JPH10198114A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a developing means from being actuated and stopped in the midst of image exposure without prolonging the timing of forming an image at the time of switching a mode whether the mode is a color image forming mode or a monochrome image forming mode. SOLUTION: In the color image forming mode, means for the image exposure for yellow(Y), magenta(M), cyan(C) and black(K) are operated in a state where the respective corresponding developing means are turned on; at the time of switching the mode to the monochrome image forming mode for yellow(Y) continuously, the means for the image exposure for yellow(Y) is actuated when a little time t1 elapses after the on-state of the developing means for yellow(Y) is continued and other developing means are turned off; and at the time of switching the mode to the color image forming mode again, the respective image exposure means are started to be actuated by turning on other developing means when a little time t2 elapses after finishing the image exposure for yellow(Y).

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 such as a copying machine, a printer, a facsimile, etc., which forms an image by forming a charging means, an image exposing means and a developing means on the peripheral surface of an image forming body. More particularly, the present invention relates to a color image forming apparatus having a monochrome image forming function.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image, a photoconductor, a charger, a developing device and the like as image forming bodies of the same number as required colors are provided, each of which is an image forming body. A color image forming apparatus in which a single-color toner image formed on a photoreceptor is superimposed on a transfer body or the like to form a color image, or a single photoreceptor is rotated a plurality of times to repeatedly charge, image expose, and develop each color to obtain a color image A color image forming apparatus for forming an image and a color image forming apparatus for forming a color image by sequentially performing charging, image exposure, and development for each color within one rotation of one photoconductor are also known.

[0003] Each of the above-mentioned apparatuses can also have a function of forming a monochrome image of a specified color by controlling operations of charging, image exposure and development corresponding to each color.

[0004]

However, when the image exposure is continuously performed from color to monochrome or from monochrome to color, the speed of the photosensitive member is reduced due to a change in the load accompanying the start or stop of the operation of the developing means during the exposure. If it changes, the formed image will be distorted or misaligned, and the image quality will be significantly impaired.

[0005] The present invention solves this problem and improves the results.
It is an object of the present invention to provide a color image forming apparatus capable of forming both color and monochrome images with high quality by appropriately regulating the operation timing of the developing unit.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to dispose a plurality of charging means, image exposing means and developing means around an image forming body, and charge, image exposing and developing during rotation of the image forming body. A color image forming apparatus for forming a color toner image by superimposing the toner images, wherein the apparatus has a monochrome image forming mode and a color image forming mode, and has a monochrome image forming mode. In, the operation of the specific image exposure means is during the operation of the specific development means, and in the color image forming mode, the operation of each image exposure means is during the operation of all the development means, and is continuous from the color image formation mode. When switching to the monochrome image forming mode, the operation of the developing means other than the specific one is stopped after the operation of each image exposing means is completed, and the operation of the specific image exposing means is opened. A plurality of charging means, an image exposing means, and a developing means provided around the image forming body, respectively, while the image forming body is rotating. A color image forming apparatus that forms a toner image by repeating charging, image exposure and development to form a color toner image by superimposing the toner images, the device includes a monochrome image forming mode and a color image forming mode. In the monochrome image formation mode, the operation of the specific image exposure unit is during the operation of the specific development unit, and in the color image formation mode, the operation of each image exposure unit is during the operation of all the development units, When continuously switching from the monochrome image forming mode to the color image forming mode, all the developing units are in the operating state after the operation of the specific image exposing unit is completed. It is accomplished by a color image forming apparatus characterized by starting the operation of the image exposure means (invention according to claim 3).

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A basic configuration of a color image forming apparatus as one example of the present invention and an image forming process will be described with reference to FIGS.

FIG. 1 is a sectional view of a color image forming apparatus, FIG. 2 is a front view showing a support structure of a drum unit, FIG. 3 is a sectional view showing a support structure of a photosensitive drum, and FIG. FIG. 5 is an external view of the drum unit, and FIG. 5 is a front view showing a support structure of the intermediate transfer belt.

