JP2001318506A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device such that the life of a developing roller is prolonged, so that the durability is improved. SOLUTION: The color image forming device includes plural image forming units 5 which contain toner in plural colors and are arranged in a tandem manner, and an endless intermediate transfer belt 1 which rotates in the direction of the arrangement of the units. Each image forming unit 5 has a photoreceptor drum 5a for forming an electrostatic latent image on by an exposure unit 4 and a developing roller 5d for developing the electrostatic latent image on the corresponding photoreceptor drum with the corresponding toner, and transfers the toner image, developed by the developing roller 5d, to the intermediate transfer belt 1. In the color image forming device, toner development is carried out by bringing the developing roller 5d into contact with the photoreceptor drum 5a only while the electrostatic latent image on the photoreceptor drum 5a is developed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming a composite image by superimposing image information using electrophotographic technology or the like.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic technique, an electrophotographic photosensitive member as an image carrier is charged by a charger, and the photosensitive member is irradiated with light according to image information. 2. Description of the Related Art A latent image is formed, and the latent image is developed by a developing device, and a visualized toner image is transferred to a sheet material or the like to form an image.

On the other hand, a plurality of image carriers on which such a series of image forming processes are developed in accordance with colorization of an image are provided, and each color image of a cyan image, a magenta image, a yellow image, and preferably a black image is provided. A number of tandem-type image forming apparatuses that form a full-color image by forming a color image on each image carrier and superimposing and transferring each color image on a sheet material at a transfer position of each image carrier have been proposed. I have. Such a tandem-type multiplex image forming apparatus has an image forming unit for each color, and is said to be advantageous for speeding up. FIG. 14 is a schematic view showing a conventional color image forming apparatus.

As shown in FIG. 14, a color image forming apparatus includes a yellow (Y), a magenta (M), a cyan (C),
Image forming units 51, 52, 53, 54 for forming toner images of each color of black (K), and an exposing device 55 for outputting an image signal to form an electrostatic latent image.
And the intermediate transfer belt 5 which is formed in a closed loop and travels
6 and a fixing device 57, and transfers the toner image on the intermediate transfer belt 56 to the sheet P supplied from the sheet cassette 58 and fixes the toner image on the sheet P by the fixing device 57.

A black (K) image forming unit 54
Is a photoreceptor drum 54a having an electrostatic latent image formed on its peripheral surface by a laser beam from an exposure unit 55, a charger 54b for charging the same, and a toner attached to visualize the electrostatic latent image. And a cleaner 54d for removing residual toner after transferring the toner image to the intermediate transfer belt 56. The other image forming units 51 to 53 have the same configuration.

In the multiplex image forming apparatus having such a configuration, for example, first, a black (K) image forming unit 5 is provided.
The latent image of the black component color of the image information is formed on the photosensitive drum 54a of No. 4 by the exposure device 55. This latent image is visualized as a black toner image by the developing roller 54c, and is transferred onto the intermediate transfer belt 56. During this time, a latent image of the cyan component color is formed, and the cyan toner image is visualized by the cyan toner in the developing device. Then, the cyan toner image is transferred to the intermediate transfer belt 52 on which the transfer of the black toner image has been completed, and is superimposed on the black toner image. Thereafter, image formation is performed in the same manner for the magenta toner image and the yellow toner image.
The superimposition of the four color toner images is completed.

Here, the photosensitive drums of the image forming units 51 to 54 are driven to rotate, and at the same time, the intermediate transfer belt 56 is driven to run. At this time, in order to prevent abrasion and wear of the photosensitive drum and the intermediate transfer belt 56 due to a speed difference between the peripheral speed of the photosensitive drum and the running speed of the intermediate transfer belt 56,
6 are brought into contact with each other when the operation is completed, and image formation is performed at an operation timing at which the operation is completed after the separation. That is,
Each of the image forming units 51 to 54 starts rotating before the photosensitive drum contacts the intermediate transfer belt 56, and makes the photosensitive drum contact when the intermediate transfer belt 56 is driven. Then, the photosensitive drum is irradiated with a laser by the exposing device 55 to form an electrostatic latent image, and then a toner image is formed by a developing roller. The formed toner image is transferred to the intermediate transfer belt 56. Thereafter, the paper cassette 58
After the toner image on the intermediate transfer belt 56 is transferred to the paper P from the printer, the intermediate transfer belt 56 is separated from the photosensitive drum, and finally, the operations of the image forming units 51 to 54 and the intermediate transfer belt 56 are stopped. I do.

