JPH0583485A - Color image forming device - Google Patents

Abstract

PURPOSE:To reduce color slurring in a sub scan direction by storing the dot data of an exposure main scan line, which are written in the different main scan direction of symmetric optical systems, in a memory while dividing those data, and alternately writing the data in that line and the data in the preceding line. CONSTITUTION:Plural laser beams from a laser write unit are passed through a collimation lens and a cylindrical lens 123B, turned to parallel beams, scanned by rotary polygon mirrors 125A and 125B and form scan lines L1-LL while irradiating a photo-sensitive belt 1 through ftheta lens 126A and 126B and mirrors 1271A, and 127B. The formed latent images are developed by plural developers and color images are obtained. The dot data to be written in the main scan direction are detected by using photodetecting sensors PS1-PS4, the plural data are stored in the memory means while being divided, and the data in that line and the data in the preceding line are alternately written. Thus, the position shift of one line to be written in the different main scan direction is suppressed less than 1/2 dot in the sub scan direction.

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 a toner image is formed on an image forming body by an electrophotographic method and is 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, three colors of yellow, magenta, and cyan or four colors including black) are arranged around the formed body, and a drum-shaped image formed body as a second example. There is an apparatus in which an exposing device and a developing device according to the number of colors are arranged around the.
Among these, a color image forming apparatus including a belt-shaped image forming body will be described.

In a color image forming apparatus, a tension roller is attached to a belt-shaped image forming body in which a photoconductor is applied or vapor-deposited on a flexible belt, and a tension roller is used to slide a tension roller against a reference guide member. By rotating while keeping the contact state, the surface of the belt-shaped image forming body is always kept at a constant position and conveyed, and a charger, an exposure device, and color toners of different colors are provided around the belt-shaped image forming body. An image forming unit composed of a plurality of developing devices accommodating (yellow, magenta, cyan, black) is arranged, and these image forming units are arranged at regular intervals on a belt-shaped image forming body which rotates.

In recent years, an image forming apparatus using a laser writing unit has been widely used in which a laser beam modulated or flickered by a laser light source and output is rotationally scanned by a rotary polygonal mirror (polygon mirror) to perform scanning exposure on an image forming body. It is commonly used.

[0006]

A conventional color image forming apparatus has a plurality of photoconductors corresponding to respective colors of yellow (Y), magenta (M), cyan (C) and black (K). A corresponding color signal is formed with a modulated light beam to form a latent image, and the latent image is formed by color toner development of a developing unit corresponding to each color.

In this method, since variations in sensitivity and positional variations of a plurality of (generally four) photoconductors cannot be avoided, registration of a plurality of colors (Y, M, C, K) can be obtained. It was difficult.

Further, when the symmetrical optical system is used, the same line is written by a laser writing beam whose scanning directions are opposite to each other with respect to the writing method, and the main scanning directions of the respective beams are not parallel, so that the dots are accurately aligned. A dot shift in the sub-scanning direction occurs in areas other than the area to be scanned.

[0009]

SUMMARY OF THE INVENTION The present invention provides a color image forming apparatus which eliminates the difficulty of alignment due to the use of a plurality of photoconductors, and uses a symmetrical optical system to reduce the main scanning direction. It is an object of the present invention to provide a color image forming apparatus intended to reduce color misregistration in the sub-scanning direction due to generation of different laser beams.

The color image forming apparatus of the present invention which achieves the above object corresponds to a laser writing unit for irradiating a plurality of positions on one image forming body with a laser beam and each laser beam irradiation position by the writing unit. A plurality of charging units and a plurality of developing units form a superposed toner image on the image forming body, and by transfer and fixing,
In a color image forming apparatus for obtaining a multi-color or full-color image, the laser writing unit makes a plurality of laser beams incident on different planes of symmetry of one polygon mirror, and each laser reflected light is emitted in the opposite direction to form an image. The symmetric optical system for scanning the body is constructed, and the dot data of the exposure main scanning line written in different main scanning directions of the symmetric optical system is divided into a plurality of pieces of memory and stored in the memory means. By alternately writing the data before the line, the positional deviation of one line written in different main scanning directions in the sub-scanning direction is set to 1/2 dot or less.

