecting the position, and send the suitable signals to the means 15, 17 for actuating the motor means 11, 12 and to the movement means 7, through a software program, however the processing and the sending of the signals can also occur by means of other equivalent systems, for example through a hard-wired logic.

The angular displacement value a, i.e. the size of the angle a, is a function of different parameters that are characteristic of the palletised load 2, amongst which the height of the load 2, the weight and/or the shape of the products forming the load 2, the type of sheet that is placed between one layer and the other of the products that form the load, etcetera .

The size of the angle a can be determined based upon tests carried out on different types of loads to be palletised.

As an example the angle value a can be set between 0 and 10 degrees and preferably between 3 and 7 degrees . The forward variation of the angular position of the cover 61 with respect to the angular position of the platform 3, in combination with the movement of the wrapping head 4, makes it possible to contrast the tension with which the plastic film 5 is wrapped around the upper layers of the load 2.

Thanks to the forward variation of the angular position of the cover 61, also the aforementioned upper layers of the load 2 are slightly rotated forwards, so that the tension of the plastic film 5 tending to twist the load 2 at the upper layers, brings the upper layers back obtaining a correct shape of the load 2 without warping or twisting even under the vertical stresses which are present during transportation .

The palletised loads 2 thus bound are wrapped and compressed by the plastic film 5 with a tension that is lower at the top 22 and greater at the base 21 of the load 2.

The operation of the present invention is as follows .

Initially, the palletised load 2, after being positioned on the rotating platform 3, is set in rotation around the first rotation axis 13.

The wrapping head 4 is, or is positioned, near to the top 22 of the load 2 and wraps the upper layers of the load, through at least one layer of plastic film 5, for example with a few layers of wrapping, obtaining a partial wrapping of the load.

In such a way, the products present in the upper part of the load are stabilised through a compression exerted by the plastic film 5 on the side walls of the load.

Subsequently, the wrapping head 4 drops in a relatively quick manner to the base 21 of the load 2 to then rise back with a slower movement. The plastic film 5 continues to be wrapped around the side walls of the load 2 so as to wrap the load 2 with a wrapping that is substantially helical with layers on top of one another.

During the quick downward stroke of the wrapping head 4, the electronic control means, after a suitable processing, send to the second inverter 17 of the second motor 12, a suitable effective voltage and/or current value, so as to vary, and in particular increase, the angular speed of the cover 61.

The aforementioned step of varying the angular speed of the cover 61 approximately occurs in the same period of time in which the wrapping head 4 carries out the quick downward stroke.

At the end of the variation step of the angular speed, the second motor 12 returns to rotating with the same rotation speed as the first motor 11 connected to the platform 3, and therefore the cover 61 rotates again with the same angular speed as the platform 3.

However, the cover 61 is rotated with respect to the platform 3 itself, and in particular, the cover 61 is rotated forwards by an angle a with respect to the rotation direction of the platform 3 and to the wrapping direction of the plastic film 5.

The angular displacement a of the cover 61 with respect to the platform 31 is thus maintained until the end of the wrapping of the load 2 with the plastic film 5.

After finishing wrapping the load 2, the plastic film 5 is cut and the cover 61 is raised from the top 22 of the load 2.

Finally, through its second motor 12 that is suitably actuated by the control unit 10, the cover 61 is rotated bringing it back into a position that is aligned with the platform 3, and therefore the machine 1 is ready to house another load 2 to be wrapped with the plastic film 5. Thanks to the twisting along the vertical direction of the palletised load 2, the plastic film 5 has a different tension between its top 22 and its base 21 that makes it possible to stabilise and counteract the tendency of the load 2 to twist during the following transportation steps.

In practice, as soon as the wrapping has finished, the load 2 has a slight bend in the direction in which the cover 61 (figure 2) had been rotated, however after a short time, for example after about a day, due to the elastic return of the plastic film 5, the load is completely aligned.

The same operation logic as described can also be applied to an apparatus 101 for wrapping a palletised load of the type with a fixed table, according to what has been illustrated in the example of figure 3.

For the sake of greater clarity in the description of this embodiment the same reference numerals as the previous embodiment have been used to indicate same parts or components.

The apparatus 101 for wrapping a palletised load 2 comprises a fixed platform 3 for supporting the load, a wrapping head 4 equipped with a plastic film 5, suitable for being wrapped around the side walls of the palletised load 2, the palletised load 2 having a base 21 and a top 22.

