JPH05216323A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a small sized device where an image displaying bright colors on OHP or paper is obtained by making processing speed in a low speed mode to be 1/n ((n) is an integer) of processing speed of a normal mode. CONSTITUTION:When OHP mode is selected by pressing a mode selection key, changeover of the processing condition to improve the fixing function is carried out through control by CPU. Then, when the lowering of the speed is carried out, the operation speed of an image reading system A is changed over to the low speed of 1/n and the image reading is carried out. Therefore, the image reading is carried out with high density which is (n) times in the direction of sub scanning. On the other hand, the operation speed of laser writing units 24 to 27 is not varied but maintained constant. Then, when the processing speed is reduced to 1/n, image data is discarded for n-1 lines for every (n) lines of scanning or transported while being changed to white signals. Therefore, semiconductor lasers of the laser writing units 24 to 27 stop light-emission for n-1 scannings.

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 for forming a latent image on a belt-shaped photoreceptor by a writing device using a laser beam, and more particularly to a transparent member for an overhead projector (hereinafter referred to as OHP). (Hereafter, O
The present invention relates to a color image forming apparatus capable of forming a toner image on HP paper) or thick paper to obtain a clear color image. The present invention also relates to a color image forming apparatus capable of improving glossiness.

[0002]

2. Description of the Related Art Many methods and apparatuses have been proposed for obtaining a color image using electrophotography. For example, JP-A-61
As disclosed in Japanese Patent Laid-Open No. -100770, a latent image is formed and developed on a photosensitive drum, which is an image forming body, according to the number of separated colors of an original image, and the latent image is transferred to the transfer drum each time the image is developed. There is a method in which a multicolor image is formed on the upper surface and then transferred onto a recording paper to obtain a color copy. The device by this method is
In addition to the photoconductor drum, it is necessary to provide a transfer drum having a size capable of transferring an image for one sheet on the peripheral surface thereof, and it is inevitable that the apparatus has a large size and a complicated structure.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-149972, latent images are formed and developed on the photosensitive drum in accordance with the number of separated colors of the original image, and the latent image is formed on the transfer material each time the development is performed. There is a method of transferring to obtain a multicolor color copy. With this method, it is difficult to accurately superimpose multicolor images, and it is impossible to obtain a good color copy.

Also, a latent image is formed on the photosensitive drum in accordance with the number of separated colors of the original image and development with color toner is repeated, the color toner images are superposed on the photosensitive drum, and then transferred to obtain a color image. There is. The basic process for forming this multicolor image is described in Japanese Patent Application Laid-Open No. 60-75850 and 60
-76766, 60-95456, 60-95458, 60-158475
It is disclosed in Japanese Patent Publication No.

In a multicolor image forming apparatus which obtains a color image by such superposition, a plurality of developing devices accommodating color toners of different colors are arranged around the periphery of the photosensitive drum. Generally, the photosensitive drum is rotated a plurality of times to develop a latent image on the photosensitive drum to obtain a color image.

As for the image forming body, as described above, the photosensitive drum having the photoconductor coated or vapor-deposited on the peripheral surface thereof and the belt-shaped body having the photoconductor coated or vapor-deposited on the flexible belt are used. Photoconductors have also been proposed.
The shape of the belt-shaped photoconductor (hereinafter also referred to as a photoconductor belt) is determined by stretching it between rotating rollers including a drive roller, so that the space is effectively used to form a compact color image forming apparatus. It is effective when doing. Further, since the photoconductor belt can run along a small curvature, it is possible to prevent transfer material separation failure by using a small-diameter rotating roller to separate the transfer material using this curvature portion. it can.

Further, when forming an image on OHP paper or thick paper, the toner of each color is sufficiently melted so that reflection at the boundary surface of the toner does not occur, color turbidity is prevented, and a vivid color image is obtained. For this reason, there is one in which the linear velocity is decreased and the fixing nip time is increased (Japanese Patent Laid-Open No. 60-808).
85, JP-A-60-86574).

In these prior arts, when an image is formed on a photoconductor, it is executed at a normal speed as in the case of normal paper, and the linear speed is set after the OHP or the rear end of the paper passes through the transfer portion. Switching to low speed.

[0009]

The above-described conventional technique has an advantage that image defect unevenness can be eliminated without requiring switching of process conditions during image formation, but has the following problems. There is.

