JP2000347116A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use an exposure scanning optical system including optical parts such as a polygon mirror and an f-θcorrecting means, etc., among plural kinds of image light for forming an image, and also, to easily adjust the positional deviation of the image light in order to accurately form the image. SOLUTION: In the image forming device, four kinds of image light La to Ld for forming the image are made incident on adjacent positions on the same plane of the polygon mirror 13, and also, an optical conjugation relationship is established between the incident positions on the polygon mirror 13 and the irradiation positions on the surfaces of photoreceptor drums 51a to 51d. The displacement of the incident position on the polygon mirror 13 coincides with the displacement of the irradiation position on each photoreceptor drum 51a to 51d, then, by adjusting the incident positions on the polygon mirror 13, the irradiation positions for four kinds of light on the photoreceptor drums 51a to 51d are adjusted together.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an electrophotographic image based on image light modulated by a plurality of image data.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus for forming an image of a plurality of colors using electrophotographic image formation, a photoconductor on which an electrostatic latent image is formed is rotated once for each color of a developer. There is something like that. For example, when a full-color image is formed using four color developers of yellow, magenta, cyan and black, the photoconductor is rotated four times.

[0003] Such a four-rotation type image forming apparatus includes:
As shown in FIG. 13, around the photosensitive drum 107, a charging roller 102, a laser writing unit 115, a developing unit 118 (118a to 118d), a transfer drum 122
And the cleaning unit 123 and the like
7, the fixing unit 105, the contact roller 108, the paper feed roller 117, and the like are arranged at predetermined positions.

In the four-rotation type image forming apparatus having the above-described configuration, the above-described units are controlled by a control unit (not shown), and the following image forming process is executed.

(1) The paper P is fed to the transfer drum 122 when the paper feed roller 117 rotates. The fed paper P is charged by a contact roller 108 connected to a power supply 121 and electrostatically attracted to a transfer drum 122.
The contact roller 108 is configured to freely contact and separate from the surface of the transfer drum 122.

(2) After the surface of the photosensitive drum 107 is uniformly charged with a single-polarity charge by the charging roller 102, the surface of the photosensitive drum 107 is irradiated with the first image light from the laser writing unit 115, and the photoconductive function Accordingly, an electrostatic latent image is formed on the surface of the photosensitive drum 107. In this first image light,
Light irradiation is performed according to image data corresponding to the color of the developer stored in the developing unit 118a.

(3) Photosensitive drum 1 on which electrostatic latent image is formed
A developer is supplied from the developing unit 118 a to the surface of the photoconductor 07, and a developer image obtained by visualizing the electrostatic latent image is carried on the surface of the photosensitive drum 107.

(4) The developer image carried on the surface of the photosensitive drum 107 faces the paper P electrostatically attracted to the surface of the transfer drum 122. At this time, due to the potential difference between the photosensitive drum 107 and the transfer drum 122, the developer image
Is electrostatically transferred to the surface of the substrate.

(5) After the transfer process is completed, the developer remaining on the surface of the photosensitive drum 107 is removed by the cleaning unit 123.

(6) Developing unit 118 for supplying image light emitted from laser writing unit 115 and developer
By sequentially switching b to 118d, the above (2) to
The process of (5) is repeatedly executed. That is, based on the second to fourth image light corresponding to the color of each developer stored in each of the developing units 118b to 118d.
The process of (2) to (5) is repeated, and 4
The color developer images are sequentially transferred.

(7) The sheet P is separated from the surface of the transfer drum 122 by the separation claw 109a and the separation charger 109b, and heated and pressed by the fixing unit 105. The four-color developer images transferred to the paper P are melted by being heated, and then firmly fixed to the surface of the paper P by being pressed.

As described above, in the four-rotation type color image forming apparatus, the electrostatic latent image corresponding to each of the four color image data and the development are formed on the surface of the photoconductor while the single photoconductor rotates four times. Since the developer images are formed in order, a single laser writing unit (exposure / scanning optical system) may be provided, adjustment of errors of optical components constituting the exposure / scanning optical system, and
There is an advantage that control of operation timing for exposure scanning is easy. However, in a four-rotation type color image forming apparatus, when forming a color image, the image forming process is performed in four times.
There is a disadvantage that the image forming speed needs to be repeated and repeated, and the image forming speed is reduced.

On the other hand, as a conventional color image forming apparatus, an individual process unit is provided for each color of a developer, and an image is formed by transporting a sheet so as to sequentially face a plurality of photosensitive members. Therefore, there is a tandem type color image forming apparatus in which the image forming time is shortened. For example,
A device that forms a full-color image using four color developers of yellow, magenta, cyan, and black includes four process units.

This tandem-type color image forming apparatus includes:
As shown in FIG. 14, the paper feed tray 16 containing the paper P
0 and the fixing unit 180, a pair of rollers 17
Along the transport path formed by the transport belt 171 stretched by the two process units 150a to 1503
0d is arranged. The developer images of four colors of yellow, magenta, cyan and black are processed by the process units 150a to 150a.
Each of the papers 150d is individually formed, and is sequentially transferred to the surface of the paper P conveyed in the conveyance path by the conveyance belt 171. The paper P to which the four color developer images are transferred is
Heat and pressure are applied in the fixing unit 180, and the four color developer images are firmly fixed on the surface of the paper P.

The processing units 150a to 150d have the same configuration as each other. As an example, the process unit 150 a that forms a yellow developer image includes a charging roller 152, a laser writing unit 153, a developing unit 155, a transfer roller 155, and a cleaner 156 around the photosensitive drum 151. Are arranged in this order along the rotation direction of. Image data corresponding to a yellow image is input to the laser writing unit 153, and the developing unit 155 contains a yellow developer. The transfer roller 155 is disposed to face the photosensitive drum 151 with the transport belt 171 interposed therebetween. In addition,
In the processing units 150b to 150d, image data corresponding to images of magenta, cyan, and black are input to the laser writing unit 153, and the developing unit 1
Reference numeral 55 stores magenta, cyan, and black developers.

In the tandem-type color image forming apparatus configured as described above, the developer images of four colors are formed almost simultaneously in the individual process sections, so that the time substantially coincides with the time of one image forming process. There is an advantage that a color image is formed and the image forming time can be shortened. However, in the tandem type color image forming apparatus, it is necessary to provide an individual process unit for each color, a plurality of exposure scanning optical systems are required, adjustment of errors of optical components constituting the exposure scanning optical system, and, There is a disadvantage that control of operation timing for exposure scanning is complicated.

Therefore, by sharing the optical components constituting the exposure scanning optical system in a plurality of process units,
There has been proposed a tandem-type color image forming apparatus that simplifies adjustment of errors of optical components constituting an exposure scanning optical system and control of operation timing for exposure scanning. As an example, Japanese Patent Application Laid-Open No. 5-100540 discloses that a polygon mirror, which is an optical component constituting an exposure scanning optical system, is coaxially arranged in two stages, and two upper and lower polygon mirrors are driven by a single motor. There is disclosed a configuration and a control method in which four image lights are emitted through each of two surfaces of a two-stage polygon mirror.

Japanese Patent Application Laid-Open No. Hei 5-270051 discloses a configuration in which three laser beams having different wavelengths are irradiated separately from each other by an optical filter via one polygon mirror. .

