Machine and method for producing bags

Abstract

A machine for producing bags includes a station for forming a tube, which forms a band of transversely perforated flexible material into a tube, a holding station for retaining the tube, a folding station for forming a bottom at the end of the tube, a folding roller having a folding blade for folding a flap at the end of the tube and a tear-off bar for pinching the tube against the drum, the folding station and the holding station being configured to jointly exert a traction on the tube and detach a portion of the tube. The tear-off bar is disposed behind the folding blade, the machine controlling the rotation of the folding station to synchronize the drum with the front of the tube.

Claims

1. A machine for producing bags, comprising: a station for forming a tubular body from a band of flexible material that is transversely perforated at intervals; a holding station for retaining the tubular body; a folding station for forming a bottom at an end of the tubular body, the folding station comprising: a drum rotating about a first axis; and a folding roller mounted to rotate about a second axis that is parallel to the first axis, the folding roller comprising a folding blade that folds a flap at the end of the tubular body in co-operation with a clamp at a periphery of the drum to form the bottom; a tear-off bar that clamps the tubular body against the drum, wherein the folding station and the holding station are configured jointly to exert traction on the tubular body when perforations of the band of flexible material are between the folding station and the holding station and to detach a portion of the tubular body, wherein the tear-off bar is arranged to separate the tubular body when the bottom of the tubular body has already been formed; the machine further comprising a controller that controls rotation of the drum to synchronize the drum with a front of the tubular body.

2. The machine according to claim 1, wherein the drum and the folding roller are mechanically synchronized.

3. The machine according to claim 1, wherein rotation of the drum and rotation of the folding roller are controlled separately.

4. The machine according to claim 1, wherein the tear-off bar is carried by the folding roller.

5. The machine according to claim 1, wherein the tear-off bar comprises a tear-off roller carrying the tear-off bar.

6. The machine according to claim 1, further comprising a perforation station to perforate transversally the band of flexible material.

7. The machine according to claim 6, wherein the perforation station is controlled to perforate the band of flexible material at a chosen location.

8. The machine according to claim 1, wherein the controller controls the holding station.

9. The machine according to claim 1, wherein the drum comprises two clamps arranged on a periphery to grasp the front of the tubular body.

10. The machine according to claim 1, wherein the folding blade is cyclically retractable.

11. A method of producing bags comprising: transversely perforating a band of flexible material at intervals; forming, at a folding station, a bottom at an end of the tubular body, the folding station comprising: a drum mounted to rotate about a first axis; and a folding roller mounted to rotate about a second axis that is parallel to the first axis; the bottom being formed by folding a flap at the end of the tubular body by a folding blade carried by the folding roller in co-operation with a clamp at a periphery of the drum; detaching a portion of the tubular body by clamping the tubular body against the drum with a tear-off bar; retaining, in a holding station, the tubular body by exerting traction on the tubular body when perforations of the band of flexible material are between the folding station and the holding station; wherein the portion of tubular body is detached after the formation of the bottom and rotation of the drum is controlled to synchronize the drum with a front of the tubular body.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be better understood and other particular features and advantages will become apparent on reading the following description which refers to the appended drawings, in which:

(2) FIG. 1 shows schematically a machine in accordance with first and second embodiments of the invention;

(3) FIGS. 2 to 4 show schematically various steps executed by the machine from FIG. 1;

(4) FIG. 5 is a view similar to FIG. 1 of a machine according to a third embodiment of the invention;

(5) FIG. 6 is a view similar to FIG. 1 of a machine according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

(6) According to one embodiment shown in FIG. 1 a machine for producing bags includes an unwinding station, not shown, for unwinding a band 2 of flexible material and then, in the direction of unwinding of the band 2 indicated by the arrow F1, a perforation station 3 for perforating the band 2 of flexible material transversely at regular or irregular intervals, a station 4 for forming a tubular body 2a for forming the band 2 into a tubular body 2a, a driving station 5, a holding station 6 for retaining the tubular body 2a, and a folding station 7 for forming a bottom 20 at the end of the tubular body 2a. The machine further includes transport means, not shown, disposed between the various stations to guide and to transport the tubular body 2a between the stations and the bags formed after folding.

