JP3217170B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to a vertical type developing apparatus using a two-component developer applied to a color copying machine.

[0002]

2. Description of the Related Art Conventionally, development using a two-component developer in an electrophotographic image forming apparatus has been performed using a vertical developing apparatus as shown in FIG. In the figure,
A developing device 1 is disposed in proximity to a photosensitive drum 2 serving as an image carrier, and the developing device 1 includes a replenishing tank 3 for storing replenished toner 11 and a developing tank 4. In the supply tank 3, a supply roller 6 and a thin layer blade 7 that are in contact with the supply roller 5 are arranged. A bias circuit 20 for applying a bias voltage is connected to each of the supply roller 5, the supply roller 6, and the thin layer blade 7, and the bias circuit 20 is connected to a reference density pattern 21 formed on the photosensitive drum 2. The amount of charge of the replenishment toner 11 is corrected according to.

A developing sleeve 8 is disposed in the developing tank 4, and a plurality of magnets 8a including a magnet constituting a main developing pole are provided inside the developing sleeve 8 in a support plate 8a.
b, and this developing main pole is set at a position facing the photosensitive drum 2. Then, an upper stirring screw 12 for stirring the developer and a lower stirring screw 14
Is arranged. In the above configuration, the replenishment toner 11 stored in the replenishment tank 3 is rubbed against the surface of the replenishment roller 5 by the supply roller 6 and is carried on the surface, and the thickness of the toner layer is made uniform by the thin layer blade 7. It is transported in the direction of the developing sleeve 8. Then, the toner carried to the developing tank 4 and carried on the surface of the developing sleeve 8 forms a magnetic brush by a plurality of magnets 8a, which is exposed from the opening of the developing tank 4 and is already formed on the photosensitive drum 2. By contacting the electrostatic latent image, the image is visualized and developed.

[0004]

However, in the above-mentioned conventional developing device, it is very difficult to stir and mix the toner magnetically adhered onto the developing sleeve 8 and the carrier. This is remarkable in the above-mentioned vertical developing device having a developer stirring section above the developer.
When insufficient stirring and mixing occurs in the developing device having this configuration,
This causes fluctuations in the density of the toner of each copy, unevenness in the spiral pitch of the upper and lower agitating screws 12, 14, and unevenness in the front and rear density due to poor lateral agitation of the developer. In addition, if the linear velocity of the developing sleeve 8 is reduced for improving the image quality, the stirring and mixing (particularly, the lateral stirring ability) is necessarily reduced, so that there is a problem that the image quality cannot be improved. . Therefore, the present invention solves the above-mentioned conventional problems, and can perform good stirring and mixing of the toner and the carrier of the developer on the developing sleeve, and also has a horizontal stirring ability, thereby enabling high image quality development. It is another object of the present invention to provide a developing device having a simple configuration.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a developing sleeve for carrying a two-component developer comprising a toner and a carrier, an upper stirring screw and a lower stirring screw for mixing the toner and the carrier. A screw, a supply roller for supplying toner, and a supply roller. The lower stirring screw is disposed close to the upper side of the developing sleeve, has a magnet inside, and conveys the developer upward. A conveying roller for the lower stirring screw is provided so as to have a central axis above the central axis,
In the developing device in which the upper stirring screw has a central axis above the center axis of the transport roller, the lower stirring screw has a larger spiral pitch and a larger spiral diameter than the upper stirring screw. It is in.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a developing sleeve which carries a two-component developer composed of a toner and a carrier and forms a developing area between an image carrier and the toner. A replenishing roller for supplying the surface of the two-component developer carried on the developing sleeve, and a two-component developer on the developing sleeve having a magnet therein and supplied with toner by the replenishing roller. A transport roller for transporting upward, an upper stirring screw for stirring and mixing the two-component developer transported upward by the transport roller, and the two-component developer dropped by being stirred and mixed by the upper stirring screw; And a lower agitating screw for agitating and mixing the two-component developer carried on the developing sleeve in the moving direction of the two-component developer. Wherein with the developing region are disposed in this order, the stirring screw is arranged close to the upper side of the developing sleeve, the conveying rollers and,
A developing device provided with a central axis above the central axis of the lower stirring screw, and the upper stirring screw is arranged to have a central axis above the central axis of the transport roller, The spiral pitch of the lower stirring screw is larger than the spiral pitch of the upper stirring screw.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a developing device 1 is arranged close to a photosensitive drum 2 serving as an image carrier, and the developing device 1 includes a supply tank 3 for storing a supply toner 11 and a developing tank 4. In the supply tank 3, a supply sponge roller 6 and a thin layer blade 7 which are in contact with the supply roller 5 are arranged. In the developing tank 4, a developing sleeve 8 and its developing doctor 15, an upper conveying roller 10, a lower conveying roller (conveying roller) 9, an upper conveying screw 12, a screw casing 13, and a lower conveying screw 14 are arranged. Inside the developing sleeve 8, a plurality of magnets (not shown) including a magnet constituting a developing main pole are attached, and the developing main pole is set at a position facing the photosensitive drum 2. Above the developing sleeve 8, a lower conveying roller 9 having an NS 2-pole block magnet provided therein is disposed. Above the lower conveying roller 9, an upper conveying roller 10 having the same internal structure as the lower conveying roller 9 is disposed. . An upper stirring screw 12 and a screw casing 13 are provided at a substantially intermediate position between the upper conveying roller 10 and the lower conveying roller 9, and a lower stirring screw 14 is provided below these.
The screw casing 13 has a slit opening (not shown). Also, the lower stirring screw 14
Has a larger spiral diameter than the upper stirring screw 12,
The spiral pitch is also large. This is because the filling amount of the developer in the portion of the lower stirring screw 14 is larger than the sub-stirring space of the screw casing 13 of the upper stirring screw 12.

