JPH0980856A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a good image and also to simplify the attaching/detaching work of a fixed developing device, a mobile developing device and an intermediate transfer body by preventing the positional deviation of the developing device due to that the torque of a rotary body is unbalanced and the shortage of a time for switching the developing device in the case when the toner capacity of a specified developing device is increased. SOLUTION: The fixed developing device 21B for black is arranged above a photoreceptor drum 15, and rotary developing devices 20Y, 20M and 20C for respective yellow, magenta and cyan loaded on a rotary body 23 are arranged on the side of the drum 15, and the intermediate transfer body 9 is arranged under the drum 15. Even in the case where the toner capacity of the frequently used developing device 21B is increased, the torque balance of the rotary body 23 and the time for switching the developing device are not affected by the increase of the capacity. And also, as for the attaching/detaching direction with reference to the image forming device main body, the developing device 21B is attached/detached in up and down directions, the developing devices 20Y, 20M and 20C are attached/detached in the left and right directions (the axial direction of the photoreceptor drum), the intermediate transfer body 9 is attached/detached in forward and backward directions so that these devices and the rotary body are easily attached/detached.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser beam printer or an electrostatic recording type image forming apparatus.

[0002]

2. Description of the Related Art FIG. 5 shows a schematic structure of a color laser beam printer as an example of a color image forming apparatus.

This printer is provided with a photosensitive drum (image carrier) 104a which is rotatably supported in the direction of the arrow in the center of the apparatus main body 109. Above the photosensitive drum 104a, a charging roller 104b to which a charging voltage is applied is applied.
(Primary charger) is arranged, and the photosensitive drum 104a
The surface is uniformly charged to a predetermined potential.

The exposure of the photosensitive drum 104a is performed by the scanner section 110 having a laser diode. The laser light L emitted from the laser diode corresponding to the image signal is a polygon mirror 11 that rotates at high speed.
0a, the lens 110b, the mirror 110c and the like, the surface of the photosensitive drum 104a is selectively exposed. As a result, electrostatic latent images of respective colors are sequentially formed on the surface of the photosensitive drum 104a.

The rotary developing device 105 is a developing device of each color, and developing devices 105M, 105C, 105Y, 1 equipped with toners of respective colors of magenta, cyan, yellow and black.
Has 05K. These four color developing devices are shaft 105e
It is mounted on a rotating body 105b that is rotatably supported around the center. Each of the four color developing devices is configured to maintain a constant posture regardless of the rotation of the rotating body 105b, and has a constant toner capacity to keep the torque distribution to the shaft 105e constant. For example, each toner contains toner capable of printing about 2000 A4 images. At the time of image formation, the developing device for the color corresponding to the electrostatic latent image is rotationally moved to the developing position facing the photosensitive drum 104a, and along with this, the developing sleeve 105a moves the photosensitive drum 1a.
It is positioned so as to face the surface 04a through a minute gap. The developing device is connected to a high-voltage power source and a driving means, and when rotated to a developing position, the developing sleeve 1
A development bias is applied to 05a, and a predetermined rotation is performed. At the time of development, the developing sleeve 105a receives the application of the developing bias and the rotation drive, so that the photosensitive drum 1
The electrostatic latent image on 04a is developed as a toner image.

A paper feeding unit 101 is for feeding the transfer material 102 to a transfer drum (intermediate transfer member) 103, and a paper feeding cassette 101a for accommodating the transfer material 102 is arranged at the bottom of the apparatus main body 109. Has been done. During image formation, the paper feed roller 101b rotates according to the image forming operation, and the transfer materials 102 are separated one by one from the paper feed cassette 101a and fed to the transfer drum 103.

The transfer drum 103 winds a transfer material 102 fed from a paper supply unit 101 and forms a photosensitive drum 104a.
In order to transfer the above-described toner images of the respective colors onto the transfer material 102 at the transfer portion, the peripheral speed V equals to the surface speed of the photosensitive drum 104a V = 75.4 mm / sec (hereinafter referred to as "process speed"). The transfer drum 103 has a diameter of 180 mm
The elastic layer 103b is formed of sponge or rubber on the outer periphery of the aluminum cylinder 103a of
c is formed, and a dielectric layer 103d is further formed on the outermost layer. Further, a gripper 103f that holds the leading end of the fed transfer material 102 is provided at a predetermined position on the outer periphery of the transfer drum 103. Furthermore, the transfer drum 10
An electrostatic attraction roller 103g is provided on the surface of the transfer roller 103 so as to be able to come into contact with and separate from it, and the attraction roller 103g presses against the surface of the transfer drum 103 so as to sandwich the transfer material 102 with the transfer drum 103. Then, by applying a voltage between the attraction roller 103g and the transfer drum 103,
Electric charges are induced in the transfer material 102, which is a dielectric, and the dielectric layer 103d of the transfer drum 103, and the transfer material 102 is electrostatically adsorbed on the surface of the transfer drum 103.

