Developing device having a powder conveyor, process cartridge, and image forming apparatus including the same

A developing device includes a housing to store a powder, a developing roller to hold the powder, a supplying roller to supply the powder to the developing roller, a regulator to regulate the powder held by the developing roller, a powder conveyer to convey the powder for image forming, a first powder storing chamber, and a second powder storing chamber. The powder conveyor includes a first conveying part that includes a rotating axis, and a conveying surface inclined with respect to the rotating axis along a direction of the rotating axis. The powder conveyor further includes a second conveying part that includes a conveying surface parallel to the rotating axis along the direction of the rotating axis, and the first conveying part and the second conveying part are disposed alternately along the direction of the rotating axis.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2014-078763, filed on Apr. 7, 2014, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

I. Technical Field

The present disclosure relates to a powder conveying member for use in an image forming apparatus such as a copier, printer, and facsimile machine; and a powder conveying device, a process cartridge, and an image forming apparatus using the developing device.

II. Description of the Related Art

An image forming apparatus, such as a copier, printer, facsimile machine, and combined machine thereof, generally includes a powder conveyer to covey a powder, such as toner, to develop a latent image. A conveying screw which has a shaft and a spiral vane, and a conveying paddle which has a plate around a shaft are known as a powder conveyer.

SUMMARY

In accordance with some embodiments of the present invention, a powder conveyer is provided.

The powder conveyer includes a first conveying part, and a second conveying part. The first conveying part includes a rotating axis, and a conveying surface inclined with the rotating axis along a direction of the rotating axis. The second conveying part includes a conveying surface parallel to the rotating axis along the direction of the rotating axis. The first conveying part and the second conveying part are disposed alternately along the direction of the rotating axis.

In accordance with some embodiments of the present invention, a conveying device is provided. The powder conveying device includes a driver to drive the powder conveyer, a housing, and the above-described powder conveyer.

In accordance with some embodiments of the present invention, a developing device is provided. The developing device includes a housing, a developing roller, a supplying roller, a regulator, and a developer conveyer that includes the above-described powder conveyer.

In accordance with some embodiments of the present invention, a process unit is provided. The process unit includes a photoreceptor, and the above-described developing device.

In accordance with some embodiments of the present invention, an image forming apparatus is provided. The image forming apparatus includes the above-described powder conveyer.

DETAILED DESCRIPTION

An image forming apparatus according to an embodiment of the present invention is described below with reference toFIG. 1. An image forming apparatus1illustrated inFIG. 1is a color laser printer. An intermediate transfer belt30is disposed approximately at a center part of the printer in a height direction. Four process cartridges4Y,4M,4C, and4K are disposed below the intermediate transfer belt30. The process cartridges4Y,4M,4C, and4K have the same configuration except for storing developers with different colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively, corresponding to the color separation components of a color image. Descriptions of the present embodiment are made with a case in which a one-component developer consisting of only toner is used, however, a two-component developer consisting of toner and carrier may also be used.

The toner may be a pulverized toner or polymerized toner. An external additive for toner may include silicone with silicone oil.

The external additive is obtained in a manner that the pulverized toner or the polymerized toner (100 parts by mass) is added to hydrophobic silica RY50 (2 parts by mass) (product of Nippon Aerosil Co., Ltd), and mixed together by a 20 L HENSCHEL MIXER (rotating speed 40 m/s for 5 minutes). Then the resultant mixture is caused to pass through a sieve with an opening size of 75 μm to remove coarse particles and aggregates.

Each of the process cartridges4Y,4M,4C, and4K includes a photoreceptor5in a drum-like shape serving as a latent image carrier, a charger6to charge a surface of the photoreceptor5, a developing device7to supply toner to a surface of the photoreceptor5, a cleaner8to clean a surface of the photoreceptor5, and an irradiator9to irradiate a surface of the photoreceptor5. In the present embodiment, an LED unit is employed as the irradiator9.

A transfer device3is disposed above the process cartridges4Y,4M,4C, and4K. The transfer device3includes the intermediate transfer belt30serving as an intermediate transfer medium, four primary transfer rollers31serving as primary transfer means, a secondary transfer roller36serving as secondary transfer means, a secondary transfer backup roller32, and a belt cleaner35.

The intermediate transfer belt30is in the form of an endless belt and stretched taut with the secondary transfer backup roller32and a roller33. The intermediate transfer belt30rotates in a direction indicated by an arrow inFIG. 1as the secondary transfer backup roller32is driven to rotate.

