This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-073259 filed on Mar. 25, 2009.
The present invention relates to a developing unit and an image forming apparatus.
[1] According to an aspect of the invention, a developing unit includes a developer retainer, a developing vessel, a first conveyance member, a second conveyance member, a layer thickness limiting member and a reduction portion. The developer retainer includes a magnet member and a retaining member. The magnet member has magnetic poles. The retaining member is supported on an outer circumference of the magnet member and retains a developer magnetized and sucked on a surface of the retaining member by a magnetic force of the magnet member. The developing vessel receives the developer internally and includes a retainer receiving portion, a first agitation portion and a second agitation portion. The retainer receiving portion receives the developer retainer. The first agitation portion is adjacent to the retainer receiving portion. The second agitation portion is adjacent to the first agitation portion. The first conveyance member is received in the first agitation portion and conveys the developer in the first agitation portion in a first conveyance direction. The second conveyance member is received in the second agitation portion and conveys the developer in the second agitation portion in a second conveyance direction which is reverse to the first conveyance direction. The layer thickness limiting member is provided in opposition to the developer retainer to limit a layer thickness of the developer retained on the surface of the retaining member, which is disposed between the second conveyance member and the developer retainer and which is made of a magnetic material. The reduction portion is disposed on an entrance side of the layer thickness limiting member and in a space between the layer thickness limiting member and the second agitation portion. The reduction portion reduces entrance of the developer on an upstream side of the layer thickness limiting member into the space.
Exemplary embodiments of the invention will be described in detail based on the following figures, wherein:
Although specific examples of modes for carrying out the invention (hereinafter referred to as “embodiments”) will be described below with reference to the drawings, the invention is not limited to the following embodiments.
In order to facilitate understanding of the following description, in the drawings, the front/rear direction is indicated as an X-axis direction, the left/right direction is indicated as a Y-axis direction and the up/down direction is indicated as a Z-axis direction, and directions or sides designated by the arrows X, -X, Y, -Y, Z and -Z are indicated as the front direction, the rear direction, the right direction, the left direction, the upper direction and the lower direction, or the front side, the rear side, the right side, the left side, the upper side and the lower side respectively.
In the drawings, each arrow with “.” written in “∘” means an arrow directed from the back side of the sheet to the front side thereof and each arrow with “x” written in “∘” means an arrow directed from the front side of the sheet to the back side thereof.
In the following description using the drawings, any other member than members required for description is omitted from the drawings suitably for the purpose of facilitating understanding.
In
In
In
The image processing portion GS converts print information into image information for forming latent images corresponding to images of four colors of yellow, magenta, cyan and black, that is, Y, M, C and K. The print information is inputted from a personal computer PC or the like as an example of an external information transmitting apparatus. The image processing portion GS outputs the converted image information to the latent image forming unit drive circuit DL.
When an original image is a unicolor image or a so-called monochrome image, image information of only black is inputted to the latent image forming unit drive circuit DL.
The latent image forming unit drive circuit DL has not-shown drive circuits of yellow Y, magenta M, cyan C and black K to output signals corresponding to the input image information to LED heads LHy, LHm, LHc and LHk at given times respectively. Each LED head LHy, LHm, LHc, LHk is an example of a latent image forming unit disposed for each color.
In
According to the first embodiment, the magenta and cyan visible image forming units UM and UC are configured in the same manner as the black visible image forming unit UK, but the developing unit Gy of the yellow visible image forming unit UY has a different shape while the other members of the yellow visible image forming unit UY, that is, a photoconductor Py, the charging roll CRy, the LED head LHy and a photoconductor cleaner CLy are configured in the same manner. Detailed description about the developing units Gy to Gk will be made later.
