JP2009216882A - Optical writing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide an optical writing device which is made thin and provides a high image quality. <P>SOLUTION: An optical housing 20 of the optical writing device 10 is made of one metallic plate composed of: side plates 20a on both sides in a main scanning direction; a bottom plate 20b; and side plates 20c on both sides in a subscanning direction, and is composed in a rectangular box. Optical elements 7, 8, 9, and 11 are held positioning by inserted into openings provided on the side plates 20a of the housing. Since the positioning accuracy of the respective optical elements 7, 8, 9, and 11 is determined by the openings provided on the side plates 20a, the accuracy is remarkably easily improved compared to the case where the accuracy is determined by the vertical direction on the bottom plate 20b of the housing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical writing device (optical scanning device) in an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

Japanese Patent Laid-Open No. 3-150174 Japanese Patent Laid-Open No. 9-127444 Japanese Patent Laid-Open No. 10-3048 JP-A-10-282440

  Currently, market demand for image forming apparatuses includes small size, light weight, and low cost. In particular, since a color image forming apparatus has a large number of components, it is much larger than a conventional monochrome apparatus, and there is a high demand for downsizing.

  An optical writing device (optical scanning device) that uses a plurality of light beams used in an image forming apparatus that has been commercially available in the past, refracts the light beam by a plurality of reflection mirrors, thereby supporting each image. Although it irradiates the scanned surface of the body, it is necessary to arrange a plurality of mirrors so that the respective light beams do not interfere with each other. Therefore, a space is inevitably necessary, and the height in the vertical direction is not particularly large. I do not get.

  Further, in Patent Document 1, using a plurality of light sources having different oscillation wavelengths, the irradiated beams are substantially overlapped by the color synthesizing means, the synthesized light is scanned for each wavelength, and the color separating means is used. An optical scanning device for color separation is described.

Further, Patent Document 2 describes a multi-beam scanning device that can improve the workability of maintenance work and improve the color overlay accuracy.
Further, Patent Document 3 describes an optical scanning device of a multicolor image forming apparatus that scans a plurality of photoconductors using two light sources having different polarization directions or wavelengths.

  Patent Document 4 describes an optical scanning apparatus and an electrophotographic recording apparatus that distribute and irradiate a plurality of photosensitive drums using a multi-chip semiconductor laser light source in which a plurality of semiconductor laser chips having different emission wavelengths are arranged side by side. Has been.

  However, in each of the above-mentioned patent documents, the synthesized light beam is separated using a separating means. However, the optical path lengths to the respective photosensitive members are different from each other, or polygons are used to match the optical path lengths. The surface connecting the mirror scanning surface and the irradiation position on each photoconductor is not parallel. Further, the incident angle of the light beam to each photoconductor is also different.

  As in Patent Document 1 and Patent Document 2, when the polygon mirror scanning surface and the surface connecting the irradiation positions of the respective photosensitive members are not parallel, the optical scanning device can be miniaturized, but a plurality of folding mirrors are used. However, the image forming apparatus cannot be thinned and becomes large. In addition, in the configuration in which the optical elements are arranged substantially symmetrically around the polygon mirror for the four colors, it is difficult to arrange the photoconductors in a horizontal line, and tandem type color image formation that is currently widely used is formed. There is a problem that it is difficult to apply to the apparatus.

  In addition, since the optical path lengths to the respective photoconductors are different from those described in Patent Document 3 and Patent Document 4, the incident angles of the light beams to the respective photoconductors are also different. There are problems that the beam diameters of the respective light beams on the surface to be scanned are different, or that the configuration is disadvantageous when the color images formed on the respective photoconductors are superimposed.

  In addition, when scanning using light beams having different wavelengths, the magnification varies depending on the wavelength when the same scanning optical system lens is used for the light beams having different wavelengths. There is a problem in that the beam diameters are different and a uniform and high-quality electrostatic latent image cannot be formed on each photoconductor.

  Further, in the conventional optical scanning device, it is necessary to support optical elements such as a mirror and a lens in a three-dimensionally complicated positional relationship, which inevitably complicates the configuration of the optical housing, which is necessary for manufacturing the optical housing. There is also a problem that time and cost increase.

