Suction box for a system for conveying flat media and printing machine thus equipped

Abstract

A suction box, intended for a system for transporting flat media (4) includes at least one endless belt (6), formed with a plurality of through-holes, in a media-printing machine (1), equipped with at least one printing unit (2). The suction box has a face (16) past which the belt (6) passes. A suction device (17) generates a vacuum in the suction box. The face (16) of the suction box is formed with at least one zone at a first suction pressure (22, 23, 24), which is in communication with the suction device (17), so as to apply the vacuum through the holes in the belt (6) to the media being transported by the belt (6), and the face of the suction box has at least one zone at a second pressure (26, 27). The zone at a second pressure is situated in the region of the printing unit (2). The magnitude of the second pressure is greater than the magnitude of the first pressure.

Claims

1. A suction box configured for use in a system for conveying flat media, the system having at least one endless belt configured and operable for conveying the media, the belt being provided with a plurality of through holes, the suction box and the belt being configured for use in a printing machine for printing on media, the printing machine comprising at least one printing unit which includes a print head; the suction box comprising: a face which the belt passes the box; and a suction device located and configured for generating a vacuum in the suction box; the face of the suction box including: at least one first zone of the suction box is at a first suction pressure due to communicating with the suction device, the first zone being configured for applying a vacuum through the through holes in the belt, the first zone being away from the print head and applying vacuum to the media conveyed by the belt wherein those media are then away from the print head; and at least one second zone of the suction box is at a second pressure and situated in a region of the printing unit, the second zone being at the print head, wherein, the second pressure is greater than the first pressure.

2. A box according to claim 1, further comprising the at least one second zone at a second pressure is oriented at a right angle to at least one of the digital print heads with which the printing unit is equipped, and the zone at a first suction pressure is situated longitudinally offset from the print head at an angle which is different from the right angle to the at least one of the print heads.

3. A box according to claim 1, further comprising two of the first zones at a first suction pressure, and one of the first zones at a first suction pressure surrounding the second zone at a second pressure.

4. A box according to claim 1, in which the zones are oriented transversely to a direction of the belt conveying and the media.

5. A box according to claim 1, further comprising a stationary plate pierced with orifices, the plate being located at the first zone at a first suction pressure.

6. A box according to claim 1, further comprising a respective suction compartment associated with each first zone at a first suction pressure.

7. A box according to claim 1, further comprising the suction device comprises at least one suction duct and one suction system supplying vacuum to the suction device.

8. A box according to claim 7, wherein each compartment communicates with a respective one of the suction ducts.

9. A system for conveying flat media comprising: at least one endless belt driven to convey the media for being printed, the belt provided with a plurality of through holes, the belt being located in a printing machine for printing media and wherein the printing machine includes at least one printing unit, and the system comprising at least one suction box according to claim 1.

10. A system according to claim 9, further comprising first and second rollers between which the endless belt is mounted to be driven in rotation by at least one drive motor configured for driving the belt in the direction of conveying.

11. A printing machine for flat media comprising at least one printing unit, and comprising a system for conveying the media, according to claim 9.

12. A machine according to claim 11, wherein each printing unit is associated with a respective suction box.

13. A machine according to claim 11, wherein each printing unit is equipped with at least one digital print head for printing the flat media conveyed past the print head.

14. A machine according to claim 11, further comprising: a first series of digital print heads arranged transversely of a direction of conveying of the media, a first sector from the at least one second zone at a second pressure situated at a right angle to the first series; a second series of digital print heads arranged transversely of a direction of conveying the media, and a second sector from the at least one second zone at a second pressure being situated at a right angle to the second series.

15. A printing machine for flat media which is equipped with at least one printing unit, and the machine comprising a system for conveying the media through the printing unit, and comprising at least one suction box according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be readily understood and its various advantages and different features will become more apparent from the following description of the non-limiting exemplary embodiment, with reference to the attached schematic drawings:

(2) FIG. 1 shows a perspective view of a printing machine, comprising a conveying system and suction boxes according to the invention;

(3) FIGS. 2 and 3 show a perspective plan view of a suction box, according to a first and a second embodiment of the invention, respectively;

(4) FIGS. 4 and 5 show a plan view of the box in FIG. 2 and the box in FIG. 3, respectively;

(5) FIG. 6 shows a perspective plan view of the box in FIG. 2, with no plate;

(6) FIG. 7 shows a plan view of the box in FIG. 2, with no plate; and

(7) FIG. 8 shows a perspective view of the underside of the box in FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

(8) As illustrated in FIG. 1, a printing machine 1 is used for printing media in the form of plate-like elements, for example sheets of corrugated cardboard. In the main exemplary embodiment, the machine 1 is a digital printing machine which includes, for example, some constituent parts described in U.S. Pat. No. 6,471,430 incorporated herein by reference. The machine 1 comprises in particular a set of four printing units 2 arranged in a line, one after the other. Water-based black, cyan, magenta, and yellow inks are printed in succession by the printing units 2 onto the sheets.

