JP2000081784A - Developing device and image forming device using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of improving the quality of image formed on a recording paper sheet by equalizing the distance between a photoreceptor drum and a developing roller in a developing area at the time of image forming. SOLUTION: This developing device is provided with the developing roller 117 feeding toner on the photoreceptor drum 102, and the developing roller 117 is composed in a shape that its center part 117a in the lengthwise direction thereof is thinner as compared to both end parts 117b in the lengthwise direction of the same. As a result of the above, when the developing roller 117 receives various kind of force, the center part 117a of the developing roller 117 is pressed toward the photoreceptor drum 102 side, and thus the distance between the developing roller 117 and the photoreceptor drum 102 is equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for, for example, a mono-color or full-color copying machine or printer, and an image forming apparatus using the same. More specifically, the quality of an image formed on a recording medium such as recording paper is improved by equalizing the distance between the image carrier and the image carrier in the developing region during image formation. And an image forming apparatus using the same.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a photosensitive drum that has been charged over its entire surface by exposure of an optical writing unit, and then a developing blade is used to regulate the amount of developer carried by a developing roller. Then, the developer is adhered to the electrostatic latent image on the photosensitive drum to visualize the image and form an image on recording paper. Both the developing roller and the photosensitive drum are composed of cylindrical rotating bodies,
The distance between the photosensitive drum and the developing roller may differ from device to device, or the distance between the photosensitive drum and the developing roller may vary along its longitudinal direction. When such a phenomenon occurs, the development efficiency varies,
The quality of the image formed on the recording paper also deteriorates. In order to cope with such a variation in the distance between the photosensitive drum and the developing roller, for example, in Japanese Patent Application Laid-Open No. 4-350864,
The correction is made by adjusting the developing voltage applied to the photosensitive drum and the developing roller.
In Japanese Patent Publication No. 80, the charging intensity of the charger, the magnitude of the bias voltage, the frequency of the AC bias voltage, and the light intensity of the light source are adjusted or a combination thereof.

[0003]

However, Japanese Unexamined Patent Publication No.
In the technology disclosed in Japanese Patent Application Laid-Open No. 350864 and Japanese Patent Application Laid-Open No. 5-72880, correction is performed at the same rate in the longitudinal direction of the photosensitive drum and the developing roller. If the variation is different in the longitudinal direction, it may be difficult to correct. In particular, since the developing roller and the like rotate during image formation, a frictional force acts between the developing roller and the regulating blade, the supply roller, and the like, so that the developing roller is likely to bend, and the photosensitive drum and the developing roller It is difficult to make the distance between them uniform over its length. If the variation in the distance between the photosensitive drum and the developing roller is considered to be due to insufficient strength of the developing roller, the developing roller may be increased in size and weight in order to increase the strength of the developing roller. This is one solution. However, even if it is intended to increase the size and weight of the developing roller,
There is a limit in recent years when miniaturization and weight reduction of products are required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has been made by making the distance between an image carrier and a developer carrier in a developing area at the time of image formation uniform. For example, it is an object to provide a developing device capable of improving the quality of an image formed on a recording medium such as a recording sheet, and an image forming apparatus using the same.

[0005]

According to the present invention, there is provided a developing apparatus having a developer carrier for holding a developer, wherein the developer carrier is provided at a center in a longitudinal direction. The portion is thinner than both ends in the same longitudinal direction. During image formation, various forces act on the developer carrier, causing the developer carrier to bend, but the central portion in the longitudinal direction of the developer carrier is thinner than both ends in the same longitudinal direction. As a result, the central portion is pressed toward the image carrier and moves toward the image carrier. As a result, the distance between the image carrier and the developer carrier in the development area during image formation is made uniform. be able to. In this case, assuming in advance the unevenness between the image carrier and the developer carrier in the development area during image formation, the central portion in the longitudinal direction of the developer carrier is compared with both ends in the same longitudinal direction. It is desirable that the shape be as thin as possible. In particular, it is good to take into account a bending curve or the like generated in the developer carrying member.

