JP2002236267A - Image forming device and exposure device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize image forming where the deviation of an image, that is, color slurring is restrained with simple constitution and also to realize inexpensive high-speed image formation. SOLUTION: This image forming device is equipped with a plurality of photoreceptors 1Y, 1M, 1C and 1K and an exposure means 40 scanning and exposing the respective photoreceptors by deflecting laser beams modulated according to an image signal. The exposure means 40 is composed of a plurality of laser beam sources and one rotary polygon mirror reflecting and deflecting the respective laser beams from the laser beam sources so as to perform scanning, and the respective laser beam sources are arranged at positions where the laser beams are reflected on the common reflection surface of the rotary polygon mirror. Then, the respective laser beam sources are arranged at positions where the laser beams are made incident on the common reflection surface from different angles respectively and the respective photoreceptors 1Y, 1M, 1C and 1K are arranged at positions where their optical path lengths from the reflection surface are nearly the same. In the respective laser beam sources, the laser beams are modulated by using a common clock signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a color image on a sheet material such as a printer or a facsimile, and more particularly, to a mechanism structure thereof.

[0002]

2. Description of the Related Art A typical example of a conventional color image forming apparatus is disclosed in JP-B-4-51829 or JP-A-63-93.
61 is generally known, and in Japanese Patent Publication No. 4-51829, a plurality of laser beams corresponding to each color component are firstly deflected by a rotating polygon mirror in a first deflection direction. Latent images are formed on a plurality of photoconductors by performing deflection scanning while being divided in a direction opposite to the second deflection direction, and the first image information and the second image are formed.
It is a configuration in which the output order of image information in each scan is converted and output in the opposite direction, and a plurality of reflection mirrors are required to guide the image information conversion means and the deflected and scanned laser beam to the photoconductor, Further, since a plurality of laser beams are divided and deflected and scanned in directions opposite to the first deflection direction and the second deflection direction by different reflecting surfaces of the rotary polygon mirror, if the parallel accuracy of the reflecting surfaces is poor, the relative parallelism is reduced. Since the difference appears as a relative difference in the sub-scanning direction and results in image quality deterioration in which color misregistration occurs, a high-precision rotating polygon mirror is required, and the structure is not only complicated but also expensive.

Further, if the relative positions of the rotating polygon mirror, the plurality of reflection mirrors, and the plurality of photoconductors change due to environmental changes such as temperature, the images of the plurality of photoconductors are particularly transferred when sequentially transferred to a recording sheet. This appeared as a relative shift in the sub-scanning direction, and caused image quality degradation in which color shift occurred.

On the other hand, Japanese Patent Application Laid-Open No. 63-9361 attempts to solve the former problem, but not only the latter problem remains, but also the laser beam of the rotating polygon mirror. If the optical path length reaching each photoconductor from the reflection surface is different, the scanning width will be different,
The formation of the image signal needs to be modulated based on the individual data clock frequency corresponding to each laser light source, and the formation of the image signal is complicated and expensive.

[0005]

As described above, in the prior art, not only the image quality deteriorates due to a color shift due to a relative shift in the sub-scanning direction due to an environmental change such as a temperature, but also a mechanical structure. However, it is an expensive color image forming apparatus because the formation of image signals and image signals are complicated and a rotating polygon mirror specially configured with high precision is required.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problem, and an object thereof is to prevent a relative shift in the sub-scanning direction, that is, an image quality in which color shift occurs. Suppresses image misalignment, i.e., color misregistration, without the need for a special configuration, no special high-precision rotating polygon mirror, and no special configuration for forming image signals. It is an object of the present invention to provide a color image forming apparatus capable of forming images at a reduced cost and capable of forming images at high speed at low cost.

[0007]

SUMMARY OF THE INVENTION To this end, the present invention provides an image forming apparatus comprising a plurality of photoreceptors and an exposing means for deflecting and scanning each of the photoreceptors with a laser beam modulated by an image signal. In the apparatus, the exposure means includes:
It comprises a plurality of laser light sources and one rotary polygon mirror for reflecting and deflecting and scanning each laser beam of the plurality of laser light sources, and each of the laser light sources reflects the laser beam on a common reflection surface of the rotary polygon mirror. Wherein each of the laser light sources is disposed at a position where the laser beam is incident on the common reflection surface from a different angle, and each of the photoconductors has an optical path length from the reflection surface. Are arranged at substantially the same position, and each of the laser light sources has a laser beam modulated using a common clock signal,
The laser beam is arranged at a position where the laser beam enters a common position on the reflection surface from different angles.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to FIGS. 1 to 4 show a suitable embodiment of the image forming apparatus of the present invention, FIGS. 5 and 6 show a suitable embodiment of the flexible endless sleeve material of the present invention, and FIG. 7 shows the present invention. FIG. 8 shows a suitable embodiment of the flexible endless sleeve driving device of the present invention, and FIG. 8 shows a suitable forming example of the flexible endless sleeve material of the present invention.

FIG. 1 is a cross-sectional view showing the entire configuration of the image forming apparatus of the present invention, and FIG. 2 is a cross-sectional view of a main part of a developing device, showing a part of a developing section of the image forming apparatus of the present invention in an enlarged manner. FIG. 3 is a partial cross-sectional view of a main part of the exposure device of the image forming apparatus of the present invention, showing a main part of the exposure device. FIG. 4 is an explanatory diagram of a photoconductor arrangement for explaining an arrangement relationship of photoconductors in the image forming apparatus of the present invention.

First, the image forming section of the image forming apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2 and other drawings. As shown in FIG. 1, the main part of the image forming section of the present embodiment includes a plurality of photosensitive drums 1Y, 1M, 1C, and 1K arranged vertically adjacent to each other at a substantially central portion, and a plurality of photosensitive drums 1Y and 1K.
M, 1C, and 1K, and a plurality of charging rollers 2Y,
2M, 2C, 2K and photosensitive drum cleaners 3Y, 3M, 3
C, 3K and developing units 10Y, 10M, 10C, 10K.

As for the developing units 10Y, 10M, 10C and 10K, the two sets of upper developing units 10Y and 10M and the lower two sets of developing units 10C and 10K have the same configuration. 2 sets of developing unit 10
Some of C and 10K are not shown.

The order of the image forming process will be described with reference to FIGS. 1 and 2. The charging rollers 2Y and 2 in this embodiment will be described.
M, 2C, and 2K are formed of a semiconductive elastic body such as rubber, for example, and are photosensitive drums 1Y and 1 that rotate in the direction of the arrow in the figure.
When a bias of about DC (-) 2 kv or less is applied while following each of M, 1C and 1K, the photosensitive drums 1Y and 1K are applied.
Each of M, 1C and 1K is (-) 600 V to (-) 700 V
It can be charged to a charging potential of.

The charging rollers 2Y, 2M, 2C, and 2K are respectively pressed and supported toward the photosensitive drums 1Y, 1M, 1C, and 1K by a pressing mechanism constituted by a spring or the like (not shown), and a total pressure of approximately 1 kg. With photosensitive drum 1
Y, 1M, 1C, 1K.

Next, different image signals are supplied from the exposure device 40, which is disposed substantially in the horizontal direction to the photosensitive drums 1Y, 1M, 1C, 1K disposed in the vertical direction, which will be described in detail later, so that different image signals are shared by a common data clock frequency. The photosensitive drums 1Y, 1M, 1C, 1 are modulated by light beams incident on the optical paths 49Y, 49M, 49C, 49K and emitted therefrom.
K is image-exposed to form a latent image, and the potential of the image-exposed portion becomes (-) 10V to (-) 150V.

