JP2009063739A - Optical writing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To thin an optical writing device, and to miniaturize an image forming apparatus. <P>SOLUTION: The optical writing device deflects two optical beams having different wavelengths with a polygon mirror 4 by composing on the same axis in a sub-scanning direction. A dichroic mirror 8 transmits or reflects the optical beam according to the wavelength; and a photoreceptor 101a is scanned with the optical beam transmitting the dichroic mirror 8 and scanning a photoreceptor 101b by allowing the optical beam reflected on the dichroic mirror 8 to be reflected on a polarizing beam splitter 6. Since the optical beam need not be guided to a photoreceptor by using a plurality of mirrors, the optical writing device can be thinned. <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.

JP 58-79215 A Japanese Patent Laid-Open No. 9-127444 Japanese Patent Laid-Open No. 10-3048 JP-A-10-282440 Japanese Patent No. 3084829

  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. 7 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.

Patent Document 1 describes an optical system for a laser printer that can print in two colors, for example, black and red.
Further, Patent Document 2 describes a multi-beam scanning device that can improve the workability of maintenance work and improve the color overlay accuracy.

Patent Document 3 describes an optical scanning device of a multicolor image forming apparatus that writes and scans a plurality of light beams onto a plurality of photoreceptor surfaces with a single polygon mirror.
Patent Document 4 describes an optical scanning device in which laser light from light sources having different emission wavelengths is separated according to the wavelength and exposed to a photosensitive drum.

  Patent Document 5 discloses an image forming apparatus that forms an electrophotographic image by separating a plurality of laser beams by a separating unit (beam splitter) and irradiating the laser beams at different positions.

  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, Patent Document 2, and Patent Document 5, when the polygon mirror scanning surface and the surface connecting the irradiation positions on each photosensitive member are not parallel, the optical scanning device can be miniaturized, but a plurality of foldings are possible. Since the mirror is used, the thickness cannot be reduced, and the image forming apparatus 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.

  The present invention provides an optical writing apparatus that solves the above-described problems in the conventional optical writing apparatus, realizes a reduction in the thickness of the optical writing apparatus, and contributes to downsizing of the color image forming apparatus. This is the issue.

  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 different wavelengths. The light beams emitted from the light source are combined on the same axis in the sub-scanning direction, deflected by the deflector, and arranged so that the light beams deflected by the deflector enter, and the light beams are changed according to the beam entrance direction. A first beam separating means for transmitting or reflecting; and a second beam separating means for transmitting or reflecting each light beam after passing through the first beam separating means according to its wavelength. One surface to be scanned is scanned by the light beam that has passed through the separating means, and the light beam reflected by the second beam separating means is reflected by the first beam separating means to make another one. Configured to scan a surface to be scanned, wherein to compensate for differences in focal length of each light beam is solved by are provided at different optical path lengths of the respective light beams.

Further, it is preferable that the optical path lengths of the respective light beams are provided differently on the upstream side of the deflector in the beam traveling direction.
Further, it is preferable to have beam combining means for combining the light beams emitted from the respective light sources.

Moreover, it is preferable that the optical path lengths of the respective light beams are provided differently on the downstream side of the deflector in the beam traveling direction.
Further, it is preferable that the second beam separation means is provided so that the position in the optical axis direction can be adjusted.

Moreover, it is preferable that the beam intensity of each light source is provided to be changeable.
Preferably, the first beam separation means is a polarization beam splitter, and a quarter-wave plate is disposed between the first beam separation means and the second beam separation means.

The second beam separation means is preferably a dichroic mirror.
And a light beam detecting means used for synchronous detection of each light source, so that the light beam detecting means is incident before the light beam deflected by the deflector is incident on the first beam separating means. It is preferable that it is provided.

The number of the light beam detecting means is preferably one.
Further, it is preferable that each of the light sources is controlled to be turned on with a predetermined time difference.
Further, it is preferable that each of the light sources is arranged so as to have a predetermined angle in the same plane in the sub-scanning direction and to irradiate each light beam at the same position in the main scanning direction of the deflector.