The color image forming apparatus of the present invention is
A laser writing unit that irradiates a plurality of positions on one image forming body with laser light, a plurality of charging units and a plurality of developing units corresponding to the respective laser light irradiation positions by the laser writing unit, and a superimposed toner image. In a color image forming apparatus for forming a multi-color image or a full-color image by transferring and fixing the same on a photoconductor, the laser writing unit makes a plurality of laser beams incident on different planes of symmetry of one polygon mirror. A symmetrical optical system in which reflected laser light is emitted in the opposite direction and scans the image forming body, the polygon mirror is rotated at an integer (n) times the basic number of revolutions, and every 1 / n line. The dot data write signal is applied intermittently to reduce the deviation in the sub-scanning direction of one line written in different main scanning directions from 1 / n or less. And it is characterized in and.

[0012]

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 provided with a belt-shaped image forming body according to an embodiment of the present invention, and FIG. 2 is a schematic view of the belt-shaped image forming body and laser scanning exposure. 3 is a perspective view showing an optical system of the apparatus, FIG.
FIG. 4 is a plan view showing the positional relationship between the laser scanning exposure apparatus of this embodiment and the image forming body.

In FIG. 1, the color image forming apparatus of this embodiment has a plurality of chargers 11 around the belt-shaped image forming body 1.
0, 210, 310, 410, exposure scanning lines L1, L2, L3
L4 and developing device 13 loaded with four different color toners
Image forming means consisting of 0, 230, 330, and 430 are arranged, and the yellow, magenta, cyan, and black toner images are superposed by one rotation of the image forming body 1 to form a color image.

The belt-shaped image forming member 1 is a belt-shaped photosensitive member (hereinafter, referred to as a photosensitive member belt) in which a photoconductor is applied or vapor-deposited on a flexible belt, and the rotating roller 2 is used.
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.

Further, 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 and a scorotron charging device are used. It is 410.

The exposure means is a semiconductor laser writing unit (laser scanning exposure device) 120, and the charger 110,
The surface of the photoconductor belt 1 charged by 210, 310, 410 is exposed to form an electrostatic latent image.

The developing means is composed of four developing devices 130 each containing a developer of a different color, for example, a toner (developer) of each color of yellow (Y), magenta (M), cyan (C) and black (K). , 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, and is provided so as to clean the photosensitive belt 1 by pressing it against the surface of the photosensitive belt 1 only at the time of cleaning.

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 writing unit 120, a laser beam is emitted from the semiconductor laser 121 in the laser writing unit 120. Is generated. The laser beam is collimation lens 12
2, drive motor 124 through cylindrical lens 123
It is rotated and scanned by the polygon mirror 125 rotated by, and passes through the fθ lens 126, and is projected on the peripheral surface of the photoconductor belt 1 which is uniformly charged to a predetermined charge by the chargers 110 to 410 to form a bright line. ..

On the other hand, in the sub-scanning direction, the photosensor detects a registration mark corresponding to a specific position on the photoconductor belt 1, and the modulation of the semiconductor laser 121 by the image signal is started based on this detection signal. The main scan line is determined. When the scanning is started, a fixed position is detected by the laser beam in the main scanning direction, and the semiconductor laser 12 based on the image signal of the first color is detected based on the detected signal.
The modulation of 1 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 230 containing yellow toner, and a yellow toner image is formed on the surface of the photosensitive belt 1. 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 photosensitive 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. It is charged by 210 and then the photoconductor belt 1
The specific position of the
Modulation of the semiconductor laser of the laser writing unit 120 is started by the image signal of, and the laser light generated by the semiconductor laser is rotationally scanned by the polygon mirror rotated by the collimation lens drive motor, and the fθ lens,
After passing through the cylindrical lens, a latent image is formed by being projected onto the peripheral surface of the photosensitive belt 1 which is uniformly charged to a predetermined electric charge by the charger 210. 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 above-mentioned image signal of the second color, the charger 310 continues to remove the image. Charged, laser writing unit 120
A latent image is formed by the developer and contains cyan toner.
Develop at 330 to form a cyan toner image. Further, the photoconductor belt 1 on which the cyan toner image of the third color is formed is further conveyed and is uniformly charged by the charger 410 as in the case of the image signals of the second and third colors. A latent image is formed by the laser writing unit 120, and a black toner image is developed by the developing device 430 containing black toner.
Formed on the surface of. 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 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. 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 means 17, the paper is ejected from the apparatus main body by the paper ejection 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
Around the photosensitive belt 1, a plurality of chargers 110 to 410, an exposure device 120, and a developing device 1 in which four different color toners are loaded.
An image forming unit composed of 30 to 430 is arranged, and the photoreceptor belt 1
This is a so-called one-pass method in which the yellow, magenta, cyan, and black toner images are superposed in one rotation to form a color image. 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.