Further, Japanese Patent Application Laid-Open No. Hei 6-286226 discloses that a laser beam emitted from a laser array in a very close proximity is deflected in the main scanning direction via a single polygon mirror, and then deflected by a single f- There is disclosed a configuration in which the scanning speed is made uniform by the θ correction means, and the four photosensitive members are separately irradiated in the respective directions via the beam separation means.

[0020]

However, in the configuration disclosed in Japanese Patent Laid-Open No. 5-80631, individual f-.theta. Correction means is required for each color image light, and the error of the f-.theta. Adjustment is complicated. Further, it is necessary to adjust the error between the upper and lower polygon mirrors. further,
Since the two image lights are scanned in the opposite direction to the other two image lights via the upper and lower two-stage polygon mirrors, the rotation unevenness of the polygon mirror causes scanning unevenness in the opposite direction, resulting in a large image defect. .

In the configuration disclosed in Japanese Patent Application Laid-Open No. 5-270051, the amount of laser light is reduced by the optical filter when the optical paths of the laser light are made coincident or when the laser light is separated and deflected. Further, when the wavelengths of the laser beams of the respective colors are close to each other, it is necessary to use an optical filter capable of separating and deflecting a plurality of laser beams having similar wavelengths. However, this is generally expensive and the cost increases. on the other hand,
When the wavelengths of the laser beams of the respective colors are separated from each other, a relatively inexpensive optical filter can be used. Manufacturing is difficult, and the imaging correction means must be expensive, and in any case, an increase in cost cannot be avoided.

Further, in the configuration disclosed in JP-A-6-286226, the four positions of the laser array, the reflecting surface of the polygon mirror, the beam separating means, and the surface of the photosensitive member must be optically conjugate. This is a great limitation in designing an exposure scanning optical system. Further, the beam separation means needs to separate the laser beams that are very close together, and high precision is required for the shape and arrangement position of the components.
Further, since the laser beam is obliquely incident on the f-θ correction unit, the shape of the f-θ correction unit is complicated. The f-θ correction means having a complicated shape as described above cannot easily specify the deformation due to the temperature change, and it is difficult to form a high-quality image.

The most important problem in a color image forming apparatus is a color shift for each color. This color shift is that the image formation for each color by a plurality of laser beams is deviated from a prescribed position in image formation (resist failure).
Caused by The registration failure is caused by a displacement of the laser beam in the main scanning direction and a displacement of the laser beam in the sub-scanning direction.

The positional deviation in the main scanning direction is caused by the deviation of the incident position of each laser beam on the reflecting surface of the polygon mirror from a predetermined position in the main scanning direction. As a cause, as shown in FIG. 15, a single start sensor 193 detects the scanning start position of each laser beam to compare the allowable accuracy of a general misalignment of 1/8 dot or less. Can be easily achieved.

However, the positional deviation in the sub-scanning direction caused by the deviation of the incident position of each laser beam on the reflecting surface of the polygon mirror 191 from the predetermined position in the sub-scanning direction is as follows.
Since it cannot be detected by the start sensor 193, it appears as an error on the surface of the photoconductor 195 as it is, and when a displacement of one or more dots in the sub-scanning direction occurs for a plurality of laser beams, a plurality of colors of developer The images cannot be superimposed on each other, and the images cannot be faithfully reproduced.

For this reason, in the configuration shown in FIG. 15, the irradiation position of the laser beam on the surface of the photoconductor 195 in the sub-scanning direction is corrected by changing the reflection angle of the deflecting mirror 194. It becomes necessary to adjust the deflection mirror 194 in addition to the adjustment of the 191 and the f-θ correction means 192, and the control form becomes complicated.

An object of the present invention is to make it possible to share an exposure scanning optical system including optical components such as a polygon mirror and f-θ correction means among a plurality of image lights when an image is formed by a plurality of image lights. Another object of the present invention is to provide a tandem-type image forming apparatus capable of realizing miniaturization of the apparatus and easily adjusting a position shift of image light for forming a high-precision image.

[0028]

The present invention has the following arrangement as means for solving the above-mentioned problems.

(1) A plurality of image light beams are focused on a polygon mirror in the sub-scanning direction, deflected by the polygon mirror at a constant angular velocity in the main scanning direction, and then at a uniform speed in the main scanning direction via the correction means. In an image forming apparatus that deflects and forms an image on the surface of a photoreceptor, a plurality of image light beams are focused at close positions on the reflection surface of a single polygon mirror.

In this configuration, a plurality of image lights are reflected from the light source at positions close to each other on the reflection surface of the single polygon mirror, and reach the surface of the photoreceptor from the light source via the reflection surface of the polygon mirror. In the optical path of each image light, the reflection position of the polygon mirror and the irradiation position of the photoconductor have an optically conjugate relationship. Therefore, the displacement of the irradiation position on the photosensitive member (resist failure) between the plurality of image lights is reduced.

In addition, the irradiation position on the photoconductor is displaced in a substantially similar manner for a plurality of image lights corresponding to the displacement of the reflection position on a single polygon mirror, and a plurality of image lights are adjusted by adjusting only the reflection position on a single polygon mirror. The irradiation position of the image light on the photoconductor is adjusted at the same time. Therefore, when correcting a registration defect, it is only necessary to adjust the inclination angle of the rotation axis of a single polygon mirror (correction of the tilt of the polygon mirror). There is no need to consider combinations of adjustment states.

Further, the distortion states of the reflection positions of the plurality of image lights substantially match. Therefore, a large registration defect does not occur between the plurality of image lights due to the difference in the state of the reflection position.

In addition, only one polygon mirror for deflecting image light in the main scanning direction is provided for a plurality of image lights. Therefore, the number of parts is reduced, and the size of the apparatus is reduced and the cost is reduced.

(2) The beam waists of the plurality of image lights overlap at least partially or entirely in the sub-scanning direction.

In this configuration, the error in the sub-scanning direction of the reflection positions of the plurality of image lights on the polygon mirror is made within the range of the beam waist of each image light. Therefore, the registration failure among a plurality of image lights falls within the range of 1 dot or less, and there is no significant shift in the image.

(3) A plurality of light sources for irradiating the plurality of image lights are provided, and the plurality of light sources are arranged at substantially the same position in the main scanning direction and at different positions in the sub-scanning direction. I do.

In this configuration, a plurality of light sources for irradiating each image light to the polygon mirror are arranged at substantially the same position in the main scanning direction. Therefore, by irradiating the image light from a plurality of light sources to a position close to the reflection surface of the polygon mirror, the optical path ranges of the plurality of image lights in the main scanning direction substantially match. For this reason, the length of the reflection surface of the polygon mirror in the main scanning direction is maximized by the plurality of image lights constituting the image.

Further, the plurality of light sources are arranged at different positions in the sub-scanning direction. Therefore, the light emitted from each light source is emitted from the reflection surface of the polygon mirror toward different positions in the sub-scanning direction. For this reason, a plurality of image lights constituting an image are easily separated after being reflected by the polygon mirror.