The cleaner 104d is for cleaning the toner remaining on the photosensitive drum 104a after the transfer of the toner image, and is located downstream of the transfer portion of the photosensitive drum 104a.
It is arranged around.

The fixing section 106 is driven by the pressure roller 10.
6a, and a fixing roller 106b that is pressed against this and applies heat and pressure to the transfer material 102. The toner images of four colors are transferred to the surface, and the transfer material 102 separated from the surface of the photosensitive drum 103 passes between the pressure roller 106a and the fixing roller 106b, whereby the toner images of four colors are fixed. It

The image forming operation of the above-mentioned image forming apparatus is summarized as follows.

A transfer material 102 in a paper feed cassette 101a is fed to a transfer drum 103 by a paper feed roller 101b. The transfer drum 103 is a transfer material 102 that has been fed.
Is gripped by the gripper 103f and electrostatically attracted to the surface thereof. On the other hand, the photosensitive drum 104a whose surface is uniformly charged by the primary charger 104b is exposed with a magenta image by the scanner 110a, and an electrostatic latent image of a magenta image is formed on the surface. Simultaneously with the formation of this latent image, the magenta developing device 105M is driven to be rotationally moved to the developing position, and in order to attach the magenta toner to the magenta latent image formed on the photosensitive drum 104a, it has substantially the same polarity as the charging polarity of the photosensitive drum 104a. A developing bias voltage of the same potential is applied to develop the image, and a magenta toner image is formed on the photosensitive drum 104a. And the transfer drum 10
A transfer voltage having a polarity opposite to that of the magenta toner is applied to 3 to transfer the magenta toner image on the photosensitive drum 104a to the transfer drum 1.
03 is transferred onto the transfer material 102.

When the transfer of the magenta toner image is completed, the next developing device 105C rotationally moves to the developing position, and in the same process, formation of a latent image of cyan, development, and transfer of the toner image are sequentially performed, and the transfer material 102 is transferred. The cyan toner image is superimposed on the magenta toner image of. Similarly, yellow and black toner images are also superimposed on the transfer material 102 to form a four-color full-color image.

By rotating the transfer drum 103 carrying the transfer material 102 on its surface four times, one full-color image of four colors can be obtained. That is, as described above, the diameter of the transfer drum 103 is set to 180 mm and the process speed is set to 75.4 mm / sec.
One full-color image is output in π × 4 / 75.4 = 30 seconds.

Transfer material 1 after transfer of four color toner images
02 is separated from the transfer drum 103 and fixed to the fixing unit 106.
The toner image is fixed by the fixing unit 106 and then discharged onto the discharge tray 108 by the discharge roller pair 107.

[0015]

By the way, in general, 4
In a full-color image forming apparatus, the amount of black toner consumed is larger than that of other colors. For this reason, the amount of toner in the black developing device 105K is changed to the developing devices 10K of other colors.
If it is larger than the amount of toner in 5M, 105C, and 105Y, the number of times of toner replenishment is reduced, which is convenient.

However, in the above-mentioned conventional technique, since the developing devices of four colors are all rotatably arranged, increasing the toner of the developing devices of a specific color breaks the torque balance when the developing devices are rotated. In addition, there is a problem that the time for switching the developing device is insufficient or the position of the developing device is displaced, which hinders the formation of a good color image.

Further, in the image forming apparatus shown in FIG. 5, when the transfer drum 103 is exchanged, the transfer drum 103 is pulled out in the vertical direction with respect to FIG. .

