Abstract:
An offset printing unit has a first plate cylinder, a first blanket cylinder, at least one first inker roller, and a motor that drives the plate cylinder. The first plate cylinder supports a first printing plate and drive the first blanket cylinder. The first blanket cylinder supports a first printing blanket, rollingly engages the first plate cylinder, and rollingly engages a substrate. The at least one first inker roller supplies ink to the first plate and blanket cylinders and rollingly engages the first plate cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/199,061, filed Nov. 13, 2008, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to offset printing units, and, at least in some embodiments, to novel drive train configurations for offset printing units and their associated methods of use. 
         [0003]    A conventional offset printing unit typically includes a rotationally supported plate cylinder (or “printing cylinder”) carrying a printing plate. The printing plate has oleophilic surfaces defining an image area, and hydrophilic surfaces defining a non-image area. An inker (or “inker roller”) applies ink to the printing plate. The ink collects on the oleophilic surfaces to form an image which transfers to a blanket cylinder, and which, in turn, transfers to media, such as a web or sheet of paper, plastic, metal, or other substrate running between the blanket cylinder and an impression cylinder. The grouping of a plate cylinder and a blanket cylinder is often referred to as a “cylinder couple” or a “couple.” By transferring the image first from the printing plate to a blanket roller, and then to the web, the printing plate does not directly print the image on the web, hence the term “offset” printing. Moreover, by placing a cylinder couple (with accompanying inkers) on both sides of the paper, images are applied to both sides of the paper simultaneously, often referred to as perfecting printing. Application of an image on only a single side of the paper, on the other hand, is commonly known as non-perfecting printing. 
         [0004]    The circumference of the rotating cylinders determines the length of each repeated pattern printed onto the web passing therethrough. Therefore, in order to permit a press to be modified to permit printing of different sized repeated pattern, plate and blanket cylinders of selected circumferences are used to vary the repeat size provided by the press. Quality printing requires at least some degree of accurate synchronization of the cylinders. The cylinders may also be configured to permit throw off (separation for accessibility during routine maintenance and/or to allow the web to be fed therethrough). During this process, the precisely set contact stripe between the cylinders may be lost. 
         [0005]    The gear teeth that mesh between a driving gear and a driven gear tend to separate circumferentially (contact forms from one gear flank to another) when the gears rotate during the printing process. Thus, in a printing unit, the gear teeth on a driving gear, fixed to a blanket cylinder, tend to separate circumferentially from the gear teeth on a driven gear, fixed to an adjoining plate cylinder, when the cylinders rotate during printing. The circumferential separation experienced by such gear teeth in a printing unit may cause defects in the printed product. 
         [0006]    Typically, a plate cylinder of a printing unit may be circumferentially adjusted, and/or laterally adjusted. Poor quality such as color to color register variation or doubling of a printed image on a web or sheet of paper or material occurs when, among other things, the plate cylinder rotationally moves with respect to the blanket cylinder during the previously described separation of their respective gear teeth, the rate of movement per revolution of the plate cylinder varies as a function of the rate of revolution, i.e. the rotational speed, of the plate cylinder. Doubling occurs when the blanket cylinder prints the same image onto a web or sheet more than once, or prints a doubled image. One printing may result from the residual (leftover) ink of an image applied by the printing plate on the plate cylinder to one location on the blanket cylinder during one revolution of the blanket cylinder, as the ink remains on the blanket cylinder after the one revolution of the blanket cylinder. Another printing may be from ink of the same image applied by the printing plate on the plate cylinder to another location on the blanket cylinder after the one revolution of the blanket cylinder and after adjustment of the plate cylinder. The image on the web or sheet from the one printing and the image on the web or sheet from the other printing may vary from each other enough to give the appearance of a double image, i.e. doubling of an image. Doubling results in poor quality and/or wasted paper. Further, increased plate/blanket gear tooth contact load increases the operating margin which decreases register variation and/or doubling. There can be more than one residual image. 
       SUMMARY 
       [0007]    The present invention relates to offset printing units, and, at least in some embodiments, to novel drive train configurations for offset printing units and their associated methods of use. 
         [0008]    In some embodiments, an offset printing unit comprises: a first plate cylinder configured to support a first printing plate during printing; a first blanket cylinder configured to support a first printing blanket during printing, rollingly engage the first plate cylinder during printing, and rollingly engage a substrate during printing; at least one first inker roller configured to supply ink to the first plate and blanket cylinders during printing and rollingly engage the first plate cylinder during printing; and a first motor configured to drive the first plate cylinder during printing. 
         [0009]    In some embodiments, a method of driving the offset printing unit comprises the steps of: driving the first plate cylinder with the first motor; and driving the first blanket cylinder with the first plate cylinder. 
         [0010]    In some embodiments, a method of driving the offset printing unit comprises driving the first plate cylinder with the first motor; driving a second plate cylinder with a second motor; driving the first blanket cylinder with the first plate cylinder; and driving a second blanket cylinder with the second plate cylinder. 
         [0011]    The features and advantages of the present invention will be apparent to those skilled in the art. While those skilled in the art may make numerous changes, such changes are within the spirit of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not limit or define the invention. 
