JPH04335665A - Color image forming device - Google Patents

Abstract

PURPOSE:To precisely eliminate the deviation of a write position caused by the deviation of the sub-scanning direction of a belt-like photosensitive body and to obtain a high-resolution image without color slippage in a color image forming device which obtains a multicolor image by plurally superposing toner image obtained by forming and developing an electrostatic latent image on the belt-like photosensitive body by an optical write device using laser light. CONSTITUTION:A triangular mark 1A, for example, is provided at the prescribed place of a photosensitive belt 1 and a mark sensor 23 which detects the mark 1A by a laser beam L is provided at the prescribed position of the device main body. Based on a signal obtained by the sensor 23, the rotational phase deviation of a rotary polygon mirror 74 caused by the deviation of the sub-scanning direction of the belt 1 is corrected and the write timing of image data is made precise.

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 that forms a latent image on a belt-shaped photoreceptor using an optical writing device using a laser beam.

0002

2. Description of the Related Art Many methods and devices have been proposed for obtaining color images using electrophotography. For example, JP-A-6
As disclosed in Japanese Patent No. 1-100770, a latent image is formed and developed in accordance with the number of separated colors of the original image on a photosensitive drum serving as an image forming member, and is transferred onto a transfer drum each time the development is performed. There is a method in which a multicolor image is formed on a drum and then transferred onto recording paper to obtain a color copy. A device using this method requires a transfer drum large enough to transfer one sheet of image onto its circumferential surface in addition to the photoreceptor drum, and the device does not have a large and complicated structure. Inevitable.

For example, as disclosed in Japanese Patent Laid-Open No. 61-149972, a latent image is formed and developed on a photosensitive drum according to the number of separated colors of an original image, and a latent image is formed on a transfer material each time the development is performed. This is a method to obtain multicolor copies by transferring. With this method, it is difficult to overlap multicolor images with high precision, and it is impossible to obtain a high-quality color image.

[0004] Also, by repeating the formation of a latent image on the photosensitive drum according to the number of separated colors of the original image and the development with color toner,
There is a method of superimposing color toner images on a photoreceptor drum and then transferring them to obtain a color image. The basic process of forming a multicolor image is described in Japanese Patent Application Laid-Open No. 60-75850 by the present applicant.
No. 60-76766, No. 60-95456, No. 60
This method is disclosed in Japanese Patent No. 95458, No. 60-158475, and the like.

[0005] In a multicolor image forming apparatus that obtains a color image by superimposing color images as described above, a plurality of developing units containing different color toners are arranged around the periphery of the photoreceptor drum. Generally, the photoreceptor drum is rotated multiple times to develop the latent image on the photoreceptor drum to obtain a color image.

Regarding image forming bodies, as described above, in addition to photosensitive drums having a photoconductor coated or vapor-deposited on the circumferential surface of the drum, belt-shaped bodies having a photoconductor coated or attached to a flexible belt are used. Photoreceptors have also been proposed. The shape of the belt-shaped photoreceptor (hereinafter also referred to as photoreceptor belt) is determined by stretching it between rotating rollers including a drive roller, so space is effectively utilized to construct a compact color image forming device. It is effective if In addition, since the photoreceptor belt can run along a small curvature, it is possible to prevent poor separation of the transfer material by using a rotating roller with a small diameter and using this curvature to separate the transfer material. can.

[0007]

[Problems to be Solved by the Invention] As a result of further study by the inventor of the present invention regarding the technology using a belt-shaped photoreceptor, the following problems have become clear.

(1) When performing multiple writing using an optical writing device using a laser beam to form a multicolor image (when writing images of each color superimposed on a photoreceptor), the belt is separated. Because it is driven by rollers, relative positional deviation occurs in the vertical direction due to slippage, etc., and positional deviation occurs in the (vertical) direction of movement of the belt-shaped photoreceptor, resulting in color deviation in the sub-scanning direction and a decrease in resolution. There was a problem.