Photosensitive drum 1 as a drum-shaped image forming body
Numeral 0 denotes, for example, a cylindrical transparent substrate formed by a transparent member of a transparent acrylic resin provided inside, and a transparent conductive layer and an organic photoconductor layer (OPC) formed on the outer periphery of the substrate. In this state, it is rotated in the direction shown by the arrow in FIG.

In the present embodiment, it is sufficient that the photoconductive layer of the photosensitive drum has an exposure light amount capable of providing an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photoreceptor drum in the present embodiment does not need to be 100%, and may be such that a certain amount of light is absorbed when the exposure light is transmitted. As a material of the light-transmitting substrate, an acrylic resin, particularly one polymerized using a methyl methacrylate monomer, is preferably used because it is excellent in transparency, strength, precision, surface properties, and the like, but is used for other general optical members and the like. Used fluorine, polyester, polycarbonate, polyethylene terephthalate,
Various translucent resins, such as, for example, can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. The refractive index of these resins is approximately 1.5. As a method of forming the light-transmitting conductive layer, indium tin oxide (ITO), alumina, tin oxide, lead oxide, and the like can be used by vacuum evaporation, active reaction evaporation, various sputtering methods, and various CVD methods. Indium oxide, copper iodide, Au, Ag, Ni,
A light-transmitting thin film made of Al or the like is used,
A conductive resin composed of the above-mentioned metal fine particles and a binder resin is used by a dip coating method, a spray coating method or the like. Further, as the photoconductor layer, various organic photoreceptor layers (O
PC) can be used.

Examples of preferred image forming bodies are shown below.

After adding a catalyst for synthesizing and polymerizing the plastic material monomer, pour it into a cylindrical mold, seal and fix it with side plates, rotate it at high speed, and heat it appropriately. Promotes uniform polymerization. After completion of the polymerization, the mixture is cooled, the obtained transparent resin substrate is taken out of the mold, cut, and, if necessary, subjected to a finishing step to produce a transparent substrate for a photosensitive drum of an image forming apparatus (centrifugal polymerization method).

As a material of a transparent base material of a transparent plastic molded by centrifugal polymerization, as described above, a material obtained by polymerizing a methacrylic acid methyl ester monomer is used.
The best in transparency, strength, precision, surface properties, etc., but other polyethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polybutyl acrylate, polystyrene, polyimide, polyester or polyvinyl chloride, or these Copolymers and the like can be used. In the centrifugal polymerization method, since the roundness is determined by the mold used for molding, a highly accurate substrate can be obtained. In addition, uneven thickness varies depending on rotation unevenness and viscosity during polymerization and heating conditions during polymerization.

As the light-transmitting conductive layer provided on the base, indium tin oxide (ITO), tin oxide, lead oxide,
Indium oxide, alumina, copper iodide, Au, Ag,
A conductive resin obtained by mixing a resin and conductive fine particles made of Ni, Al, or the like is used. As a film forming method, a dip coating method, a spray coating method, or the like is preferably used.

The organic photoreceptor layer is composed of a charge generation material (CGM)
And a charge transport layer (CTL) containing a charge transport material (CTM) as a main component. The organic photoreceptor layer having a two-layer structure has a low CGL, and thus has good transparency of image exposure light and is suitable for the present invention. The organic photoreceptor layer may have a single-layer structure containing a charge generation material (CGM) and a charge transport material (CTM) in one layer, and may have the single-layer structure or the two-layer structure. Usually contains a binder resin.

In the photoreceptor drum having the two-layer organic photoreceptor layer, the CGM contained in the CGL may be an azo pigment, an azulenium pigment, a phthalocyanine pigment which is sensitive to light from a light source such as an LED or LD. , A perylene pigment is used, and infrared light (600 nm to 8
The CGM of the OPC photoreceptor sensitive to 50 nm) is as follows.
Copper phthalocyanine pigments and titanyl phthalocyanine pigments are preferably used.

As a binder resin used for CGL, a polyvinyl butyral resin or a polycarbonate resin is used, which is excellent in sensitivity, potential change upon repeated use, and the like. These binder resins can be used alone or as a mixture of two or more.

As a solvent or a dispersion medium used for forming CGL, a ketone-based or halogen-based solvent is preferably used, and sensitivity and potential change upon repeated use are further improved. These solvents can be used alone or as a mixture of two or more solvents.

