JP2003015066A - Optical writing device and image forming device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical writing device capable of reducing the deterioration of image quality occurring on a color when the difference of light quantity is caused by the difference of shading characteristics. SOLUTION: The housing 50 of the optical writing device 5 is constituted of a base 50A where a light deflector 62 and an optical system are disposed, and a frame- shaped side wall 50B surrounding the periphery of the base 50A, and is partitioned up and down by the base 50A. Light source units 52 to 55 are arranged on the side wall 50B, the light deflector 62 is arranged nearly in the center of the base 50A, and optical members constituting the optical system are separately disposed on both top and bottom surfaces of the base 50A. By setting the size of the housing 50 to be equal to or under the half of the optical path length of the entire optical system while securing the optical path length, the housing 50 is made compact. Light beams L1 and L2 and light beams L3 and L4 are arranged by two colors symmetrically with respect to the vertical axis Y and the horizontal shaft X of the light deflector 62, and the shading characteristics and droop characteristics are combined to make the shading characteristics flat, so that irregular density and irregular color are reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an optical writing device for irradiating a light beam on the surface to be scanned of a plurality of image carriers arranged in parallel to write a latent image, and the optical writing device. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a plotter that forms a multicolor image.

[0002]

2. Description of the Related Art A latent image is written by irradiating four image carriers (for example, photoconductor drums) arranged in parallel with light beams emitted from a plurality of light sources. The latent images formed on the image carriers are developed with different color developers (for example, yellow, magenta, cyan, and black toners) to form visible images, and then carried on a transfer / transport belt or the like. Transfer material such as recording paper is sequentially conveyed to the transfer section of each image carrier, and the visible image of each color formed on each image carrier is transferred onto the transfer material, and then transferred onto the transfer material. There is known a tandem type color image forming apparatus for fixing a formed image to obtain a multicolor image.

In such a tandem type color image forming apparatus, conventionally, there is known one in which a latent image is written on each image carrier by an optical writing device individually provided for each image carrier. However, an optical writing device that uses an optical deflector consisting of a polygon mirror and a drive motor for driving the polygon mirror is relatively expensive, and providing an individual optical writing device for each image carrier is a component cost and a manufacturing cost. There is a problem with.

Further, a large installation space is required to install a plurality of optical writing devices having an optical deflector in correspondence with the number of image carriers, which causes a problem that the entire image forming apparatus becomes large. is there.

Therefore, in order to reduce the cost and the size of the tandem type color image forming apparatus, an optical deflector is shared by a plurality of light sources as a means for performing optical writing on a plurality of image carriers, and a single light deflector is used. 2. Description of the Related Art An optical writing device is known in which an optical deflector simultaneously deflects and scans light beams from a plurality of light sources to irradiate a plurality of image carriers to perform optical writing.

As described above, one optical deflector simultaneously deflects and scans light beams from a plurality of light sources to irradiate a plurality of image carriers to perform optical writing, and an optical writing device includes a plurality of light source units. One optical deflector, and an optical system symmetrically arranged in two directions with the optical deflector as a center and guiding a plurality of light beams deflected and scanned by the optical deflector onto corresponding scan surfaces to form an image. And a configuration in which these optical members are housed in a single housing. Therefore, the number of parts can be reduced and the installation space can be reduced as compared with the conventional configuration including a plurality of optical writing devices, so that the cost and size of the image forming apparatus can be reduced.

In the case of an image forming apparatus having the above-described optical writing device and forming a full-color image, usually, as a plurality of light source units, a light source unit for black and three light source units for color ( For example, cyan, magenta, and yellow light source units are provided, and only the black light source unit is used in the monochrome mode for forming a monochrome image, and the four light source units are used in the color mode for forming a color image. used.

In the color mode, four light source units, one for black and one for color, are used, and the light beams from the four light source units are simultaneously deflected and scanned by one optical deflector to pass through the respective optical systems. The four image carriers are irradiated with light to perform optical writing. When the four image carriers are irradiated with light to form a latent image, a synchronization sensor is provided to align the writing positions of the light from the four light sources in the main scanning direction. The writing timing of each of the four colors is adjusted by the output of this synchronous sensor.

1 and 2 show the arrangement of the LD units in the conventional machine as described above. Illustrated optical writing device 5
Are four light source units 52, 53, 54, 55 and an optical deflector 62 for deflecting and scanning the light beams L1, L2, L3, L4 from the respective light source units in two symmetrical directions.
(For example, two-stage polygon mirror) and a plurality of light beams which are arranged symmetrically with respect to a vertical axis passing through the optical deflector 62 and are deflected and scanned by the optical deflector 62 respectively correspond to the photoconductor drums 1 and 2. An optical system (comprising optical members such as imaging lenses 63 and 64 and mirrors 65, 66, 67 and 68 for folding the optical path) that guides and forms an image on the surface to be scanned 3, 4 is provided. The constituent members of (1) are housed in one housing 50.

