Image forming apparatus and developing device

An image forming apparatus comprises: a developing device having an outlet from which a two-component developer is partially discharged while the two-component developer is conveyed; a hopper to which (i) a first cartridge containing a first developer including carriers and (ii) a second cartridge containing a second developer including toner and not carriers are attachable, and operable, when the first cartridge is attached thereto, to supply the first developer to the developing device, and when the second cartridge is attached thereto, to supply the second developer to the developing device; and a switching part operable, when the first developer is supplied, to switch the developing device to a first state in which the two-component developer is partially discharged from the outlet, and when the second developer is supplied, to switch the developing device to a second state in which the two-component developer is not discharged from the outlet.

This application is based on application No. 2010-151323 filed in Japan, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an image forming apparatus and a developing device for developing an electrostatic latent image on an image carrier using a developer, the image forming apparatus including the developing device.

(2) Description of the Related Art

An image forming apparatus, such as a copier or a printer, includes a developing device which contains a two-component developer including carriers and toner, and develops an electrostatic latent image formed on a photosensitive drum.

Examples of a developing method include a so-called trickle developing method. In this method, a developer including fresh carriers (i.e., fresh developer) is supplied into a housing of a developing device little by little via an inlet of the housing. At the same time, developer in the housing is agitated and circularly conveyed. While the developer is being conveyed, an excess amount of developer due to the supply of the fresh developer overflows and is discharged outside the housing via an outlet of the housing (Japanese examined patent application publication No. H02-21591).

According to the trickle developing method, the fresh developer is supplied into the housing from a cartridge, and whereby old carriers in the housing are replaced by fresh carriers and discharged outside the housing. Therefore, deteriorated carriers are less likely to remain in the housing, and deterioration in the developer is suppressed for a long period of time. This realizes high image quality in forming images.

Although realizing high image quality, the use of a developing device for the trickle developing method as described above is costly. This is because such a developing device requires a large amount of fresh developer for supply, and a two-component developer is discharged from the developing device.

Suppose here that a user sometimes needs to print out images having high image quality, such as pictures, but other times needs to print out images that do not require high image quality, such as images including only characters. In this case, the user may not wish to use the developing device for the trickle developing method all the time, since it is costly although providing high image quality.

Here, a normal developing method, which is not the trickle developing method, is less costly. In this method, a two-component developer in a housing is not discharged via an outlet, and a fresh developer including toner and not carriers is supplied into the housing from a cartridge. However, such a normal developing method cannot provide high image quality for a long period of time.

For example, it is possible to prepare two developing devices, i.e., one for the trickle developing method and the other for a normal non-trickle developing method. Then, the user may switch between the two developing devices as necessary. This structure, however, is costly as it requires two types of developing devices. Also, the user needs to keep one of the developing devices not mounted in the image forming apparatus somewhere different from the image forming apparatus, which is bothersome.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above problems, and an aim thereof is to provide an image forming apparatus and a developing device that realize high image quality and low cost as desired by a user.

The above aim is achieved by an image forming apparatus for developing an electrostatic latent image on an image carrier with use of a two-component developer including carriers and toner, the image forming apparatus comprising: a developing device having (i) a conveyance path in which the two-component developer is conveyed and (ii) an outlet from which the two-component developer is partially discharged while the two-component developer is conveyed; a hopper to which (i) a first cartridge containing a first developer including carriers and (ii) a second cartridge containing a second developer including toner and not carriers are attachable, and operable, when the first cartridge is attached thereto, to supply the first developer to the developing device, and when the second cartridge is attached thereto, to supply the second developer to the developing device; and a switching part operable, when the first developer is supplied, to switch the developing device to a first state in which the two-component developer is partially discharged from the outlet, and when the second developer is supplied, to switch the developing device to a second state in which the two-component developer is not discharged from the outlet.

Also, the above aim is achieved by a developing device mounted in an image forming apparatus, and for developing an electrostatic latent image on an image carrier with use of a two-component developer including carriers and toner, the developing device comprising: a conveyance path in which the two-component developer is conveyed, an outlet that is provided in the conveyance path and from which the two-component developer is partially discharged while the two-component developer is conveyed; an inlet that is provided in the conveyance path and from which (i) a first developer including carriers is supplied when a cartridge containing the first developer is attached to the image forming apparatus and (ii) a second developer including toner and not carrier is supplied when a cartridge containing the second developer is attached to the image forming apparatus; and a switching part operable, when the first developer is supplied, to switch the developing device to a first state in which the two-component developer is discharged from the outlet, and when the second developer is supplied, to switch the developing device to a second state in which the two-component developer is not discharged from the outlet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes an embodiment of an image forming apparatus according to the present invention, by taking a tandem-type color digital copier (hereinafter, simply “copier”) as an example.

FIG. 1shows an overall structure of a copier10according to Embodiment 1.

As shown inFIG. 1, the copier10includes an image reader11, an image former12, a paper feeder13, a fixer14, a controller15, an operation panel16, etc. The copier10forms a color image using yellow (Y), magenta (M), cyan (C) and black (K) or a monochrome image using black, for example, and reproduces the image on a recording sheet. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, respectively.

The image reader11obtains image data by reading an image on a document set thereto, and outputs the image data.

The image former12includes imaging parts20Y to20K that respectively correspond to colors Y to K, an intermediate transfer belt21, hoppers7Y to7K, supply motors8Y to8K, etc.

The imaging parts20Y to20K respectively include photosensitive drums1Y to1K, charge rollers2Y to2K, exposure parts3Y to3K, developing devices4Y to4K, primary transfer rollers5Y to5K, cleaners6Y to6K for cleaning the photosensitive drums1Y to1K, etc, and form toner images of Y to K on the photosensitive drums1Y to1K. The charge rollers2Y to2K, the exposure parts3Y to3K, the developing devices4Y to4K, the primary transfer rollers5Y to5K, and the cleaners6Y to6K are all disposed around the photosensitive drums1Y to1K.

Each of the developing devices4Y to4K contains a two-component developer that includes carriers and toner (hereinafter “developer”), and is switchable between (i) a trickle developing method as a first developing method and (ii) a normal developing method as a second developing method (hereinafter “non-trickle developing method”).

The intermediate transfer belt21is endless and suspended by a driving roller22and a driven roller23in a tensioned manner. The intermediate transfer belt21is driven to rotate in the direction of arrow A inFIG. 1.

A cartridge9Y, which contains a Y-color developer for supply, is attachable to the hopper7Y. The hopper7Y supplies the Y-color developer to the developing device4Y by an instruction from the controller15. The cartridge9Y comes in two types, i.e., a first cartridge containing a first developer that includes carriers and toner, and a second cartridge containing a second developer that includes toner and not carriers. The cartridge9Y is exchangeable between two types of cartridges, i.e., the first and second cartridges, and either the first cartridge or the second cartridge is attached to the hopper7Y.

The cartridge9Y is exchangeable between two types and attachable to the hopper7Y, so that when the developing method is switched between the trickle developing method and the non-trickle developing method, a developer corresponding to the developing method that has been switched to is supplied. The cartridge9Y is attachable and detachable by a user (i.e., operator).

The same applies to the other hoppers7M to7K, and cartridges9M to9K are detachable from the hoppers7M to7K, respectively. The cartridges9M to9K come in two types, i.e., first and second types, and contain developers M to K, respectively. The hoppers7M to7K supply developers in the cartridges9M to9K attached thereto, to the developing devices4M to4K, by an instruction from the controller15.

The paper feeder13includes a paper feed cassette31, a feed roller32, a conveyance roller pair33, a timing roller pair34, a secondary transfer roller35, etc. The paper feed cassette31contains sheets S. The feed roller32feeds the sheets S in the paper feed cassette31, one at a time, onto a conveyance path37. The conveyance roller pair33conveys the sheet S that has been fed, and the timing roller pair34adjusts the timing for conveying the sheet S to a secondary transfer position351.