Therefore, according to the present invention, it is possible to form a good color image even when the toner amount of the developing device of a specific color which is frequently used is increased, and the fixed developing device, the moving developing device, An object of the present invention is to provide an image forming apparatus in which an intermediate transfer body (intermediate transfer drum) can be easily attached and detached.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and includes a rotatable image carrier disposed in the main body of an image forming apparatus and a periphery of the image carrier. The latent image forming means, the developing means, and the intermediate transfer means sequentially form toner images of a plurality of different colors on the image carrier, and these toner images are collectively formed on the transfer material via the intermediate transfer body. In the color image forming apparatus for transferring by means of transfer, the developing means is disposed above the image carrier and forms a first developing position with the image carrier, and the fixed developing device. It is mounted on a rotatable rotatable member disposed below the container, and is rotated and moved with the rotation of the rotatable member, and is selectively disposed at a second developing position between the image bearing member and the image bearing member. At least two moving developing devices, and the axis of the image carrier is As a rule, when the direction along the axis is the left-right direction, and the vertical direction and the horizontal direction of the directions perpendicular to the axis are the up-down direction and the front-back direction, respectively, the fixed developing device is attached to the main body of the image forming apparatus. It is characterized in that it is detachable in the vertical direction via the upper portion, and that each of the movable developing devices is detachable in the horizontal direction via the side portion of the image forming apparatus main body.

Further, the intermediate transfer means may have a cylindrical intermediate transfer member which is detachable in the front-rear direction via the front portion or the rear portion of the image forming apparatus main body.

Further, the intermediate transfer member, the fixed developing device, and the moving developing device are mounted on the main body of the image forming apparatus.
The respective predetermined portions may be brought into contact with the same positioning portion formed at the end portion of the image carrier to perform the positioning.

[Operation] Based on the above configuration, for example, the black toner, which consumes a large amount, is stored in the immovable fixed developing device, and the toners of other colors are accommodated in the rotationally movable moving developing device. As a result, even if the amount of black toner stored is made larger than the amount of toner stored in other colors to reduce the number of times of toner replenishment, if the stored amount of toner of other colors is the same, the rotating body When the moving developing device is rotatively moved, the torque balance will not be lost due to the difference in the amount of stored toner, the switching time of the moving developing device will not be short, and the displacement of the moving developing device will not occur.

Further, the predetermined portions of the intermediate transfer member, the fixed developing device, and the moving developing device are brought into contact with a common member, that is, the same positioning member formed at the end portion of the image carrier, so that the respective parts for the image carrier are contacted. The positioning accuracy of the member can be improved.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> [General Description of Image Forming Apparatus] A color image forming apparatus according to the present invention will be described with reference to a longitudinal sectional view of a color laser beam printer shown in FIG.

The color image forming apparatus shown in FIG. 1 includes a photosensitive drum 15 as an image bearing member which rotates at a constant speed, a black developing device 21B which is immovably arranged, and a rotating member 2.
Three color developing devices 20Y, 20C, 20 for rotating three colors, namely, yellow, magenta, and cyan.
An image forming unit having M and a color image composed of a plurality of eclipsed toner images developed and multiply transferred in the image forming unit, and collectively transferred to the transfer material 2 fed from the feeding unit. And a transfer body (intermediate transfer means) 9. The transfer material 2 on which the color image has been transferred is then conveyed to the fixing unit 25 to fix the color image on the transfer material 2, and a paper discharge roller 36 discharges a paper onto a paper discharge tray (discharge unit) 37 on the upper surface of the image forming apparatus body.
To be discharged to The color movable developing devices 20Y, 20M, 20C and the black fixed developing device 21B that are fixedly arranged are separately detachable from the image forming apparatus main body. There is.

Next, the structure of each part of the above-mentioned color image forming apparatus will be sequentially described in detail. [Image Bearing Unit (Drum Unit)] The drum unit (image bearing unit) 13 integrally includes a photosensitive drum 15 and a cleaner container 14 that also serves as a holder for the photosensitive drum 15. This drum unit 13
Is detachably supported on the main body of the image forming apparatus, and the unit can be easily replaced according to the life of the photosensitive drum 15. Photosensitive drum 15 of the present embodiment
Is formed by coating an organic photoconductor layer on the outside of an aluminum cylinder having a diameter of about 60 mm, and is rotatably supported by a cleaner container 14 of a cleaning device that also serves as a holder for the photosensitive drum 15. A cleaning blade 16 and a primary charging unit 17 are arranged around the photosensitive drum 15, and a drive motor (not shown) is provided at one end of the photosensitive drum 15.
By transmitting the driving force, the photosensitive drum 15 is rotated counterclockwise in the figure in accordance with the image forming operation. [Charging Means] The charging means 17 employs a contact charging method, in which a conductive roller is brought into contact with the photosensitive drum 15 and a voltage is applied to the conductive roller to make the surface of the photosensitive drum 15 uniform. It is charged. [Exposure Means] The exposure of the photosensitive drum 15 described above is performed by the scanner unit 30. That is, when the image signal is given to the laser diode, the laser diode emits image light corresponding to the image signal, and thereby illuminates the polygon mirror 31. The polygon mirror 31 is rotated at a high speed by a scanner motor, and the image light reflected by the polygon mirror 31 is rotated at a constant speed via an imaging lens 32 and a reflection mirror 33.
The surface of No. 5 is selectively exposed, and as a result, an electrostatic latent image is formed on the surface of the photosensitive drum 15. [Developing Means] The developing means includes three rotary developing devices (moving developing devices) capable of developing each color of yellow, magenta, cyan, and black in order to visualize the electrostatic latent image as a toner image. ) 20Y, 20M, 20C and one black fixed developing device 21B.