The housing 50 has a base 50A on which an optical deflector 62 and an optical system are arranged, and a frame-shaped side wall 50B surrounding the base 50A.
The structure is provided in a substantially central portion of 0B and divides the housing 50 into upper and lower parts. The four light source units 52, 53, 5
Reference numerals 4 and 55 are arranged on the side wall 50B of the housing 50, and the optical deflector 62 is arranged substantially at the center of the base 50A of the housing 50.

In the optical writing device 5, the color-separated image data input from a document reading device (scanner) or an image data output device (personal computer, word processor, facsimile receiving unit, etc.) not shown is used for driving the light source. The light source (semiconductor laser (LD)) in each of the light source units 52, 53, 54, 55 is driven in accordance with the converted signal to output a light beam. The light beams L1, L2, L3, and L4 emitted from the light source units 52, 53, 54, and 55 pass through the cylindrical lenses 56, 57, 58, and 59 for face tilt correction, directly or via the mirrors 60 and 61. To the optical deflector 62,
Deflection scanning is performed in two symmetrical directions by two-stage polygon mirrors 62a and 62b which are rotated at a constant speed by a polygon motor.

The two-stage polygon mirror of the optical deflector 62
The light beam, which is deflected and scanned in two directions beam by beam, forms an image forming lens 63, which is composed of an upper and lower two-layered fθ lens, for example.
64 and passes through the first folding mirrors 65 and 6 respectively.
After being folded back by 6, 67, 68 and passing through the opening of the base 51, the photosensitive drums for the respective colors are passed through the optical system including the second image forming device such as a long toroidal lens (WTL). It is irradiated onto the surface to be scanned and an electrostatic latent image is written.

As shown in FIG. 2, assuming that the vertical axis and the horizontal axis passing through the optical deflector 62 are the X and Y axes, respectively, L for two colors is used.
The light beams L1 and L2 from the D unit are arranged in the second quadrant, and the other light beams L3 and L4 are arranged in the first quadrant. The rotation direction of the optical deflector 62 is clockwise in the direction of the arrow in the figure. When the light deflector 62 rotates, the light beam emitted from the LD unit scans the photoconductors 1 to 4 in a constant scanning direction through the optical system as described above.

The image height is -150 to 0 to +150 depending on the reflection angle of the optical deflector 62 and the characteristics of the lenses and mirrors that form the optical system.
The shading characteristics of are as shown in FIG. On the other hand, since the LD of the LD unit, which is the light emitting source, has a droop characteristic (temperature characteristic), the amount of emitted light decreases due to the emitted heat of the LD itself even during one line scanning in the main scanning direction, and the end in the scanning direction. Then, the amount of light decreases considerably.

Due to the influence of both of the above, as shown in FIG. 4, the combined shading characteristics on the side of the light beams L1 and L2 both become brighter on the −150 side and darker on the +150 side, which is promoted. The light beams L3 and L4 cancel each other due to their characteristics, and the composite shading characteristics are close to flat. Therefore, due to the difference in the shading characteristics of the light beams L1 and L2 and the light beams L3 and L4, a difference in light amount occurs when four colors are simultaneously used or when the colors of the light beams L1 and L3 are overlapped, resulting in a tint. As a result, the image quality of the formed image deteriorates.

The present invention has been made in view of the above circumstances, and provides an optical writing device capable of reducing the occurrence of a deterioration in image quality which causes a tint and a difference in light amount due to a difference in shading characteristics. For the purpose of providing
An object of the present invention is to provide an image forming apparatus including the optical writing device and capable of improving the image quality.

[0017]

In order to achieve the above object, an optical writing apparatus according to a first aspect of the present invention has a plurality of light sources and a plurality of light beams from the plurality of light sources which are symmetrical. And a plurality of light beams, which are arranged symmetrically in the two directions with the optical deflector as a center, and which are deflected and scanned by the optical deflector. In an optical writing device having an optical system that guides and forms an image to the plurality of light sources, the optical deflector, and the optical system in one housing,
It is characterized in that two colors are arranged in opposite directions with respect to one axis included in the deflection scanning plane of the deflector.

