JP5017030B2 - Optical writing apparatus and image forming apparatus - Google Patents

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 the surface to be scanned is irradiated, the optical writing device tends to increase in the thickness direction because a plurality of mirrors are used.

  FIG. 6 is a block diagram showing an example of a conventional optical writing apparatus. In the optical writing apparatus shown in this figure, a light beam emitted from a light source (not shown) is deflected by a polygon mirror 54 and guided to a photoconductor 101 to be scanned through a plurality of mirrors (reflecting mirrors) 59. The mirrors 59 for guiding each light beam to the photosensitive member need to be arranged so that the respective light beams do not interfere with each other. Therefore, a space is inevitably required, and the height in the vertical direction is particularly large. I have to be.

  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.

  Furthermore, 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.

An object of the present invention is to solve the above-mentioned problems in a conventional optical writing apparatus, and to provide an optical writing apparatus that achieves high image quality while realizing a reduction in thickness.
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 an optical writing apparatus that scans a surface to be scanned by deflecting light from a light source by a deflector, and includes a plurality of light sources that emit light beams having the same polarization direction and different wavelengths. The light beams emitted from the plurality of light sources are combined so as to be on the same axis when viewed from the sub-scanning direction and deflected by the deflector, and the light beams deflected by the deflector enter. A first beam transmitting / reflecting means arranged to transmit or reflect the light beam according to the polarization direction of the light beam, and a second to transmit or reflect each of the light beams after passing through the first beam transmitting / reflecting means depending on its wavelength. a beam transmitting reflecting means, disposed between the first beam transmissive reflective means and the second beam transmitting reflecting means, the polarization direction of the light beam [pi / 4 rotated to 1 / And a wave plate, a light source as the upstream, the deflector, the first beam transmitting reflecting means, said quarter-wave plate and the second beam transmitted through the reflecting means are arranged in this order, the first The beam transmitting / reflecting means transmits the light beam deflected by the deflector to pass through the quarter wavelength plate, and is reflected by the second beam transmitting / reflecting means and returned to the quarter wavelength. are arranged to reflect light beams having passed through the plate again, to scan one scanning surface by the light beam transmitted through the second beam transmissive reflecting means and reflecting the second beam transmissive reflective means light by more it reflects the beam to the first beam transmitted through the reflecting means configured to scan the other one surface to be scanned, further an aperture having a beam passing portion of the magnitude of the response to the wavelength of the optical beam This is solved by forming each light beam into a desired shape by the aperture.

The plurality of light sources are mounted close to the same substrate, and the light beam emission directions from the respective light sources are inclined in different directions with respect to the normal line of the substrate, and the light beams are emitted from the respective light sources. It is preferable that the direction exhibits an opening angle at least in the main scanning direction and intersects in the vicinity of the deflection surface of the deflector.

Further, it is preferable to have beam combining means for combining light beams from the plurality of light sources, and to irradiate the deflection surface of the deflector with the light beam combined by the beam combining means.
Further, it is preferable to use a light source that emits light beams whose polarization directions are different by 90 degrees as the plurality of light sources.

Further, it is preferable that the light beams from the respective light sources are combined by the beam combining means after passing through the aperture.
Further, it is preferable that the light beams from the respective light sources are combined by the beam combining means and then passed through the aperture.

The plurality of light sources preferably have a configuration in which light sources that emit light beams having different wavelengths are arranged in a line.
Preferably, the aperture includes a plurality of apertures, and each aperture is provided with a beam passing portion having a size corresponding to the wavelength of each light beam.

Moreover, it is preferable that the said aperture is one aperture which has a beam passage part which can pass each light beam by the magnitude | size different according to the wavelength.
In addition, the beam passing portion includes a base material opening provided in a predetermined shape in a base material that does not transmit each light beam, and a predetermined shape provided in a beam transmission blocking unit provided in the base material opening. It comprises a second opening, and the beam transmission blocking means preferably transmits one of the light beams by its wavelength and blocks the other .

The beam transmission blocking means is preferably an optical filter or a dichroic mirror.
The material of the optical filter or dichroic mirror is preferably glass or transparent resin, and a dielectric multilayer film is preferably formed on the incident surface.

  Further, it is preferable that the second beam separating means is arranged so that the optical path lengths from the light sources to the scanned surfaces are equal.

Moreover, it is preferable that the incident angle of the light beam to each of the surfaces to be scanned is the same angle.
Further, it is preferable that the scanning surface by the deflector and the plane connecting the incident positions of the light beams on the scanned surfaces are parallel to each other.