Further, according to the developing device of the present invention, the developer carrying member may be configured to include the core extending in the longitudinal direction and an elastic body disposed outside the core. it can. This allows the elastic body outside the developer carrier to supply the developer while being supported by the core portion, so that the developer can be stably supplied to the image carrier side.

In this case, the developer carrying member has at least one of the core portion and the elastic member whose central portion in the longitudinal direction is thinner than both end portions in the longitudinal direction. It just has to be. Thereby, in consideration of manufacturing costs and the like, only the elastic body outside the developer carrier may be thinner at the center in the longitudinal direction than both ends in the same longitudinal direction, or Only the core may be narrower at the center in the longitudinal direction than at both ends in the same longitudinal direction. However, for both the core portion and the elastic body, the central portion in the longitudinal direction may be thinner than both end portions in the longitudinal direction.

Further, according to the developing device of the present invention, a regulating member that contacts the developer carrier to regulate the layer thickness of the developer, supplies the developer to the developer carrier,
It is possible to provide a supply and recovery unit that can recover the developer on the developer carrier after the development operation.

Thus, the developer carrying member receives a force from, for example, the regulating member and the supply / recovery means, so that
Although the developer carrier is bent, the central portion in the longitudinal direction of the developer carrier is thinner than both ends in the longitudinal direction, and the central portion is pressed toward the image carrier.

Further, according to the image forming apparatus of the present invention,
The image forming apparatus includes: the developing device; an image carrier for carrying an image; and an image forming unit for forming an image on the image carrier. In this image forming apparatus, an image is formed on an image carrier by an image forming means and a developing device. Then, the image on the image carrier is transferred to a recording medium such as a recording sheet.
Note that the image carrier may be a recording medium, and an image may be directly formed on the recording medium. Since such an image forming apparatus has the developing device of the present invention, for example, by making the distance between the image carrier and the developer carrier in the development area during image formation uniform, The quality of an image formed on a recording medium such as a recording medium can be improved.

In this image forming apparatus, it is desirable that the distance between the image carrier and the image material carrier during image formation be uniform. As a result, the development efficiency becomes substantially constant, and density unevenness does not occur in an image formed on a recording medium such as a recording sheet.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying a developing device of the present invention and an image forming apparatus using the same will be described below in detail with reference to the drawings. In the present embodiment, in an electrophotographic image forming apparatus, an image is formed using a nonmagnetic one-component toner developer (hereinafter, simply referred to as toner G1). FIG. 1 is a schematic diagram illustrating a main part of the image forming apparatus according to the embodiment.

As shown in FIG. 1, an organic photoconductive material (OPC) is provided at a substantially central portion in the main body 101 of the image forming apparatus.
Drum 102 having a thin film layer formed of
(Image carrier) is provided rotatably in the direction of arrow A. Around the photosensitive drum 102, a charger 103, a developing device 104, a transfer device 105, and a cleaner 106 are sequentially arranged along the rotation direction of the arrow A, and further, an obliquely upper side of the photosensitive drum 102. Is provided with a laser exposure device 107 as an image forming means. A controller 140 (control means) of the image forming apparatus is provided on a bottom side of the apparatus main body 101. The controller 140 includes a charger 103, a developing device 104, a transfer device 105, a cleaner 106, a laser The exposure device 107 and the like can be controlled.

The charger 103 uniformly charges the entire surface of the thin film layer on the surface of the photosensitive drum 102 while rotating the thin film layer in the direction of arrow A. Further, the laser exposure device 107
Exposes the surface of the photoconductor drum 102 with a laser beam 115 based on image information, thereby forming an electrostatic latent image on the photoconductor drum 10.
2 formed on the surface. In order to form the image information, a reading device IR for reading an image on a document is provided above the image forming apparatus main body 101. Based on the image information read by the reading device IR, the controller 140 Data for driving the exposure apparatus 107 is created. In this case, the surface potential of the photosensitive drum 102 after receiving the laser beam 115 is greatly different between the image portion where the electrostatic latent image is formed and the non-image portion where the electrostatic latent image is not formed. The toner G1 is visualized corresponding to the electrostatic latent image only on the image portion where the electrostatic latent image is formed.