According to a second aspect of the present invention, in order to achieve the above object, in the optical writing device of the first aspect, the housing is a base on which an optical deflector and an optical system are arranged, and the base. And a plurality of light sources are arranged on the side wall and the optical deflector is disposed on the side wall. It is characterized in that it is arranged substantially at the center of the base, and the optical members constituting the above-mentioned optical system are separately arranged on the upper and lower surfaces of the base.

In order to achieve the above object, the image forming apparatus according to the third aspect uses the optical writing apparatus according to the first or second aspect.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that, in the following, the same parts as those in the prior art will be denoted by the same reference numerals, and overlapping description will be omitted. 5 is a cross-sectional view of an embodiment of the optical writing device according to the present invention, and FIG. 6 is a schematic configuration diagram showing an embodiment of an image forming apparatus including the optical writing device shown in FIG. FIG. 7 is a plan view showing the structure of the optical writing device shown in FIG. 5 on the upper surface side of the substrate. Note that FIG. 5 corresponds to a cross-sectional view taken along the line AA of FIG. 7.

The image forming apparatus having the structure shown in FIG. 6 is a full-color image forming apparatus in which a plurality of drum-shaped photoconductive photoconductors (photosensitive drums) 1, 2, 3, 4 are juxtaposed as a plurality of image carriers. The four photosensitive drums 1 to 4 form images corresponding to respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk) in order from the right in the figure. To do. The order of colors is not limited to this and can be set arbitrarily. Around each of the four photosensitive drums 1 to 4, a charging unit (charging roller, charging brush, charging charger, etc.) 6, 7, 8, 9 for performing image formation by an electrophotographic process, and a light The exposure unit of the light beams L1 to L4 from the writing device 5 and the developing unit (developing device for each color of Y, M, C, Bk) 10, 11, 1
2, 13 and transfer means (transfer roller, transfer brush, etc.) 14 and 1, which are arranged on the transfer / transport belt 22a and its back surface.
A transfer / transport device 22 including 5, 16, 17 and cleaning units (cleaning blades, cleaning brushes, etc.) 18, 19, 20, 21 and the like are provided. It is possible to form an image.

The optical writing device 5 includes four photosensitive drums 1 to 1.
4 is arranged obliquely above the image forming units arranged side by side, and is positioned and fixed to the main body frame 29 of the image forming apparatus by the main reference pin A and the sub reference pin B on the housing side. A top view of the main body frame 29 is shown in FIG. 7, in which the housing main reference A side is a determining hole (round hole) and the sub reference B side is an elongated hole.

This optical writing device 5, as shown in FIG.
The four light source units 52, 53, 54 and 55 are arranged symmetrically in substantially opposite directions with respect to the axis passing through the light deflector 62. That is, as shown in FIG. 8 showing the rigidity shading characteristic of the present embodiment, the light beams L1 and L2 are arranged in the third quadrant, and the other light beams L3 and L4 are arranged in the first quadrant. Further, the plurality of light beams L1 to L4 deflected and scanned by the light deflector 62 respectively correspond to the corresponding photosensitive drums 1.
Optical systems for guiding and forming an image on the surface to be scanned (imaging lenses 63, 64, 69 to 72, mirror 65 for folding the optical path).
.About.68, 73 to 80 and other optical members. ),
These constituent members are housed in one housing 50. In the housing 50, the optical members forming the optical system (imaging lenses 63, 64, 69 to 72, mirrors 65 to 68, 73 to 80 for folding the optical path, etc.) are the base 5
It is arranged separately on both surfaces (upper surface side and lower surface side) of 0A. In addition, a cover 8 is provided on the upper and lower parts of the housing 50.
7, 88 are provided, an opening through which the light beam passes is provided in the lower cover 87, and dustproof glasses 83, 84, 85, 86 are attached to the openings.

In the optical writing device 5, the color-separated image data input from a document reading device (not shown) or the like is converted into a light source driving signal as in the conventional example, and the light source units 52 to A semiconductor laser (LD), which is a light source in 55, is driven to emit a light beam, pass through cylindrical lenses 56 to 59 for correction of surface tilt, and reach an optical deflector 62 directly or via mirrors 60, 61. , Two-stage polygon mirrors 62a and 62b rotated at a constant speed by a polygon motor 62c deflect and scan in two symmetrical directions. The polygon mirror is for the light beams L2 and L3,
Although the upper and lower stages for the light beams L1 and L4 are divided into two stages, a thick polygon mirror may be used to deflect and scan the four light beams.

