HK1050245B - Banding-reduced imaging of a printing form - Google Patents

Description

Producing images on printing plates with reduced streaking

Technical Field

The invention relates to a universal image production method for use in engraving processes, in particular printing processes or copying processes. It relates in particular to a method and a device for producing images on printing plates by means of at least two imaging modules (bibilderungsmodules) of the type mentioned in the preambles of the independent claims.

Background

In the field of engraving, in particular in the offset printing sector, known imaging modules are used for producing flat or curved printing plates by the so-called multibeam imaging method, in which a plurality of image points are exposed simultaneously on different media, such as printing plates, films, data carriers or the like.

At present, laser diode systems are mainly used for producing images on printing plates by means of light sources, and such systems involve two different solutions. In one aspect, the light beams of a single laser diode or a laser diode array can reach the medium on which the image is to be made through optical elements such as lenses, mirrors, or optical fibers; on the other hand, the light beam emitted from a laser source, typically a laser diode bar, is projected by different optical elements onto an array of n modulators, typically electro-optical or acousto-optical modulators, where n is a natural number. Wherein the selection of an individual light beam from all light beams and the modulation of its power can be achieved by n modulators that can be individually controlled. Such laser diode systems are known, for example, from EP 0878773 a2 and US5,521,748.

In addition, the so-called "interlaced raster scan line method" (hereinafter referred to as the IRS method) is known, in which raster scan lines are written on a medium by means of a multi-ray laser source. Such a method is known from US5,691,759, in which a laser source generates n image points with modulated power and intensity modulation by means of corresponding projection light, where n is a natural number. The n image points are distributed on a straight line, in other words, arranged in a row. After the imaging of the n pixels, the medium is moved relative to the pixels with a movement component perpendicular to the direction defined by the pixel axes, so that the n pixels can be rewritten at other positions on the medium. Typically, the image point axis extends substantially parallel to the axis of a cylinder which houses the printing plate to be imaged. The grid of scan lines of intensity-modulated image points is generated by these laser beams whose power is modulated in accordance with the corresponding image information. The respective blackening grey levels of the different printed dots can thus be achieved.

It is to be noted here that in this connection, "a row of printed dots" is understood in the one-dimensional case to mean a line which is produced by subsequently moving the imaging module with the plurality of light sources or the medium to be written, i.e. the printing plate, in the direction defined by the pixel columns of the imaging module. Accordingly, one row represents printed dots at the same height in different scan lines written adjacent to each other. By carrying out the IRS method once in the direction determined by a row of the matrix and once in the direction determined by a column of the matrix, the IRS method can be generalized in a simple manner to a system with (n) forming a rule₁×n₂) In the two-dimensional case of pixels of the matrix, n is used here₁And n₂Is a natural number.

According to US5,691,759, after a scan with a movement component in the vertical direction has been completed, a movement is carried out over a distance parallel to the direction defined by the axes of the n pixels. The n pixels are then moved again over the surface of the medium with a movement component perpendicular to the direction defined by the pixel axes, so that additional scan lines are generated. In this way, each grid scan line is spatially separated from its immediate neighbors by the distance of the printed dot. Accordingly, overlapping (interleaving) of the scanning lines is achieved in this way by making full use of the multiple beams of one laser source.

EP 0947950 a2 discloses an improved IRS method, in which the overlap is achieved by a suitable selection of the step width of the movement of the medium, which has been moved parallel to the axis defined by the image points, between the markings of two scan lines, i.e. a new scan line is written between the scan lines which have already been written, without any position being touched several times by an image point of the laser.

Furthermore, an IRS method is known from the previously filed german patent application DE 10031915, in which, for the production of an image on a printing plate, the printing plate is exposed to light on individual grid scanning lines by means of an image-producing mold. N image points are generated by means of a projection light fixture, which image points have a distance 1 between adjacent points. An interlaced scanning method is used, characterized in that the step width of the movement in the direction of the axis defined by the image points is larger than the distance 1 between adjacent points.

In order to achieve a faster image production on the printing plate, it is possible, in the case of a plurality of imaging modules arranged in parallel, to produce an image from each of the regions of the total area of the image to be produced from a respective one of the correspondingly arranged imaging modules. For this purpose, the area of the image to be produced is typically divided into strips. Each strip is exposed by a single imaging module. In the region in which two such strips are connected to one another, the correction errors between the two image-producing modules that produce the image become particularly pronounced due to the sharp edges between the two strips, in particular in the case of high precision requirements in the engraving technique. If two imaging modules are positioned, for example, slightly further apart from one another, a gap is created; otherwise an excessively wide line is produced. This effect is known in literature as "Banding".

