JPH05150607A - Color image forming device - Google Patents

Abstract

PURPOSE:To form a character part to sharp and high-resolution image quality and a picture part to high-grade image quality free from stepped unequalness. CONSTITUTION:Plural writing units 120,... plural electrifiers 110,... corresponding to the irradiation position of respective main scanning light beams by the writing units 120,... and plural developing devices 130,... are disposed on one image forming body 1 which is moved under auxiliary scanning. Superposed toner images are formed on an image forming body 1 and multi-color or full-color images are obtd. by transferring and fixing. The two black writing units; a black writing unit 520 to be exclusively used for a character mode and a black writing unit 420 for a picture mode, are independently disposed between one piece each of the electrifiers for forming the black image and the developing device among the plural electrifiers 110,... and the developing devices 130,.... The exposing beam diameter of the black writing unit 520 for the character mode is set smaller than the exposing beam diameter of the black writing unit 420 for the picture mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus in which toner images of a plurality of colors are formed on an image forming body by an electrophotographic method and transferred onto a transfer material to obtain an image. ..

[0002]

2. Description of the Related Art As an image forming method for obtaining a color image by using an electrophotographic method, for example, JP-A-60-75850 and 60-767.
As disclosed in No. 66, No. 60-95456, No. 60-95458, No. 60-158475, etc., latent image formation and development according to the number of separated colors of the original image on the image forming body are performed. There is a method in which a color toner image is repeatedly formed on the image forming body and then transferred to obtain a color image.

A color image forming apparatus to which an image forming method in which latent images are formed and developed according to the number of separated colors of a document image read by a color scanner on the image forming body is applied is a belt-shaped image as a first example. An exposure device and a development device corresponding to the number of separated colors (for example, four colors including yellow, magenta, cyan, and black) are arranged around the formation body. As a second example, the exposure device and the development device are arranged around the drum-shaped image formation body. There is a device in which an exposure device and a developing device are provided according to the number of colors.

Among these, a color image forming apparatus having a belt-shaped image forming body is provided with a tension roller attached to a belt-shaped image forming body in which a photoconductor is applied or vapor-deposited on a flexible belt, and the pressure roller is pressed. By rotating the belt-shaped image forming body while keeping the sliding contact state with respect to the reference guide member by the tension of the belt-shaped image forming body, the surface of the belt-shaped image forming body is always held at a constant position and conveyed. Charger, exposure device, color toner of different colors (yellow,
An image forming means including a plurality of developing devices accommodating magenta, cyan, and black) is arranged, and the belt-shaped image forming body on which these image forming means rotate is arranged at a constant interval.

[0005]

Generally, in a color image forming apparatus, when copying an original image in which a character portion and a picture portion having a halftone such as an image or a photograph are mixed, the character portion is sharper. There is a demand for a copy image with clear contrast with high resolution and a beautiful halftone image quality in the picture portion.

When the sharpness of the character portion is pursued, it is necessary to reduce the exposure beam diameter of the writing unit and increase the dot density. However, when the beam diameter of the writing unit is made small, the potential on the image forming body (photoreceptor) becomes sharp, so that the image density of the picture portion becomes conspicuous, and the image quality as a whole is significantly deteriorated.

[0007]

In view of the above-mentioned problems of the prior art, the present invention provides a color image forming apparatus in which a character portion is formed into a copy image having a sharp resolution and excellent in character quality. It is an object of the present invention to provide a color image forming apparatus having a writing unit for forming a copy image having excellent halftone reproducibility.

In the color image forming apparatus of the present invention which achieves the above object, a plurality of writing units for performing main scanning exposure to a plurality of positions on one image forming body which moves in the sub scanning direction, and main scanning light by the writing units. A multi-color or full-color image is obtained by arranging a plurality of charging devices corresponding to the irradiation positions of the two and a plurality of developing devices to form a superposed toner image on the image forming body and transferring and fixing the toner image. In the forming apparatus, a black writing unit dedicated to a character mode and a black writing unit for a picture mode are provided in the middle of one charging device and a developing device for forming a black image among the plurality of charging devices and the developing device. 2 writing units are independently arranged, and the exposure beam diameter of the black writing unit for the character mode is set to the black writing for the picture mode. It is characterized in that it has less than the exposure beam diameter of write units.