The surfaces of the photoconductors Py to Pk are charged uniformly in charging areas Q1y, Q1m, Q1c and Q1k opposed to the charging rolls CRy to CRk by the charging rolls CRy to CRk respectively. Then, latent images are written on the surfaces of the photoconductors Py to Pk by the LED heads LHy to LHk in latent image forming areas Q2y, Q2m, Q2c and Q2k respectively. The written electrostatic latent images are developed into toner images in developing areas Q3y, Q3m, Q3c and Q3k opposed to the developing units Gy to Gk respectively. The developed toner images are conveyed to primary transfer areas Q4y, Q4m, Q4c and Q4k contacting with an intermediate transfer belt B which is an example of an intermediate transfer. In the primary transfer areas Q4y, Q4m, Q4c, Q4k, primary transfer voltages whose polarities are reverse to the charged polarity of the toners are applied to primary transfer rolls T1y, T1m, T1c and T1k at given times respectively by the power supply circuit E controlled by the control portion C. Each primary transfer roll T1y, T1m, T1c, T1k is an example of a primary transfer disposed on the back surface side of the intermediate transfer belt B.
According to the first embodiment, as shown in
The toner images on the photoconductors Py to Pk are primarily transferred onto the intermediate transfer belt B by the primary transfer rolls T1y, T1m, T1c and T1k respectively.
Residual or attached materials such as untransferred toners or corona products on the surfaces of the photoconductors Py, Pm, Pc and Pk after the primary transfer are cleaned up by the photoconductor cleaners CLy, CLm, CLc and CLk respectively. The cleaned surfaces of the photoconductors Py, Pm, Pc and Pk are charged again by the charging rolls CRy, CRm, CRc and CRk respectively. Residual materials etc. that cannot be removed by the photoconductor cleaners CLy to CLk but adhere to the charging rolls CRy to CRk are cleaned up by charger cleaners CCy, CCm, CCc and CCk disposed in contact with the charging rolls CRy to CRk, respectively. Each charger cleaner CCy, CCm, CCc, CCk is an example of a charger cleaning member.
In
A belt cleaner CLb as an example of an intermediate transfer cleaner is disposed above the rear portion of the intermediate transfer belt B. The belt cleaner CLb has a cleaning vessel CLb1, a belt cleaning blade CLb2, a film CLb3 and a residual material conveyance member CLb4. The belt cleaning blade CLb2 is an example of a cleaning member, which is supported on the cleaning vessel CLb1 and brought into contact with the intermediate transfer belt B to remove and clean residual materials staying on the surface of the intermediate transfer belt B. The film CLb3 is an example of a leakage prevention member, which prevents the residual materials removed by the belt cleaning blade CLb2 from flying out and leaking out. The residual material conveyance member CLb4 is disposed in the cleaning vessel CLb1 to convey and discharge the removed residual materials. The cleaning vessel CLb1 according to the first embodiment is disposed in a position above the black photoconductor cleaner CLk.
A secondary transfer roll T2b which is an example of a secondary transfer member is disposed in opposition to the surface of the intermediate transfer belt B which is in contact with the backup roll T2a. A secondary transfer T2 as an example of a final transfer unit according to the first embodiment is constituted by the backup roll T2a and the secondary transfer roll T2b. A secondary transfer area Q5 is formed by the area where the secondary transfer roll T2b and the intermediate transfer belt B are opposed to each other.
Unicolor or multi-color toner images transferred to overlap one another in turn on the intermediate transfer belt B in the primary transfer areas Q4y, Q4m, Q4c and Q4k by the primary transfer rolls T1y, T1m, T1c and T1k respectively are conveyed to the secondary transfer area Q5.
A transfer unit T1+T2+B according to the first embodiment, which transfers the images on the surfaces of the photoconductors Py to Pk onto a medium, is constituted by the primary transfer rolls T1y to T1k, the intermediate transfer belt B, and the secondary transfer unit T2.
As shown in
Under the visible image forming units UY to UK, a paper feed tray TR1 is provided as an example of a medium storage portion. The paper feed tray TR1 has a bottom wall TR1a, a rear end wall TR1b and an upper wall TR1c. The bottom wall TR1a is an example of a lower wall. The rear end wall TR1b extends upward from the rear end of the bottom wall TR1a. The upper wall TR1c is disposed above the bottom wall TR1a and in opposition thereto. A supply port TR1d for supplying new recording sheets S is formed in the front end portion of the paper feed tray TR1. The front end portion of the upper wall TR1c is formed to ascend frontally toward the outside of the supply port TR1d. Accordingly, the distance between the upper wall TR1c and the bottom wall TR1a in the supply port TR1d becomes larger on the front side. Thus, the supply port TR1d is formed to be wider on the front side. to be wider on the front side.
