JP2003114563A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resolution in, particularly, black and perform high speed writing in a monochrome mode at low costs, in an image forming device having tandem system image forming parts for a plurality of colors. SOLUTION: A monochrome image formation unit module 131K has more lasers, 151K1 and 151K2, than the other color image forming parts 131Y, M, and C. Thus, high resolution can be accomplished only in black. In addition, a high speed image formation can be realized by performing a multi-laser operation only in monochrome mode.

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 having an image forming section for a plurality of colors including black, and more particularly to an image forming apparatus having a high performance black image forming section.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as printers and copying machines have become complicated in control of image formation such as high-speed printing, high-definition printing, and color printing. In order to realize an advanced image forming system, writing devices are parallelized.

FIG. 9 shows a laser printer which is a conventional electrophotographic four-drum tandem electrophotographic color image forming apparatus. The structure up to the generation of image data and the structure after the latent image formation by the laser are omitted for simplicity.

This image forming apparatus is provided with unit modules 931Y, M, C, K as four image forming sections corresponding to four colors of yellow, magenta, cyan and black, and each unit module 931Y, M, C, Each of the Ks includes a photoconductor drum 970Y, M, C, K, and a laser beam optical writing unit 960Y, M, C, K for writing an image on the photoconductor drum 970Y, M, C, K. . The optical writing units 960Y, M, C, K have lasers 951Y, M, C, K and polygon mirrors 952Y, M, C, K for scanning the laser beam. YMCK notation is yellow, magenta, and
Refers to each color of cyan and black.

This printer device will be described by taking the yellow unit module 931Y as an example, and is controlled by an instruction from the controller 910 to perform an image forming operation. During an image forming operation, a video signal is transmitted from the image processing block 941 through a plurality of video data signal lines 942Y corresponding to 256 gradation data, and the PWM-I
The C940Y generates and outputs one PWM signal 950Y, which drives the laser 951Y to cause laser emission, and the photosensitive drum 9 via the polygon mirror 952Y.
Irradiate 70Y to form an electrostatic latent image. Image formation is similarly performed for MCK colors.

The electrostatic latent images on the photosensitive drums 970Y, M, C, and K are developed by toners of respective colors by a developing device (not shown), and the developed images of the respective colors are conveyed on the transfer belt 980. The toner is mixed and fixed on the paper by passing through a fixing device (not shown) to form an image.

As described above, the four-series tandem type color image forming apparatus can form a color image at a higher speed than the color image forming apparatus using only one photosensitive drum.

[0008]

However, the above-mentioned four-series tandem type color image forming apparatus has the following drawbacks.

First, since it is necessary to accurately superimpose four color images, it is necessary to control each position with high precision as an electrophotographic process. Therefore, the image forming unit modules Y, M, C and K of each color are Even with high resolution, there was a problem that the resolution was not fully utilized at the stage of overlapping colors.

In the monochrome mode in which it is not necessary to control at least four-color superposition, the rotation speed of the photosensitive drum 970K, that is, image formation, is provided in the monochrome mode having a printing speed switching function for increasing the printing speed. By increasing the speed, a printing speed about 1.5 times that of the color mode is realized.

However, in the monochrome mode, the latent image forming speed by laser scanning is 1.5 times, and the exposure amount to the photosensitive drum 970K is also 2/3, so that the latent image forming ability is lowered. As a result, the image quality deteriorates, and in order to compensate for this, it is necessary to take measures such as increasing the sensitivity of the photosensitive member, resulting in high cost.

Further, since it is necessary to rotate the polygon mirror 952K at a higher speed in order to maintain the image resolution in the paper carrying direction, there is a problem that the durability life of the polygon mirror bearing is shortened.

In order to solve the problems caused by increasing the speed of these latent image forming portions, a latent image forming means using a plurality of laser beams has been proposed as an effective solving means. In this case,
There is a big problem in that the increase in cost due to the use of multiple beams, such as variations in the characteristics of the multiple beam laser diode, its drive circuit, optical parts, and factory adjustment.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus capable of increasing the resolution of black in particular and providing high-speed writing in a monochrome mode at low cost. Is to provide.