The fixer14includes a fixing roller and a pressure roller that are pressed against each other, and a heater for heating the fixing roller.

The operation panel16includes keys and a liquid crystal display17. The keys receive instructions (e.g., a copying instruction), and selections (e.g., color mode or monochrome mode). The liquid crystal display17displays information for giving a notification or a warning to a user.

Upon receiving an instruction for copying or the like via the operation panel16from the user, the controller15controls the image reader11, the image former12, etc. to start a copying operation based on the instruction. Specifically, the controller15causes the image reader11to read a document image, thereby obtaining image data. Then, the controller15drives laser diodes of the exposure parts3Y to3K, based on the image data. As a result, the laser diodes of the exposure parts3Y to3K emit laser beams L respectively corresponding to the colors Y to K, and the photosensitive drums1Y to1K are exposure-scanned on a line-by-line basis.

The photosensitive drums1Y to1K are uniformly charged by the charge roller2Y to2K before the exposure scanning, so that electrostatic latent images are formed on the photosensitive drums1Y to1K by the exposure scanning of the laser beams L. The electrostatic latent images on the photosensitive drums1Y to1K are developed (i.e., visualized) by developers contained in the developing devices4Y to4K. As a result, toner images are formed on the photosensitive drums1Y to1K.

The toner images on the photosensitive drums1Y to1K are sequentially primary-transferred onto the intermediate transfer belt21, by the electrostatic force acting between the primary transfer rollers5Y to5K and the photosensitive drums1Y to1K. At this time, the toner images are transferred to the same position on the intermediate transfer belt21at different timings, so that they are superimposed on each other at the position. After being superimposed on the intermediate transfer belt21, the toner images of the respective colors are conveyed to the secondary transfer position351by the rotation of the intermediate transfer belt21.

In the meanwhile, the paper feeder13feeds a sheet S via the timing roller pair34to the secondary transfer position351at the timing when the toner images are conveyed thereto. The sheet S, which has been fed by the paper feeder13, passes through between the intermediate transfer belt21and the secondary transfer roller35. When the sheet S passes through therebetween, the toner images on the intermediate transfer belt21are collectively secondary-transferred onto the sheet S, by the electrostatic force acting between the secondary transfer roller35and the driving roller22.

After passing the secondary transfer position351, the sheet S is conveyed to the fixer14. When the sheet S passes through the fixer14, the toner images on the sheet S are fixed onto the sheet S by heat and pressure. The sheet S passes through an ejection roller pair36and is ejected onto an ejection tray38.

The above describes an operation in the case of color mode for forming a color image. However, in the case of monochrome mode for forming only an image of the color K for example, only the imaging part20K for the color K is driven to form a K-color toner image.

FIG. 2is a sectional view showing a structure of the developing device4Y.FIG. 3schematically shows the hopper7Y supplying toner to the developing device4Y.FIG. 4shows the developing device4Y seen from the front of the copier10. For the convenience of description,FIG. 3does not show the exposure part3Y and so on. Although using developers of different colors, the developing devices4Y to4K and the hoppers7Y to7K have the same structures. Therefore, the following describes the developing device4Y and the hopper7Y, and descriptions of the structures of the other developing devices4M to4K and hoppers7M to7K are omitted.

As shown inFIG. 2, the developing device4Y includes a housing50, a developing roller51, a supply screw52, an agitation screw53, and a developer detection sensor54. The components from the housing50to the agitation screw53are elongated along an axis direction of the photosensitive drum1Y (i.e., a direction perpendicular to a paper surface: hereinafter “axis direction”).

The housing50is partitioned by a partition (i.e., dividing wall)57into upper and lower portions, i.e., a supply chamber58, an agitation chamber59, etc. The developing roller51and the supply screw52are disposed in the supply chamber58and the agitation screw53is disposed in the agitation chamber59. The supply chamber58and the agitation chamber59contain a developer D.

The developing roller51is disposed at an opening of the supply chamber58, the opening facing the photosensitive drum1Y. The developing roller51includes a developing sleeve511and a magnet roller512. The developing sleeve511is tubular, and the magnet roller512is inserted in the developing sleeve511along the axis direction.

The magnet roller512includes a plurality of magnetic poles, i.e., N-poles and S-poles. For example, the N-poles and the S-poles are disposed alternately along the circumferential direction of the magnet roller512. An edge of the magnet roller512in the axis direction is fixed to the housing50so as to prevent the magnet roller512from rotating. Each of the magnetic poles extends along the axis direction.

The developing sleeve511is partially exposed from the opening of the housing50so as to face the photosensitive drum1Y. The developing sleeve511is held by the housing50in a manner that the developing sleeve511is rotatable in the direction of an arrow shown inFIG. 2. The developing sleeve511rotates around the magnet roller512that is stationary, while holding (i.e., carrying) the developer D on its surface by the magnetic force of the magnet roller512.

The supply screw52is disposed in the supply chamber58, and faces the photosensitive drum1Y with the developing roller51in between. The supply screw52is rotatably held by the housing50parallel to the developing roller51in the axis direction. The supply screw52rotates in the direction of an arrow shown inFIG. 2, thereby conveying the developer D in the supply chamber58along the axis direction and supplying the developer D to the developing roller51.

The agitation screw53is disposed in the agitation chamber59, and is rotatably held by the housing50parallel to the developing roller51in the axis direction. The agitation screw53rotates in the direction of an arrow shown inFIG. 2, thereby conveying and agitating the developer D in the agitation chamber59along a direction opposite from the direction of the supply screw52conveying the developer D. The developing sleeve511, the supply screw52, and the agitation screw53rotate by the drive force of a motor that is not shown in figures.

The developer detection sensor54is disposed at the bottom of the agitation chamber59, and measures the ratio of carriers to toner that are both included in the developer D conveyed inside the agitation chamber59. The developer detection sensor54transmits, to the controller15, a detection signal indicating the ratio of the carriers to the toner. The controller15controls the supply of the developer from the hopper7Y to the developing device4Y, such that the ratio of the carriers to the toner falls within an appropriate range. Specifically, the controller15performs this control by driving the supply motor8Y, based on the detection signal transmitted from the developer detection sensor54. Details of this control are described later.

As shown inFIG. 3, the hopper7Y includes a cartridge housing70Y, a spiral roller71Y, and a cartridge type detection sensor72Y.

The cartridge housing70Y is provided for housing the cartridge9Y that contains a developer Da. The cartridge9Y is detachable from the cartridge housing70Y. As described above, the cartridge9Y comes in two types, i.e., the first cartridge containing the first developer that includes carriers and toner, and the second cartridge containing the second developer that includes toner and not carriers.

InFIG. 3, “9Y” denotes the first cartridge, “Da” denotes the first developer in the first cartridge9Y, “9Yb” denotes the second cartridge, and “Db” denotes the second developer in the second cartridge9Yb.

The first cartridge9Y corresponds to the trickle developing method, and the second cartridge9Yb corresponds to the non-trickle developing method. Therefore, in the case of using the trickle developing method, the first cartridge9Y is attached so as to supply the first developer that corresponds to the trickle developing method.

In the case of switching to the non-trickle developing method, the second cartridge9Yb is attached so as to supply the second developer that corresponds to the non-trickle developing method. The same applies to the case with the other colors. That is, first cartridges9M,9C, and9K correspond to the trickle developing method, and second cartridges9Mb,9Cb, and9Kb (not shown) correspond to the non-trickle developing method.

The spiral roller71Y rotates by the drive force of the supply motor8Y, and conveys, to a pipe73Y, the first developer Da (or the second developer Db) in the cartridge9Y (or the cartridge9Yb) that is attached to the hopper7Y. After being conveyed to the pipe73Y, the first developer Da (or the second developer Db) passes through the pipe73Y to be conveyed into the housing50of the developing device4Y, via a developer receiver55Y (seeFIG. 4) provided at an upper portion of the housing50.

