JP2005077972A - Optical write-in device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an existing write-in device corrected for the write-out position in a subscanning direction with a simple structure. <P>SOLUTION: The number of reflection faces of a polygon mirror is increased from a conventional number of faces (M faces) to N faces (N>M) without varying the image formation conditions (the number of revolution of the polygon mirror, the line speed of a photoreceptor or the like). Thus, the width between a first line formed with the first face of the polygon mirror and the second line formed with the second face of the polygon mirror is made to be 1/(N/M) μm. For example, if M=6, N=12 and the conventional gap between lines is 42 μm, the minimum correction amount of the deviation correction of position of a light spot P in a subsacanning direction becomes 21 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical writing apparatus including a rotary deflector that is a regular polygon having a plurality of reflecting surfaces for deflecting and scanning a light beam emitted from a light source.

  An image forming apparatus in a laser beam printer, a digital copying machine, a laser facsimile machine, or the like includes a polygon mirror formed in a regular polygon for deflecting and scanning a light beam from a light source, and a light beam scanned by the polygon mirror on a photoreceptor surface. An optical element (scanning lens) for forming an image above is provided, and a light detector is provided on the scanning start side outside the effective exposure region in order to determine the writing start position.

  In such a laser writing method, the pixel density in the sub-scanning direction is determined by the number of light beams that are light sources, the number of surfaces of the polygon mirror, and the number of rotations. Obtaining an accurate writing density to obtain good image quality is an important issue.

  In particular, in an apparatus that forms a single image by superimposing a plurality of color images by a plurality of writing systems, color drift occurs if the pixel density of each writing system is different. It is important.

  In other words, a conventional laser writing apparatus such as a color copying machine has a configuration in which one line is formed for each reflecting surface of a rotary deflector (polygon mirror) that is a regular polygon. As shown in FIG. 6, the irradiation position of the light spot P on the photosensitive member that is the scanned body of the laser light in each color (C (cyan), M (magenta), Y (yellow), Bk (black)) is as follows. Due to the assembly error of the apparatus, the variation of each part, etc., a deviation occurs with respect to the reference line, and the irradiation position is not always aligned. Further, the irradiation position of the laser beam for forming each color also changes due to thermal deformation of the optical element or the like due to temporal changes such as thermal fluctuation during image formation.

  Furthermore, since the write clock write timing is generated for each surface of the polygon mirror, the write position in the sub-scanning direction varies depending on the tilting of the polygon mirror, surface-to-surface variation, write clock timing, and the like. End up.

  Therefore, a method for correcting misregistration of each color is necessary. For example, in the case of a writing structure with a pixel density of 600 dpi employed in a laser writing device such as a general color copying machine and a polygon mirror surface number of 6 surfaces, FIG. As shown in FIG. 7, the width of the first line formed by the first surface and the second line formed by the second surface is about 42 μm. Becomes 42 μm. In other words, even if the writing position is deviated from the ideal irradiation position, the current writing apparatus cannot correct 42 μm or less.

In order to solve this problem, a technique such as Patent Document 1 is proposed. In this prior art, when detecting fluctuations in the scanning beam from the two photodetectors, data on the entire surface of the polygon mirror is detected multiple times in consideration of fluctuations in the height of the scanning beam due to the surface tilt of the polygon mirror. The distribution data is obtained and the optimum correction data is defined.
JP 2002-169112 A

  However, as described above, in the writing apparatus in which color matching is performed by a plurality of writing systems as described above, even if writing can be started from the same surface, the effect of surface tilt can be detected. Since the cause is not only the tilting of the polygon mirror, there is a problem that it is impossible to align each color.

  An object of the present invention is to solve these problems and to provide an optical writing device capable of correcting the writing position in the sub-scanning direction in a current writing device with a simple configuration.

  In order to achieve the above object, the invention described in claim 1 is directed to a rotary deflector that is a regular polygon having a plurality of reflecting surfaces for deflecting and scanning a light beam emitted from a light source, and the light that has been deflected and scanned. An optical writing apparatus comprising an optical system for forming a beam with a predetermined beam spot diameter and irradiating the surface to be scanned, wherein the number of reflecting surfaces of the rotary deflector is a writing density specification for the surface to be scanned. Is set to a positive multiple of the number of reflecting surfaces, and the rotational deflection is performed according to the amount of deviation of the imaging position on the scanned surface in the sub-scanning direction of the light beam deflected and scanned by the rotational deflector. With this configuration, the reflecting surface of the rotary deflector can be selected according to the amount of deviation of the imaging position of the deflected light beam in the sub-scanning direction. Can be aligned It becomes ability.