The weight ratio of CGM to the binder resin in the CGL is 100: 1 to 1000, the thickness of the CGL is 0.01 to 10 μm, and the coating method for forming the CGL is a blade. There are various coating methods such as coating, wire bar coating, spray coating, dip coating and slide hopper coating.

Next, as the CTM contained in the CTL, a hydrazone compound, a styryl compound, a benzidine compound, a stilbene compound or the like is used.

The binder resin used in the CTL can be selected from a wide range of insulating resins as appropriate, and preferred binder resins include silicon-alkyd resin, phenol-formaldehyde resin, and poly-N- Insulating resins such as vinyl carbazole and polysilane can be mentioned, and these binder resins can be used alone or in combination of two or more.

The mixing ratio of the binder resin and CTM is 1:
It is set to 10 to 500, more preferably 1:20 to 150. The thickness of the CTL is set to 1: 100 μm, preferably 5 to 50 μm.

As a coating method, a method similar to CGL can be used.

An intermediate layer is provided between the organic photoreceptor layer and the translucent conductive layer if necessary.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate bimaleic acid copolymer, ethyl cellulose, carboxymethyl cellulose,
It is a resin layer having a thickness of 0.01 to 2 μm, such as a copolymer type or modified type alcohol-soluble polyamide resin.

By using a plastic cylindrical transparent substrate produced by the above-described manufacturing method, the thickness is uniform, the cylindrical substrate has excellent cylindricity and roundness, and the defocus of image exposure light is reduced. No photoreceptor drum is provided.

Reference numeral 11 denotes a scorotron charger (hereinafter, simply referred to as a charger) which performs a charging action on the above-mentioned organic photoreceptor layer of the photoreceptor drum 10 by a grid maintained at a predetermined potential and corona discharge by a discharge wire. A uniform potential is applied to the photosensitive drum 10.

Reference numeral 12 denotes an image exposure means, that is, the photosensitive drum 1
An exposure optical system composed of a light emitting element such as an LED arranged in the axial direction of 0 and a SELFOC lens which is an equal-magnification image forming system. Each is input to the exposure optical system 12 as an electric signal.

Each of the exposure optical systems 12 is attached to a support member 20 provided as an optical system support means, and is accommodated in the base of the photosensitive drum 10.

Reference numerals 13Y to 13K denote developing units for accommodating yellow (Y), magenta (M), cyan (C) and black (K) developers, each having a predetermined gap with respect to the peripheral surface of the photosensitive drum 10. And a developing sleeve 130 that rotates in the same direction while maintaining the same.

Each of the developing devices 13 includes the charging device 1 described above.
The electrostatic latent image on the photosensitive drum 10 formed by the charging of the photosensitive drum 1 and the image exposure by the exposure optical system 12 is reversely developed in a non-contact state by applying a developing bias voltage.

In an image reading apparatus separate from the present apparatus, image data read from an original image by an image pickup device or image data edited by a computer is
The image signals are temporarily stored and stored in a memory as image signals for respective colors of Y, M, C and K.

At the start of image recording, the photoconductor driving motor starts to rotate the photoconductor drum 10 in a counterclockwise direction, and at the same time, the application of a potential to the photoconductor drum 10 by the charging action of the charger 11 (Y) starts. Is done.

After the photosensitive drum 10 is applied with a potential, the exposure optical system 12 (Y) starts exposure with an electric signal corresponding to a first color signal, that is, an image signal of yellow (Y). An electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface by rotational scanning.

The latent image is reversely developed by the developing device 13 (Y) in a state where the developer on the developing sleeve 130 is not in contact with the developer, and a yellow (Y) toner image is formed in accordance with the rotation of the photosensitive drum 10. .

Next, the photosensitive drum 10 is further provided with a potential on the yellow (Y) toner image by the charging action of the charger 11 (M), and the second color signal of the exposure optical system 12 (M), ie, Exposure is performed with an electric signal corresponding to the magenta (M) image signal, and the magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the developing device 13 (M). Are sequentially superimposed and formed.

