WO2002023278A2 - Device and method for exposing photosensitive plates for printing presses - Google Patents

Device and method for exposing photosensitive plates for printing presses Download PDF

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Publication number
WO2002023278A2
WO2002023278A2 PCT/EP2001/003806 EP0103806W WO0223278A2 WO 2002023278 A2 WO2002023278 A2 WO 2002023278A2 EP 0103806 W EP0103806 W EP 0103806W WO 0223278 A2 WO0223278 A2 WO 0223278A2
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WO
WIPO (PCT)
Prior art keywords
photosensitive plates
laser
laser beam
exposure
plates
Prior art date
Application number
PCT/EP2001/003806
Other languages
French (fr)
Other versions
WO2002023278A3 (en
Inventor
Bart Wattyn
Original Assignee
N.V. Strobbe Graphics
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by N.V. Strobbe Graphics filed Critical N.V. Strobbe Graphics
Priority to AU2001262166A priority Critical patent/AU2001262166A1/en
Publication of WO2002023278A2 publication Critical patent/WO2002023278A2/en
Publication of WO2002023278A3 publication Critical patent/WO2002023278A3/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
    • G02B27/0031—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration for scanning purposes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G02B26/12—Scanning systems using multifaceted mirrors
    • G02B26/127—Adaptive control of the scanning light beam, e.g. using the feedback from one or more detectors
    • 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
    • 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
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/047—Detection, control or error compensation of scanning velocity or position
    • 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
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/113—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors
    • H04N1/1135—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors for the main-scan only
    • 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
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/12—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanning
    • 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
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/19—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/024—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof deleted
    • H04N2201/02406—Arrangements for positioning elements within a head
    • H04N2201/02439—Positioning method
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/047—Detection, control or error compensation of scanning velocity or position
    • H04N2201/04701—Detection of scanning velocity or position
    • H04N2201/0471—Detection of scanning velocity or position using dedicated detectors
    • H04N2201/04712—Detection of scanning velocity or position using dedicated detectors using unbroken arrays of detectors, i.e. detectors mounted on the same substrate
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/047—Detection, control or error compensation of scanning velocity or position
    • H04N2201/04701—Detection of scanning velocity or position
    • H04N2201/04732—Detecting at infrequent intervals, e.g. once or twice per line for main-scan control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/047—Detection, control or error compensation of scanning velocity or position
    • H04N2201/04701—Detection of scanning velocity or position
    • H04N2201/04744—Detection of scanning velocity or position by detecting the scanned beam or a reference beam
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/047—Detection, control or error compensation of scanning velocity or position
    • H04N2201/04753—Control or error compensation of scanning position or velocity
    • H04N2201/04758—Control or error compensation of scanning position or velocity by controlling the position of the scanned image area
    • H04N2201/0476—Control or error compensation of scanning position or velocity by controlling the position of the scanned image area using an optical, electro-optical or acousto-optical element
    • H04N2201/04762—Control or error compensation of scanning position or velocity by controlling the position of the scanned image area using an optical, electro-optical or acousto-optical element using a reflecting element
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/047—Detection, control or error compensation of scanning velocity or position
    • H04N2201/04753—Control or error compensation of scanning position or velocity
    • H04N2201/04794—Varying the control or compensation during the scan, e.g. using continuous feedback or from line to line

Definitions

  • the invention relates to a device for exposing photosensitive plates for printing presses, comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates.
  • a problem is that the known plate exposers do not operate sufficiently accurately.
  • a disadvantage of this system is that it does not operate sufficiently fast.
  • the purpose of the invention is to provide a device and a method for exposing photosensitive plates for printing presses, whereby the above mentioned disadvantage is remedied.
  • a device for exposing photosensitive plates for printing presses comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates, whereby the controlled laser exposure apparatus comprises means for measuring and compensating variances in the laser beam orientation.
  • this purpose is achieved by a method for exposing photosensitive plates for printing presses, whereby the photosensitive plates are exposed by means of a controlled laser beam, whereby the variances in the laser beam orientation are measured and compensated.
  • the controlled laser exposure apparatus comprises a software control .
  • the variances in the laser beam orientation are measured and compensated by means of software .
  • This problem is solved by providing a device for exposing photosensitive plates for printing presses whereby the exposure apparatus comprises at least two laser sources synchronised with each other.
  • This device can also be implemented without means for measuring and compensating variances in the laser beam orientation.
  • each laser beam is controlled by means of a polygon and the software controlled exposure apparatus is provided with a software controlled measuring and calibration system for measuring the variances of each laser beam that arise through the wobble faults in the polygon, with at least a multi-quadrant photocell that is placed at an angle in relation to each laser beam, folding mirrors with which each laser beam can be directed towards the photocell quadrants, and provisions for measuring differences between the laser beam positions on each of the photocell quadrants.
  • the laser beams are controlled by means of a polygon and the software controlled exposure apparatus is provided with a software controlled measuring and synchronisation system for synchronising the various laser beams with each other, with at least a multi-quadrant photocell that is placed at an angle in relation to the laser beams, - folding mirrors with which the laser beams can be directed towards the photocell quadrants, provisions for measuring differences between the laser beam positions on each of the photocell quadrants.
  • one or more of the aforementioned folding mirrors comprise piezoelectric mirrors that can be directed to another angle by the software control .
  • the multi-quadrant photocell is a two-quadrant photocell.
  • the two- quadrant photocell is disposed at an angle between 3.5° and 10.75° in relation to the laser beams, preferably at an angle of approximately 7.125°.
  • the conveyor system for moving forward the photosensitive plates comprises a movable supporting system for the photosensitive plates during the exposure thereof, a loading and unloading system that are provided in order to convey and to handle the photosensitive plates flat.
  • the device comprises a removal system for conveying the exposed photosensitive plates to a developing apparatus, which removal system is part of the movable supporting system for the photosensitive plates during the exposure thereof .
