Developing device and image forming apparatus including the same

Abstract

A developing device (3a-3d) is provided with a developing container (20), a first stirring and conveying member (25), a second stirring 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 part (20). The first stirring and conveying member (25) has a first rotating shaft (23a) and a first stirring blade (24a). The second stirring and conveying member (26) has a second rotating shaft (23b) and a second stirring blade (24b). The developer carrier (31) faces the second stirring and conveying member (26). The first rotating shaft (23a) has, in at least a partial region in the axial direction of the first rotating shaft (23a), a tapered part (36) having a shaft diameter that increases toward the downstream side in a developer conveying direction within the first conveying chamber (21).

Description

Technical Field

[0001] The present invention relates to a developing device and an image forming apparatus including the same.

Background Art

[0002] Image forming apparatuses such as copiers, printers, facsimiles, and multifunction machines using the electrophotographic method include a developing device for developing an electrostatic latent image formed on the outer peripheral surface of an image carrier, that is, forming a toner image (visible image) in which the electrostatic latent image is made apparent.

[0003] As such a developing device, Patent Document 1 discloses a device including a developing container that stores a developer containing toner, a stirring and conveying member that stirs and conveys the developer in the developing container, and a developing roller that partially exposes from an opening formed in the developing container (Patent Document 1). The developing container includes a first conveyance chamber and a second conveyance chamber. The stirring and conveying member is disposed in each of the first conveyance chamber and the second conveyance chamber.

[0004] The stirring and conveying member has a rotating shaft rotatably supported by the developing container and stirring blades formed on the outer peripheral surface of the rotating shaft. The rotating shaft is supported by a bearing portion provided in the developing device and is rotatably supported. As the stirring blades rotate around the rotating shaft, the developer in the developing container is supplied to the developing roller while circulating in the developing container.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, in the case of a developing device using a two-component development system, for example, when developing high-density images continuously, a large amount of toner is consumed and a large amount of toner is replenished at one time. Then, the replenished toner is not sufficiently agitated in the developing container, and the toner concentration (mixing ratio of toner to carrier in the developer; T / C) around the toner supply section (around the most upstream part of the developing container in the developer transport direction) becomes higher than that in other parts. Then, there is a risk of density unevenness occurring in the formed image. In addition, since the toner and carrier in the developing container are not sufficiently agitated, it is difficult for the toner to be properly charged. For this reason, there has been a risk that so-called background fogging occurs in the image, or that the undercharged toner scatters and dirties the inside of the image forming apparatus.

[0007] An object of the present invention is to provide a developing device capable of suppressing insufficient agitation of the developer in a developing container.

Means for Solving the Problems

[0008] A first configuration of the present invention for achieving the above object is a developing device including a developing container, a first agitation and transport member, a second agitation and transport member, and a developer carrier. The developing container has a first transport chamber, a second transport chamber disposed in parallel with the first transport chamber with a partition portion interposed therebetween, and a communication portion that communicates the first transport chamber and the second transport chamber on both end sides in the longitudinal direction of the partition portion, and houses a developer containing toner. The first agitation and transport member has a first rotating shaft rotatably supported in the first transport chamber and first agitation blades formed on the outer peripheral surface of the first rotating shaft, and agitates and transports the developer in the first transport chamber. The second agitation and transport member has a second rotating shaft rotatably supported in the second transport chamber and second agitation blades formed on the outer peripheral surface of the second rotating shaft, and agitates and transports the developer in the second transport chamber. The developer carrier faces the second agitation and transport member and carries the toner in the second transport chamber on its surface. The first rotating shaft has a tapered portion in at least a part of the axial direction of the first rotating shaft, the shaft diameter of which increases as it advances downstream in the developer transport direction in the first transport chamber.

Effects of the Invention

[0009] According to the first configuration of the present invention, since the first rotating shaft has a tapered portion, the volume of the first conveyance chamber decreases from the upstream side to the downstream side. That is, the amount of developer that the first agitation conveyance member can convey gradually decreases from the upstream side to the downstream side in the developer conveyance direction. For this reason, the developer in the first conveyance chamber is conveyed while being pushed back toward the upstream side on the way to the downstream side. Thereby, the developer is conveyed to the second conveyance chamber in a state of being sufficiently agitated in the first conveyance chamber. Therefore, it is possible to provide a developing device that can suppress insufficient agitation of the developer in the developing container.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0011] Hereinafter, a first embodiment of the developing devices 3a to 3d of the present invention and the image forming apparatus 100 including the developing devices 3a to 3d will be described with reference to the drawings.

[0012] FIG. 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 in which the developing devices 3a to 3d according to the first embodiment of the present invention are mounted. Inside the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the conveyance direction (the left side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, yellow, and black images are sequentially formed by the respective processes of charging, exposure, development, and transfer.

[0013] Photoconductor drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of each color are arranged in these image forming units Pa to Pd, and further, an intermediate transfer belt 8 that rotates in the counterclockwise direction in FIG. 1 is provided adjacent to each of the image forming units Pa to Pd. The toner images formed on these photoconductor drums 1a to 1d are sequentially primary-transferred and superimposed onto the intermediate transfer belt 8 that moves while contacting each of the photoconductor drums 1a to 1d. Thereafter, the toner image primary-transferred onto the intermediate transfer belt 8 is secondary-transferred onto transfer paper S as an example of a recording medium by a secondary transfer roller 9. Further, after the toner image is fixed on the transfer paper S onto which the toner image has been secondary-transferred, the transfer paper S is discharged from the main body of the image forming apparatus 100. While rotating the photoconductor drums 1a to 1d in the clockwise direction in FIG. 1 by a main motor (not shown), an image forming process for each of the photoconductor drums 1a to 1d is executed.