Next, the photosensitive drums 1Y, 1M, 1C, 1K
The relationship between the developing units 10Y, 10M, 10C and 10K corresponding to FIG. 2 will be described with reference to FIG. 2. In FIG. 2, the relationship between the photosensitive drum 1Y and the developing unit 10Y is shown as a representative, and other photosensitive drum and developing unit relationships are omitted. For simplicity of description, the reference numerals of the respective parts are omitted from the illustration of Y, M, C, and K, but are applied to the Y, M, C, and K parts, respectively.

In the developing section 10 shown in FIG. 2, the supply roller 13 which is formed of a semiconductive elastic material such as foamed rubber and rotates in the direction of the arrow in the drawing can be charged to the same polarity as the above-mentioned charging potential. The toner in the storage unit 11 for storing the toner is coated on the surface thereof, rotated, and rubbed with the charging blade 15 to frictionally charge the coated toner to the negative polarity. Let it be coated.

Here, a positive bias may not be applied to the supply roller 13 to frictionally charge the toner to the (-) polarity, but DC (-) 200 V to (-) 400
When a bias of about V is applied, the (−) polarity charging of the toner is promoted. The toner remaining on the surface of the developing roller 12 without being coated is scraped off by the scraping blade 16.
And the supply roller 13 is refreshed to enable the above cycle to be repeated again. On the other hand, the toner scraped by the scraping blade 16 is returned into the storage unit 11 from the passage 17b by the rotation of the supply roller 13, and the above cycle can be repeated.

Next, the toner coated on the surface of the developing roller 12 formed of a semiconductive elastic material such as a rubber material, which rotates in the direction of the arrow in FIG. A total pressure of approximately 1 Kg, and the entire surface in the axial direction is brought into contact with the regulating member 14 for regulating the coated toner to a coating layer having a predetermined thickness.
The toner layer is regulated by the toner layer thinned to a certain degree, and is triboelectrically charged to a more uniform (-) polarity.

The developing roller 12 has a DC (-) 200
A bias of about V to (−) 400 V is applied,
The thinned toner layer is conveyed to the photosensitive drum 1 and reversely developed on a nip portion formed by pressing the developing roller 12 and the photosensitive drum 1 against each other and in the vicinity of the nip portion.

Next, the toner image reversely developed on the image exposure portion of the photosensitive drum 1 is transferred to a primary transfer portion 80 shown in FIG.
The toner is transferred at Y, 80M, 80C, and 80K, but the untransferred toner is scraped off by the cleaning blade 93 pressed against the photosensitive drum 1 and stored in a predetermined space (not shown).

Incidentally, the cleaned photosensitive drum 1 is supplied with a voltage of (-) 600 V by the action of the charging roller 2 described above.
(−) It is possible to transfer to the next image forming process again by charging to a charging potential of 700 V. If the potential remaining on the photosensitive drum 1 is removed by cleaning after cleaning by irradiating light (not shown), the photosensitive drum 1 The surface potential can be brought closer to the initial state.

Here, the handling of the toner will be described. First, the amount of toner in the storage unit 11 is kept to a minimum necessary amount that does not hinder the above-described image forming process.
The space is shrinking. The toner that decreases with the above-described development is configured to be dropped and replenished in the space of the storage unit 11 from a toner transport unit 30 that transports the toner, which will be described in detail later. The toner transport section 30 has a mechanism for transporting toner by toner transport means including an endless coil spring 31 which will be described in detail later. The toner transport section 30 has a structure described in detail later. , The toner is circulated and conveyed.

Next, the toner circulation / conveying function will be described. In order to compensate for the toner in the storage unit 11 consumed by the above-described development, a toner replenishing unit that falls by its own weight is disposed in a transport path for circulating the toner, which will be described in detail later. The toner is replenished, circulated and transported, and dropped and supplied from the toner transport unit 30 to the storage unit 11.

Here, the toner replenishing means and the toner conveying means for circulating and conveying the toner will be described with reference to FIG. A part of the toner roller 20 is stretched over the supply roller 13 and the developing roller 12 in the axial direction and partially extended in the axial direction. Can be freely attached to and detached from the developer case 17 (the attachment / detachment mechanism is not shown in the drawing).
A predetermined amount of toner is sealed therein, the toner is supplied in a state where the toner is sealed, and toner is replenished. When the toner is consumed, the toner tank 20 is replaced with a new toner tank.

The main part of the toner tank 20 includes a cylindrical tank case 21 having a bottom at the bottom in the figure, a cover 22 fixed above and sealing the toner, and a tank case 21 and a cover 22. Plural blades 23 that stir rotatable toner sealed with toner
The endless coil spring 31 for circulating and transporting the toner is detachably operable in a state in which the endless coil spring 31 is accommodated in the developing device case 17 (the attachment / detachment mechanism is not shown in the drawings).

Regarding the mounting position of the toner tank 20,
Each of the photosensitive drums 1Y, 1M, 1C, 1
Optical paths 49Y, 49M, 49C, 4 irradiated toward K
9K, that is, in FIG. 1, each developing unit 10Y,
10M, 10C, and 10K, the toner tank 20Y is attached to the developing unit 10Y on the front side of the optical path 49Y in the figure, and the toner tank 20M is attached to the developing unit 10M is located on the rear side of the optical path 49M in the figure. The toner tank 20C is mounted on the front side of the optical path 49Y in the figure, and the toner tank 20K is mounted on the developing unit 10K behind the optical path 49K (the toner tank 20M in the figure).
The toner tank 20K is arranged in a staggered manner (illustration is omitted), and an effective spatial arrangement avoiding mutual interference is provided.

In the image forming apparatus of this embodiment, yellow, magenta, cyan, and black color toners are stored in the respective toner tanks 20Y, 20M, 20C, and 20K, and the respective developing units 10Y. , 10
M, 10C, and 10K are configured to perform yellow, magenta, cyan, and black color development corresponding to the color toner.

On the other hand, in order to drive the endless coil spring 31 for circulating and transporting the toner, the driving means 2
5, a protruding end is formed in a wedge shape, and a rotatable convex portion 25a protrudes from the developing device case 17. When the toner tank 20 is mounted at a predetermined position, the wedge is formed. Rotatable convex part 25a formed in a shape and concave part 2 formed at one end of one agitator 23
3c is engaged and driven to rotate.

The driving means 25 of the endless coil spring 31 for circulating and conveying the toner is as follows.
The rotating body that can be engaged with the coil spring 31 can be driven. However, in this embodiment, a helical gear having a torsion angle close to the lead angle of the coil spring 31 in a stretched state is adopted, and the coil spring 31 is used. Are stabilized. The drive means 25 for the endless coil spring 31 is structured to be driven to rotate via a gear 26 by a drive mechanism (not shown).

The toner agitated by the rotation of the agitator 23 circulates and transports the toner through an opening 21a formed at the bottom of the tank case 21 and an opening 17a of the developing device case 17 provided opposite the opening 21a. The endless coil spring 31 is configured to fall under its own weight into the toner circulation / conveyance path in which the opening 21 a and the opening 17 are linked with the attachment / detachment of the toner tank 20.
a is opened and closed (not shown).

