EP1510460B1

EP1510460B1 - Method of and apparatus for the sealed overwrapping of a load using a tubular film of stretchable plastic material

Info

Publication number: EP1510460B1
Application number: EP04103938A
Authority: EP
Inventors: Franco Tacchini
Original assignee: Officina Meccanica Sestese SpA
Current assignee: Officina Meccanica Sestese SpA
Priority date: 2003-08-28
Filing date: 2004-08-17
Publication date: 2006-12-27
Anticipated expiration: 2024-08-17
Also published as: ATE349378T1; DE602004003869D1; ITMI20031674A1; DE602004003869T2; EP1510460A1; PT1510460E; ES2278279T3; DK1510460T3

Abstract

The invention relates to a method of and to an apparatus for the overwrapping of a pallet-stacked load (C) using a tubular wrapping film (P) made of a stretchable plastic material. In a rigid main support structure (1) are provided means for upwardly feeding the film, means for cutting a section of said film and for thermowelding the lower edge thereof to form a bag, as well as means for causing the upper open edge thereof to ruffle on an adjustable widening frame (13) with a similar upward movement. The adjustable widening frame (13) consists of four angular posts, mutually linked through four tubular telescopic rods. Means are provided for widening said frame and for transversally stretching said film bag, as well as means for having said adjustable widening frame slide downwards along the load (C) arranged at a wrapping station, and means for progressively releasing said film bag onto the load, simultaneously causing the turning inside-out thereof. The four angular posts of the adjustable widening frame comprise guiding means which, together with said four telescopic rods, guide said bag during its inside-out movement and brake it during the release thereof onto the load. Said welding means are associated with means cooling the finished welding. <IMAGE>

