Developing device, image forming apparatus and process cartridge in which a shock is applied intermittently to the discharged developer

A developing device capable of conveying discharged developer to the outside of the device well by preventing developer from firmly adhering within a discharge conveyance path, as well as an image forming apparatus and a process cartridge having this developing device. A developing device, having: a developing roller; a developer conveyance path having a supply screw and a supply conveyance path; a toner replenishment controller for replenishing the developer to the developer conveyance path; a discharge conveyance path for conveying the developer to the outside of the developing device; a discharge screw serving as a discharge conveying member for applying a conveying force to the developer within the discharge conveyance path; and a developer discharge port serving as developer discharge means for discharging the developer to the discharge conveyance path, wherein the conveying force is applied to the discharged developer intermittently by the discharge screw serving as a discharge conveying member, whereby a shock is applied intermittently to the discharged developer within the discharge conveyance path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a developing device used in a copying machine, a facsimile device, a printer and the like, and an image forming apparatus and a process cartridge that use the developing device.

2. Description of the Related Art

There has conventionally been widely used an image forming apparatus with a developing device using a two-component developer composed of toner and magnetic carrier. As this type of image forming apparatus, there is an image forming apparatus in which toner is replenished, according to need, from a toner container to a developer contained in a developing device that consumes toner as it conducts development, and thereby maintains the toner density of the developer within a predetermined range. In such a configuration, because the carrier within the developer is repeatedly used without being consumed significantly, the carrier degrades as an image is output. Specifically, the coated layer on the surface of the carrier is scraped off due to mechanical stress, and spent toner component is formed on the carrier surface. When the carrier degrades, the ability of the carrier to charge the toner decreases gradually, causing not only abnormal images such as scumming, image density reduction and image density irregularity, but also toner scattering. Therefore, a serviceman is sent to the user of this type of image forming apparatus to replace the carrier regularly. For this reason, the maintenance cost and the cost per image formation increase.

Japanese Patent Application No. 2891845 and Japanese Unexamined Patent Application Publication No. 2000-112238, for example, disclose a developing device in which a pre-mixed developer with a mixture of carrier and toner is replenished into a developer contained in the developing device in order to recover the toner density, and at the same time the increment of the developer is discharged from the developing device. In this configuration, old carrier is discharged little by little from the developing device by discharging the developer, and at the same time new carrier within the pre-mixed developer is replenished to the developer contained in the developing device. The carrier within the developer is replaced with the new carrier little by little by performing the above-described discharge and replenishment so that the carrier replacement work can be omitted.

However, the developer discharged from the developing device contains a larger proportion of degraded developer than the developer contained in the developing device. The degraded developer has a low fluidity, and thus there is a possibility that the developer firmly adheres to a conveying member that applies conveying force to the developer within a discharge conveyance path conveying the discharged developer. Specifically, when the conveying member that applies the conveying force to the developer in the conveyance path conveying the developer is a conveying screw, the developer having a low fluidity adheres and aggregates on a wing portion or an axis of the conveying screw, since the developer having a low fluidity has a high cohesive property.

When the developer has a high fluidity, the developer scatters easily in spite of its cohesive property, and the developer adhering to the conveying screw hardly aggregates and firmly adheres. When the developer has a low fluidity, on the other hand, the developer does not scatter once it aggregates, and thus the developer adhering to the conveying screw easily aggregates and firmly adheres. Because the developer adhering to the conveying screw only follows the rotation of the conveying screw, the rotation of the conveying screw does not apply the conveying screw to the developer. Moreover, when the fluidity of the developer to be conveyed is poor, the developer adhering firmly to the conveying screw aggregates gradually, reducing the conveying capability of the conveying screw.

Note that the problem in which the developer having a low fluidity adheres firmly to the conveying screw is not exclusive to the case where the conveying member is a screw, and thus the developer can firmly adhere to any conveying member that constantly applies a fixed conveying force to the developer.

In addition, when the developer firmly adheres to the conveying screw of the discharge conveyance path and thereby reduces the conveying performance of the developer within the conveyance path, the conveying capability of the discharge conveyance path drops in relation to the amount of developer to be discharged, which might clog up the discharge conveyance path. Also, a torque for rotating the conveying screw is increased by the firmly adhered developer, damaging the conveying member.

These problems are not exclusive to the developing device that uses a two-component developer composed of toner and magnetic carrier, and thus might occur in any developing device that uses a one-component developer, as long as such developing device is configured to discharge a developer by using developer discharge means.

SUMMARY OF THE INVENTION

The present invention was contrived in view of the above problems, and an object of the present invention is to provide a developing device capable of conveying discharged developer to the outside of the device well by preventing the developer from firmly adhering within a discharge conveyance path, and to provide an image forming apparatus and a process cartridge that have this developing device.

In an aspect of the present invention, a developing device comprises a developer carrier, which rotates while carrying a developer on a surface thereof, supplies a toner to a latent image on a surface of a latent image carrier at a section where the developer carrier faces the latent image carrier, and develops the latent image; a developer conveyance path, which has a developer conveying member conveying the developer, and conveys the developer while supplying the developer to the developer carrier in a developer supply region in which the developer is supplied to the developer carrier; a developer replenishing device for replenishing the developer to the developer conveyance path; a discharge conveyance path for conveying the developer to the outside of the developing device; a discharge conveying member, which applies a conveying force to the developer within the discharge conveyance path; and a developer discharging device for discharging at least part of the developer within the developer conveyance path to the discharge conveyance path in the form of a discharged developer. A shock is applied intermittently to the discharged developer within the discharge conveyance path.

In another aspect of the present invention, an image forming apparatus comprises at least a latent image carrier; a charging device for charging a surface of the latent image carrier; a latent image forming device for forming an electrostatic latent image on the latent image carrier; and a developing device for developing the electrostatic latent image into a toner image. The developing device comprises a developer carrier, which rotates while carrying a developer on a surface thereof, supplies a toner to a latent image on the surface of the latent image carrier at a section where the developer carrier faces the latent image carrier, and develops the latent image; a developer conveyance path, which has a developer conveying member conveying the developer, and conveys the developer while supplying the developer to the developer carrier in a developer supply region in which the developer is supplied to the developer carrier; a developer replenishing device for replenishing the developer to the developer conveyance path; a discharge conveyance path for conveying the developer to the outside of the developing device; a discharge conveying member, which applies a conveying force to the developer within the discharge conveyance path; and a developer discharging device for discharging at least part of the developer within the developer conveyance path to the discharge conveyance path in the form of a discharged developer, the discharged developer within the discharge conveyance path being applied with a shock intermittently.

