JPH0980860A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easy, small sized developing device switching mechanism for a color image forming device for developing a latent image formed on a belt-like image carrier by plural developing devices and forming a color image. SOLUTION: Four backup rollers 18 are installed at the inner peripheral part of the photoreceptor belt 10 stretched between rotary rollers 17a and 17b, and the backup rollers are moved making two pairs. At the time of developing with yellow toner, the backup roller 18Y is moved upward so that the photoreceptor belt 10 may come into contact with an yellow developing device 13Y, and also, the back up roller 18C is moved downward, and at the time of developing by magenta toner, the backup roller 18M is moved upward so that the photoreceptor belt 10 may come into contact with a magenta developing device 13M, and also, the backup roller 18K is moved downward, then, the switching of the developing device is executed while keeping the traveling path length of the photoreceptor belt 10 constant.

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, and in particular, a toner image is formed on a belt-shaped image carrier (hereinafter also referred to as "photosensitive belt") by an electrophotographic method, and the toner image is formed. The present invention relates to a color image forming apparatus that transfers a toner image onto a recording medium to form a color image.

[0002]

2. Description of the Related Art In a color image forming apparatus for forming a color image by an electrophotographic method, a plurality of developing devices filled with toners of different colors of three to four colors are sequentially changed over to develop a recording paper. A color image is formed on a recording medium such as.

As a developing device switching mechanism used in this type of color image forming apparatus, conventionally, a system in which a plurality of developing devices are mechanically moved and the developing devices are sequentially brought into contact with an image carrier, or a developing device A method of changing the developing device by adjusting the height of the brush is generally known.

FIG. 6 is a diagram for explaining a system in which the developing device is mechanically moved for switching. Note that FIG.
In the figure, the configurations other than the image carrier (photosensitive drum), the developing device, and the switching mechanism thereof are omitted.

FIG. 6A is a diagram for explaining a system in which a plurality of developing devices are rotated for switching. The rotary system in which the developing device is rotated for switching is described in, for example, the Journal of the Electrophotographic Society, Vol. 28, No. 4, 1989, page 408, and yellow (Y), magenta (M), cyan (C) and black. A rotary mechanism for rotating four developing devices 13'Y, 13'M, 13'C and 13'K for developing each color of (K) is provided, and the four developing devices are sequentially rotated by this rotary mechanism. The respective developing devices are sequentially brought into contact with the photosensitive drum 51.

FIG. 6B is a view for explaining the developing device switching mechanism disclosed in Japanese Patent Laid-Open No. 5-61339. The switching mechanism disclosed in the above-mentioned publication includes a separating / connecting spring 52 and a solenoid type pressing device 53 as its main components, and moves the developing device 13 ″ in the horizontal direction to bring it into contact with or out of contact with the photosensitive drum 51. To switch.

On the other hand, a method of switching the developing device by adjusting the height of the developer is described in Electrophotographic Society of Japan Vol. 28, No. 4, 1989, p. 416. According to this method, During development of one color, for example yellow,
The magnetic brush is cut off so that the magnetic brush of the developing device for developing other magenta, cyan and black colors does not come into contact with the photoconductor. The cutting of the magnetic brush can be performed by rotating a magnetic plate provided in the developing roller to shield the magnetic field, or by rotating the developing roller in a direction opposite to that during development.

[0008]

However, the above-mentioned conventional switching mechanism has a problem that its structure becomes complicated and the size of the apparatus becomes large.

That is, as shown in FIGS. 6A and 6B, in the conventional system in which the developing device is mechanically moved for switching, the entire developing device filled with toner and having a large volume and a large mass is used. Since it has to be moved, there is a problem that the switching mechanism becomes large and the apparatus becomes expensive. This is because if the switching mechanism does not have sufficient accuracy and rigidity adapted to the mass of the developing device, the positioning accuracy of the developing device with respect to the image carrier is deteriorated, and the image quality is greatly affected.

