Title of Invention	COMPACT IMAGING HEAD AND HIGH SPEED MULTI-HEAD LASER IMAGING ASSEMBLY AND METHOD
Abstract	The present invention relates to an imaging assembly, characterized in that the imaging assembly comprises a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area; and a plurality of imaging modules, coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules image wise produces laser light which is a summation of each .individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the image wise production of laser energy from each individual module. The present invention also relates to an imaging system, a laser imaging assembly, an optical projection head, imaging head and to a method of preparing a printing plate.

Title of Invention

COMPACT IMAGING HEAD AND HIGH SPEED MULTI-HEAD LASER IMAGING ASSEMBLY AND METHOD

Abstract

The present invention relates to an imaging assembly, characterized in that the imaging assembly comprises a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area; and a plurality of imaging modules, coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules image wise produces laser light which is a summation of each .individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the image wise production of laser energy from each individual module. The present invention also relates to an imaging system, a laser imaging assembly, an optical projection head, imaging head and to a method of preparing a printing plate.

Full Text	COMPACT IMAGING HEAD AND HIGH SPEED MULTI-HEAD LASER IMAGING ASSEMBLY AND METHOD BACKGROUND OF THE IN\'INTION 1- Field of the Invention The present invention relates to a compact imaging head, a high speed niuhi-head laser imaging assembly comprising a plurality of such heads, and a method of imaging heat or light sensitive media using such an assembly. In particular, the assembly comprises a plurality of compact imaging heads (referred to as modules when they are interchangeable) which operate in unison to direct radiation from groups of laser emitters to modulators. The assembly and method of the present invention are capable of directing radiant energy produced by each module for imaging heat or light sensitive media such as a printing plate. 2. Background Infomiation Some of die current trends in the thermal offset printing plate industry have been in the area of increased productivity, especially as they relate to so-called "Computer to Plate" (CTP) systems. However, such conventional systems are presently limited, especially as they relate to imaging of thermal offset plates. Conventional internal drum systems are limited, for example, with respect to the spinning speed of the mirror, the commutation time on/off of the laser beam (for acousto-optic modulators with YAG lasers, red and UV laser diodes and optical fiber lasers), and power of the laser sources. Conventional external drum systems which have a plurahty of laser sources such as diodes are limited, for example, with respect to respective rotational speeds, respective number of diodes and the total power generated thereby. Conventional external drums employing a spatial modulator also have power limitations as well as limitations with respect to the number of spots produced thereby. Conventional flat bed systems have 'width of plate" limitations, resolution limitations, as well as limited scanning speeds, modulation frequencies and power of the respective laser source. A conventional system in which a laser beam is widened in one dimension to cover an array of a substantial number of electro-optic gates (so that a large number of adjacent spots can be formed and thus constitute a 'wide brush") is described in U.S. Patent No. 4,746,942, which is incorporated herein by reference. In particular, this patent discloses that the beam is divided by the gates into a plurality of potential spot-forming beams. The transmission of each beam to a photosensitive surface for imaging is selectively inhibited in accordance with a pre-determined pattern or program, while the beams are swept relative to the photosensitive surface to form characters and other images. However, the number of spots of the brush described in this patent may be limited by optical aberrations. In addition, the power that a single laser source can produce limits the imaging speed of theraio-sensitive plates because of their low sensitivity. The performance of a spatial modulator with a single laser source can also be limited. Conventional "brush" systems generally use spatial modulators such as, e.g., electro-optic ferro-electric ceramic (PLZT) modulators, total internal reflection (TIR) modulators and micro-miirors, are similarly limited. TIR modulators based on the use of LiNbOs crystals are of partictilar interest because of their commutation speed. This type of modulator is described in the literature and several patents such as in U.S. Patent No. 4,281,904, which is incorporated herein by reference. However, for the imaging of thermo-sensitive plates where a high level of energy is necessary, the crystal is submitted to a strong energy density that induces photorefraction effects which negatively affect the operation of the modulator. These effects, known as "optical damage, dc drift" limit the amoimt of energy which can be handled. An imaging head" comprising a source of laser energy, associated optics, and a modulator capable of generating a line segment or "brush" is described in co-assigned U.S. Patent No. 6,137,631, which is incorporated herein by reference. Such a module or head typically projects a thin (i.e. 12 micron) line-segment or brush having a width of 5.2 mm (i.e. a 256 pixel line segment). The imaging productivity of • an imaging system is disadvantageously limited by the small size of such a line-segment. One of the objects of the present invention is to overcome the limitations and disadvantages of the above-described conventional CTP systems by increasing their productivity. Another object of the present invention is to increase the number of spots generated using a laser beam by juxtapositioning the brushes produced by a plurality of compact imaging heads such that each head produces several hundreds liglit spots. Thus, the available power and the pixel rate of conventional CTP systems can be multiphed by the number of heads provided in the assembly and method of the present invention. It is another object of this mvention that the system of tliis invention may be employed in internal and external dnmi systems, as described above, as well as in flat bed platesetter systems, such as described in WO 00/49463, the entire disclosure of which is incorporated herein by reference. It is yet another object of this invention to provide a compact imaging head which may be employed in the assembly and method of this invention, where it is also referred to as a 'module/' It is one feature of this invention that the brushes of hght produced by each module in the head assembly are controlled to provide a continuous scan line which is the aggregate of the indi\'idual brushes emitted from each head, thereby avoiding any gaps in the overall scan Ime employed for imaging. It is another feamre of this invention that the width, orientation, shape, power and dmmg of each brush is controlled to permit the aggregate of individual brushes to be employed as a continuous scan line. The svstem and method of this invention thus advantaeeouslv are able to overcome the limitations of existing "single head" systems which are usually limited to small (e.g. 256 pixel) line segments. Other objects, features and advantages of the system and method of this invention will be apparent to those skilled in the art. SUMMARY OF THE INVENTION Several optical heads are mounted on a common carriage adapted to scan a photosensitive printing plate. Each head is equipped with a laser source, a modulator and projection optics and can project an image (i.e. "brush") of the active zone of the modulator containing a plurahty of pixels. The opdcal track of beams in each head is folded several times in such a way as to reduce the width of the head. When the carriage moves from one edge of the plate to the other edge a swath of pixels is projected as if painted by the brush. Each head includes means to adjust the height, spatial position, orientation and intensity of the brush it generates. Each head is accurately positioned on die carriage so that at least two abutting swaths are projected during each sweep of the carriage to produce a wider swath. The carriage generates pulses indicative of its position relative to the location of the plate edges. Each head is capable of receiving a signal to time the projection of brushes. The relative movements between the carriage and the photosensitive plate are controlled by electronic means. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and IB illustrate an assembly of individual modules. Fig. IC rqjresents a modular imaging assembly in accordance with an embodiment of this invention. Fig. ID represents another modular assembly in accordance with an embodiment of this invention. Fig. IE illustrates the definition of various terms used in the description of this invention. Figs. 2A and 2B are elevation and side views respectively of a compact imaging module in accordance with an embodiment of this invention. Fig. 2C is a schematic representation in exploded view of the major optical components of a head. Fig. 2D is a schematic representation in exploded view of the components of Figure 2C as they affect slow-axis rays. Figs. 3 A, 3B and 3C represent exploded views of the imaging module of Figs. 2A and 2B divided into three sections located on different planes. Figs. 3A', 3B' and 3C' represent the elements involved in the adjustment of optical elements in this invention. Figs. 4A, 4B and 4C represent the effect of non-aligned laser emitters on the focalization of the fast axis rays on a modulator. Fig. 4D represents how the crystal is cut to fold the beams. Fig. 5 represents the "smile" of a laser bar. Fig. 6 is a schematic depiction of the adjustment of the power of laser diodes in each imaging module in an embodiment of the imaging assembly of this mvention. Fig. 7 is an embodiment of this invention in which the imaging assembly comprises four (4) imaging modules. Fig. 8 is a schematic depiction of the imaging of a printing plate using alternative exposure of bands in accordance with one embodiment of this invention. Fig. 9 represents an exploded view of an imaging head in accordance with another embodiment of this invention. Fig. 10 represents an external view of the imaging module of Fig. 9. Fig. 11 represents the components employed in this invention located at the end of the optical path and method of adjustment thereof DETAILED DESCRIPTION OF THE INVENTION This invention and its various embodiments will become apparent from the following detailed description and specific references to the accompanying figures. Compact Imaging Modules Figures 2A and 2B show enlarged side views of an exemplary compact imagmg module or head 36 which may be used in the assembly and method of the present invention. Figures 3A-3C show exploded elevation views of different sections of the module 36 illusn-ated in Figures 2A and 2B, located on different respective planes. This module 36 has a laser source 10 (typically a laser bar or laser diode array comprising a pluraHty of emitters) emitting a bundle of rays 5 (see Fig. 2A). and arranged thereon which is attached to a support arrangement (not shown in Figures 2A and 2B). The laser source 10 described herein is cooled by a liquid flowing through micro channels. Such as laser source may be obtained from Jenoptik Laserdiode, GmbH, as type JOLD-32-CAFC-1L, having a power of 32 warts. This particular laser source 10 described herein is a bar that is one-centimeter long and includes nineteen (19) emitters, although other laser sources may also be used. Collimating lens 20 is positioned to collimate the fast axis of the laser rays from laser source 10. In this embodiment, collimating lens 20 is a type FAC-S50D lens available from Limo-Lissotschenko Microoptik GmbH, although other lenses may also be used. When the bundle of rays 5 is projected therethrough, due to the aspherical cylindrical profile of collimating lens 20 combined with a glass of high refractive index, a resultant beam which approaches the diffraction limit is produced. The beam divergence along a slow axis is reduced by an array of cylindrical lenses 30 (shown in Fig. 2A as a single lens) provided in the module 36. Each of the cylindrical lenses 30 provided in the module 36 preferably corresponds to one emitter of the laser source 10. Upon exiting from the cylindrical lenses 30, the beams are reflected by polarizing mirror 40 and reach imaging (half-wave) blade 50. Half-wave blade 50 makes it possible, upon the beams' exit therefrom, to position the polarization plane of the beam in the direction where the efficiency of a modulator 15 (also provided in the module 36) is optimum. A group of two cylindrical lenses 60 and 70 are utilized for controlling or adjusting the divergence of the beams along the fast axis by adjusting the distance between these lenses 60 and 70. This distance adjxistment between lenses 60 and 70 effects the width of the beam output at plate location 400. In this manner, it is thus possible to adjust the beam output of the module 36 which, in its unadjusted state, produces respective beams having different beam widths. In addition, if it is determined that the module 36 is outputting a beam having beam characteristics which have been degraded or changed (e.g., a change in the beam width due a defect of a particular imaging component of the module), it is possible to use the above-described adjustment capability of the two cylindrical lenses 60 and 70 to compensate for certain irregularities of the components within the module 36. After exiting cylindrical lenses 60 and 70, the beams are projected through