IL104172A - System and method for exposing a radiation sensitive medium - Google Patents

Description

SYSTEM AND METHOD FOR EXPOSING A RADIATION SENSITIVE MEDIUM SCITEX CORPORATION LTD.

C:14712 14712il.ame 14.11.93 104172/2 FIELD OF THE INVENTION The present invention relates to step and repeat machines and to imposition machines generally, to digital step and repeat, and imposition machines and to scanning heads appropriate for such machines.

BACKGROUND OF THE INVENTION During the preparation of an offset printing plate of a single color separation, a plurality of films of that color separation are imposed onto the offset plate. Each film typically represents a page of a printed product (brochure, book, magazine, etc) and the order of imposition of the pages is determined by the final printed product and by the folding equipment which will fold the printed paper produced by printing the offset plate.

As is known in the art, step and repeat machines, as well as imposition machines, are utilized to impose the color separation films into their corresponding locations on the offset plate. The Impomaster, manufactured by Misomex AB of Hagerstrom, Sweden, is one such step and repeat machine.

A step and repeat machine is shown schematically in Fig. 1 to which reference is now made. A chase frame 10, shown in a cutout format, picks up at least one of a plurality of color separation films 12 from an "unfinished pile" 13, usually placed in a collection tray (not shown) , and accurately places the selected film or films 12 in a page location 16 on a radiation sensitive medium, such as offset plate 14 of Fig. 1, or a film. The placement is performed via accurate x-y translation apparatus 15.

Although the color separation film 12 typically fills the entire page location 16, an image 20 on the film 12 typically does not fill the entire area of the page location 16. Furthermore, certain areas of the page location 16 are "non-printing" 104172/2 areas (e.g. the margins which have no printing on them) . In order to correctly prepare the page location 16, a mask is typically utilized to blank out the sections which should not be exposed. The mask can be an opaque piece of film placed over the film 12 or, as shown in Fig. 1 and as described in U.S. Patent 4,150,991 to Dillow, it can be a rectangular aperture 22 between four individually translatable plates 24.

If the mask is an opaque film, then the chase frame 10 is operative to pick up a film 12 and a mask film at one time. The combination of film 12 and mask film will be referred to hereinafter as the film-to-be-exposed.

Once the film-to-be-exposed is placed, the step and repeat machine illuminates the page location 16 with a lamp 18, optionally having lenses 19 associated therewith, thereby to expose the section of the offset plate 14 at the page location 16. The lamp 18 and optional lenses 19 are typically mounted within the hood of chase frame 10.

After the film-to-be-exposed has been exposed, the chase frame 10 removes it from the page location 16 and places it in a "finished" pile 25, also placed in a collection tray (not shown) . The chase frame 10 then returns to the unfinished pile 13 and takes the next film-to-be-exposed. Alternatively, if the film-to-be-exposed is to be exposed at a second page location 16, the chase frame 10 moves the film-to-be-exposed to the second page location 16. The plate 14 is exposed and afterward, the film-to-be-exposed is removed to the finished pile 25.

A page 26 to be exposed at the page location 16 typically comprises a number of elements, as shown in Fig. 2 to which reference is now made. The page 26 can comprise a continuous tone image 28 and a linework image 30 produced from a continuous tone separation film 32 and a linework separation film 34.

Very often, page 26 is composed, or "stripped", at the page location 16 by the step and repeat machine. To do this, one of the films 32 or 34 and a corresponding mask film 36 or 38, respectively, are placed in its appropriate portion of location 104172/2 16. The corresponding mask film 36 or 38 is shaped to mask out all but the desired corresponding element 28 or 30. After exposure of the first film, the second film is placed with its mask film and exposed. For the purposes of clarity only, Fig. 2 indicates that the exposure occurs all at once.

Recently, apparatus performing direct digital plate exposure have been developed, such as the Raystar-CTP, commercially available from Scitex Corporation Ltd. of Herzlia, Israel, and Synardica 170, commercially available from Polychrome Corp. of Yonkers, New York, USA. Although attractive since they bypass the film stage, they have found limited use because they assume that the pages are completely digital while, in reality, pages 26 are often formed from a combination of digital data and existing art work, such as separation films.

To overcome these limitations, methods of converting existing art work to a digital form have been developed. However, these methods typically are slow and expensive to operate. 104172/2 SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a system and a method for combining digitally generated and existing art work on one offset plate.

It is also an object of the present invention to provide an on-line, digital masking ability.