  • the loading system is preferably provided in order to take the photosensitive plates out of light- and air-tight cassettes .
  • the movable supporting system for the photosensitive plates during the exposure thereof comprises a flat exposure table.
  • the conveyor system is provided in order in each case to be able to load, expose and unload at least two photosensitive plates simultaneously.
  • the simultaneous loading, exposing and unloading of two photosensitive plates has the advantage that the loading and unloading time can be very short, namely reducible to 6 seconds .
  • the loading system comprises a software controlled stepping motor that effects an up and down loading movement via a reduction gear driven link system (spindle system) and vacuum cups.
  • a stepping motor has the advantage that this blocks when a plate crash occurs during loading. It is moreover possible to separate the photosensitive plates from each other slowly and in a software controlled manner.
  • the loading system is moreover preferably provided with plate height detectors and vacuum detectors .
  • vacuum cups are adjustably provided on a profile structure.
  • the attachment of the vacuum cups on a profile structure has the advantage that they can easily be adjusted in relation to the plate format used.
  • the exposure table is moved forwards by means of a linear motor.
  • a linear motor is that a "banding-free exposure" on the plate is achieved.
  • the movement of the exposure table is preferably synchronised to the laser sources synchronised to each other.
  • the device comprises a loading magazine for light- and air-tight cassettes
  • the loading magazine or the loading system comprises a toothed wheel drive that can work together with a toothed rack provided on the light- and air-tight cassettes in order to feed the cassettes into the loading system while the cover of the cassettes remains behind in a loading magazine of the device.
  • the invention further relates to a housing for a device such as described above, whereby the housing is implemented as a light- and air-tight cassette.
  • the advantage of such a housing is that the machine need no longer be disposed in a dark room in order to be able to load the photosensitive plates into the machine.
  • the machine can be disposed in a normal working environment, the cassettes can be loaded into the machine and unloaded in normal artificial or daylight conditions and the cassettes can be kept in stock in normal conditions without danger of being exposed through exposure to whatever light source.
  • the photosensitive plates therefore remain at all times light- and air-tight during the handling and during the conveyance and can be loaded into the machine without adjustments of whatever nature.
  • the housing is preferably such that the bottom plate of the cassette is provided with adjustable positioning pegs.
  • the cassette is provided with a light- and air-tight cover that slides open.
  • the cover that can slide open is provided in order to be capable of being slid open via a linear movement in a loading magazine or loading system of a device for exposing photosensitive plates .
  • the cassette is provided with a toothed rack that can work together with a toothed wheel of a loading magazine or loading system of a device for exposing photosensitive plates.
  • This housing can also be provided with other devices for exposing photosensitive plates for printing presses than the device according to this invention.
  • the above mentioned method according to the invention is preferably such that in each case two or more photosensitive plates are exposed by means of at least two laser beams synchronised with each other.
  • the wobble faults are calibrated through a polygon by the software controlled measurement and correction of the variances of the laser beam or laser beams .
  • the synchronisation of the various laser beams is calibrated by the software controlled measurement and correction of the faults that occur in axis direction of the laser beams.
  • the method is preferably so implemented that a multi-quadrant photocell is placed at an angle in relation to the laser beams, the laser beams are directed towards the photocell quadrants by means of folding mirrors, - the differences between the laser beam positions on each of the photocell quadrants are measured, and by means of an algorithm, the direction of the software controlled piezoelectric mirror (s) is corrected until the beams predominantly fall in the middle of the photocells.
  • the photosensitive plates are preferably conveyed and handled flat .
  • the photosensitive plates are preferably picked up from a supply stack by means of a software controlled stepping motor.
  • the method is preferably such that it comprises the following steps: the downward movement of the plate loader until the height detectors detect the photosensitive plates; the picking-up of the photosensitive plates by the loader,- - the separation of the photosensitive plates from the stacks by the slow upward movement of the loader for a short time; the fast upward displacement of the photosensitive plates by the loader; the moving of the exposure table below the loader and the lowering and positioning of the photosensitive plates on to the aforementioned exposure table; the moving of the exposure table below the exposure apparatus and the exposure of the photosensitive plates in a movement synchronised with the laser beams; the further displacement of the exposure table below a plate unloader; - the picking-up of the photosensitive plates by the unloader; the return movement of the exposure table to its starting position; the lowering of the photosensitive plates on to a removal device towards a development device.
  • the picking-up of unexposed photosensitive plates by the loader and the picking-up of exposed photosensitive plates by the unloader preferably occurs simultaneously.
  • the lowering of exposed photosensitive plates on to the removal device and the lowering of unexposed photosensitive plates on to the exposure table preferably occurs simultaneously.
  • Use is preferably made of photosensitive plates that are provided in light- and air-tight cassettes.
  • figure 1 represents a view from above of the optical system
  • figure 2 is a schematic representation of the software controlled automatic laser measuring, calibration and synchronisation system
  • figure 3 is a detailed representation of a two- quadrant photocell
  • figure 4 is a representation of a photocell that is attached to a rail and is driven by a stepping motor
  • figure 5 is a schematic representation of the conveyor system
  • figure 6 up to and including 13 represent the various steps that the conveyor system performs during the loading, exposure, unloading and removal of photosensitive plates.
  • the Polaris/Platesetter D is a flatbed plate exposer that has the purpose of exposing one or several photosensitive plates over the entire width by means of lasers.
  • two photosensitive aluminium plates are exposed by means of two lasers .
  • the data to be exposed can be both text, composed of alphabetical script and of kanji characters, photographs and drawings.
  • This exposure occurs by means of 2 parallel placed laser engines, of which the writing beam of one lies in the extension of the second.
  • the exposure occurs with a speed of 800 scans per second in combination with an accuracy of 5 ⁇ m.
  • the exposure apparatus or the optical system (1) for exposing photosensitive plates by laser beam consists of a laser source (2) , with a power of 100 - 200 M atts, which produces a laser beam (100) with a wavelength of 532 nm and a diameter of approximately 1 mm.
