JP2000075642A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which prevents toner stored in a developing device above a fixing device from being softened, melted, or solidified due to heat from the fixing device. SOLUTION: Time measurement by a timer is started after the fixing device has reached a prescribed temperature, (S2). When 120 seconds has elapsed without image formation on a recording material, the developing device provided above the fixing device turns, (S8), so that a developing unit moves. This prevents the specific part of the developing device, that is, the specific developing unit in the developing device from staying in the vicinity of the fixing device for 120 seconds or longer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a copying machine and a printer.

In particular, the present invention relates to an image forming apparatus having a movable developing means.

[0003]

2. Description of the Related Art A plurality of developing devices each containing a different color toner are sequentially used to transfer a plurality of color images onto a single transfer material in a superimposed manner, and the images are fixed to form a color image. 2. Description of the Related Art Color image forming apparatuses have been widely used.
FIG. 5 shows a conventional color image forming apparatus, which will be briefly described below.

FIG. 5 is an explanatory view of the overall configuration of a color laser printer which is an embodiment of a color image forming apparatus.

[0005] The image forming section of the color laser printer is
It comprises a photosensitive drum 45 as an image carrier that rotates at a constant speed, a fixed black developing device 49B, and three rotatable color developing devices (yellow developing device 48Y, magenta developing device 48M, and cyan developing device 48C). Have been.

Below the image forming section, an intermediate transfer member 43 for holding the developed and multi-transferred color image and transferring it to the transfer material 42 fed from the feeding section is arranged.

Then, the transfer material 4 on which the color image has been transferred
2 is conveyed to a fixing section 52 to fix the color image on the transfer material 42, and is discharged by discharge rollers 58, 59 and 60 to a discharge section
It is discharged to 61.

The photosensitive drum 45 is formed by applying an organic photoconductor layer to the outside of an aluminum cylinder having a diameter of about 62 mm, and a cleaner blade 46 and a primary charging means 47 are arranged on the circumference.

A driving force of a driving motor (not shown) is transmitted to one end on the rear side in FIG. 5 so that the photosensitive drum 45 is rotated counterclockwise in FIG. 5 in accordance with an image forming operation. .

The exposure of the photosensitive drum 45 is performed by a scanner unit.
Done from 57. That is, when the image signal is sent to the laser diode, the laser diode irradiates the polygon mirror with light at a timing corresponding to the image signal.
This polygon mirror is rotated at a high speed by a scanner motor, and the light reflected by the polygon mirror selectively exposes the surface of the photosensitive drum 45 via an imaging lens and a reflecting mirror, and as a result, Form an electrostatic image.

The above electrostatic image is developed by three rotary developing devices capable of developing each color of yellow, magenta, cyan and black.
The image is visualized by 48Y, 48M, 48C and one black developing device 49B.

The black developing device 49B is a developing device that is fixed at a developing position except when the black developing device 49B is mounted on the apparatus main body. Then, a visible image is formed on the photosensitive drum 45 using black toner.

The toner capacity of the black developing device 49B is 15,000, which is more than twice the toner capacity of other YMC developing devices, in consideration of the documents and image patterns handled by the user and the toner consumption.
It contains toner equivalent to a page (A4, 5% printing).

By increasing the capacity of the black developing device in this way, it is possible to reduce the frequency of replacement of the black developing device by the user and to reduce the running cost per print.

As shown in FIG. 5, the black developing device is arranged between a laser scanner as an exposure device and a YMC developing device as a rotary developing device. Due to the above arrangement, toner leaking when the YMC developing device rotates is prevented from scattering to optical components such as a laser scanner. Accordingly, it is possible to prevent a toner from adhering to a polygon, a lens, a mirror, or the like and hinder formation of a latent image, thereby obtaining a clear output image.

On the other hand, three rotary developing units 48Y, 48M, 48C
Each contain 6,000 pages of toner (A4, 5% printing). The three rotary developing devices are detachably held by a developing rotary 51 that rotates about a shaft 50.

