EP2572999A1

EP2572999A1 - Vertical-curtain wrapping apparatus with multiformat feeder

Info

Publication number: EP2572999A1
Application number: EP12184334A
Authority: EP
Inventors: Franco Tacchini; Maurizio Orfano
Original assignee: Officina Meccanica Sestese SpA
Current assignee: Officina Meccanica Sestese SpA
Priority date: 2011-09-22
Filing date: 2012-09-13
Publication date: 2013-03-27
Anticipated expiration: 2032-09-13
Also published as: ES2446387T3; EP2572999B1; ITMI20111711A1; DK2572999T3

Abstract

A method and wrapping apparatus with plastic film curtain is disclosed. Transfer means (12) are described, apt to present a film end edge coming from at least one storage reel (8-8₃) to gripper means (21) of temporary winding means (19, 20), through support and presenting means (17), wherein both said temporary winding means (19, 20) and said transfer means (12) translate crosswise (X-X) to a transport line (1) of a load (C) to apply said curtain of plastic film (P), the transfer means (12) being first connected to a moving coupling bar (18) provided with movement drive independent with respect to a movement drive of said temporary winding means (19, 20), said temporary winding means (19, 20) rotating in a first direction to initially accumulate a length of film (P) and then rotating in a second direction to deliver the same length of film (P) during the dragging of said curtain of film (P) by the load (C), and said transfer means (12), connected to said moving coupling bar (18), and said temporary winding means (19, 20) mutually converge in a centreline area wherein a welding and cutting operation of the film occurs to define said wrapping of the load (C).

Description

Field of the Invention

The present invention concerns an improved apparatus for the packaging of products piled on pallets - in the following referred to in short by the term "load" - by means of a plastic material film. More in detail, it relates to an apparatus which allows to wrap loads which arrive sequentially, along a transport line, towards a wrapping station where a curtain of plastic film is laid.

Background Art

As known, various wrapping techniques of pallet-mounted loads exist. When it is desired to wrap a load with a plastic film during the movement thereof on a transport line, it is normally resorted to curtain-like wrapping equipment. In particular, such equipment provides to lay a curtain of plastic film, maintained on a vertical plane, transversally to the path of the transport line: when the load arrives on the plastic film, it pushes it into the same movement thereof, until part of the film is suitably guided and stretched also on the sides thereof and then on the rear surface. In correspondence of the rear surface of the load (with respect to the progressing direction), the film is then welded behind the load and hence cut to then begin the cycle with a subsequent load.
Since in these conditions loads are typically of different heights, it is necessary to provide an adjustment of the height of the film curtain, which operation is performed using reels of film having different heights.
For such purpose, a conventional multiformat wrapping machine provides to arrange a plurality of curtains having different heights, in succession along the transport line. Depending on the film height to be used, the desired curtain is maintained in the proximity of the transport line and the others are raised, so as to bring them well above the load transit path.
This construction method is convenient and effective, also in terms of format change speed, but has a cost proportional to the number of different curtain heights which it is necessary to provide, which makes it extremely burdensome when more than two or three different heights are to be managed.
Alternatively, revolving multiformat wrapping machines have proven extremely effective.
A significant example, which makes up the closest prior art to the present invention, is the one disclosed in patent IT 1,356,529 and EP2452881 , both in the name of the same Applicant, the contents of which is entirely recomprised in the present application, for a better understanding of the invention.
The wrapping machine described in these documents makes use of a pair of gripper carriages, moving crosswise to the transport line and apt to transfer to the centre of the line two opposite edges of equal-height films, edges taken out from respective reels belonging to storage stations arranged at the two sides of the transport line.
Each side station supports an equal plurality of reels of wrapping film, mounted in a revolving manner. The revolving movement is synchronised with that of the moving carriages, so as to bring the (desired-height) reels in the drawing positions of the gripper carriages in a synchronised manner on the two sides.
This equipment has implied a market improvement with respect to the solutions of the previous prior art, because it has a cost which is not overly affected by the number of reels used and is hence economically preferable when there is a large number of different heights (for example 6 reels).
However, the present Applicant has realised that there is room for further improvements.
In fact, an extremely important, if not essential, factor for the accomplishment of new wrapping lines, but especially for the rebuilding of existing lines in constrained spaces, is bulk containment. Now, the equipment according to the two above-cited documents implies- due in particular to the presence of the two reel-carrying platforms on the two sides of the transport line - a considerable overall transversal bulk, which often cannot find a suitable place even in recently built industrial buildings.
Moreover, the simultaneous use of two reels, despite making available a remarkable length of film and hence reducing idle times (necessary for the replacement of exhausted reels), inevitably produces wastes. As a matter of fact, the two opposite reels do not wear out at identical speed (there is always some consumption dissymmetry, if anything because the load position is not always perfectly aligned on the centreline between two revolving supports) and when one runs out, the other one could still have a few metres of film, but is nevertheless replaced in order not to have a double down time: this implies waste of material.
Wrapping machines have also been suggested wherein the curtain is formed using, on one side, a reel acting as film storage and, on the other side, a temporary stock device. Equipment of this type are generally known from US 3,910,005 and EP 516,602 . In these documents the general principles of exploiting a single storage reel in cooperation with a temporary stock cylinder are set forth, but no working details on the best configuration to employ are supplied. In actual fact, these systems have so far remained at the level of principle exhibition, but have never been industrially developed with practical solutions which are sufficiently economical and capable of being industrialised.

