JP2001166552A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of forming a black image high in use frequency and a high-definition image at high speed with the same dot clock frequency of image data as that at the time of forming a color image and at the same scanning speed as that at the time of forming the color image without accelerating the scanning speed of an image writing means. SOLUTION: This color image forming device is provided with at least a black processing unit in plural processing units, and plural image writing means in the black processing unit. At the time of selecting a black image forming mode, the image forming speed of the black processing unit is set higher than that at the time of selecting a color image forming mode, and the speed of writing the image on the black processing unit by plural image writing means is set to be the same as that at the time of selecting the color image forming mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus in which a charging means, an image writing means, a developing means and the like are arranged around an image carrier in a copying machine, a printer, a facsimile or the like. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image, an image carrier having the same number of colors as an image required, and a charging means, an image writing means, and a developing means are provided around the image carrier. Provided, a single color toner image formed on each image forming body,
A device that forms a color image by superimposing a recording material or an intermediate transfer member (an intermediate transfer belt or an intermediate transfer drum) conveyed on a belt member (conveyor belt), or a device in which one image carrier is rotated a plurality of times for each color A device for forming a color image superimposed on an image carrier by repeating charging, image exposure and development of a toner image formed by charging, image exposure and development on one image carrier There is known an apparatus that transfers an image onto an (intermediate transfer belt or an intermediate transfer drum), repeats this for each color, and forms a color image superimposed on the intermediate transfer member.

[0003] In particular, an image carrier having the same number of images as the required colors and image forming process means such as charging means, image writing means and developing means are provided around the image carrier, and each image forming body is provided with each image forming body. A color image forming apparatus that forms a color image by superimposing the formed single-color toner image on a recording material or an intermediate transfer body (an intermediate transfer belt or an intermediate transfer drum) conveyed on a belt member (conveyor belt) is preferable. In recent years, it has been used as a device for forming a simple color image. In particular, a rotating polygon mirror (polygon mirror) is generally used as an image writing unit of the color image forming apparatus, and is disclosed in Japanese Patent Application Laid-Open No. H11-65212. Japanese Patent Application Laid-Open No. 10-78708 discloses a method in which the above-described color image forming apparatus is used to increase the image forming speed and form a high-definition image only at the time of forming a frequently used black image. .

[0004]

However, in the color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. H11-65212, the condition for forming a black image that is frequently used is determined by the condition for forming a color image. Since the scanning speed of the image writing unit at the time of forming a color image is determined by the scanning speed at the time of forming a black image which requires a high speed, it is necessary to always scan the image writing unit at a high speed. . For this reason, similarly to the black image formation, during the color image formation, the rotation speed of the rotating polygon mirror (polygon mirror) mainly used for the image writing means is constantly rotated at a high speed, or the dot of the image data is always fast. Since scanning is performed at the clock frequency, noise from the image writing unit increases, the cost of the image writing unit increases, and the life of the rotary polygon mirror used in the image writing unit decreases. Was occurring. This problem also occurs in the case of forming a high-definition image that requires the scanning speed of the image writing unit to be higher than usual. JP-A-10-78708
In the case of forming a high-definition image disclosed in Japanese Patent Application Laid-Open Publication No. H10-157, there is a problem that the resolution is reduced. As a method for improving these problems, for example, image writing scanning is performed by thinning out image writing scanning when forming a color image and performing image writing scanning when scanning a black image or forming a high-definition image. However, the image quality of a color image is deteriorated due to a decrease in resolution.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and does not increase the scanning speed of the image writing means, but at the same scanning speed as that for forming a color image and the same dot of image data as that for forming a color image. It is an object of the present invention to provide a color image forming apparatus that performs high-speed black image formation and high-definition image formation at a clock frequency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image bearing member, a charging means for charging the image bearing member, and an image forming apparatus for forming a latent image by scanning the image bearing member charged by the charging means. And a developing means for developing the latent image formed by the image writing means, a color image forming apparatus having a plurality of process units, wherein at least a black processing unit is provided among the plurality of process units. In addition, a plurality of image writing means are provided in the black process unit, and when the black image forming mode is selected, the image forming speed of the black process unit is set faster than the image forming speed when the color image forming mode is selected. Writing the image to the black process unit by the plurality of image writing units at the same speed as when the color image forming mode is selected. It is accomplished by a color image forming apparatus characterized by a constant (the first invention).

[0007] Further, the object is to provide an image carrier, charging means for charging the image carrier, image writing means for forming a latent image by scanning the image carrier charged by the charging means, In a color image forming apparatus having a plurality of process units including a developing unit that develops a latent image formed by the image writing unit, the plurality of process units include:
At least a black process unit is provided, and a plurality of image writing means are provided in the black process unit, and when the black image forming mode is selected and when the high-definition image forming mode is selected, the image forming speed of the black process unit is selected. Is set to the same speed as the image forming speed when the color image forming mode is selected, and the image writing to the black process unit by the plurality of image writing units is performed at the same speed as when the color image forming mode is selected. A color image forming apparatus set to the same speed (second invention)
Achieved by

[0008] Further, the object is to provide an image carrier, charging means for charging the image carrier, image writing means for forming a latent image by scanning the image carrier charged by the charging means, In a color image forming apparatus having a plurality of process units each including a developing unit for developing a latent image formed by the image writing unit, one of the plurality of process units may be used.
An image forming process unit such as a charging unit, an image writing unit, and a developing unit for forming a black image, and a charging unit, an image writing unit, and a developing unit for forming an image of any other one color in one process unit This is achieved by a color image forming apparatus (third invention) that performs image formation by providing image forming process means such as.

[0009]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Further, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

Embodiment 1 A color image forming apparatus according to claims 1 to 4 will be described with reference to FIGS. FIG. 1 is a schematic sectional configuration diagram of an embodiment of a first example of a color image forming apparatus according to claims 1 to 4 of the present invention, and FIG.
FIG. 3 is a diagram illustrating an example of an image writing unit common to the present embodiment and the second embodiment. FIG.
FIG. 9 is a control block diagram of image forming mode selection common to the first embodiment.

According to FIGS. 1 to 3, in the image formation described below, as shown in FIG. 3, a color image is selected by an image reading device (not shown) or automatically determined when reading a document image. A formation mode and a black image formation mode are selected. In the black image forming mode, a high-definition image forming mode can be further selected, and a high-definition image forming mode is also selected.

Image data (in the case of a color image, image data for each color) read by a separate (not shown) image reading apparatus is stored in a memory (RAM) in a storage unit provided in the present image forming apparatus. You. When the color image forming mode is selected, the image data is stored in the memory (R
The color image formation is performed through the control unit according to the color image formation program (not shown) stored in the OM), and the image formation is performed at a predetermined speed (color image formation speed). At this time, the rotation speed of the rotating polygon mirror (polygon mirror) for each color provided in the image writing means for each color, which will be described later, is a rotation speed (predetermined speed) of a predetermined value corresponding to the color image forming speed (predetermined speed). Rotation speed,
The rotation of the rotary polygon mirror is performed at the same rotation speed for each color), and the image carrier for each color is scanned.
The dot clock frequency of the image writing unit for each color for performing image writing is a dot clock frequency (predetermined dot clock frequency, a predetermined dot clock frequency) of a predetermined value corresponding to the color image forming speed (predetermined speed). The image writing by the image writing means is performed at the same dot clock frequency.

