JP2006085072A - Multi-beam exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-beam exposure device for stably recording halftones, by using a means for selectively on/off turning a plurality of pixels of a two-dimensional optical modulator or the like, and using an FM screen. <P>SOLUTION: The multi-beam exposure device miniaturizes so as to make an exposure beam spot BS flat, in the scanning direction by arranging a means for making the diameter small at a position being a parallel light flux on an optical path, at a position having a substantially conjugate relation with the lens system imaging position on an optical path leading to the upper part of an exposure face of a recording medium, from a light source installed on an exposure head. Thereby the multi-beam exposure device makes the edge part of the both sides of the scanning direction exposure amount distribution in each beam spot BS forming one dot steep, and performs exposure processing, in a state where the longitudinal direction both sides of the edge part is along the scanning direction. The exposure head preferably suppresses image unevenness, in a direction orthogonal to the scanning direction so as not to be influenced by the variations in the coloring threshold of the recording medium and intensity variation or the like of a laser beam, and records so as to express the intermediate tone stabilized by using the FM screen. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, each light emitted from a spatial light modulation element (two-dimensional light modulator) or the like, which is means for selectively turning on / off a plurality of pixels installed in an exposure head based on image data (pattern data). The present invention relates to a multi-beam exposure apparatus that performs exposure with a predetermined pattern by condensing a light beam for each pixel by an optical element and irradiating a recording medium.

  In recent years, a recording medium such as a lithographic printing plate using a spatial light modulation element (two-dimensional light modulator) such as a digital micromirror device (DMD) as a pattern generator and a light beam modulated according to image data Development of a multi-beam exposure apparatus that performs image exposure on the top is in progress. Since this spatial light modulation element (two-dimensional light modulator) has a configuration in which pixels that modulate incident light are two-dimensionally arranged, it has the merit that it can also be used in a spatially incoherent light source, a so-called lamp. Have. Further, the spatial light modulation element (two-dimensional light modulator) can reduce the light power irradiated per unit pixel as compared with the one-dimensional light modulator arranged in one dimension depending on the method of use. Therefore, it is expected to be widely used for multi-beam exposure apparatuses.

  This DMD is a mirror device in which a large number of micromirrors whose reflecting surfaces change in response to a control signal, for example, are two-dimensionally arranged on a semiconductor substrate such as silicon, and the electrostatic force generated by charges stored in each memory cell. Thus, the angle of the reflection surface of the micromirror is changed.

  In such a multi-beam exposure apparatus using a DMD, for example, a laser beam emitted from a light source that emits a laser beam is collimated by a lens system, and a plurality of DMD micro-arrays arranged at substantially focal positions of the lens system are used. Each beam emitted after being two-dimensionally modulated by reflecting the laser beam with a mirror is condensed for each pixel by a lens system, and is exposed on the exposure surface of a recording medium (lithographic printing plate) which is a photosensitive material. An image is formed with a reduced spot diameter and image exposure is performed.

  That is, in this multi-beam exposure apparatus, each of the DMD micromirrors is controlled on / off by a control device (not shown) based on a control signal generated according to image data or the like to modulate (deflect) the laser beam. Then, exposure is performed by irradiating the exposure surface (recording surface) with the modulated laser beam.

  In this multi-beam exposure apparatus, a lithographic printing plate or the like is arranged on the recording surface, and a laser beam is irradiated onto each of the lithographic printing plate or the like from a plurality of exposure heads provided in the exposure apparatus, and the position of the beam spot imaged. The pattern exposure is performed on the flat printing plate or the like by modulating each DMD according to the image data while moving the plate relative to the flat printing plate or the like. Note that a recording medium such as a lithographic printing plate on which an image is exposed and recorded is subjected to an automatic developing machine as necessary, and a latent image formed on the recording medium such as a lithographic printing plate is converted into a visible image.

  Conventionally, a DMD used in such a multi-beam exposure apparatus is configured to arrange m rows in the scanning direction and n columns in a direction orthogonal to the scanning direction. Further, this DMD is arranged so that the row of pixels is inclined at a predetermined angle with respect to the scanning direction of the exposure head, and by performing multiple exposures N times at different times in the scanning direction, m / N-1 dots can be formed. As described above, it has been proposed to change the dot pitch and increase the resolution in the direction orthogonal to the scanning direction by adjusting the number of multiple exposures in the scanning direction (see, for example, Patent Document 1).

  However, in such a multi-beam exposure apparatus, when a row of DMD pixels is arranged so as to be inclined at a predetermined angle with respect to the scanning direction of the exposure head, and recording is performed by N times multiple exposure while shifting the time in the scanning direction. Then, exposure is performed a plurality of times by shifting the time with pixels inclined obliquely with respect to the main scanning line to form one dot on the lithographic printing plate. At this time, the position of each beam spot subjected to multiple exposure for recording one dot on the lithographic printing plate is shifted in the sub-scanning direction. For this reason, the exposure amount distribution in the recorded dots spreads in the sub-scanning direction, and the recorded dots have a so-called blurred shape in the sub-scanning direction.

  In addition, in a conventional multi-beam exposure apparatus that exposes an image to a lithographic printing plate, an AM screen (a method for forming a gray image by a halftone image) is used when a halftone is expressed by exposing the lithographic printing plate. In general, halftones are expressed in a net shape (so-called minimal checkered pattern). That is, in the AM screen, the halftone dot image of the minimum unit is composed of a relatively large number of dots, for example, a total of 196 dots of 14 (number of dots in the horizontal direction) × 14 (number of dots in the vertical direction). A grayscale image is recorded by recording point images in a two-dimensional plane. However, when halftones are expressed using this AM screen, moire fringes or tone jumps may occur.

  Further, as a technique for forming a grayscale image using a halftone dot image, there is a technique called FM screen (FM Screen). This FM screen expresses the density of a recorded image by a set density of irregular dots having no regularity. For example, an image composed of a relatively small number of dots such as 2 × 2 total 4 dots is displayed. Gradation is expressed by being distributed in a two-dimensional plane. This FM screen has the advantage that the generation of moire fringes can be suppressed in principle.

  Therefore, in a multi-beam exposure apparatus that performs image exposure on a recording medium such as a lithographic printing plate, it is desired to form a halftone with a small net shape using an FM screen.

  However, in a multi-beam exposure apparatus, when recording is performed by a system in which DMD pixel rows are arranged so as to be inclined at a predetermined angle with respect to the scanning direction of the exposure head and the time is shifted in the scanning direction and multiple exposure is performed N times. When multiple exposure is performed to record one dot on a recording medium such as a printing plate, the positions of a plurality of beam spots subjected to multiple exposure with respect to the same exposure point to be one dot are shifted in the sub-scanning direction and recorded. There is a case where the exposure amount distribution of the dots spread in the sub-scanning direction and one recorded dot becomes a so-called blurred shape in the sub-scanning direction.

One dot recorded in this way has a shape that is blurred in the sub-scanning direction, and the image when the FM screen is recorded by exposure in a state where the so-called edge cannot be kept sharp is recorded such as fluctuations in optical power and the number of printed sheets. If the circumference of the recording pixel changes even a little depending on the conditions and development conditions such as the degree of development of the automatic developing machine, the ratio of the halftone image (halftone area ratio characteristic) is likely to change abruptly, and density fluctuations are likely to occur. Therefore, an FM screen is used in a conventional multi-beam exposure apparatus that arranges a row of DMD pixels so as to be inclined at a predetermined angle with respect to the scanning direction of the exposure head and shifts the time in the scanning direction multiple times N times. There is a problem that it is difficult to do.
JP 2004-62156 A

  In view of the above-mentioned problems, the present invention uses a means for selectively turning on / off a plurality of pixels, such as a two-dimensional optical modulator, and a multi-beam exposure capable of recording a stable halftone expression using an FM screen. The object is to provide a new device.