In another aspect of the present invention, a process cartridge is configured to have at least a latent image carrier for carrying a latent image and a developing device means for developing the latent image on the latent image carrier, in a common holder as one unit, and is further configured to be detachable from a main body of an image forming apparatus that has the latent image carrier and the developing device. The developing device comprises a developer carrier, which rotates while carrying a developer on a surface thereof, supplies a toner to a latent image on the surface of the latent image carrier at a section where the developer carrier faces the latent image carrier, and develops the latent image; a developer conveyance path, which has a developer conveying member conveying the developer, and conveys the developer while supplying the developer to the developer carrier in a developer supply region in which the developer is supplied to the developer carrier; a developer replenishing device for replenishing the developer to the developer conveyance path; a discharge conveyance path for conveying the developer to the outside of the developing device; a discharge conveying member, which applies a conveying force to the developer within the discharge conveyance path; and a developer discharging device for discharging at least part of the developer within the developer conveyance path to the discharge conveyance path in the form of a discharged developer, the discharged developer within the discharge conveyance path being applied with a shock intermittently.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As an image forming apparatus to which the present invention is applied, an embodiment of a tandem color laser copying machine (simply called “copying machine500” hereinafter) in which a plurality of photoreceptors are disposed in parallel with each other will now be described hereinafter.

FIG. 1shows a schematic configuration of a copying machine500according to the present embodiment. The copying machine500has a printer portion100, a sheet feeding device200on which the printer portion100is placed, a scanner300fixedly placed on the printer portion100, and the like. The copying machine500also has an automatic original conveying device400that is placed fixedly on the scanner300.

The printer portion100has an image forming unit20that is constituted by four process cartridges18Y, M, C and K for forming images of colors of yellow (Y), magenta (M), cyan (C), and black (K) respectively. Y, M, C and K provided at the ends of the reference numerals indicate the members for the colors, yellow, cyan, magenta and black, respectively (same hereinafter). In addition to the process cartridges18Y, M, C and K, an optical writing unit21, an intermediate transfer unit17, a secondary transfer device22, a resist roller pair49, a belt fixing type fixing device25and the like are disposed.

The optical writing unit21has a light source, a polygon mirror, an f-θ lens, a reflecting mirror and the like, which are not shown, and emits a laser beam onto the surface of an after-described photoreceptor on the basis of image data.

Each of the process cartridges18Y, M, C and K has a drum-like photoreceptor1, a charging unit, a developing device4, a drum cleaning device, a destaticizing unit, and the like.

The yellow process cartridge18will now be described hereinafter.

The surface of a photoreceptor1Y is uniformly charged by the charging unit functioning as charging means. The surface of the photoreceptor1Y that is subjected to the charging processing is irradiated with a laser beam that is modulated and deflected by the optical writing unit21. Consequently, the potential of the irradiated portion (exposed portion) on the surface of the photoreceptor1Y is attenuated. Due to this attenuation of the potential of the surface, a Y electrostatic latent image is formed on the surface of the photoreceptor1Y. The formed Y electrostatic latent image is developed into a Y toner image by a developing device4Y serving as developing means.

The Y toner image formed on the Y photoreceptor1Y is primarily transferred to an intermediate transfer belt110which is described hereinafter. Transfer residual toner on the surface of the photoreceptor1Y is cleaned by the drum cleaning device after the Y toner image is primarily transferred.

In the Y process cartridge18Y, the photoreceptor1Y that is cleaned by the drum cleaning device is destaticized by the destaticizing unit. Then, the photoreceptor1Y is uniformly charged by the charging unit and thereby returns to the initial state. The series of processes described above is the same for the other process cartridges18M, C and K.

The intermediate transfer unit will now be described hereinafter.

The intermediate transfer unit17has the intermediate transfer belt110, a belt cleaning device90and the like. The intermediate transfer unit17further has a stretching roller14, a drive roller15, a secondary transfer backup roller16, four primary transfer bias rollers62Y, M, C and K, and the like.

The intermediate transfer belt110is tension-stretched by a plurality of rollers including the stretching roller14. The intermediate transfer belt110is then moved endlessly in a clockwise direction in the drawing by the rotation of the drive roller15that is driven by a belt drive motor which is not shown.

Each of the four primary transfer bias rollers62Y, M, C and K is disposed in contact with the inner peripheral surface of the intermediate transfer belt110, and is applied with a primary transfer bias from a power source, which is not shown. Furthermore, the inner peripheral surface of the intermediate transfer belt110is pressed against the photoreceptors1Y, M, C and K to form primary transfer nips. At each of the primary transfer nips, a primary transfer electric field is formed between each photoreceptor1and each primary transfer bias roller62due to the influence of the primary transfer bias.

The abovementioned Y toner image formed on the Y photoreceptor1Y is primarily transferred onto the intermediate transfer belt110due to the influence of the primary transfer electric field or nip pressure. M, C and K toner images formed on the respective M, C and K photoreceptors1M, C and K are sequentially superimposed and primarily transferred onto the Y toner image. A four-color superimposed toner image (called “four-color toner image” hereinafter), i.e., a multiple toner image, is formed on the intermediate transfer belt110due to the primary transfer performed subsequently to the superimposition of the toner images.

The four-color toner image that is transferred onto the intermediate transfer belt110is secondarily transferred onto a transfer sheet, i.e., a recording medium that is not shown, by a secondary transfer nip described hereinafter. The residual transfer toner that remains on the surface of the intermediate transfer belt110after the four-color toner image passes through the secondary transfer nip is cleaned by the belt cleaning device90that holds the belt between this belt cleaning device and the drive roller15located on the left side of the drawing.

Next, the secondary transfer device22will be described.

The secondary transfer device22that stretches a sheet conveying belt24by means of two stretching rollers23is disposed on the lower side of the intermediate transfer unit17as shown. The sheet conveying belt24is endlessly moved in a counterclockwise direction in the drawing as at least either one of the stretching rollers23is driven and rotated. Of the two stretching rollers23, the one roller disposed on the right side in the drawing holds the intermediate transfer belt110and the sheet conveying belt24between this stretching roller and the secondary backup roller16of the intermediate transfer unit17. Accordingly, the secondary transfer nip where the intermediate transfer belt110of the intermediate transfer unit17comes into contact with the sheet conveying belt24of the secondary transfer device22is formed. Then, this stretching roller23is applied with a secondary transfer bias having a polarity opposite to the polarity of the toner, by the power source that is not shown. Due to this application of the secondary transfer bias, a secondary transfer electric field that electrostatically moves the four-color toner image formed on the intermediate transfer belt110of the intermediate transfer unit17from the belt side toward this stretching roller23is formed at the secondary transfer nip. The four-color toner image that is affected by the secondary transfer electric field or nip pressure is secondarily transferred onto the transfer sheet, which is sent to the secondary transfer nip by the after-described resist roller pair49in synchronization with the four-color toner image formed on the intermediate transfer belt110. It should be noted that a charger for charging the transfer sheet in a noncontact manner may be provided in place of the secondary transfer system that applies a secondary transfer bias to this stretching roller23.

In the sheet feeding device200provided in a lower section of the main body of the copying machine500, a plurality of sheet feeding cassettes44, each of which can contain a plurality of stacked transfer sheets, are disposed vertically in a stacked manner. Each of the sheet feeding cassettes44presses the top transfer sheet of the stacked transfer sheets against a sheet feeding roller42. Then, by rotating the sheet feeding roller42, the top transfer sheet is sent out toward a sheet feeding path46.