An object of the present invention is to solve the above-described problems in a conventional optical writing apparatus, and to provide an optical writing apparatus that achieves high image quality while reducing the thickness and at a low cost.
It is another object of the present invention to provide a small and high-quality image forming apparatus provided with the optical writing device.

According to the present invention, there is provided a plurality of light sources that emit light beams having different wavelengths, and scanning optics for deflecting and scanning light beams emitted from the light sources and synthesized on the same axis in the sub-scanning direction. An optical writing apparatus that includes a system and a separation optical system for separating the combined light beams, and scans the scanned surfaces by guiding the separated light beams to different scanned surfaces. This is solved by the configuration in which the optical center of the scanning optical system and the optical center of the separation optical system substantially coincide with each other in the height direction of the optical writing device.

Further, it is preferable that the optical housing holding the optical elements constituting the scanning optical system and the separation optical system is a box-shaped housing manufactured from a single plate-like member.
Moreover, it is preferable that the optical element constituting the separation optical system is positioned and held on the side wall portion of the box-shaped housing.

Further, it is preferable that an optical element constituting the separation optical system is fitted and held in an opening provided in a side wall portion of the box-shaped housing.
Further, it is preferable that a unit holding portion for holding the housing in the image forming apparatus main body is provided on the side wall portion on the same row as the opening and the sub-scanning direction.

In addition, it is preferable that an optical element holding portion for mounting and holding an optical element constituting the scanning optical system is provided on the bottom plate portion of the box-shaped housing.
Further, it is preferable that a reinforcing portion protrudes from the bottom plate portion of the box-shaped housing so as not to interfere with optical elements constituting the scanning optical system and the separation optical system.

  Preferably, the bottom plate portion of the box-shaped housing has a beam exit for emitting a light beam to the surface to be scanned, and an imaging lens is fitted to the beam exit to function as dust-proof glass.

The plate member is preferably a metal sheet metal.
Moreover, while using a rotation deflector as one common deflection means among the optical elements with which the optical writing device of any one of Claims 1-9 is provided, optical elements other than the said rotation deflector are the said It is preferable that they are arranged substantially symmetrically on both sides of the rotary deflector and are configured to scan four scanned surfaces with light beams from four light sources.

Further, according to the present invention, the above problem is solved by an image forming apparatus including the optical writing device according to any one of claims 1 to 10.
Further, it is preferable that the tandem type full-color device is provided with four image carriers as scanning objects scanned by the optical writing device.

  According to the optical writing device of the present invention, the optical center of the scanning optical system and the optical center of the separation optical system in the height direction of the optical writing device are configured to substantially coincide with each other. The optical writing device does not increase in size in the height direction and is thin even if the scanning light emitted from the laser beam is separated by a separation optical system and each photoconductor (scanned surface) is scanned. The optical writing device can be realized.

  According to the structure of claim 2, since it is a box-shaped housing manufactured from a single plate-like member, the optical housing has a simple structure, facilitating the manufacture of the housing, cost reduction and manufacturing time by reducing manufacturing procedures. Shortening can be realized.

  With the configuration of claim 3, since the optical elements constituting the separation optical system are positioned and held on the side wall portion of the box-shaped housing, the surface accuracy and flatness are higher than necessary for the housing bottom plate which has a large area and is difficult to obtain accuracy. This is not required, and the processing cost can be suppressed. Compared with the case where the accuracy is increased (increased) in the vertical direction on the bottom plate, the accuracy improvement is greatly facilitated.

  According to the configuration of the fourth aspect, since the optical elements constituting the separation optical system are fitted and held in the openings provided in the side wall portions of the box-shaped housing, it is easy to maintain the parallelism between the optical elements. In addition, the rigidity of the housing itself can be increased. Moreover, in order to obtain the positioning accuracy of the optical element at the side wall, it is only necessary to obtain the positional accuracy of the opening for holding the optical element, so that the accuracy can be greatly improved as compared with ensuring the accuracy on the bottom plate. It becomes.

  According to the configuration of the fifth aspect, the unit holding portion for holding the housing on the image forming apparatus main body is provided on the side wall portion on the same row in the sub-scanning direction as the opening for holding the optical element of the separation optical system. The positioning accuracy of the writing device with respect to the image forming apparatus is improved, which can contribute to the improvement of the image quality.