  The multi-beam exposure apparatus according to claim 1 of the present invention scans an exposure surface of a recording medium by projecting a plurality of exposure beam spots modulated by means for selectively turning on / off a plurality of pixels. In a multi-beam exposure apparatus that performs exposure using an exposure head, a parallel light beam on the optical path is obtained at a position that is substantially conjugate with the imaging position of the lens system on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium. The present invention is characterized in that there is provided a means for reducing the diameter of the exposure beam spot arranged at a position so as to be flattened in the scanning direction.

  By configuring as described above, each light beam passing on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium is narrowed to a flat light beam by the diameter reducing means, and on the exposure surface of the recording medium. By forming the shape of each beam spot into an oval shape (a flat beam spot shape including an ellipse or a shape close to a rectangle) that is short in the scanning direction and long in the direction perpendicular to the scanning direction, one dot is formed. Edge portions of the exposure amount distribution on both sides in the scanning direction in each beam spot to be formed can be sharpened. Therefore, in this exposure head, an exposure process is performed in a state in which the beam spot that is formed into an oblong shape by being flattened is along the scanning direction on both sides in the longitudinal direction where the edge portion of the oval beam spot is steep. I do. That is, in this exposure head, the intensity distribution of each beam spot on the recording medium is oval in the direction orthogonal to the scanning direction, and the edges on both sides in the scanning direction of the condensing point are sharp. And fluctuations in the intensity of the laser beam are hardly affected, and image unevenness in the direction orthogonal to the scanning direction is suitably suppressed. Therefore, the image when the FM screen is recorded has a halftone dot so that the circumference of the recording pixel does not fluctuate at all due to recording conditions such as light power fluctuation and the number of printed sheets, development conditions such as the degree of development of the automatic processor, and the like. It is possible to prevent the image ratio (halftone dot area ratio characteristic) from changing abruptly to make it difficult to cause density fluctuations, and to record halftones stably using an FM screen.

  The multi-beam exposure apparatus according to claim 2 of the present invention scans the exposure surface of the recording medium by projecting a plurality of exposure beam spots modulated by means for selectively turning on / off the plurality of pixels. In a multi-beam exposure apparatus that performs exposure using an exposure head, a parallel light beam on the optical path is obtained at a position that is substantially conjugate with the imaging position of the lens system on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium. A plurality of light beams emitted so as to be arranged two-dimensionally from a means for reducing the diameter of the exposure beam spot so as to be flat in the scanning direction and a means for selectively turning on / off a plurality of pixels. The exposure beam is arranged on an optical system that forms an image on the exposure surface, and a plurality of exposure beams arranged two-dimensionally are divided into a plurality of blocks in the scanning direction. Exposure adjacent to the direction orthogonal to the scanning direction projected on the exposure surface by at least one block by shifting the relative position between the blocks in the direction orthogonal to the scanning direction and projecting onto the exposure surface. And a partial pixel shift member that exposes a position during exposure with the beam spot with an exposure beam spot projected onto an exposure surface by the other block.

  By configuring as described above, each light beam passing on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium is narrowed to a flat light beam by the diameter reducing means, and on the exposure surface of the recording medium. By forming the shape of each beam spot into an oval shape (a flat beam spot shape including an ellipse or a shape close to a rectangle) that is short in the scanning direction and long in the direction perpendicular to the scanning direction, one dot is formed. Edge portions of the exposure amount distribution on both sides in the scanning direction in each beam spot to be formed can be sharpened. Therefore, in this exposure head, an exposure process is performed in a state in which the beam spot that is formed into an oblong shape by being flattened is along the scanning direction on both sides in the longitudinal direction where the edge portion of the oval beam spot is steep. I do. That is, in this exposure head, the intensity distribution of each beam spot on the recording medium is oval in the direction orthogonal to the scanning direction, and the edges on both sides in the scanning direction of the condensing point are sharp. And fluctuations in the intensity of the laser beam are hardly affected, and image unevenness in the direction orthogonal to the scanning direction is suitably suppressed. Therefore, the image when the FM screen is recorded has a halftone dot so that the circumference of the recording pixel does not fluctuate at all due to recording conditions such as light power fluctuation and the number of printed sheets, development conditions such as the degree of development of the automatic processor, and the like. It is possible to prevent the image ratio (halftone dot area ratio characteristic) from changing abruptly to make it difficult to cause density fluctuations, and to record halftones stably using an FM screen. In this multi-beam exposure apparatus, the multi-beam emitted from the means for selectively turning on / off a plurality of pixels is divided into a plurality of blocks in the scanning direction by a partial pixel shift member, and the blocks are scanned with each other. By shifting in a direction orthogonal to the direction and projecting onto the exposure surface, exposure is performed, and multiple exposure is performed for each row by each of a plurality of rows of exposure beam spots arranged in the scanning direction to be exposed in one block, and two-dimensionally. Thus, each dot can be recorded. Therefore, the position of each beam spot subjected to multiple exposure for recording each dot is accurately matched to prevent the spread of the exposure amount distribution in each dot, and the FM screen while keeping the edge of the recorded dot shape sharp. Can be recorded. In addition, the number of dots that can be exposed at one time (the number of beam spots) can be increased in the direction orthogonal to the scanning direction. For this reason, in this multi-beam exposure apparatus, for example, an enlargement optical system is used to enlarge the area of the exposure area when the beam spot is projected onto the exposure surface by the two-dimensional optical modulator, and the scanning process for the recording medium is performed. The efficiency of the exposure process can be improved by improving the speed. In this multi-beam exposure apparatus, for example, the exposure process is performed in a state where the pitch between adjacent beam spots is reduced in the direction orthogonal to the scanning direction when the beam spot is projected onto the exposure surface by the two-dimensional optical modulator. Thus, so-called resolution (positional resolution) can be improved.

  According to a third aspect of the present invention, in the multi-beam exposure apparatus according to the first or second aspect of the present invention, the diameter reducing means is constituted by a beam reducer.

  By configuring as described above, in addition to the operation and effect of the invention according to claim 1 or 2, the beam reducer is provided at a predetermined position on the optical path from the light source to the exposure surface of the recording medium. Since it can be configured simply by arranging, it can be simplified and manufactured at a low cost.

  According to the multi-beam exposure apparatus of the present invention, it is possible to record a stable halftone expression using an FM screen using a means for selectively turning on / off a plurality of pixels such as a two-dimensional light modulator. There is.

  A first embodiment relating to a multi-beam exposure apparatus of the present invention will be described with reference to FIGS.

  Although not shown, the image forming apparatus as the multi-beam exposure apparatus according to the first embodiment of the present invention is configured as a so-called flatbed image forming apparatus (setter) that is driven and controlled by a control unit. As shown in FIG. 11, a recording medium 12 such as a lithographic printing plate (PS plate) is placed on the moving stage 10, and the recording medium 12 is moved in the main scanning direction by the moving stage 10 while being exposed by the exposure head 14. The control unit is configured to perform exposure processing by spatially modulating the multi-beam emitted from the light source based on the modulation signal generated from the image data and irradiating the recording medium 12 with the multi-beam.

