JP3023722B2 - Color image forming equipment - Google Patents

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 JP-A-60-767
No. 66, No. 60-95456, No. 60-95458, No. 60-158475, the latent image formation and development according to the number of separation colors of the original image on the image forming body are performed. There is a method in which a color toner image is repeatedly obtained by superimposing a color toner image on an image forming body and then transferring the same.

A color image forming apparatus to which an image forming method in which a latent image is repeatedly formed and developed in accordance with the number of separated colors of a document image read by a color scanner on the image forming body is applied. An exposure apparatus and a development apparatus corresponding to the number of separation colors (for example, three colors of yellow, magenta, and cyan or four colors including black) are arranged around a formed body. As a second example, a drum-shaped image formed body Are provided with an exposure device and a development device according to the number of colors.
Next, 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. By rotating while maintaining the contact state, the belt-shaped image forming body is always conveyed while being kept at a constant position.Around the belt-shaped image forming body, a charger, an exposure device, and color toners of different colors are provided. (Yellow, magenta, cyan, black), and an image forming means comprising a plurality of developing units, and these image forming means are arranged at a fixed interval on a belt-shaped image forming body which rotates.

[0005]

In a color image forming apparatus, for example, a registration mark is formed on an image forming body, the registration mark is detected by a sensor, and a plurality of exposure apparatuses are sequentially arranged based on the detection. By starting exposure, latent image formation may be started from the same point on the image forming body.

However, in the above color image forming apparatus, it is assumed that a single sensor or a plurality of sensors reads a registration mark formed on a belt-shaped image forming body and determines the timing of starting exposure from each exposure device. However, in this method, it is necessary to position the interval between the sensor and the exposure apparatus and the arrangement interval of the plurality of exposure apparatuses with strict accuracy (about ± 0.01 to 0.1 mm). It has been difficult to position the arrangement interval with mechanical accuracy (at the time of filing the present application, the limit is about ± 0.3 to 0.5 mm). Further, when the exposure apparatus is removed for maintenance or the like, it is extremely difficult to set the same position again.

In a color image forming apparatus for forming a color toner image by superposing a toner image on an image forming body as described above, an exposure start position on the belt-shaped image forming body is determined by a plurality of exposing devices. In the case where the shift cannot be set to a pixel unit of, for example, about 80 μm or less, there is a problem that the image quality of the color toner image is deteriorated. In particular, when a belt-shaped image forming body was used, it was difficult to control the alignment as compared with a drum-shaped image forming body.

In addition, a dedicated sensor is used for position detection to form a pattern image previously provided on an image forming body (photoreceptor), a transfer body, or a toner image on a photoreceptor or transfer body. A method for detecting this has been adopted. This is because space is controlled by providing a dedicated sensor for control.
Despite being disadvantageous in terms of cost, sufficient alignment could not be obtained, and image quality was significantly reduced.

As a writing optical system, an optical system described in Japanese Patent Application Laid-Open No. 58-95361 is known for the purpose of compactness. In this case, a laser whose scanning direction is reversed with respect to the writing direction is used. Due to the presence of light, a pattern image on a photosensitive member or a transfer member is required on both sides in the scanning direction.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and has been made in consideration of the above-described problems. Corrects color misregistration in the main scanning direction of laser light due to movement in the thrust direction or meandering at the time of body rotation, without having to perform positioning with strict mechanical accuracy.
An object of the present invention is to provide a color image forming apparatus for preventing a shift of an exposure start point for forming a latent image when a latent image is repeatedly formed a plurality of times, thereby preventing a color shift.