(2) In order to solve the above-mentioned problems, it is necessary to improve mechanical precision, but this alone is difficult to take as a sufficient countermeasure, so it is necessary to use high-precision parts. The resulting increase in costs is also a problem, and there are limits to mechanical measures alone.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to accurately control the displacement of the writing position without strictly regulating the displacement of the photoreceptor in the sub-scanning direction when performing multiple writing. The objective is to prevent color shift in the sub-scanning direction and a decrease in resolution, and to prevent unnecessary writing on the sensitive portion of the belt-shaped photoreceptor. Another object of the present invention is to provide a color image forming apparatus that achieves the above-mentioned objects while minimizing the complexity of the apparatus.

[0011]

[Means for Solving the Problems] The above object is to perform main scanning of an exposure beam on a belt-shaped photoreceptor using a rotating polygon mirror or the like, and to scan the belt-shaped photoreceptor by sub-scanning as the belt-shaped photoreceptor moves. In a color image forming apparatus, a latent image is formed on the belt-shaped photoreceptor, and toner images of different colors obtained by development are overlaid multiple times on the belt-shaped photoreceptor to obtain a multicolor image. A reflective or transmissive mark is provided at one location on the body, a mark detection means for detecting the mark by the exposure beam is provided at a predetermined position, and the timing at which the mark detection means detects the mark is used as a reference for each color exposure. to control the rotational phase of the rotating polygon mirror,
This is achieved by a color image forming apparatus characterized by controlling the timing of starting exposure in the sub-scanning direction.

Further, in the color image forming apparatus, the mark has a shape in which the width in the main scanning direction monotonically increases or decreases in the sub-scanning direction. Furthermore, a color image forming apparatus is provided in which the detection time corresponding to the width of the mark detected by the mark detecting means of the color image forming apparatus is converted into a voltage value by an integrating circuit and then used for determining the timing. This can be mentioned as a preferred embodiment.

[0013]

[Embodiment] The present invention detects a vertical positional deviation of a belt-like photoreceptor, and based on the detection result, corrects the optical writing position in accordance with the positional deviation, and also corrects the optical writing position in accordance with the positional deviation. This is a color image forming apparatus that controls an optical writing device using a laser beam so that unnecessary writing is not performed on the toner adhesion area. This also applies to color image forming apparatuses that superimpose toner images by multiple rotations of a photoreceptor, and (B) color image forming apparatuses that form color images by superimposing toner images during one rotation of a belt-shaped photoreceptor. Therefore, the following embodiments will be explained.

(Embodiment 1) Embodiment 1 shown in FIG. 1 is a color image forming apparatus using a system in which toner images are superimposed by rotating a belt-like photoreceptor a plurality of times.

In FIG. 1, reference numeral 1 denotes a photoreceptor belt, which is a flexible belt-shaped photoreceptor coated or vapor-deposited with a photoconductor. and is conveyed clockwise by the rotation roller 2. 1A is a reflective mark provided at a predetermined location on the photoreceptor belt 1 using a paint or material with high reflectance at least in a specific wavelength range, or a transmissive mark provided so that the laser beam L passes through it. . A suitable shape for the mark 1A is, for example, a triangle whose width in the main scanning direction changes monotonically in the sub-scanning direction according to a predetermined function. Reference numeral 4 denotes a guide member fixed to the main body of the apparatus so as to be inscribed in the photoreceptor belt 1. The photoreceptor belt 1 is brought into a tensioned state by the action of the tension roller 5, so that its inner peripheral surface slides on the guide member 4. Let it rub.

Reference numeral 6 denotes a scorotron type charger as a charging means; 7 an optical writing device as an exposure means for writing (exposure) with a laser beam L as an exposure beam; 8 to 1;
Reference numeral 1 denotes a plurality of developing units each containing a developer of a specific color, and these image forming units are arranged at a portion of the photoreceptor belt 1 that is in contact with the guide member 4 . Each of the developing units 8, 9, 10, and 11 accommodates, for example, yellow, magenta, cyan, and black developers, respectively, and each developing sleeve 8A, 9A, 10A maintains a predetermined gap with the photoreceptor belt 1. 11A, and has a function of making the latent image on the photoreceptor belt 1 visible by a non-contact reversal development method. Unlike contact development, this non-contact development has the advantage of not interfering with the movement of the photoreceptor belt.

