EP0569615A1

EP0569615A1 - Process and machine for wrapping articles in a stretchable film

Info

Publication number: EP0569615A1
Application number: EP92108294A
Authority: EP
Inventors: Carlo Nicoletti
Original assignee: AWAX Progettazione e Ricerca SRL
Current assignee: AWAX Progettazione e Ricerca SRL
Priority date: 1992-05-15
Filing date: 1992-05-15
Publication date: 1993-11-18

Abstract

A process and machine for wrapping articles (P)with a stretchable film (14), in which the article (P) is lifted against a length of pre-stretched film whose flaps are successively spread out under tension onto the undersurface of said article. Prior to the lifting of the article (P), the film (14) is firstly submitted to a first pre-stretching in a first direction, within the maximum value permitted by the film, and thereafter the film is submitted to a second pre-stretching in a second direction transverse to said first direction, while simultaneously said first pre-stretching is suitably and uniformly attenuated to allow the maximum stretchability of said film in said second direction. When the article is lifted and pushed against the length of pre-stretched film, said first pre-stretching and said second pre-stretching are suitably and uniformly attenuated, whereby said film is not submitted to anomalous tensions in contacting the article and whereby said article is engaged delicately, while ensuring the formation of a wrapping which engages said article intimately.

Description

In the field of packaging, and particularly in the field of packaging of foodstuffs, it is known how to provide a lightweight package consisting of a tray made of cardboard, foamed polystyrene, or other suitable material, which displays the article and which is wrapped together with it in a stretchable and transparent film made of suitable plastics material, commonly known as "stretch film".
Processes and machines are known which carry out said packaging automatically, with no previous pre-stretching of the stretchable film, as illustrated for example in document US-A-3 662 513.
Processes and machines are also known which submit the stretchable film to a pre-stretching before pushing the articles thereagainst, so as to take advantage to a maximum degree of the stretchability of the film being used. These procedures permit to wrap articles of different sizes within a wide range, without changing the width of the film being used, and they also permit to attenuate the differential tensions of the film in contact with the product, thus ensuring a better resistance of said film and a more delicate treatment of the packaged article. A machine operating according to this principle is described, for example, in document US-A-3 967 433.
The object of this invention is to improve these types of processes and machines, and to obtain the following advantages:

the maximum economy in the use of the wrapping film, by automatically feeding into the cycle a portion of film having the length required depending upon the size of the article to be wrapped, and then by submitting said portion of film to a proportionate pre-stretching, both in the longitudinal and transverse directions, to the maximum possible extent, without creating anomalous tensions in said film;
causing the pre-stretching to be attenuated automatically and uniformly in the article-wrapping step, as a function of the size of said article , in order to avoid anomalous tensions in the film and to permit delicate articles to be wrapped without damaging them.

The above and other advantages are achieved by the following process:
The film is unreeled from the feeding means and is spread out horizontally above a lifting device which carries the article to be wrapped, with a length dimension which is proportionate to the size of the article to be wrapped, and as a function of said length said film is stretched to a maximum extent in the longitudinal direction. The longitudinally pre-stretched length of film is then pre-stretched to a maximum extent in the transverse direction, as a function of its original dimensions, and during this step the longitudinal pre-stretching is suitably attenuated, to permit the required transverse pre-stretching of the film, without creating anomalous tensions in the latter.
Thereafter, during the article-wrapping step, both the longitudinal and transverse pre-stretching are attenuated proportionally to the dimensions of said article, or as a function of the original dimensions of the film, to ensure the creation of a firm wrapping exempt from anomalous tensions and which does not submit the article to any harmfull stress.
The movements of the means controlling the edges of the wrapping film, during the pre-stretching steps and during the article-wrapping step, are originated from electrical motors controlled by a computer which is programmed by means of manual inputs relating to the length of the film being used and the characteristics of the article to be wrapped (normal, soft, very delicate, etc.), and by means of opto-electronic sensors which automatically detect the dimensions of the article to be wrapped while the latter is transferred onto the lifting device.
A similar logic system is used for the folding devices and for the article-ejecting pusher in the last step of the wrapping cycle.
The characteristics of the invention and the advantages resulting therefrom will become apparent from the following description of a preferred embodiment thereof, shown by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a diagrammatic front elevational view of some of the main components of the machine in the rest position;
Figures 2-3-4-5-6-7-8 are perspective views of the main operative components of the machine, during as many stages of the article-wrapping cycle;
Figures 9-10-11-12-13-14-15-16 show, partly in front view and partly in side view, the main components of the machine during the article-wrapping stages, beginning from the lifting of the article against the pre-stretched film and ending when the wrapped article is discharged;
Figures 17-17a and 17b are side elevational and partly sectional views of the film dispenser and unreeling clamp in the spaced apart position and in the film-clamping close up position;
Figure 18 is a plan view of the electronic-controlled driving system which actuates the film pre-stretching means, the folders and the ejector;
Figure 19 shows the details of the driving pulley of the driving system of Figure 18, taken on the section line XIX-XIX;
Figure 20 is a fragmentary top plan view of the machine;
Figures 21 and 22 show further details of the machine, taken on the sectional lines XXI-XXI and XXII-XXII, respectively, of Figures 20 and 21;
Figure 23 is an elevational view of the articulated-parallelogram mechanism which controls the opening and closing of the side rear clamp;
Figure 24 is a side elevational and partly sectional view of the lifter for the article to be wrapped;
Figure 25 is a flow-chart of the machine according to the invention.