Description

The present invention relates to a process and to an apparatus for the sealed overwrapping of a pallet-stacked load by means of a film of stretchable plastic material having a tubular shape.
The general principle of apparatuses for wrapping pallet-stacked loads is the following: a pallet-stacked load is brought in a wrapping position in the middle of a main support structure of a wrapping apparatus. A plastic wrapping film, having a tubular shape but folded longitudinally on a plane to be wound onto a feeding roll, is guided from a position at the bottom of said main support structure to a position above the top of the pallet load. Such film is then guided downwards and at the same time opened at the bottom end thereof, so as to form a sort of upturned bag. Such bag is first of all removed from the feeding roll performing a horizontal cut and simultaneous thermal welding along the top end edge. Such upturned bag is then force-fitted onto and around the pallet load, until it is completely wrapped around the load.
When a thermo-shrinking film is employed, the final wrapping step consists in the shrink-welding of the bag on the load, which occurs subjecting the wrapping film to shrinking by heat. When a stretchable film is employed instead, the bag force-fitting step is preceded by a step of temporary stretching and widening of the bag itself, so that the wrapping final step consists in the release of the bag which, due to elastic action, returns into its initial condition and hence automatically shrinks around the load. The present invention relates indeed to an overwrapping apparatus of this kind, that is one which employs a film of stretchable plastic material.
Italian patent IT-1.074.012 in the name of ANVAR (corresponding to patent FR-2.316.127 filed on 4.7.1975), describes a wrapping apparatus in which means are provided to feed the tubular film above the load, and gripping means which grip the wrapping bag at the four corners thereof, open it and drag it downwards over the bottom of the pallet along four substantially vertical tracks. In actual fact, each of such tracks has a first vertical portion, which extends in height exclusively over the pallet load and which defines a plan perimeter corresponding to the bag largest unstretched size, a second vertical portion, which extends over the entire height of the pallet load and which covers a plan perimeter of a size larger than the size of the load itself, as well as a third oblique portion, which joins the bottom end of the first portion, which is the innermost and narrowest one, and the top end of the second portion, which is the outermost and widest one. That way, said third portion of the four tracks forms a path defining a plan perimeter becoming gradually wider in the bottom portion thereof; such path hence forms an oblique widening portion, along which a temporary widening of the bag is produced, due to the elastic stretching in a crosswise direction. The bag thus widened, following the second portion of the tracks, is then force-fitted on the load and on the pallet. Once finished, the gripping means are released, to let the bag elastically resume its original condition and shrink on the load.
In patent EP-0.285.855 in the name of LACHENMEIER, filed on 11.03.1988, a wrapping apparatus of the same type is disclosed, in which, however, the bag of stretchable plastic material is first collected, substantially ruffled, on four vertical pin supports, which are located at the four corners of a quadrangular support frame (which is also referred to in the following part of the description under the term of "adjustable widening frame"). These four pin supports define (similarly to the vertical sliding guides provided in IT-1.074.012) a perimeter having a smaller plan size than the load plan size.
In a second step, said support framework is horizontally widened, both longitudinally and transversally, so as to bring the four pin supports, with the ruffled bag thereon, to define a perimeter having a larger plan size than the load plan size. Finally, in a third step, said framework with the four pin supports is made to vertically slide downwards to the bottom of the pallet, while the bag is progressively released from the same pin supports and force fitted onto the load; in this third step the stretched film freely returns into its initial condition, shrinking on the load.
Wrapping apparatuses of this type, i.e. equipped with means to ruffle the bag in a first step, then to stretch it horizontally in a second step, and finally to spread it out in a third step while simultaneously applying it to the load, are also known from patents DE-39 08 957 dated 18.3.1989, EP-0.344.815 and EP-0.445.443, both filed on 5.6.1989, EP-0.798.214 filed on 27.3.1997, EP-1.072.514 filed on 21.7.2000, all in the name of BERNHARD BEUMER MASCHINENFABRIK, as well as from patent DE-43 27 450 in the name of MOELLERS, which are all based on the same operation mode and differ from each other essentially through construction details.
All the devices of the prior art illustrated in the above cited patents have a series of drawbacks, which may be summarised in the following:
a) - the film of the wrapping bag remains stretched only in a horizontal direction (i.e. transversally to the vertical axis of the upturned bag): in fact, when the pin supports, or similar, onto which the tubular film is ruffled, are mutually spaced apart, they cause a horizontal stretching of the film; when such supports are shifted vertically, to force-fit the film on the load, said film is simply released from said supports, without any vertical stretching;
b) - furthermore, in said same vertical shift, sliding of the film during the release step from the pin supports does not occur evenly, but depends on how the film has been previously ruffled; in practice it has been shown that there is often the risk of multiple ruffle folds being released simultaneously leaving the film loose and bearing folds on the vertical walls thereof;
c) - in addition to this, the film is guided only in correspondence of the four corners of the adjustable widening frame, so that said film tends, due to its elasticity and to the remarkable stretching it was subject to, to take up an arched shape along its edges, thereby affecting the release conditions on the load;
d) - the crosswise welding line at the top of the bag remains on the outside, forming folds, ears and/or pockets, which may on the one hand become entangled on fixed obstacles, in the steps of handling the finished pallet and, on the other hand, represent preferred breakage locations, as well as allowing collection of dirt or water, which may freeze;
e) - the wrapping apparatus must be much higher than the load: the tubular film is in fact fed from a roll housed in the proximity of the bottom of the apparatus, upwards and over the load, then it is deviated downwards, on the load, hence the tubular film is stretched open and guided on the pin supports to the four corners of the adjustable widening frame; that necessarily implies that the apparatus be at least as tall as the space necessary to guide and stretch open the tubular film over the top height provided for the load.
In actual fact, some of these problems are addressed, but not fully solved in EP-1.106.507. In particular, in said document it is proposed to:
lift the bag up over the load, maintaining it in an open position; as a consequence, the risk mentioned above at point b) concerning the forming of folds upon release of the bag on the load is avoided, at least in theory;