By the same process, the charger 11 (C),
The exposure optical system 12 (C) and the developing unit 13 (C) further form a cyan (C) toner image corresponding to the third color signal, and the charging unit 11 (K), the exposure optical system 12 (K) and the developing unit 13 (C). A black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed by the unit 13 (K), and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10. You.

The exposure of the organic photosensitive layer of the photosensitive drum 10 by each of the exposure optical systems 12 is performed from the inside of the drum through a substrate transparent to the above-mentioned exposure wavelength. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image. To stabilize the temperature in the photosensitive drum 10 and prevent the temperature from rising due to the heat generated by each exposure optical system 12, a material having good thermal conductivity is used for the support member 20. In the case of (1), measures such as radiating heat to the outside through the heat pipe can be suppressed to a level that does not cause any trouble. Further, at the time of the developing action by each developing device 13, a developing bias voltage to which a direct current or further alternating current is applied is applied to the developing sleeve 130, respectively, and the jumping development by the one-component or two-component developer housed in the developing device 13 is performed. And the photosensitive drum 10 for grounding the transparent conductive layer
Is subjected to non-contact reversal development.

Thus, the color toner image formed on the peripheral surface of the photosensitive drum 10 is temporarily transferred to the peripheral surface of the intermediate transfer belt 14 provided as an intermediate transfer means.

The intermediate transfer belt 14 has a thickness of 0.5 to 2.0.
mm, a semiconductive substrate of silicon rubber or urethane rubber having a resistance of 10 ⁸ to 10 ¹² Ω · cm, and a thickness of 5 to 50 μm as a toner filming preventing layer on the outside of the rubber substrate. And a two-layer structure with fluorine coating. This layer also preferably has a similar semiconductivity. 0.1-0.5m thickness instead of rubber belt base
m, a semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like can also be used. The intermediate transfer belt 14 has rollers 14A, 14B,
The photosensitive drum 10 is stretched between the rollers 14C and 14D and circulated clockwise in synchronization with the peripheral speed of the photosensitive drum 10 by the power transmitted to the roller 14D.

The intermediate transfer belt 14 has a roller 14A.
The belt surface between the roller 14B and the roller 14B is in contact with the peripheral surface of the photosensitive drum 10, while the belt surface on the outer periphery of the roller 14C is in contact with the transfer roller 15, which is a transfer member, to form a toner image transfer area at each contact point. ing.

The color toner image adhered to the peripheral surface of the photosensitive drum 10 is first subjected to intermediate transfer by applying a bias voltage having a polarity opposite to that of the toner to the roller 14B at the contact point between the intermediate transfer belt 14 and the roller 14B. The image is transferred to the peripheral surface of the belt 14. That is, the color toner image on the drum is conveyed to the transfer area without scattering the toner by the guidance of the grounded roller 14A,
The transfer is efficiently performed on the intermediate transfer belt 14 side by applying a bias voltage of about 2 kV.

On the other hand, the transfer paper P is carried out by the operation of the paper feed roller 17 of a paper feed cassette (not shown) and fed to the timing roller 18, and is synchronized with the transfer of the color toner image on the intermediate transfer belt 14. The paper is fed to the transfer area of the transfer roller 15.

The transfer roller 15 is connected to the intermediate transfer belt 14.
The transfer paper P fed in the counterclockwise direction is synchronized with the peripheral speed of the intermediate transfer in the transfer area formed by the nip portion between the transfer roller 15 and the roller 14C in the ground state. The color toner images are successively transferred onto the transfer paper P by applying a bias voltage of the opposite polarity to the toner of 1 to 2 kV to the transfer roller 15 in close contact with the color toner image on the belt 14.

The transfer paper P to which the color toner image has been transferred is neutralized, conveyed to the fixing device 91 via the conveyance plate 19, and nipped and conveyed between the heat roller 91A and the pressure roller 91B to be heated. Is fused and fixed, and then discharged to the outside of the apparatus via a discharge roller 92.

Cleaning devices 100 and 140 are installed on the photosensitive drum 10 and the intermediate transfer belt 14, respectively, and the blades of the cleaning devices 100 and 140 are always in pressure contact with each other. It is kept clean.