The black fixed developing device 21B is fixedly arranged above the photosensitive drum 15. Fixed developer 2
1B has a sleeve 21 at a position facing the photosensitive drum 15.
The BS is arranged at the first developing position with a minute gap (about 300 μm) with respect to the photosensitive drum 15.
A visible image (toner image) with black toner is formed on 5.

In the fixed developing device 21B, the toner in the container is sent by a sending mechanism, and a thin layer of the toner is applied to the surface of the sleeve 21BS rotating clockwise in the figure by the applying blade 21BB pressed against the surface of the sleeve 21BS. In addition, the toner is charged (triboelectrically charged). Further, by applying a developing bias to the sleeve 21BS, toner development is performed corresponding to the electrostatic latent image on the photosensitive drum 15.

On the other hand, as shown in FIG.
B can be inserted into the image forming apparatus main body along the guide groove G21 from the upper arrow side by providing a large opening on the upper surface of the image forming apparatus main body. Therefore,
The size of the toner container of the fixed developing device 21B can be increased, and the capacity of the fixed developing device 21B can be adjusted to other yellow, magenta, and
It is possible to store toner equivalent to 10,000 pages (calculated with A4, 5% printing) which is more than twice the toner capacity of the cyan rotary developing devices 20Y, 20M, and 20C. By increasing the capacity of the fixed developing device 21B in this way, it is possible to reduce the frequency with which the user replaces the fixed developing device 21B and reduce the running cost per print.

Three rotary developing devices 20Y, 20M, 20C
Is 4000 pages each (calculated with A4 and 5% printing)
Corresponding toner is stored and detachably held by a developing rotary (rotating body) 23 that rotates around a shaft 22, and at the time of image formation, the rotary developing units 20Y and 20Y.
While the M and 20C are held by the developing rotary 23, the M and 20C rotate around the shaft 22, and a predetermined rotary developing device (the rotary developing device 20Y in FIG. 1 and the rotary developing device 20M in FIG. 2) is attached to the photosensitive drum 15. After being stopped at the facing position, and further, the developing sleeve is positioned at the second developing position so as to face the photosensitive drum 15 with a minute gap (about 300 μm), the electrostatic latent image on the photosensitive drum 15 is dealt with. A visible image (toner image) is formed. At the time of forming a color image, the developing rotary 23 rotates for each rotation of the intermediate transfer member 9, and the yellow, magenta, and cyan rotary developing devices 20Y, 20M,
The developing process is performed in the order of 20C, and then the black fixed developing device 21B.

FIG. 1 shows a state where the yellow rotary developing device 20Y is positioned and stationary at a position facing the photosensitive drum 15. The rotary developing device 20Y sends the toner in the container to the coating roller 20YR by a feeding mechanism, and rotates clockwise in the drawing by the coating roller 20YR rotating clockwise and the blade 20YB pressed against the surface of the sleeve 20YS. A thin layer of toner is applied to the surface of the sleeve 20YS that rotates in the direction of 0, and an electric charge is applied to the toner (friction charging). By applying a developing bias to the sleeve 20YS facing the photosensitive drum 15 on which the latent image is formed, toner development is performed on the photosensitive drum 15 according to the latent image. Toner development is also performed on the magenta rotary developing device 20M and the cyan rotary developing device 20C by the same mechanism as described above.

Further, each rotary developing device 20Y, 20M, 20
The respective sleeves of C are provided for the respective rotary developing devices 20Y, 20Y.
When the M20C is rotationally moved to the second developing position, it is configured to be connected to a high-voltage power source for each color developing device and a drive provided in the image forming apparatus main body, and a voltage is selectively applied for each color developing. And the drive is connected.

