Abstract:
A printing press for one-sided or two-sided printing of a sheet includes a transfer cylinder disposed in a travel direction of the sheet between a first and a second impression cylinder, respectively, of two printing units, and a sheet support assigned to the transfer cylinder for receiving the sheet thereon before the sheet is transferred to the second impression cylinder, an inverting drum disposed in the travel direction of the sheet between the sheet support and the second impression cylinder, the inverting drum serving for picking up the sheet from the sheet support and transporting the sheet to the second impression cylinder; and a method of operation.

Description:
BACKGROUND OF THE INVENTION 
   FIELD OF THE INVENTION 
   The invention relates to a printing press for one-sided or two-sided printing of a sheet, and a method for printing a sheet in the printing press. 
   Rotary printing presses are used for producing one-sided multicolor printing or two-sided multicolor printing. In two-sided multicolor printing, it is necessary for the sheet to be printed on both the front and rear sides thereof. For that purpose, the sheet in the printing press is inverted by a transfer cylinder between two impression cylinders. For flexible use of a rotary printing press, it is desirable to convert the printing operation from one-sided to two-sided printing, so that, depending upon the set printing operation, the sheet takes different travel paths. 
   From the published German Patent Document DE 39 03 093 A1, a sheet inverter has become known heretofore, wherein, in a one-sided multicolor printing operation, the sheet is transferred between a first impression cylinder and a second impression cylinder via the transfer cylinder. In this regard, the side of the sheet to be printed is guided in like manner on both the first and the second impression cylinder. If the rear side of the sheet is then to be printed additionally, the sheet is transferred from the transfer cylinder to a storage drum. The storage drum transfers the sheet by the trailing edge thereof to an inverting drum which, in turn, transfers the sheet, with the trailing edge thereof leading, to the second impression cylinder. In this case, the side of the sheet to be printed has been changed, so that the side of the sheet that has not yet been printed is now printed by the second impression cylinder. 
   The disposition of a storage drum is relatively complicated and requires a considerable amount of installation space in the printing press. 
   From the published German Patent Document DE 37 17 093 A1, a rotary printing press for one or more-sided printing of sheets has become known heretofore wherein a transfer cylinder is disposed between a first and a second impression cylinder. The transfer cylinder has a sheet support assigned thereto, whereon a sheet, arriving from the first impression cylinder, is placed with the leading edge of the sheet leading; the trailing edge of the sheet is firmly held by the transfer cylinder and is transferred to a gripper of the second impression cylinder. The sheet support thus serves for briefly storing the sheet, by which a simple inversion of the sheet is possible. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention is to provide a more-flexible printing press for inverting a sheet. 
   With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a printing press for one-sided or two-sided printing of a sheet includes a transfer cylinder disposed in a travel direction of the sheet between a first and a second impression cylinder, respectively, of two printing units, and a sheet support assigned to the transfer cylinder for receiving the sheet thereon before the sheet is transferred to the second impression cylinder, an inverting drum disposed in the travel direction of the sheet between the sheet support and the second impression cylinder, the inverting drum serving for picking up the sheet from the sheet support and transporting the sheet to the second impression cylinder. 
   In accordance with another feature of the invention, the sheet support has a movable slide provided with a gripper for firmly holding one edge of the sheet, the slide being movably retained between the transfer cylinder and the inverting drum. 
   In accordance with a further feature of the invention, the transfer cylinder has a gripper for transferring the sheet in-register from the transfer cylinder to the gripper of the slide. 
   In accordance with an added feature of the invention, the sheet support has a suction device formed with a suction opening, the suction opening being disposed in a region of an upper side of the sheet support. 
   In accordance with an additional feature of the invention, the slide has a toothed rack via which the slide is drivable. 
   In accordance with yet another feature of the invention, the printing press includes a registration device assigned to the sheet support, the registration device having a stop for braking the moving sheet and moving the sheet, in-register, for transferring the sheet to the gripper of the inverting drum. 
   In accordance with yet a further feature of the invention, the slide has an upper and a lower toothed rack, and is drivable in an upper path via the lower toothed rack and in a lower path via the upper toothed rack. 