The apparatus 101 also comprises movement means 107 for moving the wrapping head 4 around the palletised load 2 in a substantially helical manner.

The movement means comprise a rotating arm 107 that is equipped with a vertical sliding guide 108 for the head 4; according to other non illustrated embodiments, the movement means may comprise a slide that is mobile with an almost circular movement on a frame in a closed loop, the slide being moreover equipped with a vertical sliding guide, or they can comprise other types of devices that are capable of moving the wrapping head 4 around the load standing on the pallet 2, with a movement that is substantially helical.

The apparatus 101 also comprises, as for the previous embodiment with rotating table, a presser device 106 that rests with a suitable resting force on the top 22 during the wrapping of the plastic film 5 on the palletised load 2, a control unit 110 that, moreover, drives and controls, as a function of certain vertical displacements of the wrapping head 4, the angular position of the presser device 106 with respect to the angular position of the platform 3.

The movement means 107 actuate the wrapping head 4 in rotation around the palletised load 2 with respect to a first rotation axis 113 and in translation according to a vertical direction.

The presser device 106 comprises a cover 161 that is rested with a suitable resting force on the top 22 of the load 2 during the wrapping step, through technical solutions of the known type.

The presser device 106 also comprises motor means 112 which make it possible to rotate the cover 161 by a certain angle around an axis 162 that substantially coincides with the first rotation axis 113.

As for the previous case, the control unit 110 comprises means 116 for detecting the position of the cover 161 of the presser device 106, second means 117 for actuating the motor means 112, means 118 for detecting the position of the wrapping head 4, and control means 119 that are operatively connected to position detection means 116, 118, to the actuation means 117 of the motor means 112 and to the movement means 107.

On the other hand there are no means for detecting the position and for moving the platform 3, since the latter is fixed.

The apparatus comprises, also in the present embodiment of the present invention, actuation means for varying the angular position of the cover 161 with respect to the angular position of the platform 3, as a function of the vertical displacement of the wrapping head 4 between the base 21 and the top 22 of the load 2.

As shall be made clearer in the rest of the description, said actuation means are made up, also in the present embodiment, by the same second motor means 112 and by the respective actuation means 117. When operating, the control unit 110 acts with an electronic control that is capable of detecting the position of the wrapping head 4 with respect to the top 22 of the load 2 through position detection means, which can be for example an encoder 118, and after a suitable software processing, it sends the motor means 112 a suitable signal so as to vary, when foreseen and necessary, the angular position of the cover 161 with respect to a predetermined initial position.

In particular, during the wrapping step of the load 2, the cover 161 is rotated by and angle a with respect to the predetermined initial position of the cover 161, in the opposite direction to the wrapping direction of the plastic film 5 around the load.

The angular displacement value, i.e. the size of the angle a, is substantially analogous to that of the previous case of apparatus with rotating table and it is a function of the same aforementioned characteristic parameters of the palletised load 2. Also in this case, the size of the angle a can be determined based upon tests carried out on the different types of loads to be palletised.

The operation of the present embodiment is as follows .

The palletised load 2 is positioned on a platform 3 of the fixed type.

The presser device 106 is moved at the load 2 and the cover 161 is rested, with a suitable resting force, on the top 21 of the load 2, so as to stabilise and keep the products in the correct position during the wrapping step.

The wrapping head 4, is or is moved near to the top 22 of the load and it is set in rotation around the first axis 113.

The plastic film 5 is wrapped along the side walls of the top 22 of the load 2. Also in this case the top 22 of the load 2 is wrapped through at least one layer of plastic film 5, for example with a few layers of wrapping, achieving a partial wrapping of the load so as to stabilise the products present in the upper part of the load.

In this initial step, the cover 161 and the platform 3 are angularly aligned with one another.

Subsequently, the wrapping head 4, which again rotates around the first axis 113, drops rapidly towards the base 21, with a rotary translation motion of the helical type around the load 2. In an analogous manner to the case of machine with rotating table, approximately in the time in which there is the rapid descent step of the wrapping head 4, the control unit 110 rotates the cover 161 by a certain angle a, through the motor means 112.

