JPH0580631A - Color image forming device - Google Patents

Abstract

PURPOSE:To easily and accurately realize the alignment of the dots of respective colors in a main scanning direction in a color image forming device, to prevent color slurring and to form a high-quality image. CONSTITUTION:A laser write unit is a symmetric type optical system which makes plural laser beams incident on the different symmetric surfaces of one polygon mirror 125A and 125B so that reflected laser beams are projected in an opposite direction and perform scanning on an image forming body. A pre-pattern 1A provided on one side of a photosensitive body with respect to the main scanning direction is irradiated with the write laser beams and reflected light beams are received by photosensors PS1-PS4, which output a pre-pattern position detection signal. The laser beam which performs write from the direction of the pre-pattern 1A outputs a write start timing signal in the middle of the same scanning as the pre-pattern detection signal, and the laser beam which performs write from the opposite direction to the pre- pattern 1A receives the pre-pattern detection signal one before and calculates the write start timing of next scanning to output a signal, then they respectively receive write start timing signals and start the write of the image.

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.
Next, of 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.

[0005]

In a color image forming apparatus, for example, a resist mark is formed on an image forming body, the resist mark is detected by a sensor, and a plurality of aligners are sequentially arranged based on the detection. It is conceivable that the latent image formation is started from the same point on the image forming body by starting the exposure.

However, in the color image forming apparatus described above, a single sensor or a plurality of sensors is used to read the registration mark formed on the belt-shaped image forming body and determine the timing to start the exposure from each exposure apparatus. However, in this method, it is necessary to position the interval between the sensor and the exposure device and the arrangement interval of the plurality of exposure devices with strict accuracy (about ± 0.01 to 0.1 mm). It was difficult to position the array interval with mechanical accuracy (the limit is ± 0.3 to 0.5 mm at the time of filing of the present application). Furthermore, when the exposure apparatus is removed for maintenance or the like, it is extremely difficult to set the exposure apparatus at the same position again.

Further, in the color image forming apparatus for forming the color toner image by superposing the toner images on the image forming body as described above, the exposure start position on the belt-shaped image forming body is set from a plurality of exposing devices. Has a problem that the image quality of the color toner image is deteriorated when the deviation cannot be set in a unit of one pixel, for example, about 80 μm or less. In particular, when the belt-shaped image forming body is used, it is difficult to perform the alignment control as compared with the drum-shaped image forming body.

Further, a dedicated sensor for position detection is used to form a pattern image previously provided on an image forming body (photoreceptor) or a transfer body, or a toner image on the photoconductor or the transfer body. The method of detecting this was taken. This is because a dedicated sensor is installed to control the space,
Although it is disadvantageous in terms of cost, sufficient alignment cannot be obtained, and the image quality is significantly deteriorated.

As a writing optical system, an optical system described in Japanese Patent Laid-Open No. 58-95361 is known for the purpose of compactness. In this case, a laser in which the scanning direction is opposite to the writing direction is used. Since it has light, a pattern image on the photoconductor or the transfer body is required on both sides in the scanning direction.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a variation in the mounting position of an image forming body in a writing unit of a color image forming apparatus, a shift in the writing position due to a temperature change, and an image formation. It is possible to correct the color misregistration in the main scanning direction of the laser light due to the movement in the thrust direction and the meandering when the body rotates, without positioning with strict mechanical accuracy.
An object of the present invention is to provide a color image forming apparatus intended to prevent color misregistration by preventing the exposure start point for forming a latent image from shifting when the latent image formation is repeated a plurality of times.

In the color image forming apparatus of the present invention which achieves the above object, a plurality of laser writing units for irradiating a plurality of positions on one image forming body with a laser beam, and irradiation positions of the respective laser beams by the writing unit. In the color image forming apparatus, a multi-color or full-color image is obtained by forming a superposed toner image on the image forming body by a plurality of charging units and a plurality of developing units corresponding to the above, and the laser writing unit. Is a symmetric optical system in which a plurality of laser beams are incident on different symmetry planes of one polygon mirror, and each laser reflected light is emitted in the opposite direction to scan on the image forming body. Pre-pattern provided on one side of the photoconductor is irradiated with writing laser light and reflected light is received by the light-receiving sensor to detect pre-pattern position Laser beam for writing from the direction of the pre-pattern emits a writing timing signal during the same scanning as the pre-pattern detection signal, and the laser beam for writing from the direction opposite to the pre-pattern receives the preceding pre-pattern detection signal. The writing start timing of the next scan is calculated, a signal is issued, and the writing start timing signal is received to write the image.

