Abstract:
The invention relates to a machine for processing sheets, having a deliverer for delivering the sheets which comprises a delivery drum that is acted on pneumatically. The delivery drum has vacuum applied to it. The delivery drum also has disks for carrying the sheets, each of the disks defining vacuum channels for holding the sheets. The vacuum channels have openings and a vacuum connection. The openings and the vacuum connection together form a rotary valve cyclically applying vacuum to the vacuum channels.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     The present invention relates to a machine for processing sheets, having a delivery for delivering the sheets that includes a delivery drum that is acted on pneumatically.  
         [0002]     In German Patent DE 1 561 043 corresponding to U.S. Pat. No. 3,542,358 to Schuhmann, such a machine, whose delivery drum is acted on with blown air, is described. By the application of positive pressure to the delivery drum, a thin air cushion is formed between the sheet and the drum periphery, which prevents the printing ink from the sheet being smeared onto the drum. However, the application of positive pressure does not manage to prevent the printing ink smearing from the sheet transported by the delivery drum to the machine parts adjacent to the delivery drum.  
       SUMMARY OF THE INVENTION  
       [0003]     It is accordingly an object of the invention to provide a machine for processing sheets that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that has a delivery drum the transports the sheets safely past the adjacent machine parts without smearing.  
         [0004]     With the foregoing and other objects in view, there is provided, in accordance with the invention, a machine for processing sheets, having a delivery, or deliverer, for delivering the sheets includes a delivery drum that is acted on pneumatically, is characterized by acting on the delivery drum with a vacuum.  
         [0005]     As a result of acting on the delivery drum with a vacuum, in the machine according to the invention, a route for solving the problem—which is completely opposite to the prior art (e.g., German Patent DE 1 561 043)—is followed. It has been found that, for the protection against smearing onto the adjacent machine parts, it is much more effective to keep the sheet in contact with the delivery drum for some time by a vacuum of the latter, instead of keeping the sheet at a distance from the delivery drum by a blown air cushion.  
         [0006]     Advantageous developments will be explained briefly in detail in the following text.  
         [0007]     In an advantageous development with regard to protecting the sheets against smearing of their printed image as a result of the contact between the sheet and delivery drum necessitated by the application of vacuum, in accordance with another feature of the invention, the delivery drum includes disks for carrying the sheets. Because of the narrowness of the disks, these carrying disks support the sheet only locally, as seen over its sheet width, and not over the entire sheet width. As viewed in the direction of the sheet width, the disks can be disposed after one another such that contact points determined by the disks are located within corridors that are free of a printed image and that run in the longitudinal direction of the respective sheet. What is important to the disks is primarily their narrowness and less whether the respective disk is circular, corresponding to a full circle or, instead, only has the shape of a circular segment, or whether the respective disk is produced from one piece or is assembled from a plurality of segments. As a result of the interaction between the application of vacuum and the disks of the delivery drum, the sheet is held exactly and in a stable position on its necessary transport path, and the printing ink from the sheet can smear neither onto the delivery drum nor onto the machine parts adjacent to the delivery drum. The delivery drum is, therefore, particularly well suited to transporting sheets printed on both sides.  
         [0008]     In accordance with a further feature of the invention, each of the disks includes vacuum channels for holding the sheets. Although it is also conceivable to act on a drum part adjacent to the respective disk with the vacuum holding the sheet on the delivery drum, the application of vacuum to the disks themselves, carried out by the vacuum channels, is more advantageous from a functional and constructional point of view. The vacuum channels can have openings in the peripheral surface of the respective disk, and these openings can form a row running in the peripheral direction of the disk.  
         [0009]     In a departure from this development, however, it is also conceivable to provide only a single vacuum channel for each disk and a vacuum groove that extends in the peripheral direction of the disk, in its peripheral surface, which is open toward the sheet and in the base of which the vacuum channel opens.  
         [0010]     In a development that is advantageous with regard to avoiding drawing extraneous air into the delivery drum, in accordance with an added feature of the invention, the openings of the vacuum channels and a vacuum connection together form a rotary valve for the cyclic application of vacuum to the vacuum channels. The rotary valve ensures that each of the vacuum channels is connected at least once to the vacuum in the course of a complete revolution of the disk and is, then, isolated from the vacuum again. Although it is, likewise, conceivable for a common rotary valve to be associated with the disks (whose number is at least two and, preferably, exactly two), the valve controlling the vacuum in the vacuum channels of all the disks cyclically, it can be advantageous from various points of view to assign a different, dedicated rotary valve to each of the disks so that the rotary valves work with one another in parallel operation.  