In the Figures, numerals 1 and 2 indicate the consecutive flights of the belt-conveyors which feed and arrange centrally on the lifter 3 the articles P to be wrapped, which are introduced in single file and resting substantially on the right-hand side of the conveyor 1 (see below). Upon passing from the conveyor 1 to the conveyor 2, the articles P are scanned by two banks 4 and 5 of optoelectronic sensors, one of said banks being arranged horizontally, transversely to the path of travel of the articles, and the other being arranged vertically, laterally of said path of travel, and which, in combination with an electronic computer 6, detect the three dimensions of the article, namely the width, the height and the length (s), the latter being deduced (the constant value of the advancement speed v of an article carried the conveyor 1 being known) from the equation $s= v.t$
, wherein t is the time of shadowing of at least one of the sensors of any one of the banks 4-5.
The lifter 3 comprises a plurality of vertical and parallel frames 9 provided at the top with crowned, overturnable supports 10, normally in a vertical position, with which said lifter is placed initially below the imaginary plane containing the upper flight of the conveyor 2, so as to avoid interfering with the oncoming article P. When the article has been centrally positioned on the lifter, the latter is raised to introduce said article into the wrapping station of the machine.
The stretchable film is unreeled from a roll 11 which is supported so as to be rotatable about its axis by a pair of parallel rollers 12, one of which is actuated by a geared motor 13 which causes the rotation of said roll in the film-unreeling direction. The film 14 unreeled from the roll is guided on at least one pair of parallel idle rollers 15 and, for example, on a buffer roller 16 which, in combination with the sensor 17, constitute a device which cyclically activates the geared motor 13 whereby the film will be fed to the wrapping station with no remarkable tensioning.
The film 14 is gripped at its end by a dispensing clamp or dispenser 18 (see also Figure 17) which is parallel to the axis of the roll 11 and comprises a pair of parallel rollers 19 and 20, the roller 19 being coated with rubber and rotatably supported at the ends by the frame 21 of the dispenser and its rotation is normally prevented by an axial electro-magnetic brake 22. The roller 20 is made of steel and is supported via a unidirectional rotation clutch, by a frame 23 pivoted at 24 to the frame 21 and urged by a resilient means 25 which maintain the roller 20 in engagement with the roller 19. The film 14 is guided partly on the roller 20 and partly on the roller 21 and upon leaving the latter is laid down on the top portion 121 of the frame 21 which has a comb-like configuration, is coated with felt or other suitable material and on which said film is retained by a comb-like member 123 secured to the frame 23 and, if desired, also coated with suitable material on the portions designed to contact the film, so as to permit the film to slide and to avoid any damage thereto.
Accommodated in the spaces of the upper comb-like member 121-123 of the dispenser 18 there is the inclined end portion of flat springs 26 which are secured to the frame 21. In Figure 17 it can also be seen that secured to the front side of the frame 21 of the dispenser there is an L-shaped guide 27 provided with openings in registry with the openings or spaces of the comb-like member of the dispenser and acting as a guide for a serrated blade 28 which is pivotably secured at its ends to a pair of levers 29 which are fulcrumed on the same axis of rotation of the roller 19, at the sides of the frame 21, where there are arranged springs which urge said levers upwards. Rotatably and overhangingly mounted on the outer side of said levers 29 there is a small roller 30. The levers 29 are provided with an extension beyond the fulcrum, which is directed downwards and is provided with a ferromagnetic plate 31 at the end thereof. When the blade 28 is in its lower position, below the comb-like member 121-123 of the dispenser, the plate 31 is in front of an electro-magnet 32 which is secured to the frame 21 of said dispenser. However, when the blade 28 is in its upper active position, as shown by dot-and-dash lines, the lower extension of the laver 29 is in abutment against a stop 33.
The dispenser 18 is movable on rectilinear and horizontal guides and is controlled by driving means which transfer it from the rest position shown in Figure 1 by solid lines to the position which is shown by broken lines wherein said dispenser is arranged with its comb on the imaginary vertical plane Q that is in line with the bank of sensors 7.
In Figures 1 and 17A it can be seen that arranged at the same level as the dispenser 18 and parallelly thereto is a clamp 34 comprising a single upper jaw 35 and a plurality of side-by-side lower jaws 36 interfulcrumed on a common shaft 37 and whose portion directed towards the dispenser has a comb-like configuration to become interleaved in the spaces of the comb 121-123 of said dispenser. It is apparent from Figure 3 that each jaw 36 is provided with two teeth and is urged by elastic means 38 (Figure 17A) away from the upper jaw 35. In order to achieve a firm grip on the film, the lower surface of the jaw 35 is suitably roughened, while the upper faces of the teeth of said jaws 36 is coated with rubber or other suitable material. When the jaws 36 are in the opened condition, their arms behind the fulcrum 35 engage against a stop 39, preferably made of yieldable resilient material. The rear arm of the jaws 36 carries below a small disc 40 of ferromagnetic material which, when said jaws are in the closed-clamp position shown by broken lines, is closely spaced from a respective electro-magnet 41 which is secured to the frame member 42 of said clamp. Said frame 42, similarly to the frame 21 of the dispenser 18 is movable on rectilinear and horizontal guides and is controlled by driving means which transfer it from the rest position shown in Figure 1 by solid lines to the position shown by broken lines wherein the clamp co-operates with the dispenser at the imaginary vertical plane Q.
From Figures 1 and 2 it appears that, upon control, the dispenser 18 and the clamp 34 are moved towards each other and meet at the central plane Q. At this stage, under the control of a microswitch 17, the motor 13 is actuated automatically to feed the amount of film required to permit said movement of the dispenser, thus avoiding to submit said film to particular tensions in the longitudinal direction. Before the clamp and the dispenser co-operate with each other, a linear cam 43 (Figure 17A), secured to the side frame 67 of the machine, co-operates with the small roller 30 of the rocking structure 29 carrying the blade 28 of the dispenser, thus lowering this latter component, as shown by solid lines in Figure 17b. At due time, the electro-magnet 32 will retain the disc 31 to keep the blade 28 in the opened condition even when, during the successive working steps of the machine, the cam 43 will not be present.
When the teeth of the lower jaws 36 of the clamp 34 penetrate the openings of the comb of the dispenser 18, said teeth co-operate with the inclined portions of the flat springs 26 which cause said teeth to lift and, therefore, said disc 40 to approach the electromagnet 41, against the action of the springs 38. At the end of the approaching stroke of the dispenser and clamp, the teeth of the movable jaws 36 and the stationary jaw 35 are positioned under and over the film, respectively, and are closed spaced from said film which is retained by the comb 121-123 of the dispenser 18. Under command, the electro-magnets are energized and the jaws 36 are lifted to clamp the film against the upper jaw 35.
The electromagnetic brake 22 of the roller 19 of the dispenser 18 is de-energized to let said roller rotate freely.
Upon control, the dispenser 18 and clamp 34 move away from each other as from Figure 3. The rollers 19 and 20 of the dispenser let the film unreel freely, while the clamp 34 draws from the feeding means a length of film of the same length as the stroke traveled by said clamp.
Depending upon the dimensions of the article to be wrapped, which are processed by the computer 6 (Figures 1-3-4), a suitable length of film is drawn through the dispenser 18 and this condition is controlled by the same computer via displacement transducers of the components 18 and 34, as discussed below.
When the computer detects that the length of the unreeled film is sufficient for the dimensions of the article to be wrapped, it causes the energization of the electro-magnetic brake 22 which stops the rotation of the roller 19, whereby the dispenser also operates as a clamp, in that the film cannot slide on said rubber roller 19. The dispenser 18 and clamp 34 go on moving away from each other to submit the length of film therebetween to the maximum pre-stretching in the longitudinal direction. The extent of this final portion of the stroke of the dispenser and clamp away from each other is also calculated automatically by the computer 6 on the basis of the length of the portion of film to be stretched and of the nominal stretching which said film can undergo. Figure 4 shows diagrammatically the relative position of the dispenser 18 and the clamp 34 on completion of the longitudinal pre-stretching of the length of film intended to wrap the article.
From Figures 2 and 3 it can be seen that laterally of the length of film unreeled from the dispenser 18 there are arranged two clamps 44-45 which are disposed symmetrically of the central plane Q shown in Figure 1 and at the same level as the film, so as to be able to act thereon. The clamps 44 and 45 are controlled by means for horizontal and rectilinear displacement to be mutually moved towards and away from each other, and said clamps comprise one respective stationary upper jaw having pivoted thereto at least one lower jaw. During the strokes when the dispenser 18 and clamp 34 are moved towards and away from each other, the side clamps 44 and 45 are in the most spaced apart position and they are opened, as from Figures 2 and 3, to avoid interfering with the film, the dispenser 18 and the clamp 34.
On completion of the longitudinal pre-stretching of the film, the side clamps 44 and 45 are moved towards each other to cover an intermediate portion of the longitudinal edges of the pre-stretched length of film, as shown in Figure 4, whereafter said side clamps are closed to clamp the film and, as shown the successive Figure 5, at least one of said clamps is moved away to submit the film to the maximum transverse pre-stretching (see below).
Only the clamp 45 is moved to effect the transverse pre-stretching of the film, while the clamp 44 - which clamps the edge of film which will be spread last over the bottom of the article to be wrapped, stands still in the film-clamping position. The transverse displacement of the clamp 45 is also controlled by the computer 6 (Figure 1) on the basis of the width of the film being used, of the maximum pre-stretch characteristics thereof and depending upon the length of the portion of film admitted initially into the packaging cycle. Anyway, it is to be understood that both side clamps 44 and 45 may be moved with a logic movement to effect the transverse pre-stretching of the film together.
In order to submit the film to the maximum transverse pre-stretching, the invention contemplates that during the operative movement of the clamp 45 in that direction, the longitudinal pre-stretching is suitably attenuated with a suitable movement of the dispenser 18 and clamp 34 towards each other, as shown in Figure 5.
The length of film supported by the dispenser 18, clamp 34 and clamps 44-45 is thus ready for packaging the article.
The described process has the following characteristics:

