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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not limit or define the invention.
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.
Referring to
Referring now to
Referring now to
Referring still to
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.
Referring now to
Referring generally to
Referring now to
Torque balance for steady state equilibrium about each axis requires:
F
inkergear
−F
plate/inker
−F
loss=0
F
drive
+F
plate/inker
+F
plate/blanket
'F
plate/blanketgear=0
F
plate/blanketgear
−F
plate/blanket
F
inkergear=0
Solving the above three equations for the three gear train forces yields:
F
inkergear
=F
loss
+F
plate/inker
F
plate/blanketgear
=F
loss
+F
plate/blanket
+F
plate/inker
Fdrive=Floss
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.
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.
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.
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.
Number | Date | Country | |
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61199061 | Nov 2008 | US |