         [0011]     In accordance with an additional feature of the invention, a vacuum-active angular range of the delivery drum is determined by the rotary valve or by each rotary valve, and is located in an exit pocket of a drum-cylinder nip. The rotary valve, therefore, ensures that the suction action from the delivery drum or its disks is exerted in a targeted manner in the exit pocket on the sheet section that has already emerged from the drum-cylinder nip and not on the sheet section that has not yet entered the drum-cylinder nip. In the region of an inlet pocket of the drum-cylinder nip, opposite the exit pocket, the vacuum channels are kept vacuum-inactive by the rotary valve so that the vacuum channels attract the sheet by suction at the earliest in the drum-cylinder nip in the course of its rotation.  
         [0012]     In accordance with yet a further feature of the invention, a sheet guide device that is adjacent to the delivery drum extends into the vacuum-active angular range. Such a sheet guide device is a machine element that is immediately adjacent to the delivery drum and that is intended to be protected against smearing by the application of vacuum to the delivery drum. The rotary valve or each rotary valve activates the vacuum of the delivery drum in the cycle of the sheets conveyed through between the delivery drum and the sheet guide device. The sheet guide device is, preferably, a pneumatically acting sheet guide device that is equipped with air nozzles, preferably, with blown air nozzles assisting the vacuum of the delivery drum from the opposite side. For example, the sheet guide device can be formed as a blown air box or as a blower pipe configuration.  
         [0013]     In a development that is advantageous with regard to pneumatic stabilization of the sheet position of one and the same sheet carried out simultaneously before and after the drum-cylinder nip, in accordance with yet another feature of the invention, the drum-cylinder nip is formed by the delivery drum together with an impression cylinder, and a blowing device for blowing the sheets against the impression cylinder is allocated to the impression cylinder. The blown air from the blowing device is aimed at the sheet and presses the sheet firmly against the peripheral surface of the impression cylinder. The vacuum-active angular range of the delivery drum and the blowing device are disposed to be offset from each other along the sheet transport path such that the blowing device holds the rear half of the sheet still on the impression cylinder while the front half of the sheet is already being held by the activated vacuum channels on the delivery drum.  
         [0014]     In accordance with yet an added feature of the invention, the blowing device is allocated to the impression cylinder between a press nip formed by the impression cylinder and the drum-cylinder nip. As viewed in the direction of movement of the sheets, the blowing device is, therefore, disposed after the press nip and before the drum-cylinder nip. The impression cylinder can form the press nip together with a blanket cylinder provided for offset printing or instead for full-surface varnishing or with a printing form cylinder bearing a flexographic printing form for spot varnishing.  
         [0015]     In accordance with yet an additional feature of the invention, at least one of the disks is mounted such that it can be adjusted relative to another of the disks in the direction of the width of the sheets, that is to say, transversely with respect to the transport direction of the sheets. The disk is, preferably, mounted such that it can be set as desired to various distances relative to the other disk. This setting can, preferably, be carried out continuously so that, within the adjustment range of the disk, any desired distance between the adjustable disk and the other disk can be set. The respectively selected distance, at which the disk is secured after its setting, can depend on the format of the sheets (sheet width) or on the position of the already mentioned corridors of the sheet that are free of a printed image.  
         [0016]     In accordance with again another feature of the invention, the delivery drum is disposed or mounted within a circulation path of a chain conveyor. This means that the delivery drum is disposed such that chains of the chain conveyor run around the delivery drum.  
         [0017]     In accordance with again a further feature of the invention, the machine according to the invention is, preferably, configured as a perfecting press. In such a perfecting press, each sheet is printed on both its sides in a single printing cycle. In connection with such sheets printed on both sides, the envisaged anti-smearing measures (vacuum application, disks) come fully into effect. As a result of the vacuum application, smearing of the printed image on the sheet side facing away from the delivery drum is avoided, by its contact with the sheet guide device being avoided and, by the disks, at the same time smearing of the other printed image on the sheet side facing the delivery drum is avoided by the facing sheet side being supported by the disks only in unprinted regions, that is to say, outside the printed image.  