   In accordance with yet an added feature of the invention, the printing press includes at least one drivewheel for formlockingly engaging in the toothed rack and moving the slide. 
   In accordance with yet an additional feature of the invention, the printing press includes a gear train, and wherein the drivewheel is connected via a coupling to the said gear train. 
   In accordance with still another feature of the invention, the printing press includes two overturning wheels, and further includes a guide element via which one end of the slide is guidable in a first guide path, and, via one of the overturning wheels, the other end of the slide is movable, symmetrically to the first guide path, into a second path of motion. 
   In accordance with another aspect of the invention, there is provided a method for two-sided printing of a sheet in a printing press having a transfer cylinder which is disposed in a travel direction of the sheet between a first and a second impression cylinder, respectively, of two printing units, and having a sheet support disposed in the travel direction between the transfer cylinder and the second impression cylinder, the sheet being placed on the sheet support before the sheet is transferred to the second impression cylinder, includes assigning an inverting drum to the sheet support; moving the sheet on the sheet support from a conveyor system to the inverting drum; and having the inverting drum pick up the sheet and guide the sheet to the second impression cylinder. 
   In accordance with another mode of the method of the invention, transferring the sheet, in-register, from the transfer cylinder to the conveyor system; and transferring the sheet, in-register, from the conveyor system to the inverting drum. 
   An advantage of the invention is that a sheet support and an inverting drum are disposed between the transfer cylinder and the second impression cylinder. This arrangement offers the advantage that the function of inverting the sheet is transferred from the transfer cylinder to the inverting drum, and a simple device for transferring the sheet from the transfer cylinder to the inverting drum is furnished by the sheet support. 
   The sheet support preferably has a movable slide, with a gripper that engages an edge of the sheet, and the sheet is moved by a motion of the slide to the inverting drum, which in turn grasps the sheet at one edge. Using a movable slide makes precise transporting of the sheet from the transfer cylinder to the inverting drum possible. 
   The sheet is preferably transferred from the transfer cylinder to the slide while maintaining registration; that is, the sheet is in a prescribed position relative to the slide. Thus, in-register transfer of the sheet to the inverting drum and to the second impression cylinder is possible, and as a result the sheet is located at a predetermined position relative to the printing operation that is performed at the second impression cylinder. The sheet support preferably has a suction device, with which the sheet can be firmly sucked or aspirated at the sheet support. By the firm suction of the sheet, a defined position of the sheet is prescribed, and the sheet can, for example, be tautened. 
   In a special embodiment of the invention, a suction opening of the suction device is disposed below the transfer cylinder and provided in fixed position. This affords a simple, economical disposition of the suction device. 
   In a further feature of the invention, a registration device is provided at the sheet support, and with the registration device, the location of the sheet is detected from a registration character on the sheet, and the sheet is transferred to the inverting drum in a prescribed position. 
   In this way, in-register transfer of the sheet is possible even if the sheet is not transferred in-register from the transfer cylinder to the sheet support. Thus, in this embodiment as well, precise printing of the rear side of the sheet with the second impression cylinder is possible. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a printing machine and method for printing a sheet it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary diagrammatic side elevational view of a printing press provided with a sheet support located between a transfer cylinder and an inverting drum; 
       FIG. 2  is a view like that of  FIG. 1  of the printing press with a more detailed first embodiment of the sheet support having a movable slide; 
       FIG. 3  is a view like that of  FIG. 2 , but showing a further embodiment of a conveyor system with a suction belt and a registration device; 
       FIG. 4  is a top, side and rear perspective view of the slide with a support table; 
       FIG. 5  is a diagrammatic side elevational view of a slide with a toothed rack guide; and 
       FIG. 6  is a diagrammatic side elevational view of a slide with a registration wheel. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings and, first, particularly to  FIG. 1  thereof, there is shown therein diagrammatically a detail of a printing press  1  with a first rubber blanket cylinder  10  of a first printing unit of the printing press  1 . The first rubber blanket cylinder  10  is assigned to a first impression cylinder  2 . To the first impression cylinder  2 , in turn, a transfer cylinder  3  is assigned, and to the transfer cylinder  3 , a sheet support  8  and a second impression cylinder  4  are assigned. An inverting drum  9  is disposed between the sheet support  8  and the second impression cylinder  4 . A second rubber blanket cylinder  11  of a second printing unit is assigned to the second impression cylinder  4 . The first impression cylinder  2 , the transfer cylinder  3 , the inverting drum  9  and the second impression cylinder  4 , respectively, are equipped with gripper devices for grasping and firmly holding a sheet  5  by a leading edge and/or a trailing edge  6 ,  7  thereof, respectively. The first and second rubber blanket cylinders  10 ,  11 , the first impression cylinder  2 , the transfer cylinder  3 , the inverting drum  9 , and the second impression cylinder  4 , respectively, are rotatably supported via a pivot shaft in the printing press  1  and are driven at different rotary speeds by a motor. 
