Abstract:
A flexographic rotary printing machine has a supporting structure provided with two lateral shoulders, an impression roller over which a material in sheet form to be printed passes, at least one printing element or assembly arranged adjacent to the impression roller and having an inking unit, a printing plate cylinder and an anilox roller, which are sleeve cylinders, and a drive for transmitting motion between the impression roller and each printing assembly. At each shoulder there is at least one lateral support device for the advancement-retraction of the sleeve cylinders, adapted to move them between a retracted or resting position, in which a respective sleeve can be inserted or removed, and an advanced or active position, in which the cylinders are kept in contact with, and operatively connected to, the impression roller.

Description:
This application is a division of U.S. application Ser. No. 09/29883 filed Apr. 26, 1999 and now U.S. Pat. No. 6,125,752. 
    
    
     BACKGROUND OF THE INVENTION 
     A The present invention relates to a multi-colour rotary flexographic machine of the narrow-web type. 
     As it is known, replacement of the printing plate cylinder and the anilox roller in each printing unit of a conventional flexographic rotary machine is a troublesome operation which requires long machine downtimes. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a new flexographic rotary machine with separate printing units in which changing of printing and/or printing colours can be made in a quick and easy way. 
     Another object of the present invention is to provide a high performance flexographic rotary machine which is highly reliable and precise. 
     These and other objects which will become better apparent hereinafter are achieved by a flexographic rotary printing machine according to the invention, which comprises a supporting structure, an impression roller on which a sheet material to be printed passes, at least one printing unit arranged adjacent to said impression roller and having a closed-chamber doctor-blade inking group, a printing plate cylinder and an anilox roller, which are of sleeve cylinder type, motion transmission means between said impression roller and each printing assembly, and at least one lateral support device for forward and backward movements of said sleeve cylinders which is arranged to move them between a retracted or resting position, in which a respective sleeve can be inserted or removed, and an advanced or printing position, in which they are kept in contact with, and operatively connected to, said impression roller. 
     Advantageously, said lateral support device comprises at least one slide provided with recirculating ballscrew sliding blocks and a guide of antifriction material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects and advantages of the present invention will become better apparent from the following detailed description of a currently preferred example of embodiment thereof, given merely by way of non-limitative example with reference to the accompanying drawings, wherein: 
     FIG. 1 is a schematic top view, with parts shown in cross-section along the line I—I of FIG. 2, of a colour unit arranged adjacent to the impression roller of a printing machine according to the invention; 
     FIG. 2 is a front side view on an enlarged scale of the colour unit of FIG. 1; 
     FIG. 3 is a cross-section view taken along the line III—III of FIG. 2; 
     FIG. 4 is a cross-section view taken along the line IV—IV of FIG. 2; 
     FIG. 5 is rear side view on an enlarged scale of the colour unit of FIG. 1; 
     FIG. 6 is a cross-section view taken along the line VI—VI of FIG. 5, and is also an enlarged-scale view of a detail of FIG. 1; 
     FIG. 6A shows a detail of FIG. 6 according to another embodiment; 
     FIG. 7 is a schematic side view of a holding means or cap with a conical locking pin; 
     FIG. 8 is a cross-section view taken along the line VIII—VIII of FIG. 7; 
     FIGS. 9 and 10 are a plan view and a side view, respectively, of the cap of FIG. 7 in its open position; 
     FIG. 11 shows another embodiment of a cap with a conical locking pin; 
     FIG. 12 is a cross-section view taken along the line XII—XII of FIG. 11; 
     FIG. 13 is a cross-section view taken along the line XIII—XIII of FIG. 11; 
     FIG. 14 is a side view of the cap of FIG. 11 in its open position; 
     FIG. 15 shows a side elevation view of an eight-color rotary printing machine with a central drum; and 
     FIGS. 16 and 17 are diagrammatic side elevation views of a printing machine with single in-line colour units, and with twin stacked colour units, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the accompanying drawings, identical or similar parts or components have been designated by the same reference numerals. 
     With reference to FIGS. 1 to  10  and  15 , it will be noted that a printing machine according to the invention has a supporting structure, generally designated by the reference numeral  1 . An impression roller or printing drum  2 , around which a sheet or web material to be printed passes and is partly wound, is mounted for rotation on the structure  1 . On the opposite side with respect to the vertical axis of the impression roller  2  there is provided a plurality of printing assemblies or color units  3 , e.g. eight printing units, which extend substantially in radial direction with respect to the impression roller. 
     The supporting structure  1  comprises in particular two cast-iron shoulders  1   a  and  1   b  of large thickness to ensure maximum stability and lack of vibrations and thus optimum printing quality control. 
     Each printing unit  3  comprises, as usual in the art, a closed-chamber doctor-type inking group, generally designated by SI, an anilox roller  4 , and a printing plate cylinder  5 , which can be operatively connected to each other and to the impression roller  2  by suitable motion transmission means, usually gears, as further explained hereinafter. 