The cartridge type detection sensor72Y is provided at the cartridge housing70Y, and outputs, to the controller15, a signal indicating whether the cartridge set in the cartridge housing70Y is the first cartridge9Y or the second cartridge9Yb. In the present embodiment, the first cartridge9Y and the second cartridge9Yb are provided with identification information pieces at predetermined positions thereof. Each identification information piece indicates whether the corresponding cartridge is the first cartridge9Y or the second cartridge9Yb. The cartridge type detection sensor72Y reads the identification information piece of the cartridge set to the cartridge housing70Y, and transmits the identification information piece to the controller15. For example, the identification information pieces may be marks that each have a different shape, and the cartridge type detection sensor72Y may detect a difference between the mark of the cartridge set to the cartridge housing70Y and the other mark. Alternatively, the identification information pieces may be barcodes, the cartridge type detection sensor72Y may read the barcode of the cartridge set to the cartridge housing70Y.

Upon receiving an identification information piece, the controller15judges whether the cartridge set to the cartridge housing70Y is the first cartridge9Y or the second cartridge9Yb, based on the identification information piece (judgment of the type of cartridge). Based on a result of the judgment, the controller15outputs, to the user, a warning that indicates switching of the position of a shutter (described later) of the developing device4Y. Details of the outputting of the warning are described later.

When using the trickle developing method, the user attaches the first cartridge9Y to the hopper7Y. When switching to the non-trickle developing method, the user detaches the first cartridge9Y from the hopper7Y and attaches the second cartridge9Yb to the hopper7Y. When switching from the non-trickle developing method to the trickle developing method, the user detaches the second cartridge9Yb from the hopper7Y, and attaches the first cartridge9Y to the hopper7Y. In this way, a developer corresponding to the developing method currently being used is supplied from the cartridge containing the developer to the developing device4Y.

InFIG. 3, a reference sign80shown by a dashed line denotes a collection tank (seeFIG. 10) for collecting the developer D discharged in the trickle developing method. The collection tank80is detachably attached to the copier10. In the present embodiment, an outer cover is provided on a front side of the copier10such that the outer cover can be freely opened and closed. The user can open the outer cover so as to attach/detach the collection tank80and to change the cartridge from the front of the copier10. Note that the collection tank80also collects residual toner discharged from the cleaners6Y to6K. The residual toner is removed from the photosensitive drums1Y to1K by the cleaners6Y to6K cleaning the photosensitive drums1Y to1K.

FIG. 5is a sectional view of the developing device4Y taken along the line A-A inFIG. 2.FIG. 6is a sectional view of the developing device4Y taken along the line B-B inFIG. 2. InFIGS. 5 and 6, a crosswise direction corresponds to the axis direction. The right side along the axis direction indicates the front of the copier, and the left side along the axis direction indicates the back of the copier. Note that the developer D is not shown inFIGS. 5 and 6.

As shown inFIGS. 5 and 6, the supply chamber58and the agitation chamber59in the housing50are tubular and elongated along the axis direction. The supply chamber58and the agitation chamber59are separated from each other by the partition57, but in communication with each other via (i) opening93(seeFIG. 5) at one end (right side) of the partition57along the axis direction and (ii) opening94(seeFIG. 5) at the other end (left side) of the partition57along the axis direction.

The supply screw52is composed of a rotational shaft and a spiral blade provided along the outer circumferential surface of the rotational shaft. Both ends of the supply screw52in the axis direction are rotatably held by side walls of the supply chamber58via bearings.

The agitation screw53is composed of a rotational shaft and a spiral blade provided along the outer circumferential surface of the rotational shaft. Both ends of the agitation screw53in the axis direction are rotatably held by side walls of the agitation chamber59via bearings.

A gear is attached to each of the developing roller51, the supply screw52, and the agitation screw53, specifically to each of their shaft portions at the back side of the copier10. The gears are engaged with each other, so that an external rotational drive force is transmitted to the developing roller51, the supply screw52, and the agitation screw53via the gears, thus driving the developing roller51, the supply screw52, and the agitation screw53to rotate.

When the developing roller51, the supply screw52, and the agitation screw53are driven to rotate, the developer D in the supply chamber58is conveyed by the supply screw52in an X direction shown by the arrow X. While being conveyed by the supply screw52, the developer D is supplied to the developing roller51.

When the developer D arrives at the opening93, which is located at the front side of the copier10and at the end of the supply screw52in the downstream side in the developer conveyance direction of the supply screw52, the developer D is conveyed to the agitation chamber59via the opening93.

After being conveyed to the agitation chamber59, the developer D is further conveyed by the agitation screw53in an X′ direction shown by the arrow X′ (i.e., a direction opposite from the X direction). When the developer D arrives at the opening94, which is located at the back side of the copier10and at the end of the agitation screw53in the downstream side in the developer conveyance direction of the agitation screw53, the developer D is conveyed to the supply chamber58via the opening94. In this way, the developer D is circularly conveyed in the housing50in the direction shown by the arrows X and X′ inFIG. 5.

In the supply chamber58, a conveyance path in which the developer D is conveyed by the supply screw52in the X direction is referred to as a first conveyance path92. Also, in the agitation chamber59, a conveyance path in which the developer D is conveyed by the agitation screw53is referred to as a second conveyance path92.

The opening93allows the downstream side of the first conveyance path91in the developer conveyance direction to communicate with the upstream side of the second conveyance path92in the developer conveyance direction. The opening93also serves as a first communication path93in which the developer D is conveyed from the first conveyance path91to the second conveyance path92. The opening94allows the downstream side of the second conveyance path92in the developer conveyance direction to communicate with the upstream side of the first conveyance path91in the developer conveyance direction. The opening94also serves as a second communication path94in which the developer D is conveyed from the second conveyance path92to the first conveyance path91.

As shown inFIG. 6, the first developer Da (or the second developer Db) supplied from the hopper7Y is conveyed from the developer receiver55Y of the housing50, which is provided at the front side of the copier10, to the agitation chamber59, via an inlet98of the agitation chamber59at an end portion thereof located at the front side of the copier10. When conveyed to the agitation chamber59, the first developer Da (or the second developer Db) is conveyed and agitated by the agitation screw53, together with the developer D in the agitation chamber59.

An outlet99of the developer is provided at the bottom of the supply chamber58in an end portion thereof located at the front side of the copier10. Also, a shutter56for opening and closing the outlet99is provided in the vicinity of the outlet99.

FIGS. 7A and 7Bcorrespond respectively toFIGS. 5 and 6. InFIGS. 7A and 7B, the supply screw52and the agitation screw53are not shown so that a structure of the shutter56is easily understood.FIG. 8is a schematic perspective view showing the structure of the shutter56and a part of the housing50at the front side of the copier10.

As shown inFIGS. 7A,7B and8, the shutter56includes a first shutter part61, a second shutter part62, and a holder60. The first shutter part61and the second shutter part62are formed integrally on the holder60. The shutter56is held by the housing50such that the shutter56is slidable (i.e., movable) by a predetermined distance along the axis direction (i.e., an E direction shown by an arrow E inFIG. 8).

The first shutter part61has the shape of a curved plate, and is positioned outside the housing50. The first shutter part61is bent in an arc so as to be in contact with an outer bottom surface of the supply chamber58in the housing50, and to coincide with the shape of the outer bottom surface thereof. When the shutter56is moved to the front side of the copier10, the first shutter part61moves to a closing position for closing the outlet99and closes the outlet99. When the shutter56is moved to the back side of the copier10, the first shutter part61moves away from the outlet99and to an opening position for opening the outlet99and opens the outlet99.

The second shutter part62has the shape of a flat plate elongated in the E direction, and extends inside the housing50via an elongated hole503(seeFIG. 8) that is a through-hole provided at the bottom of the housing50. The second shutter part62is held parallel to the partition57(seeFIG. 2) provided inside the housing50.

When the shutter56is moved to the back side of the copier10, an end portion621of the second shutter part62at the back side of the copier10makes contact with the partition57. As a result, the second shutter part62becomes a part of the partition57that partitions the housing50into the supply chamber58and the agitation chamber59.