[0014] The transfer paper S onto which the toner image is secondarily transferred is housed in a paper cassette 16 arranged at the lower part of the main body of the image forming apparatus 100, and is conveyed to the nip portion between the secondary transfer roller 9 and the driving roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a resist roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged on the downstream side of the secondary transfer roller 9.

[0015] Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photosensitive drums 1a to 1d, there are charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d, an exposure device 5 for exposing the photosensitive drums 1a to 1d with image information, developing devices 3a, 3b, 3c and 3d for forming a toner image on the photosensitive drums 1a to 1d, and cleaning devices 7a, 7b, 7c and 7d for removing the developer (toner) and the like remaining on the photosensitive drums 1a to 1d.

[0016] When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data to form an electrostatic latent image corresponding to the image data on each of the photosensitive drums 1a to 1d. The developing devices 3a to 3d are each filled with a predetermined amount of a two-component developer containing cyan, magenta, yellow, and black toners. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image described later, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to form a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5.

[0017] Then, a transfer electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d by the primary transfer rollers 6a to 6d, and the cyan, magenta, yellow, and black toner images on the photoreceptor drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These four-color images are formed with a predetermined positional relationship determined in advance for predetermined full-color image formation. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, toner and the like remaining on the surfaces of the photoreceptor drums 1a to 1d after primary transfer are removed by the cleaning devices 7a to 7d.

[0018] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream driving roller 11. When the intermediate transfer belt 8 starts to rotate counterclockwise with the rotation of the driving roller 11 by a belt driving motor (not shown), the transfer paper S is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper S. The transfer paper S onto which the toner image has been secondarily transferred is conveyed to the fixing unit 13.

[0019] The transfer paper S conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the transfer paper S, forming a predetermined full-color image. The transfer paper S on which the full-color image has been formed has its conveyance direction distributed by the branching portion 14 branched in a plurality of directions, and is then discharged to the discharge tray 17 by the discharge roller pair 15 (either as it is or after being sent to the duplex conveyance path 18 to form images on both sides).

[0020] FIG. 2 is a perspective view showing the developing device 3a with the cover member 61 and the developing roller 31 removed. FIG. 3 is a side cross-sectional view of the developing device 3a with the cover member 61 and the developing roller 31 attached. In the following description, the developing device 3a disposed in the image forming unit Pa of FIG. 1 is exemplified. However, since the configurations of the developing devices 3b to 3d disposed in the image forming units Pb to Pd are basically the same, the description thereof is omitted.

[0021] As shown in FIGS. 2 and 3, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and toner is stored. 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 supply portion 32.

[0022] The stirring and conveying chamber 21 and the supply and conveying chamber 22 are arranged in parallel. The partition wall 20a is provided inside the developing container 20 and divides the inside of the developing container 20 into the stirring and conveying chamber 21 and the supply and conveying chamber 22. The communication portions 20b and 20c communicate the stirring and conveying chamber 21 and the supply and conveying chamber 22 at both longitudinal ends of the partition wall 20a. The cover member 61 closes the upper part of the developing container 20 and separates the internal space of the developing container 20 from the external space.

[0023] In the stirring and conveying chamber 21 and the supply and conveying chamber 22, a first stirring and conveying member 25 and a second stirring and conveying member 26 for mixing and stirring the toner supplied from the toner container 4a (see FIG. 1) with the magnetic carrier and charging it are respectively provided. The first stirring and conveying member 25 and the second stirring and conveying member 26 are rotatably supported by a bearing portion (not shown) fixed to the developing container 20 via shaft support portions 52 provided at both axial ends.

[0024] When the first stirring and conveying member 25 and the second stirring and conveying member 26 rotate, the developer is stirred and conveyed in the axial direction (the direction perpendicular to the plane of FIG. 3), and circulates between the stirring and conveying chamber 21 and the supply and conveying chamber 22 through the communication portions 20b and 20c formed at both ends of the partition wall 20a. That is, a circulation path for the developer is formed in the developing container 20 by the stirring and conveying chamber 21, the supply and conveying chamber 22, and the communication portions 20b and 20c.

[0025] As shown in FIG. 3, in the developing container 20, above and to the upper right of the second agitation and conveyance member 26 provided in the supply and conveyance chamber 22, a developing roller (developer carrier) 31 is disposed. 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 1a. The developing roller 31 rotates in the counterclockwise direction in FIG. 3. The first agitation and conveyance member 25, the second agitation and conveyance member 26, and the developing roller 31 rotate at a predetermined rotational speed by the driving force from a main motor (not shown).

[0026] The developing roller 31 is composed of a cylindrical developing sleeve (not shown) that rotates in the counterclockwise direction in FIG. 3 and a magnet (not shown) having a plurality of magnetic poles fixed inside the developing sleeve. Here, a developing sleeve with a knurled surface is used, but a developing sleeve with a large number of concave shapes (dimples) formed on the surface, a developing sleeve with a blasted surface, or a developing sleeve that has been blasted in addition to knurling or forming concave shapes, or a plated one can also be used.