     The printing plate cylinder  5  and the anilox roller  4  of each printing unit are sleeve cylinders, since engraving is also provided on a tubular element  6 , whereby both the printing plate  7  and the tubular element  6  constitute “sleeves” insertable on, and removable from, a respective cylinder  5  or  4 . This makes it possible to considerably simplify printing or color changing operations, since it is no longer necessary to replace the cylinders  4  and  5  but simply to change or replace their respective sleeves, which is a much simpler operation that can be performed in a very short time, as no heavy loads or loads which might be dangerous for the safety of the personnel and for the components of the machine need to be handled. 
     Each printing unit  3  has at one shoulder of the machine (preferably the front shoulder  1   b ) a supporting device, generally designated by the reference numeral  8 , arranged to cause the sleeve cylinders  4  and  5  to move back and forward between a retracted or resting position, in which their respective sleeve  6 ,  7  can be inserted or removed, and an advanced or printing position, in which it is kept in contact and operatively connected to said impression roller. 
     More particularly, each supporting device  8  is mounted at a respective large opening or slot  9  formed in the front shoulder  1   b  of the printing machine for easy loading and unloading of the ceramic anilox sleeve  6  and the printing plate sleeve  7  of the sleeve cylinders  4  and  5 . A supporting device  8  comprises a slide 10 , one or more lower linear prismatic guides  11  which are fixed to the supporting structure  1 , an upper linear guide  12  for the linear sliding of the slide  10 , and control means for actuating the slide  10 , e.g. constituted by a screw  13  driven by an electric motor  14  supported by the shoulder  1   b  and controlled by a respective encoder  15 , and by a female thread  16 , secured to the slide 10 , the screw  13  being rotated by a wheel or pulley  17  which is keyed thereon and by a toothed transmission belt  18  which is driven by the motor  14 . 
     Preferably, the or each prismatic guide  11  is engaged by a respective sliding block  19 , which is fixed to the slide  10  and mates with the prismatic guide  11 , and is constituted by a suitable antifriction material having a low coefficient of friction, e.g. a material commercially known as “Turcite” and marketed by Swedish company Shamban, which besides having a very low coefficient of friction can also absorb the vibrations that might occur during printing. 
     At its upper part, the slide  10  has two recirculating-ballscrew sliding blocks  20  to ensure good smoothness and high resistance to overturning moments which might occur during a sleeve changing operation. 
     To the side of the slide  10  there is a second slide or sliding block  100  which is designed to support the cylinder  4  and can be actuated by an assembly comprising an electric motor  22 , an encoder  23 , a toothed belt  24  and a pulley  25  and arranged to rotate a screw  26  in a female thread  27  carried by the slider  10 . 
     At the upper guide  12  registering wedges  21  are also provided which are arranged to eliminate any play between the slider  10  and  100  and the shoulders of the supporting structure  1  and to apply a given preloading to the lower guide or guides  11 , thereby ensuring greater and constant rigidity of the system during printing operations. 
     The slide  10  has a through slot  30  which extends longitudinally and parallel to the guides  11  and  12  and has such dimensions as to ensure easy passage of an anilox sleeve  6  for the anilox roller  4 . 
     The distal end of the slide or sliding block  100  is equipped, i.e. it has a substantially semicircular receiving cradle or seat  31  whose inlet has chamfered edges  32  and  33  to constitute guiding surfaces for the entry of the end  34  of the end  4 . 
     Advantageously, the lower portion of the cradle  31  is constituted by a separate part which is articulated at a pivot  35  which has a horizontal axis in order to resiliently yield and assist the inlet-exit of the end  34  into and from the cradle  31 . 
     At the distal end of the slide  10 , a recess  36  delimits a cradle or seat for receiving an end  37  of the cylinder  5 . At the upper portion of the cradle  36  there is provided a removing holding device  38  which is further explained with reference to FIGS. 7 to  10 . 
     Most of the upper portion of the cradle  36  is formed by a holding lever or cap element  39 , which is articulated about a pivot  40  located in an upper region above the cradle  36 , in a backward position close to the slot  30 , thereby allowing the holding element  39  to oscillate on a plane parallel to the plane on which the slide 10  moves. 
     As shown more clearly in FIG. 8, the holding element  39  can be a U-shaped in cross-section and is slidingly inserted from below onto the upper end of the cradle  36 . Moreover, the lever element  39  is resiliently loaded, e.g. by one or more helical springs  45  which urge it to its closed position. 
     Articulation movements of the holding element  39  are prevented by an axially movable pivot  41  which has a frustum-shaped tip and is located in a lateral seat or recess  42  formed in one wing of the holding element and terminating with a frustum-shaped portion  43  provided in the slider  10 . The pivot  41  is actuated by a linear actuator  44 , e.g. a solenoid, a jack or the like, and is preferably kept slightly axially offset (FIG. 8) with respect to the axis of its seat  42  for safer holding effect in its locked position. 
