JP2007156185A - Light beam deflector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high-accuracy exposure, by stably matching the focusing position of a light beam for exposure emitted from a light source side on a face to be scanned, by making the light beam reflect on the reflecting face of a deflecting member of a light beam deflector which is rotated at a high speed. <P>SOLUTION: The light beam modulated, according to image information, is emitted from the optical system on the light source side of the light beam deflector to the deflecting member 38 in a circularly polarized state, and the light beam, emitted in the circularly polarized state, is converted into an S-polarized light with a quarter-wave polarizing plate 44 or the like, which is a conversion means, from a circularly polarized light into a linearly polarized light, disposed so as to turn linked with a reflecting face 42, made incident on the reflecting face 42 of the deflecting member 38, deflected on the reflecting face 42 of the rotationally driven deflecting member 38, and scan-exposes a recording medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is suitable for use in an inner drum exposure device (inner surface scanning type light beam scanning exposure device) that scans a photosensitive surface arranged on the inner surface of a cylindrical drum by a laser beam scanning optical system and performs exposure processing. The present invention relates to a light beam deflector that enables high-quality recording by securing a focus position.

  Generally, a photosensitive lithographic printing plate (so-called PS plate) is used for offset printing. In the field of lithographic printing, laser exposure processing is performed based on digital data from a computer or the like, and development processing is performed to convert a latent image formed on the photosensitive lithographic printing plate into a visible image by an automatic processor. A CTP (Computer to Plate) system for making a printing plate directly has been put into practical use.

  In such a CTP system, an inner drum exposure device (inner surface scanning) that conducts a scanning exposure process by introducing a light beam such as a laser beam onto the photosensitive surface of a photosensitive lithographic printing plate that is a recording medium disposed on the inner peripheral surface of a cylindrical drum. Type light beam scanning exposure apparatus) is widely used.

  This inner drum exposure apparatus includes a spinner mirror device as a light beam deflector (monogon scanner). This spinner mirror device reflects a condensed beam from the optical system on the light source side to a spinner mirror that is rotationally driven at high speed, performs deflection scanning in the main scanning direction on the photosensitive surface of the recording medium, and By performing sub-scanning by moving the spinner mirror portion at a constant speed in the axial direction of the arc central axis of the inner drum support by the sub-scanning moving means, exposure processing is performed on the entire photosensitive surface of the recording medium.

  In this light beam deflector (monogon scanner), when the spinner mirror is composed of a prism member, the reflecting surface and the incident / exit surface of the prism member are distorted by the centrifugal force due to high-speed rotation, and the deflection direction and the direction perpendicular thereto In other words, the focal position of the lens becomes different (astigmatism), making it difficult to keep the beam spot small, and the image quality deteriorates.

  For example, a conventional light beam deflector has been proposed in which a prism member is arranged inside a cylindrical housing provided with an opening along an optical path. The reflecting surface of the prism member is inclined 45 degrees with respect to the center line of the cylindrical housing.

  In this light beam deflector, the incident light beam is incident from the opening of the cylindrical housing and reflected by the reflecting surface of the prism member. The reflected light beam is emitted from a side opening formed in the side surface of the cylindrical housing and is collected on the recording medium.

  Since this cylindrical casing is rotated at a high speed (10,000 rpm or more) in order to scan the optical beam, the reflecting surface of the prism member is deformed by a centrifugal force, and aberration is generated in the optical beam.

  Therefore, in the conventional light beam deflector, an optical flat glass plate is disposed in the opening of the cylindrical housing so that the angle with respect to the reflecting surface of the prism member can be adjusted, and the prism member of this optical flat glass plate There has been proposed one that performs wavefront aberration correction to eliminate aberration by adjusting a relative angle with a reflecting surface (see, for example, Patent Document 1).

  However, in such a conventional light beam deflector, when scanning exposure is performed by rotating the prism member at a high speed, a phenomenon that the focal position changes depending on the polarization direction of the light beam reflected on the reflecting surface of the prism member is an experiment. It was confirmed by. This is considered to be a phenomenon in which the focal position changes depending on the polarization direction due to birefringence due to the photoelastic effect because stress distribution is generated inside the prism due to centrifugal force when the prism member is rotated at high speed.

