Developer conveyance device and image forming apparatus incorporating same

A developer conveyance device includes a downward conveyance path in which a developer falls under gravity, a transverse conveyance path communicating with a lower end of the downward conveyance path and extending in a transverse direction intersecting with the downward conveyance path, a transport screw disposed in the transverse conveyance path, and a floating member. The transport screw is configured to rotate in a predetermined direction to transport the developer in the transverse direction. The floating member is configured to contact the transport screw rotating in the predetermined direction to float in the downward conveyance path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2019-105807, filed on Jun. 6, 2019 and 2020-065919, filed on Apr. 1, 2020, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Embodiments of the present disclosure generally relate to a developer conveyance device to transport a developer such as excess toner, and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction peripheral (MFP) having at least two of such capabilities, incorporating the developer conveyance device.

Description of the Related Art

In certain image forming apparatuses, such as copiers, printers, and the like, a downward conveyance path and a transverse conveyance path transport a developer such as excess toner. The developer falls in the downward conveyance path under gravity. As a transport screw rotates in the transverse conveyance path, the developer flowing from the downward conveyance path is transported in a transverse direction.

SUMMARY

Embodiments of the present disclosure describe an improved developer conveyance device that includes a downward conveyance path in which a developer falls under gravity, a transverse conveyance path communicating with a lower end of the downward conveyance path and extending in a transverse direction intersecting with the downward conveyance path, a transport screw disposed in the transverse conveyance path, and a floating member. The transport screw is configured to rotate in a predetermined direction to transport the developer in the transverse direction. The floating member is configured to contact the transport screw rotating in the predetermined direction to float in the downward conveyance path.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. In addition, identical or similar reference numerals designate identical or similar components throughout the several views, and redundant descriptions are omitted or simplified below as required.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail with reference to drawings.

It is to be noted that the suffixes Y, M, C, and BK attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary.

A configuration and operation of an image forming apparatus1is described below with reference toFIG. 1.

InFIG. 1, the image forming apparatus1, which is a tandem-type color copier in the present embodiment, includes a document conveyance device3, a scanner (document reading device)4, and an exposure device (writing device)6. The document conveyance device3transports documents to the scanner4. The scanner4scans image data for the documents. The exposure device6emits a laser beam based on input image data.

The image forming apparatus1also includes a sheet feeder7, process cartridges10Y,10M,10C, and10BK, an intermediate transfer belt17, and a secondary transfer roller18. The sheet feeder7accommodates sheets of paper P or the like. The process cartridges10Y,10M,10C, and10BK are image forming units to form yellow, magenta, cyan, and black toner images, respectively. The intermediate transfer belt17serves as an image bearer onto which the toner images of multiple colors are transferred and superimposed. The secondary transfer roller18transfers the toner images on the intermediate transfer belt17to the sheet P.

The image forming apparatus1further includes a fixing device20, toner containers28, and an excess toner receptacle30. The fixing device20fixes unfixed toner images on the sheet P. The toner containers28contain toners of respective colors to be supplied to developing devices13(seeFIG. 2) of the corresponding process cartridges10Y,10M,10C, and10BK. Excess toner is collected in the excess toner receptacle30.

Each of the process cartridges10Y,10M,10C, and10BK as the image forming units includes a photoconductor drum11as an image bearer, a charging device12, the developing device13, and a cleaning device15, which are united as a single unit as illustrated inFIG. 2. Each of the process cartridges10Y,10M,10C, and10BK, which are expendable, is replaced with a new one when depleted. In the process cartridges10Y,10M,10C, and10BK, yellow, magenta, cyan, and black toner images are formed on the respective photoconductor drums11.

A description is provided below of the operation of the image forming apparatus1to form a normal color image.

A conveyance roller of the document conveyance device3transports a document on a document table onto a platen (exposure glass) of the scanner4. Then, the scanner4optically scans image data for the document on the platen. The yellow, magenta, cyan, and black image data are transmitted to the exposure device6. The exposure device6irradiates the photoconductor drums (image bearers)11of the corresponding process cartridges10Y,10M,10C, and10BK with laser beams (exposure light) L based on the yellow, magenta, cyan, and black image data, respectively.