To mitigate the above-mentioned stripe effect US5,942,745 discloses a solution in which the sharp edges are replaced by loose edges. Such a loose edge is produced in the transition region between two adjacent regions by the fact that successive rows of printed dots in the transition region are produced in a first section from the boundary with the first adjacent region up to an intermediate point by the graphic module assigned to the first region and in a second section from the intermediate point up to the boundary with the second region by the graphic module assigned to the second region, wherein the position of the intermediate point can be different for adjacent rows, i.e. rows of different height in the direction parallel to the region boundary.

Furthermore, US5,818,498 and US5,757,411 disclose solutions in which image points in the edge region between adjacent regions are each imaged at least twice.

The disadvantage of both of the above-described solutions, i.e. the production of loose edges and the multiple production of images in the transition region, is that the strip width of the image to be produced by means of an imaging module is significantly increased either in order to allow the printed points up to the intermediate point to land in different positions or to allow multiple exposures of the individual printed points. The objective of achieving rapid imaging by dividing the printing plate into different areas that are each exposed by a single imaging module may therefore be hampered. There are cases where even more imaging modules are required to be used to image strips of increased width.

Disclosure of Invention

The object of the present invention is therefore to provide a method and a device for producing an image on a printing form of the type mentioned at the outset, which overcome the above-mentioned disadvantages of the prior art and which reduce the "streak" effect as technically as simple as possible and therefore cost-effectively.

According to the invention, a method for producing an image on a printing form, the method comprising the steps of producing printing points on the printing form by means of at least a first imaging module and a second imaging module, wherein the two imaging modules are applied to the same position of the printing form for producing the image in a transition region, comprising: generating a plurality of at least partially non-singly connected first printed dots in the transition region by means of the first imaging module; generating non-singly connected second printed dots complementary to the first printed dots in the transition region by means of a second imaging module; wherein at least one singly-connected first area of the printing plate is correspondingly configured with the first image-making module, and one singly-connected second area of the printing plate is correspondingly configured with the second image-making module, the first printing point is only generated by the first image-making module in the first area, and the second printing point is only generated by the second image-making module in the second area; the first imaging module and the second imaging module each have n light sources located in a line, which light sources generate image points in a line of the printing plate, which image points have an adjacent image point distance 1, which distance 1 is a multiple of the distance p between two adjacent printing points.

The invention is based on this idea: the streak effect is reduced or even completely eliminated by specifically using or utilizing the IRS methods described above and providing an accessory device. When images are produced by the IRS method, a region is produced at the beginning and at the end of the writing process of a continuous row of printing points, i.e. image production points or printing points produced by the production of images several times, in which only a part of the printing points to be printed is imaged on the printing plate. These areas are also referred to as start edge and end edge in the following. The printed dots of the image to be produced in a consecutive row are typically situated at a distance p from adjacent dots, in other words, the dots are arranged densely at a distance p. At this time, there are exposed, i.e., landed, printed dots and unexposed, i.e., landed, printed dots within the starting edge and the ending edge. Here, the exposed or landed printed dots form a collection of dots with a non-single connected (meth-einfachzusammen-haengende) layout (Topologie). This can be understood in this connection, namely: the set of landed printed dots includes at least one dot having at least one directly adjacent dot in the row that is not landed. Accordingly, the non-landed printed dots form a complementary set within the beginning edge and the ending edge: the set of landed printed dots combined with the complementary set includes all printed dots within the starting edge and the ending edge. The printed dots of the merged set are densely packed.

The method according to the invention for producing an image on a printing form by means of at least one first and one second imaging module for producing printing spots on the printing form, wherein the two imaging modules are applied to the same position of the printing form for producing the image in a transition region, is characterized in that in the transition region at least some printing spots which are at least partially not connected in a single manner are produced by means of the first imaging module and complementary printing spots which are not connected in a single manner are produced by means of the second imaging module.

The method according to the invention for producing an image on a printing form by means of at least two imaging modules for producing printing spots on the printing form, usually m imaging modules, where m is a natural number, each having at least one, preferably several, light source, and two adjacent printing spots typically having a distance p, has the following steps in an advantageous embodiment. The printing plate is divided into m preferably singly connected strip-shaped regions with (m-1) transition regions, wherein one imaging module is assigned to each of the m regions, and two imaging modules of two adjacent regions are assigned to each of the (m-1) transition regions. By means of suitable actuators, by servomotors or the like, a relative movement is produced between the graphic element and the printing plate in such a way that the position of the printing spot to be produced is acted upon at least once by a pixel of a light source in a graphic element. The above-mentioned division of the printing plate can be determined, for example, by the amplitude of movement of the imaging module, and not specifically on the printing plate. In this way, the exposure of the printing plate in each of the m regions takes place via the image-forming modules assigned to it by means of the preferably linearly arranged image points of the light source of the image-forming module, and the exposure of the printing plate in each of the (m-1) transition regions takes place via the preferably linearly arranged image points of the light source of the image-forming module of the two adjacent regions. The method according to the invention for producing an image on a printing form is characterized in that at least in one transition region, at least partially non-singly connected printing points are produced by the image-producing mold of a first adjacent region, and complementary non-singly connected printing points are produced by the image-producing mold of a second adjacent region.

