JP2002072686A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a monochrome image forming apparatus or full color image forming apparatuses of various systems including a tandem system inexpensive and excellent in maintainability by gradually automatically exchanging developer with a simple constitution. SOLUTION: A developer recovery part 5 is provided on the backside of a developing unit 1, and a carrying screw 14 is disposed between the recovery part 5 and a developing container 2. The screw 14 continues to a return screw 13 continuing to a 2nd stirring and carrying screw 12, and is formed to make its shaft common to them and its diameter small. The developer carrying base of the screw 14 is higher than the screws. In a state where a proper amount of developer exists in the container 2, the surface of a developer layer does not exceed the base of the screw 14, but when the surface of the developer layer exceeds the base of the screw 14 because the amount of the developer is increased by the replenishment of the replenishing developer, the excess developer is carried to a developer recovery part 5 and then carried out to the outside of an image forming part by the carrying screw 15 of a recovered developer carrying-out means 16.

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 a copying machine or a printer using an electrophotographic system or the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, particularly in an image forming apparatus for forming a chromatic image, a two-component developing method in which a non-magnetic toner and a magnetic carrier are mixed and used as a developer is used. Widely used.

The two-component developing system has advantages such as image stability and durability of the apparatus as compared with other developing systems which are currently proposed. In particular, since deterioration of the carrier is inevitable, it is necessary to perform an operation of exchanging the developer with long-term use of the image forming apparatus.

Several solutions to this problem have been proposed. For example, Japanese Patent Publication No. 2-15991 discloses a developing apparatus for an electrophotographic copying machine having a stirring means for stirring a carrier and a toner, and a developing roller for supplying a developer stirred by the stirring means to a photosensitive member. A carrier replenishing device and a toner replenishing device are provided separately or integrally above the means, a developer overflow portion is provided on a side wall of the developing device housing, and new developer is replenished little by little by the replenishing device. A technique for discharging a developer from an overflow portion is disclosed.

According to the publication, the characteristics of the developer in the housing of the developing device can be kept constant, and as a result, the image quality of the copy can be kept constant. As the old developer is automatically discharged from the overflowing part of the developer automatically, remove the developing device from the copier, take out the old developer in the housing of the same device and remove the new developer as in the conventional case. The developer does not need to perform a troublesome replacement operation of the developer, such as mounting the developing device again after refilling, and the developer is prevented from being scattered.

That is, by gradually replacing the deteriorated developer (carrier) with a new one, the apparent progress of deterioration of the carrier is stopped, and the characteristics of the developer as a whole are stabilized. As a result, the operation of replacing the developer becomes unnecessary, and the maintainability is improved.

Japanese Patent Application Laid-Open No. Hei 9-218575 proposes a configuration in which this method is combined with a rotary developing device. The rotary developing device is provided with a developer replenishing means so that the developer necessary for each developing device is provided. And the excess developer in the developing device is discharged by utilizing the change in the direction of action of gravity due to the rotation of the rotating body. According to the publication, it is possible to discharge excess developer with a simple structure by utilizing the movement unique to the rotating body.

In addition, there is also a method which does not rely on a rotary developing device,
For example, various proposals have been made as shown in JP-A-10-63074.

[0009]

On the other hand, in recent years, as the market for full-color copying machines and printers has expanded and various functions have been required, for example, a plurality of photosensitive drums are arranged to provide high productivity. Many tandem-type image forming apparatuses that perform multiple transfer have been commercialized, and are considered to become one of the mainstream markets in the future.

However, in the image forming apparatus of the tandem system, since the developing devices of the respective colors are fixedly mounted on the respective photosensitive drums, a simple structure as proposed in the above-mentioned Japanese Patent Application Laid-Open No. 9-218575 is used. Can not do it. For this reason, in order to adopt a system in which the developer is gradually replaced in the tandem system, the method disclosed in Japanese Patent Application Laid-Open No. H10-630 is used.
A complicated structure as shown in FIG. 74 had to be taken. This is the same in an image forming apparatus that forms a monochromatic image.

In other words, in the prior art, a developer is used in a single-color image forming apparatus, a tandem type which produces high productivity, and various types of full-color image forming apparatuses which do not employ a rotary developing device in order to make use of various features. In order to improve maintainability by gradually and automatically replacing the device, there is a problem that on the contrary, the structure becomes complicated and the cost of the apparatus itself increases.