Each of the four primary transfer rollers31and the corresponding photoreceptor5sandwich the intermediate transfer belt30to form a primary transfer nip. Each of the primary transfer rollers31is connected to a power source which applies a predetermined direct current voltage (DC) and/or an alternating current voltage (AC) thereto.

The secondary transfer roller36and the secondary transfer backup roller32sandwich the intermediate transfer belt30to form a secondary transfer nip. The secondary transfer roller36is connected to a power source which applies a predetermined direct current voltage (DC) and/or an alternating current voltage (AC) thereto.

The belt cleaner35includes a cleaning brush and a cleaning blade both disposed in contact with the intermediate transfer belt30. The belt cleaner35is connected to a waste toner container with a waste toner transport hose.

Four toner cartridges2Y,2M,2C, and2K to store supplementary fresh toner are detachably mounted to an upper part of the printer. A supply path is provided between each of the toner cartridges2Y,2M,2C, and2K and each of the developing devices7to supply fresh toner from each of the toner cartridges2Y,2M,2C, and2K to each of the developing devices7.

The toner is supplied to process units4Y,4M,4C,4K from toner cartridges2Y,2M,2C,2K as toner supplying units. The frequency of changing each process unit is thus reduced, which leads to a long life of the process unit and a reduced print unit price.

At a lower part of the main body of the printer, a paper feed tray10to store paper sheets, serving as recording media, and a paper feed roller11to feed the paper sheets from the paper feed tray10, are provided. Other than normal paper sheets, sheets of thick paper, thin paper, coated paper, art paper, or tracing paper, postcards, envelopes, OHP sheets, etc., can be used as the recording media. It is possible to further provide a manual paper feed mechanism.

Inside the main body of the printer, a conveyance path R is provided to convey a paper sheet from the paper feed tray10to an outside of the printer via the secondary transfer nip.

On the conveyance path R, a pair of registration rollers12is provided upstream from the secondary transfer roller36relative to the direction of conveyance of the paper sheet. The pair of registration rollers12conveys the paper sheet to the secondary transfer nip at a right timing.

A fixing device20to fix an unfixed toner image on a paper sheet is provided downstream from the secondary transfer roller36relative to the direction of conveyance of the paper sheet. A pair of discharge rollers13to discharge the paper sheet to the outside of the printer is provided on the conveyance path R downstream from the fixing device20relative to the direction of conveyance of the paper sheet. On an upper surface of the main body of the printer, a discharge tray14is provided to stack paper sheets discharged from the printer.

Basic operation of this printer is explained below with reference toFIG. 1. At the beginning of an imaging operation, each of the photoreceptors5in the process cartridges4Y,4M,4C, or4K is driven to rotate clockwise inFIG. 1by a driving device.

A surface of each of the photoreceptors5is then uniformly charged to a predetermined polarity by each of the chargers6. The charged surface of the photoreceptor5is irradiated with laser light emitted from the irradiator9so that an electrostatic latent image is formed on the surface of the photoreceptor5.

The laser light contains single-color image information of yellow, magenta, cyan, or black that is separated from full-color image information. The electrostatic latent image formed on each of the photoreceptors5is supplied with toner from each of the developing devices7and developed into a toner image that is visible.

On the other hand, the secondary transfer backup roller32is driven to rotate counterclockwise inFIG. 1so that the intermediate transfer belt30is driven to rotate in the direction indicated by the arrow inFIG. 1. Each of the primary transfer rollers31is applied with a constant-voltage-controlled or constant-current-controlled voltage having an opposite polarity to that of the toner so that a transfer electric field is formed in the primary transfer nip defined between each of the primary transfer rollers31and each of the photoreceptors5.

Upon reaching the primary transfer nips as the photoreceptors5rotate, the toner images on the respective photoreceptors5are sequentially transferred onto the intermediate transfer belt30and superimposed on one another by action of the transfer electric fields formed in the primary transfer nips. Thus, a full-color composite toner image is formed on a surface of the intermediate transfer belt30.

Residual toner particles remaining on the photoreceptors5without being transferred onto the intermediate transfer belt30are removed by the cleaners8. The surface of each of the photoreceptors5is neutralized by a neutralizer to initialize the surface potential.

