JPH09329963A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good quality image and to improve durability and reliability by disposing a layer-thickness restriction roller parallel to a developing roller in a layer-thickness restriction plane, thereby restricting the thickness of a toner layer on the developing roller, and removing the accumulation of toner by means of rotation. SOLUTION: The layer-thickness restriction roller 29 restricts the thickness of the layer on the developing roller 10, and the accumulation of toner 30 is formed between the layer-thickness restriction roller 29 and developing roller 10 when printing is carried out. The toner 9 stirred and carried by a toner stirring member 8, then supplied to the surface of the developing roller 10, serving as a toner carrier, by a toner supply roller 6, and carried along the surface is subjected to toner-layer-thickness restriction by the layer-thickness restriction roller 29 and, at the same time, frictionally charged and formed into the thin layer on the periphery of the developing roller 10. Thereafter, by a bias voltage applied from a development bias power source 14, the toner 9 is transferred and attached onto a part of the surface of a photoreceptor 1 where an electrostatic latent image is formed, so that the electrostatic latent image is developed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus which visualizes an electrostatic latent image formed on a surface of a photoconductor with toner.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus mainly uses equipment using dry toner, and has been put to practical use as many copying machines, laser printers, plain paper facsimiles, etc., and has made remarkable progress. This electrophotographic device is a device to which electrophotographic process technology is applied. After the electrostatic latent image formed on the surface of the photoconductor is visualized with toner, it is transferred to recording paper, and printing is completed through a fixing process. It is a thing.

FIG. 6 is a block diagram showing a conventional image forming apparatus, and FIG. 7 is a block diagram showing the periphery of a developing roller during printing in the conventional image forming apparatus. In FIG. 6, a photosensitive member 1 is an electrostatic latent image carrier having a metal drum made of aluminum or the like as a base material, and a photosensitive receiving layer such as selenium (Se) or an organic photoconductor is applied in a thin film on the outer peripheral surface thereof. The charger 2 is disposed close to the photoconductor 1 and is composed of a charging wire 2a such as a tungsten wire, a shield plate 2b made of metal, and a grid plate 2c. The exposure optical system 3 irradiates the exposure light beam 4. The exposure light beam 4 is obtained by subjecting an image signal to light intensity modulation or pulse width modulation by a laser drive circuit (not shown). The developing device 5 includes a toner supply roller 6 that is a toner supply member, and a toner hopper 7 that stores toner 9.
A toner agitating member 8 whose both ends are rotatably supported by the toner hopper 7 and which is bent and formed in a rectangular shape; a developing roller 10 which is a toner carrier; and a metal spring plate member 13a and a layer which contacts the developing roller 10. And a layer thickness regulating blade 13 including a thickness regulating member 13b. The toner supply roller 6 is for supplying the toner 9 to the surface of the developing roller 10, and a toner supply bias power source 11 is connected to the surface of the metal shaft via a protective resistor 12.
A bias voltage is applied from the developing bias power source 14 to the metallic shaft portion of the developing roller 10. The layer thickness regulating blade 13 is attached to the blade holder 15 with screws. The layer thickness regulating member 13b is formed by integrally forming an elastic member such as silicon or urethane on one end of the metal spring plate member 13a.

The recording paper cassette 16 stores the recording paper 17, and the paper feed roller 18 sends the recording papers 17 one by one to the conveying roller 19. The registration roller 20 aligns the recording paper 17 and the toner image formed on the surface of the photoconductor 1 with each other.
The recording paper 17 is temporarily stopped and waited, and is in contact with the driven roller 21. The transfer device 22 includes a transfer line 22a made of a tungsten wire or the like and a shield plate 22b made of a metal plate. The fixing device 25 includes a heat roller 23 having a heat source inside and a pressure roller 24. The cleaning blade 26 for scraping off the residual toner on the surface of the photoconductor 1 and the toner collecting container 27 for storing the scraped residual toner constitute a cleaner part, and the static eliminator 28 is arranged on the downstream side of the cleaner part. Is
The surface of the photoreceptor 1 is electrostatically cleaned.