  According to the configuration of the sixth aspect, since the optical element holding portion for positioning and holding the optical element constituting the scanning optical system is provided on the bottom plate portion of the box-shaped housing, the rigidity of the housing bottom plate portion is increased. Can do.

  According to the configuration of the seventh aspect, since the reinforcing portion protrudes from the bottom plate portion of the box-shaped housing so as not to interfere with the optical elements constituting the scanning optical system and the separation optical system, the rigidity of the housing bottom plate portion is increased. be able to.

According to the configuration of the eighth aspect, dust and the like can be prevented from entering the housing.
With the configuration of the ninth aspect, processing becomes easy, and a high-precision optical writing device can be realized at low cost.

With the configuration of the tenth aspect, it is possible to cope with full-color scanning while suppressing an increase in the number of parts.
According to the image forming apparatus of the eleventh aspect, by providing the thin optical writing device, it is possible to reduce the size of the image forming device in the vertical direction and to reduce the size of the device.

  With the configuration of the twelfth aspect, a tandem type image forming apparatus capable of forming a full color image in a short time can be realized by reducing the size of the image forming apparatus in the vertical direction with a thin optical writing device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the main configuration of an example of an optical writing device according to the present invention. FIG. 2 is a plan view thereof. The optical writing device 10 of this example has a configuration in which two sets of components other than the polygon mirror 5 in FIG. 2 are arranged substantially symmetrically with the polygon mirror 5 as a deflecting means in common, as shown in FIG. In addition, four photosensitive members as scanning objects are scanned.

  The optical writing apparatus 10 of this example shown in these drawings includes a semiconductor laser 1, a collimating lens 2, an aperture 3, a cylindrical lens 4, a polygon mirror 5 that is a rotating polygon mirror, an fθ lens 6, and a polarization beam splitter 7 (first Beam separating means), ¼ wavelength plate 8, dichroic mirror 9 (second beam separating means), reflecting mirror 11, imaging lens 14 and the like, and these components are arranged in the optical unit 20. ing.

  In the optical writing apparatus of this example, semiconductor lasers 1a and 1b that emit light beams having different wavelengths are used, and those having a wavelength band corresponding to the dichroic mirror 9 as the light separation means are used. . Similarly, semiconductor lasers 1c and 1d that emit light beams having different wavelengths are used, and those having a wavelength band corresponding to the dichroic mirror 9 as the light separating means are used.

  Since the operation of the components arranged on each side of the polygon mirror 5 is the same, the description will be made mainly based on the left part here, but scanning is performed by the semiconductor lasers 1c and 1d shown on the right side of the polygon mirror 5. The same applies to the parts to be performed.

  Light beams having the same polarization direction and different wavelengths emitted from two different light sources, the semiconductor lasers 1a and 1b, are combined on the same axis in the sub-scanning direction via the collimating lens 2, the apertures 3a and 3b, and the cylindrical lens 4. Then, it is reflected by the polygon mirror 5 as the deflecting means, passes through the fθ lens 6 and passes through the polarizing beam splitter 7 as the beam separating means. The polarization beam splitter 7 separates light according to the polarization direction due to the difference in the rotation angle of the light beam by π / 2, and has a characteristic of transmitting or reflecting depending on the beam entrance direction. The collimating lens 2 and the cylindrical lens 4 are arranged for each light source, but since they are exactly the same, they are not distinguished by adding a and b to the reference numerals. Further, since the semiconductor lasers 1a and 1b and the apertures 3a and 3b have different parts, they are distinguished by adding a and b to the reference numerals.

  Two beams (light beams having the same polarization direction and different wavelengths) that have exited the fθ lens 6 and passed through the polarization beam splitter 7 pass through the quarter-wave plate 8. The quarter-wave plate 8 rotates the polarization direction of the light beam by π / 4, and the two light beams pass through the quarter-wave plate 8 so that they are π / 4 at the time of emission. In a state where the light beam is rotated only by one beam, one beam is transmitted and the other one beam is reflected by the dichroic mirror 9 which is a multilayer dielectric mirror placed perpendicular to the beam. The dichroic mirror 9 transmits a light beam in a certain wavelength band and reflects a light beam in a certain wavelength band. That is, the two light beams are separated into reflected light and transmitted light by the dichroic mirror 9.