  • the laser beam (100) passes through a band width lens (3) , after which the laser beam (100) still has a diameter of approximately 70 ⁇ m.
  • the laser beam (100) thereafter passes through a modulator
  • the modulator (4) which will ensure whether or not the laser beam (100) passes through a hole (5) .
  • the principle of the modulator works as follows: the data to be exposed are converted via a RIP process (Raster Image Processing) into a raster of points of light. If a point has to be placed on the photosensitive plate (200) (see figure 5) that is on the exposure table (56) , the modulator (4) will ensure that the laser beam (110) is bent so that the beam can pass through the hole (5) ; if no point has to be placed on this photosensitive plate (200) , the modulator (4) does not bend the laser beam (100) and the laser beam (100) cannot pass through the hole. What is brought on to the photosensitive plate (200) is a positive image of what has to be printed.
  • the laser beam (100) thereafter passes via a reversing mirror (6) to a piezoelectric mirror (7) .
  • the laser beam (100) now has a diameter of approximately 5 mm.
  • the laser beam (100) passes through a beam expander (8) , through which the laser beam (100) acquires a diameter of approximately 22 mm.
  • the laser beam (100) passes via a rotating polygon (9) to an F-data lens (10) , which has a threefold task: on the one hand this F-data lens (10) ensures that the focal length is evenly maintained, on the other hand this focuses the laser beam (100) on the photosensitive plate (200) and finally the polygon angular deflection is linearised to a constant scanning speed.
  • the laser beam (100) describes a circle (360°) , whereby the laser beam (100) in the course of a part of this circular movement falls on a folding mirror (11) .
  • the folding mirror (11) ensures that the laser beam (100) is deflected to the exposure table (56) lying below (see figure 5) .
  • the laser beam (100) that falls on the exposure table (56) finally has a power of approximately 52 MWatts, a diameter of approximately 20 ⁇ m and can scan a width of approximately 61 cm.
  • a software controlled automatic laser calibration and synchronisation system (20) is provided, as represented in figure 2 .
  • this system (20) the variances in the laser beam (100) that arise through the wobble faults in the polygon (9) can be measured and adjusted and the two laser beams (100) can be synchronised. These measurements are converted by means of software (11) into a compensation curve (12) in order to neutralise these variances.
  • the synchronisation of the axes of the two beams occurs with an accuracy of 5 ⁇ m.
  • the principle of the automatic calibration and synchronisation system (20) is based on a multi-quadrant photocell, more specifically a two-quadrant photocell (30), as represented in more detail in figure 3 , which is placed at a slight angle in relation to the laser beam (100) .
  • the laser beam (100) is aligned precisely in the middle of the two quadrants (31, 32) by means of the folding mirror (11) . Because of this the scan first falls on facet A (33) for the time t ⁇ (t x (A), t (B) ) and thereafter on facet B (34) for the time t 2 (t 2 (A), t 2 (B)).
  • the various scans will fall higher or lower in comparison with the middle of the photocell, with the result that the times t and t 2 are a measure for the position of each scan. These times are measured via amplifiers (23, 24) by means of 8-bit counters (25, 26) and fed into the software (21) .
  • the software (21) converts these times with an algorithm (27) and subsequently via an amplifier (28) directs the piezoelectric mirror (7) to another angle (29) for each scan. This is repeated until all scans fall precisely through the middle of the photocell (30) in order to effect the synchronisation in this manner.
  • the photocell (30) is optimally placed at an angle of 7.125°.
  • the position measurement accuracy of the scans is 0.005 mm.
  • the photocell (30) is attached to a rail (41) that is driven by a stepping motor (42) , as represented in figure 4 .
  • the latter is also driven by the software (21) .
  • a transparent conveyor system (50) has been developed, as is represented in figure 5.
  • the conveyor system (50) principally consists of four parts :
  • a loading system (51) consisting of a loader (52) , which is provided with
  • an unloading system consisting of an unloader (59) , which is provided with vacuum cups (53) , mounted in the same manner and with the same function as with the loading system (51) ;
  • a removal system (60) for the exposed photosensitive plates 200 consisting of a conveyor (61) , constructed out of • a number of belts or cords (62) ,
  • the conveyor system (50) operates, as represented in figure 6 up to and including 13 , in the following steps : - step 1 (see figure 6) : the loader (52) moves downwards until the height detectors detect the photosensitive plates (200) . The first two unexposed photosensitive plates (201) are sucked fast with vacuum to the vacuum cups (53) . - step 2 (see figure 7) : the loader (52) moves slowly upwards for a short time in order to separate well the first two unexposed photosensitive plates (201) . Thereafter the loader (52) moves upwards at full speed. - step 3 (see figure 8) : the exposure table (56) moves to the right to below the loader (52) .
  • the first two unexposed photosensitive plates (201) are blown from the vacuum cups (53) with compressed air and fall on to the exposure table (56) .
  • step 4 (see figure 9) : the exposure table (56) moves quickly to below the software controlled exposure apparatus (63) , consisting of 2 optical systems (1) and a software measuring, calibration and synchronisation system (20) , and thereafter slowly farther to the left.
  • the laser beam (100) is modulated by the modulator (4) (see figure 1) . Because of this the laser beam (100) reaches the first two unexposed photosensitive plates (201) and the image is formed.
  • step 5 the exposure table (56) moves quickly to the extreme left.
  • the unloader (59) goes down and sucks fast the first two exposed photosensitive plates (202) with vacuum.
  • step 6 (see figure 11) : the exposure table (56) moves back towards the right.
  • step 7 (see figure 12) : the unloader (59) moves downwards and blows the first two exposed photosensitive plates (202) off on to the conveyor belts (62) .
  • step 8 (see figure 13 ) •. the conveyor (61) conveys the first two exposed photosensitive plates (202) to the developing machine (not represented in the figure) .
  • the photosensitive plates (200) are delivered from the plate supplier, according to the desired format, stacked without separation paper between each plate in a housing or a cassette that is light- and air-tight.