The sheet feeding path46that receives the transfer sheet sent out from the sheet feeding cassette44has a plurality of conveying roller pairs47and the resist roller pair49that is provided in the vicinity of an end of the sheet feeding path46. The sheet feeding path46conveys the transfer sheet toward the resist roller pair49. The transfer sheet conveyed toward the resist roller pair49is sandwiched between the roller portions of the resist roller pair49. On the other hand, in the intermediate transfer unit17, the four-color toner image formed on the intermediate transfer belt110enters the secondary transfer nip as the belt endlessly moves. The resist roller pair49sends the transfer sheet, sandwiched between the roller portions, at timing at which the transfer sheet is attached to the four-color toner image at the secondary transfer nip. In this manner, the four-color toner image formed on the intermediate transfer belt110is attached to the transfer sheet at the secondary transfer nip. Then, the four-color toner image is secondarily transferred onto the transfer sheet and thereby becomes a full-color image on the white transfer sheet. The transfer sheet on which the full-color image is formed in this manner leaves the secondary transfer nip as the sheet conveying belt24endlessly moves, and is then sent from the top of the sheet conveying belt24to the fixing device25.

The fixing device25has a belt unit that is caused to move endlessly while stretching a fixing belt26by means of two rollers, and a pressure roller27that is pressed against one of the rollers of the belt unit. The fixing belt26and the pressure roller27abut against each other to form a fixing nip, and the transfer sheet received from the sheet conveying belt24is sandwiched by this nip. Of the two rollers of the belt unit, the roller that is pressed by the pressure roller27has a heat source therein, which is not shown, and heats the fixing belt26by using heat generated by the heat source. The heated fixing belt26then heats the transfer sheet sandwiched by the fixing nip. Due to the application of heat or the nip pressure, the full-color image is fixed to the transfer sheet.

The transfer sheet that is subjected to the fixing processing in the fixing device25is either stacked on a stack portion57provided outside of a plate of a printer casing on the left side of the drawing, or is returned to the abovementioned secondary transfer nip in order to form a toner image on the other side of the transfer sheet.

When making a copy of an original, which is not shown, for example, a sheaf of sheet originals is set on an original platen30of the automatic original conveying device400. However, if this original is a one-filing original closed by the subject document, the sheaf of sheet originals is set on a contact glass32. Prior to this setting operation, the automatic original conveying device400is opened with respect to the copying machine main body, and thereby the contact glass32of the scanner300is exposed. Thereafter, the one-filing original is pressed and held by the closed automatic original conveying device400.

After the original is set in this manner, a copy start switch, not shown, is pressed, whereby original reading operation is performed by the scanner300. However, if a sheet original is set on the automatic original conveying device400, the automatic original conveying device400automatically moves the sheet original to the contact glass32prior to the original reading operation. In the original reading operation, a first traveling body33and a second traveling body34start traveling together first, and light is emitted from a light source provided in the first traveling body33. Then, the light reflected from the surface of the original is reflected by a mirror provided within the second traveling body34, passes through an image forming lens35, and thereafter enters a read sensor36. The read sensor36constructs image information based on the reflected light.

In parallel with such original reading operation, each element within each of the process cartridges18Y, M, C and K, the intermediate transfer unit17, the secondary transfer device22, and the fixing device25start driving. Then, the optical writing unit21is driven and controlled based on the image information constructed by the read sensor36, and Y, M, C and K toner images are formed on the photoreceptors1Y, M, C and K respectively. These toner images become a four-color toner image by superimposing and transferring these toner images on the intermediate transfer belt110.

Moreover, at substantially the same time as when the original reading operation is performed, a sheet feeding operation is started in the sheet feeding device200. In this sheet feeding operation, one of the sheet feeding rollers42is selected and rotated, and transfer sheets are sent out from one of the sheet feeding cassettes44that are stored in multiple stages in a sheet bank43. The sent transfer sheets are separated one by one by a separation roller45. Each sheet enters a reversal sheet feeding path46and is then conveyed to the secondary transfer nip by the conveying roller pairs47. A manual tray51sometimes feeds the sheets in substitution for the sheet feeding cassettes44. In this case, after a manual sheet feeding roller50is selected and rotated to send out transfer sheets placed on the manual tray51, a separation roller52separates the transfer sheets one by one and feeds each sheet to a manual sheet feeding path53of the printer portion100.

In the present copying machine500, when forming a color image composed of toners of two or more colors, the intermediate transfer belt110is stretched such that an upper stretching surface thereof lies substantially horizontally, and all of the photoreceptors1Y, M, C and K are brought into contact with the upper stretching surface. On the other hand, when forming a monochrome image composed of the K toner only, the intermediate transfer belt110is tilted downward to the left in the drawing by using a mechanism, not shown, and the upper stretching surface is separated from the Y, M and C photoreceptors1Y, M and C. Then, out of the four photoreceptors1Y, M, C and K, only the K photoreceptor1K is rotated in the counterclockwise direction in the drawing to form a K toner image only. At this moment, for Y, M and C, driving of the respective photoreceptors1and of the developing device4is stopped to prevent each of the members of the photoreceptors1or developing device4and the developer within the developing device4from being depleted unnecessarily.

The copying machine500has a control unit, not shown, which is configured by a CPU and the like that control the elements within the copying machine500, and an operation display portion, not shown, which is configured by a liquid crystal display, various keybuttons, and the like. An operator can select one of three one-side printing modes for forming an image on one side of a transfer sheet, by sending a command to the control unit based on the implementation of a key input operation in the operation display portion. The three one-side printing modes are a direct discharge mode, a reversal discharge mode, and a reversal decal discharge mode.

FIG. 2shows the configurations of the developing device4provided in one of the four process cartridges18Y, M, C and K and of the photoreceptor1. Apart from the fact that they handle different colors, the configurations of the four process cartridges18Y, M, C and K are essentially identical and, accordingly, the letters Y, M, C and K applied to the “4” of the drawing have been omitted.

The surface of the photoreceptor1is charged by the charging device, which is not shown, as it rotates in the direction of the arrow G in the drawing shown inFIG. 2. Toner is supplied from the developing device4to a latent image, which is formed as an electrostatic latent image on the surface of the charged photoreceptor1by a laser beam irradiated from an exposure device, which is not shown, whereby a toner image is formed.

The developing device4has a developing roller5that serves as a developer carrier for supplying the toner to develop the latent image on the surface of the photoreceptor1while surface-moving in the direction of the arrow I of the drawing. The developing roller5has a rotatable developing sleeve in which a magnetic body, not shown, which is composed of a plurality of magnetic poles, is disposed. The magnetic body is required for retaining the developer on the surface of the developing roller5.

The developing device4also has a supply screw8serving as a supply conveying member for, while supplying the developer to the developing roller5, conveying the developer in the direction toward the far side ofFIG. 2along the axis line direction of the developing roller5.

A doctor blade12serving as developer regulating means for regulating the thickness of the developer supplied to the developing roller5to a thickness suitable for development is provided on the downstream side in the direction of surface movement of the developing roller5from a part where the developing roller5faces the supply screw8.

A recovery conveyance path7, which recovers the developer that passes through a developing region and is used for development after being released from the surface of the developing roller5, faces the developing roller5on the downstream side in the direction of surface movement from the developing region being a part where the developing roller5faces the photoreceptor1. The recovery conveyance path7has a spiral recovery screw6, which is disposed in parallel with the axis line direction of the developing roller5and serves as a recovery conveying member for conveying the recovered recovery developer in the same direction as the direction of the supply screw8along the axis line direction of the developing roller5. A supply conveyance path9having the supply screw8is disposed in the lateral direction of the developing roller5, and the recovery conveyance path7having the recovery screw6is disposed below the developing roller5in parallel with the supply conveyance path9.