  The light beam that has passed through the dichroic mirror 9 is reflected by the reflecting mirror 10 and passes through the imaging lens 14 and is irradiated onto the surface to be scanned of the photosensitive member 101a while being narrowed down in the sub-scanning direction. On the other hand, the light beam reflected by the dichroic mirror 9 returns the same optical path and passes through the quarter-wave plate 8 again, so that the polarization direction is rotated again by π / 4. The light beam enters the polarization beam splitter 7 in a state where the light beam is rotated. The light beam rotated by π / 2 from that at the time of emission is reflected by the polarization beam splitter 7 and is irradiated onto the surface to be scanned of the photoconductor 101b through the imaging lens 14 while being narrowed down in the sub-scanning direction. In this manner, the light beams emitted from the semiconductor lasers 1a and 1b are respectively guided to the photosensitive member 101a and the photosensitive member 101b, and scan the respective photosensitive members.

  In this example, the two light beams emitted from the semiconductor lasers 1 a and 1 b are both linearly polarized P waves, for example, and one light beam is rotated by π / 4 by the quarter-wave plate 8. In the state of circularly polarized light, the light passes through the dichroic mirror 9 and is irradiated onto the photosensitive member 101a. The other light beam is rotated by π / 4 by the quarter-wave plate 8 to become circularly polarized light, then reflected by the dichroic mirror 9 and again passes through the quarter-wave plate 8 to change the polarization direction again to π. The photosensitive member 101b is irradiated in a state of being rotated by / 4 to be a linearly polarized S wave.

  Similarly, also on the right side portion of the polygon mirror 5, the light beams emitted from the semiconductor lasers 1c and 1d are respectively guided to the photoconductor 101c and the photoconductor 101d to scan each photoconductor.

  In this example, the optical path lengths from the respective semiconductor lasers 1a, 1b, 1c, and 1d, which are light sources, to the respective photoreceptors 101a, 101b, 101c, and 101d are provided to be equal.

In this example, the incident angles of the respective light beams to the surface of the photoreceptor (shown as an angle θ in FIG. 1) are configured to be equal.
Further, in this example, the scanning plane by the polygon mirror 5 and the plane connecting the centers of the plurality of photosensitive drums (in this example, the photosensitive bodies 101a, 101b, 101c, and 101d) are configured to be parallel.

  Now, in order to separate the two light beams by the dichroic mirror 9 which is a multilayer dielectric mirror, the wavelengths of the two light beams need to be different. Although the boundary between reflection and transmission differs depending on the added multilayer film, for example, a dichroic mirror having a boundary near the wavelength of 750 nm can be preferably used. In that case, it is necessary to select a wavelength band before and after the boundary for the light beam to be used. When using a dichroic mirror having a boundary near the wavelength of 750 nm, as an example, visible light having a wavelength of about 650 nm and infrared light having a wavelength of about 780 nm can be selected (visible light having a wavelength of about 650 nm is selected. A semiconductor laser that emits light and a semiconductor laser that emits infrared light having a wavelength of about 780 nm can be used as the semiconductor lasers 1a and 1b). The same applies to the semiconductor lasers 1c and 1d.

  The dichroic mirror, which is a multilayer dielectric mirror, includes a hot mirror (heat ray reflective type) and a cold mirror (heat ray transmissive type), and either type can be employed in the present invention.

  As can be seen from FIG. 1, the optical writing device 10 according to the present invention includes an optical center of the scanning optical system upstream of the fθ lens 6 (an optical element constituting the optical center) and a separation optical system downstream of the polarization beam splitter 7. The optical center of the optical element is configured to substantially coincide with the optical center. For this reason, scanning light (light beam) emitted from a plurality of light sources (semiconductor lasers 1a and 1b or semiconductor lasers 1c and 1d) and synthesized is separated by a separation optical system to scan each photosensitive member. However, the size of the optical scanning device (optical writing device) in the height direction is not increased, and a thin optical writing device can be realized.

