JPH11254743A - Scanning optical writing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high definition image even for large size by arranging a plurality of scanning optical units for reflecting a laser beam on a scanning rotary polyhedron mirror and focusing it on a recording medium through a focus lens such that the main scanning direction of the laser beam will be parallel. SOLUTION: The scanning optical writing apparatus comprises a scanning optical unit 1, a same type unit 1', a surface plate 2, and a charger 3 wherein the scanning optical units 1, 1' on a recording medium are set with an effective scanning width of 560 mm required for individual writing. These units are arranged to abut in parallel at the end of effective scanning width on a recording medium 4. Laser beam from a semiconductor laser performs spread correction and tilt correction, scans in main scanning direction through a polygon mirror turning at high speed, and performs tilt correction while sustaining the beam diameter before being reflected perpendicularly. A focused laser beam scans on the recording medium to write a printing plate having size corresponding to 4 pages of a newspaper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical drawing apparatus used for a laser printer, a plate setter for a CTP plate, and the like.

[0002]

2. Description of the Related Art Conventionally, for exposure drawing of a laser printer or a plate setter of a CTP plate, a laser beam from a laser light source is scanned by a rotating polygon mirror, and the scanning light is imaged on a recording medium by an imaging lens. A scanning optical device is used. In particular, for the electrophotographic or silver salt type plates having high sensitivity among CTP plates, a combination of the above-described scanning optical device and a flat bed type in which the plate is placed on a flat surface and transported is suitably used. The flatbed method does not require a complicated printing plate mounting mechanism as compared with the outer drum method or the inner drum method.
In the drawing apparatus, the drawing speed is increased by rotating the rotary polygon mirror at a higher speed. In the newspaper printing field where the advantages such as shortening of the plate making time and automation can be maximized, an electrophotographic plate making device has been put to practical use.

In general, as a printing plate size used in the newspaper printing field, a newspaper vertical two-page plate (1W2L) in which two plates having a size corresponding to one page of a newspaper are connected vertically is widely used. However, recently, with the increase in the number of color pages of newspapers, the frequency of use of plate materials of the size of a spread has also increased. (2W1L) or a four-page newspaper (2
It is desired to develop a drawing apparatus capable of performing wide area scanning corresponding to a plate having a size such as W2L).

However, in the above-described exposure method, when wide area scanning is performed, the focal point shifts due to the difference in optical path length, and the curvature of field occurs, so that the shape of the laser beam differs near the center and near both ends of the scanning area. . Therefore, the line width and the like become non-uniform, and a fine image cannot be obtained.
Various control methods have been devised to correct the focus shift.However, compared to the exposure drawing method such as the outer drum method or the inner drum method, at present the wide area scanning is not good, and the above-described printing plate is not suitable. No corresponding drawing apparatus has been put to practical use.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a scanning optical drawing apparatus capable of obtaining a fine image without deteriorating the drawing speed even if the size of the printing plate is increased. The purpose is to provide.

[0006]

According to the first aspect of the present invention, a scanning optical drawing apparatus reflects a laser beam from a laser light source by a rotating polygon mirror for scanning, and reflects the reflected light by an imaging lens. A plurality of scanning optical units that form an image on a recording medium are arranged so that the main scanning direction of the laser beam is parallel.

Thus, even if the drawing width of the recording medium in the main scanning direction becomes longer, the number of scanning optical units required for the drawing width is calculated in parallel with the main scanning direction by calculating from the scanning width of one optical unit. By arranging in such a manner, drawing can be performed without lowering the drawing speed.

According to a second aspect of the present invention, the system for moving the recording medium in the sub-scanning direction is a flatbed system.

In the case where the recording medium is in the form of a sheet, for example, an electrophotographic planographic printing plate, by using a flatbed method, a complicated plate feeding mechanism, a plate discharging mechanism and a positioning mechanism are not required, and a simple CT
A system such as a P plate making machine can be easily automated, and the production cost of the plate making machine itself can be kept low. In addition, since the time required for plate feeding and plate discharging is short, the total drawing time is shortened as a result. Even when the recording medium is of the electrophotographic type, a charging device for performing a necessary charging step before the exposure / drawing step can be easily incorporated.

The invention according to claim 3 is characterized in that a scanning area of the scanning optical unit partially overlaps a scanning area of an adjacent scanning optical unit.