The toner dropped by its own weight into the toner circulating conveyance path in which the coil spring 31 is disposed is
Endless coil spring 31 driven by
When the toner is circulated and conveyed to the upper part of the storage unit 11, it falls under its own weight from the upper part of the supply roller 13 and is stored in the toner storage unit 11. The toner storage unit 11 is configured to be extremely narrow. Therefore, based on the relationship between the amount of toner consumption and the amount of supply, which differs depending on the image form, the toner storage 11
In this state, the toner is circulated and conveyed by the coil spring 31 without falling under its own weight.
The configuration is also such that the drop of the toner from the toner tank 20 by its own weight is also interrupted.

The above is the main part of the image forming means of this embodiment, and corresponds to the photosensitive drums 1Y, 1M, 1C and 1K.
Developing units 10Y, 1 that enable development of each color toner
0M, 10C, and 10K are supply rollers 13Y,
13M, 13C, 13K and developing rollers 12Y, 12M,
12C, 12K and regulating members 14Y, 14M, 14C, 1
4K and endless coil springs 31Y, 31
M, 31C, 31K, etc.
Y, 17M, 17C, and 17K are housed in a unit, and are detachable from the main body. At the time of maintenance of the structural parts, they are integrally removed and repaired or replaced. The relationship between each developing unit and the main body is determined by a positioning unit (not shown) and fixed by a fixing unit (not shown).

Next, the transfer structure of this embodiment for transferring the reversal-developed color toner image to the image exposure portions of the respective photosensitive drums 1Y, 1M, 1C and 1K will be described with reference to FIGS. 1 and 2. In the description of FIG. 2, the relationship between the photosensitive drum 1Y and the developing unit 10Y is shown as a representative illustration, and the relationship between the other photosensitive drums and the developing unit is omitted. , K will be omitted from the illustration.
Each applies to the Y, M, C, K sites).

In the transfer structure of this embodiment, a color toner image reversely developed on each of the photosensitive drums 1Y, 1M, 1C and 1K is stretched over a plurality of rollers 82, 83 and 84, and each photosensitive drum 1Y is stretched. , 1M, 1C, and 1K, the primary transfer portions 80Y and 80 are transferred onto a flexible endless sleeve-like intermediate transfer medium 85 that moves in the direction of the arrow in FIG.
M, 80C, and 80K sequentially superimpose and primary transfer to form a primary image, and the primary image is conveyed to the roller 83 by the movement of the intermediate transfer medium 85.

On the other hand, in synchronization with the movement of the intermediate transfer medium 85 on which the primary image has been primary-transferred, the uppermost sheet of a plurality of sheet materials as recording media stored in the sheet material storage unit 75 1 by a pickup roller 91 rotating in the direction of the arrow in FIG. 1, a feed roller pair 92 for feeding the sheet material, and a registration roller pair 73 for controlling the feed timing and skew of the sheet material. The sheet material is fed to a sheet material transport path formed along the arrow indicated by P in FIG.

The primary image conveyed by the movement of the fed sheet material and the intermediate transfer medium 85 merges with the sheet material at a secondary transfer portion 90, and is pressed by a pressing mechanism (not shown). Is pressed with a total pressure of several hundred g toward a roller 83 which is driven while being stretched, and has a polarity opposite to that of a color toner image reversely developed on each of the photosensitive drums 1Y, 1M, 1C and 1K described in detail later. DC2-4KV
It is provided with means for applying a front and rear bias, and is conveyed to a nip portion formed by a pressing action of a rotatable transfer roller 81 formed of a conductive or semiconductive elastic material such as rubber. The primary image formed on the intermediary transfer medium 85 by the copy unit is printed on the synchronously fed sheet material.
Next transfer is performed to form a secondary image.

Then, the color toner of the primary image remaining after the transfer in the secondary transfer is further conveyed toward the roller 84, and the intermediate transfer is performed by the intermediate transfer medium cleaner 70 disposed opposite to the roller 84. The intermediate transfer medium cleaner 71 pressed against the medium 85 scrapes and is housed in the space 72, and the intermediate transfer medium 85 is refreshed so that the above cycle can be repeated again.

Here, each of the photosensitive drums 1Y, 1
A color toner image reversely developed on M, 1C, and 1K is stretched over a plurality of rollers 82, 83, and 84 and driven while being in contact with the respective photosensitive drums 1Y, 1M, 1C, and 1K, and is driven in a direction indicated by an arrow in FIG. The primary transfer units 80Y, 80M, and 80 are placed on a flexible endless sleeve-like intermediate transfer medium 85 that moves to
Primary transfer in which a primary image is formed by sequentially superimposing primary transfer at C and 80K will be described.

In FIG. 1 and FIG.
At least one of the rollers 2, 83, 84 is arranged with a tension function (not shown) for applying tension to the intermediate transfer medium 85. Photosensitive drums 1Y, 1M, 1C, 1K
, The plurality of rollers 8
It is configured to be driven by at least one of the rollers 2,83,84.

As shown in FIG. 2, the endless sleeve-like intermediate transfer medium 85 which moves is in contact with the photosensitive drum 1 via the developed color toner image to form a desired nip. The rear surface of the transfer medium 85 is disposed so as to face the photosensitive drum 1 and is in sliding contact therewith.
For example, a conductive brush material, a conductive film, or a metal material having means for intensively applying a bias of about 1 to 3 KV having a reverse polarity to the color toner image reversely developed to 1M, 1C, and 1K is formed. Is applied to the intermediate transfer medium 85 by applying a bias from the
The primary transfer is performed and moves.

In the course of the primary transfer, the color toner images are sequentially superimposed on the primary transfer portions 80Y, 80M, 80C, and 80K and are primarily transferred onto the intermediate transfer medium 85 to form a primary image. The color toner images successively transferred to the color toner image transferred first are superimposed or primary-transferred immediately, and the transfer bias at the time of first transfer and the transfer bias at the time of successive transfer In some cases, it is necessary to at least sequentially switch to a high-voltage transfer bias. In this embodiment, the primary transfer units 80Y, 80Y
The bias voltages applied from the electrode 81 at 80M, 80C, and 80K can be set to independent bias voltages.

Next, the primary image conveyed by the movement of the intermediate transfer medium 85 is synchronously merged with the sheet material fed at the secondary transfer portion 90 and secondary-transferred onto the sheet material, thereby transferring the secondary image. A fixing unit 60 that fixes the sheet material in the process of forming and feeding the sheet material to the sheet material conveyance path formed along the arrow indicated by P in FIG. 1 will be described.

The main part of the fixing section 60 of this embodiment is disposed downstream of the sheet conveying direction, and detailed description is omitted. At least one of the fixing sections 60 has a built-in heating element such as a halogen heater and is rotatable. The fixing roller pair 63 and the fixing roller pair 6
A pressing means for pressing at least one of the rollers on the other side to the other side to press the secondary image secondary-transferred onto the sheet material against the sheet material; The image is fixed on the sheet material at a predetermined temperature in a nip formed by the fixing roller pair 63.

Next, each of the photosensitive drums 1Y, 1M, 1
An exposing device 40 for performing latent image exposure on C and 1K will be described with reference to FIG. The main part of the exposure device 40 includes a motor 41 rotating at a little less than 20,000 rpm, a control circuit board (not shown) for controlling the rotation of the motor 41, and a plurality of semiconductors mounted on an output shaft of the motor 41 and rotating. Light emitting element 4 such as laser
The light beams emitted from 2Y, 42M, 42C, and 42K are respectively deflected and scanned to form a plurality of optical paths 49Y, 49M, and 49.
It comprises a rotating polygon mirror 43 constituting C and 49K, and exposure unit cases 44 and 46 which house the above-mentioned main components and are unitized.