The dispensation of the film at the wrapping station is effected by means of a self-centering movement of the dispenser 18 and clamp 34 towards and away from each other. Therefore, it is possible to have at the wrapping station a portion of film whose length is each time proportionate to the size of the article to be wrapped and said portion of film is centered perfectly with respect to said station. The dispensation of the film at the wrapping station is effected in shorter periods because also the dispenser contributes to dispense the film during its movement towards the central plane Q of said station and because the working stroke of the clamp 34 is substantially halved with respect to the conventional art in which the dispenser is stationary and the unreeling of the film is carried out entirely by the corresponding gripper clamp.
The portion of film positioned at the wrapping station has a length which is proportionate to the size of the article to be wrapped and is submitted to the required longitudinal and transverse pre-stretching up to the maximum pre-stretching values of the film, as a function of said length and of the width of said film and its nominal stretching characteristics.
The portion of film positioned at the wrapping station is exploited up to the maximum degree as for its stretchability since, for this purpose, it is first submitted to a maximum longitudinal pre-stretching and then to a maximum transverse pre-stretching while simultaneously and uniformly attenuating the longitudinal pre-stretching.

After the film has been pre-stretched, the lifter 3 is raised, as from Figures 6 and 9. When the article P is in substantial contact with the film 14, the further ascent of the lifter will occur automatically together with a proportional self-centering movement of the dispenser 18 and clamp 34 towards each other and with a proportional movement of the side clamps 44-45 towards each other with displacement of only the clamp 45 (or also of the clamp 44 if the latter had previously pre-stretched the film transversely), whereby during the ascent of the article the condition of the wrapping film will remain substantially constant and unchanged with respect to the previous pre-stretching conditions. These movements are controlled by the computer 6 on the basis of the size of the article to be wrapped. It is apparent that this procedure enables the formation of a wrapper exempt from anomalous tensions and therefore reliable, and as a result it enables a delicate treatment of the article in the wrapping step, thus making it possible to enwrap automatically any type of product, from the most stiff to the most soft and delicate, with the minimum amount of film.
The lifter 3 terminates its upward stroke when the bottom of the article is substantially co-planar with, or just above, the folding members which shall spread out the flaps of the length of wrapping film over the bottom of said article. Since the wrapped article will get out from the side adjacent the side clamp 44 (see below), we designate as side flaps of the wrapping film, the flaps that are supported by the dispenser 18 and clamp 34, and as rear and front flaps the flaps that are supported by the clamps 45 and 44, respectively. The machine according to the invention is provided with a pair of side folders 46-47 arranged above the dispenser and respective clamp, parallelly thereto and connected to means for carrying them towards and away from each other. The operative rounded edges 146 and 147 of the side folders have a similar and opposed configuration, such as to effect a remarkable folding of the side flaps at the front flap supported by the clamp 44 without interfering therewith and which progressively decreases towards the rear flap supported by the clamp 45.
The rear folder 48 is arranged above the side folders and is connected to means for transferring it horizontally, below the article, by a displacement normally to that of the side folders. The front side of the folder 48 is rectilinear and is defined by an idle roller 49.
As shown in the succession of Figures 7 and 8, the side folders and the rear folder operate with such a sequence as to cause the crossing and partial overlapping of the side flaps and the rear flap, substantially at the diagonals of the bottom of the article-supporting tray, while at due time the dispenser 18 and clamp 34 move towards each other, the wrapping film is severed off the dispenser 18 by the action of the cutting blade 28 and is released from the clamp 34, while the rear clamp 45 moves further towards the article and then opens. The action of the side folders and of the assembly discussed above is better illustrated in Figures 10 and 11. Figure 10 shows the first operative step of the side folders 46-47 with the simultaneous movement of the dispenser 18 and clamp 34 towards each other. When the side flaps of the film have been already spread out partly on the bottom of the article, said distribution and clamp are stopped, the cutting blade 28 is actuated and said clamp 34 opens. The side folders will complete the spreading out of the flaps of the film over the bottom of the article, as shown in Figure 11. From Figures 10 and 11 it is apparent that the side folders, during their operative movement, interfere with the rocking supports 10 which carry the article, overturning them partly. From these Figures and from Figure 9, it also appears that during the wrapping step the article is controlled from above by a presser 50 of any suitable conventional type, which presses said article onto the folders upon termination of the action of the dispenser 18 and clamps on the wrapping film, thus preventing undesired movements of said article.
In the succession of Figures 12-13-14, the action of the rear folder 48-49 and the clamp 45 is pointed out. When the rear flap of the film has been spread out to a great extent on the underside of the article and when the clamp 45 has reached the lifter 3 and said article is largely supported by the side folders and rear folder, the lifter 3 is returned to the lower position to start a new cycle, while the clamp 45 is timely opened and the folder completes the spreading out of the rear flap of the wrapping film on the tray.
In the Figures 2 to 8 and 12-13-14 it can be seen that arranged above the clamp 44, substantially co-planar with the rear folder 48-49, there is a small rollerpath 51 whose rollers are parallel to the roller 49 of the rear folder and are idle rollers. The portion of the roller 51 close to the wrapping station is pivoted transversely at 52 to a supporting structure and is controlled by an actuator which, in the earlier stages of the working cycle of the machine, keeps said roller-path in a suitable raised condition with its end close to said wrapping station, to retain the article during the action of the rear folder, as shown in Figures 12-13-14.
When the rear folder has completed its working stroke and the lifter 3 has been lowered, the roller-path 51 is returned to its horizontal position, as from Figure 15. Associated with the same carriage which carries the 45 is a pusher 53 acting against the rear side of the article to discharge it onto the roller-path 51, while the front flap of the film is held fast by the respective clamp 44. When this flap has been largely spread out on the underside of the article and has been overlapped on the other flaps, the clamp 44 is either opened or kept closed through permitting it to frictionally release the rear flap of the film to enable said flap to overlap the other flaps, while the article moves on the roller-path 51, first by the action of the pusher 53 and then due to inertia. It is to be understood that if the clamp 44 has also been previously displaced to pre-stretch the film transversely, said clamp is suitably actuated to keep the tension on the film substantially unchanged, similarly to what has been said previously in connection with the rear clamp 45.
Finally, the wrapped article is removed by any suitable means (see below) and the roller-path is returned to the inclined position for a new cycle. The rear folder is returned to the rest condition and the clamp 45 is also returned to the initial position, together with the pusher 53. The clamp 44 is also moved away either by its own means or by the co-operation with a cam which is carried by either the clamp 34 or by the dispenser 18 (see below). Regardless of the size of the article to be packaged successively, the dispenser 18 and clamp 34 stand still in the position they had at the end of the preceding cycle (Figure 8) and they begin the new cycle from this position (Figure 2).
With reference to Figures 18 and 19, we will describe now the means for actuating the assembly dispenser clamp 18-34, the assembly rear clamp pusher 45-53, the rear folder 48-49 and the side folders 46-47. The carriage which carries each of these components is secured to the rectilinear flight of any suitable conveyor of the positive type 54, e.g. a toothed belt type, a perforated steel belt type or any other type, which is guided around parallel shafts 55-56, one of which is an idle shaft while the other is powered by a geared motor 57, for example, of the worm and helical gear type, with a precision electrical motor 58, for example, of the D.C. type, with double direction of rotation, with an incorporated encoder to permit the required connection with the computer 6 of Figure 1. More particularly, the conveyor 54 comprises a steel rope 59 guided around an idle pulley 60 arranged on the adjustable shaft 55 and secured at the ends thereof to the opposite faces of a driving drum 61 which is keyed on the powered shaft 56, after said rope has been suitably turned around on the circumference of said drum. The ends of the rope are provided with small heads 62-63 added and welded thereto. The head 62, which is supposed to be the leading head, is accommodated, for example, in a recess formed in the upper face of the driving drum 61 and the rope 69 originating from said head is guided around tangentially on the groove of the drum with a fraction of turn and then leaves therefrom to be guided around the driven pulley 60 wherefrom said rope is returned tangentially onto the side surface of the driving drum, below the initial point mentioned above, and said rope is wound with a plurality of turns around said drum, the total length of said turns determining the capacity of longitudinal displacement of said rope-type conveyor. The trailing head 63 of the rope is accommodated in a recess formed in the lower face of the drum 61. When the driving drum is rotated in one direction, the leading or upper portion of the rope is wound on said drum while the trailing portion is unwound to make room available for the turns being wound. When the direction of rotation of the drum is reversed, the winding and unwinding of the rope on the drum 61 is also reversed.