Further, in the conventional method in which the developing device is switched by adjusting the height of the developer, it is necessary to provide a complicated magnetic shielding mechanism or the like in the developing device, so that the switching mechanism becomes complicated and the apparatus becomes expensive. There is a problem of becoming. further,
In the conventional method in which the developing device is switched by adjusting the height of the brush, it is necessary to use a two-component developer, so that the developing device itself becomes large, and as a result, the switching mechanism of the developing device also becomes large.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a color image forming apparatus having a simple and small developing device switching mechanism.

[0012]

In order to achieve the above object, the present invention provides a color image forming method in which a latent image formed on a belt-shaped image carrier is developed by a plurality of developing devices to form a color image. In the apparatus, a traveling path of the image carrier is changed so that each of the plurality of developing devices is sequentially brought into contact with the image carrier, and a color image forming apparatus is provided.

Further, according to the present invention, a belt-shaped image bearing member stretched between a plurality of rotating rollers, a plurality of developing devices arranged so as to be able to contact the image bearing member, and the image bearing member. A plurality of backup means arranged at a position opposed to the plurality of developing devices via a developing device, and a developing device facing one of the backup means by moving one of the plurality of backup means. Provided is a color image forming apparatus characterized in that it makes contact with the image carrier and moves other backup means to keep a path length of a traveling path of the image carrier constant.

Further, according to the present invention, a flexible belt-shaped image carrier which is stretched between a plurality of rotating rollers is arranged on a predetermined arc so as to be able to contact the image carrier. A plurality of developing devices, and backup means for bringing each of the plurality of developing devices into contact with the image carrier,
The backup means is moved along the predetermined arc so that each of the plurality of developing devices is sequentially brought into contact with the image carrier while keeping the path length of the traveling path of the image carrier constant. And a color image forming apparatus.

According to the color image forming apparatus of the present invention, unlike the conventional color image forming apparatus, the developing device is fixed without moving, and the traveling path of the flexible belt-shaped image carrier is changed. By performing the separation / contact operation between the developing device and the image carrier, the switching of the developing device can be realized with a simple configuration. The traveling path of the image carrier can be easily changed by moving a backup means such as a backup roller arranged on the inner peripheral portion of the image carrier up and down.

Further, according to the color image forming apparatus of the present invention, not only the backup roller is vertically moved to change the traveling path of the image carrier, but also the traveling path of the image carrier is changed when the developing device is switched. By keeping the path length constant, it is possible to prevent problems such as elastic deformation of the image bearing member or fluctuation of the running speed of the image bearing member, thereby preventing the occurrence of three or four colors. It is possible to prevent the deterioration of the color matching accuracy of the toner image and the deterioration of the image quality due to the color shift.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018]

First Embodiment First, a color image forming apparatus according to a first embodiment of the present invention will be described.

FIG. 1 is a side view for explaining the configuration of a color image forming apparatus according to the first embodiment of the present invention.

Referring to FIG. 1, in the color image forming apparatus according to the present embodiment, a scorotron charger 11 for charging the photosensitive belt 10 around the flexible photosensitive belt 10 and a charged photosensitive belt. A laser writing unit 12 for forming a latent image on the body belt 10, and four developments in which developers of yellow (Y), magenta (M), cyan (C), and black (K) are contained, respectively. The containers 13Y, 13M, 13C and 13K, the intermediate transfer drum 14, the cleaner device 15, and the static elimination lamp 16 are arranged in this order in the counterclockwise direction.

The photosensitive belt 10 includes two rotating rollers 1.
It is stretched between 7a and 17b, and the rotation roller 17
By driving a, it is conveyed counterclockwise. Four backup rollers 18Y, 18M, 18C and 18K for switching the developing devices and two fixed rollers 19a and 19b are arranged on the inner peripheral portion of the photosensitive belt 10. Here, the developing devices 13Y, 13M, 13
C and 13K are fixed to a frame (not shown) with a predetermined distance from the photoconductor belt 10.

Next, with reference to FIG. 1, a process of actually forming a color image using the color image forming apparatus according to the present embodiment will be described.