The support member 20 is composed of a pair of front and rear members fixed to a rotation support shaft 30 of the photosensitive drum 10 as shown in FIGS.
2 has both ends adjusted so that the distance to the photosensitive surface via the attaching member 21 is in a predetermined positional relationship, and is fixed to the adjustment position by bonding.

On the other hand, the photosensitive drum 10 has flange members 10A and 10B provided at both ends thereof rotatably supported by the support member 20 via bearings B, respectively, and is driven by a gear 10G provided in the flange member 10B. It is rotated about the rotation support shaft 30 in a fixed state as a rotation center.

The rotation support shaft 30 is connected to the photosensitive drum 10
Each of the symmetrical front and rear side plates 40 formed in a U-shape and integrally connected while supporting each of the exposure optical systems 12.
The bearing is supported between.

The side plate 40 is provided with rail members 50 as hanging means at the front and rear connecting portions, and the rail members 50 are inserted into and engaged with the guide members 60 provided in the apparatus main body to be in a suspended state. By doing so, the rotation support shaft 30, and thus the photosensitive drum 10 and each of the exposure optical systems 12 are placed at substantially predetermined positions.

Further, when the rotation support shaft 30 is inserted to a regular position, the shaft end 30B protruding from the rear side plate 40 from the above-mentioned suspended state is fitted into the receiving seat 71 provided on the apparatus board, Shaft end 3 protruding from front side plate 40
0A is supported by the screw member 82 which is tapered into the receiving seat 81 provided on the support substrate 80, thereby accurately regulating the photosensitive drum 10 to a regular set position, and
Is meshed with the gear on the driving side, and each exposure optical system 12 further moves the through pin P1 provided on the shaft end 30B to the above-mentioned seat 71.
By being engaged with the V-shaped groove formed in the cross section, a predetermined angular position with respect to the apparatus main body is accurately regulated and brought into a fixed state. Thereafter, the lead wire of each optical system is connected to the window 20A of the support member 20 on the front side through the cutout portion 40 of the side plate 40.
A is connected to the power supply via A.

The support substrate 80 has upper and lower reference holes H.
1 is engaged with a pair of reference pins P2 provided on the front device board 70, the attachment position thereof is determined, and is fixed to the front device board 70 by a plurality of screwing screws. Each of the rod-shaped chargers 11 having the window 80A opened and having the above-described rod shape is inserted from the outside of the support substrate 80 to be set at a predetermined interval position with respect to the photoconductor drum 10, and a screwing screw is set in a state where the electrodes are connected. It is fixed and supported by.

Therefore, the support substrate 80 is provided with each charger 1
When the screw member 82 is removed in a state where 1 is removed through the window 80A, the screw member 82 is only released from a plurality of screw holes, and is separated from the device substrate 70. From this state, the side plate 40 is removed. The rail member 50 is slid under the guidance of the guide member 60 so that the photosensitive drum 10 and each of the exposure optical systems 12 are integrally moved in the horizontal direction, and can be taken out of the apparatus main body through the opening 70A of the apparatus substrate 70. Becomes

Prior to the start of the attaching / detaching operation of the photosensitive drum 10 supported by the side plate 40 to the apparatus main body, each developing unit 13, the intermediate transfer belt 14, and the cleaning device 100 with respect to the peripheral surface of the photosensitive drum 10 are started. Each pressing action of the blade is released in advance, and the blade is in a retracted state of about 1 to 10 mm, and is returned to the pressed state again after mounting.

After the side plate 40 is removed from the apparatus main body, the rail member 50 can be placed on the lower side as shown in FIG. 4 so that the photosensitive drum and the like can be placed in a well-balanced manner so as not to come into contact with the floor surface. Function as a table,
It is also used to protect the photoreceptor surface.

Each of the rollers 14A to 14D is formed in a U-shape in a state where the intermediate transfer belt 14 is stretched by the urging force of the tension roller T, and the front and rear side plates 45 are integrally connected. Bearings are supported between them.

Each of the side plates 45 is further formed in a U-shape, and each of the asymmetric front and rear support substrates 85 is integrally connected.
Between the cleaning device 140 and the cleaning device 140.