[0008]

However, in each of the image forming units 51 to 54, when the photosensitive drum is rotating, the developing roller is always rotating at the same time by contacting the peripheral surface thereof. On the other hand, in the case of the tandem system, in the example of FIG. 14, the printing operation is performed sequentially from the black image forming unit to the cyan image forming unit 51, and the respective printing timings are slightly shifted.
That is, in the operation of each of the image forming units 51 to 54, printing is not always performed, but an image signal is input to each of them, and the printing operation mode is set only for a predetermined period. Therefore, if the developing roller rotates at the same time as the rotation of the photosensitive drum, the developing roller remains in contact with the photosensitive drum during periods other than the printing period, and a reduction in life due to wear is inevitable.

The surface of the developing roller is made of conductive silicon rubber, and is in contact with a thinning blade for controlling the amount of toner supplied from the supply roller. Since the thinning blade comes into contact with the developing roller from the same direction as the photosensitive drum, the developing roller is also worn.

As described above, in the conventional color image forming apparatus, the developing roller always contacts the photosensitive drum which is rotated or driven in contact with or separated from the intermediate transfer belt 56 in a timely manner. For this reason, even during the non-printing period, the developing roller receives friction from the photosensitive drum, and the life is shortened due to abrasion.

In view of the above, according to the present invention, the developing roller is brought into contact with the photosensitive drum only when a toner image is formed on the photosensitive drum to form a toner image, so that the life of the developing roller can be extended and the durability can be improved. It is an object to provide a color image forming apparatus.

[0012]

According to the present invention, there are provided a plurality of image forming units each provided with a plurality of color toners and arranged in tandem, and an endless intermediate transfer which travels around in the arrangement direction of the image forming units. A belt, wherein the image forming unit includes a photosensitive drum capable of forming an electrostatic latent image by an exposure unit, and a developing roller for developing the electrostatic latent image on the photosensitive drum with the toner. In a color image forming apparatus that transfers a toner image developed by a developing roller to the intermediate transfer belt, the developing roller is brought into contact with the photosensitive drum only during a period of developing the electrostatic latent image on the photosensitive drum. It is characterized in that development with toner is enabled.

According to the present invention, it is possible to obtain a color image forming apparatus capable of extending the life of the developing roller and improving the durability.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The invention according to a first aspect of the present invention is directed to an image forming apparatus comprising: a plurality of image forming units each including a plurality of color toners arranged in tandem; The image forming unit includes a photosensitive drum capable of forming an electrostatic latent image by exposure means, and a developing roller for developing the electrostatic latent image on the photosensitive drum with toner. In a color image forming apparatus that transfers a toner image developed by the above to an intermediate transfer belt, the developing roller can be brought into contact with the photosensitive drum only during a period for developing the electrostatic latent image on the photosensitive drum, thereby enabling development with toner. This is a color image forming apparatus characterized in that the contact time between the developing roller and the photosensitive drum is shortened. It has the effect of improving the life of the roller.

According to a second aspect of the present invention, the image forming unit is connected to the first housing holding the photosensitive drum so as to be vertically swingable with respect to the first housing via a support shaft. 2. The image forming apparatus according to claim 1, further comprising a second housing for holding the developing roller, wherein the second housing is turned up and down to allow the developing roller to be moved toward and away from the photosensitive drum. Since the photosensitive drum and the developing roller can be unitized in each of the first and second housings, the separation and contact mechanism can be obtained with a simple configuration.

According to a third aspect of the present invention, the second housing is provided with a thinning blade for charging and thinning the toner in contact with the peripheral surface of the developing roller. 3. The color image forming apparatus according to claim 2, wherein the rotation of the developing roller is stopped when the developing roller is separated from the drum, and the developing roller does not rotate during a period apart from the photosensitive drum. This has the effect of preventing the abrasion of the surface of the developing roller further without sliding with the thinning blade.