Moreover, while using the said deflector as one common deflector among the optical elements with which the optical writing apparatus of any one of Claims 1-15 is provided, optical elements other than the said deflector are used for the said deflection | deviation. It is preferable that they are arranged substantially symmetrically on both sides of the device and are configured to scan four scanned surfaces with light beams from four light sources.

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 16 .
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 first beam transmission / reflection unit and the second beam transmission / reflection unit can separate the light beams emitted from the plurality of light sources. Since each light beam can be guided to each scanning object without any problem, the optical writing device can be made thinner. In addition, since each light beam is shaped to a desired beam diameter by the aperture, the beam diameter of the light beam on each scanned surface is the same even when scanning is performed using a plurality of light sources having different emission wavelengths. Thus, it is possible to form a uniform and high-quality electrostatic latent image.

With the configuration of the second aspect, it is not necessary to use a beam combining means such as a prism, and the number of parts and the cost can be reduced.
According to the configuration of the third aspect, since a plurality of light beams scan on the same plane (on the optical axis), it is possible to perform scanning with high accuracy by suppressing a shift of the scanning position on the surface to be scanned and a bending of the scanning line. it can.

With the configuration of the fourth aspect, it is possible to perform beam synthesis using the polarization characteristics of the light beam.
According to the configuration of the fifth aspect, the light beams can be synthesized after being formed into a desired shape.

According to the configuration of the sixth aspect, the light beams can be formed into a desired shape after being combined.
According to the configuration of the seventh aspect, it is not necessary to use beam combining means such as a prism, and the number of parts and the cost can be reduced.

According to the configuration of the eighth aspect, the configuration of the aperture becomes simple, and the cost can be reduced.
With the configuration of the ninth aspect, the number of apertures can be reduced, the number of parts can be reduced, and space saving can be achieved.

According to the structure of the tenth aspect, it becomes possible to form a plurality of beams by one aperture, and each light beam can be shaped according to its wavelength.
According to the configuration of the eleventh aspect, it is possible to realize the formation of a plurality of beams by one aperture using the function of the optical filter or the dichroic mirror.

  According to the structure of the twelfth aspect, an optical writing device with little change in temperature characteristics can be obtained by using glass as the material of the optical filter or dichroic mirror. In addition, when a transparent resin is used, an inexpensive optical writing device can be obtained.

According to the configuration of the thirteenth aspect, since the optical path lengths from the respective light sources to the respective scanned surfaces are equal, it is not necessary to arrange the respective scanned surfaces with respect to the optical writing device, and the optical writing device can be arranged. The space involved can be reduced in thickness.

According to the configuration of the fourteenth aspect, since the incident angles of the light beams to the scanned surfaces are the same angle, the arrangement of the scanning target is not complicated, and the image forming apparatus can be reduced in size.

According to the configuration of the fifteenth aspect, since the scanning surface by the deflector and the plane connecting the incident positions of the light beams to the respective scanned surfaces are parallel, the arrangement of the scanning objects is not complicated, and the image forming apparatus This can contribute to the downsizing.

According to the configuration of the sixteenth 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 seventeenth aspect , by providing the thin optical writing device, the size of the image forming device in the vertical direction can be reduced, and the size of the device can be reduced.

With the configuration of the eighteenth 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 showing a part 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 10, imaging imaging lens 14 and the like, and these components are included in the unit housing 12. Is arranged. In addition, the structure of each Example mentioned later can be employ | adopted for the structure of the upstream from the polygon mirror 5, respectively. FIG. 2 shows one embodiment.

  The optical writing device 10 of this example scans four photosensitive members as scanning objects, and includes four semiconductor lasers as light sources. As shown in FIG. 2, two of them are arranged on one side of the polygon mirror 5, and are shown as semiconductor lasers 1a and 1b in FIG. Further, as described above, the optical writing device 10 of the present example has a configuration in which the polygon mirror 5 is shared and two sets of other components are arranged substantially symmetrically, and the same is applied to one side of the polygon mirror 5 (not shown). Thus, semiconductor lasers 1c and 1d (not shown) as light sources are arranged.

  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 given mainly based on the left side portion shown in FIG. 2, but it is shown on the right side of the polygon mirror 5 in FIG. The same applies to the parts scanned by the semiconductor lasers 1c and 1d. The configuration upstream from the polygon mirror 5 will be described in the case of the first embodiment (other embodiments will be described later).

  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.