The rotation direction of the cover 161 is opposite to the rotation direction of the wrapping head 4 around the load 2, the cover 161 is displaced by the aforementioned angle a with respect to the platform 3.

Consequently, also the upper layers of the load 2 close to the top 22 are set in rotation by an angle a with respect to the base 21.

The wrapping head 4 is thus moved with a rotary translation motion towards the top 22, in this case the rising of the head 4 is slower with respect to the previous descent since the plastic film 5 wraps the load 2 with a wrapping that is substantially helical with layers on top of one another that makes it possible to obtain the final packaging of the load 2.

Also in this embodiment, the variation of the angular position of the cover 161 with respect to the angular position of the platform 3, in combination with the movement of the wrapping head 4, makes it possible to counteract the tension with which the plastic film 5 is wrapped around the upper layers of the load 2, ensuring a high level of compactness and a high stability of the load 2.

The present invention moreover refers to a method for wrapping a palletised load 2 of the improved type.

Such a method for wrapping a palletised load mainly comprises the steps of:

positioning a palletised load 2, comprising a top 22 and a base 21, on a support platform 3;

resting, with a suitable resting force, a presser device 6, 106 equipped with a cover 61, 161 on the top 22 of the palletised load 2;

determining a relative movement that is substantially of the rotary translation type between the load 2 and a wrapping head 4;

wrapping the side walls of the palletised load 2 through a plastic covering film 5 that is dispensed by the wrapping head 4;

displacing by an angle a. the angular position of the cover 61, 161 with respect to the angular position of the platform 3, in a direction that is opposite to the wrapping direction of the plastic film 5, so as to generate a controlled rotation of the upper layers with respect to the base 21 of the load, during the wrapping of the palletised load 2.

During the wrapping of the load 2, the position of the wrapping head 4, with respect to the top 22, and the angular displacement of the cover 61, 161, with respect to the angular position of the platform 3, are controlled by a control unit 10, 110.

The wrapping of the load 2 comprises the steps of: moving the wrapping head 5 near to the top 22;

wrapping the top 22 of the load 2 with at least one layer of plastic film 5.

After such steps, the layers of the products near to the top 22 are compacted together and are stabilised. Subsequently, the following steps are foreseen:

moving, with a relatively rapid stroke, the wrapping head 4 from the top 22 towards the base 21 of the load 2, whereas the plastic film 5 is continued to be wrapped around the load 2;

verifying through the control unit 10, 110 the position of the wrapping head 4 with respect to the top 22;

rotating, with respect to the platform 3, the cover 61, 161 around a rotation axis 62, 162, through actuator means 12, 17, 112, 117 that are actuated by the control unit 10, 110, approximately in the same period of time in which the wrapping head 4 carries out the quick downward stroke towards the base 21.

The step of rotating the cover 61, 161 comprises: rotating by an angle a the cover 61, 161 around the axis 62, 162 with respect to the platform 3, with a rotation that is opposite the wrapping direction of the plastic film 5 around the side walls of the load 2.

Through such a rotation of the cover 61, 161 and the consequent rotation of the upper layers of the load 2, the tension of the plastic film 5 is counteracted on these upper layers. This makes it possible to stabilise and keep the products of the palletised load in the correct position without twisting, in particular during their transport.

Indeed, the top 22 and its base 21 of the load 2 are subjected to a differentiated tension that is optimised for holding the top 22, which during transportation can undergo greater stresses with respect to the base.

Moreover, the method for wrapping a palletised load comprises :

lifting the cover 61, 161 from the top 22 of the load 2;

rotating the cover 61, 161 bringing it back into alignment with the platform 3.

In one alternative embodiment of the invention, illustrated in figure 4, the apparatus 201 is completely identical to that of the embodiment of figures 1 and 2, or rather it comprises a platform 203, a wrapping head 204, a presser device 206 with a respective cover 261, first motor means of the platform 203 around a first axis 213, and second motor means 212 of the presser device 206 around a second axis 262.

The apparatus 201 is however different since the second motor means 212 of the presser device 206 are mounted on a plate 250 that is rotatably supported in the upper portion 251 of the frame of the apparatus 1, around the same second axis 262 of the second motor means 212.

Moreover, in this embodiment the apparatus 201 comprises actuation means 252 comprising a linear actuator .