First, after the scorotron charger 11 uniformly charges the entire surface of the photosensitive belt 10 at about -800 V, based on a yellow image signal sent from a host computer (not shown). The laser writing unit 12 is driven to form an electrostatic latent image for a yellow image on the photoconductor belt 10. Here, the potential of the electrostatic latent image is -3
An image is formed at 00 V and a resolution of 400 dpi, for example.

On the other hand, almost simultaneously with the start of forming the electrostatic latent image for the yellow image, the yellow backup roller 18Y is moved upward as shown in FIG. 1 to bring the photosensitive belt 10 into contact with the yellow developing device 13Y. Then, the yellow developing device 13Y is connected to the photosensitive belt 1 by the one-component contact developing method.
0 to form a yellow toner image.

Here, the backup roller 1 for yellow
The cyan backup roller 18C is moved downward as shown in FIG. 1 in order to prevent the traveling path length of the photoconductor belt 10 from varying with the movement of 8Y. The relationship between the positions of the backup rollers 18Y, 18M, 18C and 18K and the travel path length of the photoconductor belt 10 will be described in detail later.

After a yellow toner image is formed on the photosensitive belt 10 by the yellow developing device 13Y, the yellow toner image on the photosensitive belt 10 is electrostatically transferred onto the intermediate transfer drum 14 at a transfer voltage V1 = + 1.5 kV. .

Thereafter, the toner remaining on the photoconductor belt 10 is scraped off by the blade of the cleaner device 15 and collected, and the photoconductor belt 1 that has passed through the cleaner device 15 is collected.
The surface charge remaining on 0 is removed by the static elimination lamp 16.

Then, the photosensitive belt 10 is uniformly charged to about -800 V by the scorotron charger 11 again, and the development is shifted to the next magenta developing device 13M.

In this manner, the same cycle as the yellow image forming cycle is sequentially repeated for images of magenta, cyan and black other than yellow,
On the intermediate transfer drum 14, four color toner images of a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are sequentially superposed.

4 superposed on the intermediate transfer drum 14
Recording paper 2 with color toner image at transfer voltage V2 = + 2.5 kV
1 is electrostatically transferred onto one sheet, and the toner is melted and fixed by the heat roll type fixing device 20, and finally the recording paper 21
Form the desired color image on top.

The toner remaining on the intermediate transfer drum 14 is removed by the brush cleaning device 22 before the next color image is formed.

Here, the backup rollers 18Y, 18
The relationship between the positions of M, 18C and 18K and the travel path length of the photoconductor belt 10 will be described by taking the switching from the yellow developing device 13Y to the magenta developing device 13M as an example.

FIG. 2 is a side view for explaining the developing device switching mechanism of the color image forming apparatus according to the first embodiment of the present invention. In FIG. 2, the photosensitive belt 10
And developing units 13Y, 13M, 13C and 13K, backup rollers 18Y, 18M, 18C and 18K,
Only the positional relationship between the fixed rollers 19a and 19b is focused, and the other configurations are omitted in the drawing.

FIG. 2A shows a state in which development is performed by the yellow developing device 13Y. 2B shows immediately before the development by the yellow developing device 13Y is completed, that is, from the development by the yellow developing device 13Y to the magenta developing device 1.
The state immediately before switching to 3M development is shown. further,
FIG. 2C shows a state where development is performed by the magenta developing device 13M.

Referring to FIG. 2, in the color image forming apparatus according to the present embodiment, the developing devices 13Y, 13M, 13C and 13K have a central portion in the left-right direction above the straight line connecting the rotating rollers 17a and 17b. Are installed side by side at equal intervals. In addition, these developing devices 13Y, 13M, 13
Four backup rollers 18Y, 18M, 18C and 18K are provided at positions facing C and 13K, respectively. The backup rollers 18Y, 18
M, 18C and 18K are supported by a simple cam mechanism (not shown) so as to be able to reciprocate in the vertical direction.

