Image forming apparatus and developer supplier capable of supplying developer at increased speed

The present application is based on and claims priority to Japanese patent application No. 2005-269285 filed on Sep. 15, 2005 in the Japan Patent Office, the entire contents of which are hereby incorporated herein by reference.

1. Field of the Invention

Exemplary aspects of the present invention relate to an image forming apparatus and a developer supplier, and more particularly to an image forming apparatus and a developer supplier for supplying a developer to be used for image forming at an increased speed.

2. Description of the Related Art

A related art image forming apparatus, such as a copying machine, a printer, a facsimile machine, or a multifunction printer including copying, printing, scanning, and facsimile functions, forms an electrostatic latent image on a photoconductor according to image data. The electrostatic latent image is developed with a developer (e.g., a toner) supplied from a development unit opposing the photoconductor to form a toner image on the photoconductor. The toner image is transferred onto a recording medium to form an image on the recording medium.

The toner to be used for development is supplied from a bottle containing the toner to a developer container of the development unit via a developer supplier. The developer supplier includes a temporary container for temporarily containing the toner supplied from the bottle and a conveyer for rotating to convey the toner in the temporary container toward the developer container. The developer supplier supplies the toner to the developer container to replenish it whenever the toner in the developer container is consumed for development. When the temporary container does not contain a sufficient amount of toner and thereby does not stably supply the toner to the developer container, the electrostatic latent image formed on the photoconductor may not be properly developed and a faulty image may be formed on the recording medium due to improper toner density.

To detect whether the temporary container contains the sufficient amount of toner or not, an exemplary developer supplier includes a sensor for detecting the toner at a specific height in the temporary container. When the sensor does not detect the toner at the specific height, the image forming apparatus notifies a user that the temporary container is almost empty and prompts the user to replace the bottle with new one. Therefore, the user may set the new bottle in the image forming apparatus before the temporary container becomes empty, preventing the faulty image from being formed on the recording medium due to improper toner density.

Another exemplary developer supplier includes an agitator for agitating the toner in the temporary container so as to prevent the toner from agglomerating and a driver for driving the conveyer and the agitator.

To form the image on the recording medium faster, the developer supplier needs to supply the toner to the development unit at an increased speed. When the conveyer is rotated at the increased speed to convey the toner faster, the agitator is also rotated at that increased speed because both the conveyer and the agitator are driven by the common driver.

The toner used in the image forming apparatus has a high flowability (i.e., a low accelerated agglomeration) so as to be conveyed at the increased speed. When the agitator is rotated at the increased speed, the agitator excessively agitates the toner in the temporary container. The toner is excessively dispersed in the air and is stirred up in the temporary container, and an amount of toner per unit volume decreases. The sensor detects the toner based on a load applied to the sensor by the toner. The excessively dispersed toner applies a decreased load to the sensor. Thus, the sensor may erroneously detect that the temporary container is almost empty even when the temporary container contains the sufficient amount of toner.

This specification describes below an image forming apparatus according to an exemplary embodiment of the invention. In one aspect of the present invention, the image forming apparatus includes an image forming mechanism configured to contain a developer and to form an image with the developer and a developer supplier configured to supply the developer to the image forming mechanism. The developer supplier includes a developer container, a conveyer, a sensor, an agitator, and a driver. The developer container is configured to contain the developer. The conveyer is configured to convey the developer from the developer container to the image forming mechanism. The sensor is disposed at a predefined position on an interior wall of the developer container and is configured to detect the developer at the predefined position in the developer container. The agitator is configured to rotate to agitate the developer, and includes a paddle formed in a plate-like shape and including an opening through which a part of the developer slips and avoids being paddled by the paddle. The driver is configured to drive the conveyer and the agitator at a variable speed.

This specification further describes a developer supplier according to one exemplary embodiment of the invention. In one aspect of the present invention, the developer supplier is configured to supply a developer to an image forming mechanism and includes a developer container, a conveyer, a sensor, an agitator, and a driver. The developer container is configured to contain the developer. The conveyer is configured to convey the developer from the developer container to the image forming mechanism. The sensor is disposed at a predefined position on an interior wall of the developer container and is configured to detect the developer at the predefined position in the developer container. The agitator is configured to rotate to agitate the developer, and includes a paddle formed in a plate-like shape which itself includes an opening through which a part of the developer slips and avoids being paddled by the paddle. The driver is configured to drive the conveyer and the agitator at a variable speed.

A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an image forming apparatus according to an exemplary embodiment of the present invention;

FIG. 2 is a sectional view of a process cartridge of the image forming apparatus shown in FIG. 1 ;

FIG. 3 is a perspective view of a toner bottle of the image forming apparatus shown in FIG. 1 ;

FIG. 4 is a perspective view of a toner supplier of the image forming apparatus shown in FIG. 1 connected with the process cartridge shown in FIG. 2 and the toner bottle shown in FIG. 3 ;

FIG. 5 is a sectional front view of a toner bottle base of the image forming apparatus shown in FIG. 1 , the toner bottle shown in FIG. 3 , and the toner supplier shown in FIG. 4 ;

FIG. 6 is a sectional front view of the toner bottle and the toner supplier shown in FIG. 5 ;

FIG. 7 is a sectional side view of the toner bottle and the toner supplier shown in FIG. 6 ;

FIG. 8 is another sectional side view of the toner bottle and the toner supplier shown in FIG. 6 ;

FIG. 9 is a sectional side view of the toner supplier shown in FIG. 8 ;

FIG. 10 is a sectional top view of the toner supplier shown in FIG. 9 ;

FIG. 11 is a sectional front view of the toner supplier shown in FIG. 9 ;

FIG. 12 illustrates an opening and an agitator of the toner supplier shown in FIG. 11 ;

FIG. 13 is a sectional side view of a tester toner supplier;

FIG. 14 is a sectional top view of the tester toner supplier shown in FIG. 13 ;

FIG. 15 is a sectional front view of the tester toner supplier shown in FIG. 13 ;

FIG. 16 is a graph illustrating a relationship between an accelerated agglomeration and an amount of toner conveyed by one rotation of an agitator of the tester toner supplier shown in FIG. 15 ;

FIG. 17A illustrates a detection result of a sensor of the toner supplier shown in FIG. 11 ;

FIG. 17B illustrates a detection result of a sensor of the tester toner supplier shown in FIG. 15 ;

FIG. 18 is a sectional top view of a toner supplier according to another exemplary embodiment of the present invention;

FIG. 19A illustrates a detection result of a sensor of the toner supplier shown in FIG. 18 ;

FIG. 19B illustrates another detection result of a sensor of the toner supplier shown in FIG. 18 ;

FIG. 19C illustrates yet another detection result of a sensor of the toner supplier shown in FIG. 18 ; and

FIG. 20 is a sectional top view of a toner supplier according to yet another exemplary embodiment of the present invention.

