AU2007201405B2

AU2007201405B2 - Developing device, image forming cartridge and image forming apparatus

Info

Publication number: AU2007201405B2
Application number: AU2007201405A
Authority: AU
Inventors: Tomoyuki Yoshii
Original assignee: Fujifilm Business Innovation Corp
Current assignee: Fujifilm Business Innovation Corp
Priority date: 2006-05-31
Filing date: 2007-03-30
Publication date: 2009-12-17
Anticipated expiration: 2027-03-30
Also published as: JP2007322696A; JP4957082B2; AU2007201405A1

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant/s: Fuji Xerox Co., Ltd. Actual Inventor/s: Tomoyuki Yoshii Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: DEVELOPING DEVICE, IMAGE FORMING CARTRIDGE AND IMAGE FORMING APPARATUS The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 53817AUP00 - la DEVELOPING DEVICE, IMAGE FORMING CARTRIDGE AND IMAGE FORMING APPARATUS Background 1. Technical Field 5 The present invention relates to a developing device, an image forming cartridge that includes a developing device, and an image forming apparatus. 2. Related Art Any discussion of the prior art throughout the 10 specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. Conventionally, a developing device, for developing an electrostatic latent image formed, for example, on a 15 photosensitive drum, is provided for an image forming apparatus that employs an electrophotographic system. As a developing device of this type, one is known wherein a developer (a two-component developer), comprising a magnetic carrier and toner, that employs as a main 20 component a color resin, is stored in a housing (a developer container) in which an opening is formed opposite the photosensitive drum, and positioned between the developer container opening and the photosensitive drum is a developing roller, arranged to the rear of which, within 25 the housing, is a pair of agitation members (transporting screws) that are provided to agitate and cyclically transport the developer (see JP-A-5-88543 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")). According to this developing 30 device, the pair of agitation members agitate and charge the toner and the magnetic carrier, and transport the thus prepared developer to the developing roller. There, the developer is attracted to the developing roller, which is oppositely charged, that carries the developer to the photosensitive drum. Thereafter, to develop the latent image on the photosensitive drum, toner is selectively transferred from the developing roller and attached to the latent image. In addition, according to the developing device described in 5 LTP-A-5-88543, a partition wall is provided that separates the two agitation members and ensures that they can smoothly agitate and transport the developer. It should be noted that communication ports, for connecting a transport path to the agitation members, are formed at both longitudinal ends of the partition wall. With 10 this arrangement, the pair of agitation members can agitate and cyclically transport the developer within the housing. Furthermore, since according to this type of developing device an electrostatic latent image on a photosensitive drum is developed using toner, accordingly, the ratio of the toner to the 15 developer (the toner density) in the housing is reduced. And should the reduction in the toner density be progressive, the toner available for developing a latent image would be gradually depleted, until finally, an image failure would occur. Therefore, according to JP-A-5-88543, a supply port, for replenishing the toner, is 20 formed in the developing device, and as new toner is supplied through the supply port, the agitation members, which agitate and mix the new toner with the developer already present in the developing device, can supply the developing roller with developer having a constant toner density. 25 In the conventional developing device, a communication port is arranged outside an image forming area (an area in the axial direction of the photosensitive drum on which a toner image is formed) in order to supply a fully agitated and mixed developer to the developing roller. That is, the developer (and the toner 2 - 3 that is supplied) is agitated by the agitation member located farthest from the developing roller, and is then carried through the communication port to the agitation member located nearer the developing roller. Thereafter, 5 the developer is agitated and mixed by the second agitation member and is supplied to the developing roller. However, when a communication port is arranged outside the image forming area, downsizing both the developing device and the image forming apparatus is difficult. 10 On the other hand, were the communication port arranged inside the image forming area, the agitation and mixing of developer would be insufficient, and should this be true, either a toner charging failure would occur, and a low density toner image be developed on the photosensitive 15 drum, or an uneven density phenomenon would occur, such as the development of a striped pattern. Summary It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the 20 prior art, or to provide a useful alternative. In order to resolve the above described technical problems, one objective of the present invention, at least in respect of some embodiments, is to provide a developing device with which, by preventing the insufficient agitation 25 or mixing of a developer, the occurrence of uneven densities can be reduced for toner images that are developed, an image forming cartridge that includes such a developing device, and an image forming apparatus. Another objection of some embodiments of the present 30 invention is to provide a developing device with which downsizing can be performed without adversely affecting the agitation and mixing of developer, an image forming - 4 cartridge that includes such a developing device, and an image forming apparatus. According to a first aspect of the present invention, a developing device includes: a housing that includes an 5 opposed portion, in which an opening is formed, opposite a latent image holding member holding an electrostatic latent image, and that has developer stored inside thereof; a developer holding member that is rotatably arranged at position facing the opening in the housing, and that holds 10 developer and develops an electrostatic latent image on the latent image holding member; a first agitation and transporting member that is extended inside of the housing, and that agitates the developer, transports the developer in an extensional direction of the developer holding member 15 and supplies the developer holding member with the developer; a second agitation and transporting member that is extended inside of the housing, and that agitates the developer and transports the developer in an opposite direction to the extensional direction of the first 20 agitation and transporting member; and a partition wall that is positioned inside of the housing, that separates a first transporting chamber, which stores the first agitation and transporting member, from a second transporting chamber, which stores the second agitation and 25 transporting member, and that is configured to form a communication port linking to communicate between the second transporting chamber and the first transporting chamber, wherein the developer in the second transporting chamber is gradually transported to the first transporting 30 chamber through the communication port across the partition wall in an extensional direction of the second agitation and transporting member and wherein the partition wall on the communication port side has a height reduced in a - 5 direction in which the developer is transported by the second agitation and transporting member. (2) The developing device as described in the item (1), wherein the first agitation and transporting member and the 5 second agitation and transporting member are arranged horizontally, and the partition wall is arranged perpendicularly. (3) The developing device as described in the item (1) or item (2), wherein the developer contains toner and a 10 carrier. (4) The developing device as described in the item (3) further including a toner supply unit that supplies the second transporting chamber with the toner. (5) According to a second aspect of the present invention, 15 an image forming cartridge, which is detachable from an image forming apparatus, includes: a latent image holding member that holds an electrostatic latent image; and a developing device that develops the electrostatic latent image on the latent image holding member, the developing 20 device including: a housing that includes an opposed portion, in which an opening is formed, opposite the latent image holding member, and that has developer stored inside thereof; a developer holding member that is rotatably arranged at position facing the opening in the housing, and 25 that holds developer and develops an electrostatic latent image on the latent image holding member; a first agitation and transporting member that is extended inside of the housing, and that agitates the developer, transports the developer in an extensional direction of the developer 30 holding member and supplies the developer holding member with the developer; a second agitation and transporting member that is extended inside of the housing, and that agitates the developer and transports the developer in an opposite direction to the extensional direction of the - 6 first agitation and transporting member; and a partition wall that is positioned inside of the housing, that separates a first transporting chamber, which stores the first agitation and transporting member, from a second 5 transporting chamber, which stores the second agitation and transporting member, and that is configured to form a communication port linking to communicate between the second transporting chamber and the first transporting chamber, wherein the communication port is enlarged from 10 upstream to downstream in a direction in which the developer is transported by the second agitation and transporting member. (6) The image forming cartridge as described in the item (5), wherein the second agitation and transporting member 15 includes: a rotary shaft; spiral blades that are spirally arranged on an outer circumferential face of the shaft; and a projection that is formed on the outer circumferential face, in an area opposite the furthest upstream position of the communication port, in a direction in which the 20 developer is transported by the second agitation and transporting member. (7) According to a third aspect of the present invention, an image forming apparatus includes: a latent image holding member; a latent image forming unit that forms an 25 electrostatic latent image on the latent image holding member; a developing unit that employs toner to develop the electrostatic latent image formed on the latent image holding member by the latent image forming unit; and a transfer unit that transfers the toner image, which is 30 formed on the latent image holding member by the developing unit, to a recording medium, wherein the developing unit includes: a housing that includes an opposed portion, in which an opening is formed, opposite the latent image holding member, and that has developer stored inside -7 thereof; a developer holding member that is rotatably arranged at position facing the opening in the housing, and that holds developer and develops an electrostatic latent image on the latent image holding member; a supply member 5 that is located inside of the housing, and that agitates and transports the developer, and supplies the developer holding member with the developer; an agitation member that is located inside of the housing, and that agitates and transports the developer so for cyclically moving the 10 developer relative to the supply member; a partition wall that is extended inside of the housing, that divides a supply chamber storing the supply member, and an agitation chamber storing the agitation member, and that is configured to form a first communication port transporting 15 the developer from the agitation chamber to the supply chamber, and a second communication port transporting the developer from the supply chamber to the agitation chamber; and a low portion that is formed on the partition wall near the first communication port, and that has a height shorter 20 than the partition wall near the second communication port. (8) The image forming apparatus as described in the item (7), wherein the partition wall has a length in an extensional direction, the length being shorter than a length, in a direction parallel to the extensional 25 direction of the partition wall, of an electrostatic latent image formed on the latent image holding member. According to some embodiments of the present invention, when the developer i's agitated and transported, the partition wall is employed to mix the developer. 30 Therefore, insufficient agitation and insufficient mixing of the developer can be eliminated, and as a result, the occurrences of uneven densities for developed toner images can be reduced.