[0015]

To achieve the above object, in the present invention, a plurality of image forming portions corresponding to a plurality of colors including black are provided, and each image forming portion includes a photoconductor and a photoconductor. An image forming apparatus provided with an optical writing unit for writing an image on the photoconductor is characterized in that only a black image forming unit is provided with a plurality of optical writing units more than color image forming units other than black.

It is preferable to provide a means for optically writing with a higher resolution than the other color image forming portions by a plurality of optical writing means of the black image forming portion.

A monochrome mode for forming only a black image and a color mode for forming a color image are provided, and one of a plurality of optical writing means of the black image forming section is driven according to switching between the monochrome mode and the color mode. A means for switching the number of means for switching the number of means is provided, and in the monochrome mode, all the optical writing means of the black image forming portion are used, and in the color mode, a part of the number of the optical writing means of the black image forming portion is used for a color image. Forming is preferred.

An image processing unit corresponding to each color is provided, and an image processing unit other than black is shared as an image processing unit of an optical writing unit used only in the monochrome mode of the black image forming unit. It is preferable to switch the operation of the image processing unit accordingly.

The image data transmitting means of each of the plurality of image forming portions and the forced non-light emitting means of the optical writing means of the black image forming portion, which is used only in the monochrome mode, are provided, and the image data transmitting means other than black is set in the monochrome mode. It is preferable that the optical writing means of the black image forming portion, which is used only in the above-mentioned image forming means, is shared as the image data transmitting means, and that each of the optical writing means that operates at the time of mode switching is selected by using the forced non-light emitting means. .

The light emitting pattern generating means for driving the light writing means of each of the plurality of image forming portions and the forced non-light emitting means of the light writing means of the black image forming portion, which is used only in the monochrome mode, are provided. The generation means is shared as the light emission pattern generation means of the optical writing means of the black image forming section used only in the monochrome mode, and the forced non-light emitting means is used to select each optical writing means operating at the time of mode switching. Is preferred.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the illustrated embodiments.

(Embodiment 1) FIG. 1 shows an image forming apparatus according to Embodiment 1 of the present invention. As in the conventional example, the present embodiment will be described by taking an example of a four-tandem tandem type electrophotographic printer of yellow, magenta, cyan, and black.

That is, the image forming apparatus includes an image forming unit module (image forming section) 1 for forming four images corresponding to four colors of yellow, magenta, cyan and black.
31Y, M, C, K are provided. Each of the unit modules 131Y, M, C, and K includes the photosensitive drum 1
70Y, M, C, K and the photoconductor drums 170Y, M,
An optical writing unit for writing an image in C and K is provided. The YMCK notation indicates each color of yellow, magenta, cyan, and black.

In the first embodiment, in order to increase the resolution of the black portion, only the black unit module 131K uses a plurality of optical writing means more than the color unit modules 131Y, M, C other than black. . In the illustrated example, the yellow, magenta, and cyan color unit modules 131Y, M, and C have one laser 151Y, M, and C that constitute an optical writing unit, and the laser 151Y, M, and C emits light. 1 laser beam 1
An image is written by using 60Y, M, and C. The black unit module 131K has a plurality of lasers 151K1 and K2, which constitute two optical writing means in the present embodiment.
Two laser beams 16 emitted from 1,151K2
A multi-beam method for writing an image using 0K1 and 160K2 is used. K1 and K2 indicate configurations corresponding to the two black beams, respectively.

The laser beams 160Y, M, C are scanned by the polygon mirrors 152Y, M, C, and the optical parts forming the optical path are constructed for one beam. The laser beams 160K1 and 160K2 are the same polygon mirror 1
The optics scanned by 52K and forming the optical path are configured for high resolution two beams.

The details will be described below.

In FIG. 1, reference numeral 100 denotes a printer main body, and each unit module 131Y, M, C, K is arranged in parallel in this printer main body 100 in order from the upstream side in the paper transport direction.