When the frequently used black image forming mode is selected, the image data is transmitted through the control unit according to a black image forming program (not shown) stored in a memory (ROM) in the storage unit. The image formation is performed at a high speed image formation speed higher than a predetermined speed (color image formation speed). On this occasion,
To form a black image, a plurality of (in the present embodiment, two or
Image writing means are used, and the rotation speeds of the rotating polygon mirrors (polygon mirrors) of the two image writing means are respectively set to a predetermined number of rotations (a predetermined number of rotations) corresponding to a predetermined speed (color image forming speed). And the rotation speeds of the rotating polygon mirrors of the two image writing means are the same).
The dot clock frequencies of the two image writing units are respectively predetermined dot clock frequencies corresponding to the predetermined speed (color image forming speed) (the predetermined dot clock frequency and the dot clock frequencies of the two image writing units are the same).
Then, image writing by the image writing means is performed.

When the high-definition image forming mode is selected in the black image forming mode, the high-definition image forming program (non-high-definition image forming program) in the black image forming program in which the image data is stored in the memory (ROM) in the storage section. 1), a high-definition image is formed through the control unit, and the image is formed at a predetermined image forming speed equal to the color image forming speed. At this time, a plurality of (two in the present embodiment) image writing means are used for forming a black image, and the rotation speeds of the rotating polygon mirrors of the two image writing means are respectively set to a predetermined speed (color image). The rotation of the rotary polygon mirror is performed at a predetermined number of rotations (the predetermined number of rotations and the number of rotations of the rotary polygon mirror of the two image writing units are the same) according to the formation speed). The dot clock frequency of the embedding means is a predetermined speed (color image forming speed).
The image writing is performed by the image writing unit at a predetermined dot clock frequency (the predetermined dot clock frequency and the dot clock frequencies of the two image writing units are the same) according to the following.

In FIG. 1, reference numeral 14a denotes a conveying belt as a belt member which conveys a recording sheet P as a recording material and is rotated in a counterclockwise direction in FIG. At the upper part of 14a, from the upstream side to the downstream side, according to the order of colors to be imaged,
A black (K) process unit 100K, a yellow (Y) process unit 100Y, a magenta (M) process unit 100M, and a cyan (C) process unit 100C are provided.

The transfer units 14K and 14K as transfer means for each color are opposed to the process units 100K, 100Y, 100M and 100C with the transport belt 14a interposed therebetween.
Y, 14M and 14C are arranged to form a transfer area for each color.

[0017] Black (K) process unit 100K
Is rotated in the clockwise direction in FIG. 1, and a photosensitive drum 10K as an image carrier that is disposed in contact with or close to the transport belt 14a in a transfer area of the transfer device 14K, and a rotation direction of the photosensitive drum 10K. Then, a cleaning device 19K as a cleaning unit, which is disposed around the photosensitive drum 10K in that order on the downstream side from the transfer area in that order.
And a scorotron charger 11K as charging means, and two exposure optical systems 121K and 122 as image writing means.
And a developing device 13K as a developing means. The exposure optical system 121K is located upstream and the exposure optical system 122K is located downstream with respect to the rotation direction of the photoconductor drum 10K. Scorotron charger 11K, exposure optical system 12
1K, 122K, developing unit 13K, etc. are image forming process means for forming a black (K) image.

Further, the yellow (Y) process unit 100Y is rotated clockwise in FIG.
A photosensitive drum 10 </ b> Y as an image carrier that is disposed in contact with or close to the transport belt 14 a in the transfer area of
A cleaning device 19Y as a cleaning unit and a scorotron charger 11 as a charging unit, which are arranged around the photoconductor drum 10Y in the rotation direction of the photoconductor drum 10Y on the downstream side of the transfer area in that order.
Y, an exposure optical system 12Y as an image writing unit, and a developing unit 13Y as a developing unit. Scorotron charger 11Y, exposure optical system 12Y, developing unit 13Y
And the like are image forming process means for forming a yellow (Y) image.

The magenta (M) process unit 100M is rotated clockwise in FIG.
A photosensitive drum 10M as an image carrier that is disposed in contact with or close to the transport belt 14a in the transfer area of
A cleaning device 19M as a cleaning unit and a scorotron charger 11 as a charging unit, which are arranged around the photoconductor drum 10M in the rotation direction of the photoconductor drum 10M on the downstream side of the transfer area in that order.
M, an exposure optical system 12M as an image writing unit, and a developing unit 13M as a developing unit. Scorotron charger 11M, exposure optical system 12M, developing unit 13M
And the like are image forming process means for forming an image of magenta (M).

The cyan (C) process unit 1
Reference numeral 00C denotes a photosensitive drum 10C as an image carrier which is rotated clockwise in FIG. 1 and is disposed in contact with or close to the transport belt 14a in the transfer area of the transfer device 14C, and rotation of the photosensitive drum 10C. A cleaning device 19C as a cleaning unit and a scorotron charger 11C as a charging unit are disposed around the photoreceptor drum 10C in this order in the direction downstream from the transfer area.
, An exposure optical system 12C as image writing means, and a developing device 13C as developing means. The scorotron charger 11C, the exposure optical system 12C, the developing device 13C, and the like are image forming process means for forming an image of cyan (C).

Photosensitive drums 10K, 10 serving as image carriers
Y, 10M, and 10C form an organic photoreceptor layer (OPC) having an overcoat layer (protective layer) on the outer periphery of a cylindrical metal substrate formed of, for example, an aluminum material, on the outer periphery of the metal substrate. In response to a driving force from a photoconductor driving motor (not shown), the photoconductor is rotated clockwise as indicated by an arrow in FIG.

Scorotron charger 11 as charging means
K, 11Y, 11M and 11C denote corona discharges of the same polarity as the toner used (toner during development) by a control grid (no sign) and a corona discharge electrode (no sign) maintained at a predetermined potential, respectively. And a uniform potential is applied to the photosensitive drums 10K, 10Y, 10M and 10C. Scorotron charger 11K,
As 11Y, 11M and 11C corona discharge electrodes,
In addition, a sawtooth electrode or a needle electrode can be used.

