CA2405206A1 - Method of exposing a printing form - Google Patents
Method of exposing a printing form Download PDFInfo
- Publication number
- CA2405206A1 CA2405206A1 CA002405206A CA2405206A CA2405206A1 CA 2405206 A1 CA2405206 A1 CA 2405206A1 CA 002405206 A CA002405206 A CA 002405206A CA 2405206 A CA2405206 A CA 2405206A CA 2405206 A1 CA2405206 A1 CA 2405206A1
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- Prior art keywords
- exposure
- row
- array
- printing form
- channels
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- 238000007639 printing Methods 0.000 title claims abstract description 101
- 238000000034 method Methods 0.000 title claims abstract description 72
- 230000004913 activation Effects 0.000 claims description 20
- 230000003213 activating effect Effects 0.000 claims description 7
- 238000004590 computer program Methods 0.000 claims description 5
- 238000001994 activation Methods 0.000 description 18
- 230000008569 process Effects 0.000 description 7
- 238000006073 displacement reaction Methods 0.000 description 6
- 238000003491 array Methods 0.000 description 5
- 238000009826 distribution Methods 0.000 description 4
- 238000003384 imaging method Methods 0.000 description 4
- 239000000654 additive Substances 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000011161 development Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 239000000123 paper Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000013519 translation Methods 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 238000002679 ablation Methods 0.000 description 1
- 230000009471 action Effects 0.000 description 1
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- 229910052804 chromium Inorganic materials 0.000 description 1
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- 125000004122 cyclic group Chemical group 0.000 description 1
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- 150000002500 ions Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000007645 offset printing Methods 0.000 description 1
- 229920000620 organic polymer Polymers 0.000 description 1
- 239000011087 paperboard Substances 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
- B41J2/447—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources
- B41J2/45—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources using light-emitting diode [LED] or laser arrays
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/20—Exposure; Apparatus therefor
- G03F7/2051—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source
- G03F7/2053—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source using a laser
- G03F7/2055—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source using a laser for the production of printing plates; Exposure of liquid photohardening compositions
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
- G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
- G06K15/12—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers
- G06K15/1238—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point
- G06K15/1242—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line
- G06K15/1247—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line using an array of light sources, e.g. a linear array
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/40—Picture signal circuits
- H04N1/40025—Circuits exciting or modulating particular heads for reproducing continuous tone value scales
- H04N1/40031—Circuits exciting or modulating particular heads for reproducing continuous tone value scales for a plurality of reproducing elements simultaneously
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
- B41C1/00—Forme preparation
- B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
- B41C1/1075—Mechanical aspects of on-press plate preparation
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/20—Exposure; Apparatus therefor
- G03F7/24—Curved surfaces
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
- General Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Health & Medical Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Theoretical Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
- Manufacture Or Reproduction Of Printing Formes (AREA)
Abstract
A method is presented of exposing a printing form (30), using a number of exposure channels (310) arranged in a two-dimensional array (38), the exposure channels of a column of the array effecting an input of energy for an image element (20) on the printing form, which is to be moved relative to the exposure channels. A first row (324) of the array of exposure channels is activated to produce a first component of the input of energy associated with each column of the array in one row of image elements. The method according to the invention is distinguished by the fact that a second row (326) of the array is activated to produce a second component of the input of energy associated with each column of the array when the point of projection (314) of the exposure channel of a second row of the array comes to lie on the image element (20) of the row already exposed by the exposure channel of the first row and the same column. This advantageously shortens the time needed to expose the printing form.
Description
Method of exposing a printing form The invention relates to a method of exposing a printing form, using a number of exposure channels which are arranged in a two-dimensional array, the exposure channels of a column of the array causing an input of energy for an image element on the printing form, the method having the steps of activating a first row of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in one row of image elements and moving the printing form relative to the exposure channels.
For imagesetting or exposing printing forms, be it in printing form exposers or in direct-imaging printing units, as they are known, in printing presses, a number of image elements are often produced in a time-parallel fashion on the printing form as a result of inputting energy by means of a number of exposure channels.
The document EP 0 947 950 A2 discloses a typical exposing method by means of a multi-beam laser exposure device. In this method, a plurality of image elements in a row are exposed in a time-parallel fashion, a relative displacement between exposure device and image carrier is then carried out in accordance with rules which avoid a position of points of projection, that is to say those points at which light falls on the image carrier, on already exposed image elements, before a plurality of image elements is again exposed in a time-parallel fashion. This procedure is repeated and comprises displacements in the two linearly independent directions of the surface of the image carrier.
_1_ For example, it is known from US 5,477,259 that parallel exposure does not have to be restricted to a plurality of exposure channels arranged in a row. This document describes a multi-beam laser exposure device which has laser light sources arranged in a two-dimensional array. It is therefore possible for a large number of rows of a number of image elements which are each associated with a number of exposure channels to be exposed in a time-parallel fashion.
In a procedure of the type described, a lower limit for the duration of the complete exposure of the printing form is equal to that time which is required for the complete production of an image element, multiplied by the total number of image elements on the printing form and divided by the number of exposure channels available in one exposure step (irrespective of a one-dimensional or two-dimensional arrangement). Furthermore, typically additional time is required in order to guide the points of projection of the exposure channels, whose number lies considerably below the total number of image elements to be exposed, over the two-dimensional surface of the printing form. Points of projection are to be understood as those points at which light falls onto the printing form when the exposure channel is open.
Furthermore, additional time for relative displacements is needed, if an image element is to be built up in a structured manner from individual exposure points. These movements are often slow or take place in steps. The exposure duration will therefore in practice generally be greater than this lower limit.
The disadvantage with the method described is that the lower time limit for the exposure duration which can be achieved by means of a plurality of imagesetting channels through the parallel processing cannot be reached, since additional time is needed as a result of relative displacements of the printing form in relation to the imagesetting channels.
It is an object of the present invention to provide a method of exposing printing forms which permits a short exposure time.
According to the invention, this object is achieved by a method having the features as claimed in claim 1. Advantageous developments of the invention are characterized in the subclaims.
In the method according to the invention of exposing a printing form, using a number of exposure channels which are arranged in a two-dimensional array, provision is made for the exposure channels of a column of the array to be used to produce an image element and, for this purpose, cause an input of energy for an image element on the printing form. Expressed in other words, the exposure channels in various rows but in the same columns are therefore used proportionally to produce an exposed point in an image element associated with the column in a raw on the printing form. The number of columns determines the number of image elements in a row. At a given instant or at a time, in this case at least points of projection from two exposure channels in one column of the array cannot coincide on the printing form. To produce a first component of the input of energy associated with each column of the array in a row of image elements, a first row of the array of exposure channels is activated at a first time. Here, activation comprises, firstly, switching the exposure channel on and off for a time period which can be one interval or a plurality of intervals and, secondly, an input of energy with a specific amount of energy, it being possible for the amount of energy either to be constant over time when the exposure _3_ channel is open (switched on) or can vary over time, the integral of the amount of energy over the time representing the input of energy.
The printing form is moved relative to the exposure channels.
For a relative movement, it is unimportant whether the exposure channels or the printing form or both are moved. A
relative movement in connection with the invention in this case has at least one velocity vector component in the direction at right angles to the optical axis of the exposure channels which strike the printing form. Expressed in other words, a change in spacing resulting from the relative movement is not necessary, preferably even not provided, while the velocity has at least one tangential component.