Reference numeral 110 denotes a control controller for controlling each section of the printer. In the illustrated portion, each photosensitive drum 170Y, M, C, K and polygon mirror 152 are shown.
The Y, M, C, K and the transfer belt 180 are drive-controlled.

Reference numeral 141 denotes an image processing block of the printer, which has an image processing unit for performing image processing of each color in parallel, and 8-bit video data of each color image constitutes video data signal lines 142Y, 142M which constitute an image data transmitting means. , C, K1,
It is output to K2. PWMs 140Y, M, C, K1, and K2 generate a laser emission pattern corresponding to the video data of 256 gradation bits from the image processing block 141.
A PWM signal line 150Y, which is a light emission pattern generation unit configured by an IC and constitutes image data transmission means,
PWM signals are output from M, C, K1, and K2. Each PWM 151Y, M, C, K1, K by this PWM signal
2 is driven.

The polygon mirrors 152Y, M, C, and K are beams 160Y of lasers 151Y, M, C, K1, and K2.
The laser beams 160Y, M, C, K1 and K2 are irradiated onto the photoconductor drums 170Y, M, C and K through predetermined optical paths.

Reference numeral 180 denotes a transfer belt, which conveys paper which is an image forming medium and forms a color image by superposing the color toner images formed on the photosensitive drums of the respective unit modules.

The image forming apparatus includes a controller 11
The image forming operation is performed under the control of the instruction of 0. In the image forming operation, a Y (yellow) image will be described as an example. From the image processing blocks 141 to 256, there are a plurality of video data signal lines 14 corresponding to 256 gradation data.
2Y, a single PWM signal is generated in the light emission pattern generation unit 140Y, and the PWM signal line 150Y is generated.
Output to. As a result, the laser 151Y is driven to emit laser light, and is irradiated onto the photoconductor drum 170Y via the polygon mirror 152Y to form an electrostatic latent image. Image formation is similarly performed for MCK colors.

The images electrophotographically developed in the respective colors are transferred by being superposed on the paper conveyed on the transfer belt 180, pass through a fixing device, and toner is mixed and fixed on the paper to form a color image. .

The color image forming unit modules 131Y, M, and C have a latent image resolution of 600 dpi in both the laser scanning direction and the drum rotation direction. In the black image forming unit module 131K,
The laser scanning interval is narrower than the image forming spot for color by the two-beam laser and the two-beam laser optical system.
The scan interval is equivalent to 200 dpi. The arrangement of the two-beam laser and the optical system for the two-beam laser that realizes this scanning interval constitute means for optically writing with a higher resolution than the other unit modules 131Y, M, and C.

FIG. 2 shows the spot diameters and positions of the laser beams imaged on the photosensitive drum side by side. Here, images are formed simultaneously in parallel in the rotation direction of the photosensitive drum (direction perpendicular to the laser scan). The black polygon mirror 152K is a color polygon mirror 152.
Since it rotates at the same speed as Y, M, C, yellow
A color image is formed with a resolution of 600 dpi for magenta / cyan and a resolution of 1200 dpi for black in the drum rotation direction.

(Second Embodiment) Next, a second embodiment of the present invention will be described.

FIG. 3 shows an image forming apparatus according to the second embodiment of the present invention.

That is, this image forming apparatus is also a unit module 331Y, M, C, K as four image forming units corresponding to four colors of yellow, magenta, cyan and black.
Each unit module 331Y, M, C, K
Are photosensitive drums 370Y, M, C and K, respectively.
An optical writing unit for writing an image on the photoconductor drums 370Y, M, C, K is provided.

Also in the second embodiment, only the black unit module 331K uses a plurality of optical writing means which are more than the color unit modules 331Y, M, C other than black. In the illustrated example, for the yellow, magenta, and cyan color unit modules 331Y, M, and C, one laser 351Y, M, and C that configures the optical writing unit is used.
1 emitted from this laser 351Y, M, C
An image is written using the laser beams 360Y, M, and C of the book. Black unit module 331
Regarding K, a plurality of lasers, in the present embodiment, two lasers 351K1 and K2 that constitute two optical writing means are provided, and an image is written by using two laser beams 360K1 and 360K2 emitted from the lasers 351K1 and 351K2. The multi-beam method is used. K1 and K2 indicate configurations corresponding to the two black beams, respectively.