There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for exposing a radiation sensitive medium. The method includes the steps of a) receiving data in the form of at least one of existing artwork and at least one digital representation of an image and b) selectively performing the following steps depending on the type of data to be exposed: c) if the existing artwork is to be exposed, continuously and scanningly illuminating at least a portion of the existing artwork and the radiation sensitive medium and d) if one of the at least one digital representation is to be exposed, scanningly illuminating the radiation sensitive medium in accordance with the one of the digital representations.

There is also provided, in accordance with a preferred embodiment of the present invention, a system for exposing a radiation sensitive medium. The system includes a) at least one pre-press workstation for providing at least one digital representation of an image, b) an imposition workstation for producing impositioning instructions for impositioning at least one of existing artwork and the at least one digital representation and c) an exposure station for exposing the radiation sensitive medium in accordance with the impositioning instructions, the exposure station including a scanning head for scanningly illuminating the radiation sensitive medium.

Alternatively, there is provided, in accordance with an embodiment of the present invention apparatus for producing images on a radiation sensitive medium which includes a) apparatus for placing existing artwork having the images thereon onto the radiation sensitive medium and b) an exposure station which scanningly illuminates at least a portion of the existing 104172/2 artwork and the radiation sensitive medium, thereby transferring the images to the radiation sensitive medium.

There is still further provided, in accordance with another preferred embodiment of the present invention, apparatus for producing images on a radiation sensitive medium which includes an exposure station for scanningly illuminating the radiation sensitive medium with at least one of existing artwork and digital representations of images. The exposure station includes apparatus for selective illumination operative to provide continuous illumination over at least a portion of the existing artwork when exposing the existing artwork and to provide selective illumination in accordance with the digital representation when exposing the digital representation.

Additionally, in accordance with the embodiments of the present invention, the portion of the existing artwork is determined by a digital mask. The digital mask can be of arbitrary shape .

Further, in accordance with some of the embodiments of the present invention, the exposure station includes a scanning head. The scanning head can be a laser beam scanning device having two mirrors or a spinner.

Alternatively, it can be a white light modulation device from one of the following group: deformable mirror device (DMD) arrays, liquid crystal valve arrays, PLZT crystal arrays, ferro-electric arrays or magneto-optic arrays. The white light modulation device can be one- or two-dimensional. 104172/2 BRIEF DESCRIPTION OF THE DRAWINGS AND ANNEX The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a schematic illustration of a prior art step and repeat machine; Fig. 2 is a schematic illustration of a prior art method of combining continuous tone and linework images; Fig. 3 is a block diagram illustration of a system for combining digital page data and existing art work, constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 4 is a schematic illustration of a step and repeat machine, constructed and operative in accordance with one embodiment of the present invention, forming part of the system of Fig. 3; Figs. 5A - 5D are schematic illustrations of four cases of exposing a page of an offset plate; Fig. 6 is a block diagram illustration of the workflow of the system of Fig. 3; Fig. 7 is a schematic illustration of an alternative step and repeat machine having a white light modulation based scanning head; and Annex A is an article describing prior art deformable mirror modulators forming part of the machine of Fig. 7. 104172/2 DETAILED DESCRIPTION OF PRESENT INVENTION Reference is now made to Figs. 3 - 6 which illustrate a system for combining digital page data and existing art work, constructed and operative in accordance with a preferred embodiment of the present invention.

The system typically comprises a digital data preparation system 40, an imposition station 42 and an exposure station 44, connected together via a communications gateway 46, such as removable media (i.e. optical disks, magnetic media, etc.) or a network connection, such as a gateway forming part of an Ethernet or a small computer system interface (SCSI) network.

The digital data preparation system 40 typically comprises a plurality of color pre-press workstations 50, such as the MicroAssembler or Star workstations manufactured by Scitex Corporation Ltd., on which digital representations of images, or "digital images", forming at least part of the pages to be imposed on an offset plate are created and a digitizer 52, such as the MG3 manufactured by SummaGraphics Corp. of Fairfield Connecticut, USA, for creating electronic layouts from hand-made ones.

The workstations 50 and digitizer 52 are typically connected together via a network 54, such as an Ethernet or a SCSI network, to which is also connected a" color proofer 56, such as the Smartjet manufactured by Iris Graphics Inc. of Bedford, Massachusetts, USA. The color proofer 56 is typically utilized to proof the images created on the workstations 50 before their exposure on the plate 14.

