Abstract:
The invention relates to a light illumination apparatus comprising at least one exposure head ( 12 ) and at least two light modulating arrangements ( 20 ), each of said two light modulating arrangements ( 20 ) comprising a spatial light modulator ( 31, 32 ) and an associated light emitter arranged for illumination of an illumination surface ( 15 ) via said spatial light modulator ( 31, 32 ), each of said two light modulating arrangements ( 20 ) being digitally controlled, said apparatus comprising means for performing a relative movement between said at least one exposure head and said illumination surface ( 15 ) in at least one direction (x;y).

Description:
FIELD OF THE INVENTION 
   The present invention relates to a light illumination apparatus according to claim  1 . 
   BACKGROUND OF THE INVENTION 
   A typical light illumination apparatus comprises an arrangement adapted for illuminating a light sensitive material. Such material may e.g. comprise printing plates, materials adapted for rapid prototyping, film, etc. The illuminating is performed for the purpose of obtaining certain changes of properties of the illuminated material. Such illumination may thus e.g. result in the establishment of an image on the illuminated material or a certain structure. 
   In order to obtain the desired illumination, light must be modulated. One prior art method of modulating light transmitting to an illumination surface is to apply a single or multiple beam laser, which may be modulated when performing a scanning movement over the illumination surface. 
   Another and more recent way of illuminating an illumination surface is to apply a so-called spatial light modulator. Examples of such modulators may be a DMD, an LCD, etc. The spatial light modulator is adapted for modulating an incoming light beam into a number of individually modulated light beams. 
   A problem of the prior art is that the obtainable modulating speed is somewhat limited due to the nature of the applied light modulators combined with the required energy and illumination speed for some applications. 
   SUMMARY OF THE INVENTION 
   The invention relates to a light illumination apparatus comprising at least one exposure head and at least two light modulating arrangements, each of said two light modulating arrangements comprising a spatial light modulator and an associated light emitter arranged for illumination of an illumination surface via said spatial light modulator,
     each of said two light modulating arrangements being digitally controlled,   said apparatus comprising means for performing a relative movement between said at least one exposure head and said illumination surface in at least one direction.   

   According to the invention it has been realized that a movable exposure head may advantageously comprise two spatial light modulators, thereby facilitating a scanning by means of a two modulators at one time. 
   In an embodiment of the invention, the light illumination apparatus comprises at least one exposure head and at least two light modulating arrangements
     each of said two light modulating arrangements comprising a spatial light modulator and an associated light emitter arranged for illumination of an illumination surface via said spatial light modulator,   each of said two light modulating arrangements being digitally controlled,   said apparatus comprising means for performing a relative movement between said at least one exposure head and said illumination surface in at least one direction.   

   In an embodiment of the invention, said at least two light modulating arrangements are arranged on the same exposure head. 
   In an embodiment of the invention, said relative movement is a scanning movement. 
   In an embodiment of the invention, said relative movement is established by moving the at least one exposure head relative to said illumination surface. 
   In an embodiment of the invention, said relative movement is established by moving said illumination surface relative to the at least one exposure head. 
   In an embodiment of the invention, at least one exposure head comprises two light modulating arrangements. It has thus been established that a cost-effective way of illuminating an illumination surface is by applying two spatial light modulation arrangements in one exposure head, thereby obtaining an illumination arrangement, which may illuminate the illumination surface in a relatively high-speed scanning movement. In this context is noted that an exposure head may be somewhat difficult to deal with when the weight of the moving arrangement increases. 
   In an embodiment of the invention, said relative movement is established by moving said illumination surface relative to the at least one exposure head. 
   In an embodiment of the invention, at least one exposure head comprises two light modulating arrangements. 
