CN117413226A - Developing device and image forming apparatus including the same - Google Patents

Abstract

The invention provides a developing device and an image forming apparatus including the same. The developing devices (3 a-3 d) are provided with a developing container (20), a first agitating and conveying member (25), a second agitating and conveying member (26), and a developer carrier (31). The developing container (20) has a first conveying chamber (21), a second conveying chamber (22), and a communication portion (20). The first stirring and conveying member (25) has a first rotation shaft (23 a) and a first stirring blade (24 a). The second stirring and conveying member (26) has a second rotation shaft (23 b) and a second stirring blade (24 b). The developer carrier (31) is opposed to the second agitating-conveying member (26). The first rotary shaft (23 a) has a tapered portion (36) whose shaft diameter increases toward the downstream side in the developer conveying direction in the first conveying chamber (21) in at least a partial region in the axial direction of the first rotary shaft (23 a).

Description

Developing device and image forming apparatus including the same

Technical Field

The present invention relates to a developing device and an image forming apparatus including the same.

Background

Image forming apparatuses such as copiers, printers, facsimile machines, and complex machines using an electrophotographic system include a developing device for developing an electrostatic latent image formed on an outer peripheral surface of an image carrier, that is, for forming a toner image (visible image) for developing the electrostatic latent image.

As such a developing device, patent document 1 discloses a developing device including: a developing container for accommodating a developer containing toner; a stirring and conveying member that stirs and conveys the developer in the developing container; and a developing roller, a part of which is exposed from an opening formed in the developing container (patent document 1). The developing container includes a first conveying chamber and a second conveying chamber. The stirring and conveying members are respectively arranged in the first conveying chamber and the second conveying chamber.

The stirring and conveying member has a rotation shaft rotatably supported by the developing container and stirring blades formed on an outer peripheral surface of the rotation shaft. The rotation shaft is supported by a bearing portion provided to the developing device and is supported rotatably. The stirring blade rotates around the rotation axis, so that the developer in the developing container is supplied to the developing roller while circulating in the developing container.

Patent document 1: japanese patent laid-open No. 2002-278271

However, for example, in the case of a developing device of the two-component development system, if an image having a high density is continuously developed, a large amount of toner is consumed and replenished at a time. Then, the replenished toner cannot be sufficiently stirred in the developing vessel, and the toner concentration (mixing ratio of the toner in the developer to the carrier: T/C) around the toner replenishing portion (the periphery of the most upstream side portion of the developing vessel in the developer conveying direction) becomes thicker than the other portions. Thus, there is a possibility that density unevenness occurs on the formed image. In addition, since the toner and the carrier in the developing container are not sufficiently stirred, it is difficult for the toner to be appropriately charged. Therefore, there is a possibility that the image may generate so-called fog of the negative film, and the toner having insufficient charging may fly and contaminate the inside of the image forming apparatus.

Disclosure of Invention

The invention aims to provide a developing device capable of inhibiting insufficient stirring of developer in a developing container.

In order to achieve the above object, a first structure of the present invention relates to a developing device including a developing container, a first agitating-conveying member, a second agitating-conveying member, and a developer carrier. The developing container accommodates a developer containing toner, and has a first conveying chamber, a second conveying chamber disposed in parallel with the first conveying chamber via a partition, and a communication portion that communicates the first conveying chamber and the second conveying chamber on both end sides in a longitudinal direction of the partition. The first agitating and conveying member agitates and conveys the developer in the first conveying chamber, and has a first rotary shaft rotatably supported in the first conveying chamber, and a first agitating blade formed on an outer peripheral surface of the first rotary shaft. The second agitating and conveying member agitates and conveys the developer in the second conveying chamber, and has a second rotation shaft rotatably supported in the second conveying chamber, and a second agitating blade formed on an outer peripheral surface of the second rotation shaft. The developer carrier is opposed to the second agitating-conveying member, and carries toner in the second conveying chamber on the surface. The first rotation shaft has a tapered portion in at least a partial region in an axial direction of the first rotation shaft, the shaft diameter of the tapered portion increasing toward a downstream side in a developer conveying direction in the first conveying chamber.

According to the first configuration of the present invention, since the first rotation shaft has the tapered portion, the volume of the first conveyance chamber becomes smaller from the upstream side to the downstream side. That is, the amount of developer that can be conveyed by the first agitation conveying member gradually decreases from the upstream side to the downstream side in the developer conveying direction. Therefore, the developer in the first conveying chamber is conveyed while being pushed back to the upstream side in the middle of being directed to the downstream side. Thereby, the developer is conveyed to the second conveying chamber in a state of being sufficiently stirred in the first conveying chamber. Accordingly, it is possible to provide a developing device capable of suppressing insufficient agitation of the developer in the developing container.

Drawings

Fig. 1 is a cross-sectional view showing an internal structure of an image forming apparatus 100 in which developing devices 3a to 3d according to a first embodiment of the present invention are mounted.

Fig. 2 is a perspective view of the developing device 3a showing a state in which the cover member 61 and the developing roller 31 are detached.

Fig. 3 is a side sectional view of the developing device 3a in a state where the cover member 61 and the developing roller 31 are mounted.

Fig. 4 is a plan sectional view showing a cross section of an agitating portion of the developing device 3a obtained by sectioning the developing device 3a with a section line A-A shown in fig. 3.

Fig. 5 is a plan view showing a modification of the developing device 3a of the present invention.

Fig. 6 is a plan view showing another modification of the developing device 3a according to the present invention.

Fig. 7 is a side sectional view showing the developing container 20 supplied to the conveying chamber 22.