It is particularly advantageous for the use of the method according to the invention to divide the printing plate into m similar singly-connected regions and (m-1) similar transition regions, which have equivalent geometries. For regions or transition regions with equivalent geometry, the relationship should be understood such that: the single connected areas have the same number of printed dots and an equal distribution in the direction of the coordinate axes of the area of the spread plate. The transition regions with equal geometric shapes are understood to mean that they likewise have the same number of printed dots, which are distributed correspondingly in the direction of the two coordinate axes of the area of the spread printing form.

It is particularly advantageous to use an imaging module having n light sources, where n is a natural number, the pixels of which have a distance 1 between adjacent pixels on the printing plate, where 1 is a multiple of the distance p between two adjacent printed pixels. Advantageously, the exposure of the printing plate by each imaging module in the area corresponding thereto and in the transition area or transition areas corresponding thereto is carried out in an interlaced manner. In such an interleaving method, the distance t traveled, measured in units of the distance p between adjacent printed dots, and the distance 1 between adjacent image dots are natural numbers without common divisor. The interlacing method is preferably used here with a step width of a movement distance t which is equal to the number n of light sources in each of the m imaging modules. The step width of the movement distance t is greater than the distance 1 between adjacent pixels.

According to the invention, there is also provided an apparatus for making an image on a printing plate, comprising: a first imaging module for directing first pixels of at least one first light source onto a transition region of the printing plate, the first pixels of the at least one first light source producing a first set of printing dots in the transition region that form a non-unilaterally connected set; a second imaging module for directing second pixels of at least one first light source or at least one second light source onto the transition region of the printing plate, the second pixels producing a second set of printing dots in the transition region that are complementary to the first set of printing dots and are not in single communication with the first set of printing dots; the first and second imaging modules being movable relative to the printing plate; wherein at least one singly-connected first area of the printing plate is correspondingly configured with the first image-making module, and one singly-connected second area of the printing plate is correspondingly configured with the second image-making module, the first printing point is only generated by the first image-making module in the first area, and the second printing point is only generated by the second image-making module in the second area; wherein the first and second imaging modules each have n light sources which lie in a line, the light sources producing pixels in a line, adjacent pixels having a distance 1 therebetween, the distance 1 being a multiple of the distance p between two adjacent printed pixels.

The device is used for making images on the printing plate by at least two image-making modules which can move relative to the printing plate, wherein, the movement of the first image-making module guides the image point of at least one light source to a transition area of the printing plate by the movement of the second image-making module, so that the printing point is generated by one-time passing of one image point of one light source. The inventive device is characterized in that the pixels of the light source of the first imaging module produce a set of printing dots in the transition region, which is a non-single connected set, and the pixels of the light source of the second imaging module produce a complementary set of non-single connected printing dots in the transition region.

In an advantageous embodiment, the device according to the invention for producing images on a printing form has at least two imaging modules which are movable relative to the printing form and each comprise at least one light source, preferably several individual light sources. The movement of the first imaging module directs the pixels of the light source of the first imaging module onto a first area and a transition area of the printing plate and the movement of the second imaging module directs the pixels of the light source of the second imaging module onto a second area and the transition area of the printing plate. The printed spots are deposited in the first region and in the transition region by the first imaging module and in the second region and in the transition region by the second imaging module in such a way that one printed spot can be produced by a single pass of the image spot of one light source. The device according to the invention is characterized in that the pixels of the light source of the first imaging module generate a set of printing dots in the transition region, which form a non-single connected set, and the pixels of the light source of the second imaging module generate a complementary set of non-single connected printing dots in the transition region. It is obvious to the expert that generalizations to m regions and (m-1) transition regions are possible.

It is particularly advantageous if each imaging module has n light sources which are situated substantially in a straight line with a distance 1 between adjacent light sources.

According to the invention, in other words, it is preferred that the printed dots landed by the first graphic module on the lines at two consecutive areas or in the transition area exposed by the light sources in a first and a second graphic module produce a pattern, which is the inverse of the pattern of the printed dots landed by the second graphic module, by using the IRS writing method, wherein the patterns have a non-single-connected layout.