   In an embodiment of the invention, said light modulating arrangements are arranged on at least two different exposure heads and where said exposure heads perform scanning movements over the illumination surface. When applying two or more free-running scanning exposure heads, the illumination may be optimized carefully to the illumination surface, thereby avoiding so-called “over-scanning”. In principle, any superfluous scanning may be avoided or at least minimized due to the fact that the scanning performed by the exposure heads may be adapted to avoid any conflicting movement between the applied exposure heads. Thus, a number of free-running exposure heads illuminating an illumination surface by scanning is quite advantageous with respect to efficiency due to the fact that the scanning movement as such ensures a high-speed illumination, while the free-running heads ensure that the illumination of the illumination area may be optimized as described above. 
   According to a further embodiment of the above-described free-running exposure heads, the number may exceed two, e.g. three or further heads in total. Moreover, each head may e.g. comprise two or further illumination arrangements, e.g. of the type described in  FIG. 2 . 
   When said spatial light modulators being arranged so as to illuminate two substantially separate sub-areas of said illumination surface, an advantageous embodiment of the invention has been obtained. 
   When said spatial light modulating arrangements being aligned so that the rows of both light modulators are parallelly oriented, an advantageous embodiment of the invention has been obtained. 
   When said spatial light modulating arrangements being aligned so that the neighboring rows of the two spatial light modulators are positioned substantially so that the distance (DN) between the two neighboring rows of the two spatial light modulators are substantially the same as the distance (DR) between the rows of the individual light modulators, an advantageous embodiment of the invention has been obtained. 
   When the “x-projection” (D 1 ) of the distance between the centers of the two spatial light modulators being less than 200 millimeters, preferably less than 150 millimeters, preferably substantially 120 millimeters, an advantageous embodiment of the invention has been obtained. 
   When the “y-projection” (D 2 ) of the distance between the centers of the two spatial light modulators being less than 50 millimeters, preferably less than 35 millimeters, preferably substantially 25.6 millimeters or 20.5 millimeters when applying SXGA, and XGA respectively, an advantageous embodiment of the invention has been obtained. 
   When the distance between the centers of the two spatial light modulators being less than 121.73 millimeters (XGA) or 122,70 millimeters (SXGA), an advantageous embodiment of the invention has been obtained. 
   According to the invention it has been recognized that a very close positioning of the light modulating arrangements facilitates an improved overall scanning speed in the sense that the effective scanning area is optimized. A minimizing of the distance therefore results in that both spatial light modulators of the exposure head are active as long as possible at the ends of the scanning lines. 
   When said exposure head comprising cooling means, an advantageous embodiment of the invention has been obtained. 
   Cooling means may e.g. comprise electrically driven fans. 
   When each spatial light modulating arrangement comprising individual cooling means, an advantageous embodiment of the invention has been obtained. 
   When said substantially separate sub-areas comprising neighboring surfaces of said illumination surface, an advantageous embodiment of the invention has been obtained. 
   When said at least one direction being substantially transverse to a relative movement of said illumination surface, an advantageous embodiment of the invention has been obtained. 
   When said at least one direction establishing that an illuminated pixel on said illumination surface is illuminated by means of a least two light modulators of said spatial light modulator, an advantageous embodiment of the invention has been obtained. 
   When said at least one direction establishing that an illuminated pixel on said illumination surface is illuminated by means of at least one modulator row of said spatial light modulator, an advantageous embodiment of the invention has been obtained. 
   When said exposure head being movable in at least two directions with respect to said illumination surface, an advantageous embodiment of the invention has been obtained. 
   When said light emitter comprising a light source, an advantageous embodiment of the invention has been obtained. 
   When said light emitter comprising at least on light emitting end of an optical guide coupled to a light source, an advantageous embodiment of the invention has been obtained. 
   When said light emitter comprising a lamp, an advantageous embodiment of the invention has been obtained. 
   When said light emitter comprising a LED matrix, an advantageous embodiment of the invention has been obtained. 
   When said spatial light modulator comprising a DMD chip, an advantageous embodiment of the invention has been obtained. 
   The spatial light modulating array of the illumination arrangements may be a transmissive micro-mechanical shutter array as disclosed in WO 98 47048 and WO 98 47042, which are hereby included by reference. 