Next, with reference to FIG. 3, each embodiment that can be used as a configuration upstream of the polygon mirror 5 (configuration that combines two light beams) will be described.
(A) The first embodiment of beam synthesis shown in the figure is called an intersection method. Two light sources (semiconductor lasers) 1a and 1b having different emission wavelengths are attached in the vicinity of the same substrate having a substantially flat plate shape around a straight line substantially parallel to the optical axis of each light source. The emission direction of each of the light sources is inclined in different directions with respect to the normal line of the substrate, and the emission direction of the light beam from each light source exhibits an opening angle at least in the main scanning direction and intersects near the deflection surface of the polygon mirror 5. Is provided. That is, the light beams La and Lb emitted from the semiconductor lasers 1a and 1b are converted into parallel lights by the collimating lens 2 and formed into desired shapes by the apertures 3a and 3b, respectively. It is narrowed down to. These light beams La and Lb are then combined so as to intersect in the vicinity of the deflection surface and deflected by the polygon mirror 5. That is, the light sources 1a and 1b are arranged such that the light beams La and Lb are irradiated at substantially the same position in the main scanning direction of the polygon mirror 5 with a predetermined angle in the same plane in the sub-scanning direction. .

  (B) In the second embodiment of the beam synthesis shown in the figure, light sources (semiconductor lasers) 1a and 1b having two different emission wavelengths that emit light beams whose polarization directions are different by 90 degrees are used. The light beams La and Lb emitted from the light sources 1a and 1b are converted into parallel light by the collimating lens 2 and formed into desired shapes by the apertures 3a and 3b, respectively, and then combined with the light beams. 15 is synthesized. The combined light beams La and Lb are focused in the sub-scanning direction by the cylindrical lens 4 and then deflected by the polygon mirror 5.

  (C) In the third embodiment of beam synthesis shown in the figure, light sources (semiconductor lasers) 1a and 1b having two different emission wavelengths that emit light beams whose polarization directions are different by 90 degrees are used. The light beams La and Lb emitted from the light sources 1a and 1b are converted into parallel light by the collimator lens 2 and synthesized by the beam synthesis prism 15. The light beams La and Lb are each formed into a desired beam diameter by passing through the aperture 13, narrowed in the sub-scanning direction by the cylindrical lens 4, and then deflected by the polygon mirror 5.

  (D) In the fourth embodiment of beam synthesis shown in the figure, light beams La and Lb emitted from a light source 1 having a configuration in which light sources having two different emission wavelengths are arranged in a line (for example, an LD array) are collimated. The lens 2 makes parallel light. The light beams La and Lb are each formed into a desired beam diameter by passing through the aperture 13, narrowed in the sub-scanning direction by the cylindrical lens 4, and then deflected by the polygon mirror 5.

  In each of the above-described embodiments, each light beam is caused by the apertures 3a and 3b or the aperture 13 so that the beam diameter (the beam size) of each light beam becomes the same on the photosensitive member scanning surface scanned by each light beam. Is formed into a desired beam diameter. As a result, even when scanning is performed using a plurality of light sources having different emission wavelengths, the beam diameter of the light beam on each photosensitive member scanning surface is made equal to form a uniform and high-quality electrostatic latent image. Is possible.

  The first to fourth embodiments of beam synthesis described here can be used as a configuration for synthesizing two light beams upstream from the polygon mirror 5, respectively. FIG. 2 shows the first embodiment shown in FIG.

Next, apertures used in the first to fourth embodiments of beam synthesis will be described with reference to FIG.
Apertures 3a and 3b shown in FIG. 4A are used in the first and second embodiments of the beam synthesis. The apertures 3a and 3b have openings 16a and 16b having different sizes, respectively, and the light beams La and Lb pass through the apertures 3a and 3b, respectively. Molded to a diameter (desired shape). In this example, the openings 16a and 16b have similar shapes and differ only in size. When used in the second embodiment (the light beams La and Lb are parallel), the apertures 3a and 3b may be arranged in parallel in the main scanning direction on one substrate. In this specification, “beam diameter” and “beam size” are equivalent. Further, “desired shape” means “desired shape and desired size”.

  The aperture 13 shown in FIG. 4B is used in the third and fourth embodiments of the beam synthesis. The aperture 13 includes an optical filter or dichroic mirror 17 having a spectroscopic function at a base opening provided in a predetermined shape (including the size as described above). The optical filter or dichroic mirror 17 is provided with an opening 16c having a predetermined shape. The optical filter or dichroic mirror 17 and the opening 16c are spectrally separated by forming a dielectric multilayer film on a portion (a portion other than the opening 16c) corresponding to the optical filter or dichroic mirror 17 of a member made of glass or transparent resin. It has a function.