- 8 Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or 5 exhaustive sense; that is to say, in the sense of "including, but not limited to". Brief Description of the Drawings Exemplary embodiment of the present invention will be described in detail based on the following figures, 10 wherein: Fig 1 is a diagram showing an example configuration of an image forming apparatus for which the present invention is applied; Fig. 2 is a diagram showing the state wherein the 15 front cover of the image forming apparatus is open; Fig. 3 is a diagram showing an example arrangement for a process cartridge; Fig. 4 is a top view of a developing device according to a first embodiment of the present invention; 20 Fig. 5 is a perspective view of the developing device according to the first embodiment; Fig. 6 is a diagram showing the partition wall, the first communication port and the second communication port of the developing device according to the first embodiment; 25 Figs. 7A and 7B are diagrams showing the movement of a developer in the vicinity of the first communication port; Fig. 8 is a diagram showing the partition wall, the first communication port and the second communication port of a developing device according to a second embodiment of 30 the present invention; and Figs. 9A and 9B are diagrams showing the movement of a developer in the vicinity of the first communication port. 5 Detailed Description The embodiments for carrying out the present invention will now be described in detail, while referring to the accompanying drawings. 10 (First Embodiment) Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus according to a first embodiment of the present invention. An image forming apparatus 10 shown in Fig. 1 is a so-called 15 tandem type, wherein four color process cartridges (image forming units and drum cartridges) 11a, 1lb, 11c and lid are vertically arranged within a main body 10a. Further, a conveying path 12, along which a sheet P is conveyed, substantially perpendicularly, from the bottom to the top, is formed at positions corresponding to those 20 of the process cartridges 1a to lid. A sheet cassette 13 is located below (the upstream side) the lowermost (the furthest upstream) process cartridge 11a for storing sheets P, each of which is to be conveyed along the conveying path 12 and to which toner images are sequentially transferred. Depending on the size of the sheets 25 P stored in the sheet cassette 13, part of the sheet cassette 13 is projected to the rear (to the reverse side or to the farther side) of the main body 10a. When the sheets P are small, the sheet cassette 13 does not project outward from the main body 10a. 9 The process cartridges 11a to lid, which are of a single image forming cartridge type, form yellow (Y) , magenta (M) , cyan (C) and black (K) toner images, from upstream, along the conveying path 12. The process cartridges 11a to lid are assembled by integrally 5 arranging photosensitive drums (image bearing members) 14, and arranging various types of electro-photographic devices around the photosensitive drums 14. An exposure device 15, used in common by the process cartridges 1a to lid, is located adjacent to the process cartridges 10 11a to ld sides that are furthest from the conveying path 12. This exposure device 15 employs color image data to emit beams from four semiconductor lasers (not shown) . Thereafter, the beams emitted by the four semiconductor lasers are deflected by polygon mirrors (not shown) , and the deflected beams are guided through an f0 lens 15 and a plurality of reflection mirrors to exposure points on the photosensitive drums 14. As a result, an optical image is formed on each of the photosensitive drums 14. A conveying belt 16 is extended past positions corresponding to the photosensitive drums 14 of the process cartridges 11a to 20 lid, and is moved cyclically along the conveying path 12. This conveying belt 16, formed of a belt material that can electrostatically attract the sheet P, is fitted around a drive roller 17A and a coupled roller 17B. Further, an attraction roller 18 is provided along the conveying path 12 to assist in the 25 electrostatic attraction of the sheet P to the conveying belt 16. Transfer rollers 19, which function as transfer portions, are provided on the reverse face of the conveying belt 16 at positions corresponding to the photosensitive drums 14 of the process cartridges 11a to lid. These transfer rollers 19 are used to closely 10 press the sheet P, on the conveying belt 16, against the photosensitive drums 14 and to transfer the toner images on the photosensitive drums 14 to the sheet P. A fixing device 20 is arranged along the conveying path 12 5 following (downstream of) the topmost (the furthest downstream) process cartridge lid. A sheet delivery portion 21, integrally formed with the main body 10a, is provided for storing the sheet P, which is discharged after the toner images have been fixed by the fixing device 20. Also provided for the main body 10a is an 10 inversion conveying path 22, for inverting the faces of the sheet P, on one side of which the images have been fixed by the fixing device 20, and for again feeding the sheet P to the conveying path 12. Additionally provided, at the front of the main body 10a of 15 the image forming apparatus 10, is a manual feeding tray 23 that pivots open, to the front (outwardly), when rotated at a fulcrum J at its lower end. Then, once the manual feeding tray 23 has been pivoted open, sheets P can be fed into an insertion slot (not shown). In essence, the manual feeding tray 23 can thus be used to supply 20 sheets P that differ from those stored in the sheet cassette 13. When a user issues a print instruction to a controller (not shown) to establish a state for the transfer, to a sheet P, of toner images, a sheet P is supplied, at a predetermined timing, from either the sheet cassette 13 or the manual feeding tray 23. Then, the sheet 25 P is fed through a plurality of conveying rollers 24 to the conveying path 12, and is transported along the conveying belt 16 to the transfer positions for the individual process cartridges 11a to 11d. Fig. 2 is a diagram for explaining the design of the front 11 cover 25. As shown in Figs. 1 to 2, the front cover 25 is provided for the main body 10a of the image forming apparatus 10, and is rotatable at the fulcrum J positioned at its lower end. When in the closed 5 state, the front cover 25, along with the main body 10, functions as an external cover. That is, the front cover 25 forms the front wall of the image forming apparatus 10 above the sheet cassette 13. The conveying belt 16, the drive roller 17a and the coupled 10 roller 17B, the attraction roller 18, the transfer rollers 19 and the inversion conveying path 22 are mounted within the front cover 25. Therefore, when the front cover 25 is open, these components, as well as the front cover 25, are separated from the main body 10a. Thus, when a user opens the front cover 25, the process 15 cartridges 11a to 11d are exposed, and the user can easily access the conveying path 12. Within the main body 10a, the individual process -cartridges 11a to lid are detachably mounted, substantially horizontally. Thus, the process cartridges 11a to lid can be readily removed by 20 opening the front cover 25. It should here be noted that a setting detection sensor (not shown) is provided to detect the statuses of the process cartridges 11a to lid, and to output the results obtained to a controller (also not shown). As described above, by opening the front cover 25, the process 25 cartridges lla to lid can be exposed and replaced. Furthermore, when a paper jam occurs, the photosensitive drums 14 can be exposed for corrective maintenance (clearing the paper jam). In this manner, the ease with which maintenance is performed for the image forming apparatus 10 is increased. 