JP2010026440A - Optical write-in apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple color image-forming apparatus which is made compact in a subscanning direction (thickness direction). <P>SOLUTION: The optical write-in apparatus includes: a plurality of beam emission means; an optical deflection means which deflects and scans the beams emitted from the beam emission means; an imaging means which images beams deflected and scanned with the optical deflection means onto a plurality of respective image carriers; and a synthesizing means which synthesizes at least two beams having different emitting light wavelengths onto one and the same path in the subscanning direction, wherein the beam synthesized with the synthesizing means is split and imaged on the plurality of image carriers by using a dichroic mirror, a wavelength plate giving a phase shift to the polarized state of the beam, a polarized light beam splitter having transmitting or reflecting characteristic depending on the polarized state, and a reflection mirror propagating the finally split beam to the last image carrier. The optical paths of the beams in the range of transmitting through or reflected on the dichroic mirror, the wavelength plate, the polarized light beam splitter and the reflection mirror are parallel to the plane which connects the points at which the respective beams are connected to the respective image carriers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method, and more particularly to optical system image writing that scans a surface to be scanned using a light beam and writes image information. is there.

  Currently, market demand for image forming apparatuses includes small size, light weight, and low cost. In recent years, high image quality has been demanded as well. In a general desktop type color printer, a color image is created by combining four colors (K (black), C (cyan), M (magenta), and Y (yellow)). Focusing on the point of improving the image quality, a method for forming a multicolor image having excellent gloss with a total of five colors using transparent toner in addition to the four basic colors CMYK, and conventional cyan and magenta as basic colors. Instead of forming images with four basic colors of yellow, black and black, the use of light toner of each of the four colors, which is the mainstream method currently used in inkjet printers, reduces the graininess of the image. A method for improving the color reproduction range or color reproducibility by using a special color such as green or orange is also considered.

  When considering a configuration using such multi-color images exceeding four colors, for example, five or six colors, if the configuration of the conventional image forming apparatus is diverted, it is applied to one side of the deflector as shown in FIGS. A general configuration is a tandem system in which two beams, three on one side, or three on one side are scanned. A multi-color image forming apparatus using a tandem method has a larger number of components than a conventional monochrome printer, has a very large structure, and is difficult to reduce in size.

  Currently, an optical writing device for an image forming apparatus using a plurality of light beams that is commercially available generally diffracts a plurality of light beams by a plurality of reflection mirrors, and thereby sensitizes each image carrier. Irradiates the scanned surface of the body. However, since the optical path is folded three-dimensionally using a plurality of mirrors, the optical writing device tends to increase in the thickness direction. In particular, in a six-color color tandem machine, the beam of each color corresponding to each photoconductor must be shifted in the sub-scanning direction to prevent interference with each optical path or optical element, and thus must be further increased in the thickness direction. In addition, in order to create a color image by combining the six colors, the deflector in the writing device has a three-stage layer structure and performs opposite scanning, so that it is about three times higher in the thickness direction than a monochrome printer. I need.

  For this reason, some proposals have been made to realize simplification and compactness of the device itself at a low cost. For example, in Patent Document 1, two laser beams having different deflections or wavelengths are used to synthesize two beams by a deflection beam splitter, irradiate the combined beam to a single polygon mirror, and pass through an fθ lens. A configuration in which a beam is separated by a polarization separation mirror and irradiated to a plurality of photosensitive members is disclosed. In Patent Document 2, a multi-chip semiconductor laser light source in which a plurality of semiconductor laser chips having different emission wavelengths are arranged side by side is used, and composite laser light output from this light source is converted into one scanning optical system (collimating lens, cylindrical lens, polygon). A configuration is disclosed in which after being deflected by a mirror, an fθ lens, and a dichroic mirror, the light is separated according to the wavelength and distributed to a plurality of photoconductors.