Fig. 8 is a plan sectional view showing a cross section of an agitating portion of the developing device 3a of the second embodiment.

Fig. 9 is a flowchart showing an example of a control flow of the driving unit 40.

Fig. 10 is a plan sectional view of the developing device in a state in which the reverse rotation mode is performed from the state of fig. 8.

Fig. 11 is a side sectional view of the developing device 3a of the second embodiment.

Detailed Description

Hereinafter, a first embodiment of the developing devices 3a to 3d and the image forming apparatus 100 including the developing devices 3a to 3d according to the present invention will be described with reference to the drawings.

Fig. 1 is a cross-sectional view showing an internal structure of an image forming apparatus 100 in which developing devices 3a to 3d according to a first embodiment of the present invention are mounted. In the main body of the image forming apparatus 100 (here, a color printer), four image forming portions Pa, pb, pc, pd are arranged in order from the upstream side in the conveying direction (left side in fig. 1). These image forming portions Pa to Pd are provided so as to correspond to images of four different colors (cyan, magenta, yellow, and black), and each sequentially forms images of cyan, magenta, yellow, and black through respective steps of charging, exposing, developing, and transferring.

Photosensitive drums (image carriers) 1a, 1b, 1c, 1d that carry visible images (toner images) of respective colors are disposed in the image forming portions Pa to Pd, and an intermediate transfer belt 8 that rotates counterclockwise in fig. 1 is disposed adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on an intermediate transfer belt 8, and the intermediate transfer belt 8 moves while being in contact with the photosensitive drums 1a to 1 d. Then, the toner image primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a transfer sheet S, which is an example of a recording medium, by a secondary transfer roller 9. Further, the transfer sheet S to which the toner image is secondarily transferred is fixed with the toner image in the fixing unit 13, and then discharged from the main body of the image forming apparatus 100. While the photosensitive drums 1a to 1d are rotated clockwise in fig. 1 by a main motor (not shown), image forming processing is performed for each photosensitive drum 1a to 1 d.

The transfer sheet S to which the toner image is secondarily transferred is accommodated in a sheet cassette 16 disposed at a lower portion of the main body of the image forming apparatus 100, and is conveyed to a nip portion between the secondary transfer roller 9 and the driving roller 11 of the intermediate transfer belt 8 by a sheet feeding roller 12a and a registration roller pair 12 b. The intermediate transfer belt 8 is a sheet made of a dielectric resin, and a seamless belt is mainly used. Further, a scraper-like belt cleaner 19 is disposed downstream of the secondary transfer roller 9, and the belt cleaner 19 is configured to remove toner and the like remaining on the surface of the intermediate transfer belt 8.

Next, image forming portions Pa to Pd will be described. Around and below the photosensitive drums 1a to 1d arranged rotatably, there are provided: charging devices 2a, 2b, 2c, 2d charge the photosensitive drums 1a to 1d; an exposure device 5 that exposes the image information to the photosensitive drums 1a to 1d; developing devices 3a, 3b, 3c, 3d for forming toner images on the photosensitive drums 1a to 1d; and cleaning devices 7a, 7b, 7c, and 7d for removing the developer (toner) remaining on the photosensitive drums 1a to 1 d.

When image data is input from a host device such as a personal computer, the surfaces of the photosensitive drums 1a to 1d are charged by the charging devices 2a to 2d in the same manner. Then, the exposure device 5 irradiates light based on the image data, and forms electrostatic latent images corresponding to the image data on the photosensitive drums 1a to 1 d. The developing devices 3a to 3d are filled with two-component developers containing toners of respective colors of cyan, magenta, yellow, and black in predetermined amounts, respectively. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d is lower than a predetermined value due to the formation of a toner image described later, the toner is supplied from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toners in these developers are supplied to the photosensitive drums 1a to 1d by the developing devices 3a to 3d, and form toner images corresponding to electrostatic latent images formed by exposure from the exposure device 5 by electrostatic adhesion.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are primarily transferred on the intermediate transfer belt 8. In order to form a predetermined full-color image, images of the four colors are formed in a predetermined positional relationship. Then, in order to prepare for the next formation of a new electrostatic latent image, the cleaning devices 7a to 7d remove the toners and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer.

The intermediate transfer belt 8 is set up between the driven roller 10 on the upstream side and the driving roller 11 on the downstream side, the secondary transfer roller 9 is provided adjacent to the driving roller 11, and if a belt driving motor (not shown) rotates the driving roller 11 and drives the intermediate transfer belt 8 to start rotating in the counterclockwise direction, the transfer sheet S is conveyed from the registration roller pair 12b to a nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 at a predetermined timing, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the transfer sheet S. The transfer sheet S to which the toner image is secondarily transferred is conveyed to the fixing portion 13.

The transfer sheet S fed to the fixing section 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer sheet S, thereby forming a predetermined full-color image. The transfer sheet S on which the full-color image is formed is conveyed in the direction of conveyance by the branching section 14 branching in a plurality of directions, and is discharged to the discharge tray 17 as it is (or after being conveyed to the duplex conveying path 18 and having images formed on both sides) by the discharge roller pair 15.

Fig. 2 is a perspective view of the developing device 3a showing a state in which the cover member 61 and the developing roller 31 are detached. Fig. 3 is a side sectional view of the developing device 3a in a state where the cover member 61 and the developing roller 31 are mounted. In the following description, the developing device 3a disposed in the image forming portion Pa of fig. 1 is exemplified, but the configuration of the developing devices 3b to 3d disposed in the image forming portions Pb to Pd is also substantially the same, and therefore, the description thereof is omitted.