Although not shown in detail, the exposure device cases 44 and 46 have a plurality of optical paths 49Y, 49M,
A predetermined position is established by engagement (not shown) of a positioning portion with a positioning portion formed on a sub-chassis 100 stretched on a main chassis which is a reference of an internal configuration of the device in which 49C and 49K are arranged in a symmetrical position sandwiching in the front-rear direction. And is fixed to the sub-chassis 100 by fixing means such as a screw 45 or the like.

The plurality of light emitting elements 42Y, 42M, 42C, 42K such as semiconductor lasers and the plurality of optical paths 49Y,
49M, 49C, and 49K correspond to each other in a relationship as shown in FIG. 3, and a plurality of light emitting elements 42Y, 42M, 42C, and 42K such as semiconductor lasers respectively emit light beams modulated by different image signals. The plurality of light beams are reflected by the reflecting surface 43a at the common position of the rotating polygon mirror 43 rotating in the direction of the arrow in the figure, respectively, are deflected and scanned in different directions, and pass through the fθ lens (not shown). A plurality of optical paths 49Y, 49M, 49 in different directions.
C, 49K.

In this embodiment, the light beams modulated by different image signals emitted from the light emitting elements 42Y, 42M, 42C and 42K such as a plurality of semiconductor lasers are used.
Each is modulated corresponding to an image of a different color.

Then, corresponding to the plurality of optical paths 49Y, 49M, 49C, and 49K in different directions, the plurality of optical paths 49Y, 49M, 49C, and 49K have an optical path length substantially the same. Each photosensitive drum 1Y,
1M, 1C, and 1K are arranged. Naturally, the scanning widths of the light beams scanned by the plurality of optical paths 49Y, 49M, 49C, and 49K are also substantially the same.

By the way, as described above, initially, each of the photosensitive drums 1Y, 1M, 1C, and 4K is located at a position where the optical path lengths of the plurality of optical paths 49Y, 49M, 49C, and 49K are substantially the same.
Even if 1K is arranged, the length may slightly change due to changes in the temperature and humidity environment inside and outside the device, and the scanning width may change.
Alternatively, the color toner images of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer medium 85 by the primary transfer unit 80.
When a primary image is formed by performing primary transfer by sequentially superposing Y, 80M, 80C, and 80K, a relative shift may occur in the primary transfer position, which may cause deterioration in image quality.

However, in the present embodiment, in view of this point, even if there is a change in the temperature or humidity environment inside and outside the apparatus, the plurality of optical paths 49Y, 49M, 49C,
As first means for suppressing the relative change of 49K, exposure unit cases 44 and 46, which house the essential components of the above-described exposure unit 40 and are unitized, are not shown in detail but are shown in FIG. Engagement of the to-be-positioned portion with a positioning portion formed on a sub-chassis 100 which is stretched on a main chassis serving as a reference for the internal configuration of the device in which the optical paths 49Y, 49M, 49C, and 49K are disposed symmetrically in the front-rear direction (not shown) ) Is positioned at a predetermined position.

The position as shown in detail in FIG.
For example, a screw 45 or the like is provided at a position substantially uniform in the surface direction of the reflecting surface 43a with respect to the reflecting surface 43a at the common position of the rotating polygon mirror 43 and substantially parallel to the plurality of photosensitive drums 1Y, 1M, 1C, 1K. The exposure unit 40 is fixed to the sub-chassis 100 by fixing means, and even if there is a change in temperature or humidity environment inside and outside the apparatus, the exposure unit 40 expands and contracts based on this fixing position, and the position of the reflection surface 43a Is fixed with a structure that does not change.

The position of the portion to be positioned with respect to the positioning unit formed on the sub-chassis 100 and the exposing unit cases 44 and 46 (not shown) does not serve as an expansion / contraction standard, but may be arranged near the screw 45. preferable.

On the other hand, as the second means, in the present embodiment, the plurality of photosensitive drums 1Y, 1M, 1C, and 1K are connected to the plurality of optical paths 49Y, 49M, and 49 in FIG.
49C and 49K are arranged at symmetrical positions sandwiching in the front-rear direction. The main chassis is used as a reference for the internal configuration of the apparatus. Have been. If there is a change in the temperature or humidity environment inside and outside the apparatus, a plurality of photosensitive drums 1 are referenced based on the position of the above-mentioned reflecting surface 43a.
The positions of Y, 1M, 1C, and 1K correspond to the optical paths 49Y and 49, respectively.
M, 49C, and 49K are configured to relatively expand and contract along the plurality of optical paths 49Y, 49M, 49C, and 49K.
The optical path length of K expands and contracts by almost the same length.
The scanning widths of the light beams scanned by the plurality of optical paths 49Y, 49M, 49C, and 49K are also substantially the same.

The above mechanism will be described in more detail with reference to FIG. 4. A plurality of photosensitive drums 1Y, 1M, 1C arranged at positions shown by solid lines in FIG. , 1K, when a change in the temperature or humidity environment inside or outside the apparatus occurs, each of the optical paths 49Y, 49 shown in FIG.
Move along M, 49C, and 49K to the positions centered on the intersections indicated by the one-dot chain line and the two-dot chain line in the figure (the content shown in FIG. 4 shows a state where the position has been changed in the extending direction, but shrinks. In the case where the position changes in the direction, the following description may be reversed.

On the other hand, a plurality of photosensitive drums 1Y, 1M, 1
C and 1K have corresponding extensions and 1 in the above figure.
The state shown by the two-dot chain line in the figure is centered on the intersection point indicated by the two-dot chain line and the two-dot chain line.
The endless sleeve-like intermediate transfer medium 85 which is driven and moved in contact with 1M, 1C, and 1K moves from a state shown by a solid line to a state shown by a two-dot chain line in FIG. The state changes to a state in which the peripheral length of the intermediate transfer medium 85 in contact with 1Y, 1M, 1C, and 1K is long.

However, in this embodiment, at least one of the plurality of rollers 82, 83, 84 shown in FIG. 1 has a tension function (not shown) for applying tension to the intermediate transfer medium 85. The intermediate transfer medium 8
The structure that does not change the state of contact with each of the photosensitive drums 1Y, 1M, 1C, and 1K by this tension, including the extension of 5, is provided.

On the other hand, the problem here is that the positions and outer diameters of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K change, and the state in which the peripheral length of the intermediate transfer medium 85 in contact with the photosensitive drums 1Y, 1M, 1C, and 1K needs to be longer. Then, each of the photosensitive drums 1Y, 1M, 1
C, 1K to the primary transfer unit 80Y,
A primary image formed by primary transfer by sequentially superimposing the images at 80M, 80C, and 80K is formed as an image that is relatively shifted by an amount corresponding to a longer peripheral length of the intermediate transfer medium 85. However, a plurality of rollers 82 for driving the intermediate transfer medium 85 of the present embodiment,
Since at least one of the rollers 83 and 84 has a corresponding expansion due to a change in the temperature and humidity environment, the intermediate transfer medium 85 is quickly driven by the corresponding expansion of the rollers, and the plurality of photosensitive drums 1Y, 1M, The intermediate transfer medium 85 moving in contact with 1C and 1K is configured to cancel a state in which the peripheral length of the intermediate transfer medium 85 needs to be long. In the present embodiment, the remaining cancellation can be reduced to about several μm.

