Image forming apparatus with toner recovery system

An image forming apparatus has an image carrier on which an electrostatic latent image is formed, a developing unit that develops the electrostatic latent image using a toner to form a toner image, and a cleaning unit that removes the toner remaining on the image carrier after transferring the toner image to a recording medium. The image forming apparatus includes a buffer housing unit that temporarily houses the toner removed by the cleaning unit, a first carrier unit comprising a carrier driving member, the first carrier unit provided between the cleaning unit and the buffer housing unit, and the first carrier unit carries the toner removed by the cleaning unit to the buffer housing unit using the a carrier driving member, a second carrier unit comprising a carrier driving member, the second carrier unit provided between the buffer housing unit and the developing unit, and the second carrier unit carries the toner housed in the buffer housing unit to the developing unit using the carrier driving member, a waste housing unit connected to the buffer housing unit, and a control unit that separately controls the carrier driving member of the first carrier unit and the carrier driving member of the second carrier unit, wherein the buffer housing unit has an upper limit of housing capacity, and the waste housing unit houses the toner exceeding the upper limit and overflowing from the buffer unit.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to an image forming apparatus that forms an image made of toner such as a printer, a copy machine, or a multifunction machine having plural functions, and particularly to an image forming apparatus suitable for retrieving the toner remaining on an image carrier because of transfer failure or the like at the time of the image formation and effectively reusing a proper quantity of the retrieved toner.

(2) Description of the Related Art

In an image forming apparatus that forms an image using toner as a developer, since toner remains on an image carrier, an intermediate transfer member and the like because of transfer failure or the like at the time of the image formation, removal of the toner by a cleaning device, recirculation of the toner to a developing device and reuse of the toner have been attempted.

For example, in order to address the problem of continuous increase of retrieved toner with the lapse of time while retrieving toner remaining on an image carrier by a cleaner unit and effectively reusing the retrieved toner, the present applicant has previously proposed an image forming apparatus having a waste toner housing unit that houses the toner retrieved by the cleaner unit and carried by a second carrier unit, and a control unit that controls the supply ratio of unused toner and retrieved toner supplied to a developing unit in accordance with a cumulative value of pixel count of image information.

Also, in order to properly process retrieved toner even when the quantity of retrieved toner supplied from a cleaning device exceeds the processing capacity of a classifying device in an image forming apparatus having a toner recycle classifying device that classifies impurities from toner retrieved by the cleaning device, there has been proposed an image forming apparatus having an excessive retrieved toner processing unit that is arranged near the classifying unit and processes excessively supplied retrieved toner, and a quantifying wall that is arranged between the classifying unit and the excessive retrieved toner processing unit and causes the quantity of retrieved toner exceeding the processing capacity of the classifying device to overflow to the excessive retrieved toner processing unit.

However, these proposed image forming apparatuses have the following problems.

In the former image forming apparatus, the second carrier unit that carries the retrieved toner to the waste toner housing unit is provided in the state of being branched from the cleaning unit, and the second carrier unit is driven while its operation is controlled. Therefore, the structure of the apparatus is complicated accordingly. Also, since the operation to carry the retrieved toner to the waste toner housing unit need to be controlled, the control operation is complicated. Moreover, since the quantity of the retrieved toner to be supplied to the developing unit is controlled in accordance with the cumulative value of pixel count or the like, the control operation is further complicated. Such complexity may be increased further when applied to a color image forming apparatus in which plural image carriers are arranged.

On the other hand, in the latter image forming apparatus, measures to prevent clogging or the like and maintenance and inspection of the classifying unit are necessary. Also, the structure of the classifying unit itself is complicated and large-scaled. Moreover, since the quantity of the classified retrieved toner to be supplied to the developing unit is not particularly adjusted, the rate of use of the retrieved toner increases and may cause occurrence of defective image quality such as image fog. Furthermore, there is another problem that the quantity of the retrieved toner to be supplied to the developing unit depends on the processing capacity of the classifying unit.

SUMMARY OF THE INVENTION

This invention has been made in view of the above circumstances and provides an image forming apparatus.