Note that the developer can be separated/released from the developing roller5by setting a section for releasing the developer within the abovementioned magnetic body of the developing sleeve into a nonmagnetic state. Moreover, the magnetic poles of the magnetic body may be arranged so as to form a repulsive magnetic field in the section for releasing the developer.

A stirring conveyance path10is provided below the supply conveyance path9in the developing device4in parallel with the recovery conveyance path7. The stirring conveyance path10has a spiral stirring screw11, which is disposed in parallel with the axis line direction of the developing roller5and serves as a stirring/conveying member for, while stirring the developer along the axis line direction of the developing roller5, conveying it in the opposite direction to the direction of the supply screw8, the opposite direction being oriented on the near side in the drawing.

The supply conveyance path9and the stirring conveyance path10are partitioned by a first partition wall133serving as a partition member. In a part of the first partition wall133that partitions the supply conveyance path9and the stirring conveyance path10an opening portion is formed at both ends in the near side and far side of the drawing to thereby allow the supply conveyance path9and the stirring conveyance path10to communicate with each other.

Note that although the supply conveyance path9and the recovery conveyance path7are also partitioned by the first partition wall133, there is no opening portion provided in the part of the first partition wall133that partitions the supply conveyance path9and the recovery conveyance path7.

The two developer conveyance paths of the stirring conveyance path10and the recovery conveyance path7are also partitioned by a second partition wall134serving as a partition member. An opening portion is formed in the second partition wall134at the near side in the drawing to allow the stirring conveyance path10and the recovery conveyance path7to communicate with each other.

The supply screw8, the recovery screw6and the stirring screw11serving as a developer conveying members are made of resin or metal. The diameter of each screw is set to φ22 [mm]. The supply screw is in the form of a double-thread screw and has a screw pitch of 50 [mm], and the recovery screw6and the stirring screw11each is in the form of a single-thread screw and has a screw pitch of 25 [mm]. The rotation speed of each screw is set to approximately 600 [rpm].

The developer that is thinned by the stainless doctor blade12on the developing roller5is conveyed to the developing region where the developing roller5faces the photoreceptor1, and then development is performed. The surface of the developing roller5made of an Al or SUS pipe stock with a diameter of φ25 [mm] has a V-shaped groove or is sandblasted. The size of the gap formed between the doctor blade12and the photoreceptor1is approximately 0.3 [mm].

The developer obtained after the development is recovered by the recovery conveyance path7, then conveyed to the near side of the cross section ofFIG. 2, and then transferred to the stirring conveyance path10at the opening portion of the first partition wall133provided in a non-image region. It should be noted that toner is supplied from an after-mentioned toner replenishing port95to the stirring conveyance path10, the toner replenishing port95being provided above the stirring conveyance path10and in the vicinity of the opening portion of the first partition wall133on the upstream side in a developer conveyance direction in the stirring conveyance path10.

Next, the circulation of the developer within the three developer conveyance paths will be described.

FIG. 3shows a perspective sectional view of the developing device4to explain a flow of the developer within the developer conveyance paths. The arrows in the drawing indicate the directions of movement of the developer.

Also,FIG. 4is a schematic diagram showing a flow of the developer within the developing device4. As withFIG. 3, the arrows in the diagram indicate the directions of movement of the developer.

In the supply conveyance path9to which the developer is supplied from the stirring conveyance path10, the developer is conveyed to the downstream side in a conveyance direction of the supply screw8, while being supplied to the developing roller5. Excess developer that is supplied to the developing roller5and conveyed to a downstream end in a conveyance direction of the supply conveyance path9without being used for the development is supplied to the stirring conveyance path10through an excess opening portion92of the first partition wall133(arrow E inFIG. 4).

On the other hand, the developer supplied to the developing roller5is used for the development in the developing region, separated/released from the developing roller5, and delivered to the recovery conveyance path7. The recovery developer that is delivered from the developing roller5to the recovery conveyance path7and conveyed to a downstream end in a conveyance direction of the recovery conveyance path7by the recovery screw6is supplied to the stirring conveyance path10through a recovery opening portion93of the second partition wall134(arrow F inFIG. 4).

The stirring conveyance path10then stirs the supplied excess developer and recovery developer, conveys thus obtained mixture to the upstream side in the conveyance direction of the supply screw8, which is also the downstream side in a conveyance direction of the stirring screw11, and supplies it to the supply conveyance path9through a supply opening portion91of the first partition wall133(arrow D inFIG. 4).

In the stirring conveyance path10, the recovery developer, excess developer, and toner replenished from a transporting portion according to need are stirred and conveyed by the stirring screw11in the direction opposite to that of the developer of the recovery path7and the supply path9. The stirred developer is transported to the upstream side in the conveyance direction of the supply conveyance path9that is communicated at the downstream side in the conveyance direction through the supply opening portion91. Note that a toner density sensor, not shown, which is configured by a permeability sensor, is provided below the stirring conveyance path10, and a toner replenishment controller, not shown, is actuated by the output of the sensor to replenish the toner from a toner container which is not shown.

In the developing device4shown inFIG. 4having the supply conveyance path9and the recovery conveyance path7, because the developer is supplied and recovered in different developer conveyance paths, the developer used for the development is prevented from being mixed in the supply conveyance path9. Accordingly, the toner density of the developer supplied to the developing roller5is prevented from decreasing as the developer is sent toward the downstream side in the conveyance direction of the supply conveyance path9. In addition, because the developing device has the recovery conveyance path7and the stirring conveyance path10and the developer is recovered and stirred in these different developer conveyance paths, loss of the developer used for the development is prevented while it is being stirred. Therefore, since the sufficiently stirred developer is supplied to the supply conveyance path9, supply of insufficiently stirred developer to the supply conveyance path9can be prevented. Because the toner density of the developer within the supply conveyance path9is prevented from decreasing and insufficient stirring of the developer in the supply conveyance path9is prevented in this manner, a constant image density can be ensured throughout development.

As shown inFIG. 4, the developer is moved from the lower part of the developing device4to the upper part of the same in the direction of the arrow D only. The developer is moved in the direction of the arrow D to raise the developer and supply it to the supply conveyance path9by pushing the developer existing on the downstream side of the stirring conveyance path10as the stirring screw11rotates.

Such movement of the developer causes stress on the developer, reducing the life of the developer.

When the developer is lifted up as described above, stress is placed on the developer, scraping a carrier film, and spent toner is formed on the stressed part of the developer, and consequently stable image quality can no longer be maintained.

Therefore, the life of the developer can be extended by alleviating the stress that is placed on the developer moving in the direction of the arrow D. By extending the life of the developer, it becomes possible to provide a developing device capable of preventing the degradation of the developer and providing stable image quality with no image density irregularity.