In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this 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.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, an image forming apparatus 100 according to an exemplary embodiment of the present invention is explained.

As illustrated in FIG. 1 , the image forming apparatus 100 includes process cartridges 6 Y, 6 M, 6 C, and 6 K, an exposure unit 7 , an intermediate transfer unit 15 , a toner bottle base 31 , toner bottles 32 Y, 32 M, 32 C, and 32 K, a paper tray 26 , a feeding roller 27 , a registration roller pair 28 , a second transfer roller 19 , a fixing unit 20 , an output roller pair 29 , and an output tray 30 .

The image forming apparatus 100 includes a copying machine, a facsimile machine, a printer, and a multifunction printer including copying, printing, scanning, and facsimile functions. According to this non-limiting exemplary embodiment of the present invention, the image forming apparatus 100 functions as a color printer for printing an image on a recording medium in an electrophotographic method.

The process cartridge 6 Y includes a photoconductor 1 Y, a charger 4 Y, a development unit 5 Y, and a cleaner 2 Y. The process cartridge 6 M includes a photoconductor 1 M, a charger 4 M, a development unit 5 M, and a cleaner 2 M. The process cartridge 6 C includes a photoconductor 1 C, a charger 4 C, a development unit 5 C, and a cleaner 2 C. The process cartridge 6 K includes a photoconductor 1 K, a charger 4 K, a development unit 5 K, and a cleaner 2 K.

The process cartridges 6 Y, 6 M, 6 C, and 6 K respectively form toner images in yellow, magenta, cyan, and black colors. The process cartridges 6 Y, 6 M, 6 C, and 6 K are attachable to and detachable from the image forming apparatus 100 so as to be replaced with new ones. The process cartridges 6 Y, 6 M, 6 C, and 6 K use as a developer toners of different colors from each other but have a common structure.

The photoconductors 1 Y, 1 M, 1 C, and 1 K rotate in a rotating direction A. The chargers 4 Y, 4 M, 4 C, and 4 K, the development units 5 Y, 5 M, 5 C, and 5 K, and the cleaners 2 Y, 2 M, 2 C, and 2 K are respectively disposed around the photoconductors 1 Y, 1 M, 1 C, and 1 K. The chargers 4 Y, 4 M, 4 C, and 4 K uniformly charge surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K respectively.

The exposure unit 7 is disposed under the process cartridges 6 Y, 6 M, 6 C, and 6 K and emits light L (e.g., a laser beam) onto each of the charged surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K according to image data so as to form an electrostatic latent image on each of the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K. In the exposure unit 7 , the laser beam emitted from a light source is scanned by a polygon mirror rotatably driven by a motor and is irradiated onto the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K via a plurality of optical lenses and mirrors.

The development units 5 Y, 5 M, 5 C, and 5 K respectively develop the electrostatic latent images formed on the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K with yellow, magenta, cyan, and black toners to form yellow, magenta, cyan, and black toner images.

The intermediate transfer unit 15 is disposed above the process cartridges 6 Y, 6 M, 6 C, and 6 K and includes an intermediate transfer belt 8 , a second transfer backup roller 12 , a cleaning backup roller 13 , a tension roller 14 , first transfer bias rollers 9 Y, 9 M, 9 C, and 9 K, and a cleaner 10 . The intermediate transfer belt 8 is formed in an endless belt-like shape and is looped over the second transfer backup roller 12 , the cleaning backup roller 13 , and the tension roller 14 . At least one of the second transfer backup roller 12 , the cleaning backup roller 13 , and the tension roller 14 drives and rotates the intermediate transfer belt 8 in a rotating direction B. The first transfer bias rollers 9 Y, 9 M, 9 C, and 9 K respectively oppose the photoconductors 1 Y, 1 M, 1 C, and 1 K via the intermediate transfer belt 8 to form first transfer nips. A transfer bias of a polarity (e.g., positive) opposite to a polarity of the toner is applied to an inner circumferential surface of the intermediate transfer belt 8 . The rollers other than the first transfer bias rollers 9 Y, 9 M, 9 C, and 9 K are grounded. The first transfer bias rollers 9 Y, 9 M, 9 C, and 9 K respectively transfer and superimpose the yellow, magenta, cyan, and black toner images formed on the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K onto an outer circumferential surface of the rotating intermediate transfer belt 8 at the first transfer nips. Thus, a color toner image is formed on the outer circumferential surface of the intermediate transfer belt 8 .

The cleaners 2 Y, 2 M, 2 C, and 2 K respectively remove residual toners remaining on the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K after the yellow, magenta, cyan, and black toner images formed on the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K are respectively transferred onto the outer circumferential surface of the intermediate transfer belt 8 . Then, dischargers (not shown) discharge the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K. Thus, the surfaces of the photoconductors 1 Y, 1 M, 1 C, and 1 K are initialized to become ready for next image forming processing.

The toner bottle base 31 is disposed above the intermediate transfer unit 15 and under the output tray 30 . The toner bottles 32 Y, 32 M, 32 C, and 32 K are arranged on the toner bottle base 31 and respectively contain the yellow, magenta, cyan, and black toners. The yellow, magenta, cyan, and black toners are respectively supplied from the toner bottles 32 Y, 32 M, 32 C, and 32 K to the development units 5 Y, 5 M, 5 C, and 5 K of the process cartridges 6 Y, 6 M, 6 C, and 6 K. The toner bottles 32 Y, 32 M, 32 C, and 32 K are attachable to and detachable from the image forming apparatus 100 separately from the process cartridges 6 Y, 6 M, 6 C, and 6 K.

The paper tray 26 is disposed under the exposure unit 7 and loads a recording medium (e.g., sheets P). The feeding roller 27 contacts an uppermost sheet P of the sheets P. When a driver (not shown) rotates the feeding roller 27 in a rotating direction C, the uppermost sheet P is fed toward a nip formed by the registration roller pair 28 . The registration roller pair 28 rotates to nip the uppermost sheet P. When the registration roller pair 28 nips the uppermost sheet P, the registration roller pair 28 temporarily stops rotating.