When the shutter56is moved to the front side of the copier10, the end portion621(seeFIG. 8) of the second shutter part62moves away from the partition57. As a result, a part of the partition57disappears, and a communication path95(seeFIG. 9B) for conveying the developer D is newly formed between the supply chamber58and the agitation chamber59.

The communication path95(hereinafter, “third communication path”) communicates a portion911(seeFIG. 5) of the first conveyance path91with a portion921(seeFIG. 5) of the second conveyance path92. The portion911is located more upstream in the developer conveyance direction in the first conveyance path91than the first communication path93, and the portion921is located more downstream in the developer conveyance direction in the second conveyance path92than the first communication path93. When the developing method is switched to the non-trickle developing method, the third communication path95is used as a part of a circulation conveyance path in which the developer D is circularly conveyed. Details of switching of the developing method are described later. The third communication path95is formed between the developing roller51and the first communication path93in the axis direction.

As shown inFIG. 8, the holder60is connected to the second shutter part62via a connecting part622. A back surface of the holder60, which is a surface closer to the back of the copier10, has a hole65(shown by a dashed line) that is elongated. The hole65extends from the back surface toward the front side of the copier10along the E direction. A pin69is disposed at a position facing the opening of the hole65of the holder60. The pin69is arranged immediately below the housing50, parallel to the E direction, pointing toward the front side of the copier10. The elongated hole503, which is a through-hole elongated in the E direction, is provided in a part of the housing50, the part being located at the front side of the copier10and between the first conveyance path91and the second conveyance path92.

The second shutter part62is inserted from the outside (bottom part) to the inside (upper part) of the housing50via the elongated hole503. In this way, the second shutter part62is arranged inside the housing50, and the connecting part622is engaged with the elongated hole503.

The pin69provided for the housing50is fit in and engaged with the hole65of the holder60. Also, the connecting part622of the shutter56is engaged with the elongated hole503of the housing50. In this state, the shutter56is held by the housing50such that the shutter56is slidable along the E direction.

The pin69is inserted in a compression coil spring68. The compression coil spring68constantly applies, to the holder60, a biasing force directed toward the front side of the copier10. The holder60has a head portion601at the front side of the copier10. The head portion601has two states, i.e., (i) a pressed state in which the head portion601is pressed toward the back side of the copier10, against the biasing force of the compression coil spring68, and (ii) a non-pressed state of not being pressed. The state of the head portion601is switched between the pressed state and the non-pressed state, thus causing the position of the shutter56to be switched between a first position corresponding to the trickle developing method and a second position corresponding to the non-trickle developing method.

FIG. 9Ashows the shutter56being placed at the first position (trickle corresponding position).FIG. 9Bshows the shutter56being placed at the second position (non-trickle corresponding position).

As shown inFIG. 9A, in the trickle corresponding position, the first shutter part61is positioned away from the outlet99so as to open the outlet99. Also, the second shutter part62is positioned at a blocking position for blocking the third communication path95by cutting across the third communication path95. As a result, the second shutter part62makes contact with the partition57to be a part of the partition57and closes the third communication path95.

When the third communication path95is blocked, the developer D conveyed in the X direction by the supply screw52in the supply chamber58cannot pass through the third communication path95. Accordingly, the developer D is conveyed toward the first communication path93at the front of the copier10, passes over the outlet99, and is thereafter conveyed to the agitation chamber59via the first communication path93. While the developer D passes over the outlet99, a part of the developer D is discharged outside the housing50from the outlet99. According to the trickle developing method described above, although the developer D in the developing device4Y gets deteriorated, the developer D is gradually replaced with fresh developer. This makes it possible to maintain high image quality over a long period of time, and to reduce the frequency of replacing the deteriorated developer with new one by a service man or the like. As a result, the life of the developer D is prolonged.

In the trickle developing method, the first conveyance path91, the first communication path93, the second conveyance path92, and the second communication path94constitute a circulation conveyance path90along which the developer D is circularly conveyed.

As shown inFIG. 9B, at the non-trickle corresponding position, the first shutter part61moves to the closing position for closing the outlet99and closes the outlet99. Also, the second shutter part62moves away from the partition57to an opening position for opening the third communication path95. In this way, a part of the partition57disappears, and the third communication path95is opened.

Due to the third communication path95being open, the developer D in the supply chamber58, which is conveyed by the supply screw52in the X direction, is mostly conveyed to the agitation chamber59via the third communication path95.

In the present Embodiment, the agitation chamber59is located obliquely downward with respect to the supply chamber58, as shown inFIG. 2. Therefore, at the time of being conveyed from the supply chamber58to the agitation chamber59, the developer D mainly drops to the agitation chamber59via the third communication path95due to gravity. The remaining part of developer D that has not dropped via the third communication path95is conveyed to the front side of the copier10by the supply screw52.

The part of the developer D conveyed to the front side of the copier10by the supply screw52passes over the outlet99. Since the outlet99is closed, the developer D is not discharged outside the housing50and conveyed to the agitation chamber59via the first communication path93. Unlike the trickle developing method, the developer D in the developing device4Y is not discharged. This makes it possible to reduce the amount of developer required for developing, thus reducing cost.

In the non-trickle developing method, the first conveyance path91, third communication path95, the second conveyance path92, and the second communication path94mainly constitute a circulation conveyance path901along which the developer D is circularly conveyed.

FIG. 10Ais a sectional view showing a state before the collection tank80is mounted in the copier10, where a part of the collection tank80is shown by a side view.FIGS. 10B and 10Ceach show a state after the collection tank80is mounted in the copier10.FIG. 10Bshows an example of the case of the trickle developing method.FIG. 10Cshows an example of the case of the non-trickle developing method.

As shown inFIG. 10A, a surface85of the collection tank80that faces the developing device4Y is provided with an open hole81. When being mounted in the copier10, the collection tank80is fixedly held by the copier10in a state where an end portion501(a portion including the outlet99) of the developing device4Y at the front side of the copier10is inserted into the collection tank80via the open hole81, as shown inFIGS. 10B and 10C.

The collection tank80has a projection82, which is slidable up and down, at a position on the surface85thereof, in particular, at a position lower than the open hole81. The projection82makes contact with the head portion601of the shutter56of the developing device4Y, so as to switch the position of the shutter56between the trickle corresponding position and the non-trickle corresponding position. The position of the projection82is manually switchable by the user. When the user applies a certain degree of pressure to the projection82, the projection82is switched between an uppermost position (shown by a solid line) and a lowermost position (shown by a dashed line) as shown inFIG. 10A. The position of the projection82is not switched by a pressure produced by, for example, vibrations of the copier10when images are formed.

In the case of switching to the trickle developing method, the user can mount the collection tank80to the copier10in the following manner. First, the user mounts the first cartridge9Y to the hopper7Y, and switches the position of the projection82to the uppermost position. Then, the user holds and inserts the collection tank80into the copier10, from the front side of the copier10in a direction shown by the arrow F (i.e., direction toward the back side of the copier10).

As shown inFIG. 10B, when the collection tank80is mounted in the copier10with the projection82being at the uppermost position, (i) the projection82makes contact with the head portion601of the shutter56of the developing device4Y, and (ii) the head portion601is pressed toward the back side of the copier10(i.e., pressed against the biasing force of the compression coil spring68), whereby the shutter56moves to the trickle corresponding position.

At the trickle corresponding position, the outlet99of the developing device4Y is open. Therefore, while the developer D is circularly conveyed in the housing50, a part of the developer D is discharged from the outlet99and collected into the collection tank80.

In the case of switching to the non-trickle developing method, the user mounts the second cartridge9Yb to the hopper7Y instead of the first cartridge9Y, and switches the position of the projection82from the uppermost position to the lowermost position, and thereafter mounts the collection tank80to the copier10.

