JPH08286455A - Color electrophotographic method - Google Patents

Abstract

PURPOSE: To correct a change in the characteristic of the startup in the electrification of a photoreceptor and to obtain a uniform, beautiful color image without lengthening the time required for image formation, in a color electrophotographic method which switches a photoreceptor for each color and synthesizes color images. CONSTITUTION: The color electrophotographic method is applied to a device comprising the photoreceptor 21, an electrifier 22, image formation units 15 and 16 comprising developing units, each having developer of a different color, a moving means which puts, in order, the image formation units 15 and 16 into an exposing position where an exposing means carries out image exposure in a single position and into an image forming position. By the method, a voltage which is applied to the electrifier 22 during the first rotation of the photoreceptor 21 after the image formation units 15 and 16 move into the image forming position and an image forming operation is started is greater than that which is applied during the second rotation and rotation thereafter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic method applicable to color printers, color copying machines, color fax machines and the like.

[0002]

2. Description of the Related Art As a conventional example, the inventors of the present invention have disclosed in Japanese Patent Laid-Open No.
The configuration will be described using the color electrophotographic apparatus filed in Japanese Patent No. 6246. FIG. 10 is an overall configuration diagram of the conventional color electrophotographic apparatus.

In the center, four sets of fan-shaped image forming units 101Bk for black, cyan, magenta, and yellow are provided.
01C, 101M, and 101Y form an image forming unit group, and are arranged in an annular shape. 102 is a photoconductor, 103
Is a charger, 104 is a developer reservoir, 105 is a cleaner, 10
6 is a developing roller. The image forming units 101Bk, 101C, 101M and 101Y arranged in an annular shape are supported by a support (not shown), and are driven by a moving motor 107 which is a moving means as a whole, and are fixed in a cylindrical shape. It is rotatable about a non-rotating shaft 108. The image forming units are sequentially connected to the intermediate transfer belt 1
It can be located at the image forming position 111 facing the transfer roller 110 supporting 09. The image forming position 111 is also an exposure position by the signal light 112. Reference numeral 113 denotes a laser exposure device, which generates a signal light 112 by a laser beam which is modulated by a signal input to the printer section. This signal light 112 passes through an optical path formed between the image forming units 101M and 101Y in FIG. , A window 11 opened in a part of the shaft 108
The light is incident on the mirror 115 fixed inside the shaft 108 through 4a, is reflected, and is reflected through the window 114b.
The photosensitive member 102 of the image forming unit in No. 1 is irradiated to form a latent image. In the state of FIG. 10, the image forming unit 1 for black is used.
It acts on 01Bk.

Next, the operation of this apparatus when forming a color image will be described. First, as shown in FIG. 10, the image forming unit has the black image forming unit 101Bk at the image forming position 111. Black signal light is input to the image forming unit 101Bk by the laser exposure device 113, and an image is formed with black toner. At the same time as the image is formed, the black toner image is formed by the action of the transfer roller 110.
It is transcribed to 09. Immediately after all the black toner images have been transferred, the image forming unit groups 101Bk, 101C, 1
The entire 01M and 101Y are driven by the moving motor 107 to rotate integrally, and rotate exactly 90 degrees to stop the image forming unit 101C at a position near the image forming position 111. The image forming unit 101C moves to the image forming position 111.
After the arrival, the laser exposure device inputs the signal light to the image forming unit 101C by the cyan signal as before, and the cyan toner image is formed and transferred. At this time, the intermediate transfer belt 109 makes one revolution, and the writing timing of the cyan signal light is controlled so that the next cyan toner image is positionally aligned with the previously transferred black toner image. The same operation as described above is performed for magenta and yellow, and toner images of four colors are positionally aligned and superposed on each other to form a color image. After the final transfer of the yellow toner image, the four color toner images are collectively transferred onto the image receiving paper 116 by the action of the second transfer roller 117 at the same timing. The toner image transferred to the image receiving paper is fixed by the fixing device 118.

The above is a brief description of the configuration and operation of the conventional example.

[0006]

In this conventional example, after the image forming unit 101 arrives at the image forming position 111, the photoconductor 102 starts rotation for image formation, and from that time, the photoconductor 102 is exposed by the charger 103. The body 102 starts to be charged. FIG. 2 shows the positional relationship between the surface position of the photoconductor of each image forming unit 101 and each device such as a charger at this time, and FIG. 3 shows the charging potential at each position of the photoconductor at that time. In FIG. 2, 119 is a corona charger, 120 is a photoconductor,
121 is an exposure by a laser signal, 122 is a developing device, 12
3 is a two-component magnetic brush developer, 124 is a developing sleeve that carries the developer, 125 is a magnet roller that attracts the developer 123 to the developing sleeve, 126 is a blade that regulates the amount of the developer 123 on the developing sleeve 124, 127 is a cleaner for cleaning the toner remaining on the photoconductor 120 after the transfer. A case where a corona charger 119 is used as the charger here instead of the charging roller 103 used in FIG. 10 will be described. The problem of this conventional example is no different from the case of using the charging roller even when the corona charger is used.