Each rotary developing device 20Y, 20M, 20C is
As shown in FIG. 2, via the side portion of the image forming apparatus main body,
The photosensitive drum 15 is configured to be detachable in the left-right direction along the axial direction. In FIG. 2, the yellow rotary developing device 20Y is mounted in the direction of the arrow (to the right) and taken out in the direction opposite to the arrow (to the left). [Intermediate Transfer Body] The intermediate transfer body 9 makes the toner images on the photosensitive drum 15 visualized by the developing devices 20Y, 20M, 20C, and 21B four times (yellow, magenta, and cyan black toners) during the color image forming operation. Image), it rotates in a clockwise direction in the figure in synchronism with the surface speed of the photosensitive drum 15 in order to receive multiple transfer, and the intermediate transfer member 9 that has received multiple transfer is transferred by a transfer roller 10 to which a voltage is applied. By sandwiching and transporting the two, the toner images of respective colors on the intermediate transfer member are simultaneously and multiple-transferred onto the transfer material 2.

The intermediate transfer member 9 according to the present embodiment has a diameter of 1
The surface of the aluminum cylinder 12 of 80 is covered with an elastic layer 11 such as a medium resistance sponge or medium resistance rubber. The intermediate transfer member 9 is rotatably supported and is rotated by being driven by a gear (not shown) fixed integrally.

Further, as shown in FIG. 3, an openable and closable door is provided above the sheet feeding section on the side surface M1 of the image forming apparatus main body.
From there, the intermediate transfer body 9 is mounted inside the main body of the image forming apparatus along the guide groove G9 in the direction of the arrow in the drawing, and is detached in the opposite direction, so that a sufficient working space for attachment / detachment can be secured. it can.

Further, as shown in FIG. 4, the end portion 9a of the intermediate transfer member 9 is abutted with the end portion 21BSa of the sleeve 21BS of the fixed developing device 21B and the end portion 20Sa of the sleeve 20S of each rotary developing device. By abutting against the same photosensitive drum end portion (positioning portion) 15a, the position of each developing device and the intermediate transfer member 9 with respect to the photosensitive drum 15,
Therefore, the relative position between each developing device and the intermediate transfer member 9 can be accurately determined. This makes it possible to stabilize the transfer performance of the toner image and reduce color misregistration. [Cleaning Means] The cleaning means has a cleaning blade 16 as shown in FIG. 1, and when the toner image visualized on the photosensitive drum 15 by the developing means is transferred to the intermediate transfer body 9, the intermediate transfer is performed. The toner remaining on the photosensitive drum 15 without being transferred to the body 9 is removed by the above-mentioned cleaning blade 16. The removed waste toner is stored in the cleaner container 14. The storage capacity of the waste toner in the cleaner container 14 is set to a size such that the cleaner container 14 is not filled with the waste toner before the life of the photosensitive drum 15 is reached.
Therefore, the cleaner container 14 is designed to be integrally replaced when the life of the photosensitive drum 15 is replaced. [Paper Feeding Unit] The paper feeding unit feeds the transfer material 2 to the image forming unit, and the paper feeding cassette 1 containing a plurality of transfer materials 2
And a sheet feeding roller 3, a feeding roller 4, a retard roller 5 for preventing double feeding, a sheet feeding guide 6, a conveying roller 7, a registration roller 8 and the like. At the time of image formation, the paper feed roller 3 is driven and rotated according to the image forming operation to separate and feed the transfer materials 2 in the paper feed cassette 1 one by one, and guide them by the paper feed guide 6 and pass through the conveyance roller 7. Then, the registration roller 8 is reached. During the image forming operation, the registration roller 8 performs a non-rotating operation of keeping the transfer material 2 stationary and a rotating operation of transporting the transfer material 2 toward the intermediate transfer body 9 in a predetermined sequence, and is a next step. The image and the transfer material 2 at the time of the transfer step are aligned. [Transfer Section] The transfer section includes a swingable transfer roller 10. The transfer roller 10 is formed by winding a metal shaft around a medium-resistance foamed elastic body, is movable up and down in the figure, and is rotationally driven by a drive means (not shown). The transfer roller 10 is indicated by a solid line in the figure so that the image is not disturbed while the toner images of four colors are formed on the above-mentioned intermediate transfer body 9, that is, while the intermediate transfer body 9 makes a plurality of rotations. , Stand by at a standby position 10A below the surface of the intermediate transfer member. Then, after the four color toner images have been formed on the intermediate transfer member 9, the transfer roller 10 is driven by a cam member (not shown) at a timing of transferring the color image onto the transfer material 2 so that the transfer roller 10 has The transfer material 2 is located between the upper operating position 10B indicated by the dashed line, that is, the surface of the intermediate transfer member 9
Is arranged at a position where it is nipped and conveyed. At this time, a bias is applied to the transfer roller 10 at the same time, and the bias on the intermediate transfer member 9
The color toner images are collectively transferred to the transfer material 2. Here, since the intermediate transfer body 9 and the transfer roller 10 are individually driven to rotate, the transfer material 2 sandwiched between the two is subjected to the transfer process and at the same time, is moved to the left in the figure by a predetermined distance. The sheet is conveyed at a speed and is sent to the fixing unit 25 which is the next step. [Fixing Unit] As shown in FIG. 1, the fixing unit 25 is sequentially formed on the photosensitive drum 15 by the developing devices 20Y, 20M, 20C, and 21B described above, and is collectively formed on the transfer material 2 via the intermediate transfer body 9. It fixes the transferred four-color toner image, and includes a fixing roller 26 for applying heat to the transfer material 2 and a pressure roller 27 for bringing the transfer material 2 into pressure contact with the fixing roller 26. Each of the rollers 26 and 27 is formed as a hollow roller and has heaters 28 and 29 inside thereof.
And is driven to rotate by drive means (not shown).
As a result, the transfer material 2 holding the toner images of four colors is heated and pressed while being nipped and conveyed by the fixing roller 26 and the pressure roller 27, and the toner images of four colors on the surface are melted and fixed and fixed. It [Image Forming Operation] An operation when an image is formed by the image forming apparatus having the above configuration will be described.