  • the cassette is constructed out of metals and aluminium parts that are mechanically connected to each other.
  • the bottom plate of the cassette is provided with positioning pegs that are adjustable.
  • the cassette is light- and air-tight by means of a cover.
  • the conveyance of the cassette into the machine occurs by means of a toothed rack attached to the cassette that is driven by a toothed wheel in the machine .
  • a toothed rack attached to the cassette that is driven by a toothed wheel in the machine .
  • this is positioned below the loader by means of the toothed wheel/toothed rack drive. This linear movement is such that the cover remains behind in the magazine and that the photosensitive plates stored in the cassette are available for the loader. As soon as the cassette slides backwards again into the magazine, this is coupled with "the automatic replacement of the cover.
  • the cover automatically remains on the cassette, in order to guarantee the light- and air-tightness during the handling and/or conveyance.

Abstract

The invention relates to a device and a method for exposing photosensitive plates (33) for printing presses, comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates. The problem with the plate exposers at present is that they are not sufficiently accurate. A device is therefore provided whereby the controlled laser exposure apparatus (63) comprises means (1, 20) for measuring and compensating the variances in the laser beam orientation. The controlled laser exposure apparatus (63) comprises a software control (21). Another problem is that one laser source cannot bridge the scanning of photosensitive plates (200) with great width. Two laser sources (2) synchronised with each other are therefore provided. The invention further relates to a housing for a device such as specified above.

Description

DEVICE AMD METHOD FOR EXPOSING PHOTOSENSITIVE PLATES FOR PRINTING PRESSES
The invention relates to a device for exposing photosensitive plates for printing presses, comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates.
A problem is that the known plate exposers do not operate sufficiently accurately.
A system that is already known for solving this problem consists of a drum (= cylinder in which there is a plate) , which rotates round a laser. A disadvantage of this system is that it does not operate sufficiently fast.
The purpose of the invention is to provide a device and a method for exposing photosensitive plates for printing presses, whereby the above mentioned disadvantage is remedied.
This purpose is on the one hand achieved by a device for exposing photosensitive plates for printing presses, comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates, whereby the controlled laser exposure apparatus comprises means for measuring and compensating variances in the laser beam orientation.
On the other hand this purpose is achieved by a method for exposing photosensitive plates for printing presses, whereby the photosensitive plates are exposed by means of a controlled laser beam, whereby the variances in the laser beam orientation are measured and compensated. In a preferred embodiment the controlled laser exposure apparatus comprises a software control .
In a preferred method the variances in the laser beam orientation are measured and compensated by means of software .
Another problem with the plate exposers known up until now, operating with the above mentioned principle, is that the exposure of photosensitive plates of great width, which for example at present is current with the newspaper formats on the Japanese and Asian market, gives problems via the laser, because of the fact that one laser cannot bridge the scanning of these great widths.
This problem is solved by providing a device for exposing photosensitive plates for printing presses whereby the exposure apparatus comprises at least two laser sources synchronised with each other.
This device can also be implemented without means for measuring and compensating variances in the laser beam orientation.
In a specific embodiment each laser beam is controlled by means of a polygon and the software controlled exposure apparatus is provided with a software controlled measuring and calibration system for measuring the variances of each laser beam that arise through the wobble faults in the polygon, with at least a multi-quadrant photocell that is placed at an angle in relation to each laser beam, folding mirrors with which each laser beam can be directed towards the photocell quadrants, and provisions for measuring differences between the laser beam positions on each of the photocell quadrants.
The introduction of a software controlled automatic laser measuring and calibration system has the advantage that the time-consuming work by a specialised service engineer for the manual measurement and compensation of the wobble faults is not necessary. Because of this a much greater accuracy can be achieved, through which a "banding-free" image comes on the plate.
In another specific embodiment the laser beams are controlled by means of a polygon and the software controlled exposure apparatus is provided with a software controlled measuring and synchronisation system for synchronising the various laser beams with each other, with at least a multi-quadrant photocell that is placed at an angle in relation to the laser beams, - folding mirrors with which the laser beams can be directed towards the photocell quadrants, provisions for measuring differences between the laser beam positions on each of the photocell quadrants.
In a preferred embodiment one or more of the aforementioned folding mirrors comprise piezoelectric mirrors that can be directed to another angle by the software control .
In a more specific preferred embodiment the multi-quadrant photocell is a two-quadrant photocell.
In a still more specific preferred embodiment the two- quadrant photocell is disposed at an angle between 3.5° and 10.75° in relation to the laser beams, preferably at an angle of approximately 7.125°.
In a preferred embodiment the conveyor system for moving forward the photosensitive plates comprises a movable supporting system for the photosensitive plates during the exposure thereof, a loading and unloading system that are provided in order to convey and to handle the photosensitive plates flat.
This has the advantage that the conveyor system is easy to understand, through which the user can maintain and repair the system themselves .
In another preferred embodiment the device comprises a removal system for conveying the exposed photosensitive plates to a developing apparatus, which removal system is part of the movable supporting system for the photosensitive plates during the exposure thereof .
This has the advantage that the total footprint of the exposer and the developing machine together are shortened by approximately one metre .
The loading system is preferably provided in order to take the photosensitive plates out of light- and air-tight cassettes .
In a preferred embodiment the movable supporting system for the photosensitive plates during the exposure thereof comprises a flat exposure table.
The use of a flat exposure table has the advantage that either "custom designed" register pins or a "custom designed" three-point locating system can be built in. This has the function of perfectly positioning the plate on the exposure table.
In a specific embodiment the conveyor system is provided in order in each case to be able to load, expose and unload at least two photosensitive plates simultaneously.
The simultaneous loading, exposing and unloading of two photosensitive plates has the advantage that the loading and unloading time can be very short, namely reducible to 6 seconds .
In a preferred embodiment the loading system comprises a software controlled stepping motor that effects an up and down loading movement via a reduction gear driven link system (spindle system) and vacuum cups.