[0011] The images at the boundary between the end of the scanning area of one scanning optical unit and the end of the scanning area of an adjacent scanning optical unit are connected by different laser beams. In an image at such a boundary portion, a shift is likely to occur between the scanning optical units due to individual differences in a laser light source, an optical system, and the like. In particular, when the scanning is performed at both ends of the scanning area, this shift becomes remarkable. However, by arranging the scanning areas of the adjacent scanning optical units so as to partially overlap each other, it is possible to suppress displacement.

The invention according to claim 4 is characterized in that the both ends of the scanning area of the scanning optical unit are arranged so as to be at the positions of unexposed portions.

As seen in newspaper printing, in a case where the drawing area of the recording medium (printing plate in this case) is fixed every time, both ends of the scanning area of the scanning optical unit are unexposed. By arranging them so as to be at the same position, it is possible to solve the above-described problem of displacement on the boundary.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of scanning optical units according to the present invention are arranged so that the main scanning direction of a laser beam is parallel. This means that a laser beam emitted from each unit is recorded on a recording medium. Indicate that the main scanning directions are arranged in parallel. This will be described with reference to FIG. FIG. 1 shows main scanning areas 1a to 1d of laser beams from four scanning optical units (not shown),
It is shown on the recording medium 4 at an arbitrary time, and the directions of the main scanning areas 1a to 1d coincide with the main scanning direction. Arranging a plurality of scanning optical units so that the main scanning direction of the laser beam is parallel means that the main scanning directions (areas) 1a to 1d in the figure need only be parallel, and The arrangement of the optical unit itself does not matter. In addition, if they are parallel, the drawing positions can be different (1a and 1c), but the same is preferable from the viewpoint of controlling the writing position. It is also possible to use a different type of scanning optical unit (1a).
And 1d), it is preferable to use the same type of unit from the viewpoint of adjustment and control (1a and 1b).

The fact that the method of moving the recording medium in the sub-scanning direction according to the present invention is the flatbed method means that drawing is performed with the recording medium placed on a flat surface. In this case, drawing may be performed while the recording medium is being conveyed, or the recording medium may be kept still and the scanning optical unit may be conveyed for drawing. In the method of transporting the recording medium,
A method of transporting on a surface plate, a belt transport method, and a roll holding transport method are suitably used.

The scanning optical unit according to the present invention is of a system in which a laser beam from a laser light source is scanned by a rotating polygon mirror and the scanning light is imaged on a recording medium by an imaging lens. A known scanning optical unit used for a film plotter, an image setter or the like can be suitably used. In particular, an optical unit of a film plotter or an image setter is more preferable because the scanning width of the unit carrier is longer than that of a laser printer, so that the total number of optical units can be reduced.

[0017]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

Embodiment 1 FIG. 2 is a schematic view of a scanning optical drawing apparatus according to the present invention when viewed from above, and is intended for a newspaper spread plate size. The scanning optical drawing apparatus includes a scanning optical unit 1,
The scanning optical unit 1 and the scanning optical unit 1 'are of the same type. The positional relationship between the scanning optical unit 1 and the scanning optical unit 1 'will be described with reference to FIG. Maximum scanning width 1 of the scanning optical unit 1 alone on the recording medium
01 is 570 mm, but without using the maximum scanning width 101, the effective scanning width 100 required for drawing is set to 560 mm.
Is set to Similarly, the maximum scanning width 101 'of the single scanning optical unit 1' is 570 mm, but the effective scanning width 100 'is set to 560 mm. The arrangement of the scanning optical unit 1 and the scanning optical unit 1 'is such that the ends of the effective scanning widths 100 and 100' are in contact with and parallel to each other on the recording medium as shown in FIG.

FIG. 4 is a schematic diagram of the scanning optical unit 1 as a single unit.
2. It comprises a cylindrical lens 13, a prism 14, a polygon mirror 15, an fθ lens 16, and a cylindrical mirror 17. A laser beam from a semiconductor laser 11 as a laser light source is applied to a collimator lens 1.
2, the polygon mirror 15 is corrected for tilt by the cylindrical lens 13, and then passes through the prism 14 to rotate the polygon mirror 15 (8
(Scan) in the main scanning direction. Next, the beam diameter is maintained by the fθ lens 16, the tilt of the polygon mirror 15 is corrected by the cylindrical mirror 17, and the laser beam reflected at right angles to form an image is scanned on a recording medium. Here, the cylindrical mirror 17 is commonly used for the scanning optical units 1 and 1 '. The polygon mirror 15 and the fθ lens 1
Although not shown in the figure, a light-shielding mask for shielding the laser light at both ends of 5 mm is installed so that the scanning width becomes 560 mm, although not shown.

