EP0395919A1

EP0395919A1 - Automatic wrapping machine for packaging products, particularly palletized units, to be wrapped with a thermoretractible tubular film

Info

Publication number: EP0395919A1
Application number: EP90106872A
Authority: EP
Inventors: Franco Tacchini
Original assignee: Officina Meccanica Sestese SpA
Current assignee: Officina Meccanica Sestese SpA
Priority date: 1989-05-02
Filing date: 1990-04-10
Publication date: 1990-11-07
Anticipated expiration: 2010-04-10
Also published as: DE69002529D1; ATE92419T1; ES2045618T3; IT8920343A0; IT1229317B; EP0395919B1; DE69002529T2

Abstract

An automatic wrapping machine for packaging products, materials and palletized units, to be wrapped with a thermoretractible tubular film, comprises a casing (1), at the centre of which the material to be packaged is positioned in order to receive a wrapping of thermoretractible tubular film formed as a bag with bottom at the top, and is equipped with heating means to carry out the thermoretraction of said film after the material has been wrapped therewith.

According to the invention, said machine is provided with a plurality of movable gripper members (6), by means of which said film wrapping is picked up in the form of a bag at the side of said casing, is lifted, is opened and is transferred into said casing above the material to be packaged, as a prismatic bag, being then lowered so as to wrap said material. Said gripper members consist of pairs of grippers which grip the folded tubular film on four edges.

The machine also provides for the reel (B) feeding the thermoretractible tubular film to be rotatably supported between two end cones (10) suspended by means of flexible elements (9) to the machine casing. Furthermore, said heating means to carry out the thermoretraction of the film consist of a ring furnace (8).

Description

The present invention concerns important improvements in automatic machines for wrapping products, groups of products or materials of various types, particularly palletized units - for packaging purposes - with a thermoretractible film already in tubular form.
There are already known to be in technique automatic wrapping machines, wherein the material to be wrapped is positioned at the centre of the base of a high casing, at the top of which the tube of thermoretractible film, unrolled from a reel positioned externally to the machine, is opened and/or guided ready open so as to envelop the material itself, the packaging being then completed by retraction of the film into a ring furnace provided in said machines.
The performances of these machines are quite satisfactory, but they all have the serious inconvenience of being oversized in height. This prevents transport thereof in fully assembled conditions, thereby considerably increasing the installation costs, and also creates at times problems of bulk for the user.
To overcome these drawbacks, automatic wrapping machines of considerably lower size have been conceived, wherein the opening of the tube of thermoretractibe film, only just started on a ring positioned to the side of the material to be wrapped, is completed when overturning said ring onto the material itself, by the air which - due to overturning at high speed - swells the moving part of said tube, which is finally guided - as in the previous case - up to complete packaging, before the thermoretraction is carried out. This solution, theoretically brilliant, does not always guarantee in practice satisfactory results, particularly due to the difficulties in centering the tube of thermoretractibe film over the material to be wrapped (whereby there is a tendency to use tubular films wider than required); furthermore, machines of this type are complicated and delicate as far as structure and working, and the setting up thereof involves considerable costs.
All the drawbacks of the abovementioned known technique are overcome with the wrapping machine according to the invention which is, on one hand, of height limited to an extent such as to allow transport thereof in fully assembled conditions and, on the other hand, of simple and reliable construction and working.
The present invention supplies in fact an automatic wrapping machine for packaging products and materials, particularly palletized units, to be wrapped with a thermoretractible tubular film, of the type comprising a casing, at the centre of which the material to be packaged is positioned in order to receive a wrapping of thermoretractible tubular film formed as a bag with bottom at the top, and which is possibly provided with heating means to carry out the thermoretraction of said film after the material has been wrapped therewith, characterized in that it comprises a plurality of movable gripper members, by means of which said bag wrapping is picked up at the side of said casing, is lifted, is opened and is transferred into said casing above the material to be packaged - as a prismatic bag - and is then lowered so as to wrap said material, said gripper members consisting of pairs of grippers which grip the folded tubular film on four edges.
Said machine preferably comprises, at the side of said casing housing the working section, a section feeding the thermoretractible tubular film.
According to a preferred embodiment of the machine according to the invention, the working section comprises a casing formed of four uprights and of two cross members projecting from the casing towards the feeding section, gripper members movable along said cross members, and bars to weld and cut the thermoretractible tubular film, acting between said gripper members and the machine feeding section, while the feeding section comprises a reel of thermoretractible tubular film wound onto a shaft rotatably supported between two end cones suspended by means of flexible elements to the ends of the portion of said cross members pro jecting from said casing, a roll to support said reel, and idle guide rollers.
Going into further detail, said movable gripper members comprise, in said working section, a carriage with two elements movable horizontally along said cross members with different laws, and each carrying a pair of vertically moving bars equipped with a pair of grippers, said pairs of bars drawing close when the carriage moves towards the feeding section, and drawing apart when the carriage moves towards the casing.
The accompanying drawings show a preferred embodiment of the wrapping machine according to the invention, which is now described in further detail. In said drawings:

Figs. 1 to 7 are diagrammatic perspective views of the machine assembly according to the invention, schematically illustrating the different working steps thereof;
Figs. 8 and 9 show some main components of the movable gripper members of the machine according to the invention, fig. 8 illustrating the vertical movements and fig. 9 the horizontal movements of said members;
Figs. 10, 11, and 12, 13, are respectively side views and top plan views of the grippers carried by the movable gripper members, in two different working steps;
Fig. 14 is a sectional view of one of the welding and cutting bars of the machine according to the invention;
Figs. 15 and 16 diagrammatically illustrate the control means for said welding and cutting bars, in two different working steps; and
Figs. 17, 18 and 19 are, respectively, a side, a front and a top plan view of the improved feeding section of the machine according to the invention.

With reference to the drawings, the wrapping machine according to the invention comprises (fig. 1) a working section L and a section A feeding the tubular film PT.
The working section L comprises a stout metal casing 1 with four uprights 2, at the centre of which the palletized unit UP (fig. 4) - or other material or product, or group of products - to be wrapped with the thermoretractible tubular film PT is positioned for packaging purposes. The four uprights 2 of the casing 1 are connected in twos by means of upper cross members 3, parallel one to the other and strongly projecting from the casing 1 towards the section A feeding the thermoretractible film PT. Along each of the cross members 3 of the casing 1 there is slidably mounted a carriage 4 carrying pairs of vertical bars 5, movable both horizontally - so that their position and reciprocal distance along said cross members depends on the position of the carriage 4 - and vertically, said bars being equipped with pairs of grippers 6, one pair at the lower end and the other higher up, designed to grip the section of tubular film PT with which the material being packaged has to be wrapped.
The working section L of the machine according to the invention is completed with a pair of bars 7, for cutting and welding the film, and with a ring furnace 8.
The feeding section A comprises means for simply suspending a reel B of thermoretractible tubular film PT, consisting of two flexible elements as chains 9 (or possibly ropes or cables) hanging from the free end of each cross member 3 of the casing 1, and of two supporting cones 10 into which are rotatably mounted the ends of the shaft 11 (fig. 18) of the reel B on which the film PT is wound up. The feeding section A also comprises an element, consisting for example of an idle roll 12, to support and guide the reel B, and three idle guide rollers to deviate the unreeled film, of which a movable roller 13 and two fixed and coupled rollers 14, parallel and close to the base of the machine.
Going into further details for what concerns the working section L, the movements of the carriage 4 along the cross members 3 are directed (fig. 8) by guides 15 and controlled by a fluid pressure cylinder 16. The carriage 4 consists of two elements 17 and 18, each carrying one of the two pairs of vertical bars 5 of said carriage. The element 18 carries an idle sprocket 19 engaging with a toothing 20 fixed to the casing 1 and with a toothing 21 projecting from the element 17. The piston rod 16A of the cylinder 16 is connected to the element 18 of the carriage 4. In this way, the movements of the elements 17 and 18 of the carriage 4, controlled by the cylinder 16, take place with different laws and, in practice, the pairs of vertical bars 5, carried by said elements, draw close when the carriage travels towards the centre of the casing 1, and move apart when the carriage travels towards the feeding section A.
The movements of the vertical bars 5 in the vertical direction are in turn directed (fig. 9) by pairs of rollers 22, 23, and controlled by bidirectional electric motors 24, 25, through toothed belts 26, 27, which wind onto driving sprockets 28 and guide rollers 28A, 28B, and which are fixed to the upper ends of said bars 5, said motors and rollers being carried by the elements 17 and 18 of the carriage 4.
The grippers 6 are mounted at the lower ends of the vertical bars 5, and about half way along their length, so as to grip the section of tubular film PT allowing to wrap the palletized unit UP (or other material to be packaged). One of said grippers is shown in detail in figs. 10 to 13. It comprises a pair of jaws 29 reciprocally pivoted, about a vertical axis 30, onto a lever 31 which is in turn pivoted on the bar 5 about a horizontal axis 32. The jaws 29 of the gripper are kept open by a pair of springs 33, while their closing is controlled by a lever 34, fulcrumed horizontally in 35 on the bar 5 and operated by the piston of a fluid pressure cylinder 36, and by a connecting rod 37 which connects the lever 34 to the lever 31. Furthermore, an element 38 is provided to stop the movement of the lever 34.