The linear actuator 252 has a first end 253 that is hinged to the upper portion 251 of the frame of the apparatus 201, and a second end 254 that is hinged to the plate 250 on which the second motor means 212 are fixed.

The linear actuator 252 can be of any type, for example a double acting pneumatic actuator, or an electric actuator, or any other type of actuator which makes it possible to obtain an active stroke both in one direction and the other.

The linear actuator 252 therefore, in this embodiment, makes it possible to obtain, with an outward stroke of its stem, the angular displacement a of the cover 261 of the presser device 206 with respect to the platform 203, with the same effects that have already been described for the embodiment of figures 1, 2.

In other words, the actuator 252 makes it possible to obtain, in this embodiment, the effect that in the embodiment of figures 1, 2, is obtained through the action of the control unit 10 that varies the rotation speed of the second motor means 12, making use however of completely mechanical means.

At the end of the wrapping step, by carrying out a return stroke of the stem of the actuator 252, the cover 261 of the presser device 206 is brought back into the initial position, as described for the embodiment of figures 1, 2.

Yet another embodiment of the invention is illustrated in figure 5.

The apparatus 301 according to the embodiment is, in its essential characteristics, identical to that of the embodiment of figure 3.

The apparatus 301 indeed comprises a fixed platform 303 for supporting the load, a wrapping head 304 that is equipped with a plastic film 5, movement means 307 for moving in a substantially helical manner the wrapping head 304 around the palletised load 2 around a first rotation axis 113.

The apparatus 301 moreover comprises a presser device 306 with a respective cover 361 that can rotate around a second axis 362.

Also in this embodiment, the apparatus 301 comprises a control unit 310 comprising means 316 for detecting the position of the cover 361 of the presser device 306, means 318 for detecting the position of the wrapping head 304, and control means 319 that are operatively connected to the position detection means 316, 318 and to the movement means 307.

It is not foreseen for there to be, on the other hand, a motor that sets the presser device 306 in rotation.

The apparatus 301 comprises, in this embodiment, actuator means comprising a linear actuator 352 that is associated with the presser device 306.

The linear actuator 352 can be of any type, for example of the double acting pneumatic type, electric, or of any other type that is suitable for obtaining an outlet and return stroke of the stem that are both active.

The linear actuator 352 is operatively slaved to the control unit 310.

More in detail, the linear actuator 352 has a first end 353 that is hinged to the frame of the apparatus, and a second end 354 that is hinged to the axis of the presser device 306, and in particular to a plate 350 that is fixedly attached to the axis of the presser device 306 itself.

The actuator 352 therefore, in this embodiment, makes it possible to obtain, with an outlet stroke of its stem, the angular displacement a of the cover

361 of the presser device 306 with respect to the platform 303, with the same effects already described for the embodiment of figure 3.

The invention thus conceived can undergo numerous modifications and variants all covered by the inventive concept.

Moreover, all the details can be replaced by technically equivalent elements. In practice the materials used, as well as the contingent shapes and sizes, may be any according to the requirements without for this reason departing from the protection of the following claims.

Claims

1. Apparatus (1; 101; 201; 301) for wrapping a palletized load (2) with a plastic film (5), the palletized load (2) having a base (21) and a top (22) , comprising a platform (3; 203; 303) for supporting the palletized load (2), a wrapping head (4; 204; 304) for distributing the plastic film (5) , which is wrapped, with a relative substantially rotating-translating motion, around the side walls of the palletized load (2), a pressing device (6; 106; 206; 306), provided with a rotating cover (61; 161; 261; 361) adapted to be laid, with a suitable laying strength, on the top (22) during the wrapping of the palletized load (2) , characterised in that it comprises actuating means (12, 17; 112, 117; 252; 352) to modify the angular position of the cover (61; 161; 261; 361) with respect to the angular position of the platform (3; 203; 303), based on vertical displacements of the wrapping head (4; 204; 304) between the base (21) and the top (22) of the load ( 2 ) .

2. Apparatus according to claim 1, wherein said actuating means (12, 17; 112, 117; 252; 352) displace the angular position of said cover (61; 161) of an angle (a) with respect to the angular position of the platform (3), said displacement of an angle (a) being opposite to the wrapping direction of the plastic film (5) .

3. Apparatus according to claim 2, wherein said angle (a) ranges from 0 to 10 degrees and preferably from 3 to 7 degrees.

