EP0044820A1

EP0044820A1 - A machine and a process for packaging articles of products

Info

Publication number: EP0044820A1
Application number: EP81830115A
Authority: EP
Inventors: Franco Pioltini
Original assignee: Pittacus AG
Current assignee: Pittacus AG
Priority date: 1980-07-22
Filing date: 1981-07-14
Publication date: 1982-01-27
Also published as: ES504165A0; ES8301808A1; IT1131751B; IT8023595A0; JPS5755810A

Abstract

A machine and a process for packaging products by wrapping a stretchable transparent film of plastic material around the products placed in trays of different sizes.

Trays (20) carrying the products are advanced transversally with respect to the plastic film (18) that unrolls from one or more supply rolls (11,12,41,42) and is cut at prefixed and adjustable lengths and then further advanced to be centered over the tray. The machine carrying out the process includes a control unit performing portions of the packaging cycle that are common to every tray and portions of the cycle dependent upon the size of the tray. The sizes of a series of trays are preset by the operator, e.g. positioning a selecting device on one of the possible values that are provided by the machine. Moreover the machine provides for a plurality of film supply rolls (11, 12, 41, 42) mounted on both sides thereof and having different width for an alternating use so as to reduce the time for changing or replacing a film roll. Conveyor means for the film comprise elastic endless cords, movable on rolls transversally displaceable to fit the different film widths.

Description

The present invention relates to a machine and a process for packaging products carried in trays by wrapping a thin foil sheet or film of plastic material.
The invention relates therefore to the forming of packages for products of different kind and more particularly food products, made up by containers, trays, boxes etc. containing the products and wrapped by a film of trasparent plastic and stretchable material, e.g. polyvinyl chloride, that is enveloped and sealed around the product and the tray in order to form discrete packages. These packages are easy to handle, exhibit a good resistance and allow for inspection of the product while storing the same under hygienic conditions.
Several and different machines of the above type are known, usually having sizes and costs rather high and being substantially designed for wrapping and packaging a well defined type of container. These machines work fully automatically and at high speed. Particular examples are the machines disclosed in U.S. Patent No.3,662,513 to Fabbri, issued on May 16, 1972 and in U.S. Patent No.3,967,433 to Bonfiglioli, issued on July 6, 1976. Such machines are mechanically controlled, substantially suitable for packaging large batches of a same pro duct so as to justify the cost and cannot be modified to accept containers having sizes quite different from the ones they were designed for.
This kind of machine is therefore unsuitable for preparing a small number of packagings employing trays with different sizes, due both to their high price and to the waste of material in packaging the smaller items. Furthermore the quality and the aspect of a packaging oversized with respect to the Volume of the content are rather unsatisfactory and packaging is not possible for trays being larger than the size for which the machine was designed.
Moreover it is to be considered that the machines of this type employ members and devices that are mostly mechanical or electropneumatic for controlling the different operations so that it is generally unfeasible even for the manufacturer to modify the machine in order to meet the user's needs.
.Further disadvantages and minor shortcomings of the known machines will be considered later.
There is a particular class of users of the mentioned packaging machines that are bound to package articles near the selling places with containers having sizes pretty variable and in number seldom higher than a hundred of pieces for each kind Of article. For such a use it is not necessary that the packaging speed is particularly high, being rather essential a high degree of flexibility.
It is therefore an object of the present invention to carry out a process for wrapping a length of transparent stretchable plastic film around an article placed in a tray, container or other supporting means having variable sizes, allowing an easy adaptation to the different sizes of the trays that are preset at the beginning of a series of trays, and wherein the packaging operations are electronically programmable in the control unit of the machine carrying out the process so that the switching from a size to another for the container does not require mechanical modifications or interventions and can be accomplished automatically by the control unit of the machine.
It is another object of the invention to realize an improved packaging machine for wrapping a transparent stretchable plastic film around an article hold by a tray that employs the above process and is therefore adapted to package series of trays having different sizes by using a precisely cut length of film.
It is still an object of the invention to realize a packaging machine entirely under electronic control having logical processing circuits and power circuits for actuating the machine mechanisms.
A further object of the invention is to realize a packaging machine having conveying means of the film formed by endless elastic cords or belts that allow for changing the width of the plastic film fed to the wrapping station.
The machine according to the invention comprises:

- means for feeding a length of film unrolling from one of a plurality of rolls to an operative location or wrapping station of the machine, said means including a plurality of elastic endless cords positioned at both sides of the film length and moving along closed loops around driving sheaves and guide sheaves, said feeding means being actuated on each operation cycle under control of a control unit, a first time for a time interval that is proportional to the width of the tray to be wrapped, after which the film is cut and successively said feeding means are actuated for a time interval long enough to have the plastic sheet centered over the tray, said time intervals being dependent upon the value preset by the operator for the width of the tray;
- means for sequentially conveying the trays containing the article from an entry position to a position laying under said operative position;
- lifting means for raising each tray and means for stretching and wrapping said length of film around the tray to form the package;
- means for extracting the packaged article from the machine; and
- an electronic control unit controlling the unwinding and cutting of prefixed lengths of the plastic film as well as their positioning and centering over the tray according to the values preset by the operator for the width of a tray.

Furthermore the process according to the invention provides for predetermining the values relating to the sizes of each series of trays to be wrapped and, successively, each operating cycle comprises the steps of:

a) completing the folding of the film edges around an enveloped tray, extracting the same and sealing together the folded edges, and supplying another tray to the lifting station;
b) unrolling and advancing a portion of film having a length suitable for the predetermined sizes of the tray, said advancing being transverse with respect to the tray;
c) cutting the film portion corresponding to such advancing;
d) unrolling a second length of film in order to prepare the machine for the next wrapping operation;
e) advancing the cut length of film over the tray until it is centered over the tray;
f) lifting the tray to a point higher than the film, the cut sheet being kept fast at least on its side edges;
g) releasing the side edges and folding them under the tray.

For controlling and handling the different working operations the machine according to the invention preferably employs a microcomputer suitably programmed to command the operations relating to the packaging of anyone of the type of trays for which it is preset, without any manual intervention but the initial set of the tray size and the selection of the film roll. The machine according to the invention provides for several novel mechanical features that will be illustrated more particularly in the following.
The above features and further advantages will become .evident from the following description relating to a preferred embodiment with reference to the attached drawings in which:

FIGURE 1 is a schematic front view of the machine according to the invention;
FIGURE 2 is a side cross-section view along line II-II of Fig. 1;
FIGURE 3 is a plan view of the machine shown in Fig. 1; _'FI'GURE 4 is a diagram illustrating the timing of the different components of the machine; and
FIGURE 5 is a block diagram of the control unit of the machine.