           [0013]      FIG. 1  is a cross-sectional view of one embodiment of an offset printing unit; 
           [0014]      FIG. 2  is a cross-sectional view of one embodiment of an offset printing unit; 
           [0015]      FIG. 3  is an exploded view of one embodiment of an offset printing unit; 
           [0016]      FIG. 4  is an exploded perspective view of one embodiment of an offset printing unit; and 
           [0017]      FIG. 5  is a perspective, exploded view of an embodiment of a plate cylinder drive offset printing unit showing primary forces and torques. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The present invention relates to offset printing units, and, at least in some embodiments, to novel drive train configurations for offset printing units and their associated methods of use. 
         [0019]    Referring to  FIG. 1 , in one embodiment offset printing unit  100  has at least one plate cylinder  102   a,  at least one blanket cylinder  104   a,  at least one set of inker rollers  106   a,  and at least one motor  108   a.  Plate cylinder  102   a  is configured to support printing plate  110   a  during printing, and to drive blanket cylinder  104   a  during printing. Blanket cylinder  104   a  is configured to support printing blanket  112   a  during printing, and to rollingly engage plate cylinder  102   a  and web  114  during printing. Inker rollers  106   a  are configured to supply ink to plate cylinder  102   a  and thus, to blanket cylinder  104   a  by rollingly engaging plate cylinder  102   a  during printing. Motor  108   a  is configured to drive plate cylinder  102   a  during printing. Optionally, impression cylinder  116  is configured to cooperate with blanket cylinder  104   a  to engage opposing sides of web  114  during printing. The configuration of  FIG. 1  enables printing on one side of web  114 . 
         [0020]    Referring now to  FIG. 2 , offset printing unit  100  is a unit configured to print both sides simultaneously, with an additional plate cylinder  102   b,  blanket cylinder  104   b,  set of inker rollers  106   b,  and/or motor  108   b  on an opposing side of web  114  from plate cylinder  102   a,  blanket cylinder  104   a,  inker rollers  106   a  and/or motor  108   a.  In this embodiment, impression cylinder  116  is omitted. Similar to the embodiment described above, the embodiment of  FIG. 2  includes plate cylinders  102   a  and  102   b  configured to support printing plates  110   a  and  110   b  respectively during printing. Plate cylinders  102   a  and  102   b  are further configured to drive blanket cylinders  104   a  and  104   b  during printing. Blanket cylinders  104   a  and  104   b  are configured to support printing blankets  112   a  and  112   b  during printing. Blanket cylinders  104   a  and  104   b  are further configured to rollingly engage plate cylinders  102   a  and  102   b  and web  114  during printing. Inker rollers  106   a  and  106   b  are configured to supply ink to plate cylinders  102   a  and  102   b  and thus, to blanket cylinders  104   a  and  104   b  by rollingly engaging plate cylinders  102   a  and  102   b  during printing. Motors  108   a  and  108   b  are configured to drive plate cylinders  102   a  and  102   b  during printing. In the embodiment of  FIG. 2 , blanket cylinders  104   a  and  104   b  engage opposing sides of web  114  during printing. 
         [0021]    Referring now to  FIG. 3 , offset printing unit  100  has motor gear  118 , plate gear  120 , and blanket gear  122 . Motor gear  118  is preferably coaxial with motor  108  and rotable therewith. Motor gear  118  has motor gear teeth  124 . Plate gear  120  is preferably coaxial with plate cylinder  102  and rotable therewith. Plate gear  120  has plate gear teeth  126  configured to meshingly engage motor gear teeth  124  and establish a driving connection between motor  108  and plate cylinder  102 . Blanket gear  122  is preferably coaxial with blanket cylinder  104  and rotable therewith. Blanket gear  122  has blanket gear teeth  128  configured to meshingly engage plate gear teeth  126  and establish a driving connection between plate cylinder  102  and blanket cylinder  104 . While  FIG. 3  illustrates a single motor gear  118 , plate gear  120 , and blanket gear  122 , any number of gears may be used to drive the various components. Additionally, offset printing unit  100  may include multiple motor gears  118 , plate gears  120 , and blanket gears  122  and associated teeth to correspond, for example, to motors  108   a  and  108   b,  plate cylinders  102   a  and  102   b,  and blanket cylinders  104   a  and  104   b  of  FIG. 2 . Further, the various gears and corresponding teeth may appear at either or both ends of the respective cylinders. 
         [0022]    Referring still to  FIG. 3 , blanket cylinder  104  is configured to drive inker rollers  106  during printing. For example, inker gear  130  is coaxial with inker rollers  106  and rotable therewith. Inker gear  130  has inker gear teeth  132  configured to meshingly engage second blanket gear teeth  134  on second blanket gear  136  and establish a driving connection between blanket cylinder  104  and the inker rollers  106  during printing. This driving connection may be established in a number of ways. For example, a gear train may provide one or more intermediate gears (e.g., gears  138 ) having teeth to provide one or more of the meshing engagements. Likewise, a similar configuration could be used to allow an additional blanket cylinder to drive additional inker rollers on an opposing side of a web in a two-sided printing operation. In other embodiments, gear  118  may be eliminated and motor  108  may drive directly into plate gear  120 . 
