JPH06208294A - Developing device - Google Patents

Abstract

PURPOSE:To provide the developing device of simple constitution which can well agitate and mix the toners and carriers of a developer on a developing sleeve, has an agitating capacity as well and can make development with high image quality HR. CONSTITUTION:This developing device has the developing sleeve 8, a supply roller 5 and a makeup roller 6. A lower agitating screw 14 is disposed in proximity on the upper side of the developing sleeve 8 and a transporting roller 9 is so provided as to have a central axis upper than the central axis of the lower agitating screw 14. In addition, an upper agitating screw 12 is disposed to have a central axis upper than the central axis of this transporting roller 9. The spiral pitch or spiral diameter of the lower agitating screw 14 is set larger than the spiral pitch or spiral diameter of the upper agitating screw 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying machine, and more particularly to a vertical developing device used in a color copying machine.

[0002]

2. Description of the Related Art Conventionally, HR development using a two-component developer in an electrophotographic image forming apparatus has been carried out using a vertical developing device as shown in FIG. In the figure, a developing device 1 is arranged close to a photosensitive drum 2 which is an image carrier, and the developing device 1 is composed of a replenishing tank 3 for accommodating replenishment toner 11 and a developing tank 4. In the supply tank 3, a supply roller 6 that contacts the supply roller 5 and a thin layer blade 7 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,
The bias circuit 20 corrects the charge amount of the replenishment toner 11 according to the reference density pattern 21 formed on the photosensitive drum 2.

Further, a developing sleeve 8 is arranged in the developing tank 4, and inside the developing sleeve 8, a plurality of magnets 8a including magnets constituting a developing main pole are supported.
The developing main pole is attached to the photosensitive drum 2 at a position facing the photosensitive drum 2. Then, the upper stirring screw 12 and the lower stirring screw 14 that stir the developer.
Are arranged. In the above-mentioned 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, is carried on the surface, and the thickness of the toner layer is made uniform by the thin layer blade 7, It is conveyed 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 the plurality of magnets 8a, which is exposed from the opening of the developing tank 4 and already formed on the photosensitive drum 2. By making contact with the electrostatic latent image being formed, the image is visualized and developed.

[0004]

However, in the above-described conventional developing device, it is very difficult to stir and mix the toner and the carrier of the developer magnetically adhered to the developing sleeve 8, and in particular, This is conspicuous in the above vertical developing device having a developer stirring section above the developing sleeve 8. In the developing device having this configuration, when the mixing and stirring are insufficient, the toner density variation of each copy, the pitch unevenness of the spiral pitch of the upper and lower stirring screws 12 and 14, and the uneven density before and after the horizontal stirring of the developer are caused. Will end up. In addition, the developing sleeve 8 for improving the image quality
When the linear velocity of rotation is reduced, the stirring and mixing (particularly, the horizontal stirring ability) is inevitably deteriorated, so that there is a problem that high image quality cannot be expected. Therefore, the present invention solves the above-mentioned problems of the related art, and can satisfactorily stir and mix the toner of the developer on the developing sleeve and the carrier, and also has a lateral stirrer capability, which enables high-quality HR development. An object of the present invention is to provide a developing device having a simple structure.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a developing sleeve carrying a two-component developer composed of a toner and a carrier, an upper stirring screw and a lower stirring for mixing the toner and the carrier. The screw includes 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 is provided so as to have a central axis above the central axis of the lower stirring screw,
And, in the developing device in which the upper stirring screw is arranged so as to have a central axis above the central axis of the conveying roller, the spiral pitch and the spiral diameter of the lower stirring screw are made larger than those of the upper stirring screw. It is in.

[0006]

Therefore, the toner is supplied onto the developing sleeve by the supply roller and the supply roller. All of the developer (toner and carrier) on the developing sleeve is peeled off by the carrying roller and carried upward, and then the developer falls on the upper stirring screw due to gravity. At this time, the developer is conveyed in the lateral direction by the upper stirring screw, and after sufficient lateral stirring is performed, the developer drops downward. Then, the dropped developer is sufficiently mixed and supplied to the developing sleeve while being laterally conveyed by the lower stirring screw. Since the filling amount of the developer in this portion is larger than that in the upper stirring screw portion, the lower pitching screw has a larger spiral pitch or spiral diameter than the upper stirring screw. It improves the mixing property and keeps the balance before and after horizontal stirring.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a developing device 1 is arranged in the vicinity of a photosensitive drum 2 which is an image carrier, and the developing device 1 is composed of a replenishing tank 3 for accommodating replenishment toner 11 and a developing tank 4. In the supply tank 3, a supply sponge roller 6 and a thin layer blade 7 that are in contact with the supply roller 5 are arranged. Further, 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 forming a developing main pole are attached, and the developing main pole is set at a position facing the photoconductor drum 2. On the upper side of the developing sleeve 8, a lower conveying roller 9 having a block magnet of NS2 pole inside is arranged, and on the upper side thereof, an upper conveying roller 10 having the same internal structure as the lower conveying roller 9 is arranged. . An upper stirring screw 12 and a screw casing 13 are provided at a substantially intermediate position between the upper transporting roller 10 and the lower transporting roller 9, and a lower stirring screw 14 is provided below them.
The screw casing 13 is provided with 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 lower stirring screw 14 is larger than the sub stirring space of the screw casing 13 of the upper stirring screw 12.