another lens 80, reflected from the mirrors 90 and 100, and directed toward lenses 110 and 120 (shown in Fig. 3A). Due to the presence of mirrors 90 and 100, the size of the module 36 may be reduced. This can be done, at least in part, by reflecting or folding the beams with mirrors 90 and 100. A further reduction of the module size by "folding" the beams is discussed in further detail below. The lenses 80, 110 and 120 are arranged in a telecentric objective arrangement which collects the beams emerging from thejaser source 10 of the module 36. These lenses 80, 110, and 120 modify the characteristics of the beams entering therein to form an image of the emitters at an input face of an optical mixer (here mixing blade 130) along the slow axis of the laser source. The optical mixer is capable of equalizing the energy beams received from the laser diode array. As described above, the group or combination of optical components 20, 30 and 80 are capable of shaping and directing energy' rays from the laser source 10 to the input of the optical mixer. Thereafter, the beams enter into a group of cylindrical lenses 140 and 150 from an output end of blade 130 (i.e., directly through the lenses 140, 150), then reflect or fold via mirrors 160 and 170 as shown, and finally enter lens 180. The miiTors 160 and 170 are preferably located in an imaging track (i.e., along the beam path) so as to reflect or fold the beam again, which facilitates the size reduction of module 36. The resultant slow axis beams exiting from the cylindrical lenses 140, 150, ISO form an image of the exit face of the mixer blade at the center 210 of modulator 15. The combination or group of lenses 140, 150 is capable of directing and focalizing slow-axis rays emerging from the output of the optical mixer 130 to the focal point 500 of lens 180, which is capable of directing slow-axis rays from the focal point 500 to the modulator 15. This arrangement of the cylindrical lenses 140, 150, 180 also has telecentric characteristics along the slow axis. Thus, a uniform distribution of hght on the modulator 15 can be generated for the image. The uniform distribution of hght using modulator 15 is also described in co-assigned U.S. Patent No. 6,137,631, the entire disclosiu'e of which is incorporated herein by reference. Before reaching the modulator, the beams are directed to another cylindrical lens 190 which focalizes and directs the beams of the fast axis to the active zone of the modulator 15. The width of the resultant beams (e.g., a bundle of rays) is limited at an entrance to the modulator 15 by certain mechanical elements 200 (e.g. stops). One exemplary modulator 15 can be a TIR-type modulator whose active zone has a column of 256 active elements which are controlled by four drivers 350 (e.g., SUPERTEX INC HV5770S, available from Supertex, Inc., Sunnyvale, Ca). The modulation of hght as well as the projection of modulated light for the projection of individual light brushes (as described below) may be achieved using the modulation and projection techniques and equipment described in, for example, U.S. Patent Nos. 4,746,942 and 6,137,631, both of which are incorporated herein by reference in their entirety. As shown and described in copending U.S. Patent No. 6,222,666, the entire disclosure of which is incorporated herein by reference, the modulator 15 can be divided into an active imaging central zone which is controlled by one or more drivers for imaging a column of 256 spots and lateral zones. These drivers (e.g., drivers 350) can be directly attached to crystal 220, and may be enc^sulated to increase their resistance to shock. The modulator 15 preferably operates in the mode known as a "bright field." Thus, the beams are directed to modulator 15 which modifies or configures these beams using drivers 350 and mechanical elements 200. In particular, the light beams 5" enter the crystal 220 via crystal face 230 angled by five degrees relative to the normal at a plane of the crystal 220. Thus, the beams are deviated in the crystal 220, and submitted to a total reflection in the active zone of the modulator 15 with a small angle of incidence. The modified beams 5'" exit the crystal 220 in a direction which is perpendicular to the plane of the crystal 220 after another reflection of the beams at prismatic face 240 of the crystal 220 takes place. The composition of the crystal 220 is preferably selected so as to avoid photorefi-action effects (e.g., imaging damage, DC drift, etc.) at high energy density. A preferred crystal composition is LiNbCh with about 5 mol% of MgO or about 7 mol% of Zn. In a particularly prefenred embodiment, the modulator is a TIR modulator comprising a total reflection crystal having at least one prismatic edge enable of deviating rays by 90 degrees. Thereafter, as shown in Figure 3B, beams 5"' reach lens 260 via another mirror 250. Lens 260 is capable of collecting rays emerging from the active zone to form an image (500') on stop element (270), which is capable of eliminating unwanted rays. Mirror 250redirectsthebeams toward stop element 270 preferably located close to the Fourier transform plane at the focus of lens 260 for the purpose of blocking rays of higher diffraction order as is well known in the art. A calibrated opening or slit of stop element 270 allows the undiflfracted rays to go through and proceed toward the following optical elements. In one embodiment of the invention. the stop element is independent of the objective group cornprismg elements 280, 290, 300, 310 and 320. The same circulating coolant such as a water circuit used by the laser bar may be used to insure thermal stability. The height of this image is adjusted by changing the distance between spherical lens 260 and stop element 270. Accurate centering of image 340' on the aperture of the stop element is obtained by the lateral displacement of lens 180. Rays emerging from the aperture of element 270 enter imaging lens group 280. 290, 300, 310, 320 and 330. These lenses relay the image 340' 01 the exit face 240 of modulator 220 to the photosensitive face of the plate 400 u'here ii is shown at 340. Lens 320 of the objective lens assembly can be used to modify the focal plane without affecting the size of image 340. It is another object of the invention to reduce the size of each head by folding beams as schematically represented in Figure 2C, placing the optical components in substantially the same plane, as shown also in Figures 2A and 2B. In this manner the height of the head is considerably reduced and the width of the head (represented by W in Figure 7) is kept at its minimum. The plane represented by the folded beams is preferably perpendicular to the bmsh image 340. It is thus possible to produce compact modules of reduced height and minimum width (W=30nmi). The objective assembly may also be provided with an optional protective cover 330 composed of quartz. A support element (not shown) can be auached to the objective assembly to allow certain accurate displacements of the objective assembly's axis which are perfonned as a fimction of the offset of the focalized bundle of rays (or beams) which fomi the image 340. Such adjustment makes it possible to obtain a spatial position of the focalized beam preferably identical for all imaging modules in the imaging assembly (discussed further herein) in relation to particular reference points. In another embodiment of this invention, the compact imaging module or head which may be employed in the assembly and method of this invention is as depicted in Figures 9 and 10. Figure 9 represents the interior view of the components of a duplex imaging head which contains laser sources 510 and 510' which are typically a laser diode as previously described with respect Figiu-es 2A-2B and 3A-3C. The beams from laser source 510 are directed to a corresponding first set of optical arrangements wnicn compnses lenses 560 ana 5/0 naii-wave blade 550, polarizing cube 540 and lens 580. Similarly, the beams from laser source 510' are directed to a corresponding optical arrangement which comprises lenses 560 and 570', half-wave blades 550 and 550', polarizing cube 540' (not shown) and lens 580' (not shown). The beams emerging from the corresponding first optical arrangements are directed to a first common optical arrangement which in this embodiment comprises mirror 600A and lenses 610A and 620A. The image of the emitters from laser sources 510 and 510' exit the first common optical arrangement via lens 620A and respectively form an image of the laser sources at the input faces of second corresponding optical arrangements which in this embodiment comprise imaging blades 630 and 630' as shown. The beams emerge from mixing blades 630 and 630' and are directed to a second common optical arrangement which in this embodiment comprises lenses 640A and 650A and mirrors 660A and 670A. The beams are then respectively directed to third corresponding optical arrangements comprising lenses 680 and 690 (for laser source 510) and lenses 680' (not shown) and 690' (for laser source 510'). The beams emerge from the third corresponding optical arrangements and the beams of the corresponding fast axes are directed to an active zone of modulators 720 and 720', respectively. These modulators are of the configuration and operate as the modulators previously described with respect to Figures 2A-2B and 3A-3C. The beams emerge from the modulators 720 and 720' and are respectively directed to corresponding fourth optical arrangements as shown in Figure 9, which comprise lens 760, mirrors 740 and 750, and imaging lens group G (for laser source 510), and lens 760', mirrors 740' and 750', and imaging lens group G' (for laser source 510'). As is also depicted in Figure 9, the imaging lens groups G and G' are offset in a direction perpendicular to the travel path of the scanning carriage as is explained further herein. The ofiset corresponds to the offset shown as 51 in Figure IC described herein. The beams are projected by imaging lens groups G and G' to the imageable medium (e.g. printing plate) to be imaged. Figure 10 depicts a view of the exterior of the imaging assembly of Figure 9. In Figure 10, the housing 1000 contains the elements previously described with respect to Figure 9, and the housing may be detachably or fixably coupled to the carriage, as is further described herein. In additional embodiments of this invention, the imaging module or head used in this invention may compromise the optical elements described m U.S. Patent No. 6,169,565, which is incorporated herein by reference. Modular Imaging Assembly A modular imaging assembly in accordance with the present invention refers to the assembly of identical interchangeable imaging heads referred to as modules detachably coupled or mounted on a common carriage. Figures lA, IB, IC and ID schematically illustrate various embodiments of the present invention. One of the objects of this invention is to increase the production speed of platesetters in which the printing plate and the imaging optics are moveable relative to each other to produce successive joining bands of pixels to image a printing plate. Such systems are described, for example, in U.S. Patent Nos. 4,746,942 and 4,819,018, and WO 00/49463, all of which are incorporated herein by reference. The number of pixels that can be produced and projected by a single imaging module to form a band of pixels is limited for the reasons discussed above. In theorx', if it were possible to manufacture an imaging module or head no larger than the width of a brush (for example 256 pixels) several heads 44 could be affixed face to face on a common carriage (as shown in Fig. 1 A), thus increasing the number of pixels that could be swept across a plate for imaging in one excursion of the carriage. However, such an arrangement is impossible in the present state of the art. The width of each head would be limited to the width of a brush, for example to 5.2 mm to produce adjacent brushes of 256 pixels of 20 microns. An assembly of four such theoretical heads, each one-brush-wide, is illustrated in Figure 1 A. Figure IB represents an assembly of four modules or heads 38 mounted side by side on a common carriage using technology available to those skilled in the art prior to this invention. For example, each head may be magnetically removably attached to the carriage on which it may be accurately positioned by pins, as is well known in the art. As shown in Fig. IB, this arrangement is unacceptable because gaps 45 would be left between each band of pixels or brushes 34*. It is an important object of this invention to eliminate such gaps. This object of the present invention is accomplished by the imaging assembly of this invention schematically illustrated in Fig. IC, representing schematically various components of a flat-bed platesetter such as described in WO 00/49463 in detail. Imaging carriage 37, sliding on rails 52 moves or traverses continuously from one edge of plate 42 to the other edge for the projection of a swath of pixels on a light or heat sensitive medium for imaging thereof Four joining bands (i.e. 34-r, 34-2', 34-3' and 34-4') each 256 pixel-wide, are projected at each excursion of carriage 37, from left to right and vice versa. The result is the projection of a swath 46 having a width of 1024 pixels at each excursion of the carriage. This result is obtained, as shown on the left side of Fig. IC, by locating individual imaging modules or heads M-1 to M-4 (projecting pixel brushes 34-1, 34-2, 34-3, and 34-4 respectively to generate respective bands 34-1', 34-2', 34-3' and 34-4') at different levels 38-1, 38-2,38-3 and 38-4 of the carriage. These levels are precisely determined such that consecutive pixel brushes 34-1, 34-2, 34-3 and 34-4 are exactly aligned, so that the bottom portion of a brush abuts exactly the top portion of an adjacent brush as per the orientation of Figures IC and ID. The modules are thus aligned with respect to one another such