Here, when the development by the yellow developing device 13Y is switched to the development by the magenta developing device 13M, the traveling path length of the photosensitive belt 10 is constant during the development of the yellow toner and the development of the magenta toner. Backup rollers 18Y, 18M, 18 to be kept
Move C and 18K.

Specifically, at the time of developing the yellow toner, the backup roller 18 is kept until the photosensitive belt 10 comes into contact with the yellow developing device 13Y as shown in FIG. 2 (A).
While moving Y upward, the backup roller 18
Move C down.

When developing magenta toner, as shown in FIG.
As shown in (C), the backup roller 18M is moved upward and the backup roller 18K is moved downward until the photoconductor belt 10 contacts the magenta developing device 13M.

Here, in order to make the traveling path length of the photosensitive belt 10 constant, the two rotating rollers 1 shown in FIG.
Photoreceptor belt 10 based on the line connecting 7a and 17b
When the upper half of the photosensitive belt 10 shown in FIG. 2A is rotated 180 degrees, the lower half of the photosensitive belt 10 shown in FIG. Of the photoconductor belt 1 that matches the running route of the photoconductor belt 1 shown in FIG.
Fig. 2 shows a state in which the lower half travel route of 0 is rotated 180 degrees.
The backup rollers 18Y and 18Y during the development of the yellow toner and the development of the magenta toner are aligned with the upper half traveling path of the photosensitive belt 10 shown in (C).
Determine the positions of M, 18C and 18K.

It should be noted that during development of the yellow toner, the backup rollers 18M and 18K are moved to positions where they do not come into contact with the photosensitive belt 10, and during development of the magenta toner, the backup rollers 18Y and 18C do not come into contact with the photosensitive belt 10. Move to.

The backup rollers 18Y and 18C and the backup roller 18M are maintained while maintaining the above relationship.
And 18K are moved as a pair, the traveling path length of the photosensitive belt 10 can be kept constant during the development of the yellow toner and the development of the magenta toner.

Similarly, during development of cyan toner,
While moving the backup roller 18C upward until the photoreceptor belt 10 contacts the cyan developing device 13C,
The backup roller 18Y is moved downward to keep the traveling path length of the photoconductor belt 10 constant.
During development of black toner, the backup roller 1 is kept until the photoconductor belt 10 comes into contact with the black developing device 13K.
8K is moved upward, and backup roller 1
8M is moved downward to keep the traveling path length of the photoconductor belt 10 constant.

The positions of the backup rollers 18C and 18Y during the development of the cyan toner, and the backup rollers 18K and 1K during the development of the black toner.
The relationship between the position of 8M and the position of 8M is such that when the two are rotated 180 degrees, their travel routes match each other.

Next, referring to FIG. 2B, regarding the relationship between the position of the backup roller 18 and the traveling path length of the photosensitive belt 10 in the transition process in which the developing device is switched, the magenta development from the yellow developing device 13Y is performed. Switching to the container 13M will be described as an example.

When switching from the yellow developing device 13Y to the magenta developing device 13M, as shown in FIG. 2B, before moving the positions of the backup rollers 18Y and 18C involved in the development of the yellow toner, Backup rollers 18M and 1 involved in the development of magenta toner
8K is moved until it contacts the inner peripheral surface of the photosensitive belt 10.

After this, the backup roller 1
In conjunction with moving 8Y downward, the backup roller 18K is moved downward by the same amount as the moving amount of the backup roller 18Y. Similarly, when the backup roller 18M is moved upward, the backup roller 18C is moved upward by the same amount as the movement amount of the backup roller 18M.

After the backup roller 18M contacts the cyan developing device 13C, the backup roller 1M
8Y and 18C are moved to a state where they do not come into contact with the photosensitive belt 10, and finally the state shown in FIG.

As described above, the backup rollers 18Y, 18M, 18C and 18K are moved up and down to switch the developing devices 13Y, 13M, 13C and 13K, so that the photosensitive member is always included in the transition process. The running path length of the belt 10 can be kept constant, and high color matching accuracy can be realized.