         [0018]     With the objects of the invention in view, there is also provided a machine for processing sheets, including a delivery for delivering the sheets, the delivery having a delivery drum with a surface and a vacuum source fluidically connected to the delivery drum and applying a negative pressure vacuum to the delivery drum to draw air from the surface of the delivery drum.  
         [0019]     With the objects of the invention in view, there is also provided a machine for processing sheets, including a delivery for delivering the sheets, the delivery having a delivery drum acted on pneumatically by having a vacuum applied thereto, disks for carrying the sheets, each of the disks defining vacuum channels for holding the sheets, and the vacuum channels having openings and a vacuum connection, the openings and the vacuum connection together forming a rotary valve cyclically applying the vacuum to the vacuum channels.  
         [0020]     Other features that are considered as characteristic for the invention are set forth in the appended claims.  
         [0021]     Although the invention is illustrated and described herein as embodied in a machine for processing sheets, it is, nevertheless, not intended to be limited to the details shown because 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.  
         [0022]     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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a cross-sectional view of an overall diagrammatic illustration of a press having a sheet delivery according to the invention;  
         [0024]      FIG. 2  is a fragmentary, cross-sectional view of a delivery drum of the sheet delivery of  FIG. 1 ; and  
         [0025]      FIG. 3  is a fragmentary, perspective view of the delivery drum of  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     Referring now to the figures of the drawings in detail and first, particularly to  FIG. 1  thereof, there is shown a machine  2  processing sheets  1 . The machine  2  is a sheet-fed press, specifically a recto and verso press, and includes a printing unit  3 . 1  for printing the front side of the sheet and a printing unit  3 . 2  for printing the rear side of the sheet. The printing unit  3 . 2  includes an impression cylinder  4  and a blanket cylinder  27 , these two cylinders  4  and  27  together forming a press nip  24 . In addition, the machine  2  includes a delivery  5  having a chain conveyor  6  and what is referred to as a delivery drum  7 . The chain conveyor  6  runs around the delivery drum  7  and deposits the sheets  1  on a stack  8 . The chain conveyor has grippers  9 , which move along a circulation path  26 , and chains  10  that carry the grippers  9  and determine the circulation path  26 . The impression cylinder  4  transfers the sheets  1  one after another to the grippers  9  at a transfer point. The transfer point is a drum-cylinder nip  23  formed by the delivery drum  7  together with the impression cylinder  4  and is located in the first quadrant of the delivery drum  7  if a sheet transport direction from right to left is used as a basis, as in  FIG. 1 .  
         [0027]     The delivery drum  7  is what is referred to as a skeleton drum and has disks  11  that carry the sheets  1  and are seated at a distance from one another on a rotating axle  25 . Each of the two disks  11  is mounted such that it can be displaced individually and relative to the other of the two disks  11  along the axle  25 . As a result of the displacement of the two disks  11 , these can be adjusted closer together or further apart as desired, and each of the two disks  11  can be positioned in a manner coordinated with the sheet format of the respective print job such that the disks  11  contact the sheets  1  only at their side edges free of a printed image. Used as the axle  25  is what is referred to as the sprocket shaft, on which there are seated sprockets  12  that engage in the chain teeth and belong to the chain conveyor  6 . The disks  11  have diametrical clearances  13 , into which the grippers  9 , formed as gripper bars, dip during their circulation. The peripheral speeds of the chain conveyor  6  and of the delivery drum  7  or the disks  11  are synchronized. In addition, each disk  11  is associated with a securing device  14 , by which the corresponding disk  11  can be fixed on the axle  12  in its respective axial position suitable for the format, for example, can be clamped firmly. The external diameter of the disks  11  substantially corresponds to that of the sprockets  12  and of the impression cylinder  4 .  
         [0028]     The delivery drum  7 , which is acted on pneumatically internally, is what is referred to as a vacuum drum and has vacuum channels  15  that are introduced into the disks  11 . The vacuum channels  15  extend longitudinally substantially radially and open in the peripheral surface of the respective disk  11 . Openings  16  of the vacuum channels  15  are disposed in rows, which run in the peripheral direction of the delivery drum  7  and extend substantially over the entire sheet length of the maximum sheet format. Each of the vacuum channels  15  is formed from a radial bore and a transverse bore that extends parallel to the axle  25  and intersects the radial bore. The transverse bores forming the inner ends of the vacuum channels  15  each have an opening  17 .  