  According to a second aspect of the present invention, in the optical writing apparatus according to the first aspect, the number of rotations of the rotary deflector can be switched to an integral multiple of the number of rotations that can achieve the writing density specification. Therefore, it is possible to perform better alignment in the sub-scanning direction.

  According to a third aspect of the present invention, in the optical writing device according to the first aspect, when a plurality of light beams are emitted from the light source, the optical axis of the light beam to be scanned first is the rotation axis, and the writing density is increased. Accordingly, the rotation angle can be adjusted accordingly, and this configuration can prevent the writing position from being shifted even when the mode for increasing the writing density is selected.

  According to a fourth aspect of the present invention, in the optical writing apparatus according to the first aspect, a plurality of optical elements are disposed in the vicinity of the rotary deflector, and an optical path of an independent scanning optical system is configured by the optical elements. Things also apply.

  According to the present invention, the number of reflecting surfaces of the rotating deflector is set to a positive multiple of the number of reflecting surfaces capable of achieving the writing density specification for the scanned surface, and the sub-scanning direction of the light beam deflected and scanned by the rotating deflector The reflection surface of the rotary deflector can be selected in accordance with the amount of deviation of the imaging position on the surface to be scanned in the sub-scanning of the light beam to be deflected and scanned by appropriately selecting the reflection surface. In accordance with the amount of deviation of the imaging position in the direction, alignment in the sub-scanning direction can be performed, and the writing position in the sub-scanning direction can be corrected, thereby realizing good optical writing.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing a configuration of a main part of a digital color writing processing system according to an embodiment of the present invention. 1 is a laser light source, 2 is a predetermined beam shaping with respect to a laser beam L emitted from the laser light source 1. 3 is a polygon mirror that has a reflecting surface on the side of a regular polygon and that rotates at high speed to deflect and scan the laser beam L, and 4 is a surface selection means that detects each reflecting surface in the polygon mirror 3. Reference numeral 5 denotes a mirror that is provided at the end of the laser scanning range of the polygon mirror 3 and guides the laser beam L to the laser beam detector 6 that detects the beam and outputs a synchronization detection signal for controlling the scanning position. .

  Reference numeral 7 denotes an fθ lens that converts equiangular motion of beam scanning into constant linear motion by the polygon mirror 3, reference numeral 8 denotes a cylindrical lens that corrects errors such as surface tilt of the polygon mirror 3, and reference numeral 9 denotes a photosensitive member that is a scanned object. A mirror 11 for guiding the laser beam L to the body 10 is a reading means for identifying an image on a member (photosensitive member or the like) capable of forming an image pattern for measuring the amount of positional deviation.

  As described above, generally, the writing density is 600 dpi (the number of reflecting surfaces of the polygon mirror is M (M is an integer)), M = 6, and the first line formed by the first surface and the first line Since the width of the second line formed by the two surfaces is about 42 μm as shown in FIG. 7, the positional deviation correction of the light spot P of the laser beam L in the sub-scanning direction is shown in FIG. Thus, the minimum correction amount is 42 μm.

  Therefore, in the present embodiment, the number of reflection surfaces of the polygon mirror 3 is set to the N surface (N> M) without changing the image forming conditions (the rotation speed of the polygon mirror 3, the linear velocity of the photoconductor 10, etc.). Thereby, the width of the first line formed by the first surface and the second line formed by the second surface can be set to 42 / (N / M) μm.

  For example, when M = 6 and N = 12, the width of the first line and the second line is 21 μm as shown in FIG. 3, so the sub-scanning direction of the light spot P as shown in FIG. In the positional deviation correction at, the minimum correction amount is 21 μm.

  Accordingly, when the laser beam L is written, the reflection surface of the polygon mirror 3 is appropriately selected, so that the minimum correction amount for the positional deviation correction in the sub-scanning direction with respect to the light spot P is 42 / (N / M) μm. Can do.