  In Patent Document 1, the irradiation angles at which the separated beams irradiate the respective photoconductors are different. The writing start timing is detected by a synchronization detection sensor provided outside the photosensitive member scanning area, and is controlled by performing synchronization detection for each beam. The difference in irradiation angle can be made the same by adjusting the positional relationship among each photoconductor, the polarization separation mirror, and the reflection mirror, but the optical path of each beam irradiated to each photoconductor by such a positional relationship change. The length will be different. Even in the configuration of Patent Document 2, the irradiation angle and the optical path length are different.

  That is, according to the above prior art, after combining the light beams in the sub-scanning direction, scanning and condensing using one optical system, the combined light beams are separated using each separating means. The length is different for each photoconductor. In Patent Document 1, the photosensitive member irradiation angle is also different.

Japanese Patent Laid-Open No. 10-3048 JP-A-10-282440

  In a writing method of a multi-color image forming apparatus using a general tandem method, a beam deflected by a light deflecting unit irradiates a scanned surface of an image carrier (photosensitive member) carrying each color with a desired optical path length. Therefore, a plurality of mirrors are used and the optical path is folded three-dimensionally, so that the optical writing device tends to increase in the thickness direction. Furthermore, in order to prevent interference of each optical path or optical element, the beam corresponding to each photoconductor is shifted in the sub-scanning direction, so that it becomes very large in the thickness direction.

  In view of the above background, the problem to be solved by the present invention is to reduce the size of the multicolor image forming apparatus in the sub-scanning direction (thickness direction).

According to the present invention, there is provided a plurality of beam emitting means, a light deflecting means for deflecting and scanning a beam emitted from the beam emitting means, and a plurality of image carriers having the beams deflected and scanned by the light deflecting means. In the optical writing device having an imaging means for forming an image on each of the optical writing apparatus, the optical writing apparatus has a synthesizing means for synthesizing at least two beams having different emission wavelengths in the same path in the sub-scanning direction. The
A dichroic mirror,
A wave plate that gives a phase difference to the polarization state of the beam;
A polarizing beam splitter having transmission and reflection characteristics depending on the polarization state;
With a reflecting mirror that propagates the finally separated beam to the last image carrier,
Each of the plurality of image carriers is separately imaged, and a beam optical path and each beam within a range that transmits and reflects these dichroic mirror, wavelength plate, polarizing beam splitter, and reflection mirror are included in the image carrier. This is solved by setting the surfaces connecting the portions to be connected to each other in parallel.

  Two each of the dichroic mirror, the wavelength plate, and the polarizing beam splitter are used, and the first set of polarizing beam splitter, wavelength plate, and dichroic mirror are arranged in order from the light deflecting unit, and the first set of dichroic mirrors are arranged. It is preferable that a second set of polarizing beam splitter, wave plate, and dichroic mirror is disposed after the mirror. At this time, the phase difference given by the first wave plate is preferably λ / 4, and the phase difference given by the second wave plate is preferably λ / 8. Further, the light quantity P1 of wavelength λ1 reflected by the first set of dichroic mirrors and turned back to the first image carrier by the first set of polarization beam splitters, and reflected by the second set of dichroic mirrors and reflected by the second set of polarizations. The ratio of the beam quantity P2 of wavelength λ2 that is folded back to the second image carrier by the beam splitter and the beam quantity P3 of wavelength λ3 that passes through the second set of dichroic mirrors and is folded back to the third image carrier by the reflection mirror. However, if P1: P2: P3 = 1: 4/3: 4/3, it is more effective.

  Preliminarily correct the combined beams of multiple emission wavelengths with a common scanning lens, and then correct them with a non-common scanning lens placed after being reflected by the reflecting section or reflecting mirror of each polarizing beam splitter and dichroic mirror. It is good to do. In addition, it is also assumed that the combined beams having a plurality of emission wavelengths are independently corrected by a non-common scanning lens disposed after being turned back by the respective polarization beam splitters and the reflecting parts of the dichroic mirrors or reflecting mirrors.