The developing device 104 visualizes the latent image formed on the photosensitive drum 102 by using the toner G1, and rotates in the direction of arrow C at a position adjacent to the photosensitive drum 102. A developing roller 117 (developer carrier) is provided. Further, the developing device 104 has a toner hopper 116 for storing the toner G1, and a regulating blade 118 (regulating member) extending toward the developing roller 117 is disposed above the toner hopper 116. Then, the developing roller 117 of the toner hopper 116
A supply / recovery roller (hereinafter, simply referred to as a supply roller) 119 as a supply / recovery unit for the toner G1 is disposed in the buffer chamber 116a located on the side. Further, a toner storage chamber 116 located on the back side of the toner hopper 116 is provided.
b includes stirring blades 120 that rotate in the direction of arrow B to agitate the toner G1 and supply the toner G1 to the supply roller 119. Further, the developing roller 117
On the lower side, a lower seal 1 that contacts the developing roller 117
21 (static elimination member), and the photosensitive drum 10
Between the developing roller 2 and the developing roller 117, a density sensor 130 for detecting a developing density is provided.

These components will be described in detail. The supply roller 119 rotates while rotating in the direction of arrow D (the same direction as the direction of arrow C) in contact with the developing roller 117.
1 can be supplied to the developing roller 117, so that the regulating blade 118 rotates in the direction of rotation of the developing roller 117 (arrow C).
), The developing roller 117 contacts the developing roller 117 on the downstream side, and the thickness of the thin layer of the toner G1 carried on the developing roller 117 is made constant. On the bottom side of the image forming apparatus main body 101, a bias power supply 114 is provided. The bias power supply 114 has a negative power with respect to the regulating blade 118 so that the toner G1 does not adhere to the regulating blade 118. Apply a bias.

When supplying the toner G1 to the photosensitive drum 102, the developing roller 117
The toner G <b> 1 is applied to the photosensitive drum 102 while rotating in the direction of arrow C while making contact in a contact area (hereinafter referred to as a “development area”) with the photosensitive drum 102. In this case, the developing roller 117
Is made of a conductive material and is connected to the bias power supply 114 so that the developing bias voltage is appropriately applied. Therefore, when the developing bias is applied to the developing roller 117, Toner G1
Moves to the photosensitive drum 102 according to the surface potential of the electrostatic latent image in the developing area. At the time of development, the bias power supply 114 generates an electric field such that the toner G1 is directed from the developing roller 117 to the portion of the photosensitive drum 102 irradiated with the laser beam 115. 1 kHz to 10 kHz
z, duty 10% to 90% offset, voltage -1
An AC bias of 00 V to -800 V is applied.

The lower seal 121 is for removing electricity by frictionally charging the toner G1 to a polarity opposite to the normal charging polarity of the toner G1. For example, a material having good conductivity in which carbon is kneaded is used. Further, the supply roller 119 is connected to the bias power supply 114, and a collection bias can be set between the developing roller 117 and the supply roller 119. Therefore, after the development operation is completed, the collection bias is set. Below, the supply roller 119 can collect the discharged toner G1 remaining on the developing roller 117. Specifically, at the time of collecting the residual toner G1 after the development, the voltage value of the supply roller 119 is set to be higher than the voltage value of the development roller 117 by about 100V.

As described above, the controller 140 can appropriately control the bias power supply device 114. Therefore, the bias power supply device 114 controls the photosensitive drum 102, the developing roller 117, the supply roller 119, the lower seal 121, and the like. A bias voltage is appropriately applied.