[0027] As shown in FIG. 3, a regulating blade 33 is attached to the developing container 20 along the longitudinal direction of the developing roller 31 (the direction perpendicular to the plane of FIG. 3). A slight gap is formed between the tip 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 onto the outer peripheral surface of the developing roller 31 to a predetermined thickness by this slight gap.

[0028] A developing voltage power source (not shown) is connected to the developing device 3a via a voltage control circuit (not shown). The developing voltage power source applies a developing voltage obtained by superimposing a DC voltage and an AC voltage to the developing roller 31. Due to the developing voltage and the magnetic force of the magnet inside the developing roller 31, a developer is attached (carried) to the surface of the developing roller 31 to form a magnetic brush.

[0029] As shown in Fig. 3, a toner density sensor 27 is arranged on the bottom surface of the stirring and conveying chamber 21 so as to face the first stirring and conveying member 25 in the height direction (the vertical direction in Fig. 3). The toner density sensor 27 is located at a predetermined position in the developer conveying direction of the stirring and conveying chamber 21 (the position where the toner density value is the highest) (see Fig. 4). The toner density sensor 27 is connected to a control unit 59 (see Fig. 1) provided at a predetermined location of the image forming apparatus 100.

[0030] The toner density sensor 27 detects the magnetic permeability of the developer in the developing container 20 and transmits the detection result to the control unit 59. Based on this detection result, the control unit 59 determines the toner density in the developer (the mixing ratio of toner to carrier in the developer; T / C) and determines whether to replenish toner. The closer the toner density is to the reference value (for example, 6%), the more preferably the toner is stirred. The control unit 59 controls the rotational drive of the first stirring and conveying member 25 and the second stirring and conveying member 26 and the replenishment of toner so that the toner density approaches the reference value.

[0031] As shown in Fig. 2, the toner replenishing unit 32 is provided on the side surface portion of the developing container 20 in the axial direction. The toner replenishing unit 32 includes a replenishing port 58 and a toner replenishing path 34. The replenishing port 58 opens at the upper part of the toner replenishing unit 32. The replenishing port 58 is connected to a toner container 4a (see Fig. 1). The toner replenishing path 34 extends downward from the replenishing port 58 and communicates with the stirring and conveying chamber 21 from the upstream side with respect to the developer conveying direction (see Fig. 4). The toner stored in the toner container 4a is replenished into the stirring and conveying chamber 21 through the replenishing port 58 and the toner replenishing path 34.

[0032] When replenishing toner, the control unit 59 transmits a control signal to a toner replenishing motor (not shown). By this 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 unit 32 (see FIG. 2). At this time, while detecting the toner concentration of the developer in the developing container 20 by the toner concentration sensor 27, the control unit 59 replenishes the toner while controlling the toner replenishing motor so that the detected toner concentration approaches a predetermined reference value (6%).

[0033] Next, the configuration of the stirring unit of the developing device 3a will be described in detail. FIG. 4 is a plan sectional view showing a cross section of the stirring unit of the developing device 3a cut along the A-A cross-sectional line shown in FIG. 3.

[0034] As described above, the partition wall 20a extends in the longitudinal direction of the developing container 20 and partitions the stirring and conveying chamber 21 and the supply and conveying chamber 22 in parallel. As shown in FIG. 4, one end in the longitudinal direction of the partition wall 20a (the left side in FIG. 4) forms an upstream communication portion 20b together with the side wall portion 29b of the developing container 20. The other end in the longitudinal direction of the partition wall 20a (the right side in FIG. 4) forms a downstream communication portion 20c together with the side wall portion 29a of the developing container 20.

[0035] As shown in FIGS. 2 and 4, a first stirring and conveying member 25 is disposed in the stirring and conveying chamber 21, and a second stirring and conveying member 26 is disposed in the supply and conveying chamber 22. The first stirring and conveying member 25 includes a first rotating shaft 23a, a first spiral blade 24a (first stirring blade), and a replenishing blade 35. The second stirring and conveying member 26 includes a second rotating shaft 23b and a second spiral blade 24b (second stirring blade).

[0036] The first rotating shaft 23a is a cylindrical shaft body extending along the longitudinal direction of the developing container 20 (the conveying direction of the developer). The first rotating shaft 23a extends to the vicinity of both axial ends of the developing container 20. The upstream end of the first rotating shaft 23a with respect to the developer conveying direction projects outward in the axial direction from the stirring and conveying chamber 21 and is located in the toner replenishing path 34.

[0037] The first rotating shaft 23a has a tapered portion 36 and a straight portion 37. The tapered portion 36 and the straight portion 37 are adjacent portions of the first rotating shaft 23a in the axial direction. The tapered portion 36 is located between the upstream end and the central portion of the first rotating shaft 23a with respect to the developer conveyance direction (preferably, at a position overlapping with the upstream communication portion 20b with respect to the developer conveyance direction).

[0038] The shaft diameter of the tapered portion 36 increases in a tapered shape from the upstream side to the downstream side in the developer conveyance direction within the agitation conveyance chamber 21. The shaft diameter D1 of the downstream end of the tapered portion 36 in the developer conveyance direction is 1.2 times or more and 1.5 times or less of the shaft diameter D2 of the upstream end of the tapered portion 36 in the developer conveyance direction.

[0039] The straight portion 37 is connected to the downstream end of the tapered portion 36 with respect to the developer conveyance direction. The shaft diameter of the straight portion 37 is the same as the shaft diameter D1 of the downstream end of the tapered portion 36 with respect to the developer conveyance direction and is constant without changing as it proceeds downstream in the developer conveyance direction.