Referring to Figs. 1, 2 and 3 a preferred embodiment of the machine according to the invention comprises a supporting frame 1, laterally equipped with a conveying device 2 for trays 20, formed by a conveying belt 25 moving around two rolls, 26 and 27, and onto which it is laid a tray containing a product to be transferred to a lifting plate 36 initally disposed in a lowered position. Above the lifter a wrapping station includes an upper plate 28 having a rectangular opening or matrix 24. Above the latter an extractor apparatus 4 is provided to drive out the enveloped trays. Extractor 4 includes a raised conveyor 34 having a moving belt 35 covered by an elastic spongy material. By friction engagement with the package it pushes the latter out of the wrapping station.
The machine contains a reduction gear unit 6 for the main (electric) motor 7 tha drives the lifting device, the extracting conveyor 4, etc. Particularly referring to Fig. 1, the machine further provides for at least two pairs of. side rolls 11, 12 of thin plastic stretchable film. On the upper part there are provided means for unrolling, conveying and cutting the film that will be better illustrated in the following.
It is an important feature of the machine according to the invention that a single electric motor, properly reduced and coupled with driving belts to the different parts of the machine, is employed to supply the main necessary movements. Some other actuators employ electromagnets so that the machine does not require any auxiliary hydraulic or pneumatic supply thus making simpler and cheaper the installation.
As can be seen in the figures, conveying plane 3 of the feeding device is equipped with a switch 54 starting each operating cycle when the machine works at steady conditions. Fingers or pushers. 37 fixed to the conveying belt 25 carry trays 20 to the lifting device 36 in proper alignement. The plastic transparent film 18 to be wrapped is drawn from rolls .such as those shown with 11 and 12 according to the size of the tray to be wrapped. More particularly, in the machine according to the invention both width and length of the wrapping sheet can be precisely adjusted since the longitudinal cutting device explained later will determine the width of the cut sheet whereas the selection of one of the rolls having different widths allows for choosing the proper length of the wrapping sheet. Moreover the machine can be simmetrically built as shown in the figures, with a further pair of wrapping material rolls 41, 42 preferably identical to rolls 11 and 12 on the left side as seen in Fig. 1. The film driving movement can be reversed quite simply to allow using the film unrolling from either group of rolls. Consequently it is possible to wrap a series of trays using a roll of one size (e.g. right hand roll 11) and simultaneously to arrange the machine for packaging the next series of trays with a film of different width (e.,g. left hand roll 42). This way stop periods to switch to another series of trays having different size are almost completely avoided, as well a stop periods for replacing an exhausted roll.
Trays are advanced transversely to the plastic film supply and the latter is cut transversely to the advancing direction by knife or cutting device 13. The plastic film is unrolled and fed through driving rolls and elastic conveyors 8 and 9 known as plasticords, formed by elastic endless cords usually with circular cross-section, movable along a closed path, around a plurality of driving and guide sheaves. More precisely the film turns around guide rolls 14, is drawn by driving and stopping rolls 17 and then is engaged between elastic cords 8 and 9. for the final positioning in the wrapping station. For further details of these memberssee the above mentioned U.S. Patent No.. 3,662,513 wherein anyhow flat belt conveyors are used.
Conveying elastics 8 and 9, that are formed by two groups of upper and lower elastic cords, respectively, the upper group being shown in Fig.. 3, move through grooves on compounded driving sheaves 21, 22, 23 that can be shifted along their supporting axles so as to be laterally displaced for fitting to different widths of the plastic film. The use of this elastic conveying means so positioned allows for relevant advantages over the usual belt conveying systems. Namely the device is quite simpler, substantially cheaper and more effective and reliable besides allowing for adjustements for the film width thanks to the side mobility of the sheaves. A length of unrolled film is cut by means of a perforating tool 13 preferably built as a saw-toothed blade that is lifted and engaged against the unwinding film 18 whereas, simultaneously, roll 14 is braked by a friction mechanism. This way one obtains a stretching of the sheet that is subsequently torn and carried to the wrapping station as a pre-stretched foil having the desired size. After the cut of the film the machine resumes unrolling and advancing another film portion for the wrapping of the next tray.
The actuators of the wrapping machine are controlled by cam 5 rotated by main motor 7, that starts a wrapping cycle upon the closure of a switch and causes the different lifting and lowering operations, through levers. 39, 40, folding operations, through lever 32 for actuating the folders, and so on.
The operation of the machine will now be illustrated referring to a wrapping cycle.'
After selecting a suitable roll, unrolling a portion and fitting the same between, the guide members and presetting in a control panel the value of the length to be cut (corresponding to a prefixed width of the tray), the operator starts the machine and places a tray 20 over microswitch 54 of the feeding device 2, thereby causing to closure of the switch 54 and the beginning of the cycle.
The real beginning of the cycle is however dependent upon the angular portion of cam 5 and comprise lowering of plate . 36 to pick up the tray 20 advancing along the conveying line . 3, and the unrolling of the film. A central control unit constantely monitors the length of unrolled film stopping the drawing when such a length is equal to the one preset for the series of tray. The film is than cut and the drawing resumed whereas at the same time the lifting device is stopped. This portion of the machine cycle has a variable duration depending upon the preset size for a series of trays. In fact, this first time interval for unrolling the film must be such as to cause a prefixed length of film be unwound. After the cutting, the sheet must be advanced for a second time interval, long enough to center the cut sheet over matrix 24. Such first and second time intervals are constant for the whole series of trays having the same size, but must be automatically changed by the machine when the operator sets another tray size. The'control circuitry carries out .such change without any delay and, at most, a dry machine cycle is required to get rid of the film portion already positioned.
