System for vacuum-refeeding sheets, in particular corrugated board sheets, to be used in printing and die cutting machines

Abstract: There is disclosed a system (11) for vacuum-refeeding sheets in printing and die cutting machines, comprising a plurality of boxes with fans, located above a conveying line composed of: sheet-dragging knurled rollers (39,41,43,45); a covering plate (49) for the initial section, with slits for the knurled rollers and rows of small holes (51) to make air pass; a central conveying line (53) and at least two side lines (55,57), composed of a plurality of idle guide rollers, single (55) or in groups of three (59,61,63), and of small, longitudinal sheet-guiding plates (65) between idle rollers; and timing belts (25) between idle roller lines (53,55,57) including on the external surface thereof small sheet-dragging blocks (67), with such pitch and speed as to adjust the phase of the outgoing sheets to the position of die cutting cylinder (27) downstream without interference with the rear side of the sheets.

Description: The present invention refers to a system for vacuum-refeeding sheets, in particular corrugated board sheets, to be used for example in printing and die cutting machines for the sheets themselves, in order to prepare packaging boxes. Systems of this type and according to the preamble of claim 1 are known from a brochure of the Company Martin S.A., in which there is disclosed a sheet-transporting device, that connects the printing station to the die cutting one in a rotary printing machine: this device allows vacuum-conveying sheets, in particular corrugated board sheets and similar ones, by applying an upward-directed suction force generated by a fan placed inside an upper hood: an horizontal sheet displacement is therefore obtained, where the sheets are grasped by two rubber rollers and then pass, pushed by two belts with small blocks, on idle rollers in contact with the upper face thereof, without having to make these sheets pass on cylindric rollers that will make the lower face thereof dirty as soon as it has been printed by the upstream printing station. The above-described device has the problem that it is necessary to have sheets available whose width is greater than the distance between the two belts, so that these latter ones can push them through their small blocks; therefore, the belts must be transversally adjusted at every work-change, with obvious operating problems; furthermore, the belts reduce the available space under the sheets, occupied in this case by a small-sized drying machine, that thereby guarantees a less effective drying operation. Purpose of the present invention is providing a system for vacuum-conveying sheets in general, and corrugated board sheets in particular, that can be easily manufactured and is immediately effective, even for long sheet displacement distances; this system allows conveying sheets provided with any thickness and any size greater than the minimum overall one pertaining to the machine, and, after printing thereof, it allows realigning them and suiting the speed thereof to the one of the following working unit, in which these sheets will be die cut. The above and other purposes and advantages of the invention, which will be apparent from the following description, are obtained with a system for vacuum-refeeding sheets having the features of Claim 1. The present invention will be better described by some preferred embodiments, with reference to the enclosed drawings, in which: Figure 1 is a side view of a printing and die cutting line for cardboard sheets including an embodiment of the sheet-refeeding system of the present invention; Figure 2 is a bottom view of an embodiment of the sheet-refeeding system of the present invention; Figure 3 is a cross view, partially in section, of the sheet-refeeding system in Fig. 2; and Figure 4 is a side view of the sheet-refeeding system in Fig. 2. Before beginning the description of the preferred embodiment of the invention, it is necessary to point out that this can be applied to any sheet-production line in which a conveyance is needed that does not make use of the lower face of the interested sheets: the preferred embodiment deals with corrugated board sheets in a rotary printing line, but the invention could be applied, for example, to lines to convey various types of wooden sheets. The rotary printing line, in the parts thereof dealing with the present invention, is schematically shown in Fig. 1. In this Figure, sheets are traveling along a direction represented by arrow A and are entering a printing unit 1, wherein there are substantially a printing roller 3, a pressure cylinder 4 and a pair of outlet rollers 5 and 7. The outlet roller 5 speed is synchronized with the first knurled roller 39 that is already part of the sheet-refeeding system 11 of the invention, which will be described in detail below. After having entered the refeeding system 11 and having been conveyed by it, the sheets enter the die cutting unit 13 through two inlet rollers 15, that are actuated by a d.c. motor 17 through adequate kinematic devices 19, 21 and 23: the rotating speed of the inlet rollers 15 is the same as the outlet speed of the sheets from the printing unit 1, and is slightly greater than that of the refeeding system 11, because the d.c. motor 17 also controls rotation of the toothed timing belts 25 of the system 11, which will be described afterwards. The sheets then pass below the die cutter-holding cylinder 27 and are cut and then further conveyed by known devices for the following workings. In the lower part of the refeeding system 11 in Fig. 1, a sheet-drying machine (not shown) is provided to be installed, that, given the wider space available provided by the novel arrangement of the timing belts 25 dragging the sheets, guarantees a more complete and effective drying. With reference to Fig. 2 to 4, the novel part of the printing and die cutting machine for corrugated board sheets shown in Fig. 1 will now be described. This novel part is composed of the system 11 for vacuum-refeeding sheets on a conveying line, system that first of all includes a support and upper closure structure 29 shaped as a hood; a central box 31 located on the upper side of the support structure 29 and that communicates therewith on the lower side thereof, that is open towards this structure 29; and at least a pair of side boxes 33 and 