Banding-reduced imaging of a printing form

Details Banding-reduced imaging of a printing form Banding-reduced imaging of a printing form

2002-02-01

2004-07-20

Pham, Hai (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S234000, C347S248000

Reexamination Certificate

active

06765604

ABSTRACT:

Priority to German Application No. 101 08 624.5, filed Feb. 22, 2001 and hereby incorporated by reference herein, is hereby claimed.
BACKGROUND INFORMATION
The present invention generally relates to image-forming methods for use in the graphics technology, in particular, in the printing technology or duplicating technology. In particular, it relates to a method and a device for imaging a printing form via at least two imaging modules according to the respective generic parts of the independent claims.
In the field of graphics technology, in particular, of offset printing technology, it is known in the production of plane or curved printing forms through so-called “multibeam imaging” to use imaging modules, with which a plurality of imaging spots are simultaneously imaged on different media such as printing plates, films, data carriers, or the like.
At the moment, for imaging printing plates through light sources, one uses primarily laser diode systems which are based on two different concepts. On the one hand, the radiation of individual laser diodes or of an array of laser diodes can be guided to the medium to be imaged via optical elements such as lenses, mirrors or fibers. On the other hand, it is possible for the radiation from a laser light source, typically laser diode bars, to be imaged via diverse optical elements onto an array of n modulators, with n being a natural number, typically electro-optical or acousto-optical modulators. In this context, the individual control of the n modulators permits the selection of individual beams from the entire radiation and the modulation of the power thereof. Such laser diode systems are revealed, for example, by European Patent Application No. 0 878 773 A2 and U.S. Pat. No. 5,521,748.
Furthermore, so-called “interleaving raster scan line methods” (hereinafter referred to as “IRS methods”) are known in which raster scan lines are written onto a medium using a multibeam laser light source.
Thus, U.S. Pat. No. 5,691,759 reveals a method of that kind in which a laser light source generates n imaging spots, with n being a natural number, with modulated power via corresponding imaging optics and intensity modulation. These n imaging spots are arranged on one line, in other words, they lie in one row. Subsequent to imaging n dots, a shifting of the medium relative to the imaging spots is carried out with a translation component perpendicular to the direction defined by the axis of the imaging spots so than n dots can be written at another location of the medium again. Typically, the axis of the imaging spots runs essentially parallel to the axis of a cylinder on which a printing form to be imaged is accommodated. Because of the laser radiation whose power is modulated in accordance with the respective image information, the mentioned raster scan lines of intensity-modulated imaging spots are formed. In this manner, an individual blackening of different printing dots can be attained.
At this point, it should already be pointed out that, in the one-dimensional case, a “line of printing dots” will be understood in this context as a line which results from a subsequent displacement of the imaging module having a number of light sources or, alternatively, of the medium to be written on, that is, of the printing form, in the direction defined by the row of imaging spots of the imaging module. Accordingly, a line denotes printing dots, which lie at the same height, of different scan lines written side by side. IRS methods can be easily generalized to the two-dimensional case with imaging spots forming an evenly spaced (n
1
×n
2
) matrix, with n
1
, and n
2
being natural numbers, by carrying out an IRS method in the direction defined by a line of the matrix as well as an IRS method in the direction defined by a column of the matrix.
According to U.S. Pat. No. 5,691,759, upon completion of a scan with a translatory component in a perpendicular direction, a displacement by a distance is carried out parallel to the direction defined by the axis of the n imaging spots. The n imaging spots are now displaced again on the surface of the medium with a translatory component perpendicular to the direction defined by the axis of the imaging spots so that further scan lines are formed. Thus, each raster scan line is spatially separated from its immediate neighbor by the spacing of the printing dots. Using a plurality of optical beams of a laser light source in this manner, an overlapping (interleave) of the scan lines is attained accordingly.
Furthermore, European Patent Application No. 0 947 950 A2 discloses an enhanced IRS method in which an overlapping is attained, i.e., new scan lines are written between previously written scan lines, without any location being multiply touched by an imaging spot of the laser, given a suitable selection of the step size of the displacement parallel to the axis defined by the imaging spots by which step size the medium is moved between the writing of two scan lines.
In addition, commonly-assigned German Patent Application No. 100 31 915 and related U.S. patent application Ser. No. 09/879,609 (which are not necessarily prior art and are herein incorporated by reference), describe an IRS method in which, for imaging printing plates via an imaging module, a printing form is imaged in separated raster scan lines. Via a projection optics, n imaging spots are generated which have a distance l between neighboring spots. An interleaf method is used which has the feature that the step size of the displacement in the direction of the axis defined by the imaging spots is larger than spacing l of neighboring spots.
When using a plurality of imaging modules in parallel, it is possible to image separate regions of the entire area to be imaged via an allocated imaging module, respectively, to attain a faster imaging of a printing form. To this end, the surface to be imaged is typically divided into strips. In the process, each of the strips is imaged by a separate imaging module. In the region in which in each case two such strips meet, adjustment errors of the two imaging modules that are imaging relative to each other become especially visible because of the sharp edge between the two strips, in particular in connection with the high precision requirements in the graphics technology. If, for instance, the two imaging modules are arranged slightly too far apart, a gap will results; otherwise, too broad a line will form. In literature, this effect is known as “banding”.
To reduce the aforementioned banding effect, U.S. Pat. No. 5,942,745 discloses a design approach in which the sharp edge is substituted by a frayed edge. This frayed edge is produced within a transition region between tow adjacent regions in that continuous lines of printing dots are generated in this transition region in each case within a first section from the boundary with the first adjacent region up to an intermediate dot by the imaging module assigned to the first region and, within a second section from the intermediate dot up to the boundary with the second region by the imaging module assigned to the section region, it being possible for the position of the intermediate dots to be different for neighboring lines, that is, lines of different height in a direction parallel to the region boundaries.
Moreover, U.S. Pat. No. 5,818,498 and U.S. Pat. No. 5,757,411 describe design approaches in which pixels in the edge region between two adjacent regions are imaged at least twice.
The two aforementioned procedures, that is, the generation of a frayed edge as well as the multiple imaging in a transition region, have the disadvantage that the strip width to be imaged by an imaging module is additionally increased considerably, either to be able to place printing dots at different locations up to intermediate dots or to be able to carry out multiple imaging of individual printing dots. Because of this, the goal of attaining a faster imaging by dividing the printing form into different regions which are each imaged by separate imaging modules can be frustrated. It

Affiliated with

Also associated with

Rating

Banding-reduced imaging of a printing form does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Banding-reduced imaging of a printing form, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Banding-reduced imaging of a printing form will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3257959