The invention proposes, in particular, to select the relative movement between the imaging module and the printing plate in the direction defined by the light source axis to be greater than the adjacent pixel distance 1 of the n light sources in each imaging module, and, in conjunction therewith, to select the relative movement such that the two successive rows are complementary in a transition region between a first region, in which the first imaging module is associated, and a second region, in which the second imaging module is associated, to the set of printing pixels which are impinged by the first imaging module in the transition region, and to the set of printing pixels which are impinged by the second imaging module in the transition region, i.e. the printing pixels which are impinged in total are arranged densely. In other words, the superposition of the beginning edge of the row landed by the second graphic module and the ending edge of the row landed by the first graphic module results in a closed engagement of the printed dots in the transition region.

It is worth mentioning that a continuous marking can be achieved, in particular if the number n of pixels does not have a common factor or common divisor of the distance 1 measured in units of the printed dot distance p, wherein each printed dot is written exactly once.

The closed engagement of the pixels is achieved by superimposing the beginning edge of the row landed by the image-forming module of the first area with the ending edge of the row landed by the image-forming module of the second area.

The first sharp edges between the strip-shaped regions are thereby eliminated and the fringe offset is distributed over a larger image area and thus attenuated for the eye of the observer. The invention thus makes it possible to achieve a reduction of the so-called fringe effect in a particularly advantageous manner without simultaneously increasing the time consumption of the image-making process.

It is emphasized that the method and the device according to the invention for producing an image on a printing form can be advantageously applied in addition to the above-described application in the field of laser-supported image production on printing forms, correspondingly also in the field of similar printing or copying technology, for example in the field of laser printing technology, inkjet printing technology or printing technology involving the spark-discharge principle and copying technology involving the selenium drum method or similar. Since the production of image media in these techniques also produces images in lines by means of discrete production image sources, the above-mentioned streak effects and side effects, which are reflected in the quality of the printed image, also occur therein.

Drawings

The invention is explained in more detail below with the aid of an exemplary embodiment shown in the drawings, from which further advantages and features of the invention can be derived. The concrete expression is as follows:

FIG. 1 is a schematic diagram of the arrangement of an imaging module with an array of light sources, for example, three beams, for making images on a printing plate;

FIG. 2 illustrates an example of an image produced on a line by an interlaced grid scan line method by an imaging module whose light source produces five image points;

FIG. 3 illustrates the division of the total area of the printing plate to be exposed into four corresponding regions with corresponding transition regions for four imaging modules;

FIG. 4 is a schematic representation of the production of an image on a printing forme of cylindrical design by means of two of the above-mentioned imaging modules, which expose the printing forme in respectively assigned regions and in a transition region;

FIG. 5 is a schematic diagram of the present invention for reducing the stripe effect.

Detailed Description

Fig. 1 cited in german patent application DE 10031915 shows a typical geometry for projecting n image points, which are emitted by an array of n light sources, for example laser diodes, in an image-generating module, where n is a natural number. The imaging module 10 is composed, for example, of a single controllable array of n stripe laser diodes (einstrifenfenr-dioden) as light sources 12, where n is particularly advantageously a power of the natural number 2, i.e. n is 2^kAnd k is a natural number. Typically, an advantageous such light source has up to 100 stripe laser diodes, preferably between 20 and 70 laser diodes. The stripe laser diode has an emission area of 1 × 5 square micrometers and a small diffraction value M²Laser radiation is emitted with a favorable radiation quality. The distance of the individual laser diodes on the array is typically between 100 and 1000 microns.

With the aid of the projection optics 16, n light beams are projected onto n image points 110 on a printing plate 18. The printing plate 18 is advantageously located at the focal distance of the beam 14. It is particularly advantageous that by means of the projection optics 16 not only the beam changes its diameter ratio (perpendicular and parallel to the axis defined by the n points) but also the mutual distance between the image points is corrected. In other words, not only the spot size of the n image points 110, but also their mutual position and distance can be adjusted. The distance between the individual light sources is generally constant, but at least the distance 1 of only the n image points 110 is required to be constant in order to produce an image advantageously. The distance 1 of the n pixels is greater than the distance p of the printed dots.

The light source 12 of the imaging module 10 may be used in a continuous mode of operation. To generate a single optical packet, the laser emission is throttled at certain time intervals. In a special embodiment, a pulsed radiation-emitting light source 12 in the imaging module 10 can also be used. For pulsed radiation, the repetition rate of the light pulses must be at least as great as the beat frequency for producing the individual printed dots, so that at least one laser pulse can be used for one printed dot. Projection optics 16 may have reflective, emissive, refractive, or similar optical components. The present invention preferably relates to micro-optical components. The projection optics 16 may not only have an enlarged or reduced projection scale, but also different projection scales in two directions parallel and perpendicular to the active area of the laser, which is particularly advantageous for divergence correction and aberration correction. The surface of the printing plate 18 is changed in physical or chemical properties by the laser beam. A removable and rewritable printing plate is advantageously used.