The method according to the invention is distinguished by the fact that, to produce a second component of the input. of energy associated with each column of the array, a second row of the array is activated at a second time when the point of projection of the exposure channel of a second row of the array comes to lie on the image element of the row already exposed by the exposure channel of the first row and the same column. In other words, as a result of the relative movement, the points of projection of the second row of the array wi)_1 come to lie at a second time on the image elements exposed by the first row at a first time, so that a second component of the input of energy can be provided. The total input of energy for an image element is provided gradually over time or successively in components through exposure channels in different rows but the same column in the array of exposure channels. In this case, an input of energy onto the printing form is performed in a time-parallel or simultaneously proportional manner for a plurality of image elements. The _q_ input of energy and the division into individual components can be determined in advance.
It should be noted, firstly, that the proportion of an exposure channel can also be zero. Secondly, it should be pointed out that either the point of projection of the exposure channel of a second row of the array can be moved into the image element from outside as a result of the relative movement as time progresses, or the point of projection is already located within the image element at the first time, but that a relative movement is used in order to exploit its shifted position for exposure at a second time.
For the case in which, in addition to the first and second row, further rows exist in the array of exposure channels, the activation step can be repeated for each further row of the array of exposure channels when the point of projection of the exposure channel of the further row of the array comes to lie on the image element already exposed by the exposure channel of the first row and the same column. It is therefore possible for an input of energy to be made proportionally by means of a plurality of rows.
Depending on the material of the printing form on which an image is to be set, and on the basic imagesetting process, the exposure channels may comprise different energy sources or originate from different energy sources. It is also possible for a plurality or for all of the exposure channels to be generated on the basis of one energy source. An energy source can be a light source, a laser light source, in particular a diode laser or solid body laser, a thermal energy source, a microwave source or the like. Different beam forming elements, such as focusing or defocusing lenses, guide elements, filters or the like, and/or intensity modulators, such as electrooptical or acousto-optical modulators for light, can act on the individual exposure channels. The number of imagesetting channels is preferably formed by the light beams originating from a number of individually activatable light sources, in particular laser light sources.
In the case of a light source as energy source (or a plurality of energy sources), this may be in particular an ultra-short pulsed laser. Ultra-short pulses from a laser are able to interact with a surface by disruptive ablation, so that. with a specific input of energy, a specific amount of material can be removed. Expressed in other words, a specific removal is possible by means of a specific, predetermined input of energy, in particular this removal can be additive for two successive inputs of energy.
In this connection, reference should be made to the electrochemical surface processes which are initiated by the input of energy, preferably by the input of laser energy, which have a linear dependence on the input of energy.
Galvanic processes can be caused by chemical reactions triggered by ions or radicals produced by means of the input of energy. Chromium is preferred as such a surface.
The printing form may in particular be a rewriteable printing form. Here, rewriteable is to be understood to mean that the printing form can be subjected both to a structuring process, which is used to produce image-carrying (for example hydrophobic ar lipophilic) and non-image-carrying (for example hydrophilic or lipophobic) macroscopic areas, and also to a destructuring process. The destructuring process can be designed, for example, in such a way that image-carrying and non-image-carrying areas are produced at the microscopic level, in particular in a stochastic arrangement (noise, as it is known).
The method according to the invention of exposing a printing form can also comprise, in addition to the above described steps, simultaneously activating the first row of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in a further row of image elements while activating the second row of the array of exposure channels to produce a second component of the input of energy predefined for each column of the array when the point of projection of the exposure channel of a second row of the array comes to lie on the image element belonging to the chronologically previously exposed row and already exposed by the exposure channel of the first row and the same column.
In an advantageous way, the method according to the invention, which comprises an input of energy in an image element in chronologically successive components, can effect a short exposure time of the printing form: an image element is exposed by a number of components of the overall input of energy, it being true of each proportional exposure that this is appropriately shorter, proportional to the component, when the action of the input of energy is additive. The necessary time for the total input of energy through the sum of the components for an image element is consequently that time for an input of energy of the entire magnitude in a single exposure.
However, as a result of the proportional exposure in chronologically successive steps, it is possible to increase the relative movement between printing form and exposure unit:
the tolerable maximum relative speed is determined by the path traced by a point of projection of an imagesetting channel on the printing form. In the exposure time, for a uniform movement, the typical case for the exposure, the path is equivalent to the exposure time multiplied by the relative speed. For the method according to the invention, it is now true that the exposure time for the component of the input of energy is shortened in proportion to the component. The time saved can be exploited to increase the relative speed. As a result, faster exposure of the printing form than in alternative methods is possible. The method according to the invention needs an exposure time which lies closer to the lower time limit, which is determined by the exposure process of the surface interaction per se, than in alternative methods. Exposure in discrete steps, that is to say alternation of exposure and displacement steps, can be avoided. As an alternative to shortening the total exposure time, it is also conceivable to exploit the time advantage for the exposure of a less sensitive surface of the printing form.
Even if the input of energy by means of components is not or only approximately additive, a short exposure time can advantageously be achieved by the method according to the invention, since the time gain of faster relative movement between printing form and exposure unit can more than compensate for the possible implicit time loss caused by a longer overall exposure time of an image element.
In this connection, it becomes clear that it is advantageous if the magnitude of the input of energy is of substantially the same size for each component. Expressed in other words, the envisaged overall input of energy or the maximum overall input of energy for an image element is represented by components which are substantially equal to the overall input of energy divided by the number of rows available in the array. It is then true that the first component and the second component for producing the input of energy are of _g_ substantially the same size. This is correspondingly true of each further component involved in the preferred use of the method according to the invention with arrays which have more than two rows. As a consequence, an exposure can be carried out in a simple manner with uniform component steps.
The time advantage gained by the method according to the invention can also be exploited advantageously in a different connection, in addition to a maximum faster relative speed:
the relative speed can be selected within certain limits, from the original relative speed up to the maximum, fast relative speed. As a result, it is possible to avoid vibrations which occur as a result of resonances at specific operating parameters, in particular relative speeds, by a relative speed that avoids the resonances being selected.
The method according to the invention can be used advantageously both for imagesetting in a dpi format (dots per inch) and for imagesetting in an lpi format (lines per inch).
In an advantageous embodiment of the method according to the invention, an array of regularly arranged imagesetting channels is used. In connection with the invention, a regular arrangement is to be understood to mean that the points of projection of the individual imagesetting channels lie substantially on grid points spaced apart uniformly from row to row (including those having a first width in columns and having a second width in the row direction) on the printing form (even on a curved surface). The directions defined by the rows and columns must not necessarily be orthogonal to one another, but can advantageously be so. The uniformity relates firstly to the projections of the distances onto the two orthogonal directions, in particular to the column direction, and secondly to the identity of the distances in a specific _g_ row and/or a specific column in each case. This uniformity can also apply globally for the entire grid of the points of projection.
An image element can be produced from a number of exposure points, produced in one image element by the input of energy at the points of projection of an exposure channel. In a first embodiment of the method according to the invention, provision is made for the point of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in the same column, to lie disjunctly in relation to each other in an image element. It is therefore possible to build up an image element from exposure points which lie beside one another, in this case also touching. The relationship between the area of the points exposed and the total area of the image element influences the tonal value of the image element, and at the same time the structure of the image element can be influenced (amplitude-modulated or frequency-modulated) by building up the image element from individual exposure points, for whose arrangement there are various possibilities.