First, the sheet feeding roller 3 shown in FIG. 1 is rotated to separate one sheet of the transfer material 2 in the sheet feeding cassette 1, and the sheet is conveyed to the registration roller 8.

On the other hand, the peripheral speed (process speed) of the photosensitive drum 15 and the intermediate transfer member 9 is V = 75.4 mm.
/ Sec rotates in the direction of the arrow. The photosensitive drum 15 having a diameter of 60 mm makes one rotation in 60π / 75.4 = 2.5 seconds, and the intermediate transfer member 9 having a diameter of 180 mm has 180π / 75.4 = 7.
One rotation in 5 seconds. Further, the photosensitive drum 15 and the intermediate transfer member 9 are connected by a gear (not shown),
When 5 rotates three times, the intermediate transfer member 9 rotates exactly one rotation.

In the figure, when an arbitrary point on the surface of the intermediate transfer member 9 reaches the position S in the figure, the point E on the surface of the photosensitive drum 15 whose surface is uniformly charged by the charging means 17 is the exposure position. An image is formed by receiving laser exposure. Photosensitive drum 15
Counterclockwise from the exposure position of the contact portion T with the intermediate transfer member 9
The distance a up to 1 and the distance b from the point S to T1 in the figure of the intermediate transfer member 9 are equal. Therefore, after a / 75.4 hours have elapsed, the point E where the exposure is started at the exposure position on the photosensitive drum 15 is started.
And the point S on the intermediate transfer body 9 coincide at the position of T1.
That is, the image is formed counterclockwise on the intermediate transfer member 9 with the point S as the tip.

Then, yellow, magenta, cyan,
The formation of the black toner images will be described. Formation of Yellow Image The scanner unit 30 irradiates a yellow image with a laser to form a yellow latent image on the photosensitive drum 15. Simultaneously with the formation of this latent image, the yellow rotary developing device 20Y is driven to apply a voltage having substantially the same potential as the charging polarity of the photosensitive drum 15 so that the yellow toner adheres to the latent image on the photosensitive drum 15. Perform yellow development. At the same time, the yellow toner image on the photosensitive drum 15 is primarily transferred onto the surface of the intermediate transfer member 9 at the first transfer position T1 slightly downstream of the developing section.
At this time, a voltage having a characteristic reverse to that of the yellow toner is applied to the intermediate transfer member 9 to perform the primary transfer.