In the preferred embodiment, the imaging module 10 is located on a cooling member 112. The graphic module 10 is connected to a control unit 116 by means of a line 114 to the current supply and control devices. The control unit 116 has individual components by means of which the individual laser diodes in the array of light sources 12 can be controlled or regulated separately from one another. The cooling element 112 is connected to a thermostat 120 by means of a line 118 for controlling the cooling element.

In order to check the function and to determine the output power for the individual light sources 12, a detector 122 is provided. The detector can be embodied such that a single measuring device is provided for each light source or a measuring device detects the individual light sources alternately or as required. The detector 122 is advantageously connected to the control unit 116 via a connection 124, so that the output power is processed as a parameter for activating the control signal in the control unit 116.

Before the IRS method is explained in detail with the aid of the embodiment in fig. 2, a general explanation of this is necessary. As already mentioned, in order to produce an image on a printing plate, the pixels are first moved onto the printing plate with a component perpendicular to the direction defined by the lines of the pixels, resulting in so-called grid scan lines. A consecutive line of printed dots can be understood as a line which is produced by subsequent displacement in a direction determined by the direction of the printed dots, whereby it is the printed dots of different scanning lines which are written next to one another and which are located at the same height.

The distance of the n pixels generated simultaneously by the n individual light sources can be selected to be constant, advantageously the length 1 between two adjacent pixels is an integer m times the printed pixel distance p, i.e. 1 m × p. If a suitable movement is selected, a continuous marking with n simultaneously written pixels at a distance of 1 m × p can always be realized, wherein each pixel is touched at least once by the pixel of a light source, wherein m denotes a natural number and p denotes the distance of the printed dot. The width of the movement is preferably equal to the number of image points.

But it may also happen here that a point is written several times. In particular, if the number of pixels n has no common factor with the adjacent pixel distance 1 measured in units of the printed pixel distance p, wherein the step width t is n × p, a continuous marking can be realized in which each printed pixel is written exactly once. In other words, n and m have no common divisor. This is the case, for example, when n and m are different prime numbers or powers of different prime numbers. An example case is where n is a power of the natural number 2 and m is an odd number. The amount of movement determined at the same time in the direction given by the straight line determined by the n image points should be chosen to be n. Where an edge of size r is generated at the beginning and end of the line to be written: r is n × m- (n + m-1). I.e. in the example of fig. 2: r is 3 × 5- (3+5-1) ═ 8.

Because the individual light sources can be individually controlled, each printed dot can be individually constructed. The power of a certain laser beam set for writing a pixel is determined in accordance with the given image data information. Thus, individual black shades of different printed dots can be achieved.

Fig. 2 shows an IRS method disclosed in german patent application nr.de 10031915 for writing on a printing plate by means of, for example, five image points, which are generated simultaneously by simultaneous irradiation with five individual laser diodes. In this figure, the printed dots are shown as a block simplification. As already mentioned, each printed point must be touched at least once by an image point of a laser, so that it can be exposed corresponding to the given image data or can remain unchanged. In this embodiment, a consecutive row to be written consists of printed dots arranged in a row without gaps. The distance is denoted by p.

In fig. 2, a group of simultaneously written printed dots of an image-forming module 20 consists of five pixels having the same distance 1. Five unit dots having a distance of 1 to 3p are written when the image 22 is first produced. The imaging module 20 is moved in such a way that a group of simultaneously produced printed dots is moved in the direction determined by the printed dot axis, here for example to the right by five unit dots, since in this example five printed dots are written simultaneously.

In a second image generation step 24, five more pixels are landed after a movement over a movement distance t. The movement through the five unit dots is repeated once again in the direction determined by the printing dot axis, here for example to the right, by the movement distance t. In the next image-making step 26, five points are landed again. From this sequence, it is seen that the plate can be written without gaps: each printed dot, indicated by a box, is touched once by the image point of the laser. After a movement of five length units measured in p as the movement distance t to the right, the same pattern is always produced on the printed dots, written and unwritten, as seen in 28, each time the image is reproduced. The line of written pixels therefore also has a certain space with unwritten pixels at its right end.

Further imaging of the five pixels on the right end of the figure now results in the same sequence of unwritten and written pixels. At the same time, the portion of the printed dot that is completely written by the row becomes longer and longer.

In the repeated image-making step 28, it can likewise be seen that the dimension r measured in units of the printed dot distance p is₁Has a starting edge and a dimension r₂In this case 8 printed dots. It is emphasized here that the set of printed dots that have been landed in the beginning and ending regions has a non-single connected layout. Also in this example it can be seen that, counting for example from left to right, an edge r starts₁Has an ordered set of printed dots with a trailing edge r₂The ordered set of printed dots in (a) is a complementary pattern.