12 is a transfer device; 13 is a cleaning device; the blade 13A and toner conveying roller 13B of the cleaning device 13 are kept at a position apart from the surface of the photoreceptor belt 1 during image formation; and during cleaning after image transfer. As shown in the figure, the surface of the photoreceptor belt 1 is pressed against the surface of the photoreceptor belt 1. 2
Reference numeral 3 denotes a mark sensor which is an optical mark detection means using, for example, a phototransistor as a light receiving element.

The process of forming a color image using such a color image forming apparatus is carried out as follows.

That is, when color-specific image data outputted from an image reading device separate from the color image forming device is input to the optical writing device 7, the optical writing device 7 uses a writing light source (not shown). A laser beam L, which is an exposure beam generated by a certain laser diode 71, passes through a collimator lens (72) and a cylindrical lens (73), and then passes through a rotating polygon mirror 7 rotated by a drive motor 79.
4, the fθ lens 75, mirror 76,
The light is projected through a cylindrical lens 73 and a mirror 77 onto the circumferential surface of the photoreceptor belt 1, which has been uniformly charged in advance by a charger 6 serving as a charging means, and is main-scanned to form a bright line.

[0020] The above-mentioned laser scanning is performed by control described later based on a signal obtained by the mark sensor 23. A laser beam L modulated by image data of the first color scans the circumferential surface of the photoreceptor belt 1. Therefore, by the main scanning by the laser beam L and the sub-scanning by the conveyance of the photoreceptor belt 1, the first
A latent image corresponding to the color is formed. This latent image is developed by a developing device 8 loaded with yellow (Y) toner (developing medium) of the developing means, and a toner image is formed on the belt surface. The obtained toner image passes under a cleaning device 13, which is a cleaning means, which is separated from the peripheral surface of the photoreceptor belt 1 while being held on the belt surface, and enters the next image forming cycle.

That is, the photoreceptor belt 1 is connected to the charger 6.
The image data of the second color output from the image data processing section is then input to the optical writing device 7, and writing on the belt surface is performed in the same manner as in the case of the first color described above. A latent image is formed. The latent image is developed by a developer 9 loaded with magenta (M) toner as a second color.

This magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

A developing device 10 has cyan (C) toner, and forms a cyan (C) toner image on the belt surface based on a control signal generated by an image data processing section.

Further, numeral 11 denotes a developing device containing black toner, which forms a black toner image superimposed on the belt surface by the same process. These developing devices 8, 9, 1
Direct current or even alternating current bias is applied to each sleeve 0 and 11, and non-contact development is performed using a two-component developer serving as a developing means, and non-contact development is performed on the photoreceptor belt 1 whose base is grounded. is now being carried out.

The color toner image thus formed on the circumferential surface of the photoreceptor belt 1 is fed from the paper feed cassette 14 via the paper feed guide 15 by applying a high voltage of opposite polarity to the toner in the transfer section. The image is transferred to the transferred transfer material.

That is, the top layer of the transfer material stored in the paper feed cassette 14 is conveyed out by the rotation of the paper feed roller 16, and is synchronized with the image formation on the photoreceptor belt 1 via the timing roller 17. and is supplied to the transfer device 12.

The transfer material to which the image has been transferred is reliably separated from the photoreceptor belt 1 which suddenly changes direction along the rotating roller 2, moves upward, and after the image is fused by the fixing roller 18. The paper is discharged onto a tray 20 via a paper discharge roller 19.

On the other hand, the photoreceptor belt 1, which has completed the transfer to the transfer material, continues to be transported, and the remaining toner is removed by the cleaning device 13 in which the blade 13A and the toner transport roller 13B are brought into pressure contact, and the process is completed. After waiting, the blade 13A is pulled away again, and a little later, the toner conveying roller 13B is pulled away to begin a new image forming process.

That is, the top layer of the transfer material stored in the paper feed cassette 14 is conveyed out by the rotation of the paper feed roller 16, and is synchronized with the image formation on the photoreceptor belt 1 via the timing roller 17. and is supplied to the transfer device 12.

The transfer material to which the image has been transferred is reliably separated from the photoreceptor belt 1 which suddenly changes direction along the rotating roller 2, moves upward, and after the image is fused by the fixing roller 18. The paper is discharged onto a tray 20 via a paper discharge roller 19.