When an image is formed, each developing unit is rotated around a shaft 50 while being held by a developing rotary 51, and a predetermined developing unit is stopped at a position facing the photosensitive drum 45. At this time, a visible image is formed corresponding to the electrostatic image on the photosensitive drum 45.

When forming a color image, one of the intermediate transfer members 43
The developing rotary 51 rotates with each rotation, and the yellow developing device 48
The developing process is performed in the order of Y, magenta developing device 48M, cyan developing device 48C, and then black developing device 49B.

For example, when the yellow rotary developing device 48Y is positioned and stopped at a position facing the photosensitive drum unit, the yellow rotary developing device 48Y performs development with the yellow toner on the photosensitive drum 45, and Form an image.

In the magenta developing unit 48M and the cyan developing unit 48C, toner development of each color is performed by the same mechanism as described above. The application of a bias and the transmission of drive to each developing roller of each of the rotary developing devices 48Y, 48M, and 48C are performed when each developing device is rotationally moved to the developing position.

The intermediate transfer member 43 performs multiple transfer of the toner image on the photosensitive drum 45 visualized by each developing unit four times (each of four colors of Y, M, C, and B) during the color image forming operation. Is what you get. Then, the photosensitive drum 45 rotates clockwise in FIG.

The intermediate transfer member 43 which has undergone multiple transfer
Is transferred by the transfer roller 44 to which the voltage is applied.
The toner images of the respective colors on the intermediate transfer member are simultaneously multiplex-transferred onto the transfer material 42 by sandwiching and transporting the two.

The intermediate transfer member 43 according to the present embodiment has a configuration in which the outer periphery of an aluminum cylinder having a diameter of 186 mm is covered with an elastic layer such as a medium resistance sponge or medium resistance rubber.

The cleaning means is a means for applying the toner visualized on the photosensitive drum 45 by the developing means to the intermediate transfer member 43.
After the transfer, the toner remaining on the photosensitive drum 45 is cleaned.

While the four-color toner image is being formed on the intermediate transfer member 43, that is, while the intermediate transfer member 43 rotates a plurality of times, the transfer roller 44 is positioned below as shown by the solid line in FIG. It is separated from the intermediate transfer member 43 so as not to disturb the image.

After the formation of the four color toner images on the intermediate transfer member 43, the transfer roller 44 moves the intermediate transfer member 4 in accordance with the timing of transferring the color image onto the transfer material 42.
3 is pressed at a predetermined pressure to an upper position shown by a chain line in FIG. At this time, a bias is applied to the transfer roller 44 at the same time, and the toner image on the intermediate transfer body 43 is transferred to the transfer material 42.

The transfer material 42 sandwiched between the intermediate transfer body 43 and the transfer roller 44 is conveyed at a predetermined speed to the left in FIG. Is transported to the fixing device.

The fixing section 52 fixes the toner image formed in the above-described steps. As shown in FIG. 5, the fixing unit 52 includes a fixing roller 53 for applying heat to the transfer material 42.
And a pressure roller 54 for pressing the transfer material 42 against the fixing roller 53. Each roller is a hollow roller, inside which heaters 55 and 56 are arranged. The transfer material 42 is transported by the rotation of each roller. That is, the transfer material 4 holding the toner image
2 is transported by the fixing roller 53 and the pressure roller 54,
By applying heat and pressure at the same time, the toner is fixed on the transfer material 42.

The fixing device 52 melts and mixes the toner image to form a color image, is fixed and fixed on a transfer material, and is then discharged out of the apparatus.

[0030]

The image forming apparatus having such a configuration has the following problems. Briefly describing this, the charger 47 disposed around the photosensitive drum 45, the image signal application position, the rotating developing device 50,
Since the order of the cleaner 46 and the like cannot be changed, in order to reduce the size of the apparatus, the developing device and the fixing device are arranged close to each other. Particularly, in a device using a transfer drum as an intermediate transfer member, a developing device that rotates above the fixing device may be disposed.