The laser beams 360Y, M, C are scanned by the polygon mirrors 352Y, M, C, and the optical component forming the optical path is constructed for one beam. The laser beams 360K1 and 360K2 are the same polygon mirror 3
The optical component which is scanned by 52K and constitutes the optical path is configured for two beams, but the difference from the first embodiment is that the optical component configuring the optical path for two beams is not configured for high resolution. .

The polygon mirrors 352Y, M, C, K scan the laser beams of the lasers 351Y, M, C, K1, K2, and laser beams 360Y, M, C, K.
1, K2 are photoconductor drums 370Y,
The M, C and K are irradiated.

The second embodiment has a monochrome mode in which only a black image is formed and a color mode in which a color image is formed, and the black unit module 331K of the black unit module 331K is switched according to the switching between the monochrome mode and the color mode. Of the two lasers 351K1 and 351K2, a light emission control switch 390 is provided as means for switching the driven laser 351K1 to one, and in the monochrome mode, the two lasers 351 of the black unit module 331K are provided.
K1 and 351K2 are used, and in the color mode, one laser 351K1 of the black unit module 331K is used to form a color image.

The details will be described below.

In FIG. 3, reference numeral 300 denotes a printer main body, and each unit module 331K, Y, M, C is arranged in parallel in this printer main body 300 in order from the upstream side in the paper transport direction.

Reference numeral 310 denotes a control controller for controlling each part of the printer, which controls a photoconductor drum rotation control signal 372Y for controlling the rotation speed of a motor 371Y for rotating the photoconductor drum 370Y, and the rotation speed and phase of the polygon mirror 352Y. Polygon rotation control signal 3 for
53Y, a transfer belt rotation control signal 382 for controlling the rotation speed of the transfer belt rotation motor 381 is output.

Reference numeral 341 denotes an image processing block of the printer, which is an image processing unit 341Y for performing image processing for each color in parallel.
Video data signal line 3 having M, C and K1 and 8-bit video data of each color image constituting image data transmission means
42Y, M, C, K1. 340Y, M,
C and K1 are light emission pattern generation units configured by a PWM-IC that generates a laser light emission pattern corresponding to video data of 256 gradation bits from the image processing block 341, and a PWM signal line that constitutes image data transmission means. A PWM signal is output from 350Y, M, C, and K1.
This PWM signal causes each laser 351Y, M, C, K
1, K2 drive.

A transfer belt 380 conveys a paper as an image forming medium and forms a color image by superposing the color toner images formed on the photosensitive drums of the respective unit modules.

The light emission control switch 390 is for forcibly turning off one laser 351K2 of the two-beam laser for black, and 391 is its control signal. Further, this control signal 391 is also connected to each of the yellow, magenta, and cyan color unit modules 331Y, M, and C so that all operations of charging, toner development, and toner image transfer in the electrophotographic process can be ON / OFF controlled. ing.

The processing of the light emission pattern of the one black laser 351K2, which can be forcibly turned off by turning off the light emission control switch 390, is performed adjacent to the cyan image processing unit 341C in the image processing block 341. The configuration is such that the 256 gradation bit video data signal line 342C, the light emission pattern generation unit 340C, and the PWM signal line 350C in the cyan unit module 331C are shared, and the PWM signal line 350C is branched from the middle, and one black side The PWM signal is also used for the laser 351K2.

In other words, the cyan video data signal lines 342C and PW forming the image data transmission means.
A part of the M signal line 350C is shared as image data transmission means of the laser 351K2 used only in the monochrome mode, and each light emission control switch 390 as a forced non-light emission means operates at the time of mode switching. A laser is selected.