On the other hand, the photoreceptor belt 1 that has completed the transfer to the transfer material continues to be transported, and the remaining toner is removed by the cleaning device 13 in which the blade 13A and the toner transport roller 13B are brought into pressure contact, and the process is completed. After waiting, the blade 13A is pulled away again, and a little later, the toner conveying roller 13B is pulled away to begin a new image forming process.

[0032] In the image forming apparatus shown in Example 1,
In the present invention, from the timing when the mark sensor 23 detects the mark 1A on the photoreceptor belt 1 by the laser beam L that is the exposure beam, the rotary polygon mirror 74 of the optical writing device 7
The timing of writing image data is corrected with high accuracy by correcting the rotational phase of the laser diode 71 and the light emission of the laser diode 71. This prevents deviations from occurring in the sub-scanning direction during the process of rotating the photoreceptor belt 1 and forming a latent image. This is designed to prevent color misregistration in the sub-scanning direction even if there is a problem.

FIG. 2 shows ON and OF signals from the mark sensor 23.
Based on the F signal and the signal from the index sensor 78 (not shown in FIG. 1), the rotational phase of the drive motor 79 directly connected to the rotating polygon mirror 74 and the light emission of the laser diode 71 which is the light emitting part of the optical writing device 7 are determined. FIG. 2 is a block diagram showing an example of a circuit that performs control. Figure 5(a),(b)
) shows a time chart of exposure (optical writing) by the optical writing device 7 controlled by such a circuit.

Conventionally, in such a device, the rotating polygon mirror 7
4 was performed independently of the movement of the photoreceptor belt 1, so the image formation start position in the sub-scanning direction for each color had an error close to one pixel, which is the pitch of each scanning line. , the amount of color shift in the sub-scanning direction could be quite large. In the case of control by the circuit shown in FIG. 2, the phase of the drive clock pulse of the drive motor 79 is corrected based on the signal obtained by the mark sensor 23, so that the correction error can be made extremely small.

The circuit shown in FIG. 2 determines the effective image range of the photoreceptor belt 1 based on a command from the overall control section 41 that controls the entire optical writing and a detection time corresponding to the width of the mark 1A detected by the mark sensor 23. A reference position related to the exposure start position is calculated, image data, which is a color signal stored in the image memory 42, is read out, pulse width modulated in the exposure control section 43, and output to the laser diode 71 via the laser diode driver 49. and controls its light emission.

When image recording is started, the overall control section 41 rotates the drive motor 79 and the drive motor of the rotating roller 2, the rotating polygon mirror 74 rotates, and the photosensitive belt 1 starts moving. The overall control section 41 also sends a signal to the exposure control section 43 to cause the laser diode 71 to emit steady light. When the mark 1A reaches the detection position of the mark sensor 23, the laser beam L passes through the mark 1A and enters the mark sensor 23, and the mark sensor 23 outputs a signal (this signal is turned ON) for a time corresponding to the width of the mark 1A. S10) is sent to the sub-scanning direction reference timing generation section 44.

The sub-scanning direction reference timing generating section 44, which receives the signal S10, generates a constant timing, which will be explained later, after the time when the photoreceptor belt 1 moves and the exposure start position of the effective image range reaches the scanning line of the laser beam L. A signal (this signal is referred to as S1) that rises at the time when the reference position, which is a fixed position that reaches a time tm earlier, reaches the scanning line of the laser beam L (this time is referred to as timing α) is generated.

FIG. 3 is an explanatory diagram showing the relationship between the signal S10 and the signal S1. In the figure, 1B is the effective image range on the photoreceptor belt 1, 61 is the scanning line, 62 is the tip of the mark 1A, and 63 is the reference position. mark 1
The distance from the tip 62 of A to the reference position 63 is d, and the time required for the photoreceptor belt 1 to move this distance is t3.
shall be. Time t0 is the time from the tip 62 of mark 1A until the laser beam L first begins to cross mark 1A,
ts is the scanning interval time of the laser beam L. mark 1
When A reaches the detection position, the mark sensor 23 changes pulse widths t1 and t2 each time the laser beam L crosses the mark 1A.
A signal S10 that gradually increases in size is sent to the sub-scanning direction reference timing generation section 44. Assume that the shape of the mark 1A is triangular as shown in FIG. 3, and its tip is on the downstream side on the photoreceptor belt 1, and if the moving speed of the photoreceptor belt 1 is vb, then t0=t1・ts/(t2− t1) t3=d/vb, and if t4 is the time from the tip of the second pulse of signal S10 to the reference position, t4 is t4=t3-ts-t0, so t4=(d/vb)-ts-t1・ts/(t2-t1
)=(d/vb)-t2*ts/(t2-t1), and since d, vd, and ts are predetermined constant values, t4 can be easily calculated from t1 and t2.