The color image forming apparatus of the present invention is
Among the plurality of writing units, two writing units, a black writing unit dedicated to a character mode and a black writing unit for a picture mode, are independently arranged as a writing unit for forming a black image,
Further, each of the two black writing units is provided with its own charger and developing device, and the exposure beam diameter of the black writing unit dedicated to the character mode is smaller than that of the black writing unit for picture mode. It is characterized by.

[0010]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of a color printer as an example of a color image forming apparatus having a belt-shaped image forming body according to an embodiment of the present invention, and FIG. 2 is the belt-shaped image forming body and a plurality of lasers. It is a perspective view which shows the optical path of a scanning exposure apparatus.

In FIG. 1, a color image forming apparatus of this embodiment has a plurality of chargers 11 around a belt-shaped image forming body 1.
0, 210, 310, 410, main exposure scanning lines L1, L2, L
3, L4 and image forming means composed of developing units 130, 230, 330 and 430 loaded with four different color toners are arranged, and one rotation of the image forming body 1 causes yellow, magenta, cyan and black toners. The images are superimposed to form a color image.

The belt-shaped image forming body 1 is a belt-shaped photoconductor (hereinafter, referred to as a photoconductor belt) in which a photoconductor is applied or vapor-deposited on a flexible belt.
3 and a guide member 4 having a curvature, and a tension roller 5 is attached to the photosensitive belt 1, and the tension due to the pressure contact keeps the sliding contact state with respect to the reference guide member 4. By rotating, the surface of the photoreceptor belt 1 is always kept at a constant position for conveyance. With the above-described structure, the photosensitive member on the outer peripheral surface of the photosensitive belt 1 is always kept in a constant relation position with respect to the surface of the guide member 4 even during conveyance, and a stable image forming surface having a large curvature is formed with a long width. Therefore, a large number of image forming means having the same shape can be arranged in parallel at regular intervals.

In this embodiment, the photoconductor belt 1 is used as the image forming body, but the present invention is not limited to this, and can be applied to an existing image forming body having a photosensitive layer such as a photoconductor drum. Applicable.

Around the photosensitive belt 1, a plurality of charging means, a plurality of exposure means, four developing means loaded with toners of different colors, a transfer means and a cleaning means are arranged.

The charging means is provided to uniformly charge the photosensitive layer on the surface of the photosensitive belt 1 with a predetermined polarity, and the existing charging devices 110, 210, 310, such as a corona charging device or a scorotron charging device, are used. It is 410.

The exposure means is a semiconductor laser writing unit (laser scanning exposure device) 120, 220, 320, 420, 520, and exposes the surface of the photoreceptor belt 1 charged by the charger 110, 210, 310, 410. To form an electrostatic latent image.

In the laser scanning exposure device, the first exposure device 120 to which the image signal corresponding to the yellow component image of the color image is input is moved to the first position on the photosensitive belt 1 by the main scanning beam. The first exposure main scanning line L1 is formed, and the second exposure device 220 to which the image signal corresponding to the magenta component image is input is moved to the second position of the photoconductor belt 1 by the main scanning beam. The third exposure device 320, which forms the scanning line L2 and receives the image signal corresponding to the cyan component image, forms the third exposure main scanning line L3 at the third position of the photosensitive belt 1 by the main scanning beam. The fourth exposure device 420 to which the image signal corresponding to the picture image of the black component image is input is formed by the main scanning beam at the fourth position of the photosensitive belt 1 to the fourth exposure main scanning line L4. To form Fifth exposure apparatus that image signals corresponding to the character image of the black component image et is input 520
Forms a fifth exposure main scanning line L5 near the fourth position of the photosensitive belt 1 by the main scanning beam (see FIG. 2).

Each of the laser scanning exposure devices 120, 220, 32
Reference numerals 0, 420 and 520 denote a laser light source (semiconductor laser) 121, a collimation lens 122, a drive motor 123,
It has a polygon mirror 124, an fθ lens 125, and a cylindrical lens 126.

The image signals of the respective color components input to the exposure devices 120 to 520 are output as time-series digital signals from a central control device or the like which controls the overall image reading device or recording device.