The front support substrate 85 has a reference hole H2 as a suspending means at the upper and lower rising portions 85A, while the rear support substrate 85 has a pair of reference pins P4 as the suspending means at the back. The reference hole H
2 has a reference pin P3 provided on the front device board 70, and a reference hole H having the reference pin P4 provided on the rear device board.
The intermediate transfer belt 14 is set at a predetermined position by screwing and fixing the upper screw engaged with the photosensitive drum 1 and the photosensitive drum 1.
0 to form a first transfer area for transferring a toner image from the photosensitive drum 10 to the intermediate transfer belt 14 by pressing the transfer material from the intermediate transfer belt 14 with the transfer roller 15. A second transfer area for transferring the toner image to the image is formed.

The support substrate 85 is provided between the front and rear device substrates 70.
On the other hand, it is supported so as to be able to be pulled out to the front side of the apparatus main body via a pair of guide rails 200 which can be extended and contracted in two steps called an accuride rail (trade name).

The support substrate 85 is formed by a pair of front and rear guide plates 86 provided on the left and right sides, respectively.
The movable part 200A is slidably held in the vertical direction, and the movable part 200A is integrated in the pulling-out direction.
It is configured to be able to descend until it hits 00A.

The support substrate 85 is released slightly from the front side of the apparatus main body after releasing the screw, and the reference pins and the reference holes described above are released from engagement with each other, so that the support substrate 85 is slightly lowered. Therefore, when the respective abutment plates 87 are mounted on the movable portions 200A, the guide rails 200 are extended to the front of the apparatus main body from the openings 70A of the apparatus substrate 70 by the extension operation of the guide rails 200. As a result, the intermediate transfer belt 14
The guide rail 200 is retracted from the peripheral surface of the photosensitive drum 10 and is pulled out in a state where the pressure contact is released. Move to the photosensitive drum 10
The operation of returning to the pressure-contact state is automatically and reliably performed.

Accordingly, the photosensitive drum 10 can be taken out without interfering with the intermediate transfer belt 14 by a very simple operation of attaching / detaching the support substrate 85, and furthermore, the jammed paper staying in the conveyance path by pulling out the support substrate 85 is removed. Maintenance such as removal processing, replacement of the intermediate transfer belt 14, and inspection can be easily performed.

Prior to the operation of pulling out the support substrate 85 from the apparatus main body, the pressing action of the transfer roller against the roller 14C which stretches the intermediate transfer belt 14 is released in advance, and after returning to the predetermined set position, the supporting board 85 is pressed again. Placed in state.

The color image forming apparatus has a function of switching between an image forming mode between a color image forming mode and a monochrome image forming mode. The mode can be switched to the formation mode, and the monochrome image formation mode for the specified color can be switched to the color image formation mode.

When the monochrome image forming mode is set,
Only the charging, image exposure and development corresponding to the specified color are activated (ON), and all the operations corresponding to the other colors are stopped (OFF).

Power is transmitted to each of the developing units 13 by the operation of a gear train as shown in FIG. 6, and when the photosensitive drum 10 is mounted at a predetermined set position in the apparatus main body, the developing unit 13 is integrated therewith. When the gear 10G provided coaxially with the photosensitive drum 10 meshes with the drive gear DG on the apparatus main body side, and the developing device 13 is mounted at a predetermined position, the electromagnetic clutch C is attached to the developing sleeve 130. The gear 130GA connected through the gear is meshed with the gear 10G.

In the color image forming mode, all the electromagnetic clutches C connecting the respective developing units 13 are turned on, whereby the developing sleeve 130 is turned on by the stirring member 131.
And in the monochrome image forming mode, only the electromagnetic clutch C connected to the specified developing device 13 is turned ON, and each developing sleeve 130 of the developing device 13 other than the specified one is turned on. And the stirring member 131
Is stopped (OFF).

When the image forming mode is switched during continuous image formation, the operation (ON) or stop (OFF) timing of each developing unit 13 is controlled as described below with reference to the image exposure timing.

The apparatus for explaining the present embodiment employs an internal image exposure system in which a plurality of image exposure means are provided inside an image forming body, but a plurality of image exposure means are provided outside the image forming body. The same can be applied to the provided external image exposure system.

(Embodiment 1) An embodiment of the invention according to claims 1 and 2 will be described with reference to FIGS.