In this configuration, the replenishment toner 11 stored in the replenishment tank 3 is rubbed against the surface of the replenishment roller 5 by the supply sponge roller 6, is carried on the surface, and the thickness of the toner layer is The toner is made uniform and transported in the direction of the developing sleeve 8. Then, the toner carried to the developing tank 4 and carried on the surface of the developing sleeve 8 forms a magnetic brush by a plurality of magnets 8a, which is exposed from the opening of the developing tank 4 and is already formed on the photosensitive drum 2. By contacting the electrostatic latent image, the image is visualized and developed.

After the development by the developing sleeve 8 is completed, the lower transport roller 9 removes the developer supplied from the replenishing roller 5 by one.
00% is peeled off and pumped up toward the upper transport roller 10, and the upper transport roller 10 also pumps the supplied developer upward. The rotation directions of the developing sleeve 8, the upper transport roller 10, and the lower transport roller 9 are all counterclockwise. Then, the developer pumped up by the upper transport roller 10 reaches a portion above the developing tank 4 which is not affected by the magnetic force, drops by the gravity below the developing tank 4, is received by the screw casing 13, and It is conveyed from the near side in the figure to the far side by the upper stirring screw 12 rotating in the direction.
At this time, the developer that has overflowed while being conveyed in the screw casing 13 falls downward from the slit opening, and all falls downward from a release port provided near the rear end of the screw casing 13. . The shape of the screw casing 13 enables efficient cross-mixing. The developer that has fallen from the slit opening and the release opening of the screw casing 13 is sufficiently mixed with the developer accumulated therearound while being conveyed from the back side in the figure to the front side by the lower stirring screw 14. Is supplied to the developing sleeve 8. At this time, by setting the rotation speed of the lower stirring screw 14 higher than the rotation speed of the upper stirring screw 12, more effective stirring and mixing is performed.

As described above, the lower stirring screw 14 has a spiral diameter and a larger diameter than the upper stirring screw 12.
And a large spiral pitch, which is necessary to maintain the mixing ratio of the developer and the balance before and after the horizontal stirring of the developer. When the relationship between the spiral pitch and the spiral diameter of the lower stirring screw 14 and the upper stirring screw 12 and the mixing ratio of the developer is examined by an experiment, as shown in FIG. 2, the upper stirring screw 12 (shown by a circle) The spiral pitch and the spiral diameter of the lower stirring screw 14 (indicated by the symbol に お け る) at the point A at which the developer mixing ratio becomes the best are larger than those of the upper stirring screw 12.