In the developing device4of the present embodiment, the supply conveyance path9is disposed obliquely above the stirring conveyance path10, as shown inFIG. 2. By disposing the supply conveyance path9in this manner, the stress placed on the developer moving in the direction of the arrow D can be alleviated more as compared with the case in which the supply conveyance path9is provided vertically above the stirring conveyance path10to lift up the developer.

Furthermore, since the supply conveyance path9and the stirring conveyance path10are disposed obliquely in the developing device4, an upper wall surface of the stirring conveyance path10is disposed higher than a lower wall surface of the supply conveyance path9as shown inFIG. 2.

By lifting up the supply conveyance path9vertically above the stirring conveyance path10, the developer is lifted up by the pressure of the stirring screw11against gravitational force, imposing stress on the developer. However, by disposing the upper wall surface of the stirring conveyance path10to be higher than the lower wall surface of the supply conveyance path9, the developer existing at the uppermost point of the stirring conveyance path10can flow into the lowermost point of the supply conveyance path9without fighting gravity, and as a result the stress placed on the developer can be reduced.

It should be noted that a fin member may be provided on the axis of the stirring screw11, which is a section through which the stirring conveyance path10and the supply conveyance path9are communicated with each other at the downstream side of the developer conveyance path of the stirring conveyance path10. This fin member is a plate-like member configured by a side parallel to the axial direction of the stirring screw11and a side perpendicular to the axial direction of the stirring screw11. By scooping up the developer using this fin member, the developer can be delivered from the stirring conveyance path10to the supply conveyance path9efficiently.

Moreover, in the developing device4the supply conveyance path9and the stirring conveyance path10are disposed such that the center distance A between the developing roller5and the supply conveyance path9is shorter than the center distance B between the developing roller5and the stirring conveyance path10. In this manner, the developer can be supplied from the supply conveyance path9to the developing roller5naturally, and the size of the device can be reduced.

Also, the stirring screw11rotates in the counterclockwise direction as viewed from the near side ofFIG. 2(direction of the arrow C in the drawing) so that the developer is lifted up along the shape of the stirring screw11and transported to the supply conveyance path9. Accordingly, the developer can be lifted up efficiently and also the stress placed thereon can be reduced.

FIG. 5is a cross-sectional view of the rotation center of the supply screw8of the developing device4, the rotation center being viewed in the direction of the arrow J shown inFIG. 3. Reference numeral H in the drawing shows the developing region in which the developing roller5serving as a developer carrier supplies the toner to the photoreceptor1serving as a latent image carrier. The width of the developing region H in the direction of the rotation axis of the developing roller5is the developing region width α.

As shown inFIG. 5, the developing device4is provided with, within the developing region width α, the supply opening portion91for lifting up the developer from the stirring conveyance path10to the supply conveyance path9, and the excess opening portion92for dropping the developer from the supply conveyance path9to the stirring conveyance path10.

FIG. 6shows a flow of the developer within the developing device4having a different configuration from the developing device shown inFIG. 4.

In the developing device4shown inFIG. 6, the supply opening portion91and the excess opening portion92are provided outside the developing region width α. Since the supply opening portion91is provided outside the developing region width α, the upstream side in the conveyance direction of the supply conveyance path9is longer than the developing roller5by a supply conveyance path upstream region β. Also, since the excess opening portion92is provided outside the developing region width α, the downstream side in the conveyance direction of the supply conveyance path9is longer than the developing roller5by a supply conveyance path downstream region γ.

On the other hand, in the developing device4with the configuration shown inFIG. 4, because the supply opening portion91is provided within the developing region width α, the upstream side in the conveyance direction of the supply conveyance path9can be made shorter than the developing device4ofFIG. 6by the supply conveyance path upstream region β. Moreover, because the excess opening portion92is provided within the developing region width α, the downstream side in the conveyance direction of the supply conveyance path9can be made shorter than the developing device4ofFIG. 6by the supply conveyance path downstream region γ.

Since the supply opening portion91and the excess opening portion92of the developing device4shown inFIG. 4are provided within the developing region width α as described above, the space of the upper part of the developing device4can be saved more, as compared with the developing device4shown inFIG. 6.

Next is described the position for replenishing the toner to the developer conveyance paths constituted by the supply conveyance path9, the stirring conveyance path10and the recovery conveyance path7of the developing device4.FIG. 7is a perspective view showing the exterior of the developing device4.

As shown inFIG. 7, the toner replenishing port95for replenishing the toner is provided above an upstream end portion in the conveyance direction of the stirring conveyance path10having the stirring screw11. Because this toner replenishing port95is provided on the outer side than the end portion in the width direction of the developing roller5, it is positioned outside the developing region width α.

The section provided with the toner replenishing port95is an extension of the conveyance direction of the supply conveyance path9and corresponds to an empty space of the supply conveyance path downstream region γ shown inFIG. 6. By providing the toner replenishing port95in the empty space obtained by providing the excess opening portion92within the developing region width α, the size of the developing device4can be reduced.

The toner replenishing port95may be provided not only above the upstream end portion in the conveyance direction of the stirring conveyance path10, but also above a downstream end portion of the recovery conveyance path7.

Moreover, the toner replenishing port95may be provided immediately above the recovery opening portion93, which is a section where the developer is delivered from the recovery conveyance path7to the stirring conveyance path10. Since the space immediately above the recovery opening portion93is also the empty space obtained by providing the excess opening portion92within the developing region width α, the size of the developing device4can be reduced by providing the toner replenishing port95at this position. Moreover, because the developer is easily mixed in the recovery opening portion93serving as a delivery portion, the developer can be stirred more efficiently by performing replenishment at this position.

As in the developing device4described with reference toFIG. 4, there are provided within the developing region width α the supply opening portion91for delivering the developer from the downstream end in the conveyance direction of the stirring conveyance path10to the upstream end in the conveyance direction of the supply conveyance path9, and the excess opening portion92for delivering the developer from the downstream end of the supply conveyance path9to the upstream end in the conveyance direction of the stirring conveyance path10. Therefore, as compared with the conventional developing device4, the space in the upper part of the developing device4can be saved, and the spaces in the entire developing device4can be also saved.

Moreover, because the toner replenishing port95is provided in the empty space that is obtained by providing the excess opening portion92within the developing region width α, the size of the developing device4can be reduced.

Because the toner is replenished from the upper part of the recovery opening portion93serving as a delivery portion for delivering the developer from the recovery conveyance path7to the stirring conveyance path10, the developer can be stirred efficiently.

In addition, since the developing device4is provided as developing means of the printer portion100of the copying machine serving as an image forming apparatus, the spaces of the entire apparatus can be saved.

The toner replenishment controller, not shown, which serves as developer replenishing means, replenishes the toner stored in the toner container, not shown, from the toner replenishing port95to the developing device4. In the developing device4of the present embodiment, the developer having toner and carrier is replenished from the toner replenishing port95of the developing device4. Hereinafter, the developer having a mixture of toner and carrier and replenished to the developing device4is referred to as “pre-mixed toner.”

FIG. 8shows the configuration of the vicinity of a near-side end portion of the developing device4in which a discharge screw2aserving as a discharge conveying member, the stirring screw11, recovery screw6and doctor blade12are removed therefrom.