When the transfer material 2 on which an image is formed is of A3 size, the length is 420 mm, and the image is transferred from a point T1 on the surface of the intermediate transfer body 9 to a point T2 on the downstream side of 420 / 180π (≈3 / 4) circumference. Is formed. When the transfer of the yellow toner to the intermediate transfer member 9 is completed, that is, when the point T2 passes the first transfer position T1, the developing rotary 23 rotates counterclockwise and the next magenta rotary developing device 20M rotationally moves. It is positioned at a second developing position facing the photosensitive drum 15. Formation of Magenta Image Next, when one point S (the tip of the yellow image) on the surface of the intermediate transfer body 9 makes a round and reaches the position S in the figure, the laser irradiation of the magenta image is similarly started by the scanner unit 30 and the yellow color is started. Similarly, the magenta toner image is developed on the latent image on the photosensitive drum 15, and the magenta toner image on the photosensitive drum 15 is similarly transferred onto the intermediate transfer body 9 at the first transfer position T1. When the transfer of the magenta toner to the intermediate transfer body 9 is completed, that is, when T2 passes the first transfer position T1, the developing rotary 23 rotates counterclockwise,
The next cyan rotary developing device 20C is rotationally moved and positioned at the second developing position facing the photosensitive drum 15. Formation of Cyan Image Next, when one point S (front end of the yellow and magenta images) on the surface of the intermediate transfer body 9 further goes around and reaches the position S in the figure, laser irradiation of the cyan image is similarly performed by the scanner unit 30. The cyan toner image is developed on the latent image on the photosensitive drum 15 in the same manner as in the case of magenta, and the cyan toner image on the photosensitive drum 15 is transferred onto the intermediate transfer member 9 at the first transfer position T1. And transfer it to. When the transfer of the cyan toner to the intermediate transfer body 9 is completed, that is, when T2 passes the first transfer position T1, the developing rotary 23 rotates counterclockwise by 60 degrees and the color developing device is located at a position facing the photosensitive drum 15. 20 does not exist. Formation of Black Image Next, one point S (front ends of the yellow, magenta, and cyan images) on the surface of the intermediate transfer member 9 further makes a round, and is shown in FIG.
Similarly, the laser irradiation of the black image is started by the scanner unit 30 and then the black toner is developed by the black developing device 21B, and the black toner image on the photosensitive drum 15 is intermediately transferred at the first transfer position T1. The image is further transferred onto the body 9 and transferred.

As described above, latent image formation and development in the order of yellow, magenta, cyan, and black and toner transfer to the intermediate transfer member 9 are successively performed four times, and yellow, magenta, cyan, and cyan are transferred to the surface of the intermediate transfer member 9. A full-color image composed of black toner of four colors is formed.

Before the transfer of the black toner to the intermediate transfer body 9 is completed, that is, the point S at the image front end of the intermediate transfer body 9 on which the full-color image is formed after the first transfer of the black toner of the fourth color is completed is the second. Before the transfer material T reaches the transfer portion T2, the transfer material 2 held by the registration rollers 8 is started to be conveyed at the same timing. When each color image is formed on the intermediate transfer body 9 four times as described above, the transfer roller 10 that is in a non-contact state with the intermediate transfer body 9 is moved downward by a cam (not shown) at the same time to move the transfer material 2 to the intermediate position. Transfer body 9
By applying pressure at the second transfer portion T2 between and, and at the same time, applying a bias having a characteristic reverse to that of the toner to the transfer roller 10,
The full-color image on the intermediate transfer member 9 is simultaneously transferred onto the transfer material 2 in four colors. The transfer material 2 that has passed through the second transfer portion T2 is separated from the intermediate transfer body 9 and is conveyed to the fixing portion 25 to perform toner fixing, and thereafter, the conveying rollers 34 and 35, and the paper discharge roller 3.
The image is discharged onto the sheet discharge tray 37 via 6 with the image surface facing downward, and the image forming operation is completed.

It is understood that the intermediate transfer member 9 basically requires four rotations and a time period of 30 seconds (7.5 seconds × 4) in order to form one full-color image in this way. it can. The intermediate transfer member 9 and its process speed V
The photosensitive drum 15 driven in the same manner is inversely proportional to the outer diameter ratio with the intermediate transfer member 9 to produce one full-color image.
Make two turns.

The intermediate transfer body 9 has a diameter of 180 mm and an outer peripheral length of about 565 mm, and a peripheral length of 420 mm is used for forming an A3 size image. That is, the distance from the point S on the surface of the intermediate transfer member 9 to the point T in the counterclockwise direction is 420 mm. That is, 420 mm of the outer circumference 565 mm of the intermediate transfer body 9 is used for image formation,
The remaining 145 mm is not used for imaging. Since the intermediate transfer member 9 rotates at a constant process speed V = 75.4 mm / sec, a non-image forming time of 145 / 75.4 = 1.92 seconds exists for forming an A3 size full-color image. , This time is the color rotary developing device 20Y, 20
Applies to switching times of M and 20C.

Laser exposure position of the photosensitive drum 15 and the first
The time that can be applied for the rotary developing device 20Y located between the transfer portion T1 and the next rotary developing device 20M to form a visible image and to replace the next rotary developing device 20M is the middle of the actual timing being shifted. The point T of the transfer body 9 corresponds to the time until the point S passes through the first transfer portion T1 and the point S reaches the first transfer portion T1 next time.