As shown inFIG. 10C, when the collection tank80is mounted in the copier10with the projection82being at the lowermost position, the projection82does not make contact with the head portion601of the shutter56of the developing device4Y. As a result, the head portion601moves toward the front side of the copier10by the biasing force of the compression coil spring68, whereby the shutter56moves to the non-trickle corresponding position.

At the non-trickle corresponding position, the outlet99of the developing device4Y is closed. Therefore, although being circularly conveyed, the developer D is not discharged from the outlet99.

Note that the collection tank80corresponds to (i.e., is commonly used by) each of the developing devices4Y to4K. Therefore, a pair of the open hole81and the projection82is provided for each of the developing devices4Y to4K, so that the position of the projection82is individually switchable for each developing device.

As described above, changing both the type of cartridge and the position of the shutter for each color enables the user to switch between the trickle developing method and the non-trickle developing method as desired at any time. Accordingly, it is not necessary to prepare both a developing device dedicated to the trickle developing method and a developing device dedicated to the non-trickle developing method, allowing the user to easily switch between the developing methods at low cost.

FIG. 11is a block diagram showing a structure of the controller15.

As shown inFIG. 11, the controller15includes a CPU151, a ROM152, a RAM153, a cartridge type judgment part154, and a display controller155. These components151to155exchange data with each other.

The CPU151controls operations of components such as the image reader11, the image former12, and the paper feeder13, based on a control program stored in the ROM152, and thereby realizes smooth operations for forming color and monochrome images. Also, the CPU151receives information input by the user using the operation panel16. Furthermore, based on the detection signals from the developer detection sensors54Y to54K, the CPU151judges whether the ratio of carriers to toner in the developer D currently contained in each of the developing devices4Y to4K falls within an appropriate range that is predetermined as a standard. When judging that the ratio of carriers and toner of any of the colors does not fall within the appropriate range, the CPU151performs control to cause one of the supply motors8Y to8K that corresponds to the color to be driven, so that the developer is supplied to the corresponding one of the developing devices4Y to4K and the ratio of carriers to toner of the color falls within the appropriate range.

This supply control is applied to both the trickle developing method and the non-trickle developing method. In this case, it is possible to employ a method in which the appropriate range is different for each color or each developing method. Alternatively, it is possible to employ a method of detecting the amount of developer contained in a developing device. Then, if the amount of developer in the developing device is detected to be smaller than an appropriate value that is a standard, an operation for supplying the corresponding developer may be performed until the amount of the developer reaches the appropriate value.

Also, the following method is possible. That is, the amount of toner consumed by developing is estimated based on the cumulative value of the number of pixels (i.e., dot count) when the laser beam emitted from an exposure part exposure-scans the corresponding photosensitive drum on a pixel-by-pixel basis. Then, the amount of developer corresponding to the estimated consumption amount is supplied to the corresponding developing device. By corresponding in advance one dot with the amount of toner supposedly consumed for forming a one-pixel image, the amount of consumed toner is estimated from the cumulative value of the dot count. Furthermore, it is possible to employ a method of detecting, with use of a reflective sensor or the like, the amount (i.e., density) of toner actually used to form a toner image on a photosensitive drum or on an intermediate transfer belt. According to this method, the detected amount of toner is considered as the amount of toner consumed for developing the toner image, and the amount of toner corresponding to the detected amount is supplied to the corresponding developing device. Also, it is possible to employ a supply method in which the aforementioned processes are combined. A supply method is selected based on the structure of a developing device, so that it is suitable for the developing device.

The RAM153is a work area for the CPU151.

The cartridge type judgment part154receives detection signals (identification information pieces each indicating the type of cartridge) from the cartridge type detection sensors72Y to72K, judges whether the cartridges set in the respective hoppers7Y to7K are the first cartridge or the second cartridge (determines the type of cartridge), and transmits results of the judgment to the display controller155.

The display controller155displays various pieces of information on the liquid crystal display17of the operation panel16. Also, based on the results of the judgment from the cartridge type judgment part154, the display controller155causes the liquid crystal display17to display a warning message which instructs the user to move the shutters56of the developing devices4Y to4K to the respective positions that correspond to the cartridges currently set to the developing devices4Y to4K.

FIG. 12is a flowchart showing the details of control for displaying the warning message.

As shown inFIG. 12, the display controller155acquires the type of each of the cartridges set to the hoppers7Y to7K (step S1). The acquisition is performed by receiving results of judgment from the cartridge type judgment part154.

When the type of cartridge is the first cartridge for the trickle developing method (“YES” in step S2), the display controller155causes the liquid crystal display17to display a warning message instructing the user to switch the position of the shutter56of the corresponding developing device to the trickle corresponding position (step S3), and ends the processing.

When the type of cartridge is the second cartridge for the non-trickle developing method (“NO” in step S2), the display controller155causes the liquid crystal display17to display a warning message instructing the user to switch the position of the shutter56of the corresponding developing device to the non-trickle corresponding position (step S4), and ends the processing.

The above processing is performed for each of the imaging parts20Y to20K.

Specifically, suppose that the first cartridges9Y,9M, and9C for the trickle developing method are used for the colors Y, M, and C, and the second cartridge9Kb for the non-trickle developing method is used for the color K. In this case, for example, the warning message indicates “Please set the projections84of the collection tank for the colors Y, M, and C to the uppermost positions, and set the projection84of the collection tank for the color K to the lowermost position”.

The user can look at the warning message on the liquid crystal display17, and switch, for each color, the position of the projection84on the collection tank80to either the trickle corresponding position (i.e., uppermost position) or the non-trickle corresponding position (i.e., lowermost position), or check whether the projections84are set to the respective positions indicated by the warning message. Note that the warning display described above is not limited to the message, and may be graphics showing the positions of the projections for the respective colors. Also, the warning described above does not always need to be displayed. For example, the warning may be provided by means of audio output or the like, as long as it can provide the user with a notification for indicating or warning about the positions of the shutters, in the same manner as the above warning message.

As for the timing for the warning, the user is preferably notified when the cartridge currently set is replaced with a new one. This is because of the following reason. If the new cartridge is of the same type as the previous one, the position of the shutter56does not need to be changed; however, if the new cartridge is of a different type from the previous one, the position of the shutter56needs to be changed to a position corresponding to the new cartridge. In the sense of encouraging the user to check the positions of the shutters56, a notification such as a warning display may be provided for the user all the time.

With the stated structure, the following advantages are obtained. During a period in which the user often needs to print out images having high image quality (e.g., pictures), the user can set the first cartridges9Y to9K for the respective colors to the hoppers7Y to7K, and switch the position of each shutter56to the trickle corresponding position (i.e., switch each projection84to the uppermost position), so as to switch the developing method to the trickle developing method that gives priority to image quality. This makes it possible to form images having high image quality.

Subsequently, when the user needs to print out K-color images that do not require high image quality, such as images including only characters, the user can switch the developing method to the non-trickle developing method with respect to only the color K so as to give priority to cost-effectiveness. Specifically, the user can replace the first cartridge9K with the second cartridge9Kb, and switch only the position of the shutter56of the developing device4K to the non-trickle corresponding position (i.e., switch the projection84to the lowermost position). This makes it possible to form character images of the color K at low cost. As described above, the developing method can be switched for each color between the trickle developing method and the non-trickle developing method.

Although it is described above that the shutter56is manually switched by the user as described above, the present invention is not limited to such. The present invention may take another structure as long as it enables switching between a first state and a second state, the first state being a state in which the two-component developer is discharged from the outlet99when the first developer Da is supplied, the second state being a state in which the two-component developer is not discharged from the outlet99when the second developer Db is supplied.

For example, it is possible, as described below, to dispose an actuator (e.g., solenoid) that has a function of switching the position of the shutter56between the trickle corresponding position and the non-trickle corresponding position by applying a pressure to the shutter56in the axis direction. Also, keys for receiving a user input specifying the position of the shutter56may be provided for the operation panel16. Then, the actuator may be driven such that, when a key operation using the keys is performed by the user, the position of the shutter56is switched to the position specified by the key operation. This improves operability since the user does not need to directly hold the projection84and move the projection84up and down in order to switch the position of the shutter56.