  An additional set of a polarizing beam splitter, a wave plate, and a dichroic mirror is disposed on the opposite side of the light deflecting means with respect to the first set, the second set of the polarizing beam splitter, the wave plate, and the dichroic mirror, or the light It is assumed that the first set, the second set of polarizing beam splitters, the wave plate, and the dichroic mirror are arranged symmetrically with respect to the deflection means.

  According to the present invention, a plurality of beam emitting means, a light deflecting means for deflecting and scanning the beam emitted from the beam emitting means, and the beam deflected and scanned by the light deflecting means are applied to each of the plurality of image carriers. An optical writing device having an imaging means for forming an image has a synthesis means for synthesizing at least two beams having different emission wavelengths in the same path in the sub-scanning direction, and the beam synthesized by the synthesis means is dichroic. A mirror, a wave plate that gives a phase difference to the polarization state of the beam, a polarization beam splitter having transmission and reflection characteristics depending on the polarization state, and a reflection mirror that propagates the finally separated beam to the last image carrier Are used to separate and form images on each of the plurality of image carriers, and these dichroic mirrors, wave plates, polarization beam splitters, reflection mirrors, and the like. Compared to the conventional method, the sub-scanning direction (thickness direction) is that the beam optical path in the range that transmits and reflects light and the plane that connects the points where each beam is coupled to each image carrier are set in parallel. In addition, the apparatus can be made thinner.

  Two dichroic mirrors, two wavelength plates, and two polarizing beam splitters are used, and a first set of polarizing beam splitter, wavelength plate, and dichroic mirror are arranged in order from the light deflection means, and after the first set of dichroic mirrors, If the second set of polarizing beam splitter, wave plate, and dichroic mirror are arranged, two sets of optical elements are arranged on a scanning plane parallel to the beam deflected and scanned from the light deflecting means, and three different emission wavelengths. The folding of the beam to the image carrier can be made on the same plane, and the apparatus can be made thin. At this time, if the phase difference given by the first set of wave plates is λ / 4 and the phase difference by the second set of wave plates is λ / 8, the emission wavelength λ 1 reflected by the first set of dichroic mirrors The beam passes through the first set of wave plates twice, giving a total of λ / 2 phase difference. When the beam re-enters the first set of polarizing beam splitters, the polarization state is λ / 2 from the first incidence. Differently, the beam having the emission wavelength λ2 that is folded back to the image carrier and reflected by the second set of dichroic mirrors passes through the second set of λ / 8 wavelength plates twice, so that the first set of wave plates and A λ / 2 phase difference is given in total, and when the light reenters the second set of polarization beam splitters, the polarization state is different from that at the first incidence by λ / 2 and is folded back to the image carrier. In this case, the beams having the emission wavelengths λ2 and λ3 incident on the second set of polarization beam splitters in the deflected state where the phase difference of λ / 4 is given by passing through the first set of wave plates are the image carrier. One-fourth of the amount of light emitted to the opposite side is reflected, which is 3/4 less than the amount of light of the beam of λ1. If this is the case, the amount of exposure will be different when each beam is applied to the image carrier, which may lead to degradation of image quality. Therefore, the light quantity P1 of wavelength λ1 reflected by the first set of dichroic mirrors and turned back to the first image carrier by the first set of polarization beam splitters, and reflected by the second set of dichroic mirrors and reflected by the second set of polarizations. The ratio of the beam quantity P2 of wavelength λ2 that is folded back to the second image carrier by the beam splitter and the beam quantity P3 of wavelength λ3 that passes through the second set of dichroic mirrors and is folded back to the third image carrier by the reflection mirror. By setting P1: P2: P3≈1: 4/3: 4/3 in advance, it is possible to match the amount of light when the image carrier is irradiated, and to prevent image deterioration.