A paper feed cassette 108 for storing the recording paper P is provided below the image forming apparatus main body 101, and a cutout for feeding the recording paper P is provided above the paper feed cassette 108. A feed roller 109 is provided.
The photosensitive drum 1 is provided above the sheet cassette 108.
02 is formed, and the recording paper P conveyed in the paper passage 110a is transferred to the photosensitive drum 102 and the transfer device 1 by a pair of paper feed rollers 110b.
05 is transferred to the transfer region 113 interposed between the transfer region 05 and the transfer region 05. Thereafter, in the transfer area 113, the transfer device 105 is sent in synchronization with the movement of the toner G1 image on the photosensitive drum 1 in order to transfer the image of the toner G1 on the photosensitive drum 102 to the recording paper P. From the back side of the recording paper P, the toner G
A transfer charge of a positive polarity opposite to the charge polarity of 1 is given. As a result, the image of the toner G1 on the photosensitive drum 102 is transferred to the recording paper P, and an image is formed on the recording paper P.

On the downstream side of the transfer area 113, a sheet guide 1 for guiding the recording sheet P separated from the photosensitive drum 102
10c, and further, a fixing device 111 is provided downstream of the paper guide 110c, so that the fixing device 111 heats the image of the toner G1 transferred in the transfer area 113 onto the recording paper P. Fix it. Then, the recording paper P sent to the fixing device 111 is discharged onto the discharge stack 112 after the heat fixing.

The cleaner 106 is for removing the toner G1 remaining on the photosensitive drum 102 after the transfer, and has a cleaning blade 106a for removing the toner G1. As a result, the cleaning blade 106a scrapes the toner G1 on the photosensitive drum 102 while contacting the photosensitive drum 102 rotating in the direction A in FIG.
Is housed in the cleaner 106.

Next, the developing roller 117 and the like will be described with reference to FIGS. FIG. 6 is a longitudinal sectional view showing the developing roller 117 in an enlarged manner. FIG. 2 shows the photosensitive drum 1
FIG. 7 is an enlarged plan view illustrating a relationship between the developing roller 117 and a developing roller 117, in which a force is not particularly applied to the developing roller 117. As shown in FIG. 2, the developing roller 117 has a shape in which a central portion 117a in the longitudinal direction is thinner than both end portions 117b in the longitudinal direction. Specifically, as shown in FIG. 6, the developing roller 117 includes a core 117s extending in the longitudinal direction thereof, and an elastic body 117d provided outside the core 117s. In this case, the core 117s is made of a drawn material having a constant diameter and is made of, for example, a metal such as aluminum, whereas the elastic body 117d has a longer center in the longitudinal direction than both ends in the same longitudinal direction. It is formed into a thin shape, for example, from a rubber material. However, if the central portion 117a in the longitudinal direction of the developing roller 117 is thinner than the both ends 117b in the longitudinal direction, for example, as shown in FIG. The elastic body 117d may be made of a rubber material having a constant thickness, which is thinner than both ends in the same longitudinal direction. Further, for both the core portion 117s and the elastic body 117d, the central portion in the same longitudinal direction may be thinner than both ends in the same longitudinal direction.

When the developing device 104 is mounted in the image forming apparatus main body 101, the developing roller 117 receives a static pressing force F1 from the regulating blade 118 as shown in FIG. The pressing roller receives a pressing force F2 from the supply roller 119, and further receives a pressing force F3 from the lower seal 121. As a result, a force F0 obtained by combining the pressing forces F1, F2, and F3 is applied to the developing roller 117.
FIG. 3 is an enlarged side view of a main part of the developing device 104, and FIG. 3A shows a force applied to the developing roller 117 when the developing device 104 is mounted in the image forming apparatus main body 101. FIG. 3B shows the developing roller 11 when the developing roller 117 shown in FIG.
7 shows the working force.