   Another type of spatial modulator may be a DMD modulator or e.g. LCD light modulator. 
   When said spatial light modulator comprising a micro-mechanical transmissive light modulator, an advantageous embodiment of the invention has been obtained. 
   When said illumination surface comprising a printing plate, an advantageous embodiment of the invention has been obtained. 
   When said illumination surface comprising a light sensitive material, such as epoxy, an advantageous embodiment of the invention has been obtained. Other light sensitive materials may be applied as well within the scope of the invention such as emulsions for silkscreen printing, PCB emulsions, etc. 
   According to the invention, the illumination arrangement may be applied for so-called rapid prototyping. 
   Moreover, the invention relates to a method of illuminating an illumination surface whereby at least two light modulating arrangements arranged on at least one exposure head, each comprising a spatial light modulator illuminate the illumination surface by a scanning movement. 
   In an embodiment of the invention, said at least two light modulating arrangements are arranged on the same exposure head. 
   In an embodiment of the invention, said at least two light modulating arrangements are arranged on different free-running exposure heads. 
   In an embodiment of the invention, the illumination is performed by means of a light illumination apparatus according to any of the claims  1 – 31 . 

   
     THE FIGURES 
     The invention will be described in the following with reference to the drawings where 
       FIG. 1  illustrates a view of an exposure system, according to an advantageous embodiment of the invention, 
       FIG. 2  illustrates a cross-section of an illuminating arrangement, according an embodiment of the invention, 
       FIG. 3   a  illustrates a scanning pattern of an exposure head with respect to an illumination surface and where 
       FIG. 3   b  illustrates a further scanning pattern of an exposure head with respect to an illumination surface 
       FIG. 4   a  illustrates an advantageous positioning of the illuminating arrangements on the exposure head and where 
       FIG. 4   b – 4   c  illustrate further embodiments of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a view of a few main components of an exposure system, according to an advantageous embodiment of the invention. 
   The illustrated system comprises an exposure head  12  comprising two illumination arrangements  20  arranged for illumination of an illumination surface  15 . The exposure head  12  is suspended in a suspension (not shown). The suspension facilitates movement in the direction of the arrows under control by suitable electronic circuits (not shown). 
   For illustrative purposes, two illumination areas I 1 , I 2  illuminated by the spatial light modulators (e.g. DMD chips) arranged in the illumination arrangements  20  are indicated on the illumination surface. The illumination areas I 1  and I 2 , may e.g. comprise 1024×768 (XGA) pixels or 1280×1024 pixels (SXGA) if applying e.g. TI DMD-chips. The modulated pixels will, if applying a scanning movement, be switched dynamically from row to row (or column to column) thereby applying several pixels (e.g. a complete row of a spatial light modulator) for illumination of a single pixel on the illumination surface. Thereby, the delivered optical energy to a single pixel is increased. 
   According to the illustrated embodiment, the exposure head is moved in the X-direction and the illumination surface  15  is moved stepwise in the Y-direction. 
   Evidently, other relative movements may be applied within the scope of the invention. A further advantageous embodiment of the invention may e.g. imply a relative movement of the exposure head  12  in both directions X and Y while keeping the illumination surface stationary. 
   The spatial light modulating array of the illumination arrangements may be a transmissive micro-mechanical shutter array as disclosed in WO 98 47048 and WO 98 47042, which are hereby included by reference. 
   Another type of spatial modulator may be a DMD modulator. 
     FIG. 2  illustrates a preferred embodiment of one of the light modulating arrangements  20  of  FIG. 1 . The first part  21  of the arrangement  20  produces a focused and uniform beam of light. It comprises a lamp  210 , a lamp driver  211 , a blower  216  and a fan  217 , a protection glass  212 , a shutter  213 , a light-integrating rod  214  and beam shaping optics  215 . 