The second transfer backup roller 12 opposes the second transfer roller 19 via the intermediate transfer belt 8 to form a second transfer nip. The registration roller pair 28 feeds the sheet P to the second transfer nip at a timing when the color toner image formed on the outer circumferential surface of the intermediate transfer belt 8 is properly transferred onto the sheet P at the second transfer nip. The second transfer roller 19 transfers the color toner image formed on the outer circumferential surface of the intermediate transfer belt 8 onto the sheet P. The cleaner 10 removes residual toners remaining on the outer circumferential surface of the intermediate transfer belt 8 after the color toner image formed on the outer circumferential surface of the intermediate transfer belt 8 is transferred onto the sheet P.

The sheet P having the color toner image is fed by the second transfer roller 19 and the intermediate transfer belt 8 toward the fixing unit 20 . In the fixing unit 20 , rollers apply heat and pressure to the sheet P having the color toner image while the sheet P is conveyed between the rollers so as to fix the color toner image on the sheet P. The sheet P having the fixed color toner image is fed toward the output roller pair 29 . The output roller pair 29 feeds the sheet P having the fixed color toner image onto the output tray 30 . The output tray 30 is disposed on top of the image forming apparatus 100 . The sheet P fed by the output roller pair 29 is stacked one by one on the output tray 30 .

FIG. 2 illustrates the structure of the process cartridge 6 M, which is common to the process cartridges 6 Y, 6 C, and 6 K. As illustrated in FIG. 2 , the image forming apparatus 100 further includes a driving motor 41 . The development unit 5 M of the process cartridge 6 M includes a development sleeve 51 M, developer containers 53 M and 54 M, screws 55 M, a sensor 56 M, a controller 57 M, and a doctor blade member 52 M.

The development sleeve 51 M includes a magnetic field generator and carries a developer. The developer includes a toner and is hereinafter referred to as the toner. The toner includes a two-component developer including magnetic carrier particles and toner particles. The developer containers 53 M and 54 M are disposed adjacent to each other and contain the toner. The screws 55 M agitate the toner. The sensor 56 M detects the density of the toner in the developer container 54 M. The controller 57 M outputs a toner supplying signal when the sensor 56 M detects a low density of the toner in the developer container 54 M. The driving motor 41 is rotated in accordance with the toner supplying signal. The development sleeve 51 M rotates in a rotating direction D to convey the toner to a development area formed between the development sleeve 51 M and the photoconductor 1 M opposing each other. The doctor blade member 52 M regulates the layer thickness of the toner carried by the development sleeve 51 M. The developer container 53 M is disposed upstream of the doctor blade member 52 M in the rotating direction D and contains the toner regulated by the doctor blade member 52 M and not conveyed to the development area.

The following describes operations of the development unit 5 M. The development unit 5 M further includes a developer layer formed on a surface of the development sleeve 51 M. The developer layer moves in accordance with the rotation of the development sleeve 51 M to pick up the toner from the developer container 53 M so as to maintain a predetermined range of density of the toner. Toner particles of the toner picked up are charged by friction with carrier particles. The toner containing the charged toner particles is supplied onto the surface of the development sleeve 51 M including a magnetic pole inside and is carried by a magnetic force. The developer layer carried by the development sleeve 51 M is conveyed in the rotating direction D in accordance with the rotation of the development sleeve 51 M. The doctor 52 M regulates the layer thickness of the developer layer. When the developer layer reaches the development area formed between the development sleeve 51 M and the photoconductor 1 M, the electrostatic latent image formed on the surface of the photoconductor 1 M is developed with the toner. The rotating development sleeve 51 M conveys the developer layer remaining on the surface of the development sleeve 51 to an upstream portion of the developer container 53 M in the rotating direction D.

As illustrated in FIG. 3 , the toner bottle 32 M includes a bottle 33 M, a resin case 34 M, a handle 35 M, a bottle rotating gear 37 M, a shutter 36 M, and a groove 38 M. The bottle 33 M contains the toner. The resin case 34 M is disposed at one end of the bottle 33 M in a longitudinal direction of the bottle 33 M. The handle 35 M is integrally molded with the resin case 34 M. The bottle rotating gear 37 M is disposed at the one end of the bottle 33 M where the resin case 34 M is disposed and rotates together with the bottle 33 M. The shutter 36 M opens and closes a toner outlet (not shown) from which the toner in the bottle 33 M is supplied. The groove 38 M is formed on an inner circumferential surface of the bottle 33 M in a spiral-like shape. When the bottle 33 M rotates, the groove 38 M guides and conveys the toner in the bottle 33 M toward the resin case 34 M.

To set the toner bottle 32 M into the image forming apparatus 100 , a user lifts the output tray 30 to expose the toner bottle base 31 . When the user places the toner bottle 32 M on the toner bottle base 31 , the user turns the handle 35 M. The resin case 34 M integrally molded with the handle 35 M turns to move the shutter 36 M in a circumferential direction of the resin case 34 M. Thus, the shutter 36 M opens the toner outlet and the resin case 34 M and the toner bottle base 31 are connected to each other.

To remove the toner bottle 32 M from the image forming apparatus 100 , the user turns the handle 35 M in an opposite direction to release the connection between the resin case 34 M and the toner bottle base 31 M. The shutter 36 M closes the toner outlet. The user may catch the handle 35 M and may pick up the toner bottle 32 M from the image forming apparatus 100 . The user may set and remove the toner bottle 32 M from a top of the image forming apparatus 100 . Therefore, the user may easily understand how to set and remove the toner bottle 32 M and thereby may easily replace the toner bottle 32 M. Since the handle 35 M is integrally molded with the resin case 34 M, the user may easily set the toner bottle 32 M onto the toner bottle base 31 M by turning the handle 35 M.

When the toner bottle 32 M is not set in the image forming apparatus 100 , the shutter 36 M does not open even when the user turns the handle 35 M integrally molded with the resin case 34 M. Thus, the toner may not spill out of the bottle 33 M while the user replaces the toner bottle 32 M.