12 The sheet cassette 13 is accommodated in a cassette storage unit 26, provided for the main body 10a, and can be removed from the front of the main body 10a. More specifically, while the manual feeding tray 23 and the front cover 2S are closed, the sheet cassette 5 13 can be removed from or inserted into the cassette storage unit 26. Fig. 3 is a diagram showing an example arrangement for a process cartridge lid. The other process cartridges 11a, 1Ib and 11c have the same structure as the process cartridge lid, differing 10 only in the colors of the stored toner. The process cartridge lid in this embodiment includes: a photosensitive drum 14; a charging device 31, a developing device 32; a charge elimination device 33 and a cleaning device 34, both of which are arranged around the photosensitive drum 14; a sub-toner 15 supply unit 35; and a grip 36. The photosensitive drum 14, on the outer circumferential face of which is formed a photosensitive layer (not shown) , is rotatably arranged and is driven by a drive motor (not shown), and serves as a latent image bearing member. 20 The charging device 31 includes: a charging roller 31a, which contacts the photosensitive drum 14; and a charge cleaner 31b, which contacts the charging roller 31a. The charging roller 31a rotates in consonance with the photosensitive drum 14, while a power source (not shown) applies a charging bias to it for the transfer to the 25 photosensitive drum 14 of a predetermined potential (a negative polarity in this embodiment) . The charge cleaner 31b can be either a rotary roller or a brush member, and is rotated with the charging roller 31a to clean off foreign matter, such as toner, transferred to the charging roller 31a from the photosensitive drum 14. In this 13 embodiment, the charging device 31 and the exposure device 15 constitute a latent image forming section. The charge elimination device 33 includes: a transparent rod member 33a, extended in the axial direction of the photosensitive 5 drum 14; a frame 33b, for holding the rod member 33a; and an LED (not shown) , located opposite the axial end face of the rod member 33a. The rod member 33a is made, for example, of a plastic material, and in it, a plurality of grooves are formed in a direction perpendicular to the axial direction of the external 10 circumferential face. The cleaning device 34 includes: a cleaning blade 34a, a bracket 34b and a toner collection mechanism 34c. The cleaning blade 34a, which is a rectangular member made, for example, of urethane rubber, is mounted in the axial direction of the 15 photosensitive drum 14, against which it is held under pressure applied in the direction opposite to that in which the photosensitive drum 14 is rotated, and is fixed to the housing of the cleaning device 34 via the bracket 34b. The toner collection mechanism 34c includes an arm 34e, arranged and rotatable at a shaft 20 34d; and a scraping member 34f, attached to the free end of the arm 34e. The sub-toner supply unit 35 includes: a sub-toner chamber 35a, for storing toner; and a first sub-agitator 35b and a second sub-agitator 35c, located in the sub-toner chamber 35a. A 25 predetermined amount of toner is stored in the sub-toner chamber 35a. In the process cartridge 1id, in order to guide to the photosensitive drum 14 an exposure beam emitted by the exposure device 15, an opening is formed between the developing device 32 14 and the assembly of the cleaning device 34 and the sub-toner supply unit 35. Thus, a connection pipe 66, connecting a sub-toner supply unit 35 to a main toner supply unit 60, is arranged at a position, near the rear of the process cartridge 11d in Fig. 3, where it will 5 not interfere with the exposure beam emitted by the exposure device 15. The grip 16 is positioned so that a user can more easily mount, or replace, the process cartridge 11d. The structure of the developing device 32 will now be 10 described in detail while referring to Figs. 3 to 6. Fig. 4 is a top view of the developing device 32 in Fig. 3, and Fig. 5 is a perspective view of the developing device 32 in Fig. 3. Fig. 6 is a diagram showing a partition wall 48, a first communication port 48a and a second communication port 48b (details will be provided 15 later) formed inside the developing device 32. It should be noted that, in Figs. 4 and 5, an upper housing 41b and a developing roller 43, which will be described later, have been removed from the developing device 32. The developing device 32, which serves as a developing section, 20 includes: a developing unit 40, for employing toner T to develop an electrostatic latent image formed on the photosensitive drum 14; and the main toner supply unit 60, for supplying the toner T to the developing unit 40. The developing unit 40 employs a developer D, which contains the toner T, and a magnetic carrier 25 (not shown) . Further, the sub-toner supply unit 35, which is also a constituent of the developing device 32, supplies the toner T to the main toner supply unit 60, as will be described later. For the developing device 32, the developing unit 40 and the main toner supply unit 60 are integrally and horizontally formed. 15 The developing device 32 has a housing 41 wherein an opening 42 is formed at a position opposite the photosensitive drum 14. In this embodiment, the developing unit 40 is located below the photosensitive drum 14, and the opening 42 is formed facing upward. 5 The housing 41 includes: a lower housing 41a; an upper housing 41b, for engaging the lower housing 41a; and a sub-housing 41c, which is located inside the lower housing 41a and the upper housing 41b and is secured to these two. The lower housing 41a, the upper housing 41b and the sub-housing 41c separate the developing unit 10 40 from the main toner supply unit 60. The developing unit 40 includes: the developing roller 43, a pair of augers (a supply auger 44 and an agitation auger 45), the partition wall 48, a partition plate 49 and a layer thickness control member 50. 15 The developing roller 43, which serves as a developer bearing member, is mounted at a position facing the opening 42 of the housing 41. The developing roller 43 includes: a magnetic roller 43a, which is fixed internally; and a developing sleeve 43b, which is rotatably arranged around the external circumferential face of the 20 magnetic roller 43a. In this case, magnetic poles are arranged in the axial direction on the outer wall of the magnetic roller 43a, and plural arrays of these poles are circumferentially arranged. Further, a gear (not shown) is located at the axial end of the developing sleeve 43b, and is rotated by a motor. Also, a 25 predetermined developing bias is applied to the developing sleeve 43b by a power source (not shown). The supply auger 44 and the agitation auger 45 are located below the developing roller 43, near the rear wall of the housing 41 in the axial direction of the developing roller 43. It should 16 be noted that the supply auger 44 is positioned near the developing roller 43, while the agitation auger 45 is positioned farther from the developing roller 43, and that the supply auger 44 and the agitation auger 45 are horizontally arranged. The partition wall 5 48 is formed in the lower housing 41a, and extends upward from the inner wall. With the partition wall 48, a supply chamber 46, which includes a developer D carrying path from the supply auger 44, is separated from an agitation chamber 47, which includes a developer D carrying path from the agitation auger 45. In this embodiment, 10 the supply auger 44 serves as a first agitation and carrying member or a supply member, and the agitation auger 45 serves as a second agitation and carrying member or an agitation member. Furthermore, the supply chamber 46 serves as a first transporting chamber and the agitation chamber 47 serves as a second transporting chamber. 