A lifting plate PL1 as an example of a media loading portion is disposed on the bottom wall TR1a. The lifting plate PL1 is supported rotatably around a rotation center PL1a and loaded with the recording sheets S as an example of media so as to lift the recording sheets S. A lifting spring PL2 as an example of an urging member for urging a rear end portion of the lifting plate PL1 upward is disposed on a rear end portion of the lifting plate PL1. When image formation is not performed, the lifting plate PL1 moves to a descending position where the lifting plate PL1 is kept in parallel with the bottom wall TR1a by depressing members PL3 shaped like eccentric cams. The depressing members PL3 are disposed in the opposite left and right end portions of the lifting plate PL1. During image formation, the depressing members PL3 are rotated so that the lifting plate PL1 is supported movably between the descending position and an ascending position where the lifting plate PL1 has been lifted by the lifting spring PL2 as shown in
When the front cover U2 is opened, the supply port TR1d is opened to the outside. Thus, a new sheaf of recording sheets S can be inserted to abut against the rear end wall TR1b so as to be loaded and received on the lifting plate PL1 in the descending position.
A paper feed roll Rp as an example of a feeding-out member is disposed at the rear of the upper wall TR1c. The paper feed roll Rp is disposed in a position where the uppermost recording sheet S of the loaded recording sheets S can be pushed against the paper feed roll Rp by the spring force of the lifting spring PL2 in the state where the lifting plate PL1 has moved to the ascending position. A retard roll Rs as an example of a separation member is disposed above the rear end wall TR1b.
The recording sheets S loaded on the paper feed tray TR1 are fed out by the paper feed roll Rp, and separated one by one in the area where the retard roll Rs and the paper feed roll Rp are in contact with each other. Each separated recording sheet S is conveyed to a medium conveyance path SH. The recording sheet S in the medium conveyance path SH is conveyed to registration rolls Rr which are examples of paper feed timing adjustment members. The recording sheet S conveyed to the registration rolls Rr is fed out to the secondary transfer area Q5 in sync with the timing when the toner images on the intermediate transfer belt B reach the secondary transfer area Q5.
From the intermediate transfer belt B where the toner images have been transferred in the secondary transfer area Q5, residual materials such as untransferred toners or corona products staying on the surface of the intermediate transfer belt B are removed and cleaned by the belt cleaner CLb.
The recording sheet S to which the toner images have been transferred is conveyed to a fixing area Q6 of a fixing unit F. The fixing unit F has a heating roll Fh as an example of a heating fixing member and a pressure roll Fp as an example of a pressure fixing member. The fixing area Q6 consists of an area where the heating roll Fh and the pressure roll Fp are in contact with each other with a predetermined pressure. The unfixed toner images on the surface of the recording sheet S are fixed by heat and pressure when the toner images pass through the fixing area Q6.
The recording sheet S where the images have been fixed is conveyed in the medium conveyance path SH, and discharged to the discharge tray TRh through discharge rollers Rh which are examples of medium discharge members.
Next, the developing units according to the first embodiment will be described. The developing units Gy to Gk for the respective colors Y, M, C and K are constituted in the same manner. Therefore, only the black visible image forming unit UK will be described, but detailed description about the other yellow, magenta and cyan developing units Gy to Gc will be omitted.
In
A developing roll chamber 2 as an example of a retainer receiving portion, a supply chamber 3 as an example of a first agitation portion and an agitation chamber 4 as an example of a second agitation portion are provided inside the developing vessel 1. The developing roll G1k as an example of a developer retainer is received in the developing roll chamber 2. The supply chamber 3 is formed to be adjacent to and continuous with the bottom of the developing roll chamber 2. The agitation chamber 4 is formed to be adjacent to the rear of the supply chamber 3.
In
In
The inlet portions 5a and 5b are formed correspondingly to the outside of an image forming area L1 where an image will be formed on the photoconductor Pk. Thus, a developer flowing in and out through the inlet portions 5a and 5b is restrained from giving an adverse effect to image formation. The image forming area L1 is an example of a retaining area where an image will be retained by the image retainer.