A color image forming apparatus according to the present invention, which achieves the above object, comprises 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 each laser beam by the writing unit. A plurality of charging units and a plurality of developing units corresponding to each other, forming a superimposed toner image on the image forming body, and transferring and fixing the multi-color or full-color image in the color image forming apparatus; 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 beam is emitted in the opposite direction to scan on the image forming body. The pre-pattern provided on one side of the photoreceptor is irradiated with writing laser light, and the reflected light is received by the light receiving sensor to detect the pre-pattern position The laser light to be written from the pre-pattern direction emits a writing timing signal during the same scan as the pre-pattern detection signal, and the laser light to be written from the opposite direction to the pre-pattern detection signal receives the immediately preceding pre-pattern detection signal. , A write timing for the next scan is calculated, a signal is issued, and an image is written in response to each write timing signal.

Further, a color image forming apparatus according to the present invention comprises:
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 corresponding to the irradiation positions of each laser light by the writing unit, and a plurality of developing units are superimposed. In a color image forming apparatus that forms a multicolor or full-color image by forming a toner image on a photoreceptor and transferring and fixing the laser writing unit, the laser writing unit shares one polygon mirror with a plurality of laser lights, Is a symmetrical optical system that emits light in the opposite direction and scans the photoreceptor, irradiates a pattern formed near one side on the photoreceptor with writing laser light in the main scanning direction, and receives reflected light by a light receiving sensor. The pattern light to be written in the pattern direction is received during the same scan as the pattern detection signal. 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,
A writing timing signal is issued, and the writing of the image is performed upon receiving the writing timing signal.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will 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 one embodiment of the present invention. FIG. FIG. 3 is a perspective view showing an optical system of the apparatus, and FIG.
FIG. 3 is a plan view showing a positional relationship between the laser scanning exposure apparatus of the present embodiment and an image forming body.

In FIG. 1, a color image forming apparatus according to this embodiment includes a plurality of chargers 11 around a belt-shaped image forming body 1.
0, 210, 310, 410, exposure scan lines L1, L2, L3
Developing device 13 loaded with L4 and four different color toners
An image forming means including 0, 230, 330, and 430 is disposed, and a single rotation of the image forming body 1 forms a color image by superimposing yellow, magenta, cyan, and black toner images.

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 deposited on a flexible belt.
A tension roller 5 is attached to the photoreceptor belt 1 and stretched between the guide member 3 and a guide member 4 having a curvature. By rotating, the photosensitive belt 1 is always conveyed while keeping the surface thereof at a fixed position. With the above-described configuration, the photosensitive member on the outer peripheral surface of the photosensitive belt 1 is always maintained at a fixed 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 a constant interval.

In this embodiment, the photoreceptor belt 1 is used as an image forming member. However, the present invention is not limited to this, and the present invention is applicable to an existing image forming member having a photosensitive layer such as a photoreceptor drum. Applicable.

Around the photoreceptor belt 1, there are provided a plurality of charging means, a plurality of exposing means, a developing means loaded with toner of four different colors, a transferring means and a cleaning means.

The charging means is provided to uniformly charge the photosensitive layer on the surface of the photoreceptor belt 1 with a predetermined polarity, and is provided with existing chargers 110, 210, 310, such as a corona charger and a scorotron charger. 410. The exposing means is a semiconductor laser writing unit (laser scanning exposing device) 120, which forms an electrostatic latent image by exposing the surface of the photoreceptor belt 1 charged by the chargers 110, 210, 310, 410.

The developing means includes developing agents of different colors, for example, yellow (Y), magenta (M), cyan (C) and black (K).
Developing units 130, 230, 330, and 430 respectively containing the respective color toners (developers). Each of these developing units 130-430
Has a function of visualizing the electrostatic latent image on the photosensitive belt 1 into a toner image by a non-contact developing method. Unlike the contact developing method, the non-contact developing 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, so that a good color image can be obtained. Can be.

The transfer means transfers the toner image formed on the photosensitive belt 1 onto a transfer material by a transfer device 14 such as a transfer corona discharger. As the transfer unit, 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 pressing against the surface of the photosensitive belt 1 only at the time of cleaning.

The process of forming a color image by the image forming apparatus having the above-described configuration is performed as follows.