The imposition station 42 typically comprises an imposition workstation 60, for preparing an impositioning program and a monochrome proofer 62 for generating a digital "blue line" proof of the impositioning scheme embodied in the impositioning program. The imposition workstation 60 typically is a personal computer running a modified version of the PCU 6.0 Software manufactured by Misomex AB or a modified version of Impostrip Software, commercially available from Ultimate Technographics of 104172/2 Montreal, Canada. Proofer 62 can be the Laser Writer NTX commercially available from Apple Computers Inc. of Cupertino, California, USA or an electrostatic plotter such as the ColorStation 424MX manufactured by Raster Graphics Inc., of Sunnyvale, California, USA.

The exposure station 44 is typically a step and repeat machine, an example one of which is schematically shown in Fig. 4. It comprises a movement system and a scanning head. The movement system can be an x-y table 64 including a chase frame 65 (Pig. 4), such as are known in the art. The scanning head 66 can be the one described in the following article which is incorporated herein by reference: "Two-mirror, Two-axis, Rapid Frame Rate Galvanometer Scanning Using a Novel Resonant Scanner/Dynamic Focusing Mechanism", SPIE Vol . 767 Medical Imaging (1987) , pp. 536 - 542. The example scanning head 66 is manufactured by General Scanning Inc. of Watertown, Massachusetts under the name Raster Photo Plotter.

Alternatively, as will be known to those skilled in the art of optical scanning, the scanning head 66 may include a spinner and an f-theta lens.

The exposure station 44 also typically comprises a control computer 68 for controlling the operation of the x-y table 64 and the scanning head 66. Computer 68 can be any suitable type of computer, such as the PS/2, commercially available from International Business Machines of the USA.

The scanning head 66 typically comprises first and second galvanometric oscillating mirrors 70 and 72 for scanning a laser beam across page location 16, and an optical system 74 for providing the laser beam to first mirror 70. Second mirror 72 provides scanning in the scanning, or X direction, and first mirror 70 provides scanning in the cross-scanning, or Y direction.

The laser beam can be provided by a HeNe gas laser, an Argon Ion laser, or a semiconductor laser as appropriate to match the sensitivity of the radiation sensitive medium 14, such as a 104172/2 plate or a film, which may be exposed with the system of the present invention.

In contrast to the prior art which utilizes lamp 18 for illumination, the present invention utilizes scanning head 66. As shown in Fig. 4, exposure station 44 controls the scanning head 66 to scan across page location 16 such that the page location 16 is illuminated only a portion, such as at least one picture element or "pixel", at a time. The exposure station 44 can expose both conventional separation films and digitally stored images, singly and in combination. Furthermore, it can expose conventional separation films in an area defined by digitally generated, arbitrary shaped masks. This is illustrated in Figs. 5A - 5D.

In Figs. 5A - 5D, the scanning of images is schematically illustrated, where a solid line indicates continuous illumination and a dotted line indicates no illumination. For the purpose of clarity, the scan lines are shown spaced relatively far apart and are shown for positive working offset plates.

As shown in Fig. 5A, exposure station 44 exposes a conventional separation film 12 with a conventional mask by continually illuminating the film and mask during scanning. If it is desired to mask out part of film 12, a digitally represented mask, or "digital mask", produced by digitizer 52, is provided to control computer 68. Based on the information in the digital mask, the control computer 68 provides illumination, via scanning head 66, only within unmasked areas, one of which, denoted 80, is shown in Fig. 5B. However, as shown, the entire film 12 is scanned.

If, as shown in Fig. 5C, a digital image is to be exposed, exposure station 44 operates as a typical imagesetter, providing illumination only where so indicated by the digital image provided to it. For purposes of clarity, the image in Fig. 5C comprises only a tree and a cloud and the background has no texture. It will be appreciated that when exposing digital images, the chase frame 65 of the exposure station 44 does not pick up any conventional films. 104172/2 Finally, the exposure station 44 can expose conventional film 12 together with a digital image. For example, as shown in Fig. 5D, the page comprises a digital image having text 82 comprised of the words "words" and a smaller version of the conventional film 12 shown in the previous figures. Using the information from the digital image and from digital masks indicating where to expose which type of element, the exposure station 44 digitally exposes the area where text 82 is to be located and continuously illuminates in the area where the conventional film 12 is placed.

Furthermore, if the text 82 is provided as a conventional film rather than as a digital image, exposure station 44 can correctly produce the page illustrated in Fig. 5D by first exposing one of the films, say text 82, with an appropriate digital mask and then exposing the film 12 with its appropriate digital mask. Alternatively, chase frame 65 can pick up both the separation film of text 82 and film 12 and expose them together in accordance with a digital mask.