At a lower part of the printer, the paper feed roller11starts rotating to feed a paper sheet from the paper feed tray10to the conveyance path R. The conveyance of the paper sheet is once stopped by the pair of registration rollers12.

The pair of registration rollers12starts rotating at a predetermined timing so that the paper sheet is conveyed to the secondary transfer nip in synchronization with an entry of the full-color composite toner image on the intermediate transfer belt30into the secondary transfer nip. The secondary transfer roller36is applied with a transfer voltage having the opposite polarity to that of the full-color composite toner image on the intermediate transfer belt30so that a transfer electric field is formed in the secondary transfer nip.

The full-color composite toner image is transferred from the intermediate transfer belt30onto the paper sheet by action of the transfer electric field. Residual toner particles remaining on the intermediate transfer belt30without being transferred onto the paper sheet are removed by the belt cleaner35and collected in the waste toner storage.

The paper sheet is then conveyed to the fixing device20and the full-color composite toner image is fixed on the paper sheet in the fixing device20. The paper sheet having the fixed full-color composite toner image is discharged onto the discharge tray14by rotation of the discharge rollers13.

In the above-described embodiment, the printer is able to print the color image on the paper sheet. A sheet transfer path forms a C-shape. The printer is able to convey a variety of sheets such as a thick sheet, an envelope, and so on, with a reduced risk of a jam.

Furthermore, the paper sheet is discharged with its printed side facing downward. The paper sheet that is stacked on the discharge tray14is stacked in a print order from up to down, when the paper sheets are picked up.

In the above-described embodiment, all of the four process cartridges4Y,4M,4C, and4K are brought into operation to form full-color images. According to another embodiment, only one of the four process cartridges4Y,4M,4C, and4K is brought into operation to form single-color images. According to another embodiment, two or three of the four process cartridges4Y,4M,4C, and4K are brought into operation to form two-color or three-color toner images, respectively.

In the present embodiment, the four process cartridges4Y,4M,4C, and4K are disposed below the intermediate transfer belt30that is rotatable in the direction indicated by the arrow inFIG. 1. In this case, a distance between the primary transfer nip (i.e., the nip formed between the photoreceptor5and the primary transfer roller31) and the secondary transfer nip (i.e., the nip formed between the secondary transfer roller36and the secondary transfer backup roller32) is shorter compared to a case in which the process cartridges are disposed above the intermediate transfer belt30.

Accordingly, a distance that the intermediate transfer belt30travels after the primary transfer is completed before the secondary transfer is executed is shorter, which means that a length of time before the first print is shorter.

The photoreceptors5keep rotating in synchronization with the rotation of the intermediate transfer belt30, to keep supplying toner from the photoreceptors5to the intermediate transfer belt30. The shorter travel distance of the intermediate transfer belt30suppresses wear of the photoreceptor or consumption of the toner.

The belt cleaner35is provided immediately downstream from the secondary transfer nip, i.e., above the intermediate transfer belt30, as illustrated inFIG. 1. If the process cartridges4Y,4M,4C, and4K are provided above the intermediate transfer belt30, the process cartridges4Y,4M,4C, and4K and the belt cleaner35should be arranged next to each other in a horizontal direction, resulting in an increase in a horizontal width of the image forming apparatus.

By contrast, when the process cartridges4Y,4M,4C, and4K are provided below the intermediate transfer belt30as illustrated inFIG. 1, the process cartridges4Y,4M,4C, and4K and the belt cleaner35need not be arranged next to each other in a horizontal direction, avoiding an increase in the horizontal width of the image forming apparatus.

FIG. 2is a cross sectional view of the process cartridge4(hereinafter the additional characters Y, M, C, and K representing the respective colors of yellow, magenta, cyan, and black are omitted for the sake of simplicity). The process cartridge4includes the photoreceptor5, the charger6, the developing device7, the cleaner8, and the irradiator9.

The charger6includes a charging member61to charge the photoreceptor5by contact therewith and may include a cleaning member to clean the charging member61. The cleaner8includes a cleaning member81to remove developer (toner) adhered to a surface of the photoreceptor5and a waste toner conveying member82to convey waste toner particles removed by the cleaning member81.

Since a two-component developing system is able to attach the toner to the toner conveyer by magnetic force, it is easier to supply the toner to the toner conveyer than with a one component developing device. However, the two-component developing system leads to an increase in size of the image forming apparatus, and increased expense. The one component developing system has an advantage of producing a small and low-priced image forming apparatus.

