JPH0344663A - Developing device - Google Patents

Abstract

PURPOSE:To effectively prevent the picture quality from degradation owing to the decrease in blade contact pressure by detecting a developer which stays between a blade and a developing roller with a pressure sensor and raising the blade pressure according to the detection result. CONSTITUTION:The blade 18 fixed to a metallic plate 20 abuts on the peripheral surface of the developing roller 11 and is pressed through a cam 24 which is driven by a stepping motor 22. Further, the pressure sensor 26 is incorporated at a proper place of a housing side wall 102 to detect the developer staying between the blade 18 and developing roller 11. When the developer stagnates between the blade 18 and developing roller 11 by more than a constant amount, the pressure sensor 26 detects that and sends a control signal to the motor 22 and the cam 24 rotates by a specific angle to raise the pressing force of the blade 18. Consequently, caking is eliminated and an electrostatic charging quantity is increased, so that the picture quality is prevented from degradation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing device provided in an image forming apparatus such as a copying machine.

[Conventional technology]

Generally, in a developing device that uses a non-magnetic component thread developer, a thin layer forming member such as a blade is pressed against the surface of a developer carrier such as a developing roller with a predetermined pressure, and frictional electrification occurs between the two. By imparting an electric charge to the developer, the developer adheres to a photoreceptor having a predetermined surface potential, thereby forming a developed image. That is, the amount of charge of the developer is determined by the contact pressure between the thin layer forming member and the developer carrier, which in turn determines the state of the image.

However, in such a developing device, as the developer gradually accumulates between the thin layer forming member and the developer carrier, the retained developer sticks to each other, and this solidified developer There is a possibility that a gap may be created between the thin layer forming member and the developer carrier due to the presence of the thin layer forming member, and the contact pressure between the two may be reduced. Since such a decrease in contact pressure directly leads to image deterioration, prevention has become a major issue.

Therefore, Japanese Utility Model Application Publication No. 63-101951 proposes a device in which a developer aggregation preventing member made of a bristle brush or the like is provided near the thin layer forming member.

Furthermore, in Japanese Patent Application Laid-open No. 58-37675, a thin layer forming member (layer thickness regulating means in the same publication) is configured to be able to approach and separate from a developer carrier, and when the number of copies exceeds a predetermined number, In this example, the thin layer forming member is largely separated from the developer carrier, and the accumulated developer is released to another area while remaining on the developer carrier.

Furthermore, Japanese Patent Application Laid-Open No. 63-118170 discloses a device in which the developer carrier is reversely rotated for a certain period of time or by a certain angle after the end of the development process or before the start of the development process, thereby removing the accumulated developer. It is shown.

[Problem to be solved by the invention]

In the device disclosed in Japanese Utility Model Application No. 63-101951, an aggregation prevention member is provided in the space formed by the developer carrier and the thin layer forming member, so that the angle formed between the two can be maintained at an obtuse angle or close to a right angle. However, in the case of a device with a small angle, there is no space for disposing an aggregation prevention member, and it is difficult to apply the method. Furthermore, there is a possibility that the aggregation prevention member itself may disturb the flow of the developer.

Furthermore, in the case of the device disclosed in Japanese Patent Application Laid-Open No. 58-37675, after the accumulated developer is carried to another area while being carried on the developer carrier, the accumulated developer on the developer carrier is scraped off. This requires a means and a container for storing the scraped developer, and there is a disadvantage that the internal structure of the developing device becomes complicated.

Furthermore, in the apparatus of this publication and the apparatus of JP-A No. 63-118170, not only is it necessary to separately perform the removal process of the stagnant developer in addition to the development process, but also the process of removing the stagnant developer is difficult. Regardless of the amount of developer, after a certain intercostal interval (
For example, after the development process has been performed a certain number of times), the processing operation may be executed even when there is not much developer accumulated, or the processing operation may be executed even though the developer has accumulated. This makes it difficult to process at the right time.

In addition, if a means for setting the contact pressure to be strong from the time of assembly and set-up is used, wear and tear of the thin layer forming member and the developer carrier will be accelerated, and the amount of charge of the developer will be excessive, causing the image to disappear. There is an inconvenience that fogging or the like tends to occur.