     With this configuration, when the slider  10  is moved against the end  37  of the cylinder  5  towards its working position, after the pivot  41  has been moved backwards from the frustum-shaped seat  43  by the actuator  44 , the cap  39  rises automatically, thereby allowing easy insertion of the end  37  into the cradle  36  and then it returns to its locking position, firmly holding in position the cylinder end  37  and therefore the cylinder  5 . At the same time, the cradle  31  on the slide  100  engages with the end  34  of the cylinder  4 , which is in turn held in its working position. 
     In the embodiment shown in FIGS. 11 to  14 , the holding device or cap  39 , instead of rotating about a pivot, can perform a translatory motion so as to be raised when the end  37  moves therethrough in contrast with the force of one or more loading springs  45 , which react against an abutment block  46  secured to the slide  10 , e.g. by means of bolts  47 . 
     At the rear shoulder  1   a  (FIGS. 1 and 5) a plate-like slide  50  is mounted movable along a lower guide  51  and an upper guide  52  which are entirely similar to the guides  11  and  12 . Sliding blocks  20  slide on the upper guides  52 . The slide  50  rotatably supports the other end of the sleeve cylinder  5  and can be actuated, similarly to the slide  10 , by a motor which, by means of a transmission belt  18 , drives a pulley  17  which is keyed to a screw  13  screwed into a female thread  16  secured to the slide. The revolutions of the screw  13  are controlled by an encoder  15 . 
     A slide or sliding block  500 , similar to the sliding block  100  on the front shoulder  1   b , is also provided on the rear shoulder  1   a  and is arranged to move parallel to the side of the slide  50 . Its movements are likewise controlled by an electric motor  22  through a transmission comprising a toothed belt  24  and a pulley  25  which is keyed on a screw  26  provided with an encoder  23 . 
     The screws  13  and  26  are preferably high-precision recirculating ballscrews. A pneumatic brake  53  is located axially aligned on each screw is to ensure effective locking in position of the slides. 
     As more clearly shown in FIGS. 1 and 6, the ends  34  and  37  of the cylinders  4  and  5  are mounted on the slide  50  and  500  by means of a respective sleeve  54  and  55  with the interposition of friction reduction means, i.e., bearings  56 , whereby allowing its respective cylinder to perform limited angular oscillations (as shown by arrow A in FIG. 6) during sleeve changing operations, and limited longitudinal movements for the necessary transverse alignment of said cylinders (arrow B). 
     In order to minimize the free bending length of the cylinder  5 , at the ends  37  of the cylinder  5  two additional roller bearings  56 A (see FIG. 6A) can be provided which are seated in the sleeve  54  on one side and in the sleeve  61  on the other side. This arrangement has also the advantage of eliminating angular oscillations indicated by double arrow A in FIG.  6 . 
     FIG. 6 also illustrates the front end of the cylinder  5  which, like the front end  34  of cylinder  4 , is provided with a cap  60  which is screwed onto a sleeve  61  for resting on the cradle  36  in the slide  10 , the sleeve  61  being loaded by one or more springs  62  for transverse registering movements. 
     The spring or springs  62  are designed to keep or automatically return the sleeve  61  to its centered position during sleeve changing operations. As more clearly shown in FIG. 6, a second sleeve  65  is slideably mounted inside the sleeve  54  and protrudes from the sleeve  54  with a widened end portion which internally receives the bearings  56 . 
     An oval external flange  66  is fixed to the sleeve  65  and to an acme-thread screw  67  secured to the oval flange  66 . The screw  67  can be screwed into a female thread  68  which can be rotated by a toothed pulley  69  which is in turn driven by a toothed belt  70  wound on a driving pulley  71  which is directly rotated by an electric motor  72 . By causing the electric motor  72  to turn in one direction or in the other the screw  67  and thus the sleeve  66  and the cylinder  5  are caused to traverse, thereby performing the precision transverse registering of the printing plate cylinder  5 . 
     It will be noted that in a printing machine as described above a very simple, quick and safe change the sleeves  6  and  7  can be performed through the openings  9  with no need of replacing the sleeve cylinders  4  and  5 . In practice, it has been found that in a color printing machine according to the invention an average sleeve changing time is on the order of a few minutes, in contrast with color changing time of a few hours required with conventional printing machines. 
     The above described invention is susceptible of numerous modifications and variations within the scope as defined by the appended claims. 
     Thus, for example, as shown in FIGS. 16 and 17, the above described embodiment of a printing machine can be applied to printing machines with a central drum (FIG.  15 ), to printing machines with separate color units (FIG. 16) and to printing machines with twin stacked color units (also known as “stack” machines in the art) see FIG.  17 . 
     The disclosures in Italian Patent Application No. VR98A000037 from which this application claims priority are incorporated herein by reference.