Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-07-09
2002-02-19
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S250000, C101S463100, C355S047000, C358S296000
Reexamination Certificate
active
06348941
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a printing plate exposure apparatus for recording image data of printing image signals from a computer on printing plates on curved surfaces of drums.
1. Prior Art
Recently, with advances in the technologies of data processing and image processing by computers, a method of effecting a drawing directly on a printing plate with a laser beam by use of image signals from a computer, without interposition of photographic film, has been invented and put to practical use, even in the field of newspaper printing and the like.
Also, a well known printing plate called a PS plate—i.e., a printing plate for which a photo-sensitive material is pre-coated on an aluminum base plate—is commonly used.
Conventionally a well known drum rotary system for facsimile apparatus is used as a mechanism for drawing on such printing plates. Although a laser beam is used for drawing on the printing plate on the drum, technology has advanced such that a system of using a plurality of beams, rather than one beam, has been adopted for increasing drawing speed. Hence, as a conventional example, a system of recording data in a band shape with a plurality of laser beams, is described hereinafter.
As described above, a multi-beam system shown in
FIG. 11
is known as an apparatus for drawing picture images on a printing plate. Reference numeral
2
is a horizontally arranged drum
2
to be rotationally driven in a direction of an arrow “a” by a motor M, with a printing plate
4
being wound on an external circumferential face of the drum
2
.
Since the printing plate
4
is wound in a regular cylindrical shape such that a start side edge line
6
of the printing plate
4
and an end side edge line
8
thereof are not skewed, a top edge line
10
of the printing plate and a bottom edge line
12
thereof are positioned in parallel to each other in a drum axial direction.
An optical apparatus is mounted on an optical stand
14
. A laser beam coming from a laser light source
16
, such as a semiconductor laser or the like, is divided into multi-beams by a multi-beam producing element
18
, such as a grating, a Wollaston polarizing prism or the like. The multi-beam passes through an AOM group (acoustical optical modulator)
20
which is switch-controlled by image signals from the computer C. Then, the beams enter into an exposure unit
22
including a light source array made of optical fibers and are irradiated onto the printing plate
4
through a lens
24
. The light source array
22
is an example of an exposure unit for directly recording images onto the printing plate. An image band
26
is recorded on the printing plate
4
within a band width B corresponding to an irradiation width of the multi-beam. A moving mechanism H causes the optical stand
14
to continuously move at a uniform speed in a direction of an arrow “b” a distance of the band width B for one revolution of the drum
2
.
2. Problems to be Solved by the Invention
The aforementioned exposure apparatus has the following problems. As shown in
FIG. 12
, the drum
2
rotates at a uniform speed while the optical stand
14
moves the distance of the band width B per revolution. Therefore, the image band
26
is spirally recorded on the printing plate
4
, axially shifting a distance of the band width B for one revolution. When the printing plate
4
is unfolded (flattened), a recording image
28
, composed of many image bands
26
is formed in the shape of a parallelogram, distorted by a distance of the band width B due to the spiral recording operation. The printing plate, having such a deformation of the recording image
28
relative to the printing plate
4
, cannot be adopted for printing use.
For a printing plate for newspaper use, when a circumference of the drum is 46 inches, a picture element density is
909
dots per inch and a light source array
22
has 128 beams, the band width B is the equivalent of 128 picture elements, i.e. 128/909=0.14 inch, or 3.6 mm. The spiral recording results in a distortion of 3.6 mm, which is not visually negligible, between a top edge line
28
c
of the recording image
28
and a bottom edge line
28
d
thereof. An inclination angle &thgr; is 0.17 degrees, as calculated from tan &thgr;=0.14/46, and hence, a start side edge line
28
a
and an end side edge line
28
b
, both parallel to each other, have the inclination of 0.17 degrees.
In order to remove the inclination of the start side edge line
28
a
of the image with respect to the start side edge line
6
of the printing plate
4
, an intermittent moving system shown in
FIG. 13
has been invented. Namely, movement of the optical stand
14
is stopped while one revolution of the drum
2
for image recording takes place. Then, the optical stand
14
is moved through a distance of the band width B by the moving mechanism H. The moving time has to be set at an integral multiple of time required for one revolution of the drum. If this intermittent moving system is adopted, a recording image
28
is recorded in a regular square shape
2
. The recording image
28
is not distorted with respect to the printing plate
2
, because the image bands
26
are formed in regular circumferential shapes, not in the spiral shapes. But, the intermittent movement has a problem in that efficiency of such a plate making operation is lowered because an overall exposure time is several times longer than for the spiral recording method.
Also, a necessity for repeatedly starting and stopping movement of the heavy optical system makes the apparatus complicated and higher in price. This also causes vibrations which are likely to cause deterioration of images and malfunctions of the apparatus.
SUMMARY OF THE INVENTION
A printing plate exposure apparatus of this invention eliminates the aforementioned problems. A printing plate exposure apparatus in which image data is recorded spirally on a surface of a printing plate wound on a drum to have a band width of a plurality of picture elements comprises basically: the printing plate being wound spirally on the drum such that when one revolution of the drum is completed an extension line of a side edge line of the printing plate is shifted by a distance of the band width; an exposure unit for recording the image data in a band shape on the printing plate; a moving mechanism for relatively moving the exposure unit a distance of the band width in a drum axial direction, relative to the drum, for each revolution of the drum; and a timing mechanism for adjusting, for each revolution of the drum, a recording start position of the band for recording the image data so that a top edge line of a recording image is parallel with, at an equal interval from, a top edge line of the printing plate.
REFERENCES:
patent: 4819018 (1989-04-01), Moyroud et al.
patent: 4822151 (1989-04-01), Tatsuno et al.
patent: 5550574 (1996-08-01), Dillow
patent: 6151099 (2000-11-01), Okamura et al.
Griffin & Szipl, P.C.
Kabushiki Kaisha Kaneda Kikai Seisakusho
Le N.
Nguyen Lamson D.
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