ES2761002T3 - Device and method for changing from continuous to intermittent the forward movement of a film inside a machine for the production of bags for flexible packaging - Google Patents

Abstract

Device (100) capable of changing the forward movement of a film (12) into a machine (10) continuously or intermittently to produce bags (1) for packaging and the like, comprising at least one cylinder (20 ) squeegee mounted movably back and forth between a feed calender (21) that operates in continuous mode and a transport calender (22) that operates in intermittent mode, the squeegee cylinder (20) moving towards the calender (22 ) transport when the latter is working, in order to feed the film (12) and moving in the opposite direction when the transport calender (22) stops in order to recover the input film that comes from the calender ( 21), characterized in that a servomotor (50) is provided for the movement of said squeegee cylinder (20), and that at least one load cell (55) is provided along the path of the film (1 2) suitable for continuously monitoring the voltage applied to the film (12) and for instantly changing the motor torque applied to the servomotor (50).

Description

DESCRIPTION

Device and method for changing from continuous to intermittent the forward movement of a film inside a machine for the production of bags for flexible packaging

Description

The object of the present invention is a device and a relative method to change from forward to intermittent the forward movement of a film inside a machine to produce bags for flexible packaging, to contain food products for human beings, feed, etc. JPH08217020 discloses a supply system for a packaging film with an oscillating device driven by a servo motor.

More particularly, the bags in question are obtained from laminated and bonded films, for example of polyester-aluminum-polyethylene, which are suitably shaped by means of longitudinal folding, formation of lateral reinforcements, longitudinal and transverse welds, folding of the base etc.

The formation of these pockets requires the welds to be repeated several times to use temperatures that do not degrade the used film. The welds then have to be cooled by cooling bars. This aspect, together with multiple other procedures that have to be performed on the bags (45 ° welds to form the square base, longitudinal welds, marking, perforations, punching for rounded corners, etc.) means that a production line can reach lengths considerable, even above 25 meters.

These lines are made up of a first part in which the material to be processed is continuously fed through cylinder uncoilers and drives that allow some operations to be carried out that necessarily have to be carried out with the film in continuous movement, such as such as longitudinal folding and reinforcement formation.

Subsequent operations, such as welding, punching, marking, etc. instead they have to be performed with the film moving intermittently (start and stop), that is, the forward movement of the film and its stop in order to carry out the aforementioned operations.

In order to switch motion from continuous to intermittent, the following are used in sequence: one pair of motorized rollers (feed calender) operating in continuous mode, one or more offset wringer cylinders, one or more pairs of motorized rollers (transport calenders) with intermittent movement. The function of the wringer cylinder is to transfer material during the forward movement phase of the film and to accumulate material when it arrives from the feed calender during the operating phases, in which the film remains still.

In order to keep the film fully taut during the different processing stages, there are normally two or more transport calendars in sequence, separated and interspersed with different adjustments that the machine is equipped with, placed after the wringer cylinder in order to interrupt the long section of the film, thus always keeping it in adequate tension.

In order to tension the material both during the forward movement and during the operations carried out on it, in particular welding, pneumatic pistons are normally used that push the draining cylinder with a force proportional to the pressure of the air fed inside the the pistons themselves. However, this pressure does not remain constant: during the forward movement phase the air in the pistons compresses, while during the stop phase in which the draining cylinder has to recover the film when it arrives, the pressure tends to decrease. This is because the draining cylinder feed cannot quickly compensate for the rapid movements of the draining cylinder.

This variation in pressure causes a variation in the tension applied to the film at the outlet of the wringer cylinder. On machines of considerable length, where the procedures are performed in sequence, this variation in tension is detrimental in that micro-slip is created in the film transport calendars following the wringer cylinder.

This slip means that the sequential operations are not performed on the same film portion and therefore the operator has to correct this slip by moving the workstations in sequence in order to match the operations. During the machine start and stop phase, for product change, in which there is a variation in the forward movement speed of the material and therefore a variation in the error due to the variable slip, considerable product rejects are generated.

The object of the invention is to eliminate the disadvantages of the prior art illustrated above.

More particularly, an object of the present invention is to provide a device for changing from continuous to intermittent forward motion of a film into a machine for producing bags for flexible packaging, such as for foodstuffs for humans, feed , etc., which allows the tension in the film to remain constant, such as to have a possible constant slip of the film in the calendars, which does not need additional corrections after the initial configuration of the machine.

Another object of the invention is to provide such a device that is simple and inexpensive to produce, as well as highly reliable.

These objects are achieved by the device according to the invention having the characteristics of the attached independent claim 1.

Advantageous embodiments of the invention will be disclosed in the dependent claims.