In addition, the laser 3 in which the cyan light emission pattern generator 340C other than black is used only in the monochrome mode
It is configured to be commonly used as 51K2 light emission pattern generation means.

A description will be given below with reference to the drawings.

This printer device has a controller 31.
The image forming operation is performed under the control of 0 instruction. A video signal is transmitted from the image processing blocks 341 through a plurality of video data signal lines 342Y corresponding to 256 gradation data, and one P signal is generated in the light emission pattern generation unit 340Y.
A WM signal is generated and output to the PWM signal line 350Y, which drives the laser 351Y to emit laser light, and irradiates the photoconductor drum 370Y via the polygon mirror 352Y to form an electrostatic latent image and form an image. . Image formation is similarly performed for MCK colors.

At this time, the controller 310
Output polygon rotation control signals 353Y, M, C, K, photoconductor drum rotation control signals 372Y, M, C, K, and transfer belt rotation control signal 382, and the polygon mirror 3
52Y, M, C, K, photoconductor drums 370Y, M, C,
K, the transfer belt 380 synchronously rotates at an appropriate speed. The image electrophotographically developed in each color of yellow, magenta, cyan, and black is transferred onto the paper conveyed on the transfer belt 380 in an overlapping manner, passes through a fixing device, and toner is mixed and fixed on the paper. Image is formed.

Here, all color image forming unit modules 331Y, M, yellow, magenta, cyan and black are provided.
C and K have a resolution of 600 dpi in both the laser scan direction and the drum rotation direction. However, in the black image forming unit module 331K, the two-beam laser 3
51K1, K2 and 2 beam laser optical system so that images are formed simultaneously in parallel in the direction of rotation of the photosensitive drum.
The spot is equivalent to 00 dpi.

FIG. 4 shows the spot diameter and position of the laser imaged on the photosensitive drum side by side.

This printer device has a color print mode and a monochrome print mode, and operates at a color image forming speed α and a monochrome image forming speed β, respectively. β is about 1.5 times faster than α.

Next, regarding the image forming operation in each mode, the difference in the operation will be described.

<Color Print Mode> A case where the image forming apparatus operates in the color print mode will be described.

FIG. 5 and FIG. 6 are diagrams simply showing the manner of operation with respect to FIG. 3 and FIG. 4, respectively.

In response to an instruction from the controller 310, the light emission control switch 390 is turned off via the control signal 391.
One of the black 2-beam lasers is controlled by 351K2
Does not emit light. Also, via the control signal 391, the yellow, magenta, and cyan color unit modules 331Y,
M and C turn on the operation in the electrophotographic process (permitted)
Is set to do.

At this time, the controller 310
Outputs a speed control signal according to the color image forming speed α, and outputs polygon rotation control signals 353Y, M, C, K, photosensitive drum rotation control signals 372Y, M, C, K, and transfer belt rotation control signal 382. Then, they rotate in synchronization with each other at an appropriate speed.

On the other hand, the video signal and the PWM signal from the image processing block 341 via the video data signal lines 342Y, M, C, K1 are also fed to the PWM signal lines 350Y, M, C ,.
Through K1, the image data is operated / transmitted according to the image forming speed α. At this time, an image of 600 dpi is formed with one beam for all colors.

<Monochrome Print Mode> A case where the image forming apparatus operates in the monochrome print mode will be described.

FIGS. 7 and 8 are diagrams simply showing the manner of operation with respect to FIGS. 3 and 4, respectively.

In response to an instruction from the controller 310, the light emission control switch 390 is turned off via the control signal 391.
The black two-beam laser can emit both lights. Further, a speed control signal according to the monochrome image forming speed β is output, and a polygon rotation control signal 353K, a photoconductor drum rotation control signal 372Y, M, C, K, and a transfer belt rotation control signal 382 are output, which are synchronized with each other. And rotate at an appropriate speed. For example, the image forming speed β is 1.
Since the speed is about 5 times, the rotation speed of the polygon is about 2/3 times that in the color print mode.