In the developing unit Gk according to the first embodiment, a supply port 5c is disposed in the right inlet portion 5a. The supply port 5c is an example of a supply portion, through which a new developer is supplied from above.
In
A trimmer 6 which is an example of a magnet member and an example of a layer thickness limiting member is supported in the developing roll chamber 2 and disposed on the upstream side of the developing area Q3k in the rotation direction of the developing roll G1k. The trimmer 6 is disposed at a predetermined distance from the developing sleeve 12 and in opposition thereto so as to limit the layer thickness of a developer layer retained on the surface of the developing roll G1k. The trimmer 6 according to the first embodiment is constituted by a columnar rod-like member made of a magnetic material. In addition, the left/right-direction length of the trimmer 6 is set to be as long as the inside distance between the right inlet portion 5a and the left inlet portion 5b, and to be longer than the length of the magnet roll 11.
In
An admix auger 8 as an example of a second agitation member extending in the left/right direction and in parallel with the supply auger 7 is rotatably supported in the agitation chamber 4. The admix auger 8 has an admix shaft 8a as an example of a second rotary shaft, which extends in the left/right direction. An admix spiral 8b as an example of a second conveyance blade is supported on the outer circumference of the admix shaft 8a. A gear G12 as an example of a gear is fixedly supported on a left end of the admix shaft 8a. The gear G12 engages with the gear G11 of the supply auger 7. In
Further, in
In
Thus, the trimmer 6 made of a magnetic material according to the first embodiment is disposed between the developing roll G1k and the admix auger 8. In addition, a front end portion of a top wall portion 13 of the cover member 1b made of a magnetic material and constituting the top of the agitation chamber 4 is also disposed between the developing roll G1k and the admix auger 8. Accordingly, the cover member 1b has a function as a wall surface forming member in the first embodiment.
Thus, in the developing unit Gk according to the first embodiment, the trimmer 6 and the top wall portion 13 are at least partially disposed on a straight line L2 connecting the position of the trimming magnetic pole N1 where the normal magnetic force of the magnetic pole is maximal and the rotation center of the developing roll G1k.
Particularly in the first embodiment, the trimmer 6 and the top wall portion 13 are received in an area surrounded by common tangents L3 and L4 of the developing roll G1k and the circumscribed circle of the admix auger as shown by the broken lines in
In
Accordingly, the eave portion 1c is disposed in a space 14 which is on the upstream side of the trimmer 6 in the rotation direction of the developing sleeve 12, that is, on the entrance side of the developer to the trimmer 6, and between the trimmer 6 and the admix auger 8. The eave portion 1c is disposed so that the front edge portion thereof is close to the surface of the trimmer 6.
In addition, the length of the eave portion 1c in the left/right direction is set to be as long as the distance between the right end of the right inlet portion 5a and the left end of the left inlet portion 5b. The eave portion 1c covers not only the image forming area L1 but also the whole areas of the right inlet portion 5a and the left inlet portion 5b. Thus, the length of the eave portion 1c in the left/right direction is set to be longer than the developing roll G1k or the trimmer 6.
In the printer U configured thus according to the first embodiment of the invention, the developer circulated in the circulating chamber 3+4 of each developing unit Gy to Gk is attracted by the magnetic force of the magnet roll 11 of the developing roll G1y to G1k in the supply chamber 3, sucked and retained on the surface of the developing sleeve 12 and used for development.
Here, in the developing unit Gy to Gk according to the first embodiment, the trimming magnetic pole N1 is disposed correspondingly to the trimmer 6, while the agitation chamber 4 and the admix auger 8 are disposed on an extended line connecting the developing unit Gy to Gk and the trimmer 6.
In the configuration of the developing unit Gy to Gk according to the first embodiment, the developing vessel 1 is miniaturized so that the distance between the developing roll G1y to G1k and the admix auger 8 becomes short. If the trimmer 6 or the top wall portion 13 were not made of a magnetic material, there is a possibility that the magnetic force of the trimming magnetic pole N1 would reach the agitation chamber 4 so that the developer might be sucked in an area A1 which is an inner side portion of the top wall portion 13 of the agitation chamber 4. The sucked developer might be so lumpy that the conveyance of the developer in the agitation chamber 4 might be unstable due to the developer staying there. Thus, there is a possibility that the image quality might deteriorate due to density unevenness caused by poor development or the like.