apply the bag on the load with an inside-out movement; as a consequence, the risks mentioned at point c) are also avoided concerning the forming of a welding line on the outside of the bag;
However, the apparatus according to EP-1.106.507, on the one hand leaves the problems mentioned at points a) and d) unsolved and, on the other hand, introduces remarkable complications in the guiding of the bag onto rod poles and ends up making the apparatus even taller than the prior art ones.
It is an object of the present invention to propose a wrapping apparatus structure which effectively solves the above mentioned problems, which has a compact structure and is easily installed, which allows to perform a safer wrapping, and which has an improved productivity. Starting from the teaching of patent DE-39 08 957, which represents the prior art closest to the invention, the object of the invention is achieved through a process and a wrapping apparatus having the features mentioned in claims 1 and 10.
Further features and advantages of the invention will in any case be clearer from the following detailed description of a preferred embodiment, given by way of a non limiting example and illustrated in the accompanying drawings, wherein:
fig. 1 is an elevated and partially sectioned diagrammatic view of the wrapping apparatus according to the invention, in the collection position of the tubular film on the adjustable widening frame, to form a ruffled bag;
fig. 2 is a view similar to that of fig. 1, but in the position of initial displacement of the tubular film from the adjustable widening frame to the load;
fig. 3 is a plan and partly sectioned diagrammatic view of the same apparatus of fig. 2;
fig. 4 is an enlarged view of the selection and collection station of different types of tubular film to feed, shown by arrow S1 in figures 1 and 2;
fig. 5 is an enlarged view of the transfer carriage mounting the adjustable widening frame, in the initial position of the step of tubular film application on the load;
figs. 6 and 7 are elevated and partly sectioned plan views, respectively, in an even more enlarged scale, of the tubular film-collecting and film-ruffling assembly on the adjustable widening frame of the transfer carriage, shown by arrow R in figure 5;
figs. 8 and 9 are views similar to those of figs. 6 and 7, showing an embodiment of the tubular film-collecting and film-ruffling assembly; and
figs. 10a to 10c show in a very diagrammatic way an embodiment of the tubular film welding and cutting assembly at the bottom end thereof, equipped with cooling means of the welding.
As diagrammatically shown in figs. 1 and 2, the wrapping apparatus according to the invention comprises a single main support structure, formed by four posts 1 (marked 1a, 1b, 1c, and 1d in fig. 3), held by crossmembers 2 and 3 at top and bottom. Said main support structure is located beside the transport line T (diagrammatically represented by a simple box in fig. 1, since it is a known device, not being part of the present invention) on which the load C, generally a pallet-stacked load to be packaged, moves (in a direction perpendicular to the plane of the drawing sheet).
According to the present invention, feeding of the tubular film and collection thereof on the adjustable widening frame occur in correspondence of the main support structure 1,2,3, whereas distribution and application of the tubular film on the load, to form the corresponding packaging, occurs outside the main support structure, in correspondence of the transport line T. For this purpose there are mainly provided:
a station S1 for selection and collection of the tubular film P to be fed, in the proximity of the bottom crossmember 2 of the main support structure 1,2,3;
a transport system S2 for upwardly feeding and guiding the tubular film towards the adjustable widening frame located inside the main support structure 1,2,3; and
a system S3 for the displacement of the adjustable widening frame from the collection position, within the main support structure, towards the distribution position above the load.
The selection and collection station S1 is represented in a diagram in fig. 1 and in greater detail in fig. 4. Said station comprises multiple supports - three supports in the case illustrated - for an equal number of rolls B1, B2, B3 feeding the tubular film P1, P2 P3. As known, the tubular film, to be wound onto rolls, is folded on a plane, that is so as to form two parallel, main plane sides, joined to two sides folded concertina-like; the cross section of this configuration, which is well known, is the one represented in fig. 3, diagrammatically represented by phantom lines and marked by reference P.
The plane sheets P1, P2 and P3 coming out of their respective feeding rolls - which sheets differ from each other generally only through their cross size, even though sheets for example of different material, resistance, colour or else may be employed, - are deviated, through a series of transmission rollers, up to the rollers 4a, 4b and 4c (for further details, see fig. 4) of a selection device; this implies a rotating cage (not shown), of which only the central support shaft 5 and the opening devices 6a, 6b e 6c can be seen in fig. 4. Every time it is desired to change the type of wrapping film, a different opening device 6a, 6b or 6c, hence a different sheet P1, P2 or P3, is brought in correspondence of the feeding and guiding station S2.
Each of said feeding and opening assemblies has a structure known per se, which is not part of the present invention, and which will therefore not be described in further detail.
Immediately above the selection station S1 is located a cutting and welding assembly (not better shown, since it is known per se and in any case it is not part of the present invention); such device is in any case diagrammatically represented in fig. 4, and comprises a pair of fixed crossmembers 7, along which cutting and welding means shift. Such means comprise, more accurately, two welding presser 7a and cutting blade 7b assemblies, operated in opposite directions by two corresponding jacks 7c. In a known manner, the two jacks 7c are capable of bringing the respective pressers 7a in mutual contact along the middle line Y―Y (see fig. 3) to perform the welding, and then blades 7b to cooperate in cutting the tubular film along the same line.
In the embodiment illustrated in figures 10a to 10c, each of the two welding presser 7a and cutting blade 7b assemblies comprises a cooling presser 7e; said cooling presser is, as is evident from the drawing, a preferably square tubular bar in which air or possibly cooling liquid is made to flow.
When the two assemblies approach each other to perform the welding, first pressers 7a are brought into mutual tight contact and grip between each other the double sheet of wrapping film to perform the thermal welding. Immediately afterwards, or with the pressers 7a still in tight contact, the cutting blades 7b are made to advance; which blades separate the film portion which has already formed the upward open bag using P3 which is fed from the corresponding roll.
According to this embodiment, upon closure of pressers 7a and of blades 7b, cooling pressers 7e are also closed (Fig. 10b); their mutual contact and clamping of the film, in a position above the welding point - as shown in fig. 10b - offers a first advantage and precisely that the welding heat does not diffuse upwards, along the film, but remains concentrated in the clamping position of the pressers 7a, allowing a more accurate welding.