   The arrangement in  FIG. 1  functions as follows: A sheet  5  is guided by a leading edge  6  thereof to the first impression cylinder  2  via a non-illustrated feed cylinder. With the gripper device, the first impression cylinder  2  grips the leading edge of the sheet  5  that is being printed and moves the respective sheet  5  past the first rubber blanket cylinder  10 . The first rubber blanket cylinder  10  transfers a printing image, which is prescribed by the first printing unit, to the upwardly facing first side of the sheet. The sheet, now printed on the first side thereof, is moved onwardly by the first impression cylinder  2  and transferred to the transfer cylinder  3 . If single-sided multicolor printing of the sheet  5  is set as the operating mode, the sheet  5  is then transferred directly to the second impression cylinder  4 . The second impression cylinder  4  grasps the sheet and moves the sheet with the first side thereof past the second rubber blanket cylinder  11 . The second rubber blanket cylinder  11  transfers a printed image, prescribed by the second printing unit, to the first side of the sheet  5 . The first and second printing units transfer a printed image in different colors, so that the sheet  5 , after being printed by the second rubber blanket cylinder  11 , has a two-colored printed image on the first side. 
   In a second operating mode, the printing press  1  is set for two-sided printing of the sheet  5 , wherein the sheet  5  is placed on the sheet support  8  by the transfer cylinder  3  with the leading edge  6  thereof leading and is moved past and underneath the inverting drum  9 . The inverting drum  9  grasps the trailing edge  7  of the sheet  5  and carries the sheet  5 , with the trailing edge  7  leading, to the second impression cylinder  4 . The second impression cylinder  4  takes over the sheet  5 , which now rests with the second side thereof facing upwardly on the second impression cylinder  4 . The second impression cylinder  4  moves the sheet  5 , by the second side thereof, upwardly past the second rubber blanket cylinder  11 . The second rubber blanket cylinder  11  prints the second side of the sheet  5  with a prescribed printed image. Thus, downline from the second rubber blanket cylinder  11 , as viewed in the travel direction of the sheets, the sheet  5  has been printed on both the first and second sides thereof. The sheet  5  is then sent onward from the second cylinder  4  to a further cylinder and is further processed by the printing press  1 . 
   An advantage of the invention is that, depending upon the operating mode which is set, a sheet  5  is printed on one or both sides thereof and, in the process, is either transferred directly from the transfer cylinder  3  to the second impression cylinder  4  or is placed on the sheet support  8  and inverted by the inverting drum  9  and transferred to the second impression cylinder  4 . The sheet support  8  is provided with at least approximately the form of a planar or slightly curved surface, whereon the sheet  5  rests and is transported onward to the inverting drum  9 . 
   Further details of the invention are shown in  FIGS. 2 and 3 .  FIG. 2  shows a transfer cylinder  3  in the form of a recessed cylinder having a circumferential wall  12  embodied in the form of two slightly curved surfaces disposed symmetrically to the pivot axis of the transfer cylinder  3 . First and second grippers  14 ,  15  are disposed on respective opposed end regions  13 . With the first and second grippers  14 ,  15 , a leading edge  6  of a sheet  5  is gripped and transferred from the first impression cylinder  2  at a first tangent point  16 . 