that the plurahty of modules imagewise produce laser hght which is a summiation of each individual light brush produced by each module. This ahgnment is achieved by employing the stair-like arrangement of the modules as described above, coupled with the delay in the imagewise projection of each brush image or swath, which is accomplished as discussed below. It will be apparent to those skilled in the art that the operation of the system described above and depicted in Fig. IC requires adequate differential timing or compensation for the projection of each band. Referring to the operation of a similar carriage as described in WO 00/49463, as carriage 37 travels from an extreme location (i.e. the near side of the imaging area) shown on the left side of Figure IC to the right (arrow F2) carriage 37 comprises an edge detector coupled with a signal generator which generates pulses that continuously inform (via detectors, etc. which are not shown) an electronic controller (not shown) of the position of carriage 37 at the plane level 400. Consequently, the beana width depends on the esseniially variable smile of the laser diodes. The width of the beam is also imposed by the value of the diffraction limit, consequently by the width and distribution of rays on lens The latter depends on the positioning accuracy of the collimating lens 20 mrefraction the emitters and on the spacing between lenses 60 and 70. A small departure ideal position of coUimating lens 20 results in a significant change of the direvitaves of the beam affecting the width of the "diffraction limited" beam at plane level For example, by reducing by one micron the distance between the emitters -and the coUimating lens 20 relative to its theoretical position where the beam is perfect t coUimated, the beam divergence is increased, thus the width of the beam on leu 1 -and the width of the "diffraction limited" spot changes from 42 to 28 micron, i in. variations in the positioning of coUimating lens 20 result in changes of the width of the beam at plane level 400. It follows from the above that increasing the smile causes an of the width of the beam whereas increased divergence causes its reduction 'therpal is to balance these two effects to obtain a beam of constant width for all module Whtn the diode has a low smile, divergence will be reduced to increase ihc width diffraction. This reduction of the divergence is obtained by increasing the spacturam lenses 60 and 70 (Fig. 4C). However, if the smile is more important, the divergence win be increased by reducing the spacing between lenses 60 and 70. The divergence may be adjusted by adjusting the spacing between lenses 60 and 70 to obtain a been of constant width at the image location at plane level 400 where the wnting focahzed and is also the location of the sensitive face of the printing plate Accordingly, for example, in one embodiment, lens 60 is negative, F= - 40 mm causing the divergence of rays and lens 70 is positive, F= + 50 mm causing tiu-convergence of rays. By adjusting the spacing between these lenses it is possible compensate for the divergence variations of different laser diodes. Theoret principle of compensation by adjustment of the divergence is possible withon: 60 and 70 by adjusting only the location of coUimating lens 20. Thus, as depreted Figs. 4A-4C and described herein, the divergence of the rays may be adjust ed 1. An imaging assembly comprising: a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area; and a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module composes at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules image wise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the image wise production of laser energy from each individual module. 2. The assembly of Claim 1, in which the carriage is capable of traversing in a single excursion a distance greater than a desired image area, and the plurality of modules produces a contmuous band of laser hght which is the summation of each individual light bums produced by each module with each traverse of the carriage across the desired image area. 3. The assembly of Claim 1, in which each module is venically offset from the other modules. 4. The assembly of Claim 1, in which the assembly contains four modules. 5. The assembly of Claim 1, in which the modulator is a TIR modulator. 6- The assembly of Claim 1, in which each module is capable of producing 256 pixels of image wise laser hght. 7. The assembly of Claim 1, in which the laser light source comprises a plurality of laser diodes. 8. An imaging assembly comprising: a moveable carriage; and apluraliry of imaging modules coupled to the carriage \ ii i MI each module is adjacent to at least one other module and each module comprise a laser light source and a modulator cooperatively arranged to produce an mdixuiu i light brush; means for aligning each module with respect to the oihci modules such that the pluraUty of modules imagewise produces laser hght whi. i; i summation of each individual light brush produced by each module; and means for delaying the imagewise production of laser energy from each individual module in response to an input signal conveying information regarding the position of the carriage relative to a desired image area. 9. An imaging system comprising: (a) an imaging assembly comprising: (i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relatively desired image area, and (ii) a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser hght source and a modulator cooperatively arranged in produce an individual light brush, and each module is aligned with respect to the modules such that the plurality of modules imagewise produces laser light which is summation of each individual hght brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of the energy from each individual module; and (b) a flat platesetter cooperatively arranged with the imaging assembly such that the imaging assembly imagewise provides laser energy a printing plate residing in the platesetter. 10. An imaging system comprising: (a) an imaging assembly comprising: (i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative desired image area, and (ii) aplurality of imaging modules coupled to the carriage, wherein each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each aligned with respect to the other modules such that the plurality of modules imagewise produces laser Hght which is a summation of each individual lighit : produced by each module, and each module comprises a signal receiver which a delay in the imagewise production of laser energy for each individual module and (b) a rotating drum cooperatively arranged uith the imaging assembly such that the imaging assembly imagewise provides laser energy a printing plate residing on a surface of the rotating drum. 11. A method of preparing a printing plate comprising: (a) providing an imaging assembly comprising. (i) a moveable carriage comprisuig a signal generator for generating a signal indicative of the location of the carnage relatively desired image area, and (ii) a plurality of imaging modules coupled to carriage, wherein each module is adjacent to at least one other module, each moduler comprises at least one laser hght source and a modulator cooperatively arranged in produce an individual hght brush, each module is aligned with respect to theother; modules such that the pIuraHty of modules imagewise produces laser light which summation of each individual hght brush produced by each module, and each n comprises a signal receiver which caiises a delay in the imagewise production of the energy from each individual module; (b) providing a printing plate for imaging; and (c) imagewise providing laser light to the printing plant using the imaging assembly. 12. The method of Claim 11, in which the plate resides in a flat platesetter cooperatively arranged with the imaging assembly. 13. The method of Claim 11, in which the plate resides on a of a rotating drum cooperatively arranged with the imaging assembly. 14. An imaging system comprising: a moveable carriage capable of traversing movement aciu width of a radiation receptive medium; a plurality of imagmg heads selectively positioned on thc carriage, wherein each head comprises at least one laser source, modulating mean modulating the laser energy and projection means for projecting the modulated la r: energy cooperatively arranged such that the laser source, modulating means amd projection means produce at least one individual light brush and each head produce at least one separate band of light brushes during each traverse of the carriage ac ic , the width of the medium; compensating means for adjusting the projection of the seprate bands such that the separate bands are projected during each traverse of the carriage form a continuous band having a width equal to the cumulative width of the seprate bands; means for stepwise moving the medium in a direction perpendicular to the traversing movement of the carriage; means for controlhng the length and position of the carriage traverse across the width of the medium; and means for detecting the location of the cairiage relative to the edges of the medium and means for timing the projection of the separate bands responsive to the detecting means. 15. The imaging assembly of Claim 1, in which the laser power: different modules is equalized by a shunt. 16. A laser imaging assembly comprising: a carriage capable of moving over a photosensitive m aplurality of optical modules selectively positioned on the carriage wherein each module comprises a laser source and associated optical components and each module projects a brush of radiant energy wherein each : is removably attached to the carriage; and locating means on the carriage to position each module n. relation to selected reference points. 17. The assembly of Claim 16, in which each module is magnetically removably attached to the carriage. 18. The assembly of Claim 16, in which the locating means comprises a signal detector, an encoder, and an electronic controller which arc operaiively associated to provide to locate the carriage. 19. The assembly of Claim 1, in which each module is provided with adjustable locating elements thereby enabhng each module to be independence adjusted on a jig to enable locadon of each module brush according to x, y and . coordinates. 20. An optical projection head comprising: a laser diode array having a plurality of emitters; a TIR modulator capable of diffracting light rays from the according to an apphed electric field; an optical mixer capable of equalizing the energy beams the array; a first group of optical components capable of shaping and directing energy rays from the laser array to the mixer; a second group of oprical components capable of direcuting emerging from the mixer to the modulator; a lens capable of focahzing rays emerging from the modulate to a stop element capable of eliminating unwanted diffracted rays; and an imaging objective assembly capable of focusing rays emerging from the stop element to a radiation sensitive media thereby producing image wherein the optical assembly comprises means for adjusting the divergence rays from the modulator to a selected value affecting the width of the image 21. An optical projection head comprising: a laser diode array having a plurality of emitters capabk i i producing energy rays along a slow axis and a fast axis which are mutually perpendicular; a TIR modulator capable of diffracting energy rays from the array according to an apphed electric field; an optical mixer capable of equalizing the energy beams from the array; a first group of optical components capable of shaping and directing energy rays from the laser array to the input of the mixer; a cylindrical lens unit capable of directing and focalizuing axis rays emerging from the output of the mixer to the focal point of a cylindrical capable of directing slow-axis rays from the focal point to the modulator; a lens capable of directing and concentrating fast-axis the active zone of the modulator ; a lens capable of coUecting rays emerging from the active to form an image of the point on a stop element capable of eliminating unwards rays; and an objective assembly capable of projecting an image on photosensitive surface. 22. The head of Claim 20, in which the adjusting means include pair of lenses. 23. An optical head comprising: a laser source of beams at an input end and image formed beams at the output end; and a plurality of optical components along said beams betweenthe input and output ends to obtain an image from the beams wherein the beams are folded a plurality of times between the input and output ends by reflecting siina 24. The head of Claim 23, in which the folded beams arc i a plurality of parallel surfaces. 25. The head of Claim 20, in which the modulator comprises LiNbOa crystal having about 5 mol. % MgO or about 7 mol. % Zn. 26. The head of Claim 21, in which the modulator comprises LiNbOs crystal having about 5 mol. % MgO or about 7 mol. % Zn. 27. The head of Claim 20, in which the modulator is a TIR modulator having one or more drivers. 2S. The bead of Claim 21, in which the modulator is a TIK modulator having one or more drivers. 29. The head of Claim 27, in which the modulator drivers are direct] V attached to a crvstal of the modulator. 30. The head of Claim 28, m which the modulator drivers ait directly attached to a crystal of the modulator. 31. The head of Claim 29, in which the crystal and dnvers are encapsulated. 32. The head of Claim 30, in which the crystal and drivers are encapsulated. 33. The head of Claim 20, in which the laser diode and the stop element are cooled by a circulating coolant. 34. The head of Claim 21, m which the laser diode and the stop element are cooled by a circulating coolant. An imaging assembly substantially as herein described with reference to the accompanying drawings, 52. An optical head substantially as herein described with reference to the accompanying drawings.