As illustrated in FIG. 4 , the image forming apparatus 100 further includes toner suppliers 40 Y, 40 M, 40 C, and 40 K. The toner suppliers 40 Y, 40 M, 40 C, and 40 K are disposed near a back side of the image forming apparatus 100 and respectively supply the yellow, magenta, cyan, and black toners from the toner bottles 32 Y, 32 M, 32 C, and 32 K to the process cartridges 6 Y, 6 M, 6 C, and 6 K. The toner suppliers 40 Y, 40 M, 40 C, and 40 K are separately provided from the toner bottles 32 Y, 32 M, 32 C, and 32 K and the process cartridges 6 Y, 6 M, 6 C, and 6 K. Therefore, the toner bottles 32 Y, 32 M, 32 C, and 32 K and the process cartridges 6 Y, 6 M, 6 C, and 6 K may have a compact size. In the image forming apparatus 100 , the toner bottles 32 Y, 32 M, 32 C, and 32 K are not disposed close to the process cartridges 6 Y, 6 M, 6 C, and 6 K. Therefore, the image forming apparatus 100 may provide flexibility and variations in design and thereby may have a compact size.

The toner outlets of the toner bottles 32 Y, 32 M, 32 C, and 32 K, the toner suppliers 40 Y, 40 M, 40 C, and 40 K, and toner inlets (not shown) of the developer containers 54 Y, 54 M, 54 C, and 54 K of the process cartridges 6 Y, 6 M, 6 C, and 6 K are disposed near one end of the intermediate transfer unit 15 in a direction perpendicular to the rotating direction B of the intermediate transfer belt 8 . Therefore, toner conveying routes of the toner suppliers 40 Y, 40 M, 40 C, and 40 K which respectively connect the toner outlets of the toner bottles 32 Y, 32 M, 32 C, and 32 K with the toner inlets of the developer containers 54 Y, 54 M, 54 C, and 54 K may become short, providing the compact image forming apparatus 100 and reducing or preventing the toner from clogging the toner conveying routes of the toner suppliers 40 Y, 40 M, 40 C, and 40 K.

FIG. 5 is a sectional front view illustrating a disposition of the toner bottle base 31 , the toner bottle 32 M, and the toner supplier 40 M, which is common to a disposition of the toner bottle base 31 , the toner bottle 32 Y, 32 C, or 32 K, and the toner supplier 40 Y, 40 C, or 40 K. FIG. 6 is a sectional front view illustrating a disposition of the toner bottle 32 M and the toner supplier 40 M, in which the toner bottle base 31 is omitted. FIG. 7 is a sectional side view of the toner bottle 32 M and the toner supplier 40 M of FIG. 6 . FIG. 8 is another sectional side view of the toner bottle 32 M and the toner supplier 40 M of FIG. 6 .

As illustrated in FIGS. 5 and 6 , the toner supplier 40 M includes the driving motor 41 M, a worm gear 42 M, a transmission gear 44 M, a gear 45 M, a sub hopper 48 M, and a pipe 43 M. As illustrated in FIGS. 7 and 8 , the toner supplier 40 M further includes a bottle driving gear 49 M.

The driving motor 41 M drives the worm gear 42 M. The worm gear 42 M coaxially rotates with the driving motor 41 M to transmit a driving force from the driving motor 41 M to the transmission gear 44 M. The transmission gear 44 M is engaged with the gear 45 M and rotates the gear 45 M. The bottle driving gear 49 M is coaxial with the transmission gear 44 M and is engaged with the bottle rotating gear 37 M. Thus, when the driving motor 41 M is rotated, the bottle 33 M rotates together with the bottle rotating gear 37 M. The rotating bottle 33 M causes the toner in the bottle 33 M to be guided and conveyed by the groove 38 M to the toner outlet of the resin case 34 M. The sub hopper 48 M receives the toner fallen from the toner outlet of the resin case 34 M. The pipe 43 M is connected to a lower portion of the sub hopper 48 M as illustrated in FIGS. 5 to 7 . The toner conveyed to the lower portion of the sub hopper 48 M is further conveyed through the pipe 43 M to the toner inlet of the developer container 54 M of the development unit 5 M. Thus, the density of the toner in the development unit 5 M is adjusted.

As illustrated in FIG. 8 , the toner supplier 40 M further includes an agitator bevel gear 46 M and a conveyer bevel gear 47 M. The agitator bevel gear 46 M is engaged with the conveyer bevel gear 47 M.

FIG. 9 is a sectional side view of the toner supplier 40 M. FIG. 10 is a sectional top view of the toner supplier 40 M. FIG. 11 is a sectional front view of the toner supplier 40 M. As illustrated in FIG. 9 , the toner supplier 40 M further includes a conveying coil 70 M, a rotating shaft 71 M, a rotating shaft 73 M, an agitator 74 M, an opening 75 M, and a sensor 72 M.

The conveying coil 70 M is disposed in the pipe 43 M with a gap in a range of from about 0.1 mm to about 0.2 mm provided between an inner circumferential surface of the pipe 43 M and an outer circumferential surface of the conveying coil 70 M. The conveying coil 70 M applies a force to the toner, which moves the toner in a toner conveyance direction, so as to prevent the toner from being accumulated in the pipe 43 M. Thus, the toner, even when accumulated in the pipe 43 M, may not flow all together into the development unit 5 M due to some impact.

The conveying coil 70 M may be coiled even if the pipe 43 M is bended. Therefore, the pipe 43 M needs not be formed in a straight shape, providing an increased flexibility in the layout of elements in the development unit 5 M. As a result, the development unit 5 M may be compact in size.

The conveying coil 70 M has an outside diameter of about 7 mm, an inside diameter of about 5 mm, and a coil pitch of about 8 mm. According to a measurement, one rotation of the conveying coil 70 M conveyed the toner of about 83.4 mg.

If the conveying coil 70 M includes a metal, friction between the outer circumferential surface of the conveying coil 70 M and the inner circumferential surface of the pipe 43 M, if any, may generate an agglomerated core of the toner, and thereby may produce a faulty image containing a white spot. In the toner supplier 40 M, the conveying coil 70 M includes a resin. Therefore, friction between the outer circumferential surface of the conveying coil 70 M and the inner circumferential surface of the pipe 43 M is weak and may not generate the agglomerated core of the toner, preventing the faulty image containing the white spot from being produced.

The driving motor 41 M which is a driving source of the conveying coil 70 M rotates in accordance with the detected density of the toner in the developer container 54 M. The detected density is updated every about 240 millisecond. A toner supplying operation starts when about 240 millisecond elapses after development starts at the latest.