   The type of lamp  210  depends on the type of plate to be exposed. Possible types comprise conventional short arc bulbs, laser sources, diode arrays and more. A preferred conventional lamp might have a power consumption of 270 W, but the present invention is not in any way limited to this value, nor to the mentioned types of lamps. Alternatives such as 250 W and 350 W may be considered. 
   The light from the lamp  210  is transmitted through a filter (e.g. IR or UV-filter depending on the application)  212 , functioning as an interference filter, and through a shutter mechanism  213 , making it possible to turn off the light beam without turning off the lamp. This is important as most lamp types need time before their light intensity and frequency is unvarying. A blower  216  and a fan  217  ensure the cooling of the lamp  210 . 
   Subsequently the light beam is transmitted through a light-integrating rod  214 . Thereby the light is mixed, making the light throughout the beam uniform with regards to intensity. This ensures that the light in the periphery of the beam has the same intensity as the light in the center of the beam. When the light leaves the light-integrating rod  214 , the beam shaping optics  215  focuses it. 
   The next part of the arrangement  20  modulates the light beam to reflect electronically stored image data. It comprises a light-modulating means  22  and means  224  for directing the unmodulated light beam towards the light-modulating means  22  without disturbing its modulated light beam output. 
   Suited light-modulating means  22  comprises DMD modulators, transmissive shutters including LCD and micro-mechanical shutters and more. For the preferred embodiment of  FIG. 2 , a DMD light-modulating chip  220  mounted on a PCB  221  with a cooling plate  222  and a temperature sensor  223  is used. 
   The light directing means  224  depends on the type of light-modulating means  22  used. For transmissive light modulating means the unmodulated light beam is directed towards one side of the light modulating means, and the modulated light beam is emitted from the other side. In such an arrangement the light directing means  224  might be excluded. 
   For DMD modulators the unmodulated light beam is directed towards the same point as where the modulated light beam is emitted. This necessitates the use of light directing means  224 . In the preferred embodiment of  FIG. 2 , a TIR-prism is used for light directing means. TIR is an abbreviation meaning ‘Total Internal Reflection’. A TIR-prism comprises a surface  225  which will act as a mirror to light coming from one direction (from the left for this specific embodiment), and will let light coming from another direction (from the top for this specific embodiment) straight through. 
   The last part of the arrangement  20  focuses the multiple modulated light beams emitted from the light modulating means  220  on an illumination surface  24  (printing plate). It comprises a set of lenses/a macro lens  230  located within a housing  23 .  FIG. 3   a  illustrates a scanning pattern of an exposure head with respect to an illumination. 
   The illustrated scanning pattern obtained by the light illumination apparatus according to the invention, e.g. the illumination arrangement as described in  FIG. 2 , involves that two illuminating arrangements  31 ,  32  of an exposure head  30   a  perform a relative movement with respect to an illumination surface. Both illumination arrangements  31 ,  32  are arranged on the same exposure head  30   a.    
   One of the illustrated illumination arrangements  31  illuminates the sub areas SUB 1  and the other illumination arrangement  32  illuminates the sub areas SUB 2 . 
   It should be noted that the exposure head  30   a  illuminates the illumination surface by modulated light in both directions in a scanning movement as indicated by the horizontal arrows while shifting between each scanning movement in steps  301 , as indicated by the vertical arrow. 
   The y-axis movement is here performed as steps corresponding to the total transverse scanning width obtained by both light illuminating arrangements in combination. 
     FIG. 3   b  illustrates a further scanning pattern of an exposure head  30   b  with respect to an illumination surface. 
   According to the illustrated embodiment of the invention, an exposure head  30   b  comprises two spatial light modulators  31 ,  32  (the illumination arrangements carrying the spatial modulators are not illustrated). The applied illumination arrangements  31 ,  32  may e.g. both be the illustrated illumination arrangement of  FIG. 2 . According to the illustrated embodiment, two spatial light modulators  31 ,  32  (or the resulting illuminated surface corresponding to I 1 , and I 2  of  FIG. 1 ) are arranged and displaced only in the Y-direction. 