In Figure 24 it can be seen that the frames 9 of the lifter 3 are supported at the bottom thereof by a bracket 64 solidary with a carriage 65 which is slidable on a vertical guide 66 secured to the frame 67. A connecting rod and crank mechanism 68 and a geared motor 69 effect the cyclic lifting and lowering of the carriage 65.
In Figures 1 and 24 it can be seen, finally, that the upper portion of each frame 9 has a fork-like configuration to pivotably support a crosspiece 70 provided on at least one end thereof with a depending lug 71 connected to a tension spring 72 secured to the frame at 73. Said spring maintains the upwardly-directed position of the protrusions 74 provided on the upper side of the crosspiece 70 and having pivoted thereon - on horizontal pivots 75 orthogonal to the axis of oscillation of said crosspiece 70 - the crowned supports 10 coated with rubber which constitute the emerging portion of the lifter, capable of supporting the article during the wrapping step. When the rear folder 48-49 becomes operative, the supports 10 will react resiliently, oscillating on the longitudinal axis of the crosspiece 70.
At the interior of each support there is an axial blind recess accommodating a spring and a ball which is urged by said spring to frictionally engage the contour of the protrusion 74, said contour being curved to permit the support 10 to be overturned towards the center of the lifter when, during the article-wrapping step, the side folders become operative. Since the supports 10 would tend to remain directed towards the center of the lifter after being oscillated on the pivots 75, the arrangement is such that the supports will be returned to the correct orientation upwards when the lifter 3 is lowered and brings the previously overturned supports to interfere with studs 76 arranged on the sides of the guides 77 on which the belts of the article feeding conveyor 2 slide. Numeral 78 indicates the electronically controlled geared motor which through the circuit 8 is connected to the computer 6 of Figure 1.
Figures 20 and 21 show that the body 42 of the clamp 34 for unreeling the film from the dispenser is secured, at the end disposed on the side of the machine from which the wrapped article is discharged, to a carriage 79 which slides on a horizontal profiled guide 80 which is orthogonal to said clamp and is secured to the frame 67 of the machine. The other end of the body of the clamp is provided with small rollers 81 which roll on a guide 82 arranged on one side of the machine frame 67.
The dispenser of the film 18 is supported slidably similarly to said clamp 34. Figure 20 also shows the carriage 79' of the dispenser, which slides on an extension of the same guide 80 which supports the carriage 79 of the unreeling clamp 34.
At the ends of the guide 80 there is mounted the power system 154 of the same type as that at 54 in Figure 18. The carriages 79-79' are connected to the two flights of the rope-type conveyor 59 so as to be actuated with the required self-centering movement.
In the Figures 20 and 21, 83 indicates the profiled guide on which the ends of the side folders 46-47 slide by means of grooved rollers 84. The numeral 254 indicates the power system of the same type as that at 54 in Figure 18, which controls the self-centering actuation of the side folders which are connected to the two flights of the rope-type conveyor 59.
Said Figures 20 and 21 also show the clamp 44 comprising a stationary upper jaw 85 having pivoted thereto at 86 a lower jaw 87 which is urged away from the upper jaw by a resilient means. The upper jaw has a lower roughened face and the lower jaw has a top side which is coated with a resilient yieldable material. The upper jaw has a depending projection 88 connected to the end of a pair of horizontal, parallel rods 89 directed away from the wrapping station and supported, through axial bearings, by the parallel sides of a structure 90 having a "U" configuration in plan view and secured at its ends to the frame 67 of the machine. The rods 89 are passed completely through the structure 90 and are interconnected at their rear ends by a crosspiece 91 which is provided centrally with a small vertical-axis roller 92 co-operating with the outer contour 93 of a cam 94 secured to the carriage 79' of the clamp 34, in such a position whereby the clamp 44 shall be retracted before interferring with the dispenser/clamp assembly 18-34 being transferred towards the central plane Q for gripping and unreeling the film. The projection 88 of the body of clamp 44 has secured thereto an end of two further rods 95 which are parallel to, and on the inner side of, the rods 89, which are passed through holes 96 in the crosspiece of the structure 90 and which are surrounded by respective springs 97 acting between said crosspiece and a shoulder 98 carried by each rod 95 and which may be adjusted by means of screws 99. The springs 97 urge the clamp 44 towards the article-wrapping station and, therefore, ensure a correct co-operation between said roller 92 and cam 94. The action of said springs also affects the force by which the lower jaw of the clamp 44 is urged against the upper jaw in gripping the film. In Figure 21, in fact, it can be seen that the lower jaw 87 of the clamp 44 is provided, beyond the fulcrum 86, with an upwardly directed projection 100 which in the movement of said clamp towards the wrapping station, interferes with an adjustable shoulder 101 secured at the centerline of the guide 83 for the side folders, thus causing the jaw 87 to lift and close the corresponding clamp which is kept in its closed condition by an electro-magnet, not shown, similarly to the clamp 34.
In is to be understood that if also the clamp 44 must be pre-set to effect a transverse pre-tensioning of the film, said clamp will be actuated by a power system of the same type as that of Figure 18 and will be provided with an electro-magnet which keeps it closed when it moves away from the mechanical stop 101 which has caused it to close.
In the Figures 20-21-22, the numeral 102 indicates the profiled guide whereon the carriage 103 slides under the action of a power system 354 of the same type as shown in Figure 18 and which overhangingly supports the rear folder 48-49.
Provided parallelly to the guide 102, on the other side of the wrapping station, there is the profiled guide 104 whereon the carriage 105 slides under the action of a power system 454 of the same type as that of Figure 18, and secured overhangingly thereon are the pusher 53 and the clamp 45. Said clamp comprises, at the centerline of the wrapping station, a stationary jaw 106 which is arranged above the film to be tensioned and which has pivoted posteriorly thereof, on a shaft 107, the lower jaw 108 secured to said shaft which, in turn, is rotatably supported by the structure carrying said upper jaw and which, as shown in the detail of Figure 22, protrudes from the outer side of the carriage 105 and carries at its end an upwardly directed lever 109 provided with a small roller 110. A spring 111 (Figure 21) urges the lower jaw to close and keeps said roller 110 against the horizontal rectilinear guide 112 (Figures 22-23) which constitutes the longer movable side of a double articulated parallelogram arranged parallel to the guide 104. The parallelogram comprises a double stationary beam 113 having inter-fulcrumed thereto at 114-114' equal links 115-115' whose lower ends are pivoted at 116-116' to the guide 112 and whose upper ends are interconnected by means of a tierod 117. The link 115 is connected to a tension spring 118 which is anchored to the beam 113, while the other link 115' is connected by means of a tierod 119 to a rectilinear motion actuator 120, e.g. an electro-magnet. In the Figure 23 the double parallelogram is shown by broken lines and by solid lines, corresponding to the opened condition and closed condition of the clamp 45.
In Figures 20 and 21, finally, there is shown the rocking roller-path 51 which contributes to spread on the undersurface of the article the last flap of the wrapping film which is held by the clamp 44. The oscillation of the roller-path about the pivot 52 is effected, for example, by a cam, not shown, carried by the carriage 103 of a side folder. The outer portion of the roller-path is arranged between the flights of a belt conveyor 122, which are parallel to the rollers of said roller-path. When the roller-path is in the lifted position, the rollers are slightly above the upper flights of the belts of the conveyor 122 which do not interfere with the sides 124 of the frame supporting said roller-path, since they are provided with recesses 125. The article arriving onto the roller-path 51, therefore, is not affected by the presence of the belts 122. When the outer-path is lowered with its outer portion, the wrapped article thereon is transferred onto the belts of the conveyor 122 which is powered by the unit 132 and which moves away the wrapped article towards an optional station where the flaps of the wrapping film are sealed, according to any known solution.
It is not to be excluded that the sealing of the wrapping-film flaps is effected while the article is travelling on the first portion of the roller-path 51 (the one directed towards the wrapping station), suitably modified for this purpose, e.g. by means of a conveyor made of teflon or other suitable material, sliding in contact over a heated plate.
The presser 50 shown in the drawings is pivotable on the fulcrum 126 (Figure 21) and is directed with its free end in the direction of discharge of the article from the wrapping station.
In Figure 1, the numerals 127-128-129-130 indicate the circuits interconnecting the computer 6, respectively, to the power units for the dispenser 18, clamp 34, clamp/pusher assembly 45-53 and side folders. By means of the computer, the various driving units can be controlled both with a variable stroke depending on the size and characteristics of the article to be wrapped, and with accelerations and decelerations as required for a correct and reliable operation of the various operating members of the machine. The numeral 131 indicates diagrammatically the input into the computer for the variables concerning the characteristics of the article to be wrapped and the width of the film being used.
The flow chart of Figure 25 shows the succession of the main operative steps of the machine. In this flow-chart:

the block A1 indicates "Select packake, normal, soft and other";
the block A2 indicates "Enter width of reel";
the block A3 indicates "Package detected?";
the block A4 indicates "Reading of distance from preceding package";
the block A5 indicates "Reading of package size: length, width, height";
the block A6 indicates "Package accepted?";
the block A7 indicates "Warning of error";
the block A8 indicates "Ejection of package at feed";
the block A9 indicates "Calculation of positions and time periods of all machine movements in connection with package";
the block A10 indicates "Synchronization with preceding cycle";
the block A11 indicates "Film unreeling with longitudinal stretching depending on package size";
the block A12 indicates "Film gripping by transverse clamps";
the block A13 indicates "Film transverse stretching depending on package size";
the block A14 indicates "Longitudinal seconding of film during transverse stretching";
the block A15 indicates "Ascent of lifter with package";
the block A16 indicates "Transverse seconding of film by approaching transverse clamps";
the block A17 indicates "Longitudinal seconding of film by approaching clamp/dispenser";
the block A18 indicates "Action of side and rear folders";
the block A19 indicates "Longitudinal attending to film by approaching clamp to dispenser";
the block A20 indicates "Transverse attending to film by approaching transverse clamps";
the block A21 indicates "Cutting of film and opening of clamps, excepted transverse front clamp";
the block A22 indicates "End of folders closure";
the block A23 indicates "Descent of lifter";
the block A24 indicates "Ejection of wrapped package and opening of transverse front clamp";
the block A25 indicates "Machine components return to rest position".