The color image forming apparatus of the present invention is
A plurality of laser writing units that irradiate a plurality of positions on one image forming body with a laser beam, a plurality of charging units corresponding to the irradiation positions of the respective laser beams by the writing unit, and a plurality of developing units, so that they are superposed. In a color image forming apparatus for obtaining a multi-color or full-color image by forming a toner image on a photosensitive member and transferring and fixing the toner image, the laser writing unit shares one polygon mirror with a plurality of laser beams, Is a symmetric optical system that emits light in the opposite direction to scan on the photoconductor, and irradiates a pattern made near one side on the photoconductor with writing laser light in the main scanning direction, and receives reflected light as a light receiving sensor. The pattern light that is received by the light source, emits the pattern position detection signal, and writes from the pattern direction. Emits a ring signal, a laser beam to write the opposite direction to the pattern, in response to one previous pattern detection signals, calculates the write timing of scan, after counting,
It is characterized in that a write-out timing signal is issued, and the write-out timing signal is received to write out an image.

[0013]

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
An image forming means composed of 0, 230, 330, and 430 is 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 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, and the rotary 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 exposing means, four developing means loaded with toners of different colors, a transferring 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 chargers 110, 210, 310 such as a corona charger and a scorotron charger are provided. It is 410. The exposure means is a semiconductor laser writing unit (laser scanning exposure device) 120, which exposes the surface of the photoreceptor belt 1 charged by the chargers 110, 210, 310, 410 to form an electrostatic latent image.

The developing means includes different color developers such as yellow (Y), magenta (M), cyan (C) and black (K).
The four developing devices 130, 230, 330 and 430 respectively contain the toners (developers) of the respective colors. Each of these developing units 130-430
Has a function of developing an 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 photoreceptor belt 1 and does not hinder the movement of the photoreceptor belt 1, thus obtaining a good color image. You can

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 that the photosensitive belt 1 is cleaned by being pressed against the surface of the photosensitive belt 1 only during 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 photosensitive 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 has a linear pre-pattern 1A formed beforehand by printing or the like in the vicinity of a side end surface of the photosensitive surface of the photosensitive belt 1 outside the image area. It is provided substantially parallel to the side end surface.
The pre-pattern 1A serves as a reference for determining an exposure start position in the main scanning direction and the sub-scanning direction by a laser beam, which will be described later, and a reference for detecting a deviation of the scanning lines L1, L2, L3, L4 in the main scanning direction.

The pre-pattern 1A and the scanning line L
1, above each position where L1, L2, L3 and L4 intersect (Fig. 2
(Refer), the light receiving sensor (reflection type photo sensor) PS
1, PS2, PS3, PS4 are provided respectively, and the pre-pattern 1A by the main scanning writing system beam of laser light is provided.
Reflected light of the light receiving sensors PS1, PS2, PS3, P
The light is received in S4.

Further, the pre-pattern 1A of the photosensitive belt 1 is formed in a transparent portion which transmits laser light, and the guide member 4 is formed with a concave portion as shown in FIG. 6, and the concave portion receives light as a light detecting means. Sensors PS11, PS12, PS13, P
By disposing S14, the exposure light of each color from the laser light source may be detected by the light receiving sensors PS1 to PS4 as the transmitted light through the pre-pattern 1A.

FIG. 4 is a partially enlarged perspective view showing a 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, a collimation lens 122A, a cylindrical lens 123A, a polygon mirror (rotary polygon mirror) 125A driven and rotated by a high-speed rotation motor 124, an fθ lens 126A, and a mirror 127A, and a first optical system. It is a symmetrical optical system including a second optical system which is symmetrically arranged and includes the above-mentioned optical components. Here, a second polygon mirror 125C is fixed coaxially with the polygon mirror 125A, and is similarly driven and rotated by a motor 124.