In the system according to the present invention, a plurality of beams having different emission wavelengths are used, the optical path length of the wavelength λ1 separated and folded by one set of optical elements, and the wavelength λ2 separated and folded by two sets of optical elements. There is a possibility that image quality deterioration may be caused by two points that there is a possibility that it is not guaranteed that the optical path length of the wavelength λ3 transmitted through the two sets of optical elements and reflected by the reflection mirror is exactly equal. . The beam diameter W0 at the beam waist position, which is a position where the laser beam is sufficiently narrowed, is the spot size of incident light when condensing the laser beam with a lens, f is the focal length, and λ is the wavelength of the laser beam. Then,
W0 = λf / πWa
The smaller the wavelength, the narrower the beam diameter W0 at the beam waist position. For this reason, when the same scanning lens is used, the beam diameter increases as the wavelength increases. Therefore, after preliminarily correcting the combined beams of a plurality of emission wavelengths with a common scanning lens, the non-common scanning lens is arranged after being reflected by the reflecting section or reflecting mirror of each polarization beam splitter and dichroic mirror. Or by independently correcting with a non-common scanning lens placed after folding the combined beams of multiple emission wavelengths by the respective polarization beam splitter and the reflecting part of the dichroic mirror or the reflecting mirror. Thus, the difference in scanning magnification due to the difference in beam diameter and optical path length is corrected, so that the optical characteristics of the beams when irradiating the respective image carriers are substantially matched.

An image forming apparatus to which the present invention is applied will be described with reference to FIGS.
FIG. 1 shows an example of a full-color image forming apparatus in which five drum-shaped photoconductors 10K, 10Y, 10C, 10M, and 10T are arranged in tandem as image carriers. These photoconductors are image forming devices 7K, 7Y, 7C, and 7M. , 7T. These image forming devices 7K, 7Y, 7C, 7M, and 7T sequentially correspond to black, yellow, cyan, magenta, and transparent, and images of other colors are also prepared by combination.

  In the image forming apparatus of FIG. 1, there is a transfer belt 14 as a transfer medium that is supported by and rotated by support rollers R <b> 1 and R <b> 2 that are opposed to each other in the left-right direction in the figure, and along a stretched line above the transfer belt 14. The image forming devices 7K, 7Y, 7C, 7M, and 7T are arranged at intervals from the upstream side in the order of the belt movement direction indicated by the arrows.

  The transfer belt 14 is configured such that the black photoconductor 10K is always in contact with the transfer roller 16 in order to conform to the black image one-color formation mode, and the other color photoconductors are movable tension rollers. The transfer belt 14 is contacted and separated by the function (not shown). In FIG. 1, the image forming devices 7K, 7Y, 7C, 7M, and 7T differ only in the color of the toner to be handled, and the mechanical configuration and the image forming process are common. Only the same reference numbers are attached, and the alphabet may be omitted for simplification of display. A configuration and an image forming process will be described for an arbitrary image forming apparatus, for example, the black image forming apparatus 7K.

  When forming a full-color image, toner images of respective colors are formed on the photoreceptors 10K, 10Y, 10C, 10M, and 10T provided in the image forming devices 7K, 7Y, 7C, 7M, and 7T as described later. Next, the toner images of different colors are transferred onto the transfer belt 14 fed from the paper feeding device 5 by using a transfer roller 16 as a transfer unit disposed opposite to each photoconductor with the transfer belt 14 interposed therebetween. Are sequentially transferred onto the sheet medium. Thereafter, the sheet medium passes between the fixing rollers of the fixing device 6, passes through the conveyance rollers, and is discharged onto a discharge tray 19 on the apparatus main body from a pair of discharge rollers (not shown), and a full color image is formed on the sheet medium. Get.

  Around the photoconductor 10K of the image forming device 7K, in the order of clockwise rotation in the figure, the charger 11 as a charging means for charging the photoconductor 10K, the irradiation position of the writing light beam 28, and the development as the developing means. A device 12, a transfer roller 16, and the like are disposed.