In the sub hopper 48 M, the rotating shaft 71 M is attached to a portion of the conveying coil 70 M facing the rotating shaft 71 M. An area E is formed from a downstream end of the sub hopper 48 M in the toner conveyance direction to a downstream head of the rotating shaft 71 M. In the area E, the conveying coil 70 M is coiled for at least one pitch and a portion of the conveying coil 70 M facing the pipe 43 M contacts the inner circumferential surface of the pipe 43 M. The rotating shaft 71 M is disposed close to the portion of the conveying coil 70 M facing the rotating shaft 71 M. Therefore, there is almost no gap provided between the rotating shaft 71 M and the portion of the conveying coil 70 M facing the rotating shaft 71 M and between the inner circumferential surface of the pipe 43 M and the portion of the conveying coil 70 M facing the pipe 43 M. Thus, the weight of the toner may not cause the toner to pass the area E. Whenever the toner is output from the toner bottle 32 M, the toner is held in the area E so that only the rotation of the conveying coil 70 M may cause the toner to pass the area E. Thus, a steady amount of the toner may pass the area E. As a result, the steady amount of the toner may be supplied to the development unit 5 M disposed downstream of the area E in the toner conveyance direction.

The rotating shaft 73 M is connected to the gear 45 M and is rotated by the driving force transmitted from the driving motor 41 M via the worm gear 42 M, the transmission gear 44 M, and the gear 45 M.

The agitator 74 M is disposed in the sub hopper 48 M and rotates to agitate the toner in the sub hopper 48 M. The agitator 74 M is formed as a paddle having a plate-like shape. The agitator 74 M is fixed to the rotating shaft 73 M and is rotated by the rotating gear 45 M. The agitator bevel gear 46 M is disposed on the rotating shaft 73 M and is engaged with the conveyer bevel gear 47 M disposed on the rotating shaft 71 M. Thus, the rotating shaft 73 M rotates the rotating shaft 71 M via the agitator bevel gear 46 M and the conveyer bevel gear 47 M. The agitator bevel gear 46 M and the conveyer bevel gear 47 M are formed with a common shape and have a common number of gear teeth. Thus, the agitator 74 M and the conveying coil 70 M rotate with a common number of revolutions per minute.

As described above, the agitator 74 M and the conveying coil 70 M may be rotated by the common driving source, that is, the driving motor 41 M. Thus, a number of elements used for driving the agitator 74 M and the conveying coil 70 M may be reduced, resulting in decreased production costs. The agitator bevel gear 46 M and the conveyer bevel gear 47 M have the common number of gear teeth. Thus, one of the agitator bevel gear 46 M and the conveyer bevel gear 47 M needs not be larger than the other, saving space in the toner supplier 40 M. The agitator bevel gear 46 M and the conveyer bevel gear 47 M are formed in the common shape, resulting in decreased production costs.

The opening 75 M is provided on the agitator 74 M. While the agitator 74 M rotates, the toner slips through the opening 75 M. Thus, the toner may not be excessively agitated by the agitator 74 M. The toner may not be excessively dispersed in the air in the sub hopper 48 M and the amount of the toner per unit volume may not be partially decreased. The sensor 72 M is disposed on an interior side wall of the sub hopper 48 M and detects the toner. As illustrated in FIG. 10 , the sensor 72 M includes a detecting surface 721 M which is provided at a predetermined height in the sub hopper 48 M. When the toner is not supplied from the toner bottle 32 M and the sensor 72 M does not detect the toner at the detecting surface 721 M, the sensor 72 M may detect an “almost empty” state that the toner bottle 32 M is empty but the sub hopper 48 M contains the toner. The sensor 72 M includes a piezoelectric vibration toner level sensor available from TDK Corporation.

The agitator 74 M includes a flexible material such as a PET (polyethylene terephthalate). The length from the rotating shaft 73 M to a foremost end of the agitator 74 M is by about 1 mm to about 3 mm longer than a distance from the rotating shaft 73 M to the detecting surface 721 M. The width of the agitator 74 M is greater than a width of the detecting surface 721 M. A length of the agitator 74 M varies depending on the size of the sub hopper 48 M and may be in a range of from about 8 mm to about 19 mm. The image forming apparatus 100 generally includes the agitator 74 M having the length of about 13 mm.

The length from the rotating shaft 73 M to the foremost end of the agitator 74 M is by about 1 mm to about 3 mm longer than the distance from the rotating shaft 73 M to the detecting surface 721 M. Thus, the foremost end of the agitator 74 M scrapes the detecting surface 721 M in a state that the foremost end of the agitator 74 M is engaged in the detecting surface 721 M by about 1 mm to about 3 mm. The foremost end of the agitator 74 M scrapes the detecting surface 721 M to prevent the toner from adhering to the detecting surface 721 M. Thus, the sensor 72 M may not erroneously detect the toner adhered to the detecting surface 721 M. Namely, the agitator 74 M may clean the detecting surface 721 M.

As illustrated in FIG. 11 , the agitator 74 M rotates in a rotating direction F. The foremost end of the agitator 74 M scrapes the detecting surface 721 M upward. The flexible material, such as the PET, of the agitator 74 M may suppress abrasion and wear of the detecting surface 721 M more effectively than an inflexible material such as a metal.

The toner supplied from the toner bottle 32 M enters the sub hopper 48 M from an upper portion of the sub hopper 48 M and is conveyed toward the development unit 5 M by the conveying coil 70 M disposed in the lower portion of the sub hopper 48 M. The toner moves from the upper portion to the lower portion of the sub hopper 48 M. The rotating shaft 73 M extends in a horizontal direction. Namely, the rotating shaft 73 M extends in a direction perpendicular to the direction in which the toner moves in the sub hopper 48 M.

FIG. 12 illustrates the opening 75 M provided on the agitator 74 M. The opening 75 M is formed in a tetragon-like shape and has dimensions shown in FIG. 12 , for example.

FIGS. 13 to 15 illustrate a tester toner supplier 40 T. FIG. 13 is a sectional side view of the tester toner supplier 40 T. FIG. 14 is a sectional top view of the tester toner supplier 40 T. FIG. 15 is a sectional front view of the tester toner supplier 40 T. As illustrated in FIGS. 13 to 15 , the tester toner supplier 40 T does not include the opening 75 M. The other elements of the tester toner supplier 40 T are common to the toner supplier 40 M as illustrated in FIGS. 9 to 11 .

