JPH09101666A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the chattering and rolling up of a cleaning blade by making the friction between a photoreceptor drum and the cleaning blade extremely little, at the time of executing the mode of stirring a developer. SOLUTION: A prescribed level image is formed on the photoreceptor drum 16, during the operation of discharging the developer from a developer recovering port, 34 by the driving of a stirring/carrying screw 32a and a returning screw 32b which are arranged in the stirring chamber 30a and developing chamber 30b of a developing unit 30 respectively. Thus, toner T is fed to between the drum 16 and a cleaner blade 23a and functions as a lubricant, so that the friction between the drum 16 and the cleaner blade 23a is made extremely little to reduce the chattering or rolling up of the cleaner blade 23a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine, and is characterized by a developing device using a two-component developer composed of a magnetic carrier and a non-magnetic toner.

[0002]

2. Description of the Related Art FIG. 5 schematically shows a digital full-color copying machine. The developing device 30 has four developing devices, that is, developing devices 30Y, 30C, 30M, and 30K for each color of yellow Y, cyan C, magenta M, and black B. Each developing device includes a toner and a carrier. The following two-component developer is used.

First, an original (original image) D is read by the CCD 1 and the obtained analog image signal is converted into an amplifier (A)
MP) 2 amplifies it to a predetermined level, and the A / D converter 3 converts it to an 8-bit (0 to 255 gradation) digital image signal. Next, this digital image signal is converted into a γ converter (2
It is composed of a 56-byte RAM and is passed through a converter 5 that performs digital conversion by a look-up table method,
After correction, it is input to the D / A converter 6.

The signal converted into an analog signal again by the D / A converter 6 is compared with a signal of a predetermined cycle generated from the triangular wave generating circuit 9 in the comparator 7, and the pulse width modulated binary image signal is compared. Is directly input to the laser drive circuit 10 to turn on the light emission of the laser diode 11.
Used for the off control signal. This laser diode 11
The laser beam emitted from is scanned by the well-known polygon mirror 12 in the main scanning direction, passes through the f / θ lens 13 and the reflection mirror 15, and then onto the photosensitive drum 16 as an image carrier rotating in the direction of arrow A. It will be illuminated to form an electrostatic latent image.

On the other hand, the photosensitive drum 16 is uniformly neutralized by the exposing device 17, and then uniformly negatively charged by the charging device 19. Thereafter, an electrostatic latent image is formed on the surface according to the image signal by receiving the laser light described above.

The developing device 30 includes four developing devices, that is, developing devices 30Y, 30C, 30M and 30K for yellow, cyan, magenta and black. In each developing device, a toner having a negative charging characteristic is attached to a portion of the photosensitive drum 16 that has been subjected to static elimination by laser light by a well-known reversal development method, and this is visualized to form a toner image. .

FIG. 7 shows the relationship between the surface potential of the photosensitive drum 16 and the development contrast in such reversal development. Here, V _D represents a negative potential uniformly charged by the charger 19 of FIG. What is V ₀₀ ?
00 _H (0 level) image signal digitized by the A / D converter 3 is a photosensitive drum surface potential irradiated by the laser light, and V _FF is the same as FF _H. The image signal of (256 levels) is the surface potential of the photosensitive drum which is driven by the laser and is irradiated with the laser light.

Here, an applied electric field (hereinafter referred to as "developing bias") applied to the developing device during development, which is V _DEV .
Then, the DC development bias and the AC development bias superposed on it, for example, a frequency of 2 kHz and a voltage of 2 kV _PP (peak to peak) are applied. Development corresponding to the development contrast represented by | V _{DE V} −V _XX | is performed. Be seen.

Therefore, as shown in FIG.
V _DEV −V _FF | is properly set as the contrast potential V _cont ,
When the developing density to be developed by the contrast potential V _cont and D _{ma x,} in order to obtain a desirable image density (about 1.2-1.8 in general electrophotography) The V
_It can be seen that the value of _cont should be set appropriately.

The fog removal potential (V _back ) in the figure is for completely removing the fog on the white background portion of the image which is irradiated with an amount of 00 _H light.