Summary of the Invention

The object of the present invention is hence to propose a curtain and multiformat wrapping apparatus, still employing a plurality of storage reels and a temporary stock cylinder, which solves the problems encountered in the prior art.
This object is achieved by the features described in the attached claims. In particular, according to a first aspect of the invention, a method for wrapping pallet-loaded loads with a film of plastic material is provided, the method comprising the steps of wrapping of a load upon running through a curtain of film coming from at least one storage reel arranged on a first side with respect to a transport line of the load, and temporary winding means which can move crosswise to said transport line, wherein at least transfer means are furthermore provided, apt to present one end edge of said film coming from said at least one storage reel to gripping means of said temporary winding means through support and presenting means, both said temporary winding means and said transfer means translating then crosswise to said transport line to lay said curtain of plastic film, said transfer means being first connected to a moving coupling bar provided with an independent drive control with respect to a movement control of said temporary winding means, and wherein said temporary winding means rotate in a first direction to accumulate initially a length of film equivalent to a perimeter portion of said load, detected and calculated in a preliminary packing phase, and then rotate in a second direction to deliver the same length of film during the dragging of said curtain of film (P) by the load, and finally said transfer means connected to said moving coupling bar and said temporary winding means converge to each other in a centre-line work area where welding and film cutting operations take place to define said wrapping of the load.
According to a preferred aspect, the movement control of said moving coupling bar depends on the movement of said temporary winding means along said direction crosswise to said transport line, the travel-end of which is reached when said gripping means face welding means at the end of said phase of delivery of the curtain of film.
Additionally, a rotation control of said temporary winding means is preferably coordinated with a translation control of the same temporary winding means and of said moving coupling bar, so that the full unwinding of the film temporarily accumulated on said temporary winding means occurs when said temporary winding means and said transfer means are mutually brought back together.
According to a further aspect, said support and presenting means are floatingly mounted on said transfer means so as to move back, after having presented said end edge of the film to the gripping means, until exposing a pair of sliding elements in contact with said film.
According to a different aspect of the invention, a curtain wrapping apparatus employing plastic film is provided, the apparatus comprising at least one gate framework defining a transport line of loads to be wrapped, at least one support carrying a series of reels of film for selecting a feeding reel based on the features of the load to be wrapped, as well as transfer means movable along a transfer path crosswise to said transport line and apt to draw an edge of film of a selected reel from said reels, so as to define a curtain of film to be applied around the load to be wrapped during the progress thereof, first welding and cutting means mounted on said transfer means being furthermore provided, wherein there is also provided
temporary winding means, opposite to said support with respect to said transfer means, apt to temporarily accumulate a certain length of film coming from said transfer means, said temporary winding means being also movable along said transfer path, so as to move away and closer with respect to said transfer means and define a curtain of film having an extension at least equal to the running front of said load to be wrapped, and wherein
said temporary winding means comprise a tubular winding /unwinding element driven in rotation, provided with gripping means apt to retain an end edge of film coming from said transfer means, as well as second welding means apt to cooperate with said first welding means in a work position wherein said transfer means and said temporary winding means are close and cooperating,
said transfer means are arranged so as to alternatively couple with a fixed post of the apparatus, in a home position, and with a movable coupling bar controlled crosswise to said transport line, in a wrapping work phase,
said movable coupling bar is controlled so as to be moved closer/further away with respect to said temporary winding means and independently from them, and
a plurality of support and presenting elements apt to present an end edge of film to said gripping means are provided, mounted projecting and retractable at different heights along said transfer means.
According to a further aspect said support and presenting means are floatingly mounted on said transfer means so as to be able to move backwards and let a pair of sliding elements come in contact with said film. Preferably, said sliding elements are idle rollers having a substantially vertical axis, mounted on said transfer means.
According to an additional aspect, said floating support and presenting elements are kept retracted through elastic means and progress into the presentation position when coming in contact with travel-end abutment means while overcoming the stress of said elastic means when said transfer means are brought into said home position. Preferably, the floating support and presenting elements are in the shape of a plurality of lamina-shaped forks apt to support flag-like a free end edge of film, said gripping means of the tubular winding/unwinding element being apt to be located between the prongs of said forks.
According to a further aspect, the tubular winding/unwinding element is driven in rotation so as to wind a length of film substantially equivalent to the plan half-perimeter of the load to be wrapped, said perimeter being detected upstream of said transfer path axis. Preferably, the tubular winding/unwinding element is driven in rotation in a coordinated manner with a translation control of said temporary winding means and of said transfer means, so that the substantial full unwinding of the film temporarily wound thereon occurs when said temporary winding means and said transfer means are close to each other in said work position and said gripping means (21) face said welding means.