Thus, the sub-scanning direction reference timing generation section 44 sends the signal S1 rising at timing α to the overall control section 41, the reference clock generation section 47, and the sub-scanning direction exposure timing generation section 46, as shown in FIG. 5(a). Exposure control for the first color shown in is started.

On the other hand, the laser beam L is incident on the index sensor 78 before the laser beam L is incident on the mark sensor 23, and a signal in which a pulse rises every time scanning is started is sent to the main scanning direction exposure timing generation section 46. do. In response to this signal, the main scanning direction exposure timing generating section 4
6 is an exposure signal S4 whose phase is corrected by the above signal (time H (ON) for writing an image during scanning of laser beam L).
) is sent to the exposure control section 43.

The reference clock generation unit 47, which receives the signal S1, outputs the pulse S2 (period ts) corrected so as to match the phase with the timing α, into a phase-locked loop (PL).
L) type PLL motor driver 48. This phase correction involves a slight delay ta, but ta is the period ts
The delay time is minute compared to . Further, the overall control section 41 that has received the signal S1 sends out a laser emission signal to the exposure control section 43.

The sub-scanning direction exposure timing generation section 45
A signal S that rises after a certain period of time tm, which is sufficient for the rotation of the rotating polygon mirror 74 to stabilize after the input of the signal S1, has elapsed.
3 is sent to the exposure control section 43. The main scanning direction exposure timing generation section 46 also sends a signal S4 to the exposure control section 43 that matches the phase of the scan start signal from the index sensor 78 and turns H (ON) for a time corresponding to the effective image range in the main scanning direction. Send. The exposure control unit 43 that receives the signals S3 and S4 performs an AND operation on both signals, and while both the signals S3 and S4 are at H level, reads image data from the image memory 42, modulates the pulse width, and sends the data through the laser diode driver 49. Light emission control is performed to cause the laser diode 71 to emit light in accordance with the transmitted image data.

FIG. 5(b) is a diagram showing a time chart during exposure of the second color. By the same control as the first color, exposure is performed with an error only due to the delay ta, and there is almost no color shift. Superposition can be performed.

In the time charts of FIGS. 5(a) and 5(b), the term "exposure (optical writing)" indicates the exposure for each scanning line. The error in the positional shift in the sub-scanning direction caused by the above control is only due to the delay ta when generating the signal S2.
a/ts, and can be kept to a much smaller error than the conventional error that is close to a maximum of one pixel pitch. In this way, positional displacement of the multicolor toner image can be accurately and reliably prevented with a simple circuit.

FIG. 4 is a block diagram showing a circuit for converting the pulse width of the signal S10 from the mark sensor 23 of FIG. 2 into a voltage value. In this circuit, the signal S10 is not directly inputted to the sub-scanning direction reference timing generating section 44 of the circuit shown in FIG. 2, but is converted into a voltage value and then inputted. The signal S10 from the mark sensor 23 is integrated by an integrating circuit consisting of an operational amplifier 51 and a capacitor C1, resulting in a signal S1.
It is converted into a voltage value proportional to the pulse width of 0H. This voltage value is determined by the signal S10, which is output by the index sensor 78 every scan and shaped into a rectangular wave by the signal processing circuit 50. The width of each pulse is accurately converted to time. By inserting this circuit, the circuit of the sub-scanning direction reference timing generation section 44 can be simplified.

[0046] In the above embodiment, the case where a transmissive mark 1A was used was explained. When using the reflective mark 1A, the mark sensor 23 may be installed at a position where it receives the reflected light of the laser beam L by the mark 1A, and the rest may be the same as in the case of the transmissive mark 1A.

(Embodiment 2) Embodiment 2 shown in FIG. 6 is a color image forming apparatus that forms a color image by superimposing toner images on a photoconductor during one rotation of a belt-like photoconductor.