From the flow chart it can be appreciated that the start command is followed by a first manual input for selecting the characteristics of the package to be wrapped, and by an additional input concerning the width of the film being used. The article or package (P) is detected by the opto-electronic sensors (4-5) arranged on the feeding conveyor (1-2), is synchronized with the preceding package and, if accepted, moves on towards the lifter (3). In the negative case, the feeding conveyor reverses its rotation and the package is ejected and the inconvenience is signalled. The computer (6) controlling the machine has received the information on the characteristics of the film being used, characteristics and dimensions of the article, has processed these functions and controls the dispenser (18) and respective clamp (34) to make them unreel a portion of film of suitable length and submit said portion of film to the required longitudinal pre-stretching. Thereafter, the transverse pre-stretching is attenuated. The article or package is lifted against the pre-stretched film while the tensioning of the latter is kept substantially constant by suitably moving the dispenser (18) and clamps (34-35) which support the flaps of said film. The side folders (46-47) and the rear folder (48-49) come into action, while the dispenser (18) and respective clamp (34) move further towards each other and while the rear clamp (4() approaches the front clamp (44), the clamps being timely opened, excepted the front clamp, and the film being cut for the separation from the dispenser. The lifter is returned to the lower position for repeating the cycle, while the package is ejected from the wrapping station and the side front clamp (44) timely releases the last flap of the film. The various operating components are returned to the rest position and the cycle is repeated.