As described above, the shutter56is formed by integrating the first shutter part61for opening and closing the outlet99with the second shutter part62for opening and closing the third communication path95, so that the outlet99and the third communication path95are opened and closed at the same time in conjunction with each other. However, the first shutter part61and the second shutter part62may be separately provided so that they can move separately from each other. In this way, the opening and closing of the outlet99may be performed separately from the opening and closing of the third communication path95.

In Embodiment 1, the shutter56has a function of opening and closing both the outlet99and the third communication path95. Embodiment 2 is different from Embodiment 1 in that the shutter opens and closes only the outlet99and an actuator opens and closes the third communication path95. Hereinafter, descriptions that are the same as in Embodiment 1 are omitted to avoid repetition, and the same reference signs are given to components that are the same as in Embodiment 1.

FIG. 13Ashows a structure of a shutter201in the present embodiment, andFIG. 13Bshows a structure of an actuator202(hereinafter also referred to as “magnetic field generators”) for opening and closing the third communication path95.

As shown inFIG. 13A, the shutter201corresponds to the first shutter part61in Embodiment 1, and does not include a part corresponding to the second shutter part62that serves as a part of the partition57between the supply chamber58and the agitation chamber59. The part corresponding to the second shutter part62is provided for the housing50as a partition203that is stationary.

Accordingly, when the shutter201is slid in the axis direction, only the outlet99is opened and closed. InFIG. 13A, the shutter201is in a closed state which corresponds to the non-trickle developing method. Note that the shutter201includes the holder60in the same manner as the shutter56in Embodiment 1. Therefore, the outlet99is opened and closed by switching the position of the projection84of the collection tank80between the uppermost position and the lowermost position.

The third communication path95is not provided with a member that mechanically closes the third communication path95. Instead, a pair of magnetic field generators202is provided outside the housing50, as shown inFIG. 13B. Specifically, one of the magnetic field generators202is provided at a first position and the other of the magnetic field generators201is provided at a second position, the first and second positions sandwiching the third communication path95therebetween and being located along a direction perpendicular to the conveyance direction of the developer D. The magnetic field generators202generate a magnetic field, and thereby form a shield that is made of the developer D to close the third communication path95.

FIG. 13Cschematically shows a state in which a shield204made of the developer D is formed in the third communication path95.

Each of the magnetic field generators202is made of an electromagnet, and generates a magnetic field when an electric current is applied thereto. The carriers included in the developer D are magnetic. Therefore, when a magnetic field is generated by the magnetic field generators202, the carriers in the developer D existing in the third communication path95and the toner attached to the carriers are attracted to the magnetic field generators202by a magnetic force, and stay in the third communication path95.

The developer D staying in the third communication path95forms a shield204that separates the supply chamber58from the agitation chamber59, and thereby blocks the third communication path95that is a path along which the developer D is conveyed. When the application of the electric current to the magnetic field generators202is stopped, the magnetic force that attracts the developer D to the magnetic field generators202disappears. As a result, the shield formed by the developer D is cleared, and the third communication path95in which the developer D is conveyed is opened.

Switching between the application and block of the electric current with respect to the magnetic field generators202is performed based on a result of judgment pertaining to the type of cartridge currently being set. That is, when the cartridge type judgment part154judges that the type of cartridge is the first cartridge for the trickle developing method, the controller15applies the electric current to the magnetic field generators202since the third communication path95needs to be closed. On the other hand, when the cartridge type judgment part154judges that the type of cartridge is the second cartridge for the non-trickle developing method, the controller15prohibits the application of the electric current to the magnetic field generators202since the third communication path95needs to be opened.

Note that the position of the shutter201is switched manually by the user in the same manner as in Embodiment 1. Therefore, a warning message is displayed that instructs the user which position the shutter201needs to be switched. The above structure is applied to each of the developing devices4Y to4K.

As described above, the third communication path95can be opened and closed by the magnetic field generated by the magnetic field generators202, instead of the shutter. Note that the generation and suspension of the magnetic field, which are performed by the magnetic field generators202, may be switched therebetween by the user using a switch or the like.

In the above embodiments, switching of the position of the shutter is manually performed by the user. Embodiment 3 is different from Embodiments 1 and 2 in that the user does not need to manually perform the switching operation.

Specifically, the actuator301(seeFIG. 11), such as a solenoid, is disposed on the developing device or the copier10itself. The actuator301can switch the position of the shutter56in Embodiment 1 between the trickle corresponding position and the non-trickle corresponding position by applying a pressure to the shutter56in the axis direction. As shown by the flowchart ofFIG. 14pertaining to control of the position of the shutter, the cartridge type judgment part154in the controller15judges the type of cartridge currently being set (step S21). When the cartridge type judgment part154judges that the type of cartridge is the first cartridge for the trickle developing method (“YES” in step S22), the controller15controls the drive of the actuator301so as to switch the shutter56to the trickle corresponding position (step S23), and ends the processing.

When the cartridge type judgment part154judges that the type of cartridge is the second cartridge for the non-trickle developing method (“NO” in step S22), the controller15controls the drive of the actuator301so as to switch the shutter56to the non-trickle corresponding position (step S24), and ends the processing. The above structure is applied to each of the developing devices4Y to4K.

With the stated structure, it is not necessary to display a warning for the user so as to encourage switching of the shutter position. Also, the user can switch between the developing methods by only setting a cartridge that corresponds to a desired developing method, to the corresponding hopper, thus improving convenience for the user.

The actuator301is not limited to a solenoid as long as it can move the shutter56by applying a pressure to the shutter56in the axis direction. For example, the actuator301may be a linear motor or a feed screw mechanism.

The present invention is not limited to an image forming apparatus and a developing device, and may be a method for switching between the aforementioned developing methods. Furthermore, the present invention may be a program that causes a computer to execute the method. Also, the program according to the present invention may be recorded on a computer-readable recording medium. Examples of such a computer-readable medium include (i) a magnetic disk such as a magnetic tape or a flexible disk, (ii) an optical recording medium such as a DVD, a CD-ROM, a CD-R, an MO, and a PD, and (iii) a flash memory-type recording medium including such as Smart Media™. The program may be manufactured and provided in the form of any of the aforementioned recording media. The program may also be transmitted and provided via a wired or wireless network including the Internet, broadcast, an electric communication line, satellite communication, etc.

Although the present invention has been described based on the embodiment, it is obvious that the present invention is not limited to the above-mentioned embodiment, and various modifications may be implemented.

(1) According to the above embodiments, one developing device is used for both the trickle developing method and the non-trickle developing method. In addition to this structure, it is possible to notify the user of the timing for switching between the developing methods.

For example, it is possible to cumulatively calculate, for each color, the operation time of the corresponding developing device in the non-trickle developing method. When the cumulative time exceeds a predetermined time length, the image forming apparatus may notify the user that the developing device needs to be switched to the trickle developing method, because the developer (especially carriers) in the developing device is deteriorated to a degree that lowers image quality by progression of abrasion of carrier particles by agitation or the like. Here, the notification may be provided for the user by, for example, display or audio as described above.

Suppose that the user is notified of switching from the non-trickle developing method to the trickle developing method, with respect to the developer device corresponding to the color Y. In this case, the user may perform the operations as described above. That is, the user may open the outer cover on the front side of the image forming apparatus, and set the first cartridge9Y to the hopper7Y, instead of the second cartridge9Yb. After detaching the collection tank80and switching the position of the projection84for the color Y from the lowermost position to the uppermost position, the user may attach the collection tank80back to the image forming apparatus.