  That is, in such a light beam deflector, the exposure laser beam emitted from the laser light source by the optical system is usually a fixed linearly polarized light.

For this reason, when performing exposure processing with such a light beam deflector, the prism member is rotated and scanned while reflecting the laser beam, which is constant linearly polarized light, by the reflecting surface of the prism member. The polarization direction of the laser beam incident on the reflecting surface of the member changes depending on the scanning position, the focus position changes on the scanning surface, astigmatism occurs depending on the location, and the beam spot is kept small on the exposure surface. Experimentation confirmed the problem that image quality deteriorates.
US Patent No. 5,768,001

  In view of the above-mentioned problems, the present invention reflects the light beam for exposure emitted from the light source side on the reflecting surface of the deflecting member rotated at high speed and performs exposure processing by scanning the photosensitive surface. A light beam that enables the recording of high image quality so that the polarization direction of the light beam from the light source incident on the reflecting surface of the deflecting member is always constant, and the focal position is stably aligned with the scanning surface. It aims at providing a deflector newly.

  In order to record an image on a recording medium, the light beam deflector according to claim 1 of the present invention deflects and scans a light beam modulated in accordance with image information on a reflection surface of a rotationally driven deflection member. In the light beam deflector, a light beam modulated in accordance with image information is emitted toward the deflecting member in a circularly polarized state, and is emitted in a circularly polarized state from the light source side optical system. The circularly polarized light that is installed so as to rotate in synchronization with the reflecting surface is converted into linearly polarized light so that the light beam is converted to S-polarized light with respect to the reflecting surface and is kept incident on the reflecting surface of the deflecting member. And a means for converting to the above.

  According to a second aspect of the present invention, in the light beam deflector according to the first aspect, the optical system on the light source side converts the linearly polarized light beam emitted from the light source into circularly polarized light by the λ / 4 polarizing plate. It is configured as described above.

  With the configuration as described above, the light beam modulated in accordance with the image information is emitted from the optical system on the light source side toward the deflecting member in a circularly polarized state, and is rotated in synchronization with the reflecting surface of the deflecting member. The moving circularly polarized light is converted into a state that becomes S-polarized light with respect to the reflecting surface by means of converting linearly polarized light, and then reflected by the reflecting surface of the deflecting member, and the focal position is stabilized on the scanning surface. Thus, the image can be exposed with high accuracy.

  According to a third aspect of the present invention, in the light beam deflector according to the first or second aspect, the circularly polarized light beam emitted from the optical system on the light source side is converted into S-polarized light with respect to the reflecting surface. A λ / 4 polarizing plate is attached to the incident surface of the deflecting member for installation.

  By configuring as described above, in addition to the operation and effect of the invention according to claim 1 or 2, the λ / 4 polarizing plate can be easily integrated with the deflecting member, and a fixing member can be provided. Since it is not used, the deflection member integrated with the λ / 4 polarizing plate can be configured to be lightweight.

  According to the light beam deflector of the present invention, the light beam for exposure emitted from the light source side is incident on the deflecting member rotating at high speed so that it always becomes S-polarized light on the reflecting surface of the deflecting member. As a result, it is possible to easily and inexpensively manufacture a light beam deflector that can form a high-quality image at high speed by making it possible to stably record the high-quality image by stably adjusting the focal position on the scanning surface. There is.

  Embodiments of the light beam deflector according to the present invention will be described with reference to FIGS. The light beam deflector according to the present embodiment uses a photosensitive lithographic printing plate (so-called PS plate) for offset printing as a recording medium, performs laser exposure processing based on digital data from a computer or the like, and performs photosensitivity with an automatic processor. It is suitable for use in a CTP system in which a latent image formed on a photolithographic printing plate is subjected to a development process for converting it into a visible image and directly plate-making a printing plate.

  1 and 2 show a schematic configuration of a CTP system including an internal drum type image forming apparatus (inner drum exposure apparatus) as a light beam deflector according to the present embodiment.