Claims

A process for wrapping articles with a stretchable film, in which the article is lifted against a length of pre-stretched film whose flaps are successively spread out under tension onto the undersurface of said article, characterized in that, prior to the lifting of the article, the film is firstly submitted to a first pre-stretching in a first direction, within the maximum value permitted by the film, and thereafter the film is submitted to a second pre-stretching in a second direction transverse to said first direction, while simultaneously said first pre-stretching is suitably and uniformly attenuated to allow the maximum stretchability of said film in said second direction.
A process according to claim 1, characterized in that when the article is lifted and pushed against the length of pre-stretched film, said first pre-stretching and said second pre-stretching are suitably and uniformly attenuated, whereby said film is not submitted to anomalous tensions in contacting the article and whereby said article is engaged delicately, while ensuring the formation of a wrapping which engages said article intimately.
A process according to claim 2, characterized in that the length of film intended to wrap the article is obtain from a feeding roll, and said first pre-stretching direction coincides with the longitudinal direction of unreeling of the film from said feeding roll.
A process according to claim 3, in which the length of film unreeled from the feeding roll is fed to a wrapping station, characterized in that said length of film introduced into the wrapping station has a length which is proportionate to the dimensions of the article to be wrapped at each time and said phases of first longitudinal pre-stretching and second transverse pre-stretching of said length of film are also proportionate to the dimensions of the article.
A machine for wrapping articles with a stretchable film, more particularly for carrying out the process of the preceding claims, characterized in that it comprises:
- at least one film-supplying roll;

- means for feeding the film to a wrapping station where said film is pre-stretched longitudinally, comprising a dispensing clamp or dispenser (18) provided with means to either lock or let the film slide therethrough, and an unreeling clamp (34) opposite to said dispenser;

- means for pre-stretching the film transversely, comprising at least one pair of opposite clamps (44-45) adapted to grip the longitudinal edges of a length of film which has been positioned under tension at the wrapping station;

- a lifter (3) arranged at the wrapping station, adapted to lift the article to be wrapped against the film which is held fast by said means for effecting the longitudinal pre-stretching and the transverse pre-stretching;

- means for severing from the feeding roll the length of film which is positioned at the wrapping station and intended to wrap the article arranged on the lifter;

- folding means for folding the flaps of the length of film onto the bottom of the article arranged on the lifter;

- means for feeding the articles to be wrapped to the lifter;