A fifth exposure device 520 dedicated to the character mode
The irradiation beam diameter on the photosensitive belt 1 according to the above is set to be smaller than the irradiation beam diameter by the fourth exposure device 420 for the picture mode. For example, assuming that the image dot density is 400 dpi (dots / inch), the irradiation beam diameter of the first to fourth exposure devices 120 to 420 in the picture mode is about 0.0635 mm.
Therefore, the irradiation beam diameter by the fifth exposure device 520 dedicated to the character mode is set to 0.06 mm or less, for example, 0.04 mm. As a result, the dot diameter is reduced and the density is increased to achieve a sharp high resolution image quality.

Of the black component image, the fourth exposure device 420 corresponding to the picture image and the fifth exposure device 520 corresponding to the character image share one charging device 410 and one developing device 430, respectively. After charging once, black picture image exposure and black character image exposure are performed, and then a black toner image is formed by the fourth developing device 430.

The developing means is composed of four developing devices 130 each containing a developer of a different color, for example, yellow (Y), magenta (M), cyan (C) and black (K) toners (developer). , 230, 330, 430. Each of the developing devices 130 to 430 has a function of developing the electrostatic latent image on the photosensitive belt 1 into a toner image by a non-contact developing method.
Unlike the contact development method, this non-contact development method does not impair the previous toner image formed on the photosensitive belt 1, and
Since the movement of the photosensitive belt 1 is not hindered, a good color image can be obtained.

The transfer means transfers the toner image formed on the photosensitive belt 1 onto the transfer material by the transfer device 14 such as a transfer corona discharger. As this transfer means, an existing transfer member such as a transfer drum may be used instead of the transfer device 14.

The cleaning means 15 has a cleaning blade 151 and a cleaning roller 152.
It is provided so as to be pressed against the surface of the photoconductor belt 1 to clean the photoconductor belt 1.

By thus setting different irradiation beam diameters and developing and transferring, a high resolution image quality can be obtained in a character image, and a high quality image quality without a step in a picture image such as a picture or a photograph. The image quality is significantly improved as a whole.

A color image forming process by the image forming apparatus having the above-mentioned structure is performed as follows.

First, when an image signal of a first color output from an image reading apparatus separate from the apparatus main body is input to the laser scanning exposure apparatus 120, the laser scanning exposure apparatus 120
A laser beam is generated by the laser light source 121 in.
A polygon mirror 124 whose laser beam is rotated by a drive motor 123 via a collimation lens 122.
Is rotated and scanned by the f.theta. Lens 125 and the cylindrical lens 126, and a bright line is formed by being projected on the peripheral surface of the photoconductor belt 1 which is uniformly charged to a predetermined charge by the chargers 110 to 410 in advance.

On the other hand, in the sub-scanning direction, drive control is performed by an encoder E and a motor M provided at the shaft end of a rotating roller 2 for rotating the photosensitive belt 1.

When the exposure scanning is started, the fixed position is detected by the photosensor PS1 by the laser light of the first laser light source 121 in the main scanning direction, and the first color of the first color is detected on the basis of the detected signal. Laser light source by image signal
The modulation of 121 is started, and the modulated laser beam scans the surface of the photosensitive belt 1. Therefore, a latent image corresponding to the first color is formed on the surface of the photosensitive belt 1 which is uniformly charged by the main scanning by the laser light and the sub scanning by the conveyance of the photosensitive belt 1. This latent image is developed by the developing device 130 containing yellow toner, and the photosensitive belt 1
Yellow toner image is formed on the surface of the. Thereafter, the photosensitive belt 1 is conveyed while holding the yellow toner image on the surface thereof, and then the image formation of the second color is started.

That is, the photoconductor belt 1 on which the yellow toner image is formed is re-charged when it is conveyed to the next position of the charger 210, as in the case of the image signal of the first color described above. After being charged by 210, and then counting a predetermined time from the start of modulation of the first laser light source 121 by a timer, a fixed position is detected by the photo sensor PS2, and the laser scanning exposure device 220 using the second image signal is detected. Modulation of the semiconductor laser is started, the laser light generated by the semiconductor laser is rotationally scanned by the polygon mirror rotated by the drive motor through the collimation lens, passes through the fθ lens and the cylindrical lens, and is predetermined by the charger 210. The latent image is formed by being projected onto the peripheral surface of the photosensitive belt 1 which is uniformly charged with the electric charges of. The latent image is developed by the developing device 230 containing magenta toner as the second color. The magenta toner image is formed in the presence of the already formed yellow toner image.