Next, the functions and operations of the main parts will be described. The developing roller 10 and the toner supply roller 6 are made of metal such as stainless steel as a base material, and elastic members such as urethane and silicon are formed in layers on the outer peripheral surfaces thereof, and both ends thereof are pivotally supported by the toner hopper 7. The toner stirring member 8 draws a circular locus along with the rotation of the toner supply roller 6, stirs the toner 9 stored in the toner hopper 7 to prevent aggregation, and conveys the toner 9 toward the toner supply roller 6. The toner 9 supplied by the toner supply roller 6 has its toner layer thickness regulated by the layer thickness regulating blade 13 and is triboelectrically charged, so that a thin layer state is formed on the outer peripheral surface of the developing roller 10. Then, the developing roller 10
Is brought into contact with or close to the photoconductor 1, and the toner 9 is transferred and adhered to a portion of the surface of the photoconductor 1 where the electrostatic latent image is formed by a bias voltage applied from the developing bias power source 14. To visualize.

The recording papers 17 stored in the recording paper cassette 16 are sent from the recording paper cassette 16 one by one to a conveying roller 19 by a half-moon shaped paper feed roller 18. The recording paper 17 sent out is conveyed in the direction indicated by the arrow A by the conveying roller 19. The recording paper 17 is temporarily stopped and waited by the registration roller 20.

In the transfer unit 22, when a high voltage is applied to the transfer line 22a, the transfer line 22a causes corona discharge, and the toner image on the surface of the photoconductor 1 is transferred onto the recording paper 17. The fixing device 25 applies pressure and heat to the recording paper 17 due to the nip rotation between the heat roller 23 and the pressure roller 24.
The toner image transferred onto the recording paper 17 is fixed and the printing is completed.

[0008]

However, in the conventional image forming apparatus, the wedge portion (the wedge portion formed by the developing roller 10 and the layer thickness regulating blade 13 as the operating time becomes long and the number of printed sheets increases). The toner 9 gradually accumulates in a narrow space 13c formed by the metal spring plate member 13a, the layer thickness regulating member 13b and the developing roller 10 to form accumulated toner. Then, the stress due to the toner conveying force of the toner supply roller 6 and the developing roller 10
The phenomenon that the accumulated toner adheres to the layer thickness regulating blade 13 occurs due to frictional heat between the layer thickness regulating blade 13 and the like. When the toner 9 adheres to the layer thickness regulating blade 13, the flatness of the layer thickness regulating blade 13 is lost, and the layer thickness of the toner 9 on the developing roller 10 becomes uneven depending on the location.
The thinned state of the toner 9 deteriorates, density unevenness such as vertical stripes occurs in the printed image, and the image quality deteriorates. Therefore, the conventional image forming apparatus requires frequent replacement of the layer thickness regulating blade 13, and has a problem that the durability and reliability of the apparatus are lacking. This problem becomes more remarkable as the peripheral speed of the developing roller 10 increases with high-speed printing.

In this image forming apparatus, it is required that the non-uniformity of the toner layer thickness on the developing roller can be eliminated to obtain a high quality image, and the durability and reliability are excellent.

The present invention eliminates the unevenness of the toner layer thickness on the developing roller to obtain a high quality image, durability,
An object is to provide an image forming apparatus having excellent reliability.

[0011]

In order to solve this problem, an image forming apparatus of the present invention is an image forming apparatus which visualizes an electrostatic latent image formed on a surface of a photoreceptor with toner.
A developing roller carrying toner for developing the electrostatic latent image formed on the surface of the photoconductor to visualize it, a toner supplying roller for supplying toner to the developing roller, and a developing roller arranged in parallel with the developing roller. The toner layer thickness of the roller is regulated and a layer thickness regulation roller that removes accumulated toner by rotation is provided.

As a result, it is possible to eliminate the unevenness of the toner layer thickness on the developing roller and obtain a high quality image, and it is possible to obtain an image forming apparatus having excellent durability and reliability.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is an image forming apparatus for visualizing an electrostatic latent image formed on a surface of a photoconductor with toner, the image forming apparatus being formed on the surface of the photoconductor. A developing roller that carries toner for developing the visualized electrostatic latent image to visualize it, a toner supply roller that supplies toner to the developing roller, and a toner layer thickness of the developing roller that is arranged in parallel with the developing roller. And a layer thickness regulation roller that removes accumulated toner by rotation, and the layer thickness regulation roller contacts the developing roller on the layer thickness regulation surface to regulate the toner layer thickness of the developing roller. At the same time, it has an effect of removing accumulated toner by rotation.