On the other hand, according to the first embodiment, the trimmer 6 and the top wall portion 13 are made of magnetic materials. The lines of magnetic force are disturbed in the agitation chamber 4 rather than in the trimmer 6. In comparison with the case where the trimmer 6 and the top wall portion 13 are made of nonmagnetic materials, the magnetic force is lowered in the agitation chamber 4. Accordingly, in each developing unit Gy to Gk according to the first embodiment, the magnetic force in the area A1 is reduced so that bad conveyance of the developer due to the suction of the developer can be suppressed, and poor development can be also reduced.
Particularly in the configuration of the first embodiment, the admix auger 8 rotates to lift the developer from the agitation chamber 4 toward the supply chamber 3. Thus, in the agitation chamber 4, the developer is apt to lean to the inner side of the front end of the top wall portion 13, that is, toward the supply chamber 3 so that the developer leaning thus is apt to be sucked. In other words, the developer is apt to be sucked conspicuously when the trimmer 6 or the top wall portion 13 is made of a nonmagnetic material. However, according to the first embodiment, the suction of the developer can be reduced due to the trimmer 6 or the top wall portion 13. Thus, the developer can be conveyed smoothly from the lower agitation chamber 4 toward the upper supply chamber 3, while bad conveyance can be reduced.
Further, the trimmer 6 made of a magnetic material according to the first embodiment may be magnetized due to the magnetic force of the trimming magnetic pole N1. If the end portions of the trimmer 6 with the developer adhering to the trimmer 6 approached the inlet portions 5a and 5b, there is a possibility that the flow of the developer in the inlet portions 5a and 5b might be disturbed by the sucked developer. However, the trimmer 6 according to the first embodiment is set to be as long as the inside distance between the right inlet portions 5a and the left inlet portion 5b. Therefore, the end portions of the trimmer 6 do not overlap the inlet portions 5a and 5b, so that bad conveyance of the developer can be suppressed.
In
However, in
On the other hand, in the developing unit Gy to Gk according to the first embodiment, as shown in
In addition, in the developing unit Gy to Gk according to the first embodiment, the partition 5 is not formed in each inlet portion 5a, 5b, but the top of the inlet portion 5a, 5b is opened so that the space 14 becomes wide. Thus, a developer is apt to stay in the space 14. In addition, the volume of the staying developer is apt to be large. On the other hand, in the developing unit Gy to Gk according to the first embodiment, the eave portion 1c is disposed also in a region corresponding to each inlet portion 5a, 5b to suppress occurrence of a developer staying to be large in volume and insufficient in electrification. Thus, it is possible to prevent an image defect such as tailing or drop stain of toner.
In addition, the left inlet portion 5b is located on the upstream side of the supply auger 7 in the conveyance direction of a developer. Accordingly, when a developer which is large in volume and insufficient in electrification leaves the trimmer 6 and falls down to the supply chamber 3, the developer may be sucked by the pickup magnetic pole S3. Thus, there is a possibility that the insufficiently charged developer might be used for development so that an image defect such as tailing or drop stain of toner might occur. On the other hand, due to the eave portion 1c disposed in an area corresponding to the left inlet portion 5b, the occurrence of a developer staying to be large in volume and insufficient in electrification can be suppressed to prevent an image defect such as tailing or drop stain of toner.
Next, the second embodiment of the invention will be described. In the description of the second embodiment, constituent members corresponding to those in the first embodiment are referred to by the same numerals, and detailed description thereof will be omitted.
The second embodiment is configured in the same manner as the first embodiment except the following points.
In
In the developing unit Gy to Gk configured thus according to the second embodiment, in the same manner as in the first embodiment, the developer on the upstream side of the trimmer 6 is blocked by the eave portion 1c′ from entering the space 14, so that an insufficiently charged developer can be restrained from being used for development. In addition, a developer dropping off from the developing sleeve 12 after the layer thickness of the developer is limited by the trimmer 6 or falling down to the downstream side of the trimmer 6 from the developing area Q3y to Q3k falls down to the connection path 16. On this occasion, a developer may be sucked on the magnetized trimmer 6 and the electrostatic charge of the developer may be lowered with age. Even when such an insufficiently charged developer falls down from the trimmer 6, the developer does not fall down to the supply chamber 3 but falls down to the agitation chamber 4. Accordingly, the insufficiently charged developer is frictionally charged when it is conveyed through the agitation chamber 4 while being agitated. Thus, the frictionally charged developer is apt to be conveyed to the supply chamber 3 so that the insufficiently charged developer can be restrained from being supplied to the developing roll G1y to G1k. Thus, the image quality can be restrained from deteriorating due to the insufficiently charged developer.