15 The partition wall 48 used as a division wall includes, as shown in Fig. 6, an upper edge 481, a first side edge 482 and a second side edge 483. A constant height is maintained along the upper edge 481 in the axial direction of the supply auger 44 and the agitation auger 20 45. The first side edge 482, with the side wall of the lower housing 41a, defines a first communication port 48a that connects the supply chamber 46 to the agitation chamber 47. That is, in this embodiment, the first side edge 482 serves as a low level portion. It should 25 be noted, as shown in Fig. 4, that the developer D is transported, via the first communication port 48a, from the agitation chamber 47 to the supply chamber 46. At this time, the first side edge 482 gradually slopes down from the upper edge 481 side to the side wall of the lower housing 41a. Therefore, the size of the first 17 communication port 48a is gradually enlarged, viewed from the direction in which the developer D is transported from the agitation chamber 47. On the other hand, the second side edge 483, with the other 5 side wall of the lower housing 41a, defines the second communication port 48b that connects the supply chamber 46 to the agitation chamber 47. The second side edge 483 is formed almost perpendicularly, and as shown in Fig. 4, the developer D is transported from the supply chamber 46 to the agitation chamber 47 via the second communication 10 port 48b. Both axial ends of the partition wall 48 are positioned inside the image forming area (an available image forming area, in the main scanning direction, on the photosensitive drum 14) provided by the developing roller 43. Therefore, the axial length of the 15 partition wall 48 is shorter than the axial length of the image forming area. In addition, as shown in Fig. 3, the partition plate 49 is formed in the upper housing 41b, extending downward from the inner w1 1. :ri with the prtitinri wall 412, cepax:ato the supply chamber 20 46 from the agitation chamber 47. Suspended from the lower end of the partition plate 49, in the axial direction, is a sealing film (not shown), the free end of which contacts the upper edge 481 of the partition wall 48. It should be noted that the axial end of the seal film does not touch the first side edge 482 or the second 25 side edge 483 of the partition wall 483. The supply auger 44 includes: a shaft 44a, extended in the axial direction of the developing roller 43; and blades (spiral blades) 44b, spirally mounted around the outer circumferential face of the shaft 44a. Also, the agitation auger 45 includes: a shaft 18 45a, extended in the axial direction of the developing roller 43; and blades (spiral blades) 45b, spirally mounted around the outer circumferential face of the shaft 45a. The agitation auger 45 also includes a first projection 45c and a second projection 45d, which 5 are plates attached to the outer circumferential face of the shaft 45a. The first projection 45c is located between the second communication port 48b and a toner supply port 68 that will be described later, and the second projection 45d is located, on the first communication port 48a side, near the starting end of the 10 first side edge 482 of the partition wall 48. The developer D containing the toner T and the carrier is stored in the supply chamber 46 and in the agitation chamber 47. It should be noted that the developer D is loaded to a level at which the supply auger 44 and the agitation auger 45 are buried 15 in it, while a level equivalent to the height of the upper edge 481 of the partition wall 48 is not exceeded. The layer thickness control member 50 is located in the housing 41, obliquely up and to the left of the developing roller 43 in Fig. 3. The layer thickness control member 50 defines a 20 predetermined gap relative to, and in the axial direction of, the developing roller 43. This layer thickness control member 50 is formed of a cylindrical shaft, and adjusts the amount of the developer D on the developing roller 43 to maintain a predetermined thickness. 25 A sealing member 51 is mounted at the end of the upper housing 41b near the opening 42. The sealing member 51 is extended in the axial direction of the developing roller 43, and its free end lightly contacts the developing roller 43 to prevent toner T from being detached from the developing roller 40. Therefore, the pressing 19 force applied by the sealing member 51, relative to the developing_ roller 43, is set so that the passage of toner T through the opening 42 can be suppressed, and so that the developer D on the developing roller 43 is not scraped off. 5 The main toner supply unit 60, which serves as a toner supply section, includes a toner storage chamber 61, a first agitator 62, a second agitator 63, a toner supply chamber 64, a supply auger 65 and the connection pipe 66. The toner storage chamber 61 is formed of the lower housing 10 41a, a lower partition wall 61a, extended upward from the inner wall of the sub-housing 41c; the upper housing 41b; and an upper partition wall 61b, extended downward from the inner wall of the upper housing 41b. The lower partition wall 61a and the upper partition wall 61b are closely attached in the axial direction of 15 the developing roller 43. It should be noted that the toner T is stored in the toner storage chamber 61. The first agitator 62 and the second agitator 63 are horizontally arranged, in parallel, in the toner storage chamber 61. The first agitator 62 is located farther from the developing 20 unit 40, while the second agitator 63 is located nearer. The first agitator 62 includes: a shaft 62a, rotatable in the axial direction of the developing roller 43; and a film member 62b, attached to the outer surface of the shaft 62a. The second agitator 63 also includes: a snart 63a, rotatable in the axial direction of the 25 developing roller 43; and a film member 63b, attached to the outer surface of the shaft 63a. The toner supply chamber 64 is defined between the lower housing 41a and the sub-housing 41c, which is bent upward from the lower housing 41a. The toner supply chamber 64 has a cylindrical 20 shape, wherein the supply auger 65 is internally provided. The supply auger 45, which serves as a transporting member, includes a shaft 65a, extended parallel to the axis of the agitation auger 45; and blades 65b, spirally attached to the outer face of the shaft 5 65a. The supply auger 65 also includes a projection 65c mounted to the outer ;ace of the shaft 65a. This projection 65c is located at a position opposite the toner supply port 68, which will be described later. Furthermore, a toner inlet 67, which connects the toner 10 storage chamber 61 to the toner supply chamber 64, is formed in one end side (at the rear in Fig. 3) of the sub-housing 41c. In the other end side (at the front in Fig. 3) of the sub-housing 41c, the toner supply port 68 is formed to connect the toner supply chamber 64 to the agitation chamber 47. 