(7) The perforation station 3 includes in the conventional manner a blade-holder roller 31 and a counter-roller 32 mounted to rotate about parallel axes. The blade-holder roller 31 includes blades 310 extending along generatrices to perforate the band 2 by clamping it against the counter-roller 32 and forming transverse perforation lines 22a, 22b.

(8) The station 4 for forming the tubular body 2a conforms the perforated band 2 into the tubular body 2a in the conventional manner, not described in detail here. It will be noted that the perforations form two offsets transverse lines 22a, 22b on respective opposite faces of the tubular body 2a.

(9) The drive station 5 includes two drive rollers 51 between which the tubular body 2a is pinched to be driven at a stable speed that determines the speed of movement of the tubular body 2a in the direction of the arrow F1.

(10) The holding station 6 includes two contra rotating holding cylinders 61, 62, the upper holding cylinder 61 including one or two holding bars 610 extending along a generatrix. The holding bars 610 come into contact with the lower holding cylinder 62 once or twice per revolution to clamp the tubular body 2a that is moving between the holding cylinders 61, 62. The speed of the holding cylinders 61, 62 is adjusted so the peripheral speed at the level of the holding bars 610 is less than or equal to the speed of movement of the tubular body 2a, at least at the time of clamping.

(11) The folding station 7 includes a drum 71 and a folding roller 72 mounted to rotate about parallel axes. The folding roller 72 includes a folding blade 720 to fold a flap 21 at the end of the tubular body 2a, a gluing bar 721 for applying glue to the tubular body 2a and a tear-off bar 722 for clamping the tubular body 2a against the drum 71. The drum 71 includes two clamps 710 distributed on the periphery to grasp the front of the tubular body 2a.

(12) The folding station 7 and the holding station 6 are configured jointly to exert traction on the tubular body 2a when the perforations are between the two stations 6, 7 and thus to detach a portion of the tubular body 2a. The tear-off bar 722 is disposed behind the folding blade 720, i.e. it intervenes to clamp the tubular body 2a when the end of the tubular body 2a is being folded or has already been folded.

(13) In a first embodiment the drum 71 and the folding roller 72 contra rotate and are synchronized mechanically. The machine further includes control means, not shown, for controlling the rotation of the folding station 7 to synchronize the drum 71 with the front of the tubular body 2a. The control means take the form of a synchronous motor for example, also termed a brushless motor, an electronic converter supplying power to the motor and an automatic control unit executing a program for controlling the various parts of the machine, including the converter.

(14) The method employed by the machine will now be described starting from an arbitrary position, knowing that each position also returns on the next cycle. The method comprises a succession of cycles, a bag being produced by each cycle.

(15) The band 2 of material is unwound by the unwinding station 1, perforated by the perforation station 3 and then formed into the tubular body 2a that is pulled by the drive station 5 in the conventional manner, not described in detail here. The tubular body 2a passes between the cylinders of the holding station 6 and then between the drum 71 and the folding roller 72. When the front of the tubular body 2a arrives between the drum 71 and the folding roller 72 and the peripheral speed thereof is the same as the speed of movement of the tubular body 2a the folding blade 720 pushes the tubular body 2a into the clamp to imprint a fold, as FIG. 2 shows. The clamp closes onto the fold so a flap 21 projects substantially radially from the drum 71. The gluing bar 721 deposits glue just behind the fold to form a glued area 23 shown in FIG. 2. The movement continuing, the flap 21 is pressed against the glued area 23 by means not shown and thus retained. The bottom 20 of the bag is then formed, as FIG. 3 shows. The tear-off bar 722 then comes into contact with the drum 71 to clamp the tubular body 2a when the perforations have passed through the holding station 6 and the retaining bars 610 also come into contact. The tubular body 2a is then tensioned to separate it from a length that is already formed into a bag 2b, as FIG. 4 shows. The clamp 710 releases the bag before or after the separation of the length, which is then evacuated in the conventional manner. The control means then command an acceleration and then a slowing down of the folding station 7, or vice versa, to move the next clamp 710 into synchronization with the front of the tubular body 2a to start a new cycle.