Upon opening of pressers 7a and of blades 7b, pressers 7e also temporarily open to allow a brief upward sliding of the film; as soon as the welding line arrives in correspondence of the pressers 7e (fig. 10c), said pressers tighten again and clamp the welding, cooling it. A second advantage is thereby obtained, i.e. that the welding, well cooled before being subjected to stretching, is much more stable and not at risk of yielding and opening during the subsequent steps of stretching and application of the bag onto the load to be wrapped.
The transport system S2 for feeding and guiding the film comprises (see also fig. 3 in the left portion of the drawing) a beam carriage 8, vertically sliding along posts 1a and 1b under the control of a motor drive 8a. On such carriage are mounted cantilevered two arms 9a and 9b, which can be shifted along the beam carriage 8, in a specularly symmetrical way to the middle transversal axis X-X, through respective motor drives 10. On each of said two arms 9a and 9b are mounted pairs of grippers 11,12, which are in turn mounted sliding along such arms in a specularly symmetrical way to the longitudinal middle axis Y-Y of the main support structure 1.
In the position represented in fig. 4, grippers 11, 12 of each pair of grippers of the tubular film P are moved closer together, at the centre of arm 9a, 9b, but are open to receive the edges Pa, Pb of the tubular film itself; said edges correspond to the upper open edge of the film carried by the opening device 6c which at that time is in correspondence of grippers 11, 12.
Once grippers 11, 12 have gripped edges Pa, Pb, carriage 8, 9a, 9b moves upwards dragging the tubular film therewith, which unrolls from the respective feeding roll. Simultaneously to this upward movement, grippers 11, 12 of each of the arms 9a, 9b are moved apart from each other (see intermediate position in fig. 1), opening the tubular film from the initial situation, marked by P and with phantom lines in fig. 3, up to the final situation, marked by P' and with phantom lines in the same figure 3.
The upward movement of carriage 8, 9, with simultaneous widening of grippers 11, 12, continues until the edge of film P', corresponding to the open upper end of the tubular film, ends up taking in the adjustable widening frame associated with the displacement system S3, in the way better described in the following.
Displacement system S3 - illustrated in figures 1 and 2 in the proximity of the top crossmember 3 of the main support structure 1, 2, 3 - in fact essentially consists of three elements: an adjustable widening frame 13, a transfer carriage 14 and a pair of support plates 15. The adjustable widening frame 13 is mounted on carriage 14 and is capable of becoming wider or narrower than carriage 14 itself. Said carriage is capable of shifting horizontally, in a crosswise direction to the movement direction of load C, along a guiding system formed on each of the two support plates 15; carriage 14 is further capable of shifting vertically, together with said two plates 15, which are capable of shifting along a guiding system formed on the pair of posts 1c and 1d. For greater clarity, it is to be noticed that:
the adjustable widening frame 13 is capable of shifting both in a crosswise direction X-X and in a longitudinal direction Y-Y, to become wider or narrower;
carriage 14 shifts in a crosswise direction X-X, i.e. parallel to the plane of the sheet of fig. 3, from a position (on the left hand side in the drawing of fig. 1) collecting the tubular film to a position (on the right hand side in the drawing of fig. 2) applying the tubular film on the load, and
the pair of plates 15 shifts only in a vertical direction Z-Z, to vertically transport both carriage 14 and the adjustable widening frame.
The two plates 15 are mounted vertically sliding along posts 1c and 1d, respectively, of the main support structure, i.e. the two posts which are on the side of the load transporter T. To ensure an integral movement of the two plates 15, said plates are mutually linked by crossmembers 15a, meant to form a rigid cage therewith; such crossmembers 15a, however, do not obstruct the free transversal movement of carriage 14. The vertical movement of cage 15, 15a is guaranteed by a guiding system integral with posts 1c, 1d, diagrammatically represented by rollers 15b and not better shown since already known and in any case not being part per se of the present invention.
From each of the two plates 15 projects a respective series of idle rollers 16, along which carriage 14 is slidingly mounted; such carriage is essentially formed by a rigid box-frame structure, which is equipped with opposite side rails, shaped so as to slide with minimal play onto said two series of rollers 16.
On the structure of transfer carriage 14 shifts the cited adjustable widening frame 13, which consists of the following elements, diagrammatically represented in fig. 3, but visible in greater detail in figures 5 to 7:
two pairs of first saddles 17, 18, which shift along two opposite sides of the box structure of carriage 14, in a specularly symmetrical way to the middle axis Y1-Y1; saddles 17 of a first pair carry a crossmember 19, whereas saddles 18 of a second pair carry a crossmember 20. The opposite and symmetrical movement of saddles 17 and crossmember 19, approaching or departing from saddles 18 and crossmember 20, occurs under the control of a single common engine 21 and of two drive chains 22, on two opposite sides of the box structure of carriage 14; to obtain said symmetrical opposite movement, saddles 17 are joined to one of the branches of each chain 22 (for example the upper branch) and saddles 18 are joined to the opposite branch (for example the lower branch);
four collection assemblies 23, 24, 25 and 26, arranged at the four corners of adjustable widening frame 13, one of which is shown in detail in figs. 6 and 7. Each collection assembly is mounted on an own saddle 23a, 24a, 25a, and 26a; such saddles are mounted sliding in pairs on crossmembers 19 and 20, in a way specularly symmetrical to the middle axis X-X. Such movement occurs under the control of two respective motors 27 and 28, each driven in perfect parallelism in correspondence of the respective crossmember 19 or 20 thereof, and by two respective drive chains, also mounted in the manner described for chains 22;
four telescopic rods 29, which connect the four collection assemblies. Such rods are preferably tubular, having a circular section, for the purpose better described in the following.
A particularly interesting advantage of the adjustable widening frame arrangement just described - with respect of the prior art of DE-39 08 957 which, for the widening of frame 13, provide two jacks arranged according to the frame diagonals - is the following: by driving the common motor 21 in a way independent from the actuation of the pair of motors 27, 28, it is possible to vary the shape and size of frame 13, i.e. it is possible to vary within wide margins the ratio between the length of a pair of opposite sides of frame 13 and the length of the other pair of sides. In other words, it is possible to adjust the shape of frame 13 to the shape of the pallet load to be wrapped, i.e. to give frame 13 a rectangular shape with the longer axis according to Y1-Y1 (as shown), or a square shape, or a rectangular shape with the longer axis according to X-X.
This adjustment of the shape of frame 13 preferably occurs before ruffling of the wrapping bag, so that, in the subsequent widening step, it is possible to control the lengthening of the sides of frame 13 so as to cause a stretching of the stretchable film of the bag, in an even way on all four sides.