In the developing device4of the present embodiment, the stirring conveyance path10serves as a circulation conveyance path for conveying the excess developer that reaches the downstream end in the conveyance direction of the supply conveyance path9to the upstream end in the conveyance direction of the supply conveyance path9. Also, the stirring screw11serves as a circulating conveying member, which applies the conveying force to the developer within the stirring conveyance path10serving as a circulation conveyance path. The excess opening portion92serves as a circulation opening portion, which is provided in the vicinity of the downstream end in the conveyance direction of the supply conveyance path9and through which the passed developer is delivered to the stirring conveyance path10serving as a circulation conveyance path. Furthermore, in the developing device4, the supply conveyance path9has a developer discharge port94that serves as developer discharge means for discharging the passed developer to the outside of the developing device4. The developer that passes through the developer discharge port94is delivered to the discharge conveyance path2as a discharged developer, and conveyed in a direction (direction toward the far side ofFIG. 2andFIG. 8) opposite to the conveyance direction of the supply conveyance path9(direction toward the near side ofFIG. 2andFIG. 8) by the rotation of the discharge screw2a.

The discharge conveyance path2is disposed on the downstream side in the conveyance direction of the supply conveyance path9such as to be adjacent to the supply conveyance path9with a partition wall135therebetween. The developer discharge port94is an opening provided on the partition wall135such that the supply conveyance path9and the discharge conveyance path2are communicated with each other.

The developing device4further has a supply downstream end wall surface80serving as developer accumulating means for accumulating, in the vicinity of the excess opening portion92serving as a circulation opening portion, the developer that reaches the vicinity of the downstream end in the conveyance direction of the supply conveyance path9but does not enter the excess opening portion92. Moreover, the developer discharge port94serving as a discharge opening port is provided so as to allow the passage of the developer that reaches the position of the developer discharge port94, the developer being part of the developer accumulated above the excess opening portion92and by the supply downstream end wall surface80. In other words, the developer that reaches the vicinity of the downstream end in the conveyance direction of the supply conveyance path9but cannot enter the excess opening portion92and thereby spills out of the excess opening portion92is blocked by the supply downstream end wall surface80in the form of the excess developer, and becomes the accumulated developer. Then, when the bulk of this accumulated developer increases, the developer that reaches the developer discharge port94provided above the excess opening portion92is allowed to pass through the developer discharge port94and discharged to the discharge conveyance path2.

FIG. 9shows a discharged-developer transfer pipe601serving as a discharge conveyance path, which receives the discharged developer conveyed to the outside of a developing casing of the developing device4through the discharge conveyance path2and conveys the discharged developer to a discharged-developer tank600serving as a discharged-developer container.

The discharged developer is conveyed from the supply conveyance path9within each of the developing devices4(Y, M, C and K) to the end portion of the developing device4opposite to the developer discharge port94via the developer discharge port94by each of the discharge conveyance paths2(Y, M, C and K), and then discharged to the outside of the developing casing of the developing device4.

The developer that is conveyed to the downstream end in the conveyance direction of the discharge conveyance path2(Y, M, C and K) and discharged from the casing of the developing device4enters the discharged-developer transfer pipe601from each of developer receiving port604(Y, M, C and K). The discharged-developer transfer pipe601has a discharge containing screw602, which serves as a discharge containing conveying member for applying the conveying force to the discharged developer within the discharged-developer transfer pipe601. One end of the discharged-developer transfer pipe601has a discharge containing screw drive source603for transferring the developer within the discharged-developer transfer pipe601successively by means of the rotation of the discharge containing screw602and causing the discharged-developer tank600serving as a discharged-developer container outside the developing device4to contain the successively transferred developer.

Note thatFIG. 9shows the configuration for conveying the discharged developer conveyed by the discharge conveyance path2(Y, M, C or K) to one discharged-developer tank600, but the discharged-developer tank600for each color may be provided individually in accordance with the each discharge conveyance path2(Y, M, C or K).

The toner that is contained in the discharged developer discharged from the developer discharge port94to the discharge conveyance path2is degraded, has poor fluidity, and thus is firmly fixed within the discharge conveyance path2easily. The discharged developer also has poor fluidity particularly under an environment with high temperature and high humidity, and thus is firmly fixed easily.

Also, in a state in which the discharge screw2aconstantly rotates at a fixed rotation speed, the force applied to the discharged developer within the discharge conveyance path2does not fluctuate. For this reason, in a state in which the discharge screw2arotates at a fixed rotation speed, the discharged developer aggregates in a section where the discharge screw2acan stop, without moving, and thereby adheres firmly within the discharge conveyance path2. As the discharged developer that exists in the section where the discharge screw2acan stop in a state in which the discharge screw2arotates at a fixed rotation speed, there is discharged developer that adheres to the axis or wing of the discharge screw2aand follows the rotation of the discharge screw2a. Such discharged developer that adheres to the discharge screw2aand follows the rotation of the discharge screw2ais not apply with the conveying force in spite of the rotation of the discharge screw2a, and thereby stops while adhering to the discharge screw2a.

Next, characterizing portions of the present embodiment will now be described.

In the developing device4of the present embodiment, the supply screw8serving as a developer conveying member, the recovery screw6, the stirring screw11, and the developing roller serving as a developer carrier continuously rotate while an image forming operation is performed. The discharge screw2a, on the other hand, rotates intermittently.

In the developing device4of the present embodiment, a shock can be applied intermittently to the discharged developer within the discharge conveyance path2by intermittently driving the discharge screw2a. The discharged developer, which is positioned so as to be applied with the conveying force by the rotation of the discharge screw2a, repeatedly accelerates and stops as the discharge screw2ais intermittently driven. Therefore, the discharged developer receives a shock intermittently at acceleration timing. Consequently, a minute vibration occurs so that the developer adhering to the discharge screw2ais prevented from aggregating and the aggregated developer can be released.

In this manner, by intermittently driving the discharge screw2aand intermittently apply the conveying force to the discharged developer by means of the discharge screw2a, shocks can be applied to the discharged developer within the discharge conveyance path2intermittently. Then, the discharged developer in a section where the conveying force of the discharge screw2awithin the discharge conveyance path2is not applied also starts moving and thereby the aggregated discharged developer can be released.

Since the aggregated discharged developer can be prevented from adhering firmly within the discharge conveyance path2, the discharged developer can be conveyed to the outside of the developing device4well.

In addition, the developing device4of the present embodiment is configured such that the discharge conveyance path2conveys the discharged developer in a horizontal direction. When the discharged developer is conveyed in the horizontal direction or upward direction, clogging by the discharged developer occurs mostly, but driving the discharge screw2aintermittently prevents the occurrence of clogging by the discharged developer even when the discharged developer is conveyed in the horizontal direction in the developing device4.

Moreover, it is desirable that the amount of carrier contained in the pre-mixed toner be small in consideration of the running cost for image formation. By reducing the amount of carrier contained in the pre-mixed toner, the amount of developer discharged from the developer discharge port94also becomes small, whereby the carrier within the developing device4does not have to be replaced so often and the carrier contained in the developer to be discharged becomes degraded more. Although the risk of firm adhesion of the degraded carrier within the discharge conveyance path2increases, driving the discharge screw2aintermittently in the developing device4of the present embodiment can prevent the firm adhesion of the discharged developer and the occurrence of clogging of the discharge conveyance path2.