Next, adjustment (correction) of the laser writing unit 120 for each laser beam described above before image formation will be described.

As shown in FIGS. 2 and 3, the photosensitive belt 1 is provided with a reflecting member as a registration mark on the photosensitive member in the vicinity of a side end surface of the photosensitive surface of the photosensitive belt 1 outside the image area. The arrangement is such that the reflected light from is received by the light receiving sensors (reflection type photosensors) PS1, PS2, PS3 and PS4. This serves as a reference for determining the exposure start position in the main scanning direction and the sub-scanning direction by the laser beam, which will be described later, and a reference for detecting the deviation of the scanning lines L1, L2, L3, L4 in the main scanning direction.

The resist mark of the photosensitive belt 1 is formed on the transparent portion which transmits the laser beam or outside the photosensitive belt 1, and the guide member 4 is formed with a concave portion as shown in FIG. Light receiving sensor as light detecting means in the recess
By arranging PS11, PS12, PS13, and PS14, each color exposure light from the laser light source may be transmitted through the pre-pattern 1A and transmitted light may be detected by each of the light receiving sensors PS1 to PS4.

FIG. 4 is a partially enlarged perspective view showing the symmetrical optical system of the laser scanning exposure apparatus according to the first embodiment of the present invention. The exposure apparatus shown in the drawing shows one of the four series of four laser beams of this embodiment, which have almost the same structure. This embodiment will be described using one laser scanning exposure device 120.

The color printer of FIG. 1 has a compact design with a refracting optical system using a plurality of mirrors in order to reduce the scanning line interval of the exposure device.

The laser scanning exposure device 120 scans the photoconductor belt 1 with a laser beam from a laser light source by a deflector. For example, the laser light source 121 as shown in FIG.
A, Collimation lens 122A, Cylindrical lens 1
23A, polygon mirror (rotary polygonal mirror) 125A driven and rotated by a high-speed rotation motor 124, fθ lens 126A, mirror 12
It is a symmetric optical system composed of a first optical system made of 7A and a second optical system made of the above-mentioned optical components and arranged symmetrically with the first optical system.

Here, a second polygon mirror 125C is fixed coaxially with the polygon mirror 125A, and the second polygon mirror 125C is also fixed.
It is coaxially driven and rotated by 124.

The laser light modulated by the image signal and collimated by the collimation lens 122 is scanned by the rotary polygon mirror 125A (125B) rotated by the motor 124. The scanned laser light is reflected by the mirror 127, and the photosensitive belt 1
Then, the scanning line L1 is formed. The photoconductor belt 1 rotates at a low speed in the direction of the arrow in the figure to perform sub-scanning of the image.

The laser light emitted from the second laser light source 121 passes through the collimation lens 122B and the cylindrical lens 123B to become parallel laser light, which is scanned by the same rotary polygon mirror 125A as described above and passes through the fθ lens 126B. The light is reflected by the mirror 127B and guided to the photosensitive belt 1 to form a scanning line L4.

Here, the scanning line L4 is formed so that the scanning direction is opposite to that of L1.

In this case, the collimation lenses 122A and 12A
As shown in the figure, each laser beam is rotated by a polygon mirror 125A.
Are installed to irradiate different planes. For example, the rotating polygon mirror 125A shown in the figure is an octahedron, and in this case, it is installed so that it illuminates every other plane independently. In the case of a hexahedron or a tetrahedron, the adjacent surfaces are irradiated.