(1) It is not suitable to change the linear velocity during the exposure or development process, because it tends to cause image distortion and unevenness. Therefore, the velocity is changed after the image transfer onto the recording paper is completed. There is. For this reason, a distance longer than the length of the OHP paper must be provided between the transfer unit and the fixing unit without fail, which leads to an increase in the size of the apparatus and a longer printing time.

(2) Similarly, a paper conveying mechanism is required between the transfer section and the fixing section, which complicates the apparatus and increases the cost.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a small-sized color image forming apparatus capable of obtaining an image expressing a vivid full color on OHP or paper.

[0013]

The above object is to perform main scanning by a plurality of optical writing means using a laser beam on an image forming body, and to perform sub-scanning accompanying the movement of the image forming body.
In a low-speed mode in a color image forming apparatus in which a latent image is formed on the image forming body and a toner image obtained by development is superposed on the image forming body a plurality of times to obtain a multicolor color image. The process speed of 1 / n of the process speed in the normal mode, and the image signal to be sent to the optical writing means in the low speed mode is sent for one scan every n scans.
The other n-1 scans are achieved by the color image forming apparatus characterized by stopping the laser emission. Where n
Is an integer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a color image forming apparatus for forming a color image by superposing toner images during one rotation by providing a plurality of optical writing means around a belt-shaped photosensitive body which is an image forming body. Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows the main structure of a color copying machine which is a color image forming apparatus provided with a belt-shaped image forming body as an embodiment of the present invention. This color copying machine is roughly classified into an image reading system A and an image forming system B.
It consists of The image forming system B of the color image forming apparatus of the present embodiment is composed of a plurality of charging means, a plurality of exposing means and a developing means in which four different color toners are loaded around the belt-shaped image forming body. An image forming means is arranged, and a toner image of black, yellow, magenta and cyan is superposed by one rotation of the belt-shaped image forming body to form a color image.

First, the image reading system A and the image data processing in the normal mode will be described with reference to FIG. 1 which is a main configuration diagram of the color copying machine and FIG. 2 which is an image data processing system diagram.

In the image reading system A, a document placed on the document table 11 is illuminated by a halogen lamp 121 attached to a carriage 12 that slides in the horizontal direction. Mirrors 131 and 132 are attached to the movable mirror unit 13, and they slide in the same horizontal direction, and in combination with the mirror 122 attached to the carriage 12, the optical image of the document is sent to the lens reading unit 14. Derive.

The carriage 12 and the movable mirror unit 13 are driven via wires (not shown) connected to a stepping motor, and V and 1/2 V, respectively.
It is slid in the same direction at the speed of.

The lens reading unit 14 has a lens 141 and a color CCD 142 at an image forming position behind the lens 141.

A color CCD 142 is used to copy the original into blue image data (B), green image data (G) and red image data (R).
The color image data is separated and output to the A / D conversion circuit 251.

The A / D conversion circuit 251 converts color image data consisting of red (R), green (G), and blue (B) image data input from the color CCD 142, or monochrome image data (Bk), For example, it is converted into image data of a digital signal of 256 gradations and output to the image data processing circuit 252.

In the image data processing circuit 252, A / D conversion 2
Of the digital signals converted in 51, the digital signal of the color image data is subjected to complementary color conversion to be converted into image data of yellow (Y), magenta (M), cyan (C), and for example, undercolor removal (called UCR). By doing, Y, M, C
Image data of black (Bk) is extracted from the image data of.

Further, masking processing, Y after UCR,
Color correction of M image data is performed.

As described above, the image data becomes the image signal of each color component which is subjected to the complementary color conversion, the black component extraction and the color correction by the image data processing circuit 252 and is sent to the selector 254 via the delay memories 253A to 253C.

The delay memories 253A to 253C are memories provided to delay the writing time point according to the writing positions of the laser writing units 24 to 27 for the respective colors, which are different from each other.

On the other hand, the normal mode signal selected by the mode selection key 50 on the operation unit of the color copying machine is CP.
Since it is input to U250, the normal mode selection signal is input to the selector 254 from the CPU250. Therefore,
The image signals of the respective color components are sent from the selector 254 as they are to the laser writing units 24 to 27 of the image forming system B through the modulation circuit 256.