  The exposure area 16 by the exposure head 14 is configured in a rectangular shape having a short side in the feed direction (main scanning direction), for example. In this case, a strip-shaped exposed region 18 is formed on the recording medium 12 in accordance with the scanning exposure moving operation. In the image forming apparatus (setter), a plurality of exposure heads 14 are arranged in an approximate matrix of m rows and n columns (for example, 2 rows and 4 columns), and a plurality of (for example, 8) exposure heads 14 are simultaneously used. You may comprise so that an exposure process may be performed.

  As shown in FIG. 1, this exposure head 14 uses a digital micromirror device as a spatial light modulator (two-dimensional light modulator) that modulates an incident light beam for each pixel in accordance with image data. (DMD) 20 is provided. The DMD 20 which is a two-dimensional optical modulator is driven and controlled by a control unit (control means) 22 having data processing means and mirror drive control means.

  The data processing unit of the control unit 22 controls driving of the micromirrors in the region to be controlled by the DMD 20 to the exposure head 14 based on the input image data (control of the angle of each micromirror reflecting surface). Control signal is generated.

  Connected to the light incident side of the DMD 20 in the exposure head 14 are bundle optical fibers 28 each drawn from a light source unit 24 that is an illumination device that emits multi-beams as laser light.

  The light source unit 24 is provided with a plurality of multiplexing modules 26 that combine laser beams such as ultraviolet rays emitted from a plurality of semiconductor laser chips and input them to an optical fiber. The optical fiber extending from each multiplexing module 26 is a multiplexing optical fiber that propagates the combined laser beam, and a plurality of optical fibers are bundled into one to form a bundle-shaped optical fiber (fiber bundle) 28. The laser beam is configured to improve the intensity of the emitted laser beam.

  On the light incident side of the DMD 20 in the exposure head 14, there is provided a mirror 32 that reflects the laser light emitted from the connection end of the bundle optical fiber 28 toward the DMD 20 through an optical lens having a rod lens or the like. Arrange the illumination optical system.

  As shown in FIG. 10, the DMD 20 is entirely monolithic as a mirror device in which a plurality of micromirrors 36 (for example, 600 × 800) constituting a pixel (pixel) are arranged in a lattice pattern. (Integrated type).

  A material having high reflectivity such as aluminum is deposited on the surface of the micromirror 36 disposed at the top of each pixel. In addition, a column 34 projects from the center of the lower surface of each micromirror 36.

  This DMD 20 is provided with a pillar 34 projecting from a micromirror 36 on a hinge 40 provided on a silicon gate CMOS SRAM cell 38 which is manufactured in a normal semiconductor memory manufacturing line corresponding to each pixel. And the micromirror 36 is mounted so as to be tiltable by ± a degrees (± 10 degrees) in the diagonal direction about the hinge 40 as an axis.

  Further, in this DMD 20, static electricity due to charges accumulated on one side or the other side of each of the mirror address electrodes 42 respectively formed at both ends in the diagonal direction in which the micromirrors 36 on the SRAM cell 38 are inclined. Utilizing force, the micromirror 36 is configured to be driven and controlled to be in a state tilted to + a degrees when the micromirror 36 is in an on state or in a state tilted to -a degrees when the micromirror 36 is in an off state.

  In the DMD 20 configured as described above, when a digital signal is written to the SRAM cell 38, the micromirrors 36 in the respective pixels of the DMD 20 correspond to the substrate side on which the DMD 20 is disposed with the diagonal line as the center in accordance with the image signal. Thus, the light is incident on the DMD 20 and is reflected in the tilt direction of each micromirror 36.

  The light reflected by the on-state micromirror 36 is modulated into an exposure state and enters a projection optical system (see FIG. 1) provided on the light exit side of the DMD 20. The light reflected by the micromirror 36 in the off state is modulated into a non-exposure state and enters a light absorber (not shown).

  Next, a projection optical system (imaging optical system) provided on the light reflection side of the DMD 20 in the exposure head 14 will be described. As shown in FIG. 1, since the projection optical system (imaging optical system) provided on the light reflection side of the DMD 20 in the exposure head 14 forms an image on the recording medium 12 on the exposure surface on the light reflection side of the DMD 20, In order from the DMD 20 side toward the recording medium 12, the first imaging optical lens systems 44 and 46, a microlens array 48 that is an intermediate imaging unit, and a rear vicinity position on the optical path from the microlens array 48. The exposure optical members of the partial pixel shift member 50, the second imaging optical lens systems 52 and 54, and the autofocus prism pair 56 are arranged. Although not shown in the drawing, the exposure head 14 may be configured by disposing aperture arrays at positions near the front and rear of the microlens array 48 on the optical path.

  In this projection optical system, the first imaging optical lens system 44, 46 has an elliptical shape in which the shape of the beam spot formed on the exposure surface on the recording medium 12 is short in the scanning direction and long in the direction perpendicular to the scanning direction. A beam reducer 61 (a means for reducing the diameter of the exposure beam spot so as to be flattened in the scanning direction) is formed for shaping into a shape (including an ellipse or a shape close to a rectangle).

  For this reason, the first imaging optical lens systems 44 and 46 are configured to be parallel light beams on an optical path between the lens system 44 on the light source side and the lens system 46 on the recording medium side.

  In the first imaging optical lens systems 44 and 46, a beam reducer 61, which is a light beam conversion lens, is disposed on an optical path between the lens system 44 on the light source side and the lens system 46 on the recording medium side. The beam reducer 61 as a diameter reducing means for reducing the size of the exposure beam spot so as to be flat in the scanning direction is configured as an optical element having optical characteristics opposite to those of the beam expander. That is, the beam reducer 61 includes a thick parallel light beam and includes an oval shape (an ellipse or a shape close to a rectangle) in which the shape of the beam spot on the exposure surface is short in the scanning direction and long in the direction orthogonal to the scanning direction. It is configured to have a function of reducing to a thin parallel light beam that is narrowed to have a flat beam spot shape.

  Further, the exposure head 14 is configured so that a position (image formation position) condensed by the microlens of the microlens array 48 and a position where a flat beam can be formed by the beam reducer 61 are in a substantially conjugate relationship. The beam spot shape collected by each microlens is configured to be a flat beam shape (flat light beam) narrowed in the scanning direction (main scanning direction).

  Further, in the exposure head 14, the light is focused on the micromirror 36 of the DMD 20 in the optical system on the light incident side from the light source unit 24 to the DMD 20 (including the illumination optical system of the exposure head 14). The image forming optical lens systems 44 and 46, the second image forming optical lens systems 52 and 54, and the image forming positions of the respective lens systems such as the microlens array 48). It may be arranged.

  As described above, the beam reducer 61 is arranged at a predetermined position on the optical path from the light source unit 24 to the condensing point on the recording surface of the recording medium 12 (for example, each position having a substantially conjugate relationship with the condensing position). In this case, each light beam passing on the optical path is narrowed into a flat light beam by the beam reducer 61, and the shape of each beam spot on the exposure surface of the recording medium 12 is shortened in the scanning direction as shown in FIG. In addition, by forming a long oval shape (a flat beam spot shape including an ellipse or a shape close to a rectangle) in a direction orthogonal to the scanning direction, the scanning direction (main scanning) in each beam spot forming one dot (Direction) Edge portions of the exposure amount distribution on both sides can be sharpened.