An exposure optical system 121K as an image writing means;
As shown in FIG. 2, 122K, 12Y, 12M, and 12C rotationally scan a laser beam emitted from a laser light source (not shown) with a rotating polygon mirror (polygon mirror) 12b, and perform fθ lens 12c, reflection mirror 12d, Consisting of
The image is read by a separate (not shown) image reading device, and FIG.
The photosensitive drums 10K, 10Y, 10M, and 10C are subjected to image exposure (image writing) in accordance with the image data of each color stored in the storage unit, and the photosensitive drums 10K,
Form electrostatic latent images on 10Y, 10M and 10C. As will be described in detail later, at the time of color image formation, one of the exposure optical system 121K and the exposure optical system 122K is operated, and the other is not operated. When forming a black image,
Alternatively, when forming a high-definition image in black, the exposure optical system 121 is used.
A latent image is formed by image writing using both the K and the exposure optical system 122K.

Developing devices 13K, 13Y, 1
3M and 13C are photosensitive drums 10K, 10Y, 10Y
The photoconductor drums 10K, 10Y, 10M, and 10C rotate in a forward direction with respect to the circumferential direction of the photoconductor drums 10K, 10Y, 10M, and 10C while maintaining a predetermined gap with respect to the peripheral surfaces of M and 10C.
It has a 25 mm cylindrical non-magnetic developing sleeve made of non-magnetic stainless steel or aluminum material (no symbol), and has black (K), yellow (Y),
It contains a one-component or two-component developer of magenta (M) and cyan (C). By applying a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve (no symbol), contact reversal development is performed, and toner images are formed on the photosensitive drums 10K, 10Y, 10M, and 10C.

The cleaning devices 19K, 19Y, 19M, and 19C, which are cleaning means, use a cleaning blade or a cleaning roller made of a rubber material such as urethane, for example, to transfer the photosensitive drums 10K, 1K after transfer.
The transfer residual toner on 0Y, 10M and 10C is cleaned.

Next, an image forming process (image forming step) when the color image forming mode is selected will be described. At this time, image formation at the time of color image formation described below is performed at an image formation speed of a predetermined speed (color image formation speed) as described above with reference to FIG. The number of rotations of the rotary polygon mirror for each color provided in the image writing means for each color is a predetermined number of rotations (a predetermined number of rotations, a rotation polygon mirror for each color) corresponding to a color image forming speed (a predetermined speed). The rotation of the rotary polygon mirror is performed, and the dot clock frequency of the image writing means for each color, which scans the image carrier for each color and writes an image, is Image writing by the image writing unit is performed at a dot clock frequency of a predetermined value corresponding to the image forming speed (predetermined speed) (the predetermined dot clock frequency and the dot clock frequency of the image writing unit for each color are the same). . Specifically, the transport belt 14
a, the rotational speeds of the photosensitive drums 10K, 10Y, 10M and 10C, and the developing speeds (developing devices 13K, 13K).
Y, rotation speeds of the developing sleeves (not numbered) of 13M and 13C), exposure optical system 121K (or exposure optical system 122K), exposure optical systems 12Y, 12M and 12K.
C, the rotation speed of the rotating polygon mirror, and the photosensitive drum 10K,
The exposure optical system 121K (or exposure optical system 122K), the dot clock frequency of the exposure optical system 12Y, 12M and 12C, the fixing speed of the fixing device 17 and the like are scanned at predetermined speeds. (settings of)
Perform at Also, scorotron chargers 11K, 11Y,
11M and 11C photoreceptor drums 10K, 10Y,
Charging at 10M and 10C is also performed at a predetermined charging potential (setting).

The start of the image recording starts the rotation of the photoconductor drive motor (not shown), whereby the photoconductor drum 10K of the black (K) process unit 100K is rotated clockwise as indicated by the arrow in FIG. 11K
, The application of a potential to the K photoconductor drum 10K is started.

On the other hand, in synchronization with the formation of the toner image on the photosensitive drum 10K (in synchronization with the image area on the photosensitive drum 10K), a paper feed cassette (not shown) serving as a transfer material storage means. From the transfer belt 14 via a timing roller (not shown) as a transfer material feeding unit.
a.

After a potential is applied to the K photosensitive drum 10K, the K exposure optical system 121K (or the exposure optical system 1K).
22K), the image writing by the first color signal, that is, the electric signal corresponding to the K image data is started, and an electrostatic latent image corresponding to the K image of the original image is formed on the surface of the K photosensitive drum 10K. Is done.

The latent image is reversely developed in a contact state by a K developing unit 13K, and a black (K) toner image is formed in accordance with the rotation of the K photosensitive drum 10K.

The K toner image formed on the K photoreceptor drum 10K as an image forming body by the above-described image forming process is transferred to a K transfer unit 14K as a transfer unit in a K transfer area (no symbol). The timing roller 16
Is transferred onto the recording paper P conveyed on the conveyor belt 14a.

The transfer residual toner remaining on the peripheral surface of the K photosensitive drum 10K after the transfer is removed by the K cleaning device 19K.
Cleaning.

Next, synchronization is established with the recording paper P on which the K toner image has been formed on the transport belt 14a, and yellow (Y)
A potential is applied by the charging action of the Y scorotron charger 11Y by the process unit 100Y, and an image writing is performed by the Y exposure optical system 12Y by an electric signal corresponding to the second color signal, that is, the Y image data. By the reversal development of the contact by the Y developing device 13Y, the Y toner image is transferred onto the Y photoreceptor drum 10Y in the Y transfer area (no sign) by the Y transfer device 14Y as the transfer means. A Y toner image is formed so as to be superimposed on the toner image.

The transfer residual toner remaining on the peripheral surface of the Y photoreceptor drum 10Y after the transfer is transferred to the Y cleaning device 19Y.
Cleaning.

By the same process, the recording paper P on which the K and Y superposed toner images are formed is synchronized, and is formed on the M photosensitive drum 10M by the magenta (M) process unit 100M. M by third color signal
The M toner image corresponding to the M image data is transferred to the M transfer device 14 serving as a transfer unit in the M transfer area (no symbol).
By M, the toner image of M is superposed on the toner image of K and Y, and the toner image is synchronized with the recording paper P on which the superposed toner image of K, Y and M is formed. The fourth color signal C formed on the photosensitive drum 10C of C by the process unit 100C of (C).
The C toner image corresponding to the C image data is transferred to the C transfer unit 14 as a transfer unit in the C transfer area (no symbol).
By C, the toner image of C is superimposed on the toner image of K, Y, and M, and the toner image of K,
A superposed color toner image of Y, M and C is formed.

M and C photosensitive drums 10M, 1 after transfer
The transfer residual toner remaining on the peripheral surface of 0C is cleaned by M and C cleaning devices 19M and 19C.

The recording paper P on which the color toner image has been transferred is
The paper is discharged by a paper separation AC static eliminator 14h, which is a separating unit, separated from the transport belt 14a, and transported to the fixing device 17.

Heat and pressure are applied between the fixing roller 17a and the pressure roller 17b of the fixing device 17 which is a fixing means composed of two rollers, a fixing roller 17a having a heater therein and a pressure roller 17b. After the superimposed color toner image on the recording paper P is fixed by the addition,
The sheet is discharged to a tray (not shown) outside the apparatus.