It is now assumed that the photoconductor 120 reaches the image forming position 111 in FIG. 10 and starts rotating. Generally, a photoreceptor has different charging characteristics immediately after being left in a cool and dark place for a long time and charging characteristics after repeating charging and exposure. This is because the number of remaining photocarriers and the state of traps inside the photoconductor layer are different. Here, the voltage applied to the charger 119 is a constant value, which is a value aimed at the target charging potential -700V. At this time, the range indicated by the arrow A, that is, the charger 11
The range from the downstream end of 9 to the developing position R is the charger 119.
Therefore, it remains at 0 V as shown in FIG. Next, the range B immediately below the charger 119 is a range in which the charging potential gradually increases according to the charging width. Next range C
Since the first charging is performed immediately after the photoconductor 120 is left in the dark for a long time, the charging potential becomes lower than the target potential −700V, and only about −600V is charged. Next, the photoconductor 1
After entering the second rotation of 20 and passing through the charging range D for the second time in a portion immediately below the charger 119 at the start of operation, the target potential reaches -700V in the range E, and then converges to this charging potential. In this example, the charger 119 is the grid 1
Since it is a scorotron charger equipped with 19 ', it is easier to control it to a constant potential than a normal corotron charger, but the dark decay characteristics of the photoconductor after passing through the charger are different after storage in the dark and during continuous use. Because of the difference, the charging potential becomes unstable in this way.

Immediately after the image forming unit group is rotationally moved to replace the image forming unit at the image forming position, the charging characteristics of the photoconductor are greatly different between the first rotation and the second rotation. Here, the diameter of the photoconductor 120 is 30 mm, and the outer peripheral length thereof is approximately 94 mm. Since this color electrophotographic apparatus prints A4 size, the length of one screen is 297 mm. Therefore, different charge potentials of the photoconductors appear on the same screen, and different image quality results when developed under the same conditions. Therefore, in order to obtain a beautiful uniform image with this color electrophotographic apparatus, it can be used for image formation only after the second rotation in which the charging potential of the photoconductor is stable. Therefore, each time each color image forming unit moves and switches to the image forming position, it is necessary to wait until the photosensitive member has completed one rotation, and it takes a long time to output one color image. .

In view of the above problems, it is an object of the present invention to provide a color electrophotographic apparatus for synthesizing a color image by switching the photoconductor for each color, and taking into consideration the rising characteristics of the charge of the photoconductor, the applied voltage of the charger and the development. A color electrophotographic method capable of obtaining a uniform and beautiful color image without unnecessarily lengthening the image formation time by adjusting the bias and the laser exposure conditions.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a plurality of image forming units each including a photoconductor, a charger, and a developing unit having a developer having a different color, and the plurality of image forming units are arranged. And a movable image forming unit group, a transfer body that transfers the toner images developed on the photoconductor by superposing them at a single transfer position to form a color image, and a single exposure unit. An exposure position for performing image exposure at a position, an image forming position corresponding to the transfer position and the exposure position, and an entire image forming unit group for sequentially positioning each of the plurality of image forming units at the image forming position. A color electrophotographic method for use in a color electrophotographic apparatus having a moving unit for moving the charging unit after the photoconductor of the image forming unit moves to the image forming position and starts the image forming operation. The applied voltage is a color electrophotographic method is characterized in that set higher than later when the second rotation at the first rotation of the photosensitive member.

Further, according to the present invention, a plurality of image forming units each provided with a photoconductor and a developing means having a developer having a different color, and an image movably arranged by disposing the plurality of image forming units. A group of forming units, a transfer body that applies a developing bias and reverse-develos the toner images on the photoconductor to form a color image by superposing and transferring the toner images at a single transfer position. An exposure position for performing image exposure, an image forming position corresponding to the transfer position and the exposure position, and an entire image forming unit group are moved to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method used in a color electrophotographic apparatus having a moving means, wherein the image forming unit is moved to the image forming position and the image forming operation is started. A color electrophotographic method, wherein a DC component of the developing bias applied to the unit is set higher later when the second rotation than during the first rotation of the photosensitive member.

Further, according to the present invention, a plurality of image forming units each having a photoconductor and a developing means having a developer having a different color, and an image movably arranged by disposing the plurality of image forming units. Exposure for performing image exposure at a single position by a laser exposure means, a forming unit group, a transfer body for superposing and transferring a toner image developed on the photoconductor at a single transfer position to form a color image A position, an image forming position corresponding to the transfer position and the exposure position, and a moving unit that moves the entire image forming unit group to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method used in a color electrophotographic apparatus having the laser exposure means after the photoconductor of the image forming unit moves to the image forming position and starts an image forming operation. A color electrophotographic method, wherein a The output is set higher later when the second rotation than during the first rotation of the photosensitive member.

Furthermore, the present invention is configured such that a plurality of image forming units each including a photoconductor and a developing means having a developer having a different color, and the plurality of image forming units are arranged and movable. Image forming unit group, a transfer body for superposing and transferring a toner image developed on the photoconductor at a single transfer position to form a color image, and image exposure is performed at a single position by a laser exposure unit. An exposure position, an image forming position corresponding to the transfer position and the exposure position, and a moving unit that moves the entire image forming unit group to sequentially position each of the plurality of image forming units at the image forming position, A color electrophotographic method used in a color electrophotographic apparatus having: a laser exposure unit after the photoconductor of the image forming unit has moved to the image forming position and starts an image forming operation. A color electrophotographic method, wherein a laser emission time was set later when the second rotation longer than when first rotation of the photosensitive member.