Meanwhile, the four photoconductor drums11rotate clockwise inFIGS. 1 and 2. With reference toFIG. 2, it can be seen that the charging device12(e.g., a charging roller) uniformly charges the surface of the photoconductor drum11at a position opposite each other (charging process). Thus, the surface of the photoconductor drum11is charged to a certain potential. Subsequently, the surface of the photoconductor drum11thus charged reaches a position where the surface of the photoconductor drum11is irradiated with the laser beam L.

The exposure device6emits the laser beams L for respective colors from a light source according to the image data. The laser beams L are reflected by a polygon mirror and transmitted through multiple lenses. The transmitted laser beams L pass through different optical paths for the different components of yellow, magenta, cyan, and black (exposure process).

The laser beam L corresponding to a yellow component is directed to the surface of photoconductor drum11in the process cartridge10Y, which is the first from the left inFIG. 1among the four process cartridges10Y,10M,10C, and10BK. Thus, an electrostatic latent image for yellow is formed on the photoconductor drum11charged by the charging device12.

Similarly, the laser beam L corresponding to a cyan component is directed to the surface of the photoconductor drum11in the second process cartridge10C from the left inFIG. 1, thus forming an electrostatic latent image for cyan on the surface of the photoconductor drum11. The laser beam L corresponding to a magenta component is directed to the surface of the photoconductor drum11in the third process cartridge10M from the left inFIG. 1, thus forming an electrostatic latent image for magenta on the photoconductor drum11. The laser beam L corresponding to a black component is directed to the surface of the photoconductor drum11in the fourth process cartridge10BK from the left inFIG. 1, thus forming an electrostatic latent image for black on the photoconductor drum11.

Then, the surface of the photoconductor drum11having the electrostatic latent image reaches a position opposite the developing device13(seeFIG. 2). The developing device13deposits toner of each color onto the surface of the photoconductor drum11and develops the electrostatic latent image on the photoconductor drum11into a toner image (development process).

Subsequently, the surface of the photoconductor drum11after the development process reaches a position facing the intermediate transfer belt17as the image bearer. The primary transfer rollers14are disposed at positions where the photoconductor drums11face the intermediate transfer belt17and in contact with an inner circumferential face of the intermediate transfer belt17, respectively. At the positions of the primary transfer rollers14, the toner images on the photoconductor drums11are transferred to and superimposed on the intermediate transfer belt17, forming a multicolor toner image thereon (primary transfer process).

After the primary transfer process, the surface of the photoconductor drum11reaches a position opposite the cleaning device15(seeFIG. 2). The cleaning device15collects untransferred toner remaining on the photoconductor drum11(cleaning process). Then, the surface of the photoconductor drum11passes through a discharge device to complete a series of image forming processes performed on the photoconductor drum11.

Meanwhile, the surface of the intermediate transfer belt17, onto which the single-color toner images on the photoconductor drums11are superimposed, moves in the direction indicated by arrow A1inFIG. 1and reaches a position opposite the secondary transfer roller18. The secondary transfer roller18secondarily transfers the multicolor toner image on the intermediate transfer belt17to the sheet P (secondary transfer process).

After the secondary transfer process, the surface of the intermediate transfer belt17reaches a position opposite a belt cleaning device9. The belt cleaning device9collects untransferred toner on the intermediate transfer belt17to complete a series of transfer processes on the intermediate transfer belt17.

The sheet P is transported to the position of the secondary transfer roller18, via a sheet conveyance guide, a registration roller pair19, and the like, from the sheet feeder7.

More specifically, a sheet feeding roller8feeds the sheet P from the sheet feeder7that accommodates a stack of sheets P, and the sheet P is then guided by the sheet conveyance guide to the registration roller pair19. The sheet P that has reached the registration roller pair19is transported toward the position of the secondary transfer roller18, timed to coincide with the arrival of the multicolor toner image on the intermediate transfer belt17.

Subsequently, the sheet P, onto which the multicolor image is transferred, is transported to the fixing device20. The fixing device20includes a fixing roller and a pressure roller pressing against each other. In a nip between the fixing roller and the pressure roller, the multicolor toner image is fixed on the sheet P.