As shown in fig. 2 and 3, the developing device 3a includes a developing container 20, and the developing container 20 accommodates a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and a toner. The developing container 20 includes a stirring and conveying chamber 21 (first conveying chamber), a supply and conveying chamber 22 (second conveying chamber), a partition wall 20a, communication portions 20b and 20c, a cover member 61, and a toner replenishing portion 32.

The stirring and transporting chamber 21 and the supplying and transporting chamber 22 are arranged in parallel. The partition wall 20a is provided inside the developing container 20, dividing the interior of the developing container 20 into a stirring and conveying chamber 21 and a supply and conveying chamber 22. The communication portions 20b and 20c communicate the stirring and transporting chamber 21 with the supply and transporting chamber 22 at both ends of the partition wall 20a in the longitudinal direction. The cover member 61 closes the upper portion of the developing container 20, and separates the inner space and the outer space of the developing container 20.

The stirring and conveying chamber 21 and the supply and conveying chamber 22 are provided with a first stirring and conveying member 25 and a second stirring and conveying member 26, respectively, and the first stirring and conveying member 25 and the second stirring and conveying member 26 are used to mix and stir the toner supplied from the toner container 4a (see fig. 1) with the magnetic carrier and charge the toner. The first stirring and transporting member 25 and the second stirring and transporting member 26 are rotatably supported by bearing portions (not shown) fixed to the developing container 20 via shaft support portions 52 provided at both end portions in the axial direction.

By rotating the first agitating and conveying member 25 and the second agitating and conveying member 26, the developer is conveyed in the axial direction (direction perpendicular to the paper surface of fig. 3) while being agitated, and the developer circulates between the agitating and conveying chamber 21 and the supply and conveying chamber 22 via the communicating portions 20b and 20c formed at both end portions of the partition wall 20 a. That is, a circulation path of the developer is formed in the developing container 20 by the agitation and conveyance chamber 21, the supply and conveyance chamber 22, and the communication parts 20b and 20c.

As shown in fig. 3, a developing roller (developer carrier) 31 is disposed obliquely above and to the right of the second agitating and conveying member 26 provided in the supply conveying chamber 22 in the developing container 20. Further, a part of the outer peripheral surface of the developing roller 31 is exposed from the opening 20e of the developing container 20, and faces the photosensitive drum 1 a. The developing roller 31 rotates in a counterclockwise direction in fig. 3. The first agitating and conveying member 25, the second agitating and conveying member 26, and the developing roller 31 are rotated at a predetermined rotational speed by a driving force from a main motor (not shown).

The developing roller 31 is composed of a cylindrical developing sleeve (not shown) that rotates counterclockwise in fig. 3, and a magnet (not shown) having a plurality of magnetic poles fixed in the developing sleeve. In addition, although a development sleeve whose surface is knurled is used here, a development sleeve whose surface is formed with a plurality of concave shapes (pits) or a development sleeve whose surface is shot-blasted may be used, and further, a development sleeve which is shot-blasted or subjected to plating treatment in addition to knurling or concave shape formation may be used.

As shown in fig. 3, the regulating blade 33 is attached to the developing container 20 along the longitudinal direction of the developing roller 31 (the direction perpendicular to the paper surface of fig. 3). A minute gap (interval) is formed between the tip end portion of the regulating blade 33 and the surface of the developing roller 31. The regulating blade 33 regulates the layer thickness of the toner supplied to the outer peripheral surface of the developing roller 31 to a predetermined thickness by the minute gap.

A developing voltage power supply (not shown) is connected to the developing device 3a via a voltage control circuit (not shown). The developing voltage power supply applies a developing voltage obtained by superimposing a direct-current voltage and an alternating-current voltage to the developing roller 31. The developer is attached (carried) to the surface of the developing roller 31 by the developing voltage and the magnetic force of the magnet in the developing roller 31 to form a magnetic brush.

As shown in fig. 3, a toner concentration sensor 27 is disposed on the bottom surface of the agitation and conveyance chamber 21 so as to face the first agitation and conveyance member 25 in the height direction (up-down direction in fig. 3). The toner concentration sensor 27 is located at a predetermined position (position where the value of the toner concentration rises to the highest) in the developer conveying direction of the agitation conveying chamber 21 (refer to fig. 4). The toner concentration sensor 27 is connected to a control unit 59 (see fig. 1), and the control unit 59 is provided at a predetermined portion of the image forming apparatus 100.

The toner concentration sensor 27 detects the magnetic permeability of the developer in the developing container 20, and sends the detection result to the control portion 59. Based on the detection result, the control unit 59 determines the toner concentration in the developer (mixing ratio of the toner in the developer to the carrier: T/C), and determines whether or not to replenish the toner. The closer the toner concentration is to the reference value (for example, 6%), the more the toner is properly stirred. The control unit 59 controls the rotation driving of the first stirring and conveying member 25 and the second stirring and conveying member 26 and the replenishment of the toner so that the toner concentration approaches the reference value.

As shown in fig. 2, the toner replenishing portion 32 is provided at a side portion of the developing container 20 in the axial direction. The toner replenishing portion 32 includes a replenishing port 58 and a toner replenishing path 34. The replenishment port 58 opens at an upper portion of the toner replenishment portion 32. The replenishment port 58 is connected to the toner container 4a (see fig. 1). The toner replenishing path 34 extends downward from the replenishing port 58 and communicates with the agitation conveying chamber 21 from the upstream side in the developer conveying direction (see fig. 4). The toner stored in the toner container 4a is replenished to the agitation and conveyance chamber 21 through the replenishment port 58 and the toner replenishment path 34.