[0014]

The function and effect of the color electrophotographic apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall structural view of a color electrophotographic apparatus of the present invention. Reference numeral 1 is an exterior casing of the color electrophotographic printer, and the right end face side in the drawing is the front face. Reference numeral 1A denotes a printer front plate, and the front plate can be freely opened and closed and raised and closed around the hinge shaft 1B on the lower side with respect to the printer outer casing 1. The state in which the front plate 1A is tilted down and opened is indicated by a one-dot chain line. The operation of attaching / detaching the intermediate transfer belt unit 2 to / from the printer, the maintenance of the printer inside such as a paper jam, and the like are performed by tilting the front plate 1A open to largely open the inside of the printer. The attachment / detachment operation of the intermediate transfer belt unit 2 is designed to be in a direction perpendicular to the direction of the rotation axis generatrix of the photoconductor, that is, in the direction of the printer front plate 1A. The intermediate transfer belt unit 2 includes a transfer belt 3, a first transfer roller 4, a second transfer roller 5, a cleaner roller 6, a scraper 7, a waste toner reservoir 8, a waste toner full detector 9, a backup roller 10, and a position detector 1.
1, tension roller 12, intermediate transfer belt unit 2
Front cover 1 that protects the surface of belt 3 when pulling out
3 and a similar rear cover 14. Details of the mechanism will be described later.

Four sets of fan-shaped image forming units 15Bk, 15Y, 15M, and 15C for black, cyan, magenta, and yellow colors form an image forming unit group 16 in the center of the left side of the printer. It is arranged in an annular shape. Each image forming unit is attachable to and detachable from a predetermined position of the image forming unit group 16 by opening the printer left face plate 1C of FIG. 1 around the hinge shaft 1D. The image forming unit 15 is properly mounted in the printer, so that the mechanical drive system and the electric circuit system on both sides of the image forming unit and the printer are connected to each other via a mutual coupling member (not shown). Mechanically and electrically.

Image forming unit 1 arranged in an annular shape
5Bk, 15C, 15M and 15Y are supports (not shown)
The image forming unit group 16 as a whole is driven by a moving motor 17 which is a moving means, and is rotatably movable around a cylindrical shaft 18 which is fixed and does not rotate. During image formation, each image forming unit can be sequentially positioned at the image forming position 19 facing the first transfer roller 4 supporting the intermediate transfer belt 3 by rotational movement. The image forming position 19 is also an exposure position by the signal light 20.

FIG. 4 shows the black image forming unit 15Bk in detail. Since each image forming unit is composed of the same constituent members except the developer contained therein, the image forming unit 15Bk for black will be described and the other colors will be omitted for simplification of description. Note that the same reference numerals are given to the same portions for each color, and when it is necessary to distinguish the configurations of the respective colors, the reference numerals are prefixed with the respective colors. In this description, the ordinary two-component magnetic brush developing method is used, but it goes without saying that any developing method used in electrophotography may be used. For example, a magnetic brush developing method, an elastic rubber roller developing method, a jumping developing method, an impression developing method, a magnetic cascade developing method or the like can be used. In FIG. 4, 20 is a laser beam signal light,
Reference numeral 21 is an organic photosensitive member mainly composed of a polycarbonate-based binder resin using phthalocyanine as a photosensitive material, 22 is a corona charger for negatively charging the photosensitive member, 23 is a grid electrode for controlling the charging potential of the photosensitive member 21, and 24 is An exposure window 25, which is an opening of the image forming unit through which the laser beam enters the image forming unit, is a developer reservoir. In the developer reservoir 25, the surface of which is coated with silicone resin has a particle size of 50.
Negative charging black toner 27Bk in which ferrite carrier 26Bk of μm and black pigment are dispersed in polyester resin
2 component developer 28Bk mixed with 10% of
It is attached to the developing roller 30 by the magnetic force of 9. 31 is a doctor blade that regulates the amount of developer on the developing roller, 3
Reference numeral 2 is an AC high voltage power source for applying a voltage to the developing roller, and 33 is a cleaner for cleaning the toner remaining on the surface of the photoconductor 21 after the transfer. The photoconductor 21 has a diameter of 30 mm and a peripheral speed of 65.
The developing roller 30 has a diameter of 16 mm and is rotated at a peripheral speed of 65 mm / s in the arrow direction.

The image forming unit in FIG. 4 is an image forming unit for black, and also shows the vertical position of the image forming unit at the image forming position. In the figure, the developer 28B
The developer reservoir 25 accommodating k is located on the upper side in the gravity direction of the photoconductor 21, and the cleaner 33 is located on the lower side. Therefore, in the developer reservoir, the developer is supplied onto the developing roller 30 by its own weight, and in the cleaner, the toner scraped off by the cleaning blade falls to the bottom of the cleaner by its own weight. It is possible to smoothly perform development and cleaning without providing a feeding mechanism or a stirring mechanism for moving the toner inside the developer reservoir or inside the cleaner. The developing units 15Y, 15M, and 15C other than black have the same configuration.

Next, referring to FIG. 5, the intermediate transfer belt unit 2
The configuration of will be described. The intermediate transfer belt unit 2 includes a unit housing 2a, a transfer belt 3, a first transfer roller 4 made of an aluminum roller, a second transfer roller 5 made of a conductive elastic rubber roller, and an aluminum member for cleaning a toner image remaining on the transfer belt. Cleaner roller 6, scraper 7 for scraping the collected toner, waste toner reservoir 8 for storing the scraped toner, waste toner full detector 9 for detecting that the amount of toner in waste toner reservoir 8 is full, It includes a backup roller 10 made of a conductive rubber facing the cleaner roller 6, a position detector 11 for detecting the transfer start position of the transfer belt, and a tension roller 12 for adjusting the tension of the transfer belt to prevent meandering. The intermediate transfer belt unit 2 is attachable / detachable to / from a predetermined storage portion in the printer outer casing 1 by folding down the printer front plate 1A in FIG.