For the rotating polygon mirror 125B which is coaxial with the rotating polygon mirror 125A and is installed above the rotating polygon mirror 125A, an optical system substantially similar to the above-mentioned symmetrical optical system is used to scan line L2.
L3 is formed. Here, the scan line L2 is formed in the same direction as the above L1, and the scan line L3 is formed in the same direction as L3S and L2.
Is the opposite of.

In this case, the scanning line L1 is for yellow,
L2 is a magenta line, L3 is a cyan bright line, and L4 is a black bright line, which is visualized by the color toners of the corresponding developing devices 130, 230, 330, and 430.

Further, as can be understood from the figure, the scanning lines L1 and L4, L2 and L3 on the photosensitive belt 1 are opposite in the main scanning direction, so that one scanning line to a few scanning lines of electricity are consumed. The color image signals are input to the laser drive circuit through the memory so that the output order of the color image signals for each line is reversed.

Next, the correction operation for detecting the deviation of the laser beam in the main scanning direction and the sub scanning direction using the light receiving sensors PS1 to PS4 provided in the vicinity of the photosensitive belt 1 according to the present invention and correcting these deviations. Will be described.

FIG. 5 is a block diagram of main scanning exposure correction for preventing deviation of the laser beam in the main scanning direction.

Here, the sub-area counter is a counter that shifts the sub-scanning direction, the main area counter is a counter that moves the main-scanning direction, and the main count setting unit is the timing from the reference detection value of the pre-pattern 1A to the start of image writing. Is the part to set.

A plurality of (four in the figure) writing laser light irradiates the pre-pattern 1A on the photosensitive belt 1 during scanning, and the reflected light is received by the light receiving sensors PS1, PS2, PS.
3, The position of the photoconductor is detected by receiving light at PS4.

The symmetric optical system for the purpose of downsizing and cost reduction of the writing unit has two rotary polygon mirrors.
Two laser beams are emitted. When this is used, the main scanning lines L1 and L4, and L2 and L3 of each laser beam are reversed, so that the pre-pattern 1A is necessary near both end faces of the photosensitive belt 1. .. This makes it difficult to increase the manufacturing cost and secure the accuracy of the distance between the two pre-patterns 1A formed on both end faces, and it is not possible to perform highly accurate color shift correction.

Therefore, in the present invention, the number of light receiving portions is one for one exposure portion, and the scanning laser light starts image writing after a certain timing dT has elapsed after detection of light reception (scan lines L1 and L2 in FIG. 2). (Of FIG. 5).

The scanning lines L3 and L4 of the laser light scanning from the direction opposite to the light receiving detector are based on the signals detected by the light receiving sensors PS3 and PS4 during the previous scanning (T ₁
-T _w -dT) has elapsed, and the FIFO method (First In First Out)
System) memory image signal is written (scan lines L3 and L4 in FIG. 3, and FIG. 5).

Here, D is the dot density (dots per inch), V _p is the linear velocity of the photosensitive belt (mm / sec), and W
Is the image area width (mm), the scanning time for one line is T ₁ = 25.4 / (D × V _P ) and the image area sub-scanning time is T _W = W / (25.4 / D).

Further, by using the light receiving sensors PS1 to PS4, the light receiving sensor can be installed at a position close to the surface of the photoconductor belt 1 and only needs to be installed on one end surface side of the photoconductor belt 1. The space for the sensor can be minimized. The light receiving sensor is not limited to the detection of reflected light of laser light, but may be detection of transmitted light.

FIG. 6 is a diagram showing the entire construction of a color copying machine having a photosensitive belt 11 having a light-transmitting resist mark formed thereon and an image reading system A on the upper portion thereof as another embodiment of the present invention. In the figure, parts having the same functions as those in the above embodiment are designated by the same reference numerals. Further, the points different from the above embodiment will be described.

A light-transmissive resist mark (not shown) is formed in the vicinity of the side end surface of the photoconductor belt 11 outside the image area, at substantially the same position as the resist mark, so that light can be transmitted. On the other hand, the guide member 4 has a concave portion formed at a position where the registration mark and each of the main scanning lines L1, L2, L3, L4 intersect, and the light receiving sensors PS11, PS12, PS13, and PS14 is arranged respectively. The light receiving sensors PS11 to PS14 detect passage of the exposure scanning laser light from the exposure device 120 through the transmissive resist mark.