  This CTP system separates and supplies an automatic feeding apparatus 10 having a printing plate supply cassette 20 and a PS plate (recording medium) 22 which is a photosensitive planographic printing plate in the printing plate supply cassette one by one. A leaf supply device 12, an inner drum exposure device 14, a buffer device 16, and a development processing device 18 are provided.

  In this CTP system, as a recording medium to be subjected to exposure processing, for example, a PS plate or a photopolymer plate in which an image recording layer containing a photosensitive material is formed on a support which is a thin aluminum plate, a silver salt type photosensitive material, or the like Can be used.

  The automatic feeding device 10 in this CTP system stores a plurality of printing plate supply cassettes 20 carried by an operator from the outside on a storage shelf 24 and supplies the required printing plate supply cassettes 20 to the sheet supply device 12. To do.

  The sheet feeding device 12 opens the lid of the supplied printing plate supply cassette 20 and separates the bundle of PS plates 22 accommodated therein by the separation roller 28 one by one while pulling up the bundle by the lifting mechanism 26. To the inner drum exposure device 14. The sheet feeding device 12 includes a slip sheet removing unit 32 that separates and stocks the slip sheet 30 sandwiched between the stacked PS plates 22 to protect the photosensitive surface.

  As shown in FIGS. 2 and 3, the inner drum exposure device 14 as a light beam deflector in the CTP system has an inner surface drum (support body) having an arc inner peripheral surface shape (a shape constituting a part of the cylindrical inner peripheral surface). ) 34 as a base body, and the PS plate 22 is supported along the inner peripheral surface of the inner surface drum 34.

  In this inner drum exposure device 14, the PS plate 22, which is an unrecorded recording medium, is held in a state of being in close contact with the inner peripheral surface of the inner drum 34 by a vacuum suction means (not shown), and then an exposure process. I do.

  In the inner drum exposure device 14, a spinner mirror device 36 as a light beam deflector is disposed at the center of the arc of the inner drum 34. As shown in FIG. 3, the spinner mirror device 36 includes a rotation shaft 40 having a prism member (spinner mirror), a so-called cubic prism (reflecting mirror member) 38 disposed on the top surface, and a spinner driver of a control device (not shown). The motor that is a drive source whose rotation is controlled by the motor can be rotated at a high speed (for example, 10,000 rpm or more). As shown in FIG. 2, the spinner mirror device 36 is configured such that the rotation center axis of the rotation shaft 40 coincides with the arc center axis of the inner surface drum 34.

  In the spinner mirror device 36, a light beam modulated according to image information projected from the optical system on the light source side is reflected on the reflecting surface 42 of the rotating cubic prism 38 which is a deflection member (prism member). Scan exposure in the main scanning direction is performed on the photosensitive surface of the PS plate 22.

  Further, in this inner drum exposure apparatus 14, an exposure light beam modulated in accordance with image information emitted from the light source side is applied to the cubic prism 38, which is a deflection member rotated at high speed, as a deflection member. By making the light incident on the reflecting surface 42 of the cubic prism 38 so as to be always S-polarized light, the focal position can be stably adjusted on the scanning surface so that high-quality recording can be performed.

  For this reason, in this inner drum exposure device 14, the light beam modulated according to the image information projected from the optical system on the light source (not shown) is circularly polarized light, and this circularly polarized light beam is a cubic prism as a deflecting member. The circularly polarized light that rotates integrally with the laser beam 38 is converted into linearly polarized light by a λ / 4 polarizing plate (λ / 4 wavelength plate) 44 that is a means for converting the linearly polarized light into linearly polarized light, and the λ / 4 polarizing plate 44 and the cubic prism 38. Is adjusted so that the light beam for exposure that is converted into linearly polarized light by the λ / 4 polarizing plate 44 and enters the cubic prism 38 is always S-polarized light with respect to the reflecting surface 42. Configure.

  As means for converting circularly polarized light into linearly polarized light (S-polarized light), in addition to the λ / 4 polarizing plate, a polarizing filter (polarizer), a Glan-Thompson prism as a polarizing prism, a Glan-Ether prism as a polarizing prism, and the like are used. Can be configured. In addition, when the λ / 4 polarizing plate 44 is used as means for converting circularly polarized light into linearly polarized light, it is advantageous because the amount of light can be prevented from decreasing when converting circularly polarized light into linearly polarized light.