When replenishing toner, the control unit 59 transmits a control signal to a toner replenishing motor (not shown). In response to the control signal, the toner replenishing motor replenishes the toner in the toner containers 4a to 4d into the developing container 20 via the toner replenishing portion 32 (see fig. 2). At this time, the control section 59 detects the toner concentration of the developer in the developing container 20 by the toner concentration sensor 27, and controls the toner replenishing motor to replenish the toner so that the detected toner concentration approaches a predetermined reference value (6%).

Next, the structure of the stirring portion of the developing device 3a will be described in detail. Fig. 4 is a plan sectional view showing a cross section of an agitating portion of the developing device 3a obtained by sectioning the developing device 3a with a section line A-A shown in fig. 3.

As described above, the partition wall 20a extends along the longitudinal direction of the developing container 20, and divides the agitation and transport chamber 21 and the supply and transport chamber 22 in parallel. As shown in fig. 4, an end portion on one side (left side in fig. 4) in the longitudinal direction of the partition wall 20a forms an upstream side communication portion 20b together with a side wall portion 29b of the developing container 20. The end portion of the other side (right side in fig. 4) of the partition wall 20a in the longitudinal direction forms a downstream side communication portion 20c together with the side wall portion 29a of the developing container 20.

As shown in fig. 2 and 4, a first agitation and conveyance member 25 is disposed in the agitation and conveyance chamber 21, and a second agitation and conveyance member 26 is disposed in the supply and conveyance chamber 22. The first agitation conveying member 25 has a first rotation shaft 23a, a first helical blade 24a (first agitation blade), and a supplementary blade 35. The second agitating-conveying member 26 has a second rotation shaft 23b and a second helical blade 24b (second agitating blade).

The first rotation shaft 23a is a cylindrical shaft body extending in the longitudinal direction of the developing container 20 (the developer conveyance direction). The first rotation shaft 23a extends to the vicinity of both end portions in the axial direction of the developing container 20. An end portion on the upstream side of the first rotation shaft 23a in the developer conveying direction protrudes outward in the axial direction from the agitation conveying chamber 21 and is located in the toner replenishing path 34.

The first rotation shaft 23a has a tapered portion 36 and a straight portion 37. The tapered portion 36 and the straight portion 37 are axially adjacent portions of the first rotation shaft 23 a. The tapered portion 36 is located between the upstream side end portion of the first rotation shaft 23a and the central portion in the developer conveying direction (preferably, at a position overlapping the upstream side communication portion 20b in the developer conveying direction).

The shaft diameter of the tapered portion 36 increases conically from the upstream side toward the downstream side in the developer conveying direction in the agitation conveying chamber 21. The shaft diameter D1 of the downstream end portion of the tapered portion 36 in the developer conveying direction is 1.2 times or more and 1.5 times or less than the shaft diameter D2 of the upstream end portion of the tapered portion 36 in the developer conveying direction.

The straight portion 37 is connected to a downstream side end portion of the tapered portion 36 in the developer conveying direction. The shaft diameter of the straight portion 37 is the same as the shaft diameter D1 of the downstream end portion of the tapered portion 36 in the developer conveying direction, and is constant without changing toward the downstream side in the developer conveying direction.

The axial length L1 of the tapered portion 36 is 0.25 to 0.9 times the total length L3 of the first rotation shaft 23 a. The axial length L1 of the tapered portion 36 is preferably 0.25 to 0.95 times (more preferably 0.4 to 0.6 times) the axial length L2 of the portion of the first rotary shaft 23a located in the stirring and transporting chamber 21.

The first helical blade 24a is formed on the outer peripheral surface of the first rotary shaft 23 a. The first helical blade 24a is formed integrally with the first rotary shaft 23a, and is formed in a spiral shape at a constant pitch in the axial direction. The first helical blade 24a extends in the developer conveying direction from a position of the agitation conveying chamber 21 overlapping the upstream side communication portion 20b to a position of the agitation conveying chamber 21 overlapping the downstream side communication portion 20c.

The outer diameter D3 of the first helical blade 24a is 1.5 times or more and 1.8 times or less (preferably 1.6 times or more and 1.7 times or less) the shaft diameter D1 of the downstream side end portion of the tapered portion 36.

The replenishment blade 35 is formed on the outer peripheral surface of the portion of the first rotation shaft 23a located in the toner replenishment path 34. The supplementary blade 35 is formed integrally with the first rotation shaft 23a, and is formed in a spiral shape at a constant pitch in the axial direction. The supplementary blade 35 is formed to be wound in reverse direction with the first helical blade 24 a. The toner conveyance amount per pitch of the replenishment blade 35 is smaller than the developer conveyance amount per pitch of the first helical blade 24a located at the upstream side end portion in the developer conveyance direction of the tapered portion 36. Specifically, the pitch of the supplementary blades 35 is smaller than the pitch of the first helical blades 24a, and the outer diameter D4 of the supplementary blades 35 is smaller than the outer diameter D3 of the first helical blades 24 a.

The axial diameter of the second rotary shaft 23b is constant over the entire axial region, and is a value of 0.9 times or more and 1.1 times or less of the axial diameter D1 of the downstream end portion of the tapered portion 36. That is, the shaft diameter of the second rotary shaft 23b is larger than the shaft diameter D2 of the upstream end portion of the tapered portion 36. The second helical blade 24b is formed on the outer peripheral surface of the second rotation shaft 23b. The second helical blade 24b is formed integrally with the second rotary shaft 23b, and is formed in a spiral shape at a constant pitch in the axial direction. The outer diameter of the second helical blade 24b is the same as the outer diameter D3 of the first helical blade 24 a. The second helical blade 24b is formed to be wound in reverse direction with the first helical blade 24 a. The second helical blade 24b extends in the developer conveying direction from a position of the agitating-conveying chamber 21 overlapping the upstream-side communication portion 20b to a position of the agitating-conveying chamber 21 overlapping the downstream-side communication portion 20c.