The use of a stepping motor has the advantage that this blocks when a plate crash occurs during loading. It is moreover possible to separate the photosensitive plates from each other slowly and in a software controlled manner.
The loading system is moreover preferably provided with plate height detectors and vacuum detectors .
In a specific embodiment the vacuum cups are adjustably provided on a profile structure.
The attachment of the vacuum cups on a profile structure has the advantage that they can easily be adjusted in relation to the plate format used.
In a preferred embodiment the exposure table is moved forwards by means of a linear motor. The advantage of the use of a linear motor is that a "banding-free exposure" on the plate is achieved.
The movement of the exposure table is preferably synchronised to the laser sources synchronised to each other.
In a preferred embodiment the device comprises a loading magazine for light- and air-tight cassettes, and the loading magazine or the loading system comprises a toothed wheel drive that can work together with a toothed rack provided on the light- and air-tight cassettes in order to feed the cassettes into the loading system while the cover of the cassettes remains behind in a loading magazine of the device.
The invention further relates to a housing for a device such as described above, whereby the housing is implemented as a light- and air-tight cassette.
The advantage of such a housing is that the machine need no longer be disposed in a dark room in order to be able to load the photosensitive plates into the machine. By means of this cassette system the machine can be disposed in a normal working environment, the cassettes can be loaded into the machine and unloaded in normal artificial or daylight conditions and the cassettes can be kept in stock in normal conditions without danger of being exposed through exposure to whatever light source. There is no longer any danger of the photosensitive plates stacked up in the cassette sticking to each other through the humidity present in the air. The photosensitive plates therefore remain at all times light- and air-tight during the handling and during the conveyance and can be loaded into the machine without adjustments of whatever nature.
The housing is preferably such that the bottom plate of the cassette is provided with adjustable positioning pegs.
In a preferred embodiment of the housing the cassette is provided with a light- and air-tight cover that slides open.
In a preferred housing the cover that can slide open is provided in order to be capable of being slid open via a linear movement in a loading magazine or loading system of a device for exposing photosensitive plates .
In a specific embodiment of the housing the cassette is provided with a toothed rack that can work together with a toothed wheel of a loading magazine or loading system of a device for exposing photosensitive plates.
This housing can also be provided with other devices for exposing photosensitive plates for printing presses than the device according to this invention.
The above mentioned method according to the invention is preferably such that in each case two or more photosensitive plates are exposed by means of at least two laser beams synchronised with each other.
In a specific method the wobble faults are calibrated through a polygon by the software controlled measurement and correction of the variances of the laser beam or laser beams .
In another specific method the synchronisation of the various laser beams is calibrated by the software controlled measurement and correction of the faults that occur in axis direction of the laser beams.
The method is preferably so implemented that a multi-quadrant photocell is placed at an angle in relation to the laser beams, the laser beams are directed towards the photocell quadrants by means of folding mirrors, - the differences between the laser beam positions on each of the photocell quadrants are measured, and by means of an algorithm, the direction of the software controlled piezoelectric mirror (s) is corrected until the beams predominantly fall in the middle of the photocells.
In the method the photosensitive plates are preferably conveyed and handled flat .
The photosensitive plates are preferably picked up from a supply stack by means of a software controlled stepping motor.
The method is preferably such that it comprises the following steps: the downward movement of the plate loader until the height detectors detect the photosensitive plates; the picking-up of the photosensitive plates by the loader,- - the separation of the photosensitive plates from the stacks by the slow upward movement of the loader for a short time; the fast upward displacement of the photosensitive plates by the loader; the moving of the exposure table below the loader and the lowering and positioning of the photosensitive plates on to the aforementioned exposure table; the moving of the exposure table below the exposure apparatus and the exposure of the photosensitive plates in a movement synchronised with the laser beams; the further displacement of the exposure table below a plate unloader; - the picking-up of the photosensitive plates by the unloader; the return movement of the exposure table to its starting position; the lowering of the photosensitive plates on to a removal device towards a development device.
The picking-up of unexposed photosensitive plates by the loader and the picking-up of exposed photosensitive plates by the unloader preferably occurs simultaneously.
The lowering of exposed photosensitive plates on to the removal device and the lowering of unexposed photosensitive plates on to the exposure table preferably occurs simultaneously.
Use is preferably made of photosensitive plates that are provided in light- and air-tight cassettes.
In a specific method in each case two photosensitive plates lying in each other's extension are exposed by means of two laser beams synchronised with each other, for the simultaneous exposure of two photosensitive plates.
In order to explain the properties of this invention further and in order to specify additional advantages and distinctive features thereof, there now follows a more detailed specification of a laser exposer for printing machines implemented according to this invention. It is clear that nothing in the following specification may be interpreted as a restriction on the protection claimed for this invention in the claims.
This invention will be explained on the basis of figures, whereby: figure 1 represents a view from above of the optical system; figure 2 is a schematic representation of the software controlled automatic laser measuring, calibration and synchronisation system; figure 3 is a detailed representation of a two- quadrant photocell; figure 4 is a representation of a photocell that is attached to a rail and is driven by a stepping motor; figure 5 is a schematic representation of the conveyor system; figure 6 up to and including 13 represent the various steps that the conveyor system performs during the loading, exposure, unloading and removal of photosensitive plates.
The Polaris/Platesetter D is a flatbed plate exposer that has the purpose of exposing one or several photosensitive plates over the entire width by means of lasers. In the example embodiment two photosensitive aluminium plates are exposed by means of two lasers . The data to be exposed can be both text, composed of alphabetical script and of kanji characters, photographs and drawings. This exposure occurs by means of 2 parallel placed laser engines, of which the writing beam of one lies in the extension of the second. The exposure occurs with a speed of 800 scans per second in combination with an accuracy of 5 μm.