According to a second aspect of the present invention, in the first aspect of the invention, the rotation direction of the layer thickness regulating roller is arranged in the same direction as the rotation direction of the developing roller during printing. It has an effect that the toner layer thickness of the developing roller is regulated and the accumulated toner is efficiently removed.

According to a third aspect of the invention, in the first aspect of the invention, the layer thickness regulating roller is electrically connected so as to rotate in a direction opposite to the rotation direction of the developing roller when removing the accumulated toner. The toner layer thickness of the developing roller is regulated and the accumulated toner is removed more efficiently.

According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, the layer thickness regulating roller is rotated to remove accumulated toner when the developing roller is not printing. In addition, the layer thickness regulating roller performs the layer thickness regulating operation during non-printing, and has an effect of not affecting the printing.

The invention according to claim 5 is the invention as defined in claims 1, 2 and
In the invention described in 3 or 4, the layer thickness regulating roller has a cleaning mechanism for removing the adhered toner, and has an effect of reliably removing the toner adhered to the layer thickness regulating roller. .

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) FIG. 1 is a block diagram showing an image forming apparatus according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing the periphery of a developing roller at the time of printing in the image forming apparatus of FIG. FIG. 2 is a configuration diagram showing the periphery of a developing roller when accumulated toner is removed in the image forming apparatus of FIG. 1 to 3, the photoconductor 1, the charger 2, the charging wire 2a, the shield plate 2
b, exposure optical system 3, exposure light beam 4, developing device 5, toner supply roller 6, toner hopper 7, toner stirring member 8, toner 9, developing roller 10, toner supply bias power source 11, protective resistor 12, layer thickness regulating blade. 13, developing bias power source 14, blade holder 15, recording paper cassette 16, recording paper 17, paper feed roller 18, conveyance roller 19, registration roller 20, driven roller 21, transfer device 22, transfer line 22.
a, the shield plate 22b, the heat roller 23, the pressure roller 24, the fixing device 25, the cleaning blade 26, the toner collecting container 27, and the charge eliminator are the same as those in FIG. Only the functions, characteristics, operations, etc. centering on the developing roller 10 will be described.
In FIG. 2, the layer thickness regulating roller 29 regulates the layer thickness of the developing roller 10, and the accumulated toner 30 is formed between the layer thickness regulating roller 29 and the developing roller 10 during printing.

Next, the toner supply roller 6 and the developing roller 1
General functions, characteristics, structures, etc. centered on 0 will be described. The toner supply roller 6 is formed by forming a conductive foam having a resistivity of 106 Ωcm or less around a metal shaft. The toner supply roller 6 supplies the toner 9 to the developing roller 10 and remains without being developed. It also has a function of scraping off the toner 9 on the developing roller 10.
A toner supply bias power source 11 is connected to the metal shaft of the toner supply roller 6 via a protective resistor 12.

The developing roller 10 has a single-layer structure in which a metal shaft is used as a base material and silicon rubber which is a conductive elastic member having a resistivity of 106 Ωcm is formed on the outer peripheral surface thereof. A developing bias power source 1 is attached to the metal shaft of the developing roller 10.
4 are connected. The rubber hardness of the developing roller 10 is preferably in the range of 30 to 60 degrees, and the surface roughness is preferably 7 μmRz or less because the higher the surface smoothness is, the more uniform the toner thin layer can be formed.

The layer-thickness regulating roller 29 is a roller which is in a fixed state (a state in which it does not rotate) at the time of printing, and a silicon rubber having a resistivity of 106 Ωcm is used on the outer periphery of its metal shaft. The linear pressure on the developing roller 10 is 60 to 10
Pressure is applied to the layer thickness regulating roller 29 so as to be 0 g / cm, preferably 70 to 90 g / cm. Thereby, the layer thickness of the toner 9 on the developing roller 10 can be regulated with high accuracy. The toner 9 has a layer thickness of 0.2 on the surface of the developing roller 10.
~ 1.0 mg / cm ² , preferably 0.4-0.6 mg
/ Cm ² is set. When the layer thickness exceeds 0.6 mg / cm ² , the variation in the charge amount of the toner 9 tends to increase, and particularly when it exceeds 1.0 mg / cm ² , this tendency becomes remarkable, which is not preferable. On the contrary, 0.4 mg
If it is less than / cm ² , the image density in the printed image tends to be reduced, and if it is less than 0.2 mg / cm ² , the image density is rapidly reduced, which is not preferable.