First, when an image signal of a first color output from an image reading device separate from the apparatus main body is input to the laser writing unit 120, a laser beam is emitted by the semiconductor laser 121 in the laser writing unit 120. Generated. The laser beam forms a collimation lens 12
2.Driving motor 124 via cylindrical lens 123
Is rotated and scanned by a polygon mirror 125 rotated by an optical scanner, and is projected through the fθ lens 126 onto the peripheral surface of the photoreceptor belt 1 which has been uniformly charged to a predetermined charge by the chargers 110 to 410 in advance to form a bright line. .

On the other hand, in the sub-scanning direction, the photo sensor detects a registration mark corresponding to a specific position of the photoreceptor belt 1, and modulation of the semiconductor laser 121 by an image signal is started based on the detection signal. The main scanning 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 over the surface of the photoreceptor belt 1. Accordingly, a latent image corresponding to the first color is formed on the surface of the photosensitive belt 1 uniformly charged by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt 1. This latent image is developed by the developing device 230 containing the yellow toner, and a yellow toner image is formed on the surface of the photoreceptor belt 1. Thereafter, the photoreceptor belt 1 is conveyed while holding the yellow toner image on the surface thereof, and subsequently enters the second color image formation.

That is, when the photosensitive belt 1 on which the yellow toner image is formed is conveyed to the next position of the charger 210 as in the case of the above-described first color image signal, the charger is recharged again. Charged by 210, then photosensitive belt 1
Is detected, and the second position is detected based on the detected signal.
The modulation of the semiconductor laser of the laser writing unit 120 by the image signal is started, and the laser light generated by the semiconductor laser is rotationally scanned by a polygon mirror rotated by a collimation lens driving motor, and an fθ lens,
After passing through the cylindrical lens, it is projected onto the peripheral surface of the photoreceptor belt 1 uniformly charged to a predetermined charge by the charger 210 to form a latent image. The latent image is developed by a developing device 230 containing magenta toner as a second color.
The magenta toner image is formed in the presence of the already formed yellow toner image.

Similarly, the photoreceptor belt 1 on which the magenta toner image of the second color is formed is further conveyed, and the charging device 310 continues to charge the photoreceptor belt 1 as in the case of the image signal of the second color. Laser writing unit 120
Developing device that forms a latent image and stores cyan toner
At 330, a cyan toner image is formed. Further, the photoreceptor belt 1 on which the cyan toner image of the third color is formed is further conveyed and uniformly charged by the charger 410 as in the case of the image signals of the second and third colors. The latent image is formed by the laser writing unit 120, developed by the developing device 430 containing the black toner, and the black toner image is superimposed on the latent image.
Formed on the surface of That is, if the photosensitive belt 1 is 1
During the rotation, a color toner image is formed.

A DC or further AC bias is applied to each of these developing units 130 to 430, so that reversal development (jumping development) is performed without contact with the photosensitive belt 1 whose base is grounded. . Incidentally, for the non-contact development, either a one-component developer or a two-component developer can be used. When a one-component developer is used, there is no need 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, so that color reproduction is improved. preferable.

The color toner image formed on the surface of the photoreceptor belt 1 as described above is supplied from a paper feed cassette 161 by a paper feed roller 162 and is transferred by a timing roller 163 to a transfer material synchronized with the color toner image. Is transferred to The transfer device 14 performs transfer by applying a high-voltage power supply having a polarity opposite to that of the toner.

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

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

The color image forming apparatus of this embodiment is
A developing device 1 in which a plurality of chargers 110 to 410, an exposing device 120, and four different color toners are loaded around a photoreceptor belt 1.
An image forming means consisting of 30 to 430 is arranged, and the photosensitive belt 1
Is a so-called one-pass method in which a yellow, magenta, cyan and black toner image is superimposed to form a color image in one rotation. Note that the present invention is not limited to the one-pass system, and it goes without saying that a multi-rotation system in which a latent image is formed and developed each time the image forming body makes one rotation may be used.