(4) A single converting means for converting a plurality of image lights reflected by the polygon mirror into light parallel to each other in the sub-scanning direction, and a plurality of image lights passing through the converting means in the main scanning direction. And a single correction means for deflecting to speed.

In this configuration, the plurality of image lights reflected by the polygon mirror are converted into light parallel to each other by the conversion means, and then deflected at a constant speed in the main scanning direction by the correction means. Therefore, after the plurality of image lights are reflected by the polygon mirror, the plurality of image lights are irradiated onto the photoconductor in a state of being surely separated. Further, the angles of incidence of the plurality of image lights with respect to the correction means become the same, and the registration failure occurring between the plurality of image lights becomes the same.

Further, one conversion means and one correction means are provided for each of a plurality of image lights. Therefore, the conversion state of the conversion unit and the correction state of the correction unit for a plurality of image lights constituting an image are constant, and the configuration is simplified.

(5) An optical path setting means for irradiating the same position on the surface of the photoconductor with a plurality of image lights is provided between the correction means and the photoconductor.

In this configuration, a plurality of image lights deflected at a constant speed in the main scanning direction by the correction means are
The light is irradiated to the same position on the surface of the photoconductor by the light setting means. Therefore, the plurality of image lights converted into light parallel to each other in the sub-scanning direction by the conversion means are deflected at a constant speed in the main scanning direction, and then irradiated to the same position on the surface of the photoreceptor while being separated from each other. By visualizing an electrostatic latent image formed by each image light with a developer corresponding to each image light, a plurality of developers are superimposed to form an image.

(6) In the plurality of image lights, the width of the image light a in the sub-scanning direction is Ba and the width of the image light b in the sub-scanning direction is two for two image lights a and b adjacent to each other in the sub-scanning direction. The width in the direction is Bb, the distance in the sub-scanning direction between the image light a and the image light b is L, the error in the sub-scanning direction of the reflection position on the polygon mirror is W, and the maximum error in the sub-scanning direction due to the surface tilt of the polygon mirror is When D, the plurality of light sources and the conversion means are arranged so as to satisfy the relationship of L- (Ba / 2)-(Bb / 2) -WD> 0.

In this configuration, for two image light beams a and b adjacent to each other in the sub-scanning direction,
(Interval L in the sub-scanning direction) to (a value of 1/2 of the width Ba of the image light a in the sub-scanning direction), (the width B of the image light b in the sub-scanning direction)
b), (the error W in the sub-scanning direction of the focal position of the polygon mirror in the sub-scanning direction), and (the maximum error D in the sub-scanning direction due to the tilting of the polygon mirror) are positive values. Is done. Therefore, even when an error occurs in the reflection position of the image light a and the image light b on the polygon mirror or the inclination of the rotation axis of the polygon mirror, the optical paths of the image light a and the image light b overlap in the sub-scanning direction. And a plurality of image lights can be reliably separated.

(7) An individual photoconductor is provided for each of the plurality of image lights, and the distance between the transfer positions of the photoconductor a and the photoconductor b is G for two photoconductors a and b adjacent to each other.
(M), the distance between the exposure position and the transfer position of the photoconductor a is Ta
(M), the distance between the exposure position of the photoconductor b and the transfer position is Tb
(M), the process speed is v (m / s), the number of revolutions of the polygon mirror is q (rpm), and an arbitrary integer is k, where G + Ta−Tb = k · 60 · v / q. And

In this configuration, for two photosensitive members a and b adjacent to each other, (the interval G between the transfer positions of the photosensitive members a and b) and (the exposure position and the transfer position of the photosensitive member a Is the integer multiple of the value obtained by subtracting (the distance Tb between the exposure position and the transfer position of the photoconductor b) from the sum of the (process distance v) and (the number of rotations q of the polygon mirror). To be. Therefore, a plurality of image lights reflected on the same surface of the polygon mirror are accurately irradiated to positions corresponding to the same dot of the image on each individual photoreceptor. Is formed.

(8) A plurality of photoconductors each having a columnar shape are individually provided for each of the plurality of image light beams.
And the radius of the photoconductor a and the photoconductor b is R (m), and the interval between the transfer positions of the photoconductor a and the photoconductor b is G.
(M), the angle between the exposure position of the photoconductor a and the transfer position is Sa (rad), the angle between the exposure position of the photoconductor b and the transfer position is Sb (rad), and the process speed is v (m). /
s), the rotation number of the polygon mirror is q (rpm), and an arbitrary integer is k, and the following relationship is established: G + R.Sa-R.Sb = k.60.v / q.

In this configuration, for the two photosensitive members a and b adjacent to each other, (the interval G between the transfer positions of the photosensitive members a and b) and (the radius R of the photosensitive member a)
The value obtained by subtracting (the radius R of the photoconductor b and the product of the angle Sb between the exposure position and the transfer position) from the sum of the product of the angle Sa between the exposure position and the transfer position is (process speed). v) is multiplied by an integral multiple of a value obtained by dividing (v) by (number of rotations q of the polygon mirror). Therefore, when a columnar photoconductor is used as a plurality of photoconductors that form a developer image corresponding to each image light, the plurality of image lights reflected on the same surface of the polygon mirror cause the image on each individual photoconductor to be different. Are accurately irradiated to the position corresponding to the same dot, the occurrence of resist failure is reliably prevented, and a high-quality image without deviation is formed.

[0050]

FIG. 1 is a diagram showing a configuration of a color image forming apparatus according to an embodiment of the present invention. In the image forming apparatus 40 according to this embodiment, a transport belt 71 stretched between a pair of rollers 72 and 73 is disposed between a paper feeding unit 60 and a fixing unit 80. The conveyor belt 71 is
On the upper surface, the recording medium supplied from the paper supply unit 60, for example, the paper P, is transported to the fixing unit 80. Conveyor belt 7
1, yellow (Y), magenta (M),
Process units 50a to 50d for forming developer images of cyan (C) and black (B) are arranged along a sub-scanning direction which is a moving direction of the upper surface of the conveyor belt 71.

Each of the process units 50a to 50d includes
They have the same configuration. As an example, a process unit 50a that forms a yellow developer image includes a cylindrical photosensitive drum 51 that rotates at a constant speed in a direction indicated by an arrow in the figure.
a, a charging roller 52a, a developing unit 54a,
The transfer roller 55a and the cleaner 56a are arranged. The developing unit 54a contains a yellow developer, and the process unit 50a forms a yellow developer image by the following process.

After a charge having a polarity opposite to that of the developer is uniformly applied from the charging roller 52a to the surface of the photosensitive drum 51a, the laser writing unit 10 irradiates image light corresponding to a yellow image. As a result, an electrostatic latent image is formed by the photoconductive action. The electrostatic latent image formed on the surface of the photosensitive drum 51a is visualized into a yellow developer image by the developer supplied from the developing unit 54a.

In synchronization with the rotation of the photoconductor drum 51a, the paper P fed from the paper supply unit 60 is conveyed by the conveyance belt 71 between the photoconductor drum 51a and the transfer roller 55a. The transfer roller 55a is arranged in contact with the inner side surface of the transport belt 71, and is applied with a bias voltage having a polarity opposite to the polarity of the charged developer. As a result, the yellow developer image formed on the surface of the photosensitive drum 51a is transferred to the surface of the sheet P. Transfer roller 55a
The developer remaining on the surface of the photosensitive drum 71 that has passed through the position opposite to the above is collected by the cleaner 56a.