When the frequently used black image forming mode is selected, black image formation is performed using only the K process unit 100K, and a plurality of image writing means, for example, the exposure optical system 121K and Exposure optical system 12
Using both (two) 2K, image writing is performed by parallel exposure in two rows in the sub-scanning direction. As described above with reference to FIG. 3, image formation is performed at a higher speed than a predetermined speed (color image formation speed). The rotation speed of the rotating polygon mirror of the black image writing means is a predetermined number of rotations (a predetermined number of rotations, two image rotations) corresponding to a predetermined speed (color image formation speed). The rotation of the rotary polygon mirror of the writing means is the same), and the rotation of the rotary polygon mirror is performed, and the dot clock frequencies of the two image writing means correspond to predetermined speeds (color image forming speeds). A predetermined value of the dot clock frequency (the predetermined dot clock frequency and the dot clock frequencies of the two image writing means are the same) and 2
Image writing is performed by two rows of simultaneous exposure in the sub-scanning direction by two image writing means. Specifically, only the black (K) process unit 100K is used, and the black (K) image is formed without using the other process units 100Y, 100M, and 100C. The rotating speed of the body drum 10K, the developing speed (the rotating speed of the developing sleeve (no symbol) of the developing device 13K), the fixing speed of the fixing device 17, and the like are higher than a predetermined speed (color image forming speed) (in this case, high speed). The charging of the photoconductor drum 10K by the scorotron charger 11K is also performed at a potential higher than the predetermined charging potential (setting). Exposure optical systems 121K and 122K for writing images by
The rotation speed of each rotary polygon mirror and the dot clock frequency are set at a predetermined speed (color image forming speed (setting)).

As described above, the frequency of use is high at the same scanning speed as that for forming a color image and at the same dot clock frequency of image data as that for forming a color image without increasing the scanning speed of the image writing means. Black image formation is performed at high speed. Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used for the image writing means, and it is used without increasing noise and increasing the cost and without reducing the life of the rotating polygonal mirror. Frequent black image formation is performed at high speed.

When the high-definition image forming mode is selected in the black image forming mode, a high-definition image is formed with a black image using only the K process unit 100K, and the image writing means is used. Using a plurality of (for example, both (two)) the exposure optical system 121K and the exposure optical system 122K, image writing is performed by two-row parallel exposure in the sub-scanning direction, and image formation is performed as described above with reference to FIG. Is performed at a predetermined image forming speed which is the same as the color image forming speed. The number of rotations of the rotating polygon mirror of the black image writing unit is a predetermined number of rotations (the predetermined number of rotations) corresponding to the predetermined speed (color image forming speed), and the number of rotations of the rotating polygon mirror of the two image writing units. Are the same), the rotation of the rotary polygon mirror is performed, and the dot clock frequencies of the two image writing units are respectively a dot clock frequency (predetermined dot) of a predetermined value corresponding to a predetermined speed (color image forming speed). The clock frequency and the dot clock frequency of the two image writing units are the same), and image writing is performed by two columns of parallel simultaneous exposure in the sub-scanning direction by the two image writing units. Specifically, only the black (K) process unit 100K is used, and the other process units 100Y, 100M, and 100C are not used, and a black (K) high-definition image is formed. Speed, photoconductor drum 10
K rotation speed, development speed (rotation speed of development sleeve (no symbol) of development unit 13K), rotation speed of each rotating polygon mirror of exposure optical systems 121K and 122K for performing image writing by two-row parallel simultaneous exposure, And the exposure optical system 121K, 1
Dot clock frequency of 22K, fixing device 1
7 is performed at a predetermined speed (color image forming speed (setting)), and the photosensitive drum 10K is also charged by the scorotron charger 11K at a predetermined charging potential (setting).

As described above, without increasing the scanning speed of the image writing means, it is possible to form a high-definition image at the same scanning speed as that for forming a color image and at the same dot clock frequency of image data as that for forming a color image. Is performed at high speed.
Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used as the image writing means, so that the noise can be increased without increasing the cost and without shortening the life of the rotating polygonal mirror. Fine image formation is performed at high speed.

In the above-described embodiment, the K, Y, M, and C toner images are sequentially transferred to the recording material conveyed on the belt member to form a superimposed color toner image, and then fixed. However, an intermediate transfer belt or an intermediate transfer drum is used as an intermediate transfer member, and K,
After the Y, M and C toner images are sequentially transferred to form a superimposed color toner image, the intermediate transfer onto a recording material fed to the intermediate transfer body is synchronized with the color toner image on the intermediate transfer body. The color toner images may be collectively transferred and fixed together on the body. It is also possible to form a black image using an intermediate transfer member and a high-definition black image.

Embodiment 2 A color image forming apparatus according to the fifth to ninth aspects will be described with reference to FIG. 4 and FIGS.
FIG. 4 is a schematic sectional configuration diagram of an embodiment of a second example of the color image forming apparatus according to claims 5 to 9 of the present invention. Members having the same structure and function as the members used in the first embodiment are given the same numbers.

FIG. 4 and FIG.
According to FIG. 3, in the image formation described below, FIG.
As shown in (1), a color image forming mode and a black image forming mode are selected by selection by an image reading device (not shown) or automatic determination at the time of reading a document image. In the black image forming mode, a high-definition image forming mode can be further selected, and a high-definition image forming mode is also selected.

Image data (in the case of a color image, image data for each color) read by a separate (not shown) image reading device is stored in a memory (RAM) in a storage unit provided in the present image forming apparatus. You. When the color image forming mode is selected, the image data is stored in the memory (R
The color image formation is performed through the control unit according to the color image formation program (not shown) stored in the OM), and the image formation is performed at a predetermined speed (color image formation speed). At this time, the rotation speed of the rotating polygon mirror (polygon mirror) for each color provided in the image writing means for each color, which will be described later, is a rotation speed (predetermined speed) of a predetermined value corresponding to the color image forming speed (predetermined speed). Rotation speed,
The rotation of the rotary polygon mirror is performed at the same rotation speed for each color), and the image carrier for each color is scanned.
The dot clock frequency of the image writing unit for each color for performing image writing is a dot clock frequency (predetermined dot clock frequency, a predetermined dot clock frequency) of a predetermined value corresponding to the color image forming speed (predetermined speed). The image writing by the image writing means is performed at the same dot clock frequency.

When the frequently used black image forming mode is selected, the image data is transmitted through the control unit according to a black image forming program (not shown) stored in a memory (ROM) in the storage unit. The image formation is performed at a high speed image formation speed higher than a predetermined speed (color image formation speed). On this occasion,
To form a black image, a plurality of (in the present embodiment, two or
One of the charging means and a plurality of (two in the present embodiment) image writing means are used, and the rotational speeds of the rotating polygon mirrors (polygon mirrors) of the two image writing means are respectively set to a predetermined speed ( The rotation of the rotary polygon mirror is performed at a predetermined number of rotations (the predetermined number of rotations and the number of rotations of the rotary polygon mirror of the two image writing units are the same) according to the color image forming speed. The dot clock frequency of the image writing means is a dot clock frequency (a predetermined dot clock frequency, a predetermined dot clock frequency, a predetermined value) corresponding to a predetermined speed (color image forming speed).
The image writing by the image writing means is performed at the same dot clock frequency of the two image writing means).