In FIG. 6, the photoreceptor belt 101 is stretched between rotating rollers 102 and 103, and the peripheral edge of the photoreceptor belt 101 moves along a fixed guide member 104 by the action of a tension roller 105. Multiple sets (
In this embodiment, there are four sets of chargers, optical writing devices, and developing devices.
(106A, 107A, 108A), (106B, 10
7B, 108B), (106C, 107C, 108C)
, (106D, 107D, 108D) are arranged in sequence. Charger 106A, 106B, 106C, 106D
Both are scorotron type chargers, and the optical writing device 10
7A, 107B, 107C, and 107D are all laser writing devices that use a laser diode as a light source and rotate and scan with a rotating polygon mirror. Also, developing devices 108A and 108B
, 108C, and 108D contain different color developers, such as yellow (Y), magenta (M), cyan (C), and black (BK) toner (developer), respectively, and non-contact reversal. It has the function of being visualized using a developing method. Further, marks 101A are provided at predetermined locations on the photoreceptor belt 101, and mark sensors 123A, 123B, 123C, and 12 are provided as detection means for the marks 101A.
3D is the charger 106A, 1 in order from upstream to downstream.
06B, 106C, 106D and developing units 108A, 108
It is arranged on the back side of the photoreceptor belt 1 between B, 108C, and 108D.

The process of forming a color image using the color image forming apparatus having the above configuration is carried out as follows. That is, modulation of the laser diode of the optical writing device 107B by the image signal of the first color (yellow) is started, and the laser beam L generated by the laser diode is uniformly charged to a predetermined charge by the charger 106A in advance. The light is projected onto the photoreceptor belt 101 and main scanned to form a bright line. A latent image corresponding to the first color is formed on the uniformly charged surface of the photoreceptor belt 101 due to the sub-scanning of the photoreceptor belt 101 as it is conveyed. This latent image is developed by a developing device 108A containing yellow toner, and a yellow toner image is formed on the surface of the photoreceptor belt 101. Thereafter, the photoreceptor belt 101 is conveyed while holding the yellow toner image on its surface, and then the second color image formation begins.

That is, when the photoreceptor belt 101 on which the yellow toner image is formed is conveyed to the position of the next charger 106B, it is again transferred to the charger as in the case of the image signal of the first color described above. 106B, the laser diode of the optical writing device 107B is then started to be modulated by a second color image signal in response to a signal from the mark sensor 123B, corresponding to a specific position on the photoreceptor belt 101. The generated laser beam L is projected onto the circumferential surface of the photoreceptor belt 101 to form a latent image. The latent image is developed by developer 108B containing magenta toner as a second color. A magenta toner image is formed in the presence of a previously formed yellow toner image.

Similarly, the photoreceptor belt 101 on which the magenta toner image of the second color has been formed is further conveyed, and is subsequently charged by the charger 106C as in the case of the image signal of the second color described above. The optical writing device 10
A latent image is formed by 7C, and developed by a developing device 108C containing cyan toner as a third color to form a cyan toner image. The photoreceptor belt 101 on which the cyan toner image has been formed is further conveyed, is uniformly charged by a charger 106D, and the latent image is formed by an optical writing device 107D, as in the case of the image signals of the second and third colors described above. is formed and developed by a developing device 108D containing black toner, and the black toner images are superimposed to form a color toner image on the surface of the photoreceptor belt 101. That is, a color toner image is formed while the photoreceptor belt 101 rotates once.

The color toner image formed on the surface of the photoreceptor belt 101 as described above is supplied from the paper feed cassette 114 by the paper feed roller 116 and then transferred to the timing roller 1.
17, the color toner image is transferred onto a transfer material in synchronization with the color toner image. The transfer device 112 performs transfer by applying a high voltage having a polarity opposite to that of the toner.

In this way, the transfer material to which the color toner image has been transferred is reliably separated from the photoreceptor belt 101, which rapidly changes direction along the rotating roller 102, and the transfer material is reliably separated from the photoreceptor belt 101, which rapidly changes direction along the rotating roller 102, and is then transferred to the fixing means 1.
After the toner is melted and fixed by the paper discharge roller 1
19, the paper is discharged onto a tray 120 at the top of the main body of the apparatus.