The cutting and welding bars 7 form part of a more complex device shown in detail in figs. 14 to 16. These bars comprise (fig. 14) a pair of longitudinal clamping shoes 39, pressed one towards the other by springs 40 and, fixed to said shoes, two resistor heating elements 41 and a cutting blade 42. The bars 7 are each carried (figs. 15 and 16) by two saddles 43, 44, movable along the cross members 3 under the control of leverages operated by a fluid pressure cylinder 45 and comprising two sets of three levers 46, 47, 48, of which, the end levers 46 are controlled by the cylinder 45, the end levers 48 control the saddles 43, 44, while the intermediate levers 47 are pivoted to an end of the casing 1.
The ring furnace 8 is of a substantially conventional type, being formed as a large square metal frame, moving vertically inside the casing 1 and housing heating means, preferably in the form of gas flames to direct the heat towards the inside of said frame, and thus towards the palletized unit UP or other material to be packaged, designed to be fully and closely enveloped by said frame.
The working of the wrapping machine described heretofore and shown on the accompanying drawings shall now be briefly illustrated.
Considering first of all the feeding section of the machine, it should be noted that it is most important for the thermoretractible tubular film PT to be unreeled with the least lateral deviation, so as to make sure that the film is wrapped around the product being packaged without exceeding in size, as far as possible, the perimeter of said product.
The solutions adopted so far, in order to obtain these conditions, are conceived with devices to shift axially the reel shaft, centering manually the film each time a new reel is mounted. It is however possible that, in a same reel, the film may not be wound perfectly straight, there being lateral deviations between the turns. Whereas, the solution adopted in the machine according to the invention makes it easier to center the reel B each time a new reel is mounted, but above all it allows to keep the reeled film centred while being unrolled. In fact, the mounting of the reel by suspension with flexible elements allows to easily and promptly move said reel in the axial sense, as may be required by the unevenness of its winding up, while the lateral shoulders of the reel keep the tubular film guided in the wanted position.
The tubular film PT, emerging - flattened and with inwardly folded sides - from the idle roll 12 supporting the reel B, winds onto the vertically moving roller 13 and onto the two fixed bottom rollers 14.
To feed the film PT to the working section L of the machine, the roller 13 of the feeding section A moves first upward, unrolling said film from the reel B of which it causes the rotation (while, downstream, the film is kept stationary as seen hereinafter), and then downward when the film PT, drawn by the machine, starts moving. The feeding to the working section L of the machine thus takes place without the reel B being dragged into rotation with negative stresses due to inertia.
At the start of the working cycle, the film is positioned as shown in fig. 1, still substantially flattened and closed at its free end, at the top of the machine, by the transversal welding performed in the previous cycle, while strikers (not shown) act on its lateral folds, below said free end, to hold it in position. The roller 13 is in top position.
The cycle starts with the downward movement of the four bars 5 (fig. 1), while the carriages 4 are positioned in correspondence of the portion of the cross members 3 projecting from the casing 1 and said bars 5 are drawn close.
With the bars 5 in this position, the grippers 6 (fig. 1) - with open jaws and spaced from the folded tubular film PT (as shown in figs. 10 and 11) - are operated so as to grip the edges of said film in correspondence of eight points, two for each bar 5. This is obtained (figs. 10 to 13) by downstroke of the piston of the cylinder 36, and by anticlockwise rotation of the lever 34 and - thanks to the connecting rod 37 - of the lever 31; the grippers 6 - with the jaws kept open by the springs 33 - move from the position (figs. 10 and 11) far from the film, to the position (figs. 12 and 13) close to the edges of the film, and in this position the lever 31 stops against the element 38. The lever 34 continues to rotate, controlled by the further downstroke of the piston 36, and thus overcomes the resistance of the springs 33, causing the closing of the jaws 29 of the grippers 6, which hence grip in correspondence of eight points (fig. 1) the edges of the thermoretractible tubular film PT, thereby opening it slightly.