According to a fourth aspect of the present invention, the guide member is arranged such that the second housing is rotated in the direction in which the image forming units are arranged, and the guide members are reciprocally movable in the direction in which the image forming units are arranged. 4. The color image forming apparatus according to claim 2, wherein a plurality of triggers are provided which rotate in conjunction with the movement of the member, and the second housing can be rotated by the rotation of the trigger. ,
This has the effect that the separation / contact operation of the photosensitive drums of a plurality of image forming units and the developing roller can be performed only by the interlocking operation of the guide member and the trigger.

According to a fifth aspect of the present invention, the developing roller is brought into contact with the photosensitive drum before the exposure by the exposing means is started, and after the transfer of the toner image onto the intermediate transfer belt by the photosensitive drum, the developing roller is moved from the photosensitive drum. The color image forming apparatus according to any one of claims 1 to 4, wherein the developing roller is brought into contact with or separated from the developing roller except when the exposure is started and when the transfer is completed. And has the effect that a good electrostatic latent image and transfer can be performed without any problem.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic side view showing the structure of a color image forming apparatus according to an embodiment of the present invention.

In FIG. 1, an intermediate transfer belt 1 driven and driven by a drive pulley 1a is arranged in a closed loop, and a sheet P from a sheet cassette 2 arranged below the intermediate transfer belt 1 is interposed between a transfer roller 1b and an intermediate transfer belt. It has a schematic configuration in which paper is fed to the fixing device 3 through the space between the transfer belt 1. That is, the color toner image formed on the intermediate transfer belt 1 is transferred to the paper P nipped between the transfer roller 1b, and the transferred toner image is fixed on the paper P by the fixing device 3. An exposure device 4 for irradiating a laser based on image information is provided above the intermediate transfer belt 1.
Are arranged between the exposing device 4 and the intermediate transfer belt 1, and the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 5, 6, 7, and 8 are intermediate-transferred. The belts 1 are arranged in order in the running direction.

Each of the image forming units 5 to 8 has the same configuration and is divided into a photosensitive unit and a developing unit. The photoreceptor unit includes photoreceptor drums 5a, 6a, 7a, 8a,
brush-type chargers 5b and 6 for charging the surfaces of a to 8a
b, 7b, 8b and the remaining toner
Cleaning blade 5 for removing from the surface of a
c, 6c, 7c and 8c. The developing unit includes developing rollers 5d, 6d, 7d, 8d,
A supply roller 5 for supplying toner from a toner tank (not shown) to the surface of these developing rollers 5d to 8d
e, 6e, 7e and 8e, and thinning blades 5f, 6f, 7f and 8f for uniformly charging the toner layers on the developing rollers 5d to 8d to a predetermined potential.

FIG. 2 is a schematic side view showing the outline of the yellow image forming apparatus together with guides and triggers. The image forming unit 5 is divided into a photoreceptor unit and a developing unit as described above, and is rotatable in a direction indicated by an arrow in the drawing via a first housing 5g and a support shaft 5i. And a second housing 5h.
A photosensitive drum 5a, a charger 5b, and a cleaning blade 5c are incorporated in the first housing 5g,
The housing 5h includes a developing roller 5d and a supply roller 5
e, The thin plate 5f is incorporated. The first housing 5g is held in the illustrated position, and the second housing 5h
Is biased counterclockwise around the support shaft 5i by a spring (not shown). That is, the second housing 5
h, the developing roller 5d held on the photosensitive drum 5a
Is always biased in the direction of contact.

On the lower left side of the second housing 5h, a trigger 9 rotatably mounted around a pin 9a fixed to the apparatus.
And the lower left end of the second housing 5h is engaged with the trigger 9. The trigger 9 has a substantially L-shaped shape,
A guide roller 9b is provided at an appropriate distance from the pin 9a.
Is provided. Then, a guide 10a for rotating the trigger 9 to rotate the second housing 5h around the support shaft 5i is provided. The guide 10a can be an opening or a sliding surface into which the guide roller 9b is movably inserted, and is shown as an opening in the illustrated example. Guide 1
Reference numeral 0a has a function of lowering the guide roller 9b into the recess 10a-1 and rotating the trigger 9 clockwise when moving left and right while partially recessing it downward. That is, when the guide 10a moves to the left in the figure, the guide roller 9b falls into the recess 10a-1, and the trigger 9 rotates clockwise. As a result, the second housing 5h rotates counterclockwise around the support shaft 5i to bring the developing roller 5d into contact with the photosensitive drum 5a.