When the high-definition image forming mode is selected in the black image forming mode, the high-definition image forming program (non-high-definition image forming program) in the black image forming program in which the image data is stored in the memory (ROM) in the storage section. 1), a high-definition image is formed through the control unit, and the image is formed at a predetermined image forming speed equal to the color image forming speed. At this time, a plurality of (two in this embodiment) charging means and a plurality of (two in this embodiment) image writing means are used to form a black image. The number of rotations of the rotating polygon mirror of the mounting means is a predetermined speed (color image forming speed).
The rotation of the rotating polygon mirror is performed at a predetermined number of rotations (the predetermined number of rotations and the rotation number of the rotating polygon mirror of the two image writing units are the same) according to the following. The dot clock frequency is a predetermined value of the dot clock frequency (the predetermined dot clock frequency and the dot clock frequencies of the two image writing units are the same) according to the predetermined speed (color image forming speed). Image writing is performed.

In FIG. 4, reference numeral 14a denotes a conveying belt as a belt member which conveys a recording sheet P as a recording material and is rotated in a counterclockwise direction in FIG. At the upper part of 14a, from the upstream side to the downstream side, according to the order of colors to be imaged,
Yellow (Y) and black (K) process units 10
A process unit 100M for 0YK and magenta (M) and a process unit 100C for cyan (C) are provided. The process unit 100YK, which is one of the plurality of process units, includes a black (K) image forming process unit for forming a black image, and another arbitrary color (in the present embodiment, yellow ( Y)) and an image forming process means for forming an image, and a black (K) and / or yellow (Y) image is formed by the process unit 100YK.

The transfer units 14YK, 14M and 1M as transfer means for each color are opposed to the process units 100YK, 100M and 100C with the transport belt 14a therebetween.
4C are arranged to form a transfer area for each color.

The yellow (Y) and black (K) process units 100YK are rotated clockwise in FIG. 4, and the image carrier is disposed in contact with or close to the transport belt 14a in the transfer area of the transfer unit 14YK. In the rotation direction of the photosensitive drum 10YK,
The photosensitive drum 10 </ b> Y is arranged downstream in that order from the transfer area.
A cleaning device 19YK as a cleaning unit, a scorotron charger 11Y as a charging unit for forming a yellow (Y) image, and an exposure optical system as an image writing unit, which are arranged around K, respectively. 12Y, a developing device 13Y as a developing device, a scorotron charger 11K as a charging device for forming a black (K) image, an exposure optical system 12K as an image writing device, and a developing device as a developing device. Developing unit 13K
It is composed of A yellow (Y) image forming process unit such as a scorotron charger 11Y, an exposure optical system 12Y, and a developing unit 13Y for forming a yellow (Y) image is provided on the upstream side with respect to the rotation direction of the photosensitive drum 10K.
A black (K) image forming process unit such as a scorotron charger 11K, an exposure optical system 12K, and a developing unit 13K for forming a black (K) image is arranged on the downstream side.

The magenta (M) process unit 100M is rotated clockwise in FIG.
A photosensitive drum 10M as an image carrier that is disposed in contact with or close to the transport belt 14a in the transfer area of
A cleaning device 19M as a cleaning unit and a scorotron charger 11 as a charging unit, which are arranged around the photoconductor drum 10M in the rotation direction of the photoconductor drum 10M on the downstream side of the transfer area in that order.
M, an exposure optical system 12M as an image writing unit, and a developing unit 13M as a developing unit. Scorotron charger 11M, exposure optical system 12M, developing unit 13M
And the like are image forming process means for forming an image of magenta (M).

The cyan (C) process unit 1
Reference numeral 00C denotes a photosensitive drum 10C serving as an image carrier which is rotated clockwise in FIG. 4 and is in contact with or close to the transport belt 14a in the transfer area of the transfer device 14C, and rotation of the photosensitive drum 10C. A cleaning device 19C as a cleaning unit and a scorotron charger 11C as a charging unit are disposed around the photoreceptor drum 10C in this order in the direction downstream from the transfer area.
, An exposure optical system 12C as image writing means, and a developing device 13C as developing means. The scorotron charger 11C, the exposure optical system 12C, the developing device 13C, and the like are image forming process means for forming an image of cyan (C).

Photosensitive drums 10YK and 1 serving as image carriers
Reference numerals 0M and 10C denote an organic photoreceptor layer (OPC) having an overcoat layer (protective layer) formed on the outer periphery of a cylindrical metal substrate formed of, for example, an aluminum material, formed on the outer periphery of the metal substrate. In response to a driving force from a photoconductor driving motor (not shown), the photoconductor is rotated clockwise as indicated by an arrow in FIG.

Scorotron charger 11 as charging means
K, 11Y, 11M and 11C denote corona discharges of the same polarity as the toner used (toner during development) by a control grid (no sign) and a corona discharge electrode (no sign) maintained at a predetermined potential, respectively. The scorotron chargers 11K and 11Y apply uniform electric potentials to the photosensitive drum 10YK, and the scorotron chargers 11M and 11C apply uniform electric potentials to the photosensitive drums 10M and 10C. Scorotron chargers 11K, 11Y, 11
As the corona discharge electrodes of M and 11C, other saw-toothed electrodes and needle-shaped electrodes can be used. As will be described in detail later, when forming a black image or when forming a high-definition image in black, both the scorotron charger 11K and the scorotron charger 12Y are used as charging means for forming a black (K) image. And scorotron charger 1
Charging for black image formation is performed by the 1K and scorotron chargers 12Y.

Exposure optical systems 12K, 1
2Y, 12M, and 12C, as shown in FIG. 2, rotationally scan laser light emitted from a laser light source (not shown) by a rotating polygon mirror (polygon mirror) 12b, and include an fθ lens 12c, a reflection mirror 12d, and the like. In accordance with image data of each color read by a separate (not shown) image reading device and stored in the storage unit of FIG.
K and 12Y perform image exposure (image writing) on the photoconductor layer of the photoconductor drum 10YK, and the exposure optical systems 12M and 12C perform image exposure on the photoconductor layer of the photoconductor drum 10M and 10C, respectively.
An electrostatic latent image is formed on the photosensitive drums 10YK, 10M, and 10C. As will be described in detail later, at the time of forming a black image or at the time of forming a high-definition image in black, both the exposure optical system 12K and the exposure optical system 12Y perform image formation for forming a black (K) image. The latent image formation for forming a black image is performed by image writing by the exposure optical system 12K and the exposure optical system 12Y.