FIG. 7 shows a state in which the first image is formed during the color image forming mode.
Is a time chart when the yellow (Y) monochrome image forming mode is inserted as an example. In forming a color image, all the developing devices 13 are turned off before the yellow (Y) image exposure is started. At the same time, the magenta (M), cyan (C), and black (K) developing units 13 are turned off at the same time when the development of black (K), which is the last image forming of the color image, is completed, and the yellow (Y) Developing device 1
The state where only 3 (Y) is ON is continued.

In the subsequent formation of a monochrome image, yellow (Y) image exposure is started after a short time t1 from the time when only the yellow (Y) developing unit 13 (Y) is turned on, and After a short period of time t2 after the end of the exposure, each of the magenta (M), cyan (C) and black (K) developing units 13 is returned to the ON state, and the yellow (Y) developing unit is maintained in the ON state. The mode is switched again to the color image forming mode together with the mode No. 13.

Since a time T required for the transfer paper P to pass at a predetermined interval is provided between each image forming process, the above-mentioned times t1 and t2 can be set with a margin. Thus, the image exposure of yellow (Y) can be started and ended while only the corresponding developing device 13 (Y) is operating, without the image forming timing being extended.

FIG. 8 shows a state in which the second
Is a time chart when the most frequently used black (K) monochrome image forming mode is inserted as an example. In forming a monochrome image, yellow (Y), magenta (M), and cyan (C) are used. ) Is turned off and only the black (K) developing device 13 (K) is turned on, and after a short time t3, the black (K) is turned on.
Is started, and after a short time t4 after the end of the image exposure, the developing units 13 for yellow (Y), magenta (M) and cyan (C) are returned to the ON state, and the color image forming mode is resumed. Can be switched to

Also in this case, the times t3 and t4
Can be sufficiently set by setting a time T required for the transfer paper P to pass at a predetermined interval, whereby the black (K) image exposure can be continuously performed without extending the image forming timing. Is the corresponding developing device 13
It is possible to start and end during the operation of only (K).

In the same manner, even when forming a magenta (M) or cyan (C) monochrome image, the image forming timing is continuously extended without extending the image forming timing while only the corresponding developing unit 13 is operating. Can be started and ended.

(Embodiment 2) An embodiment of the present invention according to claims 3 and 4 will be described with reference to FIGS. 9 and 10. FIG.

FIG. 9 shows a time chart when a color image forming mode is inserted in the middle of a yellow (Y) monochrome image forming mode as a first example. In forming a yellow (Y) monochrome image, FIG. Prior to the start of the yellow (Y) image exposure, only the yellow (Y) developing unit 13 (Y) is turned on, and the ON state is maintained even after the yellow (Y) image exposure is completed.

In the subsequent formation of a color image, the magenta (M), cyan (C) and black (K) developing units 13 are used.
Is turned on, the yellow (Y) image exposure is started after a short time t5, and a short time t6 after the end of the black (K) image exposure corresponding to the last image formation of the color image. After that, the magenta (M), cyan (C), and black (K) developing units 13 are returned to the OFF state, and the mode is switched again to the yellow (Y) monochrome image forming mode.

Since the time T required for the transfer paper P to pass at a predetermined interval is provided between each image forming process, the above-mentioned time t5 and t6 can be set with a margin. Therefore, each color image exposure can be started and ended during the operation of all the developing units 13 continuously without extending the timing of image formation.

FIG. 10 shows a second example of a time chart when the color image forming mode is inserted in the middle of the black (K) monochrome image forming mode which is most frequently used. In this case, after the development of the black (K) is completed, the yellow (Y) image exposure is performed after a short time t7 from the time when each of the yellow (Y), magenta (M) and cyan (C) developing units 13 is turned on. Is started,
After a short period of time t8 after the completion of the black (K) image exposure, the yellow (Y), magenta (M), and cyan (C) developing units 13 are returned to the OFF state, and the black (K) monochrome is returned again. The mode is switched to the image forming mode.

Also in this case, the times t7 and t8 described above are used.
Can be sufficiently set by setting the time T required for the transfer paper P to pass at a predetermined interval, so that each image exposure of the color can be continuously performed without extending the timing of image formation. Can be started and ended during the operation of the developing device 13 of FIG.