   The second impression cylinder  4  is associated with the transfer cylinder  3  at a second tangent point  17 . The second impression cylinder  4  has a third and fourth gripper  18 ,  19 , with which an edge of the sheet  5  can be grasped and firmly held. For example, in the operating mode of one-sided printing of the sheet  5 , the sheet  5  is transferred by the leading edge thereof at the second tangent point  17  from the transfer cylinder  3  directly to the second impression cylinder  4 . 
   The sheet support  8  is disposed below the transfer cylinder  3  and has a conveyor system  21 . The conveyor system  21  includes a slide  22  and a belt  23  which, in the form of an endless belt, revolves between the first and second shafts  24  and  25 . The slide  22  is solidly connected to the belt  23 . A fifth gripper  26  is disposed on the slide  22  and is movable via cam drives or other mechanical or electrical control devices for grasping and firmly holding the leading edge of a sheet  5 . 
   A support table  27  is disposed below the transfer cylinder  3  and has a suction channel  28  extending to suction openings  29  formed on the upper side of the support table  27 . The suction channel  28  is connected to a negative-pressure or suction pump, which generates a negative pressure in the suction channel  28  so that, via the suction openings  29 , a sheet  5  can be sucked down onto the support table  27 . The support table  27  is fixed in position whereas, conversely, the slide  22  is moved by the belt  23  from the first shaft  24  in a direction towards the second shaft  25 . In the course of this movement, the slide  22  is moved through a guide recess formed in the support table  27 . 
   The movement of the slide  22  and the rotation of the transfer cylinder  3 , when setting the operating mode of inverting the sheet, are synchronized so that the fifth gripper  26  of the slide  22  and the first or second gripper  14 ,  15  meet at a third tangent point  30 . In this meeting, the first or second gripper  14 ,  15  transfers the leading edge  6  of the sheet  5  to the fifth gripper  26 , which firmly clamps the sheet  5  by the leading edge  6  thereof to the slide  22 , and the slide  22  moves the sheet  5  onward in the direction towards the inverting drum  9  which is disposed below the second impression cylinder  4 . At the same time, the sheet  5  is sucked down onto the support table  27  by the suction openings  29  and, as a result, is placed on the support table  27  and the slide  22 . In addition, tension in the direction of motion of the sheet  5  is attained due to the sucking of the sheet  5 . 
   During the transfer of the leading edge  6  of the sheet  5  at the third tangent point  30  from the transfer cylinder  3  to the slide  22 , the leading edge  6  of the sheet  5  is transferred In-register, so that the location of the sheet  5  is precisely defined. In this way, it is possible for the sheet  5  to be transferred in-register from the inverting drum  9  to the second impression cylinder  4 . The sheet  5  should thereby lie completely flat. 
   The path of motion of the slide  22  is defined in such a way that the slide  22  moves the sheet  5  past the inverting drum  9  at a fourth tangent point  31 . The inverting drum  9  has a sixth gripper  32  by which an edge of the sheet can be grasped and firmly held. The rotation of the inverting drum  9  is synchronized with the motion of the slide  22  so that the sixth gripper  32  is located at the fourth tangent point  31  when the trailing edge of a sheet  5  is moved past the fourth tangent point  31  by the slide  22 . In this regard, the sixth gripper  32  grasps the trailing edge  7  and carries the sheet  5 , with the trailing edge  7  leading, to a fifth tangent point  33 , which the inverting drum  9  occupies together with the second impression cylinder  4 . The fifth gripper  26  releases the leading edge  6  of the sheet  5  the instant the sixth gripper  32  has grasped the trailing edge  7 . 
   At the fifth tangent point  33 , the trailing edge  7  is transferred to the third or fourth gripper  18 ,  19 . Next, the sheet  5 , with the second side thereof facing upwardly, is moved past the second rubber blanket cylinder  11  and printed on the second side. 
   After the transfer of the sheet  5  to the inverting drum  9 , the slide  22  is moved back from the second shaft  25  to the first shaft  24  over a second plane of motion or travel plane  34 . At the first shaft  24 , the slide  22  is moved back into the first plane of motion or travel plane  35  and, as described hereinbefore, along the first plane of motion  35 , is moved past the third and fourth tangent point  30 ,  31 . 