It is important to notice that telescopic rods 29 automatically follow the varying shape of frame 13 or the size ratio of the sides thereof, since the ends of said rods are joined directly to the four collection and ruffling assemblies. The function of such telescopic rods is essential, not so much in order to establish a structural connection among the four collection and ruffling assemblies at the four corners of the frame, as to physically set up the sides of the adjustable widening frame; such telescopic rods - having a tubular shape with a circular section - are in fact capable of offering a rounded surface, onto which the wrapping film can glide and be guided during the step of turning inside-out and release onto the load to be wrapped. The film is hence guided on a rounded surface which extends over the entire contour of the adjustable widening frame.
In figures 6 and 7 a first embodiment of one of said collection assemblies 23, 24, 25, 26 is shown in greater detail, as said, onto which tubular film P ruffles; in the following only assembly 25 is described, the other assemblies being identical thereto. Said group 25 (like each of the other three assemblies, in a symmetrical way) comprises a pair of motor-driven wheels 30, mounted on mutually perpendicular axes 31. As is well visible in the plan view of fig. 7, wheels 30 have such a periphery profile, and are positioned one in respect to the other so that their contour arrives substantially in mutual contact at a point TR representing in practice the gripping point of film P, and the dragging point, as is better described in the following.
Opposite to the point of contact TR, between the two wheels 30, a third wheel 32 is found, mounted freely rotating on a pin 32a, carried by a support triangle 33; the plane of wheel 32 is substantially oriented according to the vertical plane of the bisectrix of the angle formed by the collection assembly 25. Triangle 33 can perform a short oscillation run within said bisectrix plane, which run is controlled by jack 34. Thanks to this way of mounting, wheel 32 goes from a rest position, in which it is at a short distance from the contour of the pair of wheels 30, to a work position in which it is in close contact with said contour of wheels 30 (s. fig.7); such contact is aided by the profile shape of wheel 32, which is substantially capable of cooperating with the profile of both wheels 30 joined at the point of contact TR thereof. When the two motor-driven wheels 30 are made to rotate, they drag wheel 32 through contact, in particular when the tubular film is interposed therebetween, which film is hence in turn dragged.
Furthermore, on the vertical line of the point of contact TR, below wheels 30 and 32, is the convex-profile contour of a fourth wheel 35, mounted idle on its own axis, the function of which is to ease gliding of the tubular film when it is dragged by wheels 30, 32: that occurs not so much during the collection and ruffling step, as mainly during the step releasing the film onto the load when - as better described in the following - the film is turned inside-out, shifting it from the outside to the inside of the frame.
In the embodiment of figures 8 and 9, the arrangement is virtually inverted, at least as far as the motor drive is concerned, which is not on a pair of wheels within the adjustable widening frame (as in the case of wheels 32), but on outer wheel 40. Furthermore, within the frame the film rests - not so much on wheels 32 and on the subsequent ruffling angular post 36 - but directly on the profile of angular post 42 which, in correspondence of the resting area TR of wheel 40, is formed by a sliding block 41 made of a material having a low friction coefficient, in particular a sliding block made of Teflon® .
Both in the case of the pair of wheels 30 of the embodiment of figures 6 and 7, and in that of wheel 40 of figures 8 and 9, rotation thereof is controlled by own driving motors 37 and 43, respectively. All four motors of the four collection and ruffling assemblies are furthermore synchronised with each other so as to obtain an even sliding action, both upwards and downwards, of the tubular film.
The operation of the apparatus described above comprises the following steps:
first of all the operator provides to arrange the rolls of tubular film on the respective supports B1, B2, B3, to insert each film in the respective unwinding path P1, P2 and P3 up to transmission rollers 4a, 4b and 4c, and finally to engage the open upper side thereof with opening devices 6a, 6b and 6c, respectively.
upon start of a wrapping operation, the automatic control system of the apparatus (or the operator himself in less automated apparatuses) provides to bring opening device 6a, or 6b, or 6c - according to the type of wrapping film required - in correspondence of the pair of grippers 11, 12 of the gripping carriage 8. Once grippers 11, 12 have gripped the film, carriage 8 shifts upwards and grippers 11, 12 simultaneously depart from each other to open the tubular film in the way illustrated on the left hand side of figs. 1 and 3 (phantom profile P').
At the same time, if necessary, it is possible to change the shape and size of the adjustable widening frame, to make it more suitable to the shape of the pallet load to be wrapped, in the way shown above.
The movement of the tubular film P continues upwards as long as the free upper edge thereof is force-fitted over the four wheels 35 (fig. 6, 7) - or over sliding blocks 41 (fig. 8, 9), respectively - of collection assemblies 23, 24, 25, 26, and in the space between meeting point TR of wheels 30 with the opposite pressure wheel 32, or of wheel 40 with sliding block 41, the pressure wheel being kept apart, in this step, in its rest position.
Immediately afterwards, jack 34 is operated to bring wheel 32 in close contact with wheels 30 (or wheel 40 against sliding block 41), and hence lock the open upper end of the film bag on the adjustable widening frame 13.
afterwards it is provided to seal film P along a current line according to the axis Y-Y and to perform a cut parallel to the same axis, employing - according to a process known per se - the cutting and welding assembly 7 to separate the part of the tubular film meant to form the wrapping bag from the underlying part being fed.
It must be noticed that, according to an important feature of the invention, said welding and cutting line remains facing downwards, as diagrammatically shown by the welding footstalk PP shown in the middle lower part PI of film P, which closes below the adjustable widening frame, as diagrammatically shown in figure 5.
Such welding and cutting operation can be performed immediately after having locked the open upper end of the bag between wheels 30, 32 - as mentioned - or even shortly after the start of rotation of wheels 30, 32, with a delay depending on the desired length of the wrapping bag: such length may in fact, at least in certain cases, exceed the measure comprised between the lower end stop and the upper end stop of carriage 8, 9.
after the welding and cutting operation, rotation of wheels 30, 32 is started (or possibly continued): said wheels are made to rotate in direction F' (anti-clockwise direction with respect of fig. 6), to drag film P upwards. The film hence ruffles - along an angular section bar 36 (fig. 6) arranged vertically and having a rounded edge, in the way diagrammatically shown in PL in figure 5 - in a quantity sufficient, according to the load size, to later effect the desired wrapping. The final part PI of the film instead remains laid open on a plane below and across the adjustable widening frame.