In a second alternative embodiment of the method according to the invention, on the other hand, provision is made for the points of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in the same column, to coincide in an image element, that is to say lie substantially one above another. An image element will then have substantially one exposure point, whose area in relation to the total area of the image element influences the tonal value. Depending on the uniformity of the grid of the points of projection, explained in more detail above, these exposure points will lie uniformly on the printing form.
In order to implement the method according to the invention, it is expedient for the printing form to be held on a carrier element, and for the movement of the printing form relative to the exposure channels to be produced by means of rotation of the carrier element about an axis. This is in particular advantageous for use in a direct-imaging printing unit or a drum exposer (computer-to-plate exposer). The printing form can also in itself form the surface of the carrier element.
On the one hand, the method according to the invention can be carried out by means of an array, in which all the rows expose image elements, with interaction between the exposure channels in one column. In order to minimize the time needed for the relative movement (displacement) between printing form and exposure channels, it is therefore expedient for the first and the second row in the array of imagesetting channels to be adjacent. The same is true for each further row involved for the preferred use of the method according to the invention with arrays which have more than two rows. Exposure of the image element can then be carried out in one pass of the points of projection. On the other hand, it is also possible, in analogy with the parallel arrangement of a plurality of rows of imaging channels in a two-dimensional array, to arrange a plurality of two-dimensional arrays interacting in accordance with the method of the invention. Expressed in other words, a first subset of the total set of image elements on the printing form is produced by a first array, and a second subset is produced by a second array, the arrays being operated by the method according to the invention. This subdivision can also be understood in another way: a given array with columns and rows can be subdivided into subarrays which, according to the method of the invention, in each case produce image elements. The arrays can cross over one another or lie beside one another. For the example of dividing an array into two subarrays, it should be indicated that, in a first division, all the even rows cooperate to produce image elements and all the odd rows cooperate to produce image elements and, in a second division, the first rows up to half the number of rows and the rows from half the rows up to the last row can cooperate. Other subdivisions can also be made.
The same is true of subdivisions into larger numbers of subarrays.
In connection with the idea of the invention, there is also an apparatus for implementing the method according to the invention of exposing a printing form. The apparatus according to the invention comprises a number of exposure channels which are arranged in a two-dimensional array, and a control unit.
The exposure channels of a column of the array cause an input of energy for an image element on the printing form. The control unit has a computing unit, in which or in whose memory unit a computer program runs. The computer program is stored at least partially in the memory unit. By means of the computer program, row-by-row activation of the array of exposure channels is carried out in such a way that activation of a second row of the array of exposure channels for producing a second component of the input of energy associated with each column of the array is carried out when the point of projection of the exposure channel of a second row of the array comes to lie on the image element of the row already exposed by the exposure channel of a first row and the same column. Particularly advantageous is an apparatus according to the invention in which the two-dimensional array of exposure elements extends over the full length of the printing form (extends substantially in the direction of the rows of the array of exposure elements). If the printing form is held on a cylinder or forms the surface of a cylinder, it is the extent in the axial direction of the cylinder which is involved.
The apparatus according to the invention can be implemented in a printing unit, a direct-imaging printing unit, as it is known. In particular, the printing unit according to the invention can be a direct or indirect planographic printing unit, a flexographic printing unit, an offset printing unit (standard or waterless) or the like. A printing press according to the invention has at least one printing unit according to the invention. The printing press can be a sheet-processing or a web-processing machine. Printing materials can be paper, board, paperboard, organic polymer films or the like.
Further advantages and advantageous embodiments and developments of the invention will be illustrated using the following figures and their descriptions. In detail:
figure 1 shows a schematic flowchart of an advantageous embodiment of the method according to the invention, figure 2 shows a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points, figure 3 shows a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points in an alternative way, figure 4 shows a schematic side view of an apparatus for exposing a printing form by means of the method of the invention, and figure 5 shows a schematic view of an apparatus for exposing a printing form by means of the method of the invention.
Figure 1 shows a schematic flowchart of an advantageous embodiment of the method according to the invention based on an image element which is produced by a plurality of imagesetting channels in a column of the array of imagesetting channels. As already described in more detail above, the individual steps for the number of columns are carried out in a time-parallel manner. Expressed in other words, the individual steps are carried out line by line. In a first activation 10, to produce a first component of the input of energy associated with the image element, the intensity in the point of projection of the imagesetting channel in the first row is controlled. In a movement step 12, a relative movement of the printing form in relation to the column of the exposure channels takes place, while the intensity at the points of projection is reduced below a sufficient threshold or to zero, so that interaction between the energy transported through the exposure channel and the surface of the printing form is avoided. Tn a second activation 14, in order to produce a second component of the input of energy associated with the image element, the intensity at the point of projection of the imagesetting channel in the second row is controlled when the point of projection of the exposure channel lying in the second row of the array comes to lie on the image element of the line already exposed by the exposure channel of the first row. A repetition 16 of this procedure is carried out for all further exposure channels of the column in all the :rows involved in the array. A final activation 18 is carried out by controlling the intensity at the point of projection of the imagesetting channel in the last row in order to produce a last component of the input of energy associated with the image element. Typically, the relative movement between printing form and point of projection of the imagesetting channel is not zero during the activation steps.
Furthermore, parallelization in time can be carried out by interleaving the procedure described for one image element for a plurality of image elements to be produced by a column of imagesetting channels. While for a first image element, chronologically following activation 14, for example the second, is already being carried out, the first activation 10 can be carried out for a second image element. In an analogous way, the procedure can be the same for further image elements.
Exceptions from this time parallelization are formed, so to speak as an edge effect, in each case by the first activations for the first image elements up to the number of imagesetting channels in the column and, correspondingly, the last activations 18 for the last image elements, unless the imagesetting is cyclic in the sense that the missing components of the first image elements are supplemented by the last imagesetting steps. For example, this avoidance of the edge effect is possible for image elements which lie on a closed curve.
Figure 2 is a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively set exposure points and, by using an example of three image elements 20 which each comprise four exposure points 22, is used to explain how an exposure can be carried out in accordance with the method of the invention, using points of projection which come to lie in a disjunct manner in relation to one another in an image element 20, shown as adjacent here by way of example. In part A of the figure, the exposure of the bottom left quadrants in a first step is illustrated schematically by the number 1. Depending on the input of energy (simplified in digital terms above or below the exposure threshold), an exposed point 24 is or is not produced. Part B of the figure shows, by way of example, that the exposure points 22 in the left-hand image element 20 and in the central image element 20 are exposed points 24. In part.
B of the figure, the exposure in a second step is illustrated by the number 2 and relates to the top right quadrants of the image elements 20. Part C of the figure shows that, for the Central image element 20 and the right-hand image element 20, exposed points 24 have been set. There then follows, i.n a third step, the imagesetting of the bottom right quadrants, represented by the number 3. By way of example, part D of the figure shows that, for the central image element 20 and the right-hand image element 20, exposed points 24 have been set.
In a fourth step, the imagesetting of the top left quadrants, represented by the number 4, takes place. The chronologically successive exposure of components of the input of energy, by way of example, result in exposed areas corresponding to half-tone values, as illustrated in part E of the figure: in the left-hand image element 20, 25% of the overall area has been exposed, in the central one, 1000 of the total area has been exposed, and in the right-hand one, 750 of the total area has been exposed. Figure 2 also shows, by way of example, that the 25o exposure in the left-hand image element need not be part of the 75% exposure in the right-hand image element. The structure or screening can be configured by means of the method of the invention. In general, moreover, exposure of the quadrants (exposure points 22) in a different order or series for each individual image element 20 independently of one another is also possible.