On the other hand, the photoreceptor belt 101 that has finished transferring the color toner image to the transfer material is further conveyed clockwise to the cleaning means 113 with the cleaning blade 113A and the cleaning roller 113B in pressure contact.
The remaining toner is removed and cleaned. After cleaning is completed, a new image forming process begins again.

[0055] The optical writing devices 107A to 107D all use a laser diode as a light source and use an exposure method in which a laser beam L, which is an exposure beam emitted from the laser diode, is scanned by a rotating polygon mirror or the like. control is performed.

Optical writing device 10 in which light emission is controlled independently by signals from mark sensors 124A to 124D.
7A to 107D are controlled by the circuits shown in FIGS. 2 and 4, respectively, and only the overall control section 41 is shared, and the output signal from the overall control section 41 that controls the entire optical writing device and the mark sensors 123A to 123D and Light emission of each optical writing device 107A-107D is controlled by a signal from an index sensor (178A-178D not shown). The optical writing device 10 determines the effective image range in the sub-scanning direction based on signals from the mark sensors 123A to 123D.
7A, 107B, etc., the rotation phase of the rotating polygon mirror is corrected as in Example 1, and image data writing (exposure) timing correction is applied to the image writing means for each color, thereby changing the color in the sub-scanning direction. An image forming apparatus that prevents misalignment will be provided.

[0057]

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained.

(1) Even in a color image forming apparatus using a belt-shaped photoreceptor, by providing an automatic correction mechanism for the exposure start position, it is possible to prevent positional deviation of the photoreceptor in the sub-scanning direction when performing multiple writing of color images. It is possible to prevent the writing position from shifting without strictly regulating the color shift, and it is possible to reliably prevent color shift in the sub-scanning direction and a decrease in resolution.

(2) Before determining the timing of the writing position (exposure), the rotational phase shift of the rotating polygon mirror caused by the positional shift of the photoreceptor belt is corrected using the signal obtained by the mark sensor. The error is t
It can be reduced to a/ts.

(3) Since unnecessary writing is not performed on the sensitive area (toner-adherable area) of the photoreceptor, the means for preventing exposure and development outside the image range can be omitted.

(4) Since there is no need to extremely improve mechanical precision, an increase in device cost can be suppressed and the device can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a color image forming apparatus showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing one example of a circuit that controls the optical writing device of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between signal S10 and signal S1 in FIG. 2;

FIG. 4 is a block diagram showing a circuit that converts the pulse width of the signal S10 from the mark sensor 23 of FIG. 2 into a voltage value.

[Figure 5] Exposure (optical writing) by the optical writing device of the present invention
FIG. 2 is a diagram showing a time chart of FIG.

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

[Explanation of symbols]

1,101...Photoreceptor belt
1A, 101A... Marks 2, 3, 102, 103... Rotating roller 4, 104... Guide member 6, 106... Charger
7,107...Optical writing device 8,108...Developer
23, 123...Mark sensor 41...Overall control section
42... Image memory 43... Exposure control section
48...PLL motor driver 50...signal processing circuit
51...Operation amplifier 71...Laser diode
74... Rotating polygon mirror 75... fθ lens 78... Index sensor 79... Drive motor
L...Laser beam (exposure beam)

Claims (3)

[Claims] 1. Performing main scanning of an exposure beam on a belt-like photoreceptor using a rotating polygon mirror or the like, and forming a latent image on the belt-like photoreceptor by sub-scanning as the belt-like photoreceptor moves, In a color image forming apparatus in which toner images of different colors obtained by development are superimposed on the belt-like photoreceptor multiple times to obtain a multicolor image, reflection or transmission occurs at one location on the belt-like photoreceptor. A type mark is provided, and a mark detection means for detecting the mark by the exposure beam is provided at a predetermined position. A color image forming apparatus characterized in that the rotation phase is controlled and the timing of starting exposure in the sub-scanning direction is controlled. 2. The color image forming apparatus according to claim 1, wherein the mark has a shape in which the width in the main scanning direction monotonically increases or monotonically decreases in the sub-scanning direction. 3. The color filter according to claim 1, wherein the detection time corresponding to the width of the mark detected by the mark detection means according to claim 1 is converted into a voltage value by an integrating circuit and then used for timing determination. Image forming device.