Prediction and prevention of offset printing press problems

Details Prediction and prevention of offset printing press problems Prediction and prevention of offset printing press problems

1999-10-08

2002-08-27

Evans, Arthur G. (Department: 2622)

Facsimile and static presentation processing

Static presentation processing

Data corruption, power interruption, or print prevention

C358S001100

Reexamination Certificate

active

06441914

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to printing and graphic arts generally and more particularly to an apparatus for page composition and printing and a method for prediction and elimination of image content dependent artifacts.
GLOSSARY OF TERMS
The following terms, employed herein, are intended to have the meanings specified herein below:
Color Image
The term is intended to include image-comprising gradations of a single tone, such as black and white images.
Analog Representation of a Color Image
Any representation of a color image that resembles the original color image. The representation may appear upon a printed page, a proof or any other suitable substrate.
Digital Representation of a Color Image
Any representation of a color image which is expressed in discrete symbols, such as a computer file.
Color Characteristics of a Color Image
The characteristics of the color image, defined by individual elements of a representation of a color image, which directly represent a color or a component of a color.
Spatial Characteristics of a Color Image
Characteristics defining the arrangement of and the relationship between elements of a digital representation of a color image, such as pixels, which characteristics do not directly represent a color or a component of a color, Spatial characteristics include but arc not limited to resolution and format characteristics such as pixel by pixel encoding.
Ghost
Ghost is defined as the repeat of a previously printed image, one form roll revolution later.
Ghosting Prevention Bar
Ghosting prevention bar or ink collection bar is typically a rectangular area filled with color and placed on a signature/plate to prevent ghosting.
Plate, Signature, Imposition
Plate, Signature, Imposition have the same meaning as typically associated with that of a complete offset plate pattern that includes separate page images, registration marks, color control bars, ink collection bars and water trapping prevention bars.
Printer Spread
Imposed pages that have to keep the relative orientation between them for the printed product and pertain to the same printing form/plate.
BACKGROUND OF THE INVENTION.
The production of a book or magazine involves a large number of processes. Those processes may be grouped into five general categories: prepress, plate preparation, press set-up or “make ready”, press control operations and postpress operations.
In prepress, the principal processes are graphics, image and text editing and composition. In recent years, this area has undergone revolutionary changes through the application of computer technology. State of the art systems are available for graphics, image editing and composition and for the specific functions of scanning, image processing and film and plate setting, such as the systems manufactured and sold by Scitex Corporation Ltd. of Herzlia, Israel, under the trademarks EverSmart Scanner, Dolov and Lotem. Plate preparation involves a technique known as imposition or signature assembly, which refers to the arrangement of pages on a film in a Computer-to-Film system, on a plate in a Computer-to-Plate system or on a plate in a Computer-to-Press system. The present state of the art in signature assembly is the use of computerized systems such as the system sold under the name Brisqueimpose by Scitex Corporation Ltd. of Israel. If the imposition is performed to film, the film is later used for contact exposure of printing plates. In the ease where the imposition is performed to plate, the stage of contact exposure of printing plates is eliminated. Press set-up or “make-ready” takes place after preparation of the printing plate, and typically involves the steps of plate mounting ink key setting, which determines the supply of ink flow for that plate, solution or water setting, and other steps. If the imposition is performed on a plate in a Computer-to-Press system, plate mounting is not required. The ink key setting data is derived according to the image-on-plate coverage information, which is generated in the stage of computerized signature assembly. The ink key setting data may be generated by computerized systems such as the system sold under the InkPro trade name by Scitex Corporation Ltd. of Herzlie, Israel. Press set-up information, derived by the prepress systems, is typically communicated to the press using a standard Print Production Format communication protocol called CIP3, which is described at the Internet site http;//www.cip3.org/documents/technical_info/index.html. The ink key setting data generated by these computerized systems does not take into account, however, the wet ink trapping and accordingly does not provide correct ink key settings pen color.
U.S. Pat. No. 5,875,288 to Bronstein et al. discloses an integrated computerized system for use in color printing, having at least one digital representation of a color characteristic of at least one page to be printed and a digital storage memory for storing that digital representation. An imposition apparatus is connected to the storage memory, to receive the digital representation and arrange the digital representation in accordance with a desired plate layout, thereby to define a plate image. A press setup device extracts from the plate image the color characteristic and provides ink flow set-up data to a printing press in accordance with the extracted color characteristic.
A state of the art printing press is described in U.S. Pat. No. 4,936,211 to Pensavecchia et al. The patent discloses a printing apparatus which is intended to achieve complete computer control over the entire printing process, including plate generation, ink regulation and the start-up, print, hold, shut-down and clean up stages of the actual printing operation. Pensavecchia et al. also refer to a press including a workstation, which allows an operator to input a digital representation of an original picture to be printed. The workstation may include a CRT display and internal memory for storing image data, so that the impression to be printed may he previewed before panting. A keyboard is supplied, through which the operator may key-in instructions regarding the particular press run, such as the number of copies to be printed or the number of colors in the printed copies. The workstation is also intended to allow complete control over the operating modes of the press, including printing plate imaging, press startup procedure, ink flow regulation, dampening, print, pause, shutdown and clean-up sequences.
Despite the existence of sophisticated computerized prepress systems and printing presses, the press operator is often required to intervene in the printing process to maintain the target print quality. The deviations from the desired target print quality can be significantly reduced by taking into account the characteristics of the image to be printed. Typical examples of printing defects are ghosting, improper ink transfer, wet ink trapping, solution or water balance end others. These printing defects are typically discovered only during the printing process and in extreme cases may require complete press stop, re-imposition of the signature and the production of new plates, resulting in a significant loss of time and money.
Numerous efforts have been made to eliminate these image-dependent problems, in particular mechanical ghosting, which is the occurrence of unwanted patterns of higher or lower density created by the job layout, combined with the press's inking ability. Mechanical ghosts can be seen in heavy solids or in heavy process work on both single and multicolor presses.
There are two types of mechanical ghosts, sometimes referred to as ‘positive’ and ‘negative’. In ‘negative’ ghosts, illustrated in
FIG. 1A
, spot
20
of a slightly lighter tone (a ghost) will appear in a flat solid
22
. It takes on the form of another solid
24
on the plate
26
. 250-300 mm (10-12 inches) ahead of the ghost. The actual distance depends on the particular press construction. ‘Positive’ ghosts, illustrated in
FIG. 1B
, occur when a large solid
28
has a large rev

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