When an image is formed, as shown in FIG. 3B, the developing roller 117
The regulating blade 118, the supply roller 119, and the lower seal 121 are rotated by the
And a frictional force is generated. Therefore, the developing roller 117
Force and pressing force F generated between the blade and the regulating blade 118
1 is applied to the developing roller 117. Similarly, a synthetic force F5 is obtained by synthesizing the frictional force generated between the developing roller 117 and the supply roller 119 and the pressing force F2.
Is applied to the developing roller 117, and the developing roller 117
A resultant force F6, which is a combination of the frictional force generated between the lower seal 121 and the pressing force F3, is applied to the developing roller 117.
Thus, as shown in FIG. 3B, the developing roller 117 applies a force F7, which is a combination of the resultant forces F4, F5, and F6, to the developing roller 117.

When the pressing force F0 or the pressing force F7 is received by the developing roller 117, both ends 1 of the developing roller 117
17b is fixed to a frame (not shown) of the developing device 104, so that as shown in FIG.
17 is pressed toward the photosensitive drum 102 and the developing roller 117 is bent, so that the central portion 117a of the developing roller 117 is bent.
Approaches the photosensitive drum 102. FIG. 4 shows a state after the force shown in FIG. 3B acts on the developing roller 117 shown in FIG.

On the other hand, as shown in FIG. 7A, when the developing roller Q1 has a cylindrical shape, various forces as shown in FIG. 3B act on the developing roller Q1.
As shown in FIG. 7B, the central portion Q1a approaches the photosensitive drum Q2. As a result, the distance between the developing roller Q1 and the photosensitive drum Q2 decreases at the central portion Q1a, but increases at both ends Q1b. Therefore, the adhesion of the toner G1 is good at the central portion Q1a, the developing efficiency is high, and the image density is high. This causes a phenomenon that the image density is reduced.

Here, the case where the distance between the photosensitive drum and the developing roller changes will be specifically described. FIG.
Is a graph showing the relationship between the image density of the toner G1 attached to the photosensitive drum and the area ratio.
Is plotted on the horizontal axis of the graph, the image density increases as the area ratio increases. The distance between the photosensitive drum and the developing roller (for example, 0.20 mm to 0.35 mm
) Changes, there is a density difference depending on the distance between them. Specifically, at a point Q on the graph, the distance between the photosensitive drum and the developing roller is 0.20;
In the case of 0.30, a density difference of about 0.15 occurs. That is, the developing device 104 is connected to the image forming apparatus main body 10.
1, the photosensitive drum 102 and the developing roller 11
For example, if the distance from the image 7 is shifted by 0.1 mm, the image density changes by about 0.15. As a result, the image formed on the recording paper P has density unevenness in the paper width direction.

However, the developing roller 11 of this embodiment
The developing roller 11 has a shape in which a central portion 117a in the longitudinal direction is thinner than both ends 117b in the longitudinal direction.
7 receives the pressing force F7, the developing roller 117 is bent, and the central portion 117a approaches the photosensitive drum 102. As a result, the distance between the developing roller 117 and the photosensitive drum 102 in the developing area becomes substantially uniform (a difference of about 30 μm or less) in the longitudinal direction. The phenomenon that the adhesion of G1 becomes poor does not occur. Accordingly, as a result of the entire developing roller 117 rotating while the core portion 117s is supported by the frame of the developing device 104, the developing roller 11
The elastic body 117d located outside the photosensitive drum 7 can stably supply the toner G1 to the photosensitive drum 102.

In order to make the distance between the developing roller 117 and the photosensitive drum 102 in the developing area substantially uniform along the longitudinal direction, static and dynamic pressure applied to the developing roller 117 is required. It is desirable to predict in advance the deflection of the developing roller 117 due to the above, and to narrow the central portion 117a of the developing roller 117 based on the predicted amount. To
The shape of the developing roller 117 is preferably determined. Specifically, the roller length of the developing roller 117 is 354 mm, the diameter of the roller end is 16 mm, and the diameter of the roller center is 15.52 m.
m, diameter 14 mm, wall thickness 1 mm, pressure 7.3
The gf / mm aluminum core pipe is formed as a drawing material to reduce the cost, and the developing roller 11
The rubber thickness on the surface side of No. 7 was 1 mm at the end and 0.76 at the center.
mm, the change in the diameter from the central portion in the longitudinal direction to both ends is adjusted to the deflection curve of the developing roller 117. However, the force applied in the longitudinal direction of the developing roller 117 is not always uniform, and the amount of deflection varies depending on the roller diameter, the roller length, and the pressure. It is desirable to design the developing roller 117 appropriately in consideration of the above. As a result, the shape of the developing roller 117 from the central portion 117a toward both ends 117b in the same longitudinal direction is not necessarily symmetrical with respect to the central portion 117a.