That is, the first black (Bk) image signal is, for example, pulse width modulated by the modulation circuit 256, and then output to the laser writing unit 24 which is an optical writing unit described later. Similarly, the second color is yellow (Y) and the third color is
The magenta (M) image signal as the color of C and the cyan (C) image signal as the fourth color are respectively modulated by the modulation circuit 256.
Is pulse-width modulated, for example, and then output to laser writing units 25 to 27, which will be described later.

Next, with respect to the image forming system B, FIG. 1 showing the main construction of the color copying machine and the laser writing unit (4).
A description will be given based on FIG. 3 which is an arrangement configuration diagram excluding a mirror 248 of units, but all have the same configuration.

As shown in FIG. 3, the photosensitive belt 15 is provided with a transparent hole or a light transmitting film in the transparent hole at the upstream side in the main scanning direction at a predetermined distance from the bonded portion 151 of the photosensitive surface of the photosensitive belt 15. A resist mark 152, which is attached and transmits laser light, is formed at a position facing a photo sensor described later. The registration mark 152 serves as a reference for determining the exposure start position in the main scanning direction and the sub-scanning direction by using a photo sensor, which will be described later, as the detection of the bonded portion. As shown in the figure, the guide member 18 has recesses formed at both ends of its optical writing portion, and photosensors PS1 to PS4 are arranged in the recesses as light detecting means. The photosensors PS1 to PS4 detect the transmitted light of the laser beam, which is the exposure light from the optical writing means, through the resist mark 152. Needless to say, a reflection member may be provided as a registration mark on the photoconductor belt 15 and the reflected light of the exposure light may be received by the photosensors PS1 to PS4.

Further, in this embodiment, the photoconductor belt 15 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 15, a plurality of charging means, a plurality of optical writing means, four developing means loaded with toners of different colors, a transfer means and a cleaning means are arranged.

The charging means is provided for uniformly charging the photosensitive layer on the surface of the photosensitive belt 15 with a predetermined polarity, and is the existing chargers 20 to 23 such as a corona charger and a scorotron charger.

The optical writing means is laser writing units 24-27 using a semiconductor laser, and the surface of the photosensitive belt 15 charged by the chargers 20-23 is exposed by a laser beam to form an electrostatic latent image. ..

The developing means accommodates developers of different colors, for example, black (Bk), yellow (Y), magenta (M) and cyan (C) color toners (developer) 4 respectively.
The individual developing devices 28 to 31. Each of the developing devices 28 to 31 has a function of developing an electrostatic latent image on the photosensitive belt 15 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 photoconductor belt 15 and does not hinder the movement of the photoconductor belt 15, thus obtaining a good color image. You can

The transfer means transfers the toner image formed on the photosensitive belt 15 onto the transfer material by the transfer device 32 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 32.

The cleaning means 33 has a cleaning blade 331 and a cleaning roller 332, and is provided so as to clean the photosensitive belt 15 by pressing it against the surface of the photosensitive belt 15 only at the time of cleaning.

The recovery box 34 is for recovering and storing the residual toner on the photosensitive belt 15 removed by the cleaning means 33 through the toner recovery tube 341.

In this embodiment, each process of the photoconductor belt 15, the charging devices 20 to 23, the developing devices 28 to 31 containing toner of each color, the cleaning means 33, and the toner collecting box 34, which constitute the above-mentioned image forming section, is carried out. The parts are housed in an integrated cartridge 35 to be unitized, and can be collectively attached to and detached from the apparatus main body.

The normal mode process of color image formation by the image forming system B having the above-mentioned structure is carried out as follows.

First, when the image signal of the first color output from the image reading system A is input to the laser writing unit 24, laser light is generated by the semiconductor laser 241 in the laser writing unit 24 and is generated by the collimator lens 242. It becomes a laser beam of parallel light. This laser beam passes through a cylindrical lens 243, is rotationally scanned by a rotary polygon mirror 244 rotated by a drive motor M4, and f
It passes through the θ lens 245, the mirror 248, the cylindrical lens 246, and the dustproof glass 247, and is projected onto the peripheral surface of the photoconductor belt 15 that is uniformly charged to a predetermined charge by the charger 20 to form a bright line. Cylindrical lens here
243 and 246 correct the laser spot position variation due to the surface tilt of the rotary polygon mirror 244, and the fθ lens 245 is the photosensitive belt 15
The laser beam is imaged in the form of a spot on the upper surface, and the scanning speed of the laser spot is made constant over the entire scanning line. The index sensor 249a receives the laser beam reflected by the mirror 249b at the scanning start point of the laser beam and outputs an index signal, which is used for timing of writing image data in the main scanning direction.