In addition, it is preferable that any one of the light sources is a light source that emits visible light.
In addition, among the optical elements included in the optical writing device according to claim 1, the deflector is used as a common deflector, and an optical element other than the deflector is used as the deflector. It is preferable that one set is disposed substantially symmetrically on both sides of the device, and four scanned surfaces are scanned 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 14.
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 separation means and the second beam separation means can separate the light beams emitted from the plurality of light sources, so that a plurality of reflecting mirrors are not used. Since each light beam can be guided to each scanning object, the optical writing device can be made thin.

  Further, since the optical path lengths of the respective light beams are provided to be different so as to correct the difference in focal length of each light beam, it is possible to use light beams having different wavelengths with one lens (fθ lens), The difference in focal length caused by the difference in the number of optical elements through which each beam passes can be eliminated, and the optical path difference (difference in optical path length) of each light beam caused by the difference in wavelength between the two light beams can be obtained. It can be corrected.

According to the configuration of the second or third aspect, the optical path length of each light beam can be varied with a simple configuration.
According to the configuration of the fourth or fifth aspect, the optical path length of each light beam can be varied without adding an optical element.

According to the configuration of the sixth aspect, it is possible to correct the intensity difference between the light beams and irradiate the light beam with an appropriate intensity to the scanning target.
According to the configuration of the seventh aspect, the light beam separated by the second beam separating means can be reflected and guided to the scanning object by the polarizing beam splitter and the quarter wavelength plate as the first beam separating means.

  With the configuration according to the eighth aspect, it is possible to appropriately separate light beams having different wavelengths by using a dichroic mirror which is a multilayer dielectric mirror as the second beam separating means.

With the configuration of the ninth aspect, appropriate detection can be performed without being affected by the optical effect of the first beam separation means.
With the configuration of the tenth aspect, detection can be performed at a low cost by one light beam detection means.

According to the configuration of the eleventh aspect, a plurality of light beams can be detected by one light beam detecting means.
According to the configuration of the twelfth aspect, the configuration on the upstream side of the deflector can be simplified. In addition, synchronous detection can be performed at low cost by one light beam detection means.

According to the structure of the thirteenth aspect, since one of the light beams is visible light, the work is facilitated in an assembly work, an adjustment work, a failure analysis work, or the like.
According to the configuration of the fourteenth 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 fifteenth 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.

  According to the configuration of the sixteenth 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 in the vertical direction of the image forming apparatus with a thin optical writing device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram schematically showing an example of an optical writing device according to the present invention. FIG. 2 is a configuration diagram of the optical writing device viewed from the front side of the image forming apparatus. The optical writing apparatus 10 of this example shown in these drawings includes semiconductor lasers 1a and 1b, collimating lenses 2a and 2b, a cylindrical lens 3, a polygon mirror 4 which is a rotating polygon mirror, an fθ lens 5, and a polarizing beam splitter 6 (first beam). 1 beam separating means), a quarter wavelength plate 7, a dichroic mirror 8 (second beam separating means), a reflecting mirror 9, a beam synthesizing means 12, a synchronization detecting element 13, and the like. Arranged in the housing 11. In the optical writing apparatus of this example, the semiconductor lasers 1a and 1b are those that emit light beams having the same polarization direction and different wavelengths, respectively, and have a wavelength band corresponding to the dichroic mirror 8 as the light separating means. Is used.

  Light beams having the same polarization direction and different wavelengths emitted from semiconductor lasers 1a and 1b, which are two different light sources arranged on the same axis in the sub-scanning direction, are transmitted by collimator lenses 2a and 2b by beam combining means 12. The combined light passes through the cylindrical lens 3 and is deflected and scanned by the polygon mirror 4 as a deflecting means, passes through the fθ lens 5, and passes through the polarization beam splitter 6 that separates the light according to the polarization direction. This polarization beam splitter 6 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 two beams (light beams having the same polarization direction and different wavelengths) that have exited the fθ lens 5 and passed through the polarizing beam splitter 6 pass through the quarter-wave plate 7. The quarter-wave plate 7 rotates the polarization direction of the light beam by π / 4, and the two light beams pass through the quarter-wave plate 7 so that they are π / 4 at the time of emission. In a state where the light beam is rotated only by one, one beam is transmitted and the other one beam is reflected by the dichroic mirror 8 which is a multilayer dielectric mirror disposed perpendicular to the beam. The dichroic mirror 8 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 8.