         [0023]    In another embodiment, the gear teeth may be minimized or even eliminated and belts may drivingly connected to motor  108  and plate cylinder  102  and/or any of the other components of offset printing unit  100 . 
         [0024]    Referring now to  FIG. 4 , in a single-sided printing operation, blanket cylinder  104  is configured to drive impression cylinder  116  and impression cylinder  116  is configured to drive inker rollers  106  during printing. As indicated above, this may be done through various gears and teeth, or via belt or any other method of driving. For example, blanket gear  122  is coaxial and rotable with blanket cylinder  104 , and drives impression cylinder gear  140 , which is coaxial and rotable with impression cylinder  116 , via meshing engagement between impression cylinder gear teeth  142  and blanket gear teeth  128 . Impression cylinder  116 , in turn, drives inker gear  130  via second impression cylinder gear  144 , and one or more intermediate gears  138 . 
         [0025]    Referring generally to  FIG. 1 ,  FIG. 2 , and  FIG. 3 , driving offset printing unit  100  includes a number of steps, which may be performed in any of a number of orders, and which are not all required. In one embodiment, the user provides (1) plate cylinder  102  so as to support printing plate  110 , (2) blanket cylinder  104  so as to support printing blanket  112 , (3) inker rollers  106  so as to supply ink to the plate cylinder  102  and blanket cylinder  104 , and (4) motor  108  connected to plate cylinder  102 . The user places blanket cylinder  104  in rolling engagement with plate cylinder  102  and place inker rollers  106  in rolling engagement with plate cylinder  102 . When all appropriate connections are in place, the user activates motor  108 , thus driving plate cylinder  102  with motor  108 , and driving blanket cylinder  104  with plate cylinder  102 . This embodiment also involves driving inker rollers  106  with blanket cylinder  104 . Depending on whether a perfecting or non-perfecting operation is desired, the user may repeat the steps for similar equipment on an opposite side of web  114 , such that blanket cylinders  104   a  and  104   b  engage opposing sides of web  114 , or the user may instead provide impression cylinder  116  and drive impression cylinder  116  with blanket cylinder  104 . The user drives inker rollers  106  with impression cylinder  116  and engages opposing sides of web  114  with impression cylinder  116  and blanket cylinder  104 . Alternatively, the user drives inker rollers  106  with blanket cylinder  104 , in either perfecting or in non-perfecting embodiments. 
         [0026]    Referring now to  FIG. 5 , with respect to plate cylinder  102 , a positive gain results from both inker rollers  106  and blanket cylinder  104 . As illustrated, the improved drive path  146  produces a redistribution of system internal forces, including forces from overspeed blanket path  148  and overspeed inker path  150 , which improves loading at the mesh between plate gear  120  and blanket gear  122 . Inker gear forces do not change with changes to drive configuration. In the conventional configuration, plate/blanket nip force opposes the loss force and thus decreases the possible plate/blanket gear force. However, in the configuration of  FIG. 5 , the plate/blanket nip force reinforces the plate/blanket gear force. The various forces are represented by the following equations: 
         [0000]    Torque balance for steady state equilibrium about each axis requires: 
         [0000]        F   inkergear   −F   plate/inker   −F   loss =0 
         [0000]        F   drive   +F   plate/inker   +F   plate/blanket   &#39;F   plate/blanketgear =0 
         [0000]        F   plate/blanketgear   −F   plate/blanket   F   inkergear =0 
         [0000]    Solving the above three equations for the three gear train forces yields: 
         [0000]    
       
      
       F 
       inkergear 
       =F 
       loss 
       +F 
       plate/inker  
      
     
         [0000]    
       
      
       F 
       plate/blanketgear 
       =F 
       loss 
       +F 
       plate/blanket 
       +F 
       plate/inker  
      
     
         [0000]      F drive =F loss    
         [0027]    One of the many potential advantages of the devices and methods of the present invention, only some of which are herein disclosed, may be reduction in potential printed register variation and doubling arising from relative in-unit displacement between plate cylinder  102  and blanket cylinder  104 . Additionally, the present invention provides adequate gear and journal stiffness, thereby making the relative cylinder torsional motion essentially the same as that of the corresponding gears. Moreover, the present invention provides larger nominal contact load between plate gear  120  and blanket gear  122  in normal operation, thereby reducing the potential for dynamic loss of contact while improving the inherent performance margin relative to the performance concern here. 
         [0028]    The dimensions, structure, and composition of plate cylinder  102 , blanket cylinder  104 , inker rollers  106 , and impression cylinder  116  are similar to those commonly used in the industry, as would be understood by one or ordinary skill in the art. Likewise, drive motor  108  may be any type of motor known to those skilled in the art; for example, a Servo motor may be used. 
         [0029]    Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. For example, gears may be on either side of any cylinder and one of ordinary skill in the art will understand that a driving relationship may exist in any of a number of configurations. Likewise, relative free surface velocities may be modified to obtain overspeed, neutral, and underspeed relationships between various components, as indicated by the design engineer. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduces. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.