  The writing light beam 28 is emitted from the exposure apparatus, and internally includes a semiconductor laser as a light source, a coupling lens, an fθ lens, a cylindrical lens, a mirror, a rotating polygon mirror, and the like. . In forming an image, after the photosensitive member 10 is rotated and uniformly charged by the charging roller 11, a writing light beam 28 for each color is emitted toward each photosensitive member, and writing is performed at a writing position on the photosensitive member 10. Irradiation with the light beam 28 forms an electrostatic image. For example, in the developing device 12 of the image forming device 7K, black developer is stored, and when the electrostatic image passes through the developing device, the electrostatic latent image is visualized as a black image. The image forming apparatuses of other colors also store the developer of each color, and the latent image is visualized with the color of the stored developer.

  The black toner image on the photoconductor 10K is transferred to the sheet medium on the transfer belt 14 by the developing roller 11. The black toner image on the sheet medium includes a yellow toner image formed by the image forming device 7Y, a cyan toner image formed by the image forming device 7C, a magenta toner image formed by the image forming device 7M, and the image forming device 7T. The formed transparent toner image is superimposed and transferred. Thereby, a full-color toner image is formed.

  In the image forming apparatus of this example, the toner images on the respective photoconductors are directly transferred onto the sheet medium moving on the transfer belt 14, but in addition to such direct transfer, the toner images are temporarily transferred onto the intermediate transfer belt. There is also known a method of synthesizing a full-color image by batch-transferring overlapping toner images onto a sheet medium. The present invention can also be applied to such an image forming apparatus.

  FIG. 2 shows an example of a full-color image forming apparatus in which six drum-shaped photoconductors 10K, 10Y, 10C, 10M, 10O, and 10G are arranged in tandem as image carriers. These photoconductors are image forming devices 7K, 7Y, and 7C. , 7M, 7O, 7G. These image forming apparatuses 7K, 7Y, 7C, 7M, 7O, and 7G sequentially correspond to black, yellow, cyan, magenta, orange, and green, and images of other colors are also prepared by combinations. Other image forming members and image forming steps are the same as those of the five-color image forming apparatus shown in FIG.

The overall configuration and details of the writing apparatus according to the present invention will be described below.
FIG. 3 shows the writing device portion of the five-color full-color image forming apparatus shown in FIG. A scanning lens is placed between the polygon mirror 20 which is a deflector and the deflecting beam splitter 30a to preliminarily correct differences in scanning magnification due to differences in beam diameter and optical path length depending on the emission wavelength of the synthesized beam. To do. Also, a scanning lens is provided behind the reflecting portion of the dichroic mirror 40a and the optical path of the reflecting mirror 60, and the difference in scanning magnification due to the difference in beam diameter and optical path length depending on the emission wavelength is once again corrected. Also, the plane connecting the beam optical path in the range transmitting and reflecting through the dichroic mirrors 50a and 50b, the wave plates 40a and 40b, the polarizing beam splitters 30a and 30b, and the reflecting mirror 60 and the position where each beam is coupled to each of the photosensitive members. Are set in parallel. FIG. 4 is an enlarged detailed view of one side (left side in FIGS. 1 and 3) extracted from the writing device portion shown in FIG. FIG. 5 is a top view of one side of the writing device shown in FIG.

  4 and 5, on the left side of the polygon mirror 20, light beams emitted from light sources having three different emission wavelengths λ1, λ2, and λ3 (wavelengths are λ1 <λ2 <λ3) among the plurality of light sources are different from each other. A method of irradiating the bodies 10C, 10M, and 10T will be described. As shown in FIG. 5, after each beam emitted from each light source in the same polarization direction (in this example, vertical linear polarization: P-polarization) is once combined in the same path in the sub-scanning direction. , Enters the polygon mirror 20. The three beams scanned by the polygon mirror are first shown in the left of FIG. 8 on the basis of the polarization beam splitter 30a having transmission / reflection characteristics depending on the polarization state as shown in the left of FIG. 6, and the principle shown in FIG. The light is transmitted through a wave plate 40a that gives a phase difference of λ / 4 to the polarization state of a simple beam. Each transmitted beam becomes a light beam state (circularly polarized light) whose polarization state is rotated by λ / 4. Next, the beam of wavelength λ1 is separated into reflected light and the beams of λ2 and λ3 are separated into transmitted light by a dichroic mirror 50a having transmission / reflection characteristics due to the difference in emission wavelength as shown in the left of FIG.