When the intermediate transfer belt unit 2 is mounted on the printer main body, the first transfer roller 4 prevents the intermediate transfer belt 3 from coming into contact with the photoconductor 21, and the retracted position 4b in FIG.
It is in. When the intermediate transfer belt unit 2 is mounted on the printer body and the image forming operation is started, the first transfer roller 4
Moves to the transfer position 4a, and the transfer belt 3 moves about 1.0k.
It is pressed against the photoconductor 21 with a force of g. With this configuration,
During the rotational movement of the image forming unit group, the photosensitive member of the image forming unit and the intermediate transfer belt do not come into contact with each other, so that the photosensitive member is not damaged. Further, since the intermediate transfer body does not come into direct contact with the photosensitive body when the intermediate transfer body unit is replaced, the photosensitive body is not damaged during maintenance.

The intermediate transfer belt 3 is made of an endless belt-shaped semiconductive (medium resistance) urethane having a thickness of 100 μm as a base material, and the surface layer is made of a fluororesin such as PFA / PTFE and has a total thickness of 100 to 500 μm. It consists of sasita film. The intermediate transfer belt 3 is wound around a first transfer roller 4, a second transfer roller 5, a backup roller 10 and a tension roller 12, and is movable in the arrow Y direction.

Here, the circumference of the transfer belt is the length (297 m) in the longitudinal direction of the A4 image receiving paper which is the maximum image receiving paper size.
m) is set to 365 mm by adding a length (68 mm) slightly longer than half the circumference of the photosensitive drum 21 (diameter 30 mm). At this time, the peripheral length of the intermediate transfer belt 3 from the contact portion between the second transfer roller 5 and the third transfer roller 34 to the contact portion between the cleaner roller 6 and the backup roller 10 is:
The distance is set to 55 mm, which is shorter than the 68 mm distance.

The moving speed of the intermediate transfer belt 3 is 1.5% faster than the image forming speed of the image forming unit 15 (65 mm / s which is equal to the peripheral speed of the photoconductor 21) in order to prevent the hollow transfer of the toner image. Is set.

Second transfer roller 5 and backup roller 1
Both 0s are made of conductive rubber, and are grounded via resistors 35 and 36 of 20 MΩ respectively to prevent scattering at the time of color toner image transfer.

The medium resistance elastic layer of the second transfer roller 5 and the backup roller 10 is obtained by mixing and dispersing carbon or metal oxide in an elastic material such as silicon rubber, Teflon rubber, chloroprene rubber, urethane rubber, and EPDM. It is composed of a solid or foamed meat layer treated to have an electric resistance value (volume resistivity) of 10 ⁵ to 10 ¹⁷ Ωcm.

The first transfer roller 4 is movable between a transfer position 4a and a retreat position 4b, and when it is located at the transfer position 4a by a driving source (not shown) controlled by an electric signal, the transfer belt is moved. 3 is capable of transferring the toner image formed in contact with the photoconductor 21, and when located at the transfer position 4b, the transfer belt 3 is separated from the photoconductor 21 to a non-contact position.

When the toner image on the photoconductor 21 is transferred, a voltage of about +2.5 kV (100 μA) is applied to the first transfer roller 4 and the tension roller 12 by the high voltage power supply 37. At this time, if the first transfer roller 4 is brought into direct contact with the photoconductor 21 to transfer the toner image to the intermediate transfer belt 3, a so-called “forward jump” phenomenon occurs before the intermediate transfer belt 3 comes into contact with the photoconductor 21. The image is disturbed,
Further, it becomes difficult to uniformly adjust the contact pressure between the first transfer roller 4 and the photoconductor 21. However, when the first transfer roller 4 is moved and the intermediate transfer belt 3 stretched between the two rollers is brought into contact with the photosensitive drum 21 as in the present invention, these problems do not occur.

The third transfer roller 34 made of aluminum is
It is pressed against the second transfer roller 5 via the intermediate transfer belt 3. During formation of a color image on the intermediate transfer belt 3,
In order not to disturb the toner image on the belt, a voltage of -1 kV is applied by the high voltage power supply 38a. When transferring the color toner image to the image receiving paper 39, the high voltage power source 3
A voltage of +3 kV is applied by 8b. The configuration of the third transfer roller 34 may be a conductive elastic roller such as the second transfer roller 5, but if a metal roller having a smooth surface is used, a color image is synthesized on the intermediate transfer belt 3. It is more desirable because it does not disturb the surface of the toner image.

Reference numeral 40 is a charge elimination needle for preventing the toner image from being disturbed when the paper 39 is separated from the intermediate transfer belt 3. The third transfer roller 34 is configured to rotate 1.5% slower than the intermediate transfer belt 3 in order to prevent a hollow defect when transferring a toner image.

The cleaner roller 6 cleans the toner remaining on the intermediate transfer belt 3. In order to prevent the toner image from being transferred from the intermediate transfer belt 3 to the cleaner roller 6 while the color image is being formed on the intermediate transfer belt 3, a voltage of the same polarity as the toner is applied from the high voltage power supply 41a, here a negative voltage. Is being applied. When cleaning the toner remaining on the intermediate transfer belt 3 after transferring the toner image to the image receiving paper, a positive voltage for electrostatically attracting the toner is applied by the high voltage power supply 41b.