On the other hand, the image processing block 341 constituting the image processing unit has image processing units 341Y, M, C and K1 corresponding to respective colors to be processed in parallel, and image processing units other than black, cyan in the illustrated example. The image processing unit 341C is shared as the image processing unit of the laser 351K2 used only in the monochrome mode of the black unit module 331K, and the video signal for the laser 351K2 is output to the video data signal line 342C.

From this video signal, the light emission pattern generator 3
A PWM signal is generated by the 40K1 and 340C, and the black two-beam laser is adjusted to the image forming speed β and the PWM signal lines 350K1 and 350 serving as image data transmitting means.
Each is modulated and transmitted to K2. At this time, black is 2
The beam forms an image of 600 dpi.

The video data signal lines 342Y, 34
Since a non-emission signal is sent to 2M, the laser 351
Y and 351M do not emit light. Also, image data for the laser 351K2 is transmitted to the video data signal line 342C. The laser 351C emits light in accordance therewith, but the control signal 391 sets the yellow, magenta, and cyan color unit modules 331Y, M, and C so that the operation in the electrophotographic process is turned off (not permitted).
No image forming operation is performed in these color unit modules.

[0070]

As described above, according to the first aspect of the present invention, even if the image forming portion for each color has a high resolution in the related art, the resolution is sufficiently utilized at the stage of overlapping the colors. However, there is a problem that only a black color, which is often used as a text character or a ruled line color, can be used for high resolution by using a plurality of optical writing means, and the image forming unit can be inexpensive and the image quality can be improved. Improvement can be realized.

According to the second aspect of the invention, for example, by increasing the density of the image forming spots written by the plurality of optical writing means by the optical resolution means,
Higher resolution can be achieved.

According to the third aspect of the present invention, the light of the black image forming portion is interlocked with the speed switching function to increase the image forming speed in monochrome printing in which it is not necessary to control the superposition of a plurality of colors. By changing the number of writing means, it is possible to secure a sufficient exposure amount per spot and avoid a decrease in latent image forming ability.

Further, even when the optical writing means has, for example, a polygon mirror, the polygon mirror may be slowed down according to the change of the image forming speed, so that it is not necessary to rotate the polygon mirror at a higher speed. As a result, the durable life of the polygon mirror bearing can be extended.

According to the invention described in claim 4, since the image processing section other than black is shared as the image processing section of the optical writing means used only in the monochrome mode of the black image forming section, high speed operation is achieved. The image forming apparatus can be inexpensive.

According to the invention of claim 5, the image data transmitting means other than black is shared as the image data transmitting means of the optical writing means of the black image forming section used only in the monochrome mode. A high-speed image forming apparatus can be made inexpensive.

According to the sixth aspect of the invention, since the light emission pattern generating means other than black is used also as the light emission pattern generating means of the optical writing means of the black image forming section used only in the monochrome mode, A high-speed image forming apparatus can be made inexpensive.

As described above, according to the present invention, it is possible to inexpensively improve the image quality by increasing the resolution of black only or the image forming speed of black only.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a four-color tandem color printer as an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a YMCK color laser spot of the apparatus of FIG. 1;

FIG. 3 is an explanatory diagram of a four-color tandem color printer according to a second embodiment of the present invention.

FIG. 4 is a diagram showing YMCK color laser spots of the apparatus of FIG. 3;

FIG. 5 is a schematic diagram for explaining the operation corresponding to FIG. 3 in the color print mode of the printer according to the second embodiment of the invention.

FIG. 6 is a schematic diagram for explaining an operation corresponding to FIG. 4 in the color print mode of FIG.

FIG. 7 is a schematic diagram for explaining an operation corresponding to FIG. 3 in a monochrome print mode of the printer according to the second embodiment of the present invention.

FIG. 8 is a schematic diagram for explaining the operation corresponding to FIG. 4 in the monochrome print mode of FIG. 7.

FIG. 9 is an explanatory diagram of a four-color tandem color printer according to the related art.