According to an aspect of this invention, An image forming apparatus comprises an image carrier on which an electrostatic latent image is formed, a developing unit that develops the electrostatic latent image using a toner to form a toner image, and a cleaning unit that removes the toner remaining on the image carrier after transferring the toner image to a recording medium, and the image forming apparatus comprises:

a buffer housing unit that temporarily houses the toner removed by the cleaning unit;

a first carrier unit comprising a carrier driving member, the first carrier unit provided between the cleaning unit and the buffer housing unit, and the first carrier unit carries the toner removed by the cleaning unit to the buffer housing unit using the carrier driving member;

a second carrier unit comprising a carrier driving member, the second carrier unit provided between the buffer housing unit and the developing unit, and the second carrier unit carries the toner housed in the buffer housing unit to the developing unit using the carrier driving member;

a waste housing unit connected to the buffer housing unit;

a control unit that separately controlls the carrier driving member of the first carrier unit and the carrier driving member of the second carrier unit,

wherein the buffer housing unit has an upper limit of housing capacity of the toner, and the waste housing unit houses the toner exceeding the upper limit and overflowing from the buffer housing unit.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1shows an image forming apparatus according to a first embodiment of this invention.

In this image forming apparatus1A, its image creating unit10basically includes a photosensitive drum11having an organic photosensitive layer or the like formed on an outer circumferential surface of a drum base rotationally driven in the direction of an arrow at a predetermined speed, a charging unit12that uniformly charges the surface of this photosensitive drum11, a latent image forming unit13that exposes light corresponding to image information to the charged surface of the photosensitive drum11and forms an electrostatic latent image thereon, a developing unit14that develops the electrostatic latent image using a developer (toner) of a predetermined color (in this example, black), a primary transfer unit15that electrostatically transfers the toner image formed by the development to a recording paper P as a recording medium, and a drum cleaning unit16of a blade mode that cleans the surface of the photosensitive drum11. As the developing unit14, a two-component developing unit is used that uses a two-component developer made of toner and carrier.

In the image creating unit10as described above, after the surface of the photosensitive drum11rotated in the direction of the arrow is uniformly charged by the charging unit12, light beams corresponding to color-separated image signals are exposed from the latent image forming unit13to scan the charged surface, thus writing an electrostatic latent image thereon. After the latent image is developed by toner T, which is a two-component developer, carried on a development roll14aand supplied from the developing unit14, and a black toner image is thus formed, the toner image is electrostatically transferred to the recording paper P passing between the photosensitive drum11and the primary transfer unit. The surface of the photosensitive drum11after this transfer is cleaned by having remaining toner Ta, paper particles and the like removed by a blade16aof the drum cleaning unit16.

Next, after the recording paper P, to which the toner image has been transferred, is fed into a fixing unit, not shown, and fixing of the toner image is performed, the recording paper P is discharged to a discharge unit outside of the apparatus. Basic image formation is performed through such an image forming process.

Also, in this image forming apparatus1A, a toner supply unit30that supplies each proper quantity of unused toner Ts to the developing unit14when necessary, and a toner reuse system50that reuses toner Tc removed and retrieved by the drum cleaning unit16.

The toner supply unit30mainly includes a toner cartridge31in which unused toner Ts is housed, a toner send-out driving unit32that sends out a predetermined quantity of the unused toner Ts in the toner cartridge31toward the developing unit14at predetermined timing, and an unused toner carrier pipe34installed to be connected between the toner send-out driving unit32and the developing unit14and having an auger (carrier member formed by a carrier blade continuing spirally around a shaft)33that is rotationally driven inside and sends the toner Ts, as shown inFIG. 1. The operation of the toner supply unit30is controlled by a control unit (70), which will be described later.

The toner reuse system50mainly includes a buffer container51for temporarily housing toner Ta removed by the drum cleaning unit16, a first carrier pipe53for carrying the toner Ta removed by the cleaning unit16to the buffer container51by an auger52rotationally driven within the pipe, a second carrier pipe55for carrying retrieved toner Tc housed in the buffer container51to the developing unit14by an auger54rotationally driven within the pipe, and a waste housing bottle56that causes retrieved toner Tc′ exceeding an upper limit of housing capacity of the buffer container51to overflow and houses the overflowed toner, as shown inFIGS. 1 and 2.

The buffer container51has a housing capacity that enables temporary housing of the toner Tc removed by the drum cleaning unit16, as shown inFIG. 2. This buffer container51has a connection and attachment part51afor the first carrier pipe53, on its upper lateral side, and a connection and attachment part51bfor the second carrier pipe55, on its bottom side, as shown inFIG. 2. At a part of the lateral side of the container51, an upper limit prescription lateral surface51chaving a height equivalent to the upper limit of housing capacity with respect to the toner Tc to be housed, and a toner discharge opening51dcontinuing to the waste housing bottle56is formed above the upper limit prescription lateral surface51c.