  When the aperture 13 having such a configuration is irradiated with the combined light of the light beams La and Lb, the light beam La having a wavelength that cannot pass through the optical filter or the dichroic mirror 17 has a size (shape) by the opening 16c. It passes as a light beam. On the other hand, the light beam Lb having a wavelength that can be transmitted through the optical filter or dichroic mirror 17 has a size (shape) regulated by the base material opening (assuming that the base material cannot transmit both the light beams La and Lb). It passes as a light beam. Thereby, the light beams La and Lb are formed into a desired beam diameter (desired shape).

  Note that a mere opening (for example, the openings 16a to 16c, which may be fitted with glass or resin) through which each light beam having a different wavelength can pass only a light beam in a certain wavelength band. An opening (for example, a base material opening in which an optical filter or a dichroic mirror 17 is inserted, and a simple opening may be included in the optical filter or dichroic mirror) is also a light beam passage portion. Called.

  By the way, a light beam having a short wavelength has a higher refractive index than that of a light beam having a long wavelength. Therefore, when two light beams having different wavelengths are incident on the same aperture, it can be said that the longer the wavelength, the larger the beam diameter on the surface to be scanned. In addition, the smaller the aperture due to the aperture (the larger the opening), the easier it is to throttle (easily regulate) the beam. Therefore, if the same beam diameter is to be obtained, the aperture should have a wavelength separation characteristic that blocks a light beam having a short wavelength.

  In the optical scanning device of this example, light beams with wavelengths of 650 nm and 780 nm are used as an example. Therefore, in the aperture 13, the optical filter or dichroic mirror 17 has a wavelength separation characteristic that blocks the light beam with a wavelength of 650 nm. . In this case, the light beam La has a wavelength of 650 nm, and the light beam Lb has a wavelength of 780 nm.

  Here, the aperture shape of the aperture is described as a quadrangle, but the shape of the aperture is not limited to a quadrangle, and may be any shape, for example, a polygon other than a quadrangle, a circle, or an ellipse.

  In the optical writing apparatus according to the present invention, two light beams synthesized on the same axis in the sub-scanning direction can be separated by the first beam separation means and the second beam separation means, which will be described with reference to FIG. The plurality of light beams are guided to the respective photoconductors to be scanned without using a plurality of reflecting mirrors (mirrors) as in the conventional example (without arranging the plurality of reflecting mirrors at different positions in the vertical direction). Therefore, the optical writing device can be thinned.

  In addition, since a plurality of light beams combined in the sub-scanning direction can be shaped to a desired size by the respective apertures, the beam diameters of the light beams on each photoconductor scanning surface are made equal, and uniform and high quality. An optical writing device capable of forming an electrostatic latent image can be realized.

  The optical writing apparatus 10 of this example can be suitably used for a tandem type full-color image forming apparatus, and even when four light beams are distributed to four photosensitive members, the thickness of the optical writing apparatus does not increase. 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.

  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. 5 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 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. Further, even if the optical writing device 10 of the present example is configured to perform scanning using a plurality of light sources having different emission wavelengths, the beam diameter of the light beam on each photosensitive member scanning surface is the same, and is uniform and Since a high-quality electrostatic latent image can be formed, the image forming apparatus of this example can obtain a high-quality color image without color misregistration.

  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, those capable of separating a plurality of light beams in a combination of both can be used as appropriate. 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. Any suitable aperture for shaping each light beam into a desired shape (size) can be used 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. It is a top view which shows the part. It is a schematic diagram which shows each Example of beam composition. It is a schematic diagram which shows the example of the aperture used for this invention. 1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus including an optical writing device according to the present invention. It is a block diagram which shows an example of the conventional optical writing apparatus.

Explanation of symbols

1a, 1b Semiconductor laser 2 Collimate lens 3, 13 Aperture 4 Cylindrical lens 5 Polygon mirror (deflector)
6 fθ lens 7 polarization beam splitter (first beam separating means)
8 1/4 wavelength plate 9 Dichroic mirror (second beam separating means)
10 Optical writing device (optical scanning device)
11 Reflector (mirror)
14 imaging lens 15 beam combining prism (beam combining means)
16a, 16b, 16c Opening (light beam passage)
17 Optical filter or dichroic mirror (light beam passage)
100 image forming unit 101 photoconductor La, Lb light beam

Claims (18)