FIG. 6 is a perspective view showing the structure of the position detector 11 using a photo interrupter provided inside the intermediate transfer belt unit 2. There is a detection hole 42 at the end of the intermediate transfer belt 3, and the position detector 11 determines the leading edge position of the toner image by optically detecting the passage of the detection hole 42, and the position detector 11 detects the leading end position of the toner image. This is a configuration for aligning color images. Here, although the transmission type position detecting means is used as the position detecting means, it goes without saying that a mechanical type, an electric type, a magnetic type and the like other than the optical type may be used.

Returning to FIG. 1, the description will be continued. Reference numeral 43 denotes a laser beam scanner unit arranged on the upper side in the printer outer casing 1, and includes a semiconductor laser, a scanner motor 43a, a polygon mirror 43b, a lens system 43c, and the like.
The pixel laser signal light 20 corresponding to the time-series electric pixel signal of the image information from the scanner unit 43 passes through the optical path window 44 formed between the image forming units 15Bk and 15C of FIG. Axis 1 through a window 45 opened in the part
The exposure window 24 of the image forming unit 15Bk which is incident on the mirror 46 fixed in the image forming unit 8 and is reflected at the image forming position 19
From the inside to the image forming unit 15Bk, and the developer reservoir 25 and the cleaner 3 arranged vertically in the image forming unit.
3 through the passage between the photoconductor drum 21 and the photoconductor drum 21 and enters the exposed portion on the left side surface of the photoconductor drum 21 for scanning exposure in the generatrix direction. Here, since the optical path to the mirror 46 uses a gap formed by the exterior wall of the adjacent image forming unit and is configured by a plane substantially parallel to the optical scanning surface, it can be configured with a narrow gap without obstructing the optical path. If the gap between adjacent image forming units is large,
More stray light enters the optical path. If the width of the gap is 20 mm or less, stray light that enters the optical path of the signal light can be reduced, and the effect of stray light can be substantially eliminated.
Further, by making the exterior wall of each image forming unit black, even if stray light enters the optical path, the reflected light is weakened and the influence on the photoconductor charging potential can be reduced. The side walls (front and rear sides in the drawing) of the optical path are formed by the rotary support of the image forming unit group, and prevent stray light from entering from the side surface.

The mirror 46 is the image forming unit group 16
Since it is provided in the central part of the above, it can be configured with a single fixed mirror, which is simple and easy to align. In addition, since the optical path is set so that the laser reflection surface of the mirror 46 faces slightly downward, dust and the like inside the machine are hard to collect on the reflection surface.

Reference numeral 34 denotes a third transfer roller disposed inside the front plate 1A of the printer and above the feeding roller 47. The nip portion where the intermediate transfer belt 3 and the third transfer roller 34 are in pressure contact with each other is the printer. An image receiving paper conveying path is formed so that the image receiving paper is fed by the paper feeding roller 47 provided under the front plate 1A.

The fixing rollers 48a and 48b are provided on the upper inside of the printer, and the halogen lamp 4 is provided inside the fixing roller 48a.
9 are provided. A polyimide film 50 is stretched between 48a and 48b. This film 50
Is used for the purpose of producing the gloss of a color print. 51
Is a backup roller provided to face the fixing roller 48a, and 52 is a pair of discharge rollers arranged on the paper exit side.
The above is the description of the main configuration of the electrophotographic apparatus of the present invention.

Next, the structure and operation when the image forming unit 15 and the intermediate transfer belt unit 2 are replaced will be described. The state of FIG. 1 is a state in which image formation is being performed. This is a state in which the first transfer roller 4 has moved to the position 4a in FIG. 5 in order to transfer the toner image formed on the photoconductor 21 to the intermediate transfer belt 3. When the image forming unit group 16 rotates, or when the printer is stopped, the first transfer roller 4 retracts to the position 4b. In this state, the photoconductor 21 does not come into contact with the transfer belt 3. In this retracted state, the printer stops the printing operation and opens the printer front plate 1A so that the intermediate transfer body unit 2 can be replaced. Even if the intermediate transfer belt unit 2 is moved in and out in this state, the photoconductor 21
The intermediate transfer belt 3 and the intermediate transfer belt 3 are strongly pressed against each other without damaging them. At the same time, each image forming unit 15 can be replaced by opening the printer left side plate 1C. When replacing the other image forming unit 15,
The image forming unit group 16 stops in a state in which the image forming unit group 16 is rotated by 90 ° from this state.

The surface of the intermediate transfer belt 3 is gradually deteriorated due to toner adhesion and the like as it is used for a long period of time. When the deterioration of the belt becomes remarkable, the image is partially cut off or white or black streaks occur in the image. Therefore, it is desirable to replace the intermediate transfer belt before it deteriorates and affects the image. However, it is extremely difficult to automatically detect the deterioration phenomenon of the intermediate transfer belt in the printer device. In the present invention, as shown in FIG. 5, the intermediate transfer belt 3 is integrated with the waste toner reservoir 8 into a unit, and the waste toner is discarded at the same time when the intermediate transfer belt 3 is replaced. In such a configuration, the size of the waste toner reservoir 8 may be designed to be small so that the waste toner reservoir 8 is filled with the waste toner before the life of the intermediate transfer belt 3. By doing so, the waste toner full detector 9 installed inside the waste toner reservoir before the intermediate transfer belt deteriorates and an image defect occurs
Detects that the toner is full, and can instruct the user to replace the intermediate transfer belt unit 2. Such a structure is effective not only for the intermediate transfer belt that directly forms a toner image thereon, but also for an intermediate transfer member having a structure in which an image receiving paper is wound around the same.