The fixing device has a surface temperature of 140 ° C.
It has been widely practiced to provide a fixing roller maintained at about 180 ° C. and a pressure roller which presses against the roller, and which is configured so that a transfer material carrying an unfixed toner image is inserted through a pressure nip portion between both rollers. However, when such a fixing device is used, the temperature above the fixing device must be considerably high, so that the fixing device is located in the rotating developing device at that position, particularly on the fixing device side. In the developing device, the stored toner may be softened. Such a situation is particularly caused when the rotary developing device is stopped and a specific portion thereof is directed to the fixing device, and the temperature of the pressure roller is fixed to a predetermined value while the fixing device is operating or in a standby state. It is easy to occur when controlling.

The toner is usually obtained by crushing a resin such as polyester or styrene acrylic in which a pigment corresponding to a color is dispersed, or forming a powder having a particle diameter of several μm to several tens μm by suspension polymerization or the like. Softening starts at about ° C and completely melts at 90 ° C to 100 ° C.

When the toner in the developing device softens in this way, thereafter, the toner is agglomerated and solidified in the developing device or solidified in the developing device, so that image formation is not performed stably, and There is a problem that becomes worse.

The present invention has been proposed in order to solve the above-mentioned problems of the prior art. The purpose of the present invention is to soften, melt and solidify the toner in a developing device by heat generated from a fixing device. An object of the present invention is to provide an image forming apparatus capable of preventing occurrence of an image, performing stable image formation, and always obtaining a good image.

[0035]

To achieve the above object, according to the present invention, there is provided an image bearing member for carrying an electrostatic image, and an electrostatic image on the image bearing member containing a toner. Developing means for developing and forming a toner image; and fixing means for heating the toner image formed on the recording material to fix the toner image on the recording material, wherein the developing means is an image provided above the fixing means. The image forming apparatus is characterized in that the developing unit moves away from the fixing unit when an image is not formed on the recording material.

According to a sixth aspect of the present invention, there is provided an image carrier for carrying an electrostatic image, and a first developing means for containing toner and developing the electrostatic image on the image carrier to form a toner image. When,
A second developing unit that is different from the first developing unit; and a fixing unit that heats the toner image formed on the recording material to fix the recording material on the recording material, wherein the first developing unit is located above the fixing unit. A first image forming mode in which an image is formed on a recording material by performing development by the first developing unit; and a second developing unit that does not perform development by the first developing unit. A second image forming mode in which an image is formed on a recording material by performing development according to the first and second developing modes. In the second image forming mode, the first developing unit moves away from the fixing unit. And

(Function) According to the present invention, the toner in the developing device is prevented from being softened, melted or solidified by the heat of the fixing device, and a high quality image can be stably obtained.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> First, Embodiment 1 of the present invention
1 will be described with reference to FIG.

FIG. 1 is a schematic side sectional view of a color image forming apparatus. In FIG. 1, a developing device 1 and a transfer drum 23 are disposed in the vicinity of a rotating cylindrical image carrier 28 having an axis perpendicular to the paper surface. Are arranged in parallel. Developing devices 2Y, 2M, 2C, and 2K, which are developing means for storing toners of yellow, magenta, cyan, and black, respectively, are provided in the developing device 1 as the developing unit. At the same time, the developer sequentially arrives at a development site facing the image carrier 28.

After the photosensitive layer on the surface of the image carrier 28 is uniformly charged by the primary charger 21, an image signal is projected from the laser optical system 22 as an image signal applying means onto the charged surface to form an electrostatic image. Then, as the image carrier 28 rotates, the electrostatic image reaches a developing site facing the developing device 1. At this time, the developing device 2K containing the black toner in the developing device has reached the developing site, and a black toner image is formed by the black toner supplied from the developing device 2K.

When the black toner image reaches the transfer portion where the transfer drum 23 is opposed by the rotation of the image carrier 28, a transfer bias is applied from the transfer drum side, and the action of an electric field formed by the transfer bias is applied. The black toner image is transferred (transferred) from the image carrier 28 to the transfer drum 23.