In an optical writing device that scans a surface to be scanned by deflecting light from a light source by a deflector,
A plurality of light sources that emit light beams having the same polarization direction and different wavelengths are provided, and the light beams emitted from the plurality of light sources are combined so as to be on the same axis when viewed from the sub-scanning direction and deflected by the deflector. As well as
A first beam transmitting / reflecting means arranged so that each of the light beams deflected by the deflector enters , and transmitting or reflecting the light beam according to a polarization direction of the light beam;
A second beam transmitting reflecting means for transmitting or reflecting by its wavelength the light beams after the beam transmitted through the reflecting means transmitting the first,
A quarter-wave plate disposed between the first beam transmission / reflection unit and the second beam transmission / reflection unit and configured to rotate the polarization direction of the light beam by π / 4 ,
With the light source as the upstream side, the deflector, the first beam transmitting / reflecting means, the quarter-wave plate, and the second beam transmitting / reflecting means are arranged in this order,
The first beam transmitting / reflecting means transmits the light beam deflected by the deflector to pass through the quarter-wave plate, and is reflected and returned by the second beam transmitting / reflecting means. / 4 is arranged to reflect the light beam that has passed through the wavelength plate again,
Wherein the second light beam transmitted through the beam transmission reflecting means scans one of the scanning surface, and more reflects the light beam reflected by the second beam transmitted through the reflection means to said first beam transmissive reflecting means Configured to scan another surface to be scanned,
The optical writing apparatus further comprises an aperture having a beam passage having a size corresponding to the wavelength of each light beam, and the light beam is shaped into a desired shape by the aperture. The plurality of light sources are mounted close to the same substrate, and the light beam emission directions from the respective light sources are inclined in different directions with respect to the normal line of the substrate, and the light beam emission directions from the respective light sources are 2. The optical writing device according to claim 1, wherein the optical writing device exhibits an opening angle at least in the main scanning direction and intersects in the vicinity of a deflection surface of the deflector.   2. The light according to claim 1, further comprising a beam combining unit configured to combine light beams from the plurality of light sources, and irradiating the deflecting surface of the deflector with the light beam combined by the beam combining unit. Writing device.   The optical writing apparatus according to claim 3, wherein the plurality of light sources emit light beams whose polarization directions are different by 90 degrees.   5. The optical writing apparatus according to claim 3, wherein the light beam from each of the light sources is combined by the beam combining unit after passing through the aperture.   5. The optical writing apparatus according to claim 3, wherein the light beam from each of the light sources is combined by the beam combining unit and then allowed to pass through the aperture. 6.   The optical writing apparatus according to claim 1, wherein the plurality of light sources have a configuration in which light sources that emit light beams having different wavelengths are arranged in a line.   The aperture according to any one of claims 2 to 5, wherein the aperture includes a plurality of apertures, and each aperture is provided with a beam passing portion having a size corresponding to the wavelength of each light beam. The optical writing device described.   The aperture according to any one of claims 3, 4, 6, and 7, wherein the aperture is a single aperture having a beam passage portion that allows each light beam to pass through different sizes depending on the wavelength. The optical writing device according to claim 1. The beam passing portion includes a base material opening provided in a predetermined shape on a base material that does not transmit each light beam, and a second predetermined shape provided in a beam transmission blocking means provided in the base material opening. With an opening of
10. The optical writing device according to claim 9, wherein the beam transmission blocking means transmits one of the light beams according to its wavelength and blocks the other . 11. The optical writing device according to claim 10, wherein the beam transmission blocking means is an optical filter or a dichroic mirror.   12. The optical writing device according to claim 11, wherein a material of the optical filter or dichroic mirror is glass or transparent resin, and a dielectric multilayer film is formed on an incident surface thereof.   2. The optical writing apparatus according to claim 1, wherein the second beam separation unit is arranged so that optical path lengths from the light sources to the scanned surfaces are equal.   2. The optical writing apparatus according to claim 1, wherein the incident angles of the light beams on the respective scanned surfaces are the same angle.   2. The optical writing apparatus according to claim 1, wherein a scanning surface by the deflector and a plane connecting the incident positions of the light beams to the respective scanned surfaces are parallel to each other. Among the optical elements included in the optical writing device according to any one of claims 1 to 15 , the deflector is used as one common deflector, and an optical element other than the deflector is used for the deflector. An optical writing apparatus characterized by being arranged substantially symmetrically on both sides and configured to scan four scanned surfaces with light beams from four light sources. An image forming apparatus comprising the optical writing device according to any one of claims 1-16. The image forming apparatus according to claim 17 , wherein the image forming apparatus is a tandem type full-color apparatus including four image carriers as scanning targets scanned by the optical writing apparatus.

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