(9) The sheets are input (arrows F in FIGS. 1-5) by a feed station (not shown), mounted upstream from the printing machine 1 (not shown). The sheets are then gripped, are conveyed, circulate in longitudinal direction F, and are output in direction F after they are printed at a delivery station (not shown), mounted downstream from the printing machine 1. Two dryers 3, with steam discharge tubes, are placed downstream from the printing units 2.

(10) The sheets which are to be printed are conveyed from upstream to downstream by a conveying system 4. The conveying system 4 comprises at least one belt, in this case a single endless metal belt 6 (FIG. 1) which is mounted between a first upstream roller 7 and a second downstream roller 8. Passage of the endless belt 6 over rollers 7 and 8 defines an upper or top run of the belt and a lower or bottom run of the belt. The endless belt 6 is provided with a set of through holes 60 in FIG. 1. At least one of the two rollers 7 and 8 is driven in rotation (arrow R in FIG. 1) by means of a motor 9, which drives the belt 6. The rollers 7 and 8 and the belt 6 are mounted on a frame 10.

(11) The sheets remain applied flat to the top run of the belt 6 by virtue of suction boxes, which are also called vacuum boxes 11, located below the top run of the belt 6 and the sheets are passed by the top run of the belt 6 beneath the printing units 2 and dryers 3. Only the vacuum boxes 11 beneath the printing units 2 are shown in dashed lines in FIG. 1.

(12) In order to promote the adhesion and stability of the inks which will be deposited by printing on the cardboard sheets which are to be printed, the printing machine 1 preferably comprises an upstream coating unit 12, arranged upstream from the first printing unit 2, and just after the feed station. The upstream coating unit 12 is placed at a right angle to the upstream roller 7. In order to dry the coating, a dryer 3 may be interposed between the upstream coating unit 12 and the first printing unit 2.

(13) In order to promote stability and protection of the inks which are deposited by printing on the cardboard sheets which have been printed, the printing machine 1 preferably comprises a downstream coating unit 13. A downstream coating unit 13 is arranged downstream from the last printing unit 2 and downstream from the dryers 3, just before the delivery station. The downstream coating unit 13 is placed at a right angle to the downstream roller 8.

(14) In the printing machine 1, each of the printing units 2 is equipped with at least one contactless digital print head 14, for example of the inkjet type. For example, a set of twelve heads 14 (shown in dashed lines in FIG. 2) is provided. Each head 14 is oriented downward. The upper face of the sheets conveyed by the top run of the belt 6 are then being printed.

(15) The printing unit 2 and hence the machine 1 preferably comprise a first upstream series or row 14a of digital print heads 14 arranged transversely with respect to the belt 6. The printing unit 2 and hence the machine 1 preferably comprise a second downstream series or row 14b of digital print heads 14 arranged transversely with respect to the belt 6. In order to cover the whole width without interruption, the heads 14 of the first series 14a are offset transversely to direction F with respect to the heads 14 of the second series 14b.

(16) Four suction boxes 11 are mounted on the frame 10 under the top run of the belt 6. A box 11 is situated between the upper part of the belt run of the belt 6 which conveys the sheets and the lower part of the belt run of the belt 6 which makes the return travel. Each suction box 11 comprises a substantially flat upper face 16 oriented toward the lower face of the top run of the belt 6. The sheets are applied flat against the top face of the top run of the belt 6. The belt 6 passes at the upper face 16 of the suction box.

(17) Each suction box 11 comprises a suction device 17 capable of generating a vacuum in the suction box. The suction device 17 comprises at least one suction duct or tube 18 and a suction system 19, in the form of a motor 21.

(18) During printing with the print heads 14, it is important that micro-droplets of the inkjet emitted by the heads 14 maintain an optimum trajectory and shape in order to preserve the print quality desired by the operator. In order to ensure that these micro-droplets do not deviate from their trajectory and do not accelerate before they reach the sheet. The following is provided.

(19) According to a first embodiment of the invention (see FIGS. 2 and 4), the upper face 16 of the suction box is firstly formed with at least one zone at a first suction pressure, in this case with three such suction zones 22, 23 and 24 in sequence in direction F. The three suction zones 22, 23 and 24 communicate with the suction device 17 in order to apply vacuum through the holes 60 in the belt 6 to the media or sheets conveyed by the belt 6. For each suction box 11, the upper face 16 of the suction box is formed with an upstream suction zone 22, a central suction zone 23, and a downstream suction zone 24 with reference to the direction F of conveyance of the sheets.

(20) According to the first embodiment of the invention, the upper face 16 of the suction box is then formed with at least one zone at a second pressure. The second pressure is different from and greater than the first suction pressure. In the example shown in FIGS. 2 and 4, the upper face 16 has two zones in sequence in direction F at ambient pressure 26 and 27. Zone 26 is between zones 22 and 23. Zone 27 is between zones 23 and 24, whereby the different pressure zones alternate in direction F. For each box 11, the face 16 is formed with a first upstream zone at ambient pressure 26 and a second downstream zone at ambient pressure 27.