The developing devices 13K and 13Y, which are developing means, are provided on the peripheral surface of the photosensitive drum 10YK.
M and 13C maintain a predetermined gap with respect to the peripheral surfaces of the photosensitive drums 10M and 10C, respectively, and
K, which has a developing sleeve (not numbered) formed of a non-magnetic stainless steel or aluminum material having a thickness of, for example, 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which rotates in the forward direction of the rotation directions of K, 10M, and 10C. . Developing units 13Y, 13
K, 13M, and 13C contain one-component or two-component developers of yellow (Y), black (K), magenta (M), and cyan (C) according to the development color of each color. By applying a developing bias in which a DC voltage and an AC voltage are superimposed on a developing sleeve (unsigned), the developing device 1
In 3Y, 13M and 13C, reversal development of contact is performed,
In the developing device 13K arranged downstream of the developing device 13Y,
Performs non-contact reversal development and performs photoreceptor drums 10YK, 10M
And a toner image on 10C.

The cleaning devices 19YK, 19M and 19C, which are cleaning means, use a cleaning blade or a cleaning roller made of a rubber material such as urethane, for example, to transfer the photosensitive drums 10YK and 10M after transfer.
And the transfer residual toner on 10C is cleaned.

Next, an image forming process (image forming step) when the color image forming mode is selected will be described. At this time, image formation at the time of color image formation described below is performed at an image formation speed of a predetermined speed (color image formation speed) as described above with reference to FIG. The number of rotations of the rotary polygon mirror for each color provided in the image writing means for each color is a predetermined number of rotations (a predetermined number of rotations, a rotation polygon mirror for each color) corresponding to a color image forming speed (a predetermined speed). The rotation of the rotary polygon mirror is performed, and the dot clock frequency of the image writing means for each color, which scans the image carrier for each color and writes an image, is Image writing by the image writing unit is performed at a dot clock frequency of a predetermined value corresponding to the image forming speed (predetermined speed) (the predetermined dot clock frequency and the dot clock frequency of the image writing unit for each color are the same). . Specifically, the transport belt 14
a, the driving speed of the photosensitive drums 10YK, 10M and 10
C rotation speed, development speed (developers 13Y, 13K, 13
M and 13C (rotational speeds of developing sleeves (with no reference numeral)), exposure optical systems 12Y, 12K, 12M and 1
Rotational speed of 2C rotating polygon mirror and photosensitive drum 10Y
K, 10M, and 10C to perform image writing by exposing optical systems 12Y, 12K, 12M, and 12C (exposure optical system 1).
2Y and 12K are photosensitive drums 10YK, and exposure optical systems 12M and 12C are photosensitive drums 10M and 10C.
Is performed at a predetermined speed (set). Also, the photosensitive drums 10YK, 10M and 10C are charged by the scorotron chargers 11Y, 11K, 11M and 11C (the scorotron chargers 11Y and 11K charge the photosensitive drum 10YK, and the scorotron chargers 11M and 11C
Charge the photosensitive drums 10M and 10C) at a predetermined charging potential (setting).

Yellow (Y) and black (K) by starting a photosensitive member drive motor (not shown) at the start of image recording.
Drum 10YK of process unit 100YK
Is rotated clockwise as indicated by the arrow in FIG. 1, and at the same time, application of a potential to the photosensitive drum 10YK is started by the charging action of the Y scorotron charger 11Y. Photoconductor drum 10
After a potential is applied to YK, image writing is started by a first color signal, that is, an electrical signal corresponding to Y image data by the Y exposure optical system 12Y, and the photosensitive drum 10
An electrostatic latent image corresponding to the Y image of the original image is formed on the surface by the YK rotational scanning. This latent image is reversely developed in a contact state by a Y developing unit 13Y, and a yellow (Y) toner image is formed on the photosensitive drum 10YK.

Next, a potential is applied to the photosensitive drum 10YK on the yellow (Y) toner image by the charging action of the K scorotron charger 11K, and the second color signal of the K exposure optical system 12K, ie, Exposure is performed by an electrical signal corresponding to the black (K) image data, and a black (K) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the K developing unit 13K. It is formed by overlapping.

On the other hand, in synchronization with the formation of the superposed toner image of Y and K on the photosensitive drum 10YK (the photosensitive drum 10YK).
The recording paper P is conveyed from a paper feed cassette (not shown) as a transfer material storage means via a timing roller (not shown) as a transfer material feeding means (in synchronization with the image area on YK). It is transported to the belt 14a.

The superposed toner image of Y and K formed on the photosensitive drum 10YK, which is an image forming body, by the above-described image forming process is a transfer means in a transfer area (no symbol) of the photosensitive drum 10YK. Transfer unit 14YK
Is transferred onto the recording paper P conveyed on the conveyance belt 14a.

The transfer residual toner remaining on the peripheral surface of the photosensitive drum 10YK after the transfer is cleaned by the cleaning device 19YK.

Next, synchronization is established with the recording paper P on which the Y and K superimposed toner images on the conveyor belt 14a have been formed.
An electric potential is applied by the charging action of the M scorotron charger 11M by the magenta (M) process unit 100M, and image writing is performed by the M exposure optical system 12M using a third color signal, that is, an electrical signal corresponding to the M image data. Is performed, and the M toner image is transferred onto the M photoconductor drum 10M by the reversal development of the contact by the M developing device 13M. An M toner image is formed on top of the Y and K superposed toner images.

The untransferred toner remaining on the peripheral surface of the M photosensitive drum 10M after the transfer is transferred to the M cleaning device 19M.
Cleaning.

By the same process, the transport belt 14a
Synchronization is established with the recording paper P on which the Y, K, and M superposed toner images are formed, and a potential is applied by the charging action of the C scorotron charger 11C by the cyan (C) process unit 100C. The image writing is performed by the fourth optical signal, that is, the electric signal corresponding to the image data of C, by the exposure optical system 12C, and the C developing device 13C performs the reversal development of the contact on the C photosensitive drum 10C.
Is transferred by a C transfer unit 14C, which is a transfer unit, in the C transfer area (no sign).
A C toner image is formed by superimposing on the M superposed toner image, and a superposed color toner image of Y, K, M and C is formed on the recording paper P.

The untransferred toner remaining on the peripheral surface of the C photosensitive drum 10C after the transfer is transferred to the C cleaning device 19C.
Cleaning.

The recording paper P on which the color toner image has been transferred is
The paper is discharged by a paper separation AC static eliminator 14h, which is a separating unit, separated from the transport belt 14a, and transported to the fixing device 17.

Heat and pressure are applied between the fixing roller 17a and the pressure roller 17b of the fixing device 17 which is a fixing means composed of two rollers, the fixing roller 17a having a heater therein and the pressure roller 17b. After the superimposed color toner image on the recording paper P is fixed by the addition,
The sheet is discharged to a tray (not shown) outside the apparatus.