  Therefore, in this exposure head 14, the beam spot that is made thin and flattened into an oval shape scans both sides in the longitudinal direction where the edge portion of the oval beam spot becomes steep in the scanning direction (in the sub-scanning direction). The exposure processing is performed in a state along the (perpendicular direction). That is, in this exposure head 14, the intensity distribution of each beam spot on the recording medium 12 is oval in the sub-scanning direction, and the edges on both sides in the scanning direction of the condensing point are sharp. And fluctuations in the intensity of the laser beam are hardly affected, and image unevenness in the sub-scanning direction is suitably suppressed. Therefore, the image when the FM screen is recorded has a halftone dot so that the circumference of the recording pixel does not fluctuate at all due to recording conditions such as light power fluctuation and the number of printed sheets, development conditions such as the degree of development of the automatic processor, and the like. It is possible to prevent the image ratio (halftone dot area ratio characteristic) from changing abruptly to make it difficult to cause density fluctuations, and to record halftones stably using an FM screen.

  In this exposure head 14, instead of using the beam reducer 61, although not shown, a means for reducing the diameter of the exposure beam spot so as to be flat in the scanning direction may be configured using a beam expander. it can. When using this beam expander to configure a means for reducing the diameter of the exposure beam spot so that it is flattened in the scanning direction, the parallel beam is projected onto the exposure surface by extending it into a flat beam using the beam expander. The shape of each beam spot is extended in a direction perpendicular to the scanning direction (sub-scanning direction) to form an oval shape (a flat beam spot shape including an ellipse or a shape close to a rectangle), and the scanning direction (main The edge portions of the exposure amount distribution on both sides (scanning direction) may be configured to be sharp. In this case, the beam spot extended in the sub-scanning direction by the beam expander may be reduced to a required size by the microlens of the microlens array 48 or the like.

  The microlens array 48 serving as an intermediate imaging unit used in the projection optical system of the exposure head 14 has a one-to-one correspondence with each micromirror 36 of the DMD 20 that reflects the laser light emitted from the light source unit 24 through the optical fiber 28. A plurality of microlenses are integrally formed, and each microlens is disposed on the optical axis of each laser beam transmitted through the first imaging optical lens systems 44 and 46, respectively. In this exposure head 14, the micro lens array 48 may be omitted, and a part of the pixel shift member 50 may be arranged at the arrangement position of the micro lens array 48 shown in FIG.

  The partial pixel shift member 50 used in the exposure head 14 of this image forming apparatus has the number of dots that can be exposed at one time in the direction orthogonal to the scanning direction (beam spot number) when performing exposure processing using the DMD 20. The number of channels, which is a number, is increased by effectively using the vertical pixels of the DMD 20, and in combination with the beam reducer 61, a stable halftone expression can be recorded satisfactorily using an FM screen. It is an optical member for.

  The partial pixel shift member 50 has a plurality of exposure beam spots projected onto the exposure surface (the surface of the recording medium 12) from a group of micromirrors 36 arranged in a two-dimensional grid of M rows and N columns in the DMD 20. Are divided into a plurality of blocks with respect to the scanning direction (main scanning direction which is the feed direction) on the exposure surface, and the relative positions between these blocks are orthogonal to the scanning direction (main scanning direction) ( The DMD 20 is used so that the gap in the feed direction at the position of the plurality of exposure beam spots exposed in one block is exposed with the plurality of exposure beam spots in the other block. During the exposure process, the number of dots that can be exposed at one time (the number of channels that is the number of beam spots) is increased in the direction orthogonal to the scanning direction.

  Note that the number of dots that can be exposed at one time (by dividing the position of the exposure beam spot projected onto the exposure surface from the exposure head 14 into a plurality of blocks on the exposure surface in a direction orthogonal to the scanning direction ( The increase rate of the number of dots that can be exposed (the number of channels that is the number of beam spots) when increasing the number of channels that is the number of beam spots) is divided into blocks, and the exposure positions for each block overlap each other. Since it is proportional to the number of divisions of blocks shifted so as not to be shifted (for example, shifted to equal intervals), the required increase rate of the number of dots that can be exposed (the number of channels that is the number of beam spots) is the number of divisions It can be set by appropriately adjusting and selecting the shift amount.

  The partial pixel shift member 50 may be configured as an optical element using light refraction, an optical element using light diffraction, or an optical element using light polarization. As an element utilizing light diffraction, there are a hologram and a binary optical element blazed.

  When the partial pixel shift member 50 is configured as an optical element using light refraction, for example, the partial pixel shift member 50 is configured as shown in FIGS. 2, 3, and 8. A plurality of optical materials such as optical glass formed on a planar member having the same thickness (three in the partial pixel shift member 50 shown in FIGS. 2, 3 and 8). May be used). That is, as shown in FIG. 2, the partial pixel shift member 50 moves the first optical member 50A, the second optical member 50B, and the third optical member 50C in the scanning direction (feeding direction) on the optical path. ), The second optical member 50B is arranged so as to be orthogonal to the optical axis, and the first optical member 50A is inclined at a predetermined angle with respect to the optical axis. The third optical member 50C is disposed at a predetermined angle with respect to the other optical axis. In other words, the partial pixel shift member 50 is provided with the first optical member 50A for refraction, the second optical member 50B, and the third optical member 50C at positions located on the upper, middle, and lower stages on the optical path. The upper and lower first optical members 50A and the third optical member 50C are installed in a state (shown in FIG. 3) rotated by a predetermined angle about the scanning direction.

  Further, the second optical member 50B has a length (distance between the first optical member 50A and the third optical member 50C) with respect to the scanning direction (feeding direction) of the DMD 20 at the position where the partial pixel shift member 50 is disposed. The optical path width corresponding to the scanning direction (feeding direction) of the optical path from all the micromirrors 36 to the exposure surface (the surface of the recording medium 12) is set to a length equal to three. Further, the second optical member 50B has an optical path whose central position in the scanning direction corresponds to the scanning direction of the optical path from all the micromirrors 36 of the DMD 20 to the exposure surface at the position where the partial pixel shift member 50 is disposed. Arrange to match the center of the width.

  With this arrangement and configuration, the partial pixel shift member 50 divides the group of micromirrors 36 two-dimensionally arranged in the DMD 20 into three equal parts in the scanning direction on the exposure surface (the beam in the scanning direction). It is possible to set three blocks G1, G2, and G3 that are equally divided as illustrated in FIG.

  Further, in the partial pixel shift member 50 configured as an optical element using light refraction, the angle at which the first optical member 50A is inclined to the one side with respect to the optical axis is appropriately adjusted and set as shown in FIG. As shown in FIG. 8, the beam spot group BS1 of the first block G1 is refracted in the direction orthogonal to the scanning direction of the beam spot group BS2 in the second block G2, as shown in FIG. It is configured to shift to one side by a distance of 1/3 between adjacent lines (for example, 1/3 pitch shift to the left in FIG. 2).

  Further, in this partial pixel shift member 50, the multi-beam of laser light is refracted as shown in FIG. 3 by appropriately adjusting and setting the angle at which the third optical member 50C is inclined to the other with respect to the optical axis. Then, the beam spot group BS3 of the third block G3 is shifted to the other side by a distance of 1/3 between each other arranged adjacent to each other in the direction orthogonal to the scanning direction of the beam spot group BS2 in the second block G2. For example, it is configured to shift 1/3 pitch to the right as viewed in FIG.