  In addition, since the separation optical system for separating a plurality of scanning lights (light beams) can be arranged on both sides of the rotary deflector (polygon mirror 5), the optical writing device 10 of this example is a tandem type full-color image forming device. Even when four light beams are distributed to four photosensitive members, the thickness of the optical writing device does not increase, and a thin optical writing device can be realized. Therefore, the effect of reducing the size of the full-color image forming apparatus, in particular, suppressing the size in the vertical direction is great.

Next, the optical housing of the optical writing device 10 will be described with reference to FIGS.
FIG. 3 is a perspective view showing the optical writing device 10 described above with the upper cover of the optical housing removed. FIG. 4 is a plan view thereof. FIG. 5 is a side view thereof. FIG. 6 is a perspective view of the housing from which the optical element is omitted. FIG. 7 is a plan view of the housing. FIG. 8 is a side view of the housing. FIG. 9 is a perspective view showing the housing expanded. FIG. 10 is a plan view showing the housing expanded. FIG. 11 is a bottom view of the deployed housing as viewed from below. FIG. 12 is a side view of the deployed housing as seen from the side. Here, the upper cover that covers the upper surface of the optical housing is omitted. 7, 10, and 11 are hatched to indicate the openings provided in the housing in an easy-to-understand manner.

  In the optical writing apparatus 10 of this example, the housing body 20 excluding the upper cover is composed of a single flat plate member (in this example, a sheet metal), and side plates 20a and 20a on both sides in the main scanning direction and a bottom plate 20b. And side plates 20c, 20c on both sides in the sub-scanning direction. As can be seen from FIG. 6, a square (rectangular) box-shaped housing body 20 is formed by raising (bending) two side plates 20a and 20a and side plates 20c and 20c with respect to the bottom plate 20b.

  The side plates 20a and 20a on both sides of the main scanning direction hold the polarizing beam splitter 7 (first beam separating means), the quarter wavelength plate 8, the dichroic mirror 9 (second beam separating means), and the reflecting mirror 11. Openings 21, 22, 23, and 24 are provided. In the present example, these openings 21, 22, 23, and 24 are provided on both sides of the polygon mirror 5 in correspondence with a configuration in which two sets of optical elements are arranged on both sides of the polygon mirror 5. In addition, an opening 25 for holding the imaging lens 14 is provided in the bottom plate 20b. The opening 25 is also an opening for guiding the scanning light from the light source to the outside of the housing to scan the photosensitive drum 101 as a scanning target. In addition, a total of four openings 25 are provided, two on each side of the polygon mirror 5. In this example, the openings 21 to 25 are provided by drilling a sheet metal constituting the housing body 20.

  Each optical element of the polarizing beam splitter 7 (first beam separating means), the quarter wavelength plate 8, the dichroic mirror 9 (second beam separating means) and the reflecting mirror 11 is composed of two side plates 20a of the optical housing, It is inserted into the openings 21, 22, 23, and 24 of 20 a and is positioned and held so that the scanning optical system and the optical center substantially coincide. A plurality of contact portions 26 as shown in FIG. 13 are formed on the side plate 20a of the housing on the side surfaces of the openings 21, 22, 23, and 24, and the openings on the opposite side to the contact portions 26 are formed. A plate spring (not shown) is inserted into the gap, and the optical element (here, the polarization beam splitter 7) is pressed against the contact portion 26, whereby the optical element is positioned and held in the main scanning direction and the sub-scanning direction. In FIG. 13, the polarization beam splitter 7 is described as the optical element held in the opening, but the optical element is similarly held in the other openings.

  In this example, the imaging lens 14 held on the bottom plate 20b of the housing also functions as a dust-proof glass that prevents dust and the like from entering the housing. Therefore, no gap is generated with respect to the opening 25 provided on the bottom plate 20b. So that it is inserted and held.

  On the bottom plate 20b of the housing, a lens holding portion 27 for holding the fθ lens 6 as a scanning optical element is convexly provided. In this example, the lens holding portion 27 is formed by pressing on a sheet metal (the bottom plate 20b portion) constituting the housing body 20 so that the scanning plane of the separation optical system and the scanning plane of the scanning optical system substantially coincide. , Fθ lens 6 is held. Three convex portions 28 for positioning the fθ lens 6 are formed on the upper surface of the lens holding portion 27. The convex portion 28 is also formed by pressing in this example.