After the black toner image is transferred, a small amount of toner remaining on the image carrier is removed by the cleaner 26, and the image carrier enters the next image forming step. Forming an electrostatic image, and then forming a cyan toner image by a developing unit 2C containing the cyan toner rotating to the developing site.
This cyan toner image is superimposed and transferred onto the black toner image on the transfer drum in the same manner as the black toner image.

Subsequently, the magenta toner image and the yellow toner image are superimposedly transferred onto the toner image on the transfer drum 23.

A transfer path 24 is disposed close to the transfer drum 23 to form a secondary transfer portion with the transfer drum 23. When the transfer material 27 reaches this transfer portion from the direction indicated by the arrow A in FIG. The toner image on the drum is electrostatically transferred to a transfer material as a recording material.

The transfer material carrying the toner image travels along the transport path 24 to reach the fixing device 25, where the toner image is heated and melted and mixed to form a color image, which is then fixed and fixed to the transfer material. Is discharged outside the machine.

The image forming apparatus according to the first embodiment is provided above the fixing device in which the developing device 1 is a fixing unit, as is apparent from FIG.

In view of the above-described softening and melting temperatures of the toner, fixing in the fixing device, and the heating temperature of the pressure roller, the present invention provides a specific portion of the rotating developing device, that is, a specific developing device. The developing device is periodically rotated so that the developing device does not approach the fixing device for a long time, and the developing device close to the fixing device is separated from the fixing device. An operation sequence when applied to such an image forming apparatus will be described with reference to a block diagram shown in FIG.

In FIG. 2, after the power is turned on, the fixing device 25
When both the fixing and pressurizing rollers reach a predetermined temperature, the apparatus main body is ready for printing, and starts standby (S1).

At this time, a timer built in a CPU (not shown) sets an elapsed time T (se
The measurement of c) is started (S2).

Thereafter, when the CPU receives a print start instruction (S3-Y), after the copy operation (S4), the copy operation ends (S5), the timer T is returned to zero (S6), and Returning to S2), the measurement by the timer is continued.

If there is no print start instruction in (S3), that is, if no image is formed on the recording material (S3-N), it is determined whether or not T exceeds 120 sec (S7). If not (S9), the measurement is continued as it is.

When T exceeds 120 sec (S7-Y), the drive motor of the rotary developing device is driven by the instruction from the CPU to rotate it by 90 degrees, and the developing device facing the fixing device side until then. The device side is moved away from that position (S8).

Thereafter, the process proceeds to (S6), the timer is reset (T = 0), and the process returns to (S2) to restart the timer measurement.

As described above, while the image forming apparatus is on standby, the specific position of the rotary developing device is set to two minutes (120 minutes).
sec) By preventing the toner from being present on the fixing device side for a longer time, it is possible to reliably prevent the toner in each developing device in the developing device from softening, melting, and solidifying due to heat generated from the fixing device, and to prevent inconvenience caused by the operation. Is possible.

<Second Embodiment> Next, a second embodiment will be described.

First, an image forming apparatus according to a second embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a schematic side view of the image forming apparatus.
Parts corresponding to those of the apparatus shown in FIG. 1 are denoted by the same reference numerals, and the description of the configuration and operation thereof will be omitted. This device includes a yellow toner in a developing device 31,
Developing devices 32Y, 32M, and 32C, which are three first developing units that store magenta toner and cyan toner, are stored.

In this apparatus, a developing device 32K, which is a second developing means containing black toner, is fixedly arranged above the developing device 31 and close to the image carrier 28. With this configuration, the amount of black toner stored in the developing device 32K can be increased, and can be effectively used for monochrome images that are generally frequently used.

As is apparent from FIG. 3, a developing device 31 accommodating the first developing means is provided close to and above the fixing device.

When a large number of monochrome images are to be printed by such an apparatus, the rotation of the rotary developing device 31 is not necessary because the development of the yellow, magenta and cyan toners does not have to be performed. Sometimes it is not necessary. At the same time, since the fixing device is used even when printing a monochrome image, heat is generated.
It is assumed that a rotation operation is performed to protect the toner of the developing device in the developing device 31.