For those skilled in the art, it is clear that the regular arrangement or subdivision, shown in figure 2, of the image element 20 into four exposure points 22 which lie regularly in quadrants of the image element 20 is no restriction on the more general situation of frequency-modulated distribution of the exposure points 22 in image elements 20. Expressed in another way, figure 2 is merely based on a possible, exemplary arrangement to explain the chronologically successive or chronologically following exposure steps that have taken place in the method of the invention. Those skilled in the art will take measures aimed at performing advantageous distribution of the exposure points 22 in image elements 20, including those with different distributions in different image elements. A
procedure of this type is even advantageous as compared with a regular arrangement, distribution or subdivision.
Figure 3 shows a sequence of figure parts A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points in an alternative way in accordance with the method of the invention. In part A of the figure, by way of example, three image elements 20 are shown, each having an exposure point 22, centered here by way of example. An exposure in four steps is to be provided, using four equal components of the overall input of energy. In accordance with an exemplary first exposure step with a first component of the input of energy, exposed points 24 are produced in the left-hand image element 20 and in the central one in part B of the figure. Part C of the figure shows the situation after an exemplary second exposure step with a second component of the input of energy. The area of the central exposure point 22 has been doubled, while an exposed point 24 has been produced in the right-hand image element 20.
Part D of the figure shows the image elements 20 after an exemplary third exposure step: the area of the central exposure point 22 has increased by a half, as compared with part C of the figure, while the area of the exposed point 29 in the right-hand image element 20 has been doubled. Finally, part E of the figure shows the situation after an exemplary fourth exposure step with a fourth component of the input of energy. As a result, the left-hand image element 20 has an exposed area of 250 of the total area, the central image element 20 has been exposed over 1000 of the total area, while the right-hand image element 20 has had 75o exposed.
In general, it should further be noted that the square shape of image elements and exposure points of embodiments illustrated in the figures has been selected merely by way of example. The image elements or exposure points can in particular also be round, rectangular or oval. Furthermore, they can be distorted in the direction of movement during the activation, as a result of the relative movement between the point of projection of the exposure channel and printing form.
Figure 4 relates in schematic form to a side view or a lateral sectional image of an apparatus for exposing a printing form by means of the method of the invention. Figure 4 shows a printing form 30 which is held on a carrier element 32, here a cylinder as an example. The carrier element 32 can be rotated about an axis 34 in the direction of rotation 36, and therefore constitutes a body of rotation, here a symmetrical body of rotation. The rotation is provided by a drive, not shown here. Imagesetting channels 310 originating from an array of exposure elements 38, for example light sources, laser light sources, photon-emitting layers (infrared, visible or ultraviolet) or the like, are shown. By way of example, four exposure channels 310 are shown here, which form one column of the two-dimensional array of exposure channels, which extends in the direction at right angles to the plane of the paper. By means of a projection element 312, the exposure channels 310 are imaged at points of projection 314 on the surface of the printing form 30. The points of projection 314 lie uniformly at intervals 316. Given uniform rotational movement of the printing form 30, one point on the surface consequently needs the same time from the position of a first point of projection 314 to an adjacent point of projection 314 as from the position of a second point of projection 314 to a second point of projection 314 adjacent to the latter.
The array of exposure elements 38 is provided with a contrbl unit 318. The control unit 318 comprises a computing unit (computer or the like) with a memory unit. Stored in the memory unit of the computing unit, at least to some extent and at least for one time interval, is a program. In this embodiment, the memory unit is a familiar RAM. As an alternative to this, the memory unit can be a hard disk or a data medium on a magnetic, magneto-optical or optical basis. A
computing unit executes the program, so that activation of the imagesetting channels 314 is carried out in accordance with the invention. Expressed in other words, a computer program runs on the computing unit and performs or executes activation of the imagesetting channels 314 in steps in accordance with the method of the invention. The control unit 318, which in particular controls the intensity and/or the exposure time of the imagesetting channels 314, is connected to a data preparation unit 320. By using image information in a given format, for example following the standards pdf (portable data format), TIFF or ps (post script), data for the necessary intensities and exposure times can be made available to the control unit 318. Furthermore, the control unit 318 has a position encoder 322 for determining the position (coordinate position) of the printing form 30 on the rotatable carrier element 32.
Figure 5 shows a schematic view of an apparatus for exposing a printing form by means of the method of the invention. Figure shows a printing form 30 held on a carrier element 32 in the form of a cylinder. The carrier element 32 can be rotated about an axis 34 in a direction of rotation 36. A drive, not shown here, is provided to produce the rotational movement.
The array of exposure elements 38 extends over the full length of the printing form 30 on the carrier element 32. After exposure has been carried out, this length is used for the print. By means of an array of exposure elements 38 over the full length which is provided for the print, translation of the exposure elements, which requires additional time, in the direction of the axis 34 can be avoided. At the same time, no typically complicated translation actuator mechanism is required. Here, by way of example, the array of exposure elements 38 has a first row 324, a second row 326, a third row 328 and a fourth row 330 each having, as an example, sixteen individual exposure elements, which are associated with imagesetting channels. In other words, the apparatus comprises sixteen columns each having four exposure elements. By means of the tour imagesetting channels originating from the exposure elements in one column, points of projection 314 are produced on the printing form 30. In the apparatus shown in figure 5, the method according to the invention can be used for each of the sixteen columns to expose a printing form.
An embodiment of an apparatus according to the invention according to figure 4 or figure 5 can be implemented in a printing unit of a printing press.
Finally, it should be noted that, in an alternative embodiment, the exposure device, that is to say the array of exposure elements, which exposes a printing form by the method according to the invention, can also be designed as an in-drum exposer, as it is known. In such an arrangement, the array is arranged within the rotating carrier element (in-drum).
LIST OF DESIGNATIONS
First activation 12 Movement 14 Second activation 16 Repetition 18 Final activation Image element 22 Exposure point 24 Exposed point Printing form 32 Carrier element 34 Axis 36 Direction of rotation 38 Array of exposure elements 310 Exposure channels 312 Projection element 314 Point of projection 316 Spacing of two points of projection 318 Control unit 320 Data preparation unit 322 Position encoder 324 First row 326 Second row 328 Third row 330 Fourth row
For imagesetting or exposing printing forms, be it in printing form exposers or in direct-imaging printing units, as they are known, in printing presses, a number of image elements are often produced in a time-parallel fashion on the printing form as a result of inputting energy by means of a number of exposure channels.
The document EP 0 947 950 A2 discloses a typical exposing method by means of a multi-beam laser exposure device. In this method, a plurality of image elements in a row are exposed in a time-parallel fashion, a relative displacement between exposure device and image carrier is then carried out in accordance with rules which avoid a position of points of projection, that is to say those points at which light falls on the image carrier, on already exposed image elements, before a plurality of image elements is again exposed in a time-parallel fashion. This procedure is repeated and comprises displacements in the two linearly independent directions of the surface of the image carrier.
_1_ For example, it is known from US 5,477,259 that parallel exposure does not have to be restricted to a plurality of exposure channels arranged in a row. This document describes a multi-beam laser exposure device which has laser light sources arranged in a two-dimensional array. It is therefore possible for a large number of rows of a number of image elements which are each associated with a number of exposure channels to be exposed in a time-parallel fashion.
