Printing – Multicolor – Rotary machines
Reexamination Certificate
2002-03-26
2003-10-28
Eickholt, Eugene H. (Department: 2854)
Printing
Multicolor
Rotary machines
C101S211000, C101S248000, C101S485000, C101S486000
Reexamination Certificate
active
06637327
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a control apparatus for an image exposure apparatus which exposes an image on a printing plate, an image exposure apparatus, and a control apparatus which controls a multicolor printing press.
[Plate Making on Press]
In recent years, in order to improve the efficiency of plate making operation or to improve the registration accuracy, a plate making apparatus is attached to a printing press itself whereby plate making operation is directly performed on the printing press by the plate making apparatus. That is, instead of using a plate making apparatus separated from a printing press, a printing plate (raw plate) mounted on a plate cylinder is irradiated with a laser beam from the head of a plate making apparatus attached to a printing unit, thereby exposing an image. This operation is called plate making on press.
More specifically, the rotational speed of the printing press is increased to a designated value. When the rotational speed has stabilized, laser irradiation (exposure) from the head to the printing plate is started. After that, the head is moved in the axial direction of the plate cylinder while continuing exposure, thereby exposing an image on the entire plate mounted on the plate cylinder. The exposure time is determined by the plate size and the designated rotational speed at the time of exposure. Techniques for exposing an image on a printing plate by laser irradiation are disclosed in U.S. Pat. No. 5,379,698 (reference 1) and the like, and a detailed description thereof will be omitted.
FIG. 4
shows the attached state of plate making apparatuses to a four-color rotary printing press. Referring to
FIG. 4
, plate making apparatuses
102
-
1
to
102
-
4
are attached to printing units
101
-
1
to
101
-
4
of the respective colors. The plate making apparatuses
102
-
1
to
102
-
4
are normally at positions indicated by the alternate long and two dashed lines in FIG.
4
. When exposure operation is to be performed, they are moved close to plate cylinders
103
-
1
to
103
-
4
in the printing units
101
-
1
to
101
-
4
. Reference numerals
104
-
1
to
104
-
4
denote blanket cylinders on which blankets are mounted. Impression cylinders (not shown) are arranged under the blanket cylinders
104
-
1
to
104
-
4
.
FIG. 5
shows main part of a plate making apparatus
102
. The plate making apparatus
102
has an exposure unit
102
b
having a head
102
a.
The exposure unit
102
b
is fixed on a table
102
c.
The table
102
c
moves in the axial direction (indicated by a double-headed arrow A-B) of a plate cylinder
103
while being guided along rails
102
f
1
and
102
f
2
on a base
102
f
by a ball screw
102
e
rotated by a motor
102
d.
A printing plate (raw plate)
105
is mounted on the surface of the plate cylinder
103
.
In plate making on press, the exposure range of an image onto the printing plate
105
is set before the start of actual image exposure by causing an operator to input the X-coordinate distance (X1,0) from the origin (0,0) at the left edge on the leading edge side of the printing plate
105
to the left edge of the image range and the Y-coordinate distance (0,Y1) to the leading edge of the image range, as shown in FIG.
6
. That is, let W be the image size in the X-axis direction, and H be the image size in the Y-axis direction. The origin (0,0) is defined at the left edge on the leading edge side of the printing plate
105
. The image range is defined by X-coordinates “X1” and “X1+W” and Y-coordinates “Y1” and “Y1+H”.
Assume that the number of pixels of the image is n in the X-axis direction and m in the Y-axis direction, as shown in
FIG. 7. A
distance &Dgr;X between the pixels in the X-axis direction is given by &Dgr;X=W
, and a distance &Dgr;Y between the pixels in the Y-axis direction is given by &Dgr;Y=H/m. The plate making apparatus
102
defines &Dgr;X and &Dgr;Y as the exposure intervals in the X- and Y-axis directions and exposes image data that is input in advance within that image range.
More specifically, the head
102
a
of the plate making apparatus
102
is moved from the left to the right while rotating the plate cylinder
103
at a predetermined rotational speed. The head
102
a
is stopped at the position X1, and the pixels of one line in the Y direction are exposed at the interval &Dgr;Y. That is, pixels within the range from (X1,Y1) to (X1,Y1+H) are exposed. Next, the head
102
a
is moved to the right by &Dgr;X. At the next position, the pixels of the next line in the Y direction are exposed at the interval &Dgr;Y. This operation is repeated until the X-coordinate “X1+W”.
The image data (image “1”
on-image “0”) of each pixel is not stored in correspondence with the data of its exposure position. Only data of image “1”
on-image “0” are sequentially stored. In actual exposure, the image data are sequentially read out, and the pixels are sequentially exposed from the position (X1,Y1) at the interval &Dgr;Y in the Y direction and at the interval &Dgr;X in the X direction. This is because the number of image data to be processed is enormous. If the image data are collated with position data and exposed one by one, a very long time and large storage capacity are impractically required.
In printing by a rotary printing press, a high pressure must be applied to printing paper between the blanket cylinder and the impression cylinder. For this reason, the printing paper stretches toward the trailing edge side. Hence, the image printed by the preceding printing unit expands into a wide trapezoidal shape toward the trailing edge side, resulting in misregistration between colors. This tendency is especially conspicuous in offset printing because printing is executed with water supplied.
FIG. 8
shows an image state on printing paper after printing of the second color. A printing paper sheet
106
stretches due to printing by the second-color printing unit, and a first-color image
107
expands into a trapezoidal shape. For this reason, shifts are generated between the first-color image
107
and a second-color image
108
. That is, shifts w1 and w2 in the horizontal direction (a direction perpendicular to the sheet convey direction) of the printing paper sheet
106
, a shift h in the vertical direction (sheet convey direction), and shifts (distortion amounts) s1 and s2 due to distortions are generated. Similarly, the first- and second-color images further expand into trapezoidal shapes due to printing by the third-color printing unit. The first-, second-, and third-color images further expand into trapezoidal shapes due to printing by the fourth-color printing unit. In this way, shifts are generated between the color images, resulting in a defective printing product.
To solve this problem, the present applicant proposed in Japanese Patent Laid-Open No. 2000-309084 (U.S. Pat. No. 6,283,467; reference 2) a sheet-like object convey apparatus which stretches the trailing edge side of a printing paper sheet in the horizontal direction (right-to-left direction) upon transferring the printing paper sheet to a printing section whereby the shape of the printing paper sheet is deformed in advance into a trapezoidal shape whose width increases toward the trailing edge side to eliminate or reduce the stretch of the printing paper sheet during printing, thereby eliminating or reducing the shift of the image due to distortion by the stretch of the printing paper sheet during printing. The correction operation of the sheet-like object convey apparatus disclosed in reference 2 will be described with reference to
FIGS. 10 and 11
.
Referring to
FIG. 10
, when a swing
1
pivots from a point b to a point a, i.e., the gripping position of a feeding cylinder
4
along with rotation of a feeding cylinder shaft
4
a,
the edge portion of a paper sheet
6
is gripped by a plurality of gripper units (not shown) each formed from a gripper and gripper pad. Simultaneously, the central portion of a support shaft (not shown) that supports the
Endo Yasuji
Fuseki Takashi
Blakely & Sokoloff, Taylor & Zafman
Eickholt Eugene H.
Komori Corporation
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