However, the one component developing system has an impasse where the toner accumulates therein, at an upper of the developing device7. The impasse has a developing section which includes a developing roller71, a supply roller72, and a regulating blade73. When the process cartridges4Y,4M,4C, and4K are provided below the intermediate transfer belt30as illustrated inFIG. 1, toner is pumped up and supplied to developing section of the impasse by a rotating fin.

As shown inFIG. 2, the developing device7includes a housing70, the developing roller71serving as a developer carrier to carry toner, the supply roller72serving as a supply member to supply toner to the developing roller71, and the regulating blade73serving as a regulator to regulate a thickness of toner carried on the developing roller71.

The developing device7includes a conveying screw76serving as a first developer conveyer (first powder conveyer, first rotating member) to convey the toner, and a pumping member77serving as second developer conveyer (second powder conveyer, second rotating member).

The developer carrier is not limited to the developing roller71and may be a developing belt. The regulator is not limited to the regulating blade73and may be a regulating roller.

The space inside the housing70includes a first divider74and a holding member75which holds the first divider74. The space is divided by the first divider74and holding member75to form a mixing chamber S1serving as a first developer storing chamber and a supply chamber S2serving as a second developer storing chamber. The supply chamber S2is disposed above the mixing chamber S1.

Referring toFIG. 2, the mixing chamber S1includes the conveying screw76and the pumping member77. The supply chamber S2includes the supply roller72. The supply chamber S2and the mixing chamber S1are communicated with each other via an upper communicating path Q1, a lower communicating path Q2, and a pumping path Q4. The lower communicating path Q2is disposed at a lower end of the pumping path Q4extending in a vertical direction.

The mixing chamber S1is divided to form a first mixing space U1and a second mixing space U2. The first mixing space U1includes the conveying screw76, and is disposed above the second mixing space U2. The first mixing space U1and the second mixing space U2are divided by a second divider78that is disposed in the housing70integrally.

The supply roller72, the conveying screw76, and the pumping member77are arranged in a row. Thereby, the developing device7is able to be thin in a left and right direction inFIG. 2. This makes a distance between the photoreceptors5short.

The second divider78extends in a longitudinal direction of the conveying screw76and the pumping member77(a direction orthogonal to a paper surface ofFIG. 2.). A communicating path Q3(a first communicating path Q3aand a second communicating path Q3bare shown inFIG. 3) which is able to communicate with the first mixing chamber U1and the second mixing chamber U2, is disposed at a longitudinal direction end part side of the second divider78.

The first divider74is comprised of a flexible thin plate made of, for example, a metal or a resin. The first divider74is disposed in parallel with the developing roller71and the supply roller72in an axial direction and has the same axial dimension as the developing roller71and the supply roller72.

An upper end of the first divider74is fixed to the holding member75and disposed close to the supply roller72(i.e., immediately below the supply roller72inFIG. 2). A lower end portion of the first divider74extends obliquely downward from the fixed point. The lower end portion of the first divider74is a free end. The lower end portion of the first divider74contacts with the pumping member77over a whole region of a shaft from an upper side.

The pumping path Q4extending in the vertical direction is disposed between the first divider74and a vertical wall of the housing70. A lower end portion (an end of an upstream side) of the pumping path Q4connects to a second conveying part C of the pumping member77as the second rotating member. An upper end portion (an end of a downstream side) of the pumping path Q4connects to the supply chamber S2as the second developer storing chamber.

The conveying screw includes a rotating shaft76aparallel to the developing roller71and the supply roller72, and a spiral vane76bdisposed at a surface of the rotating shaft76a. The conveying screw76conveys the toner to one side in an axis direction of the rotating shaft76aby rotating via a drive means.

In this specification, the conveying screw76is disposed at a restriction region of the regulating blade73. In other words, the conveying screw76is disposed at a vertical lower portion of a contact point between the developer carried by developing roller71and the regulating blade73. The conveying screw76is formed longer than the pumping member77in the axis direction.

The pumping member77includes a rotating shaft77aparallel to the rotating axis of the developing roller71and supply roller72, a first conveying part B to convey the toner to the other side of the axis direction of the rotating shaft by pushing, and the second conveying part C to convey the toner in a rotating direction of the rotating shaft77a.