         [0029]     These openings  17  of the vacuum channels  15  cooperate periodically in the course of the rotation of the respective disk  11  with a stationary vacuum connection  18 , which does not co-rotate with the disk  11 . The vacuum connection  18  is a groove in the shape of a circular arc and is permanently under a negative pressure that is produced by a vacuum source  30  (only illustrated diagrammatically in  FIG. 2 ), which is connected to the vacuum connection  18 . The vacuum connection  18  is open toward the openings  17  that, in the course of the rotation of the disks  10  about the geometric axis of rotation of the axle  12 , overlap one after another with the vacuum connection  18  to which vacuum is applied conducting vacuum from the vacuum channels  15  into the vacuum connection  18 . Each of the curved rows formed by the openings  17 , as viewed in the peripheral direction, is longer than the curved length of the vacuum connection  18  so that always only a subset of the vacuum channels  15  of the respective row and never all the vacuum channels  15  of this row communicates simultaneously with the vacuum connection  18 . The vacuum channels  15 , together with the vacuum connection  18 , therefore, form a rotary valve  19 , which is placed such that the delivery drum  7  is pneumatically active with respect to the outside only within an angular range a that begins substantially only at the transfer point  10  and ends still in the fourth quadrant of the delivery drum  7 . The angular range a is located in the immediate vicinity of an exit pocket  22  from the drum-cylinder nip  23 . Because of the alignment of the rotary valve  19 , the openings  16  are active in applying vacuum to the sheets  1  only within the angular range a. Within the angular range a, it is particularly important that the sheet  1  transported to the chain conveyor  6  is attracted against the delivery drum  7  by suction by the openings  16  to which vacuum is applied and is kept in contact with the rotating disks  10  and at a distance from a sheet guide device  20 , which extends with its curved end section as far as the angular range a underneath the delivery drum  7 .  
         [0030]     The sheet guide device  20 , running in a curve partly around the delivery drum  7 , includes a guide plate provided with blower nozzles. A blowing device  21  aimed with its blown air jets at the impression cylinder  4 , substantially in the second quadrant of the impression cylinder  4 , is used to hold the sheet  1  on the impression cylinder  4 .  
         [0031]      FIG. 2  illustrates a transport phase of the sheet  1  that is particularly critical in regard to the smearing of the ink printed in the printing unit  3 . 1  from the sheet  1  to the sheet guide device  20 . In this transport phase, the leading sheet end is gripped by a gripper  9  passing the delivery drum  7  and the trailing sheet end has already emerged from the press nip  24  (cf.  FIG. 1 ) of the printing unit  3 . 2 .  
         [0032]     Without any suitable countermeasure, there would be a risk of the sheet  1  separating from the delivery drum  7  in the angular range α and forming a loop of printing material that, as a result of striking the sheet guide device  20 , could cause smearing.  
         [0033]     A countermeasure that prevents this and has been tested successfully by the applicant functions as set forth in the following text.  
         [0034]     The vacuum channels  15 , which act after the transfer point (drum-cylinder nip  23 ), and the blowing device  21  disposed before this transfer point act together such that the sheet  1  exactly maintains its substantially S-shaped longitudinal curvature following the peripheral lines of the impression cylinder  4  and of the delivery drum  7  during the critical transport phase and, thus, the disastrous formation of waves in the printing material of the sheet  1  is suppressed. In tests, it has been shown that the action of the blowing device  21  on its own is not completely adequate to force the sheet  1  into its requisite movement path and to keep it at a distance from the sheet guide device  20  within the angular range a.  
         [0035]     However, it is not ruled out that, in specific applications, by its vacuum, the delivery drum  7  is sufficiently effective on its own, that is to say, without any support by the blowing device  21 .  
         [0036]     Nonetheless, the combination of the pneumatic devices disposed on the two opposite sides of the transfer point (upstream blowing device  21 , downstream angular range a of the vacuum delivery drum  7 ) has proven to be particularly effective.  
         [0037]     This application claims the priority, under 35 U.S.C. § 119, of German patent application No. 103 32 217.5, filed Jul. 16, 2003; the entire disclosure of the prior application is herewith incorporated by reference.