Polygon mirrors 62a, 6 of the optical deflector 62
The light beams, which are deflected and scanned in two directions by two beams by 2b, respectively pass through the first imaging lenses 63 and 64 formed of, for example, upper and lower two-layer fθ lenses, and are folded by the first folding mirrors 65 to 68. After passing through the opening of the base 51, for example, a long toroidal lens (WTL)
2nd imaging lenses 69-72 consisting of
Folding mirrors 73, 75, 77, 79, third folding mirrors 74, 76, 78, 80, dustproof glasses 83 to 86
The surface to be scanned of the photoconductor drums 1, 2, 3, and 4 for each color is irradiated via the light to write an electrostatic latent image.

In the above-mentioned optical writing device 5, the four light source units 52 to 55 are composed of a semiconductor laser (LD) as a light source and a collimating lens for collimating the luminous flux emitted from the semiconductor laser. Although it is configured to be integrated into a holder, it is a black light source unit (for example, reference numeral 54) that is often used when forming a monochrome image.
The light source unit of the
A multi-beam configuration including one or more light sources (LD) and a collimator lens set may be used. Further, in the case of the multi-beam configuration, if the light source unit is configured to be rotatable around the optical axis with respect to the side wall 50B of the housing 50, the beam pitch in the sub-scanning direction can be adjusted, and at the time of monochrome image formation. Pixel density (eg 600dpi, 1200d
pi etc.) can be switched.

Further, in the optical path of each of the light beams L1 to L4, there is provided a synchronization detection mirror (not shown) for extracting the light flux at the scanning start position in the main scanning direction, and the light flux reflected by the synchronization detection mirror. Is a synchronization detector 81, 82
The light is received by and a synchronizing signal for starting scanning is output.

The scanning direction of the light beam deflected and scanned by the optical deflector 62 is the main scanning direction, which is the axial direction of the photosensitive drums 1 to 4. Further, a direction orthogonal to the main scanning direction is a sub-scanning direction, which is a rotation direction of the photosensitive drums 1 to 4 (movement direction of the surface of the photosensitive drum), and is further conveyed by a transfer / conveying belt 22a described later. Direction. That is, the width direction of the transfer / transport belt 22a is the main scanning direction, and the transport direction is the sub-scanning direction.

As shown in FIG. 6, below the four photosensitive drums 1 to 4 arranged side by side, a transfer / conveying belt 22a stretched around a driving roller and a plurality of driven rollers is disposed.
It is conveyed by the drive roller in the direction indicated by the arrow in the figure. In addition, a plurality of paper feed units 23 and 24 that store transfer materials such as recording paper are installed at the bottom of the main body of the image forming apparatus, and the transfer materials stored in these paper feed units 23 and 24 are fed. The sheet is fed to the transfer / transport belt 22a through the rollers, the transport roller, and the registration roller 25, and is carried and transported by the transfer / transport belt 22a.

The latent images formed on the photoconductors 1 to 4 by the optical writing device 5 correspond to Y, M, C and B of the developing units 10 to 13, respectively.
The toner image of each color of Y, M, C, and Bk is developed with the toner of each color of k and visualized. The images are transferred onto the transfer material carried on top of each other in sequence. Then, the transfer material on which the four-color image has been transferred is conveyed to the fixing device 26, where the image is fixed by the fixing device 26, and then discharged onto the paper discharge tray 28 by the paper discharge rollers 27.

Although the basic configuration and operation of the optical writing device and the image forming apparatus have been described above, in the optical writing device 5 of this embodiment, the housing 50 is provided with the optical deflector 62 and the optical system. And a frame-shaped side wall 50B that surrounds the periphery of the base 50A, and the base 50A is provided substantially at the center of the side wall 50B to partition the housing 50 into upper and lower parts. ˜55 are arranged on the side wall 50B of the housing 50, and the optical deflector 62 is arranged at substantially the central portion of the base 50A of the housing 50, and the optical members (imaging lenses 63, 64, 6) forming the optical system.
9-72, mirrors 65-68, 73- for folding the optical path
80) and the like are arranged separately on both sides (upper surface side and lower surface side) of the substrate 50A, so that the size of the housing 50 of the optical writing device 5 is equal to the optical path while ensuring the entire optical path length of the optical system. Since the length is less than half the length, the optical writing device 5 can be made compact.

Further, in the image forming apparatus having the structure shown in FIG. 5, the image forming section in which the four photosensitive drums 1 to 4 are arranged side by side, the optical writing device 5 and the transfer / transport device 22 are provided in the main body of the image forming apparatus. It is stored compactly and further horizontally (X in the figure
Since it is installed obliquely with respect to the (direction), the installation space is smaller than the conventional horizontal arrangement, and the tandem color image forming apparatus can be further downsized.