  In this inner drum exposure device 14, for example, λ / 4 polarized light as means for converting linearly polarized light into circularly polarized light on the optical path from a laser beam light source that emits a linearly polarized laser beam to the cubic prism 38 of the spinner mirror device 36. A plate (λ / 4 wavelength plate) 46 is disposed, and a light beam that becomes S-polarized light is applied to the cubic prism 38 between the λ / 4 polarizing plate 46 and the cubic prism 38 on the optical path from the light source to the cubic prism 38. The λ / 4 polarizing plate 44 is arranged so as to rotate integrally with the cubic prism 38 in the incident angle state.

  The λ / 4 polarizing plate 44 that is integrally attached to the cubic prism 38 in this way transmits a light beam that has been transmitted through the λ / 4 polarizing plate 44 and is linearly polarized to the reflective surface 42 of the cubic prism 38. The crystal axes are aligned so as to be incident as S-polarized light, and a rectangular plate shape corresponding to the outer shape of the incident surface of the cubic prism 38 is formed.

  The λ / 4 polarizing plate 44 thus formed in a rectangular plate shape is attached so as to create a so-called S-polarized state by positioning the outer shape so as to match the outer shape of the incident surface of the cubic prism 38.

  In attaching the λ / 4 polarizing plate 44 to the incident surface of the cubic prism 38, it is considered that the requirements for the beam spot diameter of the light beam for exposure differ depending on the photosensitive characteristics and tolerance of the photosensitive layer in the PS plate 22. Then, the accuracy of attaching the λ / 4 polarizing plate 44 to the incident surface of the cubic prism 38 for creating the S polarization state may be determined according to the required beam spot diameter.

  Further, in this inner drum exposure apparatus 14, for example, as shown in FIG. 4, a λ / 4 polarizing plate 44 is provided on a light beam incident surface of a cubic prism 38, and an adhesive for a generally used optical member (for example, an epoxy resin). Alternatively, an ultraviolet curable resin or the like can be used, and the components are integrally attached and rotated integrally. Thus, when the λ / 4 polarizing plate 44 is attached to the cubic prism 38, a separate fixing member is not used, so the cubic prism 38 portion integrated with the λ / 4 polarizing plate 44 is lightweight. And can be easily rotated at high speed.

  Alternatively, as shown in FIG. 5, the inner drum exposure apparatus 14 is configured so that both the cubic prism 38 and the λ / 4 polarizing plate 44 are integrally held by a side U-shaped holder 48. May be.

  In the inner drum exposure device 14, as described above, λ / 4 polarized light that converts linearly polarized light into circularly polarized light on the optical path from the laser beam light source that emits a linearly polarized laser beam to the cubic prism 38 of the spinner mirror device 36. The plate 46 is arranged so that a circularly polarized light beam is incident on the λ / 4 polarizing plate 44 of the cubic prism 38 in the spinner mirror device 36. However, the laser beam light source device is made using a phase plate. If the configuration is such that all the light emitted from the light source is converted into S-polarized light by the λ / 4 polarizing plate 44 and incident on the cubic prism 38 by controlling the polarization, the exposure process can be efficiently performed without loss of illuminance. Can do.

  Further, the inner drum exposure device 14 is configured to emit a circularly polarized laser beam from the laser beam light source device main body, and the circularly polarized light beam is directly incident on the cubic prism 38 from the λ / 4 polarizing plate 44. You may comprise as follows.

  The spinner mirror device 36 in the inner drum exposure device 14 is controlled to move at a constant speed in the axial direction of the center axis of the arc of the inner drum 34 (the direction penetrating from the front surface to the rear surface in FIG. 2) by a sub-scanning moving means (not shown). The sub-scan is performed.

  For this reason, in the spinner mirror device 36, the rotation of the motor is controlled by the spinner driver of the control device, and the movement is controlled in the sub-scanning direction by the sub-scanning moving means (not shown).