The first carrier pipe53is provided between the drum cleaning unit16and the buffer container51. Its auger52is connected to an auger provided within a toner housing part of the cleaning unit16and is provided up to a position where it can reach inside of the buffer container51from the connection and attachment part51aof the buffer container51. The auger52is rotationally driven by an electric motor, not shown, in a direction of carrying the toner. As this auger52is rotationally driven, the toner Ta is carried through the pipe53. The rotational driving of the auger52(electric motor) is controlled by the control unit (70), which will be described later.

The second carrier pipe55is provided between the buffer container51and the developing unit14. In this example, the connection side of the carrier pipe55to the buffer container51is connected to the connection and attachment part51b, whereas the connection part to the developing unit14is not directly connected to the developing unit14but is merged into a halfway part of the unused toner carrier pipe34in the toner supply unit30. The auger54is rotationally driven by an electric motor, not shown, in a direction of carrying the toner Tc. As this auger54is rotationally driven, the toner Tc is carried through the pipe55. The rotational driving of the auger54(electric motor) is controlled separately from the auger52by the control unit (70), which will be described later.

The waste housing bottle56has a housing capacity large enough to house the retrieved toner Tc exceeding the upper limit of housing capacity of the buffer container51(getting beyond the upper limit prescription lateral surface51c) and overflowing thereto. The waste housing bottle56is provided in a state of continuing to the toner discharge opening51dof the buffer container51.

Also, on the bottom side of the housing space of the buffer container51, a removing unit60that is driven to remove waste such as paper particles from the retrieved toner Tc housed in the buffer container51is installed. The removing unit60is formed, for example, by an ultrasonic generator that applies very small vibrations to the toner existing in the container51. As the very small vibrations are applied, the waste attached to the retrieved toner can be separated and segregated to move toward the upper side of the container51.

Moreover, in the buffer container51, a stir-driving unit65that stirs the retrieved toner Tc housed in the buffer container51is installed instead of or together with the removing unit60. The stir-driving unit65is not particularly limited as long as it can stir the retrieved toner Tc. For example, a stir-driving unit having a stirring member formed by shaping a wire member into a coil-like form or crank-like form and caused to rotate within the container is employed.

FIG. 3shows a configuration of a control system that controls each operation of this image forming apparatus1A. A numeral70inFIG. 3represents a control unit70formed by a microcomputer including a storage unit or the like. The control unit70controls the operation of the above-described image creating unit or the like in the image forming process and also controls each operation of the above-described toner supply unit30and toner reuse system50.

The control of the supply unit30by the control unit70is performed via a driving controller71that controls the driving unit for the toner send-out driving unit32in the supply unit30. Specifically, in this control, the control unit70receives signals from a toner supply detection unit72that gathers necessary detection signals for determination of toner supply, including a detection signal from a sensor that detects the presence/absence of toner in the developing unit14and a detection signal from a detection sensor that detects a patch image for density control formed on the photosensitive drum11through process control, then calculates the timing to supply the unused toner Ts and the quantity of the unused toner Ts to be supplied in accordance with a control program stored in advance in a storage unit, and sends a necessary control signal to the driving controller71for the toner send-out driving unit.

The control of the toner reused system50by the control unit70is performed via a first carrier driving controller73that controls the driving unit for the auger52in the first carrier pipe53, a second carrier driving controller74that controls the driving unit for the auger54in the second carrier pipe55, a removal driving controller75that controls the driving unit for the removing unit60, and a stir-driving controller76that controls the driving unit for the stir-driving unit65, which is provided when necessary.

Specifically, in this control, with respect to the first carrier driving controller73, when the control unit70receives a detection signal from a cleaner operation detection unit77that detects the timing of operation (driving of the auger or the like) of the drum cleaning unit16, in accordance with a toner reuse system control program stored in advance in the storage unit, a control signal that drives the first carrier driving controller73synchronously with the operation timing of the cleaning unit16is sent. The operation timing of the cleaning unit16is substantially the same as the execution timing of the image forming process. With respect to the second carrier driving controller74, when a signal is received from the toner supply detection unit72, a control signal that drives the second carrier driving controller74synchronously with the operation timing of the toner supply is sent. With respect to the removal driving controller75(and the stir-driving controller76), the same control signal as the control signal for the first carrier driving controller73is sent at the same time.

Each operation of the toner supply unit30and the toner reuse system50as described above will now be described.

In this image forming apparatus1A, every time the image forming process as described above is executed, the toner T in the developing unit14is consumed and reduced. Therefore, when a signal determining that toner supply is necessary is sent to the control unit70from the toner supply detection unit72, a control signal related to the timing to supply the unused toner Ts and the quantity of the unused toner Ts to be supplied is sent to the driving controller71in the toner supply unit30from the control unit70.