15 The basic image forming processing performed by the image forming apparatus 10 will now be described while referring to Figs. 1 and 2. First, when the image forming apparatus 10 receives image data from an image reader (a scanner) (not shown) or a computer (not shown) , an image processor (not shown) performs predetermined 20 image processing, such as shading correction, position correction, gamma correction and frame deletion and moving, for the received reflectance data. The individual color (YMCK) image data are output to the exposure device 15 after the image processing has been performed. 25 In accordance with the received color image data, the exposure device 15 exposes the photosensitive drums 14 to exposure beams emitted by the individual semiconductor lasers. The surfaces of the photosensitive drums 14 are charged to a predetermined potential by the charging devices 31 (the charging rollers 31a), and 21 thereafter, are scanned and exposed by the exposure device 15. Then, latent images are formed. Thereafter, the latent images on the photosensitive drums 14 are developed by the developing devices 32 and toner images are obtained. The developing operation 5 performed by the developing devices 32 will be explained in detail. The toner images formed on the photosensitive drums 14 are transferred to the transfer portions where the photosensitive drums 14 contact the corresponding transfer rollers 19. Meanwhile, the sheet conveying system supplies a sheet P, from either the manual 10 feeding tray 23 or the cassette storage unit 26, in accordance with a timing at which the furthest upstream yellow toner image reaches the yellow transfer portion. The sheet P, while attracted to the conveying belt 16 by the attraction roller 18, is sequentially conveyed to the transfer portions. 15 At the transfer portions for the individual colors, the sheet P is sandwiched, through the conveying belt 16, between the photosensitive drum 14 and the transfer rollers 19. At this time, a transfer bias (a positive polarity in this embodiment) , having has a polarity opposite that of the charging polarity (a negative 20 polarity in this embodiment) on the toner, is applied to each of the transfer rollers 19. Thus, charges having polarities opposite those of the toners on the photosensitive drums 14 are applied, through the transfer rollers 19, to the sheet P on the conveying belt 16. As a result, toner held on the photosensitive drums 14 25 is electrostatically attached to the sheet P, to which the toner images on the photosensitive drums 14 are thereby transferred. As the surfaces of the photosensitive drums 14 progressively pass through the transfer portions, the charge elimination devices 33 continuously remove the charges on them, and the cleaning devices 22 34 remove from the photosensitive drums 14 foreign substances, such as residual toner, in preparation for the next step in the image forming process. In the cleaning device 34, foreign substances, such as residual toner removed by the cleaning blade 34a, are swept 5 to a waste toner collection chamber by the scraping member 34, which horizontally reciprocates as the arm 34e is rotated. After the toner images have been electrostatically transferred to the sheet P, the sheet P is conveyed, while electrostatically attracted to the conveying belt 16, until it 10 reaches the fixing device 20, located downstream in the direction in which the sheet P is conveyed. The fixing device 20, using heat and pressure, performs a fixing process that securely fixes the toner images to the sheet P. The sheet P, bearing the fixed image, is then discharged to the sheet delivery portion 21 located atop 15 the image forming apparatus 10. This completes the image forming process sequence. The operation of the developing device 32 performed for the image forming processing will now be described while referring to Figs. 3 to 6. 20 In the developing unit 40, rotations of the supply auger 44 and the agitation auger 45 are initiated, and in the supply chamber 46, the supply auger 44 carries the developer D in one direction (in Figs. 3 and 6, from the rear to the front, and in Fig. 4, from the top to the bottom), while in the agitation chamber 47, the 25 agitation auger 45 carries the developer D in a direction opposite that in which carried by the supply auger 44 (in Figs. 3 and 6, from the front to the rear, and in Fig. 4, from the bottom to the top) . Since at both longitudinal ends, the supply chamber 46 and the agitation chamber 47 communicate with each other via the first 23 communication port 48a and the second communication port 48b, the developer D is agitated in the housing 41 and transported cyclically. At this time, the carrier (not shown) contained in the developer D has a positive charging polarity, while the toner T has a negative 5 charging polarity. Thus, as the developer D is agitated and carried, the toner T and the carrier in the developer rub against each other, so that the polarity of the charge on the carrier becomes positive and the polarity of the charge on the toner T becomes negative. When the thus agitated developer D is transported to the 10 supply chamber 46, opposite the developing roller 43, the carrier contained in the developer D is magnetically attracted by the magnetic force of magnetic poles provided for the magnetic roller 43a, and is transferred to the developing sleeve 43b. At this time, since the toner T carrying a negative polarity charge is 15 electrostatically attracted to the carrier carrying a positive polarity charge, the toner T is also transferred to the developing sleeve 43b, with the carrier. Therefore, the developer D, containing the toner T and the carrier, is attached to the developing sleeve 43b, and is carried thereon in consonance with the rotation 20 of the developing sleeve 43b and by the magnetic force produced by the charge on the magnetic roller 43a. Sequentially, thereafter, the layer of the developer D on the developing sleeve 43b reaches the portion facing the layer thickness control member 50, where its volume is adjusted, in accordance with a gap defined between 25 the developing sleeve 43b and the layer thickness control member 50, to provide a predetermined thickness, and as the developing sleeve 43b continues to be rotated, the developer D is carried to the opening 42, opposite the photosensitive drum 14. It should be noted that the developer D that can not pass through the portion 24 facing the layer thickness control member 50 is returned to the supply chamber 46 by gravity. At this time, a power source (not shown) applies a predetermined bias (e.g., a voltage obtained by superimposing an 5 AC voltage with a DC voltage having a negative polarity) to the developing sleeve 43b. Thus, in the neighboring developing area on the photosensitive drum 14, the toner T contained in the developer D on the developing sleeve 43b is transferred to the latent image forming area (the area exposed to the light emitted by the exposure 10 device 15) on the photosensitive drum 14, and the electrostatic latent image is developed to obtain a visible image. Since the carrier on the developing sleeve 43b is magnetically attracted by the magnetic poles of the magnetic roller 43a, it is not transferred to the photosensitive drum 14. 