Brief Description of the Drawings

Further features and advantages of the invention are in any case more evident from the following detailed description of a preferred embodiment, given purely by way of a non-limiting example and illustrated in the attached drawings, wherein:

fig. 1 is a schematic, top plan view, of a wrapping station according to the present invention, during the closing step of a wrapping;
fig. 2 is a view, similar to the one of fig. 1, which shows the sole detail of the load in an intermediate step of wrapping process;
figs. 3 and 4 are greater-detail top plan views of film transfer means, in the initial film-gripping step from the storage station and of the subsequent drawing, respectively;
fig. 5 is an elevation front view of a wrapping station according to the present invention, which shows the transfer carriage in the initial position;
fig. 6 is an elevation view, in an enlarged scale with respect to fig. 5, of the transfer carriage in the initial position; and
fig. 7 is an enlarged view of fig. 1 of the sole detail in the welding and cutting working area.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown by the top plan view of fig. 1, the wrapping apparatus according to the invention provides, in a known manner, a transport line 1 for the progression of loads C, which move in the direction indicated by arrow F. This transport line 1 is schematised in fig. 1 by a pair of rails parallel to the longitudinal axis Y-Y of transport line 1 or, in fig. 5, by a simple roller unit 1A with cylinder axes perpendicular to axis Y-Y.
Transport line 1 runs through a gate framework, consisting of a pair of posts, an inner one 2 and an outer one 3 and of two crossmembers, a lower one 4 and an upper one 5, some details of which will be described in the following.
The gate defines a pair of rails for shifting, arranged crosswise to the progressing direction F of the transport line and defining a crosswise transfer axis X-X, whereon two transfer carriages which will be illustrated in greater detail in the following are apt to move.
A single reel-carrying support 6 is furthermore provided to the side of line 1, namely beyond inner post 2 with respect to transport line 1. On this support 6 plastic film reels are installed which make up storage reels of the apparatus. The drawings show, as an example, a support of the revolving type, i.e. essentially consisting of a disc-shaped platform 6₁, rotating about a central pin 6₂ and of a plurality of supporting rotary- shaft spindles 7, 7₁, 7₂, 7₃ whereon the individual reels are mounted; in the embodiment shown only four support spindles are provided, for greater clarity of the drawing, but it is obvious that this number can be chosen at will based on the type of envisaged use.
Each one of spindles 7-7₃ supports in a freely rotatable manner a shaft with a T-shaped terminal, whereon a respective reel 8, 8₁, 8₂, 8₃ of wrapping film P is keyed on. The different reels mounted on support 6 typically have different heights (or other differentiated features, which are useful for wrapping the different loads C which pass on the transport line).
Next to rotary support 6, in a fixed position on the ground, a drive assembly 9 is provided, which determines the braked unwinding or the controlled rewinding of the reel with which it cooperates. In particular, drive assembly 9 is arranged so as to cooperate with the reel which is in turn selected each time to interact with the transfer carriages and to form the curtain of wrapping film P.
For this purpose, assembly 9 comprises a support frame 9₁ rotatably mounted on the horizontal plane on a vertical pin 9₂ under the action of a pneumatic cylinder 9₃. On frame 9₁ a pair of wheels 10 is furthermore mounted - of rubber or other material suited to cooperate with the reel surface - rotating on a respective vertical pin under the control of a respective motor 11.
Wheels 10 are preferably of a large size - for example a radius and a thickness of 80 mm - so as to have a large resting surface against the lateral surface of the respective reel; thereby, they guarantee the driving into rotation of the reel with which they come into contact, under the thrust of cylinder 9₃, but without excessive specific pressure, so as to safeguard the film.
The film P coming out of each reel is guided along a path towards respective first carriages or transfer means (one for each reel) overall referred to as 12, 12₁, 12₂, 12₃, respectively. In this path, the film runs on respective rocking rolls 13, 13₁, 13₂, 13₃, carried by an equal number of rocker arms 14, 14₁, 14₂, 14₃, as schematically shown in fig. 1, which have the function, known per se, of translating the tension changes of the film in angular displacement of arms 14-14₃: this displacement, read by a suitable sensor or encoder 15, provides a retroactive signal to proportionally drive motor 11 and hence impart the reel a faster or slower rotation, in the correct direction (winding/unwinding) to keep the tension of the film at the desired level.
As a matter of fact, during the wrapping of load C, the film P can undergo tension peaks or loosening phases, which must be seconded by the reel unwinding speed to prevent the film from ripping or becoming excessively loose (which would give rise to malfunctioning). Also in the film rewinding step, between one load and the next - as will be seen further on - it is necessary to rewind the reel in a controlled manner so that there are no overtension or undertension in the film.
In a position opposite to storage reels 8-83, the apparatus comprises a temporary winding/storage assembly, overall referred to as 19.