If the first agitating and conveying member 25 and the second agitating and conveying member 26 rotate, the developer in the developing vessel 20 is agitated by the first helical blade 24a and the second helical blade 24b, and circulated from the agitating and conveying chamber 21 to the upstream side communicating portion 20b, the supply conveying chamber 22, and the downstream side communicating portion 20c (refer to fig. 2). At this time, the developer in the supply conveyance chamber 22 is supplied to the developing roller 31.

As described above, since the first rotation shaft 23a has the tapered portion 36, the volume of the agitation and conveyance chamber 21 becomes smaller from the upstream side to the downstream side. That is, the amount of developer that can be conveyed by the first agitating-conveying member 25 gradually decreases from the upstream side to the downstream side in the developer conveying direction. Therefore, the developer in the agitation and conveyance chamber 21 is conveyed while being pushed back to the upstream side in the middle of being directed to the downstream side. Therefore, the developer is conveyed to the supply conveyance chamber 22 in a state of being sufficiently stirred in the stirring conveyance chamber 21. Accordingly, it is possible to provide the developing device 3a capable of suppressing the lack of agitation of the developer in the developing container 20.

However, there has been conventionally a developing device configured as follows: the volumes of the agitating-conveying chambers and the supply-conveying chambers themselves from which the respective agitating-conveying members are removed become smaller from the upstream side toward the downstream side in the developer conveying direction, and the outer diameters of the helical blades of the respective agitating-conveying members (the first agitating-conveying member and the second agitating-conveying member) become smaller from the upstream side toward the downstream side. In such a developing device, the amount of developer that can be conveyed by the agitating and conveying member decreases sharply from the upstream side toward the downstream side in the developer conveying direction. Therefore, at the periphery of the downstream side end portion of the agitation and conveyance member (the periphery of the communicating portion that communicates the agitation and conveyance chamber and the supply and conveyance chamber), there is a possibility that the developer becomes difficult to convey and the developer stagnates. Then, around the portion where the developer is retained, there is a possibility that the toner adheres to the rotation shaft of the stirring and conveying member, and the shaft diameter increases, so-called shaft thickness occurs.

On the other hand, the developing devices 3a to 3d of the present invention have a structure in which the shaft diameter of the first rotary shaft 23a increases in a tapered portion 36. In addition, the outer diameter D3 of the first helical blade 24a is constant, and the volume of the agitation conveying chamber 21 itself from which the first agitation conveying member 25 is removed is also constant. Therefore, the developer conveyance amount in the agitation conveyance chamber 21 gradually decreases from the upstream side to the downstream side. Therefore, the developer in the agitation and conveyance chamber 21 can be smoothly conveyed, and the retention of the developer can be suppressed.

In the present invention, the shaft diameter of the second rotary shaft 23b is equal to the shaft diameter D1 of the downstream end portion of the first rotary shaft 23a (0.9 times or more and 1.1 times the shaft diameter D1), and is constant over the entire axial region. Therefore, in the downstream communication portion 20c, the conveyance amount of the developer is less likely to change, and the developer stagnation can be suppressed. Therefore, the developing devices 3a to 3d according to the present invention can suppress the stagnation of the developer and suppress the lack of agitation of the developer, as compared with the above-described conventional developing devices.

The diameter D2 of the upstream end of the tapered portion 36 is smaller than the diameter of the second rotary shaft 23b. Therefore, when the developer flows from the supply conveying chamber 22 into the agitation conveying chamber 21 at the upstream side communicating portion 20b, the conveying amount of the developer increases, so that the developer is less likely to stay in the upstream side communicating portion 20b.

In addition, as described above, the toner conveying amount per pitch of the replenishment blade 35 is smaller than the developer conveying amount per pitch of the first helical blade 24a located at the upstream side end portion in the developer conveying direction of the tapered portion 36. Therefore, when the newly replenished toner flows into the agitation conveying chamber 21 from the toner replenishing path 34, a reduction in the conveying amount of the toner (developer) can be suppressed, and the developer is less likely to be retained. In addition, as described above, the outer diameter D4 of the supplementary blade 35 is smaller than the outer diameter D3 of the first helical blade 24 a. Therefore, the toner conveyed to the agitation conveyance chamber 21 by the replenishment blade 35 is easily conveyed to the radially inner side of the first helical blade 24 a. As a result, the toner is less likely to remain in the upstream end of the stirring and conveying chamber 21, and insufficient stirring can be suppressed.

As shown in fig. 5, the first rotation shaft 23a of the first stirring and transporting member 25 according to the above embodiment may have a larger shaft diameter. The shaft diameter D1 of the downstream end portion of the tapered portion 36 in the developer conveying direction in this case is 1.5 times or more and 2.2 times or less than the shaft diameter D2 of the upstream end portion in the developer conveying direction. In this case, the outer diameter D3 of the first helical blade 24a is 1.01 to 1.05 times (preferably 1.02 to 1.04 times) the shaft diameter D1 of the downstream end portion of the tapered portion 36.

