Note: Descriptions are shown in the official language in which they were submitted.
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A-40933/ESW
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LASER IMAGING SYSTEM AND METHOD
FOR IMPOSING PAGES FOR PRINTI~G
This invention pertains generally to laser imaging systems
and methods, and more particularly to a system and method
for imaging a plurality of pages with the proper orienta-
tions and positions for printing in an imposition format.
S In the printing of books and other publications, a
plurality of pages are printed on a single sheet which is
then folded to form a series of imposed pages known as a
signatureO In order for the pages to appear in the proper
~ sequence and orientation in the signature, they must be
positioned and oriented properly on the sheet which is
folded. The positioning and orientation of the pages on
the sheet is known as the imposition format.
In recent years, electronic page composition systems and
laser platemakers have provided greatly enhanced
flexibility and speed in page composition and plate
making. An example of a laser platemaker is found in U.S.
Patent 4,393,411, and an example of a computerized
composition and plate making system is found in U.S.
Patent 4,240,119. In these systems, the output medium is
generally scanned in raster fashion to form an image of
the page to be printed. Since the scanning is done in a
single, fixed direction, e.g. from top to bottom of the
page, these systems have heretofore not been suitable for
use in the preparation of impositions where different
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orienta~ion~i and positions are reatlired for different
p~ges.
It is in general an obj~ct of thc inv~ntion to provide a
new and improved las~r imaging system and method which
overcome the foregoing and other limitations and
; disadvantages of laser imaging systems heretofore
provided.
¦ Another object of the invention is to provide a system and
method of the above character which can image a plurality
of pages on an output medium with the orientations and
positions required for an imposition format.
These and other objects are achieved in accordance with
the invention by scanning one area of a printing plate or
other output medium with a laser beam to form an image of
one of the pages to be printed, then scanning a second
area of the medium with the beam to form an image of a
second page. In each area, the direction of beam travel
and the data with which the beam is modulated provide the
proper orientation and position of the image for the
imposition format. In one disclosed embodiment, the
images are formed in head-to-head relationship toward
opposite ends of the output medium. The beam is advanced
to a central position between the ends of the medium, then
turned on and scanned in a first direction to image one of
the pages in right reading relationship in raster fashion
between the central position and one end of the output
medium. Thereafter, the beam is returned to the central
position, then turned on and scanned in the opposite
direction to image a second page in wrong reading rela-
tionship between the central position and the other end ofthe medium. The output medium can be shifted laterally to
image additional pages beside the first two.
:
Figure 1 is a block diagram of one embodiment of a laser
imaging system according to the invention.
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F`i~ure 2 is a simplified block diagram of the l~ser
platemaker in the imaging system of Figure 1.
Figure 3 is a plan view of a sheet with an imposition
format printed in accordance with the invention.
Figure 4 is a schematic drawing of the sheet of Figure 3
folded to form a signature.
As illustrated in Figure 1, the laser imaging system
includes an electronic page composer 11 and a laser plate-
maker 12. This system can be utilized in the production
of plates for different types of printing systems
including offset lithography, direct lithography (dilitho)
and letter press systems. For offset and dilitho systems,
the output medium on which the image is formed is the
plate itself, and for letter press systems the output
medium is a film negative from which the plate is made.
'
The page composer includes a computer 13 and an interface
14 which can, for example, be of the type described in
detail in U.S. Patent 4,240,119. The computer has a
keyboard through which data and cor~ands can be entered
into the system, and it delivers data and control signals
to the platemaker.
The platernaker can be of the flatbed type described in
U.S. Patent 4,240,119 or in U.S. Patent 4,393,411, or it
can be o f another suitable type such as a drum scanner.
In addition to the elements shown in Figure 2, it can
include a reading system for scanning data from input copy
on a read platen. Data read from the input copy can be
transferred to the computer via the interface unit, where
it can be stored and cornbined with data input through the
computer for presentation to the platemaker. Plates or
negatives can be imaged in three different modes of
operation: (1) a local mode in which data read from the
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read platen is imaged directly on the output medium, ~2) a
computer mode in which data from the computer is imaged on
the output medium, and (3) a merge mode in which data from
the computer is combined with data from the read platen
S and imaged on the output medium. In addition, data stored
in the computer memory for individual files or raster
images can be combined to produce a complete page or other
composite raster image.
As illustrated in Figure 2, the platemaker includes a
write platen 16 on which the printing plate or output
medium 17 is mounted. A writing beam 18 produced by a
laser 19 is modulated by modulator 21 in accordance with
the data to be imaged on the output medium. The modulated
beam is directed to a scanner 22 which causes the beam to
- lS scan laterally across the output medium. The scanner is
mounted on a carriage 23 which is driven by a reversible
drive motor 24 in a direction generally parallel to the
longitudinal axis of the output medium. As the carriage
advances, the scanner scans the beam over the output
medium in raster fashion.