Incidentally, Japanese Patent Application Laid-Open No. 60-53970 discloses a device equipped with a means for changing the contact pressure between the thin layer forming member and the developer carrier. It controls gradation reproducibility and cannot prevent image deterioration caused by the above-mentioned staying developer.

In view of these circumstances, an object of the present invention is to provide a developing device that can effectively prevent image deterioration caused by developer accumulated between the photoreceptor carrier and the thin layer forming member. do.

[Means to solve the problem]

The present invention includes a developer carrier disposed near a photoreceptor, and a thin layer forming member that is pressed against the surface of the developer carrier to form a thin layer of developer on the developer carrier. In the developing device, the developer detecting means detects the developer accumulated between the thin layer forming member and the developer carrier, and after the developer detecting means detects a certain amount of developer, the thin layer is detected. A pressing force adjusting means for increasing the pressing force of the layer forming member.

[For production]

According to the above configuration, after a certain amount of developer actually accumulates between the developer carrier and the thin layer forming member, the thin layer forming member is pressed against the developer carrier by the action of the pressing force adjusting means. The contact pressure between the two is maintained at an appropriate level.

〔Example〕

An embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a developing device installed in an image forming apparatus such as a copying machine, and this developing device includes a housing 10 containing a non-magnetic component developer D%. The housing 10 is made up of a hopper 13 that accommodates developer and a developer container 14. Inside the developer container 14, a developer roller (developer carrier) 11 and a supply roller 1 are in contact with each other.
2 are arranged. The rotation axes of these rollers 11 and 12 are rotatably supported by both side walls 102 of the housing 10 as also shown in FIG. It is designed to be interlocked and driven in a clockwise direction.

The developing roller 11 is disposed near the photosensitive drum 16, and a blade 18 is disposed on its circumferential surface.

This blade 18 consists of a thin metal plate 20 having flexibility.
The end portion of this metal plate 20 is fixed to an inner plate 101 inside the developer container 14 .

On the other hand, a stepping motor (
) 22 constituting the pressing force adjustment means is fixed, and its drive shaft 2
A cam 24 (constituting a pressing force adjusting means) is connected to the blade 21 , and the peripheral surface of the cam 24 pushes down the metal plate 20 , so that the free end of the blade 18 touches the developing roller 1 .
It is pressed onto the circumferential surface of 1. As the cam 24 rotates through the driving of the stepping motor 22, the force that presses the metal plate 20, that is, the blade 18
The force with which it is pressed against the circumferential surface of the developing roller 11 changes. Specifically, the driving shaft 221 of the stepping motor 22 is driven counterclockwise in FIG. 1, thereby increasing the pressing force on the blade 18.

Further, as a feature of this device, as shown in FIG. 2, a pressure sensor (developer detection means) 26 is incorporated in a proper position on one side wall 102 of the housing. This pressure sensor 26 faces a space surrounded by the circumferential surface of the developing roller 11 and the lower surface of the blade 18, and is located at a position where it comes into contact with a certain amount of developer when a certain amount of developer has accumulated in this space. It is arranged in

The detection signal of this pressure sensor 26 is manually input to a control device (microcomputer; constitutes pressing force adjustment means) 28 as shown in FIG. The control device 28 sends a control signal to the stepping motor 22 when the pressure P detected by the pressure sensor 26 exceeds a predetermined value Po, in fact, when the output voltage of the pressure sensor exceeds a certain value. The stepping motor 22 is rotated by a predetermined angle to increase the pressing force of the blade 18.

Next, the operation of this developing device and the contents of control performed by the control device 28 will be explained with reference to the flowchart of FIG. 3.

First, every time the copying machine performs a copying operation, a developing device performs a developing process (step S1). Specifically, the developing roller 11 and the supply roller 12 are rotationally driven in the counterclockwise direction in FIG. At the contact portion between the supply roller 12 and the developing roller 11, a slight amount of frictional electrification causes the developer to be charged (a negative charge in this embodiment).