This temporary storage assembly 19 is in turn mounted moving along the crosswise guides of the gate frame, according to the same handling axis X-X of first transfer means 12. For such purpose, also assembly 19 is controlled in translation, through a corresponding driving system (which is illustrated in the following), on a path portion opposite to the one of transfer means 12.
According to the invention, the management of the film and the transfer thereof from the transfer means to the temporary winding assembly 19 occurs in an original and efficient manner.
Each one of the first transfer carriages 12-12₃ - one for each storage reel 8-8₃ - consists of a moving vertical bar 16 (better visible in figures 5 and 6), which defines a slot/path through which the terminal edge of the film P, which comes out of the respective reel, passes. In the rest step, the film terminal edge comes out of bar 16 and is supported flag-like (on a vertical plane) by a plurality of lamina-shaped forks 17, distributed in a vertical direction so a to be able to support all the heights of film provided in the use; as an example, in fig. 5 five forks 17 are shown and in fig. 6 only four thereof are shown, for greater clarity of the drawing.
Forks 17 are hence destined to keep a free edge of film P perfectly laid in a vertical plane and in a mechanically defined position.
The vertical bar 16 of each first transfer carriage is mounted so as to be able to slide crosswise to transport line 1 (path X-X) on the sliding guides defined on the gate frame, in the way better illustrated further on. The crosswise movement of bar 16, along the axis X-X, is guaranteed by upper and lower guides 16' apt to engage with the respective rails of the gate frame, the structure of which is within the reach of a person skilled in the field and therefore will not be described in detail.
In the rest step, i.e. when the respective reel is inoperative, bar 16 is kept securely fastened to a fixed home post 16a integral with the support 6 of the rotary storage unit, in the proximity of the respective reel. For such purpose attaching means are provided, for example two ratchet devices 16b which may be driven to open and close, which hold bar 16 adjacent and engaged with home post 16a.
In this state the film must be prevented from becoming longitudinally displaced, losing the correct positioning with respect to lamina-shaped forks 17: for such purpose first locking pad grippers 16c are provided (fig. 3), integral with home post 16a, which maintain the film pressed against bar 16. A number of locking grippers 16c, located in a vertical direction, are sufficient to keep the relative position of the film fixed with respect to lamina-shaped forks 17, until the bar is attached to home post 16a through ratchet devices 16b.
The locking grippers 16c are preferably actuated by springs, while the opening thereof is actuated by a pneumatic control, so that the retaining is guaranteed also when the supply of compressed air is missing.
On transfer rod 16 a cutting and welding unit 16s, known per se, is furthermore mounted. Unit 16s is mounted projecting on the leading edge (i.e. the edge at the film exit; the left edge in fig. 3) of bar 16.
On the leading edge of transfer bar 16 there are preferably provided also two vertical- axis cylinders 17a and 17b, mounted in close proximity to each other at both sides of lamina-shaped forks 17. On these cylinders plastic film P is meant to slide during the working step of welding and cutting - which will be illustrated further on - in which step they replace lamina-shaped fork 17 in the guiding and support of the film. As a matter of fact, forks 17 are effective for supporting flag-like the film and present it to the temporary winding assembly 19 during the gripping step (as will be seen further on), but they would end up ruining the film when said film takes on oblique attitudes in the delivery step on the load as well as in the final step of welding and cutting.
For such purpose, according to a preferred embodiment, lamina-shaped forks 17 are not mounted directly on transfer bar 16, but are mounted on a floating frame 17c, mounted translatable perpendicularly to the leading edge of bar 16 on the vertical plane.
In the embodiment shown, frame 17c is guided in the movement thereof by guiding rods 17d and is retained in a back travel-end position by elastic means 17e. In substance, frame 17c is pushed to recede with respect to transfer bar 16 by elastic means 17e, so as to cause lamina-shaped forks 17 to recede with respect to cylinders 17a and 17b (attitude illustrated in fig. 4).
When transfer bar 16 is unconstrained (ratchet devices 16b open) and distant from home post 16a (wrapping working step), forks 17 are hence kept receded with respect to cylinders 17a and 17b, so that film P which comes out of transfer carriage 12 rests on cylinders 17a and 17b.
In the home position instead, when it is necessary to retain film P flag-like through lamina-shaped forks 17 (film-presenting step to assembly 19), the position of transfer bar 16 is such that guiding rods 17d abut on a travel-end abutment 17d' - integral with home post 16a. The position of adjustable travel end abutment 17d' is such that guiding rods 17d - which frame 17c is integral with - abut against it before transfer bar 16 is fully receded (fig. 3); this results in the final recession step of bar 16 towards the home position thereof, in a relative displacement of frame 17c with respect to transfer bar 16, overcoming the elastic reaction of elastic means 17e, which causes lamina-shaped forks 17 to come out/forward with respect to cylinders 17b (attitude of fig. 3).