[0040] The axial length L1 of the tapered portion 36 is 0.25 times or more and 0.9 times or less of the total length L3 of the first rotating shaft 23a. Preferably, the axial length L1 of the tapered portion 36 is 0.25 times or more and 0.95 times or less (more preferably, 0.4 times or more and 0.6 times or less) with respect to the axial length L2 of the portion of the first rotating shaft 23a located within the agitation conveyance chamber 21.

[0041] The first spiral blade 24a is formed on the outer peripheral surface of the first rotating shaft 23a. The first spiral blade 24a is formed integrally with the first rotating shaft 23a and is formed in a spiral shape with a constant pitch in the axial direction. The first spiral blade 24a extends from a position overlapping with the upstream communication portion 20b to a position overlapping with the downstream communication portion 20c of the agitation conveyance chamber 21 with respect to the developer conveyance direction.

[0042] The outer diameter D3 of the first spiral 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 end of the tapered portion 36.

[0043] The supply blade 35 is formed on the outer peripheral surface of the portion of the first rotating shaft 23a located in the toner supply path 34. The supply blade 35 is integrally formed with the first rotating shaft 23a and is formed in a spiral shape with a constant pitch in the axial direction. The supply blade 35 is formed in a reverse spiral to the first spiral blade 24a. The conveyance amount of toner per pitch of the supply blade 35 is less than the conveyance amount of developer per pitch of the first spiral blade 24a located at the upstream end of the developer conveyance direction of the tapered portion 36. Specifically, the pitch of the supply blade 35 is smaller than the pitch of the first spiral blade 24a, and the outer diameter D4 of the supply blade 35 is smaller than the outer diameter D3 of the first spiral blade 24a.

[0044] The shaft diameter of the second rotating shaft 23b is constant over the entire axial direction, being 0.9 times or more and 1.1 times or less the shaft diameter D1 of the downstream end of the tapered portion 36. That is, the shaft diameter of the second rotating shaft 23b is larger than the shaft diameter D2 of the upstream end of the tapered portion 36. The second spiral blade 24b is formed on the outer peripheral surface of the second rotating shaft 23b. The second spiral blade 24b is integrally formed with the second rotating shaft 23b and is formed in a spiral shape with a constant pitch in the axial direction. The outer diameter of the second spiral blade 24b is equivalent to the outer diameter D3 of the first spiral blade 24a. The second spiral blade 24b is formed in a reverse spiral to the first spiral blade 24a. The second spiral blade 24b extends from the position overlapping the upstream communication portion 20b to the position overlapping the downstream communication portion 20c of the stirring conveyance chamber 21 with respect to the developer conveyance direction.

[0045] When the first stirring conveyance member 25 and the second stirring conveyance member 26 rotate, the developer in the developing container 20 is stirred while circulating from the stirring conveyance chamber 21 to the upstream communication portion 20b, the supply conveyance chamber 22, and the downstream communication portion 20c by the first spiral blade 24a and the second spiral blade 24b (see FIG. 2). At that time, the developer in the supply conveyance chamber 22 is supplied to the developing roller 31.

[0046] As described above, since the first rotation shaft 23a has the tapered portion 36, the volume of the stirring and conveying chamber 21 decreases from the upstream side to the downstream side. That is, the amount of developer that the first stirring and conveying member 25 can convey gradually decreases from the upstream side to the downstream side in the developer conveying direction. For this reason, the developer in the stirring and conveying chamber 21 is conveyed while being pushed back toward the upstream side on the way to the downstream side. Thereby, the developer is conveyed to the supply and conveyance chamber 22 in a state of being sufficiently stirred in the stirring and conveying chamber 21. Therefore, it is possible to provide the developing device 3a that can suppress insufficient stirring of the developer in the developing container 20.

[0047] By the way, conventionally, the volume of the stirring and conveying chamber excluding each stirring and conveying member and the supply and conveyance chamber itself decreases from the upstream side to the downstream side in the developer conveying direction, and the outer diameter of the spiral blades of each stirring and conveying member (the first stirring and conveying member and the second stirring and conveying member) decreases from the upstream side to the downstream side. There is a developing device configured as described above. In such a developing device, as it progresses from the upstream side to the downstream side in the developer conveying direction, the amount of developer that the stirring and conveying member can convey rapidly decreases. For this reason, in the vicinity of the downstream end of the stirring and conveying member (in the vicinity of the communication portion that communicates the stirring and conveying chamber and the supply and conveyance chamber), it becomes difficult to convey the developer, and there is a possibility that the developer may stay. Then, there is a possibility that toner adheres to the rotation shaft of the stirring and conveying member around the portion where the developer stays, and so-called shaft thickening occurs where the shaft diameter increases.

[0048] On the other hand, the developing devices 3a to 3d according to the present invention adopt a configuration in which the shaft diameter of the first rotation shaft 23a increases in a tapered shape at the tapered portion 36. Further, the outer diameter D3 of the first spiral blade 24a is constant, and the volume of the stirring and conveying chamber 21 itself excluding the first stirring and conveying member 25 is also constant. For this reason, the amount of developer conveyed in the stirring and conveying chamber 21 gradually decreases from the upstream side to the downstream side. Thereby, the developer in the stirring and conveying chamber 21 is smoothly conveyed, and the retention of the developer can be suppressed.