In the image forming apparatus 100 , the toner having an increased flowability is used so that the toner may be conveyed at an increased speed. Specifically, the toner has an accelerated agglomeration (i.e., an index showing the flowability of the toner) of about 15 percent or lower.

The accelerated agglomeration of the toner was measured as described below. A powder tester available from Hosokawa Micron Corporation was used as a measurement device.

A thermostatic vessel containing a sample toner was kept for about 24±1 hours at a temperature of about 35±2 degrees centigrade. Three sieves having a mesh of different sizes (e.g., about 75 μm, about 44 μm, and about 22 μm) were layered in a state that the sieve having a larger size mesh was layered on the sieve having a smaller size mesh. The sample toner was put into the top sieve having the largest size mesh and was screened at a predetermined vibration. The sample toner left on each sieve after screening was weighed as powder weight. The agglomeration of the sample toner left on each sieve was calculated according to the following equations. In the equations below, X1, X2, and X3 respectively represent the agglomerations of the sample toner left on the top, middle, and bottom sieves after screening. W1, W2, and W3 respectively represent the powder weights of the sample toner left on the top, middle, and bottom sieves after screening. S represents the weight of the sample toner put into the top sieve before screening.

X 1=( W 1 /S )×100

X 2=( W 2 /S )×100×⅗

X 3=( W 3 /S )×100×⅕

The accelerated agglomeration was calculated according to the following equation in which Y represents the accelerated agglomeration.

Y=X 1 +X 2 +X 3

The following describes an experiment for examining amounts of the toner conveyed by one rotation of the agitator 74 M. A plurality of toners having different flowabilities were conveyed by a test machine. The plurality of toners were conveyed for a predetermined time period and the amount of the toner conveyed by one rotation of the agitator 74 M was calculated based on the number of revolutions of the agitator 74 M and the amount of each of the toners conveyed. The result of the experiment is shown in Table 1 below and FIG. 16 .

FIG. 16 is a graph illustrating the relationship between the accelerated agglomeration and the amount of toner conveyed by one rotation of the agitator 74 M shown in table 1. Table 1 and FIG. 16 show that the amount of toner conveyed by one rotation of the agitator 74 M substantially decreased when the accelerated agglomeration was higher than 15 percent. The toner having the accelerated agglomeration of not lower than about 8 percent and not higher than about 15 percent may be preferably used. The toner having the accelerated agglomeration of lower than about 8 percent may be too flowable.

The toner supplier 40 M is requested to convey an increased amount of the toner (e.g., 12.0±(20 percent)g/min) so that the image forming apparatus 100 may form an image at a high speed. One rotation of the conveying coil 70 M conveyed the toner of an amount of about 83.4 mg. To convey the increased amount of the toner as described above, the conveying coil 70 M needs to rotate at about 144 (±20 percent) rpm. In the toner supplier 40 M, the number of revolutions per minute of the conveying coil 70 M and the agitator 74 M is common. Therefore, when the conveying coil 70 M is configured to rotate at about 144 (±20 percent) rpm, the agitator 74 M also rotates at about 144 (±20 percent) rpm.

When the conveying coil 70 M was configured to rotate at about 124 rpm or more, the sensor 72 M detected that the sub hopper 48 M was almost empty even when an accumulated toner level reached the detecting surface 741 M.

In the tester toner supplier 40 T, a toner having a high flowability (e.g., the accelerated agglomeration of about 15 percent or lower) was used so that an image may be formed on a recording medium at a high speed. When the number of revolutions per minute of the agitator 74 M was increased and the toner was excessively agitated, the toner was excessively dispersed in the air and was stirred up in the sub hopper 48 M. The amount of the toner per unit volume was partially decreased, causing the sensor 72 M to improperly detect the toner. When the agitator 74 M scraped the detecting surface 721 M, the toner was stirred up near the detecting surface 721 M and the amount of the toner per unit volume partially decreased.

The toner level sensor available from TDK Corporation was used as the sensor 72 M. The toner level sensor detected the toner in accordance with a load applied to the detecting surface 721 M by the toner. When the toner was stirred up, the load applied to the detecting surface 721 M decreased. Thus, the sensor 72 M erroneously detected that the sub hopper 48 M was almost empty even when the accumulated toner level reached the detecting surface 741 M.

The sensor 72 M detects whether the accumulated toner level reaches the detecting surface 741 M or not about every 200 millisecond. The sensor 72 M sends a detection signal to the controller 57 M about every 200 millisecond. The sensor 72 M performs detection five times as one set. When the controller 57 M receives three or more detection signals indicating that the accumulated toner level reaches the detecting surface 741 M after the sensor 72 M performs the one set of detections, the controller 57 M judges that the accumulated toner level reaches the detecting surface 741 M. When the controller 57 M receives two or less detection signals indicating that the accumulated toner level reaches the detecting surface 741 M after the sensor 72 M performs the one set of detections, the controller 57 M judges that the accumulated toner level does not reach the detecting surface 741 M.

The driving force from the driving motor 41 M is transmitted via the bottle rotating gear 37 M for rotating the toner bottle 32 M. When the number of revolutions per minute of the driving motor 41 M is increased to increase the number of revolutions per minute of the conveying coil 70 M, the number of revolutions per minute of the toner bottle 32 M is also increased. The following equation shows the ratio of the number of revolutions per minute of the toner bottle 32 M to the number of revolutions per minute of the conveying coil 70 M. In the equation below, R1 represents the number of revolutions per minute of the toner bottle 32 M and R2 represents the number of revolutions per minute of the conveying coil 70 M.

R1:R2=1:2.067

When the conveying coil 70 M rotates at 124 rpm, the toner bottle 32 M rotates at 60 rpm.

The image forming apparatus 100 stops the image forming operation when the sub hopper 48 M is almost empty. The image forming apparatus 100 resumes the image forming operation when the toner bottle 32 M is replaced with a new one or when the toner bottle 32 M is removed from the toner bottle base 31 and then is set again on the toner bottle base 31 after the amount of the toner remaining in the toner bottle 32 M is checked. Thus, when the sensor 72 M erroneously detects that the sub hopper 48 M is almost empty, an extra work is needed to resume the image forming operation, resulting in a decreased work efficiency.