  Now, the light beam that has passed through the dichroic mirror 8 is reflected by the reflecting mirror 9 and irradiated onto the surface to be scanned of the photosensitive member 101a. On the other hand, the light beam reflected by the dichroic mirror 8 returns the same optical path and passes through the quarter-wave plate 7 again, so that the polarization direction is rotated again by π / 4, and is π / 2 at the time of emission. The light beam enters the polarization beam splitter 6 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 6 and applied to the surface to be scanned of the photosensitive member 101b. 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 1a and 1b are both linearly polarized P waves, for example, and one light beam is rotated by π / 4 by the quarter wavelength plate 7. In the state of circularly polarized light, the light passes through the dichroic mirror 8 and is irradiated onto the photosensitive member 101a. The other light beam is rotated by π / 4 by the quarter-wave plate 7 to become circularly polarized light, then reflected by the dichroic mirror 8 and again passes through the quarter-wave plate 7 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.

  In the present embodiment, a difference occurs in the focal length because a single lens (fθ lens 5) uses light beams having different wavelengths and the number of optical elements that each beam transmits is different. In order to correct this, the optical path lengths of the two light beams (up to the photosensitive member) are set differently in advance. In this example, as shown in FIG. 1, the optical path lengths are made different on the upstream side of the polygon mirror 4 by synthesizing two light beams emitted from the semiconductor lasers 1a and 1b using the beam synthesizing unit 12. The focal length difference is corrected. Thereby, the optical path difference (difference in optical path length) between the two light beams caused by the difference in wavelength between the two light beams can be corrected.

  The dichroic mirror 8 is provided so as to be movable in the optical axis direction (left-right direction in FIG. 2), and the optical path length of the two light beams can be changed by adjusting the position of the dichroic mirror 8. Therefore, the dichroic mirror A configuration for correcting the difference in focal length by adjusting the position of 8 may be added.

  Furthermore, the intensity of each light beam is also different because of the difference in the number of times the optical element is transmitted through each optical path, the difference in reflectance and transmittance between the optical elements, and variations in the light sources (semiconductor lasers 1a and 1b). Each will be different. Therefore, in this example, the beam intensities of the two light sources (semiconductor lasers 1a and 1b) are provided so as to be adjustable, and by adjusting them, each photosensitive drum scanning surface is provided with a light beam with an appropriate intensity. Yes.

Next, synchronization detection of the light sources (semiconductor lasers 1a and 1b) will be described.
As shown in FIG. 1, a photodiode 13 as a synchronization detection element is disposed between the fθ lens 5 and the polarization beam splitter 6 outside the writing range in the main scanning direction. The respective light beams emitted from the semiconductor lasers 1a and 1b pass through the collimating lens 2 and are combined using the beam combining means 12, pass through the cylindrical lens 3, deflected and scanned by the polygon mirror 4, and pass through the fθ lens 5. The photodiode 13 is also irradiated. Since the scanning line (light beam) position can be detected by the photodiode 13, the writing timing can be controlled.

  In this example, the photodiode 13 is arranged in front (upstream) of the polarizing beam splitter 6 as the first beam separating means in the optical axis direction. In the present embodiment, the two light beams are combined by the beam combining means 12 and are incident on the photodiode 13 through exactly the same optical path. Therefore, the photodiodes of the respective light beams are controlled by controlling the light emission timings of the semiconductor lasers 1a and 1b. By shifting the incident timing to 13, the same (one) photodiode 13 can detect synchronization.