[0049] In addition, the shaft diameter of the second rotating shaft 23b according to the present invention is equal to the shaft diameter D1 of the downstream end portion of the first rotating shaft 23a (0.9 times or more and 1.1 times the shaft diameter D1), and is constant throughout the entire axial direction. Therefore, in the downstream communication portion 20c, the conveyance amount of the developer is less likely to change, and the retention of the developer can be suppressed. Accordingly, the developing devices 3a to 3d of the present invention can suppress the insufficient agitation of the developer while suppressing the retention of the developer as compared with the conventional developing devices as described above.

[0050] Further, the shaft diameter D2 at the upstream end portion of the tapered portion 36 is smaller than the shaft diameter of the second rotating shaft 23b. Therefore, when the developer flows from the supply conveyance chamber 22 into the agitation conveyance chamber 21 in the upstream communication portion 20b, the conveyance amount of the developer increases, so that the developer is less likely to stay in the upstream communication portion 20b.

[0051] Also, as described above, the conveyance amount of toner per pitch of the replenishing blade 35 is less than the conveyance amount of the developer per pitch of the first spiral blade 24a located at the upstream end portion in the developer conveyance direction of the tapered portion 36. Therefore, when the newly replenished toner flows from the toner replenishing path 34 into the agitation conveyance chamber 21, it is possible to suppress a decrease in the conveyance amount of the toner (developer), and it is possible to make it difficult for the developer to stay. Also, as described above, the outer diameter D4 of the replenishing blade 35 is smaller than the outer diameter D3 of the first spiral blade 24a. Therefore, the toner conveyed into the agitation conveyance chamber 21 by the replenishing blade 35 is likely to be conveyed to the radially inner side of the first spiral blade 24a. As a result, the toner is less likely to stay at the upstream end portion of the agitation conveyance chamber 21, and insufficient agitation can be suppressed.

[0052] Note that, as shown in FIG. 5, the first agitation conveyance member 25 of the above-described embodiment can have a relatively thick shaft diameter of the first rotating shaft 23a. In this case, the shaft diameter D1 at the downstream end portion in the developer conveyance direction of the tapered portion 36 is 1.5 times or more and 2.2 times or less the shaft diameter D2 at the upstream end portion in the developer conveyance direction. Also, in this case, the outer diameter D3 of the first spiral blade 24a is 1.01 times or more and 1.05 times or less (preferably 1.02 times or more and 1.04 times or less) the shaft diameter D1 at the downstream end portion of the tapered portion 36.

[0053] Further, as shown in FIG. 6, the first stirring and conveying member 25 can adopt a configuration in which a tapered portion 36 is provided over the entire axial direction of the first rotating shaft 23a. In this case, the first stirring and conveying member 25 does not include the straight portion 37 described above. By doing so, the shaft diameter of the first rotating shaft 23a gradually increases more gently as it advances from the upstream side to the downstream side in the developer conveying direction. That is, the amount of developer that the first stirring and conveying member 25 can convey gradually decreases more gently as it advances from the upstream side to the downstream side in the developer conveying direction, and the retention of the developer can be more suitably suppressed.

[0054] By the way, in the developing container 20 that stores the developer, there are small spaces formed by the retention of air here and there. When toner is introduced into the developing container 20 and the bulk density of the developer (the height from the bottom surface of the stirring and conveying chamber 21 to the surface of the developer) increases, the air in this small space is compressed by the developer, and the air pressure in the small space (hereinafter simply referred to as "air pressure") rises.

[0055] Here, in the conventional developing device 3a (a developing device in which the first rotating shaft 23a does not include the tapered portion 36 described above), since the shaft diameter of the first rotating shaft 23a is constant over both ends in the axial direction, the bulk density of the developer also becomes a constant height along the axial direction (developer conveying direction) of the first rotating shaft 23a. Then, the small space is formed in a slight gap between the top surface of the developing container 20 (the surface located above the first rotating shaft 23a and the second rotating shaft 23b among the inner wall surfaces of the developing container 20) and the surface of the developer. For this reason, the volume of the small space is relatively small. Therefore, in the small space, the rate of increase in air pressure with respect to the toner replenishment amount becomes high, and the air pressure rises relatively greatly by a small amount of toner replenishment. When the small space with the increased air pressure communicates with the toner replenishment path 34 of the developing container 20, an exhaust air flow in which air flows backward toward the toner containers 4a to 4d through the toner replenishment path 34 is generated. Then, the toner replenished from the toner replenishment path 34 may be scattered by this exhaust air flow, or the developer in the developing container 20 may be scattered by the exhaust air flow, and there is a risk that the developer will scatter outside the developing container 20.

[0056] On the other hand, in the developing device 3a of the present invention, as described above, the first rotating shaft 23a is provided with the tapered portion 36. Therefore, as shown in FIG. 7, the bulk of the developer (the hatched portion in the figure) in the stirring and conveying chamber 21 gradually increases from the upstream side to the downstream side in the developer conveying direction. As a result, the small space SP described above is less likely to be divided, and it is easier to form a relatively large integral small space SP compared to the conventional developing devices 3a to 3d described above. Then, the rate of increase in air pressure with respect to the toner supply amount becomes relatively low, and even if the small space SP communicates with the toner supply path 34, it is difficult for a discharge air flow to occur. Therefore, it is possible to suppress the toner from scattering outside the developing devices 3a to 3d.