Accordingly, an object of the present invention is to automatically and automatically change the developer with a simple configuration in a single-color image forming apparatus or an image forming apparatus that forms a full-color image by various methods such as a tandem method. It is an object of the present invention to provide an image forming apparatus which can improve the maintainability by low cost and has high maintainability at low cost.

[0013]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
The electrostatic latent image formed on the image carrier is developed by a developing unit using a two-component developer to form a visible image, the visible image is transferred to a material to be transferred, and is left on the image carrier after the transfer. An image forming apparatus that collects the collected developer by a cleaning unit, and carries out the collected developer to outside the image forming unit around the image carrier by the collected developer carrying out unit.
The developing means includes a first developer agitating / conveying means on the side closer to the developer carrier and a second developer agitating / conveying means on the far side in the developing container containing the two-component developer via a partition. And the developer agitating / conveying directions are opposite to each other, and the developer conveying means is provided downstream of the second stirring / conveying means in the developer conveying direction, and the bottom surface of the developer is higher than the second stirring / conveying means. And a developer discharge path having the following configuration. An excess developer in the developing container is discharged to the collecting developer discharging means by the developer discharge path.

According to the present invention, the first and second developer stirring / transporting means and the developer transporting means each comprise:
It consists of a rotating screw with spiral blades around it around its axis. Magnetic means may be provided between the second stirring and conveying means and the developer discharge path to magnetically restrict the conveyance of the developer. Furthermore, it has a plurality of the image carriers,
Excess developer in the developing container of the developing means provided for each image carrier is discharged to the recovered developer discharging means through the developer discharging path. A supply developer is supplied to the developing unit.

[0015]

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

Embodiment 1 FIG. 1 is a schematic sectional view showing an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a schematic sectional view showing a developing device installed in the image forming apparatus of FIG.

First, the operation of the entire image forming apparatus will be described with reference to FIG.

Referring to FIG. 1, first, the surface of the photosensitive drum 28 is uniformly charged by the charger 21.
By irradiating with laser light from Step 2 and exposing, an electrostatic latent image is formed on the surface of the photosensitive drum 28, and this latent image is developed by the developing device 1 to form a toner image on the photosensitive drum 1. Is done.

The toner image is transferred to a recording paper 27 conveyed by a transfer belt 24 by a transfer bias applied to a transfer charger 23. The recording paper 27 on which the toner image has been transferred is separated from the transfer belt 24 and fixed. To the container 25,
Then, the toner image is fixed by pressurizing and heating to form a permanent image.

The toner remaining on the photosensitive drum 28 after the transfer is removed by the cleaner 26 to prepare for the next image formation. The cleaner 26 has a transport screw 29 therein, and the transport screw 29 transfers the toner removed by the cleaner 26 to a storage unit (not shown) in the apparatus main body outside the photosensitive drum 1 and the image forming unit around the photosensitive drum 1. Transport. The toner conveyed to the storage unit is collected at an appropriate timing by a service person or the like.

Next, the developing device 1 will be described in detail with reference to FIG.

The developing device 1 contains a two-component developer composed of a non-magnetic toner and a magnetic carrier, and the mixing ratio between the toner and the carrier is about 1: 9 by weight. This ratio should be properly adjusted depending on the charge amount of the toner, the particle size of the carrier, the configuration of the image forming apparatus, and the like, and does not necessarily need to be calculated according to this numerical value.

The developing device 1 includes a photosensitive drum 28 in the developing container 2.
The developing sleeve 3 in which the magnet 4 is non-rotatably disposed is rotatably installed such that a part of the developing region facing the opening is exposed, and a part thereof is exposed to the opening. The developing sleeve 3 is formed of a non-magnetic material, rotates in the direction of the arrow in FIG. 1 during the developing operation, holds the two-component developer in the developing container 2 in a layered form, conveys it to the developing area, and moves the photosensitive drum 28 to the developing area. To the photosensitive drum 28
The electrostatic latent image formed thereon is developed. The developer after developing the latent image is collected in the developing container 2 as the developing sleeve 3 rotates.

In the developing container 2, a first developer stirring and conveying screw 11 (on the side closer to the developing sleeve 3) and a second developer stirring and conveying screw 12 (on the side farther from the developing sleeve 3) are installed. The developer is stirred and mixed by 11 and 12, and is transported and circulated in the container 2. The developer is conveyed in the direction of the first screw 11 in FIG.
2 is a direction from the near side to the back side, and a direction from the back side to the front side in FIG. 2 on the second screw 12 side.