  Incidentally, as described above, in order to separate the two light beams by the dichroic mirror 8, the wavelengths of the two light beams need to be different. Although the boundary between reflection and transmission differs depending on the dichroic mirror to be used, for example, when using a boundary having a wavelength near 750 nm, it is necessary to select a wavelength band before and after the boundary as each light beam. As an example, visible light having a wavelength of about 650 nm and infrared light having a wavelength of about 800 nm can be selected (a semiconductor laser that emits visible light having a wavelength of about 650 nm and a semiconductor laser that emits infrared light having a wavelength of about 800 nm. Can be used as the semiconductor lasers 1a and 1b).

FIG. 3 is a schematic diagram showing a second embodiment of the optical writing device. A description of the same parts as those of the optical writing apparatus of the first embodiment will be omitted, and only different points will be described.
The semiconductor lasers 1a and 1b, which are two light sources, are arranged on the same axis (same plane) in the sub-scanning direction. In the second embodiment, as shown in FIG. 1a and 1b are arranged to have a predetermined angle α. The beam combining unit 12 is not used, and two light beams are applied to the same position in the main scanning direction of the polygon mirror 4 that is a deflecting unit. That is, in the second embodiment, light beams having the same polarization direction and different wavelengths emitted from the semiconductor lasers 1a and 1b are combined on the same axis in the sub-scanning direction via the collimating lenses 2a and 2b and the cylindrical lens 3. Then, deflection scanning is performed by the polygon mirror 4 as a deflection means.

  The configuration after the polygon mirror 4 (downstream) is the same as that of the first embodiment described above. However, in the second embodiment, the optical path lengths of the two light beams on the upstream side of the polygon mirror 4 are equal. In order to correct the focal length of the two light beams, the dichroic mirror 8 is provided so as to be movable in the optical axis direction (left-right direction in FIG. 2), and the above correction is performed by adjusting the position of the dichroic mirror 8. . In the first embodiment, the beam intensities of the two light sources (semiconductor lasers 1a and 1b) are provided so as to be adjustable, and by adjusting the beam intensities, the respective photosensitive drum scanning surfaces are irradiated with the light beams with appropriate intensity. It is the same.

  As in the first embodiment, the synchronization detection in the second embodiment is performed by the photodiode 13 as a synchronization detection element arranged outside the writing range in the main scanning direction between the fθ lens 5 and the polarization beam splitter 6. Each light beam emitted from the semiconductor lasers 1 a and 1 b passes through the collimating lens 2, passes through the cylindrical lens 3, is deflected and scanned by the polygon mirror 4, passes through the fθ lens 5, and is also irradiated onto the photodiode 13. Since the scanning line (light beam) position can be detected by the photodiode 13, the writing timing can be controlled.

  In the second embodiment, the angles of the two light sources, the semiconductor lasers 1a and 1b, with respect to the polygon mirror 4 are different, and the two light sources are arranged shifted in the main scanning direction. There is no need to control the light emission timing of the conductor lasers 1a and 1b (for synchronization detection) without entering the synchronization detection element 13.

  Thus, in the optical writing device according to the present invention, it is possible to separate the two light beams synthesized on the same axis in the sub-scanning direction by the first beam separation means and the second beam separation means, As in the conventional example described with reference to FIG. 7, a plurality of reflecting mirrors (mirrors) are not used (a plurality of reflecting mirrors are not arranged at different positions in the vertical direction), and two light beams are scanned. Since it can be guided to the photoreceptor, the optical writing device can be made thin.

Next, an optical writing apparatus corresponding to the four-color full-color image forming apparatus will be described with reference to FIGS.
The optical writing device according to the third embodiment corresponding to the four-color full-color image forming apparatus is a polygon that is a deflection unit among the elements constituting the optical writing device according to the first embodiment or the second embodiment described above. 2 sets (2 sets) of components other than the mirror 4 are provided. As shown in FIG. 4 and FIG. 5, each component is arranged substantially symmetrically on both sides of the polygon mirror 4 as a center. It is a thing. Although FIG. 5 shows the configuration of the first embodiment, the configuration of the second embodiment is also possible. The polygon mirror 4 is used in common for the components on both sides.