In a procedure of the type described, a lower limit for the duration of the complete exposure of the printing form is equal to that time which is required for the complete production of an image element, multiplied by the total number of image elements on the printing form and divided by the number of exposure channels available in one exposure step (irrespective of a one-dimensional or two-dimensional arrangement). Furthermore, typically additional time is required in order to guide the points of projection of the exposure channels, whose number lies considerably below the total number of image elements to be exposed, over the two-dimensional surface of the printing form. Points of projection are to be understood as those points at which light falls onto the printing form when the exposure channel is open.
Furthermore, additional time for relative displacements is needed, if an image element is to be built up in a structured manner from individual exposure points. These movements are often slow or take place in steps. The exposure duration will therefore in practice generally be greater than this lower limit.
The disadvantage with the method described is that the lower time limit for the exposure duration which can be achieved by means of a plurality of imagesetting channels through the parallel processing cannot be reached, since additional time is needed as a result of relative displacements of the printing form in relation to the imagesetting channels.
It is an object of the present invention to provide a method of exposing printing forms which permits a short exposure time.
According to the invention, this object is achieved by a method having the features as claimed in claim 1. Advantageous developments of the invention are characterized in the subclaims.
In the method according to the invention of exposing a printing form, using a number of exposure channels which are arranged in a two-dimensional array, provision is made for the exposure channels of a column of the array to be used to produce an image element and, for this purpose, cause an input of energy for an image element on the printing form. Expressed in other words, the exposure channels in various rows but in the same columns are therefore used proportionally to produce an exposed point in an image element associated with the column in a raw on the printing form. The number of columns determines the number of image elements in a row. At a given instant or at a time, in this case at least points of projection from two exposure channels in one column of the array cannot coincide on the printing form. To produce a first component of the input of energy associated with each column of the array in a row of image elements, a first row of the array of exposure channels is activated at a first time. Here, activation comprises, firstly, switching the exposure channel on and off for a time period which can be one interval or a plurality of intervals and, secondly, an input of energy with a specific amount of energy, it being possible for the amount of energy either to be constant over time when the exposure _3_ channel is open (switched on) or can vary over time, the integral of the amount of energy over the time representing the input of energy.
The printing form is moved relative to the exposure channels.
For a relative movement, it is unimportant whether the exposure channels or the printing form or both are moved. A
relative movement in connection with the invention in this case has at least one velocity vector component in the direction at right angles to the optical axis of the exposure channels which strike the printing form. Expressed in other words, a change in spacing resulting from the relative movement is not necessary, preferably even not provided, while the velocity has at least one tangential component.
The method according to the invention is distinguished by the fact that, to produce a second component of the input. of energy associated with each column of the array, a second row of the array is activated at a second time when the point of projection of the exposure channel of a second row of the array comes to lie on the image element of the row already exposed by the exposure channel of the first row and the same column. In other words, as a result of the relative movement, the points of projection of the second row of the array wi)_1 come to lie at a second time on the image elements exposed by the first row at a first time, so that a second component of the input of energy can be provided. The total input of energy for an image element is provided gradually over time or successively in components through exposure channels in different rows but the same column in the array of exposure channels. In this case, an input of energy onto the printing form is performed in a time-parallel or simultaneously proportional manner for a plurality of image elements. The _q_ input of energy and the division into individual components can be determined in advance.
It should be noted, firstly, that the proportion of an exposure channel can also be zero. Secondly, it should be pointed out that either the point of projection of the exposure channel of a second row of the array can be moved into the image element from outside as a result of the relative movement as time progresses, or the point of projection is already located within the image element at the first time, but that a relative movement is used in order to exploit its shifted position for exposure at a second time.
For the case in which, in addition to the first and second row, further rows exist in the array of exposure channels, the activation step can be repeated for each further row of the array of exposure channels when the point of projection of the exposure channel of the further row of the array comes to lie on the image element already exposed by the exposure channel of the first row and the same column. It is therefore possible for an input of energy to be made proportionally by means of a plurality of rows.
Depending on the material of the printing form on which an image is to be set, and on the basic imagesetting process, the exposure channels may comprise different energy sources or originate from different energy sources. It is also possible for a plurality or for all of the exposure channels to be generated on the basis of one energy source. An energy source can be a light source, a laser light source, in particular a diode laser or solid body laser, a thermal energy source, a microwave source or the like. Different beam forming elements, such as focusing or defocusing lenses, guide elements, filters or the like, and/or intensity modulators, such as electrooptical or acousto-optical modulators for light, can act on the individual exposure channels. The number of imagesetting channels is preferably formed by the light beams originating from a number of individually activatable light sources, in particular laser light sources.
In the case of a light source as energy source (or a plurality of energy sources), this may be in particular an ultra-short pulsed laser. Ultra-short pulses from a laser are able to interact with a surface by disruptive ablation, so that. with a specific input of energy, a specific amount of material can be removed. Expressed in other words, a specific removal is possible by means of a specific, predetermined input of energy, in particular this removal can be additive for two successive inputs of energy.
In this connection, reference should be made to the electrochemical surface processes which are initiated by the input of energy, preferably by the input of laser energy, which have a linear dependence on the input of energy.
Galvanic processes can be caused by chemical reactions triggered by ions or radicals produced by means of the input of energy. Chromium is preferred as such a surface.
The printing form may in particular be a rewriteable printing form. Here, rewriteable is to be understood to mean that the printing form can be subjected both to a structuring process, which is used to produce image-carrying (for example hydrophobic ar lipophilic) and non-image-carrying (for example hydrophilic or lipophobic) macroscopic areas, and also to a destructuring process. The destructuring process can be designed, for example, in such a way that image-carrying and non-image-carrying areas are produced at the microscopic level, in particular in a stochastic arrangement (noise, as it is known).
The method according to the invention of exposing a printing form can also comprise, in addition to the above described steps, simultaneously activating the first row of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in a further row of image elements while activating the second row of the array of exposure channels to produce a second component of the input of energy predefined for each column of the array when the point of projection of the exposure channel of a second row of the array comes to lie on the image element belonging to the chronologically previously exposed row and already exposed by the exposure channel of the first row and the same column.
In an advantageous way, the method according to the invention, which comprises an input of energy in an image element in chronologically successive components, can effect a short exposure time of the printing form: an image element is exposed by a number of components of the overall input of energy, it being true of each proportional exposure that this is appropriately shorter, proportional to the component, when the action of the input of energy is additive. The necessary time for the total input of energy through the sum of the components for an image element is consequently that time for an input of energy of the entire magnitude in a single exposure.
However, as a result of the proportional exposure in chronologically successive steps, it is possible to increase the relative movement between printing form and exposure unit:
the tolerable maximum relative speed is determined by the path traced by a point of projection of an imagesetting channel on the printing form. In the exposure time, for a uniform movement, the typical case for the exposure, the path is equivalent to the exposure time multiplied by the relative speed. For the method according to the invention, it is now true that the exposure time for the component of the input of energy is shortened in proportion to the component. The time saved can be exploited to increase the relative speed. As a result, faster exposure of the printing form than in alternative methods is possible. The method according to the invention needs an exposure time which lies closer to the lower time limit, which is determined by the exposure process of the surface interaction per se, than in alternative methods. Exposure in discrete steps, that is to say alternation of exposure and displacement steps, can be avoided. As an alternative to shortening the total exposure time, it is also conceivable to exploit the time advantage for the exposure of a less sensitive surface of the printing form.
Even if the input of energy by means of components is not or only approximately additive, a short exposure time can advantageously be achieved by the method according to the invention, since the time gain of faster relative movement between printing form and exposure unit can more than compensate for the possible implicit time loss caused by a longer overall exposure time of an image element.