On the other hand, in the sub-scanning direction, the photosensor PS1 detects the registration mark 152 corresponding to the specific position of the photosensitive belt 15, and the modulation of the semiconductor laser 241 by the image signal is started based on this detection signal. The main scanning line to be processed is determined. When the scanning is started, the laser beam is detected by the photosensor PS1 in the main scanning direction, and the semiconductor laser 241 is started to be modulated by the image signal of the first color based on the detected signal and is modulated. The laser beam scans the surface of the photoreceptor belt 15. Therefore, a latent image corresponding to the first color is formed on the surface of the photosensitive belt 15 which is uniformly charged by the main scanning by the laser beam and the sub scanning by the conveyance of the photosensitive belt 15. This latent image is developed by the developing device 28 containing black toner, and a black toner image is formed on the surface of the photoconductor belt 15. After that, the photosensitive belt 15 is conveyed while holding the black toner image on its surface, and then the image formation of the second color is started.

That is, the photosensitive belt 15 on which the black toner image is formed is conveyed to the position of the next charging device 21 again as in the case of the image signal of the first color described above, and the charging device is again charged. Then, the registration mark 152 corresponding to a specific position on the photoconductor belt 15 is charged by the photosensor PS2.
Is detected and the modulation of the semiconductor laser of the laser writing unit 25 by the image signal of the second color is started on the basis of this detection signal, and the laser beam generated by the semiconductor laser 251 in the laser writing unit 25 is driven by the drive motor. M5
It is rotated and scanned by the rotating polygon mirror 254 which is rotated by
fθ lens 254, mirror 258, cylindrical lens 256
Then, a latent image is formed on the peripheral surface of the photoconductor belt 15 which is uniformly charged to a predetermined electric charge by the charger 21 through the dustproof glass 257. The latent image is developed by the developing device 29 containing the yellow toner as the second color. The yellow toner image is formed in the presence of the already formed black toner image.

Similarly, the photosensitive belt 15 on which the black and yellow toner images of the first and second colors have been formed is further conveyed, and as in the case of the image signal of the second color described above. Subsequently, the toner is uniformly charged by the charger 22, a latent image is formed by the laser writing unit 26 which is an optical writing means, and a latent image is formed by the developing device 30 containing magenta toner to form a magenta toner image. Further, the photoconductor belt 15 on which the magenta toner image of the third color is formed is conveyed, and is uniformly charged by the charger 23 as in the case of the image signals of the first to third colors. A latent image is formed by the laser writing unit 27, and is developed by a developing device 31 containing cyan toner to superimpose the cyan toner image, and a color toner image is formed on the surface of the photosensitive belt 15. That is, a color toner image is formed during one rotation of the photoconductor belt 15.

A direct current or an alternating current bias is applied to each of the developing devices 28 to 31, and the reversal development (jumping development) is carried out in a non-contact manner with the photoreceptor belt 15 whose base is grounded.
Is to be done. 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 the size can be reduced. However, the development method using a two-component developer is superior in terms of development stability, and therefore, color reproduction is improved. preferable.

The color toner image formed on the surface of the photosensitive belt 15 as described above is supplied from the paper feeding cassette 135 by the paper feeding roller 36 and is transferred by the timing roller 37 to the transfer material in timing with the color toner image. Transcribed. The transfer unit 32 applies a high voltage having a polarity opposite to that of the toner to transfer.

Thus, the transfer material on which the color toner image has been transferred is reliably separated along the driving roller 16 by the photoconductor belt 15 that rapidly changes direction (small-diameter curvature), and the fixing means 38 melts the toner. After being fixed, the paper is discharged from the apparatus main body by the paper discharge roller 39.

On the other hand, the photosensitive belt 15 which has finished transferring the color toner image onto the transfer material is further conveyed in the clockwise direction,
Cleaning blade 331 and cleaning roller 332
The residual toner is removed and cleaned by the cleaning means 33 in the pressure contact state. After the cleaning is completed, a new image forming process is started again.

Next, the case of the OHP mode will be described.