The above process is performed in the developing units 54b to 54b.
The same applies to the process units 50b to 50d in which magenta, cyan, and black developers are stored in each of the 54d. Each of the photosensitive drums 51b to 51d receives irradiation of image light corresponding to magenta, cyan, and black images from the laser writing unit 10. As a result, magenta, cyan, and black developer images are formed on the respective surfaces of the photosensitive drums 51b to 51d. Therefore, the paper P fed from the paper feed unit 60 is transported by the transport belt 71 to the process unit 50.
By being sequentially conveyed to a to d, yellow, magenta, cyan and black developer images are sequentially transferred to the surface.

The sheet P that has passed through the process sections 50a to 50d is guided to the fixing unit 80. Fixing unit 80
Is constituted by a pair of upper and lower rollers, and the sheet P receives heat and pressure while passing through the fixing unit 80. As a result, on the surface of the paper P, the developers of the four colors are melted and firmly fixed on the surface of the paper P, and a color image is formed.

FIGS. 2 and 3 are views showing the structure of the laser writing unit 10 provided in the image forming apparatus 40. FIG. FIG. 2 is a side view, and FIG. 3 is a plan view. The laser writing unit 10 includes a laser diode 11 as a light source.
a to 11d, lenses 12a to 12d, polygon mirror 1
3. The first cylindrical means (cylindrica)
l: Hereinafter referred to as CY. ) Lens 14, f-
θ lens 15, deflection mirrors 16a to 16
16d, and second CY lenses 17a to 17d,
Each image light emitted from the laser diodes 11a to 11d forms an optical path to the photosensitive drums 51a to 51d.

In the optical path of each image light, the optical path length from the f-θ lens 15 to the photosensitive drums 51a to 51d is made equal to each other by a mirror (not shown).

The laser diodes 11a to 11d output image light La to color corresponding to each color of YMCB according to image data.
Irradiate Ld. The lenses 12a to 12d are provided with image light La to Ld emitted from the laser diodes 11a to 11d.
And form an image on the reflection surface of the polygon mirror 13.
Therefore, the image light La to Ld is
Is focused in a direction (sub-scanning direction) orthogonal to the rotation direction (main scanning direction) of the polygon mirror 13 on the reflecting surface of (1). The laser diodes 11a to 11d and the lenses 12a to 12d are arranged side by side in the sub-scanning direction, and the incident angles of the image lights La to Ld on the reflecting surface of the polygon mirror 13 in the sub-scanning direction are different from each other.

The polygon mirror 13 is a rotary polygon mirror that rotates in the main scanning direction indicated by an arrow in the figure, and includes lenses 12a to 12a.
The image light La to Ld incident from 12d is reflected while rotating. As a result, the image lights La to Ld are deflected at a constant angular velocity in a predetermined range in the main scanning direction on the photosensitive drums 51a to 51d. Laser diode 11a
11d and lenses 12a to 12d are arranged at the same position in the main scanning direction. Therefore, the image light La
Ld are illuminated and reflected on the same reflection surface of the polygon mirror 13.

The first CY lens 14 has a lens effect only in the sub-scanning direction, and converts the image light La to Ld reflected by the polygon mirror 13 into light parallel to each other in the sub-scanning direction. The f-θ lens 15 is deflected at an equal angular velocity by the polygon mirror 13 and then converted by the first CY lens 14 into image light L converted into parallel light.
a to Ld are deflected at a constant speed. Therefore, the image light La
Ld scans the surfaces of the photosensitive drums 51s to 51d at a constant speed over the entire area in the main scanning direction.

The deflecting mirrors 16a to 16d change the optical paths of the image light La to Ld deflected at a constant speed by the f-θ lens 15 in the direction of the photosensitive drums 51a to 51d. The second CY lenses 17a to 17d are
The image lights La to Ld reflected at a to 16d are condensed and imaged on the surfaces of the photosensitive drums 51a to 51d.
Therefore, the image lights La to Ld focus on the surfaces of the photosensitive drums 51a to 51d over the entire area in the main scanning direction.

As described above, the laser writing unit 1
At 0, the image lights La to Ld emitted from the laser diodes 11a to 11d are focused on the reflection surface of the polygon mirror 13 and focused on the surfaces of the photosensitive drums 51a to 51d. That is, the reflection surface of the polygon mirror 13 and the surfaces of the photosensitive drums 51a to 51d are in an optically conjugate relationship in the sub-scanning direction.

FIG. 4 is a diagram showing the relationship between the polygon mirror 13 of the laser writing unit 10 and the photoconductors 51a to 51d (FIG. 4 shows the case of the image light La as an example). . As described above, the polygon mirror 13
Is in an optically conjugate relationship with respect to the sub-scanning direction. Therefore, the rotation axis of the polygon mirror 13 is tilted from the proper state shown in FIG. 4A as shown in FIG.
In the case where 3 has a so-called tilt, the polygon mirror 13
The incident position of the image light La to Ld in the sub-scanning direction on the reflection surface changes, but the photosensitive drum 5 of the image light La to Ld changes.
The positions in the sub-scanning direction on the surfaces 1a to 51d are maintained in an appropriate state.

As described above, the incident position of the image light La to Ld in the sub-scanning direction on the surface of the photosensitive drums 51a to 51d does not change due to the surface tilt of the polygon mirror 13, and no registration failure occurs. . Therefore, it is not necessary to correct the surface tilt of the polygon mirror 13 in order to prevent a registration failure of the image light La to Ld on the surfaces of the photosensitive drums 51a to 51d.

However, when the image light La to Ld is also focused on the surface of the polygon mirror 13 in the main scanning direction, the image light La to Ld is reflected by the polygon mirror 13 due to the surface tilt of the polygon mirror 13. , The image light La to Ld is irregularly reflected at the defective portion and is not irradiated to a predetermined position on the surface of the photosensitive drums 51a to 51d, resulting in image loss. Therefore, in the laser writing unit 10 of the color image forming apparatus according to this embodiment, the image light La to Ld is not focused on the reflection surface of the polygon mirror 13 in the main scanning direction.

FIG. 5 is a view for explaining the incident position of image light on the polygon mirror 13 of the laser writing unit 10. FIG. 5A is a sectional view in the sub-scanning direction near the reflection surface of the polygon mirror 13. FIG. 2B is a sectional view in the main scanning direction. In FIG. 5, for easy understanding,
Two image lights L adjacent to each other among a plurality of image lights
Only a and Lb are shown. Multiple image lights La to Ld
Are incident on substantially the same position on the same surface of the polygon mirror 13.

In particular, the difference W in the sub-scanning direction between the incident positions of the image lights La to Ld on the reflecting surface of the polygon mirror 13 is:
It is set to be smaller than the beam waist ω of each of the image lights La to Ld. As a result, on the reflecting surface of the polygon mirror 13, the beam waists ω of the adjacent two colors of image light in the plurality of image lights La to Ld at least partially overlap, and resist failure is suppressed.