In this connection, it becomes clear that it is advantageous if the magnitude of the input of energy is of substantially the same size for each component. Expressed in other words, the envisaged overall input of energy or the maximum overall input of energy for an image element is represented by components which are substantially equal to the overall input of energy divided by the number of rows available in the array. It is then true that the first component and the second component for producing the input of energy are of _g_ substantially the same size. This is correspondingly true of each further component involved in the preferred use of the method according to the invention with arrays which have more than two rows. As a consequence, an exposure can be carried out in a simple manner with uniform component steps.
The time advantage gained by the method according to the invention can also be exploited advantageously in a different connection, in addition to a maximum faster relative speed:
the relative speed can be selected within certain limits, from the original relative speed up to the maximum, fast relative speed. As a result, it is possible to avoid vibrations which occur as a result of resonances at specific operating parameters, in particular relative speeds, by a relative speed that avoids the resonances being selected.
The method according to the invention can be used advantageously both for imagesetting in a dpi format (dots per inch) and for imagesetting in an lpi format (lines per inch).
In an advantageous embodiment of the method according to the invention, an array of regularly arranged imagesetting channels is used. In connection with the invention, a regular arrangement is to be understood to mean that the points of projection of the individual imagesetting channels lie substantially on grid points spaced apart uniformly from row to row (including those having a first width in columns and having a second width in the row direction) on the printing form (even on a curved surface). The directions defined by the rows and columns must not necessarily be orthogonal to one another, but can advantageously be so. The uniformity relates firstly to the projections of the distances onto the two orthogonal directions, in particular to the column direction, and secondly to the identity of the distances in a specific _g_ row and/or a specific column in each case. This uniformity can also apply globally for the entire grid of the points of projection.
An image element can be produced from a number of exposure points, produced in one image element by the input of energy at the points of projection of an exposure channel. In a first embodiment of the method according to the invention, provision is made for the point of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in the same column, to lie disjunctly in relation to each other in an image element. It is therefore possible to build up an image element from exposure points which lie beside one another, in this case also touching. The relationship between the area of the points exposed and the total area of the image element influences the tonal value of the image element, and at the same time the structure of the image element can be influenced (amplitude-modulated or frequency-modulated) by building up the image element from individual exposure points, for whose arrangement there are various possibilities.
In a second alternative embodiment of the method according to the invention, on the other hand, provision is made for the points of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in the same column, to coincide in an image element, that is to say lie substantially one above another. An image element will then have substantially one exposure point, whose area in relation to the total area of the image element influences the tonal value. Depending on the uniformity of the grid of the points of projection, explained in more detail above, these exposure points will lie uniformly on the printing form.
In order to implement the method according to the invention, it is expedient for the printing form to be held on a carrier element, and for the movement of the printing form relative to the exposure channels to be produced by means of rotation of the carrier element about an axis. This is in particular advantageous for use in a direct-imaging printing unit or a drum exposer (computer-to-plate exposer). The printing form can also in itself form the surface of the carrier element.
On the one hand, the method according to the invention can be carried out by means of an array, in which all the rows expose image elements, with interaction between the exposure channels in one column. In order to minimize the time needed for the relative movement (displacement) between printing form and exposure channels, it is therefore expedient for the first and the second row in the array of imagesetting channels to be adjacent. The same is true for each further row involved for the preferred use of the method according to the invention with arrays which have more than two rows. Exposure of the image element can then be carried out in one pass of the points of projection. On the other hand, it is also possible, in analogy with the parallel arrangement of a plurality of rows of imaging channels in a two-dimensional array, to arrange a plurality of two-dimensional arrays interacting in accordance with the method of the invention. Expressed in other words, a first subset of the total set of image elements on the printing form is produced by a first array, and a second subset is produced by a second array, the arrays being operated by the method according to the invention. This subdivision can also be understood in another way: a given array with columns and rows can be subdivided into subarrays which, according to the method of the invention, in each case produce image elements. The arrays can cross over one another or lie beside one another. For the example of dividing an array into two subarrays, it should be indicated that, in a first division, all the even rows cooperate to produce image elements and all the odd rows cooperate to produce image elements and, in a second division, the first rows up to half the number of rows and the rows from half the rows up to the last row can cooperate. Other subdivisions can also be made.
The same is true of subdivisions into larger numbers of subarrays.
In connection with the idea of the invention, there is also an apparatus for implementing the method according to the invention of exposing a printing form. The apparatus according to the invention comprises a number of exposure channels which are arranged in a two-dimensional array, and a control unit.
The exposure channels of a column of the array cause an input of energy for an image element on the printing form. The control unit has a computing unit, in which or in whose memory unit a computer program runs. The computer program is stored at least partially in the memory unit. By means of the computer program, row-by-row activation of the array of exposure channels is carried out in such a way that activation of a second row of the array of exposure channels for producing a second component of the input of energy associated with each column of the array is carried out when the point of projection of the exposure channel of a second row of the array comes to lie on the image element of the row already exposed by the exposure channel of a first row and the same column. Particularly advantageous is an apparatus according to the invention in which the two-dimensional array of exposure elements extends over the full length of the printing form (extends substantially in the direction of the rows of the array of exposure elements). If the printing form is held on a cylinder or forms the surface of a cylinder, it is the extent in the axial direction of the cylinder which is involved.
The apparatus according to the invention can be implemented in a printing unit, a direct-imaging printing unit, as it is known. In particular, the printing unit according to the invention can be a direct or indirect planographic printing unit, a flexographic printing unit, an offset printing unit (standard or waterless) or the like. A printing press according to the invention has at least one printing unit according to the invention. The printing press can be a sheet-processing or a web-processing machine. Printing materials can be paper, board, paperboard, organic polymer films or the like.
Further advantages and advantageous embodiments and developments of the invention will be illustrated using the following figures and their descriptions. In detail:
figure 1 shows a schematic flowchart of an advantageous embodiment of the method according to the invention, figure 2 shows a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points, figure 3 shows a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points in an alternative way, figure 4 shows a schematic side view of an apparatus for exposing a printing form by means of the method of the invention, and figure 5 shows a schematic view of an apparatus for exposing a printing form by means of the method of the invention.
Figure 1 shows a schematic flowchart of an advantageous embodiment of the method according to the invention based on an image element which is produced by a plurality of imagesetting channels in a column of the array of imagesetting channels. As already described in more detail above, the individual steps for the number of columns are carried out in a time-parallel manner. Expressed in other words, the individual steps are carried out line by line. In a first activation 10, to produce a first component of the input of energy associated with the image element, the intensity in the point of projection of the imagesetting channel in the first row is controlled. In a movement step 12, a relative movement of the printing form in relation to the column of the exposure channels takes place, while the intensity at the points of projection is reduced below a sufficient threshold or to zero, so that interaction between the energy transported through the exposure channel and the surface of the printing form is avoided. Tn a second activation 14, in order to produce a second component of the input of energy associated with the image element, the intensity at the point of projection of the imagesetting channel in the second row is controlled when the point of projection of the exposure channel lying in the second row of the array comes to lie on the image element of the line already exposed by the exposure channel of the first row. A repetition 16 of this procedure is carried out for all further exposure channels of the column in all the :rows involved in the array. A final activation 18 is carried out by controlling the intensity at the point of projection of the imagesetting channel in the last row in order to produce a last component of the input of energy associated with the image element. Typically, the relative movement between printing form and point of projection of the imagesetting channel is not zero during the activation steps.