Further, when the balance between the spiral pitch and the spiral diameter of the lower stirring screw 14 and the upper stirring screw 12 before and after the developer is examined by an experiment,
As shown in FIG. 3, the spiral pitch and the spiral diameter of the lower stirring screw 14 (indicated by △) at the point B where the front and rear balance are balanced are larger than those of the upper stirring screw 12 (indicated by ○). .

Next, another embodiment will be described with reference to FIG. The configuration of this embodiment is substantially the same as the above embodiment,
The difference is that the upper transport roller 10 is omitted and only the lower transport roller (transport roller) 9 is provided. With this configuration, a sufficient developer transfer (pumping) volume cannot be ensured, but the apparatus becomes simpler and the entire apparatus becomes more compact. The screw casing 13
Has a function of allowing the developer conveyed by the conveying roller 9 to be filled by gravity dropping and peeling and filling. As described above, the developer on the developing sleeve 8 is entirely stripped off by the transport roller (lower transport roller) 9 and vertically transported (including the upper transport roller 10), and then dropped onto the screw casing 13 by gravity. Then, the developer is once held, and sufficient lateral stirring is performed by the upper stirring screw 12. At this time, the developer overflowing in the screw casing 13 escapes from the slit opening, and the developer conveyed laterally drops from the release port. Then, while being laterally conveyed by the lower stirring screw 14, the developer is sufficiently mixed with the developer and supplied to the developing sleeve 8.

[0013]

As described above, according to the present invention, the spiral pitch and the spiral diameter of the lower stirring screw are made larger than those of the upper stirring screw, and the rotation speed of the lower stirring screw is made larger than that of the upper stirring screw. As a result, the stirring and mixing of the toner and the carrier of the developer on the developing sleeve can be satisfactorily performed, the lateral stirring ability can be improved, and the lateral stirring in a well-balanced state can be performed. For this reason, it is possible to prevent the image from being deteriorated such as the fluctuation of the image density and the unevenness of the pitch and the like, and it is possible to perform high-quality development at a compact size and at low cost. Even if the linear velocity of the developing roller is reduced to achieve high image quality, a sufficient stirring effect can be expected.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a developing device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a developer mixing ratio and a spiral pitch (or a spiral diameter).

FIG. 3 is a characteristic diagram illustrating a relationship between a front-rear balance of developer with horizontal stirring and a spiral pitch (or a spiral diameter).

FIG. 4 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a conventional developing device.

[Explanation of symbols]

 Reference Signs List 5 supply roller 6 supply roller 8 developing sleeve 9 transport roller (lower transport roller) 11 toner 12 upper stirring screw 14 lower stirring screw

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Maruta 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Inventor Kaoru Yoshimatsu 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Katsuji Watanabe, Inventor 1-3-6 Nakamagome, Ota-ku, Tokyo Tokyo-72 Ritsuko Yoneda, Inventor Takuji Yoneda 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6, Ricoh Co., Ltd. (72) Inventor Kazuo Nojima 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (56) References JP-A-4-124685 (JP, A) Kai-63-177169 (JP, A) JP-A 2-107164 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08 110

Claims (3)

(57) [Claims] A developing sleeve for carrying a two-component developer comprising a toner and a carrier to form a development area between the image carrier and a two-component developer having a toner carried on the developing sleeve; A replenishing roller for supplying the toner to the surface, a transport roller having a magnet therein for removing the two-component developer on the developing sleeve to which the toner is supplied by the replenishing roller, and transporting the developer upward, and the transport roller An upper stirring screw for stirring and mixing the two-component developer conveyed upward, and a lower stirring screw for stirring and mixing the two-component developer dropped and stirred by the upper stirring screw, When the supply roller, the transport roller, and the developing area are arranged in this order in the moving direction of the two-component developer carried on the developing sleeve, The lower stirring screw is disposed close to the upper side of the developing sleeve, the transport roller is provided to have a central axis above the central axis of the lower stirring screw, and the upper stirring screw is A developing device arranged so as to have a central axis above a central axis of a conveying roller, wherein a spiral pitch of the lower stirring screw is formed larger than a spiral pitch of the upper stirring screw. Developing device. 2. The developing device according to claim 1, wherein a spiral diameter of said lower stirring screw is larger than a spiral diameter of said upper stirring screw. 3. The developing device according to claim 1, wherein a rotation speed of said lower stirring screw is higher than a rotation speed of said upper stirring screw.