  Further, a plurality of reinforcing portions 29 for increasing the rigidity of the housing bottom plate are formed on the bottom plate 20b of the housing. In this example, the reinforcing portion 29 is provided on the sheet metal (the bottom plate 20b portion) constituting the housing body 20 by pressing or drawing. Further, in this example, a total of six (rows) reinforcing portions 29 are provided on each side of the polygon mirror, three (rows). These reinforcing portions 29 are formed on the bottom plate 20b so as not to interfere with the respective optical elements, with the positions shifted from the openings 21 to 24 provided in the side plates 20a and 20a (shifted in the sub-scanning direction).

  Further, unit holding portions 30 for projecting the optical housing 20 (optical writing device 10) to the image forming apparatus main body are provided on the side plates 20a, 20a on both sides of the housing. In this example, the unit holding part 30 is formed on a sheet metal constituting the housing body 20 by press working. Since the unit holding unit 30 is formed on the side plates 20a and 20a in the same row as the openings 21 to 24 for holding the optical element, the processing accuracy is improved and the positioning accuracy of the optical writing device with respect to the image forming apparatus is improved. To do.

  As a manufacturing procedure of the optical housing 20 of this example, press processing (drawing processing) such as the lens holding portion 27 and the reinforcing portion 29 is performed on one sheet metal constituting the housing, and then the openings 21 to 25 are formed. The optical housing 20 is manufactured by drilling and finally bending the side plates 20a, 20a and 20c, 20c. Each optical element, light source unit, or polygon motor is attached to the optical housing 20 to constitute the optical writing device 10.

  As described above, in the optical writing device 10 of the present example, the optical housing 20 is configured in a simple square box shape, so that the housing is easy to manufacture because the optical housing 20 is not a complicated shape as in the conventional optical housing. The cost can be reduced and the production time can be shortened by reducing the production procedure.

  In addition, by forming the optical housing from a single metal plate, processing becomes easy, and a highly accurate optical writing device can be realized at low cost. The optical housing is not limited to sheet metal, and may be made of resin, for example. In that case, the opening for holding the optical element can be provided by post-opening processing.

  In addition, by positioning and holding the optical elements that constitute the separation optical system on the side surface (side wall portion) of the optical housing, a surface area and flatness that are more than necessary are required for the housing bottom plate that has a large area and is difficult to obtain accuracy. Therefore, the processing cost can be suppressed. In this example, in order to obtain the positioning accuracy of the optical element at the side plates 20a and 20a, it is only necessary to obtain the positioning accuracy of the openings 21 to 24 holding the optical element, so the accuracy in the vertical direction on the bottom plate is sufficient. Compared with the case of increasing (increasing), the accuracy improvement becomes much easier.

  Further, by positioning and holding the optical elements constituting the separation optical system through the openings 21 to 24 provided in the side plates 20a and 20a of the optical housing, it becomes easy to maintain the parallelism between the optical elements and the housing itself. It is also possible to increase the rigidity.

  Further, by providing the lens holding portion 27 for holding the fθ lens 6 so as to protrude from the bottom plate 20b of the housing, the rigidity of the housing bottom plate portion can be increased. Further, by providing the plurality of reinforcing portions 29 on the bottom plate 20b of the housing, the rigidity of the housing bottom plate portion can be increased.

  Further, the unit holding portion 30 for holding the optical housing (optical writing device) in the image forming apparatus main body is formed on the same side plate in the same row as the opening for holding the optical element, whereby the image forming device of the optical writing device The positioning accuracy with respect to can improve, and can contribute to the improvement of image quality.

  Further, the imaging lens 14 can be fitted and held in the opening 25 for letting the scanning light out of the optical housing, so that the imaging lens 14 can function as dust-proof glass, and dust and the like enter the housing. Can be prevented.