  By disposing the partial pixel shift member 50 in this way, the exposure head 14 of this image forming apparatus is configured so that the beam spots BS2 in the second block G2 are adjacent to each other with respect to the direction orthogonal to the scanning direction. Furthermore, the exposure processing can be performed in a state where the beam spots BS1 of the first block G1 and the beam spots BS3 of the third block G3 are arranged at equal intervals. Therefore, in the exposure head 14 in which the partial pixel shift member 50 is arranged and configured as described above, as a result of performing scanning exposure on the exposure surface as shown in FIG. 8, once with respect to a position on a straight line in a direction orthogonal to the scanning direction. The number of dots that can be exposed to (number of channels, which is the number of beam spots) is increased by a factor of three (the pitch between adjacent beam spots has been reduced to ３, so-called resolution (positional resolution) has been improved by a factor of three. State).

  In the exposure head 14 that sets the three blocks G1, G2, and G3 that are mutually shifted by the partial pixel shift member 50, the second imaging optical lens systems 52 and 54 are configured as, for example, an enlargement optical system, By enlarging the cross-sectional area of the light beam reflected by the DMD 20, the area of the exposure area 32 (shown in FIG. 11) by the light beam reflected by the DMD 20 on the recording medium 12 is latticed. You may comprise so that it may expand to 3 times the area of the light reflection surface comprised by arranging in a shape.

  In the case where the second imaging optical lens systems 52 and 54 are configured as an enlargement optical system, for example, a microlens array or other optical member is used to form a connection on the exposure surface of the recording medium 12. Each beam spot to be imaged may be condensed so as to be reduced in size so as to have a predetermined beam spot diameter.

  Further, in the exposure head 14, the light beam projected from the second imaging optical lens system 52, 54 is focused on the recording medium 12 placed on the exposure surface by the autofocus function of the prism pair 56. To form an image. Note that each of the first imaging optical lens systems 44 and 46 and the second imaging optical lens systems 52 and 54 in the projection optical system is shown as one lens in FIG. A lens (for example, a convex lens and a concave lens) may be combined.

  When the exposure head 14 is configured as described above, scanning is performed once in the direction orthogonal to the scanning direction on the exposure surface of the recording medium 12 under the condition that the feed speed in the scanning direction is the same. Comparison in the case where scanning exposure is performed with only a predetermined number of micromirrors 36 arranged in a direction orthogonal to the scanning direction of DMD 20 shown in FIG. 9 (when DMD 20 is tilted in the scanning direction and exposure processing is not performed). Can be 3 times the example.

  Therefore, when performing exposure processing on the entire exposed surface of the recording medium 12 while reciprocating the recording medium 12 in the scanning direction using the same number of exposure heads 14, the scanning processing speed (the same number of exposures). The efficiency of the exposure process can be improved by using the head 14 to improve the speed from the start to the completion of the exposure process for one recording medium 12.

  Further, in the exposure head 14 for setting a plurality of (here, three) blocks G1, G2, and G3 that are mutually shifted by the partial pixel shift member 50, the second imaging optical lens systems 52 and 54 are shifted. It is configured as an optical system having an enlargement ratio less than the number of blocks (here, an enlargement ratio less than 3 times), and is scanned only by a predetermined number of micromirrors 36 arranged in a direction perpendicular to the scan direction of the DMD 20 shown in FIG. Compared to the case of exposure processing in the comparative example in the case of exposure, the pitch between adjacent beam spots in the direction orthogonal to the scanning direction may be reduced to improve the so-called resolution (positional resolution). Of course.

  In the exposure head 14 for setting a plurality of (here, three) blocks G1, G2, and G3 that are mutually shifted by the partial pixel shift member 50, the three blocks G1 and G2 are formed on the exposure surface of the recording medium 12. , It is impossible to perform exposure processing by clearly distinguishing the pixels at the boundary of G3 (exposure processing by clearly separating pixels at the boundary of the three blocks G1, G2, and G3). , Crosstalk may occur between pixels at the boundary of G3. In such a case, in order to reduce the crosstalk, it is possible to cope with not using the pixel on the DMD 20 that hits the boundary.

  The partial pixel shift member 50 is configured to be divided into two blocks and shifted by a combination of the first optical member 50A or the third optical member 50C and the second optical member 50B, or the partial pixel shift. The member 50 may be configured to be divided into two blocks and shifted by a combination of the first optical member 50A and the third optical member 50C.

  Next, a configuration example in which the partial pixel shift member 50 described above is configured as an optical element using light diffraction will be described with reference to FIGS.

  The partial pixel shift member 50 configured as an optical element using light diffraction shown in FIG. 4 is a single flat plate made of optical glass or the like formed on a transparent flat member having the same thickness. It is divided into three areas (parts) of an upper stage, a middle stage, and a lower stage with respect to the (scanning direction), and the upper stage is a first diffracting unit 50D, the middle stage is a second transmitting unit 50E, and the lower stage is a third diffracting unit 50F.

  The second transmission unit 50E is configured to transmit a light beam along a straight optical path, and has a length (between the first diffraction unit 50D and the third diffraction unit 50F) with respect to the scanning direction (feed direction). The optical path width corresponding to the scanning direction (feeding direction) of the optical path from all the micromirrors 36 of the DMD 20 at the arrangement position of the partial pixel shift member 50 to the exposure surface (the surface of the recording medium 12). Set the length to Further, the second transmission portion 50E has an optical path whose central position in the scanning direction corresponds to the scanning direction of the optical path from all the micromirrors 36 of the DMD 20 to the exposure surface at the position where the partial pixel shift member 50 is disposed. Arrange to match the center of the width.

  With this arrangement and configuration, the partial pixel shift member 50 divides the group of micromirrors 36 two-dimensionally arranged in the DMD 20 into three equal parts in the scanning direction on the exposure surface (the beam in the scanning direction). It is possible to set three blocks G1, G2, and G3 that are equally divided as illustrated in FIG.

  In the partial pixel shift member 50 configured as an optical element using this light diffraction, the front and back surfaces of the first diffractive portion 50D diffract the light beam in the direction orthogonal to the scanning direction as shown in FIG. On the other hand, the first BOE (binary optics element) 51 is provided which has an effect of shifting the beam spot by a predetermined amount.

  Further, a second BOE (binary optics element) that acts to diffract the light beam on the front and back surfaces of the third diffractive portion 50F and shift the beam spot by a predetermined amount in the other direction orthogonal to the scanning direction as shown in FIG. ) 53.

  The first BOE 51 and the second BOE 53 are processed and formed as commonly used binary optics elements. For example, the first diffractive portion in the plate-shaped optical glass that partially forms the entire pixel shift member 50 is used. The front and back both surface portions of the 50D and the third diffractive portion 50F are formed by processing inclined surfaces that are fine in sectional view (actually, a so-called etching process is repeated to form a fine step-like inclination in the recesses). be able to.