A partition 9 is provided between the developer agitating and conveying screws 11 and 12 so that the developer can be smoothly circulated between the screws 11 and 12 so that the developer is smoothly circulated between the inner side and the front side of the partition 9. Is provided with an opening for transferring the developer. FIG. 2 is a cross-sectional view of the developing device 1 viewed from the back side of the image forming apparatus main body, and the near side in FIG. 2 corresponds to the back side of the apparatus main body.

Next, the replenishment and recovery of the developer, which is a characteristic part of the present embodiment, will be described in detail. FIG. 3 is a view of the developing device of the image forming apparatus and its peripheral portion as viewed from above,
FIG. 4 is a view seen from the rear.

As shown in FIGS. 3 and 4, a developer collecting section 5 is provided at the back of the developing device 1, and a discharge port is provided between the developer collecting section 5 and the developing container 2. A transport screw 14 is provided, and the excess developer in the developing container 2 can be discharged to the developer collecting section 5 by the screw 14. The transport screw 14 for discharging is provided continuously with the return screw 13 following the second developer stirring transport screw 12, has a common axis with the screws 12 and 13, and has a smaller diameter than these. Therefore, the bottom surface of the developer conveyance of the discharging screw 14 is higher than the bottom surface of the developer conveyance of the developer stirring / conveying screw 12 and the return screw 13.

The general state of the layer of the developer 7 in the developing container 2 is as schematically shown in FIGS. The height of the surface of the layer of the developer 7 is close to the center of the axis of the transport screw 12, which is optimal in terms of stirring and transport of the developer,
The screw pitch and the amount of the developer are adjusted so as to obtain the optimum height.

By the action of the return screw 13, the developer at the end of the second stirring / conveying screw 12 passes through the opening on the inner side of the partition 9 and is conveyed to the first stirring / conveying screw 11. Therefore, the surface of the developer layer further on the container end side of the return screw 13 is considerably lower than the axial center of the screw 13.

Since the bottom surface of the screw 14 for transporting the excess developer in the developing container 2 to the developer collecting section 5 is higher than the bottom surfaces of the screws 12 and 13 as described above, a normal appropriate amount of developing When the developer is in the developing container 2, the surface of the developer layer does not exceed the bottom surface of the screw 14. Further, since the screw 14 is provided at a distance from the return screw 13, even if the developer is jumped up by the rotation of the return screw 13, the developer is not conveyed to the collection unit if the amount of the developer is appropriate.

As will be described later, in the present invention, a fixed ratio (10% by weight)
%), The amount of the developer in the developing container 2 increases as the image is formed, when the toner is supplied while the toner concentration is kept constant. When the amount of the developer increases, the return screw 13
Further, the surface of the developer layer on the container end side rises. When the amount of the developer increases until the surface of the developer layer exceeds the bottom surface of the screw 14, the developer passes through the screw 14 and is transported to the developer collection unit 5. The developer conveyed to the collecting section 5 is supplied from a bottom surface of the collecting section 5 to a collecting developer carrying-out means 16 having a screw 15 as shown in FIGS.

The recovered developer carrying-out means 16 is provided with the photosensitive drum 2
The developer discharged by the transport screw 29 installed in the cleaner 26 is also collected by the collection unit 30 for the cleaner 26 in the same manner. The developer collected by the collecting unit 5 as described above is transferred together with the developer removed by the cleaner 26 together with the transport screw 15 of the collected developer discharging means 16.
As a result, the photosensitive drum 28 and its surroundings are discharged from the image forming unit including the image forming unit and conveyed to a storage unit (not shown) in the apparatus main body.

As described above, the toner consumed by the image formation is supplied as a replenishing developer containing the carrier at a fixed rate to the portion 8 on the front side of the developing container 2 according to the rotation of a replenishing screw (not shown). Replenished from above. The supply of the replenishment developer to the developing device 1 is performed from a replenishment developer hopper (not shown). The mixing ratio of the toner and the carrier of the replenishment developer is about 9: 1 by weight, but is not particularly limited to this value.