Next, the first example of intermittent rotation of the discharge screw2a(called “Example 1” hereinafter) will now be described.

FIG. 10shows the configuration on the upstream side in the conveyance direction of the discharge conveyance path2of the developing device4of Example 1. As shown inFIG. 10, the outside of the supply screw8in the axis direction of the casing of the developing device4has an eccentric cam801, which is coaxial with the supply screw8and continuously rotated and driven along with the supply screw8by drive transmitted from the drive source of the supply screw8. There is also provided an oscillating lever201, which oscillates around a rotation axis of the discharge screw2aas the eccentric cam801rotary moves.

As shown inFIG. 11, the eccentric cam801has a protruding portion802at a position eccentric with respect to the rotation axis of the supply screw8. The oscillating lever201has a groove202with which the protruding portion802is brought into engagement. When the supply screw8is rotated and driven and the eccentric cam801is rotated in the direction of the arrow M, the oscillating lever201oscillates around the rotation axis of the discharge screw2aas shown by the arrow N.

FIG. 12shows the connection between the oscillating lever201and the discharge screw2a.

As shown inFIG. 12, the oscillating lever201is connected to the rotation axis of the discharge screw2avia a one-way clutch203. The one-way clutch203transmits, to the rotation axis of the discharge screw2a, a downward motion (arrow N2) which is a one-way oscillation motion of the oscillating lever201shown by the arrow N, but does not transmit an upward motion (arrow N1) which is a backward motion. Accordingly, when the oscillating lever201oscillates as shown by the arrow N, the one-way clutch203enters a lock state with respect to the rotation axis of the discharge screw2aand transmits drive as the leading end of the oscillating lever201moves downward (arrow N2), and thereby the discharge screw2ais rotated and driven in the direction of the arrow Q in the drawing. On the other hand, the one-way clutch203enters an unlock state with respect to the rotation axis of the discharge screw2aand does not transmit drive as the leading end of the oscillating lever201moves upward (arrow N1), and thereby the discharge screw2astops.

In the developing device4of Example 1, the oscillating lever201serving as intermittent rotation transmission means and the one-way clutch203convert the drive force of the continuous rotation of the eccentric cam801serving as a rotary driving member into a drive force of intermittent rotation, and transmit the converted drive force to the discharge screw2a.

In the developing device4, the continuous rotation of the supply screw8and eccentric cam801in the direction of the arrow M in the drawing causes the oscillating lever201to oscillate in the direction of the arrow N, and then the one-way clutch203transmits the drive to the discharge screw2aso as to rotate it intermittently in the direction of the arrow Q. Specifically, in the developing device4, the drive source of the supply screw8, the supply screw8, the eccentric cam801, the oscillating lever201, the one-way clutch203and the like constitute discharge screw intermittent rotation means for rotating the discharge screw2aintermittently.

As described above, since the continuous rotation of the supply screw8is transmitted to drive the discharge screw2aintermittently, it is not necessary to provide a drive source for the discharge screw2a. Therefore, space and costs can be saved. When a drive source for the discharge screw2ais provided to drive the discharge screw2aintermittently, it is necessary to perform drive control so that the drive force of the drive source causes intermittent drive. In Example 1, however, since the oscillating lever201serving as intermittent rotation transmission means and the one-way clutch203convert the drive force of the continuous rotation of the eccentric cam801into the drive force of intermittent rotation, and transmit the converted drive force to the discharge screw2a, it is not necessary to perform drive control.

The following are the conditions for the intermittent operation performed in the developing device4of Example 1.

Rotation speed of the eccentric cam688[rpm]Oscillating angle of the oscillating lever31[°]Intermittent frequency11.5[Hz]Diameter of the discharge screwφ10[mm]Rotation speed of the discharge screw59[rpm]

Note that the copying machine500of the present embodiment is a high-speed copying machine for continuously printing 60 to 65 pages per minute, and the rotation speed of the supply screw8therein is approximately 690 [rpm]. On the other hand, the discharge screw2acan play a role of discharging the developer at a rotation speed of 60 [rpm]. Although there is no problem with the discharge screw2adischarging the developer at a rotation speed of approximately 690 [rpm], it is costly to create a screw that can tolerate such a rotation speed of 690 [rpm]. Therefore, it is desirable to use the low rotation speed, since the discharge screw2acan play such a role at a rotation speed of approximately 60 [rpm]. It is also desirable that the discharge screw2aand the supply screw8have a common drive source, in order to achieve cost reduction. However, required rotational speed differs significantly between the supply screw8and the discharge screw2a, and thus when drive is transmitted from the supply screw8the speed of driving transmission needs to be reduced to 1/10. A gear or a belt is generally used for reducing the speed, but driving transmission needs to be performed by using a large number of gears in order to achieve deceleration to 1/10. In the developing device4of Example 1, however, the deceleration by approximately 1/10 can be realized by using the eccentric cam801, oscillating lever201and one-way clutch203only.

In Example 1, the eccentric cam801serving as a rotary driving member for transmitting drive to the discharge screw2ais provided at an end portion in an axial direction of the supply screw8, but this is not the only place to provide the eccentric cam801. The stirring screw11or the recovery screw6may be provided with the eccentric cam801. Also, the developing roller5or the photoreceptor1may be provided with the eccentric cam801.

Next, the second example of intermittent rotation of the discharge screw2a(called “Example 2” hereinafter) will now be described.

As shown inFIG. 13, the developing device4of Example 2 has a discharge drive source205for the discharge screw2a, which is provided independently from the other screw members. The discharge drive source205has a motor, an electromagnetic clutch, or the like, which is not shown, and a control unit700performs ON-OFF control of driving transmission by means of the electromagnetic clutch. By performing the ON-OFF control on the discharge drive source205, the discharge screw2acan be operated intermittently as with the case of Example 1, even when the other screw of the developing device4such as the supply screw8, stirring screw11and recovery screw6rotate steadily.

The above embodiment describes the configuration in which a shock is intermittently applied to the developer existing within the discharge conveyance path2that discharges the discharged developer from the inside of the developing casing of the developing device4provided with the developing roller5serving as a developer carrier and the corresponding developer conveyance path.

The problem in which the discharged developer firmly adheres to the inner wall of the conveyance path also occurs not only in the discharge conveyance path2, but also in the discharged-developer transfer pipe601serving as a discharge conveyance path, which is provided between the developing casing of the developing device4from which the developer is discharged by the discharge conveyance path2and the discharged-developer tank600serving as a discharged-developer container.

Therefore, as with the discharge screw2a, the discharge containing screw602serving as a discharge containing conveying member may be intermittently driven. Specifically, the discharge containing screw drive source603has a motor, an electromagnetic clutch, or the like, which is not shown, and the control unit700performs ON-OFF control of driving transmission by means of the electromagnetic clutch. By performing the ON-OFF control on the discharge containing screw drive source603, the discharge containing screw602can be rotated intermittently and the discharged developer can be prevented from firmly adhering to the inner wall of the discharged-developer transfer pipe601. Consequently, the discharged developer can be conveyed to the discharged-developer tank600well.