The proposed IRS method can be used for imaging printing plates even if a single light source in the array fails. In particular, the speed of image generation is maximized when the number n of laser beam pixels is not a common divisor of the distance 1 between two adjacent pixels measured in p. In other words, a step width can be specified such that each spot to be written is touched by an image point of the laser beam only once.

In the event of a malfunction of one or more stripe laser diodes in a group of simultaneously written image points 30, marking can also be carried out by means of the IRS method. The largest neighboring pixel segments of the group that are at the same distance are always used for marking. Obviously, the step width must also be reduced in order to achieve a continuous mark. This is advantageously achieved according to the rules set out above regarding the nature of the numbers.

The production of images on a printing plate by the IRS method can be carried out with every combination of the distance 1 between adjacent pixels and the number n of pixels. However, for the purpose of continuous writing on the printing plate, suitable parameters should be selected. The speed at which images are produced can be reduced in the event of a failure of one image point.

For the IRS method described above for writing on printing plates, a plurality of laser beams is necessary. They can also be generated with other laser sources than the laser diodes preferably used. In order to vary the projection distance between the individual light sources, in an advantageous development the printing plate can be tilted by an angle different from zero relative to a plane perpendicular to the n laser beams.

Fig. 3 shows an example of the division of the entire surface of the printing plate to be exposed, corresponding to the four imaging modules, into four corresponding areas with three corresponding transition areas. FIG. 3 shows a plate 30 with two coordinate axes, coordinate Φ and coordinate z. The regions 32 of the printing plate 30 which are suitable for the image are subdivided into a plurality of strip-shaped, singly connected regions, between which there are in each case transition regions. These areas are called stripes because they have a slave coordinate o₁Starting point of the strip until having the coordinate phi₂Is the extension of the strip end point of (1). A first graphic module, not shown here, is assigned to the first region 34, the first region 34 starting from a first starting point za₁Extending to a second starting point za₂. The first region 34 is exposed by a first imaging module, not shown here. Followed by a first transition zone 36 from a second starting point za₂Extending until the first end point ze₁. Followed by a second region 38 from the first end point ze₁Extending until a third starting point za₃. A second imaging module, not shown here, is assigned to this second region. The second region 38 is exposed by the second imaging module, which is not shown here. The first transition area 36 is exposed not only by a first imaging module, not shown here, but also by a second imaging module, not shown here. In a similar continuation, a second transition region 310 is connected to the second region 38, which transition region extends from a third starting point za₃Extending until the second end point ze₂. In other words, the first imaging module, not shown here, can be moved in such a way that the image points of its light source can fall not only in the first region 34 but also in the first transition region 36, so that an image can be produced by a lateral and longitudinal movement along the strip-shaped, single-communicating first region 34 and the strip-shaped, single-communicating first transition region 36. At the same time, a second imaging module, not shown here, can be moved in such a way that it is attachedThe image point of the light source can fall not only in the first transition region 36, but also in the second region 38 and in the second transition region 310. A second end point ze having a boundary is connected after the second transition region 310₂And a fourth starting point za₄And a third region 312. Followed by a fourth starting point za with a boundary₄And a third end point ze₃And a third transition region 314. Furthermore, a fourth region 316 can be seen, which extends from the third end point ze₃Extending to the fourth end point ze₄. Third and fourth image-forming modules, not shown here, are provided, similar to the first region 34, the first transition region 36 and the second region 38 and the accompanying first and second image-forming modules, not shown here. Here, the image points of a third imaging modality, not shown here, may fall within the second transition region 310, within the third region 312 and within the fourth transition region 314, while the image points of the light source of a fourth imaging modality, not shown here, may fall within the fourth transition region 314 and within the fourth region 316.

In fig. 4, imaging of a printing plate on a rotatable cylinder is shown, for example, using a first imaging module 40 and a second imaging module 418. The printing plate is divided into a first region 414, a transition region 416 and a second region 426.

The first imaging module 40 generates n light beams, here for example three light beams 42, which are imaged on three image points 410 by means of a first projection optics 44. The three image points are advantageously of equal distance and lie on one axis. The printing plate 48 is located on a cylinder 46 which is rotatable about its axis of symmetry 45. This rotational movement is indicated by arrow B. The imaging module 40 can be moved in a linear path parallel to the axis of symmetry 45 of the roller 46, as indicated by the double arrow a. In this case, the first imaging module 40 can be moved in such a way that the corresponding image point 410 falls within the first region 414 and/or within the central region 416.

The second imaging module 418 generates n light beams, here for example three light beams 420, which are imaged by means of a second projection optics 421 onto three image points 422. The three pixels 422 are advantageously equally spaced, preferably identical to the pixels 410 of the first imaging module 40, and are located on an axis. The second imaging module 418 is movable in a linear path parallel to the axis of symmetry 45 of the cylinder 46, as indicated by the double arrow a. In this case, the second imaging module 418 can be moved in such a way that the corresponding image point 422 falls within the second region 426 and/or within the central region 416.