After the fixing process, an output roller pair29ejects the sheet P as an output image outside the image forming apparatus1, and the ejected sheet P is stacked on an output tray5to complete a series of image forming processes.

Next, the process cartridge (image forming unit)10BK of the image forming apparatus1are described in further detail below with reference toFIG. 2.FIG. 2is a schematic view of the process cartridge10BK for black. Other three process cartridges10Y,10M, and10C have a similar configuration to that of the process cartridge10BK for black except for the color of toner used in image forming processes, and thus drawings and descriptions thereof are omitted to avoid redundancy.

As illustrated inFIG. 2, the process cartridge10BK is a single unit that accommodates the photoconductor drum11as the image bearer, the charging device12to charge the photoconductor drum11, the developing device13to develop the electrostatic latent image on the photoconductor drum11, the cleaning device15to remove untransferred toner from the photoconductor drum11in a casing of the process cartridge10BK.

The photoconductor drum11used in the present embodiment is an organic photoconductor designed to be charged with a negative polarity and which includes a photosensitive layer formed on a drum-shaped conductive support. The charging device12is the charging roller including a conductive core and an elastic layer of moderate resistivity coated on the conductive core. Receiving a predetermined voltage from a power supply, the charging device12uniformly charges the surface of the photoconductor drum11opposite the charging device12.

The developing device13includes a developing roller13adisposed opposite the photoconductor drum11, a first conveying screw13b1disposed opposite the developing roller13a, a second conveying screw13b2disposed opposite the first conveying screw13b1via a partition, and a doctor blade13cdisposed opposite the developing roller13a. The developing roller13aincludes multiple magnets and a sleeve that rotates around the magnets. The magnets are stationary and generate magnetic poles around the circumference of the developing roller13a. The magnets generate a plurality of magnetic poles on the sleeve of the developing roller13ato bear a developer on the developing roller13a. The developing device13contains the two-component developer including carrier and toner.

The cleaning device15includes a cleaning blade15athat contacts the photoconductor drum11, and a conveying screw15bdisposed in a conveyance tube16to transport untransferred toner collected in the cleaning device15as excess toner toward an excess toner receptacle30(seeFIG. 3). For example, the cleaning blade15ais made of rubber, such as urethane rubber, and contacts the surface of the photoconductor drum11at a predetermined angle and with a predetermined pressure. With this configuration, substances such as untransferred toner adhering to the photoconductor drum11are mechanically scraped off and collected in the cleaning device15. An excess toner conveyance device40(seeFIG. 3) as a developer conveyance device transports the untransferred toner collected in the cleaning device15to the excess toner receptacle30via the conveyance tube16in which a conveying screw15bis disposed. The transported untransferred toner is collected in the excess toner receptacle30as excess toner. The conveying screw15bis driven by a drive motor via a gear50(seeFIG. 3) and rotates in the direction indicated by arrow A3inFIGS. 2 and 3.

Similarly, the belt cleaning device9illustrated inFIG. 1includes a cleaning blade that contacts the intermediate transfer belt17and a conveying screw disposed in a conveyance tube16to transport untransferred toner collected in the belt cleaning device9as excess toner toward the excess toner receptacle30(illustrated inFIG. 3). The excess toner conveyance device40transports the untransferred toner collected in the belt cleaning device9to the excess toner receptacle30via the conveyance tube16in which the conveying screw is disposed. Thus, the untransferred toner is collected in the excess toner receptacle30as excess toner. A detailed description of the excess toner conveyance device40is deferred.

In addition to the untransferred toner, the substances adhering to the photoconductor drum11or the intermediate transfer belt17include paper dust resulting from the sheet P, discharge products generated on the photoconductor drum11during discharge by the charging device12, additives to toner, and the like. In the present specification, such substances are collectively referred to as “untransferred toner”.

The image forming processes are described in further detail below with continued reference toFIG. 2.

The developing roller13arotates counterclockwise indicated by arrow A2inFIG. 2. In the developing device13, as the first and second conveying screws13b1and13b2arranged via the partition rotate, the developer is circulated in the longitudinal direction of the developing device13, being stirred and mixed with toner supplied from the toner container28by a toner supply device. The longitudinal direction of the developing device13is perpendicular to the surface of the paper on whichFIG. 2is drawn.