A specific operation sequence will be described with reference to the block diagrams shown in FIGS.

In FIG. 4, after the power is turned on, when the fixing and pressure rollers of the fixing device 25 reach a predetermined temperature, the apparatus main body becomes ready for printing and starts standby (S10). At this time, the timer incorporated in the CPU (not shown) starts measuring the elapsed time T (sec) from the standby state (S11).

Thereafter, when the CPU receives an instruction to start full-color printing in the first image forming mode and starts full-color printing (S12-Y), the full-color printing operation (S13) ends the full-color printing operation (S12).
After 14), the timer T is returned to 0 (zero) (S15) S1
Return to 1 to continue the timer measurement. During the full-color printing operation (S13), the first developing unit and the second developing unit
Development by the developing means is performed. At this time, the developing device 3
The rotation of 1 causes the second developing means to move, and the development of each color is performed.

When the CPU does not receive the instruction for full-color printing but receives the instruction for monochrome printing in the second image forming mode and starts printing a monochrome image (S12-
In N, S20-Y), the measurement of the continuous print number of the monochrome image is started (S21).

Thereafter, a monochrome print operation (S22),
After the end of the monochrome print operation (S25), the timer T is returned to 0 (S24), and the measured value A of the continuous print number is set to 1
Is added (S25).

During the monochrome print operation (S2
2) Development is performed by the developing device 32K that contains the black toner, which is the first developing device,
The development by 2C and 32M is not performed, and the developing device 31 does not rotate.

Thereafter, when the monochrome image is to be printed (S26-N, S28-N, S29-Y), the flow returns to S22 to start the monochrome image printing operation. When monochrome image printing is performed continuously (A ≧ 2) and the number of continuous monochrome image printing is less than 50 (S26)
In step (-Y), if a monochrome image is to be printed, the process returns to step S22 to perform the printing operation of the next monochrome image. However, when the number of continuous monochrome images reaches 50 (S26-N, S28-Y), the drive motor of the rotary developing device is driven by the instruction from the CPU to rotate it 90 degrees, and the fixing device side The side of the developing device opposed to is moved away from that position (S30). Thereafter, when the printing of the monochrome image is continued (S31), the measurement value A of the continuous print number is reset to 0, and the process returns from S32 to S21 to start the measurement again and start the printing operation of the monochrome image (S31). S22). If the printing of the monochrome image is not performed after the rotation of the developing device in S30, the process returns to S11 and the measurement of the timer is restarted.

If the subsequent monochrome image printing is not to be performed when the number of monochrome image prints is continuously 49 or less (S26-Y, S27-N), the flow advances to S33 to rotate the developing device by 90 °. Then, the process returns to S11 to start measuring the timer.

If the CPU does not receive a full-color print instruction or a monochrome print instruction in S12 (S12)
In (N, S20-N), it is determined whether or not T exceeds 120 seconds (S16). If T exceeds 120 seconds, the measurement is continued as it is (S19).

When T exceeds 120 seconds (S16-Y),
The rotary developing device is rotated by 90 ° in accordance with an instruction from the CPU, and the side of the developing device that has been opposed to the fixing device is avoided from that position (S17). Thereafter, the process proceeds to S18, where the timer is reset (T = 0), and returns to S11 to restart the timer measurement.

More specifically, the rotation of the developing device is performed in the following three cases. (1) Immediately after 50 black monochrome images have been successively formed, in this case, in order to not disturb the toner image formed on the image carrier 28, the rear end of the image immediately after 50 images have been formed The developing device 31 is rotated while the image interval portion on the side faces the developing device 1. (2) After the image formation of the continuous black single-color image is completed. (3) When the image forming apparatus is in the standby state for 120 seconds or more, in this case, the same operation as in the above embodiment may be performed.

Further, in the above three cases, when the rotation of the developing device 31 starts or ends, none of the developing devices in the developing device 1 is opposed to the image carrier 28.

With the above configuration, when a black image is printed continuously or intermittently, or when the image forming apparatus is in a standby state, a specific portion of the developing device which rotates is adversely affected by the heat of the fixing device. Can be effectively avoided.