  The beam of λ1 reflected by the first dichroic mirror 50a passes through the λ / 4 wavelength plate 40a that rotates the polarization direction by π / 4 again, and is in a state of being rotated π / 2 in total from the time of emission. It becomes a light beam (lateral linearly polarized light: S-polarized light), is folded by the characteristics of the first polarizing beam splitter 30a, and is irradiated onto the surface to be scanned of the photoconductor 10C.

  On the other hand, the λ2 and λ3 beams transmitted through the first dichroic mirror 50a are then transmitted to the second polarizing beam splitter 30b having transmission and reflection characteristics according to the polarization state as shown in the right of FIG. 6, and to the right of FIG. The light is transmitted through a second wave plate 40b that gives a phase difference of λ / 8 to the polarization state of the beam as shown. Each of the transmitted beams has a polarization state rotated by λ / 8, and a total of the phase difference given by the λ / 4 wavelength plate 40a is rotated by 3λ / 8 (elliptical polarization). Next, the second dichroic mirror 50b having the characteristics shown in the right of FIG. 9 separates the beam of wavelength λ2 into reflected light and the beam of λ3 into transmitted light.

  The beam of λ2 reflected by the second dichroic mirror 50b passes through the λ / 8 wavelength plate 40b that rotates the polarization direction by π / 8 again, and is in a state of being rotated by π / 2 in total from the time of emission. It becomes a light beam (lateral linearly polarized light: S-polarized light), is folded by the characteristics of the second polarizing beam splitter 30b, and is irradiated onto the surface to be scanned of the photoconductor 10M. The beam having the emission wavelength λ3 that has passed through the second dichroic mirror 50b is reflected by the reflection mirror 60 and irradiated onto the surface to be scanned of the photoreceptor 10T.

  By such a method, light beams having different wavelengths emitted from three different light sources and having the same polarization direction and synthesized in the sub-scanning direction are deflected and scanned by the polygon mirror 20, and different images are transmitted through the respective optical elements. Irradiation to the carrier. Compared to the counter scanning writing method using three-stage polygons used in conventional color printers, the number of polygon mirror stages can be reduced to one, and the photosensitive member can be irradiated once in the sub-scanning direction ( The height can be reduced. The beams having the emission wavelengths λ2 and λ3 incident on the second set of polarization beam splitters in the deflected state where a phase difference of λ / 4 is given by passing through the first set of wave plates are opposite to the image carrier. 1/4 of the amount of light emitted to the side is reflected, and is reduced by 3/4 compared to the amount of light of the beam of λ1, so the light amount P1 of the wavelength λ1 beam, the wavelength λ2 beam light amount P2, and the wavelength λ3 The ratio of the beam light quantity P3 is preferably set to P1: P2: P3 = 1: 4/3: 4/3 in advance to prevent image deterioration.

  Further, in order to effectively secure the layout space of the entire image forming apparatus, the optical path lengths of the beams λ1, λ2, and λ3 are set so that the polygon mirror scanning plane and the plane connecting the centers of the plurality of photosensitive drums are parallel to each other. In principle (the optical path length of λ2 must be shorter by half the thickness of the polarizing beam splitter than λ1 and λ3) and the folding position of the polarizing beam splitters 30a and 30b and the dichroic The separation position of the mirrors 50a and 50b should be determined.

  In the five-color tandem color image forming apparatus shown in FIG. 3, the above-described method is arranged on the right side of the polygon mirror 20 by two wavelengths (means for separating the wavelength beams of λ2 and λ3). Is irradiated to each photoconductor. In the 6-color tandem color image forming apparatus shown in FIG. 2, the above-described method is also arranged on the right side of the polygon mirror 20 to irradiate the respective photosensitive members with beams of 6 colors.