As represented in figure 1 , the exposure apparatus or the optical system (1) for exposing photosensitive plates by laser beam consists of a laser source (2) , with a power of 100 - 200 M atts, which produces a laser beam (100) with a wavelength of 532 nm and a diameter of approximately 1 mm.
The laser beam (100) passes through a band width lens (3) , after which the laser beam (100) still has a diameter of approximately 70 μm.
The laser beam (100) thereafter passes through a modulator
(4) , which will ensure whether or not the laser beam (100) passes through a hole (5) . The principle of the modulator works as follows: the data to be exposed are converted via a RIP process (Raster Image Processing) into a raster of points of light. If a point has to be placed on the photosensitive plate (200) (see figure 5) that is on the exposure table (56) , the modulator (4) will ensure that the laser beam (110) is bent so that the beam can pass through the hole (5) ; if no point has to be placed on this photosensitive plate (200) , the modulator (4) does not bend the laser beam (100) and the laser beam (100) cannot pass through the hole. What is brought on to the photosensitive plate (200) is a positive image of what has to be printed.
The laser beam (100) thereafter passes via a reversing mirror (6) to a piezoelectric mirror (7) . The laser beam (100) now has a diameter of approximately 5 mm. Now the laser beam (100) passes through a beam expander (8) , through which the laser beam (100) acquires a diameter of approximately 22 mm.
Thereafter the laser beam (100) passes via a rotating polygon (9) to an F-data lens (10) , which has a threefold task: on the one hand this F-data lens (10) ensures that the focal length is evenly maintained, on the other hand this focuses the laser beam (100) on the photosensitive plate (200) and finally the polygon angular deflection is linearised to a constant scanning speed. Through the rotating polygon (9) the laser beam (100) describes a circle (360°) , whereby the laser beam (100) in the course of a part of this circular movement falls on a folding mirror (11) . The folding mirror (11) ensures that the laser beam (100) is deflected to the exposure table (56) lying below (see figure 5) . The laser beam (100) that falls on the exposure table (56) finally has a power of approximately 52 MWatts, a diameter of approximately 20 μm and can scan a width of approximately 61 cm.
Since variances occur through sending the laser beam (100) on to the polygon (9) , also called the wobble fault, and the 2 laser beams (100) , each coming from an optical system (1) as shown in figure 1, have to be synchronised with each other on the exposure table (56) (see figure 5) , a software controlled automatic laser calibration and synchronisation system (20) is provided, as represented in figure 2 . With this system (20) the variances in the laser beam (100) that arise through the wobble faults in the polygon (9) can be measured and adjusted and the two laser beams (100) can be synchronised. These measurements are converted by means of software (11) into a compensation curve (12) in order to neutralise these variances. The synchronisation of the axes of the two beams occurs with an accuracy of 5 μm.
The principle of the automatic calibration and synchronisation system (20) is based on a multi-quadrant photocell, more specifically a two-quadrant photocell (30), as represented in more detail in figure 3 , which is placed at a slight angle in relation to the laser beam (100) . The laser beam (100) is aligned precisely in the middle of the two quadrants (31, 32) by means of the folding mirror (11) . Because of this the scan first falls on facet A (33) for the time tλ (tx(A), t (B) ) and thereafter on facet B (34) for the time t2 (t2(A), t2(B)). Because of the wobble faults in the polygon (9) the various scans will fall higher or lower in comparison with the middle of the photocell, with the result that the times t and t2 are a measure for the position of each scan. These times are measured via amplifiers (23, 24) by means of 8-bit counters (25, 26) and fed into the software (21) . The software (21) converts these times with an algorithm (27) and subsequently via an amplifier (28) directs the piezoelectric mirror (7) to another angle (29) for each scan. This is repeated until all scans fall precisely through the middle of the photocell (30) in order to effect the synchronisation in this manner.
After calculation it is determined that the photocell (30) is optimally placed at an angle of 7.125°. By making use of the aforementioned 8-bit counters (26, 27) the position measurement accuracy of the scans is 0.005 mm. In order to compensate the wobble over the whole scan of approximately 122 cm, the photocell (30) is attached to a rail (41) that is driven by a stepping motor (42) , as represented in figure 4 . The latter is also driven by the software (21) . In order to load, expose and unload the photosensitive plates (200) a transparent conveyor system (50) has been developed, as is represented in figure 5.
The conveyor system (50) principally consists of four parts :
1) a loading system (51) consisting of a loader (52) , which is provided with
• plate height detectors and vacuum detectors (neither represented in the figure) , • vacuum cups (53) that are attached to the loader
(52) via aluminium sectional tubes and can be adjusted in relation to the plate format used, a stepping motor (54) with reduction gear driven link system that moves the loader (52) up and down with a positioning accuracy of 0.02 mm;
2) a movable supporting system (55) for the photosensitive plates (200) during the exposure thereof consisting of an exposure table (56) that can move back and forth, which for the perfect positioning of the photosensitive plates (200) can be provided with register pins if prepunched photosensitive plates are used; if unpunched photosensitive plates are used, the exposure table can be provided with detection pins with three-stop fingers (= three-point registration system) , a linear motor (57) , which moves the exposure table (56) 1015 mm in 2 seconds;
3) an unloading system (58) , consisting of an unloader (59) , which is provided with vacuum cups (53) , mounted in the same manner and with the same function as with the loading system (51) ;
4) a removal system (60) for the exposed photosensitive plates 200, consisting of a conveyor (61) , constructed out of • a number of belts or cords (62) ,
• a small stepping motor for driving the belts and of which the speed is adjustable, in order in so doing to enable the photosensitive plates (200) to come out of the exposer with the speed of the developing machine .