By the way, in the conventional writing device having the LD unit arrangement as shown in FIG. 4, four colors are simultaneously generated or the light beam L1, L2 depending on the shading characteristics of the light beams L1, L2 and L3, 4. When the L3 color is overlapped, a difference in light amount occurs, and as a result, a tint is added, which causes deterioration in image quality. However, in the embodiment of the present invention, as shown in FIG. By arranging the LD units of two colors symmetrically with respect to the vertical axis Y and the horizontal axis X of 62, as shown in FIG. 8, the composite shading characteristics become flat due to the combination of the shading characteristics and the droop characteristics. The amount of light in the scanning direction becomes flat, and density unevenness and color unevenness can be reduced.

[0034]

As described above, the optical writing apparatus according to the first aspect and the image forming apparatus according to the first aspect using the optical writing apparatus have the arrangement of a plurality of beams and the vertical axis of the optical deflector and the horizontal axis. By arranging light sources of two colors symmetrically about the axis,
By combining the shading characteristics and the droop characteristics, the combined shading characteristics become flat, and as a result, the light amount in the main scanning direction becomes flat, which has the effect of reducing the density unevenness and color unevenness of the formed image.

In the optical writing device and the image forming apparatus using the same according to the second aspect, as described above, the housing of the optical writing device serves as a base on which the optical deflector and the optical system are arranged. , A frame-shaped side wall that surrounds the periphery of the housing, and a base is provided in the center of the side wall to partition the housing into upper and lower parts. Multiple light sources are arranged on the side wall of the housing, and the optical deflector is the base. Since the optical members that make up the optical system are arranged in the upper and lower sides of the base separately in the approximate center of the optical system, in addition to the common effects described above, the optical path length of the entire optical system is ensured. The size of the housing of the plug-in device can be less than half the optical path length, making it compact as an optical writing device,
As a result, a compact image forming apparatus can be achieved.

[Brief description of drawings]

FIG. 1 is a plan view showing an arrangement configuration of LD units in a conventional optical writing device.

FIG. 2 is a conceptual diagram of the same arrangement configuration.

3 is a diagram showing shading characteristics and droop characteristics of the optical writing device of FIG.

FIG. 4 is a conceptual diagram showing the same arrangement configuration and shading characteristics and droop characteristics.

FIG. 5 is a cross-sectional view of one embodiment of an optical writing device according to the present invention.

6 is a schematic configuration diagram showing an embodiment of an image forming apparatus including the optical writing device shown in FIG.

FIG. 7 is a plan view showing the configuration of the optical writing device shown in FIG. 5 on the upper surface side of the substrate.

FIG. 8 is a conceptual diagram showing the same arrangement configuration and shading characteristics and droop characteristics.

[Explanation of symbols]

1 to 4 photoconductor drum 5 optical writing device 6 to 9 charging unit (charging roller or the like) L1 to L4 light beam 10 to 13 developing unit 14 to 17 transfer unit (transfer roller or the like) 18 to 21 cleaning unit (cleaning blade or the like) ) 22 transfer / conveyance device 22a transfer / conveyor belt 23, 24 paper feed unit 25 registration roller 26 fixing device 27 paper ejection roller 28 paper ejection tray 29 body frame 50 housing 50A housing base 50B same side wall 52-55 light source unit 56-59 cylindrical Lenses 60, 61 Mirrors 62 Optical deflectors 62a, 62b Polygon mirrors 62c Polygon motors 63, 64, 69-72 Imaging lenses 65-68, 73-80 Mirrors 81, 82 for returning the optical path Synchronous detectors 83-86 Dustproof Glass 87, 88 cover

Claims (3)

[Claims] 1. A plurality of light sources, an optical deflector that deflects and scans a plurality of light beams from the plurality of light sources in two symmetrical directions, and a light deflector that is symmetrical about the optical deflector in the two directions. An optical system is provided, which guides a plurality of light beams deflectively scanned by the optical deflector to the respective surfaces to be scanned to form an image, and includes the plurality of light sources, the optical deflector, and the optical system in one. An optical writing device housed in a housing, wherein the plurality of light beams are arranged in two colors in substantially opposite directions with respect to one axis included in a deflection scanning plane of the deflector. . 2. The optical writing device according to claim 1, wherein the housing comprises a base on which an optical deflector and an optical system are arranged, and a frame-shaped side wall surrounding the periphery of the base. While being provided in the substantially central portion of the side wall to partition the housing vertically, the plurality of light sources are arranged on the side wall,
An optical writing device characterized in that the optical deflector is arranged substantially in the center of the base, and the optical members constituting the optical system are separately arranged on the upper and lower surfaces of the base. 3. An image forming apparatus using the optical writing device according to claim 1.