The bars 5 are then caused to move upward by operating the electric motors 26 (fig. 9) while the carriages 4 are still stationary. The film (fig. 2) moves to the top, while being kept still folded but slightly open at the edges. At the same time, the roller 13 of the feeding section L moves downward to shift forward the film without causing the rotation of the reel B, which remains still.
The cutting and welding device now starts to operate: the cylinder 45 causes, through the already described leverage, the mutual approach of the cutting and welding bars 7, until (fig. 3) the shoes 39 clamp the folded tubular film, the heating elements 41 provide for the welding thereof, and the blade 42 provides to cut said film above the welding point. In this way, the section of tubular film PT, already gripped by the grippers 6, takes up the configuration of a bag - open at the bottom and closed at the top - positioned in the upper part of the machine and apt to wrap the material to be packaged, but still folded (fig. 3). At the same time, the end of the tubular film coming from the feeding section A is clamped and closed at the top.
The aforementioned bag must now be carried over the material to be packaged: this is obtained through a horizontal movement of the carriage 4 caused by operating the fluid pressure cylinders 16 (fig. 8). The elements 17 and 18 of the carriage 4, carrying the bars 5, are moved - as seen - with different laws, so that the two front bars 5 move away from the rear ones causing the opening of the bag formed by the film PT, the opening being completed when said bag is positioned - taking up a prismatic square shape SP - at the centre of the casing 1, above the material UP to be wrapped (fig. 4).
During this step, the roller 13 of the feeding section is slowly moved upward from the previously reached lowered position. Since the free end of the folded tubular film is still clamped - and thus prevented from moving - by the shoes 39 of the welding and cutting bars, the upward movement of the roller 13 allows to unroll new film from the reel B - slowly caused to rotate - so as to form the bag for the successive cycle.
At this point, the bars 5 are moved downward (fig. 5) by operating the motors 26 in a reversed sense from the previous one (fig. 9); the palletized unit UP is then wrapped with the bag SP formed by the thermoretractible tubular film PT. At the same time, the ring furnace 8 moves down, while the welding and cutting bars 7 (fig. 5) draw apart.
The jaws 29 of the grippers 6 are now opened and the bars 5 are again moved upward (fig. 6), thereby releasing the palletized unit UP finally wrapped with the thermoretractible tubular film formed as a prismatic bag. The ring furnace 8 is turned on, while being in its lowest position, and is then slowly moved upward (fig. 7) at a speed allowing to obtain the desired degree of retraction of the film wrapping the unit UP.
The machine ends its working cycle with the return of the carriage 4, and thus of the bars 5, into the initial position in which said bars are drawn close, next to the feeding section A of the machine (fig. 1).
The heretofore described and illustrated machine - as well as for the reduced height of its structure, allowing it to be transported in fully assembled conditions - clearly differs from those of prior art in various respects, both as far as construction and as far as operation: to start with, for the first time one is able to draw - next to the material to be packaged - from a reel of tubular film (welded at the top in the previous working cycle), the desired amount of film to form the bag with which said material has to be wrapped, and to positively open said bag by means of grippers so as to give it a prismatic shape. It should be noted that, while in the solutions of known technique the positioning of the bag on the material to be wrapped involves the risk that the tubular film (which takes up a substantially circular shape due to the air being blown inside the bag) may interfere with the edges - at times sharp - of the product being wrapped, and thus break, the solution adopted in the machine according to the invention prevents this risk because, thanks to the grippers, the top part of the bag takes up a prismatic shape of rectangular or square section SP, and is kept in that shape.
It is understood that there may be other embodiments of the invention, differing from that described and illustrated, but still falling within the scope of the invention itself.
For example, the movement of the two elements 17 and 18 of the carriage 4 could be obtained (instead of using the aforedescribed and illustrated toothing and sprocket system) by means of two fluid pressure cylinders, suitably offset in operation, while the cutting system of the bars 7 could have a different configuration.
Furthermore, in the case of a limited inertia in unwinding the reel B, the feeding section A of the machine could be simplified by eliminating the movable guide roller 13.