As shown in fig. 6, the first agitating and conveying member 25 may have a configuration in which the tapered portion 36 is provided over the entire axial region of the first rotary shaft 23 a. In this case, the first agitating and conveying member 25 does not include the straight portion 37. In this way, the shaft diameter of the first rotation shaft 23a increases more gradually from the upstream side toward the downstream side in the developer conveying direction. That is, the amount of the developer that can be conveyed by the first agitating and conveying member 25 decreases more gradually from the upstream side toward the downstream side in the developer conveying direction, and the developer stagnation can be suppressed more appropriately.

However, there are some places in the developing container 20 storing the developer where a small space is formed due to air stagnation. If the height of the developer (the height from the bottom surface of the agitation and conveyance chamber 21 to the surface of the developer) is increased by charging the developer into the developing container 20, the air in the small space is pressed by the developer, and the air pressure in the small space (hereinafter simply referred to as "air pressure") is increased.

Here, since the shaft diameter of the first rotary shaft 23a of the conventional developing device 3a (developing device in which the first rotary shaft 23a does not include the tapered portion 36) is constant between both ends in the axial direction, the height of the developer is also constant along the axial direction (developer conveying direction) of the first rotary shaft 23 a. Then, the small space is formed in a minute gap between the top surface of the developing container 20 (the surface above the first rotation shaft 23a and the second rotation shaft 23b of the inner wall surface of the developing container 20) and the surface of the developer. Therefore, the volume of the small space is small. Therefore, in a small space, the air pressure increase rate with respect to the toner replenishment amount becomes high, and a small amount of toner replenishment causes a large increase in air pressure. If the small space in which the air pressure rises communicates with the toner replenishing path 34 of the developing container 20, a discharge air flow is generated in which air flows back to the toner containers 4a to 4d through the toner replenishing path 34. Then, the toner supplied from the toner supply path 34 may be scattered by the discharge air flow, and the developer in the developing container 20 may be scattered by the discharge air flow, so that the developer may be scattered to the outside of the developing container 20.

In contrast, as described above, the first rotation shaft 23a of the developing device 3a of the present invention includes the tapered portion 36. Therefore, as shown in fig. 7, the height of the developer (hatched portion in the drawing) of the agitation conveying chamber 21 becomes gradually higher from the upstream side to the downstream side in the developer conveying direction. As a result, the small space SP is difficult to be partitioned, and the small space SP is easily formed as a single body with a large volume in comparison with the conventional developing devices 3a to 3d. Then, the air pressure rise rate with respect to the toner replenishment amount becomes low, and even if the small space SP communicates with the toner replenishment path 34, it is difficult to generate the discharge air flow. Therefore, scattering of the toner to the outside of the developing devices 3a to 3d can be suppressed.

Next, developing devices 3a to 3d of an image forming apparatus 100 according to a second embodiment of the present invention will be described with reference to fig. 8 to 10. In the following description, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

Fig. 8 is a plan sectional view showing a cross section of an agitating portion of the developing device 3a of the second embodiment. Fig. 9 is a flowchart showing an example of a control flow of the driving unit 40. Fig. 10 is a plan sectional view of the developing device in a state in which the reverse rotation mode is performed from the state of fig. 8.

As shown in fig. 8, the driving unit 40 is connected to the first rotation shaft 23a and the second rotation shaft 23b. The driving unit 40 is composed of a plurality of gears, a motor, and other driving sources. The driving unit 40 transmits a rotational driving force to the first rotation shaft 23a and the second rotation shaft 23b, and rotates the first rotation shaft 23a and the second rotation shaft 23b. The driving unit 40 is connected to a control unit 59 (see fig. 1).

The control unit 59 controls the driving unit 40. The control section 59 can execute a normal rotation mode and a reverse rotation mode. In the normal rotation mode selected during execution of the print job, the driving unit 40 imparts a rotational driving force in the normal rotation direction to the first rotation shaft 23a and the second rotation shaft 23b. In the execution of the normal rotation mode, the developer is conveyed in the developer conveyance direction (counterclockwise direction shown in fig. 8) inside the developing container 20. In the reverse rotation mode, a rotational driving force in the reverse rotation direction is applied to the first rotation shaft 23a and the second rotation shaft 23b by the driving unit 40. In the execution of the reverse rotation mode, the developer is conveyed in a direction (clockwise direction shown in fig. 8) opposite to the developer conveyance direction in the developing container 20.

As shown in fig. 9, control unit 59 first determines whether or not an image forming instruction is input from a host device such as a personal computer (step S1). When no image forming instruction is input (no in step S1), the standby state is continued as it is until the image forming instruction is input. If an image forming instruction is input (yes in step S1), the above-described normal rotation mode is executed (step S2).

Next, it is determined whether the print job is ended (step S3). If the print job has not ended (no in step S3), the normal rotation mode is continued. If it is determined that the print job is ended (yes in step S3), the normal rotation mode is ended, and the reverse rotation mode (reversing the direction of the rotational drive force transmitted toward the first rotation shaft 23a and the second rotation shaft 23b from the normal rotation direction to the reverse rotation direction) is executed (step S4). After the reverse rotation mode is executed for a predetermined period, the driving unit 40 is stopped, and the transmission of the rotational driving force to the first rotation shaft 23a and the second rotation shaft 23b is stopped (step S5). Then, the control of the driving unit 40 is ended.

In the present embodiment, too, a small space SP is formed around the tapered portion 36 (see fig. 8) as in the first embodiment. Here, as described above, by executing the reverse rotation mode while the normal rotation mode is ended, the developer in the developing container 20 is conveyed in the direction opposite to the developer conveying direction. Then, as shown in fig. 10, the small space SP also moves to the upstream side in the developer conveying direction (the direction of the white arrow shown by the broken line in fig. 10). Therefore, the small space SP spreads across the communicating portion 20b to the downstream side end periphery of the supply conveyance chamber 22. Accordingly, when toner is replenished into the developing container 20, the rate of rise of the internal pressure is low, and the above-described discharge air flow is difficult to generate.