As described above, by connecting the guide roller 9b of the trigger 9 to the guide 10a having the recess 10a-1, the second housing 5h can be rotated by moving the guide 10a in the left-right direction, and the photosensitive drum 5a can be operated. The developing roller 5d can be brought into contact with or separated from the developing roller 5d. The structure for rotating the second housing 5h by the trigger 9 and the guide 10a is exactly the same for the other image forming units 6 to 8 as described later.

FIG. 3 is a perspective view showing a main part of the color image forming apparatus of the present invention, showing the arrangement of a guide member and a trigger.
(A) is a detailed perspective view of a guide member, (b) is a detailed rear view of a guide member.

A guide member 11 is attached along one side in the width direction of the intermediate transfer belt 1 so as to be movable in the left-right direction in FIG. The guide member 11 has four concave portions 11 corresponding to the image forming units 5 to 8 at four locations on the upper surface.
a, 11b, 11c, 11d and a concave portion 11e for black mode. And
A rack 11f is formed on the lower surface of the guide member 11, and two elongated holes 11g are provided at two places to be externally inserted into two holding pins 12a provided on the apparatus main body side. The rack 11f meshes with a pinion 12b rotatably arranged on the apparatus side, and the guide member 11 horizontally moves in the left-right direction in FIG. 3 by the forward and reverse rotation of the pinion 12b.

The trigger 9 is substantially L-shaped, as shown in the schematic diagram of FIG. 2, and has a pin 9a and a guide roller 9b. A pair of triggers 9 are arranged corresponding to the positions of the image forming units 5 to 8 arranged on the intermediate transfer belt 1 with the intermediate transfer belt 1 interposed therebetween. (Not shown).

FIG. 5 is a schematic diagram showing the positional relationship between each image forming unit and the guide at the time of non-printing.

The image forming units 6 to 8 are similar to the yellow (Y) image forming unit 5 shown in FIG. 2 in that the first housings 6g, 7g, 8g and the second housings 6h, 7h,
8h connected by supporting shafts 6i, 7i, 8i,
Each of the second housings 6h to 8h is the first housing 6
It is urged toward the g-8g side by a spring (not shown). A trigger 9 having the same configuration as that shown in FIG. 2 is engaged with the second housings 6h to 8h.

The guide 10a of the image forming unit 5 shown in FIG. 2 corresponds to the concave portion 11a shown by the guide member 11 in FIG. That is, the profile of the concave portion 11a of the guide member 11 and the upper surface on the left and right sides thereof correspond to the shape of the guide 10a, and the guide 10a is illustrated as a slit on which the guide roller 9b rolls for the sake of principle. Also, guides 10b, 1 corresponding to the other image forming units 6 to 8
The recesses 11b, 11c,
11d and slits corresponding to the profiles on the upper surface near the left and right sides. That is, in FIG. 5, instead of the guide member 11, the shape of the upper surface is changed to guides 10a to 10a.
In place of d, these guides 10a to 10d also change their positions to the left and right in accordance with the movement of the guide member 11 in the left and right direction.

In the above configuration, first, the charging unit 5b and the exposing unit 4 of the image forming unit 5
A latent image of the yellow component color of the image information is formed thereon. This latent image is visualized as a yellow toner image by a developing roller 5d having black toner, and is transferred onto the intermediate transfer belt 1 as a yellow toner image. On the other hand, while the yellow toner image is being transferred to the intermediate transfer belt 1, the magenta image forming unit 6 forms a magenta component color latent image on the photosensitive drum 6a. The magenta toner image is visualized. Then, the magenta toner image is transferred from the photosensitive drum 6a to the intermediate transfer belt 1 on the intermediate transfer belt 1 on which the transfer of the yellow toner image has been completed in the previous image forming unit 5. Thereafter, image formation is similarly performed on the cyan toner image and the black toner image by the image forming units 7 and 8. When the superimposition of the four color toner images on the intermediate transfer belt 1 is completed, the four color toner images are collectively transferred from the paper cassette 2 when the paper P passes between the intermediate transfer belt 1 and the transfer roller 1b. You. Then, the transferred toner image is heated and fixed on the paper P by the fixing device 3 to form a full-color image.