In the present embodiment, the main chassis and the sub-chassis 100 are arranged on a base having the same sheet metal structure. However, the present invention is not limited to the base having this sheet metal structure, and the same operation is performed. If it can be configured, for example, a substrate made of the same material formed of a plastic material impregnated with glass fiber or the like, or a substrate formed of a combination of materials having substantially the same temperature or humidity expansion coefficient may be used. I do not care.

On the other hand, a plurality of photosensitive drums 1Y, 1M, 1
C, 1K to the primary transfer unit 80Y,
When a primary image is formed by successively superimposing primary images at 80M, 80C, and 80K to form a primary image, a phenomenon caused by the above-described changes in the temperature and humidity environment with respect to the relative displacement of the primary image in the sub-scanning direction. Other than the photosensitive drums 1Y, 1
Rotational fluctuations of M, 1C, 1K, rotation jitters latent in the intermediate transfer medium 85 and the drive system of each of the photosensitive drums 1Y, 1M, 1C, 1K, etc., have a specific periodicity in the sub-scanning direction of the primary image. In some cases, it may cause a deviation.

Therefore, in this embodiment, a plurality of photosensitive drums 1
The relative circumferences of Y, 1M, 1C, and 1K are constituted by lengths of an integer ratio including 1, and the respective photosensitive drums 1Y, 1Y,
1M, 1C, and 1K transfer the developed color toner image to the primary transfer units 80Y, 80M, 80C,
The length of the intermediate transfer medium 85 between the primary transfer positions at which the primary transfer is sequentially performed at 80K in a superimposed manner is a plurality of photosensitive drums 1Y, 1M, 1
Arrangement at a position that is an integer ratio with the circumference of C and 1K prevents accumulation of a phenomenon that causes relative displacement of the primary image in the sub-scanning direction with the above specific periodicity.

Regarding the above-described image forming apparatus of the present embodiment, the points to be noted here are arranged as follows.

1). <Regarding the Configuration of the Entire Apparatus> The configuration of the image forming apparatus of the present embodiment described above with reference to FIGS. 1 and 2 feeds the sheet material in synchronization with the movement of the intermediate transfer medium 85 on which the primary image is formed. First, the primary image synchronously merges with the sheet material at the secondary transfer portion 90, and is secondary-transferred to the synchronously fed sheet material to form a secondary image. This configuration is suitable for the purpose of making the entire apparatus compact, and in particular, reducing the height direction of the entire apparatus. When priority is given to reducing the size in the horizontal direction over the size in the height direction, Although illustration is omitted, a plurality of photosensitive drums 1Y, 1M, 1C, 1K and respective developing units 10Y, 10Y are provided.
M, 10C, 10K, the intermediate transfer medium 85, and the like are rotated in the opposite directions, and the intermediate transfer medium 85 is made to attract a sheet material by, for example, an electrostatic attraction means, so as to move from the photosensitive drum 1K side to the 1Y side. The photosensitive drums 1Y, 1M, 1
C, 1K developed different color toner images
The primary transfer units 80Y and 80Y do not pass through the intermediate transfer medium 85.
The image may be formed by sequentially superimposing the images at M, 80C, and 80K and transferring them to a sheet material. In this configuration, the intermediate transfer medium 85 does not fulfill the function of forming the primary image, but fulfills the function of the sheet conveying means.

Similarly, when priority is given to reducing the size in the horizontal direction over the size in the height direction, a plurality of photosensitive drums 1Y, 1M, 1C, and 1K are substantially horizontally adjacent to each other, although not shown. The photosensitive drums 1Y, 1M,
A plurality of developing units 10Y, 10M, 1 corresponding to 1C, 1K
0C and 10K, respectively, and the photosensitive drums 1Y and 1K
Exposure device 40 is arranged above M, 1C, 1K in a similar configuration, and intermediate transfer medium 85 of the same configuration is arranged below a plurality of photosensitive drums 1Y, 1M, 1C, 1K.
The primary image is formed on the intermediate transfer medium 85 by successively superimposing and primary transferring.

The intermediate transfer medium 85 for transporting the primary image
In synchronization with the movement of the sheet, the sheet material is fed, and the fed sheet material and the primary image conveyed by the movement of the intermediate transfer medium 85 are synchronously merged at the secondary transfer portion, and the synchronously fed sheet is fed. A structure may be employed in which a secondary image is formed by secondary transfer to a material, or each of the developing units 10Y, 10M,
The rotation direction of the intermediate transfer medium 85 and the like is reversed, and the sheet material is adsorbed on the intermediate transfer medium 85 by, for example, an electrostatic attraction. The photosensitive drums 1 </ b> Y, 1 </ b> Y constitute sheet material transporting means for transporting the material.
M, 1C, and 1K color toner images of different colors developed by the primary transfer unit 80 without the intermediate transfer medium 85 interposed therebetween.
The image may be formed by sequentially superimposing and transferring the images at Y, 80M, 80C, and 80K.

On the other hand, a sheet material conveying means for adsorbing the sheet material to the intermediate transfer medium 85 by means of, for example, electrostatic attraction and conveying the sheet material from the photosensitive drum 1K side to the 1Y side is a preferred example for sheet material conveyance. Therefore, the primary transfer portions 80Y and 80Y are applied to the sheet material without passing through the intermediate transfer process.
Since an image is formed by transferring the images at 80M, 80C, and 80K in an overlapping manner, a simple and inexpensive configuration is possible.

If another configuration is given as two examples,
The photosensitive drums 1Y, 1M, 1C, 1 shown in FIG.
K have a circular shape, and if they are arranged with substantially the same optical path length as described above, the primary transfer units 80Y and 80
M, 80C, and 80K are related to each other in a substantially arc shape, and when the sheet material is fed alone toward the primary transfer portions 80Y, 80M, 80C, and 80K, the sheet material and each of the primary transfer portions 80Y. , 80M, 80C, and 80K, there is a case where a problem arises in securing the relative positional relationship. Therefore, although illustration is omitted, for example, the plurality of photosensitive drums 1Y, 1M, 1C, 1
K is a configuration with a degree of freedom such as a belt photoreceptor,
The primary transfer units 80Y, 80M, 80C, and 80K are linearly related, and the primary transfer units 80Y, 80M, 80C,
When the sheet material is fed alone toward 80K, the relative positional relationship between the sheet material and each of the primary transfer portions 80Y, 80M, 80C, and 80K is easily ensured, and the structure is simplified and the cost is reduced. Is possible.

In the configuration shown in FIG. 1, the transport path for feeding the sheet material to the secondary transfer portion 90 is not limited to a function of guiding the sheet material, and no special transport means is constructed. When a sheet material transporting means for adsorbing and transporting the sheet material by a suction means such as electrostatic attraction to the sheet material transport belt such as the intermediate transfer medium 85 is constructed, the sheet material transport is stable, and the sheet material transport speed is increased. Can also respond.

In any of the above configurations, not only high-speed image formation is possible, but also a plurality of light emitting elements 42Y, 42M, 42C and 42K such as semiconductor lasers are provided with images of different colors by different image signals. A plurality of light beams are emitted correspondingly to each other, and the plurality of light beams are respectively reflected by the reflecting surface 43a at the common position of the rotary polygon mirror 43, are scanned in different directions, and are scanned in different directions. Are constituted by the plurality of optical paths 49Y, 49M, 49C, and 49K.