To suppress excessive agitation of the toner in the sub hopper 48 M while increasing the number of revolutions per minute of the conveying coil 70 M, the agitator 74 M may be configured to rotate more slowly than the conveying coil 70 M. To vary the number of revolutions per minute of the agitator 74 M from the number of revolutions per minute of the conveying coil 70 M, the agitator bevel gear 46 M and the conveyer bevel gear 47 M may not be formed in the common shape, resulting in increased production costs. When the conveyer bevel gear 47 M for transmitting the driving force to the rotating shaft 71 M is formed larger than the agitator bevel gear 46 M to increase the number of revolutions per minute of the conveying coil 70 M, a distance between the rotating shafts 71 M and 73 M may become longer, resulting in a larger size toner supplier 40 M. Therefore, a mechanism for preventing the flowability of the toner in the sub hopper 48 M from increasing is requested without varying the number of revolutions per minute of the agitator 74 M from the number of revolutions per minute of the conveying coil 70 M.

FIGS. 17A and 17B illustrate detection results of the sensor 72 M when the sub hopper 48 M contained a sufficient amount of toner and the conveying coil 70 M rotated at about 124 rpm. FIG. 17A illustrates the detection result of the sensor 72 M of the toner supplier 40 M including the opening 75 M. FIG. 17B illustrates the detection result of the sensor 72 M of the tester toner supplier 40 T not including the opening 75 M. As illustrated in FIG. 17A , the sensor 72 M of the toner supplier 40 M has properly detected that the sub hopper 48 M contained the sufficient amount of toner. As illustrated in FIG. 17B , however, the sensor 72 M of the tester toner supplier 40 T has erroneously detected that the sub hopper 48 M did not contain the sufficient amount of toner.

The rotating speed of the driving motor 41 M varies depending on torques of the agitator 74 M, the conveying coil 70 M, and the toner bottle 32 M. Even when a signal instructing the driving motor 41 M to output a common driving force is sent to the driving motor 41 M, the rotating speed is slow when the driving motor 41 M starts rotating and the torques are high. The rotating speed is high when the torques are low. Accordingly, the rotating speeds of the conveying coil 70 M and the agitator 74 M increase.

When the conveying coil 70 M and the agitator 74 M are rotated at about 124 rpm, the opening 75 M provided on the agitator 74 M prevented the toner from being excessively agitated and the sensor 72 M did not erroneously detect that the sub hopper 48 M was almost empty. When the agitator 74 M rotated at about 155 rpm or faster, the sensor 72 M erroneously detected that the sub hopper 48 M was almost empty. When the agitator 74 M rotated at about 155 rpm, the toner bottle 32 M rotated at about 75 rpm.

FIG. 18 illustrates a toner supplier 40 Ma according to another exemplary embodiment of the present invention. As illustrated in FIG. 18 , the toner supplier 40 Ma includes a counter 76 M. The counter 76 M and the controller 57 M form a driving control mechanism for alternately driving and stopping the driving motor 41 M and functioning as an agitation adjuster for adjusting the flowability of the toner in the sub hopper 48 M. The other elements of the toner supplier 40 Ma are common to the toner supplier 40 M.

The counter 76 M counts the number of revolutions per minute of the rotating shaft 73 M and sends a signal based on the counted number of revolutions per minute of the rotating shaft 73 M to the controller 57 M. The controller 57 M sends a signal based on the signal sent from the counter 76 M to the driving motor 41 M. The driving motor 41 M performs intermittent driving (i.e., alternately drives and stops) based on the signal sent from the controller 57 M.

When the number of revolutions per minute of the rotating shaft 73 M counted by the counter 76 M is about 155 rpm or more, the controller 57 M controls the driving motor 41 M to perform intermittent driving. While the driving motor 41 M drives the agitator 74 M, the toner is dispersed in the air in the sub hopper 48 M. While the driving motor 41 M stops driving the agitator 74 M, the toner is not dispersed in the air, preventing the amount of toner per unit volume from decreasing. Thus, even when the number of revolutions per minute of the conveying coil 70 M and the number of revolutions per minute of the agitator 74 M increase, the sensor 72 M may properly detect the toner at the detecting surface 721 M. A duty ratio is represented by a time period of the drive to a total time period of the drive and the stop. In the toner supplier 40 Ma, the duty ratio is controlled to be about 75 percent or less.

FIGS. 19A , 19 B, and 19 C illustrate detection results of the sensor 72 M when the agitator 74 M with the opening 75 M rotated at about 155 rpm. FIG. 19A illustrates the detection result when the duty ratio was about 75 percent (i.e., when the driving motor 41 M was turned on for about 1.5 seconds and was turned off for about 0.5 seconds). FIG. 19B illustrates the detection result when the duty ratio was about 90 percent (i.e., when the driving motor 41 M was turned on for about 1.8 seconds and was turned off for about 0.2 seconds). FIG. 19C illustrates the detection result when the duty ratio was about 100 percent (i.e., when the driving motor 41 M was continuously turned on).

As illustrated in FIG. 19A , when the driving motor 41 M performed intermittent driving with the duty ratio of about 75 percent, the sensor 72 M properly detected that the sub hopper 48 M contained the sufficient amount of toner. As illustrated in FIG. 19B , when the driving motor 41 M performed intermittent driving with the duty ratio of about 90 percent, the sensor 72 M erroneously detected that the sub hopper 48 M was almost empty. As illustrated in FIG. 19C , when the driving motor 41 M continuously drove the agitator 74 M, the sensor 72 M erroneously detected that the sub hopper 48 M was almost empty.

FIG. 20 illustrates a toner supplier 40 Mb according to yet another exemplary embodiment of the present invention. As illustrated in FIG. 20 , the toner supplier 40 Mb includes an opening 75 Mb formed in a round-like shape. The other elements of the toner supplier 40 Mb are common to the toner supplier 40 M or 40 Ma. The opening 75 Mb may be formed in any shape other than the round-like shape as long as the opening 75 Mb decreases a surface area of the agitator 74 M used for agitating the toner.