In the same manner, even if the color image forming mode is inserted in the middle of the magenta (M) or cyan (C) monochrome image forming mode, the image exposure of each color is started while all the developing units 13 are operating. It can be terminated.

In each of the embodiments, the charging is performed only in a region including the image width in synchronization. However, since the reversal development is performed, there is a possibility that the non-image portion is solidly developed. . From this, it is possible to prevent the toner from adhering to the non-image area by sufficiently expanding the charged area only before and after the image, and to apply the developing bias applied to the developing sleeve only to the image area even when the developing sleeve is rotated. It is preferable to apply the voltage and prevent toner adhesion to the non-image area by floating or the like.

[0084]

According to the color image forming apparatus of the present invention, even if the image forming mode is switched from color to monochrome or from monochrome to color during the continuous image formation as needed.
According to Claims 1 and 3, each image exposure is performed in a stable cycle of rotation without fluctuation of the load of the image forming body in a form in which the timing of image formation is continued without being stretched. A high-quality image without deviation is provided. Further, in the developing means specifically used for monochrome image formation, unnecessary ON and OFF operations are omitted, and the durability is increased. In addition, power consumption is also reduced.

[Brief description of the drawings]

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

FIG. 2 is a front view showing a support structure of the drum unit.

FIG. 3 is a cross-sectional view illustrating a support structure of the photosensitive drum.

FIG. 4 is an external view of a drum unit.

FIG. 5 is a front view showing a support structure of the intermediate transfer belt.

FIG. 6 is a front view and a main part side view showing a drive system of the developing device.

FIG. 7 is a time chart showing the operation of the developing device when switching from color image formation to yellow (Y) monochrome image formation.

FIG. 8 is a time chart showing the operation of the developing device when switching from color image formation to black (K) monochrome image formation.

FIG. 9 is a time chart showing the operation of the developing device when switching from yellow (Y) monochrome image formation to color image formation.

FIG. 10 is a time chart showing the operation of the developing device when switching from black (K) monochrome image formation to color image formation.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 charger 12 exposure optical system (image exposure means) 13 (Y) developing device (yellow) 13 (M) developing device (magenta) 13 (C) developing device (cyan) 13 (K) developing device ( Black) 14 Intermediate transfer belt 14A to 14D Roller 15 Transfer roller 130 Developing sleeve 131 Stirring member DG Driving gear 10G, 130GA, 130GB Gears C Electromagnetic clutch

Claims (4)

[Claims] 1. A plurality of charging means, an image exposing means and a developing means are provided around an image forming body, respectively, and a toner image is formed by repeating charging, image exposing and developing during rotation of the image forming body. A color image forming apparatus that forms a color toner image by superimposing the toner images, wherein the apparatus has a monochrome image forming mode and a color image forming mode, and in the monochrome image forming mode, In the color image forming mode, the operation of each image exposing unit is in operation of all the developing units, and the operation is switched to the monochrome image forming mode continuously from the color image forming mode. When the operation of each image exposing means is completed, the operation of the developing means other than the specific one is stopped and the operation of the specific image exposing means is started. Over the image forming apparatus. 2. The color image forming apparatus according to claim 1, wherein the operation of the specific developing unit is continued even after the operation of the specific image exposing unit is completed. 3. A plurality of charging means, image exposing means and developing means are provided around the image forming body, respectively, and a toner image is formed by repeating charging, image exposing and developing during rotation of the image forming body. A color image forming apparatus that forms a color toner image by superimposing the toner images, wherein the apparatus has a monochrome image forming mode and a color image forming mode, and in the monochrome image forming mode, The operation is performed during the operation of the specific developing unit.In the color image forming mode, the operation of each image exposing unit is performed during the operation of all the developing units, and when switching from the monochrome image forming mode to the color image forming mode continuously. Is a color image forming apparatus, wherein after the operation of a specific image exposure means is completed, all the developing means are put into an operation state and the operation of each image exposure means is started. Image forming apparatus. 4. The color image forming apparatus according to claim 3, wherein the operation of the specific developing unit is continued even after the operation of the specific image exposing unit is completed.