This causes the toner send-out driving unit32to start the operation of its driving unit and thus to drive the auger33in the unused toner carrier pipe34at predetermined timing and for a predetermined period. As a result, the unused toner Ts in the toner cartridge31in the toner supply unit30is carried and supplied to the developing unit14through the unused toner carrier pipe34by the rotationally driven auger33. As the predetermined period has elapsed, the rotational driving of the auger33stops and thus the supply of the unused toner Ts ends.

Also, in the image forming apparatus1A, when the above-described image forming process is executed, the toner Ta remaining on the surface of the photosensitive drum11after the transfer is removed by the drum cleaning unit16. When the operation of this drum cleaning unit16is started, a detection signal from the cleaner operation detection unit77is sent to the control unit70and a driving signal is sent from the control unit70to the first carrier driving controller73in the toner reuse system50.

This causes the first carrier driving controller73to start the operation of its driving unit and thus to rotationally drive the auger52in the first carrier pipe53. As a result, in the toner reuse system50, the toner Ta removed by the drum cleaning unit16is carried to the buffer container51through the first carrier pipe53by the rotationally driven auger52and then housed in the buffer container51. When the image forming processing is ended, the rotational driving of the auger52stops and thus carrying the toner Ta to the buffer container51stops.

Along with the rotational driving of the auger52in this first carrier pipe53, a driving signal is sent from the control unit70to the removal driving controller75(and the stir-driving controller76). This starts the operation of the removing unit60in the buffer container51of the toner reuse system50, and waste is separated and removed from the retrieved toner Tc housed in the container51. When the stir-driving unit65is provided, the stir-driving unit65starts operating and the retrieved toner Tc housed in the container51is stirred. The retrieved toner is thus prevented from aggregating in the container51.

On the other hand, when a signal requesting toner supply is sent from the toner supply detection unit72to the control unit70, a driving signal is also sent from the control unit70to the second carrier driving controller74of the toner reuse system50.

This causes the second carrier driving controller74to start the operation of its driving unit and thus to rotationally drive the auger54in the second carrier pipe55. As a result, the retrieved toner Tc housed in the buffer container51is carried toward the developing unit14through the second carrier pipe55by the rotationally driven auger54. Since the retrieved toner Tc carried through this second carrier pipe55merges into the unused toner carrier pipe34in the toner supply unit30, the retrieved toner Tc is carried to the developing unit14as it is mixed with the unused toner Ts. Thus, the retrieved toner Tc is supplied to and reused in the developing unit14as it is mixed with the unused toner Ts. The quantity of the retrieved toner Tc to be supplied is substantially determined by the rotational driving time of the auger54. When the toner supply operation ends, the auger54stops its rotational driving and thus carrying the retrieved toner Tc to the developing unit14stops.

In this toner reuse system50, when the quantity of the retrieved toner Tc carried to and housed in the buffer container51through the first carrier pipe53exceeds the upper limit prescription lateral surface51cin the container51, the retrieved toner Tc′ corresponding the excess quantity automatically gets beyond the upper limit prescription lateral surface51cand overflows to be housed in the waste housing bottle56through the toner discharge opening51d. A test carried out by using the image forming apparatus1A having this toner reuse system50will now be described.

In this test, the same test image is formed on 10,000 recording papers P by the image forming apparatus1A. After that, a predetermined quantity of unused toner Ts is supplied to the developing unit14from the toner supply unit30, and toner is sequentially supplied while the ratio (%) of retrieved toner Tc supplied from the buffer container51to the quantity of the supplied unused toner is increased by 5% each. The occurrence of image fog in each test image that is newly formed after the toner is supplied at each ratio is observed. Then, the occurrence of image fog is evaluated on the basis of the following evaluation standards. The result of the evaluation is shown inFIG. 4.

The setting conditions in this test are as follows. As the toner T, the toner used for a color copy machine (DocuCenter Color 400CP manufactured by Fuji Xerox Co., Ltd.) is used. As the test image, an image having an image density of 10% is used.

G0: The area coverage of image fog is 0.191% or less.

G1: The area coverage of image fog is 0.971% or less.

G2: The area coverage of image fog is 1.98% or less.

G3: The area coverage of image fog is 2.43% or less.

G4: The area coverage of image fog is 4.3% or less.

The acceptable level in this evaluation is “G2 or lower”.

From the result of this test, in the toner reuse system50, the quantity of the retrieved toner Tc to be supplied to the developing unit14from the buffer container51is set to achieve 30% or less as the ratio of the retrieved toner to the quantity of the unused toner to be supplied. Specifically, a control signal is sent to the second carrier driving controller74to supply 0.3 times or less as much retrieved toner Tc as the quantity of the unused toner to be supplied that is recognized in the toner supply unit30. Also, in this case, the unused toner is supplied under a condition that the quantity of the retrieved toner Tc to be supplied is subtracted from the original quantity of supply.