Next, the operation of the image forming apparatus and the developing device 104 having the above configuration will be described. At first,
When the photosensitive drum 102 rotates in the direction A in the figure, the surface of the photosensitive drum 102 is charged to a predetermined potential when passing below the charger 103. Thereafter, when the charged portion of the photosensitive drum 102 reaches an exposure position (a position facing the laser exposure device 107) with the rotation of the photosensitive drum 102, the laser beam 11 according to the image information is there.
5, an electrostatic latent image is formed.

Next, the toner G1 in the hopper 116 is agitated by the rotation of the stirring blade 120 in the direction B in the figure and is pushed out toward the supply roller 119, and the supply roller 119 rotates in the direction D in the figure. Thus, the toner G1 is supplied to the developing roller 117 side. Developing roller 117
Is transported to the regulating blade 118 side while being carried by the developing roller 117 rotating at a predetermined speed in the direction of arrow C, and the regulating blade 118
To form a thin layer.

Next, the toner G1 uniformly carried on the developing roller 117 in the form of a thin layer is conveyed to the photosensitive drum 102 side. In this case, the distance between the developing roller 117 and the photosensitive drum 102 in the developing area is substantially uniform over the longitudinal direction as shown in FIG. Due to the action of the electric field generated by the control, the toner G
1 moves from the outer peripheral surface of the developing roller 117 to the photosensitive drum 102 in accordance with the surface potential of the electrostatic latent image. Thereby,
The toner G1 is uniformly attached to the electrostatic latent image formed on the photoconductor drum 102 to visualize the electrostatic latent image, and the photoconductor drum 102 rotates while carrying the toner G1 image on its surface. .

The image formed by the toner G1 is transferred to the transfer unit 10
5, the transfer device 10
5, a transfer electric field is applied, whereby the image of the toner G1 is sucked and transferred to the recording paper P side. Then, the recording sheet P to which the image has been transferred by the toner G1 is separated from the photosensitive drum 102, and then sent to the fixing device 111 along the sheet guide 110c.
Is discharged. On the other hand, even after passing through the transfer unit 105, the toner G1 remains slightly on the photosensitive drum 102 where the image of the toner G1 is present (the toner image trace). When the residual toner G1 reaches the cleaner 106, Then, it is scraped and removed by the blade 106a. After the development, the toner G1 remaining on the developing roller 117 moves from the developing roller 117 to the supply roller 119, and is collected by the supply roller 119. After that, the controller 140 sets a developing bias between the developing roller 117 and the supply roller 119, so that the toner G1 carried on the supply roller 119 is
7 and is carried on the developing roller 117 to be used for development.

As described above in detail, according to the present embodiment, the toner G1
In the developing device 104 having the developing roller 117 for supplying the developing roller 117, the developing roller 117
17a is thinner than both ends 117b in the same longitudinal direction, so that the developing roller 117 receives various forces, and the central portion 117a is pressed toward the photosensitive drum 102, resulting in the development in the developing area. Roller 117 and photosensitive drum 1
02 becomes uniform. This improves the quality of the image formed on the recording paper P without causing uneven density.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications can be made without departing from the gist of the present invention. For example, in order to make the contact pressure and the contact width between the supply roller 119 and the developing roller 117 uniform over the longitudinal direction, the central part in the longitudinal direction of the supply roller 119 is thicker than both ends in the same longitudinal direction. May be. In order to detect the life of the developing device 104, a controller 140 (life detecting means)
Counts the number of sheets of recording paper P on which an image is formed, and based on the count value, the controller 140
However, the bias applied to the regulating blade 118 may be changed by controlling the bias power supply 114.