As shown in fig. 8, 10, and 11, the developing container 20 of the second embodiment is preferably formed with a vent 41. The air outlet 41 is a through hole formed in the wall surface of the supply conveyance chamber 22, and communicates with the outside of the developing container 20. The exhaust port 41 is provided at a position between the downstream side end of the supply conveying chamber 22 in the developer conveying direction and the communicating portion 20b. More preferably, the air outlet 41 is provided at a position overlapping the communication portion 20b in the developer conveying direction. It is preferable that the exhaust port 41 be located at a position overlapping with the uppermost portion of the second conveying blade 24b (which is the outer peripheral edge of the second conveying blade 24 and is the uppermost portion) in the height direction, or be located further above than the uppermost portion. Further, it is preferable that the air outlet 41 is arranged at a position closer to the agitation transportation chamber 21 than the second rotation shaft 23b in the developer transportation direction. In fig. 8, the air outlet 41 is shown to be opened to the side of the developing container 20, but the air outlet 41 may be opened to the upper side (upper side shown in fig. 11).

In this way, the small space SP that expands to the supply conveyance chamber 22 due to the execution of the reverse rotation mode can be communicated with the exhaust port 41. When the toner is replenished to the developing container 20 in a state where the small space SP communicates with the air outlet 41, the air in the small space SP flows out to the outside of the developing container 20 through the air outlet 41. Therefore, the increase in the air pressure in the small space SP can be suppressed, and the discharge air flow is less likely to occur. In addition, by positioning the exhaust port 41 at a position overlapping the uppermost portion of the second conveying blade 24 in the height direction, the developer is made difficult to flow into the exhaust port 41. Therefore, outflow of the developer to the outside of the developing container 20 through the air outlet 41 can be suppressed. In addition, by positioning the air outlet 41 closer to the agitation transportation chamber 21 than the second rotation shaft 23b in the developer conveyance direction, the small space SP is easily communicated with the air outlet 41.

Further, as described above, the exhaust port 41 is provided at a position between the downstream side end of the supply conveying chamber 22 in the developer conveying direction and the communicating portion 20b. In this way, the distance between the tapered portion 36 and the exhaust port 41 in the developer conveying direction becomes shorter. Therefore, when the small space SP expands to the supply conveyance chamber 22, the small space SP easily communicates with the exhaust port 41. This makes it possible to shorten the time for executing the reverse rotation mode, and to more reliably communicate the small space SP with the exhaust port 41, thereby effectively suppressing the occurrence of the discharge air flow.

Further, a filter 42 is preferably disposed in the exhaust port 41. The filter 42 ensures ventilation between the inside and the outside of the developing container 20, and suppresses outflow of the developer flowing into the air outlet 41 to the outside of the developing container 20. Preferably, the filter 42 is formed of a polyurethane material having a plurality of void portions having an open cell configuration.

In this way, even if the developer flows into the air outlet 41, the developer is intercepted by the filter 42. Therefore, outflow of the developer to the outside of the developing container 20 through the air outlet 41 can be suppressed. Further, by forming the filter 42 from the polyurethane material having a plurality of void portions having an open-cell structure, outflow of the developer can be suppressed by a relatively simple structure, and an increase in manufacturing cost can be suppressed.

The first rotation shaft 23a of the present embodiment is configured to have the straight portion 37 in fig. 8 to 10, but is not limited thereto. For example, as in the first embodiment, the straight portion 37 may not be provided, and as shown in fig. 6, the tapered portion 36 may be provided over the entire axial region of the first rotation shaft 23 a.

The driving unit 40 of the present embodiment is configured by a plurality of driving sources such as gears and motors, but may transmit driving force of a main motor (not shown) mounted on the image forming apparatus 100 to the first rotation shaft 23a and the second rotation shaft 23b instead of the driving sources.

The effects of the present invention will be described in further detail below by way of examples.

Examples

The difference in toner concentration of the developer in the developing container 20 caused by the presence or absence of the tapered portion 36 was examined. As an experimental method, the developing device 3a shown in fig. 2 was mounted on the image forming apparatus 100 (color printer) shown in fig. 1, and the developing operation was performed, and the toner concentration (%) in the stirring and conveying chamber 21 after the toner replenishment at this time was measured. As a comparative example, the toner concentration after toner replenishment was measured in the same manner as in the present invention for the developing device 3a equipped with the first agitating and conveying member 25 having the shaft diameter of the first rotary shaft 23a constant in the longitudinal direction.

Regarding the first agitating-conveying member 25 of the comparative example, the shaft diameter of the first rotary shaft 23a was 8mm, the outer diameter of the first helical blade 24a was 13.5mm, the number of the first helical blades 24a was two windings, and the pitch of the first helical blade was 30mm.

In contrast, the shaft diameter of the first rotary shaft 23a of the first agitating and conveying member 25 of the present invention is 6mm at the upstream side end (shaft diameter D2) of the tapered portion 36 in the developer conveying direction, and 8mm at the downstream side end (shaft diameter D1) of the tapered portion 36 in the developer conveying direction. The outer diameter D3 of the first helical blade 24a is 13.5mm. The number of first helical blades 24a was two windings with a pitch of 30mm.