   For driving the belt  3 , a drive shaft  36  is provided, which is driven by a motor. The slide  22  is preferably connected formlockingly to a chain or toothed rack driven by the motor via a gearwheel. In this regard, it is noted that a formlocking connection is one that connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection, which locks the elements together by force external to the elements. The gearwheel is coupled via a coupling, in-register, to a drive train of the printing press, so that, upon acceptance and transfer of the sheet  5 , the slide  22  is guided in-register. 
   In this way, inverting in-register transfer of the sheet  5  at the third tangent point  30  is possible. Furthermore, a precise transfer of the sheet  5  to the sixth gripper  32  of the inverting drum  9  is thereby possible, so that a predetermined location with respect to the printing operation can be maintained by the second rubber blanket cylinder  11 . 
   The first plane of motion  35  is preferably embodied as a straight or slightly curved plane, because it is thereby possible to provide the printing press  1  with a smallest possible structural shape. 
     FIG. 3  shows a further embodiment of the invention, wherein a sheet support  8  is provided with a belt  23 , which revolves in the form of an endless belt between the first and second shafts  24 ,  25 . In addition, a delivery table  27  with a suction device that has a suction channel  28  and suction openings  29  is provided, but contrary to the embodiment of  FIG. 2 , it is disposed between the third and fourth tangent points  30  and  31 . In this embodiment, no slide  22  is provided; instead, the sheet  5  is taken over at the third tangent point  30  by the belt  23 , which is preferably formed with suction openings as retaining elements. In this regard, the sheet is then not taken over in-register by the transfer cylinder  3 . Thereafter, the sheet  5  is moved under the fourth tangent point  31 , with the leading edge  6  leading, and is carried by the leading edge  6  to a registration device  41 . The registration device  41  is disposed in the first plane of motion  35  and, for example, has a stop element  42 , which rotates and establishes a defined location of the sheet  5 . The sheet  5  is moved with greater speed than the rotary speed of the stop element by the slide  22  and is braked by the stop element  42  and moved in a defined path of motion, which is embodied in-register with the inverting drum  9 . To that end, the registration device  41  is coupled via a coupling into the wheel train of the printing press. Via the coupling, a calibration of the registration device  41  for in-register synchronization is possible. The sixth gripper  32  engages the trailing edge  7  of the sheet  5  at which the sheet  5  is transferred to the third or fourth gripper  18 ,  19  of the second impression cylinder  4 . By using the registration device  41 , assurance is provided that the sheet  5  will be transferred to the second impression cylinder  4  in a predetermined printing position. 
     FIG. 4  diagrammatically shows the layout of a slide  22  and a support table  27 . The support table  27  is formed with guide slits  39 , so that the support table  27  has a comblike structure. In the teeth of the comblike structure, suction openings  29  are formed, which are supplied with negative pressure or suction via the suction channel  28 . The slide  22  is embodied as an at least approximately rectangular plate, on one transverse side of which a plurality of sheet supports  38  are disposed in parallel adjacent one another, and sixth grippers  37  are associated therewith. When taking over a sheet  5 , the edge of the sheet  5  to be taken over is placed on the sheet support  38  and firmly clamped on the sheet support  38  by the seventh grippers  37 . The path of motion of the slide  22  is such that the slide  22  is moved to the support table  27  from below, and the sheet supports  38  are guided by the guide slits  39 . Next, the sheet is firmly clamped by the seventh grippers  37 , and the slide  22  is moved to the lefthand side, away from the support table  27 , in the direction towards the guide slits  39 . The clamping function of the seventh grippers  37  is performed via cam drives or other mechanical or electrical control devices, which are otherwise not explicitly shown. 