Regarding the operation of this color electrophotographic apparatus,
This will be described with reference to the drawings. The printer of FIG. 1 is in an image forming state. The image signal is sent to the printer, and the printer shifts from the stationary state to the image forming state. The photoconductor charging potential of the image forming unit 15Bk at this time will be described with reference to FIG. At the same time when the photoconductor 21 in a stationary state began to rotate, a voltage of −7 kV was applied to the charger 22 to charge the photoconductor 21. At this time, the voltage applied to the grid 23 is -70.
It was set to 0V. The photoconductor 21 is the region B of the width of the charger (the region where the photoconductor that was directly below the charger when stationary was charged for the first time).
And the charging potential converged to a constant value of −700 V in the C region (first rotation region where the photoconductor is charged for the first time). After that, when the area C passes through the development point R in FIG. 2,
The voltage applied to the charger was lowered to -6.5 kV. as a result,
A slight increase in the electric potential was observed in the width D region (the region of the second rotation immediately below the charger when stationary), but in the E region (the region where the photoconductor is charged the second time), the target charging potential It converged to about -700V.

The photosensitive member 21 thus uniformly charged was irradiated with the laser beam scanning light 20 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor was -50V. The two-component developer 28Bk was magnetically adhered onto the surface of the developing roller 30, and the surface of the photoconductor 21 was passed in front of the developing roller 30. In the passing time width of the uncharged area of the photoconductor 21 (area A in FIG. 7), 750V0-p (peak-to-peak 1.5kV) with a DC voltage of + 100V superposed on the developing roller 30 by the AC high-voltage power supply 32. ) AC voltage (frequency 2
A rectangular wave of kHz) was applied. After that, the surface of the photoconductor 21 charged to −700 V and having the electrostatic latent image written thereon (see B in FIG. 7).
-When passing through the C, D, and E regions), the developing roller 30 is superposed with a DC voltage of -500V by the AC high-voltage power source 32 at 750V0-p (peak-to-peak 1.5kV).
AC voltage (rectangular wave of frequency 2 kHz) was applied. As a result, the toner image did not adhere to the non-image portion on the photoconductor 21 and a negative-positive inverted toner image was obtained only on the image portion on the photoconductor 21. The developer on the developing roller 30 rotating in the direction of the arrow was returned to the developer reservoir 25 and used for the next image formation. In this way, a black toner image was obtained on the photoconductor 21.

Next, returning to FIG. 1, the operation of the apparatus for forming a color image will be described. The image forming unit group 16 is in the position shown in FIG. 1, and the black image forming unit 15Bk is in the image forming position 19 as shown. At this time, the photoconductor 21 is in contact with the intermediate transfer belt 3. In the image forming process of the image forming unit described above, the black signal light is input to the image forming unit 15Bk by the laser exposure device 43, and the image formation is performed by the black toner. The black toner image was transferred onto the intermediate transfer belt 3 by the action of the voltage applied to the first transfer roller 4 and the tension roller 12 simultaneously with the image formation. At this time, a DC voltage of +2.5 kV was applied to the first transfer roller 4 and the tension roller 12 as described above.

Immediately after the transfer of all the black toner images, the first transfer roller 4 is moved from the position 4a shown in FIG. 5 to the position 4b.
To the position where the intermediate transfer belt 3 does not contact the image forming unit 15Bk. Next, the entire image forming unit group 16 is driven by the moving motor 17 and
The image forming unit 15C stops at the position where the image forming unit 15C reaches the image forming position 19 after rotating by 90 ° in the direction of arrow Q. The portions of the developer reservoir 25 and the cleaner 33 other than the photoconductor of the image forming unit are located inside the rotation arc indicated by the dotted line at the tip of the photoconductor 21. In addition, the first transfer roller 4
The retreat position 4b is located outside the dotted arc. Therefore, the intermediate transfer belt 3 does not come into contact with the image forming unit during the rotational movement of the image forming unit group.

When the rotation of the image forming unit group 16 is completed and the image forming unit 15C reaches the image forming position 19, the laser exposure device 43 inputs the signal light to the image forming unit 15C by the cyan signal as before. Then, the cyan toner image is formed and transferred. By this time, the intermediate transfer belt 3 has made one rotation, and the signal from the position detector 11 shown in FIG. 5 is set so that the next cyan toner image is positionally aligned with the previously transferred black toner image. Based on this, the writing timing of the cyan signal light was controlled. During this time, the third transfer roller 34 is in contact with the intermediate transfer belt 3, but as described above, the surface of the third transfer roller is smooth and a voltage of -1 kV is applied so as to prevent the adhesion of toner. Therefore, the toner image on the transfer belt is not disturbed. The cleaner roller 6 is also in contact with the intermediate transfer belt 3,
The surface of the cleaner roller 6 is also smooth, and a voltage of -1 kV that prevents toner adhesion is applied, so that the toner image on the transfer belt is not disturbed. When these image forming units reach the image forming position 19 and start image formation, the voltage applied to the corona charger 22 is switched so as to correct the charge rising characteristics of the photoconductor as in the case of the black unit described above. The charging potential was obtained.

The same operation as described above was performed for magenta and yellow, and toner images of four colors were positionally aligned and superposed on each other on the intermediate transfer belt 3 to form a color image. After the final transfer of the yellow toner image, the toner images of four colors are collectively transferred by applying a voltage of +3 kV to the third transfer roller 34 on the image receiving paper (not shown) fed from the paper feeding cassette at the same timing. . The toner image transferred to the image receiving paper is fixed by the fixing rollers 48a and 48b, and then discharged.