The toner 9 is a non-magnetic negative component type toner, which is obtained by uniformly dispersing carbon, wax, a charge control agent, etc. in a polyester resin, and a negatively charged toner is used here. The bias voltage value of the developing bias power source 14 is −300 V, the bias voltage value of the toner supply bias power source 11 is +300 V, and the resistance value of the protective resistor 12 is 22 MΩ.
It is.

The operation of the image forming apparatus having the above-mentioned structure will be described with a focus on the toner supply roller 6 and the developing roller 10. The process speed is 96 mm / sec, the peripheral speed of the developing roller 10 is 192 mm / sec, and
The peripheral speed ratio to is 2. The layer thickness regulating roller 29 is fixed in contact with the developing roller 10 at a linear pressure of 80 g / cm. The peripheral speed of the toner supply roller 6 is 13
2 mm / sec. The photoconductor 1, the developing roller 10, and the toner supply roller 6 rotate in the directions of the arrows shown in FIG. 1, and the contact portions are in frictional contact. -700V for the photoconductor 1 by the charger 2.
By uniformly charging the photosensitive member 1 with the exposure light beam 4 emitted from the exposure optical system 3 according to the image signal, the potential of the unexposed portion is -700 V, and the potential of the exposed portion is The potential becomes about -100 V, and an electrostatic latent image is formed on the surface of the photoconductor 1.

After being stirred and conveyed by the toner stirring member 8, the toner 9 is supplied to the surface of the developing roller 10 which is a toner carrier by the toner supply roller 6 and is conveyed on the surface thereof. Due to this, the toner layer thickness is regulated, and the toner layer is triboelectrically charged to form a thin layer on the outer peripheral surface of the developing roller 10. Thereafter, the bias voltage applied from the developing bias power source 14 causes the toner 9 to be transferred and attached to the portion of the surface of the photoconductor 1 where the electrostatic latent image is formed, so that the electrostatic latent image is visualized.

Next, by applying a voltage of 1 kV to the transfer line 22a made of a tungsten wire, corona discharge is caused to transfer the toner image on the surface of the photoreceptor 1 onto the recording paper 17. The toner image transferred onto the recording paper 17 is
The fixing and fixing device 25 including the heat roller 23 and the pressure roller 24 fixes the toner on the recording paper 17 by heat and heat, and printing is completed by this fixing.

When printing is repeated by repeating the above process, the toner conveyed by the toner supply roller 6 is transferred to the wedge portion formed by the developing roller 10 and the layer thickness regulating roller 29, as shown in FIG. 9 gradually accumulates. The accumulated toner 30 may be fixed to the layer thickness regulating roller 29 due to stress due to the toner conveying force of the toner supply roller 6, frictional heat generated between the developing roller 10 and the layer thickness regulating roller 29, and the like. Layer thickness control roller 29
Before toner adhesion to the toner occurs, as shown in FIG.
By rotating the layer thickness regulating roller 29 in the counterclockwise direction, the layer thickness regulating surface 31 in contact with the developing roller 10 is renewed and the accumulated toner 30 is removed to prevent the toner sticking. The rotation timing of the layer thickness regulating roller 29 is
The number of sheets to be printed until the toner adherence is obtained in advance by experiments or the like, and the layer thickness regulating roller 2
It suffices to set 9 so that it can be rotated by 90 degrees.

As described above, according to the present embodiment, the layer thickness regulating roller 29 has the layer thickness regulating surface 31 on the developing roller 1.
Since the toner layer thickness of the developing roller 10 is regulated by contacting 0, and the accumulated toner 30 is removed by rotation, the unevenness of the toner layer thickness on the developing roller 10 is eliminated and a high quality image is obtained. Further, by preventing the toner from sticking to the layer thickness regulating roller 29 which is the layer thickness regulating member, frequent replacement of the layer thickness regulating member is unnecessary and the image forming apparatus is excellent in durability and reliability. Can be one.