In substance - what is relevant for the operation which will be described further on - lamina-shaped forks 17 are mounted retractable, so as to retain the edge of film only when the first transfer carriage 12 is in the receded home position, but in all other positions taken up by transfer bar 16, along the path on the guides transversal to transport line 1, the film edge is supported and guided by cylinders 17b while forks 17 are retracted.
The transfer bars 16 of the respective transfer carriages 12 are, for all non-working reels, kept in a home position, attached to home post 16a integral with rotary support 6, with the sole function of maintaining on the vertical plane and in the correct gripping position the film coming from the respective reels.
In the case of the working reel instead, transfer bar 16 is arranged thoroughly aligned with the guides integral with the gate frame, so as to make it available for a transfer in direction T (i.e. along the axis X-X crosswise to the progressing direction of load F), for the function better described in the following.
For such purpose, on the transfer guides of the gate frame a coupling bar 18 is slidably mounted. This coupling bar provides second attaching devices 18a, for example controlled-ratchet-gear attaching means fully similar to the ones 16b provided on home post 16a. Coupling bar 18 is driven in translation, for example through kinematic chain mechanisms actuated by an electric motor, and has the task of drawing and displacing the transfer bar 16 of transfer carriage 12.
In particular, when the desired reel is arranged in the correct delivery position, with transfer carriage 12 aligned with the direction of crosswise displacement T, coupling bar 18 is moved closer (from left to right in fig. 5) to transfer bar 16 so as to couple therewith, using the attaching devices 18a and a support shelf 18a' which couple with engaging pins 18b provided on bar 16. After having released the engagement with home post 16a (opening ratchet devices 16b), coupling bar 18 can drive into displacement with itself transfer bar 16 along the crosswise guides. The displacement occurs until about the centreline of progressing line 1, as will be better explained further on.
On the opposite side to the storage reel assembly, as mentioned above, the winding/temporary-storage assembly is provided, overall referred to as 19.
This temporary storage assembly 19 is in turn mounted moving along the crosswise guides of the gate frame, according to the same displacement axis X-X of transfer bar 16. For such purpose, also assembly 19 is driven in translation, for example through a system of chains actuated by a second electric motor, on a path portion opposite to the one of transfer bar 16 with respect to coupling bar 18. Coupling bar 18 and temporary stock assembly 19 are driven into displacement independently to be able to perform the entire curtain laying process, load winding, wrapping welding and subsequent new start of the cycle. Vice versa, bar 16 - which makes up the moving component of transfer means 12 - is not provided with independent displacement along the axis X-X, but passively follows the displacement of coupling bar 18.
This temporary storage assembly 19 comprises a vertical-rod frame 19a, similar to the transfer bar 16 of assembly 12. Frame 19a supports (as better visible in figs. 3 and 4) column winding means 20 and a corresponding motorisation suitably driven and controlled.
In particular, the column winding means are in the shape of a tubular body or drum 20 whereon plastic film P is meant to be wound.
On drum 20 a plurality of gripping means 21 is provided; said gripping means are preferably housed inside the perimeter of drum 20 and they are accessed to from the outside through a longitudinal window/slot practised in the surface of drum 20; for such purpose, drum 20 is preferably built with a profile having substantially a C-shaped section, the opening of which allows the access to gripping means 21.
Gripping means 21 are conceived for gripping the free edge of the film supported by lamina-shaped forks 17 and retaining it adjacent to tubular body 20. In particular, the position of gripping means 21 along the height of drum 20 is such as to match the gap between the prongs of lamina-shaped forks 17, when temporary winding assembly 19 is adjacent to transfer assembly 16, as shown in fig. 6: this aids perfect film gripping.
Gripping means 21, as mentioned, are preferably mounted inside tubular body 20 and are meant to grip the film edge presented and introduced into the longitudinal window of drum 20 by lamina-shaped fork 17. Once the film edge has been gripped, the rotation of tubular body 20 about the longitudinal axis thereof causes the winding of subsequent layers of plastic film in close proximity to the outer surface of tubular body 20.
For such purpose, tubular body 20 is rotatably mounted with the main axis in a vertical direction and is driven into rotation by motorisation means. Said means are, for example, in the shape of a vertical-axis motor 22 which, through a gear 22₁ and a transmission chain 22₂, drives the rotation of drum 20. Transmission chain 22₂ preferably runs also on a small vertical-axis tensioning cylinder 22₃ which may be adjusted in position, the function of which is also better described in the following.
The rotation of the tubular body 20 of the temporary winding assembly is detected through a sensing device, typically an encoder, to obtain a signal proportional to the angular position of the drum of winder 20. Such signal serves both to control motorisation means 22 during film winding on body 20 - so as to wind the desired amount of film - and to be able to determine the halting position of cylinder 20. As a matter of fact, it is important, for the correct gripping of film P and for an effective welding operation, that the position of gripping means 21 be correctly determined in the initial gripping step and in the working operation step, as will be shown further on.