(21) In the box 11, the zone at ambient pressure 26 and 27 is preferably surrounded by a suction zone 22, 23 and 24. In more detail, the two zones at ambient pressure 26 and 27 favorably alternate with the three suction zones 22, 23 and 24, each zone at ambient pressure 26 and 27 is surrounded by a suction zone 22, 23 and 24. The two zones at ambient pressure 26 and 27 are situated in the region of the printing unit 2, and more particularly under the printing unit 2. Preferably, and more precisely, the zones at ambient pressure 26 and 27 are situated at a right angle to the print heads 14. The zones at ambient pressure 26 and 27 open into the ambient.

(22) The suction zones 22, 23 and 24 are situated so that they are offset longitudinally from the print heads 14. The zones 22, 23, 24, 26 and 27 are oriented transversely with respect to the belt 6. The first zone at ambient pressure 26 is situated at a right angle to the first series of print heads 14a, and the second zone at ambient pressure 27 is situated at a right angle to the second series of heads 14b.

(23) As soon as the leading end region of the sheet has been printed by the first series of heads 14a, that end region is held in place on the belt 6 as it is picked up by the central suction zone 23, and the leading end then passes under the second series of print heads 14b to be printed, and is then again held in place as it is picked up by the downstream suction zone 24.

(24) Each suction zone 22, 23 and 24 is associated with an underlying suction compartment 28, 29 and 31, respectively, which forms part of the suction box 11 and forms part of the suction device 17 (see FIGS. 4 to 7). The upstream compartment 28 enables generating the vacuum in the region of the upstream suction zone 22. The central compartment 29 enables generating the vacuum in the region of the central suction zone 23. The downstream compartment 31 enables generating the vacuum in the region of the downstream suction zone 24. Each compartment 28, 29 and 31 forms a substantially parallelepipdal transverse volume. The compartments 28, 29 and 31 are separated from one another, which enables delimiting the zones at ambient pressure 26 and 27.

(25) Each compartment 28, 29 and 31 communicates with a suction duct 18a, 18b and 18c (see FIG. 7) which opens out in the center of each of the compartments 28, 29 and 31. The suction ducts 18a, 18b and 18c converge in the suction system 19 and form part of the suction device 17.

(26) Each suction zone 22, 23 and 24 is favorably equipped with a plate pierced with orifices 32. The plate and its orifices enable making the suction uniform in the region of the suction zones 22, 23 and 24. A single upper plate pierced with orifices 32 can cover the whole face 16. The belt 6 passes directly over the plate 32. The plate 32 comprises longitudinal rods 33 which allow the upstream suction zone 22 to be separated from and connected to the central suction zone 23, and the central suction zone 23 to be separated from and connected to the downstream suction zone 24. The length of the rods 33 defines the length of the zones at ambient pressure 26 and 27.

(27) In a second embodiment of the invention (see FIGS. 3 and 5), the upper face 16 of the suction box is initially formed with at least one zone at a first suction pressure, and in this case three suction zones, an upstream one 22, a central one 23 and a downstream one 24, which are substantially similar to one another and function in a manner which is substantially similar to the first embodiment.

(28) The upper face 16 is formed with at least one zone at a second pressure. This second pressure is different from and greater than the first suction pressure. By way of example shown in FIGS. 3 and 5, the upper face 16 has two zones at a suction pressure which is different from ambient pressure and less than ambient pressure 26 and 27.

(29) Each suction zone 22, 23 and 24 is favorably equipped with a plate pierced with orifices 32. The plate and its orifices 32 cause the suction to be uniform in the suction zones 22, 23 and 24. A single upper plate pierced with orifices 32 can cover the whole upper face 16. The belt 6 passes directly over the plate 32. In the second embodiment (FIGS. 3 and 5), the plate 32 comprises ribs, pads or runners 34 which are arranged longitudinally and allow the belt 6 to be held. The belt 6 circulates by sliding over the upper edge of these pads 34.

(30) The sheets which are being printed must be prevented from moving up and down and undulating in the region of the print heads 14, depending on the suction pressure exerted on them. It is thus interesting to reduce the pressure difference between the first suction pressure and the second pressure while retaining the first suction pressure in order to keep the first suction pressure lower than the second pressure.

(31) In order to do this, aligned orifices 36 are arranged in the region of the ribs 34 and make it possible to connect the zones at a first suction pressure 22, 23 and 24 to the zones at a second pressure 26 and 27. The orifices 36 situated upstream form an interconnection between the upstream suction zone 22, the first upstream zone at a second pressure 26, and the central suction zone 23. The orifices 36 situated downstream form an interconnection between the central suction zone 23, the second downstream zone at a second pressure 27, and the downstream suction zone 24.

(32) The number of print heads 14 and series of heads 14a and 14b may vary. The same applies to the number of suction zones 22, 23 and 24 and zones at ambient pressure 26 and 27. A common suction system may be provided as suction means 17 for multiple suction boxes 11.

(33) The present invention is not limited to the embodiments described and illustrated. Numerous modifications may be made without in so doing going beyond the scope of the claims.