- means for removing the wrapped article from the wrapping station.
A machine according to claim 5, characterized in that it comprises conventional means (12-13-15-16-17) enabling the unreeling of the film (14) with no substantial tension from the roll (11), the leading end of said film being gripped by the dispenser (18) carrying thereon a braking means (19-22) and the film-severing means (28), which under command will act transversely on the film, an unreeling clamp (34) being provided parallelly to said dispenser, and means being provided whereby said dispenser and said clamp are actuated with a self-centering movement towards and away from the central plane (Q) of the wrapping station, the arrangement being such that said dispenser (18) and clamp (34) co-operate with each other on said plane so that the unreeling clamp will grip the film, whereafter the dispenser (18) and clamp (34) will be moved apart so as to withdraw from said dispenser a length of film which is proportionate to the dimensions of the article to be wrapped and to submit said length of film to the required longitudinal pre-stretching after said transverse braking means (18-22) has timely acted on said film.
A machine according to claim 6, characterized in that the means for the self-centering actuation of the dispenser (18) and unreeling clamp (34) and for the actuation of all the other components of the machine which are to be actuated in a logic mode, is of a type which can be controlled by a computer (6) and comprises any suitable positive-type mechanical drive actuated by a geared motor, the motor being controlled electronically.
A machine according to claim 7, characterized in that it comprises laterally and below, or above, the feeding path of the articles to the lifter (3), banks of opto-electronic sensors (4-5) to be used for correctly positioning the article on said lifter and which detect the length, width and height of the article which is to be wrapped and which convey said information to the computer (6) to which is also supplied (131) the information concerning the characteristics of the articles to be wrapped and concerning the width of the film being used, so that by processing these variables the computer can control the unreeling of a portion of film whose length is proportionated to the dimensions and characteristics of the article to be wrapped and it can control the maximum longitudinal and transverse pre-stretching of said portion of film and then can suitably control the clamps, folders and pusher to form a wrapping which wraps the article intimately, which is exempt from anomalous tensions and which does not submit said article to any undesired stress.
A machine according to claim 7, characterized in that the logic and self-centering actuation of the dispensing clamp (18) and withdrawing clamp (34) is effected by means of a positive-type conveyor (59) the two parallel flights of which have secured thereto the carriages which carry said clamps; one shaft of said conveyor being actuated by a small geared motor (57) comprising an electrical reversible and electronically-controlled motor (58).
A machine according to claim 9, wherein said conveyor is a small capstan with a steel rope which is guided around an idle pulley (60) and whose ends are anchored to the two opposite ends of a groove in the drawing drum (61) on which said rope is arranged so as to be wound and unwound simultaneously, first in one direction and the in the other direction depending upon the direction of rotation given by the geared motor to said drawing drum.
A machine according to claim 7, characterized in that electronically-controlled driving systems, preferably of the same type as that which actuates the dispensing clamp (18) and withdrawing clamp (34), are used for the self-centering actuation of the side folders (46-47) and for the actuation of the side/rear clamp (45) and pusher (53) which moves the article away from the wrapping station.
A machine according to claim 9, characterized in that the shafts (55-56) of the conveyor (59) of the electronically-controlled driving system are mounted on the same guide on which the carriage or carriages carrying the operative components of the machine are slidable, the dispenser (18) and withdrawing clamp (34) being supported by sliding and guide means (81-82) also at the end opposite to that which is connected to said powered carriages, while the side folders (46-47), rear clamp (45) and pusher (53) for ejecting the article, are mounted in cantilever fashion on the respective actuating carriages.
A machine according to claim 6, characterized in that the braking means arranged on the dispenser (18) comprise, upstream of the end portion of said clamp, which has a comb-like configuration (121-123), a pair of parallel rollers (19-20) on which the film is guided so as to establish a wide contact with the larger one (19) of said rollers, which is coated with rubber and whose rotation can be locked by means of an axial electro-magnetic brake (22), while the other roller is controlled by a unidirectional rotation clutch.
A machine according to claim 6, characterized in that the means arranged on the dispenser (18) for transversely severing the film, consist of cutting means and comprises a rocking serrated blade (28), arranged immediately downstream of the comb-like front side (121-123) of said clamp, which is guided in its vertical displacement and is urged upwards by resilient means, the ends of said blade being connected to rocking levers (29), provided with a small roller (30) which during the active stroke of the dispenser interferes with a stationary cam (43) to cause said blade to be lowered, said blade being held in the lowered position by at least one electro-magnet (32) co-operating with a suitably conditioned (31) arm of said rocking levers (29) which actuate said blade.
A machine according to claim 6, characterized in that the withdrawing clamp (34) comprises an upper jaw (35) secured to the translation carriage and comprises a plurality of side-by-side lower jaws (36) articulated to the clamp body, urged in the opening direction by respective resilient means (38) and constructed so as to be closed by the co-operation with sloping portions (26) provided in the spaces of the comb (21) of the dispensing clamp (18), small electro-magnets (41) being provided to keep the lower jaws of said withdrawing clamp closed.
A machine according to claim 6, characterized in that it comprises means whereby the transverse pre-stretching of the film at the wrapping station is effected under the control of the computer 6, by actuation of both side clamps (44-45) by respective driving systems.
A machine according to claim 6, characterized in that the transverse pre-stretching of the film at the wrapping station is effected only by the rear side clamp (45) actuated together with the article-ejection pusher (53), by an electronically-controlled driving system, while the front side clamp (44) is supported by sliding and guiding means which initially move it away from the wrapping station to avoid interfering with the dispenser and the withdrawing clamp (18-34) which meet and then move apart to longitudinally pre-stretch the film, while said front side clamp is moved towards the longitudinally pre-stretched film and is closed theron and is kept in its closed condition until the last phases of the wrapping cycle, while the article is pushed to be discharged onto a collecting and discharging conveyor (51) by the action of the pusher (53) associated with said rear side clamp (45).
A machine according to claim 17, wherein the front side clamp (44) is mounted on suitable guiding and sliding means (89-90) which control it in its displacements towards and away from the wrapping station, said clamp being urged by resilient means (97) towards said station, and its sliding means being provided with a small roller (92) for co-operation with a cam (94) connected to the carriage (79) actuated by the withdrawing clamp (34) so as to be actuated by the latter component in its alternating movement, and finally the closing and opening of this side clamp being caused by the interference of a projection (100) of the lower mobile jaw (87) of said clamp against a stationary shoulder (101), and with the co-operation of said jaw with an electro-magnet carried by the stationary jaw (85).
A machine according to claim 5, characterized in that the removing conveyor (51) which collects the article in the discharge step from the wrapping station and which contributes to spread out, on its undersurface and on the previously spread out flaps, the last flap of the wrapping film, while the article is held in its position by an overlying presser (50) operative since the lifting step of the article against the film, consists of a roller-path pivotable on a transverse fulcrum (52) and actuated by suitable means whereby the end portion of said roller-path arranged at the wrapping station is kept in a raised condition until the last stages of the wrapping cycle to retain the article at the front side thereof during the action of the side folders (46-47) and rear folder (48-49), said roller-path being returned to its horizontal position while the previously lifted end is lowered, in the last stage of the cycle, when the article is to be ejected from the wrapping station and when said roller-path spreads out the last flap of the film onto the bottom of the article to overlap the other flaps.