[0047]

As described above, according to the present invention,
A developing device (fixed developing device) of a specific color (black in the description of the embodiments) that is frequently used is fixedly arranged above the image carrier, and developing devices of other colors (moving developing device) are fixed. By movably mounting the rotor on the lower part of the developing device, even if the toner capacity of the developing device of a specific color is increased and the replacement frequency is lowered, the torque balance of the rotating member is disturbed and It is possible to prevent the displacement of the developing device due to a shortage of the time for switching the developing device, and it is possible to form a good color image. Further, by attaching / detaching the fixed developing device to the up / down direction, the moving developing device to the left / right direction, and the intermediate transfer member to the image forming apparatus main body in the front / rear direction, the attachment / detachment work can be simplified. .

Further, the relative positions of each developing device and the intermediate transfer member with respect to the image carrier can be set with high accuracy, and the transfer performance of the toner image onto the intermediate transfer member can be stabilized, so that high image quality with less color misregistration can be obtained. Can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a schematic configuration of a color laser beam printer.

FIG. 2 is a perspective view illustrating an attaching / detaching operation of a black developing device and a yellow developing device with respect to the image forming apparatus main body.

FIG. 3 is a side sectional view for explaining an attaching / detaching operation of the intermediate transfer body with respect to the image forming apparatus main body.

FIG. 4 is a perspective view illustrating positioning of a black developing device sleeve, another color developing device sleeve, and an intermediate transfer member with respect to an image carrier.

FIG. 5 is a vertical sectional view showing a schematic configuration of a conventional color laser beam printer.

[Explanation of symbols]

 1 Paper Feed Cassette 2 Transfer Material 3 Paper Feed Roller 4 Feed Roller 5 Retard Roller 6 Paper Feed Guide 7 Transport Roller 8 Registration Roller 9 Intermediate Transfer Means (Intermediate Transfer Body) 10 Transfer Roller 13 Drum Unit 14 Cleaner Container 15 Image Carrier ( Photosensitive drum 16 Cleaning blade 17 Charging means 20C Moving developing device (cyan rotary developing device) 20M Moving developing device (magenta rotating developing device) 20Y Moving developing device (yellow rotating developing device) 20YB Coating blade 20YR Coating roller 20YS Development Sleeve 21B Fixed developing device (black developing device) 21BB Coating blade 21BS Developing sleeve 22 Shaft 23 Rotating body (developing rotary) 25 Fixing part 26 Fixing roller 27 Pressure roller 28, 29 Heater 30 Scanner part 31 Polygon mirror 32 Lens Third reflecting mirrors 34, 35 conveying rollers 36 discharge rollers 37 discharge tray T1 first transfer position T2 second transfer position

Claims (3)

[Claims] 1. A rotary image bearing member disposed in the main body of the image forming apparatus, and a latent image forming unit, a developing unit, and an intermediate transfer unit disposed around the image bearing member, on the image bearing member. In a color image forming apparatus that sequentially forms toner images of a plurality of different colors on one another and collectively transfers these toner images to a transfer material via the intermediate transfer member, the developing unit includes: A fixed developing device which is arranged above and forms a first developing position with the image carrier, and a rotatable developing member which is arranged below the fixed developing device and is mounted on the rotatable developing member. At least two moving developing devices that rotate and move with the rotation of the body and are selectively arranged at a second developing position between the image carrier and the image carrier. As a reference, the direction along the axis is the left-right direction, and the direction perpendicular to the axis is When the vertical direction and the horizontal direction of the image forming apparatus are the up-down direction and the front-rear direction, respectively, the fixed developing device is detachable in the up-down direction via the upper portion of the main body of the image forming apparatus, and the moving developing devices are attached to the image. A color image forming apparatus, wherein the color image forming apparatus is detachable in a lateral direction via a side portion of a main body of the forming apparatus. 2. The color image forming apparatus according to claim 1, wherein the intermediate transfer unit has a cylindrical intermediate transfer member that is detachable in a front-rear direction via a front portion or a rear portion of the image forming apparatus main body. Image forming apparatus. 3. The intermediate transfer body, the fixed developing unit, and the moving developing unit, when mounted on the main body of the image forming apparatus, contact their respective predetermined portions with the same positioning portion formed at the end portion of the image carrier. The color image forming apparatus according to claim 2, wherein the color image forming apparatus is in contact with each other for positioning.