[Explanation of symbols]

100 printer body 110 control controller 131Y, M, C unit module (color image forming part other than black) 131K unit module (black image forming part) 140Y, M, C, K light emission pattern generation part (light emission pattern generation means) 141 image Processing blocks 142Y, M, C, K1, K2 Video data signal lines (image data transmitting means) 150Y, M, C, K1, K2 PWM signal lines 151Y, M, C Lasers (light writing means other than black) 151K1, K2 Laser (black light writing means) 152Y, M, C, K Polygon mirror 160Y, M, C Non-black laser beam 160K1, K2 Black laser beam 170Y, M, C, K Photoconductor drum 180 Transfer belt 300 Printer body 310 Control Controller 331Y, M, C Unit Joule (color image forming part other than black) 331K Unit module (black image forming part) 340Y, M, C, K Light emission pattern generation part (light emission pattern generation means) 341 Image processing block 341Y, M, C, K1 Image processing part 342Y, M, C, K1 video data signal lines (image data transmission means) 350Y, M, C, K1, K2 PWM signal lines 351Y, M, C lasers (optical writing means other than black) 351K1, K2 lasers (black color) Optical writing means) 352Y, M, C, K Polygon mirrors 353Y, M, C, K Polygon rotation control signals 360Y, M, C Non-black laser beams 360K1, K2 Black laser beams 370Y, M, C, K Photoconductors Drum 371Y, M, C, K Motor 372Y, M, C, K Photoconductor drum rotation control signal 380 Transfer Belt 381 transfer belt rotating motor 382 transfer belt rotation control signal 390 light emission control switch (Forced non-emission means) 391 control signal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/46 B41J 3/00 DF term (reference) 2C362 CA17 CA18 CA33 CA39 CB62 2H030 AA06 AB02 AD07 AD17 BB02 BB63 2H076 AB06 AB12 AB18 AB22 AB60 AB61 EA01 5C074 AA12 AA20 BB17 CC22 DD14 DD24 DD28 EE02 FF15 5C079 HA13 HB03 KA08 KA11 LA31 LC20 NA04 PA03

Claims (6)

[Claims] 1. An image forming apparatus comprising a plurality of image forming units corresponding to a plurality of colors including black, each image forming unit including a photoconductor and an optical writing unit for writing an image on the photoconductor. 2. An image forming apparatus, wherein only the black image forming section is provided with a plurality of optical writing units that are more than the color image forming sections other than black. 2. The image forming apparatus according to claim 1, further comprising means for optically writing at a higher resolution than that of the other color image forming sections by a plurality of optical writing means of the black image forming section. 3. A monochrome mode for performing only a black image formation, and a color mode for performing a color image formation, and among the plurality of optical writing means of the black image forming section in response to switching between the monochrome mode and the color mode. A means for switching the number of driven means is provided. In the monochrome mode, all the optical writing means of the black image forming section are used, and in the color mode, a part of the black image forming section is used. The image forming apparatus according to claim 1, which forms a color image. 4. An image processing unit corresponding to each color is provided, and a configuration is provided in which an image processing unit other than black is shared as an image processing unit of an optical writing unit used only in the monochrome mode of the black image forming unit. The image forming apparatus according to claim 3, wherein the operation of the image processing unit is switched according to the switching. 5. An image data transmitting means for each of the plurality of image forming portions, and a forced non-light emitting means of an optical writing means of a black image forming portion which is used only in a monochrome mode are provided. The optical writing means of the black image forming section used only in the monochrome mode is commonly used as the image data transmitting means, and the forced non-light emitting means is used to select each optical writing means that operates at the time of mode switching. The image forming apparatus according to claim 3. 6. A light emission pattern generating means for driving the optical writing means of each of the plurality of image forming portions, and a forced non-light emitting means of the optical writing means of the black image forming portion, which is used only in the monochrome mode, are provided. The light emission pattern generation means is shared as the light emission pattern generation means of the light writing means of the black image forming section used only in the monochrome mode, and each of the light writing means which operates at the time of mode switching is used by using the forced non-light emitting means. The image forming apparatus according to claim 3, wherein the image forming apparatus is selected.