As a matter of fact, in the film gripping step the gripping means must be substantially aligned with transport axis X-X, so as to grip the film edge supported by lamina-shaped forks 17 (fig. 3). By contrast, in the welding working step, to have the minimum film waste, it is instead suitable for gripping means 21 to be oriented in a direction parallel to the progressing direction F of the transport line, so that the film portion between grippers 21 and the welding system be minimal (see fig. 7).
As mentioned, the system is finally completed by a welding and cutting assembly. This comprises, in a manner known per se, opposite welding blocks, 16s (the ones arranged integral with transfer bar 16) and 19s (the ones arranged on the temporary winding assembly, i.e. integral with support rod 19a), respectively.
Welding blocks 16s and 19s, traditionally heated by Joule effect, run along the entire height of assemblies 12 and 19 and are apt to come in mutual contact, clamping between them the edges of the film to be welded, during the wrapping closing step, as better detailed in the following. In the proximity of one of the welding blocks, preferably 16s of the transfer assembly 12, a cutting blade 16t is furthermore provided, on the upstream side (with respect of the unwinding direction of film P) of the welding blocks: said blade is meant to severe the wrapping, after having performed the welding, from the remaining part of film P which connects to the reel. These elements and the corresponding operation will not be described in further detail in this context, since per se they are well-known to a skilled person in the field.
During operation, a load to be wrapped is made to progress along transport line 1 in direction F. Upstream of the wrapping station the main dimensions of load C are detected. In particular, the reading of the height is used to determine reel 8-8₃ to be selected and then used, which acts on the control of rotary support 6 in order to bring the chosen reel with the corresponding transfer assembly 12 onto transfer axis X-X. Moreover, the other load dimensions are detected, to determine the extension of the plan perimeter.
Before load C arrives at line X-X, coupling bar 18 and temporary winding assembly 19 come close to transfer bar 16, sliding on the guides of crossmembers 4 and 5. Coupling bar 18 is engaged, through attaching means 18a, to transfer bar 16. At the same time lamina-shaped forks 17 present the film to gripper means 21 and said gripper means are inserted between the prongs of the forks, gripping the free edge of film P.
After that, winding assembly 19 and the bar 16 of transfer assembly 12 are displaced towards the centreline of the transport line. The film is unwound off the respective reel - starting to lay in the curtain - and lamina-shaped forks 17 recede with respect to bar 16 and hence to winding assembly 19. As a matter of fact, as better described before, the moving further away of transfer assembly 12 from home post 16a causes a recession of the frame guiding forks 17, so as to cause said forks to recede upstream of guiding cylinders 17a, 17b whereon the film P is made to slide.
At this time, tubular body 20 is driven into rotation and begins a winding step of film P: using the signal coming from the sensing device (encoder), the rotation is continued until a linear length of film substantially equal to the half-perimeter of load C is wound, less the half-width of the front side. In substance, on drum 20 a length of film sufficient to cover one half (the left one in the drawings) of the perimeter of load C must be wound, less the film which is already laid "curtain-like" through the transport line.
As a matter of fact, while winding drum 20 is driven into rotation, the entire temporary winding assembly 19 is caused to move further away from transfer means 12, i.e. it moves leftward in fig. 1. At the same time, also transfer means 12 are displaced by a short travel towards the centreline of the transport line, however, without hindering the path of load C.
When winding assembly 19 has reached the travel end thereof (fig. 2) opposite to transfer bar 16 and transfer assembly 12 is displaced forward (leftwards in fig. 1) by a certain extent, a curtain of film is found laid across transport line 1.
At this point load C arrives which, coming in contact with film P, determines its own wrapping by passing. As a matter of fact, film P is loosened both from the left, specifically by winding drum 20 which is released in rotation (by controlled friction action), and from the right, specifically by main reel 8 (itself also controlled in rotation by cylinders 10).
In other words, the load C which progresses, when coming in correspondence of vertical plane X-X, rests against the curtain formed by the film P laid between assemblies 12 and 19 and drags it in the progressing movement thereof. The film hence gradually arranges itself in the position shown in fig. 2, i.e. immediately resting on the front side of load C and increasingly resting on the lateral sides of load C. While, on the one hand, the necessary length of film guided by transfer means 12 is provided directly by reel 8, on the other hand, the length guided by assembly 19 is supplied by winding assembly 20, which gives back the one previously accumulated to the predetermined extent.