     FIG. 5  shows a conveyor system  21  wherein a slide  22  is provided, which is guided in-register via toothed racks  43  and  45 . The slide  22  has one upper and one lower toothed rack  43  and  45 , respectively, which are solidly connected to the slide  22 . The sheet supports  38  and the seventh grippers  37  are disposed in the front or leading region of the slide  22 . Also, at both ends, the slide  22  has a respective overturning peg or pin  48 . The slide  22  is driven in an upper position I by a first and second drive wheel  46  and  47 , which formlockingly or positively engage in the lower toothed rack  45 . The first and second drive wheels  46  and  47  are connected to the gearwheel train  58  of the printing press via couplings  57 . By a correspondingly synchronized engagement of the first and second drive wheels  46  and  47 , in-register guidance of the slide  22  is achieved. The slide  22  is moved from the first position I to the lefthand side, wherein the lefthand overturning peg  48 , which is secured to the lefthand side of the slide  22 , is guided laterally in a guide path  49  and revolves in a curved path. The righthand overturning peg  48  is grasped during this movement by a first overturning wheel  50  and guided downwardly in a curved path to a second position II. The slide  22  preferably remains horizontal, in this regard. In the second position II, the slide  22  is guided from the lefthand to the righthand side, again via the first and second drivewheels  46  and  47 , which forcelockingly engage in the upper toothed rack  43 . On the righthand side, the slide  22  is moved upwardly again from the second position in the direction towards the support table  27 , not shown in FIG.  5 . The righthand overturning peg  48  is guided in the guide path  49 , and the lefthand overturning peg  48  is grasped by the second overturning wheel  51  and moved upwardly. When the slide  22  reaches the upper, first position I, the slide  22  is moved a slight distance to the lefthand side by the second overturning wheel  51 , so that the second drivewheel  47  can engage in the lower toothed rack  45 , and the slide  22  moves to the lefthand side in the direction towards the first drivewheel  46 . 
   Preferably a plurality of slides  22  are provided which, at staggered times, are moved in the revolving path that is prescribed by the guide path  49 . 
     FIG. 6  shows a further embodiment of the invention, wherein the slide  22  is not guided in-register by a belt, chain or other drive, but instead, a registration wheel  54  is provided, which effects an in-register guidance of the slide  22 . In the embodiment shown, the slide  22  is moved from the righthand to the lefthand side of  FIG. 6  by a belt at a fixed speed, until the slide  22  lies with a calibration lug  55  on a calibration face  56  of the registration wheel  54 . The calibration lug  55  is guided through the slide  22  and is secured to a sheet support  38 . The slide  22  has an elongated recess, through which the calibration lug  55  is guided downwardly through the slide  22  by the sheet support  38 , and which permits motion relative to one another of the sheet support  38  and the slide  22 . Via a sliding device  44 , the sheet support  38  is connected laterally displaceably with the slide  22 . In addition, the sheet support  38  is coupled via a spring element  52  to a fastening block  53  of the slide  22 . If the calibration lug  55  engages the calibration face  56  of the registration wheel  54 , then the further motion of the sheet support  38  is prescribed by the registration wheel  54 . The registration wheel  54  is supported rotatably on a shaft and is coupled via a coupling  57  with the gearwheel train  58  of the printing press. Via the coupling  57 , an in-register calibration of the registration wheel  54  takes place, so that the sheet, which is guided by the sheet support  38  and the associated seventh gripper  37 , can be received in-register or transferred in-register. In this embodiment, the slide  22  moves faster than the rotary speed of the registration wheel  54 , so that, after the contact of the calibration lug  55  with the registration wheel  54 , the slide  22  executes a motion relative to the registration wheel  54 . However, because of the contact of the calibration lug  55  with the registration wheel  54 , the sheet support  38  is coupled directly with the rotary speed of the registration wheel  54 , so that the sheet support  38 , with the seventh gripper  37  and a sheet  5  clamped therein, executes a relational motion with respect to the slide  22 . In this regard, the spacing between the sheet support  38  and the fastening block  53  increases in the in-register guidance by the registration wheel  54 . After a prescribed angular rotation of the registration wheel  54  counterclockwise, the calibration lug  55  is released again, and the sheet support  38  is withdrawn into the starting position thereof by the spring element  52 . 
   The embodiment shown in  FIG. 6  offers the advantage that the slide  22  need not itself be guided in-register; instead, in-register calibration of the sheet support  38  and of the seventh gripper  37  is effected by a registration wheel  54 .