  The spinner mirror device 36 configured in this manner reflects the light beam projected from the optical system on the light source side and modulated in accordance with image information to the reflecting surface 42 of the rotating cubic prism 38 in the main scanning direction. The two-dimensional image is recorded on the entire recording surface of the PS plate 22 by moving the spinner mirror device 36 in the sub-scanning direction while performing the scanning exposure.

  When the exposure process is performed by the inner drum exposure apparatus 14 configured as described above, as shown in FIG. 4, a circularly polarized light beam emitted directly from the light source side or converted by the λ / 4 polarizing plate 46 is used. Rotating at a spinner rotation speed of 10,000 rpm or more, is incident on the λ / 4 polarizing plate 44 and converted to S-polarized light, and is reflected by the reflecting surface 42 of the cubic prism 38 rotating at the same spinner rotation speed. Then, as shown by an imaginary line and a dotted line in the figure, the light is condensed at one point (in particular, the same state is obtained even at 30000 rpm or more).

  That is, in this inner drum exposure device 14, the light beam becomes S-polarized light and is condensed at one point as shown in FIG. 4, and is deflected by the spinner mirror device 36 and condensed on the PS plate 22. As shown in FIG. 6, the light beam is focused on a predetermined small planar circular beam spot at the focal position and can be brought into an appropriate state in which a planar circular beam shape is formed at positions before and after the focal position. By aligning the position on the scanning plane and stably imaging a predetermined small beam spot, the image can be exposed with high accuracy, and a fine image can be formed to improve the image quality.

  For example, in the inner drum exposure apparatus 14, when the small dots of the halftone dots are exposed on the PS plate 22 on the basis of the rectangular wave exposure signal as shown in FIG. By making it steep as shown in FIG. 8C, it is possible to expose small dots of an appropriately sized dot.

  The inner drum exposure apparatus 14 has a simple configuration in which the λ / 4 polarizing plate 44 is disposed in the cubic prism 38 portion, and the λ / 4 polarizing plate 46 is disposed on the optical path on the light source side as necessary. Since the above-described appropriate exposure processing can be performed, the spinner mirror device 36 can be manufactured at low cost.

  Here, in order to show the effect of the inner drum exposure apparatus 14 according to the present embodiment, it will be described in comparison with the inner drum exposure apparatus configured to deflect the non-polarized light beam illustrated in FIG. 9 by a single cubic prism. To do.

  In this comparative inner drum exposure apparatus, as shown in FIG. 9, a linearly polarized light beam that is not synchronized with the non-polarized state or rotated is reflected by the reflecting surface 42 of a single cubic prism 38 that rotates at high speed. When an image is formed later, light of the P-polarized component is incident, and as shown by an imaginary line and a dotted line in the figure, the focus position in the main scanning direction deviates from the focus position in the sub-scanning direction (so-called non-polarity). Point aberration).

  That is, in the inner drum exposure apparatus 14 of this comparative example, the light beam deflected by the spinner mirror device 36 and collected on the PS plate 22 is a large plane at an intermediate position in the range of focusing as shown in FIG. Since it becomes a circular beam spot, it becomes an improper state that forms a plane elliptical beam shape at the position before and after the condensing range, so that the focal point is not properly focused on the scanning surface and an image is formed with a large beam spot. The recorded image quality deteriorates.

  For example, in the inner drum exposure apparatus 14 of this comparative example, when the small dots of the halftone dots are exposed on the PS plate 22 based on the rectangular wave signal as shown in FIG. As shown in FIG. 8 (B), the shape is widely distributed with a gentle slope, so that the small dots of the halftone dots cannot be exposed to an appropriate size.

  Here, in the inner drum exposure apparatus, an experiment was performed in which the shift amount d between the focus position in the sub-scanning direction and the focus position in the main scanning direction was measured while changing the rotational speed of the cubic prism 38 of the spinner mirror device 36. The result shown in FIG. 10 was obtained.

  From the experimental results shown in FIG. 10, when exposure processing is performed using an S-polarized light beam with respect to the reflecting surface 42 of the cubic prism 38, the shift amount d between the focus position in the sub-scanning direction and the focus position in the main scanning direction is obtained. For example, it can be understood that the spinner speed can be eliminated even at 40000 rpm.