1 is a schematic view of a five-color tandem color image forming apparatus to which the present invention is applied. 1 is a schematic diagram of a 6-color tandem color image forming apparatus to which the present invention is applied. 2 is an enlarged view of a writing portion of a five-color tandem color image forming apparatus to which the present invention is applied. FIG. It is a figure explaining the polarization state of the writing part. It is a top view of the writing part. It is a graph which shows the characteristic value of a polarization beam splitter. It is a figure explaining the principle of a wavelength plate. It is a graph which shows the characteristic value of a wavelength plate. It is a graph which shows the characteristic value of a dichroic mirror.

Explanation of symbols

10 Image carrier (photoreceptor)
20 Polygon mirror 30 Polarizing beam splitter 40 Wave plate 50 Dichroic mirror 60 Reflecting mirror

Claims (9)

A plurality of beam emitting means, a light deflecting means for deflecting and scanning the beam emitted from the beam emitting means, and an image forming means for forming an image of the beam deflected and scanned by the light deflecting means on each of the plurality of image carriers In an optical writing device having
It has a synthesis means for synthesizing at least two beams having different emission wavelengths in the same path in the sub-scanning direction, and the beam synthesized by the synthesis means is
A dichroic mirror,
A wave plate that gives a phase difference to the polarization state of the beam;
A polarizing beam splitter having transmission and reflection characteristics depending on the polarization state;
With a reflecting mirror that propagates the finally separated beam to the last image carrier,
Each of the plurality of image carriers is separately imaged, and a beam optical path and each beam within a range that transmits and reflects these dichroic mirror, wavelength plate, polarizing beam splitter, and reflection mirror are included in the image carrier. The plane connecting the points to be joined to each other is set in parallel,
An optical writing device.   Two each of the dichroic mirror, the wavelength plate, and the polarizing beam splitter are used, and the first set of polarizing beam splitter, wavelength plate, and dichroic mirror are arranged in order from the light deflecting unit, and the first set of dichroic mirrors are arranged. 2. The optical writing device according to claim 1, wherein a second set of polarizing beam splitter, a wave plate, and a dichroic mirror are disposed after the mirror.   3. The optical writing device according to claim 2, wherein the phase difference given by the first wave plate is λ / 4, and the phase difference caused by the second wave plate is λ / 8.   The light quantity P1 of wavelength λ1 reflected by the first set of dichroic mirrors and turned back to the first image carrier by the first set of polarization beam splitters, and reflected by the second set of dichroic mirrors and reflected by the second set of polarization beam splitters. The ratio of the beam quantity P2 of the wavelength λ2 that is folded back to the second image carrier and the beam quantity P3 of the wavelength λ3 that is transmitted through the second set of dichroic mirrors and folded to the third image carrier by the reflection mirror is 4. The optical writing device according to claim 3, wherein P1: P2: P3 = 1: 4/3: 4/3.   Preliminarily correct the combined beams of multiple emission wavelengths with a common scanning lens, and then correct them with a non-common scanning lens placed after being reflected by the reflecting section or reflecting mirror of each polarizing beam splitter and dichroic mirror. The optical writing device according to claim 1, wherein:   The combined light beams having a plurality of emission wavelengths are independently corrected by a non-common scanning lens disposed after being turned back by a reflecting portion or a reflecting mirror of each polarizing beam splitter and dichroic mirror. The optical writing apparatus as described in any one of 1-4.   A further combination of a polarizing beam splitter, a wave plate, and a dichroic mirror is arranged on the opposite side of the light deflecting means with respect to the first set and the second set of polarizing beam splitter, wave plate, and dichroic mirror. The optical writing device according to any one of claims 2 to 6.   The first set, the second set of polarizing beam splitters, the wave plate, and the dichroic mirror are arranged symmetrically on both sides of the optical deflecting means. Optical writing device.   An image forming apparatus comprising the optical writing device according to claim 1.

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