The dot line formation by laser light exposure scanning of the color image forming apparatus of this embodiment will be described below with reference to FIGS.
It will be explained based on.

FIG. 7 is a schematic diagram for explaining the conventional dot line formation.

In FIG. 7A, the exposure main scanning direction is set to be orthogonal to the conveyance direction (sub-scanning direction) X of the photoconductor belt 1 with the photoconductor belt 1 being stationary, and then the photoconductor is exposed. When the body belt 1 is conveyed, each of the exposure main scanning lines L1 to L4 forms a line inclined by the combined speed of the linear speed of the photosensitive belt 1 and the laser beam scanning speed.

Laser writing unit 120 according to the present invention
Uses a symmetric optical system for the purpose of compactness and low cost, and the scanning direction of each color laser beam is different. That is, as shown in FIGS. 2 and 3, the exposure main scanning line L1 by one polygon mirror 125A of the symmetric optical system.
The writing directions of L4 and L4 are opposite to each other. The writing directions of the exposure main scanning lines L2 and L3 by the other polygon mirror 125B are also opposite to each other as shown in FIG. 6 (A).

As described above, the scanning lines L1 to L4 are not parallel to each other in the main scanning direction, and the scanning lines L1 and L4 and L2 and L3 whose scanning directions are opposite to each other with respect to the writing direction are respectively combined to form a color image. When forming, FIG. 7 (B)
As shown in (3), the dot shift occurs in the sub-scanning direction except in the area where the dots exactly match. That is, even if the registrations are matched at the central portions of the scanning lines L3a and L2a, at least one dot (one line) is displaced in the sub-scanning direction X at both end portions of each scanning line, resulting in color misregistration.

FIG. 8 is a schematic diagram showing dot line formation according to the first embodiment of the present invention, and FIG. 9 is a flow chart showing the process.

(1) First, the scanning line timing is detected by the light receiving sensors provided near both ends of the photosensitive belt 1, and the inclination angle θ of the scanning line is detected by the CPU by the detection of the scanning line timing and the surface speed of the photosensitive belt 1. Calculate by

(2) Next, the number of divisions of the scanning line of each color and the writing memory area are calculated and converted into the writing memory of one line. Here, the data in the memory of one line (for example, L2b) to be written in the forward direction is divided into two and divided into one.
The data before the line (for example, L2a) is written alternately.
Further, the data of the memory of one line (for example, L3b) in the reverse direction is divided into four and written alternately with the data of one line before (for example, L3a).

(3) When each scanning line is divided and exposed in this way, and then developed for each color and superimposed, FIG.
As in (B), the dots of the color image overlap, and the positional deviation of one line to be written in the sub-scanning direction can be corrected. At this time, by aligning the registration of the central portion of the image in the main scanning direction, the positional deviation in the sub scanning direction X is minimized and the maximum is 1/2 dot.

In the scan line division, the positive direction is 4
The same result can be obtained by writing as divided and divided into two.

FIGS. 10A and 10B are schematic views showing the second embodiment of the present invention.

The scanning lines L1 to L4 of each laser beam on the image forming surface of the photosensitive belt 1 during image formation generally have an inclination angle θ.
Becomes Here, when the polygon mirrors 125A and 125B are rotated at n (integer) times the reference rotation speed, the inclination angle θ becomes θ / n, and the dot shift in the sub-scanning direction X is improved. At the same time, by temporarily storing data at a ratio of 1 / n (delay memory) and intermittently supplying a write signal, an image is written without excess or deficiency. The pulse width of the laser beam, the exposure amount, and the like are also the integer n.
It is necessary to change along with.

At this time, by aligning the registration of the central portion of the image in the main scanning direction, the positional deviation in the sub scanning direction X is minimized, and the maximum is 1 / n dot.
Note that FIG. 10 shows a state of n = 2, and the dot shift in the sub-scanning direction at this time is 1/2 dot. Where n = 2
, Every other line is written, and when n = 3, every two lines are written, and the dot shift at this time is 1/3.
Becomes In general, when the number is n times, writing is performed every (n-1), and the dot shift is accommodated in 1 / n dot.