Similarly, the photoconductor belt 1 on which the magenta toner image of the second color is formed is further conveyed, and as in the case of the image signal of the second color, the charger 310 continues to remove the image. Developing device 330 that is charged in the same manner, forms a latent image by the laser scanning exposure device 320, and contains cyan toner.
To develop a cyan toner image.

Subsequently, the photosensitive belt 1 on which the cyan toner image of the third color is formed is further conveyed and the charging device 41
0 is uniformly charged, a fourth laser scanning exposure device 420 forms a latent image corresponding to a black picture mode, and a fifth laser scanning exposure device 520 forms a latent image corresponding to a black character mode. Development is performed by a developing device 430 containing black toner, and the black toner images in both modes are superposed to form all color toner images on the surface of the photoconductor belt. That is, the photosensitive belt 1 is 1
A color toner image is formed during rotation.

A DC or further AC bias is applied to each of the developing devices 130 to 430, and the reversal development (jumping development) is performed in a non-contact manner on the photosensitive belt 1 whose base is grounded. .. For this non-contact development, either one-component developer or two-component developer can be used. When a one-component developer is used, it is not necessary to provide a toner concentration control means, and downsizing can be achieved. However, the development method using a two-component developer is superior in terms of development stability, so that color reproduction is improved. preferable.

The color toner image formed on the surface of the photosensitive belt 1 as described above is supplied from the paper feeding cassette 161 by the paper feeding roller 162, and the timing roller 163 transfers the color toner image in timing with the color toner image. P
Is transcribed to. The transfer device 14 applies a high voltage power source having a polarity opposite to that of the toner to transfer the toner.

Thus, the transfer material on which the color toner image has been transferred is reliably separated by the photosensitive belt 1 which rapidly changes its direction (small curvature) along the rotating roller 2,
After the toner is melted and fixed by the fixing unit 17, the paper is discharged from the apparatus main body by the paper discharge roller 18.

On the other hand, after the transfer of the color toner image onto the transfer material, the photosensitive belt 1 is further conveyed in the clockwise direction,
Cleaning blade 151 and cleaning roller 152
The residual toner is removed and cleaned by the cleaning means 15 in the pressure contact state. After the cleaning is completed, a new image forming process is started again.

The color image forming apparatus of this embodiment is
Arranged around the photosensitive belt 1 is an image forming means including four chargers 110 to 410, five exposure devices 120 to 520, and four developers 130 to 430 loaded with toners of different colors. , Forming a color image by superposing the yellow, magenta, cyan and black toner images by one rotation of the photosensitive belt 1.
This is the so-called one-pass method. Needless to say, the present invention is not limited to the one-pass method, and may be a multi-rotation method in which a latent image is formed and developed each time the image forming body makes one rotation.

Further, in the color printer of FIG. 1, since five series of exposure devices are arranged, the refracting optical system using a plurality of mirrors has a compact design.

FIG. 3 is an overall configuration diagram of a color copying machine having an image reading system A above a color image forming apparatus as another embodiment of the present invention. Also in this embodiment, similarly to the above, the fourth exposure device 420 corresponding to the picture mode for forming the black image and the fifth exposure device 5 corresponding to the character mode 5
20 is provided separately, and a common charging device 410 and developing device 430 form a black toner image in which a picture portion and a character portion are mixed. The irradiation position on the photoconductor belt 1 by the fourth exposure device 420 and the irradiation position by the fifth exposure device 520 do not necessarily have to coincide with each other, and as shown in FIG. However, the interval may be detected and controlled so that the write timings in both modes coincide.

FIG. 4 is an overall constitutional view of a color printer showing still another embodiment according to the present invention, and FIG. 5 is a perspective view showing a belt-shaped image forming body and a plurality of laser scanning exposure optical paths.

In the figure, parts having the same functions as those of the above embodiment are designated by the same reference numerals. Further, the points different from the above embodiment will be described.