The visible image (toner image having a negative charge) formed on the photosensitive drum 16 by the above method is transferred onto the transfer material (generally paper) P carried on the transfer drum 22, as shown in FIG. And is transferred by the transfer charger 21. The visible image transferred onto the transfer material P is fixed by a fixing device (not shown), and is discharged to the outside of the machine.

Further, the residual toner remaining on the surface of the photosensitive drum 16 is scraped off by the cleaner 23.

The cleaning blade of the cleaner 23 contacts the surface of the photosensitive drum in the running direction, that is, the blade edge is brought into contact with the surface of the photosensitive drum so as to be in the counter direction. Is partially burned off, and a part of the toner is present between the blade edge and the surface of the photosensitive drum to act as a lubricant, so that the cleaning mechanism is maintained.

This series of image formation is repeated for each color,
Obtain a full color image.

In addition to this series of operations, the image forming apparatus as described above is provided with a stirring mode for collecting the developer, inserting it, and taking in the initial value of the developer concentration.
When these agitation modes are carried out, generally, the photosensitive drum is rotated by the drive force of the drive source, and at the same time, the same drive force is transmitted to the agitation screw of the developing device and the like to be rotationally driven. That is, when the developer is stirred, the photosensitive drum is also rotated at the same time.

As shown in FIG. 6, each developing device 30 has an agitating chamber 30a and a developing chamber 30b, an agitating / conveying screw 32a and a returning screw 32b, respectively, and a developer at the bottom of the agitating chamber 30a. A recovery port 34 is provided.

In the above stirring mode, the photosensitive drum 1
The surface potential of 6 is controlled to V ₀₀ , an electric field is applied to the developing sleeve 31 from the developing bias power source 40, and a developing device pressing mechanism and a developing device driving mechanism (not shown) are applied between the developing sleeve 31 and the photosensitive drum 16. The developing device is pressed so as to provide a constant gap, the developing sleeve 31 is driven, and while the electrostatic latent image (V ₀₀ image) on the photosensitive drum 16 is being developed, the developer is agitated by the agitating and conveying screw 32a or the like. I was going.

[0018]

However, the agitation of the developer in the above-mentioned conventional example is for its own purpose, and at this time, the agitation operation is performed for several minutes without forming an image on the photosensitive drum 16. . For this reason, there is a shortage of toner intervening between the photosensitive drum and the edge of the cleaning blade, which acts as a lubricant, and the frictional force increases, which may cause chattering of the cleaning blade tip, blade flipping, and the like. there were.

Therefore, an object of the present invention is to provide an image forming apparatus which can reduce the friction between the image carrier and the cleaning means and reduce the chattering and the curling of the cleaning means when the developer agitation mode is carried out. Is to provide.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus that develops a latent image formed on an image carrier by a developing device using a two-component developer, developing in the developing device while forming an image of a predetermined level on the image carrier for a predetermined time. The image forming apparatus is characterized in that the agent is stirred.

When the developer is stirred, it is preferable to cut off the developer circulation path to recover the developer. It is preferable to stir the developer when the mixing ratio of the two-component developer in the developing device is taken as an initial value. According to another aspect, it is preferable that an image is formed on the image carrier by a developing device different from the developing device when the mixing ratio of the two-component developer is taken as an initial value.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. Note that the present invention is embodied in the digital full-color copying machine shown in FIG. 4, and therefore the description of the overall configuration and functions of the image forming apparatus is incorporated by reference above. The characteristic part of will be described.

First Embodiment A first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. 1 and 2. As shown in FIG.
Includes a stirring chamber 30a and a developing chamber 30b, and inside thereof, a stirring and conveying screw 32a and a returning screw 32b are arranged in parallel to the axial direction of the developing sleeve 31, which is a developer carrier. . A developer recovery port 34 is provided at the bottom of the stirring chamber 30a.

When the stirring mode for developer recovery is executed, the cap of the developer recovery port 34 is removed. Next, the photosensitive drum 16 is rotated in the direction of arrow A, and the primary charger 19 charges the photosensitive drum 16 with a predetermined potential Vd.
A laser L is used to expose to a predetermined level of image density to form a latent image. Before the surface of the photosensitive drum on which the latent image is formed passes the developing position, the developing sleeve 31, the stirring / conveying screw 32a and the returning screw 32b are rotated by the developing sleeve driving means (not shown), and the developing sleeve is rotated by the electric image bias power source 40. An electric field is applied to 31, and the developing device 30 is pressed against the photosensitive drum 16 by a developing device pressing unit (not shown).