[0057] Next, the developing devices 3a to 3d according to the second embodiment of the image forming apparatus 100 of the present invention will be described with reference to FIGS. 8 to 10. In the following, differences from the first embodiment will be described, and the same components as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

[0058] FIG. 8 is a plan sectional view showing a cross section of the stirring unit of the developing device 3a according to the second embodiment. FIG. 9 is a flowchart showing an example of the control flow of the driving unit 40. FIG. 10 is a plan sectional view of the developing device in a state where the reverse rotation mode is executed from the state of FIG. 8.

[0059] As shown in FIG. 8, a driving unit 40 is connected to the first rotating shaft 23a and the second rotating shaft 23b. The driving unit 40 is composed of a driving source such as a plurality of gears and a motor. The driving unit 40 transmits a rotational driving force to the first rotating shaft 23a and the second rotating shaft 23b to rotate the first rotating shaft 23a and the second rotating shaft 23b. The driving unit 40 is connected to a control unit 59 (see FIG. 1).

[0060] The control unit 59 controls the drive unit 40. The control unit 59 can execute a forward rotation mode and a reverse rotation mode. In the forward rotation mode selected during the execution of the printing job, the drive unit 40 applies a rotational driving force in the forward rotation direction to the first rotating shaft 23a and the second rotating shaft 23b. During the execution of the forward rotation mode, the developer is conveyed in the developer conveyance direction (counterclockwise direction shown in FIG. 8) within the developing container 20. In the reverse rotation mode, the drive unit 40 applies a rotational driving force in the reverse rotation direction to the first rotating shaft 23a and the second rotating shaft 23b. During the execution of the reverse rotation mode, the developer is conveyed in a direction opposite to the developer conveyance direction (clockwise direction shown in FIG. 8) within the developing container 20.

[0061] As shown in FIG. 9, the control unit 59 first determines whether an image formation command has been input from a host device such as a personal computer (step S1). If the image formation command has not been input (No in step S1), the standby state is continued until the image formation command is input as it is. When the image formation command is input (Yes in step S1), the above-described forward rotation mode is executed (step S2).

[0062] Next, it is determined whether the printing job has ended (step S3). If the printing job has not ended (No in step S3), the forward rotation mode is continuously executed. When it is determined that the printing job has ended (Yes in step S3), the forward rotation mode is terminated and the reverse rotation mode is executed (the direction of the rotational driving force transmitted to the first rotating shaft 23a and the second rotating shaft 23b is reversed from the forward rotation direction to the reverse rotation direction) (step S4). After the reverse rotation mode is implemented for a predetermined period, the drive unit 40 is stopped to stop the transmission of the rotational driving force to the first rotating shaft 23a and the second rotating shaft 23b (step S5). Then, the control of the drive unit 40 is terminated.

[0063] Also in this embodiment, similar to the first embodiment, a small space SP is formed around the tapered portion 36 (see FIG. 8). Here, as described above, by executing the reverse rotation mode at the end of the normal rotation mode, the developer in the developing container 20 is conveyed in the direction opposite to the developer conveyance direction. Then, as shown in FIG. 10, the small space SP also moves upstream in the developer conveyance direction (the direction of the white arrow shown by the broken line in FIG. 10). For this reason, the small space SP expands to the periphery of the downstream end portion of the supply conveyance chamber 22 across the communication portion 20b. Then, when toner is replenished into the developing container 20, the rate of increase in the internal pressure becomes relatively low, and the above-described discharge air flow is less likely to occur.

[0064] Also, as shown in FIGS. 8, 10, and 11, it is preferable that the developing container 20 according to the second embodiment is formed with an exhaust port 41. The exhaust port 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 end portion of the supply conveyance chamber 22 and the communication portion 20b with respect to the developer conveyance direction. More preferably, the exhaust port 41 is provided at a position overlapping the communication portion 20b with respect to the developer conveyance direction. The exhaust port 41 is preferably at a position overlapping in the height direction with the uppermost part of the second conveyance blade 24b (the outer peripheral edge of the second conveyance blade 24 and the portion located highest), or above this uppermost part. Also, the exhaust port 41 is preferably arranged at a position closer to the agitation conveyance chamber 21 than the second rotation shaft 23b with respect to the developer conveyance direction. In FIG. 8, the exhaust port 41 is shown as opening to the side surface of the developing container 20, but it may be made to open to the upper surface (the upper surface shown in FIG. 11).

[0065] By doing so, the small space SP extended to the supply and conveyance chamber 22 by executing the reverse rotation mode can be made to communicate with the exhaust port 41. When toner is replenished into the developing container 20 with the small space SP and the exhaust port 41 in communication, the air in the small space SP flows out to the outside of the developing container 20 through the exhaust port 41. For this reason, it becomes possible to suppress an increase in the air pressure of the small space SP, and it becomes difficult for a discharge air flow to occur. Further, since the exhaust port 41 is located at a position overlapping the uppermost part of the second conveying blade 24 in the height direction, it becomes difficult for the developer to flow into the exhaust port 41. Therefore, it is possible to suppress the developer from flowing out of the developing container 20 through the exhaust port 41. Further, since the exhaust port 41 is located closer to the agitation and conveyance chamber 21 in the developer conveyance direction than the second rotation shaft 23b, the small space SP easily communicates with the exhaust port 41.

[0066] Also, as described above, the exhaust port 41 is provided at a position between the downstream end of the supply and conveyance chamber 22 and the communication portion 20b in the developer conveyance direction. By doing so, the distance between the tapered portion 36 and the exhaust port 41 becomes relatively short in the developer conveyance direction. For this reason, when the small space SP expands to the supply and conveyance chamber 22, the small space SP easily communicates with the exhaust port 41. Thereby, while making the time for executing the reverse rotation mode relatively short, the small space SP can be more surely communicated with the exhaust port 41, and the generation of the discharge air flow can be effectively suppressed.