Claims

1) Automatic wrapping machine for packaging products and materials, particularly palletized units, to be wrapped with a thermoretractible tubular film, of the type comprising a casing, at the centre of which the material to be packaged is positioned in order to receive a wrapping of thermoretractible tubular film formed as a bag with bottom at the top, and which is possibly provided with heating means to carry out the thermoretraction of said film after the material has been wrapped therewith, characterized in that it comprises a plurality of movable gripper members, by means of which said bag wrapping is picked up at the side of said casing, is lifted, is opened and is transferred into said casing above the material to be packaged - as a prismatic bag - and is then lowered so as to wrap said material, said gripper members consisting of pairs of grippers which grip the folded tubular film on four edges.

2) Machine as in claim 1) comprising, at the side of said casing housing the working section of the machine, a section feeding the thermoretractible tubular film.

3) Machine as in claim 1), wherein said working section comprises: a casing formed of four uprights and of two cross members projecting from the casing towards the feeding section; gripper members movable along said cross members; and bars to weld and cut the thermoretractible tubular film, acting between said gripper members and the machine feeding section.

4) Machine as in claim 3), wherein said movable gripper members comprise, in said working section, a carriage with two elements movable horizontally along said cross members with different laws and each carrying a pair of vertically moving bars equipped with a pair of grippers, said pairs of bars drawing close when the carriage moves towards the feeding section and drawing apart when the carriage moves towards the casing.

5) Machine as in claim 4), wherein the horizontal movements of said carriage are controlled by at least one fluid pressure cylinder, the piston rod of which acts directly onto one of the two elements of the carriage.

6) Machine as in claim 4), wherein the vertical movements of said bars are controlled by bidirectional electric motors through driving sprockets, toothed belts and guide rollers.

7) Machine as in claim 4), wherein the grippers carried by said bars comprise a pair of jaws, kept open by springs and normally spaced from the film to be gripped, and leverages controlled by a fluid pressure cylinder so as to draw said jaws close to said film and tighten them onto its edges.

8) Machine as in claim 3), wherein the welding and cutting bars comprise clamping shoes, heating elements and a cutting blade, all carried by saddles normally spaced one from the other and drawn close by operating a fluid pressure cylinder through leverages.

9) Machine as in claim 2), wherein said feeding section comprises a reel of thermoretractible tubular film, wound onto a shaft rotatably supported between two end cones suspended by means of flexible elements to the ends of the portion of said cross members projecting from said casing, a roll to support said reel, and idle guide rollers.

10) Machine as in claim 9), wherein said cones are suspended by means of flexible elements to the free end of cross members of the casing of the wrapping machine, projecting from the casing itself.

11) Machine as in claim 9), wherein said flexible elements are chains.

12) Machine as in claim 9), wherein said flexible elements are ropes or cables.

13) Machine as in claim 9), wherein said element supporting the reeled film is an idle roll.

14) Machine as in claim 9), wherein at least one of said idle guide rollers is apt to perform a vertical rectilinear reciprocating motion.

15) Machine as in claim 1), wherein the heating means to car ry out the thermoretraction of the film, with which the material to be packaged has been wrapped, consist of a ring furnace.