Furthermore, parallelization in time can be carried out by interleaving the procedure described for one image element for a plurality of image elements to be produced by a column of imagesetting channels. While for a first image element, chronologically following activation 14, for example the second, is already being carried out, the first activation 10 can be carried out for a second image element. In an analogous way, the procedure can be the same for further image elements.
Exceptions from this time parallelization are formed, so to speak as an edge effect, in each case by the first activations for the first image elements up to the number of imagesetting channels in the column and, correspondingly, the last activations 18 for the last image elements, unless the imagesetting is cyclic in the sense that the missing components of the first image elements are supplemented by the last imagesetting steps. For example, this avoidance of the edge effect is possible for image elements which lie on a closed curve.
Figure 2 is a sequence of part images A to E to illustrate schematically the exposure of an image element by means of successively set exposure points and, by using an example of three image elements 20 which each comprise four exposure points 22, is used to explain how an exposure can be carried out in accordance with the method of the invention, using points of projection which come to lie in a disjunct manner in relation to one another in an image element 20, shown as adjacent here by way of example. In part A of the figure, the exposure of the bottom left quadrants in a first step is illustrated schematically by the number 1. Depending on the input of energy (simplified in digital terms above or below the exposure threshold), an exposed point 24 is or is not produced. Part B of the figure shows, by way of example, that the exposure points 22 in the left-hand image element 20 and in the central image element 20 are exposed points 24. In part.
B of the figure, the exposure in a second step is illustrated by the number 2 and relates to the top right quadrants of the image elements 20. Part C of the figure shows that, for the Central image element 20 and the right-hand image element 20, exposed points 24 have been set. There then follows, i.n a third step, the imagesetting of the bottom right quadrants, represented by the number 3. By way of example, part D of the figure shows that, for the central image element 20 and the right-hand image element 20, exposed points 24 have been set.
In a fourth step, the imagesetting of the top left quadrants, represented by the number 4, takes place. The chronologically successive exposure of components of the input of energy, by way of example, result in exposed areas corresponding to half-tone values, as illustrated in part E of the figure: in the left-hand image element 20, 25% of the overall area has been exposed, in the central one, 1000 of the total area has been exposed, and in the right-hand one, 750 of the total area has been exposed. Figure 2 also shows, by way of example, that the 25o exposure in the left-hand image element need not be part of the 75% exposure in the right-hand image element. The structure or screening can be configured by means of the method of the invention. In general, moreover, exposure of the quadrants (exposure points 22) in a different order or series for each individual image element 20 independently of one another is also possible.
For those skilled in the art, it is clear that the regular arrangement or subdivision, shown in figure 2, of the image element 20 into four exposure points 22 which lie regularly in quadrants of the image element 20 is no restriction on the more general situation of frequency-modulated distribution of the exposure points 22 in image elements 20. Expressed in another way, figure 2 is merely based on a possible, exemplary arrangement to explain the chronologically successive or chronologically following exposure steps that have taken place in the method of the invention. Those skilled in the art will take measures aimed at performing advantageous distribution of the exposure points 22 in image elements 20, including those with different distributions in different image elements. A
procedure of this type is even advantageous as compared with a regular arrangement, distribution or subdivision.
Figure 3 shows a sequence of figure parts A to E to illustrate schematically the exposure of an image element by means of successively placed exposure points in an alternative way in accordance with the method of the invention. In part A of the figure, by way of example, three image elements 20 are shown, each having an exposure point 22, centered here by way of example. An exposure in four steps is to be provided, using four equal components of the overall input of energy. In accordance with an exemplary first exposure step with a first component of the input of energy, exposed points 24 are produced in the left-hand image element 20 and in the central one in part B of the figure. Part C of the figure shows the situation after an exemplary second exposure step with a second component of the input of energy. The area of the central exposure point 22 has been doubled, while an exposed point 24 has been produced in the right-hand image element 20.
Part D of the figure shows the image elements 20 after an exemplary third exposure step: the area of the central exposure point 22 has increased by a half, as compared with part C of the figure, while the area of the exposed point 29 in the right-hand image element 20 has been doubled. Finally, part E of the figure shows the situation after an exemplary fourth exposure step with a fourth component of the input of energy. As a result, the left-hand image element 20 has an exposed area of 250 of the total area, the central image element 20 has been exposed over 1000 of the total area, while the right-hand image element 20 has had 75o exposed.
In general, it should further be noted that the square shape of image elements and exposure points of embodiments illustrated in the figures has been selected merely by way of example. The image elements or exposure points can in particular also be round, rectangular or oval. Furthermore, they can be distorted in the direction of movement during the activation, as a result of the relative movement between the point of projection of the exposure channel and printing form.
Figure 4 relates in schematic form to a side view or a lateral sectional image of an apparatus for exposing a printing form by means of the method of the invention. Figure 4 shows a printing form 30 which is held on a carrier element 32, here a cylinder as an example. The carrier element 32 can be rotated about an axis 34 in the direction of rotation 36, and therefore constitutes a body of rotation, here a symmetrical body of rotation. The rotation is provided by a drive, not shown here. Imagesetting channels 310 originating from an array of exposure elements 38, for example light sources, laser light sources, photon-emitting layers (infrared, visible or ultraviolet) or the like, are shown. By way of example, four exposure channels 310 are shown here, which form one column of the two-dimensional array of exposure channels, which extends in the direction at right angles to the plane of the paper. By means of a projection element 312, the exposure channels 310 are imaged at points of projection 314 on the surface of the printing form 30. The points of projection 314 lie uniformly at intervals 316. Given uniform rotational movement of the printing form 30, one point on the surface consequently needs the same time from the position of a first point of projection 314 to an adjacent point of projection 314 as from the position of a second point of projection 314 to a second point of projection 314 adjacent to the latter.
The array of exposure elements 38 is provided with a contrbl unit 318. The control unit 318 comprises a computing unit (computer or the like) with a memory unit. Stored in the memory unit of the computing unit, at least to some extent and at least for one time interval, is a program. In this embodiment, the memory unit is a familiar RAM. As an alternative to this, the memory unit can be a hard disk or a data medium on a magnetic, magneto-optical or optical basis. A
computing unit executes the program, so that activation of the imagesetting channels 314 is carried out in accordance with the invention. Expressed in other words, a computer program runs on the computing unit and performs or executes activation of the imagesetting channels 314 in steps in accordance with the method of the invention. The control unit 318, which in particular controls the intensity and/or the exposure time of the imagesetting channels 314, is connected to a data preparation unit 320. By using image information in a given format, for example following the standards pdf (portable data format), TIFF or ps (post script), data for the necessary intensities and exposure times can be made available to the control unit 318. Furthermore, the control unit 318 has a position encoder 322 for determining the position (coordinate position) of the printing form 30 on the rotatable carrier element 32.
Figure 5 shows a schematic view of an apparatus for exposing a printing form by means of the method of the invention. Figure shows a printing form 30 held on a carrier element 32 in the form of a cylinder. The carrier element 32 can be rotated about an axis 34 in a direction of rotation 36. A drive, not shown here, is provided to produce the rotational movement.