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

As shown in FIGS. 2 and 3, the photoreceptor belt 1 has a linear pre-pattern 1A formed in advance by printing or the like near a side end surface of the photoreceptor 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 a main scanning direction and a sub-scanning direction by a laser beam, which will be described later, and a reference for detecting deviation of the scanning lines L1, L2, L3, and L4 in the main scanning direction.

The pre-pattern 1A and the scanning line L
1, L2, L3, and L4 are crossed over each position (FIG. 2).
) Includes a light receiving sensor (reflective photo sensor) PS
1, PS2, PS3 and PS4, respectively, and the pre-pattern 1A by a main scanning writing system beam of laser light.
Of the reflected light from the light receiving sensors PS1, PS2, PS3, P
Light is received in S4.

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

FIG. 4 is a partially enlarged perspective view showing a symmetric optical system of the laser scanning exposure apparatus according to the first embodiment of the present invention. The exposure apparatus shown in the figure shows one of the four laser beams of the present embodiment in which two laser beams are divided into two lines, and these have almost the same configuration. This embodiment will be described using one laser scanning exposure apparatus 120. Note that the color printer of FIG. 1 has a compact design of a refraction optical system using a plurality of mirrors in order to reduce the interval between each scanning line of the exposure apparatus.

The laser scanning exposure device 120 scans the photosensitive belt 1 with a laser beam from a laser light source using a deflector. For example, as shown in FIG.
A, a first optical system including a collimation lens 122A, a cylindrical lens 123A, a polygon mirror (rotating polygon mirror) 125A driven and rotated by a high-speed rotating motor 124, an fθ lens 126A, and a mirror 127A; And a second optical system including the optical components symmetrically arranged. Here, a second polygon mirror 125C is fixed coaxially with the polygon mirror 125A, and is similarly coaxially driven and rotated by a motor 124.

The laser light modulated by the image signal and converted into parallel light by the collimation lens 122 is scanned by a rotating polygon mirror 125A (125B) rotated by a motor 124. The scanned laser beam is reflected by the mirror 127 and irradiates the photosensitive surface of the photosensitive belt 1 to form a scanning line L1. The photoreceptor belt 1 rotates at a low speed in the direction of the arrow in FIG.

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, and 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 photosensitive belt 1 to form a scanning line L4. Here, the scanning line L4 is formed with the scanning direction opposite to that of the scanning line L1.

In this case, the collimation lenses 122A and 122A
As shown in the figure, the distance between the laser beams 22B
5A is installed so as to irradiate each different plane. For example, the rotating polygon mirror 125A shown in the figure is an octahedron, and in this case, is installed so that every other plane is irradiated independently. In the case of a hexahedron or a tetrahedron, the light is applied to an adjacent surface.

The scanning line L is also applied to the rotating polygon mirror 125C, which is coaxial with the rotating polygon mirror 125A and is mounted above the rotating polygon mirror 125A, and which is substantially the same as the above-mentioned symmetric optical system.
2 and L3 are formed. Here, the scanning line L2 is the L1
And the scanning line L3 is in the same direction as L3 and opposite to L2.

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

Further, as can be understood from the figure, since the main scanning directions of the scanning lines L1 and L4 and L2 and L3 on the photoreceptor belt 1 are reversed, electric power for one to several lines of scanning is obtained. The color image signal is input to the laser drive circuit via the memory so that the output order of the color image signal for each line is reversed.

Next, a description will be given of a correction operation for detecting a 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 these deviations.

FIG. 5 is a block diagram of the main scanning exposure correction for preventing the deviation of the laser beam in the main scanning direction. Here, the sub-area counter is a counter for shifting the sub-scanning direction, the main area counter is a counter for moving in 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. Part.