Essentially, the device according to the invention, capable of changing from continuous to intermittent the forward movement of a film inside a machine for producing packaging bags and the like, comprises at least one draining cylinder movably mounted backwards and forwards between a feed calender operating in continuous mode and a transport calender operating in intermittent mode, the draining cylinder moving towards the transport calender when the latter is operated in order to feed the film and moving in the opposite direction when the transport calender is stopped in order to recover the inlet film coming from the supply calender, in which a servo motor is provided for the movement of said draining cylinder, and in which at least one load cell is provided to along the path of the film capable of continuously monitoring the voltage applied to the film and to instantly change the torque applied to the motor.

The load cell is used to have a “closed loop” control of the voltage, that is, with feedback. The motor that moves the draining cylinder will activate the appropriate correction, when receiving the information from a PID (proportional-integral-derivative) controller.

Additional features of the invention will be elucidated by the following detailed description, with reference to one of its embodiments merely by way of a non-limiting example, illustrated in the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a possible bag that can be manufactured with a machine that incorporates the device according to the invention;

Figures 2a and 2b are respectively a side view and a top plan view of a complete line for the production of these types of bags;

Figure 3 is a schematic view taken from the opposite side with respect to Figure 2a, showing the device according to the invention for changing from forward to intermittent the forward movement of the film; Figure 4 is a top plan view of the device of Figure 3;

Figure 5 is a sectional view taken along the plane V-V of Figure 4;

In figure 1 a bag or sack 1 has been shown by way of example, suitable for containing foodstuffs for human beings, feed or other products, obtained from a laminated material composed for example of polyester-aluminum-polyethylene.

Bag1 has a folded base 2, an open mouth 3 and a pair of side gussets 4.

It is obtained from a laminated material in the form of a tape, which is initially folded longitudinally on itself, then the lateral parts are folded inwards in order to create the reinforcements 4, followed by longitudinal welds along the four flanges 5, one of which serves to close the film in a tubular conformation, while the others serve to increase the sealing of the bag. Then a transverse weld 6 is formed in order to close the base 2 of the bag which can also be folded 180 ° on itself and glued.

If necessary, welds 7 to 45 ° can also be provided to determine a so-called square base. Naturally, the type of bag illustrated in FIG. 1 is merely an example, the device according to the invention being able to be used on any bag production line where it is envisaged to change the film feed from continuous to intermittent.

Figures 2a and 2b schematically illustrate a line or machine, designated generally by the number of reference 10, used for example for the production of the bag shown in figure 1.

A laminated film 12 is unwound from a roll 11 and caused to move forward continuously through a succession of stations SC ¹ ... SC ⁿ , and intermittently through a succession of stations SI ¹ YES ⁿ .

The device 100 according to the invention is placed between the stations SC and SI, which allows a continuous forward movement of the film tape 12 to be changed to an intermittent forward movement. In stations SC ¹ ... SC ⁿ , in which the film moves continuously, operations such as longitudinal folding and formation of the lateral reinforcements 4 are carried out, while in stations SI ¹ ... SI ⁿ where the film is moved forward intermittently all other operations where the film is required to stand still, such as longitudinal trimming and welds, possible 45 ° welds, multi-stage cross welding, stamping, are performed. cross section etc.

A description is now given of the device 100 according to the invention that allows the change from continuous to intermittent of the forward movement of the film 12 with reference to Figures 3 to 5, in which Figure 3 is a view taken from the opposite side with respect to figure 2a, which is with forward movement of the film from right to left.

Device 100 comprises a wringer cylinder 20, located between a film feed calender 21 and a transport calender 22, and moves forward and backward, as indicated by the arrows in Figure 3, synchronized with operations carried out at downstream stations YES ¹ ... YES ⁿ . During the forward movement phase of the film 12 the cylinder 20 moves forward, producing material, while during the film stopping phase it moves in the opposite direction, recovering the input material. The speed with which the cylinder 20 moves is the resulting one, that is to say the difference between the speed of the transport calender 22 and that of the supply calender 21. Naturally, the transport calender 22 is driven at a higher speed than the supply calender 21, which has to recover the film that has remained upstream during the stop phase.

The feed calender 21 comprises a motorized roller 23, driven by a motor 25, and a counter roller 24.

Similarly, the transport calender 22 comprises a motorized roller 26 and a counter-roller 27.

The film 12 at the outlet of the feed calender 21 traverses a plurality of idlers 30, 31, 32, 33 before rotating around the wringer cylinder 20 and going to the transport calender 22.

The ends of the shaft 40 of the draining cylinder 20 are mounted on respective shoes 41 that slide on linear guides 42.

The shoes 41 are retained by means of respective L-shaped supports 43 (Figure 5) to a pair of toothed belts 44 each wound around a respective pair of pulleys 45, 46.