The maintenance of the correct unwinding tension of the film off assembly 19, according to the exemplifying embodiment illustrated, is guaranteed by a small tensioning cylinder 22₃ which is suitably equipped with a friction device. The maintenance of the correct winding tension of the film coming from the respective reel 8 is instead ensured, in this step, by rocking roll 13 which provides the correct control to motor 11 and hence to wheels 10.
This allows to apply a vertical layer of film on the front side and on the two lateral sides of load C (fig. 2) without creating relative sliding of the film on the load.
When the load has nearly entirely overcome line X-X, both temporary winding assembly 19, and coupling bar 18 (and transfer assembly 12 therewith), simultaneously converge towards the centreline of the transport line, transferring the film also on the rear side of load C. The convergence continues until it brings the two assemblies 19 and 12 in proximity one of the other, in particular bringing in contact the respective welding blocks (figs. 1 and 7).
According to a preferred embodiment, the coupling location of the two assemblies - hence the position of the welding on the wrapping - does not necessarily fall in the centreline of transport line 1, but is defined by the encoder of motor 22: as a matter of fact, it is desired for the apparatus to be as illustrated in fig. 7, i.e. with gripper means 21 facing towards the welding blocks (which attitude guarantees the least possible film waste). Therefore the movement of transfer assembly 12 is dependent on and driven by the movement of winding assembly 19, said movement depending in turn by the signal coming from the encoder or other rotation sensor of drum 20.
In order for the process to occur as required, as already mentioned, it is suitable that the length of film wound in assembly 19 substantially corresponds to the one necessary for covering the half-perimeter of the load, less the film which is already laid between winding assembly 19 and transfer assembly 12. If the length wound in assembly 19 was shorter or longer than the required one, there would derive that the welding and cutting area of the wrapping would end up being greatly displaced from the load centreline, to one side or the other (since the cooperation position of the two assemblies, wherein the welding occurs, is determined by the detection of the full unwinding of assembly 19). If the length was much longer or shorter than the required one, it would of course not be possible to complete the wrapping, unless undesired sliding movements of the film on the load are allowed to occur.
For such purpose, as already mentioned above, it is advantageous to provide a control which detects the size of the load and wraps the correct length of film on temporary winding drum 20, as well as controlling film delivery, both from drum 20 and from the reels (8-8₃), during the unwinding step on the load.
At this point in time, winding drum 20 has fully unwound the film previously stored and retains only a short edge, between gripper means 21, which runs on the welding blocks and stretches around the load (fig. 6).
Welding blocks 16s and 19s are brought into mutual engagement, so as to perform the welding of the terminal edge of the film - now fully removed from column winding unit 20 - against the film portion carried by assembly 12 and still joined to respective reel 8.
At the end of the welding operation, the wrapping around load C has finished and it is necessary to severe it from the rest of film P which connects to the respective reel. For such purpose, the short edge of film coming from temporary winding assembly 20 is simply released by the grippers, while the other portion of film which connects to the reel is cut by blade 16t, after having locked it upstream on transfer assembly 12 through a second pad gripper 12a integral with transfer bar 16. This last edge of film, which remains laid between cylinders 17a, 17b and the point of severance on load C, is the one which is then again correctly supported by forks 17 when bar 16 returns resting on home post 16a causing again forks 17 to move forward with respect to cylinders 17a and 17b.
As a matter of fact, once this welding and cutting step has finished, temporary winding assembly 20 and transfer means 12 can return towards rotary support 6, to begin a new gripping and laying cycle of the film with the same reel or with a new reel.
As one can understand from the description reported above, the apparatus of the invention perfectly achieves the objects set forth in the premises.
In particular, the curtain wrapping apparatus according to the invention requires a single support station of the plurality of reels, to the advantage of a significant reduction of the bulks and costs. Moreover, the presence of a single reel per type makes the management more efficient and reduces idle times as well as film waste. The original cooperation between temporary stockpiling assembly 19, coupling bar 18 and transfer means 12 allows an efficient management of the film, which leads to a full absence of jamming, to a high productivity of the machine, also in the presence of reel changes, and to a minimal waste of unused plastic film.
However, it is understood that the invention must not be considered limited to the particular arrangement illustrated above, which represents only an exemplifying embodiment thereof, but that a number of variants are possible, all within the reach of a person skilled in the field, without departing from the scope of protection of the invention, as defined by the following claims.
For example, although in the description reference has always been made to a revolving support, it is not ruled out that it is replaceable in an equivalent manner with a sliding support for a plurality of reels arranged in line.