[0067] Also, it is preferable that a filter 42 is disposed at the exhaust port 41. The filter 42 suppresses the developer that has flowed into the exhaust port 41 from flowing out to the outside of the developing container 20 while ensuring ventilation between the inside and the outside of the developing container 20. The filter 42 is preferably formed of a urethane material having a plurality of void portions having a continuous bubble structure.

[0068] By doing so, even if the developer flows into the exhaust port 41, the developer is blocked by the filter 42. Therefore, it is possible to suppress the developer from flowing out of the developing container 20 through the exhaust port 41. Further, by forming the filter 42 from a urethane material having a plurality of voids having a continuous bubble structure, it becomes possible to suppress the outflow of the developer with a relatively simple structure, and an increase in manufacturing cost can be suppressed.

[0069] Note that although the first rotation shaft 23a of the present embodiment is shown as having a straight portion 37 in FIGS. 8 to 10, it is not limited thereto. For example, similar to the first embodiment, a configuration can be adopted in which the straight portion 37 is not provided and a tapered portion 36 is provided over the entire axial direction of the first rotation shaft 23a as shown in FIG. 6.

[0070] Further, although the drive unit 40 of the present embodiment is configured from a plurality of gears and a drive source such as a motor, instead of this drive source, the driving force of a main motor (not shown) mounted on the image forming apparatus 100 may be transmitted to the first rotation shaft 23a and the second rotation shaft 23b.

[0071] Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

Example

[0072] The difference in the toner concentration of the developer in the developing container 20 due to the presence or absence of the tapered portion 36 was investigated. As a test method, the developing device 3a shown in FIG. 2 was mounted on an image forming apparatus 100 (color printer) as shown in FIG. 1 to perform a developing operation, and the toner concentration (%) in the agitation conveyance chamber 21 after toner replenishment was measured. Further, as a comparative example, for a developing device 3a equipped with a first agitation conveyance member 25 having a constant shaft diameter of the first rotation shaft 23a along the longitudinal direction, the toner concentration after toner replenishment was measured in the same manner as in the present invention.

[0073] The first stirring and conveying member 25 of the comparative example has a shaft diameter of 8 mm for the first rotating shaft 23a, an outer diameter of 13.5 mm for the first spiral blade 24a, two layers of the first spiral blade 24a, and a pitch of 30 mm for the first spiral blade.

[0074] In contrast, for the first stirring and conveying member 25 of the present invention, the shaft diameter of the first rotating shaft 23a is 6 mm at the upstream end (shaft diameter D2) in the developer conveying direction of the tapered portion 36 and 8 mm at the downstream end (shaft diameter D1) in the developer conveying direction of the tapered portion 36. The outer diameter D3 of the first spiral blade 24a is 13.5 mm. The number of layers of the first spiral blade 24a is two layers, and the pitch is 30 mm.

[0075] The test was conducted 5 times (N1 to N5), and the average value of the toner concentration (%) at that time was calculated. Also, as described above, the closer the toner concentration is to the reference value, the more preferably the toner in the developing container 20 is stirred. Therefore, the reference value for the toner concentration was set to 6%, and the difference value between this reference value and the above average value was calculated. Then, the difference value in the present invention was compared and verified with the difference value in the comparative example. The results are shown in Table 1.

[0076]

Table 1

[0077] As shown in Table 1, in the developing device 3a of the present invention, the difference value of the toner concentration is smaller than the difference value of the toner concentration in the comparative example. Therefore, the developing device 3a of the present invention has a toner concentration closer to 6% and the toner in the developing container 20 is stirred more preferably than the developing device 3a of the comparative example. Accordingly, the developing device 3a according to the present invention can suppress insufficient stirring of the developer in the developing container 20 compared to the developing device 3a of the comparative example (conventional configuration).

[0078] The present invention is not limited to the above-described embodiments, and various modifications can 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 using a two-component development method, such as digital or analog monochrome copiers, monochrome printers, color copiers, facsimiles, and the like.

Industrial Applicability

[0079] The present invention can be used in a developing device including a stirring and conveying member that conveys a developer while stirring it. By using this developing device, it is possible to provide an image forming apparatus capable of suppressing defective image formation and suppressing toner scattering inside the apparatus body.

Claims

1. A first conveyance chamber, a second conveyance chamber arranged in parallel with the first conveyance chamber with a partition therebetween, and a communication portion that communicates the first conveyance chamber and the second conveyance chamber on both end sides in the longitudinal direction of the partition, and a developing container that houses a developer containing toner. A first rotating shaft rotatably supported in the first conveyance chamber, and a first stirring blade formed on the outer peripheral surface of the first rotating shaft, and a first stirring and conveying member that stirs and conveys the developer in the first conveyance chamber. A second rotating shaft rotatably supported in the second conveyance chamber, and a second stirring blade formed on the outer peripheral surface of the second rotating shaft, and a second stirring and conveying member that stirs and conveys the developer in the second conveyance chamber. In a developing device including a developer carrier that faces the second stirring and conveying member and carries toner on the surface in the second conveyance chamber. The first rotating shaft has a tapered portion provided in a region from the upstream end portion to the central portion of the first rotating shaft with respect to the developer conveyance direction, and the shaft diameter increases as it proceeds downstream in the developer conveyance direction in the first conveyance chamber, and a straight portion provided in a region from the downstream end portion of the tapered portion to the downstream end portion of the first rotating shaft with respect to the developer conveyance direction, and having the same shaft diameter as the downstream end portion of the tapered portion. The developing device is characterized by this.