Full Text

COMPACT IMAGING HEAD AND HIGH SPEED MULTI-HEAD LASER IMAGING ASSEMBLY AND METHOD
BACKGROUND OF THE IN\'INTION
1- Field of the Invention
The present invention relates to a compact imaging head, a high speed niuhi-head laser imaging assembly comprising a plurality of such heads, and a method of imaging heat or light sensitive media using such an assembly. In particular, the assembly comprises a plurality of compact imaging heads (referred to as modules when they are interchangeable) which operate in unison to direct radiation from groups of laser emitters to modulators. The assembly and method of the present invention are capable of directing radiant energy produced by each module for imaging heat or light sensitive media such as a printing plate.
2. Background Infomiation
Some of die current trends in the thermal offset printing plate industry have been in the area of increased productivity, especially as they relate to so-called "Computer to Plate" (CTP) systems. However, such conventional systems are presently limited, especially as they relate to imaging of thermal offset plates. Conventional internal drum systems are limited, for example, with respect to the spinning speed of the mirror, the commutation time on/off of the laser beam (for acousto-optic modulators with YAG lasers, red and UV laser diodes and optical fiber lasers), and power of the laser sources. Conventional external drum systems which have a plurahty of laser sources such as diodes are limited, for example, with respect to respective rotational speeds, respective number of diodes and the total power generated thereby. Conventional external drums employing a spatial modulator also have power limitations as well as limitations with respect to the number of spots produced thereby. Conventional flat bed systems have 'width of plate" limitations, resolution limitations, as well as limited scanning speeds, modulation frequencies and power of the respective laser source.