As described above, since the developing bias is set so as to correct the rising characteristics of charging of the photosensitive member, a uniform and beautiful color image can be obtained. In addition to the method of controlling the voltage applied to the charger, the method of compensating for the rising characteristics of the charging of the photoconductor includes a method of interlocking the developing bias in accordance with the change of the charging potential of the photoconductor, and a laser It is effective to make the electrostatic latent image uniform on the photoconductor by a method of changing the output of the laser or a method of exposing while changing the lighting time of the laser.

[0046]

EXAMPLE A color electrophotographic apparatus of the present invention will be described below.
This will be described with reference to the drawings.

(Specific Embodiment 1) One embodiment of the present invention will be described with reference to FIGS. 1, 2, 4 and 8.

In this embodiment, in order to correct the rising of the charging of the photosensitive member, the method of switching the developing bias according to the change of the charging potential of the photosensitive member is used. The operation of the image forming unit shown in FIG. 4 will be described with reference to FIG. When image formation was started and a voltage of -6.5 kV was applied to the charger 22, the photosensitive member 21 showed -600 in the range B (FIG. 2).
It was charged to V. The photoconductor 21 was irradiated with the signal light 20 by a laser beam to form an electrostatic latent image. At this time, the exposure potential of the photoconductor was -50V. The surface of the photoconductor 21 was passed in front of the developing roller 30 carrying the two-component developer 28Bk. At this time, the uncharged area A of the photoconductor 21
When passing through the developing point R of FIG. 2 (FIG. 2), a DC voltage of +100 V was superposed on the developing roller 30 by an AC high voltage power source.
An AC voltage (frequency 2 kHz) of 50 V0-p (peak-to-peak 1.5 kV) was applied. After that, -600
When passing through the area C (FIG. 2) of the photoconductor 21 charged with V and having the electrostatic latent image written therein, the developing roller 30 is superposed with a DC voltage of -420V by an AC high-voltage power source of 750V0-.
An AC voltage (frequency 2 kHz) of p (peak-to-peak 1.5 kV) was applied. After that, -600 to -70
When passing through the area D (FIG. 2) of the photoconductor 21 charged with 0V and having the electrostatic latent image written therein, the developing roller 30 is supplied with −450V and −450V, respectively, as shown in FIG.
750V0-p (peak
Two-peak 1.5kV AC voltage (frequency 2kH)
z) was applied in two stages. After that, when passing through the area E (FIG. 2) of the photoconductor 21 in which the electrostatic latent image is uniformly charged to −700V, the developing roller 30 is superposed with a DC voltage of −500V by a high voltage AC power source of 750V0. -
An AC voltage (frequency 2 kHz) of p (peak-to-peak 1.5 kV) was applied. As a result, a negative-positive inverted toner image was obtained only on the image portion on the photoconductor 21. The developer 28Bk carried on the developing roller 30 was returned to the developer reservoir 25 and used for the next image formation. In this way, a black toner image was obtained on the photoconductor 21. Similar operations were performed for the developing devices 15C, 15M, and 5Y other than black. Four color toner images were superposed on the intermediate transfer belt to form a color image. After the final transfer of the yellow toner image, the four color toner images are transferred onto the image receiving paper fed from the paper feeding section 47 at the same timing by the third transfer roller 34.
It was transferred all at once. The toner image transferred to the image receiving paper was fixed by the fixing device. The image receiving paper was then discharged to the outside of the apparatus via the discharge roller 52.

As described above, the DC component of the developing bias was switched and set so as to correct the rising of the charging of the photosensitive member, so that a uniform and beautiful color image was obtained.

(Specific Embodiment 2) Another embodiment of the present invention will be described with reference to FIGS. 1, 2, 4, and 9.

In this embodiment, in order to correct the rising characteristics of the charging of the photosensitive member, a method of switching the output of the laser for exposing the latent image for recording the latent image is used. The operation of the image forming unit shown in FIG. 4 will be described below with reference to FIG. After the start of image formation, when a voltage of -6.5 kV was applied to the charger 22, the photosensitive member 21 had a range of -600 in the range B.
It was charged to V. The surface of the photoreceptor 21 is covered with the two-component developer 2
It was passed in front of the developing roller 30 carrying 8 Bk. At this time, when passing through the developing point R in the uncharged area A of the photoconductor 21 (FIG. 2), the developing roller 30 is supplied with
750V 0-p (peak
Two-peak 1.5kV AC voltage (frequency 2kH)
z) was applied. After that, it was used for image formation from the C region (FIG. 2) of the photoreceptor 21 charged with −600 V and having the electrostatic latent image written therein. At this time, when passing through the area C (Fig. 2),
The laser output was adjusted to 0.45 mW and the image signal was exposed. After that, when passing through the region D (FIG. 2) of the photoreceptor 21 charged in the range of −600 to −700 V, the laser power was divided into two stages of 0.47 and 0.485 mW, and the output was gradually increased to perform exposure. After that, the area E of the photoconductor 21 in which the electrostatic latent image is uniformly charged to −700 V (FIG. 2)
Exposure was performed with the laser power of 0.5 mW. During this period, the developing roller 30 is supplied with an AC high voltage power source,
750V 0-p (peak-to-peak 1.5kV) AC voltage (frequency 2kH) with -500V DC voltage superimposed
z) was applied. As a result, a uniform toner image in which the negative and positive inversions were made was obtained on the photoconductor 21 only in the image area. The same operation was performed for the developing devices 15C, 15M, and 15Y other than black.