[0071]

As described above, the laser writing unit in the color image forming apparatus of the present invention has the dot of each color in the sub-scanning direction which is one of the most important factors for determining the recording image quality at the time of color image formation. The registration of the image is easily and accurately performed, color misregistration is prevented, and an excellent effect of forming a high-quality image is obtained. In particular, the present invention provides an extremely effective means in the exposure scanning writing unit of the color image forming apparatus of the superposition method including the electrophotographic method.

[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 of a laser scanning exposure apparatus of the color image forming apparatus of the present invention.

FIG. 3 is a plan view showing a positional relationship between the laser scanning exposure device and an image forming body.

FIG. 4 is a partially enlarged perspective view of a laser scanning exposure apparatus.

FIG. 5 is a control block diagram of the laser scanning exposure apparatus.

FIG. 6 is an overall configuration diagram of another embodiment of the color image forming apparatus according to the present invention.

FIG. 7 is a schematic diagram illustrating conventional dot line formation.

FIG. 8 is a schematic diagram showing dot line formation according to the first embodiment of the present invention.

FIG. 9 is a flowchart showing a color image forming process according to the present invention.

FIG. 10 is a schematic diagram showing dot line formation according to a second embodiment of the present invention.

[Explanation of symbols]

 1, 11, 12 Belt-shaped image forming body (photoconductor belt) 110, 210, 310, 410 Charging device 130, 230, 330, 430 Developing device 120 Laser scanning exposure device (laser writing unit) 121A, 121B Laser light source 125A, 125B polygon mirror (rotary polygonal mirror) 126A, 126B fθ lens 127A, 127B mirror L1, L2, L2a, L2b exposure main scanning line L3, L3a, L3b, L4 exposure main scanning line PS1, PS2, PS3, PS4 photo sensor Sensor) PS11, PS12, PS13, PS14 Light receiving sensor (photo sensor) PS21, PS22, PS23, PS24 Light receiving sensor (photo sensor) W Image area width X Sub scanning direction θ Scan line inclination angle

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G03G 15/01 112 A 7818-2H 15/04 116 9122-2H H04N 1/04 D 7251-5C ( 72) Inventor Tadashi Miwa 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (6)

[Claims] 1. A laser writing unit for irradiating a plurality of positions on one image forming body with a laser beam, a plurality of charging units corresponding to respective laser beam irradiation positions by the writing unit, and a plurality of developing units. In a color image forming apparatus for forming a superposed toner image on an image forming body to obtain a multi-color or full-color image by transferring and fixing, the laser writing unit has a plurality of polygon mirrors arranged on different planes of symmetry. A symmetric optical system in which a laser beam is incident and each reflected laser beam is emitted in the opposite direction to scan on the image forming body, is formed of an exposure main scanning line written in different main scanning directions of the symmetric optical system. By storing dot data divided into a plurality of pieces in the memory means and writing the data of the line and the data of the previous line alternately 1/2 1 registration error in the sub-scanning direction of the line to be written in different main scanning direction
A color image forming apparatus characterized by having dots or less. 2. The color image forming apparatus according to claim 1, wherein the laser light of the writing unit corresponds to four colors of yellow, magenta, cyan, and black. 3. The color image forming apparatus according to claim 1, wherein the image forming body is an endless belt-shaped photoconductor. 4. A laser writing unit for irradiating a plurality of positions on one image forming body with laser light, a plurality of charging units and a plurality of developing units corresponding to respective laser light irradiation positions by the laser writing unit, In a color image forming apparatus for forming a superposed toner image on a photoconductor and obtaining a multi-color or full-color image by transfer and fixing, the laser writing unit includes a plurality of laser beams on different symmetrical planes of one polygon mirror. Is formed, and each laser reflected light is emitted in the opposite direction to scan on the image forming body, and the polygon mirror is rotated by an integer (n) times the basic number of rotations. A dot data write signal is intermittently applied every n lines, and the deviation in the sub-scanning direction of one line written in different main scanning directions is set to 1 A color image forming apparatus having a ratio of / n or less. 5. The color image forming apparatus according to claim 4, wherein the laser light of the writing unit corresponds to four colors of yellow, magenta, cyan, and black. 6. The color image forming apparatus according to claim 4, wherein the image forming body is a photoconductor on an endless belt.