2. The developing device according to claim 1, wherein the shaft diameter of the downstream end portion of the tapered portion is 1.2 times or more and 2.5 times or less the shaft diameter of the upstream end portion with respect to the developer conveyance direction.

3. The developing device according to claim 1, wherein the axial length of the tapered portion is 0.25 times or more the total length of the first rotating shaft.

4. The developing container has a toner supply path that communicates with the outside of the developing container and communicates with the first conveyance chamber from the upstream side of the first conveyance chamber with respect to the developer conveyance direction. The first stirring and conveying member has a supply blade formed on the outer peripheral surface of the first rotating shaft extending into the toner supply path, and conveys the toner in the toner supply path to the first conveyance chamber. The developing device according to claim 1, wherein the conveyance amount of the toner per pitch of the supply blade is less than the conveyance amount of the developer per pitch of the first stirring blade located at the upstream end portion in the developer conveyance direction of the tapered portion.

5. The developing device according to claim 4, wherein an outer diameter of the supply blade is smaller than an outer diameter of the first stirring blade.

6. The developing device according to claim 1, wherein a shaft diameter of the second rotating shaft is 0.9 times or more and 1.1 times or less of a shaft diameter of a downstream end portion in a developer conveyance direction of the first rotating shaft over an entire axial direction.

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

8. A driving unit connected to the first rotating shaft and the second rotating shaft and applying a rotational driving force to the first rotating shaft and the second rotating shaft; A control unit for controlling the driving unit; The developing device according to claim 1, further comprising: wherein the control unit is capable of executing a normal rotation mode in which a rotational driving force in a normal rotation direction is applied to the first rotating shaft and the second rotating shaft to convey the developer 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 rotating shaft and the second rotating shaft to convey the developer in a direction opposite to the developer conveyance direction, and executes the reverse rotation mode for a predetermined period at the end of the normal rotation mode.

9. An exhaust port communicating with the outside of the developing container is provided at a position between a downstream end portion of the second conveyance chamber in the developer conveyance direction and a communication portion located downstream of the second conveyance chamber. The developing device according to claim 8, wherein the exhaust port is located at a position overlapping an uppermost portion of an outer peripheral edge of the second stirring blade or at a position above the uppermost portion.

10. The developing device according to claim 9, further comprising a filter disposed in the exhaust port and capable of suppressing outflow of the developer from the exhaust port and having air permeability.

11. The developing device according to claim 10, wherein the filter is formed of a urethane material having a plurality of void portions having a continuous bubble structure.

12. An image forming apparatus comprising: The developing device according to claim 1; and An image carrier facing the developer carrier and carrying the toner supplied from the developer carrier on a surface thereof.

13. The communication portion is an upstream communication portion located upstream of the developer conveyance direction in the first conveyance chamber or a downstream communication portion located downstream of the developer conveyance direction in the first conveyance chamber. The developing device according to claim 8, wherein the tapered portion overlaps the upstream communication portion in the developing agent conveying direction.

14. A developing device having a first conveyance chamber, a second conveyance chamber arranged in parallel with the first conveyance chamber with a partition portion therebetween, and communication portions that communicate the first conveyance chamber and the second conveyance chamber on both end sides in the longitudinal direction of the partition portion, and a developing container that houses a developer containing toner. A first stirring and conveying member having a first rotating shaft rotatably supported in the first conveyance chamber and first stirring blades formed on an outer peripheral surface of the first rotating shaft, for stirring and conveying the developer in the first conveyance chamber. A second stirring and conveying member having a second rotating shaft rotatably supported in the second conveyance chamber and second stirring blades formed on an outer peripheral surface of the second rotating shaft, for stirring and conveying the developer in the second conveyance chamber. A developing agent carrier that faces the second stirring and conveying member and carries the toner in the second conveyance chamber on a surface thereof. In the developing device, the communication portion is an upstream communication portion located on the upstream side in the developing agent conveying direction in the first conveyance chamber, or a downstream communication portion located on the downstream side in the developing agent conveying direction in the first conveyance chamber. A driving unit connected to the first rotating shaft and the second rotating shaft and applying a rotational driving force to the first rotating shaft and the second rotating shaft. A control unit for controlling the driving unit. The first rotating shaft has a tapered portion provided over the entire axial direction of the first rotating shaft and having an increasing shaft diameter as it proceeds downstream in the developing agent conveying direction in the first conveyance chamber. The control unit can execute a normal rotation mode in which a rotational driving force in the normal rotation direction is applied to the first rotating shaft and the second rotating shaft to convey the developer in the developing agent conveying direction, and a reverse rotation mode in which a rotational driving force in the reverse rotation direction is applied to the first rotating shaft and the second rotating shaft to convey the developer in a direction opposite to the developing agent conveying direction, and is characterized by executing the reverse rotation mode for a predetermined period at the end of the normal rotation mode.

15. An exhaust port that communicates with the outside of the developing container and is provided at a position between the downstream end portion of the second conveyance chamber and the downstream communication portion with respect to the developing agent conveying direction. The developing device according to claim 14, wherein the exhaust port is located at a position overlapping the uppermost portion of the outer peripheral edge of the second stirring blade or at a position above the uppermost portion.

Images