Image light La to polygon mirror 13
An error in the sub-scanning direction of the reflection position of Ld causes an error (registration failure) of the incident position of the image light La to Ld on the surface of the photosensitive drums 51a to 51d. When the incident position of any of the image lights has an error of one dot or more with respect to the incident positions of the other image lights on the surfaces of the photosensitive drums 51a to 51d, the developer images formed by these image lights are formed. Color mixing does not occur, so that a predetermined color cannot be reproduced in a color image or color turbidity may occur, resulting in deterioration of image quality. Therefore, in order to maintain a good color image formation state, it is necessary to suppress the error of the incident position between the plurality of image lights on the surfaces of the photosensitive drums 51a to 51d to one dot or less.

As shown in FIG. 6, for example, the error W 'of the incident position of the image light La, Lb on the photosensitive drums 51a, 51b is represented by W, the error on the reflection surface of the polygon mirror 13, the polygon mirror 13 and the photosensitive member Drums 51a, 51
b, the first CY lens 14, the f-θ lens 15, the deflecting mirrors 16a and 16b, and the second CY lens 1
Assuming that the optical magnification of 7a and 17b is m, it can be obtained by the following first equation.

W ′ = m · W (1) Further, the size of one dot on the surface of the photosensitive drums 51 a and 51 b is obtained by multiplying the beam waist ω on the reflection surface of the polygon mirror 13 by the optical magnification m. Value. From these facts, if the error of the reflection position in the sub-scanning direction between the image light La and Lb on the reflection surface of the polygon mirror 13 is equal to or less than the beam waist ω, the error of the incident position on the surface of the photosensitive drums 51a and 51b will be It can be suppressed to within one dot, and the formation state of the color image can be favorably maintained.

As shown in FIG. 7, the beam waist ω refers to the beam width at the focal position of the image light La to Ld. The laser writing unit 10 provided in the color image forming apparatus 40 according to this embodiment collects the image light La to Ld emitted from the laser diodes 11a to 11d by the lenses 12a to 12d,
Incident on the reflection surface. Laser diodes 11a to 11d
In general, the intensity of the laser light emitted from the light source has a Gaussian distribution. Therefore, the image lights La to L, which are laser lights,
The beam waist ω of d is obtained by the following equation (2), where λ is the wavelength of the laser beam and NA is the aperture angle of the lenses 12a to 12d.

Π · ω · NA = λ (2) Accordingly, in the color image forming apparatus 40, the difference between the incident positions of the image light La to Ld in the sub-scanning direction on the polygon mirror 13 is λ / (π -It is set to be smaller than NA).

FIG. 8 is a diagram showing a state of image light near the first CY lens 14 and the f-θ lens 15 in the laser writing unit 10. In the laser writing unit 10 of the color image forming apparatus 40 according to this embodiment, four image light beams enter the first CY lens 14 in a state where they are separated from each other at positions that do not overlap with each other in the sub-scanning direction. The first CY lens 14 converts the image lights La to Ld into light parallel to each other while maintaining a state of being separated from each other. Therefore, the separation state of the image lights La to Ld is
It is also maintained when passing through the f-θ lens 15.

For example, for the image light La and the image light Lb adjacent to each other after exiting the first CY lens 14, the distance between the image light La and the image light Lb in the sub-scanning direction is L, and the image light La and the image light Lb Where Ba and Bb are the widths in the sub-scanning direction, W is the error in the sub-scanning direction of the reflection position of the polygon mirror 13 in the sub-scanning direction, and D is the maximum error in the sub-scanning direction due to surface tilt of the polygon mirror. Have been to satisfy the relationship. L− (Ba / 2) − (Bb / 2) −WD> 0 (3) The distance L between the image lights La and Lb in the sub-scanning direction is an ideal design value (FIG. 8A )reference). From this state, if an error W occurs in the reflection position of the image light Lb on the reflection surface of the polygon mirror 13, the image light Lb passing through the f-θ lens 15 moves to the position of Lb ', and the image light La and Lb
Is (L− (Ba / 2) − (Bb / 2) −W) (see FIG. 8B).

Further, from this state, the polygon mirror 1
3 causes the surface to fall, and the image light La and Lb are changed to La ″ and L
b ", the gap H in the sub-scanning direction between the image lights La and Lb is H = L- (Ba / 2), where the difference between the movement amounts Da and Db of the image lights La and Lb is the maximum error D. )-(Bb / 2) -WD (see FIG. 8C).

Therefore, even when the image light is misaligned and the polygon mirror 13 is tilted, the value of the interval H between the image lights La and Lb in this state is positive, and the relationship of the above formula (3) is satisfied. Thereby, the separated state of the image lights La to Ld is maintained. This relationship can be realized by arranging the laser diodes 11a to 11d, the lenses 12a to 12d, the polygon mirror 13, and the first CY lens 14 appropriately.

FIG. 9 illustrates a method of irradiating a plurality of image lights to the surfaces of the photoconductors 51a to 51d using a single reflecting surface of the polygon mirror 13. In the tandem type color image forming apparatus 40 including this embodiment, as shown in FIG. 1, the paper P is constituted by a photoconductor such as photoconductor drums 51a to 51d and a transfer unit such as transfer rollers 55a to 55d. The developer image formed on the surface of the photoconductor at each transfer position is sequentially transferred to the surface of the sheet P at each transfer position.

In FIG. 9, a photoreceptor belt is used as an example of a photoreceptor, and an interval between transfer positions of two adjacent photoreceptor belts n (photoreceptor a) and n ′ (photoreceptor b) is represented by G.
(M), the distance (Ta) between the exposure position E and the transfer position F on the surface of the photosensitive belt n is T (m), and the exposure position E 'and the transfer position F' on the surface of the photosensitive belt n ' Is T '(m), the transport speed (process speed) of the paper P is v (m / s), and the rotation speed of the polygon mirror is q (rpm). In order to form a high-quality color image on the paper P by superimposing the two-color developer images N and N 'formed on the surfaces of the photoreceptor belts n and n', respectively, It is necessary to transfer the developer images N and N 'of two colors in a state where the positions of the images coincide with each other.

That is, after the developer image N is transferred from the photosensitive belt n at the transfer position F of the photosensitive belt n to the paper P being transported at a constant transport speed v (m / s), the transfer position F ′, The developer image N ′ must be transferred from the photosensitive belt n ′ to the same position as the position on the paper P to which the developer image N has been transferred. At this time, the time required for the developer image N obtained by visualizing the electrostatic latent image formed at the exposure position E of the photosensitive belt n to reach the transfer position F ′ of the photosensitive belt n ′ via the paper P is (G + T) / v until the developer image N ′, which is a visualized electrostatic latent image formed at the exposure position E ′ of the photosensitive belt n ′, reaches the transfer position F ′ of the photosensitive belt n ′. Is T '/ v.

Therefore, by starting the exposure on the photosensitive drum n 'at a timing delayed by the time t = (G + T-T') / v from the exposure start timing on the photosensitive belt n, the paper P at the transfer position F 'is started. The photosensitive drum n 'is located at the position where the developer image N is transferred.
From the developer image N '. here,
The time t is set to be equal to a value obtained by multiplying the time 60 / q required for one rotation of the polygon mirror rotating at the rotation number q (rpm) by an arbitrary integer (k), that is, the following formula (4) By satisfying the following expression, (G + T−T ′) / v = k · 60 / q G + T−T ′ = k · 60 · v / q (4) Multiple colors reflected on the same reflection surface of the polygon mirror The image formed by the image light, that is, the dot at the same position in the plurality of developer images is transferred within the range of one dot on the paper P. This allows the developer images of multiple colors to be
The image can be transferred to the same position on the sheet P to form a high-quality color image.