The replenishment developer has an overwhelmingly large amount of toner as compared with the two-component developer in the development container 2, and considering the volume ratio, it can be considered that a small amount of carrier is mixed in the toner. When supplementing toner consumed by image formation, a small amount of carrier is gradually supplied. If the ratio of the replenished developer carrier increases,
When the same amount of toner is replenished, the carrier replacement amount increases, and the developer in the developing container 2 approaches a fresh state, but the carrier consumption increases accordingly. For this reason,
It is preferable to determine an appropriate mixing ratio separately for each device.

The toner (and carrier) replenishment amount is roughly determined by the number of revolutions of the replenishment screw, and the number of revolutions is determined by a toner replenishment amount control unit (not shown). As a method of controlling the toner supply amount, a method of optically or magnetically detecting the toner concentration of the two-component developer, a method of forming a latent image of a reference image on the photosensitive drum 28, developing the image, and Various methods are known, such as a method of detecting the toner density of an image, and any one of the methods may be appropriately selected.

As described above, the replacement of the two-component developer in the developing device 1 is gradually performed.

As described above, according to this embodiment,
In the developing device fixedly installed with respect to the photoreceptor, the first and second stirring and conveying directions of the developer installed via the partition wall are opposite to each other.
Of the second developer agitating / conveying means, a developer discharge path having a higher bottom surface than the second agitating / conveying means, on the downstream side of the second agitating / conveying means in the developer conveying direction, farther from the developer carrier. Is provided, the excess developer in the developing device to which the replenishment developer is supplied is gradually discharged through the discharge path, and the developer in the developing device can be automatically replaced. The mechanism is also simple. Therefore, it is possible to realize an image forming apparatus that is inexpensive and has high maintainability.

Embodiment 2 FIG. 5 is a schematic sectional view showing another embodiment of the image forming apparatus of the present invention.

As shown in FIG. 5, the image forming apparatus includes yellow (Y), magenta (M), cyan (C), and black (K) image forming stations in the horizontal direction along the intermediate transfer belt 34. The photosensitive drums 28Y, 28M, 28C, and 28K of each station are charged by the chargers 21Y, 21M, 21C, and 21K, exposed by the exposure devices 22Y, 22M, 22C, and 22K, and the developing devices 1Y, 1M, and The yellow, magenta, cyan, and black toner images formed on the photosensitive drum by the development by 1C and 1K are transferred to transfer chargers 23Y and 23 of each station.
M, 23C, and 23K sequentially transfer the image onto the intermediate transfer belt 34 in a superimposed manner, and then collectively transfer the image onto the transfer paper 27 by the secondary transfer charger 23.

After the transfer of the toner image, the photosensitive drums 28Y, 28Y
Transfer residual toner remaining on the surfaces of 8M, 28C and 28K is cleaned by cleaners 26Y, 26M, 26C and 26K. The transfer residual toner remaining on the intermediate transfer belt 34 after the transfer of the toner image is cleaned by a belt cleaner (not shown).

In the intermediate transfer system according to the present embodiment, since the mechanism for transporting the transfer paper 27 is simplified, troubles such as paper jam are unlikely to occur, and various transfer media (materials) such as plain paper and OHP film are used. There is a feature that it can easily cope with.

In this embodiment, the four developing units 1Y to 1K are configured in the same manner as the developing unit 1 of the first embodiment, and the excess developer in the developing containers of the respective developing units 1Y to 1K is removed. The developer is discharged to a collecting section provided on the inner side of each developing device through a developer discharging path whose bottom surface is higher than the second developer stirring / conveying screw and the return screw of the developing device. Then, the developing devices 1Y, 1M, 1C, 1K are
From the cleaners 29Y, 29M, 29C, 2
The developer is collected together with the developer from 9K and can be transported outside the image forming unit.

Therefore, according to this embodiment, not only an image forming apparatus which is inexpensive and has high maintainability can be realized, but also the high productivity which is the feature of the tandem type full-color image forming apparatus and the feature of the intermediate transfer method. By taking advantage of the transfer medium transport stability, which is broadly compatible with transfer media, and by efficiently using the transporter of the cleaner,
The entire image forming apparatus can be reduced in size.

Embodiment 3 In this embodiment, as shown in FIG. 6, which shows the developing unit from the rear of the image forming apparatus, the transport screw 14 for discharging the developer on the back side of the developing container 2 of the developing unit 1 A ring-shaped magnet 17 surrounding the developer collecting section 5 is provided at the outlet of the provided discharge path to magnetically seal and regulate the flow of the developer discharged from the developing container 2. I did it.