(Embodiment 2) FIG. 4 is a block diagram showing the periphery of a developing roller when removing accumulated toner in an image forming apparatus according to Embodiment 2 of the present invention. 4, the toner supply roller 6, the developing roller 10, the toner supply bias power source 11, the protective resistor 12, the developing bias power source 14, the layer thickness regulation roller 29, the accumulated toner 30, and the layer thickness regulation surface 31 are the same as those in FIG. Therefore, the same reference numerals are given and description thereof will be omitted. Further, the configuration other than the periphery of the developing roller is the same as the configuration of the image forming apparatus according to the first embodiment of FIG. 1, and the description thereof will be omitted.

The peripheral portion of the developing roller shown in FIG. 4 is different from that shown in FIG. 3 in that the toner 32 attached to the layer thickness regulating roller,
This is that it has a layer thickness regulating roller cleaning blade 33 and a layer thickness regulating roller attached toner collection container 34. The layer-thickness-regulating-roller-attached toner 32 is toner that is attached to the layer-thickness-regulating roller 29. The attached toner 32 is removed. The layer-thickness-regulating-roller-adhered toner collecting container 34 is a container for collecting the layer-thickness-regulating-roller-adhering toner 32 removed by the layer-thickness-regulating-roller cleaning blade 33. The layer thickness regulating roller cleaning blade 33 and the layer thickness regulating roller attached toner collection container 34 constitute a cleaning mechanism.

As described above, according to the present embodiment, the toner layer thickness of the developing roller 10 is regulated by the layer thickness regulating roller 29 which rotates counterclockwise and the accumulated toner is removed, and the layer thickness regulating roller cleaning is performed. Since the toner 32 attached to the layer thickness regulating roller is removed by the blade 33, it is possible to eliminate the unevenness of the toner layer thickness on the developing roller 10 and obtain a high quality image, and it is a layer thickness regulating member. To prevent the toner from sticking to the layer-thickness regulating roller 29 more reliably, the need for frequent replacement of the layer-thickness regulating member is eliminated,
The durability and reliability of the image forming apparatus can be improved.

(Third Embodiment) FIG. 5 is a block diagram showing the periphery of a developing roller when accumulated toner is removed in an image forming apparatus according to a third embodiment of the present invention. In FIG. 5, the toner supply roller 6, the toner supply bias power supply 11, the protective resistor 12, the developing bias power supply 14, the layer thickness regulation roller 2
9, the accumulated toner 30, the layer thickness regulation surface 31, the layer thickness regulation roller adhesion toner 32, the layer thickness regulation roller cleaning blade 33, and the layer thickness regulation roller adhesion toner collection container 34 are the same as those in FIG. However, the description is omitted.
Further, the configuration other than the periphery of the developing roller is the same as in the first embodiment shown in FIG.
The configuration is the same as that of the image forming apparatus according to, and the description thereof will be omitted.

The peripheral portion of the developing roller shown in FIG. 5 is different from that shown in FIG. 4 in that the developing roller 1 rotating clockwise.
0a. That is, the layer thickness regulating roller 29
Simultaneously with the rotation operation of, the developing roller 10a rotates in the direction opposite to the rotation direction (counterclockwise direction) of the layer thickness regulating roller 29.

As described above, according to the present embodiment, the toner layer thickness of the developing roller 10a is regulated and the accumulated toner is removed by the layer thickness regulating roller 29 rotating counterclockwise and the developing roller 10a rotating clockwise. And the toner 32 adhering to the layer thickness regulating roller is removed by the layer thickness regulating roller cleaning blade 33 as in the second embodiment.
It is possible to more surely eliminate the unevenness of the toner layer thickness on a and obtain a high-quality image, and it is more certain to prevent the toner from sticking to the layer thickness regulating roller 29 which is the layer thickness regulating member. As a result, frequent replacement of the layer thickness regulating member is unnecessary, and the durability and reliability of the image forming apparatus can be improved.