By driving the developing device, the developer is agitated in the direction of arrow C in FIG.
And a part of the circulation path, here, the developer recovery port 3
By opening 4, the developer is sequentially discharged from the recovery port 34 to the outside of the developing device, and the discharge is completed after several minutes.

During the discharging operation of the developer, the photosensitive drum 16
An image of a predetermined level is formed on the toner, and the developer is agitated and collected while forming a developed image, so that the toner T is sent to the cleaner 23, which is a cleaning unit, and the friction between the cleaner blade 23a and the photosensitive drum 16 is reduced. By doing so, it is possible to reduce chattering and curling of the cleaner blade 23a, and it is possible to extend the life of the cleaner blade.

Second Embodiment Next, the second embodiment of the image forming apparatus according to the present invention will be described.
This will be described with reference to FIGS. 3 and 4. In this embodiment, as shown in FIG. 3, two developing devices are arranged upstream and downstream of the photosensitive drum.

When executing the stirring mode for developer recovery in the developing device 30M, first, the cap of the developer recovery port 34 is removed. Then, the photosensitive drum 16 is rotated in the direction of arrow A, a predetermined potential Vd is charged on the photosensitive drum 16 by the primary charger 19, and the photosensitive drum 16 is exposed to a predetermined level of image density by the laser L to form a latent image. To do.
Before the surface of the photosensitive drum on which the latent image is formed passes the developing position, the developing sleeve driving means (not shown) rotates the developing sleeve 31M, the agitating / conveying screw 32aM, and the returning screw 32bM, and the developing bias power source 40M causes the developing sleeve to rotate. Apply an electric field to 31M,
By a developing device pressurizing means (not shown), the developing device 30M
Is pressed against the photosensitive drum 16.

By driving the developing device 30M, the developer circulates in the direction of arrow C in FIG. 4, and a part of the circulation path, here, the developer collecting port 34 is opened to collect the developer. Further, the toner is sequentially discharged to the outside of the developing device 30M, and the discharge is completed after several minutes.

In the present embodiment, during the developer discharging operation of the developing device 30M, the developing device 30C located upstream of the developing device 30M forms an image of a predetermined level on the photosensitive drum 16.

As a result, even when the developer in the developer collecting and developing device 30M is collected, an image is formed on the photosensitive drum by the developing device 30C on the upstream side, and a stable amount of toner is supplied to the cleaner blade 23a. As a result, chattering and curling of the cleaner blade 23a can be reduced, and the life of the cleaner blade 23a can be extended.

As described above, in the developer collecting agitation performed by operating the two-color developing devices, the toner of the upstream side forms an image of a predetermined level, and on the other hand, the developer of the downstream developing device is used. It is desirable to collect.

Third Embodiment Next, the third embodiment of the image forming apparatus according to the present invention will be described.
The description will be made again with reference to FIGS. 1 and 2.

The present embodiment relates to the developer agitation when the initial value of the developer concentration is taken in by the initial setting of the developing device at the time of initial installation of the apparatus main body and the replacement of the developer.

In FIG. 1, the photosensitive drum 16 is rotated in the direction of arrow A, a predetermined potential Vd is charged on the photosensitive drum 16 by the primary charger 19, and the photosensitive drum 16 is exposed by the laser L so that the image density becomes a predetermined level. , Form a latent image. Before the surface of the photosensitive drum on which the latent image is formed passes through the developing position, the developing sleeve driving means (not shown) rotates the developing sleeve 31, the agitating / conveying screw 32a, and the returning screw 32b, and the developing bias power source 40 causes the developing sleeve. An electric field is applied to 31, and the developing device 30 is pressed against the photosensitive drum 16 by a developing device pressing unit (not shown).

As shown in FIG. 2, the developer is initially charged from the developer replenishing port D. After the completion of the addition of the developer, the developer is stirred and the developer concentration (mixing ratio of toner and carrier) is taken in by the detection sensor 33 of the optical reflection type.

During the period from the introduction of the developer to the end of taking in the developer concentration, the toner as the lubricant is sent to the cleaner blade 23a by developing the toner on the photosensitive drum to a predetermined level. This reduces the friction with the photosensitive drum 16 so that the cleaner blade 23c
You can reduce curling and chattering.

