Abstract:
A suction box for a system for transporting flat media ( 4 ) includes at least one endless belt ( 6 ), formed with a plurality of through-holes, used in a media printing machine ( 1 ) equipped with at least one printing unit ( 2 ). The suction box includes a suction device ( 23 ) to generate a vacuum, a suction compartment ( 16 ), divided into at least two distinct chambers ( 26, 27, 28 ), including a first suction chamber ( 28 ) of variable volume, in communication with the suction device ( 23 ) so as to apply the vacuum through the holes in the belt ( 6 ) to the media being transported by the belt ( 6 ), and a second chamber ( 26, 27 ) at ambient pressure. The first and second chambers ( 28, 26, 27 ) are separated from one another by a mobile partition ( 31, 33 ). The suction compartment ( 16 ) has an open upper face equipped with a holding arrangement ( 14, 43, 44, 46, 47, 48 ) allowing movement of the belt ( 6 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 35 U.S.C. §§371 national phase conversion of PCT/EP2015/025049, filed Jul. 15, 2015, which claims priority of European Patent Application No. 14002498.5, filed Jul. 18, 2014, the contents of which are incorporated by reference herein. The PCT International Application was published in the French language. 
     
    
     TECHNICAL BACKGROUND 
       [0002]    The present invention relates to a suction box for a system for conveying flat media in a printing machine for flat media. The invention relates to a system for conveying flat media comprising at least one suction box. The invention also relates to a printing machine for flat media, equipped with a system for conveying flat media, and the system comprising at least one suction box. 
         [0003]    A printing machine is used in the packaging industry for printing flat media such as sheets or a web of paper or cardboard. The machine comprises several stations in succession. A first infeed station, situated furthest upstream, inputs the medium in succession. The infeed station supplies several printing stations, in the form of one or more printing units placed one after the other. Each printing unit prints a specific color using an ink which has the equivalent coloration. The machine can easily accept different sizes of medium. A delivery station which collects the medium which has been printed with an image is provided at the end of the machine. 
         [0004]    In the case of printing sheets of cardboard, particularly corrugated cardboard, the technology used most frequently is flexography using a flexo unit. Digital printing is also developing, with the use of printing units equipped with digital print heads, for example of the inkjet-type. This printing technology enables the packaging manufacturer to change print jobs very quickly in order to print new sheets from a computer file representing the packaging. 
         [0005]    The printing machine comprises one or more printing units with the number of units depending on the number of colors desired. The medium is moved longitudinally from upstream to downstream from the infeed station, to the printing units and as far as the delivery station. In order to obtain a final high-quality image on the printed medium, it is in particular necessary that all the printed dots of different colors be placed exactly next to one another. It is also necessary that the printed dots not be deformed. 
         [0006]    The printing quality obtained on the flat medium depends not only on the quality of the printing machines, the quality of the inks used and the quality of the media input, but also on the quality and accuracy of the conveying system or systems used. 
         [0007]    The medium is conveyed by a vacuum conveying system using a belt, flat straps, or steel rolls driven in order to move the medium longitudinally from one printing unit to another, upstream to downstream, from the infeed station to the delivery station. In order to obtain optimal print quality, one of the fundamental principles is that the medium is conveyed at a speed which is as uniform as possible. Another principle is that the medium must be held as firmly as possible and must be guided perfectly by the conveying system so that there is no deviation during the printing by the printing unit or units or between the printing unit or units. 
       PRIOR ART 
       [0008]    U.S. Pat. No. 6,471,430 describes a printing machine for media in the form of sheets of paper or cardboard, comprising a conveying system. For the printing, the sheets are taken from a sheet feeder and conveyed on a first endless conveying belt. The sheets are held in place while they are being conveyed by a suction system and the sheets pass under first printing units and under a first ink dryer downstream from the first printing units. The sheets are then turned over and are conveyed by a second endless conveying belt under second printing units and under a second ink dryer and are then collected in an output station. 
         [0009]    The conveying belts include a series of through holes which enable air to be sucked through the belts and the holding effect obtained allows the sheets to be conveyed inside the machine. Suction boxes are placed beneath the belts in order to generate the vacuum. 
         [0010]    However, the use of a suction system for applying a vacuum beneath the conveying belt and thereby holding the sheets to be printed flat has certain disadvantages. The vacuum created has an effect on the sheets and more precisely on the position of the guided sheets. This can have consequences for the printing process because parasitical air flows are generated at the front, rear, and side edges of the sheets. 