On the other hand the sequence of the remaining operations is common, independently from the size of the trays. The sheet, cut and positioned, is fastened against surface 28 by longitudinal pressers 15 actuated by electromagnets 16. Lifter 36, thanks to levers 39, 40, raises tray 20 causing it to pass through matrix 24 thereby stretching and wrapping the film over the article. The longitudinal pressers are released and side folders 29 are closed. Thereafter the folders are opened so that the partially packaged tray can be extracted at the beginning of the next cycle after completing the wrapping and the sealing of the. folded edges.
The forward edge is folded when the tray, at the beginning of the next machine cycle, is advanced by dragger 34 (controlled by cam 5 through suitable reducing gear) toward sealing plate 44.
Rear folder 48 carries out the last folding before the package moves to the sealing plate where the folded film portions are heat sealed. As,.for the preceding operation again reference is made to the already mentioned U.S. Patent No.3,662,513.
The main difficulty in realizing a fully automatized machine for unrolling, cutting and positioning the plastic film in accordance with the tray size preset by the operator resided in measuring and checking the extract length of the unrolled and cut film with the prefixed data and getting the cut portion advanced of the precise distance to overlay the tray, or better, matrix 24.
All these elements are variable with the tray size and it would require too much complexity to carry out the operations under mechanical control. As an example of the above complexity one can consider that the machine of the invention is carried out, in a preferred embodiment, with seven possible selecting positions corresponding to as many sizes for the trays containing the products. The problem was solved by using an electronic control unit for handling and controlling the different operations. More precisely, said unit employs a programmed microcomputer for controlling both the operations common to each tray size and the ones depending upon the particular size. Usually the program is stored in a programmable memory that is written at the factory. Thus the'packaging operations are unified and the data variability is converted into a time variability of the electric control signals. Otherwise stated, the microcomputer produces timing signals for the different operations that are time offset according to the sizes of the trays. The resulting machine is highly flexible since any modification will effect only the programming of the microcomputer and this latter is easy to be changed by altering or replacing the stored program. Moreover the machine is relatively inexpensive since the working follows a standard cycle and the mechanical controls are kept to a minimum so as to obtain a simple and reliable machine.
With reference to Fig. 4 the sequence of the operations is now graphically illustrated. The microcomputer initially checks whether the switch associated with cam 5 is correctly positioned. In the negative the beginning of the operation is delayed until the cam reaches the angular position of the switch.
Thereafter the lifting device begins to lower the plate and unrolling goes on until identity is detected between the length of the unrolled film and the value preset by the operator. Upon detecting such identity the drawing mechanism and the lifting device are stopped. The film is cut, the unrolling Mechanism is started again and the brake released.
For anyone of the selections preset by the operator,a sequence subtantially similar is carried out, but with a different timing. At the end of the sequence that is controlled by a subroutine of the nicrocomputer, the lifting' device begins to raise the plate with the tray received from the feeding conveyor .25, the drawing mechanism is stopped, being now ready for the next cycle, the longitudinal pressers are closed so as to'stretch the film and after their reopening, the folding arms are activated. When cam 5 completes the rotation, the lifting device is stopped, the forward folder and the brake are released. Thus a cycle is over and another one will begin in case a further tray has been placed meanwhile over switch 54. The new cycle will begin by folding the forward and rear edges of the previous ly enveloped tray and forwarding the same to the sealing station. At the same time the film drawing and tray feeding operations will resume.
If the packaged tray is the last one of a series it will be necessary a dry cycle for having it expelled from the machine. The average time for executing a cycle, i.e. the time required to package a tray is about 5 sec. and the time relationship of the events is shown in Fig. 4. Diagram LF relates to the lifting whereas diagram FD shows the movements of the folders. Diagram RL relating to the unrolling is formed by a plurality of portions, each relating to a prefixed length of film to be cut and the same is true for diagram .CT showing that the .cut can occurs at different times. Moreover there are shown diagrams relating to the rear and front folding arms, .PZP and PZA, respectively, as well as the ones of the feeding, AL, and dragging, DR.
For sake of simplicity there were not considered the delays required for the proper and tuned working.
More particularly said delays are important in order to precisely control the film advancing before and after the cut so as to position the film exactly over the tray.
Fig. 5 is a block diagram of the control unit of the machine, comprising a clock source CK including a quartz oscillator having a frequency of 2MHz, an 8 bit microprocessor µP of general type that is able to execute an iterative aritmentic-logic program with sufficient speed, and a read only memory RM having a storage capacity of 1 Kbyte (i.e. 1024 words or characters each formed by 8 bits).
Connections between the microprocessor and the memory are carried out through a buffer unit BF1 and an 8 bit decoder-de multiplexer DD as well as through a transceiver TR1. Output signals to the actuating circuits comprise electronic pulses that are present on different leads according to timing sequences that depend upon the operation to be carried out. Such output signals, processed by the microcomputer, are transmitted to the actuating circuits through distributor D, a holding circuit or memory LT and a buffer unit BF3.
Input signals to the control unit, formed by the signals preset by the operator and by the ones received from the machine sensors, are applied to the memory and the microcomputer through buffer unit BF2 and transceiver TR2. The actuating circuitry, not shown, includes a plurality of electromagnets connected between the output of the control unit and a low voltage power supply so as to allow current flowing through those electromagnets coils having a logical 0 on their terminal.
The embodiment of the control unit that employs a microcomputer is not to be considered limiting since the control unit can be realized by means of different electric circuits, in case a cabled logic in view of the reduced amount of processing, or by means of other and simpler microcomputers. Although the invention has been illustrated with reference to a precise packaging machine and a well defined process, it is not to be limited to the described embodiments but extends to all the obvious changes and modifications that will be evident to the skilled in thp art.