The plurality of optical paths 49 in different directions are provided.
In correspondence with Y, 49M, 49C, and 49K, the photosensitive drums 1Y, 1M, and 4M are located at positions on an arc where the optical path lengths of the plurality of optical paths 49Y, 49M, 49C, and 49K are substantially the same.
When 1C and 1K are arranged, a plurality of optical paths 49Y, 49M,
The scanning width of the light beam scanned by 49C and 49K is also substantially the same scanning width, and a plurality of light emitting elements 42Y, 42M, 42C,
42K can be modulated and formed on the basis of a common data clock frequency, though it is modulated corresponding to images of different colors by different image signals.

Further, a plurality of reflection mirrors are not required to guide a laser beam deflected and scanned to a photosensitive member as in the conventional image forming apparatus disclosed in Japanese Patent Publication No. 4-51829.
Further, a plurality of laser beams are divided by the different reflecting surfaces of the rotary polygon mirror in directions opposite to the first deflection direction and the second deflection direction, and the laser beams are deflected and scanned. A specially high-precision rotating polygon mirror for preventing color misregistration caused by the relative difference between the two is unnecessary, and a simple and inexpensive color image forming apparatus can be constructed.

2). <Regarding Fixing of Exposure Unit and Correspondence to Changes in Temperature and Humidity Environment> Exposure unit cases 44 and 46 in which the main components of the above-described exposure unit 40 are housed and unitized are not shown in detail, but are shown in FIG. And a plurality of optical paths 49Y, 49M, 49C, 49
A sub-chassis 1 stretched on a main chassis serving as a reference for the internal configuration of the device in which K is disposed at a symmetrical position sandwiching in the front-rear direction.
00, the position is as shown in detail in FIG. 3, that is, the reflection surface 43a at the common position of the rotary polygon mirror 43 is substantially uniform in the surface direction of the reflection surface 43a. , And a plurality of photosensitive drums 1Y, 1M, 1C,
It is fixed to the sub-chassis 100 by a fixing means such as a screw 45 at a position substantially parallel to 1K.

Even if there is a change in the temperature and humidity environment inside and outside the apparatus, the exposure unit 40 expands and contracts based on this fixed position, and the position of the reflection surface 43a is fixed in a structure that does not change. Initially, a plurality of optical paths 49Y, 49M,
If the photosensitive drums 1Y, 1M, 1C, and 1K are arranged at arc positions at positions where the optical path lengths of 49C and 49K are substantially the same, there is a change in the temperature and humidity environment inside and outside the apparatus. The primary transfer unit 80 transfers the color toner images of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K onto the intermediate transfer medium 85.
When a primary image is formed by successively superimposing primary images in the order of Y, 80M, 80C, and 80K to form a primary image, it is possible to suppress the occurrence of a relative shift in the primary transfer position and a deterioration in image quality. As a result, stable image formation can be achieved.

The supporting means that does not change the position of the reflection surface 43a has been specifically illustrated and described as an example. However, the present invention is not limited to this specific structure. Main chassis, sub chassis 1
The relative expansion and contraction amount is canceled by a combination of expansion and contraction systems that expand and contract due to changes in the temperature and humidity environment inside and outside the apparatus, such as the exposure device cases 44 and 46.
It is possible to obtain support means in which the position of a does not change.
In the above description, the screw 45 is used as a fixing means of the exposure device 40. However, for example, a fixing means such as caulking or welding may be used.

3). <Regarding Arrangement of Photosensitive Drums and Changes in Temperature and Humidity Environment> The plurality of photosensitive drums 1Y, 1Y,
1M, 1C, and 1K are arranged on a base having a sheet metal structure of the same quality as the sub-chassis 100 to which the exposure unit 40 is fixed, and when there is a change in the temperature or humidity environment inside and outside the apparatus, the above-described reflection surface 43a Multiple photosensitive drums 1 based on position
The positions of Y, 1M, 1C, and 1K correspond to the optical paths 49Y and 49, respectively.
It is configured to have a structure that relatively expands and contracts along M, 49C, and 49K. A plurality of optical paths 49Y, 49M, 49C, 49
The optical path length of K expands and contracts by substantially the same length, and a plurality of optical paths 49 are provided.
The scanning widths of the light beams scanned by Y, 49M, 49C, and 49K are also substantially the same.

In forming an image signal, there is no need for a special configuration such as detecting temperature and humidity inside and outside the apparatus and feeding back the detected contents to the image signal forming means to form an appropriate image signal. Thus, the plurality of light emitting elements 42Y, 4
The 2M, 42C, and 42K can be modulated based on a common data clock frequency although they are modulated corresponding to images of different colors by different image signals, respectively. An image forming apparatus can be configured.

Further, a plurality of photosensitive drums 1Y, 1M, 1
Even if the positions and outer diameters of C and 1K change and the intermediate transfer medium 85 in contact therewith changes to a state in which the peripheral length of the intermediate transfer medium 85 needs to be long, the photosensitive drums 1Y, 1M, 1C, and 1K move onto the intermediate transfer medium 85. To primary transfer units 80Y, 80M, 80C, 80K
The primary image formed by the primary transfer by sequentially superimposing the at least one of the plurality of rollers 82, 83, 84 for driving the intermediate transfer medium 85 is appropriately expanded by a change in temperature or humidity environment. Therefore, the intermediate transfer medium 85 is structured to cancel a state in which the intermediate transfer medium 85 that is driven quickly and moves in contact with the plurality of photosensitive drums 1Y, 1M, 1C, and 1K requires a long circumferential length.

The remaining cancellation can be reduced to about several μm, and even if there is a change in the temperature or humidity environment inside and outside the apparatus, the color toner images on the plurality of photosensitive drums 1Y, 1M, 1C and 1K are transferred intermediately. The primary transfer unit 80Y on the medium 85,
When a primary image is formed by successively superimposing primary images at 80M, 80C, and 80K to form a primary image, it is possible to suppress the occurrence of a relative shift in the primary transfer position and a deterioration in image quality. And stable image formation.

Here, the plurality of photosensitive drums 1Y, 1M, 1
A specific example of canceling the relative displacement of the primary transfer position even when the positions and outer diameters of C and 1K change will be described in detail.

The exposing device 40 and the plurality of photosensitive drums 1Y, 1
The supporting base supporting M, 1C and 1K has a coefficient of thermal expansion of 1
It is composed of a sheet metal structure of 1.6X10-6 / ° C,
Each of the photosensitive drums 1Y, 1M, 1C, and 1K has a plurality of optical paths 4 having substantially the same length by forming an aluminum base having a thermal expansion coefficient of 23.1 × 10 −6 / ° C. with an outer diameter of 40 mm.
The optical path lengths of 9Y, 49M, 49C, and 49K are arranged at positions on an arc with a length of 300 mm, and the peripheral length of the intermediate transfer medium 85 in contact with the transfer positions of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K (see FIG. L1) of each photosensitive drum 1
62.8319 of 1/2 of the circumference of Y, 1M, 1C, 1K
mm, each photosensitive drum 1Y, 1M, 1
C and 1K are arranged.

On the other hand, the intermediate transfer medium 85 is driven by a roller 83 shown in FIG.
Outer diameter 25 mm (perimeter: 25) consisting of 1.6 × 10 -6 / ° C
π = 78.5398 mm).

Based on the detailed structure described above, during actual color image formation, initial heat is generated by a control circuit (not shown) disposed inside the apparatus, heat generated by the fixing unit 60 and the like, and a change in the installation environment of the entire apparatus. Since it is necessary to anticipate a temperature rise of about 35 ° C. from the state, a mechanism for canceling a relative displacement of the primary transfer position under the temperature rise condition will be described.