4. Apparatus according to any one of the previous claims, comprising detecting means (18) for detecting the position and the vertical displacements of the wrapping head (4) during the rotating-translating movement of the head (4) between the base (21) and the top (22) of the load (2) .

5. Apparatus according to one of the previous claims, wherein said actuating means (12, 17; 112, 117) comprise second driving means (12; 112) associated to said pressing device (6; 106).

6. Apparatus according to the previous claim, wherein the second driving means (12; 112) vary the angular position of the cover (61; 161) in response to a signal sent by the detecting means (18) .

7. Apparatus according to any one of the previous claims, comprising means (16) for detecting the angular position of the cover (61; 161).

8. Apparatus according to any one of the previous claims, wherein the second driving means (12; 112) comprise an electric engine connected to the cover (61; 161) so as to rotate the cover (61; 161) around a second rotational axis (62; 162).

9. Apparatus according to any one of the previous claims, comprising moving means (107) for actuating the wrapping head (4) .

10. Apparatus according to claim 9, wherein the moving means (107) make the wrapping head (4) rotate around a first rotational axis (113).

11. Apparatus according to any one of claims from 1 to 9, comprising first driving means (11) for making the support platform (3) rotate around a first rotational axis (13) .

12. Apparatus according to claim 10 or 11, wherein the second rotational axis (62; 162) substantially coincides with the first rotational axis (13; 113) .

13. Method for wrapping a palletized load (2) with a plastic film (5), the palletized load (2) having a base (21) and a top (22), comprising: providing an apparatus (1; 101; 201; 301) basically provided with a support platform (3; 203; 303), a pressing device (6; 106; 206; 306) with a cover (61; 161; 261; 361), a wrapping head (4; 204; 304) for distributing the plastic film (5) around the load (2);

placing the palletized load (2) on the support platform (3; 203; 303);

laying with a suitable laying strength the cover (61; 161; 261; 361) on the top (22) of the palletized load (2), so as to stabilize and keep in the proper position the load during the wrapping of the plastic film (5) ;

performing a relative rotating-translating movement, substantially helical, between the wrapping head (4; 204; 304) and the load (2); wrapping the plastic film (5) around the load (2) using the wrapping head (4; 204; 304);

characterised in that it comprises:

varying the angular position of the cover (61;

161; 261; 361) with respect to the angular position of the platform (3; 203; 303) , based on the vertical displacements of the wrapping head (4) during the translation of the head (4) between the base (21) and the top (22) of the load (2) .

14. Method for wrapping a palletized load according to claim 13, wherein said step of varying the angular position of the cover (61; 161; 261; 361) with respect to the angular position of the platform (3; 203; 303) comprises the step of displacing of an angle (a) the angular position of the cover (61; 161; 261; 361) with respect to the angular position of the platform (3; 203; 303) opposing the wrapping direction of the plastic film (5) .

15. Method for wrapping a palletized load according to claim 14, wherein said angle (a) ranges from 0 to 10 degrees and preferably from 3 to 7 degrees.

16. Method for wrapping a palletized load according to any one of claims from 13 to 15, wherein said step of varying the angular position of the cover (61, 161) with respect to the angular position of the platform (3) comprises increasing the rotational speed of the cover (61; 161) with respect to the rotational speed of the platform (3), for a given time period required to make the cover (61; 161) perform an angular displacement of an angle (a) with respect to the angular position of the platform (3).

17. Method for wrapping a palletized load according to any one of claims from 13 to 16, wherein said step of varying the angular position of the cover (61; 161) is carried out in response to given vertical displacements of the wrapping head (4) between the top (22) and the base (21) of the load (2) .

18. Method for wrapping a palletized load according to any one of claims from 13 to 17, wherein said step of varying the angular position of the cover (61; 161) is carried out after a step of wrapping the load (2) with at least a layer of plastic film (5) in the upper portion of the load (2) near to the top (22).

19. Method for wrapping a palletized load according to any one of claims from 13 to 18, wherein said step of varying the angular position of the cover (61; 161) is carried out during a step of vertical descent of the wrapping head (4) between the top (22) and the base (21) of the load (2) .

20. Method for wrapping a palletized load according to any one of claims from 13 to 19, wherein the platform (3) has a null, i.e. fixed, rotational speed.