Printing – Processes – Position or alignment
Reexamination Certificate
2003-03-26
2004-03-02
Eickholt, Eugene H. (Department: 2854)
Printing
Processes
Position or alignment
C101S211000, C101S181000, C101SDIG029, C101S365000, C356S402000, C358S296000
Reexamination Certificate
active
06698355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a patch measurement device provided in a printing apparatus, and more particularly to a patch measurement device for detecting the positions of patches constituting a control strip which is printed on printing paper.
2. Related Art Statement
There have conventionally been realized printing apparatuses which incorporate a so-called CTP (Computer To Plate) device, i.e., a prepressing device (=a printing plate recording device) that generates an image on a printing plate based on digital image data. A printing apparatus of this type, referred to as a DI (direct imaging) press, is capable of producing printed materials directly from image data, and therefore may be suitable for producing a variety of printed materials, each in relatively small quantities, over short periods of time. While prepress and other processes in such a digital printing apparatus are automated for ease of operation by non-proficient operators, further automation is desired in the control of ink supply, for example, during a printing process.
The control of ink supply in a conventional printing apparatus is generally realized by means of a separate console-type color measurement device, where a produced sample print is measured on a table. In this case, there is a problem in that a human operator needs to take out sample prints from the printing apparatus as necessary to measure the colors appearing on the printed materials.
In order to reduce the amount of work which requires the presence of a human operator as mentioned above, Japanese Patent No. 2824334 discloses a printing apparatus comprising a means for capturing an image of a printed material. In accordance with this printing apparatus, an image of a printed material is captured on an impression cylinder of the printing apparatus, whereby image data is obtained. This image data is compared against reference image data, which is previously read from a printed material that serves as a control reference, and the amount of supplied ink is controlled based on the comparison result. This printing apparatus has an advantage in that there is no need for a human operator as in the case of employing a console-type color measurement device because the printed material is imaged within the printing apparatus.
However, the aforementioned printing apparatus has a problem in that, since an image of the entire printed material must be read for comparison against the reference image, the size of the image data to be handled becomes large, thus requiring a relatively long image data processing time. Since it is necessary to prepare a reference image, this printing apparatus is not suitable for producing relatively few copies of a variety of printed materials, where agility is of the essence.
In order to solve the above problem, a printing apparatus has been proposed which prints a control strip (other than the actual printing image) on a printed material, such that the control strip is measured within the printing apparatus.
FIGS. 9A and 9B
are diagrams illustrating specific examples of such control strips. Hereinafter, the details of these control strips will be described with reference to
FIGS. 9A and 9B
.
FIG. 9A
is a diagram illustrating a printed material S which maybe obtained by using the conventional printing apparatus. As shown in
FIG. 9A
, the conventional printing apparatus prints an image im on printing paper, and thereafter prints four control strips cs
1
to cs
4
and three reference marks rm
1
to rm
3
on the same printing paper. Hereinafter, such four control strips cs
1
to cs
4
may collectively be referred to as “control strips cs”, and the three reference marks rm
1
to rm
3
as “reference marks rm”.
The image im is printed on the printing paper, beginning at a position (hereinafter referred to as a “print start position”) which is located a predetermined gripper margin f away from the leading end of the printing paper. More specifically, the image im is progressively printed in the direction of print progress indicated by the arrow (hereinafter referred to as a “first printing direction”), beginning from the print start position. The image im has a dimension m along the first printing direction, which is designated according to the image size. The control strips cs and the reference marks rm are printed beginning at a position which is a predetermined distance n away from the trailing end of the image im.
As shown in
FIG. 9A
, the control strips cs are typically printed on the printing paper with predetermined intervals therebetween along a direction (hereinafter referred to as a “second printing direction”) perpendicular to the first printing direction, and each control strip cs includes a plurality of rectangular-shaped patches arranged in a predetermined order. Each patch may be a half-tone, linework, or solid image which is printed at a predetermined density in a predetermined color.
FIG. 9B
illustrates an exemplary patch pc
1
.
As shown in
FIG. 9A
, the reference mark rm
1
is interposed between two adjoining control strips cs
2
and cs
3
. The reference mark rm
2
is interposed between the control strips cs
1
and cs
2
, and the reference mark rm
3
is interposed between the control strips cs
3
and cs
4
. As such, the reference marks rm
1
to rm
3
serve as references based on which to detect the positions of the control strips cs
1
to cs
4
. Typically, as exemplified by the reference mark rm
1
shown in
FIG. 9B
, a reference mark comprises two bars b
1
and b
2
which run parallel to the first printing direction, and a cross mark c interposed between the bars b
1
and b
2
. Each patch is printed at a position which is predetermined distances away—along the first and second printing directions—from a crosspoint P of the cross mark c. For example, the patch pc
1
is printed so that the center thereof is at a distance h (along the first printing direction) and at a distance w (along the second printing direction) from the crosspoint P of the reference mark rm
1
.
An image of the printed material S is captured by an imaging device provided in the printing apparatus, and is passed as “printed-image data” (i.e., data representing the actually produced printed material) to a patch processing device which is provided in the printing apparatus. Assuming that the patch pc
1
is currently to be processed by the patch processing device, the patch processing device first detects the crosspoint P of the reference mark rm
1
. Furthermore, the patch processing device estimates that a position which is at the patch distance h (along the first printing direction) and at the patch distance w (along the second printing direction) from the detected crosspoint P should be the relative position of the center of the patch pc
1
, which is currently to be processed. Thereafter, the patch processing device measures the color density information of the patch pc
1
at the estimated relative position.
As mentioned above, each control strip cs includes a plurality of patches which are arranged along the second printing direction. In the case where there are fifteen ink keys in the printing apparatus, the total number of patches would be 60 or more. However, due to limited spaces being available for printing the patches pc and the reference marks rm, the total number of reference marks rm which are printed on the printing paper is disproportionately small relative to the large number of patches. Even if an increased number of reference marks rm are employed, it would only invite an increase in the detection frequency of the reference marks rm, thereby resulting in more time being consumed for measuring the color density information. In this respect, the total number of reference marks rm should be minimized. In order to estimate the positions of a plurality of patches composing each control strip cs relative to a corresponding reference mark rm, the printing apparatus employs “image-to-print data”, i.e., data representing an image to be printed on the printing plat
Dainippon Screen Mfg. Co,. Ltd.
Eickholt Eugene H.
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