Thus, the toner is triboelectrically charged and attracted to the carrier. Then, the toner is carried on the developing roller13atogether with the carrier. The developer carried on the developing roller13areaches the doctor blade13c. The amount of the developer on the developing roller13ais adjusted to a suitable amount by the doctor blade13c, after which the developer is transported to a development range opposite the photoconductor drum11.

In the development range, toner in the developer adheres to the electrostatic latent image on the surface of the photoconductor drum11. Specifically, the toner adheres to the electrostatic latent image by a development electric field formed by a potential difference (i.e., a developing potential) between a latent image potential (i.e., an exposure potential) of an image area irradiated with the laser beam L and a development bias applied to the developing roller13a, thereby forming a toner image.

Subsequently, most of the toner that adheres to the photoconductor drum11in the developing process is transferred to the intermediate transfer belt17, and untransferred toner remaining on the photoconductor drum11is collected in the cleaning device15by the cleaning blade15a.

A detailed description is given below of the excess toner conveyance device40as the developer conveyance device of the image forming apparatus1according to the present embodiment with reference toFIG. 3.FIG. 3is a cross-sectional view of a part of an excess toner conveyance device of the image forming apparatus inFIG. 1. As described above, excess toner as the developer is collected by the cleaning device15and the belt cleaning device9and transported through the conveyance tube16. With reference toFIG. 3, it can be seen that the excess toner conveyance device40as the developer conveyance device transports the excess toner toward the excess toner receptacle30in the direction indicated by thick black arrow A5inFIG. 3.

That is, as illustrated inFIG. 3, the excess toner conveyance device40as the developer conveyance device includes a downward conveyance path41, a transverse conveyance path42, a transport screw43, a floating member45, and the like.

The replaceable excess toner receptacle30, which is removable, is installed in the image forming apparatus1in such a way that the excess toner receptacle30is coupled to the transverse conveyance path42of the excess toner conveyance device40. Thus, the excess toner transported by the excess toner conveyance device40is collected in the excess toner receptacle30.

In the present embodiment, the downward conveyance path41, in which toner (developer) falls under gravity, extends in the substantially vertical direction. Further, the downward conveyance path41in the present embodiment has a circular cross-section with a diameter D along line X-X inFIG. 3.

The transverse conveyance path42extends in a transverse direction intersecting the downward conveyance path41, and an upper portion of the transverse conveyance path42communicates with a lower end of the downward conveyance path41. In the present embodiment, the transverse conveyance path42extends straight in the substantially horizontal direction and has a circular cross-section slightly larger than a screw diameter of the transport screw43described below.

The transport screw43is disposed in the transverse conveyance path42and rotates in a predetermined direction indicated by arrow A4inFIG. 3to transport toner in the transverse direction. The transport screw43includes a shaft43aand a thread43bwound around the shaft43a. The transport screw43is driven by a drive motor via a gear44and rotates in the direction indicated by arrow A4inFIG. 3. Both ends of the transport screw43in an axial direction are rotatably supported by a housing of the excess toner conveyance device40. In the present embodiment, both of the shaft43aand the thread43bof the transport screw43is made of a metal material having high mechanical strength, such as stainless steel.

In the present embodiment, the downward conveyance path41extends in the substantially vertical direction. Alternatively, a downward conveyance path with any shape in which excess toner falls under gravity can be used, for example, with a sloped face inclined relative to the vertical direction, on which excess toner slides down under gravity.

Further, in the present embodiment, the transverse conveyance path42extends in the substantially horizontal direction. Alternatively, a transverse conveyance path with any shape in which excess toner is transported in the transverse direction by the transport screw43can be used. Thus, for example, a shape with a sloped face inclined relative to the horizontal direction, or with a partly or entirely curved portion, is also feasible.

In the present embodiment, a floating member45is movably disposed in the downward conveyance path41of the excess toner conveyance device40. The floating member45floats in the downward conveyance path41by contact with the transport screw43rotating in the predetermined direction indicated by arrow A4inFIG. 3and randomly hits the inner wall of the downward conveyance path41, thereby preventing excess toner from adhering to the inner wall of the downward conveyance path41.