To continuously produce images, the cylinder 46 with the printing plate 48 is rotated in accordance with a rotational movement B and the first imaging mold 40 and the second imaging mold 418 are moved longitudinally along the cylinder 46 in a direction of movement a. The speed of movement is determined by the number of beams 42 and 420 and the width p of a printed dot. Here, the image is made on a spiral path around the axis of symmetry 45 of the cylinder 46. The path of the first image point 410 is indicated by the line 412 and the path of the second image point 422 is indicated by the line 424. After the n dots have been imaged, printing plate 48 is moved relative to pixels 410 and 422 by a first determined amount with a vector component perpendicular to the direction defined by the straight line of n pixels 410 and 422, so that n dots are rewritten at another position of printing plate 48. Thus producing so-called "grid scan lines" of image points. For each defined distance of adjacent grid lines and the number n of pixels, a defined second value of the necessary movement parallel to the axis defined by the line of n pixels is generated, so that the image can be produced continuously, i.e. for each pixel arranged on the printing plate 48, by the interlaced grid line method (hereinafter referred to as the "IRS method") which will be described in more detail below.

In another embodiment, image point 410 may also be moved in a curved fashion over plate 48 by first making a full image along a line parallel to axis of symmetry 45 of cylinder 46, followed by a stepwise rotation about axis of symmetry 45.

It goes without saying that only the relative movement between the image point 410 and the printing plate 48 is important. This relative movement may also be achieved by movement of the print cylinder 46. For both directions of movement a and rotation B, it is suitable that these movements can be carried out continuously or stepwise.

Furthermore, at least one imaging module, such as the first imaging module 40, the light source 42, the projection optics 44 and the like, can also be implemented additionally inside the printing cylinder 46, so that a space-saving arrangement is obtained.

Such an image-producing device with a plurality of image-producing modules can be implemented individually or in a plurality within or outside a plate exposure device, a printing device or a printing press.

It should now be clear how the stripe effect is reduced according to the invention by means of fig. 5. Fig. 5 schematically illustrates a first region 50 in which a row 52 of printing dots of the first graphic element is arranged, a transition region 56 in which the end edge 54 of the row of printing dots of the first graphic element and the start edge 512 of the row of printing dots of the second graphic element are arranged, and a second region 58 in which a row 510 of printing dots of the second graphic element is arranged. For the sake of better illustration only, the row of printing dots 52 of the first graphic element is shown in fig. 5 at a distance from the row of printing dots 510 of the second graphic element in a direction perpendicular to the dot axis.

In this case by way of example, the transition region 56 described above extends over eight printed dots, and as in the case illustrated in fig. 2, an image is produced with five image dots having an adjacent distance l of 3p and a movement distance t of 5p, where p denotes the printed dot distance.

Here, the ending edge 54 that is struck by the first graphic element has a non-single connected set of struck printed dots, and the beginning edge 512 that is struck by the second graphic element has a non-single connected set of struck printed dots that is complementary to the set of ending edge 54.

The printing dot rows 510 of the first graphic module now define in advance the positions of the points in the transition region 56 in the end edge region 54, at which the printing dots are still to be applied between the printing dots of the finished image. Due to the deviations caused by frequent adjustment, the second imaging module is usually not able to accurately land the printed spots at these positions, but rather has an offset or deviation. By writing interleaved, that is to say in the illustration here two virtually contiguous rows produce a transition region which appears "continuous" to the naked eye and which is not defined by a discontinuous transition. This offset is distributed over the transition region 56. Furthermore, there is no spatial pattern which can be easily recognized by the naked eye, since the distribution of the printed dot rows cannot be easily recognized by the naked eye, in particular when a large number of writing channels are used, for example fifty simultaneously written dots instead of the above-mentioned five simultaneously written dots, and the transition region 56 corresponds to the width of the writing region, for example 1 cm.

By means of the method according to the invention and the use of a plurality of imaging modules in the device according to the invention, the previously sharp edges between the strip-shaped first region 50 and the second region 58 are eliminated and a deviation or adjustment deviation between the first imaging module and the second imaging module, which deviation leads to a deviation of the defined position of the printed points in the starting region 512 and the printed points not yet landed in the ending region 54, which are landed by the second imaging module, is distributed over a larger image region corresponding to the transition region 56, so that this deviation or deviation is reduced for the eye of the observer. The invention thus makes it possible to achieve a reduction of the so-called fringe effect in a particularly advantageous manner.

Unlike the prior art, this transition region is not achieved by making additional images in the case where the interlaced scanning method is preferably used, and therefore does not result in an extension of the time to make the images, since the images of the leading and trailing edges are fully utilized.