The laser light modulated by the image signal and made into parallel light by the collimation lens 122 is scanned by the rotary polygon mirror 125A (125B) rotated by the motor 124. The scanned laser beam is reflected by the mirror 127, irradiates the photosensitive surface of the photosensitive belt 1 and forms a scanning line L1. 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 the fθ lens 126B.
Then, the light is reflected by the mirror 127B and guided to the photoconductor belt 1 to form the scanning line L4. Here, the scanning line L4 is formed so that the scanning direction thereof is opposite to that of the scanning line L1.

In this case, the collimation lenses 122A and 1
As shown in the figure, each laser light is rotated by the rotating polygon mirror 12.
It is installed so that each plane of 5A is irradiated. 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.

Also for the rotary polygon mirror 125C which is coaxially installed with the rotary polygon mirror 125A and rotates above the rotary polygon mirror 125A, an optical system substantially similar to the above-mentioned symmetrical optical system is used to scan line L.
2 and L3 are formed. Here, the scanning line L2 is the L1
And the scan line L3 is in the same direction as L3 but in the opposite direction to L2.

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

Further, as understood from the figure, since the main scanning directions of the scanning lines L1 and L4 and L2 and L3 on the photoconductor belt 1 are opposite to each other, the electric lines for one to several lines of scanning are electrically charged. The color image signals are input to the laser drive circuit via 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 using the pre-pattern 1A provided on the photosensitive belt 1 according to the present invention and correcting the deviation 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 sets the timing from the reference detection value of the pre-pattern 1A to the start of image writing. It is a part.

A plurality of (four in the figure) writing laser light illuminates the pre-pattern 1A on the photosensitive belt 1 during scanning, and the reflected light thereof is received by the light receiving sensors PS1 and PS.
The position of the photoconductor is detected by receiving light at 2, PS3 and PS4.

A symmetrical optical system for the purpose of downsizing and cost reduction of a writing unit has two rotary polygon mirrors.
Two laser beams are emitted. When this is used, the main scanning lines L1 and L4, L2 and L3 of the laser beams are reversed, so that the pre-pattern 1A is necessary near both end faces of the photosensitive belt 1. .. This increases the manufacturing cost and makes it difficult to 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 misregistration correction.

Therefore, in the present invention, the pre-pattern 1A is provided at one location, and the laser light scanned from the pre-pattern side is
After the detection of the pre-pattern 1A, a predetermined timing dT has elapsed, and image writing is started (scan lines L1 and L2 in FIG. 2, and in FIG. 5).

The scanning lines L3 and L4 of the laser beam scanning from the direction opposite to the pre-pattern 1A are (T ₁ -Tw-dT) after the lapse of (T ₁ -Tw-dT) with reference to the signals detected by the light receiving sensors PS3 and PS4 during the previous scanning. , FIFO method (First
In First Out System) image signals from the memory are written (scan lines L3 and L4 in FIG. 3, and in FIG. 5).

Here, D is the dot density (dots per inch), Vp is the linear velocity of the photosensitive belt (mm / sec),
When W is the image area width (mm), the scanning time for one line is T ₁ = 25.4 / (D × Vp), and the image area width scanning time is Tw = W / (25.4 / D).

Since the time required for writing one scanning line is extremely short and the position of the photosensitive belt 1 is deviated during that period, the color misregistration in the main scanning direction can be minimized.

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.

The operation of the color image forming apparatus of this embodiment will be described below with reference to FIGS.

When the power is turned on, the photosensitive belt 1 rotates the two rotating rollers 2 and 3 in the clockwise direction at a constant velocity of about 1/5 of the constant linear velocity at the time of image formation to rotate the photosensitive belt 1 in the sub-scanning direction X. Transport to.

The laser scanning exposure device 120 corrects the deviation in the sub-scanning direction by preliminarily performing processing in the sub-scanning correction circuit and shaking the housing accommodating the exposure device 120 in the sub-scanning direction, and then waits. Enter the state.

During printing, the surface of the photoconductor is uniformly charged by the charger 110 while moving the photoconductor belt 1 at the image forming speed. Immediately before the exposure from the exposure device 120,
The pre-pattern 1A is detected by the light receiving sensor PS1 and the detection signal is used to correct the deviation in the main scanning direction,
Image exposure for one line L1 is performed. That is, the exposure device 12
0 means that the deviation in the main scanning direction on the photoconductor belt 1 is detected after a preset time has elapsed after the detection of the pre-pattern 1A, and the deviation is corrected to irradiate the laser beam, so that the photoconductor belt is always Image exposure is started from a predetermined position of 1.