         [0011]    The vacuum also generates disruption in the region of the dryers. Indeed, these dryers comprise a suction part which is required to suck up the moisture generated during the drying. In order to perform optimal drying, the suction takes place from the printed face of the sheets and upwards. However the presence of two vacuums in opposite directions, both beneath in order to hold the sheets in place on the belt and above in order to dry the sheets, will affect the flatness of the sheets and the accuracy of the conveying. 
       SUMMARY OF THE INVENTION 
       [0012]    A main object of the present invention is to provide a suction box intended for a system for conveying flat media in a printing machine for flat media. A second object is to provide a suction box for conveying media which are to be printed, which ensures that these media are held satisfactorily on the conveying belt of the conveying system. A third object is to develop a suction box which makes it possible to minimize load losses when a medium is being conveyed. A fourth object is to produce a box wherein disruptions in the belt are kept to a minimum. A fifth object is to adapt a conveying system with an endless belt for printing flat media comprising at least one suction box. A sixth object is to overcome the technical problems mentioned for the boxes and the conveying systems from the prior art. Yet another object is to improve further the print quality for a printing machine for flat media which is equipped with at least one printing unit. 
         [0013]    According to an aspect of the present invention, a suction box intended for a system for conveying flat media with at least one endless belt provided with a set of through holes, in a printing machine for media which is equipped with at least one printing unit, comprises:
       a suction device capable of generating a vacuum, and   a suction compartment which is divided into at least two separate chambers
           a first suction chamber with an adjustable volume, which communicates with the suction device, to apply the vacuum through the holes of the belt to the media conveyed by the belt, and   a second chamber at ambient pressure, wherein the first and second chamber are separated from each other by a movable partition.   
               
 
         [0018]    The suction box suction compartment has an open upper face equipped with a holding arrangement which permits the movement of the belt. 
         [0019]    As a result, the open upper face of the compartment enables the vacuum to be transferred directly to the belt and thus to the flat media. The belt is held and circulates in the region of the upper face of the compartment. 
         [0020]    The suction chamber with adjustable dimensions allows the intensity of the vacuum applied to be adjusted easily and simply. The face along which the belt passes thus has a suction zone which can be varied depending on the adjustable chambers. This makes it possible to maintain a high and optimal suction in the region of the suction zone or zones in order to preserve the flatness of the flat media, the lack of movement of the flat media relative to the conveying belt zones, and hence the accuracy of the conveying. 
         [0021]    The surface of this zone varies, for example, depending on the size of the flat media which are to be conveyed and printed. The operation of the printing machine for media will be optimal, the vacuum being applied directly beneath the conveying belt, the extent of which is limited to the zone in which the conveyed flat medium is situated. The size of the chambers supplying the vacuum beneath the conveyed media will be adapted so as not to disrupt the operation of the dryers. 
         [0022]    A flat medium is defined, by a non-limiting example, as being made from a material in the form of a sheet, a board, or a continuous strip such as paper, flat cardboard, corrugated cardboard, laminated corrugated cardboard, flexible plastic, for example polyethylene (PE), polyethylene tetraphthalate (PET), bi-oriented polypropylene (BOPP), or other polymers, or still other materials. The flat medium is defined, by a non-limiting example, as being a sheet intended to be formed into a blank and the blank into a packaging box. 
         [0023]    The longitudinal direction is defined with reference to the trajectory of the flat medium within the printing machine, along its central longitudinal axis. The upstream and downstream directions are defined with reference to the direction of movement in the trajectory of the medium, in the longitudinal direction of the overall printing machine. 
         [0024]    In another aspect of the invention, a system for conveying flat media with at least one endless belt provided with a set of through holes, in a printing machine for the media which is equipped with at least one printing unit, comprises at least one suction box having one or more of the technical features described below. 
         [0025]    In another aspect of the invention, a printing machine for flat media, which is equipped with at least one printing unit, comprises a system for conveying the media, comprising at least one suction box having one or more of the technical features described below. 
         [0026]    According to yet another aspect of the invention, a printing machine for flat media, which is equipped with at least one printing unit, comprises a system for conveying the media having one or more of the technical features described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    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, in which: 
           [0028]      FIG. 1  shows a perspective view of a printing machine, comprising a conveying system and suction boxes according to the invention; 
           [0029]      FIGS. 2 to 5  each show respectively a side view, a plan view, a plan perspective downstream view, and a plan perspective upstream view of a suction box according to a first embodiment of the invention; and 
           [0030]      FIG. 6  shows a plan perspective upstream view of a suction box according to a second embodiment of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0031]    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. 