35, each located on one of the central box 31 sides, along a transverse direction with respect to the sheet-traveling direction: the side boxes 33 and 35 are also located on the upper side of the support structure 29 and also communicate therewith on the open lower side thereof. In each one of the boxes, both the central one 31 and the side ones 33 and 35, a suction device (not shown) is placed, which is usually composed of a helical fan, whose speed can be fixed or variable according to the end user's needs. The suction device contained in the central box 31 is always operating and allows subjecting the sheets to an upward force starting from the minimum sizes that are a feature of the machine. On the contrary, the suction devices included in the side boxes 33 and 35 are usually at rest and are actuated only to transport bigger-sized sheets. Finally, in the lower part of the support structure 29 a sheet-conveying unit 37 is fixed, that is composed of a first sheet-dragging, motored knurled roller 39, located at the refeeding system 11 inlet immediately downstream of the outlet roller 5 of the sheet-printing unit 1. The first knurled roller 39 is the one performing the first sheet-grasping and traveling action and therefore has a length that is approximately equal to the transverse length of the whole sheet-conveying line. Immediately downstream of the first knurled roller 39, at least one second motored knurled roller is located (in the preferred embodiment described herein the rollers are at least three: 41, 43 and 45), also used to drag the sheets. In the preferred embodiment, since the side knurled rollers 41 and 45 only operate for quite large sheets, and since it is necessary to provide means to forward drag sheets on the line, the three second knurled rollers 41, 43 and 45 are of the same length, that is less than the length of the first roller 39 and that thereby allows inserting, between each pair of rollers 41 and 43, or 43 and 45, an idle pulley 47, whose use will be described below. The knurled rollers 41, 43 and 45 rotate with the same speed as that of the roller 39 due to the presence of an intermediate roller 46 (Fig. 1): they are conveyed by an external kinematic device (not shown) connected to the gears of the previous printing unit 1. The four knurled rollers 39, 41, 43 and 45 are the initial sheet-travel section, that is the one where the "vacuum" condition is created for an effective grasp and following conveyance of the sheet themselves. In order to generate such vacuum condition, a covering plate 49 is provided: it is equipped with a side slit through which the first knurled roller 39 projects in the lower part thereof and rotates; with at least three side slits in succession, through which the three second knurled rollers 41, 43 and 45 project in the lower part thereof and rotate; and with a plurality of rows of small circular holes 51 to make air, sucked by the upper helical fans, pass. As is apparent from Fig. 2, the rows of small holes are upstream, downstream and in the gap between the two rows of side slits. After having been taken and conveyed by the knurled rollers 39, 41, 43 and 45 at the same speed at which they had been printed, the sheets pass onto a central sheet-conveying line 53, composed of a plurality of idle guide rollers 55: this central line 53 is located below the central box 51 and is immediately downstream of the central knurled roller 43 of the second row of knurled rollers. On the central line 53 the central suction device is operating, that, though not vacuum-operating, generates a suction force that is enough to keep the sheets in contact with the line itself for the following conveyance. The central line 53 is the one being always active, as well as the upper helical fan, because the sheets always pass above it. There are also at least two side sheet-conveying lines 55 and 57, each one of which is composed of at least three small idle drive rollers 59, 61 and 63, coupled with a mutually independent rotation to reduce dragging inertia. In the two gaps between the three small rollers 59, 61 and 63 there are two small sheet-driving plates 65, that operate according to the width of the sheets to be conveyed, to prevent suction of sheets into the gaps between the small drive rollers 59, 61 and 63. In fact, the side lines 55 and 57 are not always operating, and, when they do, all three small rollers 59, 61 and 63, of which they are composed, are not always rotating. Each one of the side lines 55 and 57 is located below one of the side boxes 33 and 35 and is immediately downstream of the side knurled rollers 41 and 45. To guarantee a forward-dragging of the sheets and to be able to adjust the traveling speed to the speed of the downstream die cutting unit 13, at least two toothed timing belts 25 are provided, each respectively placed between the central line 53 and one of the side conveying lines 55 and 57. These timing belts 25 include on the external surface thereof a plurality (in the preferred embodiment the small block are three) of small blocks 67 to drag the sheets, and each one of them is driven by a driving pulley 71 and by the idle pulley 47 already mentioned with reference to Fig. 1. The small blocks 67 operate on the sheets from above and, thanks to the arrangement of the belts 25 between the rows of rollers in lines 53, 55 and 57, their transverse adjustment is avoided, as happened instead for previously known machines. The driving pulley 71 is driven by the d.c. motor 17 through the already-described kinematic devices 19, 21 and 23 and therefore the outlet speed of the sheets is made equal to the speed of the inlet roller 15 for the die cutting unit 13 downstream of the refeeding system 11. Fig. 2 shows, as an example, a corrugated board sheet 69 pushed by the small blocks 67 and conveyed to the outlet of the refeeding system 11. A further feature of the invention is allowing to solve interference problems between small blocks 67 and sheets, Immediately before they enter the die cutting unit 13: here, in fact, the small blocks 67 could nick and warp the sheets. Therefore, it has been provided that the pitch between small blocks 67 is less than the development of the downstream die cutter-holding cylinder 27, and consequently the timing belts 25 move with a traveling speed that is less than the speed of the die cutter-holding cylinder 27 and thereby prevent such an interference.