   The exposure head  30   b  is performing a scanning movement back and forth in the X-direction. Moreover, the illumination surface or the exposure head performs a relative movement in the Y-direction involving basically two different steps, a micro step  302  and a macro step  303 . 
   According to the illustrated embodiment, eight sub-areas SUB 1  and eight sub-areas SUB 2  are illuminated by performing the micro-steps  302 . Thereafter, a macro step  303  is performed and a new set of sub-areas, SUB 1  and SUB 2 , is illuminated by performing further micro steps  302 . 
   It should be emphasized that several other scanning methods (patterns) may be applied within the scope of the invention. 
     FIG. 4   a  illustrates an advantageous positioning of the illuminating arrangements (here=optical engines) on the exposure head of e.g.  FIG. 3   a . The illumination arrangement  20 , which e.g. may be the one illustrated in  FIG. 2 , is indicated by dashed lines. 
   The dimensions of the optical engine are very important for the productivity and cost of the machine. The two illuminating arrangements  20  of the exposure head are located so that the obtainable illuminated areas are adjacent in the direction of the y-axis (not to be confused with the scanning and modulator axis). This implies that there is a center distance between the optical engines in the x-axis, see  FIG. 4   a.    
   The mutual distance between the engines in the x-axis implies that it is necessary to expose longer than the actual plate length so that both heads have passed the entire plate (the illumination surface). This superfluous “over-scan” is twice the center distance D 1 . This over-scan reduces the productivity and increases the width of the x-movement and thus the width of the machine. The center distance must therefore be as low as possible. An example of such minimized distance may e.g. be
 
Center distance, x-axis: D1=120 mm
 
Center distance, y-axis: D2=(XGA) 20.48±0.002 mm and D2 (SXGA)=25.6±0.002 mm
 
   The lower limit is defined by the optics and the further illumination arrangement component, e.g. the macro lens  230  of  FIG. 2 . A fixture (not shown) will allow adjustment in the illumination plane, i.e. adjustment in x- and y-axis, and rotation about the z-axis, of the optical engines individually. This implies that the image must be accurately parallel to the flange of the macro lens house, so that both images will be in the same plane. The flange on the house is used to mount the house to the fixture, in the z-direction. The bottom side of the flange will define the focus, so that the optical engines can be mounted against a flat surface, and thus having focus in the same plane. 
     FIG. 4   b  illustrates a further embodiment of the invention, where the apparatus comprises four light modulating arrangements  53 ,  54 ,  55 ,  56 , e.g. of the type illustrated in  FIG. 2 , arranged on an exposure head  50 . 
   The four light modulating arrangements  53 ,  54 ,  55  and  56  all move together due to the fixation to the same exposure head. A scanning may advantageously be performed in several different ways, e.g. according to the principles illustrated in  FIG. 3   a.    
     FIG. 4   c  illustrates a further embodiment of the invention, where the apparatus comprises two light modulating arrangements  62 ,  63 , e.g. of the type illustrated in  FIG. 2 . 
   The illustrated embodiment comprises two separate exposure heads  60 ,  61 , each carrying a modulating arrangement  62 ,  63 . 
   The illustrated embodiment of the invention has the advantage that the illumination, when applying a scanning e.g. in the direction of the illustrated arrows, may be optimized carefully to the illumination surface, thereby avoiding the above-described “over-scanning”. In principle, any superfluous scanning may be avoided due to the fact that the scanning performed by the exposure heads  60 ,  61  may be adapted to avoid any conflicting movement between the applied exposure heads  60 ,  61 . 
   The illustrated embodiment, featuring a number of free-running exposure heads illuminating an illumination surface by scanning, is quite advantageous with respect to efficiency due to the fact that the scanning movement as such ensures a high-speed illumination, while the free-running heads ensure that the illumination of the illumination area may be optimized as described above. 
   Evidently, the embodiment of  FIG. 4   c  may be modified to incorporate fisher illumination heads, e.g. three or further heads in total.