  In the third embodiment, four (1a, 1b, 1c, 1d) semiconductor lasers are provided, and two light beams from the semiconductor lasers 1a, 1b are guided to the photoreceptors 101a, 101b, respectively, and the semiconductor laser 1c. , 1d are guided to the photoconductors 101c and 101d, respectively. The separation of each light beam is the same as that in the first embodiment and the second embodiment described above, and a description thereof will be omitted because it is redundant.

  The optical writing apparatus of the third embodiment can be suitably used for a tandem type full-color image forming apparatus, and the thickness of the optical writing apparatus can be increased even when four light beams are distributed to four photosensitive members. Therefore, 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. 6 is a color printer that can form a full-color image by adopting a tandem method. Four image forming units 100 (Y, C, M, and K) are provided at almost the center of the apparatus main body. It is arranged. 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 lower traveling side of the intermediate transfer belt 111. The intermediate transfer belt 111 wound around the support rollers 112 and 113 is driven to run counterclockwise in the figure. A belt cleaning unit 114 for cleaning the intermediate transfer belt 111 is disposed outside the left support roller 112.

  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, a developing device, a cleaning unit, and the like are arranged. Further, a transfer roller as a primary transfer unit is provided inside the intermediate transfer belt 111 so as to face each photosensitive drum 101. It has been.

  Below the four image forming units 100, an optical writing device 20 is provided. The optical writing device 20 corresponds to a four-color full-color image forming device, and here, the optical writing device 20 of the third embodiment described above is used. In each of the above embodiments, the photoconductor 101 is disposed below. However, in the present color printer, the photoconductor 101 is disposed above the optical writing device 20, and a light beam (scanning light) is emitted upward. The configuration is as follows. The optical writing device 20 irradiates the surface of the photosensitive drum 101 of each color image forming unit with laser light that is light-modulated based on image information.

  A toner accommodating portion 141 is provided on the intermediate transfer belt 111, and toner bottles accommodating toners of yellow, cyan, magenta, and black are disposed. From each toner bottle, each color toner is supplied to the developing device of each color image forming unit 100 by a toner supply mechanism (not shown).

  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 not shown.

  A secondary transfer roller 115 is provided so as to face the support roller 113 of the intermediate transfer belt 111, and a registration roller 116 is provided near the upstream side (downward in the drawing) of the secondary transfer portion in the sheet conveyance direction. Yes. A fixing device 150 is provided above the secondary transfer unit.

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 figure 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. The charged photoconductor surface is irradiated with laser light from the optical writing device 20, thereby forming an electrostatic latent image 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 to the electrostatic latent image formed in this way, and visualized as a toner image.

  Further, the intermediate transfer belt 111 is driven to run counterclockwise in the drawing, and the respective color toner images are sequentially transferred from the photosensitive drum 101 to the intermediate transfer belt 111 by the action of the primary transfer roller in each image forming unit 100. In this way, the intermediate transfer belt 111 carries a full-color toner image on its surface.

  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 after the toner image is transferred is removed from the surface of the photosensitive drum by the cleaning means, and then the surface is subjected to the action of the static eliminator to initialize the surface potential. Ready for image formation.

  On the other hand, the paper is fed from the paper feed tray 130 and is sent out toward the secondary transfer position by the registration roller pair 116 in timing with the toner image carried on the intermediate transfer belt 111. A predetermined transfer voltage is applied to the secondary transfer roller 115, whereby the toner images on the surface of the intermediate transfer belt are collectively transferred onto the paper. When the paper on which the toner image has been transferred passes through the fixing device 150, the toner image is fused and fixed to the paper by heat and pressure. The fixed paper is discharged by a paper discharge roller 151 to a paper discharge tray 140 formed on the upper surface of the apparatus main body.

  Since the optical writing device 20 is thin and has a small thickness as described above, it can be placed in a limited space inside the image forming apparatus, and is particularly effective for downsizing the color image forming apparatus. large.