In the embodiment of figures 8 and 9 operation is identical to the one described above, except for the fact that dragging of the film is performed by the motor-driven wheel 40 outside the frame, and ruffling occurs on sliding block 41 and on angular element or bar 42.
Subsequently, shifting of transfer carriage 14 is performed from the main support structure area 1, 2 (wherein station S1 selecting the tubular film and system S2 transporting and forming the ruffled bag are arranged), shown on the left hand side of fig. 1, to the area of the pallet transporter T (wherein the application station of the tubular film on the load is located), shown on the right hand side of fig. 2. This step consists exclusively in the shifting of carriage 14, together with adjustable widening frame 13, along the guide defined by rollers 16, in a crosswise direction, i.e. parallel to the axes X-X of the apparatus.
The work step just described at point E) is associated with the widening step of frame 13. In effect, when film P has ruffled on the four collection assemblies 23, 24, 25 and 26, such assemblies are mutually spaced apart, moving them in the directions shown by arrows F in fig. 3. During such movement film P is elastically stretched until it assumes a shape (such as the one shown by the phantom line on the right hand side of fig. 3) which, seen in plant, corresponds to a larger quadrilateral than the quadrilateral corresponding to load C.
Such opening step of the adjustable widening frame can be performed immediately before the crosswise shift of carriage 14 or also simultaneously therewith, or also immediately after such shift, i.e. when carriage 14 is already above transporter T.
When carriage 14 has arrived at the position illustrated in figures 2 and 5, and load C has arrived below carriage 14, the wrapping step of load C begins, during which carriage 14 is made to shift downwards until it has reached the bottom of load C.
During the initial travel step, carriage 14 first of all brings the lower plane part PI of film P into contact and resting on the top of the load. Therefore, according to a fundamental feature of the present invention, as carriage 14 travels down, the walls of the bag which free themselves from the ruffling area 36, 42, change from a position on the outside of each edge of section bar 36 (or 42), above wheels 30, which now rotate in an opposite direction to F', hence above respective wheel 35 - or above sliding block 41 - to a position on the inside of adjustable widening frame 13, after having passed over telescopic rods 29 and wheel 35 (or sliding block 41), on the inner side thereof, until said walls adhere to load C. During said step, as can be understood, the film bag turns inside out as it adheres to load C.
Such way of proceeding has a first consequence: the turning inside out of the bag, passing over wheels 35, produces by itself a braking action of the release of the tubular film. In addition thereto, such release always occurs under the control of wheels 30 or 40, which may be braked - or better, positively driven in the direction of film release - and hence achieve perfectly even and controlled film sliding. Thanks to such braked control action of the sliding of film P it is then possible - according to another fundamental feature of the invention, and unlike the prior art - to perform an important stretching action also in a vertical direction of the tubular film forming the wrapping.
This way of proceeding, however, also has another important consequence: as is easily understood, the initial resting of the closed, welded end of the film bag onto load C, takes on an upturned position with respect of the prior art arrangements; in other words, while in the prior art the film folds resulting from the cut and welding of the top of the film bag arranged themselves on the outside of the wrapping and substantially free, in the process described here, in which the bag is virtually turned inside out, it is achieved - according to another important feature of the present invention - that the welding folds remain fixed on the inside of the bag, withheld by the tension of the vertical walls of the finished wrapping. It is obvious that the length of the film bag formed in the initial steps C) and D) must be determined keeping into account also the lengthening of the film due to such stretching.
From what precedes, the advantages resulting from the present invention are evident, the main ones of which can be summarised as follows:
- apparatus height remarkably lower than that of known apparatuses. The tubular film feeding, which occurs upwards in a space adjacent to transporter T of load C - rather than being above load C as in the prior art - combined with the fact that such film is fed to be ruffled on a adjustable widening frame, allows to maintain the height of the wrapping apparatus little above the maximum height provided for the load to be wrapped. As a matter of fact, that availability of extra space above the maximum height of the load to be treated is not necessary, which is instead essential, on the one hand for operations of opening of the film bag, of cutting and welding provided in the case of DE-39 08 957, and on the other hand for the handling of the carriage with rigid posts (20) provided in EP-1.106.507. Such reduced apparatus height is evidently an advantage both in terms of transport thereof, and of the arrangement of such apparatus in a warehouse;
- continuous control of the vertical downward sliding of the wrapping film and of the adhesion thereof to the load. This control is due, first of all, to the fact that sliding is controlled by the same wheels that perform collection and ruffling of the film bag, secondly by the fact that said film comes off the adjustable widening frame not directly, but due to the turning inside-out of the bag itself, and thirdly due to the fact that the film is guided, in such turning inside-out and simultaneous release onto the load, along the whole perimeter of the adjustable widening frame, by the presence of the rounded-profile telescopic rods 29. That allows to ensure that the walls of the wrapping do not have accidental folds due to late or stepwise release of the film, as in the case of the prior art;
- even vertical stretching of the tubular film. In the braked, controlled release of the wrapping bag, the film remains stretched, as well as in a crosswise direction, also in a vertical direction, which further results in a remarkably greater stability of the wrapping compared to prior art wrapping types;
- apparatus as a portable unit assembly. The apparatus according to the invention can be manufactured, in its structure comprising posts 1 and transfer carriage 14, as a unit assembly separated from the load transport system T, so that it becomes possible, thanks to this circumstance and to the moderate height of said structure, to manufacture said assembly as an entirely prefabricated unit and then displacing it to the mounting site. That avoids having to build, mount and test the apparatus in the workshop, then taking it apart, at least partly, to move it to the site of use and there reassemble it and retest it for operation, as occurs for prior art apparatuses.
However, it is understood that the invention must not be considered limited to the particular arrangement illustrated above, which represents only an example embodiment thereof, but that different embodiments are possible, all within the reach of an expert in the field, without departing from the scope of protection of the invention itself, as defined by the following claims.