In this structure, 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 reduced by the thin layer blade 7. It is homogenized and conveyed toward 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 the plurality of magnets 8a, which is exposed from the opening of the developing tank 4 and already formed on the photosensitive drum 2. By making contact with the electrostatic latent image being formed, the image is visualized and developed.

After the development by the developing sleeve 8 is completed, the lower conveying roller 9 removes the developer supplied from the replenishing roller 5 by one.
Peel off by 00% and scoop up to the upper conveying roller 10, and the upper conveying roller 10 also scoops up the supplied developer. The developing sleeve 8, the upper transport roller 10, and the lower transport roller 9 all rotate counterclockwise. Then, the developer drawn up by the upper conveying roller 10 reaches a portion above the developing tank 4 which is not affected by the magnetic force, and falls to the lower side of the developing tank 4 due to gravity, and is received by the screw casing 13 and is received by the clock. It is conveyed from the front side to the back side in the figure by the upper stirring screw 12 rotating in the direction.
At this time, the developer overflows while being conveyed in the screw casing 13, and the developer falls downward from the slit opening portion, and also falls entirely 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. Then, the developer dropped from the slit opening portion and the release port of the screw casing 13 is sufficiently mixed with the developer accumulated in the periphery thereof while being conveyed from the back side to the front side in the figure by the lower stirring screw 14. And is supplied to the developing sleeve 8. At this time, by making the rotation speed of the lower stirring screw 14 faster than the rotation speed of the upper stirring screw 12, more effective stirring and mixing is performed.

By the way, as described above, the lower stirring screw 14 has a spiral diameter larger than that of the upper stirring screw 12.
Also, the spiral pitch is formed to be large, which is necessary for maintaining the mixing ratio of the developer and the balance before and after the lateral stirring of the developer. When the relationship between the spiral pitch of the lower stirring screw 14 and the upper stirring screw 12 and the mixing ratio of the developer with respect to the spiral diameter is examined by an experiment, as shown in FIG. 2, the upper stirring screw 12 (shown by a circle) is shown. The spiral pitch and the spiral diameter of the lower stirring screw 14 (indicated by Δ) at the point A where the developer mixing ratio is the highest are larger than those of the upper stirring screw 12.

When the balance between the front and rear of the developer with respect to the spiral pitch and the spiral diameter of the lower stirring screw 14 and the upper stirring screw 12 is examined by an experiment,
As shown in FIG. 3, the spiral pitch and the spiral diameter of the lower stirring screw 14 (shown by Δ) at point B where the front and rear balance are balanced are larger than those of the upper stirring screw 12 (shown 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 conveying roller 10 is omitted and only the lower conveying roller (conveying roller) 9 is provided. With this configuration, a sufficient transport (pumping) volume of the developer cannot be secured, but the device becomes simpler and the entire device becomes more compact. The screw casing 13
The shape of (1) has a function of performing gravity drop filling and peeling filling of the developer conveyed by the conveying roller 9. In this way, all the developer on the developing sleeve 8 is stripped off by the transport roller (lower transport roller) 9 and vertically transported in the upward direction (including the upper transport roller 10), and then dropped onto the screw casing 13 by gravity. Then, the developer is once held, and sufficient horizontal stirring is performed by the upper stirring screw 11. At this time, the developer that has overflowed in the screw casing 13 escapes from the slit opening, and the developer conveyed laterally falls from the release port. Then, while being conveyed laterally by the lower stirring screw 14, it 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 larger than those of the upper stirring screw, and the rotation speed of the lower stirring screw is higher than that of the upper stirring screw. Since the speed is increased, the toner of the developer on the developing sleeve and the carrier can be satisfactorily agitated and mixed, and the lateral agitation ability is improved, so that a well-balanced lateral agitation can be performed. For this reason, it is possible to prevent the image deterioration such as the repeat fluctuation of the image density and the pitch unevenness, and it is possible to perform the high quality HR development in a compact size and at a low cost.
Further, 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 drawings]

FIG. 1 is a schematic configuration diagram showing 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 showing a relationship between a developer front-rear balance of lateral 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]

 5 Replenishing roller 6 Supply roller 8 Developing sleeve 9 Conveying roller (lower conveying roller) 11 Toner 12 Upper stirring screw 14 Lower stirring screw

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takayuki Maruta 1-3-3 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Kaoru Yoshimatsu 1-3-3 Nakamagome, Ota-ku, Tokyo・ In Ricoh Co., Ltd. (72) Inventor Katsuji Watanabe 1-3-6 Nakamagome, Ota-ku, Tokyo ・ In Ricoh Co., Ltd. (72) Inventor Takuji Yoneda 1-3-6 Nakamagome, Ota-ku, Tokyo ・In Ricoh Co., Ltd. (72) Inventor Kazuo Nojima 1-3-6 Nakamagome, Ota-ku, Tokyo ・ In Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A developing sleeve 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,
The lower stirring screw is provided adjacent to the upper side of the developing sleeve, has a magnet inside, and is configured to convey the developer upward. In the developing device, the roller is provided so as to have a central axis above the central axis of the lower stirring screw, and the upper stirring screw is arranged so as to have a central axis above the central axis of the conveying roller. The developing device, wherein the spiral pitch of the lower stirring screw is formed larger than the spiral pitch of the upper stirring screw. 2. The developing device according to claim 1, wherein the spiral diameter of the lower stirring screw is larger than the spiral diameter of the upper stirring screw. 3. The developing device according to claim 1, wherein the rotation speed of the lower stirring screw is faster than the rotation speed of the upper stirring screw.