First, the value at which each component changes under the temperature rise condition of 35 ° C. is the outer diameter of the photosensitive drum.
323mm Optical path length ・ ・ ・ ・ ・ ・ ・ ・ 300.1
138 mm Perimeter of the intermediate transfer medium 85 (L2 in FIG. 4) 63.0
720mm Roller 83 circumference ... 78.5
398 mm. The change in the circumferential length of the intermediate transfer medium 85 between the transfer positions between the photosensitive drums 1Y and 1K is (63.0720-62.8319) × 3 = 0.072.
03 (mm) B. The change in the circumferential length of the roller 83 is 78.5717-78.
5398 = 0.0319 (mm) C.I. Initially, the intermediate transfer medium 85 is moved from the photosensitive drums 1Y to 1Y.
The number of rotations of the roller 83 for moving between K is 62.8.
319 X 3 / 78.5398 = 2.40000 (rotation) Therefore, the change in the circumferential length of the intermediate transfer medium 85 is
The remaining amount canceled by the perimeter change of 3 is 0.07
203− (0.0319 × 2.40000) = − 0.00
453 (mm).

That is, when the change in the circumferential length of the intermediate transfer medium 85 (lengthened portion) is canceled by the change in the circumferential length of the roller 83 (lengthened portion), the intermediate transfer medium 85 has a value of 4. Although it moves 5 μm faster, this remaining amount of cancellation has no substantial problem for image formation.

Based on the above relationship, the support base for supporting the exposure device 40 and the plurality of photosensitive drums 1Y, 1M, 1C, 1K is formed of, for example, plastic filled with glass fiber or the like, and the roller 83 is formed of, for example, stainless steel or the like. Even if it is formed of a plastic filled with a brass material or a glass fiber, an approximated similar relationship can be established.

In the present embodiment, the main chassis and the sub-chassis 100 are arranged on a base having the same sheet metal structure. However, the present invention is not limited to the base having the sheet metal structure, and the same operation is performed. If it can be configured, for example, a substrate made of the same material formed of a plastic material impregnated with glass fiber or the like, or a substrate formed of a combination of materials having substantially the same temperature or humidity expansion coefficient may be used. I do not care.

4). <Regarding Toner Supply to Developing Unit> As described above, each of the developing units 10Y, 10M,
10C and 10K are configured to replenish toner that decreases with development by replacing the toner tank 20.
Since each of the developing units 10Y, 10M, 10C, and 10K only needs to store a minimum necessary amount of toner that does not hinder the image forming process, an extremely small configuration is possible. As shown in FIG.
For the configuration in which Y, 10M, 10C, and 10K are arranged,
In addition to simplifying the configuration for miniaturizing the apparatus, the toner in the storage unit 11 is kept to the minimum necessary amount that does not hinder the image forming process, so that the deterioration of the toner due to the operation of the image forming process is prevented. .

Further, the toner tank 20 is
0, outside the optical paths 49Y, 49M, 49C, 49K irradiated toward the respective photosensitive drums 1Y, 1M, 1C, 1K, that is, in FIG. 1, each of the developing units 10Y, 10M,
10C and 10K, the toner tank 20Y is attached to the developing unit 10Y on the front side of the optical path 49Y in the figure, the toner tank 20M is attached to the developing unit 10M is located on the rear side of the optical path 49M in the figure, and the toner is applied to the developing unit 10C. The tank 20C is mounted in front of the optical path 49Y in the drawing,
The mounting of the toner tank 20K with respect to the K
(In the figure, the toner tank 20M and the toner tank 20K are arranged in a zigzag pattern, not shown).
Effective spatial arrangement avoiding mutual interference. Similarly, as in the color image forming apparatus of this embodiment, a plurality of developing units 1 are provided.
In the configuration in which 0Y, 10M, 10C, and 10K are arranged, not only the size of the apparatus can be easily reduced, but also the toner tank 20 is arranged in a so-called staggered arrangement (not shown), so that the operability of attachment and detachment is improved.

In the color image forming apparatus of this embodiment,
Each of the toner tanks 20Y, 20M, 20C, and 20K contains yellow, magenta, cyan, and black color toners, and each of the developing units 10Y, 10M, and 20K.
Reference numerals 10C and 10K denote yellow, magenta, cyan, and black color developments corresponding to the color toners, respectively.
Since 0C and 20K can be exchanged independently, efficient toner replenishment is possible even when the consumed yellow, magenta, cyan, and black color toners are in an uneven consumption form.

The photosensitive drums 1Y, 1M, 1C, 1K
The developing units 10Y, 10M, 10C, and 10K that have enabled color toner development correspond to the supply rollers 13Y, 13M, 13C, and 13K and the developing roller 12 described above.
Y, 12M, 12C, 12K and regulating members 14Y, 14
Main members such as M, 14C, 14K and endless coil springs 31Y, 31M, 31C, 31K are housed in developing device cases 17Y, 17M, 17C, 17K, respectively, and are unitized to be detachable from the main body. In addition, at the time of maintenance of the above-mentioned structural part, it is configured to be integrally removed and repaired or replaced, so that its operability is excellent.

5). <Relationship Between Photosensitive Drum and Intermediate Transfer Medium> As described above, in the relationship between the photosensitive drum and the intermediate transfer medium of the present embodiment, the relative circumference of the plurality of photosensitive drums 1Y, 1M, 1C, and 1K is 1 , And each of the photosensitive drums 1Y, 1M, 1C, and 1K transfers the developed color toner image onto the intermediate transfer medium 85 by primary transfer units 80Y, 80M, 80C, and 80K. The circumferential length (L1 in FIG. 4) of the intermediate transfer medium 85 between the primary transfer positions at which the primary transfer is performed sequentially in a superposed manner is a plurality of photosensitive drums 1Y, 1M, 1C, and 1K.
Are arranged at a position that is an integer ratio to the circumference of the photosensitive drums 1Y, 1M, 1C, and 1K, and the drive system of the intermediate transfer medium 85 and the photosensitive drums 1Y, 1M, 1C, and 1K. Since the accumulation of relative displacement in the sub-scanning direction of the primary image having a specific periodicity caused by latent rotation jitter and the like is prevented, the relative displacement of the primary image is suppressed to a small amount. As a result, a stable image can be formed.

On the other hand, a plurality of photosensitive drums 1Y, 1M, 1
In the relationship between C and 1K, FIG. 1 shows a common size. However, if the relative perimeter is constituted by a length of an integer ratio including 1 with respect to this size, the above-described size is obtained. Although the relationship is established, the illustration is omitted, but only the circumference of the photosensitive drum 1K on which the black toner is developed in FIG. 1 is an integer ratio of the circumference of the other photosensitive drums 1Y, 1M and 1C. In this case, the life of the photosensitive drum 1K is long even if the black toner image is used relatively frequently during actual use. Therefore, the life is set to approximately the same as the other photosensitive drums 1Y, 1M, and 1C. Things are also possible.

6). <Regarding Application of Transfer Bias to Intermediate Transfer Medium> As described above, the transfer bias application structure to the intermediate transfer medium of the present embodiment employs the reverse development of the photosensitive drums 1Y, 1M, 1C, and 1K from the back of the intermediate transfer medium 85. A bias is applied by slidably contacting an electrode 81 formed of, for example, a conductive brush material, a conductive film, or a metal material, which has means for intensively applying a bias of about DC1 to 3 KV having a polarity opposite to the polarity of the formed color toner image. A bias application structure for sequentially transferring the color toner images to the intermediate transfer medium 85 in a primary manner is not only simple and inexpensive, but also generates ozone, for example, a structure in which a bias is applied by a corona discharger. And the use environment can be improved.