Next, description will be made in accordance with the order of the processing steps of the present apparatus. As the recording medium 4, an electrophotographic planographic printing plate 4 (hereinafter, referred to as a printing plate) is used. FIG. 5 is a schematic view of the scanning optical drawing apparatus when viewed from the side. When the printing plate 4 is set at a predetermined position on the surface plate 2, the surface plate 2 once moves at a high speed and a constant speed to a position 2 'in FIG. At that time, since the charger 3 performs corona discharge at a high voltage, the printing plate 4
Is uniformly charged. Thereafter, the platen 2 moves again in the opposite direction (position 2). In synchronization with this moving operation, an external image signal (not shown) is input to an image processing unit (not shown), and an image signal input to each of the semiconductor lasers in the scanning optical units 1 and 1 'is output by a write signal (not shown). On / off along the line to start a plane scan. Then, the entire surface of the printing plate 4 is scanned for drawing as the platen 2 moves, and an electrostatic latent image is formed. The platen 2 stops when it comes to the position of 2.

With this apparatus, a large printing plate such as a four-page newspaper (2W2L) newspaper or the like, in which the size of one page of a newspaper which could not be handled so far, is arranged two by two vertically and horizontally, is drawn. I can do it. FIG. 6 shows a general newspaper 4-page version size. When this apparatus is used, in the case of FIG. 6A, the scanning optical unit 1 scans the paper surface, and the paper surface ′,
Is scanned by the scanning optical unit 1 '. In the case of a two-page spread as shown in FIG. 6B, the scanning optical unit 1 scans the paper surface and the scanning optical unit 1' scans the paper surface. Is possible by scanning. In this apparatus, the maximum scanning width 5 of the scanning optical units 1 and 1 'is
The scanning width of 560 mm is obtained by blocking the scanning light of 5 mm at both ends without using 70 mm, and the scanning area between the scanning optical unit 1 and the scanning optical unit 1 ′ is a seam of the paper. Since it is arranged so as to be an exposure part, a fine image can be obtained over the entire printing plate.

Furthermore, since the system for moving the printing plate in the sub-scanning direction is the flatbed system, a complicated transport attachment mechanism is not required as a drawing unit of an automatic plate making machine having functions from plate feeding to bender. Combinations can be made without incurring a delay in plate making time.

[0023]

As described above, the scanning optical drawing apparatus of the present invention has the above-described structure, and therefore, it is possible to obtain a fine image without impairing the drawing speed even if the size of the printing plate is increased. Can be done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a scanning direction on a recording medium related to an arrangement of a scanning optical unit according to the present invention.

FIG. 2 is a schematic configuration diagram of the scanning optical drawing apparatus according to the first embodiment as viewed from above.

FIG. 3 is a schematic diagram regarding a scanning direction on a recording medium related to the arrangement of the scanning optical unit according to the first embodiment.

FIG. 4 is a schematic configuration diagram of a scanning optical unit according to the first embodiment.

FIG. 5 is a schematic configuration diagram of the scanning optical drawing apparatus according to the first embodiment as viewed from a side.

FIG. 6 is a schematic diagram relating to a four-page newspaper size according to the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 'Scanning optical unit 2 Surface plate 3 Charger 4 Recording medium 11 Semiconductor laser 12 Collimator lens 13 Cylindrical lens 14 Prism 15 Polygon mirror 16 fθ lens 17 Cylindrical mirror

Claims (4)

[Claims] 1. A scanning optical unit which reflects a laser beam from a laser light source by a rotating polygon mirror for scanning and forms an image of the reflected light on a recording medium by an imaging lens. A scanning optical drawing apparatus, wherein a plurality of scanning optical drawing apparatuses are arranged so that a main scanning direction is parallel. 2. The scanning optical drawing apparatus according to claim 1, wherein the system for moving the recording medium in the sub-scanning direction is a flatbed system. 3. A scanning area of the scanning optical unit,
The scanning optical drawing apparatus according to claim 1, wherein the scanning optical drawing unit partially overlaps a scanning area of an adjacent scanning optical unit. 4. The scanning optical drawing apparatus according to claim 1, wherein both ends of a scanning area of the scanning optical unit are arranged at positions of unexposed portions.