The conveyor system (50) operates, as represented in figure 6 up to and including 13 , in the following steps : - step 1 (see figure 6) : the loader (52) moves downwards until the height detectors detect the photosensitive plates (200) . The first two unexposed photosensitive plates (201) are sucked fast with vacuum to the vacuum cups (53) . - step 2 (see figure 7) : the loader (52) moves slowly upwards for a short time in order to separate well the first two unexposed photosensitive plates (201) . Thereafter the loader (52) moves upwards at full speed. - step 3 (see figure 8) : the exposure table (56) moves to the right to below the loader (52) . The first two unexposed photosensitive plates (201) are blown from the vacuum cups (53) with compressed air and fall on to the exposure table (56) . - step 4 (see figure 9) : the exposure table (56) moves quickly to below the software controlled exposure apparatus (63) , consisting of 2 optical systems (1) and a software measuring, calibration and synchronisation system (20) , and thereafter slowly farther to the left. At the same moment the laser beam (100) is modulated by the modulator (4) (see figure 1) . Because of this the laser beam (100) reaches the first two unexposed photosensitive plates (201) and the image is formed. Because of the fact that due to the rotating polygon (9) (see figure 1) the laser beam (100) describes a circular movement in the vertical plane of the folding mirror (11) , which turns the laser beam (100) per optical system towards the exposure table (56) , and therefore only falls on the aforementioned folding mirror (11) for a specific period, there is a space present between each scanned-in line, which is dependent on the scanning speed and the speed with which the exposure table (56) shifts. Both first unexposed photosensitive plates (201) are exposed in this manner. step 5 (see figure 10) : the exposure table (56) moves quickly to the extreme left. The unloader (59) goes down and sucks fast the first two exposed photosensitive plates (202) with vacuum. Simultaneously two new photosensitive plates (203) are loaded with the loader (52) . step 6 (see figure 11) : the exposure table (56) moves back towards the right. step 7 (see figure 12) : the unloader (59) moves downwards and blows the first two exposed photosensitive plates (202) off on to the conveyor belts (62) . Simultaneously the two new photosensitive plates (203) are loaded on to the exposure table (56) . step 8 (see figure 13 ) •. the conveyor (61) conveys the first two exposed photosensitive plates (202) to the developing machine (not represented in the figure) .
The photosensitive plates (200) are delivered from the plate supplier, according to the desired format, stacked without separation paper between each plate in a housing or a cassette that is light- and air-tight. The cassette is constructed out of metals and aluminium parts that are mechanically connected to each other. The bottom plate of the cassette is provided with positioning pegs that are adjustable. The cassette is light- and air-tight by means of a cover.
The conveyance of the cassette into the machine occurs by means of a toothed rack attached to the cassette that is driven by a toothed wheel in the machine . In the case a cassette that is in the magazine of the machine is selected, this is positioned below the loader by means of the toothed wheel/toothed rack drive. This linear movement is such that the cover remains behind in the magazine and that the photosensitive plates stored in the cassette are available for the loader. As soon as the cassette slides backwards again into the magazine, this is coupled with "the automatic replacement of the cover. With the selection of a cassette from the magazine in order to be removed out of the machine because of the fact that this cassette is empty or because of the fact that an additional format has to be loaded, the cover automatically remains on the cassette, in order to guarantee the light- and air-tightness during the handling and/or conveyance.

Claims

C L A I S
1. Device for exposing photosensitive plates for printing presses, comprising controlled laser exposure apparatus and a conveyor system for moving forward the photosensitive plates, characterised in that the controlled laser exposure apparatus (63) comprises means
(1, 20) for measuring and compensating variances in the laser beam orientation.
2. Device according to claim 1, characterised in that the controlled laser exposure apparatus (63) comprises a software control (21) .
Device according to one of the claims 1 and 2, characterised in that the software controlled laser exposure apparatus (63) comprises at least two laser sources (2) synchronised with each other.
4. Device according to one of the claims 1 up to and including 3, characterised in that each laser beam (100) is controlled by means of a polygon (9) and that the software controlled exposure apparatus (63) is provided with a software controlled measuring and calibration system (20) for measuring the variances of each laser beam (100) that arise through wobble faults in the polygon (9) , with at least a multi-quadrant photocell (30) that is placed at an angle in relation to each laser beam (100) , folding mirrors (6, 7, 11) with which each laser beam (100) can be directed towards the photocell quadrants (31, 32) , and provisions for measuring differences between the laser beam positions on each of the photocell quadrants (31, 32) .
5. Device according to claim 3, characterised in that the laser beams (100) are controlled by means of a polygon
(9) and the software controlled exposure apparatus (63) is provided with a software controlled measuring and synchronisation system (20) for synchronising the various laser beams (100) with each other, with at least a multi-quadrant photocell (30) that is placed at an angle in relation to the laser beams (100) , folding mirrors (6, 7, 11) with which the laser beams (100) can be directed towards the photocell quadrants (31, 32) , and provisions for measuring differences between the laser beam positions on each of the photocell quadrants (31, 32) .
6. Device according to one of the claims 4 and 5, characterised in that one or more of the aforementioned folding mirrors (6, 7, 11) comprise piezoelectric mirrors (7) that can be directed to another angle (29) by the software control (21) .
7. Device according to one of the claims 4 up to and including 6, characterised in that the multi-quadrant photocell is a two-quadrant photocell (30) .
8. Device according to claim 7, characterised in that the two-quadrant photocell (30) is disposed at an angle between 3.5° and 10.75° in relation to the laser beams (100), preferably at an angle of approximately 7.125°.
9. Device according to one of the claims 1 up to and including 8, characterised in that the conveyor system (50) for moving forward the photosensitive plates (200) comprises a movable supporting system (55) for the photosensitive plates (200) during the exposure thereof and a loading (51) and unloading system (58) that are provided in order to convey and to handle the photosensitive plates (200) flat.
10. Device according to one of the claims 1 up to and including 9, characterised in that the a removal system (60) for conveying the exposed photosensitive plates (202) to a developing apparatus, which removal system (60) is part of the movable supporting system (55) for the photosensitive plates during the exposure thereof.
11. Device according to one of the claims 1 up to and including 10, characterised in that the loading system (51) is provided in order to take the photosensitive plates (200) out of light- and air-tight cassettes.