Here, in order to develop the electrostatic latent images formed on the photosensitive drums 5a to 8a with toner of each color, the developing rollers 5d to 8d are brought into contact with the photosensitive drums 5a to 8a to adhere the toner. Let it. At this time, the developing rollers 5d to 8d
If d is always in contact with the photoconductor drums 5a to 8a, as described above, abrasion is large and the durability is reduced.

Therefore, in the present invention, the photosensitive drums 5a to 5a
8a rotates the developing rollers 5d to 8d only while the intermediate transfer belt 1 runs and prints while rotating the photosensitive drums 5a to 5d.
In the non-printing period, the contact is released and the rotation of the developing rollers 5d to 8d is stopped.
The operation of the developing rollers 5d to 8d is shown in FIGS.
This will be described with reference to FIG.

FIG. 5 shows the state during the non-printing period as described above. At this time, the guide member 11 is located on the right end side as shown in FIG. Then, each image forming unit 5
8 of the trigger 9 engaged with the second housings 5h to 8h
Are separated from the recesses 10a-1 to 10d-1 of the guides 10a to 10d. Therefore,
The upper end side of each trigger 9 is in an upright posture, and the second housings 5h to 8h are rotated clockwise around the support shafts 5i to 8i. At this time, all the developing rollers 5d to 8d are separated from the photosensitive drums 5a to 8a, and are not driven to rotate.

When the printing operation is started, first, an image is written on the photosensitive drum 5a of the yellow (Y) image forming unit 5 by the laser from the exposure unit 4, and the photosensitive drum 5a
Written on the surface. Immediately before the writing, the photosensitive drum 5a starts rotating and the intermediate transfer belt 1 starts running, and the guide member 11 moves to the left by a certain distance in FIG. 3 by the rotation of the pinion 12b.
10 to 10d and the positional relationship between the image forming units 5 to 8 are shown in FIG.
It becomes as shown in. That is, only the guide roller 9b of the trigger 9 of the image forming unit 5 is recessed in the guide 10a.
When the trigger 9 falls into 0a-1, the trigger 9 rotates clockwise around the pin 9a. Thereby, the second housing 5h rotates counterclockwise around the support shaft 5i, and the developing roller 5d comes into contact with the photosensitive drum 5a. During this contact, the photosensitive drum 5a, the developing roller 5d, and the supply roller 5e are all driven to rotate in the direction of the arrow in FIG.

After the developing roller 5d comes into contact with the photosensitive drum 5a, the exposure device 4 irradiates a laser to write an electrostatic latent image on the surface of the photosensitive drum 5a. It is visualized.
The toner image on the peripheral surface is transferred as a yellow toner image onto the surface of the intermediate transfer belt 1 by the rotation of the photosensitive drum 5a. In such an operation, the developing roller 5d
The image writing is performed by the exposure device 4 after the image contacts the photosensitive drum 5a, so that the image writing that is not affected by the vibration due to the contact can be performed. In the other image forming units 6 to 8, the developing rollers 6d to 8d are all stopped and do not contact the photosensitive drums 6a to 8a.

Intermediate transfer belt 1 by image forming unit 5
After the start of the transfer operation, the guide member 11 moves to the left in FIG. 3 at a constant speed, and the image forming unit 5 continues to transfer the yellow toner. Then, at a time immediately before the transfer operation by the magenta image forming unit 6, the positional relationship between the guides 10a to 10d and the image forming units 5 to 8 changes as shown in FIG. That is, the guide roller 9b of the trigger 9 of the yellow image forming unit 5 is included in the recess 10a-1,
The guide roller 9b of the trigger 9 of the magenta image forming unit 6 falls into the recess 10b-1 of the guide 10b. Thus, as in the case of the image forming unit 5, the developing roller 6d comes into contact with the photosensitive drum 6a, and the
Image writing is performed. Then, the written electrostatic latent image is developed by the developing roller 6d, and the magenta toner image is superimposed and transferred on the previously transferred yellow toner image on the intermediate transfer belt 1.

Thereafter, the transfer of the guide member 11 causes the transfer of the cyan toner to the intermediate transfer belt 1 by the cyan image forming unit 7 as shown in FIG. 8, and subsequently the formation of the black image shown in FIG. The start of the transfer of the black toner to the intermediate transfer belt 1 by the unit 8 is performed by the same operation as in FIGS. 6 and 7, respectively. In the state of FIG. 9, in all the image forming units 5 to 8, the developing rollers 5 d to 8 d come into contact with the photosensitive drums 5 a to 8 a, and the yellow, magenta, cyan, and black toners are simultaneously transferred to the intermediate transfer belt 1. .