  The first BOE 51 and the second BOE 53 are finely extending linearly from one end to the other end in the direction orthogonal to the scanning direction on both the front and back surfaces of the first diffractive part 50D and the third diffractive part 50F. It is configured as an inclined surface having a substantially triangular cross section. In the first BOE 51 and the second BOE 53, the height of the fine substantially sectional triangle (height of the step) is n, the refractive index of the diffractive member, the refractive index of air, the light wavelength λ, and the number of steps. When N, it is formed to be an integral multiple of the following formula.

  formula

これら第１ＢＯＥ５１と、第２ＢＯＥ５３とは、理論的に、それぞれの凹部内の傾斜に形成された微細な階段部分の段数（レベル）が８レベルの傾斜面の場合に、第１ＢＯＥ５１と、第２ＢＯＥ５３とで所定の方向に回折される光の割合が約９５％となり、１６レベルの傾斜面の場合に約９８．７％，３２レベルで９９．５％となる。従って、第１ＢＯＥ５１と、第２ＢＯＥ５３とは、露光面上での迷光限界に応じて１６レベルあるいは３２レベル程度に加工することで、十分実用に耐え得るものとなる。

In theory, the first BOE 51 and the second BOE 53 are the first BOE 51, the second BOE 53, Thus, the ratio of light diffracted in a predetermined direction is about 95%, about 98.7% in the case of a 16-level inclined surface, and 99.5% in 32 levels. Therefore, the first BOE 51 and the second BOE 53 can be sufficiently put into practical use by processing them at 16 levels or 32 levels according to the stray light limit on the exposure surface.

  Further, the first diffractive portion 50D provided with the first BOE 51 and the third diffractive portion 50F provided with the second BOE 53 can be understood by comparing FIGS. 5 and 6 with the binary optics element. The direction of inclination is reversed, and the direction in which the light beam is diffracted by the first BOE 51 to shift the position of the beam spot, and the direction in which the light beam is diffracted by the second BOE 53 to shift the position of the beam spot. It is configured to be in the reverse direction.

  Furthermore, the first diffractive portion 50D provided with the first BOE 51 and the third diffractive portion 50F provided with the second BOE 53 are irradiated with beams on the exposure surface of the recording medium 12 by changing and adjusting the respective thicknesses. The shift amount of the spot position can be set to a predetermined amount.

  In addition, when the partial pixel shift member 50 provided in the exposure head 14 of the multi-beam exposure apparatus is configured as an optical element using light diffraction, the partial pixel shift member 50 described above uses light refraction. Functions and effects similar to those of the optical element can be obtained.

  Further, the partial pixel shift member 50 is configured to be divided and shifted into two blocks by a combination of the first diffractive part 50D or the third diffractive part 50F and the second transmissive part 50E, or a partial pixel shift. The member 50 may be configured to be divided into two blocks and shifted by a combination of the first diffractive part 50D and the third diffractive part 50F.

  Next, a configuration example in which the partial pixel shift member 50 described above is configured as an optical element using polarization of light will be described with reference to FIG.

  The partial pixel shift member 50 configured as an optical element using the polarization of light shown in FIG. 7 is formed on a transparent flat plate having the same thickness, and has an upper stage, a middle stage, and a scanning direction (main scanning direction). The upper stage divided into the lower three areas (parts) is the first polarizing section 50G, the middle stage is the second transmitting section 50H, and the lower stage is the third polarizing section 50I.

  The second transmission unit 50H is configured to transmit the light beam through a straight optical path, and has a length with respect to the scanning direction (feed direction) (distance between the first polarization unit 50G and the third polarization unit 50I). Is a length obtained by equally dividing the optical path width corresponding to the scanning direction (feeding direction) of the optical path from all the micromirrors 36 of the DMD 20 at the arrangement position of the partial pixel shift member 50 to the exposure surface (the surface of the recording medium 12). Set to Further, the second transmission portion 50H has an optical path whose center position in the scanning direction corresponds to the scanning direction of the optical path from all the micromirrors 36 of the DMD 20 at the arrangement position of the partial pixel shift member 50 to the exposure surface. Arrange to match the center of the width.

  With this arrangement and configuration, the partial pixel shift member 50 divides the group of micromirrors 36 two-dimensionally arranged in the DMD 20 into three equal parts in the scanning direction on the exposure surface (the beam in the scanning direction). It is possible to set three blocks G1, G2, and G3 that are equally divided as illustrated in FIG.

  Hereinafter, a case where light having a polarization direction parallel to the shift direction partially enters the pixel shift member will be considered.

In the partial pixel shift member 50 configured as an optical element using the polarization of the light, the first polarization unit 50G is formed by a generally used beam display sensor, and a light beam (light beam) is formed on the beam display sensor. ) Is shifted to one of the directions orthogonal to the scanning direction. The beam display sensor is configured such that the crystal optical axis is inclined by 45 ° in the direction of shifting the beam with respect to the normal to the incident surface. Further, the third polarizing unit 50I is generally used as a beam display. It is configured so as to shift the emission direction of the extraordinary ray generated by transmitting the light beam (light beam) through the beam display sensor to the other of the directions orthogonal to the scanning direction. That is, the light beam is polarized by the first polarizing unit 50G and the position of the beam spot projected on the exposure surface is shifted, and the light beam is polarized by the third polarizing unit 50I and projected on the exposure surface. The beam spot position is shifted in the opposite direction. Further, the first polarizing unit 50G and the third polarizing unit 50I change and adjust the thicknesses of the first polarizing unit 50G and the third polarizing unit 50I so that the shift amount of the position of the beam spot projected on the exposure surface of the recording medium 12 is set to a predetermined amount. Can be set.

  Various methods are conceivable as a method for making the polarization direction of the light parallel to the shift direction. For example, the polarizing plate 58 may be installed before entering the 50.

  Note that the partial pixel shift member 50 provided in the exposure head 14 of the multi-beam exposure apparatus is configured as an optical element using polarization of light, and the partial pixel shift member 50 described above utilizes refraction of light. Functions and effects similar to those of the optical element can be obtained.

  Further, the partial pixel shift member 50 is configured to be divided into two blocks and shifted by a combination of the first polarizing unit 50G or the third polarizing unit 50I and the second transmission unit 50H, or the partial pixel shift The member 50 may be configured to be divided into two blocks and shifted by a combination of the first polarizing unit 50G and the third polarizing unit 50I.

  Next, the exposure head 14 is arranged so that the grid-like arrangement direction of the group of micromirrors 36 coincides with the scanning direction and the direction orthogonal to the scanning direction, and the partial pixel shift member 50 described above is provided, so that the two-dimensional of the DMD 20 is provided. The group of micromirrors 36 arranged in the same manner is divided into three on the exposure surface in the scanning direction, and three blocks G1, G2, and G3 equally divided as illustrated in FIG. The operation and effect when the exposure process is performed on the image 12 will be described.

  As illustrated in FIG. 8, when the exposure head 14 exposes a first exposure point position aligned in a direction orthogonal to the scanning direction, multiple exposure is performed with three beam spot groups BS1 belonging to the block G1. To do. Further, when exposing the second exposure point position adjacent to the first exposure point position (position on the right side in FIG. 8), multiple exposure is performed with the three beam spot groups BS2 belonging to the block G2. To do. Further, when exposing a third exposure point position adjacent to the second exposure point position (position on the right side in FIG. 8), multiple exposure is performed with the three beam spot groups BS3 belonging to the block G3. . A plurality of predetermined exposure points arranged in the direction orthogonal to the scanning direction in this way are selected and subjected to multiple exposure, and the recording medium 12 is moved in the scanning direction to thereby adjust the exposure range of the recording medium 12. An exposure process is performed on the whole.