For imaging modules that produce images densely at the printed points, see for example US5,818,498, the method can also be used to reduce the stripe effect, but for this purpose transition regions must be produced in such a way that: not all dots are written with one imaging module. In this case, it is advantageous that the individual pixels can also be distributed randomly over the medium on which the image is to be produced, so that the attenuation effect is even increased.

Reference numerals

10 system image module 12 light source

14-Beam 16 projection optics

18 printing plate 110 dots

112 cooling element

114 to the current supply and control device

116 control unit

118 leads to a thermostat

120 temperature regulating device

122 probes for functional checking and power measurement

124 to the control device

Printed dots simultaneously written by 20 graphic modules

22 first creation of image 24 second creation of image

26 third creation image 28 repeat creation image

1 distance of adjacent pixels p distance of adjacent printed dots

n number of picture elements r₁Starting edge

r₂Trailing edge t movement distance

Phi strip direction coordinate axis z divides cross direction coordinate axis

ф₁Onset of banding phi₂End of strip

za₁First starting point za₂Second starting point

ze₁First end point za₃Third starting point

ze₂Second end point za₄Fourth starting point

ze₃Third end point ze₄Fourth end point

30 regions of printing plate 32 for making images

34 first region 36 first transition region

38 second region 310 second transition region

312 third region 314 third transition region

316 fourth area 40 first graphic module

42 light beam 44 first projection optics

45 axis of symmetry 46 cylinder

48 printing plate

410 image points of a first imaging modality

412 first image point path 414 first region

416 transition region 418 second imaging module

420 light beam 421 second projection optics

422 second image point of the second image module 412

426 second region

Direction of movement A

Direction of rotation B

50 first region

52 ending edge of printed dot row 54 of first imaging module

56 transition region 58 second region

510 starting edge of a print dot row 512 of a second graphic module

Claims (7)

1. Method for producing an image on a printing form (48), printing points being produced on the printing form (48) by means of at least a first imaging module (40) and a second imaging module (418), wherein, for producing the image in a transition region (416), both imaging modules (40, 418) act on the same position of the printing form (48), comprising the following steps:

-generating a plurality of at least partially non-singly connected first printed dots in the transition region (416) by means of the first image-forming module (40);

generating non-singly connected second printed dots complementary to the first printed dots in the transition region (416) by means of a second imaging module (418);

wherein at least one first, singly connected, area (414) of the printing plate (48) is associated with the first imaging module (40) and a second, singly connected, area (426) of the printing plate (48) is associated with the second imaging module (418), the first printing points being produced in the first area exclusively by the first imaging module and the second printing points being produced in the second area exclusively by the second imaging module;

the first imaging module and the second imaging module each have n light sources (12) which are located in a straight line and which generate image points in a straight line of the printing plate (48), the image points (110) having an adjacent image point distance 1, the distance 1 being a multiple of the distance p between two adjacent printing points.

2. The method of claim 1, wherein: the printing plate is exposed by each of the first and second imaging modules (40, 418) by an interleaving method at least in the transition area (416).

3. The method of claim 2, wherein: an interleaving method is used having a step width t equal to the number n of light sources in each of the first and second imaging modules, wherein the step width t is an insubstantial number with respect to the adjacent pixel distance 1 measured in units of the adjacent printed pixel distance p.

4. Apparatus for making an image on a printing plate, comprising:

a first imaging module (40) for directing first pixels (410) of at least one first light source onto a transition region (416) of the printing plate, the first pixels (410) of the at least one first light source producing a first set of printing dots in the transition region (416) that form a non-unilaterally connected set;

a second imaging module (418) for directing second pixels (422) of at least one first light source or at least one second light source onto the transition region (416) of the printing plate, the second pixels producing a second set of printed dots in the transition region (416) that is complementary to the first set of printed dots and is not singly connected;

the first and second graphic modules (40, 418) being movable relative to the printing plate (48);

wherein at least one first, singly connected, area (414) of the printing plate (48) is associated with the first imaging module (40) and a second, singly connected, area (426) of the printing plate (48) is associated with the second imaging module (418), the first printing points being produced in the first area exclusively by the first imaging module and the second printing points being produced in the second area exclusively by the second imaging module;

wherein the first and second imaging modules (40, 418) each have n light sources located in a line, the light sources producing image points in a line, adjacent image points having a distance 1 therebetween, the distance 1 being a multiple of the distance p between two adjacent printed points.

5. A plate exposure apparatus, characterized by: the printing plate exposure apparatus has at least one apparatus according to claim 4 for producing an image on a printing plate.

6. Printing device, its characterized in that: the printing unit has at least one device for producing images on printing plates according to claim 4.

7. A printing press characterized by: the printing press has at least one printing unit according to claim 6.