On the intermediate transfer belt, four color toner images were superposed to form a color image. After the final transfer of the yellow toner image, the four color toner images are collectively transferred onto the image receiving paper sent from the paper feeding section 47 at the same timing by the action of the third transfer roller 34, and fixed by the fixing device 48. Was done. In this way, the exposure output of the laser that forms the electrostatic latent image was set in accordance with the change in the charging characteristics of the photoconductor, so that a uniform and beautiful color image was obtained. Although the configuration in which the laser power is modulated is shown here, the same effect can be obtained by the method of controlling the lighting pulse width of the laser. At this time, for example, if the duty is suppressed to 75% in the C area (FIG. 2) and 100% is lit in the E area, a uniform image can be obtained.

The above is the description of the configuration and operation of the embodiment.

[0054]

According to the present invention, in a color electrophotographic apparatus for synthesizing a color image by switching the photoconductor for each color,
By adjusting the applied voltage of the charging device, the developing bias, the laser power, etc. in consideration of the charging rising characteristic of the photoconductor, without unnecessarily lengthening the time of image formation,
It is possible to obtain a color electrophotographic method capable of obtaining a uniform and beautiful color image.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus using a color electrophotographic method of the present invention.

FIG. 2 is an explanatory view of a peripheral portion of an image forming unit photoconductor for explaining problems of a conventional example.

FIG. 3 is an explanatory diagram showing the charge rising characteristics of the photoconductor, which is a problem of the conventional example.

FIG. 4 is a configuration diagram showing a configuration of an image forming unit used in a color electrophotographic apparatus according to an embodiment of the present invention.

FIG. 5 is a configuration diagram showing a configuration of an intermediate transfer belt unit used in a color electrophotographic apparatus according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram illustrating a configuration for detecting the belt position of the intermediate transfer member unit of the present invention.

FIG. 7 is an explanatory diagram illustrating a voltage application method of a charger that corrects the charging rising characteristic of the photoconductor used in the present invention.

FIG. 8 is an explanatory diagram illustrating a method of applying a voltage of a developing bias for correcting the charging rising characteristic of the photoconductor used in the present invention.

FIG. 9 is an explanatory diagram illustrating a laser power setting method for correcting the charging rising characteristic of the photoconductor used in the present invention.

FIG. 10 is a block diagram of a conventional color electrophotographic apparatus.

[Explanation of symbols]

 2 intermediate transfer body unit 3 intermediate transfer belt 4 first transfer roller 5 second transfer roller 6 cleaning roller 10 backup roller 12 tension roller 13 image forming unit 16 image forming unit group 19 image forming position 20 laser signal light 21 photoconductor 22 charging Container 30 Developing roller 32 High voltage power source for developing bias 34 Third transfer roller 43 Laser exposure device 46 Mirror

Claims (4)

[Claims] 1. A plurality of image forming units each including a photoconductor, a charger, and a developing unit having a developer having a different color, and an image movably arranged with the plurality of image forming units. Forming unit group, a transfer body that transfers the toner images developed on the photoconductor onto each other at a single transfer position to form a color image, and an exposure position where image exposure is performed at a single position by an exposure unit. And an image forming position corresponding to the transfer position and the exposure position, and moving means for moving the entire image forming unit group so as to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method used in a color electrophotographic apparatus, wherein a voltage applied to the charger after the photoconductor of the image forming unit moves to the image forming position and starts an image forming operation Color electrophotographic method characterized by the is set higher than later when the second rotation at the first rotation. 2. A plurality of image forming units each including a photoconductor and a developing unit having a developer having a different color, and an image forming unit group in which the plurality of image forming units are arranged so as to be movable. A transfer member that applies a developing bias to the toner image that has undergone reversal development on the photosensitive member to form a color image by superimposing and transferring the toner image at a single transfer position; An exposure position to be performed, an image forming position corresponding to the transfer position and the exposure position, and a moving unit for moving the entire image forming unit group to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method for use in a color electrophotographic apparatus having: a printing unit for printing on the developing unit after the photoconductor of the image forming unit has moved to the image forming position to start an image forming operation. Color electrophotographic method, wherein a DC component of the developing bias is set higher later when the second rotation than during the first rotation of the photosensitive body. 3. A plurality of image forming units each including a photoconductor and a developing means having a developer having a different color, and an image forming unit group in which the plurality of image forming units are arranged so as to be movable. A transfer member for forming a color image by superposing and transferring the developed toner images on the photosensitive member at a single transfer position; and an exposure position for performing image exposure at a single position by laser exposure means, A color electronic device including an image forming position corresponding to the transfer position and the exposure position, and a moving unit that moves the entire image forming unit group to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method used in a photographic apparatus, wherein the laser output of the laser exposure means after the photoconductor of the image forming unit is moved to the image forming position and the image forming operation is started. Color electrophotographic method is characterized in that set high since when the second rotation than during the first rotation of the photosensitive member. 4. A plurality of image forming units each including a photoconductor and a developing unit having a developer having a different color, and an image forming unit group in which the plurality of image forming units are arranged so as to be movable. A transfer member for forming a color image by superposing and transferring the developed toner images on the photosensitive member at a single transfer position; and an exposure position for performing image exposure at a single position by laser exposure means, A color electronic device including an image forming position corresponding to the transfer position and the exposure position, and a moving unit that moves the entire image forming unit group to sequentially position each of the plurality of image forming units at the image forming position. A color electrophotographic method used in a photographic apparatus, wherein a laser lighting time of the laser exposure means after the photoconductor of the image forming unit moves to the image forming position and starts an image forming operation Color electrophotographic wherein the set longer when or after the second rotation from the time the first rotation of the photosensitive member.