When the guide member 11 further moves, FIG.
As shown in the figure, the trigger 9 of the yellow image forming unit 5
Only the guide roller 9b is recessed in the guide 10a.
Get out of one. That is, in FIGS. 3 and 4, the guide roller 9 b escapes from the concave portion 11 a of the guide member 11 and reaches the upper surface of the guide member 11. Thereby, the upper end side of the trigger 9 is in a standing posture, and the second housing 5h is rotated clockwise around the support shaft 5i. Therefore, the developing roller 5d is separated from the photosensitive drum 5a and stops rotating, and the photosensitive drum 5a continues to rotate while the intermediate transfer belt 1 is running thereafter.

Here, the developing roller 5d is
The timing to move away from a is set after the transfer process from the photosensitive drum 5a to the intermediate transfer belt 1 is completed. By doing so, there is no disturbance due to reaction force vibration or the like when the developing roller 5d separates, and the transfer accuracy to the intermediate transfer belt 1 does not decrease.

Thereafter, as the guide member 11 moves,
As shown in FIG. 11, the developing roller 6d of the magenta image forming unit 6 separates from the photosensitive drum 6a and stops rotating. Then, as shown in FIG. 7d is the photosensitive drum 7
Stop rotation away from a. Then, when the guide member 11 further moves and reaches the stroke end, as shown in FIG. 13, the guide roller 9b of the trigger 9 of the black image forming unit 8 also becomes the concave 10d of the guide 10d.
-1 and the developing roller 8d is moved to the photosensitive drum 8a.
Move away from At this point in time in FIG. 13, the toner image transfer process by the image forming units 5 to 8 to the intermediate transfer belt 1 is completed.

After the completion of the step of transferring the toner image to the intermediate transfer belt 1, the intermediate transfer belt 1 continues to run, and the photosensitive drums 5a to 8a rotate to avoid abrasion due to a speed difference from the intermediate transfer belt 1. continue. Then, the intermediate transfer belt 1 runs, and the color image is transferred onto the paper P while the paper P from the paper cassette 2 is nipped with the transfer roller 1b as shown in FIG. After this transfer is completed,
When the intermediate transfer belt 1 stops, the photosensitive drums 5a to 8a of the image forming units 5 to 8 also stop rotating, and the guide member 11 moves to the position shown in FIG. 3 and waits for the next operation.

As described above, each of the image forming units 5 to 8
, The developing rollers 5 d to 8 d are brought into contact with the photosensitive drums 5 a to 8 a immediately before the exposure from the exposure device 4 to develop the electrostatic latent images on the photosensitive drums 5 a to 8 a, and the toner image is formed on the intermediate transfer belt 1. Is separated again after the transfer. That is, the developing rollers 5d to 8d do not come into contact with the photoconductive drums 5a to 8a throughout the entire printing period, but come into contact with the photoconductive drums 5a to 8a only for a period during which a toner image is formed.
Outside this period, the developing roller 5d
Stop 8d. As a result, the contact time between the developing rollers 5d to 8d and the photosensitive drums 5a to 8a is shorter than in the conventional structure, and the degree of wear can be suppressed. Also,
At the time of separation, the rotation of the developing rollers 5d to 8d is stopped, so that there is no sliding friction with the thinning blades 5f to 8f, and similarly, the degree of wear is suppressed. Therefore, even with the developing rollers 5d to 8d whose surfaces are formed of conductive silicone rubber, the generation and wear of contact friction scratches and the like can be suppressed, and the durability can be improved.

[0045]

According to the present invention, the developing roller is brought into contact with the photosensitive drum and the toner is developed only during the period of forming the toner image on the photosensitive drum, so that the wear of the developing roller can be suppressed. Therefore, the life of the developing roller, which governs the life of the image forming unit, can be greatly improved, and the service life of the apparatus can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic side view illustrating a configuration of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic side view showing an outline of a yellow image forming apparatus together with a guide and a trigger.

FIG. 3 is a perspective view showing a main part of the color image forming apparatus of the present invention and showing an arrangement of a guide member and a trigger.