According to the above-described non-limiting exemplary embodiments of the present invention, the toner supplier 40 M, 40 Ma, or 40 Mb includes the sub hopper 48 M as a developer container for containing toner to be supplied to the development unit 5 M, the conveying coil 70 M as a conveyer for conveying the toner to the developer container 54 M of the development unit 5 M, the sensor 72 M for detecting the toner in the sub hopper 48 M, the agitator 74 M as an agitator for agitating the toner in the sub hopper 48 M, and the driving motor 41 M as a driver for driving the agitator 74 M and the conveying coil 70 M. The opening 75 M or 75 Mb is provided on the agitator 74 M. When the agitator 74 M rotates to agitate the toner in the sub hopper 48 M, the toner slips through the opening 75 M or 75 Mb. Thus, the agitation of the agitator 74 M may be adjusted to prevent the toner from being excessively agitated by the agitator 74 M. As a result, the toner may not be excessively dispersed in the air in the sub hopper 48 M and the amount of toner per unit volume may not be partially decreased. Thus, even when the number of revolutions per minute of each of the conveying coil 70 M and the agitator 74 M is increased, the sensor 72 M may properly detect the toner at the detecting surface 721 M.

The agitator 74 M scrapes the detecting surface 721 M of the sensor 72 M to prevent the toner from adhering to the detecting surface 721 M so as to reduce or prevent an erroneous detection of the sensor 72 M which may occur due to the toner adhered to the detecting surface 721 M.

The flexible material, such as the PET, included in the agitator 74 M may suppress abrasion and wear of the detecting surface 721 M more effectively than the inflexible material such as the metal.

The length from the rotating shaft 73 M to the foremost end of the agitator 74 M is longer than the distance from the rotating shaft 73 M to the detecting surface 721 M. Thus, the foremost end of the agitator 74 M may properly scrape the detecting surface 721 M in a state that the foremost end of the agitator 74 M is engaged in the detecting surface 721 M. The width of the agitator 74 M is greater than the width of the detecting surface 721 M. Therefore, the agitator 74 M may properly scrape the whole width of the detecting surface 721 M. The agitator 74 M, which scrapes the detecting surface 721 M, may prevent the toner from adhering to the detecting surface 721 M and may thereby prevent an erroneous detection of the sensor 72 M which may occur due to the toner adhered to the detecting surface 721 M.

The agitator 74 M rotates to scrape the detecting surface 721 M upward. The agitator 74 M pushes back the toner falling onto the agitator 74 M. The agitator 74 M guards the detecting surface 721 M from the toner immediately after the agitator 74 M scrapes the detecting surface 721 M. Thus, the cleaned detecting surface 721 M may be maintained. If the agitator 74 M rotates to scrape the detecting surface 721 M downward, the detecting surface 721 M is exposed to the falling toner immediately after the agitator 74 M scrapes the detecting surface 721 M. The falling toner adheres to the cleaned detecting surface 721 M. Thus, the cleaned detecting surface 721 M may not be maintained.

The rotating shaft 73 M for rotating the agitator 74 M is disposed horizontally (i.e., in a direction perpendicular to a direction in which the toner moves downward in the sub hopper 48 M). If the toner bottle 32 M contains a toner having a high flowability, a substantial amount of toner may be put into the empty toner supplier 40 M, 40 Ma, or 40 Mb, for example, when the image forming apparatus 100 is set up. Namely, gravity causes an unexpected amount of toner to be flown into the toner supplier 40 M, 40 Ma, or 40 Mb. In this case, the rotating shaft 73 M and the agitator 74 M disposed in the direction perpendicular to the direction in which the toner moves downward in the sub hopper 48 M may interrupt the movement of the toner more easily than the rotating shaft 73 M and the agitator 74 M disposed in parallel to the direction in which the toner moves downward in the sub hopper 48 M. Thus, a substantial amount of toner may not flow into the sub hopper 48 M in a given time period.

The toner supplier 40 Ma or 40 Mb further includes the driving control mechanism. When the agitator 74 M rotates at about 155 rpm or more, the driving control mechanism causes the driving motor 41 M to perform intermittent driving (i.e., to alternately drive and stop). Even when the number of revolutions per minute of the agitator 74 M increases to the extent that the opening 75 M or 75 b may not suppress the flowability of the toner in the sub hopper 48 M, the toner is not dispersed into the air in the sub hopper 48 M while the agitator 74 M stops. Thus, the agitation of the agitator 74 M may be suppressed. Namely, even when the number of revolutions per minute of each of the conveying coil 70 M and the agitator 74 M is increased, the sensor 72 M may properly detect the toner at the detecting surface 721 M.

When the toner having a high flowability (e.g., an accelerated agglomeration of about 15 percent or lower) is used, the toner may be stably conveyed in the toner supplier 40 M, 40 Ma, or 40 Mb.

The conveying coil 70 M is formed in a coil-like shape which is not easily stressed by bending. The conveying coil 70 M may be coiled even if the pipe 43 M is bended. Therefore, the pipe 43 M needs not be formed in a straight shape, providing an increased flexibility in the layout of elements in the development unit 5 M. As a result, the development unit 5 M may have a compact size.

The conveying coil 70 M is disposed in the lower portion of the sub hopper 48 M. The toner is supplied into the sub hopper 48 M from the upper portion of the sub hopper 48 M and the weight of the toner moves the toner downward to the lower portion of sub hopper 48 M. Therefore, no toner conveyer for conveying the toner from the upper portion to the lower portion of the sub hopper 48 M needs to be provided in the sub hopper 48 M.

The rotating shafts 71 M and 73 M are not disposed parallel with each other. The rotating shaft 71 M slants in a manner such that a downstream portion of the rotating shaft 71 M in the toner conveyance direction is disposed downwardly. Therefore, the toner may easily move toward the downstream portion of the rotating shaft 71 M in the toner conveyance direction, resulting in a stable conveyance of the toner. The rotating shafts 71 M and 73 M respectively include the conveyer bevel gear 47 M and the agitator bevel gear 46 M. Therefore, even when the rotating shafts 71 M and 73 M are not disposed parallel with each other, the driving force from the driving motor 41 may be transmitted to the rotating shafts 71 M and 73 M via the conveyer bevel gear 47 M and the agitator bevel gear 46 M.

The conveyer bevel gear 47 M and the agitator bevel gear 46 M have the common number of gear teeth. One of the conveyer bevel gear 47 M and the agitator bevel gear 46 M needs not be larger than the other, saving space in the toner supplier 40 M, 40 Ma, or 40 Mb. The conveyer bevel gear 47 M and the agitator bevel gear 46 M may be formed so as to have a common shape, resulting in decreased production costs.

The present invention has been described above with reference to specific exemplary embodiments. Note that the present invention is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.