Specifically, the floating member45extends in substantially the same direction as the vertical direction in which the downward conveyance path41extends. The floating member45is disposed on the transport screw43and movable freely in the downward conveyance path41without being supported by any components.

The floating member45has a diameter R of the cross-section (seeFIG. 4) greater than a gap between the transport screw43and the transverse conveyance path42so that the floating member45floats on the rotating transport screw43without entering the gap.

Accordingly, the floating member45may move leftward inFIG. 3along the rotation of the transport screw43and collide with the inner wall on the left side of the downward conveyance path41, or may rebound from the inner wall or lose balance at the upper portion of the floating member45, thereby colliding with the inner wall on the other side. As a result, the floating member45randomly rocks in any direction with a free posture, and collides with the inner wall of the downward conveyance path41almost uniformly.

Thus, the floating member45moves in a relatively wide range upward from the lower end of the downward conveyance path41where the transverse conveyance path42communicates with, and collides with the substantially entire circumference of the inner wall of the downward conveyance path41, thereby preventing excess toner from adhering to the inner wall of the downward conveyance path41. Even if excess toner adheres to the inner wall of the downward conveyance path41, the toner adhering to the inner wall can be removed by the collision of the floating member45. Therefore, the adhering toner does not block the downward conveyance path41.

In particular, toner is less likely adhere to the upper portion of the inner wall of the downward conveyance path41and likely to adhere to the portion ranging from the lower end to the center. Therefore, the floating member45having a length H (seeFIG. 4) that can collide with such a range is useful to remove the adhering toner. Further, since excess toner is more likely to adhere to the inner wall of the downward conveyance path41than new toner (fresh toner), the floating member45provided in the downward conveyance path41for excess toner is useful.

In the present embodiment, the hardness of the floating member45is smaller than the hardness of the transport screw43. Specifically, in the present embodiment, the floating member45is made of a material such as a rubber material or a resin material, and softer than the transport screw43made of a metal material. The floating member45softer than the transport screw43can prevent the transport screw43from being worn due to repeated contact with the floating member45. Therefore, the good toner transportability by the transport screw43is retained over time. Note that the hardness of the floating member45may be smaller than the hardness of the transport screw43as a whole, or only at the surface of the floating member45. That is, the hardness of at least the outer surface of the floating member45can be smaller than the hardness of the transport screw43.

The floating member45can become worn due to repeated contact with the transport screw43, but the worn portion is limited to the bottom portion that contacts the transport screw43, and a portion that collides with the inner wall of the downward conveyance path41is hardly worn, and the length H (seeFIG. 4) of the portion that collides with the inner wall is sufficiently long, so that the function of preventing toner from adhering to the inner wall of the downward conveyance path41is retained over time. If a spherical floating member is used, the floating member may be caught between the threads43bof the transport screw43. However, in the present embodiment, even if the bottom of the floating member45is worn, the floating member45is not caught between the threads43bof the transport screw43, thereby preventing the malfunction or breakage of the transport screw43.

Further, in the present embodiment, the floating member45is softer than the inner wall of the downward conveyance path41, which is made of a relatively strong resin material. This configuration can prevent the downward conveyance path41from being worn due to repeated contact with the floating member45. The hardness of the floating member45may be smaller than the hardness of the inner wall of the downward conveyance path41as a whole, or only at the surface of the floating member45. That is, the hardness of at least the outer surface of the floating member45can be smaller than that of the inner wall of the downward conveyance path41.

In the present embodiment, preferably, the floating member45is elastic and made of an elastic material such as rubber. Thus, the hardness of the floating member45can be considerably reduced as compared with the hardness of the transport screw43made of a metal material, thereby preventing the transport screw43from being worn. Further, since the floating member45is elastic, the rebound when the floating member45hits the transport screw43or the inner wall of the downward conveyance path41is increased by elastic force, causing the floating member45to floats greatly. Thus, toner is prevented from adhering to the inner wall of the downward conveyance path41.