A conventional system in which a laser beam is widened in one dimension to cover an array of a substantial number of electro-optic gates (so that a large number of adjacent spots can be formed and thus constitute a 'wide brush") is described in U.S. Patent No. 4,746,942, which is incorporated herein by reference. In particular, this patent discloses that the beam is divided by the gates into a plurality of potential spot-forming beams. The transmission of each beam to a photosensitive surface for imaging is selectively inhibited in accordance with a pre-determined pattern or program, while the beams are swept relative to the photosensitive surface to form characters and other images.
However, the number of spots of the brush described in this patent may be limited by optical aberrations. In addition, the power that a single laser source can produce limits the imaging speed of theraio-sensitive plates because of their low sensitivity. The performance of a spatial modulator with a single laser source can also be limited. Conventional "brush" systems generally use spatial modulators such as, e.g., electro-optic ferro-electric ceramic (PLZT) modulators, total internal reflection (TIR) modulators and micro-miirors, are similarly limited.
TIR modulators based on the use of LiNbOs crystals are of partictilar interest because of their commutation speed. This type of modulator is described in the literature and several patents such as in U.S. Patent No. 4,281,904, which is incorporated herein by reference. However, for the imaging of thermo-sensitive plates where a high level of energy is necessary, the crystal is submitted to a strong energy density that induces photorefraction effects which negatively affect the operation of the modulator. These effects, known as "optical damage, dc drift" limit the amoimt of energy which can be handled.
An imaging *head" comprising a source of laser energy, associated optics, and a modulator capable of generating a line segment or "brush" is described in co-assigned U.S. Patent No. 6,137,631, which is incorporated herein by reference. Such a module or head typically projects a thin (i.e. 12 micron) line-segment or brush having a width of 5.2 mm (i.e. a 256 pixel line segment). The imaging productivity of • an imaging system is disadvantageously limited by the small size of such a line-segment.

One of the objects of the present invention is to overcome the limitations and disadvantages of the above-described conventional CTP systems by increasing their productivity. Another object of the present invention is to increase the number of spots generated using a laser beam by juxtapositioning the brushes produced by a plurality of compact imaging heads such that each head produces several hundreds liglit spots. Thus, the available power and the pixel rate of conventional CTP systems can be multiphed by the number of heads provided in the assembly and method of the present invention. It is another object of this mvention that the system of tliis invention may be employed in internal and external dnmi systems, as described above, as well as in flat bed platesetter systems, such as described in WO 00/49463, the entire disclosure of which is incorporated herein by reference. It is yet another object of this invention to provide a compact imaging head which may be employed in the assembly and method of this invention, where it is also referred to as a 'module/'
It is one feature of this invention that the brushes of hght produced by each module in the head assembly are controlled to provide a continuous scan line which is the aggregate of the indi\'idual brushes emitted from each head, thereby avoiding any gaps in the overall scan Ime employed for imaging. It is another feamre of this invention that the width, orientation, shape, power and dmmg of each brush is controlled to permit the aggregate of individual brushes to be employed as a continuous scan line. The svstem and method of this invention thus advantaeeouslv are able to overcome the limitations of existing "single head" systems which are usually limited to small (e.g. 256 pixel) line segments. Other objects, features and advantages of the system and method of this invention will be apparent to those skilled in the art.
SUMMARY OF THE INVENTION Several optical heads are mounted on a common carriage adapted to scan a photosensitive printing plate. Each head is equipped with a laser source, a modulator and projection optics and can project an image (i.e. "brush") of the active zone of the modulator containing a plurahty of pixels. The opdcal track of beams in each head is folded several times in such a way as to reduce the width of the head.

When the carriage moves from one edge of the plate to the other edge a swath of pixels is projected as if painted by the brush. Each head includes means to adjust the height, spatial position, orientation and intensity of the brush it generates. Each head is accurately positioned on die carriage so that at least two abutting swaths are projected during each sweep of the carriage to produce a wider swath. The carriage generates pulses indicative of its position relative to the location of the plate edges. Each head is capable of receiving a signal to time the projection of brushes. The relative movements between the carriage and the photosensitive plate are controlled by electronic means.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1A and IB illustrate an assembly of individual modules.
Fig. IC rqjresents a modular imaging assembly in accordance with an embodiment of this invention.
Fig. ID represents another modular assembly in accordance with an embodiment of this invention.
Fig. IE illustrates the definition of various terms used in the description of this invention.
Figs. 2A and 2B are elevation and side views respectively of a compact imaging module in accordance with an embodiment of this invention.
Fig. 2C is a schematic representation in exploded view of the major optical components of a head.
Fig. 2D is a schematic representation in exploded view of the components of Figure 2C as they affect slow-axis rays.
Figs. 3 A, 3B and 3C represent exploded views of the imaging module of Figs. 2A and 2B divided into three sections located on different planes.
Figs. 3A', 3B' and 3C' represent the elements involved in the adjustment of optical elements in this invention.
Figs. 4A, 4B and 4C represent the effect of non-aligned laser emitters on the focalization of the fast axis rays on a modulator.
Fig. 4D represents how the crystal is cut to fold the beams.
Fig. 5 represents the "smile" of a laser bar.

Fig. 6 is a schematic depiction of the adjustment of the power of laser diodes in each imaging module in an embodiment of the imaging assembly of this mvention.
Fig. 7 is an embodiment of this invention in which the imaging assembly comprises four (4) imaging modules.
Fig. 8 is a schematic depiction of the imaging of a printing plate using alternative exposure of bands in accordance with one embodiment of this invention.
Fig. 9 represents an exploded view of an imaging head in accordance with another embodiment of this invention.
Fig. 10 represents an external view of the imaging module of Fig. 9.
Fig. 11 represents the components employed in this invention located at the end of the optical path and method of adjustment thereof
DETAILED DESCRIPTION OF THE INVENTION This invention and its various embodiments will become apparent from the following detailed description and specific references to the accompanying
figures.
Compact Imaging Modules
Figures 2A and 2B show enlarged side views of an exemplary compact imagmg module or head 36 which may be used in the assembly and method of the present invention. Figures 3A-3C show exploded elevation views of different sections of the module 36 illusn-ated in Figures 2A and 2B, located on different respective planes. This module 36 has a laser source 10 (typically a laser bar or laser diode array comprising a pluraHty of emitters) emitting a bundle of rays 5 (see Fig. 2A). and arranged thereon which is attached to a support arrangement (not shown in Figures 2A and 2B). The laser source 10 described herein is cooled by a liquid flowing through micro channels. Such as laser source may be obtained from Jenoptik Laserdiode, GmbH, as type JOLD-32-CAFC-1L, having a power of 32 warts. This particular laser source 10 described herein is a bar that is one-centimeter long and includes nineteen (19) emitters, although other laser sources may also be used.