As described above, a color image can be formed by the three process units, and the size and cost of the apparatus can be reduced. Further, it is possible to shorten the conveying distance of the recording material on which the toner images are formed and the width of the belt member, thereby shortening the FCOT (first copy out time). Further, by making the black developing means non-contact, there is no possibility of color mixing or the like, and a color image with excellent image quality such as resolution can be formed.

When the frequently used black image forming mode is selected, the process units Y and K of one of the plurality of process units are selected.
Black image formation using only 00YK is performed, and a plurality of charging units, for example, a sulotron charger 11Y (charging unit provided in another arbitrary one-color image forming process unit) and a scorotron charger 11K (black (K )) (Charging means provided in the image forming process means)
Is used as a black charging means to perform charging, and a plurality of image writing means, for example, an exposure optical system 12Y (an image writing means provided in another arbitrary one-color image forming process means) and exposure Both the optical system 12K (image writing means provided in the black (K) image forming process means) (2
) Is used as black image writing means to perform image writing by two-row parallel simultaneous exposure at predetermined intervals in the sub-scanning direction, and using only K developing device 13K as developing means. The image is formed at a high image forming speed higher than a predetermined speed (color image forming speed) as described above with reference to FIG. Exposure optical system 1 used as means
The rotation speed of the rotating polygon mirror of the 2Y and the exposure optical system 12K) is
The rotation of the rotary polygon mirror is performed at a predetermined number of rotations (the predetermined number of rotations and the number of rotations of the rotary polygon mirrors of the two image writing units are the same) corresponding to the predetermined speed (color image formation speed), respectively. In addition, the dot clock frequencies of the two image writing units are set to a predetermined value (a predetermined dot clock frequency) corresponding to a predetermined speed (color image forming speed). The same), in the sub-scanning direction by two image writing means,
Image writing is performed by two-row simultaneous exposure at a predetermined interval. Specifically, a black (K) image is formed by using only the process unit 100YK and not using the other process units 100M and 100C.
The drive speed of 4a, the rotation speed of the photosensitive drum 10YK, the development speed (the rotation speed of the developing sleeve (no symbol) of the developing device 13K), the fixing speed of the fixing device 17, and the like are higher than a predetermined speed (color image forming speed). This is performed at a high speed (in this case, a speed twice (set) twice as high as a predetermined speed), but the photoconductor drum 10Y by the scorotron chargers 11Y and 11K is used.
The charging of K is performed at a predetermined charging potential, and the rotating polygonal surfaces of the exposure optical systems 12Y and 12K for writing an image of black (K) image data by two-row parallel exposure at predetermined intervals. The rotation speed of the mirror and the respective dot clock frequencies are performed at a predetermined speed (color image forming speed (setting)).

As described above, the frequency of use is high at the same scanning speed as that for forming a color image and at the same dot clock frequency of image data as that for forming a color image without increasing the scanning speed of the image writing means. Black image formation is performed at high speed. Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used for the image writing means, and it is used without increasing noise and increasing the cost and without reducing the life of the rotating polygonal mirror. Frequent black image formation is performed at high speed. Further, since image formation is performed using two charging units, the life of the charging unit can be extended.

When the high-definition image forming mode is selected in the black image forming mode, a black image using only the Y and K process units 100YK, which are one of the plurality of process units, is used. A high-definition image is formed, and a plurality of charging means, for example, a scorotron charger 11Y (charging means provided in another arbitrary one-color image forming process means) and a scorotron charger 11K (black (K) image) Both (two) charging means provided in the forming process means are used as black charging means to perform charging, and a plurality of image writing means are used.
For example, both the exposure optical system 12Y (an image writing unit provided in another arbitrary one-color image forming process unit) and the exposure optical system 12K (an image writing unit provided in a black (K) image forming process unit) (2) are used as black image writing means, image writing is performed by two-row parallel simultaneous exposure at predetermined intervals in the sub-scanning direction, and only K developing device 13K is used as developing means. As described above with reference to FIG. 3, image formation is performed at a high image forming speed higher than a predetermined speed (color image forming speed). Exposure optical system 12Y and exposure optical system 12K used as embedding means)
The number of rotations of the rotating polygon mirror is a predetermined number of rotations (a predetermined number of rotations, two
(The number of rotations of the rotating polygon mirror of the two image writing means is the same.)
Then, the rotating polygon mirror is rotated, and the dot clock frequencies of the two image writing units are respectively set to a predetermined value (color image forming speed). The two image writing means have the same dot clock frequency), and image writing is performed by two rows of simultaneous exposures at predetermined intervals in the sub-scanning direction by the two image writing means. Specifically, only the process unit 100YK is used, the other process units 100M and 100C are not used, and black (K) high-definition image formation is performed, the driving speed of the transport belt 14a, the photosensitive drum 10YK , The developing speed (the rotating speed of the developing sleeve (no symbol) of the developing device 13K), the fixing speed of the fixing device 17 and the like are higher than a predetermined speed (color image forming speed) (in this case, a predetermined speed of the predetermined speed). However, the charging of the photosensitive drum 10YK by the scorotron chargers 11Y and 11K is performed at a predetermined charging potential, and black is obtained by two-row parallel simultaneous exposure at a predetermined interval. The rotation speeds of the rotary polygon mirrors and the dot clock frequencies of the exposure optical systems 12Y and 12K for writing the image data of (K) are as follows. Performed at a predetermined speed (color image forming speed (setting)).

As described above, without increasing the scanning speed of the image writing means, it is possible to form a high-definition image at the same scanning speed as when forming a color image and at the same dot clock frequency of image data as when forming a color image. Is performed at high speed.
Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used as the image writing means, so that the noise can be increased without increasing the cost and without shortening the life of the rotating polygonal mirror. Fine image formation is performed at high speed.
Further, since image formation is performed using two charging units, the life of the charging unit can be extended.

In the above-described embodiment, the K and Y superimposed toner images and the M and C toner images are sequentially transferred to the recording material conveyed on the belt member to form the superimposed color toner image. After the formation, the image is fixed. However, an intermediate transfer belt or an intermediate transfer drum is used as an intermediate transfer body, and the K and Y superposed toner images are formed on the intermediate transfer belt or the intermediate transfer drum as the intermediate transfer body. After the M and C toner images are sequentially transferred to form a superimposed color toner image, the intermediate transfer onto the recording material fed to the intermediate transfer body is synchronized with the color toner image on the intermediate transfer body. The color toner images may be collectively transferred and fixed together on the body. It is also possible to form a black image using an intermediate transfer member and a high-definition black image.