The above describes a structure example of notifying of switching from the non-trickle developing method to the trickle developing method. However, it is possible to employ a structure for notifying of switching from the trickle developing method to the non-trickle developing method instead. In other words, it is possible to cumulatively calculate, for each color, the operation time of the corresponding developing device in the trickle developing method. When the cumulative time exceeds a predetermined time length, the image forming apparatus may notify the user that the developing device is recommended to be switched to the non-trickle developing method, because the deterioration of the developer is resolved by the fresh developer replacing the deteriorated developer to a sufficient extent. In a case where the user switches to the non-trickle developing method according to the notification, the user may perform operations opposite from the aforementioned operations for replacing the cartridge and switching the position of the projection84of the collection tank80.

The condition of notifying the user is not limited to the operation time, and may be information that indicates the degree of deterioration of the developer. For example, the condition may be the number of times images are formed (hereinafter “image formation count”), the remaining amount of the developer in the cartridge, the ratio of the number of times color images are formed (hereinafter “color image formation count”) to the number of times monochrome images are formed (hereinafter “monochrome image formation count”), or the like.

The larger the image formation count, the longer the operation time. This means that deterioration in the developer has progressed. Therefore, when the image formation count exceeds a predetermined count, the image forming apparatus may notify the user that the non-trickle developing method needs to be switched to the trickle developing method.

Similarly, the smaller the remaining amount of the developer in the cartridge, the longer the operation time. Therefore, when the remaining amount is smaller than a predetermined amount, the image forming apparatus may notify the user that the non-trickle developing method can be switched to the trickle developing method.

Also, the larger the ratio of the color image formation count to the monochrome image formation count, the greater the frequency of use of the developing devices4Y,4M, and4C for forming color images. This means that the deterioration of developers contained in the developing devices4Y,4M, and4C has progressed. Therefore, when the ratio exceeds a predetermined value, the image forming apparatus may notify the user that the developing methods of only the developing devices for forming color images need to be switched from the non-trickle developing method to the trickle developing method. Note that the developing method of the developing device4K may also be switched to the trickle developing method, together with the developing devices4Y,4M, and4C. The user can arbitrarily switch between the developing methods as desired.

In the case where the position of the shutter56is automatically switched as described in Embodiment 3, the following structure is possible. That is, after the user switches a cartridge according to the aforementioned notification, the position of the shutter56may be automatically switched to the position corresponding to the type of the cartridge set after the switching. Regarding the notification of switching between the developing methods as described above, it is possible to notify either one or both of (i) the switching from the non-trickle developing method to the trickle developing method and (ii) the switching from the trickle developing method to the non-trickle developing method.

(2) In Embodiment 1, the projection84is provided for the collection tank80which is a different member from the shutter56. The projection84is capable to be switched between a state of being engaged with the shutter56and a state of being disengaged with the shutter56, so as to switch the position of the shutter56between the trickle corresponding position and the non-trickle corresponding position. However, the present invention is not limited to such. The present invention may employ a different member as long as the member can switch the position of the shutter56. For example, the shutter56may be fixed to the housing50by a fixing screw at either the trickle corresponding position or the non-trickle corresponding position. When switching the position of the shutter56, the user may remove the fixing screw and, after switching the position, tighten the fixing screw again. The present invention may employ another structure or method different from those described above.

(3) In the above embodiments, the first communication path93and the third communication path95are provided as parts of the circulation conveyance path of the developer D. Also, the outlet99is arranged in the first conveyance path91, at a portion from (i) a connected portion in which the first conveyance path91is connected to the third communication path95to (ii) a connected portion in which the first conveyance path91is connected to the first communication path93located in the downstream side in the developer conveyance direction (i.e., X direction), inclusive of the connected portions. However, the position of the outlet99is not limited to such.

For example, the outlet99may be arranged in the first communication path93. Alternatively, the outlet99may be arranged in the second conveyance path92, at a portion from (i) a connected portion in which the second conveyance path92is connected to the first communication path93to (ii) the inlet98(i.e., supply position) for receiving the developer located in the downstream side in the developer conveyance direction (i.e., X′ direction), inclusive of the connected portion and exclusive of the inlet98.

Also, depending on the positional relationship with the inlet98, the outlet99may be arranged in a portion different from the aforementioned portions. For example, suppose that the inlet98is arranged in a portion of the second conveyance path92, at either the connected portion in which the second conveyance path92is connected to the third communication path95or a portion of the second conveyance path92that is located more downstream than the connected portion in the developer conveyance direction. In this case, the outlet99may be arranged in any of the following portions: (i) a portion of the first conveyance path91that is located more downstream in the developer conveyance direction than the connected portion in which the first conveyance path91is connected to the third communication path95; (ii) the first communication path93; and (iii) a portion of the second conveyance path92that is located more upstream in the developer conveyance direction than the connected portion in which the second conveyance path92is connected to the third communication path95. Note that the outlet99does not always need to be arranged at the bottom of a chamber of the housing50, such as the supply chamber58. The outlet99may be arranged at a side of a chamber of the housing50as long as the developer D currently being conveyed can be discharged outside the housing50.

Furthermore, according to the above embodiment, the shutter56opens the outlet99and closes the third communication path95in the trickle developing method. Also, the shutter56closes the outlet99and opens the third communication path95in the non-trickle developing method. However, it is not limited to such. The present invention may employ a different structure as long as the structure enables switching between a state in which the developer is discharged from the outlet and a state in which the developer is not discharged from the outlet.

For example, the following structure is possible. That is, the first conveyance path91may be split into two conveyance paths, i.e., a conveyance path A and a conveyance path B (each corresponding to a communication path), at the end of the first conveyance path91on the downstream side in the developer conveyance direction. Also, the conveyance paths A and B may be joined together at the end portion of the second conveyance path92in the upstream side in the developer conveyance direction. Further, the conveyance path A may be provided with an inlet whereas the conveyance path B may not be provided with an inlet. In this state, the image forming apparatus may be capable of switching the conveyance path of the developer D from the conveyance path A to the conveyance path B or from the conveyance path B to the conveyance path A.

In this case, the conveyance path is switched to the conveyance path A in the trickle developing method, and to the conveyance path B in the non-trickle developing method. According to the stated structure, the outlet is not opened or closed. Instead, the conveyance path for the developer D is switched between the conveyance path A having the outlet and the conveyance path B having no outlet, whereby the state of the image forming apparatus is switched between the state in which the developer is discharged from the outlet and the state in which the developer is not discharged from the outlet.

Also, the circulation conveyance path is not limited to the above embodiments. For example, the circulation conveyance path of the housing50may not include the third communication path95, and may only include the first conveyance path, the first communication path, the second conveyance path, and the second communication path. Then, the outlet may be arranged in any of the following portions: a portion of the first conveyance path that is more downstream than a portion of the first conveyance path facing the developing roller51in the developer conveyance direction; the first communication path; and a portion of the second conveyance path that is more upstream than the inlet98in the developer conveyance direction. The outlet may be opened or closed depending on whether the developing method is the trickle developing method or the non-trickle developing method. Regarding the opening and closing of the outlet, it is not limited to the structure for switching the shutter between the position for closing the outlet and the position away from the outlet to open the outlet. For example, it is possible to employ a structure where the outlet is provided with a diaphragm mechanism including a plurality of overlapping plates. In this case, the outlet is opened and closed by moving the overlapping plates.

(4) The above embodiments are described with an example of the tandem-type color digital copier. However, the present invention is not limited to such, and is applicable to a color or monochrome image forming apparatus in general, such as a printer, a FAX (facsimile), or an MFP (Multiple Function Peripheral) as long as the image forming apparatus includes at least one developing device and a hopper for supplying developer to the developing device.

Also, according to the above embodiments, the first developer Da includes carriers and toner. However, the first developer Da may include carriers and not toner. In this case, the image forming apparatus further includes another hopper for supplying toner, and performs supply control separately on each of the hoppers, i.e., (i) the hopper for supplying toner and (ii) the hopper for supplying the first developer Da including carriers and not toner. Details of a structure for supplying carriers and toner separately are disclosed in the aforementioned Japanese examined patent application publication, for example.