[Other Embodiments] In the above-described embodiment, an image forming apparatus having a mono-black mode and a full-color mode for forming an image with four color toners has been described. In addition to the two modes,
The present invention can be suitably applied to an image forming apparatus having a two-color image and a three-color image printing mode.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the technical idea of the present invention.

[0077]

As described above, according to the present invention,
2. Description of the Related Art In an image forming apparatus having a developing device rotatably formed by accommodating a plurality of developing devices, a specific portion of the developing device is opposed to a fixing device including a heating element for a long time so that a developing process is performed. It is possible to prevent the toner in the container from being softened, melted or solidified, thereby preventing inconvenience in the operation of the apparatus, and to constantly obtain a high quality image stably.

[Brief description of the drawings]

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

FIG. 2 is a block diagram for explaining Embodiment 1 of the present invention;

FIG. 3 is a schematic side sectional view illustrating a configuration of a color image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a block diagram for explaining Embodiment 2 of the present invention;

FIG. 5 is a block diagram for explaining Embodiment 2 of the present invention;

FIG. 6 is a schematic diagram illustrating a configuration of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing device 2Y, 2M, 2C, 2K developing device 21 primary charger 22 image signal applying means 23 transfer drum 24 transport path 25 fixing device 26 cleaner 27 transfer material 28 image carrier

Claims (12)

[Claims] 1. An image carrier for carrying an electrostatic image, a developing means for containing a toner and developing the electrostatic image on the image carrier to form a toner image, and a toner image formed on a recording material. Fixing means for fixing to the recording material by heating, wherein the developing means is an image forming apparatus provided above the fixing means, wherein the developing means, when not forming an image on the recording material, An image forming apparatus, wherein the image forming apparatus moves away from the fixing unit. 2. The image forming apparatus according to claim 1, wherein the developing unit moves from a developing position to a position closer to the fixing unit than a developing position when forming an image on a recording material. 3. The image forming apparatus according to claim 1, wherein the developing unit is provided in a rotatable unit, and the unit moves away from the fixing unit by rotating the unit. The image forming apparatus as described in the above. 4. The image forming apparatus according to claim 3, wherein there are a plurality of the developing units, and the plurality of the developing units are provided in the unit. 5. The image according to claim 1, wherein the developing unit moves away from the fixing unit after a lapse of a predetermined time from when the temperature of the fixing unit reaches a predetermined temperature. Forming equipment. 6. An image carrier for carrying an electrostatic image, first developing means for containing toner and developing the electrostatic image on the image carrier to form a toner image, and the first developing means Different second
An image forming apparatus comprising: a developing unit; and a fixing unit configured to heat the toner image formed on the recording material to fix the recording material on the recording material, wherein the first developing unit is provided above the fixing unit and is movable. A first image forming mode in which an image is formed on a recording material by performing development by the first developing unit; and an image is formed on the recording material by performing development by the second developing unit without performing development by the first developing unit. And a second image forming mode in which the first developing unit moves away from the fixing unit in the second image forming mode. 7. The image forming apparatus according to claim 6, wherein the first developing unit moves away from the fixing unit after forming an image on a predetermined number of recording materials in the second image forming mode. The image forming apparatus as described in the above. 8. The image according to claim 6, wherein the first developing unit moves away from the fixing unit when the image formation in the second image forming mode is completed. Forming equipment. 9. The image forming apparatus according to claim 6, wherein the first developing unit moves from a developing position to a position closer to the fixing unit than the developing position in the first image forming mode. Image forming apparatus. 10. The image forming apparatus according to claim 6, wherein the first developing unit is provided in a rotatable unit, and the first developing unit moves away from the fixing unit by rotating the unit. 10. The image forming apparatus according to 9. 11. The image forming apparatus according to claim 10, wherein there are a plurality of said first developing units, and said plurality of first developing units are provided in said unit. 12. An image forming apparatus according to claim 6, wherein said second developing means develops with black toner, and said first developing means develops with color toner.