FIG. 9 shows an example using a photosensitive belt.
The same applies to the color image forming apparatus 40 using the photosensitive drum according to this embodiment. That is, as shown in FIG. 10, the exposure positions of the photosensitive drums 51a and 51b having the radius R adjacent to each other at the interval G (m) are Ea and Eb, the transfer position is Fa and Fb, and the transfer position is between the exposure position and the transfer position. When the rotation angles are Sa (rad) and Sb (rad), the circumference Ta (corresponding to T in the fourth formula) between the exposure position Ea and the transfer position Fa of the photosensitive drum 51a is R × Sa. From the exposure position Eb of the photosensitive drum 51b to the transfer position F
The circumference Tb up to b (corresponding to T ′ in the fourth equation) is R × Sb. Substituting this into the above fourth equation, G + R.Sa-R.Sb = k.60.v / q... Fifth equation Therefore, the distance G and the radius R between the photosensitive drums 51a and 51b, the process speed v, and In accordance with the rotation speed q of the polygon mirror 13, the adjacent photosensitive drums 51a and 51a
By setting the rotation angles Sa and Sb between the exposure position and the transfer position in 1b so as to satisfy the above formula 5, the image light of a plurality of colors can be reflected on the same surface of the polygon mirror 13. In addition, the developer images of a plurality of colors can be accurately superimposed on the paper P.

Here, the operation of the laser writing unit 10 will be described. When the yellow, magenta, cyan, and black image data are input, the control unit of the laser writing unit 10 first forms an electrostatic latent image corresponding to the yellow image on the surface of the photosensitive drum 51a. To this end, a drive signal corresponding to the yellow image data is output to the laser diode 11a, and the laser diode 11a emits image light La. The image light La emitted from the laser diode 11a is transmitted through the lens 12a, the polygon mirror 13, and the sensor mirror 19 to the start sensor 20 (FIG. 3).
), The position of the reflection surface of the polygon mirror 13 and the period in the main scanning direction are detected, and the start position in the main scanning direction is determined. This start sensor 2
For 0, for example, a photodiode having a slit disposed on the light receiving surface can be used.

The image light La emitted from the laser diode 11a passes through the lens 12a to the polygon mirror 1
3, the photosensitive drum is uniformly charged in advance by the charging roller 52a via the first CY lens 14, the f-θ lens 15, the deflecting mirror 16a, and the second CY lens 17a after being reflected on the reflection surface of the polygon mirror 13. The light enters the surface of 51a. As a result, an electrostatic latent image corresponding to the yellow image is formed on the surface of the photosensitive drum 51a. This electrostatic latent image is visualized into a yellow developer image by the developing unit 54a, and is transferred to the transfer roller 55a.
Is transferred to the surface of the paper P via

Next, the control section outputs drive data based on magenta image data to the laser diode 11b at a predetermined timing after the start of forming an electrostatic latent image on the photosensitive drum 51a. Thus, the image light Lb corresponding to the magenta image data is emitted from the laser diode 11b to the photosensitive drum 51b, and an electrostatic latent image corresponding to the magenta image is formed on the surface of the photosensitive drum 51b. At this time, the timing at which the driving of the laser diode 11b is started is set so as to satisfy the relationship of the fifth equation. Therefore, the image light Lb corresponding to the magenta image data is reflected in the same state on the same reflection surface as the reflection surface of the polygon mirror 13 that reflects the image light La corresponding to the yellow image data, and the image light Lb of the photosensitive drum 51b At the transfer position, the magenta developer image is transferred to the same position as the yellow developer image formed on the paper P. Further, as shown in FIG. 5, the image lights La and Lb are made to enter the polygon mirror 13 at positions close to each other.

The control unit controls the laser diode 1 based on the cyan image data so as to satisfy the relationship of the above formula (5) and the relationship of the reflection position on the polygon mirror 13.
The timing of irradiating the image light Lc corresponding to the cyan image data from 1c and the timing of irradiating the image light Ld corresponding to the black image data from the laser diode 11d based on the black image data are determined.

In this way, the control section irradiates the image light La to Ld based on the image data of yellow, magenta, cyan and black in order from the laser diodes 11a to 11d, thereby forming the photosensitive drums 51a to 51d. The transferred developer images of the respective colors are transferred onto the paper P in a state where the respective positions match. As a result, a color image is formed on the paper P.

As described above, in the color image forming apparatus 40 according to this embodiment, the reflection positions of the four image lights on the polygon mirror 13 and the photosensitive drums 51a to 51a are detected.
The irradiation position at 51d is configured to have an optical conjugate relationship in the sub-scanning direction. Therefore, a registration failure in the sub-scanning direction due to the surface of the polygon mirror 13 does not occur. As described above, since a registration failure in the sub-scanning direction does not occur, it is necessary to provide an optical adjustment member such as a deflection mirror for adjusting the irradiation position of the image light La to Ld on the photosensitive drums 51a to 51d. That is, there is no need to adjust the relative positional relationship between the polygon mirror 13 and the other adjusting members in consideration of the combination of the two, and the manufacturing process of the image forming apparatus can be simplified and the productivity can be improved. .

Further, since the image lights La to Ld are made incident on the same reflecting surface of the polygon mirror 13, the distortion of each reflecting surface caused when a plurality of reflecting surfaces are used as in the prior art. No resist failure due to the difference occurs. Furthermore, since the image light La to Ld is incident on a position close to the reflection surface of the polygon mirror 13, resist failure due to a difference in distortion in the reflection surface of the polygon mirror 13 is suppressed. For this reason, it is possible to form a high-quality image with few registration defects even for a high-resolution image.

Further, for the four image lights La to Ld,
Since the polygon mirror 13, the first CY lens 14, and the f-θ lens 15 are provided one by one, the number of components can be reduced and the size and cost of the apparatus can be reduced. Further, there is no need to adjust the errors of the plurality of f-θ lenses 15, and the manufacturing process can be further simplified.

Further, since the laser diodes 11a to 11d for irradiating the four image lights La to Ld are arranged along the sub-scanning direction, each of the image lights La to Ld reflected by the polygon mirror 13 can be easily processed. Can be separated.

Further, as compared with the case where the laser diodes 11a to 11d are arranged along the main scanning direction, the image light L
The scanning range common to a to Ld can be maximized, and the use efficiency of the reflecting surface of the polygon mirror 13 can be optimized. That is, when a plurality of laser diodes are arranged in the main scanning direction, the scanning range of each image light reflected by the polygon mirror is shifted in the main scanning direction, and the incident range of the plurality of image lights is shifted. Only overlapping portions can be used for image formation. For this reason, there are portions that cannot be used at both ends in the main scanning direction on the reflection surface of the polygon mirror, and the area of the reflection surface formed on the polygon mirror cannot be effectively used.