Since the developer is agitated while developing the density of a predetermined level, the developer density becomes low at the time of setting, but as a correcting means, the density of the initial developer itself is made higher than an appropriate value by an amount consumed. There is a method of preserving, or a method of correcting the output of the detection sensor for the amount of developer consumed, and it is advisable to obtain an appropriate developer concentration by carrying out these methods.

Fourth Embodiment Next, a fourth embodiment of the image forming apparatus according to the present embodiment will be described with reference to FIGS.

In this embodiment, when the developer is stirred when the initial value of the developer concentration (mixing ratio of toner and carrier) is taken in, images are alternately formed on the photosensitive drum as in the two-color mode of the normal copy sequence. Then, in order to stir, one of the developing devices forms a white image of V ₀₀ , the other developing device forms a predetermined image, and the toner is supplied to the cleaner blade. The operation will be described again with reference to FIG.

The photosensitive drum 16 is rotated in the direction of arrow A, and a predetermined potential Vd is applied to the photosensitive drum 16 by the primary charger 19.
A latent image is formed by being charged upward and exposed to a predetermined level of image density by the laser L. Before the surface of the photosensitive drum on which the latent image is formed passes the developing position, the developing sleeve driving means (not shown) rotates the developing sleeve 31M, the agitating / conveying screw 32aM, and the returning screw 32bM, and the developing bias power source 40M develops the developing sleeve. An electric field is applied to 31M, and the developing device 30M is pressed against the photosensitive drum 16 by a developing device pressing unit (not shown).

After stirring the developing device 30M for one rotation of the photosensitive drum, the developing device 30C on the upstream side is driven in the same sequence to apply a developing bias to form an image of a predetermined level for one rotation. Toner is supplied to the cleaner blade 23a.

By repeating this operation, while the stirring of the developing device 30M and the image formation of a predetermined level of the developing device 30C are alternately performed, the initial density of the developer is taken in.
By supplying toner to the cleaner blade 23a, it is possible to reduce chattering and curling of the cleaner blade 23a, and it is possible to extend the life of the cleaner blade 23a. Further, the developer concentration can be taken as an initial value without changing.

[0044]

As described above, according to the present invention,
By stirring the developer in the developing device while forming an image of a predetermined level on the image carrier for a predetermined time, toner as a lubricant is supplied between the image carrier and the cleaner blade, and Friction with the cleaner blade can be reduced, chattering and curling can be reduced, and a long life of the image carrier and the cleaner blade can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining Embodiments 1 and 3 of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a developer stirring means of FIG.

FIG. 3 is an explanatory diagram for explaining Embodiments 2 and 4 of the image forming apparatus according to the present invention.

FIG. 4 is an explanatory view showing a developer stirring means of FIG.

FIG. 5 is a schematic configuration diagram showing a conventional digital full-color copying machine.

FIG. 6 is an explanatory view showing the developing system of FIG.

FIG. 7 is an explanatory diagram showing the relationship between the surface potential of the photosensitive drum and the development contrast.

[Explanation of symbols]

 16 Photosensitive Drum (Image Carrier) 23 Cleaner 23a Cleaner Blade 30 Developer 30M Magenta Developer 30C Cyan Developer 30Y Yellow Developer 30B Black Developer 31 Developing Sleeve 32a Conveying Screw 32b Return Screw 33 Detection Sensor 34 Developer Discharge Port D Developer supply port T 2 component developer

Claims (4)

[Claims] 1. An image forming apparatus for developing a latent image formed on an image carrier with a developing device using a two-component developer, wherein an image of a predetermined level is formed on the image carrier for a predetermined time. An image forming apparatus characterized by stirring a developer in a developing device. 2. The image forming apparatus according to claim 1, wherein the developer circulation path is cut off when the developer is stirred to recover the developer. 3. The image forming apparatus according to claim 1, wherein the developer is stirred when the mixing ratio of the two-component developer in the developing device is taken as an initial value. 4. The image forming method according to claim 3, wherein an image is formed on the image carrier by a developing device different from the developing device when the mixing ratio of the two-component developer is taken as an initial value. apparatus.