In this way, when the surface of the developer layer in the developing container 2 rises, only the unnecessary developer can be discharged to the outside of the developing container 2, and the amount of the developer in the container 2 can be stabilized. Further efforts can be made.

In this case, if the shaft of the second developer stirring and conveying screw 12 is made of a magnetic material, the effect of restricting the flow of the discharged developer is increased. The selection of the magnetism may be determined by the circulation of the developer in the developing container 2.

In this embodiment, the return screw 13 is also provided. However, when a magnetic seal (magnet 17) is provided, the return screw 13 may be omitted, and good results are obtained.

The three embodiments of the present invention have been described above.
The present invention is not limited to those shown in the embodiments, and various modifications and aspects can be adopted in accordance with the technical idea of the present invention.

[0049]

As described above, according to the present invention,
The developing means for developing the electrostatic latent image on the image carrier with the two-component developer is disposed on the downstream side of the developer agitating / conveying means of the developer agitating / conveying means in the developing container at the downstream side in the developer conveying direction. A developer discharge path having a developer conveying means having a higher bottom surface than that of the developer conveying means is provided. The developer is easily discharged through the developer discharge path,
By using the collected developer carrying-out means for carrying out the developer collected by the cleaning means to the outside of the image forming unit, the excess developer of the developing means can be carried out of the image forming unit.
Therefore, for a single-color image forming apparatus or an image forming apparatus that forms a full-color image by various methods such as a tandem method, the developer can be gradually and automatically replaced with a simple configuration to improve maintainability. A low price and high maintainability can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram illustrating a developing device installed in the image forming apparatus of FIG. 1;

FIG. 3 is a view of the developing device and its peripheral portion of the image forming apparatus of FIG. 1 as viewed from above.

FIG. 4 is a rear view of a developing unit of the image forming apparatus of FIG. 1;

FIG. 5 is a schematic sectional view showing another embodiment of the image forming apparatus of the present invention.

FIG. 6 is a rear view of a developing unit according to still another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing container 3 Developing sleeve 5 Developing agent recovery section 12 1st developer stirring and conveying screw 13 2nd developer stirring and conveying screw 14 Developing screw conveying screw 16 Collection developer carrying out means 17 Magnet 30 Collection section

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G03G 21/00 326 (72) Inventor Tomoyuki Sakamaki 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (Reference) 2H030 AB02 AD03 BB22 BB38 2H034 AA06 CA02 CB01 2H077 AA12 AB02 AB14 AB15 AB18 AC02 AC12 AC16 AD06 BA02 BA03 BA08 CA19 EA01 GA04 GA13

Claims (5)

[Claims] An electrostatic latent image formed on an image carrier is developed by a developing means using a two-component developer into a visible image.
The visible image is transferred to a material to be transferred, the developer remaining on the image carrier after the transfer is collected by a cleaning unit, and the collected developer is imaged around the image carrier by a collected developer discharging unit. In the image forming apparatus that is carried out of the forming unit, the developing unit includes a first developer agitating / conveying unit closer to the developer carrier and a second developer agitating / conveying unit farther from the developer container containing the two-component developer. And a second developer agitating / conveying means disposed via a partition wall and in such a manner that the developer agitating / conveying directions are opposite to each other. Also provided is a developer discharge path having a developer transfer means having a high bottom surface of the developer transfer, so that excess developer in the developing container is discharged to the recovered developer discharge means by the developer discharge path. Characteristic image forming apparatus. 2. The apparatus according to claim 1, wherein each of the first and second developer stirring / conveying means and the developer conveying means comprises a rotating screw having a spiral blade provided around the axis thereof. Image forming apparatus. 3. The image forming apparatus according to claim 1, further comprising a magnetic unit for magnetically restricting the conveyance of the developer between the second stirring and conveying unit and the developer discharge path. 4. An image forming apparatus comprising a plurality of image carriers, wherein excess developer in a developing container of a developing unit provided for each image carrier is discharged to the recovered developer discharging unit through the developer discharging path. The image forming apparatus according to claim 1, wherein: 5. The image forming apparatus according to claim 1, wherein a replenishing developer is supplied to said developing unit.