It will be appreciated that, for exposing offset plates, the registration marks, control strips and other markings of the plate can be provided either as conventional films or as digital images.

For all cases of illumination, the operation of the scanning head 66 is controlled by the control computer 68 operating in accordance with the digital data provided to it. Typically, the entirety of data relevant to a single offset plate, including individual pages, registration and folding marks, control strips and imposition data from the impositioning station 42, are stored on a storage medium (not shown) associated with control computer 68.

Fig. 6 is a block diagram of the workflow of the system of Fig. 3. Typically, at step 84, various workstation users prepare the images 20 and the desired page layouts on the prepress workstations 50. The images can be proofed with the proofer 56 and/or they can be printed as color separation films. At step 104172/2 86, the workstation users utilize the digitizer 52 to prepare digital masks for use with images on conventional films.

The registration and other, special marks forming part of the finished offset plate 14 are also typically produced by workstation users on one of the pre-press workstations 50, in step 88, and are typically utilized for more than one offset plate 14.

Typically, an operator, often separate from the workstation users, defines, in step 90, a desired impositioning scheme on the imposition workstation 60. The operator then prepares an impositioning program, in steps 92 and 94, detailing which pages are to be exposed on each offset plate 14, the type of data (conventional separation films or digital or both) forming each page, where the data is stored, the digital masks to be utilized with each page, if any, the sizes of each page, the type of registration marks, control strips and other special marks and the name of the digital files in which they are stored, etc. The impositioning program produced by the workstation 60 is then provided to the control computer 68.

In step 96, the impositioning program and any digital representations of the pages, marks, color strips, masks, etc., are transferred to the storage medium of the exposure station 44.

In step 98, which can occur in parallel with the others, any conventional separation films to be exposed are measured and taped to carrier sheets. The carrier is punched and provided to the unfinished pile 13 of the x-y table 64 (step 100) . The films are also utilized by the digitizer 52 to generate the corresponding digital masks.

In step 102, the exposure station 44 exposes the plate 14 in accordance with the impositioning program and as described hereinabove. If the impositioning program indicates that the next page is to be exposed conventionally, the chase frame 65 picks up the film and its associated conventional mask, if necessary, from the unfinished pile 13, positions it in the appropriate page location 16 and exposes it by scanning with constant illumina- 104172/2 tion.

If the impositioning program indicates the film 12 is to be exposed with a digital mask, then the exposure scanning is performed in accordance with the corresponding mask.

If the impositioning program indicates that a digital image is to be exposed next, then the exposure station 44 retrieves the relevant digital image from the storage medium, moves the chase frame 65 to the appropriate location and exposes according to the digital data it receives, without picking up any film from the unfinished pile 13.

The marks and color control strips can be exposed either as digital images or as films. They can be exposed separately from the exposure of the films 12. Alternatively, if they are digital images, they can be exposed in portions. For example, if they are to be located within or near more than one page location 16, the portion of the mark or strip forming part of each page location 16 will be exposed concurrently with exposure of that page location 16.

It will be appreciated that preparation for imposition of the next plate can occur while the exposure station 44 operates on the previous one.

Reference is now briefly made to Fig. 7 which illustrates an alternative embodiment of the step and repeat machine of the present invention having a scanning head 110 utilizing a white light modulation device. The present discussion refers to a scanning device utilizing a deformable mirror device (DMD) ; however, it will be appreciated that other white light modulation apparatus can also be utilized, such as a liquid crystal valve array, a Lead-Lanthanum-Zirconate-Titanate (PLZT) crystal array, a ferro-electric array or a magneto-optic array.

Scanning head 110, for illumination of a recording medium, is described in detail in the following article, included herein in Annex A: Larry J. Hornbeck, "Deformable-Mirror Spatial Light Modulators", SPIE Critical Reviews Series : Spatial Light Modulators and Applications III Vol. 1150, pp.86 - 102. Section 104172/2 7.3 of the article details a scanning printhead utilizing the DMD arrays described earlier in the article.

In the system of the article by Hornbeck, a tungsten halogen lamp exposes an electro-photographic drum via scanning head 110. For exposing offset plates as well as films, the lamp is typically a metal halide lamp, such as the HPO series commercially available from Philips, Eindhoven, Holland. The sensitivity of offset plates is generally low and the method described by Hornbeck may cause long exposure times. To avoid this, a method described in U.S. Patent 5,049,901, which is incorporated herein by reference, may be utilized.