  Further, by switching the rotation speed of the polygon mirror 3 to A (A: integer) times the rotation speed capable of achieving the writing density specification, the polygon mirror 3 is formed by the first line formed by the first surface and the second surface. The width with the second line can be reduced to 1 / A. Thus, the minimum correction amount for correcting the dot position deviation of each color in the sub-scanning direction can be reduced. For example, when 600 dpi and A = 2, the line width can be 21 μm (the same effect as in FIG. 2B).

  Also, as shown in FIGS. 4A and 4B, when a light source composed of a plurality of laser light sources 15 and 16 is used to emit a plurality of laser beams, conventionally, each beam in the sub-scanning direction is used. The interval (sub-scanning pitch) is adjusted by rotating the rotating shaft 17 around the interval between the laser light sources 15 and 16, as shown in FIG.

  However, in this case, although the sub-scanning pitch can be adjusted, the laser beam irradiation position is displaced.

  Therefore, in the present embodiment, as shown in FIG. 4B, the irradiation position of the first laser is determined by rotating the optical axis of the laser beam of the laser light source 15 to be scanned first as the rotation axis 18. The sub-scanning pitch can be adjusted without changing it. Thus, even when the image density mode is changed, the image density mode can be changed without changing the irradiation position.

  In the present embodiment, even if the single photoconductor 10 is deflected and scanned with respect to the single photoconductor 10 as shown in FIG. 1, a plurality (4 in this example) is used as shown in FIG. This is also applicable to an optical writing device including a polygonal mirror 21 and a plurality of fθ lenses 22, a mirror 23, a lens 24, and the like.

  The present invention is applied to an electrophotographic apparatus such as a digital copying machine or a facsimile apparatus equipped with an optical writing apparatus equipped with a polygon mirror having a plurality of reflecting surfaces for deflecting and scanning a light beam emitted from a light source. This is effective for an optical writing device mounted on an electrophotographic apparatus capable of recording an image.

The perspective view which shows the structure of the principal part of the digital color writing processing system which is embodiment of this invention. Explanatory drawing of position shift correction in the sub-scanning direction of the light spot by this embodiment Explanatory drawing of the width | variety of the 1st line formed by the 1st surface by this embodiment, and the 2nd line formed by the 2nd surface Explanatory drawing of the space | interval adjustment to the sub-scanning direction of the conventional and this embodiment in each beam in the case of emitting a plurality of laser beams Schematic configuration diagram for explaining an optical writing apparatus using a plurality of photosensitive members to which the present invention is applied as a scanned object Explanatory drawing of the shift | offset | difference with respect to the reference line in the irradiation position of the light spot P with respect to the conventional photoreceptor. Explanatory drawing of the width | variety of the 1st line formed by the 1st surface by the prior art example, and the 2nd line formed by the 2nd surface

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 3,21 Polygon mirror 4 Surface selection means 6 Laser beam detector 10,20 Photoconductor 11 Reading means 15,16 Laser light source 17,18 Rotating shaft

Claims (4)

  A rotary deflector that is a regular polygon having a plurality of reflecting surfaces for deflecting and scanning a light beam emitted from a light source, and the deflected and scanned light beam is formed to have a predetermined beam spot diameter on the surface to be scanned. In an optical writing device comprising an optical system for irradiating, the number of reflecting surfaces of the rotary deflector is set to a multiple of the number of reflecting surfaces capable of achieving a writing density specification for the scanned surface, and the rotating deflector An optical writing apparatus characterized in that the reflecting surface of the rotary deflector can be selected in accordance with the amount of deviation of the imaging position on the scanned surface in the sub-scanning direction of the light beam deflected and scanned by.   2. The optical writing apparatus according to claim 1, wherein the rotational speed of the rotary deflector can be switched to an integral multiple of the rotational speed capable of achieving the writing density specification.   2. The light source according to claim 1, wherein when a plurality of light beams are emitted from the light source, the rotation axis can be adjusted according to the writing density with the optical axis of the first light beam scanned as the rotation axis. Optical writing device.   2. The optical writing apparatus according to claim 1, wherein a plurality of optical elements are disposed in the vicinity of the rotary deflector, and an optical path of an independent scanning optical system is constituted by the optical elements.

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