  When exposure processing is performed using a P-polarized light beam with respect to the reflective surface 42 of the cubic prism 38, the shift amount d between the focus position in the sub-scanning direction and the focus position in the main scanning direction is, for example, the spinner rotational speed. It can be understood that a large value of 200 μm is obtained at 40000 rpm.

  From the above experimental results, the inner drum exposure device 14 collects the light beam that is deflected by the spinner mirror device 36 and collected on the PS plate 22 at one point by using the light beam that is S-polarized light. It can be understood that a predetermined small beam spot can be stably imaged by being illuminated.

  As shown in FIGS. 1 and 2, in this CTP system, the PS plate 22 exposed by the inner drum exposure device 14 as described above is adjusted at a required timing by adjusting the conveyance speed by the buffer device 16. It is carried out to the development processing device 18.

  The development processing device 18 performs development processing on the exposed PS plate 22 that has been carried in to visualize the latent image, and completes the plate making of the printing plate.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can take other various structures in the range which does not deviate from the summary of this invention.

It is a perspective view which shows schematic structure of the CTP system provided with the light beam deflector which concerns on embodiment of this invention. It is a schematic explanatory drawing which shows the structure inside the CTP system which concerns on embodiment of this invention. It is a principal part perspective view which takes out and shows the part of the spinner mirror apparatus of the inner drum exposure apparatus which concerns on embodiment of this invention. It is a schematic perspective view which shows the principal part of the spinner mirror apparatus concerning embodiment of this invention. It is a schematic perspective view which shows the principal part of the other structure of the spinner mirror apparatus concerning embodiment of this invention. It is explanatory drawing which shows the state of the beam spot when performing an appropriate exposure process with the spinner mirror apparatus concerning embodiment of this invention. It is explanatory drawing which illustrates the state of the beam spot when improperly exposed as a comparative example for demonstrating the effect of the spinner mirror apparatus concerning embodiment of this invention. (A) is explanatory drawing which shows the exposure signal which exposes a beam spot, in order to demonstrate the effect of the spinner mirror apparatus concerning embodiment of this invention. (B) is explanatory drawing which shows the distribution shape of the improper beam spot irradiated based on an exposure signal as a comparative example. (C) is explanatory drawing which shows the distribution shape of the appropriate beam spot irradiated based on an exposure signal. It is explanatory drawing which illustrates a state when it exposes improperly with the cubic prism as a comparative example for demonstrating the effect of the spinner mirror apparatus concerning embodiment of this invention. It is a graph which shows the experimental result for supporting the effect by the spinner mirror apparatus concerning embodiment of this invention.

Explanation of symbols

14 Inner drum exposure device 22 PS plate 34 Inner drum 36 Spinner mirror device 38 Cubic prism 40 Rotating shaft 42 Reflecting surface 44 λ / 4 polarizing plate 46 λ / 4 polarizing plate 48 Holder

Claims (3)

In order to record an image on a recording medium, a light beam deflector that deflects and scans a light beam modulated according to image information on a reflecting surface of a rotationally driven deflection member,
An optical system on the light source side that emits a light beam modulated according to the image information toward the deflecting member in a circularly polarized state;
The light beam emitted in a circularly polarized state from the optical system on the light source side is converted so as to be S-polarized with respect to the reflecting surface so as to be kept incident on the reflecting surface of the deflecting member. Means for converting circularly polarized light installed to rotate in synchronization with the reflecting surface into linearly polarized light,
A light beam deflector characterized by comprising: 2. The light beam deflection according to claim 1, wherein the optical system on the light source side is configured to convert a linearly polarized light beam emitted from the light source into circularly polarized light by a λ / 4 polarizing plate. vessel. The λ / 4 polarizing plate for converting the circularly polarized light beam emitted from the optical system on the light source side into the S-polarized light with respect to the reflecting surface is fixed to the incident surface of the deflecting member. The light beam deflector according to claim 1, wherein the light beam deflector is a light beam deflector.

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