The image forming process in this case is the same as that in the normal mode except that the process speed is different from that of the optical writing method. Therefore, only the optical writing process will be described. Further, the fixing temperature may be set according to the linear velocity, OHP and the degree of gloss.

When the mode selection key 50 is pressed to select the OHP mode, the CPU 250 controls the process conditions to improve the fixing performance. At this time, in the present invention, the process speed of the image forming system B together with the image reading system A is reduced to, for example, 1/5. However, the drive motors M4, M5, M of the laser writing units 24-27 are
6 and M7 are kept constant as in the normal mode, and therefore the scanning speed does not change.

When the speed reduction is executed, the scanning speed of the image reading system A is also switched to the low speed of ⅕ to read the image. Therefore, the image reading is performed at a high density of 5 times in the sub-scanning direction. On the other hand, the operating speed of the laser writing units 24-27 does not change and is kept constant. Therefore, the image data obtained by the image reading system A is subjected to various processes in the image data processing circuit 252 of FIG. 2 to become an image signal, and then signals other than the black signal are selected via the delay memories 253A to 253C. Sent to 254. A selector 250 receives an OHP mode selection signal from the CPU 250. So 1 for every 5 scans
An image signal corresponding to the scanning is sent to the modulation circuit 256, and the other 4
For the scanning, the white signal input from the white signal generation circuit 255 is sent to the modulation circuit 256. That is, when the process speed is reduced to 1 / n, the image data for n-1 lines is discarded every n scans, or transferred after being converted into a white signal (when reverse development is performed). It Therefore, the semiconductor laser 24 of the laser writing unit 24-27 is
For 1-271, the light emission is stopped for the above n-1 scans. This enables the rotary polygon mirrors 244-247 of the laser writing units 24-27.
The writing density of the image exposure can be kept constant regardless of the process speed without changing the rotation speed.

The above description has been made on the case where there are two kinds of modes, that is, the normal mode and the OHP mode. However, a large number of modes are provided, n is changed according to each mode, and the process speed is 1
It can be changed to / n to support various recording modes. That is, for the gloss mode, the process speed is set to 1/2, 1/3, ... 1 / according to the desired gloss level.
5, 1/6 ... Can be selected and corresponded.

Similarly, a recording material (for example, thick paper or waste paper)
The process speed can be selected in accordance with the above.

[0054]

As described above, according to the present invention, in a color image forming apparatus in which an image forming means including a plurality of optical writing means is arranged around a moving image forming body, in the case of an OHP mode or a gloss mode, Since the scanning speed of the optical writing means is not changed, the process speed is reduced to 1 / n, and the optical writing is performed only for one scanning every n scannings.
The following effects can be obtained.

(1) The control is simple, the fixing performance is improved without extremely improving the mechanical accuracy, the transparency and smoothness of the toner are improved, and a clear color image can be reproduced on OHP or paper. In addition, since the fixing is made suitable for the material of the recording material, offset, wrinkle, winding, and blurring of characters do not occur even in the case of plain paper.

(2) Since the fixing conditions are changed by switching the process speed, it is not necessary to provide a distance between the transfer portion and the fixing portion, and a paper feeding device is not required. Therefore, the cost increase of the device can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a main configuration of a color copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of an image data processing system of the present invention.

FIG. 3 is a diagram showing an arrangement configuration of a laser writing unit in FIG.

[Explanation of symbols]

 14 Lens reading part 15 Photosensitive belt 16, 17 Rotating roller 18 Guide member 20,21,22,23 Charger 24,25,26,27 Laser writing unit 241 Semiconductor laser 28,29,30,31 Developer 50 mode Selection key 152 Registration mark 250 CPU 252 Image data processing circuit 253A, 253B, 253C Delay memory 254 Selector 255 White signal generation circuit A Image reading system B Image forming system

Claims (2)

[Claims] 1. A main scanning is performed on the image forming body by a plurality of optical writing means using a laser beam, and a latent image is formed on the image forming body by a sub-scanning accompanying the movement of the image forming body, In a color image forming apparatus in which a toner image obtained by development is superposed a plurality of times on the image forming body to obtain a multicolored color image, the process speed in the low speed mode is 1 / the process speed in the normal mode. and a color image forming apparatus. Here, n is an integer. 2. The image signal to be sent to the optical writing means in the low speed mode is sent for one scan every n scans, and the laser emission is stopped for the other n-1 scans. 1. Color image forming apparatus.