15 Thereafter, the developer D that was passed through the opening 42 in the housing 41 and was used for image development continues to be retained and carried by the developing sleeve 43b. Thereafter, because of a repulsive magnetic field that is formed between magnetic poles having the same polarity, which are 20 adjacently located in the circumferential direction of the developing sleeve 43b, the carrier D is separated from the developing sleeve 43b and dropped into the supply chamber 46. The developer D dropped into the supply chamber 46 is agitated and again transported by the supply auger 44 and the agitation auger 45 in 25 preparation for its subsequent use for image development. As the process for developing an electrostatic latent image on the photosensitive drum 14 is continued to obtain a visible image, the ratio (the toner density) of the toner T to the developer D in the developing unit 40 is gradually reduced. Therefore, the 25 developing device 32 employs the main toner supply unit 60 to supply new toner T to the developer D in the developing unit 40, where the toner density has been reduced. Next, the operation for supplying the toner T to the 5 developing unit 40 will be described. In the toner storage chamber 61 of the main toner supply unit 60, the first agitator 62 and the second agitator 63 are rotated and transport the toner T from the toner storage chamber 61 to the developing unit 40. The film member 63b, suspended from the second 10 agitator 63, is so designed that the toner T can be carried upward in Fig. 4. As a result, the toner T is moved toward the toner inlet 67, and then, part of the toner T stored in the toner storage chamber 61 enters the toner supply chamber 64 through the toner inlet 67. When the toner density in the developing unit 40 is lowered, 15 the rotation of the supply auger 65 in the toner supply chamber 64 is started. As the supply auger 65 is rotated in the toner supply chamber 64, it transports the toner T in one direction (in Figs. 3 and 6, from the rear to the front, and in Fig. 4, from the top to the bottom) . Thus, the toner T that is moved from the toner supply 20 chamber 64 through the toner inlet 67 is transported by the supply auger 65 until it reaches the vicinity of the toner supply port 68. Since the projection 65c is located at the supply auger 65 in the vicinity of the toner supply port 68, the toner T transported by the rotating blades 65b settles near the position at which the 25 projection 65c is formed. The number of rotations performed by the supply auger 65 and the turning ON/OFF of the supply auger 65 can be appropriately controlled, and when the toner density in the developing unit 40 is very low, the supply auger 65 need only be rotated fast, or be continuously driven to increase the amount of 26 the toner T to be transported (the supply rate). Furthermore, in the developing unit 40, the developer D is cyclically transported by the supply auger 44 and the agitation auger 45. Downstream of the second communication port 48b and 5 upstream of the toner supply port 68, in the direction in which the developer D is transported, the projection 45c is arranged for the agitation auger 45, and the developer D transported by the rotating blades 45b settles at the position where the projection 4Sc is formed. Therefore, in the agitation chamber 47, the amount 10 of the developer D that settles in the vicinity of the projection 45c is increased, while the amount of the developer D that settles near the toner supply port 68 located downstream is reduced. That is, the surface level of the developer D in the vicinity of the toner supply port 68 is lowered. 1s Then, in the vicinity of the toner supply port 68, the pressure applied by the toner T in the toner supply chamber 64 is increased, and the pressure applied by the developer D in the agitation chamber 47 is reduced. As a result, the toner T in the toner supply chamber 64 enters the agitation chamber 48 of the developing unit 40 through 20 the toner supply port 68. Therefore, new toner T is supplied to the agitation chamber 47. The new toner T supplied to the agitation chamber 47 is agitated, by the agitation auger 45, with the developer D present in the agitation chamber 47. Then, the resultant developer D in 25 the agitation chamber 47 is moved toward the first communication port 48a. Figs. 7A and 7B are schematic diagrams for explaining the transportation of the developer D from the agitation chamber 47 to the supply chamber 46 through the first communication port 48a. 27 That is, Fig. 7A is a top view of the developing device 32 showing the movement of the developer D, and the Fig. 7B is a side view of the developing device 32 showing the movement of the developer D. In these diagrams, thick arrows are used to indicate the 5 direction in which the developer D is moved. The first side edge 482 is the inclined edge of the partition wall 48 on the first communication port 48a side. When the developer D has reached the second projection 45d provided for the agitation auger 45 in the agitation chamber 47, the transporting of the 10 developer D by the agitation auger 45 is temporarily interrupted, and the developer D settles near the second projection 45d, i.e., near the first side edge 482. Then, this developer D is again agitated by the agitation auger 45, and is gradually carried across the first side edge 482 and to the supply chamber 46. During this 15 process, the developer D in the agitation chamber 47 is sequentially moved across the first side edge 482 in the axial direction of the agitation auger 45. The developer D that was not carried across the first side edge 482 is transported along a detour, and also enters the supply chamber 46. 20 As a result, while being stirred horizontally and vertically, the developer D in the agitation chamber 47 is supplied to an inlet area M in the supply chamber 46 furthest upstream in the developer D transporting direction. As a result, in the inlet area M, new toner T and old developer D are mixed together, or developer D having 25 a high toner density and developer D having a low toner density are mixed together. Therefore, in the supply chamber 46, the developer D is more appropriately mixed than when it is in the agitation chamber 47, and developer D for which the toner density is almost uniform can be transported. Thus, a variance in the toner 28 density does not occur for the developer D to be supplied to the developing roller 43, and when a toner image is obtained by developing an electrostatic latent image on the photosensitive drum 14, uneven toner density can be suppressed. 5 In this embodiment, especially, the developing device 32 is compactly made in order for the image forming apparatus 10 to be downsized. However, conventionally, the axial lengths of the supply chamber 46 and the agitation chamber 47 can not be extended to agitate and transport the developer D. That is, like the 10 conventional developing device, it is difficult to form the first communication port 48a and the second communication port 48b outside the image forming area. On the other hand, in this embodiment, when the supply auger 44 and the agitation auger 45 are employed to cyclically agitate the developer D, the partition wall 48 15 (specifically, the first side edge 482) is used to stir the developer D. As a result, when the partition wall 48 is provided inside the image forming area, the function for agitating and transporting the developer D and the toner charging function can be obtained. Further, in this embodiment, the second projection 45d is 20 arranged for the agitation auger 45, located near the first side edge 482 of the partition wall 48, in order to settle the developer D near the second projection 45d. Therefore, regardless of the amount of developer D in the developing unit 40, the developer D near the first side edge 482 can be maintained substantially at 25 a constant level. Therefore, almost a constant amount of developer D is transported from the agitation chamber 47 to the supply chamber 46 across the first side edge 482, regardless of how the amount of developer D is changed in accordance with the amount of toner T in the developing unit 40. 