Collimating lens 20 is positioned to collimate the fast axis of the laser rays from laser source 10. In this embodiment, collimating lens 20 is a type FAC-S50D lens available from Limo-Lissotschenko Microoptik GmbH, although other lenses may also be used. When the bundle of rays 5 is projected therethrough, due to the aspherical cylindrical profile of collimating lens 20 combined with a glass of high refractive index, a resultant beam which approaches the diffraction limit is produced. The beam divergence along a slow axis is reduced by an array of cylindrical lenses 30 (shown in Fig. 2A as a single lens) provided in the module 36.
Each of the cylindrical lenses 30 provided in the module 36 preferably corresponds to one emitter of the laser source 10. Upon exiting from the cylindrical lenses 30, the beams are reflected by polarizing mirror 40 and reach imaging (half-wave) blade 50. Half-wave blade 50 makes it possible, upon the beams' exit therefrom, to position the polarization plane of the beam in the direction where the efficiency of a modulator 15 (also provided in the module 36) is optimum. A group of two cylindrical lenses 60 and 70 are utilized for controlling or adjusting the divergence of the beams along the fast axis by adjusting the distance between these lenses 60 and 70. This distance adjxistment between lenses 60 and 70 effects the width of the beam output at plate location 400. In this manner, it is thus possible to adjust the beam output of the module 36 which, in its unadjusted state, produces respective beams having different beam widths. In addition, if it is determined that the module 36 is outputting a beam having beam characteristics which have been degraded or changed (e.g., a change in the beam width due a defect of a particular imaging component of the module), it is possible to use the above-described adjustment capability of the two cylindrical lenses 60 and 70 to compensate for certain irregularities of the components within the module 36.
After exiting cylindrical lenses 60 and 70, the beams are projected through another lens 80, reflected from the mirrors 90 and 100, and directed toward lenses 110 and 120 (shown in Fig. 3A). Due to the presence of mirrors 90 and 100, the size of the module 36 may be reduced. This can be done, at least in part, by reflecting or folding the beams with mirrors 90 and 100. A further reduction of the module size by "folding" the beams is discussed in further detail below. The lenses

80, 110 and 120 are arranged in a telecentric objective arrangement which collects the beams emerging from thejaser source 10 of the module 36. These lenses 80, 110, and 120 modify the characteristics of the beams entering therein to form an image of the emitters at an input face of an optical mixer (here mixing blade 130) along the slow axis of the laser source. The optical mixer is capable of equalizing the energy beams received from the laser diode array. As described above, the group or combination of optical components 20, 30 and 80 are capable of shaping and directing energy' rays from the laser source 10 to the input of the optical mixer.
Thereafter, the beams enter into a group of cylindrical lenses 140 and 150 from an output end of blade 130 (i.e., directly through the lenses 140, 150), then reflect or fold via mirrors 160 and 170 as shown, and finally enter lens 180. The miiTors 160 and 170 are preferably located in an imaging track (i.e., along the beam path) so as to reflect or fold the beam again, which facilitates the size reduction of module 36. The resultant slow axis beams exiting from the cylindrical lenses 140, 150, ISO form an image of the exit face of the mixer blade at the center 210 of modulator 15. The combination or group of lenses 140, 150 is capable of directing and focalizing slow-axis rays emerging from the output of the optical mixer 130 to the focal point 500 of lens 180, which is capable of directing slow-axis rays from the focal point 500 to the modulator 15. This arrangement of the cylindrical lenses 140, 150, 180 also has telecentric characteristics along the slow axis. Thus, a uniform distribution of hght on the modulator 15 can be generated for the image. The uniform distribution of hght using modulator 15 is also described in co-assigned U.S. Patent No. 6,137,631, the entire disclosiu'e of which is incorporated herein by reference.
Before reaching the modulator, the beams are directed to another cylindrical lens 190 which focalizes and directs the beams of the fast axis to the active zone of the modulator 15. The width of the resultant beams (e.g., a bundle of rays) is limited at an entrance to the modulator 15 by certain mechanical elements 200 (e.g. stops). One exemplary modulator 15 can be a TIR-type modulator whose active zone has a column of 256 active elements which are controlled by four drivers 350 (e.g., SUPERTEX INC HV5770S, available from Supertex, Inc., Sunnyvale, Ca). The modulation of hght as well as the projection of modulated light for the projection of

individual light brushes (as described below) may be achieved using the modulation and projection techniques and equipment described in, for example, U.S. Patent Nos. 4,746,942 and 6,137,631, both of which are incorporated herein by reference in their entirety. As shown and described in copending U.S. Patent No. 6,222,666, the entire disclosure of which is incorporated herein by reference, the modulator 15 can be divided into an active imaging central zone which is controlled by one or more drivers for imaging a column of 256 spots and lateral zones. These drivers (e.g., drivers 350) can be directly attached to crystal 220, and may be enc^sulated to increase their resistance to shock. The modulator 15 preferably operates in the mode known as a "bright field." Thus, the beams are directed to modulator 15 which modifies or configures these beams using drivers 350 and mechanical elements 200.
In particular, the light beams 5" enter the crystal 220 via crystal face 230 angled by five degrees relative to the normal at a plane of the crystal 220. Thus, the beams are deviated in the crystal 220, and submitted to a total reflection in the active zone of the modulator 15 with a small angle of incidence. The modified beams 5'" exit the crystal 220 in a direction which is perpendicular to the plane of the crystal 220 after another reflection of the beams at prismatic face 240 of the crystal 220 takes place. The composition of the crystal 220 is preferably selected so as to avoid photorefi-action effects (e.g., imaging damage, DC drift, etc.) at high energy density. A preferred crystal composition is LiNbCh with about 5 mol% of MgO or about 7 mol% of Zn. In a particularly prefenred embodiment, the modulator is a TIR modulator comprising a total reflection crystal having at least one prismatic edge enable of deviating rays by 90 degrees.
Thereafter, as shown in Figure 3B, beams 5"' reach lens 260 via another mirror 250. Lens 260 is capable of collecting rays emerging from the active zone to form an image (500') on stop element (270), which is capable of eliminating unwanted rays. Mirror 250redirectsthebeams toward stop element 270 preferably located close to the Fourier transform plane at the focus of lens 260 for the purpose of blocking rays of higher diffraction order as is well known in the art. A calibrated opening or slit of stop element 270 allows the undiflfracted rays to go through and proceed toward the following optical elements. In one embodiment of the invention.

the stop element is independent of the objective group cornprismg elements 280, 290, 300, 310 and 320. The same circulating coolant such as a water circuit used by the laser bar may be used to insure thermal stability. The height of this image is adjusted by changing the distance between spherical lens 260 and stop element 270. Accurate centering of image 340' on the aperture of the stop element is obtained by the lateral displacement of lens 180. Rays emerging from the aperture of element 270 enter imaging lens group 280. 290, 300, 310, 320 and 330. These lenses relay the image 340' 01 the exit face 240 of modulator 220 to the photosensitive face of the plate 400 u'here ii is shown at 340. Lens 320 of the objective lens assembly can be used to modify the focal plane without affecting the size of image 340.
It is another object of the invention to reduce the size of each head by folding beams as schematically represented in Figure 2C, placing the optical components in substantially the same plane, as shown also in Figures 2A and 2B. In this manner the height of the head is considerably reduced and the width of the head (represented by W in Figure 7) is kept at its minimum. The plane represented by the folded beams is preferably perpendicular to the bmsh image 340. It is thus possible to produce compact modules of reduced height and minimum width (W=30nmi).
The objective assembly may also be provided with an optional protective cover 330 composed of quartz. A support element (not shown) can be auached to the objective assembly to allow certain accurate displacements of the objective assembly's axis which are perfonned as a fimction of the offset of the focalized bundle of rays (or beams) which fomi the image 340. Such adjustment makes it possible to obtain a spatial position of the focalized beam preferably identical for all imaging modules in the imaging assembly (discussed further herein) in relation to particular reference points.
In another embodiment of this invention, the compact imaging module or head which may be employed in the assembly and method of this invention is as depicted in Figures 9 and 10. Figure 9 represents the interior view of the components of a duplex imaging head which contains laser sources 510 and 510' which are typically a laser diode as previously described with respect Figiu-es 2A-2B and 3A-3C. The beams from laser source 510 are directed to a corresponding first set of