Referring toFIG. 3, the first mixing chamber U1and the second mixing chamber U2are communicating with each other through the first communicating path Q3aand the second communicating path Q3b, which are disposed in a longitudinal direction at both sides of end parts of the second divider78. The upstream end part of the first mixing chamber U1and the downstream end part of the second mixing chamber U2are connected by the first communicating path Q3a. The downstream end part of the first chamber U1and the upstream end part of the second mixing chamber U2are connected by the second communicating path Q3b.

Referring toFIG. 3, the length in the axis direction of the conveying screw76is longer than that of the pumping member77. The first mixing chamber U1including the conveying screw76is longer than the second mixing chamber U2including the pumping member77.

The housing70includes a main body part70astoring the pumping member77and the developing roller71, and a projecting portion70bprojected from the main body part70ain the axis direction, and covering one end side portion of the conveying screw (the right side inFIG. 3).

An upper portion of the projecting portion70bhas a tonner supplying opening79to supply the one-component toner from the toner cartridges2to the developing device7. The toner supplying opening79has a shutter serving as an opening/closing member.

Usually the toner supplying opening79is closed, however when an amount of the toner detected by a toner detector90becomes below a reference value, the opening/closing member moves to open the toner supplying opening79. Thereby, new toner is supplied to the first mixing chamber U1from the toner cartridges2via the toner supplying opening79.

Since the first communicating path Q3ais disposed immediately downstream of the toner supplying opening79, a mixing time for mixing old toner with new toner is able to gain time from the first communication path Q3as a start position to a developing area. Thereby, the new toner and old toner is mixed well, and the image forming apparatus can obtain a stable output of images free of density variation and ground staining. The toner supplying opening79can be provided at the second mixing chamber U2. In this case, the projecting portion70bis not disposed at the housing70, the conveying screw76, the pumping member77and developing roller71are a same length in the axis direction, and the conveying screw76and the pumping member77are stored in the main body part70a.

When the conveying screw76rotates, the toner is conveyed in a direction of an arrow F inFIG. 3. On the other hand, when the pumping member77rotates, the toner is conveyed in a direction of an arrow G direction inFIG. 3by vanes77bdisposed on the first conveying part B. The conveying screw76and the pumping member77convey the toner in opposite directions.

The toner conveyed by the conveying screw76and the pumping member77is pressed to an inside of the housing70at each downstream of conveying direction. The toner is conveyed from the first mixing chamber U1to the second mixing chamber U2, or from the second mixing chamber U2to the first mixing chamber U1via the first and second communicating paths Q3a, Q3b.

In this way, the toner is conveyed in the opposite directions by the conveying screw76and the pumping member77. The toner is thus conveyed along a circulation path H indicated by a broken line inFIG. 3.

When the new toner is supplied from the toner cartridge2to the first mixing chamber U1via the toner supplying opening79, the new toner is conveyed along a conveying path K shown inFIG. 3by the conveying screw76. The new toner is joined with not-new toner (old toner) conveyed along the circulation path H at a side downstream of the conveying direction

A detail of the pumping member77is described inFIGS. 4(a) to 4(c).FIG. 4(a)is a perspective view of the pumping member77;FIG. 4(b)is a side view; andFIG. 4(c)is a cross section view.

Referring toFIGS. 4(a) to 4(c), the pumping member77has the first conveying part B and the second conveying part C alternately along a direction of the axis of the rotating shaft77a.

The first conveying part B has the spiral vane77bserving as a conveying surface b1inclined with respect to the rotating shaft77a. The spiral vane77bis arranged at a length of the axial direction of the rotating shaft77a.

The spiral vane77bis a one spiral blade. However, the spiral vane77bcan be two or more spiral blades. Instead of the spiral vane77b, one or more paddles inclined with the rotating shaft77acan be disposed on the rotating shaft77a.

The second conveying part C has a polygonal rod77cextending along the direction of axis of the shaft. The second conveying part C is a right quadrangular prism in theFIG. 4. However, the polygonal rod77ccan be a triangular prism, other polygonal shape, or an elliptic shape rod.

The second conveying part C can be a plate shape member77das shown inFIGS. 8(a) to 8(c). The second conveying part C including the polygonal rod77chas a conveying surface c1parallel with the rotating shaft77aalong the direction of the axis of the shaft. InFIG. 4, four surfaces of the polygonal rod77cinclude a rectangular conveying surface c1at intervals of 90 degrees.