29 In this embodiment, the first side edge 482 of the partition wall 48 has been linearly formed. However, the first side edge 482 is not limited to this shape, and may be curved, or may be shaped like a wave. 5 (Second Embodiment) A second embodiment of the present invention is substantially the same as the first embodiment, except that the shape of a partition wall 48 that defines a first communication port 48a differs from that in the first embodiment. In this embodiment, the 10 same reference numerals as used in the first embodiment are also employed to denote corresponding components, and no detailed explanation for them will be given. Fig. 8 is a diagram for explaining the structure and shapes of the partition wall 48 and first communication ports 48a and 48b 15 used for this embodiment. The partition wall 48 includes an upper edge 481, a first side edge 484, a second side edge 483 and a notch 485 (specifically, 485a, 485b, 485c and 485d) formed near the first side edge 484. The upper edge 484 maintains a constant level in the axial 20 direction of a supply auger 44 and an agitation auger 45, as in the first embodiment. The notch 485 is formed in the end of the upper edge 481 near the first communication port 48a. The first side edge 484 defines, with one side wall of a lower housing 41a, the first communication port 48a that connects a supply 25 chamber 46 to an agitation chamber 47. Unlike in the first embodiment, the fist side edge 484 in this embodiment is formed substantially perpendicularly. Further, in this embodiment, the first notch 485a, the second notch 485b, the third notch 485c and the fourth notch 485d comprising the notch 485 also function as 30 part of the first communication port 48a. As in the first embodiment, deve-loper D is transported, through the first communication port 48a, from the agitation chamber 47 to the supply chamber 46. As in the first embodiment, the second side edge 482, with 5 the other side wall of the lower housing 41a, defines the second communication port 48b that connects the supply chamber 46 to the agitation chamber 47. The second side edge 483 is formed substantially perpendicularly. And as in the first embodiment, the developer D is transported through the second communication port 10 48b from the supply chamber 46 to the agitation chamber 47. The two axial ends of the partition wall 48 are positioned inside the image forming enabled area (an area on a photosensitive drum 14 in which image forming can be performed in the main scanning direction) using a developing roller 43 (see Fig. 4). 15 The notch 485 will now be described. As described above, the notch 485 includes the first notch 485a, the second notch 485b, the third notch 485c and the fourth notch 485d. In this embodiment, the fourth notch 485d, the third notch 485c, the second notch 485b and the first notch 485a are formed in the named order near the 20 first side edge 484, and'the depth is increased in the order the first notch 485a, the second notch 485b, the third notch 485c and fourth notch 485d. Figs. 9A and 9B are schematic diagrams for explaining the transportation of the developer D from the agitation chamber 47 25 to the supply chamber 46 through the first communication port 48a. That is, Fig. 9A is a top view of a developing device 32 showing the movement of the developer D, and the Fig. 9B is a side view of the developing device 32 showing the movement of the developer D. In these diagrams, thick arrows are used to indicate the 31 direction in which the developer D is moved.. The notch 485 (the first, second, third and fourth notches 485a, 485b, 485c and 485d) are formed in the partition wall 48 on the first communication port 48a side. When the developer D has 5 reached a second projection 45d provided for the agitation auger 45 in the agitation chamber 47, the transporting of the developer D by the agitation auger 45 is temporarily interrupted, and the developer D settle near the second projection 45d, i.e., near the notch 485. Then, this developer D is again agitated by the agitation 10 auger 45, and is gradually transported across the first, second, third and fourth notches 485a, 485b, 485c and 485d and to the supply chamber 46. During this process, the developer D in the agitation chamber 47 is sequentially moved across the first, second, third and fourth notches 485a, 485b, 485c and 485d in the axial direction 15 of the agitation auger 45. The developer D that was not carried across the notch 485 is also transported past the first side edge 484 to the supply chamber 46. As a result, as in the first embodiment, while being stirred horizontally and vertically, the developer D in the agitation 20 chamber 47 is supplied to an inlet area M in the supply chamber 46 furthest upstream in the developer transporting direction. As a result, in the inlet area M, new toner T and old developer D are mixed together, or developer D having a high toner density and developer D having a low toner density are mixed together. 25 Therefore, in the supply chamber 46, the developer D is more appropriately mixed than when it is in the agitation chamber 47, and developer D for which the toner density is almost uniform can be transported. Thus, as in the first embodiment, a variance in the toner density does not occur for the developer D to be supplied 32 to the developing roller 43, and when a toner image is obtained by developing an electrostatic latent image on the photosensitive drum 14, uneven toner density can be suppressed. In this embodiment, the notch 485 (first, second, third and 5 fourth notches 485a, 485b, 485c and 485d) has been formed at four places in the partition wall 48. However, the number of notches is not limited to four, and an arbitrary number may be selected. In addition, in this embodiment, the notch 485 has been formed perpendicular to the partition wall 48. However, a notch may be 10 formed horizontally. Furthermore, in this embodiment, the developer D has been transported by forming the notch 485 in the partition wall 48. However, any method can be employed so long as the developer D can be transported across the partition wall 48, and a hole may be formed 15 in the partition wall 48 through which the developer D may be transported. In the first and second embodiments, the developing device 32 that employs a developer (a so-called two-component developer) containing toner T and a carrier has been explained. However, any 20 other developer can be employed. For example, the above described arrangement can be applied for a developer (a so-called one-component developer) that contains toner T and does not contain a carrier, and the developer in the fully mixed state can be supplied to the developing roller 43. 25 Moreover, in the first and second embodiment, the supply auger 44 and the agitation auger 45 have been employed to cyclically convey the developer D. However, in addition to the supply auger 44 and the agitation auger 45, one or more augers may be provided, and the developer D may be agitated and transported by all of the augers. 33