optical arrangements wnicn compnses lenses 560 ana 5/0 naii-wave blade 550, polarizing cube 540 and lens 580. Similarly, the beams from laser source 510' are directed to a corresponding optical arrangement which comprises lenses 560* and 570', half-wave blades 550 and 550', polarizing cube 540' (not shown) and lens 580' (not shown). The beams emerging from the corresponding first optical arrangements are directed to a first common optical arrangement which in this embodiment comprises mirror 600A and lenses 610A and 620A. The image of the emitters from laser sources 510 and 510' exit the first common optical arrangement via lens 620A and respectively form an image of the laser sources at the input faces of second corresponding optical arrangements which in this embodiment comprise imaging blades 630 and 630' as shown. The beams emerge from mixing blades 630 and 630' and are directed to a second common optical arrangement which in this embodiment comprises lenses 640A and 650A and mirrors 660A and 670A. The beams are then respectively directed to third corresponding optical arrangements comprising lenses 680 and 690 (for laser source 510) and lenses 680' (not shown) and 690' (for laser source 510'). The beams emerge from the third corresponding optical arrangements and the beams of the corresponding fast axes are directed to an active zone of modulators 720 and 720', respectively. These modulators are of the configuration and operate as the modulators previously described with respect to Figures 2A-2B and 3A-3C. The beams emerge from the modulators 720 and 720' and are respectively directed to corresponding fourth optical arrangements as shown in Figure 9, which comprise lens 760, mirrors 740 and 750, and imaging lens group G (for laser source 510), and lens 760', mirrors 740' and 750', and imaging lens group G' (for laser source 510'). As is also depicted in Figure 9, the imaging lens groups G and G' are offset in a direction perpendicular to the travel path of the scanning carriage as is explained further herein. The ofiset corresponds to the offset shown as 51 in Figure IC described herein. The beams are projected by imaging lens groups G and G' to the imageable medium (e.g. printing plate) to be imaged.
Figure 10 depicts a view of the exterior of the imaging assembly of Figure 9. In Figure 10, the housing 1000 contains the elements previously described

with respect to Figure 9, and the housing may be detachably or fixably coupled to the carriage, as is further described herein.
In additional embodiments of this invention, the imaging module or head used in this invention may compromise the optical elements described m U.S. Patent No. 6,169,565, which is incorporated herein by reference.
Modular Imaging Assembly
A modular imaging assembly in accordance with the present invention refers to the assembly of identical interchangeable imaging heads referred to as modules detachably coupled or mounted on a common carriage. Figures lA, IB, IC and ID schematically illustrate various embodiments of the present invention. One of the objects of this invention is to increase the production speed of platesetters in which the printing plate and the imaging optics are moveable relative to each other to produce successive joining bands of pixels to image a printing plate. Such systems are described, for example, in U.S. Patent Nos. 4,746,942 and 4,819,018, and WO 00/49463, all of which are incorporated herein by reference. The number of pixels that can be produced and projected by a single imaging module to form a band of pixels is limited for the reasons discussed above. In theorx', if it were possible to manufacture an imaging module or head no larger than the width of a brush (for example 256 pixels) several heads 44 could be affixed face to face on a common carriage (as shown in Fig. 1 A), thus increasing the number of pixels that could be swept across a plate for imaging in one excursion of the carriage. However, such an arrangement is impossible in the present state of the art. The width of each head would be limited to the width of a brush, for example to 5.2 mm to produce adjacent brushes of 256 pixels of 20 microns. An assembly of four such theoretical heads, each one-brush-wide, is illustrated in Figure 1 A.
Figure IB represents an assembly of four modules or heads 38 mounted side by side on a common carriage using technology available to those skilled in the art prior to this invention. For example, each head may be magnetically removably attached to the carriage on which it may be accurately positioned by pins, as is well known in the art. As shown in Fig. IB, this arrangement is unacceptable

because gaps 45 would be left between each band of pixels or brushes 34*. It is an important object of this invention to eliminate such gaps.
This object of the present invention is accomplished by the imaging assembly of this invention schematically illustrated in Fig. IC, representing schematically various components of a flat-bed platesetter such as described in WO 00/49463 in detail. Imaging carriage 37, sliding on rails 52 moves or traverses continuously from one edge of plate 42 to the other edge for the projection of a swath of pixels on a light or heat sensitive medium for imaging thereof Four joining bands (i.e. 34-r, 34-2', 34-3' and 34-4') each 256 pixel-wide, are projected at each excursion of carriage 37, from left to right and vice versa. The result is the projection of a swath 46 having a width of 1024 pixels at each excursion of the carriage. This result is obtained, as shown on the left side of Fig. IC, by locating individual imaging modules or heads M-1 to M-4 (projecting pixel brushes 34-1, 34-2, 34-3, and 34-4 respectively to generate respective bands 34-1', 34-2', 34-3' and 34-4') at different levels 38-1, 38-2,38-3 and 38-4 of the carriage. These levels are precisely determined such that consecutive pixel brushes 34-1, 34-2, 34-3 and 34-4 are exactly aligned, so that the bottom portion of a brush abuts exactly the top portion of an adjacent brush as per the orientation of Figures IC and ID. The modules are thus aligned with respect to one another such that the plurahty of modules imagewise produce laser hght which is a summiation of each individual light brush produced by each module. This ahgnment is achieved by employing the stair-like arrangement of the modules as described above, coupled with the delay in the imagewise projection of each brush image or swath, which is accomplished as discussed below.
It will be apparent to those skilled in the art that the operation of the system described above and depicted in Fig. IC requires adequate differential timing or compensation for the projection of each band. Referring to the operation of a similar carriage as described in WO 00/49463, as carriage 37 travels from an extreme location (i.e. the near side of the imaging area) shown on the left side of Figure IC to the right (arrow F2) carriage 37 comprises an edge detector coupled with a signal generator which generates pulses that continuously inform (via detectors, etc. which are not shown) an electronic controller (not shown) of the position of carriage 37

at the plane level 400. Consequently, the beana width depends on the esseniially variable smile of the laser diodes. The width of the beam is also imposed by the value of the diffraction limit, consequently by the width and distribution of rays on lens The latter depends on the positioning accuracy of the collimating lens 20 mrefraction the emitters and on the spacing between lenses 60 and 70. A small departure ideal position of coUimating lens 20 results in a significant change of the direvitaves of the beam affecting the width of the "diffraction limited" beam at plane level For example, by reducing by one micron the distance between the emitters -and the coUimating lens 20 relative to its theoretical position where the beam is perfect t coUimated, the beam divergence is increased, thus the width of the beam on leu 1 -and the width of the "diffraction limited" spot changes from 42 to 28 micron, i in. variations in the positioning of coUimating lens 20 result in changes of the width of the beam at plane level 400.
It follows from the above that increasing the smile causes an of the width of the beam whereas increased divergence causes its reduction 'therpal is to balance these two effects to obtain a beam of constant width for all module Whtn the diode has a low smile, divergence will be reduced to increase ihc width diffraction. This reduction of the divergence is obtained by increasing the spacturam lenses 60 and 70 (Fig. 4C). However, if the smile is more important, the divergence win be increased by reducing the spacing between lenses 60 and 70. The divergence may be adjusted by adjusting the spacing between lenses 60 and 70 to obtain a been of constant width at the image location at plane level 400 where the wnting focahzed and is also the location of the sensitive face of the printing plate Accordingly, for example, in one embodiment, lens 60 is negative, F= - 40 mm causing the divergence of rays and lens 70 is positive, F= + 50 mm causing tiu-convergence of rays. By adjusting the spacing between these lenses it is possible compensate for the divergence variations of different laser diodes. Theoret principle of compensation by adjustment of the divergence is possible withon: 60 and 70 by adjusting only the location of coUimating lens 20. Thus, as depreted Figs. 4A-4C and described herein, the divergence of the rays may be adjust ed

1. An imaging assembly comprising:
a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative to a desired image area; and
a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module composes at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each module is aligned with respect to the other modules such that the plurality of modules image wise produces laser light which is a summation of each individual light brush produced by each module, and each module comprises a signal receiver which causes a delay in the image wise production of laser energy from each individual module.
2. The assembly of Claim 1, in which the carriage is capable of traversing in a single excursion a distance greater than a desired image area, and the plurality of modules produces a contmuous band of laser hght which is the summation of each individual light bums produced by each module with each traverse of the carriage across the desired image area.
3. The assembly of Claim 1, in which each module is venically offset from the other modules.
4. The assembly of Claim 1, in which the assembly contains four modules.
5. The assembly of Claim 1, in which the modulator is a TIR modulator.
6- The assembly of Claim 1, in which each module is capable of
producing 256 pixels of image wise laser hght.