An experiment was performed 5 times (N1 to N5), and the average value of the toner concentration (%) at this time was calculated. In addition, as described above, the closer the toner concentration is to the reference value, the more appropriately the toner in the developing container 20 is stirred. Therefore, the reference value of the toner concentration is set to 6%, and the difference between the reference value and the average value is calculated. Further, the above-described difference in the present invention and the above-described difference in the comparative example were compared and verified. The results are shown in Table 1.

TABLE 1

As shown in table 1, in the developing device 3a of the present invention, the difference in toner concentration is smaller than that of the comparative example. Therefore, the developing device 3a of the present invention has a toner concentration close to 6% as compared with the developing device 3a of the comparative example, and the toner in the developing container 20 is more appropriately stirred. Therefore, the developing device 3a of the present invention can suppress insufficient agitation of the developer in the developing container 20, as compared with the developing device 3a of the comparative example (conventional configuration).

In addition, the present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the present invention is not limited to the tandem color printer shown in fig. 1, and can be applied to various image forming apparatuses employing a two-component development system, such as a digital or analog monochrome copier, a black-and-white printer, a color copier, and a facsimile machine.

Industrial applicability

The present invention can be applied to a developing device including a stirring and conveying member for stirring and conveying a developer. By using the developing device, an image forming apparatus capable of suppressing image formation failure and suppressing scattering of toner in the apparatus main body can be provided.

Claims (13)

1. A developing device, comprising:

a developing container that accommodates a developer containing toner and includes a first conveying chamber, a second conveying chamber disposed in parallel with the first conveying chamber via a partition, and a communicating portion that communicates the first conveying chamber and the second conveying chamber at both end portions of the partition in a longitudinal direction;

a first stirring and conveying member that stirs and conveys the developer in the first conveying chamber, and that has a first rotation shaft rotatably supported in the first conveying chamber, and a first stirring blade formed on an outer peripheral surface of the first rotation shaft;

a second stirring and conveying member that stirs and conveys the developer in the second conveying chamber, and has a second rotation shaft rotatably supported in the second conveying chamber, and a second stirring blade formed on an outer peripheral surface of the second rotation shaft; and

a developer carrier that carries the toner in the second conveyance chamber on a surface thereof opposite to the second agitating and conveying member,

the developing device is characterized in that,

the first rotation shaft has a tapered portion in at least a partial region in an axial direction of the first rotation shaft, and an axial diameter of the tapered portion increases toward a downstream side in a developer conveying direction in the first conveying chamber.

2. A developing device according to claim 1, wherein a shaft diameter of a downstream side end portion of said tapered portion in said developer conveying direction is 1.2 times or more and 2.5 times or less than a shaft diameter of an upstream side end portion.

3. A developing device according to claim 1, wherein said tapered portion is provided over an entire area in an axial direction of said first rotation shaft.

4. The developing device according to claim 1, wherein,

the first rotation shaft has a straight portion provided in a region from a downstream side end portion of the tapered portion in the developer conveying direction to a downstream side end portion of the first rotation shaft, an axial diameter of the straight portion is the same as an axial diameter of the downstream side end portion of the tapered portion,

the axial length of the tapered portion is 0.25 to 0.9 times the total length of the first rotation shaft.

5. The developing device according to claim 1, wherein,

the developing container has a toner replenishing path that communicates with an outside of the developing container and communicates with the first conveying chamber from an upstream side of the first conveying chamber in the developer conveying direction,

the first conveying member has a replenishment blade formed on an outer peripheral surface of the first rotation shaft extending in the toner replenishment path, conveys the toner in the toner replenishment path to the first conveying chamber,

the toner conveyance amount per pitch of the replenishment blade is smaller than the developer conveyance amount per pitch of the first stirring blade located at an upstream side end portion of the tapered section in the developer conveyance direction.

6. The developing device according to claim 5, wherein an outer diameter of the replenishment blade is smaller than an outer diameter of the first conveyance blade.

7. A developing device according to claim 1, wherein an entire area of an axial diameter of said second rotation shaft in the axial direction is 0.9 times or more and 1.1 times or less of an axial diameter of a downstream side end portion of said first rotation shaft in the developer conveying direction.

8. The developing device according to claim 1, wherein the developer is a two-component developer containing the toner and a magnetic carrier.

9. The developing device according to claim 1, comprising:

a driving unit connected to the first rotation shaft and the second rotation shaft, for applying a rotational driving force to the first rotation shaft and the second rotation shaft; and

a control part for controlling the driving part,

the control section may perform: a normal rotation mode in which a rotational driving force in a normal rotation direction is applied to the first rotation shaft and the second rotation shaft, and the developer is conveyed in the developer conveyance direction; and a reverse rotation mode in which a rotational driving force in a reverse rotation direction is applied to the first rotation shaft and the second rotation shaft, the developer is conveyed in a direction opposite to the developer conveyance direction,

the control unit executes the reverse rotation mode for a predetermined period when the forward rotation mode ends.

10. The developing device according to claim 9, wherein,

comprises an exhaust port provided from a downstream side end portion of the second conveying chamber in the developer conveying direction to a position between the communicating portions located on the downstream side of the second conveying chamber and communicating with the outside of the developing container,

the exhaust port is located at a position overlapping with an uppermost portion of an outer peripheral edge of the second stirring blade or at a position above the uppermost portion.

11. A developing device according to claim 10, comprising a filter having air permeability, said filter being disposed in said air discharge port and being capable of suppressing outflow of said developer from said air discharge port.

12. The developing device according to claim 11, wherein the filter is formed of a polyurethane material having a plurality of void portions having an open-cell configuration.

13. An image forming apparatus, comprising:

the developing device of claim 1; and

an image carrier that carries the toner supplied from the developer carrier on a surface thereof, opposite to the developer carrier.