When a color image is formed by the switching mechanism of the developing device according to the present embodiment, it is possible to obtain a high quality color image with a color misalignment accuracy of about 50 μm.

FIG. 5 is a side view for explaining a developing device switching mechanism for changing the traveling path of the photosensitive belt without keeping the traveling path length of the photosensitive belt constant.

In the color image forming apparatus according to this embodiment, as described above, the backup rollers 18Y and 18Y are provided.
M, 18C and 18K are appropriately moved to move the photosensitive belt 1
Although the travel route length of 0 was kept constant, (1) Fig. 5
As shown in (1), one backup roller 18 is used to simply switch the developing device, or (2) for example, when developing yellow toner, only the backup roller 18Y is simply moved upward, and magenta, cyan, and black are used. Even when developing the toner of each color, the corresponding backup rollers 18M, 18C and 18K are simply moved upward so that the timing of the movement of the backup roller 18 at the time of switching the developing device is not considered at all. Can also be formed.

In such a method in which the traveling path length of the photosensitive belt 10 is not kept constant, the developing devices 13Y, 13M, 1
Since the traveling path length of the photosensitive belt 10 changes at the time of switching between 3C and 13K, the color misalignment accuracy is deteriorated as compared with the above-mentioned method, but if the color misalignment accuracy is within an allowable range,
It can be adopted as a simpler developing device switching mechanism.

[0053]

Second Embodiment Next, a color image forming apparatus according to a second embodiment of the present invention will be described. The overall configuration of the color image forming apparatus according to this exemplary embodiment is the same as that of the first image forming apparatus shown in FIG.
This is the same as the color image forming apparatus according to the embodiment.

FIG. 3 is a side view for explaining the developing device switching mechanism of the color image forming apparatus according to the second embodiment of the present invention. Further, FIG. 4 is a side view for explaining the movement trajectory of the backup roller in the color image forming apparatus according to the second embodiment of the present invention.

Referring to FIGS. 3 and 4, the color image forming apparatus according to the present embodiment includes developing units 13Y, 13M, 1
By arranging 3C and 13K as shown in FIG. 3 and moving one backup roller 18 as shown in FIG. 4, the photosensitive belt 10 sequentially contacts the developing devices 13Y, 13M, 13C and 13K. In this way, the developing device is switched.

That is, as shown in FIG. 4, the distance L1 between the central axes of the rotating roller 17a and the backup roller 18 is set.
Then, the backup roller 18 is moved so as to draw a locus such that the sum (= L1 + L2) of the rotation roller 17b and the distance L2 between the central axes of the backup rollers 18 is constant, and such a locus is drawn. Photosensitive belt 10 having flexibility as the backup roller 18 moves
4 developing units 13 according to the positions where the
Place Y, 13M, 13C and 13K.

Then, the backup roller 18 is moved along the above-mentioned locus to develop the developing devices 13Y, 13M, 13
The developing device is switched so that the photosensitive belt 10 sequentially contacts C and 13K.

When a color image is formed by the switching mechanism of the developing device according to the present embodiment, it has substantially the same color misalignment accuracy (up to about 55 μm) as the color image forming apparatus according to the first embodiment. A high quality color image can be obtained.

Although some embodiments of the present invention have been described above, the present invention is not limited to such embodiments and includes various embodiments according to the principle of the present invention.

For example, in the color image forming apparatus according to the first and second embodiments, the backup roller is moved to switch the developing device, but a plate-shaped backup plate is used instead of such a backup roller. Even if it is moved, the same effect can be obtained.

Further, in the color image forming apparatus according to the first and second embodiments, the developing devices 13Y, 13M and 13 are used.
The backup path 18Y, 18M, 18C and 18K for contacting the photosensitive belt 10 with C and 13K is used to keep the running path length of the photosensitive belt 10 constant, but the running path length is kept constant. Alternatively, a dedicated backup roller or backup plate may be prepared.