[0077]

According to the first or second aspect of the present invention, without increasing the scanning speed of the image writing means, the dot of the image data at the same scanning speed as when forming a color image and the same as when forming a color image is formed. At the clock frequency, a frequently used black image is formed at high speed. Therefore, the image writing means
Using a rotating polygonal mirror (polygon mirror) with the number of rotations conventionally used, high-speed black image formation that is frequently used can be performed at high speed without increasing noise and cost, and without reducing the life of the rotating polygonal mirror. Done in

According to the third or fourth aspect, without increasing the scanning speed of the image writing means, the dot clock frequency of the same image data as that of the color image formation at the same scanning speed as that of the color image formation. Thus, high-definition image formation is performed at high speed. Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used as the image writing means, so that the noise can be increased without increasing the cost and without shortening the life of the rotating polygonal mirror. Fine image formation is performed at high speed.

According to the fifth aspect, the size and cost of the device can be reduced. Further, it is possible to shorten the conveying distance of the recording material on which the toner images are formed and the width of the belt member, thereby shortening the FCOT (first copy out time).

According to the sixth, eighth, and ninth aspects of the present invention, without increasing the scanning speed of the image writing unit, the dots of the same image data at the same scanning speed as in the color image formation and at the same scanning speed as in the color image formation can be obtained. At the clock frequency, a frequently used black image is formed at high speed. Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used for the image writing means, and it is used without increasing noise and increasing the cost and without reducing the life of the rotating polygonal mirror. Frequent black image formation is performed at high speed. Further, since image formation is performed using two charging units, the life of the charging unit can be extended.

According to the seventh, eighth and ninth aspects of the present invention, without increasing the scanning speed of the image writing means, the dot of the image data at the same scanning speed as in the color image formation and the same as the color image formation can be obtained. With the clock frequency, high-definition image formation is performed at high speed. Therefore, a rotating polygonal mirror (polygon mirror) having a conventionally used number of rotations is used as the image writing means, so that the noise can be increased without increasing the cost and without shortening the life of the rotating polygonal mirror. Fine image formation is performed at high speed. Further, since image formation is performed using two charging units, the life of the charging unit can be extended.

In particular, according to the ninth aspect, a color image having excellent image quality such as resolution can be formed without fear of color mixing.

[Brief description of the drawings]

FIG. 1 is a schematic sectional configuration diagram of an embodiment of a first example of a color image forming apparatus according to claims 1 to 4 of the present invention.

FIG. 2 is a diagram illustrating an example of an image writing unit common to the present embodiment and a second embodiment.

FIG. 3 is a control block diagram for selecting an image forming mode common to the present embodiment and the second embodiment.

FIG. 4 is a schematic sectional configuration diagram of an embodiment of a second example of the color image forming apparatus according to claims 5 to 9 of the present invention.

[Explanation of symbols]

10C, 10K, 10YK, 10M, 10Y Photoconductor drum 11C, 11K, 11M, 11Y Scorotron charger 12b Rotating polygon mirror (polygon mirror) 12C, 12K, 12M, 12Y, 121K, 122K
Exposure optical system 13C, 13K, 13M, 13Y Developing device 14a Conveying belt 14C, 14K, 14YK, 14M, 14Y Transfer device 17 Fixing device 100C, 100K, 100YK, 100M, 100Y
Process unit P Recording paper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G03G 21/00 384 F term (reference) 2C362 BA51 BA56 BA66 CA39 CB08 CB14 CB59 CB62 CB63 CB80 2H027 DB01 DB02 DE07 DE09 EA02 EB04 ED04 ED06 FA16 FA28 FA30 FA35 FB05 FB07 FB19 2H030 AB02 AD02 AD05 AD08 AD17 BB02 BB12 BB23 BB41 BB63 BB71 2H076 AB02 AB12 AB16 AB68 EA05 EA06

Claims (9)

[Claims] An image carrier, a charging unit for charging the image carrier, an image writing unit for scanning the image carrier charged by the charging unit to form a latent image, and the image writing unit A color image forming apparatus having a plurality of process units including a developing unit that develops a latent image formed by the unit, wherein at least a black process unit is provided in the plurality of process units, and A plurality of image writing units are provided, and when the black image forming mode is selected, the image forming speed of the black process unit is set faster than the image forming speed when the color image forming mode is selected, and the plurality of image writing units are set. Setting the image writing to the black process unit by the same speed as when the color image forming mode is selected. Image forming apparatus. 2. The color image forming apparatus according to claim 1, wherein a rotating polygon mirror is used as said image writing means. 3. An image carrier, charging means for charging the image carrier, image writing means for scanning the image carrier charged by the charging means to form a latent image, and image writing A color image forming apparatus having a plurality of process units including a developing unit that develops a latent image formed by the unit, wherein at least a black process unit is provided in the plurality of process units, and A plurality of image writing means are provided, and when the black image forming mode is selected, and when the high definition image forming mode is selected, the image forming speed of the black process unit is the same as the image forming speed when the color image forming mode is selected. And writing the image to the black process unit by the plurality of image writing units at the speed when the color image forming mode is selected. A color image forming apparatus, wherein the color image forming apparatus is set at the same speed. 4. The color image forming apparatus according to claim 3, wherein a rotating polygon mirror is used as said image writing means. 5. An image carrier, charging means for charging the image carrier, image writing means for scanning the image carrier charged by the charging means to form a latent image, and image writing A color image forming apparatus having a plurality of process units including a developing unit that develops a latent image formed by the unit, a charging unit configured to form a black image on one of the plurality of process units, and an image. Image forming process means such as writing means and developing means, and any other optional
1. A color image forming apparatus comprising: a charging unit for forming a color image; an image forming unit such as an image writing unit and a developing unit; and an image forming unit. 6. When the black image forming mode is selected, the first
The image forming speed of one process unit is set higher than the image forming speed when the color image forming mode is selected, and the charging by the charging unit and the image writing unit provided in the other arbitrary one color image forming process unit are performed. Image formation is performed by image writing, charging by charging means provided in the black image forming process means, image writing by image writing means, and development by developing means. 6. The color image forming apparatus according to claim 5, wherein the image writing by the arbitrary one color image writing unit is set to the same speed as when the color image forming mode is selected. 7. When the black image forming mode is selected and when the high definition image forming mode is selected, the image forming speed of the one process unit is set to be the same as the image forming speed when the color image forming mode is selected. The charging by the charging unit and the image writing by the image writing unit provided in the other one-color image forming process unit, and the charging and the image writing unit by the charging unit provided in the black image forming process unit The image writing by the image writing unit and the image writing by the developing unit are performed, and the image writing by the black image writing unit and the other arbitrary one-color image writing unit is performed by the image writing unit when the color image forming mode is selected. The color image forming apparatus according to claim 5, wherein the speed is set to the same speed as the speed. 8. The color image forming apparatus according to claim 5, wherein a rotating polygon mirror is used as said image writing means. 9. An image forming process unit, such as a charging unit, an image writing unit, and a developing unit, which is used for forming an image of another arbitrary one color, is provided with a black image forming process in a rotation direction of the image carrier. And developing by the developing means provided in the other arbitrary one-color image forming process means is contact development, and developing by the developing means provided in the black image forming process means is not performed. The color image forming apparatus according to any one of claims 5 to 8, wherein the development is performed by contact development.