That is, as described above, a negative voltage is applied to the regulating blade 118 to prevent the toner G1 from adhering.
When using No. 4, leakage of the toner G1 and the like occur, which adversely affects the image forming apparatus main body 101. Therefore, when the developing device 104 has exceeded the endurance period, the regulating blade 118
By switching the bias applied to the regulating blade 118.
To make the image formation impossible. As a result, it is impossible to use the developing device 104 when it has exceeded the endurance period, and the image forming apparatus main body 10
Prevents adverse effects on 1. It goes without saying that the present invention may be applied to a full-color copying machine, a facsimile machine, or the like. The present invention can be applied not only to an electrophotographic image forming apparatus but also to a direct recording type image forming apparatus.

[0038]

As described above, according to the developing apparatus of the present invention, the distance between the image carrier and the developer carrier in the developing area during image formation is made uniform, so that, for example, recording paper The quality of an image formed on a recording medium such as a recording medium can be improved. Further, according to the image forming apparatus of the present invention, since the developing device of the present invention is used, an image formed on a recording medium such as a recording sheet does not have density unevenness and a good image is always formed. Is done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a main part of an image forming apparatus according to an embodiment.

FIG. 2 is an enlarged plan view showing a relationship between a photosensitive drum and a developing roller in the image forming apparatus.

FIG. 3 is an enlarged side view of a main part of the developing device, and FIG.
3A shows the force applied to the developing roller when the developing device is mounted on the image forming apparatus. FIG. 3B shows the force acting on the developing roller when the developing roller shown in FIG. Is shown.

4 is an enlarged plan view showing a positional relationship between a developing roller and a photosensitive drum according to the present invention, and shows a state after a force shown in FIG. 3B is applied to the developing roller of FIG. Is shown.

FIG. 5 is a graph showing a relationship between an image density of toner adhered to the photosensitive drum and an area ratio when a distance between the photosensitive drum and a developing roller changes.

FIG. 6 is an enlarged longitudinal sectional view showing a developing roller of the embodiment.

7A is a plan view illustrating a positional relationship between a cylindrical developing roller and a photosensitive drum, and FIG. 7A illustrates a state before a force acts on the developing roller, and FIG. 3) shows a state after the force shown in FIG. 3B acts on the developing roller.

FIG. 8 is a diagram corresponding to FIG. 6 of another embodiment.

[Explanation of symbols]

 G1 Toner 101 Image forming apparatus main body 102 Photoreceptor drum 103 Charger 104 Developing device 107 Laser exposure device 114 Bias power supply 116 Toner hopper 117 Developing roller 117a Central portion of developing roller 117b Both ends of developing roller 117s Core 117d Elastic body 118 Regulation Blade 119 Supply roller 120 Stirrer blade 140 Controller

Claims (6)

[Claims] 1. A developing device having a developer carrier for holding a developer, wherein the developer carrier has a shape in which a central portion in a longitudinal direction is thinner than both end portions in the longitudinal direction. Developing device. 2. The developing device according to claim 1, wherein the developer carrier includes a core extending in the longitudinal direction and an elastic body disposed outside the core. Developing device. 3. The developing device according to claim 2, wherein in the developer carrier, at least one of the core and the elastic body has a center in the longitudinal direction and both ends in the same longitudinal direction. A developing device having a shape smaller than that of the developing unit. 4. The developing device according to claim 1, wherein a regulating member that contacts the developer carrier to regulate a layer thickness of the developer, and supplies the developer to the developer carrier and develops the developer. A developing device comprising: a supply and recovery unit configured to recover the developer on the developer carrier after the operation is completed. 5. The method according to claim 1, wherein:
An image forming apparatus comprising: a developing device described above, an image carrier for carrying an image, and image forming means for forming an image on the image carrier. 6. The image forming apparatus according to claim 5, wherein the distance between the image carrier and the image material carrier during image formation is uniform.