In the present embodiment, as illustrated inFIGS. 4 and 5A, the floating member45has a columnar shape. As illustrated inFIG. 5B, when the floating member145is cubic, the corners of the floating member45hit the inner wall41aof the downward conveyance path41and wear down. As a result, the state of collision with the inner wall41achanges over time. Therefore, the effect of preventing toner from adhering to the inner wall41amay change with time. A columnar floating member like the columnar floating member45can prevent such a problem.

As illustrated inFIG. 5B, even when the cubic floating member145is used, the effect of preventing toner from adhering to the inner wall41acan be attained similarly to the case of the columnar floating member45inFIG. 5A. However, when the columnar floating member45inFIG. 5Ais used, regions, which are not close to the inner wall41a, surrounded by broken lines can be reduced as compared with the cubic floating member145inFIG. 5B. Accordingly, the effect of preventing toner from adhering to the inner wall41ais more likely to being attained.

Further, the floating member45in the present embodiment can have a hollow tubular shape having a hollow45aformed therein as illustrated inFIG. 4. Since the hollow45aof the floating member45reduces the weight of the floating member45, the transport screw43and the inner wall41aare prevented from being worn due to the collision of the floating member45. Further, since the weight of the floating member45is reduced, the rebound when the floating member45hits the transport screw43or the inner wall41aof the downward conveyance path41is increased, causing the floating member45to floats greatly. Thus, toner is prevented from adhering to the inner wall of the downward conveyance path41.

In addition, some excess toner falls through the hollow45aof the floating member45under gravity. As compared with no hollow45a, the flow (transportability) of the excess toner in the downward conveyance path41can be improved.

With reference toFIGS. 3 and 4, in the present embodiment, the excess toner conveyance device40(the floating member45and the transport screw43) satisfies a relation R>M−N. Here, R represents a diameter of an inscribed circle of a bottom face (cross-section) of the floating member45, M represents a screw pitch of the transport screw43, and N represents a thickness of the thread43bof the transport screw43. Note that, in the case of the columnar floating member45as illustrated inFIG. 5A, the diameter R of the inscribed circle equals an outer diameter of the floating member45. In the case of the cubic floating member145as illustrated inFIG. 5B, the diameter R of the inscribed circle equals a diameter of an inscribed circle of the square cross-section of the floating member145.

If the above-described relation is not satisfied, then, as illustrated inFIG. 6, the floating member45may enter between the threads43bof the transport screw43, thereby hindering the floating member45from floating by contact with the rotating transport screw43or causing the floating member45to be damaged. On the other hand, in the present embodiment, the dimensions of the related components (e.g., the floating member45and the transport screw43) are determined so that the floating member45does not enter between the threads43bof the transport screw43, thereby preventing such a problem.

With continued reference toFIGS. 3 and 4, in the present embodiment, the excess toner conveyance device40(the floating member45and the downward conveyance path41) satisfies a relation H>D. Here, H represents the length of the floating member45, and D represents the diameter of the cross-section inside of the downward conveyance path41(the inner diameter of the inner wall41a). If the above-described relation is not satisfied, the floating member45may fall down, and the longitudinal direction of the floating member45may be greatly inclined with respect to the vertical direction, thereby fitting in the inner wall41aof the downward conveyance path41. In such a case, the floating member45does not float, and the function of preventing toner from adhering to the inner wall41ais not attained.

On the other hand, in the present embodiment, since the length H of the floating member45is sufficiently greater than the diameter D of the cross-section of the downward conveyance path41, thereby reducing such a problem. Note that, when the cross-section inside the downward conveyance path41is rectangular as illustrated inFIG. 7, the length of the diagonal of the cross-section is defined as the diameter D of the cross-section.

In the present embodiment, the specific gravity of the floating member45is greater than the specific gravity of excess toner (developer). Thus, the floating member45is less likely to rise greatly above the transport screw43via excess toner because a large amount of excess toner is not interposed between the transport screw43and the floating member45.

That is, even when a large amount of excess toner is in the transverse conveyance path42, the floating member45sinks into the excess toner and comes into contact with the transport screw43due to difference of the specific gravity. Therefore, the floating member45can come into contact with the rotating transport screw43and float in the downward conveyance path41, thereby maintaining the effect of preventing toner from adhering to the inner wall41a.