  Finally, an example of an image forming apparatus including the optical writing device according to the present invention will be described. The image forming apparatus shown in FIG. 14 is a direct transfer type tandem type full-color printer, and four image forming units 100 (Y, C, M, K) are arranged at substantially the center of the apparatus main body. The image forming units 100 (Y, C, M, K) corresponding to the respective colors of yellow, cyan, magenta, and black are arranged in parallel along the upper running side of the transfer conveyance belt 108. The transfer conveyance belt 108 wound around the support rollers 106 and 107 and the like is driven to run counterclockwise in the drawing. A registration roller 109 is disposed on the side of the right support roller 107, and a fixing device 110 is disposed on the side of the left support roller 106.

  Each image forming unit 100 has the same configuration except for the color of the toner to be handled, and includes a photosensitive drum 101 as an image carrier. Around the photosensitive drum 101, a charging unit 102, a developing device 103, and the like are arranged, and a transfer roller 105 as a transfer unit is provided inside the transfer conveyance belt 108 so as to face each photosensitive drum 101. ing. The developing device 103 is provided with a toner storage container 104. In the figure, among the four image forming units, only the black image forming unit 100K is representatively given a reference numeral for each device constituting the image forming unit.

  An optical writing device 10 is provided at the top of the device above the four image forming units 100. The optical writing device 10 corresponds to a four-color full-color image forming device and has been described above. The optical writing device 10 irradiates the surface of the photosensitive drum 101 of each color image forming unit with a laser beam L that is optically modulated based on image information.

  A sheet feeding tray 130 for loading sheets is disposed at the lower part of the apparatus, and a sheet feeding apparatus 131 for feeding sheets from the sheet feeding tray is provided. Details of the separation mechanism and the like are omitted.

An image forming operation in the color printer configured as described above will be briefly described.
The photosensitive drum 101 of the image forming unit 100 is rotated in the clockwise direction in the drawing by a driving unit (not shown), and the surface of the photosensitive drum 101 is uniformly charged to a predetermined polarity by the charging unit 102. The charged photoconductor surface is irradiated with laser light from the optical writing device 10, whereby an electrostatic latent image is formed on the photoconductor drum 101 surface. At this time, the image information exposed on each photosensitive drum 101 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device 103 to the electrostatic latent image formed in this way, and visualized as a toner image.

  On the other hand, paper is fed from the paper feed tray 130 and the fed paper is once abutted against the registration roller pair 109. The paper is sent out in synchronism with the visible image, and is sucked and conveyed by the belt 108. Each time the paper reaches the transfer position facing each photoconductor drum 101, the toner images of the respective colors are sequentially transferred onto the paper by the action of the transfer means 105. In this way, a full-color toner image is carried on the paper.

  Note that any one of the image forming units 100 can be used to form a single-color image or a two-color or three-color image. In the case of monochrome printing, image formation is performed using the rightmost black (K) unit in the drawing among the four image forming units.

  The residual toner adhering to the surface of the photosensitive drum 101 after the toner image is transferred is removed from the surface of the photosensitive drum by a cleaning unit (not shown), and then the surface is subjected to the action of a static eliminator (not shown) so that the surface potential is increased. Initialized to prepare for the next image formation.

  The sheet on which the toner image has been transferred is separated from the transfer conveyance belt 108 and sent to the fixing device 110, where the toner image is fused and fixed on the sheet by heat and pressure. The fixed paper is discharged out of the apparatus and stacked on a paper discharge tray (not shown).

  Since the optical writing device 10 is thin and thin as described above, the optical writing device 10 can be arranged in a limited space inside the image forming apparatus. The effect of reducing the thickness in the direction is great. In addition, the optical housing of the optical writing device is configured in a simple square box shape, so it is not a complicated shape like the conventional optical housing, making it easier to manufacture the housing and reducing costs by reducing manufacturing procedures. In addition, manufacturing time can be shortened. Therefore, it is possible to contribute to cost reduction of the image forming apparatus.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, as each light source and the second beam separating means (dichroic mirror), those capable of separating a plurality of light beams in a combination of both can be appropriately employed. Also, the first beam separating means can be of an appropriate configuration. In addition, the incident angle of the light beam to the scanning target can be set as appropriate. The photosensitive member to be scanned is not limited to a drum shape, and a belt-like photosensitive member is also possible. The shape and size of the optical element and the opening for holding the optical element can be set as appropriate. The shape and size of the optical housing can be changed as appropriate within the scope of the present invention.