4A is a detailed perspective view of a guide member, and FIG. 4B is a detailed rear view of a guide member.

FIG. 5 is a schematic diagram showing a positional relationship between each image forming unit and a guide at a non-printing time.

FIG. 6 is a schematic diagram of a main part showing a time of transfer by a yellow image forming unit.

FIG. 7 is a schematic diagram of a main part showing a time of transfer by the yellow and magenta image forming units.

FIG. 8 is a schematic diagram of a main part showing a time of transfer by image forming units of yellow, magenta, and cyan.

FIG. 9 is a schematic diagram of a main part showing a time of transfer by image forming units of yellow, magenta, cyan, and black.

FIG. 10 is a schematic diagram of a main part showing a state after transfer of a yellow image forming unit is completed.

FIG. 11 is a schematic view of a main part showing a state after the transfer of the magenta image temper unit is completed, following FIG. 10;

FIG. 12 is a schematic view of a main part after the transfer of the cyan image temper unit is completed, following FIG. 11;

FIG. 13 is a schematic diagram of a main part showing a state after the transfer of the black image temper unit is completed, following FIG. 12;

FIG. 14 is a schematic view showing a conventional color image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 1a Drive pulley 1b Transfer roller 2 Paper cassette 3 Fixer 4 Exposure unit 5, 6, 7, 8 Image forming unit 5a, 6a, 7a, 8a Photoconductor drum 5b, 6b, 7b, 8b Charger 5c, 6c, 7c, 8c Cleaning blade 5d, 6d, 7d, 8d Developing roller 5e, 6e, 7e, 8e Supply roller 5f, 6f, 7f, 8f Thinning blade 5g, 6g, 7g, 8g First Housing 5h, 6h, 7h, 8h Second housing 5i, 6i, 7i, 8i Support shaft 9 Trigger 9a Pin 9b Guide roller 10a, 10b, 10c, 10d Guide 10a-1, 10b-1, 10c-1, 10d-1 Recess 11 guide member 11a, 11b, 11c, 11d, 11e recess 11f rack 11g long hole 12a Holding pin 12b Pinion P paper

Continued on the front page (72) Inventor Yoshiaki Ijima 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Tadashi Shimokaraminato 1006 Kadoma, Kazuma, Kazuma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Junichi Tanizaki 1006 Kadoma, Kazuma, Kazuma, Osaka Pref. 2H077 AD06 AD13 BA07 BA08 DB18 EA14 EA15 GA03 GA13

Claims (5)

[Claims] An image forming apparatus comprising: a plurality of image forming units each including a plurality of color toners and arranged in tandem; and an endless intermediate transfer belt that runs around in an arrangement direction of the image forming units. The unit includes a photosensitive drum capable of forming an electrostatic latent image by exposure means, and a developing roller for developing the electrostatic latent image on the photosensitive drum with the toner, and a toner image developed by the developing roller. In the color image forming apparatus that transfers the developing roller to the intermediate transfer belt, the developing roller is brought into contact with the photosensitive drum only during a period for developing the electrostatic latent image on the photosensitive drum, thereby enabling development with the toner. A color image forming apparatus. 2. The image forming unit is connected to a first housing for holding the photosensitive drum so as to be vertically swingable with respect to the first housing via a support shaft. And a second housing for holding the developing roller, wherein the second housing is rotated up and down to allow the developing roller to move toward and away from the photosensitive drum. Color image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the second housing is provided with a thinning blade for charging and thinning the toner by contacting a peripheral surface of the developing roller. 3. The color image forming apparatus according to claim 2, wherein the rotation of the developing roller is stopped when the developing roller is separated. 4. The image forming unit according to claim 1, wherein said second housing is rotated in a direction in which said image forming units are arranged, and guide members which are reciprocally movable in the direction in which said image forming units are arranged are arranged. 4. The color image forming apparatus according to claim 2, wherein a plurality of triggers are provided which are rotated in conjunction with the second housing, and the second housing is capable of being rotated by the rotation of the triggers. 5. The developing roller is brought into contact with the photosensitive drum before the exposure by the exposure means is started, and after the transfer of the toner image to the intermediate transfer belt by the photosensitive drum is completed, the developing roller is moved from the photosensitive drum. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is configured to be separated.