This developer is transported to the photosensitive drum 16 while adhering to the circumferential surface of the developing roller 11, and is formed into a thin layer at the contact area between the circumferential surface of the developing roller 11 and the blade 18.
It is further strongly triboelectrically charged and adheres to the circumferential surface of the photoreceptor drum 16, which has been given a positive surface potential in advance, thereby forming a developed image on the photoreceptor drum 16.

When such a developing process is repeated many times, a developer accumulates between the blade 18 and the circumferential surface of the developing roller 11, as shown in FIG. 1, and the amount thereof gradually increases. and,
When the amount of accumulated developer exceeds a certain amount, this amount of accumulated developer begins to come into contact with the pressure sensor 26 (double-dashed line in FIG. 1), and the pressure P detected by the pressure sensor 26 increases, and the amount of the accumulated developer increases. Due to the presence of the agent, the contact pressure between the blade 18 and the developing roller II' begins to decrease.

Here, when the detected pressure P exceeds the predetermined value Po (YES in step S2), a control signal is output from the control device 28 to the stepping motor 22, and the drive shaft 221 and cam 24 of the stepping motor 22 are rotated at a predetermined angle. It is rotationally driven (step S3). As a result, the force that presses the blade 18 toward the developing roller 11 increases, and the contact pressure between the two is maintained appropriately.

As described above, this device actually detects the developer accumulated between the blade 18 and the developing roller 11, and increases the contact pressure of the blade 18 at an appropriate timing based on the detection result. Therefore, image deterioration caused by the above-mentioned staying developer can be effectively prevented.

Note that the present invention is not limited to such embodiments, and may take the following embodiments as examples.

(1> In the present invention, regardless of the specific structure of the pressing force adjusting means, a rotary solenoid or the like may be used in addition to the stepping motor 22, or the pressing force can be adjusted by vertically displacing the blade 18 itself. Alternatively, the circuit may be configured so that the pressing force adjusting means is operated directly by the detection signal of the developer detecting means without using a microcomputer.

(2) In the present invention, other types of sensors such as photosensors may be used in addition to the pressure sensor described above, regardless of the specific structure of the developer detection means. For example, when using a photosensor, as shown in FIG.
02, and the other housing side wall 1.
By incorporating the light-receiving element 32 into 02, it is possible to detect the presence or absence of developer accumulated between the two.

(3) In the present invention, it is also possible to switch the pressing force of the thin layer forming member in multiple stages according to the amount of retained developer. The stepping motor 22 may be rotated in multiple stages.

(4) In the present invention, when the amount of retained developer is reduced, such as when the retained developer is removed by cleaning, the pressing force may be lowered to the original state.

〔Effect of the invention〕

As described above, the present invention actually detects the developer accumulated between the thin layer forming member and the developer carrier, and applies the pressing force to the thin layer forming member at an appropriate timing based on the detection result. Therefore, it is possible to effectively prevent a decrease in the contact pressure of the thin layer forming member due to the presence of the developer and image deterioration caused by this decrease in contact pressure. Further, there is no need to provide a new aggregation prevention means in the developing device, and there is no need to perform a process for removing the accumulated developer separately from the development process.

[Brief explanation of drawings]

FIG. 1 is a sectional side view of a developing device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. The flowchart shown in FIG. 4 is a sectional view corresponding to FIG. 2 of a developing device in another embodiment. D... Developer, 11... Developing roller (developer carrier) 16... Photosensitive drum, 18... Blade (thin layer forming member), 22... Stepping motor (pressing force adjustment means) ), 24... cam (pressing force adjustment means), 26...
... Pressure sensor (developer detection means), 28 ... Control device (pressing force adjustment means), 31 ... Light emitting element (developer detection means), 32 ... Light receiving element (developer detection means).

Claims (1)

[Claims] 1. A developer carrier disposed near the photoreceptor, and a thin layer forming member that is pressed against the surface of the developer carrier to form a thin layer of developer on the developer carrier. In the developing device, a developer detecting means detects the developer accumulated between the thin layer forming member and the developer carrier, and the thin layer is formed after the developer detecting means detects a certain amount of developer. A developing device comprising a pressing force adjusting means for increasing the pressing force of the member.