  The image forming apparatus is not limited to the direct transfer method, but may be an intermediate transfer method. The order of colors in the tandem type is also arbitrary. In addition, the present invention can be applied not only to a full-color machine of four colors but also to a multi-color machine using a plurality of colors, for example, two colors of toner. The configuration of each part of the image forming apparatus is also arbitrary. Of course, the image forming apparatus is not limited to a printer, and may be a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

It is sectional drawing which shows the principal part structure in an example of the optical writing apparatus which concerns on this invention. FIG. It is a perspective view which shows an optical writing device in the state which removed the upper cover of the optical housing. FIG. It is the side view. It is a perspective view of a housing which omitted an optical element. It is a top view of a housing. It is a side view of a housing. It is a perspective view which expands and shows a housing. It is a top view which expands and shows a housing. It is the bottom view which looked at the expanded housing from the lower part. It is the side view which looked at the expanded housing from the side. It is a partial side view which shows a mode that an optical element is hold | maintained at the opening provided in the side wall part of the housing. 1 is a schematic configuration diagram of a direct transfer tandem full-color printer that is an example of an image forming apparatus including an optical writing device according to the present invention.

Explanation of symbols

1a, 1b, 1c, 1d Semiconductor laser 5 Polygon mirror (rotary deflector)
6 fθ lens 7 polarizing beam splitter 8 quarter wave plate 9 dichroic mirror 10 optical writing device (optical scanning device)
11 Reflector (mirror)
DESCRIPTION OF SYMBOLS 14 Imaging lens 20 Housing main body 20a Side plate 20b Bottom plate 20c Side plate 21-25 Opening 27 Lens holding part 29 Reinforcement part 30 Unit holding part 100 Image forming unit 101 Photoconductor

Claims (12)

A plurality of light sources that emit light beams having different wavelengths;
A scanning optical system for deflecting and scanning light beams respectively emitted from the plurality of light sources and combined on the same axis in the sub-scanning direction;
A separation optical system for separating the synthesized light beam,
An optical writing device that guides the separated light beams to different scanned surfaces and scans the scanned surfaces,
An optical writing apparatus, wherein the optical center of the scanning optical system and the optical center of the separation optical system in the height direction of the optical writing apparatus substantially coincide with each other.   2. The light according to claim 1, wherein the optical housing holding the optical elements constituting the scanning optical system and the separation optical system is a box-shaped housing manufactured from a single plate-like member. Writing device.   The optical writing device according to claim 2, wherein the optical element constituting the separation optical system is positioned and held on a side wall portion of the box-shaped housing.   The optical writing device according to claim 3, wherein an optical element constituting the separation optical system is fitted and held in an opening provided in a side wall portion of the box-shaped housing.   The optical writing device according to claim 4, wherein a unit holding portion for holding the housing in the image forming apparatus main body is provided on the side wall portion on the same row in the sub-scanning direction as the opening.   3. The optical writing according to claim 2, wherein an optical element holding portion that mounts and holds an optical element constituting the scanning optical system is projected from a bottom plate portion of the box-shaped housing. apparatus.   The light according to claim 2, wherein a reinforcing portion protrudes from a bottom plate portion of the box-shaped housing so as not to interfere with optical elements constituting the scanning optical system and the separation optical system. Writing device.   The bottom plate portion of the box-shaped housing has a beam exit for emitting a light beam to a scanned surface, and an imaging lens is fitted to the beam exit to function as dust-proof glass. Item 3. The optical writing device according to Item 2.   The optical writing device according to claim 2, wherein the plate-like member is a metal sheet metal.   A rotary deflector is used as a common deflecting means among the optical elements included in the optical writing device according to claim 1, and an optical element other than the rotary deflector is used as the rotational deflection. An optical writing device, wherein the optical writing device is arranged substantially symmetrically on both sides of the device, and is configured to scan four scanned surfaces with light beams from four light sources.   An image forming apparatus comprising the optical writing device according to claim 1.   12. The image forming apparatus according to claim 11, wherein the image forming apparatus is a tandem-type full-color apparatus including four image carriers as scanning objects scanned by the optical writing device.

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