In this respect, in the color image forming apparatus 40 according to this embodiment, since the laser diodes 11a to 11d are arranged along the sub-scanning direction, the image light La to Ld on the reflection surface of the polygon mirror 13 is not affected. Since the incident positions are all the same, there is no unusable portion at both ends of the reflection surface of the polygon mirror 13, and the entire surface of the reflection surface formed on the polygon mirror 13 is effectively used to reduce the size of the polygon mirror 13. Can be

Further, in the color image forming apparatus according to this embodiment, the image light La to Ld is supplied to the first CY lens 14
Are converted into parallel lights, and are incident on the f-θ lens 15 at the same incident angle. For this reason, even when the f-θ lens 15 is deformed due to thermal expansion or the like, the four image lights La to Ld after exiting the f-θ lens 15 have the same positional deviation, and each image light La To Ld can be suppressed. Further, the configuration of the f-θ lens 15 can be simplified.

In the laser writing unit 10 of the color image forming apparatus 40 according to this embodiment, the configuration is shown in which the four laser diodes 11a to 11d irradiate the image lights La to Ld. The number of light sources of ~ Ld is not limited to four. For example, as shown in FIG. 11, two laser diodes 11 are provided for each image light.
a, 11a ', 11b, 11b', 11c, 11c ',
11d, 11d 'and two lenses 12a, 1
2a ', 12b, 12b', 12c, 12c ', 12
The present invention can be similarly implemented in a multi-beam laser writing unit provided with d and 12d '.

In this case, the image light, for example, the image light La, La ′, which irradiates the same photosensitive drum, enters the range of the beam waist on the same surface of the polygon mirror 13 and is reflected by the polygon mirror 13. After that,
First CY lens 14, f-θ lens 15, deflection mirror 1
The light is combined into one light via the 6a and the second CY lens 17a and irradiated onto the photosensitive drum 51a. Similarly, for the other image light, the two image lights emitted from the two laser diodes are combined into one and irradiated to the photosensitive drum.

Further, in the multi-beam laser writing unit, as shown in FIG. 12A, two image light beams radiated to the same photosensitive drum are used to irradiate an image beam irradiated to another photosensitive drum. Provided that the light is separated from the light, the light may be incident on the first CY lens 14 in a state where they are overlapped with each other in the sub-scanning direction. For example, FIG.
As shown in (B), in the vicinity of the F-θ lens 15, the optical path of the image light Lb and the image light Lb 'is separated from the optical paths of the adjacent image light La' and image light Lc in the sub-scanning direction. Thus, they can be configured at positions overlapping each other.

In the color image forming apparatus 40 according to this embodiment, the cylindrical photosensitive drums 51a to 51d
However, a photoreceptor belt constituted by an endless belt can also be used. In this case, the laser writing unit 10 transfers the developer image formed on each photoconductor belt onto the paper P without causing a displacement by performing the configuration and control satisfying the fourth formula. be able to.

Further, in the laser writing unit 10 of the color image forming apparatus 40 according to the present embodiment, the first CY lens 14 for converting four image lights into parallel lights,
The f-θ lens 15 for performing f-θ correction is separately provided.
It is also possible to provide a single conversion correction unit having a function of performing correction.

Further, as the aperture angle (angle α in FIG. 2) of the second CY lenses 17a to 17d increases, the image resolution improves. Therefore, the second C
It is desirable to increase the aperture angles of the Y lenses 17a to 17 as much as possible.

[0100]

According to the present invention, the following effects can be obtained.

(1) A plurality of image light beams are reflected from the light source at positions close to each other on the reflecting surface of a single polygon mirror, and each image light is transmitted from the light source to the surface of the photoreceptor via the reflecting surface of the polygon mirror. By making the reflection position of the polygon mirror and the irradiation position of the photoreceptor have an optically conjugate relationship in the optical path of light, it is possible to reduce the deviation of the irradiation position on the photoreceptor (resist failure) between a plurality of image lights. ,
A clear color image can be formed.

Further, the irradiation position on the photosensitive member can be displaced in a substantially similar manner for a plurality of image lights in accordance with the displacement of the reflection position on a single polygon mirror, and adjustment of only the reflection position on a single polygon mirror can be performed. Thereby, the irradiation positions of the plurality of image lights on the photoconductor can be adjusted at the same time. Therefore, when correcting a registration defect, it is only necessary to adjust the inclination angle of the rotation axis of a single polygon mirror (correction of the tilt of the polygon mirror). Since there is no need to consider the combination of the adjustment states, the assembling work of the optical components can be simplified.

Further, the distortion state of the reflection position can be made substantially the same for a plurality of image lights. Therefore, it is possible to prevent a large resist failure from occurring between a plurality of image lights due to a change in the reflection state.

In addition, only one polygon mirror for deflecting image light in the main scanning direction needs to be provided for a plurality of image lights. Therefore, it is possible to reduce the number of parts, to reduce the size of the device, and to reduce the cost.

(2) The errors in the sub-scanning direction of the reflection positions of the plurality of image lights on the polygon mirror can be made within the range of the beam waist of each image light. Therefore, the registration failure among a plurality of image lights falls within a range of 1 dot or less, and a clear image can be formed without causing a significant shift in the image.

(3) By arranging a plurality of light sources for irradiating each image light to the polygon mirror at substantially the same position in the main scanning direction, the scanning ranges of the plurality of image lights in the main scanning direction substantially coincide with each other. Thus, the length of the reflection surface of the polygon mirror in the main scanning direction can be maximized by the plurality of image lights constituting the image.

Further, by arranging a plurality of light sources at mutually different positions in the sub-scanning direction, light emitted from each light source can be emitted from the reflection surface of the polygon mirror toward different positions in the sub-scanning direction. I have to. Therefore, a plurality of image lights constituting an image can be easily separated after being reflected by the polygon mirror.

(4) After converting a plurality of image lights reflected by the polygon mirror into light parallel to each other by the conversion means, the correction means deflects the light at a constant speed in the main scanning direction, thereby being reflected by the polygon mirror. A plurality of subsequent image lights can be irradiated to the photoconductor in a state of being surely separated. In addition, since the incident angles of the plurality of image lights with respect to the correction means are the same, the registration failure occurring between the plurality of image lights becomes the same, and the adjustment work of the optical component can be simplified.

Further, by providing one conversion means and one correction means for each of the plurality of image lights, the conversion state of the conversion means and the correction state of the correction means for the plurality of image lights constituting the color image can be kept constant. And the configuration can be simplified.

(5) A plurality of image lights deflected at the same speed in the main scanning direction by the correction means are irradiated to the same position on the surface of the photoreceptor by the light setting means. After deflecting the plurality of image lights into uniform light at a constant speed in the main scanning direction, the plurality of image lights can be irradiated to the same position on the surface of the photoconductor while being separated from each other. Therefore, the electrostatic latent image formed by each image light can be visualized by the developer corresponding to each image light, and an image can be formed by overlapping a plurality of developers.