Thereafter, exposure scanning is performed based on the yellow data for one screen. As a result, a latent image is formed at a predetermined position on the photoconductor belt 1. The latent image is developed by the developing device 130 with yellow toner.

Next, in the image formation based on magenta data, cyan data and black data, the main scanning correction circuit detects the deviation of each exposure device on the photoconductor belt 1 in the main scanning direction, and corrects it. At the same time, after correcting the deviation in the sub-scanning direction, the exposure is started from the exposure device 120 after a preset time elapses, and the exposure is always started from a predetermined position of the photoconductor belt 1, so that a plurality of exposure devices can be set. Even if the positioning is not performed with strict mechanical accuracy, it is possible to prevent the deviation of the exposure start point for forming the latent image when the latent images are repeatedly formed according to the number of colors, thereby preventing the color shift.

The main scanning width adjustment (dot clock adjustment) is preferably performed after correcting the deviation in the sub-scanning direction before the standby state. Further, subsequently, the writing start position in the main scanning direction may be set before the standby state.

FIG. 6 is an overall configuration diagram of a color copying machine having a photosensitive belt 11 on which a light-transmitting pre-pattern is formed and having an image reading system A on the upper portion as a second 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 translucent pre-pattern (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 pre-pattern 1A so that light can be transmitted. On the other hand, the guide member 4 has a concave portion formed at a position where the pre-pattern and each of the main scanning lines L1, L2, L3, L4 intersect, and the light receiving sensors PS11, PS12, PS13, as light detecting means are formed in the concave portion. PS14 is arranged respectively. The light receiving sensors PS11 to PS14 detect the passage of the exposure scanning laser light from the exposure device 120 through the translucent pre-pattern.

Next, the color image forming apparatus of the third embodiment will be described. FIG. 7 is a perspective view of a laser scanning exposure apparatus of the present invention, and FIG. 8 is a block diagram of main scanning correction for preventing deviation of laser light in the main scanning direction. When the reference numerals used in the embodiments described below are the same as those used in the first embodiment, they have the same configurations and functions as those of the first embodiment unless otherwise specified. ..

By the laser beam of the laser scanning exposure device 120, a latent image of the exposure scanning line L1 is formed on the surface of the photoreceptor belt 12 which is charged in advance, and prior to this, the latent image of the reference line 12A is formed in the vicinity of the end face of the non-image area. An image is formed. The reference line 12A
Is developed by the first developing device 130 and is the reference line 12A of the visible image.
To form. PS21 is a beam detector (light receiving sensor)
That is, the laser beam incident from the rotary polygon mirror 125A through the fθ lens 126A is received, an output signal is emitted, and a beam detect signal having a rectangular wave shape based on an arbitrary set value is output by the beam detect detection circuit.

A plurality of (usually three) writing system beams downstream from the main scanning line L1 irradiate the visualized reference line 12A during scanning, and the reflected light thereof is received by the light receiving sensors PS22 and PS23, respectively. , PS24 receives light to detect and control the thrust direction start position of the photosensitive belt 1.

In general, a symmetrical optical system for the purpose of downsizing and cost reduction of a laser writing unit, that is, an optical system which irradiates two surfaces of one rotating polygon mirror with laser light and emits reflected light in symmetrical directions. When the system is used, the scanning directions of the respective laser lights (L1 and L4, L2 and L3) are opposite to each other, and therefore the reference line 12A after development is required on both end surfaces of the photosensitive belt 12. This results in unnecessary consumption of toner, a risk of toner scattering and contamination, and a large size in the width direction of the developing device, the photoconductor belt, and the cleaning device.

Therefore, only one reference line 12A is provided on one side of the photosensitive belt 12, and the scanning line L2 is written after a certain timing dT has elapsed after the detection of the reference line 12A, as in the first embodiment. And start with the baseline
The scanning lines L3 and L4 that scan from the direction opposite to 12A are
The image signal from the FIFO type memory is written after (T ₁ -Tw-d) has elapsed with reference to the signal obtained by detecting the reference line 12A in the previous scan.