The array of exposure elements 38 extends over the full length of the printing form 30 on the carrier element 32. After exposure has been carried out, this length is used for the print. By means of an array of exposure elements 38 over the full length which is provided for the print, translation of the exposure elements, which requires additional time, in the direction of the axis 34 can be avoided. At the same time, no typically complicated translation actuator mechanism is required. Here, by way of example, the array of exposure elements 38 has a first row 324, a second row 326, a third row 328 and a fourth row 330 each having, as an example, sixteen individual exposure elements, which are associated with imagesetting channels. In other words, the apparatus comprises sixteen columns each having four exposure elements. By means of the tour imagesetting channels originating from the exposure elements in one column, points of projection 314 are produced on the printing form 30. In the apparatus shown in figure 5, the method according to the invention can be used for each of the sixteen columns to expose a printing form.
An embodiment of an apparatus according to the invention according to figure 4 or figure 5 can be implemented in a printing unit of a printing press.
Finally, it should be noted that, in an alternative embodiment, the exposure device, that is to say the array of exposure elements, which exposes a printing form by the method according to the invention, can also be designed as an in-drum exposer, as it is known. In such an arrangement, the array is arranged within the rotating carrier element (in-drum).
LIST OF DESIGNATIONS
First activation 12 Movement 14 Second activation 16 Repetition 18 Final activation Image element 22 Exposure point 24 Exposed point Printing form 32 Carrier element 34 Axis 36 Direction of rotation 38 Array of exposure elements 310 Exposure channels 312 Projection element 314 Point of projection 316 Spacing of two points of projection 318 Control unit 320 Data preparation unit 322 Position encoder 324 First row 326 Second row 328 Third row 330 Fourth row
Claims (14)
1. A method of exposing a printing form (30), using a number of exposure channels (310) which are arranged in a two-dimensional array (38), the exposure channels of a column of the array causing an input of energy for an image element (20) on the printing form, the method having the steps:
- activating (10) a first row (324) of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in one row of image elements;
- moving (12) the printing form relative to the exposure channels;
characterized by:
- activating (14) a second row (326) of the array of exposure channels to produce a second component of the input of energy associated with each column of the array when the point of projection (314) of the exposure channel of a second row of the array comes to lie on the image element (20) of the row already exposed by the exposure channel of the first row and the same column.
- activating (10) a first row (324) of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in one row of image elements;
- moving (12) the printing form relative to the exposure channels;
characterized by:
- activating (14) a second row (326) of the array of exposure channels to produce a second component of the input of energy associated with each column of the array when the point of projection (314) of the exposure channel of a second row of the array comes to lie on the image element (20) of the row already exposed by the exposure channel of the first row and the same column.
2. The method of exposing a printing form (30) as claimed in claim 1, characterized in that at least two points of projection (314) of two exposure channels in a column of the array do not coincide at one time on the printing form.
3. The method of exposing a printing form (30) as claimed in claim 1 or 2, characterized in that the activation step is repeated (16) for each further row (328, 330) of the array (38) of exposure channels when the point of projection (314) of the exposure channel of the further row (328, 330) of the array (38) comes to lie on the image element already exposed by the exposure channel of the first row (324) and the same column.
4. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized by:
- simultaneously activating the first row (324) of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in a further row of image elements while activating the second row (326) of the array of exposure channels to produce a second component of the input of energy predefined for each column of the array when the point of projection of the exposure channel of a second row of the array comes to lie on the image element belonging to the chronologically previously exposed row and already exposed by the exposure channel of the first row and the same column.
- simultaneously activating the first row (324) of the array of exposure channels to produce a first component of the input of energy associated with each column of the array in a further row of image elements while activating the second row (326) of the array of exposure channels to produce a second component of the input of energy predefined for each column of the array when the point of projection of the exposure channel of a second row of the array comes to lie on the image element belonging to the chronologically previously exposed row and already exposed by the exposure channel of the first row and the same column.
5. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized in that an array of regularly arranged imagesetting channels is used.
6. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized in that the point of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in. the same column, are located disjunctly in relation to each other in an image element.
7. The method of exposing a printing form (30) as claimed in one of claims 1 to 5, characterized in that the points of projection of an exposure channel in the first row and in a specific column, and the point of projection of an exposure channel in the second row and in the same column coincide in an image element.
8. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized in that the printing form (30) is held on a carrier element (32), and the movement of the printing form (30) relative to the exposure channels is produced by means of rotation of the carrier element (32) about an axis (34).
9. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized in that the first component and the second component for producing the input of energy are of substantially the same size.
10. The method of exposing a printing form (30) as claimed in one of the preceding claims, characterized in that the number of imagesetting channels is formed by the light beams originating from a number of individually activatable laser light sources.
11. An apparatus for implementing a method of exposing a printing form (30) as claimed in one of the preceding claims, having a number of exposure channels (310) which are arranged in a two-dimensional array (38), and a control unit (318), the exposure channels of a column of the array causing an input of energy for an image element (20) on the printing form, characterized in that the control unit (318) comprises a computing unit, in which a computer program runs which is at least partially stored in a memory unit and by means of which row-by-row activation of the array of exposure channels is carried out in such a way that a second row (326) of the array of exposure channels is activated to produce a second component of the input of energy associated with each column of the array when the point of projection (314) of the exposure channel of a second row of the array comes to lie on the image element (20) of the row already exposed by the exposure channel of a first row (324) and the same column.
12. The apparatus for implementing a method of exposing a printing form (30) as claimed in claim 11, characterized in that the two-dimensional array of exposure elements (38) extends over the full length of the printing form (30).
13. A printing unit characterized by at least one apparatus as claimed in claim 11 or 12.
14. A printing press characterized by at least one printing unit as claimed in claim 13.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10152846.9 | 2001-10-25 | ||
| DE10152846 | 2001-10-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2405206A1 true CA2405206A1 (en) | 2003-04-25 |
Family
ID=7703782
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002405206A Abandoned CA2405206A1 (en) | 2001-10-25 | 2002-09-25 | Method of exposing a printing form |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JP2003195515A (en) |
| CA (1) | CA2405206A1 (en) |
| DE (1) | DE10244766A1 (en) |
| IL (1) | IL152377A (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102011106799A1 (en) | 2010-08-04 | 2012-02-09 | Heidelberger Druckmaschinen Aktiengesellschaft | Process for re-imaging a printed printing form |
| KR101632577B1 (en) * | 2011-07-18 | 2016-06-22 | 동우 화인켐 주식회사 | Film developing system and method |
| GB2495499B (en) | 2011-10-11 | 2019-02-06 | Hs Products Ltd | Hybrid spring |
| GB2500366A (en) * | 2012-02-01 | 2013-09-25 | Lumejet Holdings Ltd | Media exposure device system and method |
| GB2506104B (en) | 2012-08-10 | 2018-12-12 | Hs Products Ltd | Resilient unit with different major surfaces |
| GB201708635D0 (en) | 2017-05-31 | 2017-07-12 | Hs Products Ltd | Pocketed spring unit and method manufacture |
| GB201708639D0 (en) | 2017-05-31 | 2017-07-12 | Hs Products Ltd | Transportation Apparatus and method |
-
2002
- 2002-09-25 CA CA002405206A patent/CA2405206A1/en not_active Abandoned
- 2002-09-26 DE DE10244766A patent/DE10244766A1/en not_active Withdrawn
- 2002-10-20 IL IL15237702A patent/IL152377A/en not_active IP Right Cessation
- 2002-10-25 JP JP2002310519A patent/JP2003195515A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE10244766A1 (en) | 2003-05-08 |
| JP2003195515A (en) | 2003-07-09 |
| IL152377A0 (en) | 2003-05-29 |
| IL152377A (en) | 2005-08-31 |
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| FZDE | Discontinued |