         [0032]    Each of the printing units  2  is equipped with at least one digital contactless print head, for example an inkjet print head. By way of example, a set of heads is directed downward, so that the upper faces of the sheets conveyed by the belt  6  are then printed. The black, cyan, magenta and yellow inks are successively printed by the printing units  2  onto the sheets. 
         [0033]    The sheets are input (arrows F in  FIG. 1 ) by a feed station (not shown), mounted upstream from the printing machine  1  (not shown). The sheets are then gripped, are conveyed, circulate longitudinally F, and are output 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 . 
         [0034]    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  which is mounted between a first upstream roller  7  and a second downstream roller  8 . The endless belt  6  is provided with a set of through holes (not visible 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 . 
         [0035]    The sheets remain applied flat on the belt  6  by virtue of suction boxes which are also called vacuum boxes  11  located below the belt  6 , and the sheets pass beneath the printing units  2  and dryers  3 . Only the vacuum boxes  11  at one of upstream from the printing units  2 , between the printing units  2 , and downstream from the printing units  2  are shown in dashed lines in  FIG. 1 . 
         [0036]    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 . 
         [0037]    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 an upstream coating unit  12 . 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 . 
         [0038]    Seven suction boxes  11  are mounted on the frame  10  under the belt  6 . The boxes  11  are 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 an upper face oriented toward the lower face of the belt  6 . The sheets are applied flat against the top face of the belt  6 . The belt  6  passes in the region of the upper face of each suction box. Each of the dryers  3  is associated with a suction box  11 . Each gap between the printing units  2  is associated with a suction box  11 . 
         [0039]    The box  11  according to a first embodiment comprises, in the region of the upper face, an arrangement for holding the belt  6  in place, comprising a series of transverse, equidistant, and mutually parallel rolls  14  ( FIGS. 2, 3, 4 and 5 ). For clarity, the central roll  14  has been removed for the box  11  shown in  FIG. 3 . The rolls  14  are held so that they are free to rotate by means of bearings. The rolls  14  are flush with the upper face of the compartment  16 . The belt is moved on the rolls  14 , which limits friction and vibration. 
         [0040]    The suction box  11  comprises ( FIGS. 2 and 3 ) a suction compartment  16 , delimited by two upstream and downstream side walls  17  and  18 , two front and rear longitudinal walls  19  and  21 , and a base  22 . For clarity, the front wall  19  has been removed for the box  11  shown in  FIG. 4 . The box  11  with the suction compartment  16  has an open upper face. 
         [0041]    The box  11  with its compartment  16  communicates with a suction device  23  comprising, for example, a motor  24  capable of generating a vacuum in the compartment  16 . 
         [0042]    The compartment  16  is divided into at least two chambers. In this case, three chambers  26 ,  27  and  28  are included. A second front chamber  26  and a second rear chamber  27  surround a first central suction chamber  28 . The central chamber  28  is adjustable and has a variable pressure capacity which is selected by the operator. The two front and rear chambers  26  and  27  remain at ambient pressure. 
         [0043]    The central chamber  28  communicates with the suction device  23  to apply vacuum through the holes of the belt  6  and to the media conveyed by the belt  6 . In the center of the box  11 , of the compartment  16 , and hence of the central chamber is situated an opening  29  which is connected to the suction device  23  used to create the vacuum. 
         [0044]    The central chamber  28  is delimited by two movable partitions  31  and  33 . A front movable partition  31  separates the second front chamber  26  from the first central chamber  28 . A rear movable partition  33  separates the second rear chamber  27  from the first central chamber  28 . The suction box  11  is adjustable to the size of the conveyed sheet. Flexible plastic seals or skirts (which cannot be seen) ensure that the central chamber  28  is leakproof by rubbing against the upstream and downstream side walls  17  and  18  and against the base  22 . 
         [0045]    The central chamber  28  and the chambers at ambient pressure  26  and  27  are preferably oriented longitudinally, and the movable partitions  31  and  33  are oriented longitudinally overall, from upstream to downstream. 