  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), a light source having a wavelength capable of separating a plurality of light beams in a combination of both can be used as appropriate. Further, the first beam separation means is not limited to the polarization beam splitter, and an appropriate configuration can be adopted. The photosensitive member to be scanned is not limited to a drum shape, and a belt-like photosensitive member is also possible.

  The image forming apparatus is not limited to the intermediate transfer system but may be a direct transfer system. Further, the present invention can be applied not only to a four-color full-color machine 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 a perspective view which shows the principal part structure of 1st Embodiment of an optical writing device. It is sectional drawing seen from the front direction of the optical writing device. It is a block diagram which shows 2nd Embodiment of an optical writing device. It is sectional drawing which shows the optical writing apparatus of 3rd Embodiment corresponding to a full-color image forming apparatus of 4 colors. FIG. 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 2a, 2b Collimating lens 3 Cylindrical lens 4 Polygon mirror (deflector)
5 fθ lens 6 polarization beam splitter (first beam separation means)
7 1/4 wavelength plate 8 Dichroic mirror (second beam separating means)
9 Reflector (mirror)
10, 20 Optical writing device 12 Beam combining means 13 Photodiode (synchronous detection element)
100 Image forming unit 101 Photoconductor 111 Intermediate transfer belt

Claims (16)

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 each emitting light beams having different wavelengths, and combining the light beams emitted from the plurality of light sources on the same axis in the sub-scanning direction and deflecting by the deflector;
A first beam separating unit arranged so that each of the light beams deflected by the deflector enters, and transmitting or reflecting the light beam according to a beam entering direction; and each of the light beams after passing through the first beam separating unit. Second beam separating means for transmitting or reflecting the light depending on the wavelength,
One surface to be scanned is scanned with the light beam that has passed through the second beam separation means, and the light beam reflected by the second beam separation means is reflected by the first beam separation means to cause another one to be scanned. Configured to scan the surface to be scanned,
An optical writing apparatus, wherein the optical path lengths of the respective light beams are provided differently so as to correct a difference in focal length of the respective light beams. 2. The optical writing device according to claim 1, wherein the optical path lengths of the respective light beams are provided differently on the upstream side of the deflector in the beam traveling direction. The optical writing apparatus according to claim 2, further comprising a beam combining unit configured to combine the light beams emitted from the light sources. 2. The optical writing device according to claim 1, wherein the optical path lengths of the respective light beams are provided differently on the downstream side of the deflector in the beam traveling direction. 5. The optical writing device according to claim 3, wherein the second beam separation unit is provided so that a position in an optical axis direction can be adjusted. 6. The optical writing device according to claim 1, wherein a beam intensity of each light source is changeable. The said 1st beam separation means is a polarization beam splitter, The quarter wavelength plate is arrange | positioned between this 1st beam separation means and the said 2nd beam separation means, The said 1st beam separation means is characterized by the above-mentioned. The optical writing device according to 1. 8. The optical writing device according to claim 1, wherein the second beam separation unit is a dichroic mirror. 9. A light beam detecting means used for synchronous detection of each light source;
9. The light beam detecting means according to claim 1, wherein the light beam detecting means is provided so that the light beam deflected by the deflector enters before entering the first beam separating means. The optical writing device according to claim 1. The optical writing apparatus according to claim 9, wherein the number of the light beam detecting means is one. 11. The optical writing device according to claim 9, wherein each of the light sources is controlled to be turned on with a predetermined time difference. Each of the light sources is disposed at a predetermined angle in the same plane in the sub-scanning direction, and is provided to irradiate each light beam at the same position in the main scanning direction of the deflector. The optical writing device according to claim 1. The optical writing device according to claim 1, wherein any one of the light sources is a light source that emits visible light. Among the optical elements included in the optical writing device according to any one of claims 1 to 13, the deflector is used as a common one deflector, and an optical element other than the deflector is used for the deflector. An optical writing apparatus characterized in that one set is disposed substantially symmetrically on both sides, and four scanned surfaces are scanned with light beams from four light sources. An image forming apparatus comprising the optical writing device according to claim 1. The image forming apparatus according to claim 15, 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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