Claims: System (11) for vacuum refeeding sheets, in particular corrugated board sheets, to be used in printing and die cutting machines, comprising: a support and upper closure structure (29) shaped as a hood; a central box (31) located on an upper side of said support structure (29) and communicating therewith on a lower side thereof, said box (31) including a suction device inside it; a sheet-conveying unit, fixed to the lower side of said support structure (29), said sheet-conveying unit comprising: a first, sheet-dragging motored knurled roller (39), located at an inlet of said refeeding system (11) immediately downstream of an outlet roller (5) of a sheet-printing unit (1); at least one sheet-conveying line (53), composed of a plurality of idle drive rollers (55), said line (53) being located below said central box (31); and at least a pair of timing belts (25), said timing belts (25) including on the external surface thereof a plurality of small blocks (67) to drag the sheets, each of said timing belts (25) being driven by a driving pulley (71) and an idle pulley (47) to adjust the outlet speed of the sheets to the speed of inlet rollers (15) of a die cutting unit (13) downstream of said refeeding system (11); characterized by: said sheet-conveying unit further comprising: at least one second, sheet-dragging motored knurled roller (41, 43, 45), placed immediately downstream of said first knurled roller (39); a covering plate (49) of an initial sheet-travel section, said covering plate (49) being equipped with at least two side slits through which said knurled rollers (39, 41, 43, 45) project in the lower part thereof and rotate, and with a plurality of rows of small holes (51), said rows of small holes (51) being upstream, downstream and inside said side slits; said at least one sheet-conveying line (53) being immediately downstream of said at least one second knurled roller (41, 43, 45); the timing belts (25) of said at least pair of timing belts (25) being located on each side of said conveying line (53); and said small blocks (67) operating on the sheets from above. System (11) for vacuum refeeding sheets according to Claim 1, characterized in that a pitch between said small blocks (67) is less than a development of the die cutter-holding cylinder (27) of the die cutting unit (13), said timing belts (25) moving with a traveling speed that is less than the speed of said die cutter-holding cylinder (27) to prevent interference between small blocks and sheets at said system (11) outlet. System (11) for vacuum refeeding sheets according to Claim 1 or 2, characterized in that said system (11) further comprises at least a pair of side boxes (33, 35) each one located on one of the sides of said central box (31) in a transverse direction with respect to the sheet-traveling direction and each including a suction device; three second, sheet-dragging motored knurled rollers (41, 43, 45), said three second knurled rollers (41, 43, 45) being all of the same length; and in that said conveying line (53) is composed of a central conveying line (53) and of a pair of side conveying lines (55, 57), each one of said side lines (55, 57) being composed of at least three small idle drive rollers (59, 61, 63) coupled with a mutually independent rotation and of at least a pair of small sheet-guiding plates (65), each one longitudinally inserted, respectively, between two of said small guiding rollers (59, 61, 63), said small plates (65) preventing suction of the sheets in gaps between said small guiding rollers (59, 61, 63). System (11) for vacuum refeeding sheets according to Claim 3, characterized in that said suction devices are composed of helical fans that generate a vacuum condition in an initial part of said sheet-conveying unit, where said knurled rollers (39, 41, 43, 45) are located, and instead create a constant suction force towards the sheets in the remaining part of said conveying unit.

Inventors: GAGGIO GIANFRANCO, GAGGIO, GIANFRANCO
Applicants: TEXO SRL, TEXO S.R.L.
Application year: 1995
Main classification: B65H5
IPC codes: B65H5