A position sensor 26 monitors the longitudinal position of
the carriage. In one presently preferred embodiment, this
sensor includes limit switches which are actuated when the
carriage reaches opposite ends of its travel. The sensor
also includes an optical encoder which provides a signal
corresponding to the position of the carriage between the
i extremes of its travel. If desired, this signal can also
I be utilized to indicate the end points of the carriage
; travel.
Means is also provided for shifting the position of the
write platen in the lateral direction to permit images of
pages to be formed side by side on the output medium. In
the embodiment illustrated, this means includes a lateral
I positioning motor 27 connected to the write platen, and
, 35 the platen can also be positioned manually, if desired.
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- Data from the elect~onic page co~poser lI is applied to
the modulating input of modulato~ 2I via a memory 29.
Data is read into this memory one line at a time, and it
can be read out of the memory either in a forward direc-
tion for read-right imaging or in a reverse direction for
read-wrong imaging. Data read out of the memory can also
be complemented to produce negative images, as in the
exposure of negatives for letter press plates.
Operation of the platemaker is controlled by a micro-
processor 31 which receives inputs from electronic page
composer 11 and carriage position sensor 26. The
processor delivers output signals to the page composer and
to YariOUS elements of the platemaker including modulator
26, memory 29, drive motor 24 and lateral positioning
motor 27.
Operation and use of the imaging system, and therein the
method of the invention, can be described with reference
to the imposition format of Figure 3. This figure
illustrates a sheet 36 having an imposition format for the
- 20 8-page signa~ure shown in Figure 4. Each side of the
sheet is divided into four areas by fold lines 37, 38, and
the numbers on the sheet designate the pages to be printed
in the different areas. The circled numbers represent
pages to be printed on the front side of the sheet, and
the uncircled numbers represent pages to be pr~nted on the
back side. The numbers are oriented in accordance with
the directions in which the respective pages should face
when they are printed. Thus, pages 1 and 8 are printed
side by side on the lower half of the front side of the
sheet, pages 4 and 5 are printed upside down on the upper
half of the front side, pages 2 and 7 are printed right
side up on the lower half of the bac~ side, and pages 3
and 6 are printed upside down on the upper half of the
back side. After all of the pages have been printed, the
top half of the sheet is folded rearwardly and down along
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line 37, then the sh~et is folded along line 38 to form
the signature shown in Fiyure 4.
A printing plate for printing the front side of the
imposition format illustrated in Figure 3 in an offset
S process is produced by mounting the plate in a fixed
position on write platen 16. Drive motor 24 is actuated
to advance carriage 23 at a relatively high speed from its
home position near one end of its travel to a central
position in which the beam is located midway between the
ends of the output medium. Once the carriage reaches the
central position, the drive motor advances the carriage at
the normal scanning speed in the forward direction, and
the beam is turned on and modulated with data for imaging
pages 1 and 8 in a read-right fashion on the lower half of
lS the output medium. When these images have been formed,
the writing beam is turned off, and the drive motor is
reversed to return the carriage to the central position at
the relatively high speed. Thereafter, the drive motor
advances the carriage back toward the home position at the
normal scanning speed, and the writing beam is turned on
~ and modulated with data to image pages 4 and S in an
inverted position on the top half of the plate. These
pages are imased from top to bottom in a read-wrong
fashion as the beam travels from the center of the plate
toward the top edge of the plate. A plate for printing
the back side of sheet 36 can be prepared in a similar
mannex.
A plate for dilitho printing is produced in a similar
manner, with the images reversed so that the pages on the
bottom half of the plate are imaged in a read-wrong
fashion and the pages on the top are imaged in a read-
right relationship. For a negative, the data with which the
beam is modulated is complemented to produce the negative
image.
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A wide variety of imposition formats can be produccd with
the invention. ~dditiona1 pages can be imaged both at the
sides and at the ends of the original pages si~ply by
shifting the output medium laterally or longitudinally.
In the embodiment disclosed, proper orientation of the
images for different paqes is achieved by the direction in
which the pages are scanned and the order in which the
data for each scan line is read out of memory 29. The
orientation and positioning of the images can also be
controlled by the computer and the page composer, in which
case the images can be oriented in other directions by
rotation of the data supplied to the platemaker. In this
~- manner, for example, the output images can be rotated 90
to produce plates for printing tabloid newspaper plates
side by side.
While the invention has been described with specific
reference to printing plates and negatives for making
printing plates, it can also be utilized with other
~ photosensitiv~ materials such as films, papers, and
proofing materials. For example, images can be formed
directly on DYLUX (DuPont trademark) paper for proofing
purposes.
It is apparent from the foregoing that a new and improved
laser imaging system and method have been provided. While
only certain presently preferred embodiments have been
described in detail, as will be apparent to those familiar
with the art, certain changes and modifications can be
made without departing rom the scope of the invention as
defined by the following claims.