[0034]

As described above, according to the image forming apparatus of the present invention, the layer thickness regulating roller is arranged parallel to the developing roller on the layer thickness regulating surface to regulate the toner layer thickness of the developing roller and to rotate the toner layer. Since I tried to remove the accumulated toner,
It is possible to eliminate the unevenness of the toner layer thickness on the developing roller to obtain a good quality image, and to prevent the toner from sticking to the layer thickness regulating roller, which is the layer thickness regulating member. There is an advantageous effect that the image forming apparatus can be made highly durable and reliable without frequent replacement.

Further, by arranging the rotation direction of the layer thickness regulating roller in the same direction as the rotation direction of the developing roller at the time of printing, the toner layer thickness of the developing roller is regulated and the accumulated toner is removed efficiently. The advantageous effect that it is possible is obtained.

Further, when the accumulated toner is removed, the layer thickness regulating roller is electrically connected so as to rotate in the direction opposite to the rotation direction of the developing roller, so that the toner layer thickness of the developing roller is regulated and the accumulated toner is removed. The advantageous effect that it can be performed more efficiently is obtained.

Further, by rotating the layer thickness regulating roller for removing the accumulated toner when the developing roller is not printing, the layer thickness regulating operation by the layer thickness regulating roller is performed during non-printing, which affects printing. The advantageous effect of not giving is obtained.

Further, by providing the layer thickness regulating roller with a cleaning mechanism for removing the adhered toner, the advantageous effect that the toner adhered to the layer thickness regulating roller is surely removed can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing the vicinity of a developing roller during printing in the image forming apparatus of FIG.

FIG. 3 is a configuration diagram showing the periphery of a developing roller when accumulated toner is removed in the image forming apparatus of FIG.

FIG. 4 is a configuration diagram showing a periphery of a developing roller when accumulated toner is removed in an image forming apparatus according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing the periphery of a developing roller when accumulated toner is removed in an image forming apparatus according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a conventional image forming apparatus.

FIG. 7 is a configuration diagram showing the periphery of a developing roller during printing in a conventional image forming apparatus.

[Explanation of symbols]

 1 Photoreceptor 2 Charging Device 2a Charging Line 2b Shield Plate 3 Exposure Optical System 4 Exposure Ray 5 Developing Device 6 Toner Supply Roller 7 Toner Hopper 8 Toner Stirring Member 9 Toner 10, 10a Developing Roller 11 Toner Supply Bias Power Supply 12 Protection Resistor 16 Recording Paper cassette 17 Recording paper 18 Paper feed roller 19 Conveying roller 20 Registration roller 21 Follower roller 22 Transfer device 22a Transfer line 22b Shield plate 23 Heat roller 24 Pressure roller 25 Fixing device 26 Cleaning blade 27 Toner collecting container 28 Static eliminator 29 Layer thickness Regulation roller 30 Accumulated toner 31 Layer thickness regulation surface 32 Layer thickness regulation roller adhesion toner 33 Layer thickness regulation roller cleaning blade 34 Layer thickness regulation roller adhesion toner collection container

Claims (5)

[Claims] 1. An image forming apparatus for visualizing an electrostatic latent image formed on a surface of a photoconductor with toner, wherein the electrostatic latent image formed on the surface of the photoconductor is developed and visualized. For carrying toner, a toner supply roller for supplying toner to the developing roller, and a toner layer thickness of the developing roller arranged in parallel with the developing roller to regulate the toner layer thickness and remove accumulated toner by rotation. And an image forming apparatus having a layer thickness regulating roller. 2. The image forming apparatus according to claim 1, wherein the rotation direction of the layer thickness regulating roller is arranged in the same direction as the rotation direction of the developing roller during printing. 3. The image forming apparatus according to claim 1, wherein the layer thickness regulating roller is electrically connected so as to rotate in a direction opposite to a rotating direction of the developing roller when removing the accumulated toner. 4. The image forming apparatus according to claim 1, 2 or 3, wherein the layer thickness regulating roller rotates for removing accumulated toner when the developing roller is not printing. 5. The image forming apparatus according to claim 1, wherein the layer thickness regulating roller has a cleaning mechanism for removing the adhered toner.