An edge of the spiral vane77bis not protruding from the conveying surface c1when viewed from the axis direction. On the other hand, even if the edge of the spiral vane77bis protruding from the conveying surface c1, it is better for the edge not to protrude greatly. In this case, the conveying surface c1keeps a pumping effect.

The mixing chamber S1has a toner detector90serving as a developer detector to detect the amount of toner stored in the mixing chamber S1. Referring toFIG. 5, the toner detector90includes a first light guiding member91and a second light guiding member92both fixed to the housing70, and a cleaning member93fixed to a conveyance member (i.e., the conveying screw76in the present embodiment).

One end of the first light guiding member91is connected to a light-emitting element and the other end functions as a light-emitting surface91a. One end of the second light guiding member92is connected to a light-receiving element and the other end functions as a light-receiving surface92a. The light-emitting surface91aof the first light guiding member91and the light-receiving surface92aof the second light guiding member92are facing each other in an axial direction.

The cleaning member93is comprised of a flexible plate member made of, for example, a PET sheet. The cleaning member93rotates along with the conveying screw76. As the cleaning member93rotates, the cleaning member93slidably contacts the light-emitting surface91aof the first light guiding member91and the light-receiving surface92aof the second light guiding member92to remove toner particles adhered to the light-emitting surface91aand the light-receiving surface92a. Moreover, as the cleaning member93rotates, toner particles accumulated at a lower part of the mixing chamber S1are scraped up by the cleaning member93and allowed to pass through between the light-emitting surface91aand the light-receiving surface92a.

While the scraped-up toner particles are passing through between the light-emitting surface91aand the light-receiving surface92a, light emitted from the light-emitting surface91acannot reach the light-receiving surface92aand the light-receiving element detects no signal. During the rest of the time, light emitted from the light-emitting surface91areaches the light-receiving surface92aand the light-receiving element detects a signal.

Since an amount of toner scraped up by the cleaning member93varies depending on an amount of toner in the mixing chamber S1, the light-receiving time of the light-receiving element also varies. Accordingly, by detecting the light-receiving time of the light-receiving element, the amount of toner in the mixing chamber S1can be detected.

A toner conveying operation is explained as follows. First, toner pumping operation by the pumping member77is explained based onFIGS. 6(a) to 6(c).FIGS. 6(a) to 6(c)describe steps in which the toner is pumped by the pumping member.

When the pumping member77is rotated in a direction of an arrow A by the drive means M shown inFIG. 3, the conveying surface c1of the second conveying part C which is formed like polygonal rod, an inner surface of the housing70, and the first divider74work together. In this case, the toner T in the second mixing chamber U2is pumped upwardly. Then the toner is pushed into the supply chamber S2via the lower communicating path Q2(See,FIGS. 6(a) to 6(c)).

As the pumping member77rotates, the toner held on the conveying surface c1of the polygonal second conveying part C is struck by a lower end of the first divider74, and is pumped. The toner in the second mixing chamber U2is supplied to the supply chamber S2by repeating same action. The lower end of the first divider74works like a check valve. The pumping member77may rotate continuously or only rotate when a rotate command is made.

The lower end portion of the first divider74is pushed to the pumping member77with a carving shape while the pumping member77is rotating. If the pumping member77rotates, the first divider74contacts with the pumping member77constantly.

The toner T pumped by the pumping member77is prevented from returning to the second mixing chamber U2through the gap between the first divider74and the pumping member77. By rotating the pumping member77all the time, the toner is pushed from the lower end of the second mixing chamber U2. Thus, the toner is prevented from running back to the second mixing chamber U2.

At the lower end part of the first divider74there may be formed a plurality cuts in a vertical direction to surely strike. An interval of these cuts may correspond to the length of the polygonal rod77cin the axis direction. To form the cuts, the lower portion of the first divider74may have independent parts between the cuts, and the independent parts each strike an outer surface of a respective one of the polygonal rods77c.

If the edge of the spiral vane77bprotrudes from a surface of the polygonal rod77cto improve a conveying power, it is better that the cuts are formed at the lower end part of the first divider74to keep the conveying power of the first conveying part B and the second conveying part C. The lower end of the first divider74may contact the first conveying part B and second conveying part C while the pumping member77is rotating.

The toner conveying operation is explained referring toFIG. 2. When a developing operation starts, the photoreceptor5, the developing roller7, and the supply roller72each rotate in a direction of the arrows.