Second Embodiment

FIG. 5shows an image forming apparatus according to a second embodiment of this invention.

This image forming apparatus1B has plural image creating units10and employs an intermediate transfer mode to enable formation of a color image. Therefore, the image forming apparatus1B has the same configuration as the image forming apparatus1A according to the first embodiment except that a part of the configuration of the toner reuse system50is changed.

First, this color image forming apparatus1B has four image creating units10Y,10M,10C and10K that are dedicated to forming toner images of four colors, that is, yellow (Y), magenta (M), cyan (C) and black (K), respectively. The toner images of the four colors formed by the individual image creating units10(Y, M, C, K) are primarily transferred to overlap each other on the surface of an intermediate transfer belt20. After that, the transferred image is secondarily transferred from the intermediate transfer belt20to a recording paper P as a recording medium. Thus, a so-called full-color image can be formed.

Each of the image creating units10is basically similar to the image creating unit in the first embodiment and includes a photosensitive drum11having an organic photosensitive layer or the like formed on the outer circumferential surface of a drum base that is rotationally driven in the direction of an arrow at a predetermined speed, a charging unit12that uniformly charges the surface of this photosensitive drum11, a latent image forming unit13that exposes light corresponding to image information to the charged surface of the photosensitive drum11and thus forms an electrostatic latent image thereon, a developing unit14that develops the electrostatic latent image by using a developer of predetermined color (one of Y, M, C and K), a primary transfer unit15that electrostatically transfers the toner image formed by the development to the intermediate transfer belt20, and a drum cleaning unit16of a blade mode that cleans the surface of the photosensitive drum11.

Next, the intermediate transfer belt20is an endless belt having a double-layer structure formed by stacking a surface layer of silicone rubber or the like on a belt base made of a polyimide film or the like with its volume resistivity adjusted by containing a conductive material or the like. The intermediate transfer belt20is tensioned on a driving roll21, a backup roll22of a secondary transfer unit, plural slave rolls23,24and the like, and is arranged to contact the photosensitive drums11of the individual image creating units10(Y, M, C, K) between the slave rolls23and24. The intermediate transfer belt20travels in a rotating manner in the direction of an arrow by the rotational power of the driving roll21. The slave roll23is a tension roll that applies predetermined tension to the intermediate transfer belt20.

Around this intermediate transfer belt20, a secondary transfer roll25that presses the intermediate transfer belt20to the backup roll22to form a pressure contact area of the secondary transfer unit is provided. At a position on the intermediate transfer belt20facing the driving roll21, a belt cleaning unit26of a blade mode that cleans the surface of the belt20is provided.

In each of the image creating units10(Y, M, C, K) as described above, after the surface of the photo sensitive drum11rotating in the direction of the arrow is uniformly charged by the charging unit12, a light beam corresponding to a color-separated image signal is exposed from the latent image forming unit13to scan the charged surface, thus writing an electrostatic latent image thereon. Then, after the latent image is developed by toner, which is a two-component developer, supplied from the developing unit14, and a toner image of predetermined color is formed, the toner image is primarily transferred sequentially and electrostatically onto the surface of the intermediate transfer belt20passing between the photosensitive drum11and a transfer roll15aof the primary transfer unit. The surface of the photosensitive drum11after the primary transfer is cleaned as the remaining toner or the like is removed from the surface of the photosensitive drum11by the blade of the drum cleaning unit16.

The toner image transferred (multiple-transferred) on the intermediate transfer belt20as described above is carried by the rotation of the belt20to the secondary transfer unit that faces the secondary transfer roll25arranged to face the backup roll22. Then, in the secondary transfer unit, the toner image on the intermediate transfer belt20is secondarily transferred electrostatically onto a recording paper P transported to the secondary transfer unit from a paper feeder system, not shown, at predetermined timing in accordance with the timing of the image creation of the toner image and the timing of the secondary transfer. The surface of the intermediate transfer belt20after the secondary transfer is cleaned as the remaining toner Tb of each color component, paper particles and the like after the secondary transfer are removed from the surface of the intermediate transfer belt20by a blade26aof the belt cleaning unit26.

Next, the recording paper P on which the toner image has been transferred is fed into a fixing unit, not shown, and the toner image is fixed. After that, the recording paper P is discharged to a discharge unit outside of the apparatus. A basic color image is formed through such an image forming process.