The present embodiment describes the configuration of the developing device4in which intermittent driving of the discharge screw2acan apply shocks to the discharged developer within the discharge conveyance path2intermittently. The configuration for intermittently applying shocks to the discharged developer within the discharge conveyance path2is not limited to the configuration for intermittently driving the discharge screw2a. For example, a protruding portion that slightly contacts the wing of the discharge screw2amay be provided on the inner wall of the discharge conveyance path2. By providing such a protruding portion, the wing comes into contact with the protruding portion every time the discharge screw2arotates, whereby the discharge screw2aoscillates and a shock can be applied intermittently to the discharged developer within the discharge conveyance path2.

As described above, according to the present embodiment, in the developing device, which has: the developing roller5serving as a developer carrier, which rotates while carrying a developer on a surface thereof, supplies a toner to a latent image on the surface of the photoreceptor1serving as a latent image carrier at a section where the developing roller5faces the photoreceptor1, and develops the latent image; the developer conveyance path, which has the supply screw8serving as a developer conveying member for conveying the developer and the supply conveyance path9that conveys the developer while supplying the developer to the developing roller5at a developer supply region for supplying the developer to the developing roller5; the toner replenishment controller serving as developer replenishing means for replenishing the developer to the developer conveyance path; the discharge conveyance path2that conveys the developer to the outside of the developing device4; the discharge screw2aserving as a discharge conveying member for applying a conveying force to the developer within the discharge conveyance path2; and the developer discharge port94serving as developer discharge means for discharging at least part of the developer within the developer conveyance path to the discharge conveyance path2in the form of discharged developer, a shock is applied intermittently to the discharged developer within the discharge conveyance path2so that even discharged developer that is not applied with the conveying force of the discharge screw2ain the discharge conveyance path2starts moving and thereby the aggregated discharged developer can be released. Consequently, the aggregated discharged developer can be prevented from firmly adhering within the discharge conveyance path2and thereby the discharged developer can be conveyed to the outside of the developing device4well.

Moreover, by intermittently applying the conveying force of the discharge screw2aserving as a discharge conveying member, a shock can be applied intermittently to the discharged developer within the discharge conveyance path2, the aggregated discharged developer can be prevented from firmly adhering within the discharge conveyance path2, and the discharged developer can be conveyed to the outside of the developing device4well.

In addition, the discharge conveying member is the discharge screw2a, which has a rotation axis and a spiral wing provided on the rotation axis and rotates to convey the developer in the direction of the rotation axis. The discharge screw2ais intermittently rotated by the discharge screw2aintermittent rotation means that is configured by the drive source of the supply screw8, the supply screw8, the eccentric cam801, the oscillating lever201and the one-way clutch203. Consequently, the conveying force can be applied intermittently. Therefore, a shock can be applied intermittently to the discharged developer within the discharge conveyance path2, the aggregated discharged developer can be prevented from firmly adhering within the discharge conveyance path2, and the discharged developer can be conveyed to the outside of the developing device4well.

There is provided the eccentric cam801serving as a rotary driving member which is continuously rotated and driven by the drive force transmitted from the drive source of the supply screw8. The discharge screw2aintermittent rotation means has the intermittent rotation transmission means for converting the drive force for continuous rotation of the eccentric cam801into a drive force for intermittent rotation and transmitting the converted drive force to the discharge screw2a. Therefore, it is not necessary to provide a drive source for the discharge screw2aso that space and costs can be saved.

The are also provided the oscillating lever201serving as a oscillating member, which oscillates around the rotation axis of the discharge screw2aas the eccentric cam801rotary moves, and the one-way clutch203, which transmits one-way oscillation motion of the oscillating lever201to the discharge screw2abut does not transmit an upward motion which is a backward motion. Accordingly, the drive force for the continuous rotation of the eccentric cam801can be converted into a drive force for intermittent rotation and then transmitted to the discharge screw2a.

There are also provided the discharge drive source205serving as a discharge screw drive source for transmitting a drive force to the discharge screw2a, and the control unit700serving as discharge drive source control means for controlling the discharge screw drive source. The control unit700controls the discharge drive source205so as to rotate the discharge screw2aintermittently, whereby the conveying force can be applied intermittently by the discharge screw2aserving as a discharge conveying member.

When the discharge conveyance path2conveys the developer in the horizontal direction or upward direction, clogging by the discharged developer occurs mostly, but driving the discharge screw2aintermittently can prevent the occurrence of clogging by the discharged developer even when the discharged developer is conveyed in the horizontal direction in the developing device4.

When the developer to be used is a two-component developer composed of toner and carrier, the carrier that is not consumed in development processing deteriorates, causing an image failure. However, since the pre-mixed toner containing carrier is replenished from the toner replenishing port95so that the developer containing the deteriorated carrier can be discharged from the developer discharge port94, the carrier within the developing device4can be replaced and good image formation can be carried out.

Furthermore, by applying a shock intermittently to the developer existing within the discharge conveyance path2within the developing casing of the developing device4that is provided with the developer conveyance paths having at least the supply conveyance path9, stirring conveyance path10and recovery conveyance path7and the developing roller5serving as a developer carrier, the discharged developer can be discharged to the outside of the developing casing well.

Moreover, a shock is applied intermittently to the developer that is discharged from the developing casing of the developing device4provided with the developer conveyance paths having at least the supply conveyance path9, stirring conveyance path10and recovery conveyance path7and the developing roller5serving as a developer carrier and exists within the discharge developer transfer pipe601serving as a discharge conveyance path between the developing casing and the discharged-developer tank600serving as a discharged-developer container for containing the discharged developer. Accordingly, the discharged developer that is discharged from the developing casing can be conveyed to the discharged-developer tank600well.

The developing device4serving as developing means is provided in the copying machine500serving as an image forming apparatus, which has at least the photoreceptor1serving as a latent image carrier, the charging unit serving as charging means for charging the surface of the photoreceptor1, the optical writing unit21serving as latent image forming means for forming an electrostatic latent image on the photoreceptor1, and the developing means for developing the electrostatic latent image into a toner image. Therefore, the discharged developer can be conveyed to the outside of the developing device4well, whereby the carrier within the developing device4can be replaced and good image formation can be carried out.

In addition, the developing device4serving as developing means is provided in the process cartridge18, which is configured to have at least the photoreceptor1serving as a latent image carrier for carrying a latent image and the developing means for developing the latent image on the photoreceptor1, in a common holder as one unit, and is also configured detachably from the main body of the copying machine500serving as an image forming apparatus that has the photoreceptor1and the developing means. Accordingly, the discharged developer can be conveyed to the outside of the developing device4well, whereby the carrier within the developing device4can be replaced and the developing device4which enables good image formation can be easily attached to/detached from the copying machine500.

According to the present invention, since the discharged developer can be prevented from remaining aggregated in the discharge conveyance path as described above, the present invention can exert the effects of preventing the aggregated discharged developer from firmly adhering within the discharge conveyance path and conveying the discharged developer to the outside of the developing device well. In addition, by applying a shock intermittently to the discharged developer within the discharge conveyance path conveying the developer to the outside of the developing device, even the discharged developer that is not applied with the conveying force of the discharge conveying member in the discharge conveyance path starts moving and thereby the aggregated discharged developer can be released.