Claims

Method for overwrapping pallet-stacked loads (C), in which a wrapping film (P) made of stretchable material, of a tubular shape, is dispensed from a feeding roll (B1, B2, B3), a section of said tubular film then being separated from said roll and closed by thermowelding (7) at one of the ends thereof in order to form a bag open at the opposite end, from which end said bag is ruffled on an adjustable widening frame (13), which frame is finally opened wide, causing a transversal elastic stretching of the tubular film, and is finally moved downwards along the load (C) to release said film bag onto the load itself, characterised in that
- said tubular film section is fed upwards, thermowelded at the lower end (7) thereof to form a bag of a preset size, with an upward opening, separated from the feeding roll and fixed at said upper end open onto said adjustable widening frame (13), and said bag is collected and ruffled (TR) onto said adjustable widening frame with an upward movement,

- said frame (13) is opened wide, subjecting said ruffled bag to stretching in a horizontal direction,
said tubular film is turned inside-out and braked during the step of release and adhesion to the load, with a downward movement, subjecting it to stretching in a vertical direction, while it is made to move and guided along the whole of the contour of the adjustable widening frame.
Method for overwrapping pallet-stacked loads (C) as claimed in claim 1, characterised in that the step of preparing the ruffled bag,
consisting in the operations of feeding the film (P) with an upward movement, of separating the film from the feeding roll thereof, of thermowelding the lower edge thereof and of collecting and ruffling said bag onto said adjustable widening frame (13),
is performed in an operating area (1, 2, 3) adjacent to the area (T) wherein the pallets to be wrapped are handled.
Method for overwrapping pallet-stacked loads (C) as claimed in claims 1 or 2, characterised in that it comprises a step of displacing the adjustable widening frame (13), with a movement of horizontal shifting from the position in which said step of preparing the ruffled bag takes place to a position above the pallet (C) to be overwrapped, and in that the opening wide of said adjustable widening frame (13) to elastically stretch the ruffled bag in a horizontal direction, takes place during said displacement step.
Method for overwrapping pallet-stacked loads (C) as claimed in claims 1 or 3, characterised in that the tubular film (P) is braked while it is being released over the load, in order to cause a vertical stretching thereof also.
Method for overwrapping pallet-stacked loads (C) as claimed in claim 1, characterised in that the preparation step of the ruffled bag,
consisting in the operations of feeding the film (P) upwards, of separating the film from the feeding roll (B1, B2, B3) thereof, of thermowelding the lower edge thereof and of collecting and ruffling of the bag onto said adjustable widening frame,
is preceded by a step of determining the initial shape and size of said adjustable widening frame (13).
Method for overwrapping pallet-stacked loads (C) as claimed in claim 5, characterised in that said step of determining the shape of the adjustable widening frame is obtained elongating or shortening a pair of opposite frame sides (29), independently from the elongation or shortening of the other pair of opposite sides (29) of said frame.
Method for overwrapping pallet-stacked loads as claimed in claims 5 or 6, characterised in that the ratio between the length of a pair of opposite frame sides (29) and the length of the other pair of opposite sides (29) established in said step of determining the shape of the adjustable widening frame (13), is maintained unchanged during the step of the opening wide of the frame.
Method for overwrapping pallet-stacked loads as claimed in claim 1, characterised in that the preparation step of the ruffled bag,
consisting in the operations of feeding the film with an upward movement, of separating said film from the feeding roll thereof, of thermowelding the lower end thereof and of collecting and ruffling said bag onto said adjustable widening frame,
is preceded by a step of selecting the size of the tubular film (P1, P2 or P3) meant to form the wrapping bag.
Method for overwrapping pallet-stacked loads as claimed in claim 1, or in any one of claims 1, 5 and 8, characterised in that the thermowelding line of the lower edge of the wrapping bag is subjected to cooling before being subjected to stretching.
Apparatus for overwrapping a pallet-stacked load,
comprising a rigid main support structure (1, 2, 3), means (S1; B1, B2, B3) to feed a wrapping film (P1, P2, P3) of tubular stretchable material, means (7, 7b) for cutting a section of said tubular film, and means (7, 7a) for thermowelding a first edge thereof to shape said film section as a bag, means (11, 12) for opening said bag-shaped film (P) along the other edge thereof and to ruffle it on an adjustable widening frame (13) means (17, 18, 21, 22; 23, 24, 25, 26, 27, 28) for opening wide said frame and for transversally stretching said bag-shaped film, as well as means (15, 15a, 15b) for sliding said adjustable widening frame (13) along the load (C) positioned in a wrapping station (T) progressively releasing the bag-shaped film (P) onto the load (C) itself, characterised in that
- said adjustable widening frame is formed by four film collection and ruffling assemblies (23, 24, 25, 26), located at the frame corners, and by four telescopic rods (29) which connect said collection assemblies (23 to 26) and represent the frame sides,

- feeding rolls (B1, B2, B3) are provided in a selection station S1, which rolls are capable of dragging upwards said bag-shaped film, of opening the upper edge thereof and of fitting it onto said adjustable widening frame (13), outside of said collection assemblies (23 to 26) and of said telescopic rods (29).

- each of said four collection assemblies (23 to 26) comprise means (30, 32, 37; 40, 41, 43) for causing the ruffling of said film (P) with an upward movement, during the film loading step onto the frame (13), and means (30, 32, 37; 40, 41, 43) for guiding said film and/or for braking it during the release step onto the load (C), in the course of said downward sliding of the adjustable widening frame (13) along the load,