One of the two pulleys, in the example the pulley 45 is shown placed on one of the sides of the machine, it is driven by a servomotor 50 by means of a belt 47, and it is connected to the pulley 45 located on the other side of the machine by means of a shaft 48, so that the torque of the servomotor 50 is transmitted simultaneously to both side belts 44.

The maximum stroke of the draining cylinder 20 is determined by two limit stops 51, 52 located in each linear guide 42.

Figure 3 shows respectively by solid lines and dotted lines two possible positions taken by the wringer cylinder 20, respectively during the film recovery phase at the entrance and production of the film to the downstream stations.

The motor 50 driving the wringer cylinder 20 supplies a torque proportional to the current supplied thereto, and therefore a force will be applied to the film drive wringer cylinder 20 proportional to the motor torque.

At least one load cell is provided along the section of the film 12, in particular in the illustrated embodiment two load cells 55 are provided on the axis of the idler roller 33 located immediately upstream of the wringer cylinder 20 in order to continuously monitor the voltage applied to the film 12 being processed and to perform a "closed loop" control with a PID (proportional-integral-derivative) regulator.

The load cell can also be installed in the draining cylinder 20 or in other successive cylinders.

Based on the voltage detected by the load cells 55, a control system, not shown, which is to be considered known in itself, instantaneously changes the torque applied to the motor 50, and therefore the movement of the system in order to maintaining a constant tension in the film 12. When the tension decreases, more torque is supplied, while when the tension increases, less torque is supplied.

In this way, thanks to the used motor drive, it is possible to intervene instantaneously in the draining cylinder 20, avoiding successive adjustments of the different stations of the machine in order to compensate for the slippage of the film after the adjustment of the machine.

From what is disclosed, the advantages of the invention seem clear.

Naturally, the invention is not limited to the particular embodiment previously described and illustrated in the accompanying drawings, but numerous changes of detail may be made therein, within the scope of one skilled in the art, without thereby departing from the scope of the Invention as defined by the appended claims.

Claims (9)

i. Device (100) capable of changing the forward movement of a film (12) inside a machine (10) continuously to intermittently to produce bags (1) for packaging and the like, comprising at least one cylinder (20 ) drainer mounted movably back and forth between a feed calender (21) operating in continuous mode and a transport calender (22) operating in intermittent mode, the wringer cylinder (20) moving towards the calender (22 ) of transport when the latter is operated, in order to feed the film (12) and moving in the opposite direction when the transport calender (22) stops in order to recover the input film that comes from the calender ( 21), characterized in that a servo motor (50) is provided for the movement of said draining cylinder (20), and in that at least one load cell (55) is provided along the path of the film (1 2) suitable for continuously monitoring the tension applied to the film (12) and for instantly changing the motor torque applied to the servomotor (50). Device according to claim 1, characterized in that a PID regulator for closed loop control is provided in combination with said at least one load cell. Device according to claim 1 or 2, characterized in that said at least one load cell (55) is placed on an idler roller (33) for guiding the film (12) located immediately upstream of the wringer cylinder (20) or on another roll. Device according to claim 1, 2 or 3, characterized in that said draining cylinder (20) is mounted on a pair of lateral shoes (41) that slide in respective linear guides (42), said shoes (41) being actuated by means of belts ( 44) respective serrations actuated by said servomotor (50). Device according to claim 4, in which said toothed belts (44) run around respective pairs of pulleys (45, 46), one of these pulleys (45) being driven by the servomotor (50) by means of a belt ( 47) and connecting by means of a shaft (48) to the opposite pulley (45). Device according to claim 4 or 5, characterized in that two limit stops (51,52) are arranged in said linear guides (42), apt to limit the maximum stroke of the draining cylinder (20). Device according to any one of the preceding claims, wherein said feed calender (21) and transport calender (22) comprise a respective motorized roller (21), (26) and a counter-roller (24), (27) respective. 8. Method for changing from continuous to intermittent the forward movement of a film (12) inside a machine (10) to produce bags (1) for flexible packaging, characterized by using the device according to claim 1, wherein the film (12) exiting a continuously operating feed calender (21) is passed over a plurality of idler rollers (31, 32, 33) having a fixed axis and onto a movable wringer cylinder (20) back and forth towards an intermittently operating transport calender (22), where it provides continuous monitoring of the tension applied to the film (12) by means of at least one load cell (55) provided throughout of the film path (12) with instantaneous variation of the motor torque applied to a servomotor (50) for the movement of said draining cylinder (20). 9. Machine (10) for the production of bags (1) for flexible packaging from a laminated film (12), comprising a plurality of stations SC1 ... SCn capable of performing operations on the film with continuous forward movement and a plurality of stations SI1 ... .SIn capable of performing operations on the film with intermittent forward movement, characterized in that a device (100) according to any one of claims 1 to 7 is provided between said stations SC1 ... SCn and said stations SI1 ... SL to transform the forward movement of the film (12) continuously to intermittently.