The configuration in which a bias is applied from the electrode 81 formed of, for example, a conductive brush material, a conductive film, or a metal material is suitable for intensively applying a bias. Are sequentially transferred onto the intermediate transfer medium 85, the scattering phenomenon of the color toner image is small, and a stable primary image can be formed.

On the other hand, the primary transfer sections 80Y, 80M, 8
The bias voltage applied from the electrode 81 at 0C and 80K is
In the primary transfer process, the color toner images are sequentially superimposed on the primary transfer units 80Y, 80M, 80C, and 80K, and are set on the intermediate transfer medium 85 in the primary transfer process. Even if a primary image is formed by transfer, it is easy to transfer color toner images that are transferred one after another with respect to the color toner image that has been transferred first by using an appropriate bias voltage. The transfer bias at the time of transfer and the transfer bias at the time of successive transfer can be easily switched at least sequentially to a high-voltage transfer bias, and a stable primary image can be formed.

7). <Regarding Unit Structure of Intermediate Transfer Medium and Photosensitive Drum> Each photosensitive drum 1 is stretched over a plurality of photosensitive drums 1Y, 1M, 1C, 1K and a plurality of rollers 82, 83, 84.
When the intermediate transfer medium 85 in the form of a flexible endless sleeve that is driven in contact with Y, 1M, 1C, and 1K and moves in the direction of the arrow in FIG. 1 is unitized and configured to be detachable from the main body. , Each photosensitive drum 1Y, 1M, 1C, 1K
During maintenance of the intermediate transfer medium 85 and the intermediate transfer medium 85, it is convenient to take out the unit and facilitate repair or replacement, and to stabilize the relative positional relationship and drive relationship between the intermediate transfer medium 85 and the plurality of photosensitive drums 1Y, 1M, 1C and 1K. Maintenance can be achieved.

[0096]

As described above, according to the image forming apparatus of the present invention, a plurality of photosensitive members and an exposing means for deflecting and scanning each of the photosensitive members with a laser beam modulated by an image signal are used. In the image forming apparatus provided with, the exposure unit includes a plurality of laser light sources and one rotary polygon mirror that reflects and deflects and scans each laser beam of the plurality of laser light sources. The laser light source is arranged at a position where the laser beam is reflected from the reflection surface, and each laser light source is arranged at a position where the laser beam is incident on the common reflection surface from a different angle. Are placed at positions where the optical path lengths of the
In each laser light source, the laser beam is modulated by using a common clock signal, and the laser beams are arranged at positions where the laser beams are incident on the common position on the reflecting surface from different angles. And the scanning width of the laser beam scanned by a plurality of optical paths can be easily made substantially the same. Further, in forming an image signal, different color signals are formed by different image signals. Despite being modulated in accordance with an image, modulation can be formed based on a common data clock frequency without requiring a special configuration. Further, the surface accuracy and rotation accuracy of the reflection surface are canceled, and the reflection of the plurality of laser beams becomes uniform. Therefore, it is not necessary to use a plurality of reflection mirrors to guide a plurality of laser beams to the photoreceptor, and further, it is not necessary to use a rotating polygon mirror configured with a particularly high precision.
An inexpensive color image forming apparatus having a simple structure and a high speed can be configured.

According to the present invention, not only is the structure simple and effective for miniaturization, but also a more inexpensive configuration is possible, and stable image formation without color shift is possible. Not only can the degree of freedom be improved and the entire apparatus can be made compact, it is not necessary to use a plurality of reflection mirrors to guide a plurality of laser beams to the photoreceptor. The plurality of laser beams are divided by the reflecting surface in a direction opposite to the first deflection direction and the second deflection direction, and deflecting scanning is performed, so that a color shift caused by a relative difference in the sub-scanning direction due to a relative parallel difference of the reflecting surface. It does not require a specially high-precision rotating polygon mirror to prevent it, and it is possible to configure a simple and high-speed inexpensive color image forming apparatus. of When forming an image by sequentially superimposing and transferring toner images developed on an optical body onto a recording medium, a stable image is suppressed by suppressing a relative shift from occurring in a transfer position and deteriorating image quality. The present invention has many practical effects, such as being able to form, and the practical effects are extremely large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the entire configuration of a color image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view of a main part of a development, in which a part of a development part of the color image forming apparatus of the present invention is enlarged and illustrated.

FIG. 3 is a partial cross-sectional view of a main part of the exposure device of the color image forming apparatus of the present invention, showing a main part of the exposure device.

FIG. 4 is a photoconductor arrangement explanatory view for explaining an arrangement relationship of photoconductors in the color image forming apparatus of the present invention.

[Explanation of symbols]

1Y, 1M, 1C, 1K: photosensitive drum, 2Y, 2M, 2
C, 2K: charging roller, 10Y, 10M, 10C, 10
K: developing unit, 20Y, 20M, 20C, 20K: toner tank, 30: toner conveying unit, 31: coil spring, 40: exposure unit, 42Y, 42M, 42C, 42K ...
Light-emitting element, 49Y, 49M, 49C, 49K ... optical path, 6
0: fixing unit, 80Y, 80M, 80C, 80K: primary transfer unit, 81: transfer roller, 82, 83, 84: roller,
85 ... Intermediate transfer medium

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H04N 1/113 H04N 1/04 104A F-term (Reference) 2C362 AA42 BA52 BA54 BA83 BA90 CA22 CA39 DA04 2H030 AA01 AA06 AB02 AD07 AD13 AD16 BB02 BB13 BB23 BB63 2H045 AA01 BA22 BA34 5C072 AA01 BA19 CA06 CA09 CA11 DA04 DA21 HA02 HA06 HA13 HB01 HB08 HB13 QA14 XA04

Claims (6)

[Claims] 1. An image forming apparatus comprising: a plurality of photoconductors; and an exposure unit configured to deflect and scan each of the photoconductors with a laser beam modulated by an image signal for exposure.
The exposure means comprises a plurality of laser light sources and one rotary polygon mirror that reflects and deflects and scans each laser beam of the plurality of laser light sources. Each of the laser light sources is a common reflection surface of the rotary polygon mirror. An image forming apparatus, wherein the image forming apparatus is arranged at a position where the laser beam is reflected. 2. The image forming apparatus according to claim 1, wherein each of the photoconductors is arranged at a position where an optical path length from the reflection surface is substantially the same. 3. An exposure apparatus for exposing a plurality of photosensitive members by deflecting and scanning with a laser beam modulated by an image signal, wherein the plurality of laser light sources and the respective laser beams of the plurality of laser light sources are reflected. An exposure apparatus comprising one rotary polygon mirror for deflecting and scanning, wherein each of the laser light sources is arranged at a position where the laser beam is reflected by a common reflection surface of the rotary polygon mirror. 4. The image forming apparatus according to claim 1, wherein each of the laser light sources is arranged at a position where the laser beam enters the common reflection surface from a different angle. Exposure equipment. 5. The image forming apparatus according to claim 1, wherein each of the laser light sources modulates a laser beam using a common clock signal. 6. The image forming apparatus according to claim 1, wherein each of the laser light sources is arranged at a position where a laser beam enters a common position on the reflection surface from a different angle. Exposure equipment.