In this embodiment, Y in picture mode,
Image forming units corresponding to four colors of M, C and K, that is, four chargers 110, 210, 310 and 410 and four exposure devices
120, 220, 320, 420 and 4 developing units 130, 230, 330, 4
And a fifth charging device 510, a fifth exposure device 520, and a fifth developing device 530 as the fifth unit exclusively for character images. The laser exposure beam diameter of the fifth exposure device 520 corresponding to the character mode is set smaller than the laser exposure beam diameter of the fourth exposure device 420 corresponding to the picture mode, as in the first embodiment. This makes it possible to reduce the dot diameter to a high density and obtain a high resolution image quality with sharp characters.
At the same time, high-quality image quality including the halftone image quality of the picture part is obtained.

FIG. 6 is an overall configuration diagram of a color copying machine equipped with an image reading system A as still another embodiment of the present invention. The details of this image forming unit are the same as in FIG.

[0045]

As described above, according to the color image forming apparatus of the present invention, a sharp high-resolution image can be obtained in a character portion and a high-quality image having no step in a picture portion such as a picture or a photograph. Image formation is achieved.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing optical paths of a belt-shaped image forming body and a plurality of laser scanning exposure devices.

FIG. 3 is an overall configuration diagram showing another embodiment of a color image forming apparatus according to the present invention.

FIG. 4 is an overall configuration diagram of still another embodiment of the color image forming apparatus according to the present invention.

FIG. 5 is a perspective view of a laser scanning exposure apparatus according to the above embodiment.

FIG. 6 is an overall configuration diagram of a color copying machine as a further embodiment of the present invention.

[Explanation of symbols]

1 Belt-shaped image forming body (photosensitive belt) 2, 3 Rotating roller 4 Guide member 14 Transfer means (transfer device) 110, 210, 310, 410, 510 Charging device 120, 220, 320 Laser scanning exposure device (laser writing) Unit) 420 Laser scanning exposure device (picture mode compatible) 520 Laser scanning exposure device (character mode compatible) 121 Laser light source (semiconductor laser) 124 Polygon mirror (rotating polygon mirror) 125 fθ lens 130, 230, 330, 430, 530 Development L1, L2, L3, L4, L5 exposure main scanning line

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B41J 3/54 G03G 15/04 116 9122-2H H04N 1/29 G 9186-5C

Claims (5)

[Claims] 1. A plurality of writing units that perform main scanning exposure at a plurality of positions on one image forming body that moves in the sub-scanning direction, and a plurality of chargers that correspond to the irradiation positions of the respective main scanning lights by the writing units. A color image forming apparatus, in which a plurality of developing devices are arranged to form a superposed toner image on an image forming body, and a multicolor or full-color image is obtained by transfer and fixing, wherein the plurality of charging devices and the developing devices are provided. Among them, two writing units, that is, a black writing unit dedicated to the character mode and a black writing unit for the picture mode are independently arranged between each one charger for black image formation and the developing device. The feature is that the exposure beam diameter of the black writing unit for the character mode is smaller than that of the black writing unit for the picture mode. Color image forming apparatus to be used. 2. A plurality of writing units that perform main scanning exposure at a plurality of positions on one image forming body that moves in the sub-scanning direction, and a plurality of chargers that correspond to the irradiation positions of the main scanning lights by the writing units, respectively. In a color image forming apparatus, in which a plurality of developing devices are arranged, a superimposed toner image is formed on an image forming body, and a multi-color or full-color image is obtained by transfer and fixing, among the plurality of writing units, As a writing unit for forming a black image, two writing units, that is, a black writing unit dedicated to a character mode and a black writing unit for a picture mode are separately arranged, and the two black writing units are respectively charged exclusively. A developing unit and a developing unit are provided, and the exposure beam diameter of the black writing unit dedicated to the character mode is A color image forming apparatus characterized in that it is smaller than the exposure beam diameter of a black writing unit for a char mode. 3. The color image forming apparatus according to claim 1, wherein the writing unit is a laser beam scanning exposure device. 4. The color image forming apparatus according to claim 1, wherein the main scanning light of the writing unit corresponds to four colors of yellow, magenta, cyan, and black. 5. The color image forming apparatus according to claim 1, wherein the image forming body is an endless belt-shaped photoreceptor.