(16) Thus the only adjustment to be effected to change the bag length is intervention at the level of the perforation station 3 to modify the distance between the lines of perforations and the programming of the control means.

(17) The operation of separating the length 2b necessitates a speed difference between the drum 71, which must turn faster, and the holding station 6. This difference can be obtained if the drum 71 has released the bag and has begun to accelerate before the separation operation. In the opposite case, in particular when the bag is short and must be separated when the drum has not released the front of the tubular body, the holding station 6 must slow down the tubular body 2a for a short time during the separation operation.

(18) In a second embodiment, not specifically shown, the rotation of the drum 71 and the rotation of the folding roller 72 are controlled separately. This is achieved for example by giving the folding roller 72 its own motor, also controlled by the control means. The machine therefore has a greater adjustment possibility. Indeed, the folding roller 72 can be controlled so it intervenes only during the passage of one clamp 710 in two or three. It is thus possible to produce bags longer than the developed drum 71 between two successive clamps 710 with no limit on the length. It is moreover possible to await the appropriate time for the tear-off bar 722 to come into contact with the drum 71 so the perforations are between the holding station 6 and the folding station 7. The speed of the holding station 6 is adjusted so one revolution corresponds to the length of a bag.

(19) According to an improvement, the control means control the perforation station 3 to perforate the band 2 at a chosen location. Accordingly, even the adjustment of the distance between the perforations, determining the length of the bags, can be adjusted in a controlled manner.

(20) According to another improvement, the control means control the holding station 6. Thus even the holding frequency of the tubular body 2a and the peripheral speed at the holding station during the tear-off phase can be adjusted in a controlled manner with no necessity for mechanical intervention.

(21) In a third embodiment shown in FIG. 5 the folding station 7 differs from that of the first embodiment in that it further includes a tear-off roller 73 carrying the tear-off bar 732. The folding roller 72 therefore no longer includes a tear-off bar. The tear-off roller 73 is mounted to rotate on a shaft offset in the upstream direction relative to the folding roller 72. The tear-off roller 73 is also controlled by the control means independently of the folding roller 72 to clamp the tubular body 2a onto the drum 71 at the appropriate moment and to separate the tubular body by cooperation with the holding station 6.

(22) A fourth embodiment of the invention shown in FIG. 6 differs from the third embodiment in that the tear-off roller 73 is positioned downstream of the folding roller 72 in the same folding station 7. The tear-off roller 73 carrying the tear-off bar 731 is also controlled by the control means independently of the folding roller 72 to clamp the tubular body 2a onto the drum 71 at the appropriate moment, after the production of the bottom, and to separate the tubular body by cooperation with the holding station 6. Separation can thus be effected when the separation line is very close to the folding holder 72.

(23) In each embodiment the rollers are controlled to obtain the required speed during the working phases and thus at a very accurate time. This is obtained for example by increasing and then reducing the rotation speed if it is necessary to catch up a delay or to the contrary by reducing and then increasing the rotation speed, or even stopping the roller if necessary. It is even possible to reverse the rotation direction to provide an acceleration travel sufficient to reach the appropriate speed.

(24) The invention is not limited to the embodiments that have just been described by way of example. The drum can include only one clamp, or even three or four. Although the drum 71 is shown as larger than the folding roller, the latter could have an equivalent diameter, or even a smaller diameter, in particular if it carries only one clamp 710. The distance between the perforations need not be regular, to produce successions of bags of different lengths, the machine being capable of adapting to each bag length with no other adjustment.