7. The assembly of Claim 1, in which the laser light source
comprises a plurality of laser diodes.
8. An imaging assembly comprising:
a moveable carriage; and
apluraliry of imaging modules coupled to the carriage \ ii i MI each module is adjacent to at least one other module and each module comprise a laser light source and a modulator cooperatively arranged to produce an mdixuiu i light brush;
means for aligning each module with respect to the oihci modules such that the pluraUty of modules imagewise produces laser hght whi. i; i summation of each individual light brush produced by each module; and
means for delaying the imagewise production of laser energy from each individual module in response to an input signal conveying information regarding the position of the carriage relative to a desired image area.
9. An imaging system comprising:
(a) an imaging assembly comprising:
(i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relatively desired image area, and
(ii) a plurality of imaging modules coupled to the carriage, wherein each module is adjacent to at least one other module, each module comprises at least one laser hght source and a modulator cooperatively arranged in produce an individual light brush, and each module is aligned with respect to the modules such that the plurality of modules imagewise produces laser light which is summation of each individual hght brush produced by each module, and each module comprises a signal receiver which causes a delay in the imagewise production of the energy from each individual module; and
(b) a flat platesetter cooperatively arranged with the
imaging assembly such that the imaging assembly imagewise provides laser energy
a printing plate residing in the platesetter.

10. An imaging system comprising:
(a) an imaging assembly comprising:
(i) a moveable carriage comprising a signal generator for generating a signal indicative of the location of the carriage relative desired image area, and
(ii) aplurality of imaging modules coupled to the carriage, wherein each module comprises at least one laser light source and a modulator cooperatively arranged to produce an individual light brush, each aligned with respect to the other modules such that the plurality of modules imagewise produces laser Hght which is a summation of each individual lighit : produced by each module, and each module comprises a signal receiver which a delay in the imagewise production of laser energy for each individual module and
(b) a rotating drum cooperatively arranged uith the
imaging assembly such that the imaging assembly imagewise provides laser energy
a printing plate residing on a surface of the rotating drum.
11. A method of preparing a printing plate comprising:
(a) providing an imaging assembly comprising.
(i) a moveable carriage comprisuig a signal generator for generating a signal indicative of the location of the carnage relatively desired image area, and
(ii) a plurality of imaging modules coupled to carriage, wherein each module is adjacent to at least one other module, each moduler comprises at least one laser hght source and a modulator cooperatively arranged in produce an individual hght brush, each module is aligned with respect to theother; modules such that the pIuraHty of modules imagewise produces laser light which summation of each individual hght brush produced by each module, and each n comprises a signal receiver which caiises a delay in the imagewise production of the energy from each individual module;
(b) providing a printing plate for imaging; and
(c) imagewise providing laser light to the printing plant using the imaging assembly.

12. The method of Claim 11, in which the plate resides in a flat platesetter cooperatively arranged with the imaging assembly.
13. The method of Claim 11, in which the plate resides on a of a rotating drum cooperatively arranged with the imaging assembly.
14. An imaging system comprising:
a moveable carriage capable of traversing movement aciu width of a radiation receptive medium;
a plurality of imagmg heads selectively positioned on thc carriage, wherein each head comprises at least one laser source, modulating mean modulating the laser energy and projection means for projecting the modulated la r: energy cooperatively arranged such that the laser source, modulating means amd projection means produce at least one individual light brush and each head produce at least one separate band of light brushes during each traverse of the carriage ac ic , the width of the medium;
compensating means for adjusting the projection of the seprate bands such that the separate bands are projected during each traverse of the carriage form a continuous band having a width equal to the cumulative width of the seprate bands;
means for stepwise moving the medium in a direction perpendicular to the traversing movement of the carriage;
means for controlhng the length and position of the carriage traverse across the width of the medium; and
means for detecting the location of the cairiage relative to the edges of the medium and means for timing the projection of the separate bands responsive to the detecting means.
15. The imaging assembly of Claim 1, in which the laser power:
different modules is equalized by a shunt.

16. A laser imaging assembly comprising:
a carriage capable of moving over a photosensitive m aplurality of optical modules selectively positioned on the
carriage wherein each module comprises a laser source and associated optical
components and each module projects a brush of radiant energy wherein each :
is removably attached to the carriage; and
locating means on the carriage to position each module n.
relation to selected reference points.
17. The assembly of Claim 16, in which each module is magnetically removably attached to the carriage.
18. The assembly of Claim 16, in which the locating means comprises a signal detector, an encoder, and an electronic controller which arc operaiively associated to provide to locate the carriage.
19. The assembly of Claim 1, in which each module is provided with adjustable locating elements thereby enabhng each module to be independence adjusted on a jig to enable locadon of each module brush according to x, y and . coordinates.
20. An optical projection head comprising:
a laser diode array having a plurality of emitters;
a TIR modulator capable of diffracting light rays from the according to an apphed electric field;
an optical mixer capable of equalizing the energy beams the array;
a first group of optical components capable of shaping and directing energy rays from the laser array to the mixer;
a second group of oprical components capable of direcuting emerging from the mixer to the modulator;
a lens capable of focahzing rays emerging from the modulate to a stop element capable of eliminating unwanted diffracted rays; and

an imaging objective assembly capable of focusing rays emerging from the stop element to a radiation sensitive media thereby producing image wherein the optical assembly comprises means for adjusting the divergence rays from the modulator to a selected value affecting the width of the image
21. An optical projection head comprising:
a laser diode array having a plurality of emitters capabk i i producing energy rays along a slow axis and a fast axis which are mutually perpendicular;
a TIR modulator capable of diffracting energy rays from the array according to an apphed electric field;
an optical mixer capable of equalizing the energy beams from the array;
a first group of optical components capable of shaping and directing energy rays from the laser array to the input of the mixer;
a cylindrical lens unit capable of directing and focalizuing axis rays emerging from the output of the mixer to the focal point of a cylindrical capable of directing slow-axis rays from the focal point to the modulator;
a lens capable of directing and concentrating fast-axis the active zone of the modulator ;
a lens capable of coUecting rays emerging from the active to form an image of the point on a stop element capable of eliminating unwards rays; and
an objective assembly capable of projecting an image on photosensitive surface.
22. The head of Claim 20, in which the adjusting means include pair of lenses.
23. An optical head comprising:
a laser source of beams at an input end and image formed beams at the output end; and

a plurality of optical components along said beams betweenthe input and output ends to obtain an image from the beams wherein the beams are folded a plurality of times between the input and output ends by reflecting siina
24. The head of Claim 23, in which the folded beams arc i a plurality of parallel surfaces.
25. The head of Claim 20, in which the modulator comprises LiNbOa crystal having about 5 mol. % MgO or about 7 mol. % Zn.
26. The head of Claim 21, in which the modulator comprises LiNbOs crystal having about 5 mol. % MgO or about 7 mol. % Zn.
27. The head of Claim 20, in which the modulator is a TIR modulator having one or more drivers.
2S. The bead of Claim 21, in which the modulator is a TIK modulator having one or more drivers.
29. The head of Claim 27, in which the modulator drivers are direct] V attached to a crvstal of the modulator.
30. The head of Claim 28, m which the modulator drivers ait directly attached to a crystal of the modulator.
31. The head of Claim 29, in which the crystal and dnvers are encapsulated.
32. The head of Claim 30, in which the crystal and drivers are encapsulated.
33. The head of Claim 20, in which the laser diode and the stop
element are cooled by a circulating coolant.
34. The head of Claim 21, m which the laser diode and the stop
element are cooled by a circulating coolant.

An imaging assembly substantially as herein described with reference to the accompanying drawings,
52. An optical head substantially as herein described with reference to the accompanying drawings.

Documents:

1837-chenp-2003 abstract granted.pdf

1837-chenp-2003 claims granted.pdf

1837-chenp-2003 description(complete) granted.pdf

1837-chenp-2003 drawings granted.pdf

1837-chenp-2003-assignement.pdf

1837-chenp-2003-claims.pdf

1837-chenp-2003-correspondnece-others.pdf

1837-chenp-2003-correspondnece-po.pdf

1837-chenp-2003-description(complete).pdf

1837-chenp-2003-drawings.pdf

1837-chenp-2003-form 1.pdf

1837-chenp-2003-form 3.pdf

1837-chenp-2003-form 5.pdf

1837-chenp-2003-other documents.pdf

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Patent Number

227067

Indian Patent Application Number

1837/CHENP/2003

PG Journal Number

07/2009

Publication Date

13-Feb-2009

Grant Date

01-Jan-2009

Date of Filing

21-Nov-2003

Name of Patentee

KODAK POLYCHROME GRAPHICS GMBH

Applicant Address

AN DER BAHN 80 37520 OSTERODE/HARZ.

Inventors:

#	Inventor's Name	Inventor's Address
1	MOULIN, MICHAEL	RUE D'ENHAUT 16 CH-1143 APPLES.

PCT International Classification Number

G02B26/08

PCT International Application Number

PCT/US02/14780

PCT International Filing date

2002-05-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	09/865,345	2001-05-25	U.S.A.