Claims

1. A machine for packaging articles of products by wrapping a plastic film around the products, particularly products placed in trays having different sizes, comprising:

- means for feeding a length of film (18) unrolling from one of a plurality of rolls (11, 12, 41, 42) to an operative location or wrapping station of the machine, said means including a plurality of elastic endless cords (8, 9) positioned at both sides of the film length and moving along closed loops around sheaves (21, 22, 23), said feeding means being actuated on each operation cycle under control of a control unit, a first time for a time interval that is proportional to the width of the tray (20) to be wrapped, after which the film is cut and successively said feeding means are actuated for a time interval long enough to have the plastic sheet centered over the tray, said time intervals being dependent upon the value preset by the operator for the width of the tray;

- means for sequentially conveying the trays (20) containing the article from an entry position to a position laying under said operative position;

- lifting means .(36) for raising each tray and means for stretching and wrapping said length of film around the tray to form the package;

- means for extracting the packaged article from the machine;

- an electronic control unit controlling the unwinding and cutting of prefixed lengths of the plastic film as well as their positioning and centering over the tray according to the values preset by the operator for the width of a tray:

2. A machine as claimed in claim 1, characterized in that the control unit includes a microcomputer programmed to timely control the operations according to the values of the width for the trays preset by the operator, said microcomputer executing a cycle having an initial portion and a final portion that are the same for each size of the tray to be wrapped, and a central portion depending upon the size of the tray, said central portion relating to the unrolling, cutting and positioning the plastic film.

. 3. A machine as claimed in claim 2, characterized in that said control unit generates signals in form of timed electric pulses having a variable width on a plurality of leads connected to the actuating devices through a power circuit comprising a d.c. power supply for'feeding the excitation coils of a corresponding plurality of relais, each of said relais coils having a terminal connected to said power supply voltage and the second terminal to one of the control leads so as to be energized when the logic level of the voltage on the control lead is zero.

4. A machine as claimed in claim 3, characterized in that the sheaves of the conveying plastic cords are axially displaceable so as to fit the different widths of the unrolling plastic sheet.

5. A machine as claimed in claim 4, characterized in that it comprises an extracting or dragger mechanism built up by a raised conveyor having a moving endless belt covered by an elastic spongy material to drag the packagings out of the wrapping station by friction engaging the packages.

6. A machine as claimed in claims 4 or 5, characterized in that the supply rolls of the plastic material to be wrapped are at least two, symmetrically placed on both sides of the machine, and that the feeding means of the film are movable in both directions.

7. A machine as claimed in claim 6, characterized in that a cam driven by the main motor controls the lifting of the tray, through a system of levers and articulated joints, the folding of the edges, the advancing of the tray along the feeding means and the engagement of the packaged'tray with the extracting means.

8. A machine as claimed in claim 7, characterized in that it provides side and longitudinal pressers to fasten the sheet of plastic material to be wrapped against the lower surface of a supporting plate having an opening to allow the passage of the trays to be enveloped.

9. A process for wrapping araund products a stretchable film of plastic material unrolling from a roll, particularly products placed in trays having different sizes, preliminarily setting the values relating to a series of tray to be wrapped, said process comprising the steps of:

a) completing the. folding of the film edges around an enveloped tray, extracting the same and sealing together the folded edges, and supplying another tray to a lifting station;

b) unrolling and advancing a portion of film having a length suitable for the predetermined sizes of the tray, said advancing being transverse with respect to the tray;

c) cutting the film portion corresponding to such advancing;

d) unrolling a second length of film in order to prepare the machine for the next wrapping operation;

e) advancing the cut length of film over the tray until it is centered over the tray;

.f) lifting the tray to a point higher than the film, the cut sheet being kept fast at least on its side edges;'

g) releasing the side edges and folding them under the tray.