Then, the conveying screw76and the pumping member77start rotating. The toner in the second mixing chamber U2is pumped by the rotation of the pumping member77to the supply chamber S2via the pumping path Q4and the toner is stored in the supply chamber S2.

When an upper surface of the toner T reaches the supply roller72, the toner is transferred to the developing roller71via the supply roller72. Since the supply chamber S2does not have a screw as a conveyer, the upper surface of the toner keeps horizontal to a direction of the axis, and the toner is supplied to an area of developing roller71in the direction of the axis.

A surface of the first divider74, and an inner surface of the housing70which is opposed to a surface of the first divider74forming an inner wall of the supply chamber S2, are smooth surfaces without concavities or convexities. Thus, retaining the toner at the inner wall of the supply chamber S2is prevented.

Surplus toner among the toner caught by the developing roller71is regulated by the regulating blade73, and the regulated surplus toner falls down to the conveying screw76disposed under the regulating area.

When the opening/closing member of the toner supplying opening79opens, the new toner is supplied to the conveying screw76from a toner cartridge. The toner is circulated in the mixing chamber S1by the conveying screw76and the pumping member77, and the new toner and old toner are mixed. The toner mixed in the mixing chamber S1is supplied to the supply chamber S2by the pumping member77. In the developing device7, the toner regulated by the regulating blade73falls down to the first mixing chamber U1. Referring toFIG. 2, a circulation path M (a first circulation path) of the toner is thus formed. In one example, this circulation path is connected as follows: the first mixing chamber U1—the communicating path Q3(a second communicating path)—the second mixing chamber U2—the communicating path Q2—the pumping path Q4—the supply chamber S2—the supplying roller72—the developing roller71—the communicating path Q1—the first mixing chamber U1. Circulating the toner in the developing device7prevents the deterioration of the toner.

Referring toFIG. 3, in the mixing chamber S1, the toner is conveyed along a circulation path H (a second circulation path) by the conveying screw76and the pumping member77. The conveying screw76and the pumping member77convey the toner in the opposite directions. The toner is mixed in the mixing chamber S1.

Supplying the toner to a middle of the circulation path H from the toner supplying opening79, the new toner and the old toner are mixed enough. Supplying the mixed toner to the supply chamber S2, the old toner is prevented from being distributed unevenly to the developing roller71. A thin spot on the image occurring by unevenly distributed toner is thus prevented.

The pumping member77includes the first conveying part B conveying the toner in the direction of the axis, and the second conveying part C conveying the toner in the rotating direction of the axis. In this case, one conveyer (the pumping member77) can convey the toner in each of directions to mix the toner in the mixing chamber S1, and to pump the toner to the supply chamber S2. Therefore, it is not necessary to install two or more conveyers for different conveying directions. This is particularly useful to make the developing device7small, and to convey the toner efficiently to the directions along the two circulation paths H, M.

By the way, if there is a gap between the first divider74and the pumping member77, the toner pumped by pumping member77is not supplied to the second supply chamber S2and runs back to the second mixing chamber U2via the gap. As a result, the toner supply efficiency decreases.

Therefore, as mentioned above, the first divider74contacts constantly to the pumping member77by elastically deforming. This configuration avoids forming the gap between the first divider74and the pumping member77. Thus, the toner is supplied more efficiently.

Moreover, since the first divider74contacts the pumping member77by elastically deforming, a small vibration occurs according to the rotating of the pumping member77. The toner conveyed by the first conveying part B and second conveying part C is thus loosened up and prevented from condensing by the vibration.

Preferably, a toner carrying capacity of the pumping member77to the supply chamber S2is greater than a toner carrying capacity of the conveying screw76to the second mixing chamber U2. The capacity of the conveying screw76and the pumping member77are easily adjusted by changing a rotating speed or a size of the conveying screw76and the pumping member77. By adjusting the toner conveying capacity, enough of the toner is present near the developing roller71to prevent deterioration in development.

Moreover, preferably, the toner carrying capacity of the pumping member77to the mixing chamber U1is greater than the toner carrying capacity of the conveying screw76to the second mixing chamber U2. By this configuration, the toner retaining at a bottom part of the second mixing chamber U2is mixed efficiently.

As described above, disposing the conveying screw76under the regulating area of the regulating blade73, the old toner divided from the developing roller71at this area may fall to above the rotating conveying screw76.