In the present embodiment, the arrangement order of the toner colors of the developing devices 130 to 430 is not limited to Y, M, C, K, and for example, to facilitate the detection of the first reference line 12A. The first developing device 130 may be loaded with black toner.

Further, in the present embodiment, first, after arranging each laser writing unit 120 with ordinary mechanical accuracy (± 0.3 to 0.5 mm), the focus of the laser beam is adjusted and one scanning width unit is set. Alternatively, it corrects a slight deviation in a unit of one dot width and finely adjusts each scanning line to form an image even if the rotating photosensitive belt causes meandering or movement in the thrust direction. In particular, it is particularly effective in color image formation in which images are superposed.

[0070]

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 main scanning direction which is one of the most important factors for determining the recording image quality at the time of color image formation. It is possible to realize the position alignment of (2) easily and with high accuracy, prevent color misregistration, and form an excellent effect of forming a high-quality image. 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 showing a first embodiment of a laser scanning exposure device of a 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 the laser scanning exposure apparatus according to the first embodiment.

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

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

FIG. 7 is a perspective view of a laser scanning exposure apparatus according to a third embodiment of the present invention.

FIG. 8 is a control block diagram of the laser scanning exposure apparatus.

[Explanation of symbols]

1,11,12 Belt-shaped image forming body (photosensitive belt) 1A Pre-pattern 2,3 Rotating roller 4 Guide member 12A Reference line 14 Transfer means (transfer device) 15 Cleaning means 17 Fixing means 18 Paper discharge roller 110,210,310,410 Charger 120 Laser scanning exposure device (laser writing unit) 121A, 121B Laser light source 125A, 125C Polygon mirror (rotary polygon mirror) 126A, 126B fθ lens 127A, 127B mirror 130,230,330,430 Developer 161 Paper cassette L1, L2, L3, L4 Exposure scanning Line PS1, PS2, PS3, PS4 Light receiving sensor (photo sensor) PS11, PS12, PS13, PS14 Light receiving sensor (photo sensor) PS21, PS22, PS23, PS24 Light receiving sensor (photo sensor) W Image area width

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Matsuoka 2970 Ishikawacho, Hachioji City, Tokyo Konica Stock Company

Claims (6)

[Claims] 1. A plurality of laser writing units 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 the irradiation positions of the respective laser lights by the writing unit. In the color image forming apparatus, in which a superimposed toner image is formed on the image forming body and a multi-color or full-color image is obtained by transfer and fixing, the laser writing unit is provided on different symmetrical planes of one polygon mirror. A pre-pattern provided on one side of the photoconductor in the main scanning direction, which is a symmetrical optical system in which a plurality of laser beams are incident and each laser reflected beam is emitted in the opposite direction to scan the image forming body. Irradiate with writing laser light,
The laser light that receives the reflected light with the light receiving sensor and outputs the pre-pattern position detection signal and writes from the pre-pattern direction emits the write timing signal during the same scan as the pre-pattern detection signal, and the laser light that writes from the opposite direction to the pre-pattern ,
A color image forming apparatus, which receives a pre-pattern detection signal one line before, calculates a writing timing for the next scanning, issues a signal, and receives an writing timing signal to write an image. 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 photosensitive body. 4. A plurality of laser writing units 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 the irradiation positions of the respective laser lights by the writing unit. In the color image forming apparatus for forming a multi-colored or full-color image by forming a superposed toner image on a photoconductor by transfer and fixing, the laser writing unit includes a plurality of lasers on different symmetric planes of one polygon mirror. Is a symmetric optical system in which the laser light of (1) is incident and the reflected light of each laser is emitted in the opposite direction to scan on the photoconductor, and a writing laser on the most upstream side of the image forming body in the main scanning direction. The developing device forms a development pattern on a non-image forming portion near one end of the image forming body, and the development pattern is formed on a plurality of writing layers downstream. Laser light that irradiates with light, receives reflected light with a light receiving sensor, emits a pattern position detection signal, and writes from the pattern direction.The laser light emits a write timing signal during the same main scanning as the pattern detection signal and writes from the direction opposite to the pattern. The light is characterized by receiving the pattern detection signal of the previous line, calculating the writing timing of the main scanning, counting, and then issuing the writing timing signal, and receiving the writing timing signals respectively to write the image. Image forming apparatus. 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 an endless belt-shaped photosensitive body.