  Therefore, when the above-described grid-like arrangement of the group of micromirrors 36 is arranged so as to coincide with the scanning direction and exposure processing is performed on the recording medium 12 by the exposure head 14 provided with a partial pixel shift member 50, the main scanning line. A plurality of exposures are performed at different times with pixels arranged along the line to form one dot on the recording medium 12. At this time, since one dot is recorded on the recording medium 12, the position of each beam spot subjected to multiple exposure can be accurately matched (matched to the same position), so that the exposure amount distribution in one dot to be recorded is sub-scanned. The edge of the recorded dot shape can be kept sharp without spreading in the direction. For this reason, in this exposure head 14, the beam reducer 61 described above forms the shape of the beam spot into an oval shape (including an ellipse or a shape close to a rectangle) that is short in the scanning direction and long in the direction perpendicular to the scanning direction. Since the FM screen can be recorded with dots with sharp edges by multiple exposure at the same position in combination with the action and effect of the above, recording conditions such as optical power fluctuation and number of printed sheets, automatic processor Depending on development conditions such as the degree of development, the perimeter of the recording pixel changes and the ratio of halftone images (halftone area ratio characteristic) is prevented from changing suddenly to prevent density fluctuations. Record key expressions.

  Next, the operation of the exposure head of the multi-beam exposure apparatus configured as described above will be described.

  In this multi-beam exposure apparatus, image data corresponding to the exposure pattern is input to the control unit 22 connected to the DMD 20 and temporarily stored in a memory in the control unit 22. This image data is data representing the density of each pixel constituting the image by binary values (whether or not dots are recorded).

  The recording medium 12 is moved after the exposure head performs one scan from the upstream side to the downstream side in the scanning direction while being attracted to the surface of the moving stage (not shown) (the moving stage is stopped during scanning). When the recording medium 12 on the moving stage passes under the exposure head 14, the image data stored in the memory is sequentially read out for each of a plurality of lines, and the read image data is read by a control device as a data processing unit. The control signal (control data) corresponding to the two-dimensional arrangement of the exposure beam spot divided into a plurality of blocks and shifted by a predetermined distance in the direction orthogonal to the scanning direction is generated based on Is done.

  Based on the generated control signal, each of the micromirrors of the DMD 20 installed in the exposure head 14 is on / off controlled. When the control unit 22 is irradiated with laser light from the light source unit 24, the laser light reflected when the micromirror of the DMD 20 is in an on state is imaged in an oval shape at the required exposure beam spot position. Is done.

  Further, the recording medium 12 is exposed two-dimensionally by the exposure head 14 by repeating the movement of the recording medium 12 after the scanning of the exposure head together with the moving stage.

  In the multi-beam exposure apparatus according to the first embodiment, the DMD is used as the spatial light modulation element used in the exposure head 14. For example, a MEMS (Micro Electro Mechanical Systems) type spatial light modulation element (SLM; Spatial light modulators other than MEMS types, such as Special Light Modulators, optical elements that modulate transmitted light by electro-optic effects (PLZT elements), and liquid crystal light shutters (FLC) can be used instead of DMDs.

  In addition to the spatial light modulation element that takes only the on / off state, a spatial light modulation element that takes a plurality of intermediate values and can express gradation in addition to the on / off state may be used.

  Note that MEMS is a general term for a micro system that integrates micro-sized sensors, actuators, and control circuits based on a micro-machining technology based on an IC manufacturing process. A MEMS-type spatial light modulator is an electrostatic force. It means a spatial light modulator driven by electromechanical operation using

  In the multi-beam exposure apparatus according to the present embodiment, the DMD 20 that is a spatial light modulation element used in the exposure head 14 may be replaced with a unit that selectively turns on / off a plurality of pixels. The means for selectively turning on / off the plurality of pixels includes, for example, a laser light source that can selectively emit on / off a laser beam corresponding to each pixel, or each minute laser emission surface. Is arranged corresponding to each pixel to form a surface-emitting laser element, and each micro-laser light-emitting surface can be selectively turned on / off so as to be able to emit light.

  Next, a second embodiment of the present invention will be described with reference to FIGS. In the exposure head according to the second embodiment, only the beam reducer 61 is provided and some pixel shift members are not provided.

  The exposure head 14 shown in FIG. 12 includes a digital micromirror device (DMD) 20 as a spatial light modulation element (two-dimensional light modulator) that is driven and controlled by a control unit (control means) 22.

  Further, the exposure head 14 includes illumination optical lens systems 63 and 65 for emitting laser light emitted from the light source unit 24 as an illumination device toward the DMD 20 on the light incident side of the DMD 20.

  Further, the exposure head 14 is provided with a projection optical system (imaging optical system) on the light reflection side of the DMD 20. Since this projection optical system (imaging optical system) forms an image on the recording medium 12 on the exposure surface on the light reflection side of the DMD 20, the first imaging optical system sequentially from the DMD 20 side toward the recording medium 12. Optical members for exposure of the lens systems 44 and 46, a microlens array 48 as an intermediate imaging unit, second imaging optical lens systems 52 and 54, and an autofocus prism pair (not shown) are arranged. Configured. Further, in this projection optical system, the first image-forming optical lens systems 44 and 46 have a beam spot shape focused on the exposure surface on the recording medium 12 that is short in the scanning direction and long in the direction perpendicular to the scanning direction. A beam reducer 61 for forming a circular shape (a shape including an ellipse or a shape close to a rectangle) is disposed.

  For this reason, the first imaging optical lens systems 44 and 46 are configured to be parallel light beams on an optical path between the lens system 44 on the light source side and the lens system 46 on the recording medium side.

  Further, in the first imaging optical lens systems 44 and 46, a beam reducer 61, which is a light beam conversion lens, is disposed on the optical path between the lens system 44 on the light source side and the lens system 46 on the recording medium side. To do. The beam reducer 61 is configured as an optical element having optical characteristics opposite to those of the beam expander. That is, the beam reducer 61 includes a thick parallel light beam and includes an oval shape (an ellipse or a shape close to a rectangle) in which the shape of the beam spot on the exposure surface is short in the scanning direction and long in the direction orthogonal to the scanning direction. It is configured to have a function of reducing to a thin parallel light beam that is narrowed to have a flat beam spot shape.

  In addition, the exposure head 14 is configured so that the position where the light is condensed on the recording medium 12 by the microlens of the microlens array 48 and the position where a flat beam can be formed by the beam reducer 61 are in a conjugate relationship. As shown in FIG. 14, the beam spot shape condensed by each microlens becomes a flat beam shape (flat light beam) narrowed in the scanning direction (main scanning direction), and the exposure surface on the recording medium 12 To be projected onto the screen.

  In the exposure head 14 according to the second embodiment, as shown in FIG. 13, in the optical system on the light incident side from the light source unit 24 to the DMD 20 (including the illumination optical system of the exposure head 14). The position where light is focused on the micromirror 36 of the DMD 20 (the imaging positions of the lens systems such as the first imaging optical lens systems 44 and 46, the second imaging optical lens systems 52 and 54, and the microlens array 48). The beam reducer 61 may be arranged at a position substantially in a conjugate relationship with (including). In this case, the illumination optical lens systems 63 and 65 are configured to be parallel light beams on the optical path between the lens system 63 on the light source side and the lens system 65 on the recording medium side.