Supplying the new toner to the conveying path with the conveying screw76from the toner supplying opening79starts to mix the old toner and the new toner. Since the first communicating path Q3is disposed downstream of the toner supplying opening79, mixing of the old toner divided at the regulating area and the new toner is started from the first communicating path Q3.

Therefore, a mixing time before a developing time and a toner moving distance are able to be long. Thus, the toner is homogenized. Thereby, the new toner and old toner are mixed well, and the image forming apparatus can obtain a stable output of images free of density variation and ground staining.

In the above embodiment, a contact direction of the first divider74to the pumping member77is a counter direction (an edge of the first divider74faces an opposite direction of the rotating direction of the pumping member77). However, for example, as illustrated inFIG. 7, it is possible to be a trailing direction (the edge of the first divider74faces a same direction as the rotating direction of the pumping member77). In this case, when the contact direction of the first divider74is in the trailing direction, a turning up of the first divider74by rotating the pumping member77can be prevented.

Another embodiment of the pumping member77is described inFIGS. 8(a) to 8(c).FIG. 8(a)is a perspective view of the pumping member77;FIG. 8(b)is a side view; andFIG. 8(c)is a cross section view.

This embodiment is about the second conveying part C that includes a plurality of plate-like members77dprotruding from the rotating axis77ain a radial direction. Other components are the same as components inFIG. 4.

The first conveying part B and the second conveying part C are disposed alternately along the direction of the axis of the rotating axis77a.

A surface of each of the plate-like members77dfacing the rotating direction is a conveying surface dl that has a prescribed length along a direction parallel to the rotating axis77a. On the other hand, the first conveying part B has a spiral vane77bdisposed along the axis direction. The plate-like members77dare formed to a total of 4, every 90 degrees, around the rotating axis77a. However, it is possible to change the spacing degree and amount of plate-like members.

An edge of the spiral vane77bis not protruding from the edge of the plate-like members77dwhen viewed from the axis direction. On the other hand, even if the edge of the spiral vane77bdoes protrude from the edge of the plate-like members77d, it is better for the edge not to protrude greatly. In this case, the plate-like members77dkeep the pumping effect.

When the pumping member77is rotated as described inFIGS. 9 and 10, the toner is pushed to the rotating direction. The inner surface of the housing70and the first divider74work together. In this case, the toner T in the second mixing chamber U2is pumped upwardly, and then the toner is pushed into the supply chamber S2via the lower communicating path Q2. At that time, the toner is conveyed to the axis direction by each of the spiral vanes77bof the first conveying part B.

The embodiment described inFIGS. 8 to 10can convey the toner in two different directions at a same time by one conveyer (the pumping member77). One of the two different directions is a conveying direction for mixing the toner in the mixing chamber S1described inFIG. 3. Another one of the two different directions is a conveying direction for pumping the toner to the supply chamber S2described inFIG. 9.

In this embodiment, the plate-like members77dserving as the second conveying part C form a paddle. Thus, an amount of toner held by the second conveying part C increases. Therefore, the amount of toner struck by the first divider74with rotation of the pumping member77increases, and the capacity of pumping can be increased.

As shown inFIG. 11, the developing device handles a toner supply process. In a step S1, when a result of a detection by a toner detector is that the developing device is out of toner (step S1being yes), the process moves to a step S2. In the step S2, the toner is replenished by new toner being supplied to the developing device via a toner supplying opening.

In one non-limiting illustrative embodiment, control steps in this toner supply process, or in any other processes described in this patent specification, may be executed utilizing hardware, software, or any combination thereof. In a non-limiting illustrative example, a controller, or its equivalents, such as a processor/microprocessor, a central processing unit (CPU), at least one application specific processor (ASP), or other circuitry, may implement such control steps, and may utilize a computer readable storage medium (e.g., ROM, EPROM, EEPROM, flash memory, static memory, DRAM, SDRAM, and their equivalents).

The disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.

An image forming apparatus for installing the developing device according to an embodiment of the invention is not limited to the printer illustrated inFIG. 1and may be any of a copier, a facsimile machine, and a combined machine thereof.

The conveyer (the pumping member77) can be used for a powder conveying device different from the developing device. For example, the conveyer may be used for a waste toner container that contains the waste toner collected by the cleaning device of the photoreceptor or a middle transfer belt. Therefore, the waste toner is conveyed in two directions (the axis direction and the rotating direction), so that the waste toner is contained effectively.