Further, in the color image forming apparatus according to the first and second embodiments, four developing devices of yellow, magenta, cyan and black are provided, but three developing devices of yellow, magenta and cyan excluding black are provided. One developing device may be provided, or if necessary, various developing devices different from these may be provided. In order to realize the first embodiment in a color image forming apparatus provided with three developing devices, for example, a black developing device 13K is used.
The black back-ac roller 18K corresponding to No. 1 may be left as it is, and the backup roller 18K may be moved up and down as in the case of the first embodiment so as to keep the traveling path length constant.

In the color image forming apparatus according to the first and second embodiments, the photoconductor belt is used as the image carrier and the laser writing unit is used as the latent image forming means. Vinylidene fluoride (PV
DF) using a latent image forming belt having pyroelectricity,
The latent image may be formed by heating means such as a laser and a thermal head.

[0064]

As described above, according to the color image forming apparatus of the present invention, the traveling path of the belt-shaped image bearing member is changed, and a plurality of developing devices are attached to the image bearing member while the developing devices are fixed. Since the contacts can be sequentially performed, the switching of the developing device can be realized with a simple configuration.

Further, according to the color image forming apparatus of the present invention, since the path length of the traveling path of the image carrier is kept constant even if the developing device is switched, the color image is formed with high color matching accuracy. Forming can take place.

[Brief description of drawings]

FIG. 1 is a side view for explaining the configuration of a color image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a side view for explaining a developing device switching mechanism of the color image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a side view for explaining a developing device switching mechanism of the color image forming apparatus according to the second embodiment of the present invention.

FIG. 4 is a side view for explaining a movement trajectory of a backup roller in the color image forming apparatus according to the second embodiment of the present invention.

FIG. 5 is a side view for explaining a switching mechanism of a developing device that changes the traveling path of the photosensitive belt without keeping the traveling path length of the photosensitive belt constant.

FIG. 6 is a view for explaining a developing device switching mechanism of a conventional color image forming apparatus.

[Explanation of symbols]

 10 Photoconductor Belt 11 Scorotron Charger 12 Laser Writing Unit 13Y Yellow Developer 13M Magenta Developer 13C Cyan Developer 13K Black Developer 14 Intermediate Transfer Drum 15 Cleaner Device 16 Elimination Lamp 17a, 17b Rotating Roller 18Y Yellow Backup Roller 18M Backup roller for magenta 18C Backup roller for cyan 18K Backup roller for black 18 Backup roller 18a, 19b Fixed roller 20 Fixer 21 Recording paper 22 Brush cleaning device 51 Photosensitive drum 52 Separation spring 53 Solenoid type pressing device

Claims (5)

[Claims] 1. A color image forming apparatus for forming a color image by developing a latent image formed on a belt-shaped image carrier with a plurality of developing devices, wherein a traveling path of the image carrier is changed, A color image forming apparatus, wherein each of the plurality of developing devices is brought into contact with the image carrier in order. 2. The color image forming apparatus according to claim 1, wherein the path length of the traveling path is kept constant when the traveling path of the image carrier is changed. 3. A belt-shaped image bearing member stretched between a plurality of rotating rollers, a plurality of developing devices arranged so as to be able to contact the image bearing member, and the image bearing member via the image bearing member. A plurality of backup units arranged at positions facing the plurality of developing units; and a developing unit facing the backup unit by moving one of the plurality of backup units and the image carrier. And the other backup means are moved to keep the path length of the traveling path of the image carrier constant. 4. A flexible belt-shaped image bearing member stretched between a plurality of rotating rollers, and a plurality of flexible image bearing members disposed on a predetermined arc and capable of contacting with the image bearing member. A developing unit; and a backup unit for bringing each of the plurality of developing units into contact with the image carrier, the backup unit being moved along the predetermined arc, and a traveling path of the image carrier. A color image forming apparatus, wherein each of the plurality of developing devices is brought into contact with the image carrier in order while keeping the path length of the image forming device constant. 5. The color image forming apparatus according to claim 3, wherein the backup means is composed of a roller rotatable about an axis.