As illustrated inFIG. 8, an excess toner conveyance device40according to a first variation includes a floating member45whose bottom portion45bof enlarged diameter surrounded by the broken-line circle inFIG. 8bulges. Thus, the bulging bottom portion45band a slim portion45cother than the bottom portion of the floating member45can reduce the weight of the floating member45and minimize wear of the transport screw43and the floating member45while preventing the floating member45from entering between the threads43bof the transport screw43.

As illustrated inFIG. 9, an excess toner conveyance device40according to a second variation includes a floating member45having rounded corners surrounded by the broken-line circles inFIG. 9. Specifically, the corners of the columnar floating member45are chamfered. Such a floating member45reduces the contact pressure with the transport screw43, thereby minimizing wear of the transport screw43and the floating member45.

To prevent the rounded corner portion of the floating member45from entering between the threads43bof the transport screw43, preferably, the diameter of the bottom face that is not rounded is greater than the screw pitch M of the transport screw43. In addition to the rounded corner portions of the floating member45only at the bottom to attain the above-described effect, all corner portions of the floating member45including the ceiling portion are chamfered. As a result, the floating member45with no orientation facilitates assembly of the floating member45to the excess toner conveyance device40.

As illustrated inFIG. 10, an excess toner conveyance device40according to a third variation includes a downward conveyance path41having a rectangular cross-section therein. The columnar floating member45made of a rubber material is provided in the downward conveyance path41. In the third variation, the diameter R of the floating member45is 40% or more of the diagonal length (the diameter D) of the cross-section of the downward conveyance path41(i.e., R≥D×0.4).

Specifically, the cross-section of the downward conveyance path41has a long side length A of about 17.2 mm, a short side length B of about 13.6 mm, and the diameter D of the cross-section of about 21.93 mm. The diameter R of the floating member45is about 10 mm. Satisfying the above-described relation R≥D×0.4 can prevent excess toner from adhering to the inner wall of the downward conveyance path41without causing the malfunction or breakage of the transport screw43.

As described above, the excess toner conveyance device40as a developer conveyance device in the above-described embodiments includes the downward conveyance path41in which excess toner as a developer falls under gravity, the transverse conveyance path42communicating with the lower end of the downward conveyance path41and extending in the transverse direction intersecting with the downward conveyance path41, and the transport screw43disposed in the transverse conveyance path42. The transport screw43is configured to rotate in a predetermined direction to transport the excess toner in the transverse direction. The excess toner conveyance device40further includes the floating member45movably disposed in the downward conveyance path41and configured to contact the transport screw43rotating in the predetermined direction to float in the downward conveyance path41.

This configuration can prevent excess toner from adhering to the inner wall41aof the downward conveyance path41without causing the malfunction or breakage of the transport screw43.

According to the present disclosure, a developer conveyance device and an image forming apparatus incorporating the developer conveyance device can be provided that can prevent a developer from adhering to the inner wall of the downward conveyance path without causing the malfunction or breakage of the transport screw.

In the above-described embodiments, the present disclosure is applied to the excess toner conveyance device40as a developer conveyance device in which untransferred toner collected by the cleaning device15or the belt cleaning device9is transported as excess toner toward the excess toner receptacle30. However, the present disclosure is not limited to the above-described embodiments, and can readily be applied to, for example, an excess toner conveyance device in which only untransferred toner collected in the cleaning device15for the photoconductor drum11is transported as excess toner toward the excess toner receptacle30.

Further, in the above-described embodiments, the present disclosure is applied to the excess toner conveyance device40as a developer conveyance device in which excess toner as a developer is transported. However, the present disclosure is not limited to the above-described embodiments, and can readily be applied to, for example, a developer conveyance device in which untransferred toner collected by the cleaning device15is transported as recycle toner toward the developing device13, a developer conveyance device in which fresh toner or two-component developer is transported toward the developing device13, or the like.

In such configurations, effects similar to those of the above-described embodiments are also attained.

The above-described embodiments are illustrative and do not limit the present disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the present disclosure, the present disclosure may be practiced otherwise than as specifically described herein. The number, position, and shape of the components described above are not limited to those embodiments described above. Desirable number, position, and shape can be determined to perform the present disclosure.