Claims

Method for wrapping pallet-loaded loads with a film of plastic material, the method providing a wrapping of the load (C) upon running through a curtain of film (P) coming from at least one storage reel (8-8₃) arranged on a first side with respect to a transport line (1) of the load (C), and temporary winding means (19, 20) which can move crosswise (X-X) to said transport line (1), characterised in that
at least transfer means (12) are furthermore provided, apt to present one end edge of said film coming from said at least one storage reel (8-8₃) to gripping means (21) of said temporary winding means (19, 20) through support and presenting means (17)
both said temporary winding means (19, 29) and said transfer means (12) translating then crosswise (X-X) to said transport line (1) to lay said curtain of plastic film (P),
said transfer means (12) being first connected to a moving coupling bar (18) provided with an independent drive control with respect to a movement control of said temporary winding means (19, 20),
said temporary winding means (19, 20) rotate in a first direction to accumulate initially a length of film (P) equivalent to a perimeter portion of said load (C), detected and calculated in a preliminary packing phase, and then rotate in a second direction to deliver the same length of film (P) during the dragging of said curtain of film (P) by the load (C),
finally said transfer means (12) connected to said moving coupling bar (18) and said temporary winding means (19, 20) converge to each other in a centre-line work area where welding and film cutting operations take place to define said wrapping of the load (C).
Wrapping method as claimed in claim 1, wherein the movement control of said moving coupling bar (18) depends on the movement of said temporary winding means (19, 20) along said direction (X-X) crosswise to said transport line (1), the travel-end of which is reached when said gripping means (21) face welding means (16s, 19s) at the end of said phase of delivery of the curtain of film (P).
Wrapping method as claimed in claim 2, wherein a rotation control of said temporary winding means (19, 20) is coordinated with a translation control of the same temporary winding means (19, 20) and of said moving coupling bar (18), so that the full unwinding of the film (P) temporarily accumulated on said temporary winding means (19, 20) occurs when said temporary winding means and said transfer means (12) are mutually brought back together.
Wrapping method as claimed in claim 1, 2 or 3, wherein said support and presenting means (17) are floatingly mounted on said transfer means (12) so as to move back, after having presented said end edge of the film (P) to the gripping means (21), until exposing a pair of sliding elements (17a, 17b) in contact with said film (P).
Curtain wrapping apparatus employing plastic film (P), comprising at least one gate framework defining a transport line (1) of loads to be wrapped (C), at least one support (6) carrying a series of reels (8-8₃) of film for selecting a feeding reel based on the features of the load to be wrapped, as well as transfer means (12) movable along a transfer path (X-X) crosswise to said transport line (1) and apt to draw an edge of film of a selected reel from said reels (8-83), so as to define a curtain of film to be applied around the load to be wrapped (C) during the progress thereof, first welding and cutting means (16s, 16t) mounted on said transfer means (12) being furthermore provided, characterised in that
temporary winding means (19, 20) are furthermore provided, opposite to said support (6) with respect to said transfer means (12), apt to temporarily accumulate a certain length of film (P) coming from said transfer means (12), said temporary winding means (19, 20) being also movable along said transfer path (X-X), so as to move away and closer with respect to said transfer means (12) and define a curtain of film (P) having an extension at least equal to the running front of said load to be wrapped (C),
said temporary winding means (19, 20) comprise a tubular winding /unwinding element (20) driven in rotation, provided with gripping means (21) apt to retain an end edge of film (P) coming from said transfer means (12), as well as second welding means (19s) apt to cooperate with said first welding means (16s) in a work position wherein said transfer means (12) and said temporary winding means (19, 20) are close and cooperating,
said transfer means (12) being arranged so as to alternatively couple with a fixed post (16a) of the apparatus, in a home position, and with a movable coupling bar (18) controlled crosswise (X-X) to said transport line, in a wrapping work phase,
said movable coupling bar (18) being controlled so as to be moved closer/further away with respect to said temporary winding means (19, 20) and independently from them, and in that
a plurality of support and presenting elements (17) apt to present an end edge of film (P) to said gripping means (21) are provided, mounted projecting and retractable at different heights along said transfer means (12).
Apparatus as claimed in claim 5, wherein said support and presenting means (17) are floatingly mounted on said transfer means (12) so as to be able to move backwards and let a pair of sliding elements (17a, 17b) come in contact with said film (P).
Apparatus as claimed in claim 6, wherein said sliding elements are idle rollers (17a, 17b) having a substantially vertical axis, mounted on said transfer means (12).
Apparatus as claimed in claim 6 or 7, wherein said floating support and presenting elements (17) are kept retracted through elastic means (17e) and progress into the presentation position when coming in contact with travel-end abutment means (17d) while overcoming the stress of said elastic means (17e) when said transfer means (12) are brought into said home position.
Apparatus as claimed in claim 8, wherein said floating support and presenting elements are in the shape of a plurality of lamina-shaped forks (17) apt to support flag-like a free end edge of film (P), said gripping means (21) of the tubular winding/unwinding element (20) being apt to be located between the prongs of said forks (17).
Apparatus as claimed in any one of the preceding claims 5 to 9, wherein said tubular winding/unwinding element (20) is driven in rotation so as to wind a length of film substantially equivalent to the plan half-perimeter of the load to be wrapped (C), said perimeter being detected upstream of said transfer path axis (X-X).
Apparatus as claimed in claim 10, wherein said tubular winding/unwinding element (20) is driven in rotation in a coordinated manner with a translation control of said temporary winding means (19, 20) and of said transfer means (12), so that the substantial full unwinding of the film (P) temporarily wound thereon occurs when said temporary winding means (19, 20) and said transfer means (12) are close to each other in said work position and said gripping means (21) face said welding means (16s, 19s).