Briefly, the scanning head 110 comprises a lamp 112, as described hereinabove, condenser lenses 114, a DMD array 116 and an imaging lens 118. The DMD array 116 is typically a linear array, typically of 512 elements, wherein desired ones of the 512 elements are imaged on the recording medium at one time. DMD array 116 is described in detail in sections 1 - 6 of the above-mentioned article.

Elements 112 - 118 are typically mounted on an x-y table 120, such as the ATS 3260 translation stage, commercially available from Aerotech of Pittsburgh, Pennsylvania, USA, shown as a box in dotted lines, which provides translation across the page location 16. The x and y directions are marked. The swathe which is produced by DMD array 116, as it is translated in the y direction, is denoted 122.

In this embodiment, the control computer 68 provides groups of data to the scanning head 110, wherein the number of pixels in each group is the number of array elements of DMD array 116. The pixels can be all "on", as is the case for exposure of a conventional film or part on and part off, as is the case for exposure of a digital image or of a conventional film with a digital mask.

It will be appreciated that the system of the present invention is operative for illuminating any suitable radiation 104172/2 sensitive medium with both existing artwork and digitally represented data.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow: 104172/2

Claims (21)

1. A method for exposing a radiation sensitive medium, the method comprising the steps of: receiving data in the form of at least one of existing artwork and at least one digital representation of an image; and selectively performing the following steps depending on the type of data to be exposed: if said existing artwork is to be exposed, continuously and scanningly illuminating at least a portion of said existing artwork and said radiation sensitive medium; if one of said at least one digital representation is to be exposed, scanningly illuminating said radiation sensitive medium in accordance with said digital representation to be exposed.

2. A method according to claim 1 and wherein said portion of said existing artwork is determined by a digital mask.

3. A system for exposing a radiation sensitive medium, the system comprising: o at least one pre-press workstation for providing at least one digital representation of an image; an imposition workstation for producing impositioning instructions for impositioning at least one of existing artwork and said at least one digital representation; and an exposure station for exposing said radiation sensitive medium in accordance with said impositioning instructions, including: ^ a scanning head for scanningly illuminating said radiation sensitive medium.

4. Apparatus for producing images on a radiation sensitive medium, the apparatus comprising: 104172/2 means for placing existing artwork having said images thereon onto said radiation sensitive medium; and an exposure station which scanningly illuminates at least a portion of said existing artwork and said radiation sensitive medium, thereby transferring said images to said radiation sensitive medium.

5. Apparatus for producing images on a radiation sensitive medium, the apparatus comprising: an exposure station for scanningly illuminating said radiation sensitive medium with at least one of existing artwork and digital representations of images, the exposure station comprising means for selective illumination operative to provide continuous illumination over at least a portion of said existing artwork when exposing said existing artwork and to provide selective illumination in accordance with said digital representation when exposing said digital representation.

6. Apparatus according to either of claims 4 or 5 and wherein said portion of said existing artwork is determined by a digital mask.

7. Apparatus according to claim 6 and wherein said digital mask is of arbitrary shape.

8. Apparatus according to any of claims 4 - 7 and wherein said exposure station includes a scanning head.

9. Apparatus according to claim 8 and wherein said scanning head is a laser beam scanning device.

10. Apparatus according to claim 9 and wherein said scanning head comprises two mirrors. 104172/3

11. Apparatus according to claim 9 and wherein said scanning head comprises a spinner.

12. Apparatus according to claim 8 and wherein said scanning head is a white light modulation device.

13. Apparatus according to claim 12 and wherein said white light modulation device is one of the following group: deformable mirror device (DMD) arrays, liquid crystal valve arrays, PLZT crystal arrays, ferro-electric arrays or magneto-optic arrays.

14. Apparatus according to claim 12 and wherein said white light modulation device is one-dimensional.

15. Apparatus according to claim 12 and wherein said white light modulation device is two-dimensional.

16. A method according to any of claims 1 - 2 substantially as described hereinabove.

17. A method according to any of claims 1 - 2 substantially as illustrated in any of the drawings.

18. A system according to claim 3 substantially as described hereinabove.

19. A system according to claim 3 substantially as illustrated in any of the drawings.

20. Apparatus according to any of claims 4 - 15 substantially as described hereinabove.

21. Apparatus according to any of claims 4 - 15 substantially as illustrated in any of the drawings. For the Applicant, A. Tally Eitan-Zeev Pearl & Co. C: P-719-IL 17 719 pjvpl7.v3