The embodiments of the invention have been described above in detail. The invention is not limited to the embodiments, but various modifications can be made thereon without departing from the gist of the invention stated in the appending claims. Modifications (H01) to (H11) of the invention will be described below by way of example.
(H01) In each of the aforementioned embodiments, the printer U is constituted by a so-called printer. However, the invention is not limited thereto. For example, the invention can be applied to a copying machine, a facsimile machine, or a composite machine with a plurality of or all of those functions of the copying machine and the facsimile machine.
(H02) In each of the aforementioned embodiments, the printer U is not limited to a configuration where toners of four colors are used, but may be applied to a configuration where toners of five or more colors or toners of two or three colors are used.
(H03) In the first embodiment, it is desired that the relationship in height in the direction of gravity between the supply chamber 3 and the agitation chamber 4, the inclination of the intermediate transfer belt B, the rotation directions of each developing roll G1y to G1k, the supply auger 7 and the admix auger 8, etc. are set in the illustrated manner. However, the invention is not limited to such a configuration, but may be changed suitably in accordance with design, specification or the like.
(H04) In the first embodiment, it is desired that both the trimmer 6 and the cover member 1b are made of magnetic materials. However, either the trimmer 6 or the cover member 1b may be made of a magnetic material. Also in this case, bad conveyance can be reduced in comparison with the case where both the trimmer 6 and the cover member 1b are made of nonmagnetic materials.
(H05) In each of the aforementioned embodiments, the trimmer 6 is formed to have a shape like a round bar member. However, the invention is not limited to such a configuration, but the trimmer 6 may be formed into any shape such as a plate-like shape.
(H06) In each of the aforementioned embodiments, the whole of the cover member 1b is made of a magnetic material. However, the invention is not limited to such a configuration. For example, only the top wall portion 13 may be made of a magnetic material, or the cover member may be made of a nonmagnetic material such as resin while a plate or the like made of a magnetic material is pasted onto the wall surface of the cover member.
(H07) In each of the aforementioned embodiments, the eave portion 1c, 1c′ may be formed into any shape. For example, the eave portion 1c, 1c′ may be formed into any shape such as a shape which extends not toward the trimmer 6 but forward from the top wall portion 13, or a shape whose wall surface swells.
(H08) In each of the aforementioned embodiments, the eave portion 1c, 1c′ as an example of a reduction portion is formed integrally with the cover member 1b or the partition 5. However, the invention is not limited to such a configuration. For example, the eave portion 1c, 1c′ may be formed out of another member.
(H09) In each of the aforementioned embodiments, the length of the blocking portion along the axis of the developing roll G1y to G1k is not limited to the illustrated configuration, but may be set into any length. In addition, the blocking portion does not have to be provided in the axially central portion but the blocking portion may be provided only in the area corresponding to each inlet portion 5a, 5b that is an axial end portion.
(H010) In each of the aforementioned embodiments, the configuration is made so that each developing roll G1y to G1k includes the magnet roll 11 which is fixed supported and the developing sleeve 12 which rotates. However, the invention is not limited to such a configuration. For example, the invention may be applied to a developing roll including a magnetic roll which rotates to convey a developer.
(HO11) In each of the aforementioned embodiments, the configuration is made so that the intermediate transfer belt B is used as an example of an intermediate transfer. However, the invention is not limited to such a configuration. For example, the invention may be applied to a configuration in which an intermediate transfer such as an intermediate transfer drum is used. In addition, the invention can be also applied to an image forming apparatus in which images are transferred from the photoconductors Py to Pk directly to the sheet S without using any intermediate transfer.
Number | Date | Country | Kind |
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2009-073259 | Mar 2009 | JP | national |