         [0046]    The movable partitions  31  and  33  diverge from each other, each being advantageously being inclined with respect to the other. As can be seen in  FIG. 3 , the partitions  31  and  33  are favorably inclined relative to each other (at angles a 1 ) with respect to a central longitudinal vertical plane passing through the central longitudinal axis L of the box  11  and the machine  1 . In such a configuration, it becomes impossible to completely close the central chamber  28  between the two movable partitions  31  and  33 . The partitions have a V-shaped configuration when seen from above, when they are close to each other, which makes it possible to prevent the opening  29  of the suction means  23  from being blocked. 
         [0047]    The box  11  preferably comprises an actuation device  34  for the two movable partitions  31  and  33  (see  FIGS. 2 and 4 ). The actuation device  34  preferably comprise at least one motor, in this case a single motor  36  which actuates and moves the two partitions  31  and  33  in translation. The motor  36  is installed in a housing situated behind the front wall  19 . This housing is particularly advantageous as it allows the motor  36  to be added inside the volume of the suction box  11  rather than outside it. 
         [0048]    The actuating device  34  can comprise an endless screw  37 . The screw  37  extends transversely through the compartment  16  substantially in its center. The screw  37  is held in rotation by means of bearings. The screw  37  traverses each of the two movable partitions  31  and  33  with the aid of a piece forming a slide. 
         [0049]    A cog  38  is fixed to the endless screw  37  at its front end. The motor  36  is mechanically connected to a drive, such as a chain or a belt  39 , which causes the endless screw  37  to rotate (arrows A and B in  FIG. 2 ) via the cog  38 . 
         [0050]    The rotation of the endless screw  37  enables bringing the partitions  31  and  33  closer together or further apart, depending on the direction of rotation of the screw  37 . The two partitions  31  and  33  are favorably positioned symmetrically relative to each other. The two partitions  31  and  33  move transversely from front to back and vice versa (arrows C and S in  FIG. 3 ), symmetrically relative to each other. 
         [0051]    The box  11  preferably comprises a guide device for each of the movable partitions  31  and  33 . The guide device may have the form of guide bars  41 . The bars  41  extend transversely through the compartment  16  substantially in the region of the upstream and downstream side walls  17  and  18 . Four bars  41  are provided, including an upstream upper bar, an upstream lower bar, a downstream upper bar, and a downstream lower bar. 
         [0052]    In a second embodiment of the invention (see  FIG. 6 ), a suction box  42  comprises the suction compartment  16 , delimited by the two upstream and downstream side walls  17  and  18 , the two front and rear longitudinal walls  19  and  21 , and the base  22 . The box  42  and the suction compartment  16  have an open upper face. 
         [0053]    The box  42  with its compartment  16  communicates with a suction device  23 . In the center of the box  42 , of the compartment  16 , and hence of the central chamber  28  is situated an opening  29  which is connected to the suction device  23  used to create vacuum in the central chamber. The two partitions  31  and  33  used are substantially similar to those of the first embodiment in design and operation. 
         [0054]    The box  42  according to the second embodiment comprises, in the region of the upper face, an arrangement for holding the belt  6 , comprising a first series of front rolls  43 . These front rolls  43 , for example five in number, are transverse to the belt, equidistant from each other, and mutually parallel. The arrangement for holding the belt  6  also comprises a first series of rear rolls  44 . These rear rolls  44 , for example five in number, are also transverse to the belt, equidistant, and mutually parallel. The front  43  and rear  44  rolls are held such that they are free to rotate by means of bearings. The front rolls  43  are situated in line with the rear rolls  44 . 
         [0055]    The holding arrangement comprises three runners arranged longitudinally, a front runner  46 , a central runner  47 , and a rear runner  48 . The front rolls  43  are separated from the rear rolls  44  by the runners  46 ,  47  and  48 . The upper edges of these runners  46 ,  47  and  48  are flush with the upper face of the compartment  16 . 
         [0056]    The belt  6  is moved, while it is held on the front  43  and rear  44  rolls. The central part of the belt  6  slides on the upper edge of these runners  46 ,  47  and  48 . Because the belt  6  is held by the series of rolls  43  and  44  and by the runners  46 ,  47  and  48 , it makes it possible to prevent the belt  6  from vibrating and consequently from disrupting the printing of the sheets by the printing units  2 . 
         [0057]    It is also possible to use such a box  11  in other parts of the printing machine  1 , for example beneath the printing units  2  or other modules. Alternatively, one motor can be provided per partition  31  and  33  with independent actuation means (endless screw or other means) for each motor/movable partition pair. 
         [0058]    The present invention is not limited to the embodiments described and illustrated. Numerous modifications can be made without in so doing going beyond the scope of the claims.