Furthermore, the present invention may include a structure where the developing device in the image forming apparatus is detachable by the user or the like.

Also, according to the above embodiments, the photosensitive drums are used as image carriers for forming an electrostatic latent image. However, it is not limited to such. For example, it is possible to employ belt-like image carriers. Furthermore, it is described above that the developing roller having the sleeve is used as a developer carrier for carrying the developer D. However, it is not limited to such. It is possible to employ a different member as a developer carrier, as long as it carries the developer D.

Also, the present invention may be any combination of the embodiments and the modifications described above.

CONCLUSION

Each of the embodiment and modifications shown above is an aspect of the present invention to solve the problems discussed in the section of “BACKGROUND OF THE INVENTION”. The embodiment and modifications shown above are summarized as follows.

(1) A first aspect of the present invention is an image forming apparatus for developing an electrostatic latent image on an image carrier with use of a two-component developer including carriers and toner, the image forming apparatus comprising: a developing device having (i) a conveyance path in which the two-component developer is conveyed and (ii) an outlet from which the two-component developer is partially discharged while the two-component developer is conveyed; a hopper to which (i) a first cartridge containing a first developer including carriers and (ii) a second cartridge containing a second developer including toner and not carriers are attachable, and operable, when the first cartridge is attached thereto, to supply the first developer to the developing device, and when the second cartridge is attached thereto, to supply the second developer to the developing device; and a switching part operable, when the first developer is supplied, to switch the developing device to a first state in which the two-component developer is partially discharged from the outlet, and when the second developer is supplied, to switch the developing device to a second state in which the two-component developer is not discharged from the outlet.

(2) A second aspect of the present invention is the image forming apparatus of (1), wherein the switching part switches the developing device to the first state by opening the outlet, and switches the developing device to the second state by closing the outlet.

(3) A third aspect of the present invention is the image forming apparatus of (2), wherein the conveyance path is a circulation conveyance path in which the two-component developer is circularly conveyed, and includes: a first conveyance path that is linear and in which the two-component developer is conveyed in a first conveyance direction; a second conveyance path that is arranged parallel to the first conveyance path, and in which the two-component developer is conveyed in a second conveyance direction opposite the first conveyance direction; a first communication path for communicating a first portion of the first conveyance path located downstream in the first conveyance direction, with a first portion of the second conveyance path located upstream in the second conveyance direction; a second communication path for communicating a second portion of the second conveyance path located downstream in the second conveyance direction, with a second portion of the first conveyance path located upstream in the first developer conveyance path; and a third communication path for communicating a third portion of the first conveyance path with a third portion of the second conveyance path, the third portion of the first conveyance path located more upstream in the first conveyance direction than the first portion thereof, the third portion of the second conveyance path located more downstream in the second conveyance direction than the first portion thereof, the outlet is arranged in any of the following portions: (i) a portion of the first conveyance path located more downstream in the first conveyance direction than the third portion of the first conveyance path; (ii) the first communication path; and (iii) a portion of the second conveyance path located more upstream in the second conveyance direction than the third portion of the second conveyance path, and the switching part closes the third communication path when opening the outlet, and opens the third communication path when closing the outlet.

(4) A fourth aspect of the present invention is the image forming apparatus of (3), wherein the switching part includes: a first shutter operable to move between a first opening position and a first closing position, the first opening position being for opening the outlet by the first shutter separating from the outlet, the first closing position being for closing the outlet by the first shutter covering the outlet; and a second shutter operable to move between a second opening position and a second closing position, the second opening position being for opening the third communication path by the second shutter separating from the third communication path, the second closing position being for closing the third communication path by the second shutter cutting across the third communication path.

(5) A fifth aspect of the present invention is the image forming apparatus of (4), wherein the first shutter is integrated with the second shutter to constitute an integrated shutter, and the integrated shutter is operable to move between a first position and a second position, the first position being a position at which the first shutter is located at the first opening position for opening the outlet and the second shutter is located at the second closing position for closing the third communication path, the second position being a position at which the first shutter is located at the first closing position for closing the outlet and the second shutter is located at the second opening position for opening the third communication path.

(6) A sixth aspect of the present invention is the image forming apparatus of (5), wherein the integrated shutter is manually movable by a user.

(7) A seventh aspect of the present invention is the image forming apparatus of (6) further comprising: a detector operable to detect a type of cartridge mounted in the hopper; and a notifier operable to notify the user that the integrated shutter needs to be located at the first position when the type of cartridge is detected to be the first cartridge, and that the integrated shutter needs to be located at the second position when the type of cartridge is detected to be the second cartridge.

(8) An eighth aspect of the present invention is the image forming apparatus of (5) further comprising: a detector operable to detect a type of cartridge mounted in the hopper; an actuator operable to move the integrated shutter between the first position and the second position; and a controller operable to control the actuator, wherein the controller operable to drive the actuator to cause the integrated shutter to move to the first position when the type of cartridge is detected to be the first cartridge, and to cause the integrated shutter to move to the second position when the type of cartridge is detected to be the second cartridge.

(9) A ninth aspect of the present invention is the image forming apparatus of (3), wherein the switching part includes: a shutter operable to open and close the outlet; and a magnetic field generator operable to switch between generation and suspension of a magnetic field, the magnetic field being for forming a developer shield by causing the two-component developer existing in the third communication path to stay therein.

(10) A tenth aspect of the present invention is the image forming apparatus of (9), wherein the shutter is manually movable by a user between (i) an opening position for opening the outlet by the shutter separating from the outlet and (ii) a closing position for closing the outlet by the shutter covering the outlet.

(11) An eleventh aspect of the present invention is the image forming apparatus of (10) further comprising: a detector operable to detect a type of cartridge mounted in the hopper; a notifier operable to notify the user that the shutter needs to be located at the opening position when the type of cartridge is detected to be the first cartridge, and that the shutter needs to be located at the closing position when the type of cartridge is detected to be the second cartridge; and a controller operable to control the magnetic field generator to generate the magnetic field when the type of cartridge is detected to be the first cartridge, and to suspend the generation of the magnetic field when the type of cartridge is detected to be the second cartridge.

(12) A twelfth aspect of the present invention is the image forming apparatus of (1) further comprising: an acquisition part operable to acquire information indicating a degree of deterioration of the two-component developer contained in the developing device; and a switching notifier operable to notify a user of a timing of switching between a first developing method and a second developing method based on the information acquired by the acquisition part, the first developing method being a method for developing the electrostatic latent image with a supply of the first developer, the second developing method being a method for developing the electrostatic latent image with a supply of the second developer.

(13) A thirteenth aspect of the present invention is a developing device mounted in an image forming apparatus, and for developing an electrostatic latent image on an image carrier with use of a two-component developer including carriers and toner, the developing device comprising: a conveyance path in which the two-component developer is conveyed, an outlet that is provided in the conveyance path and from which the two-component developer is partially discharged while the two-component developer is conveyed; an inlet that is provided in the conveyance path and from which (i) a first developer including carriers is supplied when a cartridge containing the first developer is attached to the image forming apparatus and (ii) a second developer including toner and not carrier is supplied when a cartridge containing the second developer is attached to the image forming apparatus; and a switching part operable, when the first developer is supplied, to switch the developing device to a first state in which the two-component developer is discharged from the outlet, and when the second developer is supplied, to switch the developing device to a second state in which the two-component developer is not discharged from the outlet.

According to the stated structure, the user can switch between the first developing method and the second developing method as desired. Specifically, when the user desires high image quality, images are developed by means of the first developing method in which, while the first developer is supplied from the cartridge containing the first developer, the two-component developer in the developing device is discharged from the outlet. Also, when the user desires low cost, images are developed by means of the second developing method in which, although the second developer is supplied from the cartridge containing the second developer, the two-component developer in the developing device is not discharged from the outlet. As a result, the user does not need to prepare two types of developing devices, i.e., one for the first developing method and the other for the second developing method. This eliminates the need for the user to manage two types of developing devices, and thus improves convenience for the user.