A plurality (four in FIG. 4) of writing laser beams irradiate the pre-pattern 1A on the photoreceptor belt 1 during scanning, and reflect the reflected light to the light receiving sensors PS1 and PS.
2, PS3 and PS4 detect the position of the photoconductor by receiving light.

A symmetrical optical system for the purpose of reducing the size and cost of the writing unit has two rotating polygon mirrors.
When two laser beams are 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 required near the both end surfaces of the photosensitive belt 1. . This increases the manufacturing cost and makes it difficult to ensure the accuracy of the interval between the two pre-patterns 1A formed on both side 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 position, and the laser beam scanned from the pre-pattern side is
After the detection of the pre-pattern 1A, the image writing is started after a lapse of a fixed timing dT (scan lines L1 and L2 in FIG. 2, and FIG. 5).

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

Here, D is the dot density (the number of dots per inch), Vp is the linear speed of the photosensitive belt (mm / sec),
Assuming that W is an image area width (mm), scanning time for one line; T ₁ = 25.4 / (D × Vp) Image area width scanning time; Tw = W / (25.4 / D).

The time required for writing one scanning line is extremely short, and the displacement of the photosensitive belt 1 during that time can be practically ignored. Therefore, 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 photoreceptor belt 1 and only needs to be installed on one end surface side of the photoreceptor belt 1. The space for the sensors can be minimized. The light receiving sensor is not limited to detection of reflected light of laser light, but may be detection of transmitted light.

Hereinafter, the operation of the color image forming apparatus according to the present embodiment will be described with reference to FIGS.

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

The laser scanning exposure apparatus 120 corrects the deviation in the sub-scanning direction by pre-processing the sub-scanning correction circuit and swinging the housing housing the exposure apparatus 120 in the sub-scanning direction. Enter the state.

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

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

Next, in the image formation based on the magenta data, cyan data and black data, similarly to the above, the main scanning correction circuit detects the deviation of each exposure device on the photosensitive belt 1 in the main scanning direction and corrects it. After the displacement in the sub-scanning direction is corrected, the exposure is started from the exposure device 120 after a preset time has elapsed, and the exposure is always started from a predetermined position on the photoreceptor belt 1, thereby enabling a plurality of exposure devices to be used. Even when positioning is not performed with strict mechanical precision, when a latent image is formed repeatedly in accordance with the number of colors, a shift of an exposure start point for forming a latent image can be prevented and a color shift can be prevented.

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

FIG. 6 is an overall structural view of a color copying machine according to a second embodiment of the present invention, which has a photosensitive belt 11 on which a translucent pre-pattern is formed, and has an image reading system A on the upper part. . In the drawings, parts having the same functions as those of the above embodiment are denoted by the same reference numerals. Further, points different from the above embodiment will be described.

A translucent pre-pattern (not shown) is formed near the side end face of the photoreceptor belt 11 outside the image area and substantially at the same position as the pre-pattern 1A so as to be able to transmit light. On the other hand, the guide member 4 forms a concave portion 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, PS14 is arranged respectively. The light receiving sensors PS11 to PS14 detect the passage of the transmitted scanning laser beam from the exposure device 120 through the translucent pre-pattern.

Next, a color image forming apparatus according to a 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 a laser beam in the main scanning direction. When the reference numerals shown in the following embodiments are the same as those shown in the first embodiment, unless otherwise specified, the same configuration and function as those of the first embodiment are performed. .

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

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

In general, a symmetrical optical system for the purpose of reducing the size and cost of a laser writing unit, that is, an optical system that irradiates two surfaces of one rotating polygonal mirror with laser light and emits reflected light in symmetric directions. When the system is used, the scanning direction of each laser beam (L1 and L4, L2 and L3) is reversed, so that the developed reference line 12A is required on both end surfaces of the photosensitive belt 12. This results in unnecessary consumption of toner, and furthermore, there is a risk that toner is scattered and scattered. Further, there are disadvantages in that the width dimension of the developing device, the photosensitive belt, and the cleaning device is increased.