(6) Two adjacent pixels in the sub-scanning direction
For one image light a and one image light b, (a value of 1/2 of the width Ba of the image light a in the sub-scanning direction) from (interval L in the sub-scanning direction), (the width Bb of the image light b in the sub-scanning direction) A value obtained by subtracting (値 value), (error W in the sub-scanning direction of the focal position of the polygon mirror in the sub-scanning direction), and (maximum error D in the sub-scanning direction due to surface tilt of the polygon mirror) is set to a positive value. Accordingly, even when an error occurs in the reflection position of the image light a and the image light b on the polygon mirror or the inclination of the rotation axis of the polygon mirror, the optical paths of the image light a and the image light b can be reliably set in the sub-scanning direction. Can be separated.

(7) Regarding two photosensitive members a and b adjacent to each other, (the distance G between the transfer positions of the photosensitive members a and b) and (the distance between the exposure position and the transfer position of the photosensitive member a) T
A value obtained by subtracting (the distance Tb between the exposure position and the transfer position of the photosensitive member b) from the sum of (a) is an integral multiple of a value obtained by dividing (process speed v) by (number of rotations q of the polygon mirror). This makes it possible to accurately irradiate a plurality of image lights reflected on the same surface of the polygon mirror to positions corresponding to the same dot of an image formed on each individual photoreceptor, thereby reliably preventing the occurrence of registration failure. Thus, it is possible to form a high-quality image without displacement.

(8) Regarding two photosensitive members a and b adjacent to each other, (the distance G between the transfer positions of the photosensitive members a and b), (the radius R, the exposure position, and the transfer position of the photosensitive member a) And the angle Sb between the exposure position and the transfer position.
The product obtained by subtracting (product speed) is an integral multiple of a value obtained by dividing (process speed v) by (number of rotations q of the polygon mirror), thereby forming a plurality of developer images each having a color corresponding to each image light. When a cylindrical photoconductor is used as the photoconductor of
It is possible to accurately irradiate a plurality of image lights reflected on the same surface of the polygon mirror to the positions corresponding to the same dot of the image on each individual photoreceptor, thereby reliably preventing the occurrence of resist failure, and ensuring no misalignment. High quality images can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a side view illustrating a configuration of a laser writing unit provided in the image forming apparatus.

FIG. 3 is a plan view illustrating a configuration of a laser writing unit provided in the image forming apparatus.

FIG. 4 is a diagram showing a relationship between a polygon mirror and a photoconductor of the laser writing unit.

FIG. 5 is a diagram illustrating an incident position of image light on a polygon mirror of the laser writing unit.

FIG. 6 is a diagram illustrating a relationship between an error in an incident position of image light on a photosensitive drum and an error in a reflection surface of a polygon mirror.

FIG. 7 is a diagram illustrating a beam waist of image light.

FIG. 8 is a diagram showing a state of image light near a first CY lens and an f-θ lens in the laser writing unit.

FIG. 9 is a diagram illustrating a method of irradiating a surface of a photoreceptor belt with a plurality of image lights using a single reflection surface of a polygon mirror.

FIG. 10 is a diagram illustrating a method of irradiating a surface of a photosensitive drum with a plurality of image lights using a single reflecting surface of a polygon mirror.

FIG. 11 is a diagram showing an optical path of a laser beam in a multi-beam laser writing unit.

FIG. 12 is a diagram showing an optical path of a laser beam in a multi-beam laser writing unit.

FIG. 13 is a diagram illustrating the configuration and operation of a conventional four-rotation type color image forming apparatus.

FIG. 14 is a diagram illustrating the configuration and operation of a conventional tandem type color image forming apparatus.

FIG. 15 is a perspective view illustrating a configuration of a laser writing unit in a conventional color image forming apparatus.

[Explanation of symbols]

 10-laser writing unit 11a-11d-laser diode (light source) 12a-12d-lens 13-polygon mirror 14-first CY lens (conversion means) 15-f-θ lens (correction means) 16a-16d-deflection mirror ( Light path setting means) 17a-17d-second CY lens (light path setting means) 40-color image forming apparatus 51a-51d-photosensitive drum

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA11 AA14 AA48 BA54 BA58 BA83 BA85 BA90 BB03 CA22 CA39 DA03 DA09 2H030 AA01 AA05 AB02 BB02 BB16 BB56 2H045 AA01 BA02 BA22 BA34 CA03 CA63

Claims (8)

[Claims] 1. A plurality of image lights are focused on a polygon mirror in a sub-scanning direction, polarized at a constant angular velocity in a main scanning direction by a polygon mirror, and then deflected at a constant velocity in a main scanning direction via a correction means. An image forming apparatus for forming an image on a surface of a photoreceptor, wherein a plurality of image lights are focused at a position close to the same reflecting surface of a single polygon mirror. 2. The image forming apparatus according to claim 1, wherein beam waists of the plurality of image lights overlap at least partially or entirely in the sub-scanning direction. A plurality of light sources for irradiating the plurality of image lights, wherein the plurality of light sources are arranged at substantially the same position in the main scanning direction and at mutually different positions in the sub-scanning direction. The image forming apparatus according to claim 1. 4. A single conversion means for converting a plurality of image lights reflected by the polygon mirror into light parallel to each other in a sub-scanning direction, and a plurality of image lights passing through the conversion means at a constant speed in a main scanning direction. The image forming apparatus according to claim 1, further comprising a single correction unit that deflects the image. 5. An image forming apparatus according to claim 4, wherein an optical path setting means for irradiating a plurality of image lights to the same position on the surface of the photoconductor is provided between the correction means and the photoconductor. apparatus. 6. In the plurality of image lights, the width of the image light a in the sub-scanning direction is Ba, and the width of the image light a in the sub-scanning direction is two for two image lights a and b adjacent to each other in the sub-scanning direction. Is Bb, the distance between the image light a and the image light b in the sub-scanning direction is L, the error of the focal position of the polygon mirror in the sub-scanning direction is W, and the maximum error of the polygon mirror in the sub-scanning direction due to surface tilt is D. Wherein the plurality of light sources and the conversion means are arranged so as to satisfy the following relationship: L- (Ba / 2)-(Bb / 2) -WD> 0. The image forming apparatus as described in the above. 7. An image forming apparatus according to claim 1, wherein each of the plurality of image light beams includes a separate photosensitive member, and the two adjacent photosensitive members a and b have a distance G between transfer positions between the photosensitive members a and b.
(M), the distance between the exposure position and the transfer position of the photoconductor a is Ta
(M), the distance between the exposure position of the photoconductor b and the transfer position is Tb
(M), the process speed is v (m / s), the number of revolutions of the polygon mirror is q (rpm), and an arbitrary integer is k, where G + Ta−Tb = k · 60 · v / q. The image forming apparatus according to claim 1. 8. A photoconductor having a columnar shape for each of the plurality of image lights is individually provided. For two photoconductors a and b adjacent to each other, the radii of the photoconductors a and b are set to R.
(M), the distance between the transfer positions of the photoconductor a and the photoconductor b is G
(M), the angle between the exposure position of the photoconductor a and the transfer position is Sa (rad), the angle between the exposure position of the photoconductor b and the transfer position is Sb (rad), and the process speed is v (m). /
s), the rotation number of the polygon mirror is q (rpm), and an arbitrary integer is k, and the following relationship is established: G + R.Sa-R.Sb = k.60.v / q. Image forming apparatus.