This image forming apparatus1B also has a toner supply unit30B that supplies each proper quantity of unused toner Ts (Y, M, C, K) of each color to the four developing units14(Y, M, C, K) when necessary, and a toner reuse system50B that reuses toner Tc removed and retrieved by the belt cleaning unit26.

The toner supply unit30B mainly includes toner cartridges31(Y, M, C, K) in which the unused toner Ts of each color is housed, a toner send-out driving unit32that sends out a predetermined quantity of the unused toner Ts of each color in each of the toner cartridges31toward the developing units14at predetermined timing, and unused toner carrier pipes34installed to be connected between the toner send-out driving unit32and each of the developing units14(Y, M, C, K) and having an auger33that is rotationally driven inside and sends the toner Ts. As for the toner carrier pipes34, only the unused toner carrier pipe for black (K) is shown inFIG. 5while the unused toner carrier pipes for the other colors are not shown. The operation of this toner supply unit30B is controlled by a control unit (70), which will be described later.

The toner reuse system50B mainly includes a buffer container51for temporarily housing toner Tb removed by the belt cleaning unit26, a first carrier pipe53B for carrying the toner Tb removed by the cleaning unit26to the buffer container51by an auger52rotationally driven within the pipe, a second carrier pipe55B for carrying retrieved toner Tc housed in the buffer container51to the black developing unit14K by an auger54rotationally driven within the pipe, and a waste housing bottle56that causes retrieved toner Tc′ exceeding an upper limit of housing capacity of the buffer container51to overflow and houses the overflowed toner, as shown inFIGS. 5 and 6.

The buffer container51, the first carrier pipe53B, the second carrier pipe55B and the waste housing bottle56, which form this toner reuse system50B, basically include the same constituent components as those of the toner reuse system50in the first embodiment. Particularly, also in this buffer container51, a removing unit60and a stirring unit65may be installed when necessary, as in the buffer container of the toner reuse system50in the first embodiment.

However, the configuration of this toner reuse system is different from the configuration of the toner reuse system50in the first embodiment in that the first carrier pipe53B is not connected to the drum cleaning unit16of the image creating unit10but to the belt cleaning unit26and that the second carrier pipe55B is not connected to all the developing units14in the image creating units10but only to the black developing unit14.

FIG. 7shows a configuration of a control system that controls each operation of this image forming apparatus1B. A numeral70inFIG. 7represents a control unit70, as in the configuration of the control system in the first embodiment. The control unit70controls the operation of each of the above-described image creating units or the like in the image forming process and also controls each operation of the above-described toner supply unit30B and toner reuse system50B.

The control of the toner supply unit30B by the control unit70is performed via a driving controller71that controls the driving unit for the toner send-out driving unit32in the supply unit30B. Specifically, in this control, basically the same control is performed as in the toner supply unit30in the first embodiment (seeFIG. 3), except that a detection signal from a toner supply detection unit72(Y, M, C, K) of each color is received for performing similar control.

The control of the toner reused system50B by the control unit70is performed via a first carrier driving controller73, a second carrier-driving controller74, a removal driving controller75, and a stir-driving controller76, which is provided when necessary, as in the control of the toner reuse system50in the first embodiment (seeFIG. 3). Also in this control, basically the same control as the control of the toner reuse system50in the first embodiment is performed. The control in this embodiment is different from the first embodiment in that only for the first carrier driving controller73, when a detection signal is received from a cleaner operation detection unit77B that detects the timing of operation (driving of the auger or the like) of the belt cleaning unit26, a control signal that drives the first carrier driving controller73synchronously with the operation timing of the cleaning unit26is sent. The operation timing of the cleaning unit26is substantially the same as the execution timing of the image forming process.

Each operation of the toner supply unit30B and the toner reuse system50B as described above will now be described.

In this image forming apparatus1B, every time the image forming process as described above is executed, each toner T in the developing unit14(Y, M, C, K) of each image creating unit10is consumed and reduced. Therefore, when a signal determining that toner supply is necessary is sent to the control unit70from each of the toner supply detection units72(Y, M, C, K), a control signal related to the type of toner (color) of unused toner Ts to be supplied, the timing to supply the unused toner Ts and the quantity of the unused toner Ts to be supplied is separately sent to each of the driving controllers71(Y, M, C, K) in the toner supply unit30B from the control unit70.

This causes the toner send-out driving unit32to start the operation of the driving unit of the supply target and thus to drive the auger33in the unused toner carrier pipe34at predetermined timing and for a predetermined period each. As a result, the unused toner Ts in the toner cartridge31(Y, M, C, K) of the supply target in the toner supply unit30B is carried and supplied to the predetermined developing unit14(Y, M, C, K) through the unused toner carrier pipe34by the rotationally driven auger33. As the predetermined period has elapsed, the rotational driving of the auger33stops and thus the supply of the unused toner Ts ends.