Claims

1. A developing device comprising: a housing that includes an opposed portion, in which 5 an opening is formed, opposite a latent image holding member holding an electrostatic latent image, and that has developer stored inside thereof; a developer holding member that is rotatably arranged at position facing the opening in the housing, and that 10 holds developer and develops an electrostatic latent image on the latent image holding member; a first agitation and transporting member that is extended inside of the housing, and that agitates the developer, transports the developer in an extensional 15 direction of the developer holding member and supplies the developer holding member with the developer; a second agitation and transporting member that is extended inside of the housing, and that agitates the developer and transports the developer in an opposite 20 direction to the extensional direction of the first agitation and transporting member; and a partition wall that is positioned inside of the housing, that separates a first transporting chamber, which stores the first agitation and transporting member, from a 25 second transporting chamber, which stores the second agitation and transporting member, and that is configured to form a communication port linking to communicate between the second transporting chamber and the first transporting chamber, 30 wherein the developer in the second transporting chamber is gradually transported to the first transporting chamber through the communication port across the partition wall in - 35 an extensional direction of the second agitation and transporting member; and wherein the partition wall on the communication port side has a height reduced in a direction in which the 5 developer is transported by the second agitation and transporting member.

2. The developing device as claimed in claim 1, wherein the first agitation and transporting member and the 10 second agitation and transporting member are arranged horizontally, and the partition wall is arranged perpendicularly.

3. The developing device as claimed in claim 1 or claim 2, wherein the developer contains toner and a carrier. 15

4. The developing device as claimed in claim 3, further comprising a toner supply unit that supplies the second transporting chamber with the toner.

5. An image forming cartridge, which is detachable from an image forming apparatus, comprising: 20 a latent image holding member that holds an electrostatic latent image; and a developing device that develops the electrostatic latent image on the latent image holding member, the developing device comprising: 25 a housing that includes an opposed portion, in which an opening is formed, opposite the latent image holding member, and that has developer stored inside thereof; a developer holding member that is rotatably arranged at position facing the opening in the housing, and that 30 holds developer and develops an electrostatic latent image on the latent image holding member; - 36 a first agitation and transporting member that is extended inside of the housing, and that agitates the developer, transports the developer in an extensional direction of the developer holding member and supplies the 5 developer holding member with the developer; a second agitation and transporting member that is extended inside of the housing, and that agitates the developer and transports the developer in an opposite direction to the extensional direction of the first 10 agitation and transporting member; and a partition wall that is positioned inside of the housing, that separates a first transporting chamber, which stores the first agitation and transporting member, from a second transporting chamber, which stores the second 15 agitation and transporting member, and that is configured to form a communication port linking to communicate between the second transporting chamber and the first transporting chamber, wherein 20 the communication port is enlarged from upstream to downstream in a direction in which the developer is transported by the second agitation and transporting member.

6. The image forming cartridge as claimed in claim 5, 25 wherein the second agitation and transporting member comprises: a rotary shaft; spiral blades that are spirally arranged on an outer circumferential face of the shaft; and 30 a projection that is formed on the outer circumferential face, in an area opposite the furthest upstream position of the communication port, in a direction - 37 in which the developer is transported by the second agitation and transporting member.

7. An image forming apparatus comprising: a latent image holding member; 5 a latent image forming unit that forms an electrostatic latent image on the latent image holding member; a developing unit that employs toner to develop the electrostatic latent image formed on the latent image 10 holding member by the latent image forming unit; and a transfer unit that transfers the toner image, which is formed on the latent image holding member by the developing unit, to a recording medium, wherein 15 the developing unit comprises: a housing that includes an opposed portion, in which an opening is formed, opposite the latent image holding member, and that has developer stored inside thereof; a developer holding member that is rotatably arranged 20 at position facing the opening in the housing, and that holds developer and develops an electrostatic latent image on the latent image holding member; a supply member that is located inside of the housing, and that agitates and transports the developer, and 25 supplies the developer holding member with the developer; an agitation member that is located inside of the housing, and that agitates and transports the developer so for cyclically moving the developer relative to the supply member; 30 a partition wall that is extended inside of the housing, that divides a supply chamber storing the supply member, and an agitation chamber storing the agitation member, and that is configured to form a first - 38 communication port transporting the developer from the agitation chamber to the supply chamber, and a second communication port transporting the developer from the supply chamber to the agitation chamber; and 5 a low portion that is formed on the partition wall near the first communication port, and that has a height shorter than the partition wall near the second communication port.

8. The image forming apparatus as claimed in claim 7, 10 wherein the partition wall has a length in an extensional direction, the length being shorter than a length, in a direction parallel to the extensional direction of the partition wall, of an electrostatic latent image formed on the latent image holding member. 15

9. A developing device substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.

10. An image forming cartridge substantially as herein 20 described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings and/or examples.

11. An image forming apparatus substantially as herein described with reference to any one of the embodiments of 25 the invention illustrated in the accompanying drawings and/or examples.