12. Device according to one of the claims 1 up to and including 11, characterised in that the movable supporting system (55) for the photosensitive plates during the exposure thereof comprises a flat exposure table (56)
13. Device according to one of the claims 1 up to and including 12, characterised in that the conveyor system (50) is provided in order in each case to be able to load, expose and unload at least two photosensitive plates (201, 203) simultaneously.
14. Device according to one of the claims 1 up to and including 13 , characterised in that the loading system (51) comprises a software controlled stepping motor (54) that effects an up and down loading movement via a reduction gear driven link system (spindle system) and vacuum cups (53) .
15. Device according to claim 14, characterised in that the loading system (51) is provided with plate height detectors and vacuum detectors .
16. Device according to one of the claims 14 and 15, characterised in that the vacuum cups (53) are adjustably provided on a profile structure.
17. Device according to claim 16, characterised in that the exposure table (56) is moved forwards by means of a linear motor (57) .
18. Device according to claim 17, characterised in that the movement of the exposure table (56) is synchronised to the laser sources synchronised to each other.
19. Device according to one of the claims 1 up to and including 18, characterised in that the device comprises a loading magazine for light- and air-tight cassettes, and the loading magazine or the loading system comprises a toothed wheel drive that can work together with a toothed rack provided on the light- and air-tight cassettes in order to feed the cassettes into the loading system while the cover of the cassettes remains behind in a loading magazine of the device.
20. Housing for a device according to one of the claims 1 up to and including 19, characterised in that the housing is implemented as a light- and air-tight cassette.
21. Housing according to claim 20, characterised in that the bottom plate of said cassette is provided with adjustable positioning pegs.
22. Housing according to one of the claims 20 and 21, characterised in that the cassette is provided with a light- and air-tight cover that slides open.
23. Housing according to claim 22, characterised in that the cover that can slide open is provided in order to be capable of being slid open via a linear movement in a loading magazine or loading system of a device for exposing photosensitive plates.
24. Housing according to one of the claims 1 up to and including 23, characterised in that the cassette is provided with a toothed rack that can work together with a toothed wheel of a loading magazine or loading system of a device for exposing photosensitive plates.
25. Method for exposing photosensitive plates for printing presses, whereby the photosensitive plates are exposed by means of a controlled laser beam, characterised in that the variances in the laser beam orientation are measured and compensated.
26. Method according to claim 25, characterised in that the variances in the laser beam orientation are measured and compensated by means of software (21) .
27. Method according to one of the claims 25 and 26, characterised in that in each case two or more photosensitive plates (201, 203) are exposed by means of at least two laser beams (100) synchronised with each other.
28. Method according to one of the claims 1 up to and including 27, characterised in that wobble faults are calibrated through a polygon (9) by the software controlled measurement and correction of the variances of the laser beam or laser beams (100) .
29. Method according to claim 28, characterised in that the synchronisation of the various laser beams (100) is calibrated by the software controlled measurement and correction of the faults that occur in axis direction of the laser beams (100) .
30. Method according to claim 28 and 29, characterised in that a multi-quadrant photocell (30) is placed at an angle in relation to the laser beams (100) , the laser beams (100) are directed towards the photocell quadrants (31, 32) by means of folding mirrors (6, 7,
11), the differences between the laser beam positions on each of the photocell quadrants (31, 32) are measured, and by means of an algorithm (27) , the direction of the software controlled piezoelectric mirror (s) (7) is corrected until the laser beams predominantly fall in the middle of the photocell (s) (30) .
31. Method according to one of the claims 25 up to and including 30, characterised in that the photosensitive plates (200) are conveyed and handled flat.
32. Method according to one of the claims 25 up to and including 31, characterised in that the photosensitive plates (200) are picked up from a supply stack by means of a software controlled stepping motor (54) .
33. Method according to one of the claims 25 up to and including 32, characterised in that this comprises the following steps: the downward movement of the plate loader (52) until the height detectors detect the photosensitive plates (200) ; the picking-up of the photosensitive plates (201) by the loader (52) ; the separation of the photosensitive plates (201) from the stacks by the slow upward movement of the loader (52) for a short time; the fast upward displacement of the photosensitive plates (201) by the loader (52) ; the moving of the exposure table (56) below the loader (52) and the lowering and positioning of the photosensitive plates (201) on to the aforementioned exposure table (56) ; the moving of the exposure table (56) below the exposure apparatus (63) and the exposure of the photosensitive plates (201) in a movement synchronised with the laser beams (100) ; the further displacement of the exposure table (56) below a plate unloader (59) ; the picking-up of the photosensitive plates (202) by the unloader (59) ; - the return movement of the exposure table (56) to its starting position; the lowering of the photosensitive plates (202) on to a removal device (60) towards a development device.
34. Method according to claim 33, characterised in that the picking-up of unexposed photosensitive plates (201, 203) by the loader (52) and the picking-up of exposed photosensitive plates (202) by the unloader (59) occurs simultaneously.
35. Method according to one of the claims 33 and 34, characterised in that the lowering of exposed photosensitive plates (202) on to the removal device and the lowering of unexposed photosensitive plates (203) on to the exposure table (56) occurs simultaneously.
36. Method according to one of the claims 25 up to and including 35, characterised in that use is made of photosensitive plates (200) that are provided in light- and air-tight cassettes.
37. Method according to one of the claims 25 up to and including 36, characterised in that in each case two photosensitive plates (201, 203) lying in each other's extension are exposed by means of two laser beams (100) synchronised with each other, for the simultaneous exposure of two photosensitive plates (201, 203) .
PCT/EP2001/003806 2000-09-15 2001-04-04 Device and method for exposing photosensitive plates for printing presses WO2002023278A2 (en)

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Title
PATENT ABSTRACTS OF JAPAN vol. 017, no. 416 (P-1584), 3 August 1993 (1993-08-03) & JP 05 080260 A (ASAHI OPTICAL CO LTD), 2 April 1993 (1993-04-02) *

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