  As described above, the beam reducer 61 is placed at a predetermined position on the optical path from the light source unit 24 to the condensing point on the recording surface of the recording medium 12 (for example, each predetermined position having a substantially conjugate relationship with the condensing position). When arranged, each light beam passing through the optical path is narrowed into a flat light beam by the beam reducer 61, and the shape of each beam spot on the exposure surface of the recording medium 12 is changed in the scanning direction as shown in FIG. Are formed in an elliptical shape (a flat beam spot shape including an ellipse or a shape close to a rectangle) that is long and short in a direction perpendicular to the scanning direction. The edge portions of the exposure amount distribution on both sides (in the main scanning direction) can be sharpened. Compared with the comparative example shown in FIG. 15, the difference in exposure amount distribution on both sides in the scanning direction (main scanning direction) in each beam spot forming one dot is clear. Further, in the case shown in FIG. 14 in which the beam reducer 61 is installed in the exposure head 14, compared to the comparative example in FIG. 15, the line shape recorded in the direction perpendicular to the scanning direction on the exposure surface of the recording medium 12. These images can be formed so that the width in the scanning direction is narrow and continuous in the direction orthogonal to the scanning direction.

  Therefore, in this exposure head 14, the beam spot that is made thin and flattened into an oval shape scans both sides in the longitudinal direction where the edge portion of the oval beam spot becomes steep in the scanning direction (in the sub-scanning direction). The exposure process is performed in a state along the (perpendicular direction). That is, in this exposure head 14, the intensity distribution of each beam spot on the recording medium 12 is oval in the sub-scanning direction, and the edges on both sides in the scanning direction of the condensing point are sharp. And fluctuations in the intensity of the laser beam are hardly affected, and image unevenness in the sub-scanning direction is suitably suppressed. Therefore, the image when the FM screen is recorded has a halftone dot so that the circumference of the recording pixel does not fluctuate at all due to recording conditions such as light power fluctuation and the number of printed sheets, development conditions such as the degree of development of the automatic processor, and the like. It is possible to prevent the image ratio (halftone dot area ratio characteristic) from changing abruptly to make it difficult to cause density fluctuations, and to record halftones stably using an FM screen.

  The exposure head 14 may be configured using a beam expander (not shown) instead of using the beam reducer 61.

  Further, when the exposure head 14 performs exposure processing, each beam spot on the recording medium 12 becomes an oval shape in the sub-scanning direction as shown in FIG. In the case where inconvenience occurs in the formation of the recording medium, the DMD 20 may be inclined so that the exposure processing of the recording medium 12 may be performed so that there is no blank between the columns.

  Since the configurations, operations, and effects of the second embodiment other than those described above are the same as those of the first embodiment described above, the same members as those of the first embodiment are denoted by the same reference numerals, Description is omitted.

  Note that the multi-beam exposure apparatus of the present invention is not limited to the above-described embodiments, and is suitable for being configured as a PS plate exposure setter, and in a range not departing from the gist of the present invention. Of course, various other configurations can be adopted.

It is a schematic block diagram which shows the exposure head part of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. It is a schematic perspective view showing a partial pixel shift member using refraction of light used for the exposure head of the multi-beam exposure apparatus according to the first embodiment of the multi-beam exposure apparatus of the present invention. It is a schematic explanatory drawing which shows the effect | action of the partial pixel shift member using the refraction of the light used for the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. FIG. 3 is a schematic perspective view showing a partial pixel shift member using diffraction of light used for the exposure head of the multi-beam exposure apparatus according to the first embodiment of the multi-beam exposure apparatus of the present invention. It is a schematic explanatory drawing which shows the effect | action of the 1st diffraction part in the partial pixel shift member using the diffraction of the light used for the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. . It is a schematic explanatory drawing which shows the effect | action of the 3rd diffraction part in the partial pixel shift member using the diffraction of the light used for the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. . FIG. 2 is a schematic perspective view showing a partial pixel shift member using the polarization of light used for the exposure head of the multi-beam exposure apparatus according to the first embodiment of the multi-beam exposure apparatus of the present invention. It is a schematic explanatory drawing which shows the state of the beam spot projected on an exposure surface at the time of exposing with the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. The comparative example of the state of the beam spot projected on the exposure surface in order to compare and explain the effect under exposure by the exposure head of the multi-beam exposure apparatus according to the first embodiment of the multi-beam exposure apparatus of the present invention It is a schematic explanatory drawing shown. It is a perspective view which shows schematic structure of DMD used for the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. It is a perspective view of the principal part which shows the state which is performing the exposure process with the exposure head of the multi-beam exposure apparatus based on 1st Embodiment regarding the multi-beam exposure apparatus of this invention. It is a schematic block diagram which shows the exposure head part of the multi-beam exposure apparatus based on 2nd Embodiment regarding the multi-beam exposure apparatus of this invention. It is a schematic block diagram which shows the other structural example regarding the exposure head part of the multi-beam exposure apparatus based on 2nd Embodiment regarding the multi-beam exposure apparatus of this invention. It is a schematic explanatory drawing which shows the state of the beam spot projected on the exposure surface from the exposure head of the multi-beam exposure apparatus based on 2nd Embodiment regarding the multi-beam exposure apparatus of this invention. A beam spot shape projected on an exposure surface without using a beam reducer for comparison with a beam spot projected from an exposure head of the multi-beam exposure apparatus according to the second embodiment of the multi-beam exposure apparatus of the present invention It is a schematic explanatory drawing which shows the comparative example.

Explanation of symbols

12 Recording medium 14 Exposure head 24 Light source unit 44 First imaging optical lens system 46 First imaging optical lens system 50 Partial pixel shift member 52 Second imaging optical lens system 54 Second imaging optical lens System 61 Beam reducer 63 Illumination optical lens system 65 Illumination optical lens system

Claims (3)

In a multi-beam exposure apparatus that exposes an exposure head that projects and scans a plurality of exposure beam spots modulated by means for selectively turning on / off a plurality of pixels on an exposure surface of a recording medium.
An exposure beam spot arranged at a position where a parallel light flux on the optical path is formed at a position that is substantially conjugate with the imaging position of the lens system on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium. A multi-beam exposure apparatus provided with a diameter reducing means for reducing the size of the sensor so as to be flat in the scanning direction. In a multi-beam exposure apparatus that exposes an exposure head that projects and scans a plurality of exposure beam spots modulated by means for selectively turning on / off a plurality of pixels on an exposure surface of a recording medium.
An exposure beam spot arranged at a position where a parallel light flux on the optical path is formed at a position that is substantially conjugate with the imaging position of the lens system on the optical path from the light source installed on the exposure head to the exposure surface of the recording medium. A diameter reducing means for reducing the size so as to be flat in the scanning direction;
A plurality of exposure beams emitted so as to be two-dimensionally arranged from the means for selectively turning on / off the plurality of pixels are disposed on an optical system that forms an image on an exposure surface, and the two-dimensional Are divided into a plurality of blocks in the scanning direction, and the relative positions of the blocks are shifted in a direction perpendicular to the scanning direction to project onto the exposure surface. Thus, the exposure position projected on the exposure surface by the other block is the position during exposure by the exposure beam spot adjacent in the direction orthogonal to the scanning direction projected on the exposure surface by at least one of the blocks. A partial pixel shift member exposed by a beam spot;
A multi-beam exposure apparatus comprising: 3. The multi-beam exposure apparatus according to claim 1, wherein the diameter reducing means is constituted by a beam reducer.

Images