Also, in the image forming apparatus1B, when the above-described image forming process is executed, the toner Tb remaining on the surface of the intermediate transfer belt20after the secondary transfer is removed by the belt cleaning unit26. When the operation of this belt cleaning unit26is started, a detection signal from the cleaner operation detection unit77B is sent to the control unit70and a driving signal is sent from the control unit70to the first carrier driving controller73in the toner reuse system50B.

This causes the first carrier driving controller73to start the operation of its driving unit and thus to rotationally drive the auger52in the first carrier pipe53. As a result, in the toner reuse system50B, the toner Tb of mixed color components removed by the belt cleaning unit26is carried into the buffer container51through the first carrier pipe53by the rotationally driven auger52and then housed in the buffer container51. Again, when the image forming processing or the like is ended, the rotational driving of the auger52stops and thus carrying the toner Tb to the buffer container51stops.

Along with the rotational driving of the auger52in this first carrier pipe53, a driving signal is sent from the control unit70to the removal driving controller75(and the stir-driving controller76). This starts the operation of the removing unit60in the buffer container51of the toner reuse system50B, and waste is separated and removed from the retrieved toner Tc housed in the container51. When the stir-driving unit65is provided, the stir-driving unit65starts operating and the retrieved toner Tc housed in the container51is stirred. The retrieved toner of mixed colors is thus prevented from aggregating in the container51.

On the other hand, when a signal requesting toner supply of black (K) is sent from any of the toner supply detection units72(Y, M, C, K) to the control unit70, a driving signal is also sent from the control unit70to the second carrier driving controller74of the toner reuse system50B.

This causes the second carrier driving controller74to start the operation of its driving unit and thus to rotationally drive the auger54in the second carrier pipe55. As a result, the retrieved toner Tc of mixed colors housed in the buffer container51is carried toward the black developing unit14K through the second carrier pipe55by the rotationally driven auger54. Since the retrieved toner Tc carried through this second carrier pipe55merges into the black unused toner carrier pipe34K in the toner supply unit30B, the retrieved toner Tc is carried to the developing unit14as it is mixed with black unused toner Tsk. Thus, the retrieved toner Tc is supplied to and reused in the black developing unit14K as it is mixed with the black unused toner Tsk. The quantity of the retrieved toner Tc to be supplied is substantially determined by the rotational driving time of the auger54. When the toner supply operation ends, the auger54stops its rotational driving and thus carrying the retrieved toner Tc to the black developing unit14K stops.

In this toner reuse system50B, as in the first embodiment, when the quantity of the retrieved toner Tc carried to and housed in the buffer container51through the first carrier pipe53exceeds an upper limit prescription lateral surface51cin the container51, the retrieved toner Tc′ corresponding the excess quantity automatically gets beyond the upper limit prescription lateral surface51cand overflows to be housed in the waste housing bottle56through the toner discharge opening51d.

A test carried out by using the image forming apparatus1B having this toner reuse system50B will now be described.

In this test, the same test image is formed on 10,000 recording papers P by the image forming apparatus1B. After that, a predetermined quantity of black unused toner Tsk is supplied to the black developing unit14K from the toner supply unit30B, and toner is sequentially supplied while the ratio (%) of retrieved toner Tc supplied from the buffer container51to the quantity of the supplied unused toner is increased by 5% each. The occurrence of image fog in each test image that is newly formed after the toner is supplied at each ratio is observed and the saturation (C*) of black image is examined. Then, the occurrence of image fog is evaluated on the basis of the above-described evaluation standards. The saturation is measured by a measuring device (X-Rite 938 manufactured by X-Rite Inc.). The result of the measurement is shown inFIG. 8.

The setting conditions in this test are as follows. The toner T and the test image used in this test are the same as those employed in the foregoing test. The acceptable level of saturation in this test is “less than 3.0”.

From the result of this test, in the toner reuse system50B, the quantity of the retrieved toner Tc to be supplied to the black developing unit14K from the buffer container51is set to achieve 20% or less as the ratio of the retrieved toner to the quantity of the unused black toner to be supplied. Specifically, a control signal is sent to the second carrier driving controller74to supply 0.2 times or less as much retrieved toner as the quantity of the unused black toner to be supplied that is recognized in the toner supply unit30B. Also, in this case, the unused black toner is supplied under a condition that the quantity of the retrieved toner Tc to be supplied is subtracted from the original quantity of supply.