- said telescopic rods (29) being capable of cooperating with said guiding means (30, 32, 37; 40, 41, 43) of the collection assemblies, to guide the film (P) to turn inside-out during the release step onto the load (C).
Apparatus for overwrapping as claimed in claim 10, characterised in that said four film collection and ruffling assemblies (23, 24, 25, 26) are mounted mutually mobile on a horizontal plane, both in a transversal direction (X-X) and in a longitudinal direction (Y-Y), on a transfer carriage (14) having a rigid box structure.
Apparatus for overwrapping as claimed in claim 11, characterised in that said four film collection and ruffling assemblies (23, 24, 25, 26) are mounted each on respective guiding and sliding means (17, 18, 19, 20, 23a, 24a, 25a,26a)
Apparatus for overwrapping as claimed in claim 12, characterised in that said guiding and sliding means comprise two pairs of first saddles (17,17; 18, 18), slidable along two opposite sides of said transfer carriage (14) having a box-like structure, and two parallel support crossmembers (19, 20), each of which is mounted with the ends thereof integral with a pair of said first saddles, and in that said pairs of saddles and crossmembers (17,17,19; 18,18,20) are mutually movable in a specularly symmetrical way with respect of a first middle axis (Y1-Y1) of said carriage (14) having a box-like structure.
Apparatus for overwrapping as claimed in claim 12 or 13, characterised in that said guiding and sliding means further comprise two pairs of second saddles (23a,26a; 24a,25a), the saddles of each pair being mutually movable in a specularly symmetrical way with respect of a second middle axis (X-X) of said box-like structure (14) said second axis being perpendicular to the first one.
Apparatus for overwrapping as claimed in claims 13 and 14, characterised in that each of said second saddles (23a, 24a, 25a, 26a) carries one of said four film-collecting assemblies (23, 24, 25, 26), said saddles being mounted in pairs each onto a respective one of said crossmembers (19;20), slidable in opposite directions.
Apparatus for overwrapping as claimed in claims 13, 14 or 15, characterised in that said pairs of saddles (23a, 24a, 25a, 26a) and/or crossmembers (17,19; 18,20) are slidable under the control of a single motor (21), operating through driving means working in opposite directions.
Apparatus for overwrapping as claimed in claims 13, 14 or 15, characterised in that said pairs of saddles (23a, 24a, 25a, 26a) are slidable under the control of two respective motors (27, 28), operating through driving means working in opposite directions.
Apparatus for overwrapping as claimed in claims 16 or 17, characterised in that said driving means working in opposite directions consist of chains (22) each running along a circular path, every two saddles (17,18; 23a-24a; 25a-26a) movable in opposite directions being connected to a chain branch and to the opposite branch of the same chain, respectively.
Apparatus for overwrapping as claimed in claim 10, characterised in that each of said four film-collecting and film-ruffling assemblies (23, 24, 25, 26) forms an angular element of said adjustable widening frame (13) and comprises, as a film-guiding and/or film-braking means, at least one transport wheel (32, 40) arranged on the outside and substantially according to the bisectrix of the angular element, and the surface of which rests on an opposite ruffling guide (30,36; 41,42) at a film-gripping point and at a film-dragging point (TR) of the film (P).
Apparatus for overwrapping as claimed in claim 19, characterised in that said transport wheel (40) is motor-driven and said ruffling guide consists of an assembly of a guide section bar (42) and of a sliding block (41) associated with the bottom of said section bar (42)
Apparatus for overwrapping as claimed in claim 19,
characterised in that said transport wheel(32) is idle and said ruffle guide is formed by the assembly of a guide section bar(36) and of a pair of motor-driven wheels (30),arranged at 90° and mutually positioned so that their contour substantially establishes mutual contact at said gripping point (TR) of the film P.
Apparatus for overwrapping as claimed in claim 10, characterised in that said telescopic rods (29) are tubular, with a circular section.
Apparatus for overwrapping as claimed in claim 10,
characterised in that
- said main support structure (1, 2, 3) forms a unitary assembly adjacent to the means (T) for transporting the load (C) and

- said adjustable widening frame (13), with its respective means (23, 24, 25, 26) for collecting and ruffling the film (P) on the frame (13) itself, is mounted movable between a position inside the main support structure, intended for the preparation of the ruffled film bag, and a position outside said main support structure and above the load (C) to be wrapped,

- said adjustable widening frame further being vertically movable in order to apply said film bag (P) onto the load (C).
Apparatus as claimed in claims 10 or 23, characterised in that said adjustable widening frame (13) is mounted on a transfer carriage (14), of a rigid box-like structure, movable along a horizontal plane between said position intended for the preparation of the ruffled film bag and said position above the load (C).
Apparatus as claimed in claim 10, characterised in that said means (7, 7a, 7b) for cutting and thermowelding are mounted on a fixed support, located at the bottom of said main support structure (1, 2, 3), and they comprise a pair of saddles, movable the one towards the other and each carrying a cutting blade (7b) and a welding presser (7a), extending along the whole width of the tubular film (P).
Overwrapping apparatus as claimed in claim 25,
characterised in that each welding presser (7a) is associated with a cooling presser (7e) equally extending along the whole width of the tubular film (P).
Overwrapping apparatus as claimed in claim 26,
characterised in that said cooling presser (7e) consists of a tubular bar, within which air or cooling liquid flows.
Overwrapping apparatus as claimed in claim 25,
characterised in that each of said saddles is operated by a respective pneumatic jack (7c).
Overwrapping apparatus as claimed in claim 10,
characterised in that said means for feeding upwards said tubular film comprise a beam carriage (8), gliding along two posts (1a, 1b) of said main support structure (1, 2, 3) driven by respective motor means (8a).
Overwrapping apparatus as claimed in claim 29,
characterised in that said beam carriage (8) has an axis parallel to the longitudinal middle axis Y-Y of the main support structure (1, 2, 3).
Overwrapping apparatus as claimed in claims 29 or 30, characterised in that two supporting arms (9a, 9b) of the means (11, 12) for gripping the tubular film (P) are associated with said beam carriage (8), said arms (9a, 9b) being mounted cantilevered on two respective saddles, movable one towards the other onto said beam carriage (8), in a specularly symmetrical way with respect of a transversal middle axis X-X of the apparatus.
Overwrapping apparatus as claimed in claim 31,
characterised in that said film-gripping means consist of two pairs of grippers (11, 12), the grippers of each pair being mounted movable on a respective supporting arm (9a, 9b), said grippers moving closer to or further apart from each other in a specularly symmetrical manner with respect of said longitudinal middle axis Y-Y of the main support structure.
Overwrapping apparatus as claimed in claim 10,
characterised in that it comprises a tubular-film selection and feeding station (S1), located at the bottom of said main support structure (1, 2, 3).