Therefore, only one reference line 12A is provided on one side of the photoreceptor belt 12, and as in the first embodiment, the scanning line L2 is written after a certain timing dT has elapsed after the detection of the reference line 12A. To start with the reference line
Scan lines L3 and L4 that scan from the opposite direction to 12A are:
An image signal is written from a FIFO type memory after a lapse of (T ₁ −T w−d) with reference to a signal detected on the reference line 12A by the immediately preceding scan.

In this embodiment, the arrangement order of the toner colors of the developing units 130 to 430 is not limited to Y, M, C, and K. For example, in order to easily detect the first reference line 12A. Alternatively, the first developing device 130 may be loaded with black toner.

In this embodiment, first, after each laser writing unit 120 is provided with normal 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 is to correct a subtle shift in units of one dot width, and to form an image by finely adjusting each scanning line even if the rotating photosensitive belt moves in a meandering or thrust direction. This is particularly effective in forming a color image in which images are superimposed.

[0070]

As described above, the laser writing unit in the color image forming apparatus according to the present invention, when forming a color image, uses dots of each color in the main scanning direction, which are one of the most important factors that determine the recording image quality. Is achieved simply and with high accuracy, and has an excellent effect of preventing color misregistration and forming a high-quality image. Particularly, the present invention provides an extremely effective means in an exposure scanning writing unit of a color image forming apparatus of a superposition type such as an electrophotographic type.

[Brief description of the 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 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 apparatus 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 the 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 (photoreceptor belt) 1A Pre-pattern 2, 3 Rotating roller 4 Guide member 12A Reference line 14 Transfer unit (transfer unit) 15 Cleaning unit 17 Fixing unit 18 Discharge roller 110, 210, 310, 410 Charger 120 Laser scanning exposure device (laser writing unit) 121A, 121B Laser light source 125A, 125C Polygon mirror (rotating polygon mirror) 126A, 126B fθ lens 127A, 127B Mirror 130, 230, 330, 430 Developing device 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 (56) References JP-A-59-52216 (JP, A) JP-A-2-107463 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/44 G03G 15/01 112

Claims (6)

(57) [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 each laser light by the writing unit. A multi-color or full-color image is formed by forming a superimposed toner image on an image forming body, and transferring and fixing the laser image. A pre-pattern provided on one side of the photoreceptor in the main scanning direction, wherein a plurality of laser beams are incident, and each laser reflected beam is emitted in the opposite direction to scan on the image forming body. Is irradiated with a writing laser beam,
The reflected light is received by the light receiving sensor, a pre-pattern position detection signal is emitted, and the laser light to be written from the pre-pattern direction emits a write timing signal during the same scan as the pre-pattern detection signal, and the laser light to be written from the opposite direction to the pre-pattern is ,
A color image forming apparatus comprising: receiving a pre-pattern detection signal immediately before, calculating a writing start timing of a next scan, generating a signal, and receiving a 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 photoconductor. 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 each laser light by the writing unit. A multi-color or full-color image is obtained by forming a superimposed toner image on a photoreceptor and transferring and fixing the laser image. Is a symmetrical optical system that scans the photoreceptor with each laser reflected light emitted in the opposite direction, with respect to the main scanning direction, and a writing laser at the most upstream side of the image forming body. A developing device for forming a development pattern on a non-image forming portion near one end on the image forming body, and transferring the development pattern to a plurality of downstream writing layers; Laser light is emitted, the reflected light is received by the light receiving sensor, the pattern position detection signal is emitted, and the laser light to be written from the pattern direction is the same as the pattern detection signal. The color is characterized by receiving the previous pattern detection signal, calculating the writing timing of the main scanning, counting, emitting a writing timing signal after counting, and receiving each writing timing signal to write an image. Image forming device. 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 photoconductor.