Other Embodiments

In the second embodiment, the color image forming apparatus1B of a tandem type is described in which the image creating units10(Y, M, C, K) of four colors are arranged in series on the intermediate transfer belt20along the direction of rotation of the intermediate transfer belt20. However, color image forming apparatuses of other types than the tandem type can be similarly used as long as the intermediate transfer mode is utilized.

As described above, some embodiments of the invention are outlined below.

According to an aspect of the invention, an image forming apparatus has an image carrier on which an electrostatic latent image is formed, a developing unit that develops the electrostatic latent image by toner, and a cleaning unit that removes toner remaining on the image carrier after the developed toner image is transferred to a recording medium. The image forming apparatus includes a buffer housing unit that temporarily houses the toner removed by the cleaning unit, a first carrier unit that is provided between the cleaning unit and the buffer housing unit and that carries the toner removed by the cleaning unit to the buffer housing unit by a carrier driving member, a second carrier unit that is provided between the buffer housing unit and the developing unit and that carries retrieved toner housed in the buffer housing unit to the developing unit by a carrier driving member, a waste housing unit that is provided to be connected to the buffer housing unit and that causes the retrieved toner exceeding an upper limit of housing capacity of the housing unit to overflow and then houses the overflowed toner, and a control unit that separately controls driving of the carrier driving member of the first carrier unit and driving of the carrier driving member of the second carrier unit.

According to another aspect of the invention, an image forming apparatus has an image carrier on which an electrostatic latent image is formed, a developing unit that develops the electrostatic latent image by toner, an intermediate transfer member that holds the developed toner image by primary transfer and carries the toner image to a secondary transfer unit that performs secondary transfer to a recording medium, and a second cleaning unit that removes toner remaining on the intermediate transfer member after the secondary transfer.

The image forming apparatus includes a buffer housing unit that temporarily houses the toner removed by the second cleaning unit, a first carrier unit that is provided between the second cleaning unit and the buffer housing unit and that carries the toner removed by the second cleaning unit to the buffer housing unit by a carrier driving member, a second carrier unit that is provided between the buffer housing unit and the developing unit and that carries retrieved toner housed in the buffer housing unit to the developing unit by a carrier driving member, a waste housing unit that is provided to be connected to the buffer housing unit and that causes the retrieved toner exceeding an upper limit of housing capacity of the housing unit to overflow and then houses the overflowed toner, and a control unit that separately controls driving of the carrier driving member of the first carrier unit and driving of the carrier driving member of the second carrier unit.

According to another aspect of the invention, the image forming apparatus may have a toner supply unit that supplies unused toner to the developing unit, wherein the control unit may control the driving of the carrier driving member of the first carrier unit synchronously with operation timing of the cleaning unit and may control the driving of the carrier driving member of the second carrier unit synchronously with operation timing of the toner supply unit.

According to another aspect of the invention, the image forming apparatus may have a toner supply unit that supplies unused toner to the developing unit, wherein the control unit may control the driving of the carrier driving member of the first carrier unit synchronously with operation timing of the second cleaning unit and may control the driving of the carrier driving member of the second carrier unit synchronously with operation timing of the toner supply unit.

According to another aspect of the invention, in the image forming apparatus, a removing unit that is driven to remove waste from the retrieved toner housed in the buffer housing unit may be installed in the buffer housing unit.

When the removing unit is provided, the control unit may further control the driving of the removing unit synchronously with the driving timing of the carrier driving member of the first carrier unit.

According to another aspect of the invention, in the image forming apparatus, a stir-driving unit that stirs the retrieved toner housed in the buffer housing unit may be installed in the buffer housing unit.

According to another aspect of the invention, in the image forming apparatus in which the toner supply unit is provided, the control unit may control the driving of the carrier driving member of the second carrier unit to achieve 30% or less as the ratio of the retrieved toner to the quantity of unused toner to be supplied from the toner supply unit.

According to another aspect of the invention, in the image forming apparatus, as the image carrier and the developing unit, plural image carriers and developing units that individually form toner images of plural color components including at least black may be provided, and the first carrier unit may be connected only to a black developing unit that uses black toner, of the plural developing units.

When the foregoing configuration is employed, toner supply units that individually supply unused toner of color components corresponding to each of the plural developing units may be provided, and the control unit may control the driving of the carrier driving member of the second carrier unit to achieve 20% or less as the ratio of the retrieved toner to the quantity of unused black toner to be supplied from the toner supply unit.

The entire disclosure of Japanese Patent Application No. 2005-089793 filed on Mar. 25, 2005 including specification, claims, drawings and abstract is incorporated herein by reference in its entirety.