Printing – Rolling contact machines – Rotary
Reexamination Certificate
2001-02-09
2002-11-12
Hirshfeld, Andrew H. (Department: 2854)
Printing
Rolling contact machines
Rotary
C101S053000, C101S183000, C101S420000
Reexamination Certificate
active
06477951
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a sheet-fed press in which the paper feed is stabilized. More specifically, the invention concerns stabilizing the movement of the sheet of paper in a sheet-fed press. The sheet-fed press according to this invention has first and second press cylinders. The first press cylinder is defined as an intermediate cylinder or a delivery cylinder whose curved surface serves to guide the sheet through the space between the curved surface and a sheet guide unit. The second press cylinder is defined as an impression cylinder or the like which is positioned next to the first press cylinder via a reception area.
2. Description of the Related Art
Multiple-color sheet-fed presses which employ a series of printers each of which prints a different color ink are well known in the prior art. As can be seen in
FIG. 6
, the basic structural elements of such presses are feeder unit A, which consists of feeder device
39
; printer unit B, which has four printers,
132
a
,
132
b
,
132
c
and
132
d
, arrayed in tandem to print cyan, magenta, yellow and black; and delivery unit C, here paper delivery unit
04
.
In multiple-color sheet-fed presses with this configuration, a sucker unit with an inlet for sheets
11
, which are piled on table
141
of the feed unit
39
, separates a single sheet and transports it on conveyor
120
. Swing gripper
121
a
delivers the sheet to intermediate cylinder
121
b
of printer
132
a
. The sheet is fed between blanket cylinder
22
a
and impression cylinder
23
a
, and the first color is printed.
Once the first color has been printed, the sheet is fed out between the blanket cylinder
22
a
and impression cylinder
23
a
and taken up by intermediate cylinder
27
a
of the second printer
132
b
. From the intermediate cylinder
27
a
, the sheet is delivered to impression cylinder
23
b
. The next process, the printing of the second color, is executed by blanket cylinder
22
b
and impression cylinder
23
b.
The subsequent colors are printed one after the other. When sheet
11
is fed out between blanket cylinder
22
d
and impression cylinder
23
d
, which perform the final-stage printing, it is pulled onto delivery cylinder
35
of delivery unit C. From delivery cylinder
35
, the now completely printed sheet
11
is taken onto chain conveyor
124
and transported to delivery unit
04
, where it is added to the stack on table
40
of the unit
04
.
Generally, the sheets
11
which are printed in a sheet-fed press are of a thickness which ranges from 0.04 m/m to 0.8 m/m. At times, high-rigidity sheets of metal plate or synthetic resin might also be printed. As the sheet is fed from printer
132
a
to printer
132
b
to print the various colors, various mishaps may occur. A thin sheet of paper will generally have low rigidity, and its rear portion will tend to flap. A thicker sheet of paper or sheet metal will have high rigidity, and its reaction force (stability) against the centrifugal force of rotation and its own curvature will cause its rear portion to separate from impression cylinder
23
, and collide with the sheet guide unit
1
′ below the cylinder resulting a paper rebounding.
When the paper flaps or rebounds in this way, the print may be smudged or the paper folded or torn. This phenomenon is a significant cause of a reduction in print quality. Two typical methods employed to counteract this problem are to use a skeleton cylinder or a drum cylinder for the intermediate cylinder
27
. This allows the most appropriate scheme to be used for the rigidity of whatever sheet is being printed.
The example shown in FIG.
7
(A) is a skeleton-type intermediate cylinder
27
, which is used primarily when printing thicker sheets of paper. One of these skeleton cylinders
27
is placed on each side of each printer
132
. Each skeleton cylinder consists of a pair of rotors (arms)
271
which rotate on axis
270
. Each arm
271
has a series of pawls
29
on its shaft
272
(see FIG.
8
(A)) running from the end of arm
271
to the end of arm
271
on the opposite side of the shaft. The distinguishing feature of the skeleton cylinder
27
is that the area of the cylinder which comes in contact with impression cylinder
23
when the paper passes between them is extremely small. The sheet
100
which is being rotated forward is allowed to bend beyond point P where it comes into contact with pawls
29
. In other words, the point of contact P becomes the point of action. By lengthening the distance from this point to the end of sheet
100
, we reduce the reactive force exerted by the sheet in its attempt to return to its original shape.
As a result, we reduce the amount of rebounding at the end of the sheet which strikes sheet guide unit
1
′, the curved guide which conforms to the hypothetical circumference of the lower portion of skeleton-type intermediate cylinder
27
. This scheme minimizes tears and folds; but on the other hand, because this sort of skeleton cylinder
27
provides a larger region in which the end of sheet
100
is free, a thin sheet will have more opportunity to flap.
The example shown in FIG.
7
(B) is drum cylinder-type intermediate cylinder
27
′, which is used primarily for thinner sheets of paper. This sort of drum cylinder
27
′ has a number of pawls
29
in two places along the circumference of a roller which rotates on axis
270
.
The feature which distinguishes drum cylinder
27
′ is that the amount of its surface area which comes in contact with impression cylinder
23
as sheet
100
is fed between them is maximized. Because the portion of sheet
100
which is beyond pawls
29
is guided along the circumference of the drum cylinder (
27
′), this scheme makes it very difficult for the end of the sheet to flap, so it minimizes doubling, tearing and other defects resulting from the end of the sheet wrinkling or flapping. However, when this sort of drum cylinder
27
′ is used to convey thicker varieties of paper, the fact that there is very little area where the end of the sheet is free will result in significant rebounding.
In recent years, as print quality has improved, there has been a tendency to use the skeleton cylinders even for thinner papers. To keep thin sheets from flapping, a sheet guide unit
1
is provided which has a sheet guide surface
1
d
following the contour of the lower portion of intermediate cylinder
27
(or
27
′) and delivery unit
35
(hereafter referred to as the intermediate cylinder). In order to address the problems in this sort of sheet-fed press, a sheet guide unit is provided in which specifically pressurized air is blown through a number of vents in the sheet guide unit into the space between intermediate cylinder
27
and surface
1
d
of the sheet guide unit. This air is blown along the bottom of sheet
11
as it passes through the space along sheet guide surface
1
d
. Because of the Bernoulli effect, the air blown through the vents causes the sheet
11
to be suspended.
One such sheet guide unit is described in Japanese Patent Publication (Kokai) Hei 10-109404. We shall explain the relevant technology with reference to FIG.
8
. The sheet guide unit, which runs along the circumference of skeleton-type intermediate cylinder
27
or delivery cylinder
35
, both of which are studded with pawls
29
, consists of air ducts
06
. On the upper surface of the air ducts
06
are numerous air vents
4
a
and
4
b
. The vents
4
a
and
4
b
face in opposite directions and are located on either side of the center of the intermediate cylinder
27
or of delivery cylinder
35
. The vents distribute the air toward the outer edges of the intermediate cylinder
27
. The vents
4
a
and
4
b
produce two streams of air which originate at the vents and continue to move in the directions determined by the vents. These air streams keep the sheet of paper suspended at a specified height, thus stabilizing the travel of the sheet.
In the prior art technique, then, air is